Following are more than 700 publications — that we know of — with reference to the use of ADINA. Since there are numerous papers published in renowned journals, we can only give here a selection. 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:
Resonant pumping in a multilayer impedance pump
L. Loumes,1 I. Avrahami,2 and M. Gharib1
1Division of Engineering and Applied Sciences, California Institute of Technology, 1200 E, California Blvd., MC 205-45, Pasadena, California 91125, USA
2Medical Engineering, AFEKA ý Tel Aviv Academic College of Engineering, Israel
Physics Of Fluids 20, 023103, 2008
Abstract: This paper introduces the concept of multilayer impedance pump, a novel pumping mechanism inspired by the embryonic heart structure. The pump is a composite two-layer fluid-filled elastic tube featuring a thick gelatinous internal. Pumping is based on the impedance pumping mechanism. In an impedance pump, elastic waves are generated upon external periodic compressions of the elastic tube. These waves propagate along the tube’s walls, reflect at the tube’s extremities, and drive the flow in a preferential direction. The originality in the multilayer impedance pump design relies on the use of the thick internal gelatinous layer to amplify the elastic waves responsible for the pumping. As a consequence, only small excitations are needed to produce significant flow. This fully coupled fluid-structure interaction problem is solved for the flow and the structure using the finite element method over a relevant range of frequencies of excitation. Results show that the multilayer impedance pump is a complex system that exhibits a resonant response. Flow output and inner wall motion are maximal when the pump is actuated at the resonant frequency. The wave interaction mechanism present in an impedance pump is described here in details for the case of a multilayer impedance pump. Using energy balance for the passive portion of the elastic tube, we show that the elastic tube itself works as a pump and that at resonance maximum energy transmission between the elastic tube and the fluid occurs. Finally, the pump is especially suitable for many biomedical applications.
Numerical Simulation of Hydraulic Turbine Based on Fluid-Structure Coupling
Demin Liu1, Shuhong Liu1, Yulin Wu1 and Xiao-bing Liu2
1State Key Laboratory of Hydroscience & Engineering, Dept. of Thermal Engineering, Tsinghua University, China
2Schoolof Energy and Environment, Xihua University, Chengdu, China
Proc. The 4th International Symposium on Fluid Machinery and Fluid Engineering, 345-351, 2008
Abstract: By adopting the arbitrary Lagrange-Euler (ALE) method of software ADINA, fluid-structure coupling (FSC) calculation of a Francis turbine is conducted. The vibration frequency and mode-of the runner in the air and water are obtained. The calculation results show that runner frequency of the turbine is reduced in certain degree under the effect of water pressure and viscous force, and the mode is changed, too. By using dynamic fracture mechanics, the possible cracking damage of the runner is predicated.
Keywords: fluid-structure coupling - hydraulic turbine – vibration - numerical simulation
Three-Dimensional Finite Element Simulations of Compression Tests on Bimrock
M. Barbero, M. Bonini, M. Borri-Brunetto
Department of Structural and Geotechnical Engineering, Politecnico di Torino, Italy
Proc. 12th Int. Conf. IACMAG, 2008
Abstract: The paper deals with the mechanical behaviour of “bimrock” (block in matrix rock), characterized by a heterogeneous structure, constituted by rock blocks included in a small-grained, well-cemented material (matrix) with lower mechanical characteristics. The bimrock is a very peculiar material that may give rise to serious problems in engineering applications. To properly model this kind of problems it is necessary to suitably characterize the bimrock. In order to contribute to the understanding of the bimrock mechanical behaviour and to individuate strength and deformability laws suitable for the bimrock as an equivalent continuum, as the problem is clearly three-dimensional, 3D numerical analyses have been carried out by using the finite element method implemented in the Adina code. Uniaxial and triaxial compression tests on bimrock laboratory samples are simulated. Different volumetric proportions of the blocks are considered. The numerical results show the influence of the volume proportion of the blocks on the strength and deformability of bimrock, confirming the results obtained with previous 2D analyses. Furthermore, the results suggest that the interfaces between the blocks and the matrix play an important role, and may have an influence on the mechanical behaviour of bimrock.Keywords: Bimrock — melange — heterogeneous materials — numerical modelling
Seismic Design Of Two New York Bridges
Hardesty & Hanover, LLP, New York, USA
Proc. The 14th World Conference on Earthquake Engineering, 2008
Abstract: The Third Avenue Bridge and Willis Avenue Bridge are two adjacent bridges each
carrying one directional traffic across Harlem River in New York City. The replacement of 100-year old Third Avenue Bridge is complete. The new 5-lane crossing consists of 17 approach spans and a 107-m long swing span for an overall bridge length of 457m. Including on-grade approaches, the overall project length is 1067m. Construction of the $118.8 million bridge replacement project began in 2001 and completed in 2005. The Willis Avenue Swing Bridge over the Harlem River is being replaced under a $612 million project which is massive in scope as it extends over a mile in length, passes over the Harlem River and an adjoining railyard and provides connections between two major highways as well as three major arterial streets. The new alignment not only dramatically improves the alignment from that of the 100 year old existing bridge but also facilitates maintaining 70,000 vehicles per day of roadway traffic as well as maintaining navigation on the river. The project centerpiece is a new four lane, 106 meter long swing span. This paper focuses on the seismic analysis and seismic design of the two bridges. Challenges faced by the designers of the new bridge, and solutions developed to meet these challenges will be introduced. Since similarities exist between these two bridges, more detailed description will be on one of them, i.e. Third Avenue Bridge, and the other one is only in brief.
Keywords: Seismic — Design — Swing Bridge — Harlem River — Pivot Pier — Pivot Bearing — Truss — New York — Non-linear
Modelling of Tracer Tests in a Shear Zone at the Grimsel Test Site
Institut für Nukleare Entsorgung
Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft — Wissenschaftliche Berichte FZKA 7417, 2008Abstract: In the Colloid Formation and Migration (CFM) Project at the Grimsel Test Site an experiment has been planned in order to study the generation of bentonite colloid and colloid facilitated radionuclides transport in a low gradient groundwater flow. During the first phase of this project a series of tracer tests have been performed to evaluate suitable flow fields for long-term colloid migration experiments within the fractured shear zone. The tracer tests with uranine have been accompanied by numerical modelling to support the in situ measurements. The overall objective of this modelling work is to understand the flow path and the relevant transport processes within the water-conducting shear zone, considering the low hydraulic gradients. The numerical analysis was performed with the ADINA-F finite element code. The mathematical model is based on the Darcy’s law for groundwater flow and the advection-dispersion equation for the uranine transport through a porous shear zone. For the numerical simulation a two dimensional model in the plane of the shear zone has been used. The computational domain considers the circular tunnel sealed with a surface packer, both injection wells and the extraction hole. Both field data and modelling results provide a fairly consistent picture of the flow and transport characteristics in the shear zone at the planned CFM location. Furthermore, the simulation results match the experimental breakthrough curves fairly well and give confidence in the numerical model used. The estimated hydraulic and transport parameters from calibration work for two dipole fields show somewhat differences caused by natural heterogeneities in the hydraulic conductivity of the shear zone.
