Granular dampers are systems used to attenuate undesired vibrations produced by mechanical devices. They consist of cavities filled by granular particles. In this work, we consider a granular damper filled with a binary mixture of frictionless spherical particles of the same material but different size using numerical discrete element method simulations. We show that the damping efficiency is largely influenced by the composition of the binary mixture.
We have experimentally investigated the bouncing behavior and damping performance of a container partially filled with granular chains, namely a chain-filled damper. The motion of the chain-filled damper, recorded by a particle tracing technology, demonstrates that the granular chains can efficiently absorb the collisional energy of the damper. We extract both the restitution coefficient of the first collision and the total flight time to characterize the dissipation ability of the damper. Two containers and three types of granular chains, different in size, stiffness and restitution coefficie…
We study analytically and numerically the distribution of granular temperatures in granular mixtures for different dissipation mechanisms of inelastic inter-particle collisions. Both driven and force-free systems are analyzed. We demonstrate that the simplified model of a constant restitution coefficient fails to predict even qualitatively a granular temperature distribution in a homogeneous cooling state. At the same time we reveal for driven systems a stunning result -- the distribution of temperatures in granular mixtures is universal. That is, it does not depend on a particular dissipation…
Using particle trajectory data obtained from x-ray tomography, we determine two kinds of effective temperatures in a cyclically sheared granular system. The first one is obtained from the fluctuation-dissipation theorem which relates the diffusion and mobility of lighter tracer particles immersed in the system. The second is the Edwards compactivity defined via the packing volume fluctuations. We find robust excellent agreement between these two temperatures, independent of the type of the tracers, cyclic shear amplitudes, and particle surface roughness. We further elucidate that in granular s…
We study the dynamic process occurring when a granular assembly is displaced by a solid impactor. The momentum transfer from the impactor to the target is shown to occur through sporadic, normal collisions of high force carrying grains at the intruder surface. We therefore describe the stopping force of the impact through a collisional based model. To verify the model in impact experiments, we determine the forces acting on an intruder decelerating through a dense granular medium using high-speed imaging of its trajectory. By varying the intruder shape and granular target, intruder-grain inter…
Stress induced yielding/fluidization in disordered solids, characterized by irreversibility and enhanced dissipation, is important for a wide range of industrial and geological processes. Although, such phenomena in thermal systems have been extensively studied, they remain poorly understood for granular solids. Here, using oscillatory shear rheology and in-situ optical imaging, we study energy dissipation in a dense granular suspension of adhesive particles that forms yield stress solids far below the isotropic jamming point obtained in the limit of hard-sphere repulsion. We find interesting …
We report a joint experimental and theoretical investigation of cyclic training of amorphous frictional granular assemblies, with special attention to memory formation and retention. Measures of dissipation and compactification are introduced, culminating with a proposed scaling law for the reducing dissipation and increasing memory. This scaling law is expected to be universal, insensitive to the details of the elastic and frictional interactions between the granules.
The impact-induced energy transfer and dissipation in granular targets without any confining walls are studied by microgravity experiments. A solid projectile impacts into a granular target at low impact speed ($0.045 \leq v_p \leq 1.6$~m~s$^{-1}$) in a laboratory drop tower. Granular clusters consisting of soft or hard particles are used as targets. Porous dust agglomerates and glass beads are used for soft and hard particles, respectively. The expansion of the granular target cluster is recorded by a high-speed camera. Using the experimental data, we find that (i)~a simple energy scaling can…
We study, via DEM simulations, the apparent mass $m$ and loss factor $η$ of particle dampers (PD) attached to a vertically driven, single degree of freedom mechanical system. Although many studies focus on $η$, less work has been devoted to $m$. It has been recently demonstrated [M. Masmoudi \textit{et al}. Granular Matter 18 (2016) 71.] that $m$ non-linearly depends on the driving acceleration $γ$ according to a power law, $m\proptoγ^k$. Experiments using 3D packings of particles suggest $k=-2$. However, simulations with 1D columns of particles on a vibrating plate and theoretical predictions…
根据玻尔兹曼方程并考虑到最近在法国国家空间研究中心和欧空局的几次活动中的微重力实验结果，讨论了颗粒耗散气体理论[9，11]。这是回顾，玻尔兹曼的分布是一个稳定的解决方案，只有当碰撞是弹性的，因此它是不适用的情况下，耗散颗粒气体。第一个实验的情况下，非相互作用的球在一个振动的圆柱形盒子，这证明了旋转引起的耗散有重要的后果：它减少了有效的相空间维数从13-d到1-d，这个台球状系统，因为运动是1d和准周期足够大的迫使;结果仍然有效，与2个球。第二个实验是关于小颗粒数（N= 12，24，36，48）情况下相互作用粒子的动力学：球的典型速度随活塞速度线性变化，但随着球数N的增加而减小。在连续的球规碰撞之间的等待时间T1的分布遵循指数分布实验，即P（T1）= exp（-T1/To），证明不相关的球的运动。发现球规碰撞的振幅I呈指数衰减p（I）=exp（-I/Io），用与“velostat”概念相联系的“a la Boltzmann”模型对此作了暂时解释，并提出了基于耗散的第二个模型。实验表明，在碰撞过程中，旋转和平移之间的耦合不可忽略，因为它产生有效的耗散。
Energy dissipation in sheared dry and wet granulates is considered in the presence of an externally applied confining pressure. Discrete element simulations reveal that for sufficiently small confining pressures, the energy dissipation is dominated by the effects related to the presence of cohesive forces between the particles. The residual resistance against shear can be quantitatively explained by a combination of two effects arising in a wet granulate: i) enhanced friction at particle contacts in the presence of attractive capillary forces, and ii) energy dissipation due to the rupture and …
Department of Mechanical Engineering, Massachusetts Institute of Technology（麻省理工学院机械工程系）；Department of Mechanical Engineering, University of California Berkeley（加州大学伯克利分校机械工程系）
The viscosity of suspensions of large ($\geq10{μm}$) particles diverges at high solid fractions due to proliferation of frictional particle contacts. Reducing friction, to allow or improve flowability, is usually achieved by tuning the composition, either changing particle sizes and shapes or by adding lubricating molecules. We present numerical simulations that demonstrate a complementary approach whereby the viscosity divergence is shifted by driven flow tuning, using superimposed shear oscillations in various configurations to facilitate a primary flow. The oscillations drive the suspension…
In this article, we study the spreading of droplets of density-matched granular suspensions on the surface of a solid. Bidispersity of the particle size distribution enriches the conclusions drawn from monodisperse experiments by highlighting key elements of the wetting dynamics. In all cases, the relation between the dynamic contact angle and the velocity of the contact line follows a similar relation as that of a simple fluid, despite the complexity introduced by the presence of particles. We extract from this relation an apparent wetting viscosity of the suspensions that differs from that m…
The paper addresses a common assumption of elastoplastic modeling: that the recoverable, elastic strain increment is unaffected by alterations of the elastic moduli that accompany loading. This assumption is found to be false for a granular material, and discrete element (DEM) simulations demonstrate that granular materials are coupled materials at both micro- and macro-scales. Elasto-plastic coupling at the macro-scale is placed in the context of thermomechanics framework of Tomasz Hueckel and Hans Ziegler, in which the elastic moduli are altered by irreversible processes during loading. This…
