In order to investigate the wind effects on large structures, such as high-rise buildings, long suspension bridges, etc., new-type multiple-fan wind tunnels are being developed in our laboratory In these tunnels, flow turbulence has been actively generated by multiple-fans and oscillating airfoils. Usually, a wide range of power spectrum can be observed in an atmospheric turbulence under neutral conditions. Therefore, the corresponding large-scale turbulence should be reproduced to simulate the atmospheric turbulence in the tunnel. As a result of the experiments, a wide range of power spectra was achieved in the tunnel, and it was shown clearly that these spectra were well fitted to Kolmogorov's law. This means that a wide range of the inertial subrange corresponding to the atmospheric turbulence was observed.

View full abstract

Data gathered from a number of field and laboratory experiments concerned with the wind pressures acting on low- rise buildings are reviewed, and selected experimental results are presented in this paper. Particular attention is paid to works related to cladding design. Only either full- scale studies or those done under conditions simulating the atmospheric boundary layer have been considered. Comparison of the data from various sources, including code specifications, is made for the characteristics of the mean and fluctuating wind pressures.
The results indicate that the statistical properties of fluctuating pressures on the roof edge and corner regions can be predicted based on a quasi-steady approach. Furthermore, the p eak factor approach is found to be useful for evaluating the peak pressures

View full abstract

Research work by Study Committee on Fluid Dynamic Experiment and Its Similarity law has continued forthese 6 years. Topics on effect of Reynolds number is very strong initial motivation to organize this corrnnittee and to invite experts in fluid dynamics to the corrnnittee, who can cover almost all of fields related to the fluid problems. Ibis report is summary of the committee work and subjects in this report are the essence of the fluid engineering dynamics.

View full abstract

When a Shinkansen train enters a tunnel at a high speed, a compression wave is generated and propagated through the tunnel at a sound speed. At the tunnel exit, the greater part of the compression wave is reflected to the tunnel entrance and a part of the compression wave is radiated out of the tunnel exit as a pressure pulse which is called micro.pressure wave. This wave causes an environmental problem near the tunnel exit. Here model experiments for decreasing the micro-pressure waver are described.

View full abstract

How around an automobile is usually considered as steady phenomenon. Aerodynamic coefficients, the most imponant of which is the drag coefficient, are regarded as constants because of the steady flow around the vehicle body. Them is a thought however, the flow separations and the vortical motions around the body me unsteady and the constant drag coefficient can be obtained as a time averaged value of unsteady forces. The present study has been carried out horn this view point The unsteady wake structure up to 300 Hz of a scale vehicle model was measured using 252 total pressure probes. The measuring system is based on ESP (Electronically Scanned Pressure) sensors, which is very popular in the wind engineering field. The results show the wake of the vehicle model has unsteady structure.

View full abstract

Aeroelastic instability of a circular cylinder was experimentally studied by free-oscillation tests in a wind tunnel. For an in-line oscillation in the subcritical regime of Reynolds number, detailed data of response amplitude of a cylinder have been obtained in a wide range of Scruton number (values of a mass-damping parameter), 0.80-2.82 by free-oscillation tests of two-dimensional cylinder spring-mounted to oscillate as a rigid cylinder, There are certified to be two excitation regions; one within a range of reduced velocities Vr between roughly 1.4 and 2.4, and the other above Vr=2.6. It is found that aeroelastic characteristics of two unstable regions are quite different; i.e., the response amplitude are very sensitive to the Scanlan number in the first unstable region, while those of the second region are rather insensitive. Also a fixed splitter plate with the longitudinal length of 8d (d: a cylinder diameter) was mounted behind a cylinder to eliminate the vortex shedding of alternate vortices from the cylinder, after Aguirre's experiments, and the results were compared with those without a splitterplate.

View full abstract

This paper summarizes an essential dynamic Instability of Tainter gates and its dynamic similarity. Experimental modal analysis in air test results for a remaining gate under the samc design as a failed 87-ton Tainter gate at Folsom dam in California arc presented, thus resulting in a possible dynamic instability that Tainter gates induce a self excited vibration under certain conditions, even if the skinplate is centric exactly on the trunnion pin. Theoretical calculations for flow induced vibrations are outlined to present key factors dominating its dynamic similarity.

View full abstract

This paper describes new ideas and some improvements in the development of a multi-degree-of freedom aeroelastic model of a high-rise building. With this model, the mass, the eccentric distance, the frequency ratio of a torsional mode vibration to sway mode vibration, and the structural damping can be changed easily. A structural skin which reproduces the exterior geometry is discontinuous with slits separating the various zones of the model. The effect on the wind responses with these slits is in farther investigation.

View full abstract

Membrane structures are very light weight structure and those deflection at strong wind are very large, frequently. Therefore, wind tunnel tests has been planned to investigate aerodynamic behavior. The model for test requir that many similarity parameters are matched for model and prototype. In practice, it is almost impossible to match all similarity parameters. In this paper, relaxations of similarity law for air supported membrane structure, as an example.

View full abstract

In recent years, tall and long-spanned buildings have been builts at many snowy areas in Japan. So, wind tunnel experiments using model snow are carried out to predict snowdrifts around the buildings and snow load on a building's roof. This paper describes the similarity requirements for the modeling of snowdrifting and research results on wind tunnel experiments using model snow.

View full abstract

The aerodynamic vibration of inclined cables of cable stayed bridges becomes more concerns to bridge designers. In this brief paper, the observed fundamental behavior of them and the generation mechanism are explained and also the similarity rule for wind tunnel test and their complexity are briefly touched.

View full abstract

The aeroclastic analysis of flexible structures, i.e. the flutter analysis of long span suspension bridge, is increasing importance in the wind resistant design., One of its key points is reliabilityof the unsteady aerodynamic force as one of the input data Most of existing research works are based on feasibility of the measurement itself., and extension in numerical 3D model has been almost ignored In this paper, some problems in the unsteady aerodynamic force are discussed and its key issues are proposed.

View full abstract

The papa describes the strong winds caused by the typhoon 9119 in Miyajima island and Misuzugaoka residential area as a hardly explicable example with the neutral temperature condition The State of the strong wind region far form the center of the typhoon, the salt disaster in Hiroshima City and the concentrated down blows behind ground heights are attributable to the gradual downdrail of cool and dry air from the tropopause and the unstably stratified stream successively fanned on the sea surface.

View full abstract

In order to simulate turbulent flow with a large scale, several studies have been reported. Small multiple fans are driven by numerically controlled AC servo-motors in most cases. Some results are encouraging to create a turbulent now with specified spectral characteristics up to a frequency range of a few Hz. Three dimensional simulation and wind direction fluctuation will be made in a further development.

View full abstract

Some features of the 0.2m supersonic wind tunnel at National Aerospace Laboratory relating to the quiet flow establishment are described. Pressure fluctuations were measured along the tunnel circuit. The pressure fluctuation ratio at the settling chamber exit satisfies a goal of the value less than 0.2 % for the quiet wind tunnel. However, the measured velocity fluctuation ratio does not satisfy another goal of the value less than 1 %. Measured Pitot pressure fluctuation ratio at the test section does not satisfy a goal of the value less than 0.1 % for the quiet flow although the value is near the goal.

View full abstract