Radar detection in sandstorm environments is confronted with the problem of sand-dust clutter interference. By combining experimental measurements with theoretical analysis, this study discusses statistical characteristics and distribution models of sand-dust(SDS) clutter. Based on on-site measurements carried out in the X~Ka frequency bands using a vector network analyzer(VNA), sand-dust clutter data were obtained. The maximum likelihood estimation method was employed to conduct fitting analysis on the Rayleigh distribution, Weibull distribution, and lognormal distribution. The results show that under low sand-dust concentration conditions, the Weibull distribution can more accurately characterize the clutter amplitude characteristics. In high-concentration sand-dust environments, the clutter in low-frequency bands (X and Ku bands) exhibits obvious bimodal distribution characteristics, which gradually transform into a unimodal distribution as the frequency increases to the Ka band. Further comparative verification through various distribution models reveals that the double Gaussian mixture distribution achieves the optimal fitting effect on sand-dust clutter regardless of high or low concentration conditions.

This paper proposes a reverse electromagnetic coil configuration for generating controlled multi-stage deceleration/overload histories, supported by an electromagnetic‑thermal‑ structural numerical framework. Unlike traditional impact testing that relies on physical contact, this method utilizes electromagnetic induction to produce controllable and reproducible eddy-current-induced deceleration, enabling precise multi-stage overload waveforms. A comprehensive modeling framework encompassing multi-stage coils and their associated circuits is established, and the fundamental equations for magnetic, thermal, structural deformation, and electric circuit behaviors are derived systematically. The reliability of the model is verified by comparing the model results with the analytical solution and the experimental results. Key findings reveal that the overload level is significantly influenced by the armature’s inner radius and initial velocity. However, at an initial velocity of 800 m/s, the predicted armature temperature locally exceeds 1240 °C, above the melting point of copper (1083 °C), indicating a critical operational limit. Furthermore, while Von Mises stress in the armature significantly exceeds the yield strength of the armature material, the resulting plastic deformation severely degrades overload repeatability. This degradation is quantitatively mitigated by adopting a copper-titanium composite armature, which reduces overload decay from 60.75 % to 26.85 % on the final stage coil. Consequently, this method offers a complementary, laboratory-friendly approach for evaluating the survivability of electronic components under programmable multi-stage high-G environments, distinct from traditional impact tests used for material characterization.

Simulating the propagation of the electromagnetic (EM) wave in the plasma sheath is crucial for solving the communication “blackout” phenomenon. The plasma flow field data around the vehicle at different reentry altitudes are determined by the USIM software in this article. The plasma flow field data are then imported into the COMSOL Multiphysics software based on the finite element method to build the EM wave propagation model. The validity of the model is checked through observations of the field distributions. The propagation characteristics of the EM wave in the magnetized plasma sheath under the effect of the “magnetic window” are analyzed by calculating and observing the wave loss coefficients. The results show that the wave frequency, the strength of the background magnetic field, and the “magnetic window” position all have an influence on wave propagation. We have determined that decreasing the wave frequency facilitates the propagation of the whistler wave within a weakly magnetized plasma sheath. Whistler waves can be used as a communication window due to their good anti-jamming properties. On this basis, the position of the “magnetic window” most conducive to the propagation of whistler modes in weakly magnetized plasma sheath is analyzed and compared. The integrated approach proposed in this article improves simulation efficiency and optimizes overall performance.

Precise and contactless manipulation of microstructures remains a major challenge in microassembly and lab-on-chip systems. Here, we introduced a Robotic Acoustic Streaming Tweezers (RAST) system that used an MEMS-based gigahertz resonator to generate localized acoustic streaming for programmable 2D and 3D manipulation of microgels. By tuning the power and height of the resonator, RAST achieved versatile, gentle operations of microgels. Our results demonstrated that the low-power enabled precise 2D translation and planar assembly of linear, layered, and patterned structures; intermediate power induced controlled flipping and rotation for orientation-specific alignment; and high power lifted microgels into 3D vortex traps, enabling accurate spatial nesting along guiding scaffolds. By integrating computer vision and path-planning algorithms, the system also enabled the high-throughput assembly of multiple microgels without human intervention. The RAST system offered a mild, label-free, and powerful strategy for complex microscale construction, providing a robust and scalable new solution for microrobots, biomedical devices, and advanced microfabrication technologies.

