Torpedo anchors have been used in mooring systems for deep-water oil and gas projects owing to their prominent advantages, such as low cost and easy installation. The maximum force of torpedo anchors is crucial not on...Torpedo anchors have been used in mooring systems for deep-water oil and gas projects owing to their prominent advantages, such as low cost and easy installation. The maximum force of torpedo anchors is crucial not only to the safety and stability of vessels and other marine facilities, but also for an economical design. It is necessary to develop reliable formula for fast predicting their maximum inclined force of a torpedo anchor in cohesive beds. In this study, the maximum inclined force of a torpedo anchor vertically embedded in cohesive beds was extensively investigated. 316 sets of inclined pullout laboratory tests were carried out for 9 differently shaped torpedo anchors which were vertically embedded in different cohesive beds. The loading curves were automatically acquisitioned and their characteristics were analyzed. The load angle relative to the horizontal varied from 20° to 90°. A new formula for fast calculating the maximum inclined force of the torpedo anchor vertically embedded in cohesive beds was obtained based on force analysis and a nonlinear regression on the data from the present and other studies. Effect aspects on the tests are discussed and further studies are highlighted.展开更多
The penetration depth of torpedo anchor in two-layered soil bed was experimentally investigated. A total of 177 experimental data were obtained in laboratory by varying the undrained shear strength of the two-layered ...The penetration depth of torpedo anchor in two-layered soil bed was experimentally investigated. A total of 177 experimental data were obtained in laboratory by varying the undrained shear strength of the two-layered soil and the thickness of the top soil layer. The geometric parameters of the anchor and the soil properties(the liquid limit, plastic limit, specific gravity, undrained shear strength, density, and water content) were measured. Based on the energy analysis and present test data, an empirical formula to predict the penetration depth of torpedo anchor in two-layered soil bed was proposed. The proposed formula was extensively validated by laboratory and field data of previous researchers. The results were in good agreement with those obtained for two-layered and single-layered soil bed.Finally, a sensitivity analysis on the parameters in the formula was performed.展开更多
Offshore structures are subject to environmental loads such as waves,currents,or wind,which may induce cyclic lateral vibration at the foundations.These cyclic vibration loadings may affect the rheological property of...Offshore structures are subject to environmental loads such as waves,currents,or wind,which may induce cyclic lateral vibration at the foundations.These cyclic vibration loadings may affect the rheological property of the sediments adjacent to the foundation and the stability of the structures.This is especially true when the structures are founded on cohesive sedimentary bed.In this study,the viscosity of soft cohesive sediments adjacent to a vibrating pillar was considered,and as a primary index of the rheological characteristics of the sediments.The investigation was performed using the sinking ball method.The experimental findings indicated that the viscosity of cohesive sediments decrease with increase of the liquidity index and vibration intensity.A simple semi-empirical formula was proposed.The structures of the cohesive sediments were destroyed due to the mechanical vibration,and the sediments were fluidized during vibration loads.The shear strength of the cohesive sediments decreased with increased vibration intensity,not only because of the increased pore water pressure but also the decreased viscosity of cohesive sediments following sediment fluidization.展开更多
Analyzing the rheological properties of silty beds subjected to continuous oscillatory shear loading is crucial for understanding the morphological deformation of the seabed and ensuring safety in geological and marin...Analyzing the rheological properties of silty beds subjected to continuous oscillatory shear loading is crucial for understanding the morphological deformation of the seabed and ensuring safety in geological and marine engineering applications.In this study,the effects of oscillatory shearing properties on the yield stress(S_(u))of silty sediments were quantitatively investigated.The effects of oscillatory shear strength(0-3),water content(26.6%-70.84%),and particle diameter(8.79-50μm)were examined extensively through a series of laboratory tests.The results indicated that the three aforementioned parameters were the major factors that affected the rheological characteristics of silty sediments.Furthermore,their effects could be elucidated using the yield stress of cohesive sediments as the indicator parameter.The ratio of yield stress(S_(u)/S_(u0))varied as the oscillatory shear strength increased up to a critical value,Λ_(cr).S_(u)bsequently,the ratio remained at a constant value.It was deduced that the yield stress decreased with increasing oscillatory shear strength forΛ<Λ_(cr),when