bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress Singularities at Equal Angle Biwedges and Two-Material Composite Half Planes With Rough Interfaces
Authors: Theocaris P. S. , Gdoutos E. E.
Published: November 2010

The order of the elastic stress singularity developed either at the apex of an equal angle biwedge or at the vertex of a composite half plane is studied for the case when the two wedges adhere along their common interface according to Coulomb’s law of friction. The other two faces of the wedges are considered free from tractions in the vicinity of the apices of both types of biwedges. The study uses the well-known theory of complex variables, and the numerical results obtained for some special geometrical configurations and particular values of the friction coefficient are presented in Dundurs’ parallelograms which cover all physically interesting material combinations of the two wedges.
A Theoretical Investigation of the Multileaf Journal Bearing
Authors: Oh K. P. , Rohde S. M.
Published: November 2010

The finite-element method is used to solve the compressible Reynolds equation which governs the fluid flow between the journal surface and the leaves in a multileaf journal bearing. The solution obtained is then coupled with the load-deflection equations of the leaves to obtain such information as liftoff speed and minimum film thickness. In addition, the load-deflection equations yield the initial preload on the journal, the startup torque, the stiffness coefficients, and the equivalent damping coefficients. Such details as leaf curvature, friction between leaves, and between leaves and journal surface are considered in the load-deflection equations. Results are obtained for a wide range of operating parameters.
Convective Heat Transfer in a Liquid Saturated Porous Layer
Authors: Buretta R. J. , Berman A. S.
Published: November 2010

The convective heat transfer in fluid saturated porous beds either heated from below or heated by distributed sources is investigated for several bed thicknesses and permeabilities. For the case of heating from below Rayleigh numbers range from about 10–10,000. For distributed heat sources Rayleigh numbers range from about 10–1000. Critical Rayleigh numbers for the onset of convection are estimated as 38 for heating from below and 31.8 for distributed heat sources. Heat transfer results for convection induced by heating from below are in good agreement with analytical upper bound estimates obtained by Gupta and Joseph.
Thermal Stresses in Heat-Treated Fibrous Composites
Authors: Dvorak G. J. , Rao M. S. M.
Published: November 2010

A new axisymmetric plasticity theory of fibrous composites which was developed by the authors is applied to problems involving large uniform thermal changes. The determination of loading surfaces and internal microstress fields is described. To verify the accuracy of the theory, a simulation of the T6 temper, followed by uniaxial extension of a W-Al composite has been made. The resulting microstresses show an excellent agreement with available experimental magnitudes measured in situ by an X-ray technique. In addition, there is a very satisfactory agreement with results obtained by the finite-element method.
Plastic Wave Speeds in Isotropically Work-Hardening Materials
Authors: Ting T. C. T.
Published: November 2010

Plastic wave speeds in materials whose elastic response is linear and isotropic while the plastic flow is incompressible and isotropically work-hardening are obtained. One of the three plastic wave speeds is identical to the elastic shear wave speed regardless of the form of the yield condition. The other two plastic wave speeds, cf and cs, are determined for materials obeying the von Mises yield condition. The dependence of cf and cs on the stress state and the direction of propagation is investigated in detail. The largest and smallest cf and cs, and the directions along which they occur are also presented. For materials obeying the Tresca’s yield condition, it is shown that one can obtain the corresponding results by simply specializing the results for the von Mises materials. Unlike in one-dimensional analyses where the plastic wave speed becomes zero for perfectly plastic solids, the three-dimensional analyses show that the ratio of cf to c1, where c1 is the elastic dilatation wave speed, is always larger than 3/7 for the von Mises materials and 1/2 for the Tresca’s materials. For most materials under moderate loadings, this ratio is much higher.
On the Influence of Hardening and Anisotropy on the Plane-Strain Compression of Thin Metal Strip
Authors: Collins I. F. , Meguid S. A.
Published: November 2010

This paper presents a theoretical investigation into the continued quasi-static compression of a thin metal strip between two rigid, parallel rough dies. Three different constitutive postulates for the strip material are considered: (a) rigid isotropic hardening, (b) rigid-perfectly plastic with an anisotropic yield criterion, and (c) rigid-kinematic (anisotropic) hardening. An initially homogeneous such strip develops inhomogeneities through its thickness as it is compressed. This is due to the dependence of the yield locus on the rigid-body spin for an anisotropic material and on the strain-history for a hardening material. The length of the dies is supposed to be much greater than the current strip thickness. The solution is hence effectively independent of position along the length of the strip and can be found by integrating an ordinary differential equation.
Stability Analysis of Straight and Buckled Two-Dimensional Channels Conveying an Incompressible Flow
Authors: Matsuzaki Y. , Fung Y.-C.
Published: November 2010

