## Vertical Blinds Phenomenon Swaying

A senior-level undergraduate course entitled "Vibration and Flutter" was taught for many years at Georgia Tech under the quarter system. This course dealt with elementary topics involving the static and/or dynamic behavior of structural elements, both without and with the influence of a flowing fluid. The course did not deal with the static behavior of structures in the absence of fluid flow, because this is typically considered in courses in structural mechanics. Thus, the course essentially dealt with the fields of "Structural Dynamics" (when fluid flow is not considered) and "Aeroelasticity" (when it is).

As the name suggests, structural dynamics is concerned with the vibration and dynamic response of structural elements. It can be regarded as a subset of aeroelasticity, the field of study concerned with interaction between the deformation of an elastic structure in an airstream and the resulting aerodynamic force. Aeroelastic phenomena can be observed on a daily basis in nature (e.g., the swaying of trees in the wind, the humming sound Venetian blinds make in the wind, etc. ). The most general aeroelastic phenomena include dynamics, but static aeroelastic phenomena are also quite important. The course has been expanded to cover a full semester, and the course title has been appropriately changed to "Introduction to Structural Dynamics and Aeroelasticity."

Aeroelastic and structural dynamic phenomena can result in dangerous static and dynamic deformations and instabilities and, thus, have very important practical consequences in many areas of technology. Especially when one is concerned with the design of modern aircraft and space vehicles, both of which are characterized by the demand for extremely lightweight structures, the solution of many structural dynamics and aeroelasticity problems is a basic requirement for achieving an operationally reliable and structurally optimal system. Aeroelastic phenomena can also play an important role in turbomachinery, civil engineering structures, wind energy converters, and even in the sound generation of musical instruments.

Aeroelastic problems may be roughly classified into the categories of response and stability. Although stability problems are the principal focus of the material presented herein, this is not because response problems are any less important. Rather, because the amplitude of deformation is indeterminate in linear stability problems, one may consider an exclusively linear treatment and still manage to solve many practical problems. However, because the amplitude is important in response problems, one is far more likely to need to be concerned with nonlinear behavior when attempting to solve them. Although nonlinear equations come closer to representing reality, analytical solution of nonlinear equations is problematic, especially in the context of undergraduate studies.

The purpose of this text is to provide an introduction to the fields of structural dynamics and aeroelasticity. The length and scope of the text are intended to be appropriate for a semester-length, senior-level, undergraduate course or a first-year graduate course in which the emphasis is placed on conventional aircraft. For curricula that provide a separate course in structural dynamics, an ample amount of material has been added to the aeroelasticity chapters so that a full course on aeroelasticity alone could be developed from this text.

This text has been built on the foundation provided by Prof. Pierce's course notes, which had been used for the Vibration and Flutter course since the 1970s. After Prof. Pierce's retirement in 1995, when the responsibility for the course was transferred to Prof. Hodges, the idea was conceived of turning the notes into a more substantial text. This process began with the laborious conversion of Prof. Pierce's original set of course notes to 2f: format in the fall of 1997. The authors are grateful to Margaret Ojala, who was at that time Prof. Hodges's administrative assistant and who facilitated that conversion. Prof. Hodges then began the process of expanding the material and adding problems to all chapters. Some of the most substantial additions were in the aeroelasticity chapters, partly motivated by Georgia Tech's conversion to semesters. Dr. Mayuresh J. Patil, while he was a PostDoctoral Fellow in the School of Aerospace Engineering, worked with Prof. Hodges to add material on aeroelastic tailoring and unsteady aerodynamics mainly during academic year 1999-2000. The authors thank Prof. David A. Peters of Washington University for his comments on the unsteady aerodynamics section. Finally, Prof. Pierce, while enjoying his retirement and building a new house and amidst a computer hardware failure and visits from grandchildren, still managed to add material on the history of aeroelasticity and on the k and p—k methods in the early summer of 2001.

## Post a comment