[Objective]This study aims to investigate the multi-body hydrodynamic interaction mechanisms during offshore lifting operations of aquaculture net cages in wind-fishery integration systems.By integrating numerical sim...[Objective]This study aims to investigate the multi-body hydrodynamic interaction mechanisms during offshore lifting operations of aquaculture net cages in wind-fishery integration systems.By integrating numerical simulations and dynamic analysis methods,this study systematically investigates the coupled dynamic response characteristics during the cage-carrier vessel separation process to reveal its dynamic evolution patterns and key influence mechanisms.[Method]Based on potential flow theory,a fully coupled dynamic analysis model of crane vessel-net cage-semi-submersible barge was established for a marine ranch project in Guangdong.The complete lifting process was dynamically simulated using SESAM software.Five typical operating sea states were configured to investigate the influence of wave parameters on the system's motion response under combined wave-current-wind actions.[Result]The results demonstrate that wave period dominates the system stability.Under short-period conditions,the system maintains stable motion with relatively small horizontal relative displacements,while long-period conditions excite low-frequency resonance,leading to significant slow-drift motions.Vertical response analysis reveals that long-period waves cause severe relative displacement fluctuations between the cage and semi-submersible vessel,with actual displacement amplitudes doubling the preset safety target of 2.045 m.Quantitative analysis further indicates that when significant wave height increases from 1.0 m to 1.5 m,the actual displacement amplitude increases by approximately 20%relative to the target displacement of 2.045 m,demonstrating that its influence is significantly weaker than the displacement variations induced by wave period changes.The complete dynamic simulation successfully captures the continuous dynamic response characteristics during the lifting process.[Conclusion]This research clarifies the influence mechanisms of wave parameters on the cage lifting process,identifying wave period as the crucial factor for operational safety.An operation window assessment method incorporating multi-body coupling effects is established,proposing a safety criterion with peak period not exceeding six seconds as the core requirement.The findings provide theoretical foundation for safe installation of marine ranch net cages and offer valuable references for similar offshore lifting operations.展开更多
This study presents an effective hybrid simulation approach for simulating broadband ground motion in complex near-fault locations.The approach utilizes a deterministic approach based on the spectral element method(SE...This study presents an effective hybrid simulation approach for simulating broadband ground motion in complex near-fault locations.The approach utilizes a deterministic approach based on the spectral element method(SEM),which is used to simulate low-frequency ground motion(f<1 Hz)by incorporating an innovative efficient discontinuous Galerkin(DG)method for grid division to accurately model basin sedimentary layers at reduced costs.It also introduces a comprehensive hybrid source model for high-frequency random scattering and a nonlinear analysis module for basin sedimentary layers.Deterministic outcomes are combined with modified three-dimensional stochastic finite fault method(3D-EXSIM)simulations of high-frequency ground motion(f>1 Hz).A fourth-order Butterworth filter with zero phase shift is employed for time-domain filtering of low-and high-frequency time series at a crossover frequency of 1 Hz,merging the low and high-frequency ground motions into a broadband time series.Taking an Ms 6.8 Luding earthquake,as an example,this hybrid method was used for a rapid and efficient simulation analysis of broadband ground motion in the region.The accuracy and efficiency of this hybrid method were verified through comparisons with actually observed station data and empirical attenuation curves.Deterministic method simulation results revealed the effects of mountainous topography,basin effects,nonlinear effects within the basin’s sedimentary layers,and a coupling interaction between the basin and the mountains.The findings are consistent with similar studies,showing that near-fault sedimentary basins significantly focus and amplify strong ground motion,and the soil’s nonlinear behavior in the basin influences ground motion to varying extents at different distances from the fault.The mountainous topography impacts the basin’s response to ground motion,leading to barrier effects.This research provides a scientific foundation for seismic zoning,urban planning,and seismic design in nearfault mountain basin regions.展开更多
This study employed a computational fluid dynamics model with an overset mesh technique to investigate the thrust and power of a floating offshore wind turbine(FOWT)under platform floating motion in the wind–rain fie...This study employed a computational fluid dynamics model with an overset mesh technique to investigate the thrust and power of a floating offshore wind turbine(FOWT)under platform floating motion in the wind–rain field.The impact of rainfall on aerodynamic performance was initially examined using a stationary turbine model in both wind and wind–rain conditions.Subsequently,the study compared the FOWT’s performance under various single degree-of-freedom(DOF)motions,including surge,pitch,heave,and yaw.Finally,the combined effects of wind–rain fields and platform motions involving two DOFs on the FOWT’s aerodynamics were analyzed and compared.The results demonstrate that rain negatively impacts the aerodynamic performance of both the stationary turbines and FOWTs.Pitch-dominated motions,whether involving single or multiple DOFs,caused significant fluctuations in the FOWT aerodynamics.The combination of surge and pitch motions created the most challenging operational environment for the FOWT in all tested scenarios.These findings highlighted the need for stronger construction materials and greater ultimate bearing capacity for FOWTs,as well as the importance of optimizing designs to mitigate excessive pitch and surge.展开更多
This study investigates the effect of nacelle motions on the rotor performance and drivetrain dynamics of floating offshore wind turbines(FOWTs)through fully coupled aero-hydro-elastic-servo-mooring simulations.Using ...This study investigates the effect of nacelle motions on the rotor performance and drivetrain dynamics of floating offshore wind turbines(FOWTs)through fully coupled aero-hydro-elastic-servo-mooring simulations.Using the National Renewable Energy Laboratory 5 MW monopile-supported offshore wind turbine and the OC4 DeepCwind semisubmersible wind turbine as case studies,the research addresses the complex dynamic responses resulting from the interaction among wind,waves,and turbine structures.Detailed multi-body dynamics models of wind turbines,including drivetrain components,are created within the SIMPACK framework.Meanwhile,the mooring system is modeled using a lumped-mass method.Various operational conditions are simulated through five wind-wave load cases.Results demonstrate that nacelle motions significantly influence rotor speed,thrust,torque,and power output,as well as the dynamic loads on drivetrain components.These findings highlight the need for advanced simulation techniques for the design and optimization of FOWTs to ensure reliable performance and longevity.展开更多
