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Following are some publications with reference to the use of ADINA. The pages give the Abstracts of some papers published since 1986 referring to ADINA. The most recent papers are listed first. All these papers may be searched using the box:

Numerical simulation of the dynamic thermostructural response of a composite rocket nozzle throat

E.V. Morozov^a, J.F.P. Pitot de la Beaujardiere^b

^aSchool of Aerospace, Civil & Mechanical Engineering, University of New South Wales, The Australian Defence Force Academy, Canberra, Australia
^bDepartment of Mechanical Engineering, University of KwaZulu-Natal, Howard College Campus, Durban, South Africa

Composite Structures 91 (2009) 412–420

Abstract: The finite element method, in the form of the commercial finite element code ADINA, is used to investigate the dynamic thermostructural response of a composite rocket nozzle throat. ADINA’s thermoelastic analysis capability is validated by the comparison of its solution for the thermoelastic response of a thick, homogeneous, cylindrically orthotropic tube heated internally, to an analytical one. The spatially reinforced Carbon–Carbon nozzle throat examined here forms part of a low-erosion solid rocket motor nozzle model that is subjected to structural and thermal loading, with the effects of material ablation being neglected. An initial transient quasi-static thermostructural analysis is performed to determine the validity of the nozzle design, following which, an uncoupled dynamic thermostructural analysis of the nozzle’s throat and entrance section for the initial transient phase of the nozzle’s operation, is carried out. The results of this analysis are then compared to those of the equivalent transient quasi-static analysis to assess the degree of variance in either solution. It is found that the dynamic response oscillates about the quasi-static response in all cases, and that, in general, the variance in stress magnitudes between the two solution techniques is significant.

Keywords: Thermoelastic finite element analysis - Composite rocket nozzle - Dynamic response

A Phenomenological Approach Toward Patient-Specific Computational Modeling of Articular Cartilage Including Collagen Fiber Tracking

David M. Pierce¹, Werner Trobin², Siegfried Trattnig³, Horst Bischof², Gerhard A. Holzapfel^1,4

¹Institute of Biomechanics, Center of Biomedical Engineering, Graz University of Technology, Kronesgasse 5-I, 8010 Graz, Austria
²Institute for Computer Graphics and Vision, Graz University of Technology, Inffeldgasse 16-II, 8010 Graz, Austria
³Department of Radiology, Center of Excellence for High Field MR, Medical University of Vienna, Lazarettgasse 14, 1090 Vienna, Austria
⁴Department of Solid Mechanics, School of Engineering Sciences, Royal Institute of Technology (KTH), Osquars Backe 1, 100 44 Stockholm, Sweden

Journal of Biomechanical Engineering, September 2009, Vol. 131 / 091006-1

Abstract: To model the cartilage morphology and the material response, a phenomenological and patient-specific simulation approach incorporating the collagen fiber fabric is proposed. Cartilage tissue response is nearly isochoric and time-dependent under physiological pressure levels. Hence, a viscoelastic constitutive model capable of reproducing finite strains is employed, while the time-dependent deformation change is purely isochoric. The model incorporates seven material parameters, which all have a physical interpretation. To calibrate the model and facilitate further analysis, five human cartilage specimens underwent a number of tests. A series of magnetic resonance imaging (MRI) sequences is taken, next the cartilage surface is imaged, then mechanical indentation tests are completed at 2–7 different locations per sample, resulting in force/displacement data over time, and finally, the underlying bone surface is imaged. Imaging and mechanical testing are performed with a custom-built robotics-based testing device. Stereo reconstruction of the cartilage and subchondral bone surface is employed, which, together with the proposed constitutive model, led to specimen-specific finite element simulations of the mechanical indentation tests. The force-time response of 23 such indentation experiment simulations is optimized to estimate the mean material parameters and corresponding standard deviations. The model is capable of reproducing the deformation behavior of human articular cartilage in the physiological loading domain, as demonstrated by the good agreement between the experiment and numerical results (R2 =0.95 ± 0.03, mean ± standard deviation of force-time response for 23 indentation tests). To address validation, a sevenfold cross-validation experiment is performed on the 21 experiments representing healthy cartilage. To quantify the predictive error, the mean of the absolute force differences and Pearson’s correlation coefficient are both calculated. Deviations in the mean absolute difference, normalized by the peak force, range from 4% to 90%, with 40 ± 25% (M ± SD). The correlation coefficients across all predictions have a minimum of 0.939, and a maximum of 0.993 with 0.975 ± 0.013 (M ± SD), which demonstrates an excellent match of the decay characteristics. A novel feature of the proposed method is 3D sample-specific numerical tracking of the fiber fabric deformation under general loading. This feature is demonstrated by comparing the estimated fiber fabric deformation with recently published experimental data determined by diffusion tensor MRI. The proposed approach is efficient enough to enable large-scale 3D contact simulations of knee joint loading in simulations with accurate joint geometries.

