Creating an accurate model of wind and wave behavior has long challenged sailors and naval architects. The problem's always been the niggling gap between mathematical calculations and physical tests. But science now has a way of closing that margin that could revolutionize sailing with a simulation said to behave as accurately as real-world tests.
Ignazio Maria Viola, head of the the Yacht and Superyacht Research Group at Newcastle University, set out to simulate how water and air behave around a boat in different sea and wind conditions. The goal was to predict how a yacht will behave during a particular race under particular circumstances. He worked with the Yacht Research Unit of the University of Auckland and the Italian supercomputer center CILEA to develop a virtual test he says matches physical trials. The models could save race teams money and help them prepare more thoroughly for events like the Volvo Ocean Race or America's Cup by modeling different boats in different conditions.
"We believe that today we are experiencing an overturning of the traditional hierarchy between physical and numerical experiments, which will become more and more dramatic in the future years," Viola said.
The primary difficulty in achieving accurate measurements lies in determining the mean flow field — essentially the average velocity of water moving around the boat's hull. Viola's team modeled the resistance on the hull in a range of scenarios, racing virtual crews in state-of-the-art yacht designs and comparing the results with scale-model towing tank tests. The key aspect of these latest models is tracking the chaotic micro-movements of air and water over the hull. Viola found that for a truly accurate picture, he needed readings that measure the behavior of the water around a 30-meter yacht with the resolution of a tenth of a millimeter.
That's where the Italians stepped in with the heavy-duty hardware and software needed to complete the calculations. Simulations were run on the CILEA cluster in Milan. The cluster, named Lagrange, is comprised of 208 two-way Intel Xeon 3.16 GHz quad core nodes with 16GB per node, running Red Hat Enterprise.
"Computational resources are 10 times more powerful every three years," Viola said. "Last year, we could compute these micro-fluctuations of the water in 20 days instead of 200."
The simulations also can predict the aerodynamic forces wind on sails, along with predicting the speed and direction of wind a team will encounter. Beyond sailing, the ability to accurately model such things could help build better windmills and offshore platforms. The group's research was published this month in International Journal of Small Craft Technology.
Over the past decade, Viola has lent his numerical modeling expertise to several Olympic Sailing teams and America's Cup teams, including Luna Rossa and Emirates Team New Zealand. Seven-time Cup veteran Ian Burns of Oracle Team USA says modeling and simulations have grown exponentially more accurate in the 25 years that he's been with the team. In that time, he said, the number of elements in the best simulations has increased from 10,000 to 20,000 to as many as 3 million, giving teams greater confidence in the computer models. Slight differences remain between digital tests and physical tests, but if there are discrepancies between results from a computer and results from a towing tank experiment, teams now usually suspect the tank is wrong.
You don't need Larry Ellison's deep pockets to make the simulations work for you. Viola says he can run numerical models for as little as a few thousand dollars, making the simulations available to any sailor, designer or researcher.
"You tell me where you want to win," Viola said. "I will do the rest."
|4 Jul 2012
Research output: Contribution to journal › Article › peer-review