Self-noise Prediction Method. Flank Array Sonar Platform Structure Vibration Study

Flank Array Sonar is a new type of sonar appeared in 1980s, it lies at the broadside of the submarine as passive sonar. And it is of submarine just corresponds to eyes and ears for human being. How to protect"the eyes and ears"from disturbing noise, especially from the disturbing machine noise is a hot task. In order to cut down the disturbing noise, we need to predict the levels and characters of the noise. But at present there are no effective methods to do that, an effective method is used to investigate noise at the place of Flank Array Sonar in this paper. Due to less of correlative references, it will not choose the factual submarine but some simple model as research objects.Firstly a new method which is the Wave Based Method (WBM) is brought forward for structure-acoustic studies to take place of conventional Finite Element Method (FEM) in this paper. The WBM models of uncoupled plate, uncoupled cavity, structure-acoustic coupled systems, structure-acoustic coupled unbounded systems and double plate-acoustic coupled systems are deduced in detail. Most of them validated with numerical examples, and the results show that the method has great advantage in convergence rate, calculation precision and calculation speed comparing with FEM, and also the method can extend the calculation range to mid-frequency.Secondly another new method which is the Wave Superposition Method (WSM) is brought forward for sound radiation studies to take place of conventional Boundary Element Method (BEM) in this paper. 3 kinds of radiators and the positions, shapes and number of dummy sources are considered. The results show that this method also has great advantage in convergence rate, calculation precision and calculation speed comparing with BEM, and the precision is higher as the radius of the dummy source is smaller, but usually the precision is enough when the radius is in the scope of 0.1 to 0.2. The node number of the dummy boundary surface should be taken as half of the one of the real boundary surface at least. And the node number of the real boundary surface should not be smaller than the one of the dummy boundary surface. For the slender radiator the precision is lowest with a single dummy source, the precision is highest with double dummy sources when they properly located, and the precision is higher with scaled dummy source.Thirdly as the traditional wave superposition method relies solely on mesh geometry, it cannot accommodate fast shape changes in the design stage of a consumer product or machinery, where many iterations of shape changes are required. And a new approach for representing geometry is introduced by constructing a uniform lattice in a 3-D digital work space. In the presented method, geometry is represented with boundary nodes or small lattice that can easily adapt to shape changes, therefore it is more suitable for shape optimization. The new method was validated by computing sound radiation of simple structures, and the results show that the aforementioned method was entirely feasible, but also the calculation precision is relatively higher.Fourthly according to the aforementioned complexions, the WBM combining with the WSM is used to sound radiation studies, and this method excels in convergence rate and calculation speed comparing with FEM/BEM.Lastly the WSM is presented to calculate the pressure field generated close to the surface of model using measured vibration data which obtained from a model experiment. And the results show that the near-field pressure field created by internal mechanical sources and the effects could be predicted from vibration measurements inside the model in the low-frequency band.