R-3 Repository :: Browsing by Author "Walker, William F."

Browsing by Author "Walker, William F."

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A geometric solution of rotational flow fields
(1967) Morehouse, Jeffrey Herbert; Walker, William F.
This paper presents a geometric method of solving rotational flow fields. As a prior condition for this method to be applicable, streamlines must be known along the two boundaries of the flow region in question. This method is an extension of a geometric method aE solving potential flows developed by F.O. Ringleb. The method is based on the piecewise approximation of streamlines and their orthogonal trajectories by circular arcs. For both potential and rotational flows, only two-dimensional and axisymmetric flows may be solved, but the fluid may be compressible or incompressible. Examples are worked where curved shock waves have induced rotational flow. Both axisymmetric and two-dimensional flows are treated in the examples.
An analysis of the performance of clamp-type flowline connectors with tapered hub faces
(1983) Hirschberg, Alan J.; Walker, William F.; Paslay, Paul R.; Cheatham, John B.; Douglas, Andrew S.
The use of clamp-type connectors with flat hub faces for flaw-line applications results in undesirable separations between the hub faces in the area of the pressure seal. Tapered hub faces are proposed as a design solution to the seal separation problem and a displacement analysis is presented. The axial symmetry of the problem and the symmetry about the radial plane of the hub faces interface are both utilized in the analysis. The equations resulting from the analysis are incorporated into a FORTRAN computer program allowing parametric studies to be conducted easily. The results from these studies provide a basis for the effective design of the tapered hubs. Finite element analyses of a particular clamp-type connector with flat and then tapered hub faces are conducted for the dual purposes of comparison with the thesis analytical solutions for the same design and detailed examination of the stress levels induced under various loading conditions.
An experimental study of switching in a Coanda wall attachment device
(1969) Spargo, William Jay; Walker, William F.
An experimental study was conducted to determine the effect of wall angle, wall offset, and power jet pressure on the control signal required to switch the flow in a Coanda wall attachment device. A stability parameter was defined as the ratio of the power jet pressor to the change in control pressure required for switching to occur. When this ratio is a minimum, maximum stability has been attained. Data was obtained for wall angles from zero to fifty degrees; wall offsets from one-half to none inches; and power jet pressures in the range from 0.7 to 4.0 inches of mercury. Comparisons were made between the stability parameter, the wall angle, and the wall offset to find the most stable configuration of the wall. This configuration was a wall angle of thirty degrees and a wall offset of one inch. The stability parameter remained approximately constant for different power jet pressures at each geometric configuration.
An experimental study of the effect of aspect ratio, wall angle and wall offset on the resultant force on the two-dimensional jet in bistable fluid amplifiers
(1967) McCoy, James Joseph; Walker, William F.
An experimental study was conducted to determine the effect of aspect ratio, wall angle and wall offset on the force that results due to the pressure differential across the jet, on a two-dimensional jet in a bistable fluid amplifier. A dimensional analysis was made of the variables involved and a model was constructed to give the variable geometry needed. Data was obtained for aspect ratios of four, six, eight, and ten; offsets of two, four and six nozzle widths; and wall angles of ten, twenty, and thirty degrees. Graphs were made of the pressure gradient near attachment to show the effect of these variables on the resultant force on the jet. Ways of maximizing the force on the jet are suggested from the results obtained.
An experimental study of the pressure contours in the turbulent reattachment of a bistable fluid amplifier
(1968) Kirkpatrick, John R; Walker, William F.
An experimental study was conducted to determine the effect of aspect ratio, wall angle, and wall offset on the shape of pressure contours in the reattachment bubble of a symmetrical bistable fluid amplifier. The model was operated without control flow at a nominal nozzle exit Mach number of .45 and a nominal exit stagnation pressure of 4.05 "Hg. gauge exhausted to atmosphere. special attention was paid to trends in the location of and pressure within the minimum pressure region of the recirculation bubble. Pressure contour maps were graphed for aspect ratios of four, six, eight, and ten; offsets of two, four, and six nozzle widths; and wall angles of ten, twenty, and thirty degrees. The results are expressed as a series of pressure maps. The reattachment distances obtained were in fairly good agreement with the results found by others at lower Mach numbers.
