Abstract:To study the development status of air-based boost phase interception and the key challenges faced by interception and guidance, the guidance technology of air-based anti-boost phase missiles was analyzed and summarized. Air-based anti-boost phase missiles are launched by carrier aircrafts and intercept missiles in boost phase, which is an important part of the ballistic missile defense system. First, the development status of air-based missile system and guidance methods for boost phase interception was reviewed. The combat process of typical schemes, the structure and performance of typical missiles were introduced, and the research progress of guidance technology at home and abroad was summarized. Next, the challenges faced by the boost phase interception guidance of air-based missiles were analyzed, which are reflected in the limited interceptor capability, short available time, strong target maneuverability, complex interception conditions, and high uncertainty. Then, the key technologies that need to be solved for the air-based interception guidance in boost phase were put forward, including power system configuration, rapid calculation of firing data, online correction of guidance commands, hangover plan between midcourse guidance and terminal guidance, and high-precision guidance law for intercepting maneuvering targets. Finally, the development direction of guidance technology was summarized as online guidance, high-precision multi-mode compound guidance, and intelligent and coordinated guidance. Existing research results show that the boost phase interception guidance technology of air-based missiles is not yet mature. There are still some key technical issues that need to be studied and resolved. Theories such as autonomous planning and artificial intelligence can provide references for breakthroughs in key technologies.

Abstract:To overcome the speed limit of the traditional satellite orbit prediction method and lay foundation for independent orbital transfer planning of on-orbit satellites, the graphics processing unit (GPU) parallel computing method was utilized to accelerate the multi-satellite orbit calculation, and the parallel prediction module of orbit prediction was constructed, which realized the acceleration of satellite orbit prediction. In order to improve the calculation speed when the calculation amount is low, a monolithic GPU acceleration method was proposed, which substituted the simplified general perturbation version 4 (SGP4) calculation model into the kernel function. The computer memory only needed to interact with the GPU once, which greatly shortened the data transmission time between the memory and the GPU. Compared with the modular GPU acceleration method, the speed for medium or low scale calculations was increased greatly. The proposed monolithic acceleration method was implemented on two devices based on compute unified device architecture (CUDA) library. On NIVIDA TX2, a small embedded development board, it could realize the orbit prediction of 500 satellites for one day in 5 s (86 400 steps for each satellite), while the GPU acceleration ratio on the laptop was 4.6 times more than that of the central processing unit (CPU), and the precision loss after the acceleration was low. The experiment showed that the monolithic acceleration method was suitable for the parallel calculation of low and medium scale calculations (the number of steps is less than four million), and the modular acceleration method was suitable for the parallel calculation of large scale calculations (the number of steps is more than four million).

Abstract:To study the motion characteristics of moving bodies in the course of high-speed water entry in parallel, and to predict the mutual influence trends between moving bodies, combined with the results of numerical simulations, the prediction formulas for the lateral and yaw motions of the moving body were derived, and strategies to avoid instability were proposed. Firstly, the validity of the numerical calculation method was verified, and based on the numerical calculation results, a restrictive hypothesis about jerk was put forward, so as to obtain the prediction formula for the lateral displacement and yaw angle of parallel water-entry revolution bodies. Secondly, the effects of initial cavitation number and initial clearance distance on lateral and yaw motion characteristics were studied through the prediction formula. Finally, based on the concept of kinematic factor, the kinematics of collision and excessive distance was studied, and a strategy to avoid the instability of revolution bodies was proposed. Results show that the prediction formula was in good agreement with the numerical calculation results. When the initial cavitation number was small, the head pressure promoted lateral and yaw movements, and the smaller the initial cavitation number was, the greater the nominal lateral jerk and yaw angle were, indicating that the lateral and yaw motions were promoted more strongly. When the initial clearance distance was small, the inner pressure inhibited the lateral and yaw movements, and the smaller the initial clearance distance was, the larger the lateral correction factor and the yaw angle correction factor were, indicating that the lateral and yaw motions were inhibited more strongly. The initial conditions and the shape of the revolution body together determine the state of the revolution body. The initial speed of water entering and the initial clearance distance should be controlled within a reasonable range to avoid motion instability.

