bluuebunny/crossref_metadata_2025 huggingface dataset:
Expander Design in the Tube Expanding Process: The Influence of the Number of Rollers
Authors: Sukhawarn P. , Culver L. E.
Published: February 2007

This paper describes tests which have been made to study the influence of the design of tube expanders on the characteristics of rolled joints. Of the various features of the propulsive type tool, that of the number of rollers was chosen as the point from which to start such an investigation. Three expanders, otherwise identical in all particulars but with three, five, and seven rollers were used and a series of tests were carried out with each tool to varying degrees of expanding.

Comparisons are made of the values of push-out load, extrusion of the tube away from the front and back faces of the plate, mean seat pressure and hardness distributions in the tube plates. The results show that, judged on the maximum push-out strength, a three-roller expander makes the best joint, the strength falling as the number of rollers increases but there is no difference in the maximum value of mean seat pressure in joints rolled with the different expanders. The number of rollers also has a marked effect on the extrusion of the tube and on the extent of the plastic zones in the tube plates. Care is therefore necessary in selecting the appropriate criterion for optimum joint strength.
Holography as a Routine Method of Vibration Analysis
Authors: Hockley B. S. , Butters J. N.
Published: February 2007

The application of holography as a routine method of analysing the vibrations in aero-engine compressor and turbine blades and discs is studied to overcome the disadvantages of the usual sand pattern and piezo-electric crystal contact probe methods. The Stetson-Powell time average fringe hologram technique of vibration analysis is used to investigate the nodal patterns of a 3-in and 6-in compressor blade together with those of a 10-in diameter turbine disc and the disc with a full set of blades. Two real time holographic methods of vibration analysis are also studied.

The hologram system and apparatus are simplified to enable the normal methods of clamping the vibrating components to be utilized. A completely self-contained unit that is capable of both taking the hologram and photographing the reconstructed image has been developed. The unit is a box-like structure which is simple to operate and can be used in a normal inspection bay environment for objects up to 2 ft diameter.
A Review of Cascade Data on Secondary Losses in Turbines
Authors: Dunham J.
Published: February 2007

Theories and experiments on secondary losses in axial turbine cascades without end clearance are reviewed. A formula is given which correlates the effect of blade loading on secondary losses more successfully than hitherto. However, it is also shown that secondary losses increase with upstream wall boundary layer thickness. Only a tentative expression for that effect can be suggested. In order to predict secondary losses reliably more must be known about these wall boundary layers.
Calculation of Change-Gear Combinations
Authors: Merritt H. E.
Published: February 2007

Given a desired ratio r not expressible as a proper fraction, limits r1 and r2 are set within which ratios afforded by feasible tooth-number combinations must lie. From the properties of conjugate fractions developed by Brocot, Rasche and the author, a pair of conjugate fractions approximating to r1 and r2 are first derived. Fractions intermediate in value are then expressed as series, the numerators and denominators of which are successively registered on a desk calculating machine. These are tested for factors, and potential solutions containing suitable factors are recorded. Best solutions are usually accurate to about 1 in 106.
Vibration of Beams Subjected to End and Axially Distributed Loading
Authors: Pilkington D. F. , Carr J. B.
Published: February 2007

This Note describes an approximate analysis which determines a lower bound to the fundamental frequency of beams subjected to both end and axially distributed loads. Comparison with results for the fixed-free and hinged-hinged beams gives good agreement.
Analysis of the Taper-Land Bearing Pad
Authors: Neal P. B.
Published: February 2007

A computational analysis of hydrodynamically lubricated rectangular taper-land pads is presented. The geometrical parameters in the analysis are width/length ratio, land extent and film ratio. To permit assessment of the influence of variable viscosity, a linear decrease of viscosity along the pad length was provided for. Performance data have been derived for load capacity, friction, lubricant flow rate and operating temperature. Attention is given to the influence of hot lubricant carry-over from one pad to the next in a multi-pad bearing and accordingly two distinctly different situations, namely, isolated pad and compact bearing, are considered. Apart from the practical desirability of a land to carry any load under stationary conditions, it is shown that a short land is beneficial under operating conditions but that a land greater than about 0·3 of pad length is undesirable.

An example illustrating the application of the data to bearing performance prediction is given.
Dynamic Stability of a Cantilever Boring Bar with Machined Flats under Regenerative Cutting Conditions
Authors: Parker E. W.
Published: February 2007

The paper is concerned primarily with the stability of a slender boring bar which can be represented at the tool point by a simple two-degree-of-freedom, mass-spring-damper system. Its purpose is to determine how the vibration behaviour during machining is affected by coupling between modes.

The stability behaviour is investigated for machining processes in which the cutting operation is of the regenerative type, when successive passes of the workpiece cause cuts to overlap. Account is taken of variations in certain system parameters, including the effect of workpiece speed, and results derived from practical cutting tests are described. Particular attention is paid to the effect on chatter-free machining performance of variations in the angle of setting of the boring head relative to the two planes of vibration.

