Hybrid Simulation Results Research Articles

Solar wind plasma interaction with Gerasimovich lunar magnetic anomaly

AbstractWe present the results of the first local hybrid simulations (particle ions and fluid electrons) for the solar wind plasma interaction with realistic lunar crustal fields. We use a three‐dimensional hybrid model of plasma and an empirical model of the Gerasimovich magnetic anomaly based on Lunar Prospector observations. We examine the effects of low and high solar wind dynamic pressures on this interaction when the Gerasimovich magnetic anomaly is located at nearly 20∘ solar zenith angle. We find that for low solar wind dynamic pressure, the crustal fields mostly deflect the solar wind plasma, form a plasma void at very close distances to the Moon (below 20 km above the surface), and reflect nearly 5% of the solar wind in charged form. In contrast, during high solar wind dynamic pressure, the crustal fields are more compressed, the solar wind is less deflected, and the lunar surface is less shielded from impinging solar wind flux, but the solar wind ion reflection is more locally intensified (up to 25%) compared to low dynamic pressures. The difference is associated with an electrostatic potential that forms over the Gerasimovich magnetic anomaly as well as the effects of solar wind plasma on the crustal fields during low and high dynamic pressures. Finally, we show that an antimoonward Hall electric field is the dominant electric field for ∼3 km altitude and higher, and an ambipolar electric field has a noticeable contribution to the electric field at close distances (<3 km) to the Moon.

Hybrid Simulations of Particle Acceleration at Shocks

We present the results of large hybrid (kinetic ions – fluid electrons) simulations of particle acceleration at non-relativistic collisionless shocks. Ion acceleration efficiency and magnetic field amplification are investigated in detail as a function of shock inclination and strength, and compared with predictions of diffusive shock acceleration theory, for shocks with Mach number up to 100. Moreover, we discuss the relative importance of resonant and Bell's instability in the shock precursor, and show that diffusion in the self-generated turbulence can be effectively parametrized as Bohm diffusion in the amplified magnetic field.

On lunar exospheric column densities and solar wind access beyond the terminator from ROSAT soft X-ray observations of solar wind charge exchange

We analyze the Rontgen satellite (ROSAT) position sensitive proportional counter soft X-ray image of the Moon taken on 29 June 1990 by examining the radial profile of the surface brightness in three wedges: two 19 deg wedges (one north and one south) 13-32 deg off the terminator toward the dark side and one wedge 38 deg wide centered on the antisolar direction. The radial profiles of both the north and the south wedges show significant limb brightening that is absent in the 38 deg wide antisolar wedge. An analysis of the soft X-ray intensity increase associated with the limb brightening shows that its magnitude is consistent with that expected due to solar wind charge exchange (SWCX) with the tenuous lunar atmosphere based on lunar exospheric models and hybrid simulation results of solar wind access beyond the terminator. Soft X-ray imaging thus can independently infer the total lunar limb column density including all species, a property that before now has not been measured, and provide a large-scale picture of the solar wind-lunar interaction. Because the SWCX signal appears to be dominated by exospheric species arising from solar wind implantation, this technique can also determine how the exosphere varies with solar wind conditions. Now, along with Mars, Venus, and Earth, the Moon represents another solar system body at which SWCX has been observed.

Viscous dissipation effect in nano-confined shear flows: a comparative study between molecular dynamics and multi-scale hybrid simulations

In this work, a full molecular dynamics simula- tion (MDS) of nano-confined shear flows has been conducted to examine the effect of viscous dissipation and applicability of multi-scale hybrid simulation. In the cases of high shear rate and strong solid-liquid interaction, the difference is clearly seen between the MDS and hybrid simulation results. The applicability of the hybrid simulation is found highly dependent on the effect of viscous dissipation. The non- monotonic variation of the average temperature found in pressure-driven flows is also found in the present shear-driven flows. By comparatively analyzing the molecular dynamics and hybrid simulation results, it is confirmed that the hybrid simulation is valid and the explicit correlation between the slip and Kapitza lengths is valid in the ranges of shear rate ( _ c ¼ 0:012� 0:094 s � 1 , s being the time scale) and solid- liquid interaction factor (b = 0.1-10). Although the hybrid simulation results deviate from the MDS results due to the effect of viscous dissipation, the explicit correlation between the slip and Kapitza lengths still holds.

