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In this article, a three-axis attitude manoeuvre spacecraft consisting of a central rigid body and a rotating solar array is studied. The rotating solar array is considered a disturbance to the spacecraft. In the design of the controller, the coupled terms and the rotating solar array are considered a disturbance. The improved extended state observer is proposed by combing the sliding mode observer with the originally extended state observer to estimate the disturbance. The sliding mode control method is adopted to adjust the attitude of the spacecraft. Numerical simulations are presented to demonstrate the outstanding performance of the present observer.

We present an analysis of the Navier-Stokes equations based on a spatial filtering technique to elucidate the multi-scale nature of fully developed turbulence. In particular, the advection of a band-pass-filtered small-scale contribution by larger scales is considered, and rigorous upper bounds are established for the various dynamically active scales. The analytical predictions are confirmed with direct numerical simulation data. The results are discussed with respect to the establishment of effective large-scale equations valid for turbulent flows., 14 pages, 6 figures

Turbulence transportation across permeable interfaces is investigated using direct numerical simulation, and the connection between the turbulent surface flow and the pore flow is explored. The porous media domain is constructed with an in-line arranged circular cylinder array. The effects of Reynolds number and porosity are also investigated by comparing cases with two Reynolds numbers (Re≈3000,6000) and two porosities (φ=0.5,0.8). It was found that the change of porosity leads to the variation of flow motions near the interface region, which further affect turbulence transportation below the interface. The turbulent kinetic energy (TKE) budget shows that turbulent diffusion and pressure transportation work as energy sink and source alternatively, which suggests a possible route for turbulence transferring into porous region. Further analysis on the spectral TKE budget reveals the role of modes of different wavelengths. A major finding is that mean convection not only affects the distribution of TKE in spatial space, but also in scale space. The permeability of the wall also have an major impact on the occurrence ratio between blow and suction events as well as their corresponding flow structures, which can be related to the change of the Kármán constant of the mean velocity profile., Deutsche Forschungsgemeinschaft, Projekt DEAL, Cluster of Excellence SimTech

Mixing and evaporation processes play an important role in fluid injection and disintegration. Laser-induced thermal acoustics (LITA) also known as laser-induced grating spectroscopy (LIGS) is a promising four-wave mixing technique capable to acquire speed of sound and transport properties of fluids. Since the signal intensity scales with pressure, LITA is effective in high-pressure environments. By analysing the frequency of LITA signals using a direct Fourier analysis, speed of sound data can be directly determined using only geometrical parameters of the optical arrangement no equation of state or additional modelling is needed at this point. Furthermore, transport properties, like acoustic damping rate and thermal diffusivity, are acquired using an analytical expression for LITA signals with finite beam sizes. By combining both evaluations in one LITA signal, we can estimate mixing parameters, such as the mixture temperature and composition, using suitable models for speed of sound and the acquired transport properties. Finally, direct measurements of the acoustic damping rate can provide important insights on the physics of supercritical fluid behaviour., Deutsche Forschungsgemeinschaft, Projekt DEAL

Due to current and future environmental and safety issues in space propulsion, typical propellants for upper stage or satellite rocket engines such as the toxic hydrazine are going to be replaced by green propellants like the combination of liquid oxygen and hydrogen or methane. The injection of that kind of cryogenic fluids into the vacuum atmosphere of space leads to a superheated state, which results in a sudden and eruptive atomization due to flash boiling. For a detailed experimental investigation of superheated cryogenic fluids, the new cryogenic test bench M3.3 with a temperature controlled injection system was built at DLR Lampoldshausen. After a first test campaign with high-speed shadowgraphy of flash boiling liquid nitrogen sprays, a laser-based Phase Doppler system was set-up to determine the spatial distributions of droplet velocities and diameters in highly superheated sprays. The spatial distributions revealed a core region with high mean velocities close to the injector orifice. With increasing distance from the injector orifice, the sprays develop a more and more monodisperse pattern. These distributions also showed that atomization due to flash boiling generates finer sprays with growing degrees of superheat. In certain spray regions, two droplet populations varying in their direction of motion, velocity and diameter due to possible recirculation zones were observed. The experimental data of flash boiling liquid nitrogen generated within this study provide a comprehensive data base for the validation of numerical models and further numerical investigations., Deutsche Forschungsgemeinschaft, Projekt DEAL

The target's threat prediction is an essential procedure for the situation analysis in an aerial defense system. However, the traditional threat prediction methods mostly ignore the effect of commander's emotion. They only predict a target's present threat from the target's features itself, which leads to their poor ability in a complex situation. To aerial targets, this paper proposes a method for its potential threat prediction considering commander emotion (PTP-CE) that uses the Bi-directional LSTM (BiLSTM) network and the backpropagation neural network (BP) optimized by the sparrow search algorithm (SSA). Furthermore, we use the BiLSTM to predict the target's future state from real-time series data, and then adopt the SSA-BP to combine the target's state with the commander's emotion to establish a threat prediction model. Therefore, the target's potential threat level can be obtained by this threat prediction model from the predicted future state and the recognized emotion. The experimental results show that the PTP-CE is efficient for aerial target's state prediction and threat prediction, regardless of commander's emotional effect.

To improve the safety of HMX, HMX/NH2-GO composite was prepared with aqueous ammonia functionalized graphene oxide (NH2-GO). The composite was characterized by SEM, Zeta potential, XPS, Raman spectrum, XRD, HPLC, DSC and BAM sensitivity test. The results indicated that the functionalization with aqueous ammonia can enhance the interaction between GO and HMX, and more efficiently desensitize the explosive. The optimal impact sensitivity of the HMX/NH2-GO composite can be not less than 40 J, which is also the most insensitivity compared to the previous reports prepared by coating desensitization with non-energetic desensitized material. Moreover, the potential reason for the different impact and friction sensitivity was also discussed, which may bring a novel perspective to achieve the desensitization of energetic material.

Ti6Al4V is widely applied in the integral cascades of aero engines. As an effective machining method, electrochemical trepanning (ECTr) has unique advantages in processing surface parts made of hard-to-cut materials. In ECTr, the state of the flow field has a significant effect on processing stability and machining quality. To improve the uniformity of the flow field when ECTr is applied to Ti6Al4V, two different flow modes are designed, namely full-profile electrolyte supply (FPES) and edges electrolyte supply (EES). Different from the traditional forward flow mode, the flow directions of the electrolyte in the proposed modes are controlled by inlet channels. Simulations show that the flow field under EES is more uniform than that under FPES. To further enhance the uniformity of the flow field, the structure of EES is optimized by modifying the insulating sleeve. In the optimized configuration, the longitudinal distance between the center of the inlet hole and the center of the blade is 6.0 mm, the lateral distance between the centers of the inlet holes on both sides is 16.5 mm, the length to which the electrolyte enters the machining area is 1.5 mm, and the height of the insulating sleeve is 13.5 mm. A series of ECTr experiments are performed under the two flow modes. Compared with EES, the blade machined by FPES is less accurate and has poorer surface quality, with a surface roughness (Ra) of 3.346 μm. Under the optimized EES, the machining quality is effectively enhanced, with the surface quality improved from Ra = 2.621 μm to Ra = 1.815 μm, thus confirming the efficacy of the proposed methods.

