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.
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).
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.
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.
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.