Main Factors of Ice Sheet-Conical Structure Interaction Process Based on Field Monitoring

2009 ◽  
Author(s):  
Ning Xu ◽  
Yan Qu ◽  
Qianjin Yue ◽  
Xiangjun Bi ◽  
Andrew Clennel Palmer
Keyword(s):  
Ice Sheet ◽  
Field Work ◽  
Interaction Process ◽  
Structure Interaction ◽  
Interaction Processes ◽  
Ice Conditions ◽  
Conical Structure ◽  
Ice Loads ◽  
Ice Forces ◽  
Conical Structures

Ice-structure interaction plays a central part in determining ice loads and ice-induced vibrations. This is a controversial research issue, and many factors make the problem more complicated. The authors have been monitoring several ice resistant structures in the Bohai Sea for twenty years, and have measured ice forces and simultaneously observed ice-structure interaction processes. This paper describes typical physical ice sheet-conical structure interaction processes, field data and theoretical explanations, for different ice conditions and structure dimensions. The conclusions are more widely applicable, and we relate them to field work on ice-resistant conical structures in other ice-covered regions. Further work will quantify ice loads on conical structures once the interaction process is understood.

Results of Field Monitoring on Ice Actions on Conical Structures

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Ning Xu ◽  
Qianjin Yue ◽  
Yan Qu ◽  
Xiangjun Bi ◽  
Andrew Palmer
Keyword(s):  
Bohai Sea ◽  
Field Work ◽  
Interaction Process ◽  
Structure Interaction ◽  
Interaction Processes ◽  
Ice Conditions ◽  
Conical Structure ◽  
Ice Loads ◽  
Ice Forces ◽  
Conical Structures

Ice-structure interaction plays a central part in determining ice loads and ice-induced vibrations. This is a controversial research issue, and many factors make the problem more complicated. The authors have been monitoring several ice resistant structures in the Bohai Sea for 20 years and have measured ice forces and simultaneously observed ice-structure interaction processes. This paper describes typical physical ice sheet–conical structure interaction processes, field data, and theoretical explanations for different ice conditions and structure dimensions. The conclusions are more widely applicable, and we relate them to field work on ice resistant conical structures in other ice-covered regions. Further work will quantify ice loads on conical structures once the interaction process is understood.

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.

Numerical Simulations of Continuous Icebreaking Process With Different Heel Angles in Level Ice

2018 ◽  
Author(s):  
Feng Wang ◽  
Zao-Jian Zou ◽  
Hai-Peng Guo ◽  
Yi-Zhou Ren
Keyword(s):  
Measured Data ◽  
Interaction Process ◽  
Marine Structures ◽  
Structure Interaction ◽  
Ice Loads ◽  
Level Ice ◽  
Breaking Length ◽  
Increasing Trends ◽  
Ice Resistance ◽  
Good Agreement

Based on cohesive element method (CEM), the continuous icebreaking process with different heel angles in level ice are simulated in this paper. The simulations are established in FEM software LS-DYNA and an icebreaking tanker - MT Uikku is assumed advancing with the certain heel angle in level ice. Firstly, the comparisons are made between the simulations and the model tests for the cases with zero heel angle. A good agreement is obtained between the simulated and measured data. Then the effects of different heel angles on ice resistance and ice breaking patterns are investigated and analyzed. The results show that ice resistance, average ice breaking length and average broken channel width present increasing trends with the increase of ship heel angle. The applied methods show a wide prospect to predict ice loads on marine structures in the level ice and simulate the ice-structure interaction process.

