Abstract
Accurate calculation of the roll damping moment at resonance condition is essential for roll motion prediction. Because at the resonance condition, the moment of inertia counteracts restoring moment and only the damping moment resists increase in the roll angle. There are various methods to calculate the roll damping moment which are based on potential flow theory. These methods have limitations to taking into account the viscous effects in estimating the roll motion, while, CFD as a numerical method is capable of considering the viscous effects. In this study, a CFD method based on a harmonic excited roll motion (HERM) technique is used to compute the roll motion and the roll damping moment of a containership’s model in different conditions. The influence of excitation frequency, forward speed and degrees of freedom at beam-sea and oblique-sea realizations are considered in estimating the roll damping coefficients. The results are validated against model tests, where a good agreement is found.
Highlights
Large roll motions in parametric roll and dead ship conditions are serious risks for the safety of a ship in rough sea conditions
The results showed that the method can be used to predict a ship roll motion accurately compared to the potential flow method and empirical methods
There are a couple of methods available to determine the roll damping coefficient, this paper focuses on the relationship of EA = EE where the roll damping can be calculated by the following formula: N44
Summary
Large roll motions in parametric roll and dead ship conditions are serious risks for the safety of a ship in rough sea conditions. The model was constrained to three degrees of freedom where it was free in roll, heave and sway motion This numerical simulation used a random vortex method applied on a rectangular box in a beam wave condition. In numerical simulations, based on a free surface random vortex method (FSRVM), the model was forced to roll and results were in good agreement with the experimental data. Zhou, Ning Zhou, Ning [18] conducted numerical and experimental simulations to estimate the roll damping of four different types of ships based on roll decay technique in zero forward speed. Wassermann and Feder Wassermann, Feder [21] carried out model tests based on roll decay and HERM technique to calculate the roll damping of a container ship They proposed various methods without additional filtering, curve fitting and offset manipulation of the recorded time series. The impact of forward speed, DOF and excitation frequency at beam sea and oblique sea conditions on roll motion characteristics and roll damping coefficients are investigated
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