bluuebunny/crossref_metadata_2025 huggingface dataset:
Motion of a Large Dusty Buoyant Thermal With a Vortex Ring
Authors: Chang Stephen S.-H.
Published: November 2010

This paper presents a method for computing the motion and decay of a large dusty, buoyant thermal (cloud) carried by a vortex ring generated from a strong near ground explosion and ascending in an inhomogeneous atmosphere. A system of equations is derived describing the motion of the vortex ring, the thermal, and the pollutants which consist of numerous solid spherical particles. The interior properties and the trajectories of the thermal and the pollutants are obtained. The numerical solution for the thermal trajectory is in excellent agreement with experiment.
Finite Extension of an Elastic Strand With a Central Core
Authors: Huang N. C.
Published: November 2010

This paper deals with the finite extension of an elastic strand with a central core surrounded by a single layer of helical wires subjected to axial forces and twisting moments. The central core is considered as a straight rod of circular cross section and the helical wires are regarded as slender curved rods with circular cross section. The theory of slender curved rods is used in the analysis. Geometrical nonlinearities due to the reductions in helical angle and cross section of the core and wires are included. It is found that as a result of the contact between the central core and helical wires, a separation between helical wires can occur during the extension of the strand. Stresses in the core and wires as well as the contact forces between the core and wires are analyzed for strands with various helical angles subjected to different axial forces. Examples are presented for the finite extension of strands with fixed ends and strands with free ends.
Nonlinear Material Damping for Nonsinusoidal Strain
Authors: Plunkett R. , Sax M.
Published: November 2010

The damping in uniform and nonuniform cantilever beams was measured at resonance for a range of amplitudes of simultaneous steady-state first and second mode vibration. For two linear materials, aluminum and crossply fiberglas, the damping factor in each mode is independent of amplitude and unaffected by the presence of the other mode. For a fully annealed tool steel with highly nonlinear damping, the damping factor in each mode is markedly increased by the presence of the other mode.
The Response of an Oscillator With Bilinear Hysteresis to Stationary Random Excitation
Authors: Roberts J. B.
Published: November 2010

By applying the technique of stochastic averaging, a simple analytical result is obtained for the joint distribution of the displacement and velocity of a bilinear oscillator excited by a stationary random process. A comparison of theoretical results deduced from this distribution with corresponding digital simulation results shows that the theory is accurate in circumstances where the response is narrow-band in nature.
Stress-Concentration Factors for a Countersunk Hole in a Flat Bar in Tension and Transverse Bending
Authors: Cheng Y. F.
Published: November 2010

A series of three-dimensional photoelastic experiments was performed to determine the maximum stresses and stress-concentration factors at countersunk holes in a flat bar in tension and transverse bending. In the tension case, the maximum stress was found at the base of the countersunk and the stress-concentration factor was approximately 33 percent higher than those found in a straight hole. In the bending case, the neutral plane was shifted toward the surface containing the straight part of the hole and the stress-concentration factor was practically the same as those found in straight holes.
Axisymmetric Flexural Vibrations of a Thick Free Circular Plate
Authors: Hutchinson J. R.
Published: November 2010

A series solution of the general three-dimensional equations of linear elasticity is used to find accurate natural frequencies and mode shapes for the flexural vibrations of thick free circular plates. The approximate solution for thick plates, which includes shear and rotary inertia effects, is compared with the accurate series solution. It is found that the approximate solution yields frequencies of sufficient accuracy for most engineering applications within the range of applicability of the approximate theory.
Nonlinear Stability Analysis of a Two-Dimensional Model of an Elastic Tube Conveying a Compressible Flow
Authors: Matsuzaki Y. , Fung Y.-C.
Published: November 2010

This paper examines the dynamic behavior of a two-dimensional channel whose upper and lower walls deform symmetrically with respect to the center line of the channel. Unsteady fluid dynamic forces acting on the internal wall are analytically evaluated on the basis of a linearized compressible potential flow theory. The effects of distributed springs outside the channel and an internal pressure on the stability characteristics are studied by considering small disturbances about flat and buckled equilibrium configurations of the wall. The analytic methods indicate that no flutter of the flat or buckled wall is predicted when the Mach number is small and the viscous damping coefficient is positive. Numerical results by the Runge-Kutta-Gill method suggest that nonlinear effect of flow should be taken into account to fully examine the dynamic characteristics of the channel conveying a flow.
Collapse of Thin Orthotropic Elliptical Cylindrical Shells Under Combined Bending and Pressure Loads
Authors: Spence J. , Toh S. L.
Published: November 2010

The elastic collapse of thin orthotropic elliptical cylindrical shells subject to pure bending alone or combined bending and uniform normal pressure loads has been studied. Nonlinear finite deflection thin shell theory is employed and this reduces the problem to a set of nonlinear ordinary differential equations. The resulting two-point nonlinear boundary-value problem is then linearized, using quasi-linearization, and solved numerically by the “shooting technique.” Some experimental work has been carried out and the results are compared with the theoretical predictions.
Estimation of the Collapse Loads of Thin-Walled Cylinders in Axial Compression
Authors: Foster C. G.
Published: November 2010

