Reflection and transmission of ocean wave spectra by a band of randomly distributed ice floes

A new ocean wave/sea-ice interaction model is proposed that simulates how a directional wave spectrum evolves as it travels through an arbitrary finite array of circular ice floes, where wave/ice dynamics are entirely governed by wave scattering effects. The model is applied to characterise the wave reflection and transmission properties of a strip of ice floes, such as an ice edge band. A method is devised to extract the reflected and transmitted directional wave spectra produced by the array. The method builds upon an integral mapping from polar to Cartesian coordinates of the scattered wave components. Sensitivity tests are conducted for a row of floes randomly perturbed from a regular arrangement. Results for random arrays are generated using ensemble averaging. A realistic ice edge band is then reconstructed from field experiments data. Simulations show a good qualitative agreement with the data in terms of transmitted wave energy and directional spreading. In particular, it is observed that short waves become isotropic quickly after penetrating the ice field

Generalised eigenfunction expansion and singularity expansion methods for canonical time-domain wave scattering problems

The generalised eigenfunction expansion method (GEM) and the singularity expansion method (SEM) are applied to solve the canonical problem of wave scattering on an infinite stretched string in the time domain. The GEM, which is shown to be equivalent to d'Alembert's formula when no scatterer is present, is also derived in the case of a point-mass scatterer coupled to a spring. The discrete GEM, which generalises the discrete Fourier transform, is shown to reduce to matrix multiplication. The SEM, which is derived from the Fourier transform and the residue theorem, is also applied to solve the problem of scattering by the mass-spring system. The GEM and SEM are also applied to the problem of scattering by a mass positioned a fixed distance from an anchor point, which supports more complicated resonant behavior.Comment: 18 pages, 5 figure

Generalised eigenfunction expansion and singularity expansion methods for two-dimensional acoustic time-domain wave scattering problems

Time-domain wave scattering in an unbounded two-dimensional acoustic medium by sound-hard scatterers is considered. Two canonical geometries, namely a split-ring resonator (SRR) and an array of cylinders, are used to highlight the theory, which generalises to arbitrary scatterer geometries. The problem is solved using the generalised eigenfunction expansion method (GEM), which expresses the time-domain solution in terms of the frequency-domain solutions. A discrete GEM is proposed to numerically approximate the time-domain solution. It relies on quadrature approximations of continuous integrals and can be thought of as a generalisation of the discrete Fourier transform. The solution then takes a simple form in terms of direct matrix multiplications. In parallel to the GEM, the singularity expansion method (SEM) is also presented and applied to the two aforementioned geometries. It expands the time-domain solution over a discrete set of unforced, complex resonant modes of the scatterer. Although the coefficients of this expansion are divergent integrals, we introduce a method of regularising them using analytic continuation. The results show that while the SEM is usually inaccurate at $t=0$, it converges rapidly to the GEM solution at all spatial points in the computational domain, with the most rapid convergence occurring inside the resonant cavity.Comment: 24 pages, 9 figure

Hyperoxemia and excess oxygen use in early acute respiratory distress syndrome : Insights from the LUNG SAFE study

Publisher Copyright: © 2020 The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Background: Concerns exist regarding the prevalence and impact of unnecessary oxygen use in patients with acute respiratory distress syndrome (ARDS). We examined this issue in patients with ARDS enrolled in the Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE (LUNG SAFE) study. Methods: In this secondary analysis of the LUNG SAFE study, we wished to determine the prevalence and the outcomes associated with hyperoxemia on day 1, sustained hyperoxemia, and excessive oxygen use in patients with early ARDS. Patients who fulfilled criteria of ARDS on day 1 and day 2 of acute hypoxemic respiratory failure were categorized based on the presence of hyperoxemia (PaO2 > 100 mmHg) on day 1, sustained (i.e., present on day 1 and day 2) hyperoxemia, or excessive oxygen use (FIO2 ≥ 0.60 during hyperoxemia). Results: Of 2005 patients that met the inclusion criteria, 131 (6.5%) were hypoxemic (PaO2 < 55 mmHg), 607 (30%) had hyperoxemia on day 1, and 250 (12%) had sustained hyperoxemia. Excess FIO2 use occurred in 400 (66%) out of 607 patients with hyperoxemia. Excess FIO2 use decreased from day 1 to day 2 of ARDS, with most hyperoxemic patients on day 2 receiving relatively low FIO2. Multivariate analyses found no independent relationship between day 1 hyperoxemia, sustained hyperoxemia, or excess FIO2 use and adverse clinical outcomes. Mortality was 42% in patients with excess FIO2 use, compared to 39% in a propensity-matched sample of normoxemic (PaO2 55-100 mmHg) patients (P = 0.47). Conclusions: Hyperoxemia and excess oxygen use are both prevalent in early ARDS but are most often non-sustained. No relationship was found between hyperoxemia or excessive oxygen use and patient outcome in this cohort. Trial registration: LUNG-SAFE is registered with ClinicalTrials.gov, NCT02010073publishersversionPeer reviewe

