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
Complicated loads encountered by floating offshore wind turbines(FOWTs)in real sea conditions are crucial for future optimization of design,but obtaining data on them directly poses a challenge.To address this issue,w...Complicated loads encountered by floating offshore wind turbines(FOWTs)in real sea conditions are crucial for future optimization of design,but obtaining data on them directly poses a challenge.To address this issue,we applied machine learning techniques to obtain hydrodynamic and aerodynamic loads of FOWTs by measuring platform motion responses and wave-elevation sequences.First,a computational fluid dynamics(CFD)simulation model of the floating platform was established based on the dynamic fluid body interaction technique and overset grid technology.Then,a long short-term memory(LSTM)neural network model was constructed and trained to learn the nonlinear relationship between the waves,platform-motion inputs,and hydrodynamic-load outputs.The optimal model was determined after analyzing the sensitivity of parameters such as sample characteristics,network layers,and neuron numbers.Subsequently,the effectiveness of the hydrodynamic load model was validated under different simulation conditions,and the aerodynamic load calculation was completed based on the D'Alembert principle.Finally,we built a hybrid-scale FOWT model,based on the software in the loop strategy,in which the wind turbine was replaced by an actuation system.Model tests were carried out in a wave basin and the results demonstrated that the root mean square errors of the hydrodynamic and aerodynamic load measurements were 4.20%and 10.68%,respectively.展开更多
The comprehensive numerical simulation of the tower shadow effect on floating offshore wind turbines(FOWTs),an area less explored compared to fixed-bottom wind turbines,is presented in this study.The atmospheric bound...The comprehensive numerical simulation of the tower shadow effect on floating offshore wind turbines(FOWTs),an area less explored compared to fixed-bottom wind turbines,is presented in this study.The atmospheric boundary layer inflow and the joint north sea wave project random wave are used as the operating conditions for FOWT.The combination of computational fluid dynamics(CFD)software simulator for wind farm applications and turbine simulation tool OpenFAST is used to implement fluid-structure interaction calculations.The output power,platform motion,wake velocity deficit and vortex structures are analyzed to reveal the influence of the tower shadow effect on the FOWT.The results indicate that due to the fluctuation caused by the turbulent wind and the floating platform motion,the tower shadow effect of FOWT is less significant for its periodic power decay than that of fixed-bottom wind turbines.And according to the velocity deficit analysis,the influence area of the tower shadow effect on the wake is mainly in the near wake region.展开更多
Recently,semisubmersible floating offshore wind turbine technologies have received considerable attention.For the coupled simulation of semisubmersible floating offshore wind energy,the platform is usually considered ...Recently,semisubmersible floating offshore wind turbine technologies have received considerable attention.For the coupled simulation of semisubmersible floating offshore wind energy,the platform is usually considered a rigid model,which could affect the calculation accuracy of the dynamic responses.The dynamic responses of a TripleSpar floating offshore wind turbine equipped with a 10 MW offshore wind turbine are discussed herein.The simulation of a floating offshore wind turbine under regular waves,white noise waves,and combined wind-wave conditions is conducted.The effects of the tower and platform flexibility on the motion and force responses of the TripleSpar semisubmersible floating offshore wind turbine are investigated.The results show that the flexibility of the tower and platform can influence the dynamic responses of a TripleSpar semisubmersible floating offshore wind turbine.Considering the flexibility of the tower and platform,the tower and platform pitch motions markedly increased compared with the fully rigid model.Moreover,the force responses,particularly for tower base loads,are considerably influenced by the flexibility of the tower and platform.Thus,the flexibility of the tower and platform for the coupled simulation of floating offshore wind turbines must be appropriately examined.展开更多
The offshore renewable energy industry has been developing farms of floating offshore wind turbines in water depths up to 100 m.In Vietnam,floating offshore wind turbines have been developed to increase the production...The offshore renewable energy industry has been developing farms of floating offshore wind turbines in water depths up to 100 m.In Vietnam,floating offshore wind turbines have been developed to increase the production of clean and sustainable energy.The mooring system,which is used to keep the turbine stable and ensure the safety and economic efficiency of wind power production,is an important part of a floating offshore wind turbine.Appropriate selection of the mooring type and mooring line material can reduce the risks arising from the motion of wind turbines.Different types of mooring line material have been simulated and compared in order to determine the optimal type with the minimum motion risk for a floating wind turbine.This study focused on numerical modeling of semi-taut mooring systems using nonlinear materials for a semi-submersible wind turbine.Several modeling approaches common to current practice were applied.Hydrodynamic analysis was performed to investigate the motion of the response amplitude operators of the floating wind turbine.Dynamic analysis of mooring systems was performed using a time domain to obtain the tension responses of mooring lines under the ultimate limit states and fatigue limit states in Vietnamese sea conditions.The results showed that the use of nonlinear materials(polyester and/or nylon)for mooring systems can minimize the movement of the turbine and save costs.The use of synthetic fibers can reduce the maximum tension in mooring lines and the length of mooring lines.However,synthetic fiber ropes showed highly nonlinear load elongation properties,which were difficult to simulate using numerical software.The comparison of the characteristics of polyester and nylon mooring lines showed that the maximum and mean tensions of the nylon line were less than those of the polyester line.In addition,the un-stretched length of the polyester line was greater than that of the nylon line under the same mean tension load.Therefore,nylon material is recommended for the mooring lines of a floating offshore wind turbine.展开更多
