Abstract:In hypersonic thermochemical nonequilibrium flow calculations, a large difference between the numerical time step and the molecular vibration relaxation time or the chemical reaction time can bring about serious numerical stiffness problems, which are exacerbated by grid refinement in strong interaction areas such as near-wall or corner. The initial maximum CFL number and convergence rate are thus limited under high Reynolds conditions. The original LU-SGS algorithm only considers the implicit treatment of the source term and convection term. Two fully implicit LU-SGS algorithms, the FLU-SGS algorithm and the BLU-SGS algorithm, were developed by deriving and implementing the diagonal approximation of the spectral radius of the viscous Jacobian matrix. The convergence speeds of the three algorithms were investigated in cases of high enthalpy two-dimensional cylinder flow and axisymmetric re-entry capsule flow. The results show that strong viscous interaction and large separation can be quickly established and 3~5 orders of increase of the maximum CFL number can be reached with FLU-SGS and BLU-SGS algorithms. Thus the newly developed algorithms are efficient in accelerating convergence in the calculation of complex thermochemical non-equilibrium flows.

Abstract:Aiming at the ‘Black Fly’ problem of UAV (unmanned aerial vehicle), a program of the anti-UAV tethered-net capture system consisting of platform flying, flexible tethered-net arresting and parachute recycling was proposed, and a dynamic model of the whole process was conducted. The platform flight trajectory model and the tethered-net dynamic model were compared and verified with the test data. The results show that the proposed system dynamics modeling and simulation program is feasible and has guiding significance for engineering system design.

Abstract:The flutter behavior of thermoplastic composite structures in high-speed flow is a key problem in the design of reusable spacecraft. Based on the classical Mindlin thick theory, the Von-Karman larger deformation theory and the piston theory, the thermoplastic composite structure panel and its aerodynamics were described, along with the consideration of both the thermal stress and the variation of mechanical properties caused by the temperature. The aeroelastic model of the thermoplastic composite panel was established based on the principle of virtual work and the finite element method,and the V-g method and the Newmark method were used to solve the thermal flutter characteristics of the thermoplastic panel from frequency domain and time domain, respectively. After the validity and convergence of the presented method were verified, the effects of temperature on mode coupling in frequency domain, limit cycle oscillation in time-domain and stress response were investigated.The results show that the flutter dynamic pressure obtained by considering the temperature variation of thermoplastic materials will further reduce the flutter dynamic pressure of the panel, and the equivalent stress of thermoplastic panels under the limit cycle oscillation is lower than the material yield limit.

Abstract:Based on the Timoshenko beam theory and the Tsai-Hill yield criterion, a mathematical model for elastic-plastic analysis for cantilever beams by bending moment was established. Meanwhile, the analytical solutions of stress and displacement were obtained. The solutions were verified in comparison with the ones available in the literature and finite element. Furthermore, the effects of fiber orientation angle, bending moment, aspect ratio and fiber volume fraction on the elastic-plastic stress and displacement of the beam were examined in detail. The results can provide important references for the design and engineering applications of thermoplastic composites.

Abstract:The tonal noise, radiated by interaction between stator and rotor, is the main noise source of the subsonic axial fan. A rapid method to predict the noise is significant to the parameter design in early stage of the fan low radiation noise design. Therefore, a semi-analytic prediction formula of the power of radiated tonal noise of the interaction between stator rotor cascade was derived, by considering the interaction of stator and rotor blades based on the cascades response function theory, and by simulating the rotor wakes using empirical rotor wake model. The applicability of the formula was verified by comparing with the results of the existing experimental model and computational model from NASA. Based on NASA experiment model, the effect of rotor-stator spacing and stator blade parameters on tonal noise of fan was analyzed further. And the results show that increase of the rotor-stator spacing and lean design of stator blades suppresses the tonal noise caused by the interaction between stator and rotor effectively .

