Institute Of Mechanics,Chinese Academy of Sciences
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Surface waves in a sheared liquid film on a horizontal plane at moderate Reynolds numbers
No full textWhen a liquid film on a horizontal plate is driven in motion by a shear stress, surface waves are easily generated. This paper studies such flow at moderate Reynolds numbers, where the surface tension and inertial force are equally important. The governing equations for two-dimensional flows are derived using the long-wave approximation along with the integral boundary-layer theory. For small disturbances, the dispersion relation and neutral curves are determined by the linear stability analysis. For finite-amplitude perturbations, the numerical simulation suggests that the oscillations generated by the perturbation in a certain place continuously spread to the surrounding areas. When the effects of surface tension and gravity reach equilibrium, steady-state solutions will emerge, which include two cases: solitary waves and periodic waves. The former have heteroclinic trajectories between two stationary points, while the latter include five patterns at different parameters. In addition, there are also periodic waves that do not converge after a long period of time. During these evolution processes, strange attractors appear in the phase space. By examining the Poincar & eacute; section and the sensitivity to initial values, we demonstrate that these waves can be divided into two types: quasi-periodic and chaotic solutions. The specific type depends on parameters and initial conditions
Optimization of Magnetic Nozzle Configuration and Hybrid Propellant for Radio-Frequency Plasma Micro-Thrusters in Very Low Earth Orbit Applications
No full textVery low Earth orbit (VLEO) satellites are confronted with the challenge of orbital decay caused by thin atmospheres, and the volume and power limitations of micro satellites further restrict the application of traditional electric propulsion systems. In response to the above requirements, this study proposes an innovative scheme of radio frequency plasma micro-thrusters based on magnetic nozzle acceleration technology. By optimizing the magnetic nozzle configuration through the system, the plasma confinement efficiency was significantly enhanced. Combined with the mixed working medium (5 sccm Xe + 10 sccm air), the thrust reached 1.7 mN at a power of 130 W. Experiments show that the configuration of the magnetic nozzle directly affects the plasma beam morphology and ionization efficiency, and a multi-magnet layout can form a stable trumpet-shaped plume. The air in the mixed working medium has a linear relationship with the thrust gain (60 mu N/sccm), but xenon gas is required as a "seed" to maintain the discharge stability. The optimized magnetic nozzle enables the thruster to achieve both high thrust density (13.1 mu N/W) and working medium adaptability at a power level of hundreds of watts. This research provides a low-cost and miniaturized propulsion solution for very low Earth orbit satellites. Its magnetic nozzle-hybrid propellant collaborative mechanism holds significant engineering significance for the development of air-aspirating electric propulsion technology
Numerical Simulation of the Bank Slope Stability Associated with Reservoir Water Drawdown
No full textAfter the construction of the Three Gorges Dam, geological hazards frequently occur, and landslides are the most widespread disasters in the reservoir area. The rapid landslide induced by rainfall is an important natural disaster in the Three Gorges Reservoir area. The rapid landslide induced by rainfall is an important natural disaster in the Three Gorges Reservoir area. Rainfall can cause changes in pore water pressure. To study the slope stability with the pore water pressure, Yangjialing landslide located in Three Gorges Reservoir area is performed using stress-seepage-slope stability coupled analysis after water drawdown. Meanwhile the phreatic line from the simulation results is compared with the analytical solution. Lower permeability and higher drawdown velocity will result in a higher pore water pressure and it is harmful to the slope stability. The zone with smaller permeability will spend longer time to change from saturated state to unsaturated state if the water level descends at the same speed. Through the research of this paper, the main factors of landslide are obtained, which lays a theoretical foundation for the prevention of landslide in the Three Gorges Reservoir area. © 2025 The Authors.</p
