Significant contributions have been made to understanding the processing of various metal materials using laser powder bed fusion (LPBF) for the design and fabrication of high-performance metal components in many fiel...Significant contributions have been made to understanding the processing of various metal materials using laser powder bed fusion (LPBF) for the design and fabrication of high-performance metal components in many fields. For laser additive manufacturing, aluminum-based materials are regarded as difficult-to-fabricate materials be- cause of their special physical properties, including low density, low laser absorption, high thermal conductivity, and ease of oxidation. Currently, LPBF-formed structural materials require high densification, fine grains, high specific strength, high ductility, and optimized physical or chemical properties. Therefore, comprehensive un- derstanding of the fabrication and performance of Al-based materials processed by LPBF is of significant value. This paper covers emerging research on aluminum-based materials using LPBF, providing an overall view of the basic scientific mechanisms behind manufacturing. The state-of-the-art researches of aluminum-based materials for LPBF formability as well as the microstructures, properties and corresponding metallurgical mechanisms are reviewed. The mechanisms of some of the main defects (pores, cracks, balling, and oxide inclusions) and control measures are also discussed. A summary and outlook for the further development of Al-based materials for LPBF are addressed.展开更多
Volume diffuse dielectric barrier discharge （DBD） plasma is produced in subsonic airflow by nanosecond high-voltage pulse power supply with a plate-to-plate discharge cell at 6 mm air gap length. The discharge image...Volume diffuse dielectric barrier discharge （DBD） plasma is produced in subsonic airflow by nanosecond high-voltage pulse power supply with a plate-to-plate discharge cell at 6 mm air gap length. The discharge images, optical emission spectra （OES）, the applied voltage and current waveforms of the discharge at the changed airflow rates are obtained. When airflow rate is increased, the transition of the discharge mode and the variations of discharge intensity, breakdown characteristics and the temperature of the discharge plasma are investigated. The results show that the discharge becomes more diffuse, discharge intensity is decreased accompanied by the increased breakdown voltage and time lag, and the temperature of the discharge plasma reduces when airflow of small velocity is introduced into the discharge gap. These phenomena are because that the airflow changes the spatial distribution of the heat and the space charge in the discharge gap.展开更多
In this paper, the double-discharge plasma generated by radio frequency （RF） and direct current （DC） has been investigated. In comparison with their single-frequency counterpart, the interaction between the two ex...In this paper, the double-discharge plasma generated by radio frequency （RF） and direct current （DC） has been investigated. In comparison with their single-frequency counterpart, the interaction between the two excitations is significant and beneficial. The results show that the RF discharge can effectively increase the DC discharge current and decrease the DC voltage; meanwhile the DC discharge is favorable to feed abundant high energy seed electrons to the ICP discharge sustaining at 13.56 MHz for the latter to acquire higher plasma density and lower plasma potential by increasing the ionization rate. The innovative design has been demonstrated to facilitate more homogeneous performance with higher plasma density.展开更多
The stability margin is a vital indicator for assessing the safety level of aircraft control systems.It should maintain sufficient stability margin to ensure safety during flight,especially in the process of large man...The stability margin is a vital indicator for assessing the safety level of aircraft control systems.It should maintain sufficient stability margin to ensure safety during flight,especially in the process of large maneuver operations.The stability margin is generally quantified by the Bode diagram,which strictly depends on the system parameters and the open-loop transfer function.However,due to the uncertain flight environments,transmission delays of sensors and mode switchings,etc.,there exist large parameter and structure uncertainties in the aircraft control systems,which make it difficult to precisely configure the stability margin to the desired value by the usual control methods.To address this problem,an indirect adaptive control strategy is proposed in this paper,where an adaptive PI control law with the capability of self-configuration of stability margin is developed.The developed control law not only achieves stable time-varying command tracking in the time domain,but also is able to automatically configure the phase margin and gain margin in the frequency domain.Finally,the simulation of the one-degree-of-freedom roll rate control model of the air vehicle verifies the validity of the proposed control method.展开更多
