bluuebunny/crossref_metadata_2025 huggingface dataset:
A Constitutive Equation for Extensional-Thickening Fluids Flowing Through Porous Media
Authors: Souza Mendes Paulo R. , Naccache Moˆnica F.
Published: June 2008

A constitutive relation between the pressure gradient and the seepage velocity has been developed that carries information about the liquid behavior on extension. The relation was developed in two steps. Firstly the pressure drop/flow rate relationship for an ideal pore channel was obtained. Then a capillaric model theory was applied to obtain the sought-for constitutive equation. The proposed relation was validated comparing pressure drop/flow rate results with experimental data obtained in a geometry similar to the one used in the theoretical model. Also, some comparisons with experimental data for a M1 Boger fluid flowing in a model porous medium were performed. The results showed that the proposed relation has good predictions capabilities in a representative range of pressure gradients.
A Hydrodynamic Theory for Solutions of Nonhomogeneous Nematic Liquid Crystalline Polymers With Density Variations
Authors: Wang Qi , Forest M. Gregory , Zhou Ruihai
Published: June 2008

The hydrodynamic theory developed in [31] for solutions of nonhomogeneous nematic liquid crystalline polymers (LCPs) of spheroidal molecular configurations is extended to account for translational diffusion and the related spatial density variation. The new theory augments the added effect of the density variation to the Smoluchowski equation and the elastic stress. It accounts for the molecular aspect ratio as well as the finite range molecular interaction so that it is applicable to liquid crystals ranging from the rodlike liquid crystal at large aspect ratios to the discotic one at small aspect ratios. It also exhibits enhanced shape effects in the viscous stress and warrants a positive entropy production, thereby, the second law of thermodynamics. Moment averaged, approximate, mesoscopic theories for complex flow simulations are obtained via closure approximations.
Instability Boundaries of a Vocal Fold Modelled as a Flexibly Supported Rigid Body Vibrating in a Channel Conveying Fluid
Authors: Hora´cˇek J. , Sˇvec J. G.
Published: June 2008

A generalised leakage-flow induced vibration model for vibration onset of the vocal folds in the airflow is presented. Especially the influence of various physical properties of the vocal folds (e.g., their shape, adduction, mass and mass distribution) on the thresholds of instability is studied. A vibrating element with two-degrees-of-freedom (rotation and translation) placed on an elastic foundation and vibrating in the wall of a channel conveying air is used to approximate the vocal fold. The inviscid incompressible 1-D fluid flow theory is used. A generally defined shape of the vocal fold is considered for expressing the unsteady aerodynamic forces in the glottis. The parameters of the mechanical part of the model, i.e., the mass, stiffness and damping matrices are related to the known geometry, size and material density of the vocal folds as well as to the fundamental natural frequencies and damping known from the experiments. The numerical solution yields the natural frequencies, damping, mode shapes of vibration and the instability thresholds of the system. The calculated vibration and stability characteristics appear to be close to the known physiological data. The developed aeroelastic model is able to provide qualitative information, e.g., on conditions for a soft voice onset or for breathy voicing and could be helpful also in design of artificial voice prosthesis.
Optical Fiber Cable Vibrations Induced by Leakage Flow During Coating Process
Authors: Kaneko Shigehiko , Ozaki Yuichi , Watanabe Tatsuo
Published: June 2008

Optical fiber cables constitute one the key elements supporting current information technology society. Recently, the price reduction is becoming competitive among optical fiber manufacturers. In order to meet such a need, the manufacturers are now trying to increase the operating process speed when they manufacture optical fiber cables. Under these circumstances, severe vibrations were observed on a fiber cable traveling at a high speed during coating process. This paper summarizes a case study concerning traveling optical fiber vibrations and the examination results on the mechanism of vibrations. First, we outline the characteristics of traveling cable vibrations, secondly, we explain the results of model cable vibration tests and finally, we describe the theory to clarify the mechanism of the traveling cable vibrations. In the analytical part, we start with the equation of motion of a traveling cable together with the effect of the fluid force due to the leakage flow induced in a coating dice. The effect of the leakage flow in a coating dice is formulated based on annular leakage flow theory developed by author’s group where the effect of viscosity of the coating material on the instability is taken into account. Then, the equation of a traveling cable under the effect of the leakage flow at the supporting point is successfully formulated. Based on the linearized equation of motion for the traveling cable, eigenvalue analysis was performed which leads to instability criteria selecting dice configuration and the temperature of the coating material as parameters. Finally, calculated results were compared with test experimental results and discussion on the design parameters for the stable operation is made.
Steady Secondary Flows of Phan-Thien-Tanner Fluids in the Vicinity of a Corner
Authors: Letelier Mario F. , Acosta Mauricio , Co´rdova Juan , Siginer Dennis A.
Published: June 2008

Secondary flows of Phan-Thien-Tanner fluids in channels formed by two intersecting walls, and driven by a pressure gradient parallel to the intersection line, are studied by means of perturbation analysis, where the perturbing parameter is the relaxation time. The velocity field is analysed in relation to the opening angle and distance from the corner within the fluid region. An analytically exact solution is found at 0(λ3), through the mathematical structure of which is possible to draw some general and important conclusions about the dynamics of the transversal flow. Such results are of potential interest in the design of devices aimed at exploiting the transport capacity of secondary flows.
Using Ultrasonic Signal Reflection to Characterize the Density and Viscosity of Fluids and Slurries
Authors: Bamberger Judith Ann , Greenwood Margaret S.
Published: June 2008

