bluuebunny/crossref_metadata_2025 huggingface dataset:
Asymmetric Branching of Cracks
Authors: Theocaris P. S.
Published: November 2010

The problem of asymmetric branching of a crack in an infinite plate under generalized plane stress conditions and loading in a direction perpendicular to the main crack at infinity can be solved by reduction to a system of three complex Cauchy-type singular integral equations or, further, six real Cauchy-type singular integral equations. This system can be numerically solved by reduction to a system of linear equations after applying it at properly selected points of the integration interval and approximating the integrals by using the Gauss and/or Lobatto-Legendre numerical integration rules. The values of the stress-intensity factors at the crack tips, resulting directly from the solution of this system of linear equations, were computed for several geometries of asymmetrically branched cracks and found in satisfactory agreement with the corresponding experimental values determined by the method of caustics.
Equivalence of a Constrained Minimum Weight and Maximum Column Buckling Load Problem With Solution
Authors: Hornbuckle J. C. , Boykin W. H.
Published: November 2010

Packaged computer programs are available for solving the two-point boundary-value problems resulting from well-posed structural optimization problems. These methods generally require a standard form of representation of the structure’s equations and the other necessary conditions for optimization. At the same time there is a duality between minimum weight designs of structures and maximum load designs. If the maximum load design problem is an eigenvalue problem associated with the mini-max problem of the Rayleigh quotient, standard forms of representation are complex. This complexity has lead to a simple equivalence statement of the problems of minimum column weight and maximum buckling load; and, has produced a straight forward solution technique for maximum load problems.
On the Contact Problem of a Highly Inflated Spherical Nonlinear Membrane
Authors: Lardner T. J. , Pujara P.
Published: November 2010

Observations on the solution of the problem of compression of an inflated spherical membrane between two rigid plates [1] are presented. A similarity property of the solution for Neo-Hookean material for the case of λs > 1.7, approximately, is noted.
Elastic Buckling of Infinitely Long Trapezoidally Corrugated Plates in Shear
Authors: Perel D. , Libove C.
Published: November 2010

Buckling loads are calculated for a class of infinitely long trapezoidally corrugated plates under uniform in-plane edge shear. This class consists of corrugated plates in which all interior plate elements are of equal width, with the end elements clamped. The energy method is used as the basis of analysis, which considers the corrugated plate as a nonplanar assemblage of flat plates. Buckling loads calculated using this method are compared to those obtained by using orthotropic plate theory, which represents the corrugated plate by an orthotropic flat plate. The comparison shows significant differences in predicted buckling loads.
A Three-Dimensional Treatment of Transient Thermal Stresses in a Circular Cylinder Due to an Arbitrary Heat Supply
Authors: Takeuti Y. , Noda N.
Published: November 2010

We deal with a transient thermal stress problem in an infinitely long circular cylinder due to a nonuniform heat supply in circumferential and longitudinal directions on its cylindrical surface. The analysis is developed using the Boussinesq-Papkovich functions. Numerical results are given for several forms of heat supply.
Contribution to Computer Construction of Active Chain Models Via Lagrangian Form
Authors: Vukobratovic´ M. , Potkonjak V.
Published: November 2010

Basic principles underlying the computer construction of the models of open kinematic chains using the recurrent relations from the rigid body kinematics are briefly presented in this paper. A new method for automatic setting of the aforementioned models via second-order Lagrange’s equations is presented. This method provides a realistic basis for the application of complete dynamic models to the real-time control of robots and manipulators.
Lubrication Flow of a Particle-Fluid Mixture
Authors: Drew D. A.
Published: November 2010

The lubrication approximation is derived for a dilute particle-fluid mixture. The resulting equations are solved for the simple geometry of a flat plate slider bearing. The particles tend to avoid the upper plate, especially near the outlet.
Linearized k-ε Analysis of Free Turbulent Mixing in Streamwise Pressure Gradients With Experimental Verification
Authors: Hokenson G.
Published: November 2010

The equations of momentum, turbulent kinetic energy, and dissipation are subjected to a coordinate transformation and linearized to obtain approximate closed-form solutions of free mixing problems. The linearization involves not only an assumption regarding the relative transverse uniformity of free mixing flow fields, but also a turbulence modeling approach in which a preliminary estimate of the length scale is a necessary input. As a by-product of this linearization, the equations partially decouple from one another and may, therefore, be solved sequentially. In order to provide the length scale and free-stream velocity dependence upon the transformed streamwise coordinate, a temporary transformation from the physical to the mathematical plane is developed on the basis of a classical eddy viscosity formula. Due to the analytical nature of the process, the input velocity and length scale thus obtained may be adjusted to conform with the desired velocity distribution in physical space, and the appropriate length scale computed from the solution of the equations. The analysis is favorably compared to experimental data on the turbulent mixing of two-dimensional wakes in adverse pressure gradients.
A Finite-Element Model for Plane-Strain Plasticity
Authors: Hodge P. G. , van Rij H. M.
Published: November 2010

