AU2021103583A4

AU2021103583A4 - Device and experimental method for simulating the effect of submarine tidal sand waves on pipeline engineering

Info

Publication number: AU2021103583A4
Application number: AU2021103583A
Authority: AU
Inventors: Zhixiong Chen; Cong Wang; Zhipeng Zang; Jinfeng Zhang; Qinghe Zhang
Original assignee: Cnpc Engineering Tech Research Co Ltd; Tianjin University
Current assignee: Cnpc Engineering Technology Research Co Ltd; Tianjin University
Priority date: 2021-06-24
Filing date: 2021-06-24
Publication date: 2021-08-26
Anticipated expiration: 2029-06-24

Abstract

The invention discloses a device and experimental method for simulating the effect of submarine tidal waves on pipeline engineering, which includes an experimental water tank and tide generation system, a terrain scanning system, a submarine pipeline simulation measurement system, and a data acquisition processing and controller. The experimental tank and tide generation system create reciprocal tidal flows using pumps to act on the sandy seabed in order to generate submarine sand waves. The terrain scanning system uses an ultrasonic topographer to collect the sand wave pattern and transmit the data to the data acquisition processing and controller; the submarine pipeline simulation measurementsimulation measurement system uses the fiber optic strain sensors, which are stuck on the side wall of the pipeline model, to collect the pipeline deformation data, and uses a high-speed camera to collect the pipeline displacement information and transmit the information to the data acquisition processing and controller. In this invention, the periodically changing flow, instead of steady flow or waves in former experiments, is generated with a pump to simulate the tidal flows and then to simulate the formation of tidal sand waves. This device can be used to conduct experiments on the impact of submarine tidal sand waves on pipeline engineering with realistic conditions and high accuracy. 1/2 FIGURES I-) CNC Cr, / 04 N 21 Fiur I

Description

1/2

FIGURES I-) CNC

Cr,

/ 04

N 21

Fiur I

Device and experimental method for simulating the effect of submarine tidal

sand waves on pipeline engineering

TECHNICAL FIELD

The present invention relates to the field of ocean engineering, sediment transport,

ocean measurement, and in particular to an device and experimental method for

simulating the effect of submarine sand tidal waves on pipeline engineering.

BACKGROUND

With the development of offshore oil and gas resources, submarine pipelines have

become the main way of offshore oil and gas transportation. Submarine sand waves are

large rhythmic bedforms developed on sandy bottoms on continental shelves, with

characteristic wavelengths ranging from tens of meters to hundreds of meters and wave

heights reaching a few meters or more. Ocean observation data show that the tidal

current is one of the main reasons for the formation of submarine sand waves. The

seabed sand waves are generally active. Under certain circumstances, the submarine

sand waves will move rapidly and cause the exposure or suspension of the submarine

pipeline, which will eventually lead to the fatigue damage of the submarine pipeline.

Therefore, it is of great engineering significance and scientific value to study the

submarine sand wave activity and the pipeline spans caused by it.

Current research on submarine sand waves mainly relies on in-situ observations

and mathematical methods. Generally, in-situ observations are costly and the

observation period is usually long, while mathematical methods are simplified models

that cannot fully simulate the transient process of sand wave activity and also need experimental results to verify the correctness of the models. Thus, laboratory simulation is effective and necessary method to research the submarine sand waves. At present, the laboratory mainly uses waves or unidirectional flow to simplify the reciprocal tidal flows, but the obtained topography scale is very small, the wavelength is only a few centimetres long, which essentially is in the category of sand ripples (a kind of smaller topography than sand waves), which is not the real sense of the tidal sand waves.

SUMMARY

In order to solve the above technical problems, the present invention provides a

device and experimental method for simulating the impact of submarine tidal sand

waves on pipeline engineering, using a variable frequency controller to control a

two-way variable frequency pump to realize the periodic change of water flow,

simulating the real tidal reciprocating flow, and combining the initial artificial terrain

interference to simulate the formation of tidal sand waves, further simulating the impact

of sand waves on submarine pipelines, the collecting data is real and high reference

value.

An device for simulating the effect of submarine tidal sand waves on pipeline

engineering, including an experimental water tank and tidal generation system, a terrain

scanning system, a submarine pipeline simulation measurement system and a data

acquisition processing and controller.

The experimental water tank and tide generation system includes a water tank, a

circulation pipe, a gently sloping sand pit, a two-way variable frequency pump, a variable frequency controller and a flow rate meter; the gently sloping sand pit is set in the middle of the water tank, and its two ends are raised and the middle is depressed to form a cavity for holding sea sand, while the raised part is provided with a gentle slope near the end of the water tank, and the height of the gentle slope gradually decreases.

