Effects of Wave Drift Forces on Maneuvering of Ship

2008 ◽  
Author(s):  
Takeshi Kinoshita ◽  
Weiguang Bao ◽  
Motoki Yoshida ◽  
Yasunori Nihei ◽  
Yongze Xu ◽  
...  
Keyword(s):  
Dynamic Positioning ◽  
Positioning System ◽  
Ocean Engineering ◽  
Sea State ◽  
Dynamic Positioning System ◽  
Wave Drift ◽  
Wave Basin ◽  
Wave Drift Damping ◽  
Wave Drift Forces ◽  
Drift Forces

The dynamic positioning system of floating ocean structures requires hydrodynamic force derivatives to construct an accurate maneuvering model. In a severe sea state, the effects of ambient wave field on the maneuvering properties are not negligible. To investigate wave drift forces affecting on maneuvering of a ship relating to dynamic positioning system, an innovative model test, i.e. the Planer Motion Mechanism (PMM) test in waves is discussed in the present paper. Meanwhile, a theory to evaluate wave drift force including wave drift damping and wave drift added mass is summarized. Some examples of experiments done in Ocean Engineering Wave Basin of Institute of Industrial Science, University of Tokyo are presented and compared with calculated results based on the above theory.

Current Effects on a Moored Floating Platform in a Sea State

2008 ◽  
Author(s):  
Carl Trygve Stansberg
Keyword(s):  
Irregular Waves ◽  
Mooring Line ◽  
Viscous Effects ◽  
Floating Platform ◽  
Sea State ◽  
Scaled Model ◽  
Wave Drift ◽  
Wave Basin ◽  
Wave Drift Damping ◽  
Non Gaussian

The significance of current-induced forces and effects on a moored semisubmersible production platform in various sea state conditions is explored, with emphasis on surge motions. Experimental data from 1:55 scaled model tests in a 50m × 80m wave basin are investigated. A description of the current generation is given first. The current in the actual basin is modelled by use of a return current under a false bottom. The importance of modelling a “real” physical current for the proper reproduction of platform responses is pointed out. The semisubmersible tests are carried out with the platform in current only, in irregular waves only, and in combined waves and current conditions. The effects from the current on platform motions and mooring line tensions are investigated. Vortex-Induced motions (VIM) are observed in pure current, depending on the actual combination of current velocity and natural sway period. In combined waves and current the VIM seems to be more or less disappearing. A large effect is seen on the wave drift responses. Both drift forces, non-Gaussian properties and resulting extreme motions and line tensions are significantly increased, especially in high sea states. This is explained through a combination of wave drift damping and viscous effects. At the same time the damping is also increased, but this only partly compensates for the increased forces.

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.

Realistic Adaptive DP Controller for Flotel Operating in Side-by-Side Configuration With FPSO

2019 ◽  
Author(s):  
A. Yenduri ◽  
A. R. Magee ◽  
J. Liu ◽  
W. Xu ◽  
A. Choudhary ◽  
...  
Keyword(s):  
Neural Network ◽  
Shielding Effect ◽  
Dynamic Positioning ◽  
Positioning System ◽  
Sea State ◽  
Large Wave ◽  
Dynamic Positioning System ◽  
The Neural Network ◽  
Ocean Environment ◽  
State Detector

Abstract Side-by-side operation of multiple floaters in the ocean environment is very challenging and the operators always prefer a maximum operable weather window, in order to minimise the cost incurred from the downtime. The safety of the gangway connecting the floaters is very crucial and its dynamic response in the ocean environment raises concerns during operations. Therefore, an efficient dynamic positioning system is essential to maintain the floater and ultimately, the gangway response within the desired limits. In this work, a novel dynamic positioning system for floater operating aside another vessel is presented. The system includes an adaptive controller combined an optimised thruster allocation law and with a sea state detector. The adaptive control is achieved by using the barrier Lyapunov function and a predictor-based method in combination with the neural network scheme. The limitations include the saturation of inputs and the forbidden zones due to thruster-thruster or thruster-hull interaction. An optimised allocation for lower fuel consumption, wear and tear of the thruster equipment and to ensure the resultant command in the respective direction of the azimuth thrusters is designed. The optimisation here is a non-convex problem and a locally convex reformulation of second order is implemented. The presence of unknown shielding effect due to nearby vessel in a side-by-side configuration and input time delay is also considered in the development of this thruster allocation law. In order to overcome these effects, a novel sea state detector is designed. The sea state detector can effectively monitor the variation of drift wave-induced force on the vessel and activate the neural network compensator in the controller when a large wave drift force is identified. Simulation studies are conducted to verify the efficiency of this dynamic position system and a demonstration of flotel in side-by-side configuration with a turret moored FPSO is presented for the non-collinear ocean environment.

