Nonlinear Coupled Hydrostatics of Arctic Conical Platforms

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Oddgeir Dalane ◽  
Finn Faye Knudsen ◽  
Sveinung Løset
Keyword(s):  
Operation Time ◽  
Open Water ◽  
Floating Structures ◽  
Good Design ◽  
Arctic Conditions ◽  
Restoring Forces ◽  
Ice Conditions ◽  
Exact Analytic Expression ◽  
Analytic Expression ◽  
Metacentric Height

The increased exploration of deeper Arctic waters motivates the designs of new floating structures to operate under harsh Arctic conditions. Based on several model tests and investigations, structures with conical sections at the waterline have been shown to be a good design for waters where drifting ice is present, because the approaching ice fails in bending, which induces smaller loads than a crushing failure of ice. However, in most Arctic waters ice features are only present during part of the year and a large portion of the operation time of these structures will be in open water. Therefore, the floating structures must perform well in both conditions.Conical sections at the waterline will induce nonlinear coupling in the hydrostatic restoring forces and moments. It is important to understand how this affects the behavior in both ice and open water conditions. In order to investigate the nonlinear coupled hydrostatic restoring forces, an exact analytic expression for the metacentric height of a regular cone is presented. This is further used to develop an exact analytic expression for the hydrostatic restoring forces and moments for any body whose waterline intersects the frustum of a cone. A platform of the shallow draft-type, the platform type for which exact hydrostatics is most important, is used as a basis for the discussion and the effect of the coupled nonlinear restoring forces is illustrated by comparison to a model test performed in both open water and ice conditions.

Nonlinear Coupled Hydrostatics of Floating Conical Platforms

2009 ◽  
Author(s):  
Oddgeir Dalane ◽  
Finn Faye Knutsen ◽  
Sveinung Lo̸set
Keyword(s):  
Degrees Of Freedom ◽  
Operation Time ◽  
Open Water ◽  
Conical Body ◽  
Floating Structures ◽  
Arctic Conditions ◽  
Restoring Forces ◽  
Exact Analytic Expression ◽  
Analytic Expression ◽  
Metacentric Height

The increased exploration of deeper Arctic waters motivates the designs of new floating structures to operate under harsh Arctic conditions. Based on several model tests and investigations, structures with conical sections at the waterline have been shown to be a good design for waters where drifting ice is present, because the approaching ice fails in bending which induces smaller loads than crushing failure. However, in most Arctic waters ice features are only present parts of the year and a large portion of the operation time of these structures will be in open water. Therefore, the floating structures must perform well in both these conditions. Conical sections at the waterline will induce nonlinear coupling in the hydrostatic restoring forces and moments. It is important to understand how this affects the behaviour in both ice and open water conditions. In order to investigate the nonlinear coupled hydrostatic restoring forces, an exact analytic expression for the metacentric height of a regular cone is presented. This is further derived to a frustum cone that can be used to develop an exact analytic expression for the hydrostatic restoring forces and moments for any conical body. A platform of the shallow draught-type is used as a basis for the discussion and the effect of the coupled nonlinear restoring forces is illustrated by two-degrees-of-freedom (2DOF) pitch-heave time domain simulations.

Ice Tank Testing of a Surface Buoy for Arctic Conditions

2008 ◽  
Author(s):  
Oddgeir Dalane ◽  
Ove Tobias Gudmestad ◽  
Sveinung Lo̸set ◽  
Jo̸rgen Amdahl ◽  
Tor Erik Hilde`n ◽  
...  
Keyword(s):  
Test Results ◽  
Floating Structures ◽  
Deep Waters ◽  
Ice Drift ◽  
Arctic Conditions ◽  
Ice Conditions ◽  
Level Ice ◽  
Ridged Ice ◽  
Ice Forces ◽  
Multiyear Ice

A moored Shallow Draught Buoy (SDB) for potential operations in Arctic waters was tested during the summer of 2006 in the model laboratory basin at the Hamburg Ship Model Basin (HSVA) in Hamburg. The conceptual design of this buoy was based on the design of the Kulluk exploration vessel which operated in the Beaufort Sea in the 1980’s and early 1990’s. The concept was tested in ice conditions representing level ice, multiyear ice and ridged ice, where the ice thickness, ice drift velocity and flexural strength were varied in the different test runs. Moored structures are believed to be favourable in deep waters with ice present, but there exist insufficient information and data about the actions on and behaviour of moored floating structures in ice to support this. The purpose of the present paper is to evaluate the model test results and look at the dynamic ice loading and response of the structure. The ice forces on the structure were calculated from the structure’s response and response power density spectra were used to evaluate the periodic forces and displacements. Based on the analysis of the test data, an increased understanding of the behaviour of the surface buoy is presented.

