bluuebunny/crossref_metadata_2025 huggingface dataset:
A Cantilever Conveying Fluid: Coherent Modes Versus Beam Modes
Authors: Sarkar A. , Paidoussis M. P.
Published: June 2008

A semianalytical approach to obtain the proper orthogonal modes (POMs) is described for the non-linear oscillation of a cantilevered pipe conveying fluid. Theoretically, while the spatial coherent structures are the eigenfunctions of the time-averaged spatial autocorrelation functions, it emerges that once the Galerkin projection of the proper orthogonal modes is carried out using the uniform cantilever-beam modes, the spatial dependency of the integral eigenvalue problem can be eliminated by analytical manipulation which avoids any spatial discretization error. As the solution of the integral equation is obtained semianalytically by linearly projecting the proper orthogonal modes on the cantilever-beam modes, any linear or non-linear operation can be carried out analytically on the proper orthogonal modes. Futhermore, the reduced-order eigenvalue problem minimizes the numerical pollution which leads to spurious eigenvectors, as may arise in the case of a large-scale eigenvalue problem (without the Galerkin projection of the eigenvectors on the cantilever-beam modes). This methodology can conveniently be used to study the convergence of the numerically calculated proper or-thogonal modes obtained from the full-scale eigenvalue problem.
Study on Mechanism for Unstable Vibrations of an Axisymmetric Body in a Cavitating Leakage Flow
Authors: Arai Masaaki
Published: June 2008

An axisymmetric body in a cavitating narrow annular parallel passage attains the self-excited vibrations when the apparent passage formed by the cavitation bubbles becomes certain conditions. This paper presents experimental and analytical studies on the mechanism for such unstable vibrations. In order to examine the apparent passage, the cross-sections of the leakage flow containing the cavitation are observed in the one-dimensional leakage model. When the self-excited vibrations occur, the cavitation bubbles disappear in the vicinity of the exit. Relating these apparent passages to the annular passage, the fluid-dynamic forces acting on an axisymmetric body are investigated theoretically. The theoretical results show that the fluid-dynamic damping is negative when the unstable vibrations occur experimentally.
Flow Structure, Pressure Fluctuations and Resulting Vibrations Caused by the Interaction of a Turbulent Jet With Cross Flow Over a Flexible Flat Plate
Authors: Gopalan Shridhar , Abraham Bruce M. , Katz Joseph
Published: June 2008

The objective of this study is to characterize the velocity, vorticity, wall pressure fluctuations and resulting structural vibrations caused by injection of a round, turbulent jet into a turbulent boundary layer. The experiments are performed in a quiet water channel with back ground noise well below the local pressure fluctuations. One of the channel walls is replaced by a vibration isolated, 1m long, aluminum plate from which the 1cm-diameter jet is injected. The cross flow velocity is fixed at 2 m/s and the velocity ratio, r (ratio of mean jet velocity to the cross flow), varies from 0.5 to 2.5 and Re based on cross flow and jet diameter is 20,000. High-resolution PIV is used to measure the flow field and high sensitivity, low-noise pressure sensors are used for the wall pressure measurements. The flush-mounted transducers are installed at several locations ranging from 2–15 diameters behind the jet. Auto-spectra of the pressure signals show that the effect of the jet is in the 15–100Hz range, and increase the wall pressure levels by 25dB for r=2.5. The fluctuations increase with velocity ratio and decrease with distance from the jet, although there is only a 6dB increase in overall levels at r=2.5 as compared to r=1. Hilbert-Huang “amplitude” spectrum shows the frequency content of the signal as it evolves in time, and is found to be a useful tool to characterize such unsteady phenomena. Velocity and pressure measurements have been performed simultaneously and thousands of frames have been recorded. Analysis of these frames demonstrates the relationship between the wall pressure fluctuations and the vortical structures. Several striking differences in the flow structure between high and low velocity ratios are described in the paper. Acceleration measurements describe the effect of the jet and cross flow on the vibrations of the side-wall. Cross flow boundary layer dominates structural vibrations below 1000Hz, and jet velocity effects are visible at 1000Hz–2000Hz. At higher jet velocities effects are seen even below 1000Hz and large narrow band frequency peaks occur. (CD ROM version includes color figures).
The Mechanics of a Helically Wrapped Thin-Shell Supported by an Externally Pressurized Air Cushion
Authors: Mu¨ftu¨ Sinan
Published: June 2008

The mechanics of the fluid structure interactions between a flexible web and an externally pressurized air cushion is modeled. The web is wrapped around the porous cylindrical air-reverser at an oblique angle. The air reverser supplies pressurized air into the web/air-reverser clearance. This model is an extension of a previous model and allows the web to be wrapped around the cylinder in a helical fashion. The geometric relations are based on Rongen’s work (1994) and steady state equilibrium equations are developed based on the work of Mu¨ftu¨ and Cole (1999). This paper describes the theory. A case study is presented.
Relationships Between Mass Transfer and Morphology in Deformable Complex Interfacial Systems
Authors: El Afif A. , De Kee D. , Cortez R. , Gaver D. P.
Published: June 2008