Simulating the coupled motions of multiple bodies in the time domain is a complex problem because of the strong hydrodynamic interactions and coupled effect of various mechanical connectors. In this study, we investig...Simulating the coupled motions of multiple bodies in the time domain is a complex problem because of the strong hydrodynamic interactions and coupled effect of various mechanical connectors. In this study, we investigate the hydrodynamic responses of three barges moored side-by-side in a floatover operation in the frequency and time domains. In the frequency domain, the damping lid method is adopted to improve the overestimated hydrodynamic coefficients calculated from conventional potential flow theory. A time-domain computing program based on potential flow theory and impulse theory is compiled for analyses that consider multibody hydrodynamic interactions and mechanical effects from lines and fenders. Correspondingly, an experiment is carried out for comparison with the numerical results. All statistics, time series, and power density spectra from decay and irregular wave tests are in a fairly good agreement.展开更多
Nonlinear interactions among incident wave, tank-sloshing and floating body coupling motion are investigated. The fully nonlinear sloshing and body-surface nonlinear free surface hydrodynamics is simulated using a Non...Nonlinear interactions among incident wave, tank-sloshing and floating body coupling motion are investigated. The fully nonlinear sloshing and body-surface nonlinear free surface hydrodynamics is simulated using a Non-Uniform Rational B-Spline （NURBS） higher-order panel method in time domain based on the potential theory. A robust and stable improved iterative procedure （Yan and Ma, 2007） for floating bodies is used for calculating the time derivative of velocity potential and floating body motion. An energy dissipation condition based on linear theory adopted by Huang （2011） is developed to consider flow viscosity effects of sloshing flow in nonlinear model. A two-dimensional tank model test was performed to identify its validity. The present nonlinear coupling sway motion results are subsequently compared with the corresponding Rognebakke and Faltinsen （2003）＇s experimental results, showing fair agreement. Thus, the numerical approach presented in this paper is expected to be very efficient and realistic in evaluating the coupling effects of nonlinear sloshing and body motion.展开更多
This paper presents the results from a numerical study on the nonlinear dynamic behaviors including bifurcation and chaos of a truss spar platform. In view of the mutual influences between the heave and the pitch mode...This paper presents the results from a numerical study on the nonlinear dynamic behaviors including bifurcation and chaos of a truss spar platform. In view of the mutual influences between the heave and the pitch modes, the coupled heave and pitch motion equations of the spar platform hull were established in the regular waves. In order to analyze the nonlinear motions of the platform, three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs were constructed, the Poincare maps and the power spectrums of the platform response were calculated. It was found that the platform motions are sensitive to wave fre- quency. With changing wave frequency, the platform undergoes complicated nonlinear motions, including 1/2 sub-harmonic motion, quasi-periodic motion and chaotic motion. When the wave frequency approaches the natural frequency of the heave mode of the platform, the platform moves with quasi-periodic motion and chaotic motional temately. For a certain range of wave frequencies, the platform moves with totally chaotic motion. The range of wave frequencies which leads to chaotic motion of the platform increases with increasing wave height. The three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs reveal the nonlinear motions of the spar platform under different wave conditions.展开更多
The production of hydrogen on offshore platform can decrease reliance on the power grid,mitigate transmission losses of electricity,and diminish investment costs for subsea cables.In this study,the hydrodynamic perfor...The production of hydrogen on offshore platform can decrease reliance on the power grid,mitigate transmission losses of electricity,and diminish investment costs for subsea cables.In this study,the hydrodynamic performances of platforms equipped with two types of tanks separately are evaluated and are comprehensively compared with each other.The Volume of Fluid(VOF)two-phase flow model and the Shear−Stress Transport(SST)k−omega turbulence model are applied to simulate the motion responses of the C-type and Moss-type tanks under the same excitation force of platform based on the time-frequency response results of platforms.Comparisons are made among the shape of the liquid hydrogen surface,variations of the wall pressures,changes of the gas-liquid temperatures,and the pressure drop phenomena induced by phase changes inside the tanks.The results indicate that the interaction between wave-induced excitation force and sloshing force from tanks can either increase or decrease the amplitude of platform’s motion.Meanwhile,the thermodynamic responses of liquid hydrogen sloshing inside the tanks correlate positively with the dynamic behavior.Compared with Moss-type tanks,the sloshing of liquid hydrogen in C-type tanks is more intense,accompanied by jetting and breaking wave phenomena.For the C-type tanks,the substantial increase in interfacial area significantly enhances phase change condensation and heat transfer,leading to the rapid decline in temperature and pressure inside the tanks.The results of this study can provide valuable insights for the future design of floating hydrogen storage platform and the selection of tanks on the platform.展开更多
Numerical simulations on the coupling actions between the free surface oscillation in the moonpool and the heave motion response of hulls with vertical mooring stiffness are carried out in this study,where the influen...Numerical simulations on the coupling actions between the free surface oscillation in the moonpool and the heave motion response of hulls with vertical mooring stiffness are carried out in this study,where the influences of edge profiles,including sharp and convex edge profiles,on the coupling actions are considered.Two-peak variations in the free surface oscillations in the moonpool with incident wave frequencies can be observed,which are defined as the first and second peak frequencies.The free surface oscillations and heave motion responses show in-phase and out-of-phase relationships at the first and second peak frequencies,respectively.The convex edge profiles are able to generate effective suppressing actions at the second peak frequencies.However,it is only efficient for large vertical stiffness at the first peak frequency.The relative velocity between the fluid flow along the moonpool bottom and the heave motion of the hulls is the essential reason.展开更多