the sediments were in a non-equilibrium fluidization stage.WhenΛ>Λ_(cr),the sediments entered an equilibrium fluidization stage,and the yield stress remained almost constant,irrespective of the oscillatory shear strength.Furthermore,during the equilibrium fluidization stage,it was observed that the ratio S_(u)/S_(u0)did not vary with water content but decreased as the particle diameter increased.Finally,based on regression analysis of the experimental data for non-equilibrium and equilibrium fluidization stages,a correlation between yield stress of silty sediments and continuous oscillatory shearing properties was proposed.This correlation can aid in understanding the changes in solid resistance and assessing safety in piling engineering.Furthermore,it can provide a theoretical guidance for reducing soil resistance in marine structures using mechanical vibrations.展开更多
Local scour threatens the safety of marine structures,necessitating the precise prediction of scour evo-lution around these structures.A visually oriented deep learning model,called Disentangled Physics-constrained Pr...Local scour threatens the safety of marine structures,necessitating the precise prediction of scour evo-lution around these structures.A visually oriented deep learning model,called Disentangled Physics-constrained Prediction(DPP),was proposed in this study to predict scour evolution at monopiles reliably.It integrates scouring physics with advanced video prediction techniques through a two-branch architec-ture.The Physics-constrained Recurrent Module(PRModule)branch leverages Recurrent Neural Networks(RNNs)for temporal differentiation,ensuring accurate prediction of scouring-related physical information.Meanwhile,the Convolutional Long-Short-Term Memory(ConvLSTM)branch captures spatial and tempo-ral dynamics in scouring videos,focusing on the prediction of residual features.DPP outperformed three baseline models in predicting the scour evolution at monopiles.Across three scouring scenarios,DPP achieved a 14.2%decrease in Root Mean Squared Error,a 14.7%reduction in Mean Absolute Error,and an 8.1%increase in Structural Similarity on average,compared to the best-performing baseline model.The predicted scouring frames are found to agree well with the true frames,demonstrating DPP’s potential as a valuable tool to protect marine infrastructures.展开更多
Local scour at a pile or pier in current or wave environments threats the safety of the upper structure all over the world.The application of a net-like matt as a scour protection cover at the pile or pier was propose...Local scour at a pile or pier in current or wave environments threats the safety of the upper structure all over the world.The application of a net-like matt as a scour protection cover at the pile or pier was proposed.The matt weakens and diffuses the flow in the local scour pit and thus reduces local scour while enhances sediment deposition.Numerical simulations were carried out to investigate the flow at the pile covered by the matt.The simulation results were used to optimize the thickness dt(2.6 d_(95)∼17.9 d_(95))and opening size dn(7.7 d_(95)∼28.2 d_(95))of the matt.It was found that the matt significantly reduced the local velocity and dissipated the vortex at the pile,substantially reduced the extent of local scour.The smaller the opening size of the matt,the more effective was the flow diffusion at the bed,and smaller bed shear stress was observed at the pile.For the flow conditions considered in this study,a matt with a relative thickness of T=7.7 and relative opening size of S=7.7 could be effective in scour protection.展开更多
This paper presents our numerical study of the scale effects on a tip-rake propeller,the PPTC-II,based on the RANS simulations using software FLUENT 6.3.The low Re option in SST k-ωmodel is adopted at model scale,tog...This paper presents our numerical study of the scale effects on a tip-rake propeller,the PPTC-II,based on the RANS simulations using software FLUENT 6.3.The low Re option in SST k-ωmodel is adopted at model scale,together with fine prism grids to resolve the viscous sub-layer.At full scale,standard wall function is adopted.The scale-effect corrections yielded by our RANS simulations are compared with those obtained from the ITTC method.To explain the CFD results,an analysis of sectional forces is performed.To investigate how the tip rake influences propeller scale effects,the geometry of PPTC-II is modified by removing the tip rake only,and the RANS-predicted scale effects for the modified propeller,PPTC-II-m,are compared with those for the PPTC-II.The study indicates that the scale effect on propeller thrust can be as important as that on the torque;somehow the RANS-and ITTC-based predictions for full-scale efficiency agree quite well;the tip-rake reduces tip loading and tip vortex strength,and brings about large differences in the scale effects as compared with the propeller without tip-rake.展开更多
基金financially supported by the Ministry of Education of China(Grant No.6141A02022337)
