bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability of Cylindrical Shells Under Moving Loads by the Direct Method of Liapunov
Authors: Hegemier G. A.
Published: October 2011

The stability of a long, thin, elastic circular cylindrical shell subjected to axial compression and an axisymmetric load moving with constant velocity along the shell axis is studied. With the aid of the direct method of Liapunov, and employing a nonlinear Donnell-type shell theory, sufficient conditions for local stability of the axisymmetric response are established in a functional space whose metric is defined in an average sense. Numerical results, which are presented for the case of a moving decayed step load, reveal that the sufficient conditions for stability developed here and the sufficient conditions for instability obtained in a previous paper lead to the actual stability transition boundary.
On Nonconservative Stability Problems of Elastic Systems With Slight Damping
Authors: Herrmann G. , Jong I. C.
Published: October 2011

A linear two-degree-of-freedom system with slight viscous damping and subjected to nonconservative loading is analyzed with the aim of studying the effects of damping on stability of equilibrium. It is found that, in such systems, multiple ranges of stability and instability may exist in a richer variety than in corresponding systems without damping. Further, for certain systems, instability either by divergence (static buckling) or by flutter may occur first as the compressive load increases, depending upon the ratio of the damping coefficients in the two degrees of freedom. It is shown finally that systems exist for which the destabilizing effect of slight viscous damping cannot be removed completely whatever the ratio of the (positive) damping coefficients.
Forced Convection of a Dissipative Liquid in a Channel With Neumann Conditions
Authors: Tyagi V. P.
Published: October 2011

In this paper, we consider a heat transfer problem of forced convection of liquids in an arbitrary straight channel with arbitrarily prescribed wall heat flux when the flow is steady, laminar, and of constant-property type and when the effect of viscous dissipation is taken into account. The assumption of fully developed flow has been made. An arbitrary heat source is assumed to be present in the channel. The general solution of the problem, in terms of integral formulas, is directly presented by using the methods of conformal transformation. In a separate section, some aspects of the problem are discussed briefly, especially with respect to wall heat-flux function, heat-source function, and mapping function, and a general series solution is then given. In the end, the problem of a cardioid duct is investigated numerically, and the results of nondissipative and dissipative cases are compared.
Asymptotic Analysis of the Axisymmetric Vibrations of Shells
Authors: Ross E. W.
Published: October 2011

An asymptotic analysis is carried out for the equations of axisymmetric vibrations of thin shells, somewhat analogous to the procedure by which geometrical optics is obtained from electromagnetic theory. It is found that two types of asymptotic solutions are obtained, roughly classifiable as high-frequency membrane solutions and bending solutions. Two explicit representations of these solutions are obtained, one for the shallow region of a shell and the other for the nonshallow region. A number of interesting conclusions emerge from the analysis.
Dynamic Flexural Buckling of Rods Within an Axial Plastic Compression Wave
Authors: Abrahamson G. R. , Goodier J. N.
Published: October 2011

Rods impacting a rigid target at velocities sufficient to produce several percent axial strain are found to buckle plastically with a fairly reproducible wavelength. This phenomenon is investigated for materials which exhibit strain-hardening, a property which is crucial to the theory. The buckling motion is treated as a perturbation of the motion associated with the axial compression. It is assumed that the axial strain rate dominates the extensional strain rate due to bending, so that no strain-rate reversal occurs until after the buckling is well developed. Elastic deformations are neglected, and the material is taken to follow a linear strain-hardening law. It is found that the predicted wavelength and buckling time are in reasonable agreement with experimental results.
Dynamic Response of a Viscoelastic Cylinder With Ablating Inner Surface
Authors: Achenbach J. D.
Published: October 2011

The effects of ablation and viscoelasticity on the vibratory response of a hollow cylinder are investigated. The cylinder is subjected to a time-dependent internal pressure. Solutions are presented for the circumferential stress at the eroding inner surface and for the displacement in radial direction. It is found that, due to ablation, frequencies decrease and amplitudes increase. The increases in amplitudes due to ablation are counteracted by viscoelastic damping. In this analysis, it is assumed that the material is incompressible in bulk and viscoelastic in shear.
Instability of Cylindrical Shells Subjected to Axisymmetric Moving Loads
Authors: Hegemier G. A.
Published: October 2011

Using a Donnell-type nonlinear theory and the stability in the small concept of Poincare´, the instability of an infinite-length cylindrical shell subjected to a broad class of axisymmetric loads moving with constant velocity is studied. Special cases of the general loading function include the moving-ring, step, and decayed-step loads. The analysis is carried out with a double Laplace transform, functional-difference technique. Numerical results are presented for the case of the moving-ring load.
On Some Problems in Transversely Isotropic Elastic Materials
Authors: Chen W. T.
Published: October 2011

This paper treats some problems in a homogeneous transversely isotropic elastic material, occupying an infinite space, or an infinitely long circular cylinder. The analysis is based upon the potential function method by Elliott, with the addition of another potential function. The static solution is extended to include quasi-static, or steady-state problems. Closed-form solution is found for the problem of an arbitrarily oriented concentrated force in an infinite medium. The case of discontinuous pressure over an infinitely long circular cylinder is also studied with the aid of a numerical method of integration. The applied forces are assumed to be moving with uniform velocity along the anisotropic direction.
The Stress Field Created by a Circular Sliding Contact
Authors: Hamilton G. M. , Goodman L. E.
Published: October 2011