Sensitivity of a Floating Bridge Global Responses to Different Wave Drift Force Models

2021 ◽  
Author(s):  
Carlos Eduardo Silva de Souza ◽  
Nuno Fonseca ◽  
Marit Irene Kvittem
Keyword(s):  
Mooring Line ◽  
Sea State ◽  
Mooring Lines ◽  
Wave Drift ◽  
Floating Bridge ◽  
Promising Solution ◽  
Bridge Girder ◽  
Wave Drift Forces ◽  
Wave Incidence ◽  
Drift Forces

Abstract Floating bridges are a promising solution for replacing ferries in the crossing of Norwegian fjords. Their design involves the adoption of accurate, but at the same time efficient models for the loads the structure is subjected to. Wave drift forces at the bridge’s pontoon may excite the bridge’s lower horizontal modes, with consequences to the loads on the bridge and mooring lines. Newman’s approximation is normally adopted to calculate the wave drift forces in such applications. A common simplification is to assume that the pontoons are fixed in the calculation of wave drift coefficients, while it is known that wave frequency motions may significantly influence drift loads. This paper evaluates the consequences of this simplification, in comparison to coefficients obtained considering the pontoons’ motions. First, the effect of the bridge deflection, due to mean drift, on the pontoon’s motions, is evaluated. It is found that this effect is negligible. Then, the RAOs are used in the calculation of wave drift coefficients, showing very different results than those obtained with fixed pontoons. Time-domain simulations are then performed with wave drift coefficients calculated with both approaches, with focus on the bridge girder moments and mooring line tensions. It is shown that using wave drift coefficients obtained with fixed pontoon is a non-conservative simplification, depending on sea state and wave incidence direction.

scholarly journals Experimental and Numerical Analysis of Wave Drift Force on KVLCC2 Moving in Oblique Waves

2021 ◽  
Vol 9 (2) ◽  
pp. 136
Author(s):  
Min Guk Seo ◽  
Yoon Jin Ha ◽  
Bo Woo Nam ◽  
Yeongyu Kim
Keyword(s):  
Numerical Analysis ◽  
Ocean Engineering ◽  
Validation Data ◽  
Wave Drift ◽  
Motion Responses ◽  
Direct Pressure ◽  
Korea Research Institute ◽  
Drift Force ◽  
Wave Drift Forces ◽  
Drift Forces

In this study, experimental and numerical methods were applied to estimate surge and sway wave drift forces and yaw drift moment acting on KVLCC2, advancing in oblique wave. An experiment was carried out in the ocean engineering basin of the Korea Research Institute of Ships and Ocean Engineering (KRISO). A series of regular wave tests under various heading conditions were conducted to investigate ship motion responses and wave drift forces. A Rankine panel method based on potential flow was adopted in the numerical analysis, and the direct pressure integration method that integrates second-order pressure on the hull surface was applied to compute wave drift force. Through this study, validation data of wave drift force acting on KVLCC2 was established, and the computation capability of the potential-based numerical method was systematically analyzed.

Modeling and Simulation of Ship Motion for Dynamic Positioning Vessel

2014 ◽  
Vol 919-921 ◽  
pp. 2127-2130
Author(s):  
Pei Wen Yu ◽  
Hui Chen
Keyword(s):  
Modeling And Simulation ◽  
Wind Wave ◽  
Ship Motion ◽  
Dynamic Positioning ◽  
Positioning System ◽  
Dynamic Positioning System ◽  
Oil Supply ◽  
Mmg Model ◽  
Simulation Results

The paper presents a method to build MMG model of ship motion for a oil supply vessel (OSV) with dynamic positioning system. It is assumed that the ship motion exposed to environment disturbances like wind, wave & currents, The simulation results show that the model of the vessel and environment disturbances are suitable, and the method is practicable .

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