arXiv subjects

Ishan Sharma

Publications and source records attributed to Ishan Sharma.

9 recordsLinked to original sources

arXiv2026

Depth and slip ratio dependencies of friction for a sphere rolling on a granular slope

We experimentally investigate the dynamics of a sphere rolling down a granular slope by varying the initial velocity, slope angle, and sphere density. The results show that the sphere rolls down with constant deceleration while sinking into the granular bed. $\delta/R$ (the sinking depth $\delta$ normalized to the sphere radius $R$) is scaled by the sphere density normalized by the bulk density of the granular layer. To evaluate the translational energy dissipation, we introduce an effective friction coefficient $\mu_\mathrm{d}$. We demonstrate that $\mu_\mathrm{d}$ decreases with increasing the slope angle and the slip ratio. Furthermore, systematic measurements over a wide range of sphere densities reveal that $\mu_\mathrm{d}$ increases linearly with $\delta/R$ : $\mu_\mathrm{d}=\beta(\delta/R)+\mu_0$. The value of $\mu_0$ is linearly decreasing with slip ratio and its coefficient $\beta(\simeq0.41)$ does not vary significantly. The results suggest that the normalized depth and slip ratio determine the effective friction of a rolling sphere.

cond-mat.soft↗

arXiv2025

Axisymmetric landslides on small planetary bodies

We aim to understand how landslides affect the shape and rotational motion of small rubble planetary bodies. We limit ourselves to axisymmetric global landslides, and take the primordial shape of the body to also be axisymmetric. The landslides are modeled through depth-averaging, while also incorporating the effect of the body's rotation, topographical changes due to multiple landslides, the body's non-uniform gravity field and possible surface mass shedding. The body's rotational dynamics is coupled to its shape change due to landsliding, and also includes the action of radiation torque. We utilize our model to investigate regolith motion on actual asteroids. We then study the evolution of the shape and spin state of an initially spherical rubble asteroid due to impact-induced global landsliding events over its lifetime. We find that rotational fission is suppressed by regolith redistribution to the body's equator by landsliding. Furthermore, top shapes are rapidly formed and this may explain the abundance of top-shaped asteroids in near-Earth orbits.

astro-ph.EP↗

arXiv2025

Coupled shape and spin evolution of small near spherical asteroids due to global regolith motion

Recent space missions have provided substantial evidence of regolith movement on the surfaces of near Earth asteroids. To investigate this phenomenon, we present a continuum-based model that describes regolith motion on nearly spherical asteroids. The theoretical framework employs a depth averaged approach, traditionally used for simulating terrestrial landslides, and is extended to include additional terms that account for spherical geometry, shallow topography and the asteroids rotation. The governing equations couple the resurfacing process with the asteroids spin evolution through angular momentum conservation. The axisymmetric form of these equations is then employed to study the transition of an initially spherical asteroid into a top-shaped.

astro-ph.EP↗

arXiv2024

Chatting with Logs: An exploratory study on Finetuning LLMs for LogQL

Logging is a critical function in modern distributed applications, but the lack of standardization in log query languages and formats creates significant challenges. Developers currently must write ad hoc queries in platform-specific languages, requiring expertise in both the query language and application-specific log details -- an impractical expectation given the variety of platforms and volume of logs and applications. While generating these queries with large language models (LLMs) seems intuitive, we show that current LLMs struggle with log-specific query generation due to the lack of exposure to domain-specific knowledge. We propose a novel natural language (NL) interface to address these inconsistencies and aide log query generation, enabling developers to create queries in a target log query language by providing NL inputs. We further introduce ~\textbf{NL2QL}, a manually annotated, real-world dataset of natural language questions paired with corresponding LogQL queries spread across three log formats, to promote the training and evaluation of NL-to-loq query systems. Using NL2QL, we subsequently fine-tune and evaluate several state of the art LLMs, and demonstrate their improved capability to generate accurate LogQL queries. We perform further ablation studies to demonstrate the effect of additional training data, and the transferability across different log formats. In our experiments, we find up to 75\% improvement of finetuned models to generate LogQL queries compared to non finetuned models.

cs.DB↗

arXiv2024

Granular flows over normally vibrated inclined bases

We investigate granular flows over an inclined rigid base, which is vibrated externally in a direction normal to itself, through discrete element simulations. We vary the base inclination angle theta, vibration frequency f, and amplitude A to study changes in the granular flow profile and the mass flow rate Q. We find that the flow velocity profiles for the vibrated bases are nonlinear, unlike their fixed base counterparts. Our study reveals that Q may be maintained nearly constant in flows over vibrated bases utilizing appropriate combinations of theta, A, and f. At the same time, by vibrating the base at a fixed inclination, we may increase the mass flow rate by as much as 30 times the value found in flows over a stationary base. Finally, we show that Q depends upon a nondimensional number S obtained by taking the ratio of vibrational and gravitational energies.

