bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Response in a One-Dimensional Model of Thermoelastic Contact
Authors: Olesiak Z. S. , Pyryev Yu. A.
Published: February 2008

We consider two layers of different materials with the initial gap between them in the field of temperature with imperfect boundary conditions in Barber’s sense. The model we discuss is that of two contacting rods (Barber and Zhang, 1988) which in the case of a single rod was devised and discussed by Dundurs and Comninou (1976, 1979). In this paper we try to make a step further in the investigation of the essentially nonlinear problem. Though we consider a system of the linear equations of thermoelasticity the nonlinearity is induced by the boundary conditions dependent on the solution. We present an algorithm for solving the system of equations based on Laplace’s transform technique. The method of solution can be used also in the dynamical problems with inertial terms taken into account. The numerical results have been obtained by a kind of computational simulation.
The Debonded Interface Anticrack
Authors: Markenscoff X. , Ni Luqun
Published: February 2008

The debonded interface anticrack is treated analytically and the singularity at the tip is found to vary between 1/2 and 1, with the dependence on the material constants combination explicitly obtained. While the case of uniform tension and shear loading at infinity has been solved, the method of solution, which consists of distributing dislocation and line load densities, readily lends itself to solution for other point loadings, such as concentrated forces or dislocations.
The Matrix-Fiber Crack in an Elastic Solid
Authors: Selvadurai A. P. S. , Singh B. M. , Au M. C.
Published: February 2008

In the presence of strong interface adhesion, the fracture of an embedded fiber can also result in the cracking of the surrounding matrix. While the orientation of such matrix cracks can be varied, the flat penny-shaped crack represents a critical crack orientation which is of particular interest to the study of the micromechanics of fracture processes in fiber-reinforced solids. This paper considers the axisymmetric problem of the uniform straining of a composite elastic solid which contains a penny-shaped crack occupying both the fiber and matrix regions. The isolated cracked fiber-matrix crack interaction is formulated as a mixed boundary value problem related to a two-domain half-space region. The resulting integral equations are solved in a numerical fashion to evaluate the stress intensity factor at the boundary of the penny-shaped crack. The numerical results presented, in the paper illustrate the influence of the elasticity mismatch between the fiber and the matrix on the stress intensity factor at the crack-tip located in the matrix. The numerical results are presented for typical fiber-reinforced composites consisting of epoxy and ceramic matrices reinforced with silicon, glass, and kevlar fibers.
Micromechanical Definition of the Strain Tensor for Granular Materials
Authors: Kruyt N. P. , Rothenburg L.
Published: February 2008

In order to develop constitutive relations for granular materials from the micromechanical viewpoint, general expressions relating macroscopic stress and strain to contact forces and particle displacements are required. Such an expression for the stress tensor under quasi-static conditions is well established in the literature, but a corresponding expression for the strain tensor has been lacking so far. This paper presents such an expression for two-dimensional assemblies. This expression is verified by computer simulations of biaxial and shear tests. As a demonstration of the use of the developed expression, a study is made of the elastic moduli of two-dimensional, isotropic assemblies of bonded, nonrotating disks. Theoretical expressions are given for the elastic moduli in terms of micromechanical parameters, such as coordination number and contact stiffnesses. Comparison with the results from computer simulations show that the agreement is fairly good over a wide range of coordination numbers and contact stiffness ratios.
Scaled Memory Description of Hysteretic Material Behavior
Authors: Bardet J. P.
Published: February 2008

Herein the concept of scaled memory (SM) is proposed to describe hysteretic material behaviors. SM scales the nonlinear variation of tangential modulus during monotonic loadings into a piecewise linear distribution, which can easily be modified to simulate specific characteristics of material behavior during cyclic loadings. As an example, SM is applied to eliminate artificial ratchetting in bounding surface plasticity, and to produce closed stress-strain loops during cyclic loadings, without introducing a single material constant. SM is generalized to six dimensions in the particular case of pressure-independent materials, and is applied to simulate the hysteretic responses of metals.
Stochastic Analysis of Nonlinear Responses of a Moored Structure Under Narrow Band Excitations
Authors: Yim Solomon C. , Yuk Dongjun , Naess Arvid , Shih I-Ming
Published: February 2008

A semianalytical method is developed for the stochastic analysis of a nonlinear moored ocean structure subjected to narrow band random waves. The method is then used to investigate the probability distribution of extreme values of the responses. To verify the accuracy and capability of the method in handling complex nonlinear behavior of the nonlinear moored ocean structure, experimental results are employed to calibrate numerical simulations and the resulting probability distributions obtained from the semianalytical method. A nonlinear-structure nonlinearly damped model is employed to model the moored structure considered and the system coefficients are identified through the reverse multiple-input/single-output technique. An examination of the comparisons indicates that the structural response extreme value probability distributions obtained from the semianalytical predictions are quite accurate.
Modeling of Facet Articulation as a Nonlinear Moving Contact Problem: Sensitivity Study on Lumbar Facet Response
Authors: Sharma M. , Langrana N. A. , Rodriguez J.
Published: February 2008

