RU2191132C1 - Marine semi-submersible platform of high wave resistance - Google Patents

Abstract

FIELD: shipbuilding; semi-submersible platforms. SUBSTANCE: proposed marine semi-submersible platform includes upper working structure on which main equipment is arranged depending on purpose of platform (for example, drilling equipment; two rows of columns at section S_c and height H_c, which carry upper working structure ; two pontoons having volume V_p and height H_p, which give support for columns; these pontoons are also used for mounting the power plant, fuel tanks and ballast tanks; horizontal strips of wing profile found between pontoons perform function of strength members and other special functions. When ballast tanks are blown-off, platform is in surface cruise position at draft T_w and preset transverse metacentric height and reserve of buoyancy. When ballast tanks are filled, platform lowers to semi-submersible position at draft T_er, and preset transverse metacentric height and reserve of buoyancy. Proposed invention includes mathematical relationships for determination of total height and cross-section area of columns, distance between columns along pontoons, volume and height of pontoons and distances between them, volume of ballast tanks and permissible height of center of mass of platform according to preset payload, rated height and length of waves, preset reserve of buoyancy in cruise position, as well as metacentric heights for cruise and working position. EFFECT: minimization of wave disturbance forces acting on platform in design range of swell and motions, as well as its displacement at simultaneous satisfying of requirement imposed on reserve of buoyancy, stability and seaworthiness. 3 cl, 2 dwg

Description

 The invention relates to floating technical devices that are required to function reliably in conditions of sea waves up to 5-7 points, inclusive, in compliance with increased requirements to minimize vertical and angular vibrations of the platform itself, as well as its wave drift. Semi-submersible offshore platform (PMP) can be used to deliver ballistic missiles to the launch site and launch artificial Earth satellites into near-earth orbit, place intelligence and mining tools on it from the sea bottom, helicopter landing site, and perform other functions on waves.

 Known self-propelled marine platform for launching ballistic missiles: Ocean launching apparatus for space rockets IR Patents, Application GB 2187680 A (analogue 1). It includes a transport ship dock carrying two launch platforms with a launching device and storage of spare missiles, a crane unit and a tugboat. All of them are located on the deck of the transport ship-dock. Actually launching platforms have an upper working deck, which is held by four vertical cylindrical columns. The columns themselves below are supported by ship-shaped rams that play the role of pitching dampers.

 This semi-submersible offshore platform is used as follows: a dock transport vessel enters the area of the proposed launch and immerses so that the launch platforms, the crane platform and the tugboat emerge from the dock deck. Then the tug pulls out the crane and launch platforms in sequence. They plunge along the launch waterline and prepare to launch missiles. The main drawback of this entire design is its complexity and the long time from the start of the operation of the ship’s diving to the launch of the rocket for at least 10 hours. During this time, a significant disturbance may appear at sea, and the launch will be frustrated. In addition, this patent does not stipulate conditions for the dimensions of columns, rams and their deepening, namely, the relationship between the geometric dimensions of columns, rams and their deepening determines the parameters of the vertical and angular pitching of the PMF and its horizontal displacement - wave drift.

 A technical solution is known for the patent 2011599 (Razumeenko Yu.V., Pylnev Yu. V. Semi-submerged base of offshore structures. RF patent 2011599 with priority 08.07.91), which leads to a significant reduction in wave perturbing forces (4-5 times) acting on semi-submerged marine objects, due to giving them a special wave-resistant shape (analogue 2). In accordance with the recommendations of the patent 2011599 in the operating position of the PMP, the upper working structure (WRC) and the deck of the pontoons should be removed from the calm surface by 1.2-1.5 amplitudes of the calculated wave (3-5 m, not 25-30 m, as is customary in most modern PMP), and the optimal volume of pontoons should be consistent with the estimated wavelength, the total area of the vertical columns and their depth. However, the ideas of this technical solution did not find application in the well-known PMP designed to launch ballistic missiles.

