An investigation has been made of the effectiveness of reinforced flexible hoses in decreasing pressure fluctuations in a hydraulic circuit. An understanding has been obtained of the properties and length of hose required to achieve a quieter system. The existing theory of longitudinal wave propagation in hoses has been extended by considering the effect of fluid viscosity and by making an accurate allowance for the inner lining. The theory has been checked by comparing the wave properties obtained from resonance tests with those calculated from the physical properties of hose and fluid by using the theory. A method of calculating pressure fluctuations in a complete hydraulic system consisting of one or more lengths of hose has been developed. In many cases, motion of the ends of hoses can be neglected which simplifies the calculations. The results for simple circuits have been compared with those obtained experimentally. A theoretical investigation has been made of the effects of the physical properties of a hose on the wave properties. It has been found helpful to split up wall stiffness into two components corresponding to actual or effective extension of the reinforcing cords and to changes in cord angle. There are two ways in which hoses can be used to reduce the pressure fluctuations in a system. A short tuned length of hose can be used to reduce pressure fluctuation at a particular frequency, or a longer length can be used for broadband attenuation. Both approaches have been investigated theoretically and experimentally, although only the latter is of general practical applicability. High attenuation is achieved with extensible cords and with high loss factors associated with wall deformation. For this reason nylon reinforced hoses are effective. The theory also enables the normal surface velocity of a hose, and hence the sound power radiated from it, to be calculated.

A thorough study of standing waves in hydraulic lines is carried out using transmission line theory. Special emphasis is attached to the representation of standing wave patterns of different systems by three dimensional graphs. From this study a new experimental test method has been developed for evaluating the fluid borne noise characteristics of pumps and other hydraulic components. The validity and accuracy of this test method, named the "tuned length method", was assessed by comparison with other existing methods. Unlike many other experimental methods, the tuned length method is capable of testing hydraulic components at low mean pressures. The "tuned length method" was used to evaluate the inlet fluid borne noise characteristics of three gear pumps and an axial piston pump. A purpose built pressurized reservoir was used to control pump inlet conditions. Large pressure fluctuations were measured at some positions in pressurized suction lines and were found to be similar to fluctuations measured in pump discharge lines. The levels of pressure ripple in a pump suction line were found to have a significant affect on the air borne levels generated by the hydraulic system. There is strong evidence of air release occurring in the pump inlet passageway under normal operating conditions. This accounts for the very low pressure ripples in the suction line of a normally aspirated pump. However, this does not affect the volumetric efficiency of the pump. When the pump inlet is pressurized air release is inhibited and the pressure ripple can be very large. An axial piston pump was tested when boosted by another piston pump and the inlet characteristics were evaluated. These characteristics are very similar to those obtained when the pump is supplied by a pressurized reservoir. In order to maintain low fluid borne noise in pump suction lines the mean inlet pressure must be kept as low as possible. The existence of air disolved in the fluid in small quantities is favourable as it prevents very low instantaneous pressures and hence limit the possibility of cavitation. The use of a pressurized reservoir is reccommended for this purpose, as long as steps are taken to avoid solution of additional quantities of air.

This thesis describes the design, development and testing of a distributed parameter hydraulic system simulation program based on the method of characteristics, and is intended to extend and complement the work being carried out at Bath University on the computer aided design of fluid power systems on small computers. The first part of the thesis is an extensive literature review of distributed parameter techniques and related topics, and represents a stock-taking of current simulation methods and their applicability to fluid power system modelling. The method of characteristics is a numerical technique for analysing wave propagation effects in the time domain. A general program structure was designed whereby various systems could be analysed by subroutines modelling the behaviour of individual hydraulic components linked together by pipe models based on the method of characteristics. General aspects of the program operation were tested by simulating a hydrostatic transmission, good correlation was obtained with analytical results, and with a lumped parameter simulation. More specific problems of component modelling were investigated by simulating a Barmag type, 3 port pressure compensated flow control valve. The program was applied to the analysis of pump generated pressure ripple. Good agreement was obtained with experimental results demonstrating the ability of the method of characteristics, as programmed, to accurately predict high frequency effects in hydraulic systems. The program providing an alternative tool for analysing fluid borne noise, which is especially suitable for situations where transient effects are important. 006. The method of characteristics is not ideal for general hydraulic system simulation and the recommendations for future work include a scheme for incorporating it into the existing lumped parameter simulation language (HGSP) developed at Bath University.

