Modeling the random fiber distribution of a fiber-reinforced composite is of great importance for studying the progressive failure behavior of the material on the micro scale. In this paper, we develop a new algorithm for generating random representative volume elements (RVEs) with statistical equivalent fiber distribution against the actual material microstructure. The realistic statistical data is utilized as inputs of the new method, which is archived through implementation of the probability equations. Extensive statistical analysis is conducted to examine the capability of the proposed method and to compare it with existing methods. It is found that the proposed method presents a good match with experimental results in all aspects including the nearest neighbor distance, nearest neighbor orientation, Ripley’s K function, and the radial distribution function. Finite element analysis is presented to predict the effective elastic properties of a carbon/epoxy composite, to validate the generated random representative volume elements, and to provide insights of the effect of fiber distribution on the elastic properties. The present algorithm is shown to be highly accurate and can be used to generate statistically equivalent RVEs for not only fiber-reinforced composites but also other materials such as foam materials and particle-reinforced composites.

Membrane-type acoustic metamaterial (MAM) has exhibited superior sound isolation properties, as well as thin and light characteristics. However, the anti-resonance modes of traditional MAMs are generated intermittently in a wide frequency range causing discontinuities in the anti-resonance modes. Achieving broadband low-frequency sound attenuation with lightweight MAM design is still a pivotal research aspect. Here, we present a strategy to realize wide sound-attenuation bands in low frequency range by introducing the design concept of bionic configuration philosophy into the MAM structures. Built by a polymeric membrane and a set of resonators, two kinds of MAM models are proposed based on the insight of a spider web topology. The sound attenuation performance and physical mechanisms are numerically and experimentally investigated. Multi-state anti-resonance modes, induced by the coupling of the bio-inspired arrangement and the host polymer film, are systematically explored. Significant sound attenuation is numerically and experimentally observed in both the lightweight bio-inspired designs. Remarkably, compared with a traditional MAM configuration, a prominent enhancement in both attenuation bandwidth and weight-reduction performance is verified. In particular, the bio-inspired MAM Model I exhibits a similar isolation performance as the reference model, but the weight is reduced by nearly half. The bio-inspired Model II broadens the sound attenuation bandwidth greatly; meanwhile, it retains a lighter weight design. The proposed bio-inspired strategies provide potential ways for designing sound isolation devices with both high functional and lightweight performance.

This paper, based on the CFD-DPM model coupled with sliding grid technology, constructs a simulation analysis method for the aerodynamic effects of propellers and wings under heavy rainfall. The mechanism of the influence of raindrops on the aerodynamic characteristics of this configuration is deeply analyzed, and the influence of the laws of different rainfall parameters is explored. The conclusion indicates that the local attack angle of the propeller decreases due to the influence of the falling speed of raindrops, resulting in a decrease in blade thrust and a maximum loss of 2.35%. The torque increases due to the increase in the rotational drag of the propeller. The maximum torque increment reaches 2.15%. With a decrease in the local angle of the attack and the effects of raindrop impact, film covering, and splashing, the maximum lift loss is 1.84%, and the drag increases by more than 12%. Raindrops will further influence the pitching, rolling, and yawing moment variation effect, combined with the rotation of the propeller. The greater the terminal velocity, diameter, and rainfall are, close to the surface of the propeller–wing combination configuration, the more severe the deterioration of the blade performance, and the stronger the lift reduction, drag increase, and moment variation effects of the wing.

Aircraft structural design is undergoing a profound transformation driven by increasingly demanding requirements in lightweight construction