bluuebunny/crossref_metadata_2025 huggingface dataset:
Research Note: Vibrations Resulting from Thermal Conduction between Non-Rigid Contacting Bodies
Authors: Watson A.
Published: February 2007

A piece of metal which has few points of contact when standing on a plane surface, and which will rock when disturbed, will continue rocking indefinitely if a sufficient temperature difference is maintained between the metal and the plane. By analysing the thermal conduction between the points of contact, the work output and thermal efficiency of the rocker are calculated. A survey of materials shows that ceramic-metal interfaces are capable of high work output. Vibrations between components made of these materials could thus be sustained by this mechanism.
On the Equations Governing the Free and Forced Vibrations of a General Non-Conservative System
Authors: Wahed I. F. A. , Bishop R. E. D.
Published: February 2007

An expression is derived for the steady forced response of a system governed by the equation

in which A, B and C are real but not symmetric. The theory is effectively an adaptation and exploration of previous work by Woodcock (1)‡. His studies were published in the ‘Hamiltonian’ form, while in the present paper the Lagrange approach is used.
Compressor-Diffuser Interaction with Circumferential Flow Distortion
Authors: Greitzer E. M. , Griswol H. R.
Published: February 2007

An analytical and experimental study of axial compressor-diffuser interaction in circumferentially non-uniform flow is reported. An analysis of non-axisymmetric flow in an annular diffuser is presented, based on an inviscid rotational core flow plus the use of a diffuser effective area ratio to account for boundary layer blockage. The analysis is applied to the prediction of the diffuser flow field associated with the presence of a circumferential total pressure distortion. It is found that large static pressure non-uniformities can exist at the inlet of diffusers that are short compared with their mean circumferences, as is usually the case in turbomachinery applications. The analysis is coupled to an asymmetric compressor flow field prediction to provide a method for calculating the effect of an exit diffuser on compressor performance with distortion. It is shown that the velocity defect seen by the compressor can be substantially increased by the presence of the diffuser.

The experiments were directed at assessing the method used to predict the flow in the diffuser. Measurements were carried out of the inlet static pressure distortion associated with a circumferentially non-uniform total pressure distribution. The results are found to be in good agreement with the theoretical predictions.
The Reduction of Pressure Surge in a Simple Pipe Flow System
Authors: Driels M. R.
Published: February 2007

Two methods are presented for reducing the magnitude of the propagated pressure waves resulting from the reduction of flow in a reservoir-valve-pipe system. The theoretical performances of the two methods are investigated and compared with a third method developed by Streeter (1)†, and with that resulting from simple linear closure of the valve controlling the flow. The two methods indicate a maximum reduction of around 80 per cent in the magnitude of the pressure wave, and a significant reduction for valve closure in one pipe period.
The Immiscible Liquid Binary Rankine Cycle
Authors: Burnside B. M.
Published: February 2007

An analysis of the immiscible liquid binary Rankine cycle using aqueous/perfluorocarbon binaries has been carried out. Six such binaries have been studied and it has been shown that the cycle is characterized principally by the volatility of its organic component. The cycle performance has been compared with that of promising pure organic working fluid cycles. Although having generally lower efficiency than the optimum organic pure fluid cycle, practical considerations may favour the binary cycle at the bottom end of the Rankine cycle power range.
Dynamic Characteristics of a Structure with Modifications at its Supports
Authors: Mahalingam S.
Published: February 2007

The paper is concerned with the free and forced vibrations of an undamped system in which rigid supports are removed or replaced by new subsystems. Since the modifications involve the constraints of the system, special techniques based on the receptances and transfer ratios associated with displacement excitation at a support are employed. The results are formulated in the modal parameters of the whole of the original unmodified system and any added subsystems; the characteristics of the removed subsystem play no part in the solution. Starting with the problem of the removal of one or more rigid supports, the analysis is extended to modifications of a greater complexity at the supports.
Research Note: The Influence of Surface Preparation on Machining Forces and Chip Geometry
Authors: Woodward R. L.
Published: February 2007

In machining practice, repeated passes result in the presentation of pre-strained material to the cutting edge. The effect of such strains on machining forces and chip geometry is investigated in a series of machining experiments performed on α-brass using a variety of cutting conditions. It is found that both thrust force and chip side spread depend on surface preparation, but cutting force and chip length ratio are not significantly affected by surface preparation under the conditions of the experiments. Surface preparation is also found to affect the scatter of results.
Research Note: An Alternative Scheme to Solve the Equations for Unsteady Gas Flow
Authors: MacLaren J. F. T. , Tramschek A. B. , Pastrana O. F. , Sanjines A.
Published: February 2007

A scheme which combines the ‘leap-frog’ method and the method of characteristics was found to be an efficient way to solve the unsteady gas flow equations which form the basis of mathematical models of compressor or engine systems.
The Distortion and Buckling of Long Viscoelastic Cylinders in Pure Bending
Authors: Croll S. G.
Published: February 2007

The behaviour in pure bending of moderately thick polypropylene cylinders is examined. The distortion into an oval cross-section is measured as the bulging and flattening displacements. The bending radius at buckling is also determined.

