Name: visualization of flow field around a vibrating pipeline within an equilibrium scour hole
Uploaded: 2019-08-26T14:00:00
Description: Watch this Scientific Journal Video about Visualization of Flow Field Around a Vibrating Pipeline Within an Equilibrium Scour Hole at JoVE.com

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 ...

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