Large undercoolings up to 395K (0.28TE) are obtained for 15g samples of Ni-32.5%Sn eutectic alloy by superheating the alloy melt to 108-700K above its eutectic temperature and consequently destroying most of the inher...Large undercoolings up to 395K (0.28TE) are obtained for 15g samples of Ni-32.5%Sn eutectic alloy by superheating the alloy melt to 108-700K above its eutectic temperature and consequently destroying most of the inherent heterogeneous nuclei. The recalcscence phenomenon and its dependence on undercooling and on crystal nuclcation and growth, as well as its relationship to solidification microstructures are studied. The crystalli/ation fraction during recalcsccnce is also calculated. Experiments reveal that recalcscence degree increases with undercooling when the latter is below a certain critical value∧Te, but it decreases as undercooling increases above A 7'( (under present conditions∧Te= 245K, i. c. 0.17TE). The greater the recalescencc degree, the larger the proportion of anomalous eutectic in solidified structures. It is inferred that anomalous eutectic is the product of rapid solidification while lamellar eutectic forms at much slower nuclcation rate and growth velocity.展开更多
In this paper three types of dual- chamber shock- struts are considered in dynamic analyses of landing-gear behavior during impact and taxi. Their dynamic characteristics are compared with each other according to calc...In this paper three types of dual- chamber shock- struts are considered in dynamic analyses of landing-gear behavior during impact and taxi. Their dynamic characteristics are compared with each other according to calculation results, and some conclusions are presented.It is very helpful for selecting a suitable type of dual-chamber shock-strut in landing-gear design.展开更多
The growth behaviors of short through cracks (0.2 < △a < 2.2mm) and long cracks are compared using CT type specimens in aluminum-lithium alloy 8090 T651. It is found that the short cracks grow much more than lo...The growth behaviors of short through cracks (0.2 < △a < 2.2mm) and long cracks are compared using CT type specimens in aluminum-lithium alloy 8090 T651. It is found that the short cracks grow much more than long ones and are observed to grow at the stress intensity ranges far below the long crack threshold. The distinction of growth bahavior between short and long cracks is attributed to the difference of their crack closure effect. The growth behavior of short cracks can be rationalized with that of long ones in terms of effective stress intensity ranges. The upper demarcation value of short through cracks for aluminum-lithium alloy 8090 is presented.展开更多
A fast algorithm is proposed for recursively computing the DFTs of prime length. Only (N-1) / 2 real multiplications are required to compute all N frequency components in terms of permuting the input data. The multipl...A fast algorithm is proposed for recursively computing the DFTs of prime length. Only (N-1) / 2 real multiplications are required to compute all N frequency components in terms of permuting the input data. The multiplication in recursive computation is replaced by shifting. Complexity of the algorithm is studied. A factor η is introduced and presented. When the ratio of multiplier's period Tm to adder's period Ta is greater than the factor η (i.e.Tm / Ta >η), the new algorithm is faster than FFT. The necessary condition and error of the algorithm are studied. The signal-to-noise ratio for different length N is presented. A high accuracy scheme is proposed for improving the SNR about 20 -30dB.展开更多
In this paper, the eigen function expansions of displacements and stresses of bi-metal laminates with interface cracks are obtained. Furthermore, the stress intensity factors are determined by the variational method t...In this paper, the eigen function expansions of displacements and stresses of bi-metal laminates with interface cracks are obtained. Furthermore, the stress intensity factors are determined by the variational method to satisfy the boundary conditions and there are only line integrals in the variational equations due to the previous satisfaction of all basic equations. The computations show that this method of solution has the advantages of rapid convergency and time-saving. The results obtained by this method for homogeneous material agree with the known ones very well.展开更多
The paper discusses the system function, structure of hardware and software of the ground simulating testing system for airborne electronic devices; an example of a practical simulation and inspection system is given....The paper discusses the system function, structure of hardware and software of the ground simulating testing system for airborne electronic devices; an example of a practical simulation and inspection system is given. The system connects different kinds of microcomputers as DIMENSION 68000. SDK86, TP80T to form a distributed simulation and inspection network through an 8-terminal optic fiber communication net. The system can imitate the signal of the radar of a motional object and the ARINC429 signal of the navigation subsystem and atmosphere subsystem. It can be directly connected to the airborne electronic devices, receiving and processing real-time data from the airborne electronic devices, storing the data, fulfilling error analysis, drawing curves of the motive objects, printing tables of various test parameters. The system is easy to operate with perfect functions. The technique index accomplished and appraisal of the system are also given.展开更多
