The accuracy of fluctuating pressure test in wind tunnel is affected by the tube system. By employing contradistinctive experimental method, systematic study was conducted to investigate the effects of the tube system...The accuracy of fluctuating pressure test in wind tunnel is affected by the tube system. By employing contradistinctive experimental method, systematic study was conducted to investigate the effects of the tube system on fluctuating pressure. The analyzed tube system parameters include tube length, inside diameter, curvature, deflection angle, thickness, material, restrictor length,restrictor inside diameter, and restrictor place. It is found that all the tube system parameters mentioned above except tube curvature have non-negligible effects on fluctuating pressure. Based on the research results, test methods were presented for the fluctuating pressure measurement in low-speed wind tunnel, which can obviously improve the data accuracy but not lose test efficiency. The effectiveness of the method is verified by the wind tunnel test.展开更多
In the anticorrosive coating line of a welded tube plant, the current status and existing problems of the medium-frequency induction heating equipment were discussed.Partial renovations of the power control cabinet ha...In the anticorrosive coating line of a welded tube plant, the current status and existing problems of the medium-frequency induction heating equipment were discussed.Partial renovations of the power control cabinet have been conducted.Parameters such as the DC current, DC voltage, intermediate frequency power, heating temperature, and the positioning signal at the pipe end were collected.A data acquisition and processing system, which can process data according to user needs and provide convenient data processing functions, has been developed using LabVIEW software.This system has been successfully applied in the coating line for the automatic control of high-power induction heating equipment, production management, and digital steel tube and/or digital delivery.展开更多
In recent years,there has been a growing demand for more efficient and robust control strategies in cooperative multi-robot systems.This paper introduces the cascade explicit tube model predictive controller(CET-MPC),...In recent years,there has been a growing demand for more efficient and robust control strategies in cooperative multi-robot systems.This paper introduces the cascade explicit tube model predictive controller(CET-MPC),a control architecture designed specifically for distributed aerial robot systems.By integrating an explicit model predictive controller(MPC)with a tube MPC,our approach significantly reduces online computational demands while enhancing robustness against disturbances such as wind and measurement noise,as well as uncertainties in inertia parameters.Further,we incorporate a cascade controller to minimize steady-state errors and improve system performance dynamically.The results of this assessment provide valuable insights into the effectiveness and reliability of the CET-MPC approach under realistic operating conditions.The simulation results of flight scenarios for multi-agent quadrotors demonstrate the controller’s stability and accurate tracking of the desired path.By addressing the complexities of quadrotors’six degrees of freedom,this controller serves as a versatile solution applicable to a wide range of multi-robot systems with varying degrees of freedom,demonstrating its adaptability and scalability beyond the quadrotor domain.展开更多
Electro-hydraulic screw down servo system（HSDS） is widely used in seamless tube rolling mill in western companies.But in Chinese companies,mechanical screw down system（MSDS） is popularly equipped and has a serious...Electro-hydraulic screw down servo system（HSDS） is widely used in seamless tube rolling mill in western companies.But in Chinese companies,mechanical screw down system（MSDS） is popularly equipped and has a serious disadvantage that the roller would often be locked when it is overloaded.For the purpose of designing the first set of domestic twin-roller,four-cylinder and six-framework electro-hydraulic HSDS of seamless tube rolling mill,an experiment system that can simulate the process of seamless tube rolling is constructed.A digital simulation model of the experiment system is built with AMESim software and validated by comparing the simulation results with experiment results.The sudden load response of the screw piston position is studied with the built model and the experiment system.To improve the HSDS＇s positioning accuracy with large load,a hybrid control scheme of combining load disturbance feedforward compensation（LDFC） method based on servo valve＇s pressure-stroke feature and anti-saturation integral control（ASIC） is proposed.Both results of simulation and experiment indicate that the transient response time of the single-roller HSDS with the proposed scheme decreases from 0.65 s to less than 0.2 s without static error.To improve the system dynamic stiffness and production qualified rate,a flow rate feedforward compensation（FFC） control strategy based on oil compressibility to dynamic position error is proposed.This FFC strategy is validated with experiments in which the transient error caused by sudden load is reduced to less than 25% of that without FFC.By extending the simulation model to HSDS of a twin-roller,four-cylinder rolling mill,analyzing the mill deformation,and applying the LDFC,ASIC and FFC to the HSDS,the dynamic performance and positioning accuracy of compensated multi-roller HSDS at biting moment are predicted.The research results provide a theoretical and experimental basis for the design of HSDS of seamless steel tube rolling mill.展开更多
