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David R Fuhrman - One of the best experts on this subject based on the ideXlab platform.
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numerical investigation of wave plus current induced scour beneath two Submarine Pipelines in tandem
Coastal Engineering, 2020Co-Authors: Yuzhu Li, David R Fuhrman, Bjarke Eltard LarsenAbstract:Abstract Two-dimensional (2D) local scour beneath two Submarine Pipelines in tandem under wave-plus-current conditions is investigated numerically. A fully-coupled hydrodynamic and morphologic model based on unsteady Reynolds-averaged Navier-Stokes (URANS) equations with the k − ω turbulence closure is applied. The model is validated against existing experimental measurements involving live-bed scour beneath a single pipeline and beneath two Pipelines in tandem, respectively. The model is then employed to simulate scour beneath two tandem Pipelines under wave-plus-current conditions for a variety of Keulegan-Carpenter ( K C ) numbers and relative current strengths. Horizontal gap ratios (the horizontal gap distance between two Pipelines divided by the pipeline diameter) ranging from 1 to 4 are modelled. It is found that for conditions involving waves plus a low-strength current, the scour pattern beneath two Pipelines behaves like that in the pure-wave condition. Conversely, when the current has equal strength to the wave-induced flow, the scour pattern beneath two Pipelines resembles that in the pure-current condition. It is also observed that in the pure-wave condition the equilibrium scour depth beneath each pipeline is affected by both K C and the horizontal gap ratio, except for K C = 5.6 . For such a small K C , the horizontal gap ratio has insignificant influence on the equilibrium scour depth, since vortex shedding does not occur. When the current strength relative to the waves is low, the scour development beneath the upstream and the downstream Pipelines are similar. However, when the current has equal strength to the waves, the scour development beneath the downstream pipeline has a different pattern to that upstream. Namely, smaller horizontal gap ratios result in delayed scour beneath the downstream pipeline.
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generalized time scale for wave induced backfilling beneath Submarine Pipelines
Coastal Engineering, 2019Co-Authors: Kim Bastian, Stefan Carstensen, David R FuhrmanAbstract:Abstract This paper presents 25 new laboratory experiments involving the wave-induced backfilling of wave-induced scour holes beneath Submarine Pipelines (so-called wave-to-wave backfilling scenarios). The experiments complement the previous 8 wave-to-wave backfilling experiments of Fredsoe et al., as well as recent current-to-wave backfilling experiments of Bayraktar et al. It is found that the wave-induced backfilling time scale is generally an order of magnitude larger than for scour, and is relatively insensitive to the initial (current- or wave-induced) pre-backfilling scour profile. Based on this, the data sets involving wave-induced backfilling are collectively analyzed, resulting in a new generalized expression for estimating the wave-induced backfilling time scale beneath Pipelines in the live-bed regime. This expression accounts for primary dependence on the Shields parameter, as well as secondary dependence based on the difference between the (estimated or known) initial and expected final equilibrium scour depth due to the backfilling wave condition.
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experimental and numerical study of wave induced backfilling beneath Submarine Pipelines
Coastal Engineering, 2016Co-Authors: Deniz Bayraktar, Bjarke Eltard Larsen, Stefan Carstensen, Joseph Ahmad, David R FuhrmanAbstract:Abstract This paper presents results of complementary experimental and numerical studies involving wave-induced backfilling of current-generated scour holes beneath Submarine Pipelines. The laboratory experiments are conducted in a wave-plus-current flume, utilizing Laser Doppler Anemometry to measure velocities, synchronized flow visualizations using digital image technology, along with live-bed scour and backfilling measurements. Each experiment is based on a two-stage process: (1) initial scour induced by a pure current, followed by: (2) backfilling induced by pure waves (either regular or irregular). The time series of scour depths are closely monitored through video recordings. Systematic analysis of these has resulted in a closed form expression for the backfilling time scale, which is demonstrated to be a full order of magnitude greater than the well-known time scale of scour (with both governed primarily by the Shields parameter). The developed expression is strictly valid for the current-to-wave backfilling scenarios considered, while likely serving as an upper limit for more general wave-induced backfilling circumstances. The experiments are complemented by similar backfilling simulations utilizing a fully-coupled hydrodynamic and morphodynamic CFD model. The numerical simulations demonstrate the ability of the model to predict backfilling towards expected equilibrium scour depths based on the new wave climate, with time scales reasonably in line with experimental expectations.
