Simcenter Testing Solutions Simcenter Testlab Virtual Prototype Assembly

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The Simcenter Testlab Virtual Prototype Assembly (VPA) software is used to predict the noise or vibration performance of an assembled dynamic system.  The user creates components based on structural Frequency Response Functions (FRFs) and load functions (spectrums, orders, waterfalls, etc). Using a graphical interface, multiple components can be connected directly or with stiffness modules as shown in Figure 1.
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Figure 1: Assembly of components in the Simcenter Testlab Virtual Prototype Assembly software interface.

The loads and FRFs can be derived by simulation or test data.  The total system performance can be calculated and understood.

This article describes how to use the VPA software: 
1. Background
2. Components
   2.1 Structural Components
   2.2 Loads 
   2.3 Test Scenarios
3. Getting Started
4. Example
5. VPA Definition
6. VPA Assembly

1. Background

The reduced availability of physical prototypes, together with the increase in complexity brought by the electrification put the validation of the noise and vibration (NVH) attributes at risk. Addressing NVH issues late in the product development cycle is expensive and creates delays in product launches.

SImcenter Testlab Virtual Prototype Assembly (VPA) is a solution designed to overcome the challenges faced by NVH engineers.  This is done by creating virtual prototypes to assess in early project phases the noise and vibration target performance and set more realistic sub-system design targets.  This solution is not only designed for test engineers, but also for simulation engineers, since it is possible to use and combine both data types. 

This solution is based on the Dynamic Substructuring (DS) concept and benefits from the FRF Based Substructuring (FBS) theory. The Dynamic Substructuring technique is often applied to complex structures to determine their structural dynamics. The complex structure is divided in substructures or sub-systems that are characterized separately and after assembled to predict or evaluate the assembled dynamics. This approach permits not only the evaluation of the components separately, calculating their impact on the whole assembly, but also the opportunity to create virtual prototypes assessing the target performance at critical conditions. Furthermore, several components’ combinations can be evaluated on different test conditions.
2. Components

Six types of components are used in Simcenter Testlab Virtual Prototype Assembly:

2.1 Structural Components (defined by FRFs):
  • Body Receiver: Defined as the system receiver where the target points are present. For a strongly coupled system, a Blocked Forces model is used and, in this case, the FRF’s between the Input Degree of Freedom (DOF) Ids and to the Response (Target) points are needed. For this case, the effect on the loads of the interaction of source and receiver is taken into account. For weakly coupled system, just the FRFs between Input and Response are needed. The total assembled transfer functions are required for the noise prediction. These are calculated from the combined information from the individual components. An example of a Body Receiver component is a vehicle body, ship structure, tractor body, etc.
  • Connectors: Used to model bushing or system mounts. These components are usually characterized by the dynamic stiffness curves between Inputs and Outputs DOF Ids. They can incorporate one or multiple Degrees of Freedom (DOF) – translational and rotational. Even multiple mounts can be stored in a single connector component.
  • Passive Components: Structural parts between the sources and receivers of a mechanical structure. To publish such component in the VPA Definition application the FRF’s between Input DOFs and Output DOFs is needed. Also, the driving points for Input and Output DOFs are needed. The number of input and outputs can be different. 
  • Active Components: These components will store the FRF’s of the source. If the Loads are characterized at the interface/connection, the Blocked Forces model will be used, hence the FRF’s between connections points should be available. If, the Loads are defined as Pseudo Forces, at the source center for example, the FRF’s between Input and Output DOFs are needed and the FRF’s between the Output points (connection points).
2.2 Loads

Load components are designed to store force excitations (orders, spectrum, autopower, waterfalls) that are applied to the system.  These forces can be blocked forces, pseudo forces, or free velocities.  These forces will pair with the Active Components, creating the system excitation.

More information on the how to use block forces properly in the knowledge article: Blocked Forces versus Contact Forces in Transfer Path Analysis (TPA).

2.3 Test Scenarios

The Test Scenarios can also be interpreted as the operating conditions of the product. This component will provide the dependencies values for a certain test conditions, such as motor rpm, speed, torque, position, etc.

