bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Analysis of Heterogeneous, Atherosclerotic Human Aorta
Authors: Beattie D. , Xu C. , Vito R. , Glagov S. , Whang M. C.
Published: February 2008

An experimental technique was developed to determine the finite strain field in heterogeneous, diseased human aortic cross sections at physiologic pressures in vitro. Also, the distributions within the cross sections of four histologic features (disease-free zones, lipid accumulations, fibrous intimal tissue, and regions of calcification) were quantified using light microscopic morphometry. A model incorporating heterogeneous, plane stress finite elements coupled the experimental and histologic data. Tissue constituent mechanical properties were determined through an optimization strategy, and the distributions of stress and strain energy in the diseased vascular wall were calculated. Results show that the constituents of atherosclerotic lesions exhibit large differences in their bilinear mechanical properties. The distributions of stress and strain energy in the diseased vascular wall are strongly influenced by both lesion structure and composition. These results suggest that accounting for heterogeneities in the mechanical analysis of atherosclerotic arterial tissue is critical to establishing links between lesion morphology and the susceptibility of plaque to mechanical disruption in vivo.
An Approach for the Stress Analysis of Transversely Isotropic Biphasic Cartilage Under Impact Load
Authors: Garcia J. J. , Altiero N. J. , Haut R. C.
Published: February 2008

Stress analysis of contact models for isotropic articular cartilage under impacting loads shows high shear stresses at the interface with the subchondral bone and normal compressive stresses near the surface of the cartilage. These stress distributions are not consistent, with lesions observed on the cartilage surface of rabbit patellae from blunt impact, for example, to the patello-femoral joint. The purpose of the present study was to analyze, using the elastic capabilities of a finite element code, the stress distribution in more morphologically realistic transversely isotropic biphasic contact models of cartilage. The elastic properties of an incompressible material, equivalent to those of the transversely isotropic biphasic material at time zero, were derived algebraically using stress-strain relations. Results of the stress analysis showed the highest shear stresses on the surface of the solid skeleton of the cartilage and tensile stresses in the zone of contact. These results can help explain the mechanisms responsible for surface injuries observed during blunt insult experiments.
A Global Relationship Between Trabecular Bone Morphology and Homogenized Elastic Properties
Authors: Zysset P. K. , Goulet R. W. , Hollister S. J.
Published: February 2008

An alternative concept of the relationship between morphological and elastic properties of trabecular bone is presented and applied to human tissue from several anatomical locations using a digital approach. The three-dimensional morphology of trabecular bone was assessed with a microcomputed tomography system and the method of directed secants as well as the star volume procedure were used to compute mean intercept length (MIL) and average bone length (ABL) of 4 mm cubic specimens. Assuming isotropic elastic properties for the trabecular tissue, the general elastic tensors of the bone specimens were determined using the homogenization method and the closest orthotropic tensors were calculated with an optimization algorithm. The assumption of orthotropy for trabecular bone was found to improve with specimen size and hold within 6.1 percent for a 4 mm cube size. A strong global relationship (r2 = 0.95) was obtained between fabric and the orthotropic elastic tensor with a minimal set of five constants. Mean intercept length and average bone length provided an equivalent power of prediction. These results support the hypothesis that the elastic properties of human trabecular bone from an arbitrary anatomical location can be estimated from an approximation of the anisotropic morphology and a prior knowledge of tissue properties.
A Parametric Study of Acetabular Cup Design Variables Using Finite Element Analysis and Statistical Design of Experiments
Authors: Mantell S. C. , Chanda H. , Bechtold J. E. , Kyle R. F.
Published: February 2008

To isolate the primary variables influencing acetabular cup and interface stresses, we performed an evaluation of cup loading and cup support variables, using a Statistical Design of Experiments (SDOE) approach. We developed three-dimensional finite element (FEM) models of the pelvis and adjacent bone. Cup support variables included fixation mechanism (cemented or noncemented), amount of bone support, and presence of metal backing. Cup loading variables included head size and cup thickness, cup/head friction, and conformity between the cup and head. Interaction between and among variables was determined using SDOE techniques. Of the variables tested, conformity, head size, and backing emerged as significant influences on stresses. Since initially nonconforming surfaces would be expected to wear into conforming surfaces, conformity is not expected to be a clinically significant variable. This indicates that head size should be tightly toleranced during manufacturing, and that small changes in head size can have a disproportionate influence on the stress environment. In addition, attention should be paid to the use of nonmetal backed cups, in limiting cup/bone interface stresses. No combination of secondary variables could compensate for, or override the effect of, the primary variables. Based on the results using the SDOE approach, adaptive FEM models simulating the wear process may be able to limit their parameters to head size and cup backing.
An Elastic–Viscoplastic Model for Excised Facial Tissues
Authors: Rubin M. B. , Bodner S. R. , Binur N. S.
Published: February 2008

