bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Growth Before Coupled-Mode Flutter
Authors: Schmid Peter , de Langre Emmanuel
Published: June 2008

Transient growth of energy is known to occur even in stable dynamical systems due to the non-normality of the underlying linear operator. This has been the object of growing attention in the field of hydrodynamic stability, where linearly stable flows may be found to be strongly nonlinearly unstable as a consequence of transient growth. We apply these concepts to the generic case of coupled-mode flutter, which is a mechanism with important applications in the field of fluid-structure interactions. Using numerical and analytical approaches on a simple system with two degrees of freedom and anti-symmetric coupling we show that the energy of such a system may grow by a factor of more than 10, before the threshold of coupled-mode flutter is crossed. This growth is a simple consequence of the non-orthogonality of modes arising from the non-conservative forces. These general results are then applied to three cases in the field of flow-induced vibrations: (a) panel flutter (two-degrees-of-freedom model, as used by Dowell (1995)), (b) follower force (two-degrees-of-freedom model as used by Bamberger (1981)), and (c) fluid-conveying pipes (two-degree-of-freedom model, as used by Benjamin (1961) and Paidoussis (1998)), for different mass ratios. For these three cases we show that the magnitude of transient growth of mechanical energy before the onset of coupled-mode flutter is substantial enough to cause a significant discrepancy between the apparent threshold of instability and the one predicted by linear stability theory.
Wave Propagation in Flows Across Junctions Between Rigid and Flexible Walls
Authors: Carpenter P. W. , Sen P. K. , Hegde S. , Davies C.
Published: June 2008

The generic problem considered is the propagation of vortical waves across junctions between one wave-bearing medium and another. It is assumed that the eigensolutions are known for the corresponding spatially homogeneous problems. The task is how to determine the amplitudes of the reflected and transmitted waves given the amplitude of the incident wave. In general, there may be more than one incident, reflected or transmitted wave. It is shown how this sort of problem may be solved in terms of the homogeneous eigensolutions by drawing an analogy between the junction and a wave-driver. The particular illustrative problem studied is that of a Tollmien-Schlichting wave, propagating along a rigid-walled channel flow, that is incident on a section of the channel where the walls consist of compliant panels. It is shown how the wave system over the compliant panels and the amplitude of the Tollmien-Schlichting wave leaving the compliant section may be determined in terms of the incident wave. The technique developed for this problem is considered to be generic.
Axial Leakage Flow-Induced Vibration of Thin Cylindrical Shell With Respect to Circumferential Vibration
Authors: Fujita Katsuhisa , Shintani Atsuhiko , Ono Masakazu
Published: June 2008

In this paper, the dynamic stability of a thin cylindrical shell subjected to axial leakage flow is discussed. In this paper, the third part of a study of the axial leakage flow-induced vibration of a thin cylindrical shell, we focus on circumferential vibration, that is, the ovaling vibration of a shell. The coupled equations of motion between shell and liquid are obtained by using Donnell’s shell theory and the Navier-Stokes equation. The added mass, added damping and added stiffness in the coupled equations of motion are described by utilizing the unsteady fluid pressure acting on the shell. The relations between axial velocity and the unstable vibration phenomena are clarified concerning the circumferential vibration of a shell. Numerical parametric studies are done for various dimensions of a shell and an axial leakage flow.
Fraction Solid Measurements on A319 Aluminum Alloy
Authors: Bakhtiyarov Sayavur I. , Overfelt Ruel A. , Teodorescu Sorin G.
Published: June 2008

A new indirect method to measure fraction solid on molten metals is presented. The method is based on the phenomena that when a metal sample (solid or liquid) rotates in a magnetic field (or the magnetic field rotates around a stationary sample), circulating eddy currents are induced in the sample, which generate an opposing torque proportional to amount of solid phase that precipitates in a solidifying melt between the liquidus and solidus temperatures. A new technique is applied for measuring fraction solid on commercial A319 aluminum alloy. The solidification curves obtained by the proposed method at different cooling rates are in a good agreement with the predictions made by the Scheil model.
Automatic Sequence Planning by Subassembly Detection for Automobile Body Assembly
Authors: Zhang Yizhu , Ni Jun , Lin Zhongqin , Lai Xinmin
Published: June 2008

In the modern global economy, automotive manufactures need to shorten the product development time and concurrently improve the design for new products, However, the majority of assembly planning tasks in automobile body design is still manually performed by assembly designers according to their experiences. This has prolonged the production lead time and time to market. This paper describes a procedure to automatically derive all the feasible assembly sequences for automobile body assembly. This procedure is based on a mathematical model of the automobile body, obtained through the definitions of the connection matrix and contracted matrix. These two matrices represent the precedence constraint knowledge among components and subassemblies. The possible subassemblies are automatically detected by satisfying some mathematical conditions applicable to these matrices. For each subassembly and the whole product, all the possible assembly sequences are generated by rearranging the initial connection sub-matrix and the contracted matrix. The procedure can solve the ‘combinatorial explosion’ problem efficiently by hierarchical subassembly detection.
Theory and Simulation of a Novel Viscosity Measurement Method for High Temperature Semiconductor Melt
Authors: Lin Bochuan , Li Chao , Ban Heng , Scripa Rosalia N. , Zhu Shen , Su Ching-Hua , Lehoczky Sandor L.
Published: June 2008

