ADINA Publications

Page 39

The Theory used in ADINA is richly documented in the following books by K.J. Bathe and co-authors


Finite Element Procedures
 

Finite Element Procedures in Engineering Analysis

Numerical Methods in Finite Element Analysis
 


The Mechanics of Solids and Structures — Hierarchical ...


The Finite Element Analysis of Shells — Fundamentals


Inelastic Analysis of Solids and Structures

 
 
To Enrich Life
(Sample pages here)
 

 

Following are more than 700 publications — that we know of — 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:

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Computational Flow Dynamics Study in Severe Carotid Bulb Stenosis with Ulceration

T.S. Oh1, Y.B. Ko3, S.-T. Park4, K. Yoon3, S.-W. Lee5, J.W. Park1, J.L. Kim1, B. Kim1, S.-O. Park1, J.S. Kim2, D.C. Suh1

1 Departments of Radiology and Research Institute of Radiology,
2 Department of Neurology, University of Ulsan, College of Medicine, Asan Medical Center;
3 Department of Mechanical Engreering, Dankook University;
4 Department of Radiology, Soonchunhyang University Hospital;
5 School of Mechanical and Automotive Engineering University of Ulsan, Seoul, Korea

Neurointervention, 5:97-102, 2010

Abstract:
Purpose: Computational fluid dynamics (CFD) applications for atherosclerotic carotid stenosis have not been widely used due to limited resolution in the severely stenotic lumen as well as small flow dimension in the stenotic channel.
Materials and Methods: CT data in DICOM format was transformed into 3 dimensional (3D) CFD model of carotid bifurcation. For computational analysis of blood flow in stenosis, commercial finite element software (ADINA Ver. 8.5) was used. The blood flow was assumed to be laminar, viscous, Newtonian, and incompressible. The distribution of wall shear stress (WSS), peak velocity and pressure across the average systolic and diastolic blood pressures permitted construction of a contour map of the velocity in each cardiac cycle.
Results: Computer simulation of WSS, flow velocity and wall pressure could be demonstrated three dimensionally according to flow vs. time dimension. Such flow model was correlated with angiographic finding related to maximum degree of stenosis associated with ulceration. Combination of WSS map and catheter angiogram indicated that the highest WSS corresponded to the most severely stenotic segment at systolic phase, whereas ulceration, which is the weakest point of the plaque, appeared at the downstream side of the carotid bulb stenosis.
Conclusion: Our preliminary study revealed that 3D CFD analysis in carotid stenosis was feasible from CT angiography source image and could reveal WSS, flow velocity and wall pressure in the severe carotid bulb stenosis with ulceration. Further CFD analysis is warranted to apply such hemodynamic information to the atherosclerotic lesion in the more practical way.

Keywords: Carotid arteries - Hemodynamic - Stenosis - CTA - ulceration - Wall shear stress

 

Patient-Based Abdominal Aortic Aneurysm Rupture Risk Prediction with Fluid Structure Interaction Modeling

M. Xenos,1 S.H. Rambhia,1 Y. Alemu,1 S. Einav,1 N. Labropoulos,3 A. Tassiopoulos,3 J.J. Ricotta,2,3 And D. Bluestein1

1 Department of Biomedical Engineering, Stony Brook University, HSC T18-030, Stony Brook, NY 11794-8181, USA
2 Department of Surgery, Washington Hospital Center, Washington, DC, USA
3 Department of Surgery, Stony Brook University Hospital, Stony Brook, NY, USA

Annals of Biomedical Engineering, 38(11): 3323–3337, 2010

Abstract: Elective repair of abdominal aortic aneurysm (AAA) is warranted when the risk of rupture exceeds that of surgery, and is mostly based on the AAA size as a crude rupture predictor. A methodology based on biomechanical considerations for a reliable patient-specific prediction of AAA risk of rupture is presented. Fluid–structure interaction (FSI) simulations conducted in models reconstructed from CT scans of patients who had contained ruptured AAA (rAAA) predicted the rupture location based on mapping of the stresses developing within the aneurysmal wall, additionally showing that a smaller rAAA presented a higher rupture risk. By providing refined means to estimate the risk of rupture, the methodology may have a major impact on diagnostics and treatment of AAA patients.

Keywords: Ruptured abdominal aortic aneurysm - Aneurysmal strength - Rupture potential index - Fluid–structure interaction - Reconstruction of patient based geometry

 

Scantling of Mast and Rigging of Sail Boats: a Few Hints from a Test Case to Develop Improved Design Procedures

C.M. Rizzo, D. Boote

DINAEL- Faculty of Engineering, University of Genova, Genova, Italy

Proc. 11th Int. Symp. on Practical Design of Ships and Other Floating Structures, 613-623, 2010

Abstract: In this paper, the structural design of mast and rigging of sail yachts is presented from a practical viewpoint, highlighting main idealization concepts of structural behavior. At fi rst, the analytical procedures available in open literature are briefl y reviewed, considering current industrial practice in scantling design of sail yachts. Applicable rules are considered as well. Then, more complex scantling procedures, taking advantage of modern computation facilities, are presented. Indeed, fi nite element (FE) analyses are more and more routinely used by designers. However, large deformations and slacking behavior of rigging and sails require nonlinear calculations, making convergence of algorithms diffi cult. In this case, limit states should be carefully defi ned; description of environmental actions and loads application on the structural system need engineering judgment, skill of FE analysts and sailing practice to completely understand the performance of the structure. Examples of applications on a typical modern sail yacht highlight that the design of these fascinating slender structures is really challenging and their design is still largely based on empiricism.

