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Ian Reid - One of the best experts on this subject based on the ideXlab platform.
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topographic disturbance of subaqueous gravel substrates by signal crayfish pacifastacus leniusculus
Geomorphology, 2010Co-Authors: Matthew F Johnson, Stephen P Rice, Ian ReidAbstract:Abstract The impact of signal crayfish ( Pacifastacus leniusculus ) on the topography and fabric of six narrowly graded, gravel substrates was investigated using repeat laser scanning of sediment surfaces in still-water aquaria. Digital Elevation Models (DEMs) of the gravel surfaces were obtained before and after exposure to crayfish for five predetermined periods. The impact on the substrate was quantified by establishing topographic and volumetric changes using DEMs of difference (DoD). The presence of an individual, medium sized crayfish for 24 h resulted in an average volume change in surface topography of 450 cm 3 over an area of 2400 cm 2 , giving a sediment displacement of 1.7 kg m −2 d − 1 . The majority (78%) of this volume change was associated with small scale (≤ 1 median grain diameter) movements of surface grains. This fabric adjustment altered grain orientations and friction angles. Crayfish also constructed pits and mounds that increased significantly the roughness of the gravel substrates and altered the protrusion of individual grains. Crayfish were able to move material up to 38 mm in diameter that had a Submerged Weight six times that of the individuals used in this study. By modifying the arrangement of grains on the surface of fluvial substrates, signal crayfish may counteract the low flow physical consolidation of gravel beds and reduce the entrainment stresses required to move river bed material. The results of this study suggest that signal crayfish, an internationally widespread invasive species, may have substantial impacts on the physical environment of streams and rivers, as well as on local benthic ecological communities.
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topographic disturbance of subaqueous gravel substrates by signal crayfish pacifastacus leniusculus
Geomorphology, 2010Co-Authors: Matthew F Johnson, Stephen P Rice, Ian ReidAbstract:Abstract The impact of signal crayfish ( Pacifastacus leniusculus ) on the topography and fabric of six narrowly graded, gravel substrates was investigated using repeat laser scanning of sediment surfaces in still-water aquaria. Digital Elevation Models (DEMs) of the gravel surfaces were obtained before and after exposure to crayfish for five predetermined periods. The impact on the substrate was quantified by establishing topographic and volumetric changes using DEMs of difference (DoD). The presence of an individual, medium sized crayfish for 24 h resulted in an average volume change in surface topography of 450 cm 3 over an area of 2400 cm 2 , giving a sediment displacement of 1.7 kg m −2 d − 1 . The majority (78%) of this volume change was associated with small scale (≤ 1 median grain diameter) movements of surface grains. This fabric adjustment altered grain orientations and friction angles. Crayfish also constructed pits and mounds that increased significantly the roughness of the gravel substrates and altered the protrusion of individual grains. Crayfish were able to move material up to 38 mm in diameter that had a Submerged Weight six times that of the individuals used in this study. By modifying the arrangement of grains on the surface of fluvial substrates, signal crayfish may counteract the low flow physical consolidation of gravel beds and reduce the entrainment stresses required to move river bed material. The results of this study suggest that signal crayfish, an internationally widespread invasive species, may have substantial impacts on the physical environment of streams and rivers, as well as on local benthic ecological communities.
Matthew F Johnson - One of the best experts on this subject based on the ideXlab platform.
