bluuebunny/crossref_metadata_2025 huggingface dataset:
A Design Methodology to Replicate the Sub-Micron Land-Groove Structure in DVD-RAM Substrates by Injection-Compression Molding
Authors: Seong Kibyung , Moon Su-dong , Kim Hyun , Kang Shinill , Lee Jun-Seok , Lee Dongcheol
Published: November 2021

Recently, the sub-micron structured substrates of 0.74 μm track pitch and 800 Å groove depth are required for DVD-RAM, and the track pitch is expected to be narrower as the storage density for optical disk is getting higher. For the accurate replication of the land-groove structure in the stamper to the plastic substrates, it is important to control the injection-compression molding process such that the integrity of the replication for the land-groove structure is maximized. However, the determination of the processing conditions has been relied on experience or trial-and-error. In the present study, polycarbonate substrates were fabricated by injection compression molding and the land-groove structure regarded as one of the most important geometrical properties for DVD-RAM substrates was measured. The effects of the mold temperature and the compression pressure on the integrity of the replication were examined experimentally. An efficient design methodology using the response surface method (RSM) and the central composite design (CCD) technique was developed to obtain the optimum processing conditions which maximize the integrity of the replication with a limited number of experiments. The model used in this study was verified using the analysis-of-variance (ANOVA), and it was found to be adequate within the confidence limit.
On the Role of Continuum Models in Mechanobiology
Authors: Kamm R. D. , McVittie A. K. , Bathe M.
Published: November 2021

Models of cellular and subcellular mechanics are essential in gaining an understanding of the link between forces applied to a cell and its biological response. Various approaches can be used to construct these models, but one that holds considerable promise is through the use of continuum solid and fluid mechanics, coupled when necessary with molecular dynamic simulations. Here we present a continuum mechanics model of the effects of normal stress applied to a layer of airway epithelial cells. The model predicts widely differing stress distributions associated with basolateral membrane deformation, intercellular flow, or mechanical forcing by other methods such as in the use of adherent beads. When coupled with experimental results obtained from cell culture, these simulations can help to identify the site and possibly the underlying mechanisms of mechanotransduction. We also present some hypotheses concerning the nature of mechanotransduction at the molecular scale.
Flow in the Atherosclerotic Carotid Artery
Authors: Berger Stanley A. , Stroud Jennifer S.
Published: November 2021

The carotid artery bifurcation is vulnerable to the buildup of atherosclerotic plaque. This buildup may lead to vessel occlusion or to embolism or plaque rupture. Numerical simulations of blood flow in severely stenotic vessels, when considered in conjunction with experimental and in vivo data, can contribute to the understanding of plaque rupture. The Navier-Stokes equations are solved in their finite-volume formulation for carotid bifurcation geometries based on surgically removed specimens. Aspects of plaque morphology are isolated so that their effect on flow patterns and fluid mechanical stresses may be independently evaluated; results suggest that a measure of such features as plaque asymmetry and surface irregularity may usefully complement percent stenosis in the diagnosis of vulnerable plaques. The resulting flows contain large recirculation zones and high spatial variations in wall shear. Even steady flows exhibit unsteadiness (e.g. vortex shedding) due to the complex plaque morphology. The computed flow patterns and fluid stresses in different atherosclerotic vessels may be compared to identify critical features of plaque geometry and “risk factors” for plaque rupture. In this way, numerical simulations can help determine the risk of plaque rupture posed by a particular plaque deposit.
Damage Behavior of Trabecular Bone
Authors: Yeh Oscar C. , Niebur Glen L. , Jaasma Michael J. , Keaveny Tony M.
Published: November 2021

In trabecular bone, damage refers to both the physical microstructural changes which can occur in the tissue due to mechanical loads as well as to the degradations in mechanical properties which may result from such morphological changes. One hypothesis to explain age-related increases in osteoporotic fracture risk is that a history of overloads or falls can cause damage to accumulate in trabecular bone and ultimately lead to a catastrophic fracture. The purpose of this paper is to review what is known about the complex damage behavior of trabecular bone and to suggest further avenues of research.
Hydrostatic Pressurization and Depletion of Trapped Lubricant Pool During Creep and Sliding Contact of a Rippled Indenter Against a Biphasic Articular Cartilage Layer
Authors: Soltz Michael A. , Ateshian Gerard A.
Published: November 2021

This study presents an analysis of the contact of a rippled rigid impermeable indenter against a cartilage layer, which represents a first simulation of the contact of rough cartilage surfaces with lubricant entrapment. Cartilage was modeled with the biphasic theory for hydrated soft tissues, to account for fluid flow into or out of the lubricant pool. The findings of this study demonstrate that under contact creep, the trapped lubricant pool gets depleted within a time period on the order of seconds as a result of lubricant flow into the articular cartilage, while for steady state sliding contact a lubricant pool cannot be sustained. These results suggest that the classical cartilage lubrication models of weeping and boosted lubrication may have to be revised. More recent mixture-based models described in the literature are able to predict the frictional response of articular cartilage without necessarily assuming or requiring entrapment of lubricant pools at the articular contact interface.
High Velocity Coating: Effect of the Air Entrapped on the Contact Line Temporal Stability
Authors: Woehl Pierre , Bourgin Patrick
Published: November 2021

