Determination of Roll Damping Coefficients for an FPSO Through Model Tests and CFD Analysis

2017 ◽  
Vol 27 (2) ◽  
pp. 193-203 ◽  
Author(s):  
Chang Seop Kwon ◽  
Hyun Joe Kim ◽  
Dong Woo Jung ◽  
Sung Wook Lee
Keyword(s):  
Model Tests ◽  
Cfd Analysis ◽  
Roll Damping ◽  
Damping Coefficients

Experimental Determination of Roll Damping Coefficient for FPSO

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.

scholarly journals DETERMINATION OF LINEAR AND NONLINEAR ROLL DAMPING COEFFICIENTS OF A SHIP SECTION USING CFD

Brodogradnja ◽  
2019 ◽  
Vol 70 (4) ◽  
pp. 17-33 ◽  
Author(s):  
Soon-Seok Song ◽  
◽  
Sang-Hyun Kim ◽  
Kwang-Jun Paik ◽  
Keyword(s):  
Roll Damping ◽  
Damping Coefficients ◽  
Linear And Nonlinear

Estimation of Roll Damping Coefficients Based on Model Tests Responses of a FPSO in Waves

2019 ◽  
Author(s):  
Claudio A. Rodríguez ◽  
Paulo T. T. Esperança ◽  
Mauro C. Oliveira
Keyword(s):  
Model Tests ◽  
Viscous Effects ◽  
Roll Damping ◽  
Damping Coefficients ◽  
Numerical Predictions ◽  
Intact Stability ◽  
Calm Water ◽  
Wave Conditions ◽  
Decay Tests ◽  
Damping Estimation

Abstract Roll damping estimation is of great concern for the prediction of motions in waves of ship and offshore platforms, especially when viscous effects are relevant. Although this problem dates back to the times of William Froude, it has regained much attention in the context of the development of the second-generation intact stability criteria of ships, especially because there are still not accurate and efficient tools for roll damping prediction. For offshore applications, a common approach for roll damping estimation is to perform roll decay tests with scale models in calm water and then use the resultant values in the roll equation to predict motions in waves. However, for some wave conditions, the damping coefficients obtained from those tests may not be representative of the actual damping in waves. To assess the influence of wave conditions in the roll damping coefficients, the present work proposes a simplified hybrid approach that combines experimental results from model tests with numerical predictions of roll motion in waves. The numerical tool adopted here is based on a frequency domain single-degree-of-freedom model with linearized external damping that includes viscous effects. A series of experimental model tests with a typical FPSO hull in regular and irregular has been analyzed to obtain the roll damping coefficients in waves. These results are compared with those from decay tests in calm-water as well as from semi-empirical predictions based on Ikeda’s method. Despite the linearized assumption, it is expected that the damping coefficients from wave tests provide a more realistic representation of the roll dynamics than those from typical decay tests.

Realistic estimation of roll damping coefficients in waves based on model tests and numerical simulations

2020 ◽  
Vol 213 ◽  
pp. 107664
Author(s):  
Claudio A. Rodríguez ◽  
Ieza S. Ramos ◽  
Paulo T.T. Esperança ◽  
Mauro C. Oliveira
Keyword(s):  
Numerical Simulations ◽  
Model Tests ◽  
Roll Damping ◽  
Damping Coefficients

A Mathematical Model for Roll Damping Prediction

2015 ◽  
Author(s):  
Henry Piehl ◽  
Ould el Moctar
Keyword(s):  
Mathematical Model ◽  
Regression Analysis ◽  
Shape Parameter ◽  
Roll Motion ◽  
Damping Properties ◽  
Roll Damping ◽  
Ship Hulls ◽  
Damping Coefficients ◽  
Analytic Expression

A ship in seaway is always prone to roll motion. For the safety of personnel, ship and cargo it is essential to optimize the roll damping properties of the hull shape in order to prevent exceeding roll angles. Therefore, a tool for the prediction of roll damping is an important requirement during the design phase of ship hulls. The objective of this study is to use regression analysis and numerical simulation of roll motion to develop an analytic expression for the determination of roll damping. The development procedure starts with a variation of several hull shape parameter that influence the roll damping. For each of the parameter variants, a numerical roll simulation is conducted and the according roll damping coefficients are determined by time series analysis. Finally, regression analysis is applied to the computed results in order to derive a mathematical model that allows to determine the roll damping coefficient depending on the hull shape parameter.

