13,060 research outputs found
Thermophysical Phenomena in Metal Additive Manufacturing by Selective Laser Melting: Fundamentals, Modeling, Simulation and Experimentation
Among the many additive manufacturing (AM) processes for metallic materials,
selective laser melting (SLM) is arguably the most versatile in terms of its
potential to realize complex geometries along with tailored microstructure.
However, the complexity of the SLM process, and the need for predictive
relation of powder and process parameters to the part properties, demands
further development of computational and experimental methods. This review
addresses the fundamental physical phenomena of SLM, with a special emphasis on
the associated thermal behavior. Simulation and experimental methods are
discussed according to three primary categories. First, macroscopic approaches
aim to answer questions at the component level and consider for example the
determination of residual stresses or dimensional distortion effects prevalent
in SLM. Second, mesoscopic approaches focus on the detection of defects such as
excessive surface roughness, residual porosity or inclusions that occur at the
mesoscopic length scale of individual powder particles. Third, microscopic
approaches investigate the metallurgical microstructure evolution resulting
from the high temperature gradients and extreme heating and cooling rates
induced by the SLM process. Consideration of physical phenomena on all of these
three length scales is mandatory to establish the understanding needed to
realize high part quality in many applications, and to fully exploit the
potential of SLM and related metal AM processes
Eulerian-Lagrangian method for simulation of cloud cavitation
We present a coupled Eulerian-Lagrangian method to simulate cloud cavitation
in a compressible liquid. The method is designed to capture the strong,
volumetric oscillations of each bubble and the bubble-scattered acoustics. The
dynamics of the bubbly mixture is formulated using volume-averaged equations of
motion. The continuous phase is discretized on an Eulerian grid and integrated
using a high-order, finite-volume weighted essentially non-oscillatory (WENO)
scheme, while the gas phase is modeled as spherical, Lagrangian point-bubbles
at the sub-grid scale, each of whose radial evolution is tracked by solving the
Keller-Miksis equation. The volume of bubbles is mapped onto the Eulerian grid
as the void fraction by using a regularization (smearing) kernel. In the most
general case, where the bubble distribution is arbitrary, three-dimensional
Cartesian grids are used for spatial discretization. In order to reduce the
computational cost for problems possessing translational or rotational
homogeneities, we spatially average the governing equations along the direction
of symmetry and discretize the continuous phase on two-dimensional or
axi-symmetric grids, respectively. We specify a regularization kernel that maps
the three-dimensional distribution of bubbles onto the field of an averaged
two-dimensional or axi-symmetric void fraction. A closure is developed to model
the pressure fluctuations at the sub-grid scale as synthetic noise. For the
examples considered here, modeling the sub-grid pressure fluctuations as white
noise agrees a priori with computed distributions from three-dimensional
simulations, and suffices, a posteriori, to accurately reproduce the statistics
of the bubble dynamics. The numerical method and its verification are described
by considering test cases of the dynamics of a single bubble and cloud
cavitaiton induced by ultrasound fields.Comment: 28 pages, 16 figure
The LifeV library: engineering mathematics beyond the proof of concept
LifeV is a library for the finite element (FE) solution of partial
differential equations in one, two, and three dimensions. It is written in C++
and designed to run on diverse parallel architectures, including cloud and high
performance computing facilities. In spite of its academic research nature,
meaning a library for the development and testing of new methods, one
distinguishing feature of LifeV is its use on real world problems and it is
intended to provide a tool for many engineering applications. It has been
actually used in computational hemodynamics, including cardiac mechanics and
fluid-structure interaction problems, in porous media, ice sheets dynamics for
both forward and inverse problems. In this paper we give a short overview of
the features of LifeV and its coding paradigms on simple problems. The main
focus is on the parallel environment which is mainly driven by domain
decomposition methods and based on external libraries such as MPI, the Trilinos
project, HDF5 and ParMetis.
