Programs PMD and GFEM
Software PMD (Package for Machine Design) is based on the finite element method (FEM) and allows a solution of general problems of continuum mechanics. PMD consists of original files of programs and subroutines written in Fortran.
PMD as a system has been developed, tested and used in the Czech Republic since 1977.
The PMD package was recommended by the statement No. 515 of the "Special Commission for the Analyses of Components and Piping Systems" dated November 19, 2009 for the creation of documents for nuclear safety documentation of VVER nuclear power plants. Prior to that date PMD had been attested by the State Office for Nuclear Safety under the registration number 531.
The system PMD allows the analysis of the following problems:
Both stationary and transient temperature fields
Linear thermal – elasto - statics
Nonlinear statics, thermo - elastic - plasticity and creep
Nonlinear statics - large deformations, displacements and rotations
Linear (bifurcation) elastic stability
Nonlinear transient dynamics – both implicit and explicit integration.
Independent problem-oriented programming blocks have been compiled within PMD to enable solutions of typical engineering practices problems. The mutual communication of programs within the PMD system is streamlined by using unformatted data files. Input files (ASCII) for the programming block contain only data necessary to control the calculation. Each programming block processes a properly defined segment of the algorithm.
Since the year 1997, PMD has been developed and used together with the Institute of Thermomechanics of the Academy of Sciences of the Czech Republic.
The GFEM software is a graphic preprocessor and postprocessor of the PMD system. GFEM allows mesh generation, setting of boundary conditions and materials, the start of calculation and plotting of the results on the finite element mesh. Program interface allows processing models generated outside the PMD-GFEM system. It is also possible to load finite element meshes generated by programs such as ANSYS, FEMAP, DYNA, PATRAN and others.
Advantages of pre- and post-processor GFEM:
Complete overview of the finite element mesh
Minimized degeneration of finite elements
Focus on mapped meshes reduces computational demands
Perfected support of the utilization of quadratic elements and effective use of edge (midside) nodes
Correcting meshes created by commercial generators.
Easier state of stress evaluation according to different methodologies and standards.
The GFEM-PMD system has strict limits of tolerance to degenerated elements. This condition ensures that the FEM calculation releases only high-quality meshes, resulting in more credible solutions.
The slightly more time consuming creation of a mesh by GFEM processor is well compensated for with meaningful results which can be easily interpreted.
Inputs and outputs of GFEM processor and interconnection with PMD.
The GFEM processor is based on the kinematic formulation of the mesh. A kinematically generated mesh has many advantages not only during the calculation itself, but also for assessing the results. The creation of the mesh can be described as follows:
GFEM preprocessor environment
Each new mesh starts by creating one single point. From this point a line is drawn out and divided into segments - formed by line finite elements. The application of kinematic features such as rotation gives rise to area elements that are then similarly used to create volume finite elements. The kinematic approach to the creation of mesh can be characterized by the sequence: point - line - area - volume.
At each stage of mesh generation a number of different functions can be used to transform the existing mesh, e.g. projection on a variety of geometric shapes, use of generalized displacement. Resulting finite element models can be composed together to create complex technical structures that retain the characteristic properties of geometric submodels.
The input for the GFEM can be a ready made mesh of finite elements, which can be loaded as input text files written in a prescribed format. Input files have the characteristic of an incidental table that carries all details of the geometry of nodes and elements. These files form a pair – the first one with the extension .NOD (nodes) and the second one with the extension .ELE (elements), both with quite a simple structure. Mesh geometry can be read from all other FEM programs by the means of setting up the communication protocol. Every task, whether newly processed, downloaded or modified is stored as a binary file .TSK. The TSK file holds all the necessary information for the entire task (geometry, boundary conditions, materials, loads and load conditions) and is used for any additional work as needed.
The output of GFEM are files that are used by PMD for calculations and control of tasks. For the most commonly used linear thermoelastic analyses, the relevant input consists of the files with extensions .IB, .I1, I2, I3, I4 and I5. For other types of calculation, e.g. the determination of natural frequencies, seismic response, nonlinear and dynamic behavior of structures other input files, with extensions e.g. .IM, .IE, .IF and .ID are used. All PMD input files are generated automatically by GFEM by means of a preset user’s interface.