IBM method was first introduced by Peskin and Peskin andMcQueen to study the blood flow through heart valves. In the IBM, the solid structure is considered as an immersed boundary,which can be represented by a singular force in the Navier–Stokes(N–S) equations to mimic the no-slip condition on the structure. The IBM uses a mixture of Eulerian and Lagrangian variables, which are connected by a smoothed approximation of the Dirac delta function. For the numerical implementation, the Eulerian variables are defined on a fixed Cartesian mesh while the Lagrangian variables representing the immersed boundary are defined on a curvilinear grid that lies on top of the fixed Cartesian mesh. For immersed flexible boundaries, the Lagrangian forcing can be derived by the principle of virtual work.