Which is a type of static instability that is analyzed using finite displacement analysis to study the wind force-deformation relation?

• A. Divergence
• B. Flutter
• C. Buckling
• D. Torsional Instability

Answer: (A)

The concept being tested is static aeroelastic instability under wind loading, specifically divergence. Divergence is a static instability where aerodynamic forces interact with the structure in a way that effectively softens or negates stiffness as deflection grows. As wind force increases, the equilibrium deflection can rise dramatically, leading to a large, non-oscillatory displacement without requiring dynamic motion. To study this behavior, nonlinear or finite displacement analysis is used because it captures geometric changes as the structure deflects and how those changes alter the wind force distribution and the overall force–deflection path. This lets you trace the entire equilibrium curve and identify the divergence point where stable equilibrium ceases.

Flutter, by contrast, is a dynamic aeroelastic instability involving time-dependent oscillations. Buckling is a static instability caused by compressive forces in members and is typically analyzed for critical loads in a linear or nonlinear static sense, not the wind–deflection relationship that divergence focuses on. Torsional instability is a broader term not as specifically tied to the static wind-deflection phenomenon described here.