Abstract:The amount of helium used in a balloon is an important issue, which directly affects balloon′s ascent velocity and altitude, and then affects the reliability and stability of the platform. Therefore, the study of accurate calculation method of helium is requested. Vertical dynamic model of balloons was established and the theoretical values of initial ascent velocity were calculated. It can be used to compare with the actual initial ascent velocity and provide a basis for evaluating helium inflation calculation methods. Three helium inflation calculation methods of high-altitude balloon were summarized, the accuracy and error range of the three methods were analyzed and compared according to the flight experiments. The buoyancy compensation law was put forward, and three methods have been evaluated. Through the study, it shows that the existing helium inflation calculation methods can be modified effectively, and then it can provide guidance for future flight experiments.

Abstract:Based on the Hamiltonian principle and taking nonlocal effect, piezoelectric effect and flexoelectric effect into consideration, the vibration governing equation and boundary conditions of the Timoshenko nano-beam in the viscoelastic medium were established, and the method of solving the governing equation of flexoelectric nano-beam with simply supported boundary conditions was adopted. The effects of nonlocal parameters, flexoelectric effect and viscoelastic medium on the vibration characteristics of the flexoelectric nano-beam were systematically studied. The results show that the transverse flexoelectric coefficient can significantly increase the structural stiffness of the flexoelectric nano-beam, while the nonlocal parameters and the tangential flexoelectric coefficient can reduce the structural stiffness of the system. In addition, the critical damping coefficient of the viscoelastic medium, in which the flexoelectric nanobeam no longer reciprocating vibration, can be obtained by studying the effects of viscoelastic medium. Research results can provide a theoretical basis for the extension and application of flexoelectric nano-beam in energy harvester.

Abstract:In order to reduce the diurnal in TWSTFT (two-way satellite time and frequency transfer), based on the fact that there is no diurnal in BeiDou common view link, the Vondrak-Cepek combined filtering was applied to combine BeiDou common view and SATRE (satellite time and ranging equipment) TWSTFT or SDR (software-defined radio) TWSTFT among NTSC (national time service center), Chinese Academy of Sciences, PTB (physikalisch-technische bundesanstalt) and NIM (national institute of metrology). Two indexes, namely time deviation and amplitude spectrum, were used to evaluate the gain factors in reducing the diurnal of the fusion results, and the agreement of the two types of links was revealed by taking GPS PPP (precise point positioning) time comparison as reference. Results show that the diurnal of the fusion results is greatly improved after Vondrak-Cepek combined filtering, and the absolute value of the differences between the fusion solutions and GPS PPP solutions is kept within the calibration uncertainty of time link. For the baseline of NTSC-PTB, the gain factors of 1-day time deviation(TDEV) of fusion results versus SATRE TWSTFT and SDR TWSTFT are 1.85 and 1.81, respectively. For the baseline of NTSC-NIM, the gain factors are 1.69 for SATRE TWSTFT and 1.59 for SDR TWSTFT. The short-term stability of fusion results is significantly improved.

Abstract:The compression, bending and tensile properties of C/SiC composites at elevated temperature air were tested. The microstructures of fractures at room temperature and elevated temperature were analyzed by scanning electron microscope, respectively. Results show that, when the test temperature varies from room temperature to 1 000 ℃, the compressive strength, flexural strength and tensile strength of C/SiC composites decreases from 247 MPa to 78 MPa, 480 MPa to 277 MPa and 247 MPa to 152 MPa, respectively. The performance of these three mechanical parameters of C/SiC composites is reduced by 68%, 42% and 38%, respectively. High temperature oxidation leads to interface degradation and carbon fiber structural damage, which aggravates the degree of fiber breakage, and changes the state of fiber-matrix bonding. As a result, the fiber toughening mechanism gradually disappears, and composite properties decays.

Abstract:In order to deal with various complex telemetry problems, such as high dimensionality, huge volume, unbalanced categories and failure to intuitively make sense about states of payload, and considering the requirement of interpretability in space mission, a general method for fast identification of payload based on information gain and integrated learning method was proposed. Sample statistics and information gain was used to select features and reduce the dimension of the telemetry data; meanwhile, the integrated learning algorithm was used to complete the adaptive recognition and classification about payload states. The proposed method combined the advantages of the parameter classification information evaluation criteria of the information gain and strong modeling, high accuracy and strong anti-noise ability under unbalanced category samples. Furthermore, the model had to possess the property of being explanatory and able to find the key parameters. The method was verified by experiments using actual mission data, which was tested using the payload telemetry data on operational scientific satellite mission. Following that, an state-of-art result, of which the overall recognition accuracy is higher than 90 percent and a few samples can also be identified, covered mission requirement in all and proved the effectiveness and practicability.