Conventional X-ray tube-based cone-beam computed tomography(CX-CBCT) systems have great potential in industrial applications. Such systems can rapidly obtain a three-dimensional(3D) image of an object.Conventional X-r...Conventional X-ray tube-based cone-beam computed tomography(CX-CBCT) systems have great potential in industrial applications. Such systems can rapidly obtain a three-dimensional(3D) image of an object.Conventional X-ray tubes fulfill the requirements for industrial applications, because of their high tube voltage and power. Continuous improvements have been made to CX-CBCT systems, such as imaging time shortening,acquisition strategy optimization, and imaging software development, etc. In this study, a CX-CBCT system is developed. Additionally, some improvements to the CX-CBCT system are proposed based on the hardware conditions of the X-ray tube and detector. A near-detector(ND)geometry condition is employed to obtain a sharper image and larger detection area. An improved acquisition strategy is proposed to simplify operations and reduce total imaging time. In the ND geometry condition, a simplified method called FBP slice stacking(SS-FBP) is proposed, which can be applied to 3D image reconstruction. SS-FBP is timesaving relative to traditional methods. Furthermore, imaging software for the CX-CBCT system is developed in the MATLAB environment. Several imaging experiments were performed. The results suggest that the CX-CBCT system works properly, and that the above improvements are feasible and practical.展开更多
Thermo-hydraulic characteristics of TiO_2-water nanofluids in thin-wall stainless steel test tubes(corrugated tube and circular tube) filled with copper foam(40 PPI) are experimentally investigated and compared with t...Thermo-hydraulic characteristics of TiO_2-water nanofluids in thin-wall stainless steel test tubes(corrugated tube and circular tube) filled with copper foam(40 PPI) are experimentally investigated and compared with those in test tubes without copper foam. The effects of nanoparticle mass concentration on flow and heat transfer performances are investigated. In addition, the mutual restriction relationships between Reynolds number(Re), Nusselt number(Nu) and resistance coefficient(f) are discussed respectively. Also, the comprehensive coefficient of performance(CCP) between heat transfer and pressure drop is evaluated. The results show that core-enhancement region for heat transfer using experimental tubes filled with copper foam is notably different from that of tubes without copper foam. There is a corresponding Reynolds number(about Re = 2400) for the maximum CCP of each condition. And the heat transfer can be enhanced dramatically and sustained at 8000 ≤ Re ≤ 12000.展开更多
The so-called Evacuated Tube Train(ETT)is currently being proposed as a high-speed transportation system potentially competitive with airplane transportation.Aerodynamic resistance is one of the most crucial factors f...The so-called Evacuated Tube Train(ETT)is currently being proposed as a high-speed transportation system potentially competitive with airplane transportation.Aerodynamic resistance is one of the most crucial factors for the successful design of an ETT.In the present work,a three-dimensional concept ETT model has been elaborated.The aerodynamic characteristics of the subsonic ETT have been numerically simulated under different conditions.The train’s running speed varies from 600 km/h up to 1200 km/h,and the blockage ratio is in the range between 0.1 and 0.3.As the blocking ratio and running speed increase,the resistance of the head car increases greatly,while the resistance of the middle car changes slightly.The aerodynamic resistance of the tail car is affected by the shock wave emerging in the wake flow.Two different design criteria for the maximum allowed aerodynamic resistance are proposed for aerodynamic parameter matching.With an increase in the blockage ratio and running speed,the atmospheric pressure in the tube should be decreased to achieve a balance.展开更多
Advanced high strength steels are the group of material with high strength and good formability, because high strength lesser gauge thickness can be used without compromising the function of component. In terms of eco...Advanced high strength steels are the group of material with high strength and good formability, because high strength lesser gauge thickness can be used without compromising the function of component. In terms of economic forming process, hydroforming is the manufacturing option which uses a fluid medium to form a component by using high internal pressure. This process gained steep interest in the automotive and aerospace industries because of its many advantages such as part consolidation, good quality of the formed part etc. The main advantage is that the uniform pressure can be transferred to whole projected part at the same time. Low pressure tube hydroforming considered an inexpensive option for forming these advanced high strength steel. This paper investigates the pressurization system used during the low pressure tube hydroforming cycle. It is observed that the usage of ramp pressure cycle during forming the part from low pressure tube hydroforming results in lesser die holding force. Also, the stress, strain and thickness distribution of the part during low pressure tube hydroforming are critically analysed.展开更多
An integrated CAD/CAPP/CAM system of tube manufacturing based on integration frame is presented. In this system, two kinds of data conventions describing tube shape are presented in tube CAD subsystem, the object-orie...An integrated CAD/CAPP/CAM system of tube manufacturing based on integration frame is presented. In this system, two kinds of data conventions describing tube shape are presented in tube CAD subsystem, the object-oriented concept and the goal-driven inference mechanism have been applied in the development of the knowledge-based CAPP subsystem and simulation of tube processing under tube bending simulation subsystem is performed based on the tube model＇s piecewise representation. A tube product case is considered to give the application of the integrated system, and the advantages of the system in the use of tube bending are revealed.展开更多
