This work was supported by the Young Scientists Fund of the National Natural Science Foundation of China (51709082) and the Fundamental Research Funds for the Central Universities (2018B13014).

1. Laboratory safety check
<ol>
	<li>Review the safety rules relating to the use of the laser and flume system.</li>
	<li>Ensure that the safety training requirements of the laboratory have been met. 
	NOTE: In this experiment, a set of 5W air-cooling continuous wave laser with a wavelength of 532 nm and a glass-sided straight flume (Figure 1) with dimensions of 11 m length, 0.6 m width, and 0.6 m depth are used. The basic safety recommendations for these two apparatuses are as follow...

<ol>
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The protocol presented in this paper describes a method for visualization of the two-dimensional flow fields and determination of the near-boundary flow stress fields around a forced vibrating pipeline in an equilibrium scour hole by using the PIV techniques. Since the designed pipeline motion is one-dimensional along the y direction, preparing and adjusting the pipeline model and vibration system to fulfill this objective are critical prerequisites for a successful outcome. Any undesirable motions of the pipeli...

Subsea pipelines are widely used in offshore environments for the purpose of fluid or hydro-carbon products conveyance. When a pipeline is placed on an erodible seabed, a scour hole around the pipeline is likely to form because of the waves, currents or dynamic motions of the pipeline itself (forced-vibration or vortex-induced-vibration)1,2. To improve the understanding of the scour mechanism around a subsea pipeline, measurements of the turbulent flow fields and estimations of the bed shear and normal stresses within the pipeline-fluid-seabed interaction region are essential in addition to measurements of the scour hole dimension1,2,3,4,5,6,7. In an environment where the bed shear and normal stresses are extremely difficult to be determined because the flow field is unsteady and the bottom boundary is rough, measured instantaneous near-boundary stresses (at approximately 2 mm above the boundary) could be used as their surrogate8,9. In the past few decades, scour around a vibrating pipeline has been studied and published without quantitatively presenting the values of the sophisticated flow fields around the pipeline within the scour hole3,4,5,10,11,12,13,14,15,16,17,18. Therefore, the goal of this method paper is to provide a novel experimental protocol for visualizing the detailed flow fields and to determine the near-boundary shear and normal stresses within an equilibrium scour hole induced by a forced vibrating pipeline. It should be noted that the pipeline-fluid-seabed interaction process in this study is in a quiescent water environment rather than those with unidirectional currents and waves.
This experimental method consists of two important components, namely, (1) simulation of pipeline (forced) vibrations; and (2) measurements of the flow fields around the pipeline. In the first component, the vibrating pipeline was simulated in an experimental flume by using a vibrating system, which has a servo motor, two connecting springs, and pipeline supporting frames. Different vibration frequencies and amplitudes can be simulated by adjusting the motor speed and location of the connecting springs. In the second component, the time-resolved particle image velocimetry (PIV) and wavelet transform techniques were adopted to obtain high temporal and spatial resolution flow field data at different pipeline vibration phases. The time-resolved PIV system consists of a continuous wave laser, a high-speed camera, seeding particles, and cross-correlation algorithms. Although PIV techniques have been widely used in obtaining steady turbulent flow fields19,20,21,22,23,24,25, applications in complex unsteady flow field conditions, such as cases of pipeline-fluids-seabed interaction, are relatively limited8,9,26,27. The reason probably is because traditional single-time-interval cross-correlation algorithm of PIV techniques is unable to accurately capture the flow features in unsteady flow fields where a relatively high velocity gradient is present9,20. The method described in this paper can solve this problem by using the multiple-time-interval cross-correlation algorithm9,28.

