bluuebunny/crossref_metadata_2025_split huggingface dataset:
Externally-Pressurized Gas-Lubricated Floating-Ring Porous Journal Bearings Part 2: Dynamical State Analysis
Authors: Malik M , Hori Y 
Published: February 2007

Theoretical stability characteristics of a new type of floating-ring bearing, proposed in an earlier paper, are presented. The results bring out the essential features of dynamical behaviour of the proposed bearing against the externally-pressurized plain porous journal bearing. The numerical scheme for the computation of the stability margin adopted in this work is different, yet simple and very efficient.
Integral Calculations of Transitional Boundary Layers
Authors: Fraser C J , Milne J S 
Published: February 2007

A method is presented for the calculation of two-dimensional, incompressible, transitional boundary layers under small pressure gradient and moderate freestream turbulence conditions. Established integral techniques are used in conjunction with an intermittency weighted model of the transitional boundary layer, and empirical correlations are used to predict the onset and length of the transition region. The only input data required to compute the entire unseparated boundary layer are the ambient pressure and temperature, the freestream turbulence level and the freestream velocity distribution in a power law, or a polynomial form. Alternatively, the freestream velocity can be input in tabular form as a function of x. The computed integral parameters and mean velocity profiles are seen to compare favourably with present and other published experimental data.
Elastohydrodynamic Film Thickness in Concentrated Contacts: Part 1: Experimental Investigation for Lubricant Entrainment Aligned with the Major Axis of the Contact Ellipse
Authors: Chittenden R J , Dowson D , Taylor C M 
Published: February 2007

Experimental investigations of the lubricant film thickness generated in elastohydrodynamic elliptical contacts have been undertaken since the early 1960s. The majority of these studies has been concerned with circular or near circular contact situations, although a wide range of geometries in which lubricant entrainment was directed along the minor axis of the contact ellipse has also been considered. The information available on lubricant film thickness in geometrical conditions where lubricant entrainment was aligned with the major axis of the contact ellipse has, however, been severely limited. The experimental investigation described in this paper is therefore concerned with the measurement of lubricant film thickness in the unusual geometrical conditions recently analysed theoretically by the authors (1, 2). The measurements were made with the aid of a twin disc machine for geometries ranging from a radius ratio of unity down to a value of 0.112. The experimental apparatus is described and details are given of the special test discs which were manufactured to produce such geometries. The capacitance measurement technique adopted is detailed along with the numerical model developed to allow the measured values of inter-disc capacitance to be interpreted in terms of the lubricant film thickness. The lubricant film thickness developed in four geometrical situations was investigated at four rotational speeds and five loads. This allowed a comparison to be made with the film thickness values predicted by recent elastohydrodynamic theory for changes in both speed and load. The film thickness deduced from the capacitance measurements was considered to be representative of that found at the centre of contact, and good agreement was found between experiment and all aspects of the theoretical predictions.
Elastohydrodynamic Film Thickness in Concentrated Contacts: Part 2: Correlation of Experimental Results with Elastohydrodynamic Theory
Authors: Chittenden R J , Dowson D , Taylor C M 
Published: February 2007

The existence of a coherent film of lubricant between highly loaded machine elements has been recognized for many years. Over this period of time measurements of film thickness have gone hand in hand with theoretical analyses in the field now known as elastohydrodynamic lubrication. The experimental techniques of capacitance, electrical resistance and X-ray measurement have been supplemented by the use of optical interferometry while the analytical expressions obtained with the use of elegant simplifications have been superseded by those developed from extensive and comprehensive computational procedures. These developments in experimental techniques have yielded a substantial number of measurements of both minimum and central film thickness. Likewise, the advent of the digital computer has allowed the derivation of a large number of solutions to the problem of elastohydrodynamic lubrication of concentrated contacts. All these results, covering a wide range of geometrical conditions, are to be found in the literature, yet little attempt appears to have been made to assemble a representative set of experimental data to permit a detailed evaluation of the theoretical formulae for elliptical contacts. The second part of this paper therefore considers the correlation between a number of experimental studies covering a wide range of operating conditions and geometries, and the predictions of recent elastohydrodynamic theory. Some of the important aspects of each set of experimental results are then considered and examples are provided which illustrate the following points: 1. Good estimates of lubricant film thickness may be obtained from the theoretical expressions recently derived, even when the dimensionless parameters involved are outside the ranges considered in the derivation of the formulae. 2. The discrepancies which exist between theoretical predictions and some of the measured film thicknesses are nevertheless quite large, even when the dimensionless parameters are within their usual limits. On the whole there is good agreement between experiment and theory, while the general trend of the results indicates that theoretical predictions may underestimate the minimum film thickness by about 10 per cent and the central film thickness by about 25 per cent. This measure of agreement is quite remarkable when the extreme difficulty of interpreting the magnitudes of effective and very thin mean film thicknesses between machined components in various forms of experimental equipment is considered.
Regimes of Traction in Elastohydrodynamic Lubrication
Authors: Evans C R , Johnson K L 
Published: February 2007