Modeling, Simulation and Design Optimization of a Series Hydraulic Hybrid Vehicle

Crude oil resources in the world continue to diminish; automobile, agricultural machinery and construction machinery manufacturing companies are placing more emphasis on energy efficient series hydraulic hybrid systems which can replace their conventional transmission systems. Series hydraulic hybrid system is a mechatronics system with two source of power (that includes prime mover and hydro-pneumatic accumulator) which drives the vehicle. Even though, it has been proven as an energy efficient system, sizing of the components or sub-system for automobiles has got a major influence on energy efficiency of vehicle. In this paper, a power bond graph approach is used to model the dynamics of series hydraulic hybrid system and simulation results elucidate various modes of operations. It also shows the dynamic response of hydro-pneumatic accumulator, prime-mover and system output speed. Further, design optimization of system is carried out to optimize the physical /process parameters for the maximum system's output energy that, leads to increase in energy efficiency and environmental friendly vehicle.

Observations of energetic particles in the upstream of a quasi-parallel collisionless shock

通过Cluster卫星在2005年3月16日观测到的一个准平行激波观测事例，研究了准平行激波上游低频等离子体波动与能量离子之间的关系.卫星观测结果表明，在准平行激波上游，离子微分能通量受到了非线性波动的调制.在磁场强度较小区域，离子微分能通量较高.产生这种现象的可能原因是准平行激波上游的非线性波动可以捕获离子，被捕获的离子在波动中来回弹跳并被电场加速，从而导致磁场强度较小区域离子微分能通量较高.这一观测结果与已有的混合模拟结果相吻合.

Control Design and Implementation for High Performance Shunt Active Filters in Aircraft Power Grids

This paper presents the design and implementation of a Shunt Active Filter (SAF) for aircraft power networks using an accurate wide-band current control method based on Iterative Learning Control (ILC). The SAF control system is designed to compensate harmonic currents, with a 400 Hz supply voltage. This work introduces useful design strategies to increase the error-decay speed and improve the robustness of the SAF control system by using a hybrid P-type ILC controller. Detailed design of the hybrid P-type ILC controller and simulation results are presented. The overall system implementation is demonstrated through experimental results on a laboratory prototype.

Bayesian Updating of Fragility Functions Using Hybrid Simulation

The accuracy of fragility functions is critical for regional risk and loss estimations. This paper proposes a two-stage approach to generate improved fragility functions for engineering structures using field measurement and experimental data. In the first stage, the linear and nonlinear parameters of the bridge model are calibrated using measured earthquake responses and cyclic testing data; analytical fragilities are then generated with the calibrated model. In the second stage, a Bayesian updating approach is used to further update the derived fragilities using hybrid (analytical-experimental) simulation results. To illustrate the effectiveness of the proposed approach, fragility functions are generated for the Meloland Road Overcrossing Bridge considering four cases that represent an increasing level of data availability. A comparison of the four sets of fragility functions shows that appropriate calibration of bridge model is critical to the accuracy of the fragilities. In addition, hybrid simulation provides an economic and efficient way of validating and improving the accuracy of fragility functions through Bayesian updating.

Hardware-in-the-loop hybrid simulation of pantograph–catenary interaction

The paper addresses the use of hybrid simulation to study pantograph-catenary interaction. Based on this approach, also known as ‘Hardware-in-the-loop’, a physical pantograph is set in interaction with a numerical model of the catenary which is run in real time. To this aim, a dedicated test bench was designed and built to reproduce pantograph–catenary interaction in the 0–20Hz frequency range also including the effect of stagger in the contact wire. To appraise the accuracy of the simulation method, results of hybrid simulations were compared with line test measurements, considering two different pantograph–catenary couples presently used in the European high-speed railway network.

Large‐scale real‐time hybrid simulation involving multiple experimental substructures and adaptive actuator delay compensation