Keywords: articular cartilage - collagen fibers - finite viscoelasticity - finite element simulation - indentation testing

Local critical stress correlates better than global maximum stress with plaque morphological features linked to atherosclerotic plaque vulnerability: an in vivo multi-patient study

Dalin Tang¹, Zhongzhao Teng¹, Gador Canton², Thomas S Hatsukami³, Li Dong², Xueying Huang1 and Chun Yuan²

¹Worcester Polytechnic Institute, Mathematical Sciences Department 100 Institute Road, Worcester, MA, USA
²University of Washington, Department of Radiology, Seattle, WA 98195 USA
³University of Washington, Division of Vascular Surgery, Seattle, WA 98195 USA

BioMedical Engineering OnLine 2009, 8:15

Abstract
Background: It is believed that mechanical stresses play an important role in atherosclerotic plaque rupture process and may be used for better plaque vulnerability assessment and rupture risk predictions. Image-based plaque models have been introduced in recent years to perform mechanical stress analysis and identify critical stress indicators which may be linked to rupture risk. However, large-scale studies based on in vivo patient data combining mechanical stress analysis, plaque morphology and composition for carotid plaque vulnerability assessment are lacking in the current literature.
Methods: 206 slices of in vivo magnetic resonance image (MRI) of carotid atherosclerotic plaques from 20 patients (age: 49–71, mean: 67.4; all male) were acquired for model construction. Modified Mooney-Rivlin models were used for vessel wall and all plaque components with parameter values chosen to match available data. A morphological plaque severity index (MPSI) was introduced based on in vivo plaque morphological characteristics known to correlate with plaque vulnerability. Critical stress, defined as the maximum of maximum-principal-stress
(Stress-P1) values from all possible vulnerable sites, was determined for each slice for analysis. A computational plaque stress index (CPSI, with 5 grades 0–4, 4 being most vulnerable) was defined for each slice using its critical stress value and stress interval for each CPSI grade was optimized to reach best agreement with MPSI. Correlations between CPSI and MPSI, plaque cap thickness, and lipid core size were analyzed.
Results: Critical stress values correlated positively with lipid core size (r = 0.3879) and negatively with cap thickness (r = 0.3953). CPSI classifications had 71.4% agreement with MPSI classifications. The Pearson correlation coefficient between CPSI and MPSI was 0.849 (p < 0.0001). Using global maximum Stress-P1 value for each slice to define a global maximum stress-based CPSI (G-CPSI), the agreement rate with MPSI was only 34.0%. The Pearson correlation coefficient between G-CPSI and MPSI was 0.209.
Conclusion: Results from this in vivo study demonstrated that localized critical stress values had much better correlation with plaque morphological features known to be linked to plaque rupture risk, compared to global maximum stress conditions. Critical stress indicators have the potential to improve image-based screening andplaque vulnerability assessment schemes.

Ultimate strength and ductility characteristics of intermittently welded stiffened plates

Mohammad Reza Khedmati^a, Mehran Rastani^b, Khosrow Ghavami^c

^aFaculty of Marine Technology, Amirkabir University of Technology, 424 Hafez Avenue, Tehran 15914, Iran
^bStateoil-Petropars JV, No. 255 Mirdamad Blvd Postal code 1918933931, Tehran, Iran
^cDepartment of Civil Engineering, Pontificia Universidade CatÛlica (PUC-Rio), 22453-900 Rio de Janeiro, Brazil

Journal of Constructional Steel Research 65 (2009) 599_610

Abstract: A series of detailed numerical analyses of stiffened steel plates subjected to in plane longitudinal or transverse compressive load is performed. Stiffened plates are selected from the deck structure of real sea-going ships and inland waterway vessels. Three different stiffener-to-plate welding procedures are considered: continuous welding, chain intermittent fillet welding and staggered intermittent fillet welding. Special attention is paid to finite element modelling of the fillet welds as applied in practice to verify the reliability of the FEM. Some available experimental results are simulated verifying the reliability of the finite element method. Full-range equilibrium paths are traced for non-linear elasto-plastic response of the stiffened plates, using a commercially available FEM programme, ADINA. Strength and ductility characteristics of the stiffened plates are discussed in details.

