Browsing by Author "Wilhoit, James C."
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Item Approximation of the plastic behavior of rocks at elevated mean pressures using a bi-linear yield envelope(1980) Gerecci, Gultekin S.; Cheatham, John B.; Wilhoit, James C.; Merwin, John E.In this study, the stress-strain curves of four different rocks are obtained by using true tri-axial test apparatus. First, results using this test apparatus are compared with results using conventional tri-axial test equipment and the dependability is confirmed. Mohr circles, based on the stress-strain curves have been drawn to provide yield envelopes for the rocks tested in this study. The yield envelope is approximated by a bi-linear curve and by extending the wedge indentation theory for this case, the penetration force equation is derived. The calculated values for the penetration force are then compared with the experimental results obtained by previous investigations. The rocks tested are: Danby Marble, Carthage Marble, Ohio Sandstone and Indiana Limestone. These rocks are tested under confining pressures of 25, 5, 75, 1,, 2, and 3, psi.Item Inertia effects in consolidation problems(1981) Lockett, Robert R.; Bowen, Ray M.; Wang, C. C.; Wilhoit, James C.The dynamic behavior of a chemically inert, isothermal mixture of an isotropic elastic solid with an elastic fluid is studied. Geometrically, this mixture is assumed to comprise a layer of fixed depth, bounded below by a rigid, impervious surface, and above by a free surface to which loads are applied. The resulting boundary-initial value problem is solved by use of a Green's function. Two different loading conditions are used to demonstrate the effect of including inertia terms in the equations of motion. In the first example of a constant compressive load, our result is found to agree with the inertia-free solution only for very long times. The second example shows that for a harmonically varying compression, resonance displacements occur at certain loading frequencies, whereas the solution obtained by neglecting inertia does not predict this behavior.Item One dimensional shear motions in fluid saturated porous media(1981) Roberson, Kyle R.; Bowen, Ray M.; Wilhoit, James C.; Wang, C. C.An analytic solution is presented for shear motions in a binary mixture of a chemically inert, isothermal, elastic isotropic solid and elastic fluid subject to a sinusoidally varying solid displacement on one boundary and free of tractions on the other. It is demonstrated that the retention of inertial terms, and the resulting resonance phenomenon, can cause solid displacements in the interior of the region orders of magnitude greater than the exciting solid displacement on the boundary. Displacement spectra are presented for certain well known porous media.Item Stress distribution in the human buttocks(1980) Scott, Allison Cooper; Wilhoit, James C.; Walker, William F.; Merwin, John E.One of the foremost problems in rehabilitation today is the prevention of bedsores or decubitus ulcers in spinal cord-injured patients. For those patients who must spend great lengths of time in a wheelchair, the wheelchair cushion is of vital importance in avoiding the high forces on the skin that could cause tissue breakdown. The finite element method was used to analyze a two-dimensional model of the human buttocks. The normal and shear stresses in the flesh were determined for several body types supported by a variety of cushion materials. Results permitted a comparison of external pressure measurements made experimentally with calculated internal stresses. Thus, analysis supplemented clinical observations in evaluating the ability of cushion materials to minimize stresses in the flesh.Item The effects of plastic yielding and tension on suspended pipelines(1974) Serpas, Raymond Joseph; Wilhoit, James C.In this thesis, a method for determining the shape of an underwater pipeline suspended under tension together with the forces acting on it is derived for the purpose of evaluating the effect of yielding on the pipeline. This yielding may occur either before the pipe is suspended from a lay barge or in the suspended portion. The method employs a trilinear approximation to the experimental nonlinear moment versus curvature diagram for the pipe in order to account for any yielding. A Taylor's Series approach along with a finite element, initial value method, is used to solve the nonlinear shape description equation for the pipe. A 16-inch O.D. pipe is used as a test case. It is concluded that yielding of the pipe has no significant effect on the depth attainable, and a small amount of horizontal tension can be used to eliminate the yielding and also control the moment distribution in the pipe.Item Unsteady flow in a gas bubble plume(1981) Fahrenthold, Eric P.; Beckmann, Herbert K.; Wilhoit, James C.; Bayazitoglu, YildizThe characteristics of a gas bubble plume produced by the discharge of gas from a submerged orifice at high flowrates is investigated. Flow of the gas and liquid mixture into the plume has been found to develop pulsations at high gas flowrates, resulting in a plume structure different from that produced by uniform bubble flow. The plume is modeled as a column of gas bubble "clouds." The frequencies of the flow pulsations in the plume are obtained by evaluation of the forces acting on a bubble cloud forming at the discharge nozzle. The vertical current in the plume is investigated by consideration of the wake produced by bodies of revolution traveling in line. Expressions for the drag force on cylinders (two-dimensional), spheres, and disks arranged in line are determined. Available experimental data on flow fluctuations in gas bubble plumes and drag forces on cylinders, spheres, and disks arranged in line are used to evaluate the derived expressions.