The circulation pipe is installed on the lower side of the water tank, and its inlet and

outlet ends are respectively installed on the bottom surfaces of two opposite ends of

the water tank; the gently sloping sand pit is filled with sea sand; the two-way inverter

pump is installed on the circulation pipe, and the inverter controller is connected to

the two-way inverter pump and data acquisition processing and controller,

respectively, and can control the two-way inverter pump according to the commands

of data acquisition processing and controller working; the flow velocity meter is

installed inside the water tank, which is connected to the data acquisition processing

and controller.

The terrain scanning system comprises an ultrasound topographer, a connecting

rod and a motion device. The ultrasound topographer's probe is mounted on the

connecting rod, the connecting rod is mounted on the motion device and its motion

trajectory is controlled by the motion device; the connecting rod is capable of

changing the position of the ultrasound topographer's probe by means of telescoping;

the ultrasound topographer is connected to the data acquisition processing and

controller;

The submarine pipeline simulation measurement system includes a pipeline

model, a counterweight, a fiber optic strain sensor and a high speed camera; the high speed camera is mounted above the water tank and connected to the data acquisition processing and controller for photographing the shape of the sandy bed in the sand pit; the pipeline model is placed in the sand pit, which is partially or fully buried in the sea bed. The pipe model is provided with a counterweight inside; the fiber optic strain sensors are fixed longitudinally on the side wall of the pipe model with a certain interval and connected to the data acquisition processing and controller for detecting the strain data of the pipe model.

Further, the movement device includes a track on the side wall of the water tank,

a roller device capable of moving along the track, and an electric motor driving the

roller device.

Further, the circulation pipe is parallel to the long side of the water tank.

Further, the cross-section of the gentle slope is a class of right triangle with a

ratio of height to bottom side of 1:25 to 1:15.

Further, there are four strings of the fiber optic strain sensors, which are

distributed along the axis of the pipe model and are evenly distributed around the

circumference of the pipeline model with 90°.

Further, the pipe model is a PVC pipe.

Further, the counterweight is water or sea sand.

An experimental method for simulating the effect of submarine tidal sand waves

on a submarine pipeline, comprising the following steps:

1 Loading sand samples into gently sloping sand pits, then leveling the sand

surface in general and processing local areas of the sand surface into tiny bumps or

grooves.

2 Slowly injecting water into the water tank to reach the depth required for the

experiment without disturbance of the state of the sand sample in the sand pit.

3 Using the variable frequency controller to preset the period and maximum flow

rate of reciprocating flow and control the two-way frequency pump to form

reciprocating flow in the water tank.

4 Using flow velocity meters and ultrasonic topographer probes to collect the

morphology of the sea bed and transmit the collected data to the data acquisition

processing and controller (In practice, the data acquisition processing and controller is

often a computer).

5 When the sand sample forms a simulated submarine sand wave, empty the

water in the tank, lay the pipe model on the submarine sand wave, refilling water to

the original height, and create reciprocal flows in the tank to simulate the tidal flows.

6 Using flow velocity meter, ultrasonic topographer, high-speed camera and fiber

optic strain sensor, the water flow velocity, the morphology of the sea bed and the

movement and deformation of the submarine pipeline are observed synchronously;

and the collected data are transmitted to the data acquisition processing and controller

for analysis and processing.

The device to simulate the impact of submarine tidal sand waves on pipeline

engineering uses a variable frequency controller to control bi-directional variable frequency pumps to realize the periodic change of water flow, simulate the real tidal reciprocal flow, and combine the initial artificial terrain interference to simulate the formation of tidal sand waves, and further simulate the sand waves and their impact on submarine pipelines, with real conditions and high accuracy.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic diagram of the structure of the device provided by the

present invention for simulating the effect of submarine tidal sand waves on pipeline

engineering.

Figure 2 shows a schematic diagram of the structure of the submarine pipeline

simulation and measurement system 3.

Figure 3 shows an enlarged view of the side view of Figure 2.

DESCRIPTION OF THE INVENTION

The technical solutions of the present invention are described in detail below in

conjunction with the accompanying drawings and specific embodiments.

An device for simulating the effect of submarine tidal sand waves on pipeline

engineering, including an experimental water tank and tidal generation system 1, a

terrain scanning system 2, a submarine pipeline simulation measurement system 3 and

a data acquisition processing and controller 4.

