bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Interaction of Intense Acoustic Fields and Viscous Fluid Flows
Authors: Hribar A. E. , Purdy K. R.
Published: November 2011

A survey is given of several analytical techniques that can be applied to acoustic streaming phenomena. A method is selected for examining intense acoustic field-viscous fluid flow interaction problems in which the flow oscillation magnitude is much larger than any time-mean flow component. The method itself has a wide range of applicability and provides a clear and explicit statement of the approximations involved. The major goal of the paper is to illustrate this method by applying it to a new problem; namely, the interaction of an intense transverse resonant acoustic field with simple channel flow. The solution, while simple, possesses some very interesting heat transfer aspects.
Pulsatile Flow Behavior in Elastic Systems Containing Wave Reflection Sites
Authors: Campbell J. L. , Yang T.
Published: November 2011

An analytical study is presented for one-dimensional, pulsatile flow of an incompressible fluid in systems of elastic tubing. Nonlinear terms are retained in the system of describing equations. Three experimental test systems with characteristics similar in some respects to those of the human cardiovascular system are described. These systems were used for experimental verification of the analytical predictions. Comparisons of the analytical predictions and experimental results show that pressures, mass flow rates, and velocities can be predicted with reasonable accuracy for all test conditions employed on the three models.
Nonlinear Optimal Control by Use of Extra Linear States to Represent Nonlinearities
Authors: Gustafson R. D. , Harwood R. A.
Published: November 2011

This paper describes a technique which extends the application of the Kalman linear state variable feedback controller to practical nonlinear systems. This technique involves the linearization of the system model with residual nonlinearities retained. Extra linear states are then used to represent the residual nonlinearities in formulating the optimal controller. The use of the technique is illustrated by generating a controller for a simplified model of a hydroelectric plant. The advantages are shown by a comparison between the response of the nonlinear system with a controller generated using all of the nonlinearities as extra states and one using only one of the nonlinearities as an extra state. This technique could be used to design a nonlinear analog controller with fixed coefficients or an extremely simple control routine for an online digital computer.
Optimal Control of Linear Distributed Parameter Systems With Constrained Inputs
Authors: Weigand W. A. , D’Souza A. F.
Published: November 2011

The optimal open loop control of systems described by a set of linear partial differential equations is investigated. The performance index is of quadratic type and the mean square error is considered as a special case. Energy type inequality constraints are imposed on the control inputs. The problem is formulated as a minimization problem in Hilbert space. The necessary and sufficient conditions for a minimum are obtained and it is proved that these conditions yield the global minimum. It is shown how the solution to the constrained problem can be obtained from the solution of the unconstrained problem. The optimal control functions satisfy Fredholm integral equations with symmetric kernels. The paper presents an example where the solution is obtained by eigenfunction expansion.
The Use of Piecewise Continuous Expansions in the Identification of Nonlinear Systems
Authors: Sprague C. H. , Kohr R. H.
Published: November 2011

This paper describes an experimental method of establishing an ordinary differential equation to represent, or describe, a nonlinear physical system. Each nonlinear function that appears in the differential equation is approximated by a piecewise continuous collection of simple power series expansions. A given elementary expansion is used to represent a function over only a small fraction of the total range of the corresponding argument. These expansions are characterized by a few coefficients which are determined, during the identification process, by a steep descent adjustment procedure. It is assumed that the system may be excited by a specified input and that neither the input nor the output is significantly corrupted by noise. Systems of any order, and with any number of unknown constant coefficients and continuous, single-valued nonlinear functions may be identified with this procedure. Prior knowledge required to implement the method includes the form and order of a differential equation to describe the unknown system, and the location and arguments of functions in this equation assumed or known to be nonlinear. Examples are given to illustrate the efficacy of the method.
A Multiplier Rule for a Functional Subject to Certain Integrodifferential Constraints
Authors: Wittler M. , Shen C. N.
Published: November 2011

A problem in the optimal control of a nuclear rocket requires the minimization of a functional subject to an integral equation constraint and an integrodifferential inequality constraint. A theorem giving first-order necessary conditions is derived for this problem in the form of a multiplier rule. The existence of multipliers and the arbitrariness of certain variations is shown. The fundamental lemma of the calculus of variations is applied. A simple example demonstrates the applicability of the theorem.
Optimal State Variable Feedback With Bounded Gains
Authors: Millers H. F. , Takahashi Y.
Published: November 2011

The optimization of bounded feedback gains with respect to an arbitrary integral performance criterion is performed using nonlinear programming. The gradient projection method has been applied to several examples of fifth order, linear, and nonlinear, with good results.
Switching Analysis for Constrained Bilinear Distributed Parameter System With Applications
Authors: Briggs D. L. , Shen C. N.
Published: November 2011

