The mechanical behavior of cohesive soil is sensitized to drying-wetting cycles under confinements.However,the hydromechanical coupling effect has not been considered in current constitutive models.A macro-micro analy...The mechanical behavior of cohesive soil is sensitized to drying-wetting cycles under confinements.However,the hydromechanical coupling effect has not been considered in current constitutive models.A macro-micro analysis scheme is proposed in this paper to investigate the soil deformation behavior under the coupling of stress and drying-wetting cycles.A new device is developed based on CT(computerized tomography)workstation to apply certain normal and shear stresses on a soil specimen during drying-wetting cycles.A series of tests are conducted on a type of loess with various coupling of stress paths and drying-wetting cycles.At macroscopic level,stress sensor and laser sensor are used to acquire stress and strain,respectively.The shear and volumetric strain increase during the first few drying-wetting cycles and then become stable.The increase of the shear stress level or confining pressure would cause higher increase rate and the value of shear strain in the process of drying-wetting cycles.At microscopic level,the grayscale value(GSV)of CT scanning image is characterized as the proportion of soil particles to voids.A fabric state parameter is proposed to characterize soil microstructures under the influence of stress and drying-wetting cycle.Test results indicate that the macroand micro-responses show high consistence and relevance.The stress and drying-wetting cycles would both induce collapse of the soil microstructure,which dominants degradation of the soil mechanical properties.The evolution of the macro-mechanical property of soil exhibits a positive linear relationship with the micro-evolution of the fabric state parameter.展开更多
Plasma electrolytic oxidation(PEO)coatings were prepared on Al−Mg laminated macro composites(LMCs)using both unipolar and bipolar waveforms in an appropriate electrolyte for both aluminum and magnesium alloys.The tech...Plasma electrolytic oxidation(PEO)coatings were prepared on Al−Mg laminated macro composites(LMCs)using both unipolar and bipolar waveforms in an appropriate electrolyte for both aluminum and magnesium alloys.The techniques of FESEM/EDS,grazing incident beam X-ray diffraction(GIXRD),and electrochemical methods of potentiodynamic polarization and electrochemical impedance spectroscopy(EIS)were used to characterize the coatings.The results revealed that the coatings produced using the bipolar waveform exhibited lower porosity and higher thickness than those produced using the unipolar one.The corrosion performance of the specimens’cut edge was investigated using EIS after 1,8,and 12 h of immersion in a 3.5 wt.%NaCl solution.It was observed that the coating produced using the bipolar waveform demonstrated the highest corrosion resistance after 12 h of immersion,with an estimated corrosion resistance of 5.64 kΩ·cm^(2),which was approximately 3 times higher than that of the unipolar coating.Notably,no signs of galvanic corrosion were observed in the LMCs,and only minor corrosion attacks were observed on the magnesium layer in some areas.展开更多
Owing to their high flexibility and directional actuation capabilities,macro fiber composites(MFCs)have attracted significant attention for the active control of structures,especially in the nonlinear vibration suppre...Owing to their high flexibility and directional actuation capabilities,macro fiber composites(MFCs)have attracted significant attention for the active control of structures,especially in the nonlinear vibration suppression applications for large-scale flexible structures.In this paper,an MFC-based self-feedback system is introduced for the active control of geometrically nonlinear steady-state forced vibrations in functionally graded carbon nanotube reinforced composite(FG-CNTRC)plates subject to transverse mechanical loads.Based on the first-order shear deformation theory and the von Kármán nonlinear strain-displacement relationship,the nonlinear vibration control equations of the plate with MFC sensor and actuator layers are derived by Hamilton's principle.These equations are discretized by the finite element method(FEM),and solved by the Newton-Raphson and direct iterative methods.A velocity feedback control algorithm is introduced,and the effects of the control gain and the MFC actuator position on the nonlinear vibration active control effectiveness are analyzed.Additionally,a nonlinear resonance analysis is carried out,considering the effects of carbon nanotube(CNT)volume fraction and distribution type.The results indicate that the intrinsic characteristics of the structures significantly influence the vibration behavior.Furthermore,the appropriate selections of control gain and MFC position are crucial for the effective active control of the structures.The present work provides a promising route of the active and efficient nonlinear vibration suppression for various thin-walled structures.展开更多