Response Plans for Arctic Oil and Ice Encounters

1999 ◽  
Vol 1999 (1) ◽  
pp. 639-646 ◽  
Author(s):  
Nick W. Glover ◽  
David F. Dickins
Keyword(s):  
Open Water ◽  
North Slope ◽  
Action Plans ◽  
Response Strategies ◽  
Arctic Conditions ◽  
Oil Spill Response ◽  
Ice Conditions ◽  
Ground Truthing ◽  
And Behavior ◽  
Alaskan North Slope

ABSTRACT Ice conditions, in dynamic stages of development and degradation, are present for over 280 days out of every calendar year in the Beaufort Sea adjacent to the operating oilfields on the Alaskan North Slope. Additionally, wind driven ice invasions during the open water season, July through September typically, may also occur for short periods throughout the season. This presence combined with extreme arctic conditions routinely presents a challenge to mounting a safe and effective oil spill response action. In order to overcome this challenge responders must develop response action plans not only with an understanding of the physical environment but also with a basic understanding of the effect this environment will have on the fate and behavior of the spilled oil. Arctic spill response strategies, worldwide, have been developed through years of experience with both offshore and onshore drilling and production operations in all types of sea and ice conditions. North Slope response action plans are based on this experience, intense field training, and ground truthing of related research and development projects.

scholarly journals ENERGY EXTRACTION FROM GRAVITATIONAL COLLAPSE TO STATIC BLACK HOLES

2003 ◽  
Vol 12 (01) ◽  
pp. 121-127 ◽  
Author(s):  
REMO RUFFINI ◽  
LUCA VITAGLIANO
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Extraction Process ◽  
Maximum Efficiency ◽  
Energy Extraction ◽  
Mass Energy ◽  
Classical Level ◽  
Static Black Hole ◽  
Exact Analytic Expression ◽  
Analytic Expression

The mass-energy formula of black holes implies that up to 50% of the energy can be extracted from a static black hole. Such a result is reexamined using the recently established analytic formulas for the collapse of a shell and the expression for the irreducible mass of a static black hole. It is shown that the efficiency of energy extraction process during the formation of the black hole is linked in an essential way to the gravitational binding energy, the formation of the horizon and the reduction of the kinetic energy of implosion. Here a maximum efficiency of 50% in the extraction of the mass energy is shown to be generally attainable in the collapse of a spherically symmetric shell: surprisingly this result holds as well in the two limiting cases of the Schwarzschild and extreme Reissner–Nordström space–times. Moreover, the analytic expression recently found for the implosion of a spherical shell to an already formed black hole leads to a new exact analytic expression for the energy extraction which results in an efficiency strictly less than 100% for any physical implementable process. There appears to be no incompatibility between General Relativity and Thermodynamics at this classical level.

scholarly journals Airborne River-Ice Thickness Profiling with Helicopter-Borne UHF Short-Pulse Radar

1987 ◽  
Vol 33 (115) ◽  
pp. 330-340 ◽  
Author(s):  
Steven A Arcone ◽  
Allan J Delaney
Keyword(s):  
Short Pulse ◽  
Hanging Wall ◽  
Open Water ◽  
High Water ◽  
High Water Content ◽  
Ice Thickness ◽  
Frazil Ice ◽  
Pulse Radar ◽  
Detailed Surface ◽  
Ice Conditions

AbstractThe ice-thickness profiling performance of a helicopter-mounted short-pulse radar operating at approximate center frequencies of 600 and 900 MHz was assessed. The antenna packages were mounted 1.2 m off the skid of a small helicopter whose speed and altitude were varied from about 1.8 to 9 m/s and 3 to 12 m. Clutter from the helicopter offered minimal interference with the ice data. Data were acquired in Alaska over lakes (as a proving exercise) and two rivers, whose conditions varied from open water to over 1.5 m of solid ice with numerous frazil-ice formations. The most readily interpretable data were acquired when the ice or snow surface was smooth. Detailed surface investigations on the Tanana River revealed good correlations of echo delay with solid ice depth, but an insensitivity to frazil-ice depth due to its high water content. On the Yukon River, coinciding temporally coherent surface and bottom reflections were associated with solid ice and smooth surfaces. All cases of incoherent surface returns (scatter) occurred over ice rubble. Rough-surface scattering was always followed by the appearance of bottom scattering but, in many cases, including a hanging-wall formation of solid frazil ice, bottom scattering occurred beneath coherent, smooth-surface reflections. Areas of incoherent bottom scattering investigated by drilling revealed highly variable ice conditions, including frazil ice. The minimum ice thickness that could be resolved from the raw data was about 0.2 m with the 600 MHz antenna and less than 0.15 m with the 900 MHz antenna.

