14,741 research outputs found
A well-balanced meshless tsunami propagation and inundation model
We present a novel meshless tsunami propagation and inundation model. We
discretize the nonlinear shallow-water equations using a well-balanced scheme
relying on radial basis function based finite differences. The inundation model
relies on radial basis function generated extrapolation from the wet points
closest to the wet-dry interface into the dry region. Numerical results against
standard one- and two-dimensional benchmarks are presented.Comment: 20 pages, 13 figure
Simulation of gain stability of THGEM gas-avalanche particle detectors
Charging-up processes affecting gain stability in Thick Gas Electron
Multipliers (THGEM) were studied with a dedicated simulation toolkit.
Integrated with Garfield++, it provides an effective platform for systematic
phenomenological studies of charging-up processes in MPGD detectors. We
describe the simulation tool and the fine-tuning of the step-size required for
the algorithm convergence, in relation to physical parameters. Simulation
results of gain stability over time in THGEM detectors are presented, exploring
the role of electrode-thickness and applied voltage on its evolution. The
results show that the total amount of irradiated charge through electrode's
hole needed for reaching gain stabilization is in the range of tens to hundreds
of pC, depending on the detector geometry and operational voltage. These
results are in agreement with experimental observations presented previously
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Numerical investigations on bubble-induced jetting and shock wave focusing: application on a needle-free injection
The formation of a liquid jet into air induced by the growth of a laser-generated bubble inside a needle-free device is numerically investigated by employing the compressible Navier–Stokes equations. The three co-existing phases (liquid, vapour and air) are assumed to be in thermal equilibrium. A transport equation for the gas mass fraction is solved in order to simulate the non-condensable gas. The homogeneous equilibrium model is used in order to account for the phase change process between liquid and vapour. Thermodynamic closure for all three phases is achieved by a barotropic Equation of State. Two-dimensional axisymmetric simulations are performed for a needle-free device for which experimental data are available and used for the validation of the developed model. The influence of the initial bubble pressure and the meniscus geometry on the jet velocity is examined by two different sets of studies. Based on the latter, a new meniscus design similar to shaped-charge jets is proposed, which offers a more focused and higher velocity jet compared to the conventional shape of the hemispherical gas–liquid interface. Preliminary calculations show that the developed jet can penetrate the skin and thus, such configurations can contribute towards a new needle-free design
The Propagation of Magneto-Centrifugally Launched Jets: I
We present simulations of the propagation of magnetized jets. This work
differs from previous studies in that the cross-sectional distributions of the
jets's state variables are derived from analytical models for
magneto-centrifugal launching. The source is a magnetized rotator whose
properties are specfied as boundary conditions. The jets in these simulations
are considerably more complex than the ``top-hat''constant density etc.
profiles used in previous work. We find that density and magnetic field
stratification (with radius) in the jet leads to new behavior including the
separation of an inner jet core from a low density collar. We find this {\it
jet within a jet} structure, along with the magnetic stresses, leads to
propagation behaviors not observed in previous simulation studies. Our
methodology allows us to compare MHD jets from different types of sources whose
properties could ultimately be derived from the behavior of the propagating
jets.Comment: 42 pages, accepted by the Ap
Testing and Analysis Correlation of Composite Sandwich Longitudinal Bonded Joints for Space Launch Vehicle Structures
The NASA Composite Technology for Exploration (CTE) Project has been developing and demonstrating critical composite technologies with a focus on joints; incorporating materials, design/analysis, manufacturing, and tests that utilize NASA expertise and capabilities. The CTE project has focused on the development of composite longitudinal bonded joint technologies for conical structures such as the SLS Payload Attach Fitting (PAF) due to challenging joint geometries and loads compared to cylindrical jointed structures. The CTE team selected and designed a double-lap composite bonded joint as the most advantageous longitudinal joint to advance for the CTE project. This paper reports on the longitudinal bonded joint sub-element test articles that were fabricated and tested for several loading conditions to test the capability of the bonded joint design. Test and analysis correlation to the sub-element test articles are presented in the paper
WavePacket: A Matlab package for numerical quantum dynamics. III: Quantum-classical simulations and surface hopping trajectories
WavePacket is an open-source program package for numerical simulations in
quantum dynamics. Building on the previous Part I [Comp. Phys. Comm. 213,
223-234 (2017)] and Part II [Comp. Phys. Comm. 228, 229-244 (2018)] which dealt
with quantum dynamics of closed and open systems, respectively, the present
Part III adds fully classical and mixed quantum-classical propagations to
WavePacket. In those simulations classical phase-space densities are sampled by
trajectories which follow (diabatic or adiabatic) potential energy surfaces. In
the vicinity of (genuine or avoided) intersections of those surfaces
trajectories may switch between surfaces. To model these transitions, two
classes of stochastic algorithms have been implemented: (1) J. C. Tully's
fewest switches surface hopping and (2) Landau-Zener based single switch
surface hopping. The latter one offers the advantage of being based on
adiabatic energy gaps only, thus not requiring non-adiabatic coupling
information any more.
The present work describes the MATLAB version of WavePacket 6.0.2 which is
essentially an object-oriented rewrite of previous versions, allowing to
perform fully classical, quantum-classical and quantum-mechanical simulations
on an equal footing, i.e., for the same physical system described by the same
WavePacket input. The software package is hosted and further developed at the
Sourceforge platform, where also extensive Wiki-documentation as well as
numerous worked-out demonstration examples with animated graphics are
available
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