The interlink between particle-scale properties and macroscopic behavior of three-dimensional granular media subjected to mechanical loading is studied intensively by scientists and engineers, but not yet well understood. Here we study the role of key particle-scale properties, such as interparticle friction and particle elastic modulus, in the functioning of dual contact force networks, viz., strong and weak contacts, in mobilizing shear strength in dense granular media subjected to quasistatic shearing. The study is based on three-dimensional discrete element method in which particle-scale constitutive relations are based on well-established nonlinear theories of contact mechanics. The underlying distinctive contributions of these force networks to the macroscopic stress tensor of sheared granular media are examined here in detail to find out how particle-scale friction and particle-scale elasticity (or particle-scale stiffness) affect the mechanism of mobilization of macroscopic shear strength and other related properties. We reveal that interparticle friction mobilizes shear strength through bimodal contribution, i.e., through both major and minor principal stresses. However, against expectation, the contribution of particle-scale elasticity is mostly unimodal, i.e., through the minor principal stress component, but hardly by the major principal stress. The packing fraction and the geometric stability of the assemblies (expressed by the mechanical coordination number) increase for decrease in interparticle friction and elasticity of particles. Although peak shear strength increases with interparticle friction, the deviator strain level at which granular systems attain peak shear strength is mostly independent of interparticle friction. Granular assemblies attain peak shear strength (and maximum fabric anisotropy of strong contacts) when a critical value of the mechanical coordination number is attained. Irrespective of the interparticle friction and elasticity of the particles, the packing fraction and volumetric strain are constant during steady state. Volumetric strain in sheared granular media increases with interparticle friction and elasticity of the particles. We show that the elasticity of the particles does not enhance dilation in frictionless granular media. The results presented here provide additional understanding of the role of particle-scale properties on the collective behavior of three-dimensional granular media subjected to shearing.

Renewable energy sources prevail as a clean energy source and their penetration in the power sector is increasing day by day due to the growing concern for climate action. However, the intermittent nature of the renewable energy based-power generation questions the grid security, especially when the utilized source is solar radiation or wind flow. The intermittency of the renewable generation can be met by the integration of distributed energy resources. The virtual power plant (VPP) is a new concept which aggregates the capacities of various distributed energy resources, handles controllable and uncontrollable loads, integrates storage devices and empowers participation as an individual power plant in the electricity market. The VPP as an energy management system (EMS) should optimally dispatch the power to its consumers. This research work is proposed to analyze the optimal scheduling of generation in VPP for the day-ahead market framework using the beetle antenna search (BAS) algorithm under various scenarios. A case study is considered for this analysis in which the constituting energy resources include a photovoltaic solar panel (PV), micro-turbine (MT), wind turbine (WT), fuel cell (FC), battery energy storage system (BESS) and controllable loads. The real-time hourly load curves are considered in this work. Three different scenarios are considered for the optimal dispatch of generation in the VPP to analyze the performance of the proposed technique. The uncertainties of the solar irradiation and the wind speed are modeled using the beta distribution method and Weibull distribution method, respectively. The performance of the proposed method is compared with other evolutionary algorithms such as particle swarm optimization (PSO) and the genetic algorithm (GA). Among these above-mentioned algorithms, the proposed BAS algorithm shows the best scheduling with the minimum operating cost of generation.

The prevalence of particulate materials in modern industrial processes and products provides a significant motivation to achieve fundamental understanding of the bulk behaviour of particulate media. The rapid progress being made with atomic force microscopy and related particle characterization techniques pushes the limits of micro- and nanotechnologies such that interparticle interactions can be engineered to fabricate particulate assemblies to deliver specific functionalities. In this paper, primarily based on discrete element method simulations that we performed over the past 10 years, we summarize the key findings on the role of force transmission networks in dense particulate systems subjected to shearing. In general, the macroscopic strength characteristics in particulate systems is dictated by the distribution of heavily loaded contacts, also referred to as ‘strong’ force chains. Surprisingly, they constitute only a limited proportion of all contacts in particulate systems. They act like a ‘granular brain’ (memory networks) at particle scale. We show that the structural arrangement of the force chains and their evolution during loading depends on the single-particle properties and the initial packing condition in particulate assemblies. Further, the ‘nature’ of force chains in sheared granular media induces larger ‘solid’ grains to behave like ‘fluid’ particles, retarding their breakage. Later, we probe for ways by which we can control the signature of memory networks in packed beds, for example by applying an external electrical field in a densely packed particulate bed subjected to shearing (combined electromechanical loading). Though further research is required to account for more realistic conditions and preferably to allow particles to self-organize to strength specifications, understanding the hidden memory networks in particulate materials could be exploited to optimize their collective strength.

To describe the heterogeneous nature of stress transmission in granular materials, the concept of the “strong” network consisting of contacts with large normal forces has been proposed by Radjaï et al. [Phys. Rev. Lett. 80, 61 (1998)]. The shear stress is mainly determined by this strong network. The dual viewpoint is adopted here, by not only considering the forces at contacts, but also the deformation. It is shown that the strain increments are determined by the tangential component of the relative displacements at the contacts. A “mobile” network consisting of contacts with large tangential relative displacements is defined that primarily accounts for the strain increments. The investigation of the relation between the strong and the mobile networks shows that these networks are largely unrelated. An alternative network is defined that consists of contacts at which the contribution to the work input is large. It is found that this work input occurs primarily through the tangential forces and tangential relative displacements.

Healthy eyes are vital for a better quality of human life. Historically, for man-made materials, scientists and engineers use stress concentration factors to characterise the effects of structural non-homogeneities on their mechanical strength. However, such information is scarce for the human eye. Here we present the shear stress distribution profiles of a healthy human cornea surface in vivo using photo-stress analysis tomography, which is a non-intrusive and non-X-ray based method. The corneal birefringent retardation measured here is comparable to that of previous studies. Using this, we derive eye stress concentration factors and the directional alignment of major principal stress on the surface of the cornea. Similar to thermometers being used for monitoring the general health in humans, this report provides a foundation to characterise the shear stress carrying capacity of the cornea and a potential bench mark for validating theoretical modelling of stresses in the human eye in future.