The Study Of Dynamical Optimizing On Stiffened Plates With Frequency Preserve Of Hull

The hull vibration(whether the hole hull vibration or the local vibration) can bring on the discomfort of the person in the ship, affect the work of the equipment and the instrument, as well as it can bring on the alternate stress of the component, speedup the fatigue damage of the structure. Since the ship engine room and the superstructure are the working and living area, the designer should calculate the inherent specialty of the each deck in the design phase, so that the vibration frequency can be distinguish whether it is satisfied the frequency preserve or not (the ratio between the inherent frequency of the local structure and exciting frequency is little than 0.7 or great than 1.3). If the vibration frequency was satisfied the need of preserve, the resonance and the bad vibration will be avoid. As a result, it's significant to predict the local vibration of the decks exactly. And another critical problem is how to design the structure reasonable to avoid the frequency preserve and resonance, on the basis of predicting inherent specialty of the hull local vibration exactly. Previously the structural dynamic design is based on experiences, so it will take a lot of time and is hard to find the best plan. This thesis presents a dynamic optimization calculation method for stiffened plates. This method can find the optimization solution to avoid the frequency preserve in dynamics and save more time and cost.Following jobs were done in the course of graduate:First, the quadrangle element with 4 nodes and the void beam element with 2 nodes and 12 freedom were conformed on the Mindlin suppose condition, as well as the calculate model of the stiffened plates. It can well reflect the characteristic of the structure to disperse deck structure to stiffened plates model, and the calculate result of the inherent specialty will be close to the real. The beam' inertia moment in the stiffened plates was studied, and a new and useful beam element was put forward. While the FORTRAN language was compiled to calculate the geometry specialty of the beam element and the inherent specialty of the stiffened plates model.Then, the dynamical sensitivity of the stiffened plates was analyzed. The dynamic sensitivity analysis is the important content of structure dynamics, and it can be used to the dynamical optimizing and amending of the structure as well as parameter identifying. On the basis of discussing on the beam element, the thickness of the plate element t and the inertia Iy as the parameters of sensitivity analysis were discussed to analyze the structure parameter by themethod of the difference sensitivity analysis. The more sensitive parameters were get after analysis, and it can be used to the amending of dynamical optimize.At last, the stiffened plates were optimized. The sensitivity analysis of the stiffened plates has show way for the amending of dynamical optimize. The reasonable parameters avoiding the frequency preserve were deduced according to the result of sensitivity analysis, amending the parameters of the plate element and the beam element, and feeling the demand of static stress, craftworks etc, at the same time, changing the boundary restriction and centralizing or distributing the mass can also be taken into account to avoid the frequency preserve. That is the process of dynamical optimizing.