Analysis Engine Calculation

<< Click to Display Table of Contents >>

Navigation:  PipeLay > Technical Notes > Technical Note 8 - Calculation of Support Fine Tune Offsets >

Analysis Engine Calculation

Previous page Next page

Once the user interface has achieved the specified pipe radii of curvature and a static analysis is run, you may find that the predicted radii of curvature at the supports differ to what was specified in the Radii of Curvature dialog. This is because under tensile loading the pipe tends to straighten in the spans between the supports and so the profile it adopts is somewhat more piecewise linear rather than curved. The net effect of this is that you get a concentration of curvature at the supports themselves, which could in theory be higher than the curvature specified in the Radii of Curvature dialog. To address this issue the analysis engine can, if requested, carry out a Support Elevation Optimisation step during the static analysis procedure. The Support Elevation Optimisation step attempts to maintain the radii of curvature as applied by the user interface even after the pipe has undergone tensile loading and support concentration effects. The Support Elevation Optimisation step only affects the supports that have Analysis Optimisation set to Yes in the Radii of Curvature dialog.

If a Support Elevation Optimisation step has been requested, it only runs if any of the radii of curvature at the supports have deviated by more than 1% of the specified value.

At the start of the Support Elevation Optimisation step, the analysis engine must decide which support to move (this will be referred to as the governing support from here on) as only one support is adjusted at a time. To do this the analysis engine checks the predicted static radius of curvature at the different supports and compares them to the corresponding radii specified by the user. The governing support is the support whose static radius of curvature is less than the associated user defined value by the greatest amount.

Once the governing support is found, its elevation is adjusted along the Fine Tune Direction to bring the current radius of curvature at the support closer to the requested value. While the governing support is being adjusted, the radius of curvature at the rest of the supports is constantly monitored and the analysis engine will switch the governing support when a more suitable support is found; suitability is based on the same criteria when picking the original governing support. The engine will also switch to a different support should the current governing support become unloaded as a result of the elevation adjustment. This switching of supports is important as adjusting the governing support obviously affects the radius of curvature at adjacent supports. It also ensures that radius of curvature values at supports will not deviate too far from the desired value during the optimisation process.

The analysis engine continues on in this manner, constantly switching and adjusting supports, until all the supports have been optimised or a max number of attempts have been reached. The default number of attempts for Support Elevation Optimisation is 500, but this can be changed if Criteria are present in the Analysis. To elaborate, if the Max Iterations for the specified Criteria is greater than 500, then this takes precedence over the default value. The Support Elevation Optimisation also stops if the model runs into convergence difficulties or if no more support adjustments can be made without worsening the achieved curvature profile.

Once a Support Elevation Optimisation step has run, a Support Data CSV file is created in the corresponding Stage Results directory. This file contains a summary of the adjustments made to the supports Fine Tune Offset values and can be accessed via the View Support Data button on the Results tab of the Analysis component. This CSV file contains the same data columns as the corresponding user interface output described previously, but the data here is distinctly different in some ways. For example, the Radius of Curvature value in this instance is the predicted radius of curvature as achieved by the analysis engine after optimisation. Also, the X Movement, Y Movement and Fine Tune Offset values are the sum of the adjustments applied by both the analysis engine and the user interface.

In the Progress tab of the Analysis component, a summary of the Support Elevation Optimisation step is presented to the user. This summary simply states the maximum percentage difference of any pipe support curvature below the corresponding specified value before and after the optimisation process. This is a good indication of how much the support profile has improved after the Support Elevation Optimisation, but nonetheless a full review of the Support Data CSV file is advised to ensure the profile meets expectations.

If a Criteria analysis or a Sheave analysis is run, then the model adjustments made during these analysis steps could change the radii of curvature achieved by the Support Elevation Optimisation step. For this reason, a Support Elevation Optimisation step is run before and after these particular analysis steps. This is to ensure that all pipe curvatures achieved during the first Support Elevation Optimisation step are maintained after any Criteria or Sheave analysis has made model adjustments. The second Support Elevation Optimisation step only runs if the 1% tolerance measure previously outlined is no longer maintained. Please note that the Support Data CSV file produced by the second Support Elevation Optimisation step overrides the file produced by the first step and the X Movement, Y Movement and Fine Tune Offset are the sum of the offsets applied by the UI and both Support Elevation Optimisation steps carried out by the analysis engine. All other entries will remain the same.