A novel viscosity measurement technique was developed in which angular deflection-oscillation of a sealed quartz ampoule containing a semiconductor melt is measured upon application of a rotating magnetic field. This paper provides a theoretical basis for this novel method. Equations for coupled fluid flow and ampoule torsional oscillation were solved numerically. The predictions of the melt flow and ampoule oscillation were in good agreement with the experimental data. The results also showed that both electrical conductivity and viscosity could be calculated from the experimental data by a numerical fitting procedure. The transient velocity of the melt caused by the rotating magnetic field was found to reach steady state in about one minute, within which both the electrical conductivity and the viscosity of the melt can be obtained. This is a significant improvement over the existing oscillation cup method, which requires about one hour of measurement to obtain viscosity.
Virtual Manufacturing and Its Application to Making Oil Pumps
Authors: Tseng A. A. , Yan J. Q. , Fan X. M. , Ma D. Z.
Published: June 2008

Advances in manufacturing systems have led to the increasing importance of the information processing techniques. Many tasks in manufacturing have been transferred from workshops to computers, and now large portions of activities in manufacturing systems are presently considered for being carried out as information processing activities within computers. As a result, system architectures and virtual reality have emerged as necessary components in today’s global manufacturing industry in an attempt to enhance both process and production operations. A system structure and related design methodology of a general virtual manufacturing system is proposed here. Prototype software based on the proposed system has been developed. The system was developed on a network-based platform, which can integrate with wide variety of software. Applications of the proposed system to virtual product design of oil pumps are then presented to demonstrate its feasibility and versatility.
Size and Frequency of Defects in Silicon MEMS
Authors: LaVan David A. , Boyce B. L. , Buchheit T. E.
Published: June 2008

Mechanical testing of thin films for MEMS has progressed from a developmental stage to a point where validated techniques are used to study the behavior of devices and materials at a very fine scale. Tensile data covering a range of sizes and test techniques have been analyzed to examine the distribution of defects that would be responsible for the observed fracture strengths. For each sample, a critical defect size was calculated based on a published fracture toughness and a half-circular surface crack fracture toughness model. For polysilicon produced using the SUMMiT V process in the period 1998–1999, the calculated mean defect size was 115 nm. For polysilicon produced using the MUMPS process, the calculated mean defect size was 389 nm.
An Architecture for the Development of Multi-Component Software Tools for Virtual Manufacturing
Authors: Bless Patrick N. , Kapoor Shiv G. , DeVor Richard E.
Published: June 2008

This paper proposes an integrated infrastructure to support the large and growing body of software tools for Computer Aided Manufacturing. The proposed infrastructure is based on an ontology-driven systematization of the CAM component domain, an agent-based communication framework, and algorithmic strategies. Such will allow researchers and other users to combine separately developed models for manufacturing processes, data repositories, optimization routines and geometry analysis tools into more comprehensive simulation software tools for analysis and optimization. An application to optimize hole quality in drilling is used as an example to illustrate the functionality of the proposed infrastructure.
A DAI-Based Framework for the Virtual Prototyping of Fluid Power Systems
Authors: Fok S. C. , Thimm G. L. , Xiang W.
Published: June 2008

This paper proposes a distributed artificial intelligence framework to address the co-ordination of interactions among the different standard virtual components during the virtual prototyping of fluid power systems. The approach considers the hydraulic system as a multi-agent system and associates each virtual hydraulic component to a domain agent. A control agent is used to co-ordinate the interactions in the multi-agent system. The representation of the proposed domain agents and the co-ordinated communication via the control agent are discussed in this paper. The paper also presents some details on the implementation of the proposed agent-based architecture and explains how agent communication and collaboration has been accomplished using Java and VRML.
A Supervisory Data-Traffic Controller in Collaborative Virtual Reality Simulations
Authors: Akgunduz Ali , Banerjee Pat
Published: June 2008

In this paper an efficient technique for distributing the data in collaborative virtual reality is presented. The described technique incorporates the culling and level of detail concepts in virtual reality to obtain cell based bounding volumes in each virtual environment. Defined bounding volumes are utilized in filtering the data that is transferred between different virtual environments in the simulation system. To orchestrate the communication between virtual environments and their bounding volumes, a supervisory control system is presented in the paper.
Radiative Properties of Polar Bear Hair
Authors: Preciado Jessica A. , Rubinsky Boris , Otten David , Nelson Brent , Martin Michael C. , Greif Ralph
Published: June 2008

