@article{zhang_kleinstreuer_kim_2009, title={Comparison of analytical and CFD models with regard to micron particle deposition in a human 16-generation tracheobronchial airway model}, volume={40}, ISSN={["1879-1964"]}, DOI={10.1016/j.jaerosci.2008.08.003}, abstractNote={A representative human tracheobronchial tree has been geometrically represented with adjustable triple-bifurcation units (TBUs) in order to effectively simulate local and global micron particle depositions. It is the first comprehensive attempt to compute micron-particle transport in a (Weibel Type A) 16-generation model with realistic inlet conditions. The CFD modeling predictions are compared to experimental observations as well as analytical modeling results. Based on the findings with the validated computer simulation model, the following conclusions can be drawn: (i) Surprisingly, simulated inspiratory deposition fractions for the entire tracheobronchial region (say, G0–G15) with repeated TBUs in parallel and in series agree rather well with those calculated using analytical/semi-empirical expressions. However, the predicted particle-deposition fractions based on such analytical formulas differ greatly from the present simulation results for most local bifurcations, due to the effects of local geometry and resulting local flow features and particle distributions. Clearly, the effects of realistic geometries, flow structures and particle distributions in different individual bifurcations accidentally cancel each other so that the simulated deposition efficiencies during inspiration in a relatively large airway region may agree quite well with those obtained from analytical expressions. Furthermore, with the lack of local resolution, analytical models do not provide any physical insight to the air–particle dynamics in the tracheobronchial region. (ii) The maximum deposition enhancement factors (DEF) may be in the order of 102 to 103 for micron particles in the tracheobronchial airways, implying potential health effects when the inhaled particles are toxic. (iii) The presence of sedimentation for micron particles in lower bronchial airways may change the local impaction-based deposition patterns seen for larger airways and hence reduces the maximum DEF values. (iv) Rotation of an airway bifurcation cause a significant impact on distal bifurcations rather than on the proximal ones. Such geometric effects are minor when compared to the effects of airflow and particle transport/deposition history, i.e., upstream effects.}, number={1}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Zhang, Zhe and Kleinstreuer, Clement and Kim, Chong S.}, year={2009}, month={Jan}, pages={16–28} }
 @article{zhang_kleinstreuer_kim_2006, title={Transport and uptake of MTBE and ethanol vapors in a human upper airway model}, volume={18}, ISSN={["1091-7691"]}, DOI={10.1080/08958370500434172}, abstractNote={Potential human exposure to vapors of methyl tertiary-butyl ether (MTBE) and ethanol is of increasing concern because these materials are widely used as gasoline additives. In this study we analyzed numerically the transport and deposition of MTBE and ethanol vapors in a model of the human upper respiratory airway, consisting of an oral airway and the first four generations of the tracheobronchial tree. Airflow characteristics and mass transfer processes were analyzed at different inspiratory flow conditions using a three-dimensional computational fluid and particle dynamics method. The deposition data were analyzed in terms of regional deposition fractions (DF = regional uptake/mouth concentration) and deposition enhancement factors (DEF = local DF/average DF) at local micro surface areas. Results show that DF in the entire upper airway model is 21.9%, 12.4%, and 6.9% for MTBE and 67.5%, 51.5%, and 38.5% for ethanol at a flow rate of 15, 30, and 60 L/min, respectively. Of the total DF, 65–70% is deposited in the oral airway for both vapors. Deposition is localized at various sites within the upper airway structure, with a maximum DEF of 1.5 for MTBE and 7.8 for ethanol. Local deposition patterns did not change with inhalation conditions, but DF and the maximum DEF increased with diffusivity, solubility, and the degree of airway wall absorption of vapors, as shown by a greater deposition of ethanol than MTBE. The vapor deposition efficiency as expressed by the dimensionless mass transfer coefficient correlated well with a product of Reynolds (Re) and Schmidt (Sc) numbers. In conclusion, MTBE and ethanol vapors deposit substantially in the upper airway structure with a marked enhancement of dose at local sites, and the deposition dose may be reasonably estimated by a functional relationship with dimensionless fluid flow and diffusion parameters.}, number={3}, journal={INHALATION TOXICOLOGY}, author={Zhang, Z and Kleinstreuer, C and Kim, CS}, year={2006}, month={Mar}, pages={169–184} }
