A taste of what's new in VMGSim 9.0 Dynamics

By Kyle Macfarlan - VMG Houston

A large number of exciting new features have been introduced in VMG version 9.0.  In addition to new analyses, such as pipeline pigging, several features were implemented to achieve better accuracy, performance, and productivity. These include variable integrator stepsize, a min-max value tracker, and the ability to playback and record stream data. This article will show how these tools can be used in the context of a vessel depressuring, although they are applicable to many other processes. In the future, we will be discussing other capabilities including pipeline pigging and slug catchers. Stay tuned!

We will use as an example a very simple single-vessel depressuring scenario, as shown below.


The vessel is filled with Nitrogen at 200 kPa and 25 C. We will open the valve and allow the vessel to depressure.

Min-Max Value Tracker 

In many processes, such as depressuring, the important parameters for analysis are minimum and maximum values. For example, in our scenario we are interested in the minimum temperature in the vessel, to ensure that it does not go below the minimum temperature rating for the vessel walls. When we run our scenario, the temperature (shown in red) reaches a clear minimum at about 20 seconds into the depressuring. In this case, there is only one vessel, so it is easy to identify and analyze. But in more complex models, identifying these values is more difficult.


To facilitate this analysis, a min-max tracker has been implemented. You can access it from the Dynamics menu. This tool will keep track of the minimum and maximum values for variables during the course of the simulation.


The min-max tracker clearly shows that the minimum temperature in the vessel was 250.8 Kelvin, and this temperature occurred 22 seconds into the simulation.

Stream Recording

The stream record and playback feature allows us to take a more modular approach to modeling systems. Instead of having to model the entire system at once, each piece can be built and analyzed separately, and the necessary data from upstream processes can be passed to downstream processes. This allows models to be split along organizational considerations; for example, a process team can build a process model, and a flare team can build the associated flare network. The data from a process team analysis can then be passed to the flare team for the flare network analysis. Because the data can be copied and pasted to and from Excel, sharing data is very easy.

To begin playback or record, change the Recording Mode found in the settings tab of the material stream. When the mode is either Record or Playback, the Record/Play tab is visible.


 The recorded data from the blowdown scenario looks like this:


Variable Stepsize

Depressuring scenarios like this are characterized by fast changes at the beginning of the simulation, and then slower changes towards the end. The variable stepsize will automatically shrink the stepsize if the gradients are large, allowing the calculation to better track the evolution of the system over time. But when the system is approaching a steady-state, it will allow the stepsize to expand back to the base size, allowing better performance. In other words, it changes the stepsize to achieve an optimal mix of accuracy and performance.

The variable stepsize options are located on the integrator form.


The integration mode changes whether the integrator uses the variable stepsize, or a fixed stepsize. The step tolerance is what controls whether the stepsize will shrink. A smaller number will force a stepsize shrink more often. The step ratio is the maximum ratio by which the stepsize will shrink. This is only a partial list of the exciting changes in VMGSim 9.0. Be sure to follow us on LinkedIn or subcribe to our newletter to hear more about VMGSim Dynamics.

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