Madison, AL, United States
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Clayton J.D.,Impact Physics | Knap J.,Computational Sciences, LLC
International Journal of Fracture | Year: 2014

Phase field theory is developed for solids undergoing potentially large deformation and fracture. The elastic potential depends on a finite measure of elastic strain. Surface energy associated with fracture can be anisotropic, enabling description of preferred cleavage planes in single crystals, or isotropic, applicable to amorphous solids such as glass. Incremental solution of the Euler–Lagrange equations corresponds to local minimization of an energy functional for the solid, enabling prediction of equilibrium crack morphologies. Predictions are in close agreement with analytical solutions for pure mode I or pure mode II loading, including the driving force for a crack to extend from a pre-existing plane onto a misoriented cleavage plane. In an isotropic matrix, the tendency for a crack to penetrate or deflect around an inclusion is shown to depend moderately on the ratio of elastic stiffness in matrix and inclusion and strongly on their ratio of surface energy. Cracks are attracted to (shielded by) inclusions softer (stiffer) than the surrounding matrix. The theory and results apparently report the first fully three-dimensional implementation of phase field theory of fracture accounting for simultaneous geometric nonlinearity, nonlinear elasticity, and surface energy anisotropy. © 2014, Springer Science+Business Media Dordrecht (outside the USA).


Cucinotta C.S.,College Green Dublin | Cucinotta C.S.,Computational Sciences, LLC | Bernasconi M.,University of Milan Bicocca | Parrinello M.,Computational Sciences, LLC
Physical Review Letters | Year: 2011

By means of abinitio simulations we here provide a comprehensive scenario for hydrogen oxidation reactions at the Ni/zirconia anode of solid oxide fuel cells. The simulations have also revealed that in the presence of water chemisorbed at the oxide surface, the active region for H oxidation actually extends beyond the metal/zirconia interface unraveling the role of water partial pressure in the decrease of the polarization resistance observed experimentally. © 2011 American Physical Society.


Angioletti-Uberti S.,Imperial College London | Ceriotti M.,Computational Sciences, LLC | Lee P.D.,Imperial College London | Finnis M.W.,Imperial College London
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The solid-liquid interface free energy γsl is a key parameter controlling nucleation and growth during solidification and other phenomena. There are intrinsic difficulties in obtaining accurate experimental values, and the previous approaches to compute γsl with atomistic simulations are computationally demanding. We present an approach which is to obtain γsl from a free-energy map of the phase transition reconstructed by metadynamics. We apply this to the benchmark case of a Lennard-Jones potential, and the results confirm the most reliable data obtained previously. We demonstrate several advantages of our approach: it is simple to implement, robust and free of hysteresis problems, it allows a rigorous and unbiased estimate of the statistical uncertainty, and it returns a good estimate of the thermodynamic limit with system sizes of a just a few hundred atoms. It is therefore attractive for applications which require more realistic and specific models of interatomic forces. © 2010 The American Physical Society.


Lin L.,Princeton University | Morrone J.A.,Princeton University | Morrone J.A.,Columbia University | Car R.,Princeton University | Parrinello M.,Computational Sciences, LLC
Physical Review Letters | Year: 2010

The proton momentum distribution, accessible by deep inelastic neutron scattering, is a very sensitive probe of the potential of mean force experienced by the protons in hydrogen-bonded systems. In this work we introduce a novel estimator for the end-to-end distribution of the Feynman paths, i.e., the Fourier transform of the momentum distribution. In this formulation, free particle and environmental contributions factorize. Moreover, the environmental contribution has a natural analogy to a free energy surface in statistical mechanics, facilitating the interpretation of experiments. The new formulation is not only conceptually but also computationally advantageous. We illustrate the method with applications to an empirical water model, ab initio ice, and one dimensional model systems. © 2010 The American Physical Society.


Patent
Computational Sciences, LLC | Date: 2013-02-14

A dual use of a heater core that enables heating the cabin, cooling the engine or both on demand regardless of the passengers cabin heating and cooling requirements. This use of the heater core is enabled by an HVAC airbox system with a cooling door that can be selectively positioned such that at least some of the air moving through the heater core is directed to the underhood area of a vehicle thereby providing supplemental engine cooling on demand regardless of the passengers cabin heating and cooling requirements. The cooling door can be positioned automatically by the Engine Control Unit (ECU) dependent on any parameter, or combination of parameters, of the engine such as the engine coolant temperature or the engine oil temperature. The blower speed and the position of the cooling door are adjusted by the ECU depending on the whether and how much supplemental engine cooling is required.


Grant
Agency: Department of Defense | Branch: Navy | Program: STTR | Phase: Phase I | Award Amount: 84.78K | Year: 2015

Computational Sciences LLC will collaborate with the Rensselaer Polytechnic Institute (RPI) to develop and validate a stand-alone computational module that naturally accounts for the effects of turbulence. Such fluctuations and transitions may be associated with compressible flows and boundary layer interactions. The module will be designed for implementation in to existing legacy codes for use in characterization of unsteady vorticity-dominated flows.The approach is based on a novel, regularized set of Navier-Stokes equations (RNS) that is extended to account for turbulence effects (fluctuations) in the continuum approximation. RNS has several important features not found in classical NS equations that are of direct relevance turbulent flows: (a) Kolmogorov-scale field fluctuations resulting from a mathematical model that accounts for turbulent diffusion in a natural manner that allows direct simulation of phenomena such as laminar-turbulence transition and wall slip effects; and (b) Natural accounting of growth of small-scale turbulent structures without refining down to Kolmogorovs scale.Phase I will focus on a simplified 3D working version of the approach by removing the selected restrictions. The validation of the model will be provided by comparison of the simulation results with the experimental data for a set of representative turbulent flows. The software module will be connected to a high order compressible flow code and will be exercised and evaluated against experimental data for selected model problems that contain elements of both nearfield and farfield wakes. Phase II will refine the approach to include generalized vortical flows generated by 6 degree-of-freedom hard body interactions, and will validate it on problems of interest to the Navy.


