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DENG Kai WU Yunfei LI Hua FANG Deming ZHONG Yingjie 《声学学报:英文版》2011,(4):417-426
Based on the energy conservation relationship,nonlinear thermo-acoustic effects of Rijke tube including instability range,saturation processes and higher harmonics modes were investigated.With coupling between the external flow and the inner space of a Rijke tube, the acoustic characteristics of self-excited oscillation were simulated.The experimental study was also carried out and the results were compared with those from simulation.The nonlinear factors which distort the acoustic waveform distortion were analyzed.From the results,it is seen that varying size of the nozzle outlet changes the acoustic impedance in the boundary, and leads to reduction of the nonlinear effects.The results show that the modes of self-excited oscillation could be influenced by the position of higher harmonics.In the large amplitude oscillation,the distortion of pressure wave within Rijke tube could be induced by the acoustic losses due to vortices on nozzle.It is found that the waveform distortion could be avoided by the shrinkage of nozzle. 相似文献
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XU Xiaodong CHEN Xiang LI Kaiyuan LIU Xiaojun CHENG Jianchun Christ Glorieux 《声学学报:英文版》2011,(4):391-397
A laser ultrasonics method is used to characterize the propagation properties of surface wave traveling on the surface of materials with sub-surface defect in 2D.Linear and nonlinear propagation properties of ultrasonics caused by the defects have been detected in experiment. A theoretical model is proposed and used to study the linear and nonlinear properties of ultrasonics caused by the defect.The numerical results indicate that the nonlinear ultrasonic wave will be excited when a finite amplitude ultrasonics propagates on the surface of materials with sub-surface defect.The theoretical analysis confirms that the nonlinear wave is caused by the "clapping"of the interface of defect instead of the mode conversions of ultrasonics. 相似文献
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The characteristics of ion beam extraction and focused to a volume as small as possible were investigated with the aid of computer code SIMION 3D version 7. This has been used to evaluate the extraction characteristics (accel-decel system) to generate an ion beam with low beam emittance and high brightness. The simulation process can provide a good study for optimizing the extraction and focusing system of the ion beam without any losses and transported to the required target. Also, a study of a simulation model for the extraction system of the ion source was used to describe the possible plasma boundary curvatures during the ion extraction that may be affected by the change in an extraction potential with a constant plasma density meniscus. 相似文献