Seismic performance of a long span arch bridge taking account of fluctuation of axial force
H. Chavez and J.J. Alvarez
Universidad Michoacana de San Nicolas de Hidalgo, Mexico
Proc. The 14th World Conference on Earthquake Engineering, 2008
Abstract: The seismic behavior of a long-span arch bridge is investigated based on a series of nonlinear dynamic analyses. The bridge was modeled with ADINA by means of elements with nonlinear behavior Since the axial force and bending moment interaction is significant in the arch rib under strong ground motions, this effect is included in the analyses by frame elements varying their moment-curvature relations. It was found from the analyses that large axial forces, as much as 1.5 times the dead axial force are developed in the arch rib during excitations, so moment-curvature relations change in the arch rib and hence should be considered in design.
Keywords: Arch bridges — nonlinear dynamic analysis — seismic performance
Experimental And Numerical Study On Dynamic Properties Of Friction-Resistant Dry-Masonry Structures
S. Dorjpalam1, H. Kawase2, K. Yamaguchi3, and S.O.Citak4
1 Structural Engineer
2 Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan
3 Grad. School of Human-Environment Studies, Kyushu University, Fukuoka, Japan
4 Ohsaki Research Institute, Tokyo, Japan
Proc. The 14th World Conference on Earthquake Engineering, 2008
Abstract: Dynamic properties of friction-resistant dry-masonry SRB-DUP (Steel Reinforced Brick based on Distributed Unbond Prestress) structures and structural elements are studied through experimental tests and numerical simulation analyses. First, dynamic tests are conducted on masonry wall elements, and basic dynamic properties are found. Next, a numerical model is formulated using micro-modeling technique, where constituent materials (bricks and reinforcing steel elements) are modeled as separate entities. The model is verified by analyzing the experimental wall models. Then simulation models of various wall elements are built and analyzed. Based on the analyses results a macro-model of a real size structure is built and analyzed for strong ground motion records. We found that the SRB-DUP structure shows quite strong seismic resistance.
Keywords: Friction-resistant — Reinforced Masonry — umerical Modeling — Simulation — FEM Analysis — Environmentally Friendly Structural System
Old and new solutions for contact splices in columns
TU Berlin, Department of Steel Structures, c/o Consulting office, Bismarckallee 4, 14193 Berlin, Germany
Journal of Constructional Steel Research, 64:833–844, 2008
Abstract: Compression forces in a splice can be transferred by contact. Accordingly additional imperfections can be noticed and have to be accounted for. If a contact splice is placed inside the length of a column these initial additional imperfections will have an influence on the buckling behaviour and thus the load carrying capacity of the column. Report on theoretical investigations on the member behaviour and on the design of a splice and its fastenings is given. Also full scale tests on different types of splices are referred to. The test results are compared to ultimate load calculations and respective design methods are proposed. Especially for contact splices in columns arranged directly one on top of the other the stability behaviour for a splice at midspan is examined and leads to a special buckling curve.
Keywords: Columns — Splices — Contact — Stability — Initial imperfections — Full scale tests — Ultimate load calculations — Steel structures
Stability analysis of gravity dams on sloping layered rock foundation against deep slide
L. Zhang, D. Wang, H. Zhang, and W. Wang
Hohai University, Nanjing, China, 210098
Proc. 11th ASCE Aerospace Division International Conference (Earth and Space 2008),
Modal Identification Study of Vincent Thomas Bridge Using Simulated Wind-Induced Ambient Vibration Data
X. He1, B. Moaveni1, J.P Conte2, A. Elgamal2, S.F. Masri2
1 Tufts University
2 University of California, San Diego
Postprints, UC San Diego, DOI: 10.1111/j.1467-8667.2008.00544.x, 2008
Abstract: In this paper, wind-induced vibration response of Vincent Thomas Bridge, a suspension bridge located in San Pedro near Los Angeles, California, is simulated using a detailed three-dimensional finite element model of the bridge and a state-of-the-art stochastic wind excitation model. Based on the simulated wind-induced vibration data, the modal parameters (natural frequencies,damping ratios, and mode shapes) of the bridge are identified using the data-driven stochastic subspace identification method. The identified modal parameters are verified by the computed eigenproperties of the bridge model. Finally, effects of measurement noise on the system identification results are studied by adding zero-mean Gaussian white noise processes to the simulated response data. Statistical properties of the identified modal parameters are investigated under increasing level of measurement noise. The framework presented in this paper will allow to investigate the effects of various realistic damage scenarios in long-span cable-supported (suspension and cable-stayed) bridges on changes in modal identification results. Such studies are required in order to develop robust and reliable vibration-based structural health monitoring methods for this type of bridges, which is a long-term research objective of the authors.Keywords: Vincent Thomas Bridge — experimental modal analysis — ambient vibration — system identification
Fluid-structure interaction for a jacket model structure with imposed displacement
A.C. Mendes, H.J.D. Correia
Laboratory of Fluid Mechanics, Universidade da Beira Interior, Covilhã, Portugal.
Proc. Eighteenth Int. Offshore and Polar Eng. Conf., 2008
Abstract: In this paper we describe a series of experimental tests performed with
a 1:45 scale jacket structure in a water basin. The model structure is assembled on a seismic table that performs a controlled motion, with amplitudes and frequencies that could correspond to actual earthquake conditions translated to the scale of the model. The structural response to the imposed displacement is analyzed in terms of the accelerations and reaction forces at the base of the structure, first in air and afterwards in water. The experimental measurements are equally correlated with the computer predictions of dynamic loading that have been obtained with a FEM commercial software - the ADINA.
Flexural Strengthening of RC Beams with Externally Bonded CFRP Systems: Test Results and 3D Nonlinear FE Analysis
Renata Kotynia1, Hussien Abdel Baky2, Kenneth W. Neale3, and Usama A. Ebead4
1 Assistant Professor, Dept. of Concrete Structures, Technical Univ. of Lodz, Al. Politechnik 6, 90-924 Lodz, Poland.
2 Ph.D. Candidate, Dept. of Civil Engineering, Univ. of Sherbrooke, Sherbrooke, Quebec, Canada J1K 2R1.
3 Canada Research Chair in Advanced Engineered Material Systems, Dept. of Civil Engineering, Univ. of Sherbrooke, Sherbrooke, Quebec, Canada J1K 2R1
4 Assistant Professor, Dept. of Civil and Environmental Engineering, College of Engineering, United Arab Emirates Univ., P.O. Box 17555, Al Ain, United Arab Emirates
Journal Of Composites For Construction, DOI 10.1061/(ASCE)1090-0268(2008)12:2(190), 2008
Abstract: This paper presents experimental results and a numerical analysis of the reinforced concrete (RC) beams strengthened in flexure with various externally bonded carbon fiber-reinforced polymer (CFRP) configurations. The aim of the experimental work was to investigate the parameters that may delay the intermediate crack debonding of the bottom CFRP laminate, and increase the load carrying capacity and CFRP strength utilization ratio. Ten rectangular RC specimens with a clear span of 4.2 m, categorized in two series, were tested to evaluate the effect of using the additional U-shaped CFRP systems on the intermediate crack debonding of the bottom laminate. Two different configurations of the additional systems were proposed, namely, continuous U-shaped wet layup sheets and spaced side-bonded CFRP L-shaped laminates. The fiber orientation effect of the side-bonded sheets was also investigated. A numerical analysis using an incremental nonlinear displacement-controlled 3D finite-element (FE) model was developed to investigate the flexural and CFRP/concrete interfacial responses of the tested beams. The finite-element model accounts for the orthotropic behavior of the CFRP laminates. An appropriate bond-slip model was adopted to characterize the behavior of the CFRP/concrete interface. Comparisons between the FE predictions and experimental results show very good agreement in terms of the load-deflection and load-strain relationships, ultimate capacities, and failure modes of the beams.
