Offshore wind power is a kind of important clean renewable energy and has attracted increasing attention due to the rapid consumption of non-renewable energy.To reduce the high cost of energy,a possible try is to util...Offshore wind power is a kind of important clean renewable energy and has attracted increasing attention due to the rapid consumption of non-renewable energy.To reduce the high cost of energy,a possible try is to utilize the combination of wind and wave energy considering their natural correlation.A combined concept consisting of a semi-submersible wind turbine and four torus-shaped wave energy converters was proposed and numerically studied under normal operating conditions.However,the dynamic behavior of the integrated system under extreme sea conditions has not been studied yet.In the present work,extreme responses of the integrated system under two different survival modes are evaluated.Fully coupled time-domain simulations with consideration of interactions between the semi-submersible wind turbine and the torus-shaped wave energy converters are performed to investigate dynamic responses of the integrated system,including mooring tensions,tower bending moments,end stop forces,and contact forces at the Column-Torus interface.It is found that the addition of four tori will reduce the mean motions of the yaw,pitch and surge.When the tori are locked at the still water line,the whole integrated system is more suitable for the survival modes.展开更多
This article provides a method by which the scour depth and scour width below pipelines,and the scour depth around single vertical piles as well as the time scales of scour for both structures due to bichromatic and b...This article provides a method by which the scour depth and scour width below pipelines,and the scour depth around single vertical piles as well as the time scales of scour for both structures due to bichromatic and bidirectional waves are calculated.The scour and time scale formulae summarized by Sumer and Fredsøe(2002)as well as the bottom shear stress formulae under bichromatic and bidirectional waves by Myrhaug et al.(2023)are used.Results for unidirectional bichromatic waves and symmetrically bidirectional monochromatic waves are provided,showing qualitative agreement with what is expected physically.Qualitative comparisons are made with the data from Schendel et al.’s(2020)small scale laboratory tests on scour around a monopile induced by directionally spread waves.Applications to related cases for pipelines are also suggested.In order to conclude regarding the validity of the method for pipelines and vertical piles,it is required to compare with data in its validity range.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
Splash zone crossing of the structures with large horizontal surface （e.g. manifolds） and the structures having large weight variation in water and air （e.g. suction anchors） is a critical marine operation. This i...Splash zone crossing of the structures with large horizontal surface （e.g. manifolds） and the structures having large weight variation in water and air （e.g. suction anchors） is a critical marine operation. This is due to the large slamming forces and added mass of the structure, which results in high dynamic loads on the crane. The solution to this could be attaching a PHC （Passive Heave Compensator） between the crane hook and the payload. This paper analyzes the deployment of a subsea manifold with and without PHC unit in North Sea at a water depth of approximately 370 m. A detailed dynamic analysis is done for a seastate of 3 m significant wave height （Hs） over a range of zero up-crossing period （Tz） varying from 3s to 13 s. For better understanding of the result analysis has been done in two stages. The first stage covers the lowering of manifold through the splash zone while second stage covers the seabed landing of the manifold. Based on the results of the analyses it is concluded that PHC tends to reduce the dynamic peak load on the crane. Besides this, it also mitigates the risk of slack wire situations during splash zone crossing of the payload. Furthermore, reduction in both landing velocity and crane tip velocity is also achieved by using a well-designed PHC unit.展开更多
Subsea templates are steel structures used to support subsea well components.Normally,offshore crane vessels are employed to install them to the target location on the seabed.Crossing the splash-zone during the ...Subsea templates are steel structures used to support subsea well components.Normally,offshore crane vessels are employed to install them to the target location on the seabed.Crossing the splash-zone during the lowering of a subsea template is considered the most critical phase during the installation due to slamming loads and needs to be studied to provide the operational weather criterion during the planning phase.In this study,dynamic response analysis has been carried out to evaluate the allowable sea states for the plash-zone crossing phase of the subsea templates.The numerical model of the lifting system,including the crane vessel and the subsea template,is firstly built in the state-of-the-art numerical program SIMA-SIMO.Then,dynamic analysis with time-domain simulations is carried out for the lifting system under various sea states.The disturbed wave field due to the shielding effects from the installation vessel is considered when calculating the hydrodynamic forces on the template.Statistical modelling of the dynamic responses from different wave realizations is used to estimate the extreme responses of various sea states.The application of the generalized extreme value distribution and Gumbel distribution in fitting the extreme responses is discussed.Moreover,the influence of the shielding effects from the vessel,as well as the influence of the changing size of the suction anchor on the hydrodynamic responses and the allowable sea states are studied.展开更多
