MHD simulation of laboratory jets and comparison with laser experiments

2018 ◽  
Vol 27 (10) ◽  
pp. 1844017
Author(s):  
O. D. Toropina ◽  
G. S. Bisnovatyi-Kogan ◽  
S. G. Moiseenko
Keyword(s):  
Numerical Method ◽  
Plasma Flow ◽  
Initial Conditions ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Laser Experiments ◽  
Laser Installation

The results of MHD simulations of the formation and development of magnetized jets on a NEODIM laser installation are presented. We simulated a plasma flow and chose the numerical method, boundary and initial conditions. We investigated the picture of the flow and compared it with the experiment.

scholarly journals Three-dimensional flow near a reconnection site at the dayside magnetopause: analytical solutions coupled with MHD simulations

2007 ◽  
Vol 73 (6) ◽  
pp. 811-819 ◽  
Author(s):  
LARS G. WESTERBERG ◽  
J. VEDIN ◽  
A. EKENBÄCK ◽  
H. O. ÅKERSTEDT
Keyword(s):  
Plasma Flow ◽  
Three Dimensional ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Three Dimensional Flow ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Dayside Magnetopause ◽  
Global Mhd Simulation ◽  
Reconnection Site

AbstractWe present a coupling between an analytical three-dimensional model covering the plasma flow behaviour through the magnetopause transition layer near a reconnection site, with results from a global MHD simulation describing the plasma flow in the magnetosheath. The structure of the plasma flow near a reconnection site at the dayside terrestrial magnetopause is investigated, together with the development of the magnetopause transition region.

scholarly journals A Rational Numerical Method for Simulation of Drop-Impact Dynamics of Oleo-Pneumatic Landing Gear

2021 ◽  
Vol 11 (9) ◽  
pp. 4136
Author(s):  
Rosario Pecora
Keyword(s):  
Numerical Method ◽  
Initial Conditions ◽  
Impact Load ◽  
Numerical Models ◽  
Landing Gear ◽  
Design Stage ◽  
Impact Dynamics ◽  
State Variables ◽  
Adopted Model ◽  
The Impact

Oleo-pneumatic landing gear is a complex mechanical system conceived to efficiently absorb and dissipate an aircraft’s kinetic energy at touchdown, thus reducing the impact load and acceleration transmitted to the airframe. Due to its significant influence on ground loads, this system is generally designed in parallel with the main structural components of the aircraft, such as the fuselage and wings. Robust numerical models for simulating landing gear impact dynamics are essential from the preliminary design stage in order to properly assess aircraft configuration and structural arrangements. Finite element (FE) analysis is a viable solution for supporting the design. However, regarding the oleo-pneumatic struts, FE-based simulation may become unpractical, since detailed models are required to obtain reliable results. Moreover, FE models could not be very versatile for accommodating the many design updates that usually occur at the beginning of the landing gear project or during the layout optimization process. In this work, a numerical method for simulating oleo-pneumatic landing gear drop dynamics is presented. To effectively support both the preliminary and advanced design of landing gear units, the proposed simulation approach rationally balances the level of sophistication of the adopted model with the need for accurate results. Although based on a formulation assuming only four state variables for the description of landing gear dynamics, the approach successfully accounts for all the relevant forces that arise during the drop and their influence on landing gear motion. A set of intercommunicating routines was implemented in MATLAB® environment to integrate the dynamic impact equations, starting from user-defined initial conditions and general parameters related to the geometric and structural configuration of the landing gear. The tool was then used to simulate a drop test of a reference landing gear, and the obtained results were successfully validated against available experimental data.

scholarly journals Relation of polar auroral arcs to magnetotail twisting and IMF rotation: a systematic MHD simulation study

2004 ◽  
Vol 22 (3) ◽  
pp. 951-970 ◽  
Author(s):  
A. Kullen ◽  
P. Janhunen
Keyword(s):  
Magnetic Field ◽  
Simulation Study ◽  
Large Scale ◽  
Detailed Examination ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Sign Change ◽  
Auroral Arcs ◽  
Good Agreement ◽  
Imf Clock Angle

Abstract. We investigate with the help of a magnetohydrodynamic (MHD) model how the large-scale topology of the magnetosphere develops for a constant interplanetary magnetic field (IMF) with different IMF clock angles and for an IMF By sign change during northward IMF. A detailed examination of the topological changes in the tail and the ionosphere for different IMF conditions shows a good agreement with observational results. The MHD simulations for different constant IMF clock angle cases show the expected field-line bending and tail twisting for nonzero IMF By. The tail becomes longer and at its tailward end stronger twisted for IMF Bz>∣By∣ than for IMF Bz

scholarly journals The surprisingly small impact of magnetic fields on the inner accretion flow of Sagittarius A* fueled by stellar winds

2019 ◽  
Vol 492 (3) ◽  
pp. 3272-3293 ◽  
Author(s):  
S M Ressler ◽  
E Quataert ◽  
J M Stone
Keyword(s):  
Angular Momentum ◽  
Magnetic Fields ◽  
Event Horizon ◽  
Initial Conditions ◽  
Rotational Instability ◽  
Stellar Winds ◽  
Accretion Flow ◽  
Sagittarius A ◽  
Mhd Simulations ◽  
Sgr A

