Acta Mechanica Sinica最新文献

This study develops a trans-scale dynamic shear-lag model based on strain gradient theory and the Gurtin-Murdoch model to investigate the dynamic behaviors and wave attenuation performance in nacre-like staggered composites. This model provides an analytical expression for the wave attenuation factor of staggered composites that incorporate nanoscale tablets and matrices. Our model shows that the strain gradient and surface energy effects of the nanoscale matrix and tablets significantly influence the dynamic behavior and wave attenuation performance of staggered composites. The strain gradient intensifies the localization of stress wave amplitude in tablets and matrices, while interface energy mitigates this effect. As the strain gradient increases or the interface modulus decreases, the first bandgap shifts to higher frequencies, resulting in a diminished low-frequency filtering capability. Furthermore, we show that the width and position of the first bandgap exhibit a non-monotonic variation with microstructural parameters, such as Young’s modulus of the tablets and the thickness of the matrix. The results of this study provide valuable insights for designing advanced composites with nanoscale structures to achieve superior dynamic performance.

To address challenges in architectural extensibility and cross-module collaboration of CAE software, this study proposes OPFEM (open-source Python-based finite element modeling)—an open-source framework featuring a unified four-layer architecture. The geometric modeling framework achieves plug-in support for geometric kernels through an interface abstraction layer and adapter patterns, decoupling kernel-specific implementations while enabling state machine-driven interaction design and parametric sketching. The pre-processing modules establish multi-level associations among materials, sections, and geometric entities using Composite and Factory patterns, while implementing Observer pattern to ensure geometric-mesh consistency and employing finite-state machines to optimize boundary workflows. The computational modules implement a modular finite element library that decouples topology from element attributes, along with a surface boundary element technique for load conversion and task-scheduling management, validated through a cantilever beam large-deformation case. The post-processing module facilitates standardized data storage and dynamic field visualization through architecture-level standardized interface definitions and hierarchical component design. Collectively, OPFEM achieves full-process integration from parametric modeling to nonlinear solving and visualization, enhancing configuration efficiency and providing an extensible, pattern-driven solution for complex CAE challenges.

Bistable beams have shown remarkable performance in vibration energy harvesting, attracting considerable attention. However, their potential for vibration reduction remains largely unexplored. To achieve an integrated design for energy harvesting and vibration control, this study focuses on a bistable buckled beam absorber (BBBA) structure to evaluate its vibration suppression capabilities. The findings provide new insights into the synergistic application of bistable beams for effective vibration control and potential energy harvesting. The core structure of the BBBA comprises an elastic beam with two stable equilibrium positions. By applying a driving torque, the potential energy barrier is reduced, enhancing snap-through behavior and improving vibration control performance. A novel modeling approach for the BBBA is proposed to systematically analyze its dynamic behavior. The buckling characteristics of the structure are analyzed, and a dynamic model of the buckled beam is established. Finite element simulations are conducted to compute the snap-through process and natural frequencies, revealing the relationship between the movable hinge position and the critical snap-through load. Finally, a BBBA prototype is fabricated, and sweep frequency tests are performed to determine its effective operating frequency range, identified as 4–17 Hz. The BBBA’s vibration suppression performance is evaluated using a manipulator model, demonstrating up to a 60% reduction in vibration amplitude within this frequency range. These findings provide both theoretical and experimental support for the application of BBBAs in engineering vibration mitigation.

Numerical simulations of pulmonary airway flow are carried out based on patient-specific geometry reconstructed from computed tomography scans. The study includes four patients, for each patient, three simulations are run on models reconstructed from data acquired in different years. As the flow rate increases, the flow in the trachea and bronchi becomes more vortical and inhomogeneous. The pressure drop between inlet and outlets and the wall shear stress show significant variation among different years due to the change of geometry. The correlation coefficients of four hydrodynamical indicators and pulmonary function tests are then examined. Indicators based on wall shear stress exhibit stronger correlation to pulmonary ventilation indices than those based on pressure drop. Especially, strong correlation is observed between the airway resistance in clinical test and wall shear stress in simulations, suggesting that the current simulations can reasonably capture the flow state in central airway.

The adjoint method is widely used in gradient-based optimization with high-dimensional design variables. However, the cost of solving the adjoint equations in each iteration is comparable to that of solving the flow field, resulting in expensive computational costs. To improve the efficiency of solving adjoint equations, we propose a physics-constrained graph neural networks for solving adjoint equations, named ADJ-PCGN. ADJ-PCGN establishes a mapping relationship between flow characteristics and adjoint vector based on data, serving as a replacement for the computationally expensive numerical solution of adjoint equations. A physics-based graph structure and message-passing mechanism are designed to endow its strong fitting and generalization capabilities. Taking transonic drag reduction and maximum lift-drag ratio of the airfoil as examples, results indicate that ADJ-PCGN attains a similar optimal shape as the classical direct adjoint loop method. In addition, ADJ-PCGN demonstrates strong generalization capabilities across different mesh topologies, mesh densities, and out-of-distribution conditions. It holds the potential to become a universal model for aerodynamic shape optimization involving states, geometries, and meshes.

