Abstract:The modeling and performance calculation for the deeply precooled combined cycle engine—SABRE(synergistic air-breathing rocket engine) were carried out. A steady componentlevel model of the engine was constructed. The rule of performance variation of the engine in the air-breathing mode along the flight trajectory was obtained, and the altitude-velocity characteristic of the engine was studied. The model is reliable with thrust error less than 6%, and it can be used to calculate performance of SABRE under the air-breathing mode. It is indicated that the SABRE is characterized by both large thrust as rocket engines and high specific impulse as aircraft engines, and its specific impulse is between 21 300~27 380 m/s; along with the increase of altitude and velocity, the thrust and specific impulse of SABRE increase first and then decrease. By decreasing the inlet airstream temperature with precooler, the range of height and velocity of SABRE can be enlarged to 25 km and 5Ma, which is required by hypersonic flight; the lower limitation of velocity is decided by the maximum mass flow rate of compressor, and the higher limitation is decided by the operation rule of helium loop.

Abstract:Dynamic grid deformation method with higher robustness is critical for unsteady flow problems which include moving boundaries. Two of rational and effective mesh quality parameters were introduced, namely Patrick parameters and Baker parameters. Then, a modified dynamic grid method was presented, which can optimize mesh quality on term of mesh quality feedback. Combined with large-pitching of 2D NACA0012 airfoil and 3D ONERA M6 wing, the difference between modified method and classical method was fully analyzed. Modified method has obvious advantage in mesh quality, and at the largest moving degree, it can significantly enhance the robustness of grid mainly through perfecting the worse element. Finally, the modified method was applied to simulate the pitching motion of NACA0012 airfoil and ONERA M6 wing, and the calculations were compared with the experimental values and literature. Result shows that the modified method can improve stronger robustness, therefore it can provide better support for unsteady flow problems.

Abstract:A novel fault tolerant attitude control scheme was proposed based on ILO (iterative learning observer) for satellite with unknown reaction wheel faults, uncertainties and unknown external disturbances. More specially, an iterative learning observer was derived to estimate reaction wheel faults and uncertainties accurately with less online computing power. Secondly, based on the estimated information, a sliding mode controller was derived to achieve the attitude stability of satellite rapidly with unknown external disturbances and reaction wheel faults. Furthermore, the stability of the ILO and the controller were approved by using the Lyapunov stability theory. Finally, simulations were carried out for satellite with unknown reaction wheel faults, uncertainties and disturbances. Results demonstrate that the proposed control scheme is more effectively and displays more feasibility by comparing with other fault tolerant control approach.

Abstract:In allusion to the trajectory tracking process of interception against hypersonic targets in near space, a novel tracking guidance law based on linear quadratic regulator theory and Gauss pseudospectral method was designed. In order to track the nominal trajectory accurately, the linear quadratic tracking problem was considered, while the sufficient and necessary conditions for optimal solutions were deduced with the optimal control theory to acquire the expression of linear state feedback control variables. Based on Gauss pseudospectral method, the time-varying difference matrixes and coefficient matrixes were calculated by using the information of the nominal trajectory on the Legendre-Gauss points to obtain the state disturbances feedback control law. Simulation results show that, compared with the method by solving Riccati equation, this method can obtain the feedback control variables with high accuracy and computation efficiency by less nodes and satisfy the requirement of on-line implementation.

Abstract:A new algorithm based on intersection fault-tolerant fusion and unscented Kalman filter was proposed for fault diagnosis, isolation and reconstruction of skew redundant strapdown inertial navigation system. Considering the error coefficients of gyros, a unified model was built for redundancy configuration. A single point of failure can be isolated rapidly with the intersection fusion model, and an unscented Kalman filter was used for the error coefficients of isolated gyros, which can determine soft failure caused by error coefficients′ change. The simulation with configuration of 5 gyros shows the validity of algorithm under 2 soft failure caused by error coefficients′ change.

