New in Version 6.0

When FLAC is run in large strain mode, the grid may become sufficiently distorted that the simulation halts with a "bad geometry" error message. Automatic rezoning logic is now available to generate new, more regular meshes during the solution process to replace the old, distorted mesh and transfer mesh-dependent information from the old mesh to the new mesh. The new command REZONE initiates the rezoning process.

FLAC Version 6.0 is compiled with a different compiler than that used for FLAC 5.0. The result is that the (double-precision) code runs significantly faster. (The calculation speed of the single precision version is not affected.) The speed increase for basic models (without FISH operations during cycling) is approximately 35%. For models that include the use of FISH functions during cycling, an even greater increase in speed is seen. The increase in speed depends on the model design. For this reason, only the double-precision executable is provided with FLAC Version 6.0. It is no longer necessary to provide a single-precision version to increase the calculation speed for simple models, as was offered with previous versions of FLAC.

A single command input line can now contain up to 200 characters (instead of the 80 character limit in previous versions of FLAC).

Contour plots of zone-based variables can now be extrapolated to gridpoints by using the SET extrap gp command. Either a simple extrapolation procedure or a least-squares extrapolation procedure can be applied.

New GENERATE commands are available to define grid shapes. The keywords bilinear, column, line and row are provided to facilitate positioning of gridpoints along different shapes. These are used primarily to convert virtual grids to FLAC grids.

The SET rez_func command is provided so that the automatic rezoning logic can be invoked whenever a “bad geometry” error is encountered.

Substantial additions to the grid generation tools in FLAC Version 6.0 make model construction easier, faster and tremendously flexible. A new "virtual grid" mode of grid generation is provided. In this mode, commands are not executed until the grid is completely constructed. When working in virtual-grid mode, limitless undo/redo operations are possible, which eliminates the extensive effort required to correct errors after a grid is created. In addition, the virtual grid is stored with the model as an object separate from the executed grid. This allows the user to return to the virtual grid for other purposes, such as to modify the model or use the virtual grid as a basis for a new model.

The new Cap-yield soil (Cysoil) material model is a simple strain-hardening/softening constitutive model for soils, characterized by a frictional Mohr-Coulomb shear failure envelope (zero cohesion) and a non-linear volumetric cap. The model can be customized to fit different characteristics of soil behavior through the selection of hardening laws. These include a cap-hardening power law that captures the volumetric behavior observed in isotropic compaction tests, a friction-hardening law that reproduces the hyperbolic stress-strain behavior observed in drained triaxial tests, and a compaction/dilation law that models the irrecoverable volumetric strain taking place as a result of monotonic soil shearing. The Cysoil model is implemented as a built-in constitutive model in FLAC 6.0.

The dynamic analysis chapter, previously provided in the Optional Features volume, is now greatly expanded and available as a separate FLAC volume. New sections have been added to provide additional guidance and recommendations for dynamic, and especially seismic liquefaction, analysis. Verification and example application problems have also been added to the dynamic analysis volume.

The OPT command now works with the FLAC 6.0 double-precision executable. The use of the optimizer will provide a substantial increase in speed when running FISH constitutive models.

A new FISH function, “MODRED.FIS,” is provided. This function computes the modulus reduction factor and damping ratio in a one-zone model at different shear strain levels for comparison laboratory measurements.

The intrinsic function rez exe causes commands contained within a given string to be executed. The function is used to facilitate grid regeneration during cycling when the automatic rezoning logic is used.

The thermal analysis and creep material models chapters, previously provided in the Optional Features volume, are now available as separate FLAC volumes. The section describing used-defined constitutive models written in C++ is now part of the Theory and Background volume.

The entire Command Reference, FISH in FLAC and Example Applications volumes are included as an HTML help file for ease of reference. These volumes are accessed through the Help menu in the GIIC.