When compared with an existing theory for thin-walled Hookean cylinders both the distortion and buckling are found to be functions of a single reduced parameter involving the tube dimensions and the bending curvature, as predicted. However, the amount of distortion and the buckling radius are both less than the theoretical values. These discrepancies are explained by the mechanical nonlinearity of polypropylene.
A Qualitative Evaluation of Phenomenological Creep Rupture Theories
Authors: Westlund R.
Published: February 2007

Predictions of the creep rupture lifetime under constant uniaxial tensile load according to various theories are compared. Both purely ductile and purely brittle rupture mechanisms are included as well as some recently proposed combined mechanisms of failure.

One of these latter mechanisms is shown to yield results which describe quite well the dependence of the creep rupture lifetime on load in the entire region from instantaneous, usually rather ductile, rupture at high loads to long delayed, usually rather brittle, creep rupture at smaller loads.
On the Pressure Distribution between Stock and Rolls in Ring Rolling
Authors: Mamalis A. G. , Johnson W. , Hawkyard J. B.
Published: February 2007

The technique of incorporating pin-type pressure transducers into the rolls and accurate measurements of the normal pressure are reported for various rolling parameters when rolling plain and profiled rings.

Experiments have been carried out using tellurium lead at room temperature to obtain quantitative information about pressure distribution relevant to hot rolling, i.e. when frictional effects are pronounced. The results indicate that, in contrast to conventional strip rolling, the normal pressure distribution in ring rolling shows an early peak soon after the entry plane.
The Stability of Viscous Axial Flow in the Entry Region of an Annulus with a Rotating Inner Cylinder
Authors: Martin B. W. , Hasoon M. A.
Published: February 2007

The stability of developing tangential flow induced by the imposition of an axial velocity on the tangential velocity distribution created by core rotation is theoretically and experimentally investigated. A linear stability analysis is used to examine the influence of axial length, axial Reynolds number and annulus radius ratio on the critical Taylor number for neutral stability when the axial velocity is assumed uniform. Predictions compare favourably with measurements obtained by hot-wire anemometer for air flowing in an annulus of radius ratio 0·9, particularly at small Reynolds number and large values of the axial length parameter.
Effect of Shaft Eccentricity and Whirl on Sealing by a Sleeve Gland
Authors: Davies M. G.
Published: February 2007

The diffusion of one gas in the stream of another in the annular space between a sleeve gland and a rotating shaft is considered. Experiments are described for finding under what conditions the distribution of concentration of the diffusing gas agrees with that given by simple theory. It is concluded that the theory is inadequate when the shaft runs eccentrically or whirls in the sleeve; the effective length of the gland can easily be halved. An attempt is made to correlate the degree of enhanced back diffusion with the factors causing it.
A Study of the Lubrication and Dynamics of Geometrically Perfect, Lightly Loaded, Cylindrical Roller Bearings with Particular Reference to Shaft Loci
Authors: Markho P. H. , Dowson D.
Published: February 2007

The principal objective of this paper is to ascertain and quantify the cyclic movement of the centre of a shaft in a geometrically perfect, lubricated, cylindrical roller bearing exhibiting initial clearance and subjected to a light and steady load. The movement may be important in relation to the accuracy of location of shafts in roller bearings, and it is shown that a detailed consideration of the rolling element assembly predicts some interesting effects.

The study also covers more conventional features of bearing performance such as lubricant film thickness and coefficient of friction, and shows the effect of squeeze to be negligible under steady bearing loads.
A Perturbation Analysis of the Electroforming Process
Authors: McGeough J. A. , Rasmussen H.
Published: February 2007

A theoretical model of electroforming, which includes the effects of current efficiency and periodic reversal of polarity, is derived. The model is analysed by a perturbation procedure for a case where a metal layer is formed upon a mandrel-electrode carrying sinusoidal irregularities on its surface. Analytic solutions of the resulting equations are shown to be so complicated that numerical methods offer the best means of solution. The latter methods are therefore used to demonstrate how the achievement of a uniform thickness for the layer is influenced by the time intervals of the polarity-cycle and the current efficiencies for deposition and dissolution. Extensions of the model to cover arbitrarily shaped surfaces on the mandrel are shown to impose limitations on the amplitude of the irregularities that can be so treated.
Strength of Cylinders Containing Radial or Offset Cross-Bores
Authors: Cole B. N. , Craggs G. , Ficenec I.
Published: February 2007

The introduction of a small transverse opening or cross-bore into the wall of a cylindrical pressure vessel is sometimes necessary. Under static conditions such a cross-bore may have little effect on the bursting pressure of a plain cylinder, but under cyclic stress conditions, the fatigue life of the vessel is severely reduced. If the cross-bore axis is offset from the radial centre-line of the cylinder, then the fatigue life of such a vessel is shown to be substantially greater than that of a similar vessel containing a radial cross-bore.
Fatigue Tests on Specimens Containing Skew Holes
Authors: Ficenec I. , Craggs G. , Cole B. N.
Published: February 2007

