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CONTENTS
Volume 19, Number 1, July 2014
 

Abstract
Rail-mounted cranes can be easily damaged by a sudden gust of wind while working at a running speed, due to the large mass and high barycenter positions. In current designs, working rail-mounted cranes mainly depend on wheel braking torques to resist large wind load. Regular brakes, however, cannot satisfactorily stop the crane, which induces safety issues of cranes and hence leads to frequent crane accidents, especially in sudden gusts of wind. Therefore, it is necessary and important to study the braking performance of working rail mounted cranes under wind load. In this study, a simplified mechanical model was built to simulate the working rail mounted gantry crane, and dynamic analysis of the model was carried out to deduce braking performance equations that reflect the qualitative relations among braking time, braking distance, wind load, and braking torque. It was shown that, under constant braking torque, there existed inflection points on the curves of braking time and distance versus windforce. Both the braking time and the distance increased sharply when wind load exceeded the inflection point value, referred to as the threshold windforce. The braking performance of a 300 ton shipbuilding gantry crane was modeled and analyzed using multibody dynamics software ADAMS. The simulation results were fitted by quadratic curves to show the changes of braking time and distance versus windforce under various mount of braking torques. The threshold windforce could be obtained theoretically by taking derivative of fitted curves. Based on the fitted functional relationship between threshold windforce and braking torque, theoretical basis are provided to ensure a safe and rational design for crane wind-resistant braking systems.

Key Words
rail mounted crane; dynamic analysis; braking performace; ADAMS; wind-resistant design

Address
Hui Jin and Da Chen: Jiangsu Key Laboratory of Engineering Mechanics & Key Laboratory of Concrete and Prestressed Concrete Structures of Ministy of Education, Southeast University, Nanjing, 210096, China

Abstract
This paper describes partial turbulence simulation and validation of the aerodynamic pressures on building models for an open-jet small-scale 12-Fan Wall of Wind (WOW) facility against their counterparts in a boundary-layer wind tunnel. The wind characteristics pertained to the Atmospheric Boundary Layer (ABL) mean wind speed profile and turbulent fluctuations simulated in the facility. Both in the wind tunnel and the small-scale 12-Fan WOW these wind characteristics were produced by using spires and roughness elements. It is emphasized in the paper that proper spectral density parameterization is required to simulate turbulent fluctuations correctly. Partial turbulence considering only high frequency part of the turbulent fluctuations spectrum was simulated in the small-scale 12-Fan WOW. For the validation of aerodynamic pressures a series of tests were conducted in both wind tunnel and the small-scale 12-fan WOW facilities on low-rise buildings including two gable roof and two hip roof buildings with two different slopes. Testing was performed to investigate the mean and peak pressure coefficients at various locations on the roofs including near the corners, edges, ridge and hip lines. The pressure coefficients comparisons showed that open-jet testing facility flows with partial simulations of ABL spectrum are capable of inducing pressures on low-rise buildings that reasonably agree with their boundary-layer wind tunnel counterparts.

Key Words
wall of wind; low-rise building; spectrum; roof; partial turbulence; pressure coefficient

Address
Tuan-Chun Fu:Department of Civil and Environmental Engineering, Florida International University, 10555 West Flagler St., Miami, FL, 33174, USA
Arindam Gan Chowdhury:Department of Civil and Environmental Engineering, International Hurricane Research Center, Florida International University, 10555 West Flagler St., Miami, FL, 33174, USA
Girma Bitsuamlak: Department of Civil and Environmental Engineering, The University of Western Ontario, London, ON, Canada
Thomas Baheru: Department of Civil and Environmental Engineering, Florida International University, 10555 West Flagler St., Miami, FL, 33174, USA


Abstract
A numerical simultaneous solution involving a linear elastic model was applied to study the fluid-structure interaction (FSI) of membrane structures under wind actions, i.e., formulating the fluid-structure system with a single equation system and solving it simultaneously. The linear elastic model was applied to managing the data transfer at the fluid and structure interface. The monolithic equation of the FSI system was formulated by means of variational forms of equations for the fluid, structure and linear elastic model, and was solved by the Newton-Raphson method. Computation procedures of the proposed simultaneous solution are presented. It was applied to computation of flow around an elastic cylinder and a typical FSI problem to verify the validity and accuracy of the method. Then fluid-structure interaction analyses of a saddle membrane structure under wind actions for three typical cases were performed with the method. Wind pressure, wind-induced responses, displacement power spectra, aerodynamic damping and added mass of the membrane structure were computed and analyzed.