Equations are obtained for the complete stress field due to a circular contact region carrying a “hemispherical” Hertzian normal pressure and a proportional distributed shearing traction. The equations are illustrated by graphs of a constant-yield parameter and graphs of maximum tensile stress.
Analytic Approximations of Boundary-Layer Problems
Authors: Schetz J. A.
Published: October 2011

The investigation of the approximate solution of boundary-layer problems by variational techniques is extended beyond earlier work based on a single-parameter collocation approach. A multiparameter treatment is considered and shown to result in a much improved approximation. More powerful minimization conditions for the single-parameter case are also studied. Finally, an approximate solution to a flow problem concerning the development of a boundary layer on a constant pressure surface after having traversed an upstream pressure gradient is presented and discussed.
Lubrication of a Porous Bearing—Reynolds’ Solution
Authors: Shir C. C. , Joseph D. D.
Published: October 2011

The problem of lubrication of a journal in a porous bearing is considered. A Reynolds equation modified to accommodate mass transfer with the fluid-saturated bearing is solved, and the influence of the permeability and radius ratio of the bearing is examined. The effects of the bearing flow are such as to reduce the magnitude of the pressure and shift the maximum away from the position of minimum gap. In extreme cases, the integrated resultant of the pressure forces is so reduced as to become comparable in magnitude with the normally negligible shear stress resultant. This latter resultant has an opposing sense so that the total load capacity of the bearing is greatly reduced as a result of bearing flow.
Some Studies of Nonlinear Lateral Sloshing in Rigid Containers
Authors: Abramson H. N. , Chu W. H. , Kana D. D.
Published: October 2011

Some experimental data, primarily on total force response, are presented for nonlinear lateral sloshing in rigid tanks of various geometries. Some effect of excitation amplitude on liquid swirl boundaries in an open circular cylindrical tank is noted. Data for the circular cylindrical tank are also compared with theoretical predictions. The primary nonlinear effects observed in all tanks were decreasing response frequency with increasing excitation amplitude and jump phenomena.
Bounds on the Maximum Thermoelastic Stress and Deflection in a Beam and Plate
Authors: Boley Bruno A.
Published: October 2011

It is shown in this paper that the thermal stress in a beam or plate cannot exceed the value kαEΔT, where ΔT is the maximum instantaneous temperature excursion in a cross section, and k is a coefficient dependent on the shape of the cross section. A simple general formula for k is found, and results for several special cases of practical interest are given. For rectangular beams (suitably oriented) and for plates, for example, k = 4/3. For any section, k = 1 if the thermal moment is zero; simplifications also occur if the thermal force is zero. The corresponding results for beam deflections are also carried out: The maximum deflection cannot exceed the value kδ kδ′αLΔT, where kδ and kδ′ are coefficients depending respectively on the cross-sectional shape and on the end conditions. For example, for rectangular cross sections, kδ = 3/4; and for a simply supported beam, kδ′ = 1/8.
A Distributed-Element Model for Hysteresis and Its Steady-State Dynamic Response
Authors: Iwan W. D.
Published: October 2011

A model for the hysteretic behavior of materials and structures is presented. This model is based on an approach which views the system as consisting of a series of ideal elastoplastic elements. The steady-state dynamic response of the model when subjected to trigonometric excitation is determined. The effect of the roundedness of the hysteresis loop on the nature of the response is investigated, and steady-state results, predicted by the theoretical model, are compared with experimental results from an actual structure.
On the Contact Problem of Thin Circular Rings
Authors: Wu Chien-Heng , Plunkett Robert
Published: October 2011

It is well known that the solution of an elastica subjected to end loads can be obtained in terms of elliptic functions. In the present paper, the combined problem of elastic contact between uniform circular rings or cylinders is reduced to a set of end-loaded elasticas. The approach is demonstrated by finding the complete solution in closed form for two unequal rings pressed between rigid anvils of constant curvature. Numerical results are obtained for the set of problems of two rings with equal stiffness but unequal radii compressed between two rigid flat plates.
On the Bending Problem of Prismatical Beam by Terminal Transverse Load
Authors: Leko Toma
Published: October 2011

Although the Saint-Venant solution on the bending problem of a prismatical beam by terminal transverse load is presented in all the literature on applied elasticity, the arbitrary constant in that solution has not been determined adequately. The different assumptions on this constant are cited, and it is shown in one particular example that the shearing stress on the cross section is not statically equivalent to the bending force. The definition of the shear center is critically reviewed, as well as some of its implications on recent investigations of turbine-blade vibration.
Buckling of a Long Fiber-Wound Cylindrical Shell Due to Stresses Caused by Windings
Authors: Langhaar H. , Boresi A. , Marcus L. , Love G.
Published: October 2011