The fatigue life of uniaxial fatigue specimens containing a skew hole is investigated. Contrary to expectation, fatigue life and fatigue endurance limit show no discernible change for vertical skew angles up to 45 when stress is calculated using the gross cross-sectional area. The point of fatigue crack initiation moves from the tip of the minor axis of the ellipse towards the tip of the major axis as skew angle increases.
Research Note: Film Rupture in a Dynamically-Loaded, Non-Conformal Contact
Authors: Dowson D. , Smith E. H. , Taylor C.M.
Published: February 2007

This note is concerned with the rupture of hydrodynamically lubricated films in infinitely-wide non-conformal contacts. An attempt to correlate previous experimental work with new analytical results using separation cavitation boundary conditions is reported. The correlation shows no overall improvement compared with that obtained using analytical results employing the more common Swift–Stieber boundary conditions. It is suggested that a more detailed examination of the physical processes at work when rupture occurs in dynamically-loaded thin-film contacts is needed.
Analysis of a Journal Bearing with Self-Boosted Pressure Generation
Authors: Alexandrov V. A. , Ettles C. M. M.
Published: February 2007

The shaft of a journal bearing is covered with a resilient layer containing perforations. These act as varying volume pockets, owing to the elasticity of the material, and force lubricant into the film as the shaft rotates. An improvement in load capacity is given for eccentricity ratios greater than 0.7 which is accompanied by a proportional increase in flow and a slight increase in friction. A range of suitable lining materials is considered.
‘Wavy’ Modes of Instability in the Flow between Eccentric Rotating Cylinders
Authors: Markho P. H. , Jones C. D. , Mobbs F. R.
Published: February 2007

This paper concerns the stability of the flow of a fluid contained between a rotating inner cylinder and a stationary outer cylinder. Visual observations as well as torque measurements are used to examine the influence of eccentricity on the further modes of instability which occur when the Taylor number of the flow is increased above its critical value. Successive transitions to wavy vortex modes of higher azimuthal wave numbers are found to be associated with sudden reductions in the slope of the torque–Taylor-number curve and in the coefficient of friction, particularly at low eccentricity ratios. This effect, which occurs throughout the ‘spectrum of transitions' to turbulence, is of considerable importance to the operation of high-speed journal bearings in modern power-generating plant.
The Partially Lubricated Piston Ring
Authors: Brown S. R. , Hamilton G. M.
Published: February 2007

The discrepancy between measured and calculated oil-film thickness under a piston ring is shown to be due to oil starvation. If care is taken to keep the inlet region filled with oil, the film thickness is found to obey the theory. A simple formula is derived for predicting the degree of starvation to be expected when more than one piston ring is fitted.
A Numerical Solution of the Dynamic Characteristics of an Aerostatic, Porous Thrust Bearing Having a Uniform Film Subjected to Linear Axial Load Variations
Authors: Taylor R.
Published: February 2007

A numerical method of solution is presented for the pressure distribution in the uniform air film of a porous thrust bearing in which the top plate is subjected to vertical vibrational motion. From this pressure distribution it is possible to compute the bearing's dynamic characteristics, the knowledge of which is essential for the design of these bearings if unstable operating regions are to be avoided.
The Elastohydrodynamic Lubrication of Heavily Loaded Contacts
Authors: Hooke C. J.
Published: February 2007

An analytical solution is presented to the problem of the lubrication of highly deformed contacts, including the effect of pressure on viscosity. It is shown that the character of the lubrication process depends on the value of a single non-dimensional parameter, and that for each value of this parameter there is a unique non-dimensional value for minimum film thickness. Results are presented for general line contacts and for cylindrical contacts.
Heat Transfer in Rotating Cylindrical Cavities
Authors: Owen J. M. , Bilimoria E. D.
Published: February 2007

Nusselt numbers are measured on the heated disc of a rotating cylindrical cavity, with either an axial throughflow or a radial outflow of coolant, over a range of gap ratios, 0.13 ≤ G ≤ 0.4, flow rates up to Re z ≈ 1.8 × 105, rotational speeds up to Reø ≈ 2.5 × 106, and Grashof numbers up to Gr ≈ 1.7 times 1012. For the axial throughflow case, dramatic increases in the values of local Nusselt numbers are observed at certain Rossby numbers; these increases are consistent with the vortex breakdown observed on a separate, isothermal, laser Doppler anemometry (L.D.A.) rig For the radial outflow case, the mean Nusselt numbers show three separate régimes which depend on Re z and Reø but are only weakly affected by G. These three régimes have been identified on the L.D.A. rig and are associated with the presence or absence of Ekman layers on the rotating discs.
Non-Hertzian Elastohydrodynamic Contacts: An Experimental Investigation
Authors: Varnam C. J. , Hooke C. J.
Published: February 2007

Interferometry is used to measure lubricant film thicknesses in a heavily loaded non-Hertzian contact. The results describing the sliding of a rigid plane over an elastic layer bonded to a rigid cylindrical substrate agree closely with theoretical values given by Hooke and O'Donoghue (1)†.
A Technique for Accelerating Block Load Fatigue Programmes
Authors: Power E. M.
Published: February 2007

Recent improvements in cycle counting methods have increased the value of the block load programme as a method of simulating the fatigue damage caused by random service loading.

