CN117932803A - Main scale design and optimization method for catenary single-point mooring platform - Google Patents
Main scale design and optimization method for catenary single-point mooring platform Download PDFInfo
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Abstract
The invention discloses a main scale design and optimization method of a catenary single point mooring platform, which comprises the following steps: (1) Acquiring wind wave flow and water depth data of a designed sea area, and ship type data of an oil tanker; (2) Calculating the horizontal force required by mooring the tanker and the pontoon under the action of the stormy waves and currents through the data; (3) Taking the horizontal force, the water depth and the dead weight of an anchor chain required by mooring the buoy as parameters into a catenary equation; (4) Grouping anchor chains pairwise, and selecting an included angle corresponding to the relatively smaller tension and displacement; (5) Calculating the maximum tension of the anchor chain and the maximum displacement of the pontoon under different parameter combinations; (6) Calculating and analyzing the transverse displacement of the pontoon on the basis of the completion of the anchor chain design; (7) optimizing the length of the underwater hose; (8) simulation calculations select a dolphin length. The invention aims to provide a method for optimizing design of a catenary single-point mooring platform from hydrodynamic force calculation and finite element calculation.
Description
Technical Field
The invention relates to the technical field of design of ship and ocean engineering structures, in particular to a main scale design and optimization method of a catenary single-point mooring platform.
Background
With the recent economic and social developments, the demand for oil and gas resources in the international market is increasing. The catenary single point mooring device has the advantages of low cost, simple structure, easy construction and the like, and is a common oil storage and discharge device. In the catenary mooring system, anchor cable connection points are arranged on the periphery of a pontoon, and a plurality of anchor cables are radially distributed on the periphery of the pontoon and have a certain laying distance on the seabed. The pontoon provides necessary buoyancy for driving the anchor cable to suspend, so that the pontoon always maintains a floating state in the mooring process, and meanwhile, equipment such as a rotary joint and the like is loaded. The prior catenary single point mooring related technology is mainly monopolized by foreign companies at present, and research in the related field is necessary. Therefore, there is a need for a method of design optimization of a catenary single point mooring platform from hydrodynamic calculations and finite element calculations.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and aims to provide a method for optimizing the design of a catenary single-point mooring platform from hydrodynamic calculation and finite element calculation.
In order to achieve the above purpose, the invention is realized by the following technical scheme:
A catenary single point mooring platform main scale design and optimization method comprises the following steps:
(1) Acquiring wind wave flow and water depth data of a designed sea area, selecting a conventional value and an extreme value in the data as environmental conditions during design, and acquiring ship type data of a designed tanker;
(2) The transverse force and the longitudinal force of wind wave currents acting on the tanker and the pontoon are calculated or obtained by using software Orcaflex, and the horizontal force required by mooring the tanker and the pontoon under the wind wave current condition is calculated by using the transverse force and the longitudinal force data;
(3) Taking the horizontal force, the water depth and the dead weight of the anchor chain required by mooring the buoy as parameters into a catenary equation:
wherein, F is horizontal force at the end point of the catenary, omega is gravity of unit length of the catenary, h is water depth, and when the length of the catenary is S 0≥Sm, the catenary is a self-catenary; when S 0<Sm is carried out, the catenary is a constraint chain, so that the minimum initial length of the anchor chain formed by the catenary is calculated;
(4) Grouping the anchor chains in pairs, wherein each group is two adjacent anchor chains, changing the included angle of the anchor chains in the group, performing systematic hydrodynamic response calculation on the conditions of different included angles to obtain the maximum tension of the anchor chains and the maximum displacement of the pontoon, and selecting the included angle corresponding to the relatively smaller tension and displacement;
(5) The length of the anchor chain and the anchoring radius are adjusted, i groups of different anchoring radii r i are selected, and the range of the anchoring radii is Wherein h is the water depth, S 0 is the initial length of the anchor chain, j anchor chain lengths S j are selected under each group of anchoring radius, and the range of the anchor chain lengths is/>Calculating the maximum tension of the anchor chain and the maximum displacement of the pontoon under different parameter combinations, and selecting the corresponding parameter combination when the tension and the displacement are relatively smaller;
(6) Calculating and analyzing the transverse displacement of the pontoon on the basis of the completion of the anchor chain design, wherein when the transverse drift amplitude of the pontoon is less than 20% of the water depth, a Chinese lantern type underwater hose can be adopted; if the transverse drift amplitude of the pontoon is not lower than 20% of the water depth, a slow-s-shaped underwater hose can be adopted, and meanwhile, the upper limit and the lower limit of the length of the underwater hose are determined according to the water depth, and the initial length l 0 of the underwater hose is determined;
(7) Optimizing the length of the underwater hose, and analyzing the bending radius and the tension of the underwater hose to obtain the condition that the minimum bending radius is relatively large and the maximum tension is relatively small;
(8) Simulation calculations performed by software Orcaflex to select the length of the dolphin, and the longest dolphin may be selected as the initial value Gradually shorten the mooring line length/>Until the calculation is carried out when the tanker collides with the pontoonThen choose/>As the final hawser length.