The polar bear’s ability to survive in the harsh arctic night fascinates scientific and lay audiences alike, giving rise to anecdotal and semi-factual stories on the radiative properties of the bear’s fur which permeate the popular literature, television programs, and textbooks [1–5]. One of the most interesting radiative properties of polar bear fur is that it is invisible in the infrared region. Some theories have attempted to explain this by claiming that the outer temperature of the fur is the same as that of the environment. However, this explanation is unsatisfactory because surface radiation depends on both the surface temperature and the surface radiative properties [6].
Function of the Anterior Band of the Inferior Glenohumeral Ligament During the Load and Shift Test
Authors: Newman William J. , Debski Richard E. , Gardiner John C. , Moore Susan M. , Weiss Jeffrey A.
Published: June 2008

The anterior band of the inferior glenohumeral ligament (AB-IGHL) plays a crucial role in anterior shoulder stability. This capsulo-ligamentous structure originates on the anterior edge of the glenoid and labrum and inserts on the anterior/lateral edge of the articular surface of the humeral head. AB-IGHL detachment from the anterior glenoid and labrum (Bankart lesion) as well as capsular stretching are frequent injuries for which initial diagnosis is often difficult. The load and shift test is a clinical exam used to assess the magnitude of anterior instability by applying an anterior load to the humeral head with the shaft in 60 degrees of abduction [1]. Information on the magnitudes and distribution of stress and strain can help in the interpretation of motion during the exam as well as assist in localizing instabilities to particular regions of the capsule. The objectives of this study were to examine the stress and strain in the AB-IGHL during the load and shift test using finite element (FE) modeling techniques.
The Effects of Cortical Bone Viscoelasticity on the Short-Term Fixation of Press-Fit Cylindrical Intramedullary Rods
Authors: Shultz Travis R. , Norman Timothy L. , Gruen Thomas A. , Blaha J. David
Published: June 2008

Cementless femoral implants have demonstrated widespread clinical success, particularly in the patient populations for which various cemented techniques have been troublesome [1–4]. Long-term fixation and consequent clinical stability occurs primarily via bony ingrowth into a porous-coated implant surface. The adequacy of this biologic fixation depends in part upon the initial or short-term fixation of the implant with respect to the adjacent bone [5,6]. Short-term fixation refers to the post-operative limitation of relative motion between the porous-coated implant surface and the adjacent bone structure. This relative motion, or micromotion, may be limited by utilizing a porous implant coating in concert with a stem press-fit — both increase the frictional resistance to motion [7]. The holding power of the press-fit over time is dependent upon the viscoelastic nature of cortical bone. Data has long been available in the literature for the viscoelastic behavior of cortical bone in the longitudinal direction [8]; however, a transverse viscoelasticity model is required to evaluate a press-fit since it generates considerable radial and circumferential stress but very little axial stress. Only recently has such a model become available [9].
A Quantitative Oil Dot Streak Method for Measuring Near-Wall Shear Stresses Applied to the Heartquest™ LVAD
Authors: Lemire Phillip P. , Day Steven W. , McDaniel James C. , Wood Houston G.
Published: June 2008

Experimental investigation of the fluid dynamics inside any blood pumping device is necessary for several reasons. First, improved understanding about the flow near the walls of a blood pump is important since thrombus formation (blood clotting) may occur when the shear stress is nearly zero. If the shear stress is in the opposite direction to the main body of the flow, a region of stagnation or recirculation is indicated, which may also lead to thrombosis. A second problem of importance to blood flows is hemolysis, the destruction of red blood cells. Hemolysis can be caused by high shear stresses imposed on the blood cells by the flow. Since hemolysis is a function of at least shear stress and residence time, an understanding of how these two variables are coupled is desirable. Third, an accurate measurement of wall shear stress and flow patterns is also necessary to validate computational fluid dynamics (CFD) predictions in the design of blood pumps. It is widely known that improper meshing of the numerical pump model, the use of an incorrect turbulence model, or errors in choosing boundary conditions can lead to a model that is in contradiction to experimental results. Quantitative oil streaking has been implemented in order to measure the wall shear stresses in the pump and supply the necessary information needed to ensure a good pump design.
Regional Association of Biological and Hemodynamic Parameters in Distal End-to-Side Vascular Anastomoses Perfused Ex Vivo
Authors: Kute Stephanie M. , Vorp David A.
Published: June 2008

Vascular bypass graft failure is a significant clinical problem and is frequently due to the formation of intimal hyperplasia (IH) [1–3]. IH is characterized by the accumulation of smooth muscle cells (SMC) and extracellular matrix in the intima of the vessel, which occurs when the normal balance between vascular cell proliferation and apoptosis (regulated cell death) is altered [4]. The disturbed flow present at the anastomosis has been implicated in the formation of IH and the link between hemodynamics and graft failure is via a complex cascade of events whereby biomechanical forces cause biological responses [5, 6]. For example, immediate early genes (IEG) such as c-fos, c-jun and egr-1 are involved in the signaling pathways for proliferation and apoptosis. When extracellular biomechanical stimuli (e.g. shear stress) cause the expression of IEG, their protein products translocate to the nucleus. These proteins regulate the expression of a number of genes implicated in cardiovascular disease including growth factors, adhesion molecules, proapoptotic substrates and coagulation factors [7–9]. Because IEG are involved in both proliferation and apoptosis, their expression may upset the normal balance between cell proliferation and apoptosis and could play a vital role in the IH formation in vascular bypass grafts.
Computational Fluid Dynamics Simulation of the Blood Flow in the Circle of Willis
Authors: Harazawa M. , Yamaguchi T.
Published: June 2008

