Transactions of Nanjing University of Aeronautics & Astronautics
Volume 36,Issue 3,2019 Table of Contents
2019, 36(3):361-375.
DOI: 10.16356/j.1005-1120.2019.03.001
Abstract:
Weight reduction is a key driving force for materials development in aerospace industry, which leads to extensive usage of lightweight structural materials such as fiber reinforced polymer (FRP), titanium alloy, aluminum alloy, etc. Hole making is indispensable to assembling these lightweight components by riveted or bolted joints. However, hole making of FRP/metal stacks is always the most challenging task due to differences of material properties between FRP and metals. A comprehensive literature review on hole making of FRP/metal stacks in the last decade is given with a focus on four main aspects including drilling operation, drilling damages and machining parameter optimization, tool performance and wear, and developments in hole making technology. Finally, in order to ensure the precise and efficient hole making of FRP/metal stacks, an idea of low frequency vibration assisted drilling (LFVAD) FRP/metal stacks based on material removal characteristics is put forward by fully exploiting the unique advantages of LFVAD technology.
Weight reduction is a key driving force for materials development in aerospace industry, which leads to extensive usage of lightweight structural materials such as fiber reinforced polymer (FRP), titanium alloy, aluminum alloy, etc. Hole making is indispensable to assembling these lightweight components by riveted or bolted joints. However, hole making of FRP/metal stacks is always the most challenging task due to differences of material properties between FRP and metals. A comprehensive literature review on hole making of FRP/metal stacks in the last decade is given with a focus on four main aspects including drilling operation, drilling damages and machining parameter optimization, tool performance and wear, and developments in hole making technology. Finally, in order to ensure the precise and efficient hole making of FRP/metal stacks, an idea of low frequency vibration assisted drilling (LFVAD) FRP/metal stacks based on material removal characteristics is put forward by fully exploiting the unique advantages of LFVAD technology.
2019, 36(3):376-386.
DOI: 10.16356/j.1005-1120.2019.03.002
Abstract:
Biomachining utilizing chemolithotrophic microorganisms for material removal is one of the recently developed non-traditional machining methods offering innovative, low cost and environment-friendly benefits. However, its shortcomings are also obvious, low material removal rate (MRR), poor stability and low surface quality. The effects of temperature, shaking rate, pH value and bacteria concentration on the MRR, machining stability (linearity of material removal-time relationship) and surface roughness (Ra) are investigated using Taguchi methodology. The results indicate that the shaking rate is the most crucial parameter for the MRR and stability of MRR; while temperature is the most influential parameter for surface Ra. The optimum process parameters for overall machining property are temperature of 20 ℃, shaking rate of 160 r/min, pH of 1.8 and bacteria concentration of 3.32 × 107 cells/ml.
Biomachining utilizing chemolithotrophic microorganisms for material removal is one of the recently developed non-traditional machining methods offering innovative, low cost and environment-friendly benefits. However, its shortcomings are also obvious, low material removal rate (MRR), poor stability and low surface quality. The effects of temperature, shaking rate, pH value and bacteria concentration on the MRR, machining stability (linearity of material removal-time relationship) and surface roughness (Ra) are investigated using Taguchi methodology. The results indicate that the shaking rate is the most crucial parameter for the MRR and stability of MRR; while temperature is the most influential parameter for surface Ra. The optimum process parameters for overall machining property are temperature of 20 ℃, shaking rate of 160 r/min, pH of 1.8 and bacteria concentration of 3.32 × 107 cells/ml.
2019, 36(3):387-400.
DOI: 10.16356/j.1005-1120.2019.03.003
Abstract:
The tooth surface friction stiffness and friction torque coefficient equations of cylindrical gear are derived. On the basis of factors such as time-varying friction coefficient and mesh stiffness, support stiffness, torsional stiffness and comprehensive error, the dynamic equations of the gear trains with bending-torsional coupling are established. Using the Fourier series method, the total response of the system is obtained, and the influence of friction on it is analyzed. The results show that when the spur gear enters the meshing, the frictional amplitude of the tooth surface is larger than that of the gear when it is withdrawn from engagement, and the meshing force fluctuates greatly. The frictional force and dynamic meshing force of the herringbone gear tooth surface are relatively stable, and the fluctuation amplitude is much smaller than that of the spur gear. The amplitude of the bearing vibration is not affected by the friction, but the friction has a certain influence on the bearing force of the output shaft. The first-order natural frequency of the split stage and the power confluence stage has a large influence on the vibration of the bearing force. In general, the natural frequency of the power confluence stage has a large proportion of influence.