Abstract:Thermal sensation is human’s perception of the surrounding temperature, humidity, and other environments. In order to study the thermal sensation of ethnic minority groups in fluctuating climatic environments and make them adapt to different environments more quickly, the classroom environment of Dalian in winter was tested on the spot, and the clothing and thermal sensation of 80 Han students and 88 ethnic minority students (24 Hui, 12 Mongol, 14 Tujia, and other minorities) from different climatic zones were investigated by questionnaires. The results were analyzed by regression. The data of different ethnic minorities were compared, the reasons for the differences were analyzed, and the experimental results were verified. Results show that the comfortable temperature range of the minority students was between 18.5 ℃ and 19.4 ℃, which was different from that of Han students. According to the thermal sensory voting (TSV) model, the actual thermal neutral temperatures of students of different ethnics were 18.5 ℃ for Hui, 16.9 ℃ for Mongol, and 15.0 ℃ for Tujia. The predicted mean vote (PMV) model could not accurately predict the true thermal sensation. On the basis of the thermal sensation adaptability model (aPMV), parameter λ was put forward as a reference for all ethnicgroups, namely, Hui -0.79, Mongol -0.90, and Tujia 0.97. There were great differences in the indicators of different ethnics. It indicates that students have certain adaptability to the local climate, while studying in Dalian is accompanied by climate fluctuations, which makes students unable to adapt quickly to the new environment. Hence, the aPMV model was used to predict the thermal sensation of ethnic minority students, and a scheme of laboratory thermal reconstruction was provided.

Abstract:To accurately measure the installation matrix between magnetometers and star sensors in satellite geomagnetic measurement system on the ground, a calibration system based on the single axis non-magnetic turntable was designed, which is composed of non-magnetic turntable, geomagnetic field monitoring equipment, etc. First, the error sources in the system were analyzed, and the corresponding coordinate systems were established for transferring the errors. The indicated output of the magnetometer was obtained by combining the error model of the magnetometer with the geomagnetic field. Thus, a method of calibrating installation matrix by using single axis vertical non-magnetic turntable was proposed. In this method, the error coefficients in the indicated output of the magnetometer were obtained by harmonic analysis, and the attitude of the magnetometer coordinate system in the initial geographical coordinate system was derived. The attitude of the star sensor coordinate system in the inertial space was determined by star sensor observation, and that in the initial geographical coordinate system was obtained according to the local longitude and latitude and Greenwich Sidereal Time. Finally, the installation matrix among the magnetometers and the star sensors was solved by using the geographic coordinate system as a bridge. Based on the Monte Carlo method and uncertainty synthesis formulae, simulation experiment and error analysis were conducted on the proposed method. Results show that the uncertainty of each element of the installation matrix was within 1.14×10^-5 rad when the observation error of the magnetometer was 1 nT and the measurement accuracy of the star sensor was 1″, indicating the correctness of the calibration method.

Abstract:Rocket engine has the advantages of high-power density and large thrust, which is often used as the thruster to attack high speed underwater weapons. However, the outlet pressure of the nozzle pulsates violently when the rocket engine is working underwater, which affects the thrust performance of the engine and even causes accidents. To investigate the operating characteristics and wake field characteristics of underwater rocket engine, based on the VOF multiphase flow model and the ideal gas model, a numerical model of supersonic gas jet under high temperature and pressure was established. The internal and external flow field of the rocket engine was simulated under the conditions of single-phase water flow and ventilated supercavitation, and the influence of factors such as ventilated supercavity and operating pressure on the gas jet flow of the rocket engine was obtained. Results show that under the condition of fully wetted vehicle, unsteady phenomena including neck shrinkage, bulge, and back attack occurred in the gas jet flow, and the engine thrust pulsated violently. Under the condition of ventilated supercavitation, the gas of the rocket engine mixed with the gas in the supercavity and discharged, the unsteady characteristic of the wake field was significantly reduced, and there was no violent pulsation. When the operating pressure was increased to the twice of the design pressure, under the condition of fully wetted vehicle, the oscillations of gas mass flow rate and engine thrust were 30.4% and 20.6% respectively. However, the operating performance of the engine was hardly affected by the operating pressure under the condition of ventilated supercavitation.

