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The spoiler is a kind of device to disturb current and promote burying. At present, all submarine pipeline spoilers at home and abroad are parallel spoilers, that is, the plane of the spoiler is parallel to the vertical plane of the pipeline axis. According to the results of indoor experiments, when the pipeline with the forward spoiler is installed perpendicular to the direction of water flow, the spoiler will accelerate the seabed erosion and cause the pipeline to endure downward pressure, which will eventually cause the pipeline self-buried to form a protection. However, when the pipeline direction is consistent with the flow direction, the self-buried behavior and protective effect is vanished. By aiming at the defect that the forward spoiler cannot be self-buried when the direction of the pipeline and the flow are basically parallel, the spoiler burying aid device perpendicular to the pipeline axis has been innovatively developed, and the hydrodynamic changes and sediment erosion characteristics near the pipeline after the installation of the device were studied based on the experiment. Results reveal that although the perpendicular spoiler cannot generate downforce, it can greatly increase the turbulent kinetic energy of the flow and the rate of sediment erosion. The larger the angle between the pipeline axis and the spoiler plane is, the larger the increase in turbulent energy will be. The increase in turbulent energy near the bed surface can reach up about 70% when the angle is 90°, while serious sediment erosion mainly occurs along both sides of the pipeline with a distance of about 2–4 times the pipe diameter. In the future, we can further explore the influence of the perpendicular spoiler size and installation position on the pipeline downforce and the effect of burying promotion. At the same time, field tests on the perpendicular spoiler burying aid device currently developed will conduct to observe the actual effect of perpendicular spoiler promoting pipeline scouring and burying, and improve submarine pipeline safety protection technology. [ABSTRACT FROM AUTHOR]

Changes in the external geometry of the pipeline laid on the erodible beds may affect the local scour around pipe. If the scouring process below the pipe is accelerated, the pipe buries on the bed (known as self-burial of the pipe) and can be used as a cheap alternative to mechanical trench digging. In this study, the effect of changes in the external geometry of the pipe in order to accelerate the scouring and self-burial pipe processes by spoiler and piggy back under unidirectional flow on the erodible bed is investigated. The results showed that the time scale of self-burial process is less than that of the scouring process. At the angles of 180, 135 and 225°, the Spoiler and piggy back reduced the time scale of self-burial and scouring process and increased the scour and self-burial depths, as well as the lee erosion length as compared with the simple pipe. At angles of 90 and 270°, the scale time of scour and self-burial processes are increased, the scour and self-burial depths and the lee erosion length are decreased as compared with the simple pipe. It can be concluded that the performance of piggy back is similar to the spoiler, therefore, they are of similar application and could be a suitable alternative for the spoiler. [ABSTRACT FROM AUTHOR]

Providing safe conditions for water pipelines or other fluids on erodible beds is an important issue in the field of hydraulic engineering. Studies show that the installation of a plate called Spoiler on top of the pipeline increases the amount of the erosion around the pipe and its self burial stimulation. Most studies about spoiler have been done on a fixed pipe, but in reality, when the scouring hole underneath the pipe is deep enough, the pipe begins to lower as a result of the weight, at when the pipe reaches the bottom of the scour hole, the erosion process stops and then the pipe is covered with sand and buried. The self burial phenomenon has not been studied with the use of a spoiler in the case of actual displacement of the pipe, and due to the fact that the studied pipes have been fixed, the transitional and sedimentary phases have not been observed. Considering the role of pipe displacement in changing the scouring profile, the study of the spatial phenomenon of the pipe during displacement and observing the actual effect of the spoiler on the self burial performance and its effective parameters are necessary. In this study, this phenomenon has been studied experimentally.

Free spanning of subsea pipelines caused by local scour is a primary concern during its operation. This study aims to propose an effective method to protect the pipeline form spanning. The experiments were conducted in clear-water scour conditions. Impermeable spoiler, porous spoiler and flexible spoiler were considered for both fixed and self-burial test. The flow fields around the pipeline were obtained using the particle image velocimetry (PIV) technique. The scour of a fixed subsea pipeline indicates the spoiler can accelerates the erosion rate significantly. When the pipeline leaves the seabed, the scour profile is featured by two scour pits and two sand dunes. The scour process of flexible spoilers includes two stages: quasi-steady and flapping and the flapping downward motion is the main cause for sediment burst. The shelter effect of flexible spoiler protects the pipeline form vigorous scouring and achieves a 10% decrease of the maximum scour depth. The trapped vortex and disturbance propagation caused by the orifice jet flow inhibits the scour process to some extent for porous spoiler. However, the self-burial results indicate the porous spoiler can accelerates the self-burial process up to 5.5 times compared to smooth pipeline and shows a better performance than impermeable spoiler. • This paper illustrates the interactive coupling between the vortex systems and sand grains via PIV and POD method. • Porous spoiler facilitates the self-burial process and shows a better performance than traditional impermeable spoiler. • Elaboration of scour process and self-burial mechanism of pipelines attached with porous and flexible spoilers. [ABSTRACT FROM AUTHOR]