<table border="0" cellpadding="0" cellspacing="0" style="width:1299px;" width="1298">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">Camera control software</td>
			<td style="width:359px;">Vision Research</td>
			<td style="width:175px;">Phantom PCC 2.6</td>
			<td style="width:555px;">Camera control, image data acquisition and processing</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">Camera lens</td>
			<td style="width:359px;">Nikon Chiyoda</td>
			<td style="width:175px;"></td>
			<td>Nikor&#160; 60mm, f=2.8 prime lens</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Continuous wave laser&#160;</td>
			<td style="width:359px;">Beijing Laserwave optoelectronics technology co. ltd.</td>
			<td style="width:175px;"></td>
			<td>PIV Laser source; Nd:YAG laser, 532 nm; air-cooling</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">High-speed camera</td>
			<td style="width:359px;">Vision Research</td>
			<td style="width:175px;">Phantom Miro 120</td>
			<td>Image data recording</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">Laser sheet forming optics&#160;</td>
			<td style="width:359px;">Thorlabs Inc</td>
			<td style="width:175px;"></td>
			<td>Transform the point laser to a thin laser sheet</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Pipeline model</td>
			<td style="width:359px;">ZONCEPZ SOLUTIONS</td>
			<td style="width:175px;"></td>
			<td>Acrylic cylinder with a diameter of 35 mm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Pipeline vibration system</td>
			<td style="width:359px;">ZONCEPZ SOLUTIONS</td>
			<td style="width:175px;"></td>
			<td>Consists of a sever motor, two connecting springs and pipeline supporting frames.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">PIV calcuation software</td>
			<td>AXESEA Engineering Technology Limited Co.</td>
			<td style="width:175px;">PISIOU</td>
			<td>Image data processing for obtaining flow fields and pipeline displacements</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">PIV seeding materials</td>
			<td style="width:359px;">Shimakyu</td>
			<td style="width:175px;"></td>
			<td>Aluminum powder with a diameter of 10um</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">Recirculating flume&#160;</td>
			<td style="width:359px;">SZU ENGINEERING PTE LTD</td>
			<td style="width:175px;"></td>
			<td>Glass-sided, 11 m long, 0.6 m wide, and 0.6 m deep</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:211px;">Tri-pod</td>
			<td style="width:359px;">MANFROTTO</td>
			<td style="width:175px;">SKU MT190GOC4US 410</td>
			<td>Camara supporting</td>
		</tr>
	</tbody>
</table>

visualization of flow field around a vibrating pipeline within an equilibrium scour hole

An experimental method is presented in this paper to facilitate visualization of the detailed flow fields and determination of the near-boundary shear and normal stresses within an equilibrium scour hole induced by a vibrating pipeline. This method involves the implementation of a pipeline vibration system in a straight flume, a time-resolved particle image velocimetry (PIV) system for pipeline displacement tracking and flow fields measurements. The displacement time-series of the vibrating pipeline are obtained by using the cross-correlation algorithms. The steps for processing raw particle laden images obtained by using the time-resolved PIV are described. The detailed instantaneous flow fields around the vibrating pipeline at different vibrating phases are calculated by using a multiple-time-interval cross-correlation algorithm to avoid displacement bias error in the flow regions with a large velocity gradient. By applying the wavelet transform technique, the captured images that have the same vibrating phase are accurately cataloged before the phase-averaged velocity fields are obtained. The key advantages of the flow measurement technique described in this paper are that it has a very high temporal and spatial resolution and can be simultaneously used to obtain the pipeline dynamics, flow fields, and near-boundary flow stresses. By using this technique, more in-depth studies of the 2-dimensional flow field in a complex environment, such as that around a vibrating pipeline, can be conducted to better understand the associated sophisticated scour mechanism.

An example of the comparison between the raw image and processed image of the pipeline displacements tracking and instantaneous velocity calculation is shown in Figure 3. As shown in Figure 3b, the seeding particles and noise in the raw image are filtered out and the shining pipeline edge is retained to obtain the displacement time series. As shown in Figures 3c, light scatters/reflections around the seeding particles, pipeline ...

Watch this Scientific Journal Video about Visualization of Flow Field Around a Vibrating Pipeline Within an Equilibrium Scour Hole at JoVE.com

Visualization of Flow Field Around a Vibrating Pipeline Within an Equilibrium Scour Hole

The goal of the protocol is to enable visualization of the detailed flow fields and determination of the near-boundary shear and normal stresses within an equilibrium scour hole induced by a vibrating pipeline.

An experimental method is presented in this paper to facilitate visualization of the detailed flow fields and determination of the near-boundary shear and ...

