2023 Vol.37(6)
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2023, 37(6): 885-896.
doi: 10.1007/s13344-023-0074-7
Abstract:
Serious ice accumulating, pile-up and ice jamming occur around the conductor array of offshore jacket platforms during the winter every year in Bohai Sea, which could cause grave threats to the stability of platform structure, the safety of people and equipment, and even severer calamity. Therefore, the process of ice accumulation and ice jamming in the jacket platform area needs more concern. This study focuses on ice accumulation and jamming behaviors in the jacket platform conductor area by using a coupled two-dimensional hydro-ice dynamics model. A series of cases are conducted with different flow conditions, such as flow velocity, drifting direction and oscillatory flow. Through the simulation, the ice pile-up process is described and changes in ice-jamming thickness, ice pile-up location and ice pile-up volume are investigated. The differences in ice pile-up in the steady flow and oscillatory flow are analyzed. This study proposes a new approach to simulate the ice jamming process in the jacket platform conductor area, providing a reference for ice management on the platform.
Serious ice accumulating, pile-up and ice jamming occur around the conductor array of offshore jacket platforms during the winter every year in Bohai Sea, which could cause grave threats to the stability of platform structure, the safety of people and equipment, and even severer calamity. Therefore, the process of ice accumulation and ice jamming in the jacket platform area needs more concern. This study focuses on ice accumulation and jamming behaviors in the jacket platform conductor area by using a coupled two-dimensional hydro-ice dynamics model. A series of cases are conducted with different flow conditions, such as flow velocity, drifting direction and oscillatory flow. Through the simulation, the ice pile-up process is described and changes in ice-jamming thickness, ice pile-up location and ice pile-up volume are investigated. The differences in ice pile-up in the steady flow and oscillatory flow are analyzed. This study proposes a new approach to simulate the ice jamming process in the jacket platform conductor area, providing a reference for ice management on the platform.
2023, 37(6): 897-911.
doi: 10.1007/s13344-023-0075-6
Abstract:
In this work, a novel fluid?structure coupling method called the common node discrete element-smoothed particle hydrodynamics (DS-SPH) method is introduced. This framework combines the principles of the common node discrete element method (DEM) and smoothed particle hydrodynamics (SPH) to construct DEM-SPH particles situated on the same node. By doing so, the DEM particles can interact with the SPH particles within their support domain, enabling fluid-structure interaction (FSI). To determine the DEM microscopic parameters required for this method, uniaxial compression and three-point bending tests are conducted on sea ice. To verify the proposed model, we select the interaction between sea ice and structures as a case study. Through simulation, the model’s capability of accurately depicting sea ice deformation and fracture has been demonstrated. The results indicate that the inclusion of SPH particles with fluid properties in the DEM model has minimal impact on the main mechanical parameters of sea ice. Additionally, it helps prevent the occurrence of particle splashing during cement failure. However, it is observed that the size of DEM particles and the friction between DEM particles and the structure significantly influence the macroscopic mechanical behavior of the common-node DEM-SPH model. Finally, we compare the fracture behavior of sea ice and the ice forces acting on structures obtained from the current model with on-site measured results. The agreement between the two sets of data is excellent, further validating the effectiveness of the proposed model in practical applications.
In this work, a novel fluid?structure coupling method called the common node discrete element-smoothed particle hydrodynamics (DS-SPH) method is introduced. This framework combines the principles of the common node discrete element method (DEM) and smoothed particle hydrodynamics (SPH) to construct DEM-SPH particles situated on the same node. By doing so, the DEM particles can interact with the SPH particles within their support domain, enabling fluid-structure interaction (FSI). To determine the DEM microscopic parameters required for this method, uniaxial compression and three-point bending tests are conducted on sea ice. To verify the proposed model, we select the interaction between sea ice and structures as a case study. Through simulation, the model’s capability of accurately depicting sea ice deformation and fracture has been demonstrated. The results indicate that the inclusion of SPH particles with fluid properties in the DEM model has minimal impact on the main mechanical parameters of sea ice. Additionally, it helps prevent the occurrence of particle splashing during cement failure. However, it is observed that the size of DEM particles and the friction between DEM particles and the structure significantly influence the macroscopic mechanical behavior of the common-node DEM-SPH model. Finally, we compare the fracture behavior of sea ice and the ice forces acting on structures obtained from the current model with on-site measured results. The agreement between the two sets of data is excellent, further validating the effectiveness of the proposed model in practical applications.