For intermediate water depths(typically ranging from 50 m to 80 m),designing steel catenary mooring systems for floating marine renewable energy(FMRE)platforms can be challenging due to the limited weight of suspended...For intermediate water depths(typically ranging from 50 m to 80 m),designing steel catenary mooring systems for floating marine renewable energy(FMRE)platforms can be challenging due to the limited weight of suspended mooring lines.This can substantially increase mooring line tensions following large platform offsets.In contrast,mooring systems using synthetic fibre ropes offer the potential to prevent large platform offsets while reducing peak mooring line tensions.In this study,novel semi-taut moor-ing systems incorporating polyester ropes and steel chains are proposed for a combined wind and wave energy system-the semi-submersible flap torus combination(STFC)concept,deployed at a 50 m wa-ter depth.The STFC integrates a semi-submersible floating offshore wind turbine(FOWT),a torus wave energy converter(WEC)and three flap-type WECs.The dynamic responses of the STFC with different semi-taut mooring configurations under operational and survival environmental conditions are assessed in terms of key performance parameters such as the platform’s motion responses and mooring line ten-sions.These performance parameters are compared against those of a chain-catenary mooring system.With the use of semi-taut mooring systems,significantly smaller mooring footprints as compared to the chain-catenary mooring systems can be achieved.Moreover,it is demonstrated that the semi-taut moor-ing systems are effective in reducing the maximum tension of the mooring lines.A basic cost analysis further indicates that semi-taut mooring systems offer substantial cost advantages over chain-catenary moorings in intermediate water depths.展开更多
Monolithic catalysts for CO_(2) methanation have become an active research area for the industrial development of Power-to-Gas technology.In this study,we developed a facile and reproducible synthesis strategy for the...Monolithic catalysts for CO_(2) methanation have become an active research area for the industrial development of Power-to-Gas technology.In this study,we developed a facile and reproducible synthesis strategy for the preparation of structured NiFe catalysts on washcoated cordierite monoliths for CO_(2) methanation.The NiFe catalysts were derived from in-situ grown layered double hydroxides(LDHs)via urea hydrolysis.The influence of different washcoat materials,i.e.,alumina and silica colloidal suspensions on the formation of LDHs layer was investigated,together with the impact of total metal concentration.NiFe LDHs were precipitated on the exterior surface of cordierite washcoated with alumina,while it was found to deposit further inside the channel wall of monolith washcoated with silica due to different intrinsic properties of the colloidal solutions.On the other hand,the thickness of in-situ grown LDHs layers and the catalyst loading could be increased by high metal concentration.The best monolithic catalyst(COR-AluCC-0.5M)was robust,having a thin and well-adhered catalytic layer on the cordierite substrate.As a result,high methane yield was obtained from CO_(2) methanation at high flow rate on this structured NiFe catalysts.The monolithic catalysts appeared as promising structured catalysts for the development of industrial methanation reactor.展开更多
Wind farms generally consist of a single turbine installed with the same hub height. As the scale of turbines increases,wake interference between turbines becomes increasingly significant, especially for floating wind...Wind farms generally consist of a single turbine installed with the same hub height. As the scale of turbines increases,wake interference between turbines becomes increasingly significant, especially for floating wind turbines(FWT).Some researchers find that wind farms with multiple hub heights could increase the annual energy production(AEP),while previous studies also indicate that wake meandering could increase fatigue loading. This study investigates the wake interaction within a hybrid floating wind farm with multiple hub heights. In this study, FAST.Farm is employed to simulate a hybrid wind farm which consists of four semi-submersible FWTs(5MW and 15MW) with two different hub heights. Three typical wind speeds(below-rated, rated, and over-rated) are considered in this paper to investigate the wake meandering effects on the dynamics of two FWTs. Damage equivalent loads(DEL) of the turbine critical components are computed and analyzed for several arrangements determined by the different spacing of the four turbines. The result shows that the dynamic wake meandering significantly affects downstream turbines’ global loadings and load effects. Differences in DEL show that blade-root flapwise bending moments and mooring fairlead tensions are sensitive to the spacing of the turbines.展开更多