Keywords: Fiber reinforced polymers - Concrete beams – Concrete – reinforced - Flexural strength - Finite element method
Tensile radial stress in the spinal cord related to arachnoiditis or tethering: a numerical model
C.D. Bertram1, L.E. Bilston1 and M.A. Stoodley2
1 Biofluid Mechanics Laboratory, Faculty of Engineering, University of New South Wales, Sydney 2052, Australia
2 Prince of Wales Medical Research Institute, UNSW, Barker Street, Randwick 2031, New South Wales, Australia
Med Biol Eng Compu, 46:701–707, 2008
Abstract: Abstract Spinal arachnoiditis comprises fibrous scarring of the subarachnoid space, following spinal trauma or inflammation, and is often associated with syringomyelia. We hypothesised that cord-to-dura attachments could cause transient tensile cord radial stress, as pressure waves propagate. This was tested in a fluid-structure interaction model, simulating three types of cord tethering, with ‘arachnoiditis’ confined to a short mid-section of the cord. The annular system was excited abdominally with a short transient, and the resulting Young and Lamb waves and reflections were analysed. Radial mid-section tethering was less significant than axial tethering, which gave rise to tensile radial stress locally when the cord was not fixed cranially. Simulated as inextensible string connections to the dura, arachnoiditis caused both localised tensile radial stress and localised low pressure in the cord as the transient passed. The extent of these effects was sensitive to the relative stiffness of the dura and cord. Tensile radial stress may create a syrinx in previously normal cord tissue, and transiently lowered pressure may draw in interstitial fluid, causing the syrinx to enlarge if fluid exit is inhibited. The suggested mechanism could also explain the juxtaposition of syrinxes to regions of arachnoiditis.
Keywords: Fluid-structure interaction — Finite-element model — Cerebrospinal fluid — Wave propagation — Syringomyelia
Modeling Of Electro Resistance Welding Tube Forming Process
Sebastián D’hers1, Pablo A. Bucello1, Martín N. Arregui1, Alberto P. Sibileau1, Miguel A. Cavaliere2 and Esteban Baralla3
1 Instituto Tecnológico de Buenos Aires. Av. E. Madero 399 C1106ACD, Buenos Aires, Argentina.
2 Tenaris Siderca, Dr. Simini 250, B2804MHA Campana, Buenos. Aires, Argentina.
3 Tenaris SIAT, Guatemala 3400, B1822AXZ Valentín Alsina, Buenos Aires, Argentina.
Mecánica Computacional, 27:627-638, 2008
Abstract: During the forming process in an electro resistance welding (ERW) forming line, a flat skelp evolves from a flat surface to a round shape, enforced by a series of roll stages. The formed round shape determines, together with welding parameters, the obtained weld and tube quality. In order to improve the process and achieve a better understanding of the skelp evolution towards the welding station, a finite element model has been developed. The process has been usually studied with analytical techniques and “trial and error” plant testing, while the use of finite element in modeling this type of process is quite recent. Process complexity imposes great computing efforts and heavy pre and post processing work. A finite element model has been proposed to predict the skelp behavior along the critical stages of the forming line. Large displacement, contact algorithms and J2 material models have been used in the problem description. Agreement with plant measurements, computational speed and robustness are the
main achieved goals.
Key Words: Metal forming - finite element method - roll forming - edge shape - electric resistance welding
Numerical Analysis Of Soil Response To Ice Scouring
E. Evgin and Z. Fu
Department of Civil Engineering, University of Ottawa, Ottawa, Ontario, Canada
Proceedings of the ASME 27th International Conference on Offshore Mechanics and Arctic Engineering, OMAE2008-57293, 2008
Abstract: Icebergs and ice ridges frequently scour the surface of seabed deposits. Ice scouring can be problematic for offshore pipelines and other seabed installations. In order to reduce the risk of failure, pipelines are buried in the seabed. However, a stationary or moving ice feature could cause a significant increase in stresses and deformation in the seabed soil deposits below the contact surface between the soil and the ice, and consequently, might result in structural failure of buried pipeline. Safe burial depth for pipelines has been the subject of both experimental and numerical studies. In this paper, two and three dimensional analyses are conducted using PLAXIS and ADINA. In these analyses, geometric and material nonlinearities are considered. In order to establish the validity of the finite element calculations, the experimental results reported in the literature and the numerical results obtained in the present study are compared. The emphasis is placed on determining the importance of (1) using interface elements between different materials such as soil and ice, soil and pipelines; (2) using the soil model correctly, and (3) using a three dimensional analysis rather than a two dimensional analysis. The changes taking placed in the deformation pattern and the stress states in the seabed soils resulting from ice scouring are determined. The effects of pipeline burial depth, the shape of the ice feature, and the characteristics of seabed soils on the stresses acting on the pipeline are evaluated.
Influence of different load models on gear crack path shapes and fatigue lives
S. Podrug1, D. Jelaska1 and S. Glodez2
1 University of Split, Faculty of Electrical Engineering, Mechanical Engineering and Naval Architecture, R. Boskovica bb, 21000 Split, Croatia
2 University of Maribor, Faculty of Mechanical Engineering, Smetanova 17, 2000 Maribor, Slovenia
Fatigue Fract Engng Mater Struct, 31:327–339, 2008
Abstract: A computational model for determination of the service life of gears with regard to bending fatigue at gear tooth root is presented. In conventional fatigue models of the gear tooth root, it is usual to approximate actual gear load with a pulsating force acting at the highest point of the single tooth contact. However, in actual gear operation, the magnitude as well as the position of the force changes as the gear rotates. A study to determine the effect of moving gear tooth load on the gear service life is performed. The fatigue process leading to tooth breakage is divided into crack-initiation and crack-propagation period. The critical plane damage model has been used to determine the number of stress cycles required for the fatigue crack initiation. The finite-element method and linear elastic fracture mechanics theories are then used for the further simulation of the fatigue crack growth.
Keywords: crack closure - crack initiation - crack propagation - gear tooth root - moving load
Numerical simulation of fluid-structure interaction for wind induced dynamic response of the 3rd Jinan Yellow River cable stayed bridge
Qi-Lin Zhang, Zhen-Hua Liu, Ying Zhou
Department of Building Engineering, Tongji University, Shanghai 200092, P.R. China
Proc. 6th Int. Conf. on Comp. of Shell and Spatial Structures, IASS-IACM 2008: “Spanning Nano to Mega”, Cornell University, Ithaca, NY, USA, 2008
Abstract: The bridge aerodynamic design has considerably progressed to a more and more analytical methodology by which the mechanical aspects concerning bridge stability are deeply understood and characterized. In this paper, a response analysis was carried out using ADINA to evaluate wind-induced dynamic response of the 3rd Jinan Yellow River cable-stayed steel box girder bridge. The wind induced dynamic coefficients and the wind pressure distribution coefficient of the steel box girder can be calculated.
