Dynamic Response Of The Cylindrical Structure And Its Vicinal Seabed Soil Subjected To Ocean Waves

Cylinder or column structure is one of the most common onshore or offshore marine installations. Appropriately calculating the wave loads acting on the cylinder and studying the vicinity seabed soil response to wave action is the important prestige for stability analysis of the structure as a whole.The cylinder can be divided into small diameter cylinder and big diameter according to the ratio of cylinder diameter D to wavelength L, and different wave theories shall be employed to calculate the wave forces. For small cylinder (D/L 0.2), the influence on wave approaching field exerted by the cylinder can be neglected, and Small Amplitude Theory and Morison Formula are employed. However, when H/d 0.2 and d/L <0.2, or H/d>0.2 and d/L<0.35, the horizontal velocity of water particle calculated with Small Amplitude Theory is obviously small, therefore, the values of PD max and MD-max, calculated with Morison Formula shall be multiplied by a coefficient and . When 0.04 d/L 0.2, the values of PD max and MD max calculated with Morison Formula shall be multiplied by a coefficient p and m. For small cylinder (D/Z>0.2), diffusive waves shall be formed as the approaching waves meet the cylinder. When the superimposed waves formed by incident waves and the diffusive waves reach a stable state, a new wave filed is then formed which can be assumed as a potential movement and the micro-amplitude wave theory can be adapted to calculate the wave force.For a square pile or column, the diversion point is the edge of pile. When waves propagate perpendicular to the pile, the flow will diverse to either side of the pile. When waves approach with an angle less than 90? the flow will pass two plans of pile, resulting in great wave forces on the pile. This typical diffusion phenomenon is quite different from thecylinder case. The dynamic for coefficient square pile or column has the following characteristics: even for a small KC number, eddy flow may occur and the drag coefficient is considerable; the drag coefficient in each direction is larger than that of the cylinder pile; the inertial coefficient is however less than that of cylinder pile; since the total width of pile against waves propagating at an angle of 45 is 2 times that of waves approaching perpendicular, the resultant force reaches the maximum value then.Linear wave theory can be used to calculate the wave forces on a cylinder array. However, in shallow water, non-linear must be considered due to great wave height and wavelength, and Stokes 5th rank wave theory, ellipse cosine theory etc. maybe employed. Wave forces on the cylinder array are quite different from that on a single cylinder, since one cylinder yields impacts or dynamic response on the other if the interval of cylinder is small. The geometric factors governing such dynamic response are mainly the relative interval,number of cylinder, formation of array and position, and the wave parameters.Physical model tests have been conducted for the horizontal forces on cylinder array at small intervals at Trondheim University of Science and Technology, Norway and Norwegian National Marine Laboratory, thanks to an academic cooperation dedicated to this doctorial study. So far, cylinder array of small intervals, say, 1.0