Background:To estimate cardiovascular and cancer death rates by regions and time periods.Design:Novel statistical methods were used to analyze clinical surveillance data.Methods:A multicenter,population-based medical ...Background:To estimate cardiovascular and cancer death rates by regions and time periods.Design:Novel statistical methods were used to analyze clinical surveillance data.Methods:A multicenter,population-based medical survey was performed.Annual recorded deaths from cardiovascular diseases were analyzed for all 195 countries of the world.It is challenging to model such data;few mathematical models can be applied because cardiovascular disease and cancer data are generally not normally distributed.Results:A novel approach to assessing the biosystem reliability is introduced and has been found to be particularly suitable for analyzing multiregion environmental and healthcare systems.While traditional methods for analyzing temporal observations of multiregion processes do not deal with dimensionality efficiently,our methodology has been shown to be able to cope with this challenge.Conclusions:Our novel methodology can be applied to public health and clinical survey data.展开更多
This paper first describes the importance of using location specific S-N curves for fatigue damage assessment of existing steel structures. It discusses the existing concepts and methods for developing S-N curves usin...This paper first describes the importance of using location specific S-N curves for fatigue damage assessment of existing steel structures. It discusses the existing concepts and methods for developing S-N curves using empirical formulae and monotonic strength parameters, such as the ultimate tensile strength and hardness. It also discusses relationships among these monotonic parameters. Then it presents formulae for developing hardness-based full range S-N curves for medium strength steels. The formulae are verified using experimental data obtained from both monotonic and cyclic testing. Finally, it describes the advantages of these hardness-based formulae for developing location specific S-N curves as hardness testing is a non-destructive test which can be carried out on specific locations in structures.展开更多
This paper presents a study where artificial neural networks are used as a curve fitting method applying measured data from an axial compressor test rig to predict the compressor map. Emphasis is on models for predict...This paper presents a study where artificial neural networks are used as a curve fitting method applying measured data from an axial compressor test rig to predict the compressor map. Emphasis is on models for prediction of pressure ratio, compressor mass flow and mechanical efficiency. Except for evaluation of interpolation and extrapolation capabilities, this study also investigates the effect of the design parameters such as number of neurons and size of training data. To reduce the effect of noise, the auto associative neural network has been applied for noise filtering of the data from the parameters used to calculate the efficiency. In summary, the results show that artificial neural network can be used for compressor map prediction, but it should be emphasized that the selection of data normalisation scale is crucial for the model where compressor mass flow is predicted. Furthermore, it is shown that the AANN （auto associative neural network） can be used to the reduce noise in measured data and thereby enhance the quality of the data.展开更多
This study presents a conceptual design for a cost-effective submersible gravity-type fish cage with a single-point mooring design.The performance of the new design in reducing environmental loads under extreme sea co...This study presents a conceptual design for a cost-effective submersible gravity-type fish cage with a single-point mooring design.The performance of the new design in reducing environmental loads under extreme sea con-ditions is demonstrated using an in-house numerical code package.The effectiveness of the submerging and surfacing operations of the fish cages is validated through numerical simulations.In the present code package,irregular wave modelling is employed to generate the wave elevations,velocities and accelerations,and the hydrodynamic forces acting on the fish cages and mooring system are calculated using the Morison model.A submersible model for the floating collar is developed to simulate the submerging and surfacing operations of the fish cages.The deformations of the fish cage system are calculated using a modified extended position based dynamics(XPBD)method combined with a mode superposition method.Results show that tension in the mooring system is significantly reduced when fish cages are submerged in the water layer with lower current speeds,and extending the buoy line to lower the conjunction point helps maintain fish cages in the desired water layer under extreme sea conditions.Flooding the outer tubes of the floating collar allows the fish cages to smoothly submerge to the desired water depth.The surfacing designs based on the compressed air and the lifting operation of the bottom sinker can enable the cages to ascend to the water surface.The submerging and surface operations are proved to be completed within six minutes.The new design based on the lifting operation of the bottom sinker,is safer and more cost-effective than the design based on compressed air for the surfacing operation.The design of the submersible single-point mooring gravity-type fish cage is thereby validated through the present numerical methods,offering valuable insights for future aquaculture design and implementation.展开更多