A distributed parameter thermal and stress model is developed for a nuclear rocket. The resultant equations for the optimal control problem are a pair of coupled, bilinear, partial differential equations. The thermal stress constraint forms an inequality which is a function of both the state and the control. The initial conditions are steady state, and the terminal condition is that the coolant flow obtain a fixed, higher level. The distributed parameter system is discretized in the space dimension to give an arbitrary order set of ordinary differential, state equations. It is shown how a result based on the Weierstrass necessary condition and derived by Berkovitz from the calculus of variations using a slack variable technique may be applied. This condition is shown to require the optimal control to be “boundary control” with no switching. The optimal control program must make the inequality constraint an equality at some location throughout the transient. Based on the result that boundary control is the optimal control, an algorithm is developed to compute the optimal control program. The algorithm was programmed on a digital computer and numerical results are given for the optimal flow program and the resultant stress distributions for various cases.
An Implantable Valveless Heart Assist Pump
Authors: Turner M. C. , Pierce W. S. , Metz H. D. , Goodman L.
Published: November 2011

An intracorporeal left ventricular bypass, incorporating an electrically driven roller pump, has operated successfully in unrestrained calves for periods up to 11 days. A pneumatically powered prototype, designed for eventual human application, extends potential effective pumping periods to two months in tests simulating implanted conditions. Mechanical design and materials maintain clotting and cell damage below traumatic levels and no subsequent ill effects are indicated.
A Model for the Control of the Rat Estrous Cycle
Authors: Schwartz Neena B.
Published: November 2011

This paper first reviews the basic elements of the reproduction system in female mammals and indicates the adaptive significance of the cyclicity of structure and function always observed in this system. A detailed description of the reproductive cycle in the laboratory rat is then presented, and a theoretical model of the control of the rat estrous cycle is described. The purpose of the model is to “explain” the mechanism of cyclic function of reproduction in the rat. Some examples of the heuristic value of the model are then outlined, including the beginning of computer simulation.
Experiences on Startup and Trial Operation at Yards Creek Pumped Storage Project
Authors: Swed R. J. , Yang K. H.
Published: November 2011

Many problems were encountered during the startup and trial operation at Yards Creek. This paper describes the major problems and how they were resolved. There are many questions about pump-turbine operation that remain unanswered. Exchange of information and experience is needed. The authors hope that this article will help to stimulate this exchange of information.
Response of a Fluidic Air Gauge
Authors: Moses H. L. , Small D. A. , Cotta G. A.
Published: November 2011

The response of the back pressure signal resulting from nozzle flow suddenly restricted by a downstream surface is described. Experimental results are presented for the periodic signal from a small nozzle in close proximity to a rotating gear. A simplified analysis for the back pressure as a function of time is developed and the calculated signal amplitude versus frequency is compared with the experimental results.
Electron Paramagnetic Resonance Measurements of Strain Induced Ozone Cracking in Rubber
Authors: DeVries K. L. , Simonson E. R. , Williams M. L.
Published: November 2011

An electron paramagnetic resonance (EPR) method for monitoring the rate of atomic bond rupture in rubber subjected to uniaxial tensile strain in an ozone environment is described. The free radicals so formed are found to be quite stable and present in large, easily detectable concentrations. The initial rate of bond rupture was found to be approximately proportional to ozone concentration at fixed strain. Below a prestrain of three percent, no effect of the ozone environment was detected; above this threshold, the rate of rupture increases with strain up to strains of approximately 20 percent. It appears that this EPR technique is very sensitive and can yield information not readily obtainable by more conventional techniques.
Three-Dimensional Boundary-Layer Flow About an Ablating Slender Cone
Authors: Fannelop T. K. , Smith P. C.
Published: November 2011

A theoretical analysis is presented for three-dimensional laminar boundary-layer flow about slender conical vehicles including the effect of transverse surface curvature. The boundary-layer equations are solved by standard finite difference techniques. Numerical results are presented for hypersonic flow about a slender blunted cone. The influences of Reynolds number, cone angle, and mass transfer are studied for both symmetric flight and at angle-of-attack. The effects of transverse curvature are substantial at the low Reynolds numbers considered and are enhanced by blowing. The crossflow wall shear is largely unaffected by transverse curvature although the peak velocity is reduced. A simplified “channel flow” analogy is suggested for the crossflow near the wall.
Electrodynamic Oscillating Compressors: Part 1—Design Based on Linearized Loads
Authors: Cadman R. V. , Cohen R.
Published: November 2011

An approximate method for the design of electrodynamic oscillating gas compressors is developed. A linear spring-damper load is used to approximate the gas load at a single design point. Equations are presented for the linear load and for the design of components. A scheme is developed for the determination of design trends, and the trends are discussed. The design method is applied to two existing designs, an experimental and a commercial electrodynamic compressor, as an independent check.
Analysis and Modeling of the Vortex Amplifier
Authors: Bichara R. T. , Orner P. A.
Published: November 2011