The collapse of a cylindrical shell due to tight fiber windings is investigated theoretically and experimentally. Buckling in the infinitesimal sense of Euler appears to be possible, if the fibers are not bonded well to the shell. Perhaps more significant than the Euler critical load is a dangerous snap-through condition that may develop.
Shells With Edge Loads of Rapid Variation—II
Authors: Steele C. R.
Published: October 2011

The previously obtained solution for the thin elastic shell with edge loads whose wave-length is smaller than the shell radii of curvature is shown to provide a transition from “thin-shell” behavior to “flat-plate” behavior. The general character of the interior stress distribution is discussed in this paper. An examination is made of the properties of the “stiffness” matrix, which give the edge stresses due to prescribed edge displacements, and the properties of the inverse (“flexibility”) matrix. A solution is provided for the paradax of the shell of negative curvature with “shear-beam” supported edges, for which the membrane theory indicates a spectrum of edge loads that produce infinite stress.
Externally Pressurized Bearings With Inherent Friction Compensation
Authors: Hirs G. G.
Published: October 2011

Inherent friction compensation can be obtained by grooving one of the bearing surfaces in such a way that the through-flow of lubricant (oil or gas) exerts viscous forces in the direction of motion. In this study, theoretical and experimental data have been presented and many applications suggested. An experiment concerning an application as a continuous viscometer has been successful.
The Effect of Finite Pressure-Pulse Duration on the Uniform Deformation of a Long Cylindrical Shell
Authors: Nachbar William
Published: October 2011

A long cylindrical shell without end loads or restraints is considered to be loaded uniformly by external pressure applied as a rectangular-shaped pulse in time. It is assumed that the shell material is elastic and perfectly plastic, that the material points in the shell are displaced only in the radial direction, and that all points on the middle surface of the shell have the same motion in time. This paper investigates the total impulse which must be delivered to the shell in order to bring the inward radial displacement to a prescribed maximum value. The impulse needed to cause the prescribed displacement is calculated as a function of pulse-duration time and compared with the impulse for zero-pulse-duration time, which is calculated using the Dirac delta function. The ratio, a function of maximum displacement and pulse-duration time, always increases with increasing pulse-duration time, but the rate of increase is relatively less severe for more ductile materials. The duration of the plastic regime is also calculated, since this affects the growth of buckling displacements according to the analysis of Abrahamson and Goodier.2 It is found that, for a given total impulse, the plastic-regime duration time decreases with increasing pulse-duration time. Thus, buckling would be most severe for the shortest pulse-duration time.
An Experimental Study of Plane Plastic Straining of Notched Bars
Authors: Findley W. N. , Drucker D. C.
Published: October 2011

Test results are presented for symmetrically notched 1-in-wide steel and aluminum tension bars having a 0.30-in-wide net section between sharp 90-deg notches. They show clearly that the limit load is close to the plane-stress value for a ratio of specimen thickness to net width of 1/2 and is but half-way to the plane-strain value for a ratio of 6. Strikingly different behavior is exhibited by the thin specimens of steel and aluminum. The apparent raising of the yield strength of aluminum but not of the steel is explained by reference to the difference between the Mises and the Tresca criteria of yielding. Special coupon tests in which plastic deformation is restricted to out-of-plane shearing demonstrate the validity of this concept. Both longitudinal extension and lateral contraction data help to give a physical picture of the changes in the pattern of deformation from thin to thick bars. The great importance of concentricity of loading is brought out and the techniques of testing are described in considerable detail.
On Nonsymmetric Dynamic Problems of Elastic Spherical Shells
Authors: Wilkinson J. P. , Kalnins A.
Published: October 2011

Homogeneous separable solutions are derived for the deformation of thin spherical shells explicitly in terms of Legendre functions. These solutions are exact within the scope of the theory of shells in which the effects of transverse shear and rotatory inertia are fully accounted for. It is shown how the solutions are calculated from their hypergeometric series. For application, the problem of an open spherical shell with a rigid insert subjected to horizontal force and/or moment is solved in detail, and the numerical results are compared with those given earlier for shallow shells and for spherical shells with a large insert.
A Contact Stress Problem for a Rigid Smooth Sphere in an Extended Elastic Solid
Authors: Wang I-Chih
Published: October 2011

A three-dimensional axisymmetric elasticity problem pertaining to the contact stresses between a smooth rigid sphere and an infinite elastic solid with a smooth spherical cavity of the same diameter has been considered. Uniaxial loading is applied to the solid at infinity, resulting in a separation along a portion of the boundary between the sphere and the solid. The problem has been considered as a mixed boundary-value problem of elasticity. The angle of contact and the stress distributions along the contact surface are determined by solving a set of dual-series equations associated with Legendre polynomials. Numerical results are presented.
Heat Transfer to Laminar Flow in Tapered Passages
Authors: Sparrow E. M. , Starr J. B.
Published: October 2011