In the present study,a numerical model is first calibrated against the crack networks and pressure attenuation data in laboratory blasting test.Then,based on the calibrated numerical model,two-hole plane models are de...In the present study,a numerical model is first calibrated against the crack networks and pressure attenuation data in laboratory blasting test.Then,based on the calibrated numerical model,two-hole plane models are developed and used to perform a series of sim-ulations of smoothwall blasting in deep tunnelling subjected to in-situ stress.The evolutions of rock fracture and excavation damage zone in the roof/floor and sidewalls under different far-field hydrostatic pressure and anisotropic in-situ stress conditions are numerically investigated.The findings in numerical modelling are also analytically interpreted with the stress distributions around the designed tunnel perimeter and perimeter borehole.The numerical and analytical results show that the variations of rock cracking and excavation dam-aged zone induced by smoothwall blasting with in-situ stress are mainly attributed to the high tangential compressive stress concentration around the remaining rock after inner primary blasts and the tensile stress acting on the wall of perimeter hole,which control the crack propagation and initiation respectively.At last,the implications of findings for practical smoothwall blasting in deep tunnelling are discussed.展开更多
Subsea templates are normally transported to the installation site on the deck of a crane vessel.After being lifted off from the deck,the template is 1)over-boarded from the initial location to the target position by ...Subsea templates are normally transported to the installation site on the deck of a crane vessel.After being lifted off from the deck,the template is 1)over-boarded from the initial location to the target position by the side of the vessel;2)lowered through the splash zone;3)further lowered down to the seabed and 4)finally positioned and landed.All the mentioned phases should be evaluated.Usually,the splash zone crossing phase is taken as the critical phase and analyzed to define the installation weather criterion.The over-boarding phase has not been the focus of analysis due to a large involvement of human actions and little involvement of hydrodynamic effects.During offshore operations,the offshore manager may decide to decrease the defined installation weather criterion if the risk of the personnel safety on deck during over-boarding phase is considered high.Thus,it is of great need to quantify the operational criterion for such operation.The objective of this paper is to perform numerical analyses and define the allowable sea states for a safe over-boarding operation.The numerical analyses using time-domain simulations have been performed in various sea states.Tugger lines have been modelled to control the motions of the template during the operation.The pendulum motions of the subsea template are considered as the critical responses for the assessment of the allowable sea states.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52171289,42176210,and 52201330)the Guangdong Basic and Applied Basic Research Foundation,China(Grant No.2022B1515250005)Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(Grant No.311023014).
文摘Offshore wind power is a kind of important clean renewable energy and has attracted increasing attention due to the rapid consumption of non-renewable energy.To reduce the high cost of energy,a possible try is to utilize the combination of wind and wave energy considering their natural correlation.A combined concept consisting of a semi-submersible wind turbine and four torus-shaped wave energy converters was proposed and numerically studied under normal operating conditions.However,the dynamic behavior of the integrated system under extreme sea conditions has not been studied yet.In the present work,extreme responses of the integrated system under two different survival modes are evaluated.Fully coupled time-domain simulations with consideration of interactions between the semi-submersible wind turbine and the torus-shaped wave energy converters are performed to investigate dynamic responses of the integrated system,including mooring tensions,tower bending moments,end stop forces,and contact forces at the Column-Torus interface.It is found that the addition of four tori will reduce the mean motions of the yaw,pitch and surge.When the tori are locked at the still water line,the whole integrated system is more suitable for the survival modes.