The distributed load with loaded area being extended over the whole structure (i.e., the extended moving load) that occurs during the operation of an electromagnetic launch rail-structure, is different from loading cases studied previously such as the concentrated load or distributed load on a finite segment (i.e., the single moving load), or a series of single moving loads in a periodic pattern (i.e., the periodic moving load). In this paper, a nonlinear finite element model is proposed by modeling the rail-structure as a Euler-Bernoulli based beam on an elastic foundation to study the dynamics of rail-beam under such an extended moving load. The proposed model is firstly verified by comparison with the analytical solution for the rail-vibration response under the extended moving load at constant speed, and the model feasibility is further revealed by comparison with the experimental results of rail strain. The significant differences of rail vibration modes are observed between the extended moving load and the single, or periodic moving load. Moreover, the maximum error of the middle of the rail between the linear forcing and nonlinear forcing will decrease with the increase in the foundation elastic modulus, but increases with the increase in the pulse current. Those results will improve our understanding on dynamics of beam under the more comprehensive loading cases.

The handling of individual cells is the basis for single-cell studies. Richer modes, wider ranges, and higher resolution are the goals that various microgripper techniques are chasing, yet few techniques satisfy these metrics. Herein, we propose a versatile microgripper technology, which uses hydrodynamics and acoustics to peel and trap cells as a programmable microgripper. We choose a mini-packaged GHz resonator to generate micro vortices, inducing up to 2500 Pa shear stress on a microscale region. Controllable detachment based on spatial position and adhesion status, three-dimensional movement, and the assembly of individual cells is achieved by integrating with the displacement stage. This noncontact and label-free technology provides a user-friendly strategy for single-cell manipulation in Petri dish, which conforms to the preferences of researchers and realizes flexible operations that traditionally require multiple platforms and promises to provide an automated solution for a variety of biological and pharmaceutical research.

A numerical method is employed to examine the impact of different transport models on the flow field in classic hypersonic models, including high enthalpy shock tunnel Göttingen (HEG), Electre flight data, and radio attenuation measurements (RAMC-II) for Mach numbers ranging from 8.98 to 25.9, by comparing the results with experimental data under thermochemical nonequilibrium conditions. Existing methods for calculating viscosity coefficients (Blottner curve fit and Gupta collision integral model) and thermal conductivity remain valid under specific flow conditions, with negligible differences between them. However, under the RAMC-II case, the influence of the diffusion coefficient becomes significant. Comparing the performance of different diffusion methods, including the collision integral model, the National Aeronautics and Space Administration (NASA) Ames code data-parallel line relaxation (DPLR) and the NASA Langley code Langley aerothermodynamic upwind relaxation algorithm (LAURA), constant Lewis number (CLN) model, and Schmidt number, the results indicate that the relative temperature difference reaches 13.5%. The error primarily stems from the high sensitivity of the diffusion coefficient to temperature. This requires careful consideration for accurate hypersonic flow calculations. Further exploration of relevant theoretical models is still needed.

The electromagnetic energy can be efficiently converted into kinetic energy by using the coil-structure electromagnetic launcher. However, the design of such a device is hampered by the limited understanding of the extreme multi-physical coupling fields involved. In this paper, the mathematical modelling of the electrical-magnetic-thermal-mechanical coupling behavior is firstly proposed by solving the problems of current conduction, transient magnetic diffusion, transient heat transfer and structural dynamics based on finite element method for the coil-structure electromagnetic launcher. The proposed model is verified by comparison with the analytical solution for magnetic induction intensity and the model feasibility is further revealed by comparison with the experimental results of the final armature speed. It is found that the structural and muti-field characteristics of the coil-structure launcher will be affected by the initial armature position and armature length, and the optimal energy conversion efficiency can be achieved by adjusting the initial armature position. More importantly, the front material of the armature is completely under the yielding stress state, therefore, the structure design with outer layer of the copper alloy and the inner layer of titanium alloy is suggested to suppress the plastic deformation for armature component. These results will be significant to understand the engineering structure modelling and design with multi-field coupling behavior.