Ultrasonic signals can be used to interrogate many forms of two-phase systems, dense slurry-laden and three-phase suspensions. This paper describes using ultrasonic signal reflection at a fluid-sensor interface to characterize fluid and slurry density and viscosity. The sensor consists of a series of transducers mounted on a wedge with the base of the wedge in contact with the liquid. Ultrasonic beams, striking the wedge base at several angles, are reflected at the base-liquid interface to the receive transducers. The amount of reflection at this interface depends upon the density of the liquid, the speed of sound in the liquid, and the wedge parameters. The response of a shear wave transducer, in conjunction with a density measurement, is used to determine the viscosity. The sensor can be mounted in a pipeline configuration or submerged in a tank for process control of food products. Novel features include: the small size of the probe and the sensor robustness. Performance is not affected by fluid flow rate, entrained air, or vibration. Experimental measurements of the density and viscosity for fluids and slurries are presented.
Numerical Study of the Turbulent Flow Around a Square Cylinder Near a Wall
Authors: Guilmineau Emmanuel , Queutey Patrick
Published: June 2008

Calculations are reported for the flow around a two-dimensional, square cylinder at Re = 22,000 (based on the prism side dimension, D, and the free-stream velocity) placed at various distances from an adjacent wall. The nominal boundary layer thickness is 1.5D. Experiments have indicated that unsteady vortex shedding is suppressed when the wall is relatively close to the cylinder. The turbulent fluctuations are simulated with three turbulence models: the one-equation model of Spalart & Allmaras (1992), the two-equations SST K–ω model (Menter, 1993) and a Reynolds stress Rij–ω closures (Deng & Visonneau, 1999). The paper consists in comparing simulation and experimental results for configurations S/D = 1 (periodic case) and S/D = 0.25 (stationary case). Predicted and measured distributions of the mean velocity, Reynolds stress tensor and surface pressures are compared. Although the agreement is very good in general, observed discrepancies are discussed.
Numerical Solutions of a Viscous Uniform Approach Flow Past Square and Diamond Cylinders
Authors: Dalton Charles , Zheng Wu
Published: June 2008

Numerical results are presented for a uniform approach flow past square and diamond cylinders, with and without rounded corners, at Reynolds numbers of 250 and 1000. This unsteady viscous flow problem is formulated by the 2-D Navier-Stokes equations in vorticity and stream-function form on body-fitted coordinates and solved by a finite-difference method. Second-order Adams-Bashforth and central-difference schemes are used to discretize the vorticity transport equation while a third-order upwinding scheme is incorporated to represent the nonlinear convective terms. A grid generation technique is applied to provide an efficient mesh system for the flow. The elliptic partial differential equation for stream-function and vorticity in the transformed plane is solved by the multigrid iteration method. The Strouhal number and the average in-line force coefficients agree very well with the experimental and previous numerical values. The vortex structures and the evolution of vortex shedding are illustrated by vorticity contours. Rounding the corners of the square and diamond cylinders produced a noticeable decrease on the calculated drag and lift coefficients.
Modeling Heat and Mass Transfer and Fluid Flow in Three-Dimensional Gas Metal Arc Welding
Authors: Wang Y. , Tsai H. L. , Marin S. P. , Wang P. C.
Published: June 2008

This paper extends a mathematical model and numerical techniques previously developed for simulating stationary 2-D gas metal arc welding (GMAW), to moving 3-D GMAW. The filler droplets carrying mass, momentum, thermal energy, and species periodically impinge onto the weld pool, while moving at a certain speed in the welding direction. The complicated transport phenomena in the weld pool are caused by the combined effect of droplet impingement, gravity, electromagnetic force, plasma arc force, and surface tension force (Marangoni effect). The weld pool shape and the distributions of temperature, species, and velocity in the weld pool are calculated as functions of time. For the first time, the phenomena of “open and close-up” for a crater and the formation of ripples at the surface of a solidified weld bead are predicted by mathematical modeling. Under the welding conditions used in the present study, detailed mechanisms leading to the formation of ripples are discussed.
Enhancement of Fatigue Life of Self-Piercing Riveted Joints by Coining
Authors: Jin Zheng , Mallick P. K.
Published: June 2008

Self-piercing riveting is receiving attention in the automotive industry as an alternative to spot welding for body panels and structures, especially if they are made of aluminum alloys. In this paper, we explore the possibility of enhancing fatigue life of self-piercing riveted joints in 5754-O aluminum alloy sheets. Different sheet thickness combinations are considered. Coining is found to increase fatigue life significantly for self-piercing riveted joints in thinner sheets. However, the fatigue life enhancement is found to be less significant if the sheet thickness is in the range of 3 mm. The enhancement of fatigue life is attributed to residual compressive stresses around the coined area.
Compliant Assembly Variation Analysis Using Components Geometric Covariance
Authors: Camelio Jaime A. , Hu S. Jack
Published: June 2008