Unified constitutive equations for elastic–viscoplastic materials were modified and used to model the highly nonlinear elastic and rate-dependent inelastic response exhibited in recent experiments on excised facial tissues. These included the skin and the underlying supportive tissue SMAS (the Superficial Musculoaponeurotic System). This study indicates a number of relevant results: The skin is more strain rate dependent than the SMAS; the nonlinearity of the elasticity of the skin is greater than that of the SMAS; both tissues exhibit a hardening effect indicated by increased resistance to inelastic deformation due to stress acting over a time period; the hardening effect leads to a decrease in time dependence and an increased elastic range, which is more pronounced for SMAS. Consequently, the SMAS can be viewed as the firmer elastic foundation of the more viscous skin. Moreover, the relaxation time for the skin is fairly short so the skin would be expected to conform to the deformation of the SMAS if it remained attached to the SMAS during stretching. This is relevant when it is undesirable to separate the skin from the SMAS for physiological reasons.
Static and Dynamic Bending Responses of the Human Cervical Spine
Authors: Voo L. M. , Pintar F. A. , Yoganandan N. , Liu Y. K.
Published: February 2008

The quasi-static and dynamic bending responses of the human mid-lower cervical spine were determined using cadaver intervertebral joints fixed at the base to a six-axis load cell. Flexion bending moment was applied to the superior end of the specimen using an electrohydraulic piston. Each specimen was tested under three cycles of quasi-static load-unload and one high-speed dynamic load. A total of five specimens were included in this study. The maximum intervertebral rotation ranged from 11.0 to 15.4 deg for quasi-static tests and from 22.9 to 34.4 deg for dynamic tests. The resulting peak moments at the center of the intervertebral joint ranged from 3.8 to 6.9 Nm for quasi-static tests and from 14.0 to 31.8 Nm for dynamic tests. The quasi-static stiffness ranged from 0.80 to 1.35 Nm/deg with a mean of 1.03 Nm/deg (±0.11 Nm/deg). The dynamic stiffness ranged from 1.08 to 2.00 Nm/deg with a mean of 1.50 Nm/deg (±0.17 Nm/deg). The differences between the two stiffnesses were statistically significant (p < 0.01). Exponential functions were derived to describe the quasi-static and dynamic moment-rotation responses. These results provide input data for lumped-parameter models and validation data for finite element models to better investigate the biomechanics of the human cervical spine.
Estimates of the Peak Pressures in Bone Pore Water
Authors: Zhang D. , Weinbaum S. , Cowin S. C.
Published: February 2008

The maximum pore fluid pressures due to uniaxial compression are determined for both the vascular porosity (Haversian and Volkmann’s canals) and the lacunar–canalicular porosity of live cortical bone. It is estimated that the peak pore water pressure will be 19 percent of the applied axial stress in the vascular porosity and 12 percent of the applied axial stress in the lacunar–canalicular porosity for an impulsive step loading. However, the estimated relaxation time for the vascular porosity (1.36 μs) is three orders of magnitude faster than that estimated for the lacunar–canalicular porosity (4.9 ms). Thus, under physiological loading, which has a stress rise time generally larger than 1 ms, pressures higher than the vascular pressure cannot be sustained in the vascular porosity due to the swift pressure relaxation in this porosity (unless the fluid drainage through the boundary is obstructed). The model also predicts a slight hydraulic stiffening of the bulk modulus due to longer draining time of the lacunar–canalicular porosity. The undrained bulk modulus is 6 percent higher than the drained bulk modulus in this case.
Analysis of Acute Mechanical Insult in an Animal Model of Post-traumatic Osteoarthrosis
Authors: Newberry W. N. , Garcia J. J. , Mackenzie C. D. , Decamp C. E. , Haut R. C.
Published: February 2008

Chronic degeneration of articular cartilage and bone in a rabbit model of post-traumatic osteoarthrosis has been hypothesized to occur due to acute stresses that exceed a threshold for injury. In this study, we impacted the rabbit patellofemoral joint at low and high intensities. High-intensity impacts produced degenerative changes in the joint, such as softening of retropatellar cartilage, as measured by indentation, an increase in histopathology of the cartilage, and an increase in thickness of sub-chondral bone underlying the cartilage. Low-intensity impacts did not cause these progressive changes. These data suggest that low-intensity impacts produced acute tissue stresses below the injury threshold, while high-intensity impacts produced stresses that exceeded the threshold for disease pathogenesis. This study begins to identify “safe” and “unsafe” ranges of acute tissue stress, using the rabbit patella, which may have future utility in the design of injury prevention devices for the human.
Theoretical and Experimental Study of Intermittent Blood Flows in Microcirculation: Application to the in-Vivo Determination of Compliance
Authors: Guiffant G. , Gabet L. , Dufaux J.
Published: February 2008

