Showing papers on "Vortex-induced vibration published in 1973"

Vortex shedding from bluff bodies in a shear flow

Abstract: Experiments are described in which the vortex shedding from a bluff body and the base pressure coefficient have been measured in a shear flow. It is shown that the shedding breaks down into a number of spanwise cells in each of which the frequency is constant. The division between the cells is thought to be marked by a longitudinal vortex in the stream direction and this is supported by evidence from experiments where a longitudinal vortex was generated in an otherwise uniform flow.

Vibratory dynamics of flow-excited struts in water

Abstract: The general problem of the response of a cantilevered beam to flow over its surface is considered experimentally and theoretically. The measured flow induced modal vibratory motion of a nonsinging beam is compared to theoretical estimates of inflow turbulence excitation and boundary-layer excitation. The comparison indicates that while the response to turbulent inflow is dominant at low frequencies, the response of the strut to its own boundary layer is important at high frequencies. The magnitude of hydrodynamically induced damping is also characterized experimentally. It is shown that results agree favorably with an approximate expression based on finite-aspect-ratio, unsteady airfoil theory. Loss factors, based on entrained mass, are found to be inversely proportional to a reduced frequency based on the width of the strut and inflow speed. Finally, a wind tunnel study of the statistical properties of the boundary layer formed on the strut is described. The results disclose that flow separation at the leading edge, which is sensitive to angles of attack, generates a low-frequency pressure field that is markedly higher than that normally encountered in boundary layers. At high frequencies the pressure field is influenced by the local flow parameters normally used in boundary-layer studies.

Measurements of the Response of Bluff Cylinders to Flow-Induced Vortex Shedding

Abstract: The prediction and measurement of vortex-excited vibrations and associated fluid forces are important in such ocean engineering applications as the determination of the flow-induced lift and drag forces on sea floor pipelines and structural members, tow and mooring cables, and suspended pipelines which must be known in order to implement proper design procedures and to prevent costly failures. This paper discusses a study wherein measurements were made of the response characteristics and flow about circular cylinders that were mounted on springs in a wind tunnel. Free stream Reynolds numbers for two cylindrical models ranged respectively from 350 to 550 and from 550 to 900. The measured vibration frequencies, amplitudes, and phase angles are compared with predictions made with an heuristic wake oscillator model for the vortex-excited vibrations. Steady drag measurements were made and show that the drag coefficient increases by as much as 75 percent at the maximum vibration amplitude from the measured stationary cylinder value. Lift amplification and energy transfer from the flow during resonance are compared over the range of the experiments. Energy determinations made from the measured response and damping data are in good agreement with the results of the theory. The agreement between theory and experiment indicated that further development of the wake oscillator model is warranted.

Crossflow-Induced Vibration of a Circular Cylinder in Water

Abstract: A circular cylinder elastically mounted to have equal flexibility in all lateral directions was exposed to cross (transverse) flow of water. The amplitudes and frequencies of flow-induced vibrations were measured as a function of flow velocity. Resonance-type responses were observed when the vortex-shedding frequency coincided with 50% (Condition A), and 100% (Condition B) of the natural frequency of the cylinder. As expected, Condition B resulted in large-amplitude vibrations in the lift (transverse to flow) direction. However, water excitation at the lower flow velocity of Condition A, which is generally considered unimportant for airflow exposures, resulted in drag (parallel to flow) direction vibrations of moderately large amplitudes. It appears that design applications subject to waterflow under exposure Condition A warrant individual investigation.