bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Mathematical Model of the Locomotor Apparatus
Authors: Calderale P M , Scelfo G 
Published: February 2007

This study presents a mathematical model for the musculo-skeletal system of the locomotor apparatus. Muscle forces and joint reactions are calculated for the static problem of leaning and squatting and for the dynamic problem of walking on a level surface. Muscle forces thus calculated are compared with electromyographic (EMG) patterns. The model follows previous statically indeterminate mathematical models, from which it differs chiefly in introducing intermediate constraints (in addition to the points of insertion) for the muscles, and in setting bounds on muscle tensile stress depending on system geometry, kinematics, and loading.
Frictional Properties of Artificial Hip Joints
Authors: Unsworth A , Pearcy M J , White E F T , White G 
Published: February 2007

A new generation of hip replacements has been designed incorporating compliant layers to promote fluid film lubrication when the joints are implanted in patients. Tests in the Durham hip function simulator show that the friction in these joints is up to an order of magnitude lower than in currently used prostheses, and because this is due to complete separation of the rubbing surfaces, wear ought to be vastly reduced. Experiments have shown that the best results are achieved with compliant surfaces of hardness between 4 and 8 N/mm2. Such surfaces produce coefficients of friction of the order of 5 × 10-3.
Wear and Contact Stress Studies of the Minns Meniscal Knee Prosthesis
Authors: Minns R J 
Published: February 2007

This paper describes the results of wear testing and contact area studies of a Minns meniscal knee prosthesis and compares the results of previous work on wear and contact stress studies of other knee prosthesis designs. Although stresses that arise at the surface of the polyethylene meniscus components are large, after repetitive loading the contact area rises, as a consequence of plastic flow and creep, and they reduce to a fifth of the initial stress after 1 million cycles. Contact area studies show that asymmetrical loading of the meniscus give proportionally high stresses on the higher loaded meniscus and, at large values of flexion, have similar values to a more conforming but fixed polyethylene tibial component design of knee prosthesis.
Effect of Hydrostatic Pressure on the Direct-Stress Fatigue Strength of an Alloy Steel
Authors: White D. J. , Crossland B. , Morrison J. L. M. 
Published: February 2007

This paper describes tests in which specimens are subjected to cyclically varying direct stress, that is, in ‘push-pull’ with additional tensile and compressive mean stress, both at atmospheric pressure and also while the material is subjected to ambient fluid pressure of the order 3000 atm (20 ton/in2); for this work a novel testing machine was developed. The results of tests at atmospheric pressure are in good agreement with earlier tests and show that the range of direct stress leading to fatigue failure is a continuous function over the range of mean stress used. When fluid pressure of 20 ton/in2 is superimposed on the stress system, the range of reversed stress required to cause fatigue failure is increased by a small, but definite, amount. For the tensile mean stress values investigated the fatigue limit appears to have been raised until it coincides with the range of stress required to cause ‘gross yielding’ with a reduction in area greater than that which occurs in a static tension test at atmospheric pressure. For the compressive mean stress values investigated, fatigue failure has been entirely eliminated.
Stress and Deflection Studies of Flat-Plate and Toroidal Expansion Bellows, Subjected to Axial, Eccentric or Internal Pressure Loading
Authors: Turner C. E. 
Published: February 2007

Tests in axial compression, eccentric (hinge) loading and internal pressure are described for corrugated-pipe and flat-plate bellows. Strain gauge surveys and deflection readings were made for each test. A recently developed theory for the small elastic deflection of toroidal elements is briefly described and its application to a wide range of bellows shapes and loadings is discussed. For some flat-plate bellows, where the depth of convolution is much smaller than the overall radius of the bellows, an approximate theory neglecting circumferential effects is possible, and comparison is made between this approximate and the more exact theory. Both theory and experiment show that the location of the maximum stresses depends markedly upon the proportions of the bellows. General bellows design and construction problems are examined in the light of the stresses likely to be caused by actual service conditions of operation.
Experimental Determination of the Centre-of-Flexure and Centre-of-Torsion Co-Ordinates of an Asymmetrical Aerofoil Cross-Section
Authors: Carnegie William 
Published: February 2007

The differential equations of motion (1)† of a vibrating cantilever blade contain coupling terms dependent upon the co-ordinates of the centre-of-flexure relative to the centroid of the blading cross-section. Complete solution of the equations, therefore, requires a knowledge of the co-ordinates. The general theoretical problem of flexure of a cantilever blade has not yet been solved but a solution (2) based on St. Venant's theory of torsion is available for the case of a blade of uniform cross-section with symmetry about one of its principal axes but asymmetrical about the other. The accuracy of the theory is confirmed by experiment (***3). The present paper describes an extension of the flexure experiment to the case of a blade of asymmetrical aerofoil cross-section, the most usual form of cross-section found in turbine and compressor blading. For a cross-section with symmetry about one of its principal axes but asymmetrical about the other it has been shown by reasoning and confirmed by experiment (3) that, providing the root fixing is encastré, the centre-of-flexure is coincident with the centre-of torsion. A second experiment is presently described in which the centre-of-torsion coordinates are determined when the cross-section is asymmetric. Close agreement is shown to exist between the co-ordinates of the centre-of-torsion and those of the centre-of-flexure of the asymmetrical aerofoil cross-section blade.
Design of Small Isolator Units for the Suppression of Low-Frequency Vibration
Authors: Tobias S. A. 
Published: February 2007