The coupling effect between ship motion and liquid sloshing in a beam sea is investigated,with a focus on the influence of liquid types,namely,water and liquefied natural gas(LNG),on the coupling dynamics.A hybrid num...The coupling effect between ship motion and liquid sloshing in a beam sea is investigated,with a focus on the influence of liquid types,namely,water and liquefied natural gas(LNG),on the coupling dynamics.A hybrid numerical model,combining a potential flow model and computational fluid dynamics methods,is employed to simulate these interactions.Numerical validation is performed using experimental data from water sloshing tests.Comparisons between water and LNG reveal that liquid type has minimal effects on the ship’s roll motion response in a beam sea,provided the total liquid masses are the same.Regarding sloshing impact pressure,although differences between LNG and water results are minor,substituting LNG with water in physical experiments is shown to yield reliable results.展开更多
The integrated system composed of wave energy converters and floating wind turbines offers substantial potential for reducing the levelized cost of energy(LCOE) by sharing the infrastructure, mooring system, substatio...The integrated system composed of wave energy converters and floating wind turbines offers substantial potential for reducing the levelized cost of energy(LCOE) by sharing the infrastructure, mooring system, substations and cables.This paper proposes an integrated system consisting of a semi-submersible wind turbine platform and three Wave Star flap-type wave energy converters. The coupled motion model of the integrated system is established and validated on the basis of viscously corrected potential flow theory. This study investigates the influence of two key parameters,the arm length and hinge points of flap-type wave energy converters, on system performance. The results reveal that variations in the arm length of flap-type wave energy converters(WECs) are the primary determinants of the integrated system's dynamic characteristics, whereas changes in hinge points predominantly affect device power generation.Additionally, incorporating WECs reduces the pitch and heave motions of the platform within a specific wave frequency range, thereby enhancing the energy output of the integrated system at the operational sea site. The performance of this hybrid system at a selected sea site is further assessed via the proposed aero-hydroservo coupling simulations.展开更多
The effect of coupling between sloshing and ship motions in the evaluation of slosh-induced interior pressures is studied. The coupling between sloshing loads and ship motions is modelled through a hybrid algorithm wh...The effect of coupling between sloshing and ship motions in the evaluation of slosh-induced interior pressures is studied. The coupling between sloshing loads and ship motions is modelled through a hybrid algorithm which combines a potential flow solution based on transient Green function for the external ship hydrodynamics with a viscous flow solution based on a multiphase interface capturing volume of fluid(VOF) technique for the interior sloshing motion. The coupled algorithm accounts for full nonlinear slosh forces while the external forces on the hull are determined through a blended scheme of linear radiationdiffraction with nonlinear Froude-Krylov and restoring forces. Consideration of this level of nonlinearities in ship motions is found to have non-negligible effects on the slosh-coupled responses and slosh-induced loads. A scheme is devised to evaluate the statistical measure of the pressures through long-duration simulation studies in extreme irregular waves. It is found that coupling significantly influences the tank interior pressures, and the differences in the pressures between coupled and uncoupled cases can be as much as 100% or more. To determine the RAO over the frequency range needed for the simulation studies in irregular waves, two alternative schemes are proposed, both of which require far less computational time compared to the conventional method of finding RAO at each frequency, and the merits of these are discussed.展开更多
The launching and recovery process of a human-occupied vehicle(HOV)faces more complex wave effects than other types of submersible operations.However,due to the nonlinearity between the HOV and its mother ship,difficu...The launching and recovery process of a human-occupied vehicle(HOV)faces more complex wave effects than other types of submersible operations.However,due to the nonlinearity between the HOV and its mother ship,difficulties occur in theoretically simulating their coupled motion and hydrodynamics.The coupled motion responses and the load under different regular wave conditions are investigated experimentally in this study.The optimized design of the experimental scheme simulated the launching and recovery process of the mother ship and HOV in regular waves.The attitude sensor performed synchronous real-time measurement of the coupled motion between the mother ship and HOV as well as obtained the load data on the coupled motion under different cable lengths.The results show that models in heading waves mainly lead to the vertical motion of the hoisting point.In beam waves,the transverse and vertical motions of the hoisting point occur in a certain frequency of waves.Under the heading and beam wave conditions,the longer the hoisting cable is,the greater the movement amplitude of the submersible is.Moreover,compared with the condition of the beam waves,the hoisting submersible has less influence on the mother ship under the condition of the heading waves.The findings provide theoretical support for the design optimization of the launching and recovery operation.展开更多
For general dynamic positioning systems,controllers are mainly based on the feedback of motions only in the horizontal plane.However,for marine structures with a small water plane area and low metacentric height,undes...For general dynamic positioning systems,controllers are mainly based on the feedback of motions only in the horizontal plane.However,for marine structures with a small water plane area and low metacentric height,undesirable surge and pitch oscillations may be induced by the thruster actions.In this paper,three control laws are investigated to suppress the induced pitch motion by adding pitch rate,pitch angle or pitch acceleration into the feedback control loop.Extensive numerical simulations are conducted with a semi-submersible platform for each control law.The influences of additional terms on surge−pitch coupled motions are analyzed in both frequency and time domain.The mechanical constraints of the thrust allocation and the frequency characters of external forces are simultaneously considered.It is concluded that adding pitch angle or pitch acceleration into the feedback loop changes the natural frequency in pitch,and its performance is highly dependent on the frequency distribution of external forces,while adding pitch rate into the feedback loop is always effective in mitigating surge−pitch coupled motions.展开更多