An interactive computer solution for thermal systems
(1985) Reynolds, Frank Fisher; Walker, William F.; Chapman, Alan J.; Wierum, Frederic A.
The Thermal Analysis System is an attempt to automate the analysis of a closed thermodynamic system. A first law analysis is performed on each device in the system using the properties initially entered by the user at selected states. The known data for a problem to be solved is entered via interactive prompts. The program then manipulates the data and attempts to solve the system. If enough data is not known to solve the system completely, all known data is printed out and an error message will appear.
Diffusion of hydrogen in metal membranes deformed in tension
(1984) Lee, Kelly A. (b. 1976); McLellan, Rex B.; Brotzen, Franz R.; Walker, William F.
Three well known electrochemical techniques were used to study the diffusion of hydrogen in tensilely deformed iron and nickel membranes. Constant current permeation tests, current pulse tests and potentiostatic depletion tests were performed to determine which test produced the most reliable and reproduceable data. The bulk lattice diffusivity in annealed nickel at 22°C was found to be 3.24 X 1 cm2/sec while the bulk lattice diffusivity in annealed iron at 21°C was found to be 1.59 X 1”6 cm2/sec.
Flow visualization studies of a left ventricular bypass pump
(1975) Lloyd, John Morgan (1880-1960); Walker, William F.
A flow visualization method was implemented in the study of the fluid flow characteristics of a swirl type left ventricular bypass pump. A systematic combination of pump spatial inlet orientations, pump valves, and pump body geometry were examined in order to determine pump flow characteristics. Both still and high speed motion photography were made of operating, transparent pumps in a mock circulatory loop with a blood analogue fluid. Regions of pump stasis, low velocity flows, and eddy formation were identified. In -redesigning the bypass pump, several changes were implemented that stemmed from these flow visualization studies. The final pump design incorporated an angled, tangential inlet duct with a tilting disc valve and a tilting disc valve in the outflow tract. A low profile, nonocclusive diaphragm was used with a nozzle shaped pump body to improve internal pump flow. These modifications should minimize areas of possible clot formation and fibrin deposition in the pump.
Hydraulic evaluation of filter screens for power plant water intake
(1979) Kamata, Masahiro; Walker, William F.; Beckmann, Herbert K.; Picologlou, Basil F.
An investigation has been performed of hydrodynamic losses through filter screens used in power plant water intakes. For the experimental phase of the investigation, screens with aspect ratio up to 3.8 were tested. The Reynolds number range for the test was from 15-1 and the ratio of traveling screen velocity to water approach velocity varied from -1.. It was found that the characteristics of flow through slot mesh screens are similar to those for flow through square mesh screens. The losses through round wire screens can be estimated from the approach water velocity, wire diameter, and a function of the ratio of opening area to frontal area of the screen. If a finer screen mesh is desired for filtering purposes, slot mesh screens sustain smaller hydrodynamic losses than square mesh screens because the ratio of openings is larger. It was also found that the screen motion in the water could be easily simulated. It was determined that the losses for a traveling screen are the same as those for a stationary screen of the same design so long as the normal component of the approach velocity remains unchanged.
Hydrodynamic considerations of coronary blood flow with and without stenosis
(1976) Brugger, Jean-Pierre; Walker, William F.
Coronary stenosis is one of the most common heart diseases. Though not much is known concerning the growth of the stenosis in the coronary arteries, it is nevertheless possible to study the effects of the stenosis on the blood flow, and thus to determine its influence on myocardial perfusion. In summary, this thesis is concerned with the effects of the stenosis on left coronary blood flow. To determine these effects it has been necessary in a first step to understand left coronary blood flow and its regulation. This is done by computing coronary blood flow as a function of the hydraulic power delivered by the heart. In a second step the hydrodynamic effects of the stenosis have been computed and experimentally tested in vitro. It has been found that the resistance to the flow presented by the stenosis is a strong function of the percentage of stenosis, its inner radius and its length. Apparently. the geometrical inlet shape of the stenosis is not an important factor. It has been shown also that for given conditions a 75% stenosis can present a high enough resistance to impede myocardial blood flow such as to lead to myocardial infarction. This is true even if the required blood supply is far from being excessive.
