Transactions of Nanjing University of Aeronautics & Astronautics
Volume 33,Issue 5,2016 Table of Contents
1 Development of Composite Cellular Cores for Sandwich Panels Based on Folded Polar Quadra-Structures
2016, 33(5):519-528.
Abstract:
An idea to develop a family of cellular cores for sandwich panels using a technology of prepreg folding is presented. Polar folded quadra-structures are regarded as a geometric basis for these cores whose standard fragment has the fourth degree of axial symmetry. The classification of the polar structures are described and a method of various quadra-structure synthesis is developed. A possibility to provide high strength of the structure due to preservation of faces reinforcement pattern is presented. Arrangement of the plane core on a bi-curvature surface is also introduced. Besides, provision of isotropy of the core in two or three directions are described. Finally, examples of cellular folded coresmanufactured from basalt reinforced plastic are demonstrated.
An idea to develop a family of cellular cores for sandwich panels using a technology of prepreg folding is presented. Polar folded quadra-structures are regarded as a geometric basis for these cores whose standard fragment has the fourth degree of axial symmetry. The classification of the polar structures are described and a method of various quadra-structure synthesis is developed. A possibility to provide high strength of the structure due to preservation of faces reinforcement pattern is presented. Arrangement of the plane core on a bi-curvature surface is also introduced. Besides, provision of isotropy of the core in two or three directions are described. Finally, examples of cellular folded coresmanufactured from basalt reinforced plastic are demonstrated.
2016, 33(5):529-535.
Abstract:
Ultra-violet(UV) curing is an efficient method for composite molding. Firstly, thermophysical properties of UV cured glass-fiber reinforced plastics are conducted. Material properties are studied for various kinds of postcuring modes. Then the UV curing method is suggested in manufacturing V-crimp folded core for sandwich panels. Two kinds of processing schemes for V-crimp folded core manufacturing using UV curing are presented. Finally, the effect of post-curing on the mechanical properties of folded core sandwiches is experimentally studied, and optimum modes of post-curing are determined. The experimental results show that the ultimate compressive strength of the folded sandwiches is increased by 60% after post-curing with the optimum post-curing mode.
Ultra-violet(UV) curing is an efficient method for composite molding. Firstly, thermophysical properties of UV cured glass-fiber reinforced plastics are conducted. Material properties are studied for various kinds of postcuring modes. Then the UV curing method is suggested in manufacturing V-crimp folded core for sandwich panels. Two kinds of processing schemes for V-crimp folded core manufacturing using UV curing are presented. Finally, the effect of post-curing on the mechanical properties of folded core sandwiches is experimentally studied, and optimum modes of post-curing are determined. The experimental results show that the ultimate compressive strength of the folded sandwiches is increased by 60% after post-curing with the optimum post-curing mode.
2016, 33(5):536-545.
Abstract:
Personal desktop platform with teraflops peak performance of thousands of cores is realized at the price of conventional workstations using the programmable graphics processing units (GPUs). A GPU-based parallel Euler/Navier-Stokes solver is developed for 2-D compressible flows by using NVIDIA′s Compute Unified Device Architecture (CUDA) programming model in CUDA Fortran programming language. The techniques of implementation of CUDA kernels, doublelayered thread hierarchy and variety memory hierarchy are presented to form the GPU-based algorithm of Euler/Navier-Stokes equations. The resulting parallel solver is validated by a set of typical test flow cases. The numerical results show that dozens of times speedup relative to a serial CPU implementation can be achieved using a single GPU desktop platform, which demonstrates that a GPU desktop can serve as a cost-effective parallel computing platform to accelerate computational fluid dynamics(CFD) simulations substantially.
Personal desktop platform with teraflops peak performance of thousands of cores is realized at the price of conventional workstations using the programmable graphics processing units (GPUs). A GPU-based parallel Euler/Navier-Stokes solver is developed for 2-D compressible flows by using NVIDIA′s Compute Unified Device Architecture (CUDA) programming model in CUDA Fortran programming language. The techniques of implementation of CUDA kernels, doublelayered thread hierarchy and variety memory hierarchy are presented to form the GPU-based algorithm of Euler/Navier-Stokes equations. The resulting parallel solver is validated by a set of typical test flow cases. The numerical results show that dozens of times speedup relative to a serial CPU implementation can be achieved using a single GPU desktop platform, which demonstrates that a GPU desktop can serve as a cost-effective parallel computing platform to accelerate computational fluid dynamics(CFD) simulations substantially.
