Damping calibration method based on cylindrical FPSO ship model experiment

Abstract

The present invention relates to a ship model experiment damping calibration method based on a cylindrical FPSO, comprising the following steps: establishing a scaled model of a cylindrical FPSO; performing numerical simulation before the scaled model experiment to determine the sea conditions that need to be paid attention to when performing the scaled model experiment; performing a free decay experiment on the scaled model of the cylindrical FPSO to obtain the viscosity coefficient in the hydrodynamic analysis; performing an irregular wave experiment on the scaled model of the cylindrical FPSO; establishing a damping calibration model, comparing the results of the irregular wave experiment on the scaled model of the cylindrical FPSO, and selecting the damping suitable for different sea conditions. The method can calibrate the most suitable damping at the matching position according to the special structural properties of the cylindrical FPSO, so as to achieve the best match with the results of the scaled model experiment.

Description

Technical Field

[0001] The invention relates to a ship model experimental damping calibration method based on a cylindrical FPSO, belonging to the technical field of offshore oil development. Background Art

[0002] Since my country has abundant offshore oil and gas reserves, the main battlefield for oil and gas development and exploration in my country has now shifted from inland and shallow seas to deep seas. In order to exploit deep-sea oil and gas, it is usually necessary to build an oil and gas production platform on the surface of the deep sea that integrates deep-sea drilling, oil and gas processing, oil storage, oil unloading, power generation, heating and living functions, and then transport oil and natural gas to oil tankers or land-based oil or gas tanks through pipelines. Oil and gas production platforms are generally suspended on the surface of deep sea water. In order to drill in the deep sea and transport the drilled oil and gas, the current mainstream deep-sea oil and gas field development solutions mainly include semi-submersible platforms, floating production storage and offloading units (FPSO), SPAR, and tension leg platforms. These production platforms have different economic and technical applicability for different sea conditions and different stages of oil field development.

[0003] The cylindrical FPSO has a large waterline area and complex hydrodynamic performance. The motion performance during actual operation is difficult to predict and capture. In addition, there are few projects with past applications and the relevant project information is extremely limited. Therefore, it is very dependent on the results of model experiments. However, due to the excessive sea conditions during the actual operation of the platform, it is difficult for model experiments to simulate all operating sea conditions. In addition, due to the conditions of the water tank used in the model experiment, it is difficult to simulate all the factors of concern. For example, because the mooring system needs to be truncated, the tension and fatigue strength of the mooring are difficult to simulate to be consistent with the actual operating sea conditions. Therefore, it is necessary to perform damping correction and calibration on the calculation model of numerical simulation based on the experimental results.

[0004] At the same time, because conventional potential flow commercial software such as aqwa and orcaflex do not consider the effect of viscous loads by default, it is necessary to reasonably select damping to replace the viscous load effect based on the experimental results. The characteristics of the cylindrical FPSO's own structure determine that it is difficult to accurately capture its motion characteristics using conventional damping correction methods for ship types, so it is also necessary to reasonably calibrate the damping applicable to numerical simulation based on experimental results. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a ship model experimental damping calibration method based on a cylindrical FPSO, which is used to solve the problem that it is difficult to accurately predict the motion performance of the cylindrical FPSO in the design stage, and effectively ensures the reliability and rationality of the design.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A ship model experimental damping calibration method based on a cylindrical FPSO comprises the following steps:

[0008] Build a scaled model of a cylindrical FPSO;

[0009] Numerical simulations are conducted before the scale model experiment to determine the sea conditions that need to be paid attention to when conducting the scale model experiment;

[0010] A free decay test was conducted on a scaled model of a cylindrical FPSO to obtain the viscous force coefficient in the hydrodynamic analysis.

[0011] Conduct irregular wave experiments on a scaled model of a cylindrical FPSO;

[0012] A damping calibration model is established, and the results of irregular wave experiments on a scaled model of a cylindrical FPSO are compared to select the damping suitable for different sea conditions.

