Transactions of Nanjing University of Aeronautics & Astronautics
Volume 35,Issue 6,2018 Table of Contents
2018, 35(6):913-923.
DOI: 10.16356/j.1005-1120.2018.06.913
Abstract:
The space target imaging is important in the development of space technology. Due to the availability of trajectory information of the space targets and the arising of rapid parallel processing hardware, the back projection (BP) method has been applied to synthetic aperture radar (SAR) imaging and shows a number of advantages as compared with conventional Fourier-domain imaging algorithms. However, the practical processing shows that the insufficient accuracy of the trajectory information results in the degrading of the imaging results. On the other hand, the autofocusing algorithms for BP imaging are not well developed, which is a bottleneck for the application of BP imaging. Here, an analysis of the effect of trajectory errors on the space target imaging using microlocal technology is presented. Our analysis provides an explicit quantitative relationship between the trajectory errors of the space target and the positioning errors in the reconstructed images. The explicit form of the position errors for some typical trajectory errors is also presented. Numerical simulations demonstrate our theoretical findings. The measured position errors obtained from the reconstructed images are consistent with the analytic errors calculated by using the derived formulas. Our results will be used in the development of effective autofocusing methods for BP imaging.
The space target imaging is important in the development of space technology. Due to the availability of trajectory information of the space targets and the arising of rapid parallel processing hardware, the back projection (BP) method has been applied to synthetic aperture radar (SAR) imaging and shows a number of advantages as compared with conventional Fourier-domain imaging algorithms. However, the practical processing shows that the insufficient accuracy of the trajectory information results in the degrading of the imaging results. On the other hand, the autofocusing algorithms for BP imaging are not well developed, which is a bottleneck for the application of BP imaging. Here, an analysis of the effect of trajectory errors on the space target imaging using microlocal technology is presented. Our analysis provides an explicit quantitative relationship between the trajectory errors of the space target and the positioning errors in the reconstructed images. The explicit form of the position errors for some typical trajectory errors is also presented. Numerical simulations demonstrate our theoretical findings. The measured position errors obtained from the reconstructed images are consistent with the analytic errors calculated by using the derived formulas. Our results will be used in the development of effective autofocusing methods for BP imaging.
2018, 35(6):924-941.
DOI: 10.16356/j.1005-1120.2018.06.924
Abstract:
The incidence and mortality of cardiovascular diseases and gastrointestinal cancer have gradually increased in recent years, and these diseases have become major social and public-health concerns. New requirements have been proposed for the clinical diagnosis of these diseases in the hope that, by accessing accurate structural information, to further grasp the functional information which closely related to the development of the diseases. Photoacoustic imaging is a new imaging method in which ultrasonic signals are generated from biological samples by laser-pulse irradiation. It has the advantages of high optical contrast, large ultrasound penetration depth, and high resolution. Additionally, it can acquire spectral information. The integration of a photoacoustic imaging system into a tiny imaging catheter can realize interventional imaging based on photoacoustic principles. The combination of structural imaging of cardiovascular and gastrointestinal lesion regions with photoacoustic spectroscopy to identify and quantify tissue components can realize highly sensitive functional imaging. After surveying the recent progress in the development of the photoacoustic imaging method for interventional application, with a particular emphasis on intravascular photoacoustic imaging, photoacoustic endoscopy, and photoacoustic spectroscopy, we summarize and identify future research directions for interventional photoacoustic imaging.
The incidence and mortality of cardiovascular diseases and gastrointestinal cancer have gradually increased in recent years, and these diseases have become major social and public-health concerns. New requirements have been proposed for the clinical diagnosis of these diseases in the hope that, by accessing accurate structural information, to further grasp the functional information which closely related to the development of the diseases. Photoacoustic imaging is a new imaging method in which ultrasonic signals are generated from biological samples by laser-pulse irradiation. It has the advantages of high optical contrast, large ultrasound penetration depth, and high resolution. Additionally, it can acquire spectral information. The integration of a photoacoustic imaging system into a tiny imaging catheter can realize interventional imaging based on photoacoustic principles. The combination of structural imaging of cardiovascular and gastrointestinal lesion regions with photoacoustic spectroscopy to identify and quantify tissue components can realize highly sensitive functional imaging. After surveying the recent progress in the development of the photoacoustic imaging method for interventional application, with a particular emphasis on intravascular photoacoustic imaging, photoacoustic endoscopy, and photoacoustic spectroscopy, we summarize and identify future research directions for interventional photoacoustic imaging.
