bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional Analysis of Pre and Post-Knee Surgery: Total Knee Arthroplasty and ACL Reconstruction
Authors: Andriacchi T. P.
Published: March 2008

This paper examines the biomechanics of total knee arthroplasty as a treatment for arthritis and anterior cruciate ligament (ACL) reconstruction for repair of torn anterior cruciate ligaments of the knee. These are two of the most frequent reconstructive procedures for the knee joint. Functional testing of patients while performing various activities of daily living was used to study the relationship between the intrinsic biomechanics of the knee and function. The results of the study of patients following total knee replacement demonstrated a dynamic interaction between the posterior cruciate ligament and quadriceps function during stairclimbing. The study of patients with ACL-deficient knees demonstrated that loss of the anterior cruciate ligament can cause the avoidance of quadriceps contraction during activities when the knee is near full extension. Other studies demonstrated a relationship between tibiofemoral joint mechanics and patellofemoral mechanics. In addition, the importance of combined ligamentous laxity with higher than normal adduction moments during gait was examined in relationship to progressive degenerative changes to the medial compartment of the knee. In summary, functional testing such as gait analysis has proven to be an important basic research tool as well as extremely effective for clinical testing of new procedures and devices.
Lipid Transport Aspects of Atherogenesis
Authors: Weinbaum Sheldon , Chien Shu
Published: March 2008

In this review we shall examine the current understanding of events that lead to the incipient formation of the early foam cell lesion in atherogenesis and its localization. Particular emphasis will be placed on the intimal transport mechanisms that lead to the growth of extracellular lipid liposomes in the intima, since there is now substantial evidence that this growth is the triggering event in the complex sequence of processes that leads to the recruitment of blood borne monocytes into the sub-endothelial intima and their subsequent conversion to macrophages. The role of the endothelium, intimal proteoglycans and internal elastic lamina (IEL) in modulating the transport of low density lipoproteins (LDL) in the subendothelial space will be analyzed and a new hypothesis for the co-localization of liposome formation, cellular level endothelial leakage and monocyte entry described. The possible modifications of LDL in the lipsomes that facilitate the conversion of monocytes into foam cells is summarized. We also discuss the fluid dynamic aspects of intimal transport and the relationship of fluid shear stress to the localization of cellular level endothelial leakage of LDL. The effect of fluid shear on other endothelial cell functions has been recently reviewed in [1].
Flow Dynamics in the Human Aorta
Authors: Chandran K. B.
Published: March 2008

The aorta is the major blood vessel transporting blood pumped by the left ventricle to the systemic circulation. The tricuspid aortic valve at the root of the aorta provides a centralized flow with nearly uniform velocity profile into the ascending aorta. The aorta consisting of the ascending limb, the aortic arch, and the descending segment is a vessel of complex geometry including curvature in multiple planes, branches and bifurcation as well as taper. The understanding of the development of blood flow in this distensible vessel has been the subject of several theoretical as well as experimental investigations. Flow development in the aorta and in the branch vessels has been of interest in delineating the role of wall shear stresses on the etiology of atherosclerosis. In this paper, a review of the current status on our understanding of the complex flow dynamics in the aorta is presented. With the advent of transesophageal echocardiography and magnetic resonance velocity mapping, further evidence of the presence of secondary flows even in the descending aorta has been reported. The importance of the effect of secondary flow in the descending aorta on the perfusion of distal blood vessels (such as superior mesenteric and renal arterial branches) as well as in the iliac bifurcation is also included in the discussion.
Indentation Analysis of Biphasic Articular Cartilage: Nonlinear Phenomena Under Finite Deformation
Authors: Suh Jun-Kyo , Spilker Robert L.
Published: March 2008

The nonlinear indentation response of hydrated articular cartilage at phsiologically relevant rates of mechanical loading is studied using a two-phase continuum model of the tissue based on the theory of mixtures under finite deformation. The matrix equations corresponding to the governing mixture equations for this nonlinear problem are derived using a total Lagrangian penalty finite element method, and solved using a predictor-corrector iteration within a modified Newton-Raphson scheme. The stress relaxation indentation problem is examined using either a porous (free draining) indenter or solid (impermeable) indenter under fast and slow compression rates. The creep indentation problem is studied using a porous indenter. We examine the finite deformation response and compare with the response obtained using the linear infinitesimal response. Differences between the finite deformation response and the linear response are shown to be significant when the compression rate is fast or when the indenter is impermeable. The finite deformation model has a larger ratio of peak-to-equilibrium reaction force, and higher relaxation rate than the linear model during the early relaxation period, but a similar relaxation time. The finite deformation model predicts a slower creep rate than the linear model, as well as a smaller equilibrium creep displacement. The pressure distribution below the indenter, particularly near the loaded surface is also larger with the finite deformation model.
Computing Body Segment Trajectories in the Hybrid III Dummy Using Linear Accelerometer Data
Authors: Shea Rex T. , Viano David C.
Published: March 2008