This paper analyzes the stability of a two-dimensional flexible channel of finite length by evaluating the fluid dynamic pressure analytically, and solving a plate equation with the aid of a two-term Galerkin approach. The walls of the channel are collapsible, flat plates supported laterally by a set of uniformly distributed springs and at the ends by pins. The nonlinear relationship between axial and lateral displacement is taken into account in order to examine the behavior of the walls when they deviate from the flat configuration after an onset of aerodynamic buckling or classical buckling due to the fluid force or endshortening, respectively. As the flow is increased from zero the walls become statically unstable at a certain flow speed and start to collapse in the first axial mode when there are no distributed springs. With further increase in flow speed the deflection of the buckled walls increases continuously. The analysis of limit cycle oscillations indicates that no flutter of the flat and buckled walls is predicted when damping exists.
Optimal Beam Layouts: The Free Edge Paradox
Authors: Hill R. D. , Rozvany G. I. N.
Published: November 2010

In optimizing plane flexural systems such as grillages and fiber-reinforced plates of a prescribed depth, the solution can now be obtained relatively easily for any combination of clamped and simply supported boundaries. However, attempts to extend the same theory to systems with free (unsupported) edges failed in the past and it has even been suggested that solutions for such boundary conditions may not have to satisfy certain generally accepted static-kinematic optimality criteria. The reasons for these difficulties are explained herein by considering the optimization of a simple grillage subjected to point loads. It is demonstrated that, when discrete solutions having a prescribed number of beams are considered, then the optimal structural weight can be reduced further by increasing the number of beams specified. The limiting case giving the absolute minimum structural weight appears to consist of an infinite number of beams some of which take on an infinitesimal length. The foregoing layout satisfies the Prager-Shield optimality criterion and is made plausible by establishing very close upper and lower bounds on it. The proposed solution is useful both in furnishing the absolute limits of economy and in providing efficient beam directions for the design of discrete grillages with free edges.
A Modal Analysis for the Damped Linear Gyroscopic Systems
Authors: Hablani H. B. , Shrivastava S. K.
Published: November 2010

A modal analysis of a flexible linear damped gyroscopic system is developed here. The simple structure of the corresponding real constant generally nonsymmetric dynamic matrix allows the use of the biorthogonality relation and dual-expansion theorem for a linear operator in a vector space. A closed-form response to both periodic forces and general initial conditions is thus obtained. The method is illustrated by deriving the response of an inertially coupled gravity-stabilized pervasively damped satellite.
Uniqueness of Damping and Stiffness Distributions in the Identification of Soil and Structural Systems
Authors: Udwadia F. E. , Sharma D. K. , Shah P. C.
Published: November 2010

As the interest in the seismic design of structures has increased considerably over the past few years, accurate predictions of the dynamic responses of soil and structural systems has become necessary. Such predictions require a knowledge of the dynamic properties of the systems under consideration. This paper is concerned with the uniqueness of the results in the identification of such properties. More specifically, the damping and stiffness distributions, which are of importance in the linear range of response, have been investigated. An N-storied structure or an N-layered soil medium is modeled as a coupled, N-degree-of-freedom, lumped system consisting of masses, springs, and dampers. Then, assuming the mass distribution to be known, the problem of identification consists of determining the stiffness and damping distributions from the knowledge of the base excitation and the resulting response at any one mass level. It is shown that if the response of the mass immediately above the base is known, the stiffness and damping distributions can be uniquely determined. Following this, some nonuniqueness problems have been discussed in relation to the commonly used ideas of system reduction in the study of layered soil media. A numerical example is provided to verify some of these concepts and the nature of nonuniqueness of identification is indicated by showing how two very different (yet physically reasonable) systems could yield identical excitation-response pairs. Errors in the calculation of the dynamic forces, due to erroneous identification have also been illustrated thus making the results of the present study useful from the practical standpoint of the safe design of structures to ground shaking.
Wave Motion in Multilayered Liquid Films
Authors: Akhtaruzzaman A. F. M. , Wang C. K. , Lin S. P.
Published: November 2010

The governing equation of the linear interfacial wave motion in an n-layered liquid film, which possesses n degree of freedoms, flowing steadily down an inclined plane is obtained. The effects of density, viscosity, and thickness variations on the various modes of wave motion are elucidated with aid of some numerical experiments for a three-layered system. It is found that the wave speed of the interfacial mode is much smaller than that of the free-surface mode. The interfaces seem to oscillate in phase for the free-surface mode but can be either out-of-phase or in-phase for the interfacial modes. It is shown that a limited control of wave speeds can be achieved by adjusting the variation in thickness, viscosity, and density of each layer.
Nonparallel Effects on the Stability of Jet Flows
Authors: Garg V. K. , Round G. F.
Published: November 2010

A theoretical analysis of the linear, spatial stability of Bickley’s jet is presented. The analysis takes into account the effects of transverse velocity component and the axial variations of the basic flow and of the disturbance amplitude, wavenumber and spatial growth rate. The integration of stability equations is started from the outer region of the jet toward the jet axis using the solution of the asymptotic forms of the governing equations. Results are compared with those for the parallel-flow stability analysis. It is found that the nonparallel effects decrease the wave number at low frequencies but increase it at high frequencies. Thus the nonparallel effects make Bickley’s jet unstable over a wider frequency range.
Solution of Navier’s Equation in Cylindrical Curvilinear Coordinates
Authors: Berger B. S. , Alabi B.
Published: November 2010

