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CONTENTS
Volume 16, Number 2, February 2013
 

Abstract
A wind tunnel test of a scaled-down model and field measurement were effective methods for elucidating the aerodynamic behavior of a chimney under a wind load. Therefore, the relationship between the results of the wind tunnel test and the field measurement had to be determined. Accordingly, the set-up and testing method in the wind tunnel had to be modified from the field measurement to simulate the real behavior of a chimney under the wind flow with a larger Reynolds number. It enabled the results of the wind tunnel tests to be correlated with the field measurement. The model surface roughness and different turbulence intensity flows were added to the test. The simulated results of the wind tunnel test agreed with the full-scale measurements in the mean surface pressure distribution behavior.

Key Words
chimney; full-scale measurement; Reynolds number; pressure; surface roughness; wind tunnel test

Address
Chern-Hwa Chen : 1Department of Civil and Environmental Engineering, National University of Kaohsiung, Kaohsiung, Taiwan
Cheng-Hsin Chang and Yuh-Yi Lin : Department of Civil Engineering, Tamkang University, New Taipei City, Taiwan

Abstract
Output-only modal parameter identification is based on the assumption that external forces on a linear structure are white noise. However, harmonic excitations are also often present in real structural vibrations. In particular, it has been realized that the use of forced acceleration responses without knowledge of external forces can pose a problem in the modal parameter identification, because an external force is imparted to its impulse acceleration response function. This paper provides a three-stage identification procedure as a solution to the problem of harmonic and white noise excitations in the acceleration responses of a linear dynamic system. This procedure combines the uses of the mode indicator function, the complex mode indication function, the enhanced frequency response function, an iterative rational fraction polynomial method and mode shape inspection for the correlation-related functions of the force-embedded acceleration responses. The procedure is verified via numerical simulation of a five-floor shear building and a two-dimensional frame and also applied to ambient vibration data of a large-span roof structure. Results show that the modal parameters of these dynamic systems can be satisfactorily identified under the requirement of wide separation between vibration modes and harmonic excitations.

Key Words
acceleration; ambient vibration; correlation; excitations; frequency response; identification; modal model; mode indication function

Address
C.J. Ku, Y. Tamura and A. Yoshida : 1Department of Architectural Engineering, Tokyo Polytechnic University, Iiyama, Japan
K. Miyake: MHS Planners, Architects & Engineers, Tokyo, Japan
L.S. Chou: Yuh-Ing Junior College of Health Care & Management, General Education Center, Kaohsiung, Taiwan

Abstract
The flow around two rectangular cylinders with aspect ratio of 0.5 in a tandem arrangement, was investigated using pressure measurements (in a wind tunnel) and flow visualizations (in a water tunnel) in the range of P/h from 0.6 to 4.0. Four flow patterns were identified, and processes of shear layers wrapping around, the shear layer reattachment, vortices wrapping around and vortices impingement, were observed. Mean and rms pressure distributions, flow visualizations and Strouhal numbers were presented and discussed. The paper revealed that the variations of Strouhal numbers were associated with the shear layers or vortex interference around two cylinders.

Key Words
rectangular cylinders; pressure distributions; flow visualizations; flow patterns

Address
Letian Yang, Xuejun Zhao and Weimin Zhang : China Academy of Aerospace Aerodynamics, Beijing, China, 100074
Letian Yang and Zhifu Gu : LTCS and College of Engineering, Peking University, Beijing, China, 100871

Abstract
This paper presents results from a wind tunnel study that examined the drag coefficient and wind flow over an asymmetric wave train immersed in turbulent boundary layer flow. The modeled wavy surface consisted of eight replicas of a statistically-valid hurricane-generated wave, located near the coast in the shoaling wave region. For an aerodynamically rough model surface, the air flow remained attached and a pronounced speed-up region was evident over the wave crest. A wavelength-averaged drag coefficient was determined using the wind profile method, common to both field and laboratory settings. It was found that the drag coefficient was approximately 50% higher than values obtained in deep water hurricane conditions. This study suggests that nearshore wave drag is markedly higher than over deep water waves of similar size, and provides the groundwork for assessing the impact of nearshore wave conditions on storm surge modeling and coastal wind engineering.

Key Words
drag coefficient; shoaling wave; wind stress; profile method; log-law

Address
Brian C. Zachry and Delong Zuo: Wind Science and Engineering Research Center, Texas Tech University, Lubbock, TX 79409, USA
Brian C. Zachry : AIR Worldwide, Boston, MA 02116, USA
Chris W. Letchford : Department of Civil and Environmental Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA
Andrew B. Kennedy : Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556,
USA

Abstract
One of the key issues affecting the promotion of solar water heaters in Taiwan is the severe impact of typhoon each year. An experimental study was conducted to investigate the wind uplift characteristic of a solar collector model with and without a guide plate. The guide plate with different lengths and orientations with respect to wind direction was adopted. It is found that the wind uplift of a solar collector is associated with the tilt angle of the flat panel as expected. A cavity formed between the guide plate and the flat panel has a significant effect on the distributions of streamwsie and lateral pressure. Reduction in uplift is essentially coupled with the projected area of a guide plate on the lower surface of the tilt flat panel.

Key Words
guide plate; solar collector; uplift; wind load, typhoon

Address
K.M. Chung : Aerospace Science and Technology Research Center, National Cheng Kung University, Tainan, Taiwan
K.C. Chang , C.K. Chen and C.C. Chou : Department of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan


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