A Nonlinear Numerical Algorithm for Time-Domain Hydrodynamic Simulations of Vessel Motions in the Presence of Waves

2012 ◽  
Author(s):  
Eduardo Pasquetti ◽  
Luiz Cristóvão G. Coelho ◽  
Marcelo A. S. Neves ◽  
Mauro C. Oliveira ◽  
Paulo T. T. Esperança ◽  
...  
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Relative Position ◽  
Geometric Modeling ◽  
Domain Model ◽  
Irregular Waves ◽  
Wave Forces ◽  
Hydrodynamic Simulations ◽  
Non Linear ◽  
Hull Forms

Linear approaches have been traditionally employed to simulate the dynamic behavior of floating vessels and its interaction with regular or irregular waves. Some difficulties arise when large waves and vessel motions occur. Under these circumstances, the linear assumptions to compute the restoring and wave forces, which are computed on the mean position of body and water surface, are not capable of accurately representing the physics of the interactions between waves and vessels. Hydrostatic analysis of generic hull forms has already been implemented with a geometrical face representation of the hull and also internal ballast and oil tanks [1]. With the goal of improving the modeling the non-linear computation of hydrostatic in waves (at the instantaneous free surface) is implemented, thus using a generic geometric modeling of the hull to perform hydrodynamic simulations of vessel motions in the presence of waves. Additionally, for the computation of the instantaneous non-linear Froude-Krylov force (6 DOF time-domain model) the contribution of each geometrical face to the global Froude-Krylov force is calculated at the exact relative position of the vessel and the incident waves. After computing the relative position of each face, possibly being cut at the free surface, the pressure at the wetted face centers determines the contribution to the integral calculation. The paper presents the main aspects of the proposed methodology and highlights its capabilities and differences with respect to the linear approach. Complementarily, comparisons with model experiments are discussed.

Frequency, Stochastic and Time Domain Models for an Articulated Wave Power Device

2008 ◽  
Author(s):  
Jose´ J. Caˆndido ◽  
Paulo A. P. Justino
Keyword(s):  
Stochastic Model ◽  
Time Domain ◽  
Domain Model ◽  
Irregular Waves ◽  
Power Device ◽  
Wave Power ◽  
Regular Waves ◽  
Sea State ◽  
Frequency Model ◽  
Non Linear

A frequency domain model to describe the behaviour of an articulated system in regular waves is developed. A stochastic model is found for the articulated wave power device. Probability density functions for relevant parameters that characterize the wave power system behaviour are found for different sea state conditions. Average values for useful power and capture length are also obtained for these sea state conditions. A time domain model is also developed for the articulated wave power device. Results for a linear power take-off configuration and regular waves are obtained and compared to the results obtained from the frequency model. A non-linear power take-off configuration is found. Results in regular wave conditions are obtained for this configuration, set in terms of different characteristic parameters. Results for this non-linear configuration for the power take-off and irregular waves are also computed and presented. Finally, these results are compared to the results obtained from the stochastic model.

scholarly journals Prediction of deepwater riser VIV with an improved time domain model including non-linear structural behavior

2021 ◽  
Vol 236 ◽  
pp. 109508
Author(s):  
Sang Woo Kim ◽  
Svein Sævik ◽  
Jie Wu ◽  
Bernt Johan Leira
Keyword(s):  
Time Domain ◽  
Domain Model ◽  
Structural Behavior ◽  
Non Linear ◽  
Deepwater Riser

Coupled Time-Domain Hydro-Elastic Simulation for Submerged Floating Tunnel Under Wave Excitations

2021 ◽  
Author(s):  
Chungkuk Jin ◽  
Sung-Jae Kim ◽  
MooHyun Kim
Keyword(s):  
Time Domain ◽  
Domain Model ◽  
Mooring Line ◽  
Wave Forces ◽  
Rod Theory ◽  
Discrete Module ◽  
Simulation Based ◽  
Submerged Floating Tunnel ◽  
The Time Domain ◽  
Elastic Simulation

