The objective of this study is to propose an optimal plant design for blue hydrogen production aboard a liquefiednatural gas(LNG)carrier.This investigation focuses on integrating two distinct processes—steam methaner...The objective of this study is to propose an optimal plant design for blue hydrogen production aboard a liquefiednatural gas(LNG)carrier.This investigation focuses on integrating two distinct processes—steam methanereforming(SMR)and ship-based carbon capture(SBCC).The first refers to the common practice used to obtainhydrogen from methane(often derived from natural gas),where steam reacts with methane to produce hydrogenand carbon dioxide(CO_(2)).The second refers to capturing the CO_(2) generated during the SMR process on boardships.By capturing and storing the carbon emissions,the process significantly reduces its environmental impact,making the hydrogen production“blue,”as opposed to“grey”(which involves CO_(2) emissions without capture).For the SMR process,the analysis reveals that increasing the reformer temperature enhances both the processperformance and CO_(2) emissions.Conversely,a higher steam-to-carbon(s/c)ratio reduces hydrogen yield,therebydecreasing thermal efficiency.The study also shows that preheating the air and boil-off gas(BOG)before theyenter the combustion chamber boosts overall efficiency and curtails CO_(2) emissions.In the SBCC process,puremonoethanolamine(MEA)is employed to capture the CO_(2) generated by the exhaust gases from the SMR process.The results indicate that with a 90%CO_(2) capture rate,the associated heat consumption amounts to 4.6 MJ perkilogram of CO_(2) captured.This combined approach offers a viable pathway to produce blue hydrogen on LNGcarriers while significantly reducing the carbon footprint.展开更多
Substantial advancements have been achieved in Tunnel Boring Machine(TBM)technology and monitoring systems,yet the presence of missing data impedes accurate analysis and interpretation of TBM monitoring results.This s...Substantial advancements have been achieved in Tunnel Boring Machine(TBM)technology and monitoring systems,yet the presence of missing data impedes accurate analysis and interpretation of TBM monitoring results.This study aims to investigate the issue of missing data in extensive TBM datasets.Through a comprehensive literature review,we analyze the mechanism of missing TBM data and compare different imputation methods,including statistical analysis and machine learning algorithms.We also examine the impact of various missing patterns and rates on the efficacy of these methods.Finally,we propose a dynamic interpolation strategy tailored for TBM engineering sites.The research results show that K-Nearest Neighbors(KNN)and Random Forest(RF)algorithms can achieve good interpolation results;As the missing rate increases,the interpolation effect of different methods will decrease;The interpolation effect of block missing is poor,followed by mixed missing,and the interpolation effect of sporadic missing is the best.On-site application results validate the proposed interpolation strategy's capability to achieve robust missing value interpolation effects,applicable in ML scenarios such as parameter optimization,attitude warning,and pressure prediction.These findings contribute to enhancing the efficiency of TBM missing data processing,offering more effective support for large-scale TBM monitoring datasets.展开更多
This work investigates the potential of low-pressure,medium-speed dual-fuel engines for cleaner maritime transportation.The thermodynamic performance of these engines is explored using three alternative fuels:liquefie...This work investigates the potential of low-pressure,medium-speed dual-fuel engines for cleaner maritime transportation.The thermodynamic performance of these engines is explored using three alternative fuels:liquefied natural gas(LNG),methanol,and ammonia.A parametric analysis examines the effect of adjustments to key engine parameters(compression ratio,boost pressure,and air-fuel ratio)on performance.Results show an initial improvement in performance with an increase in compression ratio,which reaches a peak and then declines.Similarly,increases in boost pressure and air-fuel ratio lead to linear performance gains.However,insufficient cooling reduces the amount of fuel burned,which hinders performance.Exergy analysis reveals significant exergy destruction within the engine,which ranges from 69.96%(methanol)to 78.48%(LNG).Notably,the combustion process is the leading cause of exergy loss.Among the fuels tested,methanol exhibits the lowest combustion-related exergy destruction(56.41%),followed by ammonia(62.12%)and LNG(73.77%).These findings suggest that methanol is a promising near-term alternative to LNG for marine fuel applications.展开更多
Effective forest regeneration is essential for sustainable forestry practices.In Sweden,mechanical site preparation and manual planting is the dominating method,but sourcing labour for the physically demanding work is...Effective forest regeneration is essential for sustainable forestry practices.In Sweden,mechanical site preparation and manual planting is the dominating method,but sourcing labour for the physically demanding work is difficult.An autonomous scarifying and planting system(Autoplant)could meet the requirements of the forest industry and,for this,a tool for regeneration planning and routing is needed.The tool,Pathfinder,plans the regeneration and routes based on the harvested production(hpr)files,soil moisture and parent material maps,no-go areas(for culture or nature conservation),digital elevation models(DEM),and machine data(e.g.,working width,critical slope,time taken for different turn angles).The overall planting solution is either a set of capacity constrained routes or a continuous route and could be used for any planting machine as well as for traditional scarifiers as disc trenchers or mounders pulled by forwarders.Pathfinder was tested on eleven regeneration areas throughout Sweden,both with continuous routes and routes based on a carrying capacity of 1500 seedlings.The net operation area,species and seedling density suggestions were deemed relevant by expert judgement in the field.The routes provided by Pathfinder were compared with solutions given by two experienced drivers and a third solution based on the actual soil scarification at the site.Total driving distance did not differ significantly between the suggestions,but Pathfinder included less side-slope driving on steep slopes(≥27%or 15°)and medium slopes(15–27%).The chosen threshold value for steep slopes(where side-slope driving should be avoided)affects the routing,and a lower threshold means more turning and longer driving distance.Pathfinder is not only a tool for routing of planting machines,but also helps in planning of traditional regeneration by providing a more correct net area and tree species suggestions based on the growth of the previous stand.It also diminishes the risk of severe soil disturbance by excluding the wettest area in the planning.展开更多