Mooring cable tension is a crucial parameter for evaluating the safety and reliability of a floating platform mooring system.The real-time mooring tension in an actual marine environment has always been essential data...Mooring cable tension is a crucial parameter for evaluating the safety and reliability of a floating platform mooring system.The real-time mooring tension in an actual marine environment has always been essential data that mooring system designers aim to acquire.To address the need for long-term continuous monitoring of mooring tension in deep-sea marine environments,this paper presents a mooring cable tension monitoring method based on the principle of direct mechanical measurement.The developed tension monitoring sensors were installed and applied in the mooring system of the"Yongle"scientific experimental platform.Over the course of one year,a substantial amount of in-situ tension monitoring data was obtained.Under wave heights of up to 1.24 m,the mooring tension on the floating platform reached 16.5 tons.Through frequency domain and time domain analysis,the spectral characteristics of mooring tension,including waveinduced force,slow drift force,and mooring cable elastic restoring force,were determined.The mooring cable elastic restoring force frequency was approximately half of that of the wave signal.Due to the characteristics of the hinge connection structure of the dual module floating platform,under some specific working conditions the wave-induced force was the maximum of the three different frequency forces,and restoring force was the smallest.展开更多
This paper presents an overview of the recent developments in hybrid wind-wave energy.With the focus on floating concepts,the possible configurations introduced in the literature are categorized and depicted,and the m...This paper presents an overview of the recent developments in hybrid wind-wave energy.With the focus on floating concepts,the possible configurations introduced in the literature are categorized and depicted,and the main conclusions obtained from the references are summarized.Moreover,offshore wind and wave resources are discussed in terms of complementarity and supplementarity,offering a new perspective to developing hybrid wind-wave energy systems that look for synergies not limited to maximizing power output.Then,the feasibility of the concepts under development is discussed in detail,with focus on technical feasibility,dynamic feasibility and limitations of the methods employed.The hybrid configurations that surpassed the experimental validation phase are highlighted,and the experimental results are summarized.By compiling more than 40 floating wind turbine concepts,new relations are drawn between power,wind turbine dimensions,platforms’draft and displacement,which are further related to the payload allowance of the units to accommodate wave devices and onboard power take-off systems.Bearing in mind that it is a challenge to model the exact dynamics of hybrid floating wind-wave platforms,this paper elucidates the current research gaps,limitations and future trends in the field.Lastly,based on the overview and topics discussed,several major conclusions are drawn concerning hybrid synergies,dynamics and hydrodynamics of hybrid platforms,feasibility of concepts,among other regards.展开更多
Modularfiloating structures(MFS)offer a sustainable pathway towards the expansion of coastal cities in adaptation tofilooding and sea level rise driven by climate change.It is therefore necessary to develop analytical...Modularfiloating structures(MFS)offer a sustainable pathway towards the expansion of coastal cities in adaptation tofilooding and sea level rise driven by climate change.It is therefore necessary to develop analytical methods easily accessible to architects or structural engineers for the rapid prototyping of MFS designs.This work develops novel closed‑form expressions describing the rigid body dynamics of symmetrically loaded rectangular pontoons across all six degrees of freedom(DOF)excited by surface waves approaching from any arbitrary direction.The derivations were based on Airy wave theory assuming frequency‑independent added mass and damping.When benchmarked against numerical solutions from ANSYS/AQWA for two MFS prototypes,the analytical approach proved capable of predicting the response amplitude operators(RAO)across all DOFs,wave directions,and structural confiigurations.However,while the response of mass‑dominated DOFs(surge,sway,and yaw)were well captured,the damping ratio for stiffness‑dominated DOFs(heave,roll,and pitch)must be judiciously selected to yield accurate RAO results.A parametric investigation further elucidated the contribution of structural geometry and wave directionality on the critical accelerations experienced by an idealizedfiloating structure founded upon a square pontoon under realistic sea states.It was discovered that the largest accelerations were triggered by waves approaching orthogonally to the pontoon.Ultimately,this work facilitates a more streamlined approach for the dynamic analysis of compliantfiloating bodies to supplement detailed modeling efforts via numerical methods.展开更多
Offshore floating photovoltaic systems have tremendous potential to address the energy crisis.As a novel type of float-ing photovoltaic system,membrane structures are increasingly applied due to their advantages of be...Offshore floating photovoltaic systems have tremendous potential to address the energy crisis.As a novel type of float-ing photovoltaic system,membrane structures are increasingly applied due to their advantages of being lightweight and cost-effective.A 1:40 scaled model for laboratory experiments was designed and developed,considering Ocean Sun’s membrane structure.The study aims to investigate the hydrodynamic characteristics of the membrane structure under wave loading by testing its various mo-tion responses and mooring forces at different wave heights and periods.The conclusions indicate that as the wave period decreases within the range of 1.75 to 1.25 s,the heave motion response of the structure decreases,whereas pitch,surge motion response,heave acceleration,and mooring force increase.The amplitudes of various motions and mooring forces of the structure decrease with de-creasing wave height.The hydrodynamic responses under irregular and regular waves follow similar patterns,but the responses and mooring forces induced by irregular waves are more significant.The structure should be designed based on the actual wave height.In addition,the same frequency resonance phenomenon is avoided because the movement period of each degree of freedom is close to the wave period.展开更多
Siwa Oasis,one of Egypts most remote settlements,is also a popular tourist destination thanks to the beautiful salt pools with water that people can float in.Salt is both a blessing and a curse in Siwa.Years ago,peopl...Siwa Oasis,one of Egypts most remote settlements,is also a popular tourist destination thanks to the beautiful salt pools with water that people can float in.Salt is both a blessing and a curse in Siwa.Years ago,people started realizing that there was money to be made in the salt trade,and salt mining operations created the salt lakes that the oasis is now famous for.展开更多
