How To: Boundary Conditions¶

Boundary Condition Surfaces¶

Boundary conditions in Intact.Simulation are specified as triangle mesh surfaces (*.ply or *.stl files) rather than directly on finite element meshes. This is due to Intact’s non-conforming mesh technology.

Important notes:

Multiple disconnected components in one mesh may not yield high quality results. Create separate boundary condition instances for each fully connected component.
Boundary conditions disconnected from the geometry will result in a runtime warning but are not errors. Forces distributed over disconnected surfaces may not be fully accounted for.
Point and edge constraints/forces/moments are not supported.

Defining Boundary Conditions¶

Boundary conditions are defined in the boundary_conditions array:

{
  "boundary_conditions": [ ]
}

Each boundary condition must specify a type and a boundary surface (path to *.ply or *.stl file). Additional fields depend on the boundary condition type.

Restraints¶

Fixed Boundary¶

A “Fixed Boundary” restraint fixes the selected geometry in all directions.

The fixed boundary only has one input:

the boundary surface to be fixed

{
  "boundary": "restraint.ply",
  "type": "fixed"
}

Fixed Vector¶

A “Fixed Vector” restraint allows for each direction to be optionally set to a specified displacement value, 0 being fixed and ‘None’ being un-restrained. Note that a structural problem must have all three directions restrained somewhere to be valid.

A fixed vector has five inputs:

the boundary surface to be fixed
the x_value to set the displacement for the x-axis direction (optional)
the y_value to set the displacement for the y-axis direction (optional)
the z_value to set the displacement for the z-axis direction (optional)
the units that apply to the displacement values

{
  "boundary": "restraint.stl",
  "type": "fixed_vector",
  "x_value": 0.2,
  "z_value": 0.0,
  "units": "FootPoundSecond"
}

In this example, the X-direction has a displacement of 0.2 ft, the Y-direction is un-restrained, and the Z-direction is fixed.

Sliding Restraint¶

A “Sliding Restraint” allows for motion tangential to a specified surface, but fixes motion normal to the specified surface.

A sliding restraint only has one input:

the boundary surface for the sliding restraint condition

{
  "boundary": "restraint.stl",
  "type": "sliding"
}

Structural Loads¶

Vector Force¶

“Vector Force” load is a surface load applied to a face in a specified direction. An example of this load is pressing on the top of a book to push it across a table.

A vector load requires four inputs:

the boundary surfaces where the load is applied
the direction vector of the force
the magnitude of the force
the units that apply to the magnitude

{
  "boundary": "load.stl",
  "direction": [0, 0, -1],
  "magnitude": 100,
  "type": "vector_force",
  "units": "InchPoundSecond"
}

Torque¶

“Torque” load is a surface load that applies a twisting force around an axis. The direction of the torque is determined using the right-hand rule: using your right hand, point your thumb in the direction of the axis. A positive torque value applies a torque acting in the direction the fingers of your right hand would wrap around the axis. The torque load is applied among the load faces with a distribution that varies linearly from zero at the axis.

A torque load requires five inputs:

the boundary surfaces where the load is applied
the origin for the axis of rotation
the axis vector defining the axis of rotation
the magnitude of the torque
the units that apply to the magnitude

{
  "boundary": "load.stl",
  "origin": [10, 1, 1],
  "axis": [1, 0, 0],
  "magnitude": 10,
  "type": "torque_force",
  "units": "MeterKilogramSecond"
}

Pressure¶

A “Pressure” load is a surface load specified in terms of force per unit area. Positive pressures ‘push’ into the surface, and negative pressures ‘pull’.

A pressure load requires three inputs:

the boundary surfaces where the load is applied
the units that apply to the magnitude
the magnitude of the pressure.

{
  "boundary": "load.stl",
  "magnitude": 10,
  "type": "pressure_force",
  "units": "MeterKilogramSecond"
}

Bearing Force¶

A “Bearing Force” is a surface load applied to a (typically) cylindrical face to approximate the effects of a shaft pressing against the side of a hole. The applied force gets converted to a varying pressure distribution on the portion of the face experiencing compressive pressure. The pressure distribution is computed automatically to achieve the specified overall bearing force.

A bearing force requires four inputs:

the boundary surfaces where the load is applied
the direction vector of the bearing force
the units that apply to the magnitude
the magnitude of the force

{
  "boundary": "load.stl",
  "direction": [0, 0, -1],
  "magnitude": 100,
  "type": "bearing_force",
  "units": "MeterKilogramSecond"
}

Hydrostatic Load¶

A “Hydrostatic” load is a spatially varying pressure on the surfaces submerged in a fluid due to the weight of that fluid. The pressure at any point depends on the height and density of the fluid, increasing from zero at the fluid surface to a maximum at the deepest point.

A hydrostatic load requires four inputs:

the boundary surfaces where the load is applied
the height of the fluid surface
the density of the fluid
the units that apply to the fluid height and density

{
  "boundary": "load.stl",
  "height": 78,
  "density": 1.0,
  "type": "hydrostatic_force",
  "units": "CentimeterGramSecond"
}

Flexible Remote Load¶

A “Flexible Remote Load” allows specifying the force and moment at a remote location that is then applied to a surface. It can be used in a similar manner to NASTRAN’s RBE3 load or Abaqus coupling elements.

A flexible remote load requires seven inputs:

the boundary surfaces where the load is applied
the direction vector of the remote force
the force of the remote force
the axis of rotation about which the moment acts
the moment magnitude of the remote moment
the remote_point where the force and moment are applied
the units that apply to the magnitude and moment

The direction and axis vectors should be unit vectors to describe the direction. They will be normalized if they are not unit vectors.

{
  "boundary": "load.stl",
  "direction": [0, -1, 0],
  "force": 100,
  "axis": [1, 0, 0],
  "moment": 200,
  "remote_point": [1, 1, 1],
  "type": "flexible_remote_load",
  "units": "MeterKilogramSecond"
}

Thermal Loads¶

Fixed Boundary (Fixed Temperature)¶

A “Fixed Boundary” load fixes the selected boundary to a specified temperature when the value is specified and non-zero.

The fixed temperature boundary condition has three inputs:

the boundary surface to be fixed
the value of the temperature to fix at the boundary surface
the units that apply to the temperature

{
  "boundary": "fixed_temp.ply",
  "type": "fixed",
  "value": 320
}

Convection¶

A “Convection” load specifies the transfer of heat from a surrounding medium.

A thermal convection boundary condition requires four inputs:

the boundary surface where the convection is applied
the heat transfer coefficient
the environment_temperature of the surrounding medium
the units that apply to the coefficient and environment temperature

{
  "boundary": "face.ply",
  "coefficient": 25,
  "environment_temperature": 300,
  "type": "convection",
  "units": "MeterKilogramSecond"
}

Surface Flux¶

Surface “Thermal or Heat Flux” specifies the heat flow per unit of surface area.

A surface thermal flux requires three inputs:

the boundary surface where the flux is applied.
the magnitude of the heat flux
the units that apply to the magnitude

{
  "boundary": "face.ply",
  "magnitude": 500,
  "type": "constant_flux",
  "units": "MeterKilogramSecond"
}