This paper discusses the numerical modeling of the dynamic coupled analysis of the floating platform and mooring/risers using the asynchronous coupling algorithm with the purpose to improve the computational efficienc...This paper discusses the numerical modeling of the dynamic coupled analysis of the floating platform and mooring/risers using the asynchronous coupling algorithm with the purpose to improve the computational efficiency when multiple lines are connected to the platform. The numerical model of the platform motion simulation in wave is presented. Additionally, how the asynchronous coupling algorithm is implemented during the dynamic coupling analysis is introduced. Through a comparison of the numerical results of our developed model with commercial software for a SPAR platform, the developed numerical model is checked and validated.展开更多
In this paper, numerical simulations of FPSO ship motion coupled with LNG tank sloshing with low-filling ratios are conducted. The fully coupled problem is addressed with our own unsteady RANS solver: naoe-FOAM-SJTU d...In this paper, numerical simulations of FPSO ship motion coupled with LNG tank sloshing with low-filling ratios are conducted. The fully coupled problem is addressed with our own unsteady RANS solver: naoe-FOAM-SJTU developed based on the open source tool librar- ies of OpenFOAM. The internal tank sloshing and external wave flow are solved simultaneously. The FPSO model includes 2 LNG tanks. For the ship 3-DOFs are released in the regular beam waves. The filling ratios of the 2 tanks are 20% - 20%, lower than the external free surface. This kind of low-filling condition reduces ship roll motion significantly, and produces complex free surface shapes in tanks. 4 different incident wave frequencies are considered in the simulation in comparison with the existing experimental data. The comparison shows that the numerical re- sults are in good agreement with the experimental data, proving the reliability of the proposed method. The filling conditions with large wave amplitudes are studied further, and due to the coupling effect, violent sloshing occurs in tanks and impulsive pressure forms on bulkhead.展开更多
As one of the most important daily motor activities, human locomotion has been investigated intensively in recent decades. The locomotor functions and mechanics of human lower limbs have become relatively well underst...As one of the most important daily motor activities, human locomotion has been investigated intensively in recent decades. The locomotor functions and mechanics of human lower limbs have become relatively well understood. However, so far our understanding of the motions and functional contributions of the human spine during locomotion is still very poor and simultaneous in-vivo limb and spinal column motion data are scarce. The objective of this study is to investigate the delicate in-vivo kinematic coupling between different functional regions of the human spinal column during locomotion as a stepping stone to explore the locomotor function of the human spine complex. A novel infrared reflective marker cluster system was constrncted using stereophotogrammetry techniques to record the 3D in-vivo geometric shape of the spinal column and the segmental position and orientation of each functional spinal region simultaneously. Gait measurements of normal walking were conducted. The preliminary results show that the spinal column shape changes periodically in the frontal plane during locomotion. The segmental motions of different spinal functional regions appear to be strongly coupled, indicating some synergistic strategy may be employed by the human spinal column to facilitate locomotion. In contrast to traditional medical imaging-based methods, the proposed technique can be used to investigate the dynamic characteristics of the spinal column, hence providing more insight into the functional biomechanics of the human spine.展开更多
Objective： To observe the tested results of the segmental range of motion （ROM） of lumbar spine by charge couple device （CCD）-based system for 3-dimensional real-time positioning （CCD system）, and to analyze it...Objective： To observe the tested results of the segmental range of motion （ROM） of lumbar spine by charge couple device （CCD）-based system for 3-dimensional real-time positioning （CCD system）, and to analyze its clinical significance. Methods： Seven patients with lumbar joint dysfunction and 8 healthy subjects were tested twice by the CCD-based system with an interval of 10 min. Results： The ROM of the patients was obviously lesser than that of the healthy subjects. The measuring data of segmental ROM of lumbar spine by CCD system is correlated significantly to the same data checked later on the same subjects in every direction of the movements. The differences between two checks are usually less than 1 degree. Conclusion： Specially designed CCD based system for 3-dimensional real-time positioning could objectively reflect the segmental ROM of lumbar spine. The system would be of great clinical significance in the assessment of the biomechanical dysfunction of lumbar spine and the effect of the treatment applied.展开更多
This paper presents a design of boundary controllers implemented at the top end for global stabilization of a marine riser in a three dimensional space under environmental loadings. Based on the energy approach, nonli...This paper presents a design of boundary controllers implemented at the top end for global stabilization of a marine riser in a three dimensional space under environmental loadings. Based on the energy approach, nonlinear partial differential equations of motion, including bending-bending and longitudinal-bending couplings for the risers are derived. The couplings cause mutual effects between the three independent directions in the riser＇s motions, and make it difficult to minimize its vibrations. The Lyapunov direct method is employed to design the boundary controller. It is shown that the proposed boundary controllers can effectively reduce the riser＇s vibration. Stability analysis of the closed-loop system is performed using the Lyapunov direct method. Numerical simulations illustrate the results.展开更多
In Fluid Structure Interaction(FSI) problems encountered in marine hydrodynamics, the pressure field and the velocity of the rigid body are tightly coupled. This coupling is traditionally resolved in a partitioned man...In Fluid Structure Interaction(FSI) problems encountered in marine hydrodynamics, the pressure field and the velocity of the rigid body are tightly coupled. This coupling is traditionally resolved in a partitioned manner by solving the rigid body motion equations once per nonlinear correction loop, updating the position of the body and solving the fluid flow equations in the new configuration. The partitioned approach requires a large number of nonlinear iteration loops per time–step. In order to enhance the coupling, a monolithic approach is proposed in Finite Volume(FV) framework,where the pressure equation and the rigid body motion equations are solved in a single linear system. The coupling is resolved by solving the rigid body motion equations once per linear solver iteration of the pressure equation, where updated pressure field is used to calculate new forces acting on the body, and by introducing the updated rigid body boundary velocity in to the pressure equation. In this paper the monolithic coupling is validated on a simple 2D heave decay case. Additionally, the method is compared to the traditional partitioned approach(i.e. "strongly coupled" approach) in terms of computational efficiency and accuracy. The comparison is performed on a seakeeping case in regular head waves, and it shows that the monolithic approach achieves similar accuracy with fewer nonlinear correctors per time–step. Hence, significant savings in computational time can be achieved while retaining the same level of accuracy.展开更多
