Abstract:The very wide SIMD (single instruction multiple data) digital signal processor often supports vector memory access mode of regular applications with contiguous or equal address strides, but its access bandwidth utilization is usually very low for the irregular application accesses that exist widely in scientific and engineering computations. It reduces the overall computing performance of digital signal processor. In order to improve the vector access performance for the irregular applications, the vector memory called GSVM to support the Gather/Scatter access was designed on the basis of the architecture of a SIMD digital signal processor. The vector address generation unit and the conflict buffer array matching the SIMD width were designed to realize the full pipeline operations of Gather/Scatter instruction. The experimental results show that compared with the vector memory without Gather/Scatter, the GSVM obtains 2~8 times speedup for sparse-matrix vector multiplication test programs with the 22% hardware overhead.

Abstract:In order to enhance data access efficiency between front-end nodes of Internet of things and edge computing applications, a novel RZCFS(remote zero-copy file system) was proposed. The zero-copy data transmission framework based on generic network interface card was realized without special hardware. The random-access character of non-volatile memory was fully utilized by RZCFS to reduce data caches and copies, which yields a significant throughput improvement for data access. A buffer pool was implemented, the traditional network stack and storage stack were simplified and converged to shorten the file access path, which can eliminate software overhead and reduce data access latency. As a result, RZCFS provides the low-latency and high-bandwidth remote data access. Simulation results show that it achieves 42.26%~99.19% latency reductions for traditional NFS (network file system). The throughput of fine-grained access can reach 1297 times faster than those of NFS. The RZCFS significantly reduces the processor cycles and cache misses.

Abstract:Aimed at the anti-radiation requirements of the aerospace electronic system control module for integrated circuits, a controller chip based on the proportion, integral and differential algorithms was designed on a 130 nm partially depleted SOI (silicon-on-insulator) process platform. The TID (total ionizing dose) radiation reinforcement was investigated in terms of SOI wafer, fabrication process and layout design, respectively. The test results of the chip show that the adjustment accuracy of the chip reaches 5×10-12, which is equivalent to the imported radiation-tolerant FPGA (field programmable gate array); the chip is superior to the foreign anti-radiation FPGA in terms of long-term frequency stability. TID experiments were carried out and the results show that the chip can function normally under the total dose of 300 krad (Si).

Abstract:ROP (return-oriented programming) is a technique which is able to bypass the protection of the DEP (data execution prevention). The ROP can constitute a program that performs a specific function by searching for an appropriate assembly instruction fragment in the memory code area. Previous methods for automatic generation of ROP do not consider the limitation of the layout of ROP caused by the program memory requirement, which leads to poor practicability of ROP. In order to solve this problem, a new method for automatic fragmented layout of multi-module ROP based on symbolic execution was proposed. The ROP chain was divided into different modules on the basis of automatic ROP generation framework Q; the controllability of memory was dynamically analyzed by using symbolic execution tool S2E; the controllable memory areas for each ROP module was found, and the fragmented layout ROP was automatically constructed. Experiments show that, compared with the previous methods, the ROP chain generated by the proposed method can effectively reduce the requirements for the program memory controllability.

Abstract:Aiming to reduce conservatism of the optimal solution with regard to robust optimization model, a light robust optimization approach was proposed to solve the open vehicle routing problem with travel time uncertainty. This approach yields routes that minimize the weighted sum of the number of defaulted vehicles and the total penalty cost. For each realizations of the uncertain data set, the optimal solution of the approach can ensure that its optimal value never exceeds a certain value, thus improving the conservatism of the optimal solution. To improve the probability of finding the optimal solution, the automatic design of genetic algorithms was proposed to solve the model. Its main idea is to use the particle swarm optimization algorithm to search components of genetic algorithm which can expectedly enable the genetic algorithm to generate the optimal solution and then to combine these components to generate a new genetic algorithm to solve the model. The new genetic algorithm was used to solve the model continuously and give rise to a new optimal solution. Calculation results show that the conservatism of the optimal solution solved by the proposed light robust optimization approach is significantly reduced comparing with the past robust optimization method.