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topographic disturbance of subaqueous gravel substrates by signal crayfish pacifastacus leniusculus
Geomorphology, 2010Co-Authors: Matthew F Johnson, Stephen P Rice, Ian ReidAbstract:Abstract The impact of signal crayfish ( Pacifastacus leniusculus ) on the topography and fabric of six narrowly graded, gravel substrates was investigated using repeat laser scanning of sediment surfaces in still-water aquaria. Digital Elevation Models (DEMs) of the gravel surfaces were obtained before and after exposure to crayfish for five predetermined periods. The impact on the substrate was quantified by establishing topographic and volumetric changes using DEMs of difference (DoD). The presence of an individual, medium sized crayfish for 24 h resulted in an average volume change in surface topography of 450 cm 3 over an area of 2400 cm 2 , giving a sediment displacement of 1.7 kg m −2 d − 1 . The majority (78%) of this volume change was associated with small scale (≤ 1 median grain diameter) movements of surface grains. This fabric adjustment altered grain orientations and friction angles. Crayfish also constructed pits and mounds that increased significantly the roughness of the gravel substrates and altered the protrusion of individual grains. Crayfish were able to move material up to 38 mm in diameter that had a Submerged Weight six times that of the individuals used in this study. By modifying the arrangement of grains on the surface of fluvial substrates, signal crayfish may counteract the low flow physical consolidation of gravel beds and reduce the entrainment stresses required to move river bed material. The results of this study suggest that signal crayfish, an internationally widespread invasive species, may have substantial impacts on the physical environment of streams and rivers, as well as on local benthic ecological communities.
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topographic disturbance of subaqueous gravel substrates by signal crayfish pacifastacus leniusculus
Geomorphology, 2010Co-Authors: Matthew F Johnson, Stephen P Rice, Ian ReidAbstract:Abstract The impact of signal crayfish ( Pacifastacus leniusculus ) on the topography and fabric of six narrowly graded, gravel substrates was investigated using repeat laser scanning of sediment surfaces in still-water aquaria. Digital Elevation Models (DEMs) of the gravel surfaces were obtained before and after exposure to crayfish for five predetermined periods. The impact on the substrate was quantified by establishing topographic and volumetric changes using DEMs of difference (DoD). The presence of an individual, medium sized crayfish for 24 h resulted in an average volume change in surface topography of 450 cm 3 over an area of 2400 cm 2 , giving a sediment displacement of 1.7 kg m −2 d − 1 . The majority (78%) of this volume change was associated with small scale (≤ 1 median grain diameter) movements of surface grains. This fabric adjustment altered grain orientations and friction angles. Crayfish also constructed pits and mounds that increased significantly the roughness of the gravel substrates and altered the protrusion of individual grains. Crayfish were able to move material up to 38 mm in diameter that had a Submerged Weight six times that of the individuals used in this study. By modifying the arrangement of grains on the surface of fluvial substrates, signal crayfish may counteract the low flow physical consolidation of gravel beds and reduce the entrainment stresses required to move river bed material. The results of this study suggest that signal crayfish, an internationally widespread invasive species, may have substantial impacts on the physical environment of streams and rivers, as well as on local benthic ecological communities.
Fu-ping Gao - One of the best experts on this subject based on the ideXlab platform.
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Physical modeling of the axial pipe-soil interaction for pipeline walking on a sloping sandy seabed
Ocean Engineering, 2019Co-Authors: Yu-min Shi, Fu-ping Gao, Ning Wang, Jun-qin WangAbstract:Abstract Axial pipe-soil interaction is crucial for the prediction of pipeline walking, especially on a sloping seabed. In this study, a mechanical-actuator facility has been specially designed and utilized to simulate the axial pipe-soil interactions along a sloping sandy seabed. Based on dimensional analyses, an apparent axial anti-sliding coefficient is proposed to describe the anti-sliding capacity for pipeline walking on a sloping seabed under the fully-drained condition. Effects of the pipeline surface roughness, the Submerged Weight (G) of the pipeline and the slope angle ( α ) of the seabed on the apparent axial anti-sliding coefficient are investigated experimentally. The experimental results indicate that, for a fixed value of the non-dimensional Submerged pipeline Weight, both the ultimate anti-sliding capacity and the corresponding mobilization displacement increase with the increase of the slope angle of the seabed. There exist approximately linear correlations between the apparent anti-sliding coefficient and the examined seabed slope angle ( − 9 o ≤ α ≤ 9 o ) or the non-dimensional Submerged pipeline Weight ( 0.34 ≤ G ≤ 0.81 ). An expression for the apparent axial anti-sliding coefficient incorporating an updated wedging factor is finally deduced and validated with the present experimental results. This axial pipe-soil interaction model may help assessing the pipeline walking along subsea continental slopes.
