2020 Vol.34(3)
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2020, 34(3): 299-313.
doi: 10.1007/s13344-020-0028-2
Abstract:
Influenced by weather, the estuaries and bays often exhibit recurring oscillations in flow and water level similar to astronomical tides. The weather impact however is less regular than tides and more difficult to predict. The spectrum of weather induced motions in estuaries and bays is mostly at the low-frequency end with time scales longer than those of diurnal tides. The repeated weather impact produces meteorological tide: the recurring flood and ebb and flushing of the estuaries and bays but at lower frequencies than those of tides. The variation in weather conditions is quasi-periodic and of large scale nature (~1000?3000 km) because of the alternating low- and high- atmospheric pressure systems of extra-tropical cyclones and anti-cyclones and associated fronts. By examining 40 years of data between Jan. 1, 1977 and Dec. 31, 2016, we identified 1648 frontal events (averaging ~41.2±4.7 per year) influencing the northern Gulf of Mexico for time periods in the spring, fall and winter. The late spring and summer months (May, Jun, July, and August) were not included in the calculation because of much weaker activities involving synoptic weather systems with fronts during these months. It is found that the number of frontal events reached the maximum in Jan. and Dec. while the minimum occurred in April and Sept. It is found that there is an increasing trend of number of fronts over the 40-year period. Our data show that the low pass filtered water level, velocity, and vorticity (velocity shear) all vary in response to the weather and appear as the meteorological tide. The particle excursions of meteorological tides are much larger than those from the astronomical tides. In addition, the irregular nature of the meteorological tide makes the inward flux and outward flux asymmetric in general and thus it has a significant implication to dispersion and transport of waterborne materials. A scaling analysis shows that the meteorological tide generally reaches quasi-steady state; and as a result, a regression model is established which can be very useful for predicting the weather produced quasi-periodic motions.
Influenced by weather, the estuaries and bays often exhibit recurring oscillations in flow and water level similar to astronomical tides. The weather impact however is less regular than tides and more difficult to predict. The spectrum of weather induced motions in estuaries and bays is mostly at the low-frequency end with time scales longer than those of diurnal tides. The repeated weather impact produces meteorological tide: the recurring flood and ebb and flushing of the estuaries and bays but at lower frequencies than those of tides. The variation in weather conditions is quasi-periodic and of large scale nature (~1000?3000 km) because of the alternating low- and high- atmospheric pressure systems of extra-tropical cyclones and anti-cyclones and associated fronts. By examining 40 years of data between Jan. 1, 1977 and Dec. 31, 2016, we identified 1648 frontal events (averaging ~41.2±4.7 per year) influencing the northern Gulf of Mexico for time periods in the spring, fall and winter. The late spring and summer months (May, Jun, July, and August) were not included in the calculation because of much weaker activities involving synoptic weather systems with fronts during these months. It is found that the number of frontal events reached the maximum in Jan. and Dec. while the minimum occurred in April and Sept. It is found that there is an increasing trend of number of fronts over the 40-year period. Our data show that the low pass filtered water level, velocity, and vorticity (velocity shear) all vary in response to the weather and appear as the meteorological tide. The particle excursions of meteorological tides are much larger than those from the astronomical tides. In addition, the irregular nature of the meteorological tide makes the inward flux and outward flux asymmetric in general and thus it has a significant implication to dispersion and transport of waterborne materials. A scaling analysis shows that the meteorological tide generally reaches quasi-steady state; and as a result, a regression model is established which can be very useful for predicting the weather produced quasi-periodic motions.
2020, 34(3): 314-327.
doi: 10.1007/s13344-020-0029-1
Abstract:
The interaction between structure and wave is a typical phenomenon in naval architecture and ocean engineering. In this paper, numerical simulation is carried out to study the interaction between a two-dimensional submerged, fixed, horizontal rigid plate and solitary wave with our in-house meshless particle CFD solver MLParticle-SJTU. First, the in-house CFD solver is verified by experimental results conducted at the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. During the verification, the plate is submerged under water and the solitary wave with a given amplitude is generated by a piston-type wave maker. Free surface elevation of the wave and the pressure impacting on the plate is recorded and compared with experimental data respectively. The predicted pressure and surface elevation agree well with the experimental results. Then in order to further investigate factors affecting wave-structure interaction, wave height, submerged depth and plate length are analyzed.
