Conventional rotary actuators mainly rely on electric or hydraulic/pneumatic motors to convert energy into mechanical motion, making them one of the most widely used actuation methods in industrial manufacturing, robotics, and automation control. However, these traditional actuators often suffer from limitations in operability and applicability due to their complex structures, bulky systems, high energy consumption, and severe mechanical wear. Liquid crystal elastomers (LCEs) have been increasingly used for programmable actuation applications, owing to their ability to undergo large, reversible, and anisotropic deformations in response to external stimuli. In this work, we propose a compact flexible rotary joint (FRJ) based on LCEs. To describe the thermo-mechanical coupled behaviors, a constitutive model is developed and further implemented for finite element analysis (FEA). Through combining experiments and simulations, we quantify the dynamic rotational behavior of the rotor rotating relative to the base driven by the induced strain of the FRJ under cyclic thermal stimuli. The proposed rotary joint features a simple structure, lightweight design, low energy consumption, and easy control. These characteristics endow it with significant potential for miniaturization and integration in the field of soft actuation and robotics.

To break the limitations of the multi-dimensional (M-D) vibration isolation (VI) platforms with the Stewart-Gough design, such as strongly coupling motions, excessive friction in connections, heavy weight, and limited workspace, this study processes a novel platform integrated by a stiffness-adjustable origami spring sub-structure and a parallel mechanism. The origami-based stiffness-adjustable spring realizes low-frequency VI, and the parallel mechanism symmetry design realizes motions decoupling. In the origami-based sub-leg, the parallel-stack-assembly (PSA) design mechanism with two Miura origami configurations is proposed to generate a symmetrical negative stiffness property. Paired with a linear positive stiffness spring, the origami-based sub-leg has wide-amplitude-high-static-low-dynamic stiffness (WA-HSLDS) characteristics in one direction. Then, with construction of the parallel mechanism connected with origami-based sub-legs, an M-D VI platform is achieved, whose motions in the vertical direction and yaw direction are decoupled with the motions in the other directions. Based on the dynamic model and incremental harmonic balance (IHB) with the arc-length continuation method, appropriate structural parameters in the parallel mechanism part are figured out, and the accurate transmissibility in different directions is defined, which gives the parametric influencing investigations for realization of low-frequency VI performances. Finally, experiments are conducted to validate the accuracy and feasibility of the theoretical methods, and to demonstrate the performance of M-D low-frequency isolation with load-carrying capacity of the proposed VI platform. The integration of the origami into the parallel mechanism results in a compact, efficient, and flexible platform with nonlinear adjustability, offering new possibilities for lightweight M-D VI, and developing the practical applications in high-precision platforms in ocean and aerospace environments.

Reducing the vibration transmission in beams is of significant interest, as beams are among the most widely used basic structures in numerous practical engineering applications. However, achieving broadband suppression of multi-polarization low-frequency vibration in beams presents a challenge. This study proposes a single-phase multi-resonant metabeam, which consists of a host beam with subwavelength arrays of tunable local resonators. These resonators exhibit adjustable multi-polarization resonant modes that strongly couple with the host beam, enabling simultaneous suppression of multi-type waves over a broad frequency range. The theoretical analysis demonstrates that under the fixed total added-mass ratio ({\gamma }_{\text{total}}=1.5), the tailored frequency spacing (\delta =25–50 Hz) and the controlled loss factor (\eta =0.03–0.07) act synergistically to broaden bandgaps through resonant zone overlapping and attenuation peak smoothing. The experimental validation with monolithic three-dimensional (3D)-printed specimens confirms the efficacy of this design in multi-polarization vibration control within a deep-subwavelength bandgap, opening a new avenue for designing multi-polarization vibration suppression structures.

The incomplete understanding of nanoscale surface interactions arising from underlying atomistic long-range forces limits our ability to simulate and design their performance. In this paper, the surface elasticity is constructed from underlying atomistic nonlocal interactions in spherical nanoparticles. By introducing an intrinsic length scale, we quantify the surface region thickness, and demonstrate the progressive elastic modulus transition caused by asymmetric atomistic nonlocal interactions. The universal surface scaling law, relating the intrinsic length scale to the particle dimensions, is established, and a surface-dominated criterion is developed for quantifying the transition to the surface-dominated behaviors. The model is thoroughly validated through the molecular static simulations and experimental data with the material-specific intrinsic length constants.

In this paper, we investigate the interfacial behavior of a thin, penny-shaped, one-dimensional (1D) hexagonal functionally graded (FG) piezoelectric quasicrystal (PQC) film bonded on a temperature-dependent elastic substrate under thermal and electrical loads. The problem is modeled as axisymmetric based on the membrane theory, with the peeling stress and bending moment being disregarded. A potential theory method, combined with the Hankel transform technique, is utilized to derive the displacement field on the substrate surface. With perfect interfacial bonding assumption, an integral equation governing the phonon interfacial shear stress is formulated and numerically solved by the Chebyshev polynomials. Explicit expressions are derived for the interfacial shear stress, the internal stresses within the PQC film and the substrate, the axial strain, and the stress intensity factors (SIFs). Numerical simulations are conducted to investigate the effects of the film’s aspect ratio, material inhomogeneity, material mismatch, and temperature-dependent material properties on its mechanical response. The results provide insights for the functional design and reliability assessment of FG PQC film/substrate systems.