Skull structures are important for biomechanical head simulations,but they are mostly reconstructed frommedical images.These reconstruction methods harmthe human body and have a long processing time.Currently,skull st...Skull structures are important for biomechanical head simulations,but they are mostly reconstructed frommedical images.These reconstruction methods harmthe human body and have a long processing time.Currently,skull structures canbe straightforwardly predictedfromthe head,but a fullheadshapemust be available.Most scanning devices can only capture the face shape.Consequently,a method that can quickly predict the full skull structures from the face is necessary.In this study,a novel face-to-skull prediction procedure is introduced.Given a threedimensional(3-D)face shape,a skull mesh could be predicted so that its shape would statistically fit the face shape.Several prediction strategies were conducted.The optimal prediction strategy with its optimal hyperparameters was experimentally selected through a ten-fold cross-validation with 329 subjects.As a result,the face-to-skull prediction strategy based on the relations between face head shape and back head shape,between face head shape and face skull shape,and between back head shape and back skull shape was optimal.The optimal mean mesh-to-mesh distance(mean±SD)between the predicted skull shapes and the ground truth skull shapes was 1.93±0.36 mm,and those between the predicted skull meshes and the ground truth skull meshes were 2.65±0.36 mm.Moreover,the prediction errors in back-skull and muscle attachment regions were 1.7432±0.5217 mm and 1.7671±0.3829 mm,respectively.These errors are within the acceptable range of facial muscle simulation.In perspective,this method will be employed in our clinical decision support system to enhance the accuracy of biomechanical head simulation based on a stereo fusion camera system.Moreover,we will also enhance the accuracy of the face-to-skull prediction by diversifying the dataset intomore varied geographical regions and genders.More types of parameters,such as BodyMass Index(BMI),coupled with head-to-skull thicknesses,will be fused with the proposed face-to-skull procedure.展开更多
Data-driven reduced-order modeling opens new avenues of understanding,predicting,controlling,and optimizing system behavior.Simple systems may have state spaces in which sparse human-interpretable dynamical systems ca...Data-driven reduced-order modeling opens new avenues of understanding,predicting,controlling,and optimizing system behavior.Simple systems may have state spaces in which sparse human-interpretable dynamical systems can be identified.This approach has been pioneered by Brunton et al.(2016,PNAS)with sparse identification of nonlinear dynamics.Complex systems,however,cannot be expected to benefit from such simple analytical descriptions.Yet,smoothness may be exploited by analytical local descriptions.In this paper,we identify a clusterwise polynomial dynamics from time-resolved snapshot data.The full state space is partitioned into clusters with a reduced-order polynomial description for each cluster and a global patching strategy.The resulting clusterwise modeling is entirely data-driven and requires no prior knowledge of the system dynamics.We illustrate the approach on the well-known chaotic Lorenz and Rössler systems,on the more challenging chaotic fluid flow dynamics of higher state-space dimensions,on a noisy electrocardiogram signal,and finally on the time evolution of the monthly sunspot number.Clusterwise modeling offers a powerful and interpretable paradigm for dynamical modeling.Nonlinear dynamics can be approximated by assembling many simple local models of different resolutions,opening new paths to understand and control intricate nonlinearities.展开更多
The plastic flow behaviors of AA6061-T4 sheets at different temperatures(21-300°C)and strain rates(0.002-4 s^(-1))were studied.Significant nonlinear effects of temperature and strain rate on flow behaviors were r...The plastic flow behaviors of AA6061-T4 sheets at different temperatures(21-300°C)and strain rates(0.002-4 s^(-1))were studied.Significant nonlinear effects of temperature and strain rate on flow behaviors were revealed,as well as underlying micromechanical factors.Phenomenology and machine learning-based constitutive models were developed.Both models were formulated in the framework of a temperature-dependent linear combination regulated by a transition function to capture the evolution of strain-hardening behavior with increasing temperature.Novel mathematical functions for describing temperature and strain rate sensitivities were formulated for the phenomenological constitutive model.The threshold temperature related to microstructure evolution was considered in the modeling.A data-enrichment strategy based on extrapolating experimental data via classical strain hardening laws was adopted to improve neural network training.An efficient inverse identification strategy,focusing solely on the transition function,was proposed to enhance the prediction accuracy of post-necking deformation by both constitutive models.展开更多
Understanding the structure-property relationship and the mechanisms by which catalysts promote polysulfide conversion is crucial for the rational design of room-temperature sodium-sulfur(RT Na-S)battery catalysts.Her...Understanding the structure-property relationship and the mechanisms by which catalysts promote polysulfide conversion is crucial for the rational design of room-temperature sodium-sulfur(RT Na-S)battery catalysts.Herein,we systematically investigate Fe-,Co-,and Ni-incorporated Mo_(2)C as catalysts for RT Na-S battery to elucidate the intrinsic correlation between the d band center of Mo in Mo_(2)C and its catalytic activity.Combining experimental and theoretical analysis revealed that Ni-substituted Mo_(2)C elevates the d band center while significantly reducing antibonding orbitals(π^(*))occupancy compared to Fe-substituted Mo_(2)C and Co-substituted Mo_(2)C counterparts.This electronic restruction enhances d-p hybridization at the Mo-S interface,which strengthens sodium polysulfides adsorption energy and enhances charge transfer,thereby steering sulfur redox pathways toward thermodynamically favorable configurations.Our findings elucidate the intricate interplay between the electronic structure and catalytic activity of Mo_(2)C,advancing a novel perspective for the rational design of RT Na-S battery catalysts through tailored modulation of antibonding orbital occupancy.展开更多