A solution has been derived for the Navier equations in orthogonal cylindrical curvilinear coordinates in which the axial variable, X3, is suppressed through a Fourier transform. The necessary coordinate transformation may be found either analytically or numerically for given geometries. The finite-difference forms of the mapped Navier equations and boundary conditions are solved in a rectangular region in the curvilinear coordinaties. Numerical results are given for the half space with various surface shapes and boundary conditions in two and three dimensions.
On the Onset of Breakup in Inviscid and Viscous Jets
Authors: Caulk D. A. , Naghdi P. M.
Published: November 2010

This paper is concerned with the instability of inviscid and viscous jets utilizing the basic equations of the one-dimensional direct theory of a fluid jet based on the concept of a Cosserat (or a directed) curve. First, a system of differential equations is derived for small motions superposed on uniform flow of an inviscid straight circular jet which can twist along its axis. Periodic wave solutions are then obtained for this system of linear equations; and, with reference to a description of growth in the unstable mode, the resulting dispersion relation is found to agree extremely well with the classical (three-dimensional) results of Rayleigh. Next, constitutive equations are obtained for a viscous elliptical jet and these are used to discuss both the symmetric and the antisymmetric small disturbances in the shape of the free surface of a circular jet. Through a comparison with available three-dimensional numerical results, the solution obtained is shown to be an improvement over an existing approximate solution of the problem.
Finite-Element Solution of the Fredholm Integral Equation With Weak Singularity
Authors: Dang D. Q. , Norrie D. H.
Published: November 2010

The solution of the Fredholm integral equation with weak singularity using the finite-element approach is described. Several methods of evaluating the elemental integrals are considered in relation to an analytic test problem. Comparison of the results shows that although explicit integration will usually give a more accurate solution, there are advantages in approximate integration for more complicated systems.
Exact Equations for the Inextensional Deformation of Cantilevered Plates
Authors: Simmonds J. G. , Libai A.
Published: November 2010

A set of first-order ordinary differential equations with initial conditions is derived for the exact, nonlinear, inextensional deformation of a loaded plate bounded by two straight edges and two curved ones. The analysis extends earlier approximate work of Mansfield and Kleeman, Ashwell, and Lin, Lin, and Mazelsky. For a plate clamped along one straight edge and subject to a force and couple along the other, there are 13 differential equations, but an independent set of 9 may be split off. In a subsequent paper, we consider alternate forms of these 9 equations for plates that twist as they deform. Their structure and solutions are compared to Mansfield’s approximate equations and particular attention is given to tip-loaded triangular plates.
Elasticity Theory of Plates and a Refined Theory
Authors: Cheng Shun
Published: November 2010

A method for the solution of three-dimensional elasticity equations is presented and is applied to the problem of thick plates. Through this method three governing differential equations, the well-known biharmonic equation, a shear equation and a third governing equation, are deduced directly and systematically from Navier’s equations. It is then shown that the solution of the second fundamental equation (the shear equation) is in fact related to the shear deformation in the bending of plates, hence it may be appropriately called the shear solution and the equation the shear equation. Moreover, it is found that the solution of the third fundamental equation does not yield transverse shearing forces. Because of these results, a refined plate theory which takes into account the transverse shear deformation can now be explicitly established without employing assumptions. With the present theory three boundary conditions at each edge of the plate and all the fundamental equations of elasticity can be satisfied. As an illustrative example, the present theory is applied to the problem of torsion resulting in exactly the same solution as the Saint Venant’s solution of torsion, although the two approaches are appreciably different. The second example also illustrates that accurate solutions, as compared with exact solutions, can be obtained by means of the refined plate theory.
Optimum Hole Shapes in Finite Plates Under Uniaxial Load
Authors: Durelli A. J. , Rajaiah K.
Published: November 2010

This paper presents optimized hole shapes in plates of finite width subjected to uniaxial load for a large range of hole to plate widths (D/W) ratios. The stress-concentration factor for the optimized holes decreased by as much as 44 percent when compared to circular holes. Simultaneously, the area covered by the optimized hole increased by as much as 26 percent compared to the circular hole. Coefficients of efficiency between 0.91 and 0.96 are achieved. The geometries of the optimized holes for the D/W ratios considered are presented in a form suitable for use by designers. It is also suggested that the developed geometries may be applicable to cases of rectangular holes and to the tip of a crack. This information may be of interest in fracture mechanics.
Reference Stress and Temperature for Nonisothermal Creep of Structures
Authors: Williams J. J. , Cocks A. C. F.
Published: November 2010

