The rayed structure of the fin is found in greater than 99% of all living fish species – a testament to its versatility. Among many other maneuvers, fish use it to stay still in moving waters, or to propel themselves in explosive bursts of motion. The fins themselves are mechanically passive – that is, they have no biological motors (muscles) embedded within them.
So how exactly do they work? A better understanding of the design principles underlying the fin’s biomechanics could shed light on the reasons behind its overwhelming dominance in the aquatic realm, and lead to applications in underwater robotics.
A team of researchers, including Madhusudhan Venkadesan, assistant professor of mechanical engineering & materials science, took a closer look – research that included use of a three-dimensional reconstruction of a mackerel (Scomber japonicus) pectoral fin. Their results are published in the Journal of the Royal Society Interface. In addition to Venkadesan and lead author Dr. Shreyas Mandre of Brown University, the paper’s authors include Khoi Nguyen, Ning Yu, Mahesh M. Bandi.
Critical to the fin’s function is its ability to curve and stiffen, like a dollar bill that you’re inserting into a vending machine. Unlike a piece of paper, though, it also has bony rays connected by a thin membrane. The rays splay apart when water pushes against the fin, thereby engaging the interconnecting membrane and stiffening the fin.
For more about the science of fins, watch the video below:
School of Engineering & Applied Science on 6th of June 2017
Source: Yale University