CFD Simulation of Roll Damping Characteristics of a Ship Mid-Section With Bilge Keel

2016 ◽  
Author(s):  
Mohsin A. R. Irkal ◽  
S. Nallayarasu ◽  
S. K. Bhattacharyya
Keyword(s):  
Fluid Dynamics ◽  
Cfd Simulation ◽  
Experimental Studies ◽  
Ship Hull ◽  
Estimation Methods ◽  
Accurate Estimation ◽  
Roll Motion ◽  
Roll Damping ◽  
Damping Characteristics ◽  
Bilge Keel

The prediction of nonlinear roll motion of ships depends highly on the accurate estimation of roll damping. The nonlinear nature of roll damping arises from the viscous flow and the associated phenomenon of flow separation around the ship hull. Roll damping changes noticeably with a slight change in the ship hull geometry and appendages. The estimation methods employed in industry are highly empirical in nature. These empirical methods were derived from combinations of model tests conducted in wave flumes and basins, and some selected formulae used in fluid dynamics. These methods have limitations and the roll damping prediction show large variation with change in the ship parameters. The advances made in Computational Fluid Dynamics (CFD) in recent times, and validation of the CFD results using experimental studies, can help in predicting roll motion and damping more accurately. The present work uses CFD as a tool to estimate roll damping of a ship mid-section with bilge keel with validation using published experimental results.

A Piecewise Model for Prediction of Large Amplitude Total Ship Roll Damping

2011 ◽  
Author(s):  
Christopher C. Bassler ◽  
Arthur M. Reed ◽  
Alan J. Brown
Keyword(s):  
Large Amplitude ◽  
Roll Motion ◽  
Practical Implementation ◽  
Roll Damping ◽  
Damping Characteristics ◽  
Ship Roll ◽  
Piecewise Model ◽  
Physical Changes ◽  
Physical Phenomena ◽  
Bilge Keel

A piecewise model is presented to model total ship roll damping, with considerations for large amplitude roll motion effects, such as bilge keel interaction with the free-surface. The model is based on the consideration of distinct ship-specific physical phenomena, such as bilge keel emergence. Abrupt physical changes occur with these events, resulting in significant changes in the damping characteristics of the system. Without these considerations, roll motion may be under-predicted. Some additional considerations needed for the practical implementation of the proposed piecewise model are also discussed.

scholarly journals Analysis on Rolling Damping of a Conventional Boat fitted with T-shaped Bilge Keels

2018 ◽  
Vol 202 ◽  
pp. 02007
Author(s):  
Yam Ke San ◽  
Gordon Chiew ◽  
Chin Howe ◽  
Vincent Chieng Chen Lee ◽  
Sukanta Roy
Keyword(s):  
Fluid Dynamics ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Large Aspect Ratio ◽  
Roll Damping ◽  
Damping Characteristics ◽  
Grid Approach ◽  
The Impact ◽  
Bilge Keel ◽  
Dynamics Method

This work presents a numerical study on the effect of T-shaped bilge keels on the roll damping of a conventional boat. A scaled boat model with the same dimensions as that of Irkal et al. [2] was fitted with two T-shaped bilge keels at the edges of the model. Computational Fluid Dynamics method was employed to simulate the roll decay motion of the boat. The motion of the boat is captured using a 6DOF model and the Overset grid approach. Comparison was performed on the damping characteristics of the conventional I-shaped and the T-shaped bilge keels. In addition, the impact of the aspect ratio of the keel bilges on the roll damping of the boat was evaluated. It was found that the bilge keel aspect ratio influences the damping coefficient non-linearly. Sufficiently large aspect ratio, i.e. an aspect ratio greater than 2, is necessary in order to obtain an effective damping on the peak angle.

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.

