NEA-1692 FFT-BM.

1. NAME OR DESIGNATION OF PROGRAM:  FFT-BM.

3. DESCRIPTION OF PROGRAM OR FUNCTION

FFT-BM is an integrated version of the programs package performing code accuracy evaluations with the 1D Fast Fourier Transform (FFT) methodology. It contains two programs:
  
- CASEM: Takes care of the complete manipulation of data in order to evaluate the quantities through which the FFT method quantifies the code accuracy.
  
- AAWFTO completes the evaluation of the average accuracy (AA) and related weighted frequency (WF) values in order to obtain the AAtot and WFtot values characterising the global calculation performance.

4. METHODS

The Fast Fourier Transform, or FFT, which is based on the Fourier analysis method is an optimised method for calculating the amplitude Vs frequency, of functions or experimental or computed data.
In order to apply this methodology, after selecting the parameters to be analyzed, it is necessary to choose the following parameters:
  
- number of curves (exp + calc) to be analyzed
- number of time windows to be analyzed
- sampling frequency
- cut frequency
- time begin and time end of each time window.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

Up to 30 curves (exp + calc) and 5 time windows may be analyzed.

6. TYPICAL RUNNING TIME:  Machine dependent.

7. UNUSUAL FEATURES

Two steps are foreseen in the application of the method. In the first step the average accuracy (AA) and the related weighted frequency (WF) of each considered parameter in the analysis are evaluated. In the second one the AA and WF of the whole parameter set characterizing the analyzed transient are calculated. The user's manual gives typical values of AA and WF for the two steps to be taken as reference values in the application of FFT-BM to nuclear power plant related analyses.

10. REFERENCES

Leonardi M., D'Auria F., Pochard R.:
"The FFT based method in the frame of the UMAE",
Spec. Workshop on Uncertainty Analysis Methods, London, March 1994.

- F. D'Auria:
FFT Method Description

13. SOFTWARE REQUIREMENTS

IBM VM/370 mainframe, CRAY UNICOS, UNIX SUN workstations, PC DOS Windows 3.1 and higher, Microsoft FORTRAN 5.1 and Compaq Visual Fortran 6 compilers.

15. NAME AND ESTABLISHMENT OF AUTHORS

F. D'Auria
Department of Mechanical, Nuclear and Production Engineering (DIMNP)
University of Pisa
Via Diotisalvi, 2
56100 Pisa (Italy)
tel. no.: +39.050.836653
fax no.: +39.050.836665
e-mail: dauria@ing.unipi.it

casem.for  Source file of the FFT-BM in fortran 77
casem.exe   Executable file in windows environment
FFT_BM_description.doc  Method description, source list and user's manual
Sub folder "Example" containing some example files:
1. exp_txt   Archive of reference experimental data
2. fft_sx0    Archive of reference calculated data and related output file obtained
3. fft_inp    Archive of the used input files