Search Results (252)

As key driving and supporting components of spacecraft, pod-type space self-deployable structures have terminal pointing accuracy that directly affects overall spacecraft performance. To clarify the influence of the structure’s machining deformation on its pointing accuracy, this study focuses on two key processes, namely laser welding and hot forming. Based on the bionic symmetric structural characteristics of pod-type structures, a laser welding finite element model with a surface Gaussian heat source and a hot forming constitutive model coupled with creep aging were established. An orthogonal experimental design was adopted: for laser welding, three parameters, namely laser power, spot diameter, and welding speed, each with three levels, were selected, and an L₉(3³) orthogonal table was constructed to conduct nine groups of simulations; for hot forming, two parameters, namely processing temperature and holding time, each with three levels, were chosen, and nine groups of simulations were designed based on the first two columns of the L₉(3⁴) orthogonal table. The combined method of residual analysis and analysis of variance was used to quantitatively identify the influence of each process parameter on pointing accuracy. The results show that in laser welding, welding speed has the most significant impact on deformation, followed by laser power, and spot diameter has the least; in hot forming, processing temperature and holding time have similar effects on deformation. Physical machining verification was performed, and the actually measured deformations are 0.164 mm and 0.034 mm, which are close to the simulation results of 0.176 mm and 0.047 mm, meeting the index requirement that the terminal pointing deformation of a single pod structure is less than 0.2 mm. The results can provide a theoretical basis and engineering reference for the actual machining of such structures. Full article

This study analyzes a hybrid computational framework that combines peridynamics (PD) and the finite element (FE) method to model wave propagation in a one-dimensional bar, focusing on their integration for enhanced accuracy and efficiency. The analysis investigates PD’s ability to capture non-local interactions in regions near loading points, with computationally efficient coarse discretization in other areas through finite element methods. The dynamic response to symmetric and asymmetric axial loading, including loading and unloading phases, is analyzed through time-dependent external forces, solving displacement, velocity, and acceleration fields at each time step. The effects of PD-specific parameters, such as the horizon size, and the FE–PD node spacing size ratios on the performance of the hybrid model in wave propagation are investigated. Additionally, the study examines the von Neumann stability for PD to ensure stability and reliability, offering a robust framework for integrating PD and FE in dynamic analyses. Full article

The Survey Camera (SC) is the key instrument of the China Space Station Telescope (CSST), with its imaging performance significantly constrained by microvibrations from internal sources such as the shutter and cryocoolers. This paper proposes a systematic microvibration suppression scheme integrating disturbance source control, payload isolation, and transfer path optimization to meet the stringent requirements. The Cryocooler Assembly (CCA) compressor adopts a symmetric piston layout and a real-time vibration cancellation algorithm to reduce the vibration. Coupled with a vibration isolator designed by combining hydraulic damping and a flexible structure, it achieves a vibration isolation efficiency of 95%. The shutter adopts dual-blade symmetric design with sinusoidal angular acceleration control, ensuring its vibrations fall within the compensable range of the Fast Steering Mirror (FSM). And the finite element optimization method is used to optimize the dynamic characteristics of the Support Structure (SST) made of M55J carbon fiber composite material, to avoid resonance in the critical frequency bands. System-level tests on the integrated SC show that the RMS values of vibration force and torque within 8–300 Hz are 0.25 N and 0.08 N·m, respectively, meeting design specifications. This scheme validates effective microvibration control, guaranteeing the SC’s high-resolution imaging capability for the CSST mission. Full article

This paper develops a fully discrete finite element scheme for the fractional wave equation with order $\alpha \in (1,2)$, whose solution typically exhibits a weak singularity near the initial time $t=0$. By introducing an auxiliary variable, we first reformulate the fractional wave problem into an equivalent coupled system of two fractional equations. The resulting coupled system is then discretized using the nonuniform Alikhanov formula in time and the standard finite element method on triangular meshes in space. Through rigorous analysis, we establish a pointwise-in-time error estimate for the proposed scheme in the $H^1$ semi-norm. A key advantage of the proposed methodology is its ability to employ a sparser mesh near the initial time to achieve optimal convergence of local errors. In particular, our analysis shows that away from the initial time, the local rate of convergence reaches $O\left(N^{-2}\right)$ in time for $r\ge 2$. Finally, numerical experiments are given to verify the sharpness of the theoretical convergence rates. Full article

