Narrow Results

Long-period ground motions pose potential risks to the safety and serviceability of supertall buildings, which was not paid sufficient attention in the past of structural seismic design. To address this issue, the comparative study presented in this paper systematically investigates the dynamic responses of a 600-m-high supertall building subjected to natural hazards including long-period ground motions, ordinary ground motions and a super typhoon with the same return periods of 50 years. The seismic responses and wind-induced responses of the supertall building are obtained based on the building’s finite element model under earthquake excitation records and structural health monitoring system installed in the skyscraper, respectively. The long-period ground motions cause larger dynamic responses of the supertall building than those resulted by the ordinary ground motions or the super typhoon. This combined study of numerical analysis and field measurement provides valuable insights into the dynamic responses of a supertall building under different natural hazards, especially the long-period ground motions. The findings are expected to be of interest and practical use to the design of supertall buildings.

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The gust response factors (GRFs) of transmission towers in current standards are reviewed for synoptic winds. The collapse of most transmission towers has occurred under the high-intensity wind (HIW) caused by events such as typhoons, hurricanes, and downbursts. Thus, this paper studies the GRF of a transmission tower under the typhoon. First, the definition of GRF and its extended form for the transmission towers are developed. Then the wind speed simulation of a typhoon event is introduced. Based on the structural health monitoring (SHM) system installed on tower #32, the measured GRFs under the super typhoon Mangkhut are calculated. Then the finite element model (FEM) of the transmission tower-line system is established to simulate the dynamic response to further calculate the GRFs, which agrees well with the field measurements. Both the field measurement and simulation results show that the GRFs under the typhoon are larger than those under the synoptic wind and that the recommended GRFs in the Chinese standard underestimate the peak responses. Finally, a parametric analysis is performed, which demonstrates that the turbulence intensity, wind speed, and power-law exponent all have great effects on the GRFs of transmission towers. In the HIW-prone areas, it is recommended that the characteristics of the HIW can be considered in improving the GRF values to guarantee the structural safety of transmission towers.

Many long-span bridges are located at typhoon prone regions. With the continuous increase of the bridge span, the typhoon-induced buffeting becomes more and more prominent. In this study, based on the structural health monitoring system installed in the Sutong Bridge, the recorded buffeting responses of the main girder during typhoons Damrey and Haikui were analyzed. The run test method demonstrated that the recorded acceleration responses can be regarded as zero-mean non-stationary random processes. Hence, to capture the energy distribution of the recorded data in the time-frequency domain, the evolutionary power spectral density (EPSD) estimation was conducted using efficient generalized harmonic wavelet (GHW) and filtered harmonic wavelet (FHW), respectively. Compared with the GHW, narrower wavelet bandwidth is required by the FHW to yield a compromise between the time and frequency resolution. For the FHW-based method, the power spectral density amplitudes of the averaging EPSDs are slightly larger for certain major frequency components than those obtained by the Pwelch method. Results show that the non-stationary features of the buffeting of long-span bridges during Typhoon events should be considered. This study can also provide references for non-stationary buffeting analysis of other long-span bridges during extreme wind events.

Steel sheeting is usually provided at the upper flange of purlin in steel roof with screw connections. The resulting diaphragm effect provided by the sheeting enhances the buckling resistance of the purlin. However, this diaphragm effect will be reduced due to any abnormality in the screw connection caused by wind-induced fatigue particularly from typhoon. This would reduce the buckling resistance of the purlin with sheeting (the purlin-sheeting system), and it would affect subsequent condition evaluation during their service life. This problem is addressed in this paper with a framework of time-dependent reliability evaluation of the buckling limit state of the purlin-sheeting system. The buckling resistance reduction due to the degradation of the diaphragm effect from typhoon is taken into account in the resistance model. The randomness of wind intensity and landfall occurrence of typhoon during the service life of purlin are also accounted for in the wind load effect model. The time-dependent reliability of the purlin at different positions of a roof is studied. Then the variation of reliability of the system due to the effect of climatic changes in the design service life is discussed. The proposed strategy is then applied to the evaluation of a purlin-sheeting system in eleven cities in China with typhoon occurrences with some useful results for future studies in the provisions of the design code.