2018, 35(6):942-951.
DOI: 10.16356/j.1005-1120.2018.06.942
Abstract:
Effects of tip slots on the aerodynamic characteristics of helicopter rotor were investigated numerically by solving three-dimensional Navier-Stokes equations based on unstructured overset grids algorithm. Improved delayed detached eddy simulation (IDDES) based on the Spalart-Allmaras turbulence model and adaptive grid refinement technique were employed. Several slots in the rotor blade tip were designed on the base of Caradonna-Tung rotor to study the effect of tip slots. Numerical results show that tip slots are able to introduce the airflow from the leading edge and turn it in the spanwise direction to be ejected out of the face at the rotor blade tip, which can reduce the strength of the rotor blade tip vortex and accelerate the dissipation process. Although tip slots may lead to the decrease of airfoils' lift coefficient at the root of the rotor blade, it can increase the lift coefficient of airfoils at the rotor blade tip, so the lift of the rotor with tip slots is almost the same as that of the rotor without tip slots. In addition, tip slots can also reduce the intensity of the tip shock wave, which is beneficial to reduce the wave drag of the rotor.
Effects of tip slots on the aerodynamic characteristics of helicopter rotor were investigated numerically by solving three-dimensional Navier-Stokes equations based on unstructured overset grids algorithm. Improved delayed detached eddy simulation (IDDES) based on the Spalart-Allmaras turbulence model and adaptive grid refinement technique were employed. Several slots in the rotor blade tip were designed on the base of Caradonna-Tung rotor to study the effect of tip slots. Numerical results show that tip slots are able to introduce the airflow from the leading edge and turn it in the spanwise direction to be ejected out of the face at the rotor blade tip, which can reduce the strength of the rotor blade tip vortex and accelerate the dissipation process. Although tip slots may lead to the decrease of airfoils' lift coefficient at the root of the rotor blade, it can increase the lift coefficient of airfoils at the rotor blade tip, so the lift of the rotor with tip slots is almost the same as that of the rotor without tip slots. In addition, tip slots can also reduce the intensity of the tip shock wave, which is beneficial to reduce the wave drag of the rotor.
2018, 35(6):952-961.
DOI: 10.16356/j.1005-1120.2018.06.952
Abstract:
Due to the complexity of strong metal interference and multiple occlusions in aircraft assembly workshop, the random "drift" phenomenon often happens in the ultra wide band (UWB) based positioning system. To solve this, a fusion positioning optimization algorithm is proposed based on median filtering, hidden Markov model (HMM) and Kalman filtering. Firstly, based on the three-dimensional (3D) median filtering, a queue optimization method with weights is introduced to smooth the measurement data and eliminate the abnormal value. Secondly, taking Singer model as a reference, a single-dimension acceleration distribution model is designed. In order to further consider the spatial motion characteristics of objects in workshop, the distribution is extended from 1D to 3D, and discretized into the state quantity of HMM. Subsequently, the data obtained by the two methods are fused by taking Kalman filter as an iterator, and then the optimized location solution is obtained based on dynamic weights. Finally, an experiment is conducted in an aircraft assembly workshop. Results show that 99.3% of dynamic positioning errors are less than 15 cm after using the proposed algorithm. Even in the situation with large signal-fluctuation, there are 71.6% of positioning data whose errors are reduced. The random "drift" is greatly decreased.