The numerical solution of space-fractional diffusion problems is investigated focusing on stability and non-negativity issues. The extension of classical schemes is analyzed for the case of the spectral fractional Dirichlet Laplacian operator. For the spatial discretization, both finite differences and finite elements are used. The finite element case needs special care and is discussed in detail. Both spatial discretizations are combined with the matrix transformation method, leading to fractional powers of matrices in the discretized problems. In the time stepping, $\theta$-methods are utilized with $\theta =0,{\displaystyle \frac{1}{2}}$ and 1. In the analysis, it is pointed out that the stability condition in the case of $\theta =0$ depends on the fractional power $\alpha \in (0,1]$, which results in a weaker condition on the time discretization compared to the conventional diffusion. In this case, we also obtain non-negativity preservation. Also, unconditional stability is established for $\theta ={\displaystyle \frac{1}{2}}$ and $\theta =1$, where for the spatial discretization rather general conditions are posed. The results containing stability conditions are also confirmed in a series of numerical experiments. In the course of the corresponding algorithms, an efficient matrix power–vector product procedure is employed to keep simulation time at an affordable level. The associated computational algorithm is also described in detail. Full article

The stability of underground excavations is a critical factor in the safety and efficiency of mining operations, particularly in structurally complex and geomechanically variable rock mass. This study presents a comparative evaluation of empirical and numerical methods for the design of tunnel support systems in the Gilar underground mine, located in the Gedabek Contract Area of Azerbaijan. To validate and optimize the empirical Q-system-based support designs, Finite Element Method (FEM) simulations were conducted using RS2 software. These simulations enabled the modeling of stress distribution, deformation, and support–rock interaction under in situ conditions. Critical sections along the main ramp were analyzed in detail to determine safety factors during excavation and post-support installation. The study reveals that, although the Q-system provides a practical and time-efficient method for support selection, it may underestimate the reinforcement required in highly fractured or low-strength zones. Numerical modeling proved to be essential in identifying zones with low strength factors and in optimizing support configurations by adjusting rockbolt spacing and shotcrete thickness. The hybrid approach adopted in this study—empirical classification followed by numerical verification and optimization—demonstrated significant improvements in long-term tunnel stability. This research highlights the importance of integrating empirical and numerical approaches for robust ground support design in underground mining. The proposed methodology not only enhances the accuracy of support recommendations but also provides a more reliable basis for decision-making in complex geological settings. The results are particularly relevant for deep and geologically active mines requiring long-term stability of access tunnels. Full article

Due to the large mass, high end load, and long action distance of a mill relining manipulator, gravity effects inevitably lead to a reduction in end effector positioning accuracy. To solve this problem, an online calculation method is proposed to realize real-time end effector deformation prediction. First, a manipulator is simplified into two cantilever beams: the upper arm and the forearm. Second, a reaction force and moment transformation model is established based on the coupling relationship between the forearm and upper arm. Third, finite element (FE) static analysis and simulation are carried out to obtain the end deformation. A total of 3528 discrete joint configurations are selected to cover the entire joint space, and their corresponding FE solutions are used to establish the end deformation offline dataset. Finally, an online deformation calculation algorithm based on Kolmogorov–Arnold networks (KANs) is developed to predict end deformation in any working condition. Visualization analysis and validation experiments are conducted and demonstrate the superiority of the proposed method in reducing gravity effects and improving computational efficiency. In summary, the proposed method provides support for end position compensation, especially for heavy-duty manipulators. Full article

