Although a wind speed in ground-based observation is strongly influenced by a surrounding terrain, measurement of atmospheric pressure is not thought so. A local wind suitably estimated using observed pressure data is useful for the investigation and prediction of wind disaster. In this paper, we compared ground-based observed wind speed with the corresponding wind speed estimated using the barometric pressure gradients which is based on measured pressure data when Typhoon Chaba(0416), Songda(0418) and ShanShan(0613) passed. Although reductions to mean sea level of the measured pressures were mostly distributed on concentric circles agreeing with values guessed using a formula of Schloemer, the projected wind speeds overestimated the mean wind ground-based. However we could approximately estimate maximum values and their areas where wind speeds became the largest.

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The flow and temperature characteristics within an unstable surface boundary layer were determined using a hot-wire anemometer and a cold-wire thermometer. Results of experiments on the unstable surface boundary layer flow showed that the peak frequency of power spectrum density in instability was shifted more toward the low-frequency side than in the neutral condition. The co-spectra of heat flux had similar tendencies to the results of Kaimal. The logarithm of the ratio between roughness lengths for momentum and heat showed similar results to those which were obtained from field observation in grass plain fields by Brutseart.

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We report on the structure of atmospheric turbulence especially focusing on the spatial correlations of three fluctuating components of wind speed using our record measured at a transmission tower located at the tip of a cape, which are required for simulations of the dynamic response of a coupled tower-and-conductor system and of the trajectory of a flying debris under a strong wind. According to our results, the profiles of longitudinal and lateral wind speeds in typhoons were different from those in non typhoons. And we showed that cross-correlations between the longitudinal and lateral components of the fluctuating wind speeds were explained by the theoretical expressions in the isotropic turbulence theory, using the covariance coefficients of the longitudinal and lateral components normalized by the longitudinal scale of turbulence of the longitudinal wind speed.

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The frequency of extreme wind speed was examined using data of daily maximum gust wind speed at synoptic stations in Japan from 1967 to 2007. Correction to temporal inhomogeneity arising from changes in sites, anemometer height and types, and land use of the surrounding area was attempted using surface geostrophic wind speed as reference. It is found that part of the stations, especially those in the inland area of western Japan, have a few cases of unusually high wind that deviates from the Gumbel distribution. At these stations, wind speed is reduced for some range of wind direction due to orographic barrier effects, so that extremely high wind tends to be observed only in limited occasions.

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The land of Japan is characterized by complex and steep terrains, which influence the strength of severe local storms. Due to high variability of wind speed, gusty winds are not only affected by mesoscale and/or microscale weather disturbances but also by small-scale terrains. This study investigates the variability of severe local winds associated with mesoscale weather disturbances by conducting high-resolution meteorological simulation. It is shown that the high-resolution simulation can represent the short-term and small-scale variability of surface winds. The model well reproduces small-scale vortical structure embedded in mesoscale disturbances that were observed by a Doppler radar implemented for the safety of railroad transport. The vortical disturbances induce locally high winds, which are also affected by small-scale terrain features.

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Since the Akashi Kaikyo Bridge is the world's longest suspension bridge with the main span of 1,991m, various researches and developments were conducted in design for the Akashi Kaikyo Bridge. However, the design methods were based on several assumptions, and it was necessary to be verified. Therefore, many sensors including accelerometers, anemometers, velocity gauges and GPS, were installed to the Akashi Kaikyo Bridge for the design verification and the maintenance purpose. For the past 10 years after completion, approximately 32,000 data of strong wind with 10-minute time series were recorded by the monitoring system of the Akashi Kaikyo Bridge.
In this paper, the analysis results of characteristics of strong wind, focusing on the typhoon which attacked to the Akashi Kaikyo Bridge, are described.