By considering the Yoshimura pattern obtained in buckling thin-walled cylinders as a space frame and calculating the collapse loads of the compression members the critical loads of a buckling cylinder can be estimated. Excellent agreement has been obtained with one set of published experimental data in establishing both the postbuckling critical loads and the initial buckling load.
The Stability of a Moving Elastic Strip Subjected to Random Parametric Excitation
Authors: Kozin F. , Milstead R. M.
Published: November 2010

The dynamic stability of a thin strip, traveling axially, at a constant speed between two roller supports is investigated for the case of zero mean random in-plane loading. Galerkin’s method is used to reduce the equations of motion to a set of fourth-order stochastic equations. An extention of the method first proposed by Wu and Kozin is developed which allows determination of the sufficiency conditions to guarantee Almost Sure Asymptotic Stability of stochastic systems of order greater than two. Using this method, results in terms of the variance of the random loadings on the moving strip are derived. It is found that the critical noise level to guarantee stability of the strip decreases with increasing mode, approaching asymptotically a level determined solely by the strip stiffness.
Dynamic Response of a Membrane With Both Curved and Straight Line Boundaries
Authors: Nagaya K.
Published: November 2010

In this paper a method for solving vibration and dynamic response problems of a membrane having an arbitrary shaped boundary consisting of curved and straight lines is presented. The frequency equation for the arbitrary-shaped membrane is given, and the solution for the membrane subjected to general transient load is obtained in a generalized form. As a numerical example, the response of a parabolic membrane subjected to a uniformly distributed exponentially decaying load is investigated.
A Physically Consistent Method for the Prediction of Creep Behavior of Metals
Authors: Weng G. J.
Published: November 2010

A physically consistent method, which considers the deformation mechanisms, the active and latent hardening in single crystals, and their transient and steady creep, is proposed to predict the creep behavior of polycrystalline materials. This method consists of two steps: first, the material constants of single crystals are determined from the tensile creep data of the polycrystal, and then these constants are used to predict the creep properties of the same polycrystal under required loading conditions. This method simultaneously satisfies the requirements of equilibrium and compatibility over the grain boundaries, and is self-consistent. The proposed method was applied to calculate the creep strains of a 2618-T61 Aluminum alloy under pure shear, combined stress and nonradial loading; the results obtained were in good agreement with the test data.
Uniaxial Cyclic Loading of Elastic-Viscoplastic Materials
Authors: Bodner S. R. , Partom I. , Partom Y.
Published: November 2010

Elastic-viscoplastic constitutive equations based on two internal state variables are utilized to determine material response for uniaxial cyclic loading conditions. These equations are capable of representing the principal features of cyclic loading behavior including softening upon stress reversal, cyclic hardening or softening, tendency toward a stable limit cycle, cyclic relaxation, and cyclic creep. Calculations were performed for various stress and strain controlled conditions using material constants intended to represent commercially pure titanium and aluminum and OFHC copper. Capabilities and limitations of the analytical formulations are discussed in relation to computed results and corresponding test data.
A Circular Crack Under Asymmetric Loads and Some Related Integral Equations
Authors: Krenk S.
Published: November 2010

A method of solution in terms of polynomials is developed for some integral equations that arise in connection with boundary-value problems for the circular disk. The key result is a Neumann series expansion of the kernel in terms of Gegenbauer polynomials. The method is developed in connection with the problem of a circular crack under general asymmetric loads and leads to explicit relations between the applied surface stresses and the crack opening. The method completely avoids the use of Abel integrals often associated with dual integral equations and is easily adapted to numerical calculations.
Computation of Rigid-Body Rotation in Three-Dimensional Space From Body-Fixed Linear Acceleration Measurements
Authors: Mital N. K. , King A. I.
Published: November 2010

The angular acceleration of a rigid body with respect to a body-fixed (moving) frame can be reliably computed from nine acceleration field measurements. Noncommutativity of finite rotations causes computational problems during numerical integration to obtain the transformation matrix, especially when the rotation is three-dimensional and there are errors in the measured linear accelerations. A method based on the orientation vector concept is formulated and tested against hypothetical data. The rigid-body rotations computed from linear accelerometer data from impact acceleration tests are compared against those obtained from three-dimensional analysis of high speed movie films.
On the Dynamics of a Weighted Bowling Ball
Authors: Huston R. L. , Passerello C. , Winget J. M. , Sears J.
Published: November 2010

An analysis of the dynamics and performance of a weighted, slipping/rolling bowling ball is presented. The analysis uses Euler parameters and angular velocity components as dependent variables. The governing equations of motion are integrated using standard digital/numerical procedures. Particular attention is given to factors affecting ball performance (“hook”) and the lane oil tracing on the ball. It is found that factors most affecting hook are the mass-center location, the lane conditions (friction), and the initial angular velocity component parallel to the lane.
A Continuum Dislocation Theory Model for Predicting the Wall Thickness Changes of Hollow Drawn Tubing
Authors: Flinn J. E.
Published: November 2010