 @article{kim_kim_ihm_2005, title={Encapsulation and polymerization of acetylene molecules inside a carbon nanotube}, volume={416}, number={06-Apr}, journal={Chemical Physics Letters}, author={Kim, G. and Kim, Y. and Ihm, J.}, year={2005}, pages={279–282} }
 @article{shi_kleinstreuer_zhang_kim_2004, title={Nanoparticle transport and deposition in bifurcating tubes with different inlet conditions}, volume={16}, ISSN={["1089-7666"]}, DOI={10.1063/1.1724830}, abstractNote={Transport and deposition of ultrafine particles in straight, bent and bifurcating tubes are considered for different inlet Reynolds numbers, velocity profiles, and particle sizes, i.e., 1 nm⩽dp⩽150 nm. A commercial finite-volume code with user-supplied programs was validated with analytical correlations and experimental data sets for nanoparticle depositions, considering a straight tube, a tubular 90° bend, and a G3-G5 double bifurcation with both planar and nonplanar configurations. The focus is on the airflow structures as well as nanoparticle deposition patterns and deposition efficiencies, which were analyzed for planar and nonplanar bifurcating lung airway models representing part of the upper bronchial tree. Deposition takes place primarily by Brownian diffusion, and thus deposition efficiencies increase with decreasing nanoparticle size and lower inlet Reynolds numbers. Deposition in the nonplanar configuration differs only slightly from that in the planar configuration. When compared with axisymmetric inlet conditions, the more realistic, skewed inlet velocity and particle profiles generate nearly axisymmetric deposition patterns as well. This work may elucidate basic physical insight of ultrafine particle transport and deposition relevant to environmental, industrial and biomedical studies.}, number={7}, journal={PHYSICS OF FLUIDS}, author={Shi, H and Kleinstreuer, C and Zhang, Z and Kim, CS}, year={2004}, month={Jul}, pages={2199–2213} }
 @article{kim_ro_2002, title={An accurate full car ride model using model reducing techniques}, volume={124}, ISSN={["1528-9001"]}, DOI={10.1115/1.1503065}, abstractNote={In this study, an approach to obtain an accurate yet simple model for full-vehicle ride analysis is proposed. The approach involves linearization of a full car MBD (multibody dynamics) model to obtain a large-order vehicle model. The states of the model are divided into two groups depending on their effects on the ride quality and handling performance. Singular perturbation method is then applied to reduce the model size. Comparing the responses of the proposed model and the original MBD model shows an accurate matching between the two systems. A set of identified parameters that makes the well-known seven degree-of-freedom model very close to the full car MBD model is obtained. Finally, the benefits of the approach are illustrated through design of an active suspension system. The identified model exhibits improved performance over the nominal models in the sense that the accurate model leads to the appropriate selection of control gains. This study also provides an analytical method to investigate the effects of model complexity on model accuracy for vehicle suspension systems.}, number={4}, journal={JOURNAL OF MECHANICAL DESIGN}, author={Kim, C and Ro, PI}, year={2002}, month={Dec}, pages={697–705} }
 @article{zhang_kleinstreuer_kim_2002, title={Micro-particle transport and deposition in a human oral airway model}, volume={33}, ISSN={["0021-8502"]}, DOI={10.1016/S0021-8502(02)00122-2}, abstractNote={Laminar-to-turbulent air flow for typical inhalation modes as well as micro-particle transport and wall deposition in a representative human oral airway model have been simulated using a commercial finite-volume code with user-enhanced programs. The computer model has been validated with experimental airflow and particle deposition data sets. For the first time, accurate local and segmentally averaged particle deposition fractions have been computed under transitional and turbulent flow conditions. Specifically, turbulence that occurs after the constriction in the oral airways for moderate and high-level breathing can enhance particle deposition in the trachea near the larynx, but it is more likely to affect the deposition of smaller particles, say, St<0.05. Particles released around the top/bottom zone of the inlet plane more easily deposit on the curved oral airway surface. Although more complicated geometric features of the oral airway may have a measurable effect on particle deposition, the present simulations with a relatively simple geometry exhibit the main features of laminar-transitional-turbulent particle suspension flows in actual human oral airways. Hence, the present model may serve as the “entryway” for simulating and analyzing airflow and particle deposition in the lung.}, number={12}, journal={JOURNAL OF AEROSOL SCIENCE}, author={Zhang, Z and Kleinstreuer, C and Kim, CS}, year={2002}, month={Dec}, pages={1635–1652} }