Keywords: Mast - rigging - sails - FEM -  scantling – assessment

 

Patient-Based Abdominal Aortic Aneurysm Rupture Risk Prediction with Fluid Structure Interaction Modeling

M. Xenos1, S.H. Rambhia1, Y. Alemu1, S. Einav1, N. Labropoulos3, A. Tassiopoulos3, J.J. Ricotta2,3, and D. Bluestein1

1 Department of Biomedical Engineering, Stony Brook University, HSC T18-030, Stony Brook, NY 11794-8181, USA
2 Department of Surgery, Washington Hospital Center, Washington, DC, USA
3 Department of Surgery, Stony Brook University Hospital, Stony Brook, NY, USA

Annals of Biomedical Engineering, 38(11):3323-3337, 2010

Abstract: Elective repair of abdominal aortic aneurysm (AAA) is warranted when the risk of rupture exceeds that of surgery, and is mostly based on the AAA size as a crude rupture predictor. A methodology based on biomechanical considerations for a reliable patient-specific prediction of AAA risk of rupture is presented. Fluid–structure interaction (FSI) simulations conducted in models reconstructed from CT scans of patients who had contained ruptured AAA (rAAA) predicted the rupture location based on mapping of the stresses developing within the aneurysmal wall, additionally showing that a smaller rAAA presented a higher rupture risk. By providing refined means to estimate the risk of rupture, the methodology may have a major impact on diagnostics and treatment of AAA patients.

Keywords: Ruptured abdominal aortic aneurysm — Aneurysmal strength — Rupture potential index — Fluid-structure interaction — Reconstruction of patient based geometry

 

The effect of angulation in abdominal aortic aneurysms: fluid-structure interaction simulations of idealized geometries

M. Xenos1, Y Alemu1, D. Zamfir1, S. Einav1, J.J. Ricotta2,3, N. Labropoulos3, A. Tassiopoulos3, D. Bluestein1

1 Department of Biomedical Engineering, Stony Brook University, HSC T18-030, Stony Brook, NY 11794-8181, USA
2 Department of Surgery, Washington Hospital Center, Washington, DC, USA
3 Department of Surgery, Stony Brook University Hospital, Stony Brook, NY, USA

Med Biol Eng Comput, 48:1175–1190, 2010

Abstract: Abdominal aortic aneurysm (AAA) represents a degenerative disease process of the abdominal aorta that results in dilation and permanent remodeling of the arterial wall. A fluid structure interaction (FSI) parametric study was conducted to evaluate the progression of aneurysmal disease and its possible implications on risk of rupture. Two parametric studies were conducted using (i) the iliac bifurcation angle and (ii) the AAA neck angulation. Idealized streamlined AAA geometries were employed. The simulations were carried out using both isotropic and anisotropic wall material models. The parameters were based on CT scans measurements obtained from a population of patients. The results indicate that the peak wall stresses increased with increasing iliac and neck inlet angles. Wall shear stress (WSS) and fluid pressure were analyzed and correlated with the wall stresses for both sets of studies. An adaptation response of a temporary reduction of the peak wall stresses seem to correlate to a certain extent with increasing iliac angles. For the neck angulation studies it appears that a breakdown from symmetric vortices at the AAA inlet into a single larger vortex significantly increases the wall stress. Our parametric FSI study demonstrates the adaptation response during aneurysmal disease progression and its possible effects on the AAA risk of rupture. This dependence on geometric parameters of the AAA can be used as an additional diagnostic tool to help clinicians reach informed decisions in establishing whether a risky surgical intervention is warranted.

Keywords: Aneurysm — FSI — Risk of rupture — Iliac angle — Neck aneurysmal angle

 

Surprisingly Simple Mechanical Behavior of a Complex Embryonic Tissue

M. von Dassow1, J.A. Strother2, L.A. Davidson1

1 Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
2 Howard Hughes Medical Institute Janelia Farm, Ashburn, Virginia, United States of America

Embryonic Tissue. PLoS ONE 5(12): e15359. doi:10.1371/journal.pone.0015359, 2010

Abstract:
Background: Previous studies suggest that mechanical feedback could coordinate morphogenetic events in embryos. Furthermore, embryonic tissues have complex structure and composition and undergo large deformations during morphogenesis. Hence we expect highly non-linear and loading-rate dependent tissue mechanical properties in embryos.
Methodology/Principal Findings:We used micro-aspiration to test whether a simple linear viscoelastic model was sufficient to describe the mechanical behavior of gastrula stage Xenopus laevis embryonic tissue in vivo. We tested whether these embryonic tissues change their mechanical properties in response to mechanical stimuli but found no evidence of changes in the viscoelastic properties of the tissue in response to stress or stress application rate. We used this model to test hypotheses about the pattern of force generation during electrically induced tissue contractions. The dependence of contractions on suction pressure was most consistent with apical tension, and was inconsistent with isotropic contraction. Finally, stiffer clutches generated stronger contractions, suggesting that force generation and stiffness may be coupled in the embryo.
Conclusions/Significance: The mechanical behavior of a complex, active embryonic tissue can be surprisingly well described by a simple linear viscoelastic model with power law creep compliance, even at high deformations. We found no evidence of mechanical feedback in this system. Together these results show that very simple mechanical models can be useful in describing embryo mechanics.

