Papers by Keyword: Implicit Method

Abstract: The paper describes the derivation of the numerical formulation of a second order time accurate and Geometrically Conservative Backward Difference Scheme (BDF) for transient flow simulation of Arbitrary Lagrangian Eulerian (ALE) problems using the control volume approach. The required modification to implement the scheme in an implicit adaptive flow solver is explained. The accuracy and robustness of the current formulation is demonstrated by simulating unsteady flow field over a sinusoidally pitching NACA0012 airfoil with larger allowable timestep in comparison to an existing Mid-point scheme.

Abstract: Non-convergence often occurs in the solution of highly nonlinear problem by conventional implicit finite element method. As another choice, explicit method is sometimes used by researchers. Through 2 typical static and dynamic examples this paper verifies that explicit finite element method can provide the same exactness of calculation as the implicit method even in the situation that the duration of action exceeds the natural period of structure greatly. At the same time, compared with implicit method, explicit method possesses higher speed, more robust algorithm, and stronger nonlinear capability, so that explicit method can be applied in static and dynamic analysis of structures, especially in large deformation and highly nonlinear problem.

Abstract: Firstly, we introduced the development of cloth simulation in recent years. Based on physical model of cloth simulation, we established the simulation system with a simplified mass-spring model. The computational efficiency is increased with this model. A modified implicit method was proposed in this paper. This method produces plausible animation, and it is easy to be realized with a stable and good real-time performance. The paper adopted AABB (Axis-Aligned Bounding Boxes) bounding volume approach for the detection of cloth collision, it obtains an excellent real-time effect of cloth simulation.

Abstract: Based on the coupled precise time integration method and basic assumptions of constant average acceleration method in Newmark family, implicit series solution of structural dynamic equation is put forward by introducing the Taylor series expansion. Relevant time step integration formulas were designed. Stability and accuracy of the method were analyzed. Stability analyses show that the coupling implicit method is stable when damping ratio is equal to 0, and is conditionally stable when damping ratio are other values. The results show that the accuracy of the algorithm can be controlled by choosing the number of truncation order of Taylor series expansion and is better than that of traditional scheme with the increase of time step. Number examples are given to demonstrate the validity of the proposed method.

Abstract: A comparative study of different material modeling strategies in deformability analysis of rectangular cups is presented in this paper. The article focuses on application of dynamic explicit and static implicit approaches in Finite Element Methods (FEM) for metal forming simulation where different material models and contact conditions with friction are involved. The simulated results are verified using results from experimental study of the deformation on the same material. Further, a comparison between a quadratic Hill anisotropic yield criterion and von Mises yield criterion with isotropic hardening has been studied. The results confirm that the dynamic explicit method is more efficient in simulating sheet metal forming processes. The study shows also that the finite element analysis undoubtedly gives good approximate numerical results to real processes when the material and friction anisotropy are considered.

Abstract: Numerical simulations of phase separation in Fe-Cr-Mo―Ni or Fe-Cr-MoーTi quaternary alloys similar to ferrite phases in dplex stainless steeswere performed by the Cahn-Hilliard equation. We obtained that the asymptotic behaviour of minor element Ni, Mo, Ti in an Fe-Cr-X quaternary alloy along a trajectory of a peak top of the major element Cr is classified into three groups according to the sign of the second derivative of the chemical free energy with respect to the compositions of Cr and X(X=Mo, Ni or Ti]. It is also predicted that that small addition of Mo upto 10% accelerates phase separation of Cr. It seems that the optimum value of Mo exists to enhance the phase separation of Cr in Fe-Cr-Mo ternary alloys. Simulation result indicates that the phase separation of Cr is most enhanced with addition of 1% Mo. The above mentioned simulation results given by the numerical simulation by the Cahn-Hilliard equation were in good agreement with those obtained by the Monte Carlo simulation Theoretical analyses were performed in order to discuss the simulation results. On the basis of theb simulation results Optimum materials design of the duplex stainless steel has been established.

Abstract: Numerical simulations of phase separation in Fe-Cr-Mo and Fe-Cr-Ti ternary alloys and Fe-Cr-Mo-Ti quaternary alloys were performed with use of the Cahn-Hilliard equation for ternary alloys and quaternary alloys. We obtained that the asymptotic behaviours of minor element X(Mo, Ti) in Fe-Cr-X ternary alloys and Fe-Cr-Mo-Ti quaternary alloys along a trajectory of a peak top of the major element Cr was classified into three groups according to the sign of the second derivative of the chemical free energy with respect to the compositions of Cr and X(Mo, Ti). Theoretical analysis for the symptotic behavior Mo in Fe-Cr-Mo ternary has been formed in order to discuss the simulation results. Effect of the other elements, such as Ti on separation behaviours of Cr in Fe-Cr-Ti ternary alloys were also investigated. A simple theory for describing the effect of subsutitutonal element in Fe-Cr-X ternary alloys on the basis of simulations and theoretical analyses was proposed.

Abstract: Unsteady Reynolds-Averaged Navier-Stokes computations are presented for the flow over a pure plunging aerofoil and a plunging wing. The implicit RANS solver used for obtaining time-accurate solution is based on implicit finite volume nodal point spatial discretization scheme with dual time stepping. Baldwin and Lomax turbulence model has been used for the turbulence closure. The results are obtained in the form of aerodynamic coefficients, thrust coefficient and propulsion efficiency for two different cases over the aerofoil and wing and are compared with available literature.

Abstract: Unsteady Reynolds-averaged Navier-Stokes (RANS) computations are presented for low Mach number flow past a combined pitching and plunging NACA 0012 aerofoil. The Implicit RANS solver used for obtaining time-accurate solutions is based on a finite volume nodal point spatial discretization scheme with dual time stepping. The aim is to validate the unsteady solver for flapping motion of the aerofoil. Results are presented in the form of aerodynamic coefficients and compared with available literature, thus demonstrating the capability of the solver to provide useful unsteady input data for aeroelastic and aeroacoustic analysis.