@article{zeng_kim_underwood_guddati_2023, title={Asphalt mixture fatigue damage and failure predictions using the simplified viscoelastic continuum damage (S-VECD) model}, volume={174}, ISSN={["1879-3452"]}, url={https://doi.org/10.1016/j.ijfatigue.2023.107736}, DOI={10.1016/j.ijfatigue.2023.107736}, abstractNote={Fatigue cracking is a primary asphalt pavement distress and various models have been developed to predict the fatigue life of asphalt mixtures using laboratory tests. One such model is the simplified viscoelastic continuum damage (S-VECD) model, which has been implemented in the pavement performance prediction program, FlexPAVETM. The S-VECD model test protocols (AASHTO TP 133 and AASHTO T 400) and data processing tool (FlexMATTM) are widely used around the world. Over the past three decades, this model has been continuously improved and refined. However, questions remain on the model’s ability to predict the material response when stress or strain are used as the model input. Also, different fitting procedures for the model calibration were found to affect the model’s prediction accuracy. In this study, analysis was conducted using data for four typical North Carolina mixes based on single replicate tests and multiple replicate tests to compare the model’s prediction accuracy based on stress versus strain as the model input and by considering fitting errors in the different calculations. The results show that using strain as the model input, which automatically incorporates portions of permanent strain, yields more accurate predictions compared to using stress as the input, regardless of the fitting algorithm. Additionally, in the analysis of individual test data, which is not affected by replicate specimen variability, the model’s predictions match the measured data well, as long as the fitting errors of the damage characteristic curve are controlled. When the data from replicate tests are analyzed together, although specimen variability compromises the S-VECD model’s prediction accuracy, failure can still be reasonably determined when strain is used as the model input.}, journal={INTERNATIONAL JOURNAL OF FATIGUE}, author={Zeng, Zhe and Kim, Y. Richard and Underwood, B. Shane and Guddati, Murthy}, year={2023}, month={Sep} }
@article{elmeliegy_guddati_2023, title={Correlation-based full-waveform shear wave elastography}, volume={68}, ISSN={["1361-6560"]}, url={http://dx.doi.org/10.1088/1361-6560/acc37b}, DOI={10.1088/1361-6560/acc37b}, abstractNote={Objective. With the ultimate goal of reconstructing 3D elasticity maps from ultrasound particle velocity measurements in a plane, we present in this paper a methodology of inverting for 2D elasticity maps from measurements on a single line.Approach. The inversion approach is based on gradient optimization where the elasticity map is iteratively modified until a good match is obtained between simulated and measured responses. Full-wave simulation is used as the underlying forward model to accurately capture the physics of shear wave propagation and scattering in heterogeneous soft tissue. A key aspect of the proposed inversion approach is a cost functional based on correlation between measured and simulated responses.Main results. We illustrate that the correlation-based functional has better convexity and convergence properties compared to the traditional least-squares functional, and is less sensitive to initial guess, robust against noisy measurements and other errors that are common in ultrasound elastography. Inversion with synthetic data illustrates the effectiveness of the method to characterize homogeneous inclusions as well as elasticity map of the entire region of interest.Significance. The proposed ideas lead to a new framework for shear wave elastography that shows promise in obtaining accurate maps of shear modulus using shear wave elastography data obtained from standard clinical scanners.}, number={11}, journal={PHYSICS IN MEDICINE AND BIOLOGY}, publisher={IOP Publishing}, author={Elmeliegy, Abdelrahman M. and Guddati, Murthy N.}, year={2023}, month={Jun} }
@article{roy_guddati_2023, title={Full waveform inversion for arterial viscoelasticity}, volume={68}, ISSN={["1361-6560"]}, DOI={10.1088/1361-6560/acba7a}, abstractNote={Objective. Arterial viscosity is emerging as an important biomarker, in addition to the widely used arterial elasticity. This paper presents an approach to estimate arterial viscoelasticity using shear wave elastography (SWE).Approach. While dispersion characteristics are often used to estimate elasticity from SWE data, they are not sufficiently sensitive to viscosity. Driven by this, we develop a full waveform inversion (FWI) methodology, based on directly matching predicted and measured wall velocity in space and time, to simultaneously estimate both elasticity and viscosity. Specifically, we propose to minimize an objective function capturing the correlation between measured and predicted responses of the anterior wall of the artery.Results. The objective function is shown to be well-behaving (generally convex), leading us to effectively use gradient optimization to invert for both elasticity and viscosity. The resulting methodology is verified with synthetic data polluted with noise, leading to the conclusion that the proposed FWI is effective in estimating arterial viscoelasticity.Significance. Accurate estimation of arterial viscoelasticity, not just elasticity, provides a more precise characterization of arterial mechanical properties, potentially leading to a better indicator of arterial health.}, number={5}, journal={PHYSICS IN MEDICINE AND BIOLOGY}, author={Roy, Tuhin and Guddati, Murthy N.}, year={2023}, month={Mar} }
@article{eslaminia_elmeliegy_guddati_2023, title={Improved least-squares migration through double-sweeping solver}, volume={88}, ISSN={["1942-2156"]}, url={https://doi.org/10.1190/geo2021-0628.1}, DOI={10.1190/GEO2021-0628.1}, abstractNote={Based on a recently developed approximate wave-equation solver, we have developed a methodology to reduce the computational cost of seismic migration in the frequency domain. This approach divides the domain of interest into smaller subdomains, and the wavefield is computed using a sequential process to determine the downward- and upward-propagating wavefields — hence called a double-sweeping solver. A sequential process becomes possible using a special approximation of the interface conditions between subdomains. This method is incorporated into the least-squares migration framework as an approximate solver. The associated computational effort is comparable to one-way wave-equation approaches, yet, as illustrated by the numerical examples, the accuracy and convergence behavior are comparable to that of the full-wave equation.}, number={3}, journal={GEOPHYSICS}, author={Eslaminia, Mehran and Elmeliegy, Abdelrahman M. and Guddati, Murthy N.}, year={2023}, pages={S131–S141} }
@article{capron_roy_guddati_urban_2023, title={Improving group velocity based estimates of arterial stiffness}, volume={153}, ISSN={["1520-8524"]}, DOI={10.1121/10.0018801}, abstractNote={Arterial stiffness is a predictor of cardiovascular diseases, the leading causes of death worldwide. Ultrasound-based methods that measure arterial wave propagation have promise for evaluating local stiffness in vivo. However, geometric properties of arteries cause dispersion, invalidating typical assumptions underlying the relationship between shear modulus G and group velocity cg, which clinical implementations of ultrasound shear wave elastography do not consider. Here, we examine the dependence of these estimates on geometry and evaluate alternative approaches. Wave motion in the proximal wall of an artery after application of focused acoustic radiation force is simulated with a semi-analytical finite element (SAFE) model, and cg is estimated using a time-to-peak algorithm to determine G with several methods. First, the value of G a clinical scanner would report is calculated assuming a bulk medium. Second, a pulse wave velocity (PWV)-based G estimate is calculated by taking cg = PWV and applying the Moens–Korteweg equation. Third, we develop an interpolation-based method to provide a corrected G estimate using data generated by the SAFE model. Simulation results show severe geometry-dependent bias with the bulk method, which is partially ameliorated with the PWV method and substantially improved with the interpolation approach. Results are validated using arterial phantoms.}, number={3}, journal={JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA}, author={Capron, Charles and Roy, Tuhin and Guddati, Murthy and Urban, Matthew W.}, year={2023}, month={Mar} }
@article{guddati_roy_elmeliegy_urban_2023, title={Shear wave elastography: From dispersion matching to full waveform inversion}, volume={153}, ISSN={["1520-8524"]}, DOI={10.1121/10.0018796}, abstractNote={Shear Wave Elastography (SWE) involves estimating mechanical properties through inversion, i.e., matching measured and simulated propagation characteristics of shear waves in the tissue. The accuracy of the estimated properties depends significantly on the specific characteristics/responses that are being matched. These could range from simple group velocity to dispersion curves and to full-wave response (particle velocity measurements). Using specific applications of arterial, liver, and tumor elstography, we illustrate that effective SWE is performed by resorting to an inversion approach, or combination of inversion approaches, guided by the underlying physics. To this end, we present inversion approaches ranging from matching dispersion characteristics to matching full waveform responses and provide rationale for choosing the appropriate technique(s) depending on the problem at hand.}, number={3}, journal={JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA}, author={Guddati, Murthy and Roy, Tuhin and Elmeliegy, Abdelrahman M. and Urban, Matthew W.}, year={2023}, month={Mar} }
@article{roy_guddati_2022, title={Full wave simulation of arterial response under acoustic radiation force}, volume={149}, ISSN={["1879-0534"]}, DOI={10.1016/j.compbiomed.2022.106021}, abstractNote={With the ultimate goal of estimating arterial viscoelasticity using shear wave elastography, this paper presents a practical methodology to simulate the response of a human carotid artery under acoustic radiation force (ARF). The artery is idealized as a nearly incompressible viscoelastic hollow cylinder submerged in incompressible, inviscid fluid. For this idealization, we develop a multi-step methodology for efficient computation of three-dimensional response under complex ARF excitation, while capturing the fluid-structure interaction between the arterial wall and the surrounding fluid. The specific steps include (a) performing dimensional reduction through semi-analytical finite element formulation, (b) efficient finite element discretization using traditional and recent techniques. The computational efficiency is further enhanced by utilizing (c) modal superposition, followed by, where appropriate, (d) impulse response function. In addition to developing the methodology, convergence analysis is performed for a typical arterial geometry, leading to recommendations on various discretization parameters. At the end, the computational effort is shown to be several orders of magnitude less than the traditional, fully three-dimensional analysis using finite element methods, leading to a practical yet accurate simulation of arterial response under ARF excitations.}, journal={COMPUTERS IN BIOLOGY AND MEDICINE}, author={Roy, Tuhin and Guddati, Murthy N.}, year={2022}, month={Oct} }
@article{eslaminia_elmeliegy_guddati_2022, title={Full waveform inversion through double-sweeping solver}, volume={453}, ISSN={["1090-2716"]}, url={https://doi.org/10.1016/j.jcp.2021.110914}, DOI={10.1016/j.jcp.2021.110914}, abstractNote={An efficient method is proposed to accurately approximate the gradient and the Hessian operator for the full-waveform inversion (FWI) in large-scale problems. The key idea is an approximate solver called double-sweeping solver, which divides the domain into smaller slabs and sequentially solves the wavefields through a downward and an upward sweeping. The sequential solution is facilitated by approximating the continuity conditions that suppress the multiples, thus relaxing long-range coupling between the subdomains. The double-sweeping solver is incorporated into an inexact Gauss-Newton approach to perform FWI, where the gradient and the Hessian vector multiplication are computed more efficiently. Through numerical experiments, we show that the convergence of FWI with respect to the number of iterations does not degrade when the double-sweeping approximation is used. Given that the double-sweeping solver is computationally cheaper than full-wave simulation, the proposed method is more efficient than the standard FWI. This paper contains the complete formulation of the proposed methodology as well as an illustration of its effectiveness to problems of varying complexity including the inversion of the Marmousi model from the Geophysics community.}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, publisher={Elsevier BV}, author={Eslaminia, Mehran and Elmeliegy, Abdelrahman M. and Guddati, Murthy N.}, year={2022}, month={Mar} }
