The attenuation coefficient of the impressed first sound due to the scattering of random background of the second sound is calculated.The result shows that this is an important factor which gives rise the attenuation ...The attenuation coefficient of the impressed first sound due to the scattering of random background of the second sound is calculated.The result shows that this is an important factor which gives rise the attenuation of the first sound in the vicinity of transition temperature T_(λ) at very high frequencies of GHz range.The predicted value agrees with the measured data in order of magnitude.展开更多
A model is developed to calculate the distribution of first-order velocity field caused by the coupled bubbles in an ultrasound field. Using this model, numerical investigations of velocity field have been made when t...A model is developed to calculate the distribution of first-order velocity field caused by the coupled bubbles in an ultrasound field. Using this model, numerical investigations of velocity field have been made when the two identical bubbles are driven well below resonance by an acoustic field with pressure amplitude exceeding cavitation threshold. Three representative kinestates of the coupled bubbles were chosen for analyzing the velocity distribution of surrounding liquid. The results show that the nonlinear oscillations of a bubble pair affect violently the radial velocity distribution of surrounding liquid, especially in the expanding phase. Symmetry of the tangential velocity distribution implies a possibility of attraction or repulsion of the bubble pairs.展开更多
A laser ultrasonics method is used to surface wave traveling on the surface of materials characterize the propagation properties of with sub-surface defect in 2D. Linear and nonlinear propagation properties of ultraso...A laser ultrasonics method is used to surface wave traveling on the surface of materials characterize the propagation properties of 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.展开更多
Three different wall sections with step shape were applied in the finite element analysis models set up to investigate the effect on low frequency sound field by wall modification. The heights of the step in three cas...Three different wall sections with step shape were applied in the finite element analysis models set up to investigate the effect on low frequency sound field by wall modification. The heights of the step in three cases are taken as equal, random and optimized. The optimized value is obtained by using an optimization process with an objective function of minimum fluctuation in sound field. The frequency responses of rooms with original and modified walls were calculated in a range from 60 Hz to 120 Hz. The results showed that the room with an optimized wall section had the flattest frequency response. Same thing was true as the ratio of the room was changed. The largest improvement on fluctuation reached 4.5 dB, In addition, wall section with semicircle and triangle were studied. The rooms that wall section had optimized radius and heights also gave a better performance than those that had fixed radius and heights. Therefore, it is possible to use optimized wall section to improve low frequency sound field.展开更多
文摘The attenuation coefficient of the impressed first sound due to the scattering of random background of the second sound is calculated.The result shows that this is an important factor which gives rise the attenuation of the first sound in the vicinity of transition temperature T_(λ) at very high frequencies of GHz range.The predicted value agrees with the measured data in order of magnitude.
基金supported by the National Natural Science Foundation of China(Grant Nos. 10904068, 10834009, 11174138, 81127901, 11204168 and 11174139)Fundamental Research Funds for the Central Universities(Grant No. GK201002009)the Natural Science Foundation of Shaanxi Province(Grant No. 2010JQ1006)
文摘A model is developed to calculate the distribution of first-order velocity field caused by the coupled bubbles in an ultrasound field. Using this model, numerical investigations of velocity field have been made when the two identical bubbles are driven well below resonance by an acoustic field with pressure amplitude exceeding cavitation threshold. Three representative kinestates of the coupled bubbles were chosen for analyzing the velocity distribution of surrounding liquid. The results show that the nonlinear oscillations of a bubble pair affect violently the radial velocity distribution of surrounding liquid, especially in the expanding phase. Symmetry of the tangential velocity distribution implies a possibility of attraction or repulsion of the bubble pairs.
基金supported by the National Natural Science Foundation of China(11074126,10674069)NSFC-KOSEF
文摘A laser ultrasonics method is used to surface wave traveling on the surface of materials characterize the propagation properties of 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.
基金This work was supported by Excellent Youth Science Foundation of China, Grant (10105417) National Natural Science Foundation of China, Grant (10474046).
文摘Three different wall sections with step shape were applied in the finite element analysis models set up to investigate the effect on low frequency sound field by wall modification. The heights of the step in three cases are taken as equal, random and optimized. The optimized value is obtained by using an optimization process with an objective function of minimum fluctuation in sound field. The frequency responses of rooms with original and modified walls were calculated in a range from 60 Hz to 120 Hz. The results showed that the room with an optimized wall section had the flattest frequency response. Same thing was true as the ratio of the room was changed. The largest improvement on fluctuation reached 4.5 dB, In addition, wall section with semicircle and triangle were studied. The rooms that wall section had optimized radius and heights also gave a better performance than those that had fixed radius and heights. Therefore, it is possible to use optimized wall section to improve low frequency sound field.
