Numerical Simulation Of The Motion And Deformation Of Hyperelastic Capsules In Shear And Tensile Flow Fields

Capsule is a core-shell structure formed by a super-elastic film wrapped around a liquid droplet,which has excellent deformability.It is found both in nature-as in biconcave red blood cells-and in artificial products-as in drug delivery vehicles.Since the membrane of the capsule has a certain bending resistance and incompressibility,it is very easy to undergo complex deformation under flow field conditions.Therefore,the study of the dynamical behavior of capsules under different flow fields is of great importance for practical applications such as cell encapsulation design and drug delivery control.In this thesis,the motion and deformation of hyperelastic capsules under shear and tensile flow fields are systematically investigated using finite element analysis based on fluid-solid coupling,and the main findings are as follows:1.In steady-state shear flow,the shear rate and initial position height are the main factors affecting the motion and deformation of the hyperelastic capsule.The vertical velocity of the capsule increases not only with the increasing of the shear rate but also with the increasing of the initial position height;the horizontal velocity is proportional to the shear rate and the initial position height;the phase angle of the membrane decreases with the increase of the shear rate and the initial position height;the inclination angle of the membrane increases monotonically with the increase of the initial position of the center of mass,indicating that the capsule membrane is rotating continuously,and when the steady state is reached,the capsule continues with a constant inclination angle motion;finally we compare the effects of two parameters in the Arruda-Boyce hyperelastic model,where the number of segments denotes the number of molecular chains and is the physical quantity used to construct the model,and the number of segments has a negligible effect on the capsule dynamics.2.In oscillatory shear flow,shear amplitude and shear frequency are the key factors affecting the dynamic behavior of hyperelastic capsules.In addition,the initial position height,capsule film thickness and Young’s modulus also affect the capsule motion and deformation.The results show that the deformation of the capsule is divided into two kinds: at low frequency and high amplitude,the capsule shows overshoot phenomenon and the shape of the capsule is beyond the elliptical range,similar to "dumbbell" and "bowling ball bottle",and even the surface of the capsule has a large number of folds;at high frequencies and low amplitudes,the capsule returned to its original shape.3.In the tensile flow field,and the radius of the capsule,the thickness of the capsule membrane,and the shear modulus in the parameters affect the critical velocity and critical distance when the capsule is initially positioned at the bottom of the axis.The results show that the thickness of the capsule film is linearly related to both the critical velocity and the minimum boundary distance that can drive the capsule away from the lower wall.As the radius of the capsule increases,both the critical velocity and the minimum boundary distance decrease.The shear modulus only affects the critical velocity.The deformation index of capsule separation from the lower wall was also investigated,and it was found that the larger the shear modulus,the faster the capsule separation from the lower wall and the greater the degree of deformation.In this thesis,firstly,we systematically study the motion and deformation of capsules in shear flow,and the simulation results can be widely applied to cosmetics,drug carriers and cellular encapsulation;secondly,we measure the mechanical behaviour of capsule motion under tensile flow fields,which can provide a theoretical basis for the prevention of diseases such as cancer.