Ice loads from first-year ice ridges and rubble fields

1998 ◽  
Vol 25 (2) ◽  
pp. 206-219 ◽  
Author(s):  
Denis Blanchet
Keyword(s):  
Full Scale ◽  
The Arctic ◽  
First Year ◽  
Failure Behavior ◽  
Pressure Measurements ◽  
Load Models ◽  
Ice Load ◽  
Ice Loads ◽  
Scale Data ◽  
Structure Width

A method for estimating global loads from consolidated first-year ice ridges and rubble fields on wide Arctic offshore vertical-sided structures is presented. The method utilizes full-scale global ice load measurements in the Arctic to represent the failure behavior of the consolidated layer and a Mohr-Coulomb approach for the remaining layers. By including full-scale data, the model can take into account the effects of scale and non-simultaneous failure of the consolidated ice layer across the structure width. The results are compared with those obtained from several other first-year ice ridge and rubble field load models.Key words: first-year ice ridges, rubble fields, ice load and pressure measurements, Arctic structures, ice load models.

A Coupled Dynamic Ice-Load and Moored Floater Interaction Parametric Study for First Year Level Ice

2016 ◽  
Author(s):  
Aziz Ahmed ◽  
Anurag Yenduri ◽  
Ritwik Ghoshal ◽  
Zhuo Chen ◽  
Ankit Choudhary ◽  
...  
Keyword(s):  
Parametric Study ◽  
Oil And Gas ◽  
Time History ◽  
Full Scale ◽  
The Arctic ◽  
First Year ◽  
Mooring System ◽  
Oil And Gas Exploration ◽  
Ice Load ◽  
Level Ice

Arctic remains the final frontier in the oil and gas exploration regime. The diminishing presence of ice opens up the region for longer and wider exploration. However, even with the assistance of ice management, the threat of broken first-year level ice stays ubiquitous. Calculation of ice load for such ice features bases on the established formulation developed by observation from full-scale measurements and model test data over the years. However, the formulation mostly relies on the data derived from fixed structures or icebreakers. Such estimations of ice load do not account for the stiffness compliance afforded by mooring system of a floater, such as a semi-submersible or a spar. A floating oil and gas exploration system offers a number of advantages over the fixed platforms, such as the option to deploy elsewhere during the off-season in the Arctic as well as connecting and disconnecting during severe ice events such as an approaching iceberg or multi-year ice ridge. However, the current practice of employing dynamic ice load time-history available in ISO19906 or similar codes fails to account for the presence of the mooring system on these floating platforms, directly resulting in a lack of confidence in the derived response of the floater. This study aims to address this issue by developing a dynamic ice-load time-history algorithm, which, can readily couple with commercially available hydrodynamics and mooring system analysis software. This investigation puts forward the hypothesis that the evolution of ice load vs. ice feature displacement with respect to the structure remains same for both fixed and floating structures. However, the underlying assumption is that the size of the ice features remains comparable. This hypothesis accounts for the prominent influence of the size effect on the breaking strength of ice. The difference between the behavior of a fixed and a floating structure under ice load is due to the relative motion between the floater and the ice feature. The developed coupled ice-load-function accounts for this by including the relative displacement between the floater and the ice feature in the formulation. This study uses the semi-empirical formulation originally derived by Croasdale to calculate the main ice load components for a fixed structure with downward breaking slope. Subsequently, this study uses this coupled ice load subroutine to compare against the full-scale measurement data found in the literature for a floater with downward-sloped hull specifically designed to assist in ice breaking. A comparison against the peak load observed during full-scale measurements on a floater in the Arctic waters validates the proposed approach. Next, this study utilizes the coupled analysis to derive the displacement, velocity, and acceleration response of the studied floater for a range of ice parameters, such as the drift speed and thickness. Additionally, this study performs a parametric study by varying the downward breaking slope angle of the floater, the mooring configuration, and the water depth. Finally, this study summarizes the observed behavior of the floater under different ice parameters as well as floater shape and mooring systems parameters.

