Naval Vessel Shape Design Considering The Radar Stealthy Performance And Vibration Reduction Optimization

In this paper, two kinds of optimization problem were studied for stealthy ship, one was the shape of the stealthy ship optimization to reduce RCS values, and the other was the mounting of the gearbox from the ship to reduce noise.Radar cross section (RCS) reduction technologies are very important in the survivability of the military naval vessels. Ship appearance shaping as an effective countermeasure of RCS reduction redirects the scattered energy from one angular region of interest in space to another region of little or no interest. To decrease the scattering electromagnetic signals from the ship scientifically, optimization methods should be employed in the ship appearance shaping. Based on the assumption that the RCS reduction of entire naval vessel could be obtained by the shape optimal RCS reduction design of characteristic sections, the mathematical formulations for cross sectional shape optimal design are studied. Because of the computation-intensive analysis and singularity of the problem, the conventional optimization methods can not meet the requirements. In this paper, two kinds of optimization methods, response surface method (RSM) +GA, and step by step GA method, are proposed to solve the present optimization problem respectively. Comparative study on RSM+GA and step by step GA method was made through several numerical examples. It showed that RSM+GA method can reduce the computation-intensive analysis in the surrogate optimization model construction, but it maybe converges at the local optimum solution. As to the step by step GA method, the optimization model needn't to be approximated and the optimization procedure convergences very fast, but the optimization results maybe depend on the initial designs. Computational results of the conventional and the optimal design verified the effectiveness of the proposed design methodology.The structural dynamic optimization design of the novel gearbox mounting is presented to reduce the vibration transmissibility in designated frequency domain. Four kinds of structural optimization formulations minimizing weight of the mounting under vibration level difference constraints are established: 1) the size optimization of ribs; 2) the topology optimization of ribs; 3) the topology optimization of the bottom of the mount; 4) combined the free-size optimization of ribs and the topology optimization of the bottom of the mount.. The optimization results showed the improvement on vibration level difference from 5dB to 12dB of gearbox mounting. The plate which mainly affects the vibration transmission is identified by optimization. New structural topology of the plates in gearbox mounting is discussed. Further more, the optimal placement of damping material was studied under vibration level difference constraints.