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Search Results: 1 - 10 of 130416 matches for " Livescu V. "
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Mesoscale polycrystal calculations of damage in spallation in metals
Tonks D.L.,Bingert J.,Livescu V.,Luo S.
EPJ Web of Conferences , 2011, DOI: 10.1051/epjconf/20101000006
Abstract: The goal of this project is to produce a damage model forspallation in metals informed by the polycrystalline grain structure at themesoscale. Earlier damage models addressed the continuum macroscale in whichthese effects were averaged out. In this work we focus on cross sectionsfrom recovered samples examined with EBSD (electron backscattereddiffraction), which reveal crystal grain orientations and voids. We seek tounderstand the loading histories of specific sample regions by meshing upthe crystal grain structure of these regions and simulating the stress,strain, and damage histories in our hydrocode, FLAG. The stresses and strainhistories are the fundamental drivers of damage and must be calculated. Thecalculated final damage structures are compared with those from therecovered samples to validate the simulations.
Compressibility effects on the Rayleigh-Taylor instability growth between immiscible fluids
Daniel Livescu
Physics , 2003, DOI: 10.1063/1.1630800
Abstract: The linearized Navier-Stokes equations for a system of superposed immiscible compressible ideal fluids are analyzed. The results of the analysis reconcile the stabilizing and destabilizing effects of compressibility reported in the literature. It is shown that the growth rate $n$ obtained for an inviscid, compressible flow in an infinite domain is bounded by the growth rates obtained for the corresponding incompressible flows with uniform and exponentially varying density. As the equilibrium pressure at the interface $p_\infty$ increases (less compressible flow), $n$ increases towards the uniform density result, while as the ratio of specific heats $\gamma$ increases (less compressible fluid), $n$ decreases towards the exponentially varying density incompressible flow result. This remains valid in the presence of surface tension or for viscous fluids and the validity of the results is also discussed for finite size domains. The critical wavenumber imposed by the presence of surface tension is unaffected by compressibility. However, the results show that the surface tension modifies the sensitivity of the growth rate to a differential change in $\gamma$ for the lower and upper fluids. For the viscous case, the linearized equations are solved numerically for different values of $p_\infty$ and $\gamma$. It is found that the largest differences compared with the incompressible cases are obtained at small Atwood numbers. The most unstable mode for the compressible case is also bounded by the most unstable modes corresponding to the two limiting incompressible cases.
Influence of sweeping detonation-wave loading on shock hardening and damage evolution during spallation loading in tantalum
Gray G.T.,Hull L.M.,Livescu V.,Faulkner J.R.
EPJ Web of Conferences , 2012, DOI: 10.1051/epjconf/20122602004
Abstract: Widespread research over the past five decades has provided a wealth of experimental data and insight concerning the shock hardening, damage evolution, and the spallation response of materials subjected to square-topped shock-wave loading profiles. However, fewer quantitative studies have been conducted on the effect of direct, in-contact, high explosive (HE)-driven Taylor wave (unsupported shocks) loading on the shock hardening, damage evolution, or spallation response of materials. Systematic studies quantifying the effect of sweeping-detonation wave loading are yet sparser. In this study, the shock hardening and spallation response of Ta is shown to be critically dependent on the peak shock stress and the shock obliquity during sweeping-detonation-wave shock loading. Sweeping-wave loading is observed to: a) yield a lower spall strength than previously documented for 1-D supported-shock-wave loading, b) exhibit increased shock hardening as a function of increasing obliquity, and c) lead to an increased incidence of deformation twin formation with increasing shock obliquity.
étude cytogénétique des taureaux d'un centre d'insémination artificielle en roumanie
Br?ndusa Livescu
Genetics Selection Evolution , 1977, DOI: 10.1186/1297-9686-9-4-529a
Cytogenetic studies of buffaloes in Romania
Brandu?a Livescu
Genetics Selection Evolution , 1982, DOI: 10.1186/1297-9686-14-1-111a
Cytogenetic studies of buffaloes in Romania
Livescu Brandu?a
Genetics Selection Evolution , 1982, DOI: 10.1186/1297-9686-14-1-111
Direct Numerical Simulation of Single-mode Rayleigh-Taylor Instability
Tie Wei,Daniel Livescu
Physics , 2011,
Abstract: Single-mode Rayleigh-Taylor instability is investigated using Direct Numerical Simulation.
Large-Scale Approximate Kernel Canonical Correlation Analysis
Weiran Wang,Karen Livescu
Computer Science , 2015,
Abstract: Kernel Canonical correlation analysis (KCCA) is a fundamental method with broad applicability in statistics and machine learning. Although there exist closed-form solution to the KCCA objective by solving an $N\times N$ eigenvalue system where $N$ is the training set size, the computational requirements of this approach in both memory and time prohibit its usage in the large scale. Various approximation techniques have been developed for KCCA. A recently proposed approach is to first transform original inputs to a $M$-dimensional feature space using random kitchen sinks so that inner product in the feature space approximates the kernel function, and then apply linear CCA to the transformed inputs. In challenging applications, however, the dimensionality $M$ of the feature space may need to be very large in order to reveal the nonlinear correlations, and then it becomes non-trivial to solve linear CCA for data matrices of very high dimensionality. We propose to use the recently proposed stochastic optimization algorithm for linear CCA and its neural-network extension to further alleviate the computation requirements of approximate KCCA. This approach allows us to run approximate KCCA on a speech dataset with $1.4$ million training samples and random feature space of dimensionality $M=100000$ on a normal workstation.
Non-premixed Flame-Turbulence Interaction in Compressible Turbulent Flow
Daniel Livescu,Cyrus K. Madnia
Physics , 2002,
Abstract: Nonpremixed turbulent reacting flows are intrinsically difficult to model due to the strong coupling between turbulent motions and reaction. The large amount of heat released by a typical hydrocarbon flame leads to significant modifications of the thermodynamic variables and the molecular transport coefficients and thus alters the fluid dynamics. Additionally, in nonpremixed combustion, the flame has a complex spatial structure. Localized expansions and contractions occur, enhancing the dilatational motions. Therefore, the compressibility of the flow and the heat release are intimately related. However, fundamental studies of the role of compressibility on the scalar mixing and reaction are scarce. In this paper we present results concerning the fundamental aspects of the interaction between non-premixed flame and compressible turbulence.
Compressibility effects on the scalar mixing in reacting homogeneous turbulence
Daniel Livescu,Cyrus K. Madnia
Physics , 2002,
Abstract: The compressibility and heat of reaction influence on the scalar mixing in decaying isotropic turbulence and homogeneous shear flow are examined via data generated by direct numerical simulations (DNS). The reaction is modeled as one-step, exothermic, irreversible and Arrhenius type. For the shear flow simulations, the scalar dissipation rate, as well as the time scale ratio of mechanical to scalar dissipation, are affected by compressibility and reaction. This effect is explained by considering the transport equation for the normalized mixture fraction gradient variance and the relative orientation between the mixture fraction gradient and the eigenvectors of the solenoidal strain rate tensor.
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