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CONTENTS
Volume 30, Number 1, January 2020
 

Abstract
The loss prediction and assessment during extreme events such as wind hazards is always crucial for the group low-rise residential buildings. This paper analyses the effect of variation in building density on wind-induced loss for low-rise buildings and proposes a loss assessment method consequently. It is based on the damage matrices of the building envelope structures and the main load-bearing structure, which includes the influence factors such as structure type, preservation degree, building density, and interaction between different envelope components. Accordingly, based on field investigation and engineering experience, this study establishes a relevant building direct economic loss assessment model. Finally, the authors develop the Typhoon Disaster Management System to apply this loss assessment methodology to practice.

Key Words
wind hazard; loss assessment; residential buildings; Monte Carlo; ArcGIS

Address
Mingxin Li and Guoxin Wang: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China

Abstract
This paper reports the study on development and verification of numerical models and analyzes of flow at high speed around structural elements in the shape of a curved pipe (e.g., a fragment of a water slide). Possibility of engineering estimation of wind forces acting on an object in the shape of a helix is presented, using relationships concerning toroidal and cylindrical elements. Determination of useful engineering parameters (such as aerodynamic forces, pressure distribution, and air velocity field) is presented, impossible to obtain from the existing standard EN 1991-1-4 (the so-called wind standard). For this purpose, flow at high speed around a torus and helix, arranged both near planar surface and high above it, was analyzed. Analyzes begin with the flow around a cylinder. This is the simplest object with a circular cross-section and at the same time the most studied in the literature. Based on this model, more complex models are analyzed: first in the shape of half of a torus, next in the shape of a helix.

Key Words
finite volume method; finite element method; computational fluid dynamics; fluid–structure interaction; wind engineering; wind action; water slide

Address
Agnieszka Padewska-Jurczak and Piotr Szczepaniak: Department of Mechanics and Bridges, Faculty of Civil Engineering, Silesian University of Technology, Akademicka 5, 44-100 Gliwice, Poland

Zbigniew Buliński: Institute of Thermal Technology, Faculty of Energy and Environmental Engineering,
Silesian University of Technology, Konarskiego 18, 44-100 Gliwice, Poland

Abstract
This paper presents a comparative structural analysis of lattice hybrid tower with six legs with conventional tubular steel tower for an onshore wind turbine using finite element method. Usually a lattice hybrid tower will have a conventional industry standard \'L\' profile section for the lattice construction with four legs. In this work, the researcher attempted to identify and analyze the strength of six legged lattice hybrid tower designed with a special profile instead of four legged L profile. And to compare the structural benefits of special star profile with the conventional tubular tower. Using Ansys, a commercial FEM software, both static and dynamic structural analyses were performed. A simplified finite element model that represents the wind turbine tower was created using Shell elements. An ultimate load condition was applied to check the stress level of the tower in the static analysis. For the dynamic analysis, the frequency extraction was performed in order to obtain the natural frequencies of the tower.

Key Words
structural dynamics; wind energy; wind loads; finite element methods; lattice hybrid tower

Address
R. Kumaravel and A. Krishnamoorthy: School of Mechanical Engineering, Sathyabama Institute of Science and Technology, Chennai, India

Abstract
To investigate the motion-induced aeroelastic effects (or aerodynamic feedback effects) on a square cylinder in uniform flow, a series of wind tunnel tests involving the pressure measurement of a rigid model (RM) and simultaneous measurement of the pressure and vibration of an aeroelastic model (AM) have been systematically carried out. More specifically, the aerodynamic feedback effects on the structural responses, on the mean and root-mean-square wind pressures, on the power spectra and coherence functions of wind pressures at selected locations, and on the aerodynamic forces were investigated. The results indicated the vibration in the lock-in range made the shedding vortex more coherent and better organized, and hence presented unfavorable wind-induced effects on the structure. Whereas the vibration in the non-lock-in range generally showed insignificant effects on the flow structures surrounding the square cylinder.

Key Words
vortex-induced vibration; rigid model test; aeroelastic model test; square cylinder

Address
Dongmei Huang and Shiqing He: School of Civil Engineering, Central South University, Changsha, Hunan 410075, China

Teng Wu: Department of Civil, Structural and Environmental Engineering, University at Buffalo, Buffalo, NY 14260, USA

Abstract
Wind tunnel test is one of the most important means to study the flutter performance of bridges, but there are blockage effects in flutter test due to the size limitation of the wind tunnel. On the other hand, the size of computational domain can be defined by users in the numerical simulation. This paper presents a study on blockage effects of a simplified box girder by computation fluid dynamics (CFD) simulation, the blockage effects on the aerodynamic characteristics and flutter performance of a long-span suspension bridge are studied. The results show that the aerodynamic coefficients and the absolute value of mean pressure coefficient increase with the increase of the blockage ratio. And the aerodynamic coefficients can be corrected by the mean wind speed in the plane of leading edge of model. At each angle of attack, the critical flutter wind speed decreases as the blockage ratio increases, but the difference is that bending-torsion coupled flutter and torsional flutter occur at lower and larger angles of attack respectively. Finally, the correction formula of critical wind speed at 0o angle of attack is given, which can provide reference for wind resistance design of streamlined box girders in practical engineering.