@article{lee_capron_liu_roy_guddati_greenleaf_urban_2022, title={Measurement of wave propagation through a tube using dual transducers for elastography in arteries}, volume={67}, ISSN={["1361-6560"]}, DOI={10.1088/1361-6560/ac9c3f}, abstractNote={Objective.Measuring waves induced with acoustic radiation force (ARF) in arteries has been studied over the last decade. To date, it remains a challenge to quantitatively assess the local arterial biomechanical properties. The cylindrical shape and waveguide behavior of waves propagating in the arterial wall pose complexities to determining the mechanical properties of the artery.Approach. In this paper, an artery-mimicking tube in water is examined utilizing three-dimensional measurements. The cross-section of the tube is measured while a transducer is translated over 41 different positions along the length of the tube. Motion in the radial direction is calculated using two components of motion which are measured from the two orthogonal views of the cross-section. This enables more accurate estimation of motion along the circumference of tube.Main results. The results provide more information to categorize the motion in tube wall into two types of responses: a transient response and a steady state response. The transient response is caused by ARF application and the waves travel along the length of the tube for a relatively short period of time. This corresponds to the axial and circumferential propagating waves. The two circumferential waves travel along the circumference of tube in CW (clockwise) and CCW (counter-clockwise) direction and result in a standing wave. By using a directional filter, the two waves were successfully separated, and their propagation was more clearly visualized. As a steady state response, a circumferential mode is generated showing a symmetric motion (i.e. the proximal and distal walls move in the opposite direction) following the transient response.Significance.This study provides a more comprehensive understanding of the waves produced in an artery-mimicking tube with ARF application, which will provide opportunities for improving measurement of arterial mechanical properties.}, number={22}, journal={PHYSICS IN MEDICINE AND BIOLOGY}, author={Lee, Hyoung-Ki and Capron, Charles B. and Liu, Hsiao-Chuan and Roy, Tuhin and Guddati, Murthy N. and Greenleaf, James F. and Urban, Matthew W.}, year={2022}, month={Nov} }
@article{capriotti_roy_hugenberg_harrigan_lee_aquino_guddati_greenleaf_urban_2022, title={The influence of acoustic radiation force beam shape and location on wave spectral content for arterial dispersion ultrasound vibrometry}, volume={67}, ISSN={["1361-6560"]}, DOI={10.1088/1361-6560/ac75a7}, abstractNote={Objective. Arterial dispersion ultrasound vibrometry (ADUV) relies on the use of guided waves in arterial geometries for shear wave elastography measurements. Both the generation of waves through the use of acoustic radiation force (ARF) and the techniques employed to infer the speed of the resulting wave motion affect the spectral content and accuracy of the measurement. In particular, the effects of the shape and location of the ARF beam in ADUV have not been widely studied. In this work, we investigated how such variations of the ARF beam affect the induced motion and the measurements in the dispersive modes that are excited.Approach.The study includes an experimental evaluation on an arterial phantom and anin vivovalidation of the observed trends, observing the two walls of the waveguide, simultaneously, when subjected to variations in the ARF beam extension (F/N) and focus location.Main results.Relying on the theory of guided waves in cylindrical shells, the shape of the beam controls the selection and nature of the induced modes, while the location affects the measured dispersion curves (i.e. variation of phase velocity with frequency or wavenumber, multiple modes) across the waveguide walls.Significance.This investigation is important to understand the spectral content variations in ADUV measurements and to maximize inversion accuracy by tuning the ARF beam settings in clinical applications.}, number={13}, journal={PHYSICS IN MEDICINE AND BIOLOGY}, author={Capriotti, Margherita and Roy, Tuhin and Hugenberg, Nicholas R. and Harrigan, Hadiya and Lee, Hon-Chi and Aquino, Wilkins and Guddati, Murthy and Greenleaf, James F. and Urban, Matthew W.}, year={2022}, month={Jul} }
@article{liu_abbasi_ding_roy_capriotti_liu_fitzgerald_doyle_guddati_urban_et al._2021, title={Characterizing blood clots using acoustic radiation force optical coherence elastography and ultrasound shear wave elastography}, volume={66}, ISSN={["1361-6560"]}, url={https://doi.org/10.1088/1361-6560/abcb1e}, DOI={10.1088/1361-6560/abcb1e}, abstractNote={Thromboembolism in a cerebral blood vessel is associated with high morbidity and mortality. Mechanical thrombectomy (MT) is one of the emergenc proceduresperformed to remove emboli. However, the interventional approaches such as aspiration catheters or stent retriever are empirically selected. An inappropriate selection of surgical devices can influence the success rate during embolectomy, which can lead to an increase in brain damage. There has been growing interest in the study of clot composition and using a priori knowledge of clot composition to provide guidance for an appropriate treatment strategy for interventional physicians. Developing imaging tools which can allow interventionalists to understand clot composition could affect management and device strategy. In this study, we investigated how clots of different compositions can be characterized by using acoustic radiation force optical coherence elastography (ARF-OCE) and compared with ultrasound shear wave elastography (SWE). Five different clots compositions using human blood were fabricated into cylindrical forms from fibrin-rich (21% red blood cells, RBCs) to RBC-rich (95% RBCs). Using the ARF-OCE and SWE, we characterized the wave velocities measured in the time-domain. In addition, the semi-analytical finite element model was used to explore the relationship between the phase velocities with various frequency ranges and diameters of the clots. The study demonstrated that the wave group velocities generally decrease as RBC content increases in ARF-OCE and SWE. The correlation of the group velocities from the OCE and SWE methods represented a good agreement as RBC composition is larger than 39%. Using the phase velocity dispersion analysis applied to ARF-OCE data, we estimated the shear wave velocities decoupling the effects of the geometry and material properties of the clots. The study demonstrated that the composition of the clots can be characterized by elastographic methods using ARF-OCE and SWE, and OCE demonstrated better ability to discriminate between clots of different RBC compositions, compared to the ultrasound-based approach, especially in clots with low RBC compositions.}, number={3}, journal={PHYSICS IN MEDICINE AND BIOLOGY}, publisher={IOP Publishing}, author={Liu, Hsiao-Chuan and Abbasi, Mehdi and Ding, Yong Hong and Roy, Tuhin and Capriotti, Margherita and Liu, Yang and Fitzgerald, Sean and Doyle, Karen M. and Guddati, Murthy and Urban, Matthew W. and et al.}, year={2021}, month={Feb} }
@article{samu_guddati_2021, title={Field Validation of Effective Dispersion Analysis of Reflections, a New Method for Nondestructive Estimation of Pile Depth}, ISSN={["2169-4052"]}, DOI={10.1177/03611981211008186}, abstractNote={Several methods have been developed for nondestructive pile depth estimation over the past few decades, with impact-based methods remaining popular because of their ease of application. Sonic-echo techniques rely on generating nondispersive longitudinal waves by impacting the pile top and subsequently picking peaks that correspond to initial and reflected wave arrivals. Unfortunately, pile tops are often inaccessible for in-service foundations and alternate impacting techniques result in signals for which time domain peak picking can be difficult. Pile sides are often easily accessible, but side impact generates highly dispersive flexural waves resulting in complicated waveforms for which analysis is not straightforward. Existing methods to process dispersive flexural waves rely on signal processing based methods and do not explicitly incorporate the physical dispersion properties of the system, resulting in large errors. To address the current limitations, a new method called effective dispersion analysis of reflections (EDAR) was recently developed for pile length estimation. EDAR provides a simple and robust technique to analyze dispersive flexural waves generated from side impact for which time domain processing is not applicable. In this paper, length estimation through EDAR is explained for longitudinal and flexural waves using synthetic bar and Timoshenko beam models. Field validation for two types of pile, concrete filled steel tubes and prestressed concrete, with varying cross sections and embedment are presented. EDAR resulted in pile length estimates within 10% error.}, journal={TRANSPORTATION RESEARCH RECORD}, author={Samu, Vivek and Guddati, Murthy}, year={2021}, month={Apr} }
@article{roy_urban_xu_greenleaf_guddati_2021, title={Multimodal guided wave inversion for arterial stiffness: methodology and validation in phantoms}, volume={66}, ISSN={["1361-6560"]}, url={https://doi.org/10.1088/1361-6560/ac01b7}, DOI={10.1088/1361-6560/ac01b7}, abstractNote={Abstract Arterial stiffness is an important biomarker for many cardiovascular diseases. Shear wave elastography is a recent technique aimed at estimating local arterial stiffness using guided wave inversion (GWI), i.e. matching the computed and measured wave dispersion. This paper develops and validates a new GWI approach by synthesizing various recent observations and algorithms: (a) refinements to signal processing to obtain more accurate experimental dispersion curves; (b) an efficient forward model to compute theoretical dispersion curves for immersed, incompressible cylindrical waveguides; (c) an optimization framework based on the recent observation that the measured dispersion curve is multimodal, i.e. it matches for not one but two different wave modes in two different frequency ranges. The resulting inversion approach is validated using extensive experimental data from rubber tube phantoms, not only for modulus estimation but also to simultaneously estimate modulus and wall thickness. The observations indicate that the modulus estimates are best performed with the information on wall thickness. The approach, which takes less than half a minute to run, is shown to be accurate, with the modulus estimated with less than 4% error for 70% of the experiments.}, number={11}, journal={PHYSICS IN MEDICINE AND BIOLOGY}, publisher={IOP Publishing}, author={Roy, Tuhin and Urban, Matthew and Xu, Yingzheng and Greenleaf, James and Guddati, Murthy N.}, year={2021}, month={Jun} }
@article{roy_guddati_2021, title={Shear wave dispersion analysis of incompressible waveguides}, volume={149}, ISSN={["1520-8524"]}, url={https://doi.org/10.1121/10.0003430}, DOI={10.1121/10.0003430}, abstractNote={A suite of methodologies is presented to compute shear wave dispersion in incompressible waveguides encountered in biomedical imaging; plate, tube, and general prismatic waveguides, all immersed in an incompressible fluid, are considered in this effort. The developed approaches are based on semi-analytical finite element methods in the frequency domain with a specific focus on the complexities associated with the incompressibility of the solid media as well as the simplification facilitated by the incompressibility of the surrounding fluid. The proposed techniques use the traditional idea of selective reduced integration for the solid medium and the more recent idea of perfectly matched discrete layers for the surrounding fluid. Also, used is the recently developed complex-length finite element method for platelike structures. Several numerical examples are presented to illustrate the practicality and effectiveness of the developed techniques in computing shear wave dispersion in a variety of waveguides.}, number={2}, journal={JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA}, publisher={Acoustical Society of America (ASA)}, author={Roy, Tuhin and Guddati, Murthy N.}, year={2021}, month={Feb}, pages={972–982} }
