A simulation approach for local ice loads on ship structures in level ice

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.

Download Full-text

A Method to Calculate Level Ice Loads on Multi Legged Conical Structures

10.3940/rina.icsot15k.2015.01 ◽

2015 ◽

Author(s):

J M Cabrera ◽

◽

J K Paik ◽

◽

Keyword(s):

Ice Loads ◽

Level Ice ◽

Conical Structures

Download Full-text

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

Volume 5: Polar and Arctic Sciences and Technology; CFD and VIV ◽

10.1115/omae2009-79733 ◽

2009 ◽

Cited By ~ 5

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.

Download Full-text

Experimental Study of Sea Ice Forces on a Structure and its Stability

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.243-249.4750 ◽

2011 ◽

Vol 243-249 ◽

pp. 4750-4753 ◽

Cited By ~ 1

Author(s):

Ji Wu Dong ◽

Zhi Jun Li ◽

Li Min Zhang ◽

Guang Wei Li ◽

Hong Wei Han

Keyword(s):

Experimental Study ◽

Sea Ice ◽

Offshore Structures ◽

Sea Bed ◽

Ice Loads ◽

Level Ice ◽

Ice Floes ◽

The Stability ◽

Ice Forces ◽

Concrete Model

A structure was designed to reduce the large forces exerted by level ice on offshore structures in shallow icy waters, by breaking the large ice floes into small pieces from flexing-induced failure. A series of model tests was conducted to simulate ice loads on the structure. A concrete model of it was adopted to verify the stability of the structure under the action of ice floes, which had five different thicknesses. The results show that ice forces on the structure are low and that the stability of the structure under different sea bed is good.

Download Full-text

A New Icebreaking Pattern for the Application in Numerical Simulation of Ship Performance in Level Ice

Volume 8: Polar and Arctic Sciences and Technology; Petroleum Technology ◽

10.1115/omae2018-77991 ◽

2018 ◽

Author(s):

Fang Li ◽

Mikko Kotilainen ◽

Floris Goerlandt ◽

Pentti Kujala

Keyword(s):

Numerical Simulation ◽

Numerical Models ◽

Computation Time ◽

Ship Hull ◽

Large Set ◽

Ice Loads ◽

Level Ice ◽

Proper Definition ◽

Definition Of ◽

Ship Performance

For the evaluation of ship performance in ice and ice loads on the ship hull, numerical simulation methods have been increasingly developed in recent years. In these models, the shapes of ice cusps broken from the intact ice sheet are idealized as either part of a circle or a triangle. Effects arising from the geometry of the loading area are neglected or idealized. Since the proper definition of the geometry of ice cusps is one of the key factors in numerical models, this paper introduces a new icebreaking pattern based on theoretical deviation. The finite difference method is adopted to approximate the deflection field of the wedge plate. This model takes a large set of factors as input while consuming little computation time. The outcome provides some new features compared to previous models. The results are validated using full-scale measurements of ice cusps around a ship hull, based on stereo camera recording and image processing. The validation shows that the derived method is appropriate in predicting realistic icebreaking patterns. Hence, it is plausible that its implementation in numerical models for ship performance in level ice will lead to improved prediction of the ship performance and ice loads on the hull.

Download Full-text

Numerical Simulations of Continuous Icebreaking Process With Different Heel Angles in Level Ice

Volume 8: Polar and Arctic Sciences and Technology; Petroleum Technology ◽

10.1115/omae2018-77253 ◽

2018 ◽

Author(s):

Feng Wang ◽

Zao-Jian Zou ◽

Hai-Peng Guo ◽

Yi-Zhou Ren

Keyword(s):

Measured Data ◽

Interaction Process ◽

Marine Structures ◽

Structure Interaction ◽

Ice Loads ◽

Level Ice ◽

Breaking Length ◽

Increasing Trends ◽

Ice Resistance ◽

Good Agreement

Based on cohesive element method (CEM), the continuous icebreaking process with different heel angles in level ice are simulated in this paper. The simulations are established in FEM software LS-DYNA and an icebreaking tanker - MT Uikku is assumed advancing with the certain heel angle in level ice. Firstly, the comparisons are made between the simulations and the model tests for the cases with zero heel angle. A good agreement is obtained between the simulated and measured data. Then the effects of different heel angles on ice resistance and ice breaking patterns are investigated and analyzed. The results show that ice resistance, average ice breaking length and average broken channel width present increasing trends with the increase of ship heel angle. The applied methods show a wide prospect to predict ice loads on marine structures in the level ice and simulate the ice-structure interaction process.

