This study is the result of long-term efforts of the authors’team to assess ground response of gob-side entry by roof cutting(GSERC)with hard main roof,aiming at scientific control for GSERC deformation.A comprehensi...This study is the result of long-term efforts of the authors’team to assess ground response of gob-side entry by roof cutting(GSERC)with hard main roof,aiming at scientific control for GSERC deformation.A comprehensive field measurement program was conducted to determine entry deformation,roof fracture zone,and anchor bolt(cable)loading.The results indicate that GSERC deformation presents asymmetric characteristics.The maximum convergence near roof cutting side is 458 mm during the primary use process and 1120 mm during the secondary reuse process.The entry deformation is closely associated with the primary development stage,primary use stage,and secondary reuse stage.The key block movement of roof cutting structure,a complex stress environment,and a mismatch in the supporting design scheme are the failure mechanism of GSERC.A controlling ideology for mining states,including regional and stage divisions,was proposed.Both dynamic and permanent support schemes have been implemented in the field.Engineering practice results indicate that the new support scheme can efficiently ensure long-term entry safety and could be a reliable approach for other engineering practices.展开更多
Aiming at the slow convergence and low accuracy problems of the traditional non-negative tensor factorization, a local hierarchical non-negative tensor factorization method is proposed by applying the local objective ...Aiming at the slow convergence and low accuracy problems of the traditional non-negative tensor factorization, a local hierarchical non-negative tensor factorization method is proposed by applying the local objective function theory to non- negative tensor factorization and combining the three semi-non- negative matrix factorization(NMF) model. The effectiveness of the method is verified by the facial feature extraction experiment. Through the decomposition of a series of an air compressor's vibration signals composed in the form of a bispectrum by this new method, the basis images representing the fault features and corresponding weight matrices are obtained. Then the relationships between characteristics and faults are analyzed and the fault types are classified by importing the weight matrices into the BP neural network. Experimental results show that the accuracy of fault diagnosis is improved by this new method compared with other feature extraction methods.展开更多
A differential equation that is generally effective for squeeze film air damping of perforated plate and non perforated plate as well as in MEMS devices is developed.For perforated plate,the thickness and the dimens...A differential equation that is generally effective for squeeze film air damping of perforated plate and non perforated plate as well as in MEMS devices is developed.For perforated plate,the thickness and the dimensions of the plate are not limited.With boundary conditions,pressure distribution and the damping force on the plate can be found by solving the differential equation.Analytical expressions for damping pressure and damping force of a long strip holeplate are presented with a finite thickness and a finite width.To the extreme conditions of very thin plate and very thin hole,the results are reduced to the corresponding results of the conventional Reynolds' equation.Thus, the effectiveness of the generalized differential equation is justified.Therefore,the generalized Reynolds' equation will be a useful tool of design for damping structures in MEMS.展开更多
Bled air from the high pressure compressor takes up 3%—5% in the air system.However,there are not many studies on the compressor performance after bleeding.By analyzing the low-speed single-stage compressors,six blee...Bled air from the high pressure compressor takes up 3%—5% in the air system.However,there are not many studies on the compressor performance after bleeding.By analyzing the low-speed single-stage compressors,six bleeding structures are presented according to their influence mechanism on the compressor performance,and five kinds of bleeding rate are applied to one of the structures.A numerical simulation is performed to study the influence of bleeding rates and structures on the compressor performance.The results show that for the stators with the large flow separation in the corner,bleeding a small amount of air from the end-wall region can improve the total pressure increase and the stability margin.Moreover there is an optimum value of the bleeding rate in the stator casing.展开更多
A differential equation for calculating squeeze-film air damping in slotted plates is developed by modifying the Reynolds equation. A term is added to account for the effect of airflow through the slots on the air dam...A differential equation for calculating squeeze-film air damping in slotted plates is developed by modifying the Reynolds equation. A term is added to account for the effect of airflow through the slots on the air damping of the plate. The end effect of the airflow in the slots is also treated by substituting an effective channel length for the geometric channel length (i. e. the thickness of the plate)..The damping pressure distribution, damping force, and damping force coefficient of the slotted plates can be found by solving the equation under appropriate boundary conditions. With restrictions on the thickness and the lateral dimensions of the slotted plate removed,the equation provides a useful tool for analysing the squeeze-film air damping effect of slotted plates with finite thickness and finite lateral dimensions. For a typical slotted plate structure, the damping force coefficient obtained by this equation agrees well with that generated by ANSYS.展开更多
