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CONTENTS
Volume 21, Number 4, October 2015
 

Abstract
Moore, Oklahoma was hit by an EF5 tornado on May 20, 2013. The tornado track slightly overlapped with two previous tornadoes that occurred on May 3, 1999 and May 8, 2003 respectively. A research team from Texas Tech University was deployed to investigate the performance of shelters based on observation of their post-storm conditions. Sixty-one shelter units were further documented by size, manufacturer, and date of installation if available. Then they were crossed referenced with the external databases to determine their compliance with design and construction standards by the International Code Council/National Storm Shelter Association and/or criteria from the Federal Emergency Management Agency publications. Wind intensity was estimated for each shelter location using the EF scale. Results showed a marked increase in the number of exterior underground shelters as well as the popularity of a new in-garage floor underground shelter design. All of the units provided protection for their occupants with no loss of life reported. However, one older shelter had a door failure due to neglect of maintenance. Recommendations were made to improve future performance of shelters.

Key Words
tornado; storm shelter; safe room; shelter; Moore, Oklahoma 2013 tornado

Address
Pataya L. Scott:National Wind Institute, Texas Tech University, Lubbock, Texas 79409, USA
Daan Liang:National Wind Institute, Texas Tech University, Lubbock, Texas 79409, USA;
Department of Civil, Environmental, and Construction Technology, Texas Tech University, Lubbock,Texas 79409, USA



Abstract
This study investigated aerodynamic characteristics of an inclined square prism experimentally. Pressure measurements were performed on a static square prism with a series of inclinations including forward inclinations (inclined to the upwind direction) and backward inclinations (inclined to the downwind direction). The prism with a vertical attitude was also tested for comparisons. Based on the pressure data, influences of the inclinations on aerodynamic characteristics (e.g., force coefficients, pressure distributions on the surfaces, and vortex shedding features) of the square prism were evaluated in detail. The results show that the inclinations have significant effects on these aerodynamic characteristics. Furthermore, the influences of the forward and backward inclinations are quite different.

Key Words
aerodynamic characteristic; inclined prism; wind tunnel test; square prism

Address
Gang Hu and K.C.S. Kwok:Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China;
Institute for Infrastructure Engineering, Western Sydney University, Penrith, NSW, 2751, Australia
K.T. Tse and Z.S. Chen: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China



Abstract
To explore the favorable structural system of cable-stayed bridges with ultra-kilometer main span, based on a fully self-anchored cable-stayed bridge with 1400 m main span, a partially earth-anchored cable-stayed bridge scheme with the same main span is designed. Numerical investigation on the dynamic characteristics, aerostatic and aerodynamic stability of both two bridge schemes is conducted, and the results are compared to those of a suspension bridge with similar main span, and considering from the aspect of wind stability, the feasibility of using partially earth-anchored cable-stayed bridge in super long-span bridges with ultra-kilometer main span is discussed. Moreover, the effects of structural design parameters including the length of earth-anchored girder, the number of auxiliary piers in side span, the height and width of girder, the tower height etc on the dynamic characteristics, aerostatic and aerodynamic stability of a partially earth-anchored cable-stayed bridge are analyzed, and their reasonable values are proposed. The results show that as compared to fully self-anchored cable-stayed bridge and suspension bridge with similar main span, the partially earth-anchored cable-stayed bridge has greater structural stiffness and better aerostatic and aerodynamic stability, and consequently becomes a favorable structural system for super long-span bridges with ultra-kilometer main span. The partially earth-anchored cable-stayed bridge can achieve greater stiffness and better wind stability under the cases of increasing the earth-anchored girder length, increasing the height and width of girder, setting several auxiliary piers in side span and increasing the tower height.

Key Words
partially earth-anchored cable-stayed bridge; dynamic characteristics, aerostatic stability; aerodynamic stability; structural design parameters

Address
Xin-jun Zhang and Mei Yao: College of Civil Engineering & Architecture, Zhejiang University of Technology, Hangzhou 310014, P.R. China

Abstract
This paper discusses the processing of the wind loads measured in wind tunnel tests by means of multi-channel pressure scanners, in order to compute the response of 3D structures to atmospheric turbulence in the time domain. Data compression and the resulting computational savings are still a challenge in industrial contexts due to the multiple trial configurations during the construction stages. The advantage and robustness of the bi-orthogonal decomposition (BOD) is demonstrated through an example, a sail glass of the Fondation Louis Vuitton, independently from any tentative physical interpretation of the spatio-temporal decomposition terms. We show however that the energy criterion for the BOD has to be more rigorous than commonly admitted. We find a level of 99.95 % to be necessary in order to recover the extreme values of the loads. Moreover, frequency limitations of wind tunnel experiments are sometimes encountered in passing from the scaled model to the full scale structure. These can be alleviated using a spectral extension of the temporal function terms of the BOD.

Key Words
pressure loads; wind tunnel; wind gust; temporal simulation; bi-orthogonal decomposition

Address
Pascal Hémon:LadHyX, CNRS-Ecole Polytechnique, F-91128 Palaiseau, France

Abstract
In this paper, an integrator based method to estimate the effective wind speed in wind turbine systems is proposed. First, the aerodynamic torque was accurately estimated through a proportional gain based observer where the generator speed is the measured output of the system. The torque signal contains not only useful frequencies of the wind, but also high frequencies and the ones due to structural vibration. The useful information of the wind signal is low frequency. A spectral analysis permitted the determination of the useful frequencies. The high frequencies were then filtered before introducing the torque signal in the wind speed observer. The desired effective wind speed was extracted through an integrator based observer using the previously estimated aerodynamic torque. The strength of the method is to avoid numerical solutions used in literature of the wind speed estimation. The effectiveness of the proposed wind speed estimator and its use to control the generator speed has been tested under turbulent situations using the FAST software (Fatigue, Aerodynamics, Structures, and Turbulence), for large scale Megawatt turbine.

Key Words
feed forward control; wind turbine power generation system; wind speed estimation; wind turbine control; FAST software

Address
Younes Ait Elmaati, Lhoussain El Bahir and Khalid Faitah: Laboratory of Electrical Engineering and Control Systems (LGECOS), National School of Applied Sciences, Cadi Ayyad University, Av. Abdelkarim El khattabi B.P 575, Marrakech 40000, Morocco


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