A Novel Data Processing Method for Ice Pressure Statistics

2015 ◽  
Author(s):  
Karoline M. Neumann ◽  
Sören Ehlers ◽  
Bernt J. Leira ◽  
Pentti Kujala
Keyword(s):  
Data Processing ◽  
Design Parameter ◽  
Processing Method ◽  
Full Scale ◽  
Cumulative Distribution ◽  
Discrete Events ◽  
Data Processing Method ◽  
Ice Loads ◽  
Ice Pressure ◽  
Scale Data

Maritime activities in ice bound areas increase demand for design of structures to withstand ice loads. A cumulative distribution with parameter α as a function of area is published in ISO19906 [1], based on analysis of multiple different discrete full scale rams from Jordaan [2] for application on design loads of discrete impacts. Taylor [3] performs a reanalysis including more full scale data, and taking into account the effect of exposure, presents design parameter curves α-area and x0-area. These are valuable, but are to be applied for design of discrete events, and can only be obtained from discrete event data. The objective of this paper is to describe and demonstrate a data processing method based on semi-continuous ice pressure data that can be applied not only for discrete events, but also for semi-continuous interaction. A finely meshed tactile sensor is applied. Jordaan’s [2] max event method is applied on a new definition of event, based on triggered sensels that are adjacent in time and space. The method is demonstrated on a model scale data set from Aalto University, and example design parameter curves are presented. Applying the developed method on full scale data, the results can be valuable for design of semi-continuous ice loads.

Review of Measured Full Scale Ice Loads to Fixed Structures

2007 ◽  
Author(s):  
Morten Bjerka˚s
Keyword(s):  
Upper Bound ◽  
Full Scale ◽  
Data Sources ◽  
Ice Thickness ◽  
Ice Load ◽  
Main Emphasis ◽  
Ice Loads ◽  
Ice Forces ◽  
Early Phases ◽  
A Current

This paper gives a review of selected public available full scale measured ice forces to fixed structures. Altogether 31 data sources are collected where the highest ice load, a current ice thickness and a structural width is reported. The main emphasis of this study is to formulate an engineering tool to predict upper bound ice forces to structures with a low number of input parameters available. Typical applications will be in early phases of projects for estimations of costs and technical integrity of surface piercing fixed structures in ice infested oceans and rivers.

A Coupled Discrete–Finite Element Method for the Ice-Induced Vibrations of a Conical Jacket Platform with a GPU-Based Parallel Algorithm

2019 ◽  
Vol 17 (04) ◽  
pp. 1850147 ◽  
Author(s):  
Shunying Ji ◽  
Shuailin Wang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Parallel Algorithm ◽  
Beam Element ◽  
Full Scale ◽  
Bond Breaking ◽  
Ice Loads ◽  
Spherical Elements ◽  
Scale Data ◽  
Element Method

Flowing ice draws special attention due to the dynamic response of jacket platforms. In this study, a coupled discrete element method (DEM) and finite element method (FEM) are developed to analyze the interaction between sea ice and conical jacket platforms to determine the ice-induced vibrations (IIVs) of the structure. To model the ice cover and to investigate ice loads, a DEM with bond-breaking spherical elements is adopted. Meanwhile, the FEM (with a beam element) is applied to model the IIVs of the jacket platform. An efficient transmission scheme between the bond-breaking spherical elements and the beam element is proposed. The graphics processing unit-based parallel algorithm is developed to improve the computational efficiency. The simulated ice loads are verified by comparing them with the full-scale data and different ice load functions. The simulated IIV accelerations of the JZ20-2 MUQ conical platform in the Bohai Sea (China) are consistent with the full-scale data under various ice conditions (e.g., velocity and thickness). The numerical results show that the IIV acceleration increases linearly with the ice velocity and the square of the ice thickness.

Dimensioning of Rudder Systems for Ice Class Ships

2020 ◽  
Author(s):  
Rob Hindley ◽  
Jillian Adams ◽  
Ville Valtonen ◽  
Chi-Hyun Sung
Keyword(s):  
Critical Element ◽  
Element Analysis ◽  
Safety Critical ◽  
System Protection ◽  
Ice Load ◽  
Hull Structure ◽  
Protection Mechanisms ◽  
Ice Loads ◽  
Control Surfaces ◽  
Scale Data

Abstract Rudder systems (rudder control surfaces and steering gear) are a safety critical element of ships operating in ice-covered waters. Icebreaking ships equipped with single rudders are particularly vulnerable considering the remote and often isolated locations in which they operate. The IACS Polar Class Rules were developed as a set of harmonized requirements for ships operating in polar waters. First published in 2006 the rules contain requirements for dimensioning the hull structure and propulsion machinery to resist ice loads. There are however no specific requirements for rudders — the rules simply require appendages to be dimensioned using the hull ice load. This paper presents a series of studies aimed at providing guidance on dimensioning rudders and steering gear systems for operation in ice. Using existing ship reference cases and rudder ice loading scenarios found in previous rules and guidelines a simplified set of design approaches are presented. These approaches are evaluated with Finite Element Analysis and compared with selected measured full-scale data and damage incidents. Guidance is provided on system protection mechanisms for the steering gear under these design and over-load cases. In addition, a comparison is made between the results and those derived from using the hull area design pressures in the current IACS rules.