A novel fault diagnosis method for sensors in air handling unit(AHU) using wavelet energy entropy was presented. Instead of directly comparing the numerous data under noise conditiom, the wavelet energy entropy resi...A novel fault diagnosis method for sensors in air handling unit(AHU) using wavelet energy entropy was presented. Instead of directly comparing the numerous data under noise conditiom, the wavelet energy entropy residual was compared in the proposed method. Three.level wavelet analysis was used to decompose the measurement data under both fault-free and faulty operation conditions. The concept of Shannon entropy was referred to define wavelet energy entropy of the wavelet coefficients. The sensor faults were diagnosed by comparing the deviation of the wavelet energy entropy of the measured signal and the estimated one with the preset threshold. Testing results showed that the wavelet energy entropy was sensitive to diagnose the biased faults. The wavelet energy entropy residuals exceed the threshold significantly when faults occur. In addition, the severer the faults were, the larger the residuals would be. The results prove that the proposed method is feasible and effective for the fault detection and diagnosis of the sensors.展开更多
The controlling algorithm was studied for the inverter-driven multi-type air conditioner using electronic expansion valve(EEV) in outdoor unit. The performance of inverter-driven air conditioner with two different uni...The controlling algorithm was studied for the inverter-driven multi-type air conditioner using electronic expansion valve(EEV) in outdoor unit. The performance of inverter-driven air conditioner with two different units was investigated by varying the outdoor ambient temperature and compressor speed. Based on the test results, the effect of EEV opening on the indoor unit exit superheat was discussed. For the specified outdoor ambient temperature scope and the EEV opening, the superheats of indoor units decrease with the outdoor ambient temperature rising. Improper distribution of refrigerant into each indoor unit will causes excessive superheat difference between two indoor units. Suggestions were then given for the controlling of the superheat.展开更多
The centrifugal air compressor outlet pipeline vibration was not decreased after barrel viscous dampers were installed in a petrochemical plant in Tianjin.A pipeline-damper experiment apparatus was built for studying ...The centrifugal air compressor outlet pipeline vibration was not decreased after barrel viscous dampers were installed in a petrochemical plant in Tianjin.A pipeline-damper experiment apparatus was built for studying the influence factors of the barrel viscous damper and pipe hoop in pipeline vibration reduction.The performance of the damper under different frequency and amplitude was researched respectively,the results showed that damping effect dependsed mainly on frequency and was not related to amplitude.Damper will fail when its vibration frequency exceeds its limit working frequency which was 40 Hz in test.The mechanical properties and energy dissipation were analyzed by using the Maxwell model,which explains experimental results well.According to damping effect and calculation of stiffness with ANSYS in different hoop width,hoop stiffness should match pipe stiffness and keep uniform along transfer path.Damping effect will get worse when local stiffness is too small or too large.Finally,the outlet pipeline vibration was decreased by 70%after using appropriate pipe hoop width and replacing the original damping liquid.展开更多
The impact of boundary layer suction on the aerodynamic performance of a high-turning compressor cascade was numerically simulated and discussed.The aerodynamic performance of a curved and a straight cascade with and ...The impact of boundary layer suction on the aerodynamic performance of a high-turning compressor cascade was numerically simulated and discussed.The aerodynamic performance of a curved and a straight cascade with and without boundary layer suction were comparatively studied at several suction flow rates.The results showed that boundary layer suction dramatically improved the flow behavior within the flow passage.Moreover,higher loading over the whole blade height,lower total pressure loss,and higher passage throughflow were achieved with a relatively small amount of boundary layer removal.The integration of curved blade and boundary layer suction contributed to better aerodynamic performance than the cascades with only curved blade or boundary layer suction used,and the more favorable effect resulted from the weakening of the three dimensional effects of the boundary layer close to the endwalls.展开更多
