bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of the Effect of Pressure on the Thermal Conductivity of Silica Aerogel Particles
Authors: Vakil Sachin S. , Hosticka Bouvard , Norris Pamela M.
Published: November 2021

Aerogels are highly porous solids that are made out of a variety of materials such as silica, alumina, or zirconia. Silica aerogel, under a modest vacuum, has the lowest thermal conductivity of any known solid. Values as low as 0.008 W/mK have been reported. While monolithic aerogel is fragile, expensive, and difficult to work with, silica aerogel particles may pose a viable, cost-effective alternative as a thermal insulator. This study details thermal conductivity tests on silica aerogel particles at various pressures. An apparatus that enables cost effective and simple measurements of the total thermal conductivity of aerogel particles at a range of pressures is described. The apparatus employs a platinum resistor placed in the center of a glass spherical bomb filled with aerogel particles. The resistor is the heat source, whose direction of heat flow can easily be traced. Drawing on basic principles of heat transfer, the thermal conductivity of the aerogel particles is found by developing a heat balance to model the data gathered from the apparatus. Furthermore, to test the effects of pressure, a vacuum is used to reduce the pressure and to thus decrease the effective thermal conductivity. Crushed aerogel particles with diameters no greater than 300 μm were found to have thermal conductivities which fell within the same order of magnitude as bulk silica aerogel and the overall thermal conductivity decreased with decreasing pressure, as has been reported with monolithic aerogel.
Thermal-Fluid Transport Phenomena in Concentric Annulus With Inner Core Rotation Under Strong Heating
Authors: Torii Shuichi , Yang Wen-Jei
Published: November 2021

A numerical study is performed to investigate thermal-fluid transport phenomena in a concentric annulus, in which an axially rotating inner cylinder and stationary outer cylinder are strongly heated under the same heat flux. The anisotropic t 2 ¯ -εt heat-transfer model is employed to determine thermal eddy diffusivity. When the inner cylinder is at rest, the turbulent kinetic energy and temperature variance over the whole cross-section in the flow and thermal fields substantially diminish along the flow, resulting in laminartization, i.e., a deterioration in heat transfer performance at the inner and outer cylinder walls. By contrast, a substantial reduction in the turbulent kinetic energy and temperature variance in the laminarzing flow are suppressed in the presence of inner core rotation. In other words, an inner core rotation contributes to a suppression of laminarization of the strongly heated gas flow.
An Interdisciplinary Approach to Brain Tumor Growth Dynamics
Authors: Torquato Salvatore , Deisboeck Thomas S.
Published: November 2021

Intensive medical research over the last fifty years has left the prognosis for patients diagnosed with malignant brain tumors nearly unchanged. This suggests that a new perspective on the problem may offer important insight. We have undertaken an interdisciplinary research program, seeking to study brain tumors as complex systems. This research aims to develop computational models coupled with experimental assays to investigate the hypothesis of self-organizing behavior in tumor systems. Preliminary assays have revealed behavior consistent with this hypothesis. A cellular-automaton model to study the growth of the tumor core has been developed. This model has proven successful in reproducing macroscopic tumor growth from a limited parameter set. Further, it has been applied to investigate the importance of heterogeneity to determination of a clinical prognosis and has demonstrated the importance of understanding clonal composition in making an accurate prognosis.
Arthropod Motion-Sensing Hairs: Biological Models for Micro-Electro-Mechanical Systems
Authors: Humphrey Joseph A. C. , Barth Friedrich G.
Published: November 2021

The filiform hairs of terrestrial and aquatic arthropods are uniquely sensitive medium motion sensors, refined by natural selection pressures over hundreds of millions of years. These sensors provide biological models for the design and fabrication of corresponding artificial sensors that could be used for fundamental research as well as practical applications. However, the measurement and modeling of filiform hairs poses a highly complex interdisciplinary problem involving various facets of biology, mechanics and mathematics. Specifically, it is of special interest to uncover the basic “design” principles affecting the maximum angular deflection and maximum angular velocity, and their respective resonance frequencies, of the hairs as a function of the physical parameters that affect these four quantities. To this end, the physically-approximate theoretical analysis of Humphrey et al. (2000) is used to predict and understand the performance characteristics of single hairs. Calculated results obtained using the approximate analysis compare well with corresponding results from a more exact physical analysis and with previous measurements and calculations, showing that all qualitative aspects of hair behavior are correctly captured by the simplified theory. The theory is then used to explain the dependence of hair motion on the physical parameters that affect it. The findings of this study suggest that an artificial motion-sensing micro-electro-mechanical system (MEMS), patterned along the lines of an array of hairs, could be designed to detect and resolve the temporal and spatial characteristics of unsteady flow structures in the near-wall region of boundary layer flows.
Design, Fabrication and Heat Transfer Analysis of a Mesoscopic Pulse Tube as an Integrated Micro-Refrigeration System
Authors: Shinde Ninad , Bashir Rashid , Groll Eckhard , Chiu George
Published: November 2021