Further, the calculation formula of the force acting on the oil tanker and the floating pontoon in the step (2) is as follows:
Wherein, C xw is a dimensionless longitudinal wind power coefficient, C yw is a dimensionless transverse wind power coefficient, ρ w is the density of air at 20 ℃, 1.223kg/m 3,Vw is the average wind speed at the water plane 10m, A T is the transverse wind receiving area on the water surface of the ship body, A L is the longitudinal wind receiving area on the water surface of the ship body, F xw is the longitudinal force of wind on the ship body, F yw is the transverse force of wind on the ship body, C xw is a dimensionless longitudinal fluid coefficient, and C yw is a dimensionless transverse fluid coefficient;
the calculation formula of the force acting on the upward flow of the tanker and the pontoon is as follows:
Fxc＝0.5CxcρcVc 2TLBP (4)
Fyc＝0.5CyρcVc 2TLBP (5)
Wherein ρ c is the density of seawater at 20 ℃, 1025kg/m 3,Vc is the average flow rate, T is the vessel draft, F xc is the longitudinal force of the flow on the hull, F yc is the lateral force of the flow on the hull;
Wave forces acting on the tanker and buoy are calculated by the Morisen formula:
Wherein F is horizontal wave force acting on the ship at any height, V is the volume of the ship, A is the projected area of the ship vertical to the horizontal direction, mu n is the instantaneous wave fluid velocity vertical to the axis of the ship, Is the instantaneous wave fluid acceleration perpendicular to the hull axis, C D is the drag coefficient, C M is the inertial force coefficient;
Vector addition is carried out on the acting forces of wind, current and wave to obtain the horizontal force required by mooring the ship body or the pontoon under the action of wind, wave and current conditions.
Further, the included angle of the anchor chains in the group in the step (4) is 10-60 degrees.
Further, in the step (6), the lower limit of the length of the underwater hose is larger than the water depth, and the upper limit of the length of the underwater hose is not longer than 150% of the water depth.
Further, in the optimizing manner in the step (7), the selected underwater hose length l 0 is increased and decreased, and each time the underwater hose length is adjusted to be not more than 1.5m, a group of l i is obtained, the software Orcaflex is used for calculating different hose lengths, the corresponding minimum bending radius and maximum tension of the hose are obtained, and the conditions that the minimum bending radius is relatively large and the maximum tension is relatively small are selected.
Further, the initial value in step (8)Not shorter than 150m.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a new catenary single point mooring platform main scale design method based on hydrodynamic force calculation and finite element calculation, which comprises the parameters of anchor chain layout mode, anchor chain length, anchoring radius, underwater hose length, mooring rope length and the like. The design method has comprehensive system, and the main scale design methods of the anchoring system, the oil transportation system and the mooring system are all related. The design method is simple and efficient, and the CALM preliminary design is enabled to be flow-processed.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
FIG. 2 is a schematic illustration of a single point mooring buoy in an embodiment;
FIG. 3 is a simulation result of the influence of different anchor chain angles on the system response in the embodiment;
FIG. 4 is a simulation result of the maximum tension of the anchor chain and the maximum displacement of the pontoon along with the main dimension of the mooring system in the optimization process in the embodiment;
FIG. 5 illustrates various subsea hose configurations in an embodiment;
FIG. 6 is a simulation of the effect of hose length on hose response in an example;
FIG. 7 is a simulation result of the effect of hawser length on system response in an embodiment.