Consideration is given to the fully developed heat-transfer characteristics of laminar flows in converging and diverging plane-walled passages. The analysis is carried out for the two fundamental thermal boundary conditions of prescribed wall heat flux and prescribed wall temperature. As a prelude to the heat-transfer analysis, a new solution for the velocity distribution is derived on the basis of a linearized momentum equation. The Nusselt number for flow in tapered passages is found to depend on the Reynolds number; this is in contrast to the situation for passages of longitudinally unchanging cross section wherein the Nusselt number is independent of the Reynolds number. In general, the Nusselt number for flow in a plane-walled diverging passage falls below that for the parallel-plate channel, while the Nusselt number for a converging flow is usually higher than that for a parallel-plate channel. Moreover, the fully developed Nusselt numbers for prescribed wall heat flux exceed those for prescribed wall temperature.
Yield, Flow and Tensile Plastic Instability
Authors: Hillier M. J.
Published: October 2011

The effect of choice of yield criterion and flow rule on tensile plastic instability is discussed. It is shown that under certain circumstances this choice can lead to widely different values of the total strain to instability.
Study of Anisothermal Short Journal Bearings With non-Newtonian Lubricants
Authors: Tanner R. I.
Published: October 2011

The equations describing the flow of simple non-Newtonian oils in short journal bearings are solved approximately for low eccentricity ratios and small viscosity variations with temperature. An approximate method for predicting the temperature distribution is compared with available experiments and appears to give realistic results. It is also shown that the reduction in friction coefficient observed by Dubois, Ocvirk, and Wehe in experiments with non-Newtonian fluids cannot be explained by accounting for through-film viscosity variations.
A Rolling Theory for Granular Solids
Authors: Johanson J. R.
Published: October 2011

Based on the continuous plane-strain deformation of an isotropic, frictional, cohesive, compressible solid, a rolling theory for granular solids has been developed. The pressure exerted by the press is predicted as a function of the flow properties of the solid, roll size, roll gap, roll surface condition, and feed pressure. Calculated results of the theory are presented in terms of roll-separating force, roll torque, and the ratio of maximum to minimum pressure existing in the press. Examples of the effect of material properties on these results are given.
Velocity, Acceleration, and Static-Force Analyses of Spatial Linkages
Authors: Denavit J. , Hartenberg R. S. , Razi R. , Uicker J. J.
Published: October 2011

The algebraic method using 4 × 4 matrices is extended to the analysis of velocities, accelerations, and static forces in one-degree-of-freedom, single-loop, spatial linkages consisting of revolute and prismatic pairs, either singly or in combination. The methods are well suited for machine calculations and have been tested on a number of examples, one of which is presented. Velocities and accelerations are obtained by differentiation of the matrix-loop or position equation. Static forces are found by combining the method of virtual work with the matrix-loop equation to relate the virtual displacement of the load to given virtual deformations of the links.
Response of Cylindrical Shells to Moving Loads
Authors: Jones J. P. , Bhuta P. G.
Published: October 2011

The response of a circular cylindrical shell subjected to a moving ring load with a constant velocity has been examined in detail when both longitudinal and transverse coupling effects are included. It is found that the correction in the bending resonance velocity resulting from the inclusion of longitudinal coupling effects is small. The results of the analysis may be used as influence coefficients to determine, by means of Duhamel integrals, the displacements and stresses produced by varying pressure pulses.
The Plastic Deformation of a Cantilever Beam With Strain-Rate Sensitivity Under Impulsive Loading
Authors: Ting Thomas C. T.
Published: October 2011

This paper presents an analysis of the plastic deformation of a cantilever beam with an attached tip mass, based on the assumption of rigid-plastic behavior with strain-rate sensitivity, under an impulsive load at the tip. Numerical solutions of the equations of motion which appear as two nonlinear simultaneous integral equations are presented. The possibility of power-series expansion is also indicated. Finally, approximate solutions are given, and the results are compared with the more exact solutions and with experimental data.
The Reduction of the Simple Hygrosteric Fluid to the Stokesian Fluid
Authors: Marris A. W.
Published: October 2011

This paper considers the derivation of the constitutive equation of the isotropic Stokesian fluid from the general constitutive equation of the isotropic first-order stress-rate hygrosteric fluid [1] on the basis that the Stokesian fluid is the limiting case of the hygrosteric fluid as the natural time of the latter tends to zero. One suggests the hypofluent liquid as a close approximation to the general first-order, stress-rate hygrosteric fluid. More general than the linear fluent body introduced by Noll [1], the hypofluent liquid possesses a constitutive equation allowing relatively easy application to flows of simple geometry for which experimental data may be obtained.
Vibration Frequencies of Tapered Bars and Circular Plates
Authors: Conway H. D. , Becker E. C. H. , Dubil J. F.
Published: October 2011

Calculations are made of the values of the transverse vibrationa resonant frequencies for truncated-cone cantilever beams for a number of geometries, the boundary conditions being clamped/free, clamped/simply supported, and clamped/clamped. After noting an analogy which exists between the free vibration of cones and linearly tapered plates for the special case when Poisson’s ratio = 1/3, data are also given for the resonant axisymmetrical frequencies of clamped tapered circular plates. Some data for partially tapered plates are also computed. Aside from their value for design purposes, these data can be used as test cases for assessing the accuracy of various approximate methods of solution.
The Torsion of a Rigid Punch in Contact With an Elastic Layer Where the Friction Law Is Arbitrary
Authors: Keer L. M.
Published: October 2011

