In this chapter, reflection on the discovery of gate instability mechanisms is provided. Stemming from Ishii's encounter as an undergraduate with the Wachi gate failure and his subsequent development of the theory for eccentricity instability, a framework for future analyses of other gate instabilities was established. The study of two degrees-of-freedom instabilities of long-span gates created a paradigm for mode coupling in hydraulic gate vibrations. The Folsom failure occurred with eyewitness testimony claiming to have heard and felt vibration. The path to understanding the mechanism that could produce vibration of the Folsom gate was the realization that the skinplate can be easily excited to undergo streamwise vibration. To counteract such vibration, dynamic design criteria for Tainter gates are needed. A draft formulation of dynamic guidelines for Tainter gate design is developed. We hope for feedback from those who use the guidelines to provide for the continuing improvement of the guidelines.
TopPreamble
Engineers, in the fulfillment of their professional duties, shall hold paramount the safety, health, and welfare of the public. (NSPE Code of Ethics for Engineers, Fundamental Canon Number 1)
TopBeginnings
Ishii became interested in gate vibrations in 1967, when he was in his junior year at the university. As he recalls in his reflections at the end of this chapter, he first learned the details of the Wachi Dam gate failure in a lecture in his hydraulics class presented by Professor Emeritus T. Uematsu. A few years later, in 1971, when he had enrolled as a doctoral candidate, Ishii’s major professor, Professor K. Imaichi, suggested that Ishii undertake the study of the Wachi Dam gate failure as his thesis topic. His dissertation work on the failure at the Wachi Dam was completed in 1975. His research led to the identification of the eccentricity instability mechanism for Tainter gates (see Ishii, 1975; Imaichi & Ishii, 1977; Ishii et al. 1977a, 1977b, 1980, 1983; Ishii & Imaichi, 1982). In 1983 he was awarded a von Humboldt Fellowship to work with Professor E. Naudascher at the Institute of Hydromechanics in Karlsruhe, Germany. Several papers resulted from Ishii’s stay in Karlsruhe (Ishii & Naudascher, 1984; Ishii et al., 1987, Ishii & Naudascher, 1992).
Knisely was employed at the Institute of Hydromechanics in Karlsruhe and was asked to help Ishii get settled. Although these two authors met and developed a friendship while they were both working with Professor E. Naudascher in Karlsruhe, their research collaboration did not begin until a few years later, after Ishii had returned to Japan and Knisely accepted a position working with Professor H. Nakagawa at Kyoto University in 1987.
Once Knisely settled in Japan, Ishii and Knisely began a collaboration on the flow-induced vibration of long-span gates with an initial focus on the effects of the shear layer beneath wide gates with submerged discharge (see Ishii & Knisely, 1988, 1989, 1990). After the work on shear layers, Ishii and Knisely moved on to consider streamwise vibration of long-span gates and then long-span gates with two degrees- of-freedom, and then long-span gates with simultaneous over- and underflow (see Ishii, 1990a, 1990b, 1992; Ishii & Knisely, 1992; Ishii et al., 1994, 1995a, 1995b; Nakata et al., 1996).