Acta Mechanica Sinica最新文献

According to the H_∞ principle, the dynamical performance optimization of a quasi-zero-stiffness (QZS) isolation system with an additional tuned viscous inerter damper (TVID) is studied by using analytical method. The approximate analytical solutions of the QZS system coupled with TVID are solved by using the complexification-averaging method, and the expression of stability conditions for steady-state solutions is derived based on Lyapunov method and Routh-Hurwitz criterion. Based on the fixed-point theory, considering the nonlinear stiffness and weak damping of the primary system, the stiffness and damping ratios of TVID coupled to QZS system are optimized by using the equal-peak method. The detailed analysis is conducted on the impact of TVID parameters and their corresponding optimization parameters on the dynamic behavior of the QZS primary system, including saddle-node (SN) bifurcation, Hopf bifurcation, backbone curve of amplitude-frequency response, and force transmissibility. According to the analysis, it is found that the steady-state motion of the system can enter quasi-periodic motion or even chaotic motion after losing stability through Hopf bifurcation. By optimizing the parameters of TVID, the number of SN bifurcation regions of the QZS main system can be reduced from 2 to 1, the Hopf bifurcation region can be eliminated, and the number of branches of backbone curve can be reduced from 2 to 1, thereby improving the dynamical performance of the QZS system.

The turning performance of a ship is an important aspect of its maneuverability, and accurately predicting the hydrodynamic forces during ship turning motion is of great significance for the safe maneuvering design of ships. This paper investigated the hydrodynamic performance of a KRISO container ship in steady turning using experimental and numerical approaches. The rotating arm tests were carried out in rotating arm basin of Zhejiang University, while the numerical simulations were conducted in commercial computational fluid dynamics software. Hydrodynamic forces and moments, hull surface wave height, wave patterns, and vorticity are studied under different velocities, radii, and drift angles. The results show that the increase in velocity has a significant impact on the forces and moments of the hull. The changes in longitudinal and transverse forces reflect the complex fluid dynamic interactions between the hull and water. Under conditions of small radius and large drift angle, the hull experiences greater forces and moments, indicating that stability and maneuverability will be more challenged during sudden turns. This study can provide experimental data and numerical simulation references for the research of ship turning maneuvers.

Current hyperelastic constitutive models of hydrogels face difficulties in capturing the stress-strain behaviors of hydrogels under extremely large deformation because the effect of non-affine deformation of the polymer network inside is ambiguous. In this work, we construct periodic random network (PRN) models for the effective polymer network in hydrogels and investigate the non-affine deformation of polymer chains intrinsically originates from the structural randomness from bottom up. The non-affine deformation in PRN models is manifested as the actual stretch of polymer chains randomly deviated from the chain stretch predicted by affine assumption, and quantified by a non-affine ratio of each polymer chain. It is found that the non-affine ratios of polymer chains are closely related to bulk deformation state, chain orientation, and initial chain elongation. By fitting the non-affine ratio of polymer chains in all PRN models, we propose a non-affine constitutive model for the hydrogel polymer network based on micro-sphere model. The stress-strain curves of the proposed constitutive models under uniaxial tension condition agree with the simulation results of different PRN models of hydrogels very well.

This review provides recent advancements in the study of attachment-line boundary layer transition with emphasis on high-speed configurations. As a critical factor influencing aerodynamic performance and thermal management in supersonic and hypersonic systems, the transition mechanisms of three-dimensional attachment-line boundary layers have emerged as a pivotal research frontier in high-speed aerodynamics. This review systematically summarizes the evolution of research on attachment-line boundary layer transition, from early theoretical foundations to modern computational and experimental breakthroughs. A critical examination is presented for two pivotal challenges in high-speed attachment-line boundary layer transition: The resolution of the Gaillard paradox and the leading-edge contamination mechanism. Through systematic synthesis of theoretical developments and empirical evidence, this review identifies critical knowledge gaps while proposing novel methodological approaches for attachment-line boundary layer transition analysis. The review culminates in a strategic framework outlining promising avenues for both fundamental inquiry into attachment-line phenomena and applied engineering solutions in flow control strategies.

The integration of physics-based modelling and data-driven artificial intelligence (AI) has emerged as a transformative paradigm in computational mechanics, This perspective reviews the development and current status of AI-empowered frameworks, including data-driven methods, physics-informed neural networks, and neural operators, While these approaches have demonstrated significant promise, challenges remain in terms of robustness, generalisation, and computational efficiency, We delineate four promising research directions: (1) Modular neural architectures inspired by traditional computational mechanics, (2) physics informed neural operators for resolution-invariant operator learning, (3) intelligent frameworks for multiphysics and multiscale biomechanics problems, and (4) structural optimisation strategies based on physics constraints and reinforcement learning, These directions represent a shift toward foundational frameworks that combine the strengths of physics and data, opening new avenues for the modelling, simulation, and optimisation of complex physical systems.