[0013] The ship model experiment damping calibration method, preferably, the specific process of determining the sea conditions that need to be paid attention to when conducting the ship model scale model experiment is as follows:

[0014] Using isotime domain analysis software to screen and calculate under various working conditions and loading conditions, the damping of the cylindrical FPSO ship scale model was preliminarily selected;

[0015] According to the screening calculation results, the required working conditions are found as the working conditions that need to be paid attention to in the scale model experiment.

[0016] The ship model experimental damping calibration method preferably performs a free decay experiment on a scaled model of a cylindrical FPSO ship model, and the specific process is as follows:

[0017] The scaled model of the cylindrical FPSO was subjected to free decay experiments under different loading conditions, focusing on the free decay in the heave, roll and pitch directions;

[0018] A free attenuation model is established to compare the attenuation of heave, roll and pitch. The parameters and damping of the model are repeatedly adjusted until the attenuation curves of heave, roll and pitch match those of the scaled model experiment.

[0019] The ship model experimental damping calibration method preferably performs a free decay experiment on a scaled model of a cylindrical FPSO ship model, and further comprises the following steps:

[0020] The secondary damping of the heave obtained by free decay is converted into the vertical drag coefficient of the Morrison bar, which is applicable in the frequency domain calculation. The formula used is as follows:

[0021] Cd=2 / (d*Pi*D*1.025)*D2

[0022] Where: Cd is the drag coefficient of the Morrison bar; d is the diameter enclosed by the Morrison bar; Pi is 3.1415926; D is the radius of the Morrison bar itself; D2 is the secondary damping obtained by the free attenuation of the heave swing.

[0023] The ship model experiment damping calibration method preferably performs an irregular wave experiment on a scaled model of a cylindrical FPSO ship model, and the specific process is as follows:

[0024] The environmental conditions of the irregular wave experiment were set to once a year, once a decade, and once a century;

[0025] For the multi-point mooring system, the environmental load directions were selected to be directly facing one set of cables, with an angle of 30 degrees and 60 degrees with one set of cables, and three seeds were made downward for each wave;

[0026] When there is data from wind tunnel tests, wind loads and flow loads are pulled at the load application point by a winch and simulated using a load time history;

[0027] The irregular wave experimental results are processed, focusing on the maximum value, minimum value, mean value, standard deviation and fitting curve of Weibull distribution under each working condition.

[0028] The ship model experimental damping calibration method preferably establishes a damping calibration model, compares the results of the irregular wave experiment on the cylindrical FPSO ship model scale model, and selects the damping suitable for different sea conditions. The specific process is as follows:

[0029] A damping calibration model was established in the time domain analysis software, and secondary damping data was initially selected. The initial roll, pitch, and heave damping values ​​were consistent with those obtained in the free decay experiment, and the initial damping of the roll and pitch were set to 0.

[0030] The numerical calculation results were processed to obtain the maximum value, minimum value, average value, standard deviation and extreme value Weibull distribution fitting effect under each working condition, and the results were compared with the results of the scaled model experiment;

[0031] Adjust the input damping until the results of the scaled model experiment are consistent with the results of the numerical simulation.

[0032] The present invention adopts the above technical solution, which has the following advantages:

[0033] 1. The cylindrical FPSO of the present invention has a simple structure, high oil storage efficiency per unit steel volume and low construction cost compared to the ship-type FPSO, no single-point device and no need for a turret structure, low later maintenance cost, no wind direction requirements, insensitivity to the direction of environmental loads, high deck bearing capacity, small fatigue load caused by waves, etc. It is very suitable for the secondary development of isolated oil fields and marginal oil fields that have reached the middle and late stages of development.