In-vitro hydrodynamic evaluation of aortic valve protheses
(1976) Lim Cheng Chye, Lawrence; Picologlou, Basil F.; Walker, William F.; Chimoskey, J. E.
A mock circulatory loop was designed for the hydrodynamic evaluation of aortic valve prostheses. It had features of low priming volume (1 to 1.2 liters) and its fluid was protected from direct contact with air. The prostheses were mounted in the anatomic subcoronary position of a plexiglas model of the human aorta. Four commercial valve prostheses were tested in the loop in one case with the sinuses of Valsalva intact and in another case in the absence of the sinus cavities. They were the Lillehei-Kaster pivoting disc, Bjork-Shiley tilting disc Smeloff-Cutter caged ball and the Starr-Edwards caged ball valves. Tests were conducted at heart rates of 6 and 9 beats/minute and the aortic flow rates of 4 and 6 liters/minute. A valve performance index was formulated, based on the energy dissipation that occurs in flow through a valve. This dissipation coefficient, as it was called, was shown to be a fair, consistent means of rating valve performance. The results showed that the pivoting/tilting disc valves were superior in performance to the caged ball valves in terms of the mean pressure gradients across the valve, percentage backflows and energy dissipations recorded. The valves also functioned more efficiently in the straight tube section than in the section with sinuses. Plausible explanations were offered, based on the flow dynamics of the valves and their relation to the immediate geometry. The results of this work were compared with those of other investigators. Although no direct comparisons were possible because of differences in flow conditions, valve sizes and flow chamber dimensions, approximate comparisons showed fair consistency.
Microprocessor control of a combined assist system for the profound support of the failing heart
(1979) Philippe, Edouard A.; Clark, John W.; Walker, William F.; Parks, Thomas W.
Conventional non-invasive mechanical circulatory assist methods such as intra-aortic balloon pumping are of little effectiveness in cases of severe ventricular failure. The proposed study is concerned with the development and testing, on a mock circulatory loop and in a series of dog experiments, of an automated combined assist system for the profound support of the failing heart. This system is mildly invasive and consists of the synergistic use of intra-aortic balloon pumping and partial veno-arterial bypass. Previous in vivo studies using this system with no automation have shown that it is quite effective in achieving its clinical objectives, and our purpose is to investigate the ability of the control systems developed herein to match the optimal manual setting of the assist system. The end result of the project is a portable compact automatically controlled ventricular assist system that can be rapidly and easily instituted, thus improving the chance of survival and recovery of acute myocardial infarction and cardiogenic shock victims.
Sensitivity analysis and parameter identification for a model of left ventricular mechanics and the systemic arterial load
(1982) Paulsen, Robert Alan; Clark, John W.; Johnson, Don H.; Walker, William F.
An identification scheme for the determination of several parameters associated with a third-order lumped-parameter model of the systemic arterial system has been developed previously (1). In the present study, a parameter sensitivity analysis of this model is conducted in conjunction with the identification scheme. This analysis indicates that the state variables of this system are not unduly sensitive to changes in the model parameters or initial conditions. It also indicates the relative sensitivities of the individual model parameters and provides valuable insight into the behavior of the arterial model. This insight resulted in a significant simplification of the identification scheme (1) that makes it more likely to be employed in practice. The arterial model mentioned above is driven by aortic root flow f (t), and this waveform is approximated by either of two methods, one involving the measurement of left ventricular pressure, the other a measurement of left ventricular volume. Adequate specification of the model driving waveform f (t) is very important to the identification process and, therefore, the abilities of the aforementioned methods in approximating fa(t) under practiced measurement conditions are investigated. The left ventricular mechanics for an individual patient are specified by the elastance curve in this study. Two clinical approaches, the direct and the indirect, to the estimation of left ventricular elastance are presented. A multiple measurement technique is used to solve for end-diastolic volume in the direct problem and an approximate method for the determination of the aortic valve resistance is suggested for the solution of the indirect problem. A sensitivity analysis of the left ventricular model proved useful in the analysis of both approaches.
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.
The effects of upstream mass injection on downstream heat transfer
(1969) Wolfram, William Robert; Walker, William F.