The blood supply for the brain is born by four arteries, that is, two internal carotid arteries and two vertebral arteries. They are mutually connected at the cerebral base, and form a closed arterial circle, called the circle of Willis, so that the safety of the brain blood supply is increased. However their anastomoses show a very wide variety of atypism. If some of anastomses are very thin, or even do not exist, the safety of the blood supply is not secured. This is particularly important when some diseases such as cerebral thrombosis occurs and the blood flow supply stops unilaterally. Redistribution of the blood supply in such cases is thought to be strongly affected by geometrical configuration of the anastomoses. It is also known that cerebral aneurysms, which may induce serious cerebrovascular diseases, preferentially occur at the circle of Willis. Complex blood flow pattern has been suspected of having an influence on this preference. This is again dependent on complex geometry of the circle.
Flow in the Stenotic Carotid Bifurcation
Authors: Berger Stanley A. , Rayz Vitaliy L.
Published: June 2008

The carotid artery bifurcation is prone to the development of atherosclerotic plaques, and is a site where the consequences of this development can be severe. The most immediate effects are changes in lumenal cross-section, volumetric blood flow, and forces on the wall. The end result may be plaque rupture, possibly resulting in a stroke. Plaque development, and plaque rupture, are likely both strongly influenced by the changes of the shear stress, and possibly normal stress, at the artery wall [1]. Numerical simulations of the flow in the carotid bifurcation can elucidate the influence of the flow on the plaque and vice versa. The irregular geometries of severely stenotic vessels make numerical modeling of these flows particularly challenging [2, 3]. We describe simulations in fully three-dimensional, realistic geometries under steady and pulsatile flow conditions.
On the Relationship Between Added Mass and Added Damping
Authors: Goyder H. G. D.
Published: June 2008

A surprising relationship exists between the amplitude and phase of a vibrating system. For an item vibrating in a fluid flow the phase of the fluid pressure (relative to the motion of the structure) can be deduced from the amplitude of the pressure. This strong dependence of the phase on the amplitude provides a means for checking the correctness of measured data and severely constrains the form that a mathematical model can take. The relationship between amplitude and phase is completely general and the paper gives various examples from theoretical models and experimental data. One interesting consequence of this relationship follows from the observation that phase angles only exist because of damping. Hence damping, due to the fluid, is linked to added mass.
Bifurcation of Water Column Oscillator Behavior Simulating Reactor Safety System: 2nd Report, Analytical Model
Authors: Kawamata K. , Morimoto Y. , Madarame Haruki , Okamoto Koji
Published: June 2008

Behavior of a water column oscillator with a cover gas system was studied experimentally and analytically. One of the free water surfaces was sealed with the cover gas, while the other was open to the atmosphere. The cover gas was supplied with a constant rate, and it was ejected through a valve when the water level reached a certain point. As soon as the level reached another point, the valve closed and the cover gas quantity increased again. In the experiment, a bifurcation-like phenomenon was observed; the valve closed period usually had a single value, while it took two values under certain conditions. In order to examine the cause of this bifurcation-like phenomenon, a numerical analysis model was developed which described the system behavior precisely. The analytical result revealed that the bifurcation-like phenomenon was not bifurcation but an abrupt change of the value dimmed by superimposed noise. Finally the numerical model predicts that the water column oscillator behaves chaotically at certain conditions.
Measurements of In Vivo Strains in the Rat Tail Vertebra
Authors: Kim Chi Hyun , Takai Erica , Culella Nicole , Guo X. Edward
Published: June 2008

The study of bone adaptation is important in understanding the etiology of age-related bone fractures, developing optimal designs for total joint replacements, and preventing bone loss during prolonged space flight. Numerous studies have attempted to quantify the relationship between mechanical loading and bone adaptation [1,2,3,4]. An in vivo rat tail vertebra model has been developed for trabecular bone adaptation studies where a controlled mechanical load can be applied to a whole vertebra [3]. The load levels applied in vivo were selected using in vitro strain gage measurements on cadaveric rat tails, resulting strains in the cortical shell of tail vertebrae within the physiological range. However, it is not clear what the physiological strain level in the rat tail vertebrae in vivo during normal cage activities is. In addition, the in vivo strain in the rat tail vertebra subjected to mechanical loads has not been quantified.
Strain and Fracture Induced Changes in Bone Mineral Crystals
Authors: Akkus Ozan , Adar Fran , Schaffler Mitchell B.
Published: June 2008

