arXiv subjects

H. Katsuragi

Publications and source records attributed to H. Katsuragi.

31 records · Page 2Linked to original sources

arXiv2016

Geometry-dependent constitutive law for granular slow frictional drag

Frictional constitutive law for very slow vertical withdrawing of a thin rod from a granular bed is experimentally studied. Using a very precise creep meter, geometry-dependent granular frictional constitutive law is particularly examined. In some previous works, a dimensionless number $I=\dotγD_g/\sqrt{p/ρ_g}$ has been used to characterize granular frictional constitutive laws, where $\dotγ$, $D_g$, $p$, and $ρ_g$ are the shear strain rate, grain diameter, confining pressure, and bulk density of granular bed, respectively. It has been considered that granular frictional constitutive law expressed by $I$ is universal (almost geometry-independent) in dense flow regime. In this study, however, we find that the geometry of the system is much more crucial to characterize granular friction in a very slow withdrawing regime. Specifically, the ratio between rod and grain diameters must be an essential parameter to describe the granular frictional constitutive law. Physical meaning of the geometry-dependent constitutive law is discussed on the basis of grains-contact-number dependence of granular behavior.

cond-mat.soft↗

arXiv2016

Sensitivity of Granular Force Chain Orientation to Disorder-induced Metastable Relaxation

A two-dimensional system of photoelastic disks subject to vertical tapping against gravity was experimentally monitored from ordered to disordered configurations by varying bidispersity. The packing fraction $ϕ$, coordination number $Z$, and an appropriately defined force chain orientational order parameter $S$, all exhibit similar sharp transition with small increase in disorder. A measurable change in $S$, but not $ϕ~\&~Z$, was detected under tapping. We find disorder-induced metastability does not show configurational relaxation, but can be detected via force chain reorientations.

cond-mat.soft↗

arXiv2014

Fingering induced by a solid sphere impact to viscous fluid

The number of splashed fingers generated by a solid projectile's impact onto a viscous liquid layer is experimentally studied. A steel sphere is dropped onto a viscous liquid pool. Then, a fingering instability occurs around the crater's rim, depending on the experimental conditions such as projectile's inertia and the viscosity of the target liquid. When the impact inertia is not sufficient, any fingering structure cannot be observed. Contrastively, if the impact inertia is too much, the random splashing is induced and the counting of fingers becomes difficult. The clear fingering instability is observable in between these two regimes. The number of fingers $N$ is counted by using high-speed video data. The scaling of $N$ is discussed on the basis of dimensionless numbers. By assuming Rayleigh-Taylor instability, scaling laws for $N$ can be derived using Reynolds number $Re$, Weber number $We$, and Froude number $Fr$. Particularly, the scaling $N=(ρ_r Fr)^{1/4}We^{1/2}/3^{3/4}$ is obtained for the gravity-dominant cratering regime, where $ρ_r$ is the density ratio between a projectile and a target. Although the experimental data considerably scatters, the scaling law is consistent with the global trend of the data behavior. Using one of the scaling laws, planetary nano crater's rim structure is also evaluated.

physics.flu-dyn↗

arXiv2013

Drag force scaling for penetration into granular media

Impact dynamics is measured for spherical and cylindrical projectiles of many different densities dropped onto a variety non-cohesive granular media. The results are analyzed in terms of the material-dependent scaling of the inertial and frictional drag contributions to the total stopping force. The inertial drag force scales similar to that in fluids, except that it depends on the internal friction coefficient. The frictional drag force scales as the square-root of the density of granular medium and projectile, and hence cannot be explained by the combination of granular hydrostatic pressure and Coulomb friction law. The combined results provide an explanation for the previously-observed penetration depth scaling.

cond-mat.soft↗

arXiv2011

Control of polymer gel surface pattern formation and its three dimensional measurement method

We report the controllability of a gelation surface pattern formation. Recently, we have found and studied a novel kind of pattern formation that occurs during a radical polymerization (gelation) process. The pattern formation is observed in an open top boundary of quasi two dimensional gelation. In previous studies, we have used two dimensional photo based image processing to analyze the patterns. However, the actual pattern is a three dimensional surface deformation. Thus we develop a three dimensional measurement system using a line laser displacement sensor and an automatic x-stage. Patterns measured by the system are analyzed and discussed by means of pattern controllability. In particular, we focus on the possibility of the pattern control using an external temperature field. As a result, we reveal that the global structure can be controlled, whereas the characteristic length scales (wavelength and amplitude) are not controllable.

nlin.PS↗

arXiv2011

The effective surface roughness scaling of the gelation surface pattern formation

The surface pattern formation on a gelation surface is analyzed using an effective surface roughness. The spontaneous surface deformation on DiMethylAcrylAmide (DMAA) gelation surface is controlled by temperature, initiator concentration, and ambient oxygen. The effective surface roughness is defined using 2-dimensional photo data to characterize the surface deformation. Parameter dependence of the effective surface roughness is systematically investigated. We find that decrease of ambient oxygen, increase of initiator concentration, and high temperature tend to suppress the surface deformation in almost similar manner. That trend allows us to collapse all the data to a unified master curve. As a result, we finally obtain an empirical scaling form of the effective surface roughness. This scaling is useful to control the degree of surface patterning. However, the actual dynamics of this pattern formation is not still uncovered.

