Warship’s Cantilever Structure Stealth And Dynamic Characteristics Optimization

As one of the most important sources of radar reflection, enclosed mast directly affects the stealth performance quality of overall warship. Meanwhile, enclosed masts structure is quite complicated. If the structure is forced to produce a resonance, the service life and normal work of precision instruments will be disturbed, and the improvement of mast’s dynamic characteristics will be difficult. So the optimization of outside shape’s radar stealth and the internal supporting structure’s frequency of warship’s enclosed mast are very meaningful.First, the calculation and optimization method of enclosed mast’s stealth and dynamic characteristics were studied. The calculation methods for electromagnetic reflection were inducted and analyzed. Calculation formulas of Physical Optics based on triangular elements were deduced, physical optics program, which contains a multiple shade judge function, was written. Four existing stealth performance evaluation criteria in the aircraft industry were discussed, and introduced into in the field of ship stealth assessment. Quadrilateral four node isoparametric element based on the Mindlin plate bending theory was deduced. The inherent dynamic characteristics’calculation of the finite element model, which is consisted of plate element and beam element, was analyzed. Genetic Algorithm and Evolutionary Strategy were introduced and compared, and the adaptive genetic algorithm program was written in this paper. Those two evolutionary algorithms, respectively, were used to combine the physical optics program with the finite element program, and the stealth optimization and frequency constraint optimization of simple cantilever structure were realized.The mast design of Royal Navy’s type-45destroyer was taken as the RCS model to the analysis of four evaluation criteria:the maximum RCS value within the threat area, the average RCS value within the threat area, the average probability of radar detection and the probability greater than the critical RCS value. Based on the typical radar detection conditions, the RCS distribution of the octagon mast was calculate. Results showed that specular scattering of surrounded plates is the main radar scattering source of the mast. The radar cross section distributions of mast models, which have different surrounded plate’s angle, were compared and multiple evaluated. The result indicates that the initial mast model has a good stealth performance in every criterion, and the stealth design of type-45destroyer’s mast is reasonable. The feasibility of four evaluation criteria in the mast stealth performance evaluation is validated.Using the adaptive genetic algorithm, the closed-wide mast was optimized with the objective function, which was respectively made through four existing stealth criteria above-mentioned, and the comparative analysis of optimal mast design in each stealth criterion was put forward. Every optimal mast design in every criterion has a better radar stealth performance, and the RCS distribution of each optimal design has a certain similarity. The result also indicates that the optimization of the RCS value of characteristic angle of mast is invalid, and the adaptive genetic algorithm has shown good convergence to solve the mast shape stealth optimization problem.Based on an adaptive evolutionary strategy algorithm, the enclosed mast which has been stealth optimized was taken as the structure optimization model. Internal supporting structures and the frequency range was established. With the plate thickness and stiffener position of the mast structure was constant, the total quality of stiffener was taken as the objective function, and the frequency forbidden zones was taken as the constraint, the stiffener type of each stiffener position was optimized. Finally, based on the stealth optimal geometric shape, a mast design which has got the light quality and satisfies the requirement of frequency was put forward.