Transactions of Nanjing University of Aeronautics & Astronautics
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2020, 37(3):353-359.
DOI: 10.16356/j.1005-1120.2020.03.001
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The aramid fiber-reinforced composites (AFRC) can increase the durability of corresponding applications such as aerospace, automobile and other large structural parts, due to the improvement in hardness, heat build-up, wear properties and green environmental protection. However, because of its complex multiphase structure and unique heterogeneity and anisotropy, the poor compression fatigue resistance and the incident surface fibrillation are inevitable. To improve the assembly precision of AFRC, mechanical processing is necessary to meet the dimensional accuracy. This paper focuses on the influence of contour milling parameters on delamination defects during milling of AFRC laminates. A series of milling experiments are conducted and two different kinds of delamination defects including tearing delamination and uncut-off delamination are investigated. A computing method and model based on brittle fracture for the two different types of delamination are established. The results can be used for explaining the mechanism and regularity of delamination defects. The control strategy of delamination defects and evaluation method of finished surface integrity are further discussed. The results are meaningful to optimize cutting parameters, and provide a clear understanding of surface defects control.
The aramid fiber-reinforced composites (AFRC) can increase the durability of corresponding applications such as aerospace, automobile and other large structural parts, due to the improvement in hardness, heat build-up, wear properties and green environmental protection. However, because of its complex multiphase structure and unique heterogeneity and anisotropy, the poor compression fatigue resistance and the incident surface fibrillation are inevitable. To improve the assembly precision of AFRC, mechanical processing is necessary to meet the dimensional accuracy. This paper focuses on the influence of contour milling parameters on delamination defects during milling of AFRC laminates. A series of milling experiments are conducted and two different kinds of delamination defects including tearing delamination and uncut-off delamination are investigated. A computing method and model based on brittle fracture for the two different types of delamination are established. The results can be used for explaining the mechanism and regularity of delamination defects. The control strategy of delamination defects and evaluation method of finished surface integrity are further discussed. The results are meaningful to optimize cutting parameters, and provide a clear understanding of surface defects control.
2016, 33(2):129-136.
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A jet noise reduction technique by using the external chevron nozzle with lobed mixer in the double-mixing exhaust system is investigated under cold conditions. The computations of jet field and the experiments of noise field are conducted with scaled model of high-bypass-ratio turbofan engine mixing exhaust system composed of external chevron nozzle with lobed mixer. The computational results indicate that comparing with the baseline nozzle with lobed mixer, the external chevron nozzle with lobed mixer increases mixing of jet and ambient air near the nozzle exit. The experimental results show that the external chevron nozzle with lobed mixer has better jet noise reduction at low frequencies, and this reduction rises with the increase of chevron bend angle. The experimental results also show that the external chevron nozzle with lobed mixer has sound pressure level (SPL) increase which is not obvious at high frequencies. With chevron bend angle increasing, SPL has relatively marked increase at 60°(directivity angle measured from upstream jet axis) and little fluctuations at 90° and 150°. The external chevron nozzle with lobed mixer has overall sound pressure level (OASPL) reduction in varying degrees at 60° and 150°, but it has little OASPL increase at 90°.
A jet noise reduction technique by using the external chevron nozzle with lobed mixer in the double-mixing exhaust system is investigated under cold conditions. The computations of jet field and the experiments of noise field are conducted with scaled model of high-bypass-ratio turbofan engine mixing exhaust system composed of external chevron nozzle with lobed mixer. The computational results indicate that comparing with the baseline nozzle with lobed mixer, the external chevron nozzle with lobed mixer increases mixing of jet and ambient air near the nozzle exit. The experimental results show that the external chevron nozzle with lobed mixer has better jet noise reduction at low frequencies, and this reduction rises with the increase of chevron bend angle. The experimental results also show that the external chevron nozzle with lobed mixer has sound pressure level (SPL) increase which is not obvious at high frequencies. With chevron bend angle increasing, SPL has relatively marked increase at 60°(directivity angle measured from upstream jet axis) and little fluctuations at 90° and 150°. The external chevron nozzle with lobed mixer has overall sound pressure level (OASPL) reduction in varying degrees at 60° and 150°, but it has little OASPL increase at 90°.
2014, 31(1):1-15.