The customary linear vibration isolators are unsuitable for the suppression of low-frequency vibration in applications where, in addition to steady-state vibration, the danger of shock excitation exists. Linear suspensions which ensure a low natural frequency are necessarily very soft and, as a result, excessive large deflections will arise during steady accelerations or shock excitation. These undesirable features are not encountered with symmetrical nonlinear suspensions, which under steady state vibration excitation behave like linear springs, but when suffering large deflections from their ‘working point’ become progressively stiffer. One of the spring elements which has the required spring characteristic is the ‘sine spring’. The properties of this spring element are summarized and the various ways of coupling sine springs and ordinary springs are discussed. Several designs of isolator units, incorporating sine springs for the vertical degree of freedom and leaf springs for the horizontal degree of freedom are described. The Appendices contain a short discussion of various ‘constant-force’ springs suitable for low-frequency suspensions, a description of the experimental equipment used, and some experimental results regarding the behaviour of sine spring suspensions.
Temperatures Reached in Disc Brakes
Authors: Newcomb T. P. 
Published: February 2007

A solution is given to the problem of the conduction of heat through an infinite slab bounded by parallel planes, initially at zero temperature, when unit area of each surface is subjected to a flux which decreases linearly with time and loses heat at a rate which is proportional to the temperature at that surface. This solution can be used to determine the transient temperatures reached during disc braking at uniform deceleration if it is assumed that all the heat flows into the disc. Both cooled and uncooled brake discs are considered and typical curves are given showing the agreement between the temperatures determined theoretically and experimentally at the friction surface during single brake applications. The problem of repetitive braking at regular intervals is also discussed and a comparison made between the disc brake and the drum brake under similar conditions. Consideration is also given to the problem when no assumptions are made concerning the manner in which heat is shared between disc and pad.
Vibration Characteristics of Stiffened Plates
Authors: Kirk C. L. 
Published: February 2007

This paper describes methods of calculating natural frequencies of free flexural vibration of rectangular plates which have stiffeners parallel to one edge. An approximate frequency equation is derived for a clamped plate with closely spaced stiffeners by extending the Rayleigh method as applied by Warburton (1)† to rectangular isotropic plates. For a plate containing a single central stiffener, an exact frequency equation is derived for simply supported edges and an approximate fundamental frequency equation is derived for clamped edges. Comparison between observed and calculated frequencies is made and the practical effect of stiffening upon natural frequencies is discussed. The application of the Rayleigh method to the calculation of natural frequencies of integrally stiffened plates is illustrated by calculating frequencies determined by Hoppmann and Thorkildsen (2).
Localized Loads Applied to a Spherical Pressure Vessel through a Cylindrical Insert
Authors: Bailey R. , Hicks R. 
Published: February 2007

A solution is obtained for the membrane and bending stresses in a thin spherical shell due to the action of a localized bending moment or radial load which is applied through a thin cylindrical insert, for example, a duct connection on a reactor pressure vessel. The stress distribution will be affected by the nature of the duct to vessel connection. In this paper attention is confined to the case of an unreinforced junction as sketched in Fig. 1. The solution is general in so far as it is reduced to a set of four simultaneous equations which can be solved readily when dealing with practical problems. As a numerical example, the case of the Hunterston reactor pressure vessel is considered, and it is shown how the localized stresses are affected by a change in duct thickness. Furthermore, these stresses are compared with those which would be induced in the sphere if the duct insert were rigid. It is found that in this practical example, the cylinder thickness has a significant effect on the calculated values for the stresses and displacements.
A Semi-Theoretical Solution of Asymmetric Heat-Transfer in Annular Flow
Authors: Barrow Henry 
Published: February 2007

A brief account is given of the analogy between the transfer of heat and the transfer of momentum. For asymmetric heat transfer in annular flow, the distributions of friction and thermal flux associated with the transport processes are considered. By simplifying the equations describing these distributions, and using an observed experimental fact concerning the temperature profile, the analogy is modified to apply to the annular flow with a fluid having a Prandtl number equal to 1. The modification results in additional factors in the final form of the conventional heat-transfer equation. These factors are functions of the annulus radius ratio parameter. A comparison is made between the final result and the recommendation of a well known authority.
An Investigation of the Pilger Process by a Plane Strain Analogue
Authors: Sansome D. H. , Lloyd H. K. 
Published: February 2007

