Search

The paper describes some apparatus which has been developed to measure those characteristics which are of interest in vehicle ride and handling. These are: Vertical, lateral and fore-and-aft tyre stiffnesses and damper characteristics. Suspension spring rates and friction, suspension geometry and suspension roll stiffnesses. Steering gear geometry and dynamic characteristics, moments and products of inertia of the vehicle and vibration characteristics of the seats. Some relevant theory and sample results are included in the Appendices.

Surface effects can influence the friction and wear characteristics and the fatigue behaviour of materials, so that any investigation of these phenomena necessitates careful study of the surfaces involved. Changes in topography, chemical nature, structure, and physical properties of surfaces subjected to sliding, rolling, abrasion, corrosion, deformation and repeated stressing have been studied using optical and electron microscopy and micro-probe analysis to obtain information of use in the elucidation of failure mechanisms and their controlling factors. Specific information from each technique enables comprehensive data to be accumulated. The paper reviews work which has been carried out in recent years, mainly from the technological viewpoint.

Several procedures for designing externally pressurized journal bearings have been presented. These vary from simple approximate solutions based on the bearing stiffness in the concentric position to full relaxation programs. In this paper the authors compare the predicted performance of bearings with experimental results. In addition to the static results obtained by the authors on a typical four-pocket grinding spindle bearing, the dynamic results of Patrick and Chen are also treated.

This paper develops a simple relationship between distance upstream and downstream of a row of blades and the velocity disturbances created by the passage of those blades. The relationship is compared with values obtained by numerical computation and measurement in an experimental axial flow compressor rig. The magnitude of vibration exciting forces and/or noise radiation sources due to potential flow interaction on a stationary row of blades is directly related to the magnitude of these velocity fluctuations. The analysis is therefore a basis ( a) for estimating the inter-row spacings for a turbomachine such that potential flow interactions are reduced below the levels of other forms of interaction, and ( b) of translating practical experience of noise and/or vibration excitation in existing machines to give reliable predictions for future designs. It is found that while potential flow interaction effects drop rapidly with increasing blade row spacing for low-speed machines, this is not the case for high speeds and very large spacings may, in fact, be required where the rotor blade speed is equivalent to a high value of Mach number. It is also found that the rate of decrease in effect is related to the circumferential wavelength of the disturbance, and comparisons between machines based on blade chords (as is the present normal practice) are meaningless unless the ratio pitch/chord is constant.

An earlier paper (1)† investigated roller and cage motion, friction torque, film thickness, and electrical resistance of a roller bearing. Further friction-torque measurements are presented and an analysis of friction losses in a roller bearing is made. Additional measurements of resistance are discussed.

This paper describes an experimental investigation into the static performance of a floating-pad journal bearing with four pads. Up to moderate eccentricities the test bearing was found to have a somewhat greater load capacity than an equivalent plain journal bearing, and there was no evidence of instability. The geometry of the bearing also allows high lubricant flows to be used for cooling purposes without requiring excessive supply pressures. Some difficulties were experienced with starting under load and with a self-excited vibration which occurred at moderate to high eccentricities. The results of the investigation suggest that this form of bearing is most suitable for low-load, high-speed applications.

The dynamic bearing characteristics of plain seals having appreciable length-to-diameter ratio are analysed by a perturbation method giving linear results. Non-linear effects have been treated in a more precise analysis, and a summary of the method and comparison of results with the simpler linear results is given. Some experimental results are given and compared with theoretical predictions. It is shown that length-to-diameter ratio has a considerable effect on seals of appreciable length, e.g. balance pistons, and that dynamic components of bearing action due to shaft rotation are comparable with the purely hydrostatic centring forces. Experimental results are shown to be reasonably in agreement with theory. It is concluded that the linearized bearing coefficients of seals given in this paper form a sufficiently sound basis for use in the vibrations analysis of pump rotors.

