Self-excited oscillation in a collapsible tube is an important phenomenon in physiology. An experimental approach on self-excited oscillation in a thin-walled collapsi- ble tube is developed by using a high transmittance and low Young＇s modulus silicone rubber tube. The elastic tube is manufactured by the method of centrifugal casting in our laboratory. An optical method for recording the evolution of the cross-sectional areas at a certain position along the longitudinal direction of the tube is developed based on the technology of refractive index matching. With the transparent tube, the tube law is measured under the static no-flow condition. The cross section at the middle position of the tube transfers from a quasi-circular configuration to an ellipse, and then to a dumbell-shape as the chamber pressure is increased. During the self-excited oscillation, two periodic self-excited oscillating states and one transitional oscillating state are identified. They all belong to the LU mode. These different oscillating states are related to the initial cross-sectional shape of the tube caused by the difference of the downstream transmural pressure.
Complex interactions of plates with ambient fluid are common in daily lives,e.g.flags flapping in wind,aerofoils oscillating in flow.Recently,the feasibility to harvest energy using the flutter motion has been demonstrated.The objectives of this study are to systematically explore the effects of the material damping on flag flutter,and then to study the energy interchange between the fluid and the flag.In this study,a two-dimensional model was developed.Three dimensionless parameters govern the system,i.e.the mass ratio between the structure and the fluid,the dimensionless fluid velocity and the dimensionless material damping.Results show that the critical velocity increases with the increase of the material damping.The oscillation frequency of the flag decreases with the increase of the material damping,and the time-averaged energy dissipation rate initially increases and then decreases.The increase of the material damping causes the transition of the system from a higher frequency oscillating state to a lower frequency oscillating state,and from a chaotic state to a periodic state.
