Papers by Srdjan Simunovic
Thermochimica is a software library that determines a unique combination of phases and their comp... more Thermochimica is a software library that determines a unique combination of phases and their compositions at thermochemical equilibrium. Thermochimica can be used for stand-alone calculations or it can be directly coupled to other codes. This release of the software does not have a graphical user interface (GUI) and it can be executed from the command line or from an Application Programming Interface (API). Also, it is not intended for thermodynamic model development or for constructing phase diagrams. The main purpose of the software is to be directly coupled with a multi-physics code to provide material properties and boundary conditions for various physical phenomena. Significant research efforts have been dedicated to enhance computational performance through advanced algorithm development, such as improved estimation techniques and non-linear solvers. Various useful parameters can be provided as output from Thermochimica, such as: determination of which phases are stable at equ...
NTRCI sponsored the research team of Battelle, Oak Ridge National Laboratory (ORNL) and the Unive... more NTRCI sponsored the research team of Battelle, Oak Ridge National Laboratory (ORNL) and the University of Tennessee at Knoxville (UTK) to conduct a three-phase investigation to enhance and refine a FE model for simulating tractor-semitrailer crash events involving roadside safety hardware such as bridge rails and median barriers. This report documents the work completed in the third phase of the project. The objective of this investigation led by Battelle was to validate and enhance computer models of a tractor-semitrailer combination for use in analysis, design, and evaluation of roadside safety hardware. The work completed during this project phase involved: 1) Continued enhancements of the tractor and semitrailer model, 2) Validation of the model by comparing model results to two full-scale tractor-semitrailer crash tests, and 3) Development of an interactive graphics based on-line user manual and FE model website. The tractor-semitrailer vehicle FE model developed in this projec...
Additive Manufacturing, 2021
Abstract Correlation between spot-melt scan parameters (linear spot-density aka areal energy dens... more Abstract Correlation between spot-melt scan parameters (linear spot-density aka areal energy density), build geometry, and solidification microstructure evolution (columnar vs equiaxed) in a powder bed fusion technology is investigated. It is shown that to maintain the equiaxed solidification microstructure evolution in electron beam powder bed additive manufacturing (AM), the areal energy density per layer needs to be scaled with respect to the 2D cross-sectional area of the layer being melted. Samples with two different cross-sectional areas (40 × 40 mm and 20 × 20 mm) have been fabricated with varying areal energy densities. For a given square cross-section (20 × 20 mm), increasing the areal energy density (4.8 MJ/sq.m to 14.7 MJ/sq.m) transitioned the solidification microstructure from columnar to equiaxed. The observed microstructure data (Electron Back Scattered Diffraction - EBSD) is quantified by calculating the principal component (PC) score using a spatial statistics methodology. The sample with equiaxed grains is found to have a low PC score while the sample with columnar grain had a high PC score. A semi-analytical model is used to simulate the heat transfer and the local solidification conditions as a function of processing parameters (linear spot-density). The result from the heat transfer model is correlated with previously quantified microstructure data. Space-Time analysis of the melt pattern is done and correlated with the observed microstructure. In addition, from the findings, appropriate parameters have been used to additively manufacture a turbine blade with site-specific or hybrid solidification microstructure (traditional fabrication possible via a patented method of localized cold working and heat treatment).
Water, 2018
A novel numerical model for groundwater flow in karst aquifers is presented. A discrete-continuum... more A novel numerical model for groundwater flow in karst aquifers is presented. A discrete-continuum (hybrid) approach, in which a three-dimensional matrix flow is coupled with a one-dimensional conduit flow, was used. The laminar flow in the karst matrix is described by a variably saturated flow equation to account for important hydrodynamic effects in both the saturated and unsaturated zones. Turbulent conduit flow for both free surface and pressurized flow conditions was captured via the noninertia wave equation, whereas the coupling of two flow domains was established through an exchange term proportional to head differences. The novel numerical approach based on Fup basis functions and control-volume formulation enabled us to obtain smooth and locally conservative numerical solutions. Due to its similarity to the isogeometric analysis concept (IGA), we labeled it as control-volume isogeometric analysis (CV-IGA). Since realistic verification of the karst flow models is an extremely...
