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Sand B.,Norut Narvik AS | Fransson L.,Lulea University of Technology
Society of Petroleum Engineers - Arctic Technology Conference 2011 | Year: 2011

The interaction of ice sheets with rigid vertical structures is an important problem in the design of arctic offshore structures. Offshore structures often experience an enormous ice load since the ice sheet breaks by crushing into the structure. The finite element method is adopted to calculate ice forces on vertical structures of various shapes. The effect of material nonlinearities and friction between the ice and structure is taken into account. The ice is treated as a transversely isotropic, nonlinear material and formation of crushing or cracking is treated as a transformation of state. The contact interaction between the ice sheet and the structure is simulated with a contact formulation based on finite sliding interaction between a deformable body and a rigid body with Coulomb friction sliding. To verify the applicability of the proposed constitutive models, the numerical results obtained during the present study are compared with data from field measurements. Copyright 2011, Offshore Technology Conference.

Katlein C.,Alfred Wegener Institute for Polar and Marine Research | Nicolaus M.,Alfred Wegener Institute for Polar and Marine Research | Petrich C.,Norut Narvik AS
Journal of Geophysical Research: Oceans | Year: 2014

Radiative transfer in sea ice is subject to anisotropic, multiple scattering. The impact of anisotropy on the light field under sea ice was found to be substantial and has been quantified. In this study, a large data set of irradiance and radiance measurements under sea ice has been acquired with a Remotely Operated Vehicle (ROV) in the central Arctic. Measurements are interpreted in the context of numerical radiative transfer calculations, laboratory experiments, and microstructure analysis. The ratio of synchronous measurements of transmitted irradiance to radiance shows a clear deviation from an isotropic under-ice light field. We find that the angular radiance distribution under sea ice is more downward directed than expected for an isotropic light field. This effect can be attributed to the anisotropic scattering coefficient within sea ice. Assuming an isotropic radiance distribution under sea ice leads to significant errors in light-field modeling and the interpretation of radiation measurements. Quantification of the light field geometry is crucial for correct conversion of radiance data acquired by Autonomous Underwater Vehicles (AUVs) and ROVs. Key Points Anisotropic scattering coefficients in sea ice influence radiance distribution Anisotropic distribution of under-ice radiance causes deeper light penetration Isotropic assumptions lead to significant errors in radiation models © 2014. American Geophysical Union. All Rights Reserved.

Nicolaus M.,Alfred Wegener Institute for Polar and Marine Research | Petrich C.,Norut Narvik AS | Hudson S.R.,Norwegian Polar Institute | Granskog M.A.,Norwegian Polar Institute
Cryosphere | Year: 2013

The amount of solar radiation transmitted through Arctic sea ice is determined by the thickness and physical properties of snow and sea ice. Light transmittance is highly variable in space and time since thickness and physical properties of snow and sea ice are highly heterogeneous on variable time and length scales. We present field measurements of under-ice irradiance along transects under undeformed land-fast sea ice at Barrow, Alaska (March, May, and June 2010). The measurements were performed with a spectral radiometer mounted on a floating under-ice sled. The objective was to quantify the spatial variability of light transmittance through snow and sea ice, and to compare this variability along its seasonal evolution. Along with optical measurements, snow depth, sea ice thickness, and freeboard were recorded, and ice cores were analyzed for chlorophyll and particulate matter. Our results show that snow cover variability prior to onset of snow melt causes as much relative spatial variability of light transmittance as the contrast of ponded and white ice during summer. Both before and after melt onset, measured transmittances fell in a range from one third to three times the mean value. In addition, we found a twentyfold increase of light transmittance as a result of partial snowmelt, showing the seasonal evolution of transmittance through sea ice far exceeds the spatial variability. However, prior melt onset, light transmittance was time invariant and differences in under-ice irradiance were directly related to the spatial variability of the snow cover. © 2013 Author(s).

