• Title/Summary/Keyword: wind resistance

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An Improved Method for Determining Sea Margin (I) (씨마진 산정법의 개선에 관한 연구(I))

  • 권영중
    • Journal of Ocean Engineering and Technology
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    • v.18 no.3
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    • pp.40-43
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    • 2004
  • A rational method is presented for estimating the power increase of a ship at sea. A probabilistic approach is applied to determine the weather condition at sea, A comparison is made between some full-scale data and the result of Swift's method. A comparison is also made to find differences among the results of eight kind methods for the wind added resistance of a VLCC in head wind. The mean difference between the results is 7%, in general, for a given relative wind speed.

Evaluation for Fatigue Resistance of Small Wind Turbine Composite Blade according to GL Guideline (GL Guideline에 의거한 소형 풍력발전용 복합재 블레이드의 피로 저항성 평가)

  • Jang, Yun Jung;Kang, Ki Weon
    • The KSFM Journal of Fluid Machinery
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    • v.16 no.4
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    • pp.15-21
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    • 2013
  • This study aims to estimate the fatigue resistance of small wind composite blade using the fatigue life estimation formula in the GL guideline. For this, firstly, we estimated a turbine blade's bending moment spectrum by using wind profile wind profile and BEMT. And fatigue tests were performed to obtain the S-N curve of composite materials used in blade. In addition, a finite element analysis was used to identify fatigue critical locations and fatigue stress spectrum. And the fatigue resistance of composite blade were evaluated using the rainflow cycle counting, and Goodman diagram and the fatigue life estimation formula in the GL guideline.

Generalized load cycles for dynamic wind uplift evaluation of rigid membrane roofing systems

  • Baskaran, A.;Murty, B.;Tanaka, H.
    • Wind and Structures
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    • v.14 no.5
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    • pp.383-411
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    • 2011
  • Roof is an integral part of building envelope. It protects occupants from environmental forces such as wind, rain, snow and others. Among those environmental forces, wind is a major factor that can cause structural roof damages. Roof due to wind actions can exhibit either flexible or rigid system responses. At present, a dynamic test procedure available is CSA A123.21-04 for the wind uplift resistance evaluation of flexible membrane-roofing systems and there is no dynamic test procedure available in North America for wind uplift resistance evaluation of rigid membrane-roofing system. In order to incorporate rigid membrane-roofing systems into the CSA A123.21-04 testing procedure, this paper presents the development of a load cycle. For this process, the present study compared the wind performance of rigid systems with the flexible systems. Analysis of the pressure time histories data using probability distribution function and power spectral density verified that these two roofs types exhibit different system responses under wind forces. Rain flow counting method was applied on the wind tunnel time histories data. Calculated wind load cycles were compared with the existing load cycle of CSA A123.21-04. With the input from the roof manufacturers and roofing associations, the developed load cycles had been generalized and extended to evaluate the ultimate wind uplift resistance capacity of rigid roofs. This new knowledge is integrated into the new edition of CSA A123.21-10 so that the standard can be used to evaluate wind uplift resistance capacity of membrane roofing systems.

A Study on the Simplified Prediction Method of Air Resistance for Towing Force Calculation of Disabled Ships (사고선박 예인력 계산을 위한 공기저항 간편 추정법 연구)

  • Kim, Eun-Chan;Choi, Hyuek-Jin
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.17 no.3
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    • pp.198-204
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    • 2014
  • Ships sailing the seas encounter air resistance. The air resistance depends on the shape of the above-water hull, the ship speed, the wind speed and wind direction. The experimental or statistical methods which are used to predict the air resistance are one of the essential procedures of the calculation of the towing force of the disabled ships. This paper shows simplified air resistance prediction method using the variables of the projected area of the above-water hull, the speed of the ship, the wind speed and its direction. These methods have been applied to the existing computer program which had been set up to predict the towing force of the disabled ships.

