1995 Fiscal Year Final Research Report Summary
UNSTEADY WIND FORCES IN TATSUMAKI
| Project/Area Number |
06452288
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Building structures/materials
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| Research Institution | Osaka City University (1995)
Kyoto University (1994) |
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Principal Investigator |
TANIIKE Yoshihito Osaka City University, Fac.of Engineering.prof., 工学部, 教授 (00111980)
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| Co-Investigator(Kenkyū-buntansha) |
OKANAN Hiroo Osaka Prefectural College of Technology, Dept.of Civil Engineering , prof., 建設工学科, 教授 (20111924)
TANIGUCHI Tetsuro Osaka City University, Fac.of Engineering, Research Assoc., 工学部, 助手 (30231418)
KIUCHI Tatsuhiko Osaka City University, Fac.of Engineering, Lecturer, 工学部, 講師 (30112527)
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| Project Period (FY) |
1994 – 1995
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| Keywords | Tatsumaki / Unsteady Wind Force / Rankine Vortex / Added Mass / Velocity Potential / Morison's Equation / Wind Tunnel Experiment |
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| Research Abstract |
The word 'tatsumaki' is used in Japan to designate meteorological phenomena as tornadoes and waterspounts. In surbeys of tatsumaki damage, great differences are often observed in the magnitude of damage to buildings, housings, towers, pylons, poles and signboards, depending on where these structures were located relative to the path of the tatsumaki. Generally, there is little regularity in the direction these structures are torn down or in which way missiles such as roofing tiles, timbers and gravels are scattered. These are results of rotational windstorms and fluctuational velocities, that are characteristic of tatsumakis. As a tatsumaki passes over, the speed and direction of wind will change constantly, creating rapid transitions in the magnitude and direction of wind loads on structures it encounters, both in time and space. Wind forces on bodies induced by unsteady flows are inevitably different from those by steady flows with constant velocity. Therefore, tatsumaki-induced wind
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loads on structures should be different from those induced by typhoons or monsoons, as both can be approximated as steady flows.
In the present study, we assumed the swirling motion of tatsumakis as a Rankine vortex that moves with a constant velocity, and analyzed the unsteady horizontal flow at arbitrary points along the tatsumaki path. By the action of unsteady/accelerating flow, the inertial force is generated on bodies and it can be estimated by the previous experimental data or by the theoretical calculation using the velocity potential of inviscid flow. The inertial force and the drag force which is proportional to the square of fluid velocity were combined and incorporated into the Morison's equation, which was then able to express the total fluid force. The fluctuating fluid forces generated during the passage of a tatsumaki on arbitrary located structures were numerically estimated.
The velocity and acceleration at arbitrary points in the tatsumaki varied continuously with time and both reached maximum at the core of the vortex. The acceleration did not depend on the translation velocity of the tatsumaki and was directed towards the center of the vortex.
It was found that the total wind force acting on structures became maximum at the leeward core of the tatsumaki vortex. The inertial force due to the acceleration of fluid was about 30% of the drag obtained from the square of fluid velocity. The directions in which the bodies are blown down by a tatsumaki may be reversed on the different sides of the path of the vortex center. This was shown to be consistent with the results of a field survey on actual tatsumaki damage. Less
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