Abstract:To explore a jet control method for enhancing the aerodynamic performance of airfoils at small angles of attack so as to realize rudderless flight control, inspired by circulation control, it was proposed to arrange the jet at the lower surface of the NACA0012 airfoil near the trailing edge, and optimize the aerodynamic control effect of (jet on the lower surface of trailing edge) LSTE jet by analyzing the flow states and parameter variations. Firstly, three sets of grids with different scales were used to simulate the NACA0012 airfoil, and the convergence and effectiveness of the numerical simulation method were verified. Secondly, the mechanism of the influence of LSTE jet on the aerodynamic performance of the airfoil was studied by comparing the changes in the distribution of Mach number, streamline, and pressure distribution of the flow field. Finally, the variations of the aerodynamic coefficients of the airfoil with the position, the momentum coefficient, and the forward angle of the jet were analyzed. Results show that LSTE jet induced a counterclockwise vortex at the trailing edge, forming a low-pressure separation zone, which deflected the main flow of the trailing edge and increased the effective camber of the airfoil, and the suction peak of the leading edge also increased, thereby increasing the lift coefficient. The closer the LSTE jet was to the trailing edge, the greater the momentum coefficient was, and the better the effect of lift increase and drag reduction was, but the angle of attack of the airfoil decreased by 1° to 3°. Under different angles of attack and jet flow coefficients, the maximum lift and minimum drag of the airfoil could be achieved between γ=60°-70° at the same time. LSTE jet can effectively change the aerodynamic performance of the airfoil at a low angle of attack, and has certain significance for the realization of aircraft rudderless control.

Abstract:To effectively reduce the dimension of the design parameters of airship hulls, improve the design efficiency, and provide reference and guidance for the design of airship hulls in the initial stage, an evaluation system was constructed for the airship hull shape parameters associated with drag coefficient sensitivity, combined with parametric section (PARSEC) method, computational fluid dynamics (CFD) method, and Sobol global sensitivity analysis method based on variance. First, the outline of airship hull was described by PARSEC method which has clear physical significance. Then, the drag coefficient of airship hull samples produced by Latin hypercube sampling (LHS) was obtained by 2D axisymmetric CFD method. The accuracy of CFD method was verified by the experimental data of six typical streamlined bodies of revolution. Under the condition that the Reynolds number was consistent, the average relative error between the calculated and experimental drag coefficient was 1.5%. Finally, the sensitivity of the hull shape parameters was ranked by the Sobol global sensitivity analysis method. Research results show that the three parameters which were the most sensitive to the hull drag coefficient were the head radius r_h, the maximum radius r_d, and the maximum radius position x_d. On the basis of this study, the design space of the airship hull shape was formed, and the design space has positive significance for improving the efficiency of designing process and reducing the aerodynamic drag of airships.

Abstract:A joint design based on improved predictor-corrector guidance and robust fault-tolerant attitude control was proposed to realize the re-entry accurate guidance and robust fault-tolerant control for reusable launch vehicles (RLVs). First, an improved predictive guidance law with modified magnitude model of bank angle and corridor function of track angle was designed. Combined with the nominal profile of the angle of attack, the input command of the attitude system was calculated online. Then, a modified tracking differential disturbance observer was presented to estimate the system uncertainty/disturbance and the actuator faults. The estimation accuracy of compound disturbance was further improved by adding feed-forward term to the observer. Finally, an auxiliary anti-saturation system was designed to tackle the problem of the saturation of control surfaces, and a sigmoid saturation function was utilized to enhance the control performance of the backstepping method in the angular rate loop. Simulation test on 6 degree-of-freedom (DOF) guidance control system shows that the RLV was capable of tracking attitude angle commands precisely in the presence of the compound disturbance of attitude system, the actuator faults and saturation, and the RLV trajectory reached the re-entry terminal area with satisfying constraints. Thus, the proposed method can realize the re-entry guidance accurately and solve the problems of attitude system uncertainty, actuator faults and saturation, indicating its satisfactory robustness and fault-tolerant capability.