Research into the financial management of construction plant and equipment maintenance is scant, despite the increased utilisation of mechanisation to augment productivity in recent years. This thesis addresses the shortage of meaningful research by developing a methodology for predicting the total average hourly maintenance costs of tracked hydraulic excavators operating in opencast mining. Initial pilot and field studies conducted revealed that maintenance management (in the form of record keeping and attitude to used oil analysis) within the plant hire and general construction industry was generally poor. Hence, the decision was made to focus the research upon plant operated by opencast mining contractors. Here, plant managers were found to utilise an optimum blend of predictive and fixed-time-to maintenance and also maintain a depth of machine history file data. Modelling total maintenance costs using multiple regression (MR) analysis at the five percent level of significance identified four key predictor variables. These were: machine weight; attitude to used oil analysis (regular use or not); type of industry (opencast coal or slate); and type of machine (backacter or front shovel). However, in order to determine the model's robustness an alternative modelling technique, namely artificial neural networks (ANN) was applied using the same variables identified as significant predictor variables in the regression analysis. Performance analysis conducted on the predictive power of both MR and ANN models revealed that overall the ANN model exhibited greater predictive performance. The thesis concludes with direction for future research and moreover, identifies the need for a more fastidious approach to maintenance management.

An analysis of a commercial vehicle drum brake fitted with a typical asbestos free friction material has been investigated by the finite element method. The "GAPFRIC" concept has been extended to model in three dimensions the frictional interface between brake linings and drum. This approach incorporates an accurate representation of the brake itself to include such features as the brake drum stiffener and mounting flange. The brake shoe representations include the actual web and platform thus eliminating the need for shoe stiffness approximations to a curved beam of uniform section as used in previous two dimensional work. The mechanical "GAPFRIC" analysis is combined with a thermal analysis of the brake to form a brake analysis package. The package is fully automatic; the output from each stage of the analysis is post processed and the results used to modify the original data file. Variations in physical properties exist between new and used friction material and these are incorporated in a five phase idealisation of the friction pair. Modifications to allow for the change of coefficient of friction with temperature were made by means of tables within the coding. In addition friction material wear was included in the analyses using an empirically derived wear criteria. Analyses were completed to investigate the effect of combined axial and circumferential distortions on temperatures at the friction interface, interfacial pressure distributions and subsequent brake performance. Predicted results show that high temperatures are reached at certain regions on the rubbing path and the temperatures may fluctuate during a brake application. Pressure variations are seen to exist both around and across the surface of the linings. The coupling of pressure and temperature variations combined with frictional changes over the lining produce changes that result in the frictional drag per unit area tending to be reasonably constant over the interface between drum and lining. The predicted values of brake torque and brake factor f rom the three dimensional analyses have been compared with results derived f rom the earlier two dimensional brake analysis and validated by comparison with measured results from a brake mounted on a dynamometer. Similarly predicted brake drum and lining temperatures were compared with measured values and some reasonable trends established. The work itself presents a better physical description of the behaviour at the friction surface during braking to improve the determination of brake drum performance.

No description available.

The following thesis investigates the performance and economics of a Pneumatic Water Engine capable of extracting energy from differential heads of water in the two to three metre range. Initial concepts are discussed and a system configuration is physically modelled at a laboratory scale. Outline designs using a variety of materials are developed and these provide a basis for the estimation of a probable capital cost using standard Civil Engineering methods. The proposed system is mathematically modelled using a lumped mass approach to the complex hydrodynamics. The resultant differential equations are solved by means of a variable Runge Kutta numerical analysis. The model includes the thermodynamic aspects of the system's compressible airflow. A computer program has been developed from the mathematical model and Is utilized in a series of parametric studies. An economic assessment based upon both the average power output achieved during the parametric studies and the probable capital cost of the system is presented, together with an estimate of the cost per kilowatt-hour of the electricity produced. This assessment takes into account maintenance costs, expected value of the energy produced and the possible effects of both Water Abstraction Charges and Local Authority Rating. In addition to the parametric studies a final, more rigorous optimization of the system involving a number of the many interacting variables has been undertaken. This optimization is achieved via Cumulative Evolutionary Design techniques involving the use of Genetic Algorithms. An optimal design of the chamber shape is achieved in the same manner.

No description available.

No description available.

No description available.