Abstract:As an important energy source of solid rocket motors, the mechanical properties of composite solid propellants have always been the focus of attention in the engineering field. The macroscopic constitutive model and the fine-scale mechanical model in the characterisation of propellant mechanical properties was focused on. The development of the two types of models was systematically sorted out. The differences between the models were clarified. The applicable conditions of various models were pointed out. The difficulties and challenges of macro and fine mechanical models in the characterisation of propellant mechanical properties at the present stage were analysed. The proposal of mechanical models represented by cross-scale mechanical models will help to solve the problem of propellant mechanical property characterisation. The key in the future modelling of propellant mechanical characterization is the experimental research under complex conditions, focusing on the development of high precision and high performance multiscale numerical computation methods, as well as the integration of data-driven technology represented by artificial intelligence technology into model innovation.

Abstract:In order to study the mechanical properties and failure mechanism of the solid propellant under extreme low temperature environment, the uniaxial tensile test of a three-component butyl hydroxyl propellant was carried out under different temperatures, wide range of superimposed pressure values and high strain rate conditions by adopting the self-developed wide-temperature-superimposed pressure loading test system, and the fracture morphology was observed by electron microscope scanning. The effect of temperature, tensile rate and peripheral pressure value on the mechanical properties of the propellant was analysed, and the damage mechanism of the propellant under different working conditions was discussed. Results show that when the tensile rate increases, the superimposed pressure increases and the temperature decreases, the elongation of the dewetting point of the propellant decreases, the dewetting point moves forward, and dewetting occurs inside the propellant. There are superimposed pressure and strain rate thresholds, above which the propellant is more prone to dewetting behaviour. At low temperature, the maximum elongation of propellant is more sensitive to the change of high tensile rate, and its maximum tensile strength and maximum elongation both tend to increase with the increase of the value of the peripheral pressure, and the maximum elongation is 28.8% under the extreme tensile condition of -55 ℃, 10 MPa, and 4 200 mm/min. The failure mode of the propellant is affected by a combination of dewetting damage, matrix fracture, and particle cracking, as the temperature decreases and the tensile rate increases.

Abstract:To investigate the damage evolution process of low-frequency fatigue-loaded NEPE (nitrate ester plasticized polyether) solid propellant and get the influence law of fatigue loading history on tensile mechanical properties of NEPE solid propellant, the NEPE solid propellant low-frequency fatigue tests and uniaxial tensile tests with constant strain rate were conducted by the electronic universal testing machine. Based on the microscopic morphology and testing curves of test piece after fatigue loading, the influential mechanism of microscopic and mesoscopic damage on the NEPE solid propellant macroscopic mechanical behavior was further analyzed. Results indicate that the NEPE solid propellant matrix microcracks and voids at the matrix/particle interface are induced by low-frequency fatigue loads, leading to nonnegligible stress-softening behavior and residual strain. During and after fatigue loading, the attenuations of macroscopic mechanical properties of NEPE solid propellant are all exponentially related to the maximum loading strain. Part of microscopic damage by low-frequency fatigue load can recover, while the remaining fatigue damage may enhance the molecular chain orientation ability, and thus lead to the fatigue-strengthening phenomenon in materials.

Abstract:In order to analyze the effect of different combinations of stretching rates of four-component HTPB propellant on the accuracy of the parallel rheological framework model, a nonlinear viscoelastic constitutive model of the propellants was developed based on the parallel rheological framework method. A constitutive model was constructed by combining experiments with different tensile rates, the corresponding constitutive model parameters were obtained and compared with experimental results using finite element models and numerical calculations. The constitutive model errors of the calibration for different rate groups were compared and analyzed. The results show that the model can be calibrated more accurately when a combination of high rate and low rate groups is used, without the need for extensive experiments at intermediate rates. And the high rate propellant tensile test rate can be up to 3 000 mm/min, no need to increase the rate. This analysis provides justified suggestions for simplifying propellant material tests and improving the efficiency of the experiments. Concurrently, it paves an effective way to rapidly predict the mechanical properties of propellant materials.

