A Comparison of Ice Loads From Level Ice and Ice Ridges on Sloping Offshore Structures Calculated in Accordance With Different International and National Standards

2006 ◽  
Author(s):  
Per Kristian Bruun ◽  
Ove Tobias Gudmestad
Keyword(s):  
Barents Sea ◽  
Slope Angle ◽  
Offshore Structures ◽  
Interaction Process ◽  
International Standards ◽  
Structure Interaction ◽  
Ice Load ◽  
Ice Loads ◽  
Level Ice

Existing national and international standards for determination of level ice and ice ridge loads on sloping offshore structures recommend different methods for the analysis. The objective of this paper is to review the codes and standards recommendations regarding ice-sloping structures interaction process and highlight the differences between them. Development of offshore hydrocarbon fields in the Eastern Barents Sea is foreseen to take place in the near future while developments already take place in the Pechora Sea and offshore Sakhalin as well as in the Northern Caspian Sea. One of the most difficult issues facing the designer of offshore structures for these areas is how to design for loads from level ice and ice ridges. The ice load considerations will have a major effect on the form and cost of these structures. It is known that different designers use very different ice load estimates (Shkhinek et al., 1994). The standards recommend different methods for determination of the global ice loads on both cone-shaped and sloping rectangular structures. For determination of the global ice loads on these types of structures, it is obvious that the ice-structure interaction process must be identified. Rubble effects must be included in the analysis. The ice-structure interaction process for these geometries depends on many factors, such as; the ice thickness, ice strength, ice-structure friction coefficient, ice velocity, width of the structure and slope angle of the structure. The methods for determination of ice loads recommended by the different standards are very much influenced by local ice conditions and the parameters listed above are given different importance in the different standards. The differences in loads calculated by using the different standards and their validity for the ice-structure interaction process have been investigated and example calculations are presented to show these differences. It is thought that the paper may be of interest for those preparing the new ISO standard (ISO 19906) on Arctic Offshore Structures.

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

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.

Influence of Structural Compliance and Slope Angle on Ice Loads and Dynamic Response of Conical Structures

2015 ◽  
Author(s):  
Gesa Ziemer ◽  
Karl-Ulrich Evers ◽  
Christian Voosen
Keyword(s):  
Natural Frequency ◽  
Model Test ◽  
Slope Angle ◽  
Offshore Structures ◽  
Model Tests ◽  
Offshore Wind Turbine ◽  
Worst Case ◽  
Ice Load ◽  
Ice Loads ◽  
Conical Structures

Model tests in ice have been conducted at the Large Ice Basin of HSVA with cylindrical and conical, compliant structures exposed to drifting level ice to investigate the influence of slope and compliance on the ice load and its breaking frequency. Main goal of the test campaign was to study the importance of structural feedback during ice-cone interaction. This is a major issue e.g. for numerical simulation of offshore structures during design phase. Four shapes were tested: 50°, 60°, 80° and 90° slope angle. The cylinder was tested in order to define the worst case scenario regarding magnitude of ice load and severity of ice-induced vibrations. Stiffness and natural frequency of the structure were chosen similar to typical values for offshore wind turbine support structures. All shapes were tested both in a compliant and fixed configuration. The breaking frequency was found to be more pronounced for the lower slope angles where the ice failed in flexural failure only, while a transition to crushing failure as observed on a cylindrical structure takes place at 80° cone angle already. This results in significantly higher ice loads on the 80° cone than on those with lower angles, but a reduced risk of severe ice-structure interaction due to the unsteady nature of the mixed mode breaking process. Although the breaking frequency is rather constant e.g. during ice impact on the 60° cone, it was not possible during the model tests to match the ice drift speed and the dynamics of the structure in a way that causes resonance. However, model test results prove that there is a risk of conical structures with low natural frequencies and low stiffness in ice plane being excited by periodic ice failure in their natural frequency, thus response amplification may take place and pose a risk to the structural integrity of conical offshore structures exposed to sea ice. This paper presents the model test setup, analysis of the results, and general findings.

