RU2493323C2 - Ice-resistant platform - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: ice-resistant platform 1 comprises a lower 4 and an upper 2 truncated conical parts with tops directed accordingly up and down, and a cylindrical part 3 arranged between them. The platform is made in the form of a gravity platform, in which the total height of the upper truncated conical part and the cylindrical part makes not more than

where

is average depth of ice keel in the place of platform location. The lower truncated cone with the top has height equal to the water reservoir depth in the place of platform installation and the average depth of the ice keel. The angle α between the generatrix of the lower cone of the platform to the vertical line makes at least the angle defined from the ratio $$\alpha \ge arctg\left(\frac{gM}{n{F}_{\lim \text{}it}}\right),$$

but not less than 45°, where n - margin, F_limit - limit load shifting the platform, g - free fall acceleration; M - platform mass, containing useful mass and mass of accepted ballast.

EFFECT: stability of platform position on soil under action of a global ice load due to its minimisation and increased force that presses a platform when affected by large ice hummocks.

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Description

The invention relates to the field of shipbuilding and relates to the creation of ice-resistant gravity platforms designed for drilling and hydrocarbon production on the shelf of freezing seas.

Famous Varandey oil shipping terminal installed in the Barents Sea. The terminal has a truncated conical shape with an apex pointing upward and a multifaceted surface.

A disadvantage of the known is the increased level of ice load acting on it, due to the orientation of the cone. It is known that the ice load on the cones, the apex of which is directed upward, is substantially greater than on the cone with the apex directed downward.

Also known is a floating ice-resistant platform with an SPAR-type anchor retention system adopted as a prototype (Sazonov K.E., Kaitanov Yu.S., Klementyeva N.Yu. Comparative analysis of the characteristics of various variants of an offshore technological platform for SHGKM based on the results of model experiments / Transactions 9 International Conference and Exhibition on the Development of Oil and Gas Resources of the Russian Arctic and the Continental Shelf of the CIS Countries, St. Petersburg, 2009, vol. 1, pp. 160-164). Among the elements of the platform body shape there are two truncated cones of approximately equal diameters, the top of one of which is directed upwards and the other downward, as well as a cylindrical insert between them. A feature of such a platform is a large draft of more than 150 m.

The disadvantage of the prototype is the impossibility of its use in shallow areas of the shelf of the freezing seas due to the presence of an anchor retention system and high draft.

The present invention solves the problem of creating an ice-resistant platform of gravity type for operation in shallow areas of the freezing shelf with depths from 10 to 40 m, which has a reduced level of ice load, which, as a result, allows to reduce the weight of the ballast taken to ensure the stability of the platform on the ground.

где

- средняя глубина киля тороса в месте расположения платформы, при этом нижний усеченный конус с вершиной имеет высоту, равную разности между глубиной водоема в месте установки платформы и средней глубиной киля тороса, кроме этого, угол α между образующей нижнего конуса платформы к вертикали составляет не менее, чем определяемый из соотношения:For this, the ice-resistant platform is made in the form of a gravity platform, in which the total height of the upper truncated conical part and the cylindrical part is not more than

Where

- the average depth of the keel of the hummock at the location of the platform, while the lower truncated cone with the apex has a height equal to the difference between the depth of the reservoir at the installation site of the platform and the average depth of the keel of the hummock, in addition, the angle α between the generatrix of the lower cone of the platform to the vertical is at least than determined from the relation:

, но не менее 45°, $$\alpha \ge arctg\left(\frac{gM}{n{F}_{PRed}}\right)$$

but not less than 45 °

where n - the safety factor, F _before - limit shear loading platform, g - free fall acceleration; M is the mass of the platform, consisting of the net mass and the mass of the received ballast.

где

- средняя глубина киля тороса в месте расположения платформы для того, чтобы наиболее часто встречающиеся ледяные образования гарантированно взаимодействовали только с конусом, вершина которого направлена вниз, и цилиндрической частью платформы. Использование такого конуса позволит существенно снизить уровень ледовой нагрузки из-за различия в процессах поворота обломков льда. В случае конуса, сужающегося вверх, на него воздействуют силы тяжести обломков. В случае конуса, сужающегося вниз, на него воздействуют силы плавучести обломков, которые в 8-9 раз меньше (Лосет С., Шхинек К.Н., Гудместад О., Хойланд К. Воздействие льда на морские и береговые сооружения. СПб.: «Лань», 2010, 272 с.).The total length of the upper truncated conical part with the vertex pointing down and the cylindrical part is selected no more than

Where

- the average depth of the keel of the hummock at the location of the platform so that the most frequent ice formations are guaranteed to interact only with the cone, the top of which is directed downward, and the cylindrical part of the platform. The use of such a cone will significantly reduce the level of ice load due to differences in the processes of rotation of ice fragments. In the case of a cone tapering upward, it is affected by the gravity of the debris. In the case of a cone tapering downward, it is affected by the buoyancy forces of fragments, which are 8–9 times smaller (Losset S., Shkhinek K.N., Gudmestad O., Khoiland K. Effect of ice on sea and coastal structures. St. Petersburg: "Doe", 2010, 272 p.).

