Abstract
Lightness and flexibility of membrane roofs make them very sensitive to any external load. One of the most
important parameters that controls their behavior, especially under wind load is the sag/span ratio of edge cables. Based on the
value of the pretension force in the edge cables and the horizontal projection of the actual area covered by the membrane, an
optimized design range of cable sag/span ratios has been determined through carrying on several membrane form-finding
analyses. Fully coupled fluid structure dynamic analyses of these membrane roofs are performed under wind load with several
conditions using the CFD method. Through investigating the numerical results of these analyses, the behavior of membrane
roofs with cables sag/span ratios selected from the previously determined optimized design range has been evaluated.
Address
Hesham Zieneldin, Mohammed Heweity, Mohammed Abdelnabi and Ehab Hendy: Department of structural Engineering, Faculty of Engineering, Alexandria University, ElHoriya Street, Alshatby, Alexandria, Egypt
Abstract
The analytical model of tornado vortices plays an essential role in tornado wind description and tornado-resistant
design of civil structures. However, there is still a lack of guidance for the selection and application of tornado analytical models
since they are different from each other. For single-cell tornado vortices, this study conducts a comparative study on the velocity
characteristics of the analytical models based on numerically simulated tornado-like vortices (TLV). The single-cell stage TLV is
first generated by Large-eddy simulations (LES). The spatial distribution of the three-dimensional mean velocity of the typical
analytical tornado models is then investigated by comparison to the TLV with different swirl ratios. Finally, key parameters are
given as functions of swirl ratio for the direct application of analytical tornado models to generate full-scale tornado wind field.
Results show that the height of the maximum radial mean velocity is more appropriate to be defined as the boundary layer
thickness of the TLV than the height of the maximum tangential mean velocity. The TLV velocity within the boundary layer can
be well estimated by the analytical model. Simple fitted results show that the full-scale maximum radial and tangential mean
velocity increase linearly with the swirl ratio, while the radius and height corresponding to the position of these two velocities
decrease non-linearly with the swirl ratio.
Address
Han Zhang:1)Key Laboratory of Concrete & Prestressed Concrete Structures of Ministry of Education, Southeast University, Nanjing 211189, China
2)Department of Mechanical Engineering, National University of Singapore, Singapore 119260, Singapore
Hao Wang: Key Laboratory of Concrete & Prestressed Concrete Structures of Ministry of Education, Southeast University, Nanjing 211189, China
Zhenqing Liu:School of Civil and Hydraulic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Zidong Xu:Key Laboratory of Concrete & Prestressed Concrete Structures of Ministry of Education, Southeast University, Nanjing 211189, China
Boo Cheong Khoo:Department of Mechanical Engineering, National University of Singapore, Singapore 119260, Singapore
Changqing Du:State Grid Jiangsu Electric Power Co., Ltd, Nanjing, 210000, China
Abstract
The large eddy simulation (LES) of the flow around a circular cylinder is not only affected by the sub-grid scale
(SGS) model but also by the grid resolution of the computational domain. To study the influence of different grids on the LES
results, the LES simulations of the flow around a circular cylinder with different grids at Reynolds number (Re) = 3900 was
performed. A circular computational domain with different radial growth rates and circumferential and spanwise grid numbers
was adopted for the simulations. Meanwhile, the aerodynamic forces, wind pressure coefficients, mean and instantaneous flow
fields, and the effect of grid resolution on them were comprehensively analyzed. The results indicate that the lift coefficient,
wind pressure coefficient, and recirculation length are significantly affected by the radial growth rate of the grid and the
circumferential grid number. The spanwise grid number has a significant influence on the three-dimensionality of the flow and
plays an important role in velocity fluctuations in the wake region. Nevertheless, the aerodynamic coefficients and recirculation
length are not sufficiently sensitive to the grid number in the spanwise direction. By comparing the results, it can be concluded
that suitable and reliable LES results can be obtained when the radial growth rate is 1.03 or 1.05, the circumferential grid number
is 160, 200, or 240, and the spanwise grid number is 64. A radial growth rate 1.05, circumferential grid number 160, and
spanwise grid number 64 are recommended to reduce the grid amount and further improve the efficiency.