SUMMARYReal‐time hybrid simulation provides a viable method to experimentally evaluate the performance of structural systems subjected to earthquakes. The structural system is divided into substructures, where part of the system is modeled by experimental substructures, whereas the remaining part is modeled analytically. The displacements in a real‐time hybrid simulation are imposed by servo‐hydraulic actuators to the experimental substructures. Actuator delay compensation has been shown by numerous researchers to vitally achieve reliable real‐time hybrid simulation results. Several studies have been performed on servo‐hydraulic actuator delay compensation involving single experimental substructure with single actuator. Research on real‐time hybrid simulation involving multiple experimental substructures, however, is limited. The effect of actuator delay during a real‐time hybrid simulation with multiple experimental substructures presents challenges. The restoring forces from experimental substructures may be coupled to two or more degrees of freedom (DOF) of the structural system, and the delay in each actuator must be adequately compensated. This paper first presents a stability analysis of actuator delay for real‐time hybrid simulation of a multiple‐DOF linear elastic structure to illustrate the effect of coupled DOFs on the stability of the simulation. An adaptive compensation method then proposed for the stable and accurate control of multiple actuators for a real‐time hybrid simulation. Real‐time hybrid simulation of a two‐story four‐bay steel moment‐resisting frame with large‐scale magneto‐rheological dampers in passive‐on mode subjected to the design basis earthquake is used to experimentally demonstrate the effectiveness of the compensation method in minimizing actuator delay in multiple experimental substructures. Copyright © 2011 John Wiley & Sons, Ltd.

Power System Subsynchronous Oscillations Electromagnetic and Electromechanical Transient Hybrid Real-Time Simulation Based on RTDS

In this paper, power system electromagnetic and electromechanical transient hybrid real-time simulation technology is expounded in details, which has advantages of the electromagnetic transient simulation program and electromechanical ones. The more details needed to analyze the dynamic characteristics of power systems are provided by this hybrid simulation technology, and the scale of power system simulated is not limited in the hybrid simulation program. The hybrid simulation program is applied to analyze the power system subsynchronous oscillation problem occurred in a power plant with 4 turbine generators located in the northwestern China. According to the simulation results, it is clear that the stability of generators is threatened by the subsynchronous oscillations caused by capacitor series compensation in the transmission line connecting the power plant and the load center system. In meantime, the effectiveness of the countermeasure is validated simultaneously by the hybrid simulation results.

First lunar wake passage of ARTEMIS: Discrimination of wake effects and solar wind fluctuations by 3D hybrid simulations

The spacecraft P1 of the new ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun) mission passed the lunar wake for the first time on February 13, 2010. We present magnetic field and plasma data of this event and results of 3D hybrid simulations. As the solar wind magnetic field was highly dynamic during the passage, a simulation with stationary solar wind input cannot distinguish whether distortions were caused by these solar wind variations or by the lunar wake; therefore, a dynamic real-time simulation of the flyby has been performed. The input values of this simulation are taken from NASA OMNI data and adapted to the P1 data, resulting in a good agreement between simulation and measurements. Combined with the stationary simulation showing non-transient lunar wake structures, a separation of solar wind and wake effects is achieved. An anisotropy in the magnitude of the plasma bulk flow velocity caused by a non-vanishing magnetic field component parallel to the solar wind flow and perturbations created by counterstreaming ions in the lunar wake are observed in data and simulations. The simulations help to interpret the data granting us the opportunity to examine the entire lunar plasma environment and, thus, extending the possibilities of measurements alone: A comparison of a simulation cross section to theoretical predictions of MHD wave propagation shows that all three basic MHD modes are present in the lunar wake and that their expansion governs the lunar wake refilling process.

The Visualization Package "Akira" for Analyses of Various Hybrid Simulation Results

対象系全体を必要な物理精度に応じて部分系に分け，各部分系に必要精度を持つ計算手法を適用する同時並列型ハイブリッドシミュレーション法が最近注目されている．我々は，原子(粒子)描像であったり連続体描像であったりするなどのハイブリッドシミュレーションコードが出力する多様かつ多数な物理変数の数値を統一的に扱い，さらにそれらの時間変化をアニメーションとして可視化するソフトウェアAkiraを開発した．Akiraを用いると，原子描像と連続体描像を混在させたり，多彩に表示した原子群のダイナミクスを原子毎の軌跡として表示させたりするなど様々な形式で，シミュレーションの結果を物理的な解釈がしやすくなるように表現することが出来る．簡易な操作で時間変化を，静止画のシークエンスとしても出力出来る．ソースコードはJava言語でOpenGLを用いて作成しているため，プラットホームの違いを気にしないで利用出来る．ユーザーが独自に改変することも，ソースコードと共に開発資料を公開しているため容易である．本論文ではAkiraの特徴的な機能を，いくつかの応用例を通じて概説する．

An explanation for the lack of ion cyclotron wave generation by pickup ions at Titan: 1‐D hybrid simulation results