Abstract:Nonlinearity especially from aerodynamic coefficients in high orders has a significant effect on projectile dynamics. Its investigation has been hindered in the conventional analysis by the complexity in nonlinear motion equations and the lack of appropriate analysis tools. Therefore, the widely used method of normal forms was introduced for the analysis of projectile angular motion. Considering the second order damping and the seventh order static moment terms, the normal form of the angular motion was derived and thus the universal analytical solution of the angle of attack is obtained, which is verified to show good agreement with the numerical integration results over a wide range of angle of attack and also demonstrates its being applicable to the undamped case and the cases with lower or higher order of static moment. In addition, the obtained relationship between initial conditions can give a conventional but simple determination of the region of attraction to the origin. Also, the amplitude equation combined with the equilibrium analysis provides a accurate prediction for the existence and stability of limit cycle in angular motion.

Abstract:In order to meet the RBDO (reliability-based design optimization) requirement for the life of turbine blade with film holes by automatic programmed control, the local parameterization method was proposed on the basis of the unstructured mesh, which significantly reduces the time costs of FEA (finite element analysis). The turbine blade was separated into two regions:the parameterized region and the non-parameterized region. After the meshes of the non-parameterized region and control points of the parameterized region were completed, only the meshes of parameterized region were required to be reconstructed when the geometry of film holes was updated. Compared with the global deformation method based on the structured mesh, the proposed method dramatically reduces the time costs of FEA while ensuring the accuracy of finite element calculation, which highly improves the efficiency of RBDO.

Abstract:The establishment of axisymmetric cohesive force element is an important method to conduct stress analysis of the bonding interface of vertical storage motor. The reference coordinate system was established on the deformed axisymmetric cohesive force element, and the transformation relationship between elemental node displacement in the reference coordinate system and the global coordinate system was derived. The internal force vector and the stiffness matrix of the element were derived based on the elemental separation displacement. The separation test of the axisymmetric bonding plate was carried out to verify the accuracy and efficiency of the axisymmetric cohesive force element. The structural analysis of solid rocket motor in vertical storage under axial acceleration and wave load has been carried out successively, and the magnitude and the distribution pattern of stress at the bonding interface have been studied emphatically. The research method and its conclusion can provide a useful reference for the structural analysis of bonding interface of solid rocket motor.

Abstract:In order to measure the various information of the high-rotation projectile at the muzzle, a new method for estimating the position and attitude of projectiles based on the intersection of dual high-speed cameras was proposed. The error modeling and analysis of the total angle of attack function were carried out. Results show that the optical axes of the two cameras should be perpendicular to each other, and the measurement function of the camera with the optical axis far from the plane of attack should be selected to calculate the total angle of attack. Under this circumstance, the measurement error is the smallest. The conclusion of error analysis and the position and attitude estimation algorithm was verified by the shooting range experiments. Experimental results show that the conclusions of error analysis are correct, and the proposed position and attitude estimation algorithm is not based on any assumptions and its accuracy is higher than that of the POSIT(pose from orthography and scaling with iteration) algorithm. The initial velocity measurement error does not exceed 0.6 m/s, and the projectile centroid position measurement error does not exceed 0.3 m. The measurement method is a non-contact measurement and easy to implement. More importantly, the measurement information is comprehensive. So it can provide a reference basis for shooting range experiments, acceptance and other works.

Abstract:Focusing on predicting the parachute deployment load in the process of inflation accurately, a compensation calculation method of parachute deployment load with RNN (recurrent neural networks) was proposed, including the model architecture and data processing. The predicted value calculated by inflation time method was brought into the RNN for the secondary calculation, so that the final result could be close to the airdrop experiment data. The feedforward neural networks, standard recurrent networks and long short-term memory networks were used to compare the model characteristic. The research verified the applicability and accuracy of the prediction results and analyzed the effects of hyperparameters such as learning rate, input layer dimension and hidden layer dimension on the performance. The optimal training condition for reference to the compensation model was developed through the test. The results show that the utilization of RNN for parachute deployment load prediction is effective and provides a referential significance for the interdisciplinary research of machine learning and parachute industry.

Abstract:Aiming at the fact that the adaptive filtering is used to estimate the target state in the netted radar system when the tracking target is maneuvering, a deception jamming optimization strategy was proposed on the basis of the netted radar with the plot fusion data processing structure. The model of the target tracked by the netted radar was described according to the state and measurement equation, the adaptive filtering model of tracking maneuvering target was established at the same time. Based on all this, a deception jamming model was established, and the influence relationship of false target deception jamming against the adaptive filtering state estimation error covariance of the netted radar fusion center was derived under the constraint of target maneuver detection. The trace of the error covariance matrix was used to quantify the effect of deception jamming and stand for the objective function of optimization. The Schur complement theory of matrix was used to change the constraints to a linear matrix inequality, and a deception jamming optimization strategy was changed in the solution to the convex optimization problem for semidefinite programming. The simulation results verify the effectiveness of the proposed deception jamming optimization strategy.