A model has been derived to predict the steady-state input-output characteristics of vortex amplifiers operating in the incompressible flow regime. The model was correlated with experimental data to affect prediction of the influence of the operating fluid properties and the vortex valve critical dimensions on the valve characteristics. The model has been implemented in a digital computer program which includes procedures for the design of vortex valves with specified flow and pressure turndown ratios and the design of vortex amplifiers with proportional (single-valued) characteristics.
A Limited Comparison of the Mechanical Strength of Austenitic Steel in 1200 F Sodium, Air, and Helium
Authors: Kirschler L. H. , Andrews R. C.
Published: November 2011

The mechanical properties of 316 stainless steel were measured at room temperature and at 1200 F during exposure to environments of air, helium and “clean” sodium. The test results were: Test: Cyclic strain / Environment: Air - Least cycles to failure; Environment: Helium - Most cycles to failure; Environment: Sodium - Between air and helium values. Test: Rupture / Environment: Air/Helium - No significant difference in rupture strenth; Environment: Sodium - Possible increase in ductility compared to air. Test: Creep / Environment: Air - Lowest rate; Environment: Helium - Highest rate; Environment: Sodium - Between air and helium values. Test: Tensile / Environment: Air/Helium/Sodium - 5 percent or less difference in tensile strength; 6 percent or less difference in yield strength. The small changes seen in the rupture, creep, and tensile tests, due to different environments, are considered insignificant when compared to overall variations between heats of stainless steel. The differences seen in cyclic strain tests reflect changes in material surface condition produced by environment.
Parametric Influence on the Wall-Thickness Changes and the Bulk Strain Behavior of Hollow-Drawn Tubing
Authors: Flinn J. E.
Published: November 2011

The hollow-drawing behavior of tubing with γ0 values (ratio of initial wall thickness to outer radius) between 0 < γ0 < 1 was studied. The effect of various parameters on wall-thickness changes during hollow drawing through conical shaped dies was examined. The parameters which influenced the wall thickness changes were die-angle, alloy or metal, and γ0. The reduction per pass or magnitude of draft had only a slight or negligible effect. An examination of the wall-thickness changes in terms of current theories is made. The bulk true strain behavior of hollow-drawn tubing is also evaluated for several metals. These strains are the elongation, hoop, and thickness, and they are examined between the limits of a rod and an infinitely thin-wall tube. These limits and the constancy of volume principle suggest that the strains can be represented by ε = C In r/r0, where C is a coefficient peculiar to each strain.
Computerized Relaxation Applied to the Plane-Strain Indenter
Authors: Wesner J. W. , Weinstein A. S.
Published: November 2011

A computer adaptation of Southwell’s Relaxation Method was developed for the solution of elastic-perfectly plastic stress distribution problems. This method was employed to study some aspects of the problem of the plane-strain indenter. For two ratios of strip thickness to indenter width, the load for, and location of, initial yielding and the load for the onset of indentation were found. The results are compared with slip-line solutions.
The Effect of Local Yielding on the Strain-Energy Release Rate
Authors: Key P. L.
Published: November 2011

In a recent paper in the Journal of Basic Engineering [1], Forman presented numerical results for the strain-energy release rate of a crack in a finite width plate using the Dugdale model [2] of a yielded crack to describe the effects of local plastic flow. However, there appear to be several errors in the formulation of the problem by Forman. In addition, it is believed that an analytical rather than numerical approach to this problem would be more useful for applications. In this Note, an analytical form for a correction factor due to yielding is obtained for the elastic strain-energy release rate from an exact expression for the strain-energy release rale of the Dugdale model of a yielded crack in an infinite sheet. The effect of finite sheet width is treated as a separate correction factor.
The Influence of Notches on Mechanical Behavior at Elevated Temperatures: Some Metallographic Observations
Authors: Goldhoff R. M. , Brothers A. J.
Published: November 2011

A metallographic study of ruptured and unruptured notch bars is reported in this paper. The alloys are Cr-Mo-V steels tested in the range 1000–1050 deg F. Crack initiation and propagation in these alloys are studied as a function of the steel’s ductility with test bar section size and notch geometry as variables. It is shown that these factors interact in a complex way to control crack initiation and propagation. The mode and rate of crack initiation and propagation in ductile alloys depend mainly on shear processes although principal stress components are important under certain conditions. Alternatively, the maximum principal stress dominates the behavior in low ductility steels. In the former case, notched bar life is limited by crack propagation while in the latter case it is controlled by crack initiation. The influence of geometrical variables and metallurgical factors are discussed.
Effects of Gravity and Surface Tension Upon Liquid Jets Leaving Poiseuille Tubes
Authors: Lienhard J. H.
Published: November 2011

