Faculty of Aerospace Engineering, Technion, Haifa 32000, Israel.
Integr Comp Biol. 2002 Feb;42(1):127-34. doi: 10.1093/icb/42.1.127.
The dictionary definition of stability as "Firmly established, not easily to be changed" immediately indicates the conflict between stability and maneuverability in aquatic locomotion. The present paper addresses several issues resulting from these opposing requirements. Classical stability theory for bodies moving in fluids is based on developments in submarine and airship motions. These have lateral symmetry, in common with most animals. This enables the separation of the equations of motion into two sets of 3 each. The vertical (longitudinal) set, which includes motions in the axial (surge), normal (heave) and pitching directions, can thus be separated from the lateral-horizontal plane which includes yaw, roll and sideslip motions. This has been found useful in the past for longitudinal stability studies based on coasting configurations but is not applicable to the analysis of turning, fast starts and vigorous swimming, where the lateral symmetry of the fish body is broken by bending motions. The present paper will also examine some of the aspects of the stability vs. maneuverability tradeoff for these asymmetric motions. An analysis of the conditions under which the separation of equations of motions into vertical and horizontal planes is justified, and a definition of the equations to be used in cases where this separation is not accurate enough is presented.
稳定性的字典定义为“牢固确立，不易改变”，这立即表明了水动力运动中稳定性和机动性之间的冲突。本文讨论了由这些相互矛盾的要求产生的几个问题。经典的流体中物体运动稳定性理论是基于潜艇和飞艇运动的发展。这些运动具有横向对称性，与大多数动物相同。这使得运动方程可以分为两组，每组有 3 个。因此，可以将垂直（纵向）组，包括轴向（进动）、法向（升沉）和俯仰方向的运动，与包括偏航、滚转和侧滑运动的横向-水平平面分开。过去，这种方法在基于滑行配置的纵向稳定性研究中很有用，但不适用于转弯、快速启动和剧烈游泳的分析，因为鱼体的横向对称性被弯曲运动打破了。本文还将研究这些非对称运动中稳定性与机动性权衡的一些方面。分析了将运动方程分为垂直和水平平面的条件，并给出了在这种分离不够准确的情况下要使用的方程的定义。