Tailoring the specific strength of AlNbTiZr high entropy alloys via Si doping
No full textLightweight refractory high-entropy alloys (LRHEAs) have received much attention due to their attractive properties and novel design concept. However, their engineering applications are severely constrained by prominent room-temperature brittleness and insufficient strength. This study systematically investigates the effects of Si alloying on the microstructure evolution and mechanical properties of Al13Nb29Ti29Zr29 LRHEAs. The findings reveal that Si addition induces two distinct effects: on one hand, it promotes the formation of nanoscale Zr5Si3 silicide at grain boundaries; on the other hand, it significantly refines the grain size of the alloys. While the former provides second-phase strengthening at the expense of deteriorating plasticity, the latter simultaneously enhances both strength and plasticity. The synergistic interaction between these two mechanisms enables the alloy to maintain favorable deformability alongside remarkable strength enhancement. Moreover, the addition of Si significantly reduces the density of the alloys, endowing the (Al13Nb29Ti29Zr29)98Si2 alloy with an ultra-high specific strength. The novel alloys developed in this work combine high specific strength, significant plasticity, and extremely low density, which shows desirable applications in high-strength lightweight materials
Tailoring Multiple Functional Domains of Lithium-Ion Sieves for Sustainable Lithium Extraction from Low-Quality Brines
No full textLow-quality brines offer virtually infinite lithium sources to resolve the lithium shortage. Lithium-aluminum layered double hydroxides (LiAl-LDHs) have been commercialized as adsorbents in the lithium extraction industry. However, their application in low-quality brines still faces substantial challenges, including poor extraction efficiency limited by low Li+ concentration, and "poisoning effect" due to intercalated SO4 2- encapsulating adsorption sites. Here, we propose a proof-of-concept polymer side-chain structure design (SCSD) strategy for LiAl-LDHs. This approach enables synergistic intralayer/interlayer engineering of LiAl-LDHs with functional polymers, achieving efficient and highly selective Li+ extraction from low-quality brines. Moreover, sustainable lithium extraction enables ppb-level residual concentration and production of high-purity Li2CO3 from the world's largest low-quality SO4 2--type brine. By rational design of side chains of polymer building blocks, the local chemical microenvironment and spatial microstructure of LiAl-LDHs can be tailored to accommodate lithium extraction from diverse brines. This work provides a feasible strategy to expand accessible brine resources for the sustainable extraction and recovery of critical metals
Hydrodynamic performance and layout optimization of floating truncated cylinder wave energy converter arrays in front of a vertical wall under the action of regular and irregular waves
No full textThis paper introduces a novel oscillating buoy-type wave energy converter (WEC) in front of a bottom-mounted vertical wall. The cylindrical WEC is capable of oscillating and harnessing wave energy in five degrees of freedom (DOF), designated as a 5-DOF WEC. The hydrodynamic performance of WEC arrays is then methodically examined in both regular and irregular wave conditions. The presence of the bottom-mounted vertical wall substantially enhances the array performance under specific circumstances. In contrast to the 1-DOF WEC, which only oscillates and extracts wave energy in the heave direction, the 5-DOF WEC substantially boosts array performance and expands the absorption bandwidth for both regular and irregular waves. The optimal layouts and associated free surface distributions for four scenarios involving unidirectional regular waves, unidirectional irregular waves, and multidirectional real waves are presented. When compared to the 1-DOF WEC array, the optimal arrangement of the 5-DOF WEC array produces a more pronounced disturbance to the wave field, leading to greater energy absorption. Thus, the collaborative development of the 5-DOF WEC array alongside the vertical wall not only facilitates enhanced wave energy absorption but also effectively mitigates the wave load acting on the vertical wall