This paper describes details of a solution to the finite journal bearing problem, including the effects of elastic distortions in the bearing liner. Solutions for the particular case of a bearing of length to diameter ratio of 1, outside to inside diameter ratio of 1·3, and Poisson's ratio of 0·4 have been obtained and the results are compared with experimental results obtained with a Delrin plastic bearing. Good agreement between theory and experiment has been obtained. The theory, which is applicable to soft shell bearings supported in a rigid housing, predicts that: (1) the ratio of the peak pressure to the average pressure is reduced; (2) the bearing stiffness is reduced; (3) the minimum film thickness for a given load is reduced by elastic distortions at eccentricity ratios less than unity; and (4) the friction is reduced.

The C.E.G.B. are installing single shaft turbo-generators of 500 and 660 MW with solid coupled shafts. It is important to assess the extent to which the operation of these large machines might be affected by changes in alignment resulting from differential movements in the turbo-generator blocks. The paper sets out the development of turbo-blocks against the evolution of turbo-generators and associated plant; and discusses the problems which have emerged as a result. The authors investigated 12 existing reinforced concrete turbo-blocks in the 120-200 MW range to establish the extent and cause of differential movements in the concrete and their resulting effects on the machine. Level measurements were taken over a period of about three years on the machine floors and basements of these blocks. These readings were correlated with changes in concrete temperature, moisture content and variations in ambient conditions. Conclusions are drawn from the investigation which can affect the design and construction of concrete turbo-blocks and particularly certain procedures for machine alignment. The continued investigation on the 500/660 MW blocks now under construction is described, as well as methods adopted for the better distribution of heat in the turbo-blocks. Current procedures for design and construction of turbo-blocks are reviewed, relative merits of concrete and steel blocks compared, and the changing roles of plant manufacturer, civil engineer and block contractor/manufacturer considered. The tentative views formed by the authors from this study, from continental sources and from their discussions with power station superintendents and staff are submitted for discussion.

Geometrical imperfections in gears can alter significantly the ways in which load and motion are transmitted. This paper describes these effects in a manner which is applicable to all types of gears, leading to a greater understanding of the problems of accurate indexing, vibration and noise, and composite inspection techniques. Theoretical and experimental comparisons are made between single and dual flank composite testing methods, the results of which suggest that these methods need to be reviewed and extended.

In this paper the choice of design and materials for artificial human joints is considered as an engineering design problem, and some possible solutions which result from this approach are discussed. Various types of plain bearing design are examined and the use of flexible connecting members is suggested as an alternative possibility. It is considered that the plain bearing designs must be based on the requirement that they should operate with a full fluid film of synovial fluid, and possible designs and materials are discussed from this point of view. The effect of fixation problems on the total design is also examined, and designs which appear to offer a rational solution are proposed. It is concluded that for bearing engineers to make any major contribution to the design problem requires more information on the variation of joint load in both magnitude and direction in relation to the timing of joint movement. Research into the performance of plastic on plastic bearings is also desirable with more information on which plastic materials are biologically acceptable.

Existing methods of stress analysis for pistons assume axial symmetry of form and loading; they cannot predict stresses in the region of the gudgeon pin bosses. In the method of analysis proposed in this paper a piston is idealized as a portal, including the gudgeon pin bosses; allowance is made for the restraining effect of the rest of the skirt on this portal; the deformations of piston and gudgeon pin are made to conform. The idealized problem may now be formulated for solution by a standard structural analysis program; however this involves a considerable amount of hand calculation, especially for the evaulation of thermal stresses. In order to reduce this, a special purpose program was written. This uses the force method of structural analysis and can evaluate both mechanical and thermal stresses. Stresses measured during rig tests are compared with those calculated using the new method. Good agreement is obtained and, in the authors' view, the use of the ‘restrained portal’ idealization is confirmed.

