2021 Vol.35(6)
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2021, 35(6): 789-801.
doi: 10.1007/s13344-021-0070-8
Abstract:
The wave-induced fluid resonance between twin side-by-side rectangular barges coupled with the roll motion of the twin barges is investigated by both numerical simulation and physical model test. A 2D numerical wave flume, based on an open source computational fluid dynamics (CFD) package OpenFOAM, is applied for the numerical simulation. After numerical validations and convergent verifications, the characteristics of the fluid resonance in the gap between the twin rolling side-by-side barges are examined. The resonant frequency of the oscillating fluid in the gap between the twin rolling barges decreases compared with that between the twin fixed barges. Generally, the twin barges roll in the opposite directions, and their equilibrium positions lean oppositely with respect to the initial vertical direction. A physical model test is carried out for a further investigation, in which the twin barges are set oppositely leaning and fixed. From the present experimental results, a linear decrease of the resonant frequency with the increasing leaning angle is found. Combined with the numerical results, the deflection of the equilibrium positions of the twin barges is a relevant factor for the resonant frequency. Besides, the effects of the gap width and incident wave height on the fluid resonance coupled with roll motion are examined.
The wave-induced fluid resonance between twin side-by-side rectangular barges coupled with the roll motion of the twin barges is investigated by both numerical simulation and physical model test. A 2D numerical wave flume, based on an open source computational fluid dynamics (CFD) package OpenFOAM, is applied for the numerical simulation. After numerical validations and convergent verifications, the characteristics of the fluid resonance in the gap between the twin rolling side-by-side barges are examined. The resonant frequency of the oscillating fluid in the gap between the twin rolling barges decreases compared with that between the twin fixed barges. Generally, the twin barges roll in the opposite directions, and their equilibrium positions lean oppositely with respect to the initial vertical direction. A physical model test is carried out for a further investigation, in which the twin barges are set oppositely leaning and fixed. From the present experimental results, a linear decrease of the resonant frequency with the increasing leaning angle is found. Combined with the numerical results, the deflection of the equilibrium positions of the twin barges is a relevant factor for the resonant frequency. Besides, the effects of the gap width and incident wave height on the fluid resonance coupled with roll motion are examined.
2021, 35(6): 802-813.
doi: 10.1007/s13344-021-0071-7
Abstract:
Optimization theory is applied to a coastal engineering problem that is the design of a port. This approach was applied to the redesign of La Turballe Port in order to increase the exploitable surface area and simultaneously reduce the occurrence of long waves within the port. Having defined the cost function as a weighted function of wave amplitude and with the chosen parameterization of the port, results show that an extended jetty and a widened mole yield a unique optimal solution. This work demonstrates that numerical optimization may be quick and efficient in the identification of port solutions consistent with classic engineering even in the context of complex problems.
Optimization theory is applied to a coastal engineering problem that is the design of a port. This approach was applied to the redesign of La Turballe Port in order to increase the exploitable surface area and simultaneously reduce the occurrence of long waves within the port. Having defined the cost function as a weighted function of wave amplitude and with the chosen parameterization of the port, results show that an extended jetty and a widened mole yield a unique optimal solution. This work demonstrates that numerical optimization may be quick and efficient in the identification of port solutions consistent with classic engineering even in the context of complex problems.
2021, 35(6): 814-827.
doi: 10.1007/s13344-021-0072-6
Abstract:
Fully nonlinear water entry of a cone into waves with gravity effect has been analyzed based on a three-dimensional (3D) higher-order boundary method (HOBEM). The total velocity potential at the initial time is divided into the incident and scattering components. In the subsequent time steps, the solution of the velocity potential is defined as a whole through instantaneous boundary conditions. Based on the image theory, a modified Green function is applied to establish the integral equations so that only half of the calculation domain is considered and the seabed can be excluded. The free surface elevation is tracked along a given azimuth plane in the polar coordinate system, while the horizontal motion of the water particle is updated by using a segment-spring analogy method, which redistributes nodes and maintains mesh connectivity according to linear stiffness. An auxiliary function is applied to solve the pressure distribution, instead of directly calculating time derivative of the velocity potential. The high accuracy of the present numerical method is achieved through a detailed convergence study and comparison with results in the literature. Simulations are emphatically performed to examine the effects of gravity, wave nonlinearity, entry location, and oblique entry.