Ship Roll Motion Damping Using Bilge Keels – A Detailed CFD Investigation

2015 ◽  
Author(s):  
Joshua Counsil ◽  
Kevin McTaggart ◽  
Dominic Groulx ◽  
Kiari Boulama
Keyword(s):  
Experimental Studies ◽  
The Body ◽  
Navier Stokes ◽  
Roll Motion ◽  
Empirical Methods ◽  
Viscous Effects ◽  
Vortex Interactions ◽  
Ship Roll ◽  
Semi Empirical ◽  
Bilge Keel

A study has been undertaken to test the value of unsteady Reynolds-averaged Navier-Stokes (URANS) and traditional semi-empirical methods in the face of complex ship roll phenomena, and provide insight into the selection of bilge keel span for varying roll amplitudes. The computational fluid dynamics (CFD) code STAR-CCM+ is employed and two-dimensional submerged bodies undergoing forced roll motion are analyzed. The spatial resolution and timestepping scheme are validated by comparison with published numerical and experimental studies. The model is then applied to a fully-submerged circular cylinder with bilge keels of varying span and undergoing roll motion at varying angular amplitudes. Extracted hydrodynamic coefficients indicate that in general, increasing displacement amplitude and bilge keel span yields increased added mass and increased damping. The relationship is complex and highly dependent upon vortex interactions with each other and the body. The semi-empirical methods used for comparison yield good predictions for simple vortex interactions but fail where viscous effects are strong. Hence, URANS methods are shown to be necessary for friction-dominated flows while semi-empirical methods remain useful for initial design considerations.

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.

Comparison of RANS Method and Discrete Vortex Method on Simulating the Roll Motion of a Ship With Bilge Keels

2018 ◽  
Author(s):  
Yichen Jiang ◽  
Xiaojie Zhao ◽  
Zhihua Zeng ◽  
Tiezhi Sun ◽  
Jiawen Li ◽  
...  
Keyword(s):  
Numerical Models ◽  
Vortex Method ◽  
Roll Motion ◽  
Fluid Viscosity ◽  
Roll Damping ◽  
Discrete Vortex ◽  
Discrete Vortex Method ◽  
Numerical Predictions ◽  
Bilge Keel ◽  
Rans Method

The prediction of roll motion of a ship section with bilge keels is particularly difficult because the flow separation and vortex shedding under the hull significantly affect the behavior of roll damping. To predict the roll damping and roll motion directly, the numerical models must simulate the fluid viscosity. Recently, Reynolds-averaged Navier–Stokes (RANS) method and Discrete Vortex Method (DVM) have been applied in this area and show promising results. In this paper, we will use both methods to simulate the free roll-decay motion of a ship section with bilge keels. The numerical predictions of the roll time histories will be compared with experimental measurements. Besides, the numerically-predicted vorticity distributions at different time instants near a bilge keel will be shown and compared. Moreover, the computation times for both numerical methods will also be reported. In this work, we will conduct the comparison for a number of cases that are with different bilge-keel heights and bilge-keel installation angles. Thus, the accuracies and the computational efficiencies will be evaluated comprehensively.

Analysis of Roll Motion due to Asymmetric Bilge Keels

2012 ◽  
Author(s):  
Nathan Tom ◽  
Robert Seah ◽  
Dominique Roddier
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Domain Model ◽  
Roll Motion ◽  
Roll Damping ◽  
Vessel Motion ◽  
Bilge Keel ◽  
Unequal Length

Traditional frequency domain based vessel motion analyses operate under the assumption that the roll damping contribution from the port and starboard bilge keels are equivalent. In this work, we examine the roll motion of a vessel with bilge keels of unequal length using a novel methodology. Experiments conducted during the FPSO Roll JIP suggest that waves approaching from port versus starboard will induce different motion amplitudes due to the unequal bilge keel length. We examine the results from different approaches, comparing the computed response from a frequency domain analysis against those provided by a time domain model using Orcaflex with bilge keel represented by drag elements.

scholarly journals Aerodynamic study of three cars in tandem using computational fluid dynamics

2021 ◽  
Vol 15 (3) ◽  
pp. 8228-8240
Author(s):  
H. Abdul-Rahman ◽  
H. Moria ◽  
Mohammad Rasidi Mohammad Rasani
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Drag Coefficient ◽  
Model Comparison ◽  
Cfd Simulation ◽  
Positive Impact ◽  
Lift Coefficient ◽  
Experimental Studies ◽  
Intelligent Transport System ◽  
Drag Coefficients