Due to the complexity of strong metal interference and multiple occlusions in aircraft assembly workshop, the random "drift" phenomenon often happens in the ultra wide band (UWB) based positioning system. To solve this, a fusion positioning optimization algorithm is proposed based on median filtering, hidden Markov model (HMM) and Kalman filtering. Firstly, based on the three-dimensional (3D) median filtering, a queue optimization method with weights is introduced to smooth the measurement data and eliminate the abnormal value. Secondly, taking Singer model as a reference, a single-dimension acceleration distribution model is designed. In order to further consider the spatial motion characteristics of objects in workshop, the distribution is extended from 1D to 3D, and discretized into the state quantity of HMM. Subsequently, the data obtained by the two methods are fused by taking Kalman filter as an iterator, and then the optimized location solution is obtained based on dynamic weights. Finally, an experiment is conducted in an aircraft assembly workshop. Results show that 99.3% of dynamic positioning errors are less than 15 cm after using the proposed algorithm. Even in the situation with large signal-fluctuation, there are 71.6% of positioning data whose errors are reduced. The random "drift" is greatly decreased.
2018, 35(6):962-972.
DOI: 10.16356/j.1005-1120.2018.06.962
Abstract:
The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments. Reynolds numbers studied in the channel range from 1 400 to 8 000. The ratios of rib height to hydraulic diameter (e/D) are 0.2 and 0.33, respectively. The ratio of rib spacing to height(P/e) ranges from 5 to 15. The rib orientations in the opposite surfaces are symmetrical and staggered arrangements. The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number, though at the cost of higher pressure losses. When the rib spacing to height ratio is 10, it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5, 10 and 15. The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs, but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.
The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments. Reynolds numbers studied in the channel range from 1 400 to 8 000. The ratios of rib height to hydraulic diameter (e/D) are 0.2 and 0.33, respectively. The ratio of rib spacing to height(P/e) ranges from 5 to 15. The rib orientations in the opposite surfaces are symmetrical and staggered arrangements. The results show that the heat transfer coefficients are increased with the increase of rib height and Reynolds number, though at the cost of higher pressure losses. When the rib spacing to height ratio is 10, it keeps the highest heat transfer coefficient in three kinds of rib spacing to height ratios 5, 10 and 15. The heat transfer coefficient of symmetrical arrangement ribs is higher than that of the staggered arrangement ribs, but the pressure loss of the symmetrical arrangement ribs is larger than that of the staggered arrangement ribs.
2018, 35(6):973-985.
DOI: 10.16356/j.1005-1120.2018.06.973
Abstract:
A synchronization method is developed for the fluid-thermal study of hypersonic flow. Different from conventional loosely/tightly coupled methods which separately deal with the flow field and the structure temperature field, the presented method expresses the governing equations in a unified framework so that the two fields can be calculated simultaneously. For efficiently solving the unified equations, the finite volume method together with the dual-time stepping approach is employed. Like in the flow field, the local time step is also used in the temperature field, which is determined from thermal conductivity spectral radii. In order to treat the fluid-structure interface more conveniently, an expanded virtual boundary is introduced. For validation, several fluid-thermal hypersonic flow problems are simulated. The computed results are compared with those obtained from the coupled methods and the experiment. In the continuous heating problems, the stagnation temperatures predicted by both the coupled and synchronization methods are in good agreements with the experimental data. In the unsteady flow-thermal hypersonic flows, the stagnation heat fluxes predicted by the presented method and tightly coupled method are basically the same, which agree better with the experimental data than those predicted by the loosely coupled method. In terms of prediction of the stagnation temperature, the synchronization method shows better accuracy than the tightly coupled method.
A synchronization method is developed for the fluid-thermal study of hypersonic flow. Different from conventional loosely/tightly coupled methods which separately deal with the flow field and the structure temperature field, the presented method expresses the governing equations in a unified framework so that the two fields can be calculated simultaneously. For efficiently solving the unified equations, the finite volume method together with the dual-time stepping approach is employed. Like in the flow field, the local time step is also used in the temperature field, which is determined from thermal conductivity spectral radii. In order to treat the fluid-structure interface more conveniently, an expanded virtual boundary is introduced. For validation, several fluid-thermal hypersonic flow problems are simulated. The computed results are compared with those obtained from the coupled methods and the experiment. In the continuous heating problems, the stagnation temperatures predicted by both the coupled and synchronization methods are in good agreements with the experimental data. In the unsteady flow-thermal hypersonic flows, the stagnation heat fluxes predicted by the presented method and tightly coupled method are basically the same, which agree better with the experimental data than those predicted by the loosely coupled method. In terms of prediction of the stagnation temperature, the synchronization method shows better accuracy than the tightly coupled method.