A finite element (FE) based scheme for modeling facet articulation in a spinal motion segment is proposed. The algorithm presented models the facet articulation as a nonlinear progressive contact problem. This algorithm is used to perform a nonlinear FE analysis of a complete L3-L4 motion segment. The role of facets in load transmission through a motion segment and its sensitivity to facet geometric parameters (i.e., spatial orientation of the facets and the gap between the facet articular surfaces) on this load transmission are studied. Compression, flexion, extension, and torsion loads are used in this study. The effect of facetectomy on gross segment response and disk fiber strains is studied by comparing the response of FE models of motion segment with and without facets. Large facet loads are obtained when the motion segment is subjected to torsional and large extension rotations, whereas minimal facet loads are observed under compression and flexion loading. Removal of facets reduces the segment stiffness considerably in torsion and results in higher strain levels in disk fibers. The facet load transmission is sensitive to facet geometric parameters, i.e., spatial orientation and initial facet joint gap. The facet loads increase uniformly with decrease in initial gap between the facet articular surfaces under compression, extension, and torsional loads. The sensitivity to spatial orientation angles of the facet is, however, found to vary with the type of loading. This sensitivity may account for the wide variation in the facet response reported in literature.
The Effect of Fluid Loss on the Viscoelastic Behavior of the Lumbar Intrevertebral Disc in Compression
Authors: Lu Y. M. , Hutton W. C. , Gharpuray V. M.
Published: February 2008

A viscoelastic finite element model of a L2-L3 motion segment was constructed and used to study: (1) the behavior of the intervertebral disc with different amounts of nucleus fluid loss; and (2) the effect of different rates of fluid loss on the viscoelastic behavior of the disc. The results indicate that: (1) The viscoelastic behavior of the intervertebral disc depends to a large extent on the rate of fluid loss from the disc; the intrinsic properties of disc tissue play a role only at the early stage of compressive loading; (2) the axial strain increases, whereas the intradiscal pressure and the posterior radial disc bulge decrease with increasing fluid loss; (3) a decreasing fluid loss rate with a total fluid loss of 10 to 20 percent (from the nucleus) during the first hour of compressive loading best predicts the overall viscoelastic behavior of a disc.
Measurement of Mechanical Characteristics of Tibial Periosteum and Evaluation of Local Differences
Authors: Uchiyama E. , Yamakoshi K. , Sasaki T.
Published: February 2008

Stress–strain relationships of bovine tibial periosteum, harvested from anterior, medial, lateral, and posterior aspects of tibia, were successfully measured using a newly developed experimental system. Results showed a curvilinear stress–strain pattern having three regions, i.e., toe, almost linear, and rupture regions, which resembled those of biological soft tissues like ligaments, skin, etc. Tensile moduli in the toe region (Ee) and in the linear region (Ec) were obtained by linear regressional analyses. These values and the tensile strength (σt) showed clear local differences. The values of Ee, Ec, and σt, in the longitudinal direction in the metaphyseal regions where ligaments or connective tissues attach were approximately two times larger than those in the diaphysis, where muscles or connective tissues attach. However, these properties in the metaphyseal and diaphyseal regions with muscle attachments were almost the same. In the transverse direction, these properties in the anterior proximal metaphysis were approximately two times larger than those in the diaphysis and in the distal metaphysis. In the other regions, these properties appeared not to be significantly different. These results clearly demonstrate that the mechanical properties of periosteum are strongly influenced by the ligament and muscle attachments.
Measurement of Water Transport During Freezing in Mammalian Liver Tissue: Part II—The Use of Differential Scanning Calorimetry
Authors: Devireddy R. V. , Bischof J. C.
Published: February 2008

There is currently a need for experimental techniques to assay the biophysical response (water transport or intracellular ice formation, IIF) during freezing in the cells of whole tissue slices. These data are important in understanding and optimizing biomedical applications of freezing, particularly in cryosurgery. This study presents a new technique using a Differential Scanning Calorimeter (DSC) to obtain dynamic and quantitative water transport data in whole tissue slices during freezing. Sprague-Dawley rat liver tissue was chosen as our model system. The DSC was used to monitor quantitatively the heat released by water transported from the unfrozen cell cytoplasm to the partially frozen vascular/extracellular space at 5°C/min. This technique was previously described for use in a single cell suspension system (Devireddy, et al. 1998). A model of water transport was fit to the DSC data using a nonlinear regression curve-fitting technique, which assumes that the rat liver tissue behaves as a two-compartment Krogh cylinder model. The biophysical parameters of water transport for rat liver tissue at 5°C/min were obtained as Lpg = 3.16 x 10−13 m3/Ns (1.9 μm/min-atm), ELp = 265 kJ/mole (63.4 kcal/mole), respectively. These results compare favorably to water transport parameters in whole liver tissue reported in the first part of this study obtained using a freeze substitution (FS) microscopy technique (Pazhayannur and Bischof, 1997). The DSC technique is shown to be a fast, quantitative, and reproducible technique to measure dynamic water transport in tissue systems. However, there are several limitations to the DSC technique: (a) a priori knowledge that the biophysical response is in fact water transport, (b) the technique cannot be used due to machine limitations at cooling rates greater than 40°C/min, and (c) the tissue geometric dimensions (the Krogh model dimensions) and the osmotically inactive cell volumes Vb, must be determined by low-temperature microscopy techniques.
Load Sharing Between Solid and Fluid Phases in Articular Cartilage: II — Comparison of Experimental Results and u-p Finite Element Predictions
Authors: Mukherjee N. , Wayne J. S.
Published: February 2008