@article{hugenberg_roy_harrigan_capriotti_lee_guddati_greenleaf_urban_aquino_2021, title={Toward improved accuracy in shear wave elastography of arteries through controlling the arterial response to ultrasound perturbation in-silico and in phantoms}, volume={66}, ISSN={["1361-6560"]}, url={https://doi.org/10.1088/1361-6560/ac38fe}, DOI={10.1088/1361-6560/ac38fe}, abstractNote={Abstract Dispersion-based inversion has been proposed as a viable direction for materials characterization of arteries, allowing clinicians to better study cardiovascular conditions using shear wave elastography. However, these methods rely on a priori knowledge of the vibrational modes dominating the propagating waves induced by acoustic radiation force excitation: differences between anticipated and real modal content are known to yield errors in the inversion. We seek to improve the accuracy of this process by modeling the artery as a fluid-immersed cylindrical waveguide and building an analytical framework to prescribe radiation force excitations that will selectively excite certain waveguide modes using ultrasound acoustic radiation force. We show that all even-numbered waveguide modes can be eliminated from the arterial response to perturbation, and confirm the efficacy of this approach with in silico tests that show that odd modes are preferentially excited. Finally, by analyzing data from phantom tests, we find a set of ultrasound focal parameters that demonstrate the viability of inducing the desired odd-mode response in experiments.}, number={23}, journal={PHYSICS IN MEDICINE AND BIOLOGY}, publisher={IOP Publishing}, author={Hugenberg, Nicholas R. and Roy, Tuhin and Harrigan, Hadiya and Capriotti, Margherita and Lee, Hyoung-Ki and Guddati, Murthy and Greenleaf, James F. and Urban, Matthew W. and Aquino, Wilkins}, year={2021}, month={Dec} }
@article{samu_guddati_2020, title={Nondestructive length estimation of an embedded pile through combined analysis of transverse and longitudinal waves}, volume={110}, ISSN={["1879-1174"]}, DOI={10.1016/j.ndteint.2019.102203}, abstractNote={This paper presents an important modification of the recently developed nondestructive testing method for estimating embedded depth of pile foundations – EDAR – effective dispersion analysis of reflections. The original EDAR method is based on processing dispersive bending wave signals in the frequency-effective wavenumber domain, thus eliminating the need to perform time-domain peak picking that is difficult due to over-distortion of reflected signals. While EDAR was successful in laboratory settings, preliminary field validation resulted in significant errors. After careful examination of the wave physics, it is discovered that both longitudinal and transverse waves need to be carefully included in EDAR analysis. Specifically, it is shown that the initial arrival is dominated by transverse waves, while the reflections are dominated by longitudinal waves, owing to significant attenuation of transverse waves due to compacted soil around the pile. This observation led to a refined EDAR methodology and accurate estimation of embedded pile depth in field settings.}, journal={NDT & E INTERNATIONAL}, author={Samu, Vivek and Guddati, Murthy}, year={2020}, month={Mar} }
@article{samu_guddati_2019, title={Nondestructive Method for Length Estimation of Pile Foundations Through Effective Dispersion Analysis of Reflections}, volume={38}, ISSN={["1573-4862"]}, DOI={10.1007/s10921-019-0583-8}, number={2}, journal={JOURNAL OF NONDESTRUCTIVE EVALUATION}, author={Samu, Vivek and Guddati, Murthy}, year={2019}, month={Jun} }
@article{cho_karshenas_tayebali_guddati_kim_2017, title={A mechanistic approach to evaluate the potential of the debonding distress in asphalt pavements}, volume={18}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2016.1149837}, abstractNote={The debonding distress in asphalt pavement structures is a critical problem that affects the performance of asphalt concrete pavements. It occurs at the layer interface due to the poor bond quality between adjacent asphalt concrete layers and/or when stresses at the layer interface exceed the strengths of the material at the interface. The debonding of the adjacent layers, especially the top surface layer of an asphalt pavement, is a contributing factor to the premature cracking of pavements. Hence, the debonding distress can lead to a reduction in the life of the pavement. This paper presents an analytical and experimental framework to evaluate the potential for debonding at the layer interface of asphalt concrete pavements. Computational analysis was performed to determine the critical stress and strain states in layered asphalt pavements under moving vehicle loads using the Layered ViscoElastic pavement analysis for Critical Distresses (LVECD) computer program developed at North Carolina State University. This computational analysis enables a greater understanding of the critical stress that is involved in debonding and the ways that such stress is affected by pavement design parameters and environmental conditions. In addition, a prediction model was developed that can determine the shear bond strength at the interface of asphalt concrete layers with different tack coat materials at various temperatures, loading rates and normal confining stresses. The systematic and mechanistic framework developed in this study employs the maximum shear ratio concept as a shear failure criterion and provides a tool to evaluate the effects of various loading, environmental and pavement factors on the debonding potential of asphalt pavements. The overall advantages of the mechanistic framework and approach using the LVECD analysis tool will help lead to better understanding of the debonding mechanism, proper selection of the tack coats, and economic benefit in highway pavement maintenance and rehabilitation costs.}, number={12}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Cho, Seong-Hwan and Karshenas, Afshin and Tayebali, Akhtarhusein A. and Guddati, Murthy N. and Kim, Y. Richard}, year={2017}, pages={1098–1110} }
@article{astaneh_urban_aquino_greenleaf_guddati_2017, title={Arterial waveguide model for shear wave elastography: implementation and in vitro validation}, volume={62}, ISSN={["1361-6560"]}, DOI={10.1088/1361-6560/aa6ee3}, abstractNote={Arterial stiffness is found to be an early indicator of many cardiovascular diseases. Among various techniques, shear wave elastography has emerged as a promising tool for estimating local arterial stiffness through the observed dispersion of guided waves. In this paper, we develop efficient models for the computational simulation of guided wave dispersion in arterial walls. The models are capable of considering fluid-loaded tubes, immersed in fluid or embedded in a solid, which are encountered in in vitro/ex vivo, and in vivo experiments. The proposed methods are based on judiciously combining Fourier transformation and finite element discretization, leading to a significant reduction in computational cost while fully capturing complex 3D wave propagation. The developed methods are implemented in open-source code, and verified by comparing them with significantly more expensive, fully 3D finite element models. We also validate the models using the shear wave elastography of tissue-mimicking phantoms. The computational efficiency of the developed methods indicates the possibility of being able to estimate arterial stiffness in real time, which would be beneficial in clinical settings.}, number={13}, journal={PHYSICS IN MEDICINE AND BIOLOGY}, author={Astaneh, Ali Vaziri and Urban, Matthew W. and Aquino, Wilkins and Greenleaf, James F. and Guddati, Murthy N.}, year={2017}, month={Jul}, pages={5473–5494} }
@article{astaneh_guddati_2017, title={Dispersion analysis of composite acousto-elastic waveguides}, volume={130}, ISSN={["1879-1069"]}, DOI={10.1016/j.compositesb.2017.07.040}, abstractNote={Abstract Propagation characteristics of guided waves are widely utilized for nondestructive characterization of laminated composites which are often immersed in fluid. These propagation characteristics are quantified through dispersion and attenuation curves, and need to be computed for a large number of estimated structure and material property combinations, over a wide range of frequencies. To solve this central problem, an efficient approach is proposed for dispersion analysis of three types of immersed waveguides: laminated plates; laminated rods and pipes; composite waveguides with generic cross-section. The approach is based on Semi-Analytical Finite Element (SAFE) method enhanced with two novel discretization methods: Complex-length Finite Element Method (CFEM) for the solid domain and Perfectly Matched Discrete Layers (PMDL) for the surrounding fluid. The resulting approach is computationally more efficient than the existing methods in that it keeps the underlying eigenvalue problem linear and substantially smaller. The paper presents the basic ideas of the proposed approach, specific algorithms for determining the discretization parameters, and open-source implementation of the resulting waveguide models. Several numerical examples are presented to illustrate the method's efficiency. Finally, the theoretical predictions from the method are validated using experimental observations for several structural members.}, journal={COMPOSITES PART B-ENGINEERING}, author={Astaneh, Ali Vaziri and Guddati, Murthy N.}, year={2017}, month={Dec}, pages={200–216} }
@article{eslaminia_guddati_2016, title={A double-sweeping preconditioner for the Helmholtz equation}, volume={314}, ISSN={["1090-2716"]}, DOI={10.1016/j.jcp.2016.03.022}, abstractNote={A new preconditioner is developed to increase the efficiency of iterative solution of the Helmholtz equation. The key idea of the proposed preconditioner is to split the domain of interest into smaller subdomains and sequentially approximate the forward and backward components of the solution. The sequential solution is facilitated by approximate interface conditions that ignore the effect of multiple reflections. The efficiency of the proposed method is tested using various 2-D heterogeneous media. We observe that the proposed preconditioner results in good convergence, with number of iterations growing very slowly with increasing frequency. We also note that the mesh size and number of subdomains do not affect the convergence rate. Finally, we find that the overall computational time is much smaller than that of the sweeping preconditioner.}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Eslaminia, Mehran and Guddati, Murthy N.}, year={2016}, month={Jun}, pages={800–823} }
@article{astaneh_guddati_2016, title={A two-level domain decomposition method with accurate interface conditions for the Helmholtz problem}, volume={107}, ISSN={["1097-0207"]}, DOI={10.1002/nme.5164}, abstractNote={Summary A new and efficient two‐level, non‐overlapping domain decomposition (DD) method is developed for the Helmholtz equation in the two Lagrange multiplier framework. The transmission conditions are designed by utilizing perfectly matched discrete layers (PMDLs), which are a more accurate representation of the exterior Dirichlet‐to‐Neumann map than the polynomial approximations used in the optimized Schwarz method. Another important ingredient affecting the convergence of a DD method, namely, the coarse space augmentation, is also revisited. Specifically, the widely successful approach based on plane waves is modified to that based on interface waves, defined directly on the subdomain boundaries, hence ensuring linear independence and facilitating the estimation of the optimal size for the coarse problem. The effectiveness of both PMDL‐based transmission conditions and interface‐wave‐based coarse space augmentation is illustrated with an array of numerical experiments that include comprehensive scalability studies with respect to frequency, mesh size and the number of subdomains. Copyright © 2015 John Wiley & Sons, Ltd.}, number={1}, journal={INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING}, author={Astaneh, Ali Vaziri and Guddati, Murthy N.}, year={2016}, month={Jul}, pages={74–90} }
@article{dehghan banadaki_guddati_kim_2016, title={An algorithm for virtual fabrication of air voids in asphalt concrete}, volume={17}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2014.979822}, abstractNote={Motivated by the virtual testing of asphalt concrete, the North Carolina State University research team has developed an algorithm to computationally generate air voids. After examining the X-ray tomographic images of real asphalt concrete microstructure, we concluded that the air void's shape and size are affected primarily by the surrounding local aggregate structure. Building on this observation, we developed an algorithm to generate random but representative air void configurations inside a given microstructure. By applying the algorithm to scanned aggregate structures, we show that the generated air voids not only look visually similar to actual air voids, but also are effective in capturing modulus reduction. The algorithm is included in a virtual aggregate structure generation framework, resulting in a streamlined virtual fabrication procedure for asphalt concrete that can qualitatively capture the effects of accelerated degradation due to the presence of air voids.}, number={3}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Dehghan Banadaki, Arash and Guddati, Murthy N. and Kim, Y. Richard}, year={2016}, month={Mar}, pages={225–232} }
