DRILLBITS
Monthly eNewsletter from the IADC

The IADC Lexicon is an oil and gas dictionary of upstream-related terms, which, unlike conventional glossaries, are official definitions drawn from legislation, regulation and regulatory guidance, standards (global, national and regional), IADC guidelines, and Well Control Institute. Terms often have multiple definitions from different sources.

This July’s Featured Term is:

“Spectral Moment” Source: APIRP 2MET, Derivation of Metocean Design and Operating Conditions, First Edition, November 2014. Global Standards.

Integral over frequency of the spectral density function multiplied by the nth power of the frequency, either expressed in hertz (cycles per second) as

m_n( ƒ ) = ∫ ƒ^{n S( ƒ ) dƒ}

or expressed in circular frequency (radians/second) as

m_n( ω ) = ∫ ωⁿ S (_ω) ^_dω

NOTE 1 As ω = 2πƒ, the relationship between the two moment expressions is:

m_n( ω ) = ∫ (2π)ⁿ m_n( ƒ )

NOTE 2 The integration extends over the entire frequency range from zero to infinity. In practice, the integration is often truncated at a frequency beyond which the contribution to the integral is negligible and/or the sensor no long responds accurately.