 A technical solution is known for a / c 1320327 of the USSR (Simkin L.M., Polyak K.V. Deepwater support, a / c 1320327, bull. 24, 1987) (analogue 3), which neutralizes the wave drift forces of semi-immersed marine objects. In accordance with recommendations of a / c 1320327, rigidly interconnected PMF columns should be located at a distance of half the length of the calculated wave.

 The closest in technical essence to the claimed invention is a semi-submerged shelf structure (PSC) according to the patent (Semi-cabmersible offshore structure IR Patent application GB 2184402 A) - prototype.

It contains:
1. The upper working structure on which equipment can be located that determines the purpose of the entire PMP (for example, drilling wells at the bottom of the sea, launching rockets, etc.).

 2. Two rows of vertical displacement columns that support the upper structure above the water.

 3. Two ship-shaped pontoons on which the columns rest. Ballast tanks are located inside the pontoons, filling which the PShS is lowered into a semi-submerged operating position. A power plant may be located in the pontoons, and then the PMP will be self-propelled.

 In the description of the prototype patent, there is a statement that the dimensions of the pontoons and columns are selected from the conditions for neutralizing the Frud-Krylov forces by diffraction forces, which (in the opinion of the author of the patent) have the opposite sign to these forces.

 There are also many options for the location of the columns, a mention is made of the need to ensure PShS stability. However, no quantitative ratios are given either in the description or in the formula. The prototype does not have any constructive measures to neutralize the horizontal wave forces causing wave drift from the occupied place.

 For semi-submersible offshore platforms of any purpose, a serious problem is ensuring the stability of the PMF in cruising (when the air defense system is located high above the water) and in a semi-submerged working condition. The surface position is important for parking in the base at a relatively small depth of the port water area, semi-submerged - during operation. However, the patent search did not reveal the conditions under which the horizontal section and deepening areas of the columns, the waterline area of the pontoons at the surface of the PMP and the distance between the columns and the pontoons, the permissible elevation of the center of mass of the PMP in height above the main plane, which would guarantee metacentric requirements, should be obeyed height in surface and semi-submerged working condition.

 An analysis of the prototype description shows that it is impossible to create a wave-resistant platform on it without additional conditions and correcting inaccuracies in the theoretical model of the effect of waves on semi-submerged sea objects.

- ее частота, τ и λ - период и длина волны. Силы эти пропорциональны суммарной площади сечения колонн ∑S_k, амплитуде волны А_о и изменяются в фазе с волной.As shown in the article (Razumeenko Yu.V., Pylnev Yu.V. The principle of structural compensation of wave disturbing effects on the semi-submerged foundations of offshore structures. Collection of reports of the international conference. S.-P. Marine Technical University, 1994, p.148-158) , on a semisubmersible platform consisting of vertical columns and pontoons of the type of Fig. 1, the following wave action components act in the vertical direction:
1. Quasistatic F _y ^hs (Archimedes forces) from moving along the columns of the wave profile y _w = A _о cos (kx + ωt), where A _о is the wave amplitude,

- its frequency, τ and λ - period and wavelength. These forces are proportional to the total column cross-sectional area ∑S _k , the wave amplitude A _о and change in phase with the wave.

2. Inertial-wave forces F _y ^iw = F _yk ^iw + F _yn ^iw on columns and pontoons. They include the Krylov forces from changes in the dynamic pressure wave field and the inertial part of the diffraction forces. These forces are proportional to the accelerations in the wave at the level of the center of buoyancy (center of magnitude) of the columns and pontoons, as well as their displacements to the attached masses. Since accelerations are ÿ = -ω ² ÿ _w , then F _y ^iw always have the opposite sign to F _y ^hs , and they can be used to neutralize the forces of Archimedes.

3. Damping (speed) forces F _y ^d including viscous, separated and wave diffraction components on columns and pontoons F _y ^d . They are proportional to the vertical velocity at the center of buoyancy of the pontoons and columns at and damping coefficients and F _y ^hs ahead in phase by π / 2.