Abstract:The understanding of the influence of water and gas dissolution and escape on the performance of a new type of catalytic inerting system can provide guidance for the design of the system. First, a low temperature controllable oxygen consumed catalytic inerting system process was designed. Then, based on the molar flow rate of the pumped gas in the fuel tank, the flow relationship of each gas component before and after flowing through the catalytic reactor and the cooler was deduced, and the concentration variation of each gas in the gas phase space of the fuel tank was determined through the gas state equation and the gas equilibrium dissolution relationship. In addition, in the cases of fuel with or without gas dissolution and escape, the effect of two key parameters, i.e., flow rate and oil loading rate of fan, on the water production and cooling performance of the system was studied. Results show that the oxygen concentration in the gas phase space of the tank decreased with the inerting process, and the molar fraction of the water vapor increased while the growth rate gradually slowed down. The cooling power required in the reactor and the cooler, the relative humidity at the outlet of the reactor, and the water removal in the cooler all decreased with time. Besides, the dissolved and escaped gases such as oxygen, nitrogen, and carbon dioxide in the fuel had a great impact on the system performance, and the amount of cooling gas required in the cooler was about 33% higher when water precipitation was taken into account. Therefore, the influence of gas dissolution and escape and water precipitation on the performance of the inerting system should not be neglected in the design of catalytic inerting systems in the future.

Abstract:To effectively improve the operation bandwidth and efficiency of power amplifiers, an X-band high-efficiency continuous class B power amplifier was proposed based on 0.25-μm GaN high electron mobility transistor (HEMT) process. The power amplifier adopted the output second harmonic tuned method and utilized the output capacitance of the transistor to design a parallel LC harmonic tuned network, which simplified the circuit structure and optimized the parallel LC harmonic tune network. The second harmonic load impedance and fundamental load impedance were matched accordingly in wideband frequency, satisfying the requirements of continuous class B mode with high efficiency. Furthermore, combined with the second harmonic source-pull method, the power amplifier employed the input second harmonic tuned method and inputted a series LC harmonic tuned network to the output transistor. With the optimization of the series LC harmonic tuned network, the second harmonic source impedance was moved into the high-efficiency regions of the transistor, which achieved the overall improvement of the output efficiency of the power amplifier in the operation bandwidth. Results show that the proposed power amplifier chip was in the bandwidth of 8.0-10.5 GHz with a saturated output power gain of 40.8-42.2 dBm, a saturated output efficiency of 51%-59%, and a power gain of 19.8-21.2 dB. The small signal gain and input return loss of the power amplifier were 23.6-25.6 dB and below-10 dB respectively. The size of the proposed chip was 3.2 mm×2.4 mm. The circuit structure proposed in this paper provides a feasible method to improve the operation bandwidth and efficiency of microwave monolithic integrated circuit (MMIC) power amplifiers.

Abstract:To reduce the phase noise of fractional-N phase locked loops (PLLs) and suppress the output spurs of PLLs caused by doubling the frequency of reference clock with traditional exclusive-OR gates (XOR), a low-spur reference frequency doubler (RFD) with a hybrid duty cycle calibration loop (DCCL) was proposed. The RFD doubles the frequency of input clock and outputs the reference clock to the PLL, effectively suppressing the phase noise of the PLL by reducing the divide ratio. To reduce the frequency jitter of the reference clock and the output spurs of the PLL caused by the duty cycle deviation of the input clock, the RFD first roughly calibrates the duty cycle with a digital-controlled edge adjustor and then improves the precision with an analog DCCL. The two methods work collaboratively based on the proposed controlling algorithm, achieving a wider calibration range and a higher precision simultaneously. Simulation results show that the proposed RFD could reduce the duty cycle error of a 100 MHz input clock from 13.8% to 0.007%, and decrease the output frequency error to 380×10^-6. The circuit was fabricated in a 40 nm CMOS process. Test results show that it could suppress the in-band phase noise by 6.67 dB and quantization noise by 5.61 dB, and after the duty cycle calibration, the spurs at 1/2 reference frequency offset in the output signal spectrum of the PLL were reduced by 9.52 dB. The in-band noise and quantization noise of PLLs could be reduced by doubling the frequency of the reference clock of PLLs. The spurs in the output signal spectrum of PLLs could be suppressed efficiently by calibrating the input duty cycle of the RFD.