The relationship between the reference stress concept and the nesting surfaces of Calladine and Drucker is examined and the implications for nonisothermal creep are discussed. A method for evaluating a reference stress and temperature is described, which it is argued is more rigorous than methods previously proposed.
Diffraction of Torsional Waves by a Flat Annular Crack in an Infinite Elastic Medium
Authors: Shindo Y.
Published: November 2010

The problem of diffraction of normally incident torsional waves by a flat annular crack embedded in an infinite, isotropic, and homogeneous elastic medium is considered. Using an integral transform technique, the problem is reduced to that of solving a singular integral equation. The solution of the singular integral equation is obtained in the form of the product of the series of Chebyshev polynomials of the first kind and their weight functions. Thus the essential feature of the dynamic singular stress field near the crack is preserved and the crack tip dynamic stress-intensity factor is easily evaluated. Numerical calculations are also carried out and the variations of dynamic stress-intensity factors with the normalized frequency for the ratio of the inner radius to the outer one are shown graphically.
Instability of a Fiber-Reinforced Elastic Slab Subjected to Axial Loads
Authors: Kurashige M.
Published: November 2010

Following the derivation of the relations of incremental stresses and strains for an idealized fiber-reinforced isotropic elastic material, the instability problem stated in the title is analyzed on the basis of Biot’s mechanics of incremental deformations. The analysis indicates that the slab reinforced by fibers along the direction of its thickness under axial loads becomes unstable in a manner different from the case of an unreinforced slab. In the course of the analysis the material was specified as the so-called Blatz-Ko rubber, solid and foam. It was found that the slab of solid rubber buckled only under compression, while that of foam rubber became unstable under tension as well as under compression. There exist two types of buckling for foam rubber under tension: a shear buckling and an internal buckling. However, the latter does not manifest itself physically since the former always occurs first.
Discrete Frequency Noise Generation From an Axial Flow Fan Blade Row
Authors: Mani Ramani
Published: November 2010

An analysis is presented which treats the noise generation from an axial flow fan row by given forces including the effects of a moving medium. The linearization of Euler’s equations to yield tractable problems for fan noise is discussed. The three-dimensional problem is decomposed into several two-dimensional problems. Finally, full details are given of a two-dimensional analysis to predict the amounts of acoustic energy, at the blade passing frequency and its harmonics, radiated up and downstream of a blade row due to its interaction with a neighboring row.
Linearized Theory of Three-Dimensional Jet Mixing With and Without Walls
Authors: Pai S. I. , Hsieh T. Y.
Published: November 2010

The laminar jet mixing of an incompressible and viscous fluid issuing from a nozzle of rectangular cross section into a uniform stream has been studied theoretically. When the jet velocity deviates slightly from that of free stream, exact solutions have been obtained. Three different cases have been discussed. First is the three-dimensional jet in an infinite domain of uniform stream. Second is the three-dimensional jet in a finite domain of uniform flow bounded by parallel walls, and third is the three-dimensional jet with adjoining parallel walls and axial pressure gradient. The following main results are obtained: (a) The rate of decrease of maximum velocity in the jet decreases as the aspect ratio of the nozzle increases for a given jet velocity. (b) The spread of the jet is different along different directions and the cross section of the jet tends to be circular far downstream from the nozzle. (c) The adjoining walls would increase the velocity in the jet, and (d) favorable axial pressure gradient increases the velocity in the jet. Numerical results for various cases are presented.
Graphical Determination of Optimum Trajectories for Third-Order Systems
Authors: Abd-El-Fattah Yousri M.
Published: November 2010

The present paper explains the use of two phase planes in the graphical determination of optimum trajectories for third-order systems, depending on the sign of a single control function. The control function is defined on these planes by means of different contours. Accordingly, the control signal is known at the different points on these planes. Once the control signal is found, the state trajectory is determined. Most of the arbitrary initial states are treated and, in particular, the cases of separate steps in each of the error and its first as well as second time derivatives. This work also explains the use of the graphical solution in obtaining the maximum error and switching times.
On the Frequency Response of Viscous Compressible Fluids as a Function of the Stokes Number
Authors: Goldschmied F. R.
Published: November 2010

Air, carbon dioxide, and helium test data are presented for the experimental verification of Iberall’s analysis of the dynamic pressure response of viscous compressible fluids in rigid tubes with deadened volume termination against oscillatory frequency. A graphical display is given of numerical solutions of Iberall’s theory over a wide range as a function of the Stokes number and of a dimensionless frequency. Rapid engineering solutions are presented for the following problems: Given a tube, a chamber volume, and a fluid, determine the maximum frequency to be transmitted at ±10 percent amplitude distortion. Given a tube, a chamber volume, and a fluid, sketch the dynamic pressure response curve. Given a chamber volume, a fluid, and a specified frequency to be transmitted within ±10 percent amplitude distortion, plot allowable tube length against tube diameter.
An Approximate Model for the Static Operation of a Fluidic Amplifier Employing Axisymmetric Jets
Authors: Johnson R. T.
Published: November 2010