 

Numerical and analytical investigation of collapse loads of laced built-up columns

K.E. Kalochairetis, C.J. Gantes

Laboratory of Metal Structures, Department of Structural Engineering, National Technical University of Athens, 9 Heroon Polytechniou, GR-15780 Zografou, Athens, Greece

Computers and Structures, In press 2010.

Abstract: Built-up columns are often used in steel buildings and bridges providing economical solutions in cases of large spans and/or heavy loads. Two main effects should be taken into account in their design that differentiate them from other structural members. One is the significant influence of shear deformations due to their reduced shear rigidity. The second is the interaction between global and local buckling. These effects are addressed here from both a numerical and an analytical point of view for laced built-up columns. It is concluded that the largest loss of capacity occurs when the local and global Euler critical stresses and the yield stress all coincide. This reduction in capacity becomes more prominent in the presence of imperfections, reaching magnitudes in the order of 50%. Despite the detrimental effects of mode interaction many major design codes do not provide sufficient pertinent guidance. In order to address this issue, a simple analytical method is proposed for calculating the collapse load of laced built-up members taking into account the above effects as well as global imperfections, local out-of straightness and plasticity, which is then verified by means of nonlinear finite element analysis, using either beam or shell elements. The proposed method is found to provide improved accuracy in comparison to EC3 specifications in cases of global elastic failure.

Keywords: Laced built-up columns — Local buckling — Global buckling — Mode interaction — Collapse load — Nonlinear finite element analysis

 

Image-based patient-specific ventricle models with fluid–structure interaction for cardiac function assessment and surgical design optimization

D. Tang1, C. Yang1,2, T.Geva3, P.J. del Nido4

1 Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA 01609 USA
2 School of Mathematics, Beijing Normal University, Beijing, China
3 Dept of Cardiology, Children's Hospital Boston, Dept of Pediatrics, Harvard Medical School, Boston, MA 02115 USA
4 Dept of Cardiac Surgery, Children's Hospital Boston, Dept of Surgery, Harvard Medical School, Boston, MA 02115 USA

Progress in Pediatric Cardiology, 30:51–62, 2010

Recent advances in medical imaging technology and computational modeling techniques are making it possible that patient-specific computational ventricle models be constructed and used to test surgical hypotheses and replace empirical and often risky clinical experimentation to examine the efficiency and suitability of various reconstructive procedures in diseased hearts. In this paper, we provide a brief review on recent development in ventricle modeling and its potential application in surgical planning and management of Tetralogy of Fallot (ToF) patients. Aspects of data acquisition, model selection and construction, tissue material properties, ventricle layer structure and tissue fiber orientations, pressure condition, model validation and virtual surgery procedures (changing patient-specific ventricle data and perform computer simulation) were reviewed. Results from a case study using patient-specific cardiac magnetic resonance (CMR) imaging and right/left ventricle and patch (RV/LV/Patch) combination model with fluid–structure
interactions (FSI) were reported. The models were used to evaluate and optimize human  pulmonary valve replacement/insertion (PVR) surgical procedure and patch design and test a surgical hypothesis that PVR with small patch and aggressive scar tissue trimming in PVR surgery may lead to improved recovery of RV function and reduced stress/strain conditions in the patch area.

Keywords: Right ventricle — Congenital heart disease — Tetralogy of Fallot — Heart model — Fluid-structural interaction

 

Propulsion Modeling and Analysis of a Biomimetic Swimmer

N.S. Ha, N.S. Goo

Smart Microsystem Research Lab., Department of Advanced Technology Fusion, Konkuk University, Seoul 143–701, Korea

Journal of Bionic Engineering, 7:259–266, 2010

Abstract: We have studied a biomimetic swimmer based on the motion of bacteria such as Escherichia coli (E. coli) theoretically and experimentally. The swimmer has an ellipsoidal cell body propelled by a helical filament. The performance of this swimmer was estimated by modeling the dynamics of a swimmer in viscous fluid. We applied the Resistive Force Theory (RFT) on this model to calculate the linear swimming speed and the efficiency of the model. A parametric study on linear velocity and efficiency to optimize the design of this swimmer was demonstrated. In order to validate the theoretical results, a biomimetic swimmer was fabricated and an experiment setup was prepared to measure the swimming speed and thrust force in silicone oil. The experimental results agree well with the theoretical values predicted by RFT. In addition, we studied the flow patterns surrounding the filament with a finite element simulation with different Reynolds number (Re) to understand the mechanism of propulsion. The simulation results provide information on the nature of flow patterns generated by swimming filament. Furthermore, the thrust forces from the simulation were compared with the thrust forces from theory. The simulation results are in good agreement with the theoretical results.

Keywords: Biomimetic microrobots — Swimming microrobots — Propulsion of flagella — Flow visualization — Medical application

 

An implicit stress gradient plasticity model for describing mechanical behavior of planar fiber networks on a macroscopic scale

P. Isaksson

Department of Engineering Physics, Mid Sweden University, SE-851 70 Sundsvall, Sweden