Abstract:To improve the penetration ability of missiles and enhance the damage effect, the problems of impact time and impact angle control of missiles were studied. A nonsingular sliding mode guidance law was proposed based on the relative dynamics of missile and target. According to the shaping theory, a line-of-sight (LOS) polynomial satisfying impact time and impact angle constraints simultaneously was designed. The coefficient was determined using an optimization method. Since the nonsingular terminal sliding mode theory has the characteristic of fast convergence of sliding surface in finite time, a sliding surface was constructed via the error of the LOS, and a nonsingular impact time and impact angle control guidance law was designed. The proposed guidance law could change the actual LOS according to the designed LOS to satisfy the constraints of impact time and impact angle. Through theoretical analysis, it was proved that the proposed guidance law satisfied the Lyapunov stability criterion and could realize the control of the impact time and impact angle without singularities. The proposed guidance law was numerically simulated in different situations. Numerical simulation results show that the proposed guidance law could control impact time and impact angle effectively under various conditions and had certain advantages compared with existing literature. Even with a certain degree of external interference, the impact time and impact angle control could still be completed.

Abstract:To reduce the resonance hazard of helicopters, a fast calculation method for the vibration characteristics of helicopters when hovering in the air is needed. Under the action of centrifugal force, the natural frequency of the rotor changes under the influence of the stress stiffening effect, and there are coupling effects of rotor blades/blades and rotors/fuselage at the same time, which makes the dynamics analysis complicated. On the other hand, in order to improve the calculation efficiency, the low-order and stylization of the kinetics equation has become an urgent need. The transfer matrix method for multibody systems (MSTMM) can solve these problems at the same time. In order to accurately and quickly calculate the natural frequencies of hovering helicopters, a dynamic model of the coupling between the four flexible rotors and the helicopter fuselage was established based on MSTMM, and the dynamic topology model, total transfer equation, and characteristic equation of the system were derived. The transfer matrix of the spatial rotating beam and spinning axis was derived in detail, and the natural frequency of the hovering helicopter system could be quickly calculated. The research shows that the error between the MSTMM calculation results and the ANSYS Workbench simulation results of the spatial rotating beam was not more than 2%, and the MSTMM calculation results of the spinning axis were basically consistent with those in literature. Under the constraints of fixed tail, the first 13 order natural frequencies of the rotor/fuselage coupling system were calculated at the speed of 36.651 9 rad/s, which were consistent with the simulation results of ANSYS Workbench. When the hovering was not restricted, the first eight order natural frequencies of the hovering helicopter system were calculated, and the calculation speed was increased 7.1 times compared with the simulation speed. The results provide a new idea for helicopter dynamics analysis.

Abstract:To accurately forecast rogue waves and avoid the great harm to the safety of the buildings and people on the sea, by utilizing the compact wavelet neural network model, combined with the wave height test data in a three-dimensional model of reefs established based on the measured data of the topography of a reef, time series of three typical wave heights were selected from experimental data to realize the prediction of wave data containing rogue waves against conventional waves, the prediction of wave data containing approximate rogue waves against rogue waves, and the prediction of conventional waves against wave data containing rogue waves. In order to verify the accuracy of the wavelet neural network model, the conventional neural network BP model was used to predict the time series of the three typical wave heights under the same conditions. Finally, the accuracy of the two neural network prediction results was compared. Results show that the wavelet neural network could capture the rogue wave emergencies better. For the overall prediction accuracy of wave surface and the prediction accuracy of rogue waves in three working conditions, the prediction model of wavelet neural network was higher than that of BP neural network, and the predicted wave height curves had better fitting effect with the actual wave height curves. If there were rogue wave features in the neural network training samples, the prediction accuracy of future rogue waves would be further improved. This research has certain application value for the risk warning of rogue waves in ships or marine engineering.

