Abstract
Th COP28 has emphasized the governments to speed up the transition away from fossil fuels to renewables such as wind and solar power in their next round of climate commitments. The steady and less turbulent wind over the ocean draws increased attention of governments, industries and researchers on exploring advanced technologies to extract energy from offshore wind. The present study numerically investigates the hydrodynamic behavior of a SPAR-type Floating Offshore Wind Turbine (FOWT) under various wave conditions and mooring line configurations. One of the major focuses of this study is investigating a freak wave's impact on a FOWT and determining its extreme responses. The study investigates the structural response under various wave impact for different configurations of mooring lines. The present study examines the wave-structure interaction under regular and freak wave conditions using numerical modelling approach. During the study, it is ensured that the natural frequency and wave induced motions of SPAR are inline with the experimental studies; thereby increasing the confidence in using the numerical model and domain for this investigation. The study considers the behaviour of slack and taut mooring arrangements under these wave conditions. The study observed that a taut mooring configuration can be efficient in restraining the FOWT motions, especially under a freak wave scenario. The Froude-Krylov force shows a non-linearity due to the non-uniform profile of the platform under all wave conditions. Overall, the study contributes to determining the performance of the mooring configurations under different wave conditions.
Address
Arya Thomas and V.K. Srineash: Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Maharashtra, 400076, India
Manasa Ranjan Behera: Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Maharashtra, 400076, India;
Centre for Climate Studies, Indian Institute of Technology Bombay, Powai, Maharashtra, 400076, India
Abstract
Although the investigation on the effect of loaded out-of-plane braces on the values of the stress concentration factor (SCF) in offshore tubular joints has been the objective of numerous research works, a number of quite important cases still exist that have not been studied thoroughly due to the diversity of joint types and loading conditions. One of these cases is the multi-planar tubular KK-joint subjected to axial loading. Tubular KK-joints are among the most common joint types in jacket substructure of offshore wind turbines (OWTs). In the present research, data extracted from the stress analysis of 243 finite element (FE) models, verified against available experimental data, was used to study the effects of geometrical parameters on the chord-side SCFs in multi-planar tubular KK-joints subjected to axial loading. Parametric FE study was followed by a set of nonlinear regression analyses to develop three new SCF parametric equations for the fatigue analysis and design of axially loaded multi-planar KK-joints.
Address
Hamid Ahmadi: National Centre for Maritime Engineering and Hydrodynamics, Australian Maritime College,
University of Tasmania, Australia;
Centre for Future Materials, Institute for Advanced Engineering and Space Sciences,
University of Southern Queensland, Australia
Adel Alizadeh Atalo: Faculty of Civil Engineering, University of Tabriz, Iran
Abstract
Numerical investigation was carried out to analyze the hydrodynamic response of 4-column semi-submersible floaters, incorporating variations such as stepping and alterations in the shape/geometry of columns and pontoons, as well as tilting of main columns. Utilizing Ansys-AQWA, a hydrodynamic software based on panel method, simulations were executed for these scenarios. The simulations yielded insights into responses, excitation forces/moments, and pressure on the structure, facilitating a comparison between the models through a parametric study. It was observed that stepping of pontoons and tilting of columns led to reduced responses, forces, and pressures, reaching balance through appropriate stepping and tilting. Additionally, altering the geometry of columns and pontoons indicated the potential benefits of employing elliptical pontoons and pentagonal columns for enhanced response control.
Abstract
In this study, the wave-induced motion responses of modular floating structures (MFS) was investigated through a series of experiments in a two-dimensional wave tank. A 1:63 scale model test was conducted using a 1-by-2 modular floating structure consisting of two modules and connectors. Two different types of connectors were considered: a pitch-free hinge and rigid connector. The numerical analysis was performed based on the higher-order boundary element method (HOBEM) and wave Green function with potential flow theory. First, the heave and pitch RAOs of the modules from the regular wave tests were directly compared with numerical analysis results. Next, the motion spectra and their statistical values from the irregular wave tests were compared with the numerical analysis results. The study revealed that the sheltering effect of the weather side module led to a reduction in motion of the lee side module. The numerical analysis showed good agreement with the experimental data, demonstrating the validity of the numerical method. Additionally, the rigid connector, which strongly constrain all six degrees of freedom, significantly reduce pitch motion, making the modules behave as a single rigid body.
Key Words
hinge connector; hydrodynamic analysis; model test; modular floating structures; numerical analysis; rigid connector
Address
Dong-Hee Choi, Jae-Min Jeon, Min-Ju Maeng, Jeong-Hyeon Kim and Bo Woo Nam: Department of Naval Architecture and Ocean Engineering, Seoul National University,
Seoul 08826, Republic of Korea
Abstract
In this study, the lift coefficient and wave deformations for a two-dimensional flat-plate in noncavitating
condition were computed using a closed-form (analytic) solution. This plate moves at a constant
speed beneath a free surface in water of finite depth. The model represents the flat-plate using a lumped vortex
element within the constraints of potential flow theory. The kinematic and dynamic free surface conditions
were combined and linearized. This linearized free surface condition was then applied to get the total velocity
potential. The method of images was utilized to account for the effects of finite depth in the calculations. The
lift coefficient of the flat-plate and wave elevations on the free surface were calculated using the closed-form
solution. The lift coefficients derived from the present analytic solution were validated by comparing them
with Plotkin
Key Words
finite depth; flat-plate; free surface; lumped vortex element; method of images
Address
Sakir Bal: Department of Naval Architecture and Marine Engineering, Istanbul Technical University, Istanbul, Turkey