An expression, based on some concepts of continuum dislocation theory, is developed for predicting the wall thickness changes in hollow drawn tubing. This expression predicts the observed wall thickening and thinning behavior and incorporates the parametric influences on the changes of wall thickness.
Void Fraction and Pressure Drop in a Water Electrolysis Cell
Authors: Thorpe J. F. , Funk J. E. , Bong T. Y.
Published: November 2010

An experimental investigation was conducted to determine the void fraction and pressure drop occurring in a forced-convection water electrolysis cell. It was concluded that the slip ratio is essentially unity for water electrolysis cells operating at atmospheric pressure and 80–100 deg F. A frictional pressure-drop multiplier was determined by a data reduction technique that has been used extensively in the boiling heat transfer literature. This multiplier has been correlated and found to be a function of both the void fraction and the gas generation rate.
Annular Two-Phase Flow—Part 1: A Simple Theory
Authors: Wallis G. B.
Published: November 2010

A simple theory for annular two-phase flow is developed in terms of equations for the interfacial and wall shear stresses. Expressions for the pressure drop and void fraction are derived. Criteria for the minimum pressure drop, zero wall shear, and flow regime transition in vertical flow are given. The results are compared with numerous data and alternative theories from the literature.
Response Characteristics of a Pulse-Width-Modulated Electrohydraulic Servo
Authors: Tsai S. C. , Ukrainetz P. R.
Published: November 2010

Methods for analyzing the response characteristics of a pulse-width-modulated electro-hydraulic servomechanism are presented. Except for the modulator, the hydraulic control system is of conventional configuration. The modulator transfer characteristic is derived from a double Fourier series analysis of the pulse-width-modulated signal and this indicates the effect of the modulation parameters on the system performance. The valve flow which controls the mechanical load motion has been shown to be the dominant nonlinearity in a valve-controlled hydraulic system, and the system becomes more complicated due to the valve spool dither which is a consequence of the pulse-width-modulated signal. A dual-input describing function is developed for the equivalent valve flow gain in the determination of the system closed-loop frequency response. A numerical simulation is used to obtain the closed-loop transient response. Experimental verification of the theoretical analyses is carried out on a practical system. Good agreement is obtained between the predicted and the experimental responses.
A Multipurpose Frequency-Response Analyzer
Authors: Kohr R. H. , Sprague C. H.
Published: November 2010

A novel closed-loop method of obtaining the frequency response of a physical system is presented. It is assumed that the physical system to be examined may be excited by a known sinusoidal input signal and that the resulting output response may be measured. The method described herein employs this input-output information together with a steepest descent computing procedure to obtain the in-phase and quadrature components of the system’s response. The method may be mechanized on either an analog or digital computer and may be applied to either linear or nonlinear systems. Examples illustrating the application of the procedure to a variety of linear and nonlinear systems are given.
A Modified Gradient Procedure for Adaptation in Nonlinear Control Systems
Authors: Pearson A. E.
Published: November 2010

A modified gradient procedure is proposed for making discrete-time changes in the adjustable parameters of a continuous-time nonlinear control system during normal operating conditions. The algorithm employs the best available estimate of the unknown plant parameters as well as the estimates of disturbance, state, and output variables. The importance of the metric properties of a performance index is discussed, and the necessary and sufficient conditions for the integral squared error index to possess metric properties are derived. Theoretical conditions for the error correctiveness of the algorithm are formulated in terms of the constrained extrema of quadratic functionals.
Application of Bond Graph Techniques to the Study of Vehicle Drive Line Dynamics
Authors: Karnopp D. , Rosenberg R. C.
Published: November 2010

General bond graph methods for the description, analysis, and simulation of dynamic systems are illustrated through the study of vehicle drive line dynamics. Emphasis is placed upon the problem of assembling a compatible and efficient system description from multiport models of the system components. Examples show how state space descriptions for analysis and block diagrams for analog simulation may be obtained systematically from bond graphs. Digital simulation is conveniently accomplished using the ENPORT programs, which accept bond graphs directly.
Jet Pump Cavitation
Authors: Cunningham R. G. , Hansen A. G. , Na T. Y.
Published: November 2010