Experimental measurements in conjunction with theoretical predictions were used to determine the extent of load supported by the fluid phase of cartilage at the articular surface. The u-p finite element model was used to simulate the loading of six separate porcine knee joints and to predict surface deformations of the cartilage layer on the lateral femoral condyle. Representative geometry for the condyle, contact pressures, and intrinsic material properties of the cartilage layer were supplied from experimental measures (see Part I). The u-p finite element predictions for surface deformations of the cartilage layer were obtained for several load partitioning states between the solid and fluid phases of cartilage at the articular surface. These were then compared to actual surface deformations obtained experimentally. It appeared from the comparison that approximately 75 percent of the applied load was borne by the fluid phase at the articular surface under this loading regime. This was qualitatively in agreement with the hypothesis that an applied load to articular joints is partitioned at the surface to the two phases according to the surface area ratios of the solid and fluid phases. It appeared that the solid phase was shielded from the total applied stress on the articular surface by the fluid and could be a reason for the excellent durability of the tissue under the demanding conditions in a diarthrodial joint.
Effects of Inserting a Pressensor Film Into Articular Joints on the Actual Contact Mechanics
Authors: Wu J. Z. , Herzog W. , Epstein M.
Published: February 2008

Fuji film has been widely used in studies aimed at obtaining the contact mechanics of articular joints. Once sealed for practical use in biological joints, Fuji Pressensor film has a total effective thickness of 0.30 mm, which is comparable to the cartilage thickness in the joints of many small animals. The average effective elastic modulus of Fuji film is approximately 100 MPa in compression, which is larger by a factor of 100–300 compared to that of normal articular cartilage. Therefore, inserting a Pressensor film into an articular joint will change the contact mechanics of the joint. The measurement precision of the Pressensor film has been determined systematically; however, the changes in contact mechanics associated with inserting the film into joints have not been investigated. This study was aimed at quantifying the changes in the contact mechanics associated with inserting sealed Fuji Pressensor film into joints. Spherical and cylindrical articular joint contact mechanics with and without Pressensor film and for varying degrees of surface congruency were analyzed and compared by using finite element models. The Pressensor film was taken as linearly elastic and the cartilage was assumed to be biphasic, composed of a linear elastic solid phase and an inviscid fluid phase. The present analyses showed that measurements of the joint contact pressures with Fuji Pressensor film will change the maximum true contact pressures by 10–26 percent depending on the loading, geometry of the joints, and the mechanical properties of cartilage. Considering this effect plus the measurement precision of the film (approximately 10 percent), the measured joint contact pressures in a joint may contain errors as large as 14–28 percent.
Influence of Sensor Size on the Accuracy of In-Vivo Ligament and Tendon Force Measurements
Authors: Rupert M. , Grood E. , Byczkowski T. , Levy M.
Published: February 2008

In-vivo tendon forces are commonly measured using transducers, which detect tension in the tendon fibers. A poorly understood source of measurement errors is the difference in stress distribution within the tendon between experimental and transducer calibration conditions. The objective of this study was to investigate this source of error, and to determine whether these errors could be minimized by proper selection of transducer size. The study was conducted using the infrapatellar ligament (patellar tendon) of New Zealand White rabbits. Tendon force was measured with two different size implantable force transducers (IFTs), one Wide and one Narrow, and by a strain gaged load cell in series with the tendon. Tests were conducted at five different loading conditions selected to produce five different stress distributions within the tendon. One loading condition corresponded to a typical post-experiment calibration, and the data from that condition were used to develop a calibration equation for the transducer. The errors that resulted from using this calibration were determined by comparing the tendon force measured by the in-series load cell with the force predicted from the IFT output using the calibration equation. Changes in stress distribution produced measurement errors up to 64 N with the Narrow IFT but only 24 N with the Wide IFT. We found the measurement error was dependent on sensor width. Our results support the hypothesis that measurement errors can be caused by differences in tendon stress distribution between calibration and experimental conditions. We further showed that these errors can be minimized by using an IFT, which samples the tension in a large percentage of the tendon fibers. Information from this study can be used for selection of an appropriately sized implantable force transducer for measuring tendon and ligament force.
Evaluation of Temperature Distribution During Hyperthermic Treatment in Biliary Tumors: A Computational Approach
Authors: Rivolta B. , Inzoli F. , Mantero S. , Severini A.
Published: February 2008

