bluuebunny/crossref_metadata_2025 huggingface dataset:
A Modified Entrainment Theory for the Prediction of Turbulent Boundary Layer Growth in Adverse Pressure Gradients
Authors: Nicoll W. B. , Ramaprian B. R.
Published: November 2011

An approach based on the “entrainment” theory is presented as a tool for the prediction of turbulent boundary layer growth in adverse pressure gradients. The rate of entrainment of free-stream fluid by the boundary layer is assumed to be a unique function of the shape factor. A two parameter velocity profile has been assumed, which reduces to the Spalding [24] profile for zero pressure gradient flows and to the half-power profile of Stratford [26] for separating flows. The integral equations of continuity and momentum are solved with the above empirical input to predict the growth of the boundary layer parameters, both in two-dimensional and axisymmetric flows. The predictions are compared with some of the available experimental data in both the cases. The technique is found to give improved predictions compared with those of previous methods. Results in the case of conical diffusers indicate that the theory predicts slightly higher shape factors than actual, especially in the far downstream portions of the diffuser and thus furnishes a slightly conservative method for design.
Reduction of Noise and Vibrations in a Hydraulic Turbine
Authors: Sagawa T.
Published: November 2011

This paper describes test procedures and methods used to reduce the abnormal noise and vibrations which had occurred at a hydroelectric station in Japan. Noise level, vibration, and pressure were measured in various operating conditions of two turbines of this station, and the necessary conditions for the noise to grow, the substantial cause and various preventive methods were investigated for a year and a half. Finally the noise and vibrations were eliminated successfully by modification of the runner blading.
The Boundary-Layer Velocity Distribution in Turbulent Swirling Pipe Flow
Authors: Backshall R. G. , Landis Fred
Published: November 2011

An experimental study was performed to determine the boundary-layer characteristics of an incompressible swirl flow produced by the insertion of a helically twisted tape into a pipe. The resulting flow can be approximated by a uniform axial flow with a superposed forced vortex flow. Boundary-layer velocity measurements indicate that the total velocity in this three-dimensional flow is well approximated by the universal logarithmic velocity profile. Modified axial and tangential logarithmic velocity laws have also been derived and are shown to be in good agreement with the data. The wall shear stress has to be determined either by direct velocity gradient measurements at the wall or by a modified momentum balance since pressure loss measurements do not directly lead to the correct wall shear stress.
Frequency-Dependent Friction in Transient Pipe Flow
Authors: Zielke W.
Published: November 2011

An equation is derived, which relates the wall shear stress in transient laminar pipe flow to the instantaneous mean velocity and to the weighted past velocity changes. The term is applied to the method of characteristics to calculate water-hammer phenomena in viscous fluids, in which effects of frequency-dependent friction cause distortion of traveling waves. Theoretical results are compared with the experimental pressure fluctuation due to an instantaneous valve closure and show accurate prediction of the response curve.
Optimum Carbon Content for Tempered Martensitic Steels
Authors: Lubahn J. D. , Chu H. P.
Published: November 2011

Notch-tensile tests were conducted on four quenched and tempered steels to study the effect of carbon content on notch toughness. The toughness was found to decrease when the carbon content was either above or below an optimum value of about 0.35 to 0.40 percent. The general engineering concept which prefers a low-carbon steel to a high-carbon steel for better toughness is briefly discussed in view of the present and previous experimental results.
The Microplastic Strain Energy Criterion Applied to Fatigue
Authors: Esin A.
Published: November 2011

This paper describes the research work done to develop an analytical approach to fatigue failure in metals for a life in excess of 105 cycles which will enable the prediction of fatigue data to be carried out by computer. In the region of interest where the metal is nominally elastic, a localized form of plastic flow was found and termed “microplasticity.” As microplastic flow is a random and microstructure sensitive property, it was studied by means of a statistical approach. The necessary parameters to define the statistical functions were obtained from tensile test and by measuring the changes in the a-c resistance under strain, which made it possible to differentiate between elastic and plastic strain and hence detect microplasticity. Using the experimentally defined parameters, a mathematical model for generating microplastic hysteresis loops was constructed. Fatigue damage was related to the plastic hysteresis energy dissipated per cycle and the final fracture was assumed to occur when the accumulated plastic strain energy reached the value under the true stress-true strain diagram. By applying the microplastic strain energy criterion, the fatigue lives of six different types of steel were successfully determined using a computer.
Radial Flow Velocity Field for Predicting Upper-Bound Solutions for Plane Strain Extrusion
Authors: Fenton R. G.
Published: November 2011

The upper bound of the average ram pressure, based on an assumed radial flow velocity field, is derived for plane strain extrusion. Ram pressures are calculated for a complete range of reduction ratios and die angles, considering a wide range of frictional conditions. Results are compared with upper-bound ram pressures obtained by considering velocity fields other than the radial flow field, and it is shown that for a considerable range of reduction ratios and die angles, the radial flow field yields better upper bounds for the average ram pressure.
Dynamic Programming and a Distributed Parameter Maximum Principle
Authors: Brogan W. L.
Published: November 2011