A theory is developed to apply the basic principles of the coupling mechanism over a wide range of conditions. Predicted changes in chatter characteristics are compared with experimental observations.

Certain discrepancies arise between theory and practice, some of which can be resolved by re-assessing the initial assumptions for cutting forces.
Twisting and Bending of Thin-Walled Prismatic Beams of Open Cross-Sectional Profile
Authors: Harrison T.
Published: February 2007

Previous studies of the behaviour, in generalized co-ordinates, of thin-walled, prismatic beams of open cross-sectional profile have included, explicitly, only the effects of distributed transverse forces, q x and q y, distributed longitudinal forces, q z, and distributed torsional couples, m z.

Using the principle of virtual displacements, the work of previous investigators is extended to include, quite generally, the effects of the hitherto neglected distributed couples, m x and m y. The derivation of the differential equation relating to the twisting of an open-section prismatic beam is presented fully whilst those relating to transverse and axial displacements of cross-sections are merely stated.

The kinematic and static boundary conditions for a cantilever are also established from the virtual work equations. These show that the free-end shear boundary condition associated with transverse bending which is usually adopted in engineering calculations is inadequate for such a generalized loading system.
Effect of a Tensile Mean Stress on the Alternating Stress Required to Propagate an Edge-Crack in Various Materials
Authors: Frost N. E. , Greenan A. F.
Published: February 2007

The conditions governing growth or dormancy of edge-cracks in plate specimens of twelve materials subjected to the general tensile loading cycle σ m ± σ a, where σ m ≥ σ a and σ m + σ a < yield stress, have been determined. It was found that, as in the case of zero mean load, these conditions were defined by the value of the parameter σa3l; if σa3l < Cm a crack would grow whereas if σa3l < Cm it would remain dormant, where C m depended on the material and on the value of the ratio σ m/σ a. Above a certain value of σ m/σ a reached a minimum value for a given material. In general, this minimum value agreed with the value derived from the known fatigue crack growth characteristics of the material by assuming that during one loading cycle a crack will remain dormant if it cannot extend at least one atomic spacing.
Harmonic Wave Analysis of Vibration and Stress in a Longitudinally Reciprocated Bar
Authors: Beddoe B.
Published: February 2007

The wave equation in one dimension approximately represents the longitudinal motion of a uniform bar that carries regularly spaced equal point masses. Fourier analysis is used to obtain the steady-state solution when the bar is reciprocated from one end. Distributed damping is considered.

The more general system of unequal and irregularly spaced point masses on a bar consisting of sections of different mass per unit length is analysed in terms of reflection and transmission coefficients; a wave reflection method and a transfer matrix method are given for the solution of the problem of reciprocation. The limitation of the approximate equation of motion is assessed by examining wave dispersion in the uniform system.

Application to ‘traverse bars’ on machines for winding extruded synthetic fibre was the object of the investigation.
Heat Transfer Measurements on a Simple Model Representing a Poppet Exhaust Valve in an Outflowing Stream
Authors: Annand W. J. D. , Lanary R. S.
Published: February 2007

There exists no published information from which the heat transfer between the exhaust gases of a reciprocating engine and the exhaust valve may be calculated with reasonable confidence. Such information is needed for the application of cycle synthesis calculations to the analysis and prediction of the thermal loading of the valve, which is a critical component in that respect. Measurements obtained on a simplified poppet valve model in steady flow are presented. The heat transfer coefficients measured are shown to be at variance with the empirical pipe-flow equations which have previously been employed in such calculations. They can be represented by Nu = aRe0.58 where the factor a is a function of lift/diameter ratio.
Air-Generated Waves on a Moving Membrane
Authors: Binnie A. M.
Published: February 2007

When air passes over a wide flexible membrane tensioned in the direction of the air stream, waves on the membrane may be excited. An expression is found for the length of the most unstable wave in terms of the air velocity and density and of the tension and density of the membrane. A numerical example of these effects in a paper-making machine is given.
Elastic Buckling of Overbraced Frames
Authors: Godley M. H. R. , Chilver A. H.
Published: February 2007

Some simple studies are made of the characteristics of elastic buckling of overbraced frames, loaded at the joints. A frame of this type may be prestressed before the application of external loads, due to initial lack of fit of members of the frame, and this is taken into account in the analysis. Experiments on simple over-braced frames confirm the theoretical conclusions.
Steady Compressible Flow through a Single Row of Radial Holes in the Wall of a Pipeline
Authors: Trengrouse G. H.
Published: February 2007

Measured values of discharge coefficient for air flow through a single row of radial holes in the wall of a pipeline are reported, together with the values of pipe Mach numbers in the immediate vicinity of the holes. A wide range of pressure and area ratios are considered, the flow through the holes being either into or out of the pipe. It is shown that the effects on the measured values of both the pressure level at discharge from the holes and the air temperature are negligible.

