A Discrete-Vortex Method (SS-FSRVM) for Nonlinear Coupled Vertical-Plane and Lateral-Plane Ship Motions in Head Waves

Date: 
Friday, February 10, 2017 - 2:30pm
Location: 
3110 Etcheverry Hall
Speaker: 
Dr. Lu Wang, Ph.D.

Department of Mechanical Engineering

University of California, Berkeley

About: 

E-201 Ocean Engineering Seminar Series, Spring 2017

 

2:00 - 2:30pm Beverages & Refreshments

2:30 - 4:00pm Seminar

 

The Slender-Ship Free-Surface Random-Vortex Method (SS-FSRVM) is a highly efficient numerical method designed for modeling viscous-fluid flows about a slender vessel advancing in head-seas, with consideration of nonlinear coupling effects of the vertical-plane (pitch and heave) motions and possible large roll motions. In SS-FSRVM, the three-dimensional flow around the ship hull is solved in a series of two-dimensional computational planes, significantly reducing the computational workload.  In each computational plane, the flow is simulated using a combination of potential flow and discrete vortex elements to model the effects of fluid viscosity. Previously, this method was shown to be capable of predicting reliably the free roll-decay motion of a ship fitted with bilge keels in a viscous fluid, yielding results that are highly consistent with actual wave-tank measurements. In the present talk, a new formulation is developed that allows motion excitation from head seas to be incorporated into the efficient computational-plane formulation that is the hallmark of the SS-FSRVM. The restriction of this formulation requires the ratio of wave-steepness to Froude number to be small O(ε), a condition that can be met by most operational conditions. The solution procedure is applied to predict the heave and pitch responses in head seas of a Wigley-type hull with comparisons to existing experimental data. Also, a C11-class container-ship model hull is used to test the nonlinear heave-pitch and roll coupling in head seas. At certain expected synchronization conditions, moderate seas are indeed found to induce parametric rolling. In the future, the SS-FSRVM will be applied to evaluate the effectiveness of bilge keels in suppressing the head-seas-induced excessive roll motion.

 

Biography:

Dr. Lu Wang received his Ph.D. in 2016 from the Ocean Engineering group in the Department of Mechanical Engineering of UC Berkeley and is currently a lecturer. He also received his M.S. (2012) and B.S. (2011) degrees from the ME department of UCB. His research interests include simulation of viscous-fluid flows using the Discrete-Vortex Method (DVM), and the application of DVM to energy devices auch as micro-flow turbines) and ship motion. Previously, he received a SNAME Graduate Paper Honor prize and was the inaugural JV Wehausen Graduate Scholar.

 

Hosted by: Professor Simo Mäkiharju, 6179 Etcheverry Hall (makiharju@berkeley.edu)