2016, 33(5):546-551.
Abstract:
Traditional signal processing methods for turbine flowmeter are unable to solve the contradiction between the realtime performance and the accuracy during the aeroengine bench test or hardware in the loop (HIL) simulation of aeroengine control system. A dynamic flow measurement method based on cycle number of the flowmeter is proposed. And a DSP-based multi-functional dynamic signal processing module for turbine flowmeter is built to validate the method. The developed system can provide three types of output modes including PWM, frequency and D/A. At the same time, the results can be displayed instantly with the module of serial communication interface to obtain dynamic flow signal with good precision. Experimental results show that the stability of flow measurement is greatly improved with precision guaranteed and the real-time response reaches the maximum limit of turbine flowmeter.
Traditional signal processing methods for turbine flowmeter are unable to solve the contradiction between the realtime performance and the accuracy during the aeroengine bench test or hardware in the loop (HIL) simulation of aeroengine control system. A dynamic flow measurement method based on cycle number of the flowmeter is proposed. And a DSP-based multi-functional dynamic signal processing module for turbine flowmeter is built to validate the method. The developed system can provide three types of output modes including PWM, frequency and D/A. At the same time, the results can be displayed instantly with the module of serial communication interface to obtain dynamic flow signal with good precision. Experimental results show that the stability of flow measurement is greatly improved with precision guaranteed and the real-time response reaches the maximum limit of turbine flowmeter.
2016, 33(5):552-558.
Abstract:
According to the structural characteristics of embedded fluid elastomeric damper and dynamic modeling method of bearingless rotor (BR) system, a time-domain dynamic model based on multilayer elastomeric theory and fluid dynamic equations is developed. The parameters contained in the analysis model are identified by dynamic experiment data of embedded fluid elastomeric damper. The dynamic characteristics curves calculated through dynamic model are compared with those derived from experimental data. The consistent results illustrate that the model can describe the nonlinear relationship between stress and strain of embedded fluid elastomeric damper under different displacement amplitude and frequency. Due to the validity and reliability of the dynamic analysis model, it can be used in aeroelastic characteristics calculation of BR with embedded fluid elastomeric damper for helicopters.
According to the structural characteristics of embedded fluid elastomeric damper and dynamic modeling method of bearingless rotor (BR) system, a time-domain dynamic model based on multilayer elastomeric theory and fluid dynamic equations is developed. The parameters contained in the analysis model are identified by dynamic experiment data of embedded fluid elastomeric damper. The dynamic characteristics curves calculated through dynamic model are compared with those derived from experimental data. The consistent results illustrate that the model can describe the nonlinear relationship between stress and strain of embedded fluid elastomeric damper under different displacement amplitude and frequency. Due to the validity and reliability of the dynamic analysis model, it can be used in aeroelastic characteristics calculation of BR with embedded fluid elastomeric damper for helicopters.
2016, 33(5):559-565.
Abstract:
To enhance the controllability of stratosphere airship, a vectored electric propulsion system is used. By using the Lagrangian method, a kinetic model of the vectored electric propulsion system is established and validated through ground tests. The fake gyroscopic torque is first proposed, which the vector mechanism should overcome besides the inertial torque and the gravitational torque. The fake gyroscopic torque is caused by the difference between inertial moments about two principal inertial axes of the propeller in the rotating plane, appears only when the propeller is rotating and is proportional with the rotation speed. It is a sinusoidal pulse, with a frequency that is twice of the rotation speed. Considering the fake gyroscope torque pulse and aerodynamic efficiency, three blade propeller is recommended for the vectored propulsion system used for stratosphere airship.
To enhance the controllability of stratosphere airship, a vectored electric propulsion system is used. By using the Lagrangian method, a kinetic model of the vectored electric propulsion system is established and validated through ground tests. The fake gyroscopic torque is first proposed, which the vector mechanism should overcome besides the inertial torque and the gravitational torque. The fake gyroscopic torque is caused by the difference between inertial moments about two principal inertial axes of the propeller in the rotating plane, appears only when the propeller is rotating and is proportional with the rotation speed. It is a sinusoidal pulse, with a frequency that is twice of the rotation speed. Considering the fake gyroscope torque pulse and aerodynamic efficiency, three blade propeller is recommended for the vectored propulsion system used for stratosphere airship.
2016, 33(5):566-575.
