Techno Press


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CONTENTS
Volume 15, Number 3, May 2012
 

Abstract
Lock-in and drag amplification phenomena are studied for a flexible cantilever using a simplified fluid-structure interaction approach. Instead of solving the 3D domain, a simplified setup is devised, in which 2D flow problems are solved on a number of planes parallel to the wind direction and transversal to the structure. On such planes, the incompressible Navier-Stokes equations are solved to estimate the fluid action at different positions of the line-like structure. The fluid flow on each plane is coupled with the structural deformation at the corresponding position, affecting the dynamic behaviour of the system. An Arbitrary Lagrangian-Eulerian (ALE) approach is used to take in account the deformation of the domain, and a fractional-step scheme is used to solve the fluid field. The stabilization of incompressibility and convection is achieved through orthogonal quasi-static subscales, an approach that is believed to provide a first step towards turbulence modelling. In order to model the structural problem, a special one-dimensional element for thin walled cross-section beam is implemented. The standard secondorder Bossak method is used for the time integration of the structural problem.

Key Words
fluid-structure interaction; vortex-induced vibrations; slender line-like structures; lock-in; drag coefficient amplification

Address
Ali Vasallo Belver : CARTIF Centro Tecnologico, Parque Tecnologico de Boecillo, parcela 205, 47151 Boecillo (Valladolid), Spain
Antolin Lorenzana Iban : CARTIF Centro Tecnologico, Parque Tecnologico de Boecillo, parcela 205, 47151 Boecillo (Valladolid), Spain, ITAP. University of Valladolid, Paseo del Cauce 59, 47011 Valladolid, Spain
Riccardo Rossi: International Center for Numerical Methods in Engineering, Barcelona, 08034, Spain

Abstract
The flutter reliability analysis of long span bridges requires use of a software tool that predicts the uncertainty in a flutter response due to uncertainties in the model formulation and input parameters. Existing flutter analysis numerical codes are not capable of dealing with stochastic uncertainty in the analysis of long span bridges. The goal of the present work is to develop a software tool (FREASB) to enable designers to efficiently and accurately conduct flutter reliability analysis of long span bridges. The FREASB interfaces an open-source Matlab toolbox for structural reliability analysis (FERUM) with a typical deterministic flutter analysis code. The paper presents a brief introduction to the generalized first-order reliability method implemented in FREASB and key steps involved in coupling it with a typical deterministic flutter analysis code. A numerical example concerning flutter reliability analysis of a long span suspension bridge with a main span of 1385 m is presented to demonstrate the application and effectiveness of the methodology and the software.

Key Words
computer software; structural reliability; flutter; long span bridges

Address
Jin Cheng : State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China

Abstract
Multivariate simulation is necessary for cases where non-Gaussian processes at spatially distributed locations are desired. A simulation algorithm to generate non-Gaussian wind pressure fields is proposed. Gaussian sample fields are generated based on the spectral representation method using wavelet transforms method and then mapped into non-Gaussian sample fields with the aid of a CDF mapping transformation technique. To illustrate the procedure, this approach is applied to experimental results obtained from wind tunnel tests on the domes. A multivariate Gaussian simulation technique is developed and then extended to multivariate non-Gaussian simulation using the CDF mapping technique. It is proposed to develop a new wavelet-based CDF mapping technique for simulation of multivariate non- Gaussian wind pressure process. The efficiency of the proposed methodology for the non-Gaussian nature of pressure fluctuations on separated flow regions of different rise-span ratios of domes is also discussed.

Key Words
domes; wavelet; CDF mapping technique; multivariate; non-Gaussian; stochastic simulation; wind pressure field; wind tunnel experiment

Address
Nyi Nyi Aung and Ye Jihong : Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education, Southeast University, China
F.J. Masters : Department of Civil and Coastal Engineering, University of Florida, USA

Abstract
Some numerical investigations are presented concerning the response of a given plate under turbulence driven excitations. Three different input loads are simulated according to the wall pressure distributions derived from the models proposed by Corcos, Efimtsov and Chase, respectively. Modal solutions (finite element based) are used for building the modal stochastic responses in the sub-critical aerodynamic frequency range. The parametric investigations concern two different values of the structural damping and three values of the boundary layer thickness. A final comparison with available experimental data is also discussed. The results demonstrate that the selection of the adequate TBL input model is still the most critical step in order to get a good prediction.

Key Words
turbulent boundary layer; stochastic plate response; wall pressure distribution

Address
S. De Rosa, F. Franco, and D. Gaudino : Laboratory for promoting experiences in aeronautical structures and acoustics, Department of Aerospace Engineering, Universita degli Studi di Napoli

Abstract
This paper presents a framework of nonlinear dynamic analysis of a low-speed moving maglev (magnetically levitated) vehicle subjected to cross winds and controlled using a clipped-LQR actuator with time delay compensation. A four degrees-of-freedom (4-DOFs) maglev-vehicle equipped with an onboard PID (Proportional-Integral-Derivative) controller traveling over guideway girders was developed to regulate the electric current and control voltage. With this maglev-vehicle/guideway model, dynamic interaction analysis of a low-speed maglev vehicle with guideway girders was conducted using an iterative approach. Considering the time-delay issue of unsynchronized tuning forces in control process, a clipped-LQR actuator with time-delay compensation is developed to improve control effectiveness of lateral vibration of the running maglev vehicle in cross winds. Numerical simulations demonstrate that although the lateral response of the maglev vehicle moving in cross winds would be amplified significantly, the present clipped-LQR controller exhibits its control performance in suppressing the lateral vibration of the vehicle.

Key Words
cross wind; incremental-iterative method; LQR actuator; maglev system; time delay

Address
J.D. Yau : Department of Transportation Management, Tamkang University, New Taipei City, Taiwan, College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, China


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