• Proceedings of the KSR Conference
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• 2005.11a
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• pp.1241-1247
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• 2005

The ballast-flying, induced by strong underbody train gust, may damage train underbody, wheel and even cause the safety problems. For this reason, a heighter is being used to prevent the ballast-flying phenomenon through underbody now reduction. In this research, flow field around a heighter is numerically simulated. And the parametric study of various heighter shapes is performed to find out more effective heighter shape. Also the ballast-flying probabilities are calculated for various ballast types and train speeds.

• Journal of Ship and Ocean Technology
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• v.12 no.2
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• pp.16-31
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• 2008

The lifting-surface programs have been used successfully in practice for the design and global performance prediction of the marine propellers. To predict the pressures on the blade for the strength analysis, the constant panel method has been a good alternative. To meet the need for more accurate information on the pressure near the tip region and the trailing edge of the blade, the higher order panel method (HiPan, hereinafter) based on a B-spline is developed and now available. However, there is an increasing demand to get the highly reliable unsteady behavior of the pressure near the tip region by the HiPan. The ultimate goal of our efforts is to develop the fully unsteady higher order panel code for the propeller. In the present paper, we will show the numerical procedure applicable to unsteady problems of the three dimensional hydrofoil in a sinusoidal gust and heave motions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.369-373
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• 2005

To investigate the mechanism of ballast-flying phenomena by strong wind induced by high-speed trains, wind velocity in the vicinity of the track has been measured using 16-channel Kiel-probe array and detailed flow structure near the surface of the track has been analyzed. The position at which the underflow fully develop has been examined in order to assess the driving force of the turbulent flow under train and the results yields that the turbulent flow owing to the cavity of the inter-car as well as the friction force at the underbody of the train is the main reason of the strong wind under high-speed train. The preceding wind tunnel test results has been introduced to assess the probability of ballast-flying during the passage of the high-speed train by comparing the results from field-measuring. The results shows that when the G7 train as well as the KTX train runs at 300km/h, about 25m/s wind gust is induced just above the tie and the probability for small ballast under 50g to fly is about 50% when it is on the tie. If the G7 train runs at 350km/h, the wind gust just above the tie increases to 30m/s, therefore more radical countermeasure seems to be needed.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.561-564
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• 2009

In order to reduce damage from natural disasters, prevention activities through analysis and predicting based on meteorological factor and damage data is required. Other countries already have continuously studied on natural disasters and developed reducing disasters damage. But the risk assessment model for natural disaster is not to Korea. Therefore, a previous model of hurricane, Florida Public Hurricane Loss Model(FPHLM), is the basis and is applying to domestic situation. Accordingly, this study introduces the variables selecting process because input variables should be selected under Korea present state and be used. The estimating representative damage method would be necessary along with selecting housing types representing relevant areas because estimating damage amount of all over relevant areas housing was very hard during damage estimating process. But there is no exact representative housing types in the Korea. Therefore, we select housing types applicable to risk assessment model for natural disasters representing the Korea through previous studies and literature reviews. We using ASCE 7-98(Minimum Design Loads for Buildings and Other Structures, 1998) standard which estimated wind load using 3-second gust. ASCE 7-98 divided Main Wind Force Resistance System(MWFRS) and Component and Cladding(C&C) and it estimated wind load. Therefore, we estimate wind load affected by 3-second gust of a typhoon Maemi through calculating wind load process using selected representative detached house types in the process of selecting input variables for previous disaster predict model. The result of houses damage amount is about 230 hundred million won. This values are limit the 1-story detached dwelling, 19~29pyeong(62.81~95.56 $m^2$) of total area and flat roof. Therefore, this process is possible application to other type houses.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.12
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• pp.1035-1044
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• 2013

Because of the high specific stiffness and strength inherent in the sandwich structure composed of facesheet that resists in-plane loads and a core that resists out-of-plane loads, it is often used for large and light-weighted structures. However, inevitably the increased flexibility allows greater deformation-based disturbances in the structures. Thus, it is necessary to analyze the structural safety. To obtain more accurate analytical results, the input disturbances must more closely simulate real load conditions; to improve accuracy, non-linear elements such as gust effects were considered. In addition, the structural safety was analyzed for the iso-grid sandwich panel structure using fluid-structure interactions. For a more realistic simulation, flow velocity fields, which consider the effects of irregular gust fluctuation, were generated and the coupled field was analyzed by mapping the pressure and displacement.

• Wind and Structures
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• v.35 no.6
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• pp.419-430
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• 2022

In wind-resistant designs, wind velocity is assumed to be a Gaussian process; however, local complex topography may result in strong non-Gaussian wind features. This study investigates the non-Gaussian wind features over complex terrain under atmospheric turbulent boundary layers by the large eddy simulation (LES) model, and the turbulent inlet of LES is generated by the consistent discretizing random flow generation (CDRFG) method. The performance of LES is validated by two different complex terrains in Changsha and Mianyang, China, and the results are compared with wind tunnel tests and onsite measurements, respectively. Furthermore, the non-Gaussian parameters, such as skewness, kurtosis, probability curves, and gust factors, are analyzed in-depth. The results show that the LES method is in good agreement with both mean and turbulent wind fields from wind tunnel tests and onsite measurements. Wind fields in complex terrain mostly exhibit a left-skewed Gaussian process, and it changes from a softening Gaussian process to a hardening Gaussian process as the height increases. A reduction in the gust factors of about 2.0%-15.0% can be found by taking into account the non-Gaussian features, except for a 4.4% increase near the ground in steep terrain. This study can provide a reference for the assessment of extreme wind loads on structures in complex terrain.