Getting and maintaining stable conditions is one key challenge in high speed coating, like in many other processes. The temporal stability of the contact line, i.e. the three-phase junction between the moving substrate, the liquid sheet and the surrounding air, is investigated. The model exhibits a sub-critical instability which is consistent with the observations of the man-of-the-art. It is then tempting to assimilate the transition from stable to unstable regime to the onset of air entrainment. Further investigations, namely experiments, are to be carried out in order to confirm this theoretical prediction.
X-Ray Microtomography of Microcellular Polymers
Authors: Pyrz Ryszard
Published: November 2021

Among modern measuring techniques, which are designed to reconstruct and to measure three-dimensional aspects of microstructure on mesoscopic scale lengths, the X-ray microtomography seems to be very well suited to yield this information. Generally, X-ray microtomography is the X-ray based non-destructive testing method that was first developed for medical purposes and only recently applied to materials characterization. Monitoring materials’ microstructure using X-ray microtomography allows reconstructing a three-dimensional image of the specimen from non-destructive, serial sections and processing it in order to visualize and measure three-dimensional features. Thus valuable information can be deduced from the correlation of measured stress and strain values with a number of internal geometrical parameters which cannot be measured at the specimen surface.
Effect of Gas Type on Microcellular Foam Process Using Atmospheric Gases as a Blowing Agent
Authors: Chen Lee , Straff Rich , Wang Xiang
Published: November 2021

This work concerns the effects of gas type on the microcellular foam process when using atmospheric gases as a blowing agent. Three gases were investigated, CO2, N2 and argon. Gas absorption, viscosity reduction and cell formation were tested with these gases using the foaming process simulator (2) and an extruder with a capillary die. Significant differences were observed among these gases. The gas absorption of N2 and argon in polymers was much lower than CO2. The diffusion rate also seems to be lower with N2 and argon. The viscosity reduction was also lower with N2 and argon. Cell nucleation density was similar for all the three gases at high saturation pressures, but it was significantly lower with N2 or argon when the saturation pressure is low. The cell size is smaller with N2 and argon at a high saturation pressure, especially with N2. As a result, the foam density is higher with these two gases at the same foaming conditions compared to CO2.
Energy Absorption of Braided Glass Fiber Reinforced Composite Tubes
Authors: Quek Shu Ching , Waas Anthony M.
Published: November 2021

Results from an experimental and analytical study on the behavior of braided glass fiber composite tubes under quasi-static crush conditions are presented. The composite tubes have an initiator plug introduced at one open end (chamfered) while the other end is clamped. This procedure causes the tube to ‘flare’ outwards into fronds and results in the progressive failure of the tube in the axial and hoop direction without global tube buckling. Axial force and axial displacements are measured during these tests in order to assess energy absorption. In addition, readings from strain gages that are placed at critical locations on the tube walls are used to assess the state of strain on the tube walls away from the crush end. During a crush test, the axial load ascended to a maximum value and subsequently settled to a plateau value about which the load oscillated during the progressive crushing of the tube. The oscillations exhibited distinct periodicity. Results from an analytical model that best simulates the failure of these tubes are presented. The model is based on an axisymmetric formulation of the cylindrical shell equations in conjunction with ideas from classical fracture mechanics and continuum damage mechanics.
The Improved Volumetric-Efficiency of an Axial-Piston Pump Utilizing a Trapped-Volume Design
Authors: Manring N. D. , Zhang Y.
Published: November 2021

In this research, the volumetric efficiency of the axial-piston pump is examined as it relates to the compressibility losses of the fluid. In particular, two valve-plate geometries are compared to show that alterations in the valve-plate design can cause differences in the operating efficiency of the pump. In this paper, a standard valve-plate design which utilizes slots is compared to a trapped-volume design which eliminates the slots altogether. In the analytical result of this paper, it maybe shown that the standard valve-plate design introduces a volumetric loss which may be accounted for by the uncontrolled expansion and compression of the fluid that occurs through the slots themselves. By eliminating these slots, and utilizing a trapped volume design, it may be shown that improvements in the operating efficiency can be achieved. Though this paper does not claim to provide the ideal valve-plate design for all pump applications, it does provide the theoretical reason for utilizing trapped volumes and lends general insight into the overall problem of valve-plate design.
Model Identification of a High Performance Hydrostatic Actuation System
Authors: Habibi S. R. , Pastrakuljic V. , Goldenberg A. A.
Published: November 2021

