Improved Model for Ice Force on Conical Structure

2005 ◽  
Author(s):  
W. Feng ◽  
Z. M. Shi ◽  
L. M. Liu
Keyword(s):  
Ice Sheet ◽  
Bending Moment ◽  
Offshore Structures ◽  
Structure Design ◽  
Offshore Structure ◽  
Conical Structure ◽  
Offshore Structure Design ◽  
Improved Model ◽  
Ice Force ◽  
Bending Failure

Ice force is an important factor to be taken into account for offshore structures in cold region, and the calculation method of the ice force is meaningful for the offshore structure design. Cone is now used as optimal ice-resistant structure because it can cause bending failure of the ice sheet. The interaction between ice sheet and conical structure is studied in this paper and Croasdale’s model is modified based on the field observations. The newly built model separates the ice sheet into emersed part and floating part, and the equilibrium analyses are carried out respectively. The bending moment distribution of the ice sheet is analyzed to determine the position of bending failure, which serves as a supplementary restriction. Analytic solution of ice force on conical structure is got and it is verified by the experimental data of previous researches.

Offshore structures – why all offshore facilities should have a demanning requirement

2019 ◽  
Vol 59 (2) ◽  
pp. 789 ◽  
Author(s):  
Matt Keys
Keyword(s):  
Offshore Structures ◽  
Structure Design ◽  
Risk Level ◽  
Design Codes ◽  
Offshore Structure ◽  
Sea State ◽  
The North ◽  
Offshore Structure Design ◽  
Cost Implications ◽  
Level Of Risk

Most offshore structure design codes focus on setting appropriate safety factors to achieve an acceptable annual level of risk. Recent work by Atkins SNC-Lavalin, together with a large number of operators in Australian waters and the North Sea, has discovered that a large number of aging assets are implementing a demanning requirement to limit the risk of platform collapse to personnel, due to changes in loading or degradation of the structure. This work has shown there are two risk scenarios that should drive this requirement. The first scenario which is intended by the codes in limiting the overall annual risk. The second is to limit the collapse risk associated with a known forecast storm, as the level of risk from helicopter demanning is much lower. For all the older offshore fixed and permanently mooring floating structures assessed for a risk level considered acceptable for a forecast storm, this risk level would govern the sea-state demanning criteria. For recently installed facilities that are compliant with current standards, the findings were the same: that all facilities should have a demanning requirement. The level of this demanning sea-state limit has been shown to be lower than expected and is likely to occur only once in the asset’s life; therefore, the cost implications of implementing demanning procedures are minor. This paper presents the basis and range of findings for calculating the risks associated with an annual occurrence and an ‘in a forecast storm’ risk. Further, this paper proposes acceptable demanning limits for facilities designed to current and historical design codes.

Offshore structure design and development

1982 ◽  
Vol 307 (1499) ◽  
pp. 263-277
Keyword(s):  
Deep Water ◽  
Oil And Gas ◽  
Offshore Structures ◽  
Structure Design ◽  
Offshore Structure ◽  
Oil And Gas Exploration ◽  
Exploration And Production ◽  
Offshore Oil And Gas ◽  
Offshore Structure Design ◽  
Offshore Oil

The kinds of technology currently being applied to the design, construction, installation and operation of offshore structures for oil and gas exploration and production are quite sophisticated and include many examples of innovative configurations and approaches. The decade of the 1990s should see further evolution, reinterpretation and improvements of concepts that are already in service or being readied for service. The importance of offshore oil and gas may be judged by the projection that over half of overall exploration investments will go to offshore prospects in future years. This paper surveys some expected evolutions, with particular emphasis on the challenging area of deep-water applications. Some features of a tension leg platform design are discussed as an example of a deep-water oil production system. An attempt is made to recognize the problems of applying advanced engineering and analytical capabilities, when many specialists must interact, to producing a thoroughly engineered design, which is also balanced and economical, for such innovative systems.

