Study On Direct Analysis Approach To Assess Strength Of Buoyancy Supported Risers

BSR(buoyancy supported risers)is the key equipment to connect the submarine manifold and the floating production and storage device,which is of vital importance to the structural safety of the FPSO.In the working conditions,the structure is often in a more complex,harsh marine environmental load.Therefore,it is of great engineering significance to study the structural strength analysis method and strength check.For structural structures with complex geometrical shapes such as underwater riser support floats,structural strength analysis is difficult to complete by analytical solutions or normative empirical formulas,often using numerical methods such as finite element analysis(FEA).In general,the underwater riser supports the combined action of gravity,hydrostatic pressure,tension leg tension,and flow load during buoyancy.In the finite element structure analysis,the existing methods can be used to deal with the distribution of the first three loads on the structural grid.However,the method of obtaining the flow load distribution on the structural grid is still to be further studied.For the accurate calculation of the flow load distribution,it is often necessary to use computational fluid dynamics(CFD).However,the CFD method obtains the load distribution on the fluid mesh and is difficult to apply directly to the analysis on the structural grid.Therefore,it is necessary to solve the problem of the load distribution on the load and the distribution of the load distribution on the structural grid.In order to solve this problem,this paper proposes an algorithm of fluid mesh and structural grid information transfer based on the idea of block mapping,and combines this algorithm with CFD and FEA method effectively,Direct Calculation Method for Structural Strength Analysis of buoyancy supported risers.The specific research content is divided into three parts,as shown below.(1)Based on the general commercial software FLUENT and the RNG k-ε turbulence model,the surface flow load of the cylindrical underwater riser supported floating structure under typical operating conditions is taken as an example,and the accuracy of the model and method is verified by comparing the numerical solution and analytic solution of the surface flow load.Further application of the above model and method to analyze the typical underwater riser support floating body(Subsea7)in three typical conditions(forward flow,lateral flow,and back flow)under the fluid grid nodes Flow load distribution,and lay a good foundation for the next step in structural strength calculations.(2)Based on the idea of block mapping,an algorithm for information transfer between fluid mesh nodes and structural mesh nodes is proposed.A typical example of three-dimensional cylindrical model is given to verify the accuracy of the algorithm ’s information transfer between different fluid element density,structural cell density and structural element shape.According to the above algorithm,based on Fortran90 language and QT 4.8 interface language developed a corresponding grid information transfer calculation program HUSTM2 M.(3)After obtaining the flow load distribution on the structural grid by the above method,based on the FEA method,using the general finite element software ABAQUS to complete the actual operating conditions under the typical underwater riser support the floating body(Subsea 7)structural strength of the direct calculation.On the basis of the above calculation of structural strength,different measures to reduce the pressure on the support structure are proposed and their advantages and disadvantages are compared and analyzed.In this paper,the direct calculation method of the underwater riser support floating structure strength is proposed.The new method of inter-grid information transfer is used to realize the effective combination of CFD method and FEA method,and has high accuracy.And the method can deal with the problem of strength analysis of complex geometric shape structure under the action of flow load without the need of simplification,and has strong potential application value.