An advanced hydrostatic actuation system referred to as the Electro Hydraulic Actuator (EHA) has been designed and prototyped. The prototype of EHA exhibits a very high level of dynamic performance and positional accuracy. EHA’s positional accuracy with a simple outer-loop proportional controller equals its optical position-encoder resolution of 10 Micron. In this paper, a linearized mathematical model of EHA is derived and used as a basis for model identification. Open loop experiments and numerical optimization are used for tuning some of the unknown model parameters and for quantifying their influence. The resulting model is validated and matches closely the measured response.
Deformation Twinning During Impact of a Titanium Cylinder: Numerical Investigation
Authors: Lapczyk I. , Rajagopal K. R. , Srinivasa A. R.
Published: November 2021

It is well known that polycrystalline metals (especially those with bcc or hcp structures), when subjected to impact, undergo two inelastic processes — slip and twinning. Since the work of Taylor (1948) the former one has been studied extensively; while more recently, deformation twinning has attracted attention of some researchers, e.g. Bolling & Richman (1965), Armstrong & Worthington (1974) and Zerilli & Armstrong (1988). Zerilli and Armstrong (1988) suggested that the major effect of twinning is a refinement of the grain size. Based on this assumption, they proposed a model for twinning and showed that much better agreement with experiments can be obtained if, in addition to deformation by slip, deformation twinning is also considered. Similar conclusions were reached by Holt, Mock, Zerilli and Clark (1994) who analyzed the Taylor impact of a titanium specimen.

In this study, we model the Taylor impact of a titanium cylinder. We assume that the problem is axisymmetric and solve the full dynamic equations by using the Galerkin finite element method. Our results show that the energy absorbed during twinning and the deformation due to twinning are relatively small. We also demonstrate the dependence of the results on the initial grain size of the material. Specifically, by modeling two materials of widely differing grain sizes, we show that the long-grained material twins substantially more than the small-grained material.
Mechanics of Random Fiber Networks
Authors: Ostoja-Starzewski M. , Stahl D. C.
Published: November 2021

Paper has a multiscale structure, including a spectrum of features: macro-fluctuations (scale of tens, hundreds, thousands … of meters), streaks (scale of meters), flocs (scale of centimeters), single cellulose fibers (scale of millimeters), cellulose fiber being a composite helically wound from fibrils (scale of tens of microns), fibrils (submicron scale), and molecular chains (tens through thousands of Angstroms). This complexity is the root cause of various size-scale effects in mechanics (elasticity and strength) of paper. We outline a micromechanics model of paper which provides a bridge from the scale of interacting fibers to a statistical continuum approximation. The model accounts for a 3-D random geometry of fiber networks with any degree of fiber flocculation, and employs a Timoshenko beam with torsion for each fiber segment (between two contiguous fiber-fiber bonds). The fiber-fiber bonds are treated as either rigid or flexible. The model involves a computational mechanics of thousands of fibers, in which global failure occurs on microscale through fracture of a fiber segment and/or fracture of a fiber-fiber bond. We also report on the scale effects and statistics of effective mechanical (elastic and strength) responses due to a nonuniform paper formation.
Active Control of Translating Media With an Arbitrarily Varying Length
Authors: Zhu W. D. , Ni J. , Huang J.
Published: November 2021

In this paper we determine the general control laws for point-wise controllers that dissipate energies of vibration of translating strings and beams with an arbitrarily varying length. Special domain and boundary control laws that can be easily implemented result as a special case. Sufficient conditions for uniform and uniform exponential stability of controlled systems are established via Lyapunov stability criteria. Numerical simulations demonstrate the effectiveness of active controllers in stabilizing translating media during both extension and retraction. Optimal gains leading to the fastest rates of decay of energies of vibration of controlled systems are identified. It is shown that under the optimal control gains, translating media can be completely stabilized during extension and retraction.
Failure Modes in Sandwich Beams With Composite Face-Sheets and PVC Foam Cores
Authors: Steeves Craig A. , Fleck Norman A.
Published: November 2021

Sandwich beams with glass-fibre reinforced plastic faces and PVC foam cores were manufactured and tested in three point bending. The experiments were compared with analytical predictions of beam behaviour for three failure modes: face microbuckling, core shear collapse, and local indentation. A new model for indentation failure was developed which gives accurate predictions for ultimate strengths of sandwich beams that fail due to indentation.
Real Time Experimental Investigation of Dynamic Failure Mode Selection in Sandwich Structures
Authors: Xu Luoyu R. , Rosakis Ares J.
Published: November 2021