The interaction between structure and wave is a typical phenomenon in naval architecture and ocean engineering. In this paper, numerical simulation is carried out to study the interaction between a two-dimensional submerged, fixed, horizontal rigid plate and solitary wave with our in-house meshless particle CFD solver MLParticle-SJTU. First, the in-house CFD solver is verified by experimental results conducted at the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. During the verification, the plate is submerged under water and the solitary wave with a given amplitude is generated by a piston-type wave maker. Free surface elevation of the wave and the pressure impacting on the plate is recorded and compared with experimental data respectively. The predicted pressure and surface elevation agree well with the experimental results. Then in order to further investigate factors affecting wave-structure interaction, wave height, submerged depth and plate length are analyzed.
2020, 34(3): 328-340.
doi: 10.1007/s13344-020-0030-8
Abstract:
The pipe?soil interactions at shoulders can significantly affect the vortex-induced vibrations (VIV) of free-spanning pipes in the subsea. In this paper, the seabed soil reacting force on the pipe is directly calculated with a nonlinear hysteretic soil model. For the VIV in the middle span, a classic van der Pol wake oscillator is adopted. Based on the Euler?Bernoulli beam theory, the vibration equations of the pipe are obtained which are different in the middle span and at the two end shoulders. The static configuration of the pipe is firstly calculated and then the VIV is simulated. The present model is validated with the comparisons of VIV experiment, pipe?soil interaction experiment and the simulation results of VIV of free-spanning pipes in which the seabed soil is modelled with spring-dashpots. With the present model, the influence of seabed soil on the VIV of a free-spanning pipe is analyzed. The parametric studies show that when the seabed soil has a larger suction area, the pipe vibrates with smaller bending stresses and is safer. While with the increase of the shear strength of the seabed soil, the bending stresses increase and the pipe faces more danger.
The pipe?soil interactions at shoulders can significantly affect the vortex-induced vibrations (VIV) of free-spanning pipes in the subsea. In this paper, the seabed soil reacting force on the pipe is directly calculated with a nonlinear hysteretic soil model. For the VIV in the middle span, a classic van der Pol wake oscillator is adopted. Based on the Euler?Bernoulli beam theory, the vibration equations of the pipe are obtained which are different in the middle span and at the two end shoulders. The static configuration of the pipe is firstly calculated and then the VIV is simulated. The present model is validated with the comparisons of VIV experiment, pipe?soil interaction experiment and the simulation results of VIV of free-spanning pipes in which the seabed soil is modelled with spring-dashpots. With the present model, the influence of seabed soil on the VIV of a free-spanning pipe is analyzed. The parametric studies show that when the seabed soil has a larger suction area, the pipe vibrates with smaller bending stresses and is safer. While with the increase of the shear strength of the seabed soil, the bending stresses increase and the pipe faces more danger.
2020, 34(3): 341-351.
doi: 10.1007/s13344-020-0031-7
Abstract:
An experimental investigation on the disturbance effect of jet-type active vibration suppression device on vortex-induced vibration of deep-sea riser was carried out in the wave-flow combined flume. The vibration suppression device was designed in which the jet pipe was horizontally fixed to the front end of the riser. By varying three different excitation spacings and multi-stage outflow velocities, the influence law of the dominant frequency, dimensionless displacement and other dynamic response parameters was studied under different excitation spacings, and the mechanism and sensitive characteristics of the disturbance suppression were explored. The results indicate that the variation of excitation spacing makes gas curtain enter the strong disturbed flow region at different velocities and angles, and the coupling relationship between excitation spacing and reduced velocity is the key factor to enter the strong disturbed flow region to achieve the optimal disturbance suppression. In the strong disturbed flow region, the influence of gas curtain on the dominant frequency is obviously affected by the flow velocity, while the vibration displacement is stable at the same amplitude and is weakly affected by the flow velocity. Gas curtain can effectively disturb the formation of vortex shedding, destroy the strong nonlinear coupled vibration of the riser, and achieve better vibration suppression effect. In the weak disturbed flow region, the vortex length of the riser tail is prolonged, the strong nonlinear coupled vibration of the riser is gradually restored, and the vibration suppression effect of the device gradually decreases.