In the paper a new two-dimensional 'man-WCV'(water cooling vest) mathematical model is developed. This model is of practical use: it can predict transient temperature responses and body temperature distributio...In the paper a new two-dimensional 'man-WCV'(water cooling vest) mathematical model is developed. This model is of practical use: it can predict transient temperature responses and body temperature distribution for a person in a nonuniform hot environment, doing various jobs and dressed in different clothes. In addition, the results calculated from the model can be used to optimize the distribution of the tube-net lined on the WCV and to evaluate an individual thermal conditioning system with cooling water. The results obtained from the model agree well with the author's experimental data.展开更多
In this paper, a whole field solution to finite internally cracked plates is derived by complex variable method, where the equations of equilibrium and compatibility, the single value condition of displacements and th...In this paper, a whole field solution to finite internally cracked plates is derived by complex variable method, where the equations of equilibrium and compatibility, the single value condition of displacements and the traction-free condition on crack surfaces are satisfied exactly. The stress intensity factors of finite plates with central crack or eccentric crack or cracks emanating from a hole are calculated by using minimum potential energy principle to treat the boundary conditions excluding those on crack surfaces. As an application of the method to engineering problems, the computation about a finite rivet joint stiffened plate with cracks emanating from a hole is also performed. The numerical results show that the method presented in this paper gives rapid convergence and is much time-saving in computations.展开更多
This paper discusses the modal features of weakly-viscoelastic material structures both for single-modulus and multi-modulus materials. It is the eigenvalues of these structures that are the roots of a series of ratio...This paper discusses the modal features of weakly-viscoelastic material structures both for single-modulus and multi-modulus materials. It is the eigenvalues of these structures that are the roots of a series of rational fraction polynomial equations. A theorem about the roots of these equations is proved in the paper. Based on it, some important conclusions about the modal features of the weakly viscoelastic material structures are given according to their dynamic behaviors.展开更多
The experimental results on the influences of oscillating leading edge vortex-flaps of triangular wing toward the vortex breakdown are presented in this paper. The results reveal that forced oscillationscan delay the ...The experimental results on the influences of oscillating leading edge vortex-flaps of triangular wing toward the vortex breakdown are presented in this paper. The results reveal that forced oscillationscan delay the breakdown of concentrated vortices, and large reversed-flow-regions which originally appear at the upper surface of the fixed wing at high angles of attack would be suppressed to some extent, depending on the oscillation frequencies. As a consequence, the influences can be optimized by selecting proper oscillation frequencies.展开更多
The two-dimensional turbulent evaporating gas-droplet two-phase flows in an afterburner diffusor of turbo-fan jet engines are simulated by the k-ε turbulence model and the particle trajectory model. Comparison of pre...The two-dimensional turbulent evaporating gas-droplet two-phase flows in an afterburner diffusor of turbo-fan jet engines are simulated by the k-ε turbulence model and the particle trajectory model. Comparison of predicted gas velocity and temperature distributions with experimental results for the cases without liquid spray shows pretty good agreement. Gas-droplet two-phase flow predictions give plausible droplet trajectories, fuel-vapor concentration distribution, gas-phase velocity and temperature field in presence of liquid droplets. One run of computation with this method is made for a particular afterburner. The results indicate that the location of the atomizers is not favorable to flame stabilization and combustion efficiency. The proposed numerical modeling can also be adopted for optimization design and performance evaluation of afterburner combustors of turbo-fan jet engines.展开更多
This paper is a study of the quantitative evaluation on the cost-effectiveness of air defense surveillance radars. The composition of life cycle cost of the radar is analysed at first. Then the radar performance and e...This paper is a study of the quantitative evaluation on the cost-effectiveness of air defense surveillance radars. The composition of life cycle cost of the radar is analysed at first. Then the radar performance and effectiveness formulas are derived. By calculating the values of many radars' cost, performance and effectiveness, tendency curves are plotted. The application of cost-effectiveness calculation and the tendency curves in radar system analysis is discussed at last.展开更多
When the 45 and 40 Cr Steel parts are quenched in a medium with different concentrations, an isolating polymer film can form on the metal surface during the cooling cycle, resulting in deeper hardening depth and less ...When the 45 and 40 Cr Steel parts are quenched in a medium with different concentrations, an isolating polymer film can form on the metal surface during the cooling cycle, resulting in deeper hardening depth and less distortion than when quenched in water or oil. Quenching crack can also be prevented. In addition, normal microstructure and satisfactory mechanical properties can be reached. Test results show that these quenchants are particularly effective for the quenching of steel parts. This paper finally elucidates some of the managing problems of CH-202M quenchant in practical use.展开更多