Past studies of dynamic failure in sandwich structures have mostly been concerned with post-mortem investigations of failure patterns resulting from the dynamic loading of such structures through projectile impact. The final fracture patterns have typically been very complex and their time sequence, interdependence, and detailed nature (opening versus shear) were unclear. In the present work we concentrated on the real-time investigation of the generation and the subsequent evolution of dynamic failure that occurred within microseconds after impact. Model sandwich structures involving a combination of transparent polymers and metals (typically tri-layers bonded together by weak or strong adhesives) were designed and subjected to impact loadings to study the failure evolution mechanism. High-speed photography and dynamic photoelasticity were utilized to study the nature and the sequence of failure modes. A series of complex failure modes was observed. In most cases, interfacial cracks (dynamic delamination) appeared first. These cracks were shear dominated and were often intersonic. Thus, initial delamination was found to be shear driven and happen at extremely short time scales even at moderate impact speeds ranging between 20 to 50 m/s. The transition behavior between interlayer crack growth and intralayer crack formation was also observed. Opening (subsonic) intralayer cracks kinking from the dynamic shear delamination propagated into the core layer of the model sandwich structure and eventually branched as they reached a high enough growth speed.
Effect of Implanted Delamination and Core Density on the Buckling Behavior of Sandwich Composites
Authors: Mahfuz Hassan , Islam Syful , Carlsson Leif , Atkins Makeba , Jeelani Shaik
Published: November 2021

Foam core sandwich composites have been fabricated using innovative co-injection resin infusion technique and tested under in-plane compression. The sandwich construction consisted of Klegcell foam as core materials and S2-Glass/Vinyl ester composites as face sheets. Tests were conducted with various foam densities and also with implanted delamination between the core and the face sheet. The intent was to investigate the effect of core density, and the effect of core-skin debonds on the overall buckling behavior of the sandwich. Analytical and finite element calculations were also performed to augment the experimental observations. It has been observed that core density has direct influence on the global buckling of the sandwich panel, while embedded delamination seem to have minimal effect on both global as well as local buckling. Detailed description of the experimental work, finite element modeling and analytical calculations are presented in this paper.
Elasticity Solutions for a Sandwich Orthotropic Cylindrical Shell Under External/Internal Pressure, and Axial Load
Authors: Kardomateas George A.
Published: November 2021

The elasticity solution is constructed for a cylindrical sandwich shell under external and/or internal pressure and for the same shell under axial load. The solution is an extension of the one for a homogeneous, monolithic shell and is provided in closed form. All three phases, i.e., the two face-sheets and the core are assumed to be orthotropic. Moreover, there are no restrictions as far as the individual thicknesses of the face-sheets and the sandwich construction may even be asymmetric. These solutions can be used as benchmarks for assessing the performance of various sandwich shell theories. Illustrative results are provided in comparison to the sandwich shell theory.
Sandwich Shell Model With Woven Fabric Facings for Nonlinear Finite Element Simulation
Authors: Tabiei Ala , Tanov Romil
Published: November 2021

This paper presents a micromechanical model for analysis of woven fabric composites. The micro model is coupled with a shell element developed for the analysis of sandwich structures. Starting with the average strains in the representative volume cell and based on continuity requirements at the sub-cell interfaces, the strains and stresses in the composite constituents are determined as well as the average stresses in the lamina. In their formulation the developed micromechanical models take into consideration all components of the 3-D strain and stress tensors. The formulation is implemented in the explicit nonlinear finite element code DYNA3D. The performance of the model is assessed through couple of examples. The simplicity of formulation makes this model attractive for the nonlinear finite element analysis of sandwich composite structures with woven facings.
Bubble Formation at Impingement of a Liquid Droplet on a Solid Surface
Authors: Fujimoto Hitoshi , Ogino Tomoyuki , Takahashi Osamu , Takuda Hirohiko , Hatta Natsuo
Published: November 2021

The collision of liquid droplets with a solid has been studied experimentally. The time evolution of the liquid/solid contact area as well as the shape of droplets has been observed by means of a flash-photographic method using two video cameras. It has been found that some air between the solid surface and the incoming droplet is entrapped at the moment of impact. In the case where the solid temperature is high (= 450 °C), numerous vapor bubbles appear at the liquid/solid interface after the collision. The bubble formation due to the entrapment of air has been examined for various experimental conditions. Water, and ethanol are used as test liquid. The droplet diameter is 2.4 mm for water and 1.9 mm for ethanol. The impact velocity varies from 0.8 to 3.1 m/s. The entrapment of air has been observed for both liquids under all conditions in the present study.
Spark Discharge Induced Flame Kernel Growth
Authors: Arpaci Vedat , Agarwal Apoorva , Ko Yongseo
Published: November 2021

An intuitive study of the growth of a flame kernel immediately following a spark discharge is presented. It is shown that the radius of the flame kernel, R grows with time, t as R ∼ ( Δ E ρ o ) 1 / 5 t 1 / 5 where ΔE is the integrated energy (∫ Edt) deposited by the spark discharge and ρo is the initial ambient density. The 1/5 scaling law is confirmed by comparing with measurements in a quiescent combustion bomb.

If the energy is deposited or released instantly (e.g. in an atomic explosion), the growth of a blast wave can be shown to scale with time as R ∼ ( E ρ o ) 1 / 5 t 2 / 5 . This is the same result obtained by Sir Geoffrey Taylor for a blast wave formed by a very intense explosion.

