described above, and examines the comparison of the experimental valueswith the theoretical ones with respect to the dynamic displacement responses of the moored-type of soft-settled-type offshore structures having a circular cross section. Further more the dynamic characteristics of the offshore structures in question are made plain in the paper.
2. THEORETICAL ANALYSIS
2.1 Equation of motion6)
A structure, which has conventionally been believed to be an elastic body, is to be hereby regarded as a rigid body and to be dealt with as a one-particle-system model. Although seismic movement has concurrently both the components of the vertical and horizontal movement, the horizontal dynamic component is exclusively dealt with in this occasion. Therefore if the movement is dealt with as a one-degree-of-freedom system, then the equations of motion are expressed respectively as shown in Eqs. (1)and(2) in a static friction region (non-gliding region) and dynamic friction region (gliding region).
・Equation of motion in the non-gliding region
・Equation of motion in the gliding region
In this connection, damping coefficient c should be neglected in this study.
2.2 Dynamic response analysis method
For the dynamic response analysis, a step by step integration method was employed6).
2.3 Added mass
For the added mass, the one in case of a cylinder by Saunders was used.That is to say, the added mass coefficient was determined to be 1.0.
2.4 Friction coefficient
For the friction coefficient, the one measured by Ohkubo' is used. The values of the coefficient are listed in Table 1.
Table 1. Friction coefficients
3. WATER RESERVOIR EXPERIMENT
3.1 Experimental apparatus
The unit employed in this experiment is a flat water reservoir with a horizontal vibration base belonging to Nihon University (Fig.1).