We propose a model for isothermal mass transport into immiscible complex fluids. The interface is described by two, space and time dependent, structural variables: a scalar Q(r,t) denoting the interfacial area density and a traceless symmetric second order tensor q(r,t) accounting for the shape anisotropy. The mass flux expression includes new contributions attributed to the dynamical changes of the interface. The diffusion-morphology coupling is found to influence both the mass transfer and the dynamics of the interface. The former exhibits non-Fickian behavior while the latter undergoes interfacial deformations that affect both its size and shape, creating internal stresses at the same time.
Orientational Distributions of a Ferromagnetic Spherocylinder Particle in a Simple Shear Flow
Authors: Aoshima Masayuki , Satoh Akira , Coverdale Geoff N. , Chantrell Roy W.
Published: June 2008

A ferrofluid is a suspension of ferromagnetic spherical particles in a base liquid (1), and is well known as a functional fluid which responds to an external magnetic field to give a large increase in the viscosity. Such a significant increase in the viscosity is due to the fact that chain-like clusters are formed owing to magnetostatic interactions between particles in an applied magnetic field. The microstructure formation offers a large resistance to a flow field that gives rise to a significant increase of the apparent viscosity (2).
Boundary Integral Equation Formulation in Generalized Linear Thermo-Viscoelasticity With Rheological Volume
Authors: El-Karamany Ahmed S.
Published: June 2008

A general model of generalized linear thermo-viscoelasticity for isotropic material is established taking into consideration the rheological properties of the volume. As special cases the corresponding equations for the coupled thermo-viscoelasticity and the generalized thermo-viscoelasticity with one (Lord-Shulman theory) or with two relaxation times (Green-Lindsay theory) are obtained. The cases of thermo-viscoelasticity ignoring the rheological properties of volume can be obtained from the given model. The equations of the corresponding thermoelasticity theories result from the given model as special cases. A formulation of the boundary integral equation method, fundamental solutions of the corresponding differential equations are obtained and the dynamic reciprocity theorem is derived for this general model. Generalizations of Somiliana’s –Green and Maysels formulas are obtained. An example illustrating the BIE formulation is given. Special emphasis is given to the representation of primary fields, namely temperature and displacement.
Rheological and Hydraulic Properties of Drilling, Completion, and Stimulation Fluids in Straight and Coiled Tubings
Authors: Zhou Y. , Shah S. N.
Published: June 2008

The rheological properties and friction pressure losses of several fluids that are most commonly used as well drilling, completion, and stimulation fluids have been investigated experimentally. These fluids include polymeric fluids – Xanthan gum, partially hydrolyzed polyacrylamide (PHPA), guar gum, and hydroxyethyl cellulose (HEC), bentonite drilling mud, oil-based drilling mud, and guar-based fracturing slurries. Rheological measurements using a Bohlin CS 50 rheometer and a model 35 Fann viscometer showed that these fluids exhibit shear thinning and thermal thinning behavior except the bentonite drilling mud whose viscosity increased as the temperature was raised. Flow experiments using a full-scale coiled tubing test facility showed that the friction pressure loss in coiled tubing is significantly higher than in straight tubing. Since the polymeric fluids displayed drag reducing property, their drag reduction behavior in straight and coiled tubings was analyzed and compared. It was found that the drag reduction (DR) in coiled tubing is much lower than that in straight tubing. Plots of drag reduction vs. generalized Reynolds number indicate that the drag reduction in coiled tubing was not affected by polymer concentration as much as in straight tubing. The onsets of turbulence and drag reduction in coiled tubing were significantly delayed as compared with straight tubing. The effect of solids content on the friction pressure losses in coiled tubing is also briefly discussed.
Torsion Galloping of Elongated Bluff Cross Sections
Authors: Larsen Allan
Published: June 2008

Torsion galloping of slender structures in a fluid stream is often attributed to a sign reversal of the moment slope, i.e. the moment coefficient attains increasingly negative values with increasing positive angles of attack or visa versa. A numerical and experimental study has revealed that torsion galloping of certain bluff elongated cross sections can not be attributed solely to moment slope reversal but rather the formation and drift of large coherent vortex structures along the body surface.
Platelet Activation and Free Emboli Formation in Flow Past Mechanical Heart Valves
Authors: Bluestein Danny , Yin Wei , Jesty Jolyon , Saltman Adam E. , Krukenkamp Irvin B. , Bernal Oscar , Suresh Krishnamurthy
Published: June 2008

Numerical studies, in vitro, and in vivo measurements were conducted, aimed at quantifying free emboli formation and procoagulant properties of platelets induced by flow past mechanical heart valves (MHV). Pulsatile turbulent flow simulation was conducted past a St. Jude medical MHV in the aortic position, to study the effects of valve implantation technique on the thromboembolic potential of the valve. A misaligned valve with subannualarly sutured pledgets produced accelerating jet flow through the valve orifices and a wider wake of shed vortices. Shear stress histories of platelets along turbulent trajectories exposed the platelets to elevated shear stresses around the leaflets, leading them to entrapment within the shed vortices. In vitro platelet studies were conducted past the MHV mounted in a recirculation flow loop and in a model of left ventricular assist device (LVAD), using an innovative platelet activity state (PAS) assay. The platelet activation significantly increased as a function of the recirculation time past the valve, and as compared to controls. Transcranial Doppler (TCD) measurements were conducted in the carotid artery of sheep with implanted MHV, showing marked increase in the number of HITS (High Intensity Transient Signals) signifying the passage of free emboli generated by the valve. The HITS were analyzed to distinguish between gaseous and thrombi emboli. Finally, platelet activity state measurements were conducted with sheep platelets, showing marked increase of platelet activation after valve implantation.
Fatigue and Fretting of Self-Piercing Riveted Joints
Authors: Iyer K. , Brittman F. L. , Hu S. J. , Wang P. C. , Hayden D. B. , Marin S. P.
Published: June 2008