The agreement between the pressure change in the pipeline due to the holes, obtained experimentally, and that predicted by simple, one-dimensional flow theories is generally unsatisfactory. However, theoretical predictions of the jet efflux angles based on two-dimensional, incompressible, non-viscous flow arguments are in good agreement with those measured, but discrepancies do arise in the prediction of discharge coefficients.
Real Area of Contact between a Rough Surface and a Softer Optically Flat Surface
Authors: O'Callaghan P. W. , Probert S. D.
Published: February 2007

The mean number of contact spots per unit area and their mean radius were measured and hence the real area of contact deduced for a rough-to-flat interface under normal loading. The contact pressure was varied from zero to half the micro-hardness of the softer material. The resulting experimental evidence did not endorse the predictions from the recent theory of Tzukizoe and Hisakado, which incorrectly assumes that the real contact area is given by the applied pressure P divided by the micro-hardness M of the softer material. It was found that this area equalled K( P/ M) n, where the coefficient K and index n depend upon the applied pressure range. A maximum number of contact points was encountered at a dimensionless loading ( P/ M) approximately equal to 7·5 × 10-3.
Effect of Gravity on the Performance of an Impact Damper: Part 2. Stability of Vibrational Modes
Authors: Sadek M. M. , Williams C. J. H.
Published: February 2007

This paper is c oncerned with the stability of the various modes of vibration of the impact damper system described in Part 1†. Charts are presented showing the ranges of dynamically stable and kinematically viable periodic two-impact-per-cycle motion. The condition of kinematic viability ensures that the trajectory of the free mass remains within the container throughout the motion.

It is shown that in general stable, viable, two-impact-per-cycle motion of the system exists under resonant conditions of the main mass and that away from resonance, where any damper is ineffective, this type of motion is generally unstable.
A Study of Resonance Coincidence in Bladed Discs
Authors: Ewins D. J.
Published: February 2007

The failure in service of just one or two out of a batch of nominally identical units poses two urgent problems. First, it is necessary to establish the immediate cause of the failures but then, and equally important, it is essential to determine whether these isolated cases represent a few ‘rogue’ units or whether they herald the subsequent failure of many others. This latter problem is examined in relation to the vibration loads borne by turbomachinery blading. The possibility that minor dimensional variations between one unit and another can result in them exhibiting significantly different vibration characteristics is studied in two detailed cases. One example shows that the shortening of all the blades on one disc by 3 per cent can worsen their resonant response levels under operating conditions by 50 per cent, and thereby drastically shorten their fatigue life. The presence of small variations between the blades on a disc—blade detuning—can also increase response levels by as much as 90 per cent. It is concluded that apparently similar bladed disc units could well exhibit quite dissimilar vibration characteristics in service, and consequently have widely differing fatigue lives.
Stability and Step Response of a Hydraulic Servo with Special Reference to Unsymmetrical Oil Volume Conditions
Authors: Martin K. F.
Published: February 2007

This paper reports a theoretical and experimental evaluation of the stability and response of a hydraulic servomechanism used to position a mass when the oil volumes on the two sides of the jack are substantially different.

Application of small perturbation theory to the closed loop system shows that the loop gain for marginal stability is least when the oil volumes are equal and that when these volumes are unequal the response of the system is governed by a fourth order differential equation. Predictions of marginal stability gain and of the step response are in good accord with measurements made on an experimental rig. A system with unequal oil volumes is shown to be inherently more stable and to have a faster but less oscillatory response than when the oil is equally distributed about the jack piston.

Coulomb friction is accounted for analytically by a viscous friction energy equivalent. When the response approximates to a damped sinusoid it is shown that it is necessary to base the equivalent upon this response.
Analysis of ‘Boosted Lubrication’ in Human Joints
Authors: Dowson D. , Unsworth A. , Wright V.
Published: February 2007

The load-bearing human joint is a self-acting dynamically loaded bearing which employs a porous and elastic bearing material (articular cartilage) and a highly non-Newtonian lubricant (synovial fluid).

The authors' understanding is that the human joint experiences fluid-film (including elastohydrodynamic), mixed and boundary lubrication in its various operating conditions. It has been recognized that squeeze-film action is capable of providing considerable protection to the cartilage surface once a fluid film is generated (6) (8)§. Furthermore, the possibility of an increasing concentration of hyaluronic acid in synovial fluid during the squeeze-film action due to the porous nature of the cartilage and its surface topography and the known relationship between this concentration and the effective viscosity (7) has led to the concept of ‘boosted lubrication’ as an important feature of joint behaviour (10).

A mathematical analysis of the concept of boosted lubrication of human joints is presented in this paper. The predictions of the analysis are shown to be in good agreement with experimental findings (12).
Non-Linear Performance of Turbine Bearings
Authors: Holmes R.
Published: February 2007

The purpose of this paper is to consider the non-linear vibration performance of turbine bearings and to give an indication of the limits of the linear treatment.
A Study of the Cross Flow Fan
Authors: Porter A. M. , Markland E.
Published: February 2007

The cross flow fan has developed from the ideas of Mortier in the late 19th century and recently has been used with conspicuous success in small domestic appliances. No satisfactory theory is known, improvements having come from experimental development.

