Showing papers in "Archive: Journal of Mechanical Engineering Science 1959-1982 (vols 1-23) in 1968"
TL;DR: The recent advent of reliable thermocouple pairs of high melting point has provided new capabilities for high temperature gas measurement as discussed by the authors, and the errors involved in such measurements using fine wire t...
Abstract: The recent advent of reliable thermocouple pairs of high melting point has provided new capabilities for high temperature gas measurement. The errors involved in such measurements using fine wire t...
247 citations
TL;DR: In this article, the rotor and stator are regarded as linear multi-degree-of-freedom systems including damping, and dry friction at the clearance space is taken into account.
Abstract: Where a rotor runs within a clearance space, the clearance being comparable with rotor mass unbalance, the synchronous whirling behaviour of the rotor may be considerably affected by intermittent interaction with the stator at the clearance position. Discontinuity and jump phenomena may occur: in general, behaviour will be different with increasing speed from that with decreasing speed, and in either case zones may exist in which rotor-stator interaction is possible but not certain. In the analysis here presented, rotor and stator are regarded as linear multi-degree-of-freedom systems including damping; dry friction at the clearance space is taken into account. Discussion is limited to cases with radial symmetry, and interaction is assumed limited to the position of the clearance space. Polar receptances are used to establish equilibrium conditions with interaction, and speed zones are defined within which interaction may occur. Some hypothetical cases are fully explored, demonstrating that rotor-stator i...
162 citations
TL;DR: In this article, the authors measured the base pressure resulting from the abrupt expansion of an air jet from a circular nozzle into a concentric cylindrical duct or shroud, and observed that the ratio of the forcing jet pressure to base pressure remained constant.
Abstract: In the investigation described, the base pressure resulting from the abrupt expansion of an air jet from a circular nozzle into a concentric cylindrical duct or shroud has been measured. Stagnation pressure ratios of the forcing jet to atmospheric of up to six were used with shrouds of various lengths and diameters. As the primary or forcing jet pressure is increased and then decreased, the jet flow attaches and separates from the shroud wall and a hysteresis effect is exhibited by the pressure at the base of the shroud. With an attached flow, the base pressure attains a minimum value which depends mainly on the duct to nozzle area ratio and on the geometry of the nozzle, lower base pressures being obtained with convergent-divergent nozzles. When the jet pressure was increased beyond that required to attain the minimum value of the base pressure, it was observed that the ratio of the forcing jet pressure to base pressure remained constant.Noise measurements of the flow from the nozzle and shroud are prese...
66 citations
TL;DR: In this article, surface asperities are considered as wedge-shaped bodies which are plastically deformed wherever relative motion occurs between mating surfaces, and this plastic interaction produces interfacial forces.
Abstract: Surface asperities are considered as wedge-shaped bodies which are plastically deformed wherever relative motion occurs between mating surfaces. This plastic interaction produces interfacial forces...
57 citations
TL;DR: In this article, the authors examined the combustion processes in a dual-fuel engine through the computation and analysis of effective rates of heat release and the effect of deliberately introducing carbon dioxide along with the methane was also examined to simulate operation on methane sources containing carbon dioxide as a major contaminant.
Abstract: The combustion processes in a dual-fuel engine are examined through the computation and analysis of effective rates of heat release. Methane was adopted as the primary fuel and the effect of deliberately introducing carbon dioxide along with the methane was also examined to simulate operation on methane sources containing carbon dioxide as a major contaminant. An examination of the various heat release records suggests that dual-fuel combustion generally appears to undergo two distinct phases. The first phase is associated mainly with the consumption of the pilot and some associated gaseous fuel, while the second phase is dependent on the concentrations and the quality of the gaseous fuel employed. Under light audible knock, the first phase gets prolonged and persists over a much longer period than under knock-free combustion. The rates of burning are excessively high and project well over the second phase. This is indirectly indicative of the auto-ignition nature of knock and the simultaneous rapid burni...