Mixing-throat cavitation in a liquid jet pump results from high jet velocities, low suction (NPSH) pressure, or low discharge pressure. Incipient cavitation at the jet boundary has no effect on jet pump efficiency, but under severe conditions it spreads to the walls. A limiting flow condition results which is independent of discharge pressure. Efficiency deteriorates rapidly and the pump head-flow characteristics can no longer be predicted by conventional theory. Eight correlation parameters (1937–1968) and their interrelations are examined. A Cavitation Index σL is recommended for correlation of cavitation-limited flow results. Limiting flow data from 14 references on water, oils, and mercury, plus additional data on three water jet pumps are compared, showing that 11 sets of data on water, oils, and mercury can be represented by the single-number index σL, with a range of 0.8 to 1.67. Conventional jet pumps are described by σL = 1.0 to 1.4 and σL = 1.35 is recommended for conservative use. The limiting flow function Y (NPSH) is shown to be a useful tool in comparing cavitation response to design changes. System design to avoid cavitation is facilitated by a simple limiting flow equation, ML(R, σL, NPSH, Vn), and the equation is compared with recently published data. Cavitation can be avoided by reducing Vn, and R, or by raising suction port pressure. Flow passage contours, including nozzle-to-throat spacing, influence σL and the limiting flow ratio can also be improved by reducing σL (0.9 or less) through careful design. Systems handling high gas-solubility liquids can be improved by reducing gas content; fluid properties otherwise have little effect on this jet pump phenomenon.
Laminar Separation, Reattachment, and Transition of the Flow Over a Downstream-Facing Step
Authors: Goldstein R. J. , Eriksen V. L. , Olson R. M. , Eckert E. R. G.
Published: November 2010

Results of an experimental investigation of the laminar flow of air over a downstream-facing step are presented. The experiments include visual observations of smoke filaments (in the viscous layer), qualitative velocity fluctuation measurements, and mean velocity profiles. Results are reported over a range of 0.36 – 1.02 cm in step height, 0.61 – 2.44 m/sec in free stream velocity at the step, and 0.16 – 0.51 cm in boundary layer displacement thickness at the step. Laminar flow to reattachment of a free shear layer is observed for subsonic flow and two criteria for which transition to turbulence at reattachment exists are presented. The laminar reattachment length is not a constant number of step heights as for turbulent flow, but varies with Reynolds number and boundary layer thickness at the step. The shape of the velocity profile at reattachment is found to be similar to the shape of a laminar boundary layer profile at separation and the boundary layer profiles downstream of reattachment are similar to those in a laminar boundary layer developing toward separation except that they are traversed in the reverse sense.
Experiments on Coupled Parallel Flows in a Channel and a Bounding Porous Medium
Authors: Beavers G. S. , Sparrow E. M. , Magnuson R. A.
Published: November 2010

Experiments were performed to study the laminar flow characteristics and the laminar-turbulent transition in a parallel-plate channel, one of whose bounding walls is a porous medium. The flow regime investigated herein is characterized by parallel, unidirectional, fully developed flows in the channel and the porous medium. The experimental results for the laminar regime were found to be in excellent accord with theoretical predictions based on a model which admits a slip velocity at the surface of the porous material. The effect of the presence of the porous wall is to increase the mass flow and decrease the friction factor relative to the corresponding quantities for a solid-walled channel. In addition, transition to turbulence occurs at a lower Reynolds number owing to the presence of the porous wall.
Analysis of Flow Separation in a Confined Two-Dimensional Channel
Authors: Hurd A. C. , Peters A. R.
Published: November 2010

A two-dimensional incompressible isothermal laminar separation of a Newtonian fluid in steady flow was investigated. The geometry chosen for this study was a constant-width channel with a sharp 90-deg turn. It was found that an adaptation of a numerical solution for the Navier-Stokes equations first proposed by Allen gave convergence for all Reynolds numbers in the laminar range. The analytical results were compared with measured velocity profiles from a very low-speed wind tunnel.
Analysis and Physiological Monitoring of the Human Left Ventricle
Authors: Ghista D. N. , Advani S. H. , Gaonkar G. H. , Balachandran K. , Brady A. J.
Published: November 2010

Mathematical models of the human left ventricle are presented to determine the physiological response-oriented mechanical parameters of the LV, which have diagnostic significance. These parameters are (i) the rheological parameters of the left ventricular muscle, namely the instantaneous values of stiffness of series elasticity, parallel elasticity, and the stress-strain rate relationship for the contractile unit that characterizes the deviatric stress-strain response of a left ventricular muscle element, (ii) the effective modulus of the LV, and (iii) the state of stress in the LV. The rheological parameters are obtained from a continuum model of the LV whose stress state equilibrates the chamber pressure and whose strain state equals the instantaneous strains in the actual LV, obtained from instantaneous changes in the geometry of the LV (as noted from cineangiocardiography); the constitutive equations for the model incorporate the known existing rheological models for the isolated cardiac muscle. The effective moduli of the LV are obtained by correlating the fundamental frequency of vibration of a spherical model of the LV with the corresponding frequencies of the second component of the first heart sound and the third heart sound; thus the values of representative moduli (and hence indices of the left ventricular stiffnesses) at systole and diastole are obtained. The stress state in the LV is obtained by utilizing single plane cineangiocardiographic information of the irregular geometry of the LV in anteroposterior projection. Plane stress finite element analysis of this planor irregular geometry of the LV is done and the resulting stresses are reduced by a factor, heuristically determined to make allowance for the actual 3-dimensional geometry of the LV; the stresses obtained thus bring out effects of irregular boundary of varying (and at times high) curvature.
Optimum Vane Number and Angle of Centrifugal Pumps With Logarithmic Vanes
Authors: Reddy Y. R. , Kar S.
Published: November 2010