In order to achieve the highest reliability in operation of large hydraulic turbo-machines, it is essential, amongst other things, to determine the magnitude not only of the static but also of the dynamic stresses under all operating conditions. The adjustable guide vanes of reversible turbine-pumps, for example, form a particularly critical component from the point of view of dynamic stresses, especially during pumping operations. This paper deals with the possibilities of predicting resonance conditions and of obtaining the magnitude of dynamic stresses in full-size machines on the basis of tests on model machines. The laws of similarity for forced and self-excited vibrations as well as vibrations in resonance are derived. It is shown that all kinds of hydraulically excited vibrations can be examined by model tests. It is permissible to carry out these measurements under reduced test head, provided that for the tested components different materials are used for the model and full-scale machine, and that the head ratio model-prototype is chosen accordingly. Suitable materials for model tests are recommended. The evaluation of the dynamic stresses for the full-size machine, based on the measured data of model tests, is shown for resonant and non-resonant conditions. Further, as an example, vibration investigations are described on the movable guide vanes of a pump-turbine, that is, using the derived laws of similarity.

The paper begins with a description of the various types of turbine generator foundations that have been installed and those that are intended for use in the near future. Then follows a section detailing the requisite characteristics of machine foundations and the factors that must be considered in order to obtain satisfactory operation. As the foundations support rotating machinery, the subject of vibration is discussed, including fundamental equations and their practical applications to the problem of calculating frequencies in the structures. Among the many factors that have to be considered when selecting the type of foundation are the size of machine and the station arrangement. The various factors are presented with comments. Important characteristics relating to the material properties and to the erection and behaviour of steel and concrete foundations are described. The topic of alignment is considered, including methods of maintaining machine alignment relative to the foundation structure. The causes of foundation distortion and the resulting effect on the alignment of the machine are summarized and some reference is made to precompensation in anticipation of misalignment developing.

The finite element technique has been used for the prediction of natural frequencies and mode shapes of a chassis structure. The program developed in Paper 1 was extended by adding an inertia matrix. The effects of shear and tapered beams were also considered and predictions of frequencies and mode shapes are compared with experimental results.

Information available for the calculation of stresses in and flexibility of mitred pipe bends (including lobster- back bends) under elastic conditions, for internal pressure loading, and in-plane and out-of-plane bending loading, is assessed. The results of Owen and Emmerson (4) for single mitre bends under internal pressure loading and their application to lobster-back bends are discussed. The stiffening effect of a ring of varying degrees of stiffness at the joint is considered in the light of some experimental results. The results of in-plane bending tests on two separate single mitre bends of different mitre angles are compared and a further comparison is made with published results on lobster-back bends. It is concluded that the results for single mitre bends under in-plane bending cannot be applied to lobster-back bends, which are more closely approximated by smooth-bend theory. Out-of-plane bending loading is briefly discussed.

The use of a line explosive charge in the expansion of water-filled brass tubes is investigated, both on a small experimental scale and on a large industrial scale. Results are presented showing how the radial velocity of deforming tubes and the distribution of hoop and axial strain in the deformed product are related. Metallurgical and some other aspects of the process are discussed.

Currently, systems which include diesel engines are designed and modified to avoid torsional vibration trouble on the basis of experience, and usually in the case of simpler systems a feasible one is found after few attempts. However, even these few attempts can be time consuming if the analysis is performed on a digital computer on a job shop basis. The purpose of the work described here, using a computer program to start from basic design data for the engines, alternators, and the like, is to achieve automatically a practically feasible and safe solution for the system, allowing for production restraints such as standard ranges of size of the various components. Economic considerations are also included. The systems examined are unbranched; simple examples being given.

A range of tests on simple radially grooved thrust washers is reported in which the number of grooves is varied from two to six. The mode of action by free thermal distortion is confirmed, the minimum film thickness occurring at 0·6–0·8 of the pad length. A degree of random waviness is shown to be beneficial, although it is likely that only half of the bearing circumferential length contributes to load carrying. The optimum number of pads appears to be four. The authors explore the use of multiple regression analysis in the design of such bearings. If several effects interact in the usual design process, it is shown that this technique can often give the direct influence of each design parameter separately without the need for iteration.

