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Dong-sheng Jeng - One of the best experts on this subject based on the ideXlab platform.
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Wave-Induced Seabed Response around a Dumbbell Cofferdam in Non-Homogeneous Anisotropic Seabed
Journal of Marine Science and Engineering, 2019Co-Authors: Linya Chen, Dong-sheng Jeng, Chencong Liao, Dagui TongAbstract:Cofferdams are frequently used to assist in the construction of offshore structures that are built on a natural non-homogeneous anisotropic Seabed. In this study, a three-dimensional (3D) integrated numerical model consisting of a wave submodel and Seabed submodel was adopted to investigate the wave–structure–Seabed interaction. Reynolds-Averaged Navier–Stokes (RANS) equations were employed to simulate the wave-induced fluid motion and Biot’s poroelastic theory was adopted to control the wave-induced Seabed response. The present model was validated with available laboratory experimental data and previous analytical results. The hydrodynamic process and Seabed response around the dumbbell cofferdam are discussed in detail, with particular attention paid to the influence of the depth functions of the permeability K i and shear modulus G j . Numerical results indicate that to avoid the misestimation of the liquefaction depth, a steady-state analysis should be carried out prior to the transient Seabed response analysis to first determine the equilibrium state caused by Seabed consolidation. The depth function G j markedly affects the vertical distribution of the pore pressure and the Seabed liquefaction around the dumbbell cofferdam. The depth function K i has a mild effect on the vertical distribution of the pore pressure within a coarse sand Seabed, with the influence concentrated in the range defined by 0.1 times the Seabed thickness above and below the embedded depth. The depth function K i has little effect on Seabed liquefaction. In addition, the traditional assumption that treats the Seabed parameters as constants may result in the overestimation of the Seabed liquefaction depth and the liquefaction area around the cofferdam will be miscalculated if consolidation is not considered. Moreover, parametric studies reveal that the shear modulus at the Seabed surface G z 0 has a significant influence on the vertical distribution of the pore pressure. However, the effect of the permeability at the Seabed surface K z 0 on the vertical distribution of the pore pressure is mainly concentrated on the Seabed above the embedded depth in front and to the side of the cofferdam. Furthermore, the amplitude of pore pressure decreases as Poisson’s ratio μ s increases.
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Liquefaction of a poro-elastoplastic Seabed under combined wave and current loading
2015Co-Authors: Dong-sheng Jeng, Song Cui, Jian LengAbstract:Combined wave and current loading is a very common and important situation for sandy Seabeds. The dynamic Seabed response under combined these loadings, including the change of excess pore water pressure and the stress, is of great significance to the coastal structures design and construction In this paper, based on two-phase u-p theory for saturated soil, a new constitutive model, which is developed from the concept of superloading and sub-loading, is proposed to analyze the dynamic responds in a sandy Seabed under the combined wave and current loadings. Firstly, a poro-elastoplastic model for a sandy Seabed is established. The Seabed soils parameters are obtained from the un-drained triaxial cyclic loading tests. The mechanics of oscillatory excess pore water pressure and residual excess pore pressure due to waves/currents are discussed and the liquefaction depth which changes correspondingly is obtained. A comparison between the dynamic responds of elastic and elatoplastic sandy Seabeds to waves/currents loading is presented. Then, a parametric study is carried out to investigate the effects of currents on the pore pressures and liquefaction.
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Coupling model for waves propagating over a porous Seabed
Theoretical and Applied Mechanics Letters, 2015Co-Authors: C.c. Liao, Zaibin Lin, Yakun Guo, Dong-sheng JengAbstract:Abstract The wave–Seabed interaction issue is of great importance for the design of foundation around marine infrastructures. Most previous investigations for such a problem have been limited to uncoupled or one-way coupled methods connecting two separated wave and Seabed sub models with the continuity of pressures at the Seabed surface. In this study, a strongly coupled model was proposed to realize both wave and Seabed processes in a same program and to calculate the wave fields and Seabed response simultaneously. The information between wave fields and Seabed fields were strongly shared and thus results in a more profound investigation of the mechanism of the wave–Seabed interaction. In this letter, the wave and Seabed models were validated with previous experimental tests. Then, a set of application of present model were discussed in prediction of the wave-induced Seabed response. Numerical results show the wave-induced liquefaction area of coupled model is smaller than that of uncoupled model.
