MDF (Mesh Data File) Format

MDF (Mesh Data File) is a data file format to store finite element mesh data. An MDF file is a simple text file containing the definition of any finite element mesh. Also a user can either implement himself another procedure to read his finite element data or develop a simple program to convert his favorite mesh file structure to an MDF file.
The main principle here is that any information in the file is contained in a line and is defined by a keyword following the rules :

• The first line must contain at the first columns the string #MESH!
• Keyword Dim starts a line that gives the space dimension. An integer number (between 1 and 3) must follow this keyword.
• Each node must be introduced by a line starting with the keyword Node. This keyword must be followed by the following data :
  
  

  label	Label of node (integer)
  x[1]	First coordinate of node (real number)
  ...	... ...
  x[dim]	dim-th coordinate of node (real number)
  nb_dof	Number of d.o.f. associated to node (integer)
  code[1]	Code associated to first d.o.f. (integer)
  ...	... ...
  code[nb_dof]	Code associated to nb_dof-th d.o.f. (integer)

  
  

• Each element must be introduced by a line starting with the keyword Element. This keyword must be followed by the following data :
  
  

  shape	String defining the element number (string)
  el	Label of element (integer)
  nb_nod	Number of element nodes (integer)
  code	Code associated to element (integer)
  el_node[1]	Label of first node of element (integer)
  ...	... ...
  el_nod[nb_nod]	Label of nb_nod-th node of element (integer)

  The element shape is given by a string of at most 10 characters. This string must be recognized among the stored element shapes in the library. In addition, there must be an concordance between the shape and the number of nodes.
  
  

  Shape	Shape Name	Dimension	Min. Nb. of Nodes
  Line	line	2	2
  Triangle	tria	2	3
  Quadrilateral	quad	2	4
  Tetrahedron	tetra	3	4
  Hexahedron	hexa	3	8




• Of course, giving the shape of the element should not be necessary but it is used here for a rigorous check of data. The main restriction in the free structure of the MDF file is that an element (or side) node given in an Element (or Side) line must have been defined before in a Node line. Otherwise, an error message is displayed and execution stops.
  The element code can be any integer number that the developer may use to identify collections of elements (macro-elements, sub-domains, material data, ...).



• Each side must be introduced by a line starting with the keyword Side. A side is a finite element in a lower space dimension than an element. Giving information on sides enables to prescribe surface type boundary conditions as Neumann boundary conditions. The syntax of a line beginning with keyword Side is the following :
  
  

  shape	String defining the side number (string)
  sd	Label of side (integer)
  nb_nod	Number of side nodes (integer)
  sd_node[1]	Label of first node of side ( integer)
  ...	... ...
  sd_nod[nb_nod]	Label of nb_dof-th node of side (integer)
  code[1]	Code associated to first d.o.f. of side (integer)
  ...	... ...
  code[nb_nod]	Code associated to nb_dof-th d.o.f. of side (integer)

• Each used material must be defined by a line starting with the keyword Material. The syntax of a line beginning with keyword Material is the following :
  
  

  code	code number (integer)
  mat_name	Name of the material associated to code (string)

  The code number is a prescribed element code. If the material name is unknown (i.e. if it does not occur among element codes) the program looks for a class that you have probably developed with this name.
  The package contains a class called MyMaterial that gives an example of user defined material. If no material is associated to an element code, the program associates to this code a fictive material called GenericMaterial and whose properties are all equal to unity.

• Boundary condition data can be introduced in an MDF file by means of the keyword BC. To each code of a degree of freedom can be associated a value to impose. For this, to each code must correspond a line that starts with keyword BC followed by the data :
  
  

  c	Code of degrees of freedom to which a value is to be associated (integer)
  v	Value to prescribe (double)

  This method to introduce Dirichlet boundary conditions is much simpler than via a user defined class. But there are some limitations.

  • Imposed values can't depend on time.
  • They are real values.
  Notice that this series of data must be provided after node and element data.

• The last line of the MDF file must contain the keyword EOF (as End Of File).