A finite-element model is proposed which allows for both straining within each element and slip between two elements. Basic equations are derived and are shown to almost completely uncouple into two constituent components: the conventional finite-element equations for continuous displacement fields and the “slip” equations which were recently derived for a model based on slipping of rigid triangles. The model is applied to the Prandtl punch problem and is shown to combine the best features of its two constituents.
Eigenfrequencies of Continuous Plates With Arbitrary Number of Equal Spans
Authors: Elishakoff Isaac , Sternberg Alexander
Published: November 2010

An approximate analytical technique is developed for determination of the eigenfrequencies of rectangular isotropic plates continuous over rigid supports at regular intervals with arbitrary number of spans. All possible combinations of simple support and clamping at the edges are considered. The solution is given by the modified Bolotin method, which involves solution of two problems of the Voigt-Le´vy type in conjunction with a postulated eigenfrequency/wave-number relationship. These auxiliary problems yield a pair of transcendental equations in the unknown wave numbers. The number of spans figures explicitly in one of the transcendental equations, so that numerical complexity does not increase with the number of spans. It is shown that the number of eigenfrequencies associated with a given pair of mode numbers equals that of spans. The essential advantage of the proposed method is the possibility of finding the eigenfrequencies for any prescribed pair of mode numbers. Moreover, for plates simply supported at two opposite edges and continuous over rigid supports perpendicular to those edges, the result is identical with the exact solution.
On Laminar Dispersion for Flow Through Round Tubes
Authors: Yu J. S.
Published: November 2010

A general method for the solution of the axially symmetric transient diffusion-convection equation for laminar dispersion in round tubes subject to arbitrary square-integrable initial conditions is analytically developed. The solution representing the local concentration is expressed by a series in terms of the zeroth-order Bessel function, and the order of approximation (equal to the number of terms in the series) required at a given value of the dimensionless time τ for flow with a specified Peclet number Pe is clearly established. It is shown that the approximation used by Gill, et al. [5–8], is a special case of the present analysis under certain conditional assumptions. For the case of fundamental interest with an initial input concentrated at a section of the tube, the mean concentration as a function of the axial distance measured from the origin of a coordinate moving with the average flow velocity determined by the present method at given values of the Peclet number and the dimensionless time is compared with those by Taylor [1], Lighthill [4], Chatwin [9], Gill, et al. [7], and Hunt [23]. The comparison of the concentration profiles shows that Lighthill’s solution is perhaps valid as τ → 0, Hunt’s solution obtained by first-order perturbation approximation yields too large a dispersion by molecular diffusion even at small times, and the other solutions are asymptotically correct at large values of time for flow with high Peclet numbers.
Effects of Mass Transfer and Free-Convection Currents on the Flow Past an Impulsively Started Vertical Plate
Authors: Soundalgekar V. M.
Published: November 2010

An exact analysis of the effects of mass transfer on the Stokes’ (also Rayleigh’s) problem for an infinite vertical plate has been presented on taking into account the free-convection currents. It has been observed that there is a rise in the velocity due to the presence of a foreign mass. But an increase in Sc (<1), Schmidt number, leads to a fall in the velocity. The skin-friction increases due to the presence of a foreign mass and Sc< 1, but it decreases at Sc = 1.
Reflection and Transmission of Circularly Polarized Elastic Waves of Finite Amplitude
Authors: Carroll M. M.
Published: November 2010

Finite amplitude standing wave solutions, obtained previously, are specialized to the case of incompressible isotropic elastic solids with cubic or quintic shear response. This allows closed-form expressions for the motion and stress field, in terms of Jacobian elliptic functions and elliptic integrals and furnishes solutions for approximate finite elasticity theories in which terms up to sixth degree in the stress and strains are retained. The solutions for reflection from free or fixed boundaries, for resonant standing waves in a plate, and for reflection and transmission at a plane boundary are examined in the context of the third and fourth-order approximations.
Excitation of Rotationally Periodic Structures
Authors: Wildheim S. J.
Published: November 2010

A rotationally periodic structure consists of a finite number of identical substructures forming a closed ring. The vibrational behavior of such structures is considered, especially the forced response due to a rotating force. It is known that for a rotationally symmetric structure, excited by a rotating force, resonance for the n nodal diameters mode is obtained when the corresponding natural frequency is ωn = nΩ, where Ω is the angular velocity of the force. This resonance condition also holds for a rotationally periodic structure. But then additional resonance possibilities exist, given by ωn = (kN ± n)Ω, where N is the number of substructures and k = 0, 1, 2,… These resonance conditions give a zigzag line in the nodal diameters versus frequency diagram, which here is introduced as the ZZENF diagram. The deformation patterns at the resonances are both forward and backward traveling waves.
Effective Drag Coefficient for Gas-Particle Flow in Shock Tubes
Authors: Rudinger George
Published: November 2010