Fully nonlinear water entry of a cone into waves with gravity effect has been analyzed based on a three-dimensional (3D) higher-order boundary method (HOBEM). The total velocity potential at the initial time is divided into the incident and scattering components. In the subsequent time steps, the solution of the velocity potential is defined as a whole through instantaneous boundary conditions. Based on the image theory, a modified Green function is applied to establish the integral equations so that only half of the calculation domain is considered and the seabed can be excluded. The free surface elevation is tracked along a given azimuth plane in the polar coordinate system, while the horizontal motion of the water particle is updated by using a segment-spring analogy method, which redistributes nodes and maintains mesh connectivity according to linear stiffness. An auxiliary function is applied to solve the pressure distribution, instead of directly calculating time derivative of the velocity potential. The high accuracy of the present numerical method is achieved through a detailed convergence study and comparison with results in the literature. Simulations are emphatically performed to examine the effects of gravity, wave nonlinearity, entry location, and oblique entry.
2021, 35(6): 828-840.
doi: 10.1007/s13344-021-0073-5
Abstract:
The collision of ships poses a great threat to the piers in navigable waters. The kinetic energy of the moving ship can be consumed not only with the structural deformation, but also with tensile force from the proposed Floating Two-stage Buffer Collision-Prevention System (FTBCPS). The actual anti-collision effect of the current designed FTBCPS can be evaluated by the dynamic simulation. The construction method of 3D model is introduced, and the system initial state is defined. The transformation matrix and the basic kinematics vector are given, and the system basic dynamics equation is then created. The mechanical analysis on each component is carried out, and the detailed process of numerical simulation is also given. The simulation results indicate that collision direction and collision position have a great influence on the system kinematic response. Bridge pier faces the greatest threat when a ship hits the floater on the front beam in a nearly vertical direction, or on the side beam in a larger course angle. The study shows that the current designed FTBCPS can make full use of the fracture tensile property of polyester ropes and keep the tensile force acted on pier within its bearable range at the same time. The collision direction has a significant effect on the dynamic response of the colliding bodies, but no failure appeared in the simulations, which indicates that the current designed FTBCPS can protect bridge piers of all cases for the 5000-t ship with a velocity smaller than 5 m/s in navigable waters.
The collision of ships poses a great threat to the piers in navigable waters. The kinetic energy of the moving ship can be consumed not only with the structural deformation, but also with tensile force from the proposed Floating Two-stage Buffer Collision-Prevention System (FTBCPS). The actual anti-collision effect of the current designed FTBCPS can be evaluated by the dynamic simulation. The construction method of 3D model is introduced, and the system initial state is defined. The transformation matrix and the basic kinematics vector are given, and the system basic dynamics equation is then created. The mechanical analysis on each component is carried out, and the detailed process of numerical simulation is also given. The simulation results indicate that collision direction and collision position have a great influence on the system kinematic response. Bridge pier faces the greatest threat when a ship hits the floater on the front beam in a nearly vertical direction, or on the side beam in a larger course angle. The study shows that the current designed FTBCPS can make full use of the fracture tensile property of polyester ropes and keep the tensile force acted on pier within its bearable range at the same time. The collision direction has a significant effect on the dynamic response of the colliding bodies, but no failure appeared in the simulations, which indicates that the current designed FTBCPS can protect bridge piers of all cases for the 5000-t ship with a velocity smaller than 5 m/s in navigable waters.
Effect of Failure Mode of Taut Mooring System on the Dynamic Response of A Semi-Submersible Platform
2021, 35(6): 841-851.
doi: 10.1007/s13344-021-0074-4
Abstract:
Mooring system failure can lead to largely different dynamic response of floating structures when compared to the response under the condition of intact mooring system. For a semi-submersible platform with taut mooring system under extreme environmental conditions, the typical mooring system failure includes anchor line breaking failure due to the broken anchor line, and the anchor dragging failure caused by the anchor failure in the seabed soil due to the shortage of the anchor bearing capacity. However, study on the mooring failure caused by anchor failure is rare. The current work investigates the effect of three failure modes of taut mooring system on dynamic response of a semi-submersible platform, including one line breaking failure, two lines breaking failure, and one line breaking with one line attached anchor dragging failure. The nonlinear polynomial mooring line model in AQWA was used with integrating the load and displacement curve from the anchor pulling study to characterize the anchor dragging behavior for mooring system failure caused by the anchor failure. The offsets of the platform and the tension of mooring lines were analyzed for mooring system failure with 100-year return period. It is found that the mooring failure of one line breaking with one line attached anchor dragging is a case between the other two mooring failures. The traditional mooring analysis considering only the damaged condition with one line breaking is not safe enough. And the simple way of mooring analysis of two lines breaking is too conservative for the costly offshore engineering.
