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Kunpeng Wang - One of the best experts on this subject based on the ideXlab platform.

  • study of Seabed trench induced by steel catenary riser and Seabed interaction
    ASME 2016 35th International Conference on Ocean Offshore and Arctic Engineering, 2016
    Co-Authors: Kunpeng Wang
    Abstract:

    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

Dong-sheng Jeng - One of the best experts on this subject based on the ideXlab platform.

  • meshfree Model for wave Seabed interactions around offshore pipelines
    Journal of Marine Science and Engineering, 2019
    Co-Authors: Xiao Xiao Wang, Dong-sheng Jeng, Chiacheng Tsai
    Abstract:

    The evaluation of the wave-induced Seabed instability around a submarine pipeline is particularly important for coastal engineers involved in the design of pipelines protection. Unlike previous studies, a meshfree Model is developed to investigate the wave-induced soil response in the vicinity of a submarine pipeline. In the present Model, Reynolds-Averaged Navier-Stokes (RANS) equations are employed to simulate the wave loading, while Biot’s consolidation equations are adopted to investigate the wave-induced soil response. Momentary liquefaction around an offshore pipeline in a trench is examined. Validation of the present Seabed Model was conducted by comparing with the analytical solution, experimental data, and numerical Models available in the literature, which demonstrates the capacity of the present Model. Based on the newly proposed Model, a parametric study is carried out to investigate the influence of soil properties and wave characteristics for the soil response around the pipeline. The numerical results conclude that the liquefaction depth at the bottom of the pipeline increases with increasing water period (T) and wave height (H), but decreases as backfilled depth ( H b ), degree of saturation ( S r ) and soil permeability (K) increase.

  • Numerical testing on wave-induced Seabed liquefaction with a poro-elastoplastic Model
    Soil Dynamics and Earthquake Engineering, 2018
    Co-Authors: Jian Leng, Dong-sheng Jeng
    Abstract:

    Abstract Dynamic Seabed response under wave loading is one of key factors for the design and construction of offshore structures. Most previous studies were based on poroelastic Seabed Model. In this paper, based on a unified elasto-plastic constitutive Model that can describe the liquefaction of sand and two-phase u-p theory for saturated soils, numerical tests are conducted to analyze the dynamic responses of a sandy Seabed subjected to cyclic wave loads. The development of liquefaction zone, the change of excess pore water pressure (EPWP), the effective stress path, and the displacement vector are investigated. Numerical tests show that the proposed method is able to capture the mechanical behaviors of wave induced liquefaction of a sandy Seabed. The calculated effective stress path and change of EPWP are similar to those of earthquake-induced liquefaction. In other words, the mechanism of wave-induced and earthquake-induced liquefaction are similar, despite of the loading forms. The liquefaction depth increases with the number of wave cycles. Meanwhile, a phase lag is observed between the liquefied Seabed and wave motion. A comparison between the dynamic response of elastic and elasto-plastic Seabed is presented to underline the importance of considering the plastic deformation of Seabed.

  • effects of cross anisotropic soil behaviour on the wave induced residual liquefaction in the vicinity of pipeline buried in elasto plastic Seabed foundations
    Soil Dynamics and Earthquake Engineering, 2016
    Co-Authors: Dong-sheng Jeng, Hongyi Zhao, C C Liao
    Abstract:

    In this paper, a two-dimensional integrated numerical Model is developed to examine the influences of cross-anisotropic soil behaviour on the wave-induced residual liquefaction in the vicinity of a pipeline buried in a porous Seabed. In the wave Model, the RANS (Reynolds Averaged Navier–Stokes) equation is used to govern the wave motion. In the Seabed Model, the residual soil response in the vicinity of an embedded pipeline is considered with the 2-D elasto-plastic solution, where the phase-resolved shear stress is used as a source for the build-up of residual pore pressure. Classical Biot׳s consolidation equation is used for linking the solid-pore fluid interaction. The validation of the proposed integrated numerical Model is conducted by the comparisons with the previous experimental data. Numerical examples show that the pore pressures can accumulate to a large value, thus resulting in a larger area of liquefaction potential in the given anisotropic soil compared to that with isotropic solution. The influences of anisotropic parameters on the wave-induced residual soil response in the vicinity of pipeline are significant. A high rate of pore pressure accumulation and dissipation is observed and the liquefaction potential develops faster as the anisotropic parameters increase. Finally, a simplified approximation based on a detailed parametric investigations is proposed for the evaluation of maximum liquefaction depth (zL) in engineering application.

