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CONTENTS
Volume 22, Number 6, June 2016
 

Abstract
In this paper, the analysis of hyperbolic cooling tower on elastic subsoil exposed to unsymmetrical wind loading is presented. Modified Vlasov foundation model is used to determine the soil parameters as a function of vertical deformation profile within subsoil. The iterative parameter updating procedure involves the use of Open Application Programming Interface (OAPI) feature of SAP2000 to provide two way data flow during execution. A computing tool coded in MATLAB employing OAPI is used to perform the analysis of hyperbolic cooling tower with supporting columns over a hollow annular raft founded on elastic subsoil. The analysis of such complex soil-structure system is investigated under self-weight and unsymmetrical wind load. The response of the cooling tower on elastic subsoil is compared with that of a tower that its supporting raft foundation is treated as fixed at the base. The results show that the effect of subsoil on the behavior of cooling tower is considerable at the top and bottom of the wall as well as supporting columns and raft foundation. The application of a full-size cooling tower has demonstrated that the procedure is simple, fast and can easily be implemented in practice.

Key Words
hyperbolic cooling tower; modified Vlasov model; unsymmetrical wind load; open application programming interface; finite element analysis

Address
Ali I. Karakas, Korhan Ozgan and Ayse T. Daloglu: Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey

Abstract
This paper deals with the comparison of different control strategies for the Induction generators in wind energy conversion system. Mainly, two types of induction machines, Self excited induction generator (SEIG) and doubly Fed Induction generators (DFIG) are studied. The different control strategies for SEIG and DFIG are compared. For SEIG, Electronic load Controller mechanism, Static Compensator based voltage regulator are studied. For DFIG the main control strategy namely vector control, direct torque control and direct power control are implemented. Apart from these control strategies for both SEIG and DFIG to improve the performance, the ANFIS based controller is introduced in both STATCOM and DTC methods. These control methods are simulated using MATLAB/SIMULINK and performances are analyzed and compared.

Key Words
Self excited induction generator (SEIG); doubly fed induction generator (DFIG); Electronic load Controller (ELC); Static Compensator (STATCOM); Adaptive Neuro Fuzzy Interface System (ANFIS); Vector control (VC); Direct Torque control (DTC) and Direct power control (DPC)

Address
D. Giribabu and Maloy Das: NIT Kurukshetra, Department of Electrical Engineering, Kurukshetra-136119, India
Amit Kumar: NIT Kurukshetra, School of Renewable Energy, Kurukshetra-136119, India

Abstract
Conical vortices generated at the corner regions of large-span flat roofs have been investigated by using the Particle Image Velocimetry (PIV) technique. Mean and instantaneous vector fields for velocity, vorticity, and streamlines were measured at three visual planes and for two different flow angles of 15. The results indicated that conical vortices occur when the wind is not perpendicular to the front edge. The location of the leading edge corresponding to the negative peak vorticity and maximum turbulent kinetic energy was found at the center of the conical vortex. The wind pressure reaches the maximum near the leading edge roof corner, and a triangle of severe suctions zone appears downstream. The mean pressure in uniform flow is greater than that under turbulent flow condition, while a significant increase in the fluctuating wind pressure occurs in turbulent streams. From its emergence to stability, the shape of the vortex cross-section is nearly elliptical, with increasing area. The angle that forms between the vortex axis and the leading edge is much smaller in turbulent streams. The detailed flow structures and characteristics obtained through FLUENT simulation are in agreement with the experimental results. The three dimensional (3-D) structure of the conical vortices is clearly observed from the comprehensive arrangement of several visual planes, and the inner link was established between the vortex evolution process, vortex core position and pressure distribution.

Key Words
flat roof; conical vortices; PIV; flow structure; FLUENT simulation

Address
Huyue Sun and Jihong Ye: Key Laboratory of Concrete and Pre-stressed Concrete Structures of China Ministry of Education, Southeast University, Nanjing 210018, China


Abstract
Downbursts are of great harm to transmission lines and many towers can even be destroyed. The downburst wind field model by Chen and Letchford was applied, and the wind loads of two typical transmission towers in inland areas and littoral areas were calculated separately. Spatial finite element models of the transmission towers were established by elastic beam and link elements. The wind loads as well as the dead loads of conductors and insulators were simplified and applied on the suspension points by concentrated form. Structural analysis on two typical transmission towers under normal wind and downburst was completed. The bearing characteristics and the failure modes of the transmission towers under downburst were determined. The failure state of tower members can be judged by the calculated stress ratios. It shows that stress states of the tower members were mainly controlled by 45 degree wind load. For the inland areas with low deign wind velocity, though the structural height is not in the highest wind velocity zone of downburst, the wind load under downburst is much higher than that under normal wind. The main members above the transverse separator of the legs will be firstly destroyed. For the littoral areas with high deign wind velocity, the wind load under downburst is lower than under normal wind. Transmission towers are not controlled by the wind loads from downbursts in design process.

Key Words
downburst; wind speed profile; transmission tower; wind load; failure mode

Address
FengLi Yangand HongJie Zhang: Engineering Mechanics Department, China Electric Power Research Institute, Beijing 100055, China

Abstract
This paper presents a wind tunnel study of wind loads of the large billboard structures with two-plate and three-plate configurations. Synchronous dynamic pressures on the surfaces of plates are measured, and the characteristics of local pressures, integrated forces on each individual plate and on the overall structures are investigated. The influences of wind direction and plate configuration on wind load characteristics, and the contributions of overall crosswind load and torque to the stress responses are examined. The results showed that the wind load characteristics of windward plate in both two- and three-plate configurations are very similar. The contribution of overall crosswind load makes the total resultant force from both alongwind and crosswind loads less sensitive to wind direction in the case of three-plate configuration. The overall torque is lower than the value specified in current codes and standards, and its contribution is less significant in both two-plate and three-plate configurations.

Key Words
billboards; wind loading; wind tunnel tests; wind pressures; drag force; torque

Address
Dahai Wang: Department of Civil Engineering, Wuhan University of Technology, Wuhan Hubei, 430070, China;
National Wind Institute, Department of Civil, Environmental and Construction Engineering, exas Tech University, Lubbock TX, 79409, USA
Xinzhong Chen: National Wind Institute, Department of Civil, Environmental and Construction Engineering,
Texas Tech University, Lubbock TX, 79409, USA
Jie Li: The State Key Laboratory on Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, China
Hao Cheng: Department of Civil Engineering, Wuhan University of Technology, Wuhan Hubei, 430070, China







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