In this study,focusing on the geometry characteristics of spherical expanding flame,the turbulent premixed flames of natural gas/air mixtures were investigated in a fan-stirred turbulent combustor.The effects of initi...In this study,focusing on the geometry characteristics of spherical expanding flame,the turbulent premixed flames of natural gas/air mixtures were investigated in a fan-stirred turbulent combustor.The effects of initial temperature(T=300-400 K),initial pressure(P=0.1-0.3 MPa),turbulence intensity(u'=1.0-2.7 m/s),oxygen volumetric percentage(φ(O_(2))=15%-21%)and carbon dioxide volumetric percentage(φ(CO_(2))=0-20%)were delved into.The flame profile under the Cartesian coordinate system was derived from the schlieren images taken by the high-speed camera.Besides,from both macroscopic and microscopic perspectives,the influence of experimental conditions on the flame geometry characteristics was explored through flame front extraction,wavelet decomposition and network topology.The results demonstrate that for significant flame wrinkling,changes in species concentrations and turbulence intensity have more pronounced effects on the flame wrinkling ratio.The wrinkling of the flame front maintains a certain degree of similarity,as evidenced by the locally concentrated distribution of the angles of the maximum fluctuation radius.The disturbance energy under large-scale(D6-D8)disturbances exhibits relatively high values with a similar trend,exerting a significant impact on the geometry characteristics of the flame front.The peaks of correlation degree are scattered either with the decomposition scale or the development of flame radius,indicating no linear correlation between different detail components.Furthermore,the probability distribution of node degrees in key wrinkled regions exhibits different trends with that of large-scale wrinkling and disturbance energy,especially with changes in initial pressure.This occurs because the number of key wrinkles varies based on the perturbation's strength or the region's span.Consequently,an increase in the fluctuation frequency of the flame's local radius may not necessarily lead to an increase in the number of key folded regions.展开更多
Due to the portability and anti-interference ability,vision-based shipborne aircraft automatic landing systems have attracted the attention of researchers.In this paper,a Monocular Camera and Laser Range Finder(MC-LRF...Due to the portability and anti-interference ability,vision-based shipborne aircraft automatic landing systems have attracted the attention of researchers.In this paper,a Monocular Camera and Laser Range Finder(MC-LRF)-based pose measurement system is designed for shipborne aircraft automatic landing.First,the system represents the target ship using a set of sparse landmarks,and a two-stage model is adopted to detect landmarks on the target ship.The rough 6D pose is measured by solving a Perspective-n-Point problem.Then,once the rough pose is measured,a region-based pose refinement is used to continuously track the 6D pose in the subsequent image sequences.To address the low accuracy of monocular pose measurement in the depth direction,the designed system adopts a laser range finder to obtain an accurate range value.The measured rough pose is iteratively optimized using the accurate range measurement.Experimental results on synthetic and real images show that the system achieves robust and precise pose measurement of the target ship during automatic landing.The measurement means error is within 0.4in rotation,and 0.2%in translation,meeting the requirements for automatic fixed-wing aircraft landing.展开更多
The wave-absorbing materials are kinds of special electromagnetic functional materials and have been widely used in electromagnetic pollution control and military fields.In-situ integrated hierarchical structure const...The wave-absorbing materials are kinds of special electromagnetic functional materials and have been widely used in electromagnetic pollution control and military fields.In-situ integrated hierarchical structure construction is thought as a promising route to improve the microwave absorption performance of the materials.In the present work,layer-structured Co-metal-organic frameworks(Co-MOFs)precursors were grown in-situ on the surface of carbon fibers with the hydrothermal method.After annealed at 500℃ under Ar atmosphere,a novel multiscale hierarchical composite(Co@C/CF)was obtained with the support of carbon fibers,keeping the flower-like structure.Scanning electron microscope,transmission electron microscope,X-ray diffraction,Raman,and X-ray photoelectron spectroscopy were performed to analyze the microstructure and composition of the hierarchical structure,and the microwave absorption performance of the Co@C/CF composites were investigated.The results showed that the growth of the flower-like structure on the surface of carbon fiber was closely related to the metal-to-ligand ratio.The optimized Co@C/CF flower-like composites achieved the best reflection loss of−55.7 dB in the low frequency band of 6–8 GHz at the thickness of 2.8 mm,with the corresponding effective absorption bandwidth(EAB)of 2.1 GHz.The EAB of 3.24 GHz was achieved in the high frequency range of 12–16 GHz when the thickness was 1.5 mm.The excellent microwave absorption performance was ascribed to the introduction of magnetic components and the construction of the unique structure.The flower-like structure not only balanced the impedance of the fibers themselves,but also extended the propagation path of the microwave and then increased the multiple reflection losses.This work provides a convenient method for the design and development of wave-absorbing composites with in-situ integrated structure.展开更多
