Inspired by the novel flapping caudal fin and body undulatory mechanisms in nature swimmers, simplified physical models are built in Computational Fluid Dynamic(CFD) solvers, and used to investigate the self-propulsion performance under different conditions with various kinetic and geometric parameters. Two simplified physical models, three-dimensional flapping wing model with flexibilities in lateral and rotational directions and multi-body system model with rigid components connected by revolute joints, are investigated for mimicking typical bio-inspired locomotion.The study was firstly carried out on a three-dimensional wing with a freedom intranslational direction under a prescribed flapping motion. The investigation focused on how the system kinematics and structural parameters affect the dynamic response of a wing with a relatively small span length. It shows that the induced wing motion is a result of the system stability breakdown, which has only been observed by previous researches in the two-dimensional case. The results obtained indicate that the evolution of the wing locomotion is controlled not only by the flapping frequency and amplitude, but also influenced by the system inertia as well as the wing aspect ratio and density ratio. Moreover, initial perturbation effect on wings flexibility plays a role in the evolution development.Subsequently, a comprehensive investigation is carried out on the dynamics response of a three-dimensional flapping wing with two degree of freedoms in lateral and rotational direction under a zero initial velocity condition. Distinguishing from the limited existing studies, present work performs a systematic examination on the effects of wing aspect ratio, inertia, torsional stiffness and pivot point on the dynamics response of a low aspect ratio rectangular wing under an initial zero speed flow field condition. The reduced rotational pitching help with the symmetry breakdown of the flapping wing and results in a forward/backward motion. When the wing reaches its stable periodic state, the induced pitching frequency is identical to its forced flapping frequency. However, depending on various kinematic and dynamic system parameters,(i.e. flapping frequency, density ratio and pitching axis), the lateral induced velocity shows a number of different oscillating frequency. Furthermore, compared with one degree of freedom wing in lateral direction only, the propulsion performance of such a two degree of freedom wing relies very much on the magnitude of torsional stiffness adding on the pivot point, as well as its pitching axis. In all cases examined, thrust force and moment generated by a long span wing is larger than that of a short wing,which is remarkably linked to the strong reverse von Kármán vortex street formed in the wake of a wing.In a separate study, the undulatory motion of fish body is mimicked with a series of linked rigid bodies, i.e. a multi-body system. The connection between two adjacent rigid components can be modelled as the revolute hinge joint, with either a passively induced pitch motion or actively prescribed pitch motion. Emphasis is put on the development for solving the problems of coupling multi-body dynamics with fluid dynamics by implementing Mobile Multi-body System (MMS) algorithm with CFD solver. Verifications are carried out by repeating the previous work, and innovative cases are tested on a prototype with three-linked rigid body system with an active joint and a passive joint. The investigation is made on the flexibility effect of tail on the propulsion performance. It shows there are optimized stiffness and damper coefficients at the passive joint leading the most efficient propulsion and fastest velocity through varying the posture of undulatory trajectory.
|Date of Award||9 Jan 2017|
- University Of Strathclyde
|Supervisor||Qing Xiao (Supervisor) & Atilla Incecik (Supervisor)|