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Wave and current induced Seabed response around a submarine pipeline in an anisotropic Seabed
Ocean Engineering, 2014Co-Authors: Xiang-lian Zhou, Jun Zhang, Jian-hua Wang, Dong-sheng JengAbstract:A better understanding of the phenomenon of wave–Seabed-structure interactions is essential for the evaluation of the liquefaction of Seabed foundation under dynamic loading in the ocean environments. However, only a few investigations have been conducted for the cross-anisotropic Seabed under wave pressure and marine structures, despite the fact that most Seabeds are anisotropic medium. Furthermore, most previous numerical models for Biot's consolidation theory were only considered wave loading. In this study, based on Biot's partly dynamic poroelastic theory (“u-p” approximation), a two-dimensional FEM Seabed model is adopted to investigate the wave and current induced Seabed response around a submarine pipeline. The third-order solution of wave-current interactions is used to determine the dynamic pressure acting on the Seabed. Verification of the proposed model is performed against the previous experimental data and analytical result. With the proposed numerical model, the effects of wave, current and Seabed characteristics, such as Poisson's ratio, Young's modulus, degree of saturation, and pipeline buried depth on the wave-induced Seabed response will be examined. Then, the wave-current induced Seabed liquefaction is also discussed. The numerical results demonstrate significant effects of anisotropic soil behavior on Seabed liquefaction.
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Wave-Induced Seabed Response in Non-homogeneous Anisotropic Seabed
Porous Models for Wave-seabed Interactions, 2013Co-Authors: Dong-sheng JengAbstract:In a natural Seabed, the soil properties is complicated, which normally vary with soil depth, change of temperature, and geographic characteristics. Furthermore, anisotropic soil behavior is commonly observed in marine sediments. However, most previous studies have been limited to the case of isotropic Seabed with uniform soil characteristics. This chapter consists of three major components: (i) analytical solutions for a Seabed with variable permeability; (ii) analytical solution for a cross-isotropic Seabed; and (iii) numerical model for a non-homogeneous Seabed with cross-anisotropic soil behavior. With the newly analytical solutions and numerical model, effects of variable permeability and cross-isotropic soil behavior on the wave-induced Seabed response were examined.
Kunpeng Wang - One of the best experts on this subject based on the ideXlab platform.
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Coupled Dynamic Modeling and Simulation of Seabed Hexapod Robot
2019 IEEE 9th Annual International Conference on CYBER Technology in Automation Control and Intelligent Systems (CYBER), 2019Co-Authors: Jingming Zhang, Yiqun Liu, Liang Ding, Kunpeng Wang, Haibo Gao, Zongquan DengAbstract:With the development of human exploration of the ocean, the manipulation capability of underwater detection equipment in the marine has become one of the key technologies that restrict the development of deep-sea exploration and work. In this paper, we propose a new type of hexapod robot that works on the Seabed. Two manipulator arms are installed in the front of the body for mining Seabed minerals. In order to design and control a Seabed hexapod robot, the dynamics on the Seabed are analyzed. Considering the complex Seabed environment, the interactions between the arms, legs, body and Seabed environment are analyzed and calculated, and a water-terrain-robot coupled dynamic modeling method is proposed. Based on the Vortex simulation platform, a predictive simulation platform for a Seabed hexapod robot with two working arms was developed to verify the coupled dynamic model. Simulation results show that the coupled dynamic model is correct.
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fatigue sensitivity analysis of steel catenary riser near touchdown point
Journal of Shanghai Jiaotong University (science), 2017Co-Authors: Kunpeng Wang, Chunyan Ji, Wenyong TangAbstract:By transforming the platform response obtained from coupled hydrodynamic analysis to the top motions of steel catenary riser (SCR), the nonlinear dynamic analysis of the SCR is carried out in Abaqus/Aqua. In this analysis, the SCR-Seabed interaction is well taken into account by introducing the Seabed trench model and hysteretic Seabed model. The fatigue damage of the SCR near touchdown point (TDP) is calculated using rain-flow counting methodology, and the sensitivity of the fatigue damage to the Seabed and wave parameters are investigated. The results indicate that as Seabed stiffness increases, the fatigue life and its sensitivity to Seabed stiffness decrease. Seabed trenching may benefit the fatigue life of the SCR and the trench position should be elaborated for realistic fatigue damage prediction. Due to the induced platform response, significant wave height and spectral peak period have significant effects on the fatigue damage, thus the short-term sea state bins should be carefully selected from the wave scatter diagram.