The fatigue life and fretting characteristics of aluminum alloy 5754-O self-piercing riveted lap joints have been investigated experimentally and analytically. The experimental program involves a set of 27 cyclic tension tests on three different joints consisting of either 1 mm, 2 mm or 3 mm-thick sheet specimens. In most cases (85%), fatigue cracks are found to initiate on the faying surface of the upper sheet, adjacent to the hole, and at an angular location that lies on the sheet loading axis towards the loading end. Three-dimensional finite element analysis of the three joints has also been performed. Computed distributions of local stresses and rivet-sheet slips are interpreted in terms of experimental observations of fatigue life, crack initiation location and fretting damage observations. Significantly, the calculations provide a rationale for the surprising crack initiation location.
Digital Panel Assembly for Automotive Body-in-White
Authors: Cai Wayne , Lesperance Ronald M. , Marin Samuel P. , Meyer W. Weston , Oetjens Thomas J.
Published: June 2008

This paper presents the methodology of Digital Panel Assembly (DPA), a computer aided approach in automotive body panel assembly. Core to the methodology is special-purpose finite element software, EAVS, that can simulate the panel assembly processes and predict assembly dimensions by taking into considerations of the compliant nature of panels and sub-assemblies. To validate the methodology, a non-contact EOIS optical scanning procedure for panel measurement is established. The validation study shows that the reported methodology can accurately predict the 1st level panel sub-assemblies. Finally, the resource requirements, functional capabilities, and scalability of the digital panel assembly methodology towards a complete Body-in-White implementation are discussed.
A Pumping System to Enhance Production From Gas Wells
Authors: Rudolf J. J. , Heidrick T. R. , Fleck B. A. , Ridley R. K. , Rajan V. S. V.
Published: June 2008

A new pumping technology has been developed and patented by the Alberta Research Council [1–3] to address the problem of liquid loading in natural gas wells at low, depleted pressures. This technology consists of a pump installed at the bottom of the well bore that is driven by the reservoir gas pressure to bring the produced liquids to the surface as they accumulate thereby improving gas production from shallow gas wells. The above pump concept has been investigated in two stages of research. In the first stage, a mathematical model was developed to estimate the minimum reservoir pressure required to prevent liquid build up in a gas well with either: • the reservoir pressure (and flow) itself carrying the produced liquids to the surface in a two-phase flow, or • the reservoir gas pressure powering a pumping device to carry the produced liquids to the surface in the most efficient manner possible. The objective of the second stage of this investigation was to look at the feasibility of using a reciprocating pump powered by gas pressure. In particular, the effect of the pump Area Ratio (ratio of the area being pushed by the gas to the area pushing the liquid) on the use of reservoir gas pressure was investigated. There are approximately 70,000 flowing gas wells in Western Canada and these gas wells were categorized by depth and production rate. From this list of gas wells, a typical well was chosen and its production data and well characteristics were incorporated into the mathematical model. The model was tested in both the above-mentioned investigations and the results show that there is a significant increase in the operating range when the reservoir pressure is used more efficiently to produce gas from the well. It was determined that higher pump area ratios lead to a more efficient use of reservoir pressure and for the gas well investigated in this study, an optimum area ratio of 40 was identified as the best design. The concept of multistage pumping was also investigated. The results presented are the basis for experiments presently being designed that will validate the current model of the system and allow for possible improvements.
Ratiometric Laser-Induced Fluorescence (LIF) Thermography of Radiofrequency Heated Tissue Phantoms
Authors: Fron Damien J. , Aksan Alptekin , McGrath John J.
Published: June 2008

A ratiometric laser-induced fluorescence (LIF) thermographic method has been developed to quantify the temperature fields associated with radiofrequency (RF) heating probes used to treat joint instabilities associated with the shoulder, knee, and ankle. Accurate temperature field measurements in tissue phantoms represent invaluable data for the purpose of developing and verifying computer models of tissue heating. Measuring temperature fields associated with RF probe heating in physiological environments poses problems for traditional methods. Thermocouples, infrared thermometry and fluoroptic methods are limited due to inability of thermocouples to operate in an RF environment, the opaque nature of physiological solutions to IR wavelengths and the relatively large size of optical fibers used in fluoroptic thermometry respectively. Whole field temperature mapping and heat flux measurements around monopolar and bipolar radiofrequency (RF) probes have been performed in tissue phantoms using two-color laser induced fluorescence (LIF) and the ratio of the fluorescent emission intensities of Rhodamine B and Rhodamine 110. The method is described, the operating characteristics are defined and examples of the application of the method to radiofrequency (RF) heating in phantom tissues are included.
Fluorescence Correlation Spectroscopy for Detection of Trace Amount of Biological Agents
Authors: Qing De-Kui , Mengu¨c¸ M. Pinar , Payne Fred A. , Danao Mary-Grace C.
Published: June 2008

