The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Lizhong Wang - One of the best experts on this subject based on the ideXlab platform.
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Numerical investigations on pore-pressure response of Suction Anchors under cyclic tensile loadings
Engineering Geology, 2017Co-Authors: Kanmin Shen, Lizhong Wang, Zhen Guo, Dong-sheng JengAbstract:The Suction Anchor is an effective option for the Anchor foundations of floating offshore wind turbines (FOWTs). During its long-term service, in addition to the static pretension load, the Suction Anchor is subjected to a series of cyclic loads that are caused by waves, currents and the continuous motions of the floating structure. Thus, excess pore-pressure will accumulate within the soil around the embedded Anchor, and the Anchor capacity tends to be reduced. In this paper, by introducing the oscillatory and residual mechanisms, a novel numerical model is proposed to predict the instantaneous variations and accumulations of excess pore-pressures around a Suction Anchor that is subjected to long-term vertical cyclic loads. The results indicate that excess pore-pressure builds up mainly in the shallow soil near the external Anchor wall. As a consequence, the effective soil stress in this region decreases along with the interface friction between the external wall and the soil. Detailed parametric studies reveal that the accumulation of excess pore-pressure is obvious for a larger load magnitude and smaller load period. With a lower permeability, smaller shear modulus or smaller relative density of the seabed soil, the pore-pressure accumulation outside the Anchor increases significantly.
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three dimensional interaction between Anchor chain and seabed
Applied Ocean Research, 2010Co-Authors: Lizhong Wang, Feng YuanAbstract:Abstract Following the Suction Anchor installation, preloading of the Anchor chain has to be carried out to remove slack. The assessment of a pretension level should take into account not only the additional chain slippage that may occur in service, but also the chain tension at the pad-eye which is transferred from the touchdown point (TDP) at the seabed. In this paper, a novel quasi-static model, which has considered the three-dimensional (3D) characteristics of soil resistance and chain elastic elongation, is presented to provide an accurate prediction of the behavior of an embedded chain. Based on this model, the chain profiles and tension distributions under different pretension levels are first calculated. While experiencing larger environment loads in service, the embedded chain will produce further movement in 3D space, which can be obtained by taking the chain equilibrium after pretensioning as the initial condition. Finally, the influence of pretension loads and angles at the TDP on the behaviors of embedded chain are thoroughly studied, and some useful conclusions are drawn.
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Behavior of Installation for Suction Anchor in Soft Clay
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 1, 2010Co-Authors: Heng-jun Dai, Lizhong WangAbstract:Suction Anchor foundations are being increasingly used for a variety of offshore application. In designing a Suction Anchor geotechnical engineering must consider the installation process as well as the in-place performance. The main objective of the present study was to investigate the penetration behavior of the Suction Anchor in normally consolidated and sensitive clay. Numerical analyses are preformed to study the installation by Suction in soft clay. The effects of the penetration depth, the shear strength ratio along the interface between the Anchor and the clay on the installation process on the failure mechanism and the pattern of soil flow at the Anchor tip during installation are discussed in detail. The shear strength reduction factor is the key factor of the installation procedure, and it has a strong effect on the limited installable aspect ratio. The displacement vectors show that the clay beneath the Anchor tip will move up inside the Anchor when the Anchor moves down while soils beneath the tip as well as soils outside the skirt wall also flow inward at the reverse bearing capacity failure. Finally, some conclusions are made, which can be useful in practice.
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behavior of installation for Suction Anchor in soft clay
ASME 2010 29th International Conference on Ocean Offshore and Arctic Engineering, 2010Co-Authors: Heng-jun Dai, Lizhong WangAbstract:Suction Anchor foundations are being increasingly used for a variety of offshore application. In designing a Suction Anchor geotechnical engineering must consider the installation process as well as the in-place performance. The main objective of the present study was to investigate the penetration behavior of the Suction Anchor in normally consolidated and sensitive clay. Numerical analyses are preformed to study the installation by Suction in soft clay. The effects of the penetration depth, the shear strength ratio along the interface between the Anchor and the clay on the installation process on the failure mechanism and the pattern of soil flow at the Anchor tip during installation are discussed in detail. The shear strength reduction factor is the key factor of the installation procedure, and it has a strong effect on the limited installable aspect ratio. The displacement vectors show that the clay beneath the Anchor tip will move up inside the Anchor when the Anchor moves down while soils beneath the tip as well as soils outside the skirt wall also flow inward at the reverse bearing capacity failure. Finally, some conclusions are made, which can be useful in practice.Copyright © 2010 by ASME
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Quasi-static three-dimensional analysis of Suction Anchor mooring system
Ocean Engineering, 2010Co-Authors: Lizhong Wang, Zhen Guo, Feng YuanAbstract:The Suction Anchor has been widely used in taut or semi-taut mooring systems as an effective and economical solution to Anchoring problems. To ensure high reliability, the profile of the mooring cable connecting the fairlead and the pad-eye must be accurately designed. However, previous studies have rarely considered the effect of cable slippage in soil on the mooring behavior, or embedded cables have been studied with an assumed tension at the seabed. This paper, by treating the cable suspended in water and the cable embedded in soil as a single cable, presents a two-dimensional (2D) static model and a three-dimensional (3D) quasi-static model for the cable during pretensioning and in service, respectively. The two models take into account the comprehensive effects of ocean currents, soil resistance and cable elasticity, all of which are critical for the design of a mooring system. Three examples are analyzed using the models and some useful conclusions are drawn.
