Advanced Weathervaning in Ice

2011 ◽  
Author(s):  
William Hidding ◽  
Guillaume Bonnaffoux ◽  
Mamoun Naciri
Keyword(s):  
Rapid Change ◽  
Ice Sheet ◽  
Model Tests ◽  
The Arctic ◽  
Mooring System ◽  
Sudden Increase ◽  
Time Step ◽  
Ice Loads ◽  
Level Ice ◽  
Drift Direction

The reported presence of one third of remaining fossil reserves in the Arctic has sparked a lot of interest from energy companies. This has raised the necessity of developing specific engineering tools to design safely and accurately arctic-compliant offshore structures. The mooring system design of a turret-moored vessel in ice-infested waters is a clear example of such a key engineering tool. In the arctic region, a turret-moored vessel shall be designed to face many ice features: level ice, ice ridges or even icebergs. Regarding specifically level ice, a turret-moored vessel will tend to align her heading (to weather vane) with the ice sheet drift direction in order to decrease the mooring loads applied by this ice sheet. For a vessel already embedded in an ice sheet, a rapid change in the ice drift direction will suddenly increase the ice loads before the weathervaning occurs. This sudden increase in mooring loads may be a governing event for the turret-mooring system and should therefore be understood and simulated properly to ensure a safe design. The paper presents ADWICE (Advanced Weathervaning in ICE), an engineering tool dedicated to the calculation of the weathervaning of ship-shaped vessels in level ice. In ADWICE, the ice load formulation relies on the Croasdale model. Ice loads are calculated and applied to the vessel quasi-statically at each time step. The software also updates the hull waterline contour at each time step in order to calculate precisely the locations of contact between the hull and the ice sheet. Model tests of a turret-moored vessel have been performed in an ice basin. Validation of the simulated response is performed by comparison with model tests results in terms of weathervaning time, maximum mooring loads, and vessel motions.

Model Tests in Brash Ice Channels

2005 ◽  
Author(s):  
Jens-Holger Hellmann ◽  
Karl-Heinz Rupp ◽  
Walter L. Kuehnlein
Keyword(s):  
Perforated Plate ◽  
Ice Sheet ◽  
Open Water ◽  
Model Tests ◽  
Ice Thickness ◽  
Special Device ◽  
Level Ice ◽  
Set Up ◽  
Parental Level ◽  
Oil Tankers

According to the present Finnish-Swedish Ice Class Rules (FSICR) the formulas for the required main engine power for tankers led to much bigger main engines than it is needed for the demanded open water speed. Therefore model tests may be performed in order to verify the vessel’s capability to sail with less required power in brash ice channels compared to the calculations. Several model test runs have been performed in order to study the performance of crude oil tankers sailing in brash ice. The tests were performed as towed propulsion tests and the brash ice channel was prepared according to the guidelines set up by the Finnish Maritime Administration (FMA). The channel width was 2 times the beam of the tanker. The model tests were carried out at a speed of 5 knots. For the tests a parental level ice sheet of adequate thickness is prepared according to HSVA’s standard model ice preparation procedure. After a predefined level ice thickness has been reached, the air temperature in the ice tank will be raised. An ice channel with straight edges will be cut into the ice sheet by means of two ice knives. The ice stripe between the two cuts will be manually broken up into relatively small ice pieces using a special ice chisel and if required the brash ice material will be compacted. Typically the brash ice thickness will be measured prior the tests at 9 positions across the channel and every two meter over the entire length of the brash ice channel with a special device, which consists of a measuring rule with a perforated plate mounted under a right angle at the lower end of the rule. As a result of the tests it could be demonstrated that tankers with a capacity of more than 50 000 tons require 50% and even less power compared to calculations using the present FSICR formulas.

