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accounting_for_inertia [2018/06/13 13:39] marijn.nijenhuis |
accounting_for_inertia [2023/06/08 16:35] (current) marijn.nijenhuis |
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First, we need to apply a material to the SolidWorks part in order to account for the object' | First, we need to apply a material to the SolidWorks part in order to account for the object' | ||
- | Next, a coordinate system has to be created which is aligned with the global coordinate system used in the Spacar simulation (the default coordinate system in SolidWorks is likely to be different from the one in your Spacar model). It is crucial that the orientation of the coordinate system in SolidWorks and Spacar is identical. While the position of the origins can be different (the inertia properties are calculated with respect to the center of mass anyway), it is recommended that the origin of the new coordinate system in SolidWorks coincides with at least a point that is also a node in the Spacar model (in order to deal with the location | + | Next, a coordinate system has to be created which is aligned with the global coordinate system used in the Spacar simulation (the default coordinate system in SolidWorks is likely to be different from the one in your Spacar model). It is crucial that the orientation of the coordinate system in SolidWorks and Spacar is identical. While the position of the origins can be different (the inertia properties are calculated with respect to the center of mass anyway), it is recommended that the origin of the new coordinate system in SolidWorks coincides with at least a point that is also a node in the Spacar model (in order to deal with the position |
To define the orientation of this new coordinate system, two perpendicular edges/ | To define the orientation of this new coordinate system, two perpendicular edges/ | ||
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{{ : | {{ : | ||
- | Next, a new coordinate system is made (SolidWorks => Features => Reference Geometry => Coordinate system) and the axis generated in the previous step are selected for the '' | + | Next, a new coordinate system is made (SolidWorks => Features => Reference Geometry => Coordinate system) and the axes generated in the previous step are selected for the '' |
Lastly, the inertia properties can be obtained from: SolidWorks => Evaluate => Mass Properties. Here, we have to specify the generated coordinate system from the previous step at " | Lastly, the inertia properties can be obtained from: SolidWorks => Evaluate => Mass Properties. Here, we have to specify the generated coordinate system from the previous step at " | ||
- the total mass of the object | - the total mass of the object | ||
- the moments of inertia taken at the center of mass and aligned with the output coordinate system. | - the moments of inertia taken at the center of mass and aligned with the output coordinate system. | ||
- | - the location | + | - the position |
+ | |||
+ | ** Important: ** Depending on the version of SolidWorks, different conventions are used for the crossproducts (the off-diagonal components of the inertia tensor). With version 2021 and later, you can set the convention: we want the positive tensor notation. You can set this in the Options panel within the Mass Properties window. For older versions of SolidWorks where you don't have this option, be very wary of what SolidWorks returns. In that case, it's mostly likely that SolidWorks shows the inertia tensor with minus signs in front of the off-diagonal components: | ||
+ | $$ \begin{bmatrix} I_{xx} & -I_{xy} & -I_{xz} \\ -I_{xy} & I_{yy} & -I_{yz} \\ -I_{xz} & -I_{yz} & I_{zz} \end{bmatrix} $$ | ||
+ | If it's unclear, check the manual for your version to see which sign convention is being used for the off-diagonal terms. | ||
{{ : | {{ : | ||
===== Adding mass and inertia properties to Spacar ===== | ===== Adding mass and inertia properties to Spacar ===== | ||
- | For this example a single leafsprings is simulated between node 1 ([0,0,0]) and node 2 ([0 0.1 0]), with one end of the wrench attached to node 2 (which coincides with the location | + | For this example, a single leafsprings is simulated between node 1 ([0,0,0]) and node 2 ([0 0.1 0]), with one end of the wrench attached to node 2 (which coincides with the position |
+ | |||
+ | ** Check the full syntax list for the correct use of '' | ||
- | A visualization of the first two vibration modes of this system is provided | + | A visualization of the first two vibration modes of this system is provided |
{{: | {{: | ||
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%node 1 | %node 1 | ||
nprops(1).fix | nprops(1).fix | ||
- | nprops(3).mass | + | nprops(3).mass |
- | nprops(3).mominertia | + | nprops(3).mominertia |
%% ELEMENT PROPERTIES | %% ELEMENT PROPERTIES | ||
Line 79: | Line 85: | ||
eprops(1).orien | eprops(1).orien | ||
eprops(1).nbeams | eprops(1).nbeams | ||
- | eprops(1).flex | + | eprops(1).flex |
eprops(1).color | eprops(1).color | ||
eprops(1).opacity | eprops(1).opacity | ||
Line 89: | Line 95: | ||
%% SIMULATION | %% SIMULATION | ||
- | out1 = spacarlight(nodes, | + | out = spacarlight(nodes, |
</ | </ | ||