2023, 37(6): 912-922.
doi: 10.1007/s13344-023-0076-5
Abstract:
The estimation of ship speed in ice ridge fields is important for both route planning and prediction of emergency response time. An analytical method for estimating ship motion in first-year ice ridge is developed based on ice resistance models and ship motion equations, in which the effect of ship speed on ridge resistance is taken into account. Two model tests in level ice and one model test in ice ridge for an icebreaking multipurpose vessel are used to validate and benchmark the presented method. The predicted results including level ice resistances, net thrust and ship motion in the ice ridge field are compared with the model test data. The comparisons show that the presented method can generate reasonable results. The effects of input parameters on ship speed, penetration depth and number of necessary rams to transit ridge have been studied. Based on the calibrated model, insights into the ice resistance and the ship motion are obtained. It is found that the energy consumption of the keel obtained by integral calculation of the keel resistance at the penetration distance is with the same magnitude as the result of the maximum keel resistance multiplied by the ridge length. In addition, the effect of ridge width and keel depth on keel resistance and average transit speed is investigated.
The estimation of ship speed in ice ridge fields is important for both route planning and prediction of emergency response time. An analytical method for estimating ship motion in first-year ice ridge is developed based on ice resistance models and ship motion equations, in which the effect of ship speed on ridge resistance is taken into account. Two model tests in level ice and one model test in ice ridge for an icebreaking multipurpose vessel are used to validate and benchmark the presented method. The predicted results including level ice resistances, net thrust and ship motion in the ice ridge field are compared with the model test data. The comparisons show that the presented method can generate reasonable results. The effects of input parameters on ship speed, penetration depth and number of necessary rams to transit ridge have been studied. Based on the calibrated model, insights into the ice resistance and the ship motion are obtained. It is found that the energy consumption of the keel obtained by integral calculation of the keel resistance at the penetration distance is with the same magnitude as the result of the maximum keel resistance multiplied by the ridge length. In addition, the effect of ridge width and keel depth on keel resistance and average transit speed is investigated.
2023, 37(6): 923-933.
doi: 10.1007/s13344-023-0077-4
Abstract:
Combining wave energy converters (WECs) with floating offshore wind turbines proves a potential strategy to achieve better use of marine renewable energy. The full coupling investigation on the dynamic and power generation features of the hybrid systems under operational sea states is necessary but limited by numerical simulation tools. Here an aero-hydro-servo-elastic coupling numerical tool is developed and applied to investigate the motion, mooring tension, and energy conversion performance of a hybrid system consisting of a spar-type floating wind turbine and an annular wave energy converter. Results show that the addition of the WEC has no significant negative effect on the dynamic performance of the platform and even enhances the rotational stability of the platform. For surge and pitch motion, the peak of the spectra is originated from the dominating wave component, whereas for the heave motion, the peak of the spectrum is the superposed effect of the dominating wave component and the resonance of the system. The addition of the annular WEC can slightly improve the wind power by making the rotor to be in a better position to face the incoming wind and provide considerable wave energy production, which can compensate for the downtime of the offshore wind.