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The strong wind fields over Kyushu Island were simulated numerically during Typhoon Songda passed by in 2004. The mesoscale climate model, JMA NHM (Japan Meteorological Agency nonhydrostatic model) was used for the calculation. The predicted wind fields were examined comparing with the observed records. The wind speeds and directions were recorded by the anemometer's network, NeWMeK, in Kyushu Island. The time variation of calculated wind speed with 1km horizontal meshes was equivalent to the ten-minutes time averaged values of observed wind speed. The values of calculated wind speed were higher than the ten-minutes time averaged wind speed. But the calculated wind speed were well correlated to the maximum wind gust of NeWMek observation in the area with strong wind. The variation of wind direction showed good correlation

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Two types of typhoon bogus schemes which modify the initial fields of mesoscale simulation for typhoon are investigated. One typhoon bogus scheme is included Mesoscale Model 5th generation (MM5) originally and another is developed by Japan Meteorological Agency (JMA). For typhoon HIGOS (2002) case making landfall on the Kanto Plain, numerical experiments are conducted on Mesoscale Model 5th generation (MM5) using these typhoon bogus schemes and without typhoon bogus scheme. Time series of sea surface pressure and typhoon intensity calculated using JMA typhoon bogus scheme are closer to observation than those calculated using MM5 original typhoon bogus scheme or without typhoon bogus scheme.

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This paper provides a new concept for hybrid method of meso-scale meteorological model and large-eddy simulation (LES) for strong wind in urban area. It is difficult to estimate the wind flow in an urban canopy where the local flow structures and very unsteady wind gusts exist. By using the present method, we predict the wind flows at the top of tall buildings immersed in the urban canopy during the specific low-pressure cyclone passing. In comparison with the observational data, the present hybrid method is validated. Also, we show the limitation of the conventional meso-scale meteorological model and the effectiveness of the hybrid method for prediction of wind flows in the urban canopy.

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This paper compares flows around complex terrains obtained from computational fluid dynamics with those from wind tunnel tests targeting the area from the seashore at Hiratsuka to Lake Tsukuiko in a mountainous area 32km long by 4.5km wide in Kanagawa prefecture. As the first step of CFD for flow around complex terrain, the study is carried out by using a standard k-e model which is composed of basic turbulent model. The studies clarify that CFD's results are some difference from the experimental results on the profiles of mean wind speed at the wake of complex terrain. The CFD's results estimate some small value near the ground

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A combination of multi-fans and an array of rectangular cylinders was used for generating thick neutral atmospheric boundary layers within a relatively short entry distance. The multi-fans were used mainly for forming target profiles of any shape and the array of rectangular cylinders for providing turbulence energy. To attain target profiles, an iterative procedure was applied. The effects of an array of cylinders on the boudary layer and turbulent characteristics were investigated.

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In this study, wind tunnel measurements of mass flux of drifting snow and wind velocity in developing boundary layer above loose snow surface were carried out. It was aimed to investigate the characteristics of drifting snow phenomena in a non-equilibrium flowfield. This measurement clearly showed the effect of drifting snow particles which reduce the wind velocity near snow surface. In the latter part of this paper, the method for normalizing the expression of the transport rate values was investigated. The relation between the streamwise distance and the transport rate measured in the experiments with two different wind velocities could be expressed in the same line by using the new method for normalization proposed in this study.

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This paper describes a new CFD base model for predicting the effects of drifting snow particles on turbulent flowfield. In the first part of this paper, the revised type k-e model which included the buoyancy effects due to density difference and the influence of snow particles on turbulent flowfield was developed. In order to express the damping of turbulence energy by the influence of the snow particles, the model proposed by Naaim et al., which introduced extra terms in the transport equations of k and e, was modified. The model coefficients in the modified model were optimized by comparing the numerical results with those of wind tunnel experiments conducted by the present authors. In the latter part, the models of drifting snow in the saltation layer, the erosion and deposition fluxes on the snow surface were discussed.

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Currently, various studies have demonstrated some doubt about the accuracy of the flow network model analysis based on orifice equation when applied to the calculation of cross-ventilation. As a result, a computational fluid dynamic (CFD) simulation is considered the best method of analyzing cross-ventilation properties under present conditions. However, repetition of CFD analysis to determine the optimum ventilation performance is particularly complex. Accordingly, a calculation method that corresponds to cross-ventilation was developed and suggested as a more efficient means of determining the optimal opening conditions.