Abstract:Tensile and compressive creep behavior of propellants in solid motors due to the influence of the gravity and long-term storage might affect the interior ballistics and structural integrity. In order to investigate the change trends of tensile and compressive creep for HTPB propellant, the 1 000 s tensile, 1 000 s compression and 28 d tensile creep tests were designed and carried out in this work. Meanwhile, the Saint-Venant body and the compressive-tensile asymmetry factor were introduced to establish a propellant viscoelastic plastic constitutive model that takes into account compressive-tensile asymmetry. The range of application of this equation was obtained by fitting and analyzing the parameters in the constitutive equation. The results indicate that the compressive creep process of propellant was mainly dependent on stress level. At the same stress level, viscoelastic deformation of tensile creep is about 1.62 times that of compressive creep, while compressive yield stress is 3.82 times that of tensile yield stress. The tension-compression asymmetric viscoelastic plastic constitutive model can well characterize the tensile-compression creep response of propellants at the lower stress levels. The conclusions and research method in this work can provide reference for structural integrity analysis and storage life evaluation of solid motor.

Abstract:An embedded strain measurement method based on fiber bragg grating sensor was proposed to solve difficult problems in measuring the internal strain response of solid rocket motor grain. The solid rocket motor tester of embedded fiber bragg grating strain sensor was designed, and the cold pressurization test was carried out on the tester. The axial and circumferential strains in the grain structure were obtained under cold pressurization test. Research shows that the proposed test method can obtain the circumferential strain and axial strain in internal grain. The research results can lay a foundation for the further application of fiber bragg grating sensor in the measurement of solid motor grain structure, and can provide a reference for the development and application of solid motor monitoring and detection technology.

Abstract:ILET(ionic liquid electrospray thruster), one of the electrostatic micro-thrusters, has recently become a hot topic for researchers. The emitter is the core component that significantly affects the thruster performance, so its manufacturing is considered as one of the key technologies for the ILET development. Combined with the operating principle and the development history of ILET, the characteristics of propellant transport and manufacturing requirements for all three types of emitters, namely capillary, externally-fed and porous emitters, were analyzed. Based on this, the typical manufacturing materials and related manufacturing technologies were reviewed, while the advantages and disadvantages of different manufacturing technologies such as ion etching were summarized and remarked. For the proven manufacturing method of ultrafast laser ablation based on porous material, the development suggestions including emitter design, novel material fabrication, and study on laser-matter interaction mechanism were given.

Abstract:The process of grid generation and flow field simulation in CFD calculation can be automated to enhance the efficiency of CFD simulation, which has a great potential for applications. An Auto-CFD technology framework based on the tie-dye algorithm which can generate grids automatically and initiate inviscid supersonic flow field calculation quickly without geometry clean-up after inputting solid models. A 2D numerical example verifies that the calculation accuracy of this technology is comparable to that of the unstructured finite volume method, but with a significant improvement in calculation efficiency. An Auto-CFD software that can start the calculation in real time based on hand-drawn models was developed in theory, which can automatically simulate any two-dimensional irregular shape. The Auto-CFD technology was also extended from 2D to 3D space, and the irregular point cloud obtained by laser scanning the car was used as the solid model to demonstrate the adaptability of this technology to complex shape problems. The Auto-CFD technology framework developed based on the tie-dye algorithm is compatible with mainstream difference schemes and has good mesh adaptability, which is expected to solve the technical problems existing in existing Auto-CFD software.

Abstract:To investigate the dynamic uncertainty of thrust of the pintle SDACM (solid divert and attitude control motor), the study focuses on the uncertainty of the thrust performance during variable operating conditions of the SDACM was carried out with the consideration of the uncertainties of the geometric parameters of the pintle gas valve. Computation model of the thrust during variable operating condition process of the SDACM was established by combining the working principle of the SDACM, the regular mathematical model of thrust and the zero-dimensional internal ballistic equation. On this basis, the uncertainty propagation was performed by Monte Carlo simulation method according to the uncertainty models of the geometry parameters of the SDACM, and the variation law of the thrust uncertainty over time after the transient motion of the pintle was obtained, thereby the uncertainty analysis of the thrust in the process of variable operating conditions was realized, and the uncertainty variables were weighted in order of importance. Quantification and evaluation of thrust uncertainty in the real-time regulation process of the SDACM can provide more reasonable design requirements for the control system, and save the development cost of the SDACM while meeting the design requirements.