In marine application the medium speed diesel engine requires gears to adapt its operational speed to the speed with which the propeller performs highest efficiency. There are many configurations of marine gears. They depend on kind and number of engines as well as on the engine room installation. Reverse reduction gears of very different design, single input reduction gears, vertical or horizontal offset or coaxial, twin or multiple input form the main groups of this section of gear designing. The single stage gear unit of today shows very compact design and a high load carrying capacity. This is due to the surface treatment of the tooth flanks by hardening processes. Outstanding experience has been collected with carburised teeth, which have been ground for accuracy achievement. Effective profile modification for the purpose of high bending resistance, protuberance milling to keep the roots of the teeth untouched by the grinding wheel result in utmost resistance against wear and rupture. So the specific loading agreed to by the classification societies are fully justified.The required accuracy of those gears even at their low circumferential velocity is to compare with the precision of turbine gears manufactured according to BSS 1807. Important are full contact areas between the teeth, this requires careful observation of shaft deflection, bearing clearance, thermal distortions and rigidity of housing, thrust block and foundation in the hull. Another important condition to be observed satisfactory performance of marine gears is the absence of major torsional vibrations producing overload torque or even torque reversal. With diesel engines as power sources excitations of torsional vibrations are very likely to interfere with one or another of the natural ferquencies of the propulsion system. The fundamental connections required to calculate torsional vibration and the rise of torques caused by them are well known. With increasing familiarization of computer technique the calculation procedure has been refined to handle even manifold systems easily and practically reliable.The necessary over-all-elasticity of the torsional vibrating system thus can be calculated and realised. More and more there are used torsionally elastic couplings to dislocate the natural frequencies to the region of low speed. Good performance showed rubber couplings with metal bonded contact surfaces of special design, which allows a prestressing of the bonded surfaces. Their high torsional elasticity and damping property assures an overcritical operation. At the same time they allow for misalignment without any maintenance trouble. In some cases where it is advisable to avoid the turbulence zone at low speed at all, there are torsional elastic clutches available. They consist of the same elastic rubber elements combined with a clutching device with friction cones and pneumatically operated ring cylinder. Thus, it is possible to engage the whole propulsion system only after having reached the engine service speed. With disengaging and re-engaging the clutch great advantage is obtained during “crashstop”-manouvre, because the time for propeller reversal is much reduced. In any case torsionally elastic clutches are required for twin or multiple engine installations, where they have been applied originally and have proven an ample reputation of reliability. Nowadays, the tedency to install unmanned engine rooms leads to immediate measuring of engine torque : this is relatively easy with highly elastic couplings of linear characteristic, the torsional angles of which are large enough to furnish significant values for the purpose of measurement.The lecture points out the recent development which has been achieved on the side of Gearing and Couplings adequate to the development of the medium speed diesel engines.

The design theory for transmission shafting, both in the elastic and plastic states, is reviewed, with consideration of the effects of splines, fillets, and similar stress-raisers. Data are presented on the actual strengths of such shafts for various steels under static and fatigue loading, and the nature of the fatigue phenomenon briefly discussed. Some typical shafting failures are described, and the appropriate lessons drawn.

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.

The manner in which the overall energy efficiency of a small linear induction motor, previously used by the authors for impact extrusion, has been increased is described. The improved motor has been used to perform the impact blanking of 1 in and 2 in dia. circular blanks of aluminium, brass, copper, and mild steel in various thicknesses of strip. The energy required to blank when the piercing tool is initially moving at between 9 and 36 ft/s was found to be less than 50 per cent greater than that required for an identical slow-speed operation.

