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.

Structure, Salinity and Density of Multi-Year Sea Ice Pressure Ridges

1985 ◽  
Vol 107 (4) ◽  
pp. 493-497 ◽  
Author(s):  
J. A. Richter-Menge ◽  
G. F. N. Cox
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Beaufort Sea ◽  
Pressure Ridge ◽  
Sample Data ◽  
Ice Loads ◽  
Scale Properties ◽  
Ice Pressure

Data are presented on the variation of ice structure, salinity, and density in multi-year pressure ridges from the Beaufort Sea. Two continuous multi-year pressure ridge cores are examined as well as ice sample data from numerous other pressure ridges. The results suggest that the large scale properties of multi-year pressure ridges are not isotropic, and that the use of anisotropic ridge models may result in lower design ridge ice loads.

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.

scholarly journals A Statistical Approach to Extreme Ice Loads on Lighthouse Norstro¨msgrund

2006 ◽  
Author(s):  
Lennart Fransson ◽  
Jan-Eric Lundqvist
Keyword(s):  
Baltic Sea ◽  
Statistical Methods ◽  
Strong Influence ◽  
Statistical Approach ◽  
The Baltic Sea ◽  
Ice Load ◽  
Ice Conditions ◽  
Ice Loads ◽  
The Baltic ◽  
Ice Pressure

Data from full-scale measurements of ice loads on lighthouse Norstro¨msgrund has been analyzed using basic statistical methods. Questions like scaling, duration of ice interaction and correlation of extreme ice loads on different segments of the structure are discussed. Typical ice conditions in the Baltic Sea are described in general and the region is divided into areas with similar ice and ice movements. Indications of strong influence of structure diameter on the effective ice pressure were confirmed by results obtained on other lighthouses in the area. The result can be used in simulations of ice load probabilities for fixed vertical structures with small diameters located in the Baltic 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.

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’.

Velocity Effects on Conical Structure Ice Loads

2002 ◽  
Author(s):  
Dmitri G. Matskevitch
Keyword(s):  
Model Tests ◽  
Ice Load ◽  
Empirical Correction ◽  
Conical Structure ◽  
Ice Loads ◽  
Ice Velocity ◽  
Velocity Effect ◽  
Ice Failure ◽  
Bending Failure ◽  
Conical Structures

Existing design codes and most methods for ice load calculation for conical structures do not take velocity effects into account. They were developed as an upper bound estimate for the load from slow moving ice which fails in bending against the cone. Velocity effects can be ignored when the structure is designed for an area with slow ice movement, for example, the nearshore Beaufort Sea. Sakhalin structures will be exposed to ice moving at velocities up to about 1.5 m/sec. Model tests show that quasi-static methods may underestimate the ice load on a steep cone when the interaction velocity is that high. The present paper summarizes results of published model tests with conical structures that show a velocity effect. An empirical correction factor to the Ralston method is developed to account for the increase in cone load with ice velocity. The paper also discusses velocity effects on ice failure length and possible transition from bending failure to an alternative failure mode when the ice velocity is high.

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.

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