Abstract We develop a fully-coupled time-domain hydro-elasticity model for the Submerged Floating Tunnel (SFT) based on the Discrete-Module-Beam (DMB) method. Frequency-domain simulation based on 3D potential theory results in multibody’s hydrodynamic coefficients and excitation forces for tunnel sections. Subsequently, we build the time-domain model with the multibody Cummins equation and external stiffness matrix from the Euler-Bernoulli and Saint-Venant torsion theories. We establish the mooring line model with rod theory and couple components with translational springs at their respective connection locations. We then compare the dynamic motions, wave forces, and mooring tensions between the present and Morison-equation-based elastic models under regular wave excitations at different submergence depths. The present model is especially important for the shallowly submerged tunnel in which the Morison model shows exaggerated motions, especially at high-frequency range.

scholarly journals Evaluation of the Viscous Drag for a Domed Cylindrical Moored Wave Energy Converter

2019 ◽  
Vol 7 (4) ◽  
pp. 120 ◽  
Author(s):  
Majid A Bhinder ◽  
Jimmy Murphy
Keyword(s):  
Free Surface ◽  
Drag Coefficient ◽  
Wave Field ◽  
Time Domain ◽  
Potential Flow ◽  
Radiation Damping ◽  
Domain Model ◽  
Viscous Drag ◽  
Structure Interaction ◽  
D Values

Viscous drag, nonlinear in nature, is an important aspect of the fluid–structure interaction modelling and is usually not taken into account when the fluid is assumed to be inviscid. Potential flow solvers can competently compute radiation damping, which is related to the radiated wave field. However, the drag damping primarily related to the viscous effects is usually neglected in the radiation/diffraction problems solved by the boundary element method (BEM), also known as the boundary integral element method (BIEM). This drag force can have a significant impact in the case of structures extending much deeper below the free surface, or for those that are completely submerged. In this paper, the drag coefficient C d was quantified for the heave and surge response of a structure which consists of a moored horizontally oriented domed cylinder with two surface piercing square columns located at the top surface. The domed cylinder is the primary part and is submerged. The drag coefficient is estimated using the experimental measurements related to harmonic monochromatic wave–structure interaction. Finally, this estimated drag coefficient was used in the modified time domain model, which includes the nonlinear viscous correction term, and the resulting device response in heave and surge directions is presented for an irregular incoming wave field. The comparison of the numerical model and the experiments validates the estimated C d values obtained earlier. Prior to the time domain model, frequency-dependent parameters such as added mass, radiation damping, and excitation force were computed using three mainstream potential flow packages (that is, ANSYS AQWA, WAMIT, and NEMOH), and a comparison is presented. The effect of free surface on the drag coefficient is investigated through differences in C d values between heave and surge modes.

Vortex Induced Vibrations of Pipelines With Non-Linear Seabed Contact Properties

2016 ◽  
Author(s):  
Jan V. Ulveseter ◽  
Svein Sævik ◽  
Carl M. Larsen
Keyword(s):  
Frequency Domain ◽  
Linear Model ◽  
Time Domain ◽  
Structural Model ◽  
Life Time ◽  
Domain Model ◽  
Linear Interaction ◽  
Vortex Induced Vibrations ◽  
Non Linear ◽  
Soil Damping

A promising time domain model for calculation of cross-flow vortex induced vibrations (VIV) is under development at the Norwegian University of Science and Technology. Time domain, as oppose to frequency domain, makes it possible to include non-linearities in the structural model. Pipelines that rest on an irregular seabed will experience free spans. In these areas VIV is a concern with respect to the fatigue life. In this paper, a time domain model for calculation of VIV on free spanning pipelines is proposed. The model has non-linear interaction properties consisting of discrete soil dampers and soil springs turning on or off depending on the pipeline response. The non-linear model is compared to two linear models with linear stiffness and damping properties. One linear model is based on the promising time domain VIV model, while the other one is based on RIFLEX and VIVANA, which calculates VIV in frequency domain. Through four case studies the effect of seabed geometry, current velocity and varying soil damping and soil stiffness is investigated for a specific pipeline. The results show that there is good agreement between the results produced by VIVANA and the linear model. The non-linear model predicts smaller stresses at the pipe shoulders, which is positive for the life time estimations. Soil damping does not influence the response significantly.

