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.

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.

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.

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.

scholarly journals Numerical Simulation of a Polar Ship Moving in Level Ice Based on a One-Way Coupling Method

2020 ◽  
Vol 8 (9) ◽  
pp. 692
Author(s):  
Bao-Yu Ni ◽  
Zi-Wang Chen ◽  
Kai Zhong ◽  
Xin-Ang Li ◽  
Yan-Zhuo Xue
Keyword(s):  
Numerical Simulation ◽  
Failure Process ◽  
Coupling Method ◽  
Crack Propagation Process ◽  
Order Of Magnitude ◽  
Level Ice ◽  
Ice Failure ◽  
Ice Resistance ◽  
Ship Speed ◽  
Good Agreement

In most previous ice–ship interaction studies involving fluid effects, ice was taken as unbreakable. Building breakable level ice on water domain is still a big challenge in numerical simulation. This paper overcomes this difficulty and presents a numerical modeling of a ship moving in level ice on the water by using a one-way CFD-DEM (computational fluid dynamics-discrete element method) coupling method. The detailed numerical processes and techniques are introduced. The ice crack propagation process including radial and circular cracks have been observed. Numerical results are compared with previous experimental data and good agreement has been achieved. The results show that water resistance is an order of magnitude smaller than ice resistance during the ice-breaking process. Ice resistance shows strong oscillation along with ice failure process, which are affected by ship speed and ice thickness significantly.

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.

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.

Microstructural Refinement in a Commercial Aluminum Alloy Processed by ECAP Using a Die Channel Angle of 110 Degrees

2015 ◽  
Vol 1114 ◽  
pp. 3-8
Author(s):  
Nicolae Şerban ◽  
Doina Răducanu ◽  
Nicolae Ghiban ◽  
Vasile Dănuţ Cojocaru
Keyword(s):  
Grain Refinement ◽  
Cross Section ◽  
High Strength ◽  
Secondary Phase ◽  
Coarse Grained ◽  
Metallographic Analysis ◽  
Second Phase ◽  
Channel Angle ◽  
Ambient Temperatures ◽  
Fine Grained

The properties of ultra-fine grained materials are superior to those of corresponding conventional coarse grained materials, being significantly improved as a result of grain refinement. Equal channel angular pressing (ECAP) is an efficient method for modifying the microstructure by refining grain size via severe plastic deformation (SPD) in producing ultra-fine grained materials (UFG) and nanomaterials (NM). The grain sizes produced by ECAP processing are typically in the submicrometer range and this leads to high strength at ambient temperatures. ECAP is performed by pressing test samples through a die containing two channels, equal in cross-section and intersecting at a certain angle. The billet experiences simple shear deformation at the intersection, without any precipitous change in the cross-section area because the die prevents lateral expansion and therefore the billet can be pressed more than once and it can be rotated around its pressing axis during subsequent passes. After ECAP significant grain refinement occurs together with dislocation strengthening, resulting in a considerable enhancement in the strength of the alloys. A commercial AlMgSi alloy (AA6063) was investigated in this study. The specimens were processed for a number of passes up to nine, using a die channel angle of 110°, applying the ECAP route BC. After ECAP, samples were cut from each specimen and prepared for metallographic analysis. The microstructure of the ECAP-ed and as-received material was investigated using optical (OLYMPUS – BX60M) and SEM microscopy (TESCAN VEGA II – XMU). It was determined that for the as-received material the microstructure shows a rough appearance, with large grains of dendritic or seaweed aspect and with a secondary phase at grain boundaries (continuous casting structure). For the ECAP processed samples, the microstructure shows a finished aspect, with refined, elongated grains, also with crumbled and uniformly distributed second phase particles after a typical ECAP texture.

An AE Investigation on Bending Failure Process of Concrete Filled CFRP-Steel Tube

2012 ◽  
Vol 20 (1-2) ◽  
pp. 33-40
Author(s):  
Liwei Zhang ◽  
Yinghua Zhao ◽  
Alan Jiang ◽  
Yilie Hou
Keyword(s):  
Failure Process ◽  
Steel Tube ◽  
Bending Failure

Development of a Probabilistic Ice Load Model Based on Empirical Descriptions of High Pressure Zone Attributes

2014 ◽  
Author(s):  
Rocky S. Taylor ◽  
Martin Richard
Keyword(s):  
High Pressure ◽  
Failure Process ◽  
Temporal Distribution ◽  
Tactile Sensor ◽  
Companion Paper ◽  
Offshore Structures ◽  
Load Model ◽  
Ice Load ◽  
High Pressure Zone ◽  
Ice Failure

During an ice-structure interaction, the localization of contact into high pressure zones (hpzs) has important implications for the manner in which loads are transmitted to the structure. In a companion paper, new methods for extracting empirical descriptions of the attributes of individual hpzs from tactile sensor field data for thin first-year sea ice have been presented. In the present paper these new empirical hpz relationships have been incorporated into a probabilistic ice load model, which has been used to simulate ice loads during level ice interactions with a rigid structure. Additional aspects of the ice failure process, such as relationships between individual hpzs and the spatial-temporal distribution of hpzs during an interaction have also been explored. Preliminary results from the empirical hpz ice load model have been compared with existing empirical models and are discussed in the context of both local and global loads acting on offshore structures.

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