To evaluate performance and reliability of an air conditioner, the states of its refrigerant in the refrigeration cycle need to be understood. Since the isentropic exponent of the next-generation refrigerant R32 is la...To evaluate performance and reliability of an air conditioner, the states of its refrigerant in the refrigeration cycle need to be understood. Since the isentropic exponent of the next-generation refrigerant R32 is larger than that of conventional refrigerant R410A, the compressor discharge temperature of R32 is higher than that of R410A. When a wet refrigerant is entered into a compressor suction line to decrease the discharge temperature, it is generally difficult to estimate the vapor quality at the suction. This paper describes a method that estimates a vapor quality at the compressor suction by applying energy balances on the compressor with the values of suction pressure, discharge pressure, discharge temperature, etc. In the air conditioner test, the vapor qualities at the compressor suction estimated with this method agreed well with those estimated with the conventional method by measuring liquid and vapor flow-rates. Moreover, this paper derived a relational expression for estimating a compressor suction state from a discharge state and discusses the characteristics of the coefficients in the expression calculated from the test results.展开更多
As the performance of an air-cooled condenser is apt to be affected by the fluctuating ambient condition, some difficulties are brought to the use of a steam feeding water pump in an air-cooled unit. This paper introd...As the performance of an air-cooled condenser is apt to be affected by the fluctuating ambient condition, some difficulties are brought to the use of a steam feeding water pump in an air-cooled unit. This paper introduces a new design of for steam feeding the water pump of an air-cooled unit using the back-pressure steam turbine as the prime motor. Using variable condition analysis on a 600 MW direct air-cooled unit, and with consideration of the effect on the ambient conditions, the feasibility, economy, and adaptability of the design are verified.展开更多
The three dimensional variable cross-section roll forming is a kind of new metal forming technol- ogy which combines large forming force, multi-axis linkage movement and space synergic movement, and the sequential syn...The three dimensional variable cross-section roll forming is a kind of new metal forming technol- ogy which combines large forming force, multi-axis linkage movement and space synergic movement, and the sequential synergic movement of the ganged roller group is used to complete the metal sheet forming according to the shape of the complicated and variable forming part data. The control system should meet the demands of quick response to the test requirements of the product part. A new kind of real time data driving multi-axis linkage and synergic movement control strategy of 3D roll forming is put forward in the paper. In the new control strategy, the forming data are automatically generated according to the shape of the parts, and the multi-axis linkage movement together with cooperative motion among the six stands of the 3D roll forming machine is driven by the real-time information, and the control nodes are also driven by the forming data. The new control strategy is applied to a 48 axis 3D roll forming machine developed by our research center, and the control servo period is less than 10ms. A forming experiment of variable cross section part is carried out, and the forming preci- sion is better than + 0.5mm by the control strategy. The result of the experiment proves that the control strategy has significant potentiality for the development of 3D roll forming production line with large scale, multi-axis ganged and svner^ic movement展开更多
The scramjet and maglev engineering technology development and trends at home and abroad are firstly presented in this paper. A new launch mode of space transportation system is proposed based on scramjet and magnetic...The scramjet and maglev engineering technology development and trends at home and abroad are firstly presented in this paper. A new launch mode of space transportation system is proposed based on scramjet and magnetic suspension technologies, and its key technologies required are given. This paper also makes analysis on using scramjet and magnetic suspension technologies to launch a reusable rocket, and the results show that a normal temperature conductor maglev launch system is feasible.展开更多
The paper proposes a novel nano-patterning method called electrically induced nanostructuring, where an external electric field, insteadof the external mechanical pressure, is applied to generate an electrohydrody- na...The paper proposes a novel nano-patterning method called electrically induced nanostructuring, where an external electric field, insteadof the external mechanical pressure, is applied to generate an electrohydrody- namic force acting on the polymer-air interface to drive the polymer' s flow into the mold cavities. This electri- cally induced nanostrueturing method no longer requires a large mechanical pressure externally applied for actua- ting the polymer filling in the mold cavities, and has been used to successfully fabricate micro/nano pillar arrays of a high aspect ratio (up to 10), which have been usually considered to be "difficult to fabricate" by conventional molding or nanoimprinting processes.展开更多
