JP2014112061A - System and method for estimating behaviour/stress distribution of underwater linear structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system and a method for estimating the behaviour/stress distribution of an underwater linear structure.SOLUTION: The system and the method for estimating behavior/stress distribution of an underwater linear structure comprises: a riser pipe 11 of the underwater linear structure extending to a sea bottom side from a sea surface side; an accelerometer for measuring an acceleration due to a tidal velocity with a prescribed interval retained for the underwater linear structure; a measured data storage unit for storing measured data acquired from the accelerometer; a database storage unit for previously executing a calculation with the tidal velocity/distribution as a parameter, and constructing and storing the database of acceleration spectra/behavior/stress distribution of the underwater linear structure at each measurement point; calculating the acceleration spectra stemming from the accelerometer measured in a short period from a calculation result acquired from the measured data from the accelerometer at each position; and output means for making the acquired acceleration spectra match with the database of the acceleration spectra/behavior/stress distribution stored in the database storage unit, and extracting the nearest tidal velocity/distribution, and outputting the behavior/stress distribution for the underwater linear structure at the measuring time.

Description

  The present invention relates to an underwater linear structure behavior / stress distribution estimation system and method.

  Offshore platforms (for oil development, scientific research, etc.), risers for excavation for suspending long pipe risers (hereinafter also referred to as “riser pipes”) below the ship, Underwater linear structures such as production risers that are used to lift crude oil from offshore oil fields to other platforms are known. A riser for working on such a seabed has a very long structure, and the total length of the riser can reach several thousand meters.

  In recent years, riser operations have been increasing in areas where strong currents exist. Therefore, when the vibration period of the excitation force due to the vortex generated from the riser due to the tidal current matches the natural frequency of the riser, the riser will be vortex-induced (VIV) vortex induced vibration (VIV). When the riser resonates with vibrations of about 1 to several Hz excited by vortex excitation, there is a risk of fatigue failure. Therefore, the riser is measured by measuring stress and displacement over the entire riser. It is necessary to grasp the fatigue state.

  As a method for measuring the stress and displacement of the riser, for example, a method of measuring a response of the riser to the flow of seawater by attaching a sensor such as an accelerometer or an optical fiber to the surface of the riser pipe has been proposed.

  For example, a response distribution measurement system for a riser pipe is disclosed in which an optical fiber is bonded and laid on the surface of the riser pipe in advance, the reflected light with respect to the incident light of the optical fiber is received, and the stress applied to the riser pipe is calculated. (For example, refer to Patent Document 1).

  Also, when using the riser in tidal currents, streamlined, elliptical, oval, etc. to reduce fluid resistance acting on the riser and to prevent vortex excitation caused by the vortex generated from the riser It has been proposed to install a cover (fairing) having a cross-sectional shape.

  For example, when the fairing rotates around the riser pipe, the direction of the tidal current can change in the direction of the smallest resistance, and all the same shape and size are equally spaced in the water depth direction (same installation interval) (See, for example, Patent Document 2).

JP 2012-98239 A JP 2010-7434 A

By the way, since the structure of the riser pipe is very long, the mode of response of each part of the riser pipe to the flow of seawater becomes a high-order vibration mode of the tenth order to the hundredth order. Therefore, the method of measuring the response of the riser tube by attaching an accelerometer to the surface of the riser tube requires a large number of measurement points, but due to the difficulty in handling the measurement cable, only a few measurement points are required. There is a problem that it cannot be provided.
As a result, it is difficult to accurately measure stress and displacement over the entire riser.

  Therefore, the advent of a technique for estimating behavior / stress distribution in an arbitrary part over the entire riser is desired.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a system and method for estimating the behavior / stress distribution of an underwater linear structure capable of grasping the behavior of the underwater linear structure. And

  The first invention of the present invention for solving the above-mentioned problems is an underwater linear structure obtained by continuously extending a plurality of pipes in the vertical direction from the sea surface side to the sea floor side, and the underwater wire. Accelerometer that measures acceleration due to tidal flow velocity with a predetermined interval in the structure, measurement data storage unit that stores measurement data obtained by this accelerometer, and calculation using tidal flow velocity and distribution as parameters in advance The database of the acceleration spectrum, behavior and stress distribution of the underwater linear structure at each measurement point is constructed and stored, and the measurement data from the accelerometer at each position of the underwater linear structure The acceleration spectrum derived from the accelerometer measured for a short period of time is calculated from the calculation result obtained from the above, and the obtained acceleration spectrum is stored in the database storage unit as the acceleration spectrum, behavior, and stress components. An output means for extracting the nearest tidal flow velocity / distribution and outputting the behavior / stress distribution for the underwater linear structure at the time of measurement. It is in the behavior / stress distribution estimation system.