Abstract:Continuous fiber reinforced polymer matrix composite trusses are widely used in aerospace and aircraft structures due to their excellent mechanical properties and relatively light weight. The vibration characteristics of the structures are the key factors for the application of composite truss. The natural vibration characteristics of composite truss were studied by using the hammering method. Comparative analysis of the truss structure was carried out by using the finite element simulation. Results show that the structural vibration modes and vibration frequency are consistent with the experimental results, which verified the feasibility and accuracy of the hammer excitation on the vibration characteristics of composite truss.

Abstract:Quadrature element formulations for tapered partially steel-concrete composite beams were established based on the Newmark model and the plane stress model respectively. Deformation of tapered partially composite beams under distributed loading and free vibrational problems with two representative boundary conditions were examined. It is shown that for slender and slightly tapered composite beams common in engineering the proposed 1D quadrature element model is effective enough for flexural and fundamental frequency analysis. Moreover, the 2D quadrature element model is capable of providing better results when needed.

Abstract:To explore the failure modes of the targets subjected to oblique impact of the projectiles with hemispherical nose， ballistic tests were carried out and the attitude of the projectiles was captured with the high-speed camera. The damage modes of projectiles as well as targets were analyzed and the apertures of the targets were measured. It was shown that the dynamic response of the target was not completely symmetric under oblique impact and the target was divided into four partitions according to the mechanic characteristics, which were contact area, bending area, tensile area and symmetric area. The penetration process was divided into four stages which was bulge, dishing, bending and perforating, according to the deformation modes. The failure modes of the targets consist of four typical patterns with the variation of the initial velocity of the missiles. The first one was bulge-dishing-deformation when the initial velocity was low to the ballistic limit. The second one was bulge-dishing-tensile & bend tearing when the velocity was higher. The third one was bulge-dishing-tensile & bend shearing with the increase of the velocity. The fourth one was bulge- tensile & bend shearing when the velocity was largely higher than the ballistic velocity. The aperture of the targets in the front view was elliptical when subjected to oblique impact of the projectiles with hemispherical nose and it was gradually transferred to the oval with the increase of the velocity.

Abstract:A deployable sunshield generally consists of layers flexible, wrinklefree multilayer membranes with high precision, deployable booms and its control equipments. The deployable booms can orderly unfold the multilayer membrane after on-orbit to realize its light control and heat control performance, and it can effectively improve the protection on the aerospace systems. The state-of-the-art of domestic and international deployable sunshield structures were classified and summarized according to their deployable methods of one dimensional axial, two-dimensional plane and three-dimensional circumferential way, as well as the comparison to different structural design and the membrane materials. Some key scientific problems for the sunshields were presented in stray light suppression, folding and deployable deformation mechanism, more field coupling on membranes under the extreme environment, low temperature thermal control, and other aspects of solar pressure moment and computing methods. In addition, some recommendations were also given for the sunshield progress and research in China.

Abstract:To cope with the timing problem of placement in the very large integrated circuit, a timing-driven optimization method for placement was proposed. Firstly, the design was analyzed by a timing evaluation tool and the timing violation paths were collected. A rough placement method was used on the moved cells between any two successive fixed cells in those paths to smooth the nets. After that, a detailed placement based on quadratic timing model was used to optimize the timing characteristics. For the given benchmarks and the evaluation method in ICCAD 2015 contest, the experimental results show that both the worst negative slack and the total negative slack are improved, and the overall timing performance is improved by 45~350 min.

Abstract:Crystal oscillator output frequency often drifts under vibration. Therefore, based on the analysis of the acoustic active noise control technology and the mechanism of acceleration effect on crystal oscillator phase noise, a method of reducing crystal oscillator phase noise under vibration was proposed. The simulation about the acoustic active noise control system obtained that the theory of acoustic noise reduction can be used in crystal oscillator phase noise reduction. By adding acceleration sensor, analog-to-digital converter, digital-to-analog converter and digital processor in the peripheral circuit of crystal oscillator, the phase noise real time compensation active noise control system was constructed. The results show that the active noise control system achieves 20 dB phase noise compensation under the random vibration of 0.03g/Hz amplitude range and 10~850 Hz frequency range.·