As a typical in-memory computing hardware design, nonvolatile ternary content-addressable memories(TCAMs) enable the logic operation and data storage for high throughout in parallel big data processing. However,TCAM c...As a typical in-memory computing hardware design, nonvolatile ternary content-addressable memories(TCAMs) enable the logic operation and data storage for high throughout in parallel big data processing. However,TCAM cells based on conventional silicon-based devices suffer from structural complexity and large footprintlimitations. Here, we demonstrate an ultrafast nonvolatile TCAM cell based on the MoTe2/hBN/multilayergraphene (MLG) van der Waals heterostructure using a top-gated partial floating-gate field-effect transistor(PFGFET) architecture. Based on its ambipolar transport properties, the carrier type in the source/drain andcentral channel regions of the MoTe2 channel can be efficiently tuned by the control gate and top gate, respectively,enabling the reconfigurable operation of the device in either memory or FET mode. When working inthe memory mode, it achieves an ultrafast 60 ns programming/erase speed with a current on-off ratio of ∼105,excellent retention capability, and robust endurance. When serving as a reconfigurable transistor, unipolar p-typeand n-type FETs are obtained by adopting ultrafast 60 ns control-gate voltage pulses with different polarities.The monolithic integration of memory and logic within a single device enables the content-addressable memory(CAM) functionality. Finally, by integrating two PFGFETs in parallel, a TCAM cell with a high current ratioof ∼10^(5) between the match and mismatch states is achieved without requiring additional peripheral circuitry.These results provide a promising route for the design of high-performance TCAM devices for future in-memorycomputing applications.展开更多
During normal de-ballasting operations for floating docks,each ballast pump independently manages a specific group of ballast tanks.However,when a pump malfunctions,a connection valve between the two groups of ballast...During normal de-ballasting operations for floating docks,each ballast pump independently manages a specific group of ballast tanks.However,when a pump malfunctions,a connection valve between the two groups of ballast water systems is opened.This allows the adjacent pump to serve as a helper pump,simultaneously controlling two groups of ballast water systems.This study explores a full-scale floating dock’s dynamic behaviours during the de-ballasting operations under this situation through a numerical model.In the developed numerical model,the dock is described as a six-degree-of-freedom rigid body which is subjected to hydrostatic,hydrodynamic,and mooring loads.A hydraulic model of the piping network of the malfunctioning pump and the helper pump is proposed.A modified P-controller regulates opening angles of all tank valves for minimal pitch and roll.Two configurations of the floating dock,i.e.,a single floating dock and a floating dock with an onboard vessel,are considered.The numerical results show that the optimal helper pumps can be identified regarding the pumps’total de-ballasting capacity and the dock’s stability.The most severe scenarios can be determined in term of the dock’s maximum draught differences caused by its roll and pitch.The observed maximum draught differences remain small relative to the dock’s width,indicating the effectiveness of employing helper pumps and the proposed automatic ballast control strategy for one-pump malfunction scenarios.展开更多
Lithium-ion batteries(LIBs)suffer from float charge failure in the grid-scale storage market.However,the lack of a unified descriptor for the diverse reasons behind float charge failure poses a challenge.Here,a quanti...Lithium-ion batteries(LIBs)suffer from float charge failure in the grid-scale storage market.However,the lack of a unified descriptor for the diverse reasons behind float charge failure poses a challenge.Here,a quantitative analysis of active lithium loss is conducted across multiple temperatures into float charge of Li(Ni_(0.5)Co_(0.2)Mn_(0.3))O_(2)–graphite batteries.It is proposed that the active lithium loss can be used as a descriptor to describe the reasons for float charge quantitatively.Approximately 6.88%and 0.96%of active lithium are lost due to solid electrolyte interphase thickening and lithium deposition,which are primary and secondary failure reasons,respectively.These findings are confirmed by X-ray photoelectron spectroscopy depth profiling,scanning electron microscope,and accelerating rate calorimeter.Titration-gas chromatography and nuclear magnetic resonance are utilized to quantitatively analyze active lithium loss.Additionally,electrolyte decomposition at high temperatures also contributes to active lithium loss,as determined by Auger electron spectrum and nondestructive ultrasound measurements.Notably,no failure is detected in the cathode due to the relatively low working voltage of the float charge.These findings suggest that inhibiting active lithium loss can be an efficient way of delaying failure during high-temperature float charge processes in LIBs.展开更多
Floating breakwaters(FBs)are commonly employed for the protection of coastal installations.In this work,a convextype floating breakwater(FB)is proposed,and its hydrodynamic characteristics are studied through systemat...Floating breakwaters(FBs)are commonly employed for the protection of coastal installations.In this work,a convextype floating breakwater(FB)is proposed,and its hydrodynamic characteristics are studied through systematic laboratory experiments.Two different deck widths and two different mooring systems are set in the experiment.The transmission coefficients,reflection coefficients,motion responses and mooring forces of convex-type FBs are obtained in experiments.The influences of the deck width and mooring system on the hydrodynamic characteristics of the proposed FB are analyzed and compared.The experimental results show that the reflection coefficient and mooring force of the convex-type FB with a cross-mooring system are significantly larger than those of the convextype FB with a parallel-mooring system.A convex-type FB with a larger deck width has a higher reflection coefficient.The convex-type FBs with cross-and parallel-mooring systems have similar surge and heave motions,but the cross-mooring results in small roll motion.In addition,reliable prediction formulas for the transmission coefficient of convex-type FBs with different mooring systems have been developed,which are important for engineering design.展开更多
Two asymmetric types of floating breakwaters integrated with a wave energy converter(WEC-FBs),a floating square box with a triangle(trapezoidal type)or a wave baffle(L type)attached to its rear side,have been proposed...Two asymmetric types of floating breakwaters integrated with a wave energy converter(WEC-FBs),a floating square box with a triangle(trapezoidal type)or a wave baffle(L type)attached to its rear side,have been proposed.In this research,the hydrodynamic performance,including capture width ratio(CWR),wave transmission coefficient,heave motion,and force coefficient,were studied and compared between the two types.A numerical simulation model based on the Navier-Stokes equation was employed.The effects of power take-off(PTO)damping coefficient,wave periods,and draft/displacement on the hydrodynamic performance of the two structure shapes were simulated and investigated.The results reveal that the L type performs better in shorter wave periods,and the trapezoidal type exhibits a higher CWR in intermediate wave periods.This study offers knowledge of the design and protection of the two WEC-FB types.展开更多