Detailed Description
The invention will be described in detail below with reference to the drawings in connection with embodiments.
As shown in fig. 1to 7, a catenary single point mooring platform main scale design and optimization method includes the following steps:
(1) The method comprises the steps of obtaining wind wave flow and water depth data of a designed sea area, selecting conventional values and extreme values in the data as environmental conditions during design, obtaining ship type data of a designed tanker, wherein a CALM type single-point mooring device buoy analyzed by the method is shown in fig. 2, main dimensions of the buoy are shown in table 1, environmental conditions such as wind wave flow and the like are shown in table 2, and the parameters of the tethered tanker are shown in table 3.
TABLE 1 pontoon parameters
TABLE 2 environmental conditions
Table 3 tanker parameters
(2) The transverse force and the longitudinal force of wind wave and current on the tanker and the pontoon are obtained through the data calculation or the software Orcaflex, the horizontal force required by mooring the tanker and the pontoon under the wind wave and current condition is calculated by utilizing the data of the transverse force and the longitudinal force,
The calculation formula of the force acting on the windward side of the tanker and the pontoon is as follows:
Wherein, C xw is a dimensionless longitudinal wind power coefficient, C yw is a dimensionless transverse wind power coefficient, ρ w is the density of air at 20 ℃, 1.223kg/m 3,Vw is the average wind speed at the water plane 10m, A T is the transverse wind receiving area on the water surface of the ship body, A L is the longitudinal wind receiving area on the water surface of the ship body, F xw is the longitudinal force of wind on the ship body, F yw is the transverse force of wind on the ship body, C xw is a dimensionless longitudinal fluid coefficient, and C yw is a dimensionless transverse fluid coefficient;
the calculation formula of the force acting on the upward flow of the tanker and the pontoon is as follows:
Fxc＝0.5CxcρcVc 2TLBP (4)
Fyc＝0.5CyρcVc 2TLBP (5)
Wherein ρ c is the density of seawater at 20 ℃, 1025kg/m 3,Vc is the average flow rate, T is the vessel draft, F xc is the longitudinal force of the flow on the hull, F yc is the lateral force of the flow on the hull;
Wave forces acting on the tanker and buoy are calculated by the Morisen formula:
Wherein F is horizontal wave force acting on the ship at any height, V is the volume of the ship, A is the projected area of the ship vertical to the horizontal direction, mu n is the instantaneous wave fluid velocity vertical to the axis of the ship, Is the instantaneous wave fluid acceleration perpendicular to the hull axis, C D is the drag coefficient, C M is the inertial force coefficient;
The forces of wind, flow and wave can be vector added to obtain the horizontal force required by mooring the ship body or the pontoon under the action of wind, wave and current conditions, or the horizontal force is calculated by software Orcaflex, and finally the maximum bearing force of the horizontal force of the maximum anchor chain of the forward flow is about 1720kN under the condition of mooring the tanker.
(3) The horizontal force 1720kN, the water depth of 30m and the unit dead weight 1195.6N/m of the anchor chain required by mooring the buoy are taken into a catenary equation as parameters:
wherein, F is horizontal force at the end point of the catenary, omega is gravity of unit length of the catenary, h is water depth, and when the length of the catenary is S 0≥Sm, the catenary is a self-catenary; when S 0<Sm is performed, the catenary is a constraint chain, the shortest length of the catenary is 310.4m, and 1.25 can be used as a safety factor in consideration of a certain bottoming length as a safety margin, namely, the length of the anchor chain can be selected to be about 388 m.
