Analysis of U-Type Anti-Roll Tank Using URANS: Sensitivity and Validation

2014 ◽  
Author(s):  
Maarten Kerkvliet ◽  
Guilherme Vaz ◽  
Nicolas Carette ◽  
Michiel Gunsing
Keyword(s):  
Free Surface ◽  
Full Scale ◽  
Grid Resolution ◽  
Experimental Results ◽  
Green Water ◽  
Roll Motion ◽  
Time Step ◽  
Roll Damping ◽  
Maximum Acceleration ◽  
Model Scale

The roll motion of ships operating in a seaway is often limiting operations. These limits could be due to, e.g. maximum acceleration, green water, capsize risk or just comfort. Therefore additional roll damping is desired to prevent uncontrolled roll motion. Different means are available to decrease the roll motion of a ship, amongst other these include bilge keels, active fin stabilizers (either for forward or zero speed) and U-shape or free surface anti-roll tanks (ART). The amplitude and phase of the roll opposing moment resulting from the water that moves inside the ART are a function of the geometry of the tank and especially its internal damping. Due to the complex and non-linear nature of this flow, the use of Computational Fluid Dynamics (CFD) was chosen to analyse the details of the flow inside the tank and its anti-roll performance. The present paper focuses on the sensitivity and validation of the anti-roll performances of passive U-type ART using CFD. For this, the incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) code ReFRESCO was used. The sensitivity on the results for the U-tank is analysed by varying the grid resolution and the numerical time step. The two-dimensional (2D) full-scale and Froude based model-scale ReFRESCO results are compared to 2D and 3D full-scale CFD results of Delaunay (2012) [1] and Thanyamanta and Molyneux (2012) [2] and validated with model-scale experimental results of Field and Martin (1975) [3] and MARIN experimental results by Gunsing et al. (2014) [4]. This paper shows the influence of the convective scheme for capturing the free-surface interface and provides recommendations for a time step and grid resolution to effectively calculate the roll damping of an ART.

scholarly journals Cavitation on Model- and Full-Scale Marine Propellers: Steady And Transient Viscous Flow Simulations At Different Reynolds Numbers

2020 ◽  
Vol 8 (2) ◽  
pp. 141 ◽  
Author(s):  
Ville Viitanen ◽  
Timo Siikonen ◽  
Antonio Sánchez-Caja
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
Full Scale ◽  
Tip Vortex ◽  
Wake Flow ◽  
Time Step ◽  
Two Phase ◽  
Marine Propellers ◽  
Model Scale ◽  
Propeller Performance

In this paper, we conducted numerical simulations to investigate single and two-phase flows around marine propellers in open-water conditions at different Reynolds number regimes. The simulations were carried out using a homogeneous compressible two-phase flow model with RANS and hybrid RANS/LES turbulence modeling approaches. Transition was accounted for in the model-scale simulations by employing an LCTM transition model. In model scale, also an anisotropic RANS model was utilized. We investigated two types of marine propellers: a conventional and a tip-loaded one. We compared the results of the simulations to experimental results in terms of global propeller performance and cavitation observations. The propeller cavitation, near-blade flow phenomena, and propeller wake flow characteristics were investigated in model- and full-scale conditions. A grid and time step sensitivity studies were carried out with respect to the propeller performance and cavitation characteristics. The model-scale propeller performance and the cavitation patterns were captured well with the numerical simulations, with little difference between the utilized turbulence models. The global propeller performance and the cavitation patterns were similar between the model- and full-scale simulations. A tendency of increased cavitation extent was observed as the Reynolds number increases. At the same time, greater dissipation of the cavitating tip vortex was noted in the full-scale conditions.

scholarly journals Bilge-Keel Influence on Free Decay of Roll Motion of a Realistic Hull1

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Yichen Jiang ◽  
Ronald W. Yeung
Keyword(s):  
Free Surface ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Vortex Method ◽  
Roll Motion ◽  
Two Dimensional ◽  
Desktop Computer ◽  
Roll Damping ◽  
Discrete Vortex ◽  
Bilge Keel

The prediction of roll motion of a ship with bilge keels is particularly difficult because of the nonlinear characteristics of the viscous roll damping. Flow separation and vortex shedding caused by bilge keels significantly affect the roll damping and hence the magnitude of the roll response. To predict the ship motion, the Slender-Ship Free-Surface Random-Vortex Method (SSFSRVM) was employed. It is a fast discrete-vortex free-surface viscous-flow solver developed to run on a standard desktop computer. It features a quasi-three-dimensional formulation that allows the decomposition of the three-dimensional ship-hull problem into a series of two-dimensional computational planes, in which the two-dimensional free-surface Navier–Stokes solver Free-Surface Random-Vortex Method (FSRVM) can be applied. In this paper, the effectiveness of SSFSRVM modeling is examined by comparing the time histories of free roll-decay motion resulting from simulations and from experimental measurements. Furthermore, the detailed two-dimensional vorticity distribution near a bilge keel obtained from the numerical model will also be compared with the existing experimental Digital Particle Image Velocimetry (DPIV) images. Next, we will report, based on the time-domain simulation of the coupled hull and fluid motion, how the roll-decay coefficients and the flow field are altered by the span of the bilge keels. Plots of vorticity contour and vorticity isosurface along the three-dimensional hull will be presented to reveal the motion of fluid particles and vortex filaments near the keels.