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simulation of wave plus current scour beneath Submarine Pipelines
Journal of Waterway Port Coastal and Ocean Engineering-asce, 2016Co-Authors: Bjarke Eltard Larsen, David R Fuhrman, Mutlu B SumerAbstract:AbstractA fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath Submarine Pipelines. The model was based on incompressible Reynolds-averaged Navier–Stokes equations, coupled with k-ω turbulence closure, with additional bed and suspended load descriptions forming the basis for seabed morphology. The model was successfully validated against experimental measurements involving scour development and eventual equilibrium in pure-current flows over a range of Shields parameters characteristic of both clear-water and live-bed regimes. This validation complements previously demonstrated accuracy for the same model in simulating pipeline scour processes in pure-wave environments. The model was subsequently utilized to simulate combined wave-plus-current scour over a wide range of combined Keulegan–Carpenter numbers and relative current strengths. The resulting equilibrium scour depths and trends were shown to be in accordance with existing exp...
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numerical simulation of wave induced scour and backfilling processes beneath Submarine Pipelines
Coastal Engineering, 2014Co-Authors: David R Fuhrman, Mutlu B Sumer, Cuneyt Baykal, Niels Gjol Jacobsen, Jorgen FredsoeAbstract:Abstract A fully-coupled hydrodynamic/morphodynamic numerical model is presented and utilized for the simulation of wave-induced scour and backfilling processes beneath Submarine Pipelines. The model is based on solutions to Reynolds-averaged Navier–Stokes equations, coupled with k − ω turbulence closure, with additional bed and suspended load descriptions forming the basis for sea bed morphology. The morphological evolution is updated continuously, rather than being based e.g. on period- or other time-averaging techniques. Simulations involving wave-induced scour over the range of Keulegan–Carpenter number 5.6 ≤ KC ≤ 30 demonstrate reasonable match with previous experiments, both in terms of the equilibrium scour depth as well as the scour time scale. Wave-induced backfilling processes are additionally studied by subjecting initial conditions taken from scour simulations with larger KC to new wave climates characterized by lower KC values. The simulations considered demonstrate the ability of the model to predict backfilling toward expected equilibrium scour depths based on the new wave climate, in line with experimental expectations. The simulated backfilling process is characterized by two stages: (1) An initial re-distribution phase involving re-organization of sediments in the immediate vicinity of the pipeline, potentially followed by (2) a more lengthy backfilling evolution toward equilibrium scour depth. The simulated backfilling time scales are of the same order of magnitude as in experiments, though the multi-stage process complicates a more systematic characterization. The simulated sequences of scour and backfilling achieved within the present work are estimated to represent temporal durations of up to approximately 12 h at full practical scales.
Bjarke Eltard Larsen - One of the best experts on this subject based on the ideXlab platform.
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numerical investigation of wave plus current induced scour beneath two Submarine Pipelines in tandem
Coastal Engineering, 2020Co-Authors: Yuzhu Li, David R Fuhrman, Bjarke Eltard LarsenAbstract:Abstract Two-dimensional (2D) local scour beneath two Submarine Pipelines in tandem under wave-plus-current conditions is investigated numerically. A fully-coupled hydrodynamic and morphologic model based on unsteady Reynolds-averaged Navier-Stokes (URANS) equations with the k − ω turbulence closure is applied. The model is validated against existing experimental measurements involving live-bed scour beneath a single pipeline and beneath two Pipelines in tandem, respectively. The model is then employed to simulate scour beneath two tandem Pipelines under wave-plus-current conditions for a variety of Keulegan-Carpenter ( K C ) numbers and relative current strengths. Horizontal gap ratios (the horizontal gap distance between two Pipelines divided by the pipeline diameter) ranging from 1 to 4 are modelled. It is found that for conditions involving waves plus a low-strength current, the scour pattern beneath two Pipelines behaves like that in the pure-wave condition. Conversely, when the current has equal strength to the wave-induced flow, the scour pattern beneath two Pipelines resembles that in the pure-current condition. It is also observed that in the pure-wave condition the equilibrium scour depth beneath each pipeline is affected by both K C and the horizontal gap ratio, except for K C = 5.6 . For such a small K C , the horizontal gap ratio has insignificant influence on the equilibrium scour depth, since vortex shedding does not occur. When the current strength relative to the waves is low, the scour development beneath the upstream and the downstream Pipelines are similar. However, when the current has equal strength to the waves, the scour development beneath the downstream pipeline has a different pattern to that upstream. Namely, smaller horizontal gap ratios result in delayed scour beneath the downstream pipeline.
