Granular mixtures with tailored damping properties

背景：噪声和振动/共振是许多工业和地球工程应用中的缺点。公路、铁路或地震产生的声波通过“粒状”材料(如土壤、混凝土或沥青)传播，集料的特性影响着到达波的速度、振幅衰减和频率。什么？/新颖性/原创性：在这个创新的项目中，作为思想的改变者，我们提议将材料/土壤转变为“颗粒状阻尼器”。通过调节(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，我们将致力于增强衰减、量身定制衰减，并在所需的频率范围内设计能最好地利用阻尼的带隙。如何？/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，对阻尼/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，形成一个全面的颗粒混合物降阶理论模型，该模型预测影响振动，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，我们一直在研究由软颗粒和硬颗粒组成的颗粒混合物在各种静水应力条件下的波传播和衰减。重点研究了由单分散玻璃和橡胶珠组成的集料的弹性和耗散性能，以及外加应力和橡胶含量之间的相互作用。有趣的是，实验表明，通过适量的软夹杂物，可以获得与原始材料相同(甚至更高)的硬度，但更轻且具有相当强的阻尼性的丰富材料。工作计划：首先，我们将研究粒度比、刚度比和软夹杂物含量对颗粒混合料减振性能的综合影响。利用频率-空间分析，我们将解开粒子与系统参数、能量吸收/衰减频率之间的关系，并建立一个降阶随机模型(主方程)来描述波能量在空间和时间上的演化。这里的新奇之处在于对频带进行分组，而不是只关注低频本征值，因为尤其是高频可能与减振应用更相关。

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.