The phenomenon of surface heat pumping has been widely used to accomplish refrigeration in macro-scale devices such as pulse-tubes and thermo-acoustic devices. Pulse tube refrigerators are typically used to lift heat at cryogenic temperatures. The advantage of a pulse tube as a no moving part device makes it amenable to miniaturization at dimensional scales where areal effects, such as friction and viscosity, dominate. In this paper, the design and preliminary fabrication results of such a device to investigate the effect of surface heat pumping in mesoscopic glass channels are presented.
Scanning Thermal Wave Microscopy
Authors: Kwon O. , Shi L. , Miner A. , Majumdar A.
Published: November 2021

This paper reports the development of a new technique for nanometer-scale thermal imaging and thermal property measurement — scanning thermal wave microscope (STWM). By raster scanning a sharp temperature-sensing probe the STWM measures the distribution of the phase lag and the amplitude of a thermal wave on the sample surface at a certain distance away from the heat source. As a benchmark experiment for this technique, the phase lag distribution of a thermal wave generated by a line heat source on a Pyrex glass sample was measured and compared with analytical solution. The effect of liquid film at the tip-sample contact on the measured phase lag was also studied. The ability of STWM to locate sub-surface heat source in a ULSI circuit was experimentally demonstrated.
Neural Network Modeling of Molecular Beam Epitaxy
Authors: Lee Kyeong K. , Brown Terence , Dagnall Georgianna , Bicknell-Tassius Robert , Brown April , May Gary
Published: November 2021

This paper presents the systematic characterization of the molecular beam epitaxy (MBE) process to quantitatively model the effects of process conditions on film qualities. A five-layer, undoped AlGaAs and InGaAs single quantum well structure grown on a GaAs substrate is designed and fabricated. Six input factors (time and temperature for oxide removal, substrate temperatures for AlGaAs and InGaAs layer growth, beam equivalent pressure of the As source and quantum well interrupt time) are examined by means of a fractional factorial experiment. Defect density, x-ray diffraction, and photoluminescence are characterized by a static response model developed by training back-propagation neural networks. In addition, two novel approaches for characterizing reflection high-energy electron diffraction (RHEED) signals used in the real-time monitoring of MBE are developed. In the first technique, principal component analysis is used to reduce the dimensionality of the RHEED data set, and the reduced RHEED data set is used to train neural nets to model the process responses. A second technique uses neural nets to model RHEED intensity signals as time series, and matches specific RHEED patterns to ambient process conditions. In each case, the neural process models exhibit good agreement with experimental results.
Flow Regimes and Transitions in a Rapid Chemical Vapor Deposition Reactor Using Flow Visualization and Rayleigh Light Scattering
Authors: Mathews Angelo G. , Peterson Jill E.
Published: November 2021

Previous study of carrier gas flow in rapid chemical vapor deposition (RCVD) reactors has been limited mostly to numerical simulations and flow visualizations. In the present work flow regimes were observed and temperatures were measured in a vertical axisymmetric pedestal RCVD reactor using flow visualization and Rayleigh light scattering (RLS) for noninvasive temperature measurement. Flow visualizations revealed that the flow undergoes complex transitions between stable flow regimes as heating occurs. The two dominant stable flow regimes were buoyant stable (BS) and momentum stable (MS). RLS was used to determine the instantaneous carrier gas temperature at discrete points in the test section. The flow regimes and their transition points were easily recognized and agreed with flow visualization data. The flow visualizations and RLS tests showed identifiable trends in transition points between flow regimes and in the types of regimes encountered. These trends were dependent on Grashof number and Reynolds number.
Thermal Analysis of Solidification in a Czochralski-Type Rotating System
Authors: Xu J. , Ferland M. , Zhang H. , Prasad V.
Published: November 2021

A continuum solidification model is used to study transport phenomena in a simulated Czochralski system for various rotation rates of the crystal and crucible. Solidification occurs on a cylindrical seed from the top surrounded by water in the crucible. An enthalpy formulation is adopted for numerical solution of convection-diffusion controlled solidification problems. Predicted solid-liquid interface and temperature distribution are in good agreement with the liquid crystal visualization experiments.
Prediction of Heat Transfer Coefficients Under Sub-Cooled Boiling Conditions
Authors: McAssey Edward V. , Wu Jinfeng , Dougherty Thomas , Yang Bao Wen
Published: November 2021

Data are presented for sub-cooled boiling of water in the range of two to four atmospheres. The results show that the sharp increase in heat transfer coefficient associated with nucleate boiling occurs at wall superheats of 20 °C to 30 °C. Comparisons between experimental and predicted heat transfer coefficients are also presented. The two prediction methods examined are the Chen correlation and the Kandlikar correlation.
Two-Phase Flow Regime Transitions in Microchannel Tubes: The Effect of Hydraulic Diameter
Authors: Coleman John W. , Garimella Srinivas
Published: November 2021