The present work is also experimental. A closed-circuit fan test rig was constructed to obtain pressure, volume flow rate and efficiency for fans of various designs. Detailed measurements within the rotors were also obtained by hot-wire traverses. These tests were supplemented by visualization studies in a water test rig.

It is found that improved pressure–flow characteristics are obtained by constructing the casing so that the vortex which forms in the fan is allowed to move circumferentially round the rotor as the output is throttled. This preserves a strong vortex and keeps the total pressure approximately constant as the flow is throttled. In many previous designs, which do not allow this kind of displacement, the vortex tends to move towards the centre of the rotor and to diminish in strength, leading sometimes to unstable operation.
Effects of Pressure and Temperature Variation in Vibratory Cavitation Damage Test
Authors: Hammitt F. G. , Rogers D. O.
Published: February 2007

Vibratory cavitation damage tests (20 kHz, 2 mil (50·8 μm) double amplitude) have been conducted in water on SAE-660 bronze, over the temperature range 55°F to 250°F and with 1 to 4 atm static suppression pressure supplied by variation of cover gas pressure. The effects upon damage of variation of temperature at constant static suppression pressure and variation of static suppression pressure at constant temperature are presented. A comparison with the existing literature is made.
Local Heat Transfer Measurements on a Gas Turbine Blade
Authors: Turner A. B.
Published: February 2007

This paper presents an experimental method for determining the variation of the local heat transfer coefficient around gas turbine blades. The method involves the accurate determination of the distribution of metal surface temperature and the heat transfer coefficient and air coolant temperature in the internal cooling passages of the blade. It is shown that from the solution of Laplace's equation and a numerical differentiation at the blade surface of the resulting two-dimensional temperature field an estimate can be made of the normal temperature gradient in the metal which can be related directly to the local heat transfer coefficient at any point of the blade periphery.

The results of experiments on a cascade blade undertaken to demonstrate the method are presented. These results show a clear laminar–turbulent transition on the convex surface of the blade but no transition, as such, is indicated on the concave surface. The magnitude of turbulence in the main stream is shown to have a very marked effect both on the mean level of heat transfer to the blade and on the local variation of the heat transfer coefficient.
Effect of Slenderness Ratio on the Natural Frequencies of Pre-Twisted Cantilever Beams of Uniform Rectangular Cross-Section
Authors: Dawson B. , Ghosh N. G. , Carnegie W.
Published: February 2007

This paper is concerned with the vibrational characteristics of pre-twisted cantilever beams of uniform rectangular cross-section allowing for shear deformation and rotary inertia.

A method of solution of the differential equations of motion allowing for shear deformation and rotary inertia is presented which is an extension of the method introduced by Dawson (1)§ for the solution of the differential equations of motion of pre-twisted beams neglecting shear and rotary inertia effects.

The natural frequencies for the first five modes of vibration are obtained for beams of various breadth to depth ratios and lengths ranging from 3 to 20 in and pre-twist angle in the range 0–90°. The results are compared with those obtained by an alternative method (2), where available, and also to experimental results.
Some Experiments on Polymer Melt Flow in Single Screw Extruders
Authors: Fenner R. T. , Williams J. G.
Published: February 2007

A brief description is given of the various assumptions possible in theoretical predictions of polymer melt flow in single screw extruders. The various dimensionless groups in which the results of computations can be expressed are described including power consumption. Experiments are then described in which a silicone polymer is pumped in a 1½ in diameter screw and measurements are made of power consumption, flow rate and pressure for various screw geometries. It is concluded that a two-dimensional, non-Newtonian, non-isothermal solution gives the best prediction but that there are significant errors due to thermal convection and surface slip in the clearance at higher speeds.
Synthesis of Slider-Crank Mechanisms with Five Precision Points
Authors: Edwards G. , Webster J. J.
Published: February 2007

The equations for a five precision point synthesis of slider–crank mechanisms are derived and some examples illustrating the application of this synthesis to the design of function generators are given.
The Performance of Truncated Conical Diffusers
Authors: Duggins R. K.
Published: February 2007

The performance of truncated conical diffusers has been assessed for a variety of geometrical configurations and incompressible inlet flow conditions. In all the cases considered, truncation of the cone was found to yield a reduced pressure recovery, typically 4 per cent for a 50 per cent truncation. Accordingly, truncation is not recommended when an untruncated cone of the optimum angle can be accommodated. On the other hand, when there is a limitation on length, truncation is strongly recommended in preference to an untruncated, wider angle diffuser.
Accurate Pitch Checking
Authors: Sharpe J. E. , Smith J. D.
Published: February 2007

The problems involved in accurate measurement of pitch in gears are discussed and techniques for pitch measurement to 0·2 μ are described.
Analysis of the Hydraulic Jacking of Journal Bearings
Authors: Horlock J. H.
Published: February 2007

An analysis is given for the flow in the clearance space between a shaft and its bearing, when the shaft is touching the bearing at its lowest point. Solutions are given for short and long bearings.