An experimental investigation on the disturbance effect of jet-type active vibration suppression device on vortex-induced vibration of deep-sea riser was carried out in the wave-flow combined flume. The vibration suppression device was designed in which the jet pipe was horizontally fixed to the front end of the riser. By varying three different excitation spacings and multi-stage outflow velocities, the influence law of the dominant frequency, dimensionless displacement and other dynamic response parameters was studied under different excitation spacings, and the mechanism and sensitive characteristics of the disturbance suppression were explored. The results indicate that the variation of excitation spacing makes gas curtain enter the strong disturbed flow region at different velocities and angles, and the coupling relationship between excitation spacing and reduced velocity is the key factor to enter the strong disturbed flow region to achieve the optimal disturbance suppression. In the strong disturbed flow region, the influence of gas curtain on the dominant frequency is obviously affected by the flow velocity, while the vibration displacement is stable at the same amplitude and is weakly affected by the flow velocity. Gas curtain can effectively disturb the formation of vortex shedding, destroy the strong nonlinear coupled vibration of the riser, and achieve better vibration suppression effect. In the weak disturbed flow region, the vortex length of the riser tail is prolonged, the strong nonlinear coupled vibration of the riser is gradually restored, and the vibration suppression effect of the device gradually decreases.
2020, 34(3): 352-361.
doi: 10.1007/s13344-020-0032-6
Abstract:
This paper presents a systematic model test program to assess the uncertainty of the ship-bank interaction forces, using the planar motion mechanism (PMM) system in a circulating water channel (CWC). Therefore, the uncertainties due to ship-bank distance and water depth are considered, and they are calculated via the partial differentials of the regression formulae based on the test data. The general part of the uncertainty analysis (UA) is performed according to the ITTC recommended procedure 7.5-02-06.04, while the uncertainty of speed is identified as the bias limit due to the flow velocity maldistribution in the CWC. In each example test for the UA of ship-bank interaction forces, 12 repeated measurements were conducted. Results from the UA show that the contribution of water depth error and flow velocity maldistribution to the total uncertainty is noticeable, and the paper explains how they increase with the change of the test conditions. The present study will be useful in understanding the uncertainty regarding the ship-bank interaction force measurement in a CWC.
This paper presents a systematic model test program to assess the uncertainty of the ship-bank interaction forces, using the planar motion mechanism (PMM) system in a circulating water channel (CWC). Therefore, the uncertainties due to ship-bank distance and water depth are considered, and they are calculated via the partial differentials of the regression formulae based on the test data. The general part of the uncertainty analysis (UA) is performed according to the ITTC recommended procedure 7.5-02-06.04, while the uncertainty of speed is identified as the bias limit due to the flow velocity maldistribution in the CWC. In each example test for the UA of ship-bank interaction forces, 12 repeated measurements were conducted. Results from the UA show that the contribution of water depth error and flow velocity maldistribution to the total uncertainty is noticeable, and the paper explains how they increase with the change of the test conditions. The present study will be useful in understanding the uncertainty regarding the ship-bank interaction force measurement in a CWC.
2020, 34(3): 362-373.
doi: 10.1007/s13344-020-0033-5
Abstract:
Fluids and structures impact is one of the common phenomena in nature, and it widely exists in engineering practice, including ship hydrodynamic slamming, wave impact on offshore platforms, plunging wave on coastal structures, emergency landing of aircrafts at sea as well as impact of ultra-cold droplets and ice lumps under aviation conditions. In this paper, a two dimensional (2-D) solver for Navier?Stokes equations is developed and applied in the numerical simulation of the impact on a rigid plate by a liquid square. The computational domain is discretized by Finite Volume Method (FVM). The Volume of Fluid (VOF) technique is used to track the free surface and the Piecewise-Linear Interface Construction (PLIC) is used for reconstruction. The Continuum Surface Force (CSF) model is used to account for the surface tension. The convective term and the diffusive term are upwind and centrally differenced respectively. The Inner Doubly Iterative Efficient Algorithm for Linked Equations (IDEAL) is used to decouple the pressure and velocity. Based on the proposed techniques, collapse of water column is simulated and convergence study is performed for the validation of the numerical solver. Then the impact of a free falling liquid body is simulated, and the effect of volume and initial height of the liquid body is analyzed. In addition, the impact on a plate with a liquid layer is also simulated to study the effect of falling height on a liquid floor.