ABSTRACT We study the flow structure in 3D magnetohydrodynamic (MHD) simulations of accretion on to Sagittarius A* via the magnetized winds of the orbiting Wolf–Rayet stars. These simulations cover over 3 orders of magnitude in radius to reach ≈300 gravitational radii, with only one poorly constrained parameter (the magnetic field in the stellar winds). Even for winds with relatively weak magnetic fields (e.g. plasma β ∼ 106), flux freezing/compression in the inflowing gas amplifies the field to β ∼ few well before it reaches the event horizon. Overall, the dynamics, accretion rate, and spherically averaged flow profiles (e.g. density, velocity) in our MHD simulations are remarkably similar to analogous hydrodynamic simulations. We attribute this to the broad distribution of angular momentum provided by the stellar winds, which sources accretion even absent much angular momentum transport. We find that the magneto-rotational instability is not important because of (i) strong magnetic fields that are amplified by flux freezing/compression, and (ii) the rapid inflow/outflow times of the gas and inefficient radiative cooling preclude circularization. The primary effect of magnetic fields is that they drive a polar outflow that is absent in hydrodynamics. The dynamical state of the accretion flow found in our simulations is unlike the rotationally supported tori used as initial conditions in horizon scale simulations, which could have implications for models being used to interpret Event Horizon Telescope and GRAVITY observations of Sgr A*.

On a Numerical Method for Solution of the Mathieu-Hill Type Equations

1980 ◽  
Vol 102 (3) ◽  
pp. 619-626 ◽  
Author(s):  
A. Midha ◽  
M. L. Badlani
Keyword(s):  
Differential Equations ◽  
Numerical Method ◽  
Initial Conditions ◽  
Linear Equations ◽  
Solution Process ◽  
Constraint Equations ◽  
Step Functions ◽  
The Matrix ◽  
Constant Coefficients ◽  
Simultaneous Linear Equations

This paper presents a computer-programmable numerical method for the solution of a class of linear, second order differential equations with periodic coefficients of the Mathieu-Hill type. The method is applicable only when the initial conditions are prescribed and the solution is not requiried to be periodic. The solution is facilitated by representing the coefficient functions as a sum of step functions over corresponding sub-intervals of the fundamental interval. During each sub-interval, the solution form is assumed to be that of the differential equations with “constant” coefficients. Constraint equations are derived from imposing the conditions of “compatibility” of response at the end nodes of the intermediate sub-intervals. This set of simultaneous linear equations is expressed in matrix form. The matrix of coefficients may be represented as a triangular one. This form greatly simplifies the solution process for simultaneous equations. The method is illustrated by its application to some specific problems.

Combined DAE and Sliding Mode Control Methods for Simulation of Constrained Mechanical Systems

2000 ◽  
Vol 122 (4) ◽  
pp. 691-698 ◽  
Author(s):  
M. D. Compere ◽  
R. G. Longoria
Keyword(s):  
Sliding Mode Control ◽  
Numerical Method ◽  
Hybrid Method ◽  
Sliding Mode ◽  
Initial Conditions ◽  
Differential Algebraic Equations ◽  
Control Law ◽  
Stabilization Method ◽  
Mode Control ◽  
Hybrid Numerical Method

In dynamic analysis of constrained multibody systems (MBS), the computer simulation problem essentially reduces to finding a numerical solution to higher-index differential-algebraic equations (DAE). This paper presents a hybrid method composed of multi-input multi-output (MIMO), nonlinear, variable-structure control (VSC) theory and post-stabilization from DAE solution theory for the computer solution of constrained MBS equations. The primary contributions of this paper are: (1) explicit transformation of constrained MBS DAE into a general nonlinear MIMO control problem in canonical form; (2) development of a hybrid numerical method that incorporates benefits of both Sliding Mode Control (SMC) and DAE stabilization methods for the solution of index-2 or index-3 MBS DAE; (3) development of an acceleration-level stabilization method that draws from SMC’s boundary layer dynamics and the DAE literature’s post-stabilization; and (4) presentation of the hybrid numerical method as one way to eliminate chattering commonly found in simulation of SMC systems. The hybrid method presented can be used to simulate constrained MBS systems with either holonomic, nonholonomic, or both types of constraints. In addition, the initial conditions (ICs) may either be consistent or inconsistent. In this paper, MIMO SMC is used to find the control law that will provide two guarantees. First, if the constraints are initially not satisfied (i.e., for inconsistent ICs) the constraints will be driven to satisfaction within finite time using SMC’s stabilization method, urobust,i=−ηisgnsi. Second, once the constraints have been satisfied, the control law, ueq and hybrid stabilization techniques guarantee surface attractiveness and satisfaction for all time. For inconsistent ICs, Hermite-Birkhoff interpolants accurately locate when each surface reaches zero, indicating the transition time from SMC’s stabilization method to those in the DAE literature. [S0022-0434(00)02404-7]

scholarly journals Flattening of the Density Spectrum in Compressible Hall-MHD Simulations