A procedure to the trace amount of biological agents in water, based on fluorescence correlation spectroscopy and confocal microscopy, is explored. A special flow system is developed to increase the probability of detecting Escherichia coli (E. coli), and confocal microscopy is used to increase the sensitivity of the detection system. It is observed that concentrations higher than 1.5×105 E. coli per milliliter (2.5×10−16 M) are detectable with the present setup. This concentration corresponds to about 1.0 nM level of Rhodamine 6-G dyes. For detection of lower concentrations, further improvements need to be implemented to increase signal/background ratio. A detailed analysis of the optical system is presented and further improvements for the procedure are discussed.
Deformable Image Registration of Mouse Brain MRI Data Using Hyperelastic Warping
Authors: Veress Alexander I. , Weiss Jeffrey A. , Gillies Robert J. , Bowden Anton E. , Galons Jean-Philippe , Rabbitt Richard D.
Published: June 2008

Quantification of time-dependent changes in three-dimensional morphology of brain structures and neural pathways is a fundamental requirement in studies of neurodevelopment, remodeling and progression of neurological diseases [1]. However, local measures of this kind are extremely difficult due to a lack of clear fiducials. Our motivation to develop a reliable technique to quantify time-dependent changes in neuroanatomy originated with the problem of tracking progression of Niemann-Pick disease type C (NP-C), a heritable disease that causes alterations in brain development [2].
An Experimental Haptic Based Skill Training Simulator for Manufacturing Applications
Authors: Balijepalli Arvind , Kesavadas T.
Published: June 2008

In this paper we present a concept of a versatile ‘haptics’ based robotic path planning and operator training tool. Some of the earlier work in the area of robotic path planning has been visited. A suitable force model has been developed and implemented to test the method. As a first step, a system for the training of machine operators and path planners is developed. Experiments are carried out to prove the hypothesis. Preliminary results from these experiments have been presented.
Evaluating Micromechanical Properties at Surfaces Using Nanoindentation With Finite-Element Modeling
Authors: Knapp J. A. , Follstaedt D. M. , Myers S. M.
Published: June 2008

Detailed finite-element modeling of nanoindentation data is used to obtain accurate mechanical properties of very thin films or surface-modified layers independently of the properties of the underlying substrates. These procedures accurately deduce the yield strength, elastic modulus, and layer hardness, and greatly increase the usefulness of indentation testing with very thin surface layers. Moreover, extraction of the effective Young’s modulus in the near surface region should enable mechanical damage studies on a small scale. This paper presents a brief overview of the procedures involved and illustrates them with He-implanted Ni.
Damage Mechanisms in Nanolayered Metallic Composites
Authors: Misra A. , Kung H. , Hammon D. , Hoagland R. G. , Nastasi M.
Published: June 2008

The strengths of metallic multilayers, composed of alternating layers of soft metals such as Cu and Nb, approach the theoretical limit of material strength when the bilayer periods are on the order of a few nanometers. We have investigated the damage mechanisms in these ultra-high strength nanolayered composite materials subjected to monotonic deformation. Large strain plastic deformation such as room temperature rolling does not lead to any dislocation cell structure formation within the layers indicating that the deformation and dislocation storage mechanisms in nanostructured materials are completely different from the bulk. In bulk metals, dislocation pile-ups lead to heterogeneous slip, but in nano-materials, deformation by single dislocations on closely spaced glide planes results in more homogeneously distributed slip. The implications of the high tensile strengths and homogeneous slip on the fatigue properties of nanolayered materials are also discussed.
Virtual Reality Environment for Creation of Freeform Models
Authors: Maiteh Bilal Y.
Published: June 2008

A novel method has been developed using a virtual reality (VR) environment to create solid models with freeform surfaces. The VR environment emulates the physical environment for creating freeform objects, i.e. the freeform model is created in a virtual environment by shaping a virtual workpiece with a variety of virtual tools. The trajectories of the virtual tools are generated by the designer’s hand movements and they are obtained by recording the position and orientation of the motion tracker mounted on a device held by the hand. In the mathematical algorithm, the swept volumes of the design tools are computed from the tools’ geometric data and trajectories. Boolean operations are then performed on the swept volumes of the virtual tools and the virtual workpiece to create the design model.
Creating Freeform Model by Carving Virtual Workpiece With Haptic Interface
Authors: Leu Ming C. , Velivelli Aditya , Peng Xiaobo
Published: June 2008

This paper presents the development of a virtual sculpting system, with the goal of enabling the user to create a freeform model by carving a virtual workpiece with a virtual tool while providing haptic interface during the sculpting process. A virtual reality approach is taken to provide stereoscopic viewing and force feedback, thus making the process of model creation in the virtual environment easier and more intuitive. The development of this system involves integrating techniques and algorithms in geometric modeling, computer graphics, and haptic rendering. Multithreading is used in an attempt to address the different update rates required in the graphic and haptic displays.
Computational Modeling and Simulation of Atherosclerotic Plaque Growth
Authors: Breeher L. E. , Marella Saikrishna , Udaykumar H. S. , Chandran K. B.
Published: June 2008