A new theoretical approach was used to study the nonlinear response of a microvascular segment subjected to a pressure step at one end. The method is suitable for both large and small deformations of the vessel wall in the case of an elastic response of the segment. It is shown that the use of this simulation permits an indirect determination of the compliance of the vessel. The procedure is applied in two cases of major interest: first the in-vivo study of the intermittent blood flow in the microcirculation, and second, the analysis of experiments using micropipettes. The resulting values of the compliance agree with other values found in the previous studies. The theoretical method is particularly adapted to nonlinear equations.
A Point Cluster Method for In Vivo Motion Analysis: Applied to a Study of Knee Kinematics
Authors: Andriacchi T. P. , Alexander E. J. , Toney M. K. , Dyrby C. , Sum J.
Published: February 2008

A new method for deriving limb segment motion from markers placed on the skin is described. The method provides a basis for determining the artifact associated with nonrigid body movement of points placed on the skin. The method is based on a cluster of points uniformly distributed on the limb segment. Each point is assigned an arbitrary mass. The center of mass and the inertia tensor of this cluster of points are calculated. The eigenvalues and eigenvectors of the inertia tensor are used to define a coordinate system in the cluster as well as to provide a basis for evaluating non-rigid body movement. The eigenvalues of the inertia tensor remain invariant if the segment is behaving as a rigid body, thereby providing a basis for determining variations for nonrigid body movement. The method was tested in a simulation model where systematic and random errors were introduced into a fixed cluster of points. The simulation demonstrated that the error due to nonrigid body movement could be substantially reduced. The method was also evaluated in a group of ten normal subjects during walking. The results for knee rotation and translation obtained from the point cluster method compared favorably to results previously obtained from normal subjects with intra-cortical pins placed into the femur and tibia. The resulting methodology described in this paper provides a unique approach to the measurement of in vivo motion using skin-based marker systems.
A Tensegrity Model of the Cytoskeleton in Spread and Round Cells
Authors: Coughlin M. F. , Stamenovic´ D.
Published: February 2008

Measurements on adherent cells have shown that spreading affects their mechanics. Highly spread cells are stiffer than less spread cells. The stiffness increases approximately linearly with increasing applied stress and more so in highly spread cells than in less spread cells. In this study, a six-strut tensegrity model of the cytoskeleton is used to analyze the effect of spreading on cellular mechanics. Two configurations are considered: a “round” configuration where a spherically shaped model is anchored to a flat rigid surface at three joints, and a “spread” configuration, where three additional joints of the model are attached to the surface. In both configurations a pulling force is applied at a free joint, distal from the anchoring surface, and the corresponding deformation is determined from equations of equilibrium. The model stiffness is obtained as the ratio of applied force to deformation. It is found that the stiffness changes with spreading consistently with the observations in cells. These findings suggest the possibility that the spreading-induced changes of the mechanical properties of the cell are the result of the concomitant changes in force distribution and microstructural geometry of the cytoskeleton.
Effect of Impact Load on Articular Cartilage: Cell Metabolism and Viability, and Matrix Water Content
Authors: Torzilli P. A. , Grigiene R. , Borrelli J. , Helfet D. L.
Published: February 2008

Significant evidence exists that trauma to a joint produced by a single impact load below that which causes subchondral bone fracture can result in permanent damage to the cartilage matrix, including surface fissures, loss of proteoglycan, and cell death. Limited information exists, however, on the effect of a varying impact stress on chondrocyte biophysiology and matrix integrity. Based on our previous work, we hypothesized that a stress-dependent response exists for both the chondrocyte’s metabolic activity and viability and the matrix’s hydration. This hypothesis was tested by impacting bovine cartilage explants with nominal stresses ranging from 0.5 to 65 MPa and measuring proteoglycan biosynthesis, cell viability, and water content immediately after impaction and 24 hours later. We found that proteoglycan biosynthesis decreased and water content increased with increasing impact stress. However, there appeared to be a critical threshold stress (15–20 MPa) that caused cell death and apparent rupture of the collagen fiber matrix at the time of impaction. We concluded that the cell death and collagen rupture are responsible for the observed alterations in the tissue’s metabolism and water content, respectively, although the exact mechanism causing this damage could not be determined.
Chained Vesicles in Vascular Endothelial Cells
Authors: Kosawada T. , Skalak R. , Schmid-Scho¨nbein G. W.
Published: February 2008

There is extensive ultrastructural evidence in endothelium for the presence of chained vesicles or clusters of attached vesicles, and they are considered to be involved in specific transport mechanisms, such as the formation of trans-endothelial channels. However, few details are known about their mechanical characteristics. In this study, the formation mechanism and mechanical aspects of vascular endothelial chained vesicles are investigated theoretically, based on membrane bending strain energy analysis. The shape of the axisymmetric vesicles was computed on the assumption that the cytoplasmic side of the vesicle has a molecular layer or cytoskeleton attached to the lipid bilayer, which induces a spontaneous curvature in the resting state. The bending strain energy is the only elasticity involved, while the shear elasticity is assumed to be negligible. The surface area of the membrane is assumed to be constant due to constant lipid bilayer thickness. Mechanically stable shapes of chained vesicles are revealed, in addition to a cylindrical tube shape. Unfolding of vesicles into a more flattened shape is associated with increase in bending energy without a significant increase in membrane tension. These results provide insights into the formation mechanism and mechanics of the chained vesicle.
A Nonlinear Axisymmetric Model With Fluid–Wall Interactions for Steady Viscous Flow in Stenotic Elastic Tubes
Authors: Tang D. , Yang J. , Yang C. , Ku D. N.
Published: February 2008