Journal of Power Sources, 2017
Large format Li-ion cells were used to study the mechanical responses of single cells of thicknes... more Large format Li-ion cells were used to study the mechanical responses of single cells of thickness 6.5 mmand stacks of three cells under compressive loading. Various sequences of increasingdepth indentations were carried out using a 1.0 inch (25.4 mm) diameter steel ball with steel plate as a rigid support surface. The indentation depths were between 0.025" and 0.250" with main indentation increments tests of 0.025" steps. Increment steps of 0.100" and 0.005" were used to pinpoint the onset of internal-short that occurred between 0.245" and 0.250". The indented cells were disassembled and inspected for internal damage. Load vs. timecurves were compared with the developed computer models. Separator thinning leading to the short circuit was simulated using both isotropic and anisotropic mechanical properties. Our study show that separators behave differently when tested as a single layer vs. a stack in a typical pouch cell. The collective responses of the multiple layersmust be taken into account in failure analysis. A model that resolves the details of the individual internal cell components was able to simulate the internal deformation of the large format cells and the onset of failure assumed to coincide with the onset of internal short circuit.
Journal of Power Sources, 2016
The response of Li-ion cells to mechanically induced internal electrical shorts is an important s... more The response of Li-ion cells to mechanically induced internal electrical shorts is an important safety performance metric design. We assume that the battery internal configuration at the onset of electrical short influences the subsequent response and can be used to gage the safety risk. We subjected a series of prismatic Li-ion cells to lateral pinching using 0.25", 0.5", 1", 2" and 3" diameter steel balls until the onset of internal short. The external aluminum enclosure froze the internal cell configuration at the onset of short and enabled us to cross-section the cells, and take the cross-section images.. The images indicate that an internal electric short is preceded by extensive strain partitioning in the cells, fracturing and tearing of the current collectors, cracking and slipping of the electrode layers with multiple fault lines across multiple layers. These observations are at odds with common notion of homogeneous deformation across the layers and strain hardening of electrodes that eventually punch through the separator and short the cell. The faults are akin to tectonic movements of multiple layers that are characteristic of granular materials and bonded aggregates. The short circuits occur after extensive internal faulting, which implies significant stretching and tearing of separators.
Volume 6: Energy, Parts A and B, 2012
ABSTRACT Lithium-ion batteries (LiB) are widely used in the electronics industry (such as, cell p... more ABSTRACT Lithium-ion batteries (LiB) are widely used in the electronics industry (such as, cell phones and laptop computers) because of their very high energy density, which reduced the size and weight of the battery significantly. LiB also serves as a renewable energy source for the transportation industry (see Ref. [1,2]). Graphite and LiCoO2 are most frequently used as anode and cathode material inside LiB (see Ref. [2,3]). During the charging and discharging process, intercalation and de-intercalation of Li occur inside the LiB electrodes. Non-uniform distributions of Li induce stress inside the electrodes, also known as diffusion induced stress (DIS). Very high charge or discharge rate can lead to generation of significant amount of tensile or compressive stress inside the electrodes, which can cause damage initiation and accumulation (see Ref. [4]). Propagation of these micro-cracks can cause fracture in the electrode material, which impacts the solid electrolyte interface (SEI) (see Ref. [2,3,5]). Concurrent to the reduction of cyclable Li, resistance between the electrode and electrolyte also increases, which affects the performance and durability of the electrode and has a detrimental consequence on the LiB life (see Ref. [6]).
2015 IEEE Power & Energy Society General Meeting, 2015
In this paper, the merits of Adomian Decomposition Method (ADM) have been investigated for the ti... more In this paper, the merits of Adomian Decomposition Method (ADM) have been investigated for the time domain simulation of multi-machine power systems. ADM is an analytical approximation method for the solution of linear, nonlinear, deterministic and stochastic operator equations. It approximates the nonlinearities in the equations using Adomian polynomial series and that can form a rapidly convergent sequence of analytic functions. We apply the ADM approach for simulation of differential algebraic equations representing the detailed multi-machine power system. The ADM approach has been applied on the widely used IEEE 3 generator 9 bus system and IEEE 10 generator 39 bus system for 3 - φ fault simulations. In our simulations we found that the ADM approach is faster than the standard trapezoidal time integration method for the comparable accuracy.
