What are the units of displacement in the ModalStructuralResults returned by the solve function in PDE Toolbox

The 'solve' function in the PDE toolbox for solving structural analysis problems returns 'ModalStructuralResults'. To access the release-specific documentation, you can execute the following command in the MATLAB R2019b command window:

>> web(fullfile(docroot, 'pde/ug/pde.thermalmodel.solve.html'))

For more details on 'ModalStructuralResults', use the command:

>> web(fullfile(docroot, 'pde/ug/pde.modalstructuralresults.html'))

The documentation does not specify the units of the 'modal displacement values at nodes' stored in the 'ModeShapes' property of 'ModalStructuralResults'.

I was following the vibration of a square plate tutorial, which you can access by running the following command in the MATLAB R2019b command window:

>> web(fullfile(docroot, 'pde/examples/vibration-of-a-square-plate.html'))

At the bottom of the tutorial, the third component (z-component) of the solution for the seven lowest nonzero-frequency modes is plotted using the fields of 'ModeShapes'.

I want to know what are the units of the values stored in "ModeShapes.uz"?

The legends of each of the figures show that the values range from 0 to -2 X 10^-3. I want to know what are the units of these values?

 

Answer 1

[MathWorks Support Team]

Mode shapes have an arbitrary scale factor associated with them. Therefore, the magnitude of the numbers does not carry much meaning individually; it is the relative displacement that illustrates the shapes of normal modes. The primary use-case for mode shapes is to allow users to visualize them and perform other types of analysis (such as transient, frequency response, etc.) to determine the actual magnitude.

Additionally, the PDE Toolbox is unit-less, and users should ensure that the model is set up using consistent units. For example, if all inputs are in SI units, then the output displacement would be in meters.

Please follow the link below to search for the required information regarding the current release:

https://www.mathworks.com/help/