Arteries with high-grade stenoses may compress under physiologic conditions due to negative transmural pressure caused by high-velocity flow passing through the stenoses. To quantify the compressive conditions near the stenosis, a nonlinear axisymmetric model with fluid–wall interactions is introduced to simulate the viscous flow in a compliant stenotic tube. The nonlinear elastic properties of the tube (tube law) are measured experimentally and used in the model. The model is solved using ADINA (Automatic Dynamic Incremental Nonlinear Analysis), which is a finite element package capable of solving problems with fluid–structure interactions. Our results indicate that severe stenoses cause critical flow conditions such as negative pressure and high and low shear stresses, which may be related to artery compression, plaque cap rupture, platelet activation, and thrombus formation. The pressure field near a stenosis has a complex pattern not seen in one-dimensional models. Negative transmural pressure as low as −24 mmHg for a 78 percent stenosis by diameter is observed at the throat of the stenosis for a downstream pressure of 30 mmHg. Maximum shear stress as high as 1860 dyn/cm2 occurs at the throat of the stenoses, while low shear stress with reversed direction is observed right distal to the stenosis. Compressive stresses are observed inside the tube wall. The maximal principal stress and hoop stress in the 78 percent stenosis are 80 percent higher than that from the 50 percent stenosis used in our simulation. Flow rates under different pressure drop conditions are calculated and compared with experimental measurements and reasonable agreement is found for the prebuckling stage.
Mathematical Model of Gas Bubble Evolution in a Straight Tube
Authors: Halpern D. , Jiang Y. , Himm J. F.
Published: February 2008

Deep sea divers suffer from decompression sickness (DCS) when their rate of ascent to the surface is too rapid. When the ambient pressure drops, inert gas bubbles may form in blood vessels and tissues. The evolution of a gas bubble in a rigid tube filled with slowly moving fluid, intended to simulate a bubble in a blood vessel, is studied by solving a coupled system of fluid-flow and gas transport equations. The governing equations for the fluid motion are solved using two techniques: an analytical method appropriate for small nondeformable spherical bubbles, and the boundary element method for deformable bubbles of arbitrary size, given an applied steady flow rate. A steady convection-diffusion equation is then solved numerically to determine the concentration of gas. The bubble volume, or equivalently the gas mass inside the bubble for a constant bubble pressure, is adjusted over time according to the mass flux at the bubble surface. Using a quasi-steady approximation, the evolution of a gas bubble in a tube is obtained. Results show that convection increases the gas pressure gradient at the bubble surface, hence increasing the rate of bubble evolution. Comparing with the result for a single gas bubble in an infinite tissue, the rate of evolution in a tube is approximately twice as fast. Surface tension is also shown to have a significant effect. These findings may have important implications for our understanding of the mechanisms of inert gas bubbles in the circulation underlying decompression sickness.
Joint Surface Modeling With Thin-Plate Splines
Authors: Boyd S. K. , Ronsky J. L. , Lichti D. D. , Sˇalkauskas D. , Chapman M. A.
Published: February 2008

Mathematical joint surface models based on experimentally determined data points can be used to investigate joint characteristics such as curvature, congruency, cartilage thickness, joint contact areas, as well as to provide geometric information well suited for finite element analysis. Commonly, surface modeling methods are based on B-splines, which involve tensor products. These methods have had success; however, they are limited due to the complex organizational aspect of working with surface patches, and modeling unordered, scattered experimental data points. An alternative method for mathematical joint surface modeling is presented based on the thin-plate spline (TPS). It has the advantage that it does not involve surface patches, and can model scattered data points without experimental data preparation. An analytical surface was developed and modeled with the TPS to quantify its interpolating and smoothing characteristics. Some limitations of the TPS include discontinuity of curvature at exactly the experimental surface data points, and numerical problems dealing with data sets in excess of 2000 points. However, suggestions for overcoming these limitations are presented. Testing the TPS with real experimental data, the patellofemoral joint of a cat was measured with multistation digital photogrammetry and modeled using the TPS to determine cartilage thicknesses and surface curvature. The cartilage thickness distribution ranged between 100 to 550 μm on the patella, and 100 to 300 μm on the femur. It was found that the TPS was an effective tool for modeling joint surfaces because no preparation of the experimental data points was necessary, and the resulting unique function representing the entire surface does not involve surface patches. A detailed algorithm is presented for implementation of the TPS.
Contact Analysis of a Posterior Cervical Spine Plate Using a Three-Dimensional Canine Finite Element Model
Authors: Villarraga M. L. , Anderson R. C. , Hart R. T. , Dinh D. H.
Published: February 2008