(4) Next, selecting a layout mode of anchor chains, in the embodiment, six anchor chains are grouped, each group is two adjacent anchor chains, the included angle range of the anchor chains in the group is 10 degrees to 60 degrees, the embodiment is divided into four types of 15 degrees, 30 degrees, 45 degrees and 60 degrees according to the difference of the minimum included angles, and under the environmental parameters selected according to the design, software Orcaflex is used for correspondingly calculating the hydrodynamic force of the single-point mooring system with the anchor chains and adopting the different minimum included angles, and the optimal scheme is obtained by comparison. As a result, as shown in fig. 3, the tension of the forward direction of the pontoon to the anchor chain is the maximum, and when the (a) of fig. 3 is that the wave current is 120 degrees, the forward direction of the pontoon to the anchor chain is the anchor chain 6; when the wave current of (b) of fig. 3 is 180 degrees, the facing current is the anchor chain 1. Under the condition that the minimum included angle of the anchor chain is 60 degrees, the tension of the anchor chain against the flow is maximum and is about 5 percent larger; for the non-head-on flow, the anchor chain tension is significantly less than in the other cases where the minimum included angle of the anchor chain is 60 degrees. As can be seen from fig. 3 (c), when the stormy waves and currents are 120 °, the minimum included angle of the anchor chain is 60 °, and each displacement of the pontoon is smaller than other included angles; as can be seen from fig. 3 (d), the displacement of the pontoon in the Z direction is minimal when the maximum displacement of the pontoon in the Z direction is 60 ° as the minimum included angle of the anchor chain. Thus, the present design selects the minimum included angle of the anchor chain to be 60 °.
(5) And optimizing the main scale of the anchoring system, and performing sensitivity analysis on the length of the anchor chain and the anchoring radius. Wherein the anchoring radius is selected from 375m, 379m, 383m, 387m and 391m, the length of the anchor chain is equal to the anchoring radius + -5 m, and each interval is 2 m. The environmental conditions are calculated by using the conventional value and the extreme value of the oil-free wheel system when the oil-free wheel system is in the parking state, and the numerical values such as the maximum displacement of the pontoon, the maximum tension of the anchor chain and the like can be obtained by using software Orcaflex for calculation, and the result is shown in figure 4.
From the results of fig. 4, it is possible to analyze: the introduction parameter b=r/s, where r is the anchoring radius and s is the chain length. As the value b decreases, i.e. the chain length increases or the anchoring radius decreases, it can be seen from fig. 4 (c) and (d) that the pontoon displacement increases, the ability of the chain to position the pontoon decreases, and the chain tension increases after decreasing. As can be seen from fig. 4 (b), when the value of b is large, the tensioning degree of the anchor chain is high, the pretension is high, resulting in a high tension value during operation; when the value of b is smaller, the pontoon movement response is larger, and therefore the maximum tension of the anchor chain is increased. When the chain length or mooring radius changes but the b value is about the same, the buoy motion response is about the same as the chain maximum tension.
In practical applications, the b value is mainly represented by the catenary initial shape. That is, when the catenary is loosened from the tight state, the positioning capability of the anchor chain to the pontoon is weakened, the tension of the anchor chain is firstly reduced and then increased, and the maximum tension of the underwater hose is increased, which is also consistent with the experience of qualitative analysis. In the sea condition, the anchoring radius 383m and the system condition under the condition of the anchor chain length 382m are optimal, so that the anchoring radius 383m and the anchor chain length 382m are selected.
(6) The underwater hose is selected through the water depth, as shown in fig. 5, the underwater hose mainly comprises a Chinese lantern type, a slow s type and a steep s type, the transverse displacement of the pontoon is calculated and analyzed on the basis of the completion of the anchor chain design, and the Chinese lantern type underwater hose can be adopted when the transverse drift amplitude of the pontoon is less than 20% of the water depth; if the transverse drift amplitude of the pontoon is not lower than 20% of the water depth, a slow-s-shaped underwater hose can be adopted, meanwhile, the upper limit and the lower limit of the length of the underwater hose are determined according to the water depth, the lower limit of the length of the underwater hose is larger than the water depth, the upper limit of the length of the underwater hose is not longer than 150% of the water depth, and the initial length l 0 of the underwater hose is determined.