Abstract:The combustion characteristics of single-element and multi-elements splash platelet injector were studied by experimental methods, the heat load of injector faceplate under different working conditions were investigated, and the effects of different mixing ratios and different structural parameters on combustion chamber pressure and combustion efficiency were obtained. Results show that the mixing ratio of the multi-elements injector has little effect on the chamber pressure, but has a greater effect on combustion efficiency. For single-element injectors, the combustion efficiency improves with the increase of the mixing ratio. Under the same conditions, increasing the expanding angle and the length of the trapezoidal orifice is beneficial to improve the combustion efficiency, but will cause the increase of the thermal load of injector faceplate. The injector faceplate of each injectors has different degrees of deformation or failure. These results are of significance for guiding the design of the platelet injector and screening the structure of the injector.

Abstract:Based on the temperature correction model of meteorological sounding rocket, through error analysis theory, research on the method of temperature correction and uncertainty evaluation was conducted. According to the law of atmospheric density change during the falling process of rocketsonde, the mathematical model of temperature correction was established, and the formula of temperature correction was deduced. According to the error theory, eight error factors which affect the temperature correction were analyzed, and the expression of error in temperature correction was given one by one. Taking measured data as an example, using the above formula, the uncertainty of temperature inversion of sounding rocket was analyzed and calculated. The results show that the uncertainty of temperature inversion is larger in 50~60 km, and the maximum is 3.6 K; uncertainty in 40~50 km is 0.3~0.9 K; uncertainty in less than 40 km is no more than 0.3 K.The main factors that affect the uncertainty of temperature are aerodynamic heating correction, lag effect correction, structural heat conduction correction, and sensor correction for environmental heat radiation. It is not enough to use the reference atmosphere or the standard atmosphere for only single correction in data processing. Iterative correction is needed, and the maximum difference between iterative correction results and single correction results is 5.6 K.

Abstract:The imaging methods in the field of ultrasonic phased array abide by the Rayleigh criterion and its resolution is limited by ultrasonic wavelength. The time reversal with multiple signal classification, termed TR-MUSIC(time reversal-multiple signal classification), has been introduced to improve the resolution and achieve super resolution imaging under the premise of keeping the ultrasonic working frequency unchanged and maintaining the detection depth of the system. The ultrasonic array data from the test object can be captured via full matrix capture process. Then the data was post-processed by plane B scan as well as TR-MUSIC to obtain the 2-D and 3-D ultrasonic images. The test object was assessed according to the imaging results. A block of steel with six 1mm-diameter side drilled holes, which can be considered as point-like targets, has been machined as the test object. Furthermore, the detection system of ultrasonic phased array has also been built. It is shown that TR-MUSIC can distinguish and locate these targets while the method of plane B scan fails. Therefore, the TR-MUSIC based on the theory of time reversal can increase the imaging resolution, and improve the quality of ultrasonic image.

Abstract:In order to promote the application of BDS (BeiDou navigation satellite system), especially the BDS-3 to join TAI (international atomic time) calculation, BDS-3 common view time comparison was implemented by using the pseudo code measured data of BDS-3 new signal between National Time Service Center of Chinese Academy of Sciences and the Institute of Photonics and Electronics Academy of Sciences of the Czech Republic. The results show that the signal of multipath noise and signal-to-noise ratio of BDS-3 are less than those of BDS-2. Compared with the previous studies, the noise of common view time comparison based on new BDS-3(B1C & B2a) signal is much better than that of the BDS-2(B1I & B3I) compatible signal, which is broadcasted by the BDS-3 satellite, and the results are similar to those of GPS and Galileo, the standard deviation of the result based on BDS-3 signal is increased by more than 40% compared with BDS-2 signal. The noise of BDS-3 single common view is smaller than that of BDS-2, and frequency stability of result is increased by more than 10% relative to BDS-2. The experiment can provide research foundation for the BDS-3 application in the TAI calculation.