[0034] 2. The damping calibration method for the cylindrical FPSO ship model experiment of the present invention can calibrate and match the most appropriate damping according to the special structural properties of the cylindrical FPSO, so as to achieve the best match with the results of the scaled model experiment. This can ensure the accuracy, rationality and reliability of the subsequent numerical simulation, and the safety of the design can also be guaranteed, which plays a key supporting role in the design of the entire platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a model in the time domain numerical simulation provided by an embodiment of the present invention, wherein a is the time when the environmental load direction is facing a group of mooring cables, b is the angle between the environmental load direction and a group of mooring cables, which is one quarter of the angle between the two groups of mooring cables, which is 30 degrees in this example, and c is the direction of the environmental load facing the middle of the two groups of cables, which is 60 degrees in this example;

[0036] Figure 2 The FPSO model used in the frequency domain hydrodynamic analysis provided by this embodiment of the present invention;

[0037] Figure 3 The Morrison model used in the frequency domain hydrodynamic analysis provided for this embodiment of the present invention;

[0038] Figure 4-6 For a group of mooring lines facing the 255 degree environmental load direction ( Figure 1 The numerical simulation (the direction of the cable facing the west and north) Figure 4-6 b) and experimental results ( Figure 4-6 A) is a comparison of the single-seed Weibull fit of Figure 4 For the dangling, Figure 5 For the indulgence, Figure 6 For vertical shaking. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work are within the scope of protection of the present invention.

[0040] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons with ordinary skills in the field to which the present invention belongs. The words "first", "second", "third", "fourth", "upper", "lower", "left and right" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0041] The damping calibration method for the cylindrical FPSO ship model experiment provided by the present invention is completely based on the scaled model experiment. First, a suitable scale ratio is selected according to the water tank size of the model experiment while ensuring geometric approximation and Froude approximation. Generally, 1:60 is selected for engineering projects with a water depth of more than 200 meters in the South China Sea.

[0042] The damping calibration method for a cylindrical FPSO ship model experiment provided by the present invention specifically comprises the following steps:

[0043] Step S1: numerical simulation before the scaled model experiment to determine the sea conditions that need to be focused on when conducting the scaled model experiment;

[0044] Step S2: performing a free decay test on a scaled model of a cylindrical FPSO, and obtaining a viscous force coefficient in a hydrodynamic analysis through the free decay test results;

[0045] Step S3: performing an irregular wave experiment on a scaled model of a cylindrical FPSO ship model and processing the experimental results;

[0046] Step S4: Establish a damping calibration model, compare it with the irregular wave test results of the cylindrical FPSO ship scale model, and select appropriate damping under different sea conditions.

[0047] Furthermore, step S1 includes the following steps:

[0048] Step S11: For previous projects, the time domain analysis software is used to perform screening calculations under various working conditions and loading conditions, and the damping of the cylindrical FPSO ship scale model is preliminarily selected.

[0049] Step S12: Find out the key working conditions as the working conditions that should be focused on in the scaled model experiment according to the screening calculation results.

[0050] Furthermore, the step S2 comprises the following steps:

[0051] Step S21: The scaled model of the cylindrical FPSO is subjected to free decay experiments under different loading conditions, mainly focusing on the free decay in the heave, roll and pitch directions. The initial release amplitude of the free decay is generally selected as the maximum motion amplitude calculated in the time domain.

[0052] Step S22: Establish a free decay model in commercial software, and compare the attenuation of heave, roll and pitch. For cylindrical FPSO, secondary damping is generally selected to perform damping correction of free decay. Repeatedly adjust the parameters and damping of the model until the attenuation curves of heave, roll and pitch match the scaled model experiment.