Y. Cho - One of the best experts on this subject based on the ideXlab platform.
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Horizontal Capacity of Embedded Suction Anchors in Clay
Journal of Offshore Mechanics and Arctic Engineering, 2010Co-Authors: S. Bang, Y. S. Kim, K. Jones, Y. ChoAbstract:The embedded Suction Anchor (ESA) is a type of permanent offshore foundation that is installed by a Suction pile. The primary factors influencing the horizontal pullout capacity of an ESA include the loading point, the soil type, the embedment depth, and the addition of flanges. The main purpose of this study is to develop an analytical solution that is capable of estimating the horizontal pullout capacity of ESAs with the loading point being anywhere along its length with or without flanges. An analytical solution has been developed to estimate the horizontal pullout capacity of embedded Suction Anchors in clay seafloor. Validation has been made through comparisons with the centrifuge model test results. Results indicate that the horizontal pullout capacity of the embedded Suction Anchor in clay increases, reaches its peak, and then starts to decrease as the point of the load application moves downward. The effect of flanges on the horizontal pullout capacity is also found to be significant. The horizontal pullout capacity is a direct function of the loading point. The horizontal pullout capacity increases as the loading point moves downward and the maximum pullout capacity is obtained when the loading point is approximately at the mid-depth. The increase in horizontal pullout capacity can be significant, i.e., more than twice in magnitude when the maximum pullout capacity is compared with that associated with the loading point near the top or tip.
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Embedded Suction Anchors for Mooring of a Floating Breakwater
Journal of Offshore Mechanics and Arctic Engineering, 2010Co-Authors: D. J. Kwag, S. Bang, I. H. Cho, Y. ChoAbstract:A floating breakwater was built in Southern Korea. Four separate floating breakwater units were moored to ten deeply buried embedded Suction Anchors. The embedded Suction Anchor is a type of permanent offshore foundation installed by a Suction pile. The cross section of the embedded Suction Anchor is circular, with its diameter being equal to that of the Suction pile that is used to drive it into the seafloor. Vertical flanges are typically added along the circumference to increase its resistance. Determination of the loading capacity and the dimensions of embedded Suction Anchors are described. Details of the construction and installation of embedded Suction Anchors, as well as the field proof test results are also discussed. A total of ten steel embedded Suction Anchors were manufactured and installed successfully. Installation of embedded Suction Anchors was accomplished with a Suction pile attached to its top. Subsequent proof tests validated the design loading capacity of embedded Suction Anchors. A floating breakwater consisted of four separate units was constructed. Initially, embedded deadweight concrete blocks were considered to moor the floating breakwater units. Later, however, embedded Suction Anchors replaced the concrete block Anchors due to numerous environmental constraints. Each fioating unit was Anchored with four embedded Suction Anchors. Field proof tests indicate that the embedded Suction Anchors can provide necessary resistance against the anticipated wind and wave forces.
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Inclined Loading Capacity of Embedded Suction Anchors in Clay
Volume 7: Offshore Geotechnics; Petroleum Technology, 2009Co-Authors: Y. S. Kim, Y. Cho, K. O. Kim, S. Bang, K. JonesAbstract:An analytical solution has been developed to estimate the inclined pullout capacity of an embedded Suction Anchor in clay seafloor. Validation has been made through comparisons with a limited number of centrifuge model test results. Results indicate that the inclined pullout capacity of an embedded Suction Anchor in clay decreases as the load inclination angle to the horizontal increases. As the point of the load application moves downward, the inclined pullout capacity increases, reaches its peak, and then starts to decrease.Copyright © 2009 by ASME
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Embedded Suction Anchors for Mooring of a Floating Breakwater
Volume 4: Ocean Engineering; Offshore Renewable Energy, 2008Co-Authors: D. J. Kwag, S. Bang, I. H. Cho, Y. ChoAbstract:A floating breakwater is currently being built in southern Korea. Four separate floating breakwater units will be moored to ten deeply embedded Suction Anchors. The embedded Suction Anchor is permanent offshore foundation installed by a Suction pile. The cross-section of the embedded Suction Anchor is circular with its diameter being the same as that of the Suction pile that is used to drive it into the seafloor. Vertical flanges are added along the circumference to increase its resistance. The design, construction, installation, and proof testing of embedded Suction Anchors are briefly described.Copyright © 2008 by ASME
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Horizontal Capacity of Embedded Suction Anchors in Clay
Volume 4: Materials Technology; Ocean Engineering, 2007Co-Authors: S. Bang, Y. S. Kim, K. Jones, Y. ChoAbstract:An analytical solution has been developed to estimate the horizontal pullout capacity of embedded Suction Anchors in clay seafloor. Validation has been made through comparisons with the centrifuge model test results. The results indicate that the horizontal pullout capacity of the embedded Suction Anchor in clay increases, reaches its peak and then starts to decrease as the point of the load application moves downward. The effect of flanges on the horizontal pullout capacity is also found to be significant.