The hierarchical organization of bone entails the tissue level at the nanoscale up to the organ level at the macroscale. In this hierarchical perspective, skeletal fragility is the outcome of a failure cascade that initiates at the molecular level, and propagates to higher levels [1]. This failure cascade is well investigated at the microscale and the macroscale [2] whereas the deformation and fracture mechanisms at the nanoscale are largely unknown. Therefore, our understanding of how mineralized tissues fail is incomplete and requires further investigations so as to formulate the ultrastructural basis of increased fracture susceptibility during disease and aging. In this regard, the first aim of the present study was to experimentally investigate the behavior of bone mineral under mechanical strain. The second aim of this study was to determine whether irreversible changes occur in the mineral crystals following fracture.
Finite Element Analysis on Nitinol Medical Applications
Authors: Gong Xiao-Yan , Pelton Alan R.
Published: June 2008

Nitinol, an alloy of about 50% Ni and 50% Ti, is a very unique material. At constant temperature above its Austenite finish (Af) temperature, under uniaxial tensile test, the material is highly nonlinear and capable of large deformation to the ultimate strain on the order of 15%. This material behavior, known as superelasticity, along with its excellent biocompatibility and corrosion resistance, makes Nitinol a perfect material candidate for many medical device applications. However, the nonlinear material response also requires a specific material description to perform the stress analysis. The user developed material subroutine from HKS/West makes the simulation of the Nitinol devices possible. This article presents two case studies of the nonlinear finite element analysis using ABAQUS/Standard and the Nitinol UMAT.
Kinematics of the Human Pelvis Following Open Book Injury
Authors: Caruntu Dumitru I. , Hefzy Mohamed Samir , Ebraheim Nabil , Mekhail Anis , Yeasting Richard
Published: June 2008

The objective of this study is to determine the three dimensional kinematics of the human pelvis including both sacroiliac joints following a simulated open book fracture induced on cadavers by applying anterior-posterior compressive loads to the pelvis. An electromagnetic digitizing and motion tracking system was utilized to measure the morphology of the pelvis and the relative movements of its bones during this simulated open book fracture. The screw displacement axis method was used to describe the relative motions between the sacrum and each hip bone. Morphologically, it was found that the articular surfaces forming the sacroiliac joints can be approximated with planar surfaces directed from proximal and lateral to distal and medial and from posteromedial to anterolateral. The kinematic data indicate that the motion of the hip bone with respect to the sacrum on the side of the sacroiliac joint (SIJ) opening is almost a pure rotation which translates clinically on the A-P x-rays as pure opening of the SIJ without vertical displacement. The average axis of rotation was found to be almost parallel to the SIJ planar articular surface.
Biomechanical Analyses of Corpectomy and Anterior Cervical Plating: A FEM Study to Assess Stability, Implant and Bone Graft Stresses in Short and Long Constructs
Authors: Natarajan Raghu N. , Oi Nelson , Curylo Luc , Andersson Gunnar B. J. , An Howard
Published: June 2008

Anterior corpectomy of the cervical vertebral body is an established procedure to decompress the spinal cord for cervical spondylotic myelopathy, traumatic and neoplastic cases. Following corpectomy at one or more levels, the spinal column is typically reconstructed by strut grafting and plating. Modern plate-screw fixation systems provide improved rigidity, but complications still may occur such as screw loosening, screw pull-out, nonunion, construct failure, and injuries to adjacent vital structures. The stability of the plate-screw constructs as wells as the stresses and strains in the implant and bone graft depend on many factors including the number of motion segments fused, presence of intermediate screws and loading direction. It is hypothesized that the shorter constructs provide greater stability and reduced stresses in the implant and bone graft as compared to longer constructs, and intermediate screws in the longer constructs improve the stability. This study will investigate the biomechanical effects of plate-screw fixation in both short and long anterior fusion constructs, using a validated multi-segment cervical finite element model.
Computation of Trunk Muscle Forces and Internal Spinal Loads in Standing Postures
Authors: Shirazi-Adl A. , El-Rich M. , Pop D. , Parnianpour M.
Published: June 2008

The kinetic redundancy in human musculoskeletal trunk system allows for the active control of posture during a specific task while satisfying equilibrium and stability requirements. Such control could aim, for example, to minimise forces in active musculature and stresses in passive tissues. It results in a superfluous system of equations the solution of which not yet satisfactorily achieved despite its importance in evaluation and treatment of spinal disorders. Due to shortcomings in existing reduction, optimisation and EMG-driven models, and combination thereof, a novel kinematics-based finite element approach [1,2] is employed that fully accounts for the synergy between passive and active trunk sub-systems. In this study, the kinematics-based model is applied to determine spinal muscle forces and internal ligamentous passive loads at different disc levels in standing postures under gravity loads with and without 200N weights carried in both hands (positioned symmetrically close to the body, either anteriorly or on sides).
Stress Changes in Intervertebral Discs of the Cervical Spine After Arthrodesis
Authors: Tchako Abraham , Sadegh Ali
Published: June 2008

An improved and detailed 3D FE model of human cervical spine model was created using digitized geometric measurement tool. The vertebral bodies of the model were fused at three locations. The unfused and the fused models were physiologically loaded and the changes in stresses in intervertebral discs were compared. A moment of 1.5 Nm was used in combination with a 50 N compressive preload. The results showed that the lower cervical spine fusion induces the most stress changes in the neighboring discs.
An Improved Testing Protocol for Evaluating Anterior Spinal Instrumentation Using Graft Loads in a Single-Level Cervical Discectomy or Corpectomy Model
Authors: DiAngelo Denis J. , Osztheimer Geza , Foley Kevin T.
Published: June 2008