文摘[Objective]This study aims to investigate the multi-body hydrodynamic interaction mechanisms during offshore lifting operations of aquaculture net cages in wind-fishery integration systems.By integrating numerical simulations and dynamic analysis methods,this study systematically investigates the coupled dynamic response characteristics during the cage-carrier vessel separation process to reveal its dynamic evolution patterns and key influence mechanisms.[Method]Based on potential flow theory,a fully coupled dynamic analysis model of crane vessel-net cage-semi-submersible barge was established for a marine ranch project in Guangdong.The complete lifting process was dynamically simulated using SESAM software.Five typical operating sea states were configured to investigate the influence of wave parameters on the system's motion response under combined wave-current-wind actions.[Result]The results demonstrate that wave period dominates the system stability.Under short-period conditions,the system maintains stable motion with relatively small horizontal relative displacements,while long-period conditions excite low-frequency resonance,leading to significant slow-drift motions.Vertical response analysis reveals that long-period waves cause severe relative displacement fluctuations between the cage and semi-submersible vessel,with actual displacement amplitudes doubling the preset safety target of 2.045 m.Quantitative analysis further indicates that when significant wave height increases from 1.0 m to 1.5 m,the actual displacement amplitude increases by approximately 20%relative to the target displacement of 2.045 m,demonstrating that its influence is significantly weaker than the displacement variations induced by wave period changes.The complete dynamic simulation successfully captures the continuous dynamic response characteristics during the lifting process.[Conclusion]This research clarifies the influence mechanisms of wave parameters on the cage lifting process,identifying wave period as the crucial factor for operational safety.An operation window assessment method incorporating multi-body coupling effects is established,proposing a safety criterion with peak period not exceeding six seconds as the core requirement.The findings provide theoretical foundation for safe installation of marine ranch net cages and offer valuable references for similar offshore lifting operations.
基金National Natural Science Foundation of China under Grant Nos.U2139208 and 52278516Key Laboratory of Earthquake Engineering and Engineering Vibration,China Earthquake Administration under Grant No.2024D15Key Laboratory of Soft Soil Characteristic and Engineering Environment,Tianjin Chengjian University under Grant No.2022SCEEKL003。
文摘This study presents an effective hybrid simulation approach for simulating broadband ground motion in complex near-fault locations.The approach utilizes a deterministic approach based on the spectral element method(SEM),which is used to simulate low-frequency ground motion(f<1 Hz)by incorporating an innovative efficient discontinuous Galerkin(DG)method for grid division to accurately model basin sedimentary layers at reduced costs.It also introduces a comprehensive hybrid source model for high-frequency random scattering and a nonlinear analysis module for basin sedimentary layers.Deterministic outcomes are combined with modified three-dimensional stochastic finite fault method(3D-EXSIM)simulations of high-frequency ground motion(f>1 Hz).A fourth-order Butterworth filter with zero phase shift is employed for time-domain filtering of low-and high-frequency time series at a crossover frequency of 1 Hz,merging the low and high-frequency ground motions into a broadband time series.Taking an Ms 6.8 Luding earthquake,as an example,this hybrid method was used for a rapid and efficient simulation analysis of broadband ground motion in the region.The accuracy and efficiency of this hybrid method were verified through comparisons with actually observed station data and empirical attenuation curves.Deterministic method simulation results revealed the effects of mountainous topography,basin effects,nonlinear effects within the basin’s sedimentary layers,and a coupling interaction between the basin and the mountains.The findings are consistent with similar studies,showing that near-fault sedimentary basins significantly focus and amplify strong ground motion,and the soil’s nonlinear behavior in the basin influences ground motion to varying extents at different distances from the fault.The mountainous topography impacts the basin’s response to ground motion,leading to barrier effects.This research provides a scientific foundation for seismic zoning,urban planning,and seismic design in nearfault mountain basin regions.
基金Supported by the National Natural Science Foundation of China(51679080 and 51379073)the Fundamental Research Funds for the Central Universities(B230205020).
文摘This study employed a computational fluid dynamics model with an overset mesh technique to investigate the thrust and power of a floating offshore wind turbine(FOWT)under platform floating motion in the wind–rain field.The impact of rainfall on aerodynamic performance was initially examined using a stationary turbine model in both wind and wind–rain conditions.Subsequently,the study compared the FOWT’s performance under various single degree-of-freedom(DOF)motions,including surge,pitch,heave,and yaw.Finally,the combined effects of wind–rain fields and platform motions involving two DOFs on the FOWT’s aerodynamics were analyzed and compared.The results demonstrate that rain negatively impacts the aerodynamic performance of both the stationary turbines and FOWTs.Pitch-dominated motions,whether involving single or multiple DOFs,caused significant fluctuations in the FOWT aerodynamics.The combination of surge and pitch motions created the most challenging operational environment for the FOWT in all tested scenarios.These findings highlighted the need for stronger construction materials and greater ultimate bearing capacity for FOWTs,as well as the importance of optimizing designs to mitigate excessive pitch and surge.
基金Supported by the Scientific and Technological Research Program of Chongqing Municipal Education Commission of China(Grant No.:KJQN202301105,KJQN202101550)Scientific Research Fund of Chongqing University of Technology(grant No.2021ZDZ015)National Nature Science Foundation of China(No.:52205052).