This experimental protocol is to visualize the detail flow fields and the near boundary share in normal stresses within an equilibrium scour hole induced by a forced vibrating pipeline. The key advantage of this measurement technique is its capacity to simultaneously obtain pipeline dynamics, flow fields and near boundary flow stresses in high resolution. By using this technique, more in-depth studies of the two dimensional flow field in a complex environment can be conducted to better understand the scour mechanism.The experiment takes place in a flume 11 meters long. The cross section is square with side length of 0.6 meters. This schematic view of the flume provides additional details including the location of an erodible seabed model.The water level is 0.4 meters above the seabed. In the seabed model, use uniformly distributed medium sand that has been compacted and leveled. Have the structure for the vibration system in place over the flume.This consists of a fixed frame that is locked on the top rails of the flume. The fixed frame has a moveable pole that supports an aluminum frame. The aluminum supporting the frame holds the pipeline model above the seabed model in the flume.This schematic provides an overview of the setup. Note that there are four bearings that ensure the aluminum supporting frame can only vibrate vertically. A connecting rod between the movable pole and a servo motor drives the motion of the aluminum frame.The setup depends on the pipe geometry. This duplicate of the acrylic pipeline model has a diameter of 35 millimeters. Adjust the supporting frame and pole so the bottom of the pipeline is one diameter above the initial seabed surface.Respect all laser safety protocols and begin working with the laser. Place the 532 nanometer laser and optics for velocimetry on top of the flume. The optics include elements to form a sheet of illumination.With the laser on, adjust the optics so that a flat sheet of illumination is formed in the field of interest in the flume. The sheet should be along the flume center and parallel to its side walls. These schematic front and side views indicate the position of the laser and optics and the created laser sheet in the setup.Next, set up the camera of the particle image velocimetry apparatus. Use a high speed camera with the appropriate focal length directed perpendicularly to the laser sheet. Connect the camera to a computer with the correct control software.With the camera on, adjust the field of view to ensure the pipeline fluid seabed region is visible and the image is clear. To calibrate the setup, begin with the seeding particles. This aluminum powder provides particles with a diameter of 10 microns.Add about 20 grams of seeding particles to the test section of the flume. Verify that the camera brings the seeding particles into sharp focus. Then, place a calibration ruler inside the field of view on the laser sheet plane and capture a calibration image.After choosing a sampling rate for data collection, turn off the laser and camera. For the experiment, obtain a transparent acrylic plate. Support it over the test bed below the laser source and on the water surface to suppress surface fluctuations.This diagram provides details of the use of strings attached to the flume rails to support the plate in this setup. Next, turn on the servo motor on the frame. This will begin to induce forced vibrations on the pipeline model.Keep the vibration system running for 24 hours. After 24 hours, turn on the laser to create the light sheet. Start the camera and its control software using the calibrated settings.Then, turn off the lights and begin data collection. Once the data is collected, check that the seeding particle density for 32 by 32 pixel interrogation window is greater than eight before collecting additional datasets. Once all of the datasets have been collected, begin data processing.Work with the particle image velocimetry software with the calibration image opened. Next, go to the toolbar and click the scale setup button. Move the cross hairs to a mark on the ruler's image and tag it.Next, tag a second mark on the ruler's image. In the dialogue box that opens, enter the distance between the marks according to the ruler. Note the scale that is computed.Return to the toolbar and click the origin button. From there, use the mouse to set the origin of the coordinates for all of the data images. Click yes when done.Then, click on the file menu and load the first of the raw images that were collected as data. Check that the other files are accessible but return to the first file. Next, click on the parameter menu.In the dialogue box, enter the number of data files and the sample rate to load all the images. Save the values and close the box. Now, go to the image filter menu.There, apply the low pass filter. In the toolbar, click the PTV module. Follow this by clicking tracing point.Then in the image, find the center point at the right half of the pipeline circumference and select it. Okay the selection before clicking on PTV tools in the toolbar. In the dialogue box that opens, adjust the gamma, light gate and median filter settings to single out the pipeline outline in the image.After approving the changes, click the object tracking button. Use the mouse to select an identifiable portion of the pipeline on the processed image. Once this is done, the software tracks the displacement in the images and records the time series.After the data is saved, go to and click on PTV tools. In the dialogue box, click the default button and OK to recover the raw image for subsequent analysis. Click on PTV module to deactivate the module.Remain in the toolbar and open the parameter panel. Verify the velocity vector calculation parameter and others before closing the dialogue box. Then, go to the image filter menu.Apply a laplacian filter function to the raw images to highlight the seeding particles and filter out undesired scattered light. Now, go back to the toolbar and click on boundary. Use the mouse to set the geometric mask on the images to exclude the seabed region.Confirm that the boundary has been set. When done, click boundary save to save the boundary data. Finally, go to the toolbar and click the run button to calculate the instantaneous velocity fields using the cross correlation method.Export and save the instantaneous velocity field's data for further analysis. This an image of a quasi-equilibrium scour profile and vibrating pipeline taken after 24 hours of pipeline vibration. The origin for analysis is set at the intersection point at the original seabed surface and the pipeline vertical center line.Seeding particles are visible but very few sediment particles are suspended in the flow, suggesting the system is in a quasi-equilibrium stage. Data collected with the protocol allows visualization of the phase averaged velocity field and vorticity dynamics. This video consists of 72 frames of flow fields from one pipeline vibration cycle.This method can also be applied to investigate vortex induced vibration processes such as pipeline vibration induced by asymmetry vortex shedding.

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Research

JoVE Journal

Environment

5.5K visualizações.  Hohai University. Este protocolo experimental é para visualizar os campos de fluxo de detalhes e a parte próxima da fronteira em tensões normais dentro de um buraco de varredura de equilíbrio induzido por um gasoduto vibratório forçado. A principal vantagem desta técnica de medição é sua capacidade de obter simultaneamente dinâmicas de tubulação, campos de fluxo e tensões de fluxo próximos em alta resolução. Usando essa técnica, estudos mais aprofundados do campo de fluxo bidimensional em um ...