According to characteristic of hydroforming of parallel multi-branch tubes,multi-objective problems were transformed to single objective problem of relational grade comparison by grey system theory.Two different objec...According to characteristic of hydroforming of parallel multi-branch tubes,multi-objective problems were transformed to single objective problem of relational grade comparison by grey system theory.Two different objectives were selected,according to the principle that process parameters were optimal which of grey relational grade were maximum,the optimal loading parameters under different objective condition were obtained,and loading paths were optimized.The results indicated that parallel multi-branch tubes hydroformed under loading paths optimized by grey system theory could meet with the requirement that objective was optimal.And the optimal loading paths under different objectives were different,and the appropriate objective should be selected according to forming characteristic.展开更多
Deposition of diamond thin films on tungsten wire substrate with the gas mixture of acetone and hydrogen by using bias-enhanced hot filament chemical vapor deposition(CVD)with the tantalum wires being optimized arrang...Deposition of diamond thin films on tungsten wire substrate with the gas mixture of acetone and hydrogen by using bias-enhanced hot filament chemical vapor deposition(CVD)with the tantalum wires being optimized arranged is investigated.The self-supported diamond tubes are obtained by etching away the tungsten substrates.The quality of the diamond film before and after the removal of substrates is observed by scanning electron microscope(SEM)and Raman spectrum.The results show that the cylindrical diamond tubes with good quality and uniform thickness are obtained on tungsten wires by using bias enhanced hot filament CVD.The compressive stress in diamond film formed during the deposition is released after the substrate etches away by mixture of H2O2 and NH4 OH.There is no residual stress in diamond tube after substrate removal.展开更多
Hunan Weather Modification Center and Suizhou Dafang Precision Electromechanical Engineering Co.,Ltd. of Hubei commonly transformed and installed 83 double tube antiaircraft guns( 37 mm) of Hunan Province in order to ...Hunan Weather Modification Center and Suizhou Dafang Precision Electromechanical Engineering Co.,Ltd. of Hubei commonly transformed and installed 83 double tube antiaircraft guns( 37 mm) of Hunan Province in order to realize remote control of computer. After transformation,loading capacity of ammunition feeding machine became large,which could shorten the time of filling shells in the case of short airspace time;one shell launch volume was more,which could improve hail suppression effect; the degree of automation was greatly improved,which could save manpower by more than 50%. It fully embodied the modernization level of Hunan weather modification operation.展开更多
Solid-liquid suspension in an agitated tank with a draft tube was investigated witha newly developed infrared turbidimeter for measuring solid concentration.The diameter of theflared inlet transition tube and the dist...Solid-liquid suspension in an agitated tank with a draft tube was investigated witha newly developed infrared turbidimeter for measuring solid concentration.The diameter of theflared inlet transition tube and the distance from the inlet to the tank bottom are two importantparameters for draft tube design The NAX-4 impeller,developed in this study,is characterized byits high flow efficiency and low power consumption.Some modifications are made to the Bald′smodel by considering the effects of solid concentration and fluid viscosity on the critical speed forcomplete off-bottom suspension.The modified equation fits the experimental data satisfactority andcan be used in scale-up展开更多
In order to realize steady-state operation of the neutral beam injection（NBI） system with high beam energy,an accurate thermal analysis and a prediction about working conditions of heat-removal structures inside hig...In order to realize steady-state operation of the neutral beam injection（NBI） system with high beam energy,an accurate thermal analysis and a prediction about working conditions of heat-removal structures inside high-heat-flux（HHF） components in the system are key issues.In this paper,taking the HHF ion dump with swirl tubes in NBI system as an example,an accurate thermal dynamic simulation method based on computational fluid dynamics（CFD） and the finite volume method is presented to predict performance of the HHF component.In this simulation method,the Eulerian multiphase method together with some empirical corrections about the inter-phase transfer model and the wall heat flux partitioning model are considered to describe the subcooled boiling.The reliability of the proposed method is validated by an experimental example with subcooled boiling inside swirl tube.The proposed method provides an important tool for the refined thermal and flow dynamic analysis of HHF components,and can be extended to study the thermal design of other complex HHF engineering structures in a straightforward way.The simulation results also verify that the swirl tube is a promising heat removing structure for the HHF components of the NBI system.展开更多