 @article{zhang_kleinstreuer_kim_2001, title={Effects of curved inlet tubes on air flow and particle deposition in bifurcating lung models}, volume={34}, ISSN={["1873-2380"]}, DOI={10.1016/S0021-9290(00)00233-5}, abstractNote={In vivo bifurcating airways are complex and the airway segments leading to the bifurcations are not always straight, but curved to various degrees. How do such curved inlet tubes influence the motion as well as local deposition and hence the biological responses of inhaled particulate matter in lung airways? In this paper steady laminar dilute suspension flows of micron-particles are simulated in realistic double bifurcations with curved inlet tubes, i.e., 0 degrees < or =theta< or =90 degrees, using a commercial finite-volume code with user-enhanced programs. The resulting air-flow patterns as well as particle transport and wall depositions were analyzed for different flow inlet conditions, i.e., uniform and parabolic velocity profiles, and geometric configurations. The curved inlet segments have quite pronounced effects on air-flow, particle motion and wall deposition in the downstream bifurcating airways. In contrast to straight double bifurcations, those with bent parent tubes also exhibit irregular variations in particle deposition efficiencies as a function of Stokes number and Reynolds number. There are fewer particles deposited at mildly curved inlet segments, but the particle deposition efficiencies at the downstream sequential bifurcations vary much when compared to those with straight inlets. Under certain flow conditions in sharply curved lung airways, relatively high, localized particle depositions may take place. The findings provide necessary information for toxicologic or therapeutic impact assessments and for global lung dosimetry models of inhaled particulate matter.}, number={5}, journal={JOURNAL OF BIOMECHANICS}, author={Zhang, Z and Kleinstreuer, C and Kim, CS}, year={2001}, month={May}, pages={659–669} }
 @article{comer_kleinstreuer_kim_2001, title={Flow structures and particle deposition patterns in double-bifurcation airway models. Part 2. Aerosol transport and deposition}, volume={435}, ISSN={["1469-7645"]}, DOI={10.1017/s0022112001003810}, abstractNote={The flow theory and air flow structures in symmetric double-bifurcation airway models 
assuming steady laminar, incompressible flow, unaffected by the presence of aerosols, 
has been described in a companion paper (Part 1). The validated computer simulation 
results showed highly vortical flow fields, especially around the second bifurcations, 
indicating potentially complex particle distributions and deposition patterns. In this 
paper (Part 2), assuming spherical non-interacting aerosols that stick to the wall 
when touching the surface, the history of depositing particles is described. Specifically, 
the finite-volume code CFX (AEA Technology) with user-enhanced FORTRAN 
programs were validated with experimental data of particle deposition efficiencies 
as a function of the Stokes number for planar single and double bifurcations. The 
resulting deposition patterns, particle distributions, trajectories and time evolution 
were analysed in the light of the air flow structures for relatively low 
(ReD1 = 500) and high (ReD1 = 2000) 
Reynolds numbers and representative Stokes numbers, i.e. StD1 = 0.04 and 
StD1 = 0.12. Particle deposition patterns and surface concentrations 
are largely a function of the local Stokes number, but they also depend on the 
fluid–particle inlet conditions as well as airway geometry factors. While particles 
introduced at low inlet Reynolds numbers (e.g. ReD1 = 500) 
follow the axial air flow, secondary and vortical flows become important at higher Reynolds numbers, causing 
the formation of particle-free zones near the tube centres and subsequently elevated 
particle concentrations near the walls. Sharp or mildly rounded carinal ridges have 
little effect on the deposition efficiencies but may influence local deposition patterns. 