Multistage hydraulic fracturing enhances recovery from low-permeability reservoirs. Understanding stress shadow effects and fracture reorientation is essential for optimizing multistage fracturing. This study develops a fully coupled 3D hydromechanical model based on the finite–discrete element method (FDEM) to simulate echelon hydraulic fractures in dual-well systems under varying well spacings and initial perforation lengths. Results show that fracture interactions are highly sensitive to spacing and initiation asymmetry. Closely spaced fractures generate strong stress shadows, influencing propagation depending on geometry and timing. A theoretical model incorporating induced stress and the weight function further clarifies stress shadow mechanisms, introducing disturbance factors to describe promotion or inhibition effects between fractures. The findings reveal an optimal well spacing that maximizes fracture complexity and reservoir stimulation, while pronounced initiation asymmetry leads to dominant–subordinate propagation and reduced efficiency. This integrated framework improves understanding of fracture evolution and guides fracturing optimization in tight formations. Full article

Microwave ablation, as a minimally invasive technique used for the treatment of tumors, is highly dependent on the performance of ablation antennas for its therapeutic effect. Clinically, antennas are required to form roughly spherical ablation zones with sufficient volume within a limited time. To meet this requirement, this paper establishes finite element models and conducts multi-objective optimization on fully water-cooled dipole antenna and partially water-cooled choke dipole antenna based on different water-cooled structures. On the premise of minimizing reflection coefficient and maximizing ablation volume, a three-dimensional objective space is constructed by introducing the minimization of roundness error, and the set of Pareto solutions is solved. The CRITIC-TOPSIS method is used to balance multi-objective conflicts and select the unique optimal solution from the Pareto set. By analyzing the optimal solution, simulation results show that the optimized antennas can effectively form near-spherical ablation shapes while minimizing the reflection coefficient and maximizing the ablation volume. Among these, the partially water-cooled antenna exhibits superior electromagnetic characteristics and ablation profile, whereas the fully water-cooled antenna demonstrates better temperature field behavior. Full article

The construction of a high-order shape function is a key and difficulty for unstructured grid mesh and sliding boundary problems. In this paper, a construction method of space-time absolute nodal coordinate formulation quadrilateral cable (SACQ) is proposed, and the accuracy of the SACQ element is studied and verified with three different applications. First, the shape function of SACQ is constructed with spatiotemporal reduction coordinates, and the action integral of SACQ is composed with the Lagrangian function and discrete with perspective transformation. Second, the numerical convergence region is discussed and determined with the Courant number. Furthermore, a space-time nodal dislocation and its relation with the Courant number are studied. The simulation and verification are focusing on some realistic problems. Finally, a one-sided impact, a free-flexible pendulum, a taut string with a sliding boundary and a deployable guyed mast under an impact transverse wave are simulated. In these problems, an unstructured grid meshed with SACQ has similar energy convergence and accuracy to a structured grid but shows better efficiency. Full article

One of the key challenges with developing pulsed induction (PI) electromagnetic induction (EMI) sensors for use in the Arctic is the inaccessibility of the environment, which makes in situ testing prohibitively expensive. To mitigate this, sensor development can be streamlined through the creation of a robust simulation strategy with which to optimize features such as coil turns and geometry. Building on work that previously presented a method for simulating an Arctic PI sensor via a time-domain finite element model (FEM), this paper presents a method for approximating a time-domain simulation with multiple frequency-domain simulations. A comparison between the fast Fourier transform (FFT) of a time-domain simulation and a collection of frequency-domain simulations is presented. These are validated against empirical data with a PI sensor over seawater, with an air gap used as a proxy for sea ice. Using the method described, a range of coils is simulated with dimensions from $0.5\times 0.5$ m up to $1.0\times 2.0$ m, demonstrating the ability of this approach to enable comparison of sensor performance over a wider parameter space. For a parametric sweep over 10 sensor-to-seawater lift-off distances, the improvement from the time-domain simulation (of a 402 $\mathsf{\mu }$s window) to the frequency-domain simulation (comprising 100 discrete frequencies) represents a reduction in simulation time from 38,013 min to 141 min. Full article