With a numerical model of Northwestern Pacific region, the water movements associated with real time tides and actual storms were reproduced. Making use of reasonably representative model simulations together with data derived from the coastal observations can lead to the required estimates of extreme conditions for the purpose of coastal defense and design of offshore structure. Here, we used the model of 1/12° latitude by 1/12° longitude resolution. 75 typhoon and monsoon surge simulations were performed with specification of 8 boundary tides for real time tides. Typhoon and winter monsoon wind fields were computed from JWA/GPV data set applying Cardone's PMBL (Planetary Marine Boundary Layer) model over the whole region with embedding parameterized typhoon wind fields onto it. Present result is an updated version of papers presented earlier (Choi and Ko, 1999; Choi and Eum, 2000). Preliminary maps showing distribution of extreme sea levels of whole modeled area including coastal boundaries and surge induced extreme currents are presented in terms of recurrence intervals.

Mooring problems are still serious issues in port construction and operation. Although many studies have been carried out about moored ship motions or waves, effective countermeasures to reduce ship motions have not been accomplished in most harbours facing open seas. It is known that operators require detailed wave information near harbours when sea conditions become severe. In this study, a new numerical model is constructed for the prediction of the mooring limit condition due to typhoons. It is based on the theories of Kalman Filter, wave growth inside typhoons and wave decay in swells. The prediction model needs less input data than the meteorological models. The accuracy of the predicted model is verified for a port facing the Pacific Ocean when swells or wind waves propagate from typhoons in various situations. The prediction model is applied to other locations facing the Pacific Ocean. This new model allows us to predict the mooring limit condition 0.5–2 days before the influence of typhoons. Moreover, we propose a berth operation system to monitor the mooring limit condition using this prediction model in harbours facing open seas.

The present study assesses the climate change impact on local storm surges along the coasts of the Korean Peninsula and Tottori Prefecture, Japan. A series of storm surge simulations are conducted on a physical process-based storm surge model using direct forcing from general circulation model output data in the two periods of 1979–2008 and 2075–2099. It is found that the typhoon intensity is enhanced and its number increases under the future climate condition in the area of the Korean Peninsula (32${}^{\circ }$ to 40${}^{\circ }$ N and 120${}^{\circ }$ to 138${}^{\circ }$ E). In addition, the typhoon approach course moves by 0.523${}^{\circ }$ westward in the future climate. From a series of storm surge simulations, the statistical analysis showed that the climate change influences the storm surge height regionally and locally; it decreases on the west coast of the Korean Peninsula in the future, whereas it increases on the south coast of the Korean Peninsula and on the coast of Tottori Prefecture, Japan.

Sea-surface wind agitation can be considered the dominant noise sources whose intensity relies on local wind speed during typhoon period. Noise source levels in previous researches may be unappreciated for all oceanic regions and should be corrected for modeling typhoon-generated ambient noise fields in deep ocean. This work describes the inversion of wind-driven noise source level based on a noise field model and experimental measurements, and the verification of the inverted noise source levels with experimental results during typhoon period. A method based on ray approach is presented for modeling underwater ambient noise fields generated by typhoons in deep ocean. Besides, acoustic field reciprocity is utilized to decrease the calculation amount in modeling ambient noise field. What is more, the depth dependence and the vertical directionality of noise field based on the modeling method and the Holland typhoon model are evaluated and analyzed in deep ocean. Furthermore, typhoons named “Soulik” in 2013 and “Nida” in 2016 passed by the receivers deployed in the western Pacific (WP) and the South China Sea (SCS). Variations in sound speed profile, bathymetry, and the related oceanic meteorological parameters are analyzed and taken into consideration for modeling noise field. Boundary constraint simulated annealing (SA) method is utilized to invert the three parameters of noise source levels and to minimize the objective function value. The prediction results with the inverted noise source levels exhibit good agreement with the measured experiment data and are compared with predicted results with other noise sources levels derived in previous researches.

This study explores the temporal precipitation organization of 126 landfalling typhoons around Japan during 2006–2019. The internal structure particularly the cell sizes and spell durations of precipitation induced by these 126 typhoons are investigated from the Radar Automated Meteorological Data Acquisition System (Radar-AMeDAS) observed hourly precipitation dataset. The best track data from the Regional Specialized Meteorological Center (RSMC) Tokyo are utilized to identify the typhoon locations. We first stratified the independent precipitation cell sizes and precipitation spell durations with intensity exceeding various thresholds into different bins. Then the frequency distribution of the precipitation sizes and durations in each bin are computed. Our results indicate that the occurrence of typhoon induced heavier precipitation is higher compared to the typhoon induced lighter precipitation. The typhoon induced heavier precipitation over Japan last up to a day, while the lighter precipitation last about 12 hours. The long-lived precipitation cases are also noticed that last up to 2 days, but they don’t occur so frequently. We analyzed the spell durations over different regions of Japan with various radii from the typhoon center starting from 10 km to 300 km. The results also indicate that the pattern of spell durations are mostly same over all the regions within 300 km radius.