3.  Getting Started

The Simcenter Testlab Virtual Prototype Assembly software uses two add-ins: VPA Definition and VPA Assembler as shown in Figure 2.
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Figure 2: Select "Tools -> Add-ins" from the main Simcenter Testlab menu to turn on the VPA Assembler and VPA Definition add-ins.

From the main menu of Simcenter Testlab, turn on "VPA Definition" and "VPA Assembler".  They required 15 tokens and 120 tokens respectively.

More about Simcenter Testlab token licensing in the knowledge article: Simcenter Testlab Tokens: What are they, and how do they work?

4.  Example Application

The remainder of the article uses an example application to predict the noise at the driver ears’ produced by an Electric Drive Unit (EDU) mounted on an axle carrier to a vehicle body (Figure 3). 
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Figure 3: Schematic of the system being assembled used in this article.
Based on FRF Based Substructuring theory, the dynamic behavior of the assembled system can be written as follows (Figure 4):
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Figure 4: FRF Based Substructuring equation for combined assembly.

  • [H] represents the FRF matrixes
  • [K] the Dynamic Stiffness of the mounts and bushings
  • {F} the Forces from the EDU
This model can be virtually assembled using the Simcenter Testlab Virtual Prototype Assembly, by publishing the components using the VPA Definition workbook and virtually assembling them on the VPA Assembler workbook. The final goal is represented on the Figure 5.
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Figure 5: Final desired assembly of vehicle body, axle carrier, and Electric Drive Unit (EDU).

To make this assembly, first the individual components need to defined in the "VPA Definition" workbook.
5. VPA Definition 

The VPA Definition Add-In in Simcenter Testlab allow the user to create components for assembly.  Figure 6 shows the data required for each component.
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Figure 6: List of data needed to create components for the Electric Drive Unit (EDU) in vehicle example.

In this example, just the models in bold were used, but the data needed for the other models is also shown. 

The body components used will be created following the process shown in the video below:

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Once all the body components are created, it is time to publish the loads. Inside the VPA Definition, there is a dedicated minor worksheet for the load definition located near the top of the screen.

For the Electric Drive Unit, the blocked forces were identified as the main orders produced by the unit. These blocked forces were characterized on three torque conditions: 50 Nm, 75 Nm and 100 Nm. Therefore, for each torque condition, the orders are stored on the load component, using a multi-level case dependency as shown in the video below:

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The last step on the VPA Definition workbook is to create the Test Scenario component. The component stores the test conditions based on the dependencies DOFs, e.g., rotational speed (rpm), vehicle speed (km/h), torque (Nm), ….

As shown in the video below, the Test Scenario for this example will vary the rotational speed (rpm) and torque (Nm) simultaneously:

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Now the components are ready to be assembled.

6.  VPA Assembly

Once the components are available, one can move to the VPA Assembler workbook. The goal of VPA Assembler is to create the Virtual Prototypes by combining the components. The components are connected by DOF Ids.

It is important to highlight the usage of a standard naming convention for the node or point Id number, since on VPA Assembler is possible to use the Auto-connect feature to easily connect the components. To have a complete assembly the minimum requirement is one Body Receiver, one Load Component, and one Test Scenario.

The operations needed to combine the components into a complete assembly are shown in the video below:

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After the assembly is defined, press the "Run" button in the lower left to calculate the results.

After the calculations, the results are stored in a new run in the Simcenter Testlab project file. In this example, the overall levels are calculated by summation of the orders levels, for each rpm and torque combination.

The total and partial contributions are calculated per order value. Hence, similar to Simcenter Testlab Transfer Path Analysis software, the paths can be displayed on a Function-Map display as shown below:

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As shown, the VPA solution allows the engineers to assess what will be the NVH levels at the target locations, ranking the paths contributions, gaining insights on possible issues, and allowing the combination from different data sources (Test and Simulation).

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KB Article ID# KB000065651_EN_US



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