文摘This study investigates the effect of nacelle motions on the rotor performance and drivetrain dynamics of floating offshore wind turbines(FOWTs)through fully coupled aero-hydro-elastic-servo-mooring simulations.Using the National Renewable Energy Laboratory 5 MW monopile-supported offshore wind turbine and the OC4 DeepCwind semisubmersible wind turbine as case studies,the research addresses the complex dynamic responses resulting from the interaction among wind,waves,and turbine structures.Detailed multi-body dynamics models of wind turbines,including drivetrain components,are created within the SIMPACK framework.Meanwhile,the mooring system is modeled using a lumped-mass method.Various operational conditions are simulated through five wind-wave load cases.Results demonstrate that nacelle motions significantly influence rotor speed,thrust,torque,and power output,as well as the dynamic loads on drivetrain components.These findings highlight the need for advanced simulation techniques for the design and optimization of FOWTs to ensure reliable performance and longevity.
基金financially supported by Lloyd’s Register Foundation(LRF),a UK-registered charity and sole shareholder of Lloyd’s Register Group Ltd.the Youth Innovation Fund of State Key Laboratory of Ocean Engineering(Grant No.GKZD010059-21)
文摘Simulating the coupled motions of multiple bodies in the time domain is a complex problem because of the strong hydrodynamic interactions and coupled effect of various mechanical connectors. In this study, we investigate the hydrodynamic responses of three barges moored side-by-side in a floatover operation in the frequency and time domains. In the frequency domain, the damping lid method is adopted to improve the overestimated hydrodynamic coefficients calculated from conventional potential flow theory. A time-domain computing program based on potential flow theory and impulse theory is compiled for analyses that consider multibody hydrodynamic interactions and mechanical effects from lines and fenders. Correspondingly, an experiment is carried out for comparison with the numerical results. All statistics, time series, and power density spectra from decay and irregular wave tests are in a fairly good agreement.
基金Foundation item： Supported by the National Natural Science Foundation of China （Grant No. 51079032） and the ＂111 project＂ （Grant No. B07019）.
文摘Nonlinear interactions among incident wave, tank-sloshing and floating body coupling motion are investigated. The fully nonlinear sloshing and body-surface nonlinear free surface hydrodynamics is simulated using a Non-Uniform Rational B-Spline （NURBS） higher-order panel method in time domain based on the potential theory. A robust and stable improved iterative procedure （Yan and Ma, 2007） for floating bodies is used for calculating the time derivative of velocity potential and floating body motion. An energy dissipation condition based on linear theory adopted by Huang （2011） is developed to consider flow viscosity effects of sloshing flow in nonlinear model. A two-dimensional tank model test was performed to identify its validity. The present nonlinear coupling sway motion results are subsequently compared with the corresponding Rognebakke and Faltinsen （2003）＇s experimental results, showing fair agreement. Thus, the numerical approach presented in this paper is expected to be very efficient and realistic in evaluating the coupling effects of nonlinear sloshing and body motion.
基金supported by the National Natural Science Foundation of China under Grant No.51179125the Innovation Foundation of Tianjin University under Approving No.1301
文摘This paper presents the results from a numerical study on the nonlinear dynamic behaviors including bifurcation and chaos of a truss spar platform. In view of the mutual influences between the heave and the pitch modes, the coupled heave and pitch motion equations of the spar platform hull were established in the regular waves. In order to analyze the nonlinear motions of the platform, three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs were constructed, the Poincare maps and the power spectrums of the platform response were calculated. It was found that the platform motions are sensitive to wave fre- quency. With changing wave frequency, the platform undergoes complicated nonlinear motions, including 1/2 sub-harmonic motion, quasi-periodic motion and chaotic motion. When the wave frequency approaches the natural frequency of the heave mode of the platform, the platform moves with quasi-periodic motion and chaotic motional temately. For a certain range of wave frequencies, the platform moves with totally chaotic motion. The range of wave frequencies which leads to chaotic motion of the platform increases with increasing wave height. The three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs reveal the nonlinear motions of the spar platform under different wave conditions.
基金supported by the National Natural Science Foundation of China(Grant No.51979130).
文摘The production of hydrogen on offshore platform can decrease reliance on the power grid,mitigate transmission losses of electricity,and diminish investment costs for subsea cables.In this study,the hydrodynamic performances of platforms equipped with two types of tanks separately are evaluated and are comprehensively compared with each other.The Volume of Fluid(VOF)two-phase flow model and the Shear−Stress Transport(SST)k−omega turbulence model are applied to simulate the motion responses of the C-type and Moss-type tanks under the same excitation force of platform based on the time-frequency response results of platforms.Comparisons are made among the shape of the liquid hydrogen surface,variations of the wall pressures,changes of the gas-liquid temperatures,and the pressure drop phenomena induced by phase changes inside the tanks.The results indicate that the interaction between wave-induced excitation force and sloshing force from tanks can either increase or decrease the amplitude of platform’s motion.Meanwhile,the thermodynamic responses of liquid hydrogen sloshing inside the tanks correlate positively with the dynamic behavior.Compared with Moss-type tanks,the sloshing of liquid hydrogen in C-type tanks is more intense,accompanied by jetting and breaking wave phenomena.For the C-type tanks,the substantial increase in interfacial area significantly enhances phase change condensation and heat transfer,leading to the rapid decline in temperature and pressure inside the tanks.The results of this study can provide valuable insights for the future design of floating hydrogen storage platform and the selection of tanks on the platform.
基金supported by the National Natural Science Foundation of China(Grant Nos.52371267 and 52171250).
文摘Numerical simulations on the coupling actions between the free surface oscillation in the moonpool and the heave motion response of hulls with vertical mooring stiffness are carried out in this study,where the influences of edge profiles,including sharp and convex edge profiles,on the coupling actions are considered.Two-peak variations in the free surface oscillations in the moonpool with incident wave frequencies can be observed,which are defined as the first and second peak frequencies.The free surface oscillations and heave motion responses show in-phase and out-of-phase relationships at the first and second peak frequencies,respectively.The convex edge profiles are able to generate effective suppressing actions at the second peak frequencies.However,it is only efficient for large vertical stiffness at the first peak frequency.The relative velocity between the fluid flow along the moonpool bottom and the heave motion of the hulls is the essential reason.
