Papers by Koichi Miyashita
This paper provides an appropriate method for predicting strong winds acting on tall buildings er... more This paper provides an appropriate method for predicting strong winds acting on tall buildings erected in close proximity to one another at the center of a city. We first check the accuracy of strong winds estimated using the meso-meteorological model (MM5) without an urban-canopy model above and inside an urban canopy, in comparison with the observational data taken at the rooftop of a high-rise building. With regard to the predictive accuracy by MM5 for urban winds, dependency on characteristics and circumstances of a meteorological event such as cyclogenesis or typhoon has been investigated. Also, we show that the MM5 has a limit to estimate the effects of various surface roughness condition on urban flows. Finally, we clarify the effectiveness of the hybrid analysis of the meso-meteorological model and LES to predict strong winds near the ground level of a city.
Wind Engineers, JAWE, 1997
Nihon kaze kogakkai ronbunshu, 2000
Summaries of technical papers of Annual Meeting Architectural Institute of Japan. B-1, Structures I, Loads, reliability stress analyses foundation structures shell structures, space frames and membrane structures, Jul 30, 1998
Wind Engineers, JAWE, 2003
The authors et al.have developed a measurement system which can analyze meteorological data trans... more The authors et al.have developed a measurement system which can analyze meteorological data transmitted to E-mail servers from several observation sites. This measurement system is effective for observations made at remote places due to the utilization of the Internet.It also has an advantage in that the data is sent over the Internet in real time.This paper gives an outline of this system and describes observation examples obtained through its use.
Nihon kaze kogakkai ronbunshu, Oct 31, 2018
This paper describes an along-wind vibration of frame-type pylons of Hakucho Suspension Bridge fo... more This paper describes an along-wind vibration of frame-type pylons of Hakucho Suspension Bridge found from longterm vibration monitoring data. It is shown that the vibration is very harmonic although its amplitude is small and it occurs under certain ranges of wind direction (10~30 degree from the bridge perpendicular axis) and of wind velocity (13~25 m/s). The dominant frequency of the vibration is either 0.6 Hz or 0.8 Hz depending on the wind velocity and these correspond to the natural frequencies of the in-plane pylon dominant modes of the suspension bridge. A series of the wind tunnel experiments using a spring-supported scaled model are conducted under uniform flow and the alongwind pylon vibration was observed and its vibration characteristics is found to be consistent to those observed in Hakucho Bridge. It is also found that the vibration is very sensitive to the incident angle of wind and to the distance between the two columns.
Wind Engineers, JAWE, 1996
Nihon kaze kogakkai ronbunshu, Jul 31, 2018
This paper describes an along-wind vibration of frame-type pylons of Hakucho Suspension Bridge fo... more This paper describes an along-wind vibration of frame-type pylons of Hakucho Suspension Bridge found from longterm vibration monitoring data. It is shown that the vibration is very harmonic although its amplitude is small and it occurs under certain ranges of wind direction (10~30 degree from the bridge perpendicular axis) and of wind velocity (13~25 m/s). The dominant frequency of the vibration is either 0.6 Hz or 0.8 Hz depending on the wind velocity and these correspond to the natural frequencies of the in-plane pylon dominant modes of the suspension bridge. A series of the wind tunnel experiments using a spring-supported scaled model are conducted under uniform flow and the alongwind pylon vibration was observed and its vibration characteristics is found to be consistent to those observed in Hakucho Bridge. It is also found that the vibration is very sensitive to the incident angle of wind and to the distance between the two columns.
Nihon Kenchiku Gakkai kōzō-kei ronbunshū, 2009
The measurement wind velocity on the rooftop of the tall building is usually utilized as a refere... more The measurement wind velocity on the rooftop of the tall building is usually utilized as a reference wind velocity. However, after many new tall buildings have been constructed around the specified tall building, it becomes difficult to use the rooftop data as a reference. While, the wind velocity predicted by the meso-meteorological model (MM5) without the urban-canopy model has been little affected by surface shapes of buildings on the ground and expected to be accurate at sufficiently higher position. This paper examines the regional representativeness of MM5 wind velocity data by comparing the full-scale measurement data at open area. Also, in the case of measurement point within the urban canopy, rooftop wind velocity computed by large-eddy simulation (LES) is estimated by matching MM5 wind profile. The method determining an appropriate height for a reference wind velocity is provided.