In this study, the approximate and exact solutions for the stationary-state of the solids model with neglecting reactant consumption for both non-uniform and uniform temperature systems were applied on gas ignition under a constant pressure condition. The criticality conditions for a slab, an infinite cylinder, and a sphere are determined and discussed using dimensionless temperatures under constant ambient and surface temperatures for a non-uniform temperature system. Exact solution for a Semenov model with convection heat loss was also presented. The solution of the Semenov problem for constant volume or density as a solid and constant pressure were compared. The critical parameter δ is calculated and compared with those of Frank-Kamenetskii solution values. The validation of the calculated ignition temperatures with other exact solution and experimental results were offered. The relation between critical parameters form Semenov and F.K. models solution was introduced.

In the edge computing environment, app vendors can cache their data on a large number of geographically distributed edge servers to serve their users. However, those cached data are particularly vulnerable to both intentional and accidental corruption, which makes data security a major concern in the EC environment. Given limited computing resources of edge servers, how to effectively and efficiently inspect those data over tremendous edge servers is a critical and open problem. To tackle this edge data integrity (EDI) problem, we first study the entities, threats, system objectives, and the inspection mechanism, then propose a novel approach named EDI-S for inspecting the integrity of edge data and localizing the corrupted ones. Based on the elliptic curve, EDI-S generates one digital signature as the integrity proof for each replica. Then, multiple integrity proofs are aggregated to be inspected together. This mechanism allows the integrity of tremendous cache data on multiple edge servers can be inspected altogether via an aggregate verification. EDI-S also provides two methods for localizing the corrupted data on edge servers, one for small-scale scenarios and the other for large-scale scenarios. Both theoretical analysis and experimentally evaluation demonstrate that EDI-S can solve the EDI problem effectively and efficiently.

A 3D laser scanning strategy based on cascaded deep neural network is proposed for the scanning system converted from 2D Lidar with a pitching motion device. The strategy is aimed at moving target detection and monitoring. Combining the device characteristics, the strategy first proposes a cascaded deep neural network, which inputs 2D point cloud, color image and pitching angle. The outputs are target distance and speed classification. And the cross-entropy loss function of network is modified by using focal loss and uniform distribution to improve the recognition accuracy. Then a pitching range and speed model are proposed to determine pitching motion parameters. Finally, the adaptive scanning is realized by integral separate speed PID. The experimental results show that the accuracies of the improved network target detection box, distance and speed classification are 90.17%, 96.87% and 96.97%, respectively. The average speed error of the improved PID is 0.4239°/s, and the average strategy execution time is 0.1521 s. The range and speed model can effectively reduce the collection of useless information and the deformation of the target point cloud. Conclusively, the experimental of overall scanning strategy show that it can improve target point cloud integrity and density while ensuring the capture of target.

Saturation phenomena often exist due to limited system resources, and impulsive protocols can lead to a reduction in communication cost. From these issues, this article investigates a leader-based formation control problem of multiagent systems via asynchronous impulsive protocols with saturated feedback. General linear system models with and without finite time-varying time delays under asymmetric saturated feedback control are concurrently considered. The asynchronous impulsive protocols only permit communication at impulsive instants and each agent has its own communication instants independently. Moreover, to improve system performance, an offset only containing desired formation information is introduced. Finally, because the feedbacks are saturated, admissible regions are proved to exist, which are also estimated by a mean of optimization. Numerical simulations are presented to demonstrate the validity of the proposed schemes.

Unmanned Aerial Vehicles (UAVs) have received a wide range of attention for military and commercial applications. Enhanced with communication capability, UAVs are considered to play important roles in the Sixth Generation (6G) networks due to their low cost and flexible deployment. 6G is supposed to be an all-coverage network to provide ubiquitous connections for space, air, ground and underwater. UAVs are able to provide air-borne wireless coverage flexibly, serving as aerial base stations for ground users, as relays to connect isolated nodes, or as mobile users in cellular networks. However, the onboard energy of small UAVs is extremely limited. Thus, UAVs can be only deployed to establish wireless links temporarily. Prolonging the lifetime and developing green UAV communication with low power consumption becomes a critical challenge. In this article, a comprehensive survey on green UAV communications for 6G is carried out. Specifically, the typical UAVs and their energy consumption models are introduced. Then, the typical trends of green UAV communications are provided. In addition, the typical applications of UAVs and their green designs are discussed. Finally, several promising techniques and open research issues are also pointed out.

We develop a scheme for the computation of the full-counting statistics of transport described by Markovian master equations with an arbitrary time dependence. It is based on a hierarchy of generalized density operators, where the trace of each operator yields one cumulant. This direct relation offers a better numerical efficiency than the equivalent number-resolved master equation. The proposed method is particularly useful for conductors with an elaborate time-dependence stemming, e.g., from pulses or combinations of slow and fast parameter switching. As a test bench for the evaluation of the numerical stability, we consider time-independent problems for which the full-counting statistics can be computed by other means. As applications, we study cumulants of higher order for two time-dependent transport problems of recent interest, namely steady-state coherent transfer by adiabatic passage and Landau-Zener-St\"uckelberg-Majorana interference in an open double quantum dot., Comment: 7 pages, 5 figures

The intrinsic permeability is a crucial parameter to characterise and quantify fluid flow through porous media. However, this parameter is typically uncertain, even if the geometry of the pore structure is available. In this paper, we perform a comparative study of experimental, semi-analytical and numerical methods to calculate the permeability of a regular porous structure. In particular, we use the Kozeny-Carman relation, different homogenisation approaches (3D, 2D, very thin porous media and pseudo 2D/3D), pore-scale simulations (lattice Boltzmann method, Smoothed Particle Hydrodynamics and finite-element method) and pore-scale experiments (microfluidics). A conceptual design of a periodic porous structure with regularly positioned solid cylinders is set up as a benchmark problem and treated with all considered methods. The results are discussed with regard to the individual strengths and limitations of the used methods. The applicable homogenisation approaches as well as all considered pore-scale models prove their ability to predict the permeability of the benchmark problem. The underestimation obtained by the microfluidic experiments is analysed in detail using the lattice Boltzmann method, which makes it possible to quantify the influence of experimental setup restrictions., Deutsche Forschungsgemeinschaft, Projekt DEAL