Research has been conducted by the authors with the objective to produce a computational model that will clearly display the coupled nature of the hemodynamics/fluid mechanics of blood flow and atherosclerotic plaque growth in the human carotid artery. The motivation for this investigation is the serious nature of atherosclerosis. Atherosclerosis is an inflammatory disease, which occurs in medium and large size arteries. Among the many effects stemming from the disease are heart attack, stroke, ischemia, and peripheral vascular disease. In healthy arteries, the collagen and elastin allow the artery to expand and contract with blood flow. This function enables the artery to maintain constant wall shear stress [1]. Plaque existence in the arterial wall results in decreased ductility of the wall, which inhibits the wall from maintaining constant shear stress. Plaque formations along the arterial wall then protrude into the artery, disturbing the blood flow. Characteristics of the fluid flow in the artery are also altered due to the presence of a plaque. Areas of low shear stress and recirculation move downstream from the plaque. These disturbances act not only to further the plaque formation at the site, but also to make the wall around the plaque formation more prone to lesions that could lead to new plaque initiation. Complex characteristics of the blood flow give areas of an artery such as bends and bifurcations a predisposition for the disease, whereas plaques affect blood flow, creating flow patterns that promote new plaque initiation. This interdependency makes atherosclerosis a very serious disease and one which is of great importance in research.
A Kinematic Analysis on an ACL Deficient Knee
Authors: Kirkendall Andrea L. , Lopez Juan M. , Gonzalez Roger V.
Published: June 2008

A torn anterior cruciate ligament (ACL) is one of the more frequently occurring knee injuries plaguing both athletes and the general population [1]. This injury typically results in severe knee instability thereby limiting the activities the injured is able to perform. Currently, surgical reconstruction is the most common option to restore knee stability and allow the injured subject to return to full functionality (i.e. participation in athletic and recreational activities as desired). However, small populations of individuals who rupture their ACL forego surgery yet still remain fully functional [2]. We hypothesize that these subjects, referred to as “copers”, alter the control strategy of the muscles crossing the knee joint to compensate for their ACL-deficient knee.
Mechanical Properties of Active and Passive Rat Middle Cerebral Arteries
Authors: Coulson Rebecca J. , Cipolla Marilyn J. , Vitullo Lisa , Chesler Naomi C.
Published: June 2008

Cerebral arteries play an important role in the regulation of cerebral blood flow through autoregulation, a well established phenomenon which is caused by a combination of myogenic, neuronal and metabolic mechanisms [1]. Myogenic reactivity is the ability of the vascular smooth muscle cells (SMC) to contract in response to stretch or to an increase in transmural pressure (TMP), and to dilate in response to a decrease in TMP [2]. It is this active constriction of arteries within the autoregulatory range that prompts studies of not just passive mechanical properties, but also active mechanical properties. Passive properties provide an understanding of the behavior of the extracellular matrix components of arteries (i.e. collagen and elastin); but, in order to understand how the artery behaves in vivo, it is necessary to understand the mechanical properties with smooth muscle cell activation. Mechanical properties might also be altered if the vessel is diseased or damaged. Ischemia has been shown to reduce vascular tone, which might lead to brain tissue damage during stroke [3]. Therefore studying the mechanical properties of vessels in disease states to determine if they are able to adequately take part in controlling local blood flow is also important.
Computational Fluid Dynamics Simulation of the Right Coronary Artery Moving With the Cardiac Wall
Authors: Hayashi H. , Yamaguchi T.
Published: June 2008

The beating motion of the heart wall, to which the major coronary arteries are fixed, is interesting, due to its possible mechanical influence on the flow inside the artery, and hence its effect on atherogenesis [1–2]. In this study, we conducted a computational fluid dynamics (CFD) simulation using a simplified model of the right coronary artery, which deforms with heart contractions. The results are discussed with respect to the local hemodynamics characteristics, particularly the streamline pattern and the wall shear stress distribution.
Measurements of Mean Velocity and Turbulent Statistics in a Centrifugal Blood Pump
Authors: Day Steven W. , McDaniel James C. , Lemire Phillip P. , Wood Houston G.
Published: June 2008

An estimated 150,000 patients in the Western World require heart transplantation every year, while only 4,000 (2.5%) of them actually receive a donor heart [1]. This lack of available donors for heart transplantation has led to a large effort since the 1960s to develop an artificial mechanical heart as an alternative to heart transplant. Most end stage cardiac failures result from cardiac disease or tissue damage of the left ventricle. After this failure, the ventricle is not strong enough to deliver an adequate supply of oxygen to critical organs. A left ventricular assist device (LVAD) is a mechanical pump that does not replace the native heart, but rather works in concert with it. An LVAD can effectively relieve some strain from a native heart, which has been weakened by disease or damage, and increase blood flow supplied to the body to maintain normal physiologic function. The inlet to the LVAD is attached to the native left ventricle, and the output of the assist pump rejoins the output of the native heart at the aorta, as shown in Figure 1. Blood flow from both the aortic valve and the assist pump combine and flow through the body. The clinical effectiveness of LVADs has been demonstrated; however, all of the currently available pumps have a limited life because of either the damage that they cause to blood or their limited mechanical design life.
Nonlinear Dynamics of a Loosely Supported Beam Subject to Harmonic Excitation
Authors: Knudsen Jakob , Massih Ali R.
Published: June 2008