An analytical method was developed and tested using several mini-sled and Hyge sled tests to calculate the planar trajectory of a Hybrid III dummy head. Aimed at expediting the Hybrid III test analyses, it may provide an opportunity for cost savings through reduced hardware and manpower on film analyses. Transformation from the moving coordinate to the laboratory coordinate is based on the angular positions integrated from the derived angular accelerations. Gravitational correction of the linear accelerometers was found to be insignificant. The computed head trajectories were compared to the ones obtained from the high speed film images. Accuracy of the calculated head trajectory relies heavily on the accuracy of the computed angular acceleration. Strain-gaged accelerometers are not dependable at all times during an impact and an ill-behaved signal for a very short period may create a significant drift in computed displacement due to double integrations. Accuracy of the currently available accelerometers is not high enough for an angular displacement calculation. A new generation of accelerometers with higher accuracy, or an angular velocity sensor may provide more accurate angular displacement for trajectory analyses. The redundancy of the in-line accelerations helps improve the isolation of erroneous outputs and improve accuracy of the procedure.
Dynamic Response of the Human Head to Impact by Three-Dimensional Finite Element Analysis
Authors: Ruan J. S. , Khalil T. , King A. I.
Published: March 2008

The impact response of the human head has been determined by three-dimensional finite element modeling. This model represents the essential features of a 50th percentile human head. It includes a layered shell closely representing the cranial bones with the interior contents occupied by an inviscid continuum to simulate the brain. A thin fluid layer was included to represent the cerebral-spinal fluid. To validate the model, its response was obtained by applying a sine-squared pulse of 6.8 kN in magnitude and 10 ms in duration. The load was applied to a freely supported head on the frontal bone in the midsagittal plane. The computed pressure-time histories at 5 locations within the brain material compared quite favorably with previously published experimental data from cadaver experiments and provided a reasonable level of confidence in the validation of the model. A parametric study was subsequently conducted to identify the model response when the impact site (frontal, side, occipital) and the material properties of the head were varied. Interestingly, the model predicted higher contre-coup pressure in the frontal lobe (from occipital impact) than that predicted in the occipital region from frontal impact. This finding supports clinical findings of contre-coup injury being more likely to result from occipital impact than from frontal impact.
A Comprehensive Approach for Studying Muscle-Tendon Mechanics
Authors: Hawkins D. , Bey M.
Published: March 2008

A comprehensive approach for studying the mechanics of partially intact muscle-tendon (MT) complexes was developed. This approach utilizes a work station which integrates state-of-the-art equipment and software. The hardware includes a nerve stimulator, ergometer, high speed video camera and recorder, computer, and temperature regulated chamber. When used in conjunction with a small animal muscle model, the work station provides accurate control of muscle stimulation, MT length, and MT shortening or stretching velocity. Simultaneously, muscle force and both muscle and tendon kinematics can be recorded. This approach is unique in that it allows simultaneous testing of both muscle and tendon under physiological conditions. Additionally, both gross and local deformations of the muscle and tendon can be determined. Sample results from a study of a rat tibialis anterior muscle illustrate the utility of this approach.
A Mechanical Model for Radial Keratotomy: Toward a Predictive Capability
Authors: Wray W. O. , Best E. D. , Cheng L. Y.
Published: March 2008

A detailed three-dimensional finite element model for radial keratotomy has been developed. The model includes the full load-bearing tunic of the eye and employs realistic geometry. Incisions are modeled explicitly, and material parameters are obtained from in vivo data. Calculated results obtained with the model are compared with data from two independent medical studies on radial keratotomy.
The Effect of Laser Parameters on the Zone of Thermal Injury Produced by Laser Ablation of Biological Tissue
Authors: Venugopalan V. , Nishioka N. S. , Mikic´ B. B.
Published: March 2008

A thermal model to predict the effect of laser parameters on the zone of thermal injury produced by laser ablation of biological tissue is presented. The model suggests that the Pe´cle`t number based on the optical penetration depth of laser radiation is the key parameter in determining the resulting zone of thermal injury. We show that the zone of thermal injury is minimized for Pe´cle`t numbers greater than one since the transport of energy via conduction beyond the ablation front is minimized. We also show that for Pe´cle`t numbers less than one, larger zones of thermal damage are unavoidable regardless of the laser pulse duration. The predictions of the model are compared with data available in the literature. Deviations between the model predictions and published data are discussed and the potential effects of the model assumptions, optical scattering, pyrolysis, temporal pulse shape, pulse duration, irradiance and pulse repetition rate are explored.
A Small Artery Heat Transfer Model for Self-Heated Thermistor Measurements of Perfusion in the Kidney Cortex
Authors: Anderson G. T. , Valvano J. W.
Published: March 2008

A small artery model (SAM) for self-heated thermistor measurements of perfusion in the canine kidney is developed based on the anatomy of the cortex vasculature. In this model interlobular arteries and veins play a dominant role in the heat transfer due to blood flow. Effective thermal conductivity, kss, is calculated from steady state thermistor measurements of heat transfer in the kidney cortex. This small artery and vein model of perfusion correctly indicates the shape of the measured kss versus perfusion curve. It also correctly predicts that the sinusoidal response of the thermistor can be used to measure intrinsic tissue conductivity, km, in perfused tissue. Although this model is specific for the canine kidney cortex, the modeling approach is applicable for a wide variety of biologic tissues.
A Numerical Study of Plasma Skimming in Small Vascular Bifurcations
Authors: Enden G. , Popel A. S.
Published: March 2008