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In this study, a new urban canopy model based on the porous media theory is proposed. Flow around two obstacles with different porosities, i.e., pine trees and a prism are simulated and compared with measurements. The simulated results showed a good agreement with measurements. The proposed model is applied to the estimation of wind speed during a typhoon to consider the effect of surrounding buildings around a meteorological station. Wind speed measured at Miyakojima Meteorological Station located in the urban area is converted to the wind speed at a distant site based on the result of the flow simulations with the proposed urban canopy model. Estimated wind speed showed a good agreement with measurements.

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The purpose of this study is to propose a new zoning method to select appropriate countermeasures against urban warming according to the climate characteristics in each region. In this paper, numerical analyses of mesoscale climate in and around Sendai city were carried out and the sensible and latent heat balances in three regions in Sendai city were examined. The sea breeze decreases the sensible heat but increases the latent heat. It is important to evaluate the thermal and humidity environment comprehensively when the countermeasures against urban warming are selected appropriately.

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The purpose of this study is to propose a new zoning method to select appropriate countermeasures against urban warming according to the climate characteristics in each region. Numerical analyses of mesoscale climate in and around Sendai city were carried out and the spatial distributions of sensible and latent heat budgets inside Sendai were drawn as heat balance maps. These maps show the area where the effect of sea breeze decreasing air temperature is larger than those of sensible heat flux at the urban surface and anthropogenic heat release that increases air temperature. But the sea breeze also increases latent heat and humidity in some areas. A detailed zoning method which evaluated humidity environment and ventilation of outdoor space affected by urban structure was proposed.

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This study aims to clarify a relationship between drag force of buildings and urban air ventilation at pedestrian level. At the first step of the study, LES was applied to the flow fields within high dense cities with buildings of various heights, and distributions of pressures acting on building surfaces and wall shear stress were examined in details. Contributions of the pressure difference and the wall shear stress to the total drag force caused by a group of buildings were compared. It was confirmed that the pressure differences between windward and leeward surface on upper parts of high-rise buildings largely contribute to the total drag force. On the other hand, the momentum transport to the downward direction in front of the windward faces of the high-rise buildings is very large compared to those in other regions.

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Releases of harmful gaseous materials are of high concern of decision making bodies. The understanding of short-range dispersion of air-borne substances within the urban canopy is crucial to predict spread of such pollutants. The simplest description of the transport and dispersion of a passive contaminant is the equation of advection. The terms describing purely advective and turbulent transport of the passive contaminant appear after some modification of this equation. The comparison of those fluxes within 6 different arrangements of idealised urban canopies is shown and the importance of a proper determination of the turbulent fluxes at the edge of the plume and at the roof top level is emphasised

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The purpose of the present study is to develop a nowcast system of local wind velocities near the ground using the JMA GPV data and real-time wind measurements. In the system, the wind velocity and direction at a reference point are first predicted by the use of an artificial neural network, the input data of which are the GPV data or the real-time wind data obtained at several meteorological observatories. Then, the predicted data are combined with the results of a wind tunnel experiment or CFD to predict the local wind velocities near the ground. A comparison between the predicted and actual data shows a relatively good agreement, which implies the potential of the proposed system.

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A wind tunnel experiment was conducted to investigate the effects of unstable stratification on cavity flow behind a cubical building. Mean and fluctuation velocities were measured by both laser Doppler anemometry and particle image velocimetry in the thermally stratified wind tunnel. Although both mean and fluctuation velocity components showed similar profiles in the near wake of the building under neutral and unstable conditions, turbulent intensities showed higher values in the far wake in unstable stratified flow owing to strong vertical mixing. In particular, as the unstable stratification became stronger, the circular vortex behind the trailing edge of the building tended not to be formed because separation vortices shed from the roof were greatly disturbed by buoyancy.

