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In practical engineering, noise and impact hazards are pervasive, indicating the pressing demand for materials that can absorb both sound and stress wave energy simultaneously. However, the rational design of such multifunctional materials remains a challenge. Herein, inspired by cuttlebone, we present bioinspired architected metamaterials with unprecedented sound-absorbing and mechanical properties engineered via a weakly-coupled design. The acoustic elements feature heterogeneous multilayered resonators, whereas the mechanical responses are based on asymmetric cambered cell walls. These metamaterials experimentally demonstrated an average absorption coefficient of 0.80 from 1.0 to 6.0 kHz, with 77% of the data points exceeding the desired 0.75 threshold, all with a compact 21 mm thickness. An absorptance-thickness map is devised for assessing the sound-absorption efficiency. The high-fidelity microstructure-based model reveals the air friction damping mechanism, with broadband behavior attributed to multimodal hybrid resonance. Empowered by the cambered design of cell walls, metamaterials shift catastrophic failure toward a progressive deformation mode characterized by stable stress plateaus and ultrahigh specific energy absorption of 50.7 J/g—a 558.4% increase over the straight-wall design. After the deformation mechanisms are elucidated, a comprehensive research framework for burgeoning acousto-mechanical metamaterials is proposed. Overall, our study broadens the horizon for multifunctional material design.Noise and impact hazards are pervasive in engineering, necessitating materials capable of absorbing both sound and stress wave energy. Here, we present bioinspired metamaterials with exceptional sound-absorbing and mechanical properties using a weakly-coupled design strategy. These materials incorporate multi-layered resonators for superior acoustic performance and cambered cell walls for enhanced structural strength. They achieve an average absorption coefficient of 0.80 across the 1.0 to 6.0 kHz range, all within a sleek 21 mm thickness. Furthermore, the design transitions failure modes from catastrophic to progressive, resulting in a remarkable 558.4% increase in energy absorption compared to conventional designs.

Self-excited oscillations of flags attached at the leading edge of aerofoils have been investigated at post-stall angles of attack at a chord Reynolds number of 100 000. Significant increases in the time-averaged lift coefficient and stall angle have been observed for three aerofoils: one symmetric, one cambered and one with a sharp leading edge. The aerodynamic improvement is due to the periodic formation of vortices caused by the flag oscillations. When the flag is near the aerofoil surface, it is lifted upwards by the induced velocity of the growing vortex. As the flag moves up, the vortex grows in strength and reaches maximum circulation when the flag is furthest from the aerofoil surface and subsequently sheds. Flags with large stiffness exhibit better spatial and temporal coherence of flag oscillations than the compliant flags, resulting in a larger maximum lift coefficient and higher stall angle. For all aerofoils tested, the best lift enhancement with respect to the clean aerofoils is found when the angle of attack is 6° to 10° above the stall angle of the clean aerofoil. High lift is observed when the flags are locked in with the wake instability in a narrow frequency band, depending on the flag mass ratio and length.

Today’s stamping simulations are realized by ignoring the elastic deformation of the press and tooling system through the assumption of a rigid behavior and a perfect press stroke. However, in reality, the press and tool components deform elastically and are one of the major error sources for the final adjustment and blue-spotting of the dies. In order to tackle this issue, a new approach is proposed in this study that substitutes the press stiffness by means of a substitutive model composed of cost-effective shell and beam elements. The substitute model was calibrated using full-scale measurements, in which a 20,000 kN trial press was experimentally characterized by measuring its deformation under static loads. To examine the robustness of the substitute model, a medium-size tool and a large-size tool were simulated together with the substitutive model. To this end, a B-pillar tool was re-machined based on the substitute-model results and a new cambering procedure was proposed and validated throughout the blue-painting procedure. The newly developed substitute model was able to replicate the global stiffness of the press with a high accuracy and affordable calculation time. The implementation of the findings can aid toolmakers in eliminating most of the reworking and home-line trials.

