Creating virtual acoustic prototypes

COUPLE allows you to assemble, predict and optimize your NVH design in a complete modular workflow. In COUPLE, you can import test-based and numerical models of components and couple them using Dynamic Substructuring. You can also import Blocked Forces to be able to listen to the created Virtual Acoustic Prototypes (VAPs). This way, problems are recognized early and late-phase troubleshooting is avoided. Fewer iterative design cycles are needed, saving time and resources. All in all, reliable full-vehicle models are available much earlier in your development process.  

In this article, you will learn how to create a virtual acoustic prototype of a very simple structure, by coupling two components (A and B) at their interface and introducing an excitation load. The studied configuration is the following.

The components will be coupled at their interfaces, so it is vital to have good-quality FRFs at the connection points. For test-based models, you must use the Virtual Point Transformation, to obtain 6 DoF FRFs at each connection point. To couple one component with the following one, it is necessary that the Virtual Points of two connecting interfaces are located at the same place and that the interface DoFs have the same orientation. When connecting interfaces, COUPLE will link each DoF of the first component to the same DoF of the second one.

Make sure that you use models that have been measured/calculated with the correct boundary conditions. In our case, the coupled system AB should be modelled in free-free condition. So, we need models of each component in free-free condition.

If your model includes more structures than your component, e.g., a test-bench, you cannot directly couple it to the receiver because it includes the dynamics of the test-bench. Consider the case of the steering gear below: The goal is to couple it to the rest of the vehicle at its connection points. If you used a model of the steering gear connected to the test-bench to integrate into the vehicle, you would also couple the test-bench. So, you would have to decouple the test-bench from the steering gear before coupling it to the vehicle. Alternatively, you could use a model of the steering gear in free-free and directly couple it to the vehicle model.

The steps to create a Virtual Acoustic Prototype in COUPLE are the following:

1. Import models.
2. Couple the components.
3. Visualize the coupled assembly.
4. Add the excitation source.
5. Visualize the predictions.
6. Make new variants.
7. Export the results.

Step 1: Import and organize models

Libraries

The first step consists of importing all component models, loads and stiffness information. For better organization and data sharing with colleagues, we have developed libraries. A library is a “folder” in COUPLE where you store all your models. You can have multiple libraries and activate and deactivate them according to your needs. For example, some components (e.g. bushings) get used multiple times in one assembly or even re-used in different variants through the years. We do not want you to lose time looking for them in old folders or having to import all the datasets again and again. For this reason, you can have a “Bushing library” that you and your colleagues keep up to date and that you activate in your project when you need it. A library is saved as a .lib file that can be shared with colleagues. All the libraries can be visualized on the COUPLE homepage.

To learn how to create, import and activate libraries, check out this link.

The Model Library

After creating a library, you must fill it with all the components. The Model Library is the go-to place when you need to import new models, set up channels and interfaces, edit existing ones, organize them in the libraries or visualize them and their characteristics.

You can access the Model Library by clicking on the top menu.

Import models

You have to import in COUPLE all the components that you need in your design. All supported data formats per data type can be found here. When importing models, you can add a description and specify the component type, platform and stage. All this information can be used as filters to search in the library or results area.

If you are importing DIRAC models, you need to select the VP preset, where both excitation and sensor data are transformed to the VP (the connection point) in 6 DoFs (usually).

To import models in COUPLE, follow the instructions at this link.

Set up channels and interfaces

In Dynamic Substructuring, you couple components at their interfaces to model a physical assembly. Interfaces are comprised of a group of collocated reference and response degrees of freedom, i.e., the forces and moments, and the translational and rotational accelerations at the Virtual Point.

To model the physical assembly in COUPLE, you need to define interfaces in the component models. An interface is comprised of a group of channels. After the import of the model, you can investigate its channels (degrees of freedom).  You can either manually group collocated channels to an interface or automatically group them based on different conditions, e.g., channel name, position.

If the model contains additional channels that are important for your analysis, you can group them to a general channel group, e.g., target channels,. Note that, you cannot establish links at channel groups because they do not resemble an interface. Nonetheless, channel groups will later on be visible in the topology of your model.

To learn how to create interfaces and channels group in COUPLE, follow the instructions at this link.

Organize models

After importing models and setting up their interfaces, you must organize them into one or multiple libraries. You can only organize models into active libraries, in the Organize tab of the Model Library.

To organize models into libraries in COUPLE, follow the instructions at this link.

Step 2: Couple components

Now that you have imported and prepared all the components, you can create the assembly. In the design area, you have to recreate the topology of the assembly, by adding components and linking the corresponding interfaces. The idea behind the design area is to allow you to visualize the assembly in the simplest possible way, in a 2D environment.

To add a component, you need to take it from the fly-in library and drag and drop it into the design area (instructions here). Each interface will be visualized on the outer border of the component as a circle. For a better visualization, you can move the interfaces around the component model by dragging and dropping them. You can rigidly link two interfaces using the links tool. A link is visualized as a line connecting two components. You can add a mount or synthetic stiffness to the link if desired. Find more instructions about linking components here.

In the A and B structures example, I need to add components A and B to the design area and rigidly link the corresponding interface.

Step 3: Visualize coupled assemblies

After coupling the components, you can visualize the coupled FRFs in the Analysis Module. You can access it by clicking on the top menu.

Here in the Data Overview tab, you can see all input data and results, that you can plot in the Graphs tab. You can find more information about the Analysis Module here.

Step 4: Add loads

After creating the assembly by coupling the components, you can add an excitation model to it. Excitation models are marked in COUPLE as Loads, characterized by the green color. You import excitation models in your library the same way you import component models. The supported data formats can be found here.

Loads are applied to a component at an interface point, so you must ensure that the channels and Degrees of Freedom match properly. The Virtual Point Transformation allows the matching of the DoFs best, so the fastest and smartest way is to calculate Blocked Forces at the Virtual Point location.

In this example, we have calculated Blocked Forces in SOURCE, caused by an excitation source on A. The Blocked Forces are computed at the connection point of component A, where the Virtual Point (and interface) is located. We have imported the Blocked Forces to the library and added the load to the design area, applying it to component A.

Step 5: Visualize predictions

You can now visualize the predictions at the target sensors. You can plot them in the Graph card of the Analysis module. In the Data Overview card, these results are marked as “Result Type” “Prediction”. To better navigate through all results and inputs, use the filters.

Step 6: Make new variants

You can now perform variation studies of the assembly, adding different variants to the components or links.

In this example, we make a variation study of the links, by adding different bushings between components A and B. We can then visualize the effect of this compliant coupling on the coupled FRFs and the predictions. To do so, we create a variation study of the links and add the bushing stiffness as new variants to the link.

You start by expanding the Studies card, and adding a new Variation Study. Rename it, select the link, and add all the desired variants. You can find more instructions about variants here.

You can also add (off-diagonal) synthetic stiffness to a link, by building a stiffness model directly in COUPLE and adding it as model in the libraries, if desired. The stiffness model builder allows you to add stiffness and damping between any pair of interface DoFs (including cross stiffness). Read here how to do this.

You can visualize the effect of the added variants of the mounts in the Analysis module, plotting the coupled FRFs and the prediction results. You can use the filters in the Data Overview card to better navigate the results.

Step 7: Export results

When you have finished your analysis, you can export your results and graphs. Data can be exported to .MAT and .ATFX formats (read more here). You can export single plots or a full page to .png, .jpeg and .bmp formats (read more here).