Foreword 序文

by D. S. Weaver, PhD, P.Eng,, Professor Emeritus, McMaster University, Hamilton, Canada   

Dams are used worldwide to create reservoirs for flood protection, irrigation and recreation, as well as to provide the hydrostatic head required for hydroelectric power generation. In most cases, these dams must have flow control structures in the form of hydraulic gates and valves so that the dam structures can reliably serve their intended purpose. Often, there are enormous energies involved in the controlled flow and failures of the flow control devices can be catastrophic, possibly leading to incalculable loss of life and property. Clearly, reliable design of the flow control structures is essential and that is the subject of this book.

Hydraulic structures subjected to high energy flows will invariably vibrate in response to the random turbulence in the flow, but this excitation mechanism is usually managed with relative ease. The real problems arise when structural motion induces fluid forces which enhance the structural response. In this way, the fluid-structural coupling transfers energy from the flow to the structure and a flow-induced structural instability develops. As with airplane wing flutter or suspension bridge deck galloping, these phenomena can be very destructive and must be understood and eliminated at the design stage.

The book is divided into 3 parts consisting of Introduction and Fundamentals, Gate Excitation Mechanisms, and Validation and Applications.  The authors begin quite appropriately by describing the commonly used forms of dam and flow control structures and presenting an interesting world history of the failures of these structures. The latter provides a useful background and a strong motivation for the material which follows. Then the concepts discussed in the book are introduced and the contents of the book are presented in the context of the existing literature on the subject. Part I continues with 4 chapters presenting the detailed development of all the fundamentals required to understand the material presented in Parts II and III, including structural vibrations, fluid mechanics, Rayleigh wave theory, and fluid added mass and damping. Part 2 consists of 5 chapters which develop the theory for the various flow-excitation mechanisms of gates with over and underflow, long span gates, gates with skin plate vibrations, and Tainter gates with single degree-of-freedom and coupled mode instabilities. Part 3 provides an important discussion of scale model testing for validation of theoretical models with emphasis on coupled mode instabilities. This is followed by a detailed analysis of the Wachi (Japan) and Folsom (USA) Tainter gate failures as being the result of coupled mode instabilities. Because the latter has been the subject of considerable controversy, a chapter is devoted to discussing the 1941 Tacoma Narrows bridge deck failure as an analogy to coupled mode Tainter gate failures. The final chapter of Part III deals with dynamic testing of full scale gate structures in the US and Japan, bringing an impressive closure to the practical application of the theory to operating hydraulic gates. The concluding chapter brings the material covered in the book together, discusses the need to understand the complexities of flow-excited vibration mechanisms in hydraulic gates and suggest future research which could help in this regard.

The theory developed in the book is rigorous but should be readily accessible to graduate engineers, especially with the background fundamentals provided in Part I of the book. Indeed, some graduate students and practitioners may find the chapters on the fundamentals unnecessary to understand Parts II and III. The theory is nicely complemented with numerous illustrative figures as well as photographs of operating gates in service. The emphasis on rigorous mathematical development, physical insight, and practical applications is refreshing. The authors are well placed to prepare this monograph, having spent their careers working on the subject problems and being able to draw heavily on their own research and experience in its preparation.

The mechanisms causing flow-induced vibrations can be very elusive and even counterintuitive. Coupled mode flutter was discovered to cause catastrophic wing failures of early monoplanes during World War I and it took some 20 years to understand the mechanism and to develop a predictive theory. The recent failures of the San Onofre Nuclear Power Station steam generators demonstrates that 40 years of research has been insufficient to enable completely reliable design of these components against flow-induced vibrations.  In this book the authors have shown convincingly that, after nearly 75 years of research, there is little consensus on the mechanism which caused the infamous Tacoma Bridge failure.  The lessons are clear.  Flow-induced vibration problems can be extremely difficult to understand and, thus, to eliminate at the design stage. That said, failure to consider them at the design stage within the context of existing knowledge and experience can have catastrophic consequences.

This book is a very useful addition to the flow-induced vibration literature, filling a current void in relation to hydraulic structures and providing an excellent guide to the related literature. It will be a useful reference for graduate students and engineers working in the field of fluid-structure interaction, and an essential read for engineers carrying out research on dynamic instabilities of hydraulic gate structures or charged with the responsibility for designing them against these potentially dangerous excitation mechanisms.