The experimental water tank and tide generation system 1 includes a water tank

11, a circulation pipe 12, a gentle slope sand pit 13, a two-way variable frequency water

pump 14, a variable frequency controller 15 and a flow velocity meter 16; the gentle

slope sand pit 13 is set in the middle of the water tank 11, the two ends of which are raised and the middle is depressed to form a cavity for holding sea sand, while the raised part is connected to the bottom of the water tank through a gentle slope 17, the height of the gentle slope 17 gradually decreases; specifically, the cross-section of the gentle slope 17 is a right-angle triangle-like, and the ratio of the height to the bottom edge is 1:25 to 1:25, and as an embodiment of the present invention, the ratio of the height to the bottom edge is 1:20; The circulation pipe 12 is set on the lower side of the water tank 11, and its inlet and outlet ends are set on the bottom surfaces of the two opposite ends of the water tank 11; the gently sloping sand pit 13 is filled with sea sand.

Preferably, the surface of the sea sand is flat as a whole and is machined into a

mound-like disturbence at a local level; as an embodiment of the present invention, the

gently sloping sand pit 13 is rectangular, and the circulation pipe 12 is parallel to the

long side of the gently sloping sand pit 13; Two-way variable frequency water pump 14

is installed on the circulation pipe 12, and the variable frequency controller 15 is

connected to the two-way variable frequency water pump 14 and the data acquisition

processing and controller 4, respectively, and can control the two-way variable

frequency water pump 14 according to the instructions of the data acquisition

processing and controller 4; the flow velocity meter 16 is installed inside the water tank

11, and it is connected to the data acquisition processing and controller 4 to transmit to

it the water flow velocity inside the water tank 11.

The terrain scanning system 2 includes an ultrasonic topographer, a connecting

rod 22 and a motion device 23; the probe 21 of the ultrasonic topographer is mounted

on the connecting rod 22, and the connecting rod 22 is mounted on the motion device

23, and the motion trajectory is controlled by the motion device 23; the connecting rod

22 can change the position of the probe 21 of the ultrasonic topographer by means of

telescoping; the ultrasonic topographer is connected to the data acquisition processing

and controller 4.

The submarine pipeline simulation measurement system 3 includes a pipeline

model 31, a counterweight 33, a fiber optic strain sensor 32, and a high-speed camera

34; the high-speed camera 34 is installed above the water tank 11 and connected to the

data acquisition processing and controller 4 for photographing and transmitting back

the morphology of the sea sand 13 in the gently sloping sand pit; the pipeline model 31

is placed in the gently sloping sand pit 13, which is partially or completely buried by the

sea sand; preferably, the pipeline The pipe model 31 is a PVC pipe; the pipe model 31 is

provided with a counterweight 33 inside; preferably, the counterweight 33 is water or

sediment. The fiber optic strain sensor 32 is fixed on the side wall of the pipe model 31

and is connected to the data acquisition and processing and controller 4 for transmitting

the measured strain data of the pipe model 31 back. Specifically, there are multiple

fiber optic strain sensors 32, which are distributed axially in multiple locations of the

pipe model 31 and uniformly distributed circumferentially at each location; preferably,

there are four evenly distributed circumferentially at each location.

As an embodiment of the present invention, the movement device 23 includes a

track set on the wall of the tank 11, a roller device that can move along the track, and a

motor that drives the movement of the roller device.

The technical solution has the following characteristics:

(a) Simulation of tidal field using reciprocating flow

At the present stage in the laboratory tank experiments, waves or one-way flow is

used to simulate the tidal flow, acting on the sea bed to form sand waves. The

limitations are: the period of waves is a few seconds, while the period of the simulated

tide needs at least a few hours, and the difference between the two periods is

significant; if one-way flow is used, it does not reflect the period change characteristics

of the tidal flow. Therefore, the wave-like landforms currently formed in the laboratory

are small in size (only a few centimeters) and are essentially sand ripples (a much

smaller bed form), rather than true tidal sand waves. And thefield observation data

shows that the periodic action of tidal waves is one of the main reasons for the

formation of sand waves. Therefore, the present invention will use the flume and the

tidal generation system to generate a large period of reciprocal flow (period of about 2

hours) to simulate the tidal field. The generation of reciprocating flow requires the

flume to be equipped with a variable frequency pump and a variable frequency

controller to control the size and period of the reciprocating flow, which is the major

difference between the present invention and the previous sand wave simulation

experiments.

