The Influence of Vortex Formation on the Damping of FPSOs With Large Width Bilge Keels

2012 ◽  
Author(s):  
Allan C. de Oliveira ◽  
Antonio Carlos Fernandes ◽  
Hélio Bailly Guimarães
Keyword(s):  
Pressure Distribution ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Roll Damping ◽  
Flat Bottom ◽  
Long Time ◽  
Large Width ◽  
Decay Tests ◽  
Visualization Techniques ◽  
Bilge Keel

The roll damping of a FPSO assessment is a different subject than the ship case. The fact that the FPSO is not moving changes the flow hydrodynamics in such a way that the well established understanding is no longer applied. This is so at least for certain particularities such as flat bottom, no lift effect due to zero velocity, and so on. Recent researches have proven the strong effect of the vortex shedding on the roll damping of a FPSO mainly when large width bilge keel are present. Although these effects are known by a long time for ships, the increase of the vortex magnitude due the large width bilge keels on a FPSO has let to uncertainties about the behavior of the structures and the situation is challenging. It has been understood that the vortex can modify deeply the pressure distribution along the FPSO hull in such way that the final roll dissipation is higher. Surprisingly, under certain conditions the memory effects are small. The use of visualization techniques allied to the analysis of several decay tests for the same hull can help the understanding of several aspects such as the uncertainty in the measurements and the vortex behavior.

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.

Numerical Simulation of Roll Damping

2006 ◽  
Author(s):  
Juan B. V. Wanderley ◽  
Andre´ Ramiro ◽  
Thiago Reis ◽  
Antonio Carlos Fernandes ◽  
Carlos Levi
Keyword(s):  
Numerical Simulation ◽  
Stokes Equations ◽  
Vortex Formation ◽  
Integral Form ◽  
Quantitative Agreement ◽  
Navier Stokes ◽  
Roll Damping ◽  
Navier Stokes Equations ◽  
Decay Tests ◽  
Volume Method

The highly viscous flow problem of roll damping of a FPSO is investigated by means of numerical solution of the unsteady two-dimensional Navier-Stokes equations. The finite volume method using non-structured grid is used to solve the integral form of the governing equations. The cross section of the FPSO hull with an initial roll displacement is let free to oscillate in roll in an initially still fluid. The numerical simulation provides a realistic picture of the physics of the phenomenon, capturing the vortex formation around the bilge keel. Numerical results from roll free decay tests are compared with experimental data showing a fairly good qualitative and quantitative agreement of the roll damping.

Numerical Simulation of Roll Damping of a FPSO

2007 ◽  
Author(s):  
Juan B. V. Wanderley ◽  
Andre´ Ramiro ◽  
Thiago Reis ◽  
Antonio Carlos Fernandes ◽  
Carlos Levi
Keyword(s):  
Numerical Simulation ◽  
Stokes Equations ◽  
Vortex Formation ◽  
Integral Form ◽  
Quantitative Agreement ◽  
Navier Stokes ◽  
Roll Damping ◽  
Navier Stokes Equations ◽  
Volume Method ◽  
Bilge Keel

The viscous flow problem of roll damping of a FPSO is investigated by means of numerical solution of the unsteady two-dimensional Navier-Stokes equations. The finite volume method using unstructured grid is used to solve the integral form of the governing equations. The cross section of the FPSO hull with an initial roll displacement is left free to oscillate in roll, heave and sway in an initially still fluid. The numerical simulation provides a realistic picture of the physics of the phenomenon, capturing the vortex formation around the bilge keel. The numerical results are compared with experimental data showing a fairly good qualitative and quantitative agreement of the motion damping.

Roll Damping Decay of a FPSO With Bilge Keel

2013 ◽  
Author(s):  
Gustavo O. Guarniz Avalos ◽  
Juan B. V. Wanderley ◽  
Antonio C. Fernandes
Keyword(s):  
Vortex Shedding ◽  
Numerical Scheme ◽  
Strong Influence ◽  
Stokes Equations ◽  
The Body ◽  
Navier Stokes ◽  
Roll Damping ◽  
Navier Stokes Equations ◽  
Decay Test ◽  
Bilge Keel

The roll damping decay is investigated for a Floating Production Storage and Offloanding (FPSO). For this purpose, a roll decay test of FPSO is simulated by means of the numerical solution of the incompressible two-dimensional Navier-Stokes equations. The numerical results are compared with experimental data for validating the numerical scheme implemented. The simulations indicated the strong influence of the bilge radius in the damping coefficient of the FPSO section. Interesting results were obtained regarding the time series of the displacement of the body and vortex shedding around the bilge keel.