A Three-Dimensional Model for Ice Rubble Pile-Ice Sheet-Conical Structure Interaction at the Piers of Confederation Bridge, Canada

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Chee K. Wong ◽  
Thomas G. Brown
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
Offshore Structures ◽  
Flexural Behavior ◽  
Small Scale ◽  
Structure Interaction ◽  
Flexural Failure ◽  
Modes Of Failure ◽  
Conical Structure ◽  
Rubble Pile

Offshore structures constructed in waters where ice cover is prevalent for several months a year are subjected to ice loading. Some of these structures are conical or sloped-faced in shape, where flexural failure becomes the dominant mode of failure for the ice sheet. The flexural failure mode reduces the magnitude of ice-structure interaction loads in comparison to other modes of failure. Various researchers have devised flexural failure models for ice-conical structure interactions. Each model shares the same principle of the ice sheet being modeled as a beam on an elastic foundation, but each model has different limitations in precisely simulating the interaction. Some models do not incorporate the ice rubble pile, while other models make oversimplified assumptions for three-dimensional behavior. The proposed three-dimensional (3D) model aims to reduce some of these limitations with the following features: (1) modeling the geometry of the ice rubble pile around the conical pier using the results of small-scale tests, (2) modeling the loads exerted by the ice rubble pile on the conical structure and ice sheet with a rigorous method of slices, (3) adding driving forces in keeping the rubble pile intact and in upward motion during the interaction, (4) accounting for eccentric offsetting moments at the ice-structure contacts, and (5) modeling the flexural behavior of the ice sheet subject to ice rubble loads using finite element method. The proposed model is used to analyze the interaction events recorded at the conical piers of the Confederation Bridge over a period of 11 years.

Evaluation of pack ice pressure approaches and engineering implications for offshore structure design

2018 ◽  
Vol 149 ◽  
pp. 71-82
Author(s):  
Lawrence Charlebois ◽  
Robert Frederking ◽  
G.W. Timco ◽  
David Watson ◽  
Martin Richard
Keyword(s):  
Structure Design ◽  
Offshore Structure ◽  
Pack Ice ◽  
Offshore Structure Design ◽  
Ice Pressure

scholarly journals Analysis of Offshore Structures Based on Response Spectrum of Ice Force

2019 ◽  
Vol 7 (11) ◽  
pp. 417 ◽  
Author(s):  
Liu ◽  
Li ◽  
Zhang
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Response Spectrum ◽  
Time History ◽  
Offshore Structures ◽  
Potential Threat ◽  
Influence Coefficients ◽  
Design Response Spectrum ◽  
Ice Force ◽  
Bending Failure

With the development of large-scale offshore projects, sea ice is a potential threat to the safety of offshore structures. The main forms of damage to bottom-fixed offshore structures under sea ice are crushing failure and bending failure. Referred to as the concept of seismic response spectrums, the design response spectrum of offshore structures induced by the crushing and bending ice failure is presented. Selecting the Bohai Sea in China as an example, the sea areas were divided into different ice zones due to the different sea ice parameters. Based on the crushing and bending failure power spectral densities of ice force, a large amount of ice force time-history samples are firstly generated for each ice zone. The time-history of the maximum responses of a series of single degree of freedom systems with different natural frequencies under the ice force are calculated and subsequently, a response spectrum curve is obtained. Finally, by fitting all the response spectrum curves from different samples, the design response spectrum is generated for each ice zone. The ice force influence coefficients for crushing and bending failure are obtained, which can be used to estimate the stochastic sea ice force acting on a structure conveniently in a static way. A comparison of the proposed response spectrum method with the Monte Carlo method by a numerical example shows good agreement.

Dynamic Ice Force Analysis on a Conical Structure Based on Direct Observation and Measurement

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Ning Xu ◽  
Qianjin Yue
Keyword(s):  
Video Camera ◽  
Temporal Variations ◽  
Qualitative Description ◽  
Basic Model ◽  
Broken Ice ◽  
Conical Structure ◽  
Ice Failure ◽  
Ice Force ◽  
Bending Failure ◽  
Ice Forces

In order to study dynamic ice force induced by ice-structure interaction, we adopted the most reliable method to directly measure ice force on full-scale structure. This paper mainly demonstrates the qualitative description on the basic model for dynamic ice forces based on direct measurement on the jackets with ice-breaking cone in the Bohai Sea. Temporal variations of ice force are recorded by the ice load panels, and corresponding ice failure processes on conical structures are recorded by video camera. It is found that, when an ice sheet acts on the upward narrow cone, bending failure occurs and broken ice pieces are completely cleared up by the side of the cone. The basic form of dynamic ice force in time domain is a series of impulse signals with minimum load of zero.