Titan's dense atmosphere is thought to be an important source of pickup ions in the Saturnian magnetosphere. Cassini spacecraft measurements of the plasmas near Titan show evidence of pickup ions, yet electromagnetic ion cyclotron waves, which are direct indicators of ion pickup, have not yet been detected. Pickup ions and their associated ion cyclotron waves have been observed at Saturn's Extended Neutral Cloud (∼4–10 Rs), as well as at Jupiter's moon, Io, suggesting that the plasma and pickup conditions near Titan may be fundamentally different than these other environments. Using 1‐D hybrid simulations, we investigate ion cyclotron wave growth for variable conditions in the Titan environment to test which conditions could yield waves with sufficient amplitude to be clearly detected by spacecraft. Results suggest that ion cyclotron waves have not been observed at Titan because their growth time is too long compared to the convection time of background plasma through the interaction region and therefore will not be of sufficient amplitude to be observed by Cassini. Because Titan can be located in either the magnetically noisy Saturnian current sheet or in the magnetically quiet lobe region, we consider both of these environments in this study.

Mercury’s magnetosphere–solar wind interaction for northward and southward interplanetary magnetic field: Hybrid simulation results

Analysis of global hybrid simulations of Mercury’s magnetosphere–solar wind interaction is presented for northward and southward interplanetary magnetic field (IMF) orientations in the context of MESSENGER’s first two encounters with Mercury. The global kinetic simulations reveal the basic structure of this interaction, including a bow shock, ion foreshock, magnetosheath, cusp regions, magnetopause, and a closed ion ring belt formed around the planet within the magnetosphere. The two different IMF orientations induce different locations of ion foreshock and different magnetospheric properties: the dayside magnetosphere is smaller and cusps are at lower latitudes for southward IMF compared to northward IMF whereas for southward IMF the nightside magnetosphere is larger and exhibits a thin current sheet with signatures of magnetic reconnection and plasmoid formation. For the two IMF orientations the ion foreshock and quasi-parallel magnetosheath manifest ion-beam-driven large-amplitude oscillations, whereas the quasi-perpendicular magnetosheath shows ion-temperature-anisotropy-driven wave activity. The ions in Mercury’s belt remain quasi-trapped for a limited time before they are either absorbed by Mercury’s surface or escape from the magnetosphere. The simulation results are compared with MESSENGER’s observations.

Extension of a Multiscale Particle Scheme to Near-Equilibrium Viscous Flows

A recently proposed low diffusion (LD) equilibrium particle method based on the direct simulation Monte Carlo (DSMC) method is modified for use with near-equilibrium viscous flows. A finite volume discretization of the viscous terms in the compressible Navier-Stokes equations is used to incorporate diffusive transport effects into the LD particle method, and a velocity and temperature slip wall boundary condition is employed for improved accuracy in the slip flow Knudsen number regime. The modified method is compared with both DSMC and theory for a series of unsteady boundary layer problems, and excellent agreement is observed. The computational cost of the modified LD particle method is shown for a representative near-equilibrium case to be roughly four orders of magnitude lower than that of DSMC, due to reduced scatter as well as less stringent cell size and time step requirements in the LD method. Simulation procedures are outlined for a strongly coupled hybrid algorithm, where the LD particle method is used in continuum flowfield regions and DSMC is employed in nonequilibrium regions. The hybrid scheme is evaluated through a comparison with numerical and experimental data for a flow of N2 through a small convergent-divergent nozzle into a near vacuum, and hybrid simulation results are generally found to agree very well with other available data. I. Introduction AS flows involving a wide range of characteristic length scales appear in a number of different engineering applications, including those related to atmospheric flow around reentry or hypersonic vehicles, high-altitude rocket plumes, flows within and around micro-electro-mechanical systems, and any supersonic flow where internal shock structures are of interest. In these types of flows, a near-equilibrium gas velocity distribution may exist through much of the flowfield, as the equilibrating effect of intermolecular collisions dominates over other processes (such as inhomogeneous diffusive transport or gas-surface interaction) which tend to pull the velocity distribution away from equilibrium. However, some flowfield regions may have characteristic length scales comparable to or smaller than the local mean free path, so that the influence of collisions does not dominate and the velocity distribution diverges considerably from the equilibrium limit. While simulation of near-equilibrium flowfield regions may be efficiently performed using computational fluid dynamics (CFD) techniques based on the Navier-Stokes equations, nonequilibrium regions must be simulated using more expensive techniques based on the Boltzmann equation. The Boltzmann equation is the governing equation for dilute gas flows at arbitrary Knudsen numbers, and its derivation follows from assumptions of molecular chaos and binary intermolecular collisions with no approximations regarding the shape of the velocity distribution. The most mature and commonly used simulation method for the Boltzmann equation is the direct simulation Monte Carlo (DSMC) method, first introduced by Bird. 1 In a DSMC simulation, a large number of representative particles are tracked through a computational grid, and move and collide in a manner consistent with physical arguments underlying the Boltzmann equation. While this method may be applied to both nonequilibrium and continuum flowfield regions, cell size and time step limitations often make it prohibitively expensive for simulating continuum flows where global characteristic length scales are far larger than the mean free path. In practice, such multiscale flows are usually simulated using both DSMC and CFD methods, by applying CFD techniques in near-equilibrium regions where the Navier-Stokes equations are valid, and using DSMC elsewhere in the flow. In the simplest type of hybrid CFD-DSMC approach, a CFD simulation is performed on a domain which 1