Combining wave energy converters (WECs) with floating offshore wind turbines proves a potential strategy to achieve better use of marine renewable energy. The full coupling investigation on the dynamic and power generation features of the hybrid systems under operational sea states is necessary but limited by numerical simulation tools. Here an aero-hydro-servo-elastic coupling numerical tool is developed and applied to investigate the motion, mooring tension, and energy conversion performance of a hybrid system consisting of a spar-type floating wind turbine and an annular wave energy converter. Results show that the addition of the WEC has no significant negative effect on the dynamic performance of the platform and even enhances the rotational stability of the platform. For surge and pitch motion, the peak of the spectra is originated from the dominating wave component, whereas for the heave motion, the peak of the spectrum is the superposed effect of the dominating wave component and the resonance of the system. The addition of the annular WEC can slightly improve the wind power by making the rotor to be in a better position to face the incoming wind and provide considerable wave energy production, which can compensate for the downtime of the offshore wind.
2023, 37(6): 934-947.
doi: 10.1007/s13344-023-0078-3
Abstract:
To obtain the interaction characteristics between Internal solitary waves (ISWs) and submerged bodies, a three-dimensional numerical model for simulating ISWs was established in the present study based on the RANS equation. The velocity entrance method was adopted to generate the ISWs. First, the reliability of this numerical model was validated by comparing it with theoretical and literature results. Then, the influence of environmental and navigation parameters on interactions between ISWs and a fixed SUBOFF-submerged body was studied. According to research, the hydrodynamic performance of the submerged body has been significantly impacted by the ISWs when the body is nearing the central region of the wave. Besides, the pitching moment (y') will predominate when the body encounters the ISWs at a certain angle between 0° and 180°, and the lateral force is larger than the horizontal force. Additionally, the magnitude of the force acting on the body is mostly affected by the wave amplitude. The variation of the vertical force is the main way that ISWs affect the hydrodynamic performance of the bodies. The investigations and findings discussed above can serve as a guide to forecast how ISWs will interact with submerged bodies.
To obtain the interaction characteristics between Internal solitary waves (ISWs) and submerged bodies, a three-dimensional numerical model for simulating ISWs was established in the present study based on the RANS equation. The velocity entrance method was adopted to generate the ISWs. First, the reliability of this numerical model was validated by comparing it with theoretical and literature results. Then, the influence of environmental and navigation parameters on interactions between ISWs and a fixed SUBOFF-submerged body was studied. According to research, the hydrodynamic performance of the submerged body has been significantly impacted by the ISWs when the body is nearing the central region of the wave. Besides, the pitching moment (y') will predominate when the body encounters the ISWs at a certain angle between 0° and 180°, and the lateral force is larger than the horizontal force. Additionally, the magnitude of the force acting on the body is mostly affected by the wave amplitude. The variation of the vertical force is the main way that ISWs affect the hydrodynamic performance of the bodies. The investigations and findings discussed above can serve as a guide to forecast how ISWs will interact with submerged bodies.
2023, 37(6): 948-961.
doi: 10.1007/s13344-023-0079-2
Abstract:
Three-dimensional direct numerical simulations of the wake flow downstream of a near-wall circular cylinder at different gap ratios and boundary layer thicknesses are carried out by using the iterative immersed boundary method. The non-dimensional gap between the cylinder and the wall, G/D = 0.2, 0.6 and 1.0, the non-dimensional boundary layer thickness, δ/D = 0.0, 0.7 and 1.6, the Reynolds number, Re=350, and the aspect ratio of the cylinder, L/D = 25 are adopted. High-resolution visualizations of the complex vortex structures at different δ/D and G/D are presented. The transition of the streamwise vortex mode, the combined effects of δ/D and G/D on the flow statistics, the pressure and shear stress distribution and the hydrodynamic forces are analyzed. Results show that with decreasing G/D and increasing δ/D, the gap flow and its vortex-shedding are significantly weakened, together with an elongated wake and an enlarged low-velocity area near the wall, leading to the wake mode transition from the two-sided to one-sided vortex-shedding. Different relative positions of the cylinder regarding the boundary layer alter the flow features of the shear layers. With an increase in δ/D, the front stagnation point shifts to the upper surface, and the distance between the flow divergence point and the maximum pressure position increases. The mean drag coefficient and r.m.s. values of drag and lift coefficients decrease with a decrease in G/D and an increase in δ/D, while the mean lift coefficient increases with decreasing G/D but decreases with increasing δ/D.