Effective drag coefficients for flows of suspensions of spherical glass particles in air were derived from simultaneous measurements of pressure and particle concentration in the flow behind weak shock waves. Average particle diameters were 29 and 62μm. The instantaneous concentration was determined by light scattering, and the results agree well with earlier shock-tube data based on streak records. They exhibit several unexpected features: the correlation between drag coefficient and Reynolds number is much steeper (∝ Re−1.7) than the generally used “standard” curve but approaches it at Reynolds numbers of several hundred; the correlation is independent of the particle concentration over the range of the experiments, that is, for particle-to-gas flow rate ratios between about 0.05 and 0.36; if the Reynolds number immediately behind the shock front is changed by varying the shock strength, the points move along the correlation, but if it is changed by changing the particle size, the entire correlation is shifted although to a smaller extent than would correspond to the direct effect of particle diameter on the Reynolds number. To account for the observations, a flow model is developed which allows for microscopic longitudinal and lateral perturbations of the particle motion that are the result of various causes, such as particle interactions with wakes of other particles, lateral forces caused by particle rotation, or electrostatic forces. Because of the nonlinearity of the equation of motion, the averaged particle motion is different from that of a particle without perturbations. The effective drag coefficient for the average particle motion is therefore different from the standard drag coefficient applied along the actual motion. With this model and plausible assumptions for the average lateral velocity component of the particle motion, all features of the experimental data can be qualitatively explained.
The Optimal Regulator Problem for a Stationary Linear System With State-Dependent Noise
Authors: McLane P. J.
Published: November 2010

The problem of minimizing a quadratic functional of the system outputs and control for a stationary linear system with state-dependent noise is solved in this paper. Both the finite final time and infinite final time versions of the problem are treated. For the latter case existence conditions are obtained using the second method of Lyapunov. The optimal controls for both problems are obtained using Bellman’s continuous dynamic programming. In light of this, the system dynamics are assumed to determine a diffusion process. For the infinite final time version of the problem noted above, sufficient conditions are obtained for the stability of the optimal system and uniqueness of the optimal control law. In addition, for this problem, an example is treated. The computational results for this example illustrate some of the qualitative features of regulators for linear, stationary systems with state-dependent disturbances.
Mean Flow Calculations Behind Arbitrarily Spaced Cylinders
Authors: Bragg G. M. , Kohli H. S. , Seshagiri B. V.
Published: November 2010

A finite array of arbitrarily spaced parallel rods is considered. It is assumed that momentum deficit may be superposed locally. The momentum deficit is computed behind each cylinder—considering it as a single cylinder—using one of the accepted theories. Then the momentum deficits at each point due to all the cylinders are superposed. From this an overall velocity distribution is calculated. Experiments with various rod diameters and spacings were conducted. The results were within 3 percent of the theoretically predicted local velocity, and under 10 percent of the predicted local velocity defect (at locations of significant velocity deficits).
Laminar and Turbulent Incompressible Boundary Layers on Slender Bodies of Revolution in Axial Flow
Authors: Cebeci T.
Published: November 2010

The boundary-layer equations for both laminar and turbulent incompressible flows over slender bodies of revolution in axial flow are solved by an implicit finite-difference method. The Reynolds shear-stress term is eliminated by means of an eddy-viscosity concept. Velocity profiles and values of local skin-friction coefficient are obtained for various slender circular cylinders in both laminar and turbulent flows. The deviation of the cylinder skin friction from that of a flat plate is studied. The calculated velocity profiles for turbulent flow are compared with those of both Richmond’s and Yasuhara’s experimental data and with Rao’s proposed formulation of the law of the wall in thick, axisymmetric turbulent boundary layers. In both cases excellent agreement is obtained.
Precise Measurement of Differential Pressure When Calibrating a Head Class Flow Meter
Authors: Miller R. W.
Published: November 2010

When flow calibrating a head class meter to establish its discharge coefficient, measurement of the fluctuating differential pressure has caused the largest uncertainty. With conventional techniques, the reported precision of determining discharge coefficients may range from ±0.1 percent to ±0.3 percent. Improved precision and accuracy in the measurement of differential pressure can be achieved by the Null Balance Integration (NBI) instrumentation system reported in this paper. Using this system the obtainable precision ranges from ±0.02 percent to ±0.04 percent. The system provides accurate determination of the average value of the fluctuating differential pressure signal by establishing a constant, predetermined reference differential. The fluctuating differential pressure, developed by the primary element, is continuously compared to this reference differential pressure. The difference is a secondary analog signal, which includes the fluctuation of the measurement signal plus whatever average difference exists between the measured and reference signals. This secondary difference signal is integrated electronically for the calibrating period. The total is divided by the calibrating time and the resultant average difference is algebraically added to the value of the reference signal. The result is an accurate average value of the measured signal during the calibration period. Orifice coefficient data is presented using the NBI System combined with a high accuracy static-weigh/time system. The spread in coefficients was ±.022 percent.
A Statistical Approach to the Prediction of Discharge Coefficients for Concentric Orifice Plates
Authors: Dowdell R. B. , Chen Yu-Lin
Published: November 2010