Dimensional variation is one of the most critical issues in the design of assembled products. This is especially important for the assembly of compliant, non-rigid parts since clamping and joining during assembly may introduce additional variation due to part deformation and springback. This paper presents a new methodology to predict sheet metal assembly variation using the components geometric covariance. The approach combines the use of principal component analysis and finite element methods to estimate the effect of components variation on assembly variation. Principal component analysis is applied to extract deformation patterns from production data, decomposing the component covariance in the individual contribution of these deformation “modes”. Finite element methods are used to determine the effect of each deformation “mode” over the assembly variation. The proposed methodology allows significant reduction in the computation effort required for variation analysis in sheet metal assembly. A case study is presented to illustrate the methodology.
Turbulence Intensity Distribution for Flow Along a Streamwise External Corner
Authors: Moinuddin Khalid A. M. , Joubert Peter N. , Chong Min S.
Published: June 2008

This work continues the studies of Moinuddin et al. [1], where experiments were performed on a streamwise external corner. The streamwise development of turbulent boundary layer over an external corner (chine) is influenced by secondary flow which is driven three-dimensionally. The direct effect of this secondary flow is to increase the drag force. Here secondary flow, which is known as Prandtl’s second kind, is induced by inequality of Reynolds stresses around the corner. This flow is expected to exhibit symmetry about the corner bisector. Moinuddin et al. [2,3] have established the symmetry of this flow based upon mean flow measurements. Normal wire measurements for the streamwise turbulence intensity profiles u′2+, measured at about Reθ 5700 and 4.7 m from the model leading edge, are presented in this paper. Mean flow measurements show excellent agreement between Pitot tube and normal wire measurements. Comparisons are made for u′2+, profiles at equal spanwise distance, from the corner, on both surfaces. The profiles agree quite well having nominal deviation depending on spanwise and normal distance from the corner. Isointensity contours also depict symmetrical turbulence distribution. It is also revealed that far from the corner, turbulence profiles agree well with the standard two-dimensional turbulence profile. The measurements agrees with the general behaviour expected from this kind of flow as reported by Xu & Pollard [4] from their LES calculation of flow in an annular square duct.
Analysis of the Near Wake of Bluff Bodies in Ground Proximity
Authors: Balkanyi Szabolcs R. , Bernal Luis P. , Khalighi Bahram
Published: June 2008

The effect of several drag reducing devices on the near wake of a generic ground vehicle body was investigated. Drag and base pressure measurements were conducted to identify the effects of the devices on the base drag. A Particle Image Velocimetry (PIV) study was conducted to determine changes of the near wake flow field. Averages of more than 200 PIV velocity vector fields were used to compute the mean velocity and turbulent stresses at several cross section planes. The results of the drag and base pressure measurements show that significant reductions of the total aerodynamic drag (as high as 48%) can be achieved with relatively simple devices. The results also indicated that models with base cavity have lower drag than their counter parts without it. The base pressure distributions showed a strong effect of the ground, resulting in decrease of pressure towards the lower half of the base. The PIV study showed that the extent of the recirculation region is not strongly affected by the drag reducing devices. The tested devices however, were found to have a strong effect on the underbody flow. A rapid upward deflection of the underbody flow in the near wake was observed. The devices were also found to reduce the turbulent stresses in the near wake. The turbulent stresses were found to decrease in magnitude with increasing drag reduction.
A Hydrodynamic Simulation for Mobile Bay Circulation
Authors: Zheng Z. Charlie , Zhang N.
Published: June 2008

A depth-averaged equation set is solved to simulate Mobile Bay circulation. A semi-implicit algorithm with an alternating-direction-implicit technique is employed to perform numerical computations on a staggered Cartesian grid mesh that covers the Mobile Bay area. The simulation results include effects from the four major rivers around Mobile Bay. Flow patterns and elevation contours are shown during flood and ebb tides. Velocity vectors and particle tracers are used to indicate the flow patterns and related transport of Mobile Bay circulation.
Validation of a Noninvasive Thermal Perfusion System Using a Canine Medial Saphenous Fasciocutaneous Free Tissue Flap Model
Authors: Cardinali Alex V. , Diller Thomas E. , Lanz Otto , Scott Elaine P.
Published: June 2008

This work describes steps in the ongoing development of a system to noninvasively estimate blood perfusion using thermal methods. A combination thermocouple/thermopile sensor is used to record heat flux and temperature measurements on the tissue of interest. The resulting data are compared to a biothermal computer model to determine blood perfusion. The system has been tested on a canine medial saphenous fasciocutaneous free tissue flap that allows experimental control of blood flow to the measurement site. These experiments show distinct correlation between blood flow and bioprobe output demonstrating the validity of the measurement method.
Virtual Reality for Machine Tool Prototyping
Authors: Netto Antonio Valerio , Ferreira de Oliveira Maria Cristina
Published: June 2008

