近年來，全球各國都在開發海上風能，海上風力發電機可分為固定式基樁風機和浮式風機。本研究使用水槽實驗和流體/固體耦合數值模型來研究固定基樁風機與浮式風機Spar型基座在孤立波中的運動，利用三維大渦模式模擬圓柱體形基座受孤立波所受的波浪力。浮式基樁則以下重上輕的圓柱體來模擬，在靜止水中浮體簡單振盪試驗，發現數值模式的阻尼比 = 0.70與實驗結果最為接近，平均振盪週期與理論值的誤差為2.0%。在孤立波中，浮動圓柱所受的波浪力與位移與波高成線性正比，且大渦模式模擬得之波浪力十分接近由位移間接計算得之外力。此外，本研究探討不同波高對固定圓柱的波浪力，模擬結果發現：細長圓柱體的最大波浪荷載可以用一無因次阻力係數來計算，而波長的延長可使得作用在圓柱上的波浪荷載持續時間更長，儘管力的大小有所減小。並在相同流況下，比較固定圓柱和浮動圓柱所受的波浪力，發現固定圓柱所受的水平力遠大於浮動圓柱，這是由於浮動圓柱將大部分的波浪力轉換為推動圓柱之動能，導致受力減少。

This study incorporates a large eddy simulation (LES) model and a two-way coupled fluid/solid algorithm to investigate the wave loads on a fixed and a floating circular cylinder in solitary waves. The experimental results of the wave flume are used to validate the numerical simulations. The following findings are summarized based on the simulation results. In a simple oscillation test of a floating cylinder in stationary water, there is about 2.0% difference between the simulated and observed oscillation periods when the damping ratio is α = 0.70. In solitary waves, the wave loads and maximum displacements of the floating cylinder are linearly proportional to the wave height. The simulated wave loads obtained from the LES model closely match the values computed from the observed displacements of the floating cylinder. This study also examines the wave loads of a fixed cylinder under different wave heights and water depths. The simulation results indicate that the maximum wave load on a slender cylindrical body can be calculated using a dimensionless drag coefficient, and increasing the wavelength extends the duration of the wave impact on the cylinder. Furthermore, the wave loads experienced by a fixed cylinder are significantly larger than that on a floating cylinder under the same wave conditions. This is attributed to the fact that the floating cylinder converts most of the wave load into the kinetic energy of the floating cylinder.

[1] Smagorinsky, J., “General circulation experiments with the primitive equations: I. The basic experiment,” Mon. Weather Review, 91, 99-164 (1963).
[2] Cundall, P. A. and Strack, O.D.L. “A discrete numerical model for granular assemblies”. Géotechnique. 29 (1): 47-65. doi:10.1680/geot.1979.29.1.47 (1979).
[3] Hirt, C. W. and Nichols, B. D., “Volume of fluid (VOF) method for the dynamics of free boundaries,” J. Comput. Phys. 39(1), 201-225 (1981).
[4] G.T. Yates, K.H. Wang “Solitary Wave Scattering By a Vertical Cylinder: Experimental Study” The Fourth International Offshore and Polar Engineering Conference, Osaka, Japan, April (1994).
[5] DeLong, M. “Two examples of the impact of partitioning with Chaco and Metis on the convergence of additive-Schwarz preconditioned FGMRES.” Technical Report LA-UR-97-4181, Los Alamos National Laboratory, New Mexico, U.S.A. (1997).
[6] Ferziger, J. H., and Peric, M. Computational Methods for Fluid Dynamics, http://scitation.aip.org/content/aip/magazine/physicstoday/article/50/3/10.1063/1.881751 (2002).
[7] Gullbrand, J., Chow, F. K. The effect of numerical errors and turbulence models in large-eddy simulations of channel flow, with and without explicit filtering. J. Fluid Mech. Vol. 495, 322-341 (2003).