@article{astaneh_guddati_2016, title={Efficient computation of dispersion curves for multilayered waveguides and half-spaces}, volume={300}, ISSN={["1879-2138"]}, DOI={10.1016/j.cma.2015.11.019}, abstractNote={Motivated by the need to compute dispersion curves for layered media in the contexts of geophysical inversion and nondestructive testing , a novel discretization approach, termed complex-length finite element method (CFEM), is developed and shown to be more efficient than the existing finite element approaches. The new approach is exponentially convergent based on two key features: unconventional stretching of the mesh into complex space and midpoint integration for evaluating the contribution matrices. For modeling the layered half-spaces of infinite depth, we couple CFEM with the method of perfectly matched discrete layers (PMDL) to minimize the errors due to mesh truncation. A number of numerical examples are used to investigate the efficiency of the proposed methods. It is shown that the suggested combination of CFEM and PMDL drastically reduces the number of elements, while requiring minor modifications to the existing finite element codes. It is concluded that the methods’ exponential convergence and sparse computation associated with linear finite elements , result in significant reduction in the overall computational cost. • Exponentially convergent semi-discretization is proposed for multilayered waveguides. • Midpoint integration with linear finite elements is key to exponential convergence. • Finite layers are discretized using a mesh stretched into complex plane. • Half-space is modeled using an optimally graded mesh. • Implementation requires minimal modification to existing FE-based codes.}, journal={COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING}, author={Astaneh, Ali Vaziri and Guddati, Murthy N.}, year={2016}, month={Mar}, pages={27–46} }
@article{guddati_druskin_astaneh_2016, title={Exponential convergence through linear finite element discretization of stratified subdomains}, volume={322}, ISSN={["1090-2716"]}, DOI={10.1016/j.jcp.2016.06.045}, abstractNote={Motivated by problems where the response is needed at select localized regions in a large computational domain, we devise a novel finite element discretization that results in exponential convergence at pre-selected points. The key features of the discretization are (a) use of midpoint integration to evaluate the contribution matrices, and (b) an unconventional mapping of the mesh into complex space. Named complex-length finite element method (CFEM), the technique is linked to Padé approximants that provide exponential convergence of the Dirichlet-to-Neumann maps and thus the solution at specified points in the domain. Exponential convergence facilitates drastic reduction in the number of elements. This, combined with sparse computation associated with linear finite elements, results in significant reduction in the computational cost. The paper presents the basic ideas of the method as well as illustration of its effectiveness for a variety of problems involving Laplace, Helmholtz and elastodynamics equations.}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Guddati, Murthy N. and Druskin, Vladimir and Astaneh, Ali Vaziri}, year={2016}, month={Oct}, pages={429–447} }
@article{eslaminia_guddati_2016, title={Fourier-finite element analysis of pavements under moving vehicular loading}, volume={17}, ISSN={["1477-268X"]}, DOI={10.1080/10298436.2015.1007237}, abstractNote={With the goal of predicting progressive pavement distress (damage and rutting) under millions of cycles of moving vehicular loading, an efficient analysis framework is developed by combining the ideas of Fourier transform, finite element discretisation and time-scale separation. Using the simple observation of time-scale separation between evolution of pavement damage/rutting, temperature variation and traffic load variation, the analysis under millions of cycles is reduced to a few hundred analyses of stress and strain evolution under a single cycle of moving load. A new method called Fourier-finite element (FFE) method is proposed for each independent stress analysis. Essentially, Fourier analysis is used to eliminate the time dimension as well as the spatial dimension in the direction of traffic, reducing the problem to a set of two-dimensional problems, which are in turn solved using the finite element method (FEM). The FFE method is more efficient than direct three-dimensional (3D) FEM by orders of magnitude, but captures the 3D effects in an accurate manner. The FFE stress analysis technique is combined with time-scale separation-based ideas to develop a pavement performance modelling framework. A 20-year pavement simulation is presented to illustrate the efficiency of the proposed framework.}, number={7}, journal={INTERNATIONAL JOURNAL OF PAVEMENT ENGINEERING}, author={Eslaminia, Mehran and Guddati, Murthy N.}, year={2016}, month={Aug}, pages={602–614} }
@article{astaneh_guddati_2016, title={Improved inversion algorithms for near-surface characterization}, volume={206}, ISSN={["1365-246X"]}, DOI={10.1093/gji/ggw192}, abstractNote={Near-surface geophysical imaging is often performed by generating surface waves, and estimating the subsurface properties through inversion, that is, iteratively matching experimentally observed dispersion curves with predicted curves from a layered half-space model of the subsurface. Key to the effectiveness of inversion is the efficiency and accuracy of computing the dispersion curves and their derivatives. This paper presents improved methodologies for both dispersion curve and derivative computation. First, it is shown that the dispersion curves can be computed more efficiently by combining an unconventional complex-length finite element method (CFEM) to model the finite depth layers, with perfectly matched discrete layers (PMDL) to model the unbounded half-space. Second, based on analytical derivatives for theoretical dispersion curves, an approximate derivative is derived for the so-called effective dispersion curve for realistic geophysical surface response data. The new derivative computation has a smoothing effect on the computation of derivatives, in comparison with traditional finite difference (FD) approach, and results in faster convergence. In addition, while the computational cost of FD differentiation is proportional to the number of model parameters, the new differentiation formula has a computational cost that is almost independent of the number of model parameters. At the end, as confirmed by synthetic and real-life imaging examples, the combination of CFEM + PMDL for dispersion calculation and the new differentiation formula results in more accurate estimates of the subsurface characteristics than the traditional methods, at a small fraction of computational effort.}, number={2}, journal={GEOPHYSICAL JOURNAL INTERNATIONAL}, author={Astaneh, Ali Vaziri and Guddati, Murthy N.}, year={2016}, month={Aug}, pages={1410–1423} }
@inproceedings{urban_astaneh_aquino_greenleaf_guddati_2016, title={Measured wave dispersion in tubes excited with acoustic radiation force matches theoretical guided wave dispersion}, DOI={10.1109/ultsym.2016.7728821}, abstractNote={Acoustic radiation force (ARF) has been used to generate shear waves in many different tissues for the purpose of quantifying material properties of those tissues. This method has also been applied to arteries, but care must be taken in this application because waves produced in the arterial wall are guided waves. To obtain accurate measurements of mechanical properties of arteries, guided wave inversion can be used, where experimental wave dispersion is iteratively matched with theoretical dispersion curves. In this paper we study wave propagation in three sets of rubber tubes with different mechanical properties, and compare their measured and theoretical dispersion curves. Three sets of tubes were made with outer diameters of 8 mm and wall thicknesses of 1 mm to mimic an adult carotid artery. A different rubber mixture was used for each set of tubes, VytaFlex 10, VytaFlex20, and ReoFlex 30. Reference samples were also poured for testing with hyper-frequency viscoelastic spectroscopy (HFVS) instrument for measurement of the material complex modulus. Wave propagation measurements were made with a Verasonics system and linear array with water inside and surrounding the tubes. Acoustic radiation force was used to generate the waves with a 200 µs push at 4.1 MHz and plane wave imaging at a frame rate of 14.9 kHz was used for measuring the propagating waves. A two-dimensional Fourier transform method was used to extract the dispersion curves from the measured particle velocity. Theoretical dispersion curves for flexural modes with circumferential wavenumber n = 1, 2, 3 were calculated from the material properties measured with HFVS for comparison with the ultrasound-based results. The measured dispersion curve matches well with theoretical results. However, the match is not with a single theoretical dispersion curve, but with different theoretical curves at different frequencies. This new approach of matching with multiple theoretical curves can be used for better understanding of wave propagation in arterial walls and improved characterization of their mechanical properties.}, booktitle={2016 ieee international ultrasonics symposium (ius)}, author={Urban, M. W. and Astaneh, A. V. and Aquino, W. and Greenleaf, J. F. and Guddati, M. N.}, year={2016} }
@article{safavizadeh_wargo_guddati_kim_2015, title={Investigating reflective cracking mechanisms in grid-reinforced asphalt specimens use of four-point bending notched beam fatigue tests and digital image correlation}, number={2507}, journal={Transportation Research Record}, author={Safavizadeh, S. A. and Wargo, A. and Guddati, M. and Kim, Y. R.}, year={2015}, pages={29–38} }
@article{karshenas_cho_tayebali_guddati_kim_2014, title={Importance of Normal Confinement to Shear Bond Failure of Interface in Multi layer Asphalt Pavements}, ISSN={["2169-4052"]}, DOI={10.3141/2456-17}, abstractNote={Several direct shear test devices are used to evaluate the shear bond strength of tack coat materials in interlayer bonding in asphalt pavements. Some devices have the capability of evaluating strength in direct shear with normal confinement, whereas other devices do not have that capability or use passive confinement to evaluate the interlayer bond strength. The literature indicates that interlayer bond strength increases with the application of normal confinement. However, the question remains as to the level of normal confinement, if any, that should be used in direct shear testing to evaluate the interlayer bond strength for specification acceptance or design. This study presents a methodology to interpret laboratory bond strength test results in relation to the state of stress at the layer interface in a representative pavement section. The results confirm the importance of normal confinement for shear bond strength evaluation and provide guidance for the selection of the appropriate level of normal ...}, number={2456}, journal={TRANSPORTATION RESEARCH RECORD}, author={Karshenas, Afshin and Cho, Seong-Hwan and Tayebali, Akhtarhusein A. and Guddati, Murthy N. and Kim, Y. Richard}, year={2014}, pages={170–177} }
@article{subramanian_guddati_kim_2013, title={A viscoplastic model for rate-dependent hardening for asphalt concrete in compression}, volume={59}, ISSN={["1872-7743"]}, DOI={10.1016/j.mechmat.2012.10.003}, abstractNote={This paper presents a new type of viscoplastic model based on viscoelastic convolution integrals for explaining the behavior of asphalt concrete in compression under repeated loading. Triaxial compression cyclic tests carried out for long rest periods, with different loading times and two different pulse shapes, square and haversine, were used in developing and validating the model. These tests demonstrate that the evolution of permanent deformation depends on load history. This history-dependent behavior is not captured accurately by some of the existing Perzyna-type viscoplastic models in which permanent deformation evolution depends on the current values of stress and viscoplastic strain. Therefore, in this study, viscoelastic-like convolution integrals were used in the model to capture the effect of history. The proposed model is applicable to compressive creep and recovery experiments at 54 °C with (1) several hundreds of cycles of loading including the secondary creep region, (2) haversine loading shapes at three different peak deviatoric stress levels, 620 kPa, 827 kPa, and 1034 kPa, and square loading shapes at 827 kPa peak deviatoric stress, and (3) long rest periods that allow complete viscoelastic recovery.}, journal={MECHANICS OF MATERIALS}, author={Subramanian, Vijay and Guddati, Murthy N. and Kim, Y. Richard}, year={2013}, month={Apr}, pages={142–159} }
@article{zhang_sabouri_guddati_kim_2013, title={Development of a failure criterion for asphalt mixtures under fatigue loading}, volume={14}, ISSN={["2164-7402"]}, DOI={10.1080/14680629.2013.812843}, abstractNote={The failure criterion defines the applicable region associated with the continuum damage model and is important in characterising the service life of asphalt mixtures. A proper failure criterion should consistently predict the failure of the material that reaches macro-fracture. A previously developed criterion that uses the viscoelastic continuum damage (VECD) model exhibits high variability and is considered to be inefficient because it requires calibration tests at different temperatures. In this paper, a new concept that involves released pseudo strain energy is introduced. This released pseudo strain energy concept focuses on the dissipated energy that is related to stiffness reduction only and is fully compatible and predictable using the VECD model. A characteristic relationship is found between the stable rate of pseudo energy release during testing and the final fatigue life of the same mixture, independent of strain amplitude and temperature. Based on these observations, a new failure criterion ...}, journal={ROAD MATERIALS AND PAVEMENT DESIGN}, author={Zhang, Jun and Sabouri, Mohammadreza and Guddati, Murthy N. and Kim, Y. Richard}, year={2013}, month={Aug}, pages={1–15} }