Abstract:
An h-adaptive method is developed for highorder discontinuous Galerkin methods (DGM) to solve the laminar compressible Navier-Stokes (N-S) equations on unstructured mesh. The vorticity is regarded as the indicator of adaptivity. The elements where the vorticity is larger than a pre-defined upper limit are refined, and those where the vorticity is smaller than a pre-defined lower limit are coarsened if they have been refined. A high-order geometric approximation of curved boundaries is adopted to ensure the accuracy. Numerical results indicate that highly accurate numerical results can be obtained with the adaptive method at relatively low expense.
An h-adaptive method is developed for highorder discontinuous Galerkin methods (DGM) to solve the laminar compressible Navier-Stokes (N-S) equations on unstructured mesh. The vorticity is regarded as the indicator of adaptivity. The elements where the vorticity is larger than a pre-defined upper limit are refined, and those where the vorticity is smaller than a pre-defined lower limit are coarsened if they have been refined. A high-order geometric approximation of curved boundaries is adopted to ensure the accuracy. Numerical results indicate that highly accurate numerical results can be obtained with the adaptive method at relatively low expense.
2016, 33(5):576-583.
Abstract:
The performance of the designed digital electro-pneumatic cabin pressure control system for the cabin pressure schedule of transport aircraft is investigated. For the purpose of this study, an experimental setup consisting of a simulated hermetic cabin and altitude simulation chamber is configured for cabin pressure control system operation. A series of experimental tests are executed to evaluate the performance of the cabin pressure control system. The parameters of the PID controller are optimized. In the optimization process, the variation regularity of the rate of cabin pressure change under various conditions is considered. An approach to prioritize the control of the rate of change of cabin pressure based on the flight status model is proposed and verified experimentally. The experimental results indicate that the proposed approach can be adopted for the designed digital electro-pneumatic cabin pressure control system to obtain a better cabin pressure schedule and rate of cabin pressure change.
The performance of the designed digital electro-pneumatic cabin pressure control system for the cabin pressure schedule of transport aircraft is investigated. For the purpose of this study, an experimental setup consisting of a simulated hermetic cabin and altitude simulation chamber is configured for cabin pressure control system operation. A series of experimental tests are executed to evaluate the performance of the cabin pressure control system. The parameters of the PID controller are optimized. In the optimization process, the variation regularity of the rate of cabin pressure change under various conditions is considered. An approach to prioritize the control of the rate of change of cabin pressure based on the flight status model is proposed and verified experimentally. The experimental results indicate that the proposed approach can be adopted for the designed digital electro-pneumatic cabin pressure control system to obtain a better cabin pressure schedule and rate of cabin pressure change.
2016, 33(5):584-594.
Abstract:
A model of autonomous positioning through associating environment memory information is presented for unmanned combat aerial vehicle (UCAV). The representation strategy of environment by constructing place cells is used to produce the memory information, and the landmarks in memory are retrieved through perceiving and processing the environment. During UCAV′s flight, the landmarks are obtained in real-time and are matched with the landmarks in memory. Then, the idea of ranging positioning is adopted to calculate UCAV′s location based on the corresponding relationship between current obtained landmarks and the memorized landmarks. Simulation shows that the proposed model can realize autonomous positioning in the memorized environment, and the positioning performance is well when the sensor has a high precision.
A model of autonomous positioning through associating environment memory information is presented for unmanned combat aerial vehicle (UCAV). The representation strategy of environment by constructing place cells is used to produce the memory information, and the landmarks in memory are retrieved through perceiving and processing the environment. During UCAV′s flight, the landmarks are obtained in real-time and are matched with the landmarks in memory. Then, the idea of ranging positioning is adopted to calculate UCAV′s location based on the corresponding relationship between current obtained landmarks and the memorized landmarks. Simulation shows that the proposed model can realize autonomous positioning in the memorized environment, and the positioning performance is well when the sensor has a high precision.
2016, 33(5):595-601.
Abstract:
The active torsion propulsion mode of a caudal fin, composed of macro fiber composites (MFC) and carbon fiber orthotropic composite material is proposed. The caudal fin is excited by the piezoelectric structure to vibrate flexibly. The work principle is firstly analyzed by finite element method (FEM) and experiments. Then the caudal fin is optimized to increase the torque and improve the streamline, and the added mass effect from the water is discussed in terms of the frequency of the structure. The torsion resonance frequency is around 103 Hz in the air and decreased by 75% to 25 Hz in the water. Finally, the mean thrust is discussed and measured to be 11 mN at 900 V (Ｐeak to peak) driving voltage. A flexible micro robot is developed and tested. The locomotion velocity and flow velocity is 320 mm/s and 268 mm/s， respectively. The results of the simulation and experiments indicate that the locomotion of the biomimetic aquatic robot has fast movement characteristics.