Owing in part to a plasma-skimming mechanism, the distribution of red blood cells (RBCs) into branches of microvascular bifurcations typically differs from the distribution of the bulk blood flow. This paper analyzes the plasma-skimming mechanism that causes phase separation due to uneven distribution of red blood cells at the inlet cross section of the parent vessel. In a previous study, the shape of the surface that divides the flow into the branches was found by numerical simulation of three-dimensional flow of a homogeneous Newtonian fluid in T-type bifurcations. Those findings are used in this study to determine, as a first approximation, the side-to-parent vessel RBC flux ratio and discharge hematocrit ratio as a function of corresponding flow ratios. Calculations are based on the assumption that RBCs move along streamlines of a homogeneous Newtonian fluid and are uniformly distributed within a concentric core at the inlet cross section of the parent vessel. The results of our calculations agree well for a wide range of flow parameters with experimental data from in vivo and in vitro studies.
Three-Dimensional Simulation of Blood Flow in an Abdominal Aortic Aneurysm—Steady and Unsteady Flow Cases
Authors: Taylor Tad W. , Yamaguchi Takami
Published: March 2008

Atherosclerosis and atherosclerotic aneurysms can occur in the abdominal aorta. Steady and unsteady three-dimensional flow cases were simulated in abdominal aortic aneurysm using a flow simulation package on a graphics workstation. In the steady case, three aneurysm models of 8.0 cm length were simulated using Reynolds numbers of 350 and 700. In the unsteady case, blood flow in a single asymmetric aneurysm of 8.0 cm length was simulated at Reynolds numbers of 350 and 700 and 1400. In the aneurysm center, two symmetric vortices were formed, and flow separation started at the aneurysm inlet. In the unsteady flow case, the main vortex appeared and disappeared and changed position in the unsteady flow case and induced vortices were formed. Although the centerline view shows the vortices change position with time, cross-sectional views show that two symmetric vortices are present or partially formed throughout the entire flow cycle. Regions of high pressure were observed at the aneurysm exit caused by the symmetric vortices that were formed, implying that this high-pressure region could be an area where rupture is most likely. In the unsteady case, regions of maximum pressure moved depending on the flow cycle time; at peak flow, local pressure maximums were observed at the distal aneurysm; these oscillated, tending to put an additional strain on the distal portion of the aneurysm. The shear stress was low in the aneurysm portion of the vessel, and local maximum values were observed at the distal aneurysm constriction.
Matrix Macromolecules That Affect the Viscoelasticity of Calfskin
Authors: Kronick P. L. , Sacks M. S.
Published: March 2008

The chemical basis of viscoelasticity of bovine skin was explored by mechanical relaxation spectroscopy after selective enzymatic degradation. Measurements covered a wide range of time scales because water was replaced in the tissue with aqueous mixtures of ethylene glycol, which maintained a water-like electrical environment for the charged macromolecules down to −50°C. Macromolecular components that couple the fibrils to the interfibrillar matrix contribute about half the values of the resultant storage and loss moduli, while removal of components that are readily extractable, so perhaps free in the matrix, did not alter these mechanical quantities or their relaxations. The precision of the method reveals the effects of fibril-attached matrix, when conventional methods of mechanical testing fail.
Embryonic Tissue Morphogenesis Modeled by FEM
Authors: Brodland G. W. , Clausi D. A.
Published: March 2008

A three-dimensional, large-strain finite element formulation for the simulation of morphogenetic behaviors in embryonic tissues is presented. It is used to investigate aspects of invagination, neural tube morphogenesis, contraction wave propagation and mechanical pattern formation. The simulations show that the spacing of patterns and the shapes produced by certain morphogenetic movements in epithelial sheets depend only slightly on the properties of the materials which underlie these sheets. Simulations of neural tube closure show that numerous, experimentally-observed features can be produced by contraction of apical microfilament bundles alone. That certain systems of forces are mechanically equivalent and that certain patterns of deformations are equivalent set practical limits on what can be inferred from the simulations.
Stokes Flow Through a Row of Cylinders Between Parallel Walls: Model for the Glomerular Slit Diaphragm
Authors: Drumond M. Claudia , Deen William M.
Published: March 2008

As a model for flow through the slit diaphragms which connect the epithelial foot processes of renal glomerular capillaries, finite element solutions of Stokes equations were obtained for flow perpendicular to a row of cylinders confined between parallel walls. A dimensionless “additional resistance” (f), defined as the increment in resistance above the Poiseuille flow value, was computed for L/W≤4 and 0.1≤ R/L≤0.9, where L is half the distance between cylinder centers, W is half the distance between walls and R is the cylinder radius. Two factors contributed to f: the drag on the cylinders, and the incremental shear stresses on the walls of the channel. Of these two factors, the drag on the cylinders tended to be dominant. A more complex representation of the slit diaphragm, suggested in the literature, was also considered. The predicted hydraulic permeability of the slit diaphragm was compared with experimental values of the overall hydraulic permeability of the glomerular capillary wall.
Analytical Solutions of Pennes Bio-Heat Transfer Equation With a Blood Vessel
Authors: Huang H. W. , Chan C. L. , Roemer R. B.
Published: March 2008