The tooth surface friction stiffness and friction torque coefficient equations of cylindrical gear are derived. On the basis of factors such as time-varying friction coefficient and mesh stiffness, support stiffness, torsional stiffness and comprehensive error, the dynamic equations of the gear trains with bending-torsional coupling are established. Using the Fourier series method, the total response of the system is obtained, and the influence of friction on it is analyzed. The results show that when the spur gear enters the meshing, the frictional amplitude of the tooth surface is larger than that of the gear when it is withdrawn from engagement, and the meshing force fluctuates greatly. The frictional force and dynamic meshing force of the herringbone gear tooth surface are relatively stable, and the fluctuation amplitude is much smaller than that of the spur gear. The amplitude of the bearing vibration is not affected by the friction, but the friction has a certain influence on the bearing force of the output shaft. The first-order natural frequency of the split stage and the power confluence stage has a large influence on the vibration of the bearing force. In general, the natural frequency of the power confluence stage has a large proportion of influence.
2019, 36(3):401-412.
DOI: 10.16356/j.1005-1120.2019.03.004
Abstract:
To improve the cutting performance of an hourglass worm gear hob and the accuracy of the resulting worm gear, the rake angles of the teeth on the pitch circle should be reduced. A method of forming the spiral flutes by using a variable transmission ratio was developed. This method ensures that the rake angles on the indexing torus of each tooth are approximately 0°. Based on the gear meshing theory and the hourglass worm forming method, the discretization mathematical model of the rake face of a planar double-enveloping worm gear hob was established by using cylindrical generating surface, and the feed parameters for machining the rake face for a variable transmission ratio were obtained. The spiral flute was simulated and the hob was machined on a four-axis CNC milling machine. A contourgraph was used to measure the rake angle. The measurement results showed that the proposed method can reduce the absolute value of the rake angle on both sides of the cutting teeth, which can be used for machining the spiral flute rake face of an hourglass worm gear hob.
To improve the cutting performance of an hourglass worm gear hob and the accuracy of the resulting worm gear, the rake angles of the teeth on the pitch circle should be reduced. A method of forming the spiral flutes by using a variable transmission ratio was developed. This method ensures that the rake angles on the indexing torus of each tooth are approximately 0°. Based on the gear meshing theory and the hourglass worm forming method, the discretization mathematical model of the rake face of a planar double-enveloping worm gear hob was established by using cylindrical generating surface, and the feed parameters for machining the rake face for a variable transmission ratio were obtained. The spiral flute was simulated and the hob was machined on a four-axis CNC milling machine. A contourgraph was used to measure the rake angle. The measurement results showed that the proposed method can reduce the absolute value of the rake angle on both sides of the cutting teeth, which can be used for machining the spiral flute rake face of an hourglass worm gear hob.
2019, 36(3):413-423.
DOI: 10.16356/j.1005-1120.2019.03.005
Abstract:
An active design method of tooth profiles for cycloid gears based on their meshing efficiency is proposed. This method takes the meshing efficiency as one of the design variables to determine the tooth profiles. The calculation method for the meshing efficiency of planetary transmission is analyzed and the equation of the meshing efficiency is deduced. Relationships between the meshing efficiency, the radius of the pin wheel and the eccentric distance are revealed. The design constraint quations and the strength constraint quations are deduced. On the basis of this, a design procedure is laid out. Some examples using different input parameters are conducted to demonstrate the feasibility of the approach. A dynamic simulation of the rigid-flexible coupling of cycloid gears is also presented. The results show that the proposed design method is more flexible to control the tooth profiles by changing the input values of the transmission efficiency.
