Studies On The Morphological Dimensions Of The Riblet Surface Of Fast-Swimming Sharks

The skins of fast-swimming sharks,characterized by tiny placoid scales with riblets,display a distinctive riblet surface which is assumed to improve the swimming performance of these sharks by reducing drag.Hydrodynamic studies indicate that, drag reduction of riblet surface depends on the physical dimensions of riblets(rib spacings and rib height).Therefore,measuring the actual rib dimensions of placoid scales of fast sharks is of great importance,in guidance of designing a new kind of riblet surface model to reduce the drag of large-scale ships navigating in rivers and seas.Obviously,if this new kind of riblet surface model that can reduce the drag of large-scale ships was successfully developed,it will be of great importance to the economy and military of the countries.The present study is aimed at providing comprehensive and detail morphological information of riblet surface of fast sharks,including the morphologies of single scales, the arrangements of scales and especially the rib dimensions of placoid scales,to promote the application of riblet surface's bionic material onto the surface of ships.In this connection,skin samples from 6 sharks in 6 shark species,wherein especially skin samples from more than 12 different localities in the body surface of two targeted fast sharks,Sphyrna zygaena and Isurus oxyrinchus were taken.Using scanning electron microscopy(SEM) technique in combination of elaborate manipulations on skin samples,these skin samples were viewed using scanning electron microscopy and a total number of 1751 SEM photos of pkacoid scales at higher magnifications were obtained.The detail morphological information of riblet surfaces from more than 12 different localities in the body surface of two targeted fast sharks were provided,and the regional variations of the scale morphologies,the scales arrangements and especially the rib dimensions among these different surface localities were investigated systematically.Based on above morphological information of riblet surface obtained, we proposed a pair of optimal riblet dimensions that are assumed to produce the best effect of drag reduction in sea water,and moreover,we designed two kind of riblet surface model with this pair of optimal riblet dimensions.The present study is the first time that provide the comprehensive and detail morphological information of riblet surfaces that taken from mote than 12 different localities in the body surface of two typical fast-swimming sharks,and moreover,the regional difference of these three kind of morphological information were investigated systematically.