FEM SolverZ88/it

Descrizione

introduced in 1.2: The Z88 solver implementation has been completely refactored, and this page has been updated accordingly.

Installation

To use the Z88 solver, the open-source version of Z88 (Z88OS or Z88Adria - see Notes for more details) needs to be installed:

1. Download the ZIP package with the code, binaries and documentation of either version:
   • Z88OS: official Z88OS repository or forked Z88OS repository
   • Z88Adria: Z88Adria download page.
2. Extract the ZIP contents to a folder of your choice.
3. In the FEM preferences, go to the Z88 tab and set the path to the z88r binary. If you are on Windows, this would be the path to the file z88r.exe that is in the subfolder \bin\win64 for Z88OS or \z88adria_windows for Z88Adria.

Utilizzo

Properties

• DatiExclude Bending Stiffness - replaces beams with trusses, currently always checked because beams are not yet supported
• DatiModel Space:
  • 3D - uses 3D shell elements
  • plane stress - uses 2D plane stress elements
  • axisymmetric - uses 2D axisymmetric elements
  • plate - uses 3D plate elements
• DatiShell Flag - IHFLAG value: set to 2 or 3 for thin shells and to 4 for very thin shells
• DatiAnalysis Type:
  • static - regular linear static analysis
  • test - provides information about the solver parameters - this information is loaded into the text document object
• DatiDisplace Mesh - deform the mesh by the displacement field
• DatiIntegration Order Hexa - displacement integration order for hexa elements
• DatiIntegration Order Quad - displacement integration order for quad elements
• DatiIntegration Order Tetra - displacement integration order for tetra elements
• DatiIntegration Order Tria - displacement integration order for tria elements
• DatiIteration Maximum - MAXIT value: maximum number of iterations for iterative solvers
• DatiMatrix Maximum - MAXGS value: maximum number of entries in the stiffness matrix
• DatiRelaxation Factor - ROMEGA value: convergence acceleration parameter for SOR pre-conditioner
• DatiResidual Limit - EPS value: it is compared to the norm of the residual vector
• DatiShift Factor - RALPHA value: convergence acceleration parameter for SIC pre-conditioner
• DatiSolver Type:
  • choly - direct Cholesky solver recommended for small structures
  • sorcg - sparse matrix iterative SORCG solver recommended for large structures
  • siccg - sparse matrix iterative SICCG solver recommended for large structures
• DatiVector Maximum - MAXKOI value: maximum number of entries in the coincidence vector

Supported finite element types

The following types of finite elements are supported by the Z88 solver implementation:

• 2-node 3D truss,
• 8-node and 20-node hexahedron,
• 4-node and 10-node tetrahedron,
• 6-node triangle and 8-node quadrangle - 3D shell and plate, 2D plane stress and axisymmetric formulations.

Linear triangles and quadrangles are not supported at all. Beam elements are not yet supported.

Notes

• Z88Adria has the same capabilities/limitations as Z88OS, but doesn't launch its GUI when running the solver from FreeCAD, so Z88Adria is currently the preferred choice.
• Pressure applied to edges of axisymmetric models must be given as in a corresponding 3D model, i.e. in units of force per unit area; the solver converts it to an equivalent force per unit length by multiplying the pressure by ${\displaystyle 2\pi R}$ (where R is the x-coordinate of the element's middle node). For plane stress elements, there is also equivalent conversion using the element's thickness.
• For plate elements, the degrees of freedom are in order: Z displacement and rotations ${\displaystyle {\theta }_x}$ and ${\displaystyle {\theta }_y}$ (in deg).

Limitations

• Currently, only displacements (in mm), nodal forces, and nodal moments are provided as contour map results. Stress values are loaded into the text document object.
• The 3D truss elements require some additional considerations. In case of errors and missing results when using them, the following steps should be taken:
  • make sure the structural member is meshed with only one such element (adjust the min and max element size to enforce that),
  • apply displacement boundary condition to the whole member, constraining the lateral displacements,
  • use the Cholesky solver.

Preferences

See the Z88 preferences for the possible solver settings, such as the used solver method.