[0053] Step S23: Since the natural period of the heave motion of a cylindrical FPSO is generally half of the roll and pitch, the heave motion is the main control factor. The Morrison formula is generally used to convert the heave secondary damping obtained by free decay into the vertical drag force coefficient of the Morrison rod. It is applicable in frequency domain calculation. The formula used is as follows:

[0054] Cd=2 / (d*Pi*D*1.025)*D2

[0055] Where: Cd is the drag coefficient of the Morrison bar; d is the diameter enclosed by the Morrison bar, which is generally selected to be slightly smaller than the radius of the heave plate; Pi is 3.1415926; D is the radius of the Morrison bar itself, which is generally selected to be 0.02 meters, and D2 is the secondary damping obtained by the free attenuation of the heave.

[0056] Further, step S3 includes the following steps:

[0057] Step S31: An irregular wave experiment is conducted on the scaled model of the cylindrical FPSO ship model. Generally, environmental conditions of once in one year, once in ten years and once in a hundred years are required. For a multi-point mooring system, the environmental load directions generally selected are facing a group of cables, and the angles with a group of cables are 30 degrees and 60 degrees. Generally, three seeds are required for each wave downward. It should be noted that when there is data from a wind tunnel experiment, the wind load and flow load are generally pulled at the load action point by a winch, and simulated by a load time history.

[0058] Step S32: Process the irregular wave test results. Generally, it is necessary to look at the maximum value, minimum value, average value and standard deviation under each working condition. Since the extreme values ​​of the motion response of the irregular wave generally conform to the Weibull distribution, the fitting curve of the Weibull distribution also needs attention.

[0059] Further, step S4 includes the following steps:

[0060] Step S41: Establish a damping calibration model in the time domain analysis software, and preliminarily select secondary damping data. The initial roll, pitch, and heave can be consistent with the damping values ​​obtained by free decay, and the initial damping of the roll and pitch can be set to 0. Note that the properties of the model itself (such as weight, center of gravity, radius of inertia, and draft) must be completely consistent with the experimental model; the data of the mooring system must also be completely consistent with the model; it should be noted that due to the certain symmetry of the cylindrical FPSO's own structure, damping can be applied to the prosthesis fixed to the FPSO (mass and radius of inertia are very small), and the prosthesis changes with the change of the environmental load direction to ensure that the head of the prosthesis is facing the environmental load direction, so that better results matching the experiment can be obtained.

[0061] Step S42: Process the numerical calculation results, and also obtain the maximum value, minimum value, average value and standard deviation under each working condition as well as the effect of extreme value Weibull distribution fitting, and compare the results with the results of the model experiment.

[0062] Step S43: Adjust the input damping until the results of the model experiment and the results of the numerical simulation are basically the same. The acceptable error requirements are: the maximum and minimum value errors are within 10%, the average values ​​are close and the standard deviation error is within 5%, and the results of Weibull fitting are also roughly the same. In this case, the selected damping is considered reasonable.

[0063] The present invention also provides a specific embodiment for illustration, which is as follows:

[0064] The environmental conditions provided by this specific embodiment are shown in Table 1:

[0065] Table 1 shows the environmental conditions for damping calibration

[0066]

[0067]

[0068] like Figure 1 As shown, it is a model in time domain numerical simulation. The time domain analysis software is Orcaflex. The arrow in the figure indicates the direction of environmental load.

[0069] like Figure 2 , 3 As shown, it is the FPSO model and Morrison model used in the frequency domain hydrodynamic analysis. The radius D enclosed by the Morrison rod is 0.956 of the heave plate radius.

[0070] like Figure 4-6 As shown, it is facing a group of mooring cables, under the 255 degree environmental load direction ( Figure 1The comparison of the single seed Weibull fitting of the numerical simulation and experimental results shows that the Weibull fitting trends of the numerical simulation and experimental results are basically the same. Because the direction of the environmental load is 255 degrees, only the pitch ( Figure 4 )、Swing( Figure 5 ) and heave ( Figure 6 ) Results with three degrees of freedom.