Abstract:Aiming at a desirable solution to the high cost of precision navigation and positioning in the ocean, transmitting real-time service data from multi-global navigation satellite system through BeiDou short-messages device to realize real-time precise point positioning was proposed. Real-time service data was simplified to reduce the costs of communication and hardware, remedying the shortage of BeiDou short-message band width. In order to overcome the low communication frequency limitation of BeiDou short-message service, and to obtain satellite orbit position and clock correction at the time beyond minute interval, a method of forecasting real-time precise ephemeris was adopted. The data process of real-time precise point positioning in ocean based on BeiDou short-message was simulated. Post-processing ocean observation data and testing positioning performance, its accuracy can reach cm-level in horizontal direction and 10～20 cm in vertical direction. Results show that the method can provide effective technical reference for the low-cost real-time precise point positioning in the ocean.

Abstract:Aiming at the urgent need for human and remote unmanned devices to cooperate precisely and accurately, a remote situational awareness system of human-machine integration was proposed based on the robot operating system, and experiments and analysis were carried out. Based on visual positioning technology, with the integration of human-machine perception as the breakthrough point, through real-time 3D scene reconstruction technology and scene consistency fusion method, the environment and target information detected by unmanned equipment were 3D reconstructed. The result was consistent and fused with the human visual information, and displayed by the augmented reality device, realizing the coordinated positioning between the remote unmanned device and the augmented reality device worn by the person without GPS. The experimental results show that the system has better performance at close range. The accuracy of human-machine coordinated positioning is gradually reduced as the distance increases. The proposed system makes the unmanned device an extension of the human eye, realizing the ability to penetrate obstacles, and crosses the sight distance without interfering with the normal movement of personnel. It can play an important role in future information operations.

Abstract:In order to improve the design efficiency of the high-precision programmable resistance network, the physical and mathematical models of the high-precision resistance network were established, and a high-precision programmable resistance network generation algorithm was proposed. The algorithm automatically generates a high-precision programmable resistor network based on the combination of the main resistance network, compensation resistance network and offset resistance network, according to the given range and accuracy. Taking the requirement of measuring range 90~250 Ω and accuracy 5 mΩ as an example, the algorithm was simulated and verified on the MATLAB platform, and the simulation results verified the feasibility of the algorithm. The results show that the generated programmable resistor network meets the requirements of target range and accuracy, and the algorithm solution time only needs 18.128 s. Compared with the manual design, this algorithm greatly improves the design efficiency.

Abstract:The information knowledge base can improve production efficiency and reduce resource consumption in industrial production, but it frequently meets with data failure. Furthermore, erasure coding strategies for multi-node failure reconstruction are limited, and the link relationship between participating nodes during the reconstruction of failed data has not been fully considered, resulting in low reconstruction efficiency. Aiming at the data failure of the information knowledge base, a multi-node failure reconstruction method was proposed. According to the data processing capacity of the node, the new node with the highest data processing capacity was selected as the routing node; then according to the link bandwidth of the routing node, the candidate supply node and the remaining idle nodes, the supply node and the new node were determined, thereby constructing the data reconstruction network topology and improving the efficiency of reconstruct failed data. Experimental results show that this method has shorter reconstruction time and higher reconstruction success rate when compared with traditional erasure code reconstruction methods.

Abstract:Based on demand of multiple time scale dynamic characterization of power electronic devices and their combination, the recent research progress and achievements on the widely used full-control power electronic devices—IGBTs(insulated gate bipolar transistors), were analyzed systematically, including the multiple time scales electro-thermal modeling of high power IGBTs and their combinations, quantitative failure evaluation methods based on the multiple time scales model and the assisted multi-rate simulation method. Furthermore, applications of the models were introduced in power electronic instruments design. In conclusion, the dynamic characterization method of high power IGBTs and their combinations under multiple time scales were presented from four aspects of modelling method, reliability evaluation, simulation method and application design, which can bring theoretical and technical support of power electronic devices to precise design of power electronic hybrid system.

