PSI - Issue 60

Ashish Kumar et al. / Procedia Structural Integrity 60 (2024) 364–371 8 A. Kumar, Y.V.N. Bhat, S.Patri, P.A.Kumar, S.I.S.Raj, S.S.Kumar, B.K.Sreedhar / StructuralIntegrity Procedia 00 (2019) 000–000

371

6. Discussion and conclusion

The first measurements done on as-assembled ECFM of LMP gave a single natural frequency on both IGT and OGT. Validation of the same through analysis indicated that both were connected. Conclusion on the state of supports acting on IGT requires its individual natural frequency. Hence, another attempt was made to measure the natural frequency of IGT after raising it by 60 mm. A 60 mm lift was anticipated to separate the IGT from OGT; nonetheless, a single response at around 33 Hz was obtained on IGT and OGT. This indicates that although the visible connections between the two bodies were removed, they remained connected. Analysis was then carried out by simulating single/multiple connections between the IGT and OGT below the O–ring locations, and the IGT lifted by 60 mm. The natural frequency with such BC was obtained at around 33 Hz, which closely agrees with the measured value. This confirms the presence of additional connections/contacts between IGT and OGT, and the reason for such connections is attributed to the tilt of the LMP skirt and rotor assembly w.r.t. shielding box. A couple of harmonic analyses was carried out, concluding that the support conditions of IGT lying below the OGT have no role in the measured natural frequency of IGT – OGT assembly, which is obtained by exciting the top portion of IGT. The understanding developed through the study of measured natural frequencies and analyses is summarized below: i IGT & OGT always remain connected to each other. Hence, the measured frequencies correspond to a combined OGT & IGT assembly, not individual IGT or OGT. ii A single natural frequency corresponding to IGT – OGT assembly is obtained irrespective of the support conditions at the bottom portion of IGT lying below OGT. iii The portion of IGT lying below OGT does not get excited with impacts given at the top. In the light of the above discussion and absence of measured natural frequency of IGT, it was not possible to conclude on the state of supports acting / not acting on IGT. Even though the primary objective of the exercise remains unfulfilled, a better understanding of modal characteristics of assembled components is developed. Findings during experiments and analytical studies have provided valuable inputs towards exploring other design options, which would enable in-situ measurements and confirming the healthiness of ECFM assembly. Further studies with the un-tilted condition of the pump in a mock up facility are also being envisaged to know the status of connections between OGT & IGT. Meanwhile, confirmation regarding the state of IGT supports was done using a 1:1 mock-up facility, which confirmed proper assembly of IGT in the LMP.

References

Poornapushpakala, S., Gomathy, C., Sylvia, J., & Babu, B. (2014). Design, development and performance testing of fast response electronics for eddy current flowmeter in monitoring sodium flow. Flow Measurement and Instrumentation. https://doi.org/10.1016/j.flowmeasinst.2014.05.004 William Thomson, (1993), Theory of Vibration with Applications (1st ed.). CRC Press. https://doi.org/10.1201/9780203718841 French, A.P. (1971), Vibrations and Waves (1st ed.). CRC Press. https://doi.org/10.1201/9781315273372 RCC-MRx (2012), Section III - Tome 1 – Subsection Z : technical appendices Fatma Nur Kudu, Ş enay Uçak, Gökhan Osmancikli, Temel Türker , Alemdar Bayraktar (2015), Estimation of damping ratios of steel structures

by Operational Modal Analysis method.. http://dx.doi.org/10.1016/j.jcsr.2015.04.019