To effectively reduce the recoil force generated by pyrotechnic launching devices during operation, this study applies a knitted stainless steel metal wire mesh damper (MWMD) to pyrotechnic launching systems and analyzes its mechanical behavior and buffering performance. Through quasi-static cyclic compression tests and numerical simulations, the effects of wire diameter (d) and relative density (ρ) of MWMD on its mechanical and rebound characteristics were investigated, along with its impact on recoil force in shock tests. The results demonstrate that MWMDs with smaller wire diameters (d) and lower relative densities (ρ) exhibit more cyclic loading cycles and superior rebound performance. Simulation data reveal that MWMDs with smaller wire diameters and higher relative densities display stronger resistance to repeated impacts under multiple cyclic shocks, demonstrating excellent energy absorption capability with an efficiency of up to 37.59
The demand for noise and vibration control in aerospace and vehicle manufacturing is increasing, but reliable design strategies are still lacking. Here, an integrated acousto-mechanical metastructure is proposed to realize broadband low-frequency sound absorption and vibration isolation simultaneously. Due to the introduction of bistable substructures, the proposed metastructure achieves quasi-zero stiffness vibration isolation and sound energy dissipation without external loads. Rapid customized design of the optimized metastructure is achieved by the proposed optimization algorithm. An average sound absorption coefficient of 0.8 is realized by optimization design within the frequency range of 350 Hz to 800 Hz. In addition, the proposed acousto-mechanical metastructure exhibits ultra-low broadband vibration isolation performance, with an initial isolation frequency of 40.4 Hz. Theoretical calculations, numerical simulations, and experimental results show that the acoustic performance of the metastructure benefits from the intensive mode density brought by multiple geometric degrees of freedom, while its vibration isolation performance originates from the quasi-zero stiffness beams. Overall, a multi-objective optimization method under a given structural design domain is proposed to optimize the multifunctional metastructure.
High-temperature dynamic seals are the structures used to seal movable clearances in high-temperature environments. The essential components of these seals are the fiber-braided seal strips. When it is working, the strip is subjected to a transverse preload, decreasing its porosity and restricting gas flow to achieve sealing. To implement seal design, efficient numerical analysis is essential, which is supposed to involve the deformation, heat transfer, seepage, and the interactions among these physical processes. In this paper, a nonlinear thermal-mechanics-seepage coupled contact model is used to describe the seal strips with circular sections. An element differential scheme is proposed to solve the coupled governing equations, and an iterative procedure based on the element differential method (EDM) tracks the contact interfaces, which further determines the range of boundary conditions of other physical fields. The proposed method simplifies the computation by avoiding integral evaluations and reducing matrix density. Two examples are implemented to verify the correctness of the proposed scheme and to predict the variations in physical variables of the seal structures. Furthermore, a comparison between the EDM and finite element method results indicates that the EDM is more efficient because of fewer contact iterations and a sparser coefficient matrix.
To address the critical challenge of end-effector stabilization in bipedal robots while enhancing upper-body motion flexibility, this study introduces a novel bionic fully-elastically-connected tensegrity robot (BFEC-TR) inspired by the biomechanics of avian cervical construction. The proposed design transcends conventional approaches by implementing a multi-nodes bionic tensegrity structure that enables superior spatial deformation capabilities, complemented by an innovative elastic muscle control strategy for dynamic stabilization across multiple locomotion gaits: swing, walking, and running. The study encompasses three key technical contributions. First, we establish a comprehensive dynamic model of the BFEC-TR through kinematic geometric analysis. Second, we develop a feedforward control strategy that explicitly addresses the dynamic requirements of various gaits by establishing the relationship between gait parameters and control parameters, thereby ensuring segmental coordination for head stabilization. Within this control framework, we derive an optimal configuration that maintains bionic posture under energy-efficient driving criteria. Finally, extensive experimental validation demonstrates the efficacy of the proposed control strategy across different locomotion gaits. This work provides biologically-inspired design paradigm and control methodology to achieve spatial dynamic stabilization for bipedal robot end-effectors. The integration of tensegrity principles with biological inspiration from avian neck mechanics presents a novel direction for enhancing the performance and adaptability of robotic systems in dynamic environments.
This paper investigates the size-dependent axisymmetric frictionless contact problem between a rigid spherical indenter and a one-dimensional (1D) hexagonal quasicrystal (QC) half-space within the context of couple stress elasticity. By introducing the characteristic material length parameter and employing the Hankel integral transformation, the governing equations for the axisymmetric contact problem of 1D hexagonal QC under the theory of couple stress are derived and solved analytically. The least-squares integral method is also employed to obtain the expression for the contact pressure distribution with size effect. Through numerical examples, the effects of the characteristic material length parameter on the contact radius, contact pressure, and indentation depth are analyzed. The results incorporating the size effects lead to notable departures from classical elasticity predictions. The presence of the phason field leads to a reduction in peak contact pressure with the size effect.