An experimental investigation of two-phase flow mechanisms during condensation of refrigerant R134a in small diameter round and rectangular tubes was conducted. A 4.91 mm round tube, and four round tubes with hydraulic diameters ranging from 1 mm – 4 mm were studied to characterize the influence of tube miniaturization on the flow mechanisms. For each tube under consideration, flow mechanisms were recorded over the entire range of qualities 0 < x < 1, and for five different mass fluxes between 150 kg/m2-s and 750 kg/m2-s. Approximately 50 data points were recorded for each tube to obtain a comprehensive understanding of the effects of geometry, mass flux and quality on the phase-change flow mechanisms. The flow mechanisms were categorized into four different flow regimes: intermittent flow, wavy flow, annular flow, and dispersed flow. In addition, the large amount of data over a wide range of test conditions enabled the delineation of several different flow patterns within each flow regime, which provides a clearer understanding of the different modes of two-phase flow. Transition lines between the respective flow patterns and regimes on these maps were established based on the experimental data. It was found that the intermittent flow regime becomes larger as the tube hydraulic diameter is decreased. Also, the size of the wavy flow regime decreases for the small diameter tubes, and disappears completely for the 1 × 1 mm square tube. These maps and transition lines can be used to predict the flow pattern or regime that will be established for a given mass flux, quality and tube geometry.
Experimental Study of Electrohydrodynamic Pumping Through Conduction Phenomenon
Authors: Jeong S. I. , Seyed-Yagoobi J. , Atten P.
Published: November 2021

In an isothermal liquid, only the Coulomb force which is the force acting on the free charges, can contribute to permanent electrohydrodynamic motion. In the absence of a direct charge injection, pumping can be achieved due to the charges associated with the heterocharge layers of finite thickness in the vicinity of the electrodes which are based on the process of dissociation of a neutral electrolytic species and recombination of the generated ions. This type of pumping is referred to as pure conduction pumping. The conduction pumping mechanism is experimentally investigated here with three different electrode designs. Sufficient pressure heads are generated with very low electric power requirements making the EHD conduction pumping attractive to certain applications such as capillary pumped loops and heat pipes.
A Fully Developed Two-Phase Flow Model in Vertical Channels for Bubbly and Slug Flow Regimes
Authors: Moujaes Samir , Sleight Erika
Published: November 2021

A theoretical model for steady state two-phase vertical upward flow in cylindrical channels is presented. A comparison of the results of this model for a circular channel as well as a reformulated rectangular channel model is partially made with experimental data in the literature. It shows that in general the model predicts the flow characteristics somewhat better in the bubbly regime than the slug flow indicating the need to look further into some of the constitutive relationships used to close the model in this regime.
Evaporation-Combustion Affected by In-Cylinder, Reciprocating Porous Regenerator
Authors: Park Chan-Woo , Kaviany Massoud
Published: November 2021

An existing in-cylinder thermal regeneration concept for the Diesel engines is examined for the roles of the porous regenerator motion and the fuel injection strategies on the fuel evaporation and combustion and on the engine efficiency. While the heated air emanating from the regenerator enhances fuel evaporation resulting in a superadiabatic combustion (thus increasing thermal efficiency), the corresponding increase in the thermal NOx is undesirable.

A multi-gas-zone and a single-step reaction model are used with a Lagrangian droplet tracking model that allows for filtration by the regenerator. A thermal efficiency of 52 percent is predicted, compared to 45 percent of the conventional Diesel engines. The optimal regenerative cooling stroke occurs close to the peak flame temperature, thus increasing the superadiabatic flame temperature and the peak pressure, while decreasing the expansion stroke pressure and the pressure drop through the regenerator. During the regenerative heating stroke, the heated air enhances the droplet evaporation, resulting in a more uniform, premixed combustion and a higher peak pressure, and thus a larger mechanical work.
Thermal Analysis of Lubricating Oil Flow Within a Wet-Disk Clutch
Authors: Jen Tien-Chien , Nemecek Dan
Published: November 2021

A combined theoretical and experimental thermal analysis is conducted on the oil flow between the plates of a wet clutch during an extended slip engagement. An analytical model, using the separation of variables technique, is developed to simulate the temperature rise due to the non-conservative friction and relative motion between the steel plates and friction plates of the clutch. A three-dimensional numerical heat transfer and fluid flow model was developed to calculate the velocity and temperature profiles in the oil groove channel. Typical velocity profiles and temperature contours plots are demonstrated. Friction factor and Nusselt number are presented as functions of axial position. The experiment performed included a wet clutch instrumented with thermocouples and installed in a power-shift transmission where the temperature rise during one clutch engagement was measured. The total energy is then estimated by accounting for system inertia, torque and rotating speeds. Finally, the inlet, outlet temperature rises and the averaged Nusselt number of the oil groove are also presented.
Three-Dimensional Computations of Transport and Growth for Crystal Growth Systems
Authors: Derby Jeffrey J. , Yeckel Andrew
Published: November 2021