The general idea of this work is to improve the performance of CAES (compressed air energy storage) for its application in solar and wind systems through a restitution technique by creating an artificial wind. The e...The general idea of this work is to improve the performance of CAES (compressed air energy storage) for its application in solar and wind systems through a restitution technique by creating an artificial wind. The efficiency of compressed air storage is often presented as a limit to its application. The present work describes a series of manipulations carried out in order to increase the yield. As the action of the artificial wind on the wind turbine is characterized by a reduced attack surface, a treated wind, a constant direction, an adjustable speed, it is therefore a question of acting on all the controllable parameters of the artificial wind to find the best way to use it to produce more energy from a certain quantity stored in a tank. The main manipulations consisted in determining: the optimal number of points of attack of the wind turbine; the nature of the action (continuous or interrupted) of the wind; the frequency of wind action and the duty cycle.展开更多
A multicellular DCX (dc-dc transformer) using unregulated cell converters has been proposed for the environmentally friendly data centers. The high speed cell converter with the switching frequency over MHz behaves ...A multicellular DCX (dc-dc transformer) using unregulated cell converters has been proposed for the environmentally friendly data centers. The high speed cell converter with the switching frequency over MHz behaves as an ideal transformer, and this behavior solves the voltage imbalance issue in the multicellular converter topology. The analysis of the unregulated cell converter is conducted by using the state space averaging method, and the operation condition for the ideal transformer is specified. The behavior of the multicellular DCX using the high speed cell converters has been also analyzed, and the voltage imbalance issue among cell converters is discussed quantitatively. A prototype of a 19.2 kW 384 V-384 V multicellular DCX using sixty-four unregulated cell converters is fabricated and the validity of the analyses is verified.展开更多
This review mainly summarizes the latest developments in the internal flow field and external characteristics of centrifugal pumps.In particular,the latest findings of centrifugal pumps focused on turbulence and cavit...This review mainly summarizes the latest developments in the internal flow field and external characteristics of centrifugal pumps.In particular,the latest findings of centrifugal pumps focused on turbulence and cavitation models,flow visualization methods,and fault detection based on noise and vibration.The external characteristics,cavitation,and vibration of the centrifugal pump were extensively discussed.In addition,advanced multi-objective optimization methods for improving impeller’s efficiency and reducing net positive suction head(NPSH)were briefed.Although some progress was made in this field,there remain many unsolved problems,such as monitoring and modeling of cavitation,rotational stall phenomenon,and discrepancies between simulation and measurement.In the future,researchers are encouraged to employ multi-dimensional flow visualization technologies and high-performance computing facilities to advance existing understandings on these issues and create new research directions.展开更多
This paper presents a detailed experimental investigation concerning the influence of blade loading (incidence) on the three-dimensional flow in an annular compressor cascade.The data are acquired at four incidence an...This paper presents a detailed experimental investigation concerning the influence of blade loading (incidence) on the three-dimensional flow in an annular compressor cascade.The data are acquired at four incidence angles under low Mach number and low Reynolds number conditions.Experimental techniquss include the oil-film visualization on the profile and the endwall surfaces,the laser-sheet visualization of the flow field inside the blade passage,and the measurement by radial-circumferential traveress using a seven-hole probe.The behavior and nature of the three-dimensional flow with severe separations inside the blade passage and at the exit are obtained.The distributions of the total pressure loss,static pressure,velocity and outflow angle are also given. These results are valuable for establishing the physical model of the three-dimensional complex flow in axial compressors and for examining the computational procedures.展开更多
基金Project(WPUKFJJ2019-19)supported by the Open Fund of State Key Laboratory of Water Resource Protection and Utilization in Coal Mining,ChinaProject(51974317)supported by the National Natural Science Foundation of China。
文摘This study is the result of long-term efforts of the authors’team to assess ground response of gob-side entry by roof cutting(GSERC)with hard main roof,aiming at scientific control for GSERC deformation.A comprehensive field measurement program was conducted to determine entry deformation,roof fracture zone,and anchor bolt(cable)loading.The results indicate that GSERC deformation presents asymmetric characteristics.The maximum convergence near roof cutting side is 458 mm during the primary use process and 1120 mm during the secondary reuse process.The entry deformation is closely associated with the primary development stage,primary use stage,and secondary reuse stage.The key block movement of roof cutting structure,a complex stress environment,and a mismatch in the supporting design scheme are the failure mechanism of GSERC.A controlling ideology for mining states,including regional and stage divisions,was proposed.Both dynamic and permanent support schemes have been implemented in the field.Engineering practice results indicate that the new support scheme can efficiently ensure long-term entry safety and could be a reliable approach for other engineering practices.
