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Polarization saturation simulation of ferroelectric polycrystalsSheng, Jianshun January 2004 (has links)
A micro-electromechanical constitutive model for ferroelectric polycrystals is introduced and applied to determine possible uniaxial remanent strain and remanent polarization states in the material. Simulations based on the model are carried out to determine the polarization saturation states under different levels of prevailing remanent strain. The simulation results clearly demonstrate how the polarization develops to the saturation and how the saturation polarization depends upon the remanent strain. The obtained information of saturation states can be applied in phenomenological constitutive models.
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THE USE OF SURFACE HOT-FILM SENSORS IN DILUTE POLYMER FLOWSGOFORTH, MONTGOMERY BAILEY January 1987 (has links)
The purpose of this study was to assess the feasibility of using flush-mounted surface hot-film sensors in dilute polymer solutions to measure mean wall shear stress. Experiments were conducted using hot-film sensors mounted on the surface of a rotating disk. It is shown that a sensor calibration obtained in a pure water flow cannot be used directly to provide accurate skin friction measurements in a dilute polymer flow. However, the repeatability of the results suggests that a functional relation may exist between a sensor's calibration in water and in dilute polymer, thereby permitting precalibration of the sensor in pure water. It is also possible that reasonably consistent measurements may be obtained by precalibration of sensors in controlled polymer solutions.
Experiments were also conducted by injecting concentrated polymer solution (4000 ppm) into the boundary layer of the rotating disk. Drag reduction and hot-film performance comparable to that obtained with homogeneous dilute polymer solution was demonstrated.
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AN AUTOMATION ALGORITHM FOR A MODULAR APPROACH TO COMPUTER-AIDED KINEMATIC ANALYSIS OF PLANAR MECHANISMSHOU, FU JOSEPH January 1987 (has links)
Many complex mechanisms are composed of several basic parts (or modules). A library of basic parts may be defined and pre-tested. Then a complex mechanism can be analyzed by analyzing each individual basic part. This is the modular approach to kinematic analysis. In previous works, the solution order of the composing basic parts for a mechanism must be recognized by the analyst. Then one wrote a main program to call subroutines in the part library in an order the mechanism should be solved. Here an algorithm based on nodal and modular relations is developed to automate the analysis process so that the solution order is determined automatically and the input for the analysis is simplified and minimized. Sample problems are presented which prove the algorithm to be logical and efficient. The algorithm may be more applicable as the part library is expanded.
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AN INVESTIGATION OF THE EFFECTS OF DEFORMATION-INDUCED PORE PRESSURE ON THE FAILURE OF ROCK LOADED BY A PUNCHLEDGERWOOD, LEROY WILLIAM, III January 1987 (has links)
Finite Element software is developed which models deformation of poro-elastic-plastic materials. This software is used to model the effects of pore pressure generated during punch indentation on the failure of high and low permeability rocks. The growth of the plastic zone under the punch as a function of load is investigated. A Confinement Transition Load is defined based on a change in character of the growth of the plastic zone. It is shown that in highly permeable rocks, deformation induced pore pressures are always small and do not affect failure. In rocks of low permeability, dilatational hardening effects are measurable, but not large at loads below the Confinement Transition Load.
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A PHENOMENOLOGICAL STUDY OF FRICTION INDUCED TORSIONAL VIBRATIONS OF DRILL STRINGSNARASIMHAN, SURINDER January 1987 (has links)
The problem of drill string vibrations when the bit is off the bottom is addressed. It is asserted that these vibrations cannot be rationalized on the basis of linear vibration theory. The central surmise is that nonlinearity in friction induces oscillations. Plausible models for friction are propounded. Two distinct types of motion are detected, with and without stickslip. Numerical and analytical procedures are employed to solve the governing differential equation of a free-sliding, single degree of freedom system with dry friction. The results are compared with data procured at three rigs. Their close correlation substantiates the principal contention of the study.
