Typhoon Conditions Research Articles

Quantitative Estimation of Strong Winds in an Urban District during Typhoon Jebi (2018) by Merging Mesoscale Meteorological and Large-Eddy Simulations

An intense tropical cyclone, Typhoon Jebi (2018), landed the central part of Japan and caused severe damages. Quantitative assessment of strong winds in urban districts under typhoon conditions is important to understand the underlying risks. As a preliminary study, we investigate the influences of densely built urban environments on the occurrence of wind gusts in an urban district of Osaka City during Typhoon Jebi by merging mesoscale meteorological and building-resolving large-eddy simulations (LES). With the successful reproduction of the track and intensity of the typhoon in meteorological simulations, the simulated winds at the boundary-layer top of the LES model are used to quantitatively estimate the wind gusts in the urban district. The maximum wind gust in the analysis area of Osaka was estimated as 60-70 m s−1, which is comparable to the wind speed at the height of about 300 m.

Observations of typhoon effects on a high-rise building and verification of wind tunnel predictions

This paper presents the analysis results of 18-h-long field measurement data collected at a 420-m-high building and four meteorological stations in Hong Kong during the passage of Typhoon Usagi (1319) which was the most intense tropical cyclone that attacked Hong Kong in 2013. In this paper, the wind characteristics during Typhoon Usagi over five different sites in Hong Kong are presented and discussed; the modal parameters of the monitored high-rise building are estimated by a probabilistic approach in a Bayesian framework (i.e., Bayesian spectral density approach) and a deterministic method (i.e., Random decrement technique), respectively; the serviceability of the high-rise building under typhoon condition is evaluated against four comfort criteria. Furthermore, the wind tunnel predictions of structural dynamic responses of the monitored building are validated by the field measurements. The goal of this study is to further the understanding of the effects of wind on high-rise buildings so as to provide useful information for the wind-resistant structural design in tropical cyclone-prone regions.

Application of an Eddy Current-Tuned Mass Damper to Vibration Mitigation of Offshore Wind Turbines

Offshore wind turbine (OWT) structures are highly sensitive to complex ambient excitations, especially extreme winds. To mitigate the vibrations of OWT structures under windstorm or typhoon conditions, a new eddy current with tuned mass damper (EC-TMD) system that combines the advantages of the eddy current damper and the tuned mass damper is proposed to install at the top of them. In the present study, the electromagnetic theory is applied to estimate the damping feature of the eddy current within the EC-TMD system. Then, the effectiveness of the EC-TMD system for vibration mitigation is demonstrated by small-scale tests. Furthermore, the EC-TMD system is used to alleviate structural vibrations of the OWT supported by composite bucket foundations (CBF) under extreme winds at the Xiangshui Wind Farm of China. It is found that the damping of the EC-TMD system can be ideally treated as having linear viscous damping characteristics, which are influenced by the gaps between the permanent magnets and the conductive materials as well as the permanent magnet layouts. Meanwhile, the RMS values of displacements of the OWT structure can be mitigated by 16% to 28%, and the acceleration can also be reduced significantly. Therefore, the excellent vibration-reducing performance of the EC-TMD system is confirmed, which provides meaningful guidance for application in the practical engineering of OWTs.

High Winds From Combined Active and Passive Measurements of HY-2A Satellite

Conventional scatterometer wind retrieval has been proved effective for low and moderate wind conditions. Under high wind conditions, especially for typhoons, the air–sea interactions are fierce, and usually the sea surface backscattering is complicated by rain, leading to degraded scatterometer wind quality. Under such circumstances, radiometers in different frequencies can provide information of rains and the complex air–sea interface. In this paper, an artificial neural network (ANN) was employed to combine the observations of the two sensors onboard HY-2A satellite: radiometer and scatterometer (HSCAT) to achieve wind field retrieving under typhoon conditions. The ANN was trained by using global/regional assimilation and prediction system (GRAPES) wind field data as true values. The established network is then verified by an independent dataset excluded from the training data. It is shown that the wind speeds and directions retrieved from the ANN are better than those of the operational HSCAT products as compared to GRAPES winds. Further comparison with the H*Wind product proves that the proposed ANN is effective in terms of high wind field retrieval. The research of this paper provides a nice reference for the typhoon wind retrieval from the HY-2A satellite and for the data processing of the coming HY-2 satellite series.