The predictions of the analysis are compared with published experimental results. While the supply pressure required to lift a shaft off its bearing may be predicted accurately, the estimated flow rate is far less than that measured in experiments.
A Model for Dynamic Fracture
Authors: Steverding B. , Werkheiser A. H.
Published: February 2007

It is shown that the dynamic fracture criterion for metals is equivalent to the failure criterion of a Voigt body containing a non-Newtonian dashpot. Integration of the differential equation leads to the concept of a critical incubation time for fracture. Contrary to static fracture criteria, not only is a sufficiently high stress necessary but this stress has also to be present for a sufficiently long time, so that large stresses afford small duration and vice versa. Some consequences of the dynamic fracture law are applied to dynamic metal behaviour at elevated temperatures, as well as to the size of the shock loaded material.
Thermal Conductivity of Heavy Water (D2O)
Authors: Venart J. E. S. , Mani N.
Published: February 2007

Existing thermal conductivity (λ) data for heavy water (D2O) between 0 and 600°C at pressures from atmospheric to 1000 bar are correlated as simple functions of reduced pressure and temperature, utilizing orthogonal polynomial least squares analysis. Correlations in the vapour and supercritical states are made from a knowledge of the ratio λd2o/λh2o. A table of best values for the liquid, vapour and supercritical states of the pure fluid is also provided. Using these values, the thermal conductivity of heavy water can be estimated to between ±2 per cent and ±10 per cent from values of pressure and temperature only.
Heat Flow across Stacks of Steel Laminations
Authors: Williams A.
Published: February 2007

The effective thermal conductivity of stacks of enamelled steel laminations (as used in the stator cores of large turbogenerators) is shown to depend on the fluid trapped between the laminations. The results of tests on stacks in a normal atmospheric environment have been adjusted for other environments, using a simple mathematical model. It is predicted that the effective thermal conductivity of a typical stack in an atmosphere of hydrogen is increased by a factor of about 2·8 compared with that in air. Tests on small samples of laminations in air, vacuum, and helium confirm that the hypothesis is reasonable. Hysteresis in the stress–strain curves of a typical stack indicates that the thermal behaviour of a stator core of a generator may change during its operational life.
Dimensional Analysis of Wear by Particle Impact in Fluid Flows
Authors: Gibbings J. C.
Published: February 2007

Dimensional analysis is applied to the phenomenon of wear in machines and ducts through which fluid containing solid particles is flowing. A relation is obtained that contains results which have been observed experimentally whilst it contains others that have not been so observed.
The Propagation Velocity of a Small Rarefaction Wave in a Non-Equilibrium Vapour-Liquid Bubble Flow: A Prediction of the Onset of Choked Flow
Authors: Baum M. R. , Horn G.
Published: February 2007

A choked or critical flow condition can occur in a two-phase flow similar to that which is observed in a single phase compressible flow. Choking occurs when the velocity of the fluid becomes equal to the rate at which a small rarefaction wave will propagate upstream in the flow. The influence of slip and departures from thermal equilibrium on the propagation velocity of a small rarefaction wave are demonstrated.
The Influence of Sweep and Dihedral in Turbomachinery Blade Rows
Authors: Lewis R. I. , Hill J. M.
Published: February 2007

A qualitative discussion of the geometrical properties of dihedral and sweep in turbo-machine blade rows is presented with a discussion of the consequent fluid dynamic effects upon blade to blade and meridional flows. Results of blade to blade calculations for four heavily loaded turbine cascades of infinite span and various angles of sweep are presented. Annulus end wall interference effects on blade to blade flow are briefly discussed with reference to previous work. The principal analytical contribution is a development of actuator disc theory to deal with meridional flows for swept cascades and for blade rows in cylindrical annuli.
The Stability and Control of Motorcycles
Authors: Sharp R. S.
Published: February 2007

Mathematical models of a motorcycle and rider dependent on three alternative assumptions concerning the tyre behaviour are developed. Stability characteristics deduced from them are compared, and minimum requirements for the model greater than have been previously satisfied are established. Using the most sophisticated of the models, the effects of design changes are calculated, and the design implications are discussed.
A Study of the Stability of a Plate-Like Load Towed beneath a Helicopter
Authors: Sheldon D. F.
Published: February 2007

Recent experience has shown that a plate-like load suspended beneath a helicopter moving in horizontal forward flight has unstable characteristics at both low and high forward speeds. These findings have prompted a theoretical analysis to determine the longitudinal and lateral dynamic stability of a suspended pallet. Only the longitudinal stability is considered here. Although it is strictly a non-linear problem, the usual assumptions have been made to obtain linearized equations of motion. The aerodynamic derivative data required for these equations have been obtained, where possible, for the appropriate ranges of Reynolds and Strouhal number by means of static and dynamic wind tunnel testing. The resulting stability equations (with full aerodynamic derivative information) have been set up and solved, on a digital computer, to give direct indication of a stable or unstable system for a combination of physical parameters. These results have indicated a longitudinal unstable mode for all practical forward speeds. Simultaneously the important stability derivatives were found for this instability and modifications were made subsequently in the suspension system to eliminate the instabilities in the longitudinal sense.

