Mayuko Nishio

Flow field analysis of a pentagonal-shaped bridge deck by unsteady RANS

ABSTRACT Long-span cable-stayed bridges are susceptible to dynamic wind effects due to their inherent flexibility. The fluid flow around the bridge deck should be well understood for the efficient design of an aerodynamically stable long-span bridge system. In this work, the aerodynamic features of a pentagonal-shaped bridge deck are explored numerically. The analytical results are compared with past experimental work to assess the capability of two-dimensional unsteady RANS simulation for predicting the aerodynamic features of this type of deck. The influence of the bottom plate slope on aerodynamic response and flow features was investigated. By varying the Reynolds number (2 × 104 to 20 × 104) the aerodynamic behavior at high wind speeds is clarified.

Investigation of Flow Fields Around Rectangular Cylinder Under Turbulent Flow by Les

Abstract In the atmospheric boundary layer turbulent flow is continuously interacting with structures. Recently it has been found that properties of natural wind turbulence are anisotropic in nature in terms of turbulence intensity and length scale. It is important to know the bluff body response under this anisotropic turbulent flow. In the present work, anisotropic turbulence effect was investigated numerically on rectangular cylinders of varying side ratios (R=d/h), R=0.1875 to 1. Four different properties of anisotropy were considered and anisotropy of the turbulence was altered by changing the vertical wind turbulence intensity and length scale. Numerical simulations were performed employing large eddy simulation (LES) with smagornisky subgrid-scale model. Turbulence effects were discussed in terms of mean drag and base pressure coefficients. Time averaged flow pattern was plotted to understand the flow field around the rectangular cylinders. After body vortex strength was also checked for turbulent flow. It was found that the anisotropy of turbulence alters bluff body responses considerably.

Comparison of aerodynamic characteristics of pentagonal and hexagonal shaped bridge decks

Aerodynamics of the long-span bridge deck should be well understood for an efficient design of the bridge system. For practical bridges various deck shapes are being recommended and adopted, yet not all of their aerodynamic behaviors are well interpreted. In the present study, a numerical investigation was carried out to explore the aerodynamic characteristics of pentagonal and hexagonal shaped bridge decks. A relative comparison of steady state aerodynamic responses was made and the flow field was critically analyzed for better understanding the aerodynamic responses. It was found that the hexagonal shaped bridge deck has better aerodynamic characteristics as compared to the pentagonal shaped bridge deck.

NUMERICAL STUDY ON THE EFFECT OF FLAP ON VORTEX-INDUCED VIBRATION OF BOX SECTION OF A BRIDGE

In this paper, numerical analysis with Reynolds Average Navier-Stokes (RANS) equations based e − k model is performed to investigate the role of flap as a countermeasure to vortex-induced oscillation of a box section of a bridge. Mean values of force coefficients of basic box section are first compared with experimental results from a wind tunnel to ensure the reliability of numerical simulation. The effect of flap on vortex-induced oscillation of a box section is studied by changing the angle of flap and the gap between barrier and flap. The power spectrum density (PSD) of velocity at the wake region is obtained in order to evaluate the fluctuations in the intensity of vortex shedding behind box section. Thereafter, the PSD of lift coefficient derived from different flap simulations manifests the influence of shape of flap on wind flow distribution pattern. In addition, the root mean square (RMS) of pressure coefficient along the perimeter of section as well as the flow pattern visualization are expressed to comprehend the flow characteristics around box section and the vortex-induced vibration suppressing mechanism in the presence of flap with its many distinct configurations. Finally, the recommendation on application of flap for a box section is given to reduce the amplitude of vortex-induced oscillation.