An active design method of tooth profiles for cycloid gears based on their meshing efficiency is proposed. This method takes the meshing efficiency as one of the design variables to determine the tooth profiles. The calculation method for the meshing efficiency of planetary transmission is analyzed and the equation of the meshing efficiency is deduced. Relationships between the meshing efficiency, the radius of the pin wheel and the eccentric distance are revealed. The design constraint quations and the strength constraint quations are deduced. On the basis of this, a design procedure is laid out. Some examples using different input parameters are conducted to demonstrate the feasibility of the approach. A dynamic simulation of the rigid-flexible coupling of cycloid gears is also presented. The results show that the proposed design method is more flexible to control the tooth profiles by changing the input values of the transmission efficiency.
2019, 36(3):424-431.
DOI: 10.16356/j.1005-1120.2019.03.006
Abstract:
A virtual interventional surgical system with force feedback is designed to provide practice before complicated interventional operation and assistance during operation. The collision detection, vessel deformation calculating and virtual force computing of the virtual system are implemented by using skeleton-spring model as the physical modeling foundation, which is based on the mass-spring model and easy to construct with high computing efficiency. In order to increase the real-time performance, the central plane of the vessel model is extracted and then simplified to complete the skeleton filling. The initiative bending kinematics of the virtual catheter is analyzed so as to provide the virtual system with higher fidelity. The experimental results show that the virtual system can well simulate the vessel deformation and force feedback within an interventional surgery, which gives the virtual system better immersion.
A virtual interventional surgical system with force feedback is designed to provide practice before complicated interventional operation and assistance during operation. The collision detection, vessel deformation calculating and virtual force computing of the virtual system are implemented by using skeleton-spring model as the physical modeling foundation, which is based on the mass-spring model and easy to construct with high computing efficiency. In order to increase the real-time performance, the central plane of the vessel model is extracted and then simplified to complete the skeleton filling. The initiative bending kinematics of the virtual catheter is analyzed so as to provide the virtual system with higher fidelity. The experimental results show that the virtual system can well simulate the vessel deformation and force feedback within an interventional surgery, which gives the virtual system better immersion.
2019, 36(3):432-441.
DOI: 10.16356/j.1005-1120.2019.03.007
Abstract:
A method is proposed to improve the accuracy of remaining useful life prediction for rolling element bearings, based on a state space model (SSM) with different degradation stages and a particle filter. The model is improved by a method based on the Paris formula and the Foreman formula allowing the establishment of different degradation stages. The remaining useful life of rolling element bearings can be predicted by the adjusted model with inputs of physical data and operating status information. The late operating trend is predicted by the use of the particle filter algorithm. The rolling bearing full life experimental data validate the proposed method. Further, the prediction result is compared with the single SSM and the Gamma model, and the results indicate that the predicted accuracy of the proposed method is higher with better practicability.
A method is proposed to improve the accuracy of remaining useful life prediction for rolling element bearings, based on a state space model (SSM) with different degradation stages and a particle filter. The model is improved by a method based on the Paris formula and the Foreman formula allowing the establishment of different degradation stages. The remaining useful life of rolling element bearings can be predicted by the adjusted model with inputs of physical data and operating status information. The late operating trend is predicted by the use of the particle filter algorithm. The rolling bearing full life experimental data validate the proposed method. Further, the prediction result is compared with the single SSM and the Gamma model, and the results indicate that the predicted accuracy of the proposed method is higher with better practicability.
2019, 36(3):442-448.
DOI: 10.16356/j.1005-1120.2019.03.008
Abstract:
The concept of cutting platform is proposed and realized based on the latest two-step automated tape laying (Two-step ATL) technology，which separates prepreg cutting process from tape laying to improve productivity for large parts with small features. Two-step ATL is more efficient than conventional layup because ply patches are pre-cut in a separate operation. The concept of the prepreg tape cutting experimental platform with two cutters is introduced. Further, based on the automatic tape laying trajectory planning software, a two-cutter cutting algorithm is proposed. Cutting experiments are reported to validate both the concept of cutting platform and cutting algorithm.
The concept of cutting platform is proposed and realized based on the latest two-step automated tape laying (Two-step ATL) technology，which separates prepreg cutting process from tape laying to improve productivity for large parts with small features. Two-step ATL is more efficient than conventional layup because ply patches are pre-cut in a separate operation. The concept of the prepreg tape cutting experimental platform with two cutters is introduced. Further, based on the automatic tape laying trajectory planning software, a two-cutter cutting algorithm is proposed. Cutting experiments are reported to validate both the concept of cutting platform and cutting algorithm.
