Ice Forces Research Articles

Sliding on ice: Real contact area, melted film thickness, and friction force

It is easy to slide on ice because of water films arising as a consequence of frictional melting. Although the friction force of ice and a slider critically depends on the area and thickness of the liquid film as well as the sliding speed, direct experimental visualization and quantification of temporal evolutions of the contact area, film thickness, and the resulting friction force have been scarce to date. Here we develop an experimental technique to visualize the contact area of ice asperities and a high-speed sliding surface in situ based on the optical principle of total internal reflection. We construct a hydrodynamic model to predict the contact area, liquid film thickness and friction force of a model system of hemispherical ice on a flat solid surface. Upon showing good agreement between theory and experiment, we briefly discuss how the fundamental understanding of the friction behavior of a single ice bump can be extended to understand the friction behavior of flat ice surfaces.

Eurasian Cooling Linked to the Vertical Distribution of Arctic Warming

AbstractObservations show that deep Arctic winter warming, extending from surface to mid‐troposphere, has concurred with below‐average temperature over central Eurasia. Modeling studies focusing on the response to Arctic sea ice loss have shown Arctic surface warming but no consistent atmospheric changes at midlatitude. Using a large number of simulations from coupled and uncoupled climate models, we show that Eurasian below‐average temperatures are more frequent in winters with deep warming compared to shallow, near‐surface warming over the Barents‐Kara Seas. Dramatic weakening of the midlatitude jet stream and increase in Ural blocking frequency are more likely to occur in winters with deep Arctic warming. Deep warming is independent of sea ice forcing but follows increased poleward atmospheric energy and moisture advection from the North Atlantic to the Arctic, indicating that internal natural variability and not sea ice is the main driving forcing for deep Arctic warming‐cold Eurasia pattern in historical simulations.

Risk assessment of sea ice disasters on fixed jacket platforms in Liaodong Bay

Abstract. Sea ice disasters seriously threaten the structural safety of oil platforms in the Bohai Sea. Therefore, it is necessary to carry out a risk assessment of sea ice disasters on oil platforms in the Bohai Sea. In this study, a risk assessment of sea ice disasters on fixed jacket platforms in Liaodong Bay, in the Bohai Sea, was performed in five steps. Firstly, the formation mechanisms of sea ice disasters were analyzed and the sources and modes of sea ice risks were summarized. Secondly, according to the calculation formulas of extreme ice force, dynamic ice force, and accumulated force, several ice indices such as thickness, motion, strength, period, and concentration were proposed as the hazard indices, and corresponding values were then assigned to the proposed indices based on ice conditions in the Bohai Sea. Thirdly, based on four structural failure modes – structural overturning by extreme ice force (Mode 1), structural fracture failure caused by dynamic ice force (Mode 2), the damage of facilities caused by dynamic ice force (Mode 3), and structural function failure caused by accumulated ice (Mode 4) – the structural vulnerability index, overturning index, dynamic index, ice-induced vibration index, and function index were proposed, and corresponding values were assigned to the structural vulnerability index of fixed jacket platforms in Liaodong Bay. Fourthly, the weight of each risk index was determined according to previously recorded sea ice disasters and accidents, and the sea ice risk was then calculated with the weighted synthetic index method. Finally, with the above index system and risk assessment methods, the risk assessment of sea ice disasters on 10 jacket platforms in three sea areas in Liaodong Bay was carried out. The analysis results showed that efficient sea ice prevention strategies could largely mitigate the sea ice-induced vibration-related risks of jacket platforms in Liaodong Bay. If steady-state vibration occurs (usually in front of the vertical legged structure) or the structural fundamental frequency is high, the structural vulnerability is significantly increased and the calculated risk levels are high. The sea ice risk assessment method can be applied in the design, operation, and management of other engineering structures in sea ice areas.

Discrete element modelling of relationship between ice breaking length and ice load on conical structure

Conical structures are widely used in marine engineering in ice-covered area because of their icebreaking capability. The ice loads acting on the conical structures are closely related to the failure modes of sea ice. The discrete element method (DEM) is adopted to simulate the ice failure modes and ice loads during the interaction between sea ice and conical structure. In this study, the accuracy of DEM simulations is validated by comparing the simulated ice loads with the measured ice loads from the model tests in Hamburg Ship Model Basin (HSVA). A bending failure occurs when the sea ice interacts on the conical structure, and the sea ice breaks into many fragments with different breaking lengths. The influence of ice thickness, ice velocity, cone diameter at waterline and cone angle are considered to analyze the characteristics of ice breaking length. The simulation results show that the ice breaking length increases with the increase of ice thickness. The increase of ice velocity and cone diameter can lead to the change of sea ice failure mode, which can reduce the breaking length of sea ice and increase the ice load. The decrease of ice breaking length indicates that the failure mode of sea ice changes from the bending failure to the crushing failure. A static ice force formula considering the effect of ice breaking length can be proposed to predict the ice load of the structure and verify the reliability of the structure.