 4. Suction forces of the entire PMF to the surface, resulting from rarefaction in the wave field, which decreases with distance from the free surface. These forces are independent of time and act vertically upward, causing a slight subsurface of the PMF relative to the equilibrium static waterline. Usually these forces are small and are not taken into account in pitching tasks. If necessary, suction forces can be compensated by the intake of a certain amount of water in equalization tanks.

суммарное выражение для волновой возмущающей силы имеет вид:

(1)
где Т_к - осадка колонн, расстояние от свободной невозмущенной поверхности до верхней палубы понтонов;
∑S_к - суммарная площадь горизонтального сечения колонн;
H_п и V_п - высота понтона и его водоизмещение;
k_ук и k_уп - коэффициенты присоединенных масс колонн и понтонов;
N_ук и N_уп - коэффициенты демпфирования колонн и понтонов.Taking into account

the total expression for the wave disturbing force is:

(1)
where T _to - sediment columns, the distance from the free undisturbed surface to the upper deck of the pontoons;
∑S _к - total area of horizontal section of columns;
H _p and V _p - the height of the pontoon and its displacement;
k _yk and k _yn are the coefficients of the attached masses of columns and pontoons;
N _yk and N _yn - damping coefficients of columns and pontoons.

 As shown by experimental studies, the damping component (the term in front of sinωt) is no more than 20-25% of the inertial-wave ones, and with increasing frequency its role decreases even more, but does not vanish. Therefore, the statement of the author of the patent prototype that it is possible to nullify the disturbing force is erroneous. In principle, it is impossible to nullify, but it is possible to substantially reduce it. The term in front of cosωt by matching the area of the columns and the dimensions of the pontoons can be turned to zero, which reduces the total force by 4-6 times in comparison with marine objects of traditional ship forms, the same as the PMP displacement.

 It follows from (1) that the efficiency of a pontoon (damper) in neutralizing quasistatic disturbing forces is higher, the closer it is to the surface. In the majority of existing PMFs, pontoons are located at a distance of 30-40 m from the upper platform, and in working condition they are 25-30 m away from the surface. The wave hardly penetrates at such depths, and these pontoons work as passive dampers without reducing disturbing forces, but only increasing the resistance to vibrations and inertia of the whole structure. It was under this scheme that the Sea Launch self-propelled platform was created, created by a joint project of the USA, Norway, Russia and Ukraine at the Vyborg Shipyard to launch artificial Earth satellites.

 The main disadvantage of the prototype and other similar technical solutions is the relatively low stabilization efficiency of the PMP pitching and unnecessarily large displacement. The basis of these decisions is a small cross-sectional area of the columns and deep-damped dampers - pontoons. The small area of the waterline does not produce large wave perturbing forces, and in combination with large pontoons significantly reduces the frequency of natural oscillations, making it 1.5-3 times less than the frequency of the calculated waves. Such a platform filters wave disturbances, but it is very sensitive to load changes. And because of the large height of the columns and their small cross-section, problems arise with ensuring the stability of the PMP in cruising and working positions. In addition, the questions of the PMF wave displacement in the horizontal position remain open.

 The objectives of the present invention is the minimization at a given payload of the wave perturbing forces acting on the PMF in the calculated range of waves and pitching of the PMF, as well as its displacement while satisfying the requirements for the margin of buoyancy, stability and seaworthiness.

 These goals are achieved by the fact that in a semi-submersible offshore platform containing an upper working structure supported by two rows of vertical columns supported by two ship-shaped pontoons, inside which there are ballast tanks and a power plant, the geometric dimensions of the pontoons and columns, the distance between them, draft, tank volumes of the main ballast and the position of the center of mass of the PMF are determined on the basis of the simultaneous fulfillment of the buoyancy conditions for a given payload, stability, and sea Nost, volnostoykosti and low pitching.