A massive amount of plastic waste has presented an immense management challenge.This escalating ecological damage,coupled with the detrimental effects of plastics infiltrating the marine food web,poses a significant t...A massive amount of plastic waste has presented an immense management challenge.This escalating ecological damage,coupled with the detrimental effects of plastics infiltrating the marine food web,poses a significant threat to human livelihoods.To combat this,there is a call for the development of plastic detection algorithms using remote sensing data.Here we tested a new index,referred to index_(MP),to detect clusters of floating macro plastics in the ocean using satellite imagery.The index_(MP)was applied to convolution high-pass filtered(3×3)Sentinel 2 Level 1 C images,showing the potential to reduce atmospheric interference and enhance the object edges,thereby improving the clarity of detection.In the analysis,we used three scatter plots to identify and assess plastic pixels.To differentiate the common features of plastic from non-plastic objects,the Sentinel 2 bands 5,8,and 9 were plotted against index_(MP)calculated and convolution high-pass filtered Level 1 C(CHPIC)images.The plastic pixels,clustering in the three scatter plots,showed positive‘X’,i.e.,CHPIC image value and‘Y’,i.e.,each band 5,8,and 9 reflectance values,along with a CHPIC image value exceeding 0.05.Using the index_(MP)and scatter plot analysis,we identified plastic pixels containing 14%or more plastic bottles.Detection of other types of plastics,such as fishing nets and plastic bags,required pixel proportions greater than 50%.Hence,plastic bottles were notably responsive even at a low pixel fraction.We further explored the classification of plastic and non-plastic objects by analyzing reed(plant)pixels;the differentiation between plastic and reed was conducted in the band 5 and 9 scatter plots.展开更多
The experimental study on the macro and micro characteristics of the spray from a pressure swirl nozzle embraces the growth of surface unstable wave,disintegration process,spray angle,breakup length and so on.The e...The experimental study on the macro and micro characteristics of the spray from a pressure swirl nozzle embraces the growth of surface unstable wave,disintegration process,spray angle,breakup length and so on.The effects of injection pressure,nozzle geometry and liquid properties on these characteristics are also discussed.The results are helpful to understand the underlying physics of the pressure swirl nozzle and serve as the basis for the practical design,usage and improvement of the nozzle.展开更多
基金funded by National Key R&D Program of China(Grant No.2023YFC3007001)Beijing Natural Science Foundation(Grant No.8244053)China Postdoctoral Science Foundation(Grant No.2024M754065).
文摘The mechanical behavior of cohesive soil is sensitized to drying-wetting cycles under confinements.However,the hydromechanical coupling effect has not been considered in current constitutive models.A macro-micro analysis scheme is proposed in this paper to investigate the soil deformation behavior under the coupling of stress and drying-wetting cycles.A new device is developed based on CT(computerized tomography)workstation to apply certain normal and shear stresses on a soil specimen during drying-wetting cycles.A series of tests are conducted on a type of loess with various coupling of stress paths and drying-wetting cycles.At macroscopic level,stress sensor and laser sensor are used to acquire stress and strain,respectively.The shear and volumetric strain increase during the first few drying-wetting cycles and then become stable.The increase of the shear stress level or confining pressure would cause higher increase rate and the value of shear strain in the process of drying-wetting cycles.At microscopic level,the grayscale value(GSV)of CT scanning image is characterized as the proportion of soil particles to voids.A fabric state parameter is proposed to characterize soil microstructures under the influence of stress and drying-wetting cycle.Test results indicate that the macroand micro-responses show high consistence and relevance.The stress and drying-wetting cycles would both induce collapse of the soil microstructure,which dominants degradation of the soil mechanical properties.The evolution of the macro-mechanical property of soil exhibits a positive linear relationship with the micro-evolution of the fabric state parameter.
