new features in version 2

- Applications where the primary unknown is a scalar function (for example, steady-state field problems (Z&T 260) such as solving Poisson's equation - the quasi-harmonic equation - over a 2D region) involve a Dirichlet boundary where the field variable U is specified. In the original FELIPE the Dirichlet boundary values had to be obtained a function in the "main engine". In version 2, the pre-processor allows vertical or horizontal Dirichlet planes to be specified, for example "U=8.0 on the plane x=1.0".
- A more general boundary condition can now also be specified, corresponding to a radiating boundary with radiation coefficient alpha and specified normal flowrate qbar (Z&T 262). Up to 9 such boundary sets can be defined. The boundary condition datalines are written at the end of the .dat data input file.
- The above boundary condition facilities can also be used when preparing data files for advanced-level elasticity-type analyses. (The radiation-boundary datalines could be used in a "main engine" to define boundaries where in situ loads should be removed, to simulate excavation.) Or they could be used for the pore-pressure degree of freedom in a coupled elastic deformation-fluid flow analysis (see below).
- Elements can now be assigned a number indicating their material type (e.g. elastic, elasto-plastic, ...). This information will be disseminated during mesh refinement, etc.
- At advanced level, extra nodal degrees of freedom can be specified; data files for problems with up to 4 d.o.f.s per node can be generated. This is done in the "modify mesh" menu option, and it is also possible to specify degrees of freedom which exist only at corner nodes of quadratic elements; the coupled analysis in porel.for illustrates this - see below. The extra d.o.f.s can be created only for nodes in elements of a particular material type (e.g. soil elements in the POREL.FOR application below).
- A wide range of finite elements is supported by PREFEL and FELVUE, including linear and quadratic triangles and quadrilaterals, mapped infinite elements (Z&T 183), beam elements (Z&T 41), and joint elements.
- The data lines defining incremental loading and timestepping regimes can be used in all advanced-level meshes.
- Extra real and integer mesh parameters can be defined at the start of the data file, for use in the "main engine".
- When changing a node's position in the "modify mesh" option, this is now effected using the mouse to indicate the new position (whose coordinates can then be fixed exactly).
- Up to 9 different material properties can be defined in each property set.
- When the input data file contains data lines defining the loading regime, boundary inputs, etc., this data can be read in the pre-processor and edited before saving in the new data file.

- POISS.FOR (for solving Poisson's equation) now uses the Dirichlet boundary planes datalines described above, and also the radiating boundary condition (Z&T 262) is implemented. As the reflective boundary condition is the natural boundary condition, this means that all common types of boundary condition are now supported in POISS.FOR.
- POISS.FOR also calculates flow rates at the Gauss-point centroids of the triangular elements - a form of post-processing (Z&T 264) analogous to calculating Gauss-point stresses in elasticity analyses. The flow-rates can be viewed in FELVUE - see below.
- The 2D elasticity program ELAST.FOR now handles plane stress as well as plane strain analyses.
- There is a further new "main engine", BIGEL.FOR, for Advanced-level elasticity analyses (plane stress or plane strain). This includes coding
for the full range of elements produced by the pre-processor, and 2D linear and quadratic triangles and
quadrilaterals, as well as mapped infinite elements, can be mixed in the mesh. The program replaces the Gaussian elimination solver with a
solver using the frontal algorithm (Z&T 479); this enables complex meshes with thousands of degrees of freedom to be
analysed on a PC. The program also supports all forms of applied loading which can be described in the
data input:
- nodal loads and specified displacements,
- surface tractions
- body forces
- an
*in situ*stress field, with unloading of a boundary to simulate excavation.

- There is another new "main engine" named POREL.FOR. This performs an undrained poroelasticity analysis, i.e. coupled elastic deformation and fluid flow (Z&T 358). A practical application would be the modelling of the initial settlement of a building on a saturated soil; by adding a timestepping regime, soil consolidation could be modelled. The "element material type LMTYPE" facility is used here: soil elements have LMTYPE=2 while elements modelling the structure have LMTYPE=1. For soil elements, an extra degree of freedom is defined at corner nodes only - thus the element involves quadratic shape functions for the displacements but linear shape functions for the pore pressure. This "main engine" is provided to demonstrate the use of the new features (material type, extra d.o.f.s), and a sample data file FOOT3.DAT is given.
- The elasto-viscoplasticity program VPLAST.FOR now also uses the frontal solution algorithm, and also includes a modified frontal solver for non-symmetric matrices. The means that realistic Mohr-Coulomb elasto-plasticity problems with complex meshes and a non-associated flow rule, can be solved.

- For vector-variable analyses such as elasticity, the sole for of display of the nodal values was as a deformed mesh.
The nodal variables can now also be displayed as nodal vectors; this is useful for application where
the primary unknown does not represent displacements, but for example flows in the
x andy directions (in Navier-Stokes problems). - If a mesh involves one-dimensional elements, the user will be asked if these represent beams; if so, the beam bending model will be used, where the 3rd d.o.f. at the end-nodes specifies the torsion angle. Deformations of mapped infinite elements can also be shown.
- Contour plots can be produced for each individual nodal degree of freedom - thus, in the output from POREL.FOR the pore pressure field can be plotted. It is possible to specify that the d.o.f. exists only at corner nodes of elements.
- Contour plots can be produced which are restricted to elements of a particular material type.
- In stress analyses, the Gauss-point stress data can include a 4th stress component (e.g. for out-of-plane stress), and contour plots of each stress component can be obtained.
- In field problems such as Poisson analyses, Gauss-point vectors (analogous to stresses, and representing flow rates, for example) can be read and plotted as flowlines or as contours.
- PostScript files can be generated of all plots, including zoomed plots.