It has already been observed that some of the lower load levels in certain block programmes make insignificant contributions to the total fatigue damage, and that the elimination of such levels can provide a very valuable method of accelerating tests.

This paper presents further evidence in support of this observation, and proposes an analytical method by which the damage significance of each block may be predicted, thus enabling a rapid selection of those levels which may be safely omitted.
In-Plane Torsion Testing of Sheet Metal
Authors: Sowerby R. , Tomita Y. , Duncan J. L.
Published: February 2007

In this paper, the ‘in-plane’ torsion testing of sheet metal is examined. The test itself was first proposed by Marciniak in order to ascertain the work hardening behaviour and fracture strain of sheet metals. In the original work, the analysis was based on the assumption that the material was rigid-work hardening.

The present work attempts a more rigorous solution, assuming the material to be elastic-work hardening. A finite-element approximation is employed to calculate the stress and strain distribution across the sheet metal annulus at various stages in the deformation process.

A comparison is made between the results from the finite-element method and those based on a rigid-work hardening material. For certain annulus geometries, excellent agreement is obtained between both sets of results.
An Analysis of a New Type of Automatic Balancer
Authors: Hedaya M. T. , Sharp R. S.
Published: February 2007

A new type of automatic balancer which consists of a pair of two-ball balancers to compensate for unbalanced inertia forces and moments is presented. A stability analysis of the balanced condition achievable by such a balancer and the results of a parametric study of its stability are included. Conclusions are drawn regarding the satisfactory operation of the balancer.
Atmospheric Turbulence Encountered by High-Speed Ground Transport Vehicles
Authors: Balzer L. A.
Published: February 2007

The structure of atmospheric turbulence near the ground is reviewed and the statistical properties of the longitudinal, lateral and vertical velocity components of the wind presented. The statistical properties of the turbulence encountered by a high-speed ground transport vehicle travelling through a turbulent wind field of arbitrary orientation are derived. Next, the statistical properties of the atmospheric forces acting on the vehicle are determined and a method of taking account of finite vehicle length is presented. The resulting formulae are applied to a typical tracked hovercraft vehicle.
Waterhammer in Non-Rigid Pipes: Precursor Waves and Mechanical Damping
Authors: Williams D. J.
Published: February 2007

When a pipe can move, waterhammer effects are altered by the existence of precursor waves, i.e. longitudinal elastic strain waves in the pipe walls, modified by the presence of the fluid. Theory and experiment show that precursor waves cannot be ignored, if the effect of longitudinal strain is to be considered; conventional waterhammer theory is thus unsatisfactory. Flexural waves may also occur.

It was found experimentally that pipe motion caused mechanical damping of the waterhammer–greater than the viscous damping. Viscoelastic piping also gave rise to strong mechanical damping, even without pipe motion.
Large-Deflection Response of Square Frames to Concentrated Impulsive Loads
Authors: Hashmi M. S. J. , Al-Hassani S. T. S.
Published: February 2007

A study is made of the elastic-plastic responses of portal and free square frames subjected to concentrated explosive impulses. A finite-difference method, which reduces the structure to small masses connected by light links, is used to solve the equations of motion of the deforming frames. The links are assumed to have the same strength properties as the material of the structure. Dynamic strain is measured experimentally, instantaneous profiles are obtained from high-speed photographs and the final deflections substantiate the predictions of the analytical method.
Dynamic Instability of Certain Conservative and Non-Conservative Systems
Authors: Done G. T. S. , Simpson A.
Published: February 2007

This paper is concerned primarily with the analysis and resolution of the problems and contradictions that arise in the classification as conservative or non-conservative of a certain type of dynamical system. The systems concerned have equations of motion of gyroscopic type when the deflections are expressed with reference to particular co-ordinate axes, and they exhibit dynamic instability. Three examples are considered which possess their own special characteristics and subtleties; these are the rotating flexible asymmetric shaft, the helicopter ground resonance system and the clamped clamped flexible tube conveying fluid. For each of these cases, the energy input mechanism is examined and the problems of classification resolved.
The Experimental Behaviour of Double-Skinned, Composite, Circular Cylindrical Shells under External Pressure
Authors: Montague P.
Published: February 2007

The paper describes the construction and pressure-testing of fifteen cylindrical shells made by filling the space between two thin, steel, concentric membranes with a resin-glass composite. Their behaviour is compared with a previously published theory (1)†. The comparison is satisfactory over about two thirds of the length of the shell, with excellent agreement before the steel skins yield and good agreement with mean behaviour at higher pressures. All the shells remain totally stable after the steel skins have yielded and some achieve their full theoretical strength.
Further Investigation of Conical Diffusers with Annular Injection
Authors: Duggins R. K. , Lampard D. , Sanders A. T.
Published: February 2007

A comprehensive investigation is made, for a wide range of incompressible flows, into the merits of annular injection as a means of obtaining a high-performance diffuser with short axial length.