Abstract:The accurate navigation of the underwater vehicle plays an important role in the process of the ocean utilization and development. The problem of restraining the accumulation errors of the underwater navigation over time was discussed and analyzed in detail. Firstly, the development history of the inertial devices was briefly described. Secondly, the advantages and disadvantages of each navigation system were compared in detail, the research status of the gravity-aided navigation at home and abroad were introduced, and the demand for the high-precision navigation of the underwater vehicles and the scientific problems of insufficient spatial resolution of the global marine gravity reference map were analyzed. Finally, the idea and technical route of obtaining the high spatial resolution and high precision global marine gravity reference map by GNSS-R altimetry constellations are proposed in order to improve the accuracy of the underwater gravity-aided navigation.

Abstract:Satellite navigation receivers are highly susceptible to electromagnetic interference, and array-based space-time or space-frequency adaptive processing has been proved to be the most effective anti-jamming method. In actual engineering implementation, the channel mismatch is inevitable. Thus in this paper, the impact of channel mismatch on the performance of GNSS antenna array was evaluated according to the statistical evaluation method. The results show that, group delay bias and amplitude mismatch between channels are the two main factors leading to the deterioration of anti-jamming performance. The influence of the former can be eliminated by increasing the number of taps of space-time filter, while the latter is not sensitive to the number of taps and the necessary calibration is required.

Abstract:In order to fully explore the use of massive satellite network data, improve decision-making efficiency,and strengthen the analysis methods of spatial frequency and orbit resource acquisition and storage, especially for the GSO (geostationary satellite orbit) resource selection problem, a satellite network situation assessment strategy based on machine learning algorithm was proposed. By analyzing the characteristics of satellite network coordination factors, the CNN (convolutional neural network) was selected as the target algorithm model, and the training data set and label rules of the algorithm model were established. The data is reduced by the split information gain measurement method and a CNN evaluation model was established. Afterwards, a verification analysis was performed. Results show that the CNN model has a correct rate of 80% or more for the satellite network coordination situation assessment problem, and has high evaluation efficiency. Moreover, with the increase of the amount of data, the evaluation effect of CNN is gradually improved, which indicates the proposed method is an effective evaluation method for coordination situation analysis and resource reserve in satellite networks.

Abstract:In order to study the impact of different ejecting state on aerodynamic heating of hypersonic aircrafts,the square/circle hole ejecting under hypersonic flow condition was numerically simulated. The impacts of ejecting pressure, ejecting velocity and ejecting direction to the main flow field were discussed and the flow field structure, wall heat flux and center line temperature at different ejecting state were obtained. The results show that gas ejection can relieve the aerodynamic heating situation of wall to some extent. The cooling effect at whole wall ejection is remarkable. And the wall heat flux reduces nearly two-thirds when the ejecting velocity is about 1 m·s-1. Moreover, at high ejecting velocity (Ma>1), the cooling effect is strengthened by increasing the ejecting pressure and velocity appropriately. At low ejecting velocity (Ma<0.6), the ejection flows within the boundary layer, and has a weak influence on the main flow field structure; the greater the ejecting velocity is, the bigger the range of cooling is, and the better the cooling effect is. The cooling effect of downstream is better when the ejecting direction is acute angle, and the cooling effect of upstream is better when the ejecting direction is obtuse angle.

Abstract:With the increase of space accidents and failed spacecraft, the orbital resources are dwindling. Now many countries in the world are developing on-orbit service and space debris removal. As one of the most critical technology, non-cooperative target capture has become a focus in the field of space research in recent years. At present, domestic and foreign institutions have conducted in-depth studies on non-cooperative targets, while various capturing methods were proposed, and great progress was made. Firstly, the non-cooperative target was classified, and then the latest situation of non-cooperative target capture technology at home and abroad was introduced with the existing capturing methods. The principle scheme is summarized, and the capturing methods and key technologies are analyzed, which will offer a perspective for future research.