Mechanism on suppression in vortex-induced vibration of bridge deck with long projecting slab with countermeasures

  • Zhou, Zhiyong;Yang, Ting;Ding, Quanshun;Ge, Yaojun
    • Wind and Structures
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    • v.20 no.5
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    • pp.643-660
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    • 2015
  • The wind tunnel test of large-scale sectional model and computational fluid dynamics (CFD) are employed for the purpose of studying the aerodynamic appendices and mechanism on suppression for the vortex-induced vibration (VIV). This paper takes the HongKong-Zhuhai-Macao Bridge as an example to conduct the wind tunnel test of large-scale sectional model. The results of wind tunnel test show that it is the crash barrier that induces the vertical VIV. CFD numerical simulation results show that the distance between the curb and crash barrier is not long enough to accelerate the flow velocity between them, resulting in an approximate stagnation region forming behind those two, where the continuous vortex-shedding occurs, giving rise to the vertical VIV in the end. According to the above, 3 types of wind fairing (trapezoidal, airfoil and smaller airfoil) are proposed to accelerate the flow velocity between the crash barrier and curb in order to avoid the continuous vortex-shedding. Both of the CFD numerical simulation and the velocity field measurement show that the flow velocity of all the measuring points in case of the section with airfoil wind fairing, can be increased greatly compared to the results of original section, and the energy is reduced considerably at the natural frequency, indicating that the wind fairing do accelerate the flow velocity behind the crash barrier. Wind tunnel tests in case of the sections with three different countermeasures mentioned above are conducted and the results compared with the original section show that all the three different countermeasures can be used to control VIV to varying degrees.

Speed-Power Performance Analysis of an Existing 8,600 TEU Container Ship using SPA(Ship Performance Analysis) Program and Discussion on Wind-Resistance Coefficients

  • Shin, Myung-Soo;Ki, Min Suk;Park, Beom Jin;Lee, Gyeong Joong;Lee, Yeong Yeon;Kim, Yeongseon;Lee, Sang Bong
    • Journal of Ocean Engineering and Technology
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    • v.34 no.5
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    • pp.294-303
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    • 2020
  • This study discusses data collection, calculation of wind and wave-induced resistance, and speed-power analysis of an 8,600 TEU container ship. Data acquisition system of the ship operator was improved to obtain the data necessary for the analysis, which was accomplished using SPA (Ship Performance Analysis, Park et al., 2019) in conformation with ISO15016:2015. From a previous operation profile of the container, the standard operating conditions of mean draft were 12.5 m and 13.6 m, which were defined with the mean stowage configuration of each condition. Model tests, including the load-variation test, were conducted to validate new ship performance and for the speed-power analysis. The major part of the added resistance of container ship is due to the wind. To check the reliability of wind-resistance calculation results, the resistance coefficients, added resistance, and speed-power analysis results using the Fujiwara regression formula (ISO15016:2015) and Computational fluid dynamics (Ryu et al., 2016; Jeon et al., 2017) analysis were compared. Wind speed and direction measured using an anemometer were used for wind-resistance calculation and the wave resistance was calculated using the wave-height and direction-data from weather information. Also, measured water temperature was used to calculate the increase in resistance owing to the deviation in water density. As a result, the SPA analysis using measured data and weather information was proved to be valid and able to identify the ship's resistance propulsion performance. Even with little difference in the air-resistance coefficient value, both methods provide sufficient accuracy for speed-power analysis. The differences were unnoticeable when the speed-power analysis results using each method were compared. Also, speed-power analysis results of the 8,600 TEU container ship in two draft conditions show acceptable trends when compared with the model test results and are also able to show power increase owing to hull fouling and aging. Thus, results of speed-power analysis of the existing 8,600 TEU container ship using the SPA program appropriately exhibit the characteristics of speed-power performance in deal conditions.

Wavelet-transform-based damping identification of a super-tall building under strong wind loads

  • Xu, An;Wu, Jiurong;Zhao, Ruohong
    • Wind and Structures
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    • v.19 no.4
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    • pp.353-370
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    • 2014
  • A new method is proposed in this study for estimating the damping ratio of a super tall building under strong wind loads with short-time measured acceleration signals. This method incorporates two main steps. Firstly, the power spectral density of wind-induced acceleration response is obtained by the wavelet transform, then the dynamic characteristics including the natural frequency and damping ratio for the first vibration mode are estimated by a nonlinear regression analysis on the power spectral density. A numerical simulation illustrated that the damping ratios identified by the wavelet spectrum are superior in precision and stability to those values obtained from Welch's periodogram spectrum. To verify the efficiency of the proposed method, wind-induced acceleration responses of the Guangzhou West Tower (GZWT) measured in the field during Typhoon Usagi, which affected this building on September 22, 2013, were used. The damping ratios identified varied from 0.38% to 0.61% in direction 1 and from 0.22% to 0.59% in direction 2. This information is expected to be of considerable interest and practical use for engineers and researchers involved in the wind-resistant design of super-tall buildings.

