Sun, Liang (Wuhan University of Technology / University of Bath) | Zang, Jun (University of Bath) | Taylor, Rodney Eatock (University of Oxford) | Taylor, Paul H. (The University of Western Australia) | Chen, Mingsheng (Wuhan University of Technology)
In the present paper, two types of wave energy converters (WECs) in uni-/multi-directional waves are investigated using a potential-flow model. The first example is a flap-type oscillating wave surge converter (OWSC) which is similar to the configurations of Oyster wave power device. The second case is an attenuator-type WEC which is based on the Pelamis P2 machine; the modelled WEC is simplified as 5 interconnected rigid modules. Both hydrodynamic interactions and mechanical connections have been considered in the present analyses. The emphases have been put on the effects of directional spreading on the performance of the WECs. Significant reductions of power output have been found in multi-directional seas.
There have been many designs or concepts to harness wave power from the ocean. Wave energy converters (WECs) can be divided into different groups according to the method used to capture the wave power (http://www.emec.org.uk/marine-energy/wave-devices/), i.e. attenuator, point absorber, oscillating wave surge converters (OWSC), oscillating water column (OWC), overtopping/terminator device, submerged pressure differential, bulge wave, rotating mass, etc. Most wave energy devices convert kinetic energy into mechanical motions to generate electricity. They usually include moving components and complicated mechanical conversion systems (e.g. power take-off systems). So both hydrodynamic and dynamic interactions have to be considered in numerical investigations.
Numerical methods for hydrodynamic modelling fall into potential- or viscous-flow frames (Li and Yu, 2012). Linear or nonlinear wave theories can be used for potential-flow analyses. Linear wave theory is usually used for operational sea states and nonlinear wave theory is adopted for the analyses of strongly non-linear waves and extreme events (Coe and Neary, 2014). When viscous effects cannot be neglected, empirical viscous coefficients have been introduced to provide reasonable predictions. However, these coefficients are geometry dependent and limited to model scale. The difficulty of this approach has been highlighted by Pauw et al. (2007) and Sun et al. (2015). A good alternative is to use a computational fluid dynamic (CFD) model such as that presented by Wei et al. (2013).
This paper aims to provide a better understanding of the interaction between focused waves and FPSO-shaped structures. This is achieved via numerical modelling using the parallel Particle-In-Cell method based model, which solves the Navier-Stokes equations for free-surface flows and incorporates a Cartesian cut cell method for fluid-structure interaction. Focused waves are generated using a piston-type wave paddle. The generated focused waves are first validated against experimental measurements and then used for fluid-structure interaction. The wave run-up and hydrodynamic pressure at various locations on the FPSO model are discussed.
This paper presents a numerical study of focused wave impact on a fixed FPSO (Floating Production Storage and Off-loading) like structure as part of the Blind Test Workshop (Series 1) devised by the Collaborative Computational Project in Wave Structure Interaction (CCP-WSI) group (https://www. ccpwsi. ac. uk/blind_test_series_l_focused_wave). The Workshop aims to provide a better understanding of the wide issues involved in selecting or developing numerical models for simulating the interaction of waves with offshore and coastal structures. The aim of this paper is thus to test the performance of a Particle-In-Cell (PIC) method based numerical model for simulating such wave-structure interaction (WSI) problem and to provide better understanding of the physical phenomena involved.
With the increasing development of oil and gas resources in deeper and deeper waters, FPSO vessels are widely designed and used in offshore oil and gas industry. Therefore, understanding the hydrodynamic performance of FPSOs under, especially, harsh sea environment is of great importance to the design and operation of FPSOs. In the literature, extreme wave interaction with FPSO-like structures has been widely studied both experimentally and numerically. Zang et al. (2006) numerically investigated the effects of second-order wave diffraction on the wave scattering and the wave run-up around a FPSO-shaped structure under focused wave action, using the potential flow solver DIFFRACT. Mai et al. (2016) conducted a physical experimental study also on focused wave interaction with FPSO-shaped structures, with an emphasis on understanding the effects of wave steepness, wave incident angles and lengths of the FPSO model on the different harmonics of the nonlinear scattered wave field around the structure. In this paper, the setup of the physical model of Mai et al. (2016) has been used but with more results such as pressures on the structure surface to be presented.