Abstract:In order to study the influence of different factors on the current expansion speed of the thyristor during the turn-on process of the pulse condition, the equivalent circuit model of the pulse forming network based on the structural characteristics and working principle of the thyristor was established, and the simulation was carried out. Numerical simulation results show that if the forward blocking voltage increases from 3 000 V to 5 000 V, the spreading speed will increase by 24.6%. If the base width increases from 500 μm to 900 μm, the spreading speed will decrease by 31.7%. If the carrier lifetime increases from 1 μs to 10 μs, the spreading speed will increase by 56.9%. While the temperature increases from 300 K to 330 K, the spreading speed only increases by 0.3%. It can be seen that the temperature has little effect on the propagation speed. The research results are helpful to select appropriate parameters to ensure the expansion speed required for opening, and have application value for improving the design of thyristor devices and improving the performance of thyristors.

Abstract:To analyze the impact of transmitting nonideal quadrature signal on FDA (frequency diversity array) beamform, based on the signal model of FDA, the orthogonality issue of baseband signal was brought out, the beamform expression was deduced mathematically under the condition that FDA system transmitting nonideal orthogonal baseband signal, and the performance of matched reception processing was further analyzed. Based on the calculation amount of beamform transmission and matched reception of FDA system, the influencing factors were extracted, and a quantitative analysis of the relationship between the orthogonal characteristics of the baseband signals and the performance of the beamform and matched reception was constructed. Based on the numerical simulation of six kinds of typical random distribution biphasic coded baseband signals, the correctness of theoretical analysis was verified by experiments. Different random distributions show different baseband signal orthogonal characteristics, and their influence on the performance of FDA beamform transmission and matching reception varies with the orthogonal characteristics. From the perspective of orthogonality, the application potential of baseband signal based on Normal, Uniform and Logistic random distribution is better.

Abstract:In the current complex battlefield environment, low probability of intercept radar signal has been widely used due to their large time-bandwidth product, strong anti-jamming performance, high resolution and low interception. It is difficult to identify the low probability of intercept radar signal by traditional radar reconnaissance methods. Based on the analysis of typical modulation of low probability of intercept radar, a radar signal classification and recognition method based on artificial intelligence was studied. Starting from the time-frequency characteristics of low probability of intercepted radar signals, a multi-window spectrogram analysis method was proposed. In this algorithm, Hermite function was used as the window function of spectrum analysis, and multiple window functions were also used for spectrum analysis. The effective signal with better aggregation is obtained, the noise interference is dispersed, and the time-frequency analysis characteristics of signal modulation characteristics are more obvious through this algorithm. On the basis of multi-window spectrogram, the idea of transfer learning was adopted, and ImageNet-VGG-f neural network was used to complete the task of signal classification and recognition. Experimental results show that the performance of the proposed algorithm is better than the traditional Choi-William distribution and Smooth and Pseudo Wigner-Ville distribution methods at low signal-to-noise ratio.

Abstract:After the detailed analysis of the diffusion characters of bridge cables, the principle of vibrating frequency-based cable tension estimation, and the principle of interferometric deformation measuring radar, a nano 77 GHz MMW (millimeter wave) radar was developed. A set of key parameters were achieved to control the maximum range, the deformation estimation precision, and the dynamic deformation measuring performance. Field experiments were conducted to compare the performances of the MMW radar with the 24 GHz K band radar. Results show that the new radar is a compact, light-weighted, low-power consumption,and the radar is of great value in cable tension measuring applications.

