The concept of metamorphic mechanisms is presented, configuration models and configuration transformations relating to a set of new matrix operations are discussed and proposed. The configuration of a metamorphic mech...The concept of metamorphic mechanisms is presented, configuration models and configuration transformations relating to a set of new matrix operations are discussed and proposed. The configuration of a metamorphic mechanism reflects the connectivity change in the mechanism during motions which results in mobility change and presents the characteristics of the mechanism which is discussed in various applications particularly in decorative artifacts. The characteristics is further investigated with mobility analysis.展开更多
This paper puts forward a design idea for blended wing body（BWB）.The idea is described as that cruise point,maximum lift to drag point and pitch trim point are in the same flight attitude.According to this design id...This paper puts forward a design idea for blended wing body（BWB）.The idea is described as that cruise point,maximum lift to drag point and pitch trim point are in the same flight attitude.According to this design idea,design objectives and constraints are defined.By applying low and high fidelity aerodynamic analysis tools,BWB aerodynamic design methodology is established by the combination of optimization design and inverse design methods.High lift to drag ratio,pitch trim and acceptable buffet margin can be achieved by this design methodology.For 300-passenger BWB configuration based on static stability design,as compared with initial configuration,the maximum lift to drag ratio and pitch trim are achieved at cruise condition,zero lift pitching moment is positive,and buffet characteristics is well.Fuel burn of 300-passenger BWB configuration is also significantly reduced as compared with conventional civil transports.Because aerodynamic design is carried out under the constraints of BWB design requirements,the design configuration fulfills the demands for interior layout and provides a solid foundation for continuous work.展开更多
A series of experiments were performed on three types of closed loop pulsating heat pipes （PHPs）, intending to investigate various kinds of flow patterns, and to develop some improved configurations for the PHPs. Op...A series of experiments were performed on three types of closed loop pulsating heat pipes （PHPs）, intending to investigate various kinds of flow patterns, and to develop some improved configurations for the PHPs. Optical visualization results indicated that there might exist three flow patterns, i.e. bubble-liquid slug flow, semi-annular flow and annular flow, corresponding to different working conditions. For a given geometry and an adequate fill ratio, the PHPs had the self-adjusting characteristic for the flow patterns （from slug flow to semi-annular and then to annular flow） to meet the demands of the increasing heat input. Two special configurations, one with alternately varying channel diameter, the other equipped with one section of thicker tube, were found to be advantageous in establishing and maintaining reliable circulation of the working fluid. The thermal performance of the PHPs was examined over a range of working conditions. Comparing with the normal PHP with uniform diameter, either of the improved PHPs exhibited higher thermal performance.展开更多
To investigate the flame and overpressure characteristics of methane–air explosion with different obstacle configurations,an experimental study has been conducted,taking account of the number of obstacles,obstacle di...To investigate the flame and overpressure characteristics of methane–air explosion with different obstacle configurations,an experimental study has been conducted,taking account of the number of obstacles,obstacle distance from ignition source,and stream-wise and cross-wise obstacle positions.The results show that the flame speed and peak overpressure increase with the increasing number of obstacles,while the time to reach the peak is not fully determined by it.And the configuration having the farthest obstacle produces a higher overpressure and takes a longer time to reach the peak,but a slower flame propagation speed is obtained.Similar explosion characteristics are also observed in the configurations with two obstacles fixed at different stream-wise positions.Furthermore,the experimental results demonstrate that the peak overpressures and flame speeds in configurations with central or staggered obstacles are relatively higher,which should to be avoided in practical processes to minimize the risk associated with methane–air explosion.展开更多
The purpose of this article is to summarize our recent progress in high-order and high accurate CFD methods for flow problems with complex grids as well as to discuss the engineering prospects in using these methods.D...The purpose of this article is to summarize our recent progress in high-order and high accurate CFD methods for flow problems with complex grids as well as to discuss the engineering prospects in using these methods.Despite the rapid development of high-order algorithms in CFD,the applications of high-order and high accurate methods on complex configurations are still limited.One of the main reasons which hinder the widely applications of thesemethods is the complexity of grids.Many aspects which can be neglected for low-order schemes must be treated carefully for high-order ones when the configurations are complex.In order to implement highorder finite difference schemes on complex multi-block grids,the geometric conservation lawand block-interface conditions are discussed.A conservativemetricmethod is applied to calculate the grid derivatives,and a characteristic-based interface condition is employed to fulfil high-order multi-block computing.The fifth-order WCNS-E-5 proposed by Deng[9,10]is applied to simulate flows with complex grids,including a double-delta wing,a transonic airplane configuration,and a hypersonic X-38 configuration.The results in this paper and the references show pleasant prospects in engineering-oriented applications of high-order schemes.展开更多
