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Model Based Separation of Overlapping Latent Fingerprints
Qijun Zhao,Jain, A. K. IEEE 2012 IEEE transactions on information forensics and sec Vol.7 No.3
<P>Latent fingerprints lifted from crime scenes often contain overlapping prints, which are difficult to separate and match by state-of-the-art fingerprint matchers. A few methods have been proposed to separate overlapping fingerprints to enable fingerprint matchers to successfully match the component fingerprints. These methods are limited by the accuracy of the estimated orientation field, which is not reliable for poor quality overlapping latent fingerprints. In this paper, we improve the robustness of overlapping fingerprints separation, particularly for low quality images. Our algorithm reconstructs the orientation fields of component prints by modeling fingerprint orientation fields. In order to facilitate this, we utilize the orientation cues of component fingerprints, which are manually marked by fingerprint examiners. This additional markup is acceptable in forensics, where the first priority is to improve the latent matching accuracy. The effectiveness of the proposed method has been evaluated not only on simulated overlapping prints, but also on real overlapped latent fingerprint images. Compared with available methods, the proposed algorithm is more effective in separating poor quality overlapping fingerprints and enhancing the matching accuracy of overlapping fingerprints.</P>
Guoqing Zhao,Qijun Zhao,Peng Li,Bo Wang 한국항공우주학회 2021 International Journal of Aeronautical and Space Sc Vol.22 No.3
Numerical simulations are performed to investigate the effects of different RPM (revolutions per minute) and different diameter on aerodynamic performances of tiltrotor in both hovering and cruise flight modes. The CLORNS code based on embedded grid and Reynold averaged Navier–Stokes equations is employed. According to the flight state of the tiltrotor, the corresponding comprehensive performance evaluation criteria and aerodynamic trimming strategy are established. On these bases, the numerical investigations on figure of merit and cruise efficiency of XV-15 tiltrotor with different RPM and diameter are conducted, and the results indicate that a large RPM is good for improving the hovering efficiency of tiltrotor, while in cruise mode, tiltrotor with small diameter (root-cut) and RPM helps to enhance the cruise efficiency.
Yong Wang,Jiatong Du,Qijun Zhao,Haibo Zhang 한국항공우주학회 2024 International Journal of Aeronautical and Space Sc Vol.25 No.2
In order to enhance the fuel economy performance of the new-generation propeller aircraft, a power management method for serial hybrid-electric propulsion system is designed and analyzed. First, a mathematical model of the serial hybrid-electric propulsion system was established under aircraft/engine integrated framework. In addition, the performance matching of the propeller aircraft and the serial hybrid-electric propulsion system was accomplished through reverse design method. Subsequently, power management strategies were devised based on the fixed and variable turbine speeds to minimize fuel consumption of the turboprop engine and accomplish the optimal power allocation between turboprop engine and lithium battery. Finally, performance parameters variation laws of the serial hybrid-electric propulsion system under different power management methods were revealed and compared. The results demonstrate that, in the case of a consistent flight profile, the power management method based on variable turbine speed can dramatically decrease the total fuel consumption by more than 2.28%, thereby providing a substantial advantage in obtaining superior fuel economy. Furthermore, it is noteworthy that under identical flight mission phase, the optimal power turbine speeds corresponding to different cruising altitudes remain approximately constant. This observation highlights the superiority and feasibility of the power management method of the serial hybrid-electric propulsion system.
Aeroacoustic Characteristic Analyses of Coaxial Rotors in Hover and Forward Flight
Bo Wang,Chenkai Cao,Qijun Zhao,Xin Yuan,Zheng Zhu 한국항공우주학회 2021 International Journal of Aeronautical and Space Sc Vol.22 No.6
A numerical method combining computational fluid dynamics (CFD) method and Ffowcs Williams–Hawkings (FW–H) equations is established for predicting acoustic characteristics of the coaxial rigid rotor in hovering and forward flight. The unsteady Reynolds-averaged Navier–Stokes (URANS) solver coupled with the moving-embedded grid technique is established to obtain sound source information in the flowfield with high accuracy. On the basis of the accurate solution for the coaxial rotor flowfield, the blade–vortex interaction (BVI) noise in hovering state and the high-speed impulsive (HSI) noise in high-speed forward flight are estimated by the Farassat 1A formula and the FW–H equation with a penetrable data surface (FW–Hpds), respectively. Then the sound pressure distribution characteristics and sound radiation pattern for the coaxial rotor in a hovering state and in a forward flight are obtained through the comparative analysis of the sound pressure time histories and the distribution of sound pressure levels of the upper rotor, lower rotor, and coaxial rotor. The simulation results indicate that significant unsteady characteristics appear in blade aerodynamic loading due to the Venturi effect, blade–vortex interaction phenomenon, and action of the downwash existing in the coaxial rotor flowfield, causing the loading noise of the coaxial rotor to occupy the dominant position in hovering state; the counter-rotating characteristics of the upper and lower rotors cause a significant phase difference between their respective sound pressure waveforms, and the phase difference is determined by the angle between the observation point and the intersection position of the upper and lower blades; the difference with the single rotor in terms of the severe HSI noise generated in the high-speed forward flight is that the noise radiation intensity of the coaxial rotor along both sides in the forward direction exhibits an approximately symmetrical distribution.
Numerical Investigations of Bump Effects on the Performance of Double-Ended Airfoils and ABC Rotors
Xin Yuan,Guoqing Zhao,Qijun Zhao 한국항공우주학회 2024 International Journal of Aeronautical and Space Sc Vol.25 No.2
Numerical simulations based on RANS have been performed to investigate the aerodynamic characteristics of the double- ended airfoil deformed by local bumps on its lower surface, both in airfoil and coaxial rotor environments. The two-dimensional results show that the bump can reduce the magnitude of negative lift but increase the drag at large negative AoAs and high Mach numbers, and can increase the stability of the airfoil at positive AoAs in forward flow and at large negative AoAs in reverse flow. A bump has a more significant effect on airfoil performance if it is closer to the leading edge and has a larger area. A coaxial rotor with different double-ended airfoils deformed by bumps located inboard was predicted under a 0.5 advance ratio with a lift-offset of 0.3. Bumps under such flight conditions influence the root region on the advancing side more than on the retreating side. The root region at 14 ~ 33% span produces about 6% of the total thrust, so bump’s effects on the whole performance are insignificant. Through the flow details around inboard sections, it suggests that bumps have the potential to improve ABC rotor performance, and flight conditions and blade geometry should be considered in conjunction with the application of bumps for effectiveness. Although the double-ended airfoil only covers the blade range of 0.14 ~ 0.33R, the total rotor thrust is slightly increased by adding bumps, and a higher bump has a greater influence.