Units, Orientation, and Visualization
Using Units
Enter loads in any unit, independently of the base SI unit system in the model, because COMSOL automatically converts any unit to the base SI unit system. To use the feature for automatic unit conversion, enter the unit in square brackets, for example, 100[lbf/in^2].
The exception is random vibration analysis. In that case, no automatic unit conversions are available, so you must enter loads in the base units of the model.
Predefined and Custom Coordinate Systems
Different predefined coordinate systems are available when materials or boundary conditions are specified. There is always the global coordinate system. Depending on the dimensionality of the part being worked with, there can also be predefined coordinate systems such as the local tangent and normal coordinate system for boundaries.
Custom coordinate systems are also available and are useful, for example, to specify a load in any direction without splitting it into components. From the Definitions toolbar, select a Coordinate System () from the menu.
Some coordinate systems can have solution dependent axis directions. If you use such a system for defining a load, the directions of the load follow the moving coordinate axis directions if the Include geometric nonlinearity checkbox is selected under the Study settings section of the current study step. See Coordinate Systems and in the COMSOL Multiphysics Reference Manual.
Visualization
If you have switched on the physics symbols (see Displaying Physics Symbols in the Graphics Window — An Example in the COMSOL Multiphysics Reference Manual), then an applied load is indicated by a symbol together with a coordinate system indicator displaying the definition directions for the load. The actual direction or magnitude of the load you enter is not, however, reflected by the symbol. As a load in COMSOL Multiphysics can be a function of parameters, variables, the solution, or results from other physics interfaces, it is not possible to display it with only the information available in the individual load feature.
Once you have turned on the physics symbols for a certain physics interface, you can fine-tune the display. Every feature which has associated physics symbols will now have a checkbox Show physics symbols, by which you can control the display of the symbols for that specific feature.
Loads are among the results for which result templates are generated, so you will always have access to a visual feedback of the loads after the solution. How to work with the default load plots is described in detail in the Plotting Applied Loads section.
Sometimes, especially if you have entered complicated load expressions in a large model, it is important to inspect the load distribution before you run the analysis. You will then need to generate a dataset and the result templates. The fastest way to do that is to click Get Initial Value in the Study toolbar. Note that if you change the loads, you will have to delete the dataset and generate it again.
In the COMSOL Multiphysics Reference Manual:
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Physics Symbols
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Using Units
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Coordinate Systems
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Plotting Applied Loads
For an example showing how to examine the load distribution, see Bracket — Static Analysis: Application Library path Structural_Mechanics_Module/Tutorials/bracket_static. This is also the first example used in the Introduction to the Structural Mechanics Module.