A theoretical study of the K-shell ionization of hydrogen-like ions, colliding with bare nuclei, is performed within the framework of the time-dependent Dirac equation. Special emphasis is placed on the ionization probability that is investigated as a function of impact parameter, collision energy and nuclear charge. To evaluate this probability in a wide range of collisional parameters we propose a simple analytical expression for the transition amplitude. This expression contains three fitting parameters that are determined from the numerical calculations, based on the adiabatic approximation. In contrast to previous studies, our analytical expression for the transition amplitude and ionization probability accounts for the full multipole expansion of the two-center potential and allows accurate description of nonsymmetric collisions of nuclei with different atomic numbers, $Z_1 \neq Z_2$. The calculations performed for both symmetric and asymmetric collisions indicate that the ionization probability is reduced when the difference between the atomic numbers of ions increases., 8 pages, 6 figures

The use of nano phase change material in thermal energy storage applications appears promising, but the often-poor performance and the lack of understanding of the heat transfer mechanisms interconnectedness remains a challenge and hinders their widespread integration. The existing numerical work has unveiled numerous impediments in predicting the actual melting behaviour. They rarely combine the effects of conduction enhancement, convection degradation, and latent heat reduction, due to inaccurate characterization of the thermophysical properties and the limitations of their model assumptions. In the present study, an enhanced numerical approach was developed to investigate the melting performance of xGnP-octadecane filled in a vertical cylindrical enclosure at different weight concentrations. The model results for the pure phase change material were compared and validated against the experimental data. The progression of the melting front, temperature probes, energy storage capacity and heat transfer rate of the nano phase change material were thoroughly evaluated. The current numerical observations demonstrate that the addition of nanoparticles improves, up to a critical concentration of 0.5wt%, the melting rate. The results showed that by adding 0.5wt% of xGnP in the base phase change material (octadecane), the melting rate decreases by 9.7% and the heat storage rate increases by 12.6%. However, at higher loadings, the heat transfer rate is deteriorated due to worsening of other thermophysical properties provoking the prevalence of viscous forces over natural convection and latent capacity. The system overall efficacy was found to be dependent on the net effects of relative changes of all thermophysical properties with nanoparticle concentration and temperature in the solid, so called mushy, and liquid zones. Finally, when characterizing nano phase change material, the thermal conductivity cannot be considered alone as a criterion for nano phase change material selection. A high thermal conductivity is needed for maximum heat absorption in thermal transport applications. Nevertheless, low viscosity, high latent heat and specific heat capacities are also essential to ensure a better thermal energy storage efficiency in terms of capacity and heat extraction/release rate.

Single-phase natural circulation thermosiphon loops have been attracting increased interest as they represent the prototype of passive safety systems. However, the stability properties of thermosiphon loops, which can affect and compromise their functionality, are still actively investigated. Traditionally, the stability analysis of thermosiphon loops has been simplified to one-dimensional (1D) calculations, on the argument that the flow would be monodimensional when the diameter of the pipe D is orders of magnitude smaller than the length of the loop Lt. However, at lower Lt/D ratios, rectangular thermosiphon loops show that the flow presents three-dimensional (3D) effect, which also has been confirmed by stability analyses in toroidal loops. In this paper, we performed a series of high-fidelity simulations using the spectral-element code nek5000 to investigate the stability behavior of the flow in rectangular thermosiphon loops. A wide range of Lt/D ratio from 10 to 200 has been considered, and the results show many different outcomes compared to previous 1D analytical calculations or stability theory. Moreover, we analyzed the flow in rectangular thermosiphon loops using proper orthogonal decomposition (POD), and we observed that the cases without flow reversal are characterized by swirl modes typical of bent pipes and high-frequency oscillation of the related time coefficients obtained by Galerkin projection. However, the swirl mode was not observed in cases with flow reversals, and these cases are characterized by symmetric flow field at second POD mode and the similarity of low-frequency oscillation in the projection of POD modes.

Novel numerical simulations investigating the Richtmyer-Meshkov instability (RMI) with surface tension are presented. We solve the two-phase compressible Euler equation with surface tension and interface reconstruction by a volume-of-fluid method. We validate and bridge existing theoretical models of effects of surface tension on the RMI in the linear, transitional, and nonlinear postshock growth regimes. After deriving a consistent nondimensional formulation from an existing linear incompressible theory predicting perturbation development under large surface tension, we find good agreement with theoretical prediction in the small-amplitude (linear) oscillatory regime for positive Atwood numbers, and we show that negative Atwood numbers can be accommodated by an appropriate modification to the theory. Next, we show good agreement with nonlinear theory for asymptotic interface growth in the limit of small surface tension. Finally, we use the nondimensional formulation to define a heuristic criterion which identifies the transition from the linear regime to the nonlinear regime at intermediate surface tension. These results highlight the utility of this numerical method for compressible problems featuring surface tension, and they pave the way for a broader investigation into mixed compressible/incompressible problems.

The appearance of high-entropy alloys (HEAs) makes it possible for a material to possess both high strength and high ductility. It is with great potential to apply HEAs under extreme conditions such as in the penetration process. In this paper, experiments of WFeNiMo HEA and tungsten heavy alloy (WHA) projectiles penetrating medium-carbon steel were conducted by using the ballistic gun and two-stage light-gas gun that can accelerate projectiles to impact velocities ranging from 1162 m/s to 2130 m/s. Depth of penetration (DOP) at elevated impact velocities of HEA and WHA projectiles were obtained firstly. Combined with the macroscopic and microscopic analysis of the residual projectiles, the transition of the penetration mode of the WFeNiMo HEA projectile was identified systemically. The experimental results indicated that the penetration mode of the HEA projectile changes from self-sharpening to mushrooming with the increase of impact velocity, while for the WHA projectile, the penetration mode is always mushrooming. The microstructure of the residual HEA projectiles showed that the phases tangle with each other and the morphology of the microstructure of the phases differs in the two penetration modes. Besides, the evolution of shear bands and fractures varies in the two modes. The evolution of the microstructure of HEAs causes the sharp-pointed nose to disappear and the HEA projectile ultimately becomes blunt as the impact velocity increases.

