How to model the permeability evolution of rock subjected to liquid nitrogen cooling is a key issue. This paper proposes a simple but practical method to study the permeability evolution of rocks subject to liquid nit...How to model the permeability evolution of rock subjected to liquid nitrogen cooling is a key issue. This paper proposes a simple but practical method to study the permeability evolution of rocks subject to liquid nitrogen cooling. FLAC with FISH function was employed to numerically model the rock behavior under cooling. The enhanced perme- ability of the volumetric strain was defined, and the permeability was directly evaluated based on element＇s volumetric strain. Detailed procedures for implementing the evolution model of permeability in this paper were presented. A case study was carried out to simulate a coal bed where liquid nitrogen was injected in the bore hole. And a semi-submerged test of liquid nitrogen was performed. The method to model the permeability evolution of rocks subject to liquid nitrogen shock in this paper was proved to be right by the test results. This simulation results are discussed with the hope to provide some insight into understanding the nitrogen cooling practice.展开更多
As the offshore industries move from shallow to deep waters in excess of 1000 m, there has been rapid development of ocean engineering practices. Innovations in theoretical and applied me- chanics have been essential ...As the offshore industries move from shallow to deep waters in excess of 1000 m, there has been rapid development of ocean engineering practices. Innovations in theoretical and applied me- chanics have been essential in this shift and in underpinning the exploitation of offshore oil and gas and renewable energy re- sources worldwide. Understanding and predicting physical mech- anisms of structure-soil interactions are vital for the stability and safety of offshore engineering structures. Accordingly, in this spe- cial issue of Theoretical ＆ Applied Mechanics Letters （TAME）, eight letter-papers are published to present recent advances in analyti- cal and numerical analysis and in physical modeling of offshore structure-soil interactions in marine environments. They all provide examples of how enhanced understanding of mechanics can imoact on aoDlied oroiects.展开更多
As the offshore engineering moving from shallow to deep waters, the foundation types for fixed and floating platforms have been gradually evolving to minimize engineering costs and structural risks in the harsh offsho...As the offshore engineering moving from shallow to deep waters, the foundation types for fixed and floating platforms have been gradually evolving to minimize engineering costs and structural risks in the harsh offshore environments. Particular focus of this paper is on the foundation instability and its failure mechanisms as well as the relevant theory advances for the prevailing foundation types in both shallow and deep water depths. Piles, spudcans, gravity bases, suction caissons, and plate anchors are detailed in this paper. The failure phenomena and mechanisms for each type of foundations are identified and summarized, respectively. The theoretical approaches along with sophisticated empirical solutions for the bearing capacity problems are then presented. The major challenges are from flow-structure-soil coupling processes, rigorous constitutive modeling of cyclic behaviors of marine sediments, and the spatial variability of soil properties for large-spreading structures. Further researches are suggested to reveal the instability mechanisms for underpinning the evolution of offshore foundations.展开更多
Reinstallation of mobile jack-up rigs next to existing footprints is a problematic operation because the spudcan located near the footprints is subjected to eccentric and/or inclined loading conditions. Geotech- nical...Reinstallation of mobile jack-up rigs next to existing footprints is a problematic operation because the spudcan located near the footprints is subjected to eccentric and/or inclined loading conditions. Geotech- nical centrifuge studies have measured these loads for combinations of changing footprint geometry, footprint soil properties and the offset of the reinstallation from the footprint centre. These tests have been of full model spudcans in order to accurately measure the combined loads developed. They have not provided information on the mechanisms of failure occurring during this complex installation. Ob- servations from a visualisation test, where a half spudcan is penetrated against a transparent window in a geotechnical centrifuge, are reported in this paper. The mechanisms of failure at different stages during the nenetrntirm are nr^nted展开更多
Pipelines are the critical link between major offshore oil and gas developments and the mainland. Any inadequate on-bottom stability design could result in disruption and failure, having a devastating impact on the ec...Pipelines are the critical link between major offshore oil and gas developments and the mainland. Any inadequate on-bottom stability design could result in disruption and failure, having a devastating impact on the economy and environment. Predicting the stability behavior of offshore pipelines in hurricanes is therefore vital to the assessment of both new design and existing assets. The Gulf of Mexico has a very dense network of pipeline systems constructed on the seabed. During the last two decades, the Gulf of Mexico has experienced a series of strong hurricanes, which have destroyed, disrupted and destabilized many pipelines. This paper first reviews some of these engineering cases. Following that, three case studies are retrospectively simulated using an in-house developed program. The study utilizes the offshore pipeline and hurricane details to conduct a Dynamic Lateral Stability analysis, with the results providing evidence as to the accuracy of the modeling techniques developed.展开更多
