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### Browsing by Author "Wilhoit, J. C."

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Item A lumped parameter approach to longitudinal and torsional vibrations of oil well drill strings(1962) Bradbury, Robert Easton; Wilhoit, J. C.Show more The effect of tool joints on the passage of plane longitudinal and torsional waves along a drill pipe was studied. An approximate solution to the governing equations of motion found, and an idealized tool joint constructed. Calculations were made for the effect of the idealized joint on an example drill string. The results showed that tool joints had negligible effect for exciting frequencies of the same order as common rotary speeds and the drill pipe could be taken as a uniform pipe with negligible error. Equivalent systems of rigid inertias and massless springs were developed for a drill string with a uniform drill pipe and one drill collar section, for fixed-fixed or fixed-free end boundary conditions. Undamped responses of the equivalent systems were found for arbitrary periodic forces applied to any point of the drill string. Approximate responses were derived for small damping. Specific formulas were derived for responses at the top of the drill string for given periodic displacement or force at the bottom, for fixed-fixed or fixed-free boundary conditions.Show more Item A study of the quasi-frictional forces resulting on serrated clamping elements(1955) Moser, Edward Israel; Wilhoit, J. C.Show more It is intuitive that a clamping element will grip better if the surface is provided with teeth which penetrate Into the surface of the clamped object. This paper is concerned with the problem of determining a quantitative comparison of the gripping ability of various penetrator shapes. It is presumed that the effects noted for a single penetrator will be applicable to an array of penetrators as on a serrated clamping element. Mathematical considerations show that a vertical penetrator load is held in equilibrium by the vertical components of the yield pressure which act on the penetrator surfaces. This is mathematically equivalent to the force given by the yield pressure acting over the area of the indentation projected on a plane normal to the direction of the load. This paper endeavors to show that the same concept will apply to forces applied transversely. Therefore the maximum possible transverse force which can be applied to a penetrator is theoretically equal to the product of the yield pressure of the Penetrated material and the area of tie penetrator face projected on a plane normal to the transverse force. Plasticity considerations show that the, yield pressure for a given material varies according to the penetrator shape. Strain hardening is also a factor in most materials. The influence of conventional friction is also shown to vary with the penetrator shape. In same cases vectorial addition of the frictional effect is required, but special cased permit algebraic addition. It is shown analytically that a friction reversal occurs at the surface of the penetrator as the transverse force roaches its maximum value. The result of the friction reversal is to lower the yield pressure Against the penetrator face. Experiments show that the foregoing theories are justified for the cases tested*Show more Item A study of the steady state forced vibrations for coupled longitudinal, lateral, and torsional motions of constrained bars(1957) Medlock, James Donal; Wilhoit, J. C.Show more Item A two dimensional photoelastic study of the load distribution among the roller bearings in a rock bit(1955) Bleimeyer, Arthur A. E; Wilhoit, J. C.Show more The photoelastic technique was employed to investigate the adverse affect on the load distribution among the roller bearings in a rock bit cutter as a result of the relatively large radial clearance in the bearings. A mathematical solution vas obtained for the load distribution among the bearings assuming negligible radial clearance, and parts of this solution were then applied to the case of relatively large radial clearance. The possibility of achieving a more equitable load distribution through the use of hollow roller bearings was also studied.Show more Item An experimental study of the propagation of flexural waves in an elastic beam of circular cross section(1962) Stephenson, Jack G; Wilhoit, J. C.Show more An experimental study of the propagation of flexural waves in an elastic beam of circular cross section subjected to an approximate step function bending moment is given. The test beam was a low carbon steel bar 2 inches in diameter by 30 feet long and was suspended in a vertical position by a pin located near the upper end. The step moment was applied at the upper pinned end of the bar by an arrangement of two high pressure, nitrogen operated cylinders. The strains were measured with strain gages located at eight stations along the bar. The experimental results are compared with results obtained from a solution of the Timoshenko theory's differential equations by E. E. Zajac and W. Flugge. The experimental results are correlated with the predictions of the theoretical solution.Show more Item Bending of composite cylinders(1969) Aguirre G., Manuel; Wilhoit, J. C.Show more A study is made with the purpose of investigating the behavior of composite cylinders under the action of bending loads. A theoretical approach is proposed in which several simplifying assumptions are made, and an experimental analysis is carried out with the view of establishing the degree of validity of these assumptions as well as for purposes of investigating the general behavior of the composite cylinders. The principal assumptions made in the theoretical treatment of the problem are: (1) Plane transverse sections remain plane both within the elastic limit of the materials and in the post-yield stages. (2) The steel behaves in accordance with Hooke's Law up to a strain of 2000 microinches per inch (0.2%). For higher values of strain, the steel stress has a constant value determined by the "0.2% offset" standard as shown in the figure below. (3) The stress-strain relationship for concrete is as established in "A Study of Combined Bending and Axial Load in Reinforced Concrete Members", University of Illinois Engineering Experiment Station, Bulletin Series No. 399, 1951, by Eivind