The development of a three-dimensional finite element model of a posteriorly plated canine cervical spine (C3-C6) including contact nonlinearities is described. The model was created from axial CT scans and the material properties were derived from the literature. The model demonstrated sufficient accuracy from the results of a mesh convergence test. Significant steps were taken toward establishing model validation by comparison of plate surface strains with a posteriorly plated canine cervical spine under three-point bending. This model was developed to better characterize the contact pressures at the various interfaces under average physiologic canine loading. The analysis showed that the screw–plate interfaces had the highest values of all the mechanical parameters evaluated.
In Vitro Forces in the Normal and Cruciate-Deficient Knee During Simulated Squatting Motion
Authors: Singerman R. , Berilla J. , Archdeacon M. , Peyser A.
Published: February 2008

Three orthogonal components of the tibiofemoral and patellofemoral forces were measured simultaneously for knees with intact cruciate ligaments (nine knees), following anterior cruciate ligament resection (six knees), and subsequent posterior cruciate ligament resection (six knees). The knees were loaded using an experimental protocol that modeled static double-leg squat. The mean compressive tibial force increased with flexion angle. The mean anteroposterior tibial shear force acted posteriorly on the tibia below 50 deg flexion and anteriorly above 55 deg. Mediolateral shear forces were low compared to the other force components and tended to be directed medially on both the patella and tibia. The mean value of the ratio of the resultant tibial force divided by the quadriceps force decreased with increasing flexion angle and was between 0.6 and 0.7 above 70 deg flexion. The mean value of the ratio of the resultant tibiofemoral contact force divided by the resultant patellofemoral contact force decreased with increasing flexion and was between 0.8 and 1.0 above 55 deg flexion. Cruciate ligament resection resulted in no significant changes in the patellar contact forces. Following resection of the anterior cruciate ligament, the tibial anteroposterior shear force was directed anteriorly over all flexion angles tested. Subsequent resection of the posterior cruciate ligament resulted in an approximately 10 percent increase in the quadriceps tendon and tibial compressive force.
Optimization Algorithm Performance in Determining Optimal Controls in Human Movement Analyses
Authors: Neptune R. R.
Published: February 2008

The objective of this study was to evaluate the performance of different multivariate optimization algorithms by solving a “tracking” problem using a forward dynamic model of pedaling. The tracking problem was defined as solving for the muscle controls (muscle stimulation onset, offset, and magnitude) that minimized the error between experimentally collected kinetic and kinematic data and the simulation results of pedaling at 90 rpm and 250 W. Three different algorithms were evaluated: a downhill simplex method, a gradient-based sequential quadratic programming algorithm, and a simulated annealing global optimization routine. The results showed that the simulated annealing algorithm performed far superior to the conventional routines by converging more rapidly and avoiding local minima.
On Dynamics and Control of Multi-Link Flexible Manipulators
Authors: Gawronski W. , Ih C.-H. C. , Wang S. J.
Published: February 2008

This paper presents solutions of dynamics, inverse dynamics, and control problems of multi-link flexible manipulators. In deriving the manipulator dynamics, flexible deformations are assumed to be small in relation to the link length, angular rates of the links are assumed to be much smaller than their fundamental frequencies, and nonlinear terms (centrifugal and Coriolis forces) in the flexible manipulator model are assumed to be the same as those in the rigid body model. Flexible displacements are measured with respect to the rigid body configuration, obtained from its rigid body inverse kinematics. As a result, a linear time-varying system is obtained. The inverse dynamics problem consists of determination of joint torques for a given tip trajectory such that joint angles in the flexible configuration are equal to the angles in the rigid body configuration. The manipulator control system consists of the feedforward compensation and feedback control loops. Simulation results of a two-link space crane with a large payload show that the performance of this linearized dynamics and control approach is accurate, and at the same time is robust when subjected to parameter variations during slew operations.
Active Sound Attenuation in Finite-Length Ducts Using Close-Form Transfer Function Models
Authors: Hu Jwu-Sheng
Published: February 2008

In this paper, the problem of active sound cancellation in finite-length ducts is investigated. The closed-form solution of a one-dimensional wave equation is obtained as the plant model. The controllability, observability, and transmission zeros are discussed based on the transfer function model. For ducts with totally reflective boundaries, stabilization can be achieved by using a speaker (actuator) and a microphone (sensor). Cases of collocated and noncollocated sensors and actuators are presented. A repetitive control algorithm was developed to drive the actuator so that harmonic noises in a duct are attenuated. For a duct with partially reflective boundaries, the application of repetitive control prevents sound from leaking out of the duct at a chosen end. A simulation study demonstrating the effects of this feedback control scheme is also presented.
Experimental Evidence of Quasiperiodicity and Its Breakdown in the Column-Pendulum Oscillator
Authors: Mustafa G. , Ertas A.
Published: February 2008