Keywords: Stiffened plates - Fillet welds - Weld gap - Buckling strength - Ultimate strength - Finite Element Method (FEM)

High Levels of 18F-FDG Uptake in Aortic Aneurysm Wall are Associated with High Wall Stress

X.Y. Xu¹, A. Borghi², A. Nchimi², J. Leung¹, P. Gomez³, Z. Cheng¹, J.O. Defraigne⁴, N. Sakalihasan⁴

¹Department of Chemical Engineering, Imperial College London, UK
²Department of Radiology, CHC, Liege, Belgium
³Department of Nuclear Medicine, CHC, Liege, Belgium
⁴Department of Cardiovascular Surgery, University Hospital of Liege, Liege, Belgium

Eur J Vasc Endovasc Surg (In press 2009)

Abstract:
Background: Functional imaging using positron emission tomography (PET) showed
increased metabolic activities in the aneurysm wall prior to rupture, whereas separate studies using finite element analysis techniques found the presence of high wall stresses in aneurysms that subsequently ruptured. This case series aimed to evaluate the association between wall stress and levels of metabolic activities in aneurysms of the descending thoracic and abdominal aorta.
Methods: Five patients with aneurysms in the descending thoracic aorta or abdominal aorta were examined using positron emission tomographyecomputed tomography (PET-CT). Patient-specific models of the aortic aneurysms were reconstructed from CT scans, and wall tensile stresses at peak blood pressure were calculated using the finite element method. Predicted
wall stresses were qualitatively compared with measured levels of 18F-fluoro-2-deoxyglucose (18F-FDG) uptakes in the aneurysm wall.
Results: The distribution of wall stress in the aneurysm wall was highly non-uniform depending on the individual geometry. Predicted high wall stress regions co-localised with areas of positive 18F-FDG uptake in all five patients examined. In the two ruptured cases, the locations of rupture corresponded well with regions of elevated metabolic activity and high wall stress.
Conclusions: These preliminary observations point to a potential link between high wall stress and accelerated metabolism in aortic aneurysm wall and warrant further large population based studies.

Keywords: Aneurysm - Aorta - Wall stress - PET-CT examination

Abdominal Aortic Aneurysm Risk of Rupture: Patient-Specific FSI Simulations Using Anisotropic Model

Peter Rissland¹, Yared Alemu¹, Shmuel Einav¹, John Ricotta², Danny Bluestein¹

1Department of Biomedical Engineering, Stony Brook University, Stony Brook, NY 11794-8181
²Department of Surgery, Stony Brook University Hospital, 101 Nicolls Road, Stony Brook, NY 11794-8191

Journal of Biomechanical Engineering, Vol. 131 / 031001-1, March 2009

Compressive strength of concrete cylinders with variable widths CFRP wraps: Experimental study and numerical modeling

Camille A. Issa, Pedro Chami, George Saad

Department of Civil Engineering, Lebanese American University, Byblos, Lebanon

Construction and Building Materials 23 (2009) 2306–2318

Abstract: There is an urgent need for models that can accurately predict performance of fiber-wrapped concrete columns. Axial compression tests on a total of 30 carbon-wrapped concrete cylinders of normal concrete and different number of wraps and height of confinement were used to verify the finite model. A nonlinear finite element model with a non-associative Drucker–Prager plasticity was used. The model compared favorably with test results. It was concluded that the adhesive bond between concrete and the wrap would not significantly affect the confinement behavior. From tests results, one can conclude that the wider the wrap, the higher the strength, also the thicker the wrap the higher the strength. However, it was impossible to reach a clear conclusion on the effect of the combination of variation of number of CFRP wraps and height of confinement. In a couple of cases, the same amount of material resulted in the same increase in the strength of the cylinders.