Uncertainty assessments of structural loading due to first year ice based on the ISO standard by using Monte-Carlo simulation

Sea ice is the major source of loading for structural design in cold regions. The intrinsic properties of sea ice are generally associated with high degrees of uncertainty due to ice growth taking place during different environmental conditions for different areas. The thickness, ice strength coefficient and flexural strength of sea ice are the parameters for the calculation of ice loads. The aim of the present paper is to investigate the uncertainties associated with the ice loads, which are acting on vertical and sloping structures as calculated by the formulations in the ISO 19906 standard. The effect of correlation between the key parameters is investigated by using the Nataf transformation model. Monte-Carlo simulation techniques are applied in order to assess the uncertainties associated with the global ice loads due to ice-structure interaction. It is found that for increasing values of the positive correlation between the sea ice properties, the uncertainties of the global ice forces will increase the fractile for both vertical and sloping structures approximately up to 40% and 60% from the case with zero correlation. Moreover, for sloping structures, higher values of the sloping angles imply increasing levels of uncertainty associated with the ice loads.

Numerical simulation of ice loads on a ship in broken ice fields using an elastic ice model

The finite element method is used to simulate the navigation of an ice-area bulk carrier in broken ice fields. The ice material is defined as elastic, and the simulations are accomplished at four model speeds and three ice concentrations. The movements of ice floes in the simulation are consistent with those in the model test, and the percentage deviation of the numerical ice resistance from the ice resistance in the model test can be controlled to be less than 15 %. The key characteristics of ice loads, including the average ice loads, extreme ice loads, and characteristic frequency, are analyzed thoroughly in a comprehensive manner. Moreover, the effects of sailing speed and ice concentration on the ice loads are analyzed. In particular, the stress distribution of ice floes is presented to help understand how model speed and concentration affect the ice loads. The “ice pressure” phenomenon is observed at 90 % ice concentration, and it is realistically reflected both in the time–and frequency–domain ice force curves.

Numerical Study of the Interaction between Level Ice and Wind Turbine Tower for Estimation of Ice Crushing Loads on Structure

In this paper, the interaction between level ice and wind turbine tower is simulated by the explicit nonlinear code LS-DYNA. The isotropic elasto-plastic material model is used for the level ice, in which ice crushing failure is considered. The effects of ice mesh size and ice failure strain on ice forces are investigated. The results indicate that these parameters have a significant effect on the ice crushing loads. To validate and benchmark the numerical simulations, experimental data on level ice-wind turbine tower interactions are used. First, the failure strains of the ice models with different mesh sizes are calibrated using the measured maximum ice force from one test. Next, the calibrated ice models with different mesh sizes are applied for other tests, and the simulated results are compared to corresponding model test data. The effects of the impact speed and the size of wind turbine tower on the comparison between the simulated and measured results are studied. The comparison results show that the numerical simulations can capture the trend of the ice loads with the impact speed and the size of wind turbine tower. When a mesh size of ice model is 1.5 times the ice thickness, the simulations can give more accurate estimations in terms of maximum ice loads for all tests, i.e., good agreement between the simulated and measured results is achieved.

