Abstract:In order to achieve good active control effect of fluctuating-frequency and dense-frequency sinusoidal vibration induced by multi-sources which may occur in active-passive vibration isolation devices of marine machineries, the improved algorithm based on multi-channel narrowband Fx-Newton algorithm was studied. The algorithm with adaptive compensator for narrowband filter phase distortion was proposed, which can obtain high robustness for fluctuating-frequency sinusoidal vibration. Next, the multi-reference Fx-Newton algorithm was proposed to control dense-frequency multiple sinusoids in the same narrowband, under the precondition of acquiring multiple independent reference signals from vibration sources. The active control experiments show that the improved narrowband Fx-Newton algorithm can get good control effect on the fluctuating-frequency sinusoidal vibration, and can achieve stable and efficient control on the fluctuating dense-frequency sinusoidal vibration excited by two exciters or two air compressors.

Abstract:Aiming at the limitation that methods based on Kalman filtering framework can deal with the known Gaussian white noise only, an improved method was proposed to deal with the system with heterogeneous noises. The disturbance from an unknown system was classified to Gaussian white noise and unknown but bounded noise which are both added into the state equation and observation equation on the basis of the noise characteristics analyzed. The set-membership filter was employed to improve standard Kalman filtering, and the adjusted value of the gain filtering was obtained by calculating the minimum mean square error of system with two noises. The improved filtering was proposed to incorporate the estimator statistics of the set-membership filter, two noises statistics and the adjusted filter gain. The improved algorithm was applied to an uncertain vehicle navigation system, and the simulation results show that the improved filtering algorithm which overcomes the heterogeneous disturbance noise performs better than the extended Kalman filtering.

Abstract:Based on the LQR(linear quadratic regulator) control method, a frequency domain weighted LQR controller was designed. By improving the commonly used filters, a new filter design idea was proposed. When the vibration source frequency is lower than the lower limit response frequency of the actuator and the actuator produces a reduced output, the control performance of the frequency band lower than the lower limit of the actuator response is improved by changing the filter parameters, increasing the weight and control force of the low-frequency part. The simulation results show that the frequency domain weighting method can improve the control performance of the LQR controller in a specific frequency domain, and the control performance of the improved frequency domain weighted LQR controller based on the new filter is further improved beyond the lower limit response frequency.

Abstract:The importance measure analysis can find out the important feature variables of model, which can effectively reduce the variable dimension and decrease the computation time. The relationship between the important measure of random forest and the variance-based global sensitivity measure was explored, which can give a novel way to solve variance-based main sensitivity index S_i and total sensitivity index S^T_i. The importance measure of single and group variables based on random forest were established to improve the corresponding measure index system. Several examples are given to verify the validity of the proposed important measures and the correctness relation derivation about variance-based sensitivity indices.

Abstract:The rapid development of high-performance computer provides the hardware environment for high performance numerical simulations. Many numerical simulations have the ability of handling meshes from billions of elements to tens of billions. However, the development of parallel mesh generation, which is a critical step in numerical simulation, is relatively lagging behind. Thus, a multilevel parallel unstructured tetrahedral mesh generation algorithm for complex geometric models was presented. Firstly, a sizing-function of the mesh was established on the basis of the geometric features of the model, and the geometric entities were grouped on the basis of the sizing-function and the adjacency relationship between the geometric entities. The grouped geometric entities were distributed to different computing nodes. Then the triangular meshes were generated by the advancing front method among the nodes. And the triangular meshes were decomposed into sub-meshes which were distributed to each process. Finally, a multi-threaded parallel algorithm was used to generate tetrahedral meshes in the process. The proposed parallel mesh generation algorithm was validated on the Three Gorges Dam model, and the results show that the presented algorithm has good parallel efficiency and scalability, and can generate billions of high quality tetrahedral meshes for modern supercomputers with thousands of processor cores.

Abstract:An induction strategy based on position spoofing for UAV (unmanned aerial vehicle) was presented to solve the problem of effective control and disposal of unauthorized UAV. The target UAV navigation and control systems got the fictitious position information caused by the spoofing signals that were produced by combination of accurate position information of the target and the induction strategy. The target UAV changed its flying attitudes and deviation from the pre-specification air route. Experimental results demonstrate the validity and effectiveness of the proposed induction strategy.