基金The National Natural Science Foundation of China(No.50875078)the Natural Science Foundation of Jiangsu Province(No.BK2007115)the National High Technology Research and Development Program of China(863 Program)(No.2007AA04Z421)
文摘Aiming at the slow convergence and low accuracy problems of the traditional non-negative tensor factorization, a local hierarchical non-negative tensor factorization method is proposed by applying the local objective function theory to non- negative tensor factorization and combining the three semi-non- negative matrix factorization(NMF) model. The effectiveness of the method is verified by the facial feature extraction experiment. Through the decomposition of a series of an air compressor's vibration signals composed in the form of a bispectrum by this new method, the basis images representing the fault features and corresponding weight matrices are obtained. Then the relationships between characteristics and faults are analyzed and the fault types are classified by importing the weight matrices into the BP neural network. Experimental results show that the accuracy of fault diagnosis is improved by this new method compared with other feature extraction methods.
文摘A differential equation that is generally effective for squeeze film air damping of perforated plate and non perforated plate as well as in MEMS devices is developed.For perforated plate,the thickness and the dimensions of the plate are not limited.With boundary conditions,pressure distribution and the damping force on the plate can be found by solving the differential equation.Analytical expressions for damping pressure and damping force of a long strip holeplate are presented with a finite thickness and a finite width.To the extreme conditions of very thin plate and very thin hole,the results are reduced to the corresponding results of the conventional Reynolds' equation.Thus, the effectiveness of the generalized differential equation is justified.Therefore,the generalized Reynolds' equation will be a useful tool of design for damping structures in MEMS.
基金Supported by the National Natural Science Foundation of China(60934001)~~
文摘Bled air from the high pressure compressor takes up 3%—5% in the air system.However,there are not many studies on the compressor performance after bleeding.By analyzing the low-speed single-stage compressors,six bleeding structures are presented according to their influence mechanism on the compressor performance,and five kinds of bleeding rate are applied to one of the structures.A numerical simulation is performed to study the influence of bleeding rates and structures on the compressor performance.The results show that for the stators with the large flow separation in the corner,bleeding a small amount of air from the end-wall region can improve the total pressure increase and the stability margin.Moreover there is an optimum value of the bleeding rate in the stator casing.
文摘A differential equation for calculating squeeze-film air damping in slotted plates is developed by modifying the Reynolds equation. A term is added to account for the effect of airflow through the slots on the air damping of the plate. The end effect of the airflow in the slots is also treated by substituting an effective channel length for the geometric channel length (i. e. the thickness of the plate)..The damping pressure distribution, damping force, and damping force coefficient of the slotted plates can be found by solving the equation under appropriate boundary conditions. With restrictions on the thickness and the lateral dimensions of the slotted plate removed,the equation provides a useful tool for analysing the squeeze-film air damping effect of slotted plates with finite thickness and finite lateral dimensions. For a typical slotted plate structure, the damping force coefficient obtained by this equation agrees well with that generated by ANSYS.
基金National Natural Science Foundation of China(No.31101085)
文摘A novel fault diagnosis method for sensors in air handling unit(AHU) using wavelet energy entropy was presented. Instead of directly comparing the numerous data under noise conditiom, the wavelet energy entropy residual was compared in the proposed method. Three.level wavelet analysis was used to decompose the measurement data under both fault-free and faulty operation conditions. The concept of Shannon entropy was referred to define wavelet energy entropy of the wavelet coefficients. The sensor faults were diagnosed by comparing the deviation of the wavelet energy entropy of the measured signal and the estimated one with the preset threshold. Testing results showed that the wavelet energy entropy was sensitive to diagnose the biased faults. The wavelet energy entropy residuals exceed the threshold significantly when faults occur. In addition, the severer the faults were, the larger the residuals would be. The results prove that the proposed method is feasible and effective for the fault detection and diagnosis of the sensors.
文摘The controlling algorithm was studied for the inverter-driven multi-type air conditioner using electronic expansion valve(EEV) in outdoor unit. The performance of inverter-driven air conditioner with two different units was investigated by varying the outdoor ambient temperature and compressor speed. Based on the test results, the effect of EEV opening on the indoor unit exit superheat was discussed. For the specified outdoor ambient temperature scope and the EEV opening, the superheats of indoor units decrease with the outdoor ambient temperature rising. Improper distribution of refrigerant into each indoor unit will causes excessive superheat difference between two indoor units. Suggestions were then given for the controlling of the superheat.