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experimental and numerical study of wave induced backfilling beneath Submarine Pipelines
Coastal Engineering, 2016Co-Authors: Deniz Bayraktar, Bjarke Eltard Larsen, Stefan Carstensen, Joseph Ahmad, David R FuhrmanAbstract:Abstract This paper presents results of complementary experimental and numerical studies involving wave-induced backfilling of current-generated scour holes beneath Submarine Pipelines. The laboratory experiments are conducted in a wave-plus-current flume, utilizing Laser Doppler Anemometry to measure velocities, synchronized flow visualizations using digital image technology, along with live-bed scour and backfilling measurements. Each experiment is based on a two-stage process: (1) initial scour induced by a pure current, followed by: (2) backfilling induced by pure waves (either regular or irregular). The time series of scour depths are closely monitored through video recordings. Systematic analysis of these has resulted in a closed form expression for the backfilling time scale, which is demonstrated to be a full order of magnitude greater than the well-known time scale of scour (with both governed primarily by the Shields parameter). The developed expression is strictly valid for the current-to-wave backfilling scenarios considered, while likely serving as an upper limit for more general wave-induced backfilling circumstances. The experiments are complemented by similar backfilling simulations utilizing a fully-coupled hydrodynamic and morphodynamic CFD model. The numerical simulations demonstrate the ability of the model to predict backfilling towards expected equilibrium scour depths based on the new wave climate, with time scales reasonably in line with experimental expectations.
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simulation of wave plus current scour beneath Submarine Pipelines
Journal of Waterway Port Coastal and Ocean Engineering-asce, 2016Co-Authors: Bjarke Eltard Larsen, David R Fuhrman, Mutlu B SumerAbstract:AbstractA fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath Submarine Pipelines. The model was based on incompressible Reynolds-averaged Navier–Stokes equations, coupled with k-ω turbulence closure, with additional bed and suspended load descriptions forming the basis for seabed morphology. The model was successfully validated against experimental measurements involving scour development and eventual equilibrium in pure-current flows over a range of Shields parameters characteristic of both clear-water and live-bed regimes. This validation complements previously demonstrated accuracy for the same model in simulating pipeline scour processes in pure-wave environments. The model was subsequently utilized to simulate combined wave-plus-current scour over a wide range of combined Keulegan–Carpenter numbers and relative current strengths. The resulting equilibrium scour depths and trends were shown to be in accordance with existing exp...
Yeemeng Chiew - One of the best experts on this subject based on the ideXlab platform.
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three dimensional scour at Submarine Pipelines
Journal of Hydraulic Engineering, 2012Co-Authors: Yushi Wu, Yeemeng ChiewAbstract:This paper presents results of an experimental study on three-dimensional scour at Submarine Pipelines with uniform sediment under a unidirectional current in clear-water conditions. The data show that propagation of the scour hole in the transverse direction of flow may be divided into a rapid and a slack phase of development. The former is characterized by a higher and constant velocity, whereas the latter a lower and reducing propagation velocity. Four nondimensional parameters are identified and their effects examined experimentally. Pipeline embedment and water depth to pipeline diameter ratios, which represent the stability force, inhibit the scouring process, resulting in a reduced propagation velocity and a dominant slack phase of development. Conversely, Froude number and Shields parameters represent the environment force; they enhance the scouring process, causing a high propagation velocity and a dominant rapid phase of development. The experimental results reveal that the scour process is not sensitive to Shields parameter under clear-water conditions but is closely related to the other three parameters. The effect of all the parameters can be viewed in a balance between the environment and stability forces.