A method is developed for approximating the transverse velocity component in the incompressible two-dimensional boundary layer equations. The method is restricted to flows that are symmetrical in the transverse coordinate, and it facilitates easy numerical integration in such problems as the prediction of jet and wake flows. The prediction of velocity profiles and diameters for free exiting Poiseuille flows, under the influence of both gravity and surface tension, is then undertaken. Analytical results obtained by the present method are found to agree very closely with experiments. The experiments also show that, in low Weber number situations, contact angle at the exit plane can dominate the early relaxation of the exit profile.
Flow Stress of 6061 AL Alloy Composites
Authors: Gulbransen L. B.
Published: November 2011

The relationship of flow stress to the interparticle path of two phase alloy systems is discussed and the similarity of two phase alloy systems to wire or fiber reinforced composites is described. Experiments were performed on iron wire reinforced 6061 aluminum alloys which show that the flow stress in these systems can be expressed by a similar relationship as documented for two phase alloy systems, namely, σflow = C1 log λ + C2, where C1 and C2 are constants, σflow is the flow stress, and λ is the interwire spacing within 4, 6, and 8 wire aluminum alloy composites.
Laminar Flow Between a Rotating Disk and a Parallel Stationary Wall With and Without Radial Inflow
Authors: Conover R. A.
Published: November 2011

The laminar velocity field between a rotating disk and a stationary disk of the same diameter was investigated by means of a pulsed dye technique without throughflow and in the presence of radial inflow. A stability limit for steady laminar flow was experimentally determined as a function of disk Reynolds number, ReD = R2ωD/ν, and the ratio of gap width to disk radius, z0/R, for the no throughflow case and for a throughflow rate of 0.31 cfm. The basic steady-state data were obtained as a series of paired photographs, a top view and a side elevation, of a dye stream pulsed at a known rate. Data was obtained for ReD = R2ωD/ν from 4.45 × 103 to 1 × 104, z0/R from 0.0476 to 0.0952, and Kν = RωD/Vra from 1.70 to ∞.
Transient Effects in the Discharge of Compressed Air From a Cylinder Through an Orifice
Authors: Deckker B. E. L. , Chang Y. F.
Published: November 2011

The transient nature of the flow through square-edge orifices during discharge from a cylinder and the accompanying expansion of the air have been examined in systematic experiments based on dimensional considerations. It has been found that the expansion of the air in the cylinder is not adiabatic. The effects due to heat transfer to the air, to orifice geometry, and to fluid dynamical quantities on the flow through an orifice have been examined separately. The results obtained under transient conditions are compared with steady flows for which the upstream conditions are similar.
Stress-Intensity Factor for a Short Edge-Notched Specimen Subjected to Three-Point Loading
Authors: Akao H. T. , Kobayashi A. S.
Published: November 2011

Stress-intensity factors for a short edge-notched specimen with an aspect ratio of appoximately 2.7:1 and subjected to three-point loading were obtained by using Bowie’s numerical technique of expanding a mapping function. Numerical relations between the mapping function, aspect ratios, and crack depths of different specimens as well as numerical difficulty in convergence of the procedure are discussed. The results are compared with the nondimensionalized experimental results obtained by Kies, et al., for a larger aspect ratio of 8:1. The proportionality factor between bending moment and stress-intensity factor was approximately 10 percent lower than the corresponding factor for Kies’ specimen and is in substantial agreement with Gross’ results.
A Technical Note on a Semigraphical Synthesis Procedure
Authors: Rabins M. J. , Wasynczuk C. A.
Published: November 2011

The problem of synthesizing a controller to yield a specified overall system phase margin requires specification of both the time constant (or constants) and the gain of the controller, but the choice of the two is not independent. A graphical technique is developed for plotting the relationship between the gain and the time constant in a straightforward manner. A logical criterion results upon which to base the controller design. The method is presented for a first order controller, but the approach may be extended to multiple time constant controllers. The method is applied in the frequency domain to linear elements. Phase shifting nonlinearities can be accommodated by judicious use of describing function results.
Stability of Coupled-Core Nuclear Reactors: Selected Exact Results
Authors: Gage S. J. , Adler F. T.
Published: November 2011

Exact analytical stability criteria are derived for the coupled-core kinetics equations. Four approximate models for describing the time distribution of the coupling neutrons are considered and a theorem proved by Pontryagin is used to establish the asymptotic stability of the systems. The criterion based on the Single Delta Function Model is compared with the one based on the Single Step Function Model.
Fluidic Electrofluid Converter
Authors: McGlaughlin D. W. , Taft C. K.
Published: November 2011

The effects of geometry, Reynolds number, and wall temperature on the separation of a fluid jet from a curved surface are investigated. The results are used to develop an electropneumatic signal converter which has no moving parts. Resistive heating is used to control the wall temperature, which in turn controls the jet separation from the curved surface.
The Second Describing Function and Removal of Jump Resonance by Signal Stabilization
Authors: Ochiai S. , Oldenburger R.
Published: November 2011