52 citations
TL;DR: In this article, an exact solution for the natural frequency, axial distribution of phase and modal envelope is computed for a pinned-pinned, fixed-fixed and pinned-fixed span.
Abstract: The lateral vibration of a pipe conveying a fluid is investigated theoretically and experimentally. An exact solution for the natural frequency, axial distribution of phase and modal envelope is computed for a pinned-pinned, fixed-fixed and pinned-fixed span. Approximate one and two term Galerkin, Rayleigh-Ritz and Fourier series solutions are obtained and compared with the exact solution. It is found that a two term Galerkin or Rayleigh-Ritz solution is simple to evaluate and provides a good estimate of frequency and phase. The influence of axial tension and internal pressure is included.The experimental results are in agreement with theory at low flow speeds but show the difficulty of accurate buckling flow speed prediction.
50 citations
TL;DR: In this article, a series of the characteristic functions representing the normal modes of vibration are taken as the approximating functions for the bending displacements in the directions of the co-ordinate axes, leading to a considerable reduction in the number of elements in the final matrix equation and also considerably reducing the computing time.
Abstract: The Rayleigh-Ritz method is used to determine the natural frequencies and mode shapes of vibration of pre-twisted rectangular cross-section beams. The method is dependent upon a good choice of approximating functions for the dynamic deflection curves. In the present analysis, series of the characteristic functions representing the normal modes of vibration are taken as the approximating functions for the bending displacements in the directions of the co-ordinate axes. The choice of this particular series leads to a considerable reduction in the number of elements in the final matrix equation and also considerably reduces the computing time.The natural frequencies of vibration are obtained for various width-to-thickness ratio beams with pre-twist angle in the range 0-90°, and the mode shapes of vibration are presented for one particular width to thickness ratio beam. The results are compared to results obtained by other methods and to experimental results, and good agreement is shown to exist.
42 citations
TL;DR: In this paper, the free and forced transverse vibrations of a class of non-uniform beams, which includes as special cases the wedge and cone, were considered and the receptive and frequency equations, mode shapes and natural frequencies were presented.
Abstract: The free and forced transverse vibrations of a class of non-uniform beams, which includes as special cases the wedge and cone, are considered. Receptances, frequency equations, mode shapes and natural frequencies are presented for simple end conditions.
41 citations
TL;DR: In this paper, it is shown that the tube failure is a one-way buckling phenomenon where buckles can appear singly or in sequence, and that small deviations from the true cylindrical form are the critical elements in determining the value of the failure load.
Abstract: This paper describes experimental work which was undertaken to investigate the buckling characteristics of axially loaded cylindrical tubes and presents a theoretical basis for analysing tube behaviour.This is a radical departure from the existing theories in the literature which are not supported by experimental evidence. It is shown here that the tube failure is a ‘one-way’ buckling phenomenon where buckles can appear singly or in sequence. Two basic failure modes are established. One is due to an outward movement of the tube wall which produces a ripple or bellows formation and is fundamentally a yielding phenomenon. The other is inward movement which produces diamond shaped indentations and is an elastic failure. Mainly in the latter case, the small deviations from the true cylindrical form are the critical elements in determining the value of the failure load.
39 citations
TL;DR: In this paper, the problem of finding cam profiles with limited follower velocity, acceleration and jerk and minimal residual vibrations over a prescribed range of cam speeds is formulated as a mathematical optimisation problem.
Abstract: The problem of finding cam profiles with limited follower velocity, acceleration and jerk and minimal residual vibrations over a prescribed range of cam speeds is formulated as a mathematical optim...
34 citations
TL;DR: Numerical solutions of the Navier-Stokes equations have been obtained in the low range of Reynolds numbers for steady, axially symmetric, viscous, incompressible fluid flow through an orifice in a...
Abstract: Numerical solutions of the Navier-Stokes equations have been obtained in the low range of Reynolds numbers for steady, axially symmetric, viscous, incompressible fluid flow through an orifice in a ...