Abstract:To improve the authenticity and reliability of the air combat decision-making and trajectory generation process, the air combat decision-making process should focus on the reliable aerodynamic coupling model and the operational performance of the guided weapon. Therefore, the unmanned combat aerial vehicle (UCAV) trial maneuvering decision based on missile attack state assessment was proposed. First, the construction idea of the UCAV trial maneuvering decision system was analyzed. Next, a UCAV heuristic maneuver decision scheme was established based on aerodynamic coupling model, and 1 331 UCAV trial maneuver strategies were designed by means of fine division. Then, based on the operational application of air-to-air missile, a decision evaluation function including angle, distance, and energy decision factors was constructed, and a maneuver decision method was designed according to the principle of statistics. Finally, a weight factor grading model based on missile attack state assessment was proposed and constructed to ensure the weight of the decision factor changed adaptively with missile attack state. By setting up UCAV and target respectively in two sets of confrontation conditions under three different initial combat situations, simulation experiments were conducted to verify the decision-making ability and effective level of the proposed trial maneuver decision-making scheme and weight factor grading model under different combat situations. This method provides an idea for solving the air combat decision-making problems combined with actual air-to-air missile combat applications, and the constructed decision-making strategy is conducive to giving full play to the operational performance of air-to-air missile.

Abstract:In view of the problem of collaborative real-time trajectory planning during the execution of ground combat missions by multiple unmanned combat aerial vehicles (UCAV), a real-time 3D trajectory planning method based on the sine cosine optimization algorithm with self-learning strategy and Lévy flight (SCASL) for multi-UCAV cooperatively attacking multi-targets was proposed to improve the real-time performance and operability of UCAV collaborative real-time trajectory planning. Firstly, the model of 3D mission space was constructed, and the constraints of flight speed, flight altitude, relative distance, and threat avoidance were designed according to the performance of UCAV. Secondly, the decision variables of collaborative real-time trajectory planning were designed based on the three-degree-of-freedom kinematics and dynamic particle model of UCAV. Finally, the objective function was constructed by transforming the collaborative real-time trajectory planning problem into an optimization problem according to the tactical principle of UCAV operations. The proposed SCASL was applied to solve the model, and the virus search algorithm (VCS) was adopted for comparison. Simulation results show that under the same conditions, the results obtained by VCS met the requirement of collaboration but not real-time, while the results obtained by SCASL met the requirements of both real-time and collaboration, which verifies the validity and superiority of the SCASL-based multi-UCAV collaborative real-time 3D trajectory planning method proposed in this paper.

Abstract:To study the nonlinear vibration characteristics of dual rotor systems considering the elastohydrodynamic lubrication (EHL) of intershaft bearings, an intershaft bearing contact model and an intershaft bearing-dual rotor system model for aero-engine were established based on the EHL theory and the rotor dynamics theory. The dynamic characteristics of the system were obtained by numerical simulation. The amplitude-frequency response of the dual rotor system was analyzed under the conditions with or without EHL. The influences of Hertz contact stiffness, radial clearance, and viscosity of lubricating oil of intershaft bearing on the system characteristics were compared. Results show that EHL had little effect on the vibration amplitude and the position of the resonant peak of the high pressure rotor and low pressure rotor at the first order resonant peak, while it had great effect on the resonant peak in the high speed range, which made the resonant peak move to the right and decreased its amplitude. With varying Hertz contact stiffness and radial clearance of intershaft bearing, the variation of amplitude at the first order resonant peak was less than 5% when considering EHL, and that at the second order resonant peak was between 4% and 9%. The position of the first order resonant peak was not offset, while that of the second order resonant peak moved about 2%–8% to the high-frequency direction. The influence on the vibration amplitude of the low pressure rotor and high pressure rotor was less than 1% when the viscosity of lubricating oil was changed. Finally, simulation results were validated by gas-driven dual rotor experimental facility.

