scholarly journals A Plane-Parallel Wind Solution for Testing Numerical Simulations of Photoevaporation

2016 ◽  
Vol 33 ◽  
Author(s):  
Mark A. Hutchison ◽  
Guillaume Laibe
Keyword(s):  
Solar Wind ◽  
Numerical Simulations ◽  
Test Problem ◽  
Analytic Solution ◽  
Sonic Point ◽  
Plane Parallel ◽  
The Difference ◽  
Protoplanetary Discs

AbstractHere, we derive a Parker-wind-like solution for a stratified, plane-parallel atmosphere undergoing photoionisation. The difference compared to the standard Parker solar wind is that the sonic point is crossed only at infinity. The simplicity of the analytic solution makes it a convenient test problem for numerical simulations of photoevaporation in protoplanetary discs.

Modulation instability in nonlinear chiral fiber

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Demissie Jobir Gelmecha ◽  
Ram Sewak Singh
Keyword(s):  
Theoretical Model ◽  
Numerical Simulations ◽  
Pulse Propagation ◽  
Modulation Instability ◽  
Constitutive Relations ◽  
Gain Spectrum ◽  
Circularly Polarized ◽  
Left Handed ◽  
Simulation Results ◽  
The Difference

AbstractIn this paper, the rigorous derivations of generalized coupled chiral nonlinear Schrödinger equations (CCNLSEs) and their modulation instability analysis have been explored theoretically and computationally. With the consideration of Maxwell’s equations and Post’s constitutive relations, a generalized CCNLSE has been derived, which describes the evolution of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) components propagating through single-core nonlinear chiral fiber. The analysis of modulation instability in nonlinear chiral fiber has been investigated starting from CCNLSEs. Based on a theoretical model and numerical simulations, the difference on the modulation instability gain spectrum in LCP and RCP components through chiral fiber has been analyzed by considering loss and chirality into account. The obtained simulation results have shown that the loss distorts the sidebands of the modulation instability gain spectrum, while chirality modulates the gain for LCP and RCP components in a different manner. This suggests that adjusting chirality strength may control the loss, and nonlinearity simultaneously provides stable modulated pulse propagation.

scholarly journals The charge-exchange induced coupling between plasma-gas counterflows in the heliosheath

2003 ◽  
Vol 21 (6) ◽  
pp. 1289-1294 ◽  
Author(s):  
H. J. Fahr
Keyword(s):  
Solar Wind ◽  
Critical Point ◽  
Charge Exchange ◽  
Plasma Temperature ◽  
Exchange Term ◽  
Momentum Exchange ◽  
Plasma Bubble ◽  
Friction Forces ◽  
Sonic Point ◽  
Interplanetary Physics

Abstract. Many hydrodynamic models have been presented which give similar views of the interaction of the solar wind plasma bubble with the counterstreaming partially ionized interstellar medium. In the more recent of these models it is taken into account that the solar and interstellar hydrodynamic flows of neutral atoms and protons are coupled by mass-, momentum-, and energy-exchange terms due to charge exchange processes. We shall reinvestigate the theoretical basis of this coupling here by use of a simplified description of the heliospheric interface and describe the main physics of the H-atom penetration through the more or less standing well-known plasma wall ahead of the heliopause. Thereby we can show that the type of charge exchange coupling terms used in up-to-now hydrodynamic treatments unavoidably leads to an O-type critical point at the sonic point of the H-atom flow, thus not allowing for a continuation of the integration of the hydrodynamic set of differential equations. The remedy for this problem is given by a more accurate formulation of the momentum exchange term for quasi-and sub-sonic H-atom flows. With a refined momentum exchange term derived from basic kinetic Boltzmann principles, we instead arrive at a characteristic equation with an X-type critical point, allowing for a continuous solution from supersonic to subsonic flow conditions. This necessitates that the often treated problem of the propagation of inter-stellar H-atoms through the heliosheath has to be solved using these newly derived, differently effective plasma – gas friction forces. Substantially different results are to be expected from this context for the filtration efficiency of the heliospheric interface.Key words. Interplanetary physics (heliopause and solar wind termination; interstellar gas) – Ionosphere (plasma temperature and density)

scholarly journals Numerical simulations of homologous coronal mass ejections in the solar wind

