"Highly Efficient Modal Frequency Response Analysis"

The availability of the Automated MultiLevel Substructuring (AMLS) software has enabled frequency response analyses using very large FE models and many modes. With certain simplified types of damping the resulting modal matrices can be solved easily. However, modeling damping accurately can make modal frequency response problems computationally very expensive to solve. Accurately modeled damping results in matrices that are fully populated rather than diagonal. The modal frequency response then requires a matrix factorization at each frequency. The time required for each factorization is proportional to the cube of the number of modes, so analyses up to higher frequencies, for which many modes are required, become extremely expensive. FastFRS (fast frequency response solver) addresses this issue by performing only one numerical operation whose cost is proportional to the cube of the number of modes, rather than one such operation at each response frequency. The solver obtains an exact, direct solution, rather than an approximation for which the user specifies a cutoff frequency, a convergence tolerance, or some other parameter requiring special expertise or instruction. As a result, FastFRS is very reliable and easy to use.

CDH/FastFRS has been implemented with an interface to MSC.NASTRAN, MD.NASTRAN, NX-NASTRAN and ALTAIR RADIOSS software, so that it can be used in industrial vibration and acoustic analysis. CDH/FastFRS can be used in modal frequency response (NASTRAN SOL111) analysis and requires a minimum of effort on the part of the user to take advantage of drastic reduced job turnaround times.

  • Direct (FRRD1) solution requires ~m3/6 operations for factorization of a dense coefficient matrix at each frequency, where m is the number of modes.
  • It is advantageous to solve an eigenvalue problem whose cost is proportional to m3 only once, making the per-frequency cost of the remaining computation proportional to m2.
  • Demonstrated dramatic improvement on many industrial FR problems.
  • Combination of AMLS and FastFRS allows the user to solve NVH problems to even higher frequencies.
  • With many modes, diagonalizing the modal FR problem is much more efficient than solving a fully coupled problem at each frequency.
  • Result, the most efficient solution method available, with no truncation error.

Software-Hardware Support:

Supported Software:Supported Hardware: 
MSC.NASTRAN   MSC.NASTRAN is a proprietary product of MSC.Software Corporation.
MD.NASTRAN   MD.NASTRAN is a proprietary product of MSC.Software Corporation.
NX NASTRAN Linux64 (x86_64 and ia64) NX NASTRAN is a proprietary product of Siemens Product Lifecycle Management Software Inc.
Altair RADIOSS   Altair RADIOSS is a proprietary product of Altair Engineering, Inc.
Altair OPTISTRUCT   Altair OPTISTRUCT is a proprietary product of Altair Engineering, Inc.



Customer reviews

Andrzej Pietrzyk // PhD, Advanced Engineering Leader NVH CAE
Volvo Cars Corporation

The FastFRS gives exceptional scaling over many cores and unprecedented speed of FRF calculations. We are also very pleased with the support we receive. It is very responsive, fast and not hesitating to add new features when needed.”

Alexandre Bonet // NVH CAE
PSA Peugeot Citroën

Having been using CDH/AMLS at PSA for more than 10 years, we experienced CDH/FastFRS V2 with CDH/AMLS V5. Thus, on the biggest vibroacoustical analysis cases we have improved user time up to 90% over V4, thanks to our new CDH solvers configuration. As a result for NVH project design, faster computations are available and wider frequency range studies are allowed."

Christian Pieper

Contact person

Christian Pieper//
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