(7) The underwater hose length is optimized, the selected underwater hose length l 0 is increased and decreased, each time the underwater hose length is adjusted to be not more than 1.5m, a group of l i is obtained, and different hose lengths are calculated through software Orcaflex. Considering that the water depth is 30m, the initial length l 0 can be initially selected from three lengths of 32.1m, 33.6m and 35.1m for sensitivity analysis, the bending radius and the tension of the underwater hose are analyzed, the influence of the hose length on the hydrodynamic response of the hose is studied, the optimal hose length is selected in a comparison mode, and the numerical calculation is carried out by adopting Orcaflex, wherein the results are shown in fig. 6 and table 4.
TABLE 4 influence of hose length on buoy displacement and chain tension
From the above results it can be seen that the change in hose length has little effect on the single point mooring buoy displacement and the chain tension, but has a greater effect on the degree of bending and tension of the hose itself. From the calculation of graph (b) in fig. 6, the reduced hose length at normal values of operating conditions helps to increase the minimum bend radius of the hose. In extreme cases, however, the hose hydrodynamic response of (c) and (d) in fig. 6 has no significant relationship to the hose length. In contrast, the response of the underwater hose is relatively excellent at a hose length of 33.6m, and thus the underwater hose length is selected to be 33.6m.
(8) Simulation calculations performed by software Orcaflex to select the length of the dolphin, and the longest dolphin may be selected as the initial valueGradually shorten the mooring line length/>Until the calculation is carried out when the tanker collides with the pontoonThen choose/>Initial value/>, as final dolphin lengthNot shorter than 150m. In the embodiment, the comparison calculation analysis is performed by adopting the conditions that the lengths of the mooring ropes are 40m, 80m, 120m and 160m respectively. Buoy parameters, environmental conditions and tanker parameters are shown in tables 1, 2 and 3, and numerical calculations were performed using Orcaflex and the results are shown in fig. 7. The results of fig. 7 (a), (b), (c) and (d) all show that both the bow and heave values of the mooring tanker increase with increasing mooring line length. However, during the simulation, when the mooring line length is 40m, a tanker collision with the buoy occurs. With the above considerations in mind, the mooring line length may be selected to be 80m.
Through the research and analysis of the above parts, we can obtain the following design schemes: the pontoon can select a turret pontoon, 6 anchor chains with an included angle of 60 degrees are adopted to be anchored on the sea bottom, the anchoring radius is 383m, and the length of the anchor chains is 382m; the underwater hose adopts a Chinese lantern shape, and the length is 33.6m; the mooring line length is 80m.
Claims (6)
1. A catenary single point mooring platform main scale design and optimization method is characterized in that: the method comprises the following steps:
(1) Acquiring wind wave flow and water depth data of a designed sea area, selecting a conventional value and an extreme value in the data as environmental conditions during design, and acquiring ship type data of a designed tanker;
(2) The transverse force and the longitudinal force of wind wave currents acting on the tanker and the pontoon are calculated or obtained by using software Orcaflex, and the horizontal force required by mooring the tanker and the pontoon under the wind wave current condition is calculated by using the transverse force and the longitudinal force data;
(3) Taking the horizontal force, the water depth and the dead weight of the anchor chain required by mooring the buoy as parameters into a catenary equation:
wherein, F is horizontal force at the end point of the catenary, omega is gravity of unit length of the catenary, h is water depth, and when the length of the catenary is S 0≥Sm, the catenary is a self-catenary; when S 0<Sm is carried out, the catenary is a constraint chain, so that the minimum initial length of the anchor chain formed by the catenary is calculated;
(4) Grouping the anchor chains in pairs, wherein each group is two adjacent anchor chains, changing the included angle of the anchor chains in the group, performing systematic hydrodynamic response calculation on the conditions of different included angles to obtain the maximum tension of the anchor chains and the maximum displacement of the pontoon, and selecting the included angle corresponding to the relatively smaller tension and displacement;