Antarctic temperature variability and change from station data

AbstractVariability and change in near‐surface air temperature at 17 Antarctic stations is examined using data from the SCAR READER database. We consider the relationships between temperature, and atmospheric circulation, sea ice concentration and forcing by the tropical oceans. All 17 stations have their largest inter‐annual temperature variability during the winter and the annual mean temperature anomalies are dominated by winter temperatures. The large inter‐annual temperature variability on the western Antarctic Peninsula has decreased over the instrumental period as sea ice has declined. Variability in the phase of the SAM exerts the greatest control of temperatures, although tropical Pacific forcing has also played a large part, along with local atmospheric circulation variability at some locations. The relationship of positive (negative) SAM and high (low) Peninsula and low (high) East Antarctic temperatures was not present before the mid‐1970s. Thirteen of the 17 stations have experienced a positive trend in their annual mean temperature over the full length of their record, with the largest being at Vernadsky (formerly Faraday) (0.46° ± 0.15°C·dec−1) on the western side of the Antarctic Peninsula. The deepening of the Amundsen Sea low as a result of the more positive SAM and changes in the IPO and PDO have contributed to the warming of the Peninsula. Beyond the Antarctic Peninsula there has been little significant change in temperature. The two plateau stations had a small cooling from the late 1970s to the late 1990s consistent with the SAM becoming positive, but have subsequently warmed. During spring there has been an Antarctic‐wide warming, with all but one station having experienced an increase in temperature, although the only trends that were significant were at Vostok, Scott base, Vernadsky and Amundsen‐Scott. In this season, much of the Peninsula/West Antarctic warming can be attributed to tropical Pacific forcing through the IPO/PDO.

Analysis of Offshore Structures Based on Response Spectrum of Ice Force

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.

Combined impact of Greenland sea ice, Eurasian snow, and El Niño–Southern Oscillation on Indian and Korean summer monsoons

AbstractThe combined impact of Greenland sea ice, Eurasian snow, and the El Niño–Southern Oscillation (ENSO) on the out‐of‐phase relationship between the Indian summer monsoon (ISM) and Korean summer monsoon (KSM) were investigated through numerical experiments. The results revealed that Indian and Korean summer rainfalls showed nonlinear responses to ENSO and Greenland sea ice forcing when the events co‐occurred. Above‐normal Greenland sea ice and a concurrent La Niña showed a distinct in‐phase relationship with ISM and out‐of‐phase relationship with KSM. Below‐normal and above‐normal Greenland sea ice during boreal autumn surrounded the Greenland region with anomalous low pressure and high pressure, respectively. These were associated with a barotropic +west/−east or –west/+east dipole pattern, respectively, over Eurasia during the subsequent winter and spring seasons. Furthermore, these patterns led to positive and negative snow depth anomalies, respectively, over western Eurasia and the opposite snow tendency over eastern Eurasia during the subsequent spring. This variability in Eurasian snow patterns may play a crucial role in ISM and KSM. The co‐occurrence of ENSO variability also generates high‐ and low‐pressure anomaly patterns over the Indian Ocean that may be related to unfavourable or favourable ISM, respectively, while influencing the negative or positive phases of a Pacific Japan (PJ)‐like teleconnection pattern that may be related to unfavourable or favourable KSM, respectively. Therefore, coexisting ENSO forcing may play a dominant role in ISM and KSM, but Greenland sea ice forcing and Eurasian snow variation intensify the out‐of‐phase relationship between ISM and KSM.

On a simple oscillator problem describing ice-induced vibrations of an offshore structure

In this paper, a new simple oscillator model is considered describing ice-induced vibrations of upstanding, water-surrounded, and bottom-founded offshore structures. Existing models are extended by taking into account deformations of an ice floe and a moving contact interaction between an ice rod, which is cut out from the floe, and the oscillator which represents the offshore structure. Special attention is paid to a type of ice-induced vibrations of structures, known as frequency lock-in, and characterized by having the dominant frequency of the ice forces near a natural frequency of the structure. A new asymptotical approach is proposed that allows one to include ice floe deformations and to obtain a nonlinear equation for the simple oscillator vibrations. The instability onset, induced by resonance effects for the oscillator and generated by the ice rod structure interaction, is studied in detail.

The Effect of QBO Phase on the Atmospheric Response to Projected Arctic Sea Ice Loss in Early Winter

AbstractRecent modeling studies have shown an important role for stratosphere‐troposphere coupling in the large‐scale atmospheric response to Arctic sea ice loss. Evidence is growing that the Quasi‐biennial Oscillation (QBO) can contribute to or even mitigate teleconnections from surface forcing. Here, the influence of QBO phase on the atmospheric response to projected Arctic sea ice loss is examined using an atmospheric general circulation model with a well‐resolved stratosphere and a QBO prescribed from observations. The role of the QBO is determined by compositing seasons with easterly phase (QBO‐E) separately from seasons with westerly phase (QBO‐W). In response to the sea ice forcing in early winter, the polar vortex during QBO‐E weakens with strong stratosphere‐troposphere wave‐1 coupling and a negative Northern Annular Mode‐type response. At the surface, this results in more severe Siberian cold spells. For QBO‐W, the polar vortex strengthens in response to the sea ice forcing.