A line laser with high power as the background light source for the design of a new photoelectric detection target is proposed in this paper, aiming to improve the detection ability of the traditional photoelectric detection target under low background illumination. The laser emitted pulse waveform function and the laser echo pulse response function were used to establish the mathematical model of the reflected echo power of projectile in the detection area and derive the calculation function of minimum detectable echo power in the line laser detection screen, according to information of the line laser emitted power, incident angle of projectile, duration time and detection distance of projectile passing through the line laser detection screen. Calculations and experimental results showed that the design method of line laser detection screen and calculation model of laser echo power are reasonable, and the detection ability of line laser detection screen is obviously higher than that of traditional photoelectric detection screen, especially in low background illumination; at the same time, the designed line laser detection screen was used to combine a six line laser detection screen intersection test system, based on live ammunition for shooting. The test system is stable and able to obtain the dynamic parameters of the flying projectile, verifying that the design of the line laser detection screen in new photoelectric detection target can be suitable for shooting range test applications.

This paper presents a non-smooth multibody dynamic formulation and error analysis of an antenna pointing mechanism including frictional spatial revolute joints (FSRJs) with small clearance in the framework of the special Euclidian group SE(3). The formulation leads to an inertial frame-invariant, a compact and unified description for rigid bodies and spatial revolute joints (SRJs). The geometric constraint of the bearing is covered by four open semi-cylinders, which can be treated as bilateral constraints assuming that the impact effects are negligible. The frictional contact problem is formulated as a horizontal linear complementary problem (HLCP), which is embedded in the Lie-group integration scheme. Error of the antenna pointing mechanism is modeled by means of the adjoint transformation and POE-based formula. The evolution of errors is obtained through the solution of non-smooth dynamics. The obtained numerical results illustrate the influences of FSRJs in dynamics modeling and error analysis of the antenna pointing mechanism.

This paper puts forward an unprecedented avoidance-striking-arrival problem aiming to address the need for tank's uncertain mechanical systems on the intelligent battlefield. The associated system uncertainties (possibly rapid) are time-varying but bounded (possibly unknown). The goal is to design a controller that enables the tank to aim at and attack the enemy tank while keeping itself (out of the enemy fire zone). The tank maintains this condition until reaching the predefined region. In this paper, an approximate constraint following control method is adopted to solve this problem, and the original constraints are creatively divided into two categories: the avoidance - tracking constraint and the striking - arrival constraint. An adaptive robust control method is proposed and consequently verified through simulation experiments. It is proved that the system fully obeys the avoidance - tracking - constraint and strictly obeys the striking - arrival constraint under the control input τ . Besides, the control of the tank vehicle running system and tank gun bidirectional stabilization system are unified to deal with the control signal delay caused by complex uncertainties on the battlefield. Overall, this paper reduced the delay of signal transmission in the system while solved the avoidance - striking - arrival problem.

Nowadays, the mitigation of damage to a ship caused by the underwater explosion attracts more and more attention from the modern ship designers. In this study, two kinds of scale tests were conducted to investigate the effects of polyurea coatings on the blast resistance of hulls subjected to underwater explosion. Firstly, small-scale model tests with different polyurea coatings were carried out. Results indicate that polyurea has a better blast resistance performance when coated on the front face, which can effectively reduce the maximum deflection of the steel plate by more than 20% and reduce the deformation energy by 35.7%–45.4%. Next, a full-scale ship (approximately 50 m × 9 m) under loadings produced by the detonation of 33 kg of spherical TNT charges was tested, where a part of the ship was coated with polyurea on the front face (8 mm + 24 mm) and not on the contrast area. Damage characteristics on the bottom were statistically analyzed based on a 3D scanning technology, indicating that polyurea contributes to enhancing the blast protection of the ship. However, damage results of this test were different from those of the small-scale tests. Moreover, the deformation area of the bottom with polyurea was greatly increased by 40.1% to disperse explosion energy, a conclusion that cannot be drown from the small-scale tests.

The close-in weapon system (CIWS) is a combat system that faces a complex environment full of dynamic and unknown challenges, whose construction and planning require a systematic design method. Multi-living agent (MLA) theory is a methodology for the combat system design, which uses the livelihood degree to evaluate the multi-dimensional long-term operational effectiveness of the system; whereas, there is still no uniform quantization framework for the livelihood degree, and the adjustment methods of livelihood degree need to be further improved. In this paper, we propose the uniform quantization framework for the livelihood degree and detailed discuss the methods of livelihood adjustment. Based on the MLA theory, the multi-dimensional operational effectiveness of the missile-gun integrated weapon system (MGIWS) is analyzed, and the long-term combat effectiveness against the saturation attack is assessed. Furthermore, the planning problem of the equipment deployment and configuration is investigated. Two objectives, including the overall livelihood degree and cost-effectiveness (CE), are proposed, and the optimization method based on genetic algorithm (GA) is studied for the planning problem.

Based on the two-arc profile assumption, the expansion deformation and energy absorption of circular tubes compressed by conical-cylindrical dies were reconsidered. First, the deformation of the two arcs was analyzed independently and an improved model denoted as Model-I was established. Then, by further involving the coupling between the bending moment and membrane forces, a more elaborate model, i.e., Model-II was developed. Afterwards, experiments and simulations were conducted to verify the models, which show that, compared with previous theoretical models, Model-II could not only capture the prominent features of the deformation, but also improve the prediction accuracy of the steady driving force significantly. By means of this model, it was found that the critical semi-conical angle, which makes the driving force minimum, increases with the increase of the friction coefficient, expansion ratio as well as the radius/thickness ratio of the tube. And, the energy dissipation due to stretching is always greater than that of bending, while the friction dissipation can account for the largest proportion at small semi-conical angle or large friction coefficient. At a certain friction and die conditions, the specific energy absorption of expanded tubes can be much higher than that under progressive collapse mode.

In this study, based on a closed bomb test combined with computational fluid dynamics, a structural finite element method, and an acoustic boundary element method, a fluid-solid acoustic one-way coupling calculation model is established for the combustion process of energetic materials in a closed bomb, and the effectiveness of the model is verified by experiments. It is found that the maximum peak sound pressure increases exponentially with an increase in loading doses or gas pressure. However, a change in the combustion coefficient of the energetic materials has little effect on the noise generated during the combustion process in the closed bomb. When the combustion coefficient is reduced by a multiple of 16, the maximum transient sound pressure is reduced by 1.79 dB, and the sound pressure level in the frequency band is reduced by 1.75 dB. With an increase in shell thickness, the combustion noise of the energetic materials in the closed bomb decreases, and the reduction range of the combustion noise increases with the increase in shell thickness.

Aiming at the independent development of tracked vehicles, it is urgent to improve its mobility, passability and ride comfort, a new type of flexible road wheel with a “wheel-hinge-hub” combined structure is proposed in this study. The vibration model characteristics of the flexible road wheel were studied by the combination of numerical simulation and experiments. The superelasticity of rubber is obtained through uniaxial tensile experiment of the material and a detail three-dimensional nolinear finite element model of the flexible road wheel is established through finite element software ABAQUS. The free vibration equation of the flexible road wheel is solved by Lanczos vector direct superposition method, and its predicted modes and natural frequencies are compared with experimental results, which verifies the accuracy and reliability of the established finite element model. On this basis, the effects of various key structural or material factors on the natural frequencies of the flexible road wheel are studied using orthogonal experimental design method. Besides, the vibration modal characteristics of the flexible road wheel are also compared with those of the rigid road wheel. The research results provide a theoretical basis for the vibration and noise reduction of flexible road wheel.