An approximate mathematical model for the static, no-load (blocked receiver) operation of a fluidic amplifier employing axisymmetric jets is developed. The amplifier is similar in concept to the three-terminal modulator developed by the Johnson Service Co. The approach used in developing the model assumes that the complex flow phenomena can be represented by the combination of several elementary flow problems. The model employs the concept of an equivalent power nozzle in describing downstream flow with a control signal present. Experimental results are presented to justify assumptions and evaluate parameters.
Hysteresis Characteristics of Francis Pump-Turbines When Operated as Turbine
Authors: Yamabe M.
Published: November 2010

The results obtained through experiments on models concerning the phenomena of hysteresis characteristics of Francis pump-turbines generated when operated as turbine are described in the present report. It has made clear the fact that the condition for generating the phenomena is regulated by cavitation factor and guidevane openings and affected by the specific speed of a pump-turbine; furthermore, some characteristics of the flow state within a runner are pointed out.
An Interferometric Technique for Temperature and Concentration Measurement for an Air-Water Interface
Authors: Prasad C. , Chen C. S. , Beard J. T.
Published: November 2010

A new technique for the measurement of temperature and concentration for a simultaneous heat and mass transfer analysis is described. The technique employs a one wavelength Mach-Zehnder interferometer with an additional noninterferometric measurement of temperature or concentration. This overcomes the difficulties encountered in other interferometric techniques used for simultaneous heat and mass transfer analysis such as two wavelength technique and one wavelength technique with the assumption of Lewis number being unity. Computational formulas were developed, by which either temperature or concentration can be calculated from the interferograms. An air-vapor boundary layer formed due to heated water and ambient air set in parallel flow was analyzed with this technique. Better results in the air-water system were obtained for the concentration from interferogram analysis with the temperature measured by another technique.
Elevated Temperature Properties of Maraging Steel Plates and Welds
Authors: Kenyon N. , Sadowski E. P. , Hydrean P. P.
Published: November 2010

The creep rupture behavior, and the effects of elevated temperature exposure in air and hydrogen on the subsequent room temperature properties of a 12 percent Ni-5 percent Cr-3 percent Mo maraging steel are described. Tests have been made on several heats of plate and on gas tungsten-arc, gas metal-arc, and electroslag welds. On the basis of the results obtained, maraging steels offer promise as high-strength steels for service at elevated temperatures.
Holographic Detection of Microcracks
Authors: Vest C. M. , McKague E. L. , Friesem A. A.
Published: November 2010

This paper describes the application of optical holographic interferometry to the detection of microcracks in metals. In particular, detection of radial cracks extending from bolt holes in high strength aircraft steel was studied. The method was found to hvve several advantages over currently used detection methods. The results of the holographic study compared favorably with independent results obtained by magnaflux, eddy current, and X-ray inspection. Some evidence of a possible ability to detect untempered martensite deposits was also noted.
Transient Response of Fluid Lines Including Frequency Modulated Inputs
Authors: Kantola R.
Published: November 2010

In this paper, analytic descriptions for the step and impulse responses of the fluid in rigid cylindrical lines are obtained in the time domain. In all cases, the fluids considered are Newtonian liquids or perfect gases, with the effects of laminar viscous dissipation and heat transfer taken into account. In particular, a power series expansion is used to solve the partial differential equations of small amplitude signal propagation. With the advent of carrier techniques in fluid systems the study of the transmission of frequency-modulated signals in fluid-filled lines is needed. Recognizing this need, an analysis of the response of fluid-filled lines to a step modulation of carrier frequencies is presented. Experimental measurements of the step response of air filled lines are also given. An effect uncovered by the experimental work is the nonlinearity of the signals at signal amplitudes, unexpectedly as low as one percent of the mean pressure.
Some Results on the Heat Transfer Within Resonant Cavities at Subsonic and Supersonic Mach Numbers
Authors: White R. A.
Published: November 2010

An experimental investigation of the heat transfer within two cavities (L/D = 1.25 and 2.0) exhibiting self-induced pressure oscillations (commonly referred to as resonance) is discussed. The tests were conducted with free stream Mach numbers between 0.35 and 1.5 with corresponding unit Reynolds numbers of 33 × 105/ft to 41 × 105/ft. The approaching boundary layer and shear layer over the cavitieswere turbulent at all times. The pattern for the heat transfer coefficient distribution over the cavity walls is in good agreement with that found by other investigators. The effect of the self-induced pressure oscillations, however, is to cause large changes in the level of the heat transfer, with low values occurring at the distinctive peaks of the pressure oscillations. The ratio of the integrated heat transfer within the cavity to the heat transfer from a flat plate with area equal to the area of the cavity opening was found to vary from 1.10 to 0.40, depending on Mach number and cavity resonance conditions.
Development and Testing of Techniques for Oscillating Pressure Measurements Especially Suitable for Experimental Work in Turbomachinery
Authors: Weyer H. , Schodl R.
Published: November 2010

