1,721,291 research outputs found
Validità della simulazione numerica bidimensionale del comportamento aerodinamico di corpi cilindrici attraverso l’approccio alle grandi scale turbolente
No full textLa memoria presenta i risultati di uno studio rivolto a valutare l’attitudine dei modelli computazionali bidimensionali, basati sull’approccio alle grandi scale turbolente (LES), nel simulare il flusso separato ad alto numero di Reynolds intorno a corpi cilindrici di lunghezza infinita. Attraverso estesi studi parametrici, l’approccio numerico ed il modello di sottogriglia sono ottimizzati in modo da introdurre effetti di dispersione e di ridistribuzione in frequenza analoghi a quelli dovuti alle strutture vorticose tridimensionali trascurate dal modello 2D. I cilindri studiati si differenziano per sezione trasversale, “grado di tozzezza” e meccanismo di rilascio dei vortici in scia. I risultati ottenuti sono confrontati con i dati misurati in prove sperimentali e con quelli ricavati da precedenti simulazioni numeriche
The validity of 2D numerical simulations of vortical structures around a bridge deck
No full textThis paper deals with a computational study for evaluating the capability of 2D numerical simulation for predicting the vortical structure around a quasibluff bridge deck. The laminar form, a number of RANS equation models, and the LES approach are evaluated. The study was applied to the deck section of the Great Belt East Bridge. The results are compared with wind-tunnel data and previously conducted computational simulations. Sensitivity of the results with regard to the computational approaches applied for each model is discussed. Finally, the study confirms the importance of safety-barrier modelling in the analysis of bridge aerodynamics. © 2003 Elsevier Science Ltd. All rights reserved
Determination of the Aeroelastic Transfer Functions for Streamlined Bodies by means of a Navier-Stokes Solver
No full textThis paper proposes a method to determine the flutter derivatives of two-dimensional streamlined cylinders by means of a modified indicial approach adapted to a Navier-Stokes solver using an Arbitrary Lagrangian Eulerian formulation. The method relies on heave or pitch motion imposed onto the section according to smoothed-ramp time-histories and on the computational evaluation of the transient forces arising on the obstacle. Hence, the indicial transfer function relating the plate motion to the induced force in the frequency domain is obtained. Application to a flat plate of finite thickness and length is proposed. The steady viscous flow simulated around the motionless plate is compared with the well-known Blasius solution. The computed flutter derivatives are compared both with those obtained from the Theodorsen function in the frame of the thin airfoil theory and with those resulting from previous methods in the frame of the computational approac
Sand transverse dune aerodynamics: 3D coherent flow structures from a computational study
Full text linkThe engineering interest about dune fields is dictated by their interaction with a number of human infrastructures in arid environments. Sand dunes dynamics is dictated by wind and its ability to induce sand erosion, transport and deposition. A deep understanding of dune aerodynamics serves then to ground effective strategies for the protection of human infrastructures from sand, the so-called sand mitigation. Because of their simple geometry and their frequent occurrence in desert area, transverse sand dunes are usually adopted in the literature as a benchmark to investigate dune aerodynamics by means of both computational and experimental approaches, usually in nominal 2D setups. The present study aims at evaluating 3D flow features in the wake of a idealized transverse dune, if any, under different nominal 2D setup conditions by means of computational simulations and to compare the obtained results with experimental measurements available in the literatur
Crowd-structure interaction in lively footbridges under synchronous lateral excitation: A literature review
No full textThis paper aims to provide a review and critical analysis of the state of the art concerning crowd-structure interaction phenomena on footbridges. The problem of lateral vibrations induced by synchronised pedestrians, namely the Synchronous Lateral Excitation, is specifically addressed. Due to the multi-physic and multi-scale nature of the complex phenomenon, several research fields can contribute to its study, from structural engineering to biomechanics, from transportation engineering to physics and applied mathematics. The different components of the overall coupled dynamical system - the structure, the crowd and their interactions - are separately analysed from both a phenomenological and modelling point of view. A special attention is devoted to those models, which explicitly account for the interaction between mechanical and living system
Crowd-Structure Interaction in footbridges: modelling, application to a real case-study and sensitivity analyses
No full textFootbridge lateral vibrations induced by synchronized pedestrians: an overview on modelling strategies
No full textThis paper aims to provide a review and critical analysis of the state of the art concerning crowd-structure interaction phenomena on footbridges. The problem of lateral vibrations induced by synchronised pedestrians, namely the Synchronous Lateral Excitation, is specifically addressed. Due to the multi-physic and multi-scale nature of the complex phenomenon, several research fields can contribute to its study, from structural engineering to
biomechanics, from transportation engineering to physics and applied mathematics. Among the different components of the overall coupled dynamical system - the structure, the crowd and their interactions - the latter ones are separately analysed from both a phenomenological and
modelling point of view. A special attention is devoted to those models, which explicitly account for the interaction between mechanical and living systems
Determination of flutter derivatives for streamlined bodies throughout a modified indicial approach by means of CWE: part II - Sensitivity to physical parameters
No full textEdge degree-of-sharpness and integral length scale effects on the aerodynamics of a bridge deck
No full textThis paper discusses the sensitivity of the aerodynamic behaviour of a trapezoidalshaped bridge deck cross-section to its lower corner degree-of-sharpness and to the incoming flow turbulence integral length scale in conjunction with low turbulence intensity. Since these features are hard to set and measure in experimental facilities, the aerodynamic behaviour of the body has been investigated through the computational simulation of the flow around it. The results are given in term of force coefficients, Strouhal number, pressure distribution along its surface, and the mean and instantaneous flow patterns. Dramatic changes in the force coefficients and Strouhal number occur following small changes in the parameters' values. These changes have been found to be due to significant modifications in the topological structure of the flow. Special emphasis has been given to the analysis of the separation and reattachment points, the recirculation bubble length, the vortex shedding mechanisms and the wake structures. On the basis of the obtained results, four aerodynamic regimes have been pointed out in analogy with the well-known individual Re number regimes. Some of these regimes have also been recognized on the Sunshine Skyway Bridge cross-section, even when the sharping aerodynamic devices at the lower corners are taken into consideratio
A new load model of the pedestrian lateral action
No full textThis paper proposes a new load model to predict the lateral force exerted by pedestrians walking on lively footbridges. The aim of the model is to take into account some important features of the synchronous lateral excitation phenomenon, which so far has not been fully understood or modelled, e.g. the distinction between synchronization among pedestrians, due to crowd density, and between the pedestrians and the structure, caused by deck oscillations; the triggering of the lock-in phenomenon and its self-limited nature. The proposed load model has been tested with reference to two crowd events that were recorded on the T-bridge in Japan (1993) and on the Millennium Bridge in London (2001). The results obtained with the present model are compared to results predicted by other load models found in literature and are then further discusse
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