A proof of a distributed parameter maximum principle is given by using dynamic programming. An example problem involving a nonhomogeneous boundary condition is also treated by using the dynamic programming technique and by extending the definition of the differential operator. It is thus demonstrated that for linear systems the dynamic programming approach is just as powerful as the variational approach originally used to derive the maximum principle.
Application of Distributed Parameter Concepts to Dynamic Analysis and Control of Bending Vibrations
Authors: Vaughan D. R.
Published: November 2011

As an alternative to the normal vibration mode approach to dynamic analysis and control of bending vibrations, such vibrations are studied in terms of the distributed parameter concepts of propagation, reflection, and characteristic termination. In particular, the dynamics of lateral vibration of a thin uniform beam are factored into a form that separates the process of propagation from boundary effects. This allows the effects of various terminal impedance matrices to be described in terms of a reflection matrix, which is a generalization of the concept of reflection coefficient for the wave equation. It is shown that the reflection matrix can be nulled by terminating a beam in its characteristic impedance matrix. Several special cases of terminal impedance matrix are considered in detail. The reflection matrices are derived for these cases, and the response of control systems incorporating these terminal impedance matrices is studied by analog simulation.
An Active Roll Mode Suspension System for Ground Vehicles
Authors: Li Y. T. , Meiry J. L. , Roeseler W. G.
Published: November 2011

This paper describes an automatic roll mode control system for ground vehicles. The primary objective of the so-called “active suspension system” is to maintain a coordinated vehicle banking attitude during cornering and steering through traffic. Efforts were also made to render the vehicle insensitive to the undulation of the road surface, wind gusts, and other disturbance inputs. Emphasis was placed upon the development of design logic in the application of control system concepts to a physical system. Realization of the active suspension concept was achieved by parameter optimization of a simplified system on the analog computer and the design and construction of an experimental vehicle. Laboratory and road tests of the physical system confirmed the feasibility of the active suspension concept and brought to focus additional design considerations such as vehicle elastic mode and the effects of man vehicle coupling. For the road tests, a manual bias was incorporated in the automatic roll control loop to improve the transient response of the system, and the resultant man-machine multiloop interaction was investigated.
Investigation of Feedback Controlled Diffusion Systems Using a High-Speed Continuous Electrical Analog
Authors: Kural O. , Schoenhals R. J.
Published: November 2011

A high-speed, two-dimensional, nonsteady, electrical diffusion analog is discussed with emphasis on applications to heat conduction systems. The accuracy of the device is apparent from transfer function data for a one-dimensional system which compares favorably with analytical predictions. The analog was used to study automatic control aspects of surface temperature regulation. Results are presented in terms of frequency response, transient response, and stability limits. In addition, optimal design parameters are given for temperature control of both one and two-dimensional systems in the presence of random disturbances. To obtain the latter information, the analog was used to simultaneously optimize controller gain and the feedback temperature probe location.
Optimum Linear Preview Control With Application to Vehicle Suspension
Authors: Bender E. K.
Published: November 2011

The concept of preview control (a control scheme in which an input is sensed before it reaches the controlled plant) is discussed and applied to the guidance of vehicles over statistically described surfaces. Two methods are presented for optimizing the trade-off between vehicle vibration and the clearance space required for excursions of a vehicle relative to a roadway. The first approach, based on Wiener filter theory, is used to synthesize the optimum characteristics (transfer function) of a free-configuration system. Since the transfer function synthesized in this manner is very difficult to mechanize, a parameter-search technique is used to optimize a fixed-configuration system which may be more easily realized in practice. The results of this study show the reduction in vibration and clearance space that a preview control system may bring about as compared to an optimized system that does not use preview information. Preview control may account for root-mean-square vibration reduction by as much as a factor of sixteen at constant clearance space or a decrease in clearance space by a factor of 223 at constant vibration level.
Mode Oriented Design Viewpoint for Linear, Lumped-Parameter Multivariable Control Systems
Authors: Takahashi Y. , Thal-Larsen H. , Goldenberg E. , Loscutoff W. V. , Ragetly P. R.
Published: November 2011

There are multivariable systems which have free motions dominated by a limited number of clearly separable modes. In some cases it is possible to specifically control these modes, thereby improving overall control of the system. This paper is a discussion of when and how modal control may be applied.
Secondary Flow Effects in a Bounded Rectangular Jet
Authors: Foss J. F. , Jones J. B.
Published: November 2011