Facilitating rain-on-snow detection with satellite data

2021 ◽  
Author(s):  
Annett Bartsch
Keyword(s):  
Satellite Data ◽  
Open Water ◽  
The Arctic ◽  
Calibration And Validation ◽  
In Situ Data ◽  
Snow Properties ◽  
Structure Changes ◽  
Indirect Measures ◽  
Ice Conditions ◽  
Northern European Russia

<p>Rain-on-snow modifies snow properties and can lead to the formation of ice crusts which impact wildlife and also vegetation. Events in the Arctic have been recently linked to specific sea ice conditions (longer open water season) for Siberia. Specifically microwave satellite data have been shown applicable for identification of such events across the Arctic. Related snow structure changes can be observed specifically over Scandinavia, northern European Russia and Western Siberia as well as Alaska (Bartsch, 2010). Events which had severe impacts for reindeer herder herding have occurred several times in the last two decades.</p><p>Challenges further include the categorization of severity of events and attribution of observations to rain-on-snow events.</p><p>Calibration and validation of detection schemes have been largely based on indirect measures. Usually a combination of air temperature and snow height measurements, supported by reports of such events are analysed.</p><p>In this presentation, the utility of current calibration and validation approaches are discussed. Requirements towards in situ data from the viewpoint of satellite based retrievals are outlined.</p><p>Bartsch, A. Ten Years of SeaWinds on QuikSCAT for Snow Applications. Remote Sens. 2010, 2, 1142-1156.</p>

scholarly journals Ice Conditions of an Arctic Polynya: North Water in Winter

1986 ◽  
Vol 32 (112) ◽  
pp. 383-390 ◽  
Author(s):  
Konrad Steffen
Keyword(s):  
Sea Water ◽  
Surface Condition ◽  
Open Water ◽  
Sea Surface ◽  
Aerial Images ◽  
The Arctic ◽  
The North ◽  
North Water ◽  
Ice Conditions ◽  
Fast Ice

AbstractThe surface condition of the North Water was investigated during two winters (i.e. the three polynyas: Smith Sound polynya, Lady Ann Strait polynya, and Barrow Strait polynya). Since no detailed information was available on ice conditions and the extent of open water during winter, radiometric temperature measurements of the sea surface had to be taken along a flight line of 2650 km from an altitude of 300 m. From November to March 1978-79 and 1980-81, 14 remote-sensing flights were carried out. On the basis of the radiometric measurements, the following ice types were identified: ice-free, dark nilas, light nilas, grey ice, grey-white ice, and white ice. A comparison between the thermal and the visual ice classification (the latter being based on grey tones of the aerial images) showed a deviation of 3%. The analysis showed that in November, December, and January more than 50% of the Smith Sound polynya was covered by young ice, nilas, and ice-free, whereas in February and March white ice was dominant. Moreover, it was found that the two polynyas in Smith Sound and Lady Ann Strait were much smaller than previously believed. In Barrow Strait, a semi-permanent polynya was observed in the winter of 1980-81. The occurrence of polynyas in Barrow Strait seems to be connected with the location of the fast-ice edge. On the basis of the calculated ice-type distribution and heat-flux rates for different ice types, an energy loss of 178 W m-2was found on the surface of the Smith Sound polynya due to open water and thin ice for the winter months November to March. Compared with other ice-covered sea surfaces in the Arctic, the heat release by the sea-water in the Smith Sound polynya is about 100 W m-2larger.