A similarity analysis of the governing equations of mass, momentum and energy is performed to reveal the internal structure of the spark-induced flame kernel as a function of its radius.
Direct Numerical Simulation of Turbulent Spray Combustion
Authors: Réveillon J.
Published: November 2021

Turbulent combustion of two-phase flows is studied by 2D direct numerical simulation. A spray of droplets is injected inside a jet with a preheated coflow. Triple flames appear to represent the global structure of the flame around the spray. Attention is focused upon global and local flame structures and droplet histories. A whole range of combustion phenomena are observed and described. The observed prevailing occurrence, for example, of the rich premixed flame compared to the diffusion flame is of great importance for any turbulent combustion model which must accurately estimate the heat release rate. This prevailing structure depends strongly on the droplet size and combustion. A competition between premixed and diffusion regimes may also occur. It has been shown that in some cases, local clusters of droplets are able either to cross the main flame front and burn in pure oxidizer or to break through the diffusion flame. It is observed that very complex interactions can emerge locally between premixed flames, diffusion flames and droplets.
Three-Dimensional Stereo Measurements in Bubbly Pipe Flows With Particle Tracking Velocimetry
Authors: Ortiz-Villafuerte Javier , Hassan Yassin A. , Schmidl William D.
Published: November 2021

In a two-phase bubbly flow, the continuous phase velocity field can be captured using standard PIV techniques, and the gas phase configuration can be determined using, for example, a shadow technique. If the PIV system includes a three-dimensional shadow PIV measurement set up, the bubble locations in the standard PIV measurements can be determined. Then, the bubble images are removed, and a typical anlysis of the liquid phase can be performed. An experimental set up that combines the traditional PIV technique with a shadow technique will be described and sample PIV images will be analyzed to demonstrate an advanced velocity vector analysis method in a two-phase bubbly flow system.
Evolution of Vortices Behind Single Diamond-Shaped Cylinders in Free Stream
Authors: Torii Shuichi , Yang Wen-Jei , Umeda Shinzaburo
Published: November 2021

Two-dimensional flow over a single diamond-shaped cylinder in the free stream are experimentally and theoretically investigated. The experimental program includes visualization of the flow field using the tracer method. In the theoretical program, the Navier-Stoeks equations are discretized using finite difference methods to determine the time history of velocity vector distribution in the flow field. Efforts directed to examine the effects of the Reynolds number, Re, and the upstream angle of the diamond shape, θ, on flow phenomena. The study discloses that (i) the generation of von Karman vortex streets behind the diamond-shaped cylinder are intensified with an increase in the Reynolds number, (ii) the flow pattern in the wake region of the diamond-shaped island is affected by θ, and (iii) the relationship among the Strouhal number, St, Re and θ is determined and compared with the existing St-Re relationship for flow over a circular cylinder.
Effects of Riblets on Goertler Vortex Flow
Authors: Winoto S. H. , Chen X. , Shah D. A.
Published: November 2021

To investigate the effects of riblets on the onset of Goertler vortex flow transition, an experiment was carried out on a ribletted concave surface of 2.0 m radius of curvature in a perspex curved rectangular duct connected to a low speed wind tunnel. Semi circular section riblets with height (h) of 1.0 mm and spacing (s) of 2.2 mm (that is, with h/s = 0.48) were used. The investigation was carried out by means of measurements using a single sensor hot wire anemometer. The boundary layer transitions were detected by turbulent intermittency measurements using the modified turbulent energy recognition algorithm (M-TERA) method. The experimental results obtained show that for free-stream velocities of 3m/s and 6m/s, boundary layer transition on the ribletted concave surface starts and ends slightly earlier than on the corresponding smooth concave surface. However, for free-stream velocities of 9m/s and 12m/s, the boundary layer transitions (both the starts and the ends) on the ribletted concave surface were delayed compared to the Goertler vortex flows on the corresponding smooth concave surface.
Numerical Simulation of Taylor Vortex Flow by GDQ Method
Authors: Wang L. , Shu C. , Chew Y. T.
Published: November 2021

In this study, the GDQ method was used to simulate a specific flow regime, Taylor vortex flow, of the motion of fluids between two concentric cylinders with rotating inner cylinder and stationary outer cylinder. An approach combining the SIMPLE strategy and GDQ discretization based on non-staggered mesh was proposed to solve the time-dependent, three-dimensional incompressible Navier-Stokes equations in primitive variable form. The numerical solution obtained has the accuracy of second-order in temporal discretization and high-order in spatial discretization. Also, this numerical code may allow the direct numerical simulations for the various regimes of Couette-Taylor flow problem. The performance of this approach was studied through a test case of Taylor vortex flow. The reported numerical results were compared with those from others. For this approach, accurate numerical results can be obtained by using fewer grid points compared with low-order methods. As a consequence, the computational effort can be greatly reduced.
Two-Dimensional Study of the Turbulent Wake Behind a Square Cylinder Subject to Uniform Shear
Authors: Saha A. K. , Biswas G. , Muralidhar K.
Published: November 2021