In this paper, an implicit lattice Boltzmann method (LBM) to speed up the simulations of compressible plasma kinetics is presented. The Boltzmann Bhatnagar-Gross-Krook equations and magnetohydrodynamics equations are used to construct a plasma simulation model. The implicit LBM needs to solve the mesoscopic equation and the macroscopic equations in each time step. The equilibrium stage distribution function and the electromagnetic force term at next time step can be predicted, by solving the macroscopic equations implicitly. Both the macroscopic and mesoscopic implicit equations are solved by using the lower-upper symmetric Gauss-Seidel factorization. Four numerical test cases, Riemann problem, shock reflection problem, Orszag-Tang vortex problem, and three-dimensional explosion in a box, have been performed to validate the implicit algorithm. The computational efficiency of the implicit LBM for compressible plasma flow can be improved by 8–25 times with the explicit LBM, which greatly reduces the computational cost.

The mechanical behavior of fcc (face center cubic) metals and their alloys such as copper-based and aluminum-based materials changes obviously under high current density, but there is a lack of suitable constitutive model to describe the electroplastic behavior of these materials, which limits the accuracy of the mechanical response prediction in applications, such as electromagnetic launch. In this paper, a novel nonlinear constitutive model for electroplastic behavior under the high current density of fcc metals and their alloys is proposed. The model proposed is based on the theory of dislocation evolution, energy transfer theory and electron transport theory and takes into account the effects of high current density on dislocation density, strain rate and resistivity. Considering the evolution of forward and reverse dislocations caused by pulsed current, the relationship between the evolution rate of reverse dislocation and strain is established. Due to the sensitivity of the electroplastic effect to strain rate, the strain rate under electric current is obtained by combining the theory of dislocation thermal activation and energy transfer. According to the concept of thermal resistance and dislocation resistance, the relationship between resistance and current density is derived. The quantitative results demonstrate that this model can well capture the flow stress softening under high current density (>3000 A/mm2) and the transient hardening after current removal because of the consideration of a more suitable strain rate and dislocation evolution. The critical current density that has a significant effect on the strain rate and the current density corresponding to the subsection point of the resistivity are quantitatively obtained. Especially, it is shown that the evolution rate of the reverse dislocation decreases nonlinearly with the increase of strain after the current is removed. These results will be helpful to study the mechanical behavior of the rail during electromagnetic launch and further optimize the design of electromagnetic launch device.

A magnetohydrodynamic lattice Boltzmann method (MHD-LBM) model for a 2D compressible plasma based on the finite volume scheme is established. The double distribution D2Q17 discrete velocities are used to simulate the fluid field. The hyperbolic Maxwell equations, which satisfy the elliptic constraints of Maxwell's equations and the constraint of charge conservation, are used to simulate the electromagnetic field. The flow field and electromagnetic field are coupled to simulate a compressible plasma through the electromagnetic force and magnetic induction equations. Four typical cases, the Taylor vortex flow, strong blast, Orszag–Tang vortex, and one-dimensional Riemann problems, are simulated to validate the MHD-LBM model for a compressible plasma. It is found that shock waves widely exist in a compressible plasma, and strong nonequilibrium effects exist around each shock wave. The quantitative simulation for the Brio–Wu problem demonstrates that this model can easily obtain the physical characteristics of nonequilibrium effects at sharp interfaces (shock waves and detonation waves). The magnetic fields can affect the magnitudes to which the system deviates from its equilibrium state. The viscosity can increase the magnitudes to which the system deviates from its equilibrium state. Compared with existing compressible MHD, these results for nonequilibrium effects can provide mesoscopic physical insights into the flow mechanism of a shock wave in a supersonic plasma.