Mooring system failure can lead to largely different dynamic response of floating structures when compared to the response under the condition of intact mooring system. For a semi-submersible platform with taut mooring system under extreme environmental conditions, the typical mooring system failure includes anchor line breaking failure due to the broken anchor line, and the anchor dragging failure caused by the anchor failure in the seabed soil due to the shortage of the anchor bearing capacity. However, study on the mooring failure caused by anchor failure is rare. The current work investigates the effect of three failure modes of taut mooring system on dynamic response of a semi-submersible platform, including one line breaking failure, two lines breaking failure, and one line breaking with one line attached anchor dragging failure. The nonlinear polynomial mooring line model in AQWA was used with integrating the load and displacement curve from the anchor pulling study to characterize the anchor dragging behavior for mooring system failure caused by the anchor failure. The offsets of the platform and the tension of mooring lines were analyzed for mooring system failure with 100-year return period. It is found that the mooring failure of one line breaking with one line attached anchor dragging is a case between the other two mooring failures. The traditional mooring analysis considering only the damaged condition with one line breaking is not safe enough. And the simple way of mooring analysis of two lines breaking is too conservative for the costly offshore engineering.
2021, 35(6): 852-865.
doi: 10.1007/s13344-021-0075-3
Abstract:
An improved three-dimensional (3D) time-domain couple model is established in this paper to simulate the bidirectional vortex-induced vibration (VIV) of a deepwater steep wave riser (SWR) subjected to oblique currents. In this model, the nonlinear motion equations of the riser are established in the global coordinate system based on the slender rod theory with the finite element method. Van der Pol equations are used to describe the lift forces induced by the x- and y- direction current components, respectively. The coupled equations at each time step are solved by a Newmark-β iterative scheme for the SWR VIV. The present model is verified by comparison with the published experimental results for a top-tension riser. Then, a series of simulations are executed to determine the influences of the oblique angle/velocity of the current, different top-end positions and the length of the buoyancy segment on the VIV displacement, oscillating frequency as well as hydrodynamic coefficients of the SWR. The results demonstrate that there exists a coupled resonant VIV corresponding to x-direction and y-direction, respectively. However, the effective frequency is almost identical between the vibrations at the hang-off segment along x and y directions. The addition of the buoyancy modules in the middle of the SWR has a beneficial impact on the lift force of three segments and simultaneously limits the VIV response, especially at the decline segment and the hang-off segments. Additionally, the incident current direction significantly affects the motion trajectory of the SWR which mainly includes the fusiform and rectangle shapes.
An improved three-dimensional (3D) time-domain couple model is established in this paper to simulate the bidirectional vortex-induced vibration (VIV) of a deepwater steep wave riser (SWR) subjected to oblique currents. In this model, the nonlinear motion equations of the riser are established in the global coordinate system based on the slender rod theory with the finite element method. Van der Pol equations are used to describe the lift forces induced by the x- and y- direction current components, respectively. The coupled equations at each time step are solved by a Newmark-β iterative scheme for the SWR VIV. The present model is verified by comparison with the published experimental results for a top-tension riser. Then, a series of simulations are executed to determine the influences of the oblique angle/velocity of the current, different top-end positions and the length of the buoyancy segment on the VIV displacement, oscillating frequency as well as hydrodynamic coefficients of the SWR. The results demonstrate that there exists a coupled resonant VIV corresponding to x-direction and y-direction, respectively. However, the effective frequency is almost identical between the vibrations at the hang-off segment along x and y directions. The addition of the buoyancy modules in the middle of the SWR has a beneficial impact on the lift force of three segments and simultaneously limits the VIV response, especially at the decline segment and the hang-off segments. Additionally, the incident current direction significantly affects the motion trajectory of the SWR which mainly includes the fusiform and rectangle shapes.