The isotach pattern in a bounded jet with an aspect ratio of 6 suggests the presence of a secondary flow structure. A physical flow model is presented, and further measurements substantiate the model and support the conclusion that three-dimensional effects are highly significant in bounded jets of modest aspect ratio, even in the mid plane between the bounding walls.
Rough Surface Effects on Cavitation Inception
Authors: Arndt Roger E. A. , Ippen A. T.
Published: November 2011

Cavitation inception and the associated bubble dynamics in turbulent boundary layers adjacent to surfaces roughened with triangular grooves is investigated in a two-dimensional recirculating water tunnel. The experiments result in the significant conclusion that the cavitation inception index is directly related to the skin friction coefficient for both smooth and rough boundaries. Cavitation is observed to occur away from the wall approximately in the center of the boundary layer, and is apparently the result of negative peaks in static pressure having a magnitude which exceeds 5 times the expected value of root mean square wall pressure. Mean velocity and skin friction data are correlated with existing theory for equilibrium boundary layers.
Some Properties of Laminar Boundary Layers on Curved Surfaces
Authors: Massey B. S. , Clayton B. R.
Published: November 2011

Equations have been developed [1] which describe the flow in a steady, two-dimensional, incompressible, laminar boundary layer on a curved surface. The method of “similar solutions” yields a fourth-order, nonlinear, ordinary differential equation which may be solved on a digital computer. Account is taken of the effects of both surface curvature and displacement thickness, and in this paper attention is given to the influence of these effects on other boundary-layer properties up to and including the position of flow separation.
An Analytical Study of Separated Flow About Circular Cylinders
Authors: Sarpkaya T.
Published: November 2011

The forces acting on a circular cylinder by a time-dependent flow are analyzed through the use of a potential flow model. The shear layers which spring from the sides of the body are replaced by a combination of line vortices and infinite number of vortex sheets which connect the nascent vortices to their respective feeding zones. The analysis is then applied to the prediction of the kinematic and dynamic characteristics of symmetric vortex separation on circular cylinders. The results compare favorably with the latest available experimental data. The development of the wake is also traced and the results show the primary and secondary roll-ups of the shear layers as represented by the line vortices and vortex sheets.
Investigation of a Method for the General Analysis of Time Dependent Two-Dimensional Laminar Boundary Layers
Authors: Koob S. J. , Abbott D. E.
Published: November 2011

A method is given for the analysis of time dependent two-dimensional incompressible laminar boundary layers. The technique is a combination of the method of weighted residuals and the method of lines, and reduces the boundary-layer equations to an Nth order approximation in terms of a system of ordinary differential equations. The method is demonstrated by solving the transient flow over a semi-infinite flat plate and the results are compared with known asymptotic solutions. For a third approximation, the steady-state skin friction coefficient given by the present method agrees with the Blasius solution within 0.1 percent.
The Biaxial Strengthening of Textured Titanium
Authors: Babel H. W. , Eitman D. A. , McIver R. W.
Published: November 2011

The purpose of this investigation was to develop an understanding of the biaxial behavior of titanium sheet. An experimental test method was developed and found to provide homogeneous stress fields for obtaining biaxial data in a variety of stress states. Data were obtained using the same specimen geometry for 1-to-2 and 1-to-1 axial-to-hoop stress states. Significant increases in the biaxial yield strength were obtained over those predicted by von Mises’ yield criterion for isotropic materials. Very high biaxial burst strengths were also obtained; the maximum was 246 ksi for annealed Ti-5Al-2.5 Sn alloy in a 1-to-1 stress state. The data followed the general form predicted by Hill’s model for anisotropic materials.
Fluid Pressure Transients in a Tapered Transmission Line
Authors: Tarantine F. J. , Rouleau W. T.
Published: November 2011

Previous investigations have shown that a liquid-filled tapered tube can be used as a transformer for amplifying or reducing the magnitude of input pulses of pressure and volume flux, but the output pulse becomes distorted, depending on the geometry of the taper. The principal objective of this paper is to present and illustrate a method for the determination of the output from liquid-filled tapered tubes subjected to step, pulse, and time-dependent inputs of pressure and volume flux. Several output results are also included to illustrate the effect of the input condition and the taper function. The model considered consists of a rigid tapered tube terminated by a very long uniform line and filled with an inviscid liquid. The input is applied to the entrance of the tapered tube while the output is taken as the terminal end of the tapered section or entrance to the long uniform line.
Effect of Surface Roughness on Cavitation Performance of Hydrofoils—Report 3
Authors: Numachi F.
Published: November 2011

As a sequel to the first and second reports of the present series of experiments intended to gain knowledge on the effect of surface roughness on hydromechanical characteristics, particularly cavitation performance, the author has this time taken up the case of striations in the direction parallel to the chord, to determine their effect on cavitation efficiency and profile performance in general, for comparison with that of spanwise striations which were the subject of the preceding two reports.
Features and Results of Several Programs of Radiation-Damage Surveillance of Power Reactor Pressure Vessels
Authors: Serpan Charles Z. , Steele L. E. , Hawthorne J. R.
Published: November 2011