Character of extreme high tide level variations response to coastline deformation in Taizhou Bay

Taizhou Bay, which locates in the southern coast of China, is frequently influenced by human activities, leading coastline changes frequently in coastline changes visible from space. Coastline deformation in this area will obviously affect the character of extreme high tide level variations in Jiaojiang River and Estuary especially during flood and typhoon periods. Statistic data showed that 54.5% of the extreme high tide levels of Jiaojiang River were caused by typhoon and 27.3% by flood in the past twenty-two years. So, a two-dimensional (2-D) hydrodynamic numerical model including Jiaojiang River and East China Sea was established based on the Mike21 FM model. The model was calibrated with field data and then was employed to predict the extreme flood and storm high tide level changes under three different assumption plans of coastline deformation. 100-year return discharge upstream with 2-year return tide level downstream conditions were set in the model to simulate extreme flood level changes, while Typhoon 0414 with actual discharge upstream were considered to simulate extreme storm high tide level variations. According to the flood level changes simulating results, an increase of 0.01∼0.03 m in extreme flood level will happen in river section and estuarine section and a decrease of 0.01∼0.06 m will occur outside estuarine section. Predictions of the typhoon conditions show that an increase of 0.01∼0.15 m in extreme storm high tide level will happen in both river and estuarine sections with a decrease of 0.01∼0.03 m outside of the Jiaojiang Estuary. Further analysis from tide wave point illustrates that propagation direction of nearshore tide wave in Taizhou Bay will be turned by coastline deformation, thus reflection effect of tide wave will be weakened, while distribution of storm tide currents field changes shows that tidal influx of Jiaojiang Estuary increases due to the blocking effect of the seawalls, causing this kind of special extreme high tide level changing formation.

Analysis on the wind characteristics under typhoon climate at the southeast coast of China

A wind measurement system was established on Mount Wangye, Fujian, China. Multi-level three-dimensional wind measurements of two Typhoon cyclones have been recorded and analyzed to find the characteristics of the near-surface boundary layer. This paper presents wind speed profiles and related parameters, turbulence intensities, turbulence integral length scales, gust factors, and the characteristics of the fluctuating wind speed power spectra in Typhoon conditions. We found a region-specific wind speed power spectrum and its associated spectrum parameters that can be used for the design of wind-resistant structures in Typhoon prone coastal region in southeast of China.

Impact of ocean–wave coupling on typhoon-induced waves and surge levels around the Korean Peninsula: a case study of Typhoon Bolaven

Typhoon-induced waves and surges are important when predicting potential hazards near coastal regions. In this paper, we applied a coupled modeling system for ocean–wave interaction to examine prediction capabilities for typhoon-induced waves and surges around the Korean Peninsula. To identify how ocean–wave coupling impacts wave and surge simulations during typhoon conditions, a set of comparative experiments was performed during Typhoon Bolaven (2012): (1) a fully coupled ocean–wave model, (2) a one-way coupled ocean–wave model without surface current feedback and ocean-to-wave water levels, and (3) a stand-alone ocean model without considering wave-based sea surface roughness (SSR). When coupled with the ocean model, the surface current reduced significantly the wave height on the right-hand side of the advancing typhoon track and improved prediction accuracy along the southern coast of Korea. Compared with the observed surge levels, the simulated surge height yielded improved results for peak height magnitude and timing compared with the uncoupled model. For wave-to-surge feedback, we found that wave-induced SSR plays an important role by modulating wind stress in the surface layer. The modulated wind stress directly affected the surge height, which improved surge peak prediction during the typhoon.

Probabilistic assessment of vibration exceedance for a full‐scale tall building under typhoon conditions

SummaryFull‐scale wind and vibration measurements were conducted on a 270‐m tall building in Hong Kong. For the modal identification, a refined fast Bayesian fast Fourier transform method was newly developed by considering the exponential form of the modal wind force spectrum. Then, the modal parameters of the monitored building and their uncertainties were identified from the full‐scale vibration data under typhoon conditions by the proposed refined fast Bayesian fast Fourier transform method. For assessing the vibration exceedance of the monitored building under typhoon, a stochastic wind force field generation technique was developed by combining the spectral representation method and the computational fluid dynamics method. Wind‐induced vibration of the tall building under Typhoon Kammuri was reanalyzed with generated wind force time history data. Finally, a time‐domain Monte Carlo simulation framework was proposed by integrating the modal identification and the stochastic wind force field generation technique. In this framework, the Metropolis–Hastings sampling algorithm was adopted to estimate the vibration exceedance probability, which was defined through a limit state performance function associated with the ISO vibration assessment criteria.