Error estimation, double mesh as well as fore-and-aft process program are applied in the rigid-viscous-plastic finite element simulation of tube unsteady extrusions. By the error estimation, mesh can be reasonably div...Error estimation, double mesh as well as fore-and-aft process program are applied in the rigid-viscous-plastic finite element simulation of tube unsteady extrusions. By the error estimation, mesh can be reasonably divided. The double mesh includes analytical mesh and material mesh. The analytical mesh is used in the finite element analysis. The material mesh is used in the recording of distortion history. The fore-and-aft process program is used in the input-output of data and computer drawing. In the results, analytical meshes, distorted material meshes and strain contours are mapped by computer.展开更多
The finite difference method (FDM) is applied in the present paper to solve the unsteady NHS equations for incompressible fluids. ADI and SLOR methods are served for the vorticity equation and the Poisson equation for...The finite difference method (FDM) is applied in the present paper to solve the unsteady NHS equations for incompressible fluids. ADI and SLOR methods are served for the vorticity equation and the Poisson equation for ψ respectively. The upwind scheme is used for the convective terms. The moving boundary conditions are specially treated, and the effects of outlet conditions on the flow field are abo examined. Numerical results obtained show that the spoiler's oscillation induces forming, growing and shedding of the vortices. The shedding frequency of vortices is equal to that of the spoiler's oscillation. The forced unsteady separated flows under the present investigation depend mainly on the reduced frequency. At low reduced frequency, the vortices shed from the spoiler interact weakly with each other, and move downstream at an almost uniform speed of 038 V∞. At high reduced frequency, the interaction between the adjacent vortices strengthens. They close up to and rotate around each other, and eventually, merge into one vortex.展开更多
In this paper, the problem of coplanar variable-speed interception between a tactical missile and an aircraft is analysed by using the differential games theory. A unified approximate guidance law in feedback form is ...In this paper, the problem of coplanar variable-speed interception between a tactical missile and an aircraft is analysed by using the differential games theory. A unified approximate guidance law in feedback form is obtained by using the technique of forced singular perturbation (FSPT). The illustrative example with the realistic aerodynamic and propulsion data shows that this suboptimal guidance control law is available for the practical applications.展开更多
In this paper, a discussion is devoted to the theory and method of a reversed-frame normalization design to robust flight control system. The robust stability theory of the normal transfer function matrix with the sam...In this paper, a discussion is devoted to the theory and method of a reversed-frame normalization design to robust flight control system. The robust stability theory of the normal transfer function matrix with the same characteristic gain loci is proved. An example of flight control system design shows the application and advantage of this method.展开更多
The morphological structure of various epoxies toughened with a special amorphous thermoplastic PEK-C and their carbon fiber composites were studied by using SEM. For both cases, phase separation and inversion took pl...The morphological structure of various epoxies toughened with a special amorphous thermoplastic PEK-C and their carbon fiber composites were studied by using SEM. For both cases, phase separation and inversion took place to form fine epoxy-rich globules dispersing in the PEK-C matrix, in which the epoxy-rich phase had the absolutely higher volume fraction. The phase structure and the interfacial properties were also studied by means of FTIR, DSC, and DMTA as well. An accompanying mechanical determination revealed that an improved toughness was achieved both in the blend casts and in the carbon fiber composites. A composite structural model was hence suggested.展开更多
文摘Large undercoolings up to 395K (0.28TE) are obtained for 15g samples of Ni-32.5%Sn eutectic alloy by superheating the alloy melt to 108-700K above its eutectic temperature and consequently destroying most of the inherent heterogeneous nuclei. The recalcscence phenomenon and its dependence on undercooling and on crystal nuclcation and growth, as well as its relationship to solidification microstructures are studied. The crystalli/ation fraction during recalcsccnce is also calculated. Experiments reveal that recalcscence degree increases with undercooling when the latter is below a certain critical value∧Te, but it decreases as undercooling increases above A 7'( (under present conditions∧Te= 245K, i. c. 0.17TE). The greater the recalescencc degree, the larger the proportion of anomalous eutectic in solidified structures. It is inferred that anomalous eutectic is the product of rapid solidification while lamellar eutectic forms at much slower nuclcation rate and growth velocity.