Modern industrial equipment is increasingly characterized by miniaturization,integration,and high performance,necessitating the production of complex structural parts with exceptionally high internal surface quality.D...Modern industrial equipment is increasingly characterized by miniaturization,integration,and high performance,necessitating the production of complex structural parts with exceptionally high internal surface quality.Direct manufacturing often leads to high internal surface roughness,which traditional finishing and measuring methods cannot adequately address due to the decreasing size and increasing complexity of internal structures.This is especially true for components like pipes with large aspect ratios,extremely small deep holes,multi-stage bends,cross pipes,and array holes.To meet the high-performance manufacturing demands of these parts,advanced internal surface finishing and roughness measurement technologies have gained significant attention.This review focuses on the challenges and solutions related to internal surface parts with various apertures and complex structures.Internal surface finishing methods are categorized into mechanical finishing,fluid-based finishing,and energy-field-based finishing based on their characteristics.Roughness measurement technologies are divided into tool-probing and non-probing methods.The principles,required equipment,and key parameters of each finishing and measurement approach are discussed in detail.Additionally,the advantages and limitations of these methods are summarized,and future trends are forecasted.This paper serves as a comprehensive guide for researchers and engineers aiming to enhance the internal surface quality of complex structure parts.展开更多
Hydraulic fracture growth is significantly influenced by the minimum horizontal principal stress gradient and the fracturing fluid pressure gradient.However,these gradients are often neglected in scaled physical model...Hydraulic fracture growth is significantly influenced by the minimum horizontal principal stress gradient and the fracturing fluid pressure gradient.However,these gradients are often neglected in scaled physical modeling experiments due to difficulties in reproducing them.This study uses centrifugal hypergravity to simulate both gradients and investigate their effects on fracture propagation.Artificial mortar specimens(ϕ200 mm×400 mm)are fractured under 1g(normal gravity),50g,and 100g.Results show that compared to 1g,fractures under 50g and 100g exhibit increasingly uneven propagation,with higher g-values leading to greater asymmetry.To interpret this,a theoretical analysis based on fracture mechanics is conducted.When the fluid pressure gradient exceeds the stress gradient,a positive net gradient is generated,increasing net pressure at the lower fracture tip.This raises the stress intensity factor at the lower tip,promoting downward growth.As g increases,the disparity becomes more significant,resulting in greater fracture deviation.In conclusion,this study,for the first time,has verified and explained that the net gradient can change the propagation of hydraulic fractures,providing important guidance for wellbore placement under stress gradients.展开更多
The paper presents analysis of the performance and the internal flow behaviour in the vaned diffuser of a radial flow pump using PIV(particle image velocimetry)and pressure probe traverses.PIV measurements have alread...The paper presents analysis of the performance and the internal flow behaviour in the vaned diffuser of a radial flow pump using PIV(particle image velocimetry)and pressure probe traverses.PIV measurements have already been performed at middle height inside one diffuser channel passage for a given speed of rotation and various mass flow rates.These results have been already presented in several previous communications.New experiments have been performed using a three-hole pressure probe traverses from hub to shroud diffuser width at different radial locations between the two diffuser geometrical throats.Numerical simulations are also realized with the commercial codes Star CCM+7.02.011 and CFX.Frozen rotor and fully unsteady calculations of the whole pump have been performed.Comparisons between numerical results,previous experimental PIV results and new probe traverses one's are presented and discussed for one mass flow rate.In this respect,a first attempt to take into account fluid leakages between the rotating and fixed part of the pump has been checked since it may affects the real flow structure inside the diffuser.展开更多
To investigate the influence of confining pressures and temperatures on the seepage characteristics of fractured rocks, seepage tests were conducted on a fractured silty mudstone using a self-developed experimental sy...To investigate the influence of confining pressures and temperatures on the seepage characteristics of fractured rocks, seepage tests were conducted on a fractured silty mudstone using a self-developed experimental system, and the effects of different factors on coefficient of permeability were discussed. The results showed that the increasing confining pressure will gradually decrease the coefficient of permeability, and this process is divided into two stages: 1) the fast decrease stage, which corresponds to a confining pressure less than 30 kPa, and 2) the slow decrease stage, which corresponds to a confining pressure larger than 30 kPa. Unlike confining pressure, an increase in temperature will increase the coefficient of permeability. It is noted that fracture surface roughness will also affect the variation of coefficient of permeability to a certain extent. Among the three examined factors, the effect of confining pressure increases is dominant on fracture permeability coefficient. The relationship between the confining pressure and coefficient of permeability can be quantified by an exponential function.展开更多