Journal of Power Sources, 2015
Electrode microstructure and processing can strongly influence lithium-ion battery performance su... more Electrode microstructure and processing can strongly influence lithium-ion battery performance such as capacity retention, power, and rate. Battery electrodes are multi-phase composite structures wherein conductive diluents and binder bond active material to a current collector. The structure and response of this composite network during repeated electrochemical cycling directly affects battery performance characteristics. We propose the fabric tensor formalism for describing the structure and evolution of the electrode microstructure. Fabric tensors are directional measures of particulate assemblies based on inter-particle connectivity, relating to the structural and transport properties of the electrode. Fabric tensor analysis is applied to experimental data-sets for positive electrode made of lithium nickel manganese cobalt oxide, captured by X-ray tomography for several compositions and consolidation pressures. We show that fabric tensors capture the evolution of inter-particle contact distribution and are therefore good measures for the internal state of and electronic transport within the electrode. The fabric tensor analysis is also applied to Discrete Element Method (DEM) simulations of electrode microstructures using spherical particles with size distributions from the tomography. These results do not follow the experimental trends, which indicates that the particle size distribution alone is not a sufficient measure for the electrode microstructures in DEM simulations.
Annals of Nuclear Energy, 2015
This paper describes an approach for coupled-code multiphysics reactor core simulations that is b... more This paper describes an approach for coupled-code multiphysics reactor core simulations that is being developed by the Virtual Environment for Reactor Applications (VERA) project in the Consortium for Advanced Simulation of Light-Water Reactors (CASL). In this approach a user creates a single problem description, called the "VERAIn" common input file, to define and setup the desired coupled-code reactor core simulation. A preprocessing step accepts the VERAIn file and generates a set of fully consistent input files for the different physics codes being coupled. The problem is then solved using a single-executable coupled-code simulation tool applicable to the problem, which is built using VERA infrastructure software tools and the set of physics codes required for the problem of interest. The approach is demonstrated by performing an eigenvalue and power distribution calculation of a typical three-dimensional 17x17 assembly with thermal-hydraulic and fuel temperature feedback. All neutronics aspects of the problem (cross-section calculation, neutron transport, power release) are solved using the Insilico code suite and are fully coupled to a thermalhydraulic analysis calculated by the Cobra-TF (CTF) code. The single-executable coupled-code (Insilico-CTF) simulation tool is created using several VERA tools, including LIME (Lightweight Integrating Multiphysics Environment for coupling codes), DTK (Data Transfer Kit), Trilinos, and TriBITS. Parallel calculations are performed on the Titan supercomputer at Oak Ridge National Laboratory using 1156 cores, and a synopsis of the solution results and code performance is presented. Ongoing development of this approach is also briefly described.
Ultrasonics Sonochemistry, 2010
We introduce a model of cavitation based on the multiphase Lattice Boltzmann method (LBM) that al... more We introduce a model of cavitation based on the multiphase Lattice Boltzmann method (LBM) that allows for coupling between the hydrodynamics of a collapsing cavity and supported solute chemical species. We demonstrate that this model can also be coupled to deterministic or stochastic chemical reactions. In a two-species model of chemical reactions (with a major and a minor species), the major difference observed between the deterministic and stochastic reactions takes the form of random fluctuations in concentration of the minor species. We demonstrate that advection associated with the hydrodynamics of a collapsing cavity leads to highly inhomogeneous concentration of solutes. In turn these inhomogeneities in concentration may lead to significant increase in concentration-dependent reaction rates and can result in a local enhancement in the production of minor species.