In the present study, OpenFOAM has been extended for modelling hydrodynamic performance of a flap-type wave energy converter in viscous flow. The numerical results of the OpenFOAM model have been compared with analytical results based on linear potential flow theory. The effects of nonlinearity and viscosity on the wave-induced motion of the oscillating flap are studied as well as the energy absorbing capacity of the device. Parametric analysis has been performed to investigate the dependence of the hydrodynamics of the device on the power take-off system
In present paper, both potential-flow and viscous-flow solvers have been used in the numerical analysis of wave-structure interactions. In the first case, surface elevations around a fixed truncated circular column have been investigated and numerical results have been compared with experimental data. Nonlinear wave forces acting on the same column have also been estimated. In the second case, the roll motion of a rectangular floating structure in regular wave has been simulated.
Li, Xiao-Jun (Institute of Mechanics, Chinese Academy of Sciences) | Gao, Fu-Ping (Institute of Mechanics, Chinese Academy of Sciences) | Yang, Bing (Institute of Mechanics, Chinese Academy of Sciences) | Zang, Jun (Department of Architecture & Civil Engineering, University of Bath)
Li, Xiaojun (Key laboratory for Hydrodynamics and Ocean Engineering, Institute of Mechanics, Chinese Academy of Sciences) | Yang, Bing (Key laboratory for Hydrodynamics and Ocean Engineering, Institute of Mechanics, Chinese Academy of Sciences) | Gao, Fuping (Key laboratory for Hydrodynamics and Ocean Engineering, Institute of Mechanics, Chinese Academy of Sciences) | Zang, Jun (Department of Architecture & Civil Engineering, University of Bath)
Zang, Jun (Department of Architecture & Civil Engineering, University of Bath, Bath, UK) | Liu, Shuxue (The State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology, Dalian, P.R. China) | Taylor, Rodney Eatock (Department of Engineering Science, University of Oxford, Oxford, UK) | Taylor, Paul H. (Department of Engineering Science, University of Oxford, Oxford, UK)
In this paper, we present both numerical and experimental studies on wave interaction with a circular cylinder in shallow water and examine the effect of nonlinearity on the wave run-up on the structure. Second-order wave diffraction theory has been included in the numerical simulation to steep waves. Both the wave run-up time history on the cylinder and the wave response spectrum derived from the diffracted wave time series are investigated and compared with the experiments conducted in a wave tank. Numerical predictions from the 2nd-order diffraction simulations agree very well with the experimental measurements for both wave run-up and response spectrum. This validation confirmed that the 2nd-order wave diffraction solution works well for steep waves in shallow water, while linear diffraction theory incorrectly predicts the peakwater levels and response spectrum.
Wave diffraction and scattering from coastal and offshore structures are of importance in understanding the impact of nonlinear waves on structures, and resulting wave loadings for structural design. Over the past 20 years, research into nonlinear wave interaction with deep-water offshore platforms and FPSO (Kim and Yue, 1989, 1990; Chau and Eatock Taylor, 1992; Eatock Taylor and Huang, 1997; Buldakov et al., 2004; Zang et al., 2003, 2005, 2006) has indicated the importance of wave theory for estimation and safe offshore design. Second-order wave diffraction theory has been successfully applied to predict nonlinear wave forces and free-surface elevations around deep-water structures. To achieve the target of 20% of the electricity generated from all sources coming from renewable energyby2020, it is expected that large numbers of offshore wind turbines will be installed along the UK coastline in the coming decade. Deep-water offshore technology, traditionally used for the development of offshore platforms and floating vessels for the oil and gas industry, is currently used for the development of offshore wind farms.
Westphalen, Jan (University of Plymouth School of Civil Engineering Plymouth, UK) | Greaves, Deborah (University of Plymouth School of Civil Engineering Plymouth, UK) | Williams, Chris (University of Bath Department of Architecture and Civil Engineering Bath,UK) | Zang, Jun (University of Bath Department of Architecture and Civil Engineering Bath,UK) | Taylor, Paul (University of Oxford Department of Engineering Science Oxford, UK)