bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some Preliminary Results for Conical Diffusers with high Subsonic entry mach Numbers
Authors: Livesey J. L. , Hugh T. 
Published: February 2007

Some preliminary results are presented for the variation of total pressure loss coefficient with entry Mach number for conical diffusers. Included angles of 5, 8 and 12°, area ratios from 2 to 16 and entry lengths from 0 to 65 diameters are considered. In these initial tests the junction between the parallel entry pipe and the cone is sharp. The variation of Mach number and total pressure loss in the entry pipe is predicted simply using measured friction factors and typical velocity profiles. These calculations give the entry conditions to the diffusers in the absence of the diffusers. The effect of the junction of entry pipe and diffuser on the entry pipe flow is thus correctly attributed to the diffuser in the assessment of its total pressure loss. In addition a correctly specified mean entry Mach number is obtained. These considerations enable the losses in diffuser-pipe conjunctions of high Mach number to be logically analysed from separate pipe flow and diffuser data. The results obtained are unusual and indicate that previous assessments of diffuser performance at high Mach numbers have been confused by incorrect consideration of the effect of the diffuser entry pipe conjunction and incorrect specification of the effective mean entry Mach number. It is concluded that further experimental results are needed for developing compressible flows in constant area ducts in order that the present preliminary results may be made more precise. The momentum equation analysis in terms of suitable mean values is presented briefly. Previous diffuser results for low subsonic entry Mach numbers are considered briefly in comparison. Serious errors are shown to be present in these early results. Typically the errors originate in the definition of loss coefficient and static pressure efficiency and the use of the mass derived mean concept. In some cases the quoted static pressure efficiencies imply a decrease in entropy for the diffuser flow at low area ratios.
Whirling of Shafts with Asymmetric Stiffness
Authors: Bones J. A. , Hannam R. G. 
Published: February 2007

The whirling of a shaft with asymmetric stiffness and viscous external damping and with its mass concentrated at a point has been investigated. General solutions for the transient and forced whirls are given and are illustrated by records obtained from an analogue computer simulation of the shaft. Also experiments have been carried out on a test shaft with special arrangements for the control of damping and for the excitation of forced whirls. The region of instability, the forms of the transient whirls, and the forced whirls produced by out-of-balance force have all been examined in detail. In addition, it is shown that as the rotational frequency of an asymmetrically stiff shaft increases above the upper limit of instability its whirl behaviour tends towards that of a symmetrically stiff shaft.
Power-Speed Characteristics of Differential Transmissions
Authors: White G. 
Published: February 2007

An index number is proposed as a means of describing the torque-speed characteristic of a variable-ratio unit. This index number is combined with conventional relations describing a differential gear in order to deduce the limiting power-speed envelopes of a differential transmission. Input-coupled and output-coupled differential transmission systems are examined and shown to have markedly different characteristics; for this reason they cannot be considered inversions. It is evident that the general relations describing each type of transmission can be used to synthesize a transmission or to analyse an existing transmission.
Blade Loadings for Hovercraft and other Radial Flow Fans
Authors: Carter A. D. S. 
Published: February 2007

The layout of a hovercraft leads naturally to the choice of a radial outward flow fan, but the aerodynamic requirements are more stringent than those normally associated with industrial fans. In this paper a blade loading criterion used extensively in axial flow compressor practice has been adapted to the more general case of radial flow fans. Using this criterion maximum fluid deflections and maximum temperature rise coefficients have been calculated. It is shown that fluid deflections in radial fans should be substantially lower than those in axial flow machines. For high work output the ratio of rotor outside diameter to rotor inside diameter should be as close to unity as is mechanically possible. Inlet guide vanes would be of no benefit to the conventional industrial type centrifugal fan, but for such applications as hovercraft inlet guide vanes could be most beneficial. The paper outlines those areas in which further research is necessary fully to confirm the approach, and hence the quantitative values, given in this paper.
Link-Mounted Gear Trains
Authors: Merritt H. E. 
Published: February 2007

This paper distinguishes, as a subject worthy of recognition and study in its own right, the class of mechanism comprising gears mounted with axes coincident with the pivot points of a linkage. The same concept serves for the analysis of the assembly conditions of multiple-contact gear trains, in which a ‘virtual’ linkage may be visualized. A variety of known mechanisms, commonly dealt with, for design analysis purposes, on an ad hoc basis, fall within the same broad concept; no novelty is claimed for any mechanism as such, and the paper merely attempts to indicate some principal sub-divisions into which broader studies might be grouped. These fall under the two main categories of ‘kinematic’ and ‘geometrical’ analysis, although these again converge when a linked gear train is used to form a differential mechanism by which a function of the deformation of the linkage is superimposed on the angular motion of the gears and their connecting shafts. It is possible that co-ordinated studies of linkages and gears in combination, as here adumbrated, might lead to the development of new, particular mechanisms capable of engineering application.
Optimization of Vibration Absorbers: Iterative Methods for use on Systems with Experimentally Determined Characteristics
Authors: Stone B. J. , Andrew C. 
Published: February 2007

