Junji Maeda

In-plane dynamic interaction between a tower and conductors at lower frequencies

Abstract Transmission line system can be represented by several analytical models composed of towers and conductors. The contribution of normal modes of a conductor to the dynamic tension force transmitted to a tower is obtained by using a frequency response function of tensions devised for the coupled systems. The in-plane dynamic interaction between a tower and conductors is investigated with varying support stiffness. A representation of the mechanism of the in-plane free vibration of transmission line systems is proposed which covers a wide frequency range.

Characteristics of in-plane free vibration of transmission line systems

Abstract A numerical procedure for the dynamic analysis of tower-and-conductor coupled systems is introduced. Characteristics of in-plane free vibration are investigated by using two series of models. Of particular interest is the phenomenon in which a group of the natural frequencies of the system are seen near each natural frequency of the same freestanding tower. This dynamic behaviour is found to be similar to that of a simplified analogue model.

On the spatial structures of longitudinal wind velocities near the ground in strong winds

Abstract The spatial structure of longitudinal wind velocity in strong winds is investigated from the standpoint of the theory of isotropic turbulence, using observations which the authors have carried out for several years. Wind pressure transducers are used as fast-response anemometers and the fluctuations of the longitudinal component of gusty winds are measured simultaneously at several observation points. The statistical functions estimated from the observed data are normalized in nondimensional form. These are compared with the theoretical values expected in the field of isotropic turbulence. Most of the observations are explained by this theory. This suggests that in strong winds the structure of atmospheric turbulence near the ground is close to the field of isotropic turbulence.

An analysis of a pressure pattern in severe Typhoon Bart hitting the Japanese Islands in 1999 and a comparison of the gradient wind with the observed surface wind

Abstract Typhoon Bart (T9918) hit Kyushu in Japan on September 24 in 1999, and caused storm surge at Matsuai-area of Shiranui in Kumamoto Prefecture with 12 deaths. We analyzed the pressure pattern in Typhoon Bart by an objective method and computed the gradient wind from it. The computed wind was compared with the wind observed at the sites of the Network for Wind Measurement in Kyushu (NeWMeK) system. The ratio of the observed wind speed to the gradient wind speed was about 0.5 outside of the maximum wind radius, but it increased rapidly with the decrease of relative radius inside of it. In addition to wind data at six stations of the Japan Meteorological Agency, the wind ratio outside of the maximum wind radius increased with height in proportion to 0.33 power of the anemometer height.

Characteristics of gusty winds simulated by an A.R.M.A. model

Accuracy of gust simulation by fitting an autoregressive moving averaging model for the u and w components of Karmans turbulent structure is discussed. The autoregressive process is directly estimated using the theoretical autocorrelation function of the turbulent structure. The power spectra and the scales of turbulence of the autoregressive moving averaging model are compared with the theoretical values of the turbulent structure. The gust components of the Karmans turbulent structure are able to be simulated using the autoregressive moving averaging model with satisfactory accuracy.

Numerical and Experimental Investigations on Unsteady Wind Pressure on a Gable Roof Body Under a Short-Rise-Time Gust

This paper reports on an investigation into the unsteady wind pressure measured on a gable roof body subjected to short-rise-time gusts in the wind tunnel compared with the results of a computational fluid dynamics (CFD) simulation using a large eddy simulation (LES) model, and the flow pattern around the body subjected to shortrise-time gusts. It was confirmed that the overshoot phenomena of wind pressure occurred on the gable roof body subjected to a short-rise-time gust by wind tunnel tests and CFD calculations. The peak value of wind pressure simulated by CFD matched well with that of the experimental result. It was found that a vortex was generated on the leeward roof face of the gable roof body under short-rise-time gusts, and the generation of this vortex caused the overshoot phenomenon of wind pressure on the leeward roof face.