Study of Viscous Effects on Wave Drift Forces on a Rectangular Pontoon With a Damping Plate by Using CFD Code OpenFOAM

2018 ◽  
Author(s):  
Adrien Courbois ◽  
Emmanuel Tcheuko ◽  
Benjamin Bouscasse ◽  
Youngmyung Choi ◽  
Olivier Kimmoun ◽  
...  
Keyword(s):  
Wave Energy ◽  
Radiation Effects ◽  
Offshore Structures ◽  
Viscous Effects ◽  
Wave Energy Dissipation ◽  
Wave Drift ◽  
Transmitted Waves ◽  
Conventional Radiation ◽  
Wave Drift Forces ◽  
Drift Forces

Wave drift loads play a key role in station-keeping analysis of floating offshore structures. However, conventional radiation/diffraction tools have some limitations especially when the structure has sharp edges, requiring more extended validation. In this paper, a series of CFD computations are performed on a 2D simplified shape representing a rectangular-pontoon, with or without a horizontal damping plate. In the present study, the structure is considered to be fixed (radiation effects are not included). For validation, the results of CFD are compared with the results of experiments. The model tests are performed at the wave canal with an equivalent configuration. The drift forces are derived from the reflected and transmitted waves thanks to far field formulation. The incident, reflected and transmitted waves are separated by using a multi “sensors” method. The dissipation of wave energy is also investigated. The analysis is performed on two different model configurations: with and without the presence of a bottom damping plate. The effect of the damping plate on the wave energy dissipation and drift forces are discussed. The results obtained allows for a better understanding and will allow the study on more complex configurations.

Mooring of Semi Submersibles in Extreme Sea States: Simplified Models for Wave Drift Forces and Low Frequency Damping

2018 ◽  
Author(s):  
Kjell Larsen ◽  
Tjerand Vigesdal ◽  
Rune Bjørkli ◽  
Oddgeir Dalane
Keyword(s):  
Low Frequency ◽  
Scale Model ◽  
Small Scale ◽  
Mooring System ◽  
Viscous Effects ◽  
Empirical Correction ◽  
Wave Drift ◽  
Total Wave ◽  
Wave Drift Forces ◽  
Drift Forces

This paper presents results from extensive small-scale model testing of three semi submersibles together with an overview of damping contributions of low frequency motions. The objectives of the model tests were to verify empirical correction formulas for viscous wave drift forces and to recommend and validate theoretical low frequency damping models. The main parameters of the semis such as displacement, number of columns and diameter of columns were intentionally varied in order to assess the effects on total wave drift forces and corresponding damping. The results show that viscous effects significantly increase the total wave drift forces in extreme sea states. The presence of current increases the effect. As expected, the viscous contribution to wave drift is especially important for semis with slender columns. A revised empirical correction formula for wave drift forces is proposed based on model test results. An overview of the different low frequency damping effects is given. Damping from viscous forces on the hull and damping from the mooring system are the most important sources of damping for the moored semis. A simplified model to calculate mooring system damping is proposed. For accurate prediction of low frequency motions of moored semi submersibles in extreme sea states, a damping level in the range 40–70% of critical damping should be applied for surge and sway when the empirical correction formulas for wave drift forces are applied.

Estimating Second Order Wave Drift Forces and Moments for Calculating DP Capability Plots

2019 ◽  
Author(s):  
Saeed Barzegar Valikchali ◽  
Mitchell Anderson ◽  
David Molyneux ◽  
Dean Steinke
Keyword(s):  
Wind Waves ◽  
Low Frequency ◽  
Offshore Structures ◽  
Second Order ◽  
Design Stage ◽  
Wave Direction ◽  
Dynamic Positioning System ◽  
Wave Drift ◽  
Wave Drift Forces ◽  
Drift Forces

Abstract The DP capability plot is a useful tool to show the limitations of a dynamic positioning system for ships or offshore structures under loading from wind, waves and ocean currents. At the preliminary design stage, it is desirable to use fast methods for calculating the forces and moments caused by the environment, preferably without the need for CFD simulations or model experiments. Empirical methods are available for predicting aerodynamic forces and moments, and hydrodynamic forces and moments from currents, but little is published for second order wave drift forces. Wave drift forces and moment calculations have been carried out using WAMIT, for a series of ship hulls from OSVs to VLCCs and the effects of wave direction and frequency on the Surge, Sway, and Yaw forces and moment have been studied. The presentation of the results allows the user to interpolate the resulting drift forces and moments as a function of wave direction for a given ship size. In terms of wave drift loads calculation, it is found that the very large vessels are dominant in the low frequency waves, while smaller size ships are in high frequencies. The wave frequency and direction in which maximum drift load occurs depends on the ship size.