The active torsion propulsion mode of a caudal fin, composed of macro fiber composites (MFC) and carbon fiber orthotropic composite material is proposed. The caudal fin is excited by the piezoelectric structure to vibrate flexibly. The work principle is firstly analyzed by finite element method (FEM) and experiments. Then the caudal fin is optimized to increase the torque and improve the streamline, and the added mass effect from the water is discussed in terms of the frequency of the structure. The torsion resonance frequency is around 103 Hz in the air and decreased by 75% to 25 Hz in the water. Finally, the mean thrust is discussed and measured to be 11 mN at 900 V (Ｐeak to peak) driving voltage. A flexible micro robot is developed and tested. The locomotion velocity and flow velocity is 320 mm/s and 268 mm/s， respectively. The results of the simulation and experiments indicate that the locomotion of the biomimetic aquatic robot has fast movement characteristics.
2016, 33(5):602-609.
Abstract:
Nowadays, energy consumption which closely contacts with environmental impacts of manufacturing processes has been highly commented as a new productivity criterion. However, little attention has paid to the development of process planning methods that take energy consumption into account. An energy-efficient process planning model that incorporates manufacturing time and energy consumption is proposed. For solving the problem, an improved genetic algorithm method is employed to explore the optimal solution. Finally, a case study for process planning is given. The experimental result generates interesting effort, and therefore allows improving the energy efficiency of manufacturing processes in process planning.
Nowadays, energy consumption which closely contacts with environmental impacts of manufacturing processes has been highly commented as a new productivity criterion. However, little attention has paid to the development of process planning methods that take energy consumption into account. An energy-efficient process planning model that incorporates manufacturing time and energy consumption is proposed. For solving the problem, an improved genetic algorithm method is employed to explore the optimal solution. Finally, a case study for process planning is given. The experimental result generates interesting effort, and therefore allows improving the energy efficiency of manufacturing processes in process planning.
2016, 33(5):610-619.
Abstract:
We focus on the electrochemical dissolution characteristics of new titanium alloys such as near-α titanium alloy Ti60, α+β titanium alloy TC4 and β titanium alloy Ti40 which are often used for aerospace industry. The experiments are carried out by electrochemical machining tool, and the surface morphology of the specimens is observed by the scanning electron microscope (SEM) and threedimensional video microscope (DVM). The appropriate electrolyte is selected and the relationships between surface roughness and current density are achieved. The results show that the singlephase titanium alloy Ti40 has a better surface roughness after ECM compared with the α+βtitanium alloy TC4 and the near-α titanium alloy Ti60. The best surface roughness is Ra0.28 μm when the current density is 75 A/cm2. Furthermore, the surface roughness of the near-α titanium alloy Ti60 is the most sensitive with the current density because of the different electrochemical equivalents of substitutional elements and larger grains than TC4. Finally, the suitable current density for each titanium alloy is achieved.
We focus on the electrochemical dissolution characteristics of new titanium alloys such as near-α titanium alloy Ti60, α+β titanium alloy TC4 and β titanium alloy Ti40 which are often used for aerospace industry. The experiments are carried out by electrochemical machining tool, and the surface morphology of the specimens is observed by the scanning electron microscope (SEM) and threedimensional video microscope (DVM). The appropriate electrolyte is selected and the relationships between surface roughness and current density are achieved. The results show that the singlephase titanium alloy Ti40 has a better surface roughness after ECM compared with the α+βtitanium alloy TC4 and the near-α titanium alloy Ti60. The best surface roughness is Ra0.28 μm when the current density is 75 A/cm2. Furthermore, the surface roughness of the near-α titanium alloy Ti60 is the most sensitive with the current density because of the different electrochemical equivalents of substitutional elements and larger grains than TC4. Finally, the suitable current density for each titanium alloy is achieved.
2016, 33(5):620-625.