A review of the important papers and patents on the pilger process of hot-rolling seamless tubes shows that there have been divergencies of views as to the most desirable type of roll profile to use, and that there is an incomplete knowledge of the loads and torques involved. An apparatus to simulate successfully the pilger process under plane strain conditions using lead as the working material, and to measure load, torque, and speed was adapted to a milling machine. The choice of a two-dimensional analogue was made in order to eliminate some of the many variables that occur in practice. The work has shown how such factors as roll profile, amount of reduction, and feed per blow affect loads and torques, and that under given conditions the parabolic cone is more desirable than the hyperbolic. It is pointed out however that in practice it does not necessarily follow that the cam requiring the least power per blow, or generating the lowest peak load or peak torque, produces the most acceptable tube. A theory has been developed to enable loads and torques to be predicted for the plane strain analogue based on Hill's indentation theory.
Notes on Incremental Collapse in Pressure Vessels
Authors: Edmunds H. G. , Beer F. J. 
Published: February 2007

A few simple cases of incremental collapse are reviewed in the context of the design of pressure vessels. Incremental shakedown and limited-life design in terms of an allowable aggregate strain are considered. It is suggested that incremental collapse will commonly impose limitations on design which will be much more severe than high strain endurance. However it is considered that this may not be true if the high strain fatigue is complicated by questions of creep relaxation. Simple results are presented of two selected examples of exploratory experiments, one illustrating incremental collapse in a pipe bend, and the other incremental shakedown in a tie-plate.
Three-Dimensional Design of Multi-Stage Axial-Flow Compressors
Authors: Railly J. W. 
Published: February 2007

The design of multi-stage axial-flow compressors, particularly where the blade rows are closely spaced, presents a problem to the designers owing to the mutual interference of the separate blade rows. The actuator disc approximation, applied to the design of single stages at a time has been shown to be useful, and this technique can be used for the multistage machine if the mutual interference of the separate stages may be neglected. Carmichael and Horlock (1)† have carried out calculations by including only the mutual interference of adjacent rows (see also Horlock (2) for an introduction to actuator disc theory). Using the theory of simple radial equilibrium of the flow at the trailing edges of the blade rows, it has been demonstrated, Howell (3), that the flow tends to a state which is termed the ‘ultimate steady flow’ after about two stages. The design of the third stage on a machine may be attempted, making use of this assumption, treating this stage as if it were flanked by many stages. The first part of the paper deals with an extremely simple method of design, for the ultimate steady flow, using the actuator disc theory, and a particular example of this method is compared with a more exact solution of the equations, based on a modified radial equilibrium approach. Both results are then compared with a set of experimental results taken from an experimental three-stage axial-flow compressor in the Department of Mechanical Engineering at the University of Birmingham. In the second part of the paper, the validity of the above assumptions regarding the ultimate steady flow state is discussed, along with the problem of the ‘entry stages’. These problems may be resolved by an exact solution for the flow through a series of identical stages in which parameters such as number of stages, blade row spacing and blade row axial length may be systematically varied. Such an approach is described, and the results of a series of calculations are presented. It is shown that the overall behaviour of the entry stages depends upon the ratio of blade row axial length to blade row spacing. Thus, for small values of this ratio, the flow tends slowly to the ultimate state, but for small axial clearance the ultimate state is reached virtually by the third stage. The influence on the entry stages of blade row spacing and of number of stages is also discussed. It is shown that the treatment of the practical multi-stage machine, even for closely spaced blading, reduces to the separate treatment of the first stage only (inlet guide vanes plus one rotor and one stator), plus the ultimate steady flow treatment to obtain the behaviour of the third stage; otherwise the exact approach may be applied to the first three stages taken as a group, although this involves more calculation. On a high-speed digital computer, such as the Ferranti ‘Mercury’ machine which was, in fact, used for the calculations, a 3-stage compressor design would take about 15 minutes.
Heat Transfer to Air, Carbon Dioxide and Helium Flowing through Smooth Circular Tubes under Conditions of Large Surface/Gas Temperature Ratio
Authors: Barnes J. F. , Jackson J. D. 
Published: February 2007

In this paper, experiments are described on the transfer of heat from a heated tube to a gas flowing through it. Three gases were used: air, helium and carbon dioxide. The difference in temperature between the tube and the gases was large and the main objective of the work was to study the effects of radial variations of the gas properties with temperature. The conditions under which the experiments were performed were (1) essentially fully developed velocity and temperature profiles, (2) approximately uniform wall heat flux and (3) low subsonic turbulent flow. Some analysis has been developed to cover the present experimental work. Predicted Nusselt number-Reynolds number relations for the constant properties case are found to be in reasonable agreement with the experimental data for Reynolds numbers above about 10 000, provided the ratio of eddy diffusivities is assumed to vary from about 1·0 at Re = 104 to about 1·2 at Re = 105. The effects of variations of surface/gas temperature ratio, predicted by the analysis, are found to be in quite good agreement with the experimental data of both this and earlier investigations.
Hydrodynamic Lubrication in Wire Drawing
Authors: Tattersall G. H. 
Published: February 2007