@inproceedings{zhang_sabouri_guddati_kim_2013, title={Development of a failure criterion for asphalt mixtures under fatigue loading}, volume={82}, booktitle={Asphalt paving technology 2013, vol 82}, author={Zhang, J. and Sabouri, M. and Guddati, M. N. and Kim, Y. R.}, year={2013}, pages={1–22} }
@inbook{guddati_thirunavukkarasu_2013, title={Improving the Convergence of Schwarz Methods for Helmholtz Equation}, ISBN={9783642352744 9783642352751}, ISSN={1439-7358}, url={http://dx.doi.org/10.1007/978-3-642-35275-1_22}, DOI={10.1007/978-3-642-35275-1_22}, abstractNote={Various domain decompositionmethods have been proposed for the Helmholtz equation, with the Optimized Schwarz Method (OSM) being one of them (see e.g. [7] for a review of various domain decomposition methods, and [3] for the details of OSM). In this paper, we focus on OSM, which is based on the idea of using approximated half-space Dirichlet-to-Neumann (DtN) maps to improve the convergence of the Schwarz methods; current version of the OSM is based on polynomial approximation of the half-space DtN map. See [8] for a review of various approaches to approximating the half-space DtN map (more commonly referred to as Absorbing Boundary Conditions (ABCs)).}, booktitle={Lecture Notes in Computational Science and Engineering}, publisher={Springer Berlin Heidelberg}, author={Guddati, Murthy N and Thirunavukkarasu, Senganal}, year={2013}, pages={199–206} }
@article{thirunavukkarasu_guddati_2012, title={A domain decomposition method for concurrent coupling of multiscale models}, volume={92}, ISSN={0029-5981}, url={http://dx.doi.org/10.1002/nme.4362}, DOI={10.1002/nme.4362}, abstractNote={Motivated by atomistic-to-continuum coupling, we consider a fine-scale problem defined on a small region embedded in a much larger coarse-scale domain and propose an efficient solution technique on the basis of the domain decomposition framework. Specifically, we develop a nonoverlapping Schwarz method with two important features: (i) the use of an efficient approximation of the Dirichlet-to-Neumann map for the interface conditions; and (ii) the utilization of the inherent scale separation in the solution. The paper includes a detailed formulation of the proposed interface condition, along with the illustration of its effectiveness by using simple but representative numerical experiments. Copyright © 2012 John Wiley & Sons, Ltd.}, number={11}, journal={International Journal for Numerical Methods in Engineering}, publisher={Wiley}, author={Thirunavukkarasu, Senganal and Guddati, Murthy N.}, year={2012}, month={Jun}, pages={918–939} }
@inbook{eslaminia_thirunavukkarasu_guddati_kim_2012, title={Accelerated Pavement Performance Modeling Using Layered Viscoelastic Analysis}, ISBN={9789400745650 9789400745667}, url={http://dx.doi.org/10.1007/978-94-007-4566-7_48}, DOI={10.1007/978-94-007-4566-7_48}, abstractNote={An efficient pavement performance analysis framework is developed by combining the ideas of time-scale separation and Fourier transform-based layered analysis. First, utilizing the vast difference in time scales associated with temperature and traffic load variations, the number of stress analysis runs are reduced from several million to a few dozen. Second, the computational cost of the pavement stress analysis is reduced significantly by using Fourier transform-based analysis. The resulting pavement performance prediction tool, named the layered viscoelastic continuum damage (LVECD) program, can capture the effects of viscoelasticity, temperature (thermal stresses and changes in viscoelastic properties) and the moving nature of the traffic load. The efficiency of the LVECD program is shown through 20-year pavement simulations.}, booktitle={7th RILEM International Conference on Cracking in Pavements}, publisher={Springer Netherlands}, author={Eslaminia, Mehran and Thirunavukkarasu, Senganal and Guddati, Murthy N. and Kim, Y. Richard}, year={2012}, pages={497–506} }
@article{savadatti_guddati_2012, title={Accurate absorbing boundary conditions for anisotropic elastic media. Part 1: Elliptic anisotropy}, volume={231}, ISSN={["1090-2716"]}, DOI={10.1016/j.jcp.2012.05.033}, abstractNote={With the ultimate goal of devising effective absorbing boundary conditions (ABCs) for heterogeneous anisotropic elastic media, we investigate the accuracy aspects of local ABCs designed for tilted elliptic anisotropy in the frequency domain (time-harmonic case). Such media support both anti-plane and in-plane wavemodes with opposing signs of phase and group velocities (cpxcgx<0) that have long posed a significant challenge to the design of accurate (and stable) local ABCs. By first considering the simpler case of scalar anti-plane waves, we show that it is possible to overcome the challenges posed by cpxcgx<0 by simply utilizing the inevitable reflections occurring at the truncation boundaries. This understanding helps us to explain the ability of a recently developed local ABC - the perfectly matched discrete layer (PMDL) - to handle the challenges posed by cpxcgx<0without the need of intervening space-time transformations. PMDL is a simple variant of perfectly matched layers (PML) that is also equivalent to rational approximation-based local ABCs (rational ABCs); it inherits the straightforward approximation properties of rational ABCs along with the versatility of PML. The approximation properties of PMDL quantified through its reflection matrix is used to derive simple bounds on the PMDL parameters necessary for the accurate absorption of all outgoing anti-plane and in-plane wavemodes - including those with cpxcgx<0. Beyond the previously derived bound on the real parameters of PMDL sufficient for the absorption of outgoing propagating anti-plane wavemodes, we present bounds on the complex parameters of PMDL necessary for the absorption of outgoing propagating and evanescent wavemodes for both anti-plane and coupled in-plane pressure and shear waves. The validity of this work is demonstrated through a series of numerical experiments.}, number={22}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Savadatti, Siddharth and Guddati, Murthy N.}, year={2012}, month={Sep}, pages={7584–7607} }
@article{savadatti_guddati_2012, title={Accurate absorbing boundary conditions for anisotropic elastic media. Part 2: Untilted non-elliptic anisotropy}, volume={231}, ISSN={["1090-2716"]}, DOI={10.1016/j.jcp.2012.05.039}, abstractNote={With the ultimate goal of devising effective absorbing boundary conditions (ABCs) for general elastic media, we investigate the accuracy aspects of local ABCs designed for untilted non-elliptic anisotropy in the frequency domain (time-harmonic analysis). While simple space-time transformations are available to treat the wavemodes with opposing phase and group velocities present in elliptic anisotropic media, no such transformations are known to exist for the case of non-elliptic anisotropy. In this paper, we use the concept of layer groupings along with an unconventional stretching of the finite element mesh to guarantee the accuracy of local ABCs designed to treat all propagating wavemodes, even those with opposing phase and group velocities. The local ABC used here is the perfectly matched discrete layer (PMDL) which is a simple variant of perfectly matched layers (PMLs) that is also equivalent to rational approximation-based local ABCs (rational ABCs); it inherits the straightforward approximation properties of rational ABCs along with the versatility of PML. The approximation properties of PMDL quantified through its reflection matrix allow us to (a) show that it is impossible to design an accurate PMDL with wavenumber-independent parameters, (b) theoretically demonstrate the ability of wavenumber-dependent parameters to ensure accuracy, and finally (c) design a practical though unconventional stretching of the finite element PMDL mesh that facilitates the implementation of wavenumber-dependent parameters. The validity of this work is demonstrated through a series of numerical experiments.}, number={22}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Savadatti, Siddharth and Guddati, Murthy N.}, year={2012}, month={Sep}, pages={7608–7625} }
@article{ulker_rahman_guddati_2012, title={Breaking wave-induced response and instability of seabed around caisson breakwater}, volume={36}, ISSN={0363-9061}, url={http://dx.doi.org/10.1002/nag.1073}, DOI={10.1002/nag.1073}, abstractNote={Breaking-wave-induced dynamic response and instability of seabed around a caisson breakwater are investigated. A seabed-rubble-breakwater system is modeled using finite elements. The impact response of the porous seabed and rubble foundation is assumed to be governed by the coupled Biot equations, and three possible formulations are considered with respect to the inclusion of inertial terms. The response is presented in terms of shear stress and pore pressure distributions at three locations underneath the breakwater. The effect of seabed and wave parameters and the inertial terms on the impact response is investigated through parametric studies. Analyses show that usually partly dynamic formulation yields the largest response amplitudes as compared to the fully dynamic formulation, which is the most complete form. The instability of seabed and rubble mound as a result of instantaneous liquefaction is also studied. Breaking wave-induced pressures in some cases are found to cause liquefaction in the rubble and the seabed. The effect of some parameters on the instability is found to be significant. Copyright © 2011 John Wiley & Sons, Ltd.}, number={3}, journal={International Journal for Numerical and Analytical Methods in Geomechanics}, publisher={Wiley}, author={Ulker, M. B. C. and Rahman, M. S. and Guddati, M. N.}, year={2012}, month={Feb}, pages={362–390} }
@article{guddati_savadatti_2012, title={Efficient and accurate domain-truncation techniques for seismic soil-structure interaction}, volume={3}, ISSN={["2092-7622"]}, DOI={10.12989/eas.2012.3.3_4.563}, abstractNote={We modify the formulation of a recently developed absorbing boundary condition (ABC), the perfectly matched discrete layers (PMDL), to incorporate the excitation coming from the exterior such as earthquake waves. The modified formulation indicates that the effect of the exterior excitation can be incorporated into PMDL ABCs (traditionally designed to treat only interior excitation) simply by applying appropriate forces on the nodes connected to the first PMDL layer. Numerical results are presented to clearly illustrate the effectiveness of the proposed method.}, number={3-4}, journal={EARTHQUAKES AND STRUCTURES}, author={Guddati, Murthy and Savadatti, Siddharth}, year={2012}, pages={563–580} }
@article{choi_subramanian_guddati_kim_2012, title={Incremental Model for Prediction of Permanent Deformation of Asphalt Concrete in Compression}, ISSN={["2169-4052"]}, DOI={10.3141/2296-03}, abstractNote={Permanent deformation (rutting) is one of the major distresses in asphalt pavement. To predict permanent deformation of asphalt concrete, repeated creep and recovery (or flow number) tests are typically used in the laboratory. However, models for the prediction of permanent deformation that incorporate flow number testing cannot represent the primary region because they concentrate on the secondary region. A new simple permanent deformation model called the incremental model is proposed. The proposed model is derived from the rate model, which is a rigorous mechanical model based on viscoplasticity. Four parameters of the new model provide an understanding of the permanent deformation. Parameter A is related to the initial permanent strain level, and Parameter C provides information about where the secondary region starts. That is, Parameters A and C govern the primary region, where α (alpha) is the slope of the secondary region, and B represents the permanent deformation level of the secondary region. Two mixtures are selected to investigate the deformation characteristics, and repeated creep and recovery tests are performed in compression. The incremental model is verified by applying it to various loading conditions for two mixtures. Furthermore, it is found that α is the material constant and the time-temperature superposition principle is applicable to each parameter. All parameters, except a, depend on both deviatoric stress and reduced load time, which is the product of load time and temperature. The incremental model describes ways to apply the time-temperature supposition principle to permanent deformation.}, number={2296}, journal={TRANSPORTATION RESEARCH RECORD}, author={Choi, Yeong-Tae and Subramanian, Vijay and Guddati, Murthy N. and Kim, Y. Richard}, year={2012}, pages={24–35} }
