New Roll Damping, Pitch Damping and Magnus Measurement Rigs at ONERA

The nonlinear responses of ship rolling motion characterized by a roll damping moment are of great interest to naval architects and ocean engineers. Modeling and identification of the nonlinear damping moment are essential to incorporate the inherent nonlinearity in design, analysis, and control of a ship. A stochastic nonparametric approach for identification of nonlinear damping in the general mechanical system has been presented in the literature (Han and Kinoshits 2012). The method has been also applied to identification of the nonlinear damping moment of a ship at zero-forward speed (Han and Kinoshits 2013). In the presence of forward speed, however, the characteristic of roll damping moment of a ship is significantly changed due to the lift effect. In this paper, the stochastic inverse method is applied to identification of the nonlinear damping moment of a ship moving at nonzero-forward speed. The workability and validity of the method are verified with laboratory tests under controlled conditions. In experimental trials, two different types of ship rolling motion are considered: time-dependent transient motion and frequency-dependent periodic motion. It is shown that this method enables the inherent nonlinearity in damping moment to be estimated, including its reliability analysis.

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The Nonlinear Roll Damping of a FPSO Hull

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4025870 ◽

2013 ◽

Vol 136 (1) ◽

Cited By ~ 9

Author(s):

Allan C. de Oliveira ◽

Antonio Carlos Fernandes

Keyword(s):

Nonlinear Damping ◽

Challenging Problem ◽

Roll Damping ◽

Ship Hulls ◽

Damping Behavior ◽

Industry Standards ◽

Long Time ◽

Technological Developments ◽

Traditional Approaches ◽

The 19Th Century

The ship-rolling problem is a subject that has been studied for a long time. Since Froude's time (in the 19th century) to nowadays, this subject was revisited several times in order to adjust the theory to changes in ship hulls, dimensions, materials, appendages, etc. On the other hand, ship analysis technological resources, including both experimental techniques and computational capacity (that did not exist in Froude's time), have also amazingly improved. But despite all those technological developments, the assessment of the nonlinear roll damping of some types of hulls still is a challenging problem. The floating production storage and offloading (FPSO) hull fitted with larger bilge keels, for instance, has behaved in such a way that it is impossible to obtain results from nowadays industry standards via decaying tests. This paper discusses an alternative way to assess the nonlinear damping behavior of FPSO hulls with large bilge keels. Since it is fairly easy to perform decaying tests, the paper also proposes an alternative way to analyze the FPSO properties through this kind of testing by grouping multiple results instead of using only a single test. This artifice brought improvements, such as an increased agreement between the alternative model and the experimental data. The paper also compares the more traditional approaches with the alternative method and finally shows the latter's applicability.

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Wave Pressure Distributions Along the Midship Transverse Section of a VLCC

Volume 4: Ocean Engineering; Offshore Renewable Energy ◽

10.1115/omae2008-57649 ◽

2008 ◽

Cited By ~ 2

Author(s):

Zhi Shu ◽

Torgeir Moan

Keyword(s):

Transverse Section ◽

Roll Damping ◽

Wave Pressure ◽

Ship Hulls ◽

Pressure Distributions ◽

The Difference ◽

Hydrodynamic Code ◽

Long Term Prediction ◽

External Wave

The external wave pressure distributions along the transverse section in the midship region of a VLCC are evaluated in this paper. The commercial hydrodynamic code WASIM issued by DnV has been adopted to perform the hydrodynamic computation. The ship hulls have been discretized with coarser and finer mesh to investigate the effect of panel size on the hydrodynamic pressures. It is found that the difference between these two mesh finenesses is small. It is also found that the roll damping has a significant influence on the wave pressure of vessel especially in beam sea. A sensitivity analysis is carried out in the sense of assessing the influence of the roll damping on the wave pressure. Finally, the long term prediction of the wave pressure has been compared for different roll damping values.

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Development and Verification of Modeling Practice for CFD Decay Calculations to Obtain Roll Damping of FPSO

10.1115/omae2021-62411 ◽

2021 ◽

Author(s):

Arjen Koop ◽

Pierre Crepier ◽

Sebastien Loubeyre ◽

Corentin Dobral ◽

Kai Yu ◽

...

Keyword(s):

Model Test ◽

Test Results ◽

Cfd Modelling ◽

Roll Damping ◽

Natural Period ◽

Computational Mesh ◽

Safety Studies ◽

Offshore Industry ◽

Decay Tests ◽

Set Up

Abstract Estimates for roll damping are important input parameters for simulation studies on vessels operating at sea, e.g. FPSO mooring in waves, wind and current, workability and operability investigations, Dynamic Position studies, ship-to-ship operations and safety studies of vessels. To accurately predict the motions of vessels this quantity should be determined with confidence in the values. Traditionally, model experiments in water basins using so-called decay tests are carried out to determine the roll damping. With recent advancements in CFD modelling, the offshore industry has started using CFD as an alternative tool to compute the roll damping of FPSO’s. In order to help adopt CFD as a widely accepted tool, there is a need to develop confidence in CFD predictions. Therefore, a practical CFD modelling practice is developed within the Reproducible CFD JIP for roll decay CFD simulations. The Modelling Practice describes the geometry modelling, computational mesh, model set-up and post-processing for these type of CFD calculations. This modelling practice is verified and validated by three independent verifiers against available model test data. This paper provides an overview of the developed modelling practice and the calculated CFD results from the verifiers. The CFD modelling practice is benchmarked against available model test results for a tanker-shaped FPSO. By following this modelling practice, the CFD predictions for the equivalent linear damping coefficient and natural period of the roll motions are within 10% for all verifiers and within 10% from the model test results. Therefore, we conclude that when following the developed modelling practice for roll decay simulations, reliable, accurate and reproducible results can be obtained for the roll damping of tanker-shaped FPSOs.

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