BACKGROUND In rotator cuff repair surgery,the double-row technique is widely performed.Studies have shown that with increased contact area and pressure between tendon and bone interface,better healing is promoted.AIM ...BACKGROUND In rotator cuff repair surgery,the double-row technique is widely performed.Studies have shown that with increased contact area and pressure between tendon and bone interface,better healing is promoted.AIM To assess the different suture configurations with the double-row technique and how this influences the contact area of the rotator cuff tendon to bone.METHODS This was a controlled laboratory study where identical tears were created in 24 fresh porcine shoulders over a 1.5 cm×2.5 cm infraspinatus insertion footprint.Double-row repair techniques,with 3 to 4-suture anchors in different configurations(2 medial,2 lateral vs 2 medial,1 lateral vs 1 medial,2 lateral),were employed for three control groups.Each group consisted of eight shoulders with identical repair configurations.Footprint contact areas of the repaired tendon against the tuberosity were determined using pressure sensitive Fujifilm placed between the tendon and tuberosity.RESULTS The mean contact area between tendon and insertion footprint from the imprinted Fujifilm was obtained using computer software.The contact area measured from a standard 4-suture anchor double row repair was 75.1±9.3 mm2,whereas areas obtained for the 2 lateral-1 medial and 2 medial-1 lateral anchor configurations were 72.9±5.2 mm2 and 75.0±4.9 mm2 respectively.No statistical significance was noted between the three groups.CONCLUSION In the technique of double-row repair,using a 3-suture anchor configuration may offer a non-inferior alternative to the standard 4-anchor construct in terms of efficacy.This may also result in overall cost reduction and shorter surgical time.展开更多
Ion optics are crucial components of ion thrusters and the study of the different ion extraction solutions used since the beginning of the electric propulsion era is essential to understand the evolution of ion engine...Ion optics are crucial components of ion thrusters and the study of the different ion extraction solutions used since the beginning of the electric propulsion era is essential to understand the evolution of ion engines. This work describes ion engine grids＇ main functions, parameters and issues related to thermal expansion and sputter erosion, and then introduces a review of ion optics used for significant launched and tested ion thrusters since 1970. Configurations, geometries, materials and fabrication methods are analyzed to understand when typical ion thrusters use two or three grids, what are the thicknesses and aperture sizes of the screen, accelerator and decelerator grids, why molybdenum and carbon-based materials such as pyrolytic graphite and carbon–carbon are the best available options for ion optics and what is the manufacturing method for each material.展开更多
This paper examines the Shock/Shock Interactions（SSI）between the body and wing of aircraft in supersonic flows.The body is simplified to a flat wedge and the wing is assumed to be a sharp wing.The theoretical spatia...This paper examines the Shock/Shock Interactions（SSI）between the body and wing of aircraft in supersonic flows.The body is simplified to a flat wedge and the wing is assumed to be a sharp wing.The theoretical spatial dimension reduction method,which transforms the 3D problem into a 2D one,is used to analyze the SSI between the body and wing.The temperature and pressure behind the Mach stem induced by the wing and body are obtained,and the wave configurations in the corner are determined.Numerical validations are conducted by solving the inviscid Euler equations in 3D with a Non-oscillatory and Non-free-parameters Dissipative（NND）finite difference scheme.Good agreements between the theoretical and numerical results are obtained.Additionally,the effects of the wedge angle and sweep angle on wave configurations and flow field are considered numerically and theoretically.The influences of wedge angle are significant,whereas the effects of sweep angle on wave configurations are negligible.This paper provides useful information for the design and thermal protection of aircraft in supersonic and hypersonic flows.展开更多
文摘The concept of metamorphic mechanisms is presented, configuration models and configuration transformations relating to a set of new matrix operations are discussed and proposed. The configuration of a metamorphic mechanism reflects the connectivity change in the mechanism during motions which results in mobility change and presents the characteristics of the mechanism which is discussed in various applications particularly in decorative artifacts. The characteristics is further investigated with mobility analysis.