A derivative of the output of a nonlinear element is taken with respect to the input. For commonly occurring nonlinearities which are piecewise linear, this derivative is sectionally constant with respect to the input. This property of the derivative is used to reduce the computational work required for deriving the describing function. The concept of this derivative is applied to the study of the effect of a high-frequency signal on the input-output relationship of a system containing a limiter with hysteresis. This signal may be regarded as an extra signal introduced into a system to improve the performance of the nonlinear component. The mathematical analysis of the effect is simplified if the extra signal is a triangular wave instead of sinusoidal. The extra triangular signal is applied to removing the jump phenomenon which exists in a feedback control system with a limiter with hysteresis.
An Experimental Determination of Differential Equations to Describe Simple Nonlinear Systems
Authors: Hoberock L. L. , Kohr R. H.
Published: November 2011

A method is presented for the determination of ordinary differential equations to describe the performance of existing lumped-parameter, time-invariant, nonlinear physical systems. It is assumed initially that the nonlinear elements can be described by products of continuous functions of system variables and these system variables themselves, which consist of the input and output of the system and their time derivatives. It is also assumed that the system input may be specified and that the output can be measured. The method yields graphical representations of unknown nonlinear functions in an assumed system differential equation. Examples illustrating the accuracy of the procedure are presented, and results obtained in the identification of two physical systems are given.
Numerical Fourier Transform Calculations for Pulse Testing Procedures
Authors: Lees Sidney , Dougherty Ray C.
Published: November 2011

Pulse testing of systems, where the input is a controlled function of time, is a well-established procedure. One data reduction technique numerically calculates the Fourier transforms of the input and the response. The complex ratio is the FT of the system function. It is shown (a) that the correction function usually employed to improve the respective FTs cancels out and is a useless operation; (b) that the numerical system function FT fails at high frequencies because the approximation to the integral fails to converge; (c) the upper limit in frequency is ωδ ≤ 0.1π, not π as predicted by the sampled data theorem; (d) generally it is necessary to use ten times as many data points as has been the practice to attain a given bandwidth.
A Study of the Stress-Strain Relationship in the Work-Hardening Range
Authors: Hsu T. C. , Davies S. R. , Royles R.
Published: November 2011

By adopting a generalized definition of strain due to Seth, the stress-strain curves of metals in the work-hardening range can be linearized. The method of choosing the strain measure for linearization is explained and the significance of the constants in the straight line equation discussed. It is shown that the method works for cold-worked materials of unknown prestrain as well as for fully annealed materials.
An Experimental Study of Skewed Turbulent Boundary Layers in Low Speed Flows
Authors: Francis G. P. , Pierce F. J.
Published: November 2011

A detailed experimental investigation is described for the flow of air in skewed turbulent boundary layers on the floor of various curved channels. Measurements of time average velocities, flow directions, turbulence intensities, and growth are made for both the development and decay of the skewed boundary layer. All measurements were made with a unique hot wire probe arrangement. Tests were run with a free stream Reynolds number of approximately one million per ft and a free stream turbulence intensity of approximately 0.0016. The boundary layer was of the order of one inch in thickness. Both the turbulence intensity and velocity profiles indicate that the inner and outer regions, characteristic of two-dimensional profiles, are not necessarily appropriate to skewed three-dimensional flows.
Planar Free Turbulent Mixing With an Axial Pressure Gradient
Authors: Schetz J. A. , Jannone J.
Published: November 2011

An analysis of incompressible free turbulent mixing processes considering either a velocity defect or excess and both favorable and adverse pressure gradients is presented. The full nonsimilar flow field is treated directly by employing a linearized approximation to the momentum equation in the von Mises plane with the total pressure as the dependent variable. A “universal” solution results which can be used to determine the velocity field for any particular pressure gradient by simple algebraic manipulation. Satisfactory agreement with experimental data is shown, and some parametric studies of pressure gradient effects are presented.
Creep of Thick-Walled Cylinders
Authors: King R. H. , Mackie W. W.
Published: November 2011

An experimental and theoretical study is presented of the creep deformation of a thick-walled cylinder under internal pressure and supporting its own end load. In order to compare the experimental behavior with that predicted, care was taken to use an isotropic material and to supplement the pressure tests with adequate tensile data covering the stress range existing in the cylinders. The resulting correlations are discussed for a finite strain analysis neglecting elastic strains, a simple time-hardening extension of this, and for an incremental theory incorporating both elastic and creep strains.
Flanged-Mounted Ball-Bearing Fatigue Tests
Authors: Moore C. C. , Perkins P. A. , Smeaton D. A.
Published: November 2011

The test results of a 8.26-in-dia ball bearing under 51,000-lb axial load at 3710 rpm are discussed. A Weibull plot of the contact fatigue data showed about 6.95 times A FBMA life, a result to be expected with vacuum-melted M50 material and MIL-L-7808 lubricant. Due to high bending stresses, the fatigue spalls initiated ring fracture. Calculation and measurement of these stresses are discussed.
The Law of the Wake and Plane of Symmetry Flows in Three-Dimensional Turbulent Boundary Layers
Authors: Pierce F. J.
Published: November 2011