Numerical and Experimental Analysis of Water Wave Scattering by Floating Elastic Plates

The response of one or more floating compliant disks to a monochromatic linear water wave is investigated theoretically and experimentally, in a regime where scattering effects dominate. A model is constructed assuming the disks behave as thin elastic plates, moving freely in a fluid domain of finite depth and infinite extent in the horizontal directions. The response of a single disk is devised first, using a novel version of the eigenfunction matching method, that accommodates a realistic Archimedean draught. The solution to the multiple-disk problem is obtained using Graf’s addition formula. A unique series of wave tank experiments is reported that replicates as closely as possible the conditions of the model. An optical remote sensing device provides accurate measurements for the disk deflection. Theoretical and experimental data are compared in terms of the natural modes of vibration of the disk. The modal amplitudes are analysed for three different disk thicknesses, over a frequency range relevant to the regime of interest. Additional tests with two disks provide data for different spacings and angles between the disks. For tests involving a single disk, good agreement is obtained overall for the dominant modes, although discrepancies appear consistently in the results. The influence of components of the experimental setup are analysed theoretically by extension of the original model to explain or discard their effect on the motion of the disk. For tests with two disks, evidence that the disks influence each other’s motion is found and reasonable agreement is obtained with the theory

Numerical and Experimental Analysis of Water Wave Scattering by Floating Elastic Plates

The response of one or more floating compliant disks to a monochromatic linear water wave is investigated theoretically and experimentally, in a regime where scattering effects dominate. A model is constructed assuming the disks behave as thin elastic plates, moving freely in a fluid domain of finite depth and infinite extent in the horizontal directions. The response of a single disk is devised first, using a novel version of the eigenfunction matching method, that accommodates a realistic Archimedean draught. The solution to the multiple-disk problem is obtained using Graf’s addition formula. A unique series of wave tank experiments is reported that replicates as closely as possible the conditions of the model. An optical remote sensing device provides accurate measurements for the disk deflection. Theoretical and experimental data are compared in terms of the natural modes of vibration of the disk. The modal amplitudes are analysed for three different disk thicknesses, over a frequency range relevant to the regime of interest. Additional tests with two disks provide data for different spacings and angles between the disks. For tests involving a single disk, good agreement is obtained overall for the dominant modes, although discrepancies appear consistently in the results. The influence of components of the experimental setup are analysed theoretically by extension of the original model to explain or discard their effect on the motion of the disk. For tests with two disks, evidence that the disks influence each other’s motion is found and reasonable agreement is obtained with the theory

Process-informed modelling of ocean waves interactions with the marginal sea ice zone

<p>The intensification of wave climate in the Southern Ocean tends to enhance the positive ice–albedo feedback. Waves break up the sea ice increasingly deeper within the outer margin of the Antarctic sea ice cover, referred to as the marginal ice zone (MIZ). During the melting season, this process accelerates sea ice loss and acts as a controlling mechanism for sea ice extent. Although much attention has been given to study the effect of the MIZ on the propagation of ocean waves, very little is known about the impact of waves on the morphology of the sea ice. The latter is principally governed by the break-up of bent sea-ice floes as a result of wave interaction. A sub-grid scale process-informed model describing the two-way coupling between the ocean waves and sea ice systems will be discussed, with a focus on how to parametrise this coupling in the NZESM.</p