2018, 35(6):986-991.
DOI: 10.16356/j.1005-1120.2018.06.986
Abstract:
Aiming to decrease the vibration of wing induced by dual-rotor civil turbofan engines, the dynamic models of a single-degree of freedom (DOF) linear main oscillator coupled with single-DOF and two-DOF nonlinear energy sink (NES) are established. According to the related energy criteria for the optimization of the dynamic vibration absorber, focusing on the effects of external excitation on the kinetic energy of the primary mass and total system energy, the vibration suppression effects of single-DOF, two-DOF serial and parallel NES on the main oscillator system are studied. Under the condition that the characteristic parameters of the main oscillator system and additional total mass of the vibration absorber remain unchanged, results show that the two-DOF parallel NES has the best vibration energy suppression effects, which can provide data reference for the optimal design of NES vibration suppression under dual-frequency excitation.
Aiming to decrease the vibration of wing induced by dual-rotor civil turbofan engines, the dynamic models of a single-degree of freedom (DOF) linear main oscillator coupled with single-DOF and two-DOF nonlinear energy sink (NES) are established. According to the related energy criteria for the optimization of the dynamic vibration absorber, focusing on the effects of external excitation on the kinetic energy of the primary mass and total system energy, the vibration suppression effects of single-DOF, two-DOF serial and parallel NES on the main oscillator system are studied. Under the condition that the characteristic parameters of the main oscillator system and additional total mass of the vibration absorber remain unchanged, results show that the two-DOF parallel NES has the best vibration energy suppression effects, which can provide data reference for the optimal design of NES vibration suppression under dual-frequency excitation.
2018, 35(6):992-999.
DOI: 10.16356/j.1005-1120.2018.06.992
Abstract:
The fluid-structure interaction (FSI) between the canopy and flow field on the inflating and inflated conditions is investigated based on the arbitrary Lagrange-Euler (ALE) method, in both a single-and double-cruciform parachute systems. The projection area of canopy is calculated in the inflation process. The flow field characteristics and the interaction between canopies are analyzed. Results showed that, with free stream velocity of 50 m/s, overinflation phenomenon would not occur during the inflation process of the double-cruciform-parachute system, because the collision and extrusion of the two canopies during inflation obstructed the oscillation of the inner gores. Concurrently, compared with the single-cruciform parachute, the vortex motion in the wake of double-cruciform-parachute is more intense. Thus the double-cruciform parachute system oscillated at a velocity of 50 m/s with an angle of less than 6.8°. By comparison, the oscillation angle of the single-cruciform parachute was within 3.5° at the velocity of 50 m/s. The results are consistent with those of the wind tunnel test.
The fluid-structure interaction (FSI) between the canopy and flow field on the inflating and inflated conditions is investigated based on the arbitrary Lagrange-Euler (ALE) method, in both a single-and double-cruciform parachute systems. The projection area of canopy is calculated in the inflation process. The flow field characteristics and the interaction between canopies are analyzed. Results showed that, with free stream velocity of 50 m/s, overinflation phenomenon would not occur during the inflation process of the double-cruciform-parachute system, because the collision and extrusion of the two canopies during inflation obstructed the oscillation of the inner gores. Concurrently, compared with the single-cruciform parachute, the vortex motion in the wake of double-cruciform-parachute is more intense. Thus the double-cruciform parachute system oscillated at a velocity of 50 m/s with an angle of less than 6.8°. By comparison, the oscillation angle of the single-cruciform parachute was within 3.5° at the velocity of 50 m/s. The results are consistent with those of the wind tunnel test.
2018, 35(6):1000-1009.