TL;DR: In this paper, the buckling of a long thin strip column rigidly supported along its length on one side, and subjected to a uniformly distributed force on the other, was studied. But the problem was not addressed in this paper.
Abstract: This paper is concerned with the problem of the buckling of a long thin strip column rigidly supported along its length on one side, and subjected to a uniformly distributed force on the other. It ...
TL;DR: In this paper, the Fokker-Planck equations governing the stationary probability density function for two-degree-of-freedom systems were solved by representing the density function by a multiple series of Hermite polynomials, and the constants in the series expansion were determined by Galerkin's method.
Abstract: A one-degree-of-freedom system and a two-degree-of-freedom system containing Dis-placement and velocity dependent nonlinearities subjected to stationary gaussian white noise excitation have been studied by the method of the Fokker-Planck equation. Non-linearities have been represented by suitable polynomials. The Fokker-Planck equations governing the stationary probability density function for these systems have been solved by representing the density function by a multiple series of Hermite polynomials. The constants in the series expansion were determined by Galerkin's method. Analysis is developed for the system containing nonlinearities described by suitable polynomials in velocity and displacement dependent forces. Comparisons were made between series and exact solutions for those special cases for which exact solutions are known.
TL;DR: The flexural vibrations of beams can be reduced by introducing sandwiched layers of energy-dissipating materials as discussed by the authors, where the equations of motion are derived for flexural vibration of symmetrical, multi-layer sandwich beams.
Abstract: The flexural vibrations of beams can be reduced by introducing sandwiched layers of energy-dissipating materials The equations of motion are derived for flexural vibrations of symmetrical, multi-layer sandwich beams Two types of beams are considered, depending on whether the central layer is energy dissipating when the number of layers will be n = 4i − 1, where i = 1, 2,…, or whether the material of the central layer is perfectly elastic when n = 4i + 1 The total number of equations of motion will be i + 1 for each type These equations will be non-linear when the properties of the energy-dissipating materials are strain dependent A numerical method of solution has been introduced by transforming the equations of motion into sets of non-dimensional simultaneous equations and using finite difference methods The simplest type of beam has three layers but even this leads to a set of four simultaneous equations of the twelfth orderIt is shown as an example that the strain dependence of a typical viscoel
TL;DR: In this article, non-dimensional parameters used in the presentation of theories of elastohydrodynamic lubrication are judged by the extent to which they can be given an acceptable physical meaning.
Abstract: Non-dimensional parameters used in the presentation of theories of elastohydrodynamic lubrication are here judged by the extent to which they can be given an acceptable physical meaning. A suitable...
TL;DR: In this article, the parametrically excited vibrations of a system with assumed small asymmetry of the shaft cross-section are discussed in terms of the motion of a symmetric shaft having the mean cross-sectional flexibility, and the equations of motion are solved by the approximate perturbation-variation method of Hsu.
Abstract: The parametrically excited vibrations of this system with assumed small asymmetry of the shaft cross-section are discussed in terms of the motion of a symmetric shaft having the mean cross-sectional flexibility, and the equations of motion are solved by the approximate perturbation-variation method of Hsu. Both features yield a more lucid appreciation of the motions expected than previous treatments: in particular, simpler explicit expressions for unstable bounds are given and forced vibrations due to mass unbalance are discussed with greater facility. The practically important case of nearly coincident natural frequencies is examined. The theoretical results are compared with analogue computation: good agreement with the approximate theory is found even for quite large shaft asymmetry.
TL;DR: Tension and torsion creep recovery tests on commercially pure copper at 150, 200 and 250°C are reported in this article, where an empirical equation relating creep recovery to these characteristics of the initial creep test is given.
Abstract: Tension and torsion creep recovery tests on commercially pure copper at 150, 200 and 250°C are reported. Recoverable strain can range from a negligible percentage to approaching 100 per cent of the total creep strain developed, depending on stress, creep period preceding unloading, and current recovery time. An empirical equation relating creep recovery to these characteristics of the initial creep test is given.
