Effects of Wave-Current Interaction on Floating Bodies

2016 ◽  
Author(s):  
Elin Marita Hermundstad ◽  
Jan Roger Hoff ◽  
Carl Trygve Stansberg ◽  
Rolf Baarholm
Keyword(s):  
Interaction Effects ◽  
Model Tests ◽  
Floating Bodies ◽  
Wave Drift ◽  
Industry Applications ◽  
Contour Plots ◽  
Finite Water Depth ◽  
Wave Drift Damping ◽  
Current Interaction ◽  
Wave Drift Forces

Wave-current interaction effects may significantly influence the mean wave drift forces on a structure as well as the motion responses and wave elevation around the structure. Additionally, the drift force may be used to estimate the wave drift damping of a moored structure. A new numerical potential theory code for industry applications (MULDIF) has been recently developed, where the hydrodynamic interaction between waves and current of arbitrary direction with large volume structures is consistently included. The code also handles multiple bodies and finite water depth including wave-current interaction effects. The aim has been to create a robust and easy-to-use practical tool. Initial validation studies against model tests have been conducted. The numerical results show a strong heave-pitch coupling due to the presence of the current. Preliminary results for a semi-submersible show good agreement for the motions provided that the mooring used in the model tests are accounted for. The free surface elevation around the semi-submersible is presented in contour plots.

Simulation of Low Frequency Motions in Severe Seastates Accounting for Wave-Current Interaction Effects

2017 ◽  
Author(s):  
Babak Ommani ◽  
Nuno Fonseca ◽  
Carl Trygve Stansberg
Keyword(s):  
Test Data ◽  
Time Domain ◽  
Low Frequency ◽  
Interaction Effects ◽  
Force Coefficients ◽  
Wave Drift ◽  
Current Interaction ◽  
Drift Force ◽  
Wave Drift Forces ◽  
Drift Forces

Today’s industry practice assumes wave drift forces on floating structures can be computed from zero current wave drift force coefficients for the stationary floater, while simplified correction models introduce current effects and slow drift velocity effects. The paper presents an alternative approach which overcomes some of the limitations of today’s procedures. The method, to be applied together with a time domain solution of the low frequency motions, is based on pre-calculation of mean wave drift force coefficients for a range of current velocities. During the low frequency motions simulation, the wave drift forces induced by the irregular waves are computed from the mean drift coefficients corresponding to instantaneous relative velocity resulting from the current and the low frequency velocities. A simple interpolation model, based on a quasi-steady assumption, is applied to obtain the drift forces in time-domain. Since calculation of the wave drift forces on Semi-submersibles in severe sea states with fully consistent methods is out of reach, a semi-empirical model is applied to correct the potential flow wave drift force coefficients. This model takes into account viscous effects, that are important in high seastates, and wave-current interaction effects. The paper compares the wave drift forces and the related low frequency motions computed by the proposed method, with results applying “standard” methods and with model test data. The test data was obtained in the scope of the EXWAVE JIP, with model tests designed to investigate wave drift forces in severe seastates and assess the wave-current interaction effects.

Analysis of Semi-Submersible Under Combined High Waves and Current Conditions Compared With Model Tests

2018 ◽  
Author(s):  
Limin Yang ◽  
Arne Nestegård ◽  
Erik Falkenberg
Keyword(s):  
Simulation Model ◽  
Low Frequency ◽  
Model Tests ◽  
Wave Forces ◽  
Viscous Effects ◽  
Numerical Predictions ◽  
Wave Drift ◽  
Zero Current ◽  
Frequency Excitation ◽  
Wave Drift Forces

Viscous effects on the low-frequency excitation force on column based platforms are significant in extreme waves. The wave drift force as calculated by a zero-current potential flow radiation/diffraction code becomes negligible for such waves. In the present study, the effect of current and viscous contributions on the slowly varying wave forces are adjusted by a formula developed in the Exwave JIP, see e.g. [1], which is validated against model test results. This paper presents numerical predictions of low frequency horizontal motions of a semi-submersible in combined high waves and current condition. In the simulation model, frequency dependent wave drift forces from radiation/diffraction code are modified by the formula. Static current forces and viscous damping are modelled by the drag term in Morison load formula using relative velocity between current and floater and with force coefficients as recommended by DNVGL-RP-C205 [2]. Low frequency surge responses calculated by the simulation model are compared with model tests for waves only and for combined collinear and noncollinear wave and current conditions.