Abstract:In order to meet the demand of the impact protection and the buoyancy reserve of sea structure platform, a new energy absorption structure of filament wound composite constrained spherical buoyancy core material element was designed. The numerical simulation analysis and experimental test verification were carried out for the structure element by using the ABAQUS finite element software and electronic universal material testing machine in order to investigate the damage modes and energy dissipation mechanism. Further analysis of the mechanical response characteristics and damage modes shows that the key to the structural energy absorption design lies in the matching of the Poisson's ratio of the surface layer and the core material. The core material absorbs energy mainly through plastic compression damage and shear fracture damage, while the surface energy absorption is mainly through circular petal-shaped tensile fracture damage. The results show that this type of structural unit has excellent compression and energy absorption characteristics, and can realize the protection energy absorption and buoyancy reserve requirements of the offshore engineering structure platform.

Abstract:P-Q/BZ(Phenolic-quartz hybrid fabrics reinforced benzoxazine resin composites) were manufactured by compression molding. The flexural properties, ablative properties, resistance to flow erosion and failure characteristics of the P-Q/BZ specimens were investigated. The applicability of P-Q/BZ in high temperature environment was studied. Results showed that, the average flexural strength, flexural modulus and ILSS (interlaminar shear stress) of virginal P-Q/BZ specimens were 283 MPa, 10.8 GPa and 22.6 MPa, respectively. After 300 ℃ thermal treatment in N2 atmospheres:the thickness of P-Q/BZ specimens were increased by about 22%, and the flexural strength, flexural modulus and ILSS of P-Q/BZ specimens were decreased by about 58%, 41% and 58%, respectively. After the oxyacetylene flame test, the average mass loss rate and the linear ablative rate of P-Q/BZ specimens were 0.048 4 g/s and -0.081 mm/s, respectively. No delamination of the P-Q/BZ composites were observed but the microstructure of the char layer delaminated severely, the carbonaceous residue blocks which were produced by the phenolic fiber and the resin matrix were attached badly to the quartz fibers. The resistance to heat-flow erosion of the P-Q/BZ specimen was significantly affected, and the mass loss of the P-Q/BZ composite was about 59% after the exhaust plume ablative test with a small liquid motor. Pyrolysis expansion problem of the P-Q/BZ composites is in need of a solution and the resistance to heat-flow erosion of this composites is in demand of improvement as well.

Abstract:The catalytic CO oxidation on platinum group metals exhibits complex intrinsic nonlinear properties, such as reaction rate catastrophe, bistability, and hysteresis. These intrinsic nonlinear properties depend on the inherent stability and self-organization mechanism of the chemical reaction. A corresponding phenomenon is a path-dependent input-output relationship between the CO oxidation reaction rate and the control parameters. The traditional linear control method for these systems has an inherently unstable mechanism that can give rise to the oscillation of the chemical reaction rate and the instability of the control system. However, the previous application of ordinary nonlinear switching control faces a large disturbance at the initial moment of switching, which will affect the dynamic performance and stability of the control system. For this reason, a smooth switching control method based on the integral initial value reset was proposed. The results show that the proposed method can provide a smooth switching control of CO oxidation reaction rate, and thus the dynamic performance of the control system is improved.

Abstract:The researches about the LOX/LCH₄ expander cycle throttling liquid rocket engine are rare and its recognition of it is not distinct, especially at the system level. Based on the whole engine system, the theoretical method was adopted to investigate the work capacity of CH₄ and the feasibility of throttling schemes. The single-turbine and double-turbine throttling schemes were given, and the detailed comparison between them was analyzed. The results reveal that CH₄ work capacity decreases at first and then increases with the decrease of chamber pressure. And the proposed throttling schemes are feasible. Moreover, compared with the single-turbine scheme, the oxidizer and fuel mass flows can be adjusted respectively for double-turbine scheme and the mixture ratio can keep constant better. Meanwhile, the work capacity of CH₄ for double-turbine scheme is much higher, the powers of the oxygen and fuel turbines vary in a narrow range, and the turbines work in a more relaxed environment. Therefore, considering the system reliability, the double-turbine scheme is advantageous to a certain extent.