Modern finite element methods implemented on parallel supercomputers promise to allow the study of three-dimensional, time-dependent continuum phenomena in many engineering systems. This paper shows several examples of the fruitful application of these approaches to bulk crystal growth systems, where strongly nonlinear coupled phenomena are important.
Simulation of Fluid Flow, Combustion, and Heat Transfer in a Coal-Fired Cement Kiln
Authors: Karki Kailash C. , Patankar Suhas V. , Grant Jeff
Published: November 2021

This paper presents the details of a mathematical model for fluid flow, combustion, and heat transfer in cement kilns. The model is based on the finite-volume technique for the solution of the gas-phase equations. The k-ε model is used to represent the turbulence effects. A two-step kinetics scheme is employed to simulate the gas-phase combustion. The Lagrangian formulation is employed for the particle phase, and the coupling between the particle and gas phases is handled by introducing appropriate source terms in the gas-phase equations. The particle reaction model includes coal devolatilization and char oxidation. The radiation heat transfer in the kiln is modeled using the six-flux model. The feed bed is represented as a solid region that is moving in the axial direction with a uniform velocity, which is calculated from the feed rate, feed density, and the fill area. The effect of chemical reactions in the feed bed is modeled by including temperature-dependent heat release/absorption rates in the energy equation.

The model has been applied to a cement kiln in operation. The predicted results agree with the observations and experience for the kiln.
Compressor Blade and Impeller Rotating Disk Vibration Avoidance Parameters
Authors: Kushner Frank
Published: November 2021

Interaction of rotating blades with stationary vanes is a prime consideration for disk design and vibration failure investigations. For a well-designed radial-flow impeller with a cover, the structure is inherently resistant to alternating forces at normal flow conditions. Critical parameters are reviewed with respect to excitation and response. A fundamental parametric equation originally published in 1979 is further explained and verified. Comparisons to open impellers and axial compressor blades that have additional critical design considerations are also presented. Data from strain gages on an impeller gave proof that liquid ingestion was the cause of high excitation, and validated the parametric equation for blade/vane interaction. Particular emphasis is given to avoiding high cycle fatigue failures with stages employing vaned diffusers, which are now much more prevalent. Modal analyses, as well as information from other references that confirms theories are included.
A Numerical Method for the Study of Surge and Flow Instabilities in Gas Compression Systems
Authors: Akyuzlu K. M. , Sakarepalle R. , Albayrak K.
Published: November 2021

A numerical method is developed to study the effect of various geometrical and operational parameters on the stability of flow in gas compression systems. It is hoped that this and similar type of studies will help us to understand the effect of coupling of the flow characteristics of a compressor with that of a pipeline. In this study, the gas compression system is assumed to be comprised of a compressor, a throttling valve, and a long pipe. A nonlinear lumped parameter model is used to represent the compressor. The gas flow inside the pipeline is modeled by discrete elements in which the flow is assumed to be one dimensional, viscous, and compressible. The throttling valve is modeled by a single element where the pressure drop across it is predicted through an empirical relation. The governing set of equations for the comprehensive model are linearized using explicit finite difference techniques and then solved for the unknowns of the problem. The results indicate that the amplitude and frequency of the flow oscillations experienced by the coupled system depend on the length of the pipe. The frictional losses seem to dampen the amplitude of the flow oscillations experienced in the compressor and the pipeline.
Hybrid Damping of Sound Radiated by Plates
Authors: Giovanardi Marco , Degon Brian , Cabell Ran
Published: November 2021

The scope of this work was to design and build a new concept of hybrid active and passive damping system, capable of attenuating sound radiated through structural vibration both in the high and low frequencies by combining the broadband control capabilities of constrained-layer viscoelastics with the narrowband capabilities of active control with piezoceramic actuators and sensors.

The effort was concentrated on modeling the response of a passive damper as well as a piezoelectric actuator in order to optimize the characteristics of both the active and passive damping materials, on implementing a test system and on designing a closed-loop control system to show the advantages of the hybrid approach over purely active or passive approaches.

An extensive research into the available viscoelastic materials was done to find materials with near optimal characteristics. A few of these materials were procured and tested on a simple structure to validate the model and test their performance.

It was demonstrated on a real system that this approach is feasible and has advantages over both the purely active and the purely passive approach. As a test structure, an aluminum panel similar to exterior panels in airplanes was chosen, and a hybrid control system implemented on this structure. An anechoic transmission loss facility, with the panel bolted into a wall and the plate excited by a speaker on one side, was used to determine the reduction in radiated sound achieved by the hybrid damping system.

The compensator for the active part of the damping system was designed as a simple combination of positive position feedback (PPF) filters, and implemented on a digital single-board computer (SBC).