(b) Initial artificial terrain disturbance incorporated

After repeated attempts, the inventors found that on a flat seabed, even if

reciprocating currents are applied to simulate the tidal field, no tidal sand waves are

formed. Only with artificial terrain disturbance, i.e., setting some small bumps and

grooves artificially in the local position of the seabed after leveling so that the local bed becomes uneven to trigger the instability of the seabed, the tidal sand wave will be formed. The height of these preset artificial terrain disturbances is generally about 5 cm, and the length needs to be varied within a certain range (e.g., from 0.5 m to 5 m).

For operational simplicity, these artificial terrain disturbances can be set in triangular

shapes. In this way, under the combined effect of the tidal current and the initial

artificial terrain disturbance, the seabed will gradually develop and form the sand wave

geomorphology. In the experiment, without the addition of the initial artificial terrain

disturbance, the sand wave will not be formed, and this step is also the key operational

step of the current invention.

(c) sand wave topography automatic scanning system

Due to the large terrain extent of the sand-wave seabed in the experiment and the

single-point measurement method of the ultrasonic topographer, continuous scanning

of the entire seabed was required to obtain terrain data for the entire experimental area.

A terrain scanning system was designed to perform reciprocal scanning measurements

over the entire test area using a motion device. This running system allows setting the

scanning range, the speed of movement, and the distance of each step.

(d) Non-contact measurement of pipe motion and strain

The conventional submarine pipeline motion measurement method is mostly

contact measurement, which affects the structural distribution of the flow field. In this

device, a high-speed camera is used to record the motion of the submarine pipe from the

outside of the water tank. In the post-processing stage, the motion image is processed to

obtain the position change of the submarine pipe. A fiber-optic grating strain sensor is placed on the surface of the submarine pipe to measure the strain of the structure. Since the fiber optic strain sensor has a diameter of only 0.2 mm, it does not affect the structural properties after being attached to the surface of the submarine pipe, and the fiber optic strain is a dynamic strain measurement with a high acquisition frequency (up to 1000 Hz), so the strain measurement results are highly accurate.

Experimental method

1 . The formation of tidal sand waves

1) Suitable sand samples were selected, (e.g., quartz sand with a median grain

size of 0 .28 mm was used in this method), and the surface was leveled after filling in

the gently sloping sand pit 13. The initial artificial terrain disturbance was set locally

on the leveled sand surface, i.e., different triangular bumps were scraped out using a

template, with a height of about 5 cm and a length between 0 .5m and 5m. This step is

also the key to the success or failure of the whole experiment.

2) Slowly fill the water tank 11 and reach the depth required for the experiment,

taking care not to destroy the initial artificial terrain disturbance set up.

3) Start generating reciprocating flow, i.e. tidal field. By setting the parameters

of the inverter controller 15 to set the period of reciprocating flow and the maximum

flow speed (e.g., tidal reciprocating period of 2 hours, maximum flow speed of

.4m/s), the bidirectional inverter pump 14 starts to work and generates reciprocating

flow. Due to the presence of artificial initial terrain disturbance, it triggers the

instability of the seabed and changes the spatial structure of the tidal field, on the basis

of which the tidal sand waves are gradually formed.

4) Data acquisition is performed using flow velocity meters 16 and ultrasonic

topographer probes 21.

2 . Interaction of sand waves with submarine pipelines

1) Wait until the submarine sand wave is formed to a certain height, drain the

water in the tank 11, and then lay the submarine pipeline model 31 on top of the

formed submarine sand wave, and the laying angle can be changed as needed. Refill

the water to the original height and continue to simulate the tidal field.

2) Simultaneous observation of flow velocity, sand wave seabed, and submarine

pipeline motion and deformation using flow velocity meter 16, ultrasonic

topographer, high-speed camera 34, and fiber optic strain sensor 32.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1 . An device for simulating the effect of submarine tidal sand waves on pipeline

engineering, including an experimental water tank and tidal generation system (1), a

terrain scanning system (2), a submarine pipeline simulation measurement system (3)

and a data acquisition processing and controller (4), it is characterized in that: the

experimental water tank and tide generation system (1) includes a water tank (11), a

circulation pipe (12), a gentle slope sand pit (13), a two-way variable frequency water

pump (14), a variable frequency controller (15) and a flow velocity meter (16); the

gentle slope sand pit (13) is set in the middle of the water tank (11), and its two ends

are raised and the middle is depressed to form a cavity for holding sea sand, while the

raised part is connected to the bottom of the water tank through a gentle slope (17),

and the height of the gentle slope (17) gradually decreases; the circulation pipe (12) is

set on the lower side of the water tank (11), and its inlet and outlet ends are set on the

bottom surfaces of two opposite ends of the water tank (11); the gently sloping sand

