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En lättgaskanon är en typ av kanon som används vid experiment där mycket snabba förlopp är av intresse, till exempel hypersonisk strömning och höghastighetskollisioner. Kanontypen når betydligt högre hastigheter än en konventionell kanon då projektilen accelereras genom eldröret av en gas med låg molekylmassa som vätgas eller helium istället för krutgaser. Denna lättgas komprimeras först till högt tryck och temperatur i pumptuben av en kolv som accelererats av en krutladdning. Pumptuben är ett rör anslutet till eldröret som initialt är frånskild av ett membran. För kanonen kan en mängd olika parametrar varieras och hur dessa ska väljas för att en viss mynningshastighet ska nås är inte självklart. Vid FOI har val av parametrar historiskt gjorts baserat på erfarenhet och genom experiment vilket kan vara tidsödslande. Syftet med examensarbetet var därför att simulera kanonen och undersöka hur olika parametrar påverkar dess prestanda. Forskningsfrågor som skulle besvaras var hur olika parametrar påverkar projektilens mynningshastighet och vilket utav två eldrörsalternativ som är bäst lämpat för en viss projektilvikt. Det innerballistiska förloppet i kanonen har simulerats för olika parameterkombinationer med ett program utvecklat specifikt för lättgaskanoner vid NASA:s Ames Research Center och modellen har i viss mån kunnat jämföras mot experimentell data. Resultatet av simuleringarna är att mängden lättgas och krut båda har stor inverkan på mynningshastigheten och att högre kolvvikt jämnar ut trycktoppar som uppstår till följd av stötar i gasen. Att ändra membranets öppningstryck ger ingen förbättring av kanonprestandan för den undersökta projektilvikten och utav de två eldrören som undersökts är det med större kaliber mer lämpligt för de aktuella experimenten., A light gas gun is a type of gun which is used for experiments when high velocity phenomena are of interest, such as hypersonic flow and high-velocity impacts. The gun type can reach much higher velocities than a conventional gun as the projectile is accelerated down the barrel by a gas with low molecular mass such as hydrogen or helium instead of combustion gasses. This light gas is first compressed to high pressure and temperature in the pump tube with a piston which is accelerated with a propellant charge. The pump tube is connected to the barrel but initially separated from it with a membrane. A vast array of parameters can be varied on the gun in order to achieve a target muzzle velocity and their selection is not trivial. Historically parameters have been selected at FOI through experience and experiments which can be tedious. The purpose of this thesis was to simulate the gun and investigate how various parameters influence its performance. The research questions to be answered was how the parameters influence the muzzle velocity of the projectile and which of two barrels is the most suitable for a given projectile weight. The internal ballistics of the gun was simulated for various combinations of parameters using a program specifically developed for light gas guns at NASA's Ames Research Center and the model has to some extent been compared to experimental data. The result of the simulations shows that the amount of light gas and the propellant charge have a significant effect of the achieved velocity and that the weight of the piston has a reducing effect on the pressure peaks caused by shockwaves in the gas. Changing the opening pressure of the membrane does not improve gun performance for the investigated projectile weight and of the two barrels investigated the one with larger calibre is better suited for the experiments of interest.

The ability to accurately model the operation of a solid rocket motor before undergoing multiple firing tests is essential. The analysis of the internal ballistics of a solid rocket motor results in a depiction of the flow properties inside the chamber, and thus, the overall motor performance. Therefore, enhancing the internal ballistics prediction capabilities reduces the design and testing costs while increasing reliability. The present dissertation is the outcome of an extensive process of work and research driven by a great personal interest in Rocket Propulsion and Aerospace Engineering. The project was born with the purpose of developing a computer software capable of simulating the internal aerodynamics of a solid rocket motor, by means of a one-dimensional discretization, allowing to model the behaviour of three-dimensional propellant geometries. As a result, S2P2-ODIB has been developed. It is a C++ written software, designed and built in Qt Creator, which is capable of simulating the internal behaviour of a given solid rocket motor. It has been developed in a way that allows it to be expanded or merged into a larger computer application. S2P2-ODIB features both a quasi steady and an unsteady algorithm, which have been enhanced by implementing several models capable of predicting erosive combustion phenomena. This document gathers the theoretical framework, the numerical discretization, an insight into the data structure, the validation and results and, lastly, two application examples.

The dose delivered to the planning target volume by proton beams is highly conformal, sparing organs at risk and normal tissues. New treatment planning systems adapted to spot scanning techniques have been recently proposed to simultaneously optimize several fields and thus improve dose delivery. In this paper, we investigate a new optimization framework based on a genetic algorithm approach. This tool is intended to make it possible to explore new schemes of treatment delivery, possibly with future enhanced technologies. The optimization framework is designed to be versatile and to account for many degrees of freedom, without any {\it a priori} technological constraint. To test the behavior of our algorithm, we propose in this paper, as an example, to optimize beam fluences, target points and irradiation directions at the same time. The proposed optimization routine takes typically into account several thousands of spots of fixed size. The evolution is carried out by the three standard genetic operators: mutation, crossover and selection. The figure-of-merit (or fitness) is based on an objective function relative to the dose prescription to the tumor and to the limits set for organs at risk and normal tissues. Fluence optimization is carried out via a specific scheme based on a plain gradient with analytical solution. Several specific genetic algorithm issues are addressed: (i) the mutation rate is tuned to balance the search and selection forces, (ii) the initial population is selected using a bootstrap technique and (iii) to scale down the computation time, dose calculations are carried out with a fast analytical ray tracing method and are multi-threaded. In this paper implementation issues of the optimization framework are thoroughly described. The behavior of the proposed genetic algorithm is illustrated in both elementary and clinically-realistic test cases., Comment: 18 pages, 4 figures