This study was performed in order to determine the effects of upstream mass injection on downstream heat transfer in a laminar non-reacting boundary layer. The study differs from numerous previous investigations in that no similarity assumptions are made. A numerical technique known as the method of integral-matrix analysis is used. This approach is a recent outgrowth of the method of integral relations. The complete coupled set of non-reacting laminar boundary layer equations with discontinuous mass injection was solved for this problem using the integral-matrix technique. The effects of mass injection on heat transfer to both sharp and blunt-nosed isothermal flat plates were studied for a Mach 2 freestream. The amount of injection and the length of the injected region were varied for each body. Heat transfer rates were found to decrease markedly in the injected region. A sharp rise in heat transfer was found immediately downstream of the region of injection followed by an asymptotic approach to the heat transfer rates calculated for the case of no injection. An insulating effect was found to persist for a considerable distance downstream of the injection region. The distance required for this insulating effect to die out was found to depend on the length of the injection region as well as the rate of injection.
Thermal properties of frozen saline soils
(1984) Jordan, Jonathan D.; Chapman, Alan J.; Wierum, Frederic A.; Walker, William F.
The thermal properties of three soils have been studied to ascertain the effects of saturating the soils with saline water. The frozen state is the primary area studied, although data during and after a phase change in the soils is also presented. The thermal properties evaluated include the thermal conductivity and thermal diffusivity, measured by means of the transient thermal probe technique, in which a metal probe is inserted into a cylindrical soil sample. This technique allows the simultaneous determination of the two thermal properties by recording the temperature response at two locations in the sample to an ideal line heat source from the probe. The experimental apparatus is described and the results are compared to several theoretical predictive methods of calculating the thermal conductivity of soils. The data from the phase change region were determined to be inconclusive and the results of the unfrozen soil were too few to find representative results. The results from frozen.state show very little effect from the salinity of the porewater. Any effects seem to be less than the accuracy of the experiment itself. The predictions from the theoretical models support this conclusion. Finally, recommended values for the thermal properties of the frozen soils are given as independent of both the temperature and porewater salinity for the ranges considered in this work.
Use of a laboratory computer for the hydro-dynamic evaluation of aortic valve prostheses in-vitro
(1978) Bilowich, Lola Norton; Walker, William F.
A method of providing a simplified approach to the hemodynamic evaluation of prosthetic aortic valves was pursued and tested. The prostheses were tested in a closed-circuit mock circulatory loop which was designed to approximate physiological pressure and flow behavior near the valve. As operative technique may preserve the sinuses of Valsalva intact or, more commonly, effectively destroy them, the valves were tested in both configurations. Trends in valve performance were observed. Comparisons between these trends and similar results by other investigators were made when possible and found to be consistent with some while at variance with others.
Use of hierarchical elements in isoparametric finite element procedures
(1984) Kipp, Robert J.; Akin, J. E.; Wheeler, Mary F.; Walker, William F.
This thesis reports on an initial study into how hierarchical elements can best be used to enhance existing isoparametric finite element routines. Hierarchical finite elements have been used to date primarily for self-adaptive solutions, but the architecture of these programs is significantly different than conventional finite element programs. The goal is to develop methods by which hierarchical elements can be easily adapted to the large number of existing conventional programs and provide additional output to assist the analyst. The investigation discussed in this thesis is carried out in one dimension. It is demonstrated that a lower-order formulation with a higher-order hierarchical term added results in a solution equivalent to the complete higher-order solution. A technique is demonstrated by which a correct higher-order solution can be iteratively calculated using the initial lower-order stiffness matrix and without assembly of the higher-order stiffness terms. Also shown is a method for calculating a useful element-level error indicator. The one-dimensional model problem used is of a form which yields non-zero off-diagonal hierarchical stiffness terms; a situation typical in cases of higher dimension. Consequently, this work provides a basis for extension of the concepts into higher dimensions, where the benefit of the hierarchical enhancement will be most significant.
Wall pressure distributions for a turbulent attacked jet flow
(1969) Byrd, Otis Eugene; Walker, William F.
In this study a method was developed to predict the pressure distribution along the enclosed wall in a turbulent attached jet flow. The flow was assumed two dimensional and only time averaged properties were considered. A flow model was developed and used to write a momentum balance. From this balance the wall pressures were predicted. The results of these predictions are shown and suggestions for continued research are given.

Browsing by Author "Walker, William F."

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