Why prefer all-suture anchor? A new comprehensive evaluation method
No full textAll-suture anchor (ASA) is an emerging suture anchor used to fix soft tissue to bone. Composed entirely of textile material, ASA has the advantage of a small size and less damage to the bone. The purpose of this study was to analyze the mechanism of the pullout process of ASA from bone tissue and to quantitatively compare the extent of damage to cancellous bone by ASA and conventional suture anchors. First, pullout experiments were conducted on ASA in two different synthetic bone blocks to verify the effect of bone density on ASA performance, and the extraction process of ASA in the bone was simulated. In addition, a model of the proximal humerus was created, and different suture anchors were implanted. The damage to cancellous bone caused by the suture anchors was calculated and compared under the same force of 0-150 N and cyclic force of 0-100 N. The results showed that when the force was 150 N, the volume of plastic strain after implantation of conventional suture anchors was 26% larger than that after ASA implantation. The maximum plastic strain after implantation of conventional suture anchors was 1.5 times greater than that after implantation of ASA. Finally, a comprehensive evaluation method of suture anchor performance based on overall stiffness was proposed. According to this evaluation method, the performance of ASA is superior to that of conventional suture anchors
EfficientSTNet: A Deep Learning Approach for Multi-Class DDoS Detection
No full textDDoS attacks are highly destructive, capable of targeting multiple devices simultaneously and posing significant threats to network systems. Therefore, it is increasingly essential to develop effective and reliable detection methods to ensure network security. Although deep learning techniques improve DDoS detection by autonomously learning feature representations, they still face challenges due to the high dimensionality and noise inherent in network traffic data, which impair computational efficiency and real-time responsiveness. Moreover, their limited adaptability to multi-class classification hinders accurate differentiation of specific attack types. This paper proposes a multi-class DDoS attack detection method based on multi-scale feature modeling-EfficientSTNet. The method employs a selective deep autoencoder for feature selection, then uses a convolutional neural network (CNN) to capture hidden spatial features in network data. Subsequently, a self-attention mechanism extracts temporal features and captures contextual dependencies among different features, improving DDoS attack detection accuracy. Finally, a fully connected layer and normalization compute the probability distribution across different classes, enabling multi-class DDoS detection. Additionally, the method integrates convolution decomposition techniques and residual network structures to accelerate model convergence and improve inference speed. The proposed EfficientSTNet model can identify different types of DDoS attacks, achieving an overall classification accuracy of 99.14% and F1-scores of 97.97% or higher across all categories, demonstrating strong practical application potential
一种具有预电离功能的射频等离子体T形磁喷微推力器
No full text本发明设计了一种具有预电离功能的射频等离子体T形磁喷微推力器，该推力器沿着工质气体进入的方向依次设有：供气模块、预电离模块、电离模块、等离子体引出模块；预电离模块设有透过率既满足两侧的气压要求、又满足便于点火和维持要求的多孔隔板，该多孔隔板将玻璃放电室分隔为两个区域，在靠近工质气体进气口处添加一段氧化钇铱灯丝，用于对工质气体进行预电离；所述等离子体引出模块包括由两个不同尺寸的环状耐高温钐钴永磁体拼接而成的T形永磁体，靠近放电室一侧的永磁体尺寸较大，远离放电室一侧的永磁体尺寸较小，二者构成截面为T形的永磁体结构。本发明提出预电离辅助点火的方法，解决了现有推力器在低功率下效率低下，电离率低的问题
一种基于温度变化速率的激光加载参数识别方法
No full text一种基于温度变化速率的激光加载参数识别方法，包括：建立蜂窝夹层结构的有限元瞬态热分析模型，蜂窝夹层结构包括正面板、蜂窝夹层芯和背面板；在所述蜂窝夹层结构的所述正面板上加载对应多种激光加载参数的热载荷，提取正面板的时空特征序列温度响应特征信息，进行数据处理，以得到处于不同时刻时整块所述正面板的温度变化率，进而组成多组训练数据集；向激光加载参数识别训练模型中输入多组训练数据集，通过迭代训练并达到设定的迭代步数时，所述激光加载参数识别训练模型以获取训练后的最优激光加载参数识别训练模型。本发明解决了现有技术中在求解非稳态导热反问题时复杂，且无法识别热载荷的特征参数的问题