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

Summary

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.

Abstract

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.

Introduction

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....

Protocol

1. Laboratory safety check

1. Review the safety rules relating to the use of the laser and flume system.
2. 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 follows:
   1. Check the potential reflection surfaces in the laser line-of-sight prior to testing; wear safety goggles when operating the laser device.....

Results

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 .......

Discussion

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.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Camera control software	Vision Research	Phantom PCC 2.6	Camera control, image data acquisition and processing
Camera lens	Nikon Chiyoda		Nikor  60mm, f=2.8 prime lens
Continuous wave laser	Beijing Laserwave optoelectronics technology co. ltd.		PIV Laser source; Nd:YAG laser, 532 nm; air-cooling
High-speed camera	Vision Research	Phantom Miro LAB 320	Image data recording
Laser sheet forming optics	Thorlabs Inc		Transform the point laser to a thin laser sheet
Pipeline model	ZONCEPZ SOLUTIONS		Acrylic cylinder with a diameter of 35 mm
Pipeline vibration system	ZONCEPZ SOLUTIONS		Consists of a sever motor, two connecting springs and pipeline supporting frames.
PIV calcuation software	AXESEA Engineering Technology Limited Co.	PISIOU	Image data processing for obtaining flow fields and pipeline displacements
PIV seeding materials	Shimakyu		Aluminum powder with a diameter of 10um
Recirculating flume	SZU ENGINEERING PTE LTD		Glass-sided, 11 m long, 0.6 m wide, and 0.6 m deep
Tri-pod	MANFROTTO	SKU MT190GOC4US 410	Camara supporting