Abstract:With the development of microelectronic technology, people pay more and more attention to the security of integrated circuits. As the main resistance for chip anti-invasive attacks, the security of active shield (AS) is concerned with the information security of integrated circuits. In this study, a random reconstruction circuit based on Galois ring oscillator was designed to improve the security level of AS. First, by inserting reconfigurable nodes into AS, the connection relationship between channels of the AS could be changed randomly. The complexity of the shield could be increased and the failure area could be reduced, which led to the effective resistance of the rerouting attack. Then, a Galois-type true random number generator was designed by reusing the reconfigurable nodes, which solved the problem that the state of the AS was consistent after each power-up and further improved the security of the shield. An experiment was designed and conducted based on the eight-channel AS. Simulation results show that the reconfigurable nodes in this study were only 4 395 μm² using SMIC 0.18 μm process technology. The insertion of reconfigurable nodes only increased the power consumption by 0.4%, and the maximum failure area of the AS was 80% smaller. Random bit stream generated using true random number seeds passed NIST SP800-22 tests. The design circuit has the advantages of small resources occupancy and low power consumption, and it can be combined with a multi-channel AS to provide a higher level of security protection for the chip.

Abstract:To diagnose the fault types of rolling bearings, thereby improving the safety of the equipment, an intelligent fault diagnosis method based on deep residual neural network was proposed. The multi-sensor fusion technology was used to improve the deep residual neural network, so that the recognition accuracy and robustness of the diagnosis model could be further improved. Firstly, through multi-sensor technology, the rich information of the equipment operating state was obtained, and then the primary features of the original vibration signal were extracted by short-time Fourier transform. Finally, the powerful learning ability of the deep residual network was used to further extract the advanced features from the primary features and identify the types of faults, thus achieving the rolling bearing fault diagnosis. The experimental data of rolling bearing were used to verify the effectiveness of the proposed method, and deep convolution neural network-based method and single sensor-based method were taken as contrast methods to test the same dataset. Results show that the proposed method could not only accurately identify faults, but also had good generalization ability and anti-noise ability. The fault diagnosis accuracy reached 100%, and when single or multiple sensors were affected by strong noise, the diagnostic accuracy was at least 93.78% and 82.54% respectively.

Abstract:To study the drag reduction and vibration suppression effect of finite-length wavy cylinder which has a fixed end and a free end, the finite-length wavy cylinder was calculated. First, large eddy simulation numerical model was adopted to calculate finite-length straight cylinder and 12 finite-length wavy cylinders with different combinations of wavelength and amplitude at Re=3 900. Then, after post-processing the results, the lift and drag coefficients of the finite-length wavy cylinders with different combinations were compared, and corresponding drag reduction and vibration suppression effect was analyzed. Finally, flow field analysis was carried out on the combination forms with better drag reduction and vibration suppression effect, and the mechanism of drag reduction and vibration suppression of finite-length wavy cylinder was studied. Results show that for the 12 kinds of wavy cylinders, most of the wavy cylinder forms could reduce the root mean square value of the lift coefficient, which could suppress the vibration, and the best combination form reduced the mean drag coefficient by 5.36%. The flow characteristics around finite-length straight cylinder were similar with those around finite-length wavy cylinder. While due to the existence of saddle and nodal surfaces of wavy cylinder, the fluid interacted in the direction of the cylinder, weakening the development of the vortex behind the cylinder, which reduced the drag reduction and vibration suppression effect. The research results can summarize the drag reduction and vibration suppression effect of finite-length wavy cylinders, which is helpful to investigate the drag reduction and vibration suppression mechanism of finite-length wavy cylinders.

Abstract:To reduce the overall hardware cost as well as improve the synthesizability of finite impulse response (FIR) filter, a two-dimensional non-recursive optimization algorithm based on coefficient matrix was proposed and simulated. Firstly, the existing digital filter optimization algorithms were investigated, and the advantages and shortcomings of these algorithms were compared and analyzed. Then, efforts were made to optimize the existing one-dimensional non-recursive algorithm. By extracting the redundant terms of one-dimensional non-recursive optimization algorithm, a novel two-dimensional non-recursive FIR optimization method with low computing complexity was obtained. Finally, multiple groups of filters were generated to simulate and compare the performance between the proposed algorithm and one-dimensional non-recursive algorithm as well as the existing recursive algorithms. Simulation results show that the two-dimensional non-recursive FIR filter design method proposed in this paper makes full use of the redundant information of the coefficient matrix, keeps the character of minimum logic depth, and meanwhile reduces logic adder number. Compared with the existing one-dimensional non-recursive algorithm, this algorithm saved logic adder by 10.05% (12 bit quantization) and 7.21% (16 bit quantization). In the design of low-order filter, the adder cost was reduced to 30% of the conventional CSD representation, which outperforms the existing recursive and non-recursive filter design methods in terms of logic depth and adder number.

