We use chiral interactions and several ab initio methods to compute the nuclear matrix elements (NMEs) for ground-state-to-ground-state double Gamow-Teller transitions in a range of isotopes and explore the correlation of these NMEs with those for neutrinoless double beta decay produced by the exchange of a light Majorana neutrino. When all the NMEs of both isospin-conserving and isospin-changing transitions from the ab initio calculations are considered, the correlation is strong. For the experimentally relevant isospin-changing transitions by themselves, however, the correlation is weaker and may not be helpful for reducing the uncertainty in the NMEs for neutrinoless double beta decay.

Multiphase systems are a natural occurrence. One particular representative are dynamic liquid-gas systems, commonly known as free surface ows. Free surface ows appear constantly in our everyday life, be it falling rain, a shower or a cup of co ee. However, aside from being a natural phenomenon, liquid-gas systems are of great importance for many industrial applications. Sprays in combustion engines, sloshing of liquid in tanks of moving vehicles, bubbly ows in chemical reactors are a small range of examples for industrial systems, where the movement and dynamics of liquids play an important role. The traditional way to study the e ects of these phenomena is to carry out physical experiments, however, depending on the problem this may be too complex, expensive or taking just too long to be feasible. Therefore, numerical simulations became an important tool in scienti c and industrial work. To simulate free surface ows, two main components are needed: a module solving the ow eld on one hand and a module updating the deforming computational domain on the other hand. The latter is a particular notorious aspect of free surface ow simulations. Many di erent methods handling the movement of the liquid-gas interface have been developed for this over the course of the last decades, which have di erent pros and cons. An important feature of a numerical method is the order of convergence, which dictates the reduction of the error for increasingly ner domain resolutions. One speci c interface advection method is the mass exchange method which is based on the volume of uid approach. It is speci cally designed for the lattice Boltzmann method, a particular ow solver which is gaining popularity over the last years. While relatively simple to implement, recent studies have shown a low order of accuracy which lowers the the order of the whole system of methods. The goal of this work is to close this bottleneck. A more sophisticated volume of uid algorithm based on geometric operations is implemented and coupled with a lattice Boltzmann solver. The order of convergence of both methods is compared by using various advection test cases, investigating the development of the geometrical and mass error. In the end, the coupling of the geometrical method with the lattice Boltzmann solver is validated by multiple standard benchmarks.

Direct numerical simulation of liquid-gas-solid flows is uncommon due to the considerable computational cost. As the grid spacing is determined by the smallest involved length scale, large grid sizes become necessary -in particular, if the bubble-particle aspect ratio is on the order of 10 or larger. Hence, it arises the question of both feasibility and reasonability. In this paper, we present a fully parallel, scalable method for direct numerical simulation of bubble-particle interaction at a size ratio of 1-2 orders of magnitude that makes simulations feasible on currently available super-computing resources. With the presented approach, simulations of bubbles in suspension columns consisting of more than 100,000 fully resolved particles become possible. Furthermore, we demonstrate the significance of particle-resolved simulations by comparison to previous unresolved solutions. The results indicate that fully resolved direct numerical simulation is indeed necessary to predict the flow structure of bubble-particle interaction problems correctly.

The free surface lattice Boltzmann method (FSLBM) is a combination of the hydrodynamic lattice Boltzmann method with a volume-of-fluid (VOF) interface capturing technique for the simulation of incompressible free surface flows. Capillary effects are modeled by extracting the curvature of the interface from the VOF indicator function and imposing a pressure jump at the free boundary. However, obtaining accurate curvature estimates from a VOF description can introduce significant errors. This article reports numerical results for three different surface tension models in standard test cases and compares the according errors in the velocity field (spurious currents). Furthermore, the FSLBM is shown to be suited to simulate wetting effects at solid boundaries. To this end, a new method is developed to represent wetting boundary conditions in a least-squares curvature reconstruction technique. The main limitations of the current FSLBM are analyzed and are found to be caused by its simplified advection scheme. Possible improvements are suggested.