Guidelines for CFD Simulations of Spar VIM

2013 ◽  
Author(s):  
Charles Lefevre ◽  
Yiannis Constantinides ◽  
Jang Whan Kim ◽  
Mike Henneke ◽  
Robert Gordon ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Test Data ◽  
Model Test ◽  
Model Tests ◽  
Full Scale ◽  
Mooring System ◽  
Time Step ◽  
Cfd Simulations ◽  
Scaled Model ◽  
Sway Motion

Vortex-Induced Motion (VIM), which occurs as a consequence of exposure to strong current such as Loop Current eddies in the Gulf of Mexico, is one of the critical factors in the design of the mooring and riser systems for deepwater offshore structures such as Spars and multi-column Deep Draft Floaters (DDFs). The VIM response can have a significant impact on the fatigue life of mooring and riser components. In particular, Steel Catenary Risers (SCRs) suspended from the floater can be sensitive to VIM-induced fatigue at their mudline touchdown points. Industry currently relies on scaled model testing to determine VIM for design. However, scaled model tests are limited in their ability to represent VIM for the full scale structure since they are generally not able to represent the full scale Reynolds number and also cannot fully represent waves effects, nonlinear mooring system behavior or sheared and unsteady currents. The use of Computational Fluid Dynamics (CFD) to simulate VIM can more realistically represent the full scale Reynolds number, waves effects, mooring system, and ocean currents than scaled physical model tests. This paper describes a set of VIM CFD simulations for a Spar hard tank with appurtenances and their comparison against a high quality scaled model test. The test data showed considerable sensitivity to heading angle relative to the incident flow as well as to reduced velocity. The simulated VIM-induced sway motion was compared against the model test data for different reduced velocities (Vm) and Spar headings. Agreement between CFD and model test VIM-induced sway motion was within 9% over the full range of Vm and headings. Use of the Improved Delayed Detached Eddy Simulation (IDDES, Shur et al 2008) turbulence model gives the best agreement with the model test measurements. Guidelines are provided for meshing and time step/solver setting selection.

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.

A Coupled Dynamic Ice-Load and Moored Floater Interaction Parametric Study for First Year Level Ice

2016 ◽  
Author(s):  
Aziz Ahmed ◽  
Anurag Yenduri ◽  
Ritwik Ghoshal ◽  
Zhuo Chen ◽  
Ankit Choudhary ◽  
...  
Keyword(s):  
Parametric Study ◽  
Oil And Gas ◽  
Time History ◽  
Full Scale ◽  
The Arctic ◽  
First Year ◽  
Mooring System ◽  
Oil And Gas Exploration ◽  
Ice Load ◽  
Level Ice

Arctic remains the final frontier in the oil and gas exploration regime. The diminishing presence of ice opens up the region for longer and wider exploration. However, even with the assistance of ice management, the threat of broken first-year level ice stays ubiquitous. Calculation of ice load for such ice features bases on the established formulation developed by observation from full-scale measurements and model test data over the years. However, the formulation mostly relies on the data derived from fixed structures or icebreakers. Such estimations of ice load do not account for the stiffness compliance afforded by mooring system of a floater, such as a semi-submersible or a spar. A floating oil and gas exploration system offers a number of advantages over the fixed platforms, such as the option to deploy elsewhere during the off-season in the Arctic as well as connecting and disconnecting during severe ice events such as an approaching iceberg or multi-year ice ridge. However, the current practice of employing dynamic ice load time-history available in ISO19906 or similar codes fails to account for the presence of the mooring system on these floating platforms, directly resulting in a lack of confidence in the derived response of the floater. This study aims to address this issue by developing a dynamic ice-load time-history algorithm, which, can readily couple with commercially available hydrodynamics and mooring system analysis software. This investigation puts forward the hypothesis that the evolution of ice load vs. ice feature displacement with respect to the structure remains same for both fixed and floating structures. However, the underlying assumption is that the size of the ice features remains comparable. This hypothesis accounts for the prominent influence of the size effect on the breaking strength of ice. The difference between the behavior of a fixed and a floating structure under ice load is due to the relative motion between the floater and the ice feature. The developed coupled ice-load-function accounts for this by including the relative displacement between the floater and the ice feature in the formulation. This study uses the semi-empirical formulation originally derived by Croasdale to calculate the main ice load components for a fixed structure with downward breaking slope. Subsequently, this study uses this coupled ice load subroutine to compare against the full-scale measurement data found in the literature for a floater with downward-sloped hull specifically designed to assist in ice breaking. A comparison against the peak load observed during full-scale measurements on a floater in the Arctic waters validates the proposed approach. Next, this study utilizes the coupled analysis to derive the displacement, velocity, and acceleration response of the studied floater for a range of ice parameters, such as the drift speed and thickness. Additionally, this study performs a parametric study by varying the downward breaking slope angle of the floater, the mooring configuration, and the water depth. Finally, this study summarizes the observed behavior of the floater under different ice parameters as well as floater shape and mooring systems parameters.

