As the most dominative component under stress in an external combustion cam engine, the working condition of piston is very rigor. Once new design type and technical improvement is applied, it is necessary to analysis its thermal load and take secure steps. And the finite element model on each conditions of thermal is calculated, which is used to estimate the temperature field and provide a theoretical basis for further structural strength analysis and optimization design. Choosing analysis results of the piston as reference and taking five structural parameters of the piston as design variables, two objective functions including piston mass and maximal Von Mises stress are respectively considered. The optimum design of the piston is executed and the results indicate that it is feasible to improve temperature field and strength of the piston. These results enrich and develop the research on structural analysis and optimization of spatial engine, which are of guiding significance for analyzing engine strength and related problem in theoretically.
To grip control mechanism of plate structure radiation noise, a method to calculate radiation resistance was improved based on series approximation, by which the analytical solution of acoustic features were derived. And then the effects of the mutual-modal coupling were investigated in studying vibro-acoustic characteristics of a simply supported plate. Some conclusions have been given, such as the relationship between the radiated noise level and the space-time distributing, fundamental principles and measures of altering the space-time distributing, which supplied the academic and applied foundation for noise control.
To control the inertial forces and moments, the new type of the reciprocating cam engine with counter-position placement has been invented. Such a thermodynamic model based on the kinematic and dynamic analysis is developed and the engine performance is simulated. Under the same structural design parameters, the counter-position placement cam engine would have the inadequate work due to the increase of throttle loss. Then effects of the gas distributions to the dynamic performance of the engine are researched. Six variables are selected to optimize maximum average indicated power and the minimum indicated specific consumption with the method of discrete variable gridding. The results indicate that: (a) The new engine structure design can present advantage of excitation forces balance. (b) The structural design parameters and the thermal efficiency of the engine should be optimized especially those of the valve actuating mechanism to achieved desired power. (c) The parameters optimized of valve train can conform to the requirements of speed and economy, and it is feasible and reasonable to put forward the scheme of cam engine with the counter-position placement.
Abstract. To overcome the non-uniqueness of solution at eigenfrequencies in the boundary integral equation method for structural acoustic radiation, wave superposition method is introduced to study the acoustics characteristics including acoustic field reconstruction and sound power calculation. The numerical method is implemented by using the acoustic field from a series of virtual sources which are collocated near the boundary surface to replace the acoustic field of the radiator, namely the principle of equivalent. How to collocate these equivalent sources is not indicated definitely. Once wave superposition method is applied to sound power calculation, it is necessary to evaluate its accuracy and impact factors. In the paper, the basic principle of wave superposition method is described, and then the integral equation is discretized. Also, the impact factors including element numbers, frequency limitation, and distance between virtual source and integral surface are analyzed in the process of calculate the acoustic radiation from the simply supported thin plate under concentrated force. The extensive measures of acoustic field at the thin plate are compared with results obtain using different numerical methods. The results show that: (a) The agreement between the results from the above numerical methods is excellent. The wave superposition method requires fewer elements and hence is faster. But the extensive numerical modeling suggests that as long as 1 ka ≤ the volume velocity matching yields more than adequate accuracy. (b) The equivalent sources should be collocated inside the radiator. And the accuracy of a given Gauss integration formula will decrease as the source approaches the boundary surface. (c) The numerical method is applicable to the acoustic radiation of structure with complicated shape. (d) The method described in this paper can be used to perform effectively sound power calculation, and its application range can be extended on the basis of these conclusions.
Computing sound field from an arbitrary radiator is of interest in acoustics, with many significant applications, one that includes the design of classical projectors and the noise prediction of underwater vehicle. To overcome the non-uniqueness of solution at eigenfrequencies in the boundary integral equation method for structural acoustic radiation, wave superposition method is introduced to study the acoustics. In this paper, the theoretical backgrounds to the direct boundary element method and the wave superposition method are presented. The wave superposition method does not solve the Kirchoff-Helmholtz integral equation directly. In the approach a lumped parameter model is estabiled from spatially averaged quantities, and the numerical method is implemented by using the acoustic field from a series of virtual sources which are collocated near the boundary surface to replace the acoustic field of the radiator. Then the sound field over the of a pulsating sphere is calculated. Finally, comparison between the analytical and numerical results is given, and the speed of solution is investigated. The results show that the agreement between the results from the above numerical methods is excellent. The wave superposition method requires fewer elements and hence is faster, which do not need as high a mesh density as traditionally associated with BEM.
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