Surface-tension-confined microfluidic devices are platforms for manipulating 2D droplets based on patterned surfaces with special wettability.They have great potential for various applications,but are still in the ear...Surface-tension-confined microfluidic devices are platforms for manipulating 2D droplets based on patterned surfaces with special wettability.They have great potential for various applications,but are still in the early stages of development and face some challenges that need to be addressed.This study,inspired by the Wenzel and slippery transition of rose petal,develops a Patterned Oil-triggered Wenzel-slippery Surface(POWS)to examine the microfluidic devices.A laser-chemical composite method is established to fabricate POWSs,which take rose-petal-like microstructures as wettability pattern and a superamphiphobic surface as the background.The prepared POWSs switched between high adhesion superhydrophobic state and the slippery liquid-infused surface state through adding or removing the lubricant oil.In the high adhesion superhydrophobic state,the droplets can be sticked on the surface.In the slippery liquid-infused state,the droplet can slide along the wettability pattern as the designed route.A POWS-based droplet reactor is further constructed,on which,the droplets can be remotely controlled to move,mix and react,as required.Such a POWS,which manipulates droplets with surface tension controlled by the switchable wettability patterns,would be a promising candidate to construct multiple surface-tension-confined microfluidic devices.In addition,the fabrication technique and design principle proposed here may aid the development of various field related to the bio-inspired surfaces,such as water collection,desalination and high throughput analysis,etc.展开更多
Sweeping jet actuator(SJA)has been widely applied for activeflow control in openflows.In this paper,the SJA character in compressor cascade and its performance for separation control in innerflows are discussed.Time-a...Sweeping jet actuator(SJA)has been widely applied for activeflow control in openflows.In this paper,the SJA character in compressor cascade and its performance for separation control in innerflows are discussed.Time-averaged and transientflowfield measurement,together with visualization methods are utilized.It is found that endwall effects are important for both SJA behaviors and SJA performance for separation control in compressor cascades.There is a maximum of 12.7%total pressure loss reduction with SJA placed near the separation position,close to the endwall and under appropriateflowrate.The characteristic frequencies in theflowfield contribute to the capture of influence regions of vortices and excitation jets.Two concentrated shedding vortices and SJA jets impact region helped to judge that SJA energizes low momentumfluids in a large region and matches the high loss core well.To be concrete,theflow separation control mechanism of SJA lies on the interruption of the blade suction surface boundary layer development and the restriction of the lifting of the boundary layer from end-wall towards blade suction surface.展开更多
Drogue detection is one of the challenging tasks in autonomous aerial refueling due to the requirement for accuracy and rapidity.Saliency detection based on image intrinsic cues can achieve fast detection,but with poo...Drogue detection is one of the challenging tasks in autonomous aerial refueling due to the requirement for accuracy and rapidity.Saliency detection based on image intrinsic cues can achieve fast detection,but with poor accuracy.Recent studies reveal that optimization-based methods provide accurate and quick solutions for saliency detection.This paper presents a hybrid pigeon-inspired optimization method,the optimized color opponent,that aims to adjust the weight of color opponent channels to detect the drogue region.It can optimize the weights in the selected aerial refueling scene offline,and the results are applied for drogue detection in the scene.A novel algorithm aggregated by the optimized color opponent and robust background detection is presented to provide better precision and robustness.Experimental results on benchmark datasets and aerial refueling images show that the proposed method successfully extracts the saliency region or drogue and exhibits superior performance against the other saliency detection methods with intrinsic cues.The algorithm designed in this paper is competent for the drogue detection task of autonomous aerial refueling.展开更多
