Lightweight And Vibration Control Research Of Bulk Carrier Structure

With environmental and energy problem more and more serious, the importance of ship lightweight is growing. Scholars at home and abroad have done a lot of resrarch from local compartment to the ship by using finite element method and all kinds of finite element software. Application of parameterization makes greater development in the ship structure optimization. It improves the study efficiency and better effect. Through reading literature, thinking carefully, it can be found that in terms of ship structure lightweight, there are still many researches worth further study. Especially to form a kind of series of guidelines which can solve the similar problems. So for the shortcomings and deficiencies of finite element analysis, a research was done from the following several parts based on a 54 m motor bulk carrier as the research object in this paper. This ship structure lightweight research is hoped to provide more valuable references.(1) Analysis of ship dynamic characteristics. Ship’s finite element model is established. The boundary conditions are determined. Ship vibration frequency restricted zones and the entrained water quality are calculated. Dynamic analysis is done on the whole ship to get the natural frequencies of the bulk carrier. The results show that there is a certain optimization space for the ship.(2) The establishment of bulk carrier piecewise rigid body equivalent model. A new equivalent method is proposed. It transforms the elastic ship model into piecewise rigid body model, which makes the model can be analyzed in the multi-rigid-body dynamics software, to achieve the goals of reducing the model size, speeding up the analysis and adding various influence factors. The equivalent method not only retains the thought of the traditional transfer matrix method, but also makes analysis object to keep the original geometry. It can meet the engineering accuracy requirements and guarantee the meaning and necessary condition when the ship equivalent rigid body is running in multi-rigid-body dynamics software.Piecewise rigid body equivalent principle is discussed theoretically in the paper. The feasibility and the effectiveness of the equivalent method are verified by rod, shaft and beam model. Engine room machinery and equipment, entrained water quality and the equivalent method of boundary conditions of the bulk carrier are studied. The rules of the original data is determined when the bulk carrier is equivalent to piecewise rigid body, and then piecewise rigid body model of the bulk carrier is established.(3) Parametric design of the bulk carrier piecewise rigid body model. Through the analysis of ship structure, the length, width and height of main longitudinal and horizontal components are selscted as design variables. Ship components are divided into groups. The expressions of the various components are written. The general representation method is summarized. The parametric rigid body model of the ship is obtained. When any size of components changes, the model properties can change accordingly. The sensitivity analysis of the design variables is carried on. Those design variables which are sensitive to quality and the natural frequency sensitivity are selected as the ship’s lightweight design variables to establish parametric modeling. It provides the basis for parametric optimization.(4) Multi-objective optimization of the bulk carrier. The steps of optimization are expounded. The advantages of multi-objective optimization are introduced. For the bulk carriers lightweight research and passive vibration control, size constraints of the ship’s shell and components are calculated and the lightest ship quality and minimum of the second order natural frequency are selected as as the optimization goals. The results of lightest quality, the minimum second order natural frequency and the corresponding sizes are obtained. The results show that the total quality of the ship decreases by 3.88 tons. The second order natural frequency decreases by 3.089% of the original one. Multi-objective optimization can reduce the total mass, and increased the reserves of frequency in dynamics.(5) Static strength check of the optimized bulk carrier. Finite element strength check is done on the optimized bulk carrier model to test whether the optimized plate, components size can meet the strength requirements or not. The results show that the optimized ship performances meet the requirements of the specification. The results also show that the lightweight method not only has good feasibility, but also has a profound practical engineering value and social significance.(6) Research of the relative moving objects interacting with ship. The vibration of bulk carrier is calculated and added to the piecewise rigid body equivalent model. Ballast water is discussed in three cases with the knowledge of the charging system dynamics and equivalent to the form of a fixed mass and a simple pendulum. The equivalent constraint of the goods is the centre of gravity moving trajectory. The rocking ballast water and goods equivalent model are established on bulk carrier model and then the relative moving objects interact with ship is studied. The interaction between relative moving objects and bulk carrier is discussed. The results of different simulation methods of goods in rolling are compared. The effects of ballast water to the stability of the ship are proved. The stability of the optimized ship is checked. The results show that the stability of the optimized ship is good. It meets specification requirements and actual needs.