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Lateral instability and tunnel erosion of a submarine pipeline: competition mechanism
Bulletin of Engineering Geology and the Environment, 2017Co-Authors: Yu-min Shi, Fu-ping GaoAbstract:In submarine geological and hydrodynamic environments, either tunnel erosion or lateral instability could be initiated where there is a shallowly embedded pipeline. Unlike previous studies on the tunnel erosion of sand and the lateral instability of pipelines, in this study we performed correlation analyses on the competition mechanism for these two physical processes. By correlating the critical flow velocities of these two processes, the instability envelope for the pipe–soil interaction system is established, which can be described using three key parameters: the embedment-to-diameter ratio, the dimensionless Submerged Weight of the pipe, and the corresponding critical flow velocity. The analysis procedure is further proposed to first determine the instability mechanism and then the critical velocity of ocean currents. Our parametric study indicates that tunnel erosion is more prone to emerging than lateral instability with small embedment-to-diameter ratio values. With increasing pipeline embedment, tunnel erosion can be suppressed and lateral instability therefore occurs more frequently. Moreover, for light pipelines, lateral instability is more likely to be triggered than tunnel erosion.
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A numerical model for ultimate soil resistance to an untrenched pipeline under ocean currents
China Ocean Engineering, 2012Co-Authors: Fu-ping Gao, Xi-ting Han, Shuming YanAbstract:One of the main concerns for pipeline on-bottom stability design is to properly predict ultimate soil resistance in severe ocean environments. A plane-strain finite element model is proposed to investigate the ultimate soil resistance to the partially-embedded pipeline under the action of ocean currents. Two typical end-constraints of the submarine pipelines are examined, i.e. freely-laid pipes and anti-rolling pipes. The proposed numerical model is verified with the existing mechanical-actuator experiments. The magnitude of lateral-soil-resistance coefficient for the examined anti-rolling pipes is much larger than that for the freely-laid pipes, indicating that the end-constraint condition significantly affects the lateral stability of the untrenched pipeline under ocean currents. The parametric study indicates that, the variation of lateral-soil-resistance coefficient with the dimensionless Submerged Weight of pipe is affected greatly by the angle of internal friction of soil, the pipe-soil friction coefficient, etc.
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Submarine pipeline lateral instability on a sloping sandy seabed
Ocean Engineering, 2012Co-Authors: Fu-ping Gao, Xi-ting Han, Jing Cao, Yong Sha, Jinsheng CuiAbstract:Ocean-current induced pipeline on-bottom stability on a sloping sandy seabed involves a complex interaction between the hydrodynamic loading, the untrenched pipeline and the neighboring soil. In this study, a newly-designed pipe-soil interaction facility and a flow-structure-soil interaction flume have been utilized for full-scale physical modeling of the pipeline instability on a sloping sand-bed, including the downslope instability and the upslope instability. Unlike the pipeline lateral stability on the horizontal seabed, an initial lateral-soil-resistance is developed and the static-instability might be triggered for the sloping seabed. According to dimensionless analyses, an ultimate lateral-soil-resistance coefficient is proposed to describe the interaction of the pipe with the sloping sand-bed. Experimental results indicate that sand-bed slope angle, pipe Submerged Weight and end-constraints have much influence on pipe on-bottom stability. No matter for the upslope instability or the downslope instability, the corresponding lateral-soil-resistance coefficient for a sloping sand-bed is larger than that for a horizontal sand-bed.