DOI: 10.16356/j.1005-1120.2018.06.1000
Abstract:
We investigate couplings between variables of attitude dynamics for a hypersonic aircraft, and present a nonlinear robust coordinated control scheme for it. First, we design three kinds of coordinated factors to restrain the strong couplings. Then, we use projection mapping to estimate the uncertain nonlinear functions of the aircraft. Combining the coordinated factors and the designed control laws, we obtain a coordinated torque and assign it to the control deflection commands by using the allocation matrix. A stability analysis demonstrates that all the signals of the closed-loop system are uniformly and fully bounded. Finally, the robust coordinated performance of the designed scheme is verified through numerical simulations.
We investigate couplings between variables of attitude dynamics for a hypersonic aircraft, and present a nonlinear robust coordinated control scheme for it. First, we design three kinds of coordinated factors to restrain the strong couplings. Then, we use projection mapping to estimate the uncertain nonlinear functions of the aircraft. Combining the coordinated factors and the designed control laws, we obtain a coordinated torque and assign it to the control deflection commands by using the allocation matrix. A stability analysis demonstrates that all the signals of the closed-loop system are uniformly and fully bounded. Finally, the robust coordinated performance of the designed scheme is verified through numerical simulations.
10 Dynamic Constitutive Model of Physical Simulation in High-Speed Blanking for C5191 Phosphor Bronze
2018, 35(6):1010-1017.
DOI: 10.16356/j.1005-1120.2018.06.1010
Abstract:
Strain hardening, strain rate strengthening and thermal softening data of C5191 phosphor bronze at high-speed blanking are not easy to be obtained with a general measure method, therefore, it is quite difficult to establish the dynamic constitutive model. To solve this problem, the tensile properties at a strain rate of 1 s-1 by GLEEBLE-3500, and dynamic tensile conditions at strain rates of 500, 1 000 and 1 500 s-1 by split Hopkinson tensile bar (SHTB) apparatus are studied. According to these test data, the classic Johnson-Cook equation is modified. Furthermore, the modified Johnson-Cook equation is validated in the physical simulation model of high-speed blanking. The results show that the strength of C5191 phosphor bronze maintains a certain degree of increase as the strain rate increasing and presents a clear sensitivity to strain rate. The modified Johnson-Cook equation, which has better description accuracy than the classical Johnson-Cook equation, can provide important material parameters for physical simulation models of its high-speed blanking process.
Strain hardening, strain rate strengthening and thermal softening data of C5191 phosphor bronze at high-speed blanking are not easy to be obtained with a general measure method, therefore, it is quite difficult to establish the dynamic constitutive model. To solve this problem, the tensile properties at a strain rate of 1 s-1 by GLEEBLE-3500, and dynamic tensile conditions at strain rates of 500, 1 000 and 1 500 s-1 by split Hopkinson tensile bar (SHTB) apparatus are studied. According to these test data, the classic Johnson-Cook equation is modified. Furthermore, the modified Johnson-Cook equation is validated in the physical simulation model of high-speed blanking. The results show that the strength of C5191 phosphor bronze maintains a certain degree of increase as the strain rate increasing and presents a clear sensitivity to strain rate. The modified Johnson-Cook equation, which has better description accuracy than the classical Johnson-Cook equation, can provide important material parameters for physical simulation models of its high-speed blanking process.
2018, 35(6):1018-1026.
DOI: 10.16356/j.1005-1120.2018.06.1018
Abstract:
A six-axis force sensor with parallel 8/4-4 structure is introduced and its measurement principle is analyzed. Based on condition numbers of Jacobian matrix spectral norm of the sensor, the relationship between the force and moment isotropy and some structural parameters is deduced. Orthogonal test methods are used to determine the degree of primary and secondary factors that have significant effect on sensor characteristics. Furthermore, the relationship between each performance index and the structural parameters of the sensor is analyzed by the method of the atlas, which lays a foundation for structural optimization design of the force sensor.
A six-axis force sensor with parallel 8/4-4 structure is introduced and its measurement principle is analyzed. Based on condition numbers of Jacobian matrix spectral norm of the sensor, the relationship between the force and moment isotropy and some structural parameters is deduced. Orthogonal test methods are used to determine the degree of primary and secondary factors that have significant effect on sensor characteristics. Furthermore, the relationship between each performance index and the structural parameters of the sensor is analyzed by the method of the atlas, which lays a foundation for structural optimization design of the force sensor.