cond-mat.soft↗

arXiv2023

Segregation on small rubble bodies due to impact-induced seismic shaking

We present a framework to study regolith segregation on rubble-pile asteroids (self-gravitating granular aggregates) due to seismic shaking induced by impacts sustained during their lifetimes. We first relate the amplitude and frequency of surface vibrations to the location and severity of an impact, and the rubble body's geometry and bulk properties. For clarity, the body is taken to be an ellipsoid with size and spin close to that of Itokawa, although other asteroids are also easily incorporated. We then model the body's collisional history stochastically given the variability in the impact activity on an asteroid. Finally, we utilize discrete element simulations to investigate the regolith's response to impacts. In these simulations, in any sample collisional history, every time an impact occurs, a bin filled with a grain mixture and located at the region of interest on the asteroid is vibrated at that impact's associated amplitude and frequency. Utilizing this framework we find that impact-driven seismicity is sufficient to drive size segregation on small rubble-piles, but the segregation quality depends on several aspects, e.g. total impact energy supplied, placement of the region of interest, bulk wave speed, and seismic diffusivity.

astro-ph.EP↗

arXiv2022

Axial segregation of granular mixtures in laterally shaken multi-trapezium channels

We investigate axial segregation of binary mixtures in a laterally shaken horizontal channel formed by ratchet-like sidewalls that appear as concatenated trapeziums when not offset axially. Grain mixtures shaken in such a channel are observed to segregate in two stages: they first separate rapidly into two vertically arranged layers and, then, these layers move axially in opposite directions, segregating the two species. Here, we conduct experiments to study the influence on the segregation process of various parameters: the size ratio of grains, the shaking frequency and the channel's geometry. We find that (a) segregation quality depends upon shaking frequency and it is possible to find a unique optimal frequency for segregation, (b) the optimal frequency lowers with increase in size ratio, (c) segregation is generally poorer when the sidewalls are more inclined to each other, and (d) segregation is improved when the sidewalls are axially offset from each other. We then carry out discrete element simulations of the segregation process in order to relate the experimental observations to the interfacial pressure gradient mechanism of Bhateja et al. [Bhateja, A., I. Sharma and J. K. Singh 2017. Segregation physics of a macroscale granular ratchet, Phys. Rev. Fluids 2, 052301]. We demonstrate that the segregation quality correlates well with the scaled interfacial pressure gradient, which is the ratio of the interfacial pressure gradient between the layers, formed in the first stage of the segregation process, to the axial body force provided by the tapered sidewalls.

cond-mat.soft↗

arXiv2017

Stability of traveling, pre-tensioned, heavy cables

We study the dynamics of an inclined tensioned, heavy cable traveling with a constant speed in the vertical plane. The cable is modeled as a beam resisting bending and shear. The governing equation for the transverse in-plane vibrations of the cable are derived through the Newton-Euler method. The cable dynamics is also studied in the limit of zero bending stiffness. In all cases, application of en- ergy balance reveals that the total energy of the system fluctuates even though the oscillations are small and bounded in time, indicating that the system is nonconser- vative. A comprehensive stability analysis is carried out in the parameter space of inclination, traveling speed, pre-tension, bending rigidity and the slenderness of the cable. Effect of damping is also considered. We conclude that, while pre-tension, rigidity and slenderness enhance the stability of the traveling cable, the angle of inclination affects the stability adversely. These results may act as guidelines for safer design and operation.

physics.class-ph↗

arXiv2016

Rings of non-spherical, axisymmetric bodies

We investigate the dynamical behavior of rings around bodies whose shapes depart considerably from that of a sphere. To this end, we have developed a new self-gravitating discrete element N-body code, and employed a local simulation method to simulate a patch of the ring. The central body is modeled as a symmetric (oblate or prolate) ellipsoid, or defined through the characteristic frequencies (circular, vertical, epicyclic) that represent its gravitational field. Through our simulations we explore how a ring's behavior -- characterized by dynamical properties like impact frequency, granular temperature, number density, vertical thickness and radial width -- varies with the changing gravitational potential of the central body. We also contrast properties of rings about large central bodies (e.g. Saturn) with those of smaller ones (e.g. Chariklo). Finally, we investigate how the characteristic frequencies of a central body, restricted to being a solid of revolution with an equatorial plane of symmetry, affect the ring dynamics. The latter process may be employed to qualitatively understand the dynamics of rings about any symmetric solids of revolution.

astro-ph.EP↗