The initiation of pipeline spanning involves the coupling between the flow over the pipeline and the seepage-flow in the soil underneath the pipeline.The pipeline spanning initiation is experimentally observed and dis...The initiation of pipeline spanning involves the coupling between the flow over the pipeline and the seepage-flow in the soil underneath the pipeline.The pipeline spanning initiation is experimentally observed and discussed in this article.It is qualitatively indicated that the pressure-drop induced soil seepage failure is the predominant cause for pipeline spanning initiation.A flow-pipe-seepage sequential coupling Finite Element Method（FEM） model is proposed to simulate the coupling between the water flow-field and the soil seepage-field.A critical hydraulic gradient is obtained for oblique seepage failure of the sand in the direction tangent to the pipe.Parametric study is performed to investigate the effects of inflow velocity,pipe embedment on the pressure-drop,and the effects of soil internal friction angle and pipe embedment-to-diameter ratio on the critical flow velocity for pipeline spanning initiation.It is indicated that the dimensionless critical flow velocity changes approximately linearly with the soil internal friction angle for the submarine pipeline partially-embedded in a sandy seabed.展开更多
Most of the present knowledge on submarine landslides relies upon back-analysis of post-failure deposits identified using geophysical techniques.In this paper,the runout of slides on rigid bases is explored using the ...Most of the present knowledge on submarine landslides relies upon back-analysis of post-failure deposits identified using geophysical techniques.In this paper,the runout of slides on rigid bases is explored using the material point method（MPM）with focus on the geotechnical aspects of the morphologies.In MPM,the sliding material and bases are discretised into a number of Lagrangian particles,and a background Eulerian mesh is employed to update the state of the particles.The morphologies of the slide can be reproduced by tracking the Lagrangian particles in the dynamic processes.A real case history of a submarine slide is back-analyzed with the MPM and also a depth-averaged method.Runout of the slides from steep slopes to moderate bases are reproduced.Then different combinations of soil and basal parameters are assumed to trigger runout mechanisms of elongation,block sliding and spreading.The runout distances predicted by the MPM match well with those from large deformation finite element analysis for the elongation and block sliding patterns.Horst and grabens are shaped in a spreading pattern.However,the current MPM simulations for materials with high sensitivities are relatively mesh sensitive.展开更多
This paper investigates the response of a maglev structure to three under-crossing tunnels of the Shanghai Metro Line 13.The minimal distance between the tunnels and pile groups of the maglev structure is only 1.5 m,t...This paper investigates the response of a maglev structure to three under-crossing tunnels of the Shanghai Metro Line 13.The minimal distance between the tunnels and pile groups of the maglev structure is only 1.5 m,thus the deformations of the maglev structure are strictly controlled for the serviceability of the operating maglev trains.The displacements of maglev piers and ground settlements during different tunnelling stages are monitored with an automatic measuring system.Based on the observed data,the ground settlement trough and displacements of maglev piers caused by the three shield tunnelling procedures are analyzed and discussed.The maximal ground settlement after the completion of the three tunnelling procedures is -43 mm.To operate the existing maglev safely,practical construction control methods are applied,including synchronous grouting,adjustment of the shield status,shield-advancing speed control,and stabilisation of the soil chamber pressure.With these countermeasures,the tunnel-induced deformations of maglev piers are well below the predefined thresholds.All piers heave under the strict deformation criterion of 2.0 mm.The crossing project is finally completed without interruptions of the maglev operations by monitoring the progress.The presented project is a valuable example for the evaluation of shield tunnelling effects on the adjacent maglev structures and establishes criteria for similar projects in the future.展开更多
文摘How to model the permeability evolution of rock subjected to liquid nitrogen cooling is a key issue. This paper proposes a simple but practical method to study the permeability evolution of rocks subject to liquid nitrogen cooling. FLAC with FISH function was employed to numerically model the rock behavior under cooling. The enhanced perme- ability of the volumetric strain was defined, and the permeability was directly evaluated based on element＇s volumetric strain. Detailed procedures for implementing the evolution model of permeability in this paper were presented. A case study was carried out to simulate a coal bed where liquid nitrogen was injected in the bore hole. And a semi-submerged test of liquid nitrogen was performed. The method to model the permeability evolution of rocks subject to liquid nitrogen shock in this paper was proved to be right by the test results. This simulation results are discussed with the hope to provide some insight into understanding the nitrogen cooling practice.