A Simulation of Non-Simultaneous Ice Crushing Force for Wind Turbine Towers with Large Slopes

When the offshore wind energy industry attempts to develop in cold regions, ice load becomes the main technological challenge for offshore wind turbine foundation design. Dynamic ice loads acting on wind turbine foundations should be calculated in a reasonable way. The scope of this study is to present a numerical model that considers the non-simultaneous ice crushing failure acting on the vertical structure of a wind turbine’s foundation. The local ice crushing force at the contact surface between the ice sheet and structure is calculated. The boundary of the ice sheet is updated at each time step based on the indentation length of the ice sheet according to its structure. Ice loads are validated against two model tests with three different structure models developed by other researchers. The time series of the ice forces derived from the simulation and model tests are compared. The proposed numerical model can capture the main trends of ice–wind turbine foundation interaction. The simulation results agree well with measured data from the model tests in terms of maximum ice force, which is a key factor for wind turbine design. The proposed model will be helpful for assisting the initial design of wind turbine foundations in cold regions.

Numerical simulation of ice-induced vibrations of steady-state type

Ice force is one kind of nonnegligible external loads that nature exerts on structures. The action of drifting ice floes may induce strong vibrations of offshore structures, and further reduce the structural safety and serviceability. The aim of this article is to develop a method to simulate the most dangerous situation during the interaction between ice and structure, that is, the ice-induced vibrations of steady-state type. A simulation methodology to realize structural steady-state vibration is proposed; it can simulate a special phenomenon of negative damping. The calculation of effective ice pressure is accomplished by an empirical formula which considers the dependence of the crushing strength on the ice velocity. The most important contribution of the simulation method is to capture the steady-state vibration phenomenon. The presented simulation methodology is conducted on the same model test introduced in a referenced study to verify the efficacy. Calculational examples show good agreements with the results of the model test, and the frequency contents of the generations coincide well with the targets. They directly prove the validity of the proposed simulation method. In addition, the numerical simulation method can be used in connection with finite element programs to perform a steady-state vibration analysis of offshore structures.

Tether analyses of offshore triceratops under ice force due to continuous crushing

Oil exploration and production in ultra-deep ice-infested waters demands an innovative structural form to withstand the ice loads. Offshore triceratops is one such new-generation innovative, compliant platforms, which show good adaptability in extreme sea state conditions even under the combined action of wind, waves, and current. As tethers are the crucial components in compliant platforms like a triceratops, it is of paramount importance to study the effect of dynamic ice loads on tether tension variation. The main aim of this study is to carry out the tether tension analysis under the ice force action in different ice sea states. The ice force time history is developed from the continuous crushing ice spectral model, and numerical studies are carried out using Ansys Aqwa by applying the ice force on buoyant legs. The study reveals that the tether tension variation is less than 10% even under extreme ice sea state. The parametric studies are also carried out to assess the effect of ice velocity, ice crushing strength, and ice thickness on tether tension variation. It is found that the maximum stress developed in the wires of tethers is very less compared to the yield stress of the material, ensuring no tether failure. However, a large number of stress cycles may lead to fatigue failure of tethers. Hence, fatigue analysis is also carried out to assess the fatigue damage and service life of tethers. The results show that fatigue damage increases from normal to extreme ice sea state. The results are also compared with open-water load case. Studies carried out under lock-in ice condition shows the increase in the fatigue damage and reduction in the service life of the tethers.

How water, wind, waves and ice shape landscapes and landforms: Historical contributions to geomorphic science

Research over approximately 200 yr on the geomorphic effects of the force of water, wind, waves and ice is reviewed. In a changed scientific, technological, institutional and socio-political context, several trends emerge. Increased focus on measurement of processes from the 1930s onwards was facilitated by new technologies, leading eventually to a blurring of disciplinary boundaries and the emergence of geomorphology as an Earth system science. Human impact research and applications have blossomed and are contributing to an emerging understanding of the Anthropocene. Absolute dating techniques have reinvigorated landform and landscape evolution research, while remote sensing and geospatial science generally have enhanced observation, measurement and modeling of terrestrial and planetary surface and subsurface forms and processes. The historical record demonstrates that geomorphology has attained scientific vigour and societal relevance through fascinating journeys of curiosity, exploration, mapping, measurement, modeling and explanation.

