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Name of experiment: detection test of submarine pipeline suspension vibration

Research direction：Pipeline straddle diagnosis

Content of experiment: signal source, power amplifier and exciter are used to stimulate pipeline vibration, and vibration of submarine pipeline is simulated under the action of ocean current erosion, and vibration is detected by pipeline detector.

Purpose of experiment：the pipe produces vibration similar to ocean current excitation, and the vibration is detected by internal detector

Test equipment: signal source, power amplifier ATA-3080, exciter, pipes

Experimental process:

1. At one end of the pipe, the blower is used to blow air into the pipe, and the ball in the pipe is pushed forward. In order to keep the ball in a steady state as in the field pipe, the force of the wind needs to be controlled.

2. By continuously adjusting the power supply voltage of the blower to achieve the continuous regulation of wind speed, considering that the ball from static to speed stability is an acceleration process, in the upstream of the excitation pipe is connected with a buffer pipe, so that the ball in the excitation pipe before the completion of acceleration and reach the steady state of constant speed rolling.

3. Flexible rubber connection is adopted between the two pipelines so that the buffer pipeline does not interfere with the vibration of the exciting pipeline. The two ends of the exciting pipeline are fixed supports to simulate the actual suspended cross-submarine pipeline.

4. The computer controls the data acquisition card to generate the excitation signal, the power amplifier amplifies it and sent to the exciter. The excitation pipe vibrates along the vertical direction.

5. Considering that at the bottom of the sea, the ocean current is parallel to the sea bed, and the direction of VIV is perpendicular to the direction of ocean current, the excitation applied to the pipeline is vertical. The laser displacement sensor measures the vibration displacement of the pipeline in real time as a reference.

6. A 50mm diameter photosensitive resin spherical shell was made by 3D printing technology, and a fixed three-axis accelerometer structure was set inside. The accelerometer was powered by a small lithium battery.

7. Two steel columns are added inside the ball to adjust its mass distribution so that the ball rotates steadily around an axis with a large moment of inertia. After the detection is completed, the ball is taken out and connected with the computer to download data and identify pipeline vibration through offline processing of acceleration signal.

Result of experiment：

1. The following figure (e) is the sum of squares of the three components of the original acceleration signal, and Figure (f) is the sum of squares of the three components of the acceleration without dc offset.

2. It can be seen that a^2 contains strong low frequency information representing the rotation of the ball and some other high frequency information before the dc components are removed. After removing the dc component, A ^2 becomes A ~^2, which is equivalent to removing the centripetal acceleration, and the low frequency information related to F1 disappears. A ^2 contains strong high frequency information representing pipeline vibration, which is conducive to identifying pipeline vibration

3. When the pipe amplitude is large, the A ^2 frequency domain contains five peaks. The peak representing the rolling frequency f1 of the ball is easily identified by using data from other pipe segments, because the acceleration signal measured by the ball in other non-vibrating pipe segments only has F1 component. The other four peaks correspond to F2,2, F2, F2 + F1 and F2-F1. The amplitude of the last three peaks is related to many factors, and sometimes it will approach or even exceed the amplitude of F2. It is unable to determine which peak is F2. De-dc of each component processed by acceleration to obtain A ~^2, the amplitude of F2 + F1 and F2-F1 can be weakened to retain only f2 and 2 F2 peaks.

4. As shown in the frequency domain curve on the right below, the red curve is calculated by using the acceleration component with dc removed, and the blue curve is calculated by using the original acceleration component. Obviously, after DC removal, the peak values related to F1 are significantly weakened, while F2 and 2F2 are almost unchanged before and after DC removal. It is easy to determine the corresponding peaks of F2 and 2F2, and then obtain the value of F2. If the pipe amplitude is large enough, 2F2 will also be obvious, which can be further confirmed by the relationship of double frequency

The role of the amplifier in this experiment: amplify the excitation signal and feed it to the exciter.