arXiv subjects

Shravan Pradeep

Publications and source records attributed to Shravan Pradeep.

7 recordsLinked to original sources

arXiv2026

Emergence of Purely Elasto-Plastic Turbulence in Shear Flows

We observe the emergence of a distinct, elasticity-driven flow state in a yield-stress fluid in the absence of inertia. Numerical simulations show that this elasto-plastic turbulent state is characterized by a broad spectrum of fluctuations in velocity and stress. Results show a non-monotonic relationship between the volume fraction of the unyielded flow and plasticity. Surprisingly, we find that above a critical value of plasticity, the system can fluidize. Our results reveal the complex interplay between elasticity and plasticity in simple shear flows, indicating that plasticity can enhance rather than hinder momentum transport.

physics.flu-dyn↗

arXiv2025

Geomimicry: Emergent Dynamics in Earth-Mediated Complex Materials

Soils and sediments are soft, amorphous materials with complex microstructures and mechanical properties, that are also building blocks for industrial materials such as concrete. These Earth-mediated materials evolve under prolonged environmental pressures like mechanical stress, chemical gradients, and biological activity. Here, we introduce geomimicry, a new paradigm for designing sustainable materials by learning from the emergent and adaptive dynamics of Earth-mediated matter. Drawing a parallel to biomimicry, we posit that these geomaterials follow evolutionary design rules, adapting their structure and function in response to persistent natural forces through locally evolved interactions and compositions. Our central argument is that by decoding these rules - primarily through understanding the emergence of novel exotic properties from multiscale interactions between heterogenous components - we can engineer a new class of adaptive, sustainable matter. We propose two complementary approaches here. The top-down approach looks to nature to identify building blocks and map them to functional groups defined by their mechanical behaviors, and then examine how environmental training tunes interactions among these groups. The bottom up approach seeks to leverage and test this framework, building earth materials one component at a time under fluctuating environmental stresses that guide assembly of complex and out-of-equilibrium materials. The goal is to create materials with programmed functionalities, such as erosion resistance or self-healing capabilities. Geomimicry offers a pathway to re-imagine climate-resilient soils and precision agriculture to new insights into planetary terraforming, fundamentally shifting the focus from static compositions to dynamic, evolving systems that are mediated via their environment.

cond-mat.soft↗

arXiv2023

Origins of complexity in the rheology of Soft Earth suspensions

When wet soil becomes fully saturated by intense rainfall, or is shaken by an earthquake, it may fluidize catastrophically. Sand-rich slurries are treated as granular suspensions, where the failure is related to an unjamming transition. Mud flows are modeled as gels, where yielding and shear-thinning behaviors arise from inter-particle attraction and clustering. Here we show that the full range of complex flow behaviors previously reported for natural debris flows can be reproduced with three ingredients: water, silica sand, and kaolin clay. Going from sand-rich to clay-rich suspensions, we observe continuous transition from brittle to ductile yielding. We propose a general constitutive relation for soil suspensions, with a particle rearrangement time that is controlled by yield stress and jamming distance. Our experimental results are supported by models for amorphous solids, suggesting that the paradigm of non-equilibrium phase transitions can help us understand and predict the complex behaviors of Soft Earth suspensions.

cond-mat.soft↗

arXiv2023

Sedimentation dynamics of passive particles in dilute bacterial suspensions: emergence of bioconvection

Microorganisms are ubiquitous in nature and technology. They inhabit diverse environments ranging from small river tributaries and lakes to oceans, as well as wastewater treatment plants and food manufacturing. In many of these environments, microorganisms coexist with settling particles. Here, we investigate the effects of microbial activity (swimming \textit{E. coli}) on the settling dynamics of passive colloidal particles using particle tracking methods. Our results reveal the existence of two distinct regimes in the correlation length scale ($L_u$) and the effective diffusivity of the colloidal particles ($D_{e\!f\!f}$), with increasing bacterial concentration ($ϕ_b$). At low $ϕ_b$, the parameters $L_u$ and $D_{e\!f\!f}$ monotonically increases with increasing $ϕ_b$. Beyond a critical $ϕ_b$, second regime is found in which both $D_{e\!f\!f}$ and $L_u$ are independent of $ϕ_b$. We demonstrate that the transition between these regimes is characterized by the emergence of bioconvection. We use experimentally-measured particle-scale quantities ($L_u$, $D_{e\!f\!f}$) to predict the critical bacterial concentration for the diffusion-bioconvection transition.

physics.flu-dyn↗

arXiv2022

Understanding the rheology of kaolinite clay suspensions using Bayesian inference

Mud is a suspension of fine-grained particles (sand, silt, and clay) in water. The interaction of clay minerals in mud gives rise to complex rheological behaviors, such as yield stress, thixotropy and viscoelasticity. Here, we experimentally examine the flow behaviors of kaolinite clay suspensions, a model mud, using steady shear rheometry. The flow curves exhibit both yield stress and rheological hysteresis behaviors for various kaolinite volume fractions ($ϕ_k$). Further understanding of these behaviors requires fitting to existing constitutive models, which is challenging due to numerous fitting parameters. To this end, we employ a Bayesian inference method, Markov chain Monte Carlo (MCMC), to fit the experimental flow curves to a microstructural viscoelastic model. The method allows us to estimate the rheological properties of the clay suspensions, such as viscosity, yield stress, and relaxation time scales. The comparison of the inherent relaxation time scales suggests that kaolinite clay suspensions are strongly viscoelastic and weakly thixotropic at relatively low $ϕ_k$, while being almost inelastic and purely thixotropic at high $ϕ_k$. Overall, our results provide a framework for predictive model fitting to elucidate the rheological behaviors of natural materials and other structured fluids.

cond-mat.soft↗

arXiv2021

Phase-separation during sedimentation of dilute bacterial suspensions

Numerous natural systems depend on the sedimentation of passive particles in presence of swimming microorganisms. Here, we investigate the dynamics of the sedimentation of spherical colloids at various E. coli concentration within the dilute regime. Results show the appearance of two sedimentation fronts, a spherical particle front and the bacteria front. We find that the bacteria front behave diffusive at short times, whereas at long times decays linearly. The sedimentation speed of passive particles decays at a constant speed and decreases as bacteria concentration ($\phi_b$) is increased. As $\phi_b$ is increased further, the sedimentation speed becomes independent of $\phi_b$. The timescales of the bacteria front is associated with the particle settling speeds. Remarkably, all experiments collapse onto a single master line by using the bacteria front timescale. A phenomenological model is proposed that captures the sedimentation of passive particles in active fluids.

cond-mat.soft↗

arXiv2021

Jamming Distance Dictates Colloidal Shear Thickening

We report experimental and computational observations of dynamic contact networks for colloidal suspensions undergoing shear thickening. The dense suspensions are comprised of sterically stabilized poly(methyl methacrylate) hard sphere colloids that are spherically symmetric and have varied surface roughness. Confocal rheometry and dissipative particle dynamics simulations show that the shear thickening strength scales exponentially with the scaled deficit contact number and the scaled jamming distance. Rough colloids, which experience additional tangential and rolling constraints, require an average of 1.5 - 2 fewer particle contacts as compared to smooth colloids, in order to generate the same shear thickening strength. This is because the surface roughness enhances geometric friction in a way that the rough colloids do not experience a large change in the free volume near the jamming point. In contrast, smooth colloids must undergo significant reduction in the free volume to support an equivalent shear stress. The available free volume for different colloid roughness is related to the deficiency from the maximum number of nearest neighbors at jamming under shear. Our results further suggest that the force per contact is different for particles with different morphologies.

cond-mat.soft↗