Modeling and Observations of Wave Energy Attenuation in Fields of Colliding Ice Floes

2022 ◽  
pp. 167-182
Author(s):  
Agnieszka Herman ◽  
Sukun Cheng ◽  
Hayley H. Shen
Keyword(s):  
Wave Energy ◽  
Ice Floes

scholarly journals Pancake sea ice kinematics and dynamics using shipboard stereo video

2019 ◽  
Vol 61 (82) ◽  
pp. 1-11 ◽  
Author(s):  
Madison Smith ◽  
Jim Thomson
Keyword(s):  
Sea Ice ◽  
Energy Loss ◽  
Wave Energy ◽  
Wave Attenuation ◽  
Bulk Wave ◽  
Ocean Turbulence ◽  
Stereo Video ◽  
Ice Floes ◽  
Turbulence Generation

AbstractIn the marginal ice zone, surface waves drive motion of sea ice floes. The motion of floes relative to each other can cause periodic collisions, and drives the formation of pancake sea ice. Additionally, the motion of floes relative to the water results in turbulence generation at the interface between the ice and ocean below. These are important processes for the formation and growth of pancakes, and likely contribute to wave energy loss. Models and laboratory studies have been used to describe these motions, but there have been no in situ observations of relative ice velocities in a natural wave field. Here, we use shipboard stereo video to measure wave motion and relative motion of pancake floes simultaneously. The relative velocities of pancake floes are typically small compared to wave orbital motion (i.e. floes mostly follow the wave orbits). We find that relative velocities are well-captured by existing phase-resolved models, and are only somewhat over-estimated by using bulk wave parameters. Under the conditions observed, estimates of wave energy loss from ice–ocean turbulence are much larger than from pancake collisions. Increased relative pancake floe velocities in steeper wave fields may then result in more wave attenuation by increasing ice–ocean shear.

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

2019 ◽  
Vol 13 (11) ◽  
pp. 2887-2900 ◽  
Author(s):  
Agnieszka Herman ◽  
Sukun Cheng ◽  
Hayley H. Shen
Keyword(s):  
Dispersion Relation ◽  
Wave Energy ◽  
High Frequency ◽  
Water Waves ◽  
Discrete Element ◽  
Unit Surface Area ◽  
Energy Propagation ◽  
Quadratic Drag ◽  
Ice Floes ◽  
Ice Water

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.

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

2019 ◽  
Author(s):  
Agnieszka Herman ◽  
Sukun Cheng ◽  
Hayley H. Shen
Keyword(s):  
Dispersion Relation ◽  
Wave Energy ◽  
High Frequency ◽  
Water Waves ◽  
Discrete Element ◽  
Unit Surface Area ◽  
Energy Propagation ◽  
Quadratic Drag ◽  
Ice Floes ◽  
Ice Water

Abstract. The energy of water waves propagating through sea ice is attenuated due to nondissipative (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 analyzed 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 nonexponential attenuation of wave amplitude a with distance x, of a form a(x)=1/(α x+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 mass-loading dispersion relation, suitable for ice covers composed of small floes, the increase of 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 (semi)permanent contact with each other, with attenuation rates close to those analyzed theoretically. Dissipation in the collisional zone increases with 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.

scholarly journals Attenuation and directional spreading of ocean wave spectra in the marginal ice zone

2016 ◽  
Vol 790 ◽  
pp. 492-522 ◽  
Author(s):  
Fabien Montiel ◽  
V. A. Squire ◽  
L. G. Bennetts
Keyword(s):  
Wave Field ◽  
Wave Energy ◽  
Scattering Problem ◽  
Ocean Wave ◽  
Thin Elastic Plate ◽  
Linear Potential ◽  
Wave Spectra ◽  
Water Ice ◽  
Marginal Ice Zone ◽  
Ice Floes

A theoretical model is used to study wave energy attenuation and directional spreading of ocean wave spectra in the marginal ice zone (MIZ). The MIZ is constructed as an array of tens of thousands of compliant circular ice floes, with randomly selected positions and radii determined by an empirical floe size distribution. Linear potential flow and thin elastic plate theories model the coupled water–ice system. A new method is proposed to solve the time-harmonic multiple scattering problem under a multidirectional incident wave forcing with random phases. It provides a natural framework for tracking the evolution of the directional properties of a wave field through the MIZ. The attenuation and directional spreading are extracted from ensembles of the wave field with respect to realizations of the MIZ and incident forcing randomly generated from prescribed distributions. The averaging procedure is shown to converge rapidly so that only a small number of simulations need to be performed. Far-field approximations are investigated, allowing efficiency improvements with negligible loss of accuracy. A case study is conducted for a particular MIZ configuration. The observed exponential attenuation of wave energy through the MIZ is reproduced by the model, while the directional spread is found to grow linearly with distance. The directional spreading is shown to weaken when the wavelength becomes larger than the maximum floe size.

scholarly journals Wave attenuation in a marginal ice zone due to the bottom roughness of ice floes

2011 ◽  
Vol 52 (57) ◽  
pp. 118-122 ◽  
Author(s):  
Alison L. Kohout ◽  
Michael H. Meylan ◽  
David R. Plew
Keyword(s):  
Attenuation Coefficient ◽  
Internal Waves ◽  
Wave Energy ◽  
Wave Scattering ◽  
Wave Attenuation ◽  
Viscous Drag ◽  
Physical Factors ◽  
Marginal Ice Zone ◽  
Rate Of Decay ◽  
Ice Floes

AbstractWave attenuation in a diffuse marginal ice zone (MIZ) is thought to be mainly a result of wave scattering. In a compact MIZ, additional physical factors are thought to be relevant. In this paper, we propose that viscous drag, form drag and energy lost to internal waves under the ice play a role in attenuating wave energy. We derive a relation for the wave attenuation due to drag. We combine the drag attenuation coefficient with the scattering attenuation coefficient and compare the result to experimental results for compact MIZs. We find that the combined scatter and drag (CSD) model improves the rate of decay of wave attenuation in compact ice fields, but fails to predict the ‘rollover’ seen at short periods.

The Silicon Detector, and Measurement of Electric Wave Energy

1907 ◽  
Vol 63 (1638supp) ◽  
pp. 26239-26239
Author(s):  
William Maver
Keyword(s):  
Wave Energy ◽  
Silicon Detector ◽  
Electric Wave
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