The prototype,basic parameters,composition and structure of computer simulation system of stretch reducing mill for tubes were introduced.The software has an obvious style of object-oriented programming,and the module...The prototype,basic parameters,composition and structure of computer simulation system of stretch reducing mill for tubes were introduced.The software has an obvious style of object-oriented programming,and the modules were integrated in the simulation system.The system can optimize pass design,and it can automatically classify pass series according to the product syllabus,formulate the rolling table and simulate the rolling parameters in stretch reducing process.The simulation results were compared with the detailed technical data(used as experimental data) provided by Baotou Iron and Steel Company,and the comparison gave a clear proof of the precision of the models.展开更多
The thermal performance enhancement of the hydronic radiant floor heating system by tube shape refinements is investigated in this paper.Both analytical and detailed numerical modelings are carried out to predict the ...The thermal performance enhancement of the hydronic radiant floor heating system by tube shape refinements is investigated in this paper.Both analytical and detailed numerical modelings are carried out to predict the performance of the radiant system.While the simple analytical model briefly investigates the possibility of the effect of the tube shape improvement with the parametric analysis,the commercial computational fluid dynamics(CFD) code(Ansys/CFX) is used to perform the detailed 3D analysis under different tube shape conditions.The fin thickness,the number of fins,and the tube thermal conductivity turn out to have significant effects on the radiant system performance.The potential energy saving impacts of the tube shape refinements are also discussed.The tube shape improvement turns out to increase the floor surface temperature and to decrease the hot water temperature drop across the system,resulting in heating energy savings.展开更多
Evacuated Tube Transportation(ETT)systems have been claimed to have considerable strengths,including ultra-highspeed,safety,and environmentally-friendly.However,the frequent handover caused by the high-speed brings a ...Evacuated Tube Transportation(ETT)systems have been claimed to have considerable strengths,including ultra-highspeed,safety,and environmentally-friendly.However,the frequent handover caused by the high-speed brings a challenge for ETT mobile wireless communication to preserve steady link performance.Moreover,in such a special scenario,the wireless link between the base station and the passengers on the train needs to experience fading from both metal pipe and train,thus the free-wave coverage with antennas in traditional high-speed rail wireless communication systems is not suitable for ETT.Based on the characteristics of ETT,an improved architecture of wireless communication network is proposed,using distributed base stations with remote radio units(RRUs)and baseband units(BBUs)and leaky waveguides to form stable coverage.And a redundant BBUs or RRUs structure is designed for coverage enhancement.Based on this redundant architecture,a fast handover scheme is proposed to resolve the handover problem.The analytical and simulation results show that the proposed scheme is capable of reducing communication outage probability and handover failure probability remarkably.展开更多
BACKGROUND: Thoracostomy tube insertion is one of the common bedside procedures in emergency medicine and many acute specialties. Dislodgement of thoracostomy tube from the connection tube of chest drainage system is ...BACKGROUND: Thoracostomy tube insertion is one of the common bedside procedures in emergency medicine and many acute specialties. Dislodgement of thoracostomy tube from the connection tube of chest drainage system is an important problem with potential complications such as contamination, infection and pneumothorax. Besides, mere loosening can also lead to malfunction. It is a common practice to tape the connection of the system. This study aimed to evaluate the materials and methods of connection of chest drain system to minimize drainage dislodgement. METHODS: We conducted an experimental study to assess the tightness of the connection with various taping materials and methods. We selected three commonly used adhesive materials(3M^(tm) Transpore^(tm) Medical tape, 3M^(tm) Micropore^(tm) Medical tape, 3M^(tm) Soft Cloth Tape on Liner) and three different methods(cross method, straight method, nylon band) to secure the junction between the thoracostomy tube and the bi-conical adaptor in the drainage system. The measured outcome was the weight causing visible loosening of the junction between thoracotomy tube and the adaptor.RESULTS: For each taping material and taping method, 10 trials were performed. The median weight required to disconnect the junction is 26.22 lb for Transpore^(tm), 31.29 lb for Micropore^(tm) and 32.44 lb for Soft Cloth Tape on Liner. A smaller force was required to disconnect if Transpore^(tm) is used(P<0.001). There was no statistical signifi cant difference between Micropore^(tm) and Soft Cloth Tape on Liner(P=0.98). The median disconnecting force is 32.44 lb for straight taping method, 40.55 lb for cross taping method and 21.15 lb for plastic band. The cross-taping method was the more secure method(P<0.0001 when compared with plastic band)(P=0.033 when compared with straight method).CONCLUSION: Cross-taping is the most secure method among the tested varieties in connecting the thoracostomy tube to the chest drainage system. Transpore^(tm) is not a recommended material for thoracostomy tube taping.展开更多