文摘This article provides a method by which the scour depth and scour width below pipelines,and the scour depth around single vertical piles as well as the time scales of scour for both structures due to bichromatic and bidirectional waves are calculated.The scour and time scale formulae summarized by Sumer and Fredsøe(2002)as well as the bottom shear stress formulae under bichromatic and bidirectional waves by Myrhaug et al.(2023)are used.Results for unidirectional bichromatic waves and symmetrically bidirectional monochromatic waves are provided,showing qualitative agreement with what is expected physically.Qualitative comparisons are made with the data from Schendel et al.’s(2020)small scale laboratory tests on scour around a monopile induced by directionally spread waves.Applications to related cases for pipelines are also suggested.In order to conclude regarding the validity of the method for pipelines and vertical piles,it is required to compare with data in its validity range.
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.
文摘Splash zone crossing of the structures with large horizontal surface （e.g. manifolds） and the structures having large weight variation in water and air （e.g. suction anchors） is a critical marine operation. This is due to the large slamming forces and added mass of the structure, which results in high dynamic loads on the crane. The solution to this could be attaching a PHC （Passive Heave Compensator） between the crane hook and the payload. This paper analyzes the deployment of a subsea manifold with and without PHC unit in North Sea at a water depth of approximately 370 m. A detailed dynamic analysis is done for a seastate of 3 m significant wave height （Hs） over a range of zero up-crossing period （Tz） varying from 3s to 13 s. For better understanding of the result analysis has been done in two stages. The first stage covers the lowering of manifold through the splash zone while second stage covers the seabed landing of the manifold. Based on the results of the analyses it is concluded that PHC tends to reduce the dynamic peak load on the crane. Besides this, it also mitigates the risk of slack wire situations during splash zone crossing of the payload. Furthermore, reduction in both landing velocity and crane tip velocity is also achieved by using a well-designed PHC unit.
文摘Subsea templates are steel structures used to support subsea well components.Normally,offshore crane vessels are employed to install them to the target location on the seabed.Crossing the splash-zone during the lowering of a subsea template is considered the most critical phase during the installation due to slamming loads and needs to be studied to provide the operational weather criterion during the planning phase.In this study,dynamic response analysis has been carried out to evaluate the allowable sea states for the plash-zone crossing phase of the subsea templates.The numerical model of the lifting system,including the crane vessel and the subsea template,is firstly built in the state-of-the-art numerical program SIMA-SIMO.Then,dynamic analysis with time-domain simulations is carried out for the lifting system under various sea states.The disturbed wave field due to the shielding effects from the installation vessel is considered when calculating the hydrodynamic forces on the template.Statistical modelling of the dynamic responses from different wave realizations is used to estimate the extreme responses of various sea states.The application of the generalized extreme value distribution and Gumbel distribution in fitting the extreme responses is discussed.Moreover,the influence of the shielding effects from the vessel,as well as the influence of the changing size of the suction anchor on the hydrodynamic responses and the allowable sea states are studied.
文摘For intermediate water depths(typically ranging from 50 m to 80 m),designing steel catenary mooring systems for floating marine renewable energy(FMRE)platforms can be challenging due to the limited weight of suspended mooring lines.This can substantially increase mooring line tensions following large platform offsets.In contrast,mooring systems using synthetic fibre ropes offer the potential to prevent large platform offsets while reducing peak mooring line tensions.In this study,novel semi-taut moor-ing systems incorporating polyester ropes and steel chains are proposed for a combined wind and wave energy system-the semi-submersible flap torus combination(STFC)concept,deployed at a 50 m wa-ter depth.The STFC integrates a semi-submersible floating offshore wind turbine(FOWT),a torus wave energy converter(WEC)and three flap-type WECs.The dynamic responses of the STFC with different semi-taut mooring configurations under operational and survival environmental conditions are assessed in terms of key performance parameters such as the platform’s motion responses and mooring line ten-sions.These performance parameters are compared against those of a chain-catenary mooring system.With the use of semi-taut mooring systems,significantly smaller mooring footprints as compared to the chain-catenary mooring systems can be achieved.Moreover,it is demonstrated that the semi-taut moor-ing systems are effective in reducing the maximum tension of the mooring lines.A basic cost analysis further indicates that semi-taut mooring systems offer substantial cost advantages over chain-catenary moorings in intermediate water depths.