  According to a second aspect of the present invention, there is provided the underwater linear structure according to the first aspect, wherein the accelerometer is stored and installed in a pressure vessel at a joint of the riser pipe with a predetermined interval. It is in the behavior / stress distribution estimation system.

  A third invention is a method for estimating the behavior / stress distribution of a submerged linear structure obtained by continuously extending a plurality of pipes in a vertical direction from the sea surface side to the sea bottom side. A database storage step of performing calculation using the tidal velocity / distribution of the object as a parameter, and constructing and storing a database of acceleration spectrum / behavior / stress distribution of the underwater linear structure at each measurement point; and the underwater linear structure Using a measurement step to measure acceleration due to tidal flow velocity using an accelerometer installed at a predetermined interval on the object and a calculation result obtained from measurement data from the accelerometer at each position of the underwater linear structure, An acceleration spectrum calculation step for calculating an acceleration spectrum derived from the accelerometer measured for a period of time and an acceleration spectrum obtained by the measurement are mapped to the stored database. And output the behavior / stress distribution of the underwater linear structure at the time of measurement, and output the behavior / stress distribution of the underwater linear structure at the time of measurement. In the estimation method.

  According to the present invention, the acceleration spectrum is calculated from the measured acceleration data, matched with the acceleration spectrum database, the closest tidal flow velocity / distribution is extracted, and the behavior / stress distribution at that time is output by the output means. Thereby, the response of the underwater linear structure can be estimated.

FIG. 1 is a schematic configuration diagram of an underwater linear structure according to an embodiment. FIG. 2 is a schematic view showing an installation state of sensors installed at the joint of the riser pipe. FIG. 3 is a schematic diagram showing a procedure for matching a database based on measurement data. FIG. 4 is a flowchart illustrating an example of steps of the estimation method. FIG. 5 is a schematic diagram showing measurement data and calculation data. FIG. 6 is a schematic configuration diagram of another underwater linear structure according to the embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by this Example, Moreover, when there exists multiple Example, what comprises combining each Example is also included.

FIG. 1 is a schematic configuration diagram of an underwater linear structure according to an embodiment. FIG. 2 is a schematic view showing an installation state of sensors installed at the joint of the riser pipe. FIG. 3 is a schematic diagram showing a procedure for matching a database based on measurement data. FIG. 4 is a flowchart illustrating an example of steps of the estimation method. FIG. 5 is a schematic diagram showing measurement data and calculation data. FIG. 6 is a schematic configuration diagram of another underwater linear structure according to the embodiment.
As shown in FIG. 1, the underwater linear structure includes a riser pipe 11 formed by continuously extending a plurality of pipes in the vertical direction from the sea surface S side to the sea bottom G side. (For development, scientific research, etc.), a riser for excavation for suspending underwater linear structures from ships, and for production used to lift crude oil collected from offshore oil fields to an offshore platform Applies to risers etc.

  The riser pipe 11 has a structure in which, for example, 20 m to several tens of m riser pipes are connected in series, and the total length reaches several thousand m (depth D from the sea surface S to the sea floor G). It is.

  The floating body 13 floating on the ocean has the riser pipe 11 disposed in the sea from the sea, and the tip thereof reaches the seabed G. The floating body 13 is, for example, a ship or an offshore platform. As the riser pipe 11, for example, a riser pipe for excavation excavates the seabed G at the tip portion. A blowout preventer (BOP) 14 is disposed at the boundary between the riser pipe 11 and the seabed G.

FIG. 2 is an enlarged configuration diagram of the riser pipe 11 at the portion X in FIG. 1, and schematically shows the installation status of sensors installed at the joint of the riser pipe 11.
As shown in FIG. 2, a plurality of risers 11a, 11b, 11c, 11d,... Constituting the riser pipe 11 are connected using joints 17a, 17b. And pressure-resistant containers 18a, 18b, and 18c are installed in a part of the lower joint 17b of the risers 11a, 11b, and 11c.