Three-dimensional direct numerical simulations of the wake flow downstream of a near-wall circular cylinder at different gap ratios and boundary layer thicknesses are carried out by using the iterative immersed boundary method. The non-dimensional gap between the cylinder and the wall, G/D = 0.2, 0.6 and 1.0, the non-dimensional boundary layer thickness, δ/D = 0.0, 0.7 and 1.6, the Reynolds number, Re=350, and the aspect ratio of the cylinder, L/D = 25 are adopted. High-resolution visualizations of the complex vortex structures at different δ/D and G/D are presented. The transition of the streamwise vortex mode, the combined effects of δ/D and G/D on the flow statistics, the pressure and shear stress distribution and the hydrodynamic forces are analyzed. Results show that with decreasing G/D and increasing δ/D, the gap flow and its vortex-shedding are significantly weakened, together with an elongated wake and an enlarged low-velocity area near the wall, leading to the wake mode transition from the two-sided to one-sided vortex-shedding. Different relative positions of the cylinder regarding the boundary layer alter the flow features of the shear layers. With an increase in δ/D, the front stagnation point shifts to the upper surface, and the distance between the flow divergence point and the maximum pressure position increases. The mean drag coefficient and r.m.s. values of drag and lift coefficients decrease with a decrease in G/D and an increase in δ/D, while the mean lift coefficient increases with decreasing G/D but decreases with increasing δ/D.
2023, 37(6): 962-974.
doi: 10.1007/s13344-023-0080-9
Abstract:
The resonant motion of the fluid inside a narrow gap between two fixed boxes induced by incident regular waves with various wave heights is investigated by adopting a two-dimensional numerical wave flume based on an open-sourced CFD package, OpenFOAM. The two boxes have identical draft and height, but the upstream box has a variable breadth. This article focuses on the influences of the breadth ratio, defined as the ratio of the breadth of the upstream box to that of the downstream box, on the following three aspects of hydrodynamic characteristics of gap resonance: (1) the wave height amplifications inside the gap, and in front and at the rear of the structure system, (2) the reflection, transmission, and energy loss coefficients of the structure system, and (3) the response and damping time of the fluid resonance. It is found that the fluid resonant frequency, the amplification factor of the resonant wave height inside the gap and the maximum energy loss coefficient of the structure system are shown to gradually decrease with the increase of the breadth ratio. The response time of gap resonance is shown to first increase and then decrease with the breadth ratio overall, regardless of the incident wave height, and the configuration that the two boxes have the same breadth would bring the largest response time of gap resonance.
The resonant motion of the fluid inside a narrow gap between two fixed boxes induced by incident regular waves with various wave heights is investigated by adopting a two-dimensional numerical wave flume based on an open-sourced CFD package, OpenFOAM. The two boxes have identical draft and height, but the upstream box has a variable breadth. This article focuses on the influences of the breadth ratio, defined as the ratio of the breadth of the upstream box to that of the downstream box, on the following three aspects of hydrodynamic characteristics of gap resonance: (1) the wave height amplifications inside the gap, and in front and at the rear of the structure system, (2) the reflection, transmission, and energy loss coefficients of the structure system, and (3) the response and damping time of the fluid resonance. It is found that the fluid resonant frequency, the amplification factor of the resonant wave height inside the gap and the maximum energy loss coefficient of the structure system are shown to gradually decrease with the increase of the breadth ratio. The response time of gap resonance is shown to first increase and then decrease with the breadth ratio overall, regardless of the incident wave height, and the configuration that the two boxes have the same breadth would bring the largest response time of gap resonance.