Throughout this paper, all metric dimensions are given approximately.
Flow Models for Turbomachines
Authors: Horlock J. H. , Marsh H.
Published: February 2007

The equations for the flow through cascades of blades are averaged across the pitch and then compared with those for the flow through hypothetical models of blade rows; a closely spaced blade row, an axisymmetric flow with body forces and the flow on a mean stream surface. It is shown that these models can provide an accurate representation for the overall flow changes across a blade row, but they cannot give an exact local matching with the averaged properties of the flow in the real cascade. The nature of the blade forces in the real flow and the body forces in the hypothetical flow is discussed.
High Frequency Hydraulic Vibrators
Authors: Smith J. D.
Published: February 2007

Hydraulic vibrators which are powerful, cheap and compact are described and theory for their performance prediction is given. They are of use where high forces are required on structures of high dynamic stiffness at frequencies up to 1 kHz.
Biaxial Creep Testing
Authors: Wilson I. H. , Duncan J. L. , Johnson W.
Published: February 2007

A new test for investigating biaxial creep in sheet metal is described. The specimen is a thin circular diaphragm clamped at the edge and deflected by lateral hydrostatic pressure. Stress and strain in the central region of the specimen are determined from measurements of pressure and of extension and curvature at the pole.

An analysis of the time-dependent deformation of a circular diaphragm is presented and compared with experiments in which commercial purity aluminium sheet was tested in constant pressure tests at temperatures between 100 and 250°C. The biaxial creep data were compared with the results of uniaxial constant load tests, but no satisfactory correlation could be obtained. The results of constant pressure biaxial tests at different temperatures above 175°C could be correlated using the Zener–Holloman time parameter.
Apparent Strain-Hardening
Authors: Hillier M. J.
Published: February 2007

Continuous and interrupted room temperature compression tests were carried out on geometrically similar specimens of duralumin, pure copper and lead, using steel and ebonite dies. Significant differences in strain-hardening rate were ascribed to heat-transfer during deformation. It was concluded that the yield-stress is strongly sensitive to small changes in temperature occurring during deformation. It is suggested that the time dependence of the associated recovery processes is the origin of the strain-rate effect.
Hugoniot's Method Applied to Stratified Flow through a Constriction
Authors: Binnie A. M.
Published: February 2007

The discharge of a homogeneous inviscid fluid through a convergent-divergent constriction can be calculated by Hugoniot's method. The method is here extended to stratified liquids moving under gravity in an open horizontal channel.
A Linear Theory for the Heaving Response of a Hovercraft Moving over Regular Waves
Authors: Reynolds A. J.
Published: February 2007

A linear theory is developed to predict the heaving response of a single-plenum hovercraft to regular head or following seas. The response in a prescribed wave environment is found to depend on the natural heaving frequency and damping of the craft, on the frequency of wave encounter, on the cushion planform, and on the ratio of craft length to wave length. Particularly vigorous forcing is found to occur when the ratio of craft length to wave length is such that large changes occur in either cushion volume or escape area.
Experiments on the Flow of Heat across Stacks of Steel Laminations
Authors: Williams A.
Published: February 2007

Further measurements of the thermal conductivities of stacked laminations are reported. Differences in surface textures are important in a normal atmospheric environment, but not in an environment of helium, when the interface gas carries most of the heat flow across adjacent laminations.
High Strain Rate Behaviour of Iron and Nickel
Authors: Muller T.
Published: February 2007

An investigation into the mechanical behaviour of iron and nickel at high strain rates is carried out, using a split Hopkinson bar method. Some special adaptations, a correction method for the effects arising from the adiabatic conditions of dynamic deformation and a simplified data processing procedure are described in detail. The test conditions covered a range of strain rates between 500 and about 10 000/s and temperatures from 20 to 500°C. For both metals, the results are presented by means of a family of true stress-true strain curves. The strong strain rate sensitivity at high strain rates indicates that the rate controlling mechanism differs from that operative at ‘static’ strain rates.
Effect of Transverse and Longitudinal Surface Waviness on the Operation of Journal Bearings
Authors: Shelly P. , Ettles C.
Published: February 2007

An analysis is made to evaluate the effect of surface finish produced by the two final machining processes of high speed aero boring and broaching. A finite difference method of solution is used in which the number of waves superimposed on the basic geometry is successively increased. A strong asymptotic trend was found for all bearing characteristics beyond a relatively small number of waves. It is found that the load capacity compared to a smooth bearing is reduced for both processes if the surface waviness is included as an addition to the film height. If the film thickness is assumed to extend to the mean wave height, the load capacity is increased. The effect of surface waviness becomes more pronounced at higher eccentricities or as the amplitude of the waviness is increased. The variation of bearing friction and oil flow is shown. It is concluded that neither finishing process would have a serious deleterious effect on journal bearing performance.
Fully Developed Turbulent Flow through Concentric Annuli
Authors: Lawn C. J. , Elliott C. J.
Published: February 2007