Key Words
aerodynamic characteristics; circular cylinder; flow field characteristics; grid resolution; LES simulation
Address
Hongmiao Jing:1)State Key Laboratory of Mechanical Behavior and System Safety of Traffic Engineering Structures,
Shijiazhuang Tiedao University, Shijiazhuang 050043, China 2)Innovation Center for Wind Engineering and Wind Energy Technology of Hebei Province, Shijiazhuang 050043, China 3)School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang 050043, China
Jitao Zhang:School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang 050043, China
Qingkuan Liu:1)State Key Laboratory of Mechanical Behavior and System Safety of Traffic Engineering Structures,
Shijiazhuang Tiedao University, Shijiazhuang 050043, China 2)Innovation Center for Wind Engineering and Wind Energy Technology of Hebei Province, Shijiazhuang 050043, China 3)School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang 050043, China
Yangxue Wang:School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang 050043, China
Abstract
In this study, the effect of sea surface temperature (SST) on the distribution of vertical wind speed in the
atmospheric boundary layer of coastal areas was analyzed. In general, coastal areas are known to be more susceptible to various
meteorological factors than inland areas due to interannual changes in sea surface temperature. Therefore, the purpose of this
study is to analyze the relationship between sea surface temperature (ERA5) and wind resource data based on the meteorological
mast of HØvsØre, the test bed area of the onshore wind farm in the coastal area of Denmark. In addition, the possibility of coastal
disasters caused by abnormal vertical wind shear due to changes in sea surface temperature was also analyzed.
According to the analysis of the correlation between the wind resource data at met mast and the sea surface temperature by
ERA5, the wind speed from the sea and the vertical wind shear are stronger than from the inland, and are vulnerable to seasonal
sea surface temperature fluctuations. In particular, the abnormal vertical wind shear, in which only the lower wind speed was
strengthened and appeared in the form of a nose, mainly appeared in winter when the atmosphere was near-neutral or stable, and
all occurred when the wind blows from the sea. This phenomenon usually occurred when there was a sudden change in sea
surface temperature within a short period of time.
Abstract
We study the progressive full-scale wind tunnel tests on a high solidity vertical axis wind turbine (VAWT) for
various tip speeds and pitch angles to understand the VAWT shaft system's dynamics using 0-1 Test for chaos. We identify that
while varying rotor speed (tip speed) of the turbine, the system's dynamics change from periodic to chaotic through quasiperiodic and strange non-chaotic (SNA) states. The present study is the first experimental evidence for the existence of these
states in the VAWT shaft system to the best of our knowledge. Using the asymptotic growth value Kc in 0-1 test, when the
turbine operates at the low tip speeds and high pitch angles for low incoming wind speeds, the system behaves periodic (Kc ≈ 0).
However, when the incoming wind speed increases further the system's dynamics shift from periodic to chaotic vibrations
through quasi-periodic and SNA. This phenomenon is due to the dynamic stalling of blades which induces chaotic vibration in
the VAWT shaft system. Further, the singular continuous spectrum method validates the presence of SNA and differentiates the
SNA from chaotic vibrations.
Key Words
chaotic vibrations; dynamic stalling; high solidity VAWT; pitch angle; SNA; tip speed
Address
C.B. Maheswaran:Turbulence and Flow Control Lab, School of Mechanical Engineering, SASTRA Deemed University, Thanjavur-613 401, India
R. Gopal:Centre for Nonlinear Science & Engineering, School of Electrical & Electronics Engineering, SASTRA Deemed University,
Thanjavur -613 401, India
V.K. Chandrasekar:Centre for Nonlinear Science & Engineering, School of Electrical & Electronics Engineering, SASTRA Deemed University,
Thanjavur -613 401, India
S. Nadaraja Pillai:Turbulence and Flow Control Lab, School of Mechanical Engineering, SASTRA Deemed University, Thanjavur-613 401, India
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