Abstract:To fully make use of the value of BeiDou signals big data resources and expand its applications in atmospheric and oceanic fields, a method to monitor rainfall information using polarimetric phase shift of BeiDou signals was studied theoretically. Based on the frequency and polarization characteristics of BeiDou signals, the microphysical process of BeiDou signals passing through rain area and interacting with raindrops was analyzed; from the definition of polarimetric phase shift, the mathematical model between polarimetric phase shift and rainfall intensity was established and analyzed by numerical simulation method. It is concluded that the polarimetric phase shift of BeiDou signals is sensitive to rainfall intensity, which illustrates the feasibility of monitoring rainfall intensity by BeiDou signals. The influence of some key factors such as raindrop size distribution, path length of rain area and elevation angle of satellite on polarimetric phase shift is systematically studied, and reasonable suggestions are put forward for subsequent experimental verification.

Abstract:Based on 0.18 μm CMOS process, a low-variable tuning gain LC-VCO(inductance capacitance-voltage controlled oscillator) was designed for wireless communication and radar systems. The circuit includes a distributed bias varactor array and a switched capacitor array, a reasonable selection of the bias voltage can achieve the purpose of expanding the C-V(capacitance-voltage) curve, thereby effectively reducing the tuning gain within the entire tuning voltage range. The three-bit switched capacitor array divides the entire adjustable frequency range into 8 sub-bands, which is implemented by controlling the varactor array. And the switched varactor array is adopted, which can effectively suppress the variation of the LC-VCO tuning gain. Based on the model of 1P6M 0.18 μm technology, the post-layout simulation results show the good performance on property of tuning gain variation rate, which is 21.5% with the frequency tuning range from 9.13 GHz to 11.15 GHz, at the same time, the VCO DC power consumption is 9 mW with 1.8 V supply voltage, the phase noise is -105 dBc/Hz@1 MHz when the VCO oscillating frequency is around 10 GHz.

Abstract:Construction of autonomic capability on spacecraft faces such developing problems as requirements increasing, variability, more complexity, and unknowingness of trend. It is needed to alter development method and architecture design to suit these trends. Based on the research of current four methods, a fifth method, a development mode which is model-based and data-oriented, was proposed. A service model with plug-and-play capability was given, and the electronic data sheet technology was used to construct the bottom-up plug-and-play capability from device level to functional service level. An intelligent planning service instance using this service model was designed and described. The purpose of the fifth method is to provide a persistent development base for the construction of the autonomic capability on spacecraft and the intelligence management and control ability between space and ground.

Abstract:High-precision positioning of the ground target is an important premise for the UAV (unmanned aerial vehicle) to carry out target reconnaissance, firepower guidance, effectiveness evaluation, etc. However, the accuracy of the UAV′ s target positioning is limited by factors such as many error factors and long transmission chain. The method of multi-frame image registration method based on Kalman filter for ground target location was studied. By combining the multi-frame target image acquired by UAV, the high-precision fusion positioning of UAV to ground target was studied based on Kalman filter. Monte Carlo method was introduced to simulate the error convergence, value and distribution of multi-frame fusion location method based on Kalman filter. The influence of observation interval and line-of-sight elevation angle on error convergence was analyzed. Several suggestions for improving the positioning accuracy were proposed.

Abstract:In order to achieve the deterministic transmission of the massive real-time data streams in a short time on the SpaceFibre onboard data network, the time-slot allocation algorithm of QoS (quality of service) for SpaceFibre was proposed. Formally the QoS of SpaceFibre network was described and the definitions of scheduling matrix were given; the queuing model of QoS was created and the impact of time-slot allocation on delay performance was quantitatively analyzed; From the perspective of network compatibility and robustness of algorithm, an improved binary sequence scheduling sub-algorithm was derived; the improved hybrid partheno-genetic scheduling sub-algorithm with the highly evolved initial population and more genetic operators was given; the SpaceFibre communication model was established by using the Opnet network simulation platform to compare with the delay performance under different algorithms. Simulation results show that the time-slot allocation algorithm has lower average latency compared with other algorithms. The performance of the network is optimized. The research results can provide a reference for building a low-latency SpaceFibre network.