2019, 36(3):449-458.
DOI: 10.16356/j.1005-1120.2019.03.009
Abstract:
An investigation is conducted on optimizing the control allocation for trimmed flight on the compound helicopter. The compound helicopter features a single main rotor, a vectored thrust ducted propeller (VTDP) and lifting wings. Due to the redundant controls for thrust, elevator deflection, and differential and symmetric flap deflection, there is a wide range of trim solutions in forward flight for compound helicopter. A method is developed to calculate optimal trim solutions. Firstly, aerodynamics models for deferent subsystems of the compound helicopter are conducted, which consider the mutual interaction of each part. Secondly, a flight dynamics model is developed based on which the method of trim optimization is performed. Finally, the method is demonstrated using a compound helicopter UH-60L/VTDP. The trim optimization of flight conditions from hover to 370 km/h is conducted using the optimization method. The controls, fuselage attitudes as well as the allocation of lift and thrust along with the flight speed are obtained.
An investigation is conducted on optimizing the control allocation for trimmed flight on the compound helicopter. The compound helicopter features a single main rotor, a vectored thrust ducted propeller (VTDP) and lifting wings. Due to the redundant controls for thrust, elevator deflection, and differential and symmetric flap deflection, there is a wide range of trim solutions in forward flight for compound helicopter. A method is developed to calculate optimal trim solutions. Firstly, aerodynamics models for deferent subsystems of the compound helicopter are conducted, which consider the mutual interaction of each part. Secondly, a flight dynamics model is developed based on which the method of trim optimization is performed. Finally, the method is demonstrated using a compound helicopter UH-60L/VTDP. The trim optimization of flight conditions from hover to 370 km/h is conducted using the optimization method. The controls, fuselage attitudes as well as the allocation of lift and thrust along with the flight speed are obtained.
2019, 36(3):459-467.
DOI: 10.16356/j.1005-1120.2019.03.011
Abstract:
This paper presents a method to design a control scheme for nonlinear systems using fuzzy optimal control. In the design process, the nonlinear system is first converted into local subsystems using sector non-linearity approach of Takagi-Sugeno (T-S) fuzzy modeling. For each local subsystem, an optimal control is designed. Then, the parameters of local controllers are defuzzified to construct a global optimal controller. To prove the effectiveness of this control scheme, simulations are performed using the mathematical model of Esso Osaka tanker ship for set-point regulation with and without disturbance and reference tracking. In addition, the simulation results are compared with that of a PID controller for further verification and validation. It has been shown that the proposed optimal controller can be used for the nonlinear ship steering with good rise time, zero steady state error and fast settling time.
This paper presents a method to design a control scheme for nonlinear systems using fuzzy optimal control. In the design process, the nonlinear system is first converted into local subsystems using sector non-linearity approach of Takagi-Sugeno (T-S) fuzzy modeling. For each local subsystem, an optimal control is designed. Then, the parameters of local controllers are defuzzified to construct a global optimal controller. To prove the effectiveness of this control scheme, simulations are performed using the mathematical model of Esso Osaka tanker ship for set-point regulation with and without disturbance and reference tracking. In addition, the simulation results are compared with that of a PID controller for further verification and validation. It has been shown that the proposed optimal controller can be used for the nonlinear ship steering with good rise time, zero steady state error and fast settling time.
2019, 36(3):468-478.
DOI: 10.16356/j.1005-1120.2019.03.011
Abstract:
In order to enhance the safety of the catapult launch of the carrier-based aircraft, the catapult launch multi-body dynamic model is established aiming at the problem of off-center catapult launch. The whole catapult process including four stages which are buffering, tensioning, releasing and taxiing is taken into consideration and the body dynamics of the off-center catapult during each stage is analyzed. The catapult launch dynamic differences between the conditions only considering taxiing and that considering four stages are compared, and the effects of the different initial off-center distances considering four stages on the attitude, landing gear load and acceleration of the carrier-based aircraft during catapult launch are discussed. The results show that only considering taxiing may underestimate the dynamics of the carrier-based aircraft substantially. When taking four stages into consideration, the initial off-center distance has small influence on the aircraft dynamic characteristics during buffering and tensioning but has larger influence on that during releasing and taxiing. The increase of the off-center distance will cause the enhancement of the aircraft rolling and yawing, which may lead to the load difference between the left and right landing gears and the increase of the aircraft lateral acceleration. The establishment and simulation of the catapult launch multi-body dynamic model founded on buffering, tensioning, releasing and taxiing provide reference for the carrier-based aircraft design and analysis of the catapult launch dynamics.