Model-Scale and Full-Scale CFD Calculations for Current Loads on Semi-Submersible

2011 ◽  
Author(s):  
Arjen Koop ◽  
Alexei Bereznitski
Keyword(s):  
Wind Tunnel ◽  
Scale Effects ◽  
Full Scale ◽  
Grid Resolution ◽  
Wind Tunnel Experiments ◽  
Force Coefficients ◽  
Model Scale ◽  
Coarse Grids

In this paper results of CFD calculations with the MARIN in-house code ReFRESCO are presented for the JBF-14000 Semi-Submersible designed by Huisman Equipment BV. The objective of the CFD calculations is to investigate the applicability, the costs and the accuracy of CFD to obtain the current coefficients of a semi-submersible for all headings. Furthermore, full scale CFD calculations are carried out to investigate possible scale effects on the current coefficients. An extensive verification study has been carried for the model-scale current loads on a semi-submersible using 10 different grids of different grid type for 3 different headings, i.e. 180, 150 and 90 degrees. These headings represent the main different flow regions around the semi-submersible. The CFD results are compared with the results from wind tunnel experiments and tests in the Offshore Basin for a range of current headings. The results for the force coefficients are not very dependent on grid resolution and grid type. The largest differences found are less than 10% and these are obtained for CX results for 180 degrees. For the results obtained on the same grid type the results change less than 4% when the grid is refined. These verification results give good confidence in the CFD results. For the angles with larger forces, i.e. the range [180:130] for CX and the range [150:90] for CY the CFD results are within 12% or better from the experiments. Full-scale force coefficients are calculated using 5 subsequently refined grids for three different headings, i.e. 180, 150 and 90 degrees. Scale effects should only be determined when the effect of grid refining is investigated. The trend of the force coefficients when refining the grid, can be different for model-scale and full-scale. The use of coarse grids can lead to misleading conclusions. On average the full-scale values are approximately 15–20% lower than for model-scale. However, larger differences for a number of angles do exist.

On the Sensitivity of the Roll Motion of an FPSO

2002 ◽  
Author(s):  
Martijn H. J. Kragtwijk ◽  
Tone M. Vestbo̸stad ◽  
Jan H. Vugts ◽  
Ove T. Gudmestad
Keyword(s):  
Theoretical Model ◽  
Potential Theory ◽  
Computer Programs ◽  
Model Tests ◽  
Full Scale ◽  
Roll Motion ◽  
Linear Potential ◽  
Roll Damping ◽  
Linear Potential Theory

This paper describes a theoretical model that has been used to investigate the roll motion of an FPSO. The Statoil operated Norne FPSO at Haltenbanken off central Norway has been used as a reference for the investigation. The model is based on linear potential theory. The viscous roll damping has been incorporated by linearizing the effect. Problems when simultaneously using various computer programs, textbooks and the theoretical model are highlighted. Also areas of caution when working with model tests are identified. The theoretical model has been used to investigate the sensitivity of the roll motion to certain key parameters. The theoretical model has further been compared with results from model tests and with full-scale measurements. The results of these comparisons are described and conclusions and recommendations following the investigation are presented.

scholarly journals Numerical Analysis of Full-Scale Ship Self-Propulsion Performance with Direct Comparison to Statistical Sea Trail Results

2020 ◽  
Vol 8 (1) ◽  
pp. 24 ◽  
Author(s):  
Wenyu Sun ◽  
Qiong Hu ◽  
Shiliang Hu ◽  
Jia Su ◽  
Jie Xu ◽  
...  
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Scale Effect ◽  
Full Scale ◽  
Hydrodynamic Performance ◽  
Local Flow ◽  
Model Scale ◽  
Propulsion Performance ◽  
The Difference ◽  
Thrust And Torque

