Geostationary floating platform

Abstract

A system for heave neutralization of semi-submersible platforms has been demonstrated that can be built into any conceivable design of such platforms. That the system is also conceivably active and predictively controllable can be concluded by analyzing the attached calculation models. As an example, Figure 18 column E is mentioned, where the water volume increments in the riser shaft are 37 cubic meters for every half meter of wave height, so that, ref column A, from H=10.5 m to H=12 m is 4 x 37 = 148 cubic meters – over 150 tons - at the same time as the air pressure, shown in column K, increases from 123.86 to 131.05 kPa, a difference of only 6.19 kPa (0.0619 bar or 61.9 millibar). Large ballast volumes can be moved in and out of the system with small pressure changes and short response time.

Description

[0003] Geostationary floating platform

[0004]

[0005] Field and background of the invention

[0006]

[0007] The present invention describes a semi-submersible floating platform with a built-in system for constant buoyancy at varying water levels due to wave and tidal movement.

[0008]

[0009] Such platforms may have great potential for the extraction of minerals on the seabed, for the extraction of oil and gas under the seabed, as foundations for floating bridges, wind turbines, solar power or other structures.

[0010]

[0011] Summary of the invention

[0012]

[0013] A floating platform is provided, comprising a structure supported by one or more columns placed on one or more buoyancy bodies, characterized by

[0014] - that the column or columns comprise a built-in riser shaft provided with at least one opening in a lower portion so as to provide fluid communication between the riser shaft and a body of water; and

[0015] - that the volume of the riser shaft increases with increasing height, so that the riser shaft has an increasing water surface area as the water level rises.

[0016]

[0017] The ladder shaft is in gas connection with a gas-filled chamber at an upper portion.

[0018]

[0019] In one embodiment:

[0020] - the riser shaft is gas-connected to a first tank via a first valve, and the first tank contains a gas, for example air, and is configured to have a higher pressure than the highest pressure in the riser shaft when the water in the riser shaft is at an upper level, and

[0021] - the riser shaft is gas-connected to a second tank via a second valve, and the second tank contains a gas, for example air, and is configured to have a lower pressure than the pressure in the riser shaft when the water in the riser shaft is at a lower level.

[0022]

[0023] The second tank preferably comprises a third valve for venting to the atmosphere. A compressor may be gas-connected to the first tank and arranged to maintain an overpressure in the first tank.

[0024] In one embodiment, the column or columns at a portion above the ladder shaft have an outer diameter that decreases upward.

[0025]

[0026] The buoyancy body or bodies have sufficient draft to not be significantly affected by surface waves. The floating platform is preferably a semisubmersible platform.

[0027]

[0028] The platform discussed here includes one - or more - columns supported on its buoyancy body through the water surface, deep enough not to be raised or lowered by wave movements on the surface.

[0029]

[0030] The present invention describes a heave-neutralizing automatic ballast system without moving parts. The system comprises a ladder shaft with one or more openings in a lower part where the level of the water level in the ladder shaft is balanced by a confined volume of air, or other gas, with slight overpressure. The top level of the ladder shaft must be below the lowest water level around the column at the bottom of the passing wave. The air volume is connected to an appropriately sized reservoir on board. When the wave height rises, the hydrostatic pressure in the ladder shaft rises and drives the water level upwards and compresses the confined air volume. The rising water level surrounding the column provides increasing buoyancy, while the increasing water volume in the ladder shaft below the splash zone provides correspondingly reduced buoyancy as the air volume is compressed. These two volumes balance each other at all times and thus neutralize the heave forces on the floating rig.

[0031]

[0032] For the system to be energy neutral, the value of pressure multiplied by volume in the confined air reservoir must be constant, pV=constant. The cross-sectional area of ​​the column, maximum wave height and that pV=constant are the main criteria for the design basis.