New equations are developed which predict the coefficients of discharge for concentric orifice plates as functions of line size, diameter ratio, and Reynolds number. These are developed using modern statistical techniques and an IBM 360 computer. Standard deviations are calculated which show the tolerance with which these new formulas predict the coefficients. The effect of the line size and the diameter ratio on the standard deviation are also presented for the case of flange taps. These equations should be used for predicting the coefficients only in the ranges of Reynolds number, diameter ratio, and line size covered by the data from which they were deduced.
Embrittlement of Precipitation Hardenable Nickel-Base Alloys by Oxygen
Authors: Prager M. , Sines G.
Published: November 2010

A study was made of the embrittling effects of oxygen on Rene´ 41, a nickel-base alloy hardened by precipitation of gamma prime. In short time tensile tests in air it was found that from 750 to 900 deg C oxygen promoted initiation and rapid propagation of intergranular cracks, while in the absence of oxygen, tensile fractures were transgranular and ductility was much improved. Sensitivity to embrittlement by oxygen decreases with coarsening of gamma prime. When gamma prime is hyperfine, probably less than 100 Å, embrittlement is greatest and follows the predictions of a Petch-Stroh model for the initiation of cracks ahead of pile-ups of dislocations. In accordance with the model, the ductility of Rene´ 41 increased in proportion of the reciprocal of the square roo of grain size. Calculated on the basis of the model, the surface energy of Rene´ 41 in air was 400 ergs/cm2, considerably lower than would be expected for an alloy of nickel in an inert atmosphere.
Dynamic Expansion of an Open-Ended Tube
Authors: Lal G. K. , Hillier M. J.
Published: November 2010

The deformation mode of a thin tube subjected to an arbitrary time varying pressure pulse is in two phases: (i) during positive radial acceleration a zone of zero axial strain sweeps outwards from the central plane toward the ends; (ii) on deceleration to rest, the plane strain zone vanishes, the axial stress changes sign, and the stress ratio is then unconstrained. The final tube profile is essentially uniform except near the ends, and the final change in length is small.
A Method for Predicting Creep Data for Commercial Alloys on a Correlation Between Creep Strength and Rupture Strength
Authors: Goldhoff R. M. , Gill R. F.
Published: November 2010

In this paper a method is presented for correlating the creep and rupture strengths of a wide variety of commercial alloys. The ultimate aim of this correlation is to predict design creep properties from rupture data alone. This is of considerable interest because rupture parameter or isothermal rupture curves are frequently the only data available since relatively little creep data is taken today. It is demonstrated in this work that reasonable predictions, useful in design, can be made. The alloys studied range from aluminum base through low alloy and stainless steels and include iron-nickel, nickel, and cobalt-base superalloys. Very long time data for single heats of each of the alloy types has been taken from either the literature or sources willing to make such data available. The construction is simple, and common techniques for determining scatter in the correlation are developed. The predictions include scatter bands of strain-time data developed from the 15 data sets encompassing all the alloys. It is suggested that some refinement might be gained by studying numerous heats of a single specification material where such data is available. A complicating problem of structural instability arises and is discussed in the paper.
Dynamics of Large Buoyant Clouds Generated by Rocket Launches
Authors: Hart W. S.
Published: November 2010

Motion pictures of launches of Titan III solid rocket motors were used, in conjunction with conservation equations and knowledge of rocket plume properties, to determine the initial temperature and mass of the large cloud that is generated during these launches. These initial conditions were applied to a mathematical model which accounted for buoyancy, drag and entrainment. The model predicted the radius, altitude, temperature and mass of the cloud as a function of time. The results showed fair agreement with size and altitude data extracted from the movies. This methodology was applied with limited success to smaller scale rocket clouds generated at test stands. The model was also used to predict the behavior of large exhaust clouds under various external temperature profiles. There is some experimental evidence that the model correctly accounts for unstable profiles, and the predictions of cloud rise during inversion conditions agree with what intuition would predict.
The Effect of the Contents of the Human Red Blood Cell on Its Deformability
Authors: Moffatt E. A. , Harris E. H.
Published: November 2010