EVALUATION OF MIMO CHANNEL CAPACITY IN INDOOR ENVIRONMENTS USING VECTOR PARABOLIC EQUATION METHOD

In this paper, the vector parabolic equation method (VPEM) is used to investigate the Shannon capacity of multiple-input multiple-output (MIMO) communication systems in indoor corridors. This deterministic three-dimensional (3-D) full-wave method is capable to demonstrate the effects of antennas and propagation environment on the channel capacity. The VPEM can model any field depolarization effects which are caused by the corridor walls. This method is particularly useful for evaluation of MIMO channel capacity in corridors with local narrowing of cross section. The channel capacity is computed for both single and hybrid polarizations and simulation results are compared with those obtained by the ray tracing method.

Real-Time Error Monitoring for Hybrid Simulation. Part II: Structural Response Modification due to Errors

Hybrid simulation results have been shown to be highly sensitive to measurement and control errors associated with experimental substructures. In particular, systematic control errors due to the response lag of servohydraulic actuators can substantially modify the computed hybrid model response. This paper examines the changes in the hybrid model response resulting from experimental errors and verifies the use of hybrid simulation error monitors (HSEM) presented in a companion paper to predict these changes. The effects of a restoring force time delay on the hybrid model response are first examined by deriving a transfer function for such a system. In addition, numerical simulations of hybrid simulations with induced systematic and random errors are used to study the effects of experimental errors on the linear and nonlinear seismic response of structures. The numerical models with simulated experimental errors are then used to examine the relationship between HSEM and more common performance measures for quantifying the accuracy of the simulations. Based on these numerical studies, appropriate threshold values for HSEM can be determined to detect in real time whether the specified level of unacceptable accuracy has been exceeded in a hybrid simulation.

Real-Time Error Monitoring for Hybrid Simulation. Part I: Methodology and Experimental Verification

The hybrid simulation test method is a versatile technique for evaluating the seismic performance of structures by seamlessly integrating both physical and numerical simulations of substructures into a single test model. Hybrid simulation results have been shown to be reliable by comparison to shake-table simulations when propagation of experimental errors is successfully mitigated. Techniques have been proposed to assess the severity of experimental errors prior to or after tests have been completed. In this paper, an error monitoring method is presented that predicts the reliability of the test results in real time using data that is readily available. Two error monitors are derived based on estimates of energy added to the hybrid simulation as a result of errors in the experimental setup. The proposed method can provide valuable decision-making information by generating early warnings of unacceptable levels of experimental errors. The warning signals can serve as an indicator to pause the simulation, examine the source of error, and correct the problem, preferably before the specimen is irreparably damaged. Use of the proposed hybrid simulation error monitors to provide a measure of confidence of the quality of the test results is verified in two hybrid simulations.

Design of Hybrid Grating for Color Filter Application in Liquid Crystal Display

Conventional color liquid crystal displays obtain red, green, and blue (RGB) lights by three color filters which absorb other spectra and allow a specific color to transmit. Consequently, the efficiency of conventional color filter in the liquid crystal display is no more than 1/3. The hybrid grating substituted for the color filter use a cold cathode fluorescent lamp or RGB light-emitting diode backlight module in the liquid crystal display to improve the efficiency is proposed. It consists of a set of dual-grating and dual-lenticular lens array. The simulation results of hybrid grating exhibit a gain factor of 1.78 in efficiency, compared with conventional color filters.