[0033] The semi-submersible floating platform has one or more columns which are arranged to pass through the swash zone of the surrounding waves varying water levels, and which are connected to floating bodies of sufficient draft so as not to be significantly affected by the surface waves having therewith the specific limitations of varying water levels in the swash zone of the waves. The invention comprises a built-in system for constant displacement to thereby neutralize the heave effect of the platform at varying wave heights. This is achieved by incorporating in the platform, at a level below the bottom of the waves, a riser shaft with a rising water surface area with rising water levels and which is in fluid communication with the surrounding water masses through one or more openings positioned at a level lower than the lowest level in the riser shaft.The level of the water table in the riser is controlled by a confined compressed gas-filled volume in the float which is either located directly above the highest level of the water table in the riser or elsewhere in the platform and is then connected by pipes or channels. As the water level around the column rises, the hydrostatic pressure in the riser increases, and the water level in the riser rises and compresses the air volume above. As the water level rises, the buoyancy increases due to the increasing displaced volume of the column in the swash zone, and an exactly corresponding volume rises in the riser below the water surface, compressing the confined air and thereby reducing the buoyancy accordingly.The area variation of the riser shaft together with the trapped gas volume is designed such that the value of pV for the gas volume is constant within the entire volume variation, and the increasing air pressure above the water table in the riser shaft in combination with the increasing water table area gives an increasing buoyancy component which is compensated by the column's wet area in the splash zone being reduced by rising wave height.

[0034]

[0035] The invention further comprises a semi-submersible floating platform which is dynamically positioned vertically by the built-in system for neutralizing heave being equipped with a system for positive or negative additional energy to counteract unwanted heave tendencies caused by viscous frictions on the hull or hydrodynamic and / or aerodynamic resistance factors in the system. The air reservoir in the system is connected to a tank with a storage pressure less than the lowest system pressure at the lowest water level in the riser, and another tank with a storage pressure higher than the highest system pressure at the highest water level in the riser, so that a control system with developed algorithms that are in connection with geostationary references can predictively actively control this individually for each column and thus keep the platform horizontal and heave neutral.

[0036]

[0037] Description of embodiments of the invention

[0038]

[0039] In the following, three different semi-submersible platform designs with different installation options for the system will be demonstrated.

[0040] Figure 1 shows a single-column platform where the reference numeral 1 denotes a column, here with a circular cross-section. The reference numeral 2 denotes a ladder shaft, and 3 a buoyancy body, -pontoon - here extended with a deeper fixed solid mass ballast module 3a of for example concrete, to give the platform sufficient stability. The ballast module 3a is optional, and the invention should not be limited to this embodiment. Furthermore, the reference numeral 4 denotes a structure, such as e.g. a deck for payload, and 5 denotes the water level at zero wave height. The ladder shaft 2 is here built into the circular pontoon.

[0041] Figure 2 shows a three-column platform with the same elements as shown in Figure 1, but here the pontoon 3 is shaped like a hexagonal torus. The idea of ​​this construction with three columns and a 'donut'-shaped pontoon is that it should be equally affected by ocean currents regardless of direction. The ladder shafts 2 are built around the circular columns 1.

[0042] Figure 3 shows a platform with four columns 1 and two pontoons 3 in the longitudinal direction. In this embodiment, the columns 1 have an approximately square cross-section, and the ladder shafts 2 are here built into the square cross-section shaped columns 1.

[0043]

[0044] Figure 4 is a vertical center section of the platform from Figure 1. The letter designations are references to calculations in Figure 6. Sea level at zero wave is reference 6, lowest level wave bottom is 7 and wave crest is 8. The column 1 has a portion 9 with decreasing outer diameter upward, i.e. towards wave crest 8. In the riser shaft 2, which is in fluid communication with the surrounding water mass via the opening 40, the middle level 10 corresponds to zero wave level 6. The lowest level in the riser shaft is 11 and the top is 12. The inner diameter 13 of the riser shaft 2 is decreasing towards the top level 12, so that the volume of the riser shaft increases with increasing height (i.e. upwards towards the deck 4). The chamber 14 constitutes a reservoir (gas, but preferably and most conveniently, air) and is connected to the top of the ladder shaft 2 via the openings 15 internally in the structure. The column 1 in this platform structure has the through opening 16.The area difference through the waterline is thus given by the difference between the diameters D and Di.

