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.

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.

Scale Effect in Ice Flexural Strength

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Mohamed Aly ◽  
Rocky Taylor ◽  
Eleanor Bailey Dudley ◽  
Ian Turnbull
Keyword(s):  
Flexural Strength ◽  
Sea Ice ◽  
Probabilistic Models ◽  
Scale Effects ◽  
Offshore Structures ◽  
Bridge Piers ◽  
Freshwater Ice ◽  
Flexural Failure ◽  
Ice Loads ◽  
Ice Strength

Ice flexural strength is an important parameter in the assessment of ice loads on the hulls of ice-class ships, sloped offshore structures, and sloped bridge piers. While scale effects in compressive ice strength are well known, there has been debate as to the extent of scale effects in ice flexural strength. To investigate scale effects during flexural failure of both freshwater and saline ice, a comprehensive up-to-date database of beam flexural strength measurements has been compiled. The database includes 2073 freshwater ice beam tests with beam volumes between 0.00016 and 2.197 m3, and 2843 sea ice beam tests with volumes between 0.00048 and 59.87 m3. The data show a considerable decrease in flexural strength as the specimen size increases, when examined over a large range of scales. Empirical models of freshwater ice flexural strength as a function of beam volume, and of saline ice as function of beam and brine volumes have been developed using regression analysis. For freshwater ice, the scale-dependent flexural strength is given as: σf=839(V/V1)−0.13 For sea ice, the dependence of flexural strength has been modeled as: σ=1324(V/V1)−0.054e−4.969vb. Probabilistic models based on the empirical data were developed based on an analysis of the residuals, and can be used to enhance probabilistic analysis of ice loads where ice flexural strength is an input.

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.

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 A review of discrete element simulation of ice–structure interaction

2018 ◽  
Vol 376 (2129) ◽  
pp. 20170335 ◽  
Author(s):  
Jukka Tuhkuri ◽  
Arttu Polojärvi
Keyword(s):  
Sea Ice ◽  
Failure Process ◽  
Discrete Element ◽  
Offshore Structures ◽  
Lessons Learned ◽  
Structure Interaction ◽  
Large Numbers ◽  
Ice Loads ◽  
Discontinuous Medium ◽  
Ice Failure

Sea ice loads on marine structures are caused by the failure process of ice against the structure. The failure process is affected by both the structure and the ice, thus is called ice–structure interaction. Many ice failure processes, including ice failure against inclined or vertical offshore structures, are composed of large numbers of discrete failure events which lead to the formation of piles of ice blocks. Such failure processes have been successfully studied by using the discrete element method (DEM). In addition, ice appears in nature often as discrete floes; either as single floes, ice floe fields or as parts of ridges. DEM has also been successfully applied to study the formation and deformation of these ice features, and the interactions of ships and structures with them. This paper gives a review of the use of DEM in studying ice–structure interaction, with emphasis on the lessons learned about the behaviour of sea ice as a discontinuous medium. This article is part of the theme issue ‘Modelling of sea-ice phenomena’.

Auto-determination of ice forces on arctic structures

1987 ◽  
Vol 14 (4) ◽  
pp. 571-580
Author(s):  
T. G. Brown ◽  
M. S. Cheung
Keyword(s):  
Sea Ice ◽  
Structural Characteristics ◽  
Full Description ◽  
Ice Load ◽  
Primary Determinant ◽  
Ice Loads ◽  
Local Pressures ◽  
Ice Failure ◽  
Ice Pressure

This paper describes a variety of programs specifically designed for the determination of sea ice and iceberg loads on Arctic offshore and nearshore structures. As any ice load is a function of the interaction between ice feature and structure, the design of arctic structures is very much an interactive process. Many other factors determining the overall loads and local pressures are functions jointly of ice feature and structural characteristics. For example, the ice strain rate which is a primary determinant of ice strength and failure behaviour may be determined from ice velocity and structure size.The paper details the development of a number of programs directed at the evaluation of quasi-static ice loads, dynamic ice loads, and corresponding local pressures between ice and structure. Examples are provided of the use of the various programs, including the data required and the type of outputs resulting.As a number of the programs incorporate quite extensive theoretical developments or, in one case, a large number of discrete interactions, full description of each program is beyond the scope of this paper. The reader is directed to the listed references for full developments of the various programs and algorithms. Key words: sea ice, iceberg, global ice load, local ice pressure, finite element, ice/structure interaction, probabilistic analysis, ice failure mode.

Ice Loading Decrease at Life Cycle Main Stages for Fixed Offshore Structures

2015 ◽  
Author(s):  
Valery M. Shaposhnikov ◽  
Anatolii V. Aleksandrov ◽  
Oleg E. Litonov ◽  
Viktor V. Platonov
Keyword(s):  
Experimental Studies ◽  
Offshore Structures ◽  
Research Centre ◽  
Ice Load ◽  
Ice Drift ◽  
Load Monitoring ◽  
Design Values ◽  
Ice Loads ◽  
Ice Resistance ◽  
Positive Effect

At the present time design values of ice loads on fixed offshore structures are rather conservative. Conservatism of design ice loads consists in assuming the most unfavorable ice action direction and the worst ice drift speed; the most unfavorable combination of the consolidated layer thickness, ridge keel depth and ice strength; as well as supposing the ice ultimate strength value constant along the whole ice–structure contact area perimeter. With accumulation of the knowledge on ice formation failure under interaction with ice-resistant fixed platforms, the requirements contained in Rules of classification societies are reduced. For example, for the last forty years the lowering of requirements to design ice load values was equal to about four times [1]. For the last time specialists of Krylov State Research Centre have performed design and experimental studies where further tendency to decreasing design values of ice loads is traced. Ice monitoring is one of the main elements for justification of design ice load values’ decrease. Modern monitoring systems permit to warn about occurrence of a state close to a limit one, as well as to record actual ice loads. Ice load monitoring is a necessary part of accident prevention during ice-resistant structures operation. Monitoring of ice loads is a necessary part for providing safe operation of ice-resistance structures, and systematic accumulation of monitoring data for several years gives a positive effect in the form of justified decrease of static and dynamic design ice loads.

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.

Sign in / Sign up

Export Citation Format

Share Document