Abstract:The low-frequency pulsation of the marine hydraulic system is transmitted along the pipe, which can create structural vibration. For the low-frequency pulsation which is difficult to control by passive style, a by-pass secondary source was designed and the pulsation control research by active style was carried out. The designed by-pass secondary source was driven by piezoelectric ceramics, which is compact and has an amplification structure to improve response characteristics. The active control system of the hydraulic system was built, and the FxLMS adaptive algorithm was used to control the pulsation at multi-frequencies. The experimental result shows that the by-pass secondary source can effectively attenuate the low-frequency pulsation at multi-frequencies, and can reduce the vibration energy transmitted with the fluid, which has no negative effect on the working performance of the original hydraulic system.

Abstract:How to plan the tool path and obtain high-quality CNC(computer numerical control) code is one of the key techniques for machining the toric surface with slow tool servo technology. A tool path planning method based on equidistant surfaces was proposed. The surface equations of the toric surface and its equidistant surface equations were derived. Two kinds of guiding curves and two discrete methods were compared and analyzed. Optimized scheme of the tool path planning was selected. The NC code generation software for machining toric surface with the slow tool servo technology was developed by using VB.net language. The generated NC code was verified based on the Vericut CNC machining simulation platform. The residual area of the virtual machined surface relative to the theoretical surface was intuitively shown. Simulation results show that the tool path planning method based on equidistant surfaces is feasible. The results show that by changing the non-primary term of the toric surface equation from a to a+r_d, its equidistant surface equation can be obtained. The tool path planning method based on equidistant surfaces is suitable for machining convex-toric surface using slow tool servo technology. The proposed method has some reference values for processing optical elements having other surface shapes by slow tool servo technology.

Abstract:In order to realize miniaturization and low power consumption of the LF (low frequency) radio transmitter, a novel LF radio transmitting technology called as RMBMA (rotating-magnet based mechanical antenna), which is based on mechanical rotating of permanent magnet to induce electromagnetic fields, was researched theoretically and practiced in engineering. A technology scheme of RMBMA based on NdFeB magnet and permanent magnet synchronous motor, and an information loading method were presented. With electric-mechanic-electromagnetic energy conversion, a system model of RMBMA was developed to analyze the radiation efficiency and radiation power. Meanwhile, in different infinite uniform medium, the distribution and attenuation characteristics of time-varying magnetic field generated by a rotating permanent magnet were studied. Finally, by developing a prototype, the near magnetic field characteristics and 2FSK signal loading characteristics were experimentally tested, and the feasibility and effectiveness of the proposed scheme were verified.

Abstract:As a widely used pulse encoding technique in the full-digital transmitter, the DSM (Delta-Sigma modulation) can obtain a better performance by increasing the quantizer’s levels. But the multi-level DSM output cannot drive the switching amplifier directly due to the structural restriction of switching amplifier in full-digital transmitter. By using the area equivalent theory and non-uniform quantizing technique, a novel pulse encoding strategy for switching amplifier was proposed and analyzed. The theoretical analysis and simulation results reveal that the pulse output created by the novel pulse encoding strategy gives rise to a much better in-band SNR(signal noise ratio) and coding efficiency performance compared to the traditional 2-level output.

Abstract:In order to study the distribution of disturbed electric field produced by a non-metallic cylindrical target under active electric field, the second electric dipole model of a non-metallic target in shallow water environment was established on the basis of the mirror method and the regional gridding method. By using the established model, the disturbed electric field at different positions near the target was calculated and was compared with the simulation results of boundary element method software. The results show that the error of the horizontal component of the disturbed electric field is less than 3%. Then an experiment was carried out in a water tank. The result data from test were basically consistent with the calculated results, which shows that the established secondary electric dipole model is accurate.

Abstract:The thermal and dynamic properties of a pumpkin-shape super-pressure balloon with load tendons during ascent were studied. Thermal environment and forces were analyzed, and the thermal and dynamic models were proposed, and a simulation program was developed by using MATLAB. A simulation of a super-pressure balloon flight was conducted, the flight altitude, the ascent rate and temperature were analyzed during ascent. The results suggest that the thermal environment as well as the dynamic properties exert a great influence on the temperature of the Helium inside the balloon, the ascent rate and Helium temperature interact with each other, and both are relevant to the free lift ratio. The comparison between the simulation results and flight data reveal that the two sets of data match well. The theoretical analysis and simulation model are helpful in the super-pressure balloon design and mission planning.