2023, 37(6): 975-988.
doi: 10.1007/s13344-023-0081-8
Abstract:
In the process of developing offshore wind power towards deeper waters, the advantages of the bucket foundation in terms of integrated construction and economy are becoming increasingly evident. In contrast to conventional floating bodies, the air-floating bucket foundations can achieve self-floating with the help of the air in the compartment and adjust its buoyancy and stability by controlling the air volume in the compartment. The construction process of the bucket foundation involves the control of air in the compartment, thus making it more difficult to construct. Especially after the prefabrication of the bucket foundation, the stability of the bucket foundation at the floating-up stage is particularly critical. The stability of a multi-compartment bucket foundation during the floating-up process cannot be accurately evaluated as the existing theoretical method of air-floating structures does not adequately consider air compressibility. To ensure the safety of the floating-up process, a theoretical method based on the idea of intact stability has been developed to analyze the stability of the air-floating bucket foundations, which will allow accurate calculation of the righting arm for different tilt states and critical air leakage angle. At the same time, accuracy and feasibility of the proposed theoretical method are verified through indoor model tests and practical operation of the prototype structure during the floating-up process. In addition, measures to enhance the stability of the bucket foundation are proposed through sensitivity analysis of influencing factors.
In the process of developing offshore wind power towards deeper waters, the advantages of the bucket foundation in terms of integrated construction and economy are becoming increasingly evident. In contrast to conventional floating bodies, the air-floating bucket foundations can achieve self-floating with the help of the air in the compartment and adjust its buoyancy and stability by controlling the air volume in the compartment. The construction process of the bucket foundation involves the control of air in the compartment, thus making it more difficult to construct. Especially after the prefabrication of the bucket foundation, the stability of the bucket foundation at the floating-up stage is particularly critical. The stability of a multi-compartment bucket foundation during the floating-up process cannot be accurately evaluated as the existing theoretical method of air-floating structures does not adequately consider air compressibility. To ensure the safety of the floating-up process, a theoretical method based on the idea of intact stability has been developed to analyze the stability of the air-floating bucket foundations, which will allow accurate calculation of the righting arm for different tilt states and critical air leakage angle. At the same time, accuracy and feasibility of the proposed theoretical method are verified through indoor model tests and practical operation of the prototype structure during the floating-up process. In addition, measures to enhance the stability of the bucket foundation are proposed through sensitivity analysis of influencing factors.
2023, 37(6): 989-999.
doi: 10.1007/s13344-023-0082-7
Abstract:
Suction caissons are widely used for anchoring floating platform and offshore wind turbines. Penetration of the suction caisson into the desired position under the combination of its self-weight and applied suction resulted from pumping out the encased water is integral to practical engineering. Model tests were carried out to investigate the suction-assisted installation of suction caissons in clay under various undrained shear strengths. It was found that there exists a critical penetration depth value. When the penetration depth is smaller than the critical value, the soil plug undrained shear strength is higher than intact clay (i.e., clay prior to installation). However, when the penetration depth is greater than the critical penetration depth, the undrained shear strength of soil plug is lower than intact clay. The critical value decreases with the increasing consolidation time and undrained shear strength of clay. During suction-assisted installation, cracks occur around suction caissons. The installation way has little effect on the crack formation. The influence range (i.e., the maximum distance between the crack and the suction caisson edge) was found to increase with the increasing friction coefficient of interface between the suction caisson wall and soil and decreases with the increasing soil undrained shear strength. In addition, the drained condition of the clay during installation is dominated by the caisson aspect ratio, the undrained shear strength and the friction coefficient between the caisson wall and clay. Equations to estimate the penetration resistance and the required suction to install the suction caisson are summarized.