In this paper we analyze the boundary treatment of the lattice Boltzmann method (LBM) for simulating 3D flows with free surfaces. The widely used free surface boundary condition of Korner etal. [27] is shown to be first order accurate. The article presents a new free surface boundary scheme that is suitable for second order accurate simulations based on the LBM. The new method takes into account the free surface position and its orientation with respect to the computational lattice. Numerical experiments confirm the theoretical findings and illustrate the different behavior of the original method and the new method. (C) 2015 Elsevier Inc. All rights reserved.

This paper presents a numerical study of flow through static random assemblies of monodisperse, spherical particles. A lattice Boltzmann approach based on a two relaxation time collision operator is used to obtain reliable predictions of the particle drag by direct numerical simulation. From these predictions a closure law F(Re-p, phi) of the drag force relationship to the bed density phi and the particle Reynolds number Re phi is derived. The present study includes densities phi ranging from 0.01 to 0.35 with Re phi ranging up to 300, that is compiled into a single drag correlation valid for the whole range. The correlation has a more compact expression compared to others previously reported in literature. At low particle densities, the new correlation is close to the widely-used Wen & Yu - correlation.Recently, there has been reported a discrepancy between results obtained using different numerical methods, namely the comprehensive lattice Boltzmann study of Beetstra et al. (2007) and the predictions based on an immersed boundary - pseudo-spectral Navier-Stokes approach (Tenneti et al., 2011). The present study excludes significant finite resolution effects, which have been suspected to cause the reported deviations, but does not coincide exactly with either of the previous studies. This indicates the need for yet more accurate simulation methods in the future. (C) 2014 Elsevier Ltd. All rights reserved.

Simulations play an important role in many elds. This is especially true for uid ow simulations. This theses will describe uid ow simulations that are based on the lattice Boltzmann model. A framework that implements this model is waLBerla, a massively parallel multiphysics software framework. The huge amount of data created by simulations has to be made human comprehensible, in order to analyze it. This is done with the help of visualization software. One of these is VisIt, an open source, interactive, scalable, visualization, animation and analysis tool. There are di erent approaches to visualize the data. Usually simulations store their data, so it can be visualized later. Another approach is to visualize the data, while the simulation is running. Tools like VisIt are able to run in in situ mode, which means they are capable of visualizing data, as it is created. VisIt o ers a library, which programmers can use to "build the bridge" between the simulation code and the visualization tool. It will be explained how this library works and how it integrates into an existing simulation code. Furthermore the waLBerla framework was extended, using the VisIt library. This makes it possible to connect to a running waLBerla simulation with VisIt and analyze the data, as it is created. Furthermore it was explored, which possibilities VisIt o ers to steer the execution of the running simulation.

This paper presents an enhancement to the free surface lattice Boltzmann method (FSLBM) for the simulation of bubbly flows including rupture and breakup of bubbles. The FSLBM uses a volume of fluid approach to reduce the problem of a liquid-gas two-phase flow to a single-phase free surface simulation. In bubbly flows compression effects leading to an increase or decrease of pressure in the suspended bubbles cannot be neglected. Therefore, the free surface simulation is augmented by a bubble model that supplies the missing information by tracking the topological changes of the free surface in the flow. The new model presented here is capable of handling the effects of bubble breakup and coalesce without causing a significant computational overhead. Thus, the enhanced bubble model extends the applicability of the FSLBM to a new range of practically relevant problems, like bubble formation and development in chemical reactors or foaming processes.

The UNEDF project was a large-scale collaborative effort that applied high-performance computing to the nuclear quantum many-body problem. The primary focus of the project was on constructing, validating, and applying an optimized nuclear energy density functional, which entailed a wide range of pioneering developments in microscopic nuclear structure and reactions, algorithms, high-performance computing, and uncertainty quantification. UNEDF demonstrated that close associations among nuclear physicists, mathematicians, and computer scientists can lead to novel physics outcomes built on algorithmic innovations and computational developments. This review showcases a wide range of UNEDF science results to illustrate this interplay.