2021, 35(6): 866-877.
doi: 10.1007/s13344-021-0076-2
Abstract:
The comb-type breakwater (CTB) has been proposed and investigated in recent years due to its advantages in terms of deep-water adaptability, material saving and water exchanges. All existing empirical formulae for CTBs have been so far restricted to the water level above the bottom of the superstructure, which mainly occurs under the high tides or storm tides. However, based on recent engineering applications and experimental observations, the most severe conditions for CTBs are more likely to occur under a medium water level, because impulsive wave pressure may occur due to interactions between waves and the special chamber in CTBs. Meanwhile, during the most of construction and operation periods, the CTBs are mainly working under the medium water levels, i.e., water levels below the bottom of the superstructure. In this study, the effects of main influence parameters on the horizontal wave force coefficient and wave transmission coefficient for open CTBs (with partially immersed side plates) under medium water levels were investigated based on a 3D numerical wave flume and corresponding empirical formulae were proposed. It is indicated that the location of the side plate related to the main caisson has significant influence on the hydrodynamic performance of CTBs. In engineering applications, the location of the side plate can be designed at b/L≤ 0.15 or b/L ≥ 0.3 (where b is the distance between the side plate and the front face of the main caisson and L is the incident wave length) for efficiently lowering the horizontal wave force and wave transmission. The flow mechanism of impulsive wave force on CTBs was revealed based on synchronous analyses of flow fields and pressure distribution. Through appropriate design of the height of the superstructure according to H/hD ≤ 1.0 or H/hD ≥ 1.5 (where H is the incident wave height and hD is the distance between the still water level and the bottom of the superstructure), the likely impulsive wave pressure on the side plate can also be diminished.
The comb-type breakwater (CTB) has been proposed and investigated in recent years due to its advantages in terms of deep-water adaptability, material saving and water exchanges. All existing empirical formulae for CTBs have been so far restricted to the water level above the bottom of the superstructure, which mainly occurs under the high tides or storm tides. However, based on recent engineering applications and experimental observations, the most severe conditions for CTBs are more likely to occur under a medium water level, because impulsive wave pressure may occur due to interactions between waves and the special chamber in CTBs. Meanwhile, during the most of construction and operation periods, the CTBs are mainly working under the medium water levels, i.e., water levels below the bottom of the superstructure. In this study, the effects of main influence parameters on the horizontal wave force coefficient and wave transmission coefficient for open CTBs (with partially immersed side plates) under medium water levels were investigated based on a 3D numerical wave flume and corresponding empirical formulae were proposed. It is indicated that the location of the side plate related to the main caisson has significant influence on the hydrodynamic performance of CTBs. In engineering applications, the location of the side plate can be designed at b/L≤ 0.15 or b/L ≥ 0.3 (where b is the distance between the side plate and the front face of the main caisson and L is the incident wave length) for efficiently lowering the horizontal wave force and wave transmission. The flow mechanism of impulsive wave force on CTBs was revealed based on synchronous analyses of flow fields and pressure distribution. Through appropriate design of the height of the superstructure according to H/hD ≤ 1.0 or H/hD ≥ 1.5 (where H is the incident wave height and hD is the distance between the still water level and the bottom of the superstructure), the likely impulsive wave pressure on the side plate can also be diminished.
2021, 35(6): 878-890.
doi: 10.1007/s13344-021-0077-1
Abstract:
Flow-induced vibration (FIV) of a group of long, flexible cylinders involves a complex interaction between fluid and structures. Although a substantial number of studies have been devoted to assessing FIV response behaviours, fatigue damage features of staggered flexible cylinders are not fully understood. Moreover, the wake-induced flutter constitutes an intricate hydrodynamic behaviour that frequently occurs when one cylinder is in the vicinity of another one. Unfortunately, existing studies on the fatigue damage caused by wake-induced flutter are incapable of achieving better results. This paper, therefore, estimates the FIV fatigue damage of two staggered flexible cylinders with an aspect ratio of 350 and a mass ratio of 1.90 based on normal S?N curves according to Det Norske Veritas (DNV) regulations. Twelve staggered cases (cross-flow spacing ratios of 2.0, 3.0, 4.0, and 6.0 and in-line spacing ratios of 4.0, 6.0, and 8.0) are discussed for comparison, and fatigue damage caused by wake-induced flutter is thoroughly considered. Fatigue damage results indicate that the variation of the cross-flow (CF) spacing ratio has a greater influence than that of the in-line (IL) spacing ratio on the CF fatigue damage of the upstream cylinder. Lower IL fatigue damages of the upstream cylinder are observed when reduced velocity Vr≥15.03 due to the wake flow patterns with different IL spacing ratios. Moreover, wake interference, especially wake-induced flutter, predominates the fatigue damage characteristics of the downstream cylinder. When Vr=8.77?11.27, wake-induced flutter enhances the IL fatigue damage of the downstream cylinder and slightly affects that of the upstream body. Furthermore, wake-induced flutter causes considerable IL fatigue damage disparity between the two staggered cylinders by suppressing the IL fatigue damage of the upstream cylinder when Vr≥20.04.