The nonlinear dynamic behavior of damped beam oscillator with elastic two-sided amplitude constraints is analyzed. The structure is modeled by a Bernoulli-Euler beam supported by elastic springs. Finite element method is used for discretization in space and time integration is performed by Newmark’s method. Rayleigh damping is assumed for the structure. Symmetric and elastic double-impact motions, both harmonic and subharmonic, are studied by way of a Poincare´ mapping that relates the states at subsequent impacts. We have found that by increasing the forcing frequency (ω) for the beam at a certain frequency a stable period one motion (solution) turns into a stable period two motion and subsequently without bifurcation it transits to an infinite number of solutions characteristic of chaotic behavior. By further increasing ω a series of windows in the bifurcation diagram (impact velocity vs. ω) comprising periodic solutions within the chaotic domain appear.
New Insight Into Deformation-Dependent Hydraulic Permeability of Hydrogels and Cartilage
Authors: Yao Hai , Gu Weiyong
Published: June 2008

Hydrogels have numerous applications in biomedical engineering and biotechnology, such as in cellular and tissue engineering. The transient mechanical behavior of hydrogels is related to its interstitial fluid flow which is governed by hydraulic permeability. The hydraulic permeability of hydrogels and other hydrated soft tissues (e.g., cartilage and intervertebral disc) is deformation dependent [1–3]. Several empirical expressions for deformation-dependent permeability of cartilage have been proposed, in order to quantify the fluid flow within a gel or tissue under mechanical loading [1,2,4]. In this paper, we report a new approach to investigating deformation-dependent permeability of hydrogels. The objective of this study is to find a relationship between hydraulic permeability and tissue porosity (water content) for hydrogels, and in turn derive its deformation-dependent permeability. This study is important for understanding biological responses of cells to interstitial fluid flow in gels or in cartilage under mechanical loading.
Changes in Material Classification of the Urinary Bladder Wall After Spinal Cord Injury
Authors: Gloeckner D. Claire , Chancellor Michael B. , Sacks Michael S.
Published: June 2008

Changes in the mechanical properties of the urinary bladder wall following neurogenic disease or trauma can result in bladder dysfunction. We have recently reported changes in the biaxial mechanical properties of the bladder wall 10 days after spinal cord injury in a rat model [1]. Development of a constitutive model to characterize these changes would facilitate quantitative comparisons and provide the necessary information for organ-level computational modeling. However, before an appropriate constitutive model of the bladder wall can be formulated, its material class must be identified. In the present study, we applied a generalized method for material classification of biaxial mechanical data to our previous data on the urinary bladder wall.
High Spatio-Temporal Resolution Digital Particle Image Velocimetry Near Compliant, Dynamically Moving Boundaries
Authors: Etebari Ali , Abiven Claude , Pierrakos Olga , Vlachos Pavlos P.
Published: June 2008

Digital Particle Image Velocimetry (DPIV) currently represents the state of the art for non-invasive global flow velocity measurements. The instantaneous velocities are determined by cross-correlating patterns of particles between consecutive images, thus mapping in space and time the velocity distribution for thousands of points in the flow field simultaneously.
Effect of Frequency and Design Parameters on Pocket Damper Seal Performance
Authors: Vance John M. , Sharma Ashish , Jayakar Nijesh
Published: June 2008

Pocket damper seals can produce large amounts of damping in turbomachines where the working fluid is compressible. Even with non-optimum design configurations, they have solved rotordynamic instability problems in high-pressure compressors. They do not rely on viscous effects, so they are ideal for oil-free applications. It is shown here that proper sizing of the seal pockets can maximize the damping. Significant parameters and variables have been identified, both experimentally and theoretically, that reflect the fundamental effects of the pocket damper seal to produce rotordynamic damping. Dimensionless analysis was performed, resulting in significant Pi groups involving damping, stiffness and leakage parameters. Of particular interest is a Helmholtz Pi group that shows 1) the benefit from optimizing the volume of the pockets around the seal, and 2) the frequency dependence of the seal. Dimensionless prediction equations are shown graphically. The graphs were generated by a computer code that uses a single control volume model. The code has been verified experimentally on several different seal test rigs with data taken at different vibration frequencies spaced an octave apart.
Characterization of Hemodynamic Performance and Degree of Flow Redirection in the Left Ventricle Dependent on the Mitral Mechanical Heart Valve Orientation
Authors: Pierrakos Olga , Vlachos Pavlos P. , Telionis Demetri P. , Yazdani Saami , Etebari Ali
Published: June 2008

Recent groundbreaking work by Kilner et al. [1] demonstrated that a healthy functioning heart redirects the flow through the left ventricle (LV) in an asymmetric manner, which results in an energy conserving mechanism. Heart valve replacement alters the physiological operation of the heart significantly affecting its hemodynamic performance. As a result, orientation and valve design could play a significant role in the energy efficient operation of the heart; therefore, orienting MHVs so that flow disturbances are minimized enhances the hemodynamic performance of the LV.
On the Interaction of Natural and Mechanical Heart Valve Leaflets With the Chordae Tendineae
Authors: Mace Amber R. , Vlachos Pavlos P. , Telionis Demetri P.
Published: June 2008