The pressure vessel 18a... Contains an accelerometer that measures the acceleration to the riser pipe 11 caused by the tidal current 15 (see FIG. 1), and is connected to the measuring / calculating means 12 on the floating body 13 side by a cable (not shown). Measurement data is sent from time to time.
Here, the accelerometer measures acceleration due to various vibrations of the riser tube 11 at an arbitrary position.
In addition to data transmission, data transmission / reception means by ultrasonic transmission installed at a predetermined interval may be used for data transmission.

  FIG. 3 shows a procedure for matching the database based on the measurement data of the accelerometer. First, several points of the riser tube 11 (11a, 11b, 11c) (three points in this embodiment: a point, Acceleration data is measured by accelerometers installed in the pressure-resistant containers 18a, 18b, and 18c at points b and c).

  Next, the measurement data is sent to the measurement / calculation means 12, where the standard deviation of each point (three points) from the measurement data is obtained.

The standard deviation of the calculated acceleration is shown in FIG.
With the standard deviation shown in FIG. 3B, it is impossible to estimate the behavior / stress distribution between the accelerometers.

Therefore, the closest behavior / stress distribution is extracted by matching with a previously calculated database.
The output of the extracted behavior / stress distribution is shown in FIG.

  From the results shown in FIG. 3C, it was difficult to estimate the overall behavior (stress, displacement) from the measurement data measured at several points as in the past, but grasp the behavior at an arbitrary point can do.

Hereinafter, a procedure for estimating behavior / stress distribution based on behavior data (acceleration, angular acceleration) measured at several points of the underwater linear structure will be described.
FIG. 4 is a flowchart illustrating an example of steps of the estimation method. Hereinafter, the processing shown in FIG. 4 may be executed fully automatically, or may be executed by an operator operating an apparatus that executes each process.

1) Database storage step A calculation is made in advance using the tidal flow velocity / distribution of the riser pipe 11, which is an underwater linear structure, as a parameter, and the acceleration spectrum / behavior / stress distribution database of the underwater linear structure at each measurement point. Is constructed and stored (step S11).
2) Measurement step Acceleration due to the tidal velocity is measured using an accelerometer installed on the underwater linear structure with a predetermined interval (step S12).
3) Acceleration spectrum calculation step From the calculation result obtained from the measurement data from the accelerometer at each position of the underwater linear structure, an acceleration spectrum derived from the accelerometer measured for a short period is calculated (step S13).
4) Output step The acceleration spectrum obtained by this measurement is matched with the stored database, the nearest tidal velocity / distribution is extracted, and the behavior / stress distribution for the underwater linear structure at the time of measurement is output ( Step S14).

  Specifically, as the database, for example, calculations using tidal flow velocity / distribution as parameters are performed in advance, and a database of acceleration spectrum / behavior / stress distribution at the measurement point is constructed.

Next, using the measurement / calculation means 12 on the floating body 13, the acceleration spectrum is calculated from the acceleration data measured for a short period, matched with the acceleration spectrum database, and the closest tidal velocity / distribution is extracted. The behavior / stress distribution is output by the output means.
Thereby, the response of the underwater linear structure can be estimated.

  Next, FIG. 5 shows an example of extracting the behavior / stress distribution from the calculation data based on the measurement data.

1) A difference between measurement data V _m measured by an accelerometer and calculation data V _c calculated in advance under a plurality of conditions is obtained at each measurement position. In FIG. 5, as the measurement data V _m, and _{V m1, V m2, V m3} . The calculation data V _c calculated in advance under a plurality of conditions includes V _{c1 (a) to} V _{c3 (a)} , V _{c1 (b) to} V _{c3 (b)} , V _{c1 (x) to} V _{c3 (x )} .
2) Then, calculation data that minimizes the average value of V _m -V _c at each measurement position is adopted.
For example, when the average value of each difference is expressed by, for example, “Equation 1” below, the response distribution of “case (a)” that is the minimum calculation data is employed.
3) As a result of this adoption, the response distribution of case (a) is assumed to be the response of the riser tube 11.
This response indicates, for example, acceleration, strain, and vibration waveforms (amplitude and frequency) generated in the riser tube 11.
Thereby, the response of each space | interval of the riser pipe | tube 11 (11a, 11b, 11c ...) can be estimated, and grasping | ascertainment of the fatigue state to a riser pipe | tube becomes accurate.