文摘Torpedo anchors have been used in mooring systems for deep-water oil and gas projects owing to their prominent advantages, such as low cost and easy installation. The maximum force of torpedo anchors is crucial not only to the safety and stability of vessels and other marine facilities, but also for an economical design. It is necessary to develop reliable formula for fast predicting their maximum inclined force of a torpedo anchor in cohesive beds. In this study, the maximum inclined force of a torpedo anchor vertically embedded in cohesive beds was extensively investigated. 316 sets of inclined pullout laboratory tests were carried out for 9 differently shaped torpedo anchors which were vertically embedded in different cohesive beds. The loading curves were automatically acquisitioned and their characteristics were analyzed. The load angle relative to the horizontal varied from 20° to 90°. A new formula for fast calculating the maximum inclined force of the torpedo anchor vertically embedded in cohesive beds was obtained based on force analysis and a nonlinear regression on the data from the present and other studies. Effect aspects on the tests are discussed and further studies are highlighted.
基金financially supported by the Ministry of Education of China(Grant No.6141A02022337)
文摘The penetration depth of torpedo anchor in two-layered soil bed was experimentally investigated. A total of 177 experimental data were obtained in laboratory by varying the undrained shear strength of the two-layered soil and the thickness of the top soil layer. The geometric parameters of the anchor and the soil properties(the liquid limit, plastic limit, specific gravity, undrained shear strength, density, and water content) were measured. Based on the energy analysis and present test data, an empirical formula to predict the penetration depth of torpedo anchor in two-layered soil bed was proposed. The proposed formula was extensively validated by laboratory and field data of previous researchers. The results were in good agreement with those obtained for two-layered and single-layered soil bed.Finally, a sensitivity analysis on the parameters in the formula was performed.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.52001206).
文摘Offshore structures are subject to environmental loads such as waves,currents,or wind,which may induce cyclic lateral vibration at the foundations.These cyclic vibration loadings may affect the rheological property of the sediments adjacent to the foundation and the stability of the structures.This is especially true when the structures are founded on cohesive sedimentary bed.In this study,the viscosity of soft cohesive sediments adjacent to a vibrating pillar was considered,and as a primary index of the rheological characteristics of the sediments.The investigation was performed using the sinking ball method.The experimental findings indicated that the viscosity of cohesive sediments decrease with increase of the liquidity index and vibration intensity.A simple semi-empirical formula was proposed.The structures of the cohesive sediments were destroyed due to the mechanical vibration,and the sediments were fluidized during vibration loads.The shear strength of the cohesive sediments decreased with increased vibration intensity,not only because of the increased pore water pressure but also the decreased viscosity of cohesive sediments following sediment fluidization.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.51779137).
文摘Analyzing the rheological properties of silty beds subjected to continuous oscillatory shear loading is crucial for understanding the morphological deformation of the seabed and ensuring safety in geological and marine engineering applications.In this study,the effects of oscillatory shearing properties on the yield stress(S_(u))of silty sediments were quantitatively investigated.The effects of oscillatory shear strength(0-3),water content(26.6%-70.84%),and particle diameter(8.79-50μm)were examined extensively through a series of laboratory tests.The results indicated that the three aforementioned parameters were the major factors that affected the rheological characteristics of silty sediments.Furthermore,their effects could be elucidated using the yield stress of cohesive sediments as the indicator parameter.The ratio of yield stress(S_(u)/S_(u0))varied as the oscillatory shear strength increased up to a critical value,Λ_(cr).S_(u)bsequently,the ratio remained at a constant value.It was deduced that the yield stress decreased with increasing oscillatory shear strength forΛ<Λ_(cr),when the sediments were in a non-equilibrium fluidization stage.WhenΛ>Λ_(cr),the sediments entered an equilibrium fluidization stage,and the yield stress remained almost constant,irrespective of the oscillatory shear strength.Furthermore,during the equilibrium fluidization stage,it was observed that the ratio S_(u)/S_(u0)did not vary with water content but decreased as the particle diameter increased.Finally,based on regression analysis of the experimental data for non-equilibrium and equilibrium fluidization stages,a correlation between yield stress of silty sediments and continuous oscillatory shearing properties was proposed.This correlation can aid in understanding the changes in solid resistance and assessing safety in piling engineering.Furthermore,it can provide a theoretical guidance for reducing soil resistance in marine structures using mechanical vibrations.
