ABSTRACTEarth Observation optical data are critical for agriculture, supporting tasks like vegetation health monitoring, crop classification, and land use analysis. However, the large size of multispectral and hyperspectral datasets poses challenges for storage, transmission, and processing, particularly in precision farming and resource‐limited contexts. This work presents the H‐PCA‐AT (Hilbert and Huffman‐encoded Principal Component Analysis‐Adaptive Triangular) format, a novel lossy compression framework that combines PCA for spectral reduction with anisotropic mesh adaptation for spatial compression. Adaptive triangular meshes capture image features with fewer elements with respect to a standard pixel grid, while efficient encoding with Hilbert curves and Huffman coding ensures compact storage. Numerical evaluations of data reconstruction, vegetation index computation, and land cover classification demonstrate the effectiveness of the H‐PCA‐AT format, achieving superior compression compared to JPEG while preserving essential agricultural insights.

ABSTRACTIn this work, we develop a topology optimization method for elastic contact problems involving fatigue constraints under proportional loads. The method is formulated by means of B‐spline parameterization of the pseudo‐density field to describe the material layout. Both the contact pressure control on the contact surface and fatigue constraint to the whole structure domain are taken into account simultaneously. The accumulated fatigue damage related to the fatigue constraint is calculated based upon the rainflow‐counting scheme, Sines method, S–N curve and Palmgren–Miner's linear damage hypothesis. The Kreisselmeier–Steinhauser (KS) function is adopted as an aggregated measure for both the maximum contact pressure and the maximum fatigue damage. The design sensitivities are derived analytically using the adjoint method. Both frictionless and frictional contact problems are investigated. The influence of fatigue constraints on the optimization result is discussed in comparison with the standard compliance minimization. Frictional contact effects upon the optimized results and fatigue damage are highlighted. Results show that the maximum contact pressure and maximum fatigue damage can effectively be controlled to avoid fatigue failure and that the fatigue strength of the structure can be improved at the cost of structural stiffness.

ABSTRACTThis paper extends the energy‐based homogenization method (EBHM) to evaluate the effective elastic properties of two‐dimensional arc unit cells, where the periodic boundary conditions are constructed based on the polar strain–displacement relationships, and the displacement field is solved by the polar finite element method. Combining the extended EBHM with the parametric level set method (PLSM) and the augmented Lagrangian multiplier method (ALM), it is able to design the topological configurations of arc unit cells for seeking superior effective elastic properties. In addition, the level set function is first filtered by compactly supported radial basis functions (CSRBFs) in order to eliminate small holes in the configuration. Numerical examples are performed to demonstrate the advantages of the proposed method. The periodic boundary condition performs well when the circumferential angle of the arc unit cell is in the range of [0.0002, 0.2]. Results indicate that the effective elastic properties of optimized arc unit cells override those of geometrically transformed optimal square unit cells. This superiority mainly benefits from the fact that unisymmetrical configurations are allowed in arc unit cells but not in square unit cells. Results also imply that the capability of nucleation of new holes is retained even though small holes are eliminated by filtering. It contributes to the trade‐off between performance and manufacturability.

ABSTRACTAn innovative and efficient reduced order algorithm is proposed for the dynamic analysis of 2‐D and 3‐D viscoelastic structures featuring cyclic symmetry, which is applicable to complete cyclically symmetric structures with or without common nodes, as well as incomplete cyclically symmetric structures. The proposed algorithm is developed on a recursive platform based on TPAA‐SBFEM and inherits all the advantages of TPAA‐SBFEM. For complete cyclically symmetric structures with or without common nodes, the global stiffness and mass matrices are proved to be block‐circulant and can be generated via a cyclically symmetric part instead of the whole domain. And then a recursive partitioning algorithm is rendered, such that the solution scale and computational cost can be efficiently reduced via solving a series of independent problems with small scales. For incomplete cyclically symmetric structures, the complete cyclic symmetry and Woodbury formula are utilized to reduce computational expense. Four numerical examples are provided to elucidate the effectiveness and efficiency of the proposed approach with satisfactory results.

ABSTRACTAero‐engines are complex and sophisticated systems combining mechanical, thermal, and fluidic domains. Abnormal wear of mechanical components is becoming more prevalent due to severe changes in flight conditions and the external environment, which may lead to drastic performance degradation and accidents. Therefore, the diagnosis of such wear and tear faults is urgent, and based on this need, more researchers and scholars are focusing their attention on it. To address the current shortcomings of fault diagnosis algorithms that only rely on one‐dimensional datasets or two‐dimensional image analysis and the low accuracy of final fault identification, an innovative hybrid algorithm is proposed in this study. The algorithm integrates one‐dimensional time series data and two‐dimensional image data, converts the one‐dimensional dataset into a two‐dimensional image dataset through the Gramian Angle Field technique, and subsequently uses a dual‐channel GRU‐CNN (Convolutional Neural Network‐Gated Recurrent Unit) algorithm model designed for fault diagnosis, which can simultaneously analyze and map the features and fault modes of the one‐dimensional dataset and the two‐dimensional image. In order to extract features with richer semantic information and stronger discriminative ability, a multimodal fusion technique is employed, which successfully addresses the limitations of the wear‐and‐tear feature distributions of the two datasets using the cross‐extraction fusion method and combines the advantages of both in terms of trend distributions of the time series and edge feature distributions of the image sequences, respectively. The best fault diagnosis results were achieved by using the strong mapping relationship between the saliency feature expression and the fault modes. The final analysis shows that the recognition rate of typical mechanical wear of aero‐engines exceeds 97%, thus achieving the desired goal.