Strong pressure oscillations of high frequencies and high amplitudes occur in the region of turbomachine rotors. The measurement of the average pressures resulting from these oscillations is one of the most important measuring problems in turbomachinery, because the pneumatic measuring systems usually used in such tests yield average pressures which normally do not agree with the true time-integrated values. This paper deals with an investigation aimed at the development of techniques, which permit the measurement of well-defined average values of oscillating pressures. Three different methods developed and tested at DFVLR are described. Two of them—a hydraulic and a mechanical one—are able to measure the true time-averaged pressures with an accuracy better than 0.5 percent of the acting pressure amplitude. The third procedure is based on an evaluation method by means of which the average pressures indicated by special pneumatic measuring systems can be correlated to the true time-weighted values. Experimental and computed results are presented showing a very good agreement.
Bending Titanium and Beryllium Sheet in Pressurized Fluid
Authors: Meyer G. E. , Fiorentino R. J.
Published: November 2010

Bend tests were conducted to determine the effect of changes in ambient pressure on the minimum bend radii of titanium and beryllium sheet. Sheet specimens of commercially pure titanium, Ti-6Al-4V, Ti-8Mo-8V-2Fe-3Al (beta-titanium alloy), Ti-8Al-1Mo-1V, and 1.5 percent BeO beryllium sheet were bent using a series of bend radii in fluid pressurized up to 225,000 psi. All the materials could be bent to radii well below this pressure level except Ti-8Al-1Mo-1V, and beryllium. Extrapolation of the test results indicated that these latter two material would have to be pressurized to about 260,000 psi to accommodate a 1T bend. No relationship was evident between mechanical properties of the sheet and the influence of ambient pressure on minimum bend radii. Strain and reduction in area values experienced by the sheet in bending were calculated as a function of bend radius.
Conduit Representation in Closed Loop Simulation of Hydroelectric Systems
Authors: Wozniak L. , Fett G. H.
Published: November 2010

This paper develops a program for closed loop simulation of the transient behavior of a hydroelectric composite. The system modeling is comprehensive, including such factors as governor nonlinearities in mechanical compensation and servomotion. Special emphasis is given to conduit simulation in its elastic and frictional characteristics. The problem of friction is treated by appropriate attenuation of the traveling pressure wave. This point of view accounts for the phenomenon of regained head at decreased flows. The turbine characteristics are represented globally by means of polynomial approximation [1].
A Momentum Integral Solution of a Three-Dimensional Turbulent Boundary Layer
Authors: Pierce F. J. , Klinksiek W. F.
Published: November 2010

The results of a momentum integral solution of the three-dimensional turbulent boundary layer on the confining wall of an impinging jet are presented. This geometry provides a boundary layer where large gradients in the streamwise and especially the transverse direction occur and hence is a severe test of momentum integral methods. The solution utilizes the Head entrainment function and the Ludwieg and Tillmann wall shear law, with no restriction on cross flows. An extensive comparison with experimental results show good to moderate agreement in the integrated flow parameters, with a strong dependence on the free-stream or edge condition to the boundary layer flow.
A Thermodynamic Model of Biological Body: Muscle Mechanics
Authors: Brankov G. , Petrov N.
Published: November 2010

The paper is an application of the theory of chemically reacting mixtures to the mechanics of active muscle. It is indicated that some empirical rheologic models can be obtained as particular cases. Viscoelastic properties of the tissue are obtained as a result of a relaxation in the binding of actin and miosin molecules.
Instrument for Continuous Measurement of O2 Consumption and CO2 Production of Men in Hyperbaric Chambers
Authors: Troutman S. J. , Webb P.
Published: November 2010

We describe an open circuit method for measuring O2 consumption and CO2 production suitable for use in hyperbaric atmospheres and designed to yield continuous data while allowing the critical instrumentation to remain outside the hyperbaric chamber. The subject wears a light, loosely fitting, full face mask of clear plastic, through which ambient chamber gas is drawn at either 100 l/min for rest or sleep, or 200 l/min during exercise. Samples of the chamber gases and of the mixed expired gases are bled out of the chamber, then compared in differential analyzers. The analog signals from the analyzers are conditioned, proportioned to the mask ventilation rate, totalized and integrated to yield gas volumes, then printed every 10 min. A method of calibrating the system using inflows of pure CO2 was devised for use at 1 atm absolute and also at hyperbaric pressures. Data taken by this method during a 17-day saturation dive compared well to the data obtained using conventional Douglas bag techniques.
Canine Pulmonary Input Impedance Measured by Transient Forced Oscillations
Authors: Fredberg J. J. , Sidell R. S. , Wohl M. E. , DeJong R. G.
Published: November 2010