The optimum number of vanes for a given centrifugal pump or blower cannot be estimated by Pfleiderer’s equation because of its limitations. In the present investigation, Stodola’s effect is analysed for logarithmic shape vanes and theoretical equations have been obtained to estimate the vane number for optimum efficiency of the unit. The experiments conducted on six impellers whose blade number varied from 2 to 10, resulted in a maximum efficiency of 62.4 percent for the impeller having seven vanes of blade angle 30 deg, which is also the same blade number predicted by the theoretical equation. The experimental results of Varley, and Bommes regarding the optimum number of vanes are in agreement with the theoretical predictions, whereas the empirical equations of Pfleiderer and others suggested either low or high values. Optimum blade angle for maximum efficiency has been worked out for an impeller having logarithmic vanes. In the present investigations an optimum blade angle of 27.3 deg has been obtained for a seven bladed impeller. The results obtained from the present theory agree very well with the results of Varley and Kasai.
Cumulative Fatigue Damage Under Stress-Controlled Conditions
Authors: Bui Quoc Thang , Dubuc J. , Bazergui A. , Biron A.
Published: November 2010

A theoretical analysis of uniaxial cumulative fatigue damage is presented together with a large number of experimental results on unnotched specimens of A-201 and A-517 steels. The theory developed permits the prediction of fatigue curves for stress-controlled conditions with zero or positive mean stress as well as the evaluation of the damage accumulated during a fatigue test and hence the prediction of the remaining life of a specimen. Theory is in good agreement with the experimental results as well as with published data on other materials. The development may be extended to other types of tests such as strain-controlled or random loading conditions.
An Explicit Scheme for the Calculation of Three-Dimensional Turbulent Boundary Layers
Authors: Nash J. F.
Published: November 2010

An explicit finite-difference scheme is formulated for calculating the development of the incompressible turbulent boundary layer on an infinite yawed cylinder. The governing partial differential equations are similar to those used by the author in a previous paper [1], and the empirical content is the same. In their general form the difference equations define a two-step scheme containing two disposable parameters, and numerical experiments have been conducted to determine the stability boundaries, and the boundaries of acceptable numerical precision, in terms of these parameters. By a particular choice of one of the parameters the system reduces to a one-step, staggered-mesh scheme, and it is in this form that the method finally emerges. With 15 collocation points through the boundary layer the method has a typical precision of 2 percent, and with 20 points, 0.5 percent.
The Influence of State of Stress on the Stress-Strain Behavior of Rocks
Authors: Swanson S. R. , Brown W. S.
Published: November 2010

An experimental investigation of the stress-strain behavior of several rocks is described. The stress-strain response of the rocks tested is seen to be quite complicated, exhibiting a number of inelastic effects even in rocks considered brittle under pressure. The inelasticity is manifested in permanent set and hysteresis on unloading and volume changes produced by shearing stresses.
Laminar Flow of an Incompressible Fluid in a Conduit With Arbitrary Cross Section, Arbitrary Time-Varying Pressure Gradient, and Arbitrary Initial Velocity
Authors: Hepworth H. K. , Rice W.
Published: November 2010

A computer-oriented solution is given for the flow described in the title of the paper. The boundary shape is represented by specification of the coordinates of N points on the boundary; the initial velocity is represented by specification of L values of the velocity in the cross section at time zero; the arbitrary time-varying pressure gradient is implemented by use of Duhamel’s Theorem. In the solution method presented, boundary and initial conditions are satisfied in the least squares sense. The Gram determinant is used to determine eigenvalues and the Gram-Schmidt orthonormalizing procedure is used to construct a set of functions appropriate for a finite series solution. Computer programs are referenced which have been used to investigate the correctness of the solution and the accuracy obtainable with reasonable digital computational time.
Three-Dimensional Curved Wall Jets
Authors: Patankar U. M. , Sridhar K.
Published: November 2010

This paper presents an experimental investigation of mean velocities of turbulent, three-dimensional incompressible air jets from various rectangular orifices issuing tangentially to and flowing along the surface of a curved wall into quiescent ambient air. An experimental study of the jet separation is also presented. The three-dimensional curved wall jet is found to be drastically different in its mean property behavior from its so-called two-dimensional counterpart. Velocity contour plots show the resultant effect on the jet flow of two diverging tendencies—the free jet flow and the Coanda flow. This effect is found to occur earlier with smaller aspect-ratio orifices. Within the range of variables studied, three-dimensional curved wall jets may be characterized by three regions of maximum velocity decay. The rate of maximum velocity decay is dependent on orifice aspect ratio, except in the potential core region. Further, the curved wall jet differs from other three-dimensional jet flows in its growth behavior.
A Simple but Complete Solution for the Step Response of a Semi-Infinite, Circular Fluid Transmission Line
Authors: Karam J. T.
Published: November 2010