A new vibration absorbing device is introduced for large flexible structures. The phase-space of the experimental system is reconstructed via delay-coordinate embedding technique. Experimental dynamics indicate that the motion is predominantly quasiperiodic, confirming the existence of invariant tori. Within the quasi-periodic region, there are windows containing intricate webs of phase-locked periodic responses. The quasiperiodic and the phase-locked responses are clearly visualized on the cover of the torus. Increase in the amplitude of excitation results in distortion of the invariant torus due to the resonance overlap. Due to the resonance overlap, the return map extracted from the experimental data becomes noninvertible. Furthermore, a burst of frequencies appears on the Fourier spectrum. This scenario is similar to many experimental observations of hydrodynamical instabilities; the breakup of the tori in these experiments is related to the onset of turbulence.
Helicopter Track and Balance With Artificial Neural Nets
Authors: Taitel Howard J. , Danai Kourosh , Gauthier David
Published: February 2008

Before a helicopter leaves the plant, it needs to be tuned so that its vibrations meet the required specifications. Helicopter track and balance is currently performed based on “sensitivity coefficients” which have been developed statistically after years of production experience. The fundamental problem with using these sensitivity coefficients, however, is that they do not account for the nonlinear coupling between modifications or their effect on high amplitude vibrations. In order to ensure the reliability of these sensitivity coefficients, only a limited number of modifications are simultaneously applied. As such, a number of flights are performed before the aircraft is tuned, resulting in increased production and maintenance cost. In this paper, the application of feedforward neural nets coupled with back-propagation training is demonstrated to learn the nonlinear effect of modifications, so that the appropriate set of modifications can be selected in fewer iterations (flights). The effectiveness of this system of neural nets for track and balance is currently being investigated at the Sikorsky production line.
Detonation Cell Widths in Hydrogen/Oxygen/Diluent Mixtures at Low Initial Pressures
Authors: Kumar R. K. , Dewit W. A.
Published: February 2008

Detonation cell widths of hydrogen/oxygen/helium/steam mixtures were determined in 15 and 30-cm internal-diameter pipes using the smoked-foil technique. The investigations were carried out over a range of initial pressures from 13.3 to 106.6 kPa and at an initial temperature of 105°C. The concentration range investigated included hydrogen concentrations from 10 to 40 percent and steam concentrations of up to 20 percent. The measured cell widths range from about 1 mm to over 100 mm and were in good agreement with those estimated using the calculated values of induction times and post-shock gas velocities.
Characterization of Solid Wastes From Circulating Fluidized Bed Combustion
Authors: Anthony E. J. , Ross G. G. , Berry E. E. , Hemings R. T. , Kissel R. K.
Published: February 2008

The characterization of solid wastes from full-scale circulating fluidized bed combustors (CFBC) is necessary to ensure that disposal procedures or utilization strategies for the waste solids are successful. Pilot plants are extremely useful in providing hydrodynamic heat and mass transfer data that can be used to design and predict the performance of larger units. Combustion studies indicate that data from pilot-scale units can be used to approximate the behavior of a full-scale plant for different fuels and operating conditions, even when the pilot plant is not designed to properly scale the commercial unit. However, the same does not seem to be true for the determination of reduced sulphur, the other is species and geotechnical or physical properties of the solid wastes generated from pilot plants. The results of analyses of samples generated from two units are discussed. One is a 150 by 150 mm square, 7.3 m high pilot-scale CFBC located at the University of British Columbia and 22 MWe CFBC located at Chatham, New Brunswick. This unit is operated by the New Brunswick Electric Power Commission (NBEPC). Both used the same New Brunswick coal containing 7 percent sulphur. The data presented indicate that the pilot-scale unit can significantly overpredict the formation of sulphides, and compared with the full-scale unit, produces residues with much less promise for either disposal or utilization in low-strength concretes. The results strongly suggest that further work is necessary to understand better the phenomena that produce sulphides and affect the geotechnical properties of wastes.
Preliminary Investigation of Cycle-to-Cycle Variations in a Nonair-Breathing Diesel Engine
Authors: Zheng M. , Reader G. T.
Published: February 2008

The effect of nonair mixtures on cycle-to-cycle variations of cylinder pressure characteristics was investigated experimentally with an indirect-injected (IDI) diesel engine. The engine intake temperature and pressure were maintained at normal air-breathing conditions when operated with nonair mixtures. Preliminary results indicate that increases in carbon dioxide concentration can cause significant cyclic variations. Moreover, the extent of such cyclic variations is notably influenced by the oxygen concentration and inert gas constituents of the working fluids.
An Experimental Study of the Interaction of Multiple Liquid Pool Fires
Authors: Vincent J. R. , Gollahalli S. R.
Published: February 2008

The risk of accidental spills and possible fires is high in the storage and handling of large quantities of flammable liquids. Such liquid pool fires are generally buoyancy-driven and emit a large fraction of their heat release in the form of radiation. Ignition and combustion characteristics of liquid pools depend on the design parameters such as diameter, spacing, and shape of the pools. This laboratory scale study was conducted to determine the effects of these parameters on the characteristics of multiple liquid pool fires. The measurements reported include pool surface regression rate, flame height, temperature, and concentrations of carbon dioxide, soot, and oxygen.
Effect of Operating Conditions on Optimal Performance of Rotary Dehumidifiers
Authors: Zheng W. , Worek W. M. , Novosel D.
Published: February 2008