The problem of torsion of a rigid punch in contact with an elastic layer where the friction law is arbitrary is solved by the method of A. H. England [11]. The solution is seen to depend upon the further solution of two independent Fredholm integral equtaions. As a first approximation to these equations the problem for torsion on an elastic half-space is solved.
Stress and Velocity Fields in the Gravity Flow of Bulk Solids
Authors: Johanson J. R.
Published: October 2011

This paper presents the mathematical theory of stress and velocity fields for the steady gravity flow of bulk solids in converging channels. The basic equations based on the concepts of soil mechanics and plasticity are presented along with the appropriate boundary conditions. A simplified stress field (called the “radial stress field” by Jenike), compatible with straight-walled converging channels, is shown by calculated and experimental evidence to approximate closely the physical stress fields occurring in the deforming portions of the solid in plane-strain and axisymmetric straight-walled converging channels.
A Linearized Theory of Nosing of Shells
Authors: Singh Manohar
Published: October 2011

The problem of nosing of shells in finite plastic strain is analyzed by considering various methods of jointly linearizing yield condition and flow rule. The numerical results show that excellent approximations to the predictions of von Mises’ theory can be obtained.
Laminar Radial Flow Between Parallel Plates
Authors: Savage S. B.
Published: October 2011

An analysis is presented for the laminar radial flow of an incompressible fluid between two closely spaced parallel plates. A solution is obtained by perturbing the creeping-flow solution and an expansion is carried out in terms of the downstream coordinate. The solution is found to agree well with experimental measurements except near the channel entrance.
Heat Transfer and Skin Friction for Turbulent Boundary-Layer Flow Longitudinal to a Circular Cylinder
Authors: Sparrow E. M. , Eckert E. R. G. , Minkowycz W. J.
Published: October 2011

An analysis has been carried out for the turbulent velocity and thermal boundary layers which develop along a cylinder whose axis is parallel to the free-stream flow. Local and average friction factors are calculated as functions of the length Reynolds number Rex for various cylinder sizes (characterized, by the radius Reynolds number Rer0). For corresponding flow conditions, the friction factor for a cylinder always exceeds that for the flat plate. Local heat-transfer coefficients corresponding to the case of uniform wall heat flux have been obtained for Prandtl numbers of 0.7 and 5. As with the friction factors, the cylinder heat-transfer coefficients exceed those for the flat plate. This effect of the cylindrical geometry on heat transfer diminishes with increasing Prandtl number.
Extensional Waves Along the Edge of an Elastic Plate
Authors: McCoy J. J. , Mindlin R. D.
Published: October 2011

A solution of second-order equations of extensional motion of plates is obtained for waves traveling along a free edge. The usual Rayleigh-type wave is found to become more and more confined to the edge of the plate as the frequency increases. Above a certain frequency another edge wave is found.
Effect of Internal Pressure on the Influence Coefficients of Spherical Shells
Authors: Cline G. B.
Published: October 2011

Uniform asymptotic solutions are found for the differential equations governing the symmetric bending of spherical shells of constant thickness subjected to self-equilibrating edge loads and internal pressure. The solutions include the effect of nonlinear coupling of the stresses and edge loads. These solutions are used to obtain expressions for the influence coefficients of both a spherical cap and the complementary portion of the sphere. The effect of the pressure coupling on these influence coefficients is presented graphically.
Dynamic Creep Instability of Initially Straight, Centrally Loaded Columns
Authors: Jahsman W. E. , Field F. A.
Published: October 2011

An examination is made of the assumptions underlying the Rabotnov-Shesterikov theory of dynamic creep instability [1] to determine a reason for the reported poor agreement between theoretical predictions and experimental data on creep-buckling times of columns [2]. It is found that improved agreement is achieved when the mechanical equation of state is modified to account for the temporary halt in creep during unloading (more precisely, when stress and stress rate differ in sign), an effect which has been reported by several authors [3, 4, 5]. The column instability times predicted by the modified theory are, like those predicted by the Rabotnov-Shesterikov theory, generally conservative estimates of the experimentally measured column collapse times. The difference between the theoretical and experimental results is believed to represent the time which elapses between the onset of instability and the completion of collapse. A detailed examination of the creep vibration of a loaded column with an idealized I-section shows that the neutral axis moves from the center of the section to one flange, back to the center, and over to the other flange during one cycle. During each cycle a small amount of permanent creep strain is developed due to the fact that the creep strain is not reduced during unloading.
Geared Five-Bar Motion: Part 2—Arbitrary Commensurate Gear Ratio
Authors: Primrose E. J. F. , Freudenstein F.
Published: October 2011

Algebraic and geometric properties are derived for the curve generated by a point on the axis of the joint connecting the two floating links of a geared five-bar mechanism having an arbitrary, commensurate gear ratio.
Limit Analysis of Shallow Shells of Revolution
Authors: Hodge P. G. , Lakshmikantham C.
Published: October 2011

