Effective viscosity of grease ice in linearized gravity waves

Grease ice is an agglomeration of disc-shaped ice crystals, named frazil ice, which forms in turbulent waters of the Polar Oceans and in rivers as well. It has been recognized that the properties of grease ice to damp surface gravity waves could be explained in terms of the effective viscosity of the ice slurry. This paper is devoted to the study of the dynamics of a suspension of disc-shaped particles in a gravity wave field. For dilute suspensions, depending on the strength and frequency of the external wave flow, two orientation regimes of the particles are predicted: a preferential orientation regime with the particles rotating in coherent fashion with the wave field, and a random orientation regime in which the particles oscillate around their initial orientation while diffusing under the effect of Brownian motion. For both motion regimes, the effective viscosity has been derived as a function of the wave frequency, wave amplitude and aspect ratio of the particles. Model predictions have been compared with wave attenuation data in frazil ice layers grown in wave tanks.Comment: 13 pages, 3 eps figures included; one more section on inertia effect

SAISERIT: A man with sight but no seeing

The subject of this work is an interdisciplinary dance and video solo performance, involving additional audience audio-immersion, concerned with an exploration of close-mindedness; employing the definition of this trait as detailed by David Foster Wallace (2009). The performance was presented on 16th July at the Media Factory in Preston, as part of the international conference "Transdisciplinary Explorations Into Performativity" [see Supplemental Material: Conference Brochure + Introductory Clip] One of the theatres was emptied for the occasion, no seats or curtains. Access to the theatre was through the back door and exit through the front door. The whole theatre space was shared by audience and performer.The set up included: - a general dim warm lighting plan and 6 movable floor light cans pointing towards the ceiling - three projectors looping three different videos previously edited by video maker Matt Clarke [see Supplemental Material: Video Projection (number one) + (number two) + (number three)] echoing the material performed live by Giorgio de Carolis [see an extract of it in Supplemental Material: Rehearsal Footage in Studio] - six wireless headphones playing David Foster Wallace's speech 'This is Water'. The audience entering the performance space was invited to select their individual point of view, duration of engagement with the work and whether or not they wanted to listen to the audio through the headphones [see Supplemental Material: Entrance Map (Instructional Poster)]

Retrieval of the ocean wave spectrum in open and thin ice covered ocean waters from ERS Synthetic Aperture Radar images

This paper concerns with the task of retrieving ocean wave spectra from imagery provided by space-borne SAR systems such as that on board ERS satellite. SAR imagery of surface wave fields traveling into open ocean and into thin sea ice covers composed of frazil and pancake icefields is considered. The major purpose is to gain insight on how the spectral changes can be related to sea ice properties of geophysical interest such as the thickness. Starting from SAR image cross spectra computed from Single Look Complex (SLC) SAR images, the ocean wave spectrum is retrieved using an inversion procedure based on the gradient descent algorithm. The capability of this method when applied to satellite SAR sensors is investigated. Interest in the SAR image cross spectrum exploitation is twofold: first, the directional properties of the ocean wave spectra are retained; second, external wave information needed to initialize the inversion procedure may be greatly reduced using only information included in the SAR image cross spectrum itself. The main drawback is that the wind waves spectrum could be partly lost and its spectral peak wave number underestimated. An ERS-SAR SLC image acquired on April 10, 1993 over the Greenland Sea was selected as test image. A pair of windows that include open-sea only and sea ice cover, respectively, were selected. The inversions were carried out using different guess wave spectra taken from SAR image cross spectra. Moreover, care was taken to properly handle negative values eventually occurring during the inversion runs. This results in a modification of the gradient descending technique that is required if a non-negative solution of the wave spectrum is searched for. Results are discussed in view of the possibility of SAR data to detect ocean wave dispersion as a means for the retrieval of ice thickness

An energy-aware architecture : a practical implementation for autonomous underwater vehicles

Energy awareness, fault tolerance and performance estimation are important aspects for extending the autonomy levels of today’s autonomous vehicles. Those are related to the concepts of survivability and reliability, two important factors that often limit the trust of end users in conducting large-scale deployments of such vehicles. With the aim of preparing the way for persistent autonomous operations this work focuses its efforts on investigating those effects on underwater vehicles capable of long-term missions. A novel energy-aware architecture for autonomous underwater vehicles (AUVs) is presented. This, by monitoring at runtime the vehicle’s energy usage, is capable of detecting and mitigating failures in the propulsion subsystem, one of the most common sources of mission-time problems. Furthermore it estimates the vehicle’s performance when operating in unknown environments and in the presence of external disturbances. These capabilities are a great contribution for reducing the operational uncertainty that most underwater platforms face during their deployment. Using knowledge collected while conducting real missions the proposed architecture allows the optimisation of on-board resource usage. This improves the vehicle’s effectiveness when operating in unknown stochastic scenarios or when facing the problem of resource scarcity. The architecture has been implemented on a real vehicle, Nessie AUV, used for real sea experiments as part of multiple research projects. These gave the opportunity of evaluating the improvements of the proposed system when considering more complex autonomous tasks. Together with Nessie AUV, the commercial platform IVER3 AUV has been involved in the evaluating the feasibility of this approach. Results and operational experience, gathered both in real sea scenarios and in controlled environment experiments, are discussed in detail showing the benefits and the operational constraints of the introduced architecture, alongside suggestions for future research directions

Sport-Based Youth Development: An Examination of the Best Practices of Three Programs Designed for Adolescent Girls

Sports-based youth development programs have used sports to teach essential life skills to participants. Programs designed for adolescent girls have an additional ambition of closing the gender gap that still exists in physical activity levels. The purpose of this study was to determine the best practices of sports-based youth development programs worldwide that are designed specifically for adolescent females. The researcher compared program elements, lesson elements, and evaluation methods of each program with recommendations from the literature. The main instruments used for these comparisons were the published curricula of each organization. Results showed minimal variance in program elements but substantial differences in lesson elements and evaluation methods. The researcher recommended creating international standards for research-supported lesson elements and incorporating scientific measurements into the evaluation process of all sports-based youth development programs designed for adolescent girls

Diffusion of gravity waves by random space inhomogeneities in pancake-ice fields. Theory and validation with wave buoys and synthetic aperture radar

We study the diffusion of ocean waves by floating bodies such as pancakes and ice floes much smaller than a wavelength. We argue that the combined effect of hydrodynamic interaction of the ice bodies and inhomogeneities in the ice cover at scales comparable to that of the wavelength significantly increases diffusion, producing a contribution to wave attenuation comparable to what is observed in the field and usually explained by invoking viscous effects. The resulting attenuation spectrum is characterized by a peak at the scale of the inhomogeneities in the ice cover, thereby providing a new possible explanation of the rollover of the attenuation profile at small wavelengths experimentally observed over the years. The proposed attenuation mechanism has the same effect as a viscous wave model with effective viscosity linearly dependent on the ice thickness, which may explain recent findings that viscous wave models require a thickness-dependent viscosity to fit experimental attenuation data. Experimental validation is carried out using wave buoy attenuation data and synthetic aperture radar image analysis.Comment: 29 pages, 5 figure