Atmospheric motion vectors (AMVs) have produced positive impacts on global weather forecasts, but few studies have evaluated the impacts of AMVs data from Fengyun (FY) geostationary satellite series, especially from FY-2G and FY-4A, on typhoon forecasts in a regional model. In this study, the AMVs data of FY-2G and FY-4A were compared and evaluated by pre-processing methods such as height assignment, quality control, channel combination and thinning. Typhoon Haishen (No.10 super typhoon in 2020) was taken as an example. The AMVs data of the two satellites were assimilated by using 3DVAR provided by WRFDA and simulated by the WRF model to evaluate the forecast results of the two satellites, respectively. The results show that the AMV data from FY-4A are better overall than those from FY-2G, with smaller RMSEs and biases for full wind speeds. On the other hand, assimilation of AMVs data improves the forecasts of environmental fields, resulting in the simulated track closer to the best track. Another experiment shows that the assimilation of AMVs data has a good impact on precipitation prediction In general, the assimilation of FY-2G and FY-4A AMV data has a relatively positive impact on typhoon prediction, and the AMVs data combined with multiple channels can provide better prediction.

During the formation of typhoon Mike (1990), the trade wind to the north of the system was very strong over a very large domain. However, there were evident cross-equatorial flows associated with the formation of typhoon Betty (1987). The intensities of both systems increased greatly after they reached tropical storm intensity. To help understand the influences of the environmental momentum field on the formation of typhoon, we used the PSU/NCAR MM5 to simulate the formation process of Betty and Mike. The ECMWF grid point data were used as the model initial field. Results showed that the strong trade wind associated with Mike's formation and the cross-equatorial flows associated with Betty's formation were simulated reasonably well. The intensities of model typhoons were also close to the observations for Betty. However, the model vortex developed faster than the observation for Mike.

Both the tangential momentum and the vorticity budgets were analyzed using model-simulated data. Results showed that the low-level eddy horizontal angular momentum transport caused by the strong trade winds played a significant role to the spin-up of the model vortex, thus was favorable for the formation of Mike. The horizontal vorticity advection caused by the cross-equatorial flow associated with Betty's formation did not contribute significantly to the vorticity generation of model vortex. However, the low-level convergence enhanced by the cross-equatorial flow might have caused the vorticity generation near system centre and increased heating efficiency. Such effect might have played an important role on the organization of convection and helped the formation of tropical cyclone.

The present study carries out the comparison of the water level associated with the numerical methods: Finite Difference Method (FDM) and Finite Volume Method (FVM) and the simulation considered on the present climate condition along the coast of Bangladesh. The governing equations of the first model are discretized through FDM and solved by a conditionally stable semi implicit manner on an Arakawa C-grid system. For the second model, α-coordinate is used for the irrational bottom slope representation and the mesh grid of the study domain is generated by the unstructured triangular cells. The feasible study domain with coast and island boundaries are approximated through proper stair steps for the FDM and the unstructured mesh representation for FVM. A one-way nested scheme technique is applied to the first model to include coastal intricacies as well as to preserve computational cost. Both the models are applied to extrapolate sea-surface elevation associated with the catastrophic cyclone 1991(BOB 01) along the seashore of Bangladesh. The simulation results from both the models are statistically copacetic and make a good acquiescent with some observed and reported data. In the statistical viewpoint, both the method has a good acceptance in storm surge simulation, but this study ensures the strong positive reconciliation with observed data and FVM simulation data. In Bangladesh region, it will be wise decision to use Finite Volume Methods for simulating the storm surge.

In order to provide data reference in protecting Beihai Silver Beach this article used the moving average method spearman rank correlation analysis method and R/S rescaled range method to analyze the typhoon tendency in Beihai Silver Beach and predicted the future tendency from the typhoon frequency intensity and extremes. The results show that: In the past 60 years there is a downward trend in the typhoon frequency in Beihai Silver Beach with a growing trend in the intensity and extremes though those three trends aren't very obvious; the typhoon frequency in Beihai Silver Beach will rise in the future so do the intensity and extremes. For ensuring Silver Beach is not affected by the change of typhoon in the future we must make some targeted and reasonable responses.