Accurate prediction of the self-propulsion performance is one of the most important factors for the energy-efficient design of a ship. In general, the hydrodynamic performance of a full-scale ship could be achieved by model-scale simulation or towing tank tests with extrapolations. With the development of CFD methods and computing power, directly predict ship performance with full-scale CFD is an important approach. In this article, a numerical study on the full-scale self-propulsion performance with propeller operating behind ship at model- and full-scale is presented. The study includes numerical simulations using the RANS method with a double-model and VOF (Volume-of-Fluid) model respectively and scale effect analysis based on overall performance, local flow fields and detailed vortex identification. The verification study on grid convergence is also performed for full-scale simulation with global and local mesh refinements. A series of sea trail tests were performed to collect reliable data for the validation of CFD predictions. The analysis of scale effect on hull-propeller interaction shows that the difference of hull boundary layer and flow separation is the main source of scale effect on ship wake. The results of the fluctuations of propeller thrust and torque along with circulation distribution and local flow field show that the propeller’s loading is significantly higher for model-scale ship. It is suggested that the difference of vortex evolution and interaction is more pronounced and has larger effects on the ship’s powering performance at model-scale than full-scale according to the simulation results. From the study on self-propulsion prediction, it could be concluded that the simplification on free surface treatment does not only affect the wave-making resistance for bare hull but also the propeller performance and propeller induced ship resistance which can be produced up to 5% uncertainty to the power prediction. Roughness is another important factor in full-scale simulation because it has up to an approximately 7% effect on the delivery power. As a result of the validation study, the numerical simulations of full-scale ship self-propulsion shows good agreement with the sea trail data especially for cases that have considered both roughness and free surface effects. This result will largely enhance our confidence to apply full-scale simulation in the prediction of ship’s self-propulsion performance in the future ship designs.

A Comparison of the Model and Full Scale Transom Wave of the R/V Athena

2010 ◽  
Author(s):  
Thomas C. Fu ◽  
Eric Terrill ◽  
Anne M. Fullerton ◽  
Genevieve Lada Taylor
Keyword(s):  
Free Surface ◽  
Froude Number ◽  
Field Measurements ◽  
Full Scale ◽  
Scale Model ◽  
Naval Research ◽  
Ambient Conditions ◽  
Laser Altimeter ◽  
Number Range ◽  
Model Scale

Over the past few years the U.S. Office of Naval Research has sponsored a series of measurements of the transom wave of the R/V Athena and of a 1/8.25-scale model (NSWCCD Model 5365) of the ship. The objectives of the testing were to characterize the free surface wave behind the ship’s transom at both model and full scale for use in identifying hydrodynamic features and for developing and validating numerical simulation tools. The focus of this paper is the comparison of these full scale and model scale measurements, specifically a comparison of the time-averaged free-surface stern wave profiles and the dominant hydrodynamic features, the rooster tail for example. Both the field measurements and the model scale tow tank measurements were made in as calm as possible ambient conditions. Full scale data was collected in the relatively protected waters of St. Andrews Bay, Florida. The winds, which typically build as the day progresses, were minimal, and it was a new moon during the test period, so tidal excursions were also minimized. While measurements were obtained for ship speeds ranging from 3.1 to 6.2 m/s (6 to 12 knots), equivalent to Froude number range based on length (47 m) of 0.14 to 0.29, respectively, the focus of the comparison is for the 0.24 Froude number (10.5 knots full scale) case. Measurements of the full scale stern wave were made by a scanning laser altimeter, while measurements at model scale were made using a traversing set of conductivity finger probes.

scholarly journals Numerical Analysis of Full-scale Ship Self-Propulsion Performance with direct Comparison to Statistical Sea Trail Results

2019 ◽  
Author(s):  
Wenyu Sun ◽  
Qiong Hu ◽  
Shiliang Hu ◽  
Jia Su ◽  
Jie Xu ◽  
...  
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Scale Effect ◽  
Full Scale ◽  
Hydrodynamic Performance ◽  
Local Flow ◽  
Model Scale ◽  
Propulsion Performance ◽  
The Difference ◽  
Thrust And Torque