A review of the two main theories of red cell structure is given. One theory asserts that the cell structure is simply an elastic membrane around liquid contents, while the counter theory contends that there is an internal structure to the cell which supports the membrane shape. An experiment is reported which tests the effect of the structural contents of the red cell on its deformability. A comparison of the force-deformation characteristics of intact red cells and red cell ghosts is made. The deformabilities are compared by measuring the distances which intact red cells and red cell ghosts move down the inside of a tapered glass tube under the same pressure head before they lodge inside the tube. The results of the experiment indicate a negligible difference in the deformabilities of red cells and ghosts. These results do not disprove the existence of an internal structure; they do assert that the contents are structurally insignificant.
The Evaluation of the Stress Intensity Factors for Cracks Subjected to Tension, Torsion, and Flexure by an Efficient Numerical Technique
Authors: Emery A. F. , Segedin C. M.
Published: November 2010

A numerical technique for the efficient computation of singular states of stress is developed and applied to several plane strain elastic problems. The method which extracts the effect of the singularity from the field permits the use of relatively coarse nodal meshes with rapid solution times but maintains a high degree of accuracy. Using this technique, stress intensity factors are calculated for the torsion and flexure of solid and hollow cylinders and the internal pressurization of cylinders of varying thicknesses.
A Solution of a Mixed Boundary Value Problem—Acoustic Pressure Fields in a Finite Container
Authors: Solomon L. P. , Schryer N.
Published: November 2010

This paper investigates the effects of different boundary conditions in calculating pressure fields corresponding to incipient cavitation. We have utilized a technique which allows us to obtain a numerical solution of this problem for various frequencies and geometrical configurations. Our results provide evidence that determination of the pressure field is not only a function of depth but also a strong function of radius and whether or not the end conditions involve the use of a baffle. We have found that, particularly at the higher frequencies, the changing of the boundary conditions will cause large variations and differences in the pressure field. The numerical technique provides a method which allows the calculation of mixed boundary value problems associated with the reduced wave equation in finite domains. The technique specifies known error bounds. However, the distribution of errors over the domain is unknown.
Induced Flow Reciprocating Pump Theory Supported by New Performance Data
Authors: Burton J. D. , Lobo-Guerrero U. J.
Published: November 2010

Reciprocating pumps have been employed in conjunction with air vessels and fluid accumulators for a long time in order to reduce maximum cylinder pressures and energy wastage in friction. More recently, diaphragm pumps, run at high speed, have been built utilizing a hydraulic accumulator or capacitance in conjunction with a hydraulic inductance, in order to greatly increase the flow output. Volumetric efficiencies of over 250 percent have been obtained. The present paper describes briefly this induced flow principle and then compares theoretical solutions with experimental measurements taken in the first commercially available pump of this type.
Two-Phase Air-Water Nozzle Flow
Authors: Wallis G. B. , Sullivan D. A.
Published: November 2010

This paper describes an experimental investigation of two-phase, air-water nozzle flows including critical or choked flow. Five different nozzle geometries were used. The nozzles exhausted to atmospheric pressure from stagnation pressures of 16 to 55 psia. The quality (mass fraction of air flowing) ranged from 2 to 35 percent. A feature of the study was the injection system which was designed to minimize the entrainment of liquid into the gas phase. The data were found to be described within about 10 percent by modifying separated flow theory by a simple “blockage factor” correlation.
A Photographic Study of Spark-Induced Cavitation Bubble Collapse
Authors: Kling C. L. , Hammitt F. G.
Published: November 2010

The collapse of spark-induced cavitation bubbles in a flowing system was studied by means of high speed photography. The migration of cavitation bubbles toward a nearby solid boundary during collapse and rebound was observed. Near its minimum volume the bubble typically formed a high speed microjet, which struck the nearby surface causing individual damage craters on soft aluminum.
Effect of Aortic Arch Atherosclerotic Formations on Blood Mass Flow Distribution
Authors: Rodkiewicz Cz. M. , Zajac S. , Jedruch W. T. , Hsieh W. T. M.
Published: November 2010

The effect of the aortic arch atherosclerotic formations on blood mass flow distribution is determined experimentally on the aortic arch model, derived from x-ray traces, for the average values of the governing parameters: Reynolds number, unsteadiness parameter, and velocity fluctuation parameter. A computer program incorporating the experimrntal data is developed, which predicts approximately the flow distribution for various arterial blockages.
A Biomechanical Analysis of Head Impact Injuries to Children
Authors: Mohan D. , Bowman B. M. , Snyder R. G. , Foust D. R.
Published: November 2010

Head-first free falls of 30 children, 1-10 yr old, and one adult, 21 yr old, were studied to determine fall circumstances and injuries sustained. The falls of six children and one adult were simulated using the MVMA Two-Dimensional Crash Victim Simulator computer model. The data show that head-first falls of children onto rigid surfaces from heights as low as 2 m can result in serious injuries. Conservative head injury tolerance limits are estimated to be 200-250g for peak head acceleration.
Dynamic Model of a Sac-Type Pneumatically Driven Artificial Ventricle
Authors: Geselowitz D. B. , Miller G. E. , Phillips W. M.
Published: November 2010