A Comparison of the Wind Resistance Characteristic of a Container Crane According to the Increase to the Lifting Capacity (권상용량 증가에 따른 컨테이너 크레인의 내풍특성 비교)

  • Lee, Seong-Wook;Kim, Hyung-Hoon;Han, Dong-Seop;Han, Geun-Jo;Kim, Tae-Hyung
    • Proceedings of the KSME Conference
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    • 2007.05a
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    • pp.204-209
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    • 2007
  • This study was carried out to analyze the effect of wind load on the structural stability of a container crane according to the increase of the lifting capacity using wind tunnel test and provided a container crane designer with data which can be used in a wind resistance design of a container crane assuming that a wind load at 75m/s wind velocity is applied on a container crane. Data acquisition conditions for this experiment were established in accordance with the similarity. The scale of a container crane dimension, wind velocity and time were chosen as 1/200, 1/13.3 and 1/15. And this experiment was implemented in an Eiffel type atmospheric boundary-layer wind tunnel with $11.52m^{2}$ cross-section area. Each directional drag and overturning moment coefficients were investigated.

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Measurement of Aerodynamic Properties of Screens for Windbreak Fence using the Apparatus for Testing Screens (공력 저항 측정기를 이용한 방풍펜스 방진막의 공기 투과 저항력 측정)

  • Kim, Rack-Woo;Lee, In-Bok;Hong, Se-Woon;Hwang, Hyun-Seob;Son, Young-Hwan;Kim, Tae-Wan;Kim, Min-Young;Song, Inhong
    • Journal of The Korean Society of Agricultural Engineers
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    • v.55 no.6
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    • pp.145-154
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    • 2013
  • Recently, damage occurrence by wind erosion has been increasing in society. In times past, such problems only took place in desert area ; however, in recent years, the wind erosion problem is spreading out to agricultural land. Wind erosion in agricultural land can cause loss of loam soils, the disturbance of the photosynthesis of the crop fields and serious economic losses. To overcome the mentioned problems, installation of windbreak fence can be recommended which function as disturbing strong wind and wind erosion. However, there is still no proper guideline to install the windbreak fence and the installation used to rely on the intuition of the workers due to the lack of related studies. Therefore, this study measured the aerodynamic resistance of screens of the windbreak fence using the apparatus for testing screens. The apparatus for testing screens was designed to measure pressure loss around the screen. Measured pressure loss by wall friction compensated for pressure loss to calculate the aerodynamic resistance of screens. The result of pressure loss by regression analysis derived the aerodynamic coefficient of Darcy-Forchheimer equation and power law equation. The aerodynamic resistance was constant regardless of the overlapped shape when the screen was overlapped into several layers. Increasing the number of layers of the screen, internal resistance increased significantly more, and pressure loss caused by the screen also increased linearly when the wind speed was certain conditions, but permeability had no tendency. In the future, the results of this study will be applied to the computational fluid dynamics simulation. The simulation models will be also validated in advance by wind tunnel experiments. It will provide standard of a design for constructing windbreak fence.

A Study on the Appropriateness of Wind Pressure Resistance Test in KS F 2622 (KS F 2622에서 복합계열에 대한 성능 추가시 풍압 저항성 시험 평가방법의 적정성 검토)

  • Kang, Hyo-Jin;Kim, Soo-Yeon;Oh, Sang-Keun
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2018.11a
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    • pp.187-188
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    • 2018
  • In this study, wind pressure resistance test was carried out among the nine test items of KS F 2622 using five types of water-tight material. After comparing the results with the performance range of the current KS F 2622 wind pressure resistance test, it is recommended to check the adequacy of the addition of the combined series.

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