Simulation of blood flow in a small-diameter vascular graft model with a swirl (spiral) flow guider
ZhiGuo Zhang1,2, YuBo Fan1, XiaoYan Deng1, GuiXue Wang3, He Zhang3 & Robert Guidoin4
1 Department of Bioengineering, Beihang University, Beijing 100083, China
2 School of Aerospace, Tsinghua University, Beijing 100084, China
3 College of Bioengineering, Chongqing University, Chongqing 400044, China
4 Department of Surgery, Laval University and Quebec Biomaterials Institute CHUQ, Quebec G1K7P4, Canada
Sci China Ser C-Life Sci, 51(10):913-921, 2008
Abstract: Small-diameter vascular grafts are in large demand for coronary and peripheral bypass procedures, but present products still fail in long-term clinical application. In the present communication, a new type of small-diameter graft with a swirl flow guider was proposed to improve graft patency rate. Flow pattern in the graft was simulated numerically and compared with that in a conventional graft. The numerical results revealed that the swirl flow guider could indeed make the blood flow rotate in the new graft. The swirling flow distal to the flow guider significantly altered the flow pattern in the new graft and the velocity profiles were re-distributed. Due to the swirling flow, the blood velocity near the vessel wall and wall shear rate were greatly enhanced. We believe that the increased blood velocity near the wall and the wall shear rate can impede the occurrence of acute thrombus formation and intimal hyperplasia, hence can improve the graft patency rate for long-term clinical use.
Keywords: arterial prosthesis - acute thrombus formation - flow simulation - swirling (spiral) flow
Computational investigation of the tensile behaviour of the hard coated Ti-6Al-4V alloy
Department of Materials Science, Rzeszow University of Technology, ul. W. Pola 2, 35-959 Rzeszow, Poland
Journal of Achievements in Materials and Manufacturing Engineering, 26(2):175-178, 2008
Purpose: Modification of the surface layer of the titanium alloys is frequently applied in order to improve their tribological properties. Various surface engineering techniques can be used to produce hard coatings, e.g. composed of metallic carbides, nitrides or more recently DLC. The coating and substrate materials possess significantly different stiffness and strength properties. This can lead to premature failure of the usually elastic coating in case of plastic deformation of the substrate when the high stresses are encountered. Cracking of the hard coating leads to stress concentration and localized plastic deformation of the substrate that can modify macroscopic deformation behaviour of the system. In the paper the influence of coating and substrate properties on local plastic deformation of substrate material was numerically investigated.
Design/methodology/approach: Two dimensional finite element analysis of the process of tensile deformation of titanium alloy with hard elastic coating was carried out. Two cases were analyzed, i.e. with and without diffusion strengthened layer underlying the coating.
Findings: The influence of the difference in Young’s modulus between coating and substrate material, yield strength of substrate material, coating thickness and depth of the crack in the coating on local plastic deformation of substrate material was determined.
Research limitations/implications: Some extension of the numerical model should be pursued in order to take into account initiation of microcracks in surface layer of the coated material and process of coating
Practical implications: The results could be used in the element design process for selection of parameters of surface layer with complex structure for load bearing applications.
Originality/value: The mechanical behaviour of hard coated material was most frequently studied for indentation and friction conditions and much less investigations were carried out for coated systems under tension or compression.
Keywords: Computational material science - Titanium alloys - Surface layer
3D MR Flow Analysis in Realistic Rapid-Prototyping Model Systems of the Thoracic Aorta: Comparison with In Vivo Data and Computational Fluid Dynamics in Identical Vessel Geometries
C. Canstein,1 P. Cachot,2 A. Faust,2 A.F. Stalder,1 J. Bock,1 A. Frydrychowicz,1 J. Küffer,2 J. Hennig,1 and M. Markl1
1 Department of Diagnostic Radiology, Medical Physics, University Hospital,
2 Institute for Product and Production engineering, Department of Technics, University of Applied Sciences Northwestern Switzerland, Muttenz, Switzerland.
Magnetic Resonance in Medicine, 59:535–546, 2008
Abstract: The knowledge of local vascular anatomy and function in the human body is of high interest for the diagnosis and treatment of cardiovascular disease. A comprehensive analysis of the hemodynamics in the thoracic aorta is presented based on the integration of flow-sensitive 4D MRI with state-of-the-art rapid prototyping technology and computational fluid dynamics (CFD). Rapid prototyping was used to transform aortic geometries as measured by contrast-enhanced MR angiography into realistic vascular models with large anatomical coverage. Integration into a flow circuit with patient-specific pulsatile in-flow conditions and application of flow-sensitive 4D MRI permitted detailed analysis of local and global 3D flow dynamics in a realistic vascular geometry. Visualization of characteristic 3D flow patterns and quantitative comparisons of the in vitro experiments with in vivo data and CFD simulations in identical vascular geometries were performed to evaluate the accuracy of vascular model systems. The results indicate the potential of such patient-specific model systems for detailed experimental simulation of realistic vascular hemodynamics. Further studies are warranted to examine the influence of refined boundary conditions of the human circulatory system such as fluid-wall interaction and their effect on normal and pathological blood flow characteristics associated with vascular geometry.
Key words: vascular hemodynamics - phase contrast - aorta - blood flow - velocity mapping - model system - rapid prototyping - computational fluid dynamics
Evaluation of critical fracture energy parameter Gfr and assessment of its transferrability
S. Acharyya1, S. Dhar1, J. Chattopadhyay2
1 Department of Mechanical Engineering, Jadavpur University, Kolkata 700032, India
2 Reactor Safety Division, Bhabha Atomic Research Center, Mumbai 400085, India
Engineering Fracture Mechanics, 75:253–274, 2008
Abstract: Prediction of maximum load bearing capacity and crack growth for ductile materials using existing models like J-R curve approach has the problem of transferability and the use of micro-mechanical model (e.g. Gurson Tvergaard, and Needleman [Tvergaard V, Needleman A. Analysis of cup cone fracture in a round tensile bar. Acta Metall 1984;32:157–169]) are limited by the requirements of the huge computation time and large numbers of critical metallurgical parameters as input to analysis. Marie and Chapuliot [Marie S, Chapuliot S. Ductile tearing simulation based on local energy criterion. Fatigue Fract Engng Mater Struct 1998;21:215–227] of CEA, France, proposed a simple but convenient ductile crack growth model using critical fracture energy (Gfr) for crack growth and Ji for initiation, both of which are material parameters. They also proposed several schemes, namely, graphical and slope of modi.ed plastic J-integral vs crack growth, JM-pl _ Da methods for the evaluation of the value of Gfr from specimens as well as from components. In all these methods the role of non-crack displacement in the crack growth process was not considered. The necessary modifications due to non-crack displacement in the above methods to evaluate the values of Gfr was studied and published [Acharyya S, Dhar S, Chattopadhyay J. (2003). The e.ect of non-crack component on Critical fracture energy on ductile material. Int J Pressure Vessels Piping 2004;81:345–353] by the authors earlier. In this paper, the modi.ed methods and formulation have been applied to evaluate the values of Gfr from experimental and FE simulated results for compact tensile (CT), three point bend (TPB) specimens and also from components like pipes and elbows. Then statistical estimation is done from these Gfr values to assess whether Gfr can be accepted as constant value material parameter. Finally, the mean value of Gfr obtained from statistical computation is used as material constant along with crack initiation toughness parameter (Ji)SZW to consider crack growth for FE simulation of load vs load-line–displacement (LLD) and load vs crack growth curves for different specimens and components. Finite element simulated results are compared with the experimental results and good matching between the two for several components are found and maximum error in prediction of maximum load is found to be within 12%.