Mean velocity data are presented for the fully-developed flow of air in three radius ratios of concentric annulus. The shear-stress distributions were determined by location of the zero-shear position with hot-wires, and by a sliding sleeve technique. This latter technique, although not entirely satisfactory, proved the reliability of the first method and allowed non-dimensional velocity profiles to be constructed with confidence. Zero-shear and maximum velocity surfaces do not coincide.
Speed Characteristics of Hooke's Joint Transmissions
Authors: Maunder L. , Burdess J. S.
Published: February 2007

A transmission consisting of three non-collinear shafts connected in sequence by two Hooke's joints is described. Each shaft has a specified moment of inertia, and power is transmitted from one end of the system to the other. Elastic and other deformations are neglected. A single differential equation governing the motion is derived, and is solved approximately by a method of small perturbations. The solution shows that at a constant mean speed the system will experience speed fluctuations which are complex functions of its dynamic parameters, including inertia and torque characteristics, as well as the more familiar kinematic parameters such as angularities of the joints.

Special cases relating to constant speed conditions at chosen points in the system are assessed, and the effects of the significant parameters are illustrated numerically for a single-joint arrangement.
Design and Stress Analysis of No-Coning Brake Discs
Authors: Abbas S. A. , Cubitt N. J. , Hooke C. J.
Published: February 2007

During braking, the thermal gradient set up over the brake disc from the disc periphery down the bell to the mounting flange causes the disc to undergo undesirable distortions, termed ‘coning’. By proper design of the bell, this coning can be minimized, but, in so doing, there is a risk of high stresses occurring in the bell. In this paper, a numerical method of designing the bell to minimize coning and calculating the stresses in the bell is described. Comparison of results with standard analytical solutions shows that good agreement is obtained. An example of brake disc design and stress analysis by this method is given.
Optimization of Hybrid Gas Lubricated Conical Bearings
Authors: Kazimierski Z.
Published: February 2007

The motion of a short symmetrical rotor without loading by a constant radial force is described. The rotor under consideration is mounted in two hybrid conical gas lubricated bearings. It is assumed that the symmetric bearing's foundation is supported by flexible damped elements. An optimum angle of conical gas bearings which gives the maximum stability of the motion of the rotor with respect to the self-excited, cylindrical vibrations is sought. For this purpose a linear method of analysis is used. The optimum angle of the conical bearing is established for a certain family of conical gas films. The conditions of its existence in terms of parameters describing properties of the gas films and of the characteristic parameters of flexible damped elements is found. Finally, the existence of an optimum stiffness of elastic elements of support with respect to the creation of self-excited whirl vibrations of the rotor and foundation is proved.
Fatigue Crack Propagation in Polymethylmethacrylate; the Effect of Loading Frequency
Authors: Arad S. , Radon J. C. , Culvcr L. E.
Published: February 2007

The influence of loading frequency on the cyclic rate of crack propagation aN, in a glassy thermoplastic (polymethylmethacrylate, p.m.m.a.) in air, at a temperature of 21° ± 1 degC and relative humidity of approximately 50 per cent, has been investigated and linear–elastic fracture mechanics concepts have been used to analyse the results. Tests have been conducted on sheet specimens, fatigue loaded in tension, under conditions of constant maximum and minimum values of stress intensity factor, K, and at three frequency levels, namely 0·1, 5 and 20 Hz. It was found that, under these conditions, an increase in frequency led to a decrease in aN. Also, the results showed that when Kmax achieved levels equal to or greater than 750 lbf/in3/2, the contribution of ‘dynamic creep’ type damage to the crack growth process became more significant. The lower the frequency, the greater was the effect of Km, the mean level of K, on aN. It was also found that for the material under investigation the crack propagation power law index, n in equation aN = β(λ) n, where λ = Kmax – Kmin2, had an average value approximately equal to 2·25 and varied only by a small amount with frequency changes.
Heaving and Pitching Response of a Hovercraft Moving over Regular Waves
Authors: Reynolds A. J. , West R. P. , Brooks Beryl E.
Published: February 2007

Consideration is given to the pitching and heaving of a hovercraft whose plenum air cushion is divided into two compartments by a transverse barrier. Linearized equations of motion are developed, subject to the assumption that the skirt hem does not contact the surface beneath; the coefficients can be calculated in terms of craft geometry, weight and lift-fan characteristics, or in terms of natural frequencies and damping ratios for pitch and heave. In considering the response to regular head and following seas, particular attention is given to accelerations experienced at the bow and to the position of the pitch centre, where the vertical accelerations are least. The behaviour of a realistic craft is examined for waves of various lengths and for different craft speeds, and consideration is given to the effects of moving the mass centre and of modifying the barrier between cushion compartments. A relatively vigorous response is predicted for certain distinct ratios of craft length to wave length, as was the case for the pure heaving response studied earlier. Once again, it is possible to relate this maximum response to conditions at which rapid changes occur in cushion volume and escape area, but now the changes for the individual compartments must be considered as well.
Mass Transfer Technique for Investigation of Heat Transfer by Jet-Impingement Systems
Authors: Ward J. , Ideriah F. J. K. , Probert S. D. , Duggan A.
Published: February 2007