Velocity Effects on Wide Sloping Structure Ice Loads

2016 ◽  
Author(s):  
Yihe Wang ◽  
Leong Hien Poh
Keyword(s):  
Boundary Conditions ◽  
Potential Theory ◽  
Sea Water ◽  
Ice Sheet ◽  
Dynamic Effect ◽  
Added Mass ◽  
Hydrodynamic Effect ◽  
Governing Equations ◽  
Structure Interaction ◽  
Ice Loads

Sloping structures are widely used in ice-infested waters because of their ability to reduce the ice loads by changing the ice sheet failure mode from crushing to bending. Model test data showed significant velocity effects on breaking component of sloping structure ice loads (Matskevitch, 2002), which are induced by both the dynamic effect of the ice sheet and the hydrodynamic effect of the sea water beneath the ice sheet. However, existing design codes and most models idealize the underlying sea water as a Winkler-type elastic foundation, without taking into account the velocity effects in the calculation of ice loading. The added mass concept has been utilized by researchers to incorporate the hydrodynamic effect (Sørensen, 1978; Sodhi, 1987), though the potential theory was reported to be more adequate in capturing the (additional) forces from the fluid foundation because the added mass varies with time and space (Zhao and Dempsey, 1996; Lubbad et al, 2008). In general, however, there is limited work done on the incorporation of velocity effects into the computation of ice breaking loads on sloping structures. In this paper, we study the velocity effects on ice breaking load through a two-dimensional problem. The ice-structure interaction problem is studied numerically by incorporating the dynamic effect of the ice sheet and the hydrodynamic effect of the sea water beneath the ice sheet. The ice-fluid interaction is captured by adopting the Euler-Bernoulli beam theory for the ice sheet and the potential theory for the fluid foundation, leading to a set of two governing equations with two loading boundary conditions. For ease of computation, we consider sub-problems with the same set of governing equations, each with modified loading boundary conditions. The numerical models are first validated against available analytical solutions for a simple problem before solving for the sub-problems. Finally, the solution to the original set of governing equations defining the ice-structure interaction is obtained from the superposition of the solutions to two sub-problems. Initial results show that the velocity effects can have a significant influence on ice breaking loads for wide sloping structures.

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.

On the Dynamic Interaction Between Drifting Level Ice and Moored Downward Conical Structures: A Critical Assessment of the Applicability of a Beam Model for the Ice

2011 ◽  
Author(s):  
Sjoerd F. Wille ◽  
Guido L. Kuiper ◽  
Andrei V. Metrikine
Keyword(s):  
Cross Section ◽  
Failure Process ◽  
Interaction Process ◽  
Second Phase ◽  
Floating Structure ◽  
Conical Structure ◽  
Level Ice ◽  
Ice Failure ◽  
Bending Failure ◽  
Conical Structures

Downward conical structures are believed to be an interesting concept of a floating host for oil and gas developments in deeper Arctic waters. The conical structure forces the ice to fail in bending, thereby limiting the ice loads on the structure. During the last two years, several conical structures were investigated at the Hamburg Ship Model Basin (HSVA) as part of a Joint Industry Project. This paper presents a numerical model for drifting level ice interacting with a moored downward conical structure. The goal of this development was to get insight in the key processes that are important for the interaction process between moving ice and a floating structure. The level ice is modelled as a moving Euler-Bernoulli beam, whereas the moored offshore structure is modelled as a damped mass-spring system. The ice-structure interaction process is divided into two phases. During the first phase, the ice sheet bends down due to interaction with the structure until a critical bending moment is reached at a cross-section of the beam. At this moment, the beam is assumed to fail at the critical cross-section in a perfectly brittle manner. During the second phase, a broken off block of ice is pushed further down the slope of the structure. These phases were built into one, piece-wise in time continuous model. A key result found by means of the numerical analysis of the model is that the motions of the moored floating structure do not significantly influence the bending failure process of level ice. Also the influence of the in-plane deformation and the heterogeneity of ice on the bending failure process is negligible. As a consequence, the dynamic response of the structure is for the biggest part determined by the ice failure process. Although the response of the structure can be dynamically amplified due to resonance for some particular ice velocities, no frequency locking of the ice failure onto one of the natural frequencies of the structure was observed. The model output showed qualitative agreement with the HSVA test results. It was however concluded that one-dimensional beamlike models of level ice sheets cannot accurately predict loading frequencies on downward conical moored floating structures because the ice blocks that break off are too long. Modelling level ice in two dimensions using plate theory is expected to give better results, since it takes into account the curvature of a structure and both radial and circumferential ice failure.

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.

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.

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