1024
|
||
1021
|
||
1018
|
||
1015
|
||
1012
|
||
109
|
||
106
|
||
103
|
||
102
|
||
101
|
||
10-1
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||
10-2
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||
10-3
|
||
10-6
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||
10-9
|
||
10-12
|
||
10-15
|
||
10-18
|
||
10-21
|
||
10-24
|
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Adding two quantities of the same kind that use different units: 0.5[ft]+33[mm]. The COMSOL Multiphysics software converts the result to the base unit system’s length unit (0.1854 m for SI units, for example). A quantity without a unit is treated as given in the base unit’s systems unit, so, for example, 0.5+33[mm] evaluates to 0.533 m when using SI units.
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Using multiplication with a unit to get consistent units for two quantities that you want to add, for example, 14[kg]+ht.rho[m^3], which works if ht.rho represents the density for a heat transfer model. You can also concatenate several units, for example, 3.6[N][m], which is equivalent to typing 3.6[N*m] and evaluates to 3.6 N·m.
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For unit names with spaces and hyphens, such as British thermal unit and pound-force, only use the symbols when declaring units.
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If user-defined parameters or variables are used in the physics, it is good practice to use the unit syntax to define them. The Settings windows for parameters and variables display the resulting unit, in the models base unit system, of user-defined parameters and variables. It is important to verify that the variables have the expected unit before using them in the physics settings. The unit of parameters and variables is otherwise undefined.
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Most user-defined and built-in functions expect dimensionless inputs and outputs, so it is good practice to use make inputs, such as time, dimensionless using unit syntax. If the input is not dimensionless, the COMSOL Multiphysics software marks the expression in an orange color and reports an unexpected unit of input. For example, to use the time t as input to a Rectangle function rect1, use [1/s] to make the input dimensionless: rect1(t[1/s]).
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If other units than the base unit system’s units are used or if SI prefixes are included, the conversion to base units also affects the value (quantity) using a scaling factor (and an offset for temperature units). The Value column in a Settings window for Parameter displays the quantity and unit in the base unit system so that you can see the result of the unit conversion. For example, a parameter is defined as 3[ft], the result in the Value column is 0.9144 m if the base unit system is SI.
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