The flow past a square cylinder at a high Reynolds number has been simulated through direct calculations and through the calculations using turbulence models. The present investigation highlights significant differences between the two approaches in terms of instantaneous flow, Strouhal number and the aerodynamic forces. The time-averaged drag coefficient and the rms fluctuations due to the direct calculation are higher than those due to the turbulence model. However, Strouhal number is underpredicted in direct calculations. The effect of shear on the flow has also been determined using the turbulence model. The time-averaged drag coefficient is found to decrease with the increase in shear parameter up to a certain value. Then it increases with the further increase in the shear parameter. On the other hand, the lift coefficient increases with the increase in shear parameter. Strouhal number shows a decreasing trend with the increase in shear parameter whereas the rms values of the drag and lift coefficients increase with the shear parameter. Kármán Vortex Street, mainly comprising of clockwise vortices due to shear, decays slowly compared to uniform flow condition.
Characterization of Wide Area Network Computing
Authors: Freitas Christopher J. , Coffin Derrick B. , Murphy Richard L.
Published: November 2021

Distributed parallel computing using message-passing techniques on Networks of Workstations (NOW) has achieved widespread use in the context of Local Area Networks (LAN). Recently, the concept of Grid-based computing using Wide Area Networks (WAN) has been proposed as a general solution to distributed high performance computing. The use of computers and resources at different geographic locations connected by a Wide Area Network and executing a real application introduces additional variables that potentially complicate the efficient use of these resources. Presented here are the results of a study that begins to characterize the performance issues of a WAN-based NOW, connecting resources that span an international border.
Simulation of Solid-Fluid Interactions on Cartesian Grids
Authors: Udaykumar H. S. , Mittal R. , Rampunggoon P.
Published: November 2021

We present a numerical technique for computing flowfields around moving solid boundaries immersed in flows on fixed meshes. The mixed Eulerian-Lagrangian framework treats the immersed boundaries as sharp interfaces and a finite volume formulation for the flow solver allows boundary conditions at the moving surfaces to be exactly applied. A second-order accurate spatial and temporal discretization is employed with a fractional-step scheme for solving the flow equations. A multigrid accelerator for the pressure Poisson equations has been developed to apply in the presence of multiple embedded solid regions on the mesh. We validate the numerics by comparing against experimental and numerical results on two problems: 1) The flow in a channel with a moving indentation in one wall and 2) The dynamics of vortex shedding from a cylinder oscillating in the free-stream.
The Effect of Discontinuity Size on the Initiation of Shattered Rim Defects
Authors: Stone Daniel H. , Dahlman Geoffrey E.
Published: November 2021

Shattered rim defects are the result of large fatigue cracks that propagate roughly parallel to the wheel tread surface. They form and grow 12 to 20 millimeters (1/2 to 3/4 in.) below the tread surface. A typical shattered rim is shown in Figure 1. The clamshell pattern of the fracture surface is also typical of shattered rims. The clamshell pattern is formed because fatigue cracks at this depth in wheels have a shear component and, when the rolling direction is opposite, the cracks grow in a different direction forming a series of ridges and valleys. Miezoso, et alia have presented a mixed mode fracture mechanics analysis of the process of forming a clam-shell fatigue crack surface in wheels.
Rail Passenger Equipment Crashworthiness Testing Requirements and Implementation
Authors: Tyrell David , Severson Kristine , Perlman A. Benjamin , Brickle Barrie , VanIngen-Dunn Caroline
Published: November 2021

This paper describes the requirements and the implementation of a series of impact tests of rail passenger equipment. The test requirements — the desired measurements — are dictated by the characteristics of the vehicle, as well as uncertainties in the analysis techniques used to evaluate the collision behavior of the equipment. The required measurements are implemented with available measurement transducers, including accelerometers, strain gages, and string potentiometers. The measurement data are gathered using an on-board data acquisition system.
Manufacture of Multi-Direction Composites (MDC) Flywheels
Authors: Abdel-Hady Faissal , Gowayed Yasser , Flowers George T.
Published: November 2021

The design and manufacture of a universal winding and tape laying machine has been developed is presented in this paper. This machine is used to manufacture a multi-direction composite (MDC) flywheel. The machine is capable, due to its modular design, to be used in wet filament and tape laying either with thermoset or thermoplastic prepregs. The MDC flywheel rims are realized by assembling the radial plies with hoop rings in a special assembly mold.
Fatigue of Notched CMC Plates Under Variable Thermomechanical Loads
Authors: Nagar Arvind , Xie Ming
Published: November 2021

The work is a part of a major study to develop design analysis methods for strength and life of CMC structural joints. This paper describes results of thermomechanical fatigue tests conducted on open hole ceramic matrix composite laminated plates. The open hole represent the zero load transfer in a joint. The thermomechanical spectrum loads included mechanical load cycle blocks of various stress levels and stress ratios. The thermal loads were varied simultaneously with mechanical loads for the duration of a representative generic flight. The spectrum peak stress versus life data was developed for the case when the peak temperature is 1500 F. An empirical relation to describe the fatigue life is presented. The results show that a CMC laminate with an open hole spend most of the life during initiation.
An Alternative Design Approach for Vehicle Crash Safety Using Crash Pulse Optimization
Authors: Yang R. J. , Tho C. H. , Gearhart C. C. , Fu Y.
Published: November 2021

