Defining the Grass Blade Interactions

You define the behaviour of the grass blades when they interact with each other, when they hit the domain walls or when they fall to the ground.

To achieve cutting of the grass blades upon impact of the lawnmower blade, you use the Impact Cutting model. This model breaks the bonds of the flexible fiber DEM particle when the lawnmower blade hits the grass blade with an impact velocity of more than 20 m/s, which corresponds to the default setting for Impact Velocity Threshold.

At one end, the grass blades are connected to the ground by using the Particle-Wall Link model in combination with Link Mode of the Flexible Fiber model set to Single End.

To define the grass blade interactions:
  1. Define the phase interactions between the DEM particles:
    1. Navigate to Continua > Physics 1 > Models > Multiphase Interaction > Phase Interactions and rename the Phase Interaction 1 node to Particle - Particle.
    2. Double-click the Particle - Particle > Models node and select the following models, in order:
      Group Box Model
      DEM Contact Model Linear Spring*
      Optional Models Impact Cutting
    3. In the Particle - Particle Model Selection dialog, deselect Rolling Resistance.
    4. Edit the Particle - Particle > Models > Linear Spring node and set the following properties:
      Node Property Settings
      Linear Spring Normal Restitution Coefficient 0.1
      Tangential Restitution Coefficient 0.1
      Normal Spring Stiffness Method
      Constant Value ${Grass Blade Stiffness}
      Tangential Spring Stiffness Method
      Constant Value ${Grass Blade Stiffness}
  2. Define the interaction between the particles and the wall:
    1. Right-click the Multiphase Interaction > Phase Interactions node and select New > Grass Blade > Wall and rename the Phase Interaction 1 node to Particle - Wall.
    2. Double-click the Particle - Wall > Models node and select the following model:
      Group Box Model
      DEM Contact Model Linear Spring*
    3. In the Particle - Wall Model Selection dialog, deselect Rolling Resistance.
    4. Edit the Particle - Wall > Models > Linear Spring node and set the following properties:
      Node Property Settings
      Linear Spring Static Friction Coefficient 0.1
      Normal Spring Stiffness Method
      Constant Value ${Grass Blade Stiffness}
      Tangential Spring Stiffness Method
      Constant Value ${Grass Blade Stiffness}
  3. Define the interaction between the particles and the ground:
    1. Right-click the Multiphase Interaction > Phase Interactions node and select New > Grass Blade > Domain : Bottom and rename the Phase Interaction 1 node to Particle - Ground.
    2. Double-click the Particle - Ground > Models node and select the following models, in order:
      Group Box Model
      DEM Contact Model Linear Spring*
      Optional Models Particle-Wall Link
    3. In the Particle - Ground Model Selection dialog, deselect Rolling Resistance.
    4. Edit the Particle - Ground > Models > Linear Spring node and set the following properties:
      Node Property Settings
      Linear Spring Normal Restitution Coefficient 0.1
      Tangential Restitution Coefficient 0.1
      Normal Spring Stiffness Method
      Constant Value ${Grass Blade Stiffness}
      Tangential Spring Stiffness Method
      Constant Value ${Grass Blade Stiffness}
  4. Save the simulation.