Results show that injection yields considerable improvements in both the quality of the discharging flow and the magnitude of the pressure recovery. Accordingly, the technique is strongly recommended when a short, high-performance diffuser is required and when a suitable secondary supply is available. Recommendations are also made regarding the optimum cone angle and the geometry of the injection slot.
A Vibration Technique for Non-Destructively Assessing the Integrity of Structures
Authors: Adams R. D. , Cawley P. , Pye C. J. , Stone B. J.
Published: February 2007

A method of non-destructively evaluating the integrity of structures is described and applied to structures for which a one dimensional analysis is satisfactory. It is shown how vibration measurements made at a single station in the structure can be used, in conjunction with a suitable theoretical model, to indicate both the location and the magnitude of a defect. Receptance analysis is used in this instance, but the principle is equally applicable to other techniques of mathematical analysis.

Experimental results are obtained on a variety of components, including straight prismatic bars, a doubly-tapered bar, and an automobile camshaft, excellent agreement between the predicted and actual damage sites being obtained. The axial mode of vibration is generally used, although somes tests are also carried out successfully in torsion.
An Elastic Mechanism for the Micro-Sliding Characteristics between Contacting Machined Surfaces
Authors: Burdekin M. , Cowley A. , Back N.
Published: February 2007

In order to explain the deflection characteristics when two contacting machined surfaces are subjected to normal and shear forces, a simple surface model is proposed. This model assumes that contact is in the elastic regime, and it is analysed for various loading sequences of the normal and applied shear forces. The results show excellent qualitative agreement with the experimentally observed characteristics. An attempt to compare the results on a quantitative basis is also made.
The Generation of Random Surfaces Representative of Abrasion
Authors: Buttery T. C. , Hamed M. S.
Published: February 2007

Theoretical models are developed to simulate random surfaces; the geometric shapes used in the theory are also used to form actual surfaces using a ‘single-grit’ approach. A particular feature of the work is the study of the effects of pile-up (cutting efficiency, β) on surface finish ( Ra). For a unit event, the theory relates surface finish to cutter geometry, pile-up and load; the equivalent parameters for grinding are the average slope of the abraded surface, process efficiency and average load per grit. Finally, similar experimental techniques are used to synthesize the formation of a ground surface at spark-out.
High-Speed Ground Transport—A Stochastic Model of Track Roughness and Misalignment
Authors: Balzer L. A.
Published: February 2007

One of the significant disturbances to a tracked hovercraft or any other high-speed ground transport vehicle is the roughness of the guideway surface together with misalignment of the guideway structure itself. Existing methods of describing this roughness and misalignment are reviewed and their shortcomings noted. A description is proposed which is valid in both statistical and wavelength-amplitude domains. Numerical data from the Tracked Hovercraft Ltd test track at Earith are analysed and a mathematical model proposed for a typical commercial H.S.G.T. guideway. A method of computer generation of typical roughness profiles is discussed.
Hydrostatic Seal Design
Authors: Laurenson I. T. , O'Donoghue J. P.
Published: February 2007

The literature contains numerous references to applications where the designer has utilized the advantages of non-contacting hydrostatic seals to solve problems of operating under conditions of high speeds, pressures and temperatures. Examples vary from gas designs for turbines and compressors to liquid applications such as boiler feed pumps and liquid-sodium pumps for nuclear reactors. It is the view of the authors that this type of seal, proved under these very difficult operating conditions, has considerable advantages when compared to ‘balanced’ mechanical face seals. In this paper, the principles of operation of hydrostatic seals are presented and design data are given for orifice-, capillary- and slot-controlled designs, including a comparison of their performances under variable-temperature conditions. A method for optimizing the location of the seal groove is presented.
The Generating Mechanism of Surface Roughness by Random Cutting Edges
Authors: Hasegawa M. , Tsukizoe T.
Published: February 2007

This paper describes a statistical approach for predicting the generating mechanism of the surface roughness produced by random cutting edges. The two-dimensional distribution of the generated surface roughness is derived by considering the distribution of the maxima of the cutting edges. The method is used to determine the root-mean-square roughness of the ground surface.
A Surface Vorticity Theory for Propeller Ducts and Turbofan Engine Cowls in Non-Axisymmetric Incompressible Flow
Authors: Hill V. P.
Published: February 2007

Starting from the basic Fredholm integral equations, a surface vorticity theory is developed for the prediction of annular aerofoil performance in three-dimensional flow. A mathematical model is proposed for the general case of the axisymmetric body in non-axisymmetric flow, using a Fourier series to represent circumferential variations in bound vorticity strength. Using the pure incidence case as an example, it is indicated how an economical solution of the flow may be arrived at by use of a digital computer. The theoretical pressure distributions obtained are compared with the results of wind-tunnel tests on an annular aerofoil model.
The Digital Measurement of Peak Parameters on Surface Profiles
Authors: Whitehouse D. J.
Published: February 2007