Coles’ model incorporating the law of the wall and the law of the wake, proposed for two and three-dimensional turbulent boundary-layer flows, is examined for the special case of plane of symmetry flows in collateral and skewed three-dimensional boundary layers. Contrary to other published results, it is shown that the model is appropriate for adverse pressure gradient plane of symmetry flows in collateral environments away from separation. Additional, it appears that the departure from Coles’ law of the wake for recently reported three-dimensional flows is of the same basic form as that observed for plane of symmetry flows in transient development or two-dimensional flow with imminent separation. Since the Coles’ model, as most velocity profile models, is proposed only in an asymptotic sense for a well-developed flow, the fact that most of the three-dimensional flows heretofore reported are in transient or undeveloped states, suggests that the three-dimensional model be examined in well-developed three-dimensional boundary-layer flows before the question of the model’s validity can be properly answered.
Preliminary Experiments With Foil Bearings
Authors: Licht L.
Published: November 2011

A capacitive probe, coincident with the surface of a revolving drum, scans the air gap between a flexible foil and the rotating cylinder. Preliminary measurements of foil displacement are made and compared with results obtained by other investigators. The experiments confirm the existence of an undulating, and sometimes unstable foil configuration in the exit region. A comparison is made between theoretical and experimental values of local amplitude and wavelength of the undulation. The effect of side leakage on displacement is demonstrated.
The Microslip Between a Ball and Its Track in Ball-Thrust Bearings
Authors: Halling J.
Published: November 2011

An approximate solution is proposed for the microslip between a rolling ball and its track when the ball is subjected to applied moments and forces in the plane of motion together with a spin moment about the normal to the contact zone. The solution is based on the appropriate slip conditions for elemental strips in the contact zone neglecting any slip transverse to the general direction of rolling. The solution obtained is shown to be in reasonable agreement with experimental results for plane contact areas subject to spin moments. This solution is also shown to degenerate into a previous solution [3] when the spin moment tends to zero. Using these arguments, it is possible to predict a solution for the microslip patterns obtained in ball-thrust bearings.
Fatigue Failure Under Complex Stress Histories
Authors: Scharton T. D. , Crandall S. H.
Published: November 2011

An expression for predicting fatigue failure of a structure subjected to sinusoidal stress cycles of different amplitudes and different mean values is derived. The derivation is based on a steady-state model of fatigue crack growth. For two cases, predicting in-service fatigue failure and predicting crack growth in a laboratory test, the derived expression is substantially equivalent to the classical linear damage rule. The crack-growth derivation extends the classical linear damage concept to the problem of predicting the remaining fatigue life of a partially damaged structure.
A Study of the Response of a Small Porous Chamber to Forced Oscillation
Authors: Peskin R. L. , Martinez E.
Published: November 2011

An analytical investigation of the pressure response to forced volume oscillations of a shallow cylindrical chamber with a porous end is undertaken. Investigation is in the frequency domain. Both infinite and finite-length chambers are considered. The irreversible gas flow introduces a frequency-dependent phase angle between volume and pressure change. Pressure leads volume at low frequency, and the phase angle becomes zero at high frequency. Curve characteristics suggest applications such as gas damping of vibrating systems.
An Investigation of the Influence of the Boundary Layers on the Performance of Centrifugal-Compressor Impellers
Authors: Lohmann R. P.
Published: November 2011

Under certain conditions, poor performance of a centrifugal compressor can be attributed to irregularities in the velocity distribution at the entrance of the diffuser which may be caused by separation of, or secondary flows in, the boundary layers on the impeller surfaces. A detailed analysis is made of the boundary layers on the blade-suction surfaces and the shrouds of several radial-flow test impellers. Measurements of the discharge-velocity profile with a hot-wire anemometer show that the analysis successfully predicts the relative performance of the impellers. The installation of boundary-layer fences is shown to cause some reduction in the amount of secondary flow in the shroud boundary layers.
A Pressure Index for Predicting the Effect of Flow Profiles on Orifice Meter Performance
Authors: Ghazi H. S.
Published: November 2011

The influence of upstream non-normal velocity distributions on orifice meters is studied experimentally. Several parameters, based on the velocity distribution, were found to correlate with the discharge coefficient. A pressure index, based on wall-pressure measurements, was also shown to correlate with the discharge coefficient. An examination of a proposed prediction method using the pressure index, showed that it appears possible to predict the performance of orifice meters when the approach profiles are non-normal.
Steam Generator Water-Level Control
Authors: Nahavandi Amir N. , Batenburg Abram
Published: November 2011