Fluids and structures impact is one of the common phenomena in nature, and it widely exists in engineering practice, including ship hydrodynamic slamming, wave impact on offshore platforms, plunging wave on coastal structures, emergency landing of aircrafts at sea as well as impact of ultra-cold droplets and ice lumps under aviation conditions. In this paper, a two dimensional (2-D) solver for Navier?Stokes equations is developed and applied in the numerical simulation of the impact on a rigid plate by a liquid square. The computational domain is discretized by Finite Volume Method (FVM). The Volume of Fluid (VOF) technique is used to track the free surface and the Piecewise-Linear Interface Construction (PLIC) is used for reconstruction. The Continuum Surface Force (CSF) model is used to account for the surface tension. The convective term and the diffusive term are upwind and centrally differenced respectively. The Inner Doubly Iterative Efficient Algorithm for Linked Equations (IDEAL) is used to decouple the pressure and velocity. Based on the proposed techniques, collapse of water column is simulated and convergence study is performed for the validation of the numerical solver. Then the impact of a free falling liquid body is simulated, and the effect of volume and initial height of the liquid body is analyzed. In addition, the impact on a plate with a liquid layer is also simulated to study the effect of falling height on a liquid floor.
2020, 34(3): 374-386.
doi: 10.1007/s13344-020-0034-4
Abstract:
The research on the hydrodynamics of blades is mainly focused on sea areas with high-speed current. However, the average velocity in most territorial waters of China is smaller than 1 m/s, and the lift type of airfoil blades has limited application in most of these conditions. Therefore, it is of great significance to study the tidal current energy capture of blades in sub-low speed sea areas. The effect of flow impact resistance on the blade at sub-low current speed is considered and a new type of thin-walled blade based on the lift type of blade is proposed, and then the lift-impact combined hydrodynamic model of horizontal axis blade is established. Based on this model, and considering the characteristics of tidal current and velocity in the sea area of Yushan Islands, simulation and optimization of blade design are carried out. Additionally, the horizontal axis thin-walled blade and the NACA airfoil contrast blade under the same conditions are developed. By using a synthetical experimental test system, the power, torque, rotational speed and load characteristics of these two blades are tested. The performance of the thin-walled blade and the design theory are verified. It shows that this type of blade has much better energy capture efficiency in the sub-low speed sea area. This research will promote the study and development of turbines that can be used in low- speed current sea areas in the future.
The research on the hydrodynamics of blades is mainly focused on sea areas with high-speed current. However, the average velocity in most territorial waters of China is smaller than 1 m/s, and the lift type of airfoil blades has limited application in most of these conditions. Therefore, it is of great significance to study the tidal current energy capture of blades in sub-low speed sea areas. The effect of flow impact resistance on the blade at sub-low current speed is considered and a new type of thin-walled blade based on the lift type of blade is proposed, and then the lift-impact combined hydrodynamic model of horizontal axis blade is established. Based on this model, and considering the characteristics of tidal current and velocity in the sea area of Yushan Islands, simulation and optimization of blade design are carried out. Additionally, the horizontal axis thin-walled blade and the NACA airfoil contrast blade under the same conditions are developed. By using a synthetical experimental test system, the power, torque, rotational speed and load characteristics of these two blades are tested. The performance of the thin-walled blade and the design theory are verified. It shows that this type of blade has much better energy capture efficiency in the sub-low speed sea area. This research will promote the study and development of turbines that can be used in low- speed current sea areas in the future.
2020, 34(3): 387-399.
doi: 10.1007/s13344-020-0035-3
Abstract:
National navies equip their submarines with Autonomous Underwater Vehicle (AUV) technology. It has become an important component of submarine development in technologically-advanced countries. Employing advanced and reliable recovery systems directly improves the safety and operational efficiency of submarines equipped with AUVs. In this paper, based on aerial refueling technology, a cone-shaped recovery system with two different guiding covers (closed structure and frame structure) is applied to the submarine. By taking the Suboff model as the research object, STAR-CCM was used to study the influence of the installation position of the recovery system, and the length of the rigid rod, on the Suboff model. It was found that when the recovery system is installed in the middle and rear of the Suboff model at the same velocity and the same length of the rigid rod, the Suboff model has the good stability and less drag. It experiences the largest drag when being installed in the front of the rigid rod. Moreover, when the recovery system is installed in the front and middle of the rigid rod, the drag increases as its length increases, and the lift decreases as its length increases. Compared with the closed structure guiding cover, the Suboff model will have less drag and better stability when the recovery system uses the frame structure guiding cover. Besides, the deflection and vibration of the rigid rod were also analyzed via mathematical theory.