Ice Load Calculation on Semi-Submersible Platform

2017 ◽  
Author(s):  
Marc Cahay ◽  
Brian A. Roberts ◽  
Sami Sadouni ◽  
Pierre-Antoine Béal ◽  
Cyril Septseault ◽  
...  
Keyword(s):  
Complex Geometry ◽  
Vertical Wall ◽  
Ice Sheet ◽  
Development Program ◽  
Offshore Structures ◽  
User Input ◽  
Sheet Bending ◽  
Common Framework ◽  
Multi Agent ◽  
Bending Failure

In 2012 TechnipFMC, Cervval and Bureau Veritas initiated a common development program to offer a new tool for the design of offshore structures interacting with ice combining a variety of models and approaches. This numerical tool called Ice-MAS (www.ice-mas.com) is using a multi-agent technology and has the possibility to combine in a common framework multiple phenomena from various natures and heterogeneous scales (i.e. drag, friction, ice-sheet bending failure, local crushing and rubble stack up). It can simulate the ice loadings of a drifting ice-sheet (including ridge or not) on predefined structures such as conical, cylindrical, sloping & vertical wall, artificial islands or more complex geometry by user input file like semi-submersible floaters with pontoon and columns allowing to obtain the detailed results on the different parts of the structure. This paper presents the overall functionalities of Ice-MAS and the different possibilities to model a semi-submersible floater. It will focus on the results obtained for different geometries subject to ice sheet loading through different incidence angles. The issues related to the anchoring of the platform are addressed in a simplified way.

Breaking Length of Sheet Ice Against Sloping Structure

2004 ◽  
Author(s):  
W. Feng ◽  
Z. M. Shi ◽  
L. M. Liu ◽  
F. Li
Keyword(s):  
Experimental Data ◽  
Field Experiment ◽  
Analytic Solution ◽  
Ice Sheet ◽  
Bending Moment ◽  
Moment Distribution ◽  
Breaking Length ◽  
Bending Failure ◽  
Resistant Structure ◽  
Theoretical Results

The interaction between sheet ice and sloping structure was studied. Models were built up according to the emersed part and floating part of the ice sheet respectively. Bending moment distribution in ice sheet was analyzed to determine where bending failure would occur. The analytic solution of breaking length for sheet ice was got. And some new conclusions were also deduced, which could provide reference for design and field experiment of offshore ice-resistant structure. The results in this paper are consistent with the experimental data from previous researchers. The theoretical results of this paper can directly be used in the analysis of wide inclined structures.

Ice rubble attenuation of ice loads on arctic offshore structures

1991 ◽  
Vol 28 (6) ◽  
pp. 881-895 ◽  
Author(s):  
T. T. Wong ◽  
N. R. Morgenstern ◽  
D. C. Segoz
Keyword(s):  
Finite Element ◽  
Field Measurements ◽  
Offshore Structures ◽  
Force Transmission ◽  
Offshore Structure ◽  
Element Analysis ◽  
Ice Load ◽  
Broken Ice ◽  
Transmission Capability ◽  
Ice Force

A state of the art survey of ice rubble mechanics is first presented. This survey covers ice rubble morphology, laboratory testing of ice rubble, the study of the load transmission capability of existing rubble fields, and field measurements in ice rubble surrounding offshore structures. Then, the implementation of a new plasticity model for normally consolidated broken ice into an existing finite element stress analysis code is described. The resulting program is validated using triaxial test data. Using this model, a two-dimensional parametric study on ice force transmission through a grounded ice rubble field is performed. The study shows that, in addition to the mechanical properties of ice rubble, the island or berm geometry may significantly affect the ice load. Key words: constitutive model, finite element analysis, ice load, ice rubble, offshore structure, plasticity.

Dynamic Ice Forces Analysis of Conical Structure Based on Direct Measurement

2010 ◽  
Author(s):  
Ning Xu ◽  
Qianjin Yue
Keyword(s):  
Direct Measurement ◽  
Failure Process ◽  
Video Camera ◽  
Ice Load ◽  
Conical Structure ◽  
Force Variation ◽  
Ice Force ◽  
Bending Failure ◽  
Ice Forces

The dynamic ice force is produced by failure process during ice interaction with structure. The best way for describing and modeling this process is using directly measured ice force on full scale structure in situ. In this paper, the ice force variation and corresponded failure process of ice sheet were recorded by ice load panel and video camera. It is demonstrated that when ice acting on upward narrow cone and in bending failure and well clearing by side of the cone. The form of ice force history looks like impulse signal.

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