Methods are presented for the optimization of the design of an absorber, incorporating combined spring and damper elements of polymeric material, and coupled to a complex main system. These methods, which involve rapidly convergent iterative procedures, utilize directly the experimentally measured characteristics of both the absorber element material and the main system. Butyl rubber is found to be a convenient and effective absorber element material, reducing the response of a model complex main system, with damping of a level typical of engineering structures, by a factor of approximately four.
Experimental Determination of the Complete Dynamical Properties of a Two-Degree-Of-Freedom Model Having Nearly Coincident Natural Frequencies
Authors: Traill-Nash R. W. , Long G. , Bailey C. M. 
Published: February 2007

Existing techniques of resonance testing have shown a marked inability to find the principal modes, natural frequencies and levels of damping in a structure which possesses two or more close natural frequencies (1)§. This paper describes an experimental investigation on a two-degree-of-freedom model of a technique which makes use of dynamical influence coefficients (or receptances) measured at a number of stations on the structure (2) (3) (4) (5). The measured coefficients are used to calculate natural frequencies and modes of vibration, and the mass, damping and stiffness properties of the system. Several model configurations having different natural frequency separations were tested and no special difficulty resulted when natural frequencies were close or even coincident.
Interaction of a Whirling Rotor with a Vibrating Stator across a Clearance Annulus
Authors: Black H. F. 
Published: February 2007

Where a rotor runs within a clearance space, the clearance being comparable with rotor mass unbalance, the synchronous whirling behaviour of the rotor may be considerably affected by intermittent interaction with the stator at the clearance position. Discontinuity and jump phenomena may occur: in general, behaviour will be different with increasing speed from that with decreasing speed, and in either case zones may exist in which rotor-stator interaction is possible but not certain. In the analysis here presented, rotor and stator are regarded as linear multi-degree-of-freedom systems including damping; dry friction at the clearance space is taken into account. Discussion is limited to cases with radial symmetry, and interaction is assumed limited to the position of the clearance space. Polar receptances are used to establish equilibrium conditions with interaction, and speed zones are defined within which interaction may occur. Some hypothetical cases are fully explored, demonstrating that rotor-stator interactions may occur in a variety of forms and circumstances. Interactions with dry friction counterwhirling are also considered. Some experimental results on counterwhirl within a ball bearing are given and qualitatively compared with theory.
Creep of a Carbon-Manganese Steel under Cyclic Stress and Temperature Conditions
Authors: Day M. F. , Cummings W. M. 
Published: February 2007

Nearly all creep data are obtained under closely controlled constant conditions of load and temperature. Most high-temperature plant, however, is subject to cyclic variations of both, due to periodic off load or reduced load conditions. Test data for a C-Mn steel are presented for various cycles of stress and/or temperature. The effects of cycling of stress or temperature, and of in-phase changes of both, are predictable within reasonable limits. It is shown, however, that with out-of-phase changes in stress and temperature, i.e. high stress/low temperature to low stress/high temperature conditions, a very rapid acceleration of strain can occur.
One-Way Buckling of a Compressed Strip under Lateral Loading
Authors: Allan T. 
Published: February 2007

This paper is concerned with the problem of the buckling of a long thin strip column rigidly supported along its length on one side, and subjected to a uniformly distributed force on the other. It is shown that the mode of buckling failure of the strip column under these conditions is independent of its length and always occurs with the sudden formation of a single buckle. The critical load also is independent of the column length although the post-buckling load is a function of the length. It is evident that the magnitude of the critical load is profoundly influenced by the degree of initial deflection or imperfection present in the column. An analysis of the problem is given together with experimental verification. The effect of the testing machine characteristics is also examined. The particular case of strip column buckling considered here is of vital importance to the solution of a number of plate and shell buckling problems, and sheds new light on these. A further paper on this extension of the theory is in preparation.
Experimental and Analytical Investigation of the Behaviour of Cylindrical Tubes Subject to Axial Compressive Forces
Authors: Allan T. 
Published: February 2007