Laboratory studies of HO2 uptake coefficients,γ(HO2),were conducted at room temperature using an aerosol flow tube coupled with a laser induced fluorescence(LIF) system.The measurement was conducted with atmospherica...Laboratory studies of HO2 uptake coefficients,γ(HO2),were conducted at room temperature using an aerosol flow tube coupled with a laser induced fluorescence(LIF) system.The measurement was conducted with atmospherically relevant HO2 concentrations(~1×10^9 molecule/cm^3) at 51% RH.The measured γ(HO2) onto aqueous(NH4)2 SO4 aerosol was 0.001±0.0007,which was consistent with the relatively low first-order loss rate of HO2 onto aqueous(NH4)2 SO4 aerosol.Theγ(HO2) was elevated with increase of Cu(Ⅱ) concentrations in aqueous(NH4)2 SO4 aerosol.The threshold of Cu(Ⅱ) concentration was10^-3 mol/L for the dramatic increase of γ(HO2).It was found that γ(HO2) reached 0.1 when Cu(Ⅱ)concentration in aerosol was larger than 10^-3 mol/L,suggesting that γ(HO2) is very sensitive to concentration of transition metal ions in aerosol.展开更多
基金supported by the Pre-research Fund of Vibration and Noise Control Technology (No. 51334060101)
文摘The accuracy of fluctuating pressure test in wind tunnel is affected by the tube system. By employing contradistinctive experimental method, systematic study was conducted to investigate the effects of the tube system on fluctuating pressure. The analyzed tube system parameters include tube length, inside diameter, curvature, deflection angle, thickness, material, restrictor length,restrictor inside diameter, and restrictor place. It is found that all the tube system parameters mentioned above except tube curvature have non-negligible effects on fluctuating pressure. Based on the research results, test methods were presented for the fluctuating pressure measurement in low-speed wind tunnel, which can obviously improve the data accuracy but not lose test efficiency. The effectiveness of the method is verified by the wind tunnel test.
文摘In the anticorrosive coating line of a welded tube plant, the current status and existing problems of the medium-frequency induction heating equipment were discussed.Partial renovations of the power control cabinet have been conducted.Parameters such as the DC current, DC voltage, intermediate frequency power, heating temperature, and the positioning signal at the pipe end were collected.A data acquisition and processing system, which can process data according to user needs and provide convenient data processing functions, has been developed using LabVIEW software.This system has been successfully applied in the coating line for the automatic control of high-power induction heating equipment, production management, and digital steel tube and/or digital delivery.
文摘In recent years,there has been a growing demand for more efficient and robust control strategies in cooperative multi-robot systems.This paper introduces the cascade explicit tube model predictive controller(CET-MPC),a control architecture designed specifically for distributed aerial robot systems.By integrating an explicit model predictive controller(MPC)with a tube MPC,our approach significantly reduces online computational demands while enhancing robustness against disturbances such as wind and measurement noise,as well as uncertainties in inertia parameters.Further,we incorporate a cascade controller to minimize steady-state errors and improve system performance dynamically.The results of this assessment provide valuable insights into the effectiveness and reliability of the CET-MPC approach under realistic operating conditions.The simulation results of flight scenarios for multi-agent quadrotors demonstrate the controller’s stability and accurate tracking of the desired path.By addressing the complexities of quadrotors’six degrees of freedom,this controller serves as a versatile solution applicable to a wide range of multi-robot systems with varying degrees of freedom,demonstrating its adaptability and scalability beyond the quadrotor domain.
基金supported by National Natural Science Foundation of China(Grant No.50575156)Open Fund of the State Key Laboratory of Fluid Power Transmission and Control of Zhejiang University,China(Grant No.GZKF-2008006)
文摘Electro-hydraulic screw down servo system（HSDS） is widely used in seamless tube rolling mill in western companies.But in Chinese companies,mechanical screw down system（MSDS） is popularly equipped and has a serious disadvantage that the roller would often be locked when it is overloaded.For the purpose of designing the first set of domestic twin-roller,four-cylinder and six-framework electro-hydraulic HSDS of seamless tube rolling mill,an experiment system that can simulate the process of seamless tube rolling is constructed.A digital simulation model of the experiment system is built with AMESim software and validated by comparing the simulation results with experiment results.The sudden load response of the screw piston position is studied with the built model and the experiment system.To improve the HSDS＇s positioning accuracy with large load,a hybrid control scheme of combining load disturbance feedforward compensation（LDFC） method based on servo valve＇s pressure-stroke feature and anti-saturation integral control（ASIC） is proposed.Both results of simulation and experiment indicate that the transient response time of the single-roller HSDS with the proposed scheme decreases from 0.65 s to less than 0.2 s without static error.To improve the system dynamic stiffness and production qualified rate,a flow rate feedforward compensation（FFC） control strategy based on oil compressibility to dynamic position error is proposed.This FFC strategy is validated with experiments in which the transient error caused by sudden load is reduced to less than 25% of that without FFC.By extending the simulation model to HSDS of a twin-roller,four-cylinder rolling mill,analyzing the mill deformation,and applying the LDFC,ASIC and FFC to the HSDS,the dynamic performance and positioning accuracy of compensated multi-roller HSDS at biting moment are predicted.The research results provide a theoretical and experimental basis for the design of HSDS of seamless steel tube rolling mill.