A computational approach is adopted to predict the temperature distribution in the biliary tissue during hyperthermic treatments in biliary tumors. Two different models are developed: an axisymmetric model and a three-dimensional model. In the first model the Pennes bioheat transfer equation is applied. It is aimed at simulating the thermoregulatory effect of the capillary bed and it can also give a pressure criterion to determine whether the blood perfusion term should be included in the mathematical model. The second model is aimed at simulating the convective effect of the large hepatic vessels: A constant Nusselt number is assumed on the sides of the vessels. The simulations of the three-dimensional model have been carried out with and without capillary perfusion in the tissue, i.e., respectively in the worst case and in the best case that may occur during heating. The results show that it is possible to obtain therapeutic temperature values in the tissue for time intervals considered acceptable by physicians. Moreover, the model is able to give more precise information about the volumes of tumoral tissue heated above therapeutic temperatures with the hyperthermic technique considered.
A One-Dimensional Unsteady Separable and Reattachable Flow Model for Collapsible Tube-Flow Analysis
Authors: Ikeda T. , Matsuzaki Y.
Published: February 2008

Taking into account both flow separation and reattachment observed in available experimental results on flows in a quasi-two-dimensional channel, we present a onedimensional unsteady flow model, which is applicable to a flow in a collapsible tube. The flow model has been derived from the two-dimensional Navier–Stokes equations by introducing the concept of a dividing streamline, which divides a separated flow into a jet and a dead-water zone. We also present a criterion for the determination of a separation point. Numerical results show that the locations of the predicted separation points agree well with the experimental data. The predicted static pressure of the separated flow is almost constant downstream of the separation point and increases quickly just before the reattachment point, as observed in the experiment. Finally, using the present flow model and the separation criterion, we examine the oscillatory behavior of an unsteady flow in a symmetric channel whose walls move sinusoidally.
Precise Measurement of Cat Patellofemoral Joint Surface Geometry With Multistation Digital Photogrammetry
Authors: Ronsky J. L. , Boyd S. K. , Lichti D. D. , Chapman M. A. , Sˇalkauskas K.
Published: February 2008

Three-dimensional joint models are important tools for investigating mechanisms related to normal and pathological joints. Often these models necessitate accurate three-dimensional joint surface geometric data so that reliable model results can be obtained; however, in models based on small joints, this is often problematic due to limitations of the present techniques. These limitations include insufficient measurement precision, the requirement of contact for the measurement process, and lack of entire joint description. This study presents a new non-contact method for precise determination of entire joint surfaces using multistation digital photogrammetry (MDPG) and is demonstrated by determining the cartilage and subchondral bone surfaces of the cat patellofemoral (PF) joint. The digital camera–lens setup was precisely calibrated using 16 photographs arranged to achieve highly convergent geometry to estimate interior and distortion parameters of the camera–lens setup. Subsequently, six photographs of each joint surface were then acquired for surface measurement. The digital images were directly imported to a computer and newly introduced semi-automatic computer algorithms were used to precisely determine the image coordinates. Finally, a rigorous mathematical procedure named the bundle adjustment was used to determine the three-dimensional coordinates of the joint surfaces and to estimate the precision of the coordinates. These estimations were validated by comparing the MDPG measurements of a cylinder and plane to an analytical model. The joint surfaces were successfully measured using the MDPG method with mean precision estimates in the least favorable coordinate direction being 10.3 μm for subchondral bone and 17.9 μm for cartilage. The difference in measurement precision for bone and cartilage primarily reflects differences in the translucent properties of the surfaces.
Harvest of Patellar Tendon (Bone–Tendon–Bone) Autograft for ACL Reconstruction Significantly Alters Surface Strain in the Human Patella
Authors: Steen H. , Tseng K.-F. , Goldstein S. A. , Carpenter J. E.
Published: February 2008

The purpose of this study was to measure the effect of bone–patellar tendon–bone autograft harvest for anterior cruciate ligament (ACL) reconstruction on the surface strain of the human patella. Through progressive removal of bone from the patella, three different defect shapes as well as the intact patella were tested in each of seven knees. Maximum principal strain and corresponding principal direction were determined from each of three gages around the defect for the four conditions (intact plus three defect shapes). There were no statistically significant differences in overall average surface strain between any of the defect shapes. Following graft harvest, overall average strain (all three defects combined) increased in the patella both medial (15 percent increase) and lateral (34 percent increase) to the defect, while decreasing in the region directly proximal (22 percent increase) to the harvest site compared to the intact patella. A statistically significant 7.5 deg shift of principal direction from longitudinal toward a more transverse (lateral-superior to medial-inferior) direction was observed in the medial region when a shallow-dome defect was made. We conclude that removal of a bone block from the anterior, inferior part of the patella induces a significant redistribution of the surface strain. This results in greater local strain adjacent to the upper border of the bone block, increasing the risk for patella fracture. This effect may be of importance in various complications known to occur after ACL reconstruction.
Analysis of Ankle Deflection During a Forward Fall in Snowboarding
Authors: Estes M. , Wang E. , Hull M. L.
Published: February 2008

