On the Roll Damping Coefficient obtained from the Irregular and Large Amplitude Forced Rolling Experiments

Abstract In this paper, a new method to estimate roll aerodynamic characteristics of a rolling projectiles is proposed. It is estimated from the measured roll rate and trajectory positional data using Extended Kalman Filter. Modified point mass model of trajectory modelling, in state space form, is used to represent system dynamics of Extended Kalman Filter. The roll and position data at every time step constitutes the measurement vector. Along with positions and velocities, roll damping coefficient is included as a state variable. As roll damping coefficient depends on projectile configurations and Mach number. Roll damping coefficients are estimated for two configurations viz. roll stabilized shell and fin stabilized rocket. The measurements are simulated for full flight regime to cover complete Mach regime. Estimated values are compared with known results for various Mach numbers. In both the cases estimation is in close agreement with known results.

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Roll Damping Simulations of an Offshore Heavy Lift DP3 Installation Vessel Using the CFD Toolbox OpenFOAM

Volume 8: CFD and FSI ◽

10.1115/omae2020-19338 ◽

2020 ◽

Author(s):

Brecht Devolder ◽

Florian Stempinski ◽

Arjan Mol ◽

Pieter Rauwoens

Keyword(s):

Boundary Element ◽

Damping Coefficient ◽

Navier Stokes ◽

Roll Motion ◽

Viscous Effects ◽

Roll Damping ◽

Two Phase ◽

Damping Behavior ◽

External Moment ◽

Heavy Lift

Abstract In this work, the roll damping behavior of the offshore heavy lift DP3 installation vessel Orion from the DEME group is studied. Boundary element codes using potential flow theory require a roll damping coefficient to account for viscous effects. In this work, the roll damping coefficient is calculated using the Computational Fluid Dynamics (CFD) toolbox OpenFOAM. The two-phase Navier-Stokes fluid solver is coupled with a motion solver using a partitioned fluid-structure interaction algorithm. The roll damping is assessed by the Harmonic Excited Roll Motion (HERM) technique. An oscillating external moment is applied on the hull and the roll motion is tracked. Various amplitudes and frequencies of the external moment and different forward speeds, are numerically simulated. These high-fidelity full-scale simulations result in better estimations of roll damping coefficients for various conditions in order to enhance the accuracy of efficient boundary element codes for wave-current-structure interactions simulations.

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Predicting Roll Damping for Barge-Type FPSO Using CFD

Volume 2: CFD and FSI ◽

10.1115/omae2019-95306 ◽

2019 ◽

Author(s):

Arjen Koop ◽

Frédérick Jaouën ◽

Xavier Wadbled ◽

Erwan Corbineau

Keyword(s):

Turbulence Model ◽

Three Dimensional ◽

Model Tests ◽

Vortical Flow ◽

Damping Coefficient ◽

Physical Parameters ◽

Two Dimensional ◽

Roll Damping ◽

End Effects ◽

Hydrodynamic Damping

Abstract An accurate prediction of the non-linear roll damping is required in order to calculate the resonant roll motion of moored FPSO’s. Traditionally, the roll damping is obtained with model tests using decays or forced roll oscillation tests. Calculation methods based on potential flow are not capable of predicting this hydrodynamic damping accurately as it originates from the viscous nature of the fluid and the complex vortical flow structures around a rolling vessel. In recent years Computational Fluid Dynamics (CFD) has advanced such that accurate predictions for the roll damping can be obtained. In this paper CFD is employed to predict the roll damping for a barge-type FPSO. The objectives of the paper are to investigate the capability and accuracy of CFD to determine roll damping of an FPSO and to investigate whether two-dimensional calculations can be used to estimate the roll damping of a three-dimensional FPSO geometry. To meet these objectives, extensive numerical sensitivity studies are carried out for a 2D hull section mimicking the midsection of the FPSO. The numerical uncertainty for the added mass and damping coefficients were found to be 0.5% and 2%, respectively. The influence of the turbulence model was found to be significant for the damping coefficient with differences up to 14%. The 2D CFD results are compared to results from two-dimensional model tests. The calculated roll damping using the k-ω SST 2003 turbulence model matches the value from the experiments within 2%. The influence of various physical parameters on the damping was investigated through additional 2D calculations by changing the scale ratio, the roll amplitude, the roll period, the water depth, the origin of rotation and the bilge keel height. Lastly, three-dimensional calculations are carried out with the complete FPSO geometry. The 3D results agree with the 2D results except for the largest roll amplitude calculated, i.e. for 15 degrees, where the damping coefficient was found to be 7% smaller. For this amplitude end-effects from the ends of the bilge keels seem to have a small influence on the flow field around the bilge keels. This indicates that the 2D approach is a cost-effective method to determine the roll damping of a barge-type FPSO, but for large roll amplitudes or for different vessel geometries the 2D approach may not be valid due to 3D effects.

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A Time-Domain Solution to the Motions of a Steered Ship in Waves

Journal of Ship Research ◽

10.5957/jsr.1974.18.1.32 ◽

1974 ◽

Vol 18 (01) ◽

pp. 32-45

Author(s):

Leonardo Pérez y Pérez

Keyword(s):

Time Domain ◽

Experimental Results ◽

Damping Coefficient ◽

Convolution Integral ◽

Roll Damping ◽

Ship Model ◽

Frequency Independent ◽

Exciting Forces

The motions of a ship in waves are expressed as linear responses to arbitrary exciting forces by means of a convolution integral. Frequency-independent nonlinearities are considered to be part of the arbitrary forces. The method is used to numerically simulate the sway, roll, and yaw motions of a ship model in waves with nonlinear roll damping coefficient and an autopilot. The agreement of the simulation with experimental results is quite reasonable. This method is restricted neither to these modes of motion nor to these nonlinearities; it can be used for all six modes of motion and any frequency-independent nonlinearity.

