In the semi-free acoustic field, the actual acoustic pressure at any point is composed of two parts： The direct acoustic pressure and the reflected acoustic pressure. The general acoustic holographic theories and alg...In the semi-free acoustic field, the actual acoustic pressure at any point is composed of two parts： The direct acoustic pressure and the reflected acoustic pressure. The general acoustic holographic theories and algorithms request that there is only the direct acoustic pressure contained in the pressure at any point on the hologram surface, consequently, they cannot be used to reconstruct acoustic source and predict acoustic field directly. To take the reflected pressure into consideration, near-field acoustic holography for semi-free acoustic field based on wave superposition approach is proposed to realize the holographic reconstruction and prediction of the semi-free acoustic field, and the wave superposition approach is adopted as a holographic transform algorithm. The proposed theory and algorithm are realized and verified with a numerical example, and the drawbacks of the general theories and algorithms in the holographic reconstruction and prediction of the semi-free acoustic field are also demonstrated by this numerical example.展开更多
The variable flexibility of a fish body is believed to play a significant role in improving swimming performance.To explore the effect of non-uniform flexibility on the motion performance of fish under biologically re...The variable flexibility of a fish body is believed to play a significant role in improving swimming performance.To explore the effect of non-uniform flexibility on the motion performance of fish under biologically relevant conditions,we set up three different flexible distribution modes for a semi-free filament and compared the motion performance of different flexible distribution modes through numerical simulations.The filament is located in the wake of the front flapping foil;it can swing adaptively in the lateral direction according to the flow situation of the surrounding fluid and finally reach a stable position.The results show that the motion state of the filament will alter with a change in the flexibility of the filament,from moving in the vortex street to moving on the side of the vortex street.In the Bénard-von Kármán(BvK)vortex streets,the drag coefficient of the filament increases as the flexibility of the filament increases,and the value of the drag coefficient is at a minimum when the flexibility of the filament increases linearly along the length of the filament.Further investigation indicates that at 85%–90%of the filament length(starting from the leading edge),the flexibility of the filament begins to increase significantly,and the filament can obtain its best propulsion performance.The results of this work provide new insights into the role of non-uniform flexibility during the process of fish movement and provide a valuable reference for the design of bionic underwater vehicles.展开更多
From April to May in 1998, time budget and behavior patterns of semi-free Cervus nippon were studied in Pingshan Wildlife Experimental Farm. The results showed that grazing behavior accounts the most for activity time...From April to May in 1998, time budget and behavior patterns of semi-free Cervus nippon were studied in Pingshan Wildlife Experimental Farm. The results showed that grazing behavior accounts the most for activity time in spring, next for ruminating and bedding behaviors, and the least for alerting and moving behaviors. In a day, there are three grazing peaks (namely, 7∶00～10∶00, 12∶00～14∶00 and 16∶00～17∶00). The female spend more moving time than the maledo. The male spend more alert and bedding time than the female. C. nippong spend more grazing time in cloudy days than in fine and rainy days, whileC. nippon spends less alert and moving time in cloudy days. Sex and weather influence activity time budget of C. nippon. More significant differences exist between male and female’s moving behaviors (F=10 09, P<0 01), while significant differences exist between bedding (F=5 96, P<0 05) and alert (F=4 52, P<0 05) behaviors. More significant differences exist between grazing (F=8 39, P<0 01) and alert (F=6 11, P<0 01) behaviors due to weather factor, while significant differences exist between bedding (F=4 27, P<0 05) and moving (F=5 32, P<0 05) behaviors.展开更多
基金This project is supported by National Natural Science Foundation of China (No.10504006, No.50575063).
文摘In the semi-free acoustic field, the actual acoustic pressure at any point is composed of two parts： The direct acoustic pressure and the reflected acoustic pressure. The general acoustic holographic theories and algorithms request that there is only the direct acoustic pressure contained in the pressure at any point on the hologram surface, consequently, they cannot be used to reconstruct acoustic source and predict acoustic field directly. To take the reflected pressure into consideration, near-field acoustic holography for semi-free acoustic field based on wave superposition approach is proposed to realize the holographic reconstruction and prediction of the semi-free acoustic field, and the wave superposition approach is adopted as a holographic transform algorithm. The proposed theory and algorithm are realized and verified with a numerical example, and the drawbacks of the general theories and algorithms in the holographic reconstruction and prediction of the semi-free acoustic field are also demonstrated by this numerical example.
基金This work was supported by the National Natural Science Foundation of China(Grants 11862017,11462015 and 61963029).
文摘The variable flexibility of a fish body is believed to play a significant role in improving swimming performance.To explore the effect of non-uniform flexibility on the motion performance of fish under biologically relevant conditions,we set up three different flexible distribution modes for a semi-free filament and compared the motion performance of different flexible distribution modes through numerical simulations.The filament is located in the wake of the front flapping foil;it can swing adaptively in the lateral direction according to the flow situation of the surrounding fluid and finally reach a stable position.The results show that the motion state of the filament will alter with a change in the flexibility of the filament,from moving in the vortex street to moving on the side of the vortex street.In the Bénard-von Kármán(BvK)vortex streets,the drag coefficient of the filament increases as the flexibility of the filament increases,and the value of the drag coefficient is at a minimum when the flexibility of the filament increases linearly along the length of the filament.Further investigation indicates that at 85%–90%of the filament length(starting from the leading edge),the flexibility of the filament begins to increase significantly,and the filament can obtain its best propulsion performance.The results of this work provide new insights into the role of non-uniform flexibility during the process of fish movement and provide a valuable reference for the design of bionic underwater vehicles.
文摘From April to May in 1998, time budget and behavior patterns of semi-free Cervus nippon were studied in Pingshan Wildlife Experimental Farm. The results showed that grazing behavior accounts the most for activity time in spring, next for ruminating and bedding behaviors, and the least for alerting and moving behaviors. In a day, there are three grazing peaks (namely, 7∶00～10∶00, 12∶00～14∶00 and 16∶00～17∶00). The female spend more moving time than the maledo. The male spend more alert and bedding time than the female. C. nippong spend more grazing time in cloudy days than in fine and rainy days, whileC. nippon spends less alert and moving time in cloudy days. Sex and weather influence activity time budget of C. nippon. More significant differences exist between male and female’s moving behaviors (F=10 09, P<0 01), while significant differences exist between bedding (F=5 96, P<0 05) and alert (F=4 52, P<0 05) behaviors. More significant differences exist between grazing (F=8 39, P<0 01) and alert (F=6 11, P<0 01) behaviors due to weather factor, while significant differences exist between bedding (F=4 27, P<0 05) and moving (F=5 32, P<0 05) behaviors.
