Nonlinear roll damping parameter identification using free-decay data

2021 ◽  
Vol 219 ◽  
pp. 108425
Author(s):  
Jinwei Sun ◽  
Sau-Lon James Hu ◽  
Huajun Li
Keyword(s):  
Parameter Identification ◽  
Roll Damping ◽  
Decay Data ◽  
Free Decay ◽  
Damping Parameter

Effect of Bilge Radius and Bilge Keel Height on Roll Damping Performance of Floating Structures

2021 ◽  
Author(s):  
Chang Seop Kwon ◽  
Joo-Sung Kim ◽  
Hyun Joe Kim
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Kinetic Energy ◽  
Floating Body ◽  
Rectangular Section ◽  
Roll Damping ◽  
Floating Structures ◽  
Free Decay ◽  
Computational Fluid Dynamics Cfd ◽  
Bilge Keel

Abstract A round bilge with a bilge keel structure is a key element which can alleviate roll motions of ships and floating structures by transferring the roll momentum of a floating body into the kinetic energy of water. This study presents a practical guide to properly designing a bilge radius and bilge keel height of a barge-shaped and tanker-shaped FPSOs. A parametric study to figure out the effect of bilge radius and bilge keel height on the roll damping performance is conducted through a series of numerical roll free decay simulations based on Computational Fluid Dynamics (CFD). The bilge radius is normalized by the half breadth of ship, and the bilge keel height is normalized by the maximum bilge keel height which is limited by the molded lines of a side shell and bottom shell. In addition, it is investigated to identify how the roll damping performance of a rectangular section differs from the result of a typical round bilge section with maximum available bilge keel height.

scholarly journals Bilge Keel Induced Roll Damping of an FPSO With Sponsons

2016 ◽  
Author(s):  
Babak Ommani ◽  
Nuno Fonseca ◽  
Trygve Kristiansen ◽  
Christopher Hutchison ◽  
Hanne Bakksjø
Keyword(s):  
Free Surface ◽  
Two Dimensions ◽  
The Body ◽  
Proximity Effects ◽  
Roll Damping ◽  
Damping Coefficients ◽  
Free Decay ◽  
Strip Theory ◽  
Decay Tests ◽  
Bilge Keel

The bilge keel induced roll damping of an FPSO with sponsons is investigated numerically and experimentally. The influence of the bilge keel size, on the roll damping is studied. Free decay tests of a three-dimensional ship model, for three different bilge keel sizes are used to determine roll damping coefficients. The dependency of the quadratic roll damping coefficient to the bilge keel height and the vertical location of the rotation center is studied using CFD. A Navier-Stokes solver based on the Finite Volume Method is adopted for solving the laminar flow of incompressible water around a section of the FPSO undergoing forced roll oscillations in two-dimensions. The free-surface condition is linearized by neglecting the nonlinear free-surface terms and the influence of viscous stresses in the free surface zone, while the body-boundary condition is exact. An averaged center of rotation is estimated by comparing the results of the numerical calculations and the free decay tests. The obtained two-dimensional damping coefficients are extrapolated to 3D by use of strip theory argumentations and compared with the experimental results. It is shown that this simplified approach can be used for evaluating the bilge keel induced roll damping with efficiency, considering unconventional ship shapes and free-surface proximity effects.

Practical aspects of on-orbit modal identification using free-decay data

1992 ◽  
Vol 29 (2) ◽  
pp. 264-270 ◽  
Author(s):  
Axel Schenk ◽  
Richard S. Pappa
Keyword(s):  
Modal Identification ◽  
Decay Data ◽  
Free Decay

scholarly journals Estimation of Squeeze-Film Damping and Inertial Coefficients from Experimental Free-Decay Data

1986 ◽  
Vol 200 (2) ◽  
pp. 123-133 ◽  
Author(s):  
J B Roberts ◽  
R Holmes ◽  
P J Mason
Keyword(s):  
Linear Model ◽  
Transient Response ◽  
Parametric Identification ◽  
Squeeze Film ◽  
Decay Data ◽  
Operating Range ◽  
Response Data ◽  
Squeeze Film Damping ◽  
Free Decay ◽  
Theoretical Predictions

This paper describes the results obtained from an experimental programme concerned with a parametric identification of the damping and inertial coefficients of a cylindrical squeeze-film bearing, through an analysis of transient response data. The results enable the operating range for which a linear model of the squeeze-film is appropriate to be determined. Comparisons are made between the estimated coefficients and theoretical predictions.

Most often instantaneous rotation center (MOIRC) for roll damping assessment in the free decay test of a FPSO

2020 ◽  
Vol 95 ◽  
pp. 102014 ◽  
Author(s):  
Peyman Asgari ◽  
Antonio Carlos Fernandes ◽  
Ying Min Low
Keyword(s):  
Roll Damping ◽  
Rotation Center ◽  
Free Decay ◽  
Decay Test

A Decrement Method for Quantifying Non-Linear and Linear Damping

2005 ◽  
Author(s):  
Craig Meskell
Keyword(s):  
Total Force ◽  
Response Measurement ◽  
Response Data ◽  
Damped System ◽  
Free Decay ◽  
Decay Test ◽  
Damping Parameter ◽  
Non Linear ◽  
Linear Damping ◽  
Single Response

A method is presented which can estimate the linear and non-linear damping parameters in a lightly damped system. Only a single response measurement from a free decay test is required as input. This ensures that the magnitude of the damping parameters is not compromised by phase distortion between measurements. The method uses the instantaneous energy to describe the long-term evolution of the system. Practically this is achieved by using only the peak amplitudes in each period. In this way the stiffness is effectively ignored, and only the damping forces are considered. For this reason, the method is not unlike the familiar decrement method, which can be used to estimate the linear damping in linear systems. The method is developed in the context of a weakly non-linear, lightly damping system, with both linear and cubic damping. Simulated response data is used to demonstrate the accuracy of the technique. The non-linear damping parameter is extracted from the response data to within 5% of the exact value, even though the non-linear term contributes less than 1% to the total force in the system.

Estimation of Nonlinear Ship Roll Damping from Free-Decay Data

1985 ◽  
Vol 29 (02) ◽  
pp. 127-138 ◽  
Author(s):  
J. B. Roberts
Keyword(s):  
Initial Conditions ◽  
Spline Interpolation ◽  
Parametric Identification ◽  
Nonlinear Damping ◽  
Scale Model ◽  
Identification Procedure ◽  
Simulation Data ◽  
Decay Data ◽  
Free Decay ◽  
Ship Roll

A common method of assessing the damping present in ship rolling motion is to perform a free-decay experiment, in which, in the absence of waves, the ship is given an initial roll amplitude and then released. By processing the resulting decaying, oscillatory trace it is possible to estimate quantitatively the degree of damping, even when this is nonlinear. In this paper an approach to the estimation of nonlinear damping is proposed which involves the use of a cubic spline interpolation of the peak amplitudes, followed by a parametric identification procedure. This method is first applied to some simulation data and then to some real free-decay data, obtained from a scale model of a ship, with various initial conditions. The experimental data are analyzed using two alternative parametric forms, that is, linear-plus-quadratic and linear-plus-cubic damping. A principal advantage of the proposed technique is that, because nonlinearities in the restoring moment are properly accounted for, it is not limited to small angles of roll. Thus it can be applied to free-decay data relating to very large initial roll amplitudes.

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