Figure 3 in the manuscript has been corrected due to layout defects during production typesetting.
In recent years, the devices for piezoelectric energy harvesting based on phononic crystals have gained increasing prominence in the field of acoustic/elastic wave energy harvesting, owing to their ability to concentrate acoustic/elastic waves and vibration energy at specific locations. However, these devices face challenges related to robustness and efficiency degradation caused by structural defects or disturbances. To tackle this challenge, we introduce a novel piezoelectric energy harvesting utilizing elastic higher-order topological insulators in this study. Numerical modeling and experimental data collectively reveal that the attachment of a piezoelectric patch at the corner points effectively harvests elastic wave energy. Moreover, leveraging the topological protection effect, the device maintains excellent elastic wave energy harvesting capability even in the presence of point defects. Additionally, we introduce magnetostrictive materials for tuning the frequencies of corner states under different magnetic fields through numerical calculations. The results indicate that by applying various magnetic fields, it is possible to tune the corner states to match desired operating frequencies. This research presents valuable perspectives and actionable guidelines to inform the design of innovative elastic wave energy harvesting systems.
This study investigates the crack propagation behavior of transversely isotropic piezoelectric materials, with a particular focus on the influence of critical elongation anisotropy, applied electric field, and polarization angle on their fracture characteristics. Piezoelectric materials, known for their ability to interconvert mechanical and electrical energy, are widely utilized in sensors, transducers, and micro-electro-mechanical systems. However, their inherent brittleness and sensitivity to cracking make them prone to fracture under electro-mechanical coupling loads. To gain a deeper understanding of their fracture behavior, this paper introduces a nonlocal macro-meso-scale damage consistent model and employs numerical simulations based on the finite element method. We propose a new non-local influence domain and the corresponding integration strategy for the transversely isotropic materials. Besides, we define both the critical elongation and the brittleness index of the material as an elliptic function regarding the bond angle. The results demonstrate that the fracture resistance of piezoelectric materials increases significantly with an increase in the critical elongation ratio. Additionally, it was observed that a positive electric field promotes fracture, whereas a negative electric field inhibits it. These findings suggest that the fracture behavior of piezoelectric materials can be effectively regulated by adjusting the critical elongation ratio, applied electric field, and polarization angle. This provides a theoretical foundation for the design and application of piezoelectric materials in various engineering contexts.
This paper investigates the stability mechanisms and influencing factors of high-speed projectile water entry at extremely small angles through numerical simulations. The finite volume method, volume of fluid multiphase flow model, and overset grid technique are employed to simulate the water entry process. An underwater stable projectile is designed, and the ballistic characteristics of projectiles entering water at angles of 1° and 2° are analyzed. The critical entry angle and the primary causes of ricochet are identified. At an angle of 1°, the projectile experiences a whip phenomenon during water entry, causing the cavitator to rotate out of the water surface and revealing an extensive wetted area on the lower surface, ultimately leading to ricochet. According to the primary causes of ricochet, the effects of entry velocity and projectile mass on the critical range of entry angles are explored. The results indicate that at higher entry velocities (200-1200 m/s), changes in entry velocity do not affect the critical entry angle. However, at lower velocities (100 m/s), the unbalanced pressure contributes to improved entry stability, thereby reducing the critical entry angle. Furthermore, increasing the projectile mass can effectively reduce the critical entry angle and improve the ballistic characteristics.
Accurate determination of the friction velocity in wall-bounded turbulent flows is crucial for both fundamental research and engineering applications. In this work, the integral relation for friction velocity proposed by Mehdi et al. is modified based on a power-law assumption for the total shear stress within the turbulent boundary layer. The present approach requires only the mean streamwise velocity and Reynolds shear stress profiles in the logarithmic region and beyond, thereby reducing the reliance on near-wall data. Extensive validation against numerical and experimental data shows that the proposed method can accurately predict the friction velocity over a broad range of Reynolds numbers. We further extend the method by deriving a more general relation for the friction velocity through an n-fold repeated integration of the mean streamwise momentum equation. It is found that the accuracy of the present method can be improved to within ±1
Multiple network elastomers (MNEs) consist of a highly crosslinked sacrificial network and one or more loosely crosslinked matrix networks. Their outstanding mechanical properties are highly sensitive to the design of crosslinker density. This study explores how the crosslinking degree of the sacrificial network affects the mechanical behavior of double/triple network elastomers (DNE/TNE) through a combination of experiments and modeling. Cyclic loading tests show negligible hysteresis in DNEs, regardless of the crosslinking degree. In contrast, TNE exhibits prominent hysteresis that increases with crosslinker density. A progressively damaged model is further developed to describe the stress response. The results show that as the crosslinking degree increases, the peak of the probability density-chain length distribution curve becomes higher and shifts leftward, indicating a decrease in average chain length. The fracture tests reveal that the fracture toughness of MNEs first increases and then decreases with increasing crosslinker density. Notably, in TNE, although energy dissipation continues to rise with crosslinking degree, fracture toughness does not increase accordingly, suggesting that the fracture toughness of MNEs is not solely dominated by energy dissipation. These findings offer valuable insights for tailoring the modulus, energy dissipation, and fracture toughness of MNEs.