Toward the general goal of preventing ankle injuries in snowboarding accidents, the objective of this project to develop a dynamic system model of a snowboarder and assess which model parameters, particularly those attributed to the boot, most strongly influenced ankle deflections during a forward fall. To satisfy this objective, a system model was created that included the rider, the boots, the snowboard, and the snow as components. Through dynamic simulations, peak ankle deflections were computed over realistic ranges of input parameter values for each of the model components. Defining sensitivity as the total change in peak ankle deflection over the range of a particular parameter studied, results indicated that the peak ankle deflection was most sensitive to the boot stiffness. Although lower, the sensitivity of the peak ankle deflection to the snow model parameters was still significant, being roughly half of the boot sensitivity. Increases in both snow stiffness and snow damping caused higher ankle deflections. Variations in both snowboard stiffness and anthropometric parameters had little effect. Due to the strong dependence of ankle deflection on boot stiffness, the potential exists for mitigating the ankle injury problem through judicious design of the boot.
On the Determination of the Worst Allowable Persistent Bounded Disturbance for a System With Constraints
Authors: Jayasuriya Suhada
Published: February 2008

The problem of explicitly determining the worst persistent input disturbance that a closed-loop system can tolerate under prespecified state and control constraints is studied. Verification of designs specifically aimed at maximizing the size of persistent bounded disturbances while satisfying system constraints, typically requires extensive simulations because the exact nature of the worst input is not known. In this paper the exact nature of the worst input is completely characterized for both SISO and MIMO cases. A finite number of specific impulse responses of the closed-loop system determines the worst persistent input disturbance. In the case of a SISO with n state constraints (|xi| ≤ βi), a control constraint (|u| ≤ βu) and an output constraint (|y| ≤ βo), n + 2 impulse responses are generally needed. With this new result the large number of simulations that is typically needed for design verification can be significantly reduced. Two examples illustrate how the new characterization can be utilized.
Control of Flexible Structures With the Confinement of Vibrations
Authors: Choura Slim
Published: February 2008

A novel control strategy for the simultaneous suppression and confinement of vibrations in flexible structures is proposed. The key idea is to alter the original modes by appropriate feedback forces to allow parts of a flexible structure to reach their steady states at fast rates. It has been demonstrated that the convergence of these parts to zero is improved at the expense of slowing down the settling of the remaining parts to their steady states. The proposed control strategy can be applied in the rapid removal of vibration energy in sensitive parts of a flexible structure for safety or performance reasons. Such parts include communication antennas in light space structures and payloads of flexible robot manipulators. In order to gain insight into the viability of the proposed control strategy, the latter is compared with a classical feedback control strategy under the same input bound constraint. It has been shown that the new control strategy brings the sensitive parts to rest with approximately 50 percent reduction in time.
Regulation of a Two-Degree-of-Freedom Structure Using Internal Resonance
Authors: Oueini Shafic S. , Tuer Kevin L. , Golnaraghi M. Farid
Published: February 2008

In this paper, we present a first attempt at using an energy based control technique to regulate the oscillations of a flexible joint, flexible arm device, through computer simulation. This technique takes advantage of the Internal Resonance (IR) phenomenon. The plant is governed by two coupled linear differential equations. The control scheme is implemented by introducing two software based controllers which are coupled dynamically with the plant through a nonlinear feedback control law. At Internal Resonance, the nonlinear coupling generates an energy link between the plant and the controllers. Thus, energy is transferred from the plant to the controllers where two active damping mechanisms subsequently dissipate it. Here the response of the structure is regulated with a single input torque applied to one plant coordinate. The theoretical analysis is based on the two-variable expansion perturbation method. Thereafter, the analytical findings are verified numerically. Simulation results indicate that the IR control strategy is able to effectively quench the oscillations of the plant.
Explicit Solutions for the Antiplane Problem of Bonded Dissimilar Materials with Two Concentric Circular-Arc Inclusions
Authors: Chao C. K. , Wu S. P.
Published: February 2008

A general solution to the antiplane problem of two concentric circular-arc inclusions in bonded dissimilar materials is provided. Based upon the Hilbert problem formulation and the technique of analytical continuation, the expressions of the complex potentials are derived explicitly in both the unit disk and the surrounding medium. Both the stress singularity coefficients and contact stress are provided in an explicit form and the former are verified by comparison with the existing ones. The effects of material and geometrical parameters upon the contact stress and stress singularity coefficients are examined and shown in graphic form. Failure initiation of an infinite bi-material plate with two arc inclusions is also discussed.
A Mathematical Model of a Tubular Solid Oxide Fuel Cell
Authors: Bessette N. F. , Wepfer W. J.
Published: February 2008