The resulting sound radiation from the panel showed clearly the validity of the concept of hybrid damping, by achieving good reduction in sound both the low and high frequencies within the chosen band of interest, 0-800Hz, and with very little weight added. The total added mass to the aluminum panel was only about 50g, which is very small compared to the amount of mass a passive system with similar performance would weigh for the same structure.
Impact Identification Using Smart Material Sensors
Authors: Peelamedu Saravanan M. , Naganathan Nagi G.
Published: November 2021

The crash performance of an automobile largely depends on the ability to identity impact damage, maintain the passenger safety through deployment of various safety restraint systems, and steer away the vehicle from impact. So, this work is focused on the impact response of an automobile structure so as to find the location, magnitude of impact and asses the severity of damage. The results of the developed generalized forward plate model compared within 2% for FEM and previous other theoretical approaches. The inverse model compared within 7% for location and reconstructed force. Damage severity assessment is also investigated.
Dynamics of a Pipe Conveying Pulsating Flow Near Criticality
Authors: McDonald Robert J. , Sri Namachchivaya N.
Published: November 2021

In this paper, we study the dynamics of a simply supported pipe conveying pulsating flow near the flow velocity where the system first becomes unstable. We study a Galerkin discretization of this system which involves the first two modes of the pipe, near the flow velocity where the two degree of freedom Hamiltonian system possesses a nonsemisimple double zero eigenvalue and a pair of imaginary axis eigenvalues. The damping, as well as me parametric forcing due to the pulsating flow, are considered as perturbations to a conservative system. Using local bifurcation analysis and recently developed global bifurcation methods, we study the transfer of energy from the forced high frequency mode to the unforced low frequency mode. This transfer of energy causes unwanted vibrations in the mode associated with the double zero eigenvalue, due to the 0:1 resonance that this mode has with the high frequency mode.
Variation Analysis for Compliant Assembly
Authors: Hu S. Jack , Long Yufeng , Camelio Jaime
Published: November 2021

Assembly processes for compliant non-rigid parts are widely used in manufacturing automobiles, furniture, and electronic appliances. One of the major issues in the sheet metal assembly process is to control the dimensional variation of assemblies throughout the assembly line. This paper provides an overview of the recent development in variation analysis for compliant assembly. First, the unique characteristics of compliant assemblies are discussed. Then, various approaches to variation modeling for compliant assemblies are presented for single station and multi-station assembly lines. Finally, examples are given to demonstrate the applications of compliant assembly variation models.
Analysis of Sound Signal Generation Due to Flank Wear in Turning
Authors: Lu Ming-Chyuan , Kannatey-Asibu Elijah
Published: November 2021

Ramp-up is a major step in the implementation of manufacturing systems, and is even more critical in reconfigurable manufacturing systems. For a successful reduction in ramp-up time, it is essential to analyze and monitor both the overall manufacturing system and the individual machine tools/processes that comprise the system. Towards this end, we have addressed the issue of monitoring tool wear using audible sound to enable faulty conditions associated with wear to be identified during the process before the part quality gets out of specification. Audible sound generated from the cutting process is analyzed as a source for monitoring tool wear during turning, assuming adhesive wear as the predominant wear mechanism. The analysis incorporates the dynamics of the cutting process. In modeling the interaction on the flank surface, the asperities on the surfaces are represented as a trapezoidal series function with normal distribution. The effect of changing asperity height, size, spacing, and the stiffness of the asperity interaction is investigated and compared with experimental data.
Reverse Engineering Using Rapid Prototyping Technique for Biomedical Application
Authors: Yean Chow Kin , Kai Chua Chee , Hui Du Zhao
Published: November 2021

Rapid Prototyping (RP) technology has found applications in medicine. Model produced using rapid prototyping technique can enhance interpretation, visualization and physical evaluation, and is useful to pre-surgical operation. This paper presents an integrated reverse engineering system for biomedical application. The configuration of this integrated system consists of hardware and software layouts. The components within the hardware layout are completed except the fiber optic link. The components of the software layout are completed. The reverse engineering system using rapid prototyping technique is applied in the case studies of nose prosthesis and ear prosthesis.
The Mathematical Model of Radial Forging of a Hollow Continuously-Cast Ingot
Authors: Babailov Nikolai A. , Bourkine Serguey P.
Published: November 2021

The problem of a detailed research of radial forging is associated with the technological process of direct combination of continuous casting and metal forming. The mathematical model of multi-die radial forging is developed. The strain state of radial forging is investigated. The dependences of main characteristics on technological parameters for radial forging with combined loading (torsion, tension or backing) are received by the variational method.

The thermal analysis of hollow continuously cast ingot during deformation is executed.