We outline a procedure for implementing a virtual CNC lathe prototype using software for creating virtual environments. The prototype constructed focus on the lathe’s interlocking system (its functionality) and on its geometric model (its physical design). This project allowed us to identify the possibilities and limitations of applying current Virtual Reality technology for virtual prototyping of manufacturing machines, and evaluate the complexity associated to product prototyping in manufacturing or assembly. In additional, we suggest the possibility that this new approach can use for three areas: Training, Marketing/Sale and Product development.
Development and Application of a Combined Imaging and Modeling Technique for Determining Biomechanical Response of Roller Coaster Passengers
Authors: Morency Richard , Livesay Glen A. , Nauman Eric A.
Published: June 2008

Roller Coasters are one of the most popular amusement devices in use throughout the world. In their most basic form, roller coasters consist of a track system in which a car or train rolls under the force of gravity. The major design constraints of roller coasters are determined by the level of force and acceleration that the human body can safely withstand. These forces are commonly measured in multiples of the Earth’s gravitational acceleration, and are termed “G” forces.
Apparatus to Determine the Macroscopic and Microscopic Biaxial Swelling Response of the Annulus Fibrosus
Authors: Hulme Paul , Bruehlmann Sabina , Duncan Neil A.
Published: June 2008

The intervertebral disc (IVD) is a “hydrostatic load-bearing structure” [1], found between the vertebral bodies of the spine. The IVD is composed of the inner and outer annulus fibrosus and a gelatinous center, the nucleus pulposus. Fluid is the largest component of the IVD. Swelling affects the macroscopic mechanical response of the tissue, as well as the microscopic nutrient and solute transport to the cells of the IVD. Previous studies describing the macroscopic swelling behaviour of the annulus fibrosus have been uniaxial in nature [2,3]. However, the behaviour of the annulus is markedly affected by its geometry [3]. By examining a biaxial section of annulus fibrosus with a portion of the bone attachment present, the structure of the annular test section will be maintained and by inference so should its function [4]. Therefore, the objective of this study was to develop an apparatus to investigate simultaneously both the macroscopic and microscopic swelling behaviour of the annulus fibrosus subjected to realistic biaxial loading. The biaxial loading device should maintain the annulus fibrosus in vivo geometry and environment, monitor stress and control tissue strain, while positioning the tissue in a manner that allows for in situ visualization of the cells.
Computational Fluid Dynamics Simulation of the Blood Flow in the Human Aortic Arch: Effects of Three Branches of the Arch on the Flow
Authors: Mori Daisuke , Hayasaka Tomoaki , Yamaguchi Takami
Published: June 2008

The vascular diseases occurred in large arteries are suggested to relate with the blood flow as well as the vessel structure, which significantly influences the flow. In order to investigate these interactions, we have to understand the detailed flow phenomena in the complex vessel configuration.
A Harmonic Balance Approach for Modeling Three-Dimensional Nonlinear Unsteady Aerodynamics and Aeroelasticity
Authors: Thomas Jeffrey P. , Dowell Earl H. , Hall Kenneth C.
Published: June 2008

Presented is a frequency domain harmonic balance (HB) technique for modeling nonlinear unsteady aerodynamics of three-dimensional transonic inviscid flows about wing configurations. The method can be used to model efficiently nonlinear unsteady aerodynamic forces due to finite amplitude motions of a prescribed unsteady oscillation frequency. When combined with a suitable structural model, aeroelastic (fluid-structure), analyses may be performed at a greatly reduced cost relative to time marching methods to determine the limit cycle oscillations (LCO) that may arise. As a demonstration of the method, nonlinear unsteady aerodynamic response and limit cycle oscillation trends are presented for the AGARD 445.6 wing configuration. Computational results based on the inviscid flow model indicate that the AGARD 445.6 wing configuration exhibits only mildly nonlinear unsteady aerodynamic effects for relatively large amplitude motions. Furthermore, and most likely a consequence of the observed mild nonlinear aerodynamic behavior, the aeroelastic limit cycle oscillation amplitude is predicted to increase rapidly for reduced velocities beyond the flutter boundary. This is consistent with results from other time-domain calculations. Although not a configuration that exhibits strong LCO characteristics, the AGARD 445.6 wing nonetheless serves as an excellent example for demonstrating the HB/LCO solution procedure.
Validation of Flow-Induced Vibration Prediction Codes: PIPO-FE and VIBIC Versus Experimental Measurements
Authors: Han Yingke , Fisher Nigel J.
Published: June 2008