Inlet and outlet pressures and flows were obtained over a wide range of operating conditions for a pneumatically driven sac-type artificial ventricle connected to a mechanical mock circulatory system. The load presented to the ventricle by the mock circulatory system was found to be characterized by a linear resistance and capacitance. A dynamic model for the ventricle which accounted for instantaneous pressures and flows was developed. The outlet port is characterized by an inertance and square law resistance; the inlet port is characterized by a nonlinear resistance dependent on the type of valve. The input to the model is the time varying sac pressure. The model predicts the fill-limited and ejection-limited modes of the artificial ventricle.
Blood Velocity Patterns in Coronary Arteries
Authors: Wells M. K. , Winter D. C. , Nelson A. W. , McCarthy T. C.
Published: November 2010

A pulsed ultrasound Doppler velocity meter has been used to map the time varying velocity waveforms in the exposed left coronary arteries of anesthetized ponies. Velocity measurements were made without invading the vessels or disturbing the hemodynamic patterns. Typical recordings of velocity waveforms and calculated velocity profiles in the main, descending and circumflex branches are presented. Marked velocity fluctuations in the frequency range of 5 to 10 Hz were measured in the major coronary branches and may influence the stability of the flow and the development of separated flows. Peak Reynolds numbers normally ranged from 300 to 600 and the Womersley unsteadiness parameter based on the heart frequency was usually less than 4.0. Maximum shear rates at the wall were estimated from the calculated velocity profiles and ranged from 400 to 600 sec−1.
An Electrohydraulic Knee-Torque Controller for a Prosthesis Simulator
Authors: Flowers W. C. , Mann R. W.
Published: November 2010

A new approach for evaluating advanced concepts for knee-joint control in above-knee prostheses involves the use of a simulator prosthesis which can be worn by an amputee and controlled electronically to emulate proposed future prostheses. A critical element in this system is the knee-torque controller. Realization of a powerful, lightweight, easily controlled transducer was essential to the successful development of the simulator system. This paper presents the design of such a controller and evaluates its performance. Brief examples of studies in which the new system has been applied are given. The proven viability of the device suggests that similar actuators might aid other prosthesis/orthesis studies.
Simple Finite-Time Settling Control and Manipulated-Variable Softening for Reverse Reaction, Overshoot, and Oscillatory Processes
Authors: Tomizuka M. , Auslander D. M. , Takahashi Y.
Published: November 2010

An easily implemented digital control method based on a discrete-time process model has been extended to encompass many process types found in common industrial control problems. The system uses a controller and observer based on finite-time settling design; the controller and observer gains are computed directly (noniteratively) from the process model parameters. A softening filter which preserves the finite-time settling behavior of the closed loop system has been developed to minimize manipulated variable excursions.
Use of Secondary Input for Process Control—An Application to a Digester Pulping Process
Authors: Goh T. N. , Wu S. M.
Published: November 2010

Normal operating record data of a continuous digester pulping process are used to study the possibilities of improving process regulator control with stochastic discrete time series techniques. It is illustrated that inclusion of a secondary input that is uncorrelated with the main input in a univariate process model enables more efficient forecasting of disturbances to be made, resulting in better control for minimum mean squared output. The resulting control scheme is a form of feedforward control which calls for adjustments in only one main process input.
A Note on the Active Compensation of a Flexibly Mounted Stabilized Platform
Authors: Burrows C. R. , Adams T. P.
Published: November 2010

The governing equations for a flexibly mounted stabilized platform were derived and solved in an earlier paper [1]. This paper presents a simplified model of the system as a basis for interpreting the active compensation technique described in reference [1].
Quasi-Time-Optimal Feedback Control of Some Fifth-Order Systems
Authors: Ryan E. P.
Published: November 2010

A quasi-time-optimal feedback control approach is proposed for certain fifth-order systems with a single saturable control input. A pure integrator system is treated initially and the suboptimal feedback control, which achieves finite-time transition to the state origin, is shown to be piecewise constant with at most seven switches in sign; the analysis is also valid for a system with negative real eigenvalues in simple ratio. The effectiveness of the approach is demonstrated by numerical example. An extension of the control, via a linear state transformation, to more general systems with real nonpositive eigenvalues is indicated.
Bond Graphs for Flexible Multibody Systems
Authors: Margolis D. L. , Karnopp D. C.
Published: November 2010

A method is presented for the analysis and simulation of the dynamic response of systems containing several long, flexible bodies driven by actuators at joints and attachment points. Applications include remote manipulators, cranes, and complex spacecraft. The geometric nonlinearities of rigid body dynamics are retained as well as small bending mode vibrations based upon linearized analysis. Since bond graphs are used, the actuator dynamics are readily incorporated. The results of simulation of a two body system with electrical actuators and up to three bending modes per body in addition to the rigid body modes are shown.
Time Optimum Control of a Two Capacity Thermal Environmental System With Louvers
Authors: Ercan Yucel
Published: November 2010