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The paper describes the performance of a micro vertical axis wind turbine (VAWT) with variable-pitch straight blades. A main feature of the variable-pitch angle mechanism is to be able to vary the pitch angles of blades according to the azimuth angle of the main links, without actuators. The performance of the wind turbine was measured by using an open circuit type wind tunnel and a numerical calculation employed the single streamtube model combined dynamic-stall model with different airfoils (NACA0012, 0015, 0018, 0021, 634-221). The performance of self-start and power of the variable-pitch VAWT is larger than that with fixed-pitch blades. We found that VAWT with variable-pitch straight blades has the optimum swing angle and the optimum airfoil.

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Overspeed rotation is one of the most important problem for straight wing vertical axis wind turbines. Rotation is controlled by the mechanical or electromagnetic brake system in existing wind turbines. However, if any trouble occur in brake system, the possibility of breaking wind turbine becomes higher. Therefore, an inhibition mechanism for overspeed rotation was devised, and wind turbine builtin this mechanism was developed. Wind tunnel experiments and field tests with the use of this wind turbine were conducted to investigate whether the rotation can controlled autonomously or not. As a result, it was confirmed that overspeed rotation could never happen in this wind turbine, because the inhibition mechanism of overspeed rotation decelerates the rotation speed of its wind turbine when its rotation speed exceeds upper limit.

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In the present study, an influence of an inflow profile and a spatial resolution of an elevation data on wind speed of a hub height over complex terrain were investigated. For this purpose, a large-eddy simulation (LES) based on a generalized curvilinear collocated grid was done. It was shown that a speed-up ratio at a position of a hub height increased, as a power law exponent became small. About an influence of a spatial resolution of an elevation data, it was shown that a spatial resolution decreased, and a speed-up ratio at a position of a hub height decreased, too. Furthermore, an influence of inflow turbulences was investigated.

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This paper proposes a wind prediction method for wind energy production using a mini Doppler sodar. In this method, short-term wind observation is conducted by a mini Doppler sodar and its wind speed data is correlated with long-term wind observation data obtained at other nearby sites such as AMeDAS. Then long-term wind prediction at the Doppler sodar site is implemented through multiple regression analysis based on the correlation between the short-term Doppler sodar data and the wind observation data at the other nearby sites. The results show that this method can predict the wind speed at the Doppler sodar site effectively. Then it is found that taking into account the atmospheric temperature and pressure in addition to the wind speed is more effective to raise the precision of the wind prediction in the multiple regression analysis.

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On May 31, 2007, a waterspout occurred near Futtsu Coast, Chiba Prefecture. According to the Doppler radar observation at Yokosuka and the ground survey, the characteristics of the waterspout were revealed. The waterspout generated over the wind shear zone, which formed by the outflows from cumulonimbus. The direction of the vortex rotation was anticyclonic and the vortex diameter was about 25 m near the surface. The tangential velocity was estimated to be approximately 20 m/s based on the images and vorticity had on the order of 100 s–1. The Doppler velocity pattern indicates the existence of vortex (misocyclone). Both the tornado vortex and the misocyclone reached up to 3 km ASL. The lifetime of the funnel was about 7 minutes, while that of misocyclone was about 20 minutes. The waterspout was almost stationary and the funnel diameter remained unchanged.

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We experimentally examined the velocity field around a moving tornado near the surface by using hotwire anemometers with an array of four X-probes and dynamic PIV system. The resultant mean distribution obtained by the PIV showed an asymmetric pattern in which the maximum velocity was appeared in right rear side of the counterclockwise tornado to the moving direction. The tornado became stronger and inclined forward as the moving velocity increased. Therefore, the tornado may be stretched continuously, and intensified through the 'vortex stretching' mechanism. The velocity change accompanied by the passage of the moving tornado was also measured at fixed points.