The theorems of limit analysis are applicable to an approximate theory if, and only if, the approximate equilibrium and strain-rate-velocity relations are such that the principle of virtual work holds between them. A theory for which this is true may be called “consistent.” Such a consistent theory is developed for shallow shells of revolution, and the methods of limit analysis are applied to particular cases of shallow parabolic and conical shells under normal and axial loads. Bounds are obtained on the plastic interaction curves using the two-moment, limited-interaction yield curve.
Funicular Polyhedra
Authors: McKeehan L. W.
Published: October 2011

The funicular polyhedron, the three-dimensional figure bounded by the links of a net supported at some of its knots (nodes), is treated theoretically by a new method in two stages. A geometrically allowable figure, with assumed coordinates of all supported nodes and of some others, is first computed consistently with the postulate that all the links are inextensible. The necessary vertical supporting forces at all nodes and horizontal forces at the supported nodes first specified, are then computed consistently with the postulate that the links are rigid and that their weights are supported equally at both ends without friction. Here additional vertical forces at nodes may be assumed at pleasure to simulate net-supported loads. Finally, vertical forces at nodes not meant to be supported are reduced in absolute magnitude, eventually to negligible values, by repeated small changes in their coordinates as assumed or computed in the first stage. There is some discussion of simple net types, and numerical examples of symmetrical funicular polyhedra of relatively few meshes are worked out precisely.
The Influence of the Equilibrium Dissociation of a Diatomic Gas on Brayton-Cycle Performance
Authors: Jacobs T. A. , Lloyd J. R.
Published: October 2011

By employing the Lighthill “ideal dissociating gas” approximation, the influence of the equilibrium dissociation of a diatomic molecule on Brayton-cycle performance is demonstrated. For low-temperature ratios it is shown that the use of a suitably selected molecule results in a significant improvement in cycle thermal efficiency.
On the Accuracy of the Bernoulli-Euler Theory for Beams of Variable Section
Authors: Boley Bruno A.
Published: October 2011

The stresses and deflections of thin rectangular beams of arbitrary variable depth, in pure bending, according to the theory of plane stress, are considered. They are obtained in the form of series; the first term of each series is identical with the strength-of-materials solution and the others represent the necessary correction to that theory. This form of the solution is chosen because of its convenience in the study of the relationship between the Bernoulli-Euler and the exact solution. The former is found to be quite accurate for thin beams and, when certain conditions are satisfied by the ordinates (and their spanwise derivatives) of the upper and lower edges of the beam. The Bernoulli-Euler theory is ambiguous in prescribing the position of the axis of a beam of variable cross section; admissible choices for the axis are presented.
Interaction of Pressure, End Load, and Twisting Moment for a Rigid-Plastic Circular Tube
Authors: Panarelli Joseph E. , Hodge Philip G.
Published: October 2011

A thick-walled circular cylinder acted on by pressure, axial end load, and twisting moment is analyzed under the assumption that end effects are negligible. The locus of all load points (interaction surface) for which unaccelerated flow of a perfectly plastic material can occur is found parametrically. Certain special cases are considered and the results compared with those of shell theory.
Plastic Instability of Cylindrical Shells With Rigid End Closures
Authors: Salmon Martin A.
Published: October 2011

Solutions are obtained for the large plastic deformations of a cylindrical membrane with rigid end closures subjected to an internal pressure loading. A plastic linearly hardening material obeying Tresca’s yield criterion and the associated flow rule is considered. It is found that, in general, a shell passes through three stages of deformation, finally assuming a spherical shape. The instability pressure (maximum pressure) may be reached in any of the stages depending on the length/diameter ratio of the shell and the hardening modulus of the material. Although numerical integration is required to obtain solutions for shells in the first stages of deformation, the solution in the final stage is given in closed form.
Stability of Curved Flows
Authors: DiPrima R. C.
Published: October 2011

In the present paper the general formulation of the hydrodynamic-stability problem is discussed. The problem of the stability of flow between rotating cylinders is considered in some detail. Several related problems which have been investigated in a complete or preliminary manner are mentioned. Finally, the recent work on the nonlinear aspects of the hydrodynamic-stability problem, with particular reference to the stability of flow between rotating cylinders, is discussed.
Asymptotic Stability of a Time-Delayed Diffusion System
Authors: Wang P. Keng Chieh
Published: October 2011

This paper discusses the asymptotic stability of the equilibrium states of a nonlinear diffusion system with time delays. It is assumed that the system is describable by a partial differential-difference equation of the form: ∂u(t,X)∂t=ℒu(t,X)+f(t,X,u(t,X),u(t−T,X),…,∂u(t,X)∂xi,…,∂u(t−T,X)∂xi,…)i=1,…,M where ℒ is a linear operator uniformly elliptic in X defined for all XεΩ … a bounded, open M-dimensional spatial domain; f is a specified function of its arguments. In the development of this paper, the physical origin of the foregoing equation is discussed briefly. Then, conditions for asymptotic stability of the trivial solution are derived via an extended Lyapunov’s direct method. Specific results are given for a simple one-dimensional linear heat equation with time-delayed arguments.
Natural Frequencies of Uniform Grillages
Authors: Wah Thein
Published: October 2011

