In the case of a structure surrounded by liquid in a narrow gap, the added fluid mass and the damping become large number, compared with the ones in air. A new method to estimate the added damping for this case has been introduced by some of the authors in 2001, which is based on a narrow passage flow theory. Following this theory, a model test has been conducted, where the structure modified the reactor component for a newly developed PWR power plant. The test model is a cylinder type structure with four narrow passages to modify the real component. It consists of four blocks connected with tie rods and immersed in water inside a rigid shell to simulate the surrounding core barrel. The cylinder is suspended in the space to move as a rigid body. In this paper, results of a model test are shown comparing the data with the calculated ones based on the above method. The natural frequency of the structure in air decreases almost to 1/5 in water, and it shows no great trend in relation to the amplitude. However, the damping increases with amplitude, and also shows the clear effect of the gap clearance. These trends agree reasonably well with the calculated trends.
展开▼
