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.

Wave Drift Forces and Responses in Current

2013 ◽  
Author(s):  
Carl Trygve Stansberg ◽  
Jan Roger Hoff ◽  
Elin Marita Hermundstad ◽  
Rolf Baarholm
Keyword(s):  
Basic Element ◽  
Irregular Waves ◽  
Mooring Line ◽  
Vertical Column ◽  
Wave Drift ◽  
Slow Drift ◽  
Initial Comparison ◽  
Mooring Forces ◽  
Wave Drift Forces ◽  
Drift Forces

The influence from a current on wave drift forces and resulting slowly varying vessel responses can be quite significant. In this paper the effect is reviewed and further investigated. Several works have been published on this complex topic during the last 20–25 years, while it is only to a little extent taken consistently into account in standard industry tools. Simplified methods are often used, if any, and /or empirical correction from model test data. Thus there is a need to improve standard tools in this respect. The effects on slowly varying vessel motions and resulting extreme mooring line loads are demonstrated through time series sequences from selected, previous model tests with FPSO’s and semisubmersibles in steep irregular waves. Wave-current interaction effects that can be larger than the effects from current and wind alone are identified. It is also confirmed from these examples that extreme mooring forces usually occur due to extreme slow-drift motions. An overview description is given of a new, general numerical potential theory code for industry use, MULDIF-2, where wave-current-structure interaction is consistently included as a basic element in the formulation. Main items in the approach are addressed and referred to previous works in the literature. Results from an initial comparison against previous results on drift forces on a vertical column are given, and a good agreement is found. Further verification and validation work is in progress.

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.

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.

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.

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