The natural frequencies for the transverse vibration of grillages with various types of boundary conditions are studied, taking into account the distributed mass of the beams. Finite-difference calculus is used for deriving the frequency equations.
An Interpretation of Slip-Line Field Patterns in Plane Plastic Flow
Authors: Hillier M. J.
Published: October 2011

A method of interpretation of slip-line field solutions is proposed. Contour maps showing lines joining points of equal vertical or horizontal displacement velocity are plotted superimposed on the slip-line field pattern for a number of known solutions. The method has the advantage of emphasizing the nature of the theoretical characteristic curves and suggests a method of comparison with experiment.
Random Vibration of a Nonlinear System With a Set-up Spring
Authors: Crandall S. H.
Published: October 2011

Several aspects of the problem of random vibration in nonlinear systems are discussed in terms of a particular set-up spring system. Exact solutions for the mean square response and the expected frequency of zero-crossings are obtained by means of the Fokker-Planck equation. These are compared with approximate solutions obtained from equivalent linearization techniques. The distribution of response peaks is then studied and a probability density is derived for the peaks on a relative frequency basis. The probability density of the response envelope is also obtained and the relationship between the two distributions is discussed.
Stresses Due to a Band of Normal Stress at the Entrance of a Circular Hole
Authors: Blenkarn K. A. , Wilhoit J. C.
Published: October 2011

The essential difficulty in this radially symmetric problem arises from the geometry involving intersecting cylindrical and plane boundaries. The problem may be reduced by integral transformation to that of solving numerically a single integral equation.
The Effect of a Longitudinal Gravitational Field on the Supercavitating Flow Over a Wedge
Authors: Acosta A. J.
Published: October 2011

The free-streamline flow past a symmetrical wedge in the presence of a longitudinal gravitational field is determined with a linearized theory. The proportions of the cavity depend upon the cavitation number and Froude number. The drag coefficient is likewise affected by gravity, though to a smaller extent.
Extensional Vibrations of Elastic Orthotropic Spherical Shells
Authors: Hoppmann W. H. , Baker W. E.
Published: October 2011

The extensional vibrations (momentless) of spherical shells of elastic orthotropic material have been studied theoretically. Equations of motion have been derived and solved. The principal directions of the elastic compliances are assumed to be along parallels of latitude and along meridians. In addition to the case of orthotropic shells of uniform thickness, the analysis may be applied in the case of shells with stiffeners attached. Special consideration is given to the isotropic shell as a limiting case of the orthotropic shell.
Whirling of Unsymmetrical Rotors
Authors: Brosens P. J. , Crandall S. H.
Published: October 2011

A study of the motion of elastically supported rotors having unequal diametral moments of inertia is presented. It is found that some rotors are dynamically unstable above a certain speed and that some of these may return to a stable condition at a sufficiently high speed depending on the particular magnitudes of the gyroscopic coupling and the inertia inequality. The effect on rotor stability due to nonrotating inequality in the supporting stiffnesses is studied. For small stiffness inequality this effect is only of second order; as the stiffness inequality is increased, new unstable speed regions may appear. Test results on an unsymmetrical rotor verify the theoretical predictions.
The Effect of a Rigid Elliptic Inclusion on the Bending of a Thick Elastic Plate
Authors: Chow Fu
Published: October 2011

The effect of a rigid elliptic inclusion on both plain bending and pure twist of a thick elastic plate is investigated on the basis of Reissner’s plate theory [1, 2]. Comparison is made for the limiting cases of vanishing focal distance of the elliptic inclusion (a rigid circular inclusion), and vanishing thickness (Poisson-Kirchhoff plate theory), with the solutions of C. Pai [3], R. A. Hirsch [4], and M. Goland [5]. The stress-concentration factors are lower than those predicted by the classical plate theory.
Transient Response of a Dynamic System Under Random Excitation
Authors: Caughey T. K. , Stumpf H. J.
Published: October 2011

This paper analyzes the transient response of a simple harmonic oscillator to a stationary random input having an arbitrary power spectrum. The application of the results of this analysis to the response of structures to strong-motion earthquakes is discussed.
Torsional Vibrations of Shells of Revolution
Authors: Garnet H. , Goldberg M. A. , Salerno V. L.
Published: October 2011

Torsional-vibration modes are uncoupled from the bending and extensional modes in thin shells of revolution. The solution for the uncoupled torsional modes then depends upon a linear second-order differential equation. The governing equation is subsequently solved for the frequencies of a conical shell. A tabulation of the first five frequencies for varying ratios of the terminal radii is presented. These frequencies are identical to those of an annular plate which has the same supports as the conical shell.
Closed-Form Correlation of Buildings Energy Use With Key Design Parameters Calibrated Using a Genetic Algorithm
Authors: Bourisli Raed I. , AlAnzi Adnan A.
Published: October 2011