The verification of mathematical model adequacy is executed by experimental researches. The design of six-dies forging unit for direct combination with vertical continuous-casting machine is developed.
Effects of Some Modeling Parameters of Finite Element Models of Binder Forming
Authors: Chen Kuo-Kuang , Sa Chung-Yeh
Published: November 2021

This paper studies the effects of some modeling parameters on the accuracy of finite element simulation in sheet metal forming. A simple stepdie, which simulates binder forming, is used. In this two-dimensional case, a flat blank is bent into a sinusoidal shape, which has an exact solution. Four modeling parameters are studied. They are: die close speed, die gap, mass damping and width of blank. One significant finding of this study reveals that in calculations using explicit finite elements, the simulation speed should be selected with care. The dynamic effects may be prevalent if the simulation speed is too fast. Numerical errors may accumulate and renders the results erroneous if it is too slow.
Three-Dimensional Tube Geometry Control for Rotary Draw Tube Bending: Part 2—Statistical Tube Tolerance Analysis and Adaptive Bend Correction
Authors: Lou Huazhou , Stelson Kim A.
Published: November 2021

The control of each individual bend and overall process is presented in part 1 of the paper. In part 2 of the paper, statistical methods are used to analyze and improve 3-D tube bending accuracy. The relationship between bending process error and tube geometry error is obtained with Monte Carlo simulation. For the same tube tolerance requirement, the required process tolerance varies in a large range based on tube geometry. Among the three bending errors: bend angle, bend plane and distance between bends, bend angle error has the largest influence on tube error. For a tube with multiple bends, the overall tube geometry error can be minimized by intentionally modify the nominal values of the bends to be made based on the errors in the existing bends. The required modification of the bending commands is calculated with an adaptive bend correction algorithm.
The Effect of Solution Heat Treatment and Natural Ageing on the Yield Characteristics of a 2024-O Aluminium Alloy
Authors: Ashbridge M. T. J. , Leacock A. G. , Gilmour K. R. , O’Donnell M. F. , McDonnell D.
Published: November 2021

Recent advances in computational technology have allowed engineers to conduct previously impractical analyses, particularly with the development of the Finite Element Method (FEM). In turn, this has led the sheet metal forming industry into an economy drive, with an increasing necessity for ‘first time’ forming operations and reduced scrap rates. The successful prediction of large-scale plastic deformation in a sheet component relies on the accuracy of the material model used, especially when anisotropic materials are considered. Some stretch formed or deep drawn forms are geometrically complex and may require several draws with inter-stage anneals and/or solution heat treatments to achieve full form, and the varying material properties create significant difficulties in the modelling of these forming processes. Current orthotropic yield criteria do not allow for any sense of time dependency and although the atomic effects of solution heat treatment and precipitation hardening are well understood, the macroscopic effects of deformation behaviour are not.

A test program was developed to investigate the effects of an increasing age hardening time on an aerospace Alclad 2024-O material after a solution heat treatment. With access to industrial heat treatment equipment, extensive tensile tests were conducted at varying age hardening times and a test rig was manufactured to obtain balanced biaxial tension data. Through the subsequent analysis, a method of predicting the data needed to generate a materials model suitable for FEA was developed, based on a modified version of Hill’s 1990 non-quadratic yield criterion. This was used to generate yield loci for the various age hardening times and compared with the loci generated with the predicted loci. Evaluation of the accuracy of the new criterion, and hence the predictive method, was achieved through its implementation in a finite element code used to model a punch-stretch test. Modelled surface strains were then compared with those measured strains determined during an empirical validation test programme.

With the knowledge that the analysis came from data predicted from a minimum of empirical tests, the predicted results were found to be in good agreement with the experimental values.
The Effects of Tooling Imperfections on the Initiation of Wrinkling in Finite Element Modeling of a Deep Drawing Process
Authors: Hematian J. , Wild P. M.
Published: November 2021

A brief review of the literature on wrinkling in deep drawing processes is presented. It is noted that, while there is a large body of literature related to thin sheet, only one study related to thick sheet or plate has been identified. Finite element based models are used to investigate the effect of initial tooling imperfections on the initiation of wrinkling in deep drawing of thick sheet. Two sorts of tooling imperfections, punch displacement and blank tilting, are considered. The simulation results are compared qualitatively to the experimental forming operation. It is confirmed that tooling imperfections, in particular blank tilting, are an important type of imperfection governing the wrinkling behavior of the blank in deep drawing process.
Efficient Meshfree Formulation for Metal Forming Simulations
Authors: Chen J. S. , Wu C. T. , Wang H. P. , Yoon S.
Published: November 2021

A stabilized conforming (SC) nodal integration method is developed for elastoplastic contact analysis of metal forming processes. In this approach, strain smoothing stabilization is introduced to eliminate spatial instability in Galerkin meshfree methods using nodal integration. The gradient matrix associated with strain smoothing satisfies the integration constraint (IC) of linear exactness in the Galerkin approximation. Strain smoothing formulation and numerical procedures for history-dependent problems are introduced. Applications to metal forming analysis are presented, with the results demonstrating a significant improvement in computational efficiency without loss of accuracy.
The Search for Mechanism in Bone Adaptation Studies
Authors: Cowin Stephen C.
Published: November 2021