文摘Monolithic catalysts for CO_(2) methanation have become an active research area for the industrial development of Power-to-Gas technology.In this study,we developed a facile and reproducible synthesis strategy for the preparation of structured NiFe catalysts on washcoated cordierite monoliths for CO_(2) methanation.The NiFe catalysts were derived from in-situ grown layered double hydroxides(LDHs)via urea hydrolysis.The influence of different washcoat materials,i.e.,alumina and silica colloidal suspensions on the formation of LDHs layer was investigated,together with the impact of total metal concentration.NiFe LDHs were precipitated on the exterior surface of cordierite washcoated with alumina,while it was found to deposit further inside the channel wall of monolith washcoated with silica due to different intrinsic properties of the colloidal solutions.On the other hand,the thickness of in-situ grown LDHs layers and the catalyst loading could be increased by high metal concentration.The best monolithic catalyst(COR-AluCC-0.5M)was robust,having a thin and well-adhered catalytic layer on the cordierite substrate.As a result,high methane yield was obtained from CO_(2) methanation at high flow rate on this structured NiFe catalysts.The monolithic catalysts appeared as promising structured catalysts for the development of industrial methanation reactor.
基金financially supported by the National Natural Science Foundation of China (Grant Nos.51909109 and 52101314)the Natural Science Foundation of Jiangsu Province (Grant No.BK20190967)。
文摘Wind farms generally consist of a single turbine installed with the same hub height. As the scale of turbines increases,wake interference between turbines becomes increasingly significant, especially for floating wind turbines(FWT).Some researchers find that wind farms with multiple hub heights could increase the annual energy production(AEP),while previous studies also indicate that wake meandering could increase fatigue loading. This study investigates the wake interaction within a hybrid floating wind farm with multiple hub heights. In this study, FAST.Farm is employed to simulate a hybrid wind farm which consists of four semi-submersible FWTs(5MW and 15MW) with two different hub heights. Three typical wind speeds(below-rated, rated, and over-rated) are considered in this paper to investigate the wake meandering effects on the dynamics of two FWTs. Damage equivalent loads(DEL) of the turbine critical components are computed and analyzed for several arrangements determined by the different spacing of the four turbines. The result shows that the dynamic wake meandering significantly affects downstream turbines’ global loadings and load effects. Differences in DEL show that blade-root flapwise bending moments and mooring fairlead tensions are sensitive to the spacing of the turbines.
文摘Background:To estimate cardiovascular and cancer death rates by regions and time periods.Design:Novel statistical methods were used to analyze clinical surveillance data.Methods:A multicenter,population-based medical survey was performed.Annual recorded deaths from cardiovascular diseases were analyzed for all 195 countries of the world.It is challenging to model such data;few mathematical models can be applied because cardiovascular disease and cancer data are generally not normally distributed.Results:A novel approach to assessing the biosystem reliability is introduced and has been found to be particularly suitable for analyzing multiregion environmental and healthcare systems.While traditional methods for analyzing temporal observations of multiregion processes do not deal with dimensionality efficiently,our methodology has been shown to be able to cope with this challenge.Conclusions:Our novel methodology can be applied to public health and clinical survey data.
文摘This paper first describes the importance of using location specific S-N curves for fatigue damage assessment of existing steel structures. It discusses the existing concepts and methods for developing S-N curves using empirical formulae and monotonic strength parameters, such as the ultimate tensile strength and hardness. It also discusses relationships among these monotonic parameters. Then it presents formulae for developing hardness-based full range S-N curves for medium strength steels. The formulae are verified using experimental data obtained from both monotonic and cyclic testing. Finally, it describes the advantages of these hardness-based formulae for developing location specific S-N curves as hardness testing is a non-destructive test which can be carried out on specific locations in structures.