Long-term wind and wave energy resource assessment in the South China sea based on 30-year hindcast data

The long-term wind and wave characteristics, and their associated stored power, are investigated in the South China Sea (SCS) from 1986 to 2015. The Weather Research and Forecasting model (WRF) and WAVEWATCH-III (WW III) are continuously performed to simulate a 30-year wind and wave hindcasts in the entire domain. Comparisons between the simulated and observed wind and wave data show good agreement under extreme typhoon conditions as well. The spatio-temporal patterns of annual, seasonal and monthly averaged wind fields and wind power density, significant wave heights, and wave potential are presented using the 30-year simulated results. Our results show that offshore winds and waves, with mean annual energy densities reaching up to 1100 W/m2 and 65 kW/m, respectively, are relatively stronger than they are nearshore or inland. The most abundant power occurs in December and the least abundant appears in May. Furthermore, wind and wave energy roses of average power potential at 15 typical points across the SCS are calculated at length. The dominant directions for both the wind and waves are consistently NNE, NE, and ENE. Additionally, the wave energy is mainly the result of energy periods (between 6 and 11 s) and significant wave heights (between 1 and 6 m).

Monitoring of wind effects on 600 m high Ping-An Finance Center during Typhoon Haima

This paper presents analyzed results of field measurements of wind-induced pressures on building claddings and structural responses of 600 m high Ping-An Finance Center (PAFC) in Shenzhen, China during the passage of Typhoon Haima. The characteristics of cladding pressures during the typhoon were investigated with highlights on energy distribution, non-Gaussian probability and coherence features. Then, the natural frequencies, damping ratios and mode shapes of the skyscraper were presented. Based on the field measurements, the amplitude-dependent characteristics of the modal parameters were discussed and the range of selection of damping ratio for the wind-resistant design of super-tall buildings was recommended. Finally, the serviceability of the skyscraper under typhoon condition was assessed. This paper aims to further understand the wind effects on super-tall buildings and provide useful information for the design of skyscrapers in tropic cyclone prone regions.

Observational study of veering wind by Doppler wind profiler and surface weather station

The information on the variation of mean wind speed with height is useful or required in various branches of engineering practices. However, the dependence of varying wind direction on height has often been disregarded in wind engineering. This study aims to further the understanding of the dependence on height of varying wind direction based on long-term wind measurements from Doppler wind profiler and a surface weather station in Hong Kong. The veering angle profiles are obtained by means of composite analysis, and their characteristics are examined as a function of topographic condition, wind speed and storm type (i.e. monsoons and typhoons), respectively. The results suggest that, the veering angle profiles have a strong dependence on the change of upwind topographic condition, which leads to noticeable divergences in terms of the shape of veering angle profiles, the peak value of veering angle and the slope of the profiles. Second, the correlation of the veering angle profiles with wind speed is estimated under near-neutral stable condition. No clear correlation is identified between the veering angle profiles and wind speed. Furthermore, the phenomena of veering wind under monsoon and typhoon conditions are assessed, in which there are excellent agreements in respect to the veering angle profiles under 800 m. Nevertheless, significant deviations arises at higher elevations.

A comparison study on gust factor considering non-stationary effects under typhoon and monsoon conditions

This article studies the feasibility and effectiveness of a non-stationary model using field measurements. Gust factors are compared for both typhoon and monsoon winds whose maximum 10-min mean wind speeds were all greater than 20 m/s using non-stationary models. Wind speeds were recorded by three-dimensional anemometers by the Structural Health Monitoring System of Xihoumen Bridge. The study focuses on the dependences of gust factor on gust averaging time, sample duration, and mean wind speed for both typhoon and monsoon climates. The gust factor curve and the relationship between gust factor and turbulence intensity are also studied. The results suggest that a non-stationary model is more suitable for actual turbulence flow, particularly under typhoon conditions. The article also compares resulting gust factor curves with those obtained in former studies and shows that accurate gust factor curves can be obtained by field measurements for monsoon wind. It is thus recommended that gust factor research should differentiate between typhoon and monsoon winds.