In order to enhance the safety of the catapult launch of the carrier-based aircraft, the catapult launch multi-body dynamic model is established aiming at the problem of off-center catapult launch. The whole catapult process including four stages which are buffering, tensioning, releasing and taxiing is taken into consideration and the body dynamics of the off-center catapult during each stage is analyzed. The catapult launch dynamic differences between the conditions only considering taxiing and that considering four stages are compared, and the effects of the different initial off-center distances considering four stages on the attitude, landing gear load and acceleration of the carrier-based aircraft during catapult launch are discussed. The results show that only considering taxiing may underestimate the dynamics of the carrier-based aircraft substantially. When taking four stages into consideration, the initial off-center distance has small influence on the aircraft dynamic characteristics during buffering and tensioning but has larger influence on that during releasing and taxiing. The increase of the off-center distance will cause the enhancement of the aircraft rolling and yawing, which may lead to the load difference between the left and right landing gears and the increase of the aircraft lateral acceleration. The establishment and simulation of the catapult launch multi-body dynamic model founded on buffering, tensioning, releasing and taxiing provide reference for the carrier-based aircraft design and analysis of the catapult launch dynamics.
2019, 36(3):479-487.
DOI: 10.16356/j.1005-1120.2019.03.012
Abstract:
The car surface scratch detection adopts the traditional manual detection with poor efficiency and high missing rate. Because of the gray mark and the background of car surface scratches, the traditional edge detection algorithm cannot meet the needs of car surface scratch detection. Therefore, the directional SUSAN algorithm based on CIELab color space is adopted in this paper. The direction template and the circle template to calculate the color difference of the color image are used in the algorithm which has been converted to the CIELab space. The edges and scratches are eliminated by matching and contrasting the detected image with the edge template. Experimental results show that the algorithm can effectively detect scratches on the surface of cars, improve the detection speed and reduce the undetected rate.
The car surface scratch detection adopts the traditional manual detection with poor efficiency and high missing rate. Because of the gray mark and the background of car surface scratches, the traditional edge detection algorithm cannot meet the needs of car surface scratch detection. Therefore, the directional SUSAN algorithm based on CIELab color space is adopted in this paper. The direction template and the circle template to calculate the color difference of the color image are used in the algorithm which has been converted to the CIELab space. The edges and scratches are eliminated by matching and contrasting the detected image with the edge template. Experimental results show that the algorithm can effectively detect scratches on the surface of cars, improve the detection speed and reduce the undetected rate.
2019, 36(3):488-499.
DOI: 10.16356/j.1005-1120.2019.03.013
Abstract:
A three-dimensional dynamic damage model that fits both small and large damage sizes is developed to predict impact damage initiation and propagation for each lamina of T300-carbon/epoxy laminations. First, 13 specimens of the same lamination sequence are subjected to three different impact energies (10 J, 15 J, and 20 J). After the impact, the laminates are inspected by the naked eye to observe the damage in the outer layers, and subsequently X-rayed to detect the inner damage. Next, the stress analysis of laminates subjected to impact loading is presented, based on the Hertz contact law and virtual displacement principle. Based on the analysis results, a three-dimensional dynamic damage model is proposed, including the Hou failure criteria and Camanho stiffness degradation model, to predict the impact damage shape and area. The numerical predictions of the damage shape and area show a relatively reasonable agreement with the experiments. Finally, the impact damage initiation and propagation for each lamina are investigated using this damage model, and the results improve the understanding of the impact process.