文摘This paper presents a study where artificial neural networks are used as a curve fitting method applying measured data from an axial compressor test rig to predict the compressor map. Emphasis is on models for prediction of pressure ratio, compressor mass flow and mechanical efficiency. Except for evaluation of interpolation and extrapolation capabilities, this study also investigates the effect of the design parameters such as number of neurons and size of training data. To reduce the effect of noise, the auto associative neural network has been applied for noise filtering of the data from the parameters used to calculate the efficiency. In summary, the results show that artificial neural network can be used for compressor map prediction, but it should be emphasized that the selection of data normalisation scale is crucial for the model where compressor mass flow is predicted. Furthermore, it is shown that the AANN （auto associative neural network） can be used to the reduce noise in measured data and thereby enhance the quality of the data.
基金supported by the Research Council of Norway through the project“Unleashing the sustainable value creation potential of offshore ocean aquaculture”(Project number:328724).
文摘This study presents a conceptual design for a cost-effective submersible gravity-type fish cage with a single-point mooring design.The performance of the new design in reducing environmental loads under extreme sea con-ditions is demonstrated using an in-house numerical code package.The effectiveness of the submerging and surfacing operations of the fish cages is validated through numerical simulations.In the present code package,irregular wave modelling is employed to generate the wave elevations,velocities and accelerations,and the hydrodynamic forces acting on the fish cages and mooring system are calculated using the Morison model.A submersible model for the floating collar is developed to simulate the submerging and surfacing operations of the fish cages.The deformations of the fish cage system are calculated using a modified extended position based dynamics(XPBD)method combined with a mode superposition method.Results show that tension in the mooring system is significantly reduced when fish cages are submerged in the water layer with lower current speeds,and extending the buoy line to lower the conjunction point helps maintain fish cages in the desired water layer under extreme sea conditions.Flooding the outer tubes of the floating collar allows the fish cages to smoothly submerge to the desired water depth.The surfacing designs based on the compressed air and the lifting operation of the bottom sinker can enable the cages to ascend to the water surface.The submerging and surface operations are proved to be completed within six minutes.The new design based on the lifting operation of the bottom sinker,is safer and more cost-effective than the design based on compressed air for the surfacing operation.The design of the submersible single-point mooring gravity-type fish cage is thereby validated through the present numerical methods,offering valuable insights for future aquaculture design and implementation.
基金the financial support from the National Natural Science Foundation of China(Grant no.51974360)for carrying out this research work.
文摘In the present study,a numerical model is first calibrated against the crack networks and pressure attenuation data in laboratory blasting test.Then,based on the calibrated numerical model,two-hole plane models are developed and used to perform a series of sim-ulations of smoothwall blasting in deep tunnelling subjected to in-situ stress.The evolutions of rock fracture and excavation damage zone in the roof/floor and sidewalls under different far-field hydrostatic pressure and anisotropic in-situ stress conditions are numerically investigated.The findings in numerical modelling are also analytically interpreted with the stress distributions around the designed tunnel perimeter and perimeter borehole.The numerical and analytical results show that the variations of rock cracking and excavation dam-aged zone induced by smoothwall blasting with in-situ stress are mainly attributed to the high tangential compressive stress concentration around the remaining rock after inner primary blasts and the tensile stress acting on the wall of perimeter hole,which control the crack propagation and initiation respectively.At last,the implications of findings for practical smoothwall blasting in deep tunnelling are discussed.
文摘Subsea templates are normally transported to the installation site on the deck of a crane vessel.After being lifted off from the deck,the template is 1)over-boarded from the initial location to the target position by the side of the vessel;2)lowered through the splash zone;3)further lowered down to the seabed and 4)finally positioned and landed.All the mentioned phases should be evaluated.Usually,the splash zone crossing phase is taken as the critical phase and analyzed to define the installation weather criterion.The over-boarding phase has not been the focus of analysis due to a large involvement of human actions and little involvement of hydrodynamic effects.During offshore operations,the offshore manager may decide to decrease the defined installation weather criterion if the risk of the personnel safety on deck during over-boarding phase is considered high.Thus,it is of great need to quantify the operational criterion for such operation.The objective of this paper is to perform numerical analyses and define the allowable sea states for a safe over-boarding operation.The numerical analyses using time-domain simulations have been performed in various sea states.Tugger lines have been modelled to control the motions of the template during the operation.The pendulum motions of the subsea template are considered as the critical responses for the assessment of the allowable sea states.