Under severe sea conditions, wave slamming on ships and marine engineering structures may lead to structural damage and casualties. Moreover, the strong nonlinearity inherent in the wave slamming process significantly...Under severe sea conditions, wave slamming on ships and marine engineering structures may lead to structural damage and casualties. Moreover, the strong nonlinearity inherent in the wave slamming process significantly limits the accuracy of numerical analyses and finite element simulations. Therefore, this paper takes a new type of floating wind turbine as an example and performs a physical model test on the wave slamming characteristics of this floating wind turbine.Based on a 1:50 model of the Pivot Buoy floating wind turbine, an experimental study is performed under the combined effects of wind-wave loads on the peak pressure, duration, and pressure distribution of slamming. First, two sets of mooring systems, the combined scheme and the full mooring chain scheme, are designed to conduct a series of experimental studies of model slamming under different wind and wave incidence angles, wave heights, and wave periods. By doing so, the slamming characteristics of the wind turbine can be obtained. Moreover, to solve the problem of the large pitch motion response of the prototype wind turbine, a set of vertically oscillating structures is designed,and the slamming pressure characteristics of the optimized model are also investigated through model tests.展开更多
Topology optimization stands as a pivotal technique in realizing periodic microstructure design.A novel approach is proposed,integrating the energy-based homogenization method with the Floating Projection Topology Opt...Topology optimization stands as a pivotal technique in realizing periodic microstructure design.A novel approach is proposed,integrating the energy-based homogenization method with the Floating Projection Topology Optimization(FPTO)method to achieve smooth topology design.The objective is to optimize the periodic microstructure to maximize the properties of specific materials,such as bulk modulus and shear modulus,or to achieve negative Poisson's ratio.Linear material interpolation is used to eliminate the nonlinear challenges and design dependence caused by material penalty.Furthermore,the three-field density representation technique is applied to augment length scales and solid/void characteristics.Through systematic analysis and numerical simulations,the impacts of various initial designs and optimization parameters on the optimization outcomes are investigated.The results demonstrate that the optimized periodic microstructures exhibit extreme performance with clear boundaries.The identification of appropriate optimization parameters is crucial for enhancing the extreme mechanical properties of material microstructures.It can provide valuable guidance for aerospace component design involving material microstructures and metamaterials.展开更多
The wave attenuation performance of a floating breakwater is important in engineering applications.On the basis of potential flow theory,the analytical and simplified solutions of the transmission coefficient of a flo...The wave attenuation performance of a floating breakwater is important in engineering applications.On the basis of potential flow theory,the analytical and simplified solutions of the transmission coefficient of a floating breakwater are deduced via velocity potential decompositions and eigenfunction expansions.The effects of the floating breakwater configuration,working sea state and motion response on the wave attenuation performance are described,facilitating a deeper investigation into the wave attenuation mechanism of the breakwater.The results indicate that the width and draft of the breakwater,incident wavelength,and motion response significantly affect the transmission coefficient of the breakwater.The wave passability rate,α1(α1=0.5−2B/L),is defined to qualitatively explain why long-period waves are difficult to control and attenuate.The radiation effect caused by the motion of the floating breakwater on the transmission coefficient is relatively complex,and the wave attenuation efficiency of the breakwater can be improved by optimizing the motion response.The incident wavelength and breakwater width are selected as the control parameters,and transmission coefficient charts of the floating breakwater for two-dimensional conditions are drawn,providing technical guidance for the configuration selection and design of the floating breakwater.展开更多
A floating nuclear power plant(FNPP)is an offshore facility that integrates proven light-water reactor technologies with floating platform characteristics.However,frequent contact with marine environments may lead to ...A floating nuclear power plant(FNPP)is an offshore facility that integrates proven light-water reactor technologies with floating platform characteristics.However,frequent contact with marine environments may lead to wave-induced vibrations and oscillations.This study aimed to evaluate the wave danger on FNPPs,which can negatively impact FNPP functionality.We developed a hydrodynamic model of an FNPP using potential flow theory and computed the frequency-domain fluid dynamic responses.After verifying the hydrodynamic model,we developed a predictive model for FNPP responses.This model utilizes a genetic aggregation methodology for batch prediction while ensuring accuracy.We analyzed all the wave data from a selected sea area over the past 50 years using the constructed surrogate model,enabling us to identify dangerous marine areas.By utilizing the extreme value distribution of important wave heights in these areas,we determined the wave return period,which poses a threat to FNPPs.This provides an important method for analyzing wave hazards to FNPPs.展开更多
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This work is supported by the National Key Research and Development Program of China(No.2023YFB4203000)the National Natural Science Foundation of China(No.U22A20178)
文摘Complicated loads encountered by floating offshore wind turbines(FOWTs)in real sea conditions are crucial for future optimization of design,but obtaining data on them directly poses a challenge.To address this issue,we applied machine learning techniques to obtain hydrodynamic and aerodynamic loads of FOWTs by measuring platform motion responses and wave-elevation sequences.First,a computational fluid dynamics(CFD)simulation model of the floating platform was established based on the dynamic fluid body interaction technique and overset grid technology.Then,a long short-term memory(LSTM)neural network model was constructed and trained to learn the nonlinear relationship between the waves,platform-motion inputs,and hydrodynamic-load outputs.The optimal model was determined after analyzing the sensitivity of parameters such as sample characteristics,network layers,and neuron numbers.Subsequently,the effectiveness of the hydrodynamic load model was validated under different simulation conditions,and the aerodynamic load calculation was completed based on the D'Alembert principle.Finally,we built a hybrid-scale FOWT model,based on the software in the loop strategy,in which the wind turbine was replaced by an actuation system.Model tests were carried out in a wave basin and the results demonstrated that the root mean square errors of the hydrodynamic and aerodynamic load measurements were 4.20%and 10.68%,respectively.