Accurate prediction of the self-propulsion performance is one of the most important factors for energy-efficient design of a ship. In general, the hydrodynamic performance of a full-scale ship could be achieved by model-scale simulation or towing tank test with extrapolations. With the development of CFD methods and computing power, directly predict ship performance with full-scale CFD is an important approach. In this article, a numerical study on the full-scale self-propulsion performance with propeller operating behind ship at model- and full-scale is presented. The study includes numerical simulations using RANS method with double-model and VOF model respectively and scale effect analysis based on overall performance, local flow fields and detailed vortex identification. Verification study on grid convergence is also performed for full-scale simulation with global and local mesh refinements. And a series of sea trail tests were performed to collect reliable data for the validation of CFD predictions. The analysis of scale effect on hull-propeller interaction shows that the difference on hull boundary layer and flow separation is the main source of scale effect on ship wake. And the results of the fluctuations of propeller thrust and torque along with circulation distribution and local flow field show that propeller’s loading is significantly higher for model-scale ship. It is suggested that the difference on vortex evolution and interaction is more pronounced and have larger effects on ship’s powering performance at model-scale than full-scale according to the simulation results. From the study on self-propulsion prediction, it could be concluded that the simplification on free surface treatment does not only affect the wave-making resistance for bare hull but also the propeller performance and propeller induced ship resistance which can produced up to 5% uncertainty to the power prediction. Roughness is another important factor in full-scale simulation because it has up to approximately 7% effect on the delivery power. As a result of validation study, the numerical simulations of full-scale ship self-propulsion shows good agreement with the sea trail data especially for cases that have considered both roughness and free surface effects. This result will largely enhance our confidence to apply full-scale simulation in the prediction of ship’s self-propulsion performance in the future ship designs.

Bilge Keel Influence on the Free Decay of Roll Motion of a Three-Dimensional Hull

2014 ◽  
Author(s):  
Ronald W. Yeung ◽  
Yichen Jiang
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Three Dimensional ◽  
Body Motion ◽  
Roll Motion ◽  
Two Dimensional ◽  
Desktop Computer ◽  
Roll Damping ◽  
The Time Domain ◽  
Bilge Keel

The prediction of roll motion of a ship with bilge keels is particularly difficult because of the nonlinear characteristics of the viscous damping. Flow separation and vortex shedding caused by bilge keels significantly affect the roll damping and the magnitude of the roll response. To predict free response of roll, the Slender-Ship Free-Surface Random Vortex Method (SSFSRVM) developed in Seah & Yeung (2008) [1] was employed. It is a fast free-surface viscous-flow solver designed to run on a standard desktop computer. It features a quasi-three dimensional formulation that allows the decomposition of the three-dimensional hull problem into a series of two-dimensional computational planes, in which the two-dimensional free-surface Navier-Stokes solver FSRVM [2] can be applied. This SSFSRVM methodology has recently been further developed to model multi-degrees of freedom of free-body motion in the time domain. In this paper, we will first examine the effectiveness of SSFSRVM modeling by comparing the time histories of free roll-decay motion resulting from simulations and experimental measurements. Furthermore, the detailed vorticity distribution near a bilge keel obtained from the numerical model will also be compared with the experimental PIV images. Next, we will report, based on the time-domain simulation of the coupled hull and fluid motion, how the roll decay coefficients and the flow field are altered by the span of the bilge keels. Plots of vorticity contour and vorticity iso-surface along the three-dimensional hull will be presented to reveal the motion of fluid particles and vortex filaments near the keels. It is appropriate and an honor for me to present this roll-damping research in the Emeritus Professor J. R. Paulling Honoring Symposium. It was from “Randy” that I first acquired the concept of equivalent linear damping. Even more so, I am very grateful for his teaching, guidance and friendship of many years. — R. W. Yeung

scholarly journals Mathematical modelling of the overflowing cylinder experiment

2003 ◽  
Vol 474 ◽  
pp. 275-298 ◽  
Author(s):  
P. D. HOWELL ◽  
C. J. W. BREWARD
Keyword(s):  
Free Surface ◽  
Surfactant Concentration ◽  
Dynamic Properties ◽  
Vertical Cylinder ◽  
Surfactant Solution ◽  
Surface Concentration ◽  
Experimental Results ◽  
Surface Velocity ◽  
Experimental Apparatus ◽  
Finite Distance

The overflowing cylinder (OFC) is an experimental apparatus designed to generate a controlled straining flow at a free surface, whose dynamic properties may then be investigated. Surfactant solution is pumped up slowly through a vertical cylinder. On reaching the top, the liquid forms a flat free surface which expands radially before over flowing down the side of the cylinder. The velocity, surface tension and surfactant concentration on the expanding free surface are measured using a variety of non-invasive techniques.A mathematical model for the OFC has been previously derived by Breward et al. (2001) and shown to give satisfactory agreement with experimental results. However, a puzzling indeterminacy in the model renders it unable to predict one scalar parameter (e.g. the surfactant concentration at the centre of the cylinder), which must be therefore be taken from the experiments.In this paper we analyse the OFC model asymptotically and numerically. We show that solutions typically develop one of two possible singularities. In the first, the surface concentration of surfactant reaches zero a finite distance from the cylinder axis, while the surface velocity tends to infinity there. In the second, the surfactant concentration is exponentially large and a stagnation point forms just inside the rim of the cylinder. We propose a criterion for selecting the free parameter, based on the elimination of both singularities, and show that it leads to good agreement with experimental results.

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