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effect of spoilers on wave induced scour at Submarine Pipelines
Journal of Waterway Port Coastal and Ocean Engineering-asce, 1993Co-Authors: Yeemeng ChiewAbstract:This paper investigates the effect of spoiler orientations on wave-induced scour around a Submarine pipeline. Experiments conducted under pure wave action show that the spoiler can increase both the scour beneath (tunnel scour) and downstream of (lee-wake scour) the pipeline. The increase in tunnel scour depth is due to the higher blockage in the flow. This high flow blockage causes the deflection of a strong flow downwards through the tunnel beneath the pipe. The lee-wake scour depth is affected by the increase in strength of the reattached flow as flow separation occurs at the edge of the spoiler. At some spoiler orientations, the formation of a secondary hole is observed at the edge of the spoiler. Secondary scour holes form when the spoiler is located near the sediment bed. The local disturbance of flow at the edge of the spoiler is the cause of the formation of these secondary scour holes.
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effect of spoilers on scour at Submarine Pipelines
Journal of Hydraulic Engineering, 1992Co-Authors: Yeemeng ChiewAbstract:This paper investigates the effect of a spoiler on local scour around Submarine Pipelines. Experiments conducted in a unidirectional flow show that the spoiler is capable of increasing both the scour depth beneath (tunnel erosion) and downstream of (lee erosion) the pipeline. The increase is related to the location of the spoiler compared with the direction of the incoming flow. The spoiler attached on top of the pipeline is effective in increasing the blockage to the incoming flow, which deflects a large proportion of the flow downward beneath the pipe, resulting in an increased scour depth. The increase in lee erosion, due to the protrusion of the spoiler above the pipeline, is important in the stimulation of the self-burial potential of the Submarine pipeline. Spoilers attached to the lower half of the pipeline effected the formation of a wake zone beneath the pipe, which acts to deflect the flow downward, causing the formation of a deeper tunnel scour hole.
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prediction of maximum scour depth at Submarine Pipelines
Journal of Hydraulic Engineering, 1991Co-Authors: Yeemeng ChiewAbstract:This paper examines and reviews published results relating to local scour around Submarine Pipelines. It highlights the limitations of existing methods for estimating scour depth at the pipeline. Based on experimental results, the study proposes an empirical function relating the amount of gap flow through the scour hole for given flow conditions. With the aid of this function, it is possible to predict the maximum Scour depth at Submarine Pipelines for given flow and geometric boundary conditions. Published results suggest that the maximum equilibrium scour depth occurs when the pipeline is just lying on a plane bed and subjected to a pure unidirectional current. The undisturbed bed shear stress is equal to the critical shear stress for sediment entrainment. This condition implies that there is no general sediment transport away from the pipeline. The predicted maximum scour depth using the iterative method proposed in this study compares well with experimental results.
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mechanics of local scour around Submarine Pipelines
Journal of Hydraulic Engineering, 1990Co-Authors: Yeemeng ChiewAbstract:The primary objective of this study is to improve understanding of the mechanism causing scour in unidirectional current. Experiments have shown how local scour develops around Submarine Pipelines in noncohesive sediments. The study shows that piping is the dominant cause of the initiation of scour. Piping and the stagnation eddy combine to undermine the pipeline, and mark the onset of scour. The critical hydraulic gradient associated with the initiation of scour is equal to the flotation gradient of the bed sediment. The pressure drop between the stagnation pressure upstream and wake pressure downstream of the pipe induces this hydraulic gradient. When a pipe is just embedded, the onset of scour does not occur if the ratio of the flow depth to pipe diameter exceeds 3.5. Similarly, the onset of scour does not occur for half‐buried pipes. The reduction in pressure gradient across the pipeline for these flow/pipe combinations accounts for the lack of scour. The onset of scour can be prevented by placing an ...
Jinping Ou - One of the best experts on this subject based on the ideXlab platform.