基金supported by the Fundamental Research Funds for the Central Universities(Nos.lzujbky-2016-208 and lzujbky-2016-32)
文摘Conventional X-ray tube-based cone-beam computed tomography(CX-CBCT) systems have great potential in industrial applications. Such systems can rapidly obtain a three-dimensional(3D) image of an object.Conventional X-ray tubes fulfill the requirements for industrial applications, because of their high tube voltage and power. Continuous improvements have been made to CX-CBCT systems, such as imaging time shortening,acquisition strategy optimization, and imaging software development, etc. In this study, a CX-CBCT system is developed. Additionally, some improvements to the CX-CBCT system are proposed based on the hardware conditions of the X-ray tube and detector. A near-detector(ND)geometry condition is employed to obtain a sharper image and larger detection area. An improved acquisition strategy is proposed to simplify operations and reduce total imaging time. In the ND geometry condition, a simplified method called FBP slice stacking(SS-FBP) is proposed, which can be applied to 3D image reconstruction. SS-FBP is timesaving relative to traditional methods. Furthermore, imaging software for the CX-CBCT system is developed in the MATLAB environment. Several imaging experiments were performed. The results suggest that the CX-CBCT system works properly, and that the above improvements are feasible and practical.
基金Supported by the National Natural Science Foundation of China(51606214)
文摘Thermo-hydraulic characteristics of TiO_2-water nanofluids in thin-wall stainless steel test tubes(corrugated tube and circular tube) filled with copper foam(40 PPI) are experimentally investigated and compared with those in test tubes without copper foam. The effects of nanoparticle mass concentration on flow and heat transfer performances are investigated. In addition, the mutual restriction relationships between Reynolds number(Re), Nusselt number(Nu) and resistance coefficient(f) are discussed respectively. Also, the comprehensive coefficient of performance(CCP) between heat transfer and pressure drop is evaluated. The results show that core-enhancement region for heat transfer using experimental tubes filled with copper foam is notably different from that of tubes without copper foam. There is a corresponding Reynolds number(about Re = 2400) for the maximum CCP of each condition. And the heat transfer can be enhanced dramatically and sustained at 8000 ≤ Re ≤ 12000.
基金supported by Sichuan Science and Technology Program(No.2019YJ0227)China Postdoctoral Science Foundation(No.2019M663550)+1 种基金China Postdoctoral Science Foundation(No.2019M663550)Science and Technology Program of China Railway Group Limited(No.2018-S-02).
文摘The so-called Evacuated Tube Train(ETT)is currently being proposed as a high-speed transportation system potentially competitive with airplane transportation.Aerodynamic resistance is one of the most crucial factors for the successful design of an ETT.In the present work,a three-dimensional concept ETT model has been elaborated.The aerodynamic characteristics of the subsonic ETT have been numerically simulated under different conditions.The train’s running speed varies from 600 km/h up to 1200 km/h,and the blockage ratio is in the range between 0.1 and 0.3.As the blocking ratio and running speed increase,the resistance of the head car increases greatly,while the resistance of the middle car changes slightly.The aerodynamic resistance of the tail car is affected by the shock wave emerging in the wake flow.Two different design criteria for the maximum allowed aerodynamic resistance are proposed for aerodynamic parameter matching.With an increase in the blockage ratio and running speed,the atmospheric pressure in the tube should be decreased to achieve a balance.
文摘Advanced high strength steels are the group of material with high strength and good formability, because high strength lesser gauge thickness can be used without compromising the function of component. In terms of economic forming process, hydroforming is the manufacturing option which uses a fluid medium to form a component by using high internal pressure. This process gained steep interest in the automotive and aerospace industries because of its many advantages such as part consolidation, good quality of the formed part etc. The main advantage is that the uniform pressure can be transferred to whole projected part at the same time. Low pressure tube hydroforming considered an inexpensive option for forming these advanced high strength steel. This paper investigates the pressurization system used during the low pressure tube hydroforming cycle. It is observed that the usage of ramp pressure cycle during forming the part from low pressure tube hydroforming results in lesser die holding force. Also, the stress, strain and thickness distribution of the part during low pressure tube hydroforming are critically analysed.
