THEODORE Y.-T. WU (1924-2023)

BY CHRISTOPHER E. BRENNEN,
J. NICHOLAS NEWMAN, AND MELBA B. WU

THEODORE YAO-TSU WU, Emeritus Professor of Engineering Science at the California Institute of Technology and a leader in hydrodynamics, passed away Dec. 16, 2023, just a few months before his 100th birthday.

Known as Ted to his friends and colleagues, he was born on March 20, 1924, in Changzhou, Jiangsu province, China. When he was nine, his family moved to Beijing, but they returned to Changzhou in 1937 after the outbreak of the Sino-Japanese War. Despite the upheaval of war, his father, Ren-Fu Wu, a government transportation planner, instilled in him the importance of education. Ted’s perseverance through wartime disruptions eventually led him to earn a B.S. in aeronautical engineering from Jiao Tung University in 1946 – his interest was inspired by the military aircraft he had seen during the war.

In 1947, he came to the United States for graduate studies, earning an M.S. in 1948 from Iowa State University before transferring to Caltech. There, stimulated by the faculty and research staff, his interests broadened to applied mechanics and hydrodynamics. He received his Ph.D. in 1952 with a dissertation on hydrofoils moving beneath a free surface. After serving as a research fellow, he joined the Caltech Faculty in the Engineering Science Department in 1955, was promoted to full professor of engineering science in 1961, and remained at the institute for his entire career. Though he retired in 1996, he continued research and lecturing well into his later years.

Ted’s research was both prolific and distinguished. His early work focused on solutions for incompressible planar flows, particularly those involving free surfaces, with support from the Office of Naval Research. Applications included wave resistance in ships and cavitation of high-speed hydrofoils and propellers. His mathematical expertise – particularly in the use of complex variables and conformal mapping – was evident in his seminal review, “Cavity and Wake Flows,” published in the Annual Review of Fluid Mechanics.

He was widely recognized for his contributions to ship hydrodynamics and quickly became a sought-after participant in technical committees and conferences, both nationally and internationally. In 1964, he was awarded a John Simon Guggenheim Fellowship and spent a sabbatical year in Germany, working with Georg Weinblum at the Institut für Schiffbau, part of the University of Hamburg. After Weinblum died in 1974, an annual lectureship was established in his honor, and Ted was one of the first Americans invited to participate. His lecture, titled “The Shallow Water Effects – Do Steady Disturbances Always Result in Steady Responses?” reflected the originality and insight that characterized his work.

In the early 1970s, he turned to bio-inspired fluid mechanics, organizing the seminal symposium Swimming and Flying in Nature – the first of its kind. The two-volume proceedings remain widely cited. One volume explored low Reynolds number propulsion by bacteria and other small animals, while the other addressed high Reynolds number propulsion by fish and birds. One of the intriguing results in the first category was the discovery of how and why bacteria use flagella that rotate continuously relative to their heads, while eukaryotic organisms achieve a similar propulsive effect by propagating waves along their flagella.

He maintained a lifelong fascination with nonlinear water waves, especially tsunami dynamics and the propagation of permanent nonlinear surface waves in an ocean of irregular depth. Even later in his life, Ted continued working on mathematical models of wave phenomena.

He met his wife, Chin-Hua (née Shih), during their undergraduate studies at Jiao Tung University. She later came to the United States in 1949, partly to pursue an advanced degree in chemistry at the University of California, Los Angeles, and they were married in 1950. The couple settled in Pasadena, where they raised two children. Ted was predeceased by Chin-Hua in 2015 and is survived by his children, Fonda Wu and Melba Wu, two grandsons, and two great-grandchildren.

Ted enjoyed competitive games of bridge and began each day with the Los Angeles Times, flipping directly to the bridge column to read about the previous day’s play. He also had a deep appreciation for Chinese calligraphy, philosophy, and poetry; loved classical music; and practiced Tai Chi Chuan. Guests in his home relished the Chinese cuisine he prepared himself. Known for enjoying a good laugh and a talent for storytelling, he frequently wove Chinese idioms into his conversations. He traveled extensively to attend symposia and give guest lectures, forming long-lasting friendships around the world. He attracted many colleagues to collaborate with him, and he was known as a gracious host.

Ted was elected to the National Academy of Engineering in 1982. He was also elected to Academia Sinica in 1984 and became a foreign member of the Chinese Academy of Sciences in 2002. Among his many honors, he received the American Physical Society’s Fluid Dynamics Prize in 1993, the American Society of Civil Engineers’ Theodore von Karman Medal in 2004, the American Society of Mechanical Engineers’ Lifetime Achievement Award in 2004, and the Caltech Distinguished Teaching Award in 1996 – a distinction he especially cherished.