Flow Physics Of Freely Routine Swimming Of Koi Carp

Natural selection provides fishes remarkable and diversified swimming abilities. At the same time, bioinspiration and biomimetics relevant to living fish develop increasingly in last ten years. The communities of researchers interested in fish biomechanics and AUV/UUV begin to come together to explore the mechanism of fish maneuvering more comprehensively, and the multidisciplinary integrated study on fish locomotion becomes a general trend. Aiming to the "body - fluid" interaction, within the mechanical chain of fish locomotion, the following new work has been done in this dissertation.1. We take the lead in putting forward the dynamical equations of a deforming body, as well as a fish body. Based on this, we set up an integrated method solving deforming body dynamics equations and unsteady fluid dynamics equations (Navier-Stokes equations). The coupled method can be used to investigate a part of the mechanical chain of fish locomotion, which consists of active body deforming, fluid dynamical response and fish body movement. This method provides a two-dimensional numerical platform for studying mechanics of freely and self-propelled fish maneuvering.2. Burst-and-coast swimming of koi carp is studied on this platform, according to the detailed kinematics data of tracking measurements. Burst-and-coast is the most common locomotion type in freely routine swimming of koi carps, which consists of a burst phase and a coast phase in each cycle and usually leads to an almost straight-line trajectory. This study reveals the hydrodynamics and flow physics in koi carp burst-and-coast, and explores its main control mechanisms of kinematical and energetic performance. We find that at the same average velocity, burst-and-coast swimming of koi carp has lower efficiency and more cost (total output mechanical power) than its equivalent steady swimming, in contrast to the available empirical conclusion that burst-and-coast costs less than steady swimming.3. Routine turns of koi carp have been investigated, also according to the kinematics data of tracking measurements. Experiments has found that the routine turn, especially single-beat turn, is the most observed turn gait in freely routine swimming of koi carps. This thesis studies the unsteady flow physics, unsteady hydrodynamic and energetic characteristics of single-beat turns and cruising turns, the basic two turning modes. Through comparative studies of the turning maneuverability performance and energetics of above two kinds of turns, their common flow control laws and different features are discovered, such as (1) agility (defined as turning rate) is correlated positively with maneuverability (defined as the reciprocal of the turning radius), (2) the total power appears good linear relation with the turning rate, and (3) single-beat turns are more efficient than cruising turns.