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Steady flow-induced instability of a partially embedded pipeline: Pipe–soil interaction mechanism
Ocean Engineering, 2011Co-Authors: Fu-ping Gao, Shuming Yan, Bing Yang, Cheng-cai LuoAbstract:The steady flow-induced instability of a partially embedded pipeline involves a complex process of pipe-soil interaction. In accordance with the hydrodynamic loading and the dimensionless analyses, a series of pipe-soil interaction tests have been conducted with an updated pipe-soil interaction facility including a load-displacement synchronous measurement system, to reveal the underlying pipe-soil interaction mechanism. The effects of pipe surface roughness, end-constraint and initial embedment are investigated, respectively. The values of lateral-soil-resistance coefficient for the rough pipes are bigger than those for the smooth pipes. For a fixed value of non-dimensional Submerged Weight, the values of lateral-soil-resistance coefficient for the anti-rolling pipes are much larger than those for the freely laid pipes. The effects of initial embedment on the ultimate soil resistance get less with the decrease of the Submerged Weight of the pipe. A comparison is made between the results of the present mechanical-actuator tests and those of the previous water-flume tests, indicating that those results are quite comparable. For the equivalent level of dimensionless Submerged Weight, the directly laid pipe in currents has higher lateral stability than in waves. (C) 2010 Elsevier Ltd. All rights reserved.
Stephen P Rice - One of the best experts on this subject based on the ideXlab platform.
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topographic disturbance of subaqueous gravel substrates by signal crayfish pacifastacus leniusculus
Geomorphology, 2010Co-Authors: Matthew F Johnson, Stephen P Rice, Ian ReidAbstract:Abstract The impact of signal crayfish ( Pacifastacus leniusculus ) on the topography and fabric of six narrowly graded, gravel substrates was investigated using repeat laser scanning of sediment surfaces in still-water aquaria. Digital Elevation Models (DEMs) of the gravel surfaces were obtained before and after exposure to crayfish for five predetermined periods. The impact on the substrate was quantified by establishing topographic and volumetric changes using DEMs of difference (DoD). The presence of an individual, medium sized crayfish for 24 h resulted in an average volume change in surface topography of 450 cm 3 over an area of 2400 cm 2 , giving a sediment displacement of 1.7 kg m −2 d − 1 . The majority (78%) of this volume change was associated with small scale (≤ 1 median grain diameter) movements of surface grains. This fabric adjustment altered grain orientations and friction angles. Crayfish also constructed pits and mounds that increased significantly the roughness of the gravel substrates and altered the protrusion of individual grains. Crayfish were able to move material up to 38 mm in diameter that had a Submerged Weight six times that of the individuals used in this study. By modifying the arrangement of grains on the surface of fluvial substrates, signal crayfish may counteract the low flow physical consolidation of gravel beds and reduce the entrainment stresses required to move river bed material. The results of this study suggest that signal crayfish, an internationally widespread invasive species, may have substantial impacts on the physical environment of streams and rivers, as well as on local benthic ecological communities.
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topographic disturbance of subaqueous gravel substrates by signal crayfish pacifastacus leniusculus
Geomorphology, 2010Co-Authors: Matthew F Johnson, Stephen P Rice, Ian ReidAbstract:Abstract The impact of signal crayfish ( Pacifastacus leniusculus ) on the topography and fabric of six narrowly graded, gravel substrates was investigated using repeat laser scanning of sediment surfaces in still-water aquaria. Digital Elevation Models (DEMs) of the gravel surfaces were obtained before and after exposure to crayfish for five predetermined periods. The impact on the substrate was quantified by establishing topographic and volumetric changes using DEMs of difference (DoD). The presence of an individual, medium sized crayfish for 24 h resulted in an average volume change in surface topography of 450 cm 3 over an area of 2400 cm 2 , giving a sediment displacement of 1.7 kg m −2 d − 1 . The majority (78%) of this volume change was associated with small scale (≤ 1 median grain diameter) movements of surface grains. This fabric adjustment altered grain orientations and friction angles. Crayfish also constructed pits and mounds that increased significantly the roughness of the gravel substrates and altered the protrusion of individual grains. Crayfish were able to move material up to 38 mm in diameter that had a Submerged Weight six times that of the individuals used in this study. By modifying the arrangement of grains on the surface of fluvial substrates, signal crayfish may counteract the low flow physical consolidation of gravel beds and reduce the entrainment stresses required to move river bed material. The results of this study suggest that signal crayfish, an internationally widespread invasive species, may have substantial impacts on the physical environment of streams and rivers, as well as on local benthic ecological communities.