Wave Drift Forces' Calculation on Two Floating Bodies Based on the Boundary Element Method—Attempt for Improvement of the Constant Panel Method

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Qiao Li ◽  
Yasunori Nihei
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Evaluation Method ◽  
Panel Method ◽  
Floating Bodies ◽  
Wave Drift ◽  
Wave Drift Forces ◽  
Multiple Floating Bodies ◽  
Drift Forces ◽  
Element Method

An improved constant panel method for more accurate evaluation of wave drift forces and moment is proposed. The boundary element method (BEM) of solving boundary integral equations is used to calculate velocity potentials of floating bodies. The equations are discretized by either the higher-order boundary element method or the constant panel method. Though calculating the velocity potential via the constant panel method is simple, the results are unable to accurately evaluate wave drift forces and moment. An improved constant panel method is introduced to address these issues. The improved constant panel method can, without difficulty, employ the near-field method to evaluate wave drift forces and moment, especially for multiple floating bodies. Results of the new evaluation method will be compared with other evaluation method. Additionally, hydrodynamic interaction between multiple floating bodies will be assessed.

scholarly journals Wave forces on three-dimensional floating bodies with small forward speed

1991 ◽  
Vol 227 ◽  
pp. 135-160 ◽  
Author(s):  
Jan Nossen ◽  
John Grue ◽  
Enok Palm
Keyword(s):  
Velocity Potential ◽  
The Body ◽  
Wave Forces ◽  
Forward Speed ◽  
Floating Bodies ◽  
Wave Drift ◽  
Exciting Forces ◽  
Wave Exciting Forces ◽  
Wave Drift Damping ◽  
The Mean

A boundary-integral method is developed for computing first-order and mean second-order wave forces on floating bodies with small forward speed in three dimensions. The method is based on applying Green's theorem and linearizing the Green function and velocity potential in the forward speed. The velocity potential on the wetted body surface is then given as the solution of two sets of integral equations with unknowns only on the body. The equations contain no water-line integral, and the free-surface integral decays rapidly. The Timman-Newman symmetry relations for the added mass and damping coefficients are extended to the case when the double-body flow around the body is included in the free-surface condition. The linear wave exciting forces are found both by pressure integration and by a generalized far-field form of the Haskind relations. The mean drift force is found by far-field analysis. All the derivations are made for an arbitrary wave heading. A boundary-element program utilizing the new method has been developed. Numerical results and convergence tests are presented for several body geometries. It is found that the wave exciting forces and the mean drift forces are most influenced by a small forward speed. Values of the wave drift damping coefficient are computed. It is found that interference phenomena may lead to negative wave drift damping for bodies of complicated shape.

scholarly journals Near-Trapping on a Four-Column Structure and the Reduction of Wave Drift Forces Using Optimized Method

2020 ◽  
Vol 8 (3) ◽  
pp. 174 ◽  
Author(s):  
Guanghua He ◽  
Zhigang Zhang ◽  
Wei Wang ◽  
Zhengke Wang ◽  
Penglin Jing
Keyword(s):  
Numerical Model ◽  
Floating Bodies ◽  
Large Wave ◽  
Approach Angle ◽  
Wave Approach ◽  
Wave Drift ◽  
Column Structure ◽  
Wave Drift Forces ◽  
Drift Forces ◽  
Wave Elevations

The near-trapping phenomenon, which can lead to high wave elevations and large wave drift forces, is investigated by a floating four-column structure. To solve this wave-structure interaction problem, a numerical model is established by combining the wave interaction theory with a higher-order boundary element method. Based on this numerical model, behaviors of scattered waves at near-trapping conditions are studied; and the superposition principle of free-surface waves is introduced to understand this near-trapping phenomenon. To avoid the near-trapping phenomenon and protect the structure, a way for rotating the structure to change the wave-approach angle is adopted, and improvements of the wave elevations around the structure and the wave drift forces acting on each column are found. Moreover, a genetic-algorithm-based optimization method is adopted in order to minimize the total wave drift force acting on the whole structure at various wavenumbers by controlling the draft of floating bodies, the wave-approach angle and the separation distance between adjacent floating bodies. With the final optimized parameters, the wave drift forces both on each column and on the whole structure can be significantly reduced. The optimized arrangement obtained from a certain wavenumber can work not only at this target wavenumber but also at a range of wavenumbers.

scholarly journals Wave drift damping of floating bodies in slow yaw motion

1996 ◽  
Vol 319 (-1) ◽  
pp. 323 ◽  
Author(s):  
John Grue ◽  
Enok Palm
Keyword(s):  
Floating Bodies ◽  
Wave Drift ◽  
Wave Drift Damping