The effects of quantization, sampling and the numerical model on the digital assessment of peak density, peak height distribution and peak curvatures are investigated. It is shown that there are practical limits which should be adhered to in order to avoid erroneous results.
Research Note: A Twin-Rotor Cross-Flow Fan
Authors: Gunton M. C. , Holgate M. J.
Published: February 2007

A twin-rotor cross-flow fan, having two parallel-axis contra-rotating impellers at the entrance to a simple rectangular duct, is found to have a longer stable operating characteristic than an equivalent single-rotor fan.
Research Note: Influence of Pipe Surface Roughness on Friction Pressure Gradient during Two-Phase Flow
Authors: Chisholm D.
Published: February 2007

An equation is developed which enables procedures for predicting the friction pressure gradient during turbulent two-phase flow in smooth pipes to be extrapolated to pipes with rough surfaces.
A Laser-Doppler Investigation of the Flow inside a Backswept, Closed, Centrifugal Impeller
Authors: Adler D. , Levy Y.
Published: February 2007

A laser-Doppler technique is successfully applied to measure the flow field inside a closed, backswept impeller, through a rotating window. Results show that, in contrast to the flow in many radial-exit impellers, the flow in the backswept impeller is stable and attached. Further, comparison with an open impeller demonstrates the fundamental difference in the flow fields near the shroud.
Refined Theory of Damped Axisymmetric Vibrations of Double-Layered Cylindrical Shells
Authors: Markuŝ Ŝ.
Published: February 2007

The governing differential equations of vibrations of double-layered cylindrical shells are derived from classical thinshell theory. The outer layer of the shell is assumed to be viscoelastic, possessing high damping capacity to control vibrations (loss factor, β = 0.3). Decoupled torsional and coupled radial-longitudinal vibration modes are analysed by the method of ‘damped normal modes’. The present theory refines Kagawa and Krokstad's former analysis (1)‡. The results obtained point to a strong dependence of mechanical losses upon the thickness-to-radius ratio, h1/ R, even in the case of axisymmetric modes. This phenomenon was not recognized in Kagawa-Krokstad's approach.
The Characteristics of Spiral Vortex Flow at High Taylor Numbers
Authors: Sorour M. M. , Coney J. E. R.
Published: February 2007

This experimental investigation is devoted to the study of combined axial and rotational flow in a concentric annular gap, of radius ratio 0.8, formed by a stationary outer and a rotatable inner cylinder. Taylor numbers varying from the critical to an order of 106 will be considered. The investigation is divided into three parts, illustrating different aspects of spiral vortex flow. Firstly, the evolution of the flow with increasing Taylor number at a constant axial Reynolds number is studied by the analysis of the spectrum of the signal from a hot-wire anemometer. Secondly, the wave length and drift velocity of the spiral vortices are determined for the axial direction. Thirdly, the effects of hydrodynamic instability on the mean flow are investigated. It should be noted that the first and second parts are under adiabatic conditions, while the third is both adiabatic and diabatic, heat being transferred isothermally through the outer wall of the annular gap. Also, all of the measurements were made in the fully-developed region of the flow.
The Effect of Flexibly Coupled Loads on the Dynamics of Hydraulic Servomechanisms in Arm Prostheses
Authors: Broome D. R.
Published: February 2007

Hydraulic servomechanisms used as positioning control systems within arm prostheses are subject to very high loads. To investigate the effects of such loads on the dynamics of a hydraulic servo, a load-arm test has been constructed. Step-response tests on this rig show stable transients at low-load values which destabilize as load increases. At loads near system stall, a stable control system is again obtained. A mathematical model of the rig has been developed, based on a flexibly connected load, and this can be used to predict the initial destabilization. This model is further refined by the inclusion of a quasi-linear approximation to the steady gravitational load, and this then also demonstrates the further restabilization observed experimentally. It was noted during the tests that it was not possible to excite system instability when operating the servovalve manually. This then means that the servosystem will be suitable for its prosthetic operation where the user will operate the valve from anatomical sites. This stabilizing effect of manual operation is also explained.
Investing in Ideas in an R & D Department
Authors: Leech D. J. , Smart P. M.
Published: February 2007

This paper reviews some literature on project appraisal and concludes that most of the methods suggested have not been used in industry and that there are good reasons why they should not be used. One of the major criticisms of project selection methods is that most ignore the constraints imposed by limited resources. Many ignore the probabilistic nature of the problems.

A simulation model is developed in order that methods of project selection may be tested. The methods tested are a simple economic ranking procedure and a stochastic LP procedure which takes account of resource limits. A random selection is also tested in order that the benefits of the formal selection techniques may be judged.

Where the projects available are relatively small and numerous and are unlikely to cause scheduling problems in whatever order they are undertaken, the stochastic LP model does almost as well as an economic selection rule and significantly better than a random selection.