The rheological behaviour of the lubricant in an elastohydrodynamic contact depends upon the properties of the fluid and the imposed conditions of load, speed and temperature. For a lubricant of known rheological properties, it is shown how a ‘map’ can be constructed in which different areas of the map correspond to different regimes of behaviour. The coordinates chosen for the map are non-dimensional pressure and a parameter which is closely related to the film thickness. Given the load, speed and temperature, the operating conditions can be located as a point in the map. Maps have been constructed for three fluids: a mineral oil, polyphenyl ether 5P4E and a traction fluid. In general the maps display four regimes: (a) Newtonian, (b) Eyring, (c) viscoelastic and (d) elastic-plastic. Appropriate constitutive equations are proposed for each regime from which the traction forces can be predicted. The maximum traction coefficients calculated in this way are well supported by experiment.
Forces in a Heavy-Duty Drive Chain during Articulation
Authors: Hollingworth N E , Hills D A 
Published: February 2007

A rigid-body analysis is presented of the forces which occur in a chain bearing during articulation. Coulomb frictional effects due to unlubricated contact are included, as these provide the energy source for deleterious wear processes and affect the force distribution. The analysis differentiates between the two types of chain bearing—open end leading or open end trailing—and the results show that the force characteristics in each are significantly different. Experimental verification of the chain link tension is good.
Vibration of Hemi-Ellipsoidal Axisymmetric Domes Submerged in Water
Authors: Ross C T F , Johns T 
Published: February 2007

Ten thin-walled domes, of hemi-ellipsoidal form, were vibrated in air and while partially and fully submerged in water. The domes varied in shape from oblate ones of aspect ratio (AR) 0.25 to prolate ones of aspect ratio 4. The fundamental modal patterns for the oblate domes tended to be of axisymmetric form, while the fundamental modal patterns of the hemispherical and prolate domes tended to be of asymmetric or lobar form. The theoretical analysis was carried out by the finite element method, where the motion of the shell structure was represented by three different types of element and the motion of the water was represented by a solid annular element. Comparison between theory and experiment was found to be good.
Round Sudden-Expansion Flows
Authors: Khezzar L , Whitelaw J H , Yianneskis M 
Published: February 2007

This paper describes an experimental investigation of the water flows through one axisymmetric and two asymmetric round sudden expansions from a 48 mm to an 84 mm diameter pipe and eccentricities of the pipe axes of 0, 5 and 15 mm respectively. Flow visualization revealed the presence of vortex rings downstream of the plane of expansion for transitional Reynolds numbers (Re, based on the upstream pipe diameter and bulk flow velocity) and reattachment lengths were determined in the Reynolds number range 120–40 000 for all three cases. Detailed measurements of the three mean velocity components and corresponding fluctuations were obtained by laser anemometry for Re = 40000. Wall static pressure measurements are also presented. The results show that asymmetry of the inlet geometry strongly influences the distribution of mean and turbulence quantities downstream of the expansion and results in three-dimensional reattachment. In all three flows, the mean flow was nearly uniform and the turbulence nearly homogeneous at distances of seven diameters of the large pipe downstream of the expansion. Higher levels of turbulence were found in the asymmetric ducts with maxima twice those in the axisymmetric duct.
Improving the Overall Efficiency of Trucks and Buses
Authors: Hahn H W 
Published: February 2007

The paper reviews areas in which transport efficiency can be improved for heavy trucks, city buses and lightweight delivery vehicles. Areas considered include fuel consumption improvements by development of engine characteristics to suit specific operational requirements, the reduction of traction resistance, and the influence of the power-weight ratio on overall efficiency. A method of calculating efficiency is described which includes topographic data, driving regimes and alternative mission cycles, which enables alternative configurations to be evaluated. The paper concludes that powertrain components will have to be developed in future to accommodate a wider and better matched application while achieving improvements in reduced cost by greater use of standardized components.
The Relationship between Twist Axis and Effective Torsional Stiffness of a Motorcycle Frame
Authors: Raines M , Thorpe T E 
Published: February 2007

The design of a motorcycle frame has an important influence upon the machine's weave and flutter oscillation characteristics. This paper deals particularly with the torsional stiffness of the frame and it underlines the importance of the position of the axis about which the frame twists. This concept of a twist axis is introduced by reference to a simple parallel tube structure. It is demonstrated that because the twist axis moves, the torsional stiffness of a structure may reduce as individual members are stiffened. The position of the twist axis of a motorcycle frame is determined by finite element techniques and it is shown that an attempt, without due consideration of the twist axis, to improve its torsional stiffness, in fact has the opposite effect.
The Development and Performance of an Ambulance Stretcher Suspension
Authors: Leyshon D R , Stammers C W 
Published: February 2007