The meaning and purpose of reactor pressure vessel surveillance is briefly discussed. Features of the surveillance programs in the Yankee, Big Rock Point, SM-1, and SM-1A reactors are briefly described along with results of testing metallurgical specimens from these programs. Additionally, the surveillance program to be effected in the Army MH-1A reactor is described. Certain problems which have occurred in the course of these programs are discussed as well as the proposed ASTM recommendations for radiation-damage surveillance programs. The value of these programs to reactor operators is reviewed with relation to the results obtained to date.
Fatigue-Crack-Propagation Rates Under Random Excitation
Authors: Plunkett R. , Viswanathan N.
Published: November 2011

Fatigue-crack-propagation rates have been measured for 2024-T3 aluminum cantilever beams in reversed bending under constant amplitude, two-level constant amplitude, and random excitations. For the two-level tests there is a large interaction between the crack-propagation rates caused by stress cycles of different amplitudes. The high-low sequence gives a delay and the low-high sequence a higher rate than a simple no interaction assumption would predict. This is confirmed in the random-excitation tests where the crack-propagation rate for low damping is much higher than that for high damping for exactly the same distribution and level of stress peaks.
Approximate Analysis of Elastic Stress Distribution in Thin Strip Material
Authors: Feng G. C. , Goodman L. E.
Published: November 2011

The general problem of the two-dimensional state of stress in a strip of elastic material under normal loading is considered. A series expansion of displacement functions generated along lines suggested by Mindlin and Medick [1] for dynamical questions arising in plate theory is employed in the solution. The variational procedure generates a set of variational equations of motion. In order to obtain useful results the series is truncated in such a way that the analysis gives an approximate solution valid for ratios of loaded length to plate thickness greater than unity.
A New Matrix Formula for the Inverse Laplace Transformation
Authors: Chen C. F. , Yates R. E.
Published: November 2011

A new matrix formula for the inverse Laplace transformation is established. After substituting the eigenvalues and coefficients and performing some simple matrix operations, one can obtain the inverse Laplace transformation of the function in question. The regular Heaviside techniques involving partial fraction expansions, function differentiations, and so on, are avoided. Since the formula is general, it is particularly advantageous for use on high-order transfer functions; since the formula is exact, the results have no numerical errors. Hundreds of commonly used transform pairs can be replaced by this single matrix formula.
Identification of Dynamic Systems by Digital Computer Modeling in State Space
Authors: Yore E. E. , Takahashi Y.
Published: November 2011

A dynamic system identification technique is described in which a digital computer model is constructed and adjusted until the model state transient follows the system state transient to a prescribed accuracy. This identification technique does not require testing signals and the observation and computation times are short relative to the longest system time constant. The principle of this identification technique is demonstrated by an example consisting of a combination jet pipe electrohydraulic servo and analog computer system. The system’s state-space dimension was larger than the model and the system had measurement noise. Favorable results of the experiment indicate that the method will be applicable to such problems as optimal control, adaptive control, learning control, and on-line component parameter identification.
On Performance Bounds for Control Systems
Authors: Rissanen J. , Durbeck R.
Published: November 2011

A technique based on Lyapunov’s second method is described for deriving bounds for the performance of nonlinear control systems. As an illustration, a performance bound is derived for systems associated with the so-called Lurie problem. As opposed to conventional sensitivity analysis, performance bounds are also determined for systems designed using grossly inaccurate models.
Discrete-Time Models and Stability of Distributed Parameter Systems
Authors: Garvey D. C. , D’Souza A. F.
Published: November 2011

The partial differential equations describing distributed parameter systems may often be reduced to transcendental transfer functions with the aid of appropriate boundary conditions. In the analysis and synthesis of closed loop systems, the transcendental transfer functions have to be approximated in a suitable manner. In this paper, discrete-time model of distributed parameter systems is obtained. The model employs a sample and hold circuit in the loop. The response of the model system is compared with the response obtained by approximating the transcendental transfer function by root factor and other approximations. The stability of linear and nonlinear systems with distributed parameters is investigated by employing the Mikhailov stability criterion.
A New Type of Pneumatic Triangle Wave Oscillator
Authors: Goldstein Seth R.
Published: November 2011

A new type of pneumatic oscillator is presented which produces triangular waveforms of pressure versus time. The device can be used for both high power and low power applications. It utilizes a freely floating disk which translates back and forth a short distance inside a housing between two dynamically unstable flapper nozzle valves. A theoretical analysis of the performance and stability of the device is given. A simplified analysis and design procedure which accounts for load flow is shown. Several prototype units were successfully operated and the experimental results obtained with them are described and compared with the predicted results.
On the Use of the Double Cantilever Beam Specimen for Determining the Plane Strain Fracture Toughness of Metals
Authors: Hoagland R. G.
Published: November 2011