基金supported by the Key Laboratory of Ministry of Education for Coastal Disaster and Protection,Hohai University(Grant No.J202202)the National Natural Science Foundation of China(Grant No.11872174)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.B200202236)the Key Laboratory of Port,Waterway&Sedimentation Engineering Ministry of Communications,PRC(Grant No.Yk220001-2).
文摘The comprehensive numerical simulation of the tower shadow effect on floating offshore wind turbines(FOWTs),an area less explored compared to fixed-bottom wind turbines,is presented in this study.The atmospheric boundary layer inflow and the joint north sea wave project random wave are used as the operating conditions for FOWT.The combination of computational fluid dynamics(CFD)software simulator for wind farm applications and turbine simulation tool OpenFAST is used to implement fluid-structure interaction calculations.The output power,platform motion,wake velocity deficit and vortex structures are analyzed to reveal the influence of the tower shadow effect on the FOWT.The results indicate that due to the fluctuation caused by the turbulent wind and the floating platform motion,the tower shadow effect of FOWT is less significant for its periodic power decay than that of fixed-bottom wind turbines.And according to the velocity deficit analysis,the influence area of the tower shadow effect on the wake is mainly in the near wake region.
基金funded by the Key Technology Research and Development Program(Nos.2022YFB4201301,and 2022YFB4201304)the National Natural Science Foundation of China(Nos.52101333,52071058,51939002,and 52071301)+2 种基金the Zhejiang Provincial Natural Science Foundation of China(No.LQ21E090009)supported by the Natural Science Foundation of Liaoning Province(No.2022-KF-18-01)the special funds for Promoting High-Quality Development from the Department of Natural Resources of Guangdong Province(No.GDNRC[2020]016).
文摘Recently,semisubmersible floating offshore wind turbine technologies have received considerable attention.For the coupled simulation of semisubmersible floating offshore wind energy,the platform is usually considered a rigid model,which could affect the calculation accuracy of the dynamic responses.The dynamic responses of a TripleSpar floating offshore wind turbine equipped with a 10 MW offshore wind turbine are discussed herein.The simulation of a floating offshore wind turbine under regular waves,white noise waves,and combined wind-wave conditions is conducted.The effects of the tower and platform flexibility on the motion and force responses of the TripleSpar semisubmersible floating offshore wind turbine are investigated.The results show that the flexibility of the tower and platform can influence the dynamic responses of a TripleSpar semisubmersible floating offshore wind turbine.Considering the flexibility of the tower and platform,the tower and platform pitch motions markedly increased compared with the fully rigid model.Moreover,the force responses,particularly for tower base loads,are considerably influenced by the flexibility of the tower and platform.Thus,the flexibility of the tower and platform for the coupled simulation of floating offshore wind turbines must be appropriately examined.
文摘The offshore renewable energy industry has been developing farms of floating offshore wind turbines in water depths up to 100 m.In Vietnam,floating offshore wind turbines have been developed to increase the production of clean and sustainable energy.The mooring system,which is used to keep the turbine stable and ensure the safety and economic efficiency of wind power production,is an important part of a floating offshore wind turbine.Appropriate selection of the mooring type and mooring line material can reduce the risks arising from the motion of wind turbines.Different types of mooring line material have been simulated and compared in order to determine the optimal type with the minimum motion risk for a floating wind turbine.This study focused on numerical modeling of semi-taut mooring systems using nonlinear materials for a semi-submersible wind turbine.Several modeling approaches common to current practice were applied.Hydrodynamic analysis was performed to investigate the motion of the response amplitude operators of the floating wind turbine.Dynamic analysis of mooring systems was performed using a time domain to obtain the tension responses of mooring lines under the ultimate limit states and fatigue limit states in Vietnamese sea conditions.The results showed that the use of nonlinear materials(polyester and/or nylon)for mooring systems can minimize the movement of the turbine and save costs.The use of synthetic fibers can reduce the maximum tension in mooring lines and the length of mooring lines.However,synthetic fiber ropes showed highly nonlinear load elongation properties,which were difficult to simulate using numerical software.The comparison of the characteristics of polyester and nylon mooring lines showed that the maximum and mean tensions of the nylon line were less than those of the polyester line.In addition,the un-stretched length of the polyester line was greater than that of the nylon line under the same mean tension load.Therefore,nylon material is recommended for the mooring lines of a floating offshore wind turbine.