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Ship Roll Damping Coefficient Prediction Using CFD

Journal of Ship Research ◽

10.5957/josr.09180061 ◽

2019 ◽

Vol 63 (2) ◽

pp. 108-122 ◽

Cited By ~ 7

Author(s):

Seyed Sadra Kianejad ◽

Hossein Enshaei ◽

Jonathan Duffy ◽

Nazanin Ansarifard ◽

Dev Ranmuthugala

Keyword(s):

Damping Coefficient ◽

Roll Damping ◽

Ship Roll

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Experimental Determination of Roll Damping Coefficient for FPSO

Volume 1A: Offshore Technology ◽

10.1115/omae2014-23400 ◽

2014 ◽

Author(s):

Oliver A. Seelis ◽

Longbin Tao

Keyword(s):

Experimental Determination ◽

Cross Section ◽

Test Data ◽

Transfer Functions ◽

Damping Coefficient ◽

Roll Damping ◽

Damping Coefficients ◽

Decay Test ◽

Bilge Keel

The roll damping coefficient is a crucial parameter for several design and operational aspects of FPSOs. The accurate prediction of the coefficient is not a trivial task and generally performed experimentally. A polynomial linearization of the decay test data has been widely applied in the offshore industry. However, research has indicated that for FPSOs with rectangular cross section and attached bilge keels, this methodology may lead to inaccurate damping coefficients. This paper presents a study on the experimental determination of roll damping coefficients for FPSOs, obtained by free decay tests. For this purpose model tests are executed in the towing tank of the Marine Hydrodynamic Laboratory at Newcastle University. The model is based on the design of a purposely build FPSO, as typically applied in the central North Sea sector. The cross section of the FPSO is boxed shaped with a characteristic knuckle shaped bilge. The tests are conducted using three different bilge keel arrangements. The parametric change in bilge keel size results in the variation of the flow characteristics around the bilge knuckle. The damping coefficients are then established from the decay test data using a polynomial approach, a bi-linear approach and a hyperbolic approach. A comparison between the damping evolutions obtained with the different methodologies is performed for each bilge keel configuration. Further, a numerical model of the FPSO is created using DNVs Sesam software. With the established damping coefficients, damping matrices are manually defined as an input to Sesam and roll transfer functions are numerically established. The computational determined transfer functions are then compared against the RAOs obtained from the model tests in regular waves to determine the most appropriate methodology. The damping coefficient for the bare hull is well established by all three proposed methodologies. However, with the attached bilge keels the bi-linear and the hyperbolic methodologies produce damping coefficients reflecting the experimental results more accurately than the polynomial approach, indicating that the recently developed hyperbolic method is a valid alternative, and in certain cases, is more suitable to determine the roll damping coefficient. The experimental measurements could serve as a benchmark for further research and contribute to the practical application of FPSO roll damping determination.

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Modelling of Roll Damping Effects for a Fishing Vessel With Forward Speed

Volume 11: Prof. Robert F. Beck Honoring Symposium on Marine Hydrodynamics ◽

10.1115/omae2015-41856 ◽

2015 ◽

Cited By ~ 2

Author(s):

K. G. Aarsæther ◽

D. Kristiansen ◽

B. Su ◽

C. Lugni

Keyword(s):

Large Amplitude ◽

Well Being ◽

Roll Motion ◽

Ship Motions ◽

Limiting Factor ◽

Real Problem ◽

Forward Speed ◽

Roll Damping ◽

Damping Effects ◽

Wave Induced

Vessels in the ocean-going fishing fleet are in general operating in almost all weather conditions. This includes operation in high sea-states which may lead to large amplitude ship motions, depending on the seakeeping characteristics of the vessel. Wave-induced ship motions are important factors for the safety and well-being of fishermen at work. Generally, potential flow theory overpredicts wave-induced roll motion amplitudes for conventional ship hulls. This is due to the presence of viscous damping effects in reality. Large amplitude roll motion of ships can be a real problem if no anti-rolling devices (e.g. bilge keels, anti-rolling tanks or roll-damping fins) are installed, as the roll damping coefficient of a ship is the limiting factor for the resonant roll motion amplitudes. The different components of roll damping for a ship at forward speed were investigated by Ikeda et al. [1], [2] and [3] and updated guidelines for numerical estimation of roll damping have been presented by the International Towing Tank Conference [4], where a component discrete type method for estimation of the damping is suggested. The different roll-damping components of Ikeda et al. has been complemented by skeg damping for smooth hulls [5]. This paper presents comparison between model experiments and the numerical results obtained from the guidelines [4] where the effects of bilge-keels and skeg are isolated.

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Damping Coefficients for Extreme Rolling and Capsize: An Analytical Approach

Journal of Ship Research ◽

10.5957/jsr.2000.44.1.1 ◽

2000 ◽

Vol 44 (01) ◽

pp. 1-13 ◽

Cited By ~ 1

Author(s):

K. J. Spyrou ◽

J. M. T. Thompson

Keyword(s):

Hamiltonian System ◽

Closed Form ◽

Large Amplitude ◽

Analytical Approach ◽

Roll Motion ◽

Elliptic Type ◽

Roll Damping ◽

Damping Coefficients ◽

Linear And Nonlinear ◽

The Law

A method to identify the law of roll motion decay from extreme angles is presented based on perturbations of the elliptic-type solutions of the corresponding Hamiltonian system. Restoring polynomials up to the 7th order are considered. It is shown that the decay law can be expressed in closed form for up to quintic restoring. The method should be especially useful for deriving linear and nonlinear roll damping coefficients in the context of ship capsize investigations where the large amplitude behavior, near to the angle of vanishing stability, needs to be taken into account.

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