  Here, the plurality of conditions are based on “sea state weather conditions”, “specification conditions of the riser pipe 11”, “operation state conditions”, and the like, and are appropriately changed according to the measurement purpose.

  Here, as examples of “sea state meteorological conditions”, 1) wave conditions (for example, wave height, wave period, wave direction, etc.), 2) wind conditions (for example, wind speed, wind direction, etc.), 3) tidal current (sea current) conditions (for example, Flow velocity, flow direction, etc.).

  Examples of the “specification conditions of the riser pipe 11” include 1) dimensions of the riser pipe 11 (eg, length, outer diameter, inner diameter, weight, etc.), 2) rigidity of the riser pipe 11 (tensile strength, bending strength, etc.) 3) The presence or absence of a buoyant body can be examined.

Examples of the “operation state condition” are 1) excavation state (a state where the riser pipe 11 is installed on the seabed), 2) hang-off state (a state where the riser pipe is suspended from the seabed in the sea) 3) A moving state (a state of moving from the sea area in a hang-off state) can be examined.
Moreover, even if it is other than these, if it is the conditions which contribute to the grasp of a fatigue state, it can also add suitably.

FIG. 6 is a schematic configuration diagram of another underwater linear structure according to the embodiment.
Based on the behavior / stress distribution obtained as described above, it is possible to estimate a place where the tidal current 15 is strong (strong tidal current 15a).

  And the position of the fairing 21 in order to suppress the vortex excitation (VIV) of the riser pipe 11 fixed before the measurement, the moving means (not shown) via the cable 22 according to the command of the control device 23 on the floating body 13 side. Therefore, the fluid resistance acting on the riser pipe 11 can be reduced.

  This movement may be carried out by pulling up the entire riser tube 11 to the floating body 13 side, but when using a fairing 21 that can be raised and lowered, the fairing 21 is moved to a portion where stress and displacement are large. The fluid resistance acting on the riser tube 11 can be reduced, and the vortex excitation (VIV) caused by the vortex generated from the riser tube 11 can be suppressed.

11 Riser Pipe 12 Measuring / Calculating Means 13 Floating Body 14 Blowout Prevention Device 15 Current

Claims (3)

An underwater linear structure obtained by continuously extending a plurality of pipes in the vertical direction from the sea surface side to the sea floor side;
An accelerometer that measures acceleration due to tidal flow velocity with a predetermined interval in the underwater linear structure;
A measurement data storage unit for storing measurement data obtained by the accelerometer;
A database storage unit that carries out calculations using the tidal current velocity and distribution as parameters in advance, constructs and stores a database of acceleration spectra, behavior, and stress distribution of underwater linear structures at each measurement point;
From the calculation result obtained from the measurement data from the accelerometer at each position of the underwater linear structure, calculate the acceleration spectrum derived from the accelerometer measured for a short period,
The obtained acceleration spectrum is matched with the database of acceleration spectrum, behavior, and stress distribution stored in the database storage unit, and the closest tidal velocity / distribution is extracted, and the behavior / stress distribution for the underwater linear structure at the time of measurement is extracted. And an output means for outputting the behavior / stress distribution estimation system of the underwater linear structure. In claim 1,
The underwater linear structure behavior / stress distribution estimation system, wherein the accelerometer is stored and installed in a pressure-resistant container at a joint of a riser pipe with a predetermined interval. A method for estimating the behavior and stress distribution of an underwater linear structure obtained by continuously extending a plurality of pipes in the vertical direction from the sea surface side to the sea floor side,
A database storage step for performing a calculation using the tidal flow velocity / distribution for the underwater linear structure in advance as a parameter, and constructing and storing a database of acceleration spectrum / behavior / stress distribution of the underwater linear structure at each measurement point;
Using an accelerometer installed at a predetermined interval in the underwater linear structure, a measurement step for measuring acceleration due to a tidal velocity,
From a calculation result obtained from measurement data from an accelerometer at each position of the underwater linear structure, an acceleration spectrum calculation step of calculating an acceleration spectrum derived from an accelerometer measured for a short period,
The output step of matching the acceleration spectrum obtained by the measurement with the stored database, extracting the closest tidal flow velocity / distribution, and outputting the behavior / stress distribution for the underwater linear structure at the time of measurement,
A method for estimating the behavior and stress distribution of an underwater linear structure characterized by comprising:

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