The mechanosensory mechanisms in bone include (i) the cell system that is stimulated by external mechanical loading applied to the bone; (ii) the system that transduces that mechanical loading to a communicable signal; and (iii) the systems that transmit that signal to the effector cells for the maintenance of bone homeostasis and for strain adaptation of the bone structure. The effector cells are the osteoblasts and the osteoclasts. These systems and the mechanisms that they employ have not yet been unambiguously identified. The candidate systems are reviewed here. The current theoretical and experimental evidence, which suggests that osteocytes are the principal mechanosensory cells of bone, is summarized. This evidence shows that they are activated by shear stress from fluid flowing through the osteocyte canaliculi. The evidence also suggests that the electrically coupled three-dimensional network of osteocytes and lining cells is a communications system for the control of bone homeostasis and structural strain adaptation.
A General Constitutive Equation of an ER Suspension Based on the Internal Variable Theory
Authors: Wang Biao , Xiao Zhongmin
Published: November 2021

A microstructural constitutive theory of ER suspensions was formulated in this investigation. The framework was based on the internal variable theory and the mechanism analysis. The ER suspension consists of fine particles with high dielectric constant and the supporting fluid. Under the action of the electric field, the polarized particles will aggregate together to form the chain-like structures along the direction of the electric field. As the size and orientation of the particle aggregates are volatile, and they adjust according to the applied electric field and strain rate, the energy conservation equation and the force equilibrium equation were thus established to determine the orientation and size of the aggregates. Following that, a three-dimensional, explicit form of the constitutive equation was derived based on the interaction energy and the dissipation function of the system. The response of the system under the action of a simple shearing load was considered and discussed in detail. It is found that the shear-thinning viscosity of an ER suspension is well approximated by the power-law ∝ (Mn)−0.82.
Prediction of Stress Jump and Elongational Viscosity via Network Theory
Authors: Kee Daniel De , Sun Ning
Published: November 2021

The network model, originally developed for rubber like materials and later extended to model liquids, is subject to modifications. In this work, we look at the adaptation for improved elongational viscosity predictions and to allow for stress jump predictions.

A new formulation involving non-affine motion is proposed and its applications are presented. The major improvement is that a finite elongational viscosity is predicted for finite elongational rate, contrary to infinite elongational viscosities existing at some elongational rates predicted by most previous network models. Comparisons with experimental data on shear viscosity, primary normal stress coefficient and elongational viscosity are given, in terms of the same set of model parameters. The model is successfully tested with data on a polyisobutylene solution (S1).

A further extension of the network model is related to the prediction of the stress jump phenomenon which is defined as the instantaneous gain or loss of stress on startup or cessation of flow. It is not predicted by most existing models. In this work, the internal viscosity idea used in the dumbbell model is incorporated into the transient network model. Via appropriate approximations, a closed form constitutive equation, which predicts a stress jump, is obtained. Successful comparisons with the available stress jump measurements are given. In addition, the model yields good quantitative predictions of the standard steady and dynamic material functions, for xanthan solutions and for Polyacrylamide solutions.
Electromagnetohydrodynamics (EMHD): Numerical Experiments in Steady Planar Flows
Authors: Dennis Brian H. , Dulikravich George S.
Published: November 2021

A new second order theoretical model of the combined interaction of externally applied electric and magnetic fields and viscous incompressible fluid flows has been rewritten as a system of first order partial differential equations. The system was solved using least-squares finite element model on an unstructured grid. The numerical algorithm is very stable and accurate. The accuracy was confirmed by comparing the numerical results against simple analytical results for a magnetohydrodynamic flow between two parallel isothermal infinite stationary plates. Effects of Joule heating and reverse pressure gradient are correctly predicted with this algorithm which is applicable to arbitrary planar flow configurations.
A Three-Phase Hydrodynamic Model for Slurry Reactors
Authors: Gamwo Isaac K. , Soong Yee , Halow John S.
Published: November 2021

A predictive three-phase hydrodynamic model for slurry-bubble column reactors has been developed from the point of view of kinetic theory of granular flow (Gidaspow, 1994a). The model is based on first principles method and can provide a complete description of the flow field. To experimentally validate the code, local gas holdups have been measured at the National Energy Technology Laboratory (NETL) by inserting a dual conductivity probe horizontally into the reactor at various locations. Predicted gas holdups are in reasonable agreement with the experimental results in the bulk region of the reactor.
Simulation of the Film Blowing Process Using a Continuum Model for Crystallization in Polymers
Authors: Rao I. J.
Published: November 2021

In this paper we simulate the film blowing process using a model developed to study crystallization in polymers (see Rao (1999), Rao and Rajagopal (2000b)). The framework was developed to generate mathematical models in a consistent manner that are capable of simulating the crystallization process in polymers. During crystallization the polymer transitions from a fluid like state to a solid like state. This transformation usually takes place while the polymer undergoes simultaneous cooling and deformation, as in film blowing. Specific models are generated by choosing forms for the internal energy, entropy and the rate of dissipation. The second law of thermodynamics along with the assumption of maximization of dissipation is used to determine constitutive forms for the stress tensor and the rate of crystallization. The polymer melt is modeled as a rate type viscoelastic fluid and the crystalline solid polymer is modeled as an anisotropic elastic solid. The mixture region, where in the material transitions from a melt to a semi-crystalline solid, is modeled as a mixture of a viscoelastic fluid and an elastic solid. The anisotropy of the crystalline phase and consequently that of the final solid depends on the deformation in the melt during crystallization, a fact that has been known for a long time and has been exploited in polymer processing. The film blowing process is simulated using a generalized Maxwell model for the melt and an anisotropic elastic solid for the crystalline phase. The results of the simulation agree qualitatively with experimental observations and the methodology described provides a framework in which the film blowing problem can be analyzed.
Free Vibration Energy and Period of a String With Time-Varying Length
Authors: Lee Seung-Yop
Published: November 2021