The deterioration of the medical condition of stretchered patients during ambulance transport is discussed. The dominant vibration is generally low frequency (below 10 Hz) and in the vertical direction. Assessment of the sensitivity of supine patients to front-to-back vibration is referred to. Methods of alleviating the vibration experienced by stretchered patients are discussed and particular types of stretcher suspension described. This suspension has a constant natural frequency of vertical oscillations over a wide range of patient mass. A stretcher ride height (above the ambulance floor) independent of patient mass is achieved. The stretcher suspension was tested over four types o surface (one ofl-highway), using a commercial vehicle having a chassis similar to that of a commonly used ambulance. Vibration of the vehicle floor and of the stretcher in both the vertical and the pitch senses was measured using accelerometers. Transmissibility of the stretcher suspension, the stretcher frame and the stretcher mattress was obtained. The vertical vibration level (averaged over the four types of surface) experienced by the patient is compared with vibration tolerance levels for supine patients. Vibration inputs are closest in magnitude to the vibration exposure limit in the range 1.5–4 Hz. The transmissibility of the suspension in this range is between −7 and −9 dB. Subjective evaluation of the suspension has been favourable.
The Use of Reliability Techniques on Traction and Rolling Stock
Authors: Puntis R , Walley D M 
Published: February 2007

Traditionally British Rail has used experience and sound engineering practice to ensure reliable traction and rolling stock. In-service reliability has been measured in terms of frequency of train delays in traffic. Availability is measured in terms of the number of vehicles available for service at a fixed time each day. Service problems are reported to the design authority at periodic service problem meetings. Modern traction and rolling stock specifications call for higher petformance to be obtained within tighter cost, size and weight constraints. To meet these demanding specifications, new system designs of increasing complexity have to be adopted. This has resulted in an increased engineering risk that the performance specifications will not be met. To ensure that reliability and availability remain acceptable, it is becoming increasingly necessary to use reliability modelling and assessment techniques. These are used from initial concept, throughout the design phase, and during the operational life of the equipment. This paper outlines some of the basic techniques which are available to assist in the solution of today's service problems and the design of tomorrow's vehicles. The application of these techniques will be illustrated by examples.
Process Integration—A Structured Approach to Operating Cost Reduction
Authors: Hill J C 
Published: February 2007

The technology of process integration is gaining wide acceptance within the process industries as an essential tool in the design of energy efficient processes. Within ICI plc initial research into the fundamental theory of the technology was reinforced by the establishment of applications teams comprising experienced process engineers who are expert in the technology. This method of utilizing the technology has created a dialogue between the research and applications teams over the past five years and has resulted in the development of a range of techniques which, while based on the initial theoretical research, are practical design aids applicable to a wide variety of processes. This paper indicates the benefits that can be gained from the application of the full range of process integration techniques and highlights some of the lessons that have been learnt, by companies new to the technology, in recent studies. It draws on experience gained within ICI plc and in studies carried out for a variety of major industrial companies by the Energy and Process Integration Service (EPI) which is a joint ICI-Harwell venture offering energy efficiency consultancy. The understanding of processes offered by process integration techniques generates insights which enable experienced personnel to identify ways in which the process itself can be modified to further improve its energy efficiency. The latest developments in the technology have produced a structured approach to the design of processes the aim of which is to reduce the total variable cost of operation.
Review of Parameters Influencing Hydraulic Forces on Centrifugal Impellers
Authors: Guelich J , Jud W , Hughes S F 
Published: February 2007

Both radial and axial hydraulic forces act on the impeller of a centrifugal pump. The radial forces are due to three different mechanisms: (a) radial thrust due to non-uniform pressure distribution around the impeller, (b) labyrinth forces and (c) impeller-diffuser interaction forces. The nature, size and origin of these forces are discussed. Steady radial thrust depends on the specific speed of the pump, type of casing (single or double volute, diffuser), geometric parameters and operation conditions including cavitation. The impact of these factors on radial loads is demonstrated and quantitative data are presented. Four different methods for radial thrust measurements are presented. Axial thrust on pump impellers is extremely sensitive to tolerances and to the labyrinth flowrate. Two methods for predicting axial thrust are discussed and predictions are compared to measurements on a multi-stage boiler feed pump. A number of parameters influencing axial thrust are treated.
Determination of the Initial Gaps between Flat Flanges without Gaskets
Authors: Lewis L V , Fessler H , Hyde T H 
Published: February 2007