The design-point dehumidification performance (i.e., at ARI conditions) of a rotary dehumidifier wheel depends on its rotational speed, the sorption properties of the desiccant, the heat and mass transfer characteristics of the matrix, and the size of the dehumidifier. However, the real operating conditions of a rotary dehumidifier can vary significantly from the design point, given the large variations in operating conditions (i.e., the outdoor, indoor, and regeneration temperatures and humidities) for various locations during different times of the year. This paper investigates the variability of the dehumidification performance of a rotary dehumidifier and its dependence on operating conditions. Also, the effect of the operating conditions on the optimum rotational speed of a rotary dehumidifier, where the performance of a rotary dehumidifier is optimized, is described.
Optimal Sequencing Site of Hydro-Power Stations
Authors: Hayashi T. , Yoshino F. , Waka R.
Published: February 2008

At the first stage of a hydro-power survey of a river, it is important to select the optimal hydro-power site. The most important condition to be satisfied is to determine the optimal site where the greatest and most economical amount of hydro-energy can be obtained. This paper proposes a new method in which the optimal arrangement of the hydro-power stations is determined by a computational operation using discrete data at points along the river such as the drainage area, altitude, and distance along the river channel as obtained from topographical maps instead of drawing on engineers’ experiences and the intuitions of experts. The results by this method are then compared with data on existing hydro-power stations and the results planned by expert engineers to show that this new computational method is superior.
Modeling the Energetic and Exergetic Self-Sustainability of Societies With Different Structures
Authors: Sciubba E.
Published: February 2008

The paper examines global energy and exergy flows in various models of organized human societies: from primitive tribal organizations to teocratic/aristocratic societies, to the present industrial (and post-industrial) society, to possible future highly “robotized” or “central control” social organizations. The analysis focuses on the very general chain of technological processes connected to the extraction, conversion, distribution and final use of the real energetic content of natural resources (i.e., their exergy): the biological food chain is also considered, albeit in a very simplified and “humankind” sense. It is argued that, to sustain this chain of processes, it is necessary to use a substantial portion of the final-use energy flow, and to employ a large portion of the total work force sustained by this end-use energy. It is shown that if these quantities can be related to the total exergy flow rate (from the source) and to the total available work force, then this functional relationship takes different forms in different types of society. The procedure is very general: each type of societal organization is reduced to a simple model for which energy and exergy flow diagrams are calculated, under certain well-defined assumptions, which restrain both the exchanges among the functional “groups” which constitute the model, and the exchanges with the environment. It is argued that not all societies are unconditionally self-sustained, and that certain size and technology-related restrictions apply to virtually all types of societal organizations examined here. These restrictions limit in general the distribution of the active workforce among different productive sectors; this distribution cannot be arbitrarily assigned, but depends quantitatively on the technological level of the chain of processes connected with energy extraction, transformation, distribution, and use. The results can be quantified using some assumptions/projections about energy consumption levels for different stages of technological development which are available in the literature; the procedure is applied to some models of primitive and pre-industrial societies, to the present industrial/post-industrial society, and to a hypothetical model of a future, high-technology society. No attempt has been made to study transient behavior (“evolution” or “decay” of a certain type of society), nor to relate quantitatively the steady-state case to resource conservation and environmental protection. For most of the cases examined here, neither resource scarcity nor finite biosphere capacity were considered as constraints.
An Improved Method for Gas Lift Allocation Optimization
Authors: Nishikiori N. , Redner R. A. , Doty D. R. , Schmidt Z.
Published: February 2008

A new method for finding the optimum gas injection rates for a group of continuous gas lift wells to maximize the total oil production rate is established. The new method uses a quasi-Newton nonlinear optimization technique which is incorporated with the gradient projection method. The method is capable of accommodating restrictions to the gas injection rates. The only requirement for fast convergence is that a reasonable estimate of the gas injection rates must be supplied as an initial point to the optimization method. A method of estimating the gas injection rates is developed for that purpose. A computer program is developed capable of implementing the new optimization method as well as generating the initial estimate of the gas injection rates. This program is then successfully tested on field data under both unlimited and limited gas supply. The new optimization technique demonstrates superior performance, faster convergence, and greater application.
Direct Calculation of Average and Marginal Costs From the Productive Structure of an Energy System
Authors: Lazzaretto A. , Macor A.
Published: February 2008

Most of the thermoeconomic accounting and optimization methods for energy systems are based upon a definition of the productive purpose for each component. On the basis of this definition, a productive structure of the system can be defined in which the interactions among the components are described by their fuel product. The aim of this work is to calculate marginal and average unit costs of the exergy flows starting from their definitions by a direct inspection of the productive structure. As a main result, it is noticed that the only differences between marginal and average unit cost equations are located in the capital cost terms of input-output cost balance equations of the components.
The Effect of Wellbore Curvature on Tubular Buckling and Lockup
Authors: Wu J. , Juvkam-Wold H. C.
Published: February 2008

