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CONTENTS
Volume 23, Number 1, July 2016
 

Abstract
This work experimentally and numerically analyzes the flow configurations and the dynamic wind loads on panels of rectangular L/h 5:1 cross section mounted on a structural frame of rectangular bars of L/h 0.5:1, corresponding to a radar structure. The fluid dynamic interaction between panels and frame wakes imposes dynamic loads on the panels, with particular frequencies and Strouhal numbers, different from those of isolated elements. The numerical scheme is validated by comparison with mean forces and velocity spectra of a panel wake obtained by wind tunnel tests. The flow configuration is analyzed through images of the numerical simulations. For a large number of panels, as in the radar array, their wakes couple in either phase or counter-phase configurations, changing the resultant forces on each panel. Instantaneous normal and tangential force coefficients are reported; their spectra show two distinct peaks, caused by the interaction of the wakes. Finally, a scaled model of a rectangular structure comprised of panels and frame elements is tested in the boundary layer wind tunnel in order to determine the influence of the velocity variation with height and the three-dimensionality of the bulk flow around the structure. Results show that the unsteady aerodynamic loads, being strongly influenced by the vortex shedding of the supporting elements and by the global 3-D geometry of the array, differ considerably on a panel in this array from loads acting on an isolated panel, not only in magnitude, but also in frequency.

Key Words
wake interaction; dynamic loads; Strouhal number

Address
Ana Scarabino and Federico Bacchi: Grupo de Fluidodinámica Computacional, Universidad Nacional de La Plata,
Calle 116 e/47 y 48, 1900 La Plata, Argentina
Mariano García Sainz and J. Sebastián Delnero: Laboratorio de Capa Límite y Fluidodinámica Ambiental, Universidad Nacional de La Plata, Calle 116 e/47 y 48, 1900 La Plata, Argentina;
Consejo Nacional de Investigaciones Científicas y Técnicas, Avda. Rivadavia 1917, CP C1033AAJ, Cdad. de Buenos Aires, Argentina
Andrés Cánchero: Laboratorio de Capa Límite y Fluidodinámica Ambiental, Universidad Nacional de La Plata,
Calle 116 e/47 y 48, 1900 La Plata, Argentina




Abstract
In the present study, a new methodology is presented to study the ride comfort and bridge responses of a long-span bridge-traffic-wind coupled vibration system considering stochastic characteristics of traffic flow and bridge surface progressive deterioration. A three-dimensional vehicle model with 24 degrees-of-freedoms (DOFs) including a three-dimensional non-linear suspension seat model and the longitudinal vibration of the vehicle is firstly presented to study the ride comfort. An improved cellular automaton (CA) model considering the influence of the next-nearest neighbor vehicles and a progressive deterioration model for bridge surface roughness are firstly introduced. Based on the equivalent dynamic vehicle model approach, the bridge-traffic-wind coupled equations are established by combining the equations of motion of both the bridge and vehicles in traffic using the displacement relationship and interaction force relationship at the patch contact. The numerical simulations show that the proposed method can simulate rationally the ride comfort and bridge responses of the bridge-traffic-wind coupled system; and the vertical, lateral, and longitudinal vibrations of the driver seat model can affect significantly the driver\'s comfort, as expected.

Key Words
bridge; traffic; vibration; ride comfort; bridge surface

Address
Yang Liu and Xinfeng Yin: School of Civil Engineering and Architecture, Changsha University of Science & Technology,
Changsha 410004, Hunan, China
Lu Deng: College of Civil Engineering, Hunan University, Changsha 410076 Hunan, China
C.S. Cai: Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge,
Louisiana 70803, USA


Abstract
Open-cross-section composite beam (OCB) tends to suffer vortex-induced vibration (VIV) due to its bluff aerodynamic shape. A cable-stayed bridge equipped with typical OCB is taken as an example in this paper to conduct sectional model wind tunnel test. Vortex-induced vibration is observed and maximum vibration amplitudes are obtained. CFD approach is employed to calculate the flow field around original cross sections in service stage and construction stage, as well as sections added with three different countermeasures: splitters, slabs and wind fairings. Results show that flow separate on the upstream edge and cause vortex shedding on original section. Splitters can only smooth the flow field on the upper surface, while slabs cannot smooth flow field on the upper or lower surface too much. Thus, splitters or slabs cannot serve as valid aerodynamic means. Wind tunnel test results show that VIV can only be mitigated when wind fairings are mounted, by which the flow field above and below the bridge deck are accelerated simultaneously.

Key Words
open-cross-section composite beam; vortex-induced vibration; splitters; slabs; wind fairings; velocity field; vorticity field

Address
Zhou Zhiyong, Zhan Qingliang and Ge Yaojun: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 20092, China

Abstract
In this paper, a hyperbolic shear deformation beam theory is developed for free vibration analysis of functionally graded (FG) sandwich beams. The theory account for higher-order variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. The material properties of the functionally graded sandwich beam are assumed to vary according to power law distribution of the volume fraction of the constituents. The core layer is still homogeneous and made of an isotropic material. Based on the present refined beam theory, the equations of motion are derived from Hamilton\'s principle. Navier type solution method was used to obtain frequencies. Illustrative examples are given to show the effects of varying gradients and thickness to length ratios on free vibration of functionally graded sandwich beams.

Key Words
functionally graded material; sandwich beam; hamilton\'s principle; vibration

Address
K. Bouakkaz and L. Hadji: Département de Génie Civil, Université Ibn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algérie;
Laboratoire des Matériaux & Hydrologie, Université de Sidi Bel Abbes, 22000 Sidi Bel Abbes, Algérie
N. Zouatnia: Laboratoire de Structures, Géotechnique et Risques, Département de Génie Civil, Université de Chlef, Algérie
E.A. Adda Bedia: Laboratoire des Matériaux & Hydrologie, Université de Sidi Bel Abbes, 22000 Sidi Bel Abbes, Algérie



Abstract
A probabilistic approach that combines structural demand hazard analysis with cumulative damage assessment is presented and applied to a steel tower of a wind turbine. The study presents the step by step procedure to compare the reliability over time of the structure subjected to fatigue, assuming: a) a binomial Weibull annual wind speed, and b) a traditional Weibull probability distribution function (PDF). The probabilistic analysis involves the calculation of force time simulated histories, fatigue analysis at the steel tower base, wind hazard curves and structural fragility curves. Differences in the structural reliability over time depending on the wind speed PDF assumed are found, and recommendations about selecting a real PDF are given.

Key Words
fatigue; structural reliability; binomial Weibull distribution; wind turbine tower; wind speed PDF

Address
Emilio A. Berny-Brandt and Sonia E. Ruiz: Instituto de Ingeniería, Universidad Nacional Autónoma de México, Coyoacán C.P. 04510, Mexico DF


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