Where scheduling problems may be encountered, the stochastic LP model can yield significantly better results than an economic model which ignores resource limitations.
A Theory of Simple Water Curtains
Authors: Binnie A. M.
Published: February 2007

The small deflections of water curtains exposed to lateral pressures are analysed. The effects of steady and periodic pressures are examined, and some numerical results are obtained.
The Effect of Non-Steady Temperatures on Experimental Investigations of Flow Instability between Eccentric Rotating Cylinders
Authors: Markho P. H. , Mobbs F. R.
Published: February 2007

Non-steady-state operation makes it very difficult to measure the actual, ‘controlling’ fluid temperature sufficiently accurately. This effect has been quantified and shown to be significant for discrepancies in temperature measurement greater than 0.5 K. A method for correction has also been suggested and verified. It is tempting to speculate, on the basis of this study, that the general lack of quantitative agreement among experimental results of previous investigators in this research area may have been partly caused by thermal inadequacies in apparatus or procedure.
Investigation of Squeeze-Film Isolators for the Vibration Control of a Flexible Rotor
Authors: Nikolajsen J. L. , Holmes R.
Published: February 2007

This paper describes work in which the feasibility of controlling the synchronous and non-synchronous vibrational behaviour of a flexible rotor was investigated using squeeze-film isolators in series with the supporting journal bearings.
An Investigation into the Dynamic Effects on the Track of Wheelflats on Railway Vehicles
Authors: Newton S. G. , Clark R. A.
Published: February 2007

Wheelflats on railway vehicles are created by wheelslide in braking: the resulting imperfection in the running line generates dynamic forces and stresses at each subsequent revolution. The authors describe this problem and refer to earlier work on this topic. A field experiment is described, in which an irregularity in the railhead was used to simulate a wheelflat for a range of vehicles, and loads and rail stresses were monitored. The structure and solution procedures of three theoretical models of the vehicle/track system are outlined and typical results are compared with the experimental data to establish the adequacy and limitations of each of the models.

Although this paper is primarily concerned with railway track dynamics, the mathematical techniques described could be applied to any problem involving the impact loading of beams.
On the Computation of Heat-Transfer Coefficients from Imperfect Temperature Measurements
Authors: Owen J. M.
Published: February 2007

An approximate theoretical model is developed to estimate the effects of errors in temperature measurement on the computation of heat-transfer coefficients, h, from the numerical solution of Fourier's equation. The model predicts that, depending on the Biot number and the algorithm used, a small random error on temperature will produce an amplified random error on the calculated instantaneous value of h and a bias in the average value, . ‘Experimental results’, simulated using Monte Carlo methods, are in reasonable agreement with the model, and it is shown that improved estimates of the heat-transfer coefficient can be obtained by using smoothing curves to minimize the effects of noise on measured temperatures.

If the temperature measurements have a small positive bias, the theoretical model and ‘experimental results’ show that there can be a large negative bias in the calculated value of h. It is also shown that ‘missing thermocouples’ can be partially compensated for by using interpolation polynomials, but there are dangers that these will cause systematic rather than random errors.
Low Reynolds-Number Pipe Flow in the Vicinity of Three-Dimensional Obstacles
Authors: Gosman A. D. , Vlachos N. S. , Whitelaw J. H.
Published: February 2007

Numerical solutions of the three-dimensional Navier-Stokes equations are presented for boundary conditions corresponding to the laminar flow of Newtonian and non-Newtonian fluids in a round pipe with truncated sector-shaped obstacles. The influences of Reynolds number and sector angle on the velocity distributions, local shear stress and pressure drop are quantified and shown to be large. The results are complementary to those previously reported by Vlachos and Whitelaw (1)§ for axisymmetric obstacles, where related two-dimensional effects were quantified. They provide new information on three-dimensional, recirculating flow in ducts and form a basis for future calculations of corresponding turbulent flows.
On the Critical Weber Number for Coarse Water Formation in Steam Turbines
Authors: Ow C. S. , Crane R. I.
Published: February 2007

The widely quoted experiments of Moore et al. indicate that the largest stable drops resulting from atomization behind a blade, in typical low-pressure wet-steam flows, can be described by a constant critical Weber number, Wec, of about 21, obtained graphically by fitting upper-limit distribution functions (ULDF) to measured spectra. A non-subjective re-analysis of these data has been made, using Marquardt's algorithm for the least-squares estimation of nonlinear parameters to improve the fitting. It is shown that optimization of the ULDF fit increases Wec considerably in the case of supersonic blade-exit flow. However, replacement of the computed maximum size by that corresponding to a given cumulative mass is necessary to avoid distortion of the result by the small fraction of total mass contained in the largest drops. A cumulative mass of 99.9 per cent consistently gives Wec values near 21, confirming Moore's result, but indicating the need for further work on the Mach-number dependence of Wec.
A Numerical Procedure for Calculating Partly Elliptic Flows
Authors: Ideriah F. J. K.
Published: February 2007