2009 ◽  
Vol 501 (3) ◽  
pp. 1123-1130 ◽  
Author(s):  
A. Soenen ◽  
F. P. Zuccarello ◽  
C. Jacobs ◽  
S. Poedts ◽  
R. Keppens ◽  
...  
Keyword(s):  
Solar Wind ◽  
Numerical Simulations ◽  
Coronal Mass Ejections

NUMERICAL SIMULATIONS OF SOLAR WIND TURBULENCE

2005 ◽  
pp. 301-320 ◽  
Author(s):  
Melvyn L. Goldstein ◽  
Roberts D. Aaron ◽  
Arcadi V. Usmanov
Keyword(s):  
Solar Wind ◽  
Numerical Simulations ◽  
Solar Wind Turbulence ◽  
Wind Turbulence

scholarly journals Numerical Simulations of Advective Flows Around Black Holes

1997 ◽  
Vol 163 ◽  
pp. 690-691
Author(s):  
Sandip K. Chakrabarti ◽  
D. Ryu ◽  
D. Molteni ◽  
H. Sponholz ◽  
G. Lanzafame ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Periodic Oscillation ◽  
Compact Objects ◽  
Advective Flow ◽  
Sonic Point ◽  
Quasi Periodic Oscillation ◽  
Accretion Flows ◽  
Advective Flows ◽  
Cooling Effects ◽  
Implicit Code

Observational results of compact objects are best understood using advective accretion flows (Chakrabarti, 1996, 1997). We present here the results of numerical simulations of all possible types of such flows.Two parameter (specific energy ε and specific angular momentum λ) space of solutions of inviscid advective flow is classified into ‘SA’ (shocks in accretion), ‘NSA’ (no shock in accretion), ‘I’ (inner sonic point only), ‘O’ (outer sonic point only) etc. (Fig. 1 of Chakrabarti, 1997 and references therein). Fig. 1a shows examples of solutions (Molteni, Ryu & Chakrabarti, 1996; Eggum, in preparation) from ‘SA’, ‘I’ and ‘O’ regions where we superpose analytical (solid) and numerical simulations (short dashed curve is with SPH code and medium dashed curve is with TVD code; very long dashed curve is with explicit/implicit code). The agreement is excellent. In presence of cooling effects, shocks from ‘SA’ oscillate (Fig. 1b) when the cooling timescale roughly agrees with postshock infall time scale (Molteni, Sponholz & Chakrabarti, 1996). The solid, long dashed and short dashed curves are drawn for T1/2 (bremsstrahlung), T0.4 and T0.75 cooling laws respectively. In the absence of steady shock solutions, shocks for parameters from ‘NSA’ oscillate (Fig. 2) even in the absence of viscosity (Ryu et al. 1997). The oscillation frequency and amplitude roughly agree with those of quasi-periodic oscillation of black hole candidates. When the flow starts from a cool Keplerian disk, it simply becomes sub-Keplerian before it enters through the horizon. Fig. 3a shows this behaviour where the ratio of λ/λKeplerian is plotted. When the flow deviates from a hot Keplerian disk, it may develop a standing shock as well (Fig. 3b) (Molteni et al. 1996).