[0045]

[0046] Figure 5 shows an enlarged section of the pontoon 3, the ladder shaft 2, the curved inner wall 13 and the air reservoir 14. The arrows 16 mark the force component of the air pressure vertically upwards, and the arrows 17 mark the force component of the same pressure downwards. With rising water level the area of ​​the water table increases and the pressure in the reservoir increases. This results in an increasing buoyancy component which must be compensated for. This is achieved by increasing the water table surrounding the column with rising level as illustrated in figure 4 point 9.

[0047]

[0048] Mathematical description of the curvature of the internal diameter of the ladder shaft 13 and the external diameter of the column 9 is demonstrated by the calculations in figures 6, 7, 8 and 9.

[0049]

[0050] Figure 6 shows constants and input values ​​for the differential equation set up in Excel in Figure 7. The formulas below are copied from the Excel sheet.

[0051]

[0052] Explanation of the input values ​​in Figure 6 column B:

[0053]

[0054] ● The input values ​​in cells B1 to B4 are the basic criteria for the construction. ● The input for hL, cell B5, is chosen as low as possible for the equation to work.

[0055] The same applies to the value for total air volume, Va in B8.

[0056] ● The input value c, B6, is a practical trade-off.

[0057] ● The input value ∆H, B7, is the increment for the water level H in the differential equation Figure 7, from cells A2 to A26.

[0058] ● The value in cell B9 is the specific gravity of seawater.

[0059]

[0060] Based on the input values ​​mentioned above, the values ​​in cells B10 to B14 in Figure 6 are calculated.

[0061]

[0062] Explanation of the differential equation Figure 7, columns A to Q:

[0063]

[0064] ● The value in cell A2 is inserted with 0 as the starting level for H. A3 is A2 plus increment 1 which is from Figure 6, cell B7.

[0065] ● Column B calculates the air volume after incremental compression at rising wave height, H. The value in B2 is copied from Figure 6, B8. The value in B3 is the value from B1 minus the value in A3 multiplied by the area of ​​the dry column, Figure 6, B11. This is the new air volume after compression after the rise in water level H. Formula: B3=(B8 in Figure 6) - (B12 in Figure 6) * A3).

[0066] ● Column C calculates how much the air volume decreases. Formula: C3=B3-B2.

[0067] Column D calculates the new hydrostatic pressure head h. This appears by dividing the pV constant, Figure 6, B14, by the value in B3. Formula: D3=(B14 in figure 6) / B3).

[0068] ● Column E calculates the increased water volume in riser shaft 2, are the same as the values ​​in column C, but with the opposite sign.

[0069] ● Column F calculates the water level in riser 2, WL. F2 is the input value from Figure 6, B5. F3 is the value in A3 minus the value D3. Formula: F3=A3-D3.

[0070] ● Column G gives the increase in elevation for the water level WL in riser shaft 2, this is the difference between the new and the previous value in column F. Formula: G3=-F2+F3.

[0071] ● Column H gives the area of ​​the water table in riser shaft 2. This is obtained by dividing the value in column E by the value on the same line in column G. Formula: H3=E3 / G3.

[0072] ● In column I, the final internal diameter of the riser shaft 2 is calculated for each incremental level of WL. The external diameter of the riser shaft is given in figure 6, B3. The area given by this external diameter minus the values ​​in column H, gives the values ​​in column I. Formula: I3=2*ROT((((B3 in figure 6) / 2)^2*π-H3) / π).

[0073] ● Column J calculates the slope of the water surface area in riser shaft 2. The value J3 is H3 minus H2.

[0074] ● Column K converts the current hydrostatic head hi in column D to pressure in kPa. The values ​​in column D are multiplied by the specific gravity of seawater, Figure 6, B9, and the force of gravity g. Formula: K3=D3*(B9 in Figure 6)*9.81.

[0075] ● Column L gives the rise in air pressure above the water table for each increment in riser shaft 2. Formula: L3=K3-K2.