A combined digital-analog mathematical model for the dynamic analysis of vertical U-tube natural-circulation steam generators is presented. The application of this model to the optimal design of a water-level controller for a steam generating unit is demonstrated. It is shown that a control system consisting of standard proportional and reset controls on water-level deviation from a desired set point and the difference between the steam and feedwater mass flow rates can be successfully employed for the control of water level in such a plant. The optimum values, as well as the range of the controller parameter sellings for which the steam generator exhibits a desired stable response, are determined.
Uncertainty and Imprecision
Authors: Lees Sidney
Published: November 2011

The core problem in the theory of measurements is to assign a value to represent quantitatively our knowledge of a physical property, given a finite set of observations. A corollary problem is to provide a statement as to the quality of the measurement. It is asserted that measurement is a process of drawing plausible inferences from incomplete data. A procedure for treating measurement processes is developed following Jaynes’ formalism, wherein probability is interpreted subjectively as a state of knowledge. In addition to the set of possible outcomes, it is necessary to include prior knowledge. In this paper, only stationary measurement processes are considered, employing repetitive observations of the same quantity. The set of possible observations is exhaustive and mutually exclusive. A theory that predicts infinite deviations cannot be accepted. Three conclusions are presented: (a) When only the expectation value and the variance are assumed known, the least biased, probability distribution is Gaussian; (b) when consideration of a possible malfunction is included, the probability distribution is bounded at three or possibly four standard deviations; (c) when the estimate of the expectation value is studied for a single set of observations, the probability distribution reduces to a rectangular function between the specified bounds. Uncertainty is defined by Shannon’s theorem. Imprecision is defined as the bounds on the probability distribution.
Minimization of Solar Radiation Pressure Effects for Gravity-Gradient Stabilized Satellites
Authors: McElvain R. J. , Schwartz L.
Published: November 2011

The considerations necessary for minimization of solar radiation pressure effects for gravity-gradient stabilized vehicles are presented here. Owing to the rather weak restoring forces available for gravity-gradient stabilized vehicles, solar pressure torques represent a prime source of attitude errors unless steps are taken to minimize their effects. The solar torque minimization procedure generally consists of four distinct steps for a given vehicle configuration: (a) Derivation of the solar torque expressions for the characteristic vehicle configuration, including such effects as diffuse reflection, multiple reflections, and so on; (b) identification of the relative contribution of the solar torques on the various surfaces, and facilitation of solar torque minimization by balancing torque contributions of similar time variation and opposite sign against one another; (c) minimization of the torque about the vehicle axis with the weakest restoring torque (usually the local vertical) via optimization of reflectance characteristics and other physical parameters (using a steepest descent or similar approach); and (d) determination of the vehicle attitude response for the nominal configuration and reflectances, suggesting any configurational changes which might reduce peak attitude errors if necessary. The minimization procedure is performed in this paper using the NASA / Hughes Applications Technology Satellite (ATS) as a prime example of a gravity-gradient-stabilized satellite in an environment where solar pressure is the predominant external disturbance. The application of the solar balancing techniques to the ATS configuration resulted in peak yaw torques of less than 1 dyne-cm for the synchronous altitude satellite, and corresponding peak attitude errors of less than 1 deg in all axes due to solar pressure torques. Although the torque minimization procedures presented here are applicable in the general sense, the application of the techniques to a specific configuration requires derivation of the solar torque expressions for that particular configuration; therefore, the torque minimization example for the NASA/Hughes ATS vehicle can serve as a guide for other configuration applications.
Stability Conditions for a Class of Distributed-Parameter Systems
Authors: Blodgett R. E.
Published: November 2011

The purpose of this paper is to obtain stability conditions for a class of nonlinear distributed-parameter systems by using a generalization of Liapunov’s direct method. Sufficient conditions for local stability and instability of the equilibrium state are derived. An application is given in which conditions are obtained for stability of a chemical-reactor process.
Secondary Flows in an Incompressible Fluid of Varying Density in a Rotating Reference Frame
Authors: Marris A. W.
Published: November 2011

This paper presents the theory of secondary flow generation for an incompressible fluid of spatially varying density due to rotation of the frame of reference. It is pointed out that, while Coriolis forces may deflect the relative streamlines, the generation of secondary vorticity and secondary circulation generally requires an appropriately oriented momentum gradient. In particular, secondary vorticity will not be generated by rotation of the frame of reference in the absence of momentum gradients perpendicular to the flow direction when the streamlines are plane curves. Consideration is given to the rotating dishpan experiment and to the apparently analogous physical examples of the vortex formation when water drains very slowly from a large tank, and the generation of circulation in a hurricane.
Remarks on Snow Cornice Theory and Related Experiments With Sink Flows
Authors: Heskestad Gunnar
Published: November 2011