文摘In this paper three types of dual- chamber shock- struts are considered in dynamic analyses of landing-gear behavior during impact and taxi. Their dynamic characteristics are compared with each other according to calculation results, and some conclusions are presented.It is very helpful for selecting a suitable type of dual-chamber shock-strut in landing-gear design.
文摘The growth behaviors of short through cracks (0.2 < △a < 2.2mm) and long cracks are compared using CT type specimens in aluminum-lithium alloy 8090 T651. It is found that the short cracks grow much more than long ones and are observed to grow at the stress intensity ranges far below the long crack threshold. The distinction of growth bahavior between short and long cracks is attributed to the difference of their crack closure effect. The growth behavior of short cracks can be rationalized with that of long ones in terms of effective stress intensity ranges. The upper demarcation value of short through cracks for aluminum-lithium alloy 8090 is presented.
文摘A fast algorithm is proposed for recursively computing the DFTs of prime length. Only (N-1) / 2 real multiplications are required to compute all N frequency components in terms of permuting the input data. The multiplication in recursive computation is replaced by shifting. Complexity of the algorithm is studied. A factor η is introduced and presented. When the ratio of multiplier's period Tm to adder's period Ta is greater than the factor η (i.e.Tm / Ta >η), the new algorithm is faster than FFT. The necessary condition and error of the algorithm are studied. The signal-to-noise ratio for different length N is presented. A high accuracy scheme is proposed for improving the SNR about 20 -30dB.
文摘In this paper, the eigen function expansions of displacements and stresses of bi-metal laminates with interface cracks are obtained. Furthermore, the stress intensity factors are determined by the variational method to satisfy the boundary conditions and there are only line integrals in the variational equations due to the previous satisfaction of all basic equations. The computations show that this method of solution has the advantages of rapid convergency and time-saving. The results obtained by this method for homogeneous material agree with the known ones very well.
文摘The paper discusses the system function, structure of hardware and software of the ground simulating testing system for airborne electronic devices; an example of a practical simulation and inspection system is given. The system connects different kinds of microcomputers as DIMENSION 68000. SDK86, TP80T to form a distributed simulation and inspection network through an 8-terminal optic fiber communication net. The system can imitate the signal of the radar of a motional object and the ARINC429 signal of the navigation subsystem and atmosphere subsystem. It can be directly connected to the airborne electronic devices, receiving and processing real-time data from the airborne electronic devices, storing the data, fulfilling error analysis, drawing curves of the motive objects, printing tables of various test parameters. The system is easy to operate with perfect functions. The technique index accomplished and appraisal of the system are also given.
文摘In the paper a new two-dimensional 'man-WCV'(water cooling vest) mathematical model is developed. This model is of practical use: it can predict transient temperature responses and body temperature distribution for a person in a nonuniform hot environment, doing various jobs and dressed in different clothes. In addition, the results calculated from the model can be used to optimize the distribution of the tube-net lined on the WCV and to evaluate an individual thermal conditioning system with cooling water. The results obtained from the model agree well with the author's experimental data.
文摘In this paper, a whole field solution to finite internally cracked plates is derived by complex variable method, where the equations of equilibrium and compatibility, the single value condition of displacements and the traction-free condition on crack surfaces are satisfied exactly. The stress intensity factors of finite plates with central crack or eccentric crack or cracks emanating from a hole are calculated by using minimum potential energy principle to treat the boundary conditions excluding those on crack surfaces. As an application of the method to engineering problems, the computation about a finite rivet joint stiffened plate with cracks emanating from a hole is also performed. The numerical results show that the method presented in this paper gives rapid convergence and is much time-saving in computations.
文摘This paper discusses the modal features of weakly-viscoelastic material structures both for single-modulus and multi-modulus materials. It is the eigenvalues of these structures that are the roots of a series of rational fraction polynomial equations. A theorem about the roots of these equations is proved in the paper. Based on it, some important conclusions about the modal features of the weakly viscoelastic material structures are given according to their dynamic behaviors.