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study of Seabed trench induced by steel catenary riser and Seabed interaction
ASME 2016 35th International Conference on Ocean Offshore and Arctic Engineering, 2016Co-Authors: Kunpeng WangAbstract:Seabed trench profile has significant effect on the fatigue damage of steel catenary riser near touchdown point. This study briefly demonstrates an approach in literature to determine the Seabed trench induced by wave frequency response based on the cubic polynomial model. In this approach, a criterion for the matching between catenary riser and Seabed trench is proposed, which is an optimization problem, and needs iterative static analysis of catenary riser. Based on the criterion, the sensitivity of the trench length and position to three parameters is parametrically studied: riser mass per unit length, ratio of horizontal span to vertical span of catenary part, trench depth. The obtained data are employed to fit the equations of trench length and position, which is taken as surrogate model since the iterative static analysis is very complicated. For completeness, the validation against data obtained from hysteretic Seabed model is also illustrated. Based on the surrogate model, this study investigates the effect of trench depth on the fatigue damage near touchdown and the effect of the low frequency response on the Seabed trench, and some useful conclusions are obtained.Copyright © 2016 by ASME
David Andrew Barry - One of the best experts on this subject based on the ideXlab platform.
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Water wave-driven seepage in marine sediments
Advances in Water Resources, 2000Co-Authors: Dong-sheng Jeng, David Andrew BarryAbstract:The action of water waves moving over a porous Seabed drives a seepage flux into and out of the marine sediments. The volume of fluid exchange per wave cycle may affect the rate of contaminant transport in the sediments. In this paper, the dynamic response of the Seabed to ocean waves is treated analytically on the basis of pore-elastic theory applied to a porous Seabed. The Seabed is modelled as a semi-infinite, isotropic, homogeneous material. Most previous investigations on the wave-Seabed interaction problem have assumed quasi-static conditions within the Seabed, although dynamic behaviour often occurs in natural environments. Furthermore, wave pressures used in the previous approaches were obtained from conventional ocean wave theories: which are based on the assumption of an impermeable rigid Seabed. By introducing a complex wave number, we derive a new wave dispersion equation, which includes the Seabed characteristics (such as soil permeability, shear modulus, etc.). Based on the new closed-form analytical solution, the relative differences of the wave-induced Seabed response under dynamic and quasi-static conditions are examined. The effects of wave and soil parameters on the seepage flux per wave cycle are also discussed in detail. (C) 2000 Elsevier Science Ltd. All rights reserved.
Liang Cheng - One of the best experts on this subject based on the ideXlab platform.
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Subsea Cable Stability on Rocky Seabeds: Comparison of Field Observations Against Conventional and Novel Design Methods
Volume 5: Pipelines Risers and Subsea Systems, 2018Co-Authors: Terry Griffiths, Scott Draper, Feifei Tong, Antonino Fogliani, Fraser Johnson, Daniel Coles, Stephen Ingham, David White, Liang Cheng, Caroline LourieAbstract:As offshore renewable energy projects progress from concept demonstration to commercial-scale developments there is a need for improved approaches beyond conventional cable engineering design methods that have evolved from larger diameter pipelines for the oil and gas industry. New approaches are needed to capture the relevant physics for small diameter cables on rocky Seabeds to reduce the costs and risks of power transmission and increase operational reliability. This paper reports on subsea cables that MeyGen installed for Phase 1a of the Pentland Firth Inner Sound tidal stream energy project. These cables are located on rocky Seabeds in an area where severe metocean conditions occur. ROV field observation of these cables shows them to be stable on the Seabed with little or no movement occurring over almost all of the cable routes, despite conventional engineering methods predicting significant dynamic movement. We cite recent research undertaken by the University of Western Australia (UWA) to more accurately assess the hydrodynamic forces and geotechnical interaction of cables on rocky Seabeds. We quantify the conformity between the cables and the undulating rocky Seabed, and the distributions of cable Seabed contact and spanning via simulations of the centimetric scale Seabed bathymetry. This analysis leads to calculated profiles of lift, drag and Seabed friction along the cable, which show that all of these load and reaction components are modelled in an over-conservative way by conventional pipeline engineering techniques. Overall, our analysis highlights that current cable stability design can be unnecessarily conservative on rocky Seabeds. Our work foreshadows a new design approach that offers more efficient cable design to reduce project capex and enhance through-life integrity management.