Keywords: Ductile fracture - Critical fracture energy (Gfr) - Ernest’s JM-pl - Graphical method - Non-crack compliance - Reverse simulation
Delamination behaviour of very high modulus carbon/epoxy marine composites
N. Barala, P. Daviesb, C. Baleyc, B. Bigourdanb
aTrimaran Groupama, 56100 Lorient, France
bMaterials and Structures Group, IFREMER Brest Centre, 29280 Plouzane, France
cUniversite de Bretagne Sud, L2PIC, BP 92116, 56321 Lorient Cedex, France
Composites Science and Technology 68 (2008) 995–1007
Abstract: This paper presents a study of the delamination resistance of unidirectional carbon .bre reinforced epoxy composites manufactured from prepreg for racing yacht mast applications. Fibre modulus has been varied from 290 to 640 GPa. Two manufacturing methods, oven cure under vacuum and autoclave, were used to produce samples. Results show that delamination resistance under mode I and mixed mode loading decreases as fibre modulus increases. The manufacturing route affects Gc values by modifying interlaminar layer geometry but does not change the trend of lower toughness with increasing fibre modulus. For the pitch composites crack propagation is observed within the fibres, in addition to more usual matrix and interface cracking. For the very high modulus fibre composites it is no longer possible to measure the GI/IIc fracture envelope with the MMB specimen, compression failure occurs before delamination. FE analysis and instrumented specimens have been used to define the limits to the current standard test method for these materials.
Keywords: Delamination - Carbon fibres - Polymers - Fracture toughness - Mixed mode
Influence of microcalcifications on vulnerable plaque mechanics using FSI modeling
Danny Bluesteina, Yared Alemua, Idit Avrahamib,e, Morteza Gharibb, Kris Dumonta, John J. Ricottac, Shmuel Einava,d
aDepartment of Biomedical Engineering, Stony Brook University, Stony Brook, NY 11794-8181, USA
bAeronautics and Bioengineering, California Institute of Technology, Pasadena, CA, USA
cDepartment of Surgery, Stony Brook University Hospital, Stony Brook University, Stony Brook, NY 11794-8181, USA
dDepartment of Bioengineering, Tel Aviv University, Tel Aviv, Israel
eAfeka College of Engineering, Tel Aviv, Israel
Journal of Biomechanics 41 (2008) 1111–1118
Abstract: Sudden heart attacks remain one of the primary causes of premature death in the developed world. Asymptomatic vulnerable plaques that rupture are believed to prompt such fatal heart attacks and strokes. The role of microcalcifications in the vulnerable plaque rupture mechanics is still debated. Recent studies suggest the microcalcifications increase the plaque vulnerability. In this manuscript we present a numerical study of the role of microcalcifications in plaque vulnerability in an eccentric stenosis model using a transient fluid–structure
interaction (FSI) analysis. Two cases are being compared (i) in the absence of a microcalcification (ii) with a microcalcification spot fully embedded in the fibrous cap. Critical plaque stress/strain conditions were affected considerably by the presence of a calcified spot, and were dependent on the timing (phase) during the flow cycle. The vulnerable plaque with the embedded calcification spot presented higher
wall stress concentration region in the fibrous cap a bit upstream to the calcified spot, with stress propagating to the deformable parts of the structure around the calcified spot. Following previous studies, this finding supports the hypothesis that microcalcifications increase the plaque vulnerability. Further studies in which the effect of additional microcalcifications and parametric studies of critical plaque cap
thickness based on plaque properties and thickness, will help to establish the mechanism by which microcalcifications weaken the plaque and may lead to its rupture.
Keywords: Vulnerable plaque - Atherosclerosis - Fibrous cap - Rupture - Microcalcification - Numerical modeling - FSI
Non-Newtonian Bile Flow in Elastic Cystic Duct: One- and Three-Dimensional Modeling
W.G. Li1, X.Y. Luo1,S.B. Chin2,N.A. Hill1, A.G. Johnson3, and N.C. Bird3
1Department of Mathematics, University of Glasgow, Glasgow G12 8QW, UK;
2Department of Mechanical Engineering, University of Sheffield, Sheffield S1 3JD, UK; and
3Academic Surgical Unit, Royal Hallamshire Hospital, Sheffield S10 2JF, UK
Annals of Biomedical Engineering, Vol. 36, No. 11, pp. 1893–1908, 2008
Abstract: Bile flow is thought to play an essential role in the pathophysiological genesis of cholelithiasis (gallstone formation) and in gallbladder pain. In this paper, we extend our previous study of the human biliary system (Li et al., 2007, J. Biomech. Eng., 129:164–173) to include two important factors: the non-Newtonian properties of bile, and elastic deformation of the cystic duct. A one-dimensional (1D) model is analyzed and compared with three-dimensional (3D) fluid–structure interaction simulations. It is found that non-Newtonian bile raises resistance to the flow of bile, which can be augmented significantly by the elastic deformation (collapse) of the cystic duct. We also show that the 1D model predicts the pressure drop of the cystic duct flow well for all cases considered (Newtonian or non-Newtonian flow, rigid or elastic ducts), when compared with the full 3D simulations.
Keywords: Gallbladder – Gallstone - Cystic duct - Biliary system - Non-Newtonian fluid - Pressure drop - Fluid–structure interaction - 1D modeling - Finite element methods
Cyclic Bending Contributes to High Stress in a Human Coronary Atherosclerotic Plaque and Rupture Risk: In Vitro Experimental Modeling and Ex Vivo MRI-Based Computational Modeling Approach
Chun Yang1,2, Dalin Tang1, Shunichi Kobayashi3, Jie Zheng4, Pamela K. Woodard4, Zhongzhao Teng1, Richard Bach5, and David N. Ku6
1Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA 01609
2School of Mathematical Sciences, Beijing Normal University, Beijing, China
3Division of Creative Engineering, Shinshu University, Ueda, Nagano, Japan
4Mallinkcrodt Inst. of Radiology, Washington University, St. Louis, MO 63110, USA
5Division of Cardiovascular Diseases, Washington University, St. Louis, MO 63110, USA
6School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0405, USA
Mol Cell Biomech. 2008; 5(4): 259–274.
Abstract: Many acute cardiovascular syndromes such as heart attack and stroke are caused by atherosclerotic plaque ruptures which often happen without warning. MRI-based models with fluid-structure interactions (FSI) have been introduced to perform flow and stress/strain analysis for atherosclerotic plaques and identify possible mechanical and morphological indices for accurate plaque vulnerability assessment. In this paper, cyclic bending was added to 3D FSI coronary plaque models for more accurate mechanical predictions. Curvature variation was prescribed using the data of a human left anterior descending (LAD) coronary artery. Five computational models were constructed based on ex vivo MRI human coronary plaque data to assess the effects of cyclic bending, pulsating pressure, plaque structure, and axial stretch on plaque stress/strain distributions. In vitro experiments using a hydrogel stenosis model with cyclical bending were performed to observe effect of cyclical bending on flow conditions. Our results indicate that cyclical bending may cause more than 100% or even up to more than 1000% increase in maximum principal stress values at locations where the plaque is bent most. Stress increase is higher when bending is coupled with axial stretch, non-smooth plaque structure, or resonant pressure conditions (zero phase angle shift). Effects of cyclic bending on flow behaviors are more modest (21.6% decrease in maximum velocity, 10.8% decrease in flow rate, maximum flow shear stress changes were < 5%). Computational FSI models including cyclic bending, plaque components and structure, axial stretch, accurate in vivo measurements of pressure, curvature, and material properties should lead to significant improvement on stress-based plaque mechanical analysis and more accurate coronary plaque vulnerability assessment.
