Granular mixtures with tailored damping properties

背景：噪声和振动/共振在许多工业和地质工程应用中构成缺点。公路、铁路或地震产生的声波通过“颗粒”材料（如土壤、混凝土或沥青）传播，骨料的特性影响到达波的速度、振幅阻尼和频率。什么？新奇/独创性：在这个创新项目中，作为一个思想改变者，我们建议将材料/土壤变成“颗粒阻尼器”。通过调整（双分散和三分散）硬软材料混合物中的颗粒特性和物种组成，我们的目标是提高阻尼，定制衰减和设计所需频率范围内的带隙，其中阻尼可以得到最好的利用。怎么做？方法：我们将从两个方面解决这个问题：在广泛的应力水平下，阻尼/弹性材料行为的物理实验将与先进的基于粒子的数值模拟相结合，为颗粒混合物提供一个全面的降阶理论模型，预测影响振动，并可用于测试，改进和优化材料，建筑或垃圾填埋场/土壤的新设计。前期工作/经验：在过去的几年里，我们一直在研究波的传播和阻尼的颗粒混合物的软，硬颗粒受到各种静水应力条件。重点是由单分散玻璃和橡胶珠制成的骨料的弹性和耗散特性以及施加的应力和橡胶含量之间的相互作用。有趣的是，实验表明，通过最佳数量的软夹杂物，可以获得一个丰富的材料，具有相同的（甚至更高）的刚度比原来的，但更轻，并具有相当强的damping. Work计划：首先，我们将研究粒度比，刚度比和软含量的阻尼行为的颗粒混合物的综合影响。利用频率空间分析，我们将解开粒子和系统参数，能量吸收/阻尼频率之间的关系，并制定一个降阶随机模型（主方程）的能量在空间和时间的演变。这里的新奇是将频带分组而不是仅关注低频本征值，因为特别是较高的频率可能与阻尼应用更相关。

Background: Noise and vibration/resonance constitute a drawback in many industrial and geo-engineering applications. Acoustic waves produced on roads, railways or by earthquakes propagate through “granular” materials (like soil, concrete or asphalt), with the characteristics of the aggregate affecting the velocity, amplitude-damping and frequencies of the arrival wave. What?/novelty/originality: In this innovative project, as a mind-changer, we propose to turn materials/soil into “granular dampers”. By tuning particle properties and species compositions in (bi- and tri-disperse) stiff-soft material mixtures, we will aim to enhance damping, tailor attenuation and to design band gaps in desired frequency ranges, where the damping can be best exploited. How?/Approach: We will attack the problem from two sides: physical experiments on the damping/elastic material behaviour, at a wide range of stress-levels, will be combined with advanced particle-based numerical simulations to inform a comprehensive reduced order theoretical model for granular mixtures that predicts the influence vibrations, and can be applied to test, improve and optimize novel designs for materials, constructions, or landfill/soils. Preliminary work/experience: In the past years, we have been studying wave propagation and damping in granular mixtures made of soft and stiff particles subjected to various hydrostatic stress conditions. Focus was on the elastic and dissipative properties of aggregates made of monodisperse glass and rubber beads and the interplay between applied stress and rubber content. Interestingly, the experiments showed that by an optimal amount of soft inclusions one can obtain an enriched material, with the same (or even higher) stiffness than the original, yet lighter and with considerably stronger damping.Work-plan: First, we will study the combined influence of size ratio, stiffness ratio and soft content on the damping behaviour of granular mixtures. Using frequency-space analysis, we will unravel the relation between particle and system parameters, energy absorbed/damped frequencies and formulate a reduced order stochastic model (master equation) for the evolution of the energy of waves in space and time. Novelty here is to group frequency bands instead of focusing on the low frequency eigen-values only, since especially the higher frequencies might be more relevant for damping applications.