Generalised reduced masses with a set of equations governing the three relative motions between two of 3-bodies in their gravitational field are established, of which the dynamic characteristics of 3-body dynamics, fundamental bases of this paper, are revealed. Based on these findings, an equivalent system is developed, which is a 2-body system with its total mass, constant angular momentum, kinetic and potential energies same as the total ones of three relative motions, so that it can be solved using the well-known theory of the 2-body system. From the solution of an equivalent system with the revealed characteristics of three relative motions, the general theoretical solutions of the 3-body system are obtained in the curve-integration forms along the orbits in the imaged radial motion space. The possible periodical orbits with generalised Kepler’s law are presented. Following the description and mathematical demonstrations of the proposed methods, the examples including Euler’s/Lagrange’s problems, and a reported numerical one are solved to validate the proposed methods. The methods derived from the 3-body system are extended to N-body problems.

Quasi-periodic solutions with multiple base frequencies exhibit the feature of 2π-periodicity with respect to each of the hyper-time variables. However, it remains a challenge work, due to the lack of effective solution methods, to solve and track the quasi-periodic solutions with multiple base frequencies until now. In this work, a multi-steps variable-coefficient formulation is proposed, which provides a unified framework to enable either harmonic balance method or collocation method or finite difference method to solve quasi-periodic solutions with multiple base frequencies. For this purpose, a method of alternating U and S domain is also developed to efficiently evaluate the nonlinear force terms. Furthermore, a new robust phase condition is presented for all of the three methods to make them track the quasi-periodic solutions with prior unknown multiple base frequencies, while the stability of the quasi-periodic solutions is assessed by mean of Lyapunov exponents. The feasibility of the constructed methods under the above framework is verified by application to three nonlinear systems.

Since rock plasticity under in-situ conditions poses challenges during fracturing stimulation, extensive research is necessary on deep gas and oil reserves, which will be the primary area of future development. This paper created a competitive, multi-cluster fracture propagation model that considered elastoplastic rock deformation and nonlinear fracture characteristics in deep reservoirs. It also proposed an optimal fracture design of “dense fracture distribution, non-uniform perforation and alternating staged fracturing” based on stress field reconstruction. The findings indicated that suitably reducing the spacing between clusters and increasing the number of perforated clusters minimized local in-situ stress variations through stress interference among fractures. This mitigated the limiting effect of plastic deformation on the propagation of hydraulic fractures, demonstrating a viable approach for enhancing the expansion of fractures in deep reservoirs. The elastoplastic fracture propagation mechanism was examined to elucidate the advantages of close-cutting fracturing technology. The impact of various fracture techniques was analyzed using stress field reconstruction. Alternate fracturing displayed a high degree of stress reconstruction with an extensive propagation range, which facilitated the propagation of multiple fracture clusters in the subsequent fracturing section. The findings offer a theoretical basis for fracture design of deep reservoirs.

The airflow mechanics in adult nasal airways, whether healthy or abnormal, are extensively studied and investigated, but the flow mechanics in child nasal airways remain underexplored. This study investigates the airflow mechanics in the child’s nasal upper airway with adenoid hypertrophy, with an adenoid nasopharyngeal ratio (AN of 0.9), under cyclic inhalation and exhalation. An inlet respiratory cycle with three different flow rates (3.2 L/min calm breathing, 8.6 L/min normal breathing, and 19.3 L/min intensive breathing) was simulated by using the computational fluid dynamics approach. To better capture the interaction between airflow and the flexible airway tissue, fluid-structure interaction analysis was performed at the normal breathing rate. Comparing the airflow dynamics during inhalation and exhalation, the pressure drops, nasal resistance, and wall shear stress show significant differences in the nasopharyngeal region for all different flow rates. This observation suggests that the inertial effect associated with the transient flow is important during exhalation and inhalation. Furthermore, the considerable temporal variation in flow rate distribution across a specific cross-section of the nasal airway highlights the critical role of transient data in virtual surgery planning and data for clinical decisions.

This paper proposes the analytical solutions involving damping effects for the dynamic response of a simply supported thin-walled curved beam under uniformly variable two-axle moving loads in four directions: vertical, torsional, radial, and axial. The warping stiffness and damping of the thin-walled beam were comprehensively considered in the vibration control equations. Unlike traditional one-axle load cases, this study employs a more realistic two-axle vehicle load model. Based on the modal superposition method, the control vibration equations for thin-walled curved beams in-plane and out-of-plane under variable speed moving loads were solved using a combination of the Fourier sine transform method, the Galerkin method, and the Laplace transform method. Analytical solutions for the dynamic responses were derived in integral form, facilitating direct numerical computation. The proposed computational method’s effectiveness and accuracy were validated against published research. Subsequently, the dynamic responses of the thin-walled curved beam under one-axle and two-axle moving load models were compared, and the effects of initial load velocity, load acceleration, and center angle of the curved beam on the dynamic responses were investigated through extensive parameter research. The research results provide valuable insights into the structural behavior of thin-walled curved beams under the moving loading with variable speed.