The Electro-Hydrostatic Actuator(EHA)is a typical hydro-mechatronic control system.Due to the limited accuracy of measurement,inadequate knowledge,and vague judgments,hybrid uncertainties,including aleatory and episte...The Electro-Hydrostatic Actuator(EHA)is a typical hydro-mechatronic control system.Due to the limited accuracy of measurement,inadequate knowledge,and vague judgments,hybrid uncertainties,including aleatory and epistemic uncertainties,inevitably exist in the performance assessment of EHA systems.Existing methods ignored the hybrid uncertainties which can hardly obtain a satisfactory result while wasting a lot of time on the experimental design.To overcome this drawback,a metamodeling method for hybrid uncertainty propagation of EHA systems is developed via an active learning Gaussian Process(GP)model.The proposed method is bifurcated into three pillars:(A)Initializing the GP model and generating the optimum candidate sampling set by an Optimized Max-Minimize Distance(OMMD)algorithm,which aims to maximize the minimum distance between the added samples and original samples,(B)maximizing the learning function and generating new samples by a developed farthest or nearest judgment strategy,while updating the original GP model,and(C)judging the convergence by three uncertainty metrics,i.e.,the area metric,maximum variance metric,and the mean value metric.A numerical example is exemplified to evaluate the effectiveness and efficiency of the proposed method.Meanwhile,the EHA system of aircrafts is examined to show the application of the proposed method for high-dimensional problems.The effects of the uncertainties in the Proportional-Integral-Differential(PID)of the EHA system are also examined.展开更多
Selective laser melting(SLM)is a 3D printing technology with a high near-net-shape ability and forming accuracy.However,the inevitable internal defects significantly hinder its development.Therefore,it is essential to...Selective laser melting(SLM)is a 3D printing technology with a high near-net-shape ability and forming accuracy.However,the inevitable internal defects significantly hinder its development.Therefore,it is essential to fully understand the causes of internal defects in SLM processing and minimize the defects to achieve quality control accordingly.This work reviews the recent studies on internal defects in SLM,presenting the main internal defects of SLM as impurities,lack of fusion,gas pores,and micro-crack.These internal defects occur on the various phenomena in the laser-powder-melt pool(LPMP)stage.The formation of SLM internal defects is mainly affected by oxidation,denudation,balling,spatter,and keyholes;here,balling,spattering,and the keyhole phenomenon are the main factors causing internal defects in LPMP.Hence,this paper focuses on reviewing the balling effect,spatter behavior,and keyhole phenomenon,introducing the action mechanism of the above three phenomena under different process conditions.Additionally,the spatter behavior when forming internal defects is proposed.This review also considers the correlation between the spatter behavior and keyhole phenomenon and makes an important contribution to understanding and reducing SLM internal defects.It presents a reliable opinion on real-time monitoring and machine intelligent learning for SLM processing in the future,as well as supporting a systematic thinking for the suppression of defect formation in SLM.展开更多
The effect of high pressure during solidification on the microstructure and mechanical property of Mg-6Zn-1Y and Mg-6Zn-3Y was investigated using optical microscopy, scanning electronic microscopy, X-ray diffraction（...The effect of high pressure during solidification on the microstructure and mechanical property of Mg-6Zn-1Y and Mg-6Zn-3Y was investigated using optical microscopy, scanning electronic microscopy, X-ray diffraction（XRD） and Vickers-hardness testing. Under atmospheric-pressure solidification, Mg-6Zn-1Y consisted of α-Mg, Mg7Zn3 and Mg_3YZn_6; whilst Mg-6Zn-3Y consisted of α-Mg, Mg_3Y_2Zn_3 and Mg_3YZn_6. Under 6 GPa high-pressure solidification, both alloy consisted of α-Mg, MgZ n and Mg12 YZn. The shape of the main second phase changed from a lamellar structure formed for atmospheric-pressure solidification to small particles formed for solidification at 6 GPa pressure. The dendrite microstructure was refined and was more regular, and the length of the primary dendrite arm increased under 6 GPa high-pressure solidification, which was attributed to increasing thermal undercooling, compositional undercooling and kinetics undercooling. After solidification at 6 GPa pressure, the solid solubility of Y in the second phase and the Vickers-hardness increased from 15 wt.% and 69 MPa for Mg-6Zn-1Y to 49 wt.% and 97 MPa; and from 19 wt.% and 71 MPa for Mg-6Zn-3Y alloy to 20 wt.% and 92 MPa, respectively.展开更多
基金supported by National Natural Science Foundation of China(Grant No.52225503)Key Research and Development Pro-gram of Jiangsu Province(Grant Nos.BE2022069 and BE2022069-1)+2 种基金The Pre-research Project of Civil Aerospace Technology(Grant No.D020302)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX23_0366)State Key Laboratory of Mechanics and Control for Aerospace Structures(Grant No.MCAS-S-0423G01).