Anterior cervical instrumentation used in discectomy or corpectomy graft fusion should restore the mechanical integrity of the operated spine and decrease graft complications. For fusion to occur, the spinal instrumentation must load-share with the interbody graft. Recent design changes in anterior cervical plates (ACP) aim to allow motion across the fusion site and load share with the graft [1]. However, existing American Society for Testing and Materials (ASTM) standards (F1717-96) for static and fatigue testing of spinal implant constructs in a corpectomy model do not include an interbody graft in the test method [2]. The objective of this study was to develop a non-destructive testing protocol and apparatus to rank the static and low-endurance performance of ACP instrumentation in single-level discectomy and corpectomy graft-plate models.
Modelling the Ion Channel Behaviour of Articular Chondrocytes
Authors: Wilson Jim R. , Duncan Neil A.
Published: June 2008

All cells have a membrane potential; this voltage difference arises from the different intracellular and extracellular ion concentrations. In excitable tissue the cell membranes contain ion channels which control the movement of ions and hence control the cell’s membrane potential. Extensive measurements of the electrophysiology of excitable cells has allowed considerable understanding of the ion channels. The Hodgkin-Huxley model [1] was developed from measurements on a squid nerve axon, and it quantifies the changes in membrane conductance due to the opening and closing of specific ion channels. This model has been very successful in describing the electrical behaviour of neurons. Ion channels also exist in non-excitable tissue cells. Patch clamp experiments have demonstrated that ion channels in chondrocytes influence cell’s membrane potential [2]; controls the influx of Ca2+ [3] and may regulate cell proliferation [2]. The objective of this research was to develop a model of ion channel behaviour for connective tissue cells based on the Hodgkin-Huxley model, and to apply this model to reported patch clamp measurements of articular chondrocytes.
Material Properties of Cells Can Be Determined From Compression Experiments of Cell-Gel Constructs
Authors: Srinivasan Jayendran , Kish Vincent , Venkatesan Vidyashankar , Salihu Sydha , Ayyalasomayajula Madhavi , Mukherjee Nilay
Published: June 2008

Mechanical loading has been implicated in regulating cellular behavior which in turn affect tissue development, growth, maintenance and regeneration. The structural components of the cell (cell membrane, transmembrane proteins such as integrins and at least three cytoskeletal networks of actin, microtubules and intermediate filaments) are involved in converting the mechanical loading into biochemical signals which then affect cellular behavior (1). Further, cells are known to alter their cytoskeletal structure during cell division (2), differentiation (3), pathology (4) and in response to mechanical loading (5). These changes will probably be reflected in gross material properties of the cell, such as modulus of elasticity. In this work, we describe a system to determine the modulus of elasticity of cells when they are embedded in agarose gel and subjected to compressive loading.
Direct Numerical Simulation of Micro-Scale Interaction Between Ice and Biological Cells
Authors: Mao L. , Udaykumar H. S. , Karlsson J. O. M.
Published: June 2008

The freezing of biological material, such as cells and tissue, duing cryopreservation involves the interaction of ice in the extracellular medium with living cells. This cell-ice interaction critically determines the success of the cryo-preservation protocol, as measured by cell survival and viability after the freeze-thaw process. This paper presents numerical simulations of the response of a cell to freezing. The phase change of the aqueous salt solution outside the cell is computed using a sharp-interface technique. The cell is modeled as a salt solution enclosed by a semi-permeable membrane. We compute the concentration and temperature fields around a single cell in the presence of extracellular ice formation. Parametric variations in the factors affecting the cell-ice interaction are performed to describe the physics of thermo-solutal transport of the interaction. Cell water loss is quantified. The external ice front is computed for both stable and unstable (cellular/dendritic) growth modes. The results show that water egress from the cell is dependent on several controlling parameters in complex ways.
Aeroacoustic Sensitivity Analysis and Its Application for Noise Barrier Design
Authors: Baysal Oktay , Ghayour Kaveh , Idres Moumen M.
Published: June 2008

An automated design optimization method is demonstrated by computationally modeling the wheel-on-rail noise. The noise propagation is simulated by solving the wave equation using the boundary element method and compared with field test data. Then, the computational model was coupled with an optimization methodology through finite-differenced sensitivities. Using this method, a number of new designs was obtained and evaluated for their relative effectiveness. Three new designs were found to improve the insertion loss within the design space delineated by the given geometrical constraints. Finally, for improved computational efficiency, a continuous adjoint sensitivity methodology was applied to the wave equation to obtain the shape sensitivity derivatives of the acoustic pressure field. Its accuracy and validity are demonstrated for objectives defined on the barrier surface and out in the acoustic field.
An Iterative Method for the Solution of Three-Dimensional Inverse Acoustic Scattering Problems
Authors: Farhat Charbel , Tezaur Radek , Djellouli Rabia
Published: June 2008