The solid oxide fuel cell shows great potential as an efficient energy conversion system for use in central power stations. These cells can reform most hydrocarbon fuels with air to produce electricity and provide a heat source at 1000°C while maintaining an efficiency of 60–75 percent. This paper describes a steady-state model for the prediction of voltage, current, and power from a single-cell tube. The model is a distributed parameter electrical network that includes the effects of mass transfer resistance (concentration polarization), chemical kinetic resistance (activation polarization), as well as relevant electrical resistances (ohmic losses). A finite-difference heat transfer model is also incorporated to allow for radial and axial temperature variations. The model computes the fuel and oxidant stream compositions as functions of axial length from energy and mass balances performed on each cell slice. The model yields results that compare favorably with the published experimental data from Westinghouse.
A Computer-Aided Molecular Design of Fluids That Optimize Absorption Cycle COP
Authors: Kernen M. , Lee L. L. , Perez-Blanco H.
Published: February 2008

A method to generate new absorbents for water in a novel refrigeration cycle was developed. The cycle, known as the phase separation absorption cycle, relies on phase separation, rather than boiling, to generate the refrigerant. After separation, the refrigerant flows to a conventional evaporator, where it evaporates, resulting in a cooling effect. The vapor is absorbed in a conventional absorber. The phase separation process is projected to require less energy than the conventional boiling process, resulting in higher cycle performance. However, suitable fluids for this cycle have never been found. The computer program developed under this work was used for the systematic design of possible absorbents. Whereas the predictive techniques which serve as kernel of the program can only provide approximate results, they allow fast screening of candidate absorbents. A model of the cycle was run for each potential absorbent, to establish whether the cycle and absorbent were compatible. A total of over 250,000 molecules were investigated, allowing the identification of a few with the potential to work in conjunction with the cycle.
Reliability-Based Casing Design
Authors: Maes M. A. , Gulati K. C. , McKenna D. L. , Brand P. R. , Lewis D. B. , Johnson R. C.
Published: February 2008

The present paper describes the development of reliability-based design criteria for oil and/or gas well casing/tubing. The approach is based on the fundamental principles of limit state design. Limit states for tubulars are discussed and specific techniques for the stochastic modeling of loading and resistance variables are described. Zonation methods and calibration techniques are developed which are geared specifically to the characteristic tubular design for both hydrocarbon drilling and production applications. The application of quantitative risk analysis to the development of risk-consistent design criteria is shown to be a major and necessary step forward in achieving more economic tubular design.
The Use of the Second Law of Thermodynamics in Process Design
Authors: Sama D. A.
Published: February 2008

The importance of using the second law of thermodynamics in the design of heat exchangers, heat exchanger networks, and processes in general, is discussed. The optimal ΔT at a refrigerated heat exchanger is considered from a second law viewpoint. It is shown that the use of minimum total annualized cost as the single optimizing factor is unsatisfactory. Total annualized costs are based on predicted costs of fuel, equipment, and capital, which are uncertain at best. Instead of a singular or “global optimum” ΔT, there is a range of optimal ΔTs, over which the total annualized cost is essentially the same, but within which the distribution between cost of capital and cost of energy is significantly different. In selecting a design ΔT, this distribution of costs should also be considered. The possibility of only one singular, or global optimum, solution for complex processes is also considered from a philosophical viewpoint, and is again rejected. The existence and identification of design decisions which unnecessarily waste thermodynamic availability (physical exergy) are discussed and identified as “second law errors.” Elimination of a second law error from a design guarantees an improved design. An optimal design, which may be any one of a numerous set of optimal designs, will result when all second law errors are eliminated. A design procedure to develop optimal process designs, using such thermodynamic insights, is proposed.
Effect of Blood Viscosity on Oxygen Transport in Residual Stenosed Artery Following Angioplasty
Authors: Kwon Ohwon , Krishnamoorthy Mahesh , Cho Young I. , Sankovic John M. , Banerjee Rupak K.
Published: February 2008

