Wave energy attenuation in fields of colliding ice floes – Part 1: Discrete-element modelling of dissipation due to ice–water drag

Agnieszka Herman , Sukun Cheng , Hayley H. Shen

Abstract

The energy of water waves propagating through sea ice is attenuated due to non-dissipative (scattering) and dissipative processes. The nature of those processes and their contribution to attenuation depends on wave characteristics and ice properties and is usually difficult (or impossible) to determine from limited observations available. Therefore, many aspects of relevant dissipation mechanisms remain poorly understood. In this work, a discrete-element model (DEM) is used to study one of those mechanisms: dissipation due to ice–water drag. The model consists of two coupled parts, a DEM simulating the surge motion and collisions of ice floes driven by waves and a wave module solving the wave energy transport equation with source terms computed based on phase-averaged DEM results. The wave energy attenuation is analysed analytically for a limiting case of a compact, horizontally confined ice cover. It is shown that the usage of a quadratic drag law leads to non-exponential attenuation of wave amplitude a with distance x, of the form a(x)=1/(αx+1/a0), with the attenuation rate α linearly proportional to the drag coefficient. The dependence of α on wave frequency ω varies with the dispersion relation used. For the open-water (OW) dispersion relation, α∼ω4. For the mass loading dispersion relation, suitable for ice covers composed of small floes, the increase in α with ω is much faster than in the OW case, leading to very fast elimination of high-frequency components from the wave energy spectrum. For elastic-plate dispersion relation, suitable for large floes or continuous ice, α∼ωm within the high-frequency tail, with m close to 2.0–2.5; i.e. dissipation is much slower than in the OW case. The coupled DEM–wave model predicts the existence of two zones: a relatively narrow area of very strong attenuation close to the ice edge, with energetic floe collisions and therefore high instantaneous ice–water velocities, and an inner zone where ice floes are in permanent or semi-permanent contact with each other, with attenuation rates close to those analysed theoretically. Dissipation in the collisional zone increases with an increasing restitution coefficient of the ice and with decreasing floe size. In effect, two factors contribute to strong attenuation in fields of small ice floes: lower wave energy propagation speeds and higher relative ice–water velocities due to larger accelerations of floes with smaller mass and more collisions per unit surface area.
Author Agnieszka Herman (FOG / IO / DPO)
Agnieszka Herman,,
- Division of Physical Oceanography
, Sukun Cheng
Sukun Cheng,,
-
, Hayley H. Shen
Hayley H. Shen,,
-
Journal seriesCryosphere, [CRYOSPHERE], ISSN 1994-0416, e-ISSN 1994-0424, (N/A 140 pkt)
Issue year2019
Vol13
No11
Pages2887-2900
Publication size in sheets0.65
ASJC Classification1904 Earth-Surface Processes; 2312 Water Science and Technology
DOIDOI:10.5194/tc-13-2887-2019
Languageen angielski
LicenseRepository; published final; Uznanie Autorstwa (CC-BY); with publication
File
Herman_Agnieszka_Wave-energy_attenuation_2019.pdf 2.55 MB
Score (nominal)140
Score sourcejournalList
ScoreMinisterial score = 140.0, 28-01-2020, ArticleFromJournal
Publication indicators Scopus SNIP (Source Normalised Impact per Paper): 2018 = 1.551; WoS Impact Factor: 2018 = 4.79 (2) - 2018=5.921 (5)
Citation count*
Additional fields
LicencjaUtwór jest udostępniany na licencji Creative Commons Uznanie autorstwa 4.0 Międzynarodowe (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/
Cite
Share Share

Get link to the record


* presented citation count is obtained through Internet information analysis and it is close to the number calculated by the Publish or Perish system.
Back
Confirmation
Are you sure?