CDH/OPTRAN calculates the frequency response functions (FRFs), operational shapes, mode shapes, mode participation and panel participation factors for large finite element models with multiple loading conditions. After the computation of the global stiffness, mass and damping matrices in NASTRAN, the CDH/OPTRAN process releases NASTRAN licenses and tokens even before CDH/AMLS starts. The CDH/OPTRAN process is illustrated in the following diagram:

To meet NVH design requirements, comfort relevant response results must be calculated for many simulated load cases including engine idle, wheel out-of-balance, road excitation etc. Typically, the following response functions must be calculated for all load cases:

• Vibration transfer functions for seats and their connection points, foot-position panel vibrations, steering wheel vibrations, mirror and headlight vibrations
• Noise transfer functions between mechanical excitation points and driver and passenger ear sound pressures responses
• Driving point response mobility for driveline/suspension connection points and sub-frame attachment points

In practice, the number of individual NVH load cases to be considered can easily exceed 200 loadcases. Post-processing the frequency response functions is in itself a major operation. Once critical responses have been identified, it is necessary to re-repeat the analysis to obtain other information such as operational shapes and panel participation factors. CDH/OPTRAN is specifically designed for NVH analysis efficiency.

CDH/OPTRAN enables users to submit analysis jobs in batch mode after defining load cases, target responses and post-processing requirements. Uncritical responses below their target limits are automatically omitted in the output of plotted response results.

• CDH/OPTRAN allows the definition of target responses for each selected load case and response degree of freedom
• CDH/OPTRAN automatically identifies response target violations
• CDH/OPTRAN automatically identifies uncritical responses below target limits and these are omitted in the output of plotted response results. The analyst can therefore concentrate on the solution for critical responses
• CDH/OPTRAN interfaces seamlessly with CDH/AMLS and CDH/FastFRS to drastically reduce computational resources such as CPU time, I/O and disk space

• Nastran punch format
• Medina .bof format (mode and operational shape output)
• FEM post-processing supports .jpeg, .tiff, .png, .ps, .csv, or .eps format
• Element based recovery such as element strain energy, stress, etc.