Engineering Fracture Mechanics, 77:1240-1252, 2010

Abstract: The plasticity behavior of fiber networks is governed by complex mechanisms. This study examines the effect of microstructure on the macroscopic plastic behavior of two-dimensional random fiber networks such as strong-bonded paper. Remote load is a pure macroscopic mode I opening field, applied via a boundary layer assuming small scale yielding on the macroscopic scale. It is shown that using a macroscopic classical homogeneous continuum approach to describe plasticity effects due to (macroscopic) singular-dominated strain fields in planar fiber networks leads to erroneous results. The classical continuum description is too simple to capture the essential mechanical behavior of a network material since a structural effect, that alters the macroscopic stress field, becomes pronounced and introduces long-ranging microstructural effects that have to be accounted for. Because of this, it is necessary to include a nonlocal theory that bridges the gap between microscopic and macroscopic scales to describe the material response in homogeneous continuum models. An implicit stress gradient small deformation plasticity model, which is based on a strong nonlocal continuum formulation, is presented here that has the potential to describe the plasticity behavior of fiber networks on a macroscopic scale. The theory is derived by including nonlocal stress terms in the classical associated J2-theory of plasticity. The nonlocal stress tensor is found by scaling the local Cauchy stress tensor by the ratio of nonlocal and local von Mises equivalent stresses. The model is relatively easy to implement in ordinary finite element algorithms for small deformation theory. Fairly good agreements are obtained between discrete micromechanical network models and the derived homogeneous nonlocal continuum model.

Keywords: Nonlocal theory — Gradient plasticity — Network material — Crack mechanics

 

Reliability analysis of 500MWe PHWR inner containment using high-dimensional model representation

B.N. Rao1, Rajib Chowdhury1, A.M. Prasad1, R.K. Singh2, H.S. Kushwaha2

1 Structural Engineering Division, Department of Civil Engineering, Indian Institute of Technology Madras, Chennai 600 036, Tamil Nadu, India
2 Bhabha Atomic Research Centre, Mumbai, India

International Journal of Pressure Vessels and Piping, 87(5):230-238, 2010

Abstract: In this paper, uncertainty analysis of Indian 500MWe Pressurized Heavy Water Reactor (PHWR) subjected to an accidental pressure is carried out using a computational tool based on High Dimensional Model Representation (HDMR) that facilitates lower dimensional approximation of the original high dimensional implicit limit state/performance function. The method involves response surface generation of HDMR component functions, and Monte Carlo simulation. HDMR is a general set of quantitative model assessment and analysis tools for capturing the high-dimensional relationships between sets of input and output model variables. It is very efficient formulation of the system response, if higher-order variable correlations are weak, allowing the physical model to be captured by first few lower-order terms. Once the approximate form of the original implicit limit state/performance function is defined, the failure probability can be obtained by statistical simulation. Reliability estimates of PHWR inner containment subjected to an internal pressure exceeding the design pressure, considering three stages of  progressive failure prior to collapse are presented.

Keywords: High dimensional model representation — Pressurized heavy water reactor — Structural reliability — Response surface and failure probability

 

The effect of beach slope on the tsunami run-up induced by thrust fault earthquakes

C. An, Y. Cai

Department of Geophysics, Peking University, Beijing, 100871, China

Procedia Computer Science,  1:645–654, 2010

Abstract: Analytical methods for studying tsunami run-up become untenable when the tsunami wave runs on beaches. In this study, we use a finite-element procedure that includes the interaction between solid and fluid based on the potential flow theory to simulate the dynamics of tsunami wave induced by a thrust fault earthquake in order to investigate the effect of different beach slopes on the tsunami run-up. The simulated run-up shows significantly differences from that predicted by the analytical solution. The maximum run-up shows a negative linear relationship with the square root of the cotangent of the beach slope, similar to the result of the analytical solution using a solitary wave as the incident wave, but with different slopes and amplitudes.

Keywords: Earthquake — Tsunami — Run-up — Beach effect

 

Three-dimensional finite element analysis of wall pressure on large diameter silos

J. Fu, M. Luan, Q.Yang, T. Nian

State Key Laboratory of Coastal and Offshore Engineering, Institute of Geotechnical Engineering, School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian, 116085, China

Journal of Convergence Information Technology, 5(7), 2010

Abstract: With the increasing volume demand of silos, silo diameters are bigger and bigger. However, present wall pressure computation methods are mostly based on small diameter silos. There is little system research on large diameter silos. To solve this problem, systematical research by three-dimensional finite element method on large diameter silos was carried out in this paper. Static wall pressure and wall pressure at the end of filling were analyzed. And the influence of mechanical parameters of bulk materials to wall pressure was studied. Two lamination ways to simulate filling process was studied. The result shows that scale of silo take important effect to wall pressure. Wall pressures at the end of filling of large diameter silos are much larger than static wall pressures near silos bottom. Wall pressure of filling should be considered in design of large diameter silos. Study in this paper has heavy theoretical significance and provide an important basis for the large diameter silo design.

Keywords: Filling — Materials handling equipment  — Pressure effects — Three dimensional — Wall flow

 

Hemodynamic environments from opposing sides of human aortic valve leaflets evoke distinct endothelial phenotypes in vitro

E.J. Weinberg1,2, P.J. Mack2,3,4, F.J. Schoen3,4, G. García-Cardeña3,  M.R.K. Mofrad1

1 Department of Bioengineering, University of California, Berkeley, CA 94720, USA
2 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
3 Department of Pathology, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA 02115, USA
4 Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, USA