[0076] ● In column M, the effect of the increasing buoyancy due to the increasing air pressure in column L is calculated. The values ​​are obtained by multiplying the values ​​in column J by the values ​​on the same line in column L. Formula: M3=J3xL3. ● In column N, the necessary ballast volume is calculated to compensate for the increasing buoyancy in column M. Formula: N3 =M3 / (9.81*(B9 in figure 6)).

[0077] ● In column O, the area of ​​the increasing wet water table that encloses column 1 at wave height H is calculated. Formula: O3=N3 / ((B7 in Figure 6)).

[0078] ● In column P, the decreasing diameter of the column is calculated. Formula: P3=P2-O3.

[0079] (P2=(B10 in Figure 6)).

[0080] ● Column Q calculates the corrected column diameter for each increment. Formula: Q3=2*ROT(P3 / PI())

[0081]

[0082] Figure 8 shows a curve plot from columns F and I from the spreadsheet in Figure 7. The horizontal axis 'WL' refers to the water level in the riser from level hL, cell B5, Figure 6, and cell F2, Figure 7, which is minus 20 meters and rising to minus 4.8 meters, cell F26, Figure 7.

[0083] The vertical axis 'ID Cn' refers to the reduction of the inner diameter of the ladder shaft listed in Figure 7 from cell I2 to I26.

[0084]

[0085] Figure 9 is a curve plot from columns A and Q from Figure 7. The horizontal axis 'H' lists the wave height values ​​from cells A2 to A26 from Figure 7, and the vertical axis 'OD Column' shows the reduction in the column's outside diameter with increasing wave height listed in cells Q2 to Q26 in Figure 7.

[0086]

[0087] Figure 10 shows a vertical center section of one of the columns for the platform illustrated in Figure 2. Reference numbers 1 to 15 have the same designations as in Figures 4 and 5. In Figure 10, the ladder shaft 2 is built concentrically on the outside of the column 1. In order for the column through the ladder shaft to retain its structural integrity to the greatest extent possible, the ladder shaft 2 has the curvature 18 for increasing water level at rising level facing outwards in contrast to the previous example in Figure 4 (reference number) 13. In order for the system to require as little air reservoir as possible, the column through the splash zone is divided into a dry and a wet section. The dry section 19 is enclosed by the curved bulkhead 20. The wet section 21 is enclosed by the column wall 22 externally and the bulkhead 20 inwards. In order for the column through the splash zone to retain its structural integrity, the necessary ventilation area for the wet section is maintained through the openings, the scupper holes 23.

[0088]

[0089] Mathematical description of the curvature of the outside diameter of the riser shaft 18 and the outside diameter 20 of the dry section 19 of the column 1 is demonstrated by the calculations in Figures 11, 12 and 13.

[0090]

[0091] Figure 11 shows the input constants in cells B1 through B8 for the spreadsheet in Figure 12. The values ​​in cells B9 through B12 are calculated based on these constants.

[0092]

[0093] Explanation of the columns in the spreadsheet figure 12:

[0094] ● Column A calculates the wave height from 0 in cell A2 to 12 m in cell A26, based on the constants from cells B3 and B6 in Figure 11.

[0095] ● Column B calculates the air volume in the system at increasing wave height, B2 is copied in from cell B7, Figure 11. Cells B3 to B26 calculate the air volume at each increment of the increasing displacement of the column at increasing wave height. ● Column C lists the incremental reduction of the air volume and is obtained by subtracting the parallel value in column B from the previous one, for example, the cell value C3=B3 minus B2.

[0096] ● Column D calculates the hydrostatic head above the water table in the riser shaft. Cell D2 is copied from cell B4 in Figure 11. The value in cell D3 is calculated by dividing the constant in cell B12 in Figure 11 by the parallel from column B, for example, D3= constant B12 divided by B3.

[0097] ● Column E lists the incremental increase in water volume in the riser which are the same values ​​as in column C with the opposite sign.

[0098] ● Column F calculates the incremental water level in the riser. The value in F2 is the same as in cell D2 with the opposite sign. The value in cell F3 is obtained by subtracting the parallel value in column D from the parallel value in column D, for example, F3= A3 minus D3.