We study the kinematics, dynamics and flow fields generated by an oscillating, compliant membrane hydrofoil extracting energy from a uniform water stream at a chord-based Reynolds number $Re \\approx 3 \\times 10^4$. Hydrodynamic forces during the foil's motion cause the membrane to dynamically morph its shape, effectively increasing the camber during the oscillation cycle. The membrane's deflection is modelled using the Young–Laplace equation, with pressure term approximated from thin-airfoil theory. Simultaneous tracking of the membrane deformation and the surrounding flow field using laser profiling and particle image velocimetry, respectively, reveals the role of dynamic cambering in stabilizing the leading-edge vortices on the membrane. In this regime of operation, we obtain up to 160 % higher power extraction when compared to a rigid, symmetric hydrofoil. The present work provides a demonstration of how passive compliance of soft materials interacting with fluids may be exploited in tidal and fluvial energy extraction.

Wall-pressure and velocity statistics in the turbulent boundary layer (TBL) on a cambered controlled-diffusion aerofoil at $8^{\\circ }$ incidence, a Mach number of 0.25 and a chord-based Reynolds number ${Re}_c=1.5\\times 10^{5}$ are analysed at four locations on the suction side with zero and adverse pressure gradients (ZPG and APG), characterised by increasing Reynolds numbers based on momentum thickness, ${Re}_{\\theta }=319$, 390, 877 and $1036$. The strong APG yields a highly non-equilibrium TBL at the trailing edge that significantly affects the turbulent flow statistics. Different normalisations of the full wall-pressure statistics involved in trailing-edge noise are analysed for the first time in such strong APG with convex curvature, and compared with available experimental and numerical data. Good overall agreement is found in the ZPG region, and most results obtained in previous APG TBL can be extended to the present highly non-equilibrium case. The presence of strong APG augments the intensity of wall-pressure fluctuations noticeably at low frequencies, shortens the streamwise and broadens the spanwise coherence of wall-pressure fluctuations in both time and space, and significantly reduces the convection velocity. The wall-pressure power spectral density are found to scale with the displacement thickness, the Zaragola–Smits velocity and the root-mean-squared pressure, the latter possibly being replaced by the local maximum Reynolds shear stress. The other two key parameters to trailing-edge noise modelling, the spanwise coherence length and the convection velocity, rather scale with displacement thickness and friction velocity, respectively.

In this study, we propose an encoder–decoder convolutional neural network-based approach for estimating the pressure field around an airfoil. The developed tool is one of the early steps of a machine-learning-based aerodynamic performance prediction tool. Network training and evaluation are performed from a set of computational fluid dynamics (CFD)-based solutions of the 2-D flow field around a group of known airfoils involving symmetrical, cambered, thick and thin airfoils. Reynolds averaged Navier Stokes-based CFD simulations are performed at a selected single Mach number and for an angle of attack condition. The calculated pressure field, which is the main parameter for lift and drag calculations, is fed to the neural network training algorithm. Pressure data are calculated using CFD methods on high-quality structured computational grids. For the better shape learning, a distance map is generated from airfoil shape and provided to the algorithm at data locations of the pressure points relative to the airfoil shape. Experiments are conducted with unseen airfoil shapes to evaluate the predictive capability of our model. Performance analysis for airfoils with different thicknesses and cambers is conducted. We also investigated the effect of the shock on the performance of our model. Overall, our model achieves 88 % accuracy for unseen airfoil shapes and shows promise to capture the overall flow pattern accurately. Also, significant speed-up is achieved compared to time-consuming CFD simulations. We achieve almost four orders of speed-up with a much cheaper computational resource.