Suction caissons are widely used for anchoring floating platform and offshore wind turbines. Penetration of the suction caisson into the desired position under the combination of its self-weight and applied suction resulted from pumping out the encased water is integral to practical engineering. Model tests were carried out to investigate the suction-assisted installation of suction caissons in clay under various undrained shear strengths. It was found that there exists a critical penetration depth value. When the penetration depth is smaller than the critical value, the soil plug undrained shear strength is higher than intact clay (i.e., clay prior to installation). However, when the penetration depth is greater than the critical penetration depth, the undrained shear strength of soil plug is lower than intact clay. The critical value decreases with the increasing consolidation time and undrained shear strength of clay. During suction-assisted installation, cracks occur around suction caissons. The installation way has little effect on the crack formation. The influence range (i.e., the maximum distance between the crack and the suction caisson edge) was found to increase with the increasing friction coefficient of interface between the suction caisson wall and soil and decreases with the increasing soil undrained shear strength. In addition, the drained condition of the clay during installation is dominated by the caisson aspect ratio, the undrained shear strength and the friction coefficient between the caisson wall and clay. Equations to estimate the penetration resistance and the required suction to install the suction caisson are summarized.
2023, 37(6): 1000-1010.
doi: 10.1007/s13344-023-0083-6
Abstract:
Helical anchor is a kind of novel foundation for floating offshore wind turbines, which should be subjected to combined tensile loading caused by wind, wave and current. However, the research about the capacity of helical anchor was mainly examined under uniaxial loading and scarcely explored under combined loading. In this study, three-dimensional finite element limit analysis is adopted to assess the bearing capacities of single-plate rigid helical anchors with different ratios of helix to shaft diameter, DH/DS and embedment ratios L/DS. Result shows that the vertical, horizontal and moment bearing capacities increase with increasing DH/DS and L/DS. The normalized V-H failure envelopes expands with increasing L/DS, while the normalized V?M failure envelopes tend to contract with the increase of DH/DS. With increasing DH/DS or decreasing L/DS, the normalized H-M failure envelopes expand when the horizontal and moment loading act in the same direction and contract when they act in the opposite direction. The effect of DH/DS and L/DS on the shape of H?M failure envelope become insignificant when L/DS ≥ 4. A series of failure mechanisms under different loading conditions were observed and can be used to explain the trend. Besides, a series of approximate expressions were proposed to fit the uniaxial bearing capacities and the failure envelopes.
Helical anchor is a kind of novel foundation for floating offshore wind turbines, which should be subjected to combined tensile loading caused by wind, wave and current. However, the research about the capacity of helical anchor was mainly examined under uniaxial loading and scarcely explored under combined loading. In this study, three-dimensional finite element limit analysis is adopted to assess the bearing capacities of single-plate rigid helical anchors with different ratios of helix to shaft diameter, DH/DS and embedment ratios L/DS. Result shows that the vertical, horizontal and moment bearing capacities increase with increasing DH/DS and L/DS. The normalized V-H failure envelopes expands with increasing L/DS, while the normalized V?M failure envelopes tend to contract with the increase of DH/DS. With increasing DH/DS or decreasing L/DS, the normalized H-M failure envelopes expand when the horizontal and moment loading act in the same direction and contract when they act in the opposite direction. The effect of DH/DS and L/DS on the shape of H?M failure envelope become insignificant when L/DS ≥ 4. A series of failure mechanisms under different loading conditions were observed and can be used to explain the trend. Besides, a series of approximate expressions were proposed to fit the uniaxial bearing capacities and the failure envelopes.
2023, 37(6): 1011-1021.
doi: 10.1007/s13344-023-0084-5
Abstract:
Compared with the traditional wind turbine of a single rotor, dual-rotor wind turbines (DRWTs) have higher wind energy capture efficiency and a more complex structure. Therefore, the aerodynamic performance of the DRWT installed on the floating platform will be greatly affected by the motion caused by wind and wave loads. In this paper, 5 MW and 750 kW single rotor wind turbines (SRWTs) are combined into a 5 MW-5 MW DRWT and a 5 MW-750 kW DRWT, and their power output and wake field characteristics in different motions are studied. The flow field is obtained by solving the Reynolds-averaged Navier–Stokes equation (RANS). The overset grid technique is employed to achieve the large-amplitude multiple-degree-of-freedom motion of the DRWT. The overall performance of the 5 MW single rotor wind turbine is determined by a numerical method. For the DRWTs, numerical results show that the surge motion and heave motion both have a negative effect on the power output of the DRWT. The surge motion is a critical factor that causes the power output of the DRWT to periodically change with motion. The average power output of the DRWT influenced by motion is lower than that of a DRWT with a fixed bottom. The surge motion significantly disturbs the wake of the DRWT due to the mutual interference between the upstream and downstream rotors. Under the influence of heave motion, low-velocity regions downstream of the blade tip are enhanced. This study indicates that attenuating the surge and heave motion of offshore DRWT is very significant for improving its efficiency and should be taken into consideration during the design procedure.