Experiments are described in which the break-out force associated with hydraulic lock on single-land pistons is measured. The test pistons used were of 0.5-in diameter × 1 in long, with diametral clearances in their bores in the range 2-20 × 10-4 in. The pistons were subjected to axial pressure drops in the range 0-5000 lbf/in2. The finish of the pistons and bores was closely controlled as regards surface finish, roundness and parallelism. It was found in all cases that a relatively small inherent lateral force acted on the pistons. The lateral force-pressure profile was found to increase linearly with clearance. Beyond a particular pressure for each clearance used, the lateral force necessary to generate hydraulic lock disappeared. Leakage flow rates were measured and used to help assess the attitude of a test piston in its bore. An hypothesis is given which explains the presence of hydraulic lock with single-land piston configurations. The hypothesis relates the hydraulic couple due to small residual tilts of pistons in their bores, and the mechanical friction in the reaction bearing required to support the piston against axial pressure forces. Experiments designed to test the hypothesis give positive support to it.

Work so far carried out confirms that the dynamic variations of axle load are similar in magnitude to the changes of axle load due to quasi-static weight transfer. The dynamic responses of the suspension, particularly the primary stage, are therefore considered to be of appreciable significance so far as adhesion is concerned. Road test results obtained with Bo-Bo electric locomotives having spring and kinematic drives as well as axle-hung motors are presented and these indicate the effect of specific suspension arrangements on variations of axle load.

The pure braking and cornering forces of a given tyre on a given wet surface at a given speed are functions of braking slip and slip angle respectively. These functional relationships are of great importance in connection with the handling and stability of vehicles and the behaviour of brakes and antilocking devices. When cornering and braking occur simultaneously the forces interact and the functional relationships are modified, with consequent effects on vehicle characteristics. The empirical data available at the Laboratory on these relationships, both for pure forces and for forces in combination, are presented. The known effects of such factors as speed, road surface texture, tread pattern, tread resilience, and tyre construction are reported, but since the work was carried out at various times and for various purposes the coverage is incomplete and uneven. The test vehicle, test procedure and the methods of measuring and evaluating the data are briefly described. Some data have been analysed statistically to discover the dependence of the various frictional coefficients on factors such as those mentioned above. It is believed that greater use should be made of these statistical techniques in future work. Raw data can also be converted into such practical quantities as braking distances, wheel locking times, etc., by computing theoretically the behaviour of model braking systems. An example of such a study is given. The principal features of the mutual effect of braking and cornering forces may be summarized as follows: (a) If curves of sideway force against slip angle are plotted for constant values of braking force, there is little change of initial slope, but the maximum sideway force and the slip angle at which it occurs are reduced. If, however, the curves are plotted for constant braking slip, then the initial slope is decreased and the slip angle for maximum sideway force is increased; at this same angle the sideway force at zero braking slip will only be slightly greater. (b) The presence of a fixed amount of angular slip reduces the initial slope of the curve of braking force against braking slip, reduces the maximum value of the force, and increases the slip at which it is attained. (c) In a few cases examined, if resultant force is plotted against resultant slip for a given speed, tyre, and surface, there is a tendency for the points to lie in a fairly definite band having a form similar to that of the braking force–braking slip curve.

