Prakash, P. Ravi

Tunnel fires represent one of the extreme catastrophic scenarios which might result in loss of lives, property, disruption of economic activity, etc. There are no available design guidelines to quantify the damage in tunnels subjected to fire. Given the extremely costly and time-consuming nature of laboratory tests (full-scale/scaled), numerical modelling strategies are usually preferred for damage assessment studies on tunnels subjected to fire. They are generally based on multi-physics components such as heat transfer, mechanical deformations and moisture transport and work at various scales. Limited numerical frameworks are available, which explicitly explain multi-physics based theoretical developmental aspects of tunnels under fire and their potential implications. This paper provides a generalized summary of a multi-physics-based numerical modelling framework for tunnels under fire exposure. The summary includes identifying multi-physics components, formulation of governing equations, multi-physics coupling, discretization strategies, numerical solutions strategies and application aspects. The summary presented here can facilitate the generalized numerical problem formulation of tunnels under fire exposure, which can eventually culminate in applications such as performance-based design, design parameterization, etc.

Discontinuities play a significant role in the analysis and design of rock structures, e.g., tunnels, stability of slopes, blocky rock masses, etc. Therefore, the following study is conducted using a discrete element method (DEM) model in Universal Distinct Element Code (UDEC) software which takes into consideration the discontinuities present in the material medium, both load-induced as well as inherent discontinuities. The DEM model in UDEC is used for the study to simulate the Uniaxial Compressive test response of Fresh Quartzite Rock. The Quartzite Rock is taken for this study because the same rock was encountered at a project site Saundatti, Karnataka, which has been identified as an amenable place to develop an integrated project by Greenko Group. In this study, all the laboratory experiments are performed on the Quartzite rock, and its behaviour is understood with those experimental results. Out of all the experiments, Uniaxial Compressive Strength (UCS) Test is chosen for the simulation purpose. The specimen model used for simulation of UCS is 110 mm in height and 54 mm in width. The specimen is further subdivided into around 900 smaller deformable blocks to simulate the field condition accurately. The model is bounded at the top and bottom by steel platens to ascertain relatively uniform load transfer across the specimen cross-section. The contact points between the deformable blocks are characterized with the normal and shear stiffness, with their nonlinear behaviour modelled from Mohr–Coulomb failure envelope (shear regime) and Rankine tension cutoff (tension regime). These micro-mechanical parameters to the DEM model are characterized by the obtained macro-level parameters from laboratory experiments. The simulation of UCS using UDEC is carried out to quantify the deformability characteristics, fracture patterns, and the stress–strain curve of the rock specimen. The deformability characteristics obtained from the numerical model are quite consistent with that of experimental observations and is mainly due to the precisely chosen micro-mechanical parameters. Moreover, the cracks initiation and propagation, stress profiles and deformation patterns obtained in the simulation are studied intricately.

Real-time optimal path planning for robotic manipulations in task space is a very fundamental and important problem. In this paper, the problem of generating robot trajectories in an obstacle-ridden environment is formulated under an optimal control framework using Hamilton-Jacobi-Bellman (HJB) equation. The novel contribution of this paper is that a closed form HJB control solution (a necessary and sufficient condition for global optimality of a control solution with respect to a cost function) has been achieved for generating real-time optimal trajectories for a robot manipulator. In contrast with the decoupled end-effector path planning and subsequent trajectory generation, the proposed scheme can exploit sensory input for real-time trajectory generation where the end-effector path as well as the joint trajectory is recomputed online while satisfying the real-time constraints. The stability and the performance of the proposed control framework is shown theoretically via Lyapunov approach and also verified experimentally using a 6 degrees of freedom (DOF) Universal Robot (UR) 10 robot manipulator. It is shown that a significant saving in cost metrics can be obtained over similar trajectory generation approaches from the state-of-the-art with obstacle-ridden environment and also has better performance in high speed tracking applications. Warehouse applications of the proposed scheme in case of static and dynamic targets with respect to the robot manipulator is also included.

In this study, the in-plane structural behavior, capacity, and performance of dry-joint stone masonry walls (DJ-SMWs) and the effects of the vertical stress level on these factors are investigated via a stochastic discontinuum analysis that considers the material uncertainty. A discontinuum type of analysis is performed based on the discrete element method (DEM), where each stone masonry unit is explicitly represented in the computational model. To better simulate the cracking and shear failure modes within the stone units, a coupled fracture energy-based contact constitutive model is implemented into a commercial discrete element code, 3DEC. First, the proposed modeling approach is validated by comparing to experimental findings in literature. Then, the approach is used to explore the failure mechanism and the force–displacement behavior of DJ-SMWs, considering different vertical stress levels and material properties. The results of the novel modeling strategy provide a better understanding of the progressive collapse mechanism of DJ-SMWs and the influence of the vertical stress level. Furthermore, the outcomes of this research indicate the major role of the frictional resistance at the joints in the safety and performance assessment of the dry-joint load-bearing masonry walls. Finally, important inferences are made regarding the non-spatial and spatial stochastic discontinuum analysis.