Songyu Liu - One of the best experts on this subject based on the ideXlab platform.
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dynamic analysis of umbrella Suction Anchor foundation embedded in seabed for offshore wind turbines
Geomechanics for Energy and the Environment, 2017Co-Authors: Hongjun Liu, Songyu LiuAbstract:Abstract Umbrella Suction Anchor foundation, a novel Suction foundation that applied to offshore wind turbines has been proved to be a much promising potential foundation than most of the existing foundations including Gravity base, Monopile, Tripod, Jacket and so on. The dynamic analysis of the offshore foundation is more complex, comparing with the one on the land. The work presented in this paper is to conduct a comprehensive analysis on the dynamic characteristics of the umbrella Suction Anchor foundation and determine its potential damage. The general finite element program ANSYS is used in the analysis. The different model vibration modes and vibration regularities of the master cylinder, the tube skirt and the Anchor branches of the structure were all obtained. The structural harmonic response under loads of 0 ∼ 130 Hz was simulated and discussed. Additionally, the original structure vibration response to wave loads was analyzed based on power spectrum density (PSD) method. Both transient dynamic response process and damageable parts were thoroughly studied, after two types of random loads (seismic and ice load) were applied on the structure. Through the research, the basic dynamic responses of umbrella Suction Anchor foundation to different external loads have been made clear. The results of the research will play an active and instructive role in the development of umbrella Suction Anchor foundation for offshore wind turbines.
Hongjun Liu - One of the best experts on this subject based on the ideXlab platform.
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Scour characteristics of an offshore umbrella Suction Anchor foundation under the combined actions of waves and currents
Ocean Engineering, 2020Co-Authors: Qi Yang, Hongjun Liu, Yifan Liu, Peng Zhang, Quandi WangAbstract:Abstract An umbrella Suction Anchor foundation (USAF) is a novel foundation for offshore wind turbines. Compared to the local scour occurring around deep foundations such as monopiles, the scour around an USAF can significantly influence the stability of wind turbine systems. Therefore, research on the local scour around an USAF induced by waves and currents is of great value to coastal engineering projects. In this study, a series of scour tests of an USAF were carried out and the authors evaluated the influences of a steady current, waves, and the combination of waves and currents. The flow field and wave field were captured by an acoustic Doppler velocimeter (ADV) current meter and wave gauge, respectively. Moreover, the equilibrium depth, scope, and shape of the scour holes are determined using an ultrasonic topographic surveying meter. The results demonstrate that the scour profiles are definitely distinctive for the three environmental conditions. A standard k-ω turbulent model is used to simulate the turbulent flow field. The volume of fluid (VOF) method is used in computational fluid dynamic (CFD) software to deal with the free water surface and moving mesh to explore the changes in the topography over time. A dynamic three-dimensional numerical model of the local scour around the USAF is developed and validated by comparing the results with previous scour tests and other published experimental data. The scour characteristics of the USAF and the Suction Anchor foundation (SAF) are determined by solving the fully three-dimensional transient Navier-Stokes equations in a fixed Eulerian grid. The results indicate that compared with a conventional SAF, the USAF can significantly prevent scour; moreover, the scour depth is significantly different for the two foundations under the combined wave-current action and is approximately twice as large for the SAF than the USAF.