Supersonic panel flutter can be of two possible types: single-mode flutter and coupled-mode flutter. Compared to coupled-mode flutter, the physical mechanism of single-mode flutter is less studied at present. In order to reveal the inducing mechanism of single-mode flutter, the present paper constructed a reduced-order fluid model by using the system identification and the Auto Regressive with eXogenous input (ARX) model. Coupling the reduced-order model (ROM) for unsteady aerodynamics in low supersonic flow with the structural equation, a highly efficient ROM-based aeroelastic model in state space is formulated, then the flutter boundaries are obtained and the stability of aeroelastic modes are investigated by the complex eigenvalue analysis. According to the physical meaning of relevant parameters in unsteady aerodynamic reduced order model ARX, it is found that the unsteady characteristic of the flow, specifically the history effects of the unsteady aerodynamic forces, plays a dominant role in causing the single-mode panel flutter at low supersonic speeds. It is also shown that the higher modes are indeed weakly unstable in the absence of any structural damping or a viscous boundary layer.

The sand particles obtain net charges due to the friction and collision in sand and dust storms (SDS), which can produce a strong environmental electric field. The impact of the electric field in SDS on the wave propagation is unclear. A theoretical model for studying the wave attenuation is presented using the equivalent medium theory. In this model, the discrete SDS is assumed as a continuous medium, and the equivalent permittivity of the SDS medium is given based on the energy method when the polarization of the electric field on the negatively charged sand particles is considered. The calculation results show that the vertical electric field (Eh-field) in SDS can significantly enhance the wave attenuation. The attenuation intensifies only with the rise of the value of the Eh-field, regardless of the Eh-field's direction. The effect of the Eh-field on the wave attenuation is more obvious with increasing frequency, and the attenuation enhances by 77 % at 40 GHz. In addition, it is found that existing the Eh-field, the wave attenuation gradually increases as decreasing the charge-to-mass ratio.

The sand particles suspended in the atmosphere can cause the attenuation of electromagnetic waves (EWs) and affect the electromagnetic scattering properties of a target during sandstorms. In this study, a theoretical analysis is offered for the prediction of the EWs attenuation and the radar cross section (RCS) of a target in sandstorms. In the model, an equivalent medium approximation is performed by con-sidering the non-uniform charge distribution on the sand particles, and the effect of the charged sand particles on the scattering characteristics of a target is also taken into account. Numerical results show that the RCS of a target is severely affected in sandstorms. Besides, the charged sand particles have a much greater effect on the target's RCS than the case of the uncharged sand particles. It can be found that the average variation value of the target's RCS decreases nearly exponentially with the increase of visibility, and increases nearly linearly with the distance between the target and incident wave source. Finally, an empirical formula is presented to calculate the RCS of an arbitrarily shaped metal target in a homogeneous lossy medium. These investigations will be of significant benefit to radar detection tech-nology in sandstorms.(c) 2022 Published by Elsevier Ltd.

For most of materials, the properties of the materials are usually dependent on the temperature, which causes the nonlinear physical and mechanical material behaviors. In this paper, an innovative multi-scale computational method is developed for efficiently simulating nonlinear dynamic thermo-mechanical problems of composite materials. The nonlinearities of these multi-scale problems were caused by the temperature-dependent properties of each component material in the composites and the heterogeneities of composite materials are taken into account by periodic distributions of representative unit cells on the micro-scale. Firstly, a second-order two-scale (SOTS) computational model for accurately analyzing nonlinear dynamic thermo-mechanical behaviors of composite materials is established based on multi-scale asymptotic analysis and Taylor series method. The proposed SOTS computational model includes the first-order and second-order auxiliary cell problems on micro-scale, homogenized problem on macro-scale and macro–micro coupled SOTS asymptotic solutions. Then we theoretically explain the crucial importance of developing the SOTS solutions by the error analysis in the point-wise sense. Next, a rigorous error analysis with an explicit rate of the SOTS approximate solutions is given under some simplifications and assumptions in the integral sense. In addition, a multi-scale numerical algorithm is proposed in detail to effectively simulate these nonlinear multi-scale problems. Finally, several typical numerical examples are carried out to confirm the effectiveness and correctness of the proposed multi-scale numerical algorithm, especially for large-scale engineering structures. This study offers an efficient and high-accuracy multi-scale computational scheme that enables the effective simulation and analysis of nonlinear dynamic thermo-mechanical problems of composite materials with temperature-dependent properties.