We describe a transient forced oscillation method for measurement of the input impedance of excised canine lungs. The technique employs a single uncalibrated data channel to record short duration pressure transients incident upon and reflected from the airway opening, from which the input impedance up to 10,000 Hz is computed using lossy transmission line theory. Data acquisition time is less than 10 ms. The lung responses exhibit numerous resonances and anti-resonances below 10,000 Hz, and exhibit lung volume dependence. The branching structure of the airways and response of the airway walls appear to be important factors in the lung response.
Deformations and Stresses in Soft Body Tissues of a Sitting Person
Authors: Chow W. W. , Odell E. I.
Published: November 2010

This paper investigates the deformations and stresses in the buttocks of a person when he sits on a cushion. The study is motivated by the need for a better understanding of the design of wheelchair cushions and the prevention of decubitus ulcers. The finite element method is used on an axisymmetric model. Surface pressure distribution, surface friction, hydrostatic pressures and von Mises stresses are obtained. The finite element model reveals the three-dimensional state of stress at all internal locations for a typical human body. Thus the study complements the experimental measurements performed by many physicians and bioengineers.
Determination of Elastic Constants for Human Femurs
Authors: Lappi V. G. , King M. S. , Le May I.
Published: November 2010

The elastic properties of the bone constituting human femurs have been determined from measurements of the velocities of ultrasonic compressional and shear waves through wet, embalmed bone samples. The bone has been shown to be a transversely isotropic material with the axis of symmetry parallel to the longitudinal axis of the bone. The values of the elastic constants were determined to be: c11=6860±330MPaE3=5500MPac12=2700±570MPaE1=4990MPac13=3760±1570MPaν31=0.39c33=8480±760MPaν12=0.20c44=2240±180MPaG31=2240MPa where the 3-axis is that of rotational symmetry and the 1- and 2-axes are in the plane of isotropy.
Geometric Modelling of the Human Left Venticle
Authors: Yettram A. L. , Vinson C. A.
Published: November 2010

Paucity of fundamental data has held back the development of stress and displacement analysis applied to the human left ventricle. Up to the present, analyses have been based on profiles dependent upon the imposition of chosen mathematical functions on single-plane radiographs. Here a process is described for a more realistic three-dimensional modelling of the geometry of the human myocardium which makes use of biplane cineangiograms. The purpose of this procedure is to provide geometric data for subsequent finite-element analysis.
Peristaltic Pumping by a Lateral Bending Wave
Authors: Wilson D. E. , Stearman R. R. , Panton R. L.
Published: November 2010

A form of fluid transport induced by an arbitrary traveling wave in the walls of a two-dimensional channel filled with a viscous incompressible fluid is investigated. This can be considered as a more general case of peristaltic transport, the latter transport phenomena being classically restricted to a wave motion which produces a progressive wave of area contraction or expansion. A perturbation solution is found satisfying the complete Navier-Stokes equations for the case of small amplitude ratio (wave amplitude/channel half width). All other parameters are left arbitrary. Two particular types of boundary waves are investigated. First, a sinusoidal wave of identical phase is imposed on each wall (in-phase motion), and secondly, an in-phase and a π out-of-phase contraction wave are imposed simultaneously. For the case of in-phase motion, a peristaltic induced mean flow is found to be proportional to the amplitude ratio squared. However, for the second case, the mean flow is found to depend linearly on amplitude ratio when an imposed pressure gradient exists, producing a peristaltic assist. Thus we see that for the superposition of two waves, the transport mechanism can increase from a second-order to a first-order effect.
An Analysis of Sensible Respiratory Heat Exchange During Inspiration Under Environmental Conditions of Deep Diving
Authors: Johnson C. E. , Linderoth L. S. , Nuckols M. L.
Published: November 2010

Temperature of the gas stream and mucosa were measured in the upper and lower trachea and right and left main bronchi of several anesthetized, intubated and mechanically respired mongrel dogs. Airway temperatures were measured using an airway sensor probe instrumented with microthermistors. Each thermistor was integrated into an especially designed. Wheatstone bridge whose signal of millivolts was displayed on a calibrated polygraph recorder. Diving respiratory conditions were simulated by utilization of an appropriate ventilatory periodic flow through an endotracheal airway which by-passed the efficient gas conditioning nasal turbinates of the dog. Deep diving respiratory environmental conditions of gas temperature, density and thermal capacitance (ρCp) were simulated in a hyperbaric chamber. The temperatures recorded during in vivo periodic positive pressure ventilation were applied to a quasi-steady flow model based upon the morphological dimensions of the Weibel model. An empirical mathematical model of inspiratory sensible heat loss was verified and slightly modified to better reflect the overall dimensionless heat transfer relationship Nu = 0.302 (RePr)0.786 that existed in the major bronchial airways of the experimental subject. The design of the experimental instrumentation is explained in detail, as is the basic mathematical model. Significance of the experimental findings is discussed.
Thermal Stress Effects and Surface Cracking Associated With Laser Use on Human Teeth
Authors: Boehm R. , Rich J. , Webster J. , Janke S.
Published: November 2010