The heat transfer within a perfused tissue in the presence of a vessel is considered. The bio-heat transfer equation is used for the perfused tissue and a lumped capacitance analysis is used for the convection in the vessel with a constant Nusselt number. Analytical solutions are obtained for two cases: (i) the arterial temperature of the perfused blood in the bio-heat transfer equation is equal to the axially varying mixed mean temperature of the blood in the vessel and, (ii) that arterial temperature is assumed to be constant. Dimensionless equilibrium length and temperature expressions are obtained and presented.
Adhesion Strength of Human Ligament Fibroblasts
Authors: Sung K.-L. Paul , Kwan Michael K. , Maldonado Fausto , Akeson Wayne H.
Published: March 2008

The adhesive interactions of cells with other cells and the extracellular matrix (ECM) play a fundamental role in the organization of cells in differentiated organs, cell motility, and the healing process. The adhesion characteristics of ligament fibroblasts depend on the expression of cell surface molecules and their interaction with the ECM. Although many receptors mediating the effects of ECM components on ligament cell function remain poorly defined, it is known that fibronectin (FN) allows ligament cells to adhere through the VLA-5 receptor (α5β1). A direct measurement of the adhesion between anterior cruciate ligament (ACL) or medial collateral ligament (MCL) fibroblasts and fibronectin matrix proteins was achieved by using a micromanipulation technique to determine the force required to detach an ACL or MCL cell from fibronectin-coated glass. We have found that the adhesion strength is not random, but has well-defined functional relationships with the FN concentration and the seeding time (time allowed for the cell to establish attachment). The adhesion strength (i.e., force required to detach) of ACL cells shows a stronger dependence on FN concentration (1, 2, and 5 μg/ml) for short seeding times (15-30 min) than for long seeding times (38-75 min). For MCL cells, the effect of the seeding time on adhesion strength was apparent for all concentrations. For all the seeding times studied and FN concentrations used, MCL cells had higher adhesion strength than ACL cells. The adhesion strengths of ACL and MCL fibroblasts to FN are correlated to cell adhesion area. The normalized adhesion strength (adhesion force/adhesion area) of MCL fibroblasts is approximately 0.025 mdynes/μm2, which is the same as ACL cells for a seeding time from 18 to 50 minutes.
A Model for Motion and Sedimentation of Cylindrical Red-Cell Aggregates During Slow Blood Flow in Narrow Horizontal Tubes
Authors: Secomb T. W. , El-Kareh A. W.
Published: March 2008

When blood flows slowly in a narrow tube, red-cell aggregation results in formation of an approximately cylindrical “core” of red cells, which moves as a rigid body. The core is denser than the surrounding fluid, and sedimentation is observed in horizontal tubes. To model this, the Stokes flow of a fluid surrounding a long solid cylinder (the core) contained in a long hollow cylinder (the tube) is considered. The cylinder axes are parallel but not coincident. An exact analytic expression for the resistance coefficient for motion perpendicular to the axes is given. This coefficient increases rapidly with the ratio of core radius to tube radius, and core eccentricity. The predicted rate of sedimentation is comparable to that observed experimentally. The apparent viscosity of a two-phase medium consisting of a core of aggregated particles and surrounding pure fluid is calculated. For a core radius corresponding to experimental conditions, the apparent viscosity increases rapidly with increasing eccentricity of the core.
Preliminary Analysis of the Effects of Blood Vessel Movement on Blood Flow Patterns in the Coronary Arteries
Authors: Moore James E. , Guggenheim Nicolas , Delfino Antonio , Doriot Pierre-Andre´ , Dorsaz Pierre-Andre´ , Rutishauser Wilhelm , Meister Jean-Jacques
Published: March 2008

Blood flow patterns are believed to be involved in the formation and progression of arterial diseases. It is possible that the normal physiologic movement of blood vessels during the cardiac cycle affects blood flow patterns significantly. For example, the contraction of the heart in systole and subsequent relaxation in diastole create movements of the coronary arteries, as evidenced in real-time angiography. The effects of this movement on coronary artery flow patterns have never been previously analyzed. This work was undertaken to provide a preliminary estimate of the importance of the effects of such physiologic movements on blood flow patterns in the coronary arteries. A Womersley-type solution was used to determine the effect of axial movement on the wall shear rate in a simplified model of the coronary arteries. The pulsatile pressure gradient was derived from previously published coronary artery flow waveforms. The axial movement function was obtained from a three-dimensional reconstruction of a biplanar coronary angiogram. Significant changes in wall shear rate were noted when the movement was taken into account. The maximum and minimum wall shear rates were 10 percent smaller and 107 percent larger in magnitude respectively, and the Oscillatory Shear Index (OSI) was doubled. Most of the changes in wall shear rate were observed in systole, when the pressure gradient is minimal and the movement is strongest. The results indicate that blood vessel movement during the cardiac cycle has a significant effect on hemodynamic phenomena which have been associated with the development of atherosclerosis.
Steady Expiratory Flow in a Model Symmetric Bifurcation
Authors: Zhao Yao , Lieber Baruch B.
Published: March 2008