A Modeling Investigation of Northern Hemisphere Extratropical Cyclone Activity in Spring: The Linkage between Extreme Weather and Arctic Sea Ice Forcing

Arctic sea ice exhibits rapid reductions and large fluctuations during recent decades in conjunction with a warming climate. Arctic sea ice shows a prominent seasonal cycle with the maximum extent in spring and the minimum extent in fall. In this study a suite of modeling experiments, which were solely forced with observed time-varying sea-ice concentration for spring 1979 to 2008 was conducted using NCAR’s Community Atmosphere Model to identify sea ice impacts on extratropical storms and associated surface climate parameters when they at the peak of their seasonal variability. Storms are the linkage between the large-scale circulation changes, forced by Arctic sea ice and local extreme weather events through strong winds, high precipitation, and high/low air temperature. In this study, a storm identification and tracking algorithm indicates that reduced sea-ice cover enhances Arctic storm activity. As a consequence, surface climate parameters such as surface air temperature (SAT) and precipitation increases in spring over the Arctic. The changes in the Arctic have a direct and indirect effect on the extratropical storm activity over the mid-latitudes. In contrast to the Arctic, storm activity weakens over Eurasia in the years with less sea ice. Further analysis of the surface climate indicates a warmer and dryer Eurasia for years with reduced sea ice.

Some features of modeling of massive ice-resistant supports of continental shelf structures

Development of new oil and gas waters of the continental shelf of the Far North due to the need to create a unique ice-resistant oil country waterworks. To assess the impact of the power of ice on such constructions are carried out theoretical and experimental research. One of the main issues are the issues of modeling with experimental studies. Ice, as a natural material belongs to the class of solids which is characterized by both physical and mechanical properties, but the ice consists of the same basic elements as that of ordinary water, i.e., from hydrogen and oxygen molecules. In this connection, ice scaling laws can obtain an extension of standard hydraulic methods. Phenomena called similar characteristics when one of them may be prepared by conversion of other characteristics of this phenomenon using permanent relationship, similar to the transition from one unit to another system. To ensure the similarity phenomena under the influence of ice is necessary that a hydraulic or mechanical model is completely consistent nature subject to geometrical, kinematic and dynamic similarity. The article notes that the dynamic similitude ratio Fн = Fм ∙ λF is sufficient to determine all other scale model. If all the forces manifest themselves in the same ratio for the corresponding points and points in time, the mechanical equilibrium equation will be the same on the model and in nature. This simplifies the preparation of other scales of values. Article is relevant due to insufficient knowledge of the issues of modeling of ice in model studies. Finally it is noted that complete similarity to ice model that takes into account the force of gravity for the water and ice, the inertia force and friction of water ice is thus similar in Froude.

An engineering method for simulating dynamic interaction of moored ship with first-year ice ridge

This paper aims to present a new tool to simulate dynamic ice ridge-structure interaction in 6 Dofs in time domain. The global forces caused by ice ridge as well as responses of the structure are simulated. The ice ridge loads are composed of loads due to sail, consolidated layer and unconsolidated keel. The sail load is neglected since it is small compared to the other two components. The consolidated layer could be taken as level ice. The related level ice force is simulated by integrating ice breaking force and ice accumulation force. Two ice failure modes, namely bending and crushing, are used when calculating the breaking force. A numerical model is used to calculating the ice accumulation force underwater by determining the relative horizontal positions and motions of ice rubble to the strip of the structure. The ice load due to the unconsolidated keel is calculated based on a modified theoretical model in probabilistic design. The motions of the moored ship are also applied to update the waterline of the hull at each time step to estimate precisely local contact areas between ice and hull. The simulation results are compared with model test data.

Structural Performance Analysis of Simple Offshore Platforms under Ice-Vibrations in Bohai Sea

In China, the oil and natural gas resources of Bohai Sea are mainly marginal oil fields. It is necessary to build both ice-resistant and economical offshore platforms. So, several simple offshore oil platforms with a jacket sub-structure or with a single pillar have been deployed. There are very good economic benefits in the manufacture, installation, removal, and other aspects. These platforms were primarily designed to withstand extreme static ice forces. However, sea ice motion can induce significant vibrations for the platforms in the region. The structural ice-resistant performances have not been well developed. In this paper, combined with the field monitored data of some simple platforms in Bohai Sea, ice-induced vibrations are analyzed. The results show that even though these structures may effectively resist extreme static ice forces, the ice-induced acceleration is more significant. Then, spectral-based method is provided to analyze the fatigue life of a real simple platform. Lastly, the ice-resistant strategy is presented, which provides a basis for the design of these platforms in ice zone.