Abstract:Aiming at solving the problem of using the two-way "Λ" configuration to achieve high-stability time-frequency comparison between the ground station and the low earth orbit spacecraft in near circular orbits, a new method for longer-term stability calculation was proposed. The method used the statistical characteristics of the short-term data to generate pseudo-measurements and fill the data gaps. The validity of the algorithm was verified using data simulated. To analyze the influence of spacecraft orbit determination error on time and frequency transfer, the Hill equation, the relative motion model in the time-transfer model and the relativistic frequency shift model were combined to analyze and calculate the requirements of orbit error for different long-term indexes. For long-term ps level stability indexes, the requirements of orbit error are that the radial and tangential errors are around 10 m, and the normal error is about 1 200 m. For long-term sub-ps level stability indexes, the requirements of orbit error are that the radial and tangential errors are around 1 m, and the normal error is about 120 m. The results shows that the error of the orbit determination is not the factor that limits the performance of satellite-ground time-frequency comparison to achieve 0.01 ps level short-term stability and sub-ps level long-term stability.

Abstract:To accurately calculate the nonlinear bearing capacity of the CBJ(clamp band joint), through the mechanics behavior analysis of each component in the CBJ, a method for calculating the axial connection stiffness of the CBJ considering the change of preload was proposed. A fine finite element model was established considering the nonlinearity of the structure, and the accuracy of the finite element model was verified by axial tensile stiffness experiment. Combined with the finite element model, the theoretical calculation of the device connection stiffness was modified. Based on the established finite element and computational theoretical model, the influence mechanism of the distribution and variation of the belt tension and the initial belt preload on the device strength and connection stiffness was revealed. The results show that the stiffness calculation model can accurately calculate the axial connection stiffness of the device and predict the failure load of the connection, which has important engineering application value.

Abstract:Supersonic film cooling technology is widely used in active thermal protection of hypersonic aircraft. A numerical simulation method was used to investigate the effects of the Mach number at the cooling gas′s inlet, blowing ratio and the height of the spray seam on the supersonic film cooling characteristics for both flat and curved surfaces, and the effectiveness of film cooling was experimentally verified. Results show that regardless of whether the cooled wall is flat or curved, the supersonic gas film has good wall adhesion characteristics and can effectively cool the wall. In comparison, the cooling effect of supersonic gas film on curved surfaces is better than that on flat surfaces. Increasing the Mach number at the cooling gas′s inlet and blowing ratio can improve cooling efficiency. As the height of the spray seam increases, the film cooling efficiency increases and gradually reaches a constant value. When the height of the spray seam is large enough, the advantage of further increasing the height of the spray seam is not significant.

Abstract:The effects of Ti/Mg thickness ratio(abbreviated as Ti/Mg ratio), structural thickness/projectile diameter(t/D) ratio and impact angle θ on the hypervelocity impact characteristics of Ti/Al/Mg impedance gradient structures were studied with AUTODYN finite element software. Results show that the influence of Ti/Mg ratio on the expansion characteristics of the outer bubble fragment cloud is within 5%, but increasing the Ti/Mg ratio can improve the degree of fragmentation of the projectile. The structural energy absorption characteristics are best within the range of 0.625 to 1. The expansion speed of the outer bubble fragment cloud and the mass of the large fragment at the center of the projectile decrease with the increase of t/D ratio, while the unit face density energy absorption decreases. Oblique impact is beneficial to the dissipation of projectile kinetic energy by the impedance gradient structure, but it will reduce the degree of fragmentation of the projectile. After θ exceeds 40° or 50°, the "slip effect" has a significant impact on the impact characteristics of the impedance gradient structure. The perforation area of the impedance gradient structure decreases with the increase of Ti/Mg ratio and t/D ratio, and increases with the increase of θ, and an empirical formula for the dimensionless perforation area of the impedance gradient structure is obtained based on dimensional analysis.