We present a computational methodology for retrieving the shape of an impenetrable obstacle from the knowledge of some acoustic far-field patterns. This methodology is based on the well-known regularized Newton algorithm, but distinguishes itself from similar optimization procedures by (a) a frequency-aware multi-stage solution strategy, (b) a computationally efficient usage of the exact sensitivities of the far-field pattern to the specified shape parameters, and (c) a numerically scalable domain decomposition method for the fast solution of three-dimensional direct acoustic scattering problems. We illustrate the salient features and highlight the performance characteristics of the proposed computational methodology with the solution on a parallel processor of various inverse mockup submarine problems.
Influence of Upstream Turbulence on the Fluidelastic Instability of a Tube Bundle With Various Flexible Tubes
Authors: Rottmann M. , Popp K.
Published: June 2008

The stability boundaries of a single flexible tube in one of the first rows of a tube bundle can be highly dependent on the turbulence characteristics of the upstream flow, cf. (Rottmann & Popp, 2001). For certain bundle geometries increased turbulence yields a stabilization of a flexible tube in the critical row. If this stabilization also occurs on the more realistic condition of a fully flexible bundle it could be a useful effect with respect to applications. The flow rate in a heat exchanger could be increased or existing stability problems could easily be solved by inserting turbulence grids at the inlet instead of changing the entire tube bundle. Therefore, wind tunnel tests have been carried out with various flexible tubes in the tube bundle. The vibrations in the tube bundle have been carefully observed and measured by means of accelerometers. These investigations still show a significant stabilizing effect of increased upstream turbulence.
Iterative Regularization Methods for Inverse Problems in Acoustics
Authors: DeLillo Thomas K. , Hrycak Tomasz , Valdivia Nicolas
Published: June 2008

We consider the use of conjugate-gradient-like iterative methods for the solution of integral equations arising from an inverse problem in acoustics in a bounded three dimensional region. The inverse problem is the computation of the normal velocities on the boundary of a region from pressure measurements on an interior surface. The pressure satisfies the Helmholtz equation in the region. Two formulations are considered: one based on the representation of pressures by a single layer potential and the other based on the Helmholtz-Kirchhoff integral equation. Both formulations can be used to approximate the Neumann Green’s function as an alternative. The integral equations are all ill-posed and are discretized by a boundary element method. The resulting liner systems are ill-conditoned and a (smooth) regularized solutions must be sought. Two regularization rules, including a new one, for conjugate-gradient-like methods are applied and found to have advantages over a standard method based on the truncated singular value decomposition using generalized cross validation. Due to the occurence of multiple singular values for our integral operators, conjugate gradient methods compute the optimal solution in the first few iterations and prove to be particularly fast for these large scale acoustics problems.
Two-Phase Cross-Flow Excitation of a Normal Square Tube Array: Experiments and Analysis
Authors: Feenstra Paul , Weaver David S. , Nakamura Tomomichi
Published: June 2008

Laboratory experiments were conducted to determine the flow-induced vibration response and fluidelastic stability threshold of a model heat exchanger tube bundle subjected to a cross-flow of refrigerant 11 (R-11). The tube bundle consisted of a normal square array of 12 tubes with outer tube diameters of 7.11 mm and a pitch over diameter ratio of 1.485. The experiments were conducted in a flow loop that was capable of generating single-phase and two-phase cross-flows over a variety of mass fluxes and void fractions. The primary intent of the research was to improve our understanding of the flow-induced vibrations of heat exchanger tube arrays subjected to two-phase cross-flow. Of particular concern was the effect of array pattern geometry on fluidelastic instability. The experimental results are analysed and compared with existing data from the literature using various methods of parameter definition. Comparison of amplitude response in liquid flow with previous results shows a similar occurrence of symmetric vortex shedding that validates the scale model approach in single-phase flow. It was found that the introduction of a small amount of bubbles in the flow disrupted the vortex shedding and thereby caused a significant reduction in streamwise vibration amplitude. The fluidelastic stability thresholds for the present array agree well with results from previous studies. Furthermore, a good collapse of the stability data from various investigations is obtained when the fluid density is defined using the slip model of Feenstra et al. [1] and when an effective two-phase flow velocity is defined using the interfacial velocity model of Nakamura et al. [2].
Numerical Simulation of Tube Bundle Vibrations in Cross Flows
Authors: Longatte E. , Bendjeddou Z. , Souli M.
Published: June 2008