[0071] Table 2 shows the environmental load direction of a group of mooring lines at 255 degrees ( Figure 1 By comparing the statistical values ​​of the three seed averages of the numerical simulation and experimental results (the center is facing the direction of the cable on the northwest side), it can be seen that the experimental results are basically consistent with the results of the numerical simulation, whether it is the maximum and minimum values ​​or the standard deviation average value, which verifies the rationality of the damping selection in the numerical simulation.

[0072] Table 2 shows the comparison of the average statistical values ​​of the three seeds in the numerical simulation and experimental results.

[0073]

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A ship model experimental damping calibration method based on a cylindrical FPSO, characterized in that: The steps include: Build a scaled model of a cylindrical FPSO; Numerical simulations are conducted before the scale model experiment to determine the sea conditions that need to be paid attention to when conducting the scale model experiment; A free decay test was conducted on a scaled model of a cylindrical FPSO to obtain the viscous force coefficient in the hydrodynamic analysis. Conduct irregular wave experiments on a scaled model of a cylindrical FPSO; A damping calibration model was established, and the irregular wave test results were compared with the scaled model of the cylindrical FPSO ship model to select the damping suitable for different sea conditions; The specific process of determining the sea conditions that need to be paid attention to when conducting ship scale model experiments is as follows: Using isotime domain analysis software to screen and calculate under various working conditions and loading conditions, the damping of the cylindrical FPSO ship scale model was preliminarily selected; According to the screening calculation results, find the required working conditions as the working conditions that need to be paid attention to in the scaled model experiment; A free decay experiment was conducted on a scaled model of a cylindrical FPSO. The specific process is as follows: The scaled model of the cylindrical FPSO was subjected to free decay experiments under different loading conditions, focusing on the free decay in the heave, roll and pitch directions; Establish a free attenuation model, compare the attenuation of heave, roll and pitch, and repeatedly adjust the model parameters and damping until the attenuation curves of heave, roll and pitch match those of the scaled model experiment; The free decay experiment on the scaled model of the cylindrical FPSO also includes the following steps: The secondary damping of the heave obtained by free decay is converted into the vertical drag coefficient of the Morrison bar, which is applicable in the frequency domain calculation. The formula used is as follows: Cd=2 / (d*Pi*D*1.025)*D2 Where: Cd is the drag coefficient of the Morrison bar; d is the diameter of the Morrison bar; Pi is 3.1415926; D is the radius of the Morrison bar itself; D2 is the secondary damping obtained by the free attenuation of the heave; The irregular wave experiment was conducted on the scaled model of the cylindrical FPSO. The specific process is as follows: The environmental conditions of the irregular wave experiment were set to once a year, once a decade, and once a century; Process the irregular wave test results, focusing on the maximum value, minimum value, mean value, standard deviation and fitting curve of Weibull distribution under each working condition; A damping calibration model was established, and the irregular wave test results were compared with the scaled model of the cylindrical FPSO ship model to select the damping suitable for different sea conditions. The specific process is as follows: A damping calibration model was established in the time domain analysis software, and secondary damping data was initially selected. The initial roll, pitch, and heave damping values ​​were consistent with those obtained in the free decay experiment, and the initial damping of the roll and pitch were set to 0. The numerical calculation results were processed to obtain the maximum value, minimum value, average value, standard deviation and extreme value Weibull distribution fitting effect under each working condition, and the results were compared with the results of the scaled model experiment; Adjust the input damping until the results of the scaled model experiment are consistent with the results of the numerical simulation.

2. The ship model experimental damping calibration method according to claim 1, characterized in that: An irregular wave experiment is carried out on a scaled model of a cylindrical FPSO. When there is data from a wind tunnel experiment, the wind load and flow load are pulled at the load action point by a line and simulated using a load time history.

3. The ship model experimental damping calibration method according to claim 1, characterized in that: An irregular wave experiment was conducted on a scaled model of a cylindrical FPSO. For a multi-point mooring system, the environmental load directions were selected as facing a group of cables, with angles of 30 degrees and 60 degrees with a group of cables, and three seeds were made downward for each wave.

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