Solid Mechanicians have been modeling well developed granular flows by invoking various yield criteria and plastic flow relations for a long time. The most widely accepted and tested model for dense granular flows is the nonlocal granular fluidity(NGF) model. It has shown success in a variety of flow configurations, most importantly, predicting the surface flows in the split bottom flows where every continuum model has failed in the past. Currently, our collaborators are using MRI-PIV techniques and Discrete element simulations (DEM) to extract the bulk flow fields in the split bottom geometry. Experimental details can be found here. The ongoing task is to calibrate the NGF model and compare its predictions with the experimental measurements and DEM simulations. The NGF model has been summarized here [Link]

Size segregation in dense granular mixtures has been a longstanding problem. It is coupled with the flow of the granular material which in itself is challenging to characterize in an arbitrary geometry. The two main driving mechanisms of segregation identified at the continuum scale are shear-strain-rate-gradient and pressure-gradient. We propose a three dimensional segregation model based on data from DEM simulations wherein we include both the driving forces of segregation in addition to diffusion flux which opposes the segregation. The model also accounts for the anisotropic nature of the diffusion and the segregation that has been observed in the DEM simulations. To characterize the flow we modify the NGF model to account for the mixture mean grain size. When the segregation model is coupled with the NGF model, the coupled model is able to predict flow and the segregation dynamics simultaneously. The ongoing research is to compare the model predictions with the DEM simulations in different flow configurations like Inclined plane flow, planar shear with gravity, couette flow, etc. The model shows good quantitative agreement with the DEM simulations. This work is summarized here [Link]

String-bridge interactions in the string musical instruments play a key role in the determining the quality of sound produced, and it is a distinct feature of each instrument. Inspired from Indian classical instrument -Sitar , we model the vibrations of a string in the presence of a finite-sized curved obstacle(bridge). The finite size of the bridge introduces an additional wrapping nonlinearity apart from the nonlinearity caused by large deformation in the string. This nonlinearity causes strong coupling between the different vibration modes along with the coupling between the in-plane and out-of-plane motion of the string. We investigate different types of motion in the presence of obstacle. Furthermore, we show that there is a critical amplitude beyond which the planar motion become unstable, and we get whirling trajectories of the string. The critically amplitude is shown to be dictated only by the obstacle geometry. Summary here [Link]