Abstract:Aimed at the problem that the traditional tree species classification method based on LiDAR (light detection and ranging) data is difficult to directly and comprehensively use the 3D structure information of the point cloud, a tree species classification method of airborne LiDAR data based on 3D deep learning was proposed. This method directly abstracts high-dimensional features from 3D data without converting point clouds into voxels or two-dimensional images. Taking the airborne LiDAR data of white birch and larch in Saihanba National Forest Park as the research object, data filtering was performed to remove noise and ground points; the point cloud distance and improved watershed segmentation method were used to extract the individual wood and make a data set. Finally, a deep neural network composed of a weight-sharing multi-layer perceptron, a max pooling, a fully connected layer and a softmax classifier was established, which can extract the high-dimensional features of trees automatically and realize tree species classification. The experimental results show that the overall classification accuracy rate is 86.7%, the kappa coefficient is 0.73, the optimal feature dimension is 1 024, and the most advantageous point density is 2 048. Compared with the method projecting individual tree point cloud to a two-dimensional view, this algorithm provides higher classification accuracy, and can reduce the calculation cost effectively and improve work efficiency.

Abstract:The cooperative fault-tolerant for the nonlinear multi-agent system with hybrid actuator faults and multiple unknown control directions were investigated, based on the RAFSMT(robust adaptive fuzzy sliding mode technology). The piecewise Nussbaum function was used to solve the multiple unknown control directions, and the robust adaptive fuzzy technology was used to solve the nonlinear uncertainty in the system. A first-order sliding mode differentiator was introduced, and it was combined with the adaptive backstepping technique to obtain the first-order derivative of the virtual control law. At the same time, a robust bounded method was adopted to improve the convergence speed and tracking accuracy of the designed adaptive cooperative controller. Based on the algebraic graph theory, the error model of the agent system was established, the distributed consensus cooperative fault-tolerant controller was designed, and the Lyapunov candidate function was constructed to prove that the proposed controller can make the system stable. The effectiveness of the proposed method is verified by the comparison of simulation examples, which provides theoretical support for engineering practice.

Abstract:In order to solve the performance optimization problem caused by the high-dimensional nonlinear characteristics of the trajactory correction decoy and improve the traditional serial design method in the conceptual design stage, an intelligent optimization algorithm based on DOE (design of experiments) and RSM (response surface methodology) was proposed and the basic projectile structure model and related design parameters were defined. Based on the DOE, the design variables were mapped to the performance criteria to generate the stochastic Kriging response surface, and the neural network was trained to identify the unstable design. Multi population genetic algorithm was used to determine the optimal projectile design. By changing its cost function, the Pareto frontier reflecting the performance tradeoff could be generated. Simulation results show that as for the technical transformation of infrared interference decoy based on trajectory correction, the proposed algorithm can obtain the optimal design configuration quickly and accurately in the conceptual design stage, which can guarantee the following accompanying flight mission.

Abstract:The motion and mechanical characteristics of pneumatic soft manipulators are significantly affected by their structural characteristics. At present, it is urgent to improve the support reaction force and inclination angle of the pneumatic soft manipulator. Based on the script interface provided by ABAQUS, Python script was developed to establish a parametric simulation model of gas control software drive, using the size factor as the optimization variable, linking Isight and ABAQUS, and to determine the high sensitivity influence factor of inclination angle and support reaction force by single factor test method.The normalization and weighting strategy and the evolutionary optimization algorithm were used to optimize the inclination angle and the support reaction force, thereby obtaining optimal parameter combination. The results show that the support reaction force and inclination angle are increased by 29% and 136% respectively compared with the initial value of the response. The combination of finite element calculation and multi-variable optimization of the pneumatic soft manipulator is realized and the bending deformation capacity and load capacity of the pneumatic soft manipulator are improved simultaneously.

Abstract:To explore effects of different installation locations and different widths of tip winglets on the aerodynamic characteristics of compressor cascades under the condition of transonic incoming flow, the flow fields of seven diffused cascades including the prototype cascade were numerically studied at Ma=0.8. The results show that under the combined influence of various factors, the suction surface tip winglets with different incoming flow attack angles have negative effects in the flow field, and increase the complexity of the flow field. Meanwhile, the pressure surface tip winglets improve the leakage flow and reduce the flow loss. The effect of the tip winglet on the flow field is proportional to its width in both installation positions. The interference or improvement effect of the tip winglet on the flow field is more obvious at positive angle of incidence. Compared with the normal condition, the most obvious effects of the two types of tip winglets can be obtained under the condition of positive 6°. The suction surface tip winglet with a width of 2.0 times of the original width causes 4.17% flow field loss, while the pressure surface tip winglet whose width is 2.0 times of the original width is accompanied by an improvement effect of 10.15%.