A model symmetric bifurcation was employed to simulate steady expiratory flow in the upper part of the human central airways. A two color, two component laser Doppler anemometer was used to measure both the axial flow and the secondary flow at three different Reynolds numbers of 518, 1036, and 2089, corresponding to Dean numbers of 98, 196, and 395. The test section is a symmetric bifurcation of constant cross-sectional area with a branching angle of 70 degrees. The flow rate into the two daughter branches was about the same. Results show that in the junction plane, velocity profiles in the daughter branches are skewed towards the inner walls. In the parent tube, just downstream of the flow divider, the velocity profile is biconcave with a dip at the center but this is rapidly transformed into a velocity peak. In a plane transverse to the bifurcation plane, parabolic velocity distribution was conserved through the daughter branches. In the parent tube, the transverse profiles became flat downstream of the flow divider and developed a defect at the center further downsteam towards the end of the parent tube part of the bifurcation. The velocity defect was confined to a small region in the vicinity of the centerline. Helical motion typified by symmetric vortices was observed in the daughter branches. In the parent tube, a set of four vortices induced by the turning of the flow was observed.
The Effect of Angle and Flow Rate Upon Hemodynamics in Distal Vascular Graft Anastomoses: A Numerical Model Study
Authors: Fei Ding-Yu , Thomas James D. , Rittgers Stanley E.
Published: March 2008

Flow in distal end-to-side anastomoses of iliofemoral artery bypass grafts was simulated using a steady flow, three-dimensional numerical model. With the proximal artery occluded, anastomotic angles were varied over 20, 30, 40, 45, 50, 60 and 70 deg while the inlet Reynolds numbers were 100 and 205. Fully developed flow in the graft became somewhat skewed toward the inner wall with increasing angle for both Reynolds numbers. Separated flow regions were seen along the inner arterial wall (toe region) for angles ≥ 60 deg at Re = 100 and for angles ≥ 45 deg at Re = 205 while a stagnation point existed along the outer arterial wall (floor region) for all cases which moved downstream relative to the toe of the anastomosis with decreasing angles. Normalized shear rates (NSR) along the arterial wall varied widely throughout the anastomotic region with negative values seen in the separation zones and upstream of the stagnation points which increased in magnitude with angle. The NSR increased with distance downstream of the stagnation point and with magnitudes which increased with the angle. Compared with observations from chronic in vivo studies, these results appear to support the hypothesis of greater intimal hyperplasia occurring in regions of low fluid shear.
Pulsatile Velocity Measurements in a Model of the Human Abdominal Aorta Under Resting Conditions
Authors: Moore James E. , Ku David N.
Published: March 2008

Oscillations in near-wall velocity direction have been found to correlate with atherosclerotic plaque localization in the carotid sinus bifurcation. However, it remains unproven whether these conditions could account for the localization of the disease at other sites where atherosclerosis forms. The abdominal aorta is an important site of clinical disease in a relatively straight segment of artery. This study was initiated to quantify the velocity field in the abdominal aorta in order to determine if local differences in hemodynamic velocity directions could account for the localization of disease in this segment. Magnetic Resonance Imaging velocimetry was used to measure the pulsatile velocity profiles in an anatomically accurate in vitro model of the abdominal aorta. Velocities measured in the suprarenal aorta were laminar and reversed minimally, comparing well with theoretical solutions of Womersley flow (r = 0.96). The time-averaged velocity was +3.0 cm/s near-wall at a distance of 1 mm away from the wall. In the infrarenal aorta, the maximal velocities were skewed toward the anterior wall. At the posterior wall, velocity oscillated in direction and was retrograde for 82 percent of the cardiac cycle. The time-averaged velocity near the posterior wall was −12.5 cm/s as compared to +3.00 cm/s near the anterior wall. At the aortic bifurcation, the locations of maximal and minimal velocities in this slice were concentrated near the lateral posterior walls. This study quantifies the magnitude of low and oscillatory velocity that may exist in the abdominal aorta and suggests that there is a strong relationship between the velocities in the retrograde direction under resting conditions and the distribution of atherosclerotic plaque.
A Multi-Degree of Freedom System for Biomechanical Testing
Authors: Kunz David N. , McCabe Ronald P. , Zdeblick Thomas A. , Vanderby Ray
Published: March 2008