基金supported by the Natural Science Foundation of China with Grant Nos.52371267 and 52171250。
文摘The coupling effect between ship motion and liquid sloshing in a beam sea is investigated,with a focus on the influence of liquid types,namely,water and liquefied natural gas(LNG),on the coupling dynamics.A hybrid numerical model,combining a potential flow model and computational fluid dynamics methods,is employed to simulate these interactions.Numerical validation is performed using experimental data from water sloshing tests.Comparisons between water and LNG reveal that liquid type has minimal effects on the ship’s roll motion response in a beam sea,provided the total liquid masses are the same.Regarding sloshing impact pressure,although differences between LNG and water results are minor,substituting LNG with water in physical experiments is shown to yield reliable results.
基金financially supported by the National Natural Science Foundation of China National Outstanding Youth Science Fund Project (Grant No. 52222109)the National Natural Science Foundation of China (Grant No. 52201322)+1 种基金Guangdong Basic and Applied Basic Research Foundation (Grant Nos. 2024A1515240006, 2022B1515020036 and 2023A1515012144)the Project of State Key Laboratory of Subtropical Building and Urban Science (Grant No. 2023ZB14)。
文摘The integrated system composed of wave energy converters and floating wind turbines offers substantial potential for reducing the levelized cost of energy(LCOE) by sharing the infrastructure, mooring system, substations and cables.This paper proposes an integrated system consisting of a semi-submersible wind turbine platform and three Wave Star flap-type wave energy converters. The coupled motion model of the integrated system is established and validated on the basis of viscously corrected potential flow theory. This study investigates the influence of two key parameters,the arm length and hinge points of flap-type wave energy converters, on system performance. The results reveal that variations in the arm length of flap-type wave energy converters(WECs) are the primary determinants of the integrated system's dynamic characteristics, whereas changes in hinge points predominantly affect device power generation.Additionally, incorporating WECs reduces the pitch and heave motions of the platform within a specific wave frequency range, thereby enhancing the energy output of the integrated system at the operational sea site. The performance of this hybrid system at a selected sea site is further assessed via the proposed aero-hydroservo coupling simulations.
文摘The effect of coupling between sloshing and ship motions in the evaluation of slosh-induced interior pressures is studied. The coupling between sloshing loads and ship motions is modelled through a hybrid algorithm which combines a potential flow solution based on transient Green function for the external ship hydrodynamics with a viscous flow solution based on a multiphase interface capturing volume of fluid(VOF) technique for the interior sloshing motion. The coupled algorithm accounts for full nonlinear slosh forces while the external forces on the hull are determined through a blended scheme of linear radiationdiffraction with nonlinear Froude-Krylov and restoring forces. Consideration of this level of nonlinearities in ship motions is found to have non-negligible effects on the slosh-coupled responses and slosh-induced loads. A scheme is devised to evaluate the statistical measure of the pressures through long-duration simulation studies in extreme irregular waves. It is found that coupling significantly influences the tank interior pressures, and the differences in the pressures between coupled and uncoupled cases can be as much as 100% or more. To determine the RAO over the frequency range needed for the simulation studies in irregular waves, two alternative schemes are proposed, both of which require far less computational time compared to the conventional method of finding RAO at each frequency, and the merits of these are discussed.
基金National Natural Science Foundation of China(Grant No.51909039)Shandong Provincial Key Laboratory of Ocean Engineering(Grant No.201807).
文摘The launching and recovery process of a human-occupied vehicle(HOV)faces more complex wave effects than other types of submersible operations.However,due to the nonlinearity between the HOV and its mother ship,difficulties occur in theoretically simulating their coupled motion and hydrodynamics.The coupled motion responses and the load under different regular wave conditions are investigated experimentally in this study.The optimized design of the experimental scheme simulated the launching and recovery process of the mother ship and HOV in regular waves.The attitude sensor performed synchronous real-time measurement of the coupled motion between the mother ship and HOV as well as obtained the load data on the coupled motion under different cable lengths.The results show that models in heading waves mainly lead to the vertical motion of the hoisting point.In beam waves,the transverse and vertical motions of the hoisting point occur in a certain frequency of waves.Under the heading and beam wave conditions,the longer the hoisting cable is,the greater the movement amplitude of the submersible is.Moreover,compared with the condition of the beam waves,the hoisting submersible has less influence on the mother ship under the condition of the heading waves.The findings provide theoretical support for the design optimization of the launching and recovery operation.
基金the National Natural Science Foundation of China(Grant Nos.51179103 and 51979167)the Ministry of Industry and Information Technology(Grant No.[2016]22)the Hainan Provincial Joint Project of Sanya Bay Science and Technology City(Grant No.520LH051).
文摘For general dynamic positioning systems,controllers are mainly based on the feedback of motions only in the horizontal plane.However,for marine structures with a small water plane area and low metacentric height,undesirable surge and pitch oscillations may be induced by the thruster actions.In this paper,three control laws are investigated to suppress the induced pitch motion by adding pitch rate,pitch angle or pitch acceleration into the feedback control loop.Extensive numerical simulations are conducted with a semi-submersible platform for each control law.The influences of additional terms on surge−pitch coupled motions are analyzed in both frequency and time domain.The mechanical constraints of the thrust allocation and the frequency characters of external forces are simultaneously considered.It is concluded that adding pitch angle or pitch acceleration into the feedback loop changes the natural frequency in pitch,and its performance is highly dependent on the frequency distribution of external forces,while adding pitch rate into the feedback loop is always effective in mitigating surge−pitch coupled motions.