The effect of blood viscosity on oxygen transport in a stenosed coronary artery during the postangioplasty scenario is studied. In addition to incorporating varying blood viscosity using different hematocrit (Hct) concentrations, oxygen consumption by the avascular wall and its supply from vasa vasorum, nonlinear oxygen binding capacity of the hemoglobin, and basal to hyperemic flow rate changes are included in the calculation of oxygen transport in both the lumen and the avascular wall. The results of this study show that oxygen transport in the postangioplasty residual stenosed artery is affected by non-Newtonian shear-thinning property of the blood viscosity having variable Hct concentration. As Hct increases from 25% to 65%, the diminished recirculation zone for the increased Hct causes the commencement of pO2 decrease to shift radially outward by ∼20% from the center of the artery for the basal flow, but by ∼10% for the hyperemic flow at the end of the diverging section. Oxygen concentration increases from a minimum value at the core of the recirculation zone to over 90mmHg before the lumen-wall interface at the diverging section for the hyperemic flow, which is attributed to increased shear rate and thinner lumen boundary layer for the hyperemic flow, and below 90mmHg for the basal flow. As Hct increases from 25% to 65%, the average of pO2,min beyond the diverging section drops by ∼25% for the basal flow, whereas it increases by ∼15% for the hyperemic flow. Thus, current results with the moderate stenosed artery indicate that reducing Hct might be favorable in terms of increasing O2 flux and pO2,min, in the medial region of the wall for the basal flow, while higher Hct is advantageous for the hyperemic flow beyond the diverging section. The results of this study not only provide significant details of oxygen transport under varying pathophysiologic blood conditions such as unusually high blood viscosity and flow rate, but might also be extended to offer implications for drug therapy related to blood-thinning medication and for blood transfusion and hemorrhage.
An Efficient Probabilistic Methodology for Incorporating Uncertainty in Body Segment Parameters and Anatomical Landmarks in Joint Loadings Estimated From Inverse Dynamics
Authors: Langenderfer Joseph E. , Laz Peter J. , Petrella Anthony J. , Rullkoetter Paul J.
Published: February 2008

Inverse dynamics is a standard approach for estimating joint loadings in the lower extremity from kinematic and ground reaction data for use in clinical and research gait studies. Variability in estimating body segment parameters and uncertainty in defining anatomical landmarks have the potential to impact predicted joint loading. This study demonstrates the application of efficient probabilistic methods to quantify the effect of uncertainty in these parameters and landmarks on joint loading in an inverse-dynamics model, and identifies the relative importance of the parameters and landmarks to the predicted joint loading. The inverse-dynamics analysis used a benchmark data set of lower-extremity kinematics and ground reaction data during the stance phase of gait to predict the three-dimensional intersegmental forces and moments. The probabilistic analysis predicted the 1–99 percentile ranges of intersegmental forces and moments at the hip, knee, and ankle. Variabilities, in forces and moments of up to 56% and 156% of the mean values were predicted based on coefficients of variation less than 0.20 for the body segment parameters and standard deviations of 2mm for the anatomical landmarks. Sensitivity factors identified the important parameters for the specific joint and component directions. Anatomical landmarks affected moments to a larger extent than body segment parameters. Additionally, for forces, anatomical landmarks had a larger effect than body segment parameters, with the exception of segment masses, which were important to the proximal-distal joint forces. The probabilistic modeling approach predicted the range of possible joint loading, which has implications in gait studies, clinical assessments, and implant design evaluations.
Two-Phase Potentials for the Treatment of an Elastic Inclusion in Plane Thermoelasticity
Authors: Kattis M. A. , Meguid S. A.
Published: February 2008

A solution to the uncoupled two-dimensional steady-state heat conduction and thermoelastic problems of an elastic curvilinear inclusion embedded in an elastic matrix, with different thermomechanical properties, is provided. The proposed analysis describes the heat conduction problem in terms of one holomorphic complex potential and the thermoelastic problem in terms of two holomorphic potentials; known hereafter as two-phase potentials. The general results of the developed analysis are applied to specific examples and explicit forms of the solution are obtained. It is shown that a uniform heat flow at infinity induces a linear stress distribution within the elliptic inclusion.
Mechanics of the Segmentation of an Embedded Fiber, Part II: Computational Modeling and Comparisons
Authors: Selvadurai A. P. S. , ten Busschen A.
Published: February 2008

A fragmentation test has been developed for the study of the influence of the adhesive characteristics of the interface between reinforcing fibers and the matrix on the development of matrix cracking at a cracked single fiber location. The present paper examines the numerical modeling of the crack extension process within the matrix region. The numerical modeling focuses on the application of boundary element techniques to the study of an axisymmetric fiber-matrix model and quasi-static crack extension criteria are employed to determine the path of crack extension. The result for the crack extension patterns obtained from the numerical models are compared with the results derived from the experiments. It is shown that elastic fracture mechanics simulations of quasi-static crack extension can successfully model the observed experimental phenomena.
Effect of Interface Layers on Elastic Wave Propagation in a Metal Matrix Composite Reinforced by Particles
Authors: Shindo Y. , Nozaki H. , Datta S. K.
Published: February 2008

This study considers the scattering of compressional and shear waves in SiC-particle-reinforced Al composite with interfacial layers. We assume same-size inclusions and same-thickness layers with nonhomogeneous elastic properties. The effective complex wave numbers follow from the coherent wave equations which depend only upon the scattering amplitude of the single scattering problem. Numerical values of scattering cross-sections, and phase velocities and attenuations of coherent plane waves are obtained for a moderately wide range of frequencies, and the results are graphed to display the effects of concentration of scatterers and interface properties.
Optimum Shapes of Elastic Solids With Infinite Branches
Authors: Cherepanov G. P.
Published: February 2008