A system is described that allows axial, torsional, and bending testing of biomechanical specimens. The system uses electric motors under closed loop control in its grips allowing application of pure bending moments. These grips attach to an axial/torsional testing system. Thus, it provides simultaneous closed loop control of all three degrees of freedom (D.O.F), so that under any given test condition either the loads or the displacements for each D.O.F. can be maintained at zero, selected constant values, or simultaneously controlled. This enables the expedient evaluation of the mechanical behavior of biological structures under complex loadings or simple loadings (one D.O.F.) with no artificially induced constraints in the other two D.O.F.’s due to specimen mounting.
A Note on the Reduced Creep Function Corresponding to the Quasi-Linear Visco-Elastic Model Proposed by Fung
Authors: Dortmans L. J. M. G. , van de Ven A. A. F. , Sauren A. A. H. J.
Published: March 2008

For description of the visco-elastic behavior of soft biological tissues, Fung proposed a visco-elastic model formulated in terms of a relaxation function and corresponding relaxation spectrum. For the corresponding creep function, Fung proposed an expression which needs correction to obtain a consistent formulation. This creep function and the corresponding creep spectrum are derived in this note.
Investigation of Vibration Characteristics of the Ligamentous Lumbar Spine Using the Finite Element Approach
Authors: Goel Vijay K. , Park Hosang , Kong Weizeng
Published: March 2008

A nonlinear, three-dimensional finite element model of the ligamentous L4-SI segment was developed to analyze the dynamic response of the spine in the absence of damping. The effects of the upper body mass were simulated by including a mass of 40 kg on the L4 vertebral body. The modal analyses of the model indicated a resonant frequency of 17.5 Hz in axial mode and 3.8 Hz in flexion-extension mode. Accordingly, the predicted responses for the cyclic load of −400 ± 40 N applied at four different frequencies (5, 11, 16.5, and 25 Hz) were compared with the corresponding results for axial compressive static loads (−360, and −440 N). As compared to the static load cases, the predicted responses were higher for the cyclic loading. For example, the effect of cyclic load at 11 Hz was to produce significant changes (9.7 – 19.0 percent) in stresses, loads transmitted through the facets, intradiscal pressure (IDP), disk bulge, as compared to the static load predictions. The responses were found to be frequency dependent as well; supporting the in vivo observations of other investigators that the human spine has a resonant frequency. For example, the 11 Hz model (DYN11) compared to the DYN5 model showed an increase in majority of the predicted parameters. The parameters showed an increase with frequency until 17.5 Hz (resonant frequency of the model); thereafter a decrease at 25 Hz. A chronic change in these parameters, especially at the resonant frequency, beyond the “base” values may trigger the bone remodeling process leading to spinal degeneration/disorders associated with chronic vibration exposure. Future directions for extending the present model as a complement to the experimental investigations are also discussed.
Analysis of Flow in a Two-Dimensional Collapsible Channel Using Universal “Tube” Law
Authors: Matsuzaki Y. , Ikeda T. , Kitagawa T. , Sakata S.
Published: March 2008

This paper presents an extension of the previous analyses on the collapsible tubeflow problem using a simplified model based on a two-dimensional channel conveying a one-dimensional flow. The main objective of the paper is to exploit the static and dynamic behavior of the model, by comparing with available experimental data and examining the accuracy of calculated results obtained for different numerical resolutions. The main revision from the previous analyses is the incorporation of a universal “tube” law that is valid for a wide range of positive and negative transmural pressure. Most of the numerical results agree qualitatively with the experimental observations. Self-excited high-frequency oscillation with very small amplitude of the membrane wall is, however, predicted to occur in a flow range where the slope of the pressure drop curve is positive. It is seen that the high-frequency oscillation is associated with the motion of the separation point of the flow.
Additional Pressure Drop at a Bifurcation Due to the Passage of Flexible Disks in a Large Scale Model
Authors: Kiani Mohammad F. , Cokelet Giles R.
Published: March 2008

The flow of red blood cells (RBC) through a microvascular capillary bifurcation was modeled in a large scale system in which rigid circular tubes and bifurcations (diameter = .95 cm) simulated capillaries and capillary bifurcations, flexible disks (undeformed diameter = 0.75 cm) simulated RBC and glycerol simulated plasma. At low Reynolds numbers (0.01 to 0.1), pressure drop was measured in the tubes upstream and downstream from the bifurcation as well as across the bifurcation itself, for various flow splits at the bifurcation while the inflow in the upstream tube was held constant. Pressure gradient across the bifurcation is taken to be the average of the upstream and downstream pressure gradients if the additional pressure drop at the bifurcation due to the partitioning of flow and disks is negligible. For the case of glycerol alone, the ratio of pressure gradient (G) at the bifurcation to the one at the upstream region was always greater than expected and reached 1.14 when the flow in the side branch was zero. With introduction of flexible disks into the system, G at the bifurcation was as much as 10 times the G at the upstream region as disks came in contact with, or close to, the dividing line of the bifurcation and paused momentarily before they entered one or the other side of the bifurcation. The largest G was for even flow split at the bifurcation and the smallest G was for the case where the flow in the side branch was smallest. Therefore, for the range of tube hematocrits (0–30 percent) and flow splits tested here, a significant additional pressure drop at the bifurcation is observed.
Hemolysis During Membrane Plasma Separation With Pulsed Flow Filtration Enhancement
Authors: Philp Jane L. , Jaffrin Michel Y. , Ding Luhui
Published: March 2008