Hognestad. (4) Concrete has negligible tensile strength. (5) Somastic and wrap coat, component materials in the composite cylinders, have negligible capacity to withstand tension or compression. (6) The test specimens used in the experimental analysis are composite cylinders made up of an inner steel cylinder, an intermediate somastic cylinder or wrap coat cylinder, and an outer, wire reinforced concrete cylinder. In practice these composite cylinders are used in the construction of under-water pipelines (the concrete cylinder serves the primary purpose of providing negative buoyancy, while the somastic and the wrap coat are asphaltic substances for protection of the steel cylinder against corrosion).Show more Item Flexural rigidity of concrete-coated steel pipe(1965) Livingston, Louis Edward; Wilhoit, J. C.Show more Steel pipe for underwater applications may have a concrete jacket as ballast to assist in laying the pipe. The contribution of the concrete jacket to the flexural rigidity of the pipe is analyzed theoretically, and the analysis compared with experimental results. The reasons for deviation of experimental results from theory are considered, and a modified theory suggested. It is concluded that the jacket can furnish some additional flexural rigidity, provided certain conditions are met.Show more Item Forced lateral motion of deep-water drill strings(1963) Graham, R. D. (Robert Douglas); Wilhoit, J. C.Show more An equation of motion governing lateral deflection, considering elastic, dynamic, and drag forces is derived. This equation is applied to three different classes of drill string behavior: a beam with constant axial tension, a perfectly flexible cable, and a beam with linearly varying axial tension. Each equation is solved for the case of simple harmonic motion. A typical deep-water drill string is synthesized by subdivision into short beam sections at the top and bottom, joined by a flexible cable in the center. The lateral deflection of the drill string is obtained by joining the beam and cable solutions, subject to boundary conditions at each junction. The drill string considered is displaced harmonically at the surface by the ship and is built-in at the ocean floor. The deflection mode shapes are plotted and analyzed. The bending stresses at the top of the drill string are computed and compared with values observed under similar, conditions; the bending stresses in the vicinity of the ocean floor are also plotted.Show more Item Lateral vibration of drill pipe including wall reaction(1964) Xu, Fengxiang; Wilhoit, J. C.Show more The impact of a drill pipe on the wall of a bore-hole is treated as a time dependent force acting laterally on the pipe assuming the existence of periodic motion. The impact force is estimated by Hertz' theory of impact. The solution obtained must satisfy the constraint conditions to approximate the impact action.Show more Item Strength characteristics of rock samples under hydrostatic pressure(1955) Bredthauer, Raymond Otto; Wilhoit, J. C.Show more Item The dynamic stresses generated in a finite elastic body of revolution by longitudinal impact with a rigid wall(1963) Langner, Carl Gottlieb; Wilhoit, J. C.Show more General statements concerning phase and group velocities of stress waves propagating in elastic media where at least one dimension is infinite are valuable for separating the distinct characteristics of the various operating phenomena. The problem of impact of a finite body, however, is so greatly complicated by the inherent reflections, reinforcements, and cancellations of the stress pulses that little use can be made of these general statements in describing the overall transient response of such a body. Presented here is a finite difference numerical method for integrating over space and time the appropriate equations of motion and boundary conditions for determining the transient stress state in a finite elastic body of revolution resulting from longitudinal impact against a rigid wall. Also presented here are the results obtained from programming this numerical procedure for the Rice University digital computer and using this program to evaluate the transient stress states in elastic bodies of nine distinct boundary configurations.Show more Item The effect of hydrostatic stress on the drilling rates of rock formations(1955) Cunningham, Robert Ashley; Wilhoit, J. C.Show more Item The stresses in a flat circular ring with a through-cut(1963) Chen, Youcai; Wilhoit, J. C.Show more This thesis treats a new approach to the problem of a complete ring, with one cut, supported on one face of the cut and subjected to a non-self-equilibrating load. A standard method of approach makes use of the Fourier Integral. Professor J. N. Goodier of Stanford University suggested a multiple ring approach to Professor Wilhoit in 1953. Although Professor Wilhoit made a preliminary study, no comparison of the two methods was attempted. A study is made of the stresses in the flat circular ring with a through-cut subjected to an arbitrary load. It is shown by the solution of an example that certain problems can be treated by the multiple-ring method with greater ease than by the Fourier-integral method.Show more Item The stresses in the rock formation near the bottom of a hole due to overburden and drill fluid pressures(1956) Whitworth, Billie Joe; Wilhoit, J. C.Show more Item The stresses produced by uniform radial displacement of two circular hole in an infinite plate(1961) Kelly, Joseph L. (Joseph Luther), 1867-1925; Douglas, Jim, Jr.; Wilhoit, J. C.; Paslay, Paul R.Show more Item The stresses produced in an infinite plate by the uniform radial displacement of two circular holes in the absence of friction(1962) Jones, Warren Tillet; Wilhoit, J. C.Show more An analytical solution using the complex variable technique of Muskhelishvili is given for the stresses produced in an infinite plate by the insertion of rigid oversize circular members in two adjacent circular holes in the absence of friction. The center distance of the holes is held constant thereby requiring that the inserts be loaded externally. Numerical data for an original hole spacing equal to three radii are presented.Show more Item The use of Boussinesq-Papkovich stress functions to determine the stresses around the bottom of a cylindrical cavity(1960) Cheatham, John B; Wilhoit, J. C.; Paslay, Paul R.Show more