Remembering Fredric Raichlen

Fredric ("Fred") Raichlen, professor emeritus of civil and mechanical engineering in Caltech's Division of Engineering and Applied Science, passed away on December 13, 2014. He was 82 years old. Raichlen was an expert in coastal engineering whose pioneering studies of tsunami mechanics have led to standards for designing tsunami-resistant structures that have saved lives around the world.

Ordinary waves are wind-driven and propagate at and just below the ocean's surface. A tsunami, however, is driven by a displacement in the earth's crust, such as an underwater earthquake or a volcanic eruption. The entire depth of the water column is set in motion from seafloor to surface. In the open ocean, the waves are hardly noticeable—the peaks are a few feet high at most, and the interval between successive waves can be several hours. But as the tsunami approaches land, the transition to shallow water concentrates the wave's energy. This rising wall of water, focused by local topography, can flood many miles inland.

That much was known when Raichlen entered the field, says his graduate student Costas Synolakis (BS '78, MS '79, PhD '86), now a professor of civil and environmental engineering at USC and the director of USC's Tsunami Research Center. But, as Synolakis says, "There were several theories and hypotheses, but there was no laboratory validation of any of them. Further, there were very few field observations. Scientists did not even know what a tsunami looked like."

This was at least partly because funding for tsunami research was hard to come by. Tsunamis were seen as a threat to other shorelines, not American ones. "Tsunamis were not trendy," Synolakis says, "and their study was considered humdrum. For almost a decade, Fred was the only professor in the U.S. working on tsunami hydrodynamics. But the students he trained, trained others. And by the time it was realized how important tsunamis are, there were knowledgeable scientists who could rise to the challenge."

Upon arriving at Caltech in 1962, Raichlen built a set of wave tanks to analyze how tsunamis originate, how they propagate through the open ocean, and what happens when they run up on shore. The data from these experiments enabled him to develop a comprehensive, three-dimensional computer model of tsunami behavior. The first part of the model described the waves' motions through the deep sea, while the second part of the model described the waves' behavior within the harbor. The two models were fused at the harbor's entrance, with the connecting region modifying the incoming tsunami's waves as they entered the harbor.

"The work he supervised remains the world standard," Synolakis says. "Nobody else before or since has done laboratory experiments of such precision and quality. Fred believed that answers could only be mined in the laboratory and that the only numerical models that could be trusted were the ones that had been benchmarked with laboratory experiments."

Previous models had represented harbors as simple geometric shapes. This model, however, re-created the harbor's interior in great detail, rendering its basins, jetties, islands, and channels as collections of line segments. The waves' reflections off of each line segment were easy to calculate when each segment was handled individually, and the tsunami's actual behavior was derived by superimposing all the reflected waves on the incoming ones to map out where they would reinforce one another and where they would damp each other out. This approach reduced the computation to a straightforward exercise in matrix algebra that could be solved on Caltech's IBM 360/75 mainframe computer—the fastest, most sophisticated machine of its day.

In 1965, Raichlen built a 31-by-15-foot wave tank instrumented to measure wave heights and water velocities anywhere within its walls. Graduate student Jiin-Jen Lee (PhD '70), also now a professor of civil and environmental engineering at the University of Southern California and the director of USC's Foundation for Cross-Connection Control and Hydraulic Research, used the tank to verify the model's predictions of wave behavior in idealized circular and rectangular harbors. He then built a scale model of the east and west basins of the port of Long Beach, California, out of 15 sheets of quarter-inch-thick Lucite. The waves created by Lee's physical model in the wave tank were well described by the mathematical model in the computer. Says Lee, "Fred wanted a theory and the numerical analysis to go with it, but he also wanted them verified against a physical model. A lot of people would just say, 'OK, I did this, and now I'll move on.' Fred was very careful to make sure that the theory could actually be checked out."

Raichlen continued to refine and expand the model. A third section was added to reproduce the different types of seabed motions that could give a wave its initial impetus. Other experiments considered a tsunami's interactions with objects floating in the harbor, such as ships and mooring platforms, or measured how fast different regions within a wave moved as the wave broke, which allowed the force of the wave's impact to be calculated.

Raichlen's model also provided the first mathematically sound explanation of how seiches, also known as "harbor waves," are created. Seiches can persist for days and are extremely damaging due to their height. They occur because every harbor has a set of resonant frequencies. Any waves of those frequencies will reverberate, amplifying themselves. Typical tsunamis have a frequency of one wave every several hours. Raichlen's model showed that many harbors also have a fundamental resonant frequency of one wave every several hours—an unfortunate frequency match that enables such a harbor to amplify a tsunami into a seiche. The model also resolved a long-standing paradox: Harbors with narrow mouths usually offer the best shelter, but those same harbors suffer the worst seiches. The model showed that as the harbor's mouth got narrower, the wave energy trapped within the harbor had less and less chance of escaping. The only way to dissipate the energy was by friction as the water sloshed back and forth.

Raichlen's commitment to his work was matched by his commitment to his students. Lee's thesis was published in the Journal of Fluid Mechanics, an unusual periodical for a civil engineer and one read by a much wider community. Says Lee, "Normally the professor and the student are coauthors, but Fred took his name out. He said, 'This is very important for your career. You should publish it as the sole author.' At first I thought that meant maybe the paper was not so good, and he didn't want his name on it. But he wanted that study to be identified with me, so he gave me all the credit. I was really moved, because it was a pretty important study. We could have published a hundred papers, each with a different-shaped harbor."

Raichlen was a hands-on adviser, spending time with each of his students every day, says Synolakis. "I will forever treasure how he trained me in the laboratory. I was a complete novice, and for several months, he stayed with me, making sure that I didn't run into trouble. He was always eager to explain what we were seeing. His attention to detail was legendary, and he could see things that nobody else could or can." 

Raichlen earned his bachelor's degree in engineering from the Johns Hopkins University in 1953 and his master's and doctoral degrees at MIT in 1955 and 1962.  He also served in the Air Force as an environmental health officer from 1956 to 1959. He came to Caltech as an assistant professor of civil engineering in 1962; he was promoted to associate professor in 1967 and to professor in 1972. In 1969, he became one of the founding faculty members of Caltech's doctoral program in environmental engineering science. He was appointed professor of civil and mechanical engineering in 1997 and professor emeritus in 2001.

Raichlen was inducted into the National Academy of Engineering in 1993, and in 1994 he received the John G. Moffatt–Frank E. Nichol Harbor and Coastal Engineering Award from the American Society of Civil Engineers (ASCE). In 2003, he was given the ASCE's International Coastal Engineering Award, the most prestigious honor in the international coastal engineering community.

In his retirement, Raichlen devoted his time to writing a book, Waves (MIT Press Essential Knowledge series, 2012). He also became an avid and prolific watercolor painter.

Raichlen is survived by his wife, Judy; his sons, Robert and David; their wives, Amy and Sarah (respectively); his sister, Linda Millison; his brother, Sonny; and two grandchildren.