National navies equip their submarines with Autonomous Underwater Vehicle (AUV) technology. It has become an important component of submarine development in technologically-advanced countries. Employing advanced and reliable recovery systems directly improves the safety and operational efficiency of submarines equipped with AUVs. In this paper, based on aerial refueling technology, a cone-shaped recovery system with two different guiding covers (closed structure and frame structure) is applied to the submarine. By taking the Suboff model as the research object, STAR-CCM was used to study the influence of the installation position of the recovery system, and the length of the rigid rod, on the Suboff model. It was found that when the recovery system is installed in the middle and rear of the Suboff model at the same velocity and the same length of the rigid rod, the Suboff model has the good stability and less drag. It experiences the largest drag when being installed in the front of the rigid rod. Moreover, when the recovery system is installed in the front and middle of the rigid rod, the drag increases as its length increases, and the lift decreases as its length increases. Compared with the closed structure guiding cover, the Suboff model will have less drag and better stability when the recovery system uses the frame structure guiding cover. Besides, the deflection and vibration of the rigid rod were also analyzed via mathematical theory.
2020, 34(3): 400-410.
doi: 10.1007/s13344-020-0036-2
Abstract:
In this paper, a Double-stage Surrogate-based Shape Optimization (DSSO) strategy for Blended-Wing-Body Underwater Gliders (BWBUGs) is proposed to reduce the computational cost. In this strategy, a double-stage surrogate model is developed to replace the high-dimensional objective in shape optimization. Specifically, several First-stage Surrogate Models (FSMs) are built for the sectional airfoils, and the second-stage surrogate model is constructed with respect to the outputs of FSMs. Besides, a Multi-start Space Reduction surrogate-based global optimization method is applied to search for the optimum. In order to validate the efficiency of the proposed method, DSSO is first compared with an ordinary One-stage Surrogate-based Optimization strategy by using the same optimization method. Then, the other three popular surrogate-based optimization methods and three heuristic algorithms are utilized to make comparisons. Results indicate that the lift-to-drag ratio of the BWBUG is improved by 9.35% with DSSO, which outperforms the comparison methods. Besides, DSSO reduces more than 50% of the time that other methods used when obtaining the same level of results. Furthermore, some considerations of the proposed strategy are further discussed and some characteristics of DSSO are identified.
In this paper, a Double-stage Surrogate-based Shape Optimization (DSSO) strategy for Blended-Wing-Body Underwater Gliders (BWBUGs) is proposed to reduce the computational cost. In this strategy, a double-stage surrogate model is developed to replace the high-dimensional objective in shape optimization. Specifically, several First-stage Surrogate Models (FSMs) are built for the sectional airfoils, and the second-stage surrogate model is constructed with respect to the outputs of FSMs. Besides, a Multi-start Space Reduction surrogate-based global optimization method is applied to search for the optimum. In order to validate the efficiency of the proposed method, DSSO is first compared with an ordinary One-stage Surrogate-based Optimization strategy by using the same optimization method. Then, the other three popular surrogate-based optimization methods and three heuristic algorithms are utilized to make comparisons. Results indicate that the lift-to-drag ratio of the BWBUG is improved by 9.35% with DSSO, which outperforms the comparison methods. Besides, DSSO reduces more than 50% of the time that other methods used when obtaining the same level of results. Furthermore, some considerations of the proposed strategy are further discussed and some characteristics of DSSO are identified.
2020, 34(3): 411-420.
doi: 10.1007/s13344-020-0037-1
Abstract:
A combined experimental and numerical investigation is carried out to study the performance of a vertical-axis eccentric-disc variable-pitch turbine (VEVT). A scheme of eccentric disc pitch control mechanism based on double-block mechanism is proposed. The eccentric control mechanism and the deflection angle control mechanism in the pitch control structure are designed and optimized according to the functional requirements of the turbine, and the three-dimensional model of the turbine is established. Kinematics analysis of the eccentric disc pitch control mechanism is carried out. Kinematics parameters and kinematics equations which can characterize its motion characteristics are derived. Kinematics analysis and simulation are carried out, and the motion law of the corresponding mechanical system is obtained. By analyzing the force and motion of blade of VEVT, the expressions of the important parameters such as deflection angle, attack angle and energy utilization coefficient are obtained. The lateral induced velocity coefficient is acquired by momentum theorem, the hydrodynamic parameters such as energy utilization coefficient are derived, and the hydrodynamic characteristics of VEVT are also obtained. The experimental results show that the turbine has good energy capture capability at different inflow velocities of different sizes and directions, which verifies that VEVT has good self-startup performance and high energy capture efficiency.