Keywords: Coronary artery - cardiovascular - cyclic bending - fluid-structure interaction - blood flow - atherosclerotic plaque rupture
Computational studies of resonance wave pumping in compliant tube
Idit Avrahami1 And Morteza Gharib2
1Medical Engineering, AFEKA-Tel Aviv. Academic College of Engineering, Bney Efraim, Tel Aviv 69107, Israel
2Aeronautics and Bioengineering, California Institute of Technology, Pasadena, CA 91125, USA
J. Fluid Mech. (2008), vol. 608, pp. 139–160.
Abstract: The valveless impedance pump is a simple design that allows the producion or amplification of a flow without the requirement for valves or impellers. It is based on fluid-filled flexible tubing, connected to tubing of different impedances. Pumping is achieved by a periodic excitation at an off-centre position relative to the tube ends. This paper presents a comprehensive study of the fluid and structural dynamics in an impedance pump model using numerical simulations. An axisymmetric finite element model of both the fluid and solid domains is used with direct coupling at the interface. By examining a wide range of parameters, the pump’s resonance nature is described and the concept of resonance wave pumping is discussed. The main driving mechanism of the flow in the tube is the reflection of waves at the tube boundary and the wave dynamics in the passive tube. This concept is supported by three different analyses: (i) time-dependent pressure and flow wave dynamics along the tube, (ii) calculations of pressure–flow loop areas along the passive tube for a description of energy conversion, and (iii) an integral description of total work done by the pump on the fluid. It is shown that at some frequencies, the energy given to the system by the excitation is converted by the elastic tube to kinetic energy at the tube outlet, resulting in an efficient pumping mechanism and thus signi.cantly higher flow rate. It is also shown that pumping can be achieved with any impedance mismatch at one boundary and that the outlet con.guration does not necessarily need to be a tube.
Analysis of the heating process and development of a microstructure suitable for thixoforming of steel
K.P. Solek, A. Lukaszek-Solek
AGH University of Science and Technology – al. Mickiewicza 30, 30-059 Kraków, Poland
Int J Mater Form (2008) Suppl 1:1015–1018
ABSTRACT: The thixoforming processes of metal alloys are carried out in the semi-solid state. The thixotropy phenomenon is conditional upon the globular microstructure that occurs in shaped material. In order to design and optimise such processes, some procedures of the Gleeble® system could be applied. The main objective of this work is an analysis of the resistance heating of samples in different material tests which are possible on the Gleeble® 3800 simulator. An example of development of steel alloy microstructure during heating on the Gleeble® simulator will also be presented. M2 tool steel was submitted for analysis. In this case, obtaining the globular microstructure was carried out on the basis of the SIMA method (Strain Induced Melt Activated).
Key words: thixoforming - resistance heating - globular microstructure - numerical analysis
Identification of nonlinear dynamic coefficients in plain journal bearings
V. Meruane, R. Pascual
Mechanical Engineering Department, Universidad de Chile, Beauchef 850, Santiago, Chile
Tribology International 41 (2008) 743–754
Abstract: This work proposes a framework to the numerical identification of nonlinear fluid film bearing parameters from large journal orbital motion (20–60% of the bearing clearance). Nonlinear coefficients are defined by a third order Taylor expansion of bearing reaction forces and are evaluated through a least mean square in time domain technique. The journal response is obtained from a computational fluid dynamic (CFD) model of a plain journal bearing on high dynamic loading conditions. The model considers fluid–structure interaction between the fluid flow and the journal. The case in study considers a laboratory test rig. Results indicate that nonlinear coefficients have an important effect on stiffness and damping. It was found a change on nonlinear behavior occurred when the Oil Whirl phenomenon starts, which it is not seen in classical linear models.
Keywords: Journal bearing - Computational fluid dynamics - Transient - Identification - Large orbital motion - Nonlinear
Using traditional and innovative approaches in the seismic evaluation and strengthening of a historic unreinforced masonry synagogue
Terrence F. Paret, Sigmund A. Freeman, Gary R. Searer, Mahmoud Hachem, Una M. Gilmartin
Wiss, Janney, Elstner Associates, Inc., 2200 Powell Street, Suite 925, Emeryville, CA 94608, United States
Engineering Structures 30 (2008) 2114–2126
Abstract: A monumental 100-year-old multi-story brick masonry synagogue in San Francisco was threatened with closure due to non-compliance with an Unreinforced Masonry Building Ordinance. The Ordinance required demonstrating that the building would protect life safety in the event of a major earthquake or upgrading the building to do so, despite the historical record showing that the building survived the Great 1906 Earthquake with relatively little damage. Much of the minor damage that did occur is still visible today as the historic finishes have remained intact since that
earthquake. The structure consists primarily of thick, brick masonry perimeter walls, wood-framed diaphragms with diagonal and straight sheathing, and riveted structural steel trusses and columns that support the dome over the main sanctuary and a large portion of the floors and main roof. The structure was subjected to linear dynamic and non-linear static analyses to benchmark its behavior during the 1906 earthquake, to better understand its vulnerabilities in the event of potentially stronger shaking, and to develop seismic improvements that minimize disturbance of its ornately detailed stone and painted plaster finishes. The most appropriate structural solution consistent with preserving the historic fabric takes advantage of the dynamic separation between the modes predominated by in-plane and out-of-plane wall shaking. The out-of-plane wall modes have long periods and low modal mass participation. The in-plane wall modes have higher mass participation, but act rigidly with little amplification. The solution consisted of a combination of intervention techniques, each developed to minimize disturbance to the non-structural finishes and retain the original dynamic characteristics. These interventions include a system of tension ties in the attic that interconnect the four perimeter walls, yet circumvent the domed sanctuary; center-cored reinforcement of the masonry walls; and fiber-wrap of a few critical piers. The tension ties contain super-elastic nitinol wires and were designed to be lightweight, easy to install, and to restrain the walls from falling outward while maintaining the modal separation and inherent flexibility of the system that enabled the structure to survive the 1906 earthquake.
Keywords: Unreinforced masonry building - Seismic strengthening - Historic structure
Seismic vulnerability of historical masonry buildings: A case study in Ferrara
Vincenzo Mallardoa, Roberto Malvezzia, Enrico Milanib, Gabriele Milanib
aDepartment of Architecture, University of Ferrara, Via Quartieri 8, 44100 Ferrara, Italy
bDepartment of Engineering, University of Ferrara, Via Saragat 1, 44100 Ferrara, Italy
Engineering Structures 30 (2008) 2223–2241
Abstract: In this paper, the seismic behaviour of an important Renaissance Palace in Ferrara (Italy), Palazzo Renata di Francia, is investigated. In the first part, a full 3D nonlinear analysis is performed in order to obtain a first insight into its structural performance. Then, three different 2D nonlinear analyses of the main front are critically compared and discussed. The first model relies on an equivalent frame approach, the second is based on an elastic–plastic damaging Finite Element (F.E.) approach and the third stems from a kinematic collapse analysis by means of a homogenised limit surface. The facade exhibits an adequate in-plane strength, when analysed with 2D plane stress F.Es., whereas the whole building undergoes out-of-plane partial collapses even in the presence of very low intensity horizontal actions, when analysed with 3D F.Es.
