Development Of Ship Structure Program Based On Inertia Release Principle

The inertial release technology is suitable for simulating unconstrained structural mechanics problems.All major commercial finite element software developed by foreign countries have inertial release functions.However,it is difficult to see the "trace" of this function in the special ship structure finite element program developed by researchers in our country’s shipbuilding industry.When the ship is still in the water,the gravity and buoyancy are balanced,and it is in a free and unconstrained state,which is the loading state and boundary conditions of the ship in the real world.However,in the finite element analysis,due to the errors and approximations in the process of load application,it is difficult for the force system of the whole ship model to achieve absolute balance.In this situation,if the solution is solved in the traditional way,the influence of unbalanced external load on the structure will be presented in the form of concentrated force(ie,constraint reaction force),which violates the precondition of freedom and unconstrained.The use of inertial release technology to solve the problem can distribute the influence of unbalanced external loads on the structure to all nodes in the form of body force(ie,inertial load),without generating constraint reaction forces.The more balanced the load applied to the structure,the result obtained by using the inertia release technique will also be closer to the real situation,and the floating state calculation is an effective way to achieve the balance of the ship’s gravity load and buoyancy load.First of all,this paper adopts a new type of floating state algorithm to calculate the floating state of a ship with a large opening channel.The algorithm is suitable for analyzing the composite structure of convex polyhedron.Several tetrahedral elements are used in the calculation model to describe the shape of the floating body,and the inner and outer layers are iteratively used to simulate the heave and rotation of the floating body in the calculation method.After iterations,the ship’s gravity and buoyancy,and the center of gravity and the center of buoyancy meet the requirements of the code for load balance adjustment,which can be used for the ship finite element analysis provides well balanced loads.Then,according to the energy principle,this paper proposes a calculation method of the equivalent nodal inertial force from the microscopic perspective of the work done by the inertial force of a micro-block in the element.According to the derived formula,the independent calculation program of plane stress four-node isoparametric element with inertial release function is written,and the algorithm and program are verified by taking a simply supported beam under distributed load as an example;the independent calculation program of threedimensional solid eight-node isoparametric element is used,and the algorithm and program are verified by taking the rotating beam around the fixed axis and the hoisting steel pipe as an example;on the basis of the shell structure analysis software — Nautilus,the inertial release function of the shell element is developed,and the steel pipe hoisting problem is analyzed again;finally,it returns to the finite element analysis of the combined strength of bending and torsion of the channel ship with large openings.The effective balance of the load is achieved by floating state calculation,and the structural response of the ship in the water in a free and unconstrained condition is simulated by inertial release.The above results all show that the inertia release algorithm proposed in this paper is correct and reliable,can accurately balance the load,simplify the processing of boundary conditions,and is suitable for solving unconstrained structures,which has certain reference significance for the independent development of domestic finite elements.