This work aims at developing a closed-form correlation between key building design variables and its energy use. The results can be utilized during the initial design stages to assess the different building shapes and designs according to their expected energy use. Prototypical, 20-floor office buildings were used. The relative compactness, footprint area, projection factor, and window-to-wall ratio were changed and the resulting buildings performances were simulated. In total, 729 different office buildings were developed and simulated in order to provide the training cases for optimizing the correlation’s coefficients. Simulations were done using the VisualDOE TM software with a Typical Meteorological Year data file, Kuwait City, Kuwait. A real-coded genetic algorithm (GA) was used to optimize the coefficients of a proposed function that relates the energy use of a building to its four key parameters. The figure of merit was the difference in the ratio of the annual energy use of a building normalized by that of a reference building. The objective was to minimize the difference between the simulated results and the four-variable function trying to predict them. Results show that the real-coded GA was able to come up with a function that estimates the thermal performance of a proposed design with an accuracy of around 96%, based on the number of buildings tested. The goodness of fit, roughly represented by R2, ranged from 0.950 to 0.994. In terms of the effects of the various parameters, the area was found to have the smallest role among the design parameters. It was also found that the accuracy of the function suffers the most when high window-to-wall ratios are combined with low projection factors. In such cases, the energy use develops a potential optimum compactness. The proposed function (and methodology) will be a great tool for designers to inexpensively explore a wide range of alternatives and assess them in terms of their energy use efficiency. It will also be of great use to municipality officials and building codes authors.
PKA Against P Bodies
Authors: Wong Wei
Published: October 2011

Attenuation of PKA activity may be required for P body formation in yeast experiencing glucose deprivation.
VraSR Two-Component Regulatory System Contributes to
mprF
-Mediated Decreased Susceptibility to Daptomycin in
In Vivo
-Selected Clinical Strains of Methicillin-Resistant Staphylococcus aureus
Authors: Mehta Shrenik , Cuirolo Arabela X. , Plata Konrad B. , Riosa Sarah , Silverman Jared A. , Rubio Aileen , Rosato Roberto R. , Rosato Adriana E.
Published: October 2011

Daptomycin (DAP) is a new class of cyclic lipopeptide antibiotic highly active against methicillin-resistant
Staphylococcus aureus
(MRSA) infections. Proposed mechanisms involve disruption of the functional integrity of the bacterial membrane in a Ca-dependent manner. In the present work, we investigated the molecular basis of DAP resistance in a group of isogenic MRSA clinical strains obtained from patients with
S. aureus
infections after treatment with DAP. Different point mutations were found in the
mprF
gene in DAP-resistant (DR) strains. Investigation of the
mprF
L826F mutation in DR strains was accomplished by inactivation and transcomplementation of either full-length wild-type or mutated
mprF
in DAP-susceptible (DS) strains, revealing that they were mechanistically linked to the DR phenotype. However, our data suggested that
mprF
was not the only factor determining the resistance to DAP. Differential gene expression analysis showed upregulation of the two-component regulatory system
vraSR
. Inactivation of
vraSR
resulted in increased DAP susceptibility, while complementation of
vraSR
mutant strains restored DAP resistance to levels comparable to those observed in the corresponding DR wild-type strain. Electron microscopy analysis showed a thicker cell wall in DR CB5012 than DS CB5011, an effect that was related to the impact of
vraSR
and
mprF
mutations in the cell wall. Moreover, overexpression of
vraSR
in DS strains resulted in both increased resistance to DAP and decreased resistance to oxacillin, similar to the phenotype observed in DR strains. These results support the suggestion that, in addition to mutations in
mprF
,
vraSR
contributes to DAP resistance in the present group of clinical strains.
A novel approach to enhancing hope in patients with advanced cancer: a randomised phase II trial of dignity therapy
Authors: Hall Sue , Goddard Cassie , Opio Diana , Speck Peter W , Martin Pauline , Higginson Irene J
Published: October 2011

Main objective

To assess the ability of dignity therapy to reduce distress in advanced cancer patients.

Design

A phase II open-label trial.

Setting

Two UK National Health Service trusts.

Participants

45 adults with advanced cancer.

Intervention

Dignity therapy: a brief palliative care psychotherapy.

Methods

Participants were randomly allocated to receive the intervention plus standard care or standard care only (control group). Outcomes were collected at baseline and at 1- and 4-week follow-up.

Main outcome measures

The primary outcome was dignity-related distress (Palliative Dignity Inventory). Secondary outcomes were hope, anxiety and depression, quality of life, palliative-related outcomes, and self-reported study benefits.

Results

45/188 (24%) patients responded. 27/45 (60%) participants remained at 1-week and 20/45 (44%) at 4-week follow-up. Baseline levels of distress were low. Groups did not differ in dignity-related distress at any time. An effect on only one secondary outcome was found: the intervention group reported more hope than the control group at both follow-ups. Effect sizes were medium (partial η2=0.20 and 0.15) and the difference was statistically significant at 1-week follow-up (difference in adjusted means 2.55; 95% CI −4.73 to 0.36; p=0.02). The intervention group was more positive than the control group on all the self-reported benefits ratings. Effect sizes (Cohen's d) ranged from 1.34 for feeling that dignity therapy had helped to 0.31 for increasing will to live.

Conclusions

The effects of dignity therapy on people with advanced cancer are encouraging. Further investigation is warranted focusing on distressed patients and those earlier in the palliative care trajectory.

Trial register number

ISRCTN29868352.