ABSTRACTA framework is proposed to bridge coarse and fine meshes in a single simulation within the phase field method for fracture. Fine meshes are used in the vicinity of localized defects to accurately capture crack initiation, while coarse meshes are used away from initial defects and include only crack propagation paths. This reduces the prohibitive computational times associated with uniformly fine meshes over the entire domain, or with the use of complex adaptive meshes in the phase field method. The coupling between the two overlapping meshes is achieved using a variational formulation in which the energies of the models associated with the fine and coarse meshes are weighted in the superposition zone. Two situations are considered. The first includes the resolution of the phase field problem only in the fine mesh, while the coarse mesh is limited to the undamaged elastic problem. In the second situation, cracks can propagate in both the fine and coarse mesh. Variational formulations and associated finite element implementations are detailed. Numerical examples are presented, showing the potential of this approach to significantly reduce computational costs in the phase field method for cracking without affecting the accuracy.

ABSTRACTThis paper deals with the optimal control of constrained mechanical systems, with potential additional kinematic constraints at the final time. Correspondingly, the equations of motion of the underlying mechanical system assume the form of differential‐algebraic equations with end constraints. The proposed discretisation of the optimality conditions yields a scheme which is capable of preserving control angular momentum maps resulting from the rotational symmetry of the underlying optimal control problem. The numerical solution of the discretised system is first tested with two solution strategies: Monolithic and staggered approaches, and then also solved with hybrid approaches, which combine salient features of each individual strategy. The monolithic strategy solves all the optimality conditions for all time steps as a single system of non‐linear equations and relies on a Newton‐Raphson scheme, which guarantees quadratic rates of convergence in the vicinity of the optimal solution trajectory. The staggered strategy is based on the Forward‐Backward Sweep Method (FBSM), where state and adjoint equations are solved separately, and the control equations provide an update of the control variables, which we here achieve with also a Newton‐Raphson scheme. The proposed hybrid strategies combine the advantages of a conventional gradient‐based FBSM with the individual Newton‐based solution procedures once the solution is close to the optimal trajectory. The strategies are developed and compared through three representative numerical examples, which show that all schemes yield very similar solutions. However, the hybrid approaches become more advantageous in the computation time when the time‐step decreases or the size of the problem increases.

ABSTRACTThe polynomial bases usually applied in the implementation of hybrid‐Trefftz stress elements for plate bending are extended to include the formal solutions necessary to model high‐gradient stress fields associated with boundary layer and singular wedge effects. To this end, the approximation of the stress‐resultant field includes the (Trefftz) solutions of the harmonic, biharmonic, and Helmholtz governing systems of differential equations. Numerical testing problems are selected to show that the element can be used to solve the Kirchhoff model and to adequately simulate both boundary layer and singular wedge effects in thin and moderately thick Mindlin–Reissner plates.

ABSTRACTFinite periodic layout for multicomponent systems signifies a compelling design strategy for constructing complex larger structures through assembling repeating representative unit‐cells with various orientations. In addition to better transportability, handleability and replaceability, design with structural segmentation has been considered particularly valuable for additive manufacturing of large workpiece due to limited printing dimension of machine. However, existing design optimization of periodic structures has been largely restricted to simple translational placements of unit‐cells, sophisticated tessellation with differently oriented topological unit‐cells remains underexplored. This paper presents an efficient and adaptable topology optimization framework for concurrently optimizing periodic structures comprised of repeating topological unit‐cells and their tailored orientations. By introducing a weighting factor associated with different orientation states of unit‐cells, a dominant orientation for each unit‐cell can gradually emerge in the course of optimization process. The proposed procedure combines the solid isotropic material with penalization (SIMP) model for topology optimization of unit‐cell and the discrete material optimization (DMO) technique for the optimization of its orientation. The optimization objective is to minimize structural compliance subject to volume fraction constraint. Through sensitivity analysis, optimality criteria can be applied to simultaneously optimize a representative unit‐cell (RUC) topology and the orientation weighting factors in the periodic macrostructure. Several 2D and 3D examples are investigated to demonstrate significant enhancement in compliance reduction of up to 34% compared to conventional periodic design without orientation optimization. This represents a notable improvement in finite periodic structural optimization, particularly leveraging the topology optimization to tailor unit‐cell orientation rather than relying on brute‐force search approaches. Our methodology paves a new avenue for designing more efficient and readily manufacturable lightweight structures with enhanced performance metrics.