Placing the Grass Blades

A table injector injects the grass blades at locations given by an XYZ table.

A line probe derived part defines the spacing between the grass blades in the z direction and is used as input to the XYZ table. The resolution of the line probe is set to 37 as this means the spacing between grass blades is as close to the value of the grass blade separation parameter as possible (19.05 mm). The particle flow rate defines the grass blade separation in the x direction and is determined by an equation which states that once the number of grass blades in the simulation falls below a threshold value, another row of grass blades is injected into the domain. The line probe and particle flow rate definitions combined mean that the grass blades are injected in a rectangular lattice formation on the domain boundary.

Grass cutting is a highly dynamic simulation. During the simulation, grass blades that have been cut already move and can reach a position where they overlap with newly injected grass blades. In such a situation, Simcenter STAR-CCM+ removes the injected DEM flexible fiber particle because overlap with existing particles is not allowed.

To set up the injector:
  1. Create and set up a table for the table injector:
    1. Edit the Derived Parts > Line Probe node and set the following properties:
      Property Setting
      Parts Regions > Domain > Boundaries > Bottom
      Point 1 [${Domain Length}*0.5-${Grass Perimeter Offset}, 0.0, -${Domain Width}*0.5+${Grass Perimeter Offset}]
      Point 2 [${Domain Length}*0.5-${Grass Perimeter Offset}, 0.0, ${Domain Width}*0.5-${Grass Perimeter Offset}]
      Resolution 37
    2. Right-click the Tools > Tables node and select New Table > XYZ Internal Table.
    3. Select the Tables > XYZ Internal Table node and click the (Custom editor) next to the Scalars property.
    4. In the Scalars dialog, in the Select From: box, select Time Step, then click (Add selected).
    5. Click OK.
    6. Edit the XYZ Internal Table node and set the following properties:
      Node Property Setting
      XYZ Internal Table Parts Derived Parts > Line Probe
      Representation Latest Surface/Volume
    7. Right-click the Tables > XYZ Internal Table node and select Extract.
  2. Right-click the Injectors node and select New.
  3. Select the Injectors > Injector 1 node and set the following properties:
    Property Setting
    Lagrangian Phase Grass Blade
    Type Table Injector
    Inputs Domain
  4. Select the Injector 1 > Conditions node and set the following properties:
    Node Property Setting
    Flow Rate Specification Method Particle Flow Rate
    Project to Boundary Enabled Activated
    Boundaries Domain > Bottom
  5. Select the Injector 1 > Values node and set the following properties:
    Node Property Setting
    Number of Fiber Segments Value ${Grass Blade Segments}
    Fiber Length Value ${Grass Blade Height}
    Fiber Radius Value ${Grass Blade Diameter}*0.5
    Injection Points Table Table XYZ Internal Table
    X Coordinate X
    Y Coordinate Time Step
    Z Coordinate Z
    Particle Flow Rate Value 
    mod(${TimeLevel},${Grass Blade Injection Rate}) == 0 ? ${Grass Blade Number}/${Time Step} : 0
    Particle Orientation Value [90.0, 0.0, 0.0] deg
    Velocity Value [-${Lawnmower Velocity}, 0.0, 0.0]
  6. Save the simulation.