This paper presents an approach, based on numerical optimization techniques, to identify an ideal (5 star) crash pulse and generate a band of acceptable crash pulses surrounding that ideal pulse. This band can be used by engineers to quickly determine whether a design will satisfy government and corporate safety requirements, and whether the design will satisfy the requirements for a 5 star crash rating. A piecewise linear representation of the crash pulse with two plateaus is employed for its conceptual simplicity and because such a pulse has been shown to be sufficient for reproducing occupant injury behavior when used as input into MADYMO models. The piecewise linear crash pulse is parameterized with 7 design variables (5 for time domain and 2 for acceleration domain) in the optimization process. A series of sample runs are conducted to validate that pulses falling within the acceptable crash pulse band do in fact satisfy 5 star requirements.
Free Vibration of In-Planar Rotating Ring: An Analytical Solution
Authors: Hamidzadeh Hamid R.
Published: November 2021

An analytical method is presented to consider the vibration characteristics of high speed rotating rings. More specifically, a systematic approach based on an established solution for linear in-plane vibration of spinning annular disks is used to compute natural frequencies and mode shapes of rotating rings. The medium is considered to be homogenous, and elastic isotropic. The developed analytical solution is achieved by implementing the two-dimensional plane stress theory. The modal displacements and stresses at both inner and outer boundaries are determined, and the required boundary conditions are satisfied to obtain the frequency equation. The dimensionless natural frequencies for different modes, rotating speeds, and thickness ratios are computed. In addition, variations of dimensionless critical speeds for several circumferential wave numbers versus radius ratio of the ring are presented. The provided results are for the two different cases of clamped-free and free-free rings.
Blind Identification of Impact Forces From Multiple Remote Vibratory Measurements
Authors: Antunes J. , Izquierdo P. , Paulino M.
Published: November 2021

Structures and mechanical components are often subjected to impulsive forces. There is a need for identification techniques which enable monitoring of such loads under operating conditions. For safety reasons and convenience, force identification must often be based on response motions sensed at accessible locations, remote from the impact points.

In our previous work we presented techniques for the experimental identification of both isolated impacts and complex rattling forces on a beam, generated at a single and also at several impacting supports. The system dynamical behavior was modeled using traveling flexural beam waves. Although successful, these techniques obviously assume a good understanding of the system dynamic parameters.

This is not always the case, a fact that highlights the practical interest of blind identification techniques. This relatively recent field, connected with higher-order statistics, avoids any explicit knowledge of the system transfer functions or impulse responses. Our previous work, based on a single response measurement, is extended in this paper to include several simultaneous responses.

We develop a multi-trace version of Wiggins minimum-entropy blind deconvolution algorithm. From numerical simulations and experiments, it is shown that the robustness to noise contamination is increased by using multiple response data. These results suggest that blind identification techniques will prove very useful in practical situations.
Simulation of Vibration and Acoustic Radiation of Finite Underwater Cylindrical Shells
Authors: Zhang X. M. , Liu G. R. , Lam K. Y.
Published: November 2021

A coupled structural-acoustic analysis of vibration and sound radiation of underwater finite cylindrical shells is investigated in this paper. The coupled vibration and radiation problem is formulated using Finite Element Method (FEM) for the structure and Boundary Element Method (BEM) for the acoustic domain. Vibration and sound radiation under symmetrical and unsymmetrical point force excitations are examined. It is shown that the coupled modals are the causes of large vibration of the shell and high sound pressure radiation of the acoustic fields. The shapes of frequency response curves of pressure are quite similar in the far fields but change greatly in the near fields.
A Macromodel for Dynamic Simulation of Microelectromechanical Systems
Authors: Lin W. Z. , Lee K. H. , Lim S. P. , Lu P.
Published: November 2021

This paper describes a method of model reduction by using Karhunen-Loève decomposition and Galerkin procedure to effectively perform the dynamic simulation and analysis of nonlinear microelectromechanical systems and devices. The Karhunen-Loève decomposition is a procedure for extracting a basis for a modal decomposition from an ensemble of signals, e.g. numerical or experimental data, thus converts the original systems into a lumped low-order macromodel with minimum number of degree of freedom. The macromodel can be used to carry out the dynamic simulation of the original systems resulting in dramatic reduction of computation time while not losing flexibility and accuracy. The method is evaluated to simulate the pull-in dynamics of a microrelay MEMS device, e.g. doubly clamped microbeam, subjected to different input voltage spectrum of electrostatic actuation. The results are compared with those of the fully meshed finite difference method (FDM) and found to be very accurate, efficient and flexible.
Nonlinear Dynamic Analysis of Rotor Supported by Finite Journals With a New Unsteady Nonlinear Oil-Film Force Model
Authors: Zhang Wen , Guo Jianping , Qiu Pengqing
Published: November 2021