The vibration control performance of powered wearable devices (PWDs) directly affects the health and comfort of the wearer. Effective vibration isolation technology has become a fundamental aspect of next-generation wearable device design. This study proposes a highly integrated nonlinear stiffness metastructure vibration isolator design for PWDs to address vibration isolation requirements in such scenarios. In this paper, we systematically analyze and experimentally verify the static characteristics of the proposed metastructure vibration isolator through numerical analysis, analytical model and experimental methods, and deeply discuss its dynamic transmissibility characteristics. Among them, we analytically derive and calculate the cantilever beam oscillator of the metastructure vibration isolator and verify the numerical results. Utilizing the mode superposition method, we examine the variations in vibration transmissibility under different operating conditions and geometric parameters. Experimental results are consistent with the numerical calculation results and demonstrate that the isolator exhibits excellent vibration attenuation within the vibration isolation frequency range of 53-61 Hz, achieving a minimum vibration transmissibility of -38 dB. The metastructure vibration isolation system presented in this study successfully achieves the anticipated vibration suppression performance, offering a novel approach to vibration isolation design for PWDs.
Based on the discrete mechanics and optimal control framework, Hamel’s variational integrators are employed to solve the fuel-optimal and time-optimal control problems for a single rigid body. The optimal control problem is discretized via the discrete d’Alembert-Lagrange principle, and the corresponding discrete necessary conditions for optimality are derived. The sensitivity matrix is constructed and solved using the Newton-Armijo iteration method. This approach effectively linearizes the nonlinear problem, enhancing computational efficiency and ease of implementation. Finally, two numerical examples involving the optimal control of spacecraft orbital transfers are presented to verify the effectiveness and applicability of the proposed method.
Randomness and nonlinearity are essential properties of the real world, and their interaction gives rise to highly complex phenomena. With the advancement of technology, merely observing data of the current system state is no longer sufficient for prediction and application in various fields. Consequently, extracting the nonlinear evolution nature of the system from noisy data has become a prominent and challenging issue. To address this, we propose an integrated approach that combines data-driven stochastic model identification with a knowledge-based model predictive control strategy. By leveraging high-precision model identification, our data-driven control design is particularly effective for continuous target tracking problems that are difficult to address using traditional precise-model-based control theory. Furthermore, the central challenge in data science lies in maximizing the informational value of datasets while minimizing the effects of observation noise. In this study, we propose and rigorously demonstrate the stochastic Occam’s razor principle, a stochastic error estimation theory that evaluates and enhances the design of data-driven schemes to mitigate the effect of observation noise. Notably, our approach offers valuable insights for contemporary data-driven, end-to-end control challenges, particularly those involving uncertain governing equations and substantial non-Gaussian observation noise.
This paper studied the effect of synthetic jets on active flow control around a finite-length square cylinder using the large eddy simulation method. Based on the oncoming flow velocity (U∞) and the model width d, the corresponding Reynolds number is 2.78 × 104. We explored the impact of the momentum coefficient (Cμ) and the dimensionless jet frequency (f*) on a finite-length square cylinder’s aerodynamic forces and flow field characteristics. The square cylinder has an aspect ratio of 5, with one end mounted on a wall and the other end free. The synthetic jet outlet is deployed at the windward leading edge of the square cylinder. It is found that synthetic jets positioned at the top can effectively suppress the cylinder’s aerodynamic forces. Both the momentum coefficient and dimensionless jet frequency influence the control effectiveness. The maximum reductions in total mean drag coefficients (Cd,mean) and fluctuating lift coefficient (Cl,rms) are 4.01
Nickel-based single crystal superalloys are extensively used in aircraft engine turbine blades due to their superior high-temperature properties. However, geometric discontinuities in these components lead to local stress concentrations, often assessed using notched specimens. This study performed uniaxial tensile and notched fatigue tests at 760 and 980 °C under varying loading conditions, revealing comparable fatigue lives despite the temperature difference. At 760 °C, the alloy showed higher yield strength but lower ductility, with fatigue life primarily governed by rapid crack propagation and quasi-cleavage fracture. At 980 °C, reduced yield strength and enhanced ductility were observed, with crack growth dominated by creep effects and influenced by microstructural evolution and plastic deformation. Numerical simulations using a coupled damage-crystal plasticity model closely matched the experiments. The results suggest that faster crack growth at 760 °C is offset by greater local plastic energy dissipation, while at 980 °C, slower crack growth is counterbalanced by continuous creep and plastic deformation—leading to a dynamic compensation between mechanisms and ultimately similar fatigue lives.