Numerical Simulations of Regular and Irregular Wave Forces on a Horizontal Semi-Submerged Cylinder

2017 ◽  
Author(s):  
Shengnan Liu ◽  
Muk Chen Ong ◽  
Charlotte Obhrai ◽  
Sopheak Seng
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Numerical Simulations ◽  
Stokes Equations ◽  
Wave Length ◽  
Wave Structure ◽  
Numerical Results ◽  
Irregular Waves ◽  
Wave Forces ◽  
Submerged Cylinder

Two-dimensional (2D) numerical simulations have been performed using OpenFOAM (an open source CFD software package [1]) and waves2Foam (an OpenFOAM based add-on library for wave generations and absorption [2]) to investigate free surface waves past one fixed horizontally semi-submerged cylinder. The 2-D simulations are carried out by solving Navier-Stokes equations which are discretized based on finite volume method (FVM). Volume of Fluid (VOF) method is employed to capture the free surface in the numerical wave tank. Validation studies have been performed by comparing the numerical results of Stokes first-order wave past a semi-submerged circular cylinder with the published experimental data at different incident wave properties. The numerical results are in good agreement with the experimental data. Subsequently, regular and irregular waves past semi-submerged cylinder at different wave heights and the wave lengths are computed numerically to investigate the effect of the wave height and wave length on wave-structure interaction. The numerical results for irregular waves are compared with those induced by regular waves.

Frequency and Time Domain Analysis of Vortex Induced Vibrations for Free Span Pipelines

2002 ◽  
Author(s):  
Carl M. Larsen ◽  
Kamran Koushan ◽  
Elizabeth Passano
Keyword(s):  
Time Domain ◽  
Structural Model ◽  
Linear Time ◽  
Time Domain Analysis ◽  
Linear Response Theory ◽  
Domain Model ◽  
Vortex Induced Vibrations ◽  
Non Linear ◽  
New Strategy ◽  
Stress Prediction

The present paper will discuss various models for calculation of vortex induced vibrations (VIV) of free span pipelines, and present a new strategy for such analyses. Applications of traditional models are presented and their limitations discussed. The new approach is based on the combination of an empirical linear frequency domain model, and a non-linear time domain structural model. The first step is to carry out the VIV analysis according to linear response theory, and next introduce the calculated hydrodynamic forces to the non-linear structural model. The benefit from using the non-linear model is to describe stresses at the shoulders more accurately, which is important since fatigue damage in many cases will be largest in this area. The conclusion is that the interaction between pipe and seafloor is crucial for accurate stress prediction, and that a non-linear time domain model will give the most accurate result.

scholarly journals Free Surface Reconstruction for Phase Accurate Irregular Wave Generation

2018 ◽  
Vol 6 (3) ◽  
pp. 105 ◽  
Author(s):  
Ankit Aggarwal ◽  
Csaba Pákozdi ◽  
Hans Bihs ◽  
Dag Myrhaug ◽  
Mayilvahanan Alagan Chella
Keyword(s):  
Free Surface ◽  
Surface Reconstruction ◽  
Deep Water ◽  
Time Domain ◽  
Present Approach ◽  
Surface Elevation ◽  
Irregular Waves ◽  
Free Surface Elevation ◽  
Irregular Wave ◽  
The Time Domain