文摘Mooring cable tension is a crucial parameter for evaluating the safety and reliability of a floating platform mooring system.The real-time mooring tension in an actual marine environment has always been essential data that mooring system designers aim to acquire.To address the need for long-term continuous monitoring of mooring tension in deep-sea marine environments,this paper presents a mooring cable tension monitoring method based on the principle of direct mechanical measurement.The developed tension monitoring sensors were installed and applied in the mooring system of the"Yongle"scientific experimental platform.Over the course of one year,a substantial amount of in-situ tension monitoring data was obtained.Under wave heights of up to 1.24 m,the mooring tension on the floating platform reached 16.5 tons.Through frequency domain and time domain analysis,the spectral characteristics of mooring tension,including waveinduced force,slow drift force,and mooring cable elastic restoring force,were determined.The mooring cable elastic restoring force frequency was approximately half of that of the wave signal.Due to the characteristics of the hinge connection structure of the dual module floating platform,under some specific working conditions the wave-induced force was the maximum of the three different frequency forces,and restoring force was the smallest.
基金supported by the Portuguese Foundation for Science and Technology(Fundação para a Ciência e Tecnologia-FCT)it contributes to the Strategic Research Plan of the Centre for Marine Technology and Ocean Engineering(Grant No.UIDB/UIDP/00134/2020)funded the first author for his PhD Scholarship(Grant No.SFRH/BD/145602/2019).
文摘This paper presents an overview of the recent developments in hybrid wind-wave energy.With the focus on floating concepts,the possible configurations introduced in the literature are categorized and depicted,and the main conclusions obtained from the references are summarized.Moreover,offshore wind and wave resources are discussed in terms of complementarity and supplementarity,offering a new perspective to developing hybrid wind-wave energy systems that look for synergies not limited to maximizing power output.Then,the feasibility of the concepts under development is discussed in detail,with focus on technical feasibility,dynamic feasibility and limitations of the methods employed.The hybrid configurations that surpassed the experimental validation phase are highlighted,and the experimental results are summarized.By compiling more than 40 floating wind turbine concepts,new relations are drawn between power,wind turbine dimensions,platforms’draft and displacement,which are further related to the payload allowance of the units to accommodate wave devices and onboard power take-off systems.Bearing in mind that it is a challenge to model the exact dynamics of hybrid floating wind-wave platforms,this paper elucidates the current research gaps,limitations and future trends in the field.Lastly,based on the overview and topics discussed,several major conclusions are drawn concerning hybrid synergies,dynamics and hydrodynamics of hybrid platforms,feasibility of concepts,among other regards.
文摘Modularfiloating structures(MFS)offer a sustainable pathway towards the expansion of coastal cities in adaptation tofilooding and sea level rise driven by climate change.It is therefore necessary to develop analytical methods easily accessible to architects or structural engineers for the rapid prototyping of MFS designs.This work develops novel closed‑form expressions describing the rigid body dynamics of symmetrically loaded rectangular pontoons across all six degrees of freedom(DOF)excited by surface waves approaching from any arbitrary direction.The derivations were based on Airy wave theory assuming frequency‑independent added mass and damping.When benchmarked against numerical solutions from ANSYS/AQWA for two MFS prototypes,the analytical approach proved capable of predicting the response amplitude operators(RAO)across all DOFs,wave directions,and structural confiigurations.However,while the response of mass‑dominated DOFs(surge,sway,and yaw)were well captured,the damping ratio for stiffness‑dominated DOFs(heave,roll,and pitch)must be judiciously selected to yield accurate RAO results.A parametric investigation further elucidated the contribution of structural geometry and wave directionality on the critical accelerations experienced by an idealizedfiloating structure founded upon a square pontoon under realistic sea states.It was discovered that the largest accelerations were triggered by waves approaching orthogonally to the pontoon.Ultimately,this work facilitates a more streamlined approach for the dynamic analysis of compliantfiloating bodies to supplement detailed modeling efforts via numerical methods.
基金supported by the National Natural Science Foundation of China(No.52271287).
文摘Offshore floating photovoltaic systems have tremendous potential to address the energy crisis.As a novel type of float-ing photovoltaic system,membrane structures are increasingly applied due to their advantages of being lightweight and cost-effective.A 1:40 scaled model for laboratory experiments was designed and developed,considering Ocean Sun’s membrane structure.The study aims to investigate the hydrodynamic characteristics of the membrane structure under wave loading by testing its various mo-tion responses and mooring forces at different wave heights and periods.The conclusions indicate that as the wave period decreases within the range of 1.75 to 1.25 s,the heave motion response of the structure decreases,whereas pitch,surge motion response,heave acceleration,and mooring force increase.The amplitudes of various motions and mooring forces of the structure decrease with de-creasing wave height.The hydrodynamic responses under irregular and regular waves follow similar patterns,but the responses and mooring forces induced by irregular waves are more significant.The structure should be designed based on the actual wave height.In addition,the same frequency resonance phenomenon is avoided because the movement period of each degree of freedom is close to the wave period.
文摘Siwa Oasis,one of Egypts most remote settlements,is also a popular tourist destination thanks to the beautiful salt pools with water that people can float in.Salt is both a blessing and a curse in Siwa.Years ago,people started realizing that there was money to be made in the salt trade,and salt mining operations created the salt lakes that the oasis is now famous for.