This paper describes a method of finding the size and shape of the gaps which exist between the faces of an assembled but unloaded fiat-faced, metal-to-metal flange joint. The low-pressure leakage of 26 such assemblies has been measured experimentally, and pressure tappings have been used to record the pressure distribution under the contact faces of some of the flanges. Formulae are derived for the conversion from experimental data to gap size and shape. The method gives a very sensitive measure of gap height because of the cubic nature of the conversion formulae. Gap heights in the range 4–30 μm have been found. It is shown by finite element calculations that deflections due to boll loading of a perfectly flat flange are much smaller than the observed initial gaps.
Hovercraft Skirt Design and Manufacture
Authors: Wheeler R L , Key A N 
Published: February 2007

Skirts are the inflated structure which extend around and beneath a hovercraft that allow the craft to operate in rough seas and over uneven ground. The early skirts were designed on the basis of model testing and practical experience, but as the size of craft increased and improved performance was required it became evident that a more sophisticated approach was needed. This was carried out by developing computer programs to design the sectional shapes, investigate the quasi-static behaviour and derive the flat pat tern shapes from which the skirt is made. The responsive skirts fitted to large cross-Channel hovercraft, the Super 4, and the latest coastal craft, the AP 1-88/100 were developed using these techniques. Investigations into the cutting of sheets of non-metallic materials by a high-pressure water jet showed that this was ideal for the nylon woven fabric coated with either natural rubber or neoprene from which skirts are made. A cutting table with a NC tape-fed controller has been developed with a jet of 0.15 mm (0.006 in) diameter operating at 379 MPa (55000 lbf/in2). All the processes of producing a skirt, design, detailing with CADAM, part programming and cutting out are now integrated via computer links giving significant savings of time and costs.
Getting the Best Out of Your Workforce
Authors: Carter B A 
Published: February 2007

It has been found that output has increased as a result of increased interest in the workers and is not necessarily the result of improved working conditions. To this end it is important to develop a management approach that will improve a company's overall effectiveness. A common goal for all the employees must be given where the part each individual must play is detailed. This paper outlines various approaches that can be used to motivate employees. If they are implemented British industry may be able to raise itself from the bottom of the European industrial league.
A Review of Developments in the Acid Hydrolysis of Cellulosic Wastes
Authors: Anderson J , Porteous A 
Published: February 2007

The acid hydrolysis of cellulosic wastes has attracted the attention of many research workers around the world, especially in the last decade. This high temperature and pressure process results in the production of sugars which may be fermented to ethanol. By virtue of their cellulosic content, agricultural, industrial and municipal solid wastes may all be processed by acid hydrolysis with an end result of waste disposal and recycling/recovery of important energy sources. The complete process of the conversion of a cellulosic waste through to the end product and by-product utilization has to give due consideration to likely technologies. Some essential problems that have to be tackled are raw material storage, availability and preparation, the optimum acid hydrolysis and fermentation conditions and product separation methods. This paper is a review of the research that is taking place not only in the field of acid hydrolysis but also in the types of waste used, the concentration of the product sugars, the optimization of the fermentation conditions and the use of low-energy alcohol recovery methods to replace conventional distillation. Most research is at bench scale level with some pilot plants being reported. Also included is the authors' current work using a continuous reactor for the hydrolysis of newsprint.
Plastic Buckling of Imperfect Hemispherical Shells Subjected to External Pressure
Authors: Galletly G D , Blachut J , Kruzelecki J 
Published: February 2007

Plastic buckling/collapse pressures for externally pressurized imperfect hemispherical shells were calculated for several values of the yield point ( syp), the radius–thickness ratio ( R/t) and the amplitude of the initial imperfection at the pole (δ0). The well-known elastic–plastic shell buckling program BOSOR 5 was used in the calculations and two axisymmetric initial imperfection shapes were studied, viz. a localized increased-radius type and a Legendre polynomial. The numerical collapse pressures ( pc) for both types of imperfection were normalized and plotted versus λ ( a parameter proportional to[Formula: see text]. Approximate algebraic equations were then derived which give pc/ pyp as a function of λ and δ0/t. The values of pc given by these equations agree well with the computer results. Using the maximum values of the geometric shape deviations allowed by some national Codes, the corresponding theoretical buckling strengths were calculated. These were then compared with an approximate lower bound of test results obtained on externally pressurized spherical shells. The agreement between the two curves was not very good for BS 5500 but was fair for the DnV rules. The agreement with BS 5500 can be improved by increasing simp, the arc length over which the initial imperfections are measured. The foregoing lower bound of test results on externally pressurized spherical shells can also be obtained, approximately, using increased-radius and Legendre polynomial imperfections in which the ratio Rimp/ R is not restricted. The magnitude of the initial imperfection required for approximate agreement between the experimental and theoretical results was δ0/t ∼ 0.5. This seems a reasonable value. However, more study of this aspect of the problem is required in both the elastic and plastic buckling regions. The limitation of Rimp/ R ≥ 1.3 imposed by some Codes should also be reviewed, particularly in the plastic regime.