Keywords: Masonry - Nonlinear - Seismic - Homogenisation
Influence of Meniscectomy and Meniscus Replacement on the Stress Distribution in Human Knee Joint
Ashkan Vaziri,1,2 Hamid Nayeb-Hashemi,2 Arvinder Singh,2 and Bashir A. Tafti3
1School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA;
2Department of Mechanical, Industrial and Manufacturing Engineering, Northeastern University, Boston, MA 02115, USA; and
3Department of Surgery and Regenerative Medicine, Division of Plastic Surgery, Stanford University, Stanford, CA 94305, USA
Annals of Biomedical Engineering, Vol. 36, No. 8, August 2008, pp. 1335–1344
Abstract: Studying the mechanics of the knee joint has direct implications in understanding the state of human health and disease and can aid in treatment of injuries. In this work, we developed an axisymmetric model of the human knee joint using finite element method, which consisted of separate parts representing tibia, meniscus and femoral, and tibial articular cartilages. The articular cartilages were modeled as three separate layers with different material characteristics: top superficial layer, middle layer, and calcified layer. The biphasic characteristic of both meniscus and cartilage layers were included in the computational model. The developed model was employed to investigate several aspects of mechanical response of the knee joint under external loading associated with the standing posture. Specifically, we studied the role of the material characteristic of the articular cartilage and meniscus on the distribution of the shear stresses in the healthy knee joint and the knee joint after meniscectomy. We further employed the proposed computational model to study the mechanics of the knee joint with an arti.cial meniscus. Our calculations suggested an optimal elastic modulus of about 110 MPa for the arti.cial meniscus which was modeled as a linear isotropic material. The suggested optimum stiffness of the artificial meniscus corresponds to the stiffness of the physiological meniscus in the circumferential direction.
Keywords: Knee mechanics - Meniscectomy - Artificial meniscus
Collapse arrestors for deepwater pipelines. Cross-over mechanisms
Rita G. Toscano, Luciano O. Mantovano, Pablo M. Amenta, Roberto F. Charreau, Daniel H. Johnson, Andrea P. Assanelli, Eduardo N. Dvorkin
Center for Industrial Research, TENARIS, Dr. Jorge A. Simini 250, Campana 2804, Argentina
Computers and Structures 86 (2008) 728–743
Abstract: Using finite element models it is possible to determine the cross-over external pressure of different pipeline arrestor designs. In this paper these finite element models are discussed and validated by comparing their results with experimental determinations. The flipping and flattening cross-over mechanisms, that were previously described in the literature, are considered in the experimental validation of the numerical models.
Keywords: Collapse - Pipelines - Deepwater - Finite elements
Using 3D fluid–structure interaction model to analyse the biomechanical properties of erythrocyte
C.Y. Cheea, H.P. Leea,b, C. Lua
aInstitute of High Performance Computing, 1 Science Park Road, Capricorn S117528, Singapore
bDepartment of Mechanical Engineering, National University of Singapore, Singapore 119260, Singapore
Physics Letters A 372 (2008) 1357–1362
Abstract: This Letter presents a newly developed three-dimensional fluid–structure interaction model of the red blood cell (RBC). The model consists of a deformable liquid capsule modelled as Newtonian fluid enclosed by a hyperelastic membrane with viscoelastic property. Numerical results show that viscosity in the cytoplasm affects the deformed shape of RBC under loading. This observation is contrary to the earlier belief that viscosity of the cytoplasm can be neglected. Numerical simulations carried out to investigate large deformation induced on the RBC model using direct tensile forces show significant improvement in terms of correlation with experimental results. The membrane shear modulus estimated from the model ranges between 3.7 to 9.0 µNm-1 compares well with results obtained from micropipette aspiration experiments.
Keywords:Cells biomechanics - Computational fluid–structure interaction
Numerical analyses of dynamic response of saturated porous seabed-pipeline interaction under seismic loading
Xiaoling Zhang, Maotian Luan
Institute of Geotechnical Engineering, School ofCivil and Hydraulic Engineering, Dalian University ofTechnology, Dalian JJ6023, China
Geotechnical Engineering for Disaster Mitigation and Rehabilitation. Liu, Deng and Chu (eds) 2008 Science Press Beijing and Springer-Verlag GmbH Berlin Heidelberg
Abstract: Based on the Biot's theory of consolidation, the model of the seabed-pipeline interaction is established using viscous-elastic artificial boundary in this paper. The distribution ofthe pore pressure in seabed soil and the dynamic response of submarine pipeline are studied under El Centro seismic wave by virtue of the general-purpose FEM analysis package ADINA. The effects of the elastic anisotropic soil and two-layered seabed behaviors on the seismic-induced pore pressure and internal stresses are discussed emphatically. It actually shows the validity and practicality ofdynamic response ofsubmarine pipeline under seismic loading.
Mechanical behavior of segment rebar of shield tunnel in construction stage
Jun-sheng Chen, Hai-hong Mo
Department of Civil Engineering, South China University of Technology, Guangzhou 510640, China
State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou 510640, China
Journal of Zhejiang University SCIENCE A, 2008 9(7):888-899
Abstract: In this paper, a 3D finite element (FE) program ADINA was applied to analyzing a tunnel with 9 segment rings. The loads acting on these segment rings included the squeezing action of tail brush of shield machine under attitude deflection, the jacking forces, the grouting pressure and the soil pressure. The analyses focused on the rebar stress in two statuses: (1) normal construction status without shield machine squeezing; (2) squeezing action induced by shield machine under attitude deflection. The analyses indicated that the rebar stress was evidently affected by the construction loads. In different construction status, the rebar stress ranges from -80 MPa to 50 MPa, and the rebar is in elastic status. Even some cracks appear on segments, the stress of segment rebar is still at a low level. It is helpful to incorporate a certain quantity of steel fiber to improve the anti-crack and shock resistance performance.
Key words: Shield tunnel - Construction - Segment - Rebar - Finite element (FE) analysis
Tensile radial stress in the spinal cord related to arachnoiditis or tethering: a numerical model
C. D. Bertram1, L. E. Bilston2 and M. A. Stoodley2
1Biofluid Mechanics Laboratory, Faculty of Engineering, University of New South Wales, Sydney 2052, Australia
2Prince of Wales Medical Research Institute, UNSW, Barker Street, Randwick 2031, New South Wales, Australia
Med Biol Eng Comput (2008) 46:701–707
Abstract: Spinal arachnoiditis comprises fibrous scarring of the subarachnoid space, following spinal trauma or inflammation, and is often associated with syringomyelia. We hypothesised that cord-to-dura attachments could cause transient tensile cord radial stress, as pressure waves propagate. This was tested in a fluid–structure interaction model, simulating three types of cord tethering, with ‘arachnoiditis’ confined to a short mid-section of the cord. The annular system was excited abdominally with a short transient, and the resulting Young and Lamb waves and reflections were analysed. Radial mid-section tethering was less significant than axial tethering, which gave rise to tensile radial stress locally when the cord was not fixed cranially. Simulated as inextensible string connections to the dura, arachnoiditis caused both localised tensile radial stress and localised low pressure in the cord as the transient passed. The extent of these effects was sensitive to the relative stiffness of the dura and cord. Tensile radial stress may create a syrinx in previously normal cord tissue, and transiently lowered pressure may draw in interstitial fluid, causing the syrinx to enlarge if fluid exit is inhibited. The suggested mechanism could also explain the juxtaposition of syrinxes to regions of arachnoiditis.