  • 2D Model for Wave-induced Pore Pressure Accumulation Around a Rubble Mound Breakwater over Sloping Seabed
    2014
    Co-Authors: Hongyi Zhao, Dong-sheng Jeng
    Abstract:

    The evaluation of wave-induced excess pore pressure in the vicinity of marine structures is one of the key factors for coastal engineers involved in the design of foundation for the structures. Unlike previous Models, the effect of outer shape of sloping Seabed and breakwater on the wave field is considered in this study, as well as the preconsolidation due to the effect of weight of breakwater on the stress field in Seabed foundation. The phase-resolved absolute shear stress is considered as the source of pore pressure generation in the porous Seabed Model. Based on numerical results, we concluded that, the liquefaction zone develops first in front of and at the toe of the rubblemound breakwater and then extends laterally and vertically to neighbouring zones. Under certain conditions, this two liquefied zone will be eventually linked together.

  • Wave and current induced Seabed response around a submarine pipeline in an anisotropic Seabed
    Ocean Engineering, 2014
    Co-Authors: Xiang-lian Zhou, Jun Zhang, Jian-hua Wang, Dong-sheng Jeng
    Abstract:

    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.

Hodjat Shiri - One of the best experts on this subject based on the ideXlab platform.

  • influence of Seabed trench formation on fatigue performance of steel catenary risers in touchdown zone
    Marine Structures, 2014
    Co-Authors: Hodjat Shiri
    Abstract:

    Abstract The subsea survey results using remote operating vehicles (ROV) show that trenches with a depth of several riser diameters can be developed underneath the steel catenary risers (SCR). Therefore, an important question in respect of the riser–Seabed interaction is, how the trench formation beneath the riser affects the riser fatigue performance in the touchdown zone. A common methodology reported in literature to study the impact of trench formation on riser fatigue life is the insertion of an artificial mathematical expression of the riser profile into the Seabed. This study shows that such methodology can be inconsistent and leading to contradictory results. The current paper has employed ABAQUS finite element software and coded a non-linear soil hysteretic Model to automatically simulate the variable Seabed stiffness and the gradual trench development through the touchdown zone. In this method, the Seabed Model parameters are initially adjusted to extreme values allowing trench with desired depth to be developed over a moderate number of displacement cycles of the SCR. The design wave scatter diagram is then applied, simulating a generic Spar system, after switching the Model parameters to values with normal range. The paper presents the impact of trenches of different depths on the fatigue performance of SCRs in the touchdown zone.

Hongyi Zhao - One of the best experts on this subject based on the ideXlab platform.

  • effects of cross anisotropic soil behaviour on the wave induced residual liquefaction in the vicinity of pipeline buried in elasto plastic Seabed foundations
    Soil Dynamics and Earthquake Engineering, 2016
    Co-Authors: Dong-sheng Jeng, Hongyi Zhao, C C Liao
    Abstract:

    In this paper, a two-dimensional integrated numerical Model is developed to examine the influences of cross-anisotropic soil behaviour on the wave-induced residual liquefaction in the vicinity of a pipeline buried in a porous Seabed. In the wave Model, the RANS (Reynolds Averaged Navier–Stokes) equation is used to govern the wave motion. In the Seabed Model, the residual soil response in the vicinity of an embedded pipeline is considered with the 2-D elasto-plastic solution, where the phase-resolved shear stress is used as a source for the build-up of residual pore pressure. Classical Biot׳s consolidation equation is used for linking the solid-pore fluid interaction. The validation of the proposed integrated numerical Model is conducted by the comparisons with the previous experimental data. Numerical examples show that the pore pressures can accumulate to a large value, thus resulting in a larger area of liquefaction potential in the given anisotropic soil compared to that with isotropic solution. The influences of anisotropic parameters on the wave-induced residual soil response in the vicinity of pipeline are significant. A high rate of pore pressure accumulation and dissipation is observed and the liquefaction potential develops faster as the anisotropic parameters increase. Finally, a simplified approximation based on a detailed parametric investigations is proposed for the evaluation of maximum liquefaction depth (zL) in engineering application.