Cardiovasc Eng,  10:5–11, 2010

Abstract: The regulation of valvular endothelial phenotypes by the hemodynamic environments of the human aortic valve is poorly understood. The nodular lesions of calcific aortic stenosis (CAS) develop predominantly beneath the aortic surface of the valve leaflets in the valvular
fibrosa layer. However, the mechanisms of this regional localization remain poorly characterized. In this study, we combine numerical simulation with in vitro experimentation to investigate the hypothesis that the previously documented differences between valve endothelial phenotypes are linked to distinct hemodynamic environments characteristic of these individual anatomical locations. A finite-element model of the aortic valve was created, describing the dynamic motion of the valve cusps and blood in the valve throughout the cardiac cycle. A fluid mesh with high resolution on the fluid boundary was used to allow accurate computation of the wall shear stresses. This model was used to compute two distinct shear stress waveforms, one for the ventricular surface and one for the aortic surface. These waveforms were then applied
experimentally to cultured human endothelial cells and the expression of several pathophysiological relevant genes was assessed. Compared to endothelial cells subjected to shear stress waveforms representative of the aortic face, the endothelial cells subjected to the ventricular waveform showed significantly increased expression of the ‘‘atheroprotective’’ transcription factor Kruppel-like factor 2 (KLF2) and the matricellular protein Nephroblastoma overexpressed (NOV), and suppressed expression of chemokine Monocyte-chemotactic protein-1 (MCP-1). Our observations suggest that the difference in shear stress waveforms between the two sides of the aortic valve leaflet may contribute to the documented differential side-specific gene expression, and may be relevant for the development and progression of CAS and the potential role of endothelial mechanotransduction in this disease.

Keywords: Aortic valve — Calcific aortic stenosis — Endothelial mechanotransduction —  Shear stress — Cell mechanics and mechanotransduction — Valvular disease

 

Comparison of Second-Generation Stents for Application in the Superficial Femoral Artery: An In Vitro Evaluation Focusing on Stent Design

S. Müller-Hülsbeck1, P.J. Schäfer2, N. Charalambous2, H. Yagi3, M. Heller2, and T. Jahnke2

1 Department of Diagnostic and Interventional Radiology/Neuroradiology, Academic Hospitals Flensburg, Germany.
2 Department of Radiology, University Hospitals Schleswig-Holstein – Campus Kiel, Germany.
3 Terumo, Ashitaka Factory, Tokyo, Japan.

Journal of Endovascular Therapy, 17( 6):767-776, 2010

Abstract:
Purpose: To examine and compare in an ex vivo study different nitinol stent designs intended for the superficial femoral artery (SFA) with regard to the appearance of fracture.
Methods: Seven different 8-340-mm nitinol stents were evaluated (Misago; Absolute, Smart, Luminexx, Sentinol; Lifestent NT, and Sinus-Superflex). Finite element analysis (FEA) was used for digitalized stent design comparison; the strain during stent movement was calculated for bending, compression, and torsion. Additional mechanical fatigue tests for bending (70u), compression (40%), and torsion (twisted counterclockwise by 180u) were performed up to 650,000 cycles or until a fracture was observed.
Results: The FEA bending test showed that only the Misago, LifeStent, and Absolute stents presented no zones of high strain; in the torsion test, the Smart stent also had no zones of high strain. Macroscopic evaluation after mechanical bending indicated that the LifeStent performed the best (no stent fracture after 650,000 cycles). Misago and Absolute stents showed fractures at 536,000 cycles and 456,667 cycles, respectively (range 320,000–650,000 cycles). After compression and torsion testing, Misago showed no stent fracture after 650,000 cycles. The worst performing stent was Luminexx during all test cycles.
Conclusion: The 7 SFA stents showed differences in the incidence of high strain zones, which indicates a potential for stent fracture, as demonstrated by the mechanical fatigue tests. Differences in stent design might play a major role in the appearance of stent strut fracture related to restenosis and reocclusion.

Keywords: Superficial femoral artery — Stent — Nitinol — Experimental study — Finite element analysis — Stent design — Fatigue testing — Stent fracture — Compression — Bending — Torsion

 

Relative contributions of strain-dependent permeability and fixed charged density of proteoglycans in predicting cervical disc biomechanics: A poroelastic C5-C6 finite element model study

M. Hussain1, R.N. Natarajan2,3, G. Chaudhary4, H.S. An2, G.B.J. Andersson2

1 Division of Research, Logan University, 1851 Schoettler Rd, Chesterfield, MO 63017, USA
2 Department of Orthopedic Surgery, Rush University Medical Center, Chicago, IL 60612, USA
3 Department of Bioengineering, University of Illinois at Chicago, Chicago, IL 60607, USA
4 Medical Residency Applicant, St. Louis, MO 63108, USA

Medical Engineering & Physics, In press 2010.

Abstract: Disc swelling pressure (P(swell)) facilitated by fixed charged density (FCD) of proteoglycans (P(fcd)) and strain-dependent permeability (P(strain)) are of critical significance in the physiological functioning of discs. FCD of proteoglycans prevents any excessive matrix deformation by tissue stiffening, whereas strain-dependent permeability limits the rate of stress transfer from fluid to solid skeleton. To date, studies involving the modeling of FCD of proteoglycans and strain-dependent permeability have not been reported for the cervical discs. The current study objective is to compare the relative contributions of strain-dependent permeability and FCD of proteoglycans in predicting cervical disc biomechanics. Three-dimensional finite element models of a C5-C6 segment with three different disc compositions were analyzed: an SPFP model (strain-dependent permeability and FCD of proteoglycans), an SP model (strain-dependent permeability alone), and an FP model (FCD of proteoglycans alone). The outcomes of the current study suggest that the relative contributions of strain-dependent permeability and FCD of proteoglycans were almost comparable in predicting the physiological behavior of the cervical discs under moment loads. However, under compression, strain-dependent permeability better predicted the in vivo disc response than that of the FCD of proteoglycans.