文摘The experimental results on the influences of oscillating leading edge vortex-flaps of triangular wing toward the vortex breakdown are presented in this paper. The results reveal that forced oscillationscan delay the breakdown of concentrated vortices, and large reversed-flow-regions which originally appear at the upper surface of the fixed wing at high angles of attack would be suppressed to some extent, depending on the oscillation frequencies. As a consequence, the influences can be optimized by selecting proper oscillation frequencies.
文摘The two-dimensional turbulent evaporating gas-droplet two-phase flows in an afterburner diffusor of turbo-fan jet engines are simulated by the k-ε turbulence model and the particle trajectory model. Comparison of predicted gas velocity and temperature distributions with experimental results for the cases without liquid spray shows pretty good agreement. Gas-droplet two-phase flow predictions give plausible droplet trajectories, fuel-vapor concentration distribution, gas-phase velocity and temperature field in presence of liquid droplets. One run of computation with this method is made for a particular afterburner. The results indicate that the location of the atomizers is not favorable to flame stabilization and combustion efficiency. The proposed numerical modeling can also be adopted for optimization design and performance evaluation of afterburner combustors of turbo-fan jet engines.
文摘This paper is a study of the quantitative evaluation on the cost-effectiveness of air defense surveillance radars. The composition of life cycle cost of the radar is analysed at first. Then the radar performance and effectiveness formulas are derived. By calculating the values of many radars' cost, performance and effectiveness, tendency curves are plotted. The application of cost-effectiveness calculation and the tendency curves in radar system analysis is discussed at last.
文摘When the 45 and 40 Cr Steel parts are quenched in a medium with different concentrations, an isolating polymer film can form on the metal surface during the cooling cycle, resulting in deeper hardening depth and less distortion than when quenched in water or oil. Quenching crack can also be prevented. In addition, normal microstructure and satisfactory mechanical properties can be reached. Test results show that these quenchants are particularly effective for the quenching of steel parts. This paper finally elucidates some of the managing problems of CH-202M quenchant in practical use.
文摘Error estimation, double mesh as well as fore-and-aft process program are applied in the rigid-viscous-plastic finite element simulation of tube unsteady extrusions. By the error estimation, mesh can be reasonably divided. The double mesh includes analytical mesh and material mesh. The analytical mesh is used in the finite element analysis. The material mesh is used in the recording of distortion history. The fore-and-aft process program is used in the input-output of data and computer drawing. In the results, analytical meshes, distorted material meshes and strain contours are mapped by computer.
基金The project is supported by the National Nature Science Foundation of China(NNSFC)
文摘The finite difference method (FDM) is applied in the present paper to solve the unsteady NHS equations for incompressible fluids. ADI and SLOR methods are served for the vorticity equation and the Poisson equation for ψ respectively. The upwind scheme is used for the convective terms. The moving boundary conditions are specially treated, and the effects of outlet conditions on the flow field are abo examined. Numerical results obtained show that the spoiler's oscillation induces forming, growing and shedding of the vortices. The shedding frequency of vortices is equal to that of the spoiler's oscillation. The forced unsteady separated flows under the present investigation depend mainly on the reduced frequency. At low reduced frequency, the vortices shed from the spoiler interact weakly with each other, and move downstream at an almost uniform speed of 038 V∞. At high reduced frequency, the interaction between the adjacent vortices strengthens. They close up to and rotate around each other, and eventually, merge into one vortex.
文摘In this paper, the problem of coplanar variable-speed interception between a tactical missile and an aircraft is analysed by using the differential games theory. A unified approximate guidance law in feedback form is obtained by using the technique of forced singular perturbation (FSPT). The illustrative example with the realistic aerodynamic and propulsion data shows that this suboptimal guidance control law is available for the practical applications.
基金This paper has been supported by the National Natural Science Foundation of Chaina.
文摘In this paper, a discussion is devoted to the theory and method of a reversed-frame normalization design to robust flight control system. The robust stability theory of the normal transfer function matrix with the same characteristic gain loci is proved. An example of flight control system design shows the application and advantage of this method.
文摘The morphological structure of various epoxies toughened with a special amorphous thermoplastic PEK-C and their carbon fiber composites were studied by using SEM. For both cases, phase separation and inversion took place to form fine epoxy-rich globules dispersing in the PEK-C matrix, in which the epoxy-rich phase had the absolutely higher volume fraction. The phase structure and the interfacial properties were also studied by means of FTIR, DSC, and DMTA as well. An accompanying mechanical determination revealed that an improved toughness was achieved both in the blend casts and in the carbon fiber composites. A composite structural model was hence suggested.
