# Boundary Conditions

Boundary Conditions available for SimSolid.

For a breakdown of which boundary conditions are available for each analysis type, visit the Available Boundary Conditions for Analyses topic.

## Constraints

For static analyses, models must be sufficiently constrained such that all rigid body motion is removed. Rigid body motion is defined as translation or rotational movement along or about the 3 primary (X, Y and Z) geometric axes. The following types of constraints are available:
Immovable support
Enforces zero translational displacements in all directions. It is applied to one or more faces in the model.
Slider support
enforces zero displacement in directions normal to the surface direction. Displacements tangent to the surface are unconstrained. Sliding support can be used to define planes of symmetry.
Hinge support
Hinge supports allow a part to freely rotate about the center-line of a cylindrical face but constrains movement in both the radial and axial directions. Hinge supports can only be applied to full or partial cylindrical faces. The cylindrical faces may be either concave or convex.
Spring support
Spring support allow general stiffness values to be applied to a support in the global X, Y and Z directions. Optionally, these may be defined in terms of volumetric foundation factors. Factors for several common materials such as concrete, wood, hard rubber, loose soil, compacted soil and railroad ballast are provided.
General Constraint

Pressure
A pressure load is defined as force per unit area and acts perpendicular to the part face. Pressure is assumed to be constant.
Force/Displacement
Both force and prescribed displacement are defined in a single dialog. Force is defined as a load on the model. The specified value is interpreted as a total force applied to all selected part faces. Loads and prescribed displacement can be specified in global X, Y and Z directions only.
Gravity is a body load uniformly distributed over the volumes of parts of an assembly. To apply a Gravity load, specify the X, Y and Z directional components of the gravity load in the dialog. When choosing a sign, note that a negative value opposes the coordinate direction. For example, if you want to simulate a downward gravitational force in the Y-direction, you enter “-1” in the Y field of the dialog. Optionally, a gravity amplification factor may be specified. This will scale the gravity and can be used as a means to apply larger full body inertia forces. The default is a standard 1 G gravitational load. Only one gravity load can be applied per analysis. Gravity load acts on all unsuppressed parts of the assembly.
An inertia load is a body load uniformly distributed over either a group of parts or the entire assembly. In SIMSOLID Cloud, inertia loads may be either Translational or Rotational.
• Translational - Translational inertia loads are in the global XYZ reference frame and are specified in terms of acceleration in a given direction. These loads will be superposed with the gravity load if present.
• Rotational - Rotational inertia loads are applied with respect to an axis of rotation. Select a curved cylinder edge to locate the axis of rotation. If necessary, use the Flip axis button to change the way the axis points. Drag the ball and arrows to approximately position the origin point, then fine tune the text values on the dialog. Once positioned, simply specify the acceleration along the axis [α], angular velocity [ω] or angular acceleration [ε] as required and select OK to close the dialog.
Note: Inertia loads act in the opposite to direction specified. An acceleration in the +X direction will cause a force in the -X direction. This is different to the gravity load which has a force in the direction specified. As a reference, common values for gravity at sea level are 9.81 m/s^2 or 386.09 in/s^2.
Inertia Relief

Inertia Relief simulates deformations and stresses in cases where the structure is unconstrained so it can move as a rigid body, and an active load is suddenly applied to the structure. The structure starts moving with translational and rotational accelerations.

Typical applications include an airplane in flight, or a satellite in space.

The solution to the problem of analysis of unconstrained structures is based on d'Alembert principal. The principal states that the structure will be in static equilibrium if the active loads are complimented by fictitious inertia loads evaluated through the structure accelerations. Therefore, in inertia relief analysis, fictitious inertia forces are calculated and distributed over the volume of the structure in such a way that they are in exact balance with your applied forces.

In SimSolid, when analyzing the inertial relief, you don't need to apply additional constraints which would eliminate rigid body motions of the structure. You simply specify the active loads and the rest is done automatically.

Remote loads are used to apply distributed loads to select set of faces that are statically equivalent to a load applied to a single remote point. Static equivalency means that the applied traction exerts the same effect on the model as the force and/or moment applied to the selected point. The remote load is the only method for applying bending, twisting, or other moment loads to your model. To apply a remote load, first enter the remote point coordinates. Dragging the location on screen to roughly position it then use the text fields on the dialog to fine tune the values. Second, enter the force and/or moment directional components on the dialog.
Hydrostatic Pressure
Distributed mass
This can be used to apply distributed mass across selected faces. Distributed mass can be applied using total mass or mass per area.
Bolt and nut tightening
Bolt and nut tightening loads are used to simulate pre-tensioning.
Volume Expansion/Shrinkage
Temperature
Specifies a constant fixed temperature on one or more groups of part faces.
Heat Flux
Specifies rate of heat energy transfer through a given surface per unit of time. Heat rate is given in Watts. Watts are defined as Joules per second. Heat flux is then Watts per unit of area. For example, in SI units, this is given as watt/m^2.
Volumetric Heat
Specifies internal heat generation (heat sources) and internal heat absorption (heat sinks) in a given part volume. A positive volume heat value indicates a heat source, and a negative volume heat value indicates a heat sink. Volumetric heat is given as Watts per unit of volume. For example: W/m^3.
Convection
Specifies the convection coefficient and ambient temperature on a given set of faces. The Ambient temperature defines the temperature of the bulk fluid, which is assumed to remain constant during the analysis. The convection coefficient defines the rate of heat transfer between the bulk fluid (liquid or gas, buoyant or moving) and a surface of your model. The convective coefficient is equal to the heat rate per unit area per unit temperature difference between the model surface and the bulk fluid. Units for convection coefficients are: W/(m^2⋅K).