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Wave-induced Seabed instability around a buried pipeline in a poro-elastic Seabed
Ocean Engineering, 2000Co-Authors: Dong-sheng Jeng, Liang ChengAbstract:Abstract The subject of the wave–Seabed–structure interaction is important for civil engineers regarding stability analysis of foundations for offshore installations. Most previous investigations have been concerned with such a problem in the vicinity of a simple structure such as a vertical wall. For more complicated structures such as a pipeline, the phenomenon of the wave–Seabed–structure has not been fully understood. This paper proposes a finite-difference model in a curvilinear coordinate system to investigate the wave-induced Seabed response in a porous Seabed around a pipeline. Based on the present numerical model, mechanism of the wave-induced soil response is examined. Employing Mohr–Coulomb failure criterion, the wave-induced Seabed instability is also estimated. The numerical results indicate the importance of the effect of pipeline on the Seabed response.
Jun Zhang - One of the best experts on this subject based on the ideXlab platform.
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Wave and current induced Seabed response around a submarine pipeline in an anisotropic Seabed
Ocean Engineering, 2014Co-Authors: Xiang-lian Zhou, Jun Zhang, Jian-hua Wang, Dong-sheng JengAbstract:A better understanding of the phenomenon of wave–Seabed-structure interactions is essential for the evaluation of the liquefaction of Seabed foundation under dynamic loading in the ocean environments. However, only a few investigations have been conducted for the cross-anisotropic Seabed under wave pressure and marine structures, despite the fact that most Seabeds are anisotropic medium. Furthermore, most previous numerical models for Biot's consolidation theory were only considered wave loading. In this study, based on Biot's partly dynamic poroelastic theory (“u-p” approximation), a two-dimensional FEM Seabed model is adopted to investigate the wave and current induced Seabed response around a submarine pipeline. The third-order solution of wave-current interactions is used to determine the dynamic pressure acting on the Seabed. Verification of the proposed model is performed against the previous experimental data and analytical result. With the proposed numerical model, the effects of wave, current and Seabed characteristics, such as Poisson's ratio, Young's modulus, degree of saturation, and pipeline buried depth on the wave-induced Seabed response will be examined. Then, the wave-current induced Seabed liquefaction is also discussed. The numerical results demonstrate significant effects of anisotropic soil behavior on Seabed liquefaction.
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trenching effects on dynamic behavior of a steel catenary riser
Ocean Engineering, 2010Co-Authors: Ali Nakhaee, Jun ZhangAbstract:Abstract The fatigue life of a steel catenary riser (SCR) near its touch-down zone (TDZ) is substantially affected by its interaction with the Seabed. Therefore, accurate estimate of the fatigue life of a SCR requires the understanding and realistic modeling of this interaction. The interaction depends on several factors, such as soil properties, riser characteristics, and the development of trenching at the Seabed. Existing approaches for modeling the Seabed in interaction with a SCR approximate the behavior of the Seabed soil by linear or nonlinear spring and dashpot, which represent the stiffness and damping of the soil, respectively. However, these approaches do not account for certain phenomena resulting from the plastic deformation of soil, such as trenching development at the Seabed. In this study, a more realistic approach is developed for simulating the interaction between a SCR and the Seabed. In addition to the use of a realistic P–y curve (where P stands for the supporting force of the Seabed and y for the vertical penetration of the riser into the Seabed) to simulate the soil deformation during its interaction with the riser, it considers the development of a trench caused by continuous impact of a riser on the Seabed and then its feedback effect on the variation of the bending moment along the riser. It is found that the trenching development on the Seabed may decrease the maximum variation of bending moment of a riser near its TDZ. Since the variation of bending moment dictates the fatigue damage to the SCR, the results based on this approach indicate that the trenching development at the Seabed may increase the fatigue life of the SCR and hence it may have important application to the design of a SCR.