Keywords: Fixed charged density of proteoglycans — Strain-dependent permeability and porosity — Cervical disc biomechanics — Tissue swelling — Poroelastic finite element

 

Cumulative Effects of Soil Nailing under Cyclic Load Considering Bottom Boundary Conditions of Facing

F. Zhu1, X. Liao2, J. Li1 Y. Yang1

1 Institute of Geotechnical Engineering, Hunan University of Technology, Zhuzhou 412008, China
2 Second Construction Company, Zhongtian Construction Group Co. Ltd, Hangzhou 310008, China

Proc. ASCE GeoShanghai 2010 International Conference, 2010

Abstract: Based on laboratory study, cumulative effect of soil nailing under cyclic load is studied. The cyclic load is produced by a multi-channel load system, from experimental results, displacement of facing increases considerably after a certain load number, then keep almost constant, which indicates attenuation of accumulation effect. Thereafter, in order to compare with laboratory results, through ADINA system, based on Mohr-Coulomb criteria, a plain strain finite element model (FEM) is built. From both experimental and calculation results, considering different stiffness and boundary constraints at the bottom of facing facing, displacement of facing is smaller with concrete facing (greater stiffness), than with wood facing (smaller stiffness), similarly, displacement of facing is smaller with fixed bottom than with free one, moreover, load frequency has pronounced influence on displacement of facing.

Keywords: Soil nailing — Cyclic load — Displacement of facing — Load frequency

 

Association between Biomechanical Structural Stresses of Atherosclerotic Carotid Plaques and Subsequent Ischaemic Cerebrovascular Events e A Longitudinal in Vivo Magnetic Resonance Imaging-based Finite element Study

U. Sadat1,2, Z. Teng1, V.E. Young1, S.R. Walsh2, Z.Y. Li1, M.J. Graves1, K. Varty2, J.H. Gillard1

1 University Department of Radiology, University of Cambridge, Cambridge, UK
2 Cambridge Vascular Unit, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK

Eur J Vasc Endovasc Surg, 40:485-491, 2010

Abstract:
Background: High-resolution magnetic resonance (MR) imaging has been used for MR imaging-based structural stress analysis of atherosclerotic plaques. The biomechanical stress profile of stable plaques has been observed to differ from that of unstable plaques; however, the role that structural stresses play in determining plaque vulnerability remains speculative.
Methods: A total of 61 patients with previous history of symptomatic carotid artery disease underwent carotid plaque MR imaging. Plaque components of the index artery such as fibrous tissue, lipid content and plaque haemorrhage (PH) were delineated and used for finite element analysis-based maximum structural stress (M-C Stress) quantification. These patients were followed up for 2 years. The clinical end point was occurrence of an ischaemic cerebrovascular event. The association of the time to the clinical end point with plaque morphology and M-C Stress was analysed.
Results: During a median follow-up duration of 514 days, 20% of patients (n=12) experienced an ischaemic event in the territory of the index carotid artery. Cox regression analysis indicated that M-C Stress (hazard ratio (HR): 12.98 (95% confidence interval (CI): 1.32-26.67, p = 0.02), fibrous cap (FC) disruption (HR: 7.39 (95% CI: 1.61-33.82), p = 0.009) and PH (HR: 5.85 (95% CI: 1.27-26.77), p = 0.02) are associated with the development of subsequent cerebrovascular events. Plaques associated with future events had higher M-C Stress than those which had remained asymptomatic (median (interquartile range, IQR): 330 kPa (229-494) vs. 254 kPa (166-290), p = 0.04).
Conclusions: High biomechanical structural stresses, in addition to FC rupture and PH, are associated with subsequent cerebrovascular events.

Keywords: Biomechanical stress — Structural stress — Plaque — Atherosclerosis — Finite element analysis — Stroke

 

Reduction in segmental flexibility because of disc degeneration is accompanied by higher changes in facet loads than changes in disc pressure: a poroelastic C5–C6 finite element investigation

M. Hussain1, R.N. Natarajan2,3, H.S. An2, G.B.J. Andersson2

1 Division of Research, Logan University, 1851 Schoettler Rd., Chesterfield, MO 63017, USA
2 Department of Orthopedic Surgery, Rush University Medical Center, Chicago, IL 60612, USA
3 Department of Bioengineering, University of Illinois at Chicago, Chicago, IL 60607, USA