文摘Significant contributions have been made to understanding the processing of various metal materials using laser powder bed fusion (LPBF) for the design and fabrication of high-performance metal components in many fields. For laser additive manufacturing, aluminum-based materials are regarded as difficult-to-fabricate materials be- cause of their special physical properties, including low density, low laser absorption, high thermal conductivity, and ease of oxidation. Currently, LPBF-formed structural materials require high densification, fine grains, high specific strength, high ductility, and optimized physical or chemical properties. Therefore, comprehensive un- derstanding of the fabrication and performance of Al-based materials processed by LPBF is of significant value. This paper covers emerging research on aluminum-based materials using LPBF, providing an overall view of the basic scientific mechanisms behind manufacturing. The state-of-the-art researches of aluminum-based materials for LPBF formability as well as the microstructures, properties and corresponding metallurgical mechanisms are reviewed. The mechanisms of some of the main defects (pores, cracks, balling, and oxide inclusions) and control measures are also discussed. A summary and outlook for the further development of Al-based materials for LPBF are addressed.
基金supported by National Natural Science Foundation of China(No.51437002)
文摘Volume diffuse dielectric barrier discharge （DBD） plasma is produced in subsonic airflow by nanosecond high-voltage pulse power supply with a plate-to-plate discharge cell at 6 mm air gap length. The discharge images, optical emission spectra （OES）, the applied voltage and current waveforms of the discharge at the changed airflow rates are obtained. When airflow rate is increased, the transition of the discharge mode and the variations of discharge intensity, breakdown characteristics and the temperature of the discharge plasma are investigated. The results show that the discharge becomes more diffuse, discharge intensity is decreased accompanied by the increased breakdown voltage and time lag, and the temperature of the discharge plasma reduces when airflow of small velocity is introduced into the discharge gap. These phenomena are because that the airflow changes the spatial distribution of the heat and the space charge in the discharge gap.
基金supported by National Natural Science Foundation of China(No.11475038)
文摘In this paper, the double-discharge plasma generated by radio frequency （RF） and direct current （DC） has been investigated. In comparison with their single-frequency counterpart, the interaction between the two excitations is significant and beneficial. The results show that the RF discharge can effectively increase the DC discharge current and decrease the DC voltage; meanwhile the DC discharge is favorable to feed abundant high energy seed electrons to the ICP discharge sustaining at 13.56 MHz for the latter to acquire higher plasma density and lower plasma potential by increasing the ionization rate. The innovative design has been demonstrated to facilitate more homogeneous performance with higher plasma density.
基金supported in part by the National Natural Science Foundation of China under Grant Nos.62322304,61925303,62173323,62003277,62088101,and U20B2073in part by the Foundation under Grant No.2019-JCJQ-ZD-049in part by Beijing Institute of Technology Research Fund Program for Young Scholars。
文摘The stability margin is a vital indicator for assessing the safety level of aircraft control systems.It should maintain sufficient stability margin to ensure safety during flight,especially in the process of large maneuver operations.The stability margin is generally quantified by the Bode diagram,which strictly depends on the system parameters and the open-loop transfer function.However,due to the uncertain flight environments,transmission delays of sensors and mode switchings,etc.,there exist large parameter and structure uncertainties in the aircraft control systems,which make it difficult to precisely configure the stability margin to the desired value by the usual control methods.To address this problem,an indirect adaptive control strategy is proposed in this paper,where an adaptive PI control law with the capability of self-configuration of stability margin is developed.The developed control law not only achieves stable time-varying command tracking in the time domain,but also is able to automatically configure the phase margin and gain margin in the frequency domain.Finally,the simulation of the one-degree-of-freedom roll rate control model of the air vehicle verifies the validity of the proposed control method.