This paper describes experimental work which was undertaken to investigate the buckling characteristics of axially loaded cylindrical tubes and presents a theoretical basis for analysing tube behaviour. This is a radical departure from the existing theories in the literature which are not supported by experimental evidence. It is shown here that the tube failure is a ‘one-way’ buckling phenomenon where buckles can appear singly or in sequence. Two basic failure modes are established. One is due to an outward movement of the tube wall which produces a ripple or bellows formation and is fundamentally a yielding phenomenon. The other is inward movement which produces diamond shaped indentations and is an elastic failure. Mainly in the latter case, the small deviations from the true cylindrical form are the critical elements in determining the value of the failure load.
Flexural Vibration of Symmetrical Multi-Layer Beams with Viscoelastic Damping
Authors: Agbasiere J. A. , Grootenhuis P. 
Published: February 2007

The flexural vibrations of beams can be reduced by introducing sandwiched layers of energy-dissipating materials. The equations of motion are derived for flexural vibrations of symmetrical, multi-layer sandwich beams. Two types of beams are considered, depending on whether the central layer is energy dissipating when the number of layers will be n = 4 i − 1, where i = 1, 2,…, or whether the material of the central layer is perfectly elastic when n = 4 i + 1. The total number of equations of motion will be i + 1 for each type. These equations will be non-linear when the properties of the energy-dissipating materials are strain dependent. A numerical method of solution has been introduced by transforming the equations of motion into sets of non-dimensional simultaneous equations and using finite difference methods. The simplest type of beam has three layers but even this leads to a set of four simultaneous equations of the twelfth order. It is shown as an example that the strain dependence of a typical viscoelastic material has only a second order effect upon the computed response. Experimentally determined values of frequency, phase angle and mode shapes under conditions of steady state are compared with computed data and the agreements are such that the response to excitation in flexural motion of symmetrical, multi-layer damped beams can now be calculated with confidence even for the lower modes.
Electronic Analogue Computer Study of Non-Linear Effects in a Class of Hydraulic Servomechanisms
Authors: Panjaby J. 
Published: February 2007

An electronic analogue is first described, of a system comprising a prime mover controlled by a non-linear flyweight governor using a non-linear hydraulic jack/valve servomechanism as a power amplifier to operate the prime mover energy supply control valve. The governor non-linearity is due to static and Coulomb friction. When dimensionless equations of motion are used for the various components in the system, the analogue is representative of a type of control system often encountered in mechanical engineering. It is shown that the presence of static friction in the governor, of magnitude greater than the Coulomb friction, has a de-stabilizing eifect and limit cycling of the system in the autonomous and non-autonomous conditions, caused by governor friction, is examined.
A Theory on the Mechanics of Axisymmetric Extrusion through Conical Dies
Authors: Lambert E. R. , Kobayashi Shiro 
Published: February 2007

For axisymmetric extrusion through conical dies, an admissible velocity field without discontinuities was obtained by superposition of basic flow patterns. Based on this velocity field, the upper bound to the average forming pressure and the detailed mechanics were calculated for the extrusion of a rod with a semi-cone angle of 45° and a reduction of 75 per cent in area. Three different friction conditions along the die were considered and their influence on the deformation characteristics was discussed. Flow lines, velocity components, grid distortion, strain-rate components, effective strain rate, effective strain, and stress components were plotted. A comparison of the present results with those obtained experimentally (visioplasticity) shows good agreement.
Radiation-Damage Stresses in the Graphite of Power-Producing Nuclear Reactors
Authors: Head J. L. , Sockalingam K. C. 
Published: February 2007

When graphite is irradiated by fast neutrons, damage to the crystal structure causes changes of the graphite dimensions. In the graphite blocks comprising the core of a nuclear reactor, there are differential dimensional changes, thus stresses are developed, analogous to thermal stresses in a body in which there are spatial variations of temperature. The stresses are partially relaxed by an irradiation-induced creep of the graphite. In this paper the authors present a method of predicting the stresses which makes allowance for the relaxation by irradiation creep.
Zero (Or Low) Torsional Stiffness Couplings
Authors: Chapman C. W. 
Published: February 2007

In many rotating systems shaft couplings of low torsional stiffness may bring dangerous one node critical speeds below the operating speed range. However, even soft couplings on multi-mass systems may allow higher node criticals to remain in the operating range. If two sections of a system be coupled by a coupling of zero stiffness torsional impulses cannot be transmitted from one section to the other, thus eliminating criticals. Coupling stiffness must be related to the torque transmitted, and experiments indicate that a stiffness/torque ratio below about 4 is almost as effective as zero stiffness.
Dynamic Viscosity of Compressed Water to 10 Kilobar and Steam to 1500°C
Authors: Bruges E. A. , Gibson M. R. 
Published: February 2007

