Originally Posted on: March 23rd, 2015
When the summer sun reflects off the water, the results can be almost blinding. But IIHR Associate Research Scientist Yugo Sanada is using a similar technique to help researchers better visualize the water surface for advanced ship hydrodynamics research.
Sanada’s technique, the reflected light distribution (RLD) method, directs a diffused light source at the water’s surface. The surface of the water acts like a mirror, allowing researchers to better visualize the water’s surface. “When the water is still,” Sanada says, “the surface acts as a flat mirror. When the water is wavy, the surface acts as a distorting mirror. Using these phenomena, we can predict the surface shape of a wave.”
The technique uses the same algorithm as PIV measurement. Researchers can analyze the images produced with RLD to measure wave displacement compared to wave height. The team is still working to refine the quality of the images and to improve the image analysis process.
Sanada, a native of Japan, joined Fred Stern’s ship hydrodynamics team in 2011, when IIHR’s wave basin was still relatively new. Sanada had earned a PhD at Osaka University, where his research focused on towing tank experiments. He was excited about the opportunity to conduct groundbreaking research at IIHR’s wave basin, which allows researchers to test free-running model-scale navy ships under a variety of real-life conditions created by the basin’s wavemakers. Researchers can maneuver the models like real ships — straight ahead, zigzag, full circle, and even capsize.
Worldwide, no one had previously conducted such difficult experiments. There was much to learn, Sanada says, and the first experiments presented many new problems to work out. But, Sanada says, it’s definitely been worth it. “When we solve the problem and get good data, I’m very happy,” he explains. “Every day is exciting!”
Sanada says the ship hydrodynamics team at IIHR benefits from two powerful tools: the wave basin and CFDShip-Iowa, the world’s most advanced computer code for ship hydrodynamics. CFDShip-Iowa, which was developed at IIHR under Stern’s leadership, simulates the flow of air and water around a virtual ship.
The experimental research Sanada conducts at the wave basin validates the results of computational fluid dynamics or CFD modeling. Recently, Sanada and his team have been studying the wave drifting effect. A ship can turn in a perfect circle in calm water, but in waves, the ship drifts and makes a sort of loop. While analyzing the huge dataset from model-scale experiments conducted at the wave basin, Sanada’s team detected new details of the wave drifting effect. Now, CFD modelers must solve this new wrinkle and model the effect. The results are important for ship maneuvering safety.
For Sanada, the ship hydrodynamics research is never-ending challenge and responsibility. He works at the wave basin from 9 a.m. to 9 p.m., day in and day out. “I cannot finish everything!” he says. “This is my whole life, the wave basin!”
But he’s not complaining. “Fred also helps me a lot, and I have good colleagues,” he says.
He appreciates Iowa City’s strong international community, and he finds Iowans friendly and pleasant. “I think it’s a good environment for researchers from foreign countries,” he says. Outside of work, Sanada loves to cook. He enjoys using native Iowa ingredients in traditional Japanese dishes. One favorite is sukiyaki, which calls for Japanese hot pot using paper-thin cut beef. Rather than special order the beef, Sanada purchased a slicer so he can prepare his own.
He’s grateful for the opportunity to be part of IIHR’s ship hydrodynamics team. “It’s a good chance for me,” Sanada says. “Our research will help to improve safety in sea transportation.”