The appearance of the PMP and its structural elements are shown in figures 1 and 2. PMP includes:
1 - the upper working structure (WRC), on which the equipment is installed that determines the purpose of the PMP;
2 - columns in an amount of at least 2 on each pontoon;
3 - two pontoons of a ship's uniform;
4 - upper connecting bonds between the pontoons, giving rigidity to the catamaran;
5 - lower connecting connections between the pontoons having a wing profile; they give rigidity to the connection of the pontoons, and also improve the propulsion and seaworthiness of the PMP;
6 - horizontal plates on columns, performing the role of additional dampers.

The condition of the wave resilience of the PMF, the indefinability of the WRC and the non-exposure of the pontoons in the working position of the platform is achieved by the fact that the height of the columns from the bottom of the WRC to the upper deck of the pontoons N _to is assigned within 1.35-1.5 of the estimated wave height h _p . The platform in working condition is balanced by water ballast so that its waterline runs in the middle of the column. Such a technical solution at the same time provides the greatest efficiency for the pontoons to neutralize quasi-hydrostatic wave forces acting on the columns. The novelty and fundamental difference of this solution from the known one is that the total column height H _k , for example, for a design wave of 5-6 points, is in the range of 4.5-7 m, and not 30-40 as in existing, for example, oil-producing PMF .

To minimize F _yΣ, it is necessary in (1) to neutralize the expression in square brackets before cosωt.

где V_п - водоизмещение понтона при его полном погружении;
Н_п - высота понтона, которая может быть назначена по конструктивным соображениям, например из условий размещения и обслуживания энергетической установки,
k_уп=0,8-1,1 - коэффициент присоединенной массы понтона, зависящий от его формы и частоты волны,
λ_p - расчетная длина волны.Since the wave height h 3% of the coverage is ~ 0.06 of the average wavelength λ, and 1% of the coverage is 0.1λ, the draft T is selected as half the column height H _k , and the latter as (1.35-1.5) h _p , then using the statistical dependences for both h _3% and h _1% , as well as the conditions for choosing H _k = 1.5h _3% and H _k = 1.35h _1% , it is possible (1) to resolve relatively unknown pontoon sizes and obtain conditions for choosing its optimal size

where V _p - displacement of the pontoon when it is completely submerged;
N _p - the height of the pontoon, which can be assigned for design reasons, for example, from the conditions of placement and maintenance of the power plant,
k _yn = 0.8-1.1 is the coefficient of the attached mass of the pontoon, depending on its shape and frequency of the wave,
λ _p is the calculated wavelength.

 Expression (2) connects the volume of the pontoon required by the wave resistance with its reduced height, the total horizontal sectional area of the columns and the calculated wavelength.

An additional means of increasing the stability of the PMF in the wave is the installation on the columns of annular external flat plate dampers. They increase the attached masses of the columns and reduce the disturbing effect of the wave on the PMF. Experimental studies have shown that the appropriate width of this ring should be in the range (0.06-0.1) b _k , where b _k is the width (diameter) of the column.

Displacement PMP in cruising position is determined from the equations
V _cr = 2 (1 + k _sn ) ^-1 • V _p = 2δ _cr L _cr B _cr T _cr (3)
ρV _cr = m _ng + m _sg (4)
where k _zp = 0.15-0.20 - the buoyancy margin of the pontoon when cruising the PMP;
δ _cr - the coefficient of the overall completeness of the pontoon for cruising;
L _cr , In _cr , T _cr - the length, width and average draft of the pontoon in a cruising position;
ρ is the density of sea water;
m _ng is the sum of the masses of loads given and accepted for structural reasons (weapons, drilling equipment, anchor devices);
m _zg - the mass of goods, depending on the size and shape of the PMF, the given speed, range, and other technical characteristics (hull, systems, power plant, etc.).

Since the volume of one pontoon is V _p = N _p S _p , which is determined by expression (2), then for the given (or accepted) buoyancy margin k _zp according to (3) and (4), the required cruising displacement is found.