Part I. It was shown by Christopherson and Naylor that hydrodynamic lubrication in wire drawing could be provided by supplying lubricant at the entry of the die at a pressure comparable with the yield stress of the wire. The necessary pressure could be conveniently generated by causing the wire to approach the die through a tube of a diameter slightly larger than the wire diameter, sealed on to the inlet side of the die. They carried out experiments with oil as the lubricant, on wires of copper and mild steel, and developed a theory which accounted for their experimental results but suffered from the defect that all their equations contained two dependent variables, P the pressure developed and q the quantity of lubricant flowing. In the present paper a theory is developed by considering all regions up to that in which the wire deforms, and equations are obtained by means of which P and q are expressed in terms of independent variables. The calculated values of pressure for Christopherson and Naylor's conditions show good agreement with their experimental results but the theoretical values of lubricant flow are too high by a factor of two to three. The probable reason for this discrepancy is that the breakdown of the oil under shear has been ignored. Part II. In Part I of this paper a theory is developed for hydrodynamic lubrication in wire drawing with oil as the lubricant, and the calculated values of P the lubricant pressure and q the lubricant flow are compared with values taken from previously published experimental work. Part II is concerned with the case when the lubricant is a soap. Experiments were carried out, in which P and q were measured as a function of wire speed u for a series of accurately made tubes (or nozzles) of a range of dimensions, and for about a dozen soaps of widely varying rheological properties. It is shown that there is a maximum value of both P and q and that this result can be explained in terms of the theory with the additional condition that the apparent viscosity of the soap is an exponential function of wire speed of the type μ = μ0 exp (– Bu). The wire speed at which the maxima occur is the same for P and q and appears to be independent of nozzle dimensions but dependent on soap properties. It is equal to I/ B. For a given soap with different nozzles the value of the maximum pressure Pmax is proportional to l/h2 where l is the length of the parallel portion of the nozzle and h is the clearance over the wire diameter, provided the thickness of the lubricant film is small compared with 1/2 h. For a given soap with different nozzles Pmax is proportional to μ0/ B.
Dynamic Behaviour of a Rigid-Plastic Steel Beam
Authors: Rawlings B. 
Published: February 2007

The estimation of permanent damage caused to steel structures from such effects as bomb blast, earthquakes, or collisions from moving objects is a problem which has attracted the attention of engineers, especially over the past decade. Analyses of the response of complete framed structures to dynamic loads have, to date, been very idealized, representing the structure as a simple mass-inelastic spring system. Some more precise analyses have, however, been made of the behaviour of specific types of beams under particular loading conditions, but the results have remained unco-ordinated. In the present paper an attempt is made to unify these by considering the mechanics of behaviour of a flexural element under general time-dependent loading conditions, the effects of high strain-rate sensitivity being ignored. The equations derived will then form a basis for analysis of framed structures, by satisfying joint equilibrium and compatibility requirements. A number of examples are given, and the limitations of the method are discussed.
An Optimization of the Principal Design Parameters of Stirling Cycle Machines
Authors: Walker G. 
Published: February 2007

A Stirling engine is a mechanism used to convert heat into power or vice versa and operates on a closed regenerative thermodynamic cycle with compression and expansion of the working fluid at different temperatures. According to the classical theory the performance of a Stirling cycle machine is a function of six independent parameters, namely: speed, pressure of the working fluid, ratio of the temperatures in the compression and expansion spaces, ratio of the swept volumes in these two spaces, phase angle by which volume variations in the expansion space lead these in the compression space, volume of the heat exchangers and regenerator. The four parameters (3)–(6) must be selected at the design stage of the machine. The paper describes the procedure and presents the results of computations carried out to establish the optimum combinations of these four parameters for maximum engine output for the machine acting as a prime mover, maximum heat lifted for the machine acting as a refrigerator, over a combined temperature range from 30 to 3000°K. The output of a Stirling cycle machine can be expressed in terms of non-dimensional power or heat lifted in several different ways. Four methods were studied in detail, the parameters optimized and design charts prepared. Wide variations in the optimum parameter combinations were obtained and a partial explanation of this phenomenon is offered. Pressure-volume diagrams for machines of the same size were prepared for the four different parameter combinations. Maximum output was obtained from the machine designed on a basis of limited maximum pressure and total swept volume. The two charts relating to the case for prime mover and refrigerator optimized with regard to the maximum cycle pressure and total swept volume are recommended for use in future design work.