Presently, the only accurate solutions for the step response of a semi-infinite, circular fluid transmission line result from involved, time consuming, numerical finite series or integration techniques [1, 2, 3]. None of these solutions is practically suitable for either a rapid manual prediction for an arbitrary fluid line (liquid or gas), or for extension of the semi-infinite line results to the more meaningful problem of a finite line with arbitrary inputs. In the frequency domain (sinusoidal signals), a complete, verified solution exists [1, 4, 5] and theoretically could be transformed into the time domain. This was the scheme used by Brown and Nelson for liquid lines [2], but it required the numerical techniques referred to above and, in their own words, was a “very complex and tricky business.” However, simpler solutions for most operating regimes also exist in the frequency domain [6, 7]. These simple frequency domain solutions were transformed into the time domain and provided the basis for a simple solution for the step response.
Unsteady Flow Calculations by Numerical Methods
Authors: Streeter V. L.
Published: November 2010

A review of methods of handling unsteady flow problems in metal pipes by numerical methods is undertaken. The characteristic method, typifying explicit methods, and the centered implicit method are developed, including the manner various boundary conditions are introduced into the solutions. High velocity flow is briefly reviewed, i.e., flow cases with the velocity of flow of the same order of magnitude as the pulse wave speed. Three complex boundary conditions are examined: turbomachinery, column separation, and the compressed gas accumulator.
Pulsatile Waterhammer Subject to Laminar Friction
Authors: Jayasinghe D. A. P. , Leutheusser H. J.
Published: November 2010

This paper deals with elastic waves which may be generated in a fluid by the sudden movement of a flow boundary. In particular, an analysis of the classical piston, or signalling problem is presented for the special case of arbitrary velocity input into a stationary fluid contained in a circular, semi-infinite waveguide. The decay of the pulse, as well as the resulting flow development in the inlet region of the pipe are analyzed by means of an asymptotic expansion of the suitably nondimensionalized Navier-Stokes equations for a compressible, nonheat-conducting Newtonian fluid. The results differ significantly from those of the more conventional one-dimensional approach based on the so-called telegrapher’s equation of mathematical physics. The present theory realistically predicts the growth of a boundary layer both in time and position and, hence, it appears to represent the transient fluid motion in a manner which is physically more appealing.
Effects of Cold Working Under Pressure on Subsequent Yield
Authors: Hoeg J. G. , Davis R. L.
Published: November 2010

A method utilizing high pressure fluid environments is described whereby a three-dimensional subsequent yield surface was determined for 304 stainless steel. Cylindrical parent specimens of this material were prestrained in axial compression under fluid pressure and then small subspecimens were sectioned from these parent specimens. Finite element techniques were used to optimize the parent specimen size so that a zone of uniform axial stress would result during the prestraining. Longitudinal strains in this zone were monitored during the prestraining and the subspecimens were cut from this region in a manner that did not allow the machining to appreciably affect the properties of the specimens. Following this, conventional tension and compression tests were performed on the subspecimens in various fluid pressure environments to determine the yield strengths for the cold-worked material in the direction of the principal axis of prestrain and the two transverse axes. These data are used to construct the three-dimensional subsequent yield surface which clearly illustrates the effects on 304 stainless steel, of cold working under pressure.
Forming of 7075-T6 Aluminum in High Pressure Environments
Authors: Pendleton R. L. , Davis R. L.
Published: November 2010

Plates of 7075-T6 Aluminum have been folded along a major axis in pressure environments of atmospheric, 20,000 psi, and 40,000 psi. A finite element computer program is used to determine the stress state in the plates at various loads. Tension and compression tests conducted in pressure environments up to 70,000 psi were used to construct models using effective stress, effective strain, and pressure as parameters to predict the behavior of the material under various stress conditions. A prediction of the occurrence of fracture in the folded plate was possible using the computer results and the pressure dependent model. As better finite element stress analysis programs become available, both the forming operation and the test specimen can be analyzed to provide more accurate data that can be coupled with tension and compression data to predict the performance of metalforming operations under pressure.
Experiments on Flow About a Yawed Circular Cylinder
Authors: Smith R. A. , Moon Woo Taik , Kao T. W.
Published: November 2010

Experiments were performed to evaluate the influence of yaw angle on circular cylinder pressure drag and near wake characteristics in the range of Reynolds numbers 2000 to 10,000. It was found that the transition in the wake from laminar to turbulent motion was significantly promoted as the angle of yaw increased. As a result, wake properties such as base pressure and position of transition to turbulence do not obey the Independence Principle which requires that properties be dependent only on the normal component of the free-stream conditions.
Effect of Bubble Inclusions on the Mechanical Properties of Cast Poly-Methyl Metacrylate
Authors: Stachiw J. D.
Published: November 2010