Keywords: Experimental - FEM - CFRP - Concrete

Fluid–structure interaction analysis of turbulent pulsatile flow within a layered aortic wall as related to aortic dissection

Khalil Khanafer^a,b, Ramon Berguer^a,b 

^aVascular Mechanics Laboratory, Department of Biomedical Engineering, University of Michigan, AnnArbor, MI48109, United States
^bVascular Mechanics Laboratory, Section of Vascular Surgery, University of Michigan, AnnArbor, MI48109, United States

Journal of Biomechanics 42(2009)2642–2648

Turbulent pulsatile flow and wall mechanics were studied numerically in an axisymmetric three-layered wall model of a descending aorta. The transport equations were solved using the finite element formulation based on the Galerkin method of weighted residuals. A fully-coupled fluid–structure interaction (FSI) analysis was utilized in this investigation. We calculated Von Mises wall  stress, streamlines and fluid pressure contours. The finndings of this study show that peak wall stress and maximum shear stress are highest in the media layer. The difference in the elastic properties of contiguous layers of the wall of the aorta probably determines the occurrence of dissection in the media layer. Moreover, the presence of aortic intramural hematomais found to have a significant effect on the peak wall stress acting on the inner layer.

Keywords: Dissection - Finite element - Flexible wall - Three-layered model - Turbulent

Influence of single-level lumbar degenerative disc disease on the behavior of the adjacent segments—A finite element model study

Lissette M. Ruberte^a, Raghu N. Natarajan^a,b, Gunnar BJ. Andersson<sup>b

a</sup>Department of Bioengineering, University of Illinois at Chicago, USA
^bDepartment of Orthopedic Surgery, Rush University Medical Center, USA

Journal of Biomechanics 42 (2009) 341–348

Abstract: The current study investigated mechanical predictors for the development of adjacent disc degeneration. A 3-D finite element model of a lumbar spine was modi.ed to simulate two grades of degeneration at the L4–L5 disc. Degeneration was modeled by changes in geometry and material properties. All models were subjected to follower preloads of 800N and moment loads in the three principal directions of motion using a hybrid protocol. Degeneration caused changes in the loading and motion patterns of the segments above and below the degenerated disc. At the level (L3–L4) above the degenerated disc, the motion increased due to moderate degeneration by 21% under lateral bending, 26% under axial rotation and 28% under .exion/extension. At the level (L5-S1) below the degenerated disc, motion increased only during lateral bending by 20% due to moderate degeneration. Both the L3–L4 and L5-S1 segment showed a monotonic increase in both the maximum von Mises stress and shear stress in the annulus as degeneration progressed for all loading directions, expect extension at L3–L4. The most significant increase in stress was observed at the L5-S1 level during axial rotation with nearly a ten-fold increase in the maximum shear stress and 103% increase in the maximum von Mises stress. The L5-S1 segment also showed a progressive increase in facet contact force for all loading directions with degeneration. Nucleus pressure did not increase signi.cantly for any loading direction at either the caudal or cephalic adjacent segment. Results suggest that single-level degeneration can increase the risk for injury at the adjacent levels.

Keywords: Disc degeneration - Finite element - Lumbar - Spine

Determination of the dynamic stress intensity factor for the four-point bend impact test

Ihor V. Rokach, Pawel Labedzki

Kielce University of Technology, Al. Tysiclecia Panstwa Polskiego 7, 25-314 Kielce, Poland

Int J Fract (2009) 160:93–100

Abstract: A simple method for determination of the dynamic stress intensity factor (DSIF) variation with time during a four-point impact bend test has been proposed. A formula for DSIF calculation from the recorded loading has been obtained using modal superposition method. Results of calculations for different specimens have been compared with the experimental data and the results of the direct finite element analysis.

Keywords: four-point impact bend test - modal superposition method - dynamic stress intensity factor

A novel, low cost, disposable, pediatric pulsatile rotary ventricular pump (PRVP) for cardiac surgery that provides a physiological flow pattern

