Calculation Method Of Floating State And Stability Based On Tetrahedron Element

Sinking due to insufficient buoyancy and capsizing because of insufficient stability are two of the major threats to ship survivability at sea.The safety from sinking and capsizing is thus an important part of the safety of navigation with the entailed safety of life and protection of the environment in waterborne transportation.With the development of multi-hull vessels and various types of offshore engineering buildings in recent years,the hydrostatic and stability calculations of complex shape floating bodies represented by mobile offshore platforms have attracted the attention of scholars at home and abroad,which also put forward the idea of " object element method" :(1)The combination can be divided into simple object elements,such as tetrahedron,hexahedron,triangular prism,cylinder,etc.(2)Based on the relationship between each object element and the water plane,its volume of displacement and buoyancy center can be evaluated.At last the hydrostatic properties of the combination can be computed by summing up all the hydrostatic parameters of the object elements.Considering the complexity of the stability calculation of the irregular floating body,this paper proposes a new object element method based on the tetrahedral element.The algorithm is simple and reliable,and is suitable for the calculation of the floating state and static stability of any complex shape floating body.The complicated floating object can be divided into simple object elements,such as hexahedra,columns and triangle prisms.These object elements can then be disassembled again into the most basic volume element: tetrahedral element.The object element method based on the tetrahedral elements is different from the classical stability calculation method based on the table of offsets and the method based on the surface triangle elements of the floating object.It is also more general than other methods based on three-dimensional object elements,such as cuboids,cylinders etc.At the meantime,the paper also assumes that the floating body and its shape definition coordinate system are stable,and the tilt and heave of the floating body are expressed as changes in the waterline surface equation.Referring to the conventional hull and waterline intersection algorithm,this paper first gives the relationship between the tetrahedral element and the waterline surface and the calculation of the geometric characteristics,and then uses the optimization method to calculate the waterline of the floating body under the current working conditions,which is used to obtain parameters such as displacement and buoyancy center of a single tetrahedral unit,and then the hydrostatic characteristics of the entire floating body are got by summarized.Finally,with the buoyancy center of the floating body and the determination of the floating state,the static stability of the floating body can be calculated.At last,on the basis of the above theory,the corresponding program is written by Visual Studio 2013 software platform,which realizes the transformation from theoretical system to practical application.At the meantime,it is used to demonstrate the feasibility and practicability of the proposed method through the experimental data of an offshore platform model,the calculation results of the offshore platform on the MAXSURF and hydrostatic curves of 1000 t oil tanker obtained by traditional algorithm.