文摘This paper puts forward a design idea for blended wing body（BWB）.The idea is described as that cruise point,maximum lift to drag point and pitch trim point are in the same flight attitude.According to this design idea,design objectives and constraints are defined.By applying low and high fidelity aerodynamic analysis tools,BWB aerodynamic design methodology is established by the combination of optimization design and inverse design methods.High lift to drag ratio,pitch trim and acceptable buffet margin can be achieved by this design methodology.For 300-passenger BWB configuration based on static stability design,as compared with initial configuration,the maximum lift to drag ratio and pitch trim are achieved at cruise condition,zero lift pitching moment is positive,and buffet characteristics is well.Fuel burn of 300-passenger BWB configuration is also significantly reduced as compared with conventional civil transports.Because aerodynamic design is carried out under the constraints of BWB design requirements,the design configuration fulfills the demands for interior layout and provides a solid foundation for continuous work.
基金the National Natural Science Foundation of China under contract 60672151 , 60532020.
文摘A series of experiments were performed on three types of closed loop pulsating heat pipes （PHPs）, intending to investigate various kinds of flow patterns, and to develop some improved configurations for the PHPs. Optical visualization results indicated that there might exist three flow patterns, i.e. bubble-liquid slug flow, semi-annular flow and annular flow, corresponding to different working conditions. For a given geometry and an adequate fill ratio, the PHPs had the self-adjusting characteristic for the flow patterns （from slug flow to semi-annular and then to annular flow） to meet the demands of the increasing heat input. Two special configurations, one with alternately varying channel diameter, the other equipped with one section of thicker tube, were found to be advantageous in establishing and maintaining reliable circulation of the working fluid. The thermal performance of the PHPs was examined over a range of working conditions. Comparing with the normal PHP with uniform diameter, either of the improved PHPs exhibited higher thermal performance.
基金supported by the National Natural Science Foundation of China (Nos.51106044 and 51176021)the Research Foundation of Education Bureau of Henan Province of China (No.14A410007)
文摘To investigate the flame and overpressure characteristics of methane–air explosion with different obstacle configurations,an experimental study has been conducted,taking account of the number of obstacles,obstacle distance from ignition source,and stream-wise and cross-wise obstacle positions.The results show that the flame speed and peak overpressure increase with the increasing number of obstacles,while the time to reach the peak is not fully determined by it.And the configuration having the farthest obstacle produces a higher overpressure and takes a longer time to reach the peak,but a slower flame propagation speed is obtained.Similar explosion characteristics are also observed in the configurations with two obstacles fixed at different stream-wise positions.Furthermore,the experimental results demonstrate that the peak overpressures and flame speeds in configurations with central or staggered obstacles are relatively higher,which should to be avoided in practical processes to minimize the risk associated with methane–air explosion.
基金This studywas supported by the project of National Natural Science Foundation of China(Grant 11072259 and 10621062)National Basic Research Program of China(Grant No.2009CB723800).The authors would like to thank Dr.Huayong Liu,and Assistant Researcher GuangxueWang of State Key Laboratory of Aerodynamics for their contributions.
