Performance of Ray Fins in Performance of Ray Fins in Fish LocomotionFish Locomotion

Qiang Zhu and Kourosh Shoele

Department of Structural EngineeringUniversity of California San Diego

Characteristics of Ray FinsCharacteristics of Ray Fins

Characteristics: Structural lightness Deployability Multi-dimensional controllability 3D anisotropic flexibilty

Ray fins of bluegill sunfish (Alben et al. 2007)

rays

membrane

base

branches

tendonsCartilage pad

ligament

dorsal fin

pectoral finpelvic fin

anal fin

caudal fin

Tangorra et al. 2007

Lauder Lab Videos

Fluid-Structure Interaction ModelFluid-Structure Interaction ModelPotential flow model with boundary element

methodWakes are modeled as shear layers and

mathematically represented by distributions of dipoles

Valid in high Reynolds numbersNonlinear Euler-Bernoulli beam model for

embedded raysFully-coupled fluid-structure interactions

Zhu et al. JFM 2002, Zhu & Kourosh JEB 2008

Caudal Fin DynamicsCaudal Fin Dynamics

Advantages of a fin with flexible rays:Reduced lateral force

Increased propulsion efficiency

Reduced dependence on kinematic parameters

Achievement of different locomotion modes (homocercal, heterocercal)

Zhu & Kourosh JEB 2008

Pectoral Fins in Labriform Swimming

Thorsen et al. 2005

Shape and structure

Rigid Rays: All the rays are rigid (red lines)Fin A: All the rays have the same stiffness (green lines)Fin B: The ray at the leading edge is strengthened (blue lines)

Kourosh & Zhu JEB 2009, 2010

Kinematics

Flapping+rowing+baseline rotation

SummarySummaryThe ray-fin structure enables detailed control of fin

motion (since each ray can be controlled individually), and is essential to the performance of the fin in locomotion.

Flexibility of the rays may enhance fin performance. It, however, depends upon detailed distribution of the stiffness (e.g. reinforcement at the leading edge).

Broader ViewBroader ViewOther Skeleton-Reinforced Membranes in NatureOther Skeleton-Reinforced Membranes in Nature

Venation structure in the wing of a Manduca sexta (from Combes & Daniel 2003).

Insect Wings Cell Membrane

Cell membrane contains a lipid bilayer supported by a protein scaffold (the cytoskeleton) (T. Wittmann, Science Photo Library).

Mollusk Nacre

Mollusk (e.g. abalone) nacre contains a chitin network that controls the growth and mechanical properties of the shell (Asaro & Harley 2004).

Zhu et al. Biophy. J 2007; Zhu & Asaro Biophy. J. 2008; Peng et al. Phys. Review E. 2010

This study is supported by NSF.

Acknowledgements