As core components of terahertz (THz) radiation sources, photoconductive antennas (PCAs) suffer from performance limitations due to inefficient carrier generation/transport and space-charge shielding effects. This study first introduced cylindrical Au nanoarray structures within the electrode gaps of photoconductive antennas to enhance radiation performance. A combination of the finite element method solver and COMSOL Multiphysics was implemented to refine the model by accounting for the shielding field, which is often neglected in the calculations. Guided by the theoretical and simulation model, the generated current, THz radiation power and the shielding field were comparatively studied in the plasmonic nanoarray PCA and traditional PCA without the plasmonic nanoarray structure. The results demonstrate that emitters with the cylindrical nanoarray structures achieve a radiation power 3.81 times higher than that of the traditional structure, along with a 50% broader bandwidth. Further optimization of photogenerated carrier distribution through engineered metallic nanoarray structures reveals that plasmonic photoconductive THz emitters with triangular nanoarrays reduce the space-charge shielding field by 28.7% compared to the cylindrical structures while enhancing the radiation field intensity by a factor of 1.21. This work presents an effective approach to designing high-performance photoconductive THz emitters, holding significant theoretical and practical significance. Full article

Finding high-performance and low-cost materials is essential for high-quality photocatalytic water purification to expand the spectral response and improve light utilization. In this paper, we used relatively inexpensive materials such as Ag and TiO₂. The influence of particle spacing, core radius, shell thickness, environmental refractive index, and incident light direction angle on the light absorption and scattering properties, local electric field enhancement, and photothermal effect of the Ag@TiO₂ core–shell nanosphere dimer is investigated by using the finite element method and the finite difference time domain. The formation mechanism of multipole resonance mode of the dimer is revealed by means of the multipole decomposition theory and the internal current distribution of the particles. The results show that light absorption and scattering of the dimer can be tuned within the visible light range by changing the particle spacing, core radius, and shell thickness. With the azimuth angle of incident light increases, the longitudinal local surface plasmon resonance (L-LSPR) mode will transform into the transverse local surface plasmon resonance (T-LSPR) mode, and the L-LSPR mode makes the dimer have better local electric field enhancement. Strong light absorption can easily cause a sharp increase in the temperature around the dimer, accelerating the rate of catalytic oxidation reactions and the elimination of bacteria and viruses in water. Strong light scattering causes a significant enhancement of the electric field between the particles, making the generation of hydroxyl and other active oxides more efficient and convenient. This work establishes a theoretical basis for designing efficient water purification photocatalysts. Full article

This paper proposes a method to analyze the effect of the rotor’s harmonic winding design and the output of a brushless wound rotor synchronous machine (WRSM) for optimal excitation power transfer. In particular, the machine analyzed by the finite-element method was a 48-slot eight-pole 2D model. The subharmonic magnetomotive force was additionally created in the air gap flux, which induces voltage in the harmonic winding of the rotor. This voltage is rectified and fed to the field winding through a full bridge rectifier. Eventually, a direct current (DC) flows to the field winding, removing the need for external excitation through brushes and sliprings. The effect of the number of harmonic winding turns is analyzed and the field winding turns were varied with respect to the available rotor slot space. Optimization of the harmonic excitation part of the machine will maximize the rotor excitation for regulation purposes and optimize the torque production at the same time. Two-dimensional finite-element analysis has been performed in ANSYS Maxwell 19 to obtain the basic results for the design of the machine. Full article

This paper presents a rigid–flexible coupling dynamic modeling framework and a fixed-time control strategy for a flexible space-tethered satellite (STS) system. A high-fidelity rigid–flexible coupling dynamic model of STS is developed using the finite element method, accurately capturing the coupled attitude dynamics of the satellite platform and flexible tether. Leveraging a simplified representation of the STS model, a nonsingular terminal sliding-mode controller (NTSMC) is synthesized via fixed-time stability theory. Uncertainties and disturbances within the system are compensated for by a radial basis function neural network (RBFNN), ensuring strong robustness. The controller’s fixed-time convergence property—with convergence time independent of initial conditions—is established using Lyapunov stability theory, enabling reliable operation in complex space environments. Numerical simulations implemented on the STS rigid–flexible coupling model validate the controller’s efficacy. Comparative analyses demonstrate superior tracking performance and enhanced practicality over conventional sliding-mode controllers, especially in the aspect of chattering suppression for the satellite thrusters. Full article