[0099] ● Column G calculates the incremental increase in the water level in the riser, where for example G3= -F2 plus F3.

[0100] ● Column H calculates the area of ​​the stairwell for each level. The values ​​are obtained by dividing the parallel values ​​in column E by the parallel values ​​in column G, for example, H3=E3 divided by G3. H2 is extrapolated from the values ​​in H3 and H4, H2=H3-(H4-H3).

[0101] ● Column I calculates the diameter of the stairwell for each level as a function of the areas in column H and the constant from cell B9 in figure 11. For example, I2= 2 * √ ((B9 fig 11 H2) / π).

[0102] ● Column J calculates the increase in the area of ​​the stairwell for each level, where the value in J3 is obtained by subtracting the parallel value in column H from the previous one, J3=H3 minus H2.

[0103] ● Column K calculates the air pressure in the stairwell in kPa for each level, for example, K2=D2 multiplied by the constant in cell B8, fig 11, multiplied by g (9.81).

[0104] ● Column L calculates the air pressure increase kPa in the stairwell for each level where, for example, L3=K3-K2.

[0105] ● Column M calculates the increasing buoyancy effect in kN of the increasing air pressure and the increasing area of ​​the water surface in the riser shaft, where for example M3=J3 multiplied by L3.

[0106] ● Column N calculates the required ballast water volume in m3 to compensate for the increasing buoyancy effect, where for example N3=M3 / (g*constant B8 in figure 11).

[0107] ● Column O calculates the increase in area of ​​the water table around the column that is necessary to accommodate this ballast water, where for example O3=N3 divided by the constant B6 in Figure 11.

[0108] ● Column P calculates the new wet area of ​​the column for each level, where for example P3=O3+P2.

[0109] ● Column Q then calculates the new dry area of ​​the column for each level, where for example Q3=the value in cell B9 minus the value in cell P3.

[0110] ● Finally, the new diameter for the column's dry area is calculated for each level in column R, where R3=2 * √ (Q3 / π).

[0111]

[0112] Figure 13 shows the top curve plot from columns I and F from the spreadsheet in Figure 12.

[0113] The horizontal axis 'WL' refers to the water level in the riser shaft from level hL, cell B6, figure 11, and cell F2, figure 12, which is minus 8.5 meters and rising to minus 1.2 meters, cell F26, figure 12. The vertical axis 'ID Cn' refers to the increase in the outer diameter of the riser shaft listed in figure 12 from cell I2 to I26.

[0114]

[0115] Figure 13, bottom curve plot, is from columns A and R of Figure 12. The horizontal axis 'H' lists the wave height values ​​from cells A2 to A26 of Figure 12, and the vertical axis 'd' shows the reduction of the column's outside diameter of the dry area with increasing wave height listed in cells R2 to R26 of Figure 12.

[0116]

[0117] Figure 14 shows the exterior of one of the columns of the four-column platform illustrated in Figure 3, as well as a vertical cross-section thereof. The reference numbers from 1 to 23 denote the same as in Figure 4 and Figure 10. The reference numbers 11a and 12a show additions for water level in the ladder shaft at the bottom and top. The ladder shaft 2 is here built into the column 1. The ladder shaft here constitutes the space between the outer walls of the column and the curved bulkheads 25 which form a square core inside the column, and the volume of the ladder shaft increases with increasing height (i.e. upwards in the direction of deck 4). The hatches 24 connect the ladder shaft to the sea. The deck 27 isolates the wet area in the ladder shaft from the internally dry column below. The deck 28 constitutes the roof for the riser shaft and the air volume above the water table connected to the pipe 15 and the chamber (gas (air) reservoir) 14. The pipe (opening) 15 is further connected to the above arrangement, which is schematically shown.Figure 14 is best read in conjunction with Figure 15 and Figure 16 which are three-dimensional illustrations. A first valve 29 is connected to a first tank 33 which has stored air at a higher pressure than the highest in the riser shaft at level 12. Furthermore, the pipe 15 is also connected to a second valve 30 which is connected to a second tank 34 which is stored at a lower pressure than the pressure in the riser shaft at level 11. A third valve 31 is for venting to the atmosphere. The compressor 32 is a low-pressure compressor type with high volume capacity. The compressor maintains the overpressure in the first tank 33. Control of opening and closing of the valves 29, 30 and 31 is thought to be connected to a control system with input data from geostationary references. When, due to hydrodynamic inertia effects, as well as viscous hydrodynamic frictions, the platform is not held completely still, the additional capacities marked WL- and WL+, 11a and 12a, can be activated and correct for this.The system can be equipped with specially developed algorithms that can then act predictively and individually independently for the 4 columns to keep the platform stable, horizontal and lift neutral.