基金Sponsored bythe Ministerial Level Research Foundation(T29483939)
文摘An integrated CAD/CAPP/CAM system of tube manufacturing based on integration frame is presented. In this system, two kinds of data conventions describing tube shape are presented in tube CAD subsystem, the object-oriented concept and the goal-driven inference mechanism have been applied in the development of the knowledge-based CAPP subsystem and simulation of tube processing under tube bending simulation subsystem is performed based on the tube model＇s piecewise representation. A tube product case is considered to give the application of the integrated system, and the advantages of the system in the use of tube bending are revealed.
基金Sponsored by the National Natural Science Foundation of China(Grant No.U0934006)
文摘According to characteristic of hydroforming of parallel multi-branch tubes,multi-objective problems were transformed to single objective problem of relational grade comparison by grey system theory.Two different objectives were selected,according to the principle that process parameters were optimal which of grey relational grade were maximum,the optimal loading parameters under different objective condition were obtained,and loading paths were optimized.The results indicated that parallel multi-branch tubes hydroformed under loading paths optimized by grey system theory could meet with the requirement that objective was optimal.And the optimal loading paths under different objectives were different,and the appropriate objective should be selected according to forming characteristic.
基金Selected from Proceedings of the 7th International Conference on Frontiers of Design and Manufacturing(ICFDM'2006)This project is supported by National Natural Science Foundation of China(No.50475026,No.50275095,No.50575135).
文摘Deposition of diamond thin films on tungsten wire substrate with the gas mixture of acetone and hydrogen by using bias-enhanced hot filament chemical vapor deposition(CVD)with the tantalum wires being optimized arranged is investigated.The self-supported diamond tubes are obtained by etching away the tungsten substrates.The quality of the diamond film before and after the removal of substrates is observed by scanning electron microscope(SEM)and Raman spectrum.The results show that the cylindrical diamond tubes with good quality and uniform thickness are obtained on tungsten wires by using bias enhanced hot filament CVD.The compressive stress in diamond film formed during the deposition is released after the substrate etches away by mixture of H2O2 and NH4 OH.There is no residual stress in diamond tube after substrate removal.
基金Supported by Topic of the Diagnostic Analysis of Spring Hail Suppression Operation Condition in Hunan
文摘Hunan Weather Modification Center and Suizhou Dafang Precision Electromechanical Engineering Co.,Ltd. of Hubei commonly transformed and installed 83 double tube antiaircraft guns( 37 mm) of Hunan Province in order to realize remote control of computer. After transformation,loading capacity of ammunition feeding machine became large,which could shorten the time of filling shells in the case of short airspace time;one shell launch volume was more,which could improve hail suppression effect; the degree of automation was greatly improved,which could save manpower by more than 50%. It fully embodied the modernization level of Hunan weather modification operation.
文摘Solid-liquid suspension in an agitated tank with a draft tube was investigated witha newly developed infrared turbidimeter for measuring solid concentration.The diameter of theflared inlet transition tube and the distance from the inlet to the tank bottom are two importantparameters for draft tube design The NAX-4 impeller,developed in this study,is characterized byits high flow efficiency and low power consumption.Some modifications are made to the Bald′smodel by considering the effects of solid concentration and fluid viscosity on the critical speed forcomplete off-bottom suspension.The modified equation fits the experimental data satisfactority andcan be used in scale-up
基金supported by the Special Program of ITER(International Thermonuclear Experimental Reactor)in China(No.2013GB101002)
文摘In order to realize steady-state operation of the neutral beam injection（NBI） system with high beam energy,an accurate thermal analysis and a prediction about working conditions of heat-removal structures inside high-heat-flux（HHF） components in the system are key issues.In this paper,taking the HHF ion dump with swirl tubes in NBI system as an example,an accurate thermal dynamic simulation method based on computational fluid dynamics（CFD） and the finite volume method is presented to predict performance of the HHF component.In this simulation method,the Eulerian multiphase method together with some empirical corrections about the inter-phase transfer model and the wall heat flux partitioning model are considered to describe the subcooled boiling.The reliability of the proposed method is validated by an experimental example with subcooled boiling inside swirl tube.The proposed method provides an important tool for the refined thermal and flow dynamic analysis of HHF components,and can be extended to study the thermal design of other complex HHF engineering structures in a straightforward way.The simulation results also verify that the swirl tube is a promising heat removing structure for the HHF components of the NBI system.
文摘The prototype,basic parameters,composition and structure of computer simulation system of stretch reducing mill for tubes were introduced.The software has an obvious style of object-oriented programming,and the modules were integrated in the simulation system.The system can optimize pass design,and it can automatically classify pass series according to the product syllabus,formulate the rolling table and simulate the rolling parameters in stretch reducing process.The simulation results were compared with the detailed technical data(used as experimental data) provided by Baotou Iron and Steel Company,and the comparison gave a clear proof of the precision of the models.