A three-dimensional dynamic damage model that fits both small and large damage sizes is developed to predict impact damage initiation and propagation for each lamina of T300-carbon/epoxy laminations. First, 13 specimens of the same lamination sequence are subjected to three different impact energies (10 J, 15 J, and 20 J). After the impact, the laminates are inspected by the naked eye to observe the damage in the outer layers, and subsequently X-rayed to detect the inner damage. Next, the stress analysis of laminates subjected to impact loading is presented, based on the Hertz contact law and virtual displacement principle. Based on the analysis results, a three-dimensional dynamic damage model is proposed, including the Hou failure criteria and Camanho stiffness degradation model, to predict the impact damage shape and area. The numerical predictions of the damage shape and area show a relatively reasonable agreement with the experiments. Finally, the impact damage initiation and propagation for each lamina are investigated using this damage model, and the results improve the understanding of the impact process.
2019, 36(3):500-509.
DOI: 10.16356/j.1005-1120.2019.03.014
Abstract:
Considering the influencing factors of the layout of solar collectors such as the tilt angles, azimuth angles, spacing between collectors and the number of collector rows, a mathematical model of the collected energy of the solar collector with limited area on the horizontal plane is established. Two different optimized models including the cost-benefit model and the minimum annual auxiliary heating energy model are conducted in this paper. The results show that, the collected energy in a year could increase with the increase of the number of collector rows. And the collected solar radiation in a year increases firstly and then decreases with the increase of the collector tilt angles. Furthermore, the collected solar radiation in a year increases firstly and then decreases with the continuous increase of the azimuth angles from -90° to 90°. Taking Nanjing city of China as an example, based on the optimized objective of maximum benefit, the optimal layout of the solar collector array in the area of 200 m2 should include: the number of collector rows is 8, the tilt angle is 40° and the azimuth angle is 0°. Meanwhile, the optimal methods for the optimized objective of minimum annual auxiliary heating energy should include: the number of collector rows is 9, the tilt angle is 50°, and the azimuth angle is 0°.
Considering the influencing factors of the layout of solar collectors such as the tilt angles, azimuth angles, spacing between collectors and the number of collector rows, a mathematical model of the collected energy of the solar collector with limited area on the horizontal plane is established. Two different optimized models including the cost-benefit model and the minimum annual auxiliary heating energy model are conducted in this paper. The results show that, the collected energy in a year could increase with the increase of the number of collector rows. And the collected solar radiation in a year increases firstly and then decreases with the increase of the collector tilt angles. Furthermore, the collected solar radiation in a year increases firstly and then decreases with the continuous increase of the azimuth angles from -90° to 90°. Taking Nanjing city of China as an example, based on the optimized objective of maximum benefit, the optimal layout of the solar collector array in the area of 200 m2 should include: the number of collector rows is 8, the tilt angle is 40° and the azimuth angle is 0°. Meanwhile, the optimal methods for the optimized objective of minimum annual auxiliary heating energy should include: the number of collector rows is 9, the tilt angle is 50°, and the azimuth angle is 0°.
2019, 36(3):510-516.
DOI: 10.16356/j.1005-1120.2019.03.015
Abstract:
Acoustic metasurface has attracted increasing attention due to the ability of manipulating the transmitted and reflected phase of waves to generate various acoustic functionalities with planar layer of sub-wavelength structure. We design an acoustic metasurface with a semi-closed and nested slotted tube array, and it possesses the capacity of modulating the reflected phase with sub-wavelength thickness (about λ/23). The reflected phase shifts can be obtained from 0 to 2π by different rotation angles of internal slotted tubes. The theoretical results agree well with the numerical results by a finite element method. The results show that some excellent wavefront manipulations are demonstrated with the phase array by using acoustic metasurface such as anomalous reflection and sub-wavelength flat focusing. The design may offer a path for acoustic manipulation and promote the potential applications of acoustic metasurface in low frequency noise control, acoustic imaging and cloaking.
Acoustic metasurface has attracted increasing attention due to the ability of manipulating the transmitted and reflected phase of waves to generate various acoustic functionalities with planar layer of sub-wavelength structure. We design an acoustic metasurface with a semi-closed and nested slotted tube array, and it possesses the capacity of modulating the reflected phase with sub-wavelength thickness (about λ/23). The reflected phase shifts can be obtained from 0 to 2π by different rotation angles of internal slotted tubes. The theoretical results agree well with the numerical results by a finite element method. The results show that some excellent wavefront manipulations are demonstrated with the phase array by using acoustic metasurface such as anomalous reflection and sub-wavelength flat focusing. The design may offer a path for acoustic manipulation and promote the potential applications of acoustic metasurface in low frequency noise control, acoustic imaging and cloaking.