Simulation and improvement of personnel evacuation in living area of offshore platform

The living space of the offshore platform is relatively small and the staff density is generally large. This causes difficulty for evacuation in case of emergency. Combining the features of an offshore platform, the main influence factors of the personnel evacuation are discussed in this paper by qualitative analysis. In the factors system, the controllable factors were found and quantitative simulation analysis was conducted to achieve the evacuation time and attendant problems in the nearby evacuation of main deck living area under normal and typhoon conditions. The software Pathfinder was introduced to analyse the influence of different features of living area and personnel activities in the evacuation process. Through the simulation of the evacuation routes of people in different locations, the optimised evacuation route was determined. The evacuation time was shortened and the efficiency of emergency evacuation will be improved.

Field Measurements of Wind Pressure on an Open Roof during Typhoons HaiKui and SuLi

Full-scale measurements of wind action on the open roof structure of the WuXi grand theater, which is composed of eight large-span free-form leaf-shaped space trusses with the largest span of 76.79 m, were conducted during the passage of Typhoons HaiKui and SuLi. The wind pressure field data were continuously and simultaneously monitored using a wind pressure monitoring system installed on the roof structure during the typhoons. A detailed analysis of the field data was performed to investigate the characteristics of the fluctuating wind pressure on the open roof, such as the wind pressure spectrum, spatial correlation coefficients, peak wind pressures and non-Gaussian wind pressure characteristics, under typhoon conditions. Three classical methods were used to calculate the peak factors of the wind pressure on the open roof, and the suggested design method and peak factors were given. The non-Gaussianity of the wind pressure was discussed in terms of the third and fourth statistical moments of the measured wind pressure, and the corresponding indication of the non-Gaussianity on the open roof was proposed. The result shows that there were large pulses in the time-histories of the measured wind pressure on Roof A2 in the field. The spatial correlation of the wind pressures on roof A2 between the upper surface and lower surface is very weak.When the skewness is larger than 0.3 and the kurtosis is larger than 3.7, the wind pressure time series on roof A2 can be taken as a non-Gaussian distribution, and the other series can be taken as a Gaussian distribution.

Monitoring of structural modal parameters and dynamic responses of a 600m‐high skyscraper during a typhoon

SummaryThis paper presents field measurement results of structural dynamic properties and wind‐induced responses of 600m‐high Ping‐An Finance Center in Shenzhen during the passage of Typhoon Haima. The field measurements included wind speed, wind direction, and structural acceleration responses during the typhoon. Analysis of the field measurements is carried out to investigate the wind‐induced structural vibrations and dynamic properties of the skyscraper under typhoon condition. In the analysis, natural frequencies and damping ratios of Ping‐An Finance Center are estimated using Peak‐Picking method, half‐power bandwidth method in frequency domain, and random decrement technique in time domain, respectively. Two band‐pass filtering methods, namely, elliptical filtering method and Kaiser‐window FIR filter, are adopted to deal with the measured acceleration signals. Consequently, the modal parameters identified with the Peak‐Picking, half‐power bandwidth, and random decrement technique methods are presented and discussed in detail. In addition, the probabilistic characteristics of the recorded acceleration responses are analyzed using the generalized extreme value distribution, and then the serviceability of the skyscraper during the typhoon is evaluated.

Monitoring-based analysis of the static and dynamic characteristic of wind actions for long-span cable-stayed bridge

Wind action is one of the environmental actions which has substantial static and dynamic effects on the long-span bridges. The main objective of the paper is to reveal the static and dynamic characteristics of the regular wind and typhoon condition. A monitoring-based investigation has been carried out to analyze the characteristics of the wind actions. The static characteristics of regular wind and typhoon condition are investigated by analyzing the average wind speed. Moreover, the dynamic characteristics of the two conditions of wind actions are studied by analyzing the parameters of turbulence intensity and gust factors. The correlation analysis is performed between the lateral wind speed and the lateral girder displacement to reveal the static effects of the wind actions on the bridge structures. It is concluded that static and dynamic characteristics of regular wind and typhoon conditions are quite different, and the dynamic effects of wind actions obtained based on monitoring data need to be further studied.

Assimilation of Sentinel-1 Derived Sea Surface Winds for Typhoon Forecasting

High-resolution synthetic aperture radar (SAR) wind observations provide fine structural information for tropical cycles and could be assimilated into numerical weather prediction (NWP) models. However, in the conventional method assimilating the u and v components for SAR wind observations (SAR_uv), the wind direction is not a state vector and its observational error is not considered during the assimilation calculation. In this paper, an improved method for wind observation directly assimilates the SAR wind observations in the form of speed and direction (SAR_sd). This method was implemented to assimilate the sea surface wind retrieved from Sentinel-1 synthetic aperture radar (SAR) in the basic three-dimensional variational system for the Weather Research and Forecasting Model (WRF 3DVAR). Furthermore, a new quality control scheme for wind observations is also presented. Typhoon Lionrock in August 2016 is chosen as a case study to investigate and compare both assimilation methods. The experimental results show that the SAR wind observations can increase the number of the effective observations in the area of a typhoon and have a positive impact on the assimilation analysis. The numerical forecast results for this case show better results for the SAR_sd method than for the SAR_uv method. The SAR_sd method looks very promising for winds assimilation under typhoon conditions, but more cases need to be considered to draw final conclusions.