An experimental rig has been constructed to establish the vibration characteristics of plain, dammed groove, and tilting pad bearings having a variety of clearances. The rig is perhaps unusual in not being a small piece of laboratory equipment, but consisting of a naval anti-submarine frigate turbo rotor (15 000 rev/min) running in two journal bearings each supported by an isotropic cantilever system of variable stiffness. Two pairs of induction probes mounted close to the test bearing monitored the shaft movement and provided an oscilloscope display of the movement of the bearing centre. Detailed information about the shaft oscillations was obtained from a wave analyser and vibration meter. The static rig natural frequencies with various bearing housing support stiffnesses were primarily determined. From preliminary running tests a fairly stiff bearing housing support, which gave a strong vibration of approxi-mately half rotational speed, was chosen for all subsequent work. With the rotor wheel balanced the tilting pad bearing tested was found to be free from serious vibration. The dammed groove type of bearing tested was also stable at low speeds but was not capable of stable operation at 15 000 rev/min and above. The plain bearing tested produced serious vibration above 9000 rev/min. The frequencies and amplitudes of vibration which occurred in different bearings with a deliberate rotor unbalance were also measured. Increase of the clearance lowered the onset speed of serious vibration. The locus of the mean position of the journal centre of the tilting pad bearing was almost a vertical straight line whereas all the other bearings showed the usual approximate semi-circle. Instantaneous oil film pressures up to 900 lb/in2 were measured using a pressure transducer in the bearing. As the design particulars of the bearings tested differed somewhat the results were not strictly comparable but nevertheless an approximate design rule has been suggested. Practical data provided about the vibration behaviour of the different journal bearing designs can be used by the many theoretical investigators in this field. This is important in view of the lack of practical attested results to substantiate or otherwise the many theories advanced.

n/a

Work on subsonic compressors is reviewed and traditional British and American methods of design are compared. Transonic compressors are now well established and recent progress, demonstrating the necessity for properly shaped blades in machines having high tip speeds, is examined. Advances in the computer-aided design of turbomachinery are described: these include the ‘Matrix through-flow’ and ‘Streamline curvature’ methods of calculating the meridional flow. Experimental results give preliminary confirmation of a method of annulus wall boundary layer prediction. Finally, current and future developments are discussed and an attempt is made to describe how an axial flow compressor may be designed a decade hence.

The results are given from a comprehensive investigation of the exhaust pipe configurations for five-, six-, seven-and eight-cylinder turbocharged two-stroke engines. The tests were carried out under cold conditions on a multi-cylinder pulse generator. For each engine two firing orders and the maximum number of alternative pipe arrangements compatible with minimum interference between cylinders were examined. Three nozzle sizes were tested for each basic configuration. The test results were analysed to determine the maximum efficiency of the exhaust pipe, expressed as the availability factor, the average scavenge ratio and the distribution of retained air between cylinders. Results of the investigation showed that in the multi-cylinder system the scavenge ratio increased with increase in nozzle area ratio, increase in the number of cylinders discharging into the pipe system, and with decrease in pipe length. The gas retained in the cylinders was found to increase with decrease in nozzle area to pipe area ratio and decrease in pipe volume. The availability factor was found to increase with decrease in nozzle area to pipe area ratio and decrease in pipe volume.

Illustrations of various faults and effects encountered on rolling contact bearings.

Erosion test in a model counter-rotating radial flow turbine has been performed to assist in the design of a 460-MW radial flow turbine. Three rows of erosion specimens were inserted at different radial locations in the last blade ring upstream of the blades to investigate the influence of the radial distance between the stages. Results showed that small droplets were formed and that erosion diminished with increased radial spacing up to a certain distance. A theoretical model for calculating droplet trajectories, sizes, and impact velocities has been derived, taking full account of wake velocity, variable droplet drag coefficient, and atomization. The calculations explained all the experimental facts and made it possible to convert the model test results to the full-size turbine showing no risk of erosion in the latter.

n/a

Water-tunnel experiments were performed to determine the free-stream characteristics of a series of 12 rudders with systematic variations in the amount of flap area and flap balance. The results include lift, drag, rudder moment and flap moment coefficients for a range of angles of attack and flap deflections. A comparison is made of the effectiveness of all-movable rudders, rudders with a fixed skeg and movable flap, and rudders with movable skegs and flaps. The latter were found to be by far the most effective. Rudders with fixed skegs are inferior to all-movable rudders unless the proportion of flap is very large. Flap balance does not appear desirable. Maximum flap moments, even with zero balance, are generally less than or comparable to the maximum moment of an ideally balanced all-movable rudder.