Long before mitral valve replacement (MVR) became a routine operation, physiologic studies indicated that the continuity of mitral leaflets with papillary muscles, chordae tendineae (CT) and the atrioventricular ring may play a decisive role in the function of the left ventricle (LV) [1]. This led Lillehei et al. [2] to establish a procedure whereby the posterior leaflet, its CT and papillary muscles were preserved in MVRs. These and other studies indicated a significant reduction of postoperative mortality compared to conventional MVR. Though developed in the early 1960s by Lillehei, the technique of chordal preservation was not initially accepted. It wasn’t until 1983 that surgeons began to revive the concept of MVR with preservation of the CT. As this technique became more widely known, many clinical studies were performed; however, very few have been conducted which examine the effect of leaflets and CT on flow dynamics.
Computational Mechanical Simulation of the Aggregation and Dissociation of Platelets Mediated by von Willebrand Factor
Authors: Yano K. , Yamaguchi T.
Published: June 2008

Platelets play an important role in blood coagulation, particularly in the formation of primary thrombi. The aggregation of platelets, which initiates primary thrombi formation, is thought to be mediated by the von Willebrand factor (vWF). The vWF is a long-chain macromolecule that exists in a soluble form in the blood flow and an insoluble form in the vessel wall. Figure 1 schematically shows normal (a) and pathological (b) thrombus formation processees. In both cases, platelets adhere to the injured vessel wall and then form a thrombus in cooperation with the fibrin network, red cells, and other blood constituents. The vWF plays a more important role in pathological thrombosis formation than in the normal hemostatic process, due to its ability to sense and react to hemodynamic stress.
Multi-Channel Blind System Identification for Noninvasive Cardiovascular Monitoring
Authors: Zhang Yi , Reisner Andrew T. , Asada H. Harry
Published: June 2008

A novel method for diagnostic monitoring of the cardiovascular system is presented, which combines peripheral measurements obtained continuously and non-invasively with a multi-channel blind system identification technique.
Phasic Variations and Magnitude of Pressure Recovery Distal to Human Coronary Artery Stenoses During Angioplasty
Authors: Banerjee Rupak K. , Back Lloyd H. , Back Martin R.
Published: June 2008

Distal pressure recovery coefficients (cpr = kcpr∞) were determined from pulsatile hemodynamic computations for the 32 patient group of Wilson et al. 1988 during coronary angioplasty in conjunction with quantitative angiography and measurements of coronary flow reserve (CFR). Before angioplasty, values of the factor k(t) ranged 2–4 times high than a reference value, cpr∞ = 0.18, and varied during the flow acceleration and deceleration phases of the cardiac cycle. After angioplasty, values of k(t) ranged from 0.8–1.4, roughly the same magnitude as cpr∞ = 0.46, and also varied phasically.
Laminar, Transitional and Turbulent Motion of Fruit Purees Within Circular Pipes
Authors: Perona Paolo , Yeow Leong Y. , Sordo Sebastiano T.
Published: June 2008

The results of an experimental investigation aimed to study both the rheological and fluid dynamic behaviour of two kinds of fruit purees at different pulp concentrations are presented in this work. An experimental setup based on the rectilinear pipe viscometer principle was used for a preliminary rheological investigation of the analyzed products. By applying either the classical Rabinowitsch and Mooney or the recent Thikonov method of regularization of integral equations, these products could reliably be considered as purely-viscous time-independent fluids. The laminar motion was described by means of the well known Metzner and Reed method while the corresponding resistance laws for turbulent motion were modeled by using the Dodge and Metzner method. The comparison of the point onset of turbulence against the ones obtained by means of the Mishra and Thripati and Hanks formulas would, however, suggest that in transitional regime the viscoelastic effects could have non-negligible influence on the dynamics.
Analysis of Fluid-Stent Interaction via Digital Particle Image Velocimetry
Authors: Yazdani Saami K. , Vlachos Pavlos P. , Berry Joel L. , Pierrakos Olga
Published: June 2008

Vascular stents are commonly used as a scaffold to hold arteries open after angioplasty. The clinical use of stents has also extended to treatment of cerebral aneurysms and as a graft anchor for endoluminal treatment of abdominal aortic aneurysms. In spite of the clinical success of stents, very little quantitative data exist on how stent structure influences blood flow patterns. Once in place, stents alter the mechanical and geometrical properties of the arterial tree. Such alterations represent an impedance mismatch between stent and unstented vessel. These changes appear to have a profound influence on pressure and flow wave interaction. These alterations may play a role in flow mediated stent failure [1, 2].
Effect of Malalignment and Friction on Contact Pressure in the Polyethylene Component in the Total Knee Replacement
Authors: Chandran Nagarajan , Amirouche F. , Goldstein Wayne , Barmada Riad
Published: June 2008