基金Supported by the National Natural Science Foundation of China under Grant No.51109040
文摘This paper discusses the numerical modeling of the dynamic coupled analysis of the floating platform and mooring/risers using the asynchronous coupling algorithm with the purpose to improve the computational efficiency when multiple lines are connected to the platform. The numerical model of the platform motion simulation in wave is presented. Additionally, how the asynchronous coupling algorithm is implemented during the dynamic coupling analysis is introduced. Through a comparison of the numerical results of our developed model with commercial software for a SPAR platform, the developed numerical model is checked and validated.
文摘In this paper, numerical simulations of FPSO ship motion coupled with LNG tank sloshing with low-filling ratios are conducted. The fully coupled problem is addressed with our own unsteady RANS solver: naoe-FOAM-SJTU developed based on the open source tool librar- ies of OpenFOAM. The internal tank sloshing and external wave flow are solved simultaneously. The FPSO model includes 2 LNG tanks. For the ship 3-DOFs are released in the regular beam waves. The filling ratios of the 2 tanks are 20% - 20%, lower than the external free surface. This kind of low-filling condition reduces ship roll motion significantly, and produces complex free surface shapes in tanks. 4 different incident wave frequencies are considered in the simulation in comparison with the existing experimental data. The comparison shows that the numerical re- sults are in good agreement with the experimental data, proving the reliability of the proposed method. The filling conditions with large wave amplitudes are studied further, and due to the coupling effect, violent sloshing occurs in tanks and impulsive pressure forms on bulkhead.
基金supported by the Key Project of National Natural Science Foundation of China (No. 50635030)the National Basic Research Program ("973" Program) of China (No. 2007CB616913)+2 种基金was also supported by the China Scholarship Council (CSC)We also would like to thank Karin Jespers and Sharon Warner of the Structure and Motion Laboratory for their support of the experimental workJRH’s con-tributions were supported by research grants BB/C516844/1 and BB/F01169/1 from the BBSRC, whom we thank.
文摘As one of the most important daily motor activities, human locomotion has been investigated intensively in recent decades. The locomotor functions and mechanics of human lower limbs have become relatively well understood. However, so far our understanding of the motions and functional contributions of the human spine during locomotion is still very poor and simultaneous in-vivo limb and spinal column motion data are scarce. The objective of this study is to investigate the delicate in-vivo kinematic coupling between different functional regions of the human spinal column during locomotion as a stepping stone to explore the locomotor function of the human spine complex. A novel infrared reflective marker cluster system was constrncted using stereophotogrammetry techniques to record the 3D in-vivo geometric shape of the spinal column and the segmental position and orientation of each functional spinal region simultaneously. Gait measurements of normal walking were conducted. The preliminary results show that the spinal column shape changes periodically in the frontal plane during locomotion. The segmental motions of different spinal functional regions appear to be strongly coupled, indicating some synergistic strategy may be employed by the human spinal column to facilitate locomotion. In contrast to traditional medical imaging-based methods, the proposed technique can be used to investigate the dynamic characteristics of the spinal column, hence providing more insight into the functional biomechanics of the human spine.
文摘Objective： To observe the tested results of the segmental range of motion （ROM） of lumbar spine by charge couple device （CCD）-based system for 3-dimensional real-time positioning （CCD system）, and to analyze its clinical significance. Methods： Seven patients with lumbar joint dysfunction and 8 healthy subjects were tested twice by the CCD-based system with an interval of 10 min. Results： The ROM of the patients was obviously lesser than that of the healthy subjects. The measuring data of segmental ROM of lumbar spine by CCD system is correlated significantly to the same data checked later on the same subjects in every direction of the movements. The differences between two checks are usually less than 1 degree. Conclusion： Specially designed CCD based system for 3-dimensional real-time positioning could objectively reflect the segmental ROM of lumbar spine. The system would be of great clinical significance in the assessment of the biomechanical dysfunction of lumbar spine and the effect of the treatment applied.
文摘This paper presents a design of boundary controllers implemented at the top end for global stabilization of a marine riser in a three dimensional space under environmental loadings. Based on the energy approach, nonlinear partial differential equations of motion, including bending-bending and longitudinal-bending couplings for the risers are derived. The couplings cause mutual effects between the three independent directions in the riser＇s motions, and make it difficult to minimize its vibrations. The Lyapunov direct method is employed to design the boundary controller. It is shown that the proposed boundary controllers can effectively reduce the riser＇s vibration. Stability analysis of the closed-loop system is performed using the Lyapunov direct method. Numerical simulations illustrate the results.
基金sponsored by Bureau Veritas under the administration of Dr.ime Malenica
文摘In Fluid Structure Interaction(FSI) problems encountered in marine hydrodynamics, the pressure field and the velocity of the rigid body are tightly coupled. This coupling is traditionally resolved in a partitioned manner by solving the rigid body motion equations once per nonlinear correction loop, updating the position of the body and solving the fluid flow equations in the new configuration. The partitioned approach requires a large number of nonlinear iteration loops per time–step. In order to enhance the coupling, a monolithic approach is proposed in Finite Volume(FV) framework,where the pressure equation and the rigid body motion equations are solved in a single linear system. The coupling is resolved by solving the rigid body motion equations once per linear solver iteration of the pressure equation, where updated pressure field is used to calculate new forces acting on the body, and by introducing the updated rigid body boundary velocity in to the pressure equation. In this paper the monolithic coupling is validated on a simple 2D heave decay case. Additionally, the method is compared to the traditional partitioned approach(i.e. "strongly coupled" approach) in terms of computational efficiency and accuracy. The comparison is performed on a seakeeping case in regular head waves, and it shows that the monolithic approach achieves similar accuracy with fewer nonlinear correctors per time–step. Hence, significant savings in computational time can be achieved while retaining the same level of accuracy.