Muk Chen Ong - One of the best experts on this subject based on the ideXlab platform.
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On-Bottom Stability of Umbilicals and Power Cables for Offshore Wind Applications
Energies, 2019Co-Authors: Muk Chen OngAbstract:With the increase in offshore wind farms, the demands for umbilicals and power cables have increased. The on-bottom stability of umbilicals and power cables under the combined wave and current loading is the most challenging design issue, due to their light Weight and the complex fluid–cable–soil interaction. In the present study, the methodology for dynamic lateral stability analysis is first discussed; and the reliable hydrodynamic load model and cable–soil interaction model based on large experimental test data are described in detail. The requirement of the Submerged Weight of a cable w s to obtain on-bottom stability is investigated for three types of soil (clay, sand and rock), using the finite element program PONDUS, and the results are w s , r o c k > w s , c l a y > w s , s a n d under the same load conditions. Several different aspects related to optimization design of the on-bottom stability are explored and addressed. There is a significant benefit for the on-bottom stability analysis to consider the reduction factors, due to penetration for clay and sand soil. The on-bottom stability is very sensitive to the relative initial embedment z 0 / D for clay and sand soil, due to the small diameter of the cables, and therefore, reliable prediction of initial embedment is required. In the energy-based cable–soil interaction model, the friction coefficient μ and the development of penetration affect each other and the total effect of friction force F f and passive resistance F r is complicated. The effect of the friction coefficient μ on the on-bottom stability is different from engineering judgement based on the Coulomb friction model. The undrained shear strength of clay is an important parameter for the on-bottom stability of umbilicals and cables. The higher the undrained shear strength of the clay, the larger the lateral displacement. Meanwhile, the Submerged Weight of sand has a minor effect on the lateral displacement of cables. The method used in the present study significantly improves the reliability of the on-bottom stability analysis of umbilicals and power cables for offshore wind application.
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A Comparison of Simplified Engineering and FEM Methods for On-Bottom Stability Analysis of Subsea Pipelines
Volume 1: Offshore Technology; Offshore Geotechnics, 2016Co-Authors: Muk Chen OngAbstract:This paper presents a comparison between simplified engineering and FEM (Finite Element Method) methods for on-bottom stability analysis of a subsea pipeline. The simplified engineering method is first used to assess the absolute on-bottom stability of empty and filled pipelines under different scenarios. The calculations of the hydrodynamic loads for three scenarios, i.e. steady current alone, regular waves alone and combined regular waves and current, are implemented in MATLAB code. The drag and lift coefficients are determined based on Keulegan-Carpenter number, Reynolds number and surface roughness of the pipelines. Only the friction force is considered in the simplified methods. In order to achieve the absolute stability, the vertical (lift force/Submerged Weight<1) and horizontal (in-line force/friction force<1) criteria need to be fulfilled at same time. Time-domain dynamic on-bottom stability analysis is performed by PONDUS for the same cases. The results of water particle velocity, hydrodynamic force, lift force and soil resistance force are compared between the simplified engineering and advanced FEM methods. Their results are in good agreement for the cases, which fulfills the absolute on-bottom stability criterion. For the cases which the pipelines will move under the combined wave and current loadings, the soil resistance force predicted by the simplified engineering method is different from that of the FEM method. The study shows that for engineering purpose the simplified engineering method could be used to check the absolute on-bottom stability of the pipeline, whereas the more advanced FEM method needs be performed when the pipeline is allowed to move within a limited distance.