2018, 35(6):1027-1037.
DOI: 10.16356/j.1005-1120.2018.06.1027
Abstract:
Facility layout selection is a multi-criteria decision making (MCDM) problem,since it has a strategic impact on the efficiency of manufacturing system. In view of the interdependency among selection criteria, analytic network process (ANP) is proposed to analyze the structure of the facility layout selection problem and determine the weights for each criterion. A network structure is constructed that shows all elements and clusters and their interactions. Limit priorities are also calculated which help decision maker evaluate the relative importance among criterion in the alternative selection process. Moreover, a hybrid MCDM approach that employs ANP and technique for order preference by similarity to an ideal solution (TOPSIS) method to rank the optimal facility layout alternatives. Finally, an application of a new aeronautic component assembly workshop facility layout selection is conducted. To further illustrate the advantage of the proposed approach, the difference between ANP-TOPSIS and AHP-TOPSIS methods are compared and discussed. Results have demonstrated the effectiveness and feasibility of the proposed method.
Facility layout selection is a multi-criteria decision making (MCDM) problem,since it has a strategic impact on the efficiency of manufacturing system. In view of the interdependency among selection criteria, analytic network process (ANP) is proposed to analyze the structure of the facility layout selection problem and determine the weights for each criterion. A network structure is constructed that shows all elements and clusters and their interactions. Limit priorities are also calculated which help decision maker evaluate the relative importance among criterion in the alternative selection process. Moreover, a hybrid MCDM approach that employs ANP and technique for order preference by similarity to an ideal solution (TOPSIS) method to rank the optimal facility layout alternatives. Finally, an application of a new aeronautic component assembly workshop facility layout selection is conducted. To further illustrate the advantage of the proposed approach, the difference between ANP-TOPSIS and AHP-TOPSIS methods are compared and discussed. Results have demonstrated the effectiveness and feasibility of the proposed method.
2018, 35(6):1038-1046.
DOI: 10.16356/j.1005-1120.2018.06.1038
Abstract:
Space shift keying (SSK) is a spectrally efficient and low-complexity technique that only uses antenna index to convey information. Combining SSK with cooperative communication, the transmission reliability of SSK system can be improved effectively. In this paper, considering imperfect channel information, the performance of cooperative SSK system with amplify-and-forward (AF) relaying protocol is investigated, and the effect of estimation error on the performance is analyzed. According to the performance analysis, the probability density function and moment generating function of effective signal-to-noise ratio are derived, respectively. Using these results, the closed-form expression of average bit error rate (BER) can be achieved. Meanwhile, the asymptotically approximated BER and the corresponding diversity order analysis are presented for the performance evaluation. By computer simulations, the validness of the presented theoretical analysis is verified, and the theoretical BERs with different estimation errors are shown to be close to those of the corresponding simulations.
Space shift keying (SSK) is a spectrally efficient and low-complexity technique that only uses antenna index to convey information. Combining SSK with cooperative communication, the transmission reliability of SSK system can be improved effectively. In this paper, considering imperfect channel information, the performance of cooperative SSK system with amplify-and-forward (AF) relaying protocol is investigated, and the effect of estimation error on the performance is analyzed. According to the performance analysis, the probability density function and moment generating function of effective signal-to-noise ratio are derived, respectively. Using these results, the closed-form expression of average bit error rate (BER) can be achieved. Meanwhile, the asymptotically approximated BER and the corresponding diversity order analysis are presented for the performance evaluation. By computer simulations, the validness of the presented theoretical analysis is verified, and the theoretical BERs with different estimation errors are shown to be close to those of the corresponding simulations.
2018, 35(6):1047-1052.