基金Supported by the National Basic Research Program of China(No.2012CB026000)the Beijing Education Commission Special Fund andDoctoral Degree Fund(No.20110010110009)
文摘The centrifugal air compressor outlet pipeline vibration was not decreased after barrel viscous dampers were installed in a petrochemical plant in Tianjin.A pipeline-damper experiment apparatus was built for studying the influence factors of the barrel viscous damper and pipe hoop in pipeline vibration reduction.The performance of the damper under different frequency and amplitude was researched respectively,the results showed that damping effect dependsed mainly on frequency and was not related to amplitude.Damper will fail when its vibration frequency exceeds its limit working frequency which was 40 Hz in test.The mechanical properties and energy dissipation were analyzed by using the Maxwell model,which explains experimental results well.According to damping effect and calculation of stiffness with ANSYS in different hoop width,hoop stiffness should match pipe stiffness and keep uniform along transfer path.Damping effect will get worse when local stiffness is too small or too large.Finally,the outlet pipeline vibration was decreased by 70%after using appropriate pipe hoop width and replacing the original damping liquid.
基金Sponsored by the National Natural Science Foundation of China(Grant No.50646021).
文摘The impact of boundary layer suction on the aerodynamic performance of a high-turning compressor cascade was numerically simulated and discussed.The aerodynamic performance of a curved and a straight cascade with and without boundary layer suction were comparatively studied at several suction flow rates.The results showed that boundary layer suction dramatically improved the flow behavior within the flow passage.Moreover,higher loading over the whole blade height,lower total pressure loss,and higher passage throughflow were achieved with a relatively small amount of boundary layer removal.The integration of curved blade and boundary layer suction contributed to better aerodynamic performance than the cascades with only curved blade or boundary layer suction used,and the more favorable effect resulted from the weakening of the three dimensional effects of the boundary layer close to the endwalls.
文摘To evaluate performance and reliability of an air conditioner, the states of its refrigerant in the refrigeration cycle need to be understood. Since the isentropic exponent of the next-generation refrigerant R32 is larger than that of conventional refrigerant R410A, the compressor discharge temperature of R32 is higher than that of R410A. When a wet refrigerant is entered into a compressor suction line to decrease the discharge temperature, it is generally difficult to estimate the vapor quality at the suction. This paper describes a method that estimates a vapor quality at the compressor suction by applying energy balances on the compressor with the values of suction pressure, discharge pressure, discharge temperature, etc. In the air conditioner test, the vapor qualities at the compressor suction estimated with this method agreed well with those estimated with the conventional method by measuring liquid and vapor flow-rates. Moreover, this paper derived a relational expression for estimating a compressor suction state from a discharge state and discusses the characteristics of the coefficients in the expression calculated from the test results.
文摘As the performance of an air-cooled condenser is apt to be affected by the fluctuating ambient condition, some difficulties are brought to the use of a steam feeding water pump in an air-cooled unit. This paper introduces a new design of for steam feeding the water pump of an air-cooled unit using the back-pressure steam turbine as the prime motor. Using variable condition analysis on a 600 MW direct air-cooled unit, and with consideration of the effect on the ambient conditions, the feasibility, economy, and adaptability of the design are verified.
基金Supported by National Key Technology R&D Program(No.2011BAG03B03)
文摘The three dimensional variable cross-section roll forming is a kind of new metal forming technol- ogy which combines large forming force, multi-axis linkage movement and space synergic movement, and the sequential synergic movement of the ganged roller group is used to complete the metal sheet forming according to the shape of the complicated and variable forming part data. The control system should meet the demands of quick response to the test requirements of the product part. A new kind of real time data driving multi-axis linkage and synergic movement control strategy of 3D roll forming is put forward in the paper. In the new control strategy, the forming data are automatically generated according to the shape of the parts, and the multi-axis linkage movement together with cooperative motion among the six stands of the 3D roll forming machine is driven by the real-time information, and the control nodes are also driven by the forming data. The new control strategy is applied to a 48 axis 3D roll forming machine developed by our research center, and the control servo period is less than 10ms. A forming experiment of variable cross section part is carried out, and the forming preci- sion is better than + 0.5mm by the control strategy. The result of the experiment proves that the control strategy has significant potentiality for the development of 3D roll forming production line with large scale, multi-axis ganged and svner^ic movement
文摘The scramjet and maglev engineering technology development and trends at home and abroad are firstly presented in this paper. A new launch mode of space transportation system is proposed based on scramjet and magnetic suspension technologies, and its key technologies required are given. This paper also makes analysis on using scramjet and magnetic suspension technologies to launch a reusable rocket, and the results show that a normal temperature conductor maglev launch system is feasible.
