Scaling of visualisers/visualizers in Dymola

This blog post seeks to raise awareness of how objects such as visualisers/visualizers reference global settings that can be enabled and adjusted from within the Animation Setup and World objects within Dymola.

Often we want to be able to visualise the application of forces and torques to better understand what is happening in the system we are modelling. This is one of the beauties of simulation, the fact that we can animate variables as the system dynamics evolve, and is something that you cannot do in real life experimentation.

In this blog post we will take the instance of the force arrows available within Modelica.Mechanics.MultiBody.Visualizers and Modelica.Mechanics.MultiBody.Visualizers.Advanced.

Figure 1. Location of the aforementioned visualisation arrows within Modelica.Mechanics.MultiBody.Visualiizers
Figure 1. Location of the aforementioned visualisation arrows within Modelica.Mechanics.MultiBody.Visualiizers

The parameter dialog of the arrow classes, an example of which is shown in Figure 2, has a quantity field which allows the user to choose from a list of types, the physical quantity that the arrow represents. The default value for quantity in these arrows is RelativePosition. So if we are interested in using the arrows to visualise a force vector, then we should choose the type Force quantity from the drop down menu.

Figure 2. Parameter dialog for the FixedArrow class.
Figure 2. Parameter dialog for the FixedArrow class.

When we do this, we need to also check the Animation Setup to view what the underlying global scaling is for that type (see Figure 3 and 4).

Figure 3.  Location of the animation setup.
Figure 3. Location of the animation setup. Click on the animation window (or create a new one from the Simulation toolbar) and Dymola will take you to the context toolbar above.
Figure 4. Animation Setup Vectors dialog displaying the default scaling for vector types.
Figure 4. Animation Setup Vectors dialog displaying the default scaling for vector types. These will be visible after the simulation has been executed.

The Force and Torque vector scaling is derived from the World object defaults that will exist in your model. This is shown in Figure 5 below in the Defaults tab.

Figure 5. Screenshot of the world Defaults tab showing the default values for N per m and Nm per m
Figure 5. Screenshot of the world Defaults tab showing the default values for N per m and Nm per m

Video 1. Screen capture of an arrow bench test to analyse how they work. Force is ramped up from 0-1N along the X, Y and Z axis in sequence.

Wider use

Within the VeSyMA suite of libraries we use arrows to visualise forces and torques. These might be torques on drive shafts, or forces at wheel-ground contact points or indeed mesh forces in gears.

In the case of the wheel models we use the Claytex.Mechanics.MultiBody.Visualisers.ForceXYZ arrows to be able to visualise the resultant force along each axis. In this case we have bypassed the global scaling factors and just use an internal scaling factor to the Claytex.Mechanics.MultiBody.Visualisers.ForceXYZ model. This is an option you might want to consider if you do not want your scaling to depend on global values.

Video 2. Animation of one of the many rig tests we include in our VeSyMA – Suspensions library that replicates road profiles through wheel pads. The resulting contact patch force at each corner is visualised via the blue arrows.
Figure 6. Snapshot of a VeSyMA - Powertrain bench test of a manual transmission including the gear shift linkage.
Figure 6. Snapshot of a VeSyMA – Powertrain bench test of a manual transmission including the gear shift linkage. The arrows are visualisation of the forces in the helical gear meshes that are transmitting the torque.

In summary, try and use as much visualisation as possible, not only for analysis purposes but also for debugging models and be aware of the global scaling settings that are used by such visualisation objects.

Claytex can offer bespoke guidance on how to apply these visualisation techniques to your models. Please get in touch for more information on how we can help you maximise the Dymola- Modelica potential in your modelling tasks. support@claytex.com

Written by: Alessandro Picarelli – Engineering Director

Please get in touch if you have any questions or have got a topic in mind that you would like us to write about. You can submit your questions / topics via: Tech Blog Questions / Topic Suggestion

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