We report that 316L austenitic stainless steel fabricated by direct laser deposition(DLD),an additive manufacturing(AM)process,have a higher yield strength than that of conventional 316L while keeping high ductility.M...We report that 316L austenitic stainless steel fabricated by direct laser deposition(DLD),an additive manufacturing(AM)process,have a higher yield strength than that of conventional 316L while keeping high ductility.More interestingly,no clear anisotropy in tensile properties was observed between the building and the scanning direction of the 3D printed steel.Metallographic examination of the as-built parts shows a heterogeneous solidification cellular microstructure.Transmission electron microscopy observations coupled with Energy Dispersive X-ray Spectrometry(EDS)reveal the presence of chemical micro-segregation correlated with high dislocation density at cell boundaries as well as the in-situ formation of well-dispersed oxides and transition-metal-rich precipitates.The hierarchical heterogeneous microstructure in the AM parts induces excellent strength of the 316L stainless steel while the low staking fault energy of the as-built 316L promotes the occurrence of abundant deformation twinning,in the origin of the high ductility of the AM steel.Without additional post-process treatments,the AM 316L proves that it can be used as a structural material or component for repair in mechanical construction.展开更多
This paper presents a numerical study of the flow topologies of three-dimensional （3D） flows in a high pressure compressor stator blade row without and with boundary layer aspiration on the hub wall. The stator blad...This paper presents a numerical study of the flow topologies of three-dimensional （3D） flows in a high pressure compressor stator blade row without and with boundary layer aspiration on the hub wall. The stator blade is representative of the first stage operating under transonic inlet conditions and the blade design encourages development of highly complex 3D flows. The blade has a small tip clearance. The computational fluid dynamics （CFD） studies show progressive increase of hub corner stall with the increase in incidence. Aspiration is implemented on the hub wall via a slot in the comer between the hub wall and the suction surface. The CFD studies show aspiration to be sensitive to the suction flow rate; lower rate leads to very complex flow struc- tures and increased level of losses whereas higher rate renders aspiration effective for control of hub comer separation. The flow topologies are studied by trace of skin friction lines on the walls. The nature of flow can be explained by the topological rules of closed separation. Furthermore, a deeper analysis is done for a particular case with advanced criterion to test the non-degeneracy of critical points in the flow field.展开更多
We outline problems and potential solutions for feasible human-machine interfaces using cable-based parallel manipulators for physiotherapy applications.From an engineering perspective,we discuss the design constraint...We outline problems and potential solutions for feasible human-machine interfaces using cable-based parallel manipulators for physiotherapy applications.From an engineering perspective,we discuss the design constraints related to acceptance by patients and physiotherapist users.To date,most designs have focused on mobile platforms that are designed to be operated as an end-effector connected to human limbs for direct patient interaction.Some specific examples are illustrated from the authors' experience with prototypes available at Laboratory of Robotics and Mechatronics (LARM),Italy.展开更多
The present work relates to a numerical investigation of double diffusive mixed convection around a horizontal annulus with a finned inner cylinder.The solutal and thermal buoyancy forces are sustained by maintaining ...The present work relates to a numerical investigation of double diffusive mixed convection around a horizontal annulus with a finned inner cylinder.The solutal and thermal buoyancy forces are sustained by maintaining the inner and outer cylinders at uniform temperatures and concentrations.Buoyancy effects are also considered,with the Boussinesq approximation.The forced convection effect is induced by the outer cylinder rotating with an angular velocity(ω)in an anti-clockwise direction.The studies are made for various combinations of dimensionless numbers;buoyancy ratio number(N),Lewis number(Le),Richardson number(Ri)and Grashof number(Gr).The isotherms,isoconcentrations and streamlines as well as both average and local Nusselt and Sherwood numbers were studied.A finite volume scheme is adopted to solve the transport equations for continuity,momentum,energy and mass transfer.The results indicate that the use of fins on the inner cylinder with outer cylinder rotation,significantly improves the heat and mass transfer in the annulus.展开更多
The effects of aging treatment on the microstructures and mechanical properties of extruded AM50 ＋ xCa alloys （x=0, 1, 2 wt.%） were studied. The results indicated the secondary phase Mgl7Al12 precipitated from the ...The effects of aging treatment on the microstructures and mechanical properties of extruded AM50 ＋ xCa alloys （x=0, 1, 2 wt.%） were studied. The results indicated the secondary phase Mgl7Al12 precipitated from the saturated α-Mg solid solution while Al2Ca changed slightly when the aging time was increased. The hardness of extruded AM50 ＋ xCa al- loys increased initially to its peak, and then dropped to reach its original hardness with the increase in aging time. With the increase in aging temperature, the hardness of the AM50 ＋ 2Ca ahoy decreased, whereas the hardness of AM50 and AM50 ＋ 1Ca alloys decreased in the initial stages of aging treatment and increased in the later stages of aging treatment. The tensile strengths of AM50 and AM50 ＋ 1Ca alloys increased after aging treatment for the precipitation of Mg17Al12 phase, which increases the resistance against dislocation movement at the grain boundary; with increase in aging temperature, their tensile strengths increased. For AM50 ＋ 2Ca alloy, the tensile strength declined after aging at 150℃ and 175℃, while it increased slightly at 200℃. The ductility of AM50 ＋ xCa alloys （x = 0, 1, 2 wt.%） declined after aging treatment.展开更多