New records of mummified crabeater seals on islands bordering Admiralty Sound, Weddell Sea

2019 ◽  
Vol 31 (3) ◽  
pp. 109-115
Author(s):  
Javier Negrete ◽  
Leopoldo H. Soibelzon ◽  
Esteban Soibelzon ◽  
Jorge Lusky
Keyword(s):  
Open Water ◽  
Weddell Sea ◽  
Pack Ice ◽  
Breeding Grounds ◽  
Ice Conditions ◽  
Crabeater Seals ◽  
Ice Floes ◽  
Early Breakup ◽  
Natural Trap ◽  
Seymour Island

AbstractNinety-six mummified crabeater seals discovered at Seymour Island (Isla Marambio) are reported. Each specimen was georeferenced, photographed and assigned to five different taphonomic states. Previous work stated that seals at Seymour Island get stranded inland around the breeding season. However, it is not clear if the species breeds in this area. The abundance of crabeater seals and the ice condition along Admiralty Sound (Estrecho Bouchard) were obtained by aerial surveys during spring (2015–17). It appears that the species uses the strait as a passage to breeding grounds. Under heavy ice conditions, the seals become stranded in the middle section of this strait and wander inland through a valley that represents the mouth of an ephemeral stream that ends at the pack ice level. This situation was observed in 2014 and 2015 when recently dead seals were found, evidencing that this natural trap is still active. Nonetheless, in 2016 and 2017, during an early breakup of Admiralty Sound, the seals that remained in the area were more numerous than in 2015 but they did not get stranded inland. This early breakup may encourage the seals to breed there in the presence of open water areas with ice floes.

scholarly journals Long-distance swimming by polar bears (Ursus maritimus) of the southern Beaufort Sea during years of extensive open water

2012 ◽  
Vol 90 (5) ◽  
pp. 663-676 ◽  
Author(s):  
A.M. Pagano ◽  
G.M. Durner ◽  
S.C. Amstrup ◽  
K.S. Simac ◽  
G.S. York
Keyword(s):  
Sea Ice ◽  
Adult Female ◽  
Open Water ◽  
Ursus Maritimus ◽  
Polar Bears ◽  
Long Distance ◽  
Gps Collars ◽  
Movement Data ◽  
Global Positioning ◽  
Ice Conditions

Polar bears ( Ursus maritimus Phipps, 1774) depend on sea ice for catching marine mammal prey. Recent sea-ice declines have been linked to reductions in body condition, survival, and population size. Reduced foraging opportunity is hypothesized to be the primary cause of sea-ice-linked declines, but the costs of travel through a deteriorated sea-ice environment also may be a factor. We used movement data from 52 adult female polar bears wearing Global Positioning System (GPS) collars, including some with dependent young, to document long-distance swimming (>50 km) by polar bears in the southern Beaufort and Chukchi seas. During 6 years (2004–2009), we identified 50 long-distance swims by 20 bears. Swim duration and distance ranged from 0.7 to 9.7 days (mean = 3.4 days) and 53.7 to 687.1 km (mean = 154.2 km), respectively. Frequency of swimming appeared to increase over the course of the study. We show that adult female polar bears and their cubs are capable of swimming long distances during periods when extensive areas of open water are present. However, long-distance swimming appears to have higher energetic demands than moving over sea ice. Our observations suggest long-distance swimming is a behavioral response to declining summer sea-ice conditions.

Model Tests on a Spar in Level Ice and Ice Ridge Conditions

2009 ◽  
Author(s):  
John Murray ◽  
Stephane LeGuennec ◽  
Don Spencer ◽  
Chang K. Yang ◽  
Wooseuk Yang
Keyword(s):  
Full Scale ◽  
Scale Model ◽  
Test Facility ◽  
Mooring System ◽  
Scaling Effects ◽  
Line System ◽  
Restoring Forces ◽  
Ice Conditions ◽  
Ice Loads ◽  
Level Ice

1:30 and 1:50 model-scale ice tests of an ice-resistant Spar design were carried out to determine the loads on the Spar in level ice and ice ridges. Due to limitations in the depth of the ice test facility, the hull draft and mooring system were truncated. The 1:30 scale model was towed through the ice on a fixed and compliant dynamometer. The stiffness characteristics of the compliant dynamometer matched the horizontal stiffness of the full-scale mooring system. The purpose of these tests was to compare the mooring and ice loads measured in fixed and compliant conditions. The 1:50 scale model was truncated by 70 m. Its mooring system was modeled using a four-line system designed to give the same global restoring forces as the full-scale mooring system. The model was fitted with vertical plates on the exterior of the hull to compensate for loss of added mass and added moment of inertia. A limited number of tests were carried out at the two model scales in the same ice conditions to investigate scaling effects. The mooring and ice loads measured in the fixed and compliant conditions were found to be similar, indicating that loads estimated, assuming the structure is fixed, provide good estimates. Good agreement between the two models was also found for the tests carried out in the same ice conditions, suggesting that the scaling effects may be negligible.

Sign in / Sign up

Export Citation Format

Share Document