Hydroelastic Response Analysis Of VLFS Attached With Submerged Plates

Very large floating structure (VLFS) has great value in taking advantage of ocean space and exploiting ocean resources, it has been a research hotspot in the domain of the ocean engineering. China Manufacture (2025) issued by the State Council of PRC, which demands quick development of VLFS technology. VLFS is an extremely flat and flexible structure. The structural vibrations and fluid motion must be coupled together using hydroelastic theory analysis. Based on the potential theory, the eigenfunction expansion matching method is applied to analyse hydroelastic response of VLFS attached with submerged plates.Applying Euler beam theory, potoons type VLFS is simplified as a two-dimensional elastic beam. To solve fluid problem, the unified system consisted of VLFS and fluid is divided into several regions. The eigenfunction expansion method and the mode function expansion method are employed to solve the velocity potential. Radiation potential coefficient and diffraction potential coefficient are obtained by solving the equations based on continuity conditions that velocity potential and velocity are equal along the boundary of different regions, then the velocity potential is abtained. To solve the structure problem, the vibration differential equation of two-dimensional elastic beam is adopted to get the hydroelastic equation of motion of VLFS. Employing the velocity potential into the motion equation and solving the equation, the mode superposition method is used to calculate wave-induced response. The relevant computer codes are developed by Fortran programming. Comparing with literature data, calculation results show that the analytical method and the program are validity and feasibility.A submerged horizontal plate attached at the fore-end of VLFS, which can effectively mitigate hydroelastic response of VLFS at the fore-end and in the middle, but it is limited to decrease the response of VLFS at the back-end. There are optimal values of submerged plate width and depth in water, so the plate can mitigate response of VLFS in the maximal degree. Comparing the structure attached submerged plate at the fore-end with the pure structure, the hydroelastic deformation is also calculated with the change of wavelength. In a suitable incident wavelength range, submerged horizontal plate can effectively mitigate response of VLFS. Installing plate under VLFS can be considered as a good damping measure.Simplifying the model based on the symmetry of the structure, the paper further derives the velocity potential and hydroelastic equation of motion when VLFS attached with plates at the fore-end and back-end. Installing two plates under VLFS, which can extremely mitigate response of the whole structure. Optimum parameters of two submerged plates also exist, whose changes are similar to those of one plate, but values are different. The hydroelastic response of the VLFS without plate, with one optimum parameters plate, with two optimum parameters plates are analyzed and compared, and the hydroelastic deformation is also calculated with the change of wavelength in three situation above. Two plates structure has distinct advantage over one plate structure in vibration damping effect and adaptation of wavelength range. This paper discusses response of VLFS with two plates at various stiffness, which shows limitation to reduce response with the increase of stiffness. At 1m and 2m wavelength of the incident wave, with water depth increasing, the structural vibration and bending moment are increasing. On the same water depth, with wavelength increasing, the structural vibration and bending moment are also increasing. The results provide a theoretical basis for future design.