Figure 5
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Ice gouging is a dangerous natural process typical for the coastal-shelf zone of the Russian Arctic; because it leads to damaging of the infrastructure it can also be related to the category of catastrophic processes. To lower the risks of occurrence and to prevent emergencies and their consequences, comprehensive monitoring of the dangerous natura...
Context in source publication
Context 1
... this case, ice gouges form a so- called "comb", usually oriented normal to the coastline due to the pressure of ice from the open sea. In 2007, during sonar tracking from the research vessel Ivan Petrov, such a "comb" was observed with dimensions of approximately 70 m wide and 400 m long; it consisted of a system of parallel ice gouges up to 1,5 m deep ( Figure 5). Ice gouges are well preserved at this depth. ...
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Citations
... Over the past 50 years, there has been a tendency for the ice-free period to increase [24]. The sea ice of Baydaratskaya Bay consists of fast ice along the coast and drift ice offshore [25]. The maximum fast ice rim position generally varies in the range of sea depths of 10-20 m [26]. ...
... The wind and currents are the driving forces of ice drift. During the winter season, southerly and southwesterly winds prevail in the Baydaratskaya Bay area [25]. The currents here are associated with semi-diurnal tides and they are practically reversive and aligned along the axis of the bay. ...
... The currents here are associated with semi-diurnal tides and they are practically reversive and aligned along the axis of the bay. The maximum speed of the tidal current during the tidal cycle is 0.5 m/s, while the measured maximum current speed is 1 m/s [25]. Sea level fluctuations are associated with tides (up to 1.1 m) and storm surges (up to 2 m). ...
Ice scours are formed when the keels of floating icebergs or sea ice hummocks penetrate unlithified seabed sediments. Until now, ice scours have been divided into “relict” and “modern” according to the water depth that corresponds with the possible maximum vertical dimensions of the keels of modern floating icebergs. However, this approach does not consider climatic changes at the present sea level, which affect the maximum depth of ice keels. We present an application of 210Pb dating of the largest ice scour in the Baydaratskaya Bay area (Kara Sea), located at depths of about 28–32 m. Two sediment cores were studied; these were taken on 2 November 2021 from the R/V Akademik Nikolay Strakhov directly in the ice scour and on the “background” seabed surface, not processed via ice scouring. According to the results of 210Pb dating, the studied ice scour was formed no later than the end of the Little Ice Age. Based on the extrapolation of possible sedimentation rates prior to 1917 (0.22–0.38 cm/year), the age of the ice scour is estimated to be 1810 ± 30 AD. The mean rate of ice scour filling with 70 cm thick sediments from the moment of its formation is around 0.33 cm/year.
The problem on a stress-strain state of the offshore pipeline buried in sandy soil, which arises during the process of gouging the soil by keels of ice formations, is considered. It is known that from the point of view of numerical modeling, the study of ice gouging for sandy soils is more complex than for clay, since the resulting sliding surfaces are essentially narrower in the fi rst case. A fi nite element model of the soil-keel-pipe system
is proposed and implemented in LS-DYNA program complex for solving the problem. Within the framework of the model the soil is assumed to be elastoplastic with the Mohr–Coulomb yield surface and non-associated flow rule, the pipe is assumed to be linear elastic, while the keel is taken as a rigid body. The soil is modeled on an Eulerian
mesh, the pipe and keel are modeled on Lagrangian fi nite element meshes. Additional elements with nonlinear spring properties are used to describe the interaction of the pipe with the soil outside the boundaries of the Eulerian mesh. To fi nd diagrams of deformation of the springs, the results of specially conducted numerical calculations are used. The features of deformation of the considered system under ice gouging for the pipes of different sizes both in the presence and in the absence of the inner pressure are studied. The simulation results correspond to the expected deformation pattern of the system: deformation of the soil beneath the keel forces the pipe to bend, and the bending plane is not parallel to the horizontal plane, but is inclined to it at some angle, since the points in the subgouge active zone are displaced both in the direction of the keel movement and deep into the soil. It is shown that after passing the keel over the pipe there is a tendency to return the pipe to its original position. The maximum displacements, strains and stresses in the pipe are achieved at the time of passage of the keel on it. The values of maximum displacements and effective stresses arising in the buried pipeline during ice gouging are found and compared with each other
on the example of pipes of characteristic sizes
Рассматривается задача о напряженно-деформированном состоянии морского трубопровода, заглубленного в песчаный грунт, реализующемся в процессе выпахивания (экзарации) грунта килями ледяных образований. Известно, что с точки зрения численного моделирования песчаный грунт является более сложным по сравнению с глинистым, поскольку возникающие поверхности скольжения в первом случае имеют существенно меньшую толщину, чем во втором. Для решения задачи предложена и реализована в программном комплексе LS-DYNA конечно-элементная модель системы «грунт – киль – труба». В рамках модели грунт предполагается упругопластическим, удовлетворяющим критерию текучести Кулона – Мора и неассоциированному закону течения; труба
предполагается линейно упругой; киль считается абсолютно твердым. Грунт моделируется на эйлеровой сетке, труба и киль – на лагранжевых конечно-элементных сетках. Для описания взаимодействия трубы с грунтом за пределами границ эйлеровой сетки используются дополнительные элементы со свойствами нелинейной пружины. Для нахождения диаграмм деформирования пружин используются результаты специально проведенных численных расчетов. Исследованы особенности
деформирования рассматриваемой системы в процессе ледового выпахивания для труб различного размера как при наличии, так и при отсутствии в них давления. Результаты моделирования соответствуют ожидаемой картине деформирования системы: деформирование грунта под килем приводит к изгибу трубы, причем плоскость изгиба не совпадает с горизонтальной плоскостью, а наклонена к ней под некоторым углом, поскольку точки трубы в активной зоне выпахивания смещаются как в направлении движения киля, так и вглубь грунта. Показано, что после прохождения киля над
трубой наблюдается тенденция возвращения трубы в исходное положение. Максимумы перемещений, деформаций и напряжений в трубе достигаются в момент прохождения над ней киля. На примере труб характерных размеров найдены и сопоставлены друг с другом значения максимальных
перемещений и эффективных напряжений, возникающих в заглубленном трубопроводе в процессе ледового выпахивания.
