How to select more than 10 nodes to be used for a curve

23 March 2018
Since the release of PLAXIS 3D 2017 and PLAXIS 2D 2018 it's possible to select an unlimited number of points to be used for curves via the GUI, rendering the approach below obsolete for these newer versions.

In order to generate curves to show e.g. displacements in time, we should select a node for which we want to show this displacement data, or stress points to show stress related data. The Plaxis applications currently allow you to select up to 10 nodes and 10 stress points prior to calculation for which the data for all intermediate steps is stored.
For nodes and stress points selected after the calculation (post-calc), the data will be retrieved from the stored result files. By default, a phase will have the Max number of steps stored set to 1, so only the last step for this phase is remembered, hence only the result for this step will be shown for the selected post-calc node. For more detailed curves, it is needed to increase this Max number of steps stored to have more intermediate data points in a phase for the curve. If the Max number of steps stored is equal to the Max steps value then all steps will be available to be used for a curve.
For more details, see the related article on Selecting points for curves.

Note, having a lot of results steps saved will also increase the disk space needed.

For some applications, like dynamic earthquake analyses, the number of steps is usually huge, and so a lot of data will need to be stored if you want to define graphs with more than 10 nodes. However, with the use of a special file, it is possible to tell PLAXIS 2D it needs to store the nodal history for more than 10 nodes. Note: this is not available for stress points.

History file: data.hi2.rsa

This special file for these (additional) pre-calc selected nodes is an ASCII file (text file) named data.hi2.rsa and it needs to be present in the Plaxis data folder.

The structure of this file is as follows:

  • The first line contains the desired number of nodes (followed by at least one space)
  • Then on each next line, the first number must refer to the node NUMBER from the mesh, followed by at least one space. Note: any character after this space can be added as a comment and will be ignored by the calculation.
  • Using this trick, the Plaxis calculation can store the history of up to 100 nodes.

Example content to store data for 4 nodes (nodes 1492, 1829, 2045 and 2229)

4 #number of nodes 
1492 
1829 
2045 
2229

To make it work

  • First, save the Plaxis 2D project file
  • In the *.p2dxdat folder, create a file data.hi2.rsa
  • Open this file with a text editor (e.g. Notepad) and add the number of nodes on the first line.
  • Then,  per line add the node number
  • Save this data.hi2.rsa
  • Now open the Plaxis project file in PLAXIS 2D, and run the calculation.
  • Make sure to save the file after the calculation!

This data.hi2.rsa file can be altered to include a different amount of nodes:

  • make sure to change the number of selected nodes on the first line
  • then every next line should contain a node number. This node number can be retrieved in the Output program e.g. from the table when viewing the mesh.

After the calculation and saving, you will find per phase a file called data.hx2.rr# (with # the number of the phase) in which the displacement history of the stored nodes from the data.hi2.rsa-file is saved.

Content of results file

Structure

The file data.hx2.rr# (with # the number of the phase) contains per phase the history of the nodal data for each calculation step.

In this file, the data will be written for each calculation step once a calculation step is finished.
It will write:

  • two lines with general values for the current step (lines 1 and 2, see below)
  • then for each selected node from the data.hi2.rsa file one line of data with displacement values in this step: ux, uy, excess pore pressure value and optional for a dynamic calculation vx, vy, ax and ay. E.g. line 3 shows the displacement values for the first selected node number from the data.hi2.rsa file, line 4 of the second selected node, etc.
  • and finally one line with results from this step

The specific data per step also contains some legacy data (e.g. multiplier data from 2D Classic and earlier) which is not used since the PLAXIS 2D AE version and defaults to a value.

The content structure looks like this:

1[legacy][legacy][legacy]timePmaxcurrent_phase_step

2ΣMweightt_dynΣMareaΣMsf[legacy]previous_phase_step
3uxuyPexcessvxvyaxay
4uxuyPexcessvxvyaxay
....
6uxuyPexcessvxvyaxay
7FxFyΣMstage[legacy][legacy]CSP

Notes:

  • [legacy] defaults to either 0.0 or 1.0
  • the velocity and acceleration values (vx vy ax ay) are only added in dynamic phases
  • t_dyn is the dynamic time
  • Pmax is the phase’s maximum excess pore pressure
  • ΣMstage is not updated correctly in 2D AE and 2D 2015.00
  • current_phase_step and previous_phase_step refer to the internal step number of the phase. This internal numbering always starts at step 0 for each phase.

So if we take the input example as shown above and run the calculation, the image below could be part of the data.hx2.rr# - result of a dynamic calculation, opened in e.g. Notepad:

Figure 1. Example of part of data.hx2.rr# file containing steps 1 to 3

In this calculation we selected 4 nodes. This means that per step, we have 7 lines per step: 2 data lines, then 4 lines with node data, followed by 1 result line:

Figure 2. Example of part of data.hx2.rr# file highlighting data blocks for steps 1 to 3

For each step block in this example, lines 3-6 contain the results per node:
ux    uy    excess_pore_pressure    vx    vy    ax    ay

Figure 3. data.hx2.rr# file showing the data lines per step containing the node specific results

And these are the most important parameters in the general data lines (lines 1, 2, and the final line per step):

Figure 4. Parameters in the general data lines 1, 2, and the final line for step 2 of the phase

Results in Output program

Note that the data of this data.hx2.rr#-file does not follow a valid data format for the PLAXIS Output program. So it is not possible to use the history of these nodes in the PLAXIS Output program to visualize this in a curve. For this a third party application, like a spreadsheet program (e.g. Microsoft Excel), is needed.

Conclusion

With the mentioned trick, it is now possible to follow and store the complete displacement history of more than 10 nodes without the need to save all calculation results.

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