Spelling suggestions: "subject:"astrofysik""
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Analysis of spatial subdomains in the Generalized Weighted Residual Method : Optimization of the distribution of spatial subdomains in one spatial dimensionGillgren, Andreas January 2017 (has links)
The Generalized Weighted Residual Method (GWRM) is a recently developed time- spectral method for parabolic or hyperbolic initial-value partial differential equations. In this paper, spatial subdomains, used in this method, are analyzed. Subdomains are used to enhance efficiency by dividing entire domains into smaller parts that can be independently solved for and then combined to get the final solution. An automatic grid mapping algorithm for spatial subdomains, called "Compressive Method", is presented and applied to Burgers' viscous equation. The error of the solution, as compared to the analytic solution, is compared for this compressive Method and the uniform grid case. Results show that accuracy can be gained at a small extra cost, using this compressive Method. Conclusions are that this adaptive algorithm shows great potential for further development.
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Effect of the convective electric field on the ion number density around a low activity cometAlinder, Simon January 2017 (has links)
Vigren et al. (2015) presents an integral expression to calculate the ion number density around a low activity comet immersed in the solar wind's convective electric field. A certain parameter of the integral takes values of either 1 or 0 depending on whether a corresponding ion trajectory is feasible or not. The criteria used in the paper has been found not to be strict enough, yielding overestimated ion number densities in the cometary wake. The present project finds two new options for the criteria, one analytical and one numerical. The new numerical condition is tested in the same computations done in the original paper and compares the results of the old and new criteria. The new conditionis found to correct the previous error. / <p>Projektet gjort inom: Fördjupningskurs i fysik - projektkurs, 5.0 hp. Kurskod:1FA566.</p>
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Full Physics Orbital Simulation around Comet Didymos for CubeSat MissionAPEX on HERA, ESAZbinden, Jonas January 2020 (has links)
We investigate the dynamic environment of the double asteroid system (65803) Didymoswith its satellite Didymos B for stable trajectories of more than 30 days for a model cubesatcalled APEX, foreseen to visit Didymos with the HERA mission, to be launched in 2023.We find semi-stable orbits with lifetimes up to 15 days under the influence of solar radiationpressure. In comparison, in the absence of solar radiation pressure, orbit trajectories reachlifetimes of up to 90 days. We present the distribution of orbital stability for positionsof initial deployment and the related orbital lifetime for inclinations of i = 0, 6 and 30 to the ecliptic plane of the sun, to investigate expected seasonality of the Didymossystem. The influence on trajectories through solar radiation pressure on the arrangementof the solar panels of APEX is compared to trajectories without solar radiation pressure. Itbecomes clear that the influence of solar radiation pressure is the main variable for stabilityof trajectories and must be further investigated with great care. We also discuss briefly theoperation of APEX in relation to orbital corrections and the limitations for such corrections.
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Evaluation and optimization of the SMILE fluxgate magnetometerEdberg, Terry January 2007 (has links)
The report shows the development during the last six months of the SMILE fluxgate magnetometer from a basic platform into a first generation magnetometer. The purpose of the SMILE project is to develop a miniaturized digital fluxgate magnetometer for the Nanospace project. The Nanospace project is collaboration by KTH and IRF Uppsala with the goal to develop a nano satellite platform. The FPGA programming has been improved to include a functional correlation loop, 13 bit DACs and a parallel and a serial interface with several output modes. The timing of the processes in the FPGA has been improved making it more robust. Some critical changes to the analogue parts has also been made. The LEMI sensors have been tested in a number of ways to increase the understanding of their characteristics. The magnetometer has also been calibrated at the Nurmijärvi geophysical observatory in Finland.
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Numerical Modeling and Evaluation of the Small Magnetometer in Low-Mass Experiment (SMILE)Arriaga Trejo, Israel Alejandro January 2007 (has links)
Fluxgate magnetometers have played a major role in space missions due to their stability, range of operation and low energy consumption. Their principle of operation is relatively simple and easy to implement, a nonlinear magnetic material is driven into saturation by an alternating excitation current inducing a voltage that is modulated by the external field intended to be measured. With the increasing use of nanosatellites the instruments and payload on board have been reduced considerably in size and weight. The Small Magnetometer in Low-Mass Experiment, SMILE, is a miniaturised triaxial fluxgate magnetometer with volume compensation incorporating efficient signal processing algorithms within a field programmable gate array (FPGA). SMILE was designed in collaboration between the Lviv Centre of Institute of Space Research in Ukraine where the sensor was developed and the Royal Institute of Technology (KTH) in Stockholm, Sweden where the electronics used to operate the instrument were designed and programmed. The characteristic dimensions of the SMILE magnetometer and geometry of its parts make impractical the task to find an analytical expression for the voltages induced in the pick-up coils to evaluate its performance. In this report, the results of numerical simulations of the SMILE magnetometer using a commercial finite element method (FEM) based software are presented. The results obtained are compared with the experimental data available and will serve as a first step to understand the behaviour of the nonlinear components that could lead to improvements of its design in a future.
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A Simulation Approach to High-Frequency Plasma WavesKoen, Etienne January 2012 (has links)
Electrostatic waves in the form of Broadband Electrostatic Noise (BEN) have been observed in the Earth's auroral region associated with high geomagnetic activity. This broad frequency spectrum consists of three electrostatic modes, namely electron plasma, electron acoustic and beam-driven modes. These modes are excited in a plasma containing three electron components: hot, cool and beam electrons. A 1D Particle-in-Cell (PIC) simulation was developed to investigate the characteristics of the electrostatic waves found in such a plasma. Dispersion, phase space and spatial electric field diagrams were constructed from the output of the PIC simulation which were used to describe the wave dispersion and spatial field structures found in a plasma. The PIC code used a three electron component plasma with Maxwellian distributions to describe the electron velocity distributions. Beam-driven waves were found to dominate the frequency spectrum while electron plasma and electron acoustic waves are damped for a high beam velocity. Furthermore, for a high beam velocity, solitary waves are generated by electron holes (positive potentials), giving rise to a bipolar spatial electric fi eld structure moving in the direction of the beam. Increasing the beam temperature allows the beam electrons to mix more freely with the hot and cool electrons, which leads to electron plasma and electron acoustic waves being enhanced while beam-driven waves are damped. Decreasing the beam density and velocity leads to damping of beam-driven waves, while electron plasma and electron acoustic waves are enhanced. Measurements in Saturn's magnetosphere have found the co-existence of two electron (hot and cool) components. The electron velocities are best described by a kappa-distribution (instead of a Maxwellian) which has a high-energy tail. Using an adapted PIC simulation the study of electron plasma and electron acoustic waves was extended by using a kappa-distribution to describe the electron velocities with low indices. Electron acoustic waves are damped over most wave number ranges. Electron plasma waves are weakly damped at low wave numbers and damped for all other wave numbers. / <p>QC 20121205</p>
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Kinetic effects in low-temperature responses of dusty plasmasTolias, Panagiotis January 2010 (has links)
No description available.
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On the properties of magnetic pulsations in the solar windEricsson, Anders January 2005 (has links)
No description available.
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A simulation of MHD wave propagation in the magnetosheathDanielsson, Måns January 2003 (has links)
No description available.
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The influence of the y-component of the interplanetary magnetic field on the structure of the magnetotail and the auroral ovalKullen, Anita January 1996 (has links)
No description available.
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