This paper presents a frequency domain approach for the calculation of the random response of fluid-conveying steel catenary risers under random wave force.The partial differential equations of motion of the steel catenary riser under a combination of internal flow and random wave excitation are established based on a series of earlier publications.The mass matrix,stiffness matrix,damping matrix and wave loading for steel catenary riser are derived in frequency domain by using Hamilton's principle.Analysis of free vibrations is then carried out to investigate the effect of flow velocity on natural frequency.By further introducing the pseudo-excitation method,the dynamic analysis of the steel catenary riser subject to wave excitation is performed in frequency domain to see how the flow velocity affects the bending moment response of the steel catenary riser.The parametric studies on the example steel catenary riser show that flow velocity may decrease the natural frequencies and increase the dynamic response of the steel catenary riser.Moreover,the dynamic stability of fluid-conveying steel catenary risers is investigated and the critical fluid velocity is identified.
The size effects of microstructure of lattice materials on structural analysis and minimum weight design are studied with extented multiscale finite element method（EMsFEM） in the paper. With the same volume of base material and configuration, the structural displacement and maximum axial stress of micro-rod of lattice structures with different sizes of microstructure are analyzed and compared.It is pointed out that different from the traditional mathematical homogenization method, EMsFEM is suitable for analyzing the structures which is constituted with lattice materials and composed of quantities of finite-sized micro-rods.The minimum weight design of structures composed of lattice material is studied with downscaling calculation of EMsFEM under stress constraints of micro-rods. The optimal design results show that the weight of the structure increases with the decrease of the size of basic sub-unit cells. The paper presents a new approach for analysis and optimization of lattice materials in complex engineering constructions.
Tensile stiffness of ocean dynamic power umbilical is an important design parameter for functional implementation and structural safety. A column with radial stiffness which is wound by helical steel wires is constructed to predict the tensile stiffness value of umbilicals in the paper. The relationship between the tension and axial deformation is expressed analytically so the radial contraction of the column is achieved in the relationship by use of a simple finite element method. With an agreement between the theoretical prediction and the tension test results, the method is proved to be simple and efficient for the estimation of tensile stiffness of the ocean dynamic power umbilical.