文摘As the offshore industries move from shallow to deep waters in excess of 1000 m, there has been rapid development of ocean engineering practices. Innovations in theoretical and applied me- chanics have been essential in this shift and in underpinning the exploitation of offshore oil and gas and renewable energy re- sources worldwide. Understanding and predicting physical mech- anisms of structure-soil interactions are vital for the stability and safety of offshore engineering structures. Accordingly, in this spe- cial issue of Theoretical ＆ Applied Mechanics Letters （TAME）, eight letter-papers are published to present recent advances in analyti- cal and numerical analysis and in physical modeling of offshore structure-soil interactions in marine environments. They all provide examples of how enhanced understanding of mechanics can imoact on aoDlied oroiects.
基金supported by the National Natural Science Foundation of China(Grant Nos.11232012,11372319 and 51309213)the National Key Basic Research Program of China(Grant No.2014CB046204)
文摘As the offshore engineering moving from shallow to deep waters, the foundation types for fixed and floating platforms have been gradually evolving to minimize engineering costs and structural risks in the harsh offshore environments. Particular focus of this paper is on the foundation instability and its failure mechanisms as well as the relevant theory advances for the prevailing foundation types in both shallow and deep water depths. Piles, spudcans, gravity bases, suction caissons, and plate anchors are detailed in this paper. The failure phenomena and mechanisms for each type of foundations are identified and summarized, respectively. The theoretical approaches along with sophisticated empirical solutions for the bearing capacity problems are then presented. The major challenges are from flow-structure-soil coupling processes, rigorous constitutive modeling of cyclic behaviors of marine sediments, and the spatial variability of soil properties for large-spreading structures. Further researches are suggested to reveal the instability mechanisms for underpinning the evolution of offshore foundations.
基金supported as a primary node of the Australian Research Council Centre of Excellence for Geotechnical Science and Engineering(CE110001009)
文摘Reinstallation of mobile jack-up rigs next to existing footprints is a problematic operation because the spudcan located near the footprints is subjected to eccentric and/or inclined loading conditions. Geotech- nical centrifuge studies have measured these loads for combinations of changing footprint geometry, footprint soil properties and the offset of the reinstallation from the footprint centre. These tests have been of full model spudcans in order to accurately measure the combined loads developed. They have not provided information on the mechanisms of failure occurring during this complex installation. Ob- servations from a visualisation test, where a half spudcan is penetrated against a transparent window in a geotechnical centrifuge, are reported in this paper. The mechanisms of failure at different stages during the nenetrntirm are nr^nted
基金supported by the Research Development Awards of University of Western Australia,Australia-China Natural Gas Technology Partnership Fund and Lloyd's Register Foundationsupports the advancement of engineering-related education and funds research and development that enhance the safety of life at sea,on land,and in the airforms part of the activities of the Centre for Offshore Foundation Systems(COFS) above,currently supported as a primary node of the Australian Research Council Centre of Excellence for Geotechnical Science and Engineering
文摘Pipelines are the critical link between major offshore oil and gas developments and the mainland. Any inadequate on-bottom stability design could result in disruption and failure, having a devastating impact on the economy and environment. Predicting the stability behavior of offshore pipelines in hurricanes is therefore vital to the assessment of both new design and existing assets. The Gulf of Mexico has a very dense network of pipeline systems constructed on the seabed. During the last two decades, the Gulf of Mexico has experienced a series of strong hurricanes, which have destroyed, disrupted and destabilized many pipelines. This paper first reviews some of these engineering cases. Following that, three case studies are retrospectively simulated using an in-house developed program. The study utilizes the offshore pipeline and hurricane details to conduct a Dynamic Lateral Stability analysis, with the results providing evidence as to the accuracy of the modeling techniques developed.