Compared with the traditional wind turbine of a single rotor, dual-rotor wind turbines (DRWTs) have higher wind energy capture efficiency and a more complex structure. Therefore, the aerodynamic performance of the DRWT installed on the floating platform will be greatly affected by the motion caused by wind and wave loads. In this paper, 5 MW and 750 kW single rotor wind turbines (SRWTs) are combined into a 5 MW-5 MW DRWT and a 5 MW-750 kW DRWT, and their power output and wake field characteristics in different motions are studied. The flow field is obtained by solving the Reynolds-averaged Navier–Stokes equation (RANS). The overset grid technique is employed to achieve the large-amplitude multiple-degree-of-freedom motion of the DRWT. The overall performance of the 5 MW single rotor wind turbine is determined by a numerical method. For the DRWTs, numerical results show that the surge motion and heave motion both have a negative effect on the power output of the DRWT. The surge motion is a critical factor that causes the power output of the DRWT to periodically change with motion. The average power output of the DRWT influenced by motion is lower than that of a DRWT with a fixed bottom. The surge motion significantly disturbs the wake of the DRWT due to the mutual interference between the upstream and downstream rotors. Under the influence of heave motion, low-velocity regions downstream of the blade tip are enhanced. This study indicates that attenuating the surge and heave motion of offshore DRWT is very significant for improving its efficiency and should be taken into consideration during the design procedure.
2023, 37(6): 1022-1031.
doi: 10.1007/s13344-023-0085-4
Abstract:
During ship operations, frequent heave movements can pose significant challenges to the overall safety of the ship and completion of cargo loading. The existing heave compensation systems suffer from issues such as dead zones and control system time lags, which necessitate the development of reasonable prediction models for ship heave movements. In this paper, a novel model based on a time graph convolutional neural network algorithm and particle swarm optimization algorithm (PSO-TGCN) is proposed for the first time to predict the multipoint heave movements of ships under different sea conditions. To enhance the dataset’s suitability for training and reduce interference, various filter algorithms are employed to optimize the dataset. The training process utilizes simulated heave data under different sea conditions and measured heave data from multiple points. The results show that the PSO-TGCN model predicts the ship swaying motion in different sea states after 2 s with 84.7% accuracy, while predicting the swaying motion in three different positions. By performing a comparative study, it was also found that the present method achieves better performance that other popular methods. This model can provide technical support for intelligent ship control, improve the control accuracy of intelligent ships, and promote the development of intelligent ships.
During ship operations, frequent heave movements can pose significant challenges to the overall safety of the ship and completion of cargo loading. The existing heave compensation systems suffer from issues such as dead zones and control system time lags, which necessitate the development of reasonable prediction models for ship heave movements. In this paper, a novel model based on a time graph convolutional neural network algorithm and particle swarm optimization algorithm (PSO-TGCN) is proposed for the first time to predict the multipoint heave movements of ships under different sea conditions. To enhance the dataset’s suitability for training and reduce interference, various filter algorithms are employed to optimize the dataset. The training process utilizes simulated heave data under different sea conditions and measured heave data from multiple points. The results show that the PSO-TGCN model predicts the ship swaying motion in different sea states after 2 s with 84.7% accuracy, while predicting the swaying motion in three different positions. By performing a comparative study, it was also found that the present method achieves better performance that other popular methods. This model can provide technical support for intelligent ship control, improve the control accuracy of intelligent ships, and promote the development of intelligent ships.