基金financially supported by the General Program Supported by Educational Committee of Liaoning Province of China(LJKMZ20220537)the financial support from the National Science and Technology Major Project(2017-Ⅲ-0006-0031)the fundamental research funds for the universities of Liaoning Province。
文摘In this study,focusing on the geometry characteristics of spherical expanding flame,the turbulent premixed flames of natural gas/air mixtures were investigated in a fan-stirred turbulent combustor.The effects of initial temperature(T=300-400 K),initial pressure(P=0.1-0.3 MPa),turbulence intensity(u'=1.0-2.7 m/s),oxygen volumetric percentage(φ(O_(2))=15%-21%)and carbon dioxide volumetric percentage(φ(CO_(2))=0-20%)were delved into.The flame profile under the Cartesian coordinate system was derived from the schlieren images taken by the high-speed camera.Besides,from both macroscopic and microscopic perspectives,the influence of experimental conditions on the flame geometry characteristics was explored through flame front extraction,wavelet decomposition and network topology.The results demonstrate that for significant flame wrinkling,changes in species concentrations and turbulence intensity have more pronounced effects on the flame wrinkling ratio.The wrinkling of the flame front maintains a certain degree of similarity,as evidenced by the locally concentrated distribution of the angles of the maximum fluctuation radius.The disturbance energy under large-scale(D6-D8)disturbances exhibits relatively high values with a similar trend,exerting a significant impact on the geometry characteristics of the flame front.The peaks of correlation degree are scattered either with the decomposition scale or the development of flame radius,indicating no linear correlation between different detail components.Furthermore,the probability distribution of node degrees in key wrinkled regions exhibits different trends with that of large-scale wrinkling and disturbance energy,especially with changes in initial pressure.This occurs because the number of key wrinkles varies based on the perturbation's strength or the region's span.Consequently,an increase in the fluctuation frequency of the flame's local radius may not necessarily lead to an increase in the number of key folded regions.
基金co-supported by the National Natural Science Foundation of China,China(No.12272404)the Postgraduate Research Innovation Project of Hunan Province of China,China(No.CX20210016).
文摘Due to the portability and anti-interference ability,vision-based shipborne aircraft automatic landing systems have attracted the attention of researchers.In this paper,a Monocular Camera and Laser Range Finder(MC-LRF)-based pose measurement system is designed for shipborne aircraft automatic landing.First,the system represents the target ship using a set of sparse landmarks,and a two-stage model is adopted to detect landmarks on the target ship.The rough 6D pose is measured by solving a Perspective-n-Point problem.Then,once the rough pose is measured,a region-based pose refinement is used to continuously track the 6D pose in the subsequent image sequences.To address the low accuracy of monocular pose measurement in the depth direction,the designed system adopts a laser range finder to obtain an accurate range value.The measured rough pose is iteratively optimized using the accurate range measurement.Experimental results on synthetic and real images show that the system achieves robust and precise pose measurement of the target ship during automatic landing.The measurement means error is within 0.4in rotation,and 0.2%in translation,meeting the requirements for automatic fixed-wing aircraft landing.
基金financially supported by the National Natural Science of Foundation of China(No.52371097)the Shenyang Unveiling and Leading Project,China(No.22-301-1-01)。
文摘The wave-absorbing materials are kinds of special electromagnetic functional materials and have been widely used in electromagnetic pollution control and military fields.In-situ integrated hierarchical structure construction is thought as a promising route to improve the microwave absorption performance of the materials.In the present work,layer-structured Co-metal-organic frameworks(Co-MOFs)precursors were grown in-situ on the surface of carbon fibers with the hydrothermal method.After annealed at 500℃ under Ar atmosphere,a novel multiscale hierarchical composite(Co@C/CF)was obtained with the support of carbon fibers,keeping the flower-like structure.Scanning electron microscope,transmission electron microscope,X-ray diffraction,Raman,and X-ray photoelectron spectroscopy were performed to analyze the microstructure and composition of the hierarchical structure,and the microwave absorption performance of the Co@C/CF composites were investigated.The results showed that the growth of the flower-like structure on the surface of carbon fiber was closely related to the metal-to-ligand ratio.The optimized Co@C/CF flower-like composites achieved the best reflection loss of−55.7 dB in the low frequency band of 6–8 GHz at the thickness of 2.8 mm,with the corresponding effective absorption bandwidth(EAB)of 2.1 GHz.The EAB of 3.24 GHz was achieved in the high frequency range of 12–16 GHz when the thickness was 1.5 mm.The excellent microwave absorption performance was ascribed to the introduction of magnetic components and the construction of the unique structure.The flower-like structure not only balanced the impedance of the fibers themselves,but also extended the propagation path of the microwave and then increased the multiple reflection losses.This work provides a convenient method for the design and development of wave-absorbing composites with in-situ integrated structure.
