36

where the frequency response functions H and H2 are calculated according to the formula given below:


                                H1 =G22Gly -G12G2y
                                     G11 "G22 - G12 2                         (3.6)
                                   GllG2y -G21Gly
                                   2   I-2 2 -G 2


    The cross terms involving H and H2,, i.e. H1H2G12 and H2H1G21, arise because of the interaction between xj(t) and x2(t.

    The multiple coherence function, that represents the correlated output power in the test section acceleration due to the input fan and pump acceleration, is given by r2:7(f) = G,                                                                 (3.7)


Results and Conclusions

   Results of the vibration data for the case when the air speed is 64.5 m/s and water speed is 0.5 m/s are presented. Results for all other test cases, tabulated in Table 3-1, are presented in Appendix B.

   The ordinary coherent output spectra, 2tG   and '2     are shown in Figure 3-13. Also, the noise contributions G,, and the multiple coherent output spectrum (i.e., the combined vibration contributions of the fan and pump) G, are compared to the output spectrum Gy in Figure 3-13. For comparison, the measured noise floor spectrum, obtained when the blower and pump are off, is also plotted.