The aerodynamic optimization method was presented to design a propeller airfoil for a stratosphere airship at low Reynolds numbers. The delta class and shape transformation were adopted to describe the airfoil geometry as the design variables. The flow field was calculated by an open-source code XFOIL to obtain the aerodynamic characteristics as the design targets. The separated particle swarm optimization was employed as the optimization algorithm. The optimization case started with a typical low Reynolds number airfoil E387 and obtained a thicker and more cambered airfoil using the proposed method. The flow fields of the optimized and initial airfoils were analysed by CFD. Results suggested that the lift-to-drag ratio of the optimized airfoil changed from 35.7 to 45.9 with an increasing rate by 28.5% at design cruise condition. The overall aerodynamic performance of the optimized airfoil has been significantly improved at both design and off-design conditions within a wide range of attack angle. The optimization platform presented here is an efficient and effective method for the low-Reynolds-number airfoil designs.

Conventional methods for manufacturing rotor blades, such as composite construction and die casting, are hindered by high costs due to expensive molds, while 3D printing often results in poor quality or high production costs with unfavorable cost‐per‐part scaling. Moreover, conventional airfoil designs perform poorly at Reynolds numbers below 100,000, necessitating larger rotors. This becomes especially problematic in wind tunnel studies, where multiple rotors must fit within a single wind tunnel for wake or multirotor research, significantly increasing both building costs and wind tunnel requirements. To address these challenges, this study develops high‐performance rotor blades for micro wind turbines that are aerodynamically efficient under low Reynolds number conditions and easy to manufacture. Using cambered plate airfoils, the optimization process employed a class shape transformation and seventh‐degree Bernstein polynomials. Aerodynamic performance was analyzed using XFOIL, with evaluations conducted at Reynolds numbers of 30,000, 40,000, and 50,000 to ensure robust performance across realistic operating scenarios. The iterative optimization employed both single‐objective and (genetic) multi‐objective algorithms, targeting both aerodynamic efficiency and manufacturability. The blade tested with the optimized MB‐LR2‐7.5 airfoil exhibited good performance in wind tunnel tests, closely matching Blade Element Momentum (BEM) simulations. This research highlights the potential of cambered plate airfoils to improve micro wind turbine performance while maintaining ease of manufacturing, with potential applications in unmanned aerial vehicles (UAVs), drone propellers, and ventilation systems. The findings advance the understanding of aerodynamic optimization in low Reynolds number environments, paving the way for more efficient and cost‐effective rotor designs.

The dynamic anisotropy and failure mechanism of shales are greatly affected by bedding surfaces. To reveal the influence of beddings on anisotropic characteristics of shales under dynamic impact, the Brazilian splitting tests were conducted by the split Hopkinson pressure bar system. The fracturing process were monitored by the high-speed camera. Meanwhile, to understand crack initiation and propagation mechanism, the stress buildup, stress shadow and stress transfer were modelled based on the digital image processing and the rock failure process analysis method. The effect of dip angle and bedding spacing on crack initiation, propagation and coalescence was analyzed. Simultaneously, the spatial distribution and energy magnitude of crack-induced acoustic emissions were captured numerically. The results show that the shale discs continue to produce parallel cracks and cambered cracks induced by the high stresses at the tips of initial cracks; the tensile strength under dynamic splitting changes in the U-shaped trend with the bedding dip angle increasing; the cracking percentage of bedding surfaces decreases, and the cracking percentage of rock matrix increases with the bedding dip angle increasing. In addition, the acceleration of crack growth and the rapid growth of AE energy can be regarded as the effective precursors of shale failure.

Single-pin meshing pairs are widely used in light-tracked vehicles. The purpose of this paper is to establish a nonlinear contact algorithm between the sprocket and track for multibody dynamics simulation. Based on the actual configuration, the tooth groove profile is discretized into three cambered surfaces, and the track pin is modeled as a cylinder with a protrusion. A body-fixed frame is introduced for each contact surface to facilitate the geometric contact criteria and contact force evaluation. Then the features of equal-pitch, sub-pitch and extra-pitch meshing are described with multibody dynamics analysis. It indicates that track pitch and sprocket pitch are the critical process parameters. A field test was performed to excavate the cause of chassis vibration. Compared with simulation results, the proposed contact model can effectively simulate the high-frequency excitation applied on a tracked vehicle. To improve its service life, a suggestion for the sprocket and track design is developed to fully use the sub-pitch meshing.