Abstract:To study the problem of impact time control for missiles in three-dimensional space with field-of-view constraint, a three-dimensional nonlinear sliding mode guidance law was proposed. The sliding mode surface was designed by using the impact time error and then the acceleration commands in pitch and yaw were derived. By making a simple correction to the proposed guidance, the singular issue driven by zero-initial-heading-error was overcome. The stability and convergence of the proposed guidance law was proved in a rigorous mathematical manner. The value range of some certain parameters and the relationship with the pure proportional navigation guidance law and the decoupled three-dimensional guidance law were analyzed. Simulation results indicate that control of the increasing or reducing impact time can be achieved effectively with the field-of-view constraint by using the proposed guidance law. The stronger the degree of coupling between the pitch and yaw planes is, the more advantageous the proposed guidance law in control energy is.

Abstract:Based on simulation accelerated pitting corrosion test results of 7B04 aluminum alloy specimen, which combined with the pitting corrosion mechanization and microstructure of aluminum alloy and stochastic process essence of pitting corrosion, two typical damage models with complex morphology which were composed of many micro-ellipsoid corrosion pits were erected through finite element method, two models were named wedging model and encircling model respectively. The stress concentration effect which was embodied by stress concentration factor and stress nephogram was calculated and analyzed through ANSYS software and linear elastic fracture mechanics. The results show that the stress concentration effect of wedging model and encircling model is very different from the results of simplified ellipsoid corrosion pits model. The stress concentration factor value of wedging model and encircling model is almost the same, and may increase because of interference and influence and superposition of each single micro-ellipsoid corrosion pits. The obvious area or location of stress concentration effect of wedging model and encircling model almost locates at the intersection region between each micro-ellipsoidal corrosion pit, the intersection regions almost are on the side of the macro corrosion pits. The size range of wedging model and encircling model stress concentration effect are well matched with the microscopic grain size and small crack size of aluminum alloy.

Abstract:In calculating random fatigue life of structures in engineering at present, the stress life method based on the axial tension-compression fatigue life S-N(stress-number of cycles) curve is often used. Easy as it is to use, it often ignores not only the single-axis S-N curve, causing inaccurate reflection of the effect of multi-axial stress state, but also the resonance on the structure fatigue life in random vibration, as a result, the method in the prediction of fatigue life of structures under random vibration with actual life tends to have a larger error. The triaxial factor was introduced to reflect the multi-axial stress state of the structure under random vibration, and its expression in frequency domain was generalized. Based on this, the multi-axial vibration factor, a new random vibration fatigue damage parameter, was proposed. The new damage parameter not only considers the effect of multi-axial stress state and resonance on fatigue life under random vibration of the structure, but also has a simple form for engineering application. By using the new random vibration fatigue damage parameters, the multi-axis S-N curve for random vibration was obtained, and a new random vibration fatigue life prediction method was established. By predicting the random vibration fatigue life of 7075-T6 and LY12CZ aluminum alloy notch specimen, the results show that the method can accurately predict the fatigue life of two kinds of notch specimens under random vibration.

Abstract:The microstucture arrays are widely used in the fields of LED lighting, liquid crystal display and optical instruments. Due to the tiny and complex structure and the high requirements of figure and surface quality, the study on the process technology of microstructures causes wide attention. A FTS (fast tool servo) device with the combination of piezoelectric ceramics actuator and flexible hinge holder was presented. The electro-mechanical coupled model of the FTS system was established and the effect of the system parameters on the system behaviors was investigated. The optimization of the structure parameters of flexible hinge holder was performed on the basis of the finite element simulation. The linearity of the output displacement of the tool was measured by laser displacement sensor. Finally, the microstructure of sinusoidal grids on the cylindrical surface of red copper was processed with the FTS and ultra-precision turning machine, and the machining results indicate that the designed FTS is able to accurately and effectively process the microstucture arrays with complex structure.

Abstract:To completely remove oxide layer and crack layer on the inner surface of the hollow steel drill rod, deep hole reaming was processed on the inner hole of the drill rod. In view of the problems of chip discharge difficulty, high cutting temperature and poor processing quality of the inner hole surface during deep hole reaming, hydraulic low-frequency vibration assisted gun drill was adopted to improve the hole surface quality here. Experiments results showed that compared with the ordinary reaming, the hydraulic low-frequency vibration reaming can reduce the chip size and the jagged edge phenomenon on the chip surface, improve the inner hole machining surface, reduce the tool marks and scratches and the processing temperature under the condition of the speed of 500 r/min and the feed rate of 0.1 mm/r. Furthermore, Furthermore, the minimal clip size with least scratches and lowest processing temperature could be achieved when the frequency reaches 36.7 Hz with vibration amplitude at 0.58 mm. With the increase of the feed rate within the range of 0.80~0.12 mm/r, the length of chip becomes larger, and the tool marks and scratches on the surface of the inner hole increase. The speed has little effect on the chip length and the surface quality of the inner hole.