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The process of the geometrical estimation of water spouts from the digital information recorded on the photographs is explained in detail. As an example, a pair of water spouts appeared on the sea in eastern Muroran-city on January 4, 2008 is taken up. As a result, the following results are obtained. The water spouts were formed on the sea about 10,200m away from Itanki-beach. The heights of them and their interval were about 460m and 480m, respectively. The widths of the splash of them were about 40m near the sea surface.

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Wind speed near the Kokufu Tornado in Auguest 2007 was estimated by some approaches, such as the fail gravestone, the displacement of a streetligt, and the flying debris. In the case of the estimation of wind speed by the gravestone, the drag force coefficient of the gravestone was measured by wind tunnel. All the estimated wind speed was distributed in the range from 20m/s to 39 m/s. On the other hand, Japan Meteorological Agency reported that this tornado corresponds to F-1 scale. The estimated wind speed was distributed in the range corresponding the defenition of F-1 scale tornado. This paper indicated that the strength of the tornado can be appropriately classified by Fujita-scale in the case of F-1 scale tornado.

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Saroma Town in Hokkaido was subjected to a severe disaster by an F3 tornado on November 7, 2006. Nine people were killed and thirty-one injured. Many buildings were collapsed and damaged. The authors conducted a questionnaire study answered by the residents in the damaged area in order to clarify the features of tornado and damage to buildings, lifeline facilities and humans. Information on the restoration of the damaged area as well as on the measures taken by administrative bodies, such as the town office, was also obtained, which will be useful for discussing tornado disaster reduction.

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When the tornado damaged Sakata city about 1:30JST of 2 December 2007, some gust fronts were observed by the X-band Doppler radar and the array of supersonic anemometers along the Mogami river Daini bridge. The first two peaks of gusty wind were not accompanied by any apparent echo patterns. The following two peaks occurred with bow echoes. They have relatively short life time of about 10 minutes and showed the velocity change yielded by the passage of the gust front. The horizontal distribution of the gust front was not uniform, which showed that there were small scale structures in the gust front.

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Occasionally toppled grave stones are left after wind-induced disasters. This toppling of grave stones may be used as an indicator to estimate the wind speed. The conventional estimation is based on the static equilibrium condition of the aerodynamic moment and the self weight of the grave stone. In order to examine this estimation, a series of model experiments to topple down miniature grave stone models are conducted by using AC servomotor driven wind tunnel. This wind tunnel can generate quite sharp gust wind. The experimental results showed that there is no significant difference in toppling wind speeds between steady winds and sharp gust winds as well as the conventional theory overestimate the turnover wind velocity.

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A wind prediction method is investigated for railway operation under strong winds based on onsite measurement and flow simulation. The prediction method can estimate the location and the frequency of the strong wind event. Based on it, a new assessment method for the strong winds in the railway system is also proposed. The proposed method is applied to the estimation of frequency of suspension of railway operation. The proposed method shows agreement with the measurement while conventional methods overestimates or underestimates the frequency. Finally, the effect of wind directions and wind fences are taken into consideration. As a result, the frequency of the train regulation due to strong wind events decreased.

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Surface wind retrieval system by X-band radar network is being developed around the Tokyo metropolitan area for the real-time monitoring of severe wind disaster. To estimate the wind information near the ground surface, the logarithmic velocity profile is assumed below the layer on which the upper (z=1000 m ASL) wind components are calculated. The comparison between the estimated and observed surface winds suggests that the windward surface condition (roughness) should be considered in the retrieval system. The wind estimation with the windward average of roughness length improves the estimation accuracy.

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The MRI (Meteorological Research Institute) portable X-band Doppler radar (X-POD: X-band, POrtable Doppler radar) has been developed as a ground-based radar observation platform to make fine-scale observations of various phenomena. It has a 60-km observation range, a 2.0 azimuth resolution, and a pulse length of 1.0 / 0.5 / 0.2 micro-sec providing independent data points every 150 / 75/ 30 m in range. An important aspect of X-POD is its portability. X-POD is basically truck-mounted radar system. Furthermore, X-POD can be dismounted after transport and set up on top of a building. In this study, the status and applications of X-POD have been presented. We will also show examples of X-POD observations. It is expected that X-POD will increase opportunities for severe weather and hazardous wind research.