scholarly journals A Simulation of Non-Simultaneous Ice Crushing Force for Wind Turbine Towers with Large Slopes

Energies ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2608 ◽  
Author(s):  
Li Zhou ◽  
Shifeng Ding ◽  
Ming Song ◽  
Junliang Gao ◽  
Wei Shi
Keyword(s):  
Numerical Model ◽  
Wind Turbine ◽  
Ice Sheet ◽  
Model Tests ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Foundation Design ◽  
Cold Regions ◽  
Crushing Force ◽  
Ice Loads

When the offshore wind energy industry attempts to develop in cold regions, ice load becomes the main technological challenge for offshore wind turbine foundation design. Dynamic ice loads acting on wind turbine foundations should be calculated in a reasonable way. The scope of this study is to present a numerical model that considers the non-simultaneous ice crushing failure acting on the vertical structure of a wind turbine’s foundation. The local ice crushing force at the contact surface between the ice sheet and structure is calculated. The boundary of the ice sheet is updated at each time step based on the indentation length of the ice sheet according to its structure. Ice loads are validated against two model tests with three different structure models developed by other researchers. The time series of the ice forces derived from the simulation and model tests are compared. The proposed numerical model can capture the main trends of ice–wind turbine foundation interaction. The simulation results agree well with measured data from the model tests in terms of maximum ice force, which is a key factor for wind turbine design. The proposed model will be helpful for assisting the initial design of wind turbine foundations in cold regions.

Preliminary Analytical Formulation of Ice-Floater Interactions Including the Effect of Wave Load

2018 ◽  
Author(s):  
Aziz Ahmed ◽  
M. Abdullah Al Maruf ◽  
Arun Kr. Dev ◽  
Mohammed Abdul Hannan
Keyword(s):  
Oil And Gas ◽  
Ice Sheet ◽  
Sheet Thickness ◽  
The Arctic ◽  
Total Force ◽  
Wave Load ◽  
Incoming Wave ◽  
Total Load ◽  
Ice Load ◽  
Level Ice

Diminishing ice presence in the Arctic provides the potential for extended operable period for oil and gas exploration in the Arctic. Floaters are a flexible solution for such scenario whereas they can fully take advantage of the extended drilling season as well as operate in other harsh environment regions during the off-season. Such floaters can disconnect and reconnect to avoid large ice features such as icebergs and multi-year ice ridges. However, they still need to encounter relatively large level ice. Accompanying icebreakers will ideally assist in breaking the level ice into manageable pieces. The interaction of such level ice floes with floater has a significant influence on the dynamic ice load on the floater and resulting mooring load. There is significant uncertainty in the simulation of level ice-floater interaction numerically. Most of the current research focuses on the influence of ice breaking and subsequent flow of the broken ice around the floater. However, the hydrodynamic load due to the incoming level ice will also affect the response of the floater, which is usually not simulated. A recent study simulated the multibody hydrodynamics of level ice and floater Such multibody hydrodynamic analysis is computationally expensive, and complexity in the modelling is a hindrance to its implementation in the design phase. The present study, therefore, employs a conservative estimation to include the effect of wave load on the floater in addition to the ice load. Parametric studies are performed to estimate this effect by varying the incoming wave amplitude and wave period, ice sheet thickness, ice drift velocity, floater’s hull angle, mooring stiffness and the distance of large ice-sheet from the floater. Significant impacts of waves on the floater in terms of total force are observed which clearly reflects the importance of this study. The effect of mooring stiffness on total load is also investigated at the end of this study which can be considered as a foundation for further research on optimizing the mooring stiffness for such kind of arctic floater.

scholarly journals Numerical Research on Global Ice Loads of Maneuvering Captive Motion in Level Ice