We introduce a new technique to analyze free vibration energy and natural frequencies of a string with time-varying length by dealing with traveling waves. One of boundaries is vertically fixed but it moves axially at a constant rate. When the string length is varied, the free vibration energy and period also change with time. String tension and non-zero instantaneous vertical velocity at the moving boundary results in the energy variation. When the string undergoes retraction, the vibration energy increases with time. The new technique using traveling waves gives the exact amount of energy transferred into the vibrating system at the moving boundary. The free vibration energy are compared with previous results using the perturbation method and Kotera’s approach.
A New Formula to Calculate the Fundamental Frequency of a Multistory Building by Approximate Numerical Method
Authors: Weiss George
Published: November 2021

A new formula has been developed in this study, to calculate the fundamental frequency of a multistory building. This formula is derived from Dunkerley’s estimate, complies with the requirements of Uniform Building Code (UBC) and the Building Officials Code Administrators (BOCA) Code, and accounts for multistory building frames of different type and size.

A coefficient Γ, function of moments of inertia and lengths of column/girder was introduced in the formula, in order to obtain a relative simple algebraic equation.

To verify the validity of the new formula a thorough investigation has been conducted. Fundamental frequencies and periods have been calculated for different building frames using the new formula (Formula 1).

A formula for buildings with rigid floors, Formula 2, has been derived from Formula 1. Formula 2 has been used to calculate the fundamental frequency for the same type and size of buildings used in the calculations with Formula 1, considered with rigid floors. In addition, three different empirical formulas have been used to calculate the fundamental period for the same buildings. Two of these formulas are recommended in different versions of the codes.

For the same type and size of buildings the fundamental frequencies and periods have been determined by computer. Comparing with the computer values, formulas 1 and 2 give the best results and can be used in preliminary design, in vibration problems or to determine seismic lateral loads for buildings with a maximum height of 160/65 ft. The empirical formulas show large differences and have to be used with caution, only in the limited range imposed by UBC and BOCA.
Adhesive Joints for Composite Sandwich Structures
Authors: Dvorak George J. , Zhang Jian , Canyurt Olcay
Published: November 2021

A new approach is explored for joining of thick, woven E-glass/vinyl ester composite laminated plates to steel or composite plates, with applications in naval ship structures. Adhesive is applied along through-the-thickness contoured interfaces, employing tongue-and-groove geometry. Both experimental and finite element modeling results are presented. They show that adhesively bonded tongue-and-groove joints between steel and composite plates loaded in monotonically increasing longitudinal tension, are stronger than conventional strap joints even in relatively thin plates. In particular, a single 0.25 in. wide and 8 or 12 in. long steel tongue, bonded by the Dexter- Hysol 9339 adhesive to a groove in a 0.5 in. thick laminated plate, can support a 20,000 lbs tension force. This force is expected to increase in proportion to plate thickness. Simple design rules indicate that high joint efficiency can be achieved for any thickness of the joined plates.
Study of Two Cylindrical Water Columns Subjected to Planar Shock Wave Loading
Authors: Igra D. , Takayama K.
Published: November 2021

Two water columns with identical initial diameters of 4.8 mm were placed 30 mm apart inside a shock tube test section and loaded by a shock wave of Mach number 1.47 in atmospheric air. The Weber and Reynolds numbers corresponding to these flow conditions are 6,900 and 112,000, respectively. Double exposure holographic interferometry was used to visualize the shock/water columns interaction. The process of the water columns deformation, displacement, acceleration was well visualized and hence the drag coefficient of shock loaded water columns was evaluated. The water column in the front behaved virtually the same as a single water column. However the displacement and acceleration of the rear water column was less significant than that of the front one. Hence its drag coefficient is less. These results show that the frontal water column has affected the flow field around the rear water column.
Discussion on Clustering Effects in Vertical Gas-Particle Flows
Authors: Helland Eivind , Occelli Rene , Tadrist Lounes
Published: November 2021

Simulations of 2D gas-particle flows in a vertical riser using a mixed Eulerian-Lagrangian approach are addressed. The model for the interstitial gas phase is based on the Navier-Stokes equations for two-phase flow with a coupling term between the gas and solid phases due to drag forces. The motion of particles is treated by a Lagrangian approach and the particles are assumed to interact through binary, instantaneous, non-frontal, inelastic collisions with friction. In this paper different particle clustering effects in the gas-particle flow is investigated.