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Simulation of tornado-like swirl flows are attempted by means of the finite element method. The finite element models consist of two cylindrical regions of which configuration corresponds to that of the conventional experiments. A special slip condition is specified at the cylindrical surface. Sucking up the air at the top end of the region, it in observed that tornado-like swirl flows can form at some limited levels of the Reynolds number. Some of the swirling flows are well corresponding to the Rankin vortex.

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Bangladesh and Myanmar were seriously dfamaged by the severe Cyclone "Sidr" in November of 2007 and "Nargis" in May of 2008. These cyclones are severest ones in the last two decades years. The total died and missed pesons were more than four thousands in Bangladesh, and more than ahundred thousands in myanmar. In the cyclone "Sidr", the minimum pressure of 944 hPa and the peak gust of 69m/s were observed at the time of landing on the coast Bangladesh. In this paper, we reprt the statistic summary of cyclones in the northern Indian Ocean with the Arabian Sea and the Bay of Bengal. The year to year variation fo the cyclone generation and the seasonal feature of the occurrence are clarified.

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This paper presents evaluation of vulnerability of V-beam steel roofing system subjected to high wind hazard. Probabilistic model based on the structural reliability concept was developed by using Monte Carlo simulation to determine the levels of damage of component connections in the roofing model. This study also estimated damage states of the model by using the developed probabilistic model. The result of the estimation showed likely wind velocity which triggers structural minor or severe damage in case of inappropriate construction or inadequate maintenance to be considered.

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It is known that the wind damage spreading over residential houses is more strongly affected by gust speeds rather than maximum wind speeds. Authors have examined some factors of wind properties on residential damage due to typhoons. It is not easy to indicate a clear correlation between properties of wind and damage, because the structural damage associated with strong winds is strongly affected by the various characteristics of structures. In this paper, we tried the damage analyses by quantifying the characteristics of buildings based on the information associated with Typhoon Bart (1999) and Typhoon Songda (2004). It was found that a rate of wooden buildings in an area has correlation to the residential damage due to the typhoons. It is suggested that the characteristics of buildings as well as the gust speeds is a significant factor of spreading of structural damage.

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The Cabinet Office has developed "Authorized standard of damage to houses" and recommended quantitative evaluation on degrees of damage. However, some problems have been pointed out on this standard as follows: differences between the authorized results and the actual damage to houses and difficulty in the appropriate judgment on various kinds of damage. In this paper the authors arranged the problems on this standard provided by the Cabinet Office and proposed a form of a new criterion considering the application to high wind damage.

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This paper describes how to plan the emergency operation against wind disasters such as tornadoes as well as how to improve the response capabilities for local governments. The authors investigated some Local Disaster Management Plans documented by many prefectures and traced the response action of Saga City just after the occurrence of the tornado in 2004. It is recommended that the use of the tornado watch/warning system by the Japan Meteorological Agency should be included in the emergency management plan. Furthermore, key facilities which are necessary for maintaining the response action during severe events should be protected perfectly.

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In this paper, the wind-induced response prediction method of the tall building having viscoelastic damper is proposed. The frequency sensitivity of VE damper is considered by using the fractional derivative model. Accuracy of the proposed prediction method is demonstrated by comparing with the results of wind tunnel test of tall building model with VE damper, and the applicability of this method are presented.

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Characteristics of wind induced vibration of a historical wooden pagoda were investigated by a wind tunnel test. The 1/40 structural model of 5 stories pagoda was used for the aerodynamic wind tunnel test, which simulate a non-linear characteristics of load-deformation relationship. It was found that the along-wind response is much larger than the across-wind response in this type of pagoda. The along-wind displacement increases rapidly when the wind speed is larger than the critical value. When the wind speed is beyond the critical value, the period is very unstable, which can be successfully analyzed by the multi-resolution analysis of a wavelet decomposition.