Abstract:Urban gas daily load has the characteristics of randomness and variability, and single load forecasting models have certain limitations in practical applications, especially for specific time periods. To tackle such problem, five evaluation criteria were used to eliminate redundant model before combination forecasting, and a method of constructing variable weight combined forecasting model was proposed. The distribution weights of the combined forecasting model were determined by ant colony algorithm, so that the precision of the combined forecasting model was better than single models in a certain time period. First, the time-varying system of urban gas daily load and the characteristics of each forecasting model were analyzed, which contains many random and fuzzy uncertainties. Then, four kinds of single daily load forecasting models were determined, including ridge regression (Ridge), differential autoregressive integral moving average model (ARIMA), support vector machine regression (SVR), and extreme gradient lifting tree (XGB). According to the characteristics of urban gas daily load model, the parameters of each model and the input vector of the model were given. The redundant model was eliminated by using the comprehensive evaluation indexes calculated by the average relative error, root mean square error, grey correlation degree, correlation coefficient, and Theil unequal coefficient as the evaluation criteria. Finally, based on the ant colony algorithm, a weight distribution combination forecasting model was developed. Study results show that the long-term comprehensive prediction effect of the proposed model was superior to that of any single model. Compared with a single model, the combined forecasting model had higher stability and fault tolerance rate, and stronger generalization ability.

Abstract:To comprehensively evaluate the connectivity of urban gas network under different ground motion intensities, the method of seismic connectivity fragility analysis was proposed based on Monte Carlo simulation which uses the ground motion prediction equation (GMPE) as input. Firstly, the input ground motion intensity measurements (P_ga and P_gv) of each site of the gas network were determined based on GMPE conditioned on a given target magnitude. The distribution of random residual was simulated by normal distribution sampling to represent the uncertainty of the ground motion. Then, the Monte Carlo simulation was used to determine the failure probability of each element in the gas network system, and the loss index of connectivity was determined by the number of blocked nodes in the gas network after the earthquake. Finally, the seismic connectivity fragility curves of the gas network were obtained by calculating the loss index exceedance probability at different magnitudes. The gas network of a city in North China was taken as an example to evaluate its seismic connectivity fragility performance based on the proposed method, and the influence of uncertainty in GMPE was compared and analyzed. Calculation results show that the mean value of magnitude corresponding to each failure state of the gas network was 0.5 smaller when the uncertainty of ground motion was taken into account. Larger connectivity failure exceedance probability could also be observed at different magnitudes. The seismic connectivity fragility analysis method proposed in this study could provide constructive strategy for urban cities to evaluate the probability seismic risk of the whole gas network, and comprehensively take into account the seismic regional differences and uncertainties of ground motion.

Abstract:To study the effects of urban form and land cover on the surface urban heat island (SUHI), by taking Xi’an as an example, local climate zone (LCZ) and land surface temperature (LST) inversion methods were employed to investigate the LST distribution of different types of LCZ based on the Landsat8 remote sensing and building vector data. Results show that the LST of the built-up LCZ was higher than that of the land cover LCZ, but the temperature variation of the built-up LCZ was more stable than that of the land cover LCZ. In built-up LCZ, LST increased with the increase of building density. In land cover LCZ, the LST of water was the lowest, while the LST of bare land was the highest, and LST of three types of vegetation LCZ were lower than those of other two types. LST and SUHI intensity of 14 samples were also calculated. Urban form indicators of built-up LCZ were introduced to analyze the effect of urban form on the SUHI, including building surface fraction (BSF), ratio of green space (GSP), and height of roughness elements (HRE). In built-up LCZ, high-rise buildings with high density and greening could reduce LST and alleviate the SUHI effect. SUHI intensities of water body and forest were lower than those in land cover LCZ types. SUHI effect could be alleviated by increasing water body and greening and reducing building density. The use of shading devices to reduce solar radiation could also mitigate the SUHI effect.