基金supported by Key Scientific and Technological Projects of Jilin Province(20220201026GX,20220401083YY)Fundamental Research Funds for the Central Universities,Jilin University(2022-JCXK-15).
文摘Surface-tension-confined microfluidic devices are platforms for manipulating 2D droplets based on patterned surfaces with special wettability.They have great potential for various applications,but are still in the early stages of development and face some challenges that need to be addressed.This study,inspired by the Wenzel and slippery transition of rose petal,develops a Patterned Oil-triggered Wenzel-slippery Surface(POWS)to examine the microfluidic devices.A laser-chemical composite method is established to fabricate POWSs,which take rose-petal-like microstructures as wettability pattern and a superamphiphobic surface as the background.The prepared POWSs switched between high adhesion superhydrophobic state and the slippery liquid-infused surface state through adding or removing the lubricant oil.In the high adhesion superhydrophobic state,the droplets can be sticked on the surface.In the slippery liquid-infused state,the droplet can slide along the wettability pattern as the designed route.A POWS-based droplet reactor is further constructed,on which,the droplets can be remotely controlled to move,mix and react,as required.Such a POWS,which manipulates droplets with surface tension controlled by the switchable wettability patterns,would be a promising candidate to construct multiple surface-tension-confined microfluidic devices.In addition,the fabrication technique and design principle proposed here may aid the development of various field related to the bio-inspired surfaces,such as water collection,desalination and high throughput analysis,etc.
基金supported by the National Natural Science Foundation of China (Grant Nos.52076052 and U2233207).
文摘Sweeping jet actuator(SJA)has been widely applied for activeflow control in openflows.In this paper,the SJA character in compressor cascade and its performance for separation control in innerflows are discussed.Time-averaged and transientflowfield measurement,together with visualization methods are utilized.It is found that endwall effects are important for both SJA behaviors and SJA performance for separation control in compressor cascades.There is a maximum of 12.7%total pressure loss reduction with SJA placed near the separation position,close to the endwall and under appropriateflowrate.The characteristic frequencies in theflowfield contribute to the capture of influence regions of vortices and excitation jets.Two concentrated shedding vortices and SJA jets impact region helped to judge that SJA energizes low momentumfluids in a large region and matches the high loss core well.To be concrete,theflow separation control mechanism of SJA lies on the interruption of the blade suction surface boundary layer development and the restriction of the lifting of the boundary layer from end-wall towards blade suction surface.
基金This work was partially supported by Science and Technology Innovation 2030-Key Project of“New Generation Artificial Intelligence”,China(No.2018AAA0102403)the National Natural Science Foundation of China(Nos.U1913602,T2121003,91948204,62103040,and U20B2071)the Open Fund/Postdoctoral Fund of the Laboratory of Cognition and Decision Intelligence for Complex Systems,Institute of Automation,Chinese Academy of Sciences(No.CASIA-KFKT-08).
文摘Drogue detection is one of the challenging tasks in autonomous aerial refueling due to the requirement for accuracy and rapidity.Saliency detection based on image intrinsic cues can achieve fast detection,but with poor accuracy.Recent studies reveal that optimization-based methods provide accurate and quick solutions for saliency detection.This paper presents a hybrid pigeon-inspired optimization method,the optimized color opponent,that aims to adjust the weight of color opponent channels to detect the drogue region.It can optimize the weights in the selected aerial refueling scene offline,and the results are applied for drogue detection in the scene.A novel algorithm aggregated by the optimized color opponent and robust background detection is presented to provide better precision and robustness.Experimental results on benchmark datasets and aerial refueling images show that the proposed method successfully extracts the saliency region or drogue and exhibits superior performance against the other saliency detection methods with intrinsic cues.The algorithm designed in this paper is competent for the drogue detection task of autonomous aerial refueling.
基金the National Natural Science Foundation of China(Nos.72301057,72271044,72331002,and 52305010)the Sichuan Science and Technology Program,China(No.2023YFG0157).
