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.

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.

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.

Numerical Calculation of the Ice Grow and Empirical Calculation Results

2013 ◽  
Vol 834-836 ◽  
pp. 1448-1454 ◽  
Author(s):  
Dmitry Sharapov ◽  
Karl Shkhinek
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Stefan Problem ◽  
Ice Thickness ◽  
Field Observations ◽  
Ice Load ◽  
Element Simulation ◽  
Calculation Results ◽  
Ice Loads ◽  
Level Calculation

Ice loads is one of the most important parameters which should be taken into consideration for arctic structures. Ice load highly depends on the ice thickness. It is always recommended to consider the ice thickness data from field observations. However if data is not available it is necessary to calculate the thicknesses of ice level. Calculation is also important for the areas where the thermal fluxes through structure should be taken into the consideration. In this work numerical simulation of Stefan problem for determining of ice level thickness is presented. The results show good correlation between empirical, experimental data and the results from finite element simulation of Stefan problem.

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.

scholarly journals Diagnosis-prescription studies – important steps towards a national drug prescription statistics in Norway

2009 ◽  
Vol 11 (1) ◽  
Author(s):  
Jørund Straand
Keyword(s):  
General Practice ◽  
Drug Prescription ◽  
Diagnostic Information ◽  
Data Sources ◽  
Font Size ◽  
Use Of Data ◽  
National Drug ◽  
Prescribing Practice ◽  
Drug Statistics ◽  
A Current

<strong><span style="font-family: TimesNewRomanPS-BoldMT;"><font face="TimesNewRomanPS-BoldMT"><p align="left"> </p></font></span><p align="left"><span style="font-size: x-small; font-family: TimesNewRomanPS-BoldMT;"><span style="font-size: x-small; font-family: TimesNewRomanPS-BoldMT;">ABSTRACT</span></span></p></strong><span style="font-size: x-small; font-family: TimesNewRomanPSMT;"><span style="font-size: x-small; font-family: TimesNewRomanPSMT;"><p align="left">In the first part of this article, drug utilization and prescribing practice is discussed as seen from a</p><p align="left">Norwegian general practice perspective. Which are the data sources available? What kind of studies</p><p align="left">have been performed? Prescription-diagnosis studies are reviewed, in particular the Møre & Romsdal</p><p align="left">Prescription Study (MRPS). Because the wholesales drug statistics do not include information about</p><p align="left">neither patients, prescribers or diagnoses, there is a current need for establishing a more comprehensive</p><p align="left">statistics giving wider and deeper insights into the prescribing and utilization of drugs in the Norwegian</p><p align="left">society. The proposed Norwegian prescription statistics is discussed in relation to previous experiences</p><p align="left">from prescription-diagnosis studies and current needs for research and statistics in the field. Some</p><p align="left">examples are given illustrating why the 11-digit person number probably should be included in the</p><p align="left">database. Lack of diagnostic information may to some extent be compensated for by introducing a more</p><p align="left">differentiated list of diagnoses for the drugs reimbursed. The use of data from this statistics for quality</p><p align="left">assurance in e.g. general practice is discussed. Finally, some suggestions are given for how the Norwegian</p><p>prescription statistics may be organised.</p></span></span>

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.

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.

Reliability Against Drifting Ice—An Adjunct to Monte Carlo Simulation

1991 ◽  
Vol 113 (3) ◽  
pp. 253-259
Author(s):  
A. B. Dunwoody
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Normal Family ◽  
Probability Distributions ◽  
Load Model ◽  
Ice Load ◽  
Ice Loads ◽  
Drifting Ice ◽  
Log Normal ◽  
Monte Carlo Simulation Program

A method is presented for the calculation of the reliability of a structure against drifting ice subject to restrictions on the form of the ice load model and on the form of the probability distributions of the ice feature characteristics. The ice load model must have the form that the ice load is proportional to the product of the characteristics of the impacting ice feature raised to individual powers. Results from a Monte Carlo simulation program are presented to demonstrate that the ice loads for a number of useful ice interaction scenarios can be modeled by an equation of this form. The probability distributions of the ice feature characteristics must be from the log-normal family. A realistic example using publicly available ice data and ice load model is presented.

Advances in Sea Ice Mechanics in the USA

1987 ◽  
Vol 40 (9) ◽  
pp. 1232-1242 ◽  
Author(s):  
Devinder S. Sodhi ◽  
Gordon F. N. Cox
Keyword(s):  
Sea Ice ◽  
Thickness Distribution ◽  
Failure Process ◽  
Field Measurements ◽  
Small Scale ◽  
Ice Thickness ◽  
Ice Drift ◽  
Sea Ice Drift ◽  
Ice Failure ◽  
Ice Forces

A brief review of significant advances in the field of sea ice mechanics in the United States is presented in this paper. Emphasis is on ice forces on structures, as the subject relates to development of oil and gas resources in the southern Beaufort Sea. The main topics discussed here are mechanical properties, ice–structure interaction, modeling of sea ice drift, and oil industry research activities. Significant advances in the determination of ice properties are the development of testing procedures to obtain consistent results. Using stiff testing machines, researchers have been able to identify the dependence of tensile and compressive strengths on different parameters, eg, strain rate, temperature, grain size, c-axis orientation, porosity, and state of stress (uniaxial or multiaxial). Now reliable data exist on the tensile and compressive strengths of first-year and multi-year sea ice. Compressive strengths obtained from field testing of large specimens (6 × 3 × 2 m thick) were found to be within 30% of the strengths obtained from small samples tested in laboratory at the same temperature and strain rate as found in the field. Recent advances in the development of constitutive relations and yield criteria have incorporated the concept of damage mechanics to include the effect of microfracturing during the ice failure process. Ice forces generated during an ice–structure interaction are related to ice thickness and properties by conducting analytical or small-scale experimental studies, or both. Field measurements of ice forces have been made to assess the validity of theoretical and small-scale experimental results. There is good agreement between theoretical and small-scale experimental results for ice forces on conical structures. Theoretical elastic buckling loads also agree with the results of small-scale experiments. Though considerable insight has been achieved for ice crushing failure, estimation of ice forces for this mode is based on empirical relations developed from small-scale experiments. A good understanding of the ice failure process has been achieved when ice fails in a single failure mode, but our understanding of multi-modal ice failure still remains poor. Field measurements of effective pressure indicate that it decreases with increasing contact area. Research in fracture mechanics and nonsimultaneous failure is underway to explain this observed trend. Ice ridge formation and pile-up have been modeled, and the forces associated with these processes are estimated to be low. The modeling of sea ice drift has progressed to a point where it is able to determine the extent, thickness distribution, and drift velocity field of sea ice over the entire arctic basin. Components of this model relate to momentum balance, thermodynamic processes, ice thickness distribution, ice strength, and ice rheology.

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