Prediction of the Flow and Force Characteristics of Safety Relief Valves

2006 ◽  
Author(s):  
W. Dempster ◽  
C. K. Lee ◽  
J. Deans
Keyword(s):  
Operating Conditions ◽  
Cfd Analysis ◽  
Flow Conditions ◽  
Relief Valve ◽  
Good Correspondence ◽  
Geometry Modeling ◽  
Valve Opening ◽  
Satisfactory Prediction ◽  
Force Characteristics

The design of safety relief valves depends on knowledge of the expected force-lift and flow-lift characteristics at the desired operating conditions of the valve. During valve opening the flow conditions change from seal-leakage type flows to combinations of sub-sonic and supersonic flows It is these highly compressible flow conditions that control the force and flow lift characteristics. This paper reports the use of computational fluid dynamics techniques to investigate the valve characteristics for a conventional spring operated 1/4” safety relief valve designed for gases operating between 10 and 30 bar. The force and flow magnitudes are highly dependent on the lift and geometry of the valve and these characteristics are explained with the aid of the detailed information available from the CFD analysis. Experimental determination of the force and flow lift conditions has also been carried out and a comparison indicates good correspondence between the predictions and the experiment. However, attention requires to be paid to specific aspects of the geometry modeling including corner radii and edge chamfers to ensure satisfactory prediction.

Determination of the added masses and damping coefficients during coupled motions of two ships in shallow water parallel to the vertical wall

2021 ◽  
pp. 16-25
Author(s):  
В.Ю. Семенова ◽  
К.И. Баканов
Keyword(s):  
Shallow Water ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Hydrodynamic Coefficients ◽  
Damping Coefficients ◽  
Added Masses ◽  
Joint Motions ◽  
National Practice ◽  
Simultaneous Influence

В статье рассматривается определение коэффициентов демпфирования и присоединенных масс, возникающих при совместной качке двух судов в условиях мелководья параллельно вертикальной стенке на основании решения трехмерной потенциальной задачи. Определение гидродинамических коэффициентов осуществляется на основании методов интегральных уравнений и зеркальных отображений. Представленное решение в отечественной практике является новым. В статье приводятся результаты расчетов коэффициентов присоединенных масс и демпфирования, возникающих при качке двух одинаковых судов, расположенных лагом к волнению и параллельно вертикальной стенке в зависимости от изменения расстояний как между судами, так и между судами и вертикальной стенкой. Проводится исследование влияния различных фарватеров на величины гидродинамических коэффициентов, а именно: мелководного фарватера, мелководного фарватера с вертикальной стенкой, мелководного фарватера со вторым параллельно качающимся судном и мелководного фарватера с вертикальной стенкой и вторым судном. Таким образом, в работе учитывается одновременное влияния мелководья, вертикальной стенки и второго судна. Показано увеличение значений коэффициентов присоединенных масс и демпфирования при уменьшении расстояний между судами и между судами и вертикальной стенкой. Также показано значительное совместное влияние вертикальной стенки и второго судна на коэффициенты присоединенных масс и демпфирования по сравнению с другими видами стесненных фарватеров. The article discusses the determination of damping coefficients and added masses arising from the joint motions of two ships in shallow water conditions parallel to the vertical wall based on the solution of a three-dimensional potential problem. Determination of hydrodynamic coefficients is carried out on the basis of the methods of integral equations and mirror images. The solution presented in the national practice is new The article presents the results of calculating the coefficients of added masses and damping arising from the motions of two identical ships located lagged to the sea and parallel to the vertical wall, depending on the change in the distances between the ships and between the ships and the vertical wall. A study is being made of the influence of various waterways on the values ​​of hydrodynamic coefficients, namely: a shallow waterway, a shallow waterway with a vertical wall, a shallow waterway with a second parallel oscillating ship and a shallow waterway with a vertical wall and a second ship. Thus, the work takes into account the simultaneous influence of shallow water, vertical wall and the second ship. An increase in the values of the coefficients of added masses and damping with a decrease in the distances between ships and between ships and the vertical wall is shown. It also shows a significant combined effect of the vertical wall and the second ship on the added mass and damping coefficients in comparison with other types of constrained waterways.

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.

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