The displacement of the PMP in the working position with semi-immersed columns will be determined by the equation:
V _p = 2V _p + H _to ΣS _to (5)
The volume of tanks of the main ballast required to transfer the PMP from the cruising to the working semi-submerged position along the waterline W _p L _p must be equal
V _CCH = 2k _sinh V _n + H _to ΣS _k (6)
These tanks should be located inside the pontoons and lower the center of mass of the PMP in working condition.

Ensuring the transverse stability of the PMP in the cruising position requires the fulfillment of the condition
z _c + r _{cr cr} - z _{g cr>} h _{cr bottom} (7)
where z _{c cr} - the elevation of the center of buoyancy of the pontoon above the main plane;
z _{g cr} - the elevation of the center of mass of the PMF above the main plane;
r _cr - the transverse metacentric radius, which for the catamaran design of the PMF is r _cr = (2i _xп + 2S _cr Y _p ² ) V _cr ;
i _xp - own moment of inertia of the area of the cruising waterline of one pontoon;
y _p is the removal of the central longitudinal axis of the pontoon from the central longitudinal axis of the PMP.

Для понтонов, близких по форме к параллелепипеду, что характерно для ПМП, z_{с кр}≈(0,55÷0,65)Т_кр; α_кр/δ_кр≈1,05÷1,15. При В_кр/В_к<0,5, что обычно для ПМП, выполняется,

. Это позволяет получить условие на допустимое возвышение центра масс ПМП в крейсерском положении при заданной поперечной метацентрической высоте h_{кр зад}.Taking into account S _cr = α _cr L _cr B _cr , where α _cr - coefficient of completeness of the cruising waterline; _Xn i = α L _{cr cr cr} At ^3/12, V = 2δ _{cr cr cr} L B T _{cr cr} and y _p = B _k / 2 to obtain the metacentric radius

For pontoons that are close in shape to a parallelepiped, which is typical for PMP, z _{with cr} ≈ (0.55 ÷ 0.65) T _cr ; α _cr / δ _cr ≈1.05 ÷ 1.15. When В _кр / В _к <0.5, which is usually for PMP,

. This allows you to get a condition on the permissible elevation of the center of mass of the PMP in the cruising position for a given transverse metacentric height h _{cr ass} .

Выражение (9) позволяет связать z_{g кp} с заданным значением поперечной метацентрической высоты, осадкой и расстоянием между понтонами.

Expression (9) allows you to connect z _{g kp} with a given value of the transverse metacentric height, draft and the distance between the pontoons.

Ensuring the transverse stability of the PMF in the working semi-submerged position requires the fulfillment of the condition
h _p = z _cp + r _p - z _g p ≥ h _{p. back} (10)
where h _r.set - the set or assigned value of the transverse metacentric height in the working position.

To ensure this condition when designing PMP necessary to express applicate center of buoyancy z _cf., center of mass z _gp and metacentric radius r _p through the geometric characteristics and analytically tie dimensions of the pontoons, columns, the position of the center of mass PMP height z _{g KP} and the position of the center height of buoyancy z _ssgb tanks of the main ballast.

Given the fact that per one pontoon and columns on it
V ' _cr = 0.5V _cr ,
z _{with cr} ≈ (0.52 ÷ 0.58) T _cr
where V _cr - cruising displacement PMP of 2 pontoons,
T _cr - draft along the cruising waterline,
k _zp ≈0.15 ÷ 0.20 - the buoyancy margin of the pontoon in the cruising position and N _p / T _cr ≈1.15 ÷ 1.20, (N _p - average pontoon height),
the following condition has been obtained for z _bcc and a given value of the transverse metacentric height for the operating position of the PMF h ' _{r rear} assigned to the cruising displacement.

Это неравенство наряду с другими накладывает ограничение на расположение центра плавучести ЦГБ по высоте z_сЦГБ и расстояние между колоннами В_к.

