What's New in PFC 6.0

PFC 6.0 is now available as a pre-release.  This new version provides major enhancements for modeling capabilities, software interoperability, and updated graphics. When you purchase PFC 6 you will receive a license for PFC 6 which will also permit you to use either PFC 5 or the pre-release version of PFC 6 until it is officially released. TRY THE DEMO

Convex Rigid Blocks
Bonded Block Models
Integration with FLAC3D
     – Structural Element Coupling (1D)
     – Interface Coupling (2D)
     – Domain Bridging (3D)
Generic Adhesive Contact Model
Soft Bond Contact Model
Results Files
And More...

 

Convex Rigid Blocks

You can now model convex rigid polygons (2D) and polyhedra (3D). This allows modeling of non-spherical objects when the shape is of importance (granular or cohesive systems) without requiring clumps. Contact detection and resolution use a variation of the GJK (Gilbert–Johnson–Keerthi) algorithm with only one contact between two objects (i.e., no sub-contacts) to maximize efficiency. Interactions between rigid blocks and between other PFC components, such as balls, clumps, or walls, are possible using regular contact models. Similar to balls and clumps (PFC) and blocks (UDEC/3DEC), a fully dynamic solution scheme is employed.

Convex rigid block utilities include:

  • Easy shape creation
  • Shape import shape from CAD data
  • Automatic computation of convex shape from a set of vertices
  • Replication or generation of multiple blocks from templates (similar to clumps)
  • Cutting existing blocks into smaller ones (stochastically or deterministically)
  • Filtering blocks by aspect ratio or relative volume during cutting to remove slivers
  • Merging blocks
  • Rounding edges and corners to reduce the number of active contacts

The following rigid block examples show contours of block velocity for a bin flow example (left) and cylindrical blocks undergoing mixing through shaking (right).

   

The next illustration is based on a 3DEC model that demonstres the effectiveness of flying buttresses in a supporting a thin-walled arch. The structure is simulated as a collection of rigid blocks and the deformation under gravity loading is observed. The model is run with (left) and without (right) buttresses to examine their effect.

 

Bonded Block Models (BBM)

In addition to granular and cohesive systems, now it is easy to create bonded block models (BBM) similar to UDEC and 3DEC. For example, the following compares a PFC2D BBM (left) with a conventional PFC2D bonded particle model (BPM) undergoing a simulated unconfined, uniaxial compression test. The two model plots indicate sample damage and fragmentation. An xy chart of Axial Stress vs. Axial Strain is shown below the two model samples.

PFC3D Integration with FLAC3D

With the release of FLAC3D 6 users were able to model zones and particles together for the first time. With PFC3D 6, Itasca has expanded these capabilities. Now you can work with discrete particles, clumps, and walls with finite-difference zones, interfaces, and structural elements all in one program. Imagine the possibilities! With PFC3D 6, and a valid FLAC3D 6 (or later) license, you can now load FLAC3D elements into the PFC3D environment. Built-in coupling capabilities take three forms.

Structural Element Coupling (1D)

One-dimensional FLAC3D structural elements such as beams, cables, and piles can now be linked to PFC3D balls, clumps, and rigid blocks in a similar manner to zone links in FLAC3D. The following illustrates a rigid block tetrahedral wedge, supported with FLAC3D cables, that falls away from other fixed blocks but is ultimately retained.

Interface Coupling (2D)

Couple PFC3D to zone faces and shell-based structural elements in pseudo-static simulations. PFC walls can be automatically created and slaved to FLAC3D zone faces or shell-based structural element faces. The motion of the wall vertices is slaved to that of the FLAC3D nodes, and forces exerted on the walls are transferred as externally applied forces (i.e., boundary conditions) to the FLAC3D nodes, resulting in an efficient two-way coupling. This functionality was first introduced in FLAC3D 6.

For example, below (left) is a staged-excavation tunnel model created and run in PFC3D 6 (left) that consists of FLAC3D zones and a portion of bonded-particles. This is an elastic model. The bonded-particle micro-properties have been calibrated to match the mechanical properties of the FLAC3D zones (E = 40 MPa, v = 0.2). A smooth transition between the behavior of the zones and particles is clearly demonstrated.  When comparing the coupled model (left) with the FLAC3D model (right), there is a good match between the response of two models. The tunnels in both models are lined with structural shell elements to represent ground support.

 

In another example, a model shows a tunnel excavated under highly anisotropic stress conditions (σH=3σV) using FLAC3D/PFC3D coupling to apply boundary conditions. Rigid blocks (tetrahedra) are used in the PFC3D region using periodic boundaries in the out-of-plane direction. Circular inserts show plots indicating the location of damage (black for shear failure and purple for tensile failure).

The following FLAC3D 6 examples are completely transferable to PFC3D 6. The first example (left) is a series of PFC particles are shown sliding down a chute onto a conveyor belt causing the belt to sag. The other example (right) is that of a punch made up of FLAC3D zones being pushed into another material consisting of bonded PFC3D particles.