Material and Microslip Damping in a Rotor Taking Gravity and Anisotropic Bearings Into Account

2000 ◽  
Vol 123 (1) ◽  
pp. 30-35 ◽  
Author(s):  
Ha˚kan L. Wettergren
Keyword(s):  
Numerical Simulations ◽  
Rotational Frequency ◽  
Dissipated Energy ◽  
Viscous Damping ◽  
Internal Damping ◽  
Material Damping ◽  
Turbine Generator ◽  
Equivalent Viscous Damping ◽  
Sign Change ◽  
The Difference

The paper is concerned with material and microslip damping in a rotor. The horizontal rotor is carried by anisotropic bearings, which means that the shaft feels three different frequencies, the rotational frequency and the difference and the sum of the rotational and vibrational frequencies. When material damping is studied, these three frequencies lead to three different equivalent viscous damping constants and the dissipated energy can be solved analytically. The rotor slot wedges in a turbine generator are used as an example of microslip damping. In this case the damping is nonlinear and the results are obtained through numerical simulations. The results show that these two different internal damping sources give both similarities and dissimilarities. The sign change and different magnitude of the dissipated energy running sub- or supercritical are the same. However the dissipated energy for material damping is not affected by gravity which microslip damping is.

Assessment of Fracture Toughness Using Small Punch Tests of Prenotched Specimens

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Yangyan Zheng ◽  
Xiao Chen ◽  
Zheng Yang ◽  
Xiang Ling
Keyword(s):  
Fracture Toughness ◽  
Numerical Simulations ◽  
Stress Gradient ◽  
Element Model ◽  
Bending Test ◽  
J Integral ◽  
Notched Specimen ◽  
Small Punch ◽  
Three Point Bending ◽  
The Difference

In this paper, line- and ring-notched small punch test (SPT) specimens were studied; a three-dimensional (3D) model of a ring-notched SPT specimen was established using the contour integral method, and the validity of the model was verified using ring-notched specimens. The stress and strain fields were analyzed using numerical simulations of a ring-notched SPT specimen, and the change in the stress gradient during deformation was considered. To verify the finite element model, the results of the numerical simulations were compared with those of three-point bending tests and a Gurson–Tvergaard–Needleman (GTN) model. Compared with the line-notched specimen, the ring-notched specimen was more suitable for notch propagation analysis and fracture toughness evaluation. The results of the numerical simulations were in good agreement with those of the experiments, which showed that the numerical model used in this study was correct. For a notch that initiated when the load reached its maximum value, the value of the J integral was 335 × 10−6 kJ/mm2, and at time 0.85Pmax, the value of the J integral was 201 × 10−6 kJ/mm2, and the difference from the result of the three-point bending test was 14.4%. For a notch that initiated during the stretching deformation stage, the relevant fracture toughness was 225 × 10−6 kJ/mm2, and the difference from the result of the three-point bending test was 3%.

Magnetohydrodynamics (MHD) numerical simulations on the interaction of the solar wind with the magnetosphere: A review

2013 ◽  
Vol 56 (7) ◽  
pp. 1141-1157 ◽  
Author(s):  
Chi Wang ◽  
XiaoCheng Guo ◽  
Zhong Peng ◽  
BinBin Tang ◽  
TianRan Sun ◽  
...  
Keyword(s):  
Solar Wind ◽  
Numerical Simulations

Calculation of the Periodic Solution in Nakamura’s Model

2012 ◽  
Vol 256-259 ◽  
pp. 1648-1651
Author(s):  
Bin Zhen ◽  
Zhang Jun Liu
Keyword(s):  
Periodic Solution ◽  
Hopf Bifurcation ◽  
Numerical Simulations ◽  
Bifurcation Analysis ◽  
Energy Method ◽  
Analytic Solution ◽  
Measure Data ◽  
Lateral Vibration ◽  
Lateral Vibrations

Nakamura’s model is one of the most practical models describing the lateral vibrations of footbridges induced by pedestrians. This paper presents a calculation of the periodic solution in Nakamura’s model. After a Hopf bifurcation analysis of Nakamura’s model, the amplitude of the lateral vibration is computed by using the energy method. The correctness and accuracy of the calculation is demonstrated by numerical simulations. Then, how the factors and variables in Nakamura’s model effect the amplitude is investigated based on the analytic solution. Our analysis results may be used to explain why the most of the predict results of Nakamura’s model are larger than the measure data.

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