Flow-induced vibration (FIV) of a group of long, flexible cylinders involves a complex interaction between fluid and structures. Although a substantial number of studies have been devoted to assessing FIV response behaviours, fatigue damage features of staggered flexible cylinders are not fully understood. Moreover, the wake-induced flutter constitutes an intricate hydrodynamic behaviour that frequently occurs when one cylinder is in the vicinity of another one. Unfortunately, existing studies on the fatigue damage caused by wake-induced flutter are incapable of achieving better results. This paper, therefore, estimates the FIV fatigue damage of two staggered flexible cylinders with an aspect ratio of 350 and a mass ratio of 1.90 based on normal S?N curves according to Det Norske Veritas (DNV) regulations. Twelve staggered cases (cross-flow spacing ratios of 2.0, 3.0, 4.0, and 6.0 and in-line spacing ratios of 4.0, 6.0, and 8.0) are discussed for comparison, and fatigue damage caused by wake-induced flutter is thoroughly considered. Fatigue damage results indicate that the variation of the cross-flow (CF) spacing ratio has a greater influence than that of the in-line (IL) spacing ratio on the CF fatigue damage of the upstream cylinder. Lower IL fatigue damages of the upstream cylinder are observed when reduced velocity Vr≥15.03 due to the wake flow patterns with different IL spacing ratios. Moreover, wake interference, especially wake-induced flutter, predominates the fatigue damage characteristics of the downstream cylinder. When Vr=8.77?11.27, wake-induced flutter enhances the IL fatigue damage of the downstream cylinder and slightly affects that of the upstream body. Furthermore, wake-induced flutter causes considerable IL fatigue damage disparity between the two staggered cylinders by suppressing the IL fatigue damage of the upstream cylinder when Vr≥20.04.
2021, 35(6): 891-904.
doi: 10.1007/s13344-021-0078-0
Abstract:
Flow-induced vibration (FIV) of four separately mounted cantilever cylinders are experimentally investigated in a water flume. The four cylinders with top ends screwed vertically into a turntable platform are subjected to uniform flows with Reynolds number ranging from 3840 to 16520. A non-intrusive measurement with high-speed cameras is employed to simultaneously capture the time-varying in-line and cross-flow vibrations in the reduced velocity range of 3.0–12.9. Experimental results highlight the continuous adjustment of flow regime caused by the spatial-temporal alteration of cylinders. Consequently, the space-time varying flow interference contributes to the occurrence of multiple response frequencies. The transition from a dominant frequency to a broad-band response illustrates the enhancement of wake interference. The combination of wake flow interactions results in the irregular oscillation trajectories and the appearance of a response trough with the associated switching in vortex shedding mode. The dual-resonance phenomenon is observed in the four cylinders due to the complicated wake-structure interaction. The greatest mechanical energy possessed by the four cylinders in an in-line square arrangement is mainly resulted from the downstream cylinders, signifying the positive role of wake excitation in extracting hydrokinetic energy from ambient flow.
Flow-induced vibration (FIV) of four separately mounted cantilever cylinders are experimentally investigated in a water flume. The four cylinders with top ends screwed vertically into a turntable platform are subjected to uniform flows with Reynolds number ranging from 3840 to 16520. A non-intrusive measurement with high-speed cameras is employed to simultaneously capture the time-varying in-line and cross-flow vibrations in the reduced velocity range of 3.0–12.9. Experimental results highlight the continuous adjustment of flow regime caused by the spatial-temporal alteration of cylinders. Consequently, the space-time varying flow interference contributes to the occurrence of multiple response frequencies. The transition from a dominant frequency to a broad-band response illustrates the enhancement of wake interference. The combination of wake flow interactions results in the irregular oscillation trajectories and the appearance of a response trough with the associated switching in vortex shedding mode. The dual-resonance phenomenon is observed in the four cylinders due to the complicated wake-structure interaction. The greatest mechanical energy possessed by the four cylinders in an in-line square arrangement is mainly resulted from the downstream cylinders, signifying the positive role of wake excitation in extracting hydrokinetic energy from ambient flow.