Abstract:To solve the problem of high-communication latency consumption when sensor data during the round trip to the server application layer in the military IoT(Internet of Things), an in-network collaborative computing method for multiple devices with low-latency task demands was proposed. This method relied on a network architecture with P4 switches as the core and employed a data-plane programming strategy based on the P4 program to complete the packet processing within the switch. A task mapping strategy was designed to map the task set to a switch network topology, thus realizing a collaborative operation mode in which tasks were computed while being transferred on the network topology path. After that, a latency optimization model was built to find the best mapping result, and the task was further optimally scheduled through the heterogeneous earliest finish time algorithm. Experimental results show that when the data size of a single packet is 1 000 Byte, the output latency of this method is reduced by about 54.2% and 72.1% compared with the local service and cloud service, respectively. Therefore, the proposed method effectively reduces latency, offering a practical solution to meet the low-latency demands of tasks.

Abstract:Aiming at the problems of low reconciliation efficiency and key leakage of the classical Cascade protocol, an improved Cascade protocol aided by fluctuation error quantization was proposed. Before reconciliation, the statistical characteristics of the fluctuation difference of channel magnitude feature of legitimate nodes were studied and a fluctuation error quantization method was proposed by using it. Based on the proposed quantization method, an improved Cascade protocol was designed by parity grouping and partitioning reconciliation. Numerical results demonstrate that the proposed improved Cascade protocol effectively improve the reconciliation efficiency, reduces the computational complexity required for information reconciliation and the possibility of key information leakage at the cost of partial reconciliation success rate. In addition, compared with the existing key generation schemes, the key generation scheme based on the proposed improved Cascade protocol has a lower key inconsistency rate and a higher key generation rate.

Abstract:The SIoT (space-based Internet of Things) is an effective supplement and extension of the ground-based IoT, and it is a basic technical means to build the interconnection of all things and ubiquitous perception. Taking the SIoT integrated in TianTuo-5 as an example, it aims at the application requirements of multi-domain and multi-scenario covering land, sea and air. It focuses on solving the high-reliability detection of the signals of AIS (automatic identification system), ADS-B (automatic dependent surveillance-broadcast) system and the multiple access of DCS (data collection system). This achieves real-time supervision of navigation and aviation goals and the global layout of extremely massive narrowband IoT sensor terminals, and provide reference scheme for the demonstration, construction, development and scale application of our country′s SIoT.

Abstract:Aiming at low response and weak measurement ability of the all-fiber optic leakage current sensor in the ship power network, a denoising method based on the combination of VMD(variational modal decomposition) and MF(morphological filtering) was proposed to improve the ability of weak current measurement. The hunter-prey optimization algorithm was used to search for the optimal combination of model number and quadratic penalty term based on the minimum entropy of the Hilbert spectrum, and the intrinsic mode functions component were obtained by completing the variational mode decomposition. The practical modal function component was determined by setting the correlation coefficient threshold to complete the signal reconstruction. The structure factor and scale coefficient of MF were determined by the hunter-prey optimization algorithm with the signal-to-noise ratio as the fitness function. The reconstructed signal was subjected to time-domain denoising processing to further denoise in the leakage current signal. This method significantly improve the signal-to-noise ratio and reduce the minimum mean square error to the existing filtering methods by simulation analysis and experimental verification. The leakage current resolution is achieved to 3mA with the proposed denoising algorithm.

Abstract:With the continuous advancement of advanced processes and technologies, in order to ensure the accuracy of data during high-speed transmission, equalizers need to provide higher compensation and lower power consumption to achieve efficient communication. A high-gain and low-power adaptive CTLE(continuous time linear equalizer) was designed on the basis of the 12 nm CMOS(complementary metal-oxide-semiconductor) process, which adopted a two-stage cascade structure to compensate for channel attenuation and improve the quality of the received signal. In addition, the adaptive module used the SS-LMS(sign-sign least mean square) algorithm to accelerate the convergence speed of the tap coefficients. Simulation results show that when the transmission rate is 16 Gbit/s, the equalizer can compensate for a half-bit rate channel attenuation of -15.53 dB, and the equalizer coefficients converge within 16×10⁴ unit interval data. Moreover, after convergence, the received error rate is lower than 10^-12.

