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Yingyi Liu, Shigeo Yoshida, An extension of the generalized actuator disc theory for aerodynamic analysis of the diffuser-augmented wind turbines, *Energy*, 10.1016/j.energy.2015.09.114, 93, 2, 1852-1859, 2015.12, The one-dimensional momentum theory is essential for understating the physical mechanism behind the phenomena of the DAWT (Diffuser-Augmented Wind Turbines). The present work tries to extend the existing GADT (Generalized Actuator Disc Theory) that proposed by Jamieson (2008). Firstly, the GADT is modified to include an effective diffuser efficiency, which is affected by the thrust loading or axial induction. Secondly, Glauert corrections to the DAWT system in the turbulent wake state are proposed, modelled by a linear and a quadratic approximation, respectively. Finally, for prediction of the axial velocity profile at rotor plane bearing various thrust loadings, an empirical model is established, which can be further used to predict the diffuser axial induction. In addition, the 'cut-off point' in Glauert correction and the 'critical thrust loading' in axial velocity profile prediction are newly defined to assist the analysis. All the above formulations have been compared and validated with Jamieson's results and Hansen's CFD data, justifying the effectiveness of the present model. . |

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Yingyi Liu, Changhong Hu, Sueyoshi Makoto, Hidetsugu Iwashita, Masashi Kashiwagi, Motion response prediction by hybrid panel-stick models for a semi-submersible with bracings, *Journal of Marine Science and Technology*, 10.1007/s00773-016-0390-1, 21, 4, 742-757, 2016.12, A diffraction-radiation analysis is usually required when the hydrodynamic interactions between structural members occur in short waves. For bracings or small cylindrical members, which play important roles in the vicinity of the natural frequency of a floating platform, special care should be taken into account for the effect of viscous damping. Two hybrid panel-stick models are, therefore, developed, through the combination of the standard diffraction-radiation method and the Morison's formulae, considering the effect of small members differently. The fluid velocity is obtained directly by the panel model. The viscous fluid force is calculated for individual members by the stick model. A semi-submersible type platform with a number of fine cylindrical structures, which is designed as a floating foundation for multiple wind turbines, is analyzed as a numerical example. The results show that viscous force has significant influence on the hydrodynamic behavior of the floating body and can successfully be considered by the proposed hybrid models.. |

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Yingyi Liu, Hidetsugu Iwashita, Changhong Hu, A calculation method for finite depth free-surface green function, *International Journal of Naval Architecture and Ocean Engineering*, 10.1515/ijnaoe-2015-0026, 7, 2, 375-389, 2015.03, An improved boundary element method is presented for numerical analysis of hydrodynamic behavior of marine structures. A new algorithm for numerical solution of the finite depth free-surface Green function in three dimensions is developed based on multiple series representations. The whole range of the key parameter R/h is divided into four regions, within which different representation is used to achieve fast convergence. The well-known epsilon algorithm is also adopted to accelerate the convergence. The critical convergence criteria for each representation are investigated and provided. The proposed method is validated by several well-documented benchmark problems.. |

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Yingyi Liu, Bin Teng, Peiwen Cong, Changfeng Liu, Ying Gou, Analytical study of wave diffraction and radiation by a submerged sphere in infinite water depth, *Ocean Engineering*, 10.1016/j.oceaneng.2012.05.004, 51, 129-141, 2012.07, The wave diffraction and radiation of a submerged sphere in deep water are studied using the multipole method within the frame of linear wave theory. By expressing the velocity potential in spherical harmonics and formulating the problems into truncating and solving M sets of linear equation systems, simple analytical expressions are derived for the hydrodynamic characteristics. A novel analytical expression for the multipoles coefficient is derived to accelerate the numerical implementation. A similar procedure of Wu et al. (1994) and Rahman (2001) is used to condense the expression for the total wave potentials at the sphere surface in the diffraction problem. Results obtained by present model precisely coincide with other numerical schemes, and converge very rapidly with the increase of the truncation parameter that generally the number of series terms N=4 and M=0,1 are sufficient to an accuracy of 3 decimals. A further analysis shows that for large submergences, the surge and the heave exciting forces approach equal. In the mean time, there exists an exact relationship a(11)-0.5=(a(00)-0.5)/2 between the surge and the heave added mass, and b(11)=b(00)/2 between the surge and the heave damping, where j=0 and j=1 correspond to the heave and surge motion, respectively. Extensive numerical results involving convergence of the multipole method, exciting forces and hydrodynamic coefficients for various parameters are also presented.. |

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Yingyi Liu, Ying Gou, Bin Teng, Shigeo Yoshida, An Extremely Efficient Boundary Element Method for Wave Interaction with Long Cylindrical Structures Based on Free-Surface Green’s Function, *Computation*, 10.3390/computation4030036, 4, 3, 1-20, 2016.09, The present study aims to develop an efficient numerical method for computing the diffraction and radiation of water waves with horizontal long cylindrical structures, such as floating breakwaters in the coastal region, etc. A higher-order scheme is used to discretize geometry of the structure as well as the physical wave potentials. As the kernel of this method, Wehausen's free-surface Green function is calculated by a newly-developed Gauss-Kronrod adaptive quadrature algorithm after elimination of its Cauchy-type singularities. To improve its computation efficiency, an analytical solution is derived for a fast evaluation of the Green function that needs to be implemented thousands of times. In addition, the OpenMP parallelization technique is applied to the formation of the influence coefficient matrix, significantly reducing the running CPU time. Computations are performed on wave-exciting forces and hydrodynamic coefficients for the long cylindrical structures, either floating or submerged. Comparison with other numerical and analytical methods demonstrates a good performance of the present method.. |