Applying External Loads in AVL EXCITE? M

by Josip Juric

Applying external loads in AVL EXCITE? M models can be done in many different ways.

In EXCITE M the evaluation and interpolation of pressure and forces defined by tables, maps and other components mentioned in this article is done by the time domain solution solver during every time step and iteration. This makes every simulation a transient one.

How to apply external loads in EXCITE M GUI, the basics for the uninitiated

First the basics: Load Items in EXCITE M are represented by dedicated elements in the model's topology. Those elements will typically be connected to a?Link Location?at a target body where the force is applied and act at one or more nodes. Typically, the?Link Location?will already offer the default nodes where the load would be applied. However, like in the case of joint connections, the user can still opt for other specific nodes instead (note that this is only possible when?Modeling Level?is set to?EXPERT?in model Settings).

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One obvious way to create a new load item is to insert the?Load Item Force?component into topology editor and then connect the inserted element to a target link location on a body. The easier way to do the same is by using the dedicated "Apply load..." option. This is available in the context menu of a selected body, and will work everywhere: in?3D Viewer, in?Topology editor, and in?Elements tree?pane.

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What are the options?

Now, let's briefly go over the current available options for applying loads. ?

Option1: Force/Moment Load Items

The first and quickest option is to use the dedicated?Force/Moment Load Item?components. These components are very easy and intuitive to use. Just connect them to a body and select one of the available types (modes) that suits your purpose the best. The supported types of loads are:

• Constant
• Constant (Speed dependent)
• Variable load
• Variable (Speed dependent)
• Multipurpose data pool load

Obviously, they support most common and straightforward options like constant loads or table/map defined loads with the possibility to use time, or a desired reference body rotation angle for the table domain evaluation. In addition, the simple?Load Items?offer advantages like visualization of the load vectors in 3D view. Within a dedicated?Focus View?there is a convenient slider that allows a very nice 3D preview of load vectors changing over time.

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One important note about the speed dependent variants of simple?Load Items: Although the map based speed dependency of the load can be defined and a body chosen for speed measurement, the interpolation of the load will be done by the GUI prior to starting the simulation. For this evaluation, the GUI will take into consideration the initial speed of the referenced body. That means that any variation of the speed of the referenced body during the simulation will not be taken into consideration. For cases when that is needed EXCITE M has more powerful options in its arsenal, as will be described later.

Advantages: Fast/easy setup, versatile and compact. Contains scale and shift as well as preview options. Supported by?Focus View.

When to use: Constant or simpler table defined loads. ?

Option 2: Load Applicator

Load Applicator?is designed to be used as a universal bridge between various signal network components and a mechanical system. The main purpose of the?Load Applicator?is to apply the connected input signals as a force/moment acting on a set of connected body nodes. In cases where pressure is fed as a signal to a?Load Applicator, the component also provides a comfortable conversion of pressure into force by using geometry of the connected?Link Location?for estimation of the area.

The long list of possible signal sources includes?Model.CONNECT??and?MATLAB?external model connections, as well as?Cylinder Pressure?maps,?Compiled Functions?and?Speed?Controller. Therefore the?Load Applicator?is a very versatile and frequently used component.

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Advantages: Very flexible, opens the door to modelling of many new scenarios. Allows external interfacing and controller loops.

When to use: When simple?Force/Moment Load Items?won't do. ?

Option 3: Using FTAB Joints

Another way of bringing external influences and inducing loads within a mechanical system was achieved by adding signal control to tables defined in?Table Force/Moment (FTAB)?joints. By combining signal controls with already available options within FTAB joints, very powerful modelling options are opening up... and the limits are still to be explored.

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Advantages: Additional level of control for bodies connected with Table Force/Moment joints.

When to use: Advanced use cases combining classical Table Force/Moment (FTAB) joints with signal network components.

Option 4: Load Item Cylinder Pressure

In EXCITE M within IC Engine cylinders and crank train assemblies, all necessary forces are derived directly from the cylinder pressure.

Load Item Cylinder Pressure?is a pre-defined (macro) assembly component whose main purpose is to allow very easy application of cylinder pressure induced loads for all affected bodies. The cylinder pressure can be defined either as a local speed/throttle dependent multidimensional map or it can be swapped with a?Model.CONNECT?element that will allow online calculation of the cylinder pressure by linked external software.

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Within its natural habitat (which is the?IC Engine Assembly), this component is automatically set-up by the GUI according to only a few configuration parameters defined in?Engine Configuration?of the IC assembly. The Cylinder pressure map (speed and throttle demand dependent) can also be provided there.

Advantages: Very easy setup of cylinder pressure induced loads in all cylinders of the IC Engine Assembly.

When to use: In?IC Engine Assemblies, or any pressure chambers where pressure creates a force. ?

Option 5: Gravity

For the sake of completeness, let us also mention the?Gravity. This can be optionally activated and defined at top-level?Settings?of the model, and is (if activated) acting on all bodies in the model.

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Advantages: Just toggle on.

When to use: Obvious.

Conclusion

As it can be seen in this overview, EXCITE M is very rich in options for definition of loads. Using the listed options in unconventional ways, especially involving signal networks and load applicators, expands the user possibilities even further.

?As much as we love to nerd out about simulation and read lengthy articles about it, we have to cut it short at this point.

We want to thank Josip Juric for the insights and the impressive work that is performed day to day behind the scenes.

Real-world activities and their real-time limitations bring this Simulation Saturday to an end, but stay tuned for another one soon!

Cheers, Thomas and Michael

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