"Vibro Acoustic Optimization"

CDH/VAO is an intuitive Interactive Computational Engineering Tool for largeproblem structural dynamics analysis. CDH/VAO enables engineers working in the virtual product development process to provide fast and reliable solutions to design engineering and test department problems.
Using CDH/VAO users are quickly able to study the structural effects of proposed design changes and to automatically predict set design modifications to provide optimum dynamic behavior of the structural system. Using the Adaptive Modal Correction Method computational savings of factor 25 to 120 have been demonstrated compared to conventional modal analysis.



CDH/VAO uses standard NASTRAN or PERMAS finite element models and the eigenvalues and eigenvectors calculated for the baseline structure to perform a wide range of structural dynamics analyses. Where the structure is coupled to a fluid, fluid eigenvectors are used to assemble the appropriate equations of the coupled system. CDH/VAO uses the advanced state of the art numerical solver algorithms available in MATLAB.

Using the imported FEM model and result data following definitions and interactive modifications can be carried out by users to study effects of material and design changes:

2.1 Model Definition:

  • Fluid properties
  • Excitation (harmonic or enforced motion)
  • Damping (no damping, structure damping, viscous damping)
  • Sub-Models

2.2 Definition and Modification of sub-model properties:

  • Material properties
  • Thickness
  • Density, Young’s modulus, Non structural mass, Torsional stiffness
  • Structural damping - Absorption

2.3 Geometry modification of sub-models using in-situ technology:

  • Interactively create or modify swages, beads and holes, etc. using the VAO-Viewer
  • Import new FEM geometry design (sub-model) from FEM Pre-Processor
  • Allow the user to quickly determine the approximate effects of local stiffing of a particular plate modification on NVH performance
  • Requirement for a completely new modes calculation after a local geometric shape modification may be eliminated

With integrated analysis and optimization features, the CDH/VAO Software is a unique platform for computational engineers to investigate and optimize the sound & vibration performance of vehicle structures. CDH/VAO combines various analysis and optimization capabilities which required in the past the utilization of several commercial FEM software solutions. The combination of rich analysis capabilities and the opportunity to obtain immediate results of re-analysis from user modifications represents a new dimension in interactive computational engineering.

CDH/VAO offers a wide range of analysis capabilities for coupled (fluid and structure) and uncoupled operations to perform:

Fast Frequency Response Analysis using Modal Correction Method Energy Analysis:

  • complex strain and kinetic energy analysis
  • equivalent radiated power (ERP)

Acoustic Analysis:

  • acoustic panel contribution analysis
  • acoustic and tactile response

Transient Analysis:

  • direct FFT analysis
  • support of non-linear elements (e.g. shock absorbers)
  • import of Nastran TLOAD card data (time domain)
  • Combination of transient analysis with all other CDH/VAO analysis features for fast-reanalysis of full system

CDH/VAO supports the stochastic paradigm by providing a range of powerful capabilities for the analysis of uncertain structures. Stochastic simulation is being increasingly applied in the automobile industry in order to obtain robust solutions to design problems in which uncertain design parameters are important. The effects of production tolerances and variation in materials and components can be accounted for in CDH/VAO dynamics analysis leading to an enhanced prediction of actual peformance.


CDH/VAO supports the engineer with state of the art stochastic analysis features:

  • probabilistic/possibilistic analysis
  • Monte Carlo analysis using uniform, Gaussian or user-supplied distributions
  • first order variation method (FOVM)
  • first order reliability method (FORM) with robust G function
  • stochastic optimization

In design optimization numerical algorithms are utilized to achieve optimum structural responses while maintaining constraints on total structural mass etc. Design variables related to structural sub-model parameters can be defined in CDH/VAO, along with targets for performance. The design variables can then be adjusted automatically in the optimization algorithm to achieve desired targets. A unique feature in CDH/VAO allows the user to define special stochastic quantities as variables. These variables can then be used in the formulation of target functions and allow trade off studies between quality cost and performance.


Following numerical optimization algorithms are supported in CDH/VAO:

· Design Optimization by the Mean Method

· Stochastic Optimization for Robust Analysis by the Beta Method


Rich interactive post-processor features in CDH/VAO allow the user to generate quality graphical output for analysis result quantities. Additionally, graphic formats are available for reports and presentations. All x-y plot ouput may be manipulated using familiar MATLAB plotting features such as zoom and rescale etc.


Post Processing Features:

  • Virtual-SAE Tools
  • structural and acoustic modal participation factors
  • structural and acoustic mode shapes
  • damped operational shapes
  • XY-Plots for FRF results


  • RMS contours
  • ASCII – export
  • support for universal file exchange
  • acoustic panel participation factors
  • output to GNS ANIMATOR 4 and T-Systems MEDINA and other Pre- and Post-Processors

Benchmark example to evaluate effort and efficiency of CAE process:

Task: Modification of body floor to adapt new swaging design following reassessment of NVH performance



Red Hat or SUSE Linux 64

Windows 64bit


Christian Pieper

Contact person

Christian Pieper//
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