Turbine Blade Trailing Edge Flow Characteristics at High Subsonic Outlet Mach Number

2003 ◽  
Vol 125 (2) ◽  
pp. 298-309 ◽  
Author(s):  
Claus H. Sieverding ◽  
Hugues Richard ◽  
Jean-Michel Desse
Keyword(s):  
Mach Number ◽  
Pressure Distribution ◽  
Turbine Blade ◽  
Vortex Shedding ◽  
High Speed ◽  
Pressure Coefficient ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Suction Side ◽  
Trailing Edge

The paper presents an experimental investigationof the effect of the trailing edge vortex shedding on the steady and unsteady trailing blade pressure distribution of a turbine blade at high subsonic Mach number M2,is=0.79 and high Reynolds number RE=2.8×106. The vortex formation and shedding process is visualized using a high-speed schlieren camera and a holographic interferometric density measuring technique. The blade is equipped with a rotatable trailing edge cylinder instrumented side-by-side with a pneumatic pressure tap and a fast response pressure sensor for detailed measurements of the trailing edge pressure distribution. The experiments demonstrate that contrary to the isobaric dead air region demonstrated at low subsonic Mach numbers the data reveal the existence of a highly nonuniform trailing edge pressure distribution with a strong pressure minimum at the center of the trailing edge. This finding is significant for the determination of the base pressure coefficient that is in general measured with a single pressure-sensing hole at the trailing edge center. The paper investigates further the effect of the vortex shedding on the blade rear suction side and discusses the superposition of unsteady effects emanating from the trailing edge and from the neighboring blade. The experimental data are a unique source for the validation of unsteady Navier-Stokes codes.

An Experimental Study on the Vertical Flow Past a Finite-Length Horizontal Cylinder at Low Reynolds Numbers

2014 ◽  
Vol 493 ◽  
pp. 68-73 ◽  
Author(s):  
Willy Stevanus ◽  
Yi Jiun Peter Lin
Keyword(s):  
Finite Length ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
Reynolds Numbers ◽  
Horizontal Cylinder ◽  
Vortex Street ◽  
Vertical Flow ◽  
Low Reynolds Numbers ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

The research studies the characteristics of the vertical flow past a finite-length horizontal cylinder at low Reynolds numbers (ReD) from 250 to 1080. The experiments were performed in a vertical closed-loop water tunnel. Flow fields were observed by the particle tracer approach for flow visualization and measured by the Particle Image Velocimetry (P.I.V.) approach for velocity fields. The characteristics of vortex formation in the wake of the finite-length cylinder change at different regions from the tip to the base of it. Near the tip, a pair of vortices in the wake was observed and the size of the vortex increased as the observed section was away from the tip. Around a distance of 3 diameters of the cylinder from its tip, the vortex street in the wake was observed. The characteristics of vortex formation also change with increasing Reynolds numbers. At X/D = -3, a pair of vortices was observed in the wake for ReD = 250, but as the ReD increases the vortex street was observed at the same section. The vortex shedding frequency is analyzed by Fast Fourier Transform (FFT). Experimental results show that the downwash flow affects the vortex shedding frequency even to 5 diameters of the cylinder from its tip. The interaction between the downwash flow and the Von Kármán vortex street in the wake of the cylinder is presented in this paper.

Roll damping decay of a FPSO with bilge keel

2014 ◽  
Vol 87 ◽  
pp. 111-120 ◽  
Author(s):  
Gustavo O.G. Avalos ◽  
Juan B.V. Wanderley ◽  
Antonio C. Fernandes ◽  
Allan C. Oliveira
Keyword(s):  
Roll Damping ◽  
Bilge Keel

Dynamics of Interstitial Fluid Pressure in Extracellular Matrix Hydrogels in Microfluidic Devices

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Joe Tien ◽  
Le Li ◽  
Ozgur Ozsun ◽  
Kamil L. Ekinci
Keyword(s):  
Extracellular Matrix ◽  
Pressure Distribution ◽  
Interstitial Fluid ◽  
Scaling Laws ◽  
Fluid Pressure ◽  
Interstitial Fluid Pressure ◽  
External Loading ◽  
Interstitial Pressure ◽  
Time Resolved ◽  
Long Time

In order to understand how interstitial fluid pressure and flow affect cell behavior, many studies use microfluidic approaches to apply externally controlled pressures to the boundary of a cell-containing gel. It is generally assumed that the resulting interstitial pressure distribution quickly reaches a steady-state, but this assumption has not been rigorously tested. Here, we demonstrate experimentally and computationally that the interstitial fluid pressure within an extracellular matrix gel in a microfluidic device can, in some cases, react with a long time delay to external loading. Remarkably, the source of this delay is the slight (∼100 nm in the cases examined here) distension of the walls of the device under pressure. Finite-element models show that the dynamics of interstitial pressure can be described as an instantaneous jump, followed by axial and transverse diffusion, until the steady pressure distribution is reached. The dynamics follow scaling laws that enable estimation of a gel's poroelastic constants from time-resolved measurements of interstitial fluid pressure.

The Nonlinear Roll Damping of a FPSO Hull

2013 ◽  
Vol 136 (1) ◽  
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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