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We investigated the damping mechanism of granular material dampers when using a structure with a relatively high natural frequency and small vibration displacement as the target of vibration damping. For powder or granular material dampers, the movement of the powder or granular material is the basic principle of damping. Damping ratios were calculated and compared by individually modifying each parameter (other than diameter) that affects the granule’s motion. As a result, it was found that when the moment of inertia of the granules is 1/2 and the Young's modulus is 1/100 of steel, the damping effect is improved in the region where the total body weight is heavy. In addition, as a specific example of reducing the moment of inertia and optimizing Young’s modulus, when the effect was examined by calculation and experiment using rubber ball with steel core, it was found that the damping ratio can be improved in the region where the total mass of the granules is large. Furthermore, we obtained new knowledge that the hardening spring characteristics of rubber balls containing steel balls have a positive effect on damping characteristics.

Gravitational instability, which is a typical example of hydrodynamic instabilities, occurs due to density difference. When a heavy fluid lies over a light fluid in a constant gravitational field, fluctuations at the interface gradually increase and then macroscopic flows occur. The gravitational instability can be found not only in liquid-liquid interface but also in the gravitational settling of granular materials. However, the gravitational instability of liquid systems and granular systems have been discussed individually in most cases. We quantitatively find a close relationship of the gravitational instability between the physical gel and granular systems. We also find that those behaviors are determined by the thickness of the fluidization region. [ABSTRACT FROM AUTHOR]

In this study, we have performed 3D DEM simulations about granular packings with slow tilt motion. It would be expected to obtain more detailed destabilization processes of tilting granular layers using numerical simulations than using experimental methods. Our simulation results agreed well with some experimental results about rearrangements of the particles at the surface layer. Most of the previous studies relate stability of the packings with mobilization of friction forces between the particles. However our simulation results show that the mobilization of friction forces does not change when the tilt angle increases up to 10° and further, the correlation between the mobilization of friction forces and global stability is insignificant. However, the direction of contacts and distribution of contact forces changed during our simulation time. Our simulation results indicate that we can estimate stability of the packings through contact forces and their directions rather than the mobilization of friction forces. [ABSTRACT FROM AUTHOR]

We investigated the damping mechanism of a granular-material damper for a structure with a high natural frequency. We focused on the flow of the granular-material vibration energy and considered its relationship with the damping characteristics. The movement of spherical granular materials was calculated in the granular-material damper; the power of the collision force and the frictional force exerted by the granular materials on the primary vibration system were obtained and compared with the input energy. In the region in which the total mass of the granular materials was small, the collision force that the granular materials exerted on the primary vibration system affected the damping characteristics of the granular-material damper. Conversely, in the region in which the total mass of the granular materials was large, the frictional force that the granular materials exerted on the primary vibration system in addition to the impact force affected the damping characteristics of the granular-material damper. That is, the vibration of the primary vibration system is primarily affected by the collision of the granular materials on the left and right container walls, and by the energy consumption caused by the friction of the granular materials on the bottom of the container. By using the quantities of energy consumed in both collisions and frictions, it is possible to evaluate the damping characteristics of the granular-material damper.

Plate penetration into dry granular materials is numerically studied using a large-scale discrete element method (DEM). To investigate the effects penetration angle on the interactions between particles and the plate, the simulations with the different angles from 0 (vertical penetration) to 60 degree are compared. The results show that the drag force acting on the plate increases with a decrease in the penetration angle. For all cases, the formation of shear bands from the plate tip to the free surface in the bed is confirmed. The analysis of energy consumption in the bed shows that most of the energy input to the bed by the plate is locally dissipated by sliding frictions between particles in shear bands. As the penetration angle decreases, the amount of energy dissipation due to the friction increases in the shear bands formed near the plate tip. [ABSTRACT FROM AUTHOR]

The interaction between dry granular materials and a plate is numerically studied using a large-scale discrete element method (DEM) simulation. In the simulation, a vertical flat plate is dragged horizontally through closely packed materials. To examine the effects of particle size on the drag force acting on the plate, five cases with different mean particle diameter Dp50 = 4.0, 2.0, 1.6, 1.2 and 0.8 mm are compared. The results show that for larger particles, the force randomly fluctuates as the plate advances while for smaller particles, the force oscillates with a larger amplitude. The analysis of angular velocity of the particles shows that the force oscillation is attributed to the evolution of shear bands formed only in the bed of the smaller particles. [ABSTRACT FROM AUTHOR]

Tangent line method and Twomey’s non-linear iteration method are applied to retrieve a particle size distribution from the sedimentation curve measured with a sedimentation distance in sedimentation tube. It is found that it is difficult to calculate the particle size distribution by the tangent line method using the sedimentation curve drawn from visual observation of the interface. On the other hand, the particle size distribution can be predicted numerically by Twomey method although the reliability is low. In order to improve the measurement accuracy, improved method to define the sedimentation interface using image analysis is investigated. Furthermore, introduction of correction term to Twomey method improves the reliability of the particle size distribution. As a results, this calculation method can be applied to measure particle size distribution not only for glass beads but also suspension concentrate of agricultural fungicide penthiopyrad. [ABSTRACT FROM AUTHOR]

We investigated the damping mechanism of a granular material damping system applied to reducing vibration in structures that have a high natural frequency and small vibration displacement. Experiments were conducted under several conditions of total mass of granules. We also constructed a computational model of a single-degree-of-freedom vibration system with a granular material damper to study the mechanism of a granular material damping system. On the basis of the fundamental idea that the damping effect of a granular material damper is governed by the motion of the granules, we classified the granular materials as “relative motion mass” and “equivalent added mass” in the translational motion and as “rotating mass” and “not rotating mass” in the rotational motion and then considered the relationship of these mass classes to the damping characteristics. In this report, we examine the relationships of the motion of the granular materials, “relative motion mass” and “rotating mass”, and damping ratio by means of experiments and calculations for structures that have a high natural frequency and small vibration displacement.

FePt thin films with L10 ordered structure are candidates for high-density magnetic recording media because of their high uniaxial magnetic anisotropy energy. The (Fe0.395Pt0.395Cu0.15P0.02Pd0.04)100-xSbx thin films with various x were deposited directly on quartz glass substrates by a sputtering method. FePt ordered alloy thin films with (001) preferential orientation were achieved in Sb content of x ≥ 8.0 at.% with post-annealing at 600°C for 1 hour under reduced pressure in a H2 atmosphere. However, the coercivity of these thin films decreased dramatically due to growing of the crystal grains. Therefore, in this study, we prepared the PdSb-FePt-(C4F8)n granular thin films to improve the coercivity. The Fe0.44Pt0.44Pd0.04Sb0.08-(C4F8)n granular thin film deposited at C4F8 partial pressure of 0.1 mTorr then annealed at 700°C for 1 hour under reduced pressure in a H2 atmosphere exhibited a large coercivity of 30 kOe. [ABSTRACT FROM AUTHOR]