The compression behavior of the lattice-walled tubes under variable strain rates are investigated by numerical simulation, and the stress-strain relationship of the structure under quasi-static loading is theoretically analyzed. The finite element software LS-DYNA is used to simulate the structure established by the beam element, and the critical impact velocity is obtained when the structure collapses layer by layer. According to the plastic hinge theory and considering the combined action of the beam's bending moment and axial force in the structure, the stress-strain relationship of the structure under quasi-static loading is derived and compared with the experimental results. The numerical simulation results reveal that the structure of the single-layer gradient tube(SGC) does not undergo shear deformation under quasi-static and low-speed impact. The critical speed of the gradient square tube(GS) is higher than that of a cylindrical tube. The theoretical model can correctly reflect the mechanical response of the structure under uniaxial compression.

Nano-TATB was developed in microchannels by physical method and chemical method, respectively. The effects of total flow rate, number of microreactor plates, solvent/non-solvent ratio and temperature on the particle size of TATB in the physical method were studied. Prepared TATB were characterized by Nano Sizer, Scanning Electron Microscopy, Specific surface aperture analyzer, X-ray diffraction, Fourier transform infrared spectroscopy and Differential Scanning Calorimetry. The results show that the TATB obtained by physical method and chemical method are spherical, with average particle size of 130.66 nm and 108.51 nm, respectively. Specific surface areas of TATB obtained by physical and chemical methods are 21.37 m2/g and 21.91 m2/g, respectively. Compared with the specific surface area of micro-TATB (0.0808 m2/g), the specific surface area of nano-TATB is significantly increased. DSC test results show that the smaller the particle size of TATB, the lower the thermal decomposition temperature. In addition, by simulating the mixing state of fluid in microchannels and combining with the classical nucleation theory, the mechanism of preparing nano-TATB by microchannels was proposed.

Recently, reactive materials have been developed for penetrative projectiles to improve impact resistance and energy capacity. However, the design of a reactive material structure, involving shape and size, is challenging because of difficulties such as high non-linearity of impact resistance, manufacturing limitations of reactive materials and high expenses of penetration experiments. In this study, a design optimization methodology for the reactive material structure is developed based on the finite element analysis. A finite element model for penetration analysis is introduced to save the expenses of the experiments. Impact resistance is assessed through the analysis, and result is calibrated by comparing with experimental results. Based on the model, topology optimization is introduced to determine shape of the structure. The design variables and constraints of the optimization are proposed considering the manufacturing limitations, and the optimal shape that can be manufactured by cold spraying is determined. Based on the optimal shape, size optimization is introduced to determine the geometric dimensions of the structure. As a result, optimal design of the reactive material structure and steel case of the penetrative projectile, which maximizes the impact resistance, is determined. Using the design process proposed in this study, reactive material structures can be designed considering not only mechanical performances but also manufacturing limitations, with reasonable time and cost.

Particle size and content of RDX are the two main factors that affect the burning stability of RDX-based propellants. However, these effects and the corresponding mechanisms are still controversial. In this work, we investigated the physicochemical processes during burning and the corresponding mechanisms through the technologies of structure compactness analysis on the base of voidage measurement and theoretical interfacial area estimation, apparent burning rate measurement using closed vessel (CV) and extinguished burning surface characterization relying on interrupted closed vessel (ICV) and scanning electron microscope (SEM). The results indicate that the voidage increased with the increase of RDX content and particle size due to the increasing interfacial area and increasing interface gap size, respectively. The apparent burning rate increased with the increase of RDX particle size because of the decreasing RDX specific surface area on the burning surface, which could decrease the heat absorbing rates of the melting and evaporation processes of RDX in the condensed phase. Similarly, the apparent burning rate decreased with the increase of RDX content at pressures lower than around 55 MPa due to the increasing RDX specific surface area. Whereas, an opposite trend could be observed at pressures higher than around 55 MPa, which was attributed to the increasing heat feedback from the gas phase as the result of the increasing propellant energy. For propellants containing very coarse RDX particles, such as 97.8 and 199.4 μm average size, the apparent burning rate increased stably with a flat extinguished surface at pressures lower than around 30 MPa, while increased sharply above around 30 MPa with the extinguished surface becoming more and more rugged as the pressure increased. In addition, the turning degree of u-p curve increased with the increase of coarse RDX content and particle size, and could be reduced by improving the structure compactness.

Finding relevant objects in a large repository is a fundamental research problem occurring in many applications, such as: data cleaning, data integration, web search, and information retrieval. Instant type-ahead fuzzy search, where user types her query character by character and find the top-k relevant objects, has become widely involved in many applications because it provides the users with rapid response results and improves the user’s experience. The state-of-the-art algorithms are generally inefficient due to their breadth first search algorithm that results in repeated computations. To this end, we propose a novel depth-oriented instant type-ahead fuzzy search algorithm, that largely avoids repeated computations. The efficiency and effectiveness of the proposed approach are empirically demonstrated using real-world datasets. Experimental results show that our approach is 5–10 times faster than state-of-the-art approaches.

This article addresses the response of GLAss fiber REinforced aluminum to hypervelocity impacts of micrometeoroid analogs at impact velocities of 7 km/s and beyond. In relation, the damage modes of different GLAss fiber REinforced aluminum configurations have been exemplified. The GLAss fiber REinforced aluminum configurations comprised six to twelve variably thick aluminum layers and up to four plies of glass fiber reinforced epoxy per composite laminate. Hypervelocity impact experiments have been conducted with the help of a two-stage light-gas gun, wherein aluminum- and stainless steel projectiles were launched at velocities up to 7.15 km/s. Visual inspection of the damage area suggested the dissipation of impact energy in elastic-plastic deformation, petalling, delamination, debonding, tensile failure of fibers, and pyrolysis of epoxy. A prevailing damage mode was not apparent albeit. The quasi-isotropic ply orientation of S2-glass/FM94-epoxy laminates promoted the interference of shock- and rarefaction waves and suppressed the damage area of GLAss fiber REinforced aluminum. To discriminate between the impact performance of different GLAss fiber REinforced aluminum configurations, the energy dissipated in different damage modes of GLAss fiber REinforced aluminum has been assessed quantitatively. In terms of normalized energy, the cross-ply GLAss fiber REinforced aluminum dissipated higher energy in petal formation than in other primary damage modes. The normalized petalling energy was found to decline with the increase of impact energy. The outcomes of this study will help to optimize the GLAss fiber REinforced aluminum laminate, which will be employed as a bumper shield to prevent the fatal damage and the unzipping of a spacecraft pressure bulkhead.