Abstract High resolution bathymetry combined with structural modelling is used to estimate changes in the on-bottom stability of an offshore pipeline due to scour and sedimentation over an 11 year period. Detailed observations of post-lay embedment changes have been combined with the pipeline structural characteristics and an elastic-plastic model of soil resistance to estimate the vertical and horizontal stability of the pipeline using a finite difference solution to the beam bending equation. Application of the design approach indicates that post-lay increases to the critical (break-out) velocity of 1–2 m/s occur along the full 19 km of surveyed pipeline due to scour and sedimentation, which act to reduce load and increase soil resistance. The rate at which this increase in stability occurs with time is found to vary along the pipeline, and is dependent on the mechanism of pipeline lowering (i.e. whether the pipe lowered due to sagging into widely spaced scour holes, or by sinking into the shoulders between many closely spaced scour holes). By incorporating sediment transport into the pipeline design, the present results suggest potential for significant improvements in pipeline on-bottom stability and associated reductions in minimum required specific gravity and/or secondary stabilisation. Highlights • Seabed mobility driven changes to pipeline embedment are observed in the field. • The resulting changes to pipeline on-bottom stability are quantified. • Increases in critical velocity of 1–2 m/s are calculated for a steady current. • The amount of increase is dependent on the mechanism of pipeline lowering. • Increased soil resistance and hydrodynamic shielding are both shown to be important. [ABSTRACT FROM AUTHOR]

A series of laboratory experiments was carried out to investigate the effects of spoiler and piggyback on the flow field and local scour formation under single and twin submerged pipes. The shape and orientation of spoiler and piggyback were tested in single and twin pipes with different distances from each other. Three piggyback shapes of rectangular, triangular, and circular were designed and the local scour profiles were measured for five orientation angles of θ = 90, 135, 180, 225, and 270°. Flow visualization was employed to study the effects of spoiler and piggyback on the rear vortex field. The velocity field was measured with an Acoustic Doppler Velocimeter (ADV) probe and the magnitudes of Turbulent Kinetic Energy (TKE) around pipelines were extracted from the time series of velocity data. Quadrant analysis was performed based on velocity data to study the effect of spoilers on turbulent momentum transfer between twin pipes. The energy and momentum coefficients were extracted from velocity profiles indicating significant disruption of velocity field and causing additional drag in the rear pipe. A comparison of the equilibrium bed profiles indicated that the minimum and maximum peak scour depths occurred when a rectangular spoiler with θ = 180° and a circular piggyback with θ = 270° were installed, respectively. The self-burial mechanism was examined by alternating the positions of piggybacks and spoilers in twin pipes. The downstream pipe was buried when either spoiler or piggyback is in the upstream pipe. It was found that the rate of self-burial reduced as the distance between two pipes increased. • Effects of spoiler and piggyback on local scour formation of submerged pipes were tested. • The shape and orientation of spoiler and piggyback on single and twin pipes were tested. • Variations of energy and momentum indicated significant disruption of velocity field. • The minimum peak scour depth occurred in rectangular spoiler installed with θ = 180°. • The maximum peak scour depth occurred in circular piggyback installed with θ = 270°. [ABSTRACT FROM AUTHOR]

The hazardous exposure and self-burial of a submarine pipeline were studied based on the investigation of a submarine pipeline in the sand wave area in the South China Sea, as well as on statistical data and mathematical calculations. The results indicate that the pipeline free span in the area was mainly induced by seabed erosion, sand wave movement, and human disturbance. Extreme weather events cause severe impacts on seabed topography and the pipeline condition. The burial status of the pipe is mainly controlled by the evolution of local seabed topographical conditions, i.e., the amount of sediment load and the movement of seabed sand waves. The migration of the continuous small-scale sand waves facilitates the self-burial of pipes, while the migration of isolated large-scale sand waves creates potential hazards for pipelines because of the existing free span continues to grow on both sides of the sand wave. [ABSTRACT FROM AUTHOR]

The freshwater snail Pomacea canaliculata shows alarm responses to chemical cues released from injured conspecifics, but its behavioural responses in the field are unknown. We investigated effects of habitat (canals or paddy fields), vegetation, and body size on alarm responses in the field. Snails responded to crushed conspecifics within 4 min by burying themselves, but the proportions of self-buried snails were generally lower (0–28% depending on experiments) than those reported in the laboratory. Snails not only showed the alarm response, but also frequently fed on crushed conspecifics. There were no influences of habitat or body size on the proportions of individuals showing the alarm response. Nevertheless, in paddy fields with high-density vegetation a higher proportion of snails showed the alarm response than in paddy fields with low-density vegetation. [ABSTRACT FROM AUTHOR]

Flow around a pipeline with and without a spoiler near a smooth wall is simulated by solving the Navier–Stokes equations. Finite-difference formulation with a second-order upwind scheme in a curvilinear coordinate system is employed. The influences of the spoiler on hydrodynamic forces, pressure distribution, vortex shedding frequency, velocity profile under the pipe, as well as shear stress on the wall are investigated. The attachment of a spoiler significantly increases drag, root-mean-square (RMS) lift, flow through the gap between the pipe and the wall and shear stress on the seabed around the pipe. The spoiler also generates a non-zero mean downward force on the pipeline, which may enhance the self-burial of the pipeline. [Copyright &y& Elsevier]

Herein, hydraulic model experiments and numerical simulations were performed to understand the self-burial mechanism of subsea pipelines with spoilers under steady flow conditions. First, scour characteristics and self-burial functions according to the spoiler length-to-pipe diameter ratio (S/D) were investigated through hydraulic experiments. Further, the Navier–Stokes solver was verified. The experimental values of the velocity at the bottom of the pipeline with a spoiler and the pressure on the sand foundation where the pipeline rested were represented with the degree of conformity. Scour characteristics of a sand foundation were investigated from the numerical analysis results of the velocity and vorticity surrounding the pipelines with spoilers. The compilation of results from the hydraulic experiment and numerical analysis showed that the projected area increased when a spoiler was attached to the subsea pipes. This consequently increased the velocity of fluid leaving the top and bottom of the pipe, and high vorticity was formed within and above the sand foundation. This aggravated scouring at the pipe base and increased the top and bottom asymmetry of the dynamic pressure field, which developed a downward force on the pipeline. These two primary effects acting simultaneously under steady flow conditions explained the self-burial of pipelines with a spoiler attachment. [ABSTRACT FROM AUTHOR]