Ph.D Student | Sergey Gendel |
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Subject | Nonlinear Spatio-Temporal Flow-Structure Interaction of an Elastically Attached Slender Body at High Incidence |

Department | Department of Mechanical Engineering |

Supervisors | Professor Emeritus Degani David |

Full Professor Gottlieb Oded | |

Full Thesis text |

Flow-induced vibrations are motions of flexible or elastically attached
rigid-bodies that are subject to external flow. The flow field can exert an
asymmetric force on the structure leading to motion transverse to the mean flow
direction. An example of this phenomenon is the Von Kármán vortex
street in the wake of a fixed circular cylinder that results in vortex-induced
vibrations of its elastically tethered counterpart due to a periodic lift
force. Flow-induced vibration problems span many different branches of
engineering, such as civil structures (bridges, stacks, transmission lines),
marine, aerospace and land vehicles, ocean and space structures (tethered
platforms, mooring cables). In recent years, investigation of these phenomena
has become increasingly important, as structures are progressively lighter and
flexible, and are more prone to large amplitude flow-induced vibrations in
severe environmental conditions. The goal of this research is to investigate
the governing mechanisms observed in fluid-structure interaction (FSI) of
elastically attached slender bodies and, conversely, the influence of the
interactions on the downstream fluid flow patterns. In this research we
numerically investigate the flow around an inclined tangent ogive**-**cylindrical
rigid-body, mounted on torsion springs that can rotate in the pitching, yawing,
and rolling directions. The body is subjected to three-dimensional,
compressible, laminar flow at Reynolds number of 30,000 (based on body
diameter) and a low Mach number of 0.2.

A second-order implicit finite-difference scheme is employed for the flow equations, adapted to three-dimensional curvilinear coordinate system, whereas the coupled structural equations, derived using Euler angle notation, are solved by an explicit fourth-order Runge-Kutta method. The investigation is focused on the influence of the angle-of-attack, in the range of 20 to 55 degrees, on the FSI of an elastically mounted slender body.

For a fixed body with a small angle-of-attack* *the
yaw moment was found to change smoothly with the location of circumferential
disturbance, whereas for an angle of attack * * the
yaw moment was characterized by an almost a square-wave behavior with
bifurcation points at specific angles relative to the initial vertical
orientation . For an elastically mounted
body the response with small angles-of-attack resulted in large amplitude
periodic yawing and pitching moments for all disturbance locations. The
response for an angle of attack resulted in
large amplitude moments which occurred only for disturbance locations which
coincided with the bifurcation points of the fixed body. The response at the
bifurcation points was found to be quasiperiodic for * *periodic for * *and chaotic-like for.

The direct implication of this investigation is that careful decomposition of experimental measurements is essential, particularly when the balance-mounted rigid bodies in laminar flow exhibit nonstationary and chaotic-like dynamics, which are due to nonlinear and complex fluid structure interaction. The current work assumed that the computational model is deterministic, and uncertainty in the properties of the dynamical system is ignored. This should be addressed in future work.