The reliable initiation of oblique detonation waves (ODWs) represents a critical factor determining the operational performance of oblique detonation engines (ODEs). While previous research has predominantly focused on idealized semi-infinite wedge configurations, such studies have consistently revealed challenges including wave instability, detonation quenching, and compromised engine efficiency. This study presents a numerical investigation of initiation mechanisms and flow field characteristics in ODWs induced by curved surfaces. The analysis employs two-dimensional, multispecies, compressible Reynolds-averaged Navier-Stokes equations coupled with a detailed acetylene combustion model. Key results demonstrate that curved-surface-induced detonations achieve a substantially wider standing range than wedge-induced counterparts, primarily attributable to sustained compression effects generated by concave geometries. Notably, at small wedge angles, the curved surface configuration significantly reduces the detonation initiation distance. The initial formation phase reveals unstable behavior characterized by the large-angle overdriven detonation wave originating from the downstream steep wall section, which subsequently migrates upstream before stabilizing. Detailed examination of the wave structure identifies four distinct components: a curved shock wave (CSW), an overdriven detonation front, a transmitted shock wave, and a supersonic jet flow. Within this configuration, we observe an alternating reflection pattern of expansion waves and compression waves in the supersonic jet region, arising from Type IVr shock-shock interactions between the overdriven detonation wave and the CSW. Viscous effects analysis shows that the gradual curvature transition between the wall and flat plate effectively attenuates shock wave/boundary layer interactions. Furthermore, increased boundary layer thickness is found to significantly alter the ODW morphology while simultaneously inhibiting upstream propagation of the downstream overdriven detonation wave. These findings provide fundamental insights into the complex fluid dynamics governing ODEs, offering valuable implications for the development of more stable and efficient propulsion systems.
The pipe conveying fluid, typically subjected to wide-band excitation, is susceptible to multi-modal resonance, which can result in structural fatigue and failure. The inertial damper, characterized by its flat potential well, demonstrates the capability to suppress vibrations adaptively across a broad frequency range. Consequently, this paper aims to investigate the application of the inertial damper to enhance the fatigue life of the pipe within the wide-band region. The inertial damper is fabricated from visco-hyperelastic materials, and its damping characteristics are determined by the constitutive relationship of these materials. Furthermore, the governing equation for the bending vibration of the pipe system is derived based on Newton’s second law. The response of the pipe is solved using the harmonic balance method and validated through the Runge-Kutta method. Subsequently, the influence of visco-hyperelastic parameters on fatigue life is thoroughly examined and discussed. Results indicate that the inertial damper significantly improves the safety performance of the pipe. Fatigue life prediction based on the Paris theory shows that the inertial damper enhances the fatigue life of the pipe system by mitigating stress during resonance, thereby improving the reliability and durability of the pipe system. The proposed inertial damper offers a simple structural design and theoretical foundation for controlling wide-band fatigue damage in pipes.
The miniaturization of electronic components and the increasing density of solder joint arrays have made the reliability testing and simulation optimization of packaging devices increasingly challenging. Effectively capturing the stress within packaging structures has become a critical issue that needs to be addressed in the field of advanced packaging. This research focuses on wafer-level chip packaging structures, exploring the internal stress evolution under thermal cycling loads and proposing a methodology that integrates experimental and simulation approaches based on embedded silicon-based piezoresistive sensors. By leveraging these sensors for the first time, real-time monitoring of stress variations across different regions of power modules was achieved, offering precise characterization of cumulative stress behavior during thermal cycling. The results indicate that the gradual accumulation of internal stress is predominantly driven by the inherent plastic deformation and creep properties of solder materials under cyclic thermal conditions. Based on this, a unified creep-plasticity constitutive model coupled with damage was developed and compiled into a UMAT subroutine, which was then incorporated into finite element software for simulation. The simulation results closely matched the experimental data, successfully replicating the stress evolution pattern during thermal cycling. This study not only elucidates the underlying mechanisms of stress evolution in advanced packaging structures but also validates the feasibility of using embedded sensor technology and enhanced simulation models to tackle the challenge of stress measurement, providing a novel approach and technical pathway for the reliability design and optimization of packaging structures.