基金supported by the National Key Research&Development Projects of China(Grant No.2022YFA1204100)National Natural Science Foundation of China(Grant No.62488201)+1 种基金CAS Project for Young Scientists in Basic Research(YSBR-003)the Innovation Program of Quantum Science and Technology(2021ZD0302700)。
文摘As a typical in-memory computing hardware design, nonvolatile ternary content-addressable memories(TCAMs) enable the logic operation and data storage for high throughout in parallel big data processing. However,TCAM cells based on conventional silicon-based devices suffer from structural complexity and large footprintlimitations. Here, we demonstrate an ultrafast nonvolatile TCAM cell based on the MoTe2/hBN/multilayergraphene (MLG) van der Waals heterostructure using a top-gated partial floating-gate field-effect transistor(PFGFET) architecture. Based on its ambipolar transport properties, the carrier type in the source/drain andcentral channel regions of the MoTe2 channel can be efficiently tuned by the control gate and top gate, respectively,enabling the reconfigurable operation of the device in either memory or FET mode. When working inthe memory mode, it achieves an ultrafast 60 ns programming/erase speed with a current on-off ratio of ∼105,excellent retention capability, and robust endurance. When serving as a reconfigurable transistor, unipolar p-typeand n-type FETs are obtained by adopting ultrafast 60 ns control-gate voltage pulses with different polarities.The monolithic integration of memory and logic within a single device enables the content-addressable memory(CAM) functionality. Finally, by integrating two PFGFETs in parallel, a TCAM cell with a high current ratioof ∼10^(5) between the match and mismatch states is achieved without requiring additional peripheral circuitry.These results provide a promising route for the design of high-performance TCAM devices for future in-memorycomputing applications.
基金The article is a result of joined research performed during the project:“A Floating Dock Digital Twin towards Efficient,Safer and Autonomous Docking Operations”-NOR/POLNOR/DigiFloDock/0009/2019-00 which is cofinanced by the programme“Applied research”under the Norwegian Financial Mechanisms 2014-2021 POLNOR 2019-Digital and Industry.
文摘During normal de-ballasting operations for floating docks,each ballast pump independently manages a specific group of ballast tanks.However,when a pump malfunctions,a connection valve between the two groups of ballast water systems is opened.This allows the adjacent pump to serve as a helper pump,simultaneously controlling two groups of ballast water systems.This study explores a full-scale floating dock’s dynamic behaviours during the de-ballasting operations under this situation through a numerical model.In the developed numerical model,the dock is described as a six-degree-of-freedom rigid body which is subjected to hydrostatic,hydrodynamic,and mooring loads.A hydraulic model of the piping network of the malfunctioning pump and the helper pump is proposed.A modified P-controller regulates opening angles of all tank valves for minimal pitch and roll.Two configurations of the floating dock,i.e.,a single floating dock and a floating dock with an onboard vessel,are considered.The numerical results show that the optimal helper pumps can be identified regarding the pumps’total de-ballasting capacity and the dock’s stability.The most severe scenarios can be determined in term of the dock’s maximum draught differences caused by its roll and pitch.The observed maximum draught differences remain small relative to the dock’s width,indicating the effectiveness of employing helper pumps and the proposed automatic ballast control strategy for one-pump malfunction scenarios.
基金supported by the National Key Research and Development(R&D)Program of China(2022YFB4101600)Key Research and Development(R&D)Projects of Shanxi Province(202102040201003,202202040201007)+1 种基金the Fundamental Research Program of Shanxi Province(20210302123008)the ICC CAS,SCJC-XCL-2023-13,CAS Project for Young Scientists in Basic Research(Grant No.YSBR-102).
文摘Lithium-ion batteries(LIBs)suffer from float charge failure in the grid-scale storage market.However,the lack of a unified descriptor for the diverse reasons behind float charge failure poses a challenge.Here,a quantitative analysis of active lithium loss is conducted across multiple temperatures into float charge of Li(Ni_(0.5)Co_(0.2)Mn_(0.3))O_(2)–graphite batteries.It is proposed that the active lithium loss can be used as a descriptor to describe the reasons for float charge quantitatively.Approximately 6.88%and 0.96%of active lithium are lost due to solid electrolyte interphase thickening and lithium deposition,which are primary and secondary failure reasons,respectively.These findings are confirmed by X-ray photoelectron spectroscopy depth profiling,scanning electron microscope,and accelerating rate calorimeter.Titration-gas chromatography and nuclear magnetic resonance are utilized to quantitatively analyze active lithium loss.Additionally,electrolyte decomposition at high temperatures also contributes to active lithium loss,as determined by Auger electron spectrum and nondestructive ultrasound measurements.Notably,no failure is detected in the cathode due to the relatively low working voltage of the float charge.These findings suggest that inhibiting active lithium loss can be an efficient way of delaying failure during high-temperature float charge processes in LIBs.
基金financially supported by the National Natural Science Foundation of China(Grant No.52088102)New Cornerstone Science Foundation through the XPLORER PRIZE.
文摘Floating breakwaters(FBs)are commonly employed for the protection of coastal installations.In this work,a convextype floating breakwater(FB)is proposed,and its hydrodynamic characteristics are studied through systematic laboratory experiments.Two different deck widths and two different mooring systems are set in the experiment.The transmission coefficients,reflection coefficients,motion responses and mooring forces of convex-type FBs are obtained in experiments.The influences of the deck width and mooring system on the hydrodynamic characteristics of the proposed FB are analyzed and compared.The experimental results show that the reflection coefficient and mooring force of the convex-type FB with a cross-mooring system are significantly larger than those of the convextype FB with a parallel-mooring system.A convex-type FB with a larger deck width has a higher reflection coefficient.The convex-type FBs with cross-and parallel-mooring systems have similar surge and heave motions,but the cross-mooring results in small roll motion.In addition,reliable prediction formulas for the transmission coefficient of convex-type FBs with different mooring systems have been developed,which are important for engineering design.