 

Another example of interface coupling is the use of 2D shell structural elements to represent protection nets in rock fall simulations. In the below figure, complex rigid blocks (not clumps) represent boulders moving down across a hillside represented by a wall topology. Towards the bottom of the hill a barrier has been erected to impede any rock falls. Rigid blocks and the structural shell element are colored by displacement (color scales are different).

Domain Bridging (3D)

Couple PFC3D elements to FLAC3D zones. With this approach, the kinematics of PFC3D elements and FLAC3D zones is constrained within select regions of the model where they overlap, to ensure displacement continuity.

This approach can be used for quasi-static as well as for dynamic situations, and minimizes spurious energy discontinuity between the different regions of the model. For example, the following dynamic wave propagation model employs an input ground motion (Ricker wavelet) applied to the center of the inner PFC3D model while ground motion displacements are recorded in the far field FLAC3D zones. The magnitude of velocity for both the particles and the zones are plotted below on a cutout of the balls and zones. The bridged model response agrees with the analytic solution from Stoke's Equation.

Generic Adhesive Contact Model

The Adhesive Rolling Resistance Linear Model is a new contact model now available in PFC 6 to represent a simple cohesive granular material. It is based on the two-dimensional model of Gilabert et al. (2007). The cohesion arises from a short-range attraction, which is a linear approximation of the van der Waals force law. The short-range attraction differs from the PFC bonded materials in that there is no concept of breakage (i.e., the attraction is always present whenever the interacting surfaces come within a specified attraction range). Gilabert et al. (2007) state that assemblies of cohesive grains exhibit much larger variations in their equilibrium densities than do corresponding assemblies of non-cohesive grains, because the cohesive grains may form loose, solid-like cohesive granulates. Such granular systems can stay in mechanical equilibrium at lower solid fractions (down to 25-30%) than cohesionless granular systems (with typical solid fractions of 58-64%). Cohesive granular materials have much less frequently been investigated by numerical simulation than cohesionless ones. The new contact model in PFC encompasses both types of materials, and could be used to study macroscopic behavior of a variety of cohesive granular materials including cohesive powders such as xerographic toners (in which cohesion stems from van der Waals interaction) and wet bead packs (in which cohesion stems from liquid bridges joining neighboring particles).

This contact model provides the behavior of a cohesive granular material via a short-range attraction as a linear approximation of the van der Waals force by adding a cohesive component to the rolling resistance linear model. It is a linear-based model that can be installed at both ball-ball and ball-facet contacts. The cohesive component is characterized by two parameters: the maximum attractive force (F0), and the attraction range(D0), as in the following figure.

A contact with the adhesive rolling resistance linear model is active if and only if the surface gap is less than the attraction range, then the force-displacement law is skipped for inactive contacts. In addition to the energy partitions of the rolling resistance linear model, the adhesive rolling resistance linear model also partitions adhesive energy (i.e., work done by the attractive force on the contacting pieces). Refer to Gilabert et al. (2007) and Gilabert et al. (2008) for additional information about the structure and mechanical properties of cohesive granular materials as well as additional examples of cohesive packings studied in the laboratory.

Soft-Bond Contact Model

The soft bond is a new contact model now available in PFC 6, representing a linear softening contact model for bonded particle modeling (BPM) applications. Prior to reaching the bond strength in either tension or shear, the model behaves fundamentally similar to the linear parallel bond contact model. A softening parameter can be specified to modify the stiffness in the post tensile failure regime, allowing for a degradation of the tensile stiffness as a function of increasing bond elongation. Such softening can lead to increasing the ratio of UCS to tensile strength of a specimen using the soft bond model when compared with the traditional linear parallel bond model.  

Results Files

Results files are save files stripped down to contain only user-specified data. These files:

  • can be generated manually or automatically during cycling,
  • are about 5% of the size of a full save file in the case of large models,
  • are useful for sharing results with colleagues and clients and for archiving work, and
  • simplify post-processing (e.g., mass, automated bitmap generation for movie generation across many results files over the course of modeling), but
  • cannot be used to cycle the simulation any further (save files are needed for this as they retain the complete model state).

And More ...

  • Data file converter to translate PFC 5 data files into PFC 6 (please note that only a limited number of PFC 5 commands/FISH functions have been renamed for software interoperability).
  • An update to PFC 5 now includes the ability to export PFC 5 save files into a format that can be restored directly by PFC 6
  • PFC's graphics rendering engine has been upgraded
  • Now compatible with Remote Desktop Protocol (RDP)
  • Integrated Help panel
  • Integrated Technical Support Dialog
  • New archiving system to provide save file compatibility across all future major versions (starting from Version 6)
  • Python updated to version 3.6
  • A revised material-modeling support package for PFC 6 will be available shortly
  • Dynamic input wizard to assist with pre-processing dynamic signals
  • Now based on Visual Studio 2017 and QT5; provides Intel 2018 support