Convenient Design Method For Goblal Strength Of Semi-Submersible Unit

The basic design for ship structure is very mature at present.We have fixed the calculation flow of global strength.However,it depends on the experience of structural engineers when design the semi-submersible platform,especially the connection structure between column and upper hull or lower hull.We have to calculate the global strength by finite element method after drawing design.It is intent to check the yielding strength,buckling strength and fatigue strength.After that,we need reinforce base on the original drawing if the structure is not satisfied somewhat with the class requirement.Traditional design method depends upon the experience of structural engineers.In addition,the class rules describe less about structural design of semi-submersible platform.The researchful primary content in this paper is to compare the evaluated methods of DNV class rules LRFD to DNV class rules WSD.I try to find a rapid,having a engineering value,associated to rules check and FEM structural method of semi-submersible platform.In order to achieve the goal I am going to summarize all the structural design data for many semi-submersible platforms.We may get some light structural semi-submersible platforms which are satisfied with class requirement.The main items are described as follow.1.First all,we design the local structure base on ABS and DNV rules.The primary input condition is hydraulic pressure and deck loads in ABS rules.Forthmore,partly stress of global strength should be considered in DNV rules.2.We adopt the beam theory to check the global strength base on the location of semi-submersible platform and correspond to the stress property.We take the acceleration of the platform to be equal to static load in order to make the calculation simple.3.To summarize global stress distribution of a few platform and reference the difference between global strength calculation result and local strength of all parts.To design suitably the structure of the connection between columns and upper hull or lower hull,and between columns and braces.After that,the basic design structural drawing is come into being which is based on the finite element analysis.4.Checking the rapid method by finite element analysis.The main researching purpose in this article is to provide a kind of proper and viable solution for these key chains which are not noted in the class rules and relevant documents in the semi-submersible platform global strength estimation.This method is simple and easy,in addition,the deviation arrangement is accepted.After checking with the living vessel,the value is approaching to the final result and it has great reference meaning.It has enormous meaning to reduce the times of finite element analysis.Of course,the solution should be improved and perfected continually in the practice.We may conclude a formula for different parts such as the wave load formula of ship type floating body.