文摘The objective of this study is to propose an optimal plant design for blue hydrogen production aboard a liquefiednatural gas(LNG)carrier.This investigation focuses on integrating two distinct processes—steam methanereforming(SMR)and ship-based carbon capture(SBCC).The first refers to the common practice used to obtainhydrogen from methane(often derived from natural gas),where steam reacts with methane to produce hydrogenand carbon dioxide(CO_(2)).The second refers to capturing the CO_(2) generated during the SMR process on boardships.By capturing and storing the carbon emissions,the process significantly reduces its environmental impact,making the hydrogen production“blue,”as opposed to“grey”(which involves CO_(2) emissions without capture).For the SMR process,the analysis reveals that increasing the reformer temperature enhances both the processperformance and CO_(2) emissions.Conversely,a higher steam-to-carbon(s/c)ratio reduces hydrogen yield,therebydecreasing thermal efficiency.The study also shows that preheating the air and boil-off gas(BOG)before theyenter the combustion chamber boosts overall efficiency and curtails CO_(2) emissions.In the SBCC process,puremonoethanolamine(MEA)is employed to capture the CO_(2) generated by the exhaust gases from the SMR process.The results indicate that with a 90%CO_(2) capture rate,the associated heat consumption amounts to 4.6 MJ perkilogram of CO_(2) captured.This combined approach offers a viable pathway to produce blue hydrogen on LNGcarriers while significantly reducing the carbon footprint.
基金supported by the National Natural Science Foundation of China(Grant No.52409151)the Programme of Shenzhen Key Laboratory of Green,Efficient and Intelligent Construction of Underground Metro Station(Programme No.ZDSYS20200923105200001)the Science and Technology Major Project of Xizang Autonomous Region of China(XZ202201ZD0003G).
文摘Substantial advancements have been achieved in Tunnel Boring Machine(TBM)technology and monitoring systems,yet the presence of missing data impedes accurate analysis and interpretation of TBM monitoring results.This study aims to investigate the issue of missing data in extensive TBM datasets.Through a comprehensive literature review,we analyze the mechanism of missing TBM data and compare different imputation methods,including statistical analysis and machine learning algorithms.We also examine the impact of various missing patterns and rates on the efficacy of these methods.Finally,we propose a dynamic interpolation strategy tailored for TBM engineering sites.The research results show that K-Nearest Neighbors(KNN)and Random Forest(RF)algorithms can achieve good interpolation results;As the missing rate increases,the interpolation effect of different methods will decrease;The interpolation effect of block missing is poor,followed by mixed missing,and the interpolation effect of sporadic missing is the best.On-site application results validate the proposed interpolation strategy's capability to achieve robust missing value interpolation effects,applicable in ML scenarios such as parameter optimization,attitude warning,and pressure prediction.These findings contribute to enhancing the efficiency of TBM missing data processing,offering more effective support for large-scale TBM monitoring datasets.
文摘This work investigates the potential of low-pressure,medium-speed dual-fuel engines for cleaner maritime transportation.The thermodynamic performance of these engines is explored using three alternative fuels:liquefied natural gas(LNG),methanol,and ammonia.A parametric analysis examines the effect of adjustments to key engine parameters(compression ratio,boost pressure,and air-fuel ratio)on performance.Results show an initial improvement in performance with an increase in compression ratio,which reaches a peak and then declines.Similarly,increases in boost pressure and air-fuel ratio lead to linear performance gains.However,insufficient cooling reduces the amount of fuel burned,which hinders performance.Exergy analysis reveals significant exergy destruction within the engine,which ranges from 69.96%(methanol)to 78.48%(LNG).Notably,the combustion process is the leading cause of exergy loss.Among the fuels tested,methanol exhibits the lowest combustion-related exergy destruction(56.41%),followed by ammonia(62.12%)and LNG(73.77%).These findings suggest that methanol is a promising near-term alternative to LNG for marine fuel applications.
基金funded by Vinnova,the Swedish Innovation Agency as a part of the Autoplant project(Dnr 2020-04202 and 2023-02747).
文摘Effective forest regeneration is essential for sustainable forestry practices.In Sweden,mechanical site preparation and manual planting is the dominating method,but sourcing labour for the physically demanding work is difficult.An autonomous scarifying and planting system(Autoplant)could meet the requirements of the forest industry and,for this,a tool for regeneration planning and routing is needed.The tool,Pathfinder,plans the regeneration and routes based on the harvested production(hpr)files,soil moisture and parent material maps,no-go areas(for culture or nature conservation),digital elevation models(DEM),and machine data(e.g.,working width,critical slope,time taken for different turn angles).The overall planting solution is either a set of capacity constrained routes or a continuous route and could be used for any planting machine as well as for traditional scarifiers as disc trenchers or mounders pulled by forwarders.Pathfinder was tested on eleven regeneration areas throughout Sweden,both with continuous routes and routes based on a carrying capacity of 1500 seedlings.The net operation area,species and seedling density suggestions were deemed relevant by expert judgement in the field.The routes provided by Pathfinder were compared with solutions given by two experienced drivers and a third solution based on the actual soil scarification at the site.Total driving distance did not differ significantly between the suggestions,but Pathfinder included less side-slope driving on steep slopes(≥27%or 15°)and medium slopes(15–27%).The chosen threshold value for steep slopes(where side-slope driving should be avoided)affects the routing,and a lower threshold means more turning and longer driving distance.Pathfinder is not only a tool for routing of planting machines,but also helps in planning of traditional regeneration by providing a more correct net area and tree species suggestions based on the growth of the previous stand.It also diminishes the risk of severe soil disturbance by excluding the wettest area in the planning.
