Wall
Use a Wall node to specify a wall’s material properties and movement. The Accumulator (Boundary) and Force Accumulator subnodes are available from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.
Wall Material Properties
When Hertz–MD or Hertz–MD with adhesion model is selected in the Contact Force Model list in the physics interface Force section, the Specify list is available with the options
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 Young’s modulus and Poisson’s ratio (the default)
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 Young’s modulus and shear modulus
Young’s modulus and Poisson’s ratio fields appear when Young’s modulus and Poisson’s ratio is selected. Young’s modulus and Shear modulus fields appear when Young’s modulus and shear modulus is selected. These properties can be assigned to grains as follows:
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 Young’s modulus Eg (SI unit: Pa). By default this is taken From material. If User defined is selected, the default is 100 GPa.
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 Shear modulus Gg (SI unit: Pa). By default this is taken From material. If User defined is selected, the default is 45.45 GPa.
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 Poisson’s ratio νg. By default this is taken From material. If User defined is selected, the default is 0.1.
Boundary Condition
This section is only available when Compute conductive heat transfer checkbox is selected in the physics interface Grain Temperature section. Select a Specify boundary condition:
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 Specified temperature (default) — enter a value or expression for the Temperature T (SI unit: K) which defines the temperature of selected walls. The default value is 293.15 K. If another physics interface is present which computes the temperature of the walls then this can be selected from the list.
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 Insulated — select this when you want to impose insulated boundary condition on the walls.
Adhesion Properties
This section is only available when the Compute van der Waals force checkbox is selected and/or when the Hertz–MD with adhesion is selected in the Contact force model list in the physics interface Force section. Enter a value or expression for the Surface energy density γ (SI unit: J/m2). The default value is 0.05.
Wall Movement
This section controls the rigid-body motion of the selected walls. Select an option from the Wall motion list.
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 Fixed (default) — select this when you want the selected walls to be stationary.
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Translation — select this when you want to impose any arbitrary prescribed displacement to the walls. This is commonly used to specify translational motion of the wall but can also be used to prescribe any arbitrary displacement.
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Rotation — select this when you want to impose a rotational displacement to the walls.
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 Translation and rotation — select this when you want to impose a mixture of translational and rotational motion to the walls.
It is not recommended to use the Moving Mesh interface with the Granular Flow interface to describe any kind of wall movement. Use of the Moving Mesh interface with the Granular Flow interface is not fully supported and may result in unphysical grain dynamics.
When either Translation or Translation and rotation is selected, enter the values of the components of the Prescribed displacement dx (SI unit: m). The default value for each component is 0 m.
When either Rotation or Translation and rotation is selected, select an option from the Rotation type list.
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Choose Constant angular velocity (the default) to specify an angular velocity ω in the Angular velocity field (SI unit: rad/s) using only numbers and model parameters. The default value is 0. Specify an initial angle α0 in the Initial angle field (SI unit: rad). The default value is 0. This effectively sets the rotation angle to α = α0 + ωt.
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Choose General angular velocity to specify a general angular velocity ω using an expression in the Angular velocity field (SI unit: rad/s) with an initial angle α0 specified in the Initial angle field (SI unit: rad). The rotation angle is computed by solving an ODE for α, which is therefore a state variable and part of the solution.
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Choose User defined to add a user-defined expression for the rotation angle α in the Rotation angle field. The default value is 0.
Enter the base point rbp components in the Rotation axis base point fields (SI unit: m). The default value for each component is 0.
When Translation and rotation is selected, the translational motion of the rbp components is automatically accounted for and should not be explicitly included in the expressions.
For 3D components, enter the rotation axis eax in the Rotation axis fields. The default values are 0, 0, 1. In 2D, no rotation axis is specified; it is assumed to point out of the plane, toward the observer.
If you specify a General angular velocity, the Wall feature uses an ODE to integrate the rotation angle in time. This can in some situations negatively affect solver behavior. Therefore, when the rotational velocity is constant, make sure to select Constant angular velocity.