유체력을 고려한 3차원 접수구조물의 진동해석

초록

Unlike structures on air, the vibration analysis of a submerged or floating structure such as offshore structures or ships is possible only when the fluid·structure interaction is understood, as the whole or part of the structure is in contact with water. Therefore, the fluid domain and structure domain are defined in a system which has independent governing equations and boundary conditions. The compatibility condition of the wetted surface is used to solve the coupled system of structure and fluid. The added mass which is proportionate to the acceleration of the actual structure is added to the mass of the structure to present the coupled effect. However, in a large structure such as a ship which has a high slenerness, the resonance of the structure and vibration source occur at a very low range of frequency, thus usually calling attention to only the vibration mode of the entire structure. In such circumstances, it can be hypothesized that the high order vibration mode of the random section is not generated. Under such hypothesis, it is normal to perform the fluid·structure uncoupled vibration analysis in which the secondary added mass of the section of the added mass is multiplied by the tertiary collection factor J which considers the effect of the length and direction mode. The method which applies the added mass can only be adapted when the tertiary collection factor is already known. A high level of error is inevitable, as the actual approximate value is used. Also, the tertiary collection factor which is widely used in vibration analysis has been calculated only in the low order vibration mode, thus making it inapplicable to the high order vibration mode. In this study, such defects have been overcome, and an application method to the high order vibration analysis of wetted structures is explained.