Abstract:Aimed at the bottleneck of the non-uniform interface and protocol of spaceborne network caused by multiple bus standards, the time-triggered static routing and event-triggered dynamical routing based on the SpaceWire bus protocol were combined to make control data and payload data share the same network. The static routing mechanism was fully abided by the SpaceWire-D protocol to ensure deterministic data delivery, in which the heuristic scheduling algorithm was adopted to realize the multi-slot schedule for the first time, and the time-slot was designed by using the greatest common divisor to improve the throughput. And the dynamical routing mechanism can insure that the critical random event be processed by allocating priority levels to random event and payload data preferentially when the transmission routes conflict with each other. In addition, a simulation model for the network system was set up in OPNET to evaluate the proposed routing mechanism. Results show that the throughput of the network is improved significantly during static routing time as compared with the existing scheduling algorithm, and different transactions can be processed according to their priority during the dynamical routing time as expected.

Abstract:The performance of CODE′s new solar radiation pressure model, the EECOM (extended empirical CODE orbit model), was analyzed on precise orbit determination for mixed-type BeiDou constellation. This study is based on the NUDTTK software, which is a satellite orbit determination toolkit. The validation of satellite laser ranging reveals that the EECOM can improve orbital accuracy of geostationary earth orbit satellites by 17.4% and 35.1%, compared with traditional CODE′s ECOM-9 and ECOM-5 models, respectively. As to the inclined geosynchronous earth orbit and the medium earth orbit satellites, the ECOM-5 model performs better than EECOM as well as ECOM-9 model. It means that CODE′s new solar radiation pressure model is not able to improve the orbital accuracy of the inclined geosynchronous earth orbit and the medium earth orbit satellites. External orbit validation by IGS data analysis centers of GFZ, WHU and CODE indicates that the accuracy of our current BeiDou precision orbit is 1~4 m for geostationary earth orbit satellites, 25~30 cm for inclined geosynchronous earth orbit satellites and 10~20 cm for medium earth orbit satellites, respectively.

Abstract:To efficiently retrieve in multimodal data, it is essential to reduce the proportion of irrelevant documents. The image data were projected to the Hamming space by using the localitysensitive hashing algorithm, the text data were mapped on the hashing function of Hamming space by employing the neural network learning, and then a novel crossmedia retrieval approach was proposed to reduce the proportion of irrelevant documents. The experiment shows that the proportion of the relevant documents can be much improved in the proposed method. Assessments on the two public datasets also demonstrate the efficacy and the accuracy of the proposed retrieval method when compared to the baselines.

Abstract:Aimed at the problem of the traditional region-based active contour model, which was difficult to segment the noisy images and intensity inhomogeneous images, an active contour model, including global term, local term and regularization term, was proposed. Global term was derived from the data fidelity items of ChanVese model. Meanwhile, the construction of local term took the local intensity information into account and the image local entropy that reflected the grey characteristics was introduced. According to the characteristics of different images, the reasonable parameters of global item and local item were selected. The regularization term was added to ensure the smoothness of curve evolution and to guarantee the reliability of segmentation. A variable level set was used to minimize the energy function to get the gradient descent flow. Experimental results of synthetic images and real images demonstrate that the proposed approach is efficient in segmenting the noisy images and inhomogeneity images.

Abstract:In response to the smart noise jamming under multi-channel broadband digital radio frequency memory repeater jammer, an orthogonal decomposition method for anti-jamming was put forward on basis of chaotic modulation signals and multiharmonic phase modulation chirp signals. Both of these two signals have a ″thumbtack″ ambiguity function. They are not only of good resolving power in range and Doppler, but also of good sensitivity to echo frequency. By an orthogonal and diverse design, they can better adapt to the smart noise jamming under multi-channel broadband digital radio frequency memory repeater jammer. The result of analysis and validation on the anti-jamming performance of the new method through computer simulation shows that under smart noise jamming in multi-channel broadband digital radio frequency memory jammer, the electronic counter-countermeasures improvement factor of the new method can be more than 10 dB, which is much better than that of the traditional frequency and slope agility method.

