Flow Induced Vibration of Power and Process Plant Components: A Practical Workbook
Download citation file:
- Ris (Zotero)
- Reference Manager
The three principal damage mechanisms resulting from flow-induced vibrations are impact (which may result in fatigue wear), fatigue and wear. Because turbulence-induced vibration is random, the zero-to-peak vibration amplitudes can occasionally exceed several times the computed rms response. Thus, the fact that the nearest component is three times the rms vibration amplitude away does not guarantee that impacting between the two components will not occur. The number of impacts between two vibrating components over a given time period can be estimated based on the theory of probability, assuming that the vibration amplitudes follow a Gaussian distribution.
Likewise, since the zero-to-peak amplitude of vibration of a structure excited by flow turbulence can, over a long enough period of time, exceed arbitrarily large values, there is no endurance limit in random vibration. Given a long enough time, any structure excited by any random force will theoretically fail by fatigue. The cumulative fatigue usage can again be calculated based on the probabilistic theory. Since in cumulative fatigue analysis, the usage factor is computed based on the absolute value of the zero-topeak vibration amplitudes, which follow the Rayleigh distribution function if the ± vibration amplitudes follow the Gaussian distribution, the Rayleigh probability distribution function must be used in computing the cumulative fatigue usage factor of a component excited by turbulent flow. From the ASME fatigue curves (which are based on the 0-topeak vibration amplitudes), corresponding fatigue curves based on rms vibration amplitudes had been derived for several types of materials. These are given in Figures 11.6 to 11.10.