The PIPO-FE and VIBIC finite-element computer codes, developed and updated over the past 30 years, are used to calculate heat exchanger tube flow-induced vibration (FIV) response. PIPO-FE includes a linear forced-vibration analysis of heat exchanger tubes subjected to all major flow-induced excitation mechanisms, namely fluidelastic instability, random turbulence-induced excitation and periodic wake shedding. VIBIC is for both linear and non-linear transient dynamic simulations of heat exchanger tubes. When used to simulate a tube with clearance supports (non-linear case), VIBIC calculates tube wear work-rates to aid in the prediction of tube fretting-wear damage. All the excitation mechanisms included in PIPO-FE analyses can be simulated in VIBIC. In addition, VIBIC can model friction forces between a tube and its supports, squeeze film forces produced by the resistance of the fluid opposing the relative motion of the tube and supports, and constant loads. An important application of these codes is the analysis of the susceptibility of a heat exchanger tube to vibration damage. These codes may be used at the design stage to assess a new heat exchanger, or during the operational stage to investigate a tube failure and determine if the damage was caused by vibration. If a vibration problem exists, then the codes can be used to assess the effectiveness of any proposed design modifications. To properly assess tube vibration damage, the codes must predict vibration response accurately. This paper documents the validation process of code predictions against measurements from three flow-induced vibration experiments conducted at Chalk River Laboratories: 1. A single-span cantilever tube bundle subjected to two-phase air-water cross flow; 2. A single-span cantilever tube bundle subjected to single- and two-phase Freon cross flow; and 3. A single-span U-bend tube bundle subjected to single-phase water and two-phase air-water partial cross flow. PIPO-FE and VIBIC code predictions for fluidelastic instability ratio and the response to random turbulence-induced excitation are compared to each other for each of these three experiments. The predictions from the two codes are in good agreement. In addition, the predictions for frequency, damping ratio, fluidelastic instability ratio and the response to random turbulence-induced excitation from both codes are in reasonable agreement with the experimental results.
Phase Change Behavior of Biomedically Relevant Solutions
Authors: Han Bumsoo , Devireddy Ramachandra V. , Bischof John C.
Published: June 2008

Understanding the phase change behavior of biomedically relevant solutions is critical to the development of cryopreservation and cryosurgery protocols. In the present study, the phase change characteristics, particularly thermodynamically non-equilibrium phenomena including supercooled ice nucleation and eutectic formation, of various compositions and concentrations of biological solutions with/without glycerol as a cryoprotective agent (CPA) were investigated using a differential scanning calorimeter (DSC) and cryomicroscopy. The eutectic transitions (crystallization and melting) were observed in not only water-NaCl binary solutions, but also phosphate buffered saline (PBS) solutions. The eutectic transitions in both water-NaCl and PBS solutions were depressed during freezing far below their thermodynamic equilibrium eutectic temperatures. Contrary to freezing, eutectic melting starts very close to the thermodynamic equilibrium eutectic temperature during thawing. However, the eutectic transitions disappeared when a small amount of glycerol (∼0.1M) was added.
Bifurcation of Water Column Oscillator Behavior Simulating Reactor Safety System: 1st Report, Experiment
Authors: Morimoto Yuichiro , Kawamata Kenji , Madarame Haruki , Okamoto Koji
Published: June 2008

The non-periodical oscillation was reported in Water Column Oscillator, which simulates a passive safety system of a future nuclear reactor, however, the mechanism of the oscillation is not clarified. The objective of this study is to elucidate the mechanism of non-periodical oscillation in Water Column Oscillator experimentally and analytically. The U-type rectangular duct is filled with the water in a certain degree of height. An end of the duct is sealed and the other is open to the atmosphere. The electromagnetic valve is installed at the top of the sealed side. A cover gas simulating vapor generation by residual heat is injected constantly into the gas phase of the sealed side. The water column oscillation with its natural frequency continues until the free surface in the sealed side, pushed by the gas, reaches at a certain height. When the height of the water level reaches HL, the electromagnetic valve is open and the cover gas flows out from the U-type duct. The gas is ejected rapidly, and thus, the cover gas pressure decreases almost to the atmospheric pressure. The water level in the sealed side of the duct rises with water supply from the open side and reaches a certain height HU. Then the valve is closed again and the increasing gas pressure pushes down the water surface of the sealed side. The water level oscillates repeating the above process. The analytical model which agrees well with the experiment is derived. The bifurcation-like phenomenon is shown in experiment, however, it can be clear that the phenomenon is not bifurcation but noise effects by the numerical simulation with noise effects. The variation of characteristics of oscillation are investigated in detail by using Poincare´ section (Y2(N), U2(N)), which indicate cover gas pressure and water level velocity at the beginning of the Nth valve-open instant. The parameter region where the system shows bifurcation can be discovered by the numerical simulation. The bifurcation is confirmed in the experiment.
Transport Characteristics of Glycerol and Propylene Glycol in an Engineered Dermal Replacement
Authors: Hubel A. , Bidault N. , Hammer B.
Published: June 2008

The ability to cryopreserve engineered tissues is important for the clinical application of therapies based on living cells. Cryopreservation facilitates the manufacture, transport and safety of cell-based therapies. The cryopreservation of cells and tissues had typically required the use of specialized solutions containing cryoprotective agents (CPAs). The addition of a CPA to the freezing solution may result in damage if it is not done properly. Tissues and intact organs can exhibit reduced cellular viability when exposed to sufficiently large step changes in external osmolarity resulting from introduction or removal of a cryopreservation solution (Pegg, 1972). Not only are large step changes in osmolarity potentially damaging, but also long-term exposure to even low concentrations of CPAs at room temperature can be lethal (Fahy et al., 1990). Exposure of cells to CPAs (in particular dimethyl sulfoxide, Me2SO) has been associated with a loss in viability with time of exposure. Subsequent studies have quantified specific cellular changes resulting from exposure to CPA, such as cytoskeletal reorganization, cross-linking of nuclear proteins, and alterations in membrane permeability (cf. ref (Fahy et al., 1990) for review) which may account for the loss in viability.
Preliminary Near Wall Hemodynamic Evaluation of a Coronary Artery Bypass Graft Model With a Flow Streamlining Implant
Authors: Pedroso Pedro D. , Anayiotos Andreas S. , Hershey Brad L. , Eleftheriou Evangelos , Holman William L.
Published: June 2008