2023, 37(6): 1032-1043.
doi: 10.1007/s13344-023-0086-3
Abstract:
The monopile is the most common foundation to support offshore wind turbines. In the marine environment, local scour due to combined currents and waves is a significant issue that must be considered in the design of wind turbine foundations. In this paper, a full-scale numerical model was developed and validated based on field data from Rudong, China. The scour development around monopiles was investigated, and the effects of waves and the Reynolds number Re were analyzed. Several formulas for predicting the scour depth in the literature have been evaluated. It is found that waves can accelerate scour development even if the KC number is small (0.78<KC<1.57). The formula obtained from small-scale model tests may be unsafe or wasteful when it is applied in practical design due to the scale effect. A new equation for predicting the scour depth based on the average pile Reynolds number (Rea) is proposed and validated with field data. The equilibrium scour depth predicted using the proposed equation is evaluated and compared with those from nine equations in the literature. It is demonstrated that the values predicted from the proposed equation and from the S/M (Sheppard/Melville) equation are closer to the field data.
The monopile is the most common foundation to support offshore wind turbines. In the marine environment, local scour due to combined currents and waves is a significant issue that must be considered in the design of wind turbine foundations. In this paper, a full-scale numerical model was developed and validated based on field data from Rudong, China. The scour development around monopiles was investigated, and the effects of waves and the Reynolds number Re were analyzed. Several formulas for predicting the scour depth in the literature have been evaluated. It is found that waves can accelerate scour development even if the KC number is small (0.78<KC<1.57). The formula obtained from small-scale model tests may be unsafe or wasteful when it is applied in practical design due to the scale effect. A new equation for predicting the scour depth based on the average pile Reynolds number (Rea) is proposed and validated with field data. The equilibrium scour depth predicted using the proposed equation is evaluated and compared with those from nine equations in the literature. It is demonstrated that the values predicted from the proposed equation and from the S/M (Sheppard/Melville) equation are closer to the field data.
2023, 37(6): 1044-1054.
doi: 10.1007/s13344-023-0087-2
Abstract:
Many offshore marine structures are built on the seabed that are slightly or considerably sloping. To study the sloping seabed transient response during marine earthquakes, an analytical solution induced by a P-wave line source embedded in the solid is presented. During the derivation, the wave fields in the fluid layer and the semi-infinite solid are firstly constructed by using the generalized ray method and the fluid?solid interface reflection and transmission coefficients. Then, the analytical solution in the transformed domain is obtained by superposing these wave fields, and the analytical solution in the time domain by applying the analytical inverse Laplace transform method. The the head wave generation conditions and arrival times at the fluid?solid interface are derived through this solution. Through the use of numerical examples, the analytical solution is proved right and the impacts of the sloping angle on the hydrodynamic pressure in the sea, the seismic wave propagation in the seabed, the head wave, and the Scholte wave at the seawater-seabed interface are also addressed.
Many offshore marine structures are built on the seabed that are slightly or considerably sloping. To study the sloping seabed transient response during marine earthquakes, an analytical solution induced by a P-wave line source embedded in the solid is presented. During the derivation, the wave fields in the fluid layer and the semi-infinite solid are firstly constructed by using the generalized ray method and the fluid?solid interface reflection and transmission coefficients. Then, the analytical solution in the transformed domain is obtained by superposing these wave fields, and the analytical solution in the time domain by applying the analytical inverse Laplace transform method. The the head wave generation conditions and arrival times at the fluid?solid interface are derived through this solution. Through the use of numerical examples, the analytical solution is proved right and the impacts of the sloping angle on the hydrodynamic pressure in the sea, the seismic wave propagation in the seabed, the head wave, and the Scholte wave at the seawater-seabed interface are also addressed.
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