  • 2D Model for Wave-induced Pore Pressure Accumulation Around a Rubble Mound Breakwater over Sloping Seabed
    2014
    Co-Authors: Hongyi Zhao, Dong-sheng Jeng
    Abstract:

    The evaluation of wave-induced excess pore pressure in the vicinity of marine structures is one of the key factors for coastal engineers involved in the design of foundation for the structures. Unlike previous Models, the effect of outer shape of sloping Seabed and breakwater on the wave field is considered in this study, as well as the preconsolidation due to the effect of weight of breakwater on the stress field in Seabed foundation. The phase-resolved absolute shear stress is considered as the source of pore pressure generation in the porous Seabed Model. Based on numerical results, we concluded that, the liquefaction zone develops first in front of and at the toe of the rubblemound breakwater and then extends laterally and vertically to neighbouring zones. Under certain conditions, this two liquefied zone will be eventually linked together.

  • 3D numerical Model for wave-induced Seabed response around breakwater heads
    Geomechanics and Engineering, 2013
    Co-Authors: Hongyi Zhao, Dong-sheng Jeng, J.-s. Zhang, Y. Zhang, H.j. Zhang, Chi Zhang
    Abstract:

    This paper presents a three-dimensional (3D) integrated numerical Model where the wave-induced pore pressures in a porous Seabed around breakwater heads were investigated. Unlike previous research, the Navier-Stokes equation is solved with internal wave generation for the flow Model, while Biot's dynamic Seabed behaviour is considered in the Seabed Model. With the present Model, a parametric study was conducted to examine the effects of wave and soil characteristics and breakwater configuration on the wave-induced pore pressure around breakwater heads. Based on numerical examples, it was found that the wave-induced pore pressures at breakwater heads are greater than that beneath a breakwater. The wave-induced Seabed response around breakwater heads become more important with: (i) a longer wave period; (ii) a Seabed with higher permeability and degree of saturation; and (iii) larger angle between the incident waves and breakwater. Furthermore, the relative difference of wave-induced pore pressure between fully-dynamic and quasi-static solutions are larger at breakwater heads than that beneath a breakwater.

Abdolrahim Taheri - One of the best experts on this subject based on the ideXlab platform.

  • An Influence of Trench Formation on Steel Catenary Risers Based on a Hysteretic Nonlinear Seabed Model
    Iranian Journal of Oil and Gas Science and Technology, 2017
    Co-Authors: Reza Siahtiri, Abdolrahim Taheri
    Abstract:

    A steel catenary riser (SCR) attached to a floating platform at its upper end encounters fluctuations in and near its touchdown zone (TDZ), which causes the interaction with the Seabed. Subsea surveys and the analysis of SCR’s indicated that the greatest stress and highest damage occurred near the touchdown point (TDP), where the SCR first touches the Seabed. Nowadays, the linear Seabed spring is carried out, and it is assumed as a flat Seabed. Improved nonlinear hysteretic Seabed Models have recently been proposed, which simulate the different stiffness in the Seabed response in the TDZ. In this study, an advanced hysteretic nonlinear SCR-Seabed soil interaction Model has been implemented to simulate the exact behavior of the riser in the vicinity of the touchdown zone. This paper focusses on the Seabed trench, which develops progressively under the SCR due to repeated contact. Also, different important parameters such as water depth and material of riser have been investigated based on the Caspian Sea environmental conditions. This paper highlights the impact of trenches of different depths on the fatigue performance of riser at TDZ.