We consider here a new type of mixed local and nonlocal equation under suitable Neumann conditions. We discuss the spectral properties associated to a weighted eigenvalue problem and present a global bound for subsolutions. The Neumann condition that we take into account comprises, as a particular case, the one that has been recently introduced in [S. Dipierro, X. Ros-Oton, E. Valdinoci, Rev. Mat. Iberoam. (2017)]. Also, the results that we present here find a natural application to a logistic equation motivated by biological problems that has been recently considered in [S. Dipierro, E. Proietti Lippi, E. Valdinoci, preprint (2020)].

An adaptive wheel-legged shape reconfigurable mobile robot, based on a scissor-like mechanism, is proposed for an obstacle detecting and surmounting robot, moving on complex terrain. The robot can dynamically adjust its own shape, according to the environment, realizing a transformation of wheel shape into leg shape and vice versa. Each wheel-legged mechanism has one degree of freedom, which means that only the relative motion of the inner and outer discs is needed to achieve the transformation of the shape into a wheel or a leg. First, the force analysis of the conversion process of the wheel-legged mechanism is carried out, while the relationship between the driving torque and the friction factor in the non-conversion trigger stage and in the conversion trigger stage is obtained. The results showed that the shape conversion can be better realized by increasing the friction factor of the trigger point. Next, the kinematics analysis of the robot, including climbing the obstacles, stairs and gully, is carried out. The motion of the spokes tip is obtained, in order to derive the folding ratio and the surmountable obstacle height of the wheel-legged mechanism. The parameters of the wheel-legged structure are optimized, to obtain better stability and obstacle climbing ability. Finally, a dynamic simulation model is established by ADAMS, to verify the obstacle climbing performance and gait rationality of the robot, in addition to a prototype experiment. The results showed that the surmountable obstacle height of the robot is about 3.05 times the spoke radius. The robot has the stability of a traditional wheel mechanism and the obstacle surmount performance of a leg mechanism, making it more suitable for field reconnaissance and exploration missions.

In the docking process of aeroengine rotor parts, docking accuracy that indicates the gaps between the end faces is strictly required. A key issue is improving docking accuracy using automated docking equipment. In this paper, a systematic study is carried out on the error modeling and compensation of a novel six-degrees-of-freedom (6-DOF) docking equipment for aeroengine rotors. First, a new model for indicating the main indexes of docking accuracy is proposed. Then, the error model of a specially designed 6-DOF docking equipment is established based on a modified Denavit Hartenberg method with five parameters. Subsequently, two error compensation methods are proposed. Based on the above models, a docking accuracy simulation algorithm is proposed using the Monte Carlo method. Finally, verification experiments are conducted. The results show that, for the maximum values and standard deviations of the gaps between the rotor end-faces in the actual and target positions and attitudes, i.e., main indexes that represent docking accuracy, the deviation rates between the simulation and experimental results are less than 20%. The modeling methods have referential significance. The decline rates of these values are 50–65% when using the two proposed compensation methods. The compensation methods significantly improve the docking accuracy.

Penetration and internal blast behavior of reactive liner enhanced shaped charge against concrete space were investigated through experiments and simulations. The volume of the enclosed concrete space is about 15 m3. The reactive liner enhanced shaped charge utilizes reactive copper double-layered liner, which is composed of an inner copper liner and an outer reactive liner, while the reactive material liner is fabricated by PTFE/Al (Polytetrafluoroethylene/Aluminum) powders through cold-pressing and sintering. Static explosion experiments show that, compared with the shaped charge which utilizes copper liner, the penetration cavity diameter and spalling area of concrete by the novel shaped charge were enlarged to 2 times and 4 times, respectively. Meanwhile, the following reactive material had blast effect and produced significant overpressure inside the concrete closed space. Theoretical analysis indicates concrete strength and detonation pressure of reactive material both affect the penetration cavity diameter. To the blast behavior of reactive material inside the concrete space, developing TNT equivalence model and simulated on AUTODYN-3D for analysis. Simulation results reproduced propagation process of the shock wave in concrete space, and revealed multi-peaks phenomenon of overpressure-time curves. Furthermore, the empirical relationship between the peak overpressure and relative distance for the shock wave of reactive material was proposed.

Cocrystallization integrates the merits of high energy and insensitivity between energetic molecules to obtain energetics with satisfying performance. However, how to obtain supramolecular synthons accurately and rapidly for predicting the structure and property of cocrystal remains a challenging problem. In this research, an efficient systematic search approach to predict CL-20/2,4-DNI cocrystal has been proposed that 2,4-DNI revolves around CL-20 with a stoichiometric ratio of 1:1 in accordance with the specified rules (hydrogen bond length: 2.2–3.0 A; search radius: 6.5 A; the number of hydrogen bond: 1–3). Eight possible supramolecular synthons were obtained by combining quantum chemistry with molecular mechanics. Crystal structure prediction indicated that there are four structures in cocrystal, namely P21/c, P212121, Pbca and Pna21, and CL-20/2,4-DNI cocrystal is likely to be P21/c and the corresponding cell parameters are Z = 4, a = 8.28 A, b = 12.17 A, c = 20.42 A, α = 90°, β = 96.94°, γ = 90°, and ρ = 1.9353 g/cm3. To further study the intermolecular interaction of CL-20/2,4-DNI cocrystal, a series of theoretical analyses were employed including intermolecular interaction energy, electrostatic potential (ESP), Density of State (DOS), Hirshfeld surface analysis. The C–H⋯O hydrogen bonds are demonstrated as the predominant driving forces in the cocrystal formation. The mechanical properties and detonation properties of CL-20/2,4-DNI cocrystal implies that the cocrystal shows better ductility and excellent detonation performances (9257 m/s, 39.27 GPa) and can serve as a promising energetic material. Cocrystal structure predicted was compared with the experimental one to verify the accuracy of systematic search approach. There is a less than 8.8% error between experiment and predict results, indicating the systematic search approach has extremely high reliability and accuracy. The systematic search approach can be a new strategy to search supramolecular synthons and identify structures effectively and does have the potential to promote the development of energetic cocrystal by theoretical design.