• Atmosphere
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• v.33 no.4
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• pp.413-422
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• 2023

Urban Air Mobility (UAM) is promising, sustainable and efficient air transportation in a metropolitan area. Korean government has recently announced operation demonstration plans as a step toward commercialization of UAM. However, there is lack of understanding on the potential impact of weather on UAM operation. We collected weather observations from Gimpo International Airport and 5 automatic weather stations (AWS) along UAM corridor of the Han-River to assess weather barriers such as low visibility, wind gust and wind shear. The results show the frequency of low visibility near the corridor fluctuated significantly from year to year depending on the concentration of fine particulate matter (PM_2.5) in Seoul. The frequency of high wind speed-shift calculated using 1-minute wind observations was increased not only during the spring season (March, April, and May) but also the beginning of rainy season (Jun). In addition, a chance of high wind shear from 1-minute wind observations varied by the stations, suggesting that the condition is largely affected by topography including a river and high-rise buildings. These basic weather properties suggest that there are substantial weather barriers to UAM operations along the Han-River Corridor, while they cannot properly surveil micro-scale weather conditions in detail such as wind gust and wind shear over the corridor. Thus, this study suggests that potential barriers related to adverse weather need to be evaluated, building high-density weather observations infrastructure prior to UAM demonstration and commercialization.

• Structural Engineering and Mechanics
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• v.89 no.5
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• pp.479-489
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• 2024

The cracking mechanism in ceramsite aerated concrete block (CACB) infill walls were studied in low seismic fortification intensity coastal areas with frequent occurrence of typhoons. The inter-story drifts of an eight-story residential building under wind loads and a seismic fortification intensity of six degrees were analyzed by using the PKPM software. The maximum inter-story drift ratio of the structure in wind load was found to be comparable to that under the seismic fortification intensity of six degrees. However, when accounting for the large gust wind speed of typhoon, the maximum inter-story drift ratio was much larger than that obtained under reference wind load. In addition, the finite element models of RC frames were employed by displacement loading to simulate two scenarios with and without window hole in the CACB infill walls, respectively. The simulation results show no signs of cracking in both the infill walls with window hole and those without window for the inter-story drift caused by seismic loads and the reference wind load. However, both types of infill walls experienced structural creaking when assessing the gust wind pressure recorded from previous typhoon monitoring. It is concluded that an underestimate of wind loads may contribute substantially to the cracking of frame CACB infill walls in low seismic fortification intensity coastal areas. Consequently, it is imperative to adopt wind pressure values derived from gust wind speeds in the design of CACB infill walls within frame structures. Finally, the future research directions of avoiding cracks in CACB filled walls were proposed. They were the material performance improving and building structure optimizing.

• Journal of Korean Association for Spatial Structures
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• v.6 no.1 s.19
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• pp.83-90
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• 2006

The GF(Gust Factor) method is usually used as a method to evaluate equivalent static wind loads for general structures. The GF method is performed on the assumption that the shape of the equivalent static wind load profile is typically similar to that of mean wind loads. The shape of fluctuating wind loads could be quite different with that of the mean wind loads in case of large-span structures. So, the effect of higher modes as well as first mode must be considered to evaluate the wind loads. In this study, the ACS (Advanced Conditional Sampling) method is suggested to evaluate of equivalent static wind loads after investigating about GF and LRC method. The An method ran derive effective static wind loads by combining wind pressures and inertia forces of a structure chosen at a maximum load effect. The maximum load effect is assessed with the time history analysis using pressure data measured in wind tunnel tests. Equivalent static wind loads evaluated using ACS, GF, and LRC methods are compared to verify the effectiveness of ACS method.

• Journal of Bio-Environment Control
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• v.3 no.1
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• pp.1-9
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• 1994

Wind load or snow load, acting on agricultural structures is working more sensitive than any other load and therefore plays an important role in determination of design loads of agricultural structures. In this study, unit snow weight, greatest gust speed and depth of snow fall were analyzed and applied to determine the amount of frames. The unit snow weights were statistically classified and calculated in the basis of mean temperature and showed considerable differences between the unit snow weights at below and above -1$^{\circ}C$. Equations for estimating greatest gust speed with fastest wind speed were developed for inland and seaside districts. The calculated values from developed equations were little higher than those from the current equation in general. The difference between the depths of snow cover and snow fall, which shows the possibility of reduction of design loads under the adequate management. Design wind speed estimated by a modified equation suggested the amount of frames less than those by current one, and the depth of snow fall as a design snow depth suggested the amount of frames more than those of snow cover. Therefore, it is very important to select the adequate design values considering the characteristics of agricultural structures.