flotools has a library of calculated variables built in to the application. These variables are made available to plot automatically without any additional user input. However, the list of built-in calculated variables that are available to plot will depend on the list of variables available in the output files. We will start with a simple example.
A simple example of a calculated trend is the variable ACCGAG. In the OLGA manual, ACCGAG is described as the “Accumulated gas mass flow”. If you have the variable GG output at any position in your .tpl file, flotools will automatically make ACCGAG available to you at the same positions.
Note that flotools calculates ACCGAG by performing numerical integration using the trapezoidal rule at the time interval that you have chosen to output GG, whereas OLGA might calculate the integral at the internal time step.
Calculated accumulation variables
Extending from the ACCGAG example, all the accumulation variables calculated by flotools and their sources are listed below.
| Accumulation variable | Source variable |
|---|---|
| Mass variables | |
| ACCGAG | GG |
| ACCGT | GT |
| ACCLIG | GLT |
| ACCOIG | GLTHL |
| ACCWAG | GLTWT |
| Volume variables | |
| ACCGAQ | QG |
| ACCLIQ | QLT |
| ACCOIQ | QLTHL |
| ACCWAQ | QLTWT |
Other calculations based on a single source
I started with the accumulation variables as they are very easy to understand. Here I will list more calculations that are based on a single source variable including a short description of how they are calculated.
- DTM – Time derivative of temperature – Obtained by taking the numerical derivative of TM trends
- DPT – Time derivative of pressure – Obtained by taking the numerical derivative of PT trends
- DUG – Time derivative of gas velocity – Obtained by taking the numerical derivative of UG trends
- DUL – Time derivative of liquid velocity – Obtained by taking the numerical derivative of UL trends
Calculated trends with a single profile variable source
OLGA calculates some variables that are based on a profile variable of the entire branch. These can be thought of as branch statistics variables. There are two classes of these variables – statistics at any given time, and statistics for the entire simulation. Since profiles may not be output at very regular intervals, flotools does not offer to calculate the second class of statistics, i.e., for the entire duration of the simulation. The list of variables from the first class of statistics is given below.
- MAXPTBRCT – Maximum pressure in branch at current time – maximum value in PT profile for each time at which profile is recorded in .ppl
- MAXPTBRCT – Minimum pressure in branch at current time – minimum value in PT profile for each time at which profile is recorded in .ppl
- MEANPTBRCT – Average pressure in branch at current time – distance-weighted average of PT profile for each time at which profile is recorded in .ppl
- MAXTMBRCT – Maximum temperature in branch at current time – maximum value in TM profile for each time at which profile is recorded in .ppl
- MAXTMBRCT – Minimum temperature in branch at current time – minimum value in TM profile for each time at which profile is recorded in .ppl
- MEANTMBRCT – Average temperature in branch at current time – distance-weighted average of TM profile for each time at which profile is recorded in .ppl
In the next part, I will discuss the calculation of rate variables.
– Prasanna.