A new approximate method for evaluating oil-film force acting on a finite journal bearing with unsteady and larger perturbed motion is presented. The nonlinear dynamic analysis of rotor supported by finite oil-film bearings is carried out by the new oil-film force model. Unsteady and large perturbed motion of journal is considered. From the numerical results the following conclusions are obtained: 1. At very low speed, oil-film force can be ignored, the motion is synchronous whirl. It is unbalance response motion. 2. At very high speed or lager eccentricity, unbalance force prevails over the influence of oil-film force. The motion is also synchronous and stable. 3. In the middle interval of speed, oil-film force and unbalance force have the same order of magnitude, or oil-film force play the main role, the motion is much complex. The nonlinear properties are appeared obviously. The running danger of the rotor would be happened in this running interval.
Time-Varying Modal Analysis by SDOF Wavelets
Authors: Masuda Arata , Sone Akira
Published: November 2021

The purpose of this paper is to provide a modal expression of a time-varying MDOF system and to develop an identification method for it. The single-input-multi-output relation of a time-varying N-DOF system is expressed as a superposition of N time-varying SDOF subsystems in the time domain, where the expansion coefficients represent the time-varying mode-shapes, and the natural frequency and the damping ratio of each subsystem represent the time-varying modal parameters of each mode. Then we define the SDOF wavelets, which correspond to the time-varying impulse responses of SDOF subsystems and show that the output of the entire system can be expressed by a superposition of SDOF wavelets. Then, the identification problem is reduced to an atomic decomposition problem of choosing the nearly best set of SDOF wavelets and determining the expansion coefficients. We develop a modified matching pursuit algorithm, called modal pursuit, to solve the problem. Basic examples are numerically examined to show that the proposed modal representation and the identification method are applicable to track the modal characteristics of time-varying systems.
Using Analytical/Numerical Matching With Finite Element Analysis to Solve a Fluid-Loaded Structural Dynamics Problem
Authors: Park Christopher D. , Franzoni Linda P.
Published: November 2021

Two model problems are solved using a combination of Analytical/Numerical Matching (ANM) and Finite Element Analysis (FEA). The first problem is that of a thick, finite length beam driven by the motion of a small rigid support attached to its lower boundary. The second problem is a thick, infinitely long fluid-loaded beam driven by the motion of periodically spaced rigid supports (identical to the support of the first problem). The ANM process divides an original problem into local, matching, and global sub-problems through the use of a smooth force and the principle of superposition. In the two model problems presented, the same high-resolution local (in vacuo) problem is solved using FEA. The fluid loading effects can be accounted for entirely by the global problem. The problems presented show that ANM is a computationally efficient method that retains the high accuracy needed near structural discontinuities.
Theoretical and Experimental Studies of Local Tissue Temperature Oscillation Under Hyperthermic Conditions Using Preserved Pig Kidney
Authors: Chen Cuiye , Xu Lisa X.
Published: November 2021

It has been long recognized that local tissue temperature may osculate due to vascular thermo-regulation under hyperthermic conditions. To effectively heat the target tissue while sparing its surroundings, it is necessary to understand and then to control the temperature oscillation. A model based on the pig kidney vasculature was developed to study the transient temperature variations in the kidney when subjected to heating in a thermal bath. In the medullary region, a vascular model previously developed in (Chen and Xu, 2000) was used to account for the conjugate heat transfer between the paired artery and vein, and their surrounding tissue. Considering that numerous small vessels exist in the cortex region, the Pennes bio-heat transfer equation was used for modeling in this region. A code was written to numerically compute the 3-D transient temperature distribution in the kidney subjected to heating. To examine the validity of the model, experiments were performed to measure the temperatures and perfusion rates using thermistor microprobes in the cortex of the preserved pig kidney. This model will be utilized for future studies to investigate the relationships among the local blood perfusion rate, the heating rate, and the tissue temperature oscillation.
An Analysis of Unicellular Mass Transfer Using a Microfabricated Experimental Technique
Authors: Howard Kelvan , Rubinsky Boris
Published: November 2021

This study introduces a microfabricated chamber which allows individual cells to be maintained between two different flow paths while kinetic volume changes and membrane permeability are measured. For HBL-100 cells, the data yielded a water permeability (Lp) of 1.1 ±0.5 μm/(min-atm) (mean ± 1 standard deviation) (N = 5) during the uncoupled transport of water at 22°C. In the presence of 6M glycerol, the water permeability (Lp), permeability coefficient (Ps), and the reflection coefficient (σs) were determined to be 2.0± 0.63 μm/(min-atm), 2.7×10E-5 ±6.1×10E-6 cm-sec−1, and 0.76±.05 (N = 6). No previous values of these coefficients could be found for HBL-100 cells.