Effects of Forward Speed on the Linear and Nonlinear Hydrodynamic Forces Acting on Advancing Submerged Cylinders in Oscillation

동요(動搖)하는 2차원몰수체(次元沒水體)에 작용(作用)하는 선형(線形) 및 비선형(非線形) 동유체력(動流體力)에 미치는 전진속도(前進速度)의 영향(影響)

Linear and nonlinear hydrodynamic force, which acts on submerged circular and eilliptic cylinders in oscillations as well as in advancing motion, are investigated as an initial-boundary value problem using a numerical method, which makes use of the source distribution on the body surface and the spectral method for treating the free surface waves. In the numerical code developed here, the boundary condition at the body surface is linearized. Using the numerical code so attained, nonlinear effects for different forward speeds and of the large-amplitude motion are computed. One of the major findings is that, when the forward speed is large, the added mass has its minimum and the damping force change rapidly around the frequency corresponding to the speed-frequency parameter, $\tau$=0.25, Compared to the result of Grue's [10], who used linear theory to get abrupt changes in values of the added mass and the damping force at the frequency corresponding to $\tau$=0.25, the present study, which takes nonlinear effects into account, shows much smoother variations near the frequency.