Advanced

FEM Boundary Conditions

Apply loads and constraints to your model

Overview

Boundary conditions (BCs) define how your model is loaded and constrained. confBuild supports 9 boundary condition types covering mechanical loads, kinematic constraints, and thermal conditions. Each BC is applied to specific face groups on your mesh.

Force

Point and distributed forces

Pressure

Normal surface pressure

Fixed

Rigid constraint, all DOF locked

Temperature

Prescribed thermal conditions

Boundary Condition Types

All 9 supported boundary condition types with their parameters.

Force

Apply point or distributed forces in the global coordinate system.

Parameter Unit Description
fx N (Newton) Force component in X direction
fy N (Newton) Force component in Y direction
fz N (Newton) Force component in Z direction

Visualized as colored arrows showing force direction and magnitude.

Moment

Apply rotational moments (torque) around each axis.

Parameter Unit Description
mx Nm Moment around X axis
my Nm Moment around Y axis
mz Nm Moment around Z axis

Visualized as curved arrows around the rotation axis.

Pressure

Apply normal pressure to a surface. Positive pressure pushes into the face.

Parameter Unit Description
pressure Pa (Pascal) Normal pressure on the surface

Visualized as a grid of arrows normal to the surface with shading.

Fixed Support

Locks all degrees of freedom (translation and rotation) at the selected face. This is the most common constraint type.

Parameter Value Description
dx, dy, dz 0 All translations locked

Visualized as a hatched ground symbol indicating rigid support.

Displacement

Prescribe specific displacements. Set a value to constrain, or leave as null for free.

Parameter Unit Description
dx m (or null) Prescribed X displacement
dy m (or null) Prescribed Y displacement
dz m (or null) Prescribed Z displacement

Visualized as bidirectional arrows: solid for constrained, transparent for free.

Rotation

Prescribe specific rotations. Set a value to constrain, or leave as null for free.

Parameter Unit Description
rx rad (or null) Prescribed rotation around X
ry rad (or null) Prescribed rotation around Y
rz rad (or null) Prescribed rotation around Z

Temperature

Apply a prescribed temperature at a surface for thermal analysis.

Parameter Unit Description
temperature °C Prescribed surface temperature

Visualized as a thermometer icon on the surface.

Heat Flux

Apply a heat flux across a surface for thermal analysis.

Parameter Unit Description
heatFlux W/m² Heat flux through the surface

Visualized as wavy arrows indicating heat flow direction.

Gravity

Apply gravitational acceleration as a body force to the entire model.

Parameter Unit Description
acceleration m/s² Gravitational acceleration (default: 9.81)

BC Visualization

All boundary conditions are visualized in 3D with distinct colors and symbols.

BC Type Color Symbol
Force Deep Orange Directional arrows
Pressure Blue Arrow grid on surface
Fixed Green Ground/hatching symbol
Moment Purple Curved arrow arc
Displacement Amber Bidirectional arrows
Rotation Cyan Rotation arcs with lock icon
Temperature Pink Thermometer icon
Heat Flux Orange Wavy arrows

Coordinate System

Choose between global and local coordinate systems for each BC.

Global vs. Local

  • Global: Forces and displacements are defined in the world coordinate system (X, Y, Z)
  • Local: Forces and displacements are defined relative to the surface normal (useful for pressure on angled surfaces)

By default, all BCs use the global coordinate system. Switch to local when applying loads perpendicular to angled or curved surfaces.

AI-Assisted BC Generation

Let AI set up your boundary conditions from a plain-text description.

How It Works

  • Describe your load case in natural language (e.g., "1000N downward force on top, fixed at bottom")
  • The AI analyzes available face groups from your mesh
  • Appropriate loads and constraints are generated automatically
  • Review and adjust the generated BCs before running the simulation

Example Descriptions

  • "500N downward force on the top face, fixed support at the bottom"
  • "Uniform pressure of 10 kPa on the front face, fixed on left and right sides"
  • "Gravity load with fixed base, 200N lateral force on the top"
  • "Temperature of 100°C on the left face, 20°C on the right face"

Best Practices

Tips for setting up boundary conditions correctly.

Recommendations

  • Every model needs at least one constraint (fixed, displacement, or rotation) to prevent rigid body motion
  • Start with a simple load case and add complexity gradually
  • Check the BC visualization to verify loads are applied to the correct faces
  • Use symmetry to reduce model size: apply symmetry constraints on cut planes
  • For gravity, remember to assign a material with density first

Common Mistakes

  • No constraints: Solver will fail with singular matrix error if model can move freely
  • Over-constraining: Locking all faces creates artificially stiff behavior
  • Wrong units: Forces in Newtons, pressure in Pascals, displacement in meters
  • Missing face group: Ensure the target face group exists in the mesh before assigning BCs
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