Porting FEM-based thermomechanical application to Grids using
GAT

T.Olas, K. Karczewski, L. Kuczynski, G. Szwarc, R. Wyrzykowski


In  this  presentation, we deal with the problem  of  numerical
estimation  of  hot-tearing in castings during  solidification.
For  this  aim,  a  new  method for the estimation  of  such  a
phenomena in a semisolid region is used. This method  is  based
on  a  local  criterion which is valid for a single macroscopic
region  corresponding  to  a  single  finite  element.  In  the
proposed  method  we deal with two types of compact  groups  of
finite  elements: those corresponding to regions suspected  for
hot-tearing, and control elements which correspond  to  regions
which  are not subject to hot-tearing. Such an approach  allows
for the global estimation of hot-tearing in castings [1].

The   resulting  computations  are  performed  in  two  scales:
macroscopic  and  microscopic. In the  macroscopic  scale,  the
finite  element  analysis  is used to determine  the  momentary
fields  of solidification parameters. The obtained results  are
then  used to derive a set of thermo-elastoplastic problems  in
the microscopic scale, taking into account the grain  structure
of a casting.  For this aim, in a chosen region of the casting,
the macroscopic finite elements are “isolated” from the rest of
the FEM mesh. Moreover, the parameters describing the state  of
the  macroscopic elements are used as input data for subsequent
computations.

Consequently, the implementation of the proposed method on Grids
using the GAT API will consist of  two phases.

A  user  starts a GAT application, passing all the  input  data
necessary  to  solve  a given numerical problem  based  on  the
finite  element  analysis  (macroscopic  computations).   Using
mechanisms  implemented in GAT, this application (or management
module) creates a FEM computational task. It is implemented  on
a  local  cluster  as  a  parallel  MPI  application  with  the
estimated  execution  time from one hour to  200  hours.  After
finishing these computations, their results are passed  to  the
management module. It selects those finite elements  for  which
the  stress  state analysis in the semisolid region is  carried
out,  in order to estimate hot-tearing in castings (microscopic
computations).

For  each of the chosen elements (approximately 100-2000),  the
management module creates a new computational tasks, using GAT.
Each  of  these  tasks  is implemented  sequentially  with  the
estimated execution time between 2 and 5 hours.

Data  for  microscopic  computations  are  received  from   the
macroscopic ones. These two phases are performed many times (5-
20) for different conditions of casting cooling.

[1]  G.  Szwarc: Numerical modeling of hot-tearing of  castings
   in the semisolid state. Czestochowa University of Technology,
   PhD Thesis, 2003 (in Polish).