Ship Collision Load Effects On The Connector Load Of Very Large Floating Structures

The21st century is the century of ocean. Ocean is the commanding heights of competition of comprehensive national strength. Sea power has become an important part of national development strategies. International marine engineering in recent years launched a study of very large floating structures (VLFS-Very Large Floating Structure referred to VLFS) of the boom. VLFS can be used as offshore supply, or scientific research, energy and maritime cities base. For the conditions of our country, our country has begun a series of proof of concept on VLFS.VLFS studied in this paper is a kind of VLFS which is made up of several semi-submersible modules. The modules are connected with connectors. The connectors are soft to allow relative motion to minimize the connector load.VLFS may meet with accidental damage due to airplane collision, ship collision, etc. Accidental loads will not only damage local structures of VLFS, but also induce additional loads on connector which is the weakest part of VLFS.The influence of ship collision on the VLFS is calculated by numerical solution.Taking ship collision as an example, by the use of simplified RMFC model, hydrodynamic coefficient is calculated by SESAM software. Then the hydrodynamic coefficient is taken into multi-body motion differential equation, and this equation is solved with numerical methods to study the influence of impact load on the connector load. The result considering the influence between modules and without considering the influence is compared. It indicates that the influence between modules can be neglected when the wave approach or the stiffness of connector is large enough.Two numerical methods present here:the first is simplified frequency-domain solution which fixed frequency hydrodynamic coefficient and wave force is applied. The second is time-domain solution which the hydrodynamic coefficient is applied to calculate the added mass in infinite frequency and memory function. It is shown that the simplified frequency-domain solution is available in preliminary design stage of VLFS.The result of different connector stiffness and collision position is compared. The stiffness of connector which cause minimum connector load and the collision position which cause maximum connector load is found. The three kind of simplified collision load models are compared. It is shown that there is slight difference between these models. The connector load is related with load impulse. The result of different collision angle is compared. It is shown that the connector load is related with the load moment In the end of this paper, the connector load considering wave and collision load is calculated. The degree of influence is verified. The order of magnitude of connecter loads induced by collision is estimated. The result is shown that the influence of collision load cannot be neglected.