@inbook{banadaki_guddati_kim_little_2012, title={Multiscale Micromechanical Lattice Modeling of Cracking in Asphalt Concrete}, ISBN={9789400745650 9789400745667}, url={http://dx.doi.org/10.1007/978-94-007-4566-7_47}, DOI={10.1007/978-94-007-4566-7_47}, abstractNote={A multiscale micromechanical lattice modeling technique is proposed from amongst several computational methods for predicting the performance of hot mix asphalt (HMA) under service loads. Although the lattice model has shown promise, many important details need to be addressed to ensure realistic predictions. This paper presents enhancements to the original model that have been developed over the past two years. These revisions are geared towards capturing the material behavior more accurately and efficiently than was possible with the original lattice model. Among the new enhancements that are presented in this paper are the incorporation of viscoelastic fracture with the help of the work potential-based viscoelastic continuum damage model, computationally efficient simulations under a large number of load cycles, and the incorporation of air voids to capture the reduction in stiffness and strength of the material. Efficiency of the model is improved further by incorporating novel algorithms.}, booktitle={7th RILEM International Conference on Cracking in Pavements}, publisher={Springer Netherlands}, author={Banadaki, Arash Dehghan and Guddati, Murthy N. and Kim, Y. Richard and Little, Dallas N.}, year={2012}, pages={487–496} }
@inbook{baek_thirunavukkarasu_underwood_guddati_kim_2012, title={Top-Down Cracking Prediction Tool for Hot Mix Asphalt Pavements}, ISBN={9789400745650 9789400745667}, url={http://dx.doi.org/10.1007/978-94-007-4566-7_45}, DOI={10.1007/978-94-007-4566-7_45}, booktitle={7th RILEM International Conference on Cracking in Pavements}, publisher={Springer Netherlands}, author={Baek, Cheolmin and Thirunavukkarasu, Senganal and Underwood, B. Shane and Guddati, Murthy N. and Kim, Y. Richard}, year={2012}, pages={465–474} }
@article{thirunavukkarasu_guddati_2011, title={Absorbing boundary conditions for time harmonic wave propagation in discretized domains}, volume={200}, ISSN={["1879-2138"]}, DOI={10.1016/j.cma.2011.04.021}, abstractNote={While many successful absorbing boundary conditions (ABCs) are developed to simulate wave propagation into unbounded domains, most of them ignore the effect of interior discretization and result in spurious reflections at the artificial boundary. We tackle this problem by developing ABCs directly for the discretized wave equation. Specifically, we show that the discrete system (mesh) can be stretched in a non-trivial way to preserve the discrete impedance at the interface. Similar to the perfectly matched layers (PML) for continuous wave equation, the stretch is designed to introduce dissipation in the exterior, resulting in a PML-type ABC for discrete media. The paper includes detailed formulation of the new discrete ABC, along with the illustration of its effectiveness over continuous ABCs with the help of error analysis and numerical experiments. For time-harmonic problems, the improvement over continuous ABCs is achieved without any computational overhead, leading to the conclusion that the discrete ABCs should be used in lieu of continuous ABCs.}, number={33-36}, journal={COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING}, author={Thirunavukkarasu, Senganal and Guddati, Murthy N.}, year={2011}, pages={2483–2497} }
@article{savadatti_guddati_2010, title={A finite element alternative to infinite elements}, volume={199}, ISSN={["1879-2138"]}, DOI={10.1016/j.cma.2010.03.018}, abstractNote={In this paper, a simple idea based on midpoint integration rule is utilized to solve a particular class of mechanics problems; namely static problems defined on unbounded domains where the solution is required to be accurate only in an interior (and not in the far field). By developing a finite element mesh that approximates the stiffness of an unbounded domain directly (without approximating the far-field displacement profile first), the current formulation provides a superior alternative to infinite elements (IEs) that have long been used to incorporate unbounded domains into the finite element method (FEM). In contrast to most IEs, the present formulation (a) requires no new shape functions or special integration rules, (b) is proved to be both accurate and efficient, and (c) is versatile enough to handle a large variety of domains including those with anisotropic, stratified media and convex polygonal corners. In addition to this, the proposed model leads to the derivation of a simple error expression that provides an explicit correlation between the mesh parameters and the accuracy achieved. This error expression can be used to calculate the accuracy of a given mesh a-priori. This in-turn, allows one to generate the most efficient mesh capable of achieving a desired accuracy by solving a mesh optimization problem. We formulate such an optimization problem, solve it and use the results to develop a practical mesh generation methodology. This methodology does not require any additional computation on the part of the user, and can hence be used in practical situations to quickly generate an efficient and near optimal finite element mesh that models an unbounded domain to the required accuracy. Numerical examples involving practical problems are presented at the end to illustrate the effectiveness of this method.}, number={33-36}, journal={COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING}, author={Savadatti, Siddharth and Guddati, Murthy N.}, year={2010}, pages={2204–2223} }
@article{savadatti_guddati_2010, title={Absorbing boundary conditions for scalar waves in anisotropic media. Part 1: Time harmonic modeling}, volume={229}, ISSN={["1090-2716"]}, DOI={10.1016/j.jcp.2010.05.018}, abstractNote={With the ultimate goal of devising effective absorbing boundary conditions (ABCs) for general anisotropic media, we investigate the accuracy aspects of local ABCs designed for the scalar anisotropic wave equation in the frequency domain (time harmonic case). The ABC analyzed in this paper is the perfectly matched discrete layers (PMDL). PMDL is a simple variant of perfectly matched layers (PML) and is equivalent to rational approximation-based local ABCs. Specifically, we derive a sufficient condition for PMDL to accurately absorb wave modes with outgoing group velocities and this condition turns out to be a simple bound on the PMDL parameters. The reflection coefficient derived in this paper clearly reveals that the PMDL absorption is based on group velocities, and not phase velocities, and hence a PMDL can be designed to correctly identify and accurately absorb all outgoing wave modes (even those with opposing signs of phase and group velocities). The validity of the sufficient condition is demonstrated through a series of frequency domain simulations. In part 2 of this paper [S. Savadatti, M.N. Guddati, Absorbing boundary conditions for scalar waves in anisotropic media. Part 2: Time-dependent modeling, J. Comput. Phys. (2010), doi:10.1016/j.jcp.2010.05.017], the accuracy condition presented here is shown to govern both the well-posedness and accuracy aspects of PMDL designed for transient (time-dependent) modeling of scalar waves in anisotropic media.}, number={19}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Savadatti, Siddharth and Guddati, Murthy N.}, year={2010}, month={Sep}, pages={6696–6714} }
@article{savadatti_guddati_2010, title={Absorbing boundary conditions for scalar waves in anisotropic media. Part 2: Time-dependent modeling}, volume={229}, ISSN={["1090-2716"]}, DOI={10.1016/j.jcp.2010.05.017}, abstractNote={With the ultimate goal of devising effective absorbing boundary conditions (ABCs) for general anisotropic media, we investigate the well-posedness and accuracy aspects of local ABCs designed for the transient modeling of the scalar anisotropic wave equation. The ABC analyzed in this paper is the perfectly matched discrete layers (PMDL), a simple variant of perfectly matched layers (PML) that is also equivalent to rational approximation based ABCs. Specifically, we derive the necessary and sufficient condition for the well-posedness of the initial boundary value problem (IBVP) obtained by coupling an interior and a PMDL ABC. The derivation of the reflection coefficient presented in a companion paper (S. Savadatti, M.N. Guddati, J. Comput. Phys., 2010, doi:10.1016/j.jcp.2010.05.018) has shown that PMDL can correctly identify and accurately absorb outgoing waves with opposing signs of group and phase velocities provided the PMDL layer lengths satisfy a certain bound. Utilizing the well-posedness theory developed by Kreiss for general hyperbolic IBVPs, and the well-posedness conditions for ABCs derived by Trefethen and Halpern for isotropic acoustics, we show that this bound on layer lengths also ensures well-posedness. The time discretized form of PMDL is also shown to be theoretically stable and some instability related to finite precision arithmetic is discussed.}, number={18}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Savadatti, Siddharth and Guddati, Murthy N.}, year={2010}, month={Sep}, pages={6644–6662} }
@article{underwood_kim_guddati_2010, title={Improved calculation method of damage parameter in viscoelastic continuum damage model}, volume={11}, ISSN={1029-8436 1477-268X}, url={http://dx.doi.org/10.1080/10298430903398088}, DOI={10.1080/10298430903398088}, abstractNote={Modelling the performance of asphalt concrete using continuum damage theories is an approach that has gained international attention in recent years. These types of models are advantageous because they ignore many of the complicated physical interactions at the microscale level and instead characterise a material using macroscale observations. One such model, the viscoelastic continuum damage model, is used in this study to examine the fatigue performance of asphalt concrete mixtures. A mathematically rigorous exploration is undertaken to specialise the model for easy prediction and characterisation using cyclic fatigue tests on cylindrical specimens. This process reveals that certain theoretical shortcomings are evident in other similar models and corrects them with a newly developed model. The resulting model is capable of capturing the underlying material property, i.e. the damage characteristic curve, which is responsible for the performance of controlled stress, controlled crosshead strain and consta...}, number={6}, journal={International Journal of Pavement Engineering}, publisher={Informa UK Limited}, author={Underwood, B. Shane and Kim, Y. Richard and Guddati, Murthy N.}, year={2010}, month={Dec}, pages={459–476} }
@inproceedings{feng_zhang_guddati_kim_2010, title={The Development and Evaluation of a Virtual Testing Procedure for the Prediction of the Cracking Performance of Hot Mix Asphalt}, ISBN={9780784411292 9780784476086}, url={http://dx.doi.org/10.1061/41129(385)13}, DOI={10.1061/41129(385)13}, abstractNote={Motivated by the ultimate goal of linking the binder and aggregate properties to the cracking performance of asphalt concrete, a multiscale virtual testing methodology is developed in this paper. The main components of the proposed methodology are: (a) a virtual fabrication technique that generates the microstructure of asphalt concrete specimens without the need for physical fabrication, (b) a lattice modeling approach that simulates the micromechanical behavior of cracked asphalt concrete specimens, and (c) a multiscale methodology that incorporates the effects of aggregates of widely varying sizes. The resulting methodology is calibrated to simulate the load-deformation behavior of real uniaxial tension test specimens. A comparison of the predicted response against the measured response indicates that the proposed method shows promise, but requires further work aimed at the fundamental understanding of the micromechanical behavior.}, booktitle={Pavements and Materials}, publisher={American Society of Civil Engineers}, author={Feng, Zhen and Zhang, Pu and Guddati, Murthy N. and Kim, Y. Richard}, year={2010}, month={Aug} }
@article{ulker_rahman_guddati_2010, title={Wave-induced dynamic response and instability of seabed around caisson breakwater}, volume={37}, ISSN={["0029-8018"]}, DOI={10.1016/j.oceaneng.2010.09.004}, abstractNote={In this study, standing wave-induced dynamic response and instability of seabed around a caisson breakwater are investigated. A seabed-rubble-caisson breakwater system is modeled using finite elements. The dynamic response of the porous seabed-rubble foundation is assumed to be governed by the Biot’s equations of coupled flow and deformation. Three possible formulations (fully dynamic, partly dynamic and quasi-static) are considered with respect to the inclusion of inertial terms associated with the motion of fluid and solids. The response is presented in terms of stress and pore pressure distributions at three locations underneath the breakwater. The instability of seabed and rubble mound due to instantaneous liquefaction is also studied. The effects of seabed and wave parameters and the effect of inertial terms on the standing wave-induced dynamic response and instability of the system are investigated through a set of parametric studies. Analyses show that quasi-static and partly dynamic formulations yield similar results while the fully dynamic formulation provides different response. The results from different formulations suggest the use of all inertial terms (fully dynamic formulation), providing the most complete solution and the least conservative response.}, number={17-18}, journal={OCEAN ENGINEERING}, author={Ulker, M. B. C. and Rahman, M. S. and Guddati, M. N.}, year={2010}, month={Dec}, pages={1522–1545} }
