29 research outputs found
Finite volume simulation of 2-D and 3-D non-stationary magnetogasdynamic flow
This work presents the development of the ideal and real magnetogasdynamic (MGD) equations in two and three spatial dimensions, followed by a modern numerical resolution method. The equations that govern the MGD flows are continuity, momentum, energy and magnetic induction together with a state equation. The method of Roe has been applied, in a high resolution Total Variation Diminishing scheme, with modifications proposed by Yee et al. For the implementation of this method in finite volumes a FORTRAN code has been developed, and it has been applied to the resolution of the magnetogasdynamic Riemann problem and the Hartman flow. Due to the high computational cost demanded by a 3D simulation, it has been necessary to reduce the grid density, compared to that used on the unidimensional and bidimensional cases. In order to evaluate this last issue, an analysis of the effect of the grid density on the results has been included at the end of the present work. The magnetogasdynamic shock tube and the Hartman flow, used as “benchmarks”, have been satisfactorily solved.Grupo Fluidodinámica Computaciona
Finite volume simulation of 2-D and 3-D non-stationary magnetogasdynamic flow
This work presents the development of the ideal and real magnetogasdynamic (MGD) equations in two and three spatial dimensions, followed by a modern numerical resolution method. The equations that govern the MGD flows are continuity, momentum, energy and magnetic induction together with a state equation. The method of Roe has been applied, in a high resolution Total Variation Diminishing scheme, with modifications proposed by Yee et al. For the implementation of this method in finite volumes a FORTRAN code has been developed, and it has been applied to the resolution of the magnetogasdynamic Riemann problem and the Hartman flow. Due to the high computational cost demanded by a 3D simulation, it has been necessary to reduce the grid density, compared to that used on the unidimensional and bidimensional cases. In order to evaluate this last issue, an analysis of the effect of the grid density on the results has been included at the end of the present work. The magnetogasdynamic shock tube and the Hartman flow, used as “benchmarks”, have been satisfactorily solved.Grupo Fluidodinámica Computaciona
Atmospheric Reentry Dynamics of Conic Objects
One of the key issues in a reentry risk analysis is the calculation of the aerodynamic coefficients. This paper presents a methodology to obtain these coefficients and couple it to a code that computes re-entry trajectories considering six degrees of freedom. To evaluate the different flight conditions encountered during the natural re-entry of conical objects, the Euler Equations for gasdynamics flows are used. A new scheme TVD (Total Variation Diminishing) is incorporated to a finite volume unstructured cell-centred formulation, for application to three-dimensional Euler flows. Finally, numerical results are obtained for a conical body at different attack angles and Mach. With these results, the calculation of the trajectories during atmospheric re-entry is completed
Numerical simulation of dark lanes in post-flare supra-arcade
We integrate the MHD ideal equations to simulate dark void sunwardly moving
structures in post--flare supra--arcades. We study the onset and evolution of
the internal plasma instability to compare with observations and to gain
insight into physical processes and characteristic parameters of these
phenomena. The numerical approach uses a finite-volume Harten-Yee TVD scheme to
integrate the 1D1/2 MHD equations specially designed to capture supersonic flow
discontinuities. The integration is performed in both directions, the sunward
radial one and the transverse to the magnetic field. For the first time, we
numerically reproduce observational dark voids described in Verwichte et al.
(2005). We show that the dark tracks are plasma vacuums generated by the
bouncing and interfering of shocks and expansion waves, upstream an initial
slow magnetoacoustic shock produced by a localized deposition of energy modeled
with a pressure perturbation. The same pressure perturbation produces a
transverse to the field or perpendicular magnetic shock giving rise to
nonlinear waves that compose the kink--like plasma void structures, with the
same functional sunward decreasing phase speed and constancy with height of the
period, as those determined by the observations.Comment: Accepted MNRAS, 6 pages, 7 figure
Numerical simulation of the internal plasma dynamics of post-flare loops
We integrate the MHD ideal equations of a slender flux tube to simulate the
internal plasma dynamics of coronal post-flare loops. We study the onset and
evolution of the internal plasma instability to compare with observations and
to gain insight into physical processes and characteristic parameters
associated with flaring events. The numerical approach uses a finite-volume
Harten-Yee TVD scheme to integrate the 1D1/2 MHD equations specially designed
to capture supersonic flow discontinuities. We could reproduce the
observational sliding down and upwardly propagating of brightening features
along magnetic threads of an event occurred on October 1st, 2001. We show that
high--speed downflow perturbations, usually interpreted as slow magnetoacoustic
waves, could be better interpreted as slow magnetoacoustic shock waves. This
result was obtained considering adiabaticity in the energy balance equation.
However, a time--dependent forcing from the basis is needed to reproduce the
reiteration of the event which resembles observational patterns -commonly known
as quasi--periodic pulsations (QPPs)- which are related with large scale
characteristic longitudes of coherence. This result reinforces the
interpretation that the QPPs are a response to the pulsational flaring
activity.Comment: Accepted MNRAS, 10 pages, 14 figures, 1 tabl
Ultracompact microinterferometer-based fiber Bragg grating interrogator on a silicon chip
We report an interferometer-based multiplexed fiber Bragg grating (FBG) interrogator using silicon photonic technology. The photonic-integrated system includes the grating coupler, active and passive interferometers, interferometers, a 12-channel wavelength-division-multiplexing (WDM) filter, and Ge photodiodes, all integrated on a 6x8 mm2 silicon chip. The system also includes optical and electric interfaces to a printed board, which is connected to a real-time electronic board that actively performs the phase demodulation processing using a multitone mixing (MTM) technique. The device with active demodulation, which uses thermally-based phase shifters, features a noise figure of σ = 0.13 pm at a bandwidth of 700 Hz, which corresponds to a dynamic spectral resolution of 4.9 fm/Hz1/2. On the other hand, the passive version of the system, based on a 90º-hybrid coupler, features a noise figure of σ = 2.55 pm at a bandwidth of 10 kHz, also showing successful detection of a 42 kHz signal when setting the bandwidth to 50 kHz. These results demonstrate the advantage of integrated photonics, which allows the integration of several systems with different demodulation schemes in the same chip and guarantees easy scalability to a higher number of ports without increasing the dimensions or the cost
Simulation of dark lanes in post--flare supra--arcades
Using two simulations of 1.5D, for the first time, in Costa et al. (2009) and
Shulz et al. (2010) we numerically reproduce the observational dark inflows
described in Verwichte et al. (2005). We show that the dark tracks can be
explained as hot plasma vacuums generated upstream of a slow magnetoacoustic
shock wave produced by a localized deposition of energy. In this work, we show
that the overall 2D results are in agreement with the observational behaviour.
However they show a slight shift in the characteristic parameter with respect
to those found previously. Also, we confirm qualitatively the behaviour found
in the previous papers, i.e. for a given numerical domain the period of the
kink--like structure is a function of the magnetic field intensity: larger
periods are associated with lower magnetic field intensities. Contrary to the
1D result -where the sunward dynamic is independent of the magnetic field
intensity due to its exclusively waveguide role- in the 2D simulation the
sunward speed is larger for larger values of the magnetic field. This can be
interpreted as the capability of the low coronal plasma to collimate the
deposition of energy into the magnetic field direction. The moving features
consistent of low--density and high--temperature plasma cavities have larger
inside values of the structuring parameter beta than the neighboring media.
Thus, the voids seem to be the emergence structures of a whole nonlinear
interacting plasma context of shocks and waves more than voided plasma loops
magnetically structured.Comment: 5 pages, 5 figure