Nonlinear Roll Damping and Roll Motion Study of Asymmetric Catamaran With Variable Layout

2021 ◽  
Author(s):  
Zhang Yihan ◽  
Hu Jingfeng
Keyword(s):  
Roll Motion ◽  
Roll Damping ◽  
Motion Study

Nonlinear Roll Damping and Roll Motion Study of Asymmetric Catamaran With Variable Layouts

2020 ◽  
Author(s):  
Yihan Zhang ◽  
Jingfeng Hu
Keyword(s):  
Numerical Methods ◽  
Great Influence ◽  
Prediction Method ◽  
Potential Method ◽  
Roll Motion ◽  
Roll Damping ◽  
Overlapping Grids ◽  
Motion Study ◽  
Seakeeping Performance ◽  
Ship Speed

Abstract Because of the interference between the main hull and side hull, the layout of asymmetric catamaran has a great influence on the seakeeping performance. In order to assess the characteristics of roll damping and roll motion of this kind of ship, firstly, a numerical prediction method of roll damping is established by CFD with overlapping grids to simulate the roll decay curves at different transverse and longitudinal spacing and ship speed. The roll damping property is analyzed by energy method and flow field monitoring. Then, based on the correction of nonlinear roll damping, the roll motion response in waves is calculated by 3D potential method. Finally, model tests are carried out to verify the numerical methods. The change of transverse layout has a great influence on the roll damping and roll motion of the asymmetric catamaran, while the longitudinal layout has a little influence on the roll performance. The research results of this paper can provide some useful reference for the design of asymmetric catamaran.

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.

Roll Damping Simulations of an Offshore Heavy Lift DP3 Installation Vessel Using the CFD Toolbox OpenFOAM

2020 ◽  
Author(s):  
Brecht Devolder ◽  
Florian Stempinski ◽  
Arjan Mol ◽  
Pieter Rauwoens
Keyword(s):  
Boundary Element ◽  
Damping Coefficient ◽  
Navier Stokes ◽  
Roll Motion ◽  
Viscous Effects ◽  
Roll Damping ◽  
Two Phase ◽  
Damping Behavior ◽  
External Moment ◽  
Heavy Lift

Abstract In this work, the roll damping behavior of the offshore heavy lift DP3 installation vessel Orion from the DEME group is studied. Boundary element codes using potential flow theory require a roll damping coefficient to account for viscous effects. In this work, the roll damping coefficient is calculated using the Computational Fluid Dynamics (CFD) toolbox OpenFOAM. The two-phase Navier-Stokes fluid solver is coupled with a motion solver using a partitioned fluid-structure interaction algorithm. The roll damping is assessed by the Harmonic Excited Roll Motion (HERM) technique. An oscillating external moment is applied on the hull and the roll motion is tracked. Various amplitudes and frequencies of the external moment and different forward speeds, are numerically simulated. These high-fidelity full-scale simulations result in better estimations of roll damping coefficients for various conditions in order to enhance the accuracy of efficient boundary element codes for wave-current-structure interactions simulations.

A Roll Damping Analysis of a Standard US Naval Hull Form (DTMB 5415)

2021 ◽  
Vol 163 (A1) ◽  
pp. 79-86
Author(s):  
L F Hu ◽  
Q T Gong ◽  
Z M Yuan ◽  
X Y Wang ◽  
J X Duan
Keyword(s):  
Numerical Simulation ◽  
Vof Method ◽  
Navier Stokes ◽  
Roll Motion ◽  
Ship Motions ◽  
Stability Criteria ◽  
Fluid Interface ◽  
Roll Damping ◽  
Hull Form ◽  
Us Navy

Accurate prediction of roll damping is important in calculating the roll motion of a ship. This paper presents a roll decay analysis of an intact US Navy Destroyer hull form (DTMB 5415) using a Navier–Stokes (NS) solver with the volume of fluid (VOF) method. Dynamic overset mesh techniques were employed to handle mesh updating required to obtain transient ship motions. The VOF method was used to capture the fluid interface. The effect of turbulence was considered by means of a k-w and a k-e model. A sensitivity analysis was conducted, in terms of the grid, timesteps and degree of freedom. The roll decay results of the numerical simulation have been compared with those of prior physical model testing (Gokce and Kinaci, 2018), and the different roll decay responses used to predict the roll damping. It is intended that this research be a useful step towards establishing intact ship stability criteria, as part of current research.

Improvement of the Harmonic Excited Roll Motion Technique for Estimating Roll Damping

2014 ◽  
Vol 61 (3) ◽  
pp. 116-130 ◽  
Author(s):  
Sven Handschel ◽  
Moustafa Abdel-Maksoud
Keyword(s):  
Roll Motion ◽  
Roll Damping

Estimation of Roll Damping for Transportation Barges

2009 ◽  
Author(s):  
Sharad S. Dhavalikar ◽  
Amresh Negi
Keyword(s):  
Degrees Of Freedom ◽  
Diffraction Theory ◽  
Offshore Structures ◽  
Roll Motion ◽  
Roll Damping ◽  
Natural Period ◽  
Highly Nonlinear ◽  
Wave Energy Spectrum ◽  
Dynamic Amplification ◽  
Linear Radiation

For ships, barges and similar long offshore structures roll natural period generally falls within the frequency range of a typical wave energy spectrum generally experienced by them. This causes dynamic amplification of rolling motion. For these structures the roll damping is highly nonlinear. Therefore it is of utmost importance that good estimation of roll damping is made for such structures. Linear radiation diffraction theory can not predict damping for roll motion as good as for other degrees of freedom. For ships and barges radiation damping (in case of roll) is generally quite small compared to the total damping in the system. Hence, additional damping needs to be added for solving roll motion equation.

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.

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.

Roll of a Ship in Astern Seas—Response to GM Fluctuations

1989 ◽  
Vol 33 (04) ◽  
pp. 284-290
Author(s):  
A. Bruce Dunwoody
Keyword(s):  
Numerical Simulations ◽  
Narrow Band ◽  
Wide Band ◽  
Random Processes ◽  
Roll Motion ◽  
Roll Damping ◽  
Metacentric Height ◽  
Good Agreement

An effect of astern seas on a ship is to produce fluctuations in the metacentric height (GM) of the ship. GM fluctuations are shown to produce an effect analogous to a reduction in the roll damping. Roll damping reductions are predicted for two extreme types of random GM fluctuations: wide-band and narrow-band random processes. Numerical simulations of the roll motion of a ship with realistic random GM fluctuations are used to compare with the predictions of damping reduction. Good agreement is found. Implications of a reduced roll damping are discussed.

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