Characteristics of the non-smooth surface morphology of living creatures and its application in agricultural engineering

Contrasting with smoothness, non-smoothness occurs widely around the world. There are many typical non-smooth surface morphologies in living creatures. Non-smooth surfaces have some special functions during the evolution of living creatures. According to the traditional conception, the body surface is smoother, and the adhesion force is smaller. In many cases, the surfaces of some products or working parts are manufactured into smooth surfaces to reduce friction resistance and adhesion force. In nature, there are different appearances. Flying birds have non-smooth feathers or non-smooth wings, and swimming fish have non-smooth squama or non-smooth connective tissue. Typically, some soil-burrowing animals such as the dung beetle, ant, pangolin, earthworm, ground beetle, mole cricket, loach, earwig, locust, millipede, and centipede live in moist or adhesive soil, but their bodies seldom stick to the soil. The problem of soil adhesion has been solved in soil-burrowing animals. It was shown that in order to adapt to the living environment, soil-burrowing animals evolved several kinds of body surface special morphology or functions. In this paper, some characteristics of non-smooth surface morphology are summarized. The investigations for reducing friction, resistance and adhesion by the non-smoothness are reviewed. The applications of non-smoothness in engineering are discussed, and the tendency in this field in the near future are forecasted.