Second order wave kinematics

1. Input in SIMA

sima

2. Spectra

  • Input Wave spectrum

    • This is the input wave spectra, for instance Jonswap with given Hs and Tp.

    • Riflex estimates a minimum frequency fmin and a maximum frequency fmax. This is the lower and upper limits for the wave spectrum.

      • \(f_{min}=fac_{min}*\omega_{peak}\)

      • \(f_{max}=fac_{max}*\omega_{peak}\)

      • facmin and facmin is spectrum dependent

      • For numerical spectrum fmin and fmax is the first and last given frequency

that and fmin and fmax is slightly adjusted to correspond with the frequency resolution
spec

  • The 2. order wave spectrum consists of

    • Linear frequency wave energy spectrum

    • Difference frequency wave energy spectrum

    • Sum frequency wave energy spectrum

3. Pre-generation of kinematics

  • Length of kinematics time series, T:

  • Requested time series length

  • Time step used in the pre-generation, Δt

  • Time increment

  • Frequency resolution = 1/(applied time series length)

  • Applied time series length = N*Δt

timgen

4. Estimated parameters

  • Sampling frequency \(f_s=\frac{1}{\Delta t}\)

  • Nyquist frequency, \(f_{nyq}=\frac{1}{2\Delta t}=\frac{f_s}{2}\)

  • N=number of steps

5. Spectra

spec2

6. Warning in Riflex (SIMA)

  • if 2*fmax > fnyq

    • Note: wmax= 2*fmax

warning

  • The user can only affect the sampling frequency, If Δt in reduced, the Nyquist frequency will increase, fs = 1/Δt

nyquist