Analysis of ship wake transformation in the coastal zone using time-frequency methods/Kiirlaevalainete uksikute komponentide omaduste muutumine rannikuvoondis

• Published in: Proceedings of the Estonian Academy of Sciences 2015-09, p.S379
• Main Authors: Torsvik, Tomas, Herrmann, Heiko, Didenkulova, Ira, Rodin, Artem
• Format: Article
• Language: English
• Subjects: Observations; Wakes (Aerodynamics); Wakes (Fluid dynamics); Water waves; Wave propagation
• ISSN: 1736-6046

Ship wake transformation in the coastal zone is analysed based on field measurements of wave conditions at two measurement sites located about 20 m and 100 m from the shore. Analysis of single wake events recorded at both sites is carried out by transforming the time series of the wave amplitude into the time-frequency domain, using both a short-time Fourier transform and a wavelet transform. Analysis reveals that signature features of individual wake components can be tracked as the wake approaches the shore, but the wave amplitude and associated wave energy is transformed differently for different wake components. The wake energy is reduced as the waves propagate through the surf zone, which can be attributed mainly to wave breaking of the leading wave system and a significant reduction of the divergent wave system. However, the energy of transverse waves is stable or increasing, indicating that these waves undergo a non-breaking shoaling process. Key words: wave transformation, ship wake, wave energy, Fourier transform, wavelet transform. Kiirlaevalainete umberkujunemist rannikuvoondis on analuusitud 20 ja 100 m kaugusel rannajoonest tehtud mootmiste alusel. Vee pinna kuju ja lainete amplituudide aegjadad uksikutes laevalainete ruhmades on teisendatud aja-sageduse koordinaadistiku salvestuste luhikestele loikudele rakendatud Fourier' teisenduse abil ning lainikute meetodiga. On naidatud, et laevalainete susteemi uksikute komponentide signatuur on selgelt jalgitav uhest mootepunktist teise, kuid erinevaid komponente esindavate lainete amplituudid ja potentsiaalne energia muutuvad erinevas rutmis. Suur osa laevalainete susteemi koguenergia kahanemisest murdlainete voondis tuleneb susteemi esimeste, korgeimate ja pikimate lainete osalisest murdumisest ning poiklainete korguse kahanemisest. Seevastu pikilained levivad praktiliselt rannikuni ilma murdumata ja nende energia pusib peaaegu muutumatuna voi isegi suureneb veidi.