Improved Dynamic Positioning Using Wave Feed Forward

2011 ◽  
Author(s):  
Frans Quadvlieg ◽  
Rink Hallmann ◽  
Greg Hughes ◽  
Rick Harris
Keyword(s):  
Wave Field ◽  
Wave Height ◽  
Pressure Sensors ◽  
Model Tests ◽  
Wave Forces ◽  
Feed Forward ◽  
Wave Drift ◽  
Local Wave ◽  
Wave Drift Forces ◽  
Drift Forces

Jo Pinkster made the first attempt to estimate 2nd order wave drift forces. In his PhD thesis from 1980, the first practical application of wave feed forward in DP was demonstrated both theoretically and in model tests. Knowledge of the local wave field was used to estimate the 2nd order wave drift forces. The local wave field was converted in wave forces and fed back in the DP system. The use of this knowledge in a DP system should lead to a better position keeping. Since Pinksters’ thesis 30 years ago, this technique has been tried several times with varying success. However, in 2009, the ‘nut was cracked’ and a good success was undoubtedly demonstrated. In 2008–2009, this method has been developed and applied in DP model tests on a ship equipped with azimuthing thrusters. The use of Wave Feed Forward resulted in a reduction of the watch circle by a factor of two. Important for the success of wave feed forward was the filtering of the measured wave signals to predict the wave forces with a limited delay. The performance is demonstrated during model tests in MARIN’s Seakeeping and Manoeuvring Basin at two speeds of 0 knots and 4 knots, uni-directional and multidirectional seas. Besides the application of wave feed forward for a single ship, wave feed forward is used in a side-by-side condition at zero speed and ahead speed. For both speeds, wave feed forward did not provide a significant improvement in DP accuracy. The objective was to make wave feed forward applicable to: zero and forward speed; on a ship alone and on ships sailing side-by-side; in unidirectional and multi-directional waves, with a realistic amount of sensors and as target wave heights, sea state 3 and 4 were envisaged. To measure the local wave height, wave height measurement sensors as well as pressure sensors were used. The pressure sensors can be mounted below the waterline and deliver an accurate estimation for the wave drift forces as well.

Comparative Study of Motions and Drift Forces in Waves and Current

2017 ◽  
Author(s):  
Florian Sprenger ◽  
Elin Marita Hermundstad ◽  
Jan Roger Hoff ◽  
Dariusz Fathi ◽  
Ørjan Selvik
Keyword(s):  
Degrees Of Freedom ◽  
Ocean Basin ◽  
Model Tests ◽  
Measuring System ◽  
Diffraction Radiation ◽  
Station Keeping ◽  
Wave Drift ◽  
Wave Drift Forces ◽  
General Cargo ◽  
Drift Forces

Station keeping analysis is an important activity in the early stages of any vessel/DP project that eventually determines the machinery and thruster configuration and thruster size selection. In order to obtain reliable results, it is crucial to apply engineering tools that realistically represent the flow physics and resulting hydrodynamic forces. Present computer tools are based on the assumption that wave drift- and current forces can be superimposed. However, there are also mutual interaction effects between waves, current and hulls that should be accounted for in the evaluation of the wave drift forces. In MULDIF, a 3D diffraction/radiation panel code developed by SINTEF Ocean within the framework of a JIP, this wave-current-body interaction is taken into consideration by a new potential flow numerical model. A case study with offshore vessels and general cargo ships of different main dimensions has been performed to assess the capabilities of MULDIF for station keeping purposes in wave and current environments. The first-order vessel motions as well as mean second-order drift forces for 0 kn forward speed without current have been calculated. Through an interface to SINTEF Ocean’s vessel response code VERES, MULDIF offers the possibility to include viscous roll damping due to hull friction, flow separation at bilge keels, lift effects as well as normal forces acting on bilge keels and hull pressure created by the presence of bilge keels. This reduces roll motions to a realistic extent as shown by the comparison of RAOs from MULDIF calculations and model tests. Roll reduction tank effects can currently only be considered through the external damping matrix. Model tests for the selected vessels have been performed in SINTEF’s Ocean Basin in a soft-mooring arrangement in different irregular sea states and headings in deep water. The models were equipped with two two-component force transducers, measuring the x- and y- components of the forces. The yaw moments have been calculated from the y-force measurements. In order to measure the vessel motions in six degrees of freedom, an optoelectronic position measuring system has been used. Selected cases illustrate the significant influence of wave-current interaction on motions and drift forces.

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