Elzbieta Gawronska

Application of Mixed Time Partitioning Methods to Raise the Efficiency of Solidification Modeling

In this paper we focus on the application of a mixed time partitioning methods to raise efficiency of the solidification kernel in the NuscaS system. We are proposing using a fixed time step in the casting and its integer multiple in other parts of mould because the time step size determines the accuracy of the simulation results. By means of numerical experiments we show that our approach allows for up to about three times performance improvement as compared to the standard approach without loosing precision of results. Moreover, this methods will be extended to 3D numerical simulation in a future work. We notice also that our method can be combined with parallel processing to further improve performance of solidification kernels.

Estimate the Impact of Different Heat Capacity Approximation Methods on the Numerical Results During Computer Simulation of Solidification

The article presents the results of numerical modeling of the solidification process. We focused on comparing the results of calculations for various methods of the effective thermal capacity approximation used in the apparent heat capacity formulation of solidification. Apparent heat capacity formulation is one of the enthalpy formulations of solidification, which allows effective simulation of casting solidification with the one domain approach. In particular, we have shown that the choice of one of four tested methods of approximation does not significantly affect the results. Differences in the resulting temperature did not exceed a few degrees. However, it can affect the time needed to execute the numerical simulations. All presented numerical algorithms were implemented in our in-house software. The software is based on very efficient and scalable libraries that ensures applicability to real world engineering problems.

Analysis of thermomechanical states in single-pass GMAW surfaced steel element

In the paper the model of temperature field, phase changes and stress states calculation during single-pass arc weld surfacing have been presented. In temperature field solution the temperature changes caused by the heat of weld and by electric arc have been taken into consideration. Kinetics of phase changes during heating is limited by temperature values at the beginning and at the end of austenitic transformation, while progress of phase transformations during cooling has been determined on the basis of time-temperature-transformation (TTT) - welding diagram. The analysis of stress state has been presented for S235 steel flat assuming planar section hypothesis and using integral equations of stress equilibrium. It has enabled a clear interpretation of influence of temperature field and phase transformation on stresses caused by surfacing using Gas Metal Arc Welding (GMAW) method.

Numerically Stable Computer Simulation of Solidification: Association Between Eigenvalues of Amplification Matrix and Size of Time Step

The constantly increasing demand for efficient and precise computational solvers becomes the crucial factor deciding about usability of a given domain specific simulation software. The main idea of this article is the use of eigenvalues of amplification matrices to determine the size of time step in modeling of solidification. As far as numerical simulations are concerned it is very important to obtain solutions which are stable and physically correct. It is acquired by fulfilling many assumptions and conditions during the construction a numerical model and carrying out computer simulations. One of the conditions is a proper selection of time step. The size of time step has a great impact on the stability of used time integration schemes (e.g. explicit scheme), or on a proper image of physical phenomena occurring during the simulation (e.g. implicit scheme). The eigenvalues of amplification matrix in governing equations influence on the appropriate selection of size of time step in computer simulations. Hence, it allows to better fit the size of time step and time integration scheme for modeled structure.

The Use of Scalability of Calculations to Engineering Simulation of Solidification

The paper focuses on the use of scalability of available development tools to engineering simulation of solidification in the mold. An essential aspect of the considerations are the ways parallelization of computations taking into account the contact between the two materials. The implementation uses a TalyFEM and PETSc library. A problem solved with finite element method (FEM) can be parallelized in two ways: the parallelization on the mathematical formulas level and the division of tasks into smaller subtasks—assignment of nodes and elements into specific computational units. Both methods can be used in the TalyFEM library if the input files loading module is modified. We have designed our own parallel input module (finite element mesh) providing a division of loaded nodes and elements into individual computational units. Our solutions enable the full potential of parallel computing available in the TalyFEM library using the MPI protocol. This implemented software can be run on any computer system with distributed memory.