The double cantilever beam (DCB) specimen has considerable potential for application to fracture toughness testing because it facilitates the determination of a number of plane strain toughness data from a single specimen of moderate size. The relationship between the elastic strain energy release rate, load, and extension for a given crack length is obtained from compliance tests and the dependence of this relationship on the specimen geometry is presented. The effect of changing specimen geometry on the fracture toughness is also presented. Comparison with plane strain toughness data obtained by other techniques on identical materials is made to evaluate the effectiveness of the side grooves in the specimen for providing plane strain conditions at fracture. Finally, consideration of the meaning of the stress intensity at crack arrest in the DCB specimen indicates that this parameter is dependent on specimen geometry as well as the material properties.
The Influence of Stress-State and Inclusion Content on Ductile Fracture With Rotation
Authors: Tipnis V. A. , Cook N. H.
Published: November 2011

A study of flow and fracture under combined shear and normal stresses in deformation regions with rotations was undertaken using tubular specimens. The results of the microscopic study for the four resulfurized steels tested show that rotations play an important role in ductile fracture at inclusions even when the mean normal stress is compressive. Two mechanisms for ductile fracture with rotation are proposed. On the gross scale a relationship is found between the fracture strain and the stress state for a given inclusion content. Also, a strong inverse dependence of fracture strain on inclusion content is obtained. These results appear useful to determine limiting shear deformation in metal processing operations.
Elastic and Fatigue Properties of Vacuum Remelted Versus Air-Melted Ni-SPAN-C Alloy 902 for Bourdon Tubes
Authors: Duff T. A. S. , Keenan M. W. , Smith L. E. , Moeller R. H.
Published: November 2011

Under sponsorship of the ASME Subcommittee on Low Pressure Measurement, four companies participated in processing and evaluating vacuum-remelted versus air-melted NI-SPAN-C Alloy 902 (Iron-Nickel-Chromium-Titanium) Bourdon Tubes. The results substantiate the opinion that the cleaner material produced by vacuum remelting will result in a reduction in the number of stress risers, which in turn will improve the fatigue life of the material and reduce the spread in the number of pressure cycles at failure. The vacuum-remelted alloy did not display any significant improvement with respect to other physical properties, such as hysteresis.—Experimental results and data are reported, including the test methods employed for pressure cycling the Bourdon Elements to determine fatigue life.
An Approximate Theory for Developing Turbulent Free Shear Layers
Authors: Lamb J. P.
Published: November 2011

The development of a two-dimensional, free turbulent shear layer from an arbitrary initial velocity profile is analyzed theoretically. Included in the analysis are effects of both compressibility and heat transfer with unit turbulent Prandtl number. The mean flow is described by approximate velocity profiles containing an unknown position parameter which is dependent upon the development distance. Integral forms of the continuity and momentum equations are utilized to specify the flow characteristics along the streamline which separates the primary and secondary flow regions. By integrating a simplified form of the transverse motion equation for this dividing streamline, one is able to calculate the position parameter and thus complete the description of the developing flow field. For initial profiles of a power law type, the theory shows that the development distance required for any flow field variable to achieve a specified percentage of its asymptotic value is proportional to the free-stream Crocco number, to the power law exponent, and to the ratio of the ambient to jet stagnation temperatures. The theory is also utilized to estimate the effects of heat transfer and compressibility on the variation of growth rates for fully developed mixing zones.
Cavitation Damage and Correlations With Material and Fluid Properties
Authors: Garcia R. , Hammitt F. G.
Published: November 2011

A comprehensive set of cavitation damage data has been obtained in a vibratory facility using water, mercury, lithium, and lead-bismuth alloy as test fluids, and covering temperatures ranging from room temperature to 1500 deg F. Materials tested include a wide variety of metals and alloys. From this data a simple, reasonably precise, damage predicting equation has been derived, including only ultimate resilience as a material property, but also corrections for cavitation “thermodynamic effects” and NPSH. It has been found that of the conventional mechanical properties, ultimate resilience is the most successful in this regard. A direct comparison between venturi and vibratory cavitation damage shows that the relative rankings of materials remain about the same for mercury, and a good correlation is obtained between the mercury data from the venturi and ultimate resilience. Neither statement applies for the water venturi data, possibly because of the greater effects of corrosion in the low intensity cavitation field.
Hydrodynamic Entrance Lengths for Ducts of Arbitrary Cross Section
Authors: McComas S. T.
Published: November 2011

A general analytical method is presented for determination of the hydrodynamic entrance length of ducts of arbitrary cross section. Only knowledge of the fully developed velocity profile is required in order to determine this length in comparison to other approaches which require a detailed analysis of the flow development. This method is applied to circular, elliptical, annular, rectangular, and triangular ducts with numerical results presented.
Identification of Potential Failure Nuclei in Rolling Contact Fatigue
Authors: Martin J. A. , Eberhardt A. D.
Published: November 2011