The use of pulsed blood flow in membrane plasmapheresis permits enhancement of plasma filtration yet may result in high levels of hemolysis due to large increases in instantaneous transmembrane pressure (TMP). This work investigates the occurrence of hemolysis as a function of TMP and wall shear rates (γw) for both steady and pulsed blood flow conditions. Two types of hollow fiber filters with identical polypropylene membranes but different lengths and membrane areas (0.1 and 0.25 m2) were tested. Fresh citrated bovine blood was circulated through the fibers at various blood flowrates and TMP in a single pass circuit using a pulsation generator, made of a single roller peristaltic pump. The free hemoglobin concentration of the plasma, Hbm, was measured from permeate samples collected at each set of TMP and γw conditions. It was found that the net hemolysis generated by the filtration was proportional to the membrane area. This justified the introduction of an hemolysis index, IH, equal to the plasma hemoglobin per unit membrane area. The boundary for the occurrence of hemolysis was thus defined by setting IH = 30 mg/ dl.m2. For both steady and pulsed flow conditions the hemolysis boundaries were found to be straight lines in the TMP-γw plane. They were identical for the two filters under steady flow but different for pulsed flow. At the same time mean wall shear rates hemolysis occurred at a lower time mean TMP under pulsed flow conditions than under steady flow conditions.
Considerations in Applying Dynamic Programming Filters to the Smoothing of Noisy Data
Authors: Hodgson Antony J.
Published: March 2008

Dynamic programming techniques are useful in smoothing and differentiating noisy data signals according to an optimization criterion and the results are generally quite robust to noise spectra different from that assumed in the construction of the filter. If the noise properties are sufficiently different, however, the generalized cross-validation function used in the optimization can exhibit either multiple minima or no minima other than that corresponding to an insignificant amount of smoothing; in these cases, the smoothing parameter desired by the user typically does not lie at the global minimum of the generalized cross-validation function, but at some other point on the curve which can be identified heuristically. I present two cases to demonstrate this phenomenon and describe what measures one can take to ensure that the desired smoothing parameter is obtained.
Experimental Evaluation of Shaped Inputs to Reduce Vibration for a Cartesian Robot
Authors: Meckl P. H. , Seering W. P.
Published: March 2008

Since all robots have some inherent flexibility, fast motions tend to excite system vibrations. This paper develops shaped inputs that generate fast motions with minimum residual vibration. Shaped force inputs are constructed from a versine series, with coefficients of the harmonic terms chosen to maximize kinetic energy and minimize excitation energy at the system natural frequencies. These force inputs are doubly integrated to obtain position waveforms that serve as reference profiles for a closed-loop controller. A Cartesian robot is used as an experimental system to test these shaped reference inputs and to compare their responses to simple step responses. Results indicate considerable reduction in residual vibration with the shaped inputs. This is especially useful when modal coupling exists, since vibration in other axes can be prevented by driving the moving axis with shaped inputs having no excitation energy at the coupled mode frequencies.
Development and Control of an Automated Robotic Weld Bead Grinding System
Authors: Whitney D. E. , Edsall A. C. , Todtenkopf A. B. , Kurfess T. R. , Tate A. R.
Published: March 2008

In a robotic weld bead grinding system there are large interaction forces between the robot and the workpiece. Jigging errors and robot compliance make position control unreliable. Instead, metal removal can be controlled by controlling the power applied to the workpiece. The approach used in this work has been to develop a nonlinear force control law for the PUMA 560 robot and implement a structured light vision system that measures material volume in real time. A power trajectory planner has also been incorporated into the system permitting the delivery of a power (the product of force and wheel speed) trajectory to the weld bead. The resulting system is able to plan and execute a multi-pass grinding sequence for removing a weld bead.
Inverse Dynamics of Flexible Robot Arms: Modeling and Computation for Trajectory Control
Authors: Asada H. , Ma Z.-D. , Tokumaru H.
Published: March 2008

The inverse dynamics of robot manipulators based on flexible arm models are considered. Actuator torques required for a flexible arm to track a given trajectory are formulated and computed by using special moving coordinate systems, called virtual rigid link coordinates. Dynamic deformations of the flexible arm can be represented in a simple and compact form with use of the virtual coordinate systems. This eliminates a number of terms involved in the equations of motion and significantly reduces complexity in the inverse dynamics computation. An efficient algorithm for computing the actuator torques is then presented on the basis of the simplified formulation, and applied to a two-link arm problem.
Lagrangian Formulation of the Equations of Motion for Elastic Mechanisms With Mutual Dependence Between Rigid Body and Elastic Motions: Part II—System Equations
Authors: Nagarajan S. , Turcic D. A.
Published: March 2008