The experimental wave paddle signal is unknown to the numerical modellers in many cases. This makes it quite challenging to numerically reproduce the time history of free surface elevation for irregular waves. In the present work, a numerical investigation is performed using a computational fluid dynamics (CFD) based model to validate and investigate a non-iterative free surface reconstruction technique for irregular waves. In the current approach, the free surface is reconstructed by spectrally composing the irregular wave train as a summation of the harmonic components coupled with the Dirichlet inlet boundary condition. The verification is performed by comparing the numerically reconstructed free surface elevation with theoretical input waves. The applicability of the present approach to generate irregular waves by reconstructing the free surface is investigated for different coastal and marine engineering problems. A numerical analysis is performed to validate the free surface reconstruction approach to generate breaking irregular waves over a submerged bar. The wave amplitudes, wave frequencies and wave phases are modelled with good accuracy in the time-domain during the higher-order energy transfers and complex processes like wave shoaling, wave breaking and wave decomposition. The present approach to generate irregular waves is also employed to model steep irregular waves in deep water. The free surface reconstruction method is able to simulate the irregular free surface profiles in deep water with low root mean square errors and high correlation coefficients. Furthermore, the irregular wave forces on a monopile are investigated in the time-domain. The amplitudes and phases of the force signal under irregular waves generated by using the current technique are modelled accurately in the time-domain. The proposed approach to numerically reproduce the free surface elevation in the time-domain provides promising and accurate results for all the benchmark cases.

Computational Fluid Dynamics Simulations of Regular and Irregular Waves Past a Horizontal Semi-Submerged Cylinder

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Shengnan Liu ◽  
Muk Chen Ong ◽  
Charlotte Obhrai ◽  
Sopheak Seng
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Wave Height ◽  
Stokes Equations ◽  
Wave Force ◽  
Numerical Results ◽  
Irregular Waves ◽  
Wave Forces ◽  
Regular Waves ◽  
Peak Period

Two-dimensional (2D) numerical simulations have been performed to investigate both regular and irregular waves past a fixed horizontally semisubmerged circular cylinder. The 2D simulations are carried out by solving Navier–Stokes equations discretized by finite volume method. Volume of fluid (VOF) method is employed to capture the free surface in the numerical wave tank (NWT). Validation studies have been performed by comparing the numerical results of free surface waves past the cylinder with the published experimental and numerical data. The present numerical results are in good agreement with both the experimental and the other numerical results in terms of hydrodynamic forces and free surface elevation. Subsequently, the effects of the wave height and the wavelength on wave–structure interaction are investigated by conducting numerical simulations on the regular and the irregular waves past a semisubmerged cylinder at different wave heights and the wavelengths. The averaged and maximum vertical wave forces on the cylinder increase with the increasing wave height. The numerical results for the irregular waves are compared with those induced by the regular waves in terms of the maximum and averaged vertical wave forces. When the significant wave height and the spectral peak period of the irregular waves are equal to the wave height and the wave period of the regular waves, the maximum vertical wave force induced by the irregular waves is larger than that induced by the regular waves, meanwhile, the average vertical wave forces have the contrary relationship.

Comparison of Time and Frequency Domain Simulations of an Offshore Floating Wind Turbine

2011 ◽  
Author(s):  
Maxime Philippe ◽  
Aure´lien Babarit ◽  
Pierre Ferrant
Keyword(s):  
Wind Turbine ◽  
Frequency Domain ◽  
Time Domain ◽  
Degrees Of Freedom ◽  
Domain Model ◽  
Floating Platform ◽  
Floating Wind Turbine ◽  
Non Linear ◽  
Offshore Floating Wind Turbine ◽  
The Time Domain

Time domain simulations of an offshore floating wind turbine have been performed. Hydrodynamic impulse responses of the floating platform are calculated with linear hydrodynamic simulation tool ACHIL3D. A user defined module for the wind turbine design code FAST has been developed to calculate hydrodynamic and mooring loads on the structure. Resolution of the movements of the system is done with FAST. Simulation results in time domain are compared with frequency domain results. In the frequency domain model, the whole system is linearized. In the time domain model, the wind turbine model is not linearized. A good agreement between time and frequency domain calculations is observed, even for the pitch motion. Furthermore we observe a non linearity in the response of sway, roll and yaw degrees of freedom around 0.3 rad.s-1. The effect of viscous damping on the movements of the floating wind turbine system has been studied with the time domain model, and a non linear hydrostatic and Froude-Krylov load model has been developed. Effects of these non linear terms are shown.

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