Parameter Sensitivity in Numerical Modelling of Ice-Structure Interaction With Cohesive Element Method

2016 ◽  
Author(s):  
Dianshi Feng ◽  
Sze Dai Pang ◽  
Jin Zhang
Keyword(s):  
Element Model ◽  
Offshore Structures ◽  
Parameter Sensitivity ◽  
The Arctic ◽  
Cohesive Element ◽  
Structure Interaction ◽  
Marine Structure ◽  
Ice Loads ◽  
The Stability ◽  
Element Method

The increasing marine activities in the Arctic has resulted in a growing demand for reliable structural designs in this region. Ice loads are a major concern to the designer of a marine structure in the arctic, and are often the principal factor that governs the structural design [Palmer and Croasdale, 2013]. With the rapid advancement in computational power, numerical method is becoming a useful tool for design of offshore structures subjected to ice actions. Cohesive element method (CEM), a method which has been widely utilized to simulate fracture in various materials ranging from metals to ceramics and composites as well as bi-material systems, has been recently applied to predict ice-structure interactions. Although it shows promising future for further applications, there are also some challenging issues like high mesh dependency, large variation in cohesive properties etc., yet to be resolved. In this study, a 3D finite element model with the use of CEM was developed in LS-DYNA for simulating ice-structure interaction. The stability of the model was investigated and a parameter sensitivity analysis was carried out for a better understanding of how each material parameter affects the simulation results.

A Reliability-Based Method for Determining Design Ice Loads on Offshore Structures

2002 ◽  
Author(s):  
X. Wu ◽  
A. T. Wang ◽  
C. E. Heuer ◽  
T. D. Ralston ◽  
G. F. Davenport ◽  
...  
Keyword(s):  
Rational Design ◽  
Offshore Structures ◽  
Type I ◽  
Type Ii ◽  
General Applicability ◽  
Ice Load ◽  
Research Company ◽  
Ice Loads ◽  
Offshore Development ◽  
Systematic Framework

This paper describes a reliability-based methodology that has been developed at ExxonMobil Upstream Research Company (URC) for determining rational design ice loads on offshore structures. The URC methodology provides a systematic framework to account for Type I (aleatory) and Type II (epistemic) uncertainties in assessing global probabilistic ice hazards. Specifically, a logic-tree based approach is developed to model Type II uncertainties in the assessment of ice hazards. Although the method has general applicability, the present work considers a wide, vertical-sided, gravity-based structure (GBS) in a dynamic, annual ice environment. Both FORM/SORM methods and Monte Carlo simulation are used in the analyses. Results obtained from this reliability-based approach indicate that the modeling of Type II uncertainties plays a significant role in quantifying the ice hazards for determining the design ice load. Further, this effort may potentially reduce over-conservatism in typical deterministic ice load calculations. The probabilistic methodology developed in this study has broad applicability and can provide a rational framework for calculating design ice loads on other types of structures for arctic offshore development.

Methodology to Evaluate Sea Ice Loads for Seasonal Operations

2015 ◽  
Author(s):  
Jan Thijssen ◽  
Mark Fuglem
Keyword(s):  
Sea Ice ◽  
Offshore Structures ◽  
Ice Thickness ◽  
Safety Level ◽  
Site Specific ◽  
Design Load ◽  
Ice Load ◽  
Ice Conditions ◽  
Design Loads ◽  
Ice Loads

Offshore structures designed for operation in regions where sea ice is present will include a sea ice load component in their environmental loading assessment. Typically ice loads of interest are for 10−2, 10−3 or 10−4 annual probability of exceedance (APE) levels, with appropriate factoring to the required safety level. The ISO 19906 standard recommends methods to determine global sea ice loads on vertical structures, where crushing is the predominant failure mode. Fitted coefficients are proposed for both Arctic and Sub-Arctic (e.g. Baltic) conditions. With the extreme ice thickness expected at the site of interest, an annual global sea ice load can be derived deterministically. Although the simplicity of the proposed relation provides quick design load estimates, it lacks accuracy because the only dependencies are structure width, ice thickness and provided coefficients; no consideration is given to site-specific sea ice conditions and the corresponding exposure. Additionally, no term is provided for including ice management in the design load basis. This paper presents a probabilistic methodology to modify the deterministic ISO 19906 relations for determining global and local first-year sea ice loads on vertical structures. The presented methodology is based on the same ice pressure data as presented in ISO 19906, but accounts better for the influence of ice exposure, ice management and site-specific sea ice data. This is especially beneficial for ice load analyses of seasonal operations where exposure to sea ice is limited, and only thinner ice is encountered. Sea ice chart data can provide site-specific model inputs such as ice thickness estimates and partial concentrations, from which corresponding global load exceedance curves are generated. Example scenarios show dependencies of design loads on season length, structural geometry and sea ice conditions. Example results are also provided, showing dependency of design loads on the number of operation days after freeze-up, providing useful information for extending the drilling season of MODUs after freeze-up occurs.

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

2011 ◽  
Vol 243-249 ◽  
pp. 4750-4753 ◽  
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.