This inequality, along with others, imposes a restriction on the location of the center of buoyancy of the CBH along the height z of the _SCB and the distance between the columns B _to .

The minimization of the forces of the PMF wave drift is ensured by the fact that the distance between the pontoons and the columns is selected near the half-length of the calculated wave and assigned in the interval
B _to ≈ (0.4-0.6) λ _p (12)
This non-rigid condition allows it to be combined with other conditions by the distance between the pontoons and the columns.

 One of the problems that always arises when creating catamaran PMPs is the problem of the rigidity and strength of the connection between pontoons and columns. However, these compounds can be made useful for the PMP speed and its wave resistance. To do this, at the bottom level, the pontoons can be connected with the wing profiles convex up and deployed at a certain angle of attack. Such profiles during the course of the PMF against the wave create additional wave traction.

 The proposed system of equations and inequalities represents the conditions for determining, when designing the PMF, the displacement, sizes of columns and pontoons, the distance between them, the permissible elevation of the center of mass of the PMP over its buoyancy center, as well as the volumes of the main ballast tanks and the position of their buoyancy center in height.

The starting points for solving this system of equations and inequalities are:
- a given payload, for example, the mass of a rocket complex, drilling equipment, carrying capacity;
- crew and supply standards;
- set speed and range, autonomy and habitability conditions;
- requirements for longitudinal and lateral stability of the PMF in the surface and semi-submerged state;
- draft and other operational requirements;
- the maximum ballast of the sea, at which the PMP should be normally operated, and the area of its installation in the anchored version or in free navigation;
- special requirements and wishes of the customer.

The problem of a rational choice of the PMF elements during its design is fundamentally solved as follows:
1. First, the calculated range of wavelengths and heights is determined. Usually, for each sea score, according to statistics, there corresponds a range of wavelengths and heights of 3 and 1% of coverage. Depending on the rigidity of the requirements for pitching the PMF, the calculated range of wavelengths and heights and their average static values λ _p and h _p can be selected.

2. Based on h _p and conditions of wave resistance, the limits of the required column height H _k = (1.35 ÷ 1.5) h _{p are set} and T _k = 0.5N _k is assigned.

3. Under the conditions of minimizing the wave drift forces, the limits of the necessary distance between the pontoons B _to ≈ (0.4 ÷ 0.6) λ _p , the number of columns n in a row and the distance L _to between the bow columns are established. If the platform is small and there are only two columns, then L _k = (0.4 ÷ 0.6) λ _p , if the length of the pontoons and the upper platform are large, close to λ _p , and the number of columns is three or more, then the distance between the extreme bow and the feed columns are selected in the interval L _to = (0.8 ÷ 1.1) λ _p . It is possible to use 2 columns of a larger horizontal section S _k at a distance of (0.4 ÷ 0.6) λ _p from each other in a row and 2-3 additional columns of a small section in the bow and stern from the main ones to support the upper working platform.

4. If the pontoons are straight-walled or close to them, then the following relations are valid for them:
S _{cr cr} = α L In _{kr Cr,} V _Cr = V _n (1-k _sn) ≈S _{cr cr} T, V = δ _{kr kr kr} In _cr T L and T _{cr cr} ≈ (1-k _{sn) n} H ,
where In _cr and L _{cr the} greatest width and length of the pontoon in the cruising position W _cr L _cr ,
S _cr - the area of the waterline W _cr L _cr pontoon,
α _cr - the coefficient of completeness of the cruising waterline, and δ _cr - the coefficient of the overall completeness of the pontoon for cruising.

5. The height of the pontoon N _p can be assigned according to the conditions of placement and maintenance of the power plant, ship supplies of water, fuel, provisions, main ballast. For a given buoyancy margin k _zp and designated N _p, draft can be determined from the cruising waterline T _cr ≈N _p (1-k _zp ).