DOI: 10.16356/j.1005-1120.2018.06.1047
Abstract:
Eddy-current (EC) testing is an effective electromagnetic non-destructive testing (NDT) technique. Planar eddy-current sensor arrays have several advantages such as good coherence, fast response speed, and high sensitivity, which can be used for micro-damage inspection of crucial parts in mechanical equipments and aerospace aviation. The main purpose of this research is to detect the defect in a metallic material surface and identify the length of a crack using planar eddy-current sensor arrays in different directions. The principle and characteristics of planar eddy-current sensor arrays are introduced, and a crack length quantification algorithm in different directions is investigated. A damage quantitative detection system is established based on a field programmable gate array and ARM processor. The system is utilized to inspect the micro defect in a metallic material, which is carved to micro crack with size of 7 mm (length)×0.1 mm (width)×1 mm (depth). The experimental data show that the sensor arrays can be used for the length measurement repeatedly, and that the uncertainty of the length measurement is below ±0.2 mm.
Eddy-current (EC) testing is an effective electromagnetic non-destructive testing (NDT) technique. Planar eddy-current sensor arrays have several advantages such as good coherence, fast response speed, and high sensitivity, which can be used for micro-damage inspection of crucial parts in mechanical equipments and aerospace aviation. The main purpose of this research is to detect the defect in a metallic material surface and identify the length of a crack using planar eddy-current sensor arrays in different directions. The principle and characteristics of planar eddy-current sensor arrays are introduced, and a crack length quantification algorithm in different directions is investigated. A damage quantitative detection system is established based on a field programmable gate array and ARM processor. The system is utilized to inspect the micro defect in a metallic material, which is carved to micro crack with size of 7 mm (length)×0.1 mm (width)×1 mm (depth). The experimental data show that the sensor arrays can be used for the length measurement repeatedly, and that the uncertainty of the length measurement is below ±0.2 mm.
2018, 35(6):1053-1063.
DOI: 10.16356/j.1005-1120.2018.06.1053
Abstract:
The problem of joint direction of arrival (DOA) and Doppler frequency estimation in monostatic multiple-input multiple-output (MIMO) radar is studied and a computationally efficient multiple signal classification (CE-MUSIC) algorithm is proposed. Conventional MUSIC algorithm for joint DOA and Doppler frequency estimation requires a large computational cost due to the two dimensional (2D) spectral peak searching. Aiming at this shortcoming, the proposed CE-MUSIC algorithm firstly uses a reduced-dimension transformation to reduce the subspace dimension and then obtains the estimates of DOA and Doppler frequency with only one-dimensional (1D) search. The proposed CE-MUSIC algorithm has much lower computational complexity and very close estimation performance when compared to conventional 2D-MUSIC algorithm. Furthermore, it outperforms estimation of signal parameters via rotational invariance technique (ESPRIT) algorithm. Meanwhile, the mean squared error (MSE) and Cramer-Rao bound (CRB) of joint DOA and Doppler frequency estimation are derived. Detailed simulation results illustrate the validity and improvement of the proposed algorithm.
The problem of joint direction of arrival (DOA) and Doppler frequency estimation in monostatic multiple-input multiple-output (MIMO) radar is studied and a computationally efficient multiple signal classification (CE-MUSIC) algorithm is proposed. Conventional MUSIC algorithm for joint DOA and Doppler frequency estimation requires a large computational cost due to the two dimensional (2D) spectral peak searching. Aiming at this shortcoming, the proposed CE-MUSIC algorithm firstly uses a reduced-dimension transformation to reduce the subspace dimension and then obtains the estimates of DOA and Doppler frequency with only one-dimensional (1D) search. The proposed CE-MUSIC algorithm has much lower computational complexity and very close estimation performance when compared to conventional 2D-MUSIC algorithm. Furthermore, it outperforms estimation of signal parameters via rotational invariance technique (ESPRIT) algorithm. Meanwhile, the mean squared error (MSE) and Cramer-Rao bound (CRB) of joint DOA and Doppler frequency estimation are derived. Detailed simulation results illustrate the validity and improvement of the proposed algorithm.
2018, 35(6):1064-1072.