TL;DR: In this article, a closed-loop guidance control system for railway wheelset and suspension unit is presented, where the centre line of the track corresponds to the input, and the lateral position of the centroid of the wheelset to the output.
Abstract: Using a simplified mathematical model, the conventional railway wheelset and suspension unit is shown to behave as a closed-loop guidance control system. The centre-line of the track corresponds to the input, and the lateral position of the centroid of the wheelset to the output. Analysis of the system shows that, while it may be made stable at up to high speeds, the performance in the stable region is unsatisfactory in certain respects. This is attributed to the large forces of interaction between the wheels and rails at the points of contact, arising, in the case of the conventional wheelset, from creepage.These forces may be reduced and controlled by interposing a coupling having viscous characteristics between the wheels, in place of the rigid axle. The new arrangement is shown to be much more flexible, and capable of fulfilling a wide range of performance requirements.
TL;DR: In this article, the authors used secondary gas jets for providing side forces for the control of a single-stage rocket, which can be achieved by using a greater side force than the primary side force.
Abstract: Directional control of rockets can be achieved by using secondary gas jets for providing side forces. The present investigation is concerned with the fact that a greater side force can be achieved ...
TL;DR: In this paper, the results of direct-stress random-loading and block-loading fatigue tests on sharply notched mild steel specimens subjected to a tensile mean stress were given, and it was shown that the randomloading tests are more damaging than the multi-level block tests simulating the same conditions.
Abstract: Results are given of direct-stress random-loading and block-loading fatigue tests on sharply notched mild steel specimens subjected to a tensile mean stress. It is shown that the random-loading tests are more damaging than the multi-level block tests simulating the same conditions.Methods of endurance prediction in variable-amplitude conditions are discussed. In random-loading tests the hypothetical S-N curve method gives the better prediction provided that a suitable value of the slope parameter, d, is chosen; this value is not predictable from two-level block tests. The Palmgren-Miner method gave optimistic predictions.There was little difference between the two prediction methods when applied to the results of the multi-level block tests and the value of d suggested by two-level tests was satisfactory.
TL;DR: In this paper, the velocity of propagation of torsional plastic waves in metals stressed statically into the plastic range was determined for both copper and mild steel, and it was found that the velocity was the same as the elastic shear wave velocity.
Abstract: This paper is concerned with the determination of the velocity of propagation of torsional plastic waves in metals stressed statically into the plastic range. A new method was developed in which a tubular test specimen together with a concentric bar of a brittle material was twisted slowly such that when the specimen was stressed beyond its yield the brittle bar broke suddenly and transmitted a plastic torsional stress increment along the specimen. It was found that the velocity of propagation both in copper and mild steel was the same as the elastic shear wave velocity. Although consistent with the strain-rate dependent theory, the result can be explained in terms of the strain-rate independent theory provided the stress-strain curve for the appropiate strain rate is used.
TL;DR: For axisymmetric extrusion through conical dies, an admissible velocity field without discontinuities was obtained by superposition of basic flow patterns, based on this velocity field, the upper bound to the average forming pressure and the detailed mechanics were calculated for the extrusion of a rod with a semi-cone angle of 45° and a reduction of 75 per cent in area as mentioned in this paper.
Abstract: For axisymmetric extrusion through conical dies, an admissible velocity field without discontinuities was obtained by superposition of basic flow patterns. Based on this velocity field, the upper bound to the average forming pressure and the detailed mechanics were calculated for the extrusion of a rod with a semi-cone angle of 45° and a reduction of 75 per cent in area.Three different friction conditions along the die were considered and their influence on the deformation characteristics was discussed. Flow lines, velocity components, grid distortion, strain-rate components, effective strain rate, effective strain, and stress components were plotted. A comparison of the present results with those obtained experimentally (visioplasticity) shows good agreement.
