The Analysis Of Vibration Of Typical Underwater Stern Structure

The vibration characteristic of underwater stern structure is always a focused issuewidely concerned by designers. Because of the specialty of conditions, the influence offluid on the vibration of the structure should be considered. With three kinds of typicalstern structures selected, including ring-stiffened conical shell, double conical shell andhorizontal stabilizer-wing, the free vibration characteristics of fluid-structure interactionwere analyzed.First, the semi-analytical method of the free vibration of fluid loaded ring-stiffenedconical shell was proposed. The motion differential equation of fluid loadedring-stiffened conical shell was derived by using classical thin shell theory andequivalent method of ring stiffeners. In the analysis, to calculate the fluid loading ofconical shell approximately, the conical shell was divided into many narrow cylindricalstrips, of which the fluid loading were available. The semi-analytical solution of theequation in terms of power series was obtained. Using the proposed method, the freevibration frequencies of the ring-stiffened conical shell in air and in water were solvedrespectively, which matched very well with the results calculated by the finite elementsoftware ANSYS. The effect of size and frame spacing of stiffeners on the accuracy ofsemi-analytical solution were analyzed. The coupled vibration frequencies ofring-stiffened conical shell with variable values of semi-vertex angle were obtained.Along with the increasing of semi-vertex angle, the vibration frequency decrease, whilethe influence of fluid on structure increase.Second, the principles and procedures of fluid-structure interaction analysis inANSYS were described, taking the flat plate coupled with fluid on one side or both sidesrespectively as example. The key points to define shell elements coupled with fluid onboth sides were introduced typically. To perform a coupled structural fluid analysis, besides the original layer of shell, an additional layer of shell needs to be define, ofwhich the Young’s modulus and the density of material must be altered to guarantee thesame mass and stiffness as the single layer of shell. The vibration frequencies of doubleconical shell were obtained, considering the outer fluid and inner fluid between twoshells. Compared with the proposed method, the drawbacks of the method whichconsider the inner fluid according to experience were pointed out.The vibration of horizontal stabilizer-wing coupled with inner and outer fluid wereanalyzed, along with the impact of bound condition and light shell of stern structurediscussed. Last but not least, lastly, the vibration characteristic of horizontalstabilizer-wing filled with floating body material was analyzed.This research can provide a useful reference to comprehend the vibrationcharacteristic of typical underwater stern structure in the future.