Key Words
membrane structures; vibration under wind actions; fluid-structure interaction; numerical simultaneous solution

Address
Fang-jin Sun:College of Civil Engineering and Architecture, Liaoning Technical University, Fuxin, Liaoning, 123000, China;
State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
Ming Gu: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China

Abstract
This paper presents the results of wind tunnel studies and numerical studies on a \'+\' plan shaped tall building. The experiment was carried out in an open circuit wind tunnel on a 1:300 scale rigid model. The mean wind pressure coefficients on all the surfaces were studied for wind incidence angle of 0 and 45. Certain faces were subjected to peculiar pressure distribution due to irregular formation of eddies caused by the separation of wind flow. Moreover, commercial CFD packages of ANSYS were used to demonstrate the flow pattern around the model and pressure distribution on various faces. k-e and SST viscosity models were used for numerical study to simulate the wind flow. Although there are some differences on certain wall faces, the numerical result is having a good agreement with the experimental results for both wind incidence angle.

Key Words
tall building; computational fluid dynamics (CFD); vortex shedding; pressure coefficients; wind tunnel testing; wind incidence angle

Address
Souvik Chakraborty:Bengal Engineering and Science University Shibpur, India
Sujit Kumar Dalui:Faculty of Engineering (Civil), Bengal Engineering and Science University, Shibpur, India
Ashok Kumar Ahuja: Faculty of Engineering (Civil), Indian Institute of Technology Roorkee, India

Abstract
The computational fluid dynamic is used to explore new aspects of the hill flow. This analysis focuses on flow dependency and the comparison of results from measurements and simulations to show an optimization turbulent model and the possibility of replacing measurements with simulations. The first half of the paper investigates a suitable turbulence model for determining a suitable site for a wind turbine. Results of the standard k-emodel are compared precisely with the measurements taken in front of the hilltop, The Reynolds Stress Model showed exact results after 1.0 times of hill steepness but the standard k-e model and standard k-w model showed greater underestimation. In addition, velocity flow over Pha Taem hill topography and the reference geometry shape were compared to find a suitable site for a turbine in case the actual hill structure was associated with the trapezoid geometric shape. Further study of geometry shaped hills and suitable sites for wind turbines will be reported elsewhere.

Key Words
computational fluid dynamics; turbulent model; suitable site; wind turbine; trapezoid hill

Address
Thitipong Unchai:Department of Physics, Faculty of Science,Ubonratchathani Rajabhat University, Thailand
Adun Janyalertadun: Department of Mechanical Engineering, Faculty of Engineering, Ubonratchathani University, Thailand

Abstract
The dynamics of a tornado-like vortex with touching down is investigated by using the LES turbulence model. The detailed information of the turbulent flow fields is provided and the force balances in radial and vertical directions are evaluated by using the time-averaged axisymmetric Navier-Stokes equations. The turbulence has slightly influence on the mean flow fields in the radial direction whereas it shows strong impacts in the vertical direction. In addition, the instantaneous flow fields are investigated to clarify and understand the dynamics of the vortex. An organized swirl motion is observed, which is the main source of the turbulence for the radial and tangential components, but not for the vertical component. Power spectrum analysis is conducted to quantify the organized swirl motion of the tornado-like vortex. The gust speeds are also examined and it is found to be very large near the center of vortex.

Key Words
dynamics of tornado-like vortex with touching down; LES; turbulent flow fields; force balances; organized swirl motion; power spectrum; gust speed

Address
Takeshi Ishihara and Zhenqing Liu: Department of Civil Engineering , School of Engineering, The University of Tokyo, 7-3-1 Hongou, Bunkyo-ku, Tokyo 113-8656, Japan


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