基金funded by the International University,VNU-HCM,under grant number T2023-01-BME.
文摘Skull structures are important for biomechanical head simulations,but they are mostly reconstructed frommedical images.These reconstruction methods harmthe human body and have a long processing time.Currently,skull structures canbe straightforwardly predictedfromthe head,but a fullheadshapemust be available.Most scanning devices can only capture the face shape.Consequently,a method that can quickly predict the full skull structures from the face is necessary.In this study,a novel face-to-skull prediction procedure is introduced.Given a threedimensional(3-D)face shape,a skull mesh could be predicted so that its shape would statistically fit the face shape.Several prediction strategies were conducted.The optimal prediction strategy with its optimal hyperparameters was experimentally selected through a ten-fold cross-validation with 329 subjects.As a result,the face-to-skull prediction strategy based on the relations between face head shape and back head shape,between face head shape and face skull shape,and between back head shape and back skull shape was optimal.The optimal mean mesh-to-mesh distance(mean±SD)between the predicted skull shapes and the ground truth skull shapes was 1.93±0.36 mm,and those between the predicted skull meshes and the ground truth skull meshes were 2.65±0.36 mm.Moreover,the prediction errors in back-skull and muscle attachment regions were 1.7432±0.5217 mm and 1.7671±0.3829 mm,respectively.These errors are within the acceptable range of facial muscle simulation.In perspective,this method will be employed in our clinical decision support system to enhance the accuracy of biomechanical head simulation based on a stereo fusion camera system.Moreover,we will also enhance the accuracy of the face-to-skull prediction by diversifying the dataset intomore varied geographical regions and genders.More types of parameters,such as BodyMass Index(BMI),coupled with head-to-skull thicknesses,will be fused with the proposed face-to-skull procedure.
基金supported by the National Natural Science Foundation of China(Grant Nos.12172109,12202121,and 12302293)the China Postdoctoral Science Foundation(Grant Nos.2023M730866 and 2023T160166)+1 种基金the Guangdong Basic and Applied Basic Research Foundation(Grant No.2022A1515011492)the Shenzhen Science and Technology Program(Grant Nos.JCYJ20220531095605012,KJZD20230923115210021,and 29853MKCJ202300205).
文摘Data-driven reduced-order modeling opens new avenues of understanding,predicting,controlling,and optimizing system behavior.Simple systems may have state spaces in which sparse human-interpretable dynamical systems can be identified.This approach has been pioneered by Brunton et al.(2016,PNAS)with sparse identification of nonlinear dynamics.Complex systems,however,cannot be expected to benefit from such simple analytical descriptions.Yet,smoothness may be exploited by analytical local descriptions.In this paper,we identify a clusterwise polynomial dynamics from time-resolved snapshot data.The full state space is partitioned into clusters with a reduced-order polynomial description for each cluster and a global patching strategy.The resulting clusterwise modeling is entirely data-driven and requires no prior knowledge of the system dynamics.We illustrate the approach on the well-known chaotic Lorenz and Rössler systems,on the more challenging chaotic fluid flow dynamics of higher state-space dimensions,on a noisy electrocardiogram signal,and finally on the time evolution of the monthly sunspot number.Clusterwise modeling offers a powerful and interpretable paradigm for dynamical modeling.Nonlinear dynamics can be approximated by assembling many simple local models of different resolutions,opening new paths to understand and control intricate nonlinearities.
文摘The plastic flow behaviors of AA6061-T4 sheets at different temperatures(21-300°C)and strain rates(0.002-4 s^(-1))were studied.Significant nonlinear effects of temperature and strain rate on flow behaviors were revealed,as well as underlying micromechanical factors.Phenomenology and machine learning-based constitutive models were developed.Both models were formulated in the framework of a temperature-dependent linear combination regulated by a transition function to capture the evolution of strain-hardening behavior with increasing temperature.Novel mathematical functions for describing temperature and strain rate sensitivities were formulated for the phenomenological constitutive model.The threshold temperature related to microstructure evolution was considered in the modeling.A data-enrichment strategy based on extrapolating experimental data via classical strain hardening laws was adopted to improve neural network training.An efficient inverse identification strategy,focusing solely on the transition function,was proposed to enhance the prediction accuracy of post-necking deformation by both constitutive models.