6. The system of equations:
- resistance to vertical wave forces (2);
- displacement in cruising position (3);
- buoyancy in cruising position (4);
- displacement in a semi-submerged working position (5);
- the volume of tanks of the main ballast (6);
- stability in cruising position (9);
- stability in a semi-submerged working position (11);
- minimum wave drift forces (12)
streamline the process of making constructive decisions and determining the necessary dimensions of PMP during design.

 All dependencies proposed here for PMP are new. The patent search for such dependencies did not reveal. Therefore, these dependencies meet the criterion of novelty.

 These dependences indicate rational ways to achieve the specified operational properties of the PMP. Without them, the design process will be very long and there is no guarantee that optimal decisions will be made. Therefore, the proposed system of equations and inequalities meets the criterion of a significant positive effect.

Claims (3)

1. A semi-submersible offshore platform containing an upper working structure supported by two rows of vertical columns supported by two ship-shaped pontoons, inside which a power plant, ship supplies and ballast tanks are located, capable of floating in a surface (cruising) and in a semi-submerged working position, different the fact that the height of the columns H _to from the bottom of the upper working structure to the upper deck of the pontoons is accepted in the interval (1.35-1.5) h _p , where h _p is the calculated wave height, the platform in working position It is balanced by water ballast so that its waterline runs in the middle of the columns, and the total volume of one pontoon V _n is determined by the formula

where N _p - pontoon height;
∑S _к - total area of horizontal section of columns on one pontoon;
λ _p is the calculated wavelength;
k _yn = 0.8-1.1 is the coefficient of the attached mass of the pontoon, depending on its shape and frequency of the calculated wave;
the distance between the columns along the width B _{k is} taken in the range (0.4-0.6) λ _p , and the distance between the columns along the length of the pontoon is related to the number of columns and the wavelength as follows: L _k = (0.4-0 , 6) λ _p for two columns, and for three or more, the distance between the extreme columns in the bow and stern is L _k = (0.8-1.1) λ _p , the displacement of the PMF in the cruising position V _cr is associated with the full volume of the pontoon and its main dimensions dependencies
V _cr = 2 (1 + k _sn ) ^-1 V _p = 2δ _cr L _cr B _cr T _cr
and
ρV _cr = m _ng + m _sg
where k _zp = 0.15-0.20 is the specified value of the buoyancy margin of the pontoons;
δ _cr - the coefficient of the overall completeness of the pontoon along the cruising waterline;
In _cr , L _cr and T _cr - its width, length and draft along the cruising waterline;
m _ng is the sum of the masses of goods given and accepted for structural reasons;
m _zg - the sum of the masses dependent on the size of the PMP cargo,
while the displacement of the PMP in the working position is determined by the expression
V _pn = 2V _p + H _to ∑S _to ,
the total volume of tanks of the main ballast V of the central cylinder _block for two pontoons is determined by the dependence
V _CCH = k V _sn + H _{cr to} ΣS _k
the elevation of the center of mass of the PMF in height from the main plane z _{g cr} for the cruising position is determined by the expression

where h _{cr ass} - the specified value of the transverse metacentric height in the cruising position;
T _cr - draft in cruising position;
In _to - the distance between the diametrical planes of the pontoons,
and for a working semi-submerged position, the elevation of the center of buoyancy of the CBH and the distance in width between the columns B _k must satisfy the inequality

where h ' _{r back} - a given value of the transverse metacentric height for a semi-submerged working position, referred to as cruising displacement;
z _ssgb - elevation of the center of buoyancy of tanks of the main ballast over the main;
V ' _cr = 0.5V _cr - the displacement of one pontoon along the cruising waterline. 2. The semi-submersible offshore platform according to claim 1, characterized in that the vertical columns are circular or streamlined in shape, and external frames of plates with a width of 0.1 width are installed on the outer surface of the columns at a distance of 0.5-1.0 m from each other b _to columns.  3. The semi-submersible offshore platform according to claims 1 and 2, characterized in that at the bottom level the pontoons are rigidly interconnected by wing profiles, installed convex upward and deployed at an angle of attack during the PMF against the wave.

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