Key Words
blockage effects; flutter performance; numerical simulation; wind speed correction; streamlined box girder

Address
Yongle Li, Junjie Guo, Xingyu Chen, Haojun Tang and Jingyu Zhang: Department of Bridge Engineering, Southwest Jiaotong University, Chengdu 610031, China

Abstract
Modelling incompressible, neutrally stratified, barotropic, horizontally homogeneous and steady-state atmospheric boundary layer (ABL) is an important aspect in computational wind engineering (CWE) applications. The ABL flow can be viewed as a balance of the horizontal pressure gradient force, the Coriolis force and the turbulent stress divergence. While much research has focused on the increase of the wind velocity with height, the Ekman layer effects, entailing veering — the change of the wind velocity direction with height, are far less concerned in wind engineering. In this paper, a modified k-epsilon model is introduced for the ABL simulation considering wind veering. The self-sustainable method is discussed in detail including the precursor simulation, main simulation and near-ground physical quantities adjustment. Comparisons are presented among the simulation results, field measurement values and the wind profiles used in the conventional wind tunnel test. The studies show that the modified k-epsilon model simulation results are consistent with field measurement values. The self-sustainable method is effective to maintain the ABL physical quantities in an empty domain. The wind profiles used in the conventional wind tunnel test have deficiencies in the prediction of upper-level winds. The studies in this paper support future practical super high-rise buildings design in CWE.

Key Words
computational wind engineering; atmospheric boundary layer; self-sustainable method; modified k-epsilon model; Coriolis force

Address
Chengdong Feng and Ming Gu: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, China

Abstract
The accurate estimation of the buffeting response of a bridge pylon is related to the quality of the bridge construction. To evaluate the influence of wind field characteristics on the buffeting response of a pylon in a trumpet-shaped mountain pass, this paper deduced a multimodal coupled buffeting frequency domain calculation method for a variable-section bridge tower under the twisted wind profile condition based on quasi-steady theory. Through the long-term measurement of the wind field of the trumpet-shaped mountain pass, the wind characteristics were studied systematically. The effects of the wind characteristics, wind yaw angles, mean wind speeds, and wind profiles on the buffeting response were discussed. The results show that the mean wind characteristics are affected by the terrain and that the wind profile is severely twisted. The optimal fit distribution of the monthly and annual maximum wind speeds is the log-logistic distribution, and the generalized extreme value I distribution may underestimate the return wind speed. The design wind characteristics will overestimate the buffeting response of the pylon. The buffeting response of the pylon is obviously affected by the wind yaw angle and mean wind speed. To accurately estimate the buffeting response of the pylon in an actual construction, it is necessary to consider the twisted effect of the wind profile.

Key Words
bridge pylon; trumpet-shaped mountain pass; twisted wind profile; wind spectrum; coherence function; buffeting response

Address
Jiawu Li, Zhengfeng Shen, Song Xing and Guangzhong Gao: 1.) School of Highway, Chang\'an University, Xi\'an, 710064, Shaanxi, China
2.) Key Laboratory for Bridge and Tunnel of Shaanxi Province, Chang\'an University, Xi\'an, 710064, Shaanxi, China


Abstract
This paper focuses on the processes of wind flow in atmospheric boundary layer, to produce realistic full scale pressures for design of low-rise buildings. CFD with LES turbulence closure is implemented on a scale 1:1 prototype building. A proximity study was executed computationally in CFD with LES that suggests new recommendations on the computational domain size, in front of a building model, apart from common RANS-based guidelines (e.g., COST and AIJ). Our findings suggest a location of the test building, different from existing guidelines, and the inflow boundary proximity influences pressure correlation and reproduction of peak loads. The CFD LES results are compared to corresponding pressures from open jet, full scale, wind tunnel, and the ASCE 7-10 standard for roof Component & Cladding design. The CFD LES shows its adequacy to produce peak pressures/loads on buildings, in agreement with field pressures, due to its capabilities of reproducing the spectral contents of the inflow at 1:1 scale.

Key Words
Atmospheric Boundary Layer (ABL); building aerodynamics; wind loading correlation; turbulence; wind pressure measurement; Large Eddy Simulation (LES); vortex method; Component and Cladding (C&C) design; scale effects

Address
(1) Aly Mousaad Aly:
Winsdstorm Impach, Science and Engineering (WISE) Lab, Civil & Environmental Engineering, Louisiana State University, Baton Rouge, USA;
(2) Hamzeh Gol-Zaroudi:
Windstorm Impact, Science and Engineering(WISE), Louisiana State University, Research & Modeling, AIR Worldwide, Boston, USA.


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