基金supported by the National Natural Science Foundation of China (Grant No. 10532070)the Knowledge Innovation Project of Chinese Academy of Sciences (Grant No. KJCX2-YW-L02)
文摘The initiation of pipeline spanning involves the coupling between the flow over the pipeline and the seepage-flow in the soil underneath the pipeline.The pipeline spanning initiation is experimentally observed and discussed in this article.It is qualitatively indicated that the pressure-drop induced soil seepage failure is the predominant cause for pipeline spanning initiation.A flow-pipe-seepage sequential coupling Finite Element Method（FEM） model is proposed to simulate the coupling between the water flow-field and the soil seepage-field.A critical hydraulic gradient is obtained for oblique seepage failure of the sand in the direction tangent to the pipe.Parametric study is performed to investigate the effects of inflow velocity,pipe embedment on the pressure-drop,and the effects of soil internal friction angle and pipe embedment-to-diameter ratio on the critical flow velocity for pipeline spanning initiation.It is indicated that the dimensionless critical flow velocity changes approximately linearly with the soil internal friction angle for the submarine pipeline partially-embedded in a sandy seabed.
基金supported by the Australian Research Council through an ARC Discovery grant(DP120102987)supported by resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia and NVIDIA Corporation with the donation of the Tesla K40 GPU for the research
文摘Most of the present knowledge on submarine landslides relies upon back-analysis of post-failure deposits identified using geophysical techniques.In this paper,the runout of slides on rigid bases is explored using the material point method（MPM）with focus on the geotechnical aspects of the morphologies.In MPM,the sliding material and bases are discretised into a number of Lagrangian particles,and a background Eulerian mesh is employed to update the state of the particles.The morphologies of the slide can be reproduced by tracking the Lagrangian particles in the dynamic processes.A real case history of a submarine slide is back-analyzed with the MPM and also a depth-averaged method.Runout of the slides from steep slopes to moderate bases are reproduced.Then different combinations of soil and basal parameters are assumed to trigger runout mechanisms of elongation,block sliding and spreading.The runout distances predicted by the MPM match well with those from large deformation finite element analysis for the elongation and block sliding patterns.Horst and grabens are shaped in a spreading pattern.However,the current MPM simulations for materials with high sensitivities are relatively mesh sensitive.
基金financially supported by National Natural Science Foundation of China,China(Grants Nos.51978517,41772295,52090082,and 52108381)Innovation Program of Shanghai Municipal Education Commission(Grant No.2019-01-07-00-07-456 E00051)+2 种基金Shanghai Science and Technology Committee,China Program(Grants Nos.21DZ1200601,20DZ1201404)National Key Research and Development Program of China(Grant No.2021YFF0502200)China Postdoctoral Science Foundation,China(Grant No.2021M702491).
文摘This paper investigates the response of a maglev structure to three under-crossing tunnels of the Shanghai Metro Line 13.The minimal distance between the tunnels and pile groups of the maglev structure is only 1.5 m,thus the deformations of the maglev structure are strictly controlled for the serviceability of the operating maglev trains.The displacements of maglev piers and ground settlements during different tunnelling stages are monitored with an automatic measuring system.Based on the observed data,the ground settlement trough and displacements of maglev piers caused by the three shield tunnelling procedures are analyzed and discussed.The maximal ground settlement after the completion of the three tunnelling procedures is -43 mm.To operate the existing maglev safely,practical construction control methods are applied,including synchronous grouting,adjustment of the shield status,shield-advancing speed control,and stabilisation of the soil chamber pressure.With these countermeasures,the tunnel-induced deformations of maglev piers are well below the predefined thresholds.All piers heave under the strict deformation criterion of 2.0 mm.The crossing project is finally completed without interruptions of the maglev operations by monitoring the progress.The presented project is a valuable example for the evaluation of shield tunnelling effects on the adjacent maglev structures and establishes criteria for similar projects in the future.
