Tomomi Yagi

Vortex-induced cable vibration of cable-stayed bridges at high reduced wind velocity

Abstract In this paper, mechanisms of vortex-induced vibration of inclined cables at high reduced wind velocity region are discussed using results from a series of wind tunnel tests. As a conclusion, this aerodynamic instability of inclined cables would occur by the fluid interaction between Karman vortex and axial vortex. Also, the axial flow along the cable axis and the upper water rivulet control this aerodynamic instability. Furthermore, three dimensional properties of vortex shedding around the cable must play important roles in these mechanisms.

Field observation of the full-scale wind-induced cable vibration

Wind-induced vibration of inclined cables of cable-stayed bridges is one of the most serious problems in bridge aerodynamics. Especially, the rain-wind induced vibration that can be explained as vortex-induced vibration at high reduced wind velocity has been reported at many cable-stayed bridges in the world. In order to clarify the characteristics and the mechanisms of the rain-wind induced vibration, experimental setup using full-scale cable model was constructed in the field, and aerodynamic behavior of this cable model was observed under various weather conditions. Then the vibration, which might be considered as the rain-wind-induced vibration, was observed.

Rain-wind-induced vibration of inclined cables at limited high reduced wind velocity region

Aerodynamic vibration of stayed cables, especially rain-wind-induced cable vibration, has been a rather serious problem on the design of cable-stayed bridges. This well-known phenomenon occurs at particular high reduced wind velocity regions and under raining condition. From results of wind tunnel tests, it might be explained as a vortex-induced vibration, which occurs at limited high reduced wind velocity region. Then, in this study, the effects of water rivulet and the wind turbulence on the vortex-induced vibration at high reduced wind velocity are investigated by wind tunnel tests, and the mechanism of the rain-wind-induced cable vibration is tried to be understood comprehensively. Furthermore, the role of Karman vortex in this vibration is discussed.

Mechanism of, and turbulence effect on vortex-induced oscillations for bridge box girders

Abstract This paper describes the hybrid characteristics of vortex-induced oscillation (VIO), which are caused by Karman vortex shedding and motion-induced vortices of bridge box girders and its response sensitivity to turbulence.

Simulation and Visualisation of the Dynamic Behaviour of an Overhead Power System with Contact Breaking

SUMMARY For high speed rail traffic it is necessary to design overhead power systems which minimize the contact loss between pantograph head and contact wire. To predict how different design solutions will behave it is favourable to model and simulate the dynamic behaviour. In this paper a model of an overhead power system is specified and used in simulation. The model is suitable for simulation with contact loss since it includes specifications of impact conditions between pantograph head and contact wire. Two sets of equations of motion are specified, one for the contact case and one for the non-contact case. The model also includes lateral movement of the wire due to the zigzag span and friction between the pantograph head and the contact wire. It is shown how to make animations of the system behaviour using a MCAE-system. The animations are made using a geometrical model of the system together with results from numerical simulations. Through the examples provided, use of the mathematical model and the...

Flow field control to mitigate airborne sea salt adhesion on bridge girders

Abstract In order to realise effective maintenance and enhanced durability of structures, it is important to also reduce corrosion of bridges by airborne sea salt. The objective of this study is to reduce airborne sea salt adhesion amount on steel girder bridges by employing aerodynamic countermeasures. The study bridge is a typical metropolitan highway bridge with 8 I-shaped steel girders located in Japan. Aerodynamic countermeasure devices are employed to change the flow field around the bridge structure in an attempt to reduce wind velocity normal to the bridge girders. Devices existing on urban bridges such as noise barriers, median barriers, and facilities for passage of drainage pipes and electric cables, modelled as horizontal plates, are modified and investigated for their ability to reduce airborne sea salt adhesion amount. As additional devices, vertical plates are installed to change the flow separation and their applicability is also studied. Computational fluid dynamics is employed for flow field simulations and airborne sea salt adhesion amount is estimated by the improved concentration flux method. Findings indicate that horizontal plates and vertical plates significantly reduce airborne sea salt adhesion amount. Noise barriers and median barriers can also reduce airborne sea salt adhesion amount.

Karman Vortex Effect on the Aerodynamic Forces to Rectangular Cylinders

Standing on the back-ground associated with the complicated bluff body aerodynamics affected by Karman vortex, the fundamental wind tunnel tests have been carried out to clarify the role of Karman vortex on the aerostatic forces and the aerodynamic forces of 2D rectangular cylinders with various side ratios in the range from B/D=0.3 to B/D=15. For mitigation of Karman vortex, a splitter plate with suitable size was installed in a wake center. As far as stationary drag force, the sharp peak in CD -B/D diagrams, completely disappear by a splitter plate installation. On the other hand, the value of dCL /dα is significantly sensitive to the Karman vortex, in particular, even its sign changes in the range from B/D=0.6 to B/D=0.7 and B/D=3.0 to B/D=4.0, which means the significant role of the Karman vortex on the galloping instability, from the point of quasi-steady theory. Furthermore, the flutter derivatives are also drastically affected by Karman vortex in the rather wide reduced velocity far from the Karman vortex resonant reduced velocity. In summary, it would be emphasized that the substantial bluff body flow might be characterized by the side ratio of cylinders, and these fundamental flows should be significantly or slightly affected by Karman vortex depending on their side ratios of cylinders.Copyright

Flows around Inclined Cables

Rain-wind induced cable vibration is one of serious problem on design of cable-stayed bridges. This vibration usually occurs at particular high reduced wind velocity regions under raining condition. The generation mechanism of this vibration is rather complicated since the cables attitude against wind is inclined, and then there are strong three-dimensional fluids characteristics around the inclined cable. Also, a water rivulet is formed on the cable surface. To understand this phenomenon, the flow field around an inclined cable was investigated by wind tunnel tests. Flow visualization tests around inclined cable model and a series of wind tunnel tests measuring its unsteady aerodynamic force and the unsteady wind fluctuation at its wake were conducted. Then, it becomes clear that there are three-dimensional interactions related to Karman vortex and the effects of water rivulet, and the wind turbulence may be significant factors of this vibration.