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A lattice Boltzmann flux solver (LBFS) is presented for simulation of fluid flows. Like the conventional computational fluid dynamics (CFD) solvers, the new solver also applies the finite volume method to discretize the governing differential equations, but the numerical flux at the cell interface is not evaluated by the smooth function approximation or Riemann solvers. Instead, it is evaluated from local solution of lattice Boltzmann equation (LBE) at cell interface. Two versions of LBFS are presented in this paper. One is to locally apply one dimensional compressible lattice Boltzmann (LB) model along the normal direction to the cell interface for simulation of compressible inviscid flows with shock waves. The other is to locally apply multi dimensional LB model at cell interface for simulation of incompressible viscous and inviscid flows. The present solver removes the drawbacks of conventional lattice Boltzmann method (LBM) such as limitation to uniform mesh, tie-up of mesh spacing and time interval, limitation to viscous flows. Numerical examples show that the present solver can be well applied to simulate fluid flows with non-uniform mesh and curved boundary.
A lattice Boltzmann flux solver (LBFS) is presented for simulation of fluid flows. Like the conventional computational fluid dynamics (CFD) solvers, the new solver also applies the finite volume method to discretize the governing differential equations, but the numerical flux at the cell interface is not evaluated by the smooth function approximation or Riemann solvers. Instead, it is evaluated from local solution of lattice Boltzmann equation (LBE) at cell interface. Two versions of LBFS are presented in this paper. One is to locally apply one dimensional compressible lattice Boltzmann (LB) model along the normal direction to the cell interface for simulation of compressible inviscid flows with shock waves. The other is to locally apply multi dimensional LB model at cell interface for simulation of incompressible viscous and inviscid flows. The present solver removes the drawbacks of conventional lattice Boltzmann method (LBM) such as limitation to uniform mesh, tie-up of mesh spacing and time interval, limitation to viscous flows. Numerical examples show that the present solver can be well applied to simulate fluid flows with non-uniform mesh and curved boundary.
2015, 32(4).
Abstract:
According to the principle of heat transfer in limited space, the thickness formula of heat-insulating layer is deduced through the conduction analysis in this paper. Polishing experiments are conducted with the same technological parameters. Compared with polishing experiments, the heat transfer model is proved to be right. According to the result of experiments, Polyurethane heat-insulating layer can effectively increase the service life of the ice fixed abrasive pad, and smooth melting rate in the process of polishing to improve the quality of polishing. Theoretical basis for research of temperature field of ice fixed abrasive polishing can be provided by the heat transfer model.
According to the principle of heat transfer in limited space, the thickness formula of heat-insulating layer is deduced through the conduction analysis in this paper. Polishing experiments are conducted with the same technological parameters. Compared with polishing experiments, the heat transfer model is proved to be right. According to the result of experiments, Polyurethane heat-insulating layer can effectively increase the service life of the ice fixed abrasive pad, and smooth melting rate in the process of polishing to improve the quality of polishing. Theoretical basis for research of temperature field of ice fixed abrasive polishing can be provided by the heat transfer model.
2015, 32(1):1-8.
DOI: 10.16356/j.1005-1120.2015.01.001
Abstract:
To date unmanned aerial system (UAS) technologies have attracted more and more attention from countries in the world. Unmanned aerial vehicles (UAVs) play an important role in reconnaissance, surveillance, and target tracking within military and civil fields. Here one briefly introduces the development of UAVs, and reviews its various subsystems including autopilot, ground station, mission planning and management subsystem, navigation system and so on. Furthermore, an overview is provided for advanced design methods of UAVs control system, including the linear feedback control, adaptive and nonlinear control, and intelligent control techniques. Finally, the future of UAVs flight control techniques is forecasted.
To date unmanned aerial system (UAS) technologies have attracted more and more attention from countries in the world. Unmanned aerial vehicles (UAVs) play an important role in reconnaissance, surveillance, and target tracking within military and civil fields. Here one briefly introduces the development of UAVs, and reviews its various subsystems including autopilot, ground station, mission planning and management subsystem, navigation system and so on. Furthermore, an overview is provided for advanced design methods of UAVs control system, including the linear feedback control, adaptive and nonlinear control, and intelligent control techniques. Finally, the future of UAVs flight control techniques is forecasted.
2011, 28(3):294-299.
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2011, 28(2):152-156.
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2011, 28(2):163-168.
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2011, 28(2):169-175.
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2013, 30(3):221-226.
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2011, 28(3):240-245.
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2011, 28(2):192-198.
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2013, 30(3):270-275.
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2011, 28(1):1-11.
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2013, 30(2):175-184.
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2013, 30(2):202-208.
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2013, 30(2):109-117.
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2013, 30(3):260-263.
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2013, 30(3):252-256.
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2013, 30(3):248-251.
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