Robertas Navakas

Community structure of force chains in granular hopper discharge

We analyse the force chain structure in granular matter during discharge from a hopper using discrete element modeling (DEM). Having obtained the particle configurations and the mechanical forces acting between the particles from DEM simulations, we build interaction graphs for the particle configurations at the respective time moments. The particles are represented as the graph vertices, the vertices are connected by edges if the respective particles are in contact, and the edge weights are proportional to the force moduli between the particle pairs. The community structures of the resulting graphs are then identified using a “walktrap” community detection algorithm. Evolution of the community structures is analysed during the hopper discharge and its dependence on the static friction coefficient between the particles.We analyse the force chain structure in granular matter during discharge from a hopper using discrete element modeling (DEM). Having obtained the particle configurations and the mechanical forces acting between the particles from DEM simulations, we build interaction graphs for the particle configurations at the respective time moments. The particles are represented as the graph vertices, the vertices are connected by edges if the respective particles are in contact, and the edge weights are proportional to the force moduli between the particle pairs. The community structures of the resulting graphs are then identified using a “walktrap” community detection algorithm. Evolution of the community structures is analysed during the hopper discharge and its dependence on the static friction coefficient between the particles.

A fluid-structure interaction model of the internal carotid and ophthalmic arteries for the noninvasive intracranial pressure measurement method

Accurate and clinically safe measurements of intracranial pressure (ICP) are crucial for secondary brain damage prevention. There are two methods of ICP measurement: invasive and noninvasive. Invasive methods are clinically unsafe; therefore, safer noninvasive methods are being developed. One of the noninvasive ICP measurement methods implements the balance principle, which assumes that if the velocity of blood flow in both ophthalmic artery segments - the intracranial (IOA) and extracranial (EOA) - is equal, then the acting ICP on the IOA and the external pressure (Pe) on the EOA are also equal. To investigate the assumption of the balance principle, a generalized computational model incorporating a fluid-structure interaction (FSI) module was created and used to simulate noninvasive ICP measurement by accounting for the time-dependent behavior of the elastic internal carotid (ICA) and ophthalmic (OA) arteries and their interaction with pulsatile blood flow. It was found that the extra balance pressure term, which incorporates the hydrodynamic pressure drop between measurement points, must be added into the balance equation, and the corrections on a difference between the velocity of blood flow in the IOA and EOA must be made, due to a difference in the blood flow rate.