A review is made of Ringleb’s theory on snow cornice-like flows and of the published, unsuccessful attempts at experimental verification. Arguments are presented which render the theory an unlikely representation of real fluid flows. The flow over a downstream-facing step in a channel, with either of two types of sinks located immediately downstream of the step, was investigated experimentally. A vortex and associated smooth expansion of the exterior flow behind the step were established for sufficiently high sink rates. A model of the step-sink flow is suggested and found consistent with results presented here and elsewhere.
Equibiaxial Low-Cycle Fatigue Properties of Typical Pressure-Vessel Steels
Authors: Ives K. D. , Kooistra L. F. , Tucker J. T.
Published: November 2011

Large-size circular-plate specimens made of typical pressure-vessel materials were tested to determine their low-cycle fatigue strength. The test consisted of two distinct phases; i.e., development of an appropriate testing apparatus and the fatigue testing of the plate specimens. A unique apparatus was developed to test simply supported, circular plate-type specimens. Through a hydraulic system, a uniform pressure was applied to the specimen that resulted in a state of equibiaxial strain at the center of the plate. Tests were conducted to evaluate the pressure-deflection characteristics for various specimen strain levels. Biaxial fatigue data with a strain ratio (circumferential to radial) of 1:1 were generated for three pressure-vessel materials (A-201, A-302, T-1) for a completely reversed strain cycle. Initial cracking was used as a criterion of failure. Cracks were determined by monitoring electrical-resistance strain gages mounted on the specimen.
The Parameter Variation Problem in State Feedback Control Systems
Authors: Perkins W. R. , Cruz J. B.
Published: November 2011

The plant-parameter variation problem in multivariable linear systems described by state-vector equations is formulated using a new sensitivity measure. This formulation involves a direct comparison of open-loop and state-feedback performance in the presence of parameter variations and provides a basis for guaranteeing the superiority of the feedback design. Results are obtained for both continuous and discrete multi-input, multi-output systems. Furthermore, it is shown for single-input, multi-output plants that a low-sensitivity design is also an optimal feedback-control design with respect to a quadratic performance index. This provides a new interpretation of a similar result previously obtained by Kalman.
Hydromagnetic Theory for Squeeze Films
Authors: Shukla J. B.
Published: November 2011

In this paper, the hydromagnetic theory for squeeze films of conducting lubricants has been discussed with special reference to roller and slipper type of bearings. The effect of magnetic field has been theoretically investigated and it has been shown that the load capacity, pressure, and time of approach can be increased by applying the magnetic field in the system.
Investigation of a Partial Arc Pad Bearing in the Superlaminar Flow Regime
Authors: Orcutt F. K.
Published: November 2011

This paper describes the apparatus and the experiments conducted with a 60 deg partial arc journal bearing in laminar and superlaminar regimes. The experiments were conducted with two clearance ratios and over a range of Reynolds numbers (based on mean clearance) up to approximately 12,000. The data on load capacity and attitude angle are compared with laminar theory and with the currently available turbulent bearing theory. Agreement with turbulent bearing theory is satisfactory in the range where the empirical factor (k) was previously determined from other work. Beyond this range, the degree of correlation becomes progressively poorer indicating that (k) continues to vary with Reynolds number even at relatively high values of the latter parameter. The experimentally determined speeds for transition of flow from laminar to superlaminar regime compare well with the criterion for transition in eccentric bearings developed by DiPrima.
Rolling Contact Lubrication—The Application of Elastohydrodynamic Theory
Authors: Smith F. W.
Published: November 2011

A series of experiments on measurements of friction between lubricated rollers moving in combined rolling and sliding is reviewed. The classes of phenomena that occur under various combinations of sliding and rolling are listed under six headings. An elastohydrodynamic theory by Grubin is used to derive the pressure-viscosity exponent of the lubricant from friction measurements, and a value in agreement with viscosimetric measurements is obtained. The film thickness and temperature field in the lubricant when a shear plane develops in the film are also discussed.
Low Cycle Fatigue Life of Turbine Generator Retaining Rings Determined by Stress Cycling Tests
Authors: Baudry R. A. , Cooper G. D.
Published: November 2011

In a turbine generator rotor, the field winding extensions beyond the main body of the rotor forging are supported by high strength retaining rings, which are the most highly stressed components of the rotor. The availability of suitable high strength retaining rings determines the maximum diameter of the rotor which can be built. In modern generators of large rating it is desirable to use rings made of nonmagnetic material. Austenitic steel alloys strengthened by cold expansion or precipitation hardening are generally used. Extensive tests have been made to determine the necessary quality level and methods of evaluation which will assure adequacy of the rings during the entire life of the generator. Among these have been stress cycling tests of slices cut from rings simulating the expected life of a machine. Stress raisers including drilled holes, artificial cracks, non-metallic inclusions, and stress corrosion cracks were tested. As a result of these tests it has been determined that the widely used cold expanded austenitic steel rings at the stress levels used, can withstand large numbers of stress cycles with large stress raisers and thus provide the desired factor of safety.