文摘The purpose of this article is to summarize our recent progress in high-order and high accurate CFD methods for flow problems with complex grids as well as to discuss the engineering prospects in using these methods.Despite the rapid development of high-order algorithms in CFD,the applications of high-order and high accurate methods on complex configurations are still limited.One of the main reasons which hinder the widely applications of thesemethods is the complexity of grids.Many aspects which can be neglected for low-order schemes must be treated carefully for high-order ones when the configurations are complex.In order to implement highorder finite difference schemes on complex multi-block grids,the geometric conservation lawand block-interface conditions are discussed.A conservativemetricmethod is applied to calculate the grid derivatives,and a characteristic-based interface condition is employed to fulfil high-order multi-block computing.The fifth-order WCNS-E-5 proposed by Deng[9,10]is applied to simulate flows with complex grids,including a double-delta wing,a transonic airplane configuration,and a hypersonic X-38 configuration.The results in this paper and the references show pleasant prospects in engineering-oriented applications of high-order schemes.
文摘BACKGROUND In rotator cuff repair surgery,the double-row technique is widely performed.Studies have shown that with increased contact area and pressure between tendon and bone interface,better healing is promoted.AIM To assess the different suture configurations with the double-row technique and how this influences the contact area of the rotator cuff tendon to bone.METHODS This was a controlled laboratory study where identical tears were created in 24 fresh porcine shoulders over a 1.5 cm×2.5 cm infraspinatus insertion footprint.Double-row repair techniques,with 3 to 4-suture anchors in different configurations(2 medial,2 lateral vs 2 medial,1 lateral vs 1 medial,2 lateral),were employed for three control groups.Each group consisted of eight shoulders with identical repair configurations.Footprint contact areas of the repaired tendon against the tuberosity were determined using pressure sensitive Fujifilm placed between the tendon and tuberosity.RESULTS The mean contact area between tendon and insertion footprint from the imprinted Fujifilm was obtained using computer software.The contact area measured from a standard 4-suture anchor double row repair was 75.1±9.3 mm2,whereas areas obtained for the 2 lateral-1 medial and 2 medial-1 lateral anchor configurations were 72.9±5.2 mm2 and 75.0±4.9 mm2 respectively.No statistical significance was noted between the three groups.CONCLUSION In the technique of double-row repair,using a 3-suture anchor configuration may offer a non-inferior alternative to the standard 4-anchor construct in terms of efficacy.This may also result in overall cost reduction and shorter surgical time.
文摘Ion optics are crucial components of ion thrusters and the study of the different ion extraction solutions used since the beginning of the electric propulsion era is essential to understand the evolution of ion engines. This work describes ion engine grids＇ main functions, parameters and issues related to thermal expansion and sputter erosion, and then introduces a review of ion optics used for significant launched and tested ion thrusters since 1970. Configurations, geometries, materials and fabrication methods are analyzed to understand when typical ion thrusters use two or three grids, what are the thicknesses and aperture sizes of the screen, accelerator and decelerator grids, why molybdenum and carbon-based materials such as pyrolytic graphite and carbon–carbon are the best available options for ion optics and what is the manufacturing method for each material.
基金supported by the Fundamental Research Funds for the Central Universities of China (No. 31020170QD087)
文摘This paper examines the Shock/Shock Interactions（SSI）between the body and wing of aircraft in supersonic flows.The body is simplified to a flat wedge and the wing is assumed to be a sharp wing.The theoretical spatial dimension reduction method,which transforms the 3D problem into a 2D one,is used to analyze the SSI between the body and wing.The temperature and pressure behind the Mach stem induced by the wing and body are obtained,and the wave configurations in the corner are determined.Numerical validations are conducted by solving the inviscid Euler equations in 3D with a Non-oscillatory and Non-free-parameters Dissipative（NND）finite difference scheme.Good agreements between the theoretical and numerical results are obtained.Additionally,the effects of the wedge angle and sweep angle on wave configurations and flow field are considered numerically and theoretically.The influences of wedge angle are significant,whereas the effects of sweep angle on wave configurations are negligible.This paper provides useful information for the design and thermal protection of aircraft in supersonic and hypersonic flows.
