In order to investigate acoustic radiation characteristics of underwater pyrotechnic combustion, Hartmann acoustic generator was applied and its main structural parameters effecting acoustic radiation characteristics were studied by using underwater acoustic measurement system. Experimental studies have shown that, when Hartmann acoustic generator was applied, the sound pressure level of underwater pyrotechnic combustion increased significantly because of the strengthening of turbulence degree. The distance between the nozzle and the resonant cavity is an important factor of affecting acoustic radiation characteristics of Hartmann acoustic generator. When the resonant cavity was placed in the unstable pressure area, it could stimulate strong sound waves. On account of the resistance of the water, the combustion products speed of reaching resonant cavity drooped and the collision strength between the feedback combustion products and the newly generated products reduced. So when the distance was larger, the SPL(sound pressure level) was smaller. The SPL of underwater pyrotechnic combustion increased and the acoustic frequency moved to the low frequency with the depth of resonant cavity increased, which is consistent with the acoustic characteristics of Hartmann acoustic generator applied in air.

For complex systems, the inhibition of self-excited vibration has always been a difficulty in engineering field. Currently, ultrasonic field energy as a special field energy could suppress vibration significantly. Unfortunately, vibration suppression mechanism has not been elucidated and intrinsic association with vibration field is still ambiguous. Here, we clarify coupling mechanism of ultrasonic field energy and unsteady vibration field energy firstly from the perspective of energy transfer and distribution. We find that it realizes spatially controllable redistribution of vibration field by changing distribution law of excitation waves, which makes vibration frequency migrate across scales. On this basis, we establish a relationship model between ultrasonic field energy and vibration field energy innovatively to accomplish precise vibration suppression. These insights generate important significance for active vibration suppression, which have broad applicability in flexible precision manufacturing, vibration inhibition of aircraft or satellite solar array, high-precision medical equipment and rail traffic stability control.