Abstract A numerical simulation study was carried out to investigate the vortex-induced vibration (VIV) characteristics and energy harvesting performance (EHP) of flat plates with six types of concave and convex geometries at different Reynolds numbers (Re). The effects of concavity and convexity on vibration response, aerodynamic forces, and energy harvesting were analyzed, and the underlying mechanisms were elucidated from a fluid dynamics perspective. Results show that modifying the longitudinal edges of a baseline rectangular plate to concave or convex profiles significantly affects its VIV behavior. For convex plates, as the convexity increases, the VIV peak amplitude decreases, the wind velocity corresponding to this peak VIV amplitude decreases, and the vortex shedding frequency tends to increase. Both the vibration and energy harvesting efficiency of convex plates are significantly lower than those of the baseline plate. At a convex height-to-width ratio H * /D=0.35, the vibration displacement reaches its minimum, which is 99.83% lower than that of the baseline plate, demonstrating effective VIV suppression. Conversely, the concave plates exhibit higher vibration amplitudes and energy harvesting efficiency than the baseline plate. At H * /D =-0.35, the dimensionless peak vibration amplitude of the concave plate is 0.113, which is 107.57% higher than that of the baseline; correspondingly, the energy harvesting efficiency coefficient reaches its maximum. Moreover, studies under attack angles of 5° and 10° reveal that the concave plate with H * /D=-0.35 maintains enhanced energy harvesting performance across different inflow conditions, indicating good applicability in practice. Overall, these findings of this study offer valuable insights for improving energy harvesting efficiency through geometric modification.

Abstract Compression therapy is a widely used strategy for preventing post-burn scars, managing lymphedema, and rehabilitation after liposuction. However, commercially available compression garments often struggle with rapid pressure decay during clinical use. To address this issue, an adaptive fatigue-resistant knitted arm sleeve has been designed and prepared using nitinol wires in the present study, aiming to explore the feasibility of integrating shape memory wires into compression garments. The objective is to combat rapid pressure decay of the compression garments by shape memory effect of nitinol wires. Initially, nitinol wires were subjected to heat treatment at 475 °C for 20 minutes, allowing for precise control over phase transition within a narrow range of less than 5 °C. The treated wires exhibited a shape recovery rate (η) of 93.22% and a martensite finish temperature (Mf) of 30.1 °C, close to surface temperature of human skin. Next, two types of knitted sleeves were fabricated, Sleeve A (dense) and Sleeve B (loose). Moreover, comprehensive characterizations have been carried out. The results showed that both sleeves exhibited favourable temperature response and fatigue-resistant property. They showed a maximum elastic recovery rate of 96.36% and maintained a minimum stress relaxation rate as low as 2.97%. Importantly, both sleeves sustained stable pressure during cyclic loading tests simulating three consecutive days of wear (cumulatively 22.5 hours), demonstrating promising fatigue resistance during wear. Additionally, Sleeve A generated a pressure of 52.53 mmHg at 30% strain due to the shape memory effect, representing a 25.3% increase in pressure after thermal activation. The developed compression sleeves displayed remarkable shape memory properties, achieving maximum shape recovery and shape fixation rates of 97.4% and 95.37%, respectively. Overall, this study offers valuable theoretical insights and practical foundations for developing innovative, fatigue-resistant, adaptive compression garments, while highlighting the need for further clinical validation to establish therapeutic efficacy.

Abstract Growing interest in metamaterials is driven by their extraordinary properties, coupled with increasing industrial demands for reconfigurable, multifunctional vibration isolation solutions; however, research into the tunability of their performance remains insufficient. A novel metamaterial structure is proposed via the synergistic integration of star-shaped (SS) geometries and hourglass-shaped mechanisms, which enables tailorable Poisson’s ratios, bandgap tunability, and effective low-frequency vibration isolation. Based on the Floquet–Bloch theorem, the band structure of the proposed hourglass-SS metamaterials (H-SSMs) is characterized, and the boundary modes of each bandgap are analyzed to elucidate the effects of each unit cell component on bandgap formation. Theoretical and simulation studies reveal that the H-SSM induces monopole, dipolar, and quadrupolar resonances, thereby forming locally resonant bandgaps and exhibiting equivalent negative parametric characteristics. Parametric studies reveal strong correlations between the geometric dimensions of the H-SSM and its bandgap characteristics. Mechanical modulation via uniaxial tension elicits bistable behavior through geometric reconfiguration under tensile loading. Tuning of the Poisson’s ratio and bandgap is realized via buckling deformation, with results demonstrating synchronous evolution between bandgap frequency shifts and stiffness transitions—both exhibiting an initial reduction followed by amplification. Specifically, the proportion of the tuned bandgap is increased to 82.14% of the total frequency range, while the minimum bandgap frequency reaches 38.772 Hz. Notably, the structure achieves ultra-low negative Poisson’s ratios of −0.73 (in the lateral direction) and −2.563 (in the longitudinal direction), providing a potential pathway for metamaterial design.

Abstract The rapid advancement of Artificial Intelligence has continuously enhanced the self-sensing and autonomous decision-making capabilities of wearable devices, thereby further accelerating the fulfillment of growing demands for health monitoring. To address the challenges related to power supply and motion monitoring in conventional wearable technologies, a dual-modal cooperative conversion biomechanical energy harvester is proposed. It is designed to ensure wearing comfort while enabling efficient energy harvesting and accurate motion monitoring. It integrates two synergistic energy conversion mechanisms: one enables energy harvesting during the negative work phase of the knee joint, and the other achieves efficient electrical conversion through the release of stored energy from a coil spring. This dual-modal cooperative design significantly extends energy harvesting duration and improves power generation efficiency. Experimental results show that at 4 km/h treadmill speed, the harvester achieves an average output power of 263.05 mW and a peak power density of 0.26 W/kg. Moreover, the electromagnetic signals generated by the harvester can accurately identify different motions when processed using the Gated Recurrent Unit model. Consequently, this study offers a novel strategy for the development of wearable systems and is expected to advance smart health management toward safer, greener, and more sustainable solutions.

Abstract Metamaterials with thermal contraction and auxetic effect can effectively prevent irreversible damage caused by thermal stress and impact in engineering applications, playing a crucial role in aerospace and other fields. Therefore, we propose a novel double-negative metamaterial structure by combining triangular arrowhead structures and triangular thermal metamaterial structures, which can achieve thermal expansion coefficient over a wide range from -167×10-6 to 162×10-6 K-1, and Poisson's ratios range from -1.7 to 1.95. Furthermore, we study the impact of the geometric parameters of the designed structures on the coefficient of thermal expansion (CTE), elastic modulus, and Poisson's ratio of the metamaterial by using the stiffness matrix method (SMM). Results show that changing the included angle of the re-entrant triangle of the structure can change the sign of thermal expansion coefficient and Poisson's ratio. This paper provides new ideas and methods for designing mechanical metamaterials with anisotropic adjustable thermal expansion coefficients and Poisson's ratios.