Bubble inclusions present in cast acrylic plastic generally degrade the mechanical properties of the material. To evaluate the effect of bubbles on the mechanical strength of acrylic plastic, 120 tensile and compressive test specimens were machined from massive acrylic castings with bubble inclusions. The specimens were tested under uniaxial loading condition and effect of bubbles on tensile and compressive strength noted. The stress raiser effect of bubbles caused the tensile specimens to fail at stresses 7 to 30 percent lower than observed in specimens without bubbles. The compressive yield strength was not affected by bubbles. However, here the bubbles served as stress raisers also and caused cracks to initiate at the bubble surfaces when the yield strength of acrylic plastic was reached.
Differential Pressure Transmitters, Span-Shift Errors With Static Pressure
Authors: Akeley L. T.
Published: November 2010

The author reviews methods of calibrating low-differential (25–300 in. H2O) D.P. transmitters at high (up to 3000 psig) static pressure. Various test methods are described along with discussion of their merits. Included are use of one or more deadweight testers (gas or liquid) and use of a high-pressure mercury manometer as a standard. Five D.P. transmitters of different construction are tested and their static span-shift performance reported.
Analytical Solutions to the Problem of Transient Heat Transfer in Living Tissue
Authors: Shitzer A. , Chato J. C.
Published: November 2010

An analytical model of transient heat transfer in living biological tissue is considered. The model includes storage, generation, conduction, and convective transport of heat in the tissue. Solutions for rectangular and cylindrical coordinates are presented and discussed. Transient times for reaching the “locally fully developed” temperature profile were found to be of the order of 5–25 min. These transients are dominated by a geometrical parameter and, to a lesser extent, by a parameter representing the ratio of heat supplied by blood flow to heat conducted in the tissue.
A Quantitative Evaluation of the Frequency-Response Characteristics of Active Human Skeletal Muscle In Vivo
Authors: Zahalak G. I. , Heyman S. J.
Published: November 2010

This paper describes an investigation of the frequency-response characteristics of active human skeletal muscle in vivo over the frequency range 1 Hz to 15 Hz. The applied force, forearm position, and surface electromyograms (from biceps, triceps, and brachioradialis) were recorded simultaneously in four normal adult male subjects for small oscillations of the forearm about a mean position of 90 deg flexion. Two modes of oscillatory behavior are discussed: externally forced oscillations under constant muscle force and voluntary oscillations against an elastic resistance. The observed amplitude and phase relations are presented herein and are compared to the response predicted by a simple model for neuromuscular dynamics. It appears that the small amplitude frequency response of normal skeletal muscle in vivo can be represented by a second order model. The main muscle parameters of this model are a muscular stiffness K, two time constants τ1 and τ2 associated with contraction dynamics, and a time delay τ: typical values of these parameters at moderate contraction levels (approximately 20 percent of maximum voluntary effort) are K = 100 N · m/rad, τ1 and τ2 = 50 ms, and τ = 10 ms. Reflex feedback under forced-oscillation conditions was also examined and may be characterized by a gain parameter (ΔE/Δθ), the ratio of the surface EMG amplitude to the angular displacement of the forearm, and the phase by which the EMG leads muscle stretch. The reflex EMG is observed to lead muscle stretch at all frequencies between 1 Hz and 15 Hz. The muscle stiffness K and the reflex gain parameter (ΔE/Δθ) are approximately proportional to the average force of contraction.
Mechanical Properties of Human Lumbar Spine Motion Segments—Part II: Responses in Compression and Shear; Influence of Gross Morphology
Authors: Berkson M. H. , Nachemson A. , Schultz A. B.
Published: November 2010

In this second part of a three-part report, we consider the mechanical behavior of 42 fresh human cadaver lumbar motion segments in compression, and in anterior, posterior, and lateral shear. We report the motions and the intradiskal pressure increases that occurred with posterior elements both intact and destroyed. We also examine to what extent intervertebral disk gross morphology can explain the large scatter in the results presented here, as well as in the results reported in Part I concerning mechanical behavior in flexion, extension, lateral bending, and torsion.
A Simulation of the Dynamics of Counterpulsation
Authors: Nerz A. R. , Myerowitz P. D. , Blackshear P. L.
Published: November 2010

An open-loop, lumped parameter, digital computer model of the left heart, coronary artery, and aortic tree is discussed. Introduction of an external flow source (counterpulsation pump system) at any of the eight major nodal points located along the aorta is permitted. The model is run for a variety of conditions to assess the effects of counterpulsation pump timing, stroke volume, infusion/aspiration rate and pump cannula location on selected indices of cardiac performance. Simulation results are compared to appropriate data from two series of animal experiments using a thin-walled cannula and a pneumatically driven, nonhemolytic counterpulsation pump system.
The Stability of Blood Cell Suspensions to Small Disturbances in Circular Couette Flow: Experimental Results for the Taylor Problem
Authors: Deutsch S. , Phillips W. M.
Published: November 2010

