About defining a variable print interval (or variable sampling frequency) in Simcenter 3D Motion, using a print interval profile (or print interval curve).
In the context of Motion Simulations, a Solution Print Interval (or results sampling frequency) will most of the time be set as a constant value, either through a Fixed Print Interval value (e.g. 0.001s) or through a Number of Steps (e.g. 1000).
Another option for setting the Print Interval is the Variable Print Method, which can be used to control the output and often skip printing results until some special time or event in a simulation then printing results.
This option is particularly useful in case of complex simulations where a tight sampling rate is needed for certain time periods, whilst other periods can be ignored by using a larger sampling rate, thus reducing the size of the output Motion results (*.mres file).
It is important to note that the Print Interval (Fixed or Variable) does not influence the computation (solving) of the solution, and only has an effect on how often the results are written.
These options can be set through the Solution menu, in the Analysis Options page, by first selecting the Print Interval Definition, that can be:
When the Print Interval Definition is set as Variable Print Interval, the latter one will be defined using a Print Interval Profile (XY Curve).
The Print Interval Profile is an XY curve with the X values being the time at which to modify the print interval and the Y values are the corresponding print intervals.
As an example, let's look at a Print Interval Profile defined as follows:
|Time (s)||Print Interval Value (s)|
In Simcenter 3D Motion, such a Print Interval can be quickly defined using a Manual Input Profile (Fig. 1):
This print interval profile would translate as follows:
Note that the print interval is taken as discrete values defined at the X time value and remains unchanged until the next X value. In our example, between t = 0-1s, the print interval will have a constant value of 0.5s
To illustrate how a Variable Print Interval affects results in terms of their sampling rate, we will look at a simple model with two masses, connected to each other and to the ground using springs and dampers. A load is applied vertically (downwards) on Mass2, and gravity is ignored (Fig. 2):
As baseline, we will look at how the system reacts, with a Fixed Print Interval of 0.001s (Fig. 3):
In a cloned Solution, we will now make use of the previously defined Print Interval Profile to define a Variable Print Interval instead of a Fixed one (Fig. 4).
Comparing the new set of results (variable print) with the original results (fixed print) will show the effects of the variable print interval on the results extraction. (Fig. 5)
It is important to note that although the Print Interval does not affect the solving (computation) process, the value of the Print Interval can change the value of the Maximum Integration Step.
The value of the Maximum Integration Step will take the Print Interval value when the initial Max. Integration Step (from Solution: Dynamic Properties) is greater than the Print Interval value.