Abstract:
Numerical analysis is critically important to understanding the complex deformation mechanics that occur during sheet forming processes. It has been widely used in simulation of sheet metal forming processes at room temperature in the automotive industry. However, material at elevated temperature behaves more differently than at room temperature and specific material parameters and models need to be developed for the simulation of warm forming. Based on the experimental investigation of material behavior of high strength aluminum alloy 7075(AA7075), constitutive equations with strain rate sensitivity at 140, 180 and 220 ℃ are developed. Anisotropic yield criterion Barlat 89 is used in the simulation. Warm forming of limit dome height tests and limit drawing ratio tests of AA7075 at 140, 180 and 220 ℃ are performed. Forming limit diagrams developed from experiment at several elevated temperatures in the previous study are used to predict the failure in the simulation results. Punch force and displacement predicted from simulation are compared with the experimental data. Simulation results agree with experimental results, so the developed material model can be used to accurately predict material behavior during isothermal warm forming of the AA7075-T6 alloy.
Numerical analysis is critically important to understanding the complex deformation mechanics that occur during sheet forming processes. It has been widely used in simulation of sheet metal forming processes at room temperature in the automotive industry. However, material at elevated temperature behaves more differently than at room temperature and specific material parameters and models need to be developed for the simulation of warm forming. Based on the experimental investigation of material behavior of high strength aluminum alloy 7075(AA7075), constitutive equations with strain rate sensitivity at 140, 180 and 220 ℃ are developed. Anisotropic yield criterion Barlat 89 is used in the simulation. Warm forming of limit dome height tests and limit drawing ratio tests of AA7075 at 140, 180 and 220 ℃ are performed. Forming limit diagrams developed from experiment at several elevated temperatures in the previous study are used to predict the failure in the simulation results. Punch force and displacement predicted from simulation are compared with the experimental data. Simulation results agree with experimental results, so the developed material model can be used to accurately predict material behavior during isothermal warm forming of the AA7075-T6 alloy.
2016, 33(5):626-632.
Abstract:
Spare parts are critical to scheduled maintenance and fault repair, and can directly affect the readiness and combat capability of equipment. Equipment′s capacity of carrying spares is influenced by its storage space and scales, so it is necessary to consider economic factors,e.g. spares cost, as well as non-economic ones, such as spares volume, mass and scale, when optimizing spares configuration. Aiming at this problem, the optimization model based on multi-constraints for carrying spares is built by METRIC theory and system analysis. Through the introduction of Lagrange factors, the spares cost is transformed to shadow price, and the optimization method for carrying spares and the dynamic adjustment policy of Lagrange factors are proposed.The result of a given example is analyzed, and demonstrates that the proposed model can be optimized with all constraints, and the research can provide a new way for carrying spares optimization.
Spare parts are critical to scheduled maintenance and fault repair, and can directly affect the readiness and combat capability of equipment. Equipment′s capacity of carrying spares is influenced by its storage space and scales, so it is necessary to consider economic factors,e.g. spares cost, as well as non-economic ones, such as spares volume, mass and scale, when optimizing spares configuration. Aiming at this problem, the optimization model based on multi-constraints for carrying spares is built by METRIC theory and system analysis. Through the introduction of Lagrange factors, the spares cost is transformed to shadow price, and the optimization method for carrying spares and the dynamic adjustment policy of Lagrange factors are proposed.The result of a given example is analyzed, and demonstrates that the proposed model can be optimized with all constraints, and the research can provide a new way for carrying spares optimization.
2016, 33(5):633-638.
Abstract:
The mechanisms and processes of sulfate attack on roller compacted concrete (RCC) with MgO expansive agent are proposed by investigating the microstructure and hydration products in specimens immersed in 5% sodium sulfate solution for one year with the optical micrograph, scanning electron microscopy (SEM) and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS). The results show that the deterioration of concrete due to the sulfate attack is mainly loss of stiffness, strength and adhesion, and expansion cracking is mainly caused by the formation of gypsum and ettringite. In the presence of MgO expansive agent, the microstructures of RCC can be improved by hydration and un-hydrated products, the large pores and permeability are reduced, and the resistance to sulfate corrosion of concrete and durability of hydraulic structure are improved slightly.
The mechanisms and processes of sulfate attack on roller compacted concrete (RCC) with MgO expansive agent are proposed by investigating the microstructure and hydration products in specimens immersed in 5% sodium sulfate solution for one year with the optical micrograph, scanning electron microscopy (SEM) and scanning electron microscopy-energy dispersive spectrometer (SEM-EDS). The results show that the deterioration of concrete due to the sulfate attack is mainly loss of stiffness, strength and adhesion, and expansion cracking is mainly caused by the formation of gypsum and ettringite. In the presence of MgO expansive agent, the microstructures of RCC can be improved by hydration and un-hydrated products, the large pores and permeability are reduced, and the resistance to sulfate corrosion of concrete and durability of hydraulic structure are improved slightly.
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