Petrich C.,Norut Narvik AS | Tivy A.C.,National Research Council Canada | Ward D.H.,U.S. Geological Survey
Cold Regions Science and Technology | Year: 2014

Historical sea ice conditions were reconstructed for Izembek Lagoon, Bering Sea, Alaska. This lagoon is a crucial staging area during migration for numerous species of avian migrants and a major eelgrass (Zostera marina) area important to a variety of marine and terrestrial organisms, especially Pacific Flyway black brant geese (Branta bernicla nigricans). Ice cover is a common feature of the lagoon in winter, but appears to be declining, which has implications for eelgrass distribution and abundance, and its use by wildlife. We evaluated ice conditions from a model based on degree days, calibrated to satellite observations, to estimate distribution and long-term trends in ice conditions in Izembek Lagoon. Model results compared favorably with ground observations and 26. years of satellite data, allowing ice conditions to be reconstructed back to 1943. Specifically, periods of significant (limited access to eelgrass areas) and severe (almost complete ice coverage of the lagoon) ice conditions could be identified. The number of days of severe ice within a single season ranged from 0 (e.g., 2001) to ≥ 67 (e.g., 2000). We detected a slight long-term negative trend in ice conditions, superimposed on high inter-annual variability in seasonal aggregate ice conditions. Based on reconstructed ice conditions, the seasonally cumulative number of significant or severe ice days correlated linearly with mean air temperature from January until March. Further, air temperature at Izembek Lagoon was correlated with wind direction, suggesting that ice conditions in Izembek Lagoon were associated with synoptic-scale weather patterns. Methods employed in this analysis may be transferable to other coastal locations in the Arctic. © 2013 Elsevier B.V.

Truong D.C.,Vietnam National University, Ho Chi Minh City | Abburi M.,Norut Narvik AS | Thuat N.T.,Vietnam National University, Ho Chi Minh City | Bostrom T.,Norut Narvik AS | Nguyen Q.,Norut Narvik AS
International Journal of Nanotechnology | Year: 2013

In this paper we present the study of electrochemical etching of silicon in KOH solutions to improve texturisation and reflection properties of p-type multi-crystalline silicon. The influence of etching temperature on surface morphology and reflection properties of the silicon wafers has been investigated. The results of the study showed that etching at high temperatures formed isotropic textured concaves on the silicon surface which is similar to the effect of acidic etching. Etching at room temperature resulted in formation of a uniform nano-porous texture and lowest reflectance. With optimised etching conditions' the total reflectance of the textured surface reduced below 25%. These results can be utilised in further studies to improve the efficiency of solar cells based on multi-crystalline silicon. © 2013 Inderscience Enterprises Ltd.

Cardenas J.F.,Norut Narvik AS
Journal of Raman Spectroscopy | Year: 2013

Raman scattering experiments were performed on Si(60 nm)/metal/substrate structures with and without silica microspheres (with a diameter between 0.5 and 5 μm) on top. Raman scattering from the thin Si layer exhibits enhancements (~20) due to the dielectric spheres, where the enhancement factors depend on the diameter of the spheres. The interaction between light and dielectric spheres has been simulated by finite difference time domain calculations (FDTD), wherein particularly the electric energy density (ED) distribution in the thin Si layer was of concern. For microspheres with a diameter less than ~3 μm, the transverse ED distribution (perpendicular to the incident light direction) within the Si layer is characterised by a single peak centered on the optical axis. For larger diameters, a multimodal transverse ED distribution develops where the maximum is not centered on the optical axis. Using an ad-hoc approach for surface enhanced Raman scattering in combination with the FDTD calculations, the experimental Raman observations are well accounted for. Copyright © 2013 John Wiley & Sons, Ltd.