Nihon kaze kogakkai ronbunshu, 2001
Nihon kaze kogakkai ronbunshu, 2015
The accurate assessment of pedestrian-level wind environment is one of the major issues in the de... more The accurate assessment of pedestrian-level wind environment is one of the major issues in the development of urban areas, which is usually evaluated on the basis of wind tunnel experiments. The accuracy of the assessment is directly related to that of wind speed ratio obtained from the wind tunnel experiments. There are some factors producing a difference between the predicted values from the wind tunnel experiments and actual values from field measurements. The present paper focuses on the following two factors. One is the effect of deciduous trees that are not reproduced in the wind tunnel models in most cases. However, there are many deciduous trees in urban areas, which may reduce the wind speeds near the ground significantly. The other is the effect of the wind direction fluctuation at the reference point. The range of fluctuation is generally much smaller in the wind tunnel flow than in the natural winds. The effects of deciduous trees and wind direction fluctuation on the wind speed ratio are investigated based on the results of wind tunnel experiments and field measurements at various locations in Tokyo.
Nihon Kenchiku Gakkai kōzō-kei ronbunshū, 2009
In order to validate the LES(large eddy simulation) model for strong wind in actual urban area, t... more In order to validate the LES(large eddy simulation) model for strong wind in actual urban area, this research performs the direct comparison between wind data estimated by LES and full-scale measurement data. Generally, LES cannot evaluate the absolute wind velocity, but can only a relative value to the reference wind velocity. In order to introduce the absolute value, we employ the meteorological model(MM5). In this study, first, based on the observation data on the rooftop of the high-rise buildings and several surrounding ground-level points, we clarify the flow characteristics of strong winds during cyclogenesis. Second, we numerically simulated the mean wind speed and the maximum instantaneous wind speed and validated the LES method through the comparison with the observation data. Accordingly the applicability of the present LES model for an actual shape of urban area has been clarified.
Nihon kaze kogakkai ronbunshu, 2013
For the wind resistant design of low-rise buildings and the assessment of pedestrian-level wind e... more For the wind resistant design of low-rise buildings and the assessment of pedestrian-level wind environment around buildings, it is important to understand the characteristics of natural winds near the ground surface, e.g. profiles of the mean wind speed and turbulence intensity and the gust factor. In the 'AIJ Recommendations for Loads on Buildings 1) (2004)', the profile of mean wind speed is specified as constant up to a height Z b corresponding to the terrain category, beyond which it is expressed by a power function of height Z above the ground. Such a vertical profile of mean wind speed may overestimate the wind loads near the ground surface, significantly. In order to evaluate the design wind loads as well as to assess the wind environment more reasonably, the characteristics of winds near the ground surface should be understood in more detail. The authors have carried out full scale measurements of wind speeds near the ground surface at various sites with different terrains, where the time history of wind speeds at two or three heights up to 10 m was obtained. The present paper discusses the characteristics of winds near the ground surface, i.e. profiles of mean wind speed and turbulence intensity, turbulence scale, gust factor and power spectrum, based on the results of these full-scale measurements.
Nihon kaze kogakkai ronbunshu, 2017
It is important for wind resistant design and wind environmental survey to consider the wind turb... more It is important for wind resistant design and wind environmental survey to consider the wind turbulence intensity. Therefore, it is necessary to study relation between turbulence intensity, gust factor, and peak factor. Also, it is useful to propose their relational expressions which evaluate unknown values from a known value. For this reason, the present paper provides the relation between peak factor and turbulence intensity by using a lot of observation data at various locations, and proposes an empirical formula for this relation.
Journal of Wind Engineering, 2017
It is important for wind resistant design and wind environmental survey to consider the wind turb... more It is important for wind resistant design and wind environmental survey to consider the wind turbulence intensity. Therefore, it is necessary to study relation between turbulence intensity, gust factor, and peak factor. Also, it is useful to propose their relational expressions which evaluate unknown values from a known value. For this reason, the present paper provides the relation between peak factor and turbulence intensity by using a lot of observation data at various locations, and proposes an empirical formula for this relation.
Summaries of technical papers of Annual Meeting Architectural Institute of Japan. B-1, Structures I, Loads, reliability stress analyses foundation structures shell structures, space frames and membrane structures, Aug 2, 2002
Journal of Wind Engineering
This study aims to validate prediction of pollutant dispersion in urban area based on wind tunnel... more This study aims to validate prediction of pollutant dispersion in urban area based on wind tunnel experiment. For this purpose, wind tunnel experiments and filed measurements of tracer gas dispersion were conducted in the campus of Tokyo Polytechnic University, and their results were compared. In addition, wind tunnel experiment was carried out under various conditions of experimental model scale, wind speed, and pollutant emission rates to confirm similarity law. The normalized concentration obtained by the wind tunnel experiments agreed well with the field measurement data. It was also confirmed that the normalized non-dimensional concentration was nearly independent of experimental model scale, wind speed, and pollutant emission rate.
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Papers by Koichi Miyashita