Abstract:The traditional Kalman filter algorithm is not robust with uncertain parameters. In view of this and based on the ensemble robust filters, the optimal method of data assimilation constructed from observations, which was referred to as the ensemble timelocal robust filter of inflating the observational covariance matrices, was presented, and the rule of the algorithm and the inference of the formula of the approach presented were given. The approach presented was compared with the ensemble Kalman filter method on the robustness and the assimilation accuracy using the strongly nonlinear Lorenz-96 model and on the basis of the changeable condition of the performance level parameters, the force parameters, and the size of observations and ensemble. The results suggest that: the root mean square errors of the ensemble Kalman filter method are much larger than those of the time-local robust filter; the ensemble Kalman filter produces filter divergence with a relatively small observation or ensemble size, while the root mean square error of the robust filter has slightly change; compared with the traditional ensemble Kalman filter algorithm, the time-local H_∞filter approaches using the observation inflation is more robust on the changes of system parameters, and improve the accuracy of filtering.

Abstract:According to the characteristics of the airborne avionics system, a method for evaluating the RF(radio frequency) stealth performance of the airborne avionics system was presented. The factors that influence the performance of the airborne avionics system in the polarization domain, wave domain and energy domain were analyzed, the RF stealth index of the waveform domain, polarization domain and the energy domain were constructed, an RF stealth evaluation method of the traditional “radiation reception” model was broken. And a quantitative evaluation method of radio frequency stealth based on the working state and working parameters of airborne avionics system was established. Finally, a simulation evaluation of airborne radar system was carried out. Results show that the proposed method can correctly reflect the RF stealth performance of airborne radar system.

Abstract:Because of the difference of thermal physical properties between subsurface target and the soil, the temperature field distribution on the surface of the whole soil area is under its influence and the target is easily detected and destroyed by enemy. To solve this problem, taking into account the influence of solar radiation, sky radiation and wind speed, the heat transfer model of temperature distribution of the region containing buried target was established, which revealed the impact of buried target on the regional temperature field during different time. Based on the transformation thermodynamics, the thermal conductivity general expressions of spherical transient thermal cloak was derived by the means of coordinate transformation. According to the equivalent medium theory, the designed thermal physical parameters were homogenized and the feasible of target infrared stealth technology was verified based on the thermal cloak by numerical method.

Abstract:An analytic dynamic trajectory generating algorithm based on real flight data interpolation was proposed for INS/GNSS integrated navigation simulation, in order to solve the problem of generating high-precision simulated signals of gyros and accelerometers in a strapdown inertial navigation system. Accurate piecewise analytic expressions of angular rates, angular increments and specific force integral increments in body frame were obtained on the basis of the spline function interpolation for the vehicle′s attitude, position and gravity data in the earth centered inertial frame. The simulated signals of gyros and accelerometers were coincident not only with the vehicle′s kinematics and dynamic characteristics, but also with the characteristics of post-processed GNSS′s pseudo-ranges and their rate measurements. The influence of the lever arm effect of an inertial measurement unit was also simulated. A constrained analytic quaternion interpolation algorithm was proposed under the restrictive condition in which the norm of the interpolated quaternion should be 1. Based on the real flight data of an unmanned aerial vehicle, it is proved that the accuracy and the effectiveness of the proposed algorithm can meet the requirements of dynamic simulation of integrated navigation. The algorithm can also be used in other simulations, such as high-precision high-dynamic navigation and rigid body motion control, in which the simulated sensor signals in angular and linear motion are needed.

Abstract:The land-based vehicle electromagnetic launcher for unmanned aerial vehicle is a new kind of take-off device. In order to realize the high maneuverability, a bilateral moving-coil permanent magnet direct current linear motor with the stator magnet track section splicing structure scheme was presented. In order to evaluate the influence of stator magnet track splice on the performance of the motor, the permanent magnet linear 〖JP2〗motor model was established. The influence of the up and down dislocation, the left and right dislocation and the tilting dislocation of the segmented splice were analyzed by using the finite element analysis software. Based on the analysis, the allowable magnet track splicing offset range was given.