Coronary artery disease (CAD) is the leading cause of death in the world today. According to the American Heart Association 529,659 people in 1999 died as a result of CAD [1]. Starting in the 1960’s, surgeons have used Coronary Artery Bypass Graft (CABG) techniques in order to reestablish blood flow to the heart. Today, the procedure remains the same, using autologous grafts, such as the mammary artery and the saphenous vein. An unresolved problem, is that a significant number of CABGs reocclude months to years postoperatively. In the case of Saphenous Vein Grafts (SVGs) typically 50% of these bypasses are totally occluded months to years after the procedure, the remaining half being more than 50% occluded [2]. The re-occlusion of CABGs is due to a process labeled intimal hyperplasia (IH). Investigators have shown that IH, believed by some to be a remodeling process, occurs at branch sites, regions of curvature, and anastomotic junctions [3,4]. At these sites there are low residence times, slow secondary structures, disturbed flow, and areas of recirculation, therefore the onset of IH is believed to be hemodynamically linked. Most recently, floor IH has been attributed to four variables: time averaged wall shear stress (WSS), oscillating shear index (OSI), spatial wall shear stress gradients (WSSG), and temporal WSSG [5]. Adverse values of these parameters, in the case of SVGs, are believed to be caused by impedance mismatch at the anastomosis site. Over time this characteristic causes a bulge at the sinus. Such a morphology additionally contributes to disturbed flows which tend to propagate down the CABG and are believed to play a major role in the development of IH and the eventual failure of the graft.
Stent-Induced Arterial Flow Disturbance: Whole Vessel and Cellular Considerations
Authors: Schachter Levanto G. , Lieu Deborah K. , Barakat Abdul I.
Published: June 2008

Although the use of endovascular stents has significantly reduced the incidence of restenosis following balloon angioplasty, restenosis rates remain unacceptably high (20–35% of all angioplasty procedures [1]). Placement of a stent within an arterial segment locally injures vascular endothelium thereby stimulating thrombotic responses that contribute to the development of in-stent restenosis. Recent research suggests that the local fluid mechanical environment in the vicinity of a stent impacts the rate of vessel re-endothelialization following stent-induced injury [2]. This is supported by in vitro data demonstrating that endothelial repair after injury is sensitive to fluid mechanical forces [3]. Recent in vivo data suggest that in-stent restenosis preferentially develops in arterial regions exposed to low and/or oscillatory shear stress [1]. Therefore, it is essential to establish the detailed flow environment in the vicinity of a stent and to investigate the impact of this environment on EC function.
A Study of Structural Behavior in Osteoporotic Trabecular Bone: Comparison Between Finite Element Analysis and Experiments With Fused Deposition Models
Authors: Eggert Jan N. , Wright Paul K.
Published: June 2008

This project combines the topics of a) modern prototyping methods, b) studies on osteoporotic trabecular bone and c) engineering analysis using Finite Element Methods. The results are preliminary and serve as a basis for futures studies in bone mechanics. Specifically, the prototyping method of Fused Deposition Modeling was used to create a ‘scaled up’ model of a human trabecular bone. This type of bone was chosen because it is often afflicted by osteoporosis, a human condition that draws significant research attention. Thus the study described here was in part motivated by a larger research investigation into the structural behavior of degenerating human bones. The goal was to build and test a physical model and compare its behavior against a Finite Element Analysis (FEA) of the same structure. First, the model material was mechanically tested to determine Young’s modulus and Poisson’s ratio for input values to the FEA. An existing micro CT file was then adjusted for the first successful scaled bone model built on Fused Deposition Modeling. This physical model was equipped with strain gauges to determine localized strains, and successively tested in compression. (see Figure1.) The results were finally compared to the FEA, and an extensive error analysis was performed to relate physical analysis to computational assumptions.
Increased Collagen Mineralization Affects the Yield Stress But Not the Yield Strain in Cortical Bone of Rats: Implications for Age-Related Tissue Embrittlement
Authors: Akkus Ozan , Adar Fran , Schaffler Mitchell B.
Published: June 2008

It has been well documented that the fracture susceptibility of cortical bone increases significantly with age [1]. Although the age-related decline in the fracture resistance of the cortical bone is attributed to reduced bone quantity; a substantial overlap in the bone mass of normal subjects and those sustaining fractures suggests that bone mass alone does not identify the fracture risk on an individual basis [2]. Therefore, the conceptual framework should be improved to include bone quality measures in addition to bone quantity to refine fracture risk assessment. In this study, Raman microspectroscopy was used to assess two key variables of bone tissue quality in aging rat cortical bone: the relative amount of mineral with respect to the amount of collagen (i.e. collagen mineralization) and the mineral crystallinity (i.e. size and stoichiometric perfection of mineral crystals). In this regard the first aim of this study was to investigate age-related changes in the extent of mineralization of collagen fibers and to test its relationship to elastic deformability of cortical bone tissue. The second aim of the study was to investigate age-related changes in the mineral crystallinity and to test its relationship to elastic deformability of cortical bone tissue. The first hypothesis of this study is that both collagen mineralization and mineral crystallinity will increase with age. The second hypothesis of this study was that age-related changes in compositional properties will compromise the elastic deformation capacity of cortical bone tissue.
FEM Validation of a Spectral Viscoelastic Model of Posterior Sclera
Authors: Downs J. Crawford , Suh J.-K. Francis , Burgoyne Claude F. , Hart Richard T.
Published: June 2008

