A numerical investigation into the aerodynamic characteristics and aeroelastic stability of a footbridge

The results of a numerical investigation into the aerodynamic characteristics and aeroelastic stability of a proposed footbridge across a highway in the north of England are presented. The longer than usual span, along with the unusual nature of the pedestrian barriers, indicated that the deck configuration was likely to be beyond the reliable limits of the British design code BD 49/01. The calculations were performed using the discrete vortex method, DIVEX, developed at the Universities of Glasgow and Strathclyde. DIVEX has been successfully validated on a wide range of problems, including the aeroelastic response of bridge deck sections. In particular, the investigation focussed on the effects of non-standard pedestrian barriers on the structural integrity of the bridge. The proposed deck configuration incorporated a barrier comprised of angled flat plates, and the bridge was found to be unstable at low wind speeds with the plates having a strong turning effect on the flow at the leading edge of the deck. These effects are highlighted in both a static and dynamic analysis of the bridge deck, along with modifications to the design that aim to improve the aeroelastic stability of the deck. Proper orthogonal decomposition (POD) was also used to investigate the unsteady pressure field on the upper surface of the static bridge deck. The results of the flutter investigation and the POD analysis highlight the strong influence of the pedestrian barriers on the overall aerodynamic characteristics and aeroelastic stability of the bridge

Numerical investigation of the effects of pedestrian barriers on aeroelastic stability of a proposed footbridge

A numerical investigation into the aerodynamic characteristics and aeroelastic stability of a proposed footbridge across a motorway in the north of England has been undertaken. The longer than usual span, along with the unusual nature of the pedestrian barriers, indicated that the deck configuration was likely to be beyond the reliable limits of the British design code BD 49/01. In particular, the investigation focussed on the susceptibility of the bridge due to flutter, and to assess if the design wind speeds could be met satisfactorily. The calculations were performed using the discrete vortex method, DIVEX, developed at the Universities of Glasgow and Strathclyde. DIVEX has been successfully validated on a wide range of problems, including the aeroelastic response of bridge deck sections. The proposed deck configuration, which incorporated a pedestrian barrier comprised of angled flat plates, was found to be unstable at low wind speeds with the plates having a strong turning effect on the flow at the leading edge of the deck. DIVEX was used to assess a number of alternative design options, investigating the stability with respect to flutter for each configuration. Reducing the number of flat plates and their angle to the deck lessened the effect of the barrier on the overall aerodynamic characteristics and increased the stability of the bridge to an acceptable level, with the critical flutter speed in excess of the specified design speed

Poder de Mercado en las Profesiones Autorreguladas: El Desempeño Médico en Argentina.

The potentially anticompetitive nature of some practices driven by professional organizations has been approached in economic literature and appears as an important issue in the antitrust organism’s agenda. However, empirical economics lacks of a self-regulated professionals analysis. This work relates the market for professional services with vertical product differentiation models and uses a Mixed Logit model to assess the medical profession behavior in Argentina. The evidence suggests the existence of a price arrangement.profesiones autorreguladas, diferenciación vertical del producto, Logit Mixto.

Chicago Beach Resort Development - an Assessment of the Transverse Galloping Stability of the Tower Hotel Mast. G.U. Aero Report 9626.

This report forms the second part of a study, commissioned by W.S. Atkins and Partners Overseas, into the galloping stability of the prismatic elements of the Tower Hotel, which is part of the Chicago Beach Resort Development. The particular subject of this study is the mast which extends above the top of the Hotel, which was not investigated previously due to a lack of relevant aerodynamic data. The report presents aerodynamic data for a number of shapes which have been identified as possessing some of the important features of the mast cross-section. Along with the structural and modal data supplied by W.S. Atkins, an assessment of the critical galloping speeds of these shapes is made after extending the quasi-steady theory originally described in the first report. There is strong evidence to suggest that the mast will not experience an instability due to transverse galloping, however the absence of sharp comers increases significantly the sensitivity of the transverse force coefficient to body geometry and Reynolds number. Increased confidence in the assessment requires more accurate aerodynamic data, obtainable from a series of wind tunnel tests on representative scale models of the mast cross-section

A New Vortex Method for Modelling Two-Dimensional, Unsteady, Incompressible, Viscous Flows. G.U. Aero Report 9245

This report presents details of a new mathematical model of viscous, incompressible, unsteady flow around multiple closed bodies. A system of vortex particles is employed in the model, on all solid boundaries and in the wake, to represent quantities of vorticity. The method is a Lagrangian technique and does not require the generation of a flow mesh. A review of recent advances in vortex modelling is provided in the Introduction. Many of these ideas are incorporated into the model or are planned for future inclusion. Section 2 is the main core of the report where the theoretical development of the model is presented. The extensive numerical details have been omitted and will be presented in a future report. Conclusions are made regarding the development of the model and the verification procedure required to validate the algorithm