The Spine Journal, 1069–1077, 2010

Abstract:
Background context: Nerve fiber growth inside the degenerative intervertebral discs and facets is thought to be a source of pain, although there may be several other pathological and clinical reasons for the neck pain. It, however, remains difficult to decipher how much disc and facet joints contribute to overall degenerative segmental responses. Although the biomechanical effects of disc degeneration (DD) on segmental flexibility and posterior facets have been reported in the lumbar spine, a clear understanding of the pathways of degenerative progression is still lacking in the cervical spine.
Purpose: To test the hypothesis that after an occurrence of degenerative disease in a cervical disc, changes in the facet loads will be higher than changes in the disc pressure.
Study design: To understand the biomechanical relationships between segmental flexibility, disc pressure, and facet loads when the C5–C6 disc degenerates.
Methods: A poroelastic, three-dimensional finite element (FE) model of a normal C5–C6 segment was developed and validated. Two degenerated disc models (moderate and severe) were built from the normal disc model. Biomechanical responses of the three FE models (normal, moderate, and severe) were further studied under diurnal compression (at the end of the daytime activity period) and moment loads (at the end of 5 seconds) in terms of disc height loss, angular motions, disc pressure, and facet loads (average of right and left facets).
Results: Disc deformation under compression and segmental rotational motions under moment loads for the normal disc model agreed well with the corresponding in vivo studies. A decrease in segmental flexibility because of DD is accompanied by a decrease in disc pressure and an increase in facet loads. Biomechanical effects of degenerative disc changes are least in flexion. Segmental flexibility changes are higher in extension, whereas changes in disc pressure and facet loads are higher in lateral bending and axial rotation, respectively.
Conclusions: The results of the present study confirmed the hypothesis of higher changes in facet loads than in disc pressure, suggesting posterior facets are more affected than discs because of a decrease in degenerative segmental flexibility. Therefore, a degenerated disc may increase the risk of overloading the posterior facet joints. It should be clearly noted that only after degeneration simulation in the disc, we recorded the biomechanical responses of the facets and disc. Therefore, our hypothesis does not suggest that facet joint osteoarthritis may occur before degeneration in the disc. Future cervical spine–based experiments are warranted to verify the conclusions presented in this study.

Keywords: Disc degeneration — Disc height — Rotational motion — Disc pressure —  Facet load

 

Analysis of the magnet support structure for the plasma fusion experiment Wendelstein 7-X

N. Jaksic1, P. van Eeten2, V. Bykov2, F. Schauer2

1 Max-Planck-Institute for Plasma Physics, EURATOM Association, Engineer/Scientist, Boltzmannstraße 2, D-85748 Garching, Germany
2 Max-Planck-Institute for Plasma Physics, EURATOM Association, Engineer/Scientist, Branch Institute Greifswald, Germany

Computers and Structures, In press 2010.

Abstract: The world’s largest plasma fusion experimental device of the stellarator family named Wendelstein 7-X (W7-X) [http://www.ipp.mpg.de/ippcms/eng/for/projekte/w7x/index.html] is being built at the Max-Planck-Institute for Plasma Physics (IPP) in Greifswald, Germany. The mission of the experiment is to prove the fusion reactor relevance of the stellarator principle [1,2].
Main subject of this paper is the description of the numerical simulation of the highly complex and multiple nonlinear W7-X magnet system structure with the code ADINA. This code was chosen right from the start of the project and has later been used in parallel with the subsequently installed ANSYS and ABAQUS codes until now. The ADINA W7-X global structure model is the result of a long term R&D work on the superconducting coils and related support structure optimization. Despite the fact that W7-X is already in the assembly phase, there are still large structural analysis efforts going on. Their aim is to accompany the machine construction by evaluating specific assembly issues, non-conformities and design changes, but also to evaluate the operational limits of the experimental device which in many respects is an absolute prototype worldwide.

Keywords: Plasma fusion — Stellerator experiment — Superconducting coils — FE analysis

 

Numerical Analysis of a Novel Method for Temperature Gradient Measurement in the Vicinity of Warm Inflamed Atherosclerotic Plaques

Z. Aronis1, E. Massarwa2, L. Rosen3, O. Rotman1, R. Eliasy2, R. Haj-Ali2,4, and S. Einav1

1 Tel-Aviv University/Biomedical Engineering Department, Tel-Aviv, Israel
2 Tel-Aviv University/Mechanical Engineering Department, Tel-Aviv, Israel
3 CorAssist Cardiovascular Ltd., Herzliya, Israel
4 Georgia Institute of Technology/School of Civil Engineering, Atlanta, GA 30332, USA

MEDICON 2010, IFMBE Proceedings 29, pp. 584–587, 2010.

Abstract: Thermography is a method used mainly for the detection of warmer arterial wall regions, as an indication for the presence of inflamed atherosclerotic plaques. A new method, utilizing injection of cold saline to the bloodstream and measuring temperature gradients within the flow instead of the wall is numerically investigated. Results show an almost 12-fold increase in expected temperature gradients, emphasizing the usefulness of such method for novel catheter design.

Keywords: Thermography – Atherosclerosis – Plaque - Numerical Simulations

 

Simulation on the Construction Process of Double-arch Tunnel by ADINA

Y. Peng and  W. Tan

College of Hydraulic & Environmental Engineering, China Three Gorges University, Yichang, China

Proc. Third International Conference on Information and Computing, pp.60-63, 2010

Abstract: As a new tunnel structure form, double-arch tunnel is placed on the research stage at home and abroad. Since the stability of surrounding rock and its strain-stress have close relationship with the lining structure function appearance, the reliabilities of the support’s design parameters as well as the working procedure, the stress and displacement in the surrounding rock during different working stages of the double-arch tunnel and the stress and displacement law of the supporting structure achieved are analyzed in this paper; a reasonable excavation procedure, support procedure and the
best support time are put forward on the basis of that. It is significant for the design and construction of the double-arch tunnel in China.

