This study evaluates the ability of the modified Rankine vortex model, which is widely used to represent tornado-like vortices, to approximate a realistic tornado-like vortex generated within a high-resolution CM1 simulation. Horizontal wind fields at 10 m AGL were extracted from the CM1 simulation and averaged over multiple time windows to examine the influence of temporal averaging on peak wind speeds. The results show that 3-s averaging, although commonly used in engineering practice, can smooth short-lived transient flow structures and may underestimate instantaneous peak wind speeds. The CM1 wind field was then examined to determine the best-matched parameters of the Rankine vortex model. Separate decay exponents were applied inside and outside the vortex core, and a radially decaying translational velocity was incorporated. These modifications improved the near-surface wind field representation, particularly near the vortex core. Larger discrepancies were observed on the left side of the vortex, where complex asymmetric flow structures were not fully captured by the idealized Rankine vortex. Treefall patterns were simulated using different critical wind speeds, and the modified Rankine vortex produced results broadly comparable to those from the CM1 vortex. The findings of this study suggest that the Rankine vortex model, when applied with carefully selected best-matched parameters and combined with treefall modeling, could provide a practical framework for estimating near-surface tornado wind characteristics in engineering applications. Future work will examine additional cases to further assess the performance of the model under a wider range of tornado-like flow conditions.
For a tall building equipped with a friction pendulum system-tuned mass damper (FPS-TMD), a significant damper displacement can occur when the building is subjected to strong wind loads. To prevent the slider in damper from sliding out, a restraining rim is typically designed at the edge of the sliding plate, making collisions between the slider and the restraining rim inevitable. This study establishes an analytical framework for bidirectional coupling motion of tall buildings equipped with the FPS-TMD featuring restraining rim under synchronized alongwind and crosswind loads. A benchmark building is used to investigate the wind-induced response characteristics of the tall building with an FPS-TMD. The vibration reduction performance of the FPS-TMD is also evaluated. The building responses to alongwind or crosswind load are compared with those to synchronized alongwind and crosswind loads, revealing bidirectional coupling effect of the FPS-TMD. The effect of collision behavior on high modal responses is also investigated. Through parametric analysis, influences of FPS-TMD design parameters on wind-induced responses of the building are thoroughly discussed. The optimal values of important parameters associated with the FPS-TMD are determined by a genetic algorithm. The efficient method proposed ensures the excellent vibration reduction performance within the wind speed range that needs to be controlled. This research provides important theoretical foundation to study the bidirectional motion of friction-collision TMDs under wind loads.
Vortex-induced vibrations (VIVs) of stay cables frequently occur at low wind speeds, causing structural fatigue damage and public safety concerns. To clarify the VIV properties and mechanisms of stay cables with helical wires, wind tunnel tests were conducted at 1.8 × 104 < Re < 6.3 × 104. Effects of helical wire diameter (0.009D ∼ 0.10D, D: cable diameter) and pitch (3.14D ∼ 10D), inclined angle (25° and 45°), and yaw angle (−60° to 60°) were examined. Results indicate that maximum amplitudes do not occur under normal flow conditions. As the inclined angle increases, the yaw angle for maximum amplitude rises, while both amplitude and length of lock-in range decrease, with maximum reductions of 31.9% and 27.6%, respectively. At constant inclination, positive yaw angles generate larger amplitudes than equal negative ones. At the pitch of 3.14D, VIV suppression efficacy improves with increasing wire diameter. At fixed diameters (0.07D to 0.10D), suppression effectiveness depends non-monotonically on pitch, decreasing initially before increasing. Optimal suppression (>50% amplitude reduction) is achieved at 0.10D diameter with pitches of 3.14D, 8D, and 10D. Mechanistically, helical wires induce forced flow separation, disrupting vortex shedding and attenuating pressure fluctuations. Furthermore, their spanwise-varying separation points enhance three-dimensional flow behavior while reducing spanwise correlation, collectively suppress VIV.
