7.2 Matrix selections, VPT and post-processing

The measurement matrix provides a graphical overview of the complete FRF matrix in terms of the response channels (rows) and excitation points (columns). The order of the DoFs is determined by the order of sensors / impacts / VPs as defined in Prepare. Clicking on a box within the matrix will display the corresponding FRF within the Graphing card and related information in the Validate card. Right-click on an entry and choose Focus on Excitation, Focus on Response or Focus on Virtual Point to immediately focus on that measurement point in the 3D viewer.

The colors and values of the entries in the matrix each represent a certain statistic quality value, as described below. The FRF matrices can now be shown for any combination of raw and Virtual Point-transformed channels, as described next.

Matrix selections and Virtual Point Transformation

The matrix is shown for the measured FRF data by default, but several other options are available for reviewing the matrix with VP-transformed data.

The matrix mode can be changed by selecting the desired mode in the taskbar above the matrix. Additional presets are also available; the matrix modes displayed in the taskbar can be toggled on/off by selecting them in the additional context menu, as shown in the following figure.

The figure below also shows the option to add a custom preset within the context menu. Any combination of raw and VP-transformed data can be shown in the measurement matrix using the custom presets. The creation of custom presets is discussed further in the following paragraphs, and descriptions of the default presets are discussed next.

The following video explains how to use the matrix viewer in Analyze.

Measured

In Measured mode, statistics on the raw FRF matrix are shown. This is typically used right after or during measurement to ensure the collected data are of high quality. Here you can even do additional measurements to optimize specific excitation points; if an impact is triggered while in this mode, the software will confirm if it is intentional and add it to the impact location currently selected in the matrix.

VP

In VP mode, the VP FRF matrix is shown as a result of the transformation of all responses and excitations associated with Virtual Points. The matrix will become square, and the specific VP DoFs follow from the definitions as set for the respective Virtual Points in Prepare. This is useful for e.g. mount characterization and Dynamic Substructuring.

All

In All mode, statistics are shown for both the measured FRF data and the VP FRF data, for a grand overview of all possible FRFs. Obviously, any update to the data takes the longest time to refresh in this mode, as every VP DoF gets recomputed.

VP+

In VP+ mode, statistics are shown similar to VP mode, but also including any microphones, additional sensors, and control impacts that are not associated with any VP. This is useful for e.g. Dynamic Substructuring, where it is desired to include additional impact or response data in the component model.

Response-VP

In Response-VP mode, the matrix is shown as a result of VP transformation of only the responses, with the excitations kept in the original framework. This is not used for most typical applications.

Force-VP

In Force-VP mode, the matrix is shown as a result of VP transformation of only the excitations, with the responses kept in the original framework. This is useful for many source characterization and Transfer Path Analysis applications, as it typically results in a matrix that has more rows than columns, with the forces/moments located exactly at the desired (Virtual Point) interfaces.

Custom presets

Custom presets can also be defined to study any combination of measured and VP transformed excitations and responses. Custom presets can be generated from the context menu shown in the figure above, accessible by clicking Add custom preset. Here, the desired excitations and responses are selected. Note that you can also click on the Type and Virtual Point buttons near the top to sort and filter the channels.

Creating a custom selection is useful to focus on e.g. the left side of the car, a subset of VPs, etc. Additionally, to export a certain subset of data to ATFX, MAT or UFF (see Export options), it must first be defined in a custom preset here.

Matrix post-processing

Like the VP transformation, in DIRAC you can do other matrix post-processing steps. All the possible post-processing activities can be found with the custom presets in the Matrix Preset window (see picture above). To perform them, you must first tick the Matrix Post-Processing box.

You can perform three different types of matrix post-processing: matrix integration, matrix inversion, and matrix transposition.

If the matrix is square, you can also apply matrix symmetrization (done for matrix presets comprising only Virtual Point channels) and cropping (applied to square matrices that only have 2 VPs, to select the upper-diagonal square).

On the left, you can decide the type of post-processing technique to apply to the matrix. On the right, an overview of the post-processing is displayed. In particular, it shows the performed operations, the units of the Channels, and the units of the Reference Channels.