Journal of Computer-Aided Materials Design, 2007
The paper presents the state-of-the-art algorithmic developments for simulating the fracture of d... more The paper presents the state-of-the-art algorithmic developments for simulating the fracture of disordered quasi-brittle materials using discrete lattice systems. Large scale simulations are often required to obtain accurate scaling laws; however, due to computational complexity, the simulations using the traditional algorithms were limited to small system sizes. In our earlier work, we have developed two algorithms: a multiple sparse Cholesky downdating scheme for simulating 2D random fuse model systems, and a block-circulant preconditioner for simulating 3D random fuse model systems. Using these algorithms, we were able to simulate fracture of largest ever lattice system sizes (L = 1024 in 2D, and L = 64 in 3D) with extensive statistical sampling. Our recent massively parallel simulations on 1024 processors of Cray-XT3 and IBM Blue-Gene/L have further enabled us to explore fracture of 3D lattice systems of size L = 128, which is a significant computational achievement. Based on these large-scale simulations, we analyze the scaling of crack surface roughness.
SAE Technical Paper Series, 2009
Static and dynamic strength tests were performed on spot welded specimens made of dual-phase (DP)... more Static and dynamic strength tests were performed on spot welded specimens made of dual-phase (DP) 780 and mild steels (DQSK). Lap-shear (LS) and cross-tension (CT) as well as a new mixed mode specimen were studied using MTS hydraulic universal testing machine for static ...
A numerical tool is in an advanced state of development to compute the equilibrium compositions o... more A numerical tool is in an advanced state of development to compute the equilibrium compositions of phases and their proportions in multi-component systems of importance to the nuclear industry. The resulting software is being conceived for direct integration into large multi-physics fuel performance codes, particularly for providing boundary conditions in heat and mass transport modules. However, any numerical errors produced in equilibrium chemistry computations will be propagated in subsequent heat and mass transport calculations, thus falsely predicting nuclear fuel behaviour. The necessity for a reliable method to numerically verify chemical equilibrium computations is emphasized by the requirement to handle the very large number of elements necessary to capture the entire fission product inventory. A simple, reliable and comprehensive numerical verification method is presented which can be invoked by any equilibrium chemistry solver for quality assurance purposes.
Physical Review Letters, 2006
Physical Review E, 2006
Using large-scale numerical simulations and extensive sampling, we analyze the scaling properties... more Using large-scale numerical simulations and extensive sampling, we analyze the scaling properties of the crack-cluster distribution and the largest crack-cluster distribution at the peak load. The simulations are performed using both two-dimensional and three-dimensional random fuse models. The numerical results indicate that in contrast with the randomly diluted networks ͑percolation disorder͒, the crack-cluster distribution in the random fuse model at the peak load follows neither a power law nor an exponential distribution. The largest crack-cluster distribution at the peak load follows a lognormal distribution, and this is discussed in the context of whether there exists a relationship between the largest crack-cluster size distribution at peak load and the fracture strength distribution. Contrary to popular belief, we find that the fracture strength and the largest crack-cluster size at the peak load are uncorrelated. Indeed, quite often, the final spanning crack is formed not due to the propagation of the largest crack at the peak load, but instead due to coalescence of smaller cracks.
Physical Review E, 2008
The paper presents the dynamic compound wavelet method ͑dCWM͒ for modeling the time evolution of ... more The paper presents the dynamic compound wavelet method ͑dCWM͒ for modeling the time evolution of multiscale and/or multiphysics systems via an "active" coupling of different simulation methods applied at their characteristic spatial and temporal scales. Key to this "predictive" approach is the dynamic updating of information from the different methods in order to adaptively and accurately capture the temporal behavior of the modeled system with higher efficiency than the ͑nondynamic͒ "corrective" compound wavelet matrix method ͑CWM͒, upon which the proposed method is based. The system is simulated by a sequence of temporal increments where the CWM solution on each increment is used as the initial conditions for the next. The numerous advantages of the dCWM method such as increased accuracy and computational efficiency in addition to a less-constrained and a significantly better exploration of phase space are demonstrated through an application to a multiscale and multiphysics reaction-diffusion process in a one-dimensional system modeled using stochastic and deterministic methods addressing microscopic and macroscopic scales, respectively.
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Papers by Srdjan Simunovic