The articulation of the femoral and tibial component contact surface is influenced by the alignment of these components. Malalignment of the total knee is perceived to increase the contact pressure and reduces the life of the polyethylene component. In this paper the contact pressure obtained from a experimental results [2] are used as the loading condition for a normal TKA alignment. In the case of a malalignment, we assumed that the loads at the interface do not change and the malalignment is to the femur component rotation. The results show that the pressure distribution is higher in the malaligned fit, which implies a reduced lifetime for the TKA. In the analysis, the experimental loads derived from cadaver knee testing are increased by a scale factor of 5, 10, 20, 50 to predict a more realistic loading condition of the knee. The effect of malrotation on the pressure distribution under these condition shows that the percentage change in the pressure distribution is slightly larger than that from the experimental loads.
Determination of Poisson’s Ratios of Bovine Articular Cartilage in Tension and Compression Using Osmotic and Mechanical Loading
Authors: Chahine Nadeen O. , Wang Christopher C.-B. , Hung Clark T. , Ateshian Gerard A.
Published: June 2008

The existence of osmotic pressure inside cartilage gives the tissue a propensity to swell. This swelling pressure is balanced by the tensile stresses generated within the solid matrix at free-swelling [1, 2]. Recent studies have shown that cartilage exhibits significant strain-softening when compressed relative to its free-swelling state [3–5]. Such strain-softening behavior has been physically interpreted within the context of osmotic swelling pressure and tension-compression nonlinearity [4, 9]. This has provided the rationale for extracting both the tensile and compressive Young’s moduli from uniaxial compression tests on the same specimen [4, 5]. The goal of the current study is to optically determine another important elastic property, i.e. the equilibrium Poisson’s ratio of young bovine articular cartilage when uniaxially compressed along its three characteristic directions: parallel and perpendicular to the split-line direction (1- and 2-direction, respectively), and in a direction normal to the articular surface (3-direction). Furthermore, the external bath concentration effects on the Poisson’s ratios will be explored at various strain levels.
Development and Validation of a Three-Dimensional Parametric Model of the Cervical Spine
Authors: Lopez Espina Carlos G. , Amirouche Farid , Wagner Franklin C. , Guppy Kern H.
Published: June 2008

The main objective of this project is to produce an accurate parametric model of a human cervical vertebra and the intervertebral disc. This model is based on a well defined set of parameters that reflect the differences between the different vertebrae, allowing for the reconstruction of cervical segments of the spine by a simple control of these parameters.
Expulsion Testing of an Anterior Cervical Intervertebral Fusion Cage: Factors Affecting Pull Out Resistance
Authors: Goel Vijay K. , Dick David , Kuroki Hiroshi , Ebraheim Nabil
Published: June 2008

Factors affecting the expulsion resistance of an anterior cervical discectomy and fusion (ACDF) device in a cadaver model were investigated. Two specimen specific properties were considered; bone mineral density (BMD), and donor age. Also, two surgical procedures were used, representing two different degrees of destabilization of the intervertebral joint. Expulsion forces averaged 176 N (S.D. 60 N) for all specimens. No statistically significant difference in expulsion force was found between the specimens in the two surgical groups. However, expulsion force showed significant correlation to both BMD and donor age, with correlation coefficients of 0.81 and −0.83 respectively.
Biomechanics of Vertebroplasty
Authors: Higgins Kathryn B. , Harten Robert D. , Langrana Noshir A. , Cuitino Alberto M.
Published: June 2008

Osteoporosis is a skeletal disease characterized by low bone mass and deterioration of bone tissue. It affects 15–20 million women in the United States. Fractures of the vertebrae, wrist and hip are the most common. [1] In the spine, osteoporosis greatly affects the bone mass of the vertebral bodies (VB), the primary structures for transmitting loads in the spine. The VB is comprised of a shell of dense bone surrounding a more porous bony tissue called trabecular bone. Trabecular bone is a lattice-like network of trabeculae in the shape of plates or rods, depending on orientation and one’s age. When the weakened trabecular structure experiences a loss of height, acute back pain, spinal cord compression, and overall loss of mobility can ensue. A single fracture creates a region of high stress in the trabecular network, often leading to more fractures. In almost 20% of the cases one fracture in a VB may result in a secondary fracture within a one year period. [2] Many fractures go unnoticed. The high occurrence, frequent uncertainty of fracture, and gravity of subsequent injury indicate a need to improve the strength of osteoporotic vertebrae before damage can occur. It may be desirable to treat weakened bone prior to fracture. One candidate for prevention that is investigated in this study is vertebroplasty. Currently, the procedure is used to repair fractured VB by injecting acrylic bone cement into the affected level. A parametric finite element (FE) investigation and supporting experimental study was conducted to evaluate the usefulness of vertebroplasty as a preventative treatment.
Using Stereolithography Models in Planning Spinal Surgery
Authors: Ahlqvist A. , Harrysson O. , Conway T. , Nayfeh J.
Published: June 2008

CT data of two patients was used to create computer generated 3-dimensional models of portions of their spines. One of the patients suffered from scoliosis and the other patient from tortecolis. The virtual models were then used to create stereolithography models in order to assist the planning of surgery of the two patients. The models increased the surgeons understanding of the deformations of the patients spines by providing a visualization tool. Also, the surgeon was able to use the models for patient education.