[8] Mo W., Irschik K., Oumeraci H. and Liu, P.L.-F. “A 3D numerical model for computing non-breaking wave forces on slender piles” Journal of Engineering Mathematics, Vol.58, 19-30 doi.org/10.1007/s10665-006-9094-6 (2007).
[9] Utsunomiya T, Sato T, Matsukuma H, Yago K. “Experimental validation for motion of a SPAR-type floating offshore wind turbine using 1/22.5 scale model”, Proceedings of the ASME 28th International Conference on Ocean, Offshore and Arctic Engineering, Hawaii 2009, No.79695, 951-959. doi.org/10.1115/OMAE2009-79695 (2009)
[10] Wu, T.-R., Chu, C.-R., Huang, C.-J., Wang, C.-Y., Chien, S.-Y., and Chen, M.-Z., “A two-way coupled simulation of moving solids in free-surface flows,” Computers and Fluids, 100, 347-355. doi.org/10.1016/.compfluid.2014.05.010 (2014)
[11] Zhou, B. Z., Wu, G.X. and Meng, Q.C. “Interactions of fully nonlinear solitary wave with a freely floating vertical cylinder,” Engineering Analysis with Boundary Elements Vol.69, 119-131. doi.org/10.1016/j.enganabound.2016.05.004 (2016)
[12] Subbulakshmi, A., Sundaravadivelu, R. “Heave damping of spar platform for offshore wind turbine with heave plate”. Ocean Engineering; 121:24-36. doi: 10.1016/j.oceaneng.2016.05.009 (2016).
[13] Ha M., Cheong C. “Pitch motion mitigation of spar-type floating substructure for offshore wind turbine using multilayer tuned liquid damper,” Ocean Eng.; 116: 157-164. doi.org/10.1016/j.oceaneng.2016.02.036 (2016).
[14] Chu C-R, Lin Y-A, Wu T-R, and Wang C-Y. Hydrodynamic force of circular cylinder close to the water surface. Computers and Fluids; 171:154-165. doi.org/10.1016/ compfluid.2018.05.032 (2018).
[15] Chu C-R, Wu Y-R, Wang C-Y, and Wu T-R. Slosh-induced hydrodynamic force in a water tank with multiple baffles. Ocean Eng.; 167: 282-292. doi.org/10.1016/j.oceaneng.2018.08.049 (2018).
[16] Chu C-R, Wu T-R, Tu Y-F, Hu S-K, Chiu C-L. Interaction of two free- falling spheres in water. Physics of Fluids ; 32 (3): 033304. doi.org/10.1063/1.5130467 (2020).
[17] Otter, A. Murphy, J. Pakrashi, V. Robertson, A., Desmond, C. A review of modeling techniques for floating offshore wind turbines, Wind Energy, 25 (5),831-857. doi.org/10.1002/we.2701 (2021)
[18] Tsai, I.-C., Li, S.-Y., Hsiao, S.-C. and Hsiao Y., Numerical simulation of 2-D fluid-structure interaction with a tightly coupled solver and establishment of the mooring model, Intern. J. of Naval Architecture and Ocean Eng. Vol.13, 433-449. doi.org/10.1016/j.ijnaoe.2021.06.002 (2021).
[19] Chen C., Ma Y., Fan. T. “Review of model experimental methods focusing on aerodynamic simulation of floating offshore wind turbines” Renewable and Sustainable Energy Reviews;157: 112036. doi.org/10.1016/j.rser.2021.112036 (2022)
[20] Chu, C.-R., Huynh, L.E. and Wu, T.-R. Large eddy simulation of the wave loads on submerged rectangular decks. Applied Ocean Research, Vol.120, 103051. doi.org/10.1016/j.apor.2022.103051 (2022).
[21] Yang R-Y, Wang C.-W., Huang C.-C., Chung C.-H., Chen C.-P., Huang C.-J. “The 1:20 scaled hydraulic model test and field experiment of barge-type floating offshore wind turbine system” Ocean Eng. doi.org/10.1016/j.oceaneng.2021.110486 (2022).