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Numerical investigation of local scour around USAF with different hydraulic conditions under currents and waves
Ocean Engineering, 2020Co-Authors: Hu Ruigeng, Jinmu Yang, Hongjun LiuAbstract:Abstract An umbrella Suction Anchor foundation (USAF) is a new foundation type used for offshore wind turbines. In this paper, a three-dimensional numerical model was established in FLOW-3D to study the local scour characteristics under the coupled effects of waves and currents. RANS equations, closed with an RNG k-e turbulence model, were established for simulating the flow field around pile groups. The simulation results were compared with a 1:40 model test and showed good agreement. Then, the effects of different hydraulic conditions and dimensionless parameters such as water depth, wave height, velocity, Keulegan-Carpenter number (KC) and the ratio of relative wave-current velocity (Ucw) on the maximum scour depth were considered in detail, and compared with the results of other scholars. This study found that the local scour shape of a USAF is different from that of a monopile foundation. Its maximum scour depth appears downstream behind the USAF, and the Anchoring structure effectively blocks the scour in front of the USAF. The shallower water depth, the higher wave height and the faster flow velocity result in a more intense scour. When KC
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Bearing capacity of offshore umbrella Suction Anchor foundation in silty soil under varying loading modes
Marine Georesources & Geotechnology, 2018Co-Authors: Qi Yang, Hongjun Liu, Guanglai Pan, Quandi WangAbstract:ABSTRACTConsidering the current disadvantages of present offshore wind turbine foundations, a novel Anchor foundation with skirt and branches is proposed, called offshore umbrella Suction Anchor fo...
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dynamic analysis of umbrella Suction Anchor foundation embedded in seabed for offshore wind turbines
Geomechanics for Energy and the Environment, 2017Co-Authors: Hongjun Liu, Songyu LiuAbstract:Abstract Umbrella Suction Anchor foundation, a novel Suction foundation that applied to offshore wind turbines has been proved to be a much promising potential foundation than most of the existing foundations including Gravity base, Monopile, Tripod, Jacket and so on. The dynamic analysis of the offshore foundation is more complex, comparing with the one on the land. The work presented in this paper is to conduct a comprehensive analysis on the dynamic characteristics of the umbrella Suction Anchor foundation and determine its potential damage. The general finite element program ANSYS is used in the analysis. The different model vibration modes and vibration regularities of the master cylinder, the tube skirt and the Anchor branches of the structure were all obtained. The structural harmonic response under loads of 0 ∼ 130 Hz was simulated and discussed. Additionally, the original structure vibration response to wave loads was analyzed based on power spectrum density (PSD) method. Both transient dynamic response process and damageable parts were thoroughly studied, after two types of random loads (seismic and ice load) were applied on the structure. Through the research, the basic dynamic responses of umbrella Suction Anchor foundation to different external loads have been made clear. The results of the research will play an active and instructive role in the development of umbrella Suction Anchor foundation for offshore wind turbines.
Heng-jun Dai - One of the best experts on this subject based on the ideXlab platform.
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Behavior of Installation for Suction Anchor in Soft Clay
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 1, 2010Co-Authors: Heng-jun Dai, Lizhong WangAbstract:Suction Anchor foundations are being increasingly used for a variety of offshore application. In designing a Suction Anchor geotechnical engineering must consider the installation process as well as the in-place performance. The main objective of the present study was to investigate the penetration behavior of the Suction Anchor in normally consolidated and sensitive clay. Numerical analyses are preformed to study the installation by Suction in soft clay. The effects of the penetration depth, the shear strength ratio along the interface between the Anchor and the clay on the installation process on the failure mechanism and the pattern of soil flow at the Anchor tip during installation are discussed in detail. The shear strength reduction factor is the key factor of the installation procedure, and it has a strong effect on the limited installable aspect ratio. The displacement vectors show that the clay beneath the Anchor tip will move up inside the Anchor when the Anchor moves down while soils beneath the tip as well as soils outside the skirt wall also flow inward at the reverse bearing capacity failure. Finally, some conclusions are made, which can be useful in practice.
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behavior of installation for Suction Anchor in soft clay
ASME 2010 29th International Conference on Ocean Offshore and Arctic Engineering, 2010Co-Authors: Heng-jun Dai, Lizhong WangAbstract:Suction Anchor foundations are being increasingly used for a variety of offshore application. In designing a Suction Anchor geotechnical engineering must consider the installation process as well as the in-place performance. The main objective of the present study was to investigate the penetration behavior of the Suction Anchor in normally consolidated and sensitive clay. Numerical analyses are preformed to study the installation by Suction in soft clay. The effects of the penetration depth, the shear strength ratio along the interface between the Anchor and the clay on the installation process on the failure mechanism and the pattern of soil flow at the Anchor tip during installation are discussed in detail. The shear strength reduction factor is the key factor of the installation procedure, and it has a strong effect on the limited installable aspect ratio. The displacement vectors show that the clay beneath the Anchor tip will move up inside the Anchor when the Anchor moves down while soils beneath the tip as well as soils outside the skirt wall also flow inward at the reverse bearing capacity failure. Finally, some conclusions are made, which can be useful in practice.Copyright © 2010 by ASME