[0118]

[0119] Figure 17 shows the input constants in cells C1 through C9 for the spreadsheet in Figure 18. The values ​​in cells C10 through C14 are calculated based on these constants.

[0120]

[0121] Explanation of the columns in the spreadsheet in Figure 18 is in principle the same as for Figure 12, up to column H. In column I in Figure 18, the external length measurements of the sides of the square core that constitutes the inner walls of the stairwell are calculated, as this here, ref. Figures 14, 15 and 16, is built into a square column.

[0122] Furthermore, the second difference is that in column Q, the length measurement is calculated from the distance from the outer wall of the column to the curved bulkhead that separates the wet and dry areas of the column in the column's splash zone.

[0123]

[0124] Figure 19 shows at the top the curve plot from columns I and F from the spreadsheet in Figure 18.

[0125] The horizontal axis 'WL' refers to the water level in the riser shaft from level hL, cell C5, figure 17, and cell F2, figure 18, which is minus 8.9 meters and rising to minus 1.0 meters, cell F26, figure 18. The vertical axis 'B x L' refers to the increase in the external length measurements of the sides of the square core that make up the inner walls of the riser shaft listed in figure 18 from cells I2 to I26.

[0126]

[0127] Figure 19, bottom curve plot, is from columns A and Q of Figure 18. The horizontal axis 'Wave height' lists the wave height values ​​from cells A2 to A26 of Figure 18, and the vertical axis 'AD wall length' shows the increase in the length of the column outer wall to the curved bulkhead separating the column's wet and dry areas in the column's splash zone, listed in cells Q2 to Q26 of Figure 18.

Claims

Claim 1. A floating platform, comprising a structure (4) supported by one or more columns (1) placed on one or more buoyancy bodies (3), characterized in that- the column or columns (1) comprise a built-in ladder shaft (2) provided with at least one opening (40; 24) in a lower portion so as to provide fluid communication between the ladder shaft and a body of water; and- the volume of the ladder shaft increases with increasing height, so that the ladder shaft has an increasing water surface area with rising water level.

2. A floating platform as claimed in claim 1, wherein the ladder shaft (2) at an upper portion is in gas communication with a gas-filled chamber (14).3.A floating platform as claimed in claim 1 or claim 2, wherein- the riser (2) is gas-connected to a first tank (33) via a first valve (29), and wherein the first tank (33) contains a gas, for example air, and configured to have a higher pressure than the highest pressure in the riser when the water in the riser is at an upper level (12), and- the riser (2) is gas-connected to a second tank (34) via a second valve (30), and wherein the second tank (34) contains a gas, for example air, and configured to have a lower pressure than the pressure in the riser when the water in the riser is at a lower level (11).

3. A floating platform as claimed in claim 2, wherein the second tank (34) comprises a third valve (31) for venting to the atmosphere.

4. A floating platform as claimed in claim 2 or claim 3, further comprising a compressor (32) which is gas-connected to the first tank (33) and arranged to maintain an overpressure in the first tank (33).5.A floating platform as claimed in any one of claims 1-4, wherein the column or columns (1) at a portion above the ladder shaft (2) have an outer diameter (9) that decreases upwardly.

6. A floating platform as claimed in any one of claims 1-5, wherein the buoyancy body or buoyancy bodies (3) have sufficient draft to not be significantly affected by surface waves.

7. A floating platform as claimed in any one of claims 1-6, wherein the platform is a semisubmersible platform.