The first step in the derivation of the equations of motion for general elastic mechanism systems was described in Part I of this work. The equations were derived at the elemental level using Lagrange’s equation and the generalized coordinates were both the rigid body degrees of freedom, and the elastic degrees of freedom of element ‘e’. Each rigid body degree of freedom gave rise to a scalar equation of motion, and the elastic degrees of freedom of element e gave rise to a vector equation of motion. Since both the rigid body degrees of freedom and elastic degrees of freedom are considered as generalized coordinates, the equations derived take into account the mutual dependence between the rigid body and elastic motions. This is important for mechanisms that are built using lightweight and flexible members and which operate at high speeds. A schematic diagram of how the equations of motion are obtained in this work is shown in Fig. 1 in Part I. The transformation step in the figure refers to the rotational transformation of the nodal elastic displacements (which were measured in the element coordinate system), so that they are measured in terms of the reference coordinate system. This transformation is necessary in order to ensure compatibility of the displacement, velocity and acceleration of the degrees of freedom that are common to two or more links during the assembly of the equations of motion. This final set of equations after assembly are obtained in closed form, and, given external torques and forces, can be solved for the rigid body and elastic response simultaneously taking into account the mutual dependence between the two responses.
Generalized Actuator Concept for the Study of the Efficiency of Energetic Systems
Authors: Seth B. , Flowers W. C.
Published: March 2008

Energy efficiency is an important consideration for the success of many portable as well as other energetic systems. One way to improve the efficiency of an engineering system is through regeneration. A regenerative actuator returns some of the otherwise dissipated energy required for passive operation. A regenerative actuator can plow back part of energy normally lost in the passive operation of the actuator into useful energy. The amount of regenerated energy will depend on the dissipation characteristics of the actuator and the regenerative potential of the process itself. In order to analyze regeneration a bond graph model of a generalized regenerative actuator is developed. The regenerative potential is analyzed in the power phase plane trajectory. By superimposing such a trajectory with the dissipation characteristics of the actuator, a framework is developed to study the feasibility of regeneration. A possible way of optimizing the regenerated energy is also considered in some depth.
Analysis of Power Monitoring on AC Induction Drive Systems
Authors: Stein J. L. , Wang Churn-Hway
Published: March 2008

The performance of AC induction motor drive systems as torque sensors is evaluated. Their potential for monitoring tool wear or breakage as well as machine component failure is discussed. A bond graph model of the motor and drive train is developed to determine the relation between electric motor power consumption and the applied torques and to identify the machine components that dominate this dynamic relation. The model, as applied to a CNC milling machine spindle system, shows (1) that the rotor input power is linearly related to both static and dynamic cutting torques under normal process conditions and (2) that the static sensitivity of the spindle system as a sensor increases and the bandwidth of the sensor decreases as the spindle speed is increased. The sensitivity and bandwidth changes are due to changes in system parameters caused by altering the gear ratios between the motor and spindle. Experiments show that the signal-to-noise ratio is affected by the motor torque vibration induced by a geometric irregularity in the drive belt. The vibration, however, does not affect the bandwidth of the sensor system. Power monitoring appears to be a viable torque sensing technique.
Description and Analysis of a Cascade Control of Fluid Flow
Authors: Lampinen M. J. , Toivonen H. T. , Niskanen E. J. , Ka¨rkka¨inen A.
Published: March 2008

A bypass flow control valve, which is a special kind of cascade control of fluid flow, is described and analyzed in this paper. The main idea of this control method is that the flow can be kept constant at varying pressure differences by using the existing pressure difference over the control valve as an energy source for making adjustments. Some flow-technical limits for the applicability of this method are examined. A theroetical consideration of a servocontrol system, where the desired volume flow is changed by external control, is also presented.
Precomputed-Gain Nonlinear Filters for Nonlinear Systems With State-Dependent Noise
Authors: Chang R. J.
Published: March 2008

Two precomputed-gain nonlinear filters are proposed for estimating the states of nonlinear systems corrupted by both external and parametric noises and subjected to linear noisy measurement systems. The exact nonlinear filters are first formulated through the Kolmogorov and Kushner’s equations. The concepts of equivalent external excitation combined with statistical linearization or local linearization are then employed to derive two precomputed-gain nonlinear filters. The resulting filters are shown to have the same structure as that of extended Kalman filter but filter-gain histories can be precomputed. Simulation results obtained from the proposed nonlinear filters and the corresponding linear filters for Duffing-type stochastic systems are compared through Monte Carlo techniques.
System Identification of Multivariate Systems With Feedback
Authors: Shin Yung C.
Published: March 2008

System identification of linear stochastic systems has been the concern of many scientists and engineers. The same system can be described in many ways and consequently many different models have been proposed. However, the complexity of the systems and computational difficulty, especially under the presence of feedback and external disturbances, have rendered identification a difficult task. This paper deals with a general modeling procedure that can be used for identification of feedback systems. First, a brief discussion on the joint input-output process models is given, followed by the discussion on the canonical representation of the model. A simplified model is derived from the general vector model. This will lead to the validity of using the Modified Autoregressive Moving Average Vector (MARMAV) model in the identification of the general multivariate system with open-loop and closed-loop dynamics. Next, an estimation procedure is explained. The estimation is pursued to reach a maximum likelihood model by nonlinear iterative calculations. Since initial values are required to start the procedure which are critical to the estimation, two methods for the initial guess value estimation are provided in the appendices.