Research On Impedance Optimization Of Typical Bases Of Underwater Structure

There is a lot of mechanical equipment working on ship during its navigation.Their vibration will cause radiation noise.Ship noise can not only make travelers uncomfortable but also threaten sailors’ health.Sound equipment’s normal operation can be disturbed as well.As for naval ships,this kind of noise has adverse effect on their acoustic stealth performance.Bases usually connect mechanical equipment to hull.Impedance characteristics are used to describe their ability to obstruct vibration from equipment and serve as an important standard for the evaluation of base design.Therefore,it is of great theoretical and practical significance to study the size and topology optimal design of ship bases.A single object size optimization and a multi-objective size optimization of long base are studied.The thicknesses of plates constituting the base are used as design variables while the object is to minimize the impedance dispersion between different loading points.The optimization result shows that the maximum dispersion of base impedance can be reduced by 15.13% with 41.93% weight saving,while the minimum value of mechanical impedance does not decrease and the strength of the base meets the requirement.After that,improved lexicographical method is adopted in the multi-objective optimization.The objectives are to minimize the maximum value of impedance dispersion and to maximize the minimum values of loading points’ mechanical impedance.After optimization,the maximum dispersion can be reduced by 6.81% while the velocity impedance of point A increase 1.87% and B decrease 1.73% and the mass of the base can be reduced by 6.17%.A topology optimization towards webs of the base is conducted.The element densities of the webs are defined as design variables.The maximum value of impedance dispersion is set as the objective to be minimized,and the minimum values of mechanical impedance are restricted.An effective form of web hole is put forward according to the result.Result shows that the maximum dispersion can be reduced by 2.57% with 1.98% weight saving.Then the element density of the webs and brackets are defined as design variables at the same time.A long base with holes on webs and brackets is obtained through topology optimization.The final scheme’s maximum dispersion is 3.63% lower than the original one and its mass is cut by 6.85%,but the structure’s strength still meets the requirement.The topology optimization of cantilever base’s configuration is performed.A cuboid whose overall dimension is the same as the typical cantilever base is used to replace the base.The elements’ densities of the cuboid are set as design variables.Volume fraction of the design space is constrained and the objective is to maximize the minimum velocity impedance.A new structure of cantilever base is proposed according to the result.Multischeme comparison and topology optimization are used to determine the final structure and dimension.Finally the strength and vibration performance of the final scheme is calculated and proved to be acceptable.This work provides a valuable reference for the optimization design of ship bases and similar structures in terms of impedance characteristics.