Energy description for deforming bodies moving through inviscid fluids

Abstract The energy-based Lagrangian expressions for multiple deforming bodies translating and rotating through an inviscid fluid in the gravity field are proved to be equal to the momentum-type ones This implies that the energy description can be directly adopted to predict dynamic behaviors of these deforming bodies without adding the body deformation thrust to fluid as the generalized force of the body–fluid system although the total mechanical energy of the system is continuously changed by the deformation effect And it is identified that the hydrodynamic force or torque on any single deforming body includes contributions of linear and angular accelerations of all the bodies, which means that these acceleration constituents should be added to corresponding hydrodynamic loads so as to unsteadily describe motions of the deforming body. In corresponding two dimensional cases, the energy description still holds and may be transformed into the extended unsteady Blasius formulae. Therefore, one can choose any pertinent approach to deal with hydrodynamic interactions among many deformable bodies.