Analysis of Wave Drift Forces on a Floating Wave Energy Converter

2008 ◽  
Author(s):  
Nuno Fonseca ◽  
Ricardo Pascoal ◽  
Joa˜o Marinho ◽  
Tiago Morais
Keyword(s):  
Transfer Function ◽  
Wave Energy ◽  
Time History ◽  
Wave Energy Converter ◽  
Mooring System ◽  
Energy Converter ◽  
Wave Drift ◽  
The Mean ◽  
Wave Drift Forces ◽  
Drift Forces

Wave drift forces acting on floating wave energy converters (WEC) are often the most important loading component for the design of the mooring system. On one hand these forces may be, at least, one order of magnitude larger than wind and current forces, and on the other hand the floating structure and mooring system may respond dynamically to the slowly varying wave drift forces. The paper presents an analysis of the wave drift forces on an articulated floating wave energy converter. Particular attention is given to the effects of the wave energy extraction on the time history of the horizontal drift forces. The hydrodynamic calculations are carried out by a frequency domain Green function panel method, resulting on the transfer function of the WEC motions as well as the transfer function of the mean drift forces. The power takeoff system is represented by a simple linear model where the extracted power is related to the relative velocity in the articulation and the damper of the PTO. With the transfer function of the mean drift forces, the variance spectrum of these same forces is calculated for stationary irregular seastates, and finally time histories of the drift forces are produced for typical operational conditions.

Time-Domain Hydrodynamic Model for Mooring Analysis of a Spread Moored Fpso With Calibration of Wave Drift Forces

2021 ◽  
Author(s):  
Min Zhang ◽  
Junrong Wang ◽  
Junfeng Du ◽  
Nuno Miguel Magalhaes Duque Da Fonseca ◽  
Galin Tahchiev ◽  
...  
Keyword(s):  
Time Domain ◽  
Hydrodynamic Model ◽  
Wave Drift ◽  
Wave Drift Forces ◽  
Drift Forces

On Approximations of the Wave Drift Forces Acting on Semi-Submersible Platforms With Heave Plates

2016 ◽  
Author(s):  
Bernard Molin ◽  
Jean-Baptiste Lacaze
Keyword(s):  
Wave Field ◽  
Scattered Wave ◽  
Diffraction Radiation ◽  
Morison Equation ◽  
Wave Drift ◽  
Horizontal Wave ◽  
Heave Plate ◽  
Drift Force ◽  
Wave Drift Forces ◽  
Drift Forces

The horizontal wave drift force acting on a vertical floating column, without then with a heave plate, is considered. Computations are performed with a diffraction-radiation code and through the Morison and Rainey equations. Focus is on wave frequencies around the heave resonance where the drift force may be significant, even though the scattered wave-field being weak. It is found that the Morison equation overpredicts the drift force while Rainey equations perform rather well.

Motion Decay Simulations of a Moored Wave Energy Converter

2020 ◽  
Author(s):  
Changqing Jiang ◽  
Ould el Moctar ◽  
Thomas E. Schellin ◽  
Guilherme Moura Paredes
Keyword(s):  
Wave Energy ◽  
Stokes Equations ◽  
Numerical Approach ◽  
Offshore Structures ◽  
Primary Role ◽  
Viscous Effects ◽  
Restoring Force ◽  
System A ◽  
Cost Reductions ◽  
Catenary System

Abstract Significant cost reductions are required for marine renewable energy to become competitive. Aside from the deployment of arrays, one key area that has been identified as having potential for cost reductions is the mooring system. A challenge, therefore, is to design mooring systems which can satisfy their primary role of station keeping while being affordable and durable. This paper presents the effects of three different mooring configurations on the motion behavior of a buoy type wave energy convertor, considering nonlinear mooring-induced fluid-structure interactions, such as the associated viscous effects. To simulate motion decay, an overset mesh method that coupled a dynamic mooring model with the Navier-Stokes equations flow solver OpenFOAM was adopted. The mooring configurations comprised an all catenary system, a catenary system with buoys, and a catenary system with buoys and clump weights. The favorable agreement between the simulations and experimental measurements validated the coupled numerical approach for simulating different mooring configurations. The mooring systems influenced not only restoring force characteristics, but also total damping of the system, which demonstrated the importance of considering mooring-induced damping when investigating moored offshore structures.

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