Abstract:Aiming at the problems of low fuel injection pressure and inability to flexibly change the fuel injection rate in the injection process of conventional high pressure common rail system, an ultra high pressure common rail system for adjustable fuel injection rate based on domestic processing capacity and technology was proposed and designed. On the basis of introducing the working principle of this system, the simulation model of system was established via AMEsim software, the accuracy of this model was verified by experiment, and the pressure characteristics and fuel injection control characteristics of the system were studied through the model. A at the same time, the influence of the key structural parameters of the electric-controlled pressure amplifier on the system performance were analyzed. Results show that the ultra high pressure common rail system for adjustable fuel injection rate can magnify fuel pressure to the ultra high pressure state, and by changing the control signal working time of electric-controlled pressure amplifier and injector solenoid valve in system, the flexible and controllable fuel injection rate curve shape can be achieved. Compared with the control chamber volume and spool mass, the fuel outlet diameter and spool displacement have greater influence on the performance of this system, with the increase of fuel outlet diameter and spool displacement, the pressurization pressure and fuel injection rate peak value both increase, while the fuel leakage rate increases first and then decreases.

Abstract:In order to investigate the shock initiation of missile warhead (cylindrical covered charge) by multiple fragments impact under actual combat conditions, based on Jacobs-Roslund formula of single fragment initiation plane covered charge, the engineering calculation model of the impact critical initiation condition of cylindrical covered charge with single or double spherical fragments were established. The calculation model includes several parameters, such as fragment diameter, impact angle, charge radius and shell thickness. The calculation model results were in good agreement with the simulation results and experimental results, which proves that the calculation model can provide a better prediction of the impact critical initiation condition of cylindrical covered charge with single or double spherical fragments.

Abstract:The pressure wavespeed of pipe flow is the basic physical parameter to analyze and study the stability and dynamic quality of hydraulic system. The three-sensor measurement theory was deduced based on the wave equation of the transmission pipeline, the Foster equivalent shear coefficient model was introduced for high-precision estimation of various influence factors in the hydraulic line, and the Newton-Raphson iterative method was adopted to reduce the data processing error and accurately calculate the pressure wavespeed. An on-line test platform for measuring pressure wavespeed of hydraulic pipeline was built based on theoretical derivation, realizing accurate measurement and calculation of pressure wavespeed of hydraulic system under various working conditions by MATLAB software programming. The test results show that: when the system is under the typical working pressure of 20 bar,50 bar,75 bar and 100 bar, the pressure wavespeed is about 1 320 m/s, 1 338 m/s, 1 363 m/s, 1 380 m/s respectively, and the measurement error is within ±1% in the wave speed interval with a confidence level of 95%; the pressure wavespeed of pipeline increases with the rise of the working pressure, and the function relationship between the two variables was given according to the test results; the effect of pipe material on system flexibility should be considered in the precise calculation of pressure wavespeed. The results of test and analysis have important guiding significance and reference value for the on-line measurement and estimation of pressure wavespeed in hydraulic system.

Abstract:The transverse bending of cylindrical tubes embedded in Winkler elastic foundation was studied based on the higher-order shear deformation beam theory. A governing equation for bending of circular cylindrical tubes on elastic foundation or in a surrounding Winkler matrix was derived and accurate solutions were presented for four typical boundary conditions. The obtained results show that the shear stress τ_xr automatically vanishes on the inner and outer surface of cylindrical tubes when an appropriate warping shape function instead of the shear correction coefficient is chosen. And it can provide analytical solutions with sufficient accuracy for the bending problems of cylindrical tubes with different length-diameter ratios and thickness-diameter ratios. When the stiffness coefficient approaches zero, the deflection curve of cylindrical tube embedded in Winkler elastic foundation approaches the deflection curve of cylindrical tube placed in free space, which verifies the accuracy of the present method. Different from the Euler-Bernoulli beam theory, the normal stress over the cross-section is no longer linear with the abscissa from the neutral surface in this method, and it is especially obvious when the length-diameter ratio is small and the thickness-diameter ratio is large.The shear stress τ_xz decreases when the distance from the neutral surface becomes large, approaching zero at the top and bottom positions, and the maximum shear stress occurs at the neutral surface which is close to the inner surface.