Aerodynamic Noise Characterization of a Full-Scale Wind Turbine through High-Frequency Surface Pressure Measurements

2015 ◽  
Vol 14 (5-6) ◽  
pp. 729-766 ◽  
Author(s):  
Franck Bertagnolio ◽  
Helge Aa. Madsen ◽  
Christian Bak ◽  
Niels Troldborg ◽  
Andreas Fischer
Keyword(s):  
Wind Turbine ◽  
Surface Pressure ◽  
High Frequency ◽  
Full Scale ◽  
Aerodynamic Noise ◽  
Pressure Measurements ◽  
Noise Characterization

Benchmarking of Truss Spar Vortex Induced Motions Derived From CFD With Experiments

2005 ◽  
Author(s):  
John Halkyard ◽  
Senu Sirnivas ◽  
Samuel Holmes ◽  
Yiannis Constantinides ◽  
Owen H. Oakley ◽  
...  
Keyword(s):  
Scale Up ◽  
Vertical Cylinder ◽  
Reynolds Numbers ◽  
Full Scale ◽  
Scale Model ◽  
Current Direction ◽  
Test Results ◽  
Helical Strakes ◽  
Truss Spar ◽  
Scale Data

Floating spar platforms are widely used in the Gulf of Mexico for oil production. The spar is a bluff, vertical cylinder which is subject to Vortex Induced Motions (VIM) when current velocities exceed a few knots. All spars to date have been constructed with helical strakes to mitigate VIM in order to reduce the loads on the risers and moorings. Model tests have indicated that the effectiveness of these strakes is influenced greatly by details of their design, by appurtenances placed on the outside of the hull and by current direction. At this time there is limited full scale data to validate the model test results and little understanding of the mechanisms at work in strake performance. The authors have been investigating the use of CFD as a means for predicting full scale VIM performance and for facilitating the design of spars for reduced VIM. This paper reports on the results of a study to benchmark the CFD results for a truss spar with a set of model experiments carried out in a towing tank. The focus is on the effect of current direction, reduced velocity and strake pitch on the VIM response. The tests were carried out on a 1:40 scale model of an actual truss spar design, and all computations were carried out at model scale. Future study will consider the effect of external appurtenances on the hull and scale-up to full scale Reynolds’ numbers on the results.

Advanced Weathervaning in Ice

2011 ◽  
Author(s):  
William Hidding ◽  
Guillaume Bonnaffoux ◽  
Mamoun Naciri
Keyword(s):  
Rapid Change ◽  
Ice Sheet ◽  
Model Tests ◽  
The Arctic ◽  
Mooring System ◽  
Sudden Increase ◽  
Time Step ◽  
Ice Loads ◽  
Level Ice ◽  
Drift Direction

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.

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.

scholarly journals Anomalous blocking over Greenland preceded the 2013 extreme early melt of local sea ice

2017 ◽  
Vol 59 (76pt2) ◽  
pp. 181-190 ◽  
Author(s):  
Thomas J. Ballinger ◽  
Edward Hanna ◽  
Richard J. Hall ◽  
Thomas E. Cropper ◽  
Jeffrey Miller ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Regional Climate ◽  
Regional Climate Change ◽  
Circulation Pattern ◽  
The Arctic ◽  
Labrador Sea ◽  
First Year ◽  
Tropospheric Circulation ◽  
Blocking Index

ABSTRACTThe Arctic marine environment is undergoing a transition from thick multi-year to first-year sea-ice cover with coincident lengthening of the melt season. Such changes are evident in the Baffin Bay-Davis Strait-Labrador Sea (BDL) region where melt onset has occurred ~8 days decade−1 earlier from 1979 to 2015. A series of anomalously early events has occurred since the mid-1990s, overlapping a period of increased upper-air ridging across Greenland and the northwestern North Atlantic. We investigate an extreme early melt event observed in spring 2013. (~6σ below the 1981–2010 melt climatology), with respect to preceding sub-seasonal mid-tropospheric circulation conditions as described by a daily Greenland Blocking Index (GBI). The 40-days prior to the 2013 BDL melt onset are characterized by a persistent, strong 500 hPa anticyclone over the region (GBI >+1 on >75% of days). This circulation pattern advected warm air from northeastern Canada and the northwestern Atlantic poleward onto the thin, first-year sea ice and caused melt ~50 days earlier than normal. The episodic increase in the ridging atmospheric pattern near western Greenland as in 2013, exemplified by large positive GBI values, is an important recent process impacting the atmospheric circulation over a North Atlantic cryosphere undergoing accelerated regional climate change.

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