In the real flow for high altitude, the initiation mechanism of the oblique detonation involves the coupling of complex wave structures and combustion waves, which may result in the phenomenon of extinction. The approach of stable initiation is one of the key factors that restricting the oblique detonation engine from theory to practice. The wave structure, initiation characteristics and characteristic parameters of the flow field are analyzed, the two-dimensional Euler equation considering the detailed chemical reactions of multi-component are solved. First, the approaches of blunt bump and transverse jet are combined used to shorten the detonation distance of the oblique detonation. Results show that these methods can promote the accelerated initiation of the oblique detonation effectively, and the detonation distance can be shortened more than 90%. There are two wave structures induced by the blunt bump: weak coupled and strong coupled, adding the transverse jet promotes the transition between these two wave structures. Then, the shape of the bump and the characteristic parameters of the transverse jet are optimized. The streamline-shape bump can eliminate the recirculation zone formed after the circle bump and the ellipse bump. The transverse jet will produce an oblique detonation wave at the front of the jet position, which changes the wave structure and initiation mode of the oblique detonation wave. It is expected to reveal the accelerated initiation mechanism of oblique detonation under the induction zone disturbance and complex flow environment, deepen the understanding of the detonation law of oblique detonation wave under real flow conditions, and provide a scientific basic for the development of the combustor of the oblique detonation engine.

The existing space manipulator joints with permanent magnet synchronous motors (PMSMs) have many deficiencies, such as large size, low output torque, and long settling time. In this paper, the dynamic behavior of space manipulators with smart giant magnetostrictive material (GMM) joints is studied. A nonlinear dynamic model considering the magneto-thermal-mechanical coupling for the manipulator is established, and an experiment is conducted to evaluate the performance of the GMM joint. After verifying the accuracy and availability of the model, we find that comparing with the PMSM joint, manipulators with the GMM joint have better performance, which has large output torque, fast settling time, and wide temperature adaptation range. These essential investigations will be of significant benefit to the applications in space manipulators.

The “communication blackout” occurs during the reentry of hypersonic vehicles, that is, the electromagnetic wave cannot pass through the plasma sheath due to high electron density formed around the vehicle, which has drawn much attention but has not yet been solved. In this paper, a novel magnetic control approach is proposed, in which a periodic magnetic field is applied near the head of the aircraft. Based on the magnetohydrodynamic simulation, a low electron density channel across the plasma sheath of vehicle under the magnetic control is revealed for the first time, which probably make Ka-band electromagnetic wave pass through. We also find that the reason for the low electron density channel is the variation of the vortex structure in the plasma flow near the wall, by the electromagnetic force exerted on the flow. Furthermore, the optimal magnetic field frequency for generating the low electron density channel is obtained. These findings will be of significant benefit to the solutions for the communication blackout problems.

In the paper, a magneto-mechanic hysteresis model for giant magnetostrictive materials is suggested by considering the effect of the domain rotation and domain wall motion on the magnetization process under prestress and the applied magnetic field. The coercive force, which is magneto-mechanic dependent, is proposed instead of a pinning constant in the Jiles–Atherton model. The model can well predict the characteristics of a magnetization-applied field curve and magnetostrictive strain-applied field curve shown in the experiment, especially the “overturn phenomenon” under different compressive prestresses. Furthermore, the effect of the microstructure parameter, such as the ratio of the domain wall thickness to the internal stress wavelength, the amplitude of internal stress, the ratio of the domain wall thickness to the inclusion radius, and inclusion consistency, on coercive force under applied prestress can also be described by the model. The comparison between the results predicted by the model and experiment shows that the model is suited for a wide-ranging applied magnetic field.