scholarly journals Influence of Viscosity and Non-Linearities in Predicting Motions of a Wind Energy Offshore Platform in Regular Waves

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
José del Águila Ferrandis ◽  
Luca Bonfiglio ◽  
Ricardo Zamora Rodríguez ◽  
Chryssostomos Chryssostomidis ◽  
Odd Magnus Faltinsen ◽  
...  
Keyword(s):  
Boundary Element ◽  
Potential Flow ◽  
Offshore Platform ◽  
Operating Conditions ◽  
Boundary Element Methods ◽  
Linear Wave ◽  
Floating Bodies ◽  
Computational Costs ◽  
Non Linear ◽  
Flow Theories

Abstract Motion predictions of floating bodies in extreme waves represent a challenging problem in naval hydrodynamics. The solution of the seakeeping problem involves the study of complex non-linear wave-body interactions that require large computational costs. For this reason, over the years, many seakeeping models have been formulated in order to predict ship motions using simplified flow theories, usually based on potential flow theories. Neglecting viscous effects in the wave-induced forces might largely underestimate the energy dissipated by the system. This problem is particularly relevant for unconventional floating bodies at resonance. In these operating conditions, the linear assumption is no longer valid, and conventional boundary element methods, based on potential flow, might predict unrealistic large responses if not corrected with empirical viscous damping coefficients. The application considered in this study is an offshore platform to be operated in a wind farm requiring operability even in extreme meteorological conditions. In this paper, we compare heave and pitch response amplitude operators predicted for an offshore platform using three different seakeeping models of increasing complexity, namely, a frequency-domain boundary element method (BEM), a partly nonlinear time domain BEM, and a non-linear viscous model based on the solution of the unsteady Reynolds-averaged Navier–Stokes (URANS) equations. Results are critically compared in terms of accuracy, applicability, and computational costs.

scholarly journals Influence of Viscosity and Non-Linearities in Predicting Motions of a Wind Energy Offshore Platform in Regular Waves

2018 ◽  
Author(s):  
José del Águila Ferrandis ◽  
Ricardo Zamora Rodríguez ◽  
Chryssostomos Chryssostomidis ◽  
Luca Bonfiglio
Keyword(s):  
Frequency Domain ◽  
Stokes Equations ◽  
Offshore Platform ◽  
Operating Conditions ◽  
Boundary Element Methods ◽  
Linear Wave ◽  
Floating Bodies ◽  
Computational Costs ◽  
Non Linear ◽  
Flow Theories

Motion prediction of floating bodies in waves represents one of the most challenging problems in naval hydrodynamics. The solution of the seakeeping problem involves the study of complex non-linear wave-body interactions that require large computational costs. For this reason, over the years many seakeeping models have been formulated in order to predict ship motions using simplified flow theories, usually based on potential flow theories solved within the linear assumption. Neglecting viscous effects in the computation of radiation forces might largely underestimate the energy dissipated by the system while moving at the free surface. This problem is particularly relevant for unconventional floating bodies at resonance. In these operating conditions the linear assumption is no longer valid and conventional Boundary Element Methods, solved in the frequency domain, might predict unrealistic large responses if not corrected with empirical damping coefficients. The application considered in this study is an offshore platform to be operated in a wind farm requiring operability even in extreme meteorological conditions. In this paper, we compare heave and pitch Response Amplitude Operators, predicted for an offshore platform using three different seakeeping models of increasing complexity; namely a frequency-domain BEM, a high-order BEM solved in time-domain and a non-linear fully viscous model based on the solution of the Unsteady Reynolds Averaged Navier-Stokes equations (URANS). Results are critically compared in terms of accuracy, applicability and computational costs.

scholarly journals Boundary element methods for the wave equation based on hierarchical matrices and adaptive cross approximation

2021 ◽  
Author(s):  
Daniel Seibel
Keyword(s):  
Wave Equation ◽  
Boundary Element ◽  
Domain Boundary ◽  
Boundary Element Methods ◽  
Scattering Problems ◽  
Computational Costs ◽  
Adaptive Cross Approximation ◽  
Transient Problems ◽  
Matrix Compression ◽  
Convolution Quadrature Method

AbstractTime-domain Boundary Element Methods (BEM) have been successfully used in acoustics, optics and elastodynamics to solve transient problems numerically. However, the storage requirements are immense, since the fully populated system matrices have to be computed for a large number of time steps or frequencies. In this article, we propose a new approximation scheme for the Convolution Quadrature Method powered BEM, which we apply to scattering problems governed by the wave equation. We use $${\mathscr {H}}^2$$ H 2 -matrix compression in the spatial domain and employ an adaptive cross approximation algorithm in the frequency domain. In this way, the storage and computational costs are reduced significantly, while the accuracy of the method is preserved.