An environmental system with two conditioned spaces is considered. Conditioned spaces are assumed to have limited heat transfer through ducts with the ambient, a cold air source and a hot air source as well as with each other. The ducts are equipped with louvers and are idealized by variable thermal resistances. The conditions for optimal control are derived by using Pontryagin’s maximum principle. The control action is shown to be of bang-bang type. A method which makes use of the behavior of the costate variables is used to determine the optimal control sequence. Solutions for a typical physical system show that the time optimal control is achieved by switching the control variables at most two times. The state space is divided into eight regions and within each region one and the same control algorithm applies. The results also show that time optimum control of two capacity thermal systems leads to energy as well as time savings if the two capacities are interconnected by a controllable thermal resistance.
Steering and Stability of Unsymmetric Articulated Railway Vehicles
Authors: Wickens A. H.
Published: November 2010

For railway vehicles having coned wheels mounted on solid axles, there is a conflict between the stability of lateral deviations from the motion along the track and ability to steer round curves. A general theory is developed which shows that any articulated, unsymmetric vehicle, which lacks elastic members in the interconnections between wheelsets, can be made stable for running in one direction only. However, an example of a particular configuration of two-axle vehicle shows that the provision of elastic restraint can make it possible to choose vehicle parameters which ensure static and dynamic stability and perfect steering on curves in either direction of motion.
Theoretical Analysis of Laminar Pipe Flow in a Porous Wall Cylinder
Authors: Galowin L. S. , Desantis M. J.
Published: November 2010

A theoretical investigation was conducted to obtain velocity, pressure, and shear stress distributions for incompressible, steady, fully developed, laminar flow through a cylinder with a uniformly porous wall. Ejection/injection at the walls results from the pressure difference across the porous wall. Fluid flow phenomena in porous tubes and ducts have previously been investigated with the velocity prescribed as the boundary condition at the wall. An accurate wall condition must account for the variable wall velocity being dependent upon the pressure difference across the wall, the properties of the fluid, the thickness and the permeability of the structure. An integral momentum technique was employed to reduce the axisymmetric Navier-Stokes equations in cylindrical coordinates to a nonlinear, second-order ordinary differential equation with appropriate boundary conditions. The velocity condition at the wall was established for the ejection/injection at the surface resulting from the pressure difference across the porous wall derived from Darcy’s law. Numerical solutions were obtained for a range of axial flow Reynolds numbers, wall permeabilities, and initial pressure difference across the porous wall. The calculated static pressure variation in the axial flow direction, the velocity components, and the wall shear stress are presented. For the case of fluid ejection, the results of the analysis show that the wall shear stress and static pressure decrease in the axial flow direction. The rates of decrease are functions of the wall porosity, initial pressure gradient across the wall, and inlet flow Reynolds number. The present analysis treats the realistic problem of flow adjustment to the condition where zero pressure differential across the porous wall occurs (the normal wall velocity vanishes). Previous models are based upon the assumptions of constant radial velocity at the wall and/or prescribed wall shear stress without taking into account the pressure drop through the wall. Such assumptions imply that a variable pressure exists external to the pipe, or that the pipe has walls of variable permeability and thickness rather than the hypothesized condition that the pipe has uniformly porous walls. For one set of boundary conditions it is shown that the outflow through the walls completely discharges the entering flow. As a result no far downstream axial flow occurs. Such effects were not previously discussed by other investigators. For other sets of boundary conditions reductions in centerline velocity and shear stress occur.
Distributed Parameter Identification Using the Method of Characteristics
Authors: Carpenter William T. , Wozny Michael J. , Goodson Raymond E.
Published: November 2010

A method is presented for estimating parameters in distributed systems which can be analyzed by the method of characteristics. Both the very real problems of noisy measurements and limited available measurement transducers are discussed in some depth. Convergent algorithms are developed using a Robbins-Munro stochastic approximation scheme. The extension of these methods to the identification of function multidimensional systems, and diffusion terms is considered.
On the Stability of a Class of Distributed, Sampled-Data Nonlinear Systems
Authors: Nagarajan N. , Khatri H. C.
Published: November 2010

A frequency domain stability criterion (sufficient condition) for a class of distributed parameter, sampled-data systems containing a memoryless, nonlinear feedback element is presented. This criterion for absolute stability of the class of distributed systems considered here parallels the criterion for lumped systems obtained by Jury and Lee, and it requires that the following relationship be satisfied on the unit circle (|z| = 1). Re{W(pj,z)[1+q(z−1)]}+1K−K′|q|2|(z−1)W(pj,z)|2≥0forallj=0,1,2,…. This sufficient condition is limited to those systems whose dynamics can be described by a transfer function W(pi, z) which is the ratio of the multiple transform of the output to the multiple transform of the input. An example is given to illustrate the applications of the stability criterion.
Switching Dynamics of Bistable Fluidic Amplifiers With Low Setbacks
Authors: Ozgu M. R. , Stenning A. H.
Published: November 2010

