The Motion Of A Circular Cylinder In A Fluid By Coupling Of Its Deforming And Changing Of Centroid

The self-propulsion behavior of a deformable body and hydrodynamic interactions among many bodies immersed in liquid have been important topics of hydrodynamics for decades which are of extensive engineering applications,especially in the design of underwater robots and marine vehicles.However,the mechanism of the self-propelled motion of a deformable body and hydrodynamic interaction among bodies with changing center of mass is unclear.This paper investigates the locomotion of an immersed deforming circular cylinder coupled with the variation of its own centroid and then discusses the hydrodynamic interaction between two circular cylinders of variable mass centers.The force and torque acting on the single cylinder by the surrounding liquid are derived using the Kirchhoff formula,and then algebraic equations of motion are derived.The results show that a submerged circular body can makes itself move from a standstill resorting to the coupling of its deformation and center of mass movement without shedding vortices and external forces,and the average migration speed is proportional to the deformation speed.The body can move in various modes by means of changing parameter pair of circle radius and its mass center.For two submerged circular bodies with changing their centers of mass moving through a fluid,the complex potential caused by movement of the bodies is derived by employing successive offset functions.The equations of motion are derived based on the Lagrange equations of fluid-bodies system,and the 4th Runge-Kutta-Fehlberg method is used for solving those ordinary differential equations.Numerical results reveal that those circular bodies immersed in an inviscid fluid can swim from rest only resorting to changing their center of mass without deformation.They may attract each other when both of their centers of mass translate back and forth along the line of centers,whereas they push each other as these centers move up and down perpendicular to the line of centers.