Introduction

Abstract

Natural flyers and swimmers such as birds, insects, and fish have fascinated us for centuries. There exists a substantial body of literature on animal locomotion. So far, the majority of the studies were published in biology-oriented journals. However, in recent years, the situation is rapidly changing as engineers and physical scientists have been enthusiastically learning from nature and implementing similar or improved concepts in human-made machines. With advances in miniaturization, first principles-based computational mechanics, precision instrumentation, materials sciences, and multidisciplinary approach, biomimetics is now an area of active research.To help offer updated summaries of some of recent progress in this area to the mechanics community, we have collected five articles to form this special AMR issue of Animal Locomotion in Fluids, and Its Mimicry. The articles were among the invited papers presented in the 2nd International Symposium on Aqua Bio-Mechanisms (ISABMEC 2003), held in Honolulu on September 14–17, 2003. These articles review a wide range of subjects, encompassing flapping as well as fixed wings, rigid as well as flexible shapes, and air as well as aquatic-based vehicles.In the first article, entitled “Review of Hydrodynamic Scaling Laws in Aquatic Locomotion and Fish-like Swimming,” Triantafyllou, Hover, Techet, and Yue summarize the fluid mechanics-based scaling laws for both natural and human engineered swimmers. Comprehensive investigations on various aspects of flapping motion are summarized, including propulsion generation, three-dimensional effects, foil-foil and foil-body interactions, transient phenomena, and the effects of vorticity, Reynolds number, and material stiffness on foil performance. In the second article, entitled “Median and Paired Fin Controllers for Biomimetic Marine Vehicles,” Kato reviews the kinematic as well as hydrodynamic aspects of median and paired fin in fish and human-made devices. The focus is primarily on propulsion enhancement and vehicle control and dynamics. In addition to experimental and computational insight into the related physical mechanisms, interesting advances made in mechanical systems are presented. In the third article, entitled “Effect of Bow Wings on Ship Propulsion and Motions.” Naito examines the issues related to water wave-induced drag and possible remedies offered by bow wings. He also discusses the effects of wing shape, size, position, and stiffness on the characteristics of thrust and resistance, and possible control and energy conversion strategies.“Simulation-Based Biological Fluid Dynamics in Animal Locomotion” is the fourth article, wherein Liu offers a comprehensive account of the various aspects related to animal swimming and flight. The focus is on recent advances in developing suitable strategies and techniques for first principles-based simulation capabilities. Large scale computational fluid dynamics results are summarized for tadpole swimming and hawkmoth hovering flight. Detailed descriptions on the key modeling and computational techniques, including morphology, kinematics, and Navier-Stokes equation solutions are highlighted. In the fifth article, entitled “Membrane Wing-Based Micro Air Vehicles,” Shyy, Ifju, and Viieru first review the vast disparity in scales (dimension, weight, speed), and striking scalability between a wide array of natural and human-made flight vehicles. They then focus on recent progress made in analyzing as well as developing membrane wing-based micro air vehicles, those with a maximum dimension of 15 cm or less. Substantial insight has been gained from computations accounting for the coupled fluid-structure dynamics, ground-based experiments, and actual flight experiences. Salient features in fluid flow aerodynamics, especially those related to the vertical structure and deformable wings, are detailed. Substantial information in regard to design, fabrication, and flight data analysis is also presented.Together, these articles offer fascinating information of how nature allows animals to move in water and air efficiently and effectively, and what we can learn from it. There are rich mechanics issues that await the research community to further advance our understanding, and to use our new knowledge to develop engineering capabilities that we can only imagine right now. Biology and engineering are fast converging in many fronts. It is our hope that this special issue will stimulate more rigorous and forward-looking mechanics research so that we not only mimic the nature, thereby obtaining improved systems for human use, but find other improved solutions where needed.