Abstract:In order to solve the problem of high cost of structural time-variant reliability analysis, a time-variant reliability analysis strategy based on weighted stochastic simulation was proposed. Time-variant reliability analysis needs to calculate the failure probability of structure with respect to different times, which often requires multiple reliability analyses, involving hugh calculation cost. The proposed method improves and expands the conventional stochastic simulation method which is used to analyze the static reliability problem. The weighted Monte Carlo method and weighted importance sampling method respectively are developed respectively by using the weighting strategy to efficiently analyze and calculate the time-variant reliability problem. The proposed methods require only one conventional reliability analysis simulation to obtain the estimator of time-variant failure probability function. Two examples, a tubular cantilever beam and a ten-bar truss, are used for verification. Results show that the weighted methods can greatly ease the computational burden and improve the computational efficiency while ensuring the precision.

Abstract:In order to carry out a more in-depth study on the load sharing characteristics of the torque-split gear system, a nonlinear dynamic model was established. The numerical simulation method was used to calculate the load sharing coefficient of the system. The influences of the torsional stiffness of the linkage shaft, the output shaft support stiffness, the input speed and the axial angle on the load sharing coefficient were studied. Experiment of gear system was carried out, and the research results show that:the load sharing coefficient of the output end is larger than the one of the input end, and the load sharing coefficient of the high pressure input end is larger than the one of the low pressure input end; the load sharing coefficient grows with the increase of the torsional stiffness of the linkage axis; with the increase of the support stiffness, the load sharing coefficient increases first and then reduces; the load sharing coefficient shows fluctuations with the growth of input speed, and the resonance peak appears in the range from 4 100 r/min to 4 400 r/min; the value of shaft position angle a₂ can affect the change law of the load sharing coefficient with a₁, and minimizing the shaft position angle can improve the load sharing performance of the system. Experimental results verify the correctness of the model of marine gear system.

Abstract:In order to improve the lethality of the axial direction fragment field of the warhead, experimental and numerical studies were conducted to investigate the maximum velocity and ejection angle distribution characteristics of axial prefabricated fragments driven by caseless cylindrical TNT charge. The LS-DYNA software was used to numerically simulate the process of prefabricated fragments driven by the charge, and the flying process of the prefabricated fragments group was described. The theoretical calculation formula of the overall plate driven by the charge was improved to obtain the maximum initial velocity of the prefabricated fragments. Results indicated that close agreement was found between numerical, experimental and theoretical results for the maximum velocity of prefabricated fragments. With the increase of the distance from the central of TNT charge for fragments, the initial velocity and radial ejection angle decreased and increased respectively, while the circumferential ejection angle of fragments varying on a very small scale. According to the experimentally measured data and theoretical analysis, the maximum initial velocity of prefabricated fragment in the central area exceeded 2500 m/s, the maximum ejection angle in the radial direction was about 22°, and the mean value of ejection angle in the circumferential direction was less than 5°.

Abstract:Based on the principle of the function of mine clearance by the way of blasting tube, the 8.2 kg solid-state FAE(fuel air explosive) mine clearance device was designed. By changing the initial explosive position and the method of setting up, in the multiple field near ground explosion tests, the stress tests were conducted by adopting reflection pressure sensor to test forward and lateral pressure from different explosive locations, at the same time a certain type of anti-infantry mines in the corresponding burst position of the forward line pressure sensor was set, and the explosive parameters in different location′s explosive field and the scope of anti-infantry′s mines clearance was obtained. Results show that the clearance range of the horizontal charge was significantly larger than that of the vertical charge, and the optimal blast height was about 0.60 m. Moreover, the acting time curve of the positive pressure zone of the explosion field is of “V” type, and the acting range of the product is up to 63 times of the charging radius, which has obvious advantages over the acting time of equivalent TNT. The mine clearance range of this device is about 1.8~3.85 times of the current mine clearance range of blasting tube blasting, the forward reliable mine clearance range can be 77 times of the charging radius, and the side can be 69 times. Since the positive pressure action time of the explosive zone is significantly longer, so it is beneficial to the clearance of all kinds of mines, and it is a potentially efficient humanitarian mine-clearing charge.