# Variation studies in COUPLE

Developing a new vehicle is a challenging task. As an NVH engineer, you want to identify the best model of the full system as soon as possible in the development process. To do so, it is often necessary to try many combinations of different components. This can be a time-consuming task. Using the variation study feature in COUPLE, you can easily combine and match all the different component models you want to evaluate. You can perform variation studies of test-based and simulation models, as well as apply different load conditions. This way, you can study the effect of each design change on the sound pressure level at the driver’s ear.

COUPLE has been developed to simplify the study of multiple assemblies and configurations. The picture below shows 128 prediction curves generated in COUPLE using the variation study feature.

## Example: E-compressor NVH study

To understand the variation studies, let’s start with an example. In this case study, we use COUPLE to evaluate the compressor integration into a vehicle. In this example, we will take two different compressors and brackets and couple them to a vehicle, to evaluate their NVH characteristics. We will also check the effect of multiple bushings of different types, between the bracket and the vehicle.

For the case study, we will evaluate the following assembly:

The compressor is attached to the bracket at one connection point. The bracket is mounted on the vehicle body in three points. If desired, rubber bushings can be added to these three connections.

In this example, we will use test-based models of the compressors and numerical models for the brackets. We also have three parametric models of bushings and the test-based model of the trimmed body.

When built up in COUPLE, the full vehicle assembly looks like this:

With the variation studies feature, you can easily add all variants, and COUPLE will automatically compute all possible combinations.

## What is a variation study?

It is important to know the right nomenclature to understand the topic: an assembly is a configuration of connected components (experimental and/or numerical models), loads and links. For each assembly, you can perform one or more variation studies. A variation study consists of different configurations of the same assembly. In the variation study, components, loads or stiffnesses can be varied according to the user’s desire. Every single component, stiffness or load model that is varied in the study is called a variant.

In COUPLE, you create one or more variation studies, add all variants and the software will automatically compute all possible combinations. You can add variants to components (e.g., vehicle bodies, compressors of different suppliers) or links (e.g., different bushings, different stiffness values). You can also use the variation study feature to apply multiple load types (e.g., constant speed, runup, run-down, etc.) to an assembly to study the responses.

You can have models that vary independently or dependently from one another. For example, a variant of a compressor bracket depends on the variant of the compressor. They have to be changed together, and no cross-combinations are allowed. On the other hand, a variant of a bushing at one connection point can be changed independently of the other bushings. Any cross-combination is allowed.

## Variation study in COUPLE

In COUPLE, you can create variation studies in two ways. You can drag and drop the components directly into the Design Area or create the variation study in the Studies tab and fill it in with models at a later stage. The first method is explained in this paragraph, while the second is described in the COUPLE product guide (link).

To create the Variation Study in the Design Area, complete the next steps:

1. Create the assembly (with components or empty assembly parts).
2. Drag and drop the variants into the correct component/link.
3. Select Add model and move to new study (or Add model and move to existing study).
4. Map the model interfaces to the part interfaces.
5. Open the Studies tab and rename the variation study and the variants.

Each assembly part in the Design Area can only be used in one Variation Study.

## E-compressor variation study

Let’s go back to our e-compressor NVH study. To explain all features, we will break down the variation study and add complexity at each step.

### 1. Single component variation

The first variation study consists of varying a single component. For example, we can try two e-compressors and see the differences in the coupled FRFs. To do so, we create a variation study of the e-compressor model and add the two components. As a result, we will get two different full-vehicle assembly models, one with the first compressor and one with the second.

In the picture below, you can see a schematic representation of this variation study.

In COUPLE, you can set up this variation study like this:

If we go to Analyze, we can see 2 different results for the coupled FRFs, that we can plot to evaluate the differences.

### 2. Multiple components dependent variation

However, it is unlikely that two compressors from different suppliers can be attached to the same bracket. For this reason, we want to attach each compressor to its corresponding bracket. To do so, we make a dependent variation study: each compressor varies together with its bracket. As a result, we will get two different full-vehicle assembly models, one with the compressor and bracket of the first supplier and the other of the second supplier.

The picture below shows a schematic representation of this variation study. We conducted one single variation study with two different assembly parts.

In COUPLE, you can set up this variation study like this:

### 3. Multiple links dependent variation

In addition to different compressors and brackets, you can also study the effect of adding bushings between the bracket and the vehicle subframe. In the assembly, the bracket is connected to the vehicle at three different locations (left, center and right). We can try different parametric models of bushings and make a new variation study. In this case, we have three parametric models: a soft, a nominal, and a hard bushing, as well as the rigid connection case (no bushings). In total, we have three connection points and four different variants. To start, we make a dependent variation study, where the bushings vary together at all three connection points. After calculations, we will get eight different results: four bushings studies per compressor supplier. This means that we will have the following configuration.

In COUPLE, you can add a second variation study, and set it up as follows.

### 4. Multiple links independent variation

You can also decide to independently vary the bushings at the three connection points. This means that you could have, for example, soft bushings on the left connection, a hard bushing in the center and a rigid connection on the right side. In COUPLE, you can easily try all different bushing configurations to spot the best one for your assembly. To do so, you create a separate variation study per connection and add all four variants (three bushings + the rigid linking). Doing so, you end up with 128 configurations (64 per compressor supplier).

In COUPLE, you make independent variation studies, adding one of them per component.

When you open the Analysis tab, you will see 128 results of coupled FRFs. Use the filters to navigate through the data.

You can also add variation studies for loads, to compute predictions of multiple operational conditions.