2019, 36(3):517-526.
DOI: 10.16356/j.1005-1120.2019.03.016
Abstract:
This paper aims to obtain the thermodynamic characteristics of the air system control device sealing part in different compressor bleed air and ambient temperature. On the basis of considering the main factors affecting the heat exchange process and simplifying the physical model of the air system control device, the thermodynamic model of air system control device is established based on the basic theory of laminar flow heat transfer and heat conduction theory. Then the piston motion characteristics and the thermodynamic characteristics of the air system control device seal are simulated. The simulation results show that the valve actuation dynamic time of piston is about 0.13 s in the actual working conditions, and the temperature effect on the dynamic response of the piston rod is only 5 ms when the inlet air temperature at 300 ℃ and 370 ℃. The maximum temperature of the air system control device sealing part is not more than 290 ℃ under long time working condition of compressor air entraining. The highest temperature of the sealing part can reach up to 340 ℃ when the air flow temperature reaches the limit temperature of 370 ℃, and the longest duration working temperature limit is not more than 14 s. Therefore, the selection of control device sealing material should consider the work characteristic of instantaneous temperature limit.
This paper aims to obtain the thermodynamic characteristics of the air system control device sealing part in different compressor bleed air and ambient temperature. On the basis of considering the main factors affecting the heat exchange process and simplifying the physical model of the air system control device, the thermodynamic model of air system control device is established based on the basic theory of laminar flow heat transfer and heat conduction theory. Then the piston motion characteristics and the thermodynamic characteristics of the air system control device seal are simulated. The simulation results show that the valve actuation dynamic time of piston is about 0.13 s in the actual working conditions, and the temperature effect on the dynamic response of the piston rod is only 5 ms when the inlet air temperature at 300 ℃ and 370 ℃. The maximum temperature of the air system control device sealing part is not more than 290 ℃ under long time working condition of compressor air entraining. The highest temperature of the sealing part can reach up to 340 ℃ when the air flow temperature reaches the limit temperature of 370 ℃, and the longest duration working temperature limit is not more than 14 s. Therefore, the selection of control device sealing material should consider the work characteristic of instantaneous temperature limit.
2019, 36(3):527-536.
DOI: 10.16356/j.1005-1120.2019.03.017
Abstract:
The aim of the present study is to investigate the brain functional network changes of patients with frontal lobe epilepsy (FLE) by resting-state functional magnetic resonance imaging (rsfMRI) and graph theoretical analysis. rsfMRI is performed in 46 adult patients with FLE and 46 age-matched healthy controls (HCs). A functional network is built from these subjects, and the topological properties of such network are analyzed quantitatively using graph theoretical methods. According to the results, both FLE patients and HCs exhibit prominent small-world features. Compared with HCs, FLE shows a decrease in local efficiency (Eloc), clustering coefficient, nodal efficiency as well as nodal degree. Furthermore, FLE (seven) has fewer hubs than HCs (ten). The functional abnormalities in the network organization suggest functional disturbances in patients with FLE. This study helps to gain new insights into the functional disorder in patients with FLE. The networks built here can also be a set of potential biomarkers for the diagnosis, monitoring and the treatment of FLE.
The aim of the present study is to investigate the brain functional network changes of patients with frontal lobe epilepsy (FLE) by resting-state functional magnetic resonance imaging (rsfMRI) and graph theoretical analysis. rsfMRI is performed in 46 adult patients with FLE and 46 age-matched healthy controls (HCs). A functional network is built from these subjects, and the topological properties of such network are analyzed quantitatively using graph theoretical methods. According to the results, both FLE patients and HCs exhibit prominent small-world features. Compared with HCs, FLE shows a decrease in local efficiency (Eloc), clustering coefficient, nodal efficiency as well as nodal degree. Furthermore, FLE (seven) has fewer hubs than HCs (ten). The functional abnormalities in the network organization suggest functional disturbances in patients with FLE. This study helps to gain new insights into the functional disorder in patients with FLE. The networks built here can also be a set of potential biomarkers for the diagnosis, monitoring and the treatment of FLE.
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