Nucleation points for contact fatigue failures in rolling bearings are identified. In cases where bearings are made from exceptionally clean steel, fatigue failures are frequently nucleated at minute surface imperfections. These have been classified as grinding furrows, pits, and dents. Regions of plastically deformed martensite are found in the vicinity of defects that are active or potential failure nuclei. Plastic deformation is also seen in the bulk material. The plastically deformed martensite is examined by light and electron microscopy and its role in fatigue failures is described.
Influence of Oblique Channel Ends on Screw-Pump Performance
Authors: Booy M. L.
Published: November 2011

Congruent velocity distributions in parallel channel cross sections are assumed in conventional flow theories for screw pumps. That assumption leads to nonuniform pressure distributions along the oblique channel ends. These pressures should be uniform when screw-pump inlet and discharge connections do not restrict flow. A new theory for isothermal flow through channels with large aspect ratios is derived based on uniform pressures along oblique ends. End-effect correction factors for drag flow and pressure back-flow rates are given as functions of L/D and helix angle. Calculated pressure distributions, streamlines, and the end factor for pressure backflow are compared with experimental values.
Radial Flow Without Swirl Between Parallel Disks Having Both Supersonic and Subsonic Regions
Authors: Moller P. S.
Published: November 2011

A theoretical and experimental study is made of turbulent radial flow between parallel disks with choked conditions at the channel inlet. Supersonic flow is found to exist for some distance downstream of the inlet to a point in the channel where a quasi-normal shock causes the flow to become subsonic. A numerical solution is obtained for the radial pressure distribution and the location of the shock region. Agreement with experiment is good as shown both by comparison with the pressure distribution and by flow visualization. When the square inlet corner was preceded by a chamfered section, the mass flows required to choke were increased and approached the one-dimensional predictions.
Carbon and Carbon-Moly Steam Pipe After Long-Time Service
Authors: Bodzin J. J. , Freeman J. W. , Rohrig I. A.
Published: November 2011

Medium-carbon steel piping, after about 200,000 hr of service, and carbon–0.5 molybdenum steel piping, after about 150,000 hr of service, have been evaluated to determine the effect of prolonged service on the stress-rupture, creep, tensile, and impact properties of the materials. The carbon steel was in main steam service at 825 F, 600 psi, and the carbon–0.5 molybdenum steel at 900 F and 800 psi. All of the material tested would meet requirements for new piping; the original differences that probably were present in the piping as a result of fabrication or heat-treatment appeared modified as a result of service.
Recent Research on Cascade-Flow Problems
Authors: Schlichting H. , Das A.
Published: November 2011

A survey is given of extensive research work on cascade-flow problems carried out in recent years in Germany. A considerable part of this work was done in the Variable Density High Speed Cascade Wind Tunnel of the Deutsche Forschungsanstalt fu¨r Luftfahrt at Braunschweig, in which the Reynolds number and the Mach number of the cascade can be varied independently. For compressor cascades with blades of different thickness ratio extensive measurements of the aerodynamic coefficients have been carried out in a wide range of Mach numbers and Reynolds numbers. For very low Reynolds numbers, as they occur for jet engines in high-altitude flight, the influence of turbulence level on loss coefficients has been investigated. Furthermore, comprehensive investigations on secondary-flow losses are reported. The most important parameters in this connection are the ratio of blade length to blade chord, the tip clearance, the Reynolds number, and the deflection of the flow in the cascade. The influence of all these parameters on the secondary-flow losses has been clarified to a certain extent.
Some Physical Effects of Cavity Collapse in Liquids
Authors: Hickling R.
Published: November 2011

The mechanism of cavity collapse in liquids is discussed in relation to certain observed effects in the fields of cavitation damage to metals, sonoluminescence, and the nucleation of freezing by cavitation.
Condensing Vapor Lubrication of Self-Acting Long Journal Bearings
Authors: Unterberg W. , Ausman J. S.
Published: November 2011

This is a theoretical investigation into the behavior of self-acting long journal bearings lubricated with vapor which may partially condense in the high-pressure region of a loaded bearing. Thermohydrodynamic considerations indicate that the lubricant temperature remains constant throughout the bearing. When the maximum pressure in the bearing reaches the saturation vapor pressure at the constant temperature, a further increase in bearing load then causes partial condensation instead of a rise in maximum pressure. In the partial condensation regime, the fluid annulus is made up of (a) a single-phase vapor region with variable pressure, and (b) a two-phase liquid-vapor region at constant saturation pressure. The regional interface locations and the bearing pressure distribution are obtained by “linearized ph” methods under the restrictions or boundary conditions of saturation pressure at the interfaces and constant lubricant mass content. It is shown that complete condensation cannot occur, so that the maximum pressure in the condensing vapor-lubricated bearing is limited to the saturation pressure. For this reason, the resulting load capacity always lies below that of a corresponding bearing lubricated with a noncondensing gas.
Impact Strength of Austenitic Stainless-Steel Welds at −320 F—Effects of Composition, Ferrite Content, and Heat-Treatment
Authors: Bennett F. W. , Dillon C. P.
Published: November 2011

