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.

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 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.

Numerical Study on Wave Attenuation of Tsunami-Like Wave by Emergent Rigid Vegetation

2021 ◽  
pp. 1-28
Author(s):  
K. Qu ◽  
G. Y. Lan ◽  
S. Kraatz ◽  
W. Y. Sun ◽  
B. Deng ◽  
...  
Keyword(s):  
Solitary Waves ◽  
Wave Energy ◽  
Wave Attenuation ◽  
Tsunami Wave ◽  
Numerical Study ◽  
Wave Model ◽  
Indian Ocean Tsunami ◽  
Vegetation Density ◽  
Rigid Vegetation ◽  
Total Wave

The extreme surges and waves generated in tsunamis can cause devastating damages to coastal infrastructures and threaten the intactness of coastal communities. After the 2004 Indian Ocean tsunami, extensive physical experiments and numerical simulations have been conducted to understand the wave attenuation of tsunami waves due to coastal forests. Nearly all prior works used solitary waves as the tsunami wave model, but the spatial-temporal scales of realistic tsunamis differ drastically from that of solitary waves in both wave period and wavelength. More recent work has questioned the applicability of solitary waves and been looking towards more realistic tsunami wave models. Therefore, aiming to achieve more realistic and accurate results, this study will use a parameterized tsunami-like wave based on wave observations during the 2011 Japan tsunami to study the wave attenuation of a tsunami wave by emergent rigid vegetation. This study uses a high-resolution numerical wave tank based on the non-hydrostatic wave model (NHWAVE). This work examines effects of prominent factors, such as wave height, water depth, vegetation density and width, on the wave attenuation efficiency of emergent rigid vegetation. Results indicate that the vegetation patch can dissipate a considerable amount of the total wave energy of the tsunami-like wave. However, the tsunami-like wave has a higher total wave energy, but also a lower wave energy dissipation rate. Results show that using a solitary instead of a tsunami-like wave profile can overestimate the wave attenuation efficiency of the coastal forest.

scholarly journals Enhancement of a 3-DOF submerged wave energy device using bistability

2020 ◽  
Vol 3 (2) ◽  
pp. 73-82
Author(s):  
Benjamin Schubert ◽  
William S. P. Robertson ◽  
Benjamin S. Cazzolato
Keyword(s):  
Wave Energy ◽  
Degrees Of Freedom ◽  
Phase Relationship ◽  
Bistable System ◽  
Viscous Drag ◽  
Regular Waves ◽  
Point Absorber ◽  
Exciting Forces ◽  
Bistable Mechanism ◽  
The Impact

The dynamic response of a submerged CETO shaped quasi-point absorbing wave energy converter coupled to a bistable power take off is presented in this study. Whilst the impact of bistability has been shown in a limited number of situations to improve the amount of power generated, many models have been restricted to a single degree of freedom and often ignore drag effects. To overcome these model limitations, a submerged single tether point absorber with a bistable power take off was modelled using both 1 and 3 degrees of freedom. The device was subjected to regular waves and included a simple model of viscous drag. The bistable mechanism was provided by a magnetic dipole model quantified by a dimensionless parameter applicable to any bistable system. The performance of the device was is assessed by the theoretical power generated. Over each model, the previously observed benefit of bistability was not consistently obtained. Simulations of regular waves demonstrated an increase in generated power for suboptimal conditions for some frequencies, while a reduction in generated power was observed in optimal conditions. The performance increase showed strong correlation to the phase relationship between the motion and exciting forces as a result of bistability.

Plane-wave attenuation anisotropy in orthorhombic media

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. D9-D19 ◽  
Author(s):  
Yaping Zhu ◽  
Ilya Tsvankin
Keyword(s):  
Attenuation Coefficient ◽  
Wave Attenuation ◽  
Fractured Reservoirs ◽  
The Body ◽  
P Wave ◽  
Attenuation Coefficients ◽  
Velocity Anisotropy ◽  
Homogeneous Wave ◽  
Anisotropy Parameters ◽  
Attenuation Anisotropy

Orthorhombic models are often used in the interpretation of azimuthally varying seismic signatures recorded over fractured reservoirs. Here, we develop an analytic framework for describing the attenuation coefficients in orthorhombic media with orthorhombic attenuation (i.e., the symmetry of both the real and imaginary parts of the stiffness tensor is identical) under the assumption of homogeneous wave propagation. The analogous form of the Christoffel equation in the symmetry planes of orthorhombic and VTI (transversely isotropic with a vertical symmetry axis) media helps to obtain the symmetry-plane attenuation coefficients by adapting the existing VTI equations. To take full advantage of this equivalence with transverse isotropy, we introduce a parameter set similar to the VTI attenuation-anisotropy parameters [Formula: see text], [Formula: see text], and [Formula: see text]. This notation, based on the same principle as Tsvankin’s velocity-anisotropy parameters for orthorhombic media, leads to concise linearized equations for thesymmetry-plane attenuation coefficients of all three modes (P, [Formula: see text], and [Formula: see text]).The attenuation-anisotropy parameters also allow us to simplify the P-wave attenuation coefficient [Formula: see text] outside the symmetry planes under the assumptions of small attenuation and weak velocity and attenuation anisotropy. The approximate coefficient [Formula: see text] has the same form as the linearized P-wave phase-velocity function, with the velocity parameters [Formula: see text] and [Formula: see text] replaced by the attenuation parameters [Formula: see text] and [Formula: see text]. The exact attenuation coefficient, however, also depends on the velocity-anisotropy parameters, while the body-wave velocities are almost unperturbed by the presence of attenuation. The reduction in the number of parameters responsible for the P-wave attenuation and the simple approximation for the coefficient [Formula: see text] provide a basis for inverting P-wave attenuation measurements from orthorhombic media. The attenuation processing must be preceded by anisotropic velocity analysis that can be performed (in the absence of pronounced velocity dispersion) using existing algorithms for nonattenuative media.

Effect of Property of Interphase Layer on Damping Properties of Polymer Composites Using Sensitivity Analysis

2019 ◽  
Author(s):  
Shank S. Kulkarni ◽  
Alireza Tabarraei ◽  
Pratik Ghag
Keyword(s):  
Sensitivity Analysis ◽  
Attenuation Coefficient ◽  
Wave Attenuation ◽  
Volume Fraction ◽  
Matrix Material ◽  
Interphase Layer ◽  
Damping Properties ◽  
Damping Property ◽  
Interphase Region ◽  
The Matrix

Abstract This work studies the damping property of Nanocomposites through simulating wave propagation using the Finite Element Method (FEM). For this purpose Representative Volume Element (RVE) of the composite material is created using Random Sequential Absorption (RSA) algorithm. Damping property is represented using the wave attenuation coefficient. The matrix material is assumed to be isotropic visco-elastic in nature with randomly dispersed stiff elastic spherical fillers. In order to model mechanical imperfections at the boundary of fillers and matrix, the interphase layer is modeled surrounding the spherical fillers. Determining the thickness and stiffness of this interphase region is a challenging task. Therefore this study aims at investigating the effect of variation in thickness and stiffness values of the interphase region on damping property of whole composite using sensitivity analysis. Two specific cases with a volume fraction of 5 % and 8.6 % are selected for sensitivity analysis. It has been found that both the thickness and stiffness of the interphase region plays an important role in deciding the damping properties of the polymer composite. Value of attenuation coefficient is more sensitive to the thickness of interphase than stiffness and hence it is important to choose the value of thickness correctly for accurate predictions.

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.

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