This paper is devoted to the simulation of floating rigid bodies in free surface flows. For that, a lattice Boltzmann based model for liquid–gas–solid flows is presented. The approach is built upon previous work for the simulation of liquid–solid particle suspensions on the one hand, and on an interface-capturing technique for liquid–gas free surface flows on the other. The incompressible liquid flow is approximated by a lattice Boltzmann scheme, while the dynamics of the compressible gas are neglected. We show how the particle model and the interface capturing technique can be combined by a novel set of dynamic cell conversion rules. We also evaluate the behaviour of the free surface–particle interaction in simulations. One test case is the rotational stability of non-spherical rigid bodies floating on a plane water surface–a classical hydrostatic problem known from naval architecture. We show the consistency of our method in this kind of flows and obtain convergence towards the ideal solution for the heeling stability of a floating box.

We study the statistics of thermodynamic quantities in two related systems with quenched disorder: A (1+1)-dimensional planar lattice of elastic lines in a random potential and the two-dimensional random bond dimer model. The first system is examined by a replica-symmetric Bethe Ansatz (RBA) while the latter is studied numerically by a polynomial algorithm which circumvents slow glassy dynamics. We establish a mapping of the two models which allows for a detailed comparison of RBA predictions and simulations. Over a wide range of disorder strength, the effective lattice stiffness and cumulants of various thermodynamic quantities in both approaches are found to agree excellently. Our comparison provides a detailed quantitative confirmation of the replica approach and renders the planar line lattice a unique testing ground for concepts in random systems.

The three-body energy-dependent effective interaction given by the Bloch-Horowitz equation is evaluated for various shell-model oscillator spaces. The results are applied to the test cases of the three-body problem (H-3 and He-3), where it is shown that the interaction reproduces the exact binding energy, regardless of the parametrization (number of oscillator quanta or value of the oscillator parameter b) of the low-energy included space. We demonstrate a nonperturbative technique for summing the excluded-space three-body ladder diagrams, but also show that accurate results can be obtained perturbatively by iterating the two-body ladders. We examine the evolution of the effective two-body and induced three-body terms as b and the size of the included space Lambda are varied, including the case of a single included shell: Lambda(h) over bar omega=0 (h) over bar omega. For typical ranges of b, the induced effective three-body interaction, essential for giving the exact three-body binding, is found to contribute similar to10% to the binding energy.

The criteria for the existence of a glass transition in a planar vortex array with quenched disorder are studied. Applying a replica Bethe ansatz, we obtain for self-avoiding vortices the exact quenched average free energy and effective stiffness which is found to be in excellent agreement with recent numerical results for the related random bond dimer model [C. Zeng, P. L. Leath, and T. Hwa, Phys. Rev. Lett. 83, 4860 (1999)] Including a repulsive vortex interaction and a finite vortex persistence length xi, we find that for xi-->0 the system is at all temperatures in a glassy phase; a glass transition exists only for finite xi. Our results indicate that planar vortex arrays in superconducting films are glassy at presumably all temperatures.

A new approach for deriving the shell-model effective interaction from realistic nucleon-nucleon potentials V-NN is studied. We first transform VNN to a physically equivalent low-momentum potential Vlow-k within a cut-off momentum k(cut). The deuteron binding energy, low-energy phase shifts and low-momentum half-on-shell T-matrix given by VNN are exactly reproduced by Vlow-k. We have found that Vlow-k is a generally smooth potential (without a strong repulsive core) and appears to be suitable for being used directly in nuclear shell model calculations, without the need of first calculating the usual Brueckner G-matrix. Using the Vlow-k given by k(cut) = 2 fm(-1), we have carried out a folded-diagram shell model calculation of O-18 and have obtained highly encouraging results. The results given by the Bonn-A and Paris potentials are close to each other.