A statistical evaluation has been made of the effect of weld rod composition, ferrite content, and heat-treatment upon the impact strength of certain austenitic stainless-steel welds in 304 stainless-steel plate at −320 F. The data indicate that suitable and approximately equivalent properties are obtained with 310 stainless-steel rod in the as-welded condition, type 308 stainless-steel rod in the as-welded condition (ferrite less than 6 percent), and 308L stainless-steel rod either as-welded or stress-relieved at 1750 F (ferrite less than 9 percent). The impact resistance of 310 stainless steel is adversely affected by stress relief, apparently due to carbide precipitation in this alloy. The 308 and 308L stainless-steel rods are both adversely affected by a stress relief at 1550 F, indicative of sigma formation. The carbon content in 308 stainless-steel rods apparently is not a major factor, as indicated by the lack of adverse effects with a 1750 F stress relief, from which the rate of cooling through the sensitizing range of 800 to 1500 F is identical with that in the 1500 F stress relief. The basic practical conclusion to be drawn from these data is that regular carbon 304 stainless steel welded with 308L stainless-steel rod can be used in cryogenic applications, and that the decision as to whether to stress relieve or not may be left to the mechanical engineer, subject only to the stipulation of a minimum stress-relieving temperature of 1750 F.
The Effect of Strain Rate on Yielding in High Strength Steels
Authors: Kendall D. P. , Davidson T. E.
Published: November 2011

The effect of strain rates ranging from 10−4 to 10 in/in/sec on the yield strengths of several high strength alloy steels is investigated. Quenched and tempered-type alloys exhibit two regions of strain-rate sensitivity with the strain rate dividing the sensitive and insensitive regions varying from 0.5 to greater than 10 in/in/sec, depending on composition, microstructure and grain size. At the higher rates a power-law relationship is found which is consistent with a yielding model involving breakaway of dislocations from solute atmospheres. Maraging steel exhibits a continuous power law-strain rate sensitivity over the entire range.
Hydrodynamic Lubrication of Partial Porous Metal Bearings
Authors: Rhodes C. A. , Rouleau W. T.
Published: November 2011

Partial porous metal bearings are analyzed to determine their performance during steady-state operating conditions with a full film of lubricant. The pressure distribution is determined by a simultaneous solution of the two-dimensional Reynolds equation in the film region and the Laplace equation within the porous bearing material. An infinite-series solution is obtained for pressure utilizing the Galerkin method to determine coefficients. Numerical values of load capacity and coefficient of friction are presented for bearing arcs of 180, 150, and 120 deg.
Effect of Plastic Deformation on the Strain Energy Release Rate in a Centrally Notched Plate Subjected to Uniaxial Tension
Authors: Forman R. G.
Published: November 2011

This paper presents theoretical studies on the effect of plastic deformation on the strain energy release rate, G, of a plate under uniaxial tension with a central propagating crack. The linear elastic fracture mechanics solution for G is improved by using the Dugdale model for the crack and yielded region to obtain the axial rigidity of the plate. The axial rigidity is then used to obtain the solution for the strain energy release rate as the crack propagates. It is found that plastic deformation has a pronounced effect on G. A correction factor is presented for correcting the linear elastic solution for the strain energy release rate. The correction factor is found to depend upon the nominal (gross) stress to material yield stress ratio and the crack length to plate width ratio.
Optimal Feedback Solutions for a Class of Distributed Systems
Authors: Khatri H. C. , Goodson R. E.
Published: November 2011

In the design of controllers for heat transfer systems, one must often describe the plant dynamics by partial differential equations. The problem of optimizing a controller for a system described by partial differential equations is considered here using exact and approximate methods. Results equivalent to the Euler-Lagrange equations are derived for the minimization of an index of performance with integral equation constraints. These integral equation constraints represent the solution of the partial differential equations and the associated boundary conditions. The optimization of the control system using a product expansion as an approximation to the transcendental transfer function of the system is also considered. The results using the two methods are in good agreement. Two examples are given illustrating the application of both the exact and approximate methods. The approximate method requires less computation.
Multilevel Approach Applied to Control System Design
Authors: Lefkowitz I.
Published: November 2011