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a three index estimator based on active thermometry and a novel monitoring system of scour under Submarine Pipelines
Sensors and Actuators A-physical, 2012Co-Authors: Xuefeng Zhao, Qin Ba, Le Li, Peng Gong, Jinping OuAbstract:Abstract A Submarine pipeline system is a major asset. Scour monitoring under Submarine Pipelines is a tough problem and lacks research, especially for nearshore and landfill sections. While these sections are critical for the viability of the pipeline system, they are also the most vulnerable to scour. In this study, a three-index estimator (TIE 1 ) based on active thermometry was developed for solving this problem and thereby a novel scour monitoring system was designed for nearshore and landfill sections. Heat dissipates in different ways between in-water and in-sediment scenarios. TIE, consisting of three indices obtained through time history analysis of temperature change during heating and cooling, can well characterize the distinction of heat transfer behaviors between in liquids and solids. By calculating TIE, it is possible to identify whether a location along a pipe is surrounded by water or soil. Considering this, the system utilizes a thermal cable to generate heat with a heating belt and concurrently measure temperature with DS18B20s. The thermal cable was deployed parallel to the pipeline. Analyzing the acquired data by TIE, identification of free spans is achieved. Several experimental tests were conducted using the system. Results confirm the methodology and substantiate the scour monitoring system.
M Zeinoddini - One of the best experts on this subject based on the ideXlab platform.
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response of Submarine Pipelines to impacts from dropped objects bed flexibility effects
International Journal of Impact Engineering, 2013Co-Authors: M Zeinoddini, Hamid Arabzadeh, M Ezzati, Gerard ParkeAbstract:Abstract Effects of soil–pipe interaction on the response of continuously supported offshore Pipelines subjected to transverse impacts caused by dropped objects are studied. For this, the impact on an internally pressurized pipeline resting on a flexible bed has been numerically simulated. The numerical model has first been validated against different sets of experimental data from the authors and a number of researches. A relatively extensive parametric study has then been carried out to examine effects from variations in the pipe geometry, internal pressure, boundary conditions, indentor shape and orientation, embedment depth of the pipe into the soil bed and subsoil mechanical properties on the pipeline response. It has been noticed that the presence of internal pressure results in substantial increase in the impact force. It, however, reduces the denting length, causing the deformation to become spatially more localized. It has also been shown that the flexibility of pipe bed plays an important role in the impact energy dissipation. This effect becomes more pronounced when the internal pressure is relatively low.
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dynamic response of pressurized Submarine Pipelines subjected to transverse impact loads
Procedia Engineering, 2011Co-Authors: Hamid Arabzadeh, M ZeinoddiniAbstract:Accidental impacts are a common source of damage in Submarine Pipelines. In this article, response of internally pressurized steel Pipelines subjected to lateral dynamic impact loads has been studied using a three dimensional finite element simulation. The numerical model has first been validated against experimental data from other researchers. Moderately thick wall steel tubes that may show noticeable inelastic deformations during lateral impacts have been considered in the study. Geometrical and material nonlinearities in the tube body and in the sub-soil medium have been taken into consideration. Effects from internal fluid pressure, dynamic wave propagation in the internal fluid, velocity of the dropped object, embedment depth of the pipe and soil bed properties have been investigated. It was found that the sea bed properties may have important effects on the extent of denting, especially at relatively low internal pressures. It has also been shown that with increase in the embedment depth of the pipe into the bed, the maximum impact load and maximum dent depth were increasing but the permanent dent did not completely follow suite.
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nonlinear seismic analysis of free spanning Submarine Pipelines effects of pipe water interaction
ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering, 2008Co-Authors: M Zeinoddini, S M Sadrossadat, G A R ParkeAbstract:The seismic response of free spanning Submarine Pipelines has received little attention in the literature. This paper deals with this subject and its main focus is on water-pipeline interaction during the event. The added mass approach provides a simple water-pipeline interaction model which is commonly used for the dynamic analysis of Submarine Pipelines. With free spans, however, earthquake components normal to the seabed also contribute to the dynamic pressures inputs to the pipeline. The line, therefore, becomes subject to loads which might be overlooked in a simplified added mass approach. To provide a more accurate estimation for the water-pipeline interaction, the pipe body, the sea bed, the free-spanning and the surrounding water have been incorporated in a numerical finite element model. The accuracy of the model has been verified by correlating the dynamic characteristics of the model with some analytical solutions. The models have then been analyzed under both harmonic excitations and extreme ground motion records. The site effects have been ignored. Both the horizontal and vertical excitations have been considered. A non-linear incremental direct integration dynamic analysis approach has been employed. Deviations up to 14% have been observed between the model predictions and those from the simple added mass method. The maximum deviation has been found to occur when the frequency contents of the excitation has been close to the first natural frequency of the free spanning pipe.Copyright © 2008 by ASME