Abstract:In order to study the motion characteristics of a certain type of rotary selfstabilizing terminal sensitive submunition, the submunition′s asymmetric structure characteristics and its initial projection condition were fully considered. The dynamic unbalance missile model was introduced to derive the 6 degrees of freedom trajectory equation of the submunition and analyze the characteristics of steady state scanning motion of submunition. Results show that the submunition′s asymmetric mass distribution and the initial angular velocity are the necessary condition for the realization of the steady state scanning. The scanning frequency of the submunition is only determined by the projection angular velocity ω_σ0, and is positively correlated with the ω_σ0. When the initial pitch angle φ_a0≥0°, the overall trend of scanning angle is increased, and when φ_a0＜0°, the scanning angle decreases and then increases. The scanning area is positively correlated with the mass ratio of weight and projectile, the φ_a0, the initial yaw angle and the ω_σ0, and is negatively correlated with the ratio moment of inertia of the center cylinder.

Abstract:A ground-based multisensory fusion approach was proposed for the guidance of UAVs (unmanned aerial vehicles) landing in GNSS (global navigation satellite system) denied environments. Firstly, an active laser transmitter was used to irradiate the UAV. The light spot in the obtained infrared images reflected by the airborne reflection prism was recognized as the UAV. Then, a region of interest was defined in the visible-light image by coordinate transformation according to the result of the infrared image. To reduce the computation complexity, the UAV was detected and located in the region of interest. Finally, the relative position of the UAV can be obtained by combining the distance measurement and the angle of the pan-tilt unit. Results of flight experiments demonstrate that the proposed approach can offer the precise positional information of UAV and can effectively adapt the complex background of UAV autonomous landing.

Abstract:For the sake of tri-axial magnetometer calibration, an error compensation model of tri-axial magnetometer was established. The sine curve fitting method was proposed to calibrate the tri-axial magnetometer based on spin data. The calibration of triaxial magnetometer could be implemented by calculating the calibration parameters using the initial phase angles of the sine curves. The results indicate that it has high precision to calculate the calibration parameters of tri-axial magnetometer, and the measurement accuracy of calibrated magnetometer is improved significantly. It dose not require high-precision optical pumping magnetometer to measure the magnetic field intensity, thus it puts forward an effective way for calibrating tri-axial magnetometer.

Abstract:Flexible structures are widespreadly applied in fields of aerospace. In order to obtain the best dynamic performance of the structures, the optimal locations of actuator and sensor become a key problem in active vibration control. The new proposed optimization criteria based on finite element dynamic equation ensuring good controllability or observability of the structures and considering the remaining modes effect were derived. Non-linear integer programming genetic algorithm was utilized to find the optimal positions of actuator and sensor. A cantilever plate was simulated by using state-feedback linear quadratic regulation controller to validate the vibration suppression effects. The comparison results of numerical simulation demonstrate the advantages of the proposed method.

Abstract:Aiming to the problem of the inspection of small diameter bending pipes using torsional guided wave, finite element method and experiments were used to investigate the problem. ANSYS was used to simulate the propagation of torsional guided wave in bending pipe. A magnetostrictive torsional guided wave transducer was designed to inspect small diameter pipes. The exciting and receiving theoretical model of the transducer was built. The experimental signals were explained by using the theoretical model. Research results show that mode conversion happens at the elbow of the pipe and part of the T(0,1) mode converts to F(1,1) mode. The orientation of the F(1,1) mode perpendicular to the direction of extrados-intrados. The double end reflection phenomenon in inspection signal is caused by mode conversion. With the increase of frequency, the ratios between end echoes′ trend towards alleviation. The longitudinal magnetostrictive forces excited by the transducer bring about small longitudinal guided wave in the signals. Conclusions will provide theoretical guide to the inspection of small diameter bend pipes using magnetostrictive torsional guided wave.

Abstract:For long-distance interception of highspeed, large maneuvering target, not only the interception arc is longer, but also interception time is longer. Therefore the guidance law design cannot make all costs to follow the target, but also consider the energy management issues. By reducing the nonlinear kinematics problem’s order, using optimal control theory, and taking energy management into consideration, the optimal guidance law for high speed and maneuvering target was obtained, and the terminal collision angle constraint could be satisfied. By introducing the damping of the two forms of linearity and exponential, the sensitivity of the missile to the target maneuver changes with the distance of the target when it intercepts the high speed and high acceleration target, so as to achieve the goal of energy management. The performance of the guidance law was verified by two-dimensional nonlinear simulation.