Disaster Resilience of Low-cost Houses: Case Study of Thua Thien Hue Province, Vietnam

This research documents the post-flood and typhoon conditions of low income housing in the Thua Thien Hue Province, Vietnam, an area prone to extreme flooding in Central Vietnam. The cost of rebuilding houses after a natural hazard has been always a burden for low income households and it often led to the elimination of essential construction practices for disaster resistance. While there has been remarkable improvement in relief and rehabilitation, poor people have been disproportionately vulnerable to extreme events due to their low adaptive capacity and suffered the same damages every year. The research documents existing conditions of low income houses in the Thua Thien Hue province and identifies leading causes of the building failure from the natural disasters. The quality of construction and repairs are assessed based on Coastal Construction Manual and by Federal Emergency Management Agency. In order to examine people's perception toward housing reinforcement as a coping strategy as well as to identify problems and issues associated with achieving stronger and safer housing, focus group and individual interviews were conducted with local residents from four different flood and typhoon-prone communities. The research found that many households in the affected areas now realize the importance of improving housing structures as a coping strategy to resist the impacts of floods and typhoons, however due to low income and a lack of professional instruction and technical guidance in the area, many households still reside in weak and fragile housing conditions that cannot withstand climate related risks. In particular, low-income households spend a considerable amount of their income on housing repair every year. Consultation and communication with professionals about building a resilient housing is lacking. Given that the major immediate recovery action taken by the local people tends to focus on repairing damaged houses, providing proper and applicable construction practices is crucial to improve the housing condition, but also to contribute to reduce poverty in Vietnam.

Typhoon Impact on a Pure Gravel Beach as Assessed through Gravel Movement and Topographic Change at Yeocha Beach, South Coast of Korea

ABSTRACT Han, M.; Yang, D.Y.; Yu, J., and Kim, J.W., 2017. Typhoon impact on a pure gravel beach as assessed through gravel movement and topographic change at Yeocha Beach, south coast of Korea. This study investigated sediment movement and topographic change using radio frequency identifier (RFID) tracers and real-time kinematic (RTK)–global positioning system (GPS) data to examine the response of a gravel beach under typhoon conditions. Yeocha Beach, the study site and a pure gravel beach, was affected by strong wind and waves produced by Typhoon Goni on 24–26 August 2015. On 26 August, the main direction of the tracer movement was toward the upper part of the beach and toward the west relative to the onshore-offshore and alongshore directions. The average movement distance of the tracers differed according to the insertion points. The tracers inserted in the beach face showed a longer average movement distance of 12.07 m compared with 1.89 m for those inserted in the storm berm. In addition, the tracer...

Changes in High- and Low-Flow Regimes: a Diagnostic Analysis of Tropical Cyclones in the Western North Pacific

This study aims to determine the characteristics of hydrological behaviors in the basins of the representative multipurpose dams in the Korean Peninsula that depend on typhoon conditions for sustainable water management and restoration of the water ecosystem. Based on the annual maximum flow and seven-day low-flow results, trend analyses were conducted on hydrological changes, such as magnitude, timing, duration, and frequency of the extreme flows. Among the eight selected multipurpose dams in South Korea, the Chungju and Soyang dams have been subject to dramatic reduction of inflow during the spring and early summer. The Sumjin Dam was indicated the most sensitive to the severity and magnitude of typhoons and it showed a statistically significant increase in the frequency and duration of peak inflows resulting from such typhoons. As regards low flow, the Chungju and Andong dams showed a distinct reduction in this flow in the winter, but the changes resulting from typhoons were relatively subtle. This diagnostic study is expected to provide foundational data to examine the causalities related to the streamflow patterns of Korean basins. In addition, the study could aid in establishing basin-customized mid- and long-term measures for supplying of water resources in the environmental system and for managing the effects of natural disasters by analyzing various hydrological changes related to extreme events.