A new finite-difference technique, designated EMIT, is presented for calculating flows that are parabolic (that is, boundary-layer type) in some regions and elliptic in others without recirculation. The technique uses velocities and pressure as the dependent variables, and employs a marching procedure in all regions of the flow, wherein calculations are made along only one plane of the flow domain at a time, and the entire planes are visited in an ordered sequence. An application of the method is made to the plume in calm, stably-stratified surroundings. For this test case, a comparison is made between the EMIT and the SIMPLE procedure of Patankar and Spalding, and the EMIT algorithm appears to be more efficient than SIMPLE.
Adjustment of a Rotor Model to Achieve Agreement between Calculated and Experimental Natural Frequencies
Authors: Done G. T. S.
Published: February 2007

This paper is concerned with the problem of adjusting the mathematical model of a system such that the computed natural frequencies coincide with those measured experimentally. The particular system considered is a laboratory turbine-rotor model, modelled mathematically by 42 Timoshenko beam elements and lumped masses. Model adjustments are made by assuming, firstly, Young's modulus and the modulus of rigidity to be variable, a change from standard values representing overall stiffness deficiencies in the mathematical model. In this case, a best fit to the lowest six natural frequencies, as measured experimentally, is made. Secondly, stiffness diameters are assumed variable, thereby allowing for deficiencies in the model near discontinuous changes of section, and in this case, the lowest six natural frequencies are matched exactly, but an overall measure of the differences between the actual and the stiffness diameters is minimized. An analysis for the rates of change of natural frequency with the various stiffness properties (i.e. the sensitivities) is presented, and the results of the manipulation discussed.
The Effect of Temperature Gradient on the Stability of Flow between Vertical, Concentric, Rotating Cylinders
Authors: Sorour M. M. , Coney J. E. R.
Published: February 2007

The effect of a radial temperature gradient on the hydrodynamic stability in the annular gap formed by two, vertical, concentric cylinders, the inner being rotatable and the outer both stationary and isothermally heated, was studied for the cases of zero and imposed axial fluid flow in the annular gap. For zero axial flow, it was found that the temperature gradient destabilizes the flow while not affecting the form of the secondary flow, viz. the classic Taylor vortex. For imposed axial flow, the point of neutral stability was modified only when natural convection was strong enough to affect the parabolic velocity profile associated with that flow; the extent of this modification was shown to depend on the direction of the axial flow. Also, the longitudinal temperature gradients within the gap were found to influence the axial wave number and the drift-velocity ratio.
Discrete-Time Modelling of a Squeeze-Film Bearing
Authors: Stanway R. , Burrows C. R. , Holmes R.
Published: February 2007

This paper describes the application of a discrete-time approach to the estimation of the linearized velocity coefficients of a squeeze-film bearing. It is assumed that motions in the vertical and horizontal directions are uncoupled. Sampled observations from laboratory experiments are processed digitally to yield estimates of the parameters in a vector-matrix difference equation. A transformation applied to this equation produces direct estimates of the oil-film coefficients. Verification of the estimated coefficients is achieved through the prediction of the dynamical behaviour of the bearing. In this way, the effectiveness of the experimental models is assessed and compared with predictions based upon short, uncavitated bearing theory.
Dynamic Synthesis of a Timing Device with Pulse Loading
Authors: Simandiri S. , Hahn E. J. , Kothari M. , Rao A. C.
Published: February 2007

This paper describes the experimental investigations which were conducted to verify existing theoretical vibration-amplitude predictions for centrally-preloaded, squeeze-film-bearing-supported rigid rotors. Very good agreement was obtained with all aspects of these predictions, including the degree of pressurization needed to achieve full-film lubrication and the complicated bistable operation behaviour. By developing the theoretical model for the more general case of a rigid rotor supported by unequal squeeze-film bearings at the ends, it is shown how existing theoretical data, derived on the basis of a symmetric rotor with symmetric motion, are readily applicable to the case of a rotor supported by squeeze-film bearings at one end only. The experimental rig consisted of such a rotor, and, although the results are based on a given bearing having a length-to-diameter ratio of 0.167, and did not allow for any significant variation in the radial support stiffness, nor for variation in the bearing dimensions, and the rotor speed did not exceed 7500 rev/min, it is concluded that the theoretical data predictions are valid in general. Their validity is questionable, however, should conditions be such that turbulence and/or unaccounted-for cavitation effects become significant. Squeeze-film bearing behaviour under such conditions warrants further investigation.

Slider-crank mechanisms are often used as timing devices, for example, to open and close valves at specified times. Such mechanisms are subject to pulse loads and their design is difficult. Here, a slider-crank mechanism with a flexibly-attached slider subjected to pulse loading is synthesized for position co-ordination. The pulse loading is expressed in the form of a Fourier series so as to simplify the analysis. A worked example is given to illustrate the synthesis procedure.
A Rapidly Converging Theoretical Solution of the Elastohydrodynamic Problem for Rectangular Rubber Seals
Authors: Ruskell L. E. C.
Published: February 2007

A theoretical approach is described which overcomes the problems of convergence previously associated with obtaining solutions of the elastohydrodynamic equations for a reciprocating, rectangular section rubber seal. Convergence of this method is extremely rapid. Results are presented which illustrate that it is suitable both for instrokes and outstrokes at realistic sealed pressures. Experimental measurements of pressure distribution are presented for comparison.