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1162
Author(s):  
Victor Montagud-Camps ◽  
František Němec ◽  
Jana Šafránková ◽  
Zdeněk Němeček ◽  
Andrea Verdini ◽  
...  
Keyword(s):  
Transition Region ◽  
Cyclotron Frequency ◽  
Density Fluctuations ◽  
Proton Density ◽  
Spectral Slope ◽  
Plasma Parameters ◽  
Mhd Simulation ◽  
Density Spectrum ◽  
Mhd Simulations ◽  
Hall Mhd

Observations of proton density fluctuations of the solar wind at 1 au have shown the presence of a decade-long transition region of the density spectrum above sub-ion scales, characterized by a flattening of the spectral slope. We use the proton density fluctuations data collected by the BMSW instrument on-board the Spektr-R satellite in order to delimit the plasma parameters under which the transition region can be observed. Under similar plasma conditions to those in observations, we carry out 3D compressible magnetohydrodynamics (MHD) and Hall-MHD numerical simulations and find that Hall physics is necessary to generate the transition region. The analysis of the kω power spectrum in the Hall-MHD simulation indicates that the flattening of the density spectrum is associated with fluctuations having frequencies smaller than the ion cyclotron frequency.

scholarly journals Analytical-Numerical Calculation Algorithm of Algebraic Equations Roots with Specified Limits of Errors

2019 ◽  
Vol 18 (6) ◽  
pp. 1491-1514
Author(s):  
Yuri Bychkov ◽  
Elena Solovyeva ◽  
Sergei Scherbakov
Keyword(s):  
Numerical Method ◽  
Algebraic Equation ◽  
Initial Conditions ◽  
Absolute Error ◽  
Variable Order ◽  
Algebraic Equations ◽  
Adaptive Procedure ◽  
Calculation Algorithm ◽  
Mathematical Basis ◽  
Calculation Step

This paper proposes an algorithm for calculating approximate values of  roots of algebraic equations with a specified limit of absolute errors. A mathematical basis of the algorithm is an analytical-numerical method of solving nonlinear integral-differential equations with non-stationary coefficients. The analytical-numerical method belongs to the class of one-step continuous methods of variable order with an adaptive procedure for choosing a calculation step, a formalized estimate of the error of the performed calculations at each step and the error accumulated during the calculation. The proposed algorithm for calculating the approximate values of the roots of an algebraic equation with specified limit absolute errors consists of two stages. The results of the first stage are numerical intervals containing the unknown exact values of the roots of the algebraic equation. At the second stage, the approximate values of these roots with the specified limit absolute errors are calculated. As an example of the use of the proposed algorithm, defining the roots of the fifth-order algebraic equation with three different values of the limiting absolute error is presented. The obtained results allow drawing the following conclusions. The proposed algorithm enables to select numeric intervals that contain unknown exact values of the roots. Knowledge of these intervals facilitates the calculation of the approximate root values under any specified limiting absolute error. The algorithm efficiency, i.e., the guarantee of achieving the goal, does not depend on the choice of initial conditions. The algorithm is not iterative, so the number of calculation steps required for extracting a numerical interval containing an unknown exact value of any root of an algebraic equation is always restricted. The algorithm of determining a certain root of the algebraic equation is computationally completely autonomous.

scholarly journals Unusual Location of the Geotail Magnetopause Near Lunar Orbit: A Case Study

2021 ◽  
Author(s):  
Wensai Shang ◽  
Binbin Tang ◽  
Quanqi Shi ◽  
Et al
Keyword(s):  
Solar Wind ◽  
Velocity Vector ◽  
Solar Wind Velocity ◽  
Full Moon ◽  
Interplanetary Shock ◽  
Time Intervals ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Solar Wind Flow

<p>The Earth's magnetopause is highly variable in location and shape and is modulated by solar wind conditions. On 8 March 2012, the ARTEMIS probes were located near the tail current sheet when an interplanetary shock arrived under northward interplanetary magnetic field conditions and recorded an abrupt tail compression at ∼(-60, 0, -5) Re in Geocentric Solar Ecliptic coordinate in the deep magnetotail. ~ 10 minutes later, the probes crossed the magnetopause many times within an hour after the oblique interplanetary shock passed by. The solar wind velocity vector downstream from the shock was not directed along the Sun-Earth line but had a significant Y component. We propose that the compressed tail was pushed aside by the appreciable solar wind flow in the Y direction. Using a virtual spacecraft in a global magnetohydrodynamic (MHD) simulation, we reproduce the sequence of magnetopause crossings in the X-Y plane observed by ARTEMIS under oblique shock conditions, demonstrating that the compressed magnetopause is sharply deflected at lunar distances in response to the shock and solar wind Vy effects. The results from two global MHD simulations show that the shocked magnetotail at lunar distances is mainly controlled by the solar wind direction with a timescale of about a quarter hour, which appears to be consistent with the windsock effect. The results also provide some references for investigating interactions between the solar wind/magnetosheath and lunar nearside surface during full moon time intervals, which should not happen in general.</p>

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