基金supported by the National Natural Science Foundation of China(No.52372224 and 52072299)the Major Project of Shaanxi Coal Joint Fund of Shaanxi.Provincial Science and Technology Department(No.2019JLZ-07)。
文摘Understanding the structure-property relationship and the mechanisms by which catalysts promote polysulfide conversion is crucial for the rational design of room-temperature sodium-sulfur(RT Na-S)battery catalysts.Herein,we systematically investigate Fe-,Co-,and Ni-incorporated Mo_(2)C as catalysts for RT Na-S battery to elucidate the intrinsic correlation between the d band center of Mo in Mo_(2)C and its catalytic activity.Combining experimental and theoretical analysis revealed that Ni-substituted Mo_(2)C elevates the d band center while significantly reducing antibonding orbitals(π^(*))occupancy compared to Fe-substituted Mo_(2)C and Co-substituted Mo_(2)C counterparts.This electronic restruction enhances d-p hybridization at the Mo-S interface,which strengthens sodium polysulfides adsorption energy and enhances charge transfer,thereby steering sulfur redox pathways toward thermodynamically favorable configurations.Our findings elucidate the intricate interplay between the electronic structure and catalytic activity of Mo_(2)C,advancing a novel perspective for the rational design of RT Na-S battery catalysts through tailored modulation of antibonding orbital occupancy.
基金the financial supports from National Key R&D Program of China(No.2022YFB3403301)the Funds for International Cooperation and Exchange of the National Natural Science Foundation of China(No.52311530080)。
文摘Modern industrial equipment is increasingly characterized by miniaturization,integration,and high performance,necessitating the production of complex structural parts with exceptionally high internal surface quality.Direct manufacturing often leads to high internal surface roughness,which traditional finishing and measuring methods cannot adequately address due to the decreasing size and increasing complexity of internal structures.This is especially true for components like pipes with large aspect ratios,extremely small deep holes,multi-stage bends,cross pipes,and array holes.To meet the high-performance manufacturing demands of these parts,advanced internal surface finishing and roughness measurement technologies have gained significant attention.This review focuses on the challenges and solutions related to internal surface parts with various apertures and complex structures.Internal surface finishing methods are categorized into mechanical finishing,fluid-based finishing,and energy-field-based finishing based on their characteristics.Roughness measurement technologies are divided into tool-probing and non-probing methods.The principles,required equipment,and key parameters of each finishing and measurement approach are discussed in detail.Additionally,the advantages and limitations of these methods are summarized,and future trends are forecasted.This paper serves as a comprehensive guide for researchers and engineers aiming to enhance the internal surface quality of complex structure parts.
基金supports of Basic Science Center Program for Multiphase Evolution in Hyper-gravity of the National Natural Science Foundation of China(No.51988101)National Natural Science Foundation of China(Nos.52109138 and 52122403)Young Elite Scientists Sponsorship Program by CAST(No.2023QNRC001).
文摘Hydraulic fracture growth is significantly influenced by the minimum horizontal principal stress gradient and the fracturing fluid pressure gradient.However,these gradients are often neglected in scaled physical modeling experiments due to difficulties in reproducing them.This study uses centrifugal hypergravity to simulate both gradients and investigate their effects on fracture propagation.Artificial mortar specimens(ϕ200 mm×400 mm)are fractured under 1g(normal gravity),50g,and 100g.Results show that compared to 1g,fractures under 50g and 100g exhibit increasingly uneven propagation,with higher g-values leading to greater asymmetry.To interpret this,a theoretical analysis based on fracture mechanics is conducted.When the fluid pressure gradient exceeds the stress gradient,a positive net gradient is generated,increasing net pressure at the lower fracture tip.This raises the stress intensity factor at the lower tip,promoting downward growth.As g increases,the disparity becomes more significant,resulting in greater fracture deviation.In conclusion,this study,for the first time,has verified and explained that the net gradient can change the propagation of hydraulic fractures,providing important guidance for wellbore placement under stress gradients.
文摘The paper presents analysis of the performance and the internal flow behaviour in the vaned diffuser of a radial flow pump using PIV(particle image velocimetry)and pressure probe traverses.PIV measurements have already been performed at middle height inside one diffuser channel passage for a given speed of rotation and various mass flow rates.These results have been already presented in several previous communications.New experiments have been performed using a three-hole pressure probe traverses from hub to shroud diffuser width at different radial locations between the two diffuser geometrical throats.Numerical simulations are also realized with the commercial codes Star CCM+7.02.011 and CFX.Frozen rotor and fully unsteady calculations of the whole pump have been performed.Comparisons between numerical results,previous experimental PIV results and new probe traverses one's are presented and discussed for one mass flow rate.In this respect,a first attempt to take into account fluid leakages between the rotating and fixed part of the pump has been checked since it may affects the real flow structure inside the diffuser.
基金Projects(51838001, 51878070, 51908073, 51908069) supported by the National Natural Science Foundation of ChinaProject(2019SK2171) supported by the Key Research and Development Program of Hunan Province, China+2 种基金Project(kq1905043) supported by the Training Program for Excellent Young Innovators of Changsha, ChinaProject(2019IC04) supported by Double First-class Scientific Research International Cooperation Expansion Project of Changsha University of Science & Technology, ChinaProject(CX20200811) supported by Postgraduate Research and Innovation Key Project of Hunan Province, China。
文摘To investigate the influence of confining pressures and temperatures on the seepage characteristics of fractured rocks, seepage tests were conducted on a fractured silty mudstone using a self-developed experimental system, and the effects of different factors on coefficient of permeability were discussed. The results showed that the increasing confining pressure will gradually decrease the coefficient of permeability, and this process is divided into two stages: 1) the fast decrease stage, which corresponds to a confining pressure less than 30 kPa, and 2) the slow decrease stage, which corresponds to a confining pressure larger than 30 kPa. Unlike confining pressure, an increase in temperature will increase the coefficient of permeability. It is noted that fracture surface roughness will also affect the variation of coefficient of permeability to a certain extent. Among the three examined factors, the effect of confining pressure increases is dominant on fracture permeability coefficient. The relationship between the confining pressure and coefficient of permeability can be quantified by an exponential function.