A combined experimental and numerical investigation is carried out to study the performance of a vertical-axis eccentric-disc variable-pitch turbine (VEVT). A scheme of eccentric disc pitch control mechanism based on double-block mechanism is proposed. The eccentric control mechanism and the deflection angle control mechanism in the pitch control structure are designed and optimized according to the functional requirements of the turbine, and the three-dimensional model of the turbine is established. Kinematics analysis of the eccentric disc pitch control mechanism is carried out. Kinematics parameters and kinematics equations which can characterize its motion characteristics are derived. Kinematics analysis and simulation are carried out, and the motion law of the corresponding mechanical system is obtained. By analyzing the force and motion of blade of VEVT, the expressions of the important parameters such as deflection angle, attack angle and energy utilization coefficient are obtained. The lateral induced velocity coefficient is acquired by momentum theorem, the hydrodynamic parameters such as energy utilization coefficient are derived, and the hydrodynamic characteristics of VEVT are also obtained. The experimental results show that the turbine has good energy capture capability at different inflow velocities of different sizes and directions, which verifies that VEVT has good self-startup performance and high energy capture efficiency.
2020, 34(3): 421-431.
doi: 10.1007/s13344-020-0038-0
Abstract:
In order to clarify the distribution and variation of silt and fluid mud in the Waiganmen shallow section of the 50000-ton intake channel of the Xiangshan Port, and to understand the influence of the channel excavation on the surrounding flow conditions and the strength of the backsilting, especially the impact of typhoon on the sudden silting of the channel, so as to demonstrate the feasibility and stability of the channel excavation. The fluid mud, hydraulic, sediment and topographic measurements were carried out in the study area, and the thickness of the fluid mud layers, tidal current, sediment and topographic data were obtained. Dual-frequency sounder, gamma-ray densitometer and SILAS navigational fluid mud measurement system were used to monitor the fluid mud, and the results were compared and verified. The adaptability and accuracy of the three methods were analyzed. The SILAS navigational continuous density measurement system and gamma-ray fixed-point fluid mud measurement are used to detect the density, thickness and variation of the fluid mud accurately. Based on the hydrological observation data, the process of erosion and deposition in excavation channel and its influence mechanism are analyzed, and the distribution characteristics and evolution law of siltation in engineering area are given in the form of empirical formula. The research shows that the super typhoon can produce large siltation, which results in sudden siltation of the channel. The tidal current is the main dynamic factor of the change of erosion and siltation of the excavation trench. Under the influence of reciprocating tidal current and excavation topography, the trial excavation trench is silted on the whole. There is fluid mud in the monitoring area of the trench, and the distribution of fluid mud is different in space. The thickness of the fluid mud at the bottom of the trench is generally larger than that outside the trench and the slope of the trench, and the siltation of the trench tends to be slow. The research results can provide scientific evaluation for channel excavation and maintenance, and support for the implementation of the project.
In order to clarify the distribution and variation of silt and fluid mud in the Waiganmen shallow section of the 50000-ton intake channel of the Xiangshan Port, and to understand the influence of the channel excavation on the surrounding flow conditions and the strength of the backsilting, especially the impact of typhoon on the sudden silting of the channel, so as to demonstrate the feasibility and stability of the channel excavation. The fluid mud, hydraulic, sediment and topographic measurements were carried out in the study area, and the thickness of the fluid mud layers, tidal current, sediment and topographic data were obtained. Dual-frequency sounder, gamma-ray densitometer and SILAS navigational fluid mud measurement system were used to monitor the fluid mud, and the results were compared and verified. The adaptability and accuracy of the three methods were analyzed. The SILAS navigational continuous density measurement system and gamma-ray fixed-point fluid mud measurement are used to detect the density, thickness and variation of the fluid mud accurately. Based on the hydrological observation data, the process of erosion and deposition in excavation channel and its influence mechanism are analyzed, and the distribution characteristics and evolution law of siltation in engineering area are given in the form of empirical formula. The research shows that the super typhoon can produce large siltation, which results in sudden siltation of the channel. The tidal current is the main dynamic factor of the change of erosion and siltation of the excavation trench. Under the influence of reciprocating tidal current and excavation topography, the trial excavation trench is silted on the whole. There is fluid mud in the monitoring area of the trench, and the distribution of fluid mud is different in space. The thickness of the fluid mud at the bottom of the trench is generally larger than that outside the trench and the slope of the trench, and the siltation of the trench tends to be slow. The research results can provide scientific evaluation for channel excavation and maintenance, and support for the implementation of the project.