2021 ◽  
Vol 9 (12) ◽  
pp. 1404
Author(s):  
Shenyu Xuan ◽  
Chengsheng Zhan ◽  
Zuyuan Liu ◽  
Qiaosheng Zhao ◽  
Wei Guo
Keyword(s):  
Model Test ◽  
Model Tests ◽  
Numerical Results ◽  
Test Results ◽  
Ocean Engineering ◽  
Drift Angle ◽  
Ice Loads ◽  
Level Ice ◽  
Turning Radius ◽  
Maneuvering Motion

In level ice, the maneuvering motion of icebreakers has a major influence on the global ice loads of the hull. This study researched the influences of the drift angle and turning radius on the ice loads of the icebreaker Xue Long through a partial numerical method based on the linear superposition theory of ice loads. First, with reference to the Araon model tests performed by the Korea Research Institute of Ships and Ocean Engineering (KRISO), numerical simulations of Araon’s direct motion were carried out at different speeds, and the average deviation between numerical results and model test results was about 13.8%. Meanwhile, the icebreaking process and modes were analyzed and discussed, compared with a model test and a full-scale ship trial. Next, the maneuvering captive motions of oblique and constant radius were simulated to study the characteristics of ice loads under different drift angles and turning radii. Compared with the maneuvering motion model tests in the ice tank of Tianjin University and the Institute for Ocean Technology of the National Research Council of Canada (NRC/IOT), the numerical results had good agreement with the model test results in terms of the variation trend of ice loads and ice–hull interaction, and the influences of drift angle and turning radius on ice resistance and transverse force, which have a certain reference value for sailing performance research and the design of the hull form of icebreaker ships, are discussed.

scholarly journals Societal implications of a changing Arctic Ocean

AMBIO ◽  
2021 ◽  
Author(s):  
Henry P. Huntington ◽  
Andrey Zagorsky ◽  
Bjørn P. Kaltenborn ◽  
Hyoung Chul Shin ◽  
Jackie Dawson ◽  
...  
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Indigenous Peoples ◽  
Global Climate ◽  
Rapid Change ◽  
The Arctic ◽  
Cultural Continuity ◽  
Societal Implications ◽  
Arctic Ecosystems ◽  
The Many

AbstractThe Arctic Ocean is undergoing rapid change: sea ice is being lost, waters are warming, coastlines are eroding, species are moving into new areas, and more. This paper explores the many ways that a changing Arctic Ocean affects societies in the Arctic and around the world. In the Arctic, Indigenous Peoples are again seeing their food security threatened and cultural continuity in danger of disruption. Resource development is increasing as is interest in tourism and possibilities for trans-Arctic maritime trade, creating new opportunities and also new stresses. Beyond the Arctic, changes in sea ice affect mid-latitude weather, and Arctic economic opportunities may re-shape commodities and transportation markets. Rising interest in the Arctic is also raising geopolitical tensions about the region. What happens next depends in large part on the choices made within and beyond the Arctic concerning global climate change and industrial policies and Arctic ecosystems and cultures.

scholarly journals A new bedrock and surface elevation dataset for modelling the Greenland ice sheet

2003 ◽  
Vol 37 ◽  
pp. 351-356 ◽  
Author(s):  
Jonathan L. Bamber ◽  
Duncan J. Baldwin ◽  
S. Prasad Gogineni
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Detailed Comparison ◽  
Radar Data ◽  
The Arctic ◽  
Small Scale ◽  
Surface Model ◽  
Rock Outcrops ◽  
Bed Topography ◽  
Elevation Model

AbstractA new digital elevation model of the surface of the Greenland ice sheet and surrounding rock outcrops has been produced from a comprehensive suite of satellite and airborne remote-sensing and cartographic datasets. The surface model has been regridded to a resolution of 5 km, and combined with a new ice-thickness grid derived from ice-penetrating radar data collected in the 1970s and 1990s. A further dataset, the International Bathymetric Chart of the Arctic Ocean, was used to extend the bed elevations to include the continental shelf. The new bed topography was compared with a previous version used for ice-sheet modelling. Near the margins of the ice sheet and, in particular, in the vicinity of small-scale features associated with outlet glaciers and rapid ice motion, significant differences were noted. This was highlighted by a detailed comparison of the bed topography around the northeast Greenland ice stream.

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