Daniel E. Mazur*, Kathryn R. Osterholzer*, John M. Toomasian, and Scott I. Merz*

*MC3, Inc. 3550 West Liberty, Suite 3 Ann Arbor, MI 48103 USA

ASAIO J. 54(5): 523–528, 2008

Abstract: Research is underway to develop a novel, low cost, disposable pediatric pulsatile rotary ventricular pump (PRVP) for cardiac surgery that provides a physiological flow pattern. This is believed to offer reduced morbidity and risk exposure within this population. The PRVP will have a durable design suitable for use in short- to mid-length prolonged support after surgery without changing pumps. The design is based on proprietary MC3 technology which provides variable pumping volume per stroke, thereby allowing the pump to respond to hemodynamic status changes of the patient. The novel pump design also possesses safety advantages that prevent retrograde flow, and maintain safe circuit pressures upon occlusion of the inlet and outlet tubing. The design is ideal for simple, safe and natural flow support. Computational methods have been developed that predict output for pump chambers of varying geometry. A scaled chamber and pump head (diameter=4 inches) were prototyped to demonstrate target performance for pediatrics (2 L/min at 100 rpm). A novel means of creating a pulsatile flow and pressure output at constant RPM was developed and demonstrated to create significant surplus hydraulic energy (greater than 10%) in a simplified mock patient circuit.

Keywords:  pediatric pump - pulsatile - blood pump - cardiac surgery

Cantilever dynamics in atomic force microscopy

Arvind Raman, John Melcher, and Ryan Tung

Birck Nanotechnology Center and the School of Mechanical Engineering Purdue University, West Lafayette, IN 47907, USA

nanotoday, Feb-Apr 2008, Vol. 3, No.1-2

Abstract: Dynamic atomic force microscopy, in essence, consists of a vibrating microcantilever with a nanoscale tip that interacts with a sample surface via short- and long-range intermolecular forces. Microcantilevers possess several distinct eigenmodes and the tip-sample interaction forces are highly nonlinear. As a consequence, cantilevers vibrate in interesting, often unanticipated ways; some are detrimental to imaging stability, while others can be exploited to enhance performance. Understanding these phenomena can offer deep insight into the physics of dynamic atomic force microscopy and provide exciting possibilities for achieving improved material contrast with gentle imaging forces in the next generation of instruments. Here we summarize recent research developments on cantilever dynamics in the atomic force microscope.

Blood flow dynamics and fluid–structure interaction in patient-specific bifurcating cerebral aneurysms

Alvaro Valencia¹, Darren Ledermann¹, Rodrigo Rivera², Eduardo Bravo² and Marcelo Galvez²

¹Department of Mechanical Engineering, Universidad de Chile, Casilla 2777, Santiago, Chile
²Neuroradiology Department, Instituto de Neurocirugia Asenjo, Jose Manuel Infante 553, Santiago, Chile

Int. J. Numer. Meth. Fluids 2008; 58:1081–1100

Abstract: Hemodynamics plays an important role in the progression and rupture of cerebral aneurysms. The current work describes the blood flow dynamics and fluid–structure interaction in seven patient-specific models of bifurcating cerebral aneurysms located in the anterior and posterior circulation regions of the circle of Willis. The models were obtained from 3D rotational angiography image data, and blood flow dynamics and fluid–structure interaction were studied under physiologically representative waveform of inflow. The arterial wall was assumed to be elastic, isotropic and homogeneous. The flow was assumed to be laminar, non-Newtonian and incompressible. In one case, the effects of different model suppositions and boundary conditions were reported in detail. The fully coupled fluid and structure models were solved with the finite elements package ADINA. The vortex structure, pressure, wall shear stress (WSS), effective stress and displacement of the aneurysm wall showed large variations, depending on the morphology of the artery, aneurysm size and position. The time-averaged WSS, effective stress and displacement at the aneurysm fundus vary between 0.17 and 4.86 Pa, 4.35 and 170.2 kPa and 0.16 and 0.74 mm, respectively, for the seven patient-specific models of bifurcating cerebral aneurysms.

Keywords: cerebral aneurysm - wall shear stress - effective wall stress - displacement - 3D rotational X-ray angiography

Mechanical characterization of contact lenses by microindentation: Constant velocity and relaxation testing

Sung Jin Lee^a, Gerald R. Bourne^b, Xiaoming Chen^a, W. Gregory Sawyer^a, Malisa Sarntinoranont^a

^aDepartment of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA
^bDepartment of Material Science and Engineering, University of Florida, Gainesville, FL 32611, USA

Acta Biomaterialia 4 (2008) 1560–1568

Abstract: Non-destructive methods for testing material properties allow for multiple tests to be performed on the same sample, which will speed up the design and testing process for hydrogel contact lenses. The mechanical properties of contact lenses were investigated by microindentation testing. Indenter force responses were recorded for two modes of testing: constant velocity and relaxation indentation. From these tests, we characterized the biphasic properties of a hydrogel contact lens: Young’s modulus of the solid matrix and hydraulic permeability. Measured indenter force response was fit to finite element (FE) simulation results over a range of Young’s modulus (E) and hydraulic permeability (k) over a short testing time scale (2 s). Estimated hydraulic permeability, 1–5 x 10^-15 m⁴ (N s)^-1, was similar to previously measured values for Etafilcon A. However, values determined for Young’s modulus, 50–60 kPa, were lower than previously measured.