Download Full-text

Numerical Study of the Interaction between Level Ice and Wind Turbine Tower for Estimation of Ice Crushing Loads on Structure

Journal of Marine Science and Engineering ◽

10.3390/jmse7120439 ◽

2019 ◽

Vol 7 (12) ◽

pp. 439 ◽

Cited By ~ 2

Author(s):

Ming Song ◽

Wei Shi ◽

Zhengru Ren ◽

Li Zhou

Keyword(s):

Numerical Simulations ◽

Wind Turbine ◽

Numerical Study ◽

Mesh Size ◽

Impact Speed ◽

Wind Turbine Tower ◽

Comparison Results ◽

Ice Loads ◽

Level Ice ◽

The Impact

In this paper, the interaction between level ice and wind turbine tower is simulated by the explicit nonlinear code LS-DYNA. The isotropic elasto-plastic material model is used for the level ice, in which ice crushing failure is considered. The effects of ice mesh size and ice failure strain on ice forces are investigated. The results indicate that these parameters have a significant effect on the ice crushing loads. To validate and benchmark the numerical simulations, experimental data on level ice-wind turbine tower interactions are used. First, the failure strains of the ice models with different mesh sizes are calibrated using the measured maximum ice force from one test. Next, the calibrated ice models with different mesh sizes are applied for other tests, and the simulated results are compared to corresponding model test data. The effects of the impact speed and the size of wind turbine tower on the comparison between the simulated and measured results are studied. The comparison results show that the numerical simulations can capture the trend of the ice loads with the impact speed and the size of wind turbine tower. When a mesh size of ice model is 1.5 times the ice thickness, the simulations can give more accurate estimations in terms of maximum ice loads for all tests, i.e., good agreement between the simulated and measured results is achieved.

Download Full-text

The measurement accuracy of instrumented ship structures under local ice loads using strain gauges

Marine Structures ◽

10.1016/j.marstruc.2020.102919 ◽

2021 ◽

Vol 76 ◽

pp. 102919

Author(s):

Angelo Mario Böhm ◽

Rüdiger Ulrich Franz von Bock und Polach ◽

Hauke Herrnring ◽

Sören Ehlers

Keyword(s):

Measurement Accuracy ◽

Strain Gauges ◽

Ship Structures ◽

Ice Loads

Download Full-text

A Numerical Model to Initiate the Icebreaking Pattern in Level Ice

Volume 10: Polar and Arctic Science and Technology ◽

10.1115/omae2014-23409 ◽

2014 ◽

Author(s):

Sandro Erceg ◽

Sören Ehlers ◽

Rüdiger von Bock und Polach ◽

Bernt Leira

Keyword(s):

Numerical Models ◽

Numerical Approach ◽

Interaction Zone ◽

Ice Loads ◽

Level Ice ◽

Semi Empirical ◽

Model Features ◽

Radial Cracks ◽

Increased Activity

Ships navigating in ice-covered waters experience local and global ice loads due to ice-hull interaction. The design of a ship with good ice performance requires adequate assessment of these forces. Recently, an increased activity in developing numerical models of ice-hull interaction in level ice has been observed, owed to the increased computational capabilities. However, certain semi-empirical icebreaking patterns inevitably influencing the interaction process have been implemented in the majority of interaction models used for the assessment of ice performance of ships. Therefore, an attempt using a quasi-static numerical approach to model the initiation of icebreaking pattern in level ice has been made and is presented in this paper. The term initiation herein denotes the creation of circumferential cracks, disregarding thus the succeeding radial cracks. The concept used in the model features a set of radially oriented ice beams at the interaction zone. The model accounts for the bow geometry and the properties of the encountered ice. The icebreaking pattern for a case study ship is simulated using the developed model. Lastly, this paper discusses the sensitivity of the model with respect to the bow shape.

Download Full-text