The violent vibration of hydraulic pipelines in aircraft may cause faults or even an accident, especially for the large aircraft with the multi-pump system because of different vibration sources and complex pipelines system. Aiming to the vibration analysis and control of the multi-pump system, this paper proposed the clamps' locations optimization to minimize the system impedance at vibration frequencies. Firstly, the models of the flexible clamp and other components in multi-pump system were established, based on which, the system impedance was calculated by using Transfer Matrix Method (TMM); Secondly, the objective function is defined as weighted sum of system impedance at frequencies of different vibration sources. Then, the clamps’ locations were altered to change the system impedance. Moreover, The Chaotic Swarm Particle Optimization (CPSO) algorithm was applied to obtain the optimal clamps’ locations and the minimum value of objective function which decreased by 36.4% compared to the value of original clamps’ locations; Finally, the experiments from vibration and pressure test with original and optimized clamps’ locations verified the effectiveness of the system impedance calculation and clamps’ locations optimization method.

The electro-hydrostatic actuator (EHA) used in more electric aircraft (MEA) has been extensively studied due to its advantages of high reliability and high integration. However, this high integration results in a small heat dissipation area, leading to high-temperature problems. Generally, to reduce the temperature, a wet cooling method of using the pump leakage oil to cool the motor is adopted, which can also increase the difficulty of accurately predicting the system temperature in the early design stage. To solve this problem, a dynamic coupling thermal model of a wet EHA is proposed in this paper. In particular, the leakage oil of the pump is used as a coupling item between the electrical system and the hydraulic system. Then, an improved T-equivalent block model is proposed to address the uneven distribution of axial oil temperature inside the motor, and the control node method is applied to hydraulic system thermal modeling. Meanwhile, a dynamic coupling thermal model is developed that enables a dynamic evaluation of the wet EHA temperature. Then, experimental prototypes of wet motor and wet EHA are developed, while the temperature response of the wet motor at different rotation speeds and different loads and the temperature response of the wet EHA at no-load condition were verified experimentally at room temperature, respectively. The maximum temperature difference between the experimental and theoretical results of the wet motor as well as the experimental and theoretical results of the wet EHA is less than 8 °C. These test results indicate that the dynamic coupling thermal model is valid and demonstrate that the thermal coupling modeling method proposed in this paper can provide a basis for the detailed thermal design of EHA.

Koopman mode decomposition is a flow analysis technique developed by Igor Mezic in 2004, based upon the Koopman operator first proposed by Bernard Koopman in 1931. Via Koopman decomposition any non-chaotic well-sampled dynamic system - linear, non-linear, laminar or turbulent - is broken down into single-frequency repetitive components (modes). This paper presents a survey consolidating published information regarding data-driven Koopman analysis techniques. It is intended to aid researchers exploring the suitability of data-driven Koopman analysis in anticipation of developing their own modeling. A basic mathematical explanation of Koopman analysis is given with emphasis toward the data-driven Dynamic Mode Decomposition (DMD) solution, which converges to the Koopman operator given a highly-sampled dataset. The four primary uses of Koopman analysis: flow analysis, power grid analysis, building thermal analysis, and biomedical analysis are discussed, along with other publications. Finally, weaknesses and problems inherent within Koopman analysis/DMD will be enumerated, alongside potential solutions. Koopman analysis is a computationally complex, yet often suitable method for determining periodic motion in any highly-sampled dataset. When compared to a similar analysis method, Proper Orthogonal Decomposition, Koopman analysis often provides additional detail regarding the structure of less significant modes present, albeit at the cost of increased computational complexity.

Copper azide with high density was successfully synthesized by in-situ reaction of nanoporous copper (NPC) precursor with HN3 gaseous. NPC with pore size of about 529 nm has been prepared by electroless plating using polystyrene (PS) as templates. The copper shells thickness of NPC was controlled by adjusting the PS loading amount. The effects of copper shell on the morphology, structure and density of copper azide were investigated. The conversion increased from 87.12% to 95.31% when copper shell thickness decrease from 100 to 50 nm. Meanwhile, the density of copper azide prepared by 529 nm NPC for 24 h was up to 2.38 g/cm3. The hollow structure of this NPC was filled by swelling of copper azide which guaranteed enough filling volume for keeping the same shape as well as improving the charge density. Moreover, HNS-IV explosive was successfully initiated by copper azide with minimum charge thickness of 0.55 mm, showing that copper azide prepared has excellent initiation performance, which has more advantages in the application of miniaturized explosive systems.

In recent years, Chinese Long March (LM) launchers have experienced several launch failures, most of which occurred in their propulsion systems, and this paper studies Autonomous Mission Reconstruction (AMRC) technology to alleviate losses due to these failures. The status of the techniques related to AMRC, including trajectory and mission planning, guidance methods, and fault tolerant technologies, are reviewed, and their features are compared, which reflect the challenges faced by AMRC technology. After a brief introduction about the failure modes of engines that can occur during flight, and the fundamentals of trajectory planning and joint optimization of the target orbit and flight path, an AMRC algorithm is proposed for geostationary transfer orbit launch missions. The algorithm evaluates the residual performance onboard, and plans new objectives and corresponding flight path by iterative guidance mode or segmented state triggered optimization methods in real-time. Three failure scenarios that have occurred during previous LM missions are simulated to check the robustness of the algorithm: imminent risk of the boosters’ engines, thrust drop during the first stage of flight, and being unable to start the engine during the second stage. The payloads would fall from space according to the current design under these conditions, but they were saved with the AMRC algorithm in the simulations, which allowed the rocket to get into the target orbit as intended or the payloads were deployed in other orbits without crashing. Although spaceflight can be very unforgiving, the AMRC algorithm has the potential to avoid the total loss of a launch mission when faced with these kinds of typical failures.

s This paper investigates the effect of porosity on active damping of geometrically nonlinear vibrations (GNLV) of the magneto-electro-elastic (MEE) functionally graded (FG) plates incorporated with active treatment constricted layer damping (ATCLD) patches. The perpendicularly/slanted reinforced 1–3 piezoelectric composite (1–3 PZC) constricting layer. The constricted viscoelastic layer of the ATCLD is modeled in the time-domain using Golla-Hughes-McTavish (GHM) technique. Different types of porosity distribution in the porous magneto-electro-elastic functionally graded PMEE-FG plate graded in the thickness direction. Considering the coupling effects among elasticity, electrical, and magnetic fields, a three-dimensional finite element (FE) model for the smart PMEE-FG plate is obtained by incorporating the theory of layer-wise shear deformation. The geometric nonlinearity adopts the von Karman principle. The study presents the effects of a variant of a power-law index, porosity index, the material gradation, three types of porosity distribution, boundary conditions, and the piezoelectric fiber's orientation angle on the control of GNLV of the PMEE-FG plates. The results reveal that the FG substrate layers' porosity significantly impacts the nonlinear behavior and damping performance of the PMEE-FG plates.