TL;DR: In this article, the response of a mechanical system to the displacement excitation at a support is determined in terms of the natural frequencies and modes of the rigidly supported system and the cross-receptances between supports.
Abstract: The response of a mechanical system to the displacement excitation at a support is determined in terms of the natural frequencies and modes of the rigidly supported system. Receptances in closed and series forms are obtained for torsional and flexural systems and their properties are discussed. Support receptances are used to determine the modal and frequency changes caused by the introduction of flexibility at a beam support. The case of a beam on two flexible supports is then analysed using the cross-receptances between supports.
TL;DR: In this paper, the displacement analysis of a 6-bar linkage with auxiliary gearing is presented, and a method of kinematic analysis generally applicable to planar mechanisms is described.
Abstract: This note describes a method of kinematic analysis generally applicable to planar mechanisms. It is illustrated by the displacement analysis of a 6-bar linkage with auxiliary gearing.
TL;DR: In this article, the authors investigated the removal of water from the trailing edge of a low pressure steam turbine fixed blade by suction slots, experiments were made on a perspex test section in which a 1-in wide section of the suction slot was simulated.
Abstract: As part of an investigation to study the removal of water from the trailing edge of a low pressure steam turbine fixed blade by suction slots, experiments were made on a perspex test section in which a 1-in wide section of the suction slot was simulated.The flow characteristics are considered of the passage in the choked condition and a comparison is made with some two-phase critical flow theories. The theories are briefly presented and discussed, and the relevant formulae given. It is found that the homogeneous-equilibrium model grossly underestimates the discharge rates whilst all of the other flow models overestimate by at least 30 per cent.
TL;DR: In this article, a theory is presented to show that for liquid droplets evaporating in the "spheroidal" state on a hot surface, the evaporation rate may be expressed by the law:Available experimental evidence verifies the above relationship.
Abstract: A theory is presented to show that for liquid droplets evaporating in the ‘spheroidal’ state on a hot surface, the evaporation rate may be expressed by the law:Available experimental evidence verifies the above relationship.
TL;DR: In this article, a linearization of the von Mises yield criterion for plane stress problems is adopted and use of the flow rule associated with this criterion allows the variation of thickness across an element to be taken into account in the solution of the stress equilibrium equation; the strains can also be determined without resorting to numerical integration.
Abstract: A theory for the redrawing of cylindrical cups through conical dies is presented. In the absence of a pressure sleeve a zone of unconstrained drawing exists prior to the conical zone and the principle of minimum energy is used to establish the extent of the zone and the associated deformation and stresses. A linearization of the von Mises yield criterion for plane stress problems is adopted and use of the flow rule associated with this criterion allows the variation of thickness across an element to be taken into account in the solution of the stress equilibrium equation; the strains can also be determined without resorting to numerical integration. Because the deformation during redrawing takes place in a series of discrete steps, work-hardening can be conveniently included in the analysis. Bending and unbending contribute significantly to the process work and a more detailed examination of the mechanism is justified. The present theory allows the effects of friction, die angle and die intersection radiu...
TL;DR: In this paper, the effects of cycling of stress or temperature, and of in-phase changes of both, are predictable within reasonable limits, however, it is shown that with out-ofphase changes in stress and temperature, i.e. high stress/low temperature to low stress/high temperature conditions, a very rapid acceleration of strain can occur.
Abstract: Nearly all creep data are obtained under closely controlled constant conditions of load and temperature. Most high-temperature plant, however, is subject to cyclic variations of both, due to periodic off load or reduced load conditions.Test data for a C-Mn steel are presented for various cycles of stress and/or temperature. The effects of cycling of stress or temperature, and of in-phase changes of both, are predictable within reasonable limits. It is shown, however, that with out-of-phase changes in stress and temperature, i.e. high stress/low temperature to low stress/high temperature conditions, a very rapid acceleration of strain can occur.