Dedicated to the memory of Fausto Saleri.Comment: Review of the LifeV Finite Element librar
Recommended from our members
Lattice Boltzmann simulation of magnetic field effects on nanofluid
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.In this paper, the magnetic field effects on natural convection heat transfer in an enclosure filled with nanofluid are numerically investigated by using lattice Boltzmann method. The fluid in the enclosure is a water-based nanofluid containing Al2O3 nanoparticles. A uniform external magnetic field with different angles was applied. A series of simulation cases were carried out for different governing parameters including Hartmann number, Rayleigh number, the nanoparticle volume fractions and magnetic field angles. The results show that the increasing Rayleigh number and nanoparticle volume fraction improve the heat transfer in the enclosure. However, the heat transfer has been suppressed when Hartmann number increases. The results also indicate there are critical values for the Raleigh number and also the magnetic field orientation, at which the impacts of the solid volume fraction and magnetic field effects are the most pronounced
DSMC investigation of rarefied gas flow through diverging micro- and nanochannels
Direct simulation Monte Carlo (DSMC) method with simplified Bernoulli-trials
(SBT) collision scheme has been used to study the rarefied pressure-driven
nitrogen flow through diverging microchannels. The fluid behaviours flowing
between two plates with different divergence angles ranging between 0
to 17 are described at different pressure ratios
(1.52.5) and Knudsen numbers (0.03Kn12.7). The
primary flow field properties, including pressure, velocity, and temperature,
are presented for divergent microchannels and are compared with those of a
microchannel with a uniform cross-section. The variations of the flow field
properties in divergent microchannels, which are influenced by the area change,
the channel pressure ratio and the rarefication are discussed. The results show
no flow separation in divergent microchannels for all the range of simulation
parameters studied in the present work. It has been found that a divergent
channel can carry higher amounts of mass in comparison with an equivalent
straight channel geometry. A correlation between the mass flow rate through
microchannels, the divergence angle, the pressure ratio, and the Knudsen number
has been suggested. The present numerical findings prove the occurrence of
Knudsen minimum phenomenon in micro- and Nano- channels with non-uniform
cross-sections.Comment: Accepted manuscript; 25 Pages and 11 Figures; "Microfluidics and
Nanofluidics
A fast GPU Monte Carlo Radiative Heat Transfer Implementation for Coupling with Direct Numerical Simulation
We implemented a fast Reciprocal Monte Carlo algorithm, to accurately solve
radiative heat transfer in turbulent flows of non-grey participating media that
can be coupled to fully resolved turbulent flows, namely to Direct Numerical
Simulation (DNS). The spectrally varying absorption coefficient is treated in a
narrow-band fashion with a correlated-k distribution. The implementation is
verified with analytical solutions and validated with results from literature
and line-by-line Monte Carlo computations. The method is implemented on GPU
with a thorough attention to memory transfer and computational efficiency. The
bottlenecks that dominate the computational expenses are addressed and several
techniques are proposed to optimize the GPU execution. By implementing the
proposed algorithmic accelerations, a speed-up of up to 3 orders of magnitude
can be achieved, while maintaining the same accuracy
Fluid-structure interaction simulation of pulse propagation in arteries : numerical pitfalls and hemodynamic impact of a local stiffening
When simulating the propagation of a pressure pulse in arteries, the discretization parameters (i.e. the time step size and the grid size) need to be chosen carefully in order to avoid a decrease in amplitude of the traveling wave due to numerical dissipation. In this paper the effect of numerical dissipation is examined using a numerical fluid-structure interaction (FSI) model of the pulse propagation in an artery.
More insight in the influence of the temporal and spatial resolution of the wave on the results of these simulations is gained using an analytical study in which the scalar linear one-dimensional transport equation is considered. Although this model does not take into account the full complexity of the problem under consideration, the results can be used as a guidance for the selection of the numerical parameters. Furthermore, this analysis illustrates the difference in accuracy that can be obtained using a second-order implicit time integration scheme instead of a first-order scheme. The results from the analytical and numerical studies are subsequently used to determine the settings necessary to obtain a grid and time step converged simulation of the wave propagation and reflection in a simplified model of an aorta with repaired aortic coarctation. This FSI model allows to study the hemodynamic impact of a stiff segment and demonstrates that the presence of a stiff segment has an important impact on a short pressure pulse, but has almost no influence on a physiological pressure pulse. This phenomenon is explained by analyzing the reflections induced by the stiff segment
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