pit (13) is filled with sea sand; the two-way variable frequency water pump (14) is

installed on the circulation pipe (12), and the variable frequency controller (15) is

connected to the two-way variable frequency water pump (14) and data collection and

processing and controller (4), controlling the two-way inverter water pump (14)

according to the commands of the data collection processing and controller (4); the

flow velocity meter (16) is mounted inside the water tank (11), which is connected to

the data collection processing and controller (4), to which the velocity of the water

flow in the water tank (11) is transmitted; the terrain scanning system (2) comprises an ultrasonic topographer, a connecting rod (22) and a motion device (23); the probe (21) of the ultrasonic topographer is mounted on the connecting rod (22), the connecting rod (22) is mounted on the motion device (23), the trajectory of which is controlled by the motion device (23); the connecting rod (22) is capable of changing the position of the ultrasonic topographer's probe (21) by means of telescoping; the ultrasonic topographer is connected to the data collection processing and controller (4) for echoing the sea sand topography in the gently sloping sand pit; the subsea pipeline simulation measurement system (3) includes a pipeline model (31), counterweight

(33), fiber optic strain sensor (32) and high speed camera ( 34); the high-speed camera

(34) is mounted above the water tank (11) and connected to the data acquisition

processing and controller (4) for photographing and transmitting back the morphology

of sea sand (13) in a gently sloping sand pit; the pipeline model (31) is placed in the

gently sloping sand pit (13), which is partially or fully buried in sandy bed; the

pipeline model (31) is provided with a counterweight (33) inside. the fiber optic strain

sensor (32) is fixedly provided on the side wall of the pipe model (31) and is

connected to the data acquisition processing and controller (4) for transmitting back

the detected strain data of the pipe model (31).
2 . Device for simulating the effect of submarine tidal sand waves on pipeline

works as claimed in claim 1, characterized in that the movement device (23)

comprises a track set on the wall of the water tank (11), a roller device capable of

moving along the track, and an electric motor driving the movement of the roller

device.
3 . Device for simulating the effect of submarine tidal sand waves on pipeline

engineering as claimed in claim 1, characterized in that the circulation pipe (12) is

parallel to the long side of the gently sloping sand pit (13).
4 . Device for simulating the effect of submarine tidal sand waves on pipeline

engineering as claimed in claim 1, characterized in that: the gentle slope (17) has a

cross-section of a class of right-angled triangle with a ratio of height to bottom side of

1:25 to 1:15.
5 . Device for simulating the effect of submarine tidal sand waves on pipeline

engineering as claimed in claim 1, characterized in that: the sea sand in the gently

sloping sand pit (13) is locally a sand pile.
6 . Device for simulating the effect of submarine tidal sand waves on pipeline

engineering as claimed in claim 1, characterized in that: preferably, there are four

strings of the fiber optic strain sensors (32), which are attached on the wall of the

pipeline model (31) along the axis and evenly distributed in the circumferential

direction of each location with 90.
7 . Device for simulating the effect of submarine tidal sand waves on pipeline

engineering as claimed in claim 1, characterized in that: the pipe model (31) is a PVC

pipe and the counterweight (33) is water or sea sand.
8 . An experimental method for simulating the effect of submarine tidal sand

waves on a pipeline engineering, characterized in that it comprises the following

steps:

1) Loading sand samples into gently sloping sand pits (13), and after overall

leveling of the sand surface, processing localized areas of the sand surface into tiny

bumps or grooves;

2) Slowly injecting water into the water tank (11) under conditions that do not

affect the state of the sand sample in the gently sloping sand pit (13) to the depth

required for the experiment;

3) Controlling the two-way variable frequency water pump (14) to work to form

a reciprocating flow in the tank (11) by using the frequency controller (15) to preset

the period and maximum flow rate of the reciprocating flow;

4) Using flow velocity meters (16) and ultrasonic topographer probes (21) for

collecting the morphology within the gently sloping sand pit and transmitting the

collected data to the data acquisition processing and controller (4);

5) When the sand sample forms a simulated submarine sand slope, empty the

water in the tank (11), lay the pipe model (31) on the submarine sand slope, refill the

water to the original height, and form a reciprocal flow in the tank to simulate the tidal

field;

6) Using flow velocity meter (16), ultrasonic topographer, high-speed camera

(34) and fiber optic strain sensor (32), the water flow velocity, the shape inside the

gently sloping sand pit and the submarine pipeline movement and deformation are

observed simultaneously; and the collected data are transmitted to the data acquisition

processing and controller (4) for analysis and processing.

FIGURES 1/2

Figure 1