Unsteady Lifts and Wakes of Oscillating Rectangular Prisms

Side-surface openings effects on galloping instability for a rectangular cylinder

“…( 2))) and the galloping was further discussed. At high wind velocities, the linear unsteady aerodynamic damping approaches the aerodynamic damping predicted by the linear quasi-steady theory (Nakamura and Mizota, 1975;Obasaju, 1983;Washizu et al, 1978;Yagi et al, 2013). According to the quasi-steady theory, the instantaneous aerodynamic forces acting on the oscillating cylinder are equal to those of the stationary cylinder subject to relative velocity Urel = (U 2 + 𝜂𝜂̇2) 1/2 , resulting from the relative angle of attack α0 (α0 = tan −1 (𝜂𝜂̇/U)), where 𝜂𝜂̇ is the cylinder vertical velocity, and positive in the downward direction, while α0 is positive in the nose-up direction.…”

“…The quasi-steady theory is widely utilized to analyze galloping response and aerodynamic damping, especially for high wind velocities where the ratio of the body oscillation velocity to the approaching wind velocity is small. Through the forced vibration tests, the linear unsteady aerodynamic damping is identified and asymptotic to the aerodynamic damping predicted by the linear quasi-steady theory (Nakamura and Mizota, 1975;Obasaju, 1983;Washizu et al, 1978;Yagi et al, 2013). As the flow can pass through the inner space of the model, one of the concerns is whether the quasi-steady theory is valid in predicting the asymptotic behavior of the aerodynamic damping for the rectangular cylinder with openings.…”

Discovering time-varying aerodynamics of a prototype bridge by sparse identification of nonlinear dynamical systems

“…Comprehensive investigations of the mechanisms responsible for VIV have been performed. Nakamura and Mizota [37] have observed the lock-in phenomenon by measuring the lift force and characterizing wakes of rectangular prisms with various aspect ratios oscillating transversely in a uniform flow, with the short sides normal to the flow direction in a wind tunnel. It was found that the phase angles of the frequency response components of both the lift and near-wake velocity show abrupt changes when approaching the critical reduced wind velocity for vortex shedding.…”

“…Despite tremendous advances in theoretical analysis and computational modeling, accurately characterizing bridge aeroelastics remains a challenging endeavor. Wind tunnel tests with cylinders, simplified sectional models or scaled, full aeroelastic models are combined with theoretical analysis to discover bridge aerodynamics [23,24,27,36,37], leading to simplified semiempirical models and a number of corresponding aerodynamic and aeroelastic parameter identifications [10-12, 14, 16, 17, 25, 43, 45, 46]. However, wind tunnel tests may suffer from uncertainties in the wind tunnels, such as uncertainties of equipment used to produce and measure wind, and results from different laboratories can differ even while using the same experimental models and under similar conditions [42].…”

Vortex-induced vibration performance and mechanism of long-span railway bridge streamlined box girder

“…For streamlined box girder sections with relatively large aspect ratios, Larsen (2015) found that the separation vortex strength generated at the shorter bottom plate of the main girder is higher, which is the main factor that affects VIV. For rectangular sections with aspect ratios of 4:1, Nakamura (1975) found that the airflow separates at the leading edge and is impinged at the section. The velocity field changes in phase, causing a corresponding change in the vortex-induced forces.…”