Aerodynamics of vehicles account for nearly 80% of fuel losses on the road. Today, the use of the Intelligent Transport System (ITS) allows vehicles to be guided at a distance close to each other and has been shown to help reduce the drag coefficients of the vehicles involved. In this article, the aim is to investigate the effect of distances between a three car platoons, to their drag and lift coefficients, using computational fluid dynamics. To that end, a computational fluid dynamics (CFD) simulation was first performed on a single case and platoon of two Ahmed car models using the STAR-CCM+ software, for validation with previous experimental studies. Significant drop in drag coefficients were observed on platoon models compared to a single model. Comparison between the k-w and k-e turbulence models for a two car platoon found that the k-w model more closely approximate the experimental results with errors of only 8.66% compared to 21.14% by k-e turbulence model. Further studies were undertaken to study the effects of various car gaps (0.5L, 1.0L and 1.5L; L = length of the car) to the aerodynamics of a three-car platoon using CFD simulation. Simulation results show that the lowest drag coefficient that impacts on vehicle fuel savings varies depending on the car's position. For the front car, the lowest drag coefficient (CD) can be seen for car gaps corresponding to X1 = 0.5L and X2 = 0.5L, where CD = 0.1217, while its lift coefficient (CL) was 0.0366 (X1 and X2 denoting first to second and second to third car distance respectively). For the middle car, the lowest drag coefficient occurred when X1 = 1.5L and X2 = 0.5L, which is 0.1397. The lift coefficient for this car was -0.0611. Meanwhile, for the last car, the lowest drag coefficient was observed when X1 = 0.5L and X2 = 1.5L, i.e. CD = 0.263. The lift coefficient for this car was 0.0452. In this study, the lowest drag coefficient yields the lowest lift coefficient. The study also found that for even X1 and X2 spacings, the drag coefficient increased steadily from the front to the last car, while the use of different spacings were found to decrease drag coefficient of the rear car compared to the front car and had a positive impact on platoon driving and fuel-saving.

Effects of fluid dynamics on enhanced biohydrogen production in a pilot stirred tank reactor: CFD simulation and experimental studies

2016 ◽  
Vol 41 (33) ◽  
pp. 14630-14640 ◽  
Author(s):  
C. Niño-Navarro ◽  
I. Chairez ◽  
L. Torres-Bustillos ◽  
J. Ramírez-Muñoz ◽  
E. Salgado-Manjarrez ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Cfd Simulation ◽  
Experimental Studies ◽  
Biohydrogen Production ◽  
Stirred Tank ◽  
Stirred Tank Reactor ◽  
Tank Reactor

Roll Decay Model Test of a Post Panamax Container Ship: Experimental and Numerical Analysis

2013 ◽  
Author(s):  
Henry Piehl ◽  
Ould el Moctar
Keyword(s):  
Ship Hull ◽  
Roll Angle ◽  
Body Motion ◽  
Roll Motion ◽  
Numerical Comparison ◽  
Container Ship ◽  
Roll Damping ◽  
Joint Research ◽  
Decay Test ◽  
Joint Research Project

The slender shape of a modern ship hull, exhibits a roll motion that is — in contrast to heave and pitch motion — submitted to large amplitudes and weak damping. This effect explains the importance of determining the roll damping of a hull and denotes the difficulty to measure such a small dynamic property. For the joint research project Best-Roll a series of roll decay tests were conducted with the model of a post panamax container ship. To capture the influence of the draft and the ship velocity, the roll motion was measured for a systematic variation of these parameter. In addition the tests were performed with an initial roll angle of 20 degrees, in order to investigate the nonlinear damping behavior at large roll angles. The objective of the subsequent study was to test the capability of OpenFOAM to compute the overall roll damping of a ship hull and appendages. For the numerical comparison, the roll decay test was simulated with OpenFOAM, using a transient multiphase solver with a RANS turbulence model, dynamic mesh motion and a rigid body motion model of the ship. The results were compared by calculating the roll damping coefficient for both experiment and numerical simulation by means of time series analysis of the roll angle.

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