Keywords: Hydraulic conductivity - pHEMA-MAA - Poroelastic - Polymer - Hysitron

Adaptive airfoils for wind turbine blades

Branko Klarin

Faculty of Electrical and Mechanical Engineering and Naval Architecture – University of Split, R. Boskovica b.b., 21000 Split, Croatia

Proc. EWEC2008, European Wind Energy Association, 2008

Astract: This paper deals with the investigation procedure and results of applying an adaptive airfoil for wind turbine blades. A flexible airfoil skin allows deformation in the elastic zone of the adaptive part of the airfoil. This skin is attached on the stiff airfoil core. The deformation of the flexible airfoil shape depends on forces caused by the pressure field of a given wind speed. This results in a change of airfoil aerodynamic characteristics and wind turbine power regulation. Flow and elastic deformation are investigated with CFD/FSI analysis. Simulation of working characteristics of wind turbine with adaptive airfoils results in a positive energy yield when compared to the stiff airfoil shape. Further numerical and experimental investigations are proposed and described.

Keywords: adaptive airfoil - wind turbine airfoil - wind turbine blade - wind turbine regulation

Biphasic Finite Element Model of Solute Transport for Direct Infusion into Nervous Tissue

Xiaoming Chen and Malisa Sarntinoranont

Department of Mechanical and Aerospace Engineering, 212 MAE-A, University of Florida, Gainesville, FL 32611, USA

Annals of Biomedical Engineering, Vol. 35, No. 12, December 2007, pp. 2145–2158

Abstract: Infusion-based techniques are promising drug delivery methods for treating diseases of the nervous system. Direct infusion into tissue parenchyma circumvents the blood–brain barrier, localizes delivery, and facilitates transport of macromolecular agents. Computational models that predict interstitial flow and solute transport may aid in protocol design and optimization. We have developed a biphasic finite element (FE) model that accounts for local, flow-induced tissue swelling around an infusion cavity. It solves for interstitial fluid flow, tissue deformation, and solute transport in surrounding isotropic gray matter. FE solutions for pressure-controlled infusion were validated by comparing with analytical solutions. The in.uence of deformation-dependent hydraulic permeability was considered. A transient, nonlinear relationship between infusion pressure
and infusion rate was determined. The sensitivity of convection-dominated solute transport (i.e., albumin) over a range of nervous tissue properties was also simulated. Solute transport was found to be sensitive to pressure-induced swelling effects mainly in regions adjacent to the infusion cavity (r/a₀ ≤ 5 where a₀ is the outer cannula radius) for short times infusion simulated (3 min). Overall, the biphasic approach predicted enhanced macromolecular transport for small volume infusions (e.g., 2 µL over 1 h). Solute transport was enhanced by decreasing Young’s modulus and increasing hydraulic permeability of the tissue.

Keywords: Hydraulic conductivity - Poroelastic - Finite element model - FEM, Local edema - Convection-enhanced delivery - CED - Intraparenchymal infusion.

Characterization of the highly nonlinear and anisotropic vascular tissues from experimental inflation data: a validation study towards the use of clinical data for in-vivo modeling and analysis

Kinon Chen¹, Bahar Fata², and Daniel R. Einstein³

¹Department of Biomedical Engineering, University of Southern California, Los Angeles, CA
²Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA
³Biological Monitoring & Modeling, MS P7-56, Pacific Northwest National Laboratory, Richland, WA

Ann Biomed Eng. 2008 October ; 36(10): 1668–1680.