The technique of using mass transfer measurements (by sublimation of naphthalene) together with the Chilton–Colburn analogy is shown to be feasible for evaluation of heat transfers from impinging jets. The method is then used to determine heat transfer coefficients at the burner walls in models of jet–impingement furnaces.
Reference Results for Plane Stress Creep Behaviour
Authors: Sim R. G.
Published: February 2007

Dimensionless results describing the plane-stress creep behaviour of thin discs with a central rigid insert are presented. The results are non-dimensional with respect to a ‘reference stress' which is dependent on the geometry of the disc and the applied loads. To convert the dimensionless results into real terms all that is required is a knowledge of the creep strain-time response associated with the reference stress. The approach is applicable for variable, as well as steady, loading. In addition, it has been found that the dimensionless results associated with various different unit loading cases may be superimposed to give results applicable for a combined load case. This important result is a consequence of the approach used in non-dimensioning the problem.
Paper 3. Some Recent Advances in Dynamic Stability and Control of Submerged Vehicles
Authors: Gertler M.
Published: February 2007

A short survey is made of technological developments, including some recent advances, in the field of dynamic stability and control pertaining directly to submerged vehicles. The practical aspects of the subject are emphasized by highlighting those advances that have provided means for obtaining improvements in design and performance of submerged vehicles from the standpoints of stability and control.
Paper 5. Directional Stability and Control of a Vessel in Restricted Waters
Authors: Fujino M.
Published: February 2007

By way of introduction the paper discusses conflicting observations of stability behaviour of ships in restricted waters. The equations of motion of a ship in a narrow channel are given, leading to stability criteria; differences from the deep water case are highlighted. More qualitatively, the theory also illustrates the asymmetric hydrodynamic force. Criteria are outlined for an automatic control system to improve stability. However, the first-order theory is shown to provide an inadequate description of all experimental results.
Paper 6. Some Theories for Ship Manoeuvring
Authors: Newman J. N.
Published: February 2007

This paper reviews and extends the available theories for predicting the hydrodynamic force and moment acting on a ship hull or submerged vessel during manoeuvres in the horizontal plane. Effects of free-surface waves and viscous separation are not considered, but attention is focused instead on recent developments in the theory of low-aspect-ratio geometries, including the effects of vortex sheets shed from sharp trailing edges, and in the use of slender-body theory to predict the manoeuvring characteristics of ships in restricted waters.
Paper 8. A Two-Dimensional Strip Method for Surface Ship Hull Derivatives: Comparison of theory with Experiments on a Segmented Tanker Model
Authors: Clarke D.
Published: February 2007

At the present time there is no complete theory for the calculation of velocity and acceleration derivatives for surface ships. A few methods have been published but they fail to take proper account of hull geometry. A strip method is described, based on added mass concepts, which is compared with experiments conducted with a segmented model of a tanker.
Paper 20. Improvement of Control by Special Devices
Authors: Ritter H.
Published: February 2007

The paper discusses hydrodynamic devices for improving manoeuvring and control. Two hydrodynamic concepts are shown to be of practical significance for large craft: control of hydrofoil lift independent of incidence, and deflection of the propulsion jet through a large angle by means of a simple hydrofoil. Lift control independent of incidence is illustrated by the jet flap and the trailing edge rotating cylinder. Improved deflection of the propeller slipstream involves extending the rudder stall angle, and it is shown how this may be achieved by fitting the rudder with a leading edge rotating cylinder.
Paper 22. Effect of Design Modifications on the Natural Course Stability of Full Tanker Models
Authors: Glansdorp C. C. , Pijfers J. G. L.
Published: February 2007

The course stability characteristics of two full tanker afterbodies with different rudder–propeller–skeg configurations are experimentally determined. Natural course stability characteristics are improved by adding lateral force generating devices in the afterbody.
Paper 29. Yaw Control in Waves
Authors: Eda H.
Published: February 2007

Results are given of a recently broadened investigation into the stability of ships in following seas, based on a theoretical study and model tests on Series 60 hull forms. The analysis is derived from perturbations to the steady yaw, sway, surge and automatic control equations. At low frequencies of encounter, corresponding to high ship speeds, it is found that significant destabilizing effects arise from the large surge forces generated by the waves, leading to broaching: stability is greatly improved by appropriate characteristics of the control system. At higher encounter frequencies, typical of lower speed ships, oscillating yaw and sway motions are induced and the rudder has little influence. The study clarifies the influences of wave encounter frequency, encounter angle, control system constants and ship configuration.