Abstract:Blade cracks pose a serious threat to aviation safety and lead to serious aviation accidents. In order to diagnose cracks at the early stage, the nonlinear vibration of cracked blades was investigated theoretically and experimentally. A nonlinear dynamic model was established to link the crack size and the dynamic parameters. A coupling quantification expression of the coupling component power in the nonlinear vibration response was obtained. This response expression indicated that the harmonic element power was determined by the adjacent component power, component order, and positively correlated with the depth of the blade crack. Therefore, based on the relative power of the vibrational components, a crack detection method is proposed. Results of the simulation and the testbed experiment both show that the cracked blades are effectively separated from the normal blades by this method.

Abstract:Reflected lights on object surfaces are composed of specular and diffuse reflection lights. To separate the specular and diffuse reflection lights on a smooth object surface, a polarization state characterization model based on the collaborative effect of specular and diffuse reflections was proposed and was used to analyze the polarization characteristics in a mixed reflection region. Based on their polarization characteristics and their distribution relations perpendicular and parallel to the smooth object surface, the specular and diffuse reflection lights were separated by polarization orthogonal decomposition. According to the correlation features between the specular and diffuse reflection components, the normalized correlation minimum between the specular and diffuse reflection lights and its corresponding to the degrees of specular and diffuse reflection polarization were calculated by the gradient descent algorithm, thus enabling the successful separation of the reflected lights. By testing reflected light images obtained from different scenes, the results indicate that the proposed algorithm could effectively separate reflection lights.

Abstract:The existing passive exoskeletons have some defects, including the lack of assistance effect. Based on the gait characteristics of human body, the principle of transforming gravitational potential energy during walking process into kinetic energy during lifting leg process was proposed, in which a passive lower extremity mechanical exoskeleton was designed by the combination of spring, crank slider mechanism, ratchet pawl mechanism and chain drive mechanism, and the performance of exoskeleton was evaluated by kinetic analysis and physiological cost index experiment. Results of kinetic analysis show that the total peak torque of hip joint is reduced by 23.38% and the total work of hip joint is reduced by 30.59% after wearing the exoskeleton, which preliminarily verifies the effectiveness of the exoskeleton. The results of experiment show no significant effect in short distance action conversion, but is reduced by 8.1% and 10.4% in long distance walking and uphill walking, respectively. Therefore, the assisting performance of the passive exoskeleton has been verified, which provides an instance reference for research in related fields.

Abstract:Based on the theory of complex network and propagation dynamics, a social network was constructed, which conforms to the interaction characteristics of large cruise ships. The hierarchical structure of the communication network was defined, five rules of topology generation of the interaction network were analyzed, and the social networks construction method of the large cruise ships epidemic communication were given. Based on the multi-agent technology, the properties of the members of the interaction network nodes and the epidemic propagation characteristics were studied, the basic form of agent member state-space was given, the physical characteristics of protection and treatment, management and control isolation, information interaction and other factors were integrated, the algorithm of agent state transfer and behavior interaction process were constructed, and the structure and interval characteristics of attenuation function were analyzed and demonstrated. Compared with the constant-distance model and the random-walk model, the simulation calculations of the epidemic transmission process of typical large cruise ships were carried out under 4 working conditions and 12 states, respectively. Results show that the random-walk model is more suitable for the simulation of the early epidemic transmission process of large cruise ships and the analysis of epidemic prevention and control strategies with abundant information.

Abstract:The aerodynamic noise of subsonic flight trajectory is wideband non-stationary noise. A new direction of arrival estimation algorithm based on wavelet function was proposed. The time-frequency analysis method was used to obtain the significant characteristics of the aerodynamic noise. By optimizing the characteristics of space-time spectrum, the target signal in time-frequency domain was optimized to enhance the significance of the target signal in space spectrum, effectively realizing the azimuth angle estimation of the aerodynamic noise of the subsonic flight vehicle finally. The experimental data shows that array signal processing model based on time-frequency analysis can better achieve the azimuth angle estimation of aerodynamic noise of subsonic flight vehicle.

Abstract:A combination of experiment and numerical simulation was used to study the response characteristics of laser-irradiated 45# steel plate. Based on the continuous fiber laser emission system, the laser irradiation experiment of the steel plate was carried out and the temperature field distribution and the ablation and perforation characteristics of the target plate were obtained. A finite element model of the metal target plate was established on the basis of ANSYS to simulate the thermal response process of the target plate under laser irradiation. The influence rules of the target plate thickness, laser power and spot diameter on temperature distribution and perforation characteristics of the target plate were obtained.