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A hanging jumper beam is adopted to suppress a jumper conductor's large movement under strong winds. However, the hanging jumper beam is vibrated easily due to low damping and it is thought that their vibrations affect a tower's or cross arm's oscillations incrementally. This paper reports some of our findings about the basic dynamic properties of a hanging jumper beam and the tower through several vibration tests of a strain tower having hanging jumper beams, adding some measurement results during a strong wind.

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In this study, a method for the estimation of the response of wind turbine support structures is proposed by using measured wind speed. Following results were obtained. By introducing a new model for turbulence intensity, the prediction accuracy of the wind response of the wind turbine support structures at low wind speed increased. A method to combine the measured wind speed with the wind speed generation was proposed and applied for the estimation of response of the wind turbine support structures. The results show that when measured wind speed is used, better agreement with the measurement is observed.

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The fluctuating wind velocity characteristics that cause large horizontal response of a simplified cantilever bridge model in the wake of a conical hill were clarified. The flow structure was identified by conditional sampling based on the large peaks of POD 1st modal coordinate of fluctuating pressure on the cantilever model. The structure developed from the downward flow and it turned into the horizontal direction near the ground toward leeward and inward to the hill's centre line direction. The front line of the structure was skewed about 40 degrees from the normal to the approaching flow direction. The occurrence of this structure with an interval near the natural period of the cantilever model would cause even larger horizontal response.

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The unsteady aerodynamic force coefficients for the basic cross-section of the twin-box-shaped deck were assessed by a numerical simulation based on two-dimensional RANS. Then the calculated results were compared with measured data from wind tunnel test to assess the accuracy of the computation. In this investigation the k-omega-SST model was employed as the turbulent model. When the approaching wind was horizontal, the unsteady aerodynamic force coefficients by the computation were in good agreement with measured results. As the angle of attack increased, the difference of unsteady aerodynamic force was increased. Flutter analyses were conducted using the both aerodynamic coefficients. As a result, the flutter velocity using the CFD data was not so different from that using the experimental data.

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Authors reported that flutter characteristics obtained by step-by-step analysis and Complex-Eigen-Value analysis showed perfect agreement. In this paper, by using step-by-step analysis, physical meanings of coupled flutter branch are discussed in relation to fundamental flutter modes. And, flutter onset velocity and branch switch characteristics are investigated basing on these two fundamental flutter modes. By using fundamental flutter modes, flutter modes can be resolved into torsional mode T0 or T180 and heaving mode H-90 or H90. Furthermore, basing on step-by-step analysis in torsional branch characteristics, similar form of Selberg's formula which evaluates flutter onset velocity can be obtained. And, this form can estimate flutter onset velocity changing frequency ratio.

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In the wind tunnel tests of Akashi Strait Bridge elastic full-scale model performed by Honshu-Shikoku Bridge Authority, damping-velocity characteristics of could not be explained by conventional 2DOF (vertical and torsional motion) flutter analysis and 3DOF (vertical, horizontal and torsional motion) flutter analysis could show better fitting to the tests results. However, there are some questions why 3DOF flutter analysis can better fitting to the results, even though the aerodynamic derivatives associated to horizontal motion is much smaller than the other derivatives. Therefore, in this study, the effects of horizontal motion and drag force are investigated by using 3DOF or multi-mode step-by-step analysis. In consequence, the coupled flutter of Akashi Strait Bridge can be characterized by aerodynamically 2DOF coupling and structural-coupling between horizontal and torsional motion.

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Wind-induced vibration of stay cables such as the rain vibration has been studied. Typical countermeasures for that is the installation of dampers or cable-surface treatment. On the other hand, dry-state galloping of stay cables is recently more concerned, and its mechanism and design criteria are now vigorously studied. It is pointed out that there is a common mechanism in them of weakening Karman-vortex shedding by the axial flow behind a cable and critical Reynolds number effect. In this study, wind-induced response and surface pressure of an indented surface cable as well as a normal surface cable were experimentally investigated in order to study the characteristics and mechanisms for dry-state galloping.

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