@article{guddati_thirunavukkarasu_2009, title={Phonon absorbing boundary conditions for molecular dynamics}, volume={228}, ISSN={["1090-2716"]}, DOI={10.1016/j.jcp.2009.07.033}, abstractNote={With the goal of minimizing the domain size for molecular dynamics (MD) simulations, we develop a new class of absorbing boundary conditions (ABCs) that mimic the phonon absorption properties of an unbounded exterior. The proposed MD-ABCs are extensions of perfectly matched discrete layers (PMDLs), originally developed as an absorbing boundary condition for continuous wave propagation problems. Called MD-PMDL, this extension carefully targets the absorption of phonons, the high frequency waves, whose propagation properties are completely different from continuous waves. This paper presents the derivation of MD-PMDL for general lattice systems, followed by explicit application to one-dimensional and two-dimensional square lattice systems. The accuracy of MD-PMDL for phonon absorption is proven by analyzing reflection coefficients, and demonstrated through numerical experiments. Unlike existing MD-ABCs, MD-PMDL is local in both space and time and thus more efficient. Based on their favorable properties, it is concluded that MD-PMDL could provide a more effective alternative to existing MD-ABCs.}, number={21}, journal={JOURNAL OF COMPUTATIONAL PHYSICS}, author={Guddati, Murthy N. and Thirunavukkarasu, Senganal}, year={2009}, month={Nov}, pages={8112–8134} }
@article{kim_baek_underwood_subramanian_guddati_lee_2008, title={Application of viscoelastic continuum damage model based finite element analysis to predict the fatigue performance of asphalt pavements}, volume={12}, ISSN={1226-7988 1976-3808}, url={http://dx.doi.org/10.1007/s12205-008-0109-x}, DOI={10.1007/s12205-008-0109-x}, number={2}, journal={KSCE Journal of Civil Engineering}, publisher={Springer Science and Business Media LLC}, author={Kim, Y. Richard and Baek, Cheolmin and Underwood, B. Shane and Subramanian, Vijay and Guddati, Murthy N. and Lee, Kwangho}, year={2008}, month={Mar}, pages={109–120} }
@article{heidari_guddati_2007, title={Novel finite-element-based subsurface imaging algorithms}, volume={43}, ISSN={["1872-6925"]}, DOI={10.1016/j.finel.2006.11.007}, abstractNote={Through an unconventional use of the finite-element method, we have developed a new class of wave equation-based subsurface imaging algorithms. These methods, which are based on the recently developed arbitrarily wide-angle wave equations (AWWE) [M.N. Guddati, Arbitrarily wide-angle wave equations for complex media, Comput. Methods Appl. Mech. Eng. 195(1–3), 63–93], employ the finite-element concepts not just to solve, but to derive the governing equations of the imaging problem. The authors have successfully applied the AWWE imaging algorithms to both acoustic and elastic media. These implementations of AWWE imaging algorithms are discussed here, and the role of finite elements in their derivation is depicted. The stability of the AWWE imaging methods is analytically studied, and their accuracy is shown through numerical impulse responses. Finally, the effectiveness of the methods is illustrated using various synthetic problems for both acoustic and elastic media.}, number={5}, journal={FINITE ELEMENTS IN ANALYSIS AND DESIGN}, author={Heidari, A. H. and Guddati, M. N.}, year={2007}, month={Mar}, pages={411–422} }
@article{guddati_heidari_2007, title={Subsurface imaging via fully coupled elastic wavefield extrapolation}, volume={23}, ISSN={["1361-6420"]}, DOI={10.1088/0266-5611/23/1/004}, abstractNote={We develop a new space-domain wavefield extrapolation technique for subsurface imaging in heterogeneous elastic media. Unlike the existing space-domain techniques, which separately propagate pressure and shear waves, the proposed method simulates one-way propagation with strong coupling between the pressure and shear waves, thus resulting in more accurate images. This is achieved by combining downward continuation ideas with the concepts of the recently developed arbitrarily wide-angle wave equations (Guddati M N 2006 Comput. Methods Appl. Mech. Eng. 195 63–93). In this method, one-way propagation is modelled by attaching a virtual halfspace to each depth step, which is represented by special complex-length finite elements. The parameters of the method, namely the lengths of the special finite elements, are chosen such that the wavefield extrapolation is stable and accurate. The accuracy of the proposed method is illustrated by its impulse response, which accurately captures the pressure, shear and head wave fronts. Application to various synthetic imaging problems, in both homogeneous and heterogeneous domains, further confirms the effectiveness of the method.}, number={1}, journal={INVERSE PROBLEMS}, author={Guddati, Murthy N. and Heidari, A. Homayoun}, year={2007}, month={Feb}, pages={73–98} }
@article{guddati_2006, title={Arbitrarily wide-angle wave equations for complex media}, volume={195}, ISSN={["1879-2138"]}, DOI={10.1016/j.cma.2005.01.006}, abstractNote={By combining various ideas related to one-way wave equations (OWWEs), half-space stiffness relation, special finite-element discretization, and complex coordinate stretching, a systematic procedure is developed for deriving a series of highly accurate space-domain versions of OWWEs. The resulting procedure is applicable to complex media where the governing equation (full wave equation) is a second order differential system, making the procedure applicable for general heterogeneous, anisotropic, porous, viscoelastic media. Owing to their high accuracy in representing waves propagating in an arbitrarily wide range of angles, the resulting equations are named Arbitrarily Wide-angle Wave Equations (AWWEs). In order to illustrate the proposed procedure, AWWEs are derived for one-way propagation in acoustic as well as elastic media. While acoustic AWWEs can be considered as modified versions of well-known space-domain OWWEs based on rational approximations of the square root operator, the elastic AWWEs are significantly different from the existing elastic OWWEs. Unlike the existing elastic OWWEs, elastic AWWEs are displacement-based and are applicable to general anisotropic media. Furthermore, AWWEs are simple in their form, and appear amenable to easy numerical implementation.}, number={1-3}, journal={COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING}, author={Guddati, MN}, year={2006}, pages={65–93} }
@article{guddati_lim_2006, title={Continued fraction absorbing boundary conditions for convex polygonal domains}, volume={66}, ISSN={["1097-0207"]}, DOI={10.1002/nme.1574}, abstractNote={Continued fraction absorbing boundary conditions (CFABCs) are highly effective boundary conditions for modelling wave absorption into unbounded domains. They are based on rational approximation of the exact dispersion relationship and were originally developed for straight computational boundaries. In this paper, CFABCs are extended to the more general case of polygonal computational domains. The key to the current development is the surprising link found between the CFABCs and the complex co-ordinate stretching of perfectly matched layers (PMLs). This link facilitates the extension of CFABCs to oblique corners and, thus, to polygonal domains. It is shown that the proposed CFABCs are easy to implement, expected to perform better than PMLs, and are effective for general polygonal computational domains. In addition to the derivation of CFABCs, a novel explicit time-stepping scheme is developed for efficient numerical implementation. Numerical examples presented in the paper illustrate that effective absorption is attained with a negligible increase in the computational cost for the interior domain. Although this paper focuses on wave propagation, its theoretical development can be easily extended to the more general class of problems where the governing differential equation is second order in space with constant coefficients. Copyright © 2005 John Wiley & Sons, Ltd.}, number={6}, journal={INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING}, author={Guddati, Murthy N. and Lim, Keng-Wit}, year={2006}, month={May}, pages={949–977} }
@article{heidari_guddati_2006, title={Highly accurate absorbing boundary conditions for wide-angle wave equations}, volume={71}, ISSN={["1942-2156"]}, DOI={10.1190/1.2192914}, abstractNote={We develop a new class of absorbing boundary conditions (ABCs) to prevent unwanted artifacts and wraparounds associated with aperture truncation in migration/modeling using high-order, one-way wave equations. The fundamental approach behind the proposed development is the efficient discretization of the half-space, beyond the boundary of interest, using midpoint-integrated imaginary finite elements, an idea recently utilized in the development of effective one-way wave equations. The proposed absorbing boundary conditions essentially add absorbing layers at the aperture truncation points. We derive the absorbing boundary conditions, analyze their properties, and develop a stable explicit finite-difference scheme to solve the downward-continuation problem modified by these boundary conditions. With the help of numerical examples, we conclude that with as few as three absorbing layers, i.e., two additional gridpoints, the waves can be absorbed completely, thus preventing associated artifacts.}, number={3}, journal={GEOPHYSICS}, author={Heidari, A. Homayoun and Guddati, Murthy N.}, year={2006}, pages={S85–S97} }
@article{zahid_guddati_2006, title={Padded continued fraction absorbing boundary conditions for dispersive waves}, volume={195}, ISSN={["1879-2138"]}, DOI={10.1016/j.cma.2005.01.023}, abstractNote={Continued fraction absorbing boundary conditions (CFABCs) are new arbitrarily high-order local absorbing boundary conditions that are highly effective in simulating wave propagation in unbounded domains. The current versions of CFABCs are developed for the non-dispersive acoustic wave equation with convex polygonal computational domains. In this paper, the CFABCs are modified through augmentation of special padding elements, and are effective for absorbing evanescent waves occurring in dispersive wave problems while retaining their absorption properties for propagating waves. The padded CFABCs for dispersive wave equations result in fourth order evolution equations, which are solved using an efficient combination of Crank Nicholson method, Newmark time-stepping scheme, and operator splitting ideas. The effectiveness of the padded CFABCs and their implementation is illustrated through numerical examples with varying levels of dispersion.}, number={29-32}, journal={COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING}, author={Zahid, Md. A. and Guddati, Murthy N.}, year={2006}, pages={3797–3819} }
@article{mun_guddati_kim_2006, title={Viscoelastic continuum damage finite element modeling of asphalt pavements for fatigue cracking evaluation}, volume={10}, ISSN={1226-7988 1976-3808}, url={http://dx.doi.org/10.1007/bf02823927}, DOI={10.1007/bf02823927}, number={2}, journal={KSCE Journal of Civil Engineering}, publisher={Springer Science and Business Media LLC}, author={Mun, Sungho and Guddati, Murthy N. and Kim, Y. Richard}, year={2006}, month={Mar}, pages={97–104} }
@article{nukala_simunovic_guddati_2005, title={An efficient algorithm for modelling progressive damage accumulation in disordered materials}, volume={62}, ISSN={["1097-0207"]}, DOI={10.1002/nme.1257}, abstractNote={This paper presents an efficient algorithm for the simulation of progressive fracture in disordered quasi-brittle materials using discrete lattice networks. The main computational bottleneck involved in modelling the fracture simulations using large discrete lattice networks stems from the fact that a new large set of linear equations needs to be solved every time a lattice bond is broken. Using the present algorithm, the computational complexity of solving the new set of linear equations after breaking a bond reduces to a simple triangular solves (forward elimination and backward substitution) using the already Cholesky factored matrix. This algorithm using the direct sparse solver is faster than the Fourier accelerated iterative solvers such as the preconditioned conjugate gradient (PCG) solvers, and eliminates the critical slowing down associated with the iterative solvers that is especially severe close to the percolation critical points. Numerical results using random resistor networks for modelling the fracture and damage evolution in disordered materials substantiate the efficiency of the present algorithm. In particular, the proposed algorithm is especially advantageous for fracture simulations wherein ensemble averaging of numerical results is necessary to obtain a realistic lattice system response. Copyright © 2005 John Wiley & Sons, Ltd.}, number={14}, journal={INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING}, author={Nukala, PKVV and Simunovic, S and Guddati, MN}, year={2005}, month={Apr}, pages={1982–2008} }