Grant
Agency: Department of Defense | Branch: Army | Program: STTR | Phase: Phase I | Award Amount: 149.95K | Year: 2013

The project will remove a key difficulty that currently hampers many existing methods for computing unsteady electromagnetic waves on unbounded regions. Numerical accuracy and/or stability may deteriorate over long times due to the treatment of artificial outer boundaries. We propose to develop a universal algorithm and software that will correct this problem by employing the Huygens'principle and quasi-lacunae of Maxwell's equations. The algorithm will provide a guaranteed error bound, uniform in time (no deterioration at all), and the software will enable robust electromagnetic simulations in a high-performance computing environment. The methodology will apply to any geometry, any scheme, and any boundary condition. It will eliminate the long-time deterioration regardless of its origin and how it manifests itself. Dr. Tsynkov who co-invented this method is the Academic partner on the project. Phase I includes development of an innovative numerical methodology for high fidelity error-controlled modeling of a broad variety of electromagnetic and other wave phenomena. Proof-of-concept 3D computations will be conducted and verified against benchmarks, to demonstrate efficiency of the proposed approach. In Phase II our algorithms will be implemented as robust commercial software tools in a standalone module that can be combined with existing numerical schemes in computational electromagnetic codes.


Grant
Agency: Department of Defense | Branch: Army | Program: STTR | Phase: Phase II | Award Amount: 999.89K | Year: 2014

The project will remove a key difficulty that currently hampers many existing methods for computing unsteady electromagnetic waves on unbounded regions. Numerical accuracy and/or stability may deteriorate over long times due to the treatment of artificial outer boundaries. We propose to develop a universal algorithm and software that will correct this problem by employing the Huygens' principle and lacunae of Maxwell's equations. The algorithm will provide a temporally uniform guaranteed error bound (no deterioration at all), and the software will enable robust electromagnetic simulations in a high-performance computing environment. The methodology will apply to any geometry, any scheme, and any boundary condition. It will eliminate the long-time deterioration regardless of its origin and how it manifests itself. Dr. Tsynkov who co-invented this method is the Academic partner on the project. Phase I included development of an innovative numerical methodology for high fidelity error-controlled modeling of a broad variety of electromagnetic and other wave phenomena. Proof-of-concept 3D computations have been conducted that convincingly demonstrate the feasibility and efficiency of the proposed approach. In Phase II our algorithms will be implemented as robust commercial software tools in a standalone module that can be combined with existing numerical schemes in computational electromagnetic codes.


Grant
Agency: Department of Defense | Branch: Missile Defense Agency | Program: SBIR | Phase: Phase II | Award Amount: 499.83K | Year: 2010

We propose to develop stand-alone computational modules for seamlessly extending the validity of continuum CFD codes into transitional and rarefied flow regimes. The modules will be designed for implementation in to existing legacy codes for use in the characterization of high altitude plume flows. The approach is based on a novel, regularized set of Navier-Stokes equations (RNS) that is extended to account for kinetic effects (intermediate Knudsen number, fluctuations) in the continuum approximation. RNS has several important features not found in classical NS equations that are of direct relevance in high altitude plume flows: (a) Natural accounting of both continuum and rarefied gas flow regimes; and (b) Kolmogorov-scale field fluctuations resulting from a mathematical model that accounts for turbulent diffusion in a natural manner that allows direct simulation of phenomena such as laminar-turbulent transition and wall slip effects. Phase I has completed the development of stand-alone, computational module prototypes incorporating a simplified version of the RNS approach. The modules were connected to a characteristics-based high order compressible flow code with particle transport capabilities, and an unstructured finite-element code, and were successfully exercised and evaluated for a model problem that contained features of both continuum and rarefied flows. Phase II will complete the development of the modules, provide a detailed comparison to Navier-Stokes results for low and high altitude flow regimes, identify the parameter region where the approach is advised, and provide connections to plume signatures sponsored and managed by the MDA/DES modeling and simulation effort.


Grant
Agency: Department of Defense | Branch: Army | Program: STTR | Phase: Phase I | Award Amount: 99.96K | Year: 2011

The project will remove a key difficulty that currently hampers many existing methods for computing unsteady electromagnetic waves in unbounded regions. The accuracy and/or stability of the simulations may deteriorate over long times due to the treatment of the outer boundaries via artificial boundary conditions. We propose to develop a universal algorithm and software that will correct this problem by employing the Huygens"principle and quasi-lacunae in the solutions of Maxwell"s equations. The algorithm will provide a temporally uniform guaranteed error bound (no deterioration at all), and the software will enable robust electromagnetic simulations in a high-performance computing environment. The methodology will apply to any geometry, any numerical scheme and any treatment of outer boundaries. It will eliminate the long-time deterioration regardless of both its origin and the way it manifests itself. Dr. Tsynkov of NCSU, who invented this method and is referenced in the Solicitation, is the Academic partner on the project. Phase I includes development of an innovative numerical methodology for high fidelity error-controlled modeling of a broad variety of electromagnetic and other wave-dominated phenomena. Solutions to test problems will be verified against analytical and accurate numerical benchmarks, to demonstrate the feasibility of the proposed approach. In Phase II our innovative algorithms will be implemented as robust commercial software tools in a standalone computational module that can be used to fix existing numerical schemes, along with the treatment of the outer boundaries, in computational electromagnetic codes.

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