Abstract:In order to solve the problem of node screen with high precision and high real-time in the hybrid cooperative location of UAV swarm, an efficient node screen algorithm was proposed. The algorithm used the variance of positioning as the basis for evaluating positioning accuracy and used the recursive relationship between the variance of positioning caused by the removal of one node to select the specified number of nodes for positioning calculation. At the same time, the algorithm added an operation volume adjustment factor to solve the problem of large computation volume and poor real-time performance of traditional node selection algorithms in the case of a large number of nodes. Through simulation experiment, the variance and operation time consumption obtained by the algorithm are compared with the corresponding results of other optimization methods. The experimental results show that the algorithm greatly reduces the amount of calculation while ensuring the positioning accuracy, and has good real-time performance and feasibility.

Abstract:Aiming at the small sample data of launch vehicle, combining the SPOT(sequential posterior odd test）and Bayes recursive estimation method to improve the traditional sample size design from hypothesis testing and parameter estimation, respectively. When evaluating the performance indexes of launch vehicle following the normal distribution, the composite equivalent coefficient was introduced to fuse multi-source data, which can make up for the shortage of experimental data or test data. Considering the two types of risks and confidence requirements comprehensively, a reasonable evaluation scheme was designed. Through the analysis of examples, the results verified that the proposed method are authentic and credible, which can reduce the sample size demand effectively, and can be used for the sample size test design of launch vehicle under the small sample condition.

Abstract:In order to solve the problem of the real-time parameter adjustment when suppressing redundant force by the structural invariance compensation method, a mathematical model and a simulation model of a servo actuation system performance test platform were established, respectively. A decoupling control method for speed feedforward compensator was proposed, and a fuzzy controller was designed to suppress the redundant force. The inhibition effects of the three control methods including the traditional PI(proportional-integral) control, traditional PI feedforward compensation control and fuzzy PI feedforward compensation control on the redundant force of the test platform were compared. Simulation results show that the loading accuracy of the test platform can be improved by the fuzzy PI feedforward compensation control method with the most significant suppression effect on the redundant force. The effectiveness of the proposed control method was verified by the comparison between the experiments and simulations, which provides a theoretical reference for the servo actuation system test platform to loading with heavy thrust and high precision.

Abstract:Aiming at the problem that the time on the satellite deviates from the time of the entire network constellation caused by the abnormal jump of the satellite clock, an autonomous time synchronization algorithm for Beidou-3 satellites for the jump of the satellite clock is designed. By introducing robust least-squares estimation, the time synchronization algorithm of distributed satellite constellations was improved, so that it can quickly detect abnormal clock jumps and have the ability of autonomous time synchronization. Using the same simulation environment as the Beidou-3 satellite and introducing actual on-orbit test data, the algorithm was accurately evaluated. The results show that within 60 d, the time synchronization error of each satellite in the constellation does not exceed 368 ns, and when a satellite jumps abnormally, the algorithm can restore time synchronization within 1 h, which improves the reliability of the algorithm under clock jumps.

Abstract:To obtain accurate product lifetime prediction results, random parameters which obey non-conjugate distributions were introduced to describe the unit-to-unit variation of products in the reliability model. For long-life products with monotonic degradation, the reliability model was proposed based on the Gamma process with non-conjugate distribution random parameters. Extending the traditional conjugate distribution of random parameters to non-conjugate distribution, unified expression of life distribution function under different parameter distributions was derived, and the lifetime prediction values were calculated by using the Monte Carlo method. Markov chain Monte Carlo method was adopted for parameter estimation. The calculation algorithm for the likelihood function under different distributions and the selection criterion for the parameter distribution were presented, and the effect of the distribution of random parameters on the product reliability was analyzed. The simulation test and the application example show that this modeling method can select an appropriate distribution. Simultaneously, the accuracy of parameter estimation and lifetime prediction of the method is validated.