(5) The length of the anchor chain and the anchoring radius are adjusted, i groups of different anchoring radii r i are selected, and the range of the anchoring radii is Wherein h is the water depth, S 0 is the initial length of the anchor chain, j anchor chain lengths S j are selected under each group of anchoring radius, and the range of the anchor chain lengths is/>Calculating the maximum tension of the anchor chain and the maximum displacement of the pontoon under different parameter combinations, and selecting the corresponding parameter combination when the tension and the displacement are relatively smaller;
(6) Calculating and analyzing the transverse displacement of the pontoon on the basis of the completion of the anchor chain design, wherein when the transverse drift amplitude of the pontoon is less than 20% of the water depth, a Chinese lantern type underwater hose can be adopted; if the transverse drift amplitude of the pontoon is not lower than 20% of the water depth, a slow-s-shaped underwater hose can be adopted, and meanwhile, the upper limit and the lower limit of the length of the underwater hose are determined according to the water depth, and the initial length l 0 of the underwater hose is determined;
(7) Optimizing the length of the underwater hose, and analyzing the bending radius and the tension of the underwater hose to obtain the condition that the minimum bending radius is relatively large and the maximum tension is relatively small;
(8) Simulation calculations performed by software Orcaflex to select the length of the dolphin, and the longest dolphin may be selected as the initial value Gradually shorten the mooring line length/>Until the calculation is carried out when the tanker collides with the pontoonThen choose/>As the final hawser length.
2. The catenary single point mooring platform main scale design and optimization method according to claim 1, wherein: in the step (2), the calculation formula of the force acting on the oil tanker and the floating pontoon for upwind is as follows:
Wherein, C xw is a dimensionless longitudinal wind power coefficient, C yw is a dimensionless transverse wind power coefficient, ρ w is the density of air at 20 ℃, 1.223kg/m 3,Vw is the average wind speed at the water plane 10m, A T is the transverse wind receiving area on the water surface of the ship body, A L is the longitudinal wind receiving area on the water surface of the ship body, F xw is the longitudinal force of wind on the ship body, F yw is the transverse force of wind on the ship body, C xw is a dimensionless longitudinal fluid coefficient, and C yw is a dimensionless transverse fluid coefficient;
the calculation formula of the force acting on the upward flow of the tanker and the pontoon is as follows:
Wherein ρ c is the density of seawater at 20 ℃, 1025kg/m 3,Vc is the average flow rate, T is the vessel draft, F xc is the longitudinal force of the flow on the hull, F yc is the lateral force of the flow on the hull;
Wave forces acting on the tanker and buoy are calculated by the Morisen formula:
Wherein F is horizontal wave force acting on the ship at any height, V is the volume of the ship, A is the projected area of the ship vertical to the horizontal direction, mu n is the instantaneous wave fluid velocity vertical to the axis of the ship, Is the instantaneous wave fluid acceleration perpendicular to the hull axis, C D is the drag coefficient, C M is the inertial force coefficient;
Vector addition is carried out on the acting forces of wind, current and wave to obtain the horizontal force required by mooring the ship body or the pontoon under the action of wind, wave and current conditions.
3. The catenary single point mooring platform main scale design and optimization method according to claim 1, wherein: the included angle of the anchor chains in the group in the step (4) is 10-60 degrees.
4. The catenary single point mooring platform main scale design and optimization method according to claim 1, wherein: the lower limit of the length of the underwater hose in the step (6) is larger than the water depth, and the upper limit of the length of the underwater hose is not longer than 150% of the water depth.
5. The catenary single point mooring platform main scale design and optimization method according to claim 1, wherein: in the optimization mode in the step (7), the selected underwater hose length l 0 is increased and reduced, and is adjusted to be not more than 1.5m each time, so that a group of l i is obtained, different hose lengths are calculated through software Orcaflex, the corresponding minimum bending radius and maximum tension of the hose are obtained, and the conditions that the minimum bending radius is relatively large and the maximum tension is relatively small are selected.
6. The catenary single point mooring platform main scale design and optimization method according to claim 1, wherein: initial value in step (8)Not shorter than 150m.
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