Inspired by the structural adaptations of natural biological organisms, helicoidal composite architectures have shown significant potential for enhancing toughness, strength, and weight efficiency in engineering applications. However, temperature and moisture’s adverse effects pose challenges during service, potentially compromising their overall performance. This study meticulously analyzes the buckling and vibration behavior of carbon nanotube (CNT)-reinforced bioinspired helicoidal composite plates under different hygrothermal conditions. A novel aspect of this study lies in the proposition of a multiscale analysis combining the analytical and numerical techniques to assess the effects of temperature, moisture, weight fraction of CNTs, layup configurations of bioinspired designs, aspect ratios, loading and boundary conditions, and geometric shapes of bioinspired helicoidal composite structures on their vibration and buckling characteristics. In this context, the stiffness properties are computed with the Halpin-Tsai model, incorporating the size-dependent features of CNTs along with their waviness and agglomeration. In addition, the Chamis micro-mechanical equations are used to determine the elastic properties of individual layers constituting bioinspired composites, considering the effects of temperature and moisture. The kinematics of the laminated bioinspired structures are captured with the third-order shear deformation theory (TSDT) within the isogeometric framework employing the non-uniform rational B-splines (NURBSs) as the basis functions. The isogeometric framework ensures higher-order inter-element continuity and provides an exact geometric representation, offering various advantages over the traditional finite element method. The developed framework is validated against the existing literature, and thereafter several numerical examples are presented, providing valuable insights for the design and optimization of bioinspired composite structures, with potential benefits for various engineering fields, including marine and aerospace sectors.

In industrial applications, plate-like structures such as steel strips in continuous hot-dip galvanizing and papers under fan action are ubiquitous. The vibration issues that arise when these structures are in axial motion, and are influenced by fluids and thermal fields, have attracted significant attention from the academic community. This study focuses on the nonlinear dynamic behavior of axially transporting immersed viscoelastic plates with particular emphasis on internal resonance and speed-dependent tension. The governing equation and the related boundary conditions for the axially transporting viscoelastic immersed plate are derived with Hamilton’s principle, prioritizing the impact of time-varying tension induced by speed perturbations. Based on the second-order Galerkin truncation, the governing equation is discretized into a system of second-order ordinary differential equations. The multi-scale method is used to analyze the stable steady-state response of the immersed viscoelastic plate. The conditions for achieving a 3 : 1 frequency ratio between the first two orders of the system are analytically deduced. Notably, when the viscoelastic coefficient diminishes, the stability boundaries exhibit increased complexity, manifesting as the irregular W-shaped contours in the parameter space. Numerical examples comprehensively investigate the effects of viscoelasticity on both the stability region and the steady-state response under internal resonance conditions. Finally, the accuracy of the obtained results is validated through numerical computation.

Sparse identification of nonlinear dynamics (SINDy) has made significant progress in data-driven dynamics modeling. However, determining appropriate hyperparameters and addressing the time-consuming symbolic regression process remain substantial challenges. This study proposes the adaptive backward stepwise selection of fast SINDy (ABSS-FSINDy), which integrates statistical learning-based estimation and technical advancements to significantly reduce simulation time. This approach not only provides insights into the conditions under which SINDy performs optimally but also highlights potential failure points, particularly in the context of backward stepwise selection (BSS). By decoding predefined features into textual expressions, ABSS-FSINDy significantly reduces the simulation time compared with conventional symbolic regression methods. We validate the proposed method through a series of numerical experiments involving both planar/spatial dynamics and high-dimensional chaotic systems, including Lotka-Volterra, hyperchaotic Rössler, coupled Lorenz, and Lorenz 96 benchmark systems. The experimental results demonstrate that ABSS-FSINDy autonomously determines optimal hyperparameters within the SINDy framework, overcoming the curse of dimensionality in high-dimensional simulations. This improvement is substantial across both low- and high-dimensional systems, yielding efficiency gains of one to three orders of magnitude. For instance, in a 20D dynamical system, the simulation time is reduced from 107.63 s to just 0.093 s, resulting in a 3-order-of-magnitude improvement in simulation efficiency. This advancement broadens the applicability of SINDy for the identification and reconstruction of high-dimensional dynamical systems.

Transcritical and supercritical fluids widely exist in aerospace propulsion systems, such as the coolant flow in the regenerative cooling channels of scramjet engines. To numerically simulate the coolant flow, we must address the challenges in solving Riemann problems (RPs) for real fluids under complex flow conditions. In this study, an exact numerical solution for the one-dimensional RP of two-parameter fluids is developed. Due to the comprehensive resolution of fluid thermodynamics, the proposed solution framework is suitable for all forms of the two-parameter equation of state (EoS). The pressure splitting method is introduced to enable parallel calculation of RPs across multiple grid points. Theoretical analysis demonstrates the isentropic nature of weak waves in two-parameter fluids, ensuring that the same mathematical properties as ideal gas could be applied in Newton’s iteration. A series of numerical cases validate the effectiveness of the proposed method. A comparative analysis is conducted on the exact Riemann solutions for the real fluid EoS, the ideal gas EoS, and the improved ideal gas EoS under supercritical and transcritical conditions. The results indicate that the improved one produces smaller errors in the calculation of momentum and energy fluxes.

The Lagrangian integral time scale (LITS) is a crucial characteristic for investigating the changes in fluid dynamics induced by the chaotic nature, and the finite-time Lyapunov exponent (FTLE) serves as a key measure in the analysis of chaos. In this study, a new LITS model with an explicit theoretical basis and broad applicability is proposed based on the FTLE, along with a verification and evaluation criterion grounded in the Lagrangian velocity correlation coefficient. The model is used to cavitating the flow around a Clark-Y hydrofoil, and the LITS is investigated. It leads to the determination of model constants applicable to cavitating flow. The model is evaluated by the Lagrangian velocity correlation coefficient in comparison with other solution methods. All the results show that the LITS model can offer a new perspective and a new approach for studying the changes in fluid dynamics from a Lagrangian viewpoint.