@article{mun_guddati_kim_2005, title={Continuum damage finite element modeling of asphalt concrete}, volume={9}, ISSN={1226-7988 1976-3808}, url={http://dx.doi.org/10.1007/bf02829051}, DOI={10.1007/bf02829051}, number={3}, journal={KSCE Journal of Civil Engineering}, publisher={Springer Science and Business Media LLC}, author={Mun, Sungho and Guddati, Murthy N. and Kim, Y. Richard}, year={2005}, month={May}, pages={205–211} }
@article{yue_guddati_2005, title={Dispersion-reducing finite elements for transient acoustics}, volume={118}, ISSN={["1520-8524"]}, DOI={10.1121/1.2011149}, abstractNote={This paper focuses on increasing the accuracy of low-order (four-node quadrilateral) finite elements for the transient analysis of wave propagation. Modified integration rules, originally proposed for time-harmonic problems, provide the basis for the proposed technique. The modified integration rules shift the integration points to locations away from the conventional Gauss or Gauss-Lobatto integration points with the goal of reducing the discretization errors, specifically the dispersion error. Presented here is an extension of the idea to time-dependent analysis using implicit as well as explicit time-stepping schemes. The locations of the stiffness integration points remain unchanged from those in time-harmonic case. On the other hand, the locations of the integration points for the mass matrix depend on the time-stepping scheme and the step size. Furthermore, the central difference method needs to be modified from its conventional form to facilitate fully explicit computation. The superior performance of the proposed algorithms is illustrated with the help of several numerical examples.}, number={4}, journal={JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA}, author={Yue, B and Guddati, MN}, year={2005}, month={Oct}, pages={2132–2141} }
@article{underwood_heidari_guddati_kim_2005, title={Experimental Investigation of Anisotropy in Asphalt Concrete}, volume={1929}, ISBN={["0-309-09403-8"]}, ISSN={0361-1981 2169-4052}, url={http://dx.doi.org/10.1177/0361198105192900128}, DOI={10.3141/1929-28}, abstractNote={Accurate multiaxial characterization of asphalt concrete requires a thorough understanding of its anisotropic behavior. For that purpose a study has been conducted to examine the anisotropic properties of asphalt concrete in the linear viscoelastic range, with growing damage, and during volumetric deformation. Tests were conducted on specimens cored in the vertical and horizontal directions from gyratory-compacted specimens. Anisotropy was found to have no effect on the linear viscoelastic properties of the material. This finding is supported by subsequent results from monotonic constant crosshead rate uniaxial tension and uniaxial compression tests. It was also found that anisotropy contributes greatly to the behavior of asphalt concrete in compression, but shows little, if any, effect on tensile properties. In addition, the strong dependence of anisotropy on temperature and strain rate is presented. Finally, promising results from a simplified method of extracting the anisotropic behavior of asphalt concrete with the use of the hydrostatic test are also introduced.}, number={1}, journal={Transportation Research Record: Journal of the Transportation Research Board}, publisher={SAGE Publications}, author={Underwood, Shane and Heidari, A. Homayoun and Guddati, Murthy and Kim, Y. Richard}, year={2005}, month={Jan}, pages={238–247} }
@article{guddati_heidari_2005, title={Migration with arbitrarily wide-angle wave equations}, volume={70}, ISSN={["1942-2156"]}, DOI={10.1190/1.1925747}, abstractNote={We develop a new scalar migration technique that is highly accurate for imaging steep dips in heterogeneous media. This method is based on arbitrarily wide-angle wave equations (AWWEs) that are highly accurate space-domain one-way wave equations and have a form similar to the 15° equation. The accuracy of the proposed method is increased by introducing auxiliary variables, as well as adjusting the parameters of the approximation. Poststack migration is carried out by downward continuation using the AWWE, for which we have developed a stable, explicit, double-marching scheme. Up to 80° accuracy is achieved by second-order AWWE migration with only 2.3 times the computational effort of the 15° equation and requiring almost the same storage. We illustrate the performance of AWWE migration using impulse-response graphs, a single-dipping reflector, and a slice of the SEG/EAGE salt model.}, number={3}, journal={GEOPHYSICS}, author={Guddati, MN and Heidari, AH}, year={2005}, pages={S61–S70} }
@article{narasimhan_ward_kruse_guddati_mahinthakumar_2004, title={A high resolution computer model for sound propagation in the human thorax based on the Visible Human data set}, volume={34}, ISSN={["1879-0534"]}, DOI={10.1016/S0010-4825(03)00044-1}, abstractNote={A parallel supercomputer model based on realistic tissue data is developed for sound propagation in the human thorax and the sound propagation behavior is analyzed under various conditions using artificial sound sources. The model uses the Visible Human®1 male data set for a realistic representation of the human thorax. The results were analyzed in time and frequency domains. The analysis suggests that lower frequencies of around 100Hz are more effectively transmitted through the thorax and that the spatial confinement of sound waves within the thorax results in a resonance effect at around 1500Hz. The results confirm previous studies that show the size of the thorax plays a significant role in the type of sound generated at the chest wall.}, number={2}, journal={COMPUTERS IN BIOLOGY AND MEDICINE}, author={Narasimhan, C and Ward, R and Kruse, KL and Guddati, M and Mahinthakumar, G}, year={2004}, month={Mar}, pages={177–192} }
@article{mun_guddati_kim_2004, title={Fatigue cracking mechanisms in asphalt pavements with viscoelastic continuum damage finite-element program}, ISBN={["0-309-09489-5"]}, ISSN={["0361-1981"]}, DOI={10.3141/1896-10}, abstractNote={A study of fatigue-cracking mechanisms in asphalt pavements used the finite-element program VECD-FEP++. This program employs the viscoelastic continuum damage model for the asphalt layer and a nonlinear elastic model for unbound layers. Both bottom-up and top-down cracks are investigated by taking several important variables, such as asphalt layer thickness, layer stiffness, pressure distribution under loading, and load level applied on the pavement surface, into account. The cracking mechanisms in various pavement structures under different loading conditions are studied by monitoring a damage contour. Preferred conditions for top-down cracking were identified with the results from this parametric study. The conjoined damage contours in thicker pavements suggest that a through-the-thickness crack may develop as the bottom-up and top-down cracks propagate simultaneously and coalesce; that idea supports observations from field cores and raises the question of the validity of traditional fatigue performance models that account for the growth of the bottom-up cracking only.}, number={1896}, journal={PAVEMENT DESIGN AND ACCELERATED TESTING 2004}, author={Mun, S and Guddati, MN and Kim, YR}, year={2004}, pages={96–106} }
@article{guddati_yue_2004, title={Modified integration rules for reducing dispersion error in finite element methods}, volume={193}, ISSN={["1879-2138"]}, DOI={10.1016/j.cma.2003.09.010}, abstractNote={This paper describes a simple but effective technique for reducing dispersion errors in finite element solutions of time-harmonic wave propagation problems. The method involves a simple shift of the integration points to locations away from conventional Gauss or Gauss–Lobatto integration points. For bilinear rectangular elements, such a shift results in fourth-order accuracy with respect to dispersion error (error in wavelength), as opposed to the second-order accuracy resulting from conventional integration. Numerical experiments involving distorted meshes indicate that the method has superior performance in comparison with other dispersion reducing finite elements.}, number={3-5}, journal={COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING}, author={Guddati, MN and Yue, B}, year={2004}, pages={275–287} }
@article{asvadurov_druskin_guddati_knizhnerman_2003, title={On optimal finite-difference approximation of PML}, volume={41}, ISSN={["0036-1429"]}, DOI={10.1137/S0036142901391451}, abstractNote={A technique derived from two related methods suggested earlier by some of the authors for optimization of finite-difference grids and absorbing boundary conditions is applied to discretization of perfectly matched layer (PML) absorbing boundary conditions for wave equations in Cartesian coordinates. We formulate simple sufficient conditions for optimality and implement them. It is found that the minimal error can be achieved using pure imaginary coordinate stretching. As such, the PML discretization is algebraically equivalent to the rational approximation of the square root on [0,1] conventionally used for approximate absorbing boundary conditions. We present optimal solutions for two cost functions, with exponential (and exponential of the square root) rates of convergence with respect to the number of the discrete PML layers using a second order finite-difference scheme with optimal grids. Results of numerical calculations are presented.}, number={1}, journal={SIAM JOURNAL ON NUMERICAL ANALYSIS}, author={Asvadurov, S and Druskin, V and Guddati, MN and Knizhnerman, L}, year={2003}, pages={287–305} }
@article{guddati_feng_kim_2002, title={Toward a micromechanics-based procedure to characterize fatigue performance of asphalt concrete}, ISBN={["0-309-07714-1"]}, ISSN={["0361-1981"]}, DOI={10.3141/1789-13}, abstractNote={A lattice-based micromechanics approach is proposed to characterize the cracking performance of asphalt concrete. A random truss lattice model was introduced and investigated for simulating the following: ( a) linear elastic and viscoelastic deformation of homogeneous materials in axial compression and shear loading experiments, ( b) linear elastic deformation and the stress field in heterogeneous materials in an axial compression loading experiment, and ( c) damage evolution in elastic solids under an indirect tensile test. The simulation results match well with the theoretical solutions and show excellent promise in predicting cracking patterns in the indirect tensile test. A brief discussion about ongoing work is also presented.}, number={1789}, journal={BITUMINOUS PAVING MIXTURES 2002}, author={Guddati, MN and Feng, Z and Kim, YR}, year={2002}, pages={121–128} }
@inproceedings{guddati_2000, title={Comparison of continued fraction absorbing boundary conditions with perfectly matched layers}, number={2000}, booktitle={EM 2000: Fourteenth Engineering Mechanics Conference, Department of Civil Engineering, the University of Texas at Austin, Austin, Texas, U.S.A., May 21-24, 2000}, publisher={Austin, Tex.: Dept. of Civil Engineering, University of Texas at Austin,}, author={Guddati, M. N.}, editor={D. R. Maniar and Tassoulas, J.Editors}, year={2000} }
@article{guddati_tassoulas_2000, title={Continued-fraction absorbing boundary conditions for the wave equation}, volume={8}, ISSN={["0218-396X"]}, DOI={10.1142/s0218396x00000091}, abstractNote={Absorbing boundary conditions are generally required for numerical modeling of wave phenomena in unbounded domains. Local absorbing boundary conditions are generally preferred for transient analysis because of their computational efficiency. However, their accuracy is severely limited because the more accurate high-order boundary conditions cannot be implemented easily. In this paper, a new arbitrarily high-order absorbing boundary condition based on continued fraction approximation is presented. Unlike the existing boundary conditions, this one does not contain high-order derivatives, thus making it amenable to implementation in conventional C 0 finite element and finite difference methods. The superior numerical properties and implementation aspects of this boundary condition are discussed. Numerical examples are presented to illustrate the performance of these new high-order boundary condition.}, number={1}, journal={JOURNAL OF COMPUTATIONAL ACOUSTICS}, author={Guddati, MN and Tassoulas, JL}, year={2000}, month={Mar}, pages={139–156} }
@inproceedings{guddati_2000, title={Reduced dispersion finite elements for time harmonic wave propagation problems}, number={2000}, booktitle={EM 2000: Fourteenth Engineering Mechanics Conference, Department of Civil Engineering, the University of Texas at Austin, Austin, Texas, U.S.A., May 21-24, 2000}, publisher={Austin, Tex.: Dept. of Civil Engineering, University of Texas at Austin,}, author={Guddati, M. N.}, editor={D. R. Maniar and Tassoulas, J.Editors}, year={2000} }