Ice collars around freezing in the ice hydrotechnical structures

. Arctic engineering projects pose unique challenges due to severe cold conditions and the presence of ice. Among the critical factors affecting offshore constructions in these regions, ice loads stand out as a primary concern. Accurate estimation of ice loads is essential to ensure safe and cost-effective operation of marine structures in icy environments. One specific ice formation that significantly influences the total design load on marine structures is the ice collar. Ice collars are thicker thermodeveloped ice formations that occur around marine structures with high thermal conductivity when level ice stops moving. The presence of ice collars can considerably alter the total load on the structure, demanding careful consideration during the design process. Various methods to manage ice collars' impact on marine structures exist, including mechanical removal, specialized cover layers, heating systems, and design adaptations. Numerical modeling proves valuable in predicting ice collar growth and its influence on load distribution. Implementing appropriate mitigation strategies ensures the continuous operability and structural integrity of marine installations in ice-prone regions.


Introduction
Arctic regions present a unique set of challenges for engineering projects, particularly when it comes to the construction and operation of marine structures.The severe cold conditions, freezing temperatures, and the presence of ice make Arctic engineering projects complex and demand specialized designs to ensure the safety and efficiency of these structures [1][2][3][4].Among the critical factors that engineers must contend with are ice loads, which can significantly influence the behavior and performance of offshore constructions in icy environments.Ice loads arise from the interaction between marine structures and ice formations, such as level ice and icebergs, and play a pivotal role in the structural design and operation of these facilities.Proper estimation of ice loads is crucial to avoid overdesigning and unnecessary expenditure, while ensuring the safe exploitation of the structures in harsh Arctic conditions.One specific ice formation that can profoundly affect the total design load on marine structures is the ice collar [5][6][7].An ice collar is a unique ice formation that occurs around marine structures with high thermal conductivity, particularly when level ice stops moving.Unlike the majority of ice action scenarios, where level ice is in motion and behaves differently, the formation of ice collars leads to distinct load changes on the structure [8][9].Ice collars create increased ice-structure contact areas, resulting in higher loads being transferred to the structure when the level ice resumes movement.Understanding the influence of ice collars is vital for engineers to make accurate calculations and design structures that can withstand the additional loads imposed by these formations.Accurate determination of the size and shape of ice collars is critical to ensure structural integrity and to optimize the performance of marine structures.For this purpose, numerical modeling emerges as a valuable tool, allowing engineers to simulate ice collar growth and its influence on load distribution.The presence of ice collars also has implications for moorage operations and the functionality of vessels operating in icecovered waters.Ships moored for extended periods during the cold season may experience ice collars forming on their hulls and moorage walls, potentially hindering departure or complicating moorage procedures.In areas with tidal currents, the occurrence of ice bustles further complicates moorage operations, necessitating strategic planning and the implementation of measures to manage ice collar effects effectively.To prevent undesirable effects from ice collars, a range of mitigation strategies can be implemented.One traditional method is the mechanical removal of accumulated ice, which is cost-effective and does not require complex structural changes.However, other approaches involve the use of specialized cover layers, such as anti-adhesion coatings, to reduce the ice-structure contact forces.While these coatings can be effective, their current high cost and susceptibility to ice abrasion may require regular renewal.For critical structures where reliable functionality is paramount, heating systems can be utilized to prevent ice accumulation on structure walls.These heating systems can be implemented as either preventive measures or applied after ice collar formation to remove accumulated ice, ensuring the continuous operation of structures in ice-prone environments.In addition to employing these mitigation strategies, the design of marine structures can be adapted to accommodate the presence of ice collars.This may involve changes in the ice failure mechanism, the incorporation of devices to remove excess ice, or other constructive measures aimed at improving the structure's ability to handle ice collar effects.Ice collars play a significant role in altering the total design load on marine structures operating in icecovered Arctic environments.A combination of numerical modeling, mitigation strategies, and thoughtful design adaptations is essential to enhance the resilience and safety of marine structures in the face of ice collar challenges [10][11].