Engineering Properties of Sea Ice Ridges in the Barents Sea in 2012-2014 Years for Evaluation of Ice Loads on Offshore Structures

2015 ◽  
Vol 725-726 ◽  
pp. 263-269
Author(s):  
Kseniia Gorbunova ◽  
Karl Shkhinek
Keyword(s):  
Sea Ice ◽  
Barents Sea ◽  
Offshore Structures ◽  
Field Conditions ◽  
Engineering Properties ◽  
The South ◽  
Svalbard Archipelago ◽  
Layer Height ◽  
The Barents Sea ◽  
Ice Loads

Results of studies of ice ridges in field conditions are presented. Ice ridges investigated in the Barents Sea the proximity of the South-East of Svalbard archipelago. Five ice ridges are surveyed during research cruises in 2012-2014 years. Main engineering properties ice ridges as thickness of consolidated layer, height of sail and depth of keel were obtained. Results of research are of primary importance for evaluation of ice loads in studied area in Barents Sea.

scholarly journals Analysis of a Collision-Energy-Based Method for the Prediction of Ice Loading on Ships

2019 ◽  
Vol 9 (21) ◽  
pp. 4546 ◽  
Author(s):  
Sabina Idrissova ◽  
Martin Bergström ◽  
Spyros E. Hirdaris ◽  
Pentti Kujala
Keyword(s):  
International Association ◽  
Load Prediction ◽  
Practical Applications ◽  
Polar Code ◽  
Ice Load ◽  
Conservation Of Momentum ◽  
Ice Conditions ◽  
Ice Loads ◽  
Popov Method

Ships designed for operation in Polar waters must be approved in accordance with the International Code for Ships Operating in Polar Waters (Polar Code), adopted by the International Maritime Organization (IMO). To account for ice loading on ships, the Polar Code includes references to the International Association of Classification Societies’ (IACS) Polar Class (PC) standards. For the determination of design ice loads, the PC standards rely upon a method applying the principle of the conservation of momentum and energy in collisions. The method, which is known as the Popov Method, is fundamentally analytical, but because the ship–ice interaction process is complex and not fully understood, its practical applications, including the PC standards, rely upon multiple assumptions. In this study, to help naval architects make better-informed decisions in the design of Arctic ships, and to support progress towards goal-based design, we analyse the effect of the assumptions behind the Popov Method by comparing ice load predictions, calculated by the Method with corresponding full-scale ice load measurements. Our findings indicate that assumptions concerning the modelling of the ship–ice collision scenario, the ship–ice contact geometry and the ice conditions, among others, significantly affect how well the ice load prediction agrees with the measurements.

Review of Ice Load Standards and Comparison With Measurements

2017 ◽  
Author(s):  
Leon Kellner ◽  
Hauke Herrnring ◽  
Michael Ring
Keyword(s):  
Sea Ice ◽  
Offshore Structures ◽  
Classification Rules ◽  
Empirical Formulas ◽  
Ice Load ◽  
Ice Coverage ◽  
Ice Loads ◽  
Full Scale Tests ◽  
The Given

Sea ice can interact with offshore structures in regions with at least seasonal ice coverage. Therefore the prediction of ice loads on offshore structures is required by many standards or classification rules and guidelines. In order to do this, empirical formulas are often prescribed. These are based on assumptions in combination with model or full scale tests. Yet there are very few publications where the results of the formulas are actually compared to measurements. A case study is made for ice loads on the Norströmsgrund lighthouse. First of all current empirical formulas given by standards bodies or classification societies are reviewed with focus on applicability. Secondly, the ice loads predicted by the empirical formulas are compared to measurements. It was found that for the given case most methods significantly overestimate the load. The applicability of some methods is disputable.

Results of Field Monitoring on Ice Actions on Conical Structures

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Ning Xu ◽  
Qianjin Yue ◽  
Yan Qu ◽  
Xiangjun Bi ◽  
Andrew Palmer
Keyword(s):  
Bohai Sea ◽  
Field Work ◽  
Interaction Process ◽  
Structure Interaction ◽  
Interaction Processes ◽  
Ice Conditions ◽  
Conical Structure ◽  
Ice Loads ◽  
Ice Forces ◽  
Conical Structures

Ice-structure interaction plays a central part in determining ice loads and ice-induced vibrations. This is a controversial research issue, and many factors make the problem more complicated. The authors have been monitoring several ice resistant structures in the Bohai Sea for 20 years and have measured ice forces and simultaneously observed ice-structure interaction processes. This paper describes typical physical ice sheet–conical structure interaction processes, field data, and theoretical explanations for different ice conditions and structure dimensions. The conclusions are more widely applicable, and we relate them to field work on ice resistant conical structures in other ice-covered regions. Further work will quantify ice loads on conical structures once the interaction process is understood.

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