Keywords: Fluid–structure interaction - Finite-element model - Cerebrospinal fluid - Wave propagation - Syringomyelia
Fluid–solid interaction simulation of flow and stress pattern in thoracoabdominal aneurysms: A patient-specific study
A. Borghia, N.B. Wooda, R.H. Mohiaddinb, X.Y. Xua
aDepartment of Chemical Engineering, South Kensington Campus, Imperial College, London SW72AZ, UK
bRoyal Brompton and Harefield NHS Trust, Sydney Street, London, UK
Journal of Fluids and Structures 24 (2008) 270–280
Abstract: Thoracoabdominal aneurysm (TA) is a pathology that involves the enlargement of the aortic diameter in the inferior descending thoracic aorta and has risk factors including aortic dissection, aortitis or connective tissue disorders. Abnormal flow patterns and haemodynamic stress on the diseased aortic wall are thought to play an important role in the development of this pathology and the internal wall stress has proved to be more reliable as a predictor of rupture than the maximum diameter for abdominal aortic aneurysms; but this assumption has not been validated yet for aneurysms involving the thoracic aorta. In the present study, three patients with TAs of different maximum diameters were scanned using magnetic resonance imaging (MRI) techniques. Realistic models of the aneurysms were reconstructed from the in vivo MRI data acquired from the patients, and subject-specific flow conditions were applied as boundary conditions. The wall and thrombus were modelled as hyperelastic materials and their properties were derived from the literature. A normal descending aorta was also simulated to provide data for comparison. Fully coupled fluid–solid interaction (FSI) simulations as well as solid static simulations were performed using ADINA 8.2. The results show that the wall stress distribution and its magnitude are strongly dependent on the 3-D shape of the aneurysm and the distribution of thrombus. Maximum wall stresses in all TA models are higher than in the normal aorta, and values of maximum wall stress are not directly related to the maximum aneurysm diameter. Comparisons between the FSI and solid static simulation results showed no significant difference in maximum wall stress, supporting those previous studies which found that FSI simulations were not necessary for wall stress prediction.
Frictional Heat-Induced Phase Transformation on Train Wheel Surface
Su Hang1, Pan Tao1, Li Lit1, Yang Cai-fu1, Cui Yin-hui2, Ji Huai-zhong2
1 Division of Structural Material Research, Central Iron and Steel Research Institute, Beijing 100081, China
2 Ma' anshan Iron and Steel Company Limited, Ma' anshan 243000, Anhui, China
Journal Of Iron And Steel Research, International, 15(5): 49-55, 2008.
Abstract: By combining thermomechanical coupling finite element analysis with the characteristics of phase transformation [continuous cooling transformation (CCT) curve], the thermal fatigue behavior of train wheel steel under high speed and heavy load conditions was analyzed. The influence of different materials on the formation of the phase transformation zone of the wheel tread was discussed. The result showed that the peak temperature of wheel/track friction zone could be higher than the austenitizing temperature for braking. The depth of the austenitized region could reach a point of 0.9 mm beneath the wheel tread surface. The supercooled austenite is transformed to a hard and brittle martensite layer during the following rapid cooling process, which may lead to cracking and then spalling on the wheel tread surface. The decrease in carbon contents of the train wheel steel helps inhibit the formation of martensite by increasing the austenitizing temperature of the train wheel steel. When the carbon contents decrease from 0.7% to 0.4 %, the Ac3 of the wheel steel is increased by 45°C, and the thickness of the martensite layer is decreased by 30%, which is helpful in reducing the thermal cycling fatigue of the train wheel tread such as spalling.
Keywords: train wheel steel - thermal cycling fatigue - friction - martensite transformation - thermomechanical coupling
The Carrying Capacity of Conical Interference Fit Joints with Laser Reinforcement Zones
Lucjan Sniezek2, Jolanta Zimmerman1, Andrzej Zimmerman1
1 Warsaw University of Technology, Faculty of Production Engineering, Institute of Mechanics
and Printing, 85 Narbutta St., 02-524 Warsaw, Poland
2 Military University of Technology, Faculty of Mechanical Engineering, Department of Machine Design, 2 Kaliskiego St., 00-908 Warsaw, Poland
Journal of Materials Processing Technology, doi:10.1016/j.jmatprotec.2010.02.004, 2008.
The subject of the paper is the comparative research on the carrying capacity of the conical interference fit joints and the interference fit joints with the laser reinforcement paths. The calculations of strain and stress distribution in the shaft neck and the bush were carried out for three stages: during the joining process, after the interference and after the application of torsional moment. The FEM was used. The dependences of the joint carrying capacity on the interference force were determined and experimental tests of the capacity of the conical interference fit joints were carried out. The numerical calculation showed the increase in the capacity of the conical interference fit joints with the laser reinforcement zones in comparison with the standard joints by 50% in the case of the same axial displacement. Greater capability (about 25%) of this joint was achieved from experimental tests in comparison to one without
Keywords: conical interference fit joints - stress distribution - torque capacity - FEM
Estimation of NonlinearMechanical Properties of Vascular Tissues via Elastography
Reza Karimi1,2, Ting Zhu1, Brett E. Bouma3, Mohammad R. Kaazempur Mofrad4
1 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
2 Department of Bioengineering, University of California, 208A Stanley Hall #1762, Berkeley, CA 94720, USA
3 Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School,
Boston, MA, USA 02114
4 Department of Bioengineering, University of California, 208A Stanley Hall #1762, Berkeley, CA 94720, USA, e-mail: firstname.lastname@example.org
Cardiovasc Eng., 8(4):191–202, 2008.
Abstract: A new method is proposed for estimation of nonlinear elastic properties of soft tissues. The proposed approach involves a combination of nonlinear finite element methods with a genetic algorithm for estimating tissue stiffness profile. A multipoint scheme is introduced that satisfies the uniqueness condition, improves the estimation performance, and reduces the sensitivity to image noise. The utility of the proposed techniques is demonstrated using optical coherence tomography (OCT) images. The approach is, however, applicable to other imaging systems and modalities, as well, provided a reliable image registration scheme. The proposed algorithm is applied to realistic (2D) and idealized (3D) arterial plaque models, and proves promising for the estimation of intra-plaque distribution of nonlinear material properties.
Keywords: Soft tissue mechanics - Nonlinear material properties – Atherosclerosis - Elastography - Genetic algorithm - Optical coherence tomography
Nonspherical Half-Shells by Ultrasonic Cleavage of the Hollow Polyhedral Particles in Water
Shuhong Jiao1, Kai Jiang2, Yanhong Zhang3, Ming Xiao1, Lifen Xu1, and Dongsheng Xu1
1 Beijing National Laboratory for Molecular Science (BNLMS), State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
2 College of Chemistry and Environmental Science, Henan Normal University, Xinxiang, Henan 453002, China
3 China Institute of Water Resources and Hydropower Research, Beijing 100044, China
J. Phys. Chem. C, 112:3358-3361, 2008.Abstract: We present a facile route to preparing nonspherical half-shells of copper sulfide in which the octahedral mesocages of copper sulfide were grown on the substrate by a two-step electrochemical method first and then were cleaved into tetrahedral half-shells by ultrasonic vibration in water. The obtained half-shells are 1-3 µm in lengths, and the shell thickness is uniform in ˜100 nm. It is found that only centrosymmetric octahedral and six-pod shells can be equally split into two similar half-shells. Furthermore, a finite element analysis has been used to model the stress distribution in the octahedral CuS shell structure during ultrasonic vibration.