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Open Access Publications from the University of California

Scholarly Works (67 results)

  • Article
  • Peer Reviewed
UC Santa Barbara Previously Published Works (2015)
    Cover page: Mean zonal flow generated by azimuthal harmonic forcing in a rotating cylinder
    • Article
    • Peer Reviewed
    UC Santa Barbara Previously Published Works (2022)
      Creative Commons 'BY-NC-ND' version 4.0 license
      • Article
      • Peer Reviewed
      UC Santa Barbara Previously Published Works (2018)
      Applying mechanical perturbations in a granular assembly may rearrange the configuration of the particles. However, the spatial propagation of an event is not related to the size of the external perturbation alone. Thus, the characteristic length scale of an event is not well defined. In this study, we trigger rearrangements by driving two intruders through a vertical two-dimensional packing of disks. The amplitude of the rearrangements of the granular assembly appearing around the two evolving intruders is related to their separating distances. We show that there exists a characteristic distance between intruders under which the dynamics of the grains above one intruder is influenced by the other. The size of the intruders has little effect on this characteristic length. Finally, we show that the correlation between the movements of the grains decreases with the distance away from the intruders over a larger length scale.
        Cover page: Cooperative effects induced by intruders evolving through a granular medium
        • Article
        • Peer Reviewed
        UC Santa Barbara Previously Published Works (2021)
        The formation of drops of a complex fluid, for instance including dissolved polymers and/or solid particles, has practical implications in several industrial and biophysical processes. In this Letter, we experimentally investigate the generation of drops of a viscoelastic suspension, made of non-Brownian spherical particles dispersed in a dilute polymer solution. Using high-speed imaging, we characterize the different stages of the detachment. Our experiments show that the particles primarily affect the initial Newtonian necking by increasing the fluid viscosity. In the viscoelastic regime, particles do not affect the thinning until the onset of the blistering instability, which they accelerate. We find that the transition from one regime to another, which corresponds to the coil-stretch transition of the polymer chains, strongly depends on the particle content. Considering that the presence of rigid particles increase the deformation of the liquid phase, we propose an expression for the local strain rate in the suspension, which rationalizes our experimental results. This method could enable the precise measurement of local stresses in particulate suspensions.
          Cover page: Pinch-off of viscoelastic particulate suspensions
          • Article
          • Peer Reviewed
          UC Santa Barbara Previously Published Works (2022)
          SignificanceThe pinch-off of a liquid drop extruded from a nozzle is a canonical situation that involves a series of self-similar regimes ending in a finite-time singularity. This configuration allows for exploring capillary flows over a large range of scales. In the case of suspension drops, the presence of particles breaks the self-similarity by introducing a length scale that can be much larger than the particle diameter. This length scale is a signature of the heterogeneities and delimitates a regime, in which a continuum approach of a suspension can be used from a regime where the discrete nature of the particles is involved.
            Cover page: The onset of heterogeneity in the pinch-off of suspension drops
            • Article
            • Peer Reviewed
            UC Santa Barbara Previously Published Works (2024)
              Creative Commons 'BY' version 4.0 license
              • Thesis
              • Peer Reviewed
              UC Santa Barbara Electronic Theses and Dissertations (2024)

              The flow of suspensions of particles in confined systems is ubiquitous in both natural and industrial contexts, ranging from extrusion-based additive manufacturing to water infiltration in soil. However, characterizing and modeling the underlying physics, especially when the size of a constriction is similar to that of the suspended particles, remains a challenge. This PhD work has considered the interplay of particles with two distinct types of confinements featuring: soft and hard.

              Soft confinements refer to deformable liquid-air interfaces, such as the ones involved in coating processes. Two processes sharing common features are considered: withdrawing a suspension from a capillary tube, leaving a thin film on the inner wall, and dip-coating, which consists of pulling a solid substrate out of a suspension bath to deposit a thin coating film on the surface. It is demonstrated that the stagnation point at the liquid-air meniscus acts as a tunable "filter" that governs the thickness of the coating film. The local thickness controls whether particles of a certain size will be deposited in the film or repelled back to the suspension bath. The deposition threshold of single spherical and anisotropic particles is investigated, and based on these findings, a filtration method for sorting particles of various sizes and guidelines for controlling the composition of the suspension film are proposed.

              The discussion then shifts to the flow of suspension through hard confinements in millifluidic channels, where particles are confined within solid walls. The research focuses on the clogging mechanism known as bridging, where particles of a size comparable to the constriction form a stable arch, blocking the channel and prevent further particle transport. Through experimental investigations, the influence of the geometry of the constriction, including its size and angle, on the particle throughput before the formation of a clog is characterized. Additionally, unique clogging phenomena observed in three-dimensional systems are explored.

                • Article
                • Peer Reviewed
                UC Santa Barbara Previously Published Works (2017)
                The resuspension and dispersion of particles occur in industrial fluid dynamic processes as well as environmental and geophysical situations. In this paper, we experimentally investigate the ability to fluidize a granular bed with a vertical gradient of temperature. Using laboratory experiments with a localized heat source, we observe a large entrainment of particles into the fluid volume beyond a threshold temperature. The buoyancy-driven fluidized bed then leads to the transport of solid particles through the generation of particle-laden plumes. We show that the destabilization process is driven by the thermal conductivity inside the granular bed and demonstrate that the threshold temperature depends on the thickness of the granular bed and the buoyancy number, i.e., the ratio of the stabilizing density contrast to the destabilizing thermal density contrast.
                  Cover page: Resuspension threshold of a granular bed by localized heating
                  • Article
                  • Peer Reviewed
                  UC Santa Barbara Previously Published Works (2021)
                  Abstract:
                    Cover page: Falling jet of dry granular material in water
                    • Article
                    • Peer Reviewed
                    UC Santa Barbara Previously Published Works (2014)
                    In this Letter, we experimentally investigate the collapse of initially dry granular media into water and the subsequent impulse waves. We systematically characterize the influence of the slope angle and the granular material on the initial amplitude of the generated leading wave and the evolution of its amplitude during the propagation. The experiments show that whereas the evolution of the leading wave during the propagation is well predicted by a solution of the linearized Korteweg-de Vries equation, the generation of the wave is more complicated to describe. Our results suggest that the internal properties of the granular media and the interplay with the surrounding fluid are important parameters for the generation of waves at low velocity impacts. Moreover, the amplitude of the leading wave reaches a maximum value at large slope angle. The runout distance of the collapse is also shown to be smaller in the presence of water than under totally dry conditions. This study provides a first insight into tsunamis generated by subaerial landslides at low Froude number.
                      Cover page: Tsunami generated by a granular collapse down a rough inclined plane
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