2021, 35(6): 905-913.
doi: 10.1007/s13344-021-0079-z
Abstract:
Edinburgh Duck wave energy converter (ED WEC) has excellent energy extraction performance and shows a great potential to integrate with other marine structures. This paper aims to investigate its wave energy extraction performance as a WEC and wave attenuation performance as a protection method for shoreline or marine structures. The wave and ED WEC interactions in regular waves are modeled using the Star-CCM+ software and verified by comparisons with published experimental results. The motion response, energy conversion efficiency, and transmission coefficient of the ED WEC with different attack angles, rotation center, and incident wave heights are investigated. Results indicate that the ED WEC with an attack angle of 42° and a rotation center of 0.55 m below the mean water line can achieve both good wave energy extraction and wave attenuation performances. The wave energy extraction and wave attenuation performance of the ED WEC decrease significantly with the increase of wave nonlinearity characterized by the wave steepness. This paper can guide the practical application of the ED WEC at the early stage of design.
Edinburgh Duck wave energy converter (ED WEC) has excellent energy extraction performance and shows a great potential to integrate with other marine structures. This paper aims to investigate its wave energy extraction performance as a WEC and wave attenuation performance as a protection method for shoreline or marine structures. The wave and ED WEC interactions in regular waves are modeled using the Star-CCM+ software and verified by comparisons with published experimental results. The motion response, energy conversion efficiency, and transmission coefficient of the ED WEC with different attack angles, rotation center, and incident wave heights are investigated. Results indicate that the ED WEC with an attack angle of 42° and a rotation center of 0.55 m below the mean water line can achieve both good wave energy extraction and wave attenuation performances. The wave energy extraction and wave attenuation performance of the ED WEC decrease significantly with the increase of wave nonlinearity characterized by the wave steepness. This paper can guide the practical application of the ED WEC at the early stage of design.
2021, 35(6): 914-923.
doi: 10.1007/s13344-021-0080-6
Abstract:
Numerical simulations of evolution characteristics of slug flow across a 90° pipe bend have been carried out to study the fluid?structure interaction response induced by internal slug flow. The two-phase flow patterns and turbulence were modelled by using the volume of fluid (VOF) model and the Realizable k?ε turbulence model respectively. Firstly, validation of the CFD model was carried out and the desirable results were obtained. The different flow patterns and the time-average mean void fraction was coincident with the reported experimental data. Simulations of different cases of slug flow have been carried out to show the effects of superficial gas and liquid velocity on the evolution characteristics of slug flow. Then, a one-way coupled fluid–structure interaction framework was established to investigate the slug flow interaction with a 90° pipe bend under various superficial liquid and gas velocities. It was found that the maximum total deformation and equivalent stress increased with the increasing superficial gas velocity, while decreased with the increasing superficial liquid velocity. In addition, the total deformation and equivalent stress has obvious periodic fluctuation. Furthermore, the distribution position of maximum deformation and stress was related to the evolution of slug flow. With the increasing superficial gas velocity, the maximum total deformation was mainly located at the 90° pipe bend. But as the superficial liquid velocity increases, the maximum total deformation was mainly located in the horizontal pipe section. Consequently, the slug flow with higher superficial gas velocity will induce more serious cyclical impact on the 90° pipe bend.