In contrast, more drastic geometric changes to the basic double-bifurcation model, 
e.g. the 90°-non-planar configuration, alter both the aerosol wall distributions and 
surface concentrations considerably.}, journal={JOURNAL OF FLUID MECHANICS}, author={Comer, JK and Kleinstreuer, C and Kim, CS}, year={2001}, month={May}, pages={55–80} }
 @article{comer_kleinstreuer_hyun_kim_2000, title={Aerosol transport and deposition in sequentially bifurcating airways}, volume={122}, ISSN={["1528-8951"]}, DOI={10.1115/1.429636}, abstractNote={Deposition patterns and efficiencies of a dilute suspension of inhaled particles in three-dimensional double bifurcating airway models for both in-plane and 90 deg out-of-plane configurations have been numerically simulated assuming steady, laminar, constant-property air flow with symmetry about the first bifurcation. Particle diameters of 3, 5, and 7 μm were used in the simulation, while the inlet Stokes and Reynolds numbers varied from 0.037 to 0.23 and 500 to 2000, respectively. Comparisons between these results and experimental data based on the same geometric configuration showed good agreement. The overall trend of the particle deposition efficiency, i.e., an exponential increase with Stokes number, was somewhat similar for all bifurcations. However, the deposition efficiency of the first bifurcation was always larger than that of the second bifurcation, while in general the particle efficiency of the out-of-plane configuration was larger than that of the in-plane configuration. The local deposition patterns consistently showed that the majority of the deposition occurred in the carinal region. The distribution pattern in the first bifurcation for both configurations were symmetric about the carina, which was a direct result of the uniaxial flow at the inlet. The deposition patterns about the second carina showed increased asymmetry due to highly nonuniform flow generated by the first bifurcation and were extremely sensitive to bifurcation orientation. Based on the deposition variations between bifurcation levels and orientations, the use of single bifurcation models was determined to be inadequate to resolve the complex fluid–particle interactions that occur in multigenerational airways. [S0148-0731(00)01102-X]}, number={2}, journal={JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME}, author={Comer, JK and Kleinstreuer, C and Hyun, S and Kim, CS}, year={2000}, month={Apr}, pages={152–158} }
 @article{zhang_kleinstreuer_kim_2000, title={Effects of asymmetric branch flow rates on aerosol deposition in bifurcating airways}, volume={24}, number={5}, journal={Journal of Medical Engineering & Technology}, author={Zhang, Z. and Kleinstreuer, C. and Kim, C. S.}, year={2000}, month={Sep}, pages={192–202} }
 @article{hong_kim_1999, title={A note on similarity measures between vague sets and between elements}, volume={115}, ISSN={["0020-0255"]}, DOI={10.1016/S0020-0255(98)10083-X}, abstractNote={Recently, Chen (Fuzzy Sets and Systems 74 (2) (1995) 217–223; IEEE Trans. Syst. Man and Cybern., 27 (1) (1997) 153–158) proposed a set of methods for measuring the degree of similarity between vague sets and between elements, and presented some examples to illustrate the application of the said measures in handling behavior analysis problems. In this paper, we showed by examples that the similarity measures proposed by Chen do not fit well in some cases, and proposed a set of modified measures. Comparing the similarity degree of each measure, the modified similarity measures turned out to be more reasonable in more general cases than the previous one.}, number={1-4}, journal={INFORMATION SCIENCES}, author={Hong, DH and Kim, C}, year={1999}, month={Apr}, pages={83–96} }
 @article{kim_ro_kim_1999, title={Effect of the suspension structure on equivalent suspension parameters}, volume={213}, ISSN={["0954-4070"]}, DOI={10.1243/0954407991527026}, abstractNote={ This paper examines the uncertainties in modelling a real suspension system that are due to the effect of suspension linkage layout (or structure) on the equivalent suspension parameters of a corresponding mathematical model. In most research on active suspension systems, a quarter-car model of two masses is very often used. However, without considering the influence of the suspension kinematic structure, the simple model may not be as effective as might be expected because of the uncertainties in the suspension parameters. Two sets of identified parameters for different suspension systems are compared to show the effect of suspension structure on the equivalent parameters. The relationships between specific parameters and changes in certain suspension linkage layouts are also investigated. The benefits of the parameter identification are demonstrated in the process of designing two active systems (one using a sky-hook control law and the other using a sliding mode control technique). The results show that suspension structure has a strong effect on the equivalent suspension parameters and this relationship becomes more important as the structure of suspension increases in complexity. The advantage of the identification process is crucial in designing both linear and non-linear active suspension systems. }, number={D5}, journal={PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART D-JOURNAL OF AUTOMOBILE ENGINEERING}, author={Kim, C and Ro, PI and Kim, H}, year={1999}, pages={457–470} }
 @article{kim_kim_im_kim_kingon_1999, title={Ferroelectric properties of new chemical solution derived SBT thin films for non-volatile memory devices}, volume={16}, ISSN={["1573-4846"]}, DOI={10.1023/A:1008748718231}, number={1-2}, journal={JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY}, author={Kim, SH and Kim, DJ and Im, J and Kim, CE and Kingon, AI}, year={1999}, month={Oct}, pages={57–63} }