At the time of writing, AFT Impulse 8 is right around the corner. We are proud to boast of new capabilities to give you an even better user experience with transient analysis.

AFT Impulse 8 showcases new features never seen before, and ones only hinted at with the releases of AFT Fathom 11 and AFT Arrow 8. Here, we have laid out the top 5 new features to be on the lookout for.

  1. Multi-Scenario Graphing
  2. Scenario Comparison
  3. Define transient force sets from workspace
  4. New unsteady friction model
  5. Multi-level undo and redo

Each of the below features will be shown off with the same example model: valve closure with an in-line gas accumulator (bladder). 

Example model for presenting the new features of Impulse 8
Figure 1: Example model for presenting the new features of Impulse 8

1) Multi-Scenario Graphing

This is a favorite new feature of many engineers at AFT and test-users around the world. And for good reason. You can now show the results from multiple scenarios on one graph! And you can graph any parameter across multiple scenarios. (Compare this to the new Fathom 11 that allows similar functionality only for pump vs. system curves.)

Imagine testing out 2 cases of the valve closure: 1 with the accumulator inactive, and 1 with it active. We are looking at how the accumulator affects the pressure seen at the branch upstream of the accumulator. We are expecting the accumulator to mitigate and reduce that pressure surge.

Well, it is now much easier to compare those responses, side-by-side. And guess what, our expectations are supported by the graph below!

Figure 2: Multi-Scenario Graph of a valve closure both with and without an accumulator active
Figure 2: Multi-Scenario Graph of a valve closure both with and without an accumulator active

2) Scenario comparison

The next tool is just as useful, and just as loved by users. With the new version, you can now directly compare the differences (and similarities) between scenarios on a single window.

In the above example, we made some changes between the scenarios, right? One scenario had the accumulator active, and the other had it inactive. What if we wanted to double-check that was the only difference? Now it is super easy with the Scenario Comparison Tool.

Below, you can see the tool in action. For our purposes, we only want the differences to be flagged. With the click of a button, I can see that there is only a single difference between the scenarios: whether the accumulator is active or not. Perfect. That was exactly what we were going for.

Figure 3: Using the Scenario Comparison Tool to check the differences between scenarios
Figure 3: Using the Scenario Comparison Tool to check the differences between scenarios

3) Transient force sets can be defined directly from the workspace

If you deal with pipe forces, you might have thought it a pain to go into a separate window (inside Transient Control) to define the transient force sets. With a large model, it can be a challenge to match up the pipe / section numbers to what is visually presented in the workspace. What if your workspace does not have a logical sequence (visually) of numbers for pipes and junctions? Sometimes, your numbering has a mind of its own. We get that. But it makes it very hard to track down what pipes you want to include in a force set.

Fear no longer! You can directly add force sets from the workspace. Simply highlight the pipes you want to create force sets for, right-click, and choose to create forces sets.

Figure 4: Creating Force Sets for pipes from the workspace
Figure 4: Creating Force Sets for pipes from the workspace

One caveat to this is that the force sets can only be created in this way for individual pipes. It will not create a force set across multiple pipes. To do so, you will have to do a little tweaking inside the Force Output tab in Transient Control.

Figure 5: Force Sets defined for the pipes after creating from the workspace
Figure 5: Force Sets defined for the pipes after creating from the workspace

4) New unsteady friction model: the "Brunone" Model

Changing flow is an inherent part of transient analysis. That changing flow also has an affect on the frictional effects from the pipe. The pressure drop from a pipe friction, or a component, is a function of velocity. When the velocity changes, the pipe friction changes too. The "Simple" friction model in the previous versions of AFT Impulse would take that new velocity value and directly calculate a new friction factor for that.

However, with sudden changes in velocity, there is more to consider, especially as the change becomes more dramatic. This new Brunone model includes an extra unsteady shear stress term, which varies based on the velocity at the current time step. This model stems from a technical paper by Adamkowski and Lewandowski (2006).

Keep in mind, this calculation is more theoretical than the Simple model, and should be used with caution. Also note that the increased calculation intensity will cause your model to run slightly longer.

Figure 6: Applying the new “Brunone” Unsteady Pipe Friction Model
Figure 6: Applying the new “Brunone” Unsteady Pipe Friction Model

5) Multi-level undo and redo

Everyone makes mistakes. And everyone makes more than one. We used to pry perfection of the users by allowing only a single action of undo and redo. But now, you don't have to worry about that! We have implemented the long-awaited multi-level undo and redo.

This does not apply to every change made in Impulse, though. For "major" changes, such as changing the data inside a junction or pipe, no undo exists. But for the visual building of the workspace, you can undo and redo all you want. Probably the most useful is when deleting a junction (perhaps accidentally) and deciding it should come back.

Rule of thumb: if you change something without opening another window and confirming data with "OK", then you can probably undo it. Who doesn't love the old Ctrl+Z move?

Figure 7(a) : Workspace after edits (b): Undoing to get back to the original model
Figure 7(a) : Workspace after edits (b): Undoing to get back to the original model

That about sums up our top 5 features for the all-new AFT Impulse 8! If you have an active Support, Upgrade, and Maintenance (SUM), you can download AFT Impulse here - when it goes live of course. To check out a full list of features, you can find the Impulse 8 New Features Data Sheet here. Happy endeavors with your transient modeling, and, as always, contact us any time you have questions. We love to help.