In many industrial applications, mechanical structures like heat exchanger tube bundles are subjected to complex flows causing possible vibrations and damage. Part of fluid forces are coupled with tube motion and these so-called fluid-elastic forces can affect the structure dynamic behaviour generating possible instabilities and leading to short term failures through high amplitude vibrations. Most classical fluid force identification methods rely on structure response experimental measurements associated with convenient data processes. Owing to recent improvements in Computational Fluid Dynamics, numerical simulation of flow-induced vibrations is now practicable for industrial purposes. The present paper is devoted to the computation of fluid-elastic forces acting on tube bundles subjected to one-phase cross flows. What is the numerical process ? In the case where fluid-elastic effects are not significant and are restricted to added mass effects, there is no real coupling between structure and fluid motion. The structure displacement is not supposed to affect flow patterns. Thus it is possible to solve the fluid and the structure problems separately by using a fixed non-moving mesh for the fluid dynamic computation. Lift and drag forces acting on tube bundles can be computed numerically by using Large Eddy Simulation. Their spectrum and time history can be introduced as inlet conditions in the mechanical calculation providing the tube vibratory response. On the contrary when fluid-elastic effects can not be neglected, in presence tube bundles subjected to cross flows for example, a coupling between flow and structure computations is required. Such a calculation is performed in the present work. An improved numerical approach has been developed and applied to the fully numerical prediction of the dynamic behaviour of a flexible tube belonging to a fixed tube bundle subjected to cross flows. The purpose is to be able to provide a numerical estimate of the critical flow velocity for the threshold of fluidelastic instability of tube bundle without experimental investigation. The methodology consists in simulating in the same time thermohydraulics and mechanics problems by using an Arbitrary Euler Lagrange (ALE) formulation for the fluid computation. Numerical results turn out to be consistent with available experimental data obtained in the same configuration. This work is a first step in the numerical prediction of tube bundle vibrations in presence of cross flows.
Behavior of a Nutation Damper Undergoing a Coupled Horizontal/Rotational Motion
Authors: Popplewell N. , Lu M. L. , Shah A. H.
Published: June 2008

Shallow water theory is used to describe the sloshing and severe wave breaking action of water contained in a rigid nutation damper undergoing a coupled horizontal/rotational motion. Results from a simple numerical procedure are shown to agree with limited experimental data. They also demonstrate that a nutation damper’s rotation promotes a hydraulic jump that beneficially enhances damping.
Dynamic Axial Crush of Automotive Rail-Sized Composite Tubes: Part 2 — Tubes With Braided Reinforcements (Carbon, Kevlar®, and Glass) and Non-Plug Crush Initiators
Authors: Browne Alan L. , Zimmerman Kristin L.
Published: June 2008

This paper documents the braided reinforcement portion of a successful fundamental study of the dynamic axial crush of automotive rail-sized composite tubes. Braided reinforcements were comprised principally of carbon fiber but also of Kevlar® and E-glass and combinations of the three. Fourteen different braids were used, six of which were tri-axial and the remainder bi-axial. Tubes were manufactured using Resin Transfer Molding (RTM) with processing and molding techniques that are suitable for the low cost high volume needs of the automotive industry. Braids were obtained as continuous rolls of tubular sock-like material and pulled over metal mandrels one ply at a time. Carbon fiber tow sizes ranged from 6k to 48k. Dow Derakane 470 vinylester resin was used for all tubes. Tube geometry, a 88.9×88.9 mm square cross section with 2.54 mm thick walls, approximated that of the first 500 mm of the lower rail of a typical mid-size vehicle. Note in particular that tube wall thickness was fixed at a single value in this study. A 45° bevel on the outside edge of the lead end of each tube served as the crush initiator. In total 71 dynamic axial crush tests were conducted. In terms of important findings, consistent with the woven fabric portion of this program [1], desirable dynamic axial crush response was demonstrated for RTM’d automotive rail-sized carbon fiber reinforced tubes. For almost all parameter configurations, the tubes exhibited stable and progressive crush with a reasonably flat plateau force level and an acceptable crush initiation force, i.e. one that can be withstood by the backup structure. Additionally, crush debris from such tubes was found to neither contain objectionable sharp brittle splinters nor pose a health risk. Displacement average values of dynamic axial crush force ranged from 11.88 to 26.51 kN and values of SEA (specific energy absorption) ranged between 10.42 and 22.44 kJ/kg. In terms of parameter effects, the fiber type and reinforcement architecture were found to be capable of more than doubling/halving the dynamic axial crush force and SEA.
Coupled Dynamic Response of Liquid Filled Composite Cylindrical Tanks With Baffles
Authors: Biswal K. C. , Bhattacharyya S. K. , Sinha P. K.
Published: June 2008

The slosh frequencies of liquid in a liquid-filled cylindrical tank, made of laminated composites, are investigated in the present paper. An annular laminated plate is used as a baffle, which is fitted to the inner periphery of a cylindrical tank. Finite element codes are accordingly developed and are then used to analyze both the liquid domain and the structural domain i.e., the tank and the baffle. The slosh frequencies of liquid are computed for different dimensions and positions of the baffle. The coupled vibration frequencies of the tank-baffle system are computed considering the effect of sloshing of liquid. The asymmetric modes corresponding to circumferential wave number one are studied in the present investigation. The results obtained for a liquid filled elastic isotropic tank without baffle and a rigid tank with rigid baffle are compared with the available results, and they are found to be in good agreement. The results for composite tanks cover the effects of a wide range of parameters including composite baffles as well as different lamination schemes and number of layers of the tank wall on the slosh frequencies and coupled vibration frequencies.