基金supported financially by the French Alternative Energies and Atomic Energy Commissionpartially funded by the ANR under contract number(No.ANR-10EQUIPEX-37).
文摘We report that 316L austenitic stainless steel fabricated by direct laser deposition(DLD),an additive manufacturing(AM)process,have a higher yield strength than that of conventional 316L while keeping high ductility.More interestingly,no clear anisotropy in tensile properties was observed between the building and the scanning direction of the 3D printed steel.Metallographic examination of the as-built parts shows a heterogeneous solidification cellular microstructure.Transmission electron microscopy observations coupled with Energy Dispersive X-ray Spectrometry(EDS)reveal the presence of chemical micro-segregation correlated with high dislocation density at cell boundaries as well as the in-situ formation of well-dispersed oxides and transition-metal-rich precipitates.The hierarchical heterogeneous microstructure in the AM parts induces excellent strength of the 316L stainless steel while the low staking fault energy of the as-built 316L promotes the occurrence of abundant deformation twinning,in the origin of the high ductility of the AM steel.Without additional post-process treatments,the AM 316L proves that it can be used as a structural material or component for repair in mechanical construction.
文摘This paper presents a numerical study of the flow topologies of three-dimensional （3D） flows in a high pressure compressor stator blade row without and with boundary layer aspiration on the hub wall. The stator blade is representative of the first stage operating under transonic inlet conditions and the blade design encourages development of highly complex 3D flows. The blade has a small tip clearance. The computational fluid dynamics （CFD） studies show progressive increase of hub corner stall with the increase in incidence. Aspiration is implemented on the hub wall via a slot in the comer between the hub wall and the suction surface. The CFD studies show aspiration to be sensitive to the suction flow rate; lower rate leads to very complex flow struc- tures and increased level of losses whereas higher rate renders aspiration effective for control of hub comer separation. The flow topologies are studied by trace of skin friction lines on the walls. The nature of flow can be explained by the topological rules of closed separation. Furthermore, a deeper analysis is done for a particular case with advanced criterion to test the non-degeneracy of critical points in the flow field.
基金supported by the research project RORAS 2 of the Mediterranean Program funded by INRIA,France
文摘We outline problems and potential solutions for feasible human-machine interfaces using cable-based parallel manipulators for physiotherapy applications.From an engineering perspective,we discuss the design constraints related to acceptance by patients and physiotherapist users.To date,most designs have focused on mobile platforms that are designed to be operated as an end-effector connected to human limbs for direct patient interaction.Some specific examples are illustrated from the authors' experience with prototypes available at Laboratory of Robotics and Mechatronics (LARM),Italy.
文摘The present work relates to a numerical investigation of double diffusive mixed convection around a horizontal annulus with a finned inner cylinder.The solutal and thermal buoyancy forces are sustained by maintaining the inner and outer cylinders at uniform temperatures and concentrations.Buoyancy effects are also considered,with the Boussinesq approximation.The forced convection effect is induced by the outer cylinder rotating with an angular velocity(ω)in an anti-clockwise direction.The studies are made for various combinations of dimensionless numbers;buoyancy ratio number(N),Lewis number(Le),Richardson number(Ri)and Grashof number(Gr).The isotherms,isoconcentrations and streamlines as well as both average and local Nusselt and Sherwood numbers were studied.A finite volume scheme is adopted to solve the transport equations for continuity,momentum,energy and mass transfer.The results indicate that the use of fins on the inner cylinder with outer cylinder rotation,significantly improves the heat and mass transfer in the annulus.
基金This work was financially supported by the International Cooperation Foundation of Shanghai Science and Technology Committee of China (No. 02SL002) and the Regional Council of Rhone-Alpes of France.
文摘The effects of aging treatment on the microstructures and mechanical properties of extruded AM50 ＋ xCa alloys （x=0, 1, 2 wt.%） were studied. The results indicated the secondary phase Mgl7Al12 precipitated from the saturated α-Mg solid solution while Al2Ca changed slightly when the aging time was increased. The hardness of extruded AM50 ＋ xCa al- loys increased initially to its peak, and then dropped to reach its original hardness with the increase in aging time. With the increase in aging temperature, the hardness of the AM50 ＋ 2Ca ahoy decreased, whereas the hardness of AM50 and AM50 ＋ 1Ca alloys decreased in the initial stages of aging treatment and increased in the later stages of aging treatment. The tensile strengths of AM50 and AM50 ＋ 1Ca alloys increased after aging treatment for the precipitation of Mg17Al12 phase, which increases the resistance against dislocation movement at the grain boundary; with increase in aging temperature, their tensile strengths increased. For AM50 ＋ 2Ca alloy, the tensile strength declined after aging at 150℃ and 175℃, while it increased slightly at 200℃. The ductility of AM50 ＋ xCa alloys （x = 0, 1, 2 wt.%） declined after aging treatment.
