Nonparametric Identification of Roll Damping and Nonlinear Restoring Forces for a Ship from a Free Roll Decay Simulation
- Yin Jiang (Shanghai Jiao Tong University) | Renchuan Zhu (Shanghai Jiao Tong University) | Yuntao Yang (Shanghai Jiao Tong University) | Jinlong Li (Shanghai Jiao Tong University)
- Document ID
- International Society of Offshore and Polar Engineers
- International Journal of Offshore and Polar Engineering
- Publication Date
- September 2019
- Document Type
- Journal Paper
- 286 - 294
- 2019. The International Society of Offshore and Polar Engineers
- RANS method, Free roll decay, roll damping and nonlinear restoring forces, stochastic inverse method
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- 17 since 2007
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Roll damping and nonlinear restoring forces have an important influence on ship roll motion. To identify them from free roll decay behaviors, the models are generally assumed to be known a priori. Here, the stochastic inverse method is introduced, and a new nonparametric approach is adopted to identify roll damping and nonlinear restoring forces from a free roll decay simulation, which is carried out by the Reynolds-averaged Navier–Stokes method and overset mesh technology. In the nonparametric identification of roll damping and nonlinear restoring forces, the nonlinear Volterra integral equation of the first kind is solved by the Markov chain Monte Carlo (MCMC) method. The conditional expectation and covariance of the conditional component distribution used in the Gibbs sampler are derived directly in the matrix-vector form by using an analytic inversion formula. Reconstructed roll histories are compared with ones from both the earlier work of the authors and the computational fluid dynamics method. Results show that the MCMC method is an effective way to identify roll damping and nonlinear restoring forces from free roll decay.
Safety against the capsizing of a ship is very important. A ship can experience three types of displacement motions (surge, sway, and heave) and three types of angular motions (roll, pitch, and yaw). The roll motion has more influence on capsizing and is significantly influenced by fluid viscosity compared with the other motions.
Roll damping is too complex to be solved analytically because of viscous effects. Various models of roll motion containing nonlinear terms in the damping force and restoring force have been studied by many researchers, such as Taylan (2000), De Kat and Paulling (1989), and Ahmed et al. (2010). The forms of the roll damping force and restoring force need to be known a priori; the corresponding coefficients in the roll damping force are determined by the free roll decay model test. The restoring force, including the nonlinear part, can be computed according to the ship’s geometry.
|File Size||2 MB||Number of Pages||9|