The formation of donut-shaped penetration pore upon membrane fusion in a closed lipid membrane system is of biological significance, since such the structures extensively exist in living body with various functions. However, the related formation dynamics is unclear because of the limitation of experimental techniques. This work developed a new model of intra-vesicular fusion to elaborate the formation and stabilization of penetration pores by employing molecular dynamics simulations, based on simplified spherical lipid vesicle system, and investigated the regulation of membrane lipid composition. Results showed that penetration pore could be successfully formed based on the strategy of membrane fusion. The ease of intra-vesicular fusion and penetration pore formation was closely correlated with the lipid curvature properties, where negative spontaneous curvature of lipids seemed to be unfavorable for intra-vesicle fusion. Furthermore, the inner membrane tension around the pore was much larger than other regions, which governed the penetration pore size and stability. This work provided basic understanding for vesicle penetration pore formation and stabilization mechanisms.

This study presents an extension of multiscale topology optimization by integrating both yield stress and local/global buckling considerations into the design process. Building upon established multiscale methodologies, we develop a new framework incorporating yield stress limits either as constraints or objectives alongside previously established local and global buckling constraints. This approach significantly refines the optimization process, ensuring that the resulting designs meet mechanical performance criteria and adhere to critical material yield constraints. First, we establish local density-dependent von Mises yield surfaces based on local yield estimates from homogenization-based analysis to predict the local yield limits of the homogenized materials. Then, these local yield-based load factors are combined with local and global buckling criteria to obtain topology optimized designs that consider yield and buckling failure on all levels. This integration is crucial for the practical application of optimized structures in real-world scenarios, where material yield and stability behavior critically influence structural integrity and durability. Numerical examples demonstrate how optimized designs depend on the stiffness to yield ratio of the considered building material. Despite the foundational assumption of the separation of scales, the de-homogenized structures, even at relatively coarse length scales, exhibit a remarkably high degree of agreement with the corresponding homogenized predictions.

Icing of water droplets is a ubiquitous phenomenon with significant implications across natural systems and industrial applications. Despite extensive research, the intricate interplay among heat transfer, mass transport, and phase change during droplet freezing remains incompletely understood, particularly in the context of multiscale dynamics and environmental dependencies. This review critically examines recent advances in uncovering the fundamental mechanisms of droplet icing through experimental, theoretical, and computational approaches. We begin by revisiting the classical tip singularity problem in the freezing of pure water droplets, analyzing its mathematical formulation and physical significance. Subsequent sections explore how environmental boundary conditions and multicomponent effects influence freezing kinetics, solute redistribution, and ice morphology. Furthermore, we evaluate emerging hybrid numerical frameworks that resolve coupled multiphase physics during solidification processes. Finally, we identify key challenges and open questions that require further investigation in this field.

Solids in nano-scales hold the promise to exhibit extreme strength and elasticity due to the absence of interior defects and the designability of micro-arrangements. A nano-scaled bulk sample can be produced by diamond, ice, metallic twins, high entropy alloy (HEA), or cubic boron nitride (cBN). A loading stage capable of 4-DoF movements was designed and built to achieve multi-axial mechanical loading inside a transmission electronic microscope chamber with sub-nanometer loading precision. For single crystal diamond in the shape of nano-needles, we were able to achieve an extreme bending strength of 125 GPa at the tensile side, approaching the theoretical strength of diamond. For ice fibers of sub-micron radius, an extreme elastic strain of 10.9% was acquired, far exceeding the previous record of 0.3% for the elastic strain achievable by ice. For metallic twin specimens made by nano-welding, a shear strain as large as 364% was recorded parallel to the twin boundary. Cyclic shear loading aligned with the twin boundary would drive an up-and-down sweeping movement of the low-angle grain boundary, as composed by an array of dislocations. The sweep of the grain boundary effectively cleanses the lattice defects and creates a feasible scenario of unlimited cyclic endurance. For a HEA dog-bone specimen in nano-scale, an extreme elastic strain of about 10% was achieved. At this level of mechanical straining, stretch-induced melting for crystalline metals, as envisaged by Lindemann a century ago, was realized. For cBN crystals, a fracture path inclined to the stacking hexagon planes would result in a new failure mechanism of layered decohesion, triggered by the extremely large elastic strain (>7%) along the edge of the submicron-scaled specimen. These results indicate ample room for upgrading the mechanical behaviour of solids in nano-scales.

In this paper, we develop a fourth-order conservative wavelet-based shock-capturing scheme. The scheme is constructed by combining a wavelet collocation upwind method with the monotonic tangent of hyperbola for interface capturing (THINC) technique. We employ boundary variation diminishing (BVD) reconstruction to enhance the scheme’s effectiveness in handling shocks. First, we prove that wavelet collocation upwind schemes based on interpolating wavelets can be reformulated into a conservative form within the framework of wavelet theory, forming the foundation of the proposed scheme. The new fourth-order accurate scheme possesses significantly better spectral resolution than the fifth- and even seventh-order WENO-Z (weighted essentially non-oscillatory) schemes over the entire wave-number range. Moreover, the inherent low-pass filtering property of the wavelet bases allows them to filter high-frequency numerical oscillations, endowing the wavelet upwind scheme with robustness and accuracy in solving problems under extreme conditions. Notably, due to the wavelet multi-resolution approximation, the proposed scheme possesses a distinctive shape-preserving property absent in the WENO-Z schemes and the fifth-order schemes with BVD reconstruction based on polynomials. Furthermore, compared to the fifth-order scheme with BVD reconstruction based on polynomials—which is significantly superior to the WENO schemes—the proposed scheme further enhances the ability to capture discontinuities.