Frequency- and time-domain methods related to flutter instability problem

Abstract

Bridge flutter phenomenon presents an important criterion of instability, which should be considered in the bridge design phase. This paper presents different bridge flutter methods which can be used to solve the flutter problem. Most commonly used frequency-domain approach is based on the formulation of aero elastic forces with frequency dependent coefficients called flutter derivatives. The critical wind speed, as the main critical condition for the onset of flutter is obtained based on these aero elastic forces. Aero elastic forces can be also expressed in the time-domain, using so-called indicial functions. These functions are usually determined from the corresponding flutter derivatives. In situations when fluid-memory effects tend to become small the quasi-steady theory can be used as an approximation of aero elastic forces. A numerical example related to the typical bridge cross-section follows presented approaches. .

Fenomen flatera mostova predstavlja važan kriterijum stabilnosti, koji mora biti uzet u obzir tokom procesa projektovanja mosta. U ovom radu su prikazane različite metode koje se mogu koristiti pri rešavanju problema flatera. Najčešće korišćeni pristup je u frekventnom domenu i baziran je na formulaciji aeroelastičnih sila putem frekventno zavisnih koeficijenata koji se nazivaju flater derivati. Na osnovu ovako izraženih aeroelastičnih sila, određuje se kritična brzina vetra, kao glavni uslov za nastanak flatera. Aeroelastične sile mogu se takođe izraziti i u vremenskom domenu, pomoću takozvanih indicijalnih funkcija. Ove funkcije su najčešće određene iz odgovarajućih flater derivata. U slučajevima kada su efekti memorije fluida zanemarljivi, kvaziustaljena teorija može se koristiti za aproksimaciju aeroelastičnih sila. Numerički primer tipičnog poprečnog preseka mosta prati prikazane pristupe. .