2020, 34(3): 432-440.
doi: 10.1007/s13344-020-0039-z
Abstract:
In this paper, a method about the water-entry slamming of a two-dimensional (2D) bow structure has been proposed based on the experimental and simulation results. According to this method, the sensitivity analysis has been carried out about the effect of speed and inclination angle on the slamming pressure of the bow. Firstly, a 2D ship bow experimental model was performed to obtain the slamming pressure distribution at different measuring points under different speeds. Then, numerical simulation for the water-entry slamming of this experimental model was conducted to obtain the pressure distribution on the experimental model under different working conditions. Finally, the experimental results were compared with the numerical simulation results to evaluate the effect of speed and inclination angle on the slamming pressure of the bow. The results show that the slamming pressure is more sensitive to speed variation within the low-speed range. The effect of inclination angle on the slamming pressure is more obvious in the small angle condition. When the inclination angle is larger than 45°, the effect is limited.
In this paper, a method about the water-entry slamming of a two-dimensional (2D) bow structure has been proposed based on the experimental and simulation results. According to this method, the sensitivity analysis has been carried out about the effect of speed and inclination angle on the slamming pressure of the bow. Firstly, a 2D ship bow experimental model was performed to obtain the slamming pressure distribution at different measuring points under different speeds. Then, numerical simulation for the water-entry slamming of this experimental model was conducted to obtain the pressure distribution on the experimental model under different working conditions. Finally, the experimental results were compared with the numerical simulation results to evaluate the effect of speed and inclination angle on the slamming pressure of the bow. The results show that the slamming pressure is more sensitive to speed variation within the low-speed range. The effect of inclination angle on the slamming pressure is more obvious in the small angle condition. When the inclination angle is larger than 45°, the effect is limited.
2020, 34(3): 441-449.
doi: 10.1007/s13344-020-0040-6
Abstract:
Modified suction caissons (MSCs) acting as offshore wind turbine foundations will generate the accumulated rotation under cyclic loading resulted from waves. The accumulated rotation and the range of soil deformation around the MSC under long-term cyclic wave loading were studied using 3-D numerical simulations. The Morison equation was adopted to calculate the wave loadings. It was found that the MSC accumulated rotation increases linearly with the increase of the logarithm of cyclic number. The normalized expression was proposed to reflect the relationship between the accumulated rotation and cyclic number. The soil deformation range around the MSC increases when increasing the cyclic number and loading amplitude. It can also be concluded that the accumulated rotation increases rapidly with this change of excess pore pressure in the first 4000 cycles. The responses of the MSC to wave and wind loads were also investigated. Results show that the accumulated rotation of the MSC under both wave and wind loadings is larger than that under the wave loading only.
Modified suction caissons (MSCs) acting as offshore wind turbine foundations will generate the accumulated rotation under cyclic loading resulted from waves. The accumulated rotation and the range of soil deformation around the MSC under long-term cyclic wave loading were studied using 3-D numerical simulations. The Morison equation was adopted to calculate the wave loadings. It was found that the MSC accumulated rotation increases linearly with the increase of the logarithm of cyclic number. The normalized expression was proposed to reflect the relationship between the accumulated rotation and cyclic number. The soil deformation range around the MSC increases when increasing the cyclic number and loading amplitude. It can also be concluded that the accumulated rotation increases rapidly with this change of excess pore pressure in the first 4000 cycles. The responses of the MSC to wave and wind loads were also investigated. Results show that the accumulated rotation of the MSC under both wave and wind loadings is larger than that under the wave loading only.
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