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As the reinforcing phase of the composites, the preform determines the performance of the composites. The performance of the precast often depends on the spatial structure of the yarn. To reflect the spatial configuration and micro-geometric structure of the yarn inside the fabric, through the discretization of the yarn, the weaving process is simulated by numerical simulation and simulation methods. We review the progress on digital element method simulation of the weaving process of composite preforms. In terms of micro-geometric structure, this paper details the development process of digital element method research from theory to application and introduces the advanced digital element modeling method. It points out that the current model is idealized for the digital element method to simulate the textile process, and does not consider the bending stiffness of the fiber, the air damping effect and the energy loss caused by lateral compression, etc. This paper also points out that the digital element method can be further optimized in future research and parametric modeling can be realized, and that the deformation mechanism of the fiber bundle is studied to obtain a more realistic micro-geometric structure model. [ABSTRACT FROM AUTHOR]

In order to study the evolution of aircraft wake vortices more deeply and precisely, and to ensure the safe operation of aircraft, the dissipation law of A330‑300 aircraft wake at different temperature vertical decreasing rates is studied in this paper by numerical simulation. The shear stress transport (SST) k‑ω turbulence model is chosen for the numerical simulation. The temperature field under five different temperature vertical decreasing rates is constructed, and the A330‑300 aircraft wake flow field is compiled within the temperature field to realize the calculation under different temperature vertical decreasing rates. The reliability of the numerical simulation method is verified by comparing the numerical simulation results with the radar detection data. The results show that for general turbulence intensities, different rates of vertical decreases in temperature act mainly on the decay phase of the wake, affecting the evolution of the wake by changing the temperature inside and outside the wake.The smaller the temperature vertical decreasing rate is, the larger the rate of decrease of circulation in the wake vortex decay region is. The larger the vertical rate of temperature decreases, the larger the rate of tail vortex sinking is and the larger the distance between vortex cores after rapid dissipations is. [ABSTRACT FROM AUTHOR]

This paper proposes a closed⁃loop homing guidance law with the constraints of the impact time and angle for the intercepting a constant⁃velocity target. In order to achieve the required terminal constraints，the line⁃of⁃sight （LOS） profile of the missile is modeled as a polynomial with one tuning parameter that is selected via an online optimization routine. Then，a terminal sliding mode guidance law is developed to nullify the tracking error within a fixed time. The key feature of the proposed guidance law is that it does not require the information of time⁃to⁃go estimation and the predictive intercept point. Numerical simulations are conducted to demonstrate the effectiveness and robustness of the proposed guidance law. [ABSTRACT FROM AUTHOR]

Iterative learning control problem is studied for a class of discrete nonlinear partial difference systems where the trial lengths vary randomly in this paper. The considered systems are composed of parabolic partial difference equations. Firstly, for the trial lengths vary randomly in systems, a stochastic variable satisfying Bernoulli distribution is introduced. Then, according to the properties of partial difference systems and P-type distributed update schemes, iterative learning controller is designed. Through rigorous theoretical analysis, the convergence sufficient condition of output error under λ norm and contractive mapping principle is established to ensure the convergence of tracking error in the sense of norm. The convergence speed of the algorithm is faster than the classical iterative learning algorithm. Finally, the effectiveness of the algorithm is verified by the numerical simulation. [ABSTRACT FROM AUTHOR]

Aiming at the problem that unmanned aerial vehicles（UAVs）are easy to overstep the boundary when rolling around the velocity vector axis，an adaptive sliding mode-based boundary protection control scheme is studied in this paper. Firstly，the attainable equilibrium set is improved based on dichotomy，and the command limitation method is introduced to realize online boundary solution and limited command generation. Then，to restrain the adverse impacts of uncertainties and disturbances to the closed-loop-system， a radial basis function（RBF）neural network is used to approximate the system uncertainties，and a nonlinear second-order disturbance observer is used to estimate the complex disturbances. Accordingly，an adaptive sliding mode-based boundary protection control law is designed to ensure the UAV’s safety and simultaneously realize the attitude tracking. Finally，the effectiveness of the adaptive sliding mode-based boundary protection control method is verified by numerical simulation. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulation is used to analyze the effect of the trailing edge of the stationary blade sawtooth on the 3.5-stage compressor, and the influences of shape and positions of the sawtooth on the compressor speed. The results show that the full blade with high opening on the trailing edge of the inlet guide blade can broaden the stable range of the compressor at 90% speed, and barely impact the pressure ratio and efficiency. But it has little effect the compressor at 100% speed. In this study, a sawtooth with a small tooth width is better than that with a large tooth width, and a sawtooth with full high-opening blades is better than that with partial opening tip. This study deepens the understanding of the effect of serrated trailing edge blades on compressor performance, and provides a reference for research on improving compressor stability. [ABSTRACT FROM AUTHOR]

Aiming at the problem that the inflatable aerodynamic decelerator（IAD）is difficult to establish a folding model with regular folds and radial compression rate，the segmentation mapping folding （SMF） method is proposed in this paper. Firstly，flattened planes are obtained by using the segmentation mapping technique. Then the segmented planes are transformed into a continuous geometric folding model by using the matrix transformation. Finally，the initial stress is used to modify the model errors during folding process， which can reduce the problems of stress concentration and mesh distortions during inflation process. Numerical results show that surface area and volume errors of the inflated single torus are only 1.8%， demonstrating the high precision of SMF method. The initial and the full shapes of the IAD are consistent with those of the experimental，and the inflation process is stable and orderly，demonstrating the reliability and applicability of SMF method. The proposed folding method can be used in the multidimensional compression and regular folding of any surface of revolution，and also improves the accuracy and stability of the surface inflation numerical simulation. [ABSTRACT FROM AUTHOR]

Referring to the phenomenon that the state of the electrical components changes when they are excited by an external force，and at the same time they return to the initial state with the shortest time，this paper compares the real-time change of the dynamic obstacles with the external force，and proposes a path planning algorithm of the dynamic obstacles robot based on the state change. First，the robot around a single fixed obstacle is analyzed in depth. Second，the dynamic obstacle is analyzed by the way of state update. Finally，the mixed task planning area with dynamic and static obstacles is analyzed by using the superposition method，and the obstacle avoidance path is generated. In order to verify the path planning ability of the algorithm in multi⁃obstacle environment，the numerical simulation experiment is used. The results show that the robot can effectively realize the path planning of static obstacle area，dynamic obstacle area and dynamic static mixed obstacle area. [ABSTRACT FROM AUTHOR]

In recent years，the rapid development of aerospace industry has put forward an urgent demand for high efficiency and low cost manufacturing of large and high-performance advanced resin matrix composites. Resin transfer molding (RTM) is a technology for manufacturing advanced fiber reinforced resin matrix com¬posites. Compared with the existing hot-pressing technology，RTM has the advantages of simple equipment structure， high production efficiency and low manufacturing cost. In this paper， the research and application status of two typical RTM processes-Vacuum assisted-Resin transfer molding (VA-RTM ) and Light-Resin transfer molding (L-RTM) are reviewed. The existing problems of these two processes in manufacturing large high performance components are pointed out. The research status and technical difficulties of multi-field coupled numerical simulation， new simulation methods and multi-function simulation of RTM process are summarized. Based on above conclusions, the development trend for RTM process is discussed, which is ben¬eficial to provide reference for realizing rapid process optimization and obtaining high efficiency，high perfor¬mance and large components in RTM process. [ABSTRACT FROM AUTHOR]