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50208-A12 7/16 P have equivalent stiffness values that
later are subject to optimization. Using modal reduction in the full BIW and TB model, engineers can ensure that the beam concept model preserves full accuracy. As it has a limited number of degrees of freedom (DOFs), it runs quite fast in optimization loops.
Multi-attribute balancing
LMS Engineering experts vary the stiff-ness of joints and beams, and evaluate the impact on the global vehicle
Siemens PLM Software www.siemens.com/plm Americas +1 314 264 8499 Europe +44 (0) 1276 413200 Asia-Pacific +852 2230 3308 Balancing NVH and vehicle handling performance in LMS Virtual.Lab.
Body-in-white beam concept joints in LMS Virtual.Lab.
Solutions for body
Summary
LMS™ Engineering services can deploy a dedicated procedure to gain insights into the static and dynamic global stiff-ness of a car body. This approach ensures reliable global static and dynamic car body stiffness properties and provides a highly efficient testing process.
Global car body stiffness is an important design attribute in vehicle design.
A thorough understanding of the relationship between global static and dynamic car body stiffness properties is required.
Performing traditional static stiffness tests on a bench provides a single static stiffness value for a car body. It might be difficult to achieve repeatable and reliable results when static stiffness properties of the car body are acquired on a dedicated test rig. Furthermore, correct replication of the clamping conditions in computer-aided engineer-ing (CAE) proves to be a challenge, limiting the possibilities for correlating test results with CAE data.
To set body stiffness targets and bench-mark their vehicles against competitor vehicles, automotive manufacturers seek proven methodologies to link the dynamics of the car body (mode shapes, mode frequencies, etc.) with the static stiffness of the body.
LMS Engineering experts have devel-oped a simplified but dedicated meth-odology that enables you not only to quantify the body global static stiffness properties (for example, bending, torsion, etc.), but also decompose this total static stiffness into contributions of dynamic body properties (the body modes).
LMS Engineering services help you understand the static and dynamic global stiffness of a vehicle body
Benefits
• Uncover the link between dynamics and static stiffness properties by decomposing static-body perfor-mance into contributions of dynamic body modes
• Apply individual static-load cases rele-vant to handling performance
• Benchmark static-stiffness parameters against competitor vehicles
• Deploy a full or partial technology transfer
Identifying static stiffness using dynamic tests
Solutions for body
A typical static stiffness identification project is comprised of the following phases:
Body FRF measurements
In a first stage, frequency response function (FRF) measurements are carried out on a vehicle body wired with accelerometers. Vibration modes are excited by use of an impact hammer or an electrodynamic shaker. These excite the vehicle when fully suspended in so-called free-free condition. The test-based measurements are combined into a free-free FRF matrix that contains all necessary transfer functions between load inputs and response outputs at the body interface points of interest.
Identifying static stiffness using dynamic tests
© 2016 Siemens Product Lifecycle Management Software Inc. Siemens and the Siemens logo are registered trademarks of Siemens AG. LMS, LMS Imagine.Lab, LMS Imagine.Lab Amesim, LMS Virtual.Lab, LMS Samtech, LMS Samtech Caesam, LMS Samtech Samcef, LMS Test.Lab, LMS Soundbrush, LMS Smart, and LMS SCADAS are trademarks or registered trademarks of Siemens Industry Software NV or any of its affiliates. All other trademarks, registered trademarks or service marks belong to their respective holders.
52556-A7 8/16 P Analysis
LMS Engineering specialists compute an analysis of the FRF matrix using one of two possible approaches: a frequency-based substructuring method (FBS) or a free-free modal analysis. Both methods can be executed using LMS Virtual.LabTM software and allow you to extract a vehicle’s global body static stiffness based on dynamic measurements.The FBS method converts the free-free FRF-matrix into a constrained FRF FRF-matrix. As such, data output from the first phase is translated to represent a virtual
clamped body condition. Next, both virtual constraints and virtual static load cases are applied. This approach is highly suitable for torsion and vertical
Siemens PLM Software www.siemens.com/plm Americas +1 314 264 8499 Europe +44 (0) 1276 413200 Asia-Pacific +852 2230 3308 Stiffness identification in free-free condition.
Stiffness identification in constrained condition.
bending.The free-free modal approach requires identification of a modal model, which contrary to the FBS method, does not need to be
constrained and describes a virtual free-free condition. Using this approach, any static-load case can be explored. This is applied after a careful estimation of global modes and residual vectors.
Evaluating static body stiffness at zero hertz
Both analysis approaches enable the extrapolation of static body stiffness values by evaluating the virtual load cases, forces and displacements at zero hertz (Hz). Finally, the acquired output allows you to compare either test-bench or CAE results.
Solutions for body
Summary
LMSTM Engineering services reduce interior noise. By identifying the panels that radiate sound to crucial positions such as the driver and passenger seats, and by analyzing design modifications, you can increase acoustic cabin comfort.
Acoustic comfort is among the most important criteria when designing a car.
But interior noise results from a
complex interaction between several sources. Their combined effect makes panels vibrate, causing the acoustic field. When looking at panel treatment as part of the solution, it is crucial to know which ones vibrate harder, but also if they reinforce each other or cancel each other out. By making spe-cific calculations on tested or simulated data, engineers can rank panels in order of importance, see their phase relation and analyze modifications in a thought-ful way.
Panel contribution analysis takes place in various development stages. It was originally used as a test method for troubleshooting, but as technologies for modeling panel treatment have
evolved, it has gained popularity for use in early-stage simulation. The exact process depends on the available data.
Sometimes test and simulation are even combined into one hybrid model. But all projects lead to the typical postprocess-ing, which is when analysis takes place.