文摘The thermal performance enhancement of the hydronic radiant floor heating system by tube shape refinements is investigated in this paper.Both analytical and detailed numerical modelings are carried out to predict the performance of the radiant system.While the simple analytical model briefly investigates the possibility of the effect of the tube shape improvement with the parametric analysis,the commercial computational fluid dynamics(CFD) code(Ansys/CFX) is used to perform the detailed 3D analysis under different tube shape conditions.The fin thickness,the number of fins,and the tube thermal conductivity turn out to have significant effects on the radiant system performance.The potential energy saving impacts of the tube shape refinements are also discussed.The tube shape improvement turns out to increase the floor surface temperature and to decrease the hot water temperature drop across the system,resulting in heating energy savings.
基金the fundamental Research Funds for Central Universities under Grant 2018JBZ102.
文摘Evacuated Tube Transportation(ETT)systems have been claimed to have considerable strengths,including ultra-highspeed,safety,and environmentally-friendly.However,the frequent handover caused by the high-speed brings a challenge for ETT mobile wireless communication to preserve steady link performance.Moreover,in such a special scenario,the wireless link between the base station and the passengers on the train needs to experience fading from both metal pipe and train,thus the free-wave coverage with antennas in traditional high-speed rail wireless communication systems is not suitable for ETT.Based on the characteristics of ETT,an improved architecture of wireless communication network is proposed,using distributed base stations with remote radio units(RRUs)and baseband units(BBUs)and leaky waveguides to form stable coverage.And a redundant BBUs or RRUs structure is designed for coverage enhancement.Based on this redundant architecture,a fast handover scheme is proposed to resolve the handover problem.The analytical and simulation results show that the proposed scheme is capable of reducing communication outage probability and handover failure probability remarkably.
文摘BACKGROUND: Thoracostomy tube insertion is one of the common bedside procedures in emergency medicine and many acute specialties. Dislodgement of thoracostomy tube from the connection tube of chest drainage system is an important problem with potential complications such as contamination, infection and pneumothorax. Besides, mere loosening can also lead to malfunction. It is a common practice to tape the connection of the system. This study aimed to evaluate the materials and methods of connection of chest drain system to minimize drainage dislodgement. METHODS: We conducted an experimental study to assess the tightness of the connection with various taping materials and methods. We selected three commonly used adhesive materials(3M^(tm) Transpore^(tm) Medical tape, 3M^(tm) Micropore^(tm) Medical tape, 3M^(tm) Soft Cloth Tape on Liner) and three different methods(cross method, straight method, nylon band) to secure the junction between the thoracostomy tube and the bi-conical adaptor in the drainage system. The measured outcome was the weight causing visible loosening of the junction between thoracotomy tube and the adaptor.RESULTS: For each taping material and taping method, 10 trials were performed. The median weight required to disconnect the junction is 26.22 lb for Transpore^(tm), 31.29 lb for Micropore^(tm) and 32.44 lb for Soft Cloth Tape on Liner. A smaller force was required to disconnect if Transpore^(tm) is used(P<0.001). There was no statistical signifi cant difference between Micropore^(tm) and Soft Cloth Tape on Liner(P=0.98). The median disconnecting force is 32.44 lb for straight taping method, 40.55 lb for cross taping method and 21.15 lb for plastic band. The cross-taping method was the more secure method(P<0.0001 when compared with plastic band)(P=0.033 when compared with straight method).CONCLUSION: Cross-taping is the most secure method among the tested varieties in connecting the thoracostomy tube to the chest drainage system. Transpore^(tm) is not a recommended material for thoracostomy tube taping.
基金the National Natural Science Foundation of China (Nos.91544225,21522701) for the financial support
文摘Laboratory studies of HO2 uptake coefficients,γ(HO2),were conducted at room temperature using an aerosol flow tube coupled with a laser induced fluorescence(LIF) system.The measurement was conducted with atmospherically relevant HO2 concentrations(~1×10^9 molecule/cm^3) at 51% RH.The measured γ(HO2) onto aqueous(NH4)2 SO4 aerosol was 0.001±0.0007,which was consistent with the relatively low first-order loss rate of HO2 onto aqueous(NH4)2 SO4 aerosol.Theγ(HO2) was elevated with increase of Cu(Ⅱ) concentrations in aqueous(NH4)2 SO4 aerosol.The threshold of Cu(Ⅱ) concentration was10^-3 mol/L for the dramatic increase of γ(HO2).It was found that γ(HO2) reached 0.1 when Cu(Ⅱ)concentration in aerosol was larger than 10^-3 mol/L,suggesting that γ(HO2) is very sensitive to concentration of transition metal ions in aerosol.