Experimental results for the stability of human blood, red cell suspensions and blood plasma to small disturbances in circular Couette flow are presented. The viscoelastic nature of whole blood and blood cell suspensions is confirmed. Blood plasma is found to be Newtonian. Elasticity is shown to have a sizably stabilizing effect on normal Hematocrit blood behavior. Two mechanisms by which elasticity may arise in blood are identified; namely red cell deformability and red cell aggregation.
A Three-Dimensional Mathematical Simulation of Pedestrian-Vehicle Impact With Experimental Verification
Authors: Padgaonkar A. J. , Krieger K. W. , King A. I.
Published: November 2010

In an urban environment, pedestrians account for a disproportionately high percentage of traffic fatalities in comparison with the percentage of accidents in which they are involved, according to the U. S. Department of Transportation. Rural statistics are equally bad. The problem of minimizing injuries to pedestrians when struck by a vehicle involves a large number of variables, such as the type and size of the vehicle, its speed at impact, the effects of braking and vehicle pitch, the geometry and stiffness of the vehicle exterior, and the size and age of the pedestrian. Obviously, it is impractical to study the effect of all of the variables experimentally. An alternate approach is the use of a validated mathematical model to simulate this impact event. This paper deals with the comparison of the results of a three-dimensional gross motion simulator with experimental data acquired under controlled laboratory conditions.
Power Spectral Density for Constrained Long Wavelength Guideway Irregularities
Authors: Bala Krishna M. , Hullender David
Published: November 2010

An equation for the power spectral density (PSD) of guideway irregularities that have been constrained to lie within a designated band is formulated. The equation enables guideway designers to control the upper bound on the long wavelength portion of the roughness PSD. The paper also provides insight into the accuracy of two quasi-linear modeling techniques for nonlinearities with random inputs.
Identification of the Dynamic Characteristics of a Bench-Type Automotive Seat for the Evaluation of Ride Quality
Authors: Smith C. C. , Kwak Y. K.
Published: November 2010

The effect of seat transmissibility upon the spectra of motion of a typical bench-type automotive front seat is investigated. Vertical and lateral acceleration spectra arc measured at the floorboard and at the man/seat interface. System transfer functions are identified from the experimental data using spectral analysis techniques. Analytical expressions, which can be used for system ride quality simulation and investigation are determined which best fit the experimentally determined transfer functions in a least-squares sense. A significant resonance at about 4.9 Hertz, which may have a significant effect upon system ride quality, is demonstrated in the data.
Graphical Solutions for the Characteristic Roots of the First Order Linear Differential-Difference Equation
Authors: Sandquist G. M. , Rogers V. C.
Published: November 2010

Approximate values for all the apparent real and imaginary characteristic roots of the general first order linear differential-difference equation are determined (primarily graphically) without mathematical proof. These approximate values may then be iterated in a convergent form of the characteristic equation to provide any desired numerical accuracy as shown in several examples. A practical application involving the kinetic behavior of nuclear reactor systems with delayed neutrons is given and compared with the more familiar system solutions.
Distillation Columns—A Class of Dynamic Systems With Multiplicative Inputs
Authors: Espana M. , Landau I. D.
Published: November 2010

Distillation columns can be described by nonlinear state space equations but which are linear with respect to the inputs for a large domain of working conditions. For adiabatic distillation columns, these state space equations are also homogeneous with respect to the inputs and in this case the inputs act multiplicatively. Three important properties are derived from this structure concerning: 1. The equilibrium points; 2. The time scale around an equilibrium point; 3. The gain around an equilibrium point. These properties depend on the direction and the modulus of the input vector. They have been verified experimentally on the pilot distillation column of Laboratoire d’Automatique de Grenoble. The properties derived from the multiplicative effect of the inputs allow: 1) To implement a simple feedforward control technique for the compensation of the feed flow rate disturbances by maintaining the direction of the input vector. 2) To implement an open loop adaptive feedback control by taking in account the effect of the magnitude of the input vector upon the system dynamics.
An Air-Modulated Fluidic Fuel-Injection System
Authors: Woods R. L.
Published: November 2010

This paper presents a unique approach to fuel management systems applicable to spark-ignition engines and discusses a fluidic implementation. The air-modulation system is opposite from conventional systems in that the driver selects the air consumption to the engine thereby providing many desirable functions that are inherent in its operation. Fluidic control was selected for its sensing and control compatibility with the fluid variables and for its cost and reliability potential. The design and bench tests of the fluidic controller are discussed. The results of the dynamometer and vehicle evaluation are encouraging.
An Elastic Analysis of Multiroll Endless Web Systems
Authors: Soong Tsai-Chen , Li Chun
Published: November 2010

A procedure for analyzing a multiroll endless web system is presented. The web is divided into endless, parallel strips which are longitudinally elastic and possess shear rigidity. The strips are wrapped over frictional cylinders and then required to pass through predetermined points on the contact arc so that compatibility among neighboring strips is maintained. Contact is assumed to be nonslipping until transverse shear and belt tension components exceed friction. Transient and steady-state motions with and without edge guide can be studied. Problems concerning edge guide force, steering moment, pivoting cylinders, rate of drift, and effect of conicity of web, taper of cylinder, and initial unstretched length of the web, etc., can be analyzed.