The eye is biomechanical pressure vessel, and mathematical and computational modeling of the posterior pole of the primate eye can be utilized to investigate the role of intraocular pressure (IOP) in the development and progression of glaucoma. The objective of this study is to validate an experimentally-derived, spectral viscoelastic characterization of scleral material properties utilizing a finite element model under cyclic loading.
A Kelvin-Voight Fractional Derivative Model for Viscoelastic Characterization of Liver Tissue
Authors: Taylor Lawrence S. , Lerner Amy L. , Rubens Deborah J. , Parker Kevin J.
Published: June 2008

There has been interest in the mechanical properties of the non-load bearing soft body tissues (brain, liver, prostate etc.) in recent years. The motivation comes from three areas: characterizing tissue response to crash injuries [1], modeling for robotic surgical devices [2] and elastographic diagnosis of disease processes using ultrasound [3].
Shear Strength of the Pig Capital Femoral Epiphyseal Plate: An Experimental Model for Human Slipped Capital Femoral Epiphysis Fixation Studies
Authors: Ipsen Brian J. , Williams John L. , Harris Michael J. , Schmidt Thomas L.
Published: June 2008

Slipped capital femoral epiphysis (SCFE) is the most common hip disorder affecting adolescent children [1]. The etiology is not fully understood but thought to be multifactorial, related to both biological and biomechanical factors [2]. SCFE occurs when the epiphysis of the proximal femur slips in relation to the metaphysis through the growth plate, causing pain, disability and potential long-term sequellae from joint incongruity. The treatment for SCFE typically involves some form of stabilization procedure using pins, screws, bone grafting, osteotomy, or casting.
Induced Stresses and Shell/Liner Micromotions in THA Components During Dislocation: A Finite Element Study
Authors: Romero Francisco , Amirouche Farid , Gonzalez Mark , Render Todd
Published: June 2008

During total hip replacement (THR) many supporting structures for the retention of the femoral head within the acetabulum are removed. Previous studies have determined that this lack of supporting structures leads to separation of the femoral head within the UHMWPE liner. During the relocation phase the femoral head impacts with the liner creating high stress conditions that may contribute to premature polyethylene wear and instabilities.
Cartilage Interstitial Fluid Load Support in Unconfined Compression
Authors: Park Seonghun , Krishnan Ramaswamy , Nicoll Steven B. , Ateshian Gerard A.
Published: June 2008

Under physiological conditions of loading, articular cartilage is subjected to both compressive strains, normal to the articular surface, and tensile strains, tangential to the articular surface. Previous studies have shown that articular cartilage exhibits a much higher modulus in tension than compression. Theoretical analyses have suggested that this tension-compression nonlinearity enhances the magnitude of interstitial fluid pressurization during loading in unconfined compression, above a theoretical threshold of 33% of the average applied stress. The first hypothesis of this experimental study is that the peak fluid load support in unconfined compression is significantly greater than the 33% theoretical limit predicted for porous permeable tissues modeled with equal moduli in tension and compression [1]. The second hypothesis is that the peak fluid load support is higher at the articular surface side of the tissue samples than near the deep zone, because the disparity between the tensile and compressive moduli is greater at the surface zone.
A Finite Element Study of Osteoporosis in a Disc Degenerated Lumbar Spine Subject to Axial Compression
Authors: Varadarajan Ravikumar , Amirouche F. , Wagner Franklin , Guppy Kern
Published: June 2008

Disc degeneration leads to various spinal disorders like Spondylylosis, Stenosis and Osteophyte formation and Osteoporosis leads to Compression fracture of the vertebral body. Biomechanical investigation of stress changes in the lumbar spine caused by disc degeneration has been done using mathematical models and cadavaric studies (1). Osteoporosis has also been studied in a similar manner (2). However, very little is known of the combined effects of osteoporosis and disc degeneration in the lumbar spine and how it may affect the treatment planning. This paper presents our findings on the combined effect using detailed finite element model of L4-L5 segments.
Biomechanical Comparison of Single-Level Cervical Plate Fusion and Interbody Cage Fusion
Authors: DiAngelo Denis J. , Thomas Amanda L. , Foley Kevin T.
Published: June 2008

Anterior cervical graft fusion alone or supplemented with an anterior cervical plate instrumentation may be used to treat the diseased cervical spine. An anterior cervical plate is intended to restore the mechanical integrity of the operated spine and decrease graft complications. An alternative method to single-level graft fusion is to use an interbody fusion device. The objective of this study was to compare the biomechanical stability of a single-level graft-plated cervical construct with an interbody cage device.
Biomechanical Comparison of Two Atlantoaxial Arthrodeses in a Cadaveric Spine Model: Transarticular Screw Fixation Versus Screw and Rod Fixation
Authors: Goel V. K. , Kuroki H. , Holekamp S. , Pitka¨nen V. , Rengachary S. , Ebraheim N. A.
Published: June 2008