Abstract: In this study, we investigate whether an inverse modeling approach can be used to characterize vascular tissue behavior from experimental data of blood vessels subjected at various levels of internal pressure and axial stretch that mimics clinical data. In-vivo condition of blood vessel with either constant or variable axial response is considered. To compensate for the limitation of this data that does not provide axial force information, a new concept to constrain the ratio of axial to circumferential elastic moduli to a typical range is proposed. Vessel wall constitutive behavior was modeled with a transversely isotropic hyperelastic equation that accounts for dispersed collagen fibers, and both single-layer and bi-layer models were implemented for examination. The possibility of obtaining the fiber orientation in this approach was also evaluated. The characterized behavior was validated with an independent pipette-aspiration biaxial data on the same samples. It was found that homogenous assumption is an over-simplification. The constrained bi-layer model was in excellent agreement with both types of experimental data. Fiber angle is needed to be pre-defined to avoid covariance problem. Finally, our approach is relatively invariant to any particular axial response. Therefore, we believe that inverse modeling approach is suitable for in-vivo characterization.

Modeling the dynamic process of tsunami earthquake by liquid-solid coupling model

CAI Yong-en and ZHAO Zhi-dong

Department of Geophysics, Peking University, Beijing 100871, China

Acta Seismologica Sinica Vol.21 No.6 (598-607)  2008

Abstract: Tsunami induced by earthquake is an interaction problem between liquid and solid. Shallow-water wave equationis often used to modeling the tsunami, and the boundary or initial condition of the problem is determined by the displacement or velocity field from the earthquake under sea floor, usually no interaction between them is considered in pure liquid model. In this study, the potential flow theory and the finite element method with the interaction between liquid and solid are employed to model the dynamic processes of the earthquake and tsunami. For modeling the earthquake, firstly the initial stress field to generate the earthquake is set up, and then the occurrence of the earthquake is simulated by suddenly reducing the elastic material parameters inside the earthquake fault. It is different from seismic dislocation theory in which the relative slip on the fault is specified in advance. The modeling results reveal that P, SP and the surface wave can be found at the sea surface besides the tsunami wave. The surface wave arrives at the distance of 600 km from the epicenter earlier than the tsunami 48 minutes, and its maximum amplitude is 0.55 m, which is 2 times as large as that of the sea floor. Tsunami warning information can be taken from the surface wave on the sea surface, which is much earlier than that obtained from the seismograph stations on land. The tsunami speed on the open sea with 3 km depth is 175.8 m/s, which is a little greater than that predicted by long wave theory, (gh)^1/2=171.5 m, and its wavelength and amplitude in average are 32 km and 2 m, respectively. After the tsunami propagates to the continental shelf, its speed and wavelength is reduced, but its amplitude become greater, especially, it can elevate up to 10 m and run 55 m forward in vertical and horizontal directions at sea shore, respectively. The maximum vertical accelerations at the epicenter on the sea surface and on the earthquake fault are 5.9 m/s² and 16.5 m/s², respectively, the later is 2.8 times the former, and therefore, sea water is a good shock absorber. The acceleration at the sea shore is about 1/10 as large as at the epicenter. The maximum vertical velocity at the epicenter is 1.4 times that on the fault. The maximum vertical displacement at the fault is less than that at the epicenter. The difference between them is the amplitude of the tsunami at the epicenter. The time of the maximum displacement to occur on the fault is not at the beginning of the fault slipping but retards 23 s.

Key words: finite element - fluid-solid interaction - earthquake tsunami - numerical modeling

Numerical Simulations of Blood Flow in Artificial and Natural Hearts With Fluid–Structure Interaction

*Matthew G. Doyle, *Jean-Baptiste Vergniaud, *Stavros Tavoularis, and *,†Yves Bourgault

*Department of Mechanical Engineering, University of Ottawa
†Department of Mathematics and Statistics, University of Ottawa, Ottawa, Canada

Artificial Organs 32(11):870–879, 2008

Abstract: This article describes two ongoing numerical studies of fluid–structure interaction in the cardiovascular system: an idealized pulsatile ventricular assist device (VAD), consisting of two fluid chambers separated by a flexible diaphragm; and blood flow and heart wall motion during passive filling of a canine heart. Simulations have been performed for the VAD and compared with the results of a previous study and to our own preliminary experimental results. Detailed measurements of the flow field in the VAD model and additional simulations are in progress. Preliminary simulations using both an idealized model of the natural heart as well as a realistic model have identified the limitations of the current numerical methods in dealing with large three-dimensional deformations. Ongoing research aims at extending the range of simulations to include large deformations and to incorporate an anisotropic material model for the heart wall to account for the muscle fibers.

Key Words: Biomechanics - Computer simulation - Heart-assist devices - Laser-doppler velocimetry - Models - cardiovascular

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