Chicago Beach Resort Development - A Review of Galloping of Rectangular Prisms Pertinent to the Stability of the Tower Hotel External Frame. G.U. Aero Report 9619

In this report a review, commissioned by W.S. Atkins and Partners Overseas, is presented of the factors which determine the high speed galloping stability characteristics of rectangular prisms. The information is subsequently used to make an assessment of the galloping stability of the external frame of the Tower Hotel, a structure which forms part of the Chicago Beach Resort Development. The predictions of linear theory are explained, and the effects of aspect ratio, freestream turbulence and reduced damping discussed in detail. The variety of oscillatory response is explained with reference to both non-linear theory and results from wind tunnel experiments. A number of prevention methods are proposed, based on results from model and full-scale tests. It is concluded that the factors discussed can have a marked effect on the galloping tendency and response of rectangular prisms. Notwithstanding the limitations of the sectional aerodynamic theory employed, an assessment of the transverse galloping stability of the Tower Hotel external frame is made. The added dampers, originally designed to suppress vortex excitation, also play an important role in the suppression of galloping in the upper two bays of the exoskeleton. With these dampers the calculated threshold wind speeds are substantially in excess of those likely to occur in the top two bays, even in extreme conditions. Without the dampers galloping excitation would be possible, especially in low turbulence flows. The lower two bays have higher natural frequencies and mass, and experience lower wind speeds. The corresponding level of damping required may be achievable without dampers. No published data has been found to enable an assessment to be made of the aeroelastic stability of the Tower Hotel mast. Although circular sections do not gallop, very slight deviations from circularity may result in an unstable section. The situation is exacerbated by the lower turbulence intensities at this height, as well as the given slenderness, exposure and fixing arrangements. It is recommended, therefore, that a series of aerodynamic tests be performed to investigate the stability of the mast

A New Vortex Method for Modelling Two-Dimensional, Unsteady, Incompressible, Viscous Flows. G.U. Aero Report 9245

This report presents details of a new mathematical model of viscous, incompressible, unsteady flow around multiple closed bodies. A system of vortex particles is employed in the model, on all solid boundaries and in the wake, to represent quantities of vorticity. The method is a Lagrangian technique and does not require the generation of a flow mesh. A review of recent advances in vortex modelling is provided in the Introduction. Many of these ideas are incorporated into the model or are planned for future inclusion. Section 2 is the main core of the report where the theoretical development of the model is presented. The extensive numerical details have been omitted and will be presented in a future report. Conclusions are made regarding the development of the model and the verification procedure required to validate the algorithm

Calculation of the Flow Field around a Square Section Cylinder undergoing Forced Transverse Oscillations using a Discrete Vortex Method. G.U. Aero report 9814

A Discrete Vortex Method has been developed at the Department of Aerospace Engineering, University of Glasgow, to predict unsteady, incompressible, separated flows around closed bodies. The basis of the method is the discretisation of the vorticity field, rather than the velocity field, into a series of vortex particles which are free to move in the flow. The grid free nature of the method allows analysis of a wide range of problems for both stationary and moving bodies. This paper presents a brief description of the method and presents the results of a validation programme on bluff bodies undergoing forced transverse oscillations. The results demonstrate that the method successfully predicts the vortex lock-in phenomena around the resonance point, as well as capturing the various states of the flow field expected above and below vortex lock-in. Results are presented for the fluctuating lift coefficients, surface pressure coefficients and phase angle, for a square cylinder undergoing transverse oscillations over a range of frequencies and amplitudes. The results from the vortex method show good agreement, both qualitatively and quantitatively, with results from various experimental data

Poder de Mercado en las Profesiones Autorreguladas: El Desempeño Médico en Argentina

La naturaleza potencialmente anticompetitiva de las prácticas impartidas desde las organizaciones de profesionales ha sido racionalizada por la literatura económica y ha ocupado un lugar no menor en la agenda de los organismos de defensa de la competencia. Sin embargo, la economía empírica carece de estudios sobre el ejercicio profesional autorregulado. Este trabajo relaciona los mercados de servicios profesionales con los modelos de diferenciación vertical y emplea un modelo Logit Mixto para evaluar la conducta del desempeño médico en Argentina. La evidencia hallada sugiere la existencia de algún acuerdo de precios.profesiones autorreguladas, diferenciación vertical del producto, Logit Mixto, self-regulated professions, vertical product differentiation, Mixed Logit.