Xianhong Han

An iterative stabilized fractional step algorithm for finite element analysis in saturated soil dynamics

The discretization of the u–p model for saturated porous media results in the semi-discrete system of mixed type in displacements and pressures. The Babuska–Brezzi condition or the simpler patch test proposed by Zienkiewicz and Taylor precludes the use of elements with the equal low order of interpolation for u and p, unless special stabilization techniques, such as the fractional step algorithms, are used. The purpose of this paper is to present a modified version of the fractional step algorithm which allows much larger time step sizes than those for the existing ones. The method is based on introducing an iteration algorithm. The numerical experiments demonstrate the effectiveness and improved performance of the proposed modified version of the fractional step algorithm.

Equal Low-Order Finite Element Simulation of the Planar Contraction Flow for Branched Polymer Melts

The rheological characteristics of branched polymer melts is described by the modified XPP model, which is discretized by inconsistent streamline-upwind method. A finite increment calculus procedure is introduced to reformulate the mass equation and to overcome oscillations of the pressure field. Moreover, the governing equations are discretized and solved by the iterative fractional step algorithm. Thus the equal low-order finite elements for velocity-pressure-stress variables are adopted to calculate the planar contraction viscoelastic flows. The influences of the Weissenberg number and the amount of branched-arms on the rheological behavior of the Pom-Pom molecule are discussed. Results demonstrate good agreement with those given in the literatures.

Numerical studies of flow-induced defects in aluminum ingot die casting process

A numerical modeling of aluminum die casting is discussed in this paper. Emphasis is laid on the flow-induced defects including air entrainment and oxide tracking. An ingot die casting process is designed by considering both laminar zone and turbulence zone. Pure aluminum is used as the casting material. In addition, different process parameters and different shapes of sprue are presented to check their influence to the flow status and flow-induced defects.

Hybrid Optimization Approach for Gas-Assisted Injection Molding Based on Metamodeling and Particle Swarm Algorithm

As a new plastic process technique, Gas-assisted injection molding has many advantages comparing to the traditional injection molding. Meanwhile, Optimization of Gas-assisted injection molding is more complex since many additional parameters have been introduced to the process. In this paper, a hybrid optimization approach based on metamodeling and particle swarm optimization algorithm is proposed and applied for Gas-assisted injection molding. Moreover, the validation of the approach will be illustrated through the optimization process of a real panel.

Modelling of Non-Isothermal Non-Newtonian Viscoelastic Flows

An adaptive coupled finite element (FE) and meshfree (MF) method in ALE description for numerical simulation of injection molding processes is proposed. In combination with the proposed method, an iterative stabilized fractional step algorithm using Characteristic Based Split procedure for numerical simulation of incompressible non-isothermal non-Newtonian fluid flows is developed. The pressure stabilization is further enhanced with introduction of the modified version of finite increment calculus (FIC) process into the proposed algorithm. A mixed finite element formulation for viscoelastic flows is derived, in which the FIC pressure stabilization process and the DEVSS method using the Crank-Nicolson-based split are introduced within a general framework of the iterative version of the fractional step algorithm. The SU method is particularly chosen to deal with the convective terms in the constitutive equation of viscoelastic flows. With the proposed scheme the finite elements with equal low-order interpolation approximations for stress-velocity-pressure variables are successfully used with numerical stability and high convergence rate even for viscoelastic flows with high Weissenberg numbers. Numerical experiments demonstrate the significance and performance of the proposed method.