An approach to control system design is described, based on an extension of the multilevel control concept. In essence, the problem is divided into simpler subproblems: (a) The controlled process is decomposed into a number of subprocesses, each with its own control system operating on a local suboptimal performance criterion; (b) each subprocess controller is decomposed into a hierarchy of control functions which distribute the load and responsibility for satisfying the control objective. The primary effort of the paper is in the development of the control hierarchy as a useful concept in control system design and implementation. The hierarchy is described in the context of the multilevel approach; however, an important distinguishing feature is the association of levels with disturbance sets roughly classified according to the frequency dependency of their effects on the overall performance. Also associated with the hierarchy is an ordering with respect to time scale, complexity of computation, degree of uncertainty, and so on, which relate to important design considerations for the overall system.
Some Experimental Results Concerning Spread in the Rolling of Lead
Authors: Chitkara N. R. , Johnson W.
Published: November 2011

Lead bars of various height-to-width ratio have been rolled down in a model rolling mill to reductions of as great as 60 percent between rolls designated as smooth, partially rough, and rough. The results of experiments to determine the amount of spread which each bar undergoes are presented nondimensionally, and these are compared with the spread formulas of Wusatowski, Hill, and Sparling.
Cavitation Bubble Collapse Observations in a Venturi
Authors: Ivany R. D. , Hammitt F. G. , Mitchell T. M.
Published: November 2011

Bubbles collapsing in water in a cavitating venturi are photographically observed. The large pressure gradient in the venturi causes the bubbles to collapse by flattening in the direction of flow. In many cases a torus is formed, implying the existence of a central jet which, as has been suggested by other investigators, may well be the primary damaging mechanism in cavitating flows. The effect of adjacent bubbles upon each other is visually observed. Numerous bubble rebounds, even in relatively degassed water, are noted. A comparison of observed collapse rates with incompressible theory for a spherical bubble indicates that the slowing down of collapse herein observed at small bubble radii probably results primarily from the asymmetry of the collapse and perhaps also from metastable compression of vapor within the bubble.
Experimental Study of Hydrostatic Extrusion
Authors: Avitzur B. , Sortais H. C.
Published: November 2011

An experimental investigation of hydrostatic extrusion through conical dies using commercially pure lead billets was carried out with two different hydrostatic pressure systems; namely, a ram-type extrusion system (with a forced predetermined extrusion rate), and an injection pump (constant-pressure) system. Pressure characteristics, flow patterns, and the cavity, piping, and dead-zone effects were investigated. Experimental pressure results for both types of pressure systems agreed well with analytical predictions. Furthermore, dead-zone, cavity, and piping effects were found to be dependent upon the semicone angle and the amount of area reduction of the billet.
Effect of Section Size on Notch Strength
Authors: Weiss V. , Schaeffer G. , Fehling J.
Published: November 2011

The effect of section size on the room-temperature notch strength of H-11 steel, 2014-T6 and 7075-T6 aluminum alloys, and Plexiglas was investigated in three different series of notched cylindrical tensile specimens and notched rectangular bend specimens. The three test series permit the separation of the influences of the geometrical parameters, which determine the stress field near the base of the notch, on the notch strength as the size of the specimen increases. The notch strength decreases with increasing size for all series investigated. The decrease in strength is most pronounced for the sharp machine-notched and fatigue-cracked specimens but it is also observed, to a much smaller degree, in the other series of notched specimens for all materials. An analysis of the results of this study indicates that the loss in strength with increasing section size is due to at least two factors: An increase in stress concentration factor and an increase in critically stressed volume with increasing size. With a superposition of stress concentration and volumetric effects, a loss in strength with increasing size greater than that predicted by existing fracture concepts for a brittle material may be anticipated and was actually observed for sharply notched H-11 steel specimens. Insight into the size effect and experimental scatter observed in notched specimens of real materials is gained from a consideration of the behavior of a model of an inhomogeneous material in the presence of external notches. The constant-fracture stress concept applied to this model yields a size-effect prediction on notch strength and an expression for experimental scatter in terms of the interflow spacing and the notch root radius.
Wake Dispersion in Turbomachines
Authors: Smith L. H.
Published: November 2011

The motion of a wake as it passes through a blade row that moves relative to the wake generator is considered. Viscosity is neglected, and it is shown that the wake is modified by a chopping process that disperses it and also by uneven energy addition. Some hot-wire anemometer traces taken downstream of a rotor in a research compressor demonstrate the wake-chopping phenomenon.
A Noniterative Numerical Solution of Poisson’s and Laplace’s Equations With Applications to Slow Viscous Flow
Authors: Booy M. L.
Published: November 2011

A noniterative finite-difference method for solution of Poisson’s and Laplace’s equations for linear boundary conditions is given. The method is simpler and more accurate than iterative procedures. It is limited in the number of meshes that can be used, but that number is adequate to obtain accurate solutions to many engineering problems. The computational effort is reduced vastly when one differential equation must be solved in a family of domains for the same boundary condition. The same applies to calculations of the integral of the function in the domain. Examples are given for simultaneous solution in Laplace’s and Poisson’s equations and for problems with multiple boundary conditions. The results of several slow viscous-flow problems are discussed.