The term loads includes boundary conditions and externally or internally applied forcing functions. Following are examples of loading types in various disciplines:
Structural: Displacements, velocities, accelerations, forces, pressures, temperatures (for thermal strain), gravity
Thermal: Temperatures, heat flow rates, convections, internal heat generation, infinite surface
Magnetic: Magnetic potentials, magnetic flux, magnetic current segments, source current density, infinite surface
Electric: Electric potentials (voltage), electric current, electric charges, charge densities, infinite surface
Acoustic: Pressures, displacements
Diffusion: Concentration, diffusion flow rate
Loads are divided into six categories: Degree-of-freedom (DOF) constraints, forces (concentrated loads), surface loads, body loads, inertia loads, and coupled-field loads.
| Load Category | Description |
|---|---|
|
DOF constraint |
Fixes a degree of freedom (DOF) to a known value. Examples: Specified displacements and symmetry boundary conditions in a structural analysis, prescribed temperatures in a thermal analysis, and flux-parallel boundary conditions. In a structural analysis, a DOF constraint can be replaced by its differentiation form, which is a velocity constraint. In a structural transient analysis, an acceleration can also be applied, which is the second order differentiation form of the corresponding DOF constraint. |
|
Force |
A concentrated load applied at a node in the model. Examples: Forces and moments in a structural analysis, heat flow rates in a thermal analysis, and current segments in a magnetic field analysis. |
|
Surface load |
A distributed load applied over a surface. Examples: Pressures in a structural analysis, and convections and heat fluxes in a thermal analysis. |
|
Body load |
A volumetric or field load. Examples: Temperatures and fluences in a structural analysis, heat generation rates in a thermal analysis, and current densities in a magnetic field analysis. |
|
Inertia load |
A load attributable to the inertia (mass matrix) of a body, used primarily in structural analyses. Examples: Gravitational acceleration, angular velocity, and angular acceleration. |
|
Coupled-field load |
A special case of one of the loads listed above, where results from one analysis are used as loads in another. Example: Applying magnetic forces calculated in a magnetic field analysis as force loads in a structural analysis. |