Keywords: Traffic engineering — Numerical simulation — FEM — Double-arch tunnel — Construction process

 

Toward Sensitivity Enhancement of MEMS ccelerometers Using Mechanical Amplification Mechanism

A. Ya’akobovitz1 and S.Krylov2

1 Faculty of Engineering, Tel-Aviv University, Tel-Aviv 69978, Israel
2 Department of Solid Mechanics, Materials and Systems, Tel-Aviv University, Tel-Aviv 69978, Israel

IEEE Sensors Journal, 10(8):1311-1319, 2010

Abstract: report on the novel architecture and operational principle of  microelectromechanical accelerometers, which may lead to enhanced sensitivity achieved through mechanical amplification of a proof mass displacements. The integrated amplification mechanism serving also as a linear-to-angular motion transformer is realized as an eccentric elastic torsion link that transforms small out-of-plane motion of the proof mass into significantly larger motion of a tilting element whose displacements are sensed to extract acceleration. The design parameters as well as the amplification ratio were elaborated using a lumped model and numerical finite element simulations. The device was fabricated from silicon-on-insulator wafer and is distinguished by a robust single-layer architecture and simple fabrication process. The devices were operated using electrostatic and inertial actuation of the proof mass combined with the optical sensing. Theoretical and experimental results, which are in a good agreement with each other, indicate that the motion amplification scheme realized in the framework of the suggested architecture results in larger detectable displacements and could be efficiently used for sensitivity improvement of microaccelerometers.

Keywords: Accelerometer — amplification mechanism — microelectromechanical systems (MEMS) — silicon on insulator (SOI)

 

Numerical study on the effect of nozzle pressure and yarn delivery speed on the fiber motion in the nozzle of Murata vortex spinning

Z. Pei and C. Yu

College of Textiles, Donghua University, 2999 North Renmin Road, Shanghai 201620, China

Journal of Fluids and Structures, In press 2010

Absract: Murata vortex spinning (MVS) is a recently developed spinning technology which utilizes high speed swirling airflow to insert twist into the yarn. The motional characteristics of the flexible fibers in the airflow inside theMVS nozzle are of vital importance to the yarn formation mechanism and properties. The fiber motion in the MVS nozzle involves fluid-structure interaction (FSI) and contact problems. In this paper, a two-dimensional FSI model combined with the fiber–wall contact is introduced to simulate a single fiber moving in the airflow inside the MVS nozzle. The model is solved using a finite element code ADINA. Based on the model, the motional characteristics of the fiber are analyzed and the effect of two process parameters – the nozzle pressure and yarn delivery speed – on the fiber motion and, in turn, the yarn tenacity is discussed. The results indicate that the fiber firstly undergoes a false-twisting process. Subsequently, its trailing end splays out and whirls within the nozzle chamber for several turns to helically wrap and make the spun yarn. The results also show that the effect of the nozzle pressure on the tenacity of the produced MVS yarn is not obvious. The increased yarn delivery speed leads to the decreased MVS yarn tenacity. The numerical results show good agreement with the experimental results provided by other researchers.

Keywords: Murata vortex spinning — Fiber motion — Nozzle —  Fluid-structure interaction — Nozzle pressure — Yarn delivery speed

 

Vibration analysis of hydropower house based on fluid-structure coupling numerical method

S. Wei and L. Zhang

College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, P. R. China

Water Science and Engineering, 3(1):75-84, 2010

Abstract: By using the shear stress transport (SST) model to predict the effect of random flow motion in a fluid zone, and using the Newmark method to solve the oscillation equations in a solid zone, a coupling model of the powerhouse and its tube water was developed. The effects of fluid-structure interaction are considered through the kinematic and dynamic conditions applied to the fluid-structure interfaces (FSI). Numerical simulation of turbulent flow through the whole flow passage of the powerhouse and concrete structure vibration analysis in the time domain were carried out with the model. Considering the effect of coupling the turbulence and the powerhouse structure, the time history response of both turbulent flows through the whole flow passage and powerhouse structure vibration were generated. Concrete structure vibration analysis shows that the displacement, velocity, and acceleration of the dynamo floor respond dramatically to pressure fluctuations in the flow passage. Furthermore, the spectrum analysis suggests that pressure fluctuation originating from the static and dynamic disturbances of hydraulic turbine blades in the flow passage is one of the most important vibration sources.

Keywords: Hydropower house — Fluid-structure interaction — Navier-Stokes equations —  Structural vibration — Numerical simulation

 

In Vitro and Computational Thrombosis on Artificial SurfacesWith Shear Stress

S.C. Corbett1,2, A. Ajdari1, A.U. Coskun1, and H. N-Hashemi1

1 Department of Mechanical Engineering, Northeastern University, Boston
2 Research and Development, Abiomed, Inc., Danvers, MA, USA

Artificial Organs, 34(7):561-569, 2010

Abstract: Implantable devices in direct contact with flowing blood are associated with the risk of thromboembolic events. This study addresses the need to improve our understanding of the thrombosis mechanism and to identify areas on artificial surfaces susceptible to thrombus deposition.Thrombus deposits on artificial blood step transitions are quantified experimentally and compared with shear stress and shear rate distributions using computational fluid dynamics (CFD) models. Larger steps, and negative (expanding) steps result in larger thrombus deposits. Fitting CFD results to experimental deposit locations reveals a specific shear stress threshold of 0.41 Pa or a shear rate threshold of 54 s-1 using a shear thinning blood viscosity model. Thrombosis will occur below this threshold, which is specific to solvent-polished polycarbonate surfaces under in vitro coagulation conditions with activated clotting time levels of 200–220 s. The experimental and computational models are valuable tools for thrombosis prediction and assessment that may be used before proceeding to clinical trials and to better understand existing clinical problems with thrombosis.

Keywords: Thrombosis — Computational fluid dynamics — Stagnation — Shear rate — Shear stress — Surfaces

 



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