基金supported by the National Natural Science Foundation of China(Grant No.52171268)Power China Zhongnan Engineering Corporation Limited(Grant No.100-2-01-2023-2483).
文摘Local scour threatens the safety of marine structures,necessitating the precise prediction of scour evo-lution around these structures.A visually oriented deep learning model,called Disentangled Physics-constrained Prediction(DPP),was proposed in this study to predict scour evolution at monopiles reliably.It integrates scouring physics with advanced video prediction techniques through a two-branch architec-ture.The Physics-constrained Recurrent Module(PRModule)branch leverages Recurrent Neural Networks(RNNs)for temporal differentiation,ensuring accurate prediction of scouring-related physical information.Meanwhile,the Convolutional Long-Short-Term Memory(ConvLSTM)branch captures spatial and tempo-ral dynamics in scouring videos,focusing on the prediction of residual features.DPP outperformed three baseline models in predicting the scour evolution at monopiles.Across three scouring scenarios,DPP achieved a 14.2%decrease in Root Mean Squared Error,a 14.7%reduction in Mean Absolute Error,and an 8.1%increase in Structural Similarity on average,compared to the best-performing baseline model.The predicted scouring frames are found to agree well with the true frames,demonstrating DPP’s potential as a valuable tool to protect marine infrastructures.
基金supported by National Natural Science Foundation of China(No.52171268)CCCC Road&Bridge Special Engineering Co.,Ltd.
文摘Local scour at a pile or pier in current or wave environments threats the safety of the upper structure all over the world.The application of a net-like matt as a scour protection cover at the pile or pier was proposed.The matt weakens and diffuses the flow in the local scour pit and thus reduces local scour while enhances sediment deposition.Numerical simulations were carried out to investigate the flow at the pile covered by the matt.The simulation results were used to optimize the thickness dt(2.6 d_(95)∼17.9 d_(95))and opening size dn(7.7 d_(95)∼28.2 d_(95))of the matt.It was found that the matt significantly reduced the local velocity and dissipated the vortex at the pile,substantially reduced the extent of local scour.The smaller the opening size of the matt,the more effective was the flow diffusion at the bed,and smaller bed shear stress was observed at the pile.For the flow conditions considered in this study,a matt with a relative thickness of T=7.7 and relative opening size of S=7.7 could be effective in scour protection.
文摘This paper presents our numerical study of the scale effects on a tip-rake propeller,the PPTC-II,based on the RANS simulations using software FLUENT 6.3.The low Re option in SST k-ωmodel is adopted at model scale,together with fine prism grids to resolve the viscous sub-layer.At full scale,standard wall function is adopted.The scale-effect corrections yielded by our RANS simulations are compared with those obtained from the ITTC method.To explain the CFD results,an analysis of sectional forces is performed.To investigate how the tip rake influences propeller scale effects,the geometry of PPTC-II is modified by removing the tip rake only,and the RANS-predicted scale effects for the modified propeller,PPTC-II-m,are compared with those for the PPTC-II.The study indicates that the scale effect on propeller thrust can be as important as that on the torque;somehow the RANS-and ITTC-based predictions for full-scale efficiency agree quite well;the tip-rake reduces tip loading and tip vortex strength,and brings about large differences in the scale effects as compared with the propeller without tip-rake.