scholarly journals NON-LINEAR WAVE FORCES ON FLOATING BREAKWATERS

1982 ◽  
Vol 1 (18) ◽  
pp. 120
Author(s):  
C.T. Niwinski ◽  
M. De St. Q. Isaacson
Keyword(s):  
Wave Train ◽  
Wave Forces ◽  
Linear Wave ◽  
Floating Bodies ◽  
Time Stepping ◽  
Non Linear ◽  
Force Curves ◽  
Accuracy Of Results ◽  
Floating Breakwaters ◽  
Linear Nature

A non-linear numerical method for calculating wave forces on floating bodies has been developed by Isaacson (1981). The time stepping procedure is programmed for a computer solution, and an incident wave train is time stepped past a fixed two-dimensional rectangular breakwater. The influence of various input parameters on the accuracy of results is investigated, and optimal values of the parameters are determined. The optimal numerical parameters are used to generate force and transmission coefficient results, which are compared to the results of other published studies. The method is shown to compare favorably with other results, with the non-linear nature of the method being clearly demonstrated by the different force curves produced by varying the wave height.

Non Linear Wave Loading of the 3D FE Structural Model of Floating Bodies

2013 ◽  
Author(s):  
Jérôme de Lauzon ◽  
François-Xavier Sireta ◽  
Sime Malenica
Keyword(s):  
Time Domain ◽  
Potential Flow ◽  
Structural Model ◽  
Linear Wave ◽  
Impulse Response Functions ◽  
Convolution Integral ◽  
Floating Bodies ◽  
Hybrid Frequency ◽  
The Time Domain ◽  
Interaction Problem

Different numerical methods exist to treat the non-linear wave body interaction problem. These methods go from very complex CFD simulations (VoF, SPH…) to simpler potential flow based methods. Within the potential flow methods, different types of numerical approaches also exist, going from very complex fully nonlinear time domain methods to simpler hybrid frequency-time domain methods. In this paper, only the hybrid frequency-time domain potential flow methods are of concern. The basic principle of these methods is to use the linear frequency domain data and transfer them to the time domain (Cummings-1962, Ogilvie-1964) using the inverse Fourier transforms. Once in the time domain, all kind of nonlinearities can be added on top of the linear solution. This method showed to be very computationally efficient for global behavior of the floating bodies. However, in the context of the body structural response, it is not trivial to make the load transfer from the 3D hydrodynamic panel model to 3DFE model of the structure. One of the main problems concerns the radiation part of the potential which comes into the play through the well-known convolution integral of the impulse response functions. Within the hydro-structure interaction problem which is of concern here, the straightforward application of the Cummings principles leads to the convolution integral for every pressure point (either on hydrodynamic or structural mesh) which can lead to very expensive numerical simulations. Previous study by Tuitman, Sireta, Malenica and Bosman (2009) proposed the use of the fast Fourier transform (FFT) to compute the radiated wave loads at each point of the structural model, as a post-processing of the seakeeping calculations. In this way the CPU time is significantly reduced but the slight unbalancing of the 3DFE model remains. In this paper, we propose the direct use of the local radiated pressure impulse response functions and we show that a good numerical implementation of such method can result in acceptable CPU time with perfect balance of the 3DFE model.

scholarly journals Kink degeneracy and rogue potential flow for the (3+1)-dimensional generalized Kadomtsev-Petviashvili equation

2016 ◽  
Vol 20 (suppl. 3) ◽  
pp. 919-927 ◽  
Author(s):  
Han-Lin Chen ◽  
Zhen-Hui Xu ◽  
Zheng-De Dai
Keyword(s):  
Potential Flow ◽  
Rogue Wave ◽  
Soliton Solutions ◽  
Linear Wave ◽  
Test Technique ◽  
Rational Potential ◽  
Higher Dimensional ◽  
Petviashvili Equation ◽  
Non Linear ◽  
Kink Soliton

The breather-type kink soliton, breather-type periodic soliton solutions and rogue potential flow for the (3+1)-dimensional generalized Kadomtsev-Petviashvili equation are obtained by using the extended homoclinic test technique and homoclinic breather limit method, respectively. Furthermore, some new non-linear phenomena, such as kink and periodic degeneracy, are investigated and the new rational breather solutions are found out. Meanwhile, we also obtained the rational potential solution and it is just a rogue wave. These results enrich the variety of the dynamics of higher-dimensional non-linear wave field.

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