Analysis
Ice collar is thicker thermodeveloped ice formation that occurs around marine structures with high thermal conductivity (fig.1).In colder regions, such as the Arctic or Antarctic, marine structures like offshore platforms, oil rigs, and vessels are exposed to sub-zero temperatures and are in contact with freezing seawater.Due to their high thermal conductivity, these structures can cause localized freezing of the surrounding seawater.
As a result of this localized freezing, the seawater in direct contact with the marine structure freezes at a higher rate compared to the surrounding seawater.Over time, this process leads to the formation of thicker ice around the structure, which is known as an ice collar (when sea water level doesn't change significantly).The ice collar typically has a more substantial thickness compared to the surrounding ice pack, and its growth may continue as long as the thermal conditions and structural characteristics support it.
The presence of ice collars can present challenges for marine structures, including increased of ice loads and changes in the structural functionality and dynamics.Therefore, engineers and designers must consider these factors when planning and constructing marine structures in ice-prone regions.Strategies such as ice-resistant design, de-icing systems, and ice management and removal techniques may be employed to mitigate the impact of ice collars on the performance and safety of marine structures.
Ice collars play a crucial role in altering the total design load on marine structures when they are frozen in ice-covered environments.These ice formations enforce contact between the ice and the structure, and in some cases, they can even influence the ice failure scenario.Normally, the load from level ice on offshore structures is calculated considering the moving level ice scenario, where the structure cuts through the ice, forming a trench behind it and eliminating pulling forces in that area.
However, when ice collars form around the structure and cause the level ice to stop moving, the ice-structure contact area increases significantly.This can result in a higher load being transferred to the structure when the level ice starts moving again.The growth of ice all around the structure further complicates the situation, leading to pulling occurring behind the structure during the initiation of new movement in the level ice.
Another challenging situation arises when a ship is moored for an extended period during the cold season.Ice collars develop on both the ship and the moorage wall, potentially preventing the ship from leaving or hampering moorage operations if the ice collar grows on the moorage wall before the ship is moored.In areas with tides, the presence of ice bustles can further complicate moorage operations, posing significant challenges to ship movement and positioning.
The key concern for engineers is accurately determining the shape and sizes of ice collars, as they have a direct impact on the loads imposed on the frozen structures.Calculation of ice collar sizes is thus of utmost importance to ensure the safe and efficient operation of marine structures in ice-prone environments.When marine structures freeze in ice-covered environments, it can have significant implications for the loads the structure experiences from the ice.The freezing of ice around marine structures can lead to several key effects that influence the loads: The accumulation of ice on the structure adds weight to it.This additional weight can increase the loads the structure must bear and may require consideration during the design phase to ensure the structure can withstand the increased loads without compromising its integrity.
As ice forms and expands around the structure, it exerts pressure on the structure's surfaces.This pressure is known as ice pressure.Depending on the ice thickness and other factors, the ice pressure can vary significantly.Structures must be designed to withstand these pressures to prevent damage or failure.
During freezing, the ice can create thermal stresses on the marine structure.When water freezes, it expands, and this expansion can exert stress on the structure's surfaces.Repeated freezing and thawing cycles can also induce cyclic thermal stresses, which may lead to fatigue issues over time.
The presence of ice on the structure can alter its dynamic response to external loads, such as wave action or tidal forces.The ice may act as a damping agent, reducing the structure's natural frequency and altering its response characteristics.Tidal currents can affect the ice load on the structure.
To mitigate the effects of ice collars on structures and moorage operations, engineers need to consider various factors.Proper numerical modeling techniques can aid in predicting ice collar development and its influence on load distribution.Design modifications, such as the inclusion of de-icing systems or the use of specialized low adhesion covers, may be considered to manage the impact of ice collars effectively.To mitigate the adverse effects of ice collars, various measures can be implemented.One traditional approach involves mechanically removing the accumulated ice.This method offers the advantage of being cost-effective and does not require complex structural modifications.Another strategy to reduce the impact of ice collars is to use special cover layers, such as specialized paints, which lower adhesion forces between the ice and the structure.While this approach can be effective, the current high cost of these covers and their susceptibility to ice abrasion necessitate regular renewal for sustained effectiveness.
For critical structures that must function reliably at all times, heating systems can be employed to prevent ice accumulation on the structure walls.Heating can be implemented as a preventive measure or applied after ice collar formation to remove the accumulated ice.This approach ensures continuous operability of the structure even in ice-prone environments.In some cases, the design of the structure itself can be adapted to accommodate additional ice accumulation.This may involve altering the ice failure mechanism, incorporating devices to remove excess ice, or implementing other constructive measures.By making these modifications, the structure can better handle the effects of ice collars and ensure its overall stability and performance.

Conclusion and discussion
Arctic port constructions require special considerations and designs due to the severe cold conditions and the presence of ice.Among the critical factors for offshore constructions in such environments, ice loads stand out as a paramount concern.Accurate estimation of ice loads is essential to ensure the safe operation of structures without incurring unnecessary costs.While ice collars represent specific ice formations that may not be present in all ice action scenarios, their potential occurrence must be taken into account, as they can significantly alter the total load on the structure.
To calculate ice collars and assess their impact, numerical modeling is a valuable tool.The model typically includes a water basin domain with the structure, and the calculations are performed over a specified time period.The choice of the time frame for consideration should be based on real environmental conditions at the site and the maximum duration the structure could freeze in the ice.The numerical simulation yields a temperature distribution, enabling the determination of ice collar volume and dimensions.The size of the ice collar in relation to the surrounding ice directly influences the increase in ice load on the structure when it is encased in ice.Depending on the ice action scenarios being considered, ice collars can play a significant role in the total load on the structure.For structures designed to withstand ice, additional ice collar loads might be accounted for.Furthermore, it is crucial to consider the nature of the loading, as regular loading does not encompass pulling forces.Therefore, for structure paneling covers, such as pin connections, adhesive pulling forces must be taken into account.In some instances, the structure may be designed for cutting ice scenarios, but if the ice adheres to the structure, the cutting scenario may not be applicable.Thus, the potential growth of ice collars on the structure's surface and their influence on primary interaction scenarios should be thoroughly analyzed.
If ice collars can impact the possible interaction scenarios, decisions must be made on how to mitigate their effects.If the structure is already designed to withstand stronger ice actions, additional measures may not be necessary, except in cases where moorage to the structure could be hindered.Options such as heating systems, special low adhesion covers, or other tailored measures can be considered to manage ice collar effects effectively.