DOI: 10.16356/j.1005-1120.2018.06.1064
Abstract:
A position and orientation compensation mechanism for the automatic docking device of a launch rocket-was established.The docking process was simulated, and the maximum docking deviation was used for the prototype testing of the compensation mechanism.The compensation mechanism mainly comprises four column pairmotion branch chains with the same structure.When the position of the ground connector panel changes relative to the moving platform,the sliding rods in the four motion branch chains move and rotate to either compress or stretch the connected spring,thereby compensating the position and orientation. First, the dynamic simulation model of the compensation mechanism was established.The docking process was then simulated under the maximum docking deviation.Bench testing of the automatic docking device prototype was carried out.Afterwards, the device was manufactured,and a maximum load test and maximum deviation test were carried out. The results demonstrate that the compensation mechanism meets the design requirements, and the spring stiffness was found as the most important factor in determining the mechanical properties of the system.The proposed compensation mechanism has a number of advantages, including a simple structure, large load bearing capacity, small size, simple installation, and adjustment.
A position and orientation compensation mechanism for the automatic docking device of a launch rocket-was established.The docking process was simulated, and the maximum docking deviation was used for the prototype testing of the compensation mechanism.The compensation mechanism mainly comprises four column pairmotion branch chains with the same structure.When the position of the ground connector panel changes relative to the moving platform,the sliding rods in the four motion branch chains move and rotate to either compress or stretch the connected spring,thereby compensating the position and orientation. First, the dynamic simulation model of the compensation mechanism was established.The docking process was then simulated under the maximum docking deviation.Bench testing of the automatic docking device prototype was carried out.Afterwards, the device was manufactured,and a maximum load test and maximum deviation test were carried out. The results demonstrate that the compensation mechanism meets the design requirements, and the spring stiffness was found as the most important factor in determining the mechanical properties of the system.The proposed compensation mechanism has a number of advantages, including a simple structure, large load bearing capacity, small size, simple installation, and adjustment.
2018, 35(6):1073-1079.
DOI: 10.16356/j.1005-1120.2018.06.1073
Abstract:
An increment-dimensional scaled boundary finite element method (ID-SBFEM) is developed to solve the transient temperature field. To improve the accuracy of SBFEM, the effect of high frequency factor on dynamic stiffness is considered, and the first-order continued fraction technique is used. After the derivation, the SBFE equations are obtained, and the dimensions of thermal conduction, the thermal capacity matrix and the vector of the right side term in the equations are doubled. An example is presented to illustrate the feasibility and good accuracy of the proposed method.
An increment-dimensional scaled boundary finite element method (ID-SBFEM) is developed to solve the transient temperature field. To improve the accuracy of SBFEM, the effect of high frequency factor on dynamic stiffness is considered, and the first-order continued fraction technique is used. After the derivation, the SBFE equations are obtained, and the dimensions of thermal conduction, the thermal capacity matrix and the vector of the right side term in the equations are doubled. An example is presented to illustrate the feasibility and good accuracy of the proposed method.
2018, 35(6):1080-1086.
DOI: 10.16356/j.1005-1120.2018.06.1080
Abstract:
The large-scale morphing aircraft can change its shape dramatically to perform high flight performance. To ensure the transient stability of aircraft in the morphing process, a novel gain-scheduled control method is investigated numerically in this paper. Based on quasi-steady assumption, the linear parameter varying (LPV) model of the morphing vehicle is derived from its nonlinear equation. Afterwards, by solving a set of linear matrix inequalities along with the bound of the morphing rate via slowly varying system theory, the designed controller which considers the transition stability during the morphing process is obtained. Finally, the transition process simulations of the morphing aircraft are performed via the changes simultaneously in both span and sweep, and the results demonstrate the effectiveness of the proposed controller.
The large-scale morphing aircraft can change its shape dramatically to perform high flight performance. To ensure the transient stability of aircraft in the morphing process, a novel gain-scheduled control method is investigated numerically in this paper. Based on quasi-steady assumption, the linear parameter varying (LPV) model of the morphing vehicle is derived from its nonlinear equation. Afterwards, by solving a set of linear matrix inequalities along with the bound of the morphing rate via slowly varying system theory, the designed controller which considers the transition stability during the morphing process is obtained. Finally, the transition process simulations of the morphing aircraft are performed via the changes simultaneously in both span and sweep, and the results demonstrate the effectiveness of the proposed controller.
CHINA AERO-SCIENCES
Mobile website
Transactions of Nanjing University of Aeronautics & Astronautics ® 2024 All Rights Reserved