Thirteenth Canadian Geotechnical Colloquium: Ice design criteria for wide arctic structures

1990 ◽  
Vol 27 (6) ◽  
pp. 701-725 ◽  
Author(s):  
Denis Blanchet
Keyword(s):  
Key Words ◽  
Shear Zone ◽  
Design Criteria ◽  
Correction Factors ◽  
Return Periods ◽  
Ice Load ◽  
Risk Probability ◽  
Arctic Exploration ◽  
Ice Conditions ◽  
Ice Loads

The derivation of design global ice loads for wide vertical caisson-type arctic exploration structures is presented. Correction factors are applied to global ice-load data measured during ice–structure interactions to create a set of design criteria for two typical exploration structures: circular (100 m diameter) and rectangular (160 × 50 m). Return periods for the proposed deterministic design ice loads for these two structures are then determined for typical ice conditions encountered in the Harrison Bay shear zone area in 20–30 m of water. Key words: exploration structures, global design ice loads, risk, probability of exceedence, return periods.

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.

Wave and current forces on fixed offshore structures

1988 ◽  
Vol 15 (6) ◽  
pp. 937-947 ◽  
Author(s):  
Michael Isaacson
Keyword(s):  
Key Words ◽  
Recent Literature ◽  
Offshore Structures ◽  
Design Criteria ◽  
Wave Forces ◽  
Ocean Engineering ◽  
Detailed Survey ◽  
Ice Loads ◽  
Hydrodynamic Data ◽  
Design Construction

The Canadian Standards Association standard S471 "General requirements, design criteria, environment, and loads, Part 1 of the CSA code for the design, construction and installation of fixed offshore structures" contains an appendix "Wave and current loads." To compliment this appendix, the present paper provides a more detailed survey of this topic with a review of the recent literature and recommendations of hydrodynamic data needed in offshore design. In addition, hydrodynamic considerations in the calculation of earthquake and ice loads are mentioned. Key words: currents, current forces, hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

Ice action on fixed offshore structures: a state-of-the-art review

1987 ◽  
Vol 14 (3) ◽  
pp. 381-407 ◽  
Author(s):  
M. A. Nessim ◽  
M. S. Cheung ◽  
I. J. Jordaan
Keyword(s):  
Interaction Design ◽  
Size Effects ◽  
Offshore Structures ◽  
Probabilistic Methods ◽  
Background Information ◽  
Design Criteria ◽  
Load Calculation ◽  
Ice Conditions ◽  
Ice Loads ◽  
Probabilistic Load

The methods and approaches for calculating global ice loads on fixed offshore structures are critically reviewed. The review covers both the mechanical approaches used in load calculation and the probabilistic methods used to deal with the uncertainties involved. The paper gives a brief review of background information related to ice conditions, ice-load characterization, and ice mechanics. Load calculation methods for different types of ice behaviour are reviewed for vertical structures, as well as sloping-sided structures. Size effects are discussed, and the effects of rubble piles on ice loads are briefly reviewed. The emphasis of the review is on summarizing the different models and approaches reported in the literature, and making evaluations, comments, and suggestions for further research from the viewpoint of choosing design criteria. Key words: ice-structure interaction, design criteria, ice indentation, probabilistic load assessment, Arctic structures, size effects.

Factored axial compressive resistance of schifflerized angles

1991 ◽  
Vol 18 (6) ◽  
pp. 926-932 ◽  
Author(s):  
Seshu Madhava Rao Adluri ◽  
Murty K. S. Madugula
Keyword(s):  
Key Words ◽  
Design Method ◽  
Design Criteria ◽  
Design Practice ◽  
Buckling Mode ◽  
Flexural Buckling ◽  
Mode Of Failure ◽  
Current Design ◽  
Similarities And Differences ◽  
Compressive Resistance

The concept of schifflerization of 90° equal-leg angle is presented and its application in triangular-base latticed steel towers is explained. The similarities and differences between schifflerized angles and regular 90° angles are discussed. The current design practice for schifflerized angles is reviewed and its limitation is highlighted. A design method which includes the effect of the torsional-flexural buckling mode of failure is proposed. For ready use of designers, the factored axial compressive resistances of schifflerized angles are tabulated for both the present and proposed design methods. Key words: buckling, compressive resistance, design criteria, schifflerized angles, stability, standards, steel, struts, towers, guyed towers.

Station Keeping Trials in Ice: Ice Load Monitoring System

2018 ◽  
Author(s):  
Håvard Nyseth ◽  
Anders Hansson ◽  
Johan Johansson Iseskär
Keyword(s):  
Data Sets ◽  
Station Keeping ◽  
Ice Load ◽  
Hull Structure ◽  
Load Monitoring ◽  
Ice Loads ◽  
Recorded Data ◽  
Measurement Concept ◽  
Ice Impacts ◽  
Basic Philosophy

In connection with the Statoil SKT project, DNV GL have developed a method for estimating ice loads on the ship hull structure and mooring tension of the anchor handling tug supply (AHTS) vessel Magne Viking by full scale measurements. In March 2017, the vessel was equipped with an extensive measurement system as a preparation for the dedicated station-keeping trial in drifting ice in the Bay of Bothnia. Data of the ice impacts acting on the hull were collected over the days of testing together with several other parameters from the ship propulsion system. Whilst moored, the tension in the mooring chain was monitored via a load cell and logged simultaneously to the other parameters. This paper presents the processes involved in developing the measurement concept, including the actual installation and execution phases. The basic philosophy behind the system is described, including the methods used to design an effective measurement arrangement, and develop procedures for estimation of ice loads based on strain measurements. The actual installation and the process of obtaining the recorded data sets are also discussed.

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.

Interaction of Ice Floes With Columns of a Semi-Submersible Platform

1983 ◽  
Vol 105 (4) ◽  
pp. 460-463
Author(s):  
P. G. Noble ◽  
D. Singh
Keyword(s):  
Maximum Load ◽  
Test Results ◽  
Ice Load ◽  
Physical Model Tests ◽  
Ice Concentration ◽  
Drilling Unit ◽  
Ice Loads ◽  
Ice Field ◽  
Preliminary Research ◽  
Ice Floes

A preliminary research project has been carried out to determine the effect of small ice floes on a semi-submersible drilling unit. Physical model tests have been conducted with two main objectives: first, to determine the ability of the columns to prevent ice from passing between them (arching) and thus minimizing the chance of riser damage, and second, to determine the total ice load on the semi-submersible during interaction with ice field concentrations. Three models were used, representing one half of a four, six or eight-legged semi-submersible platform. The dimensions and spacing of the columns were such that the heave and pitch responses were kept constant. The tests were conducted at a model scale of 1:30 using synthetic ice. Test results showed the maximum load measured on a four-legged semi-submersible model, at 100 percent ice floe concentration, was on the order of half of that measured on six or eight-legged semi-submersible models. Also the ice loads on a four-legged semi-submersible model at lower ice floe concentration were substantially less than those for six or eight-legged semi-submersible models. The total ice load on semi-submersible models is found to be a function of ice floe concentration. Up to about 75 percent ice concentration, ice loads varied linearly. Beyond that, the loads increased exponentially for all semi-submersible models.

Peak Ice Loads on a Lifeboat in Pack Ice Conditions

2014 ◽  
Author(s):  
Allison Kennedy ◽  
António Simões Ré ◽  
Brian Veitch
Keyword(s):  
Pack Ice ◽  
Ice Conditions ◽  
Ice Loads
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