文摘The Electro-Hydrostatic Actuator(EHA)is a typical hydro-mechatronic control system.Due to the limited accuracy of measurement,inadequate knowledge,and vague judgments,hybrid uncertainties,including aleatory and epistemic uncertainties,inevitably exist in the performance assessment of EHA systems.Existing methods ignored the hybrid uncertainties which can hardly obtain a satisfactory result while wasting a lot of time on the experimental design.To overcome this drawback,a metamodeling method for hybrid uncertainty propagation of EHA systems is developed via an active learning Gaussian Process(GP)model.The proposed method is bifurcated into three pillars:(A)Initializing the GP model and generating the optimum candidate sampling set by an Optimized Max-Minimize Distance(OMMD)algorithm,which aims to maximize the minimum distance between the added samples and original samples,(B)maximizing the learning function and generating new samples by a developed farthest or nearest judgment strategy,while updating the original GP model,and(C)judging the convergence by three uncertainty metrics,i.e.,the area metric,maximum variance metric,and the mean value metric.A numerical example is exemplified to evaluate the effectiveness and efficiency of the proposed method.Meanwhile,the EHA system of aircrafts is examined to show the application of the proposed method for high-dimensional problems.The effects of the uncertainties in the Proportional-Integral-Differential(PID)of the EHA system are also examined.
基金National Natural Science Foundation of China(Grant No.51975387).
文摘Selective laser melting(SLM)is a 3D printing technology with a high near-net-shape ability and forming accuracy.However,the inevitable internal defects significantly hinder its development.Therefore,it is essential to fully understand the causes of internal defects in SLM processing and minimize the defects to achieve quality control accordingly.This work reviews the recent studies on internal defects in SLM,presenting the main internal defects of SLM as impurities,lack of fusion,gas pores,and micro-crack.These internal defects occur on the various phenomena in the laser-powder-melt pool(LPMP)stage.The formation of SLM internal defects is mainly affected by oxidation,denudation,balling,spatter,and keyholes;here,balling,spattering,and the keyhole phenomenon are the main factors causing internal defects in LPMP.Hence,this paper focuses on reviewing the balling effect,spatter behavior,and keyhole phenomenon,introducing the action mechanism of the above three phenomena under different process conditions.Additionally,the spatter behavior when forming internal defects is proposed.This review also considers the correlation between the spatter behavior and keyhole phenomenon and makes an important contribution to understanding and reducing SLM internal defects.It presents a reliable opinion on real-time monitoring and machine intelligent learning for SLM processing in the future,as well as supporting a systematic thinking for the suppression of defect formation in SLM.
基金Project supported by the China Scholarship Council(2011836024)the International Science and Technology Cooperation Project of Jiangxi Province(20151BDH80006)+5 种基金the Prior Science and Technology Program led by the Returned Overseas Chinese Talents(RSTH[2015]192-GRSZ[2015]273)the Key Program of Natural Science Foundation of Jiangxi Province(20133BAB2000820144ACB20013)the Science and Technology Innovation Project of Jiangxi Academy of Sciences(2013-YYB-12013-XTPH1-192015XTTD04)
文摘The effect of high pressure during solidification on the microstructure and mechanical property of Mg-6Zn-1Y and Mg-6Zn-3Y was investigated using optical microscopy, scanning electronic microscopy, X-ray diffraction（XRD） and Vickers-hardness testing. Under atmospheric-pressure solidification, Mg-6Zn-1Y consisted of α-Mg, Mg7Zn3 and Mg_3YZn_6; whilst Mg-6Zn-3Y consisted of α-Mg, Mg_3Y_2Zn_3 and Mg_3YZn_6. Under 6 GPa high-pressure solidification, both alloy consisted of α-Mg, MgZ n and Mg12 YZn. The shape of the main second phase changed from a lamellar structure formed for atmospheric-pressure solidification to small particles formed for solidification at 6 GPa pressure. The dendrite microstructure was refined and was more regular, and the length of the primary dendrite arm increased under 6 GPa high-pressure solidification, which was attributed to increasing thermal undercooling, compositional undercooling and kinetics undercooling. After solidification at 6 GPa pressure, the solid solubility of Y in the second phase and the Vickers-hardness increased from 15 wt.% and 69 MPa for Mg-6Zn-1Y to 49 wt.% and 97 MPa; and from 19 wt.% and 71 MPa for Mg-6Zn-3Y alloy to 20 wt.% and 92 MPa, respectively.
