Characteristics Of Aerodynamic Forces Research Articles

Characteristics of aerodynamic forces and pressures on square plan buildings with height variations

Many studies on reducing across-wind responses of tall buildings have been investigated, mainly focusing on the effect of corner shape. And it is also known that changing section along the height through tapering or set-back could reduce across-wind responses of tall buildings. In this paper, to investigate the mechanism of aerodynamic force reduction, the wind tunnel tests for fluctuating pressure and fluctuating force were carried out. Two models with different tapering ratio of 5% and 10%, one set-backed model and one prototype square prism with side ratio of unity were employed under two typical boundary layers which represent suburban and urban flow condition. It is concluded that tapering or set-back helps to reduce the mean drag force and the fluctuating lift force. Reduction ratio increases as tapering ratio increases, and the set-backed model is more effective to reduce the fluctuating lift force than the tapered model with identical surface area, reducing the coefficients about 40% in suburban flow condition. And by tapering and set-back, the power spectra of wind pressures at sideward surface become wideband and the peak frequencies depend on height, which makes the correlation near the Strouhal component low or even negative.

Experimental study on the wind-induced vibration of a dry inclined cable—Part I: Phenomena

Besides rain–wind-induced vibration, field observations and a few experimental studies in recent years show that inclined cables also manifest wind-induced instability under condition when there is no precipitation. In order to further investigate these types of motion, including the limited-amplitude high-speed vortex excitations identified recently, experimental investigations were carried out. The focus of the present paper is on describing the dynamic and static model wind tunnel tests conducted and discussing the differences between divergent galloping motion and high-speed vortex excitation. Results show that the characteristics of dynamic responses and aerodynamic forces of these two types of motion are different. The former could be explained by a mechanism similar to that of classical galloping, whereas the latter might be related to vortex formation along the cable. The issues that require further investigation are also discussed.

弾性変形する矩形膜の超音速流中での挙動及び空力特性に関する基礎研究

The results of experimental studies and numerical simulations on the characteristics of a rectangular membrane made from elastic material in supersonic flow are presented. These experiments were conducted using the supersonic wind tunnel at ISAS. The characteristics of deformation, aerodynamic forces, and oscillation of the membrane are investigated experimentally. It was found that the membrane deformation and aerodynamic forces depend mainly on the aeroelasticity parameter (the ratio of aerodynamic force to elastic force), and that severe oscillation of the membrane is not observed in the experiments. A computational model, in which the membrane is described by a finite number of virtual particles, is also proposed, and their motion is computed in a Lagrangian manner. In the present study, two-dimensional calculations are performed. For the flow simulation, Newtonian flow analysis and compressible Navier-Stokes analysis are used. The results are compared with the experimental data, and good agreement is obtained.

Wind pressures measurement on end-cell-induced vibration of a cantilevered circular cylinder

In the case of a circular tower with high aspect ratio, “end-cell-induced vibration (ECIV)” occurs at a wind speed a few times higher than the occurrence wind speed of the vortex-induced vibration (J. Fluids Struct. 13 (1999) 499–518). In order to elucidate the characteristics of aerodynamic forces due to “tip-associated vortices (TAV)” which are considered as the cause of ECIV, wind pressure acting on a rigid circular tower are measured. Proper orthogonal decomposition applied to the pressure data clarifies the structure of the fluctuating pressures due to TAV and the results of wavelet analyses indicate “non-alternate generation” of them.

Development of New Type Snow Fence with Airfoil Snow Plates for Prevention of Blowing-Snow Disasters. 2nd Report. Characteristics of Aerodynamic Fluid Forces of Airfoil Snow Plates.

The present study was to develop a new snow fence with the airfoil snow plates for the prevention of blowing-snow disasters. In the previous report, it was found that the developed new type snow fence with the airfoil snow plates had a high performance in preventing snowdrifts and improving visibility in comparison with the conventional snow fence. In this report, the characteristics of aerodynamic fluid forces and the flow-induced vibrations of the airfoil snow plates was investigated. Important results from the present study were that (i) the fluctuating fluid forces acting on the airfoil snow plates which set up the topmost part of the snow fence was the most values in all of them, (ii) the flow-induced vibrations in the airfoil snow plate attached on the topmost part was generated, and then become divergent, (iii) the fluctuating fluid forces and the flow-induced vibrations of the airfoil snow plate were completely suppressed when a perforated plate was attached at the top part of the snow fence.

Time Domain Flutter and Buffeting Response Analysis of Bridges

A time domain approach for predicting the coupled flutter and buffeting response of long span bridges is presented. The frequency dependent unsteady aerodynamic forces are represented by the convolution integrals involving the aerodynamic impulse function and structural motions or wind fluctuations. The aerodynamic impulse functions are derived from experimentally measured flutter derivatives, aerodynamic admittance functions, and spanwise coherence of aerodynamic forces using rational function approximations. A significant feature of the approach presented here is that the frequency dependent characteristics of unsteady aerodynamic forces and the nonlinearities of both aerodynamic and structural origins can be modeled in the response analysis. The flutter and buffeting response of a long span suspension bridge is analyzed using the proposed time domain approach. The results show good agreement with those from the frequency domain analysis. The example used to demonstrate the proposed scheme focuses on the treatment of frequency dependent self-excited and buffeting force effects. Application to nonlinear effects will be addressed in a future publication.

Some solvable non-linear equations related to aerodynamic instability phenomena

This article proposes some forms of aerodynamic forces, looks for accurate solutions of core - pendent non-linear differential equations and analyses the characteristics of aerodynamic forces and of equation's solution. Found solutions proves that aerodynamic forces are formed from two elements: element of non-linear and dispersion, that single solutions are usually found and aerodynamic instability easy occurs.