文摘Plasma electrolytic oxidation(PEO)coatings were prepared on Al−Mg laminated macro composites(LMCs)using both unipolar and bipolar waveforms in an appropriate electrolyte for both aluminum and magnesium alloys.The techniques of FESEM/EDS,grazing incident beam X-ray diffraction(GIXRD),and electrochemical methods of potentiodynamic polarization and electrochemical impedance spectroscopy(EIS)were used to characterize the coatings.The results revealed that the coatings produced using the bipolar waveform exhibited lower porosity and higher thickness than those produced using the unipolar one.The corrosion performance of the specimens’cut edge was investigated using EIS after 1,8,and 12 h of immersion in a 3.5 wt.%NaCl solution.It was observed that the coating produced using the bipolar waveform demonstrated the highest corrosion resistance after 12 h of immersion,with an estimated corrosion resistance of 5.64 kΩ·cm^(2),which was approximately 3 times higher than that of the unipolar coating.Notably,no signs of galvanic corrosion were observed in the LMCs,and only minor corrosion attacks were observed on the magnesium layer in some areas.
基金Project supported by the National Natural Science Foundation of China(Nos.12072003 and 12372003)Beijing Natural Science Foundation of China(No.1222001)。
文摘Owing to their high flexibility and directional actuation capabilities,macro fiber composites(MFCs)have attracted significant attention for the active control of structures,especially in the nonlinear vibration suppression applications for large-scale flexible structures.In this paper,an MFC-based self-feedback system is introduced for the active control of geometrically nonlinear steady-state forced vibrations in functionally graded carbon nanotube reinforced composite(FG-CNTRC)plates subject to transverse mechanical loads.Based on the first-order shear deformation theory and the von Kármán nonlinear strain-displacement relationship,the nonlinear vibration control equations of the plate with MFC sensor and actuator layers are derived by Hamilton's principle.These equations are discretized by the finite element method(FEM),and solved by the Newton-Raphson and direct iterative methods.A velocity feedback control algorithm is introduced,and the effects of the control gain and the MFC actuator position on the nonlinear vibration active control effectiveness are analyzed.Additionally,a nonlinear resonance analysis is carried out,considering the effects of carbon nanotube(CNT)volume fraction and distribution type.The results indicate that the intrinsic characteristics of the structures significantly influence the vibration behavior.Furthermore,the appropriate selections of control gain and MFC position are crucial for the effective active control of the structures.The present work provides a promising route of the active and efficient nonlinear vibration suppression for various thin-walled structures.
基金Supported by the Guangdong Special Support Program for Key Talents Team Program(No.2019BT02H594)the PI Project of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(No.GML2021GD0810)the Major Project of National Social Science Foundation of China(No.21ZDA097)。
文摘A massive amount of plastic waste has presented an immense management challenge.This escalating ecological damage,coupled with the detrimental effects of plastics infiltrating the marine food web,poses a significant threat to human livelihoods.To combat this,there is a call for the development of plastic detection algorithms using remote sensing data.Here we tested a new index,referred to index_(MP),to detect clusters of floating macro plastics in the ocean using satellite imagery.The index_(MP)was applied to convolution high-pass filtered(3×3)Sentinel 2 Level 1 C images,showing the potential to reduce atmospheric interference and enhance the object edges,thereby improving the clarity of detection.In the analysis,we used three scatter plots to identify and assess plastic pixels.To differentiate the common features of plastic from non-plastic objects,the Sentinel 2 bands 5,8,and 9 were plotted against index_(MP)calculated and convolution high-pass filtered Level 1 C(CHPIC)images.The plastic pixels,clustering in the three scatter plots,showed positive‘X’,i.e.,CHPIC image value and‘Y’,i.e.,each band 5,8,and 9 reflectance values,along with a CHPIC image value exceeding 0.05.Using the index_(MP)and scatter plot analysis,we identified plastic pixels containing 14%or more plastic bottles.Detection of other types of plastics,such as fishing nets and plastic bags,required pixel proportions greater than 50%.Hence,plastic bottles were notably responsive even at a low pixel fraction.We further explored the classification of plastic and non-plastic objects by analyzing reed(plant)pixels;the differentiation between plastic and reed was conducted in the band 5 and 9 scatter plots.
文摘The experimental study on the macro and micro characteristics of the spray from a pressure swirl nozzle embraces the growth of surface unstable wave,disintegration process,spray angle,breakup length and so on.The effects of injection pressure,nozzle geometry and liquid properties on these characteristics are also discussed.The results are helpful to understand the underlying physics of the pressure swirl nozzle and serve as the basis for the practical design,usage and improvement of the nozzle.