The transient switching of a model bistable fluidic amplifier with low setbacks and variable configuration has been studied. The amplifier was of conventional design with straight and convex side-walls, cusped and pointed splitters, and variable control port width. Water was used as the fluid and the element was operated at different Reynolds numbers. Effect of loading, inertia of the fluid in the output legs, bias flows from the inactive control port, and geometric changes on the transient switching times were determined. The flow field was made visible by generating hydrogen bubbles in the power nozzle and at the power nozzle exit. Using visual studies of the switching process as a guide, an analysis has been developed to predict the switching times approximately.
The Selection of Performance Indices for Optimal Control Problems
Authors: Woods R. L.
Published: November 2010

This paper investigates the proper selection of a performance index to satisfy a word statement of desired effect. A performance index formed as the time integral of Un is solved for various values of n. When viewed in this light, the classical quadratic index (n = 2) gives a seemingly arbitrary solution. From this investigation the true optimal control solution can be ascertained. For the different values of n, solutions for totally different performance can be obtained. Performance indices combining two effects of minimum control effort and minimum response error are also investigated. The differences of a summed combination and a multiplicative combination are studied.
Optimal Observation of Linear Plants Whose Dynamic Properties Are Known
Authors: Gessing R.
Published: November 2010

The paper is concerned with determination of the state components in the case of measurements of output and control signals of the plant with errors. The optimal operators have been considered, which in the case of least favorable measurement errors give a minimal value of error of component to be defined. Particularly a case of signal measurement with errors which differ from each other has been considered. It has been shown that optimal operators are certain linear operators. The way of selecting these optimal operators from linear operators has been also shown. Namely it has been proved that for all cases which are considering the so called mini-max principle preserve its validity. Other theorems which can help to select optimal operators are formulated.
On the Art of Advancing The Science of Fluidics
Authors: Sarpkaya Turgut
Published: November 2010

Limitations in our understanding of the fluid dynamic phenomena encountered in fluidic elements and the resulting difficulty of the quantitative characterization for simple cataloging of the performance of fluidic devices are discussed. Finally, a number of recommendations are made for additional experimental, analytical, and phenomenological insights and the need is stressed for the integration of the existing elements, regardless of their present state of analysis, into a variety of useful and competitively priced devices by those who are interested in sustaining motion from the field of fluidics.
Adaptive Control of Respiratory Mechanics
Authors: Ha¨ma¨la¨inen Raimo P.
Published: November 2010

A hierarchial model is proposed to describe the performance principles of the adaptive system controlling respiratory mechanics. The decision criterion of the controller is modeled by a two-level minimization criterion, where the inspiratory and expiratory flow patterns are determined on the lower level and the overall pattern of breathing on the higher level. The objective functionals are related to the effectivity of breathing. An extension of the lower level model to include control of the rib cage and abdomen separately is also reported.
A Practical Filter for Systems With Unknown Parameters
Authors: Soeda T. , Yoshimura T.
Published: November 2010

This paper deals with the problem of a practical filter for discrete-time, dynamic systems with unknown parameters whose variation cannot be estimated in advance. The modeling errors caused by unknown parameters clearly degrade the filter performance and sometimes lead to divergence of estimation errors. Divergence is said to occur when the calculated covariance of estimation errors becomes very small comparing with the actual covariance. A practical filter that modifies the calculated covariance is developed as a technique for controlling the divergence. This is done by testing whether or not the actual residual at each stage is likely to have come from the calculated distribution, and the calculated covariance is modified when the test is rejected. The numerical results of digital simulation indicate that divergence of estimation errors is observed when the a priori information for dynamic systems is in error and that the divergence is prevented by the proposed filter.
Oscillations in an Adaptive Aircraft Control System
Authors: Wisler Larry S. , Rang Edward R.
Published: November 2010

An analog simulation of an adaptive control system showed small amplitude limit cycles when large input command signals were applied. These were explained by perturbation analysis on simplified versions of the systems. The conclusions were verified by the analog computation. The oscillations were shown to be an inherent feature resulting from the servo and actuator lags and the integrations in the gain-changing mechanization. A modification was made which eliminated the limit cycles.
Design for Component Reliability: A New Challenge for the Control Systems Analyst?
Authors: Brewer J. W. , Gordon L. M.
Published: November 2010

The authors demonstrate that if feedback control and component reliability design criteria are considered simultaneously, significant gains in reliability may result. The discussion begins with a tutorial introduction to probabilistic design for reliability. Simple examples are employed to illustrate the analytical tie between feedback control and component reliability. In the case of modal control, it is demonstrated that fast response and component reliability are competing criteria. The question of system (as opposed to component) reliability is discussed in a succeeding paper.