An increase in the average keel depth by a factor of 1.1 takes into account the possibility of increasing the depth of the keel of the hummock during interaction with the platform (Alekseev Yu.N. et al. Ice-technical aspects of developing offshore oil and gas fields. St. Petersburg, Gidrometeoizdat, 2001, 360 pp.).

, обусловлен тем, чтобы обеспечить как минимум одинаковое приращение сдвигающей платформу силы и удерживающей ее на месте в случае, когда на платформу подействует торос, киль которого превышает средние размеры. Такой торос будет обязательно взаимодействовать с нижним конусом. Пусть глобальная ледовая нагрузка на нижний конус будет равна F, тогда равновесие платформы будет обеспечено, когда возникающая при этом взаимодействии прижимающая платформу сила P будет равна:The choice of the angle α between the generatrix and the axis of the lower cone using the inequality: $$\alpha \ge arctg\left(\frac{gM}{n{F}_{PRed}}\right)$$

, is due to ensuring at least the same increment of the shear force of the platform and holding it in place when a hummock whose keel exceeds average dimensions acts on the platform. Such a hummock will necessarily interact with the lower cone. Let the global ice load on the lower cone be equal to F, then the equilibrium of the platform will be ensured when the force P arising from this interaction, which is pressing the platform, is equal to:

P = F _before tgα,

where α is the angle between the generatrix of the lower cone to the vertical.

Substituting one formula into another, we obtain the above requirement for the angle α. Obviously, for any calculation results, this angle cannot be less than 45 °, because in this case, the horizontal load will exceed the vertical one.

Then, when these requirements are met when the platform interacts with a larger and rarer hummock, the keel depth of which exceeds the average value for the selected water area, the platform stability on the ground will be performed spontaneously. Therefore, the calculation of the stability on the ground of such a platform should be carried out only on the action of hummocks, which has an average keel depth. This circumstance ensures minimization of the ballast necessary to ensure the stability of the platform.

The essence of the invention is illustrated by drawings, in which Fig. 1 shows an ice-resistant platform, in Fig. 2 - the process of interaction of the platform with a small hummock, and in Fig. 3 - the process of interaction of the platform with a large hummock.

The ice-resistant platform 1 contains an upper truncated conical part, tapering down 2, a cylindrical part 3 and a lower truncated conical part, tapering up 4. The surface of the upper cone 2 intersects the surface of the water 5 and interacts with the ice cover 6 and hummocks 7. The lower cone 4 is installed at the bottom pond 8.

The proposed ice-resistant platform works as follows.

(фиг.2), на ледостойкую платформу 1, киль тороса по всей его глубине, определенной с учетом его увеличения 10 в момент взаимодействия с платформой, оказывает ледовое давление только на верхнюю коническую 2 и цилиндрическую части 3 платформы.When pushing the ice cover 6 containing a small hummock 7, the depth of the keel 9 which does not exceed

(figure 2), on the ice-resistant platform 1, the keel of the hummock over its entire depth, determined taking into account its increase of 10 at the time of interaction with the platform, exerts ice pressure only on the upper conical 2 and cylindrical parts 3 of the platform.

(фиг.3), на ледостойкую платформу 1, киль тороса начинает оказывать ледовое давление не только на верхнюю коническую 2 и цилиндрическую 3 части платформы 1, но и на нижнюю коническую часть 4. При этом угол α между образующей и осью нижнего конуса выбран таким образом, чтобы возникающее при этом прижимающее усилие P с гарантией компенсировало бы возникающее горизонтальное усилие F, обеспечивая устойчивость сооружения на дне водоема 8.When pushing the ice cover 6 containing a large hummock 7, the depth of the keel 9 which exceeds

(FIG. 3), on the ice-resistant platform 1, the keel of the hummock begins to exert ice pressure not only on the upper conical 2 and cylindrical 3 parts of the platform 1, but also on the lower conical part 4. The angle α between the generatrix and the axis of the lower cone is chosen as so that the resulting pressing force P with a guarantee would compensate for the emerging horizontal force F, ensuring the stability of the structure at the bottom of the reservoir 8.

The proposed ice-resistant platform ensures the stability of its position on the ground under the action of the global ice load due to its minimization and increase in the force pressing the platform when exposed to large hummocks.

Claims (1)

An ice-resistant platform containing the lower and upper truncated conical parts with vertices directed up and down, respectively, and a cylindrical part located between them, characterized in that it is made in the form of a gravity platform, in which the total height of the upper truncated conical part and the cylindrical part is not more

where

the average depth of the keel of the hummock at the location of the platform, while the lower truncated cone with the apex has a height equal to the difference between the depth of the pond at the installation site of the platform and the average depth of the keel of the hummock, in addition, the angle α between the generatrix of the lower cone of the platform to the vertical is at least than determined from the relation
$$\alpha \ge arctg\left(\frac{gM}{n{F}_{PRed}}\right)$$

but not less than 45 °
where n - the safety factor, F _before - limit shear loading platform, g - free fall acceleration; M is the mass of the platform, consisting of the net mass and the mass of the received ballast.

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