Numerical simulations of evolution characteristics of slug flow across a 90° pipe bend have been carried out to study the fluid?structure interaction response induced by internal slug flow. The two-phase flow patterns and turbulence were modelled by using the volume of fluid (VOF) model and the Realizable k?ε turbulence model respectively. Firstly, validation of the CFD model was carried out and the desirable results were obtained. The different flow patterns and the time-average mean void fraction was coincident with the reported experimental data. Simulations of different cases of slug flow have been carried out to show the effects of superficial gas and liquid velocity on the evolution characteristics of slug flow. Then, a one-way coupled fluid–structure interaction framework was established to investigate the slug flow interaction with a 90° pipe bend under various superficial liquid and gas velocities. It was found that the maximum total deformation and equivalent stress increased with the increasing superficial gas velocity, while decreased with the increasing superficial liquid velocity. In addition, the total deformation and equivalent stress has obvious periodic fluctuation. Furthermore, the distribution position of maximum deformation and stress was related to the evolution of slug flow. With the increasing superficial gas velocity, the maximum total deformation was mainly located at the 90° pipe bend. But as the superficial liquid velocity increases, the maximum total deformation was mainly located in the horizontal pipe section. Consequently, the slug flow with higher superficial gas velocity will induce more serious cyclical impact on the 90° pipe bend.
2021, 35(6): 924-932.
doi: 10.1007/s13344-021-0081-5
Abstract:
Hydrokinetic energy is a promising technology to harness predictable renewable energy from free-flowing water, tides and ocean currents. Many studies have been conducted by researchers and engineers to find out ways to enhance the performance of the hydrokinetic turbine. The current paper reports the experimental study of using hydrophobic coating as an alternative way to improve the performance of hydrokinetic turbine. A hydrophobic coating can lower the friction drag of a surface that is in contact with liquid. For hydrokinetic turbine blade, reduction in friction drag may allow a blade section to have a better lift/drag ratio and have its efficiency improved. In this study, a formula to predict the pattern of drag reduction over a hydrophobic surface has been derived. Two hydrophobic coatings were applied on NACA 63418 hydrofoils and their performances were tested. It was found that NACA 63418 hydrofoil with the hydrophobic coatings had its drag reduced by an average of 3%?4.0%. When the coatings were applied on a 350 mm diameter three-bladed turbine, the maximum increment of rotational speed of the turbine was found to be 2.5%. The performance of the two coatings against marine fouling was also investigated. The weight of plate with and without the coatings increased by 10% and 100%, respectively.
Hydrokinetic energy is a promising technology to harness predictable renewable energy from free-flowing water, tides and ocean currents. Many studies have been conducted by researchers and engineers to find out ways to enhance the performance of the hydrokinetic turbine. The current paper reports the experimental study of using hydrophobic coating as an alternative way to improve the performance of hydrokinetic turbine. A hydrophobic coating can lower the friction drag of a surface that is in contact with liquid. For hydrokinetic turbine blade, reduction in friction drag may allow a blade section to have a better lift/drag ratio and have its efficiency improved. In this study, a formula to predict the pattern of drag reduction over a hydrophobic surface has been derived. Two hydrophobic coatings were applied on NACA 63418 hydrofoils and their performances were tested. It was found that NACA 63418 hydrofoil with the hydrophobic coatings had its drag reduced by an average of 3%?4.0%. When the coatings were applied on a 350 mm diameter three-bladed turbine, the maximum increment of rotational speed of the turbine was found to be 2.5%. The performance of the two coatings against marine fouling was also investigated. The weight of plate with and without the coatings increased by 10% and 100%, respectively.
2021, 35(6): 933-942.
doi: 10.1007/s13344-021-0082-4
Abstract:
In this study, the Jinzhou 9-3 CEPD float-over installation project was investigated. During the undocking condition, the water depth of the motion path of the working barge gradually changed from 10.31 m to 9.41 m. The undocking clearance of the HYSY 228 is smaller than 1 m; therefore, the barge shows highly nonlinear hydrodynamic characteristics, and it is difficult to be accurately simulated by numerical analysis. Thus, it is necessary to obtain the hydrodynamic characteristics and laws of the float-over barge at different water depths by using tank model test, to provide some reference and guidance for float-over operations in shallow water.
In this study, the Jinzhou 9-3 CEPD float-over installation project was investigated. During the undocking condition, the water depth of the motion path of the working barge gradually changed from 10.31 m to 9.41 m. The undocking clearance of the HYSY 228 is smaller than 1 m; therefore, the barge shows highly nonlinear hydrodynamic characteristics, and it is difficult to be accurately simulated by numerical analysis. Thus, it is necessary to obtain the hydrodynamic characteristics and laws of the float-over barge at different water depths by using tank model test, to provide some reference and guidance for float-over operations in shallow water.
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