基金Supported by Shandong Provincial Natural Science Foundation,China(ZR2020ME259)Open Fund of Shandong Key Laboratory of Civil Engineering Disaster Prevention and Mitigation(CDPM2021KF21).
文摘Two asymmetric types of floating breakwaters integrated with a wave energy converter(WEC-FBs),a floating square box with a triangle(trapezoidal type)or a wave baffle(L type)attached to its rear side,have been proposed.In this research,the hydrodynamic performance,including capture width ratio(CWR),wave transmission coefficient,heave motion,and force coefficient,were studied and compared between the two types.A numerical simulation model based on the Navier-Stokes equation was employed.The effects of power take-off(PTO)damping coefficient,wave periods,and draft/displacement on the hydrodynamic performance of the two structure shapes were simulated and investigated.The results reveal that the L type performs better in shorter wave periods,and the trapezoidal type exhibits a higher CWR in intermediate wave periods.This study offers knowledge of the design and protection of the two WEC-FB types.
基金financially supported by the National Natural Science Foundation of China (Grant No. 52071161)。
文摘Under severe sea conditions, wave slamming on ships and marine engineering structures may lead to structural damage and casualties. Moreover, the strong nonlinearity inherent in the wave slamming process significantly limits the accuracy of numerical analyses and finite element simulations. Therefore, this paper takes a new type of floating wind turbine as an example and performs a physical model test on the wave slamming characteristics of this floating wind turbine.Based on a 1:50 model of the Pivot Buoy floating wind turbine, an experimental study is performed under the combined effects of wind-wave loads on the peak pressure, duration, and pressure distribution of slamming. First, two sets of mooring systems, the combined scheme and the full mooring chain scheme, are designed to conduct a series of experimental studies of model slamming under different wind and wave incidence angles, wave heights, and wave periods. By doing so, the slamming characteristics of the wind turbine can be obtained. Moreover, to solve the problem of the large pitch motion response of the prototype wind turbine, a set of vertically oscillating structures is designed,and the slamming pressure characteristics of the optimized model are also investigated through model tests.
基金supported by the financial support from the National Natural Science Foundation of China(No.52172356)Hunan Provincial Natural Science Foundation of China(No.2022JJ10012)。
文摘Topology optimization stands as a pivotal technique in realizing periodic microstructure design.A novel approach is proposed,integrating the energy-based homogenization method with the Floating Projection Topology Optimization(FPTO)method to achieve smooth topology design.The objective is to optimize the periodic microstructure to maximize the properties of specific materials,such as bulk modulus and shear modulus,or to achieve negative Poisson's ratio.Linear material interpolation is used to eliminate the nonlinear challenges and design dependence caused by material penalty.Furthermore,the three-field density representation technique is applied to augment length scales and solid/void characteristics.Through systematic analysis and numerical simulations,the impacts of various initial designs and optimization parameters on the optimization outcomes are investigated.The results demonstrate that the optimized periodic microstructures exhibit extreme performance with clear boundaries.The identification of appropriate optimization parameters is crucial for enhancing the extreme mechanical properties of material microstructures.It can provide valuable guidance for aerospace component design involving material microstructures and metamaterials.
基金supported by the China National Funds for Distinguished Young Scientists(Grant No.52025112)the National Natural Science Foundation of China(Grant Nos.52331011 and 52301322)the Jiangsu Provincial Natural Science Foundation(Grant No.BK20220653).
文摘The wave attenuation performance of a floating breakwater is important in engineering applications.On the basis of potential flow theory,the analytical and simplified solutions of the transmission coefficient of a floating breakwater are deduced via velocity potential decompositions and eigenfunction expansions.The effects of the floating breakwater configuration,working sea state and motion response on the wave attenuation performance are described,facilitating a deeper investigation into the wave attenuation mechanism of the breakwater.The results indicate that the width and draft of the breakwater,incident wavelength,and motion response significantly affect the transmission coefficient of the breakwater.The wave passability rate,α1(α1=0.5−2B/L),is defined to qualitatively explain why long-period waves are difficult to control and attenuate.The radiation effect caused by the motion of the floating breakwater on the transmission coefficient is relatively complex,and the wave attenuation efficiency of the breakwater can be improved by optimizing the motion response.The incident wavelength and breakwater width are selected as the control parameters,and transmission coefficient charts of the floating breakwater for two-dimensional conditions are drawn,providing technical guidance for the configuration selection and design of the floating breakwater.
文摘A floating nuclear power plant(FNPP)is an offshore facility that integrates proven light-water reactor technologies with floating platform characteristics.However,frequent contact with marine environments may lead to wave-induced vibrations and oscillations.This study aimed to evaluate the wave danger on FNPPs,which can negatively impact FNPP functionality.We developed a hydrodynamic model of an FNPP using potential flow theory and computed the frequency-domain fluid dynamic responses.After verifying the hydrodynamic model,we developed a predictive model for FNPP responses.This model utilizes a genetic aggregation methodology for batch prediction while ensuring accuracy.We analyzed all the wave data from a selected sea area over the past 50 years using the constructed surrogate model,enabling us to identify dangerous marine areas.By utilizing the extreme value distribution of important wave heights in these areas,we determined the wave return period,which poses a threat to FNPPs.This provides an important method for analyzing wave hazards to FNPPs.