Petrich C.,Norut Narvik AS | Arntsen M.,Norut Narvik AS
Proceedings of the International Conference on Port and Ocean Engineering under Arctic Conditions, POAC | Year: 2013

Oil reaching the underside of sea ice after a blow-out is able to spread laterally, governed by buoyancy and surface tension, under-ice topography, and currents. However, the possibility of lateral spread and the direct contact with the ocean are inhibited once oil begins to get encapsulated by the advancing ice front. Encapsulation removes oil largely from the environment, influencing risk management strategies. We performed laboratory tank experiments to quantify the encapsulation process. A 130 L tank was built from Perspex with removable insulation to allow for in-situ observation of the ice underside. Heat flux into the water was controlled to ensure the development of a realistic crystal fabric. Oil was injected under ice of 0.1 m thickness. Observations on crystal structure and encapsulation process are consistent with previous studies. Following the initial development of a lip around the oil lens, initial overgrowth was due to crystals with vertical c-axes. Temperature probes recorded vertical heat flux and ice growth rate under the lens. Encapsulation appeared to be governed by common thermodynamic and fluid dynamic principles. No indications were found that crystal alignment would need to be considered explicitly to describe encapsulation numerically.

Abburi M.,Norut Narvik AS | Bostrom T.,Norut Narvik AS | Olefjord I.,Norut Narvik AS
Materials Chemistry and Physics | Year: 2013

Boron doped multicrystalline Si-wafers were anodically polarized in 2 M KOH and 4 M KOH at 40 °C and 50 °C. The applied potentials were 25 V, 30 V, 40 V and 50 V. The morphology of the textured surfaces, the surface products and the light reflectivity were analyzed by utilizing SEM, XPS and Lambda UV/Vis/NIR spectrophotometer, respectively. Isotropic texturing was obtained. The lowest average reflectivity, 17%, was achieved after pre-etching for 10 min and polarization at 40 V for 10 min in 4 M KOH at 50 °C. That reflection value is half of that measured on a chemical pre-etched surface, 34%. By increasing the voltage to 50 V the reflectivity rises to 28%. Polarizations to 25 V and 30 V at 50 °C in both solutions give local pores in the μm-range. The etch attack initiation is located at protrusions on the surface. At 40 V and 50 V in both solutions the pores are extended onto the entire surface. The width of the pores is about 10 μm. Inside the micro-pores, nm-pores are formed; their lateral size is in the range 100 nm-200 nm. A mechanism for the anodic dissolution reactions is discussed. © 2013 Elsevier B.V. All rights reserved.

Petrich C.,Norut Narvik AS | Arntsen M.,Norut Narvik AS | Dayan H.,Norut Narvik AS | Nilsen R.,Norut Narvik AS
ISIJ International | Year: 2013

A study was conducted to show heat transfer over a temperature range commonly observed during transport of iron ore pellets. A thermally insulated cylindrical container was used to measure heat transfer between warm and cold pellets. It was surrounded by a rectangular box filled with insulating polyurethane foam. The box was insulated by sheets of 0.05 m-thick insulation at the 4 sides parallel to the axis of the container and 0.1 m-thick insulation at top and bottom of the container. Eleven thermocouples were mounted on a vertical pole, protruding 40 mm horizontally from the support pole. It was found that heat transfer through a bed of dry pellets between 15 and 30°C can be modeled as a homogeneous medium with a temperature-independent thermal diffusivity of k=2.7×107m2 s1. Diffusivity of wet pellets is expected to be lower, and heat exchange would be retarded even further if a phase transition from ice to water were to be observed.

Cardenas J.F.,Norut Narvik AS | Fredriksson H.,Chalmers University of Technology | Kasemo B.,Chalmers University of Technology | Chakarov D.,Chalmers University of Technology
Chemical Physics | Year: 2013

Nanostructured surfaces of highly oriented pyrolytic graphite (HOPG) were characterized by Raman spectroscopy. The disc-shape nanostructures ∼110 nm high and with two different diameters ∼147 and 217 nm are prepared on HOPG using hole-mask colloidal lithography and oxygen reactive ion etching. Significant roughening of the HOPG surface is introduced by the nano-fabrication process, but the nano-disc structures preserves their crystalline structure. Resonant light absorption results in selective heating of nanostructures, although the surrounding medium remains relatively unaffected. Temperature differences of up to 350 K were measured under irradiation with ∼11 mW/μm2. Further increase of the light intensity leads to combustion of structures. © 2013 Elsevier B.V. All rights reserved.

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