Powerful Scripting for Model Customization

In this example, particles float down a channel with a given velocity and fall into a mixing drum with rotating paddles. The channel and stirring paddles were imported into PFC from a series of CAD files and automatically converted into equivalent PFC walls. In addition to the standard contact physics inherent in PFC 5, FISH scripts are added to calculate and apply both drag and  bouancy forces to the particles (colored by elevation). 

A FISH callback function is used to apply the additional buoyancy and drag forces to each particle in the model for each calculation step or cycle. These additional model forces are are calculated as:

where ρf is the fluid density, Vd is the displaced fluid volume by the ball, g is the gravity vector, ηf is the fluid dynamic viscosity, rball is the ball radius, α is the ratio of non-immersed ball volume to the total ball volume and v is the ball velocity vector. The expression chosen for the drag force is typical for a single sphere completely immersed in a fluid in the laminar regime (e.g., large fluid viscosity). The factor α is introduced to scale down the drag force when the ball is only partially immersed.

True particle-fluid interaction would be described better by including forces that are derived from the mass continuity equation and the Navier-Stokes Law. This kind of analysis is performed with the coupled-CFD option in PFC. However, the goal for this example is to show how additional physical laws can be added to your models using FISH. Additional functionality can be added incrementally in order to minimize model complexity while increasing accuracy.