This paper studies tubular buckling in curved wellbores (such as the build section of horizontal wells) and its effect on tubular “lockup” in horizontal or extended-reach wells. New buckling load equations are derived to properly predict tubular sinusoidal and helical buckling in such wellbores. The results show that the buckling loads to initiate sinusoidal and helical buckling of tubulars in curved wellbores are usually much larger than those in straight wellbores. This is because the curved wellbore tends to hold the axially compressed tubular against the outer-curve side of the wellbore. The tubular becomes less easy to buckle until higher axial compressive loads are applied. Less tubular lockup risk is then predicted for tubulars in horizontal or extended-reach wells by using the new buckling load equations. The new buckling loads in curved wellbores agree with those in straight wellbores when wellbore curvature approaches zero. Small-scale laboratory experiments also confirmed these theoretically derived buckling loads.
Impact Analysis of Shear Deformable Laminated Composite Plates
Authors: Kam T. Y. , Chang W. J.
Published: February 2008

A method for investigating the dynamic response of shear deformable laminated composite plates subject to low-speed impact is presented. The equations of motion of the impactor and the plate are derived via a virtual work approach. The contact force between the impactor and the plate is calculated by using an experimentally established contact law. The effects of existing in-plane forces, plate aspect ratio, length-to-thickness ratio, fiber angles, and number of layer groups on the contact force with or without the consideration of ply failure are studied. Optimal fiber angles and number of layer groups for angle-ply plates with maximum first-ply failure impact velocity are determined based on the maximum stress criterion.
A Thermodynamic Analysis of the Rich Flammability Limits of Fuel-Diluent Mixtures in Air
Authors: Bade Shrestha S. O. , Wierzba I. , Karim G. A.
Published: February 2008

A simple approach is described for the calculation of the rich flammability limits of fuel-diluent mixtures in air for a wide range of initial temperatures based only on the knowledge of the flammability limit of the pure fuel in air at atmospheric temperature and pressure conditions. Various fuel-diluent mixtures that include the fuels methane, ethylene, ethane, propane, butane, carbon monoxide, and hydrogen, and the diluents nitrogen, carbon dioxide, helium, and argon have been considered. Good agreement is shown to exist between predicted values of the rich flammability limits and the corresponding available experimental values for the fuel-diluent mixtures.
Influences of Near-Wall and Induced Irrotational Motion in a Turbulent Boundary Layer on Wall Pressure Fluctuations
Authors: Wilczynski V. , Casarella M. J.
Published: February 2008

While many studies have investigated the influence of flow structure in a turbulent boundary layer on the wall pressure signature, the conclusions of these studies have often been limited due to their reliance on a single observation. These single observations include investigations using one signal processing method over a range of locations, or a variety of signal processing techniques at a single location in the boundary layer. Hence, the conclusions often include conjecture on the impact of the flow structure at other physical locations, as well as predictions on the observable effect of flow structure should the turbulence be examined with a different signal processing perspective. In the current study, experimental data of simultaneous wall pressure and velocity fluctuations across the boundary layer have been obtained in a low-noise flow facility. These data have been examined using a variety of signal processing techniques, including probability distributions and spectral analysis. The distinct features of the Reynolds stress within the boundary layer and the observed irrotational motion at the outer edge of the boundary layer were evident in the results from each signal processing method. The influence of these two flow patterns on the wall pressure spectrum was identified and support conjectures made on the correlation between turbulence source locations and frequency bands in the wall pressure spectrum. The investigation demonstrates the necessity and utility of multiple perspectives over a range of spatial locations to study turbulence.
An Experimental Study of the Drilling of Aramid Composites
Authors: Veniali F. , Di Ilio A. , Tagliaferri V.
Published: February 2008

Major drilling characteristics of Aramid fiber-reinforced plastics are experimentally investigated. The chip appears highly deformed and tends to smear on the tool. Forces and, mainly, torque are more influenced by the tool diameter than by the feed rate and cutting speed. On the contrary, the specific cutting energy strongly depends upon the feed rate due to size effects of the tool tip. The damage in the work, i.e., delamination at entry and exit side, can be controlled by taking into account the relationships between machining parameters and forces and torque. Generally, the tool fails by gross brittle failure at the periphery rather than by generalized land wear.
End Effects in Laminated Anisotropic Beams — Part I
Authors: Ackermann J. A. , Kozik T. J.
Published: February 2008

The derivation of an analytical method to examine the stress field near the end of a simply supported, laminated beam is presented. Specific effort has been directed to accurately calculate the transverse-shear and normal stress by incorporating the exact displacement relations derived, by Kozik (1970). The method accommodates any combination of material lay-up and any type of normal load on the upper and lower surfaces. The reactions at the ends of the beam may be distributed over the surface edges in a fashion most accurately characterizing the physical supports. The solution and application of the method is presented in Part II of this paper.