The causes of atlantoaxial instability include trauma, tumor, congenital malformation, or rheumatoid arthritis. Commonly available fixation techniques to stabilize the atlantoaxial complex are several posterior wiring procedures (Brooks fusion, Gallie fusion), transarticular screw procedure (Magerl technique), either alone or in combination. Wiring procedures are obviously easier to accomplish however these do not provide sufficient immobilization across the atlantoaxial complex1,3,4. On the other hand, although transarticular screw fixation (TSF) affords a much stiffer atlantoaxial arthrodesis than posterior wiring procedures. However, TSF has some drawbacks; for example the injury of vertebral artery. Furthermore, body habitus (obesity or thoracic kyphosis) may prevent from achieving the low angle needed for correct placement of screws between C1 and C2. Recently, a new technique of screw and rod fixation (SRF) that minimizes the risk of injury to the vertebral artery and allows intraoperative reduction has been reported2,6. The purpose of this study was to compare the biomechanical stability imparted to the C1 and C2 vertebrae by either TSF or SRF technique in a cadaver model.
Pediatric Airbag Injuries
Authors: Sances Anthony , Kumaresan Srirangam , Daniels David , Friedman Keith
Published: June 2008

The advent of airbag technology has helped to reduce the injuries to belted occupants in motor vehicles during moderate to severe frontal and near frontal crashes [1–3]. Airbags have been in use since the early 1970s. As of July 2001, airbags have saved 7224 lives including 6066 drivers and 1158 front right passengers. However, the airbag deployments at low crash severity showed higher injury probability of occupants. The majority of airbag fatalities are associated with low speed impacts with deployments. As of July 2001, the National Highway Traffic Safety Administration (NHTSA) has reported 144 fatalities and serious life threatening injuries to children due to passenger airbags [4]. It is also reported that four children died and one child sustained life-threatening injury due to a driver side airbag. The publication from Transport Canada noted that the airbags increase the overall risk of injury of children under the age of 10 by approximately 21% [5]. Although the airbags have saved many lives, they are also responsible for fatalities and serious injuries during low speed severity collision. The present study reports pediatric airbag injuries sustained during low speed crashes.
Effect of Head Restraint Position and Neck Injury Criteria in Rear Impact
Authors: DeRosia John , Yoganandan Narayan , Pintar Frank A.
Published: June 2008

The objective of this study was to determine the forces and bending moments at the top of the Hybrid III dummy neck secondary to rear impact acceleration and evaluate the various proposed injury criteria. Rear impact sled tests were conducted by applying the Federal Motor Vehicle Safety Standards FMVSS 202 acceleration pulse. Differing positions of the head restraint in terms of height (750 and 800 mm) and backset (zero, 50, and 100 mm) were used to determine the axial and shear forces, bending moments, and injury criteria (NIC, Nij, and Nkm). The time sequence of attainment of these parameters was determined along with peak values.
Chondrocyte Death in Articular Cartilage Due to Excessive Mechanical Loading in the Axial and Transverse Directions
Authors: Chen Chih-Tung , Torzilli Peter A.
Published: June 2008

Chondrocyte injury and death in articular cartilage can cause matrix degradation and is a risk factor for secondary osteoarthritis [1,3–5]. Chondrocyte death can occur due to excessive mechanical loading, such as with a single high traumatic impact load (≥20 MPa), repeated sub-impact loads (≥5 MPa), or extensive cyclic loads (≥1 MPa) [1–5]. Several recent studies have shown that chondrocyte death depends not only on the stress magnitude [2] but also on the stress rate [3], strain rate [5] and load duration [1–2].
Finite Element Study of Harmonic Forcing Function Scattering Mechanisms for Cylindrical Structures
Authors: Pray Carl M. , Hambric Stephen A.
Published: June 2008

Low frequency sound radiation from cylindrical structures is generally dominated by radiation from low order (M=0, 1) circumferential harmonic modes. The high order circumferential harmonic modes are inefficient radiators below the coincidence frequency. For cylindrical structures excited by low frequency, high circumferential order (e.g. N=10) forcing functions, the radiated sound will be dominated by radiation from the low order modes if the forcing function is scattered by structural asymmetries into these modes. In this study, cylindrical structures of varying levels of asymmetry are examined using finite element analysis to quantify the scattering of order N harmonic forcing functions into order M structural response harmonics. First, purely axially-symmetric structures are examined to verify the analysis method used. The models examined include a finite cylinder with constant cross-section and a finite cylinder with tapered cross-section. The constant cross-section cylinder is analyzed in vacuo, and the tapered cylinder is analyzed both in vacuo and with water loading. These structures show no harmonic scattering, as would be expected. Next, a finite tapered cylinder with cyclically symmetric impedance discontinuities and a finite tapered cylinder with an asymmetric large impedance discontinuities are analyzed, both with water loading, to determine the impact of structural discontinuity on the harmonic scattering and radiated sound spectra. The periodic and single discontinuities both show significant scattering into low order circumferential modes and corresponding increases in radiated sound.