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Damping structural vibrations by vortex shedding [Poster]

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Damping structural vibrations by vortex shedding T.G.H. Basten, H. Tijdeman University of Twente Twente Institute of Mechanics P.O. Box 217, 7500 AE Enschede, The Netherlands phone +31-(0)53-4895618/2460, email [email protected] Introduction Structural vibrations can be reduced via squeeze film damping by placing a narrow air layer parallel to the vibrating surface. This damping type is based on vis- cous shear in the air layer. The damping can be im- proved by placing barriers in the layer. The vortices formed behind the barriers increase the dissipation of vibrational energy. ��� ��� ��� ��� ��� ��� ��� ��� barrier vibrating surface ba air layer ����������������������������� ����������������������������� ����������������������������� ����������������������������� ����������������������������� ����������������������������� ����������������������������� ����������������������������� ����������������������������� ����������������������������� ����������������������������� ����������������������������� Figure 1 : Two damping mechanisms. a: Viscous shear, b: Vortex shedding. With a simple model it can be shown that the vortex damping behaves non-linear. This in contrast with the squeeze film or viscothermal damping which is a lin- ear type of damping. Experiments Experiments to validate the damping effects are per- formed with a setup which is very suitable for measur- ing the influence of an air layer on the dynamical be- haviour of a vibrating structure. Barriers are placed in a narrow air layer (12.0 mm) under a stiff, light weight panel of 1m2 suspended by springs. air layer with barriers oscillating panel panel screwjack shaker bottom spring rod upper spring lower frame Figure 2 : Experimental setup. Results The vortices are visualised with smoke during one pe- riod for a vibration of 1.0 Hz, see Figure 3. Figure 3 : Vortex visualisation. Damping levels at resonance (� 5.5 Hz) for various amplitudes

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