Experimental pitch-, yaw-, and roll-damping characteristics of a shuttle orbiter at Mach number 8

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.

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

Volume 6: Ocean Engineering ◽

10.1115/omae2011-49494 ◽

2011 ◽

Cited By ~ 1

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.

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

MATEC Web of Conferences ◽

10.1051/matecconf/201820202007 ◽

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.

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