A detailed study is reported of the potential thermal stress effects and surface cracking of human teeth after absorption of laser energy. This study was motivated by the desire to define damage thresholds if lasers are used for preventive dentistry techniques. A large group of extracted teeth was exposed to manually pulsed bursts of energy of varying durations from a CW CO2 laser. The teeth were examined photographically under magnification before and after irradiation, using fluorescent dye to facilitate observation of cracks in the tooth surface. In an attempt to understand the cracking phenomena, predictions of the temperatures and thermal stresses were made. The tooth surface in the vicinity of the focused beam impingement was assumed to behave as a semi-infinite solid for the short periods of time considered. Estimated stresses where cracking occurred are compared in the paper to measured values of the ultimate strength of tooth enamel. Results are shown to be in reasonable agreement with predictions. Based on this work, a criterion is given for minimizing surface damage to the tooth.
Developments in Nonlinear Controller Synthesis: An Overview
Authors: Garg Devendra P.
Published: November 2010

In this paper developments in nonlinear controller synthesis techniques are surveyed. First, the use of functional analysis approach for system synthesis is discussed. Next, the application of intentional nonlinear controllers for performance improvement and optimization via performance index minimization is presented. This is followed by a discussion of signal stabilization using artificial dither. Finally, approaches are given for design of controllers to meet stability requirements for both single and multiple-loop nonlinear systems.
Analysis and Design of Machine Tool Chatter Control Systems Using the Regeneration Spectrum
Authors: Srinivasan K. , Nachtigal C. L.
Published: November 2010

This paper introduces a new concept in the analysis and design of machine tool chatter control systems, the regeneration spectrum. This development follows from a recognition of the fact that the stability analysis of time delayed systems such as machining systems is considerably simplified for large values of the time delay. The regeneration spectrum is a function of frequency whose definition is based on the system characteristic equation. Features of the distribution of the system characteristic roots in the s-plane are related quantitatively to the regeneration spectrum. Moreover, a quantitative measure of the degree of system stability is provided by the closeness of the regeneration spectrum peak to unity. Minimization of the regeneration spectrum peak is therefore the basis for determining controller parameters. The application of the regeneration spectrum to prior chatter control systems is illustrated. The use of the regeneration spectrum enables the formulation of the controller design problem as a multi-parameter optimization problem. Experimental work was performed to demonstrate the efficacy of this design methodology.
Effects of Jerk Limiting on the Stability of Automated Transit Vehicles
Authors: Garrard W. L.
Published: November 2010

In this paper a method is presented for estimating the effects of jerk limiting on the stability of the longitudinal dynamic response of automated transit vehicles.
Experience With Experimental Applications of Multivariable Computer Control
Authors: Seborg D. E. , Fisher D. G.
Published: November 2010

This paper summarizes experience gained over the past ten years in applying multivariable control techniques to a pilot scale, double effect evaporator at the University of Alberta. Since this same apparatus has been used in each investigation, it is possible to make meaningful comparisons between conventional control strategies and modern multivariable techniques including: Optimal control, eigenvalue assignment, state estimation, adaptive control, frequency domain methods, time delay compensation, disturbance localization and model reference identification. The paper concludes with a discussion of the implications of this research for industrial application.
Computational Techniques in Optimal State-Estimation—A Tutorial Review
Authors: Kortu¨m Willi
Published: November 2010

The objective of this tutorial presentation is to review the main computational techniques of the state-estimation problem for linearizable dynamic systems where the design is oriented toward a minimum variance (quadratic loss, gaussian) estimation error. It almost goes without saying that the viewpoints taken and the guidelines given in this paper should not be understood as firm recipes but rather as problem-dependent, sometimes subjective and experience-dependent, recommendations. We treat both the continuous and the discrete estimation problem: the first because it is usually closer to the real process and thus allows more direct physical insight; and the latter because it is often preferred for computation and for realization on large scale or special-purpose digital computers.
Robust Multivariable Controllers for a Tubular Ammonia Reactor
Authors: Viswanadham N. , Patnaik L. M. , Sarma I. G.
Published: November 2010

The specific objective of this paper is to develop multivariable controllers that would achieve asymptotic regulation in the presence of parameter variations and disturbance inputs for a tubular reactor used in ammonia synthesis. A ninth order state space model with three control inputs and two disturbance inputs is generated from the nonlinear distributed model using linearization and lumping approximations. Using this model, an approach for control system design is developed keeping in view the imperfections of the model and the measurability of the state variables. Specifically, the design of feedforward and robust integral controllers using state and output feedback is considered. Also, the design of robust multiloop proportional integral controllers is presented. Finally the performance of these controllers is evaluated through simulation.
Synthesis by Liapunov’s Direct Method
Authors: Peczkowski J. L.
Published: November 2010

This paper discusses the inverse Liapunov problem, that is, the problem of synthesis of systems to satisfy given Liapunov functions. Vector-matrix equations are developed which represent classes of systems that satisfy specified Liapunov scalar functions. The equations form a basis for direct synthesis of systems to match Liapunov performance criteria. Examples illustrate techniques.