Hello everyone,

The **IEC 61400-3-1:2019** says that the wave period *T* can range from *11.1*sqrt(H_s / g)* to *14.3*sqrt(H_s/g)*. However, OpenFast requires **Peak spectral period**, **WaveTp** for **WaveMod=2** (JONSWAP/Pierson-Moskowitz spectrum).

Is the above range applicable to **WaveTp**? That is,

*11.1 * sqrt(H_s / g) ≤ ***WaveTp** ≤ 14.3 * sqrt(H_s/g).

Or, I noticed that the peak spectral period *T_p≈1.2T_0* for the JONSWAP spectrum, in which *T_0* is the mean wave period. Is the notation *T* in IEC 61400-3-1 Eq. (10) equivalent to *T_1*, and I should use the range

*1.2 * 11.1 * sqrt(H_s / g) ≤ ***WaveTp** ≤ 1.2 * 14.3 * sqrt(H_s/g)

Thanks for your help.

Best regards,

Xingchao Wang

Dear @Xingchao.Wang,

The equation you are referring to from IEC 61400-3-1:2019 applies only to the range of wave periods associated with the extreme individual wave height in deep water when the site-specific metocean data is insufficient to determine it. This equation does not apply to normal wave conditions or irregular sea states. This equation could be used to determine the range of wave periods associated with extreme individual wave heights to be applied via constrained NewWave theory when simulating load cases involving Extreme Sea States (ESS). Constrained NewWave theory has been added to the new SeaState module of OpenFAST that will be first released in OpenFAST v4.0: https://github.com/OpenFAST/openfast/pull/1008.

Best regards,

Dear @Jason.Jonkman,

Thank you for your detailed answer. I will refer to books on the topic of random waves.

Best regards,

Xingchao Wang