基金Major Research Plan of NSFC on Nanomanufacturing(No.90923040)National Basic Research Program of China(No.2009CB724202)
文摘The paper proposes a novel nano-patterning method called electrically induced nanostructuring, where an external electric field, insteadof the external mechanical pressure, is applied to generate an electrohydrody- namic force acting on the polymer-air interface to drive the polymer' s flow into the mold cavities. This electri- cally induced nanostrueturing method no longer requires a large mechanical pressure externally applied for actua- ting the polymer filling in the mold cavities, and has been used to successfully fabricate micro/nano pillar arrays of a high aspect ratio (up to 10), which have been usually considered to be "difficult to fabricate" by conventional molding or nanoimprinting processes.
文摘The general idea of this work is to improve the performance of CAES (compressed air energy storage) for its application in solar and wind systems through a restitution technique by creating an artificial wind. The efficiency of compressed air storage is often presented as a limit to its application. The present work describes a series of manipulations carried out in order to increase the yield. As the action of the artificial wind on the wind turbine is characterized by a reduced attack surface, a treated wind, a constant direction, an adjustable speed, it is therefore a question of acting on all the controllable parameters of the artificial wind to find the best way to use it to produce more energy from a certain quantity stored in a tank. The main manipulations consisted in determining: the optimal number of points of attack of the wind turbine; the nature of the action (continuous or interrupted) of the wind; the frequency of wind action and the duty cycle.
文摘A multicellular DCX (dc-dc transformer) using unregulated cell converters has been proposed for the environmentally friendly data centers. The high speed cell converter with the switching frequency over MHz behaves as an ideal transformer, and this behavior solves the voltage imbalance issue in the multicellular converter topology. The analysis of the unregulated cell converter is conducted by using the state space averaging method, and the operation condition for the ideal transformer is specified. The behavior of the multicellular DCX using the high speed cell converters has been also analyzed, and the voltage imbalance issue among cell converters is discussed quantitatively. A prototype of a 19.2 kW 384 V-384 V multicellular DCX using sixty-four unregulated cell converters is fabricated and the validity of the analyses is verified.
基金the National Key R&D Program of China(No.2019YFB2004604)the National Natural Science Foundation of China(No.51821093)+2 种基金the Zhejiang Provincial Natural Science Foundation of China(No.LR19E050002)the Key R&D Program of Zhejiang Province(Nos.2018C01020 and 2018C01060)the Youth Funds of the State Key Laboratory of Fluid Power and Mechatronic Systems(No.SKLoFP_QN_1804),China。
文摘This review mainly summarizes the latest developments in the internal flow field and external characteristics of centrifugal pumps.In particular,the latest findings of centrifugal pumps focused on turbulence and cavitation models,flow visualization methods,and fault detection based on noise and vibration.The external characteristics,cavitation,and vibration of the centrifugal pump were extensively discussed.In addition,advanced multi-objective optimization methods for improving impeller’s efficiency and reducing net positive suction head(NPSH)were briefed.Although some progress was made in this field,there remain many unsolved problems,such as monitoring and modeling of cavitation,rotational stall phenomenon,and discrepancies between simulation and measurement.In the future,researchers are encouraged to employ multi-dimensional flow visualization technologies and high-performance computing facilities to advance existing understandings on these issues and create new research directions.
文摘This paper presents a detailed experimental investigation concerning the influence of blade loading (incidence) on the three-dimensional flow in an annular compressor cascade.The data are acquired at four incidence angles under low Mach number and low Reynolds number conditions.Experimental techniquss include the oil-film visualization on the profile and the endwall surfaces,the laser-sheet visualization of the flow field inside the blade passage,and the measurement by radial-circumferential traveress using a seven-hole probe.The behavior and nature of the three-dimensional flow with severe separations inside the blade passage and at the exit are obtained.The distributions of the total pressure loss,static pressure,velocity and outflow angle are also given. These results are valuable for establishing the physical model of the three-dimensional complex flow in axial compressors and for examining the computational procedures.