nlin.PS↗

arXiv2010

Morphology Scaling of Drop Impact onto a Granular Layer

We investigate the impact of a free-falling water drop onto a granular layer. First, we constructed a phase diagram of crater shapes with two control parameters, impact speed and grain size. A low-speed impact makes a deeper cylindrical crater in a fluffy granular target. After high-speed impacts, we observed a convex bump higher than the initial surface level instead of a crater. The inner ring can be also observed in medium impact speed regime. Quantitatively, we found a scaling law for crater radius with a dimensionless number consisting of impact speed and density ratio between the bulk granular layer and water drop. This scaling demonstrates that the water drop deformation is crucial to understand the crater morphology.

cond-mat.soft↗

arXiv2010

Jamming and growth of dynamical heterogeneities versus depth for granular heap flow

We report on grain dynamics versus depth for steady-state gravity-driven flow of grains along a heap formed between two parallel sidewalls. Near the surface the flow is steady and fast, while far below there is no flow whatsoever; therefore, a jamming transition occurs where depth is an effective control parameter for setting the distance from the transition. As seen previously, the time-averaged velocity profile along the sidewall exhibits a nearly exponential decay vs depth. Using speckle-visiblility spectroscopy (SVS), we find that velocity fluctuations grow relative to the average on approach to jamming. Introducing an image-based order parameter and the variance in its temporal decay at a given depth, we also characterize the spatially heterogeneous nature of the dynamics and find that it increases on approach to jamming. In particular, the important time and length scales for dynamical heterogeneities are found to grow almost exponentially as a function of depth. These dynamical changes occur without noticeable change in structure, and are compared to behavior found by experiment and simulation elsewhere in order to test the universality of the jamming concept. In particular we find that the size of the heterogeneities scales as the inertia number raised to the -1/3 power, in agreement with two recent simulations.

cond-mat.soft↗

arXiv2008

Projectile interactions in granular impact cratering

We present evidence for the interactions between a ball and the container boundaries, as well as between two balls, that are mediated by the granular medium during impact cratering. The presence of the bottom boundary affects the final penetration depth only for low drop heights with shallow filling, in which case, surprisingly, the penetration becomes deeper. By contrast the presence of the side wall causes less penetration and also an effective repulsion. Repulsion is also found for two balls dropped side-by-side.

cond-mat.soft↗

arXiv2007

Avalanche statistics and time-resolved grain dynamics for a driven heap

We probe the dynamics of intermittent avalanches caused by steady addition of grains to a quasi-two dimensional heap. To characterize the time-dependent average avalanche flow speed v(t), we image the top free surface. To characterize the grain fluctuation speed dv(t), we use Speckle-Visibility Spectroscopy. During an avalanche, we find that the fluctuation speed is approximately one-tenth the average flow speed, and that these speeds are largest near the beginning of an event. We also find that the distribution of event durations is peaked, and that event sizes are correlated with the time interval since the end of the previous event. At high rates of grain addition, where successive avalanches merge into smooth continuous flow, the relationship between average and fluctuation speeds changes to dv Sqrt[v].

cond-mat.soft↗

arXiv2007

Unified force law for granular impact cratering

Experiments on the low-speed impact of solid objects into granular media have been used both to mimic geophysical events and to probe the unusual nature of the granular state of matter. Observations have been interpreted in terms of conflicting stopping forces: product of powers of projectile depth and speed; linear in speed; constant, proportional to the initial impact speed; and proportional to depth. This is reminiscent of high-speed ballistics impact in the 19th and 20th centuries, when a plethora of empirical rules were proposed. To make progress, we developed a means to measure projectile dynamics with 100 nm and 20 us precision. For a 1-inch diameter steel sphere dropped from a wide range of heights into non-cohesive glass beads, we reproduce prior observations either as reasonable approximations or as limiting behaviours. Furthermore, we demonstrate that the interaction between projectile and medium can be decomposed into the sum of velocity-dependent inertial drag plus depth-dependent friction. Thus we achieve a unified description of low-speed impact phenomena and show that the complex response of granular materials to impact, while fundamentally different from that of liquids and solids, can be simply understood.

cond-mat.soft↗

arXiv2004

Dendritic side-branching with anisotropic viscous fingering

We studied dendritic side-branching mechanism in the experiment of anisotropic viscous fingering. We measured the time dependence of growth speed of side-branch and the envelop of side-branches. We found that the speed of side-branch gets to be faster than one of the stem and the growth exponent of the speed changes at a certain time. The envelope of side-branches is represented as Y ~ X^1.47.

nlin.PS↗

arXiv2002

Asymptotic function for multi-growth surfaces using power-law noise

Numerical simulations are used to investigate the multiaffine exponent $α_q$ and multi-growth exponent $β_q$ of ballistic deposition growth for noise obeying a power-law distribution. The simulated values of $β_q$ are compared with the asymptotic function $β_q = \frac{1}{q}$ that is approximated from the power-law behavior of the distribution of height differences over time. They are in good agreement for large $q$. The simulated $α_q$ is found in the range $\frac{1}{q} \leq α_q \leq \frac{2}{q+1}$. This implies that large rare events tend to break the KPZ universality scaling-law at higher order $q$.

nlin.PS↗