PSI - Issue 48

Nurman Firdaus et al. / Procedia Structural Integrity 48 (2023) 58–64 Firdaus et al. / Structural Integrity Procedia 00 (2023) 000–000

59

2

Utsunomiya, 2019;2021; Prabowo and Prabowoputra, 2020; Tjahjana et al., 2021; Wicaksono et al., 2021; Arifin et al., 2022; Prabowoputra and Prabowo, 2020;2022; Prasetyo et al., 2023). The floating wind turbines, on the other hand, are one of the most efficient renewable energy alternatives that utilize potential locations in the sea area. In the offshore wind industry, the development of a potential source for the wind energy farm is growing rapidly towards deeper sea to cope with accelerating demand for zero emissions. The stable floating platform to support the installation of floating offshore wind turbine (FOWT) was considered in the design system (Jonkman, 2010) . The harvesting of offshore wind energy can be supported using various types of floating platforms (Chuang et al., 2021) , as each type has characteristics in field application. The workability concept of floating offshore wind turbine was performed by Kaptan et al. (2022) to study the characteristics of different platform design associated with maintenance operations. The simulated results of response model were analysed with a frequency-domain approach. The main contribution of dynamic response to the FOWT platform system is generally caused by hydrodynamic and aerodynamic load. The floating structures used to support wind turbines installed in location of deep water are vulnerable to wave loads which induce a structural and member failures (Zhang et al., 2020; Carvalho et al., 2023) . According to the results of research on the motion response of spar-type floating structures for offshore wind turbines which were carried out numerically and experimentally, the hydrodynamic damping parameters play an important role in the dynamic behavior (Yang et al., 2021). In addition to wave loads, aspects of the hydrodynamic parameters that affect the performance of floater wind turbines are the added mass coefficient and damping (Karimirad et al., 2011) . The magnitude of hydrodynamic coefficient on the floating structure are significantly affected by the platform shape which is submerged in sea water. (Shi et al., 2019) conducted the numerical calculations of hydrodynamic properties on various semisubmersible shapes for FOWT platform using the first order diffraction and radiation. The problems of hydrodynamic interaction between floating platforms and wave fluids in the approach of diffraction and radiation case can be solved by using the boundary element method (Mackay et al., 2021). In this paper, the main aim of the research is to investigate the hydrodynamic characteristics of the geometrical influence on the spar-type FOWT platform. 2. Boundary element method Boundary element method (BEM), known as panel method, is one of numerical computational technique used to solve the linear potential flow theory (Papillon et al., 2020) . This method is developed to investigate wave propagation around three-dimensional bodies in water, in which the interactions of waves and floating bodies creates hydrodynamics properties. BEM solves the potential velocity of scattering and radiating for a floating body to incident waves. The body remains in position to overcome the potential for scattering and radiation found by moving an object in the absence of an incident wave. Therefore, BEM solver as a tool to calculate the hydrodynamics properties that support design optimizations. An open-source BEM solver NEMOH is a diffraction/radiation program such as ANSYS AQWA, WAMIT, and Hydrostar to obtain hydrodynamics coefficients based on the frequency domain. In this study, the added mass, damping radiations and exciting force of floating spar-FOWT type are obtained from NEMOH. However, Boundary element method is useful code for hydrodynamic model both in research laboratories and commercial applications. In order to the fluid model in motion, we assume that the fluid flow is an incompressible, inviscid and irrotational to a set of equation for the linear potential flow theory (Babarit & Delhommeau, 2015) . According to (Teng et al., 2018) , the effect of viscosity is not very important on large offshore structures and the effect of diffraction dominates the flow. The interaction analysis of the wave flow field around the floating spar and hydrodynamic force can be explained by the velocity potential  . The velocity potential can be decomposed into 3 parts showing incident wave potential   , radiation wave potential   and disturbance of the incident wave potential  7 respectively. The radiation and scattering potential can be handled with the boundary conditions. Three parts refer to the ideal fluid assumption, the following equation: =  +  + 7 (1) To solve the velocity potential in an incompressible flow, the continuity equation from potential flow theory can be used in the fluid domain Ω which satisfies the following Laplace equation (Lin, 2008),