The coaxial mixers enhance the suspension of concentrated slurries in an agitated reactor. In this research work, the complex slurry suspension and dissemination behavior in a coaxial slurry mixing system (comprised of a close clearance anchor rotating with a low speed and an inner axial impeller rotating with a high speed) was analyzed employing ERT (electrical resistance tomography, a non-intrusive flow visualization technique), and computational fluid dynamics (CFD). The numerical models were validated by comparing the axial solid concentration profiles generated using the ERT data and the CFD simulation results. The influences of various important parameters such as the diameter of the inner axial impeller, the inner impeller type, and the inner impeller spacing on the hydrodynamic characteristics of the slurry suspensions in a coaxial mixing vessel were thoroughly analyzed. The radial and axial velocity profiles of solid particles were generated using the validated mathematical models. The assessment of energy loss due to the solid–solid collisions, the particle–fluid frictions, and the particle–vessel wall collisions was conducted. The evaluation of optimum inner impeller clearance and inner impeller diameter is essential to attain a high degree of solids suspension and dissemination in a coaxial slurry mixing system.

High velocity ballistic impact deformation behaviour of Titanium/GFRP Fiber Metal Laminates (FML) has been explored. Both single and multiple projectiles impact conditions were considered. Ti/GFRP FML targets were fabricated with addition of 5% and 10% weight percentage of boron carbide (B4C) particles. Mechanical properties of Ti/GFRP FML targets were determined as per ASTM standards. High velocity ballistic experiments were conducted using Armour Piercing Projectile (APP) of diameter 7.62 mm and velocity ranging between 350 and 450 m/s. Depth of penetration of the projectile into the target was measured. The deformation behaviour of Ti/GFRP targets with and without the presence of ceramic powder (B4C) was investigated. “Ductile hole growth” failure mode was observed for pure GFRP target when subjected to single projectile impact whereas “plugging” failure mode was noted for Ti/GFRP targets. The presence of B4C (5% by weight) particles has significantly improved the ballistic resistance of the Ti/GFRP FML target by offering frictional resistance to the projectile penetration. Further addition (10% by weight) of B4C has reduced the ballistic performance due to agglomeration. None of the targets showed ‘brittle cracking’ or ‘fragmentation’ failures. When compared to the published results of Aluminium (Al 1100/GFRP and Al 6061/GFRP) FMLs, Ti/GFRP FML showed lesser DoP which increases its potential application to aerospace industry.

Recent advances in on-board radar and missile capabilities, combined with individual payload limitations, have led to increased interest in the use of unmanned combat aerial vehicles (UCAVs) for cooperative occupation during beyond-visual-range (BVR) air combat. However, prior research on occupational decision-making in BVR air combat has mostly been limited to one-on-one scenarios. As such, this study presents a practical cooperative occupation decision-making methodology for use with multiple UCAVs. The weapon engagement zone (WEZ) and combat geometry were first used to develop an advantage function for situational assessment of one-on-one engagement. An encircling advantage function was then designed to represent the cooperation of UCAVs, thereby establishing a cooperative occupation model. The corresponding objective function was derived from the one-on-one engagement advantage function and the encircling advantage function. The resulting model exhibited similarities to a mixed-integer nonlinear programming (MINLP) problem. As such, an improved discrete particle swarm optimization (DPSO) algorithm was used to identify a solution. The occupation process was then converted into a formation switching task as part of the cooperative occupation model. A series of simulations were conducted to verify occupational solutions in varying situations, including two-on-two engagement. Simulated results showed these solutions varied with initial conditions and weighting coefficients. This occupation process, based on formation switching, effectively demonstrates the viability of the proposed technique. These cooperative occupation results could provide a theoretical framework for subsequent research in cooperative BVR air combat.

This article presents the investigation of nonlinear vibration analysis of tapered porous functionally graded skew (TPFGS) plate considering the effects of geometrical non-uniformities to optimize the thickness in the structural design. The TPFGS plate is analyzed considering linearly, bi-linearly, and exponentially varying thicknesses. The plate's effective material properties are tailor-made using a modified power-law distribution in which gradation varies along the thickness direction of the TPFGS plate. Incorporating the non-linear finite element formulation to develop the kinematic equation's displacement model for the TPFGS plate is based on the first-order shear deformation theory (FSDT) in conjunction with von Karman's nonlinearity. The nonlinear governing equations are established by Hamilton's principle. The direct iterative method is adopted to solve the nonlinear mathematical relations to obtain the nonlinear frequencies. The influence of the porosity distributions and porosity parameter indices on the nonlinear frequency responses of the TPFGS plate for different skew angles and variable thicknesses are studied for various geometrical parameters. The influence of taper ratio, variable thickness, skewness, porosity distributions, gradation, and boundary conditions on the plate's nonlinear vibration is demonstrated. The nonlinear frequency analysis reveals that the geometrical non-uniformities and porosities significantly influence the porous functionally graded plates with varying thickness than the uniform thickness. Besides, exponentially and linearly variable thicknesses can be considered for the thickness optimizations of TPFGS plates in the structural design.

In this paper, a novel method of ultra-lightweight convolution neural network (CNN) design based on neural architecture search (NAS) and knowledge distillation (KD) is proposed. It can realize the automatic construction of the space target inverse synthetic aperture radar (ISAR) image recognition model with ultra-lightweight and high accuracy. This method introduces the NAS method into the radar image recognition for the first time, which solves the time-consuming and labor-consuming problems in the artificial design of the space target ISAR image automatic recognition model (STIIARM). On this basis, the NAS model's knowledge is transferred to the student model with lower computational complexity by the flow of the solution procedure (FSP) distillation method. Thus, the decline of recognition accuracy caused by the direct compression of model structural parameters can be effectively avoided, and the ultra-lightweight STIIARM can be obtained. In the method, the Inverted Linear Bottleneck (ILB) and Inverted Residual Block (IRB) are firstly taken as each block's basic structure in CNN. And the expansion ratio, output filter size, number of IRBs, and convolution kernel size are set as the search parameters to construct a hierarchical decomposition search space. Then, the recognition accuracy and computational complexity are taken as the objective function and constraint conditions, respectively, and the global optimization model of the CNN architecture search is established. Next, the simulated annealing (SA) algorithm is used as the search strategy to search out the lightweight and high accuracy STIIARM directly. After that, based on the three principles of similar block structure, the same corresponding channel number, and the minimum computational complexity, the more lightweight student model is designed, and the FSP matrix pairing between the NAS model and student model is completed. Finally, by minimizing the loss between the FSP matrix pairs of the NAS model and student model, the student model's weight adjustment is completed. Thus the ultra-lightweight and high accuracy STIIARM is obtained. The proposed method's effectiveness is verified by the simulation experiments on the ISAR image dataset of five types of space targets.