Equations specifying the dynamic viscosity of compressed water and steam are presented. In the temperature range 0-100cC the location of the inversion locus (mu) is defined for the first time with some precision. The low pressure steam results are re-correlated and a higher inversion temperature is indicated than that previously accepted. From 100 to 600°C values of viscosity are derived up to 3·5 kilobar and between 600 and 1500°C up to 1 kilobar. All the original observations in the gaseous phase have been corrected to a consistent set of densities and deviation plots for all the new correlations are given. Although the equations give values within the tolerances of the International Skeleton Table it is clear that the range and tolerances of the latter could with some advantage be revised to give twice the existing temperature range and over 10 times the existing pressure range at low temperatures. A list of the observations used and their deviations from the correlating equations is available as a separate publication.
Large Deflections of Rectangular Plates Subjected to Uniform Lateral Pressure and Compressive Edge Loading
Authors: Brown J. C. , Harvey J. M. 
Published: February 2007

A theoretical analysis is presented for the problem of flat rectangular plates undergoing large deflections due to the action of a uniform lateral pressure or combinations of uniform lateral pressure and compressive edge loading. The governing partial differential equations are replaced by their finite difference equivalents and the resulting difference equations solved by over-relaxation using an I.C.T. 1905 computer. The results for plates subjected to lateral loads only are in good agreement with the few existing solutions. For plates subjected to lateral loads and combinations of lateral and edge loading, the results show good agreement with the results of an experimental programme carried out at the University of Strathclyde.
Vortex Shedding Frequencies of the Flow through Two-Row Banks of Tubes
Authors: Borges A. R. J. 
Published: February 2007

This paper deals with the problem of vortex shedding from parallel rows of circular cylinders of equal diameter set normal to an airstream. A single row of cylinders is first discussed. The experimental results show that when the lateral spacing between the axes of two adjacent cylinders is less than two diameters the flow downstream of the row does not exhibit any obvious single dominant frequency of vortex shedding. The flow set up by two rows of cylinders is next considered for both tandem and staggered arrangements of the cylinders. The sets of measured values reported are complete in the sense that they cover the whole range of spacings for which a dominant frequency of vortex shedding could be measured. The Reynolds numbers of these tests correspond to the high subscritical range for a cylinder in isolation.
Damping Inserts in Vibrating Structures
Authors: Wolfe C. J. , Woods C. J. , Andrew C. 
Published: February 2007

A method is presented for the prediction of the response of a vibrating system after the introduction of a damping insert between two distinct co-ordinates of the system, and procedures are given for the optimization of such inserts. The method can be extended to predict the effect of breaking the system and introducing a damping insert into the break, and may utilize the experimentally measured characteristics of both the original system and the damping insert. Butyl rubber inserts are found to reduce vibration amplitudes of models of typical engineering structures by as much as a factor of 4.
Methods of Using a Vibratory System to Measure Small Rates of Turn
Authors: Linnett J. A. 
Published: February 2007

The equations of motion for a vibratory two-degrees-of-freedom spring mass system subjected to rotation about an axis perpendicular to its plane of vibration are considered, taking into account the various couplings that may be present. The rate of turn can be measured by three alternative methods, two of which involve an exciting force in the sensing direction in addition to the one vibrating the system. The shape of the phase angle against angular velocity curve is shown to be independent of damping, enabling the transient performance to be improved without affecting the sensitivity of the device. Experimental work shows good agreement with the developed theory.
Experimental Investigation of the Energy Separation in Vortex Tubes
Authors: Bruun H. H. 
Published: February 2007

Measurements of the state and the velocity distribution of air in a counterflow vortex tube have been undertaken. In order to determine the axial variation of the flow quantities, measurements were carried out in several cross-sections. The experimental results show that the velocity is predominantly tangential. A comparison of the order of magnitude of the radial and axial convection terms in the equations of motion and energy shows that these terms are of equal importance. The energy equation in terms of the total temperature is used as a basis for discussing the influence of turbulence in the flow on the separation of energy in the vortex tube.
Fatigue and Cyclic Thermal Softening of Thermoplastics
Authors: Constable I. , Williams J. G. , Burns D. J. 
Published: February 2007

Thermoplastic components subjected to cyclic loading may distort because of localized rises in temperature and/or fracture because of incremental (fatigue) crack propagation from microscopic cracks or defects produced during the manufacturing process or by service conditions. The object of the present paper is to show quantitatively how the first mode of failure, which is referred to as cyclic thermal softening, can be related to loss compliance, specimen geometry and the frequency and magnitude of the cyclic load. The results of cyclic bending tests on polymethylmethacrylate (p.m.m.a.) and Polyvinylchloride (p.v.c.) beams of rectangular and circular cross-section are analysed. For the service conditions considered the p.m.m.a. specimens showed both failure modes whereas the p.v.c. specimens failed as a result of incremental (fatigue) crack propagation.