The classical inverse problem of the plane theory of elasticity, in which the stress along the boundary contour is rendered uniform, is considered. The exact solution to the problem delivering symmetrical optimum shapes with four infinite branches along the axes of symmetry is constructed. The method enables one to find many other optimum shapes with two, three, four, five, etc., infinite branches.
On the Ordinary, Generalized, and Pseudo-Variational Equations of Motion in Nonlinear Elasticity, Piezoelectricity, and Classical Plate Theories
Authors: Yu Yi-Yuan
Published: February 2008

Ordinary, generalized, and pseudo-variational equations of motion in three-dimensional theories of nonlinear elasticity and piezoelectricity are presented systematically. These are applied to the derivations of plate equations of the classical type. In contrast to the derivations of plate equations that include thickness and higher-order effects, it is shown that the volume and surface integrals in a three-dimensional ordinary variational equation of motion must now be used jointly in a coupled manner. Details are demonstrated by first treating a classical linear plate. Equations of the classical type for large deflections of laminated composite and piezoelectric plates are then derived, with the famous von Ka´rma´n equations of an isotropic homogeneous plate deducible as a special case. Interrelationship among various plate equations is emphasized.
Stability of a Bicomponent Fiber Spinning Flow
Authors: Lee W.-S. , Park C.-W.
Published: February 2008

Draw resonance instability in a bicomponent fiber spinning flow is investigated using a model in which a Newtonian and an upper-convected Maxwell fluid are the core and skin layers, respectively. This model is to consider a situation where the two fluids have very different extensional rheology. The results indicate a significant influence of the viscoelastic skin layer on the overall flow mechanics even when its relative flow rate is small. It is also predicted that under certain conditions the stability of the bicomponent fiber can be maintained to a higher draw ratio than obtainable with either fluids individually.
A Nonlinear Wound Roll Model Allowing for Large Deformation
Authors: Benson R. C.
Published: February 2008

A new model is developed for predicting the internal loads in a wound roll. The principal contribution is the ability to account for large deformation. This is important for applications that require tightly packed rolls with large interlayer pressure and web compression. A nonlinear, orthotropic, plane-strain, pseudoelastic constitutive law is used. Arguments are made as to why the “material symmetry condition” does not apply to the wound roll. An efficient numerical solution scheme is developed, and a good correlation is achieved with interlayer pressure measurements available in the literature.
Three-Dimensional Frictional Rigid-Body Impact
Authors: Bhatt V. , Koechling Jeff
Published: February 2008

We present an analysis of the rigid-body model for frictional three-dimensional impacts, which was originally studied by Routh. Using Coulomb’s law for friction, a set of differential equations describing the progress and outcome of the impact process for general bodies can be obtained. The differential equations induce a flow in the tangent velocity space for which the trajectories cannot be solved for in a closed form, and a numerical integration scheme is required. At the point of sticking, the numerical problem becomes ill-conditioned and we have to analyze the flow at the singularity to determine the rest of the process. A local analysis at the point of sticking provides enough information about the global nature of the flow to let us enumerate all the possible dynamic scenarios for the sliding behavior during impact. The friction coefficient, and the mass parameters at the point of contact, determine the particular sliding behavior that would occur for a given problem. Once the initial conditions are specified, the possible outcome of the impact can then be easily determined.
Viscoelastic Effects in Modeling Web Handling Systems: Steady-State Analysis
Authors: Guan X. , High M. S. , Tree D. A.
Published: February 2008

The effect of viscoelasticity in web handling systems is examined by introducing a viscoelastic equation of state into a model for tension control. Case studies and generalized results for a single open-span system and a double open-span system are presented to compare the results of the viscoelastic model to a model based on a purely elastic equation of state. The results show only small differences in the tension behavior for the single-span system. However, large differences in the magnitude and reversal of the sign of the tension in the second span of a two-span system are seen for even small degrees of viscoelasticity in the web material. The results clearly demonstrate that viscoelasticity must be considered in modeling multispan web handling systems.
Optimal Design Problems in Mechanics of Growing Composite Solids, Part II: Shape Optimization
Authors: Drozdov A. D. , Kalamkarov A. L.
Published: February 2008

Optimal design problems arising in mechanics of growing composite viscoelastic and elastic solids subjected to aging are considered. The growth means a continuous mass influx to the body surface. Due to this process, the size of the body increases in time. The mass influx with pretensioning causes the rise of stresses in the growing body. The purpose of the current study is to propose a new class of the optimal design problems for the growing viscoelastic composite solids subjected to aging, and to solve the mechanical design problems of this new type. In the current paper we analyze the optimal design of the shape of growing reinforced beams which minimizes their maximum deflection. The proposed approach and the obtained new solutions are of a special interest and importance for the design of the reinforced cantilevers and bridges.