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THE DEVELOPMENT OF AN ISOPARAMETRIC HELICAL ELEMENTNAVRATIL, PETER GEORGE January 1987 (has links)
A new isoparametric element is developed to aid in the finite element analysis of threaded joints that links the radial and axial displacements that normally occur in these types of joints, but which are ignored by axisymmetric analyses. The element is helical in shape, and gives rise to six components of stress and strain, but is implemented in such a way that it can be attached to two-dimensional axisymmetric models. The research includes the theoretical considerations for the development of such an element, the creation of the stiffness matrix, implementation in the finite element code BEGIN, verification, and comparison with experimental data. It is shown that the new element is much too stiff torsionally, and that the results are not better than in the axisymmetric case.
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DETERMINATION OF ROCK PLASTICITY PARAMETERS BY INDENTATION EXPERIMENTSTANLEY, H. MARK, III January 1987 (has links)
Indentation tests are performed on samples of Indiana Limestone and Berea Sandstone under confining pressures ranging from 0 to 2500 psi. The force-displacement data from these experiments are analyzed by comparing them to numerical results obtained for a simplified theoretical model which assumes (1) rigid-perfectly plastic behavior, (2) a Mohr-Coulomb linear yield envelope, and (3) negligible lip formation. In addition, indentation is assumed to be a quasi-static, equilibrium process.
The two Mohr-Coulomb parameters cohesive strength (c) and angle of internal friction ($\phi$) are bounded by consideration of the following two heuristic conditions: (1) The force-displacement curve generated by a perfectly rough assumption must be an upper bound to the experimentally observed curve. (2) The frictionless solution must be a lower bound. These two conditions restrict $\phi$ and c to a narrow allowable region in $\phi$-c space, and are applicable to more realistic yield conditions, as well.
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AN EXPERIMENTAL STUDY OF FORCED COOLING ACROSS HEATED RECTANGULAR BLOCKSTHAN, HUNG TRONG HOANG January 1987 (has links)
Two dimensional laminar and turbulent forced convective flows over heated rectangular obstructions on insulated plates were experimentally investigated. Velocities were measured by a three beam Laser Doppler Velocimetry system operating in the backward scattering mode with a counter type signal processor, and temperatures were measured with copper-constantan thermocouples. Assumptions such as insulated plates, constant heat production by the obstructions and uniform velocity profile at the entrance were made to render the problem controllable in the laboratory environment. Only laminar velocity and temperature profiles were compared with existing numerical values. Recirculating flow between adjacent blocks was detected. Heat removal enhancement along the bottom plate due to high local turbulence was observed. Velocity profiles and local Nusselt numbers for three Reynolds numbers are presented to assist in the design of electronic packaging.
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Numerical analysis on Strouhal frequencies in vortex shedding over square cylinders with surface suction and blowingLing, Lisa Mei January 1992 (has links)
The effects of normal surface suction and blowing on the Strouhal frequencies in vortex shedding over porous square cylinders was analyzed numerically The general characteristics determined were (1) an initial increase followed by a decreasing behavior in the Strouhal frequency with increasing suction velocity and (2) a decrease in the Strouhal frequency with increasing blowing velocity. The numerical results were compared to existing analytical predictions, yielding fairly close agreement.
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Propagation of antiplane waves in an elastic solid containing a distribution of parallel cracksKoba, Yuri Kostyantynovych January 1993 (has links)
The propagation of antiplane waves in an unbounded linearly elastic solid that contains a distribution of flat cracks is considered. The cracks are parallel to each other, the distribution is dilute, and a wave is obliquely incident on the planes of the cracks. It is assumed that the multiple scattering produces a coherent wave that loses energy as it propagates. The attenuation coefficient is specified in terms of the power scattered by a single crack and the number of cracks per unit volume. Using the Kramers-Kronig relations, the speed of the coherent wave in the cracked solid is derived as a function of the frequency and of the crack density. Curves are presented for the attenuation coefficient versus the frequency, and for the speed versus the frequency and the crack density. These curves show that the speed of the coherent wave in a cracked solid is always less than the speed in an uncracked solid.
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