This thesis presents numerical modelling and analysis of a solar Organic Rankine Cycle (ORC) for electricity generation. A regression based approach is used for the working fluid property calculations. Models of the unit&rsquo / s sub-components (pump, evaporator, expander and condenser) are also established. Steady and transient models are developed and analyzed because the unit is considered to work with stable (i.e. solar + boiler) or variable (i.e. solar only) heat input. The unit&rsquo / s heat exchangers (evaporator and condenser) have been identified as critical for the applicable method of analysis (steady or transient). The considered heat resource into the ORC is in the form of solar heated water, which varies between 80-95 0C at a range of mass flow rates between 2-12 kg/s. Simulation results of steady state operation using the developed model shows a maximum power output of around 40 kW. In the defined operation range / refrigerant mass flow rate, hot water mass flow rate and hot water temperature in the system are identified as critical parameters to optimize the power production and the cycle efficiency. The potential benefit of controlling these critical parameters is demonstrated for reliable ORC operation and optimum power production. It is also seen that simulation of the unit&rsquo / s dynamics using the transient model is imperative when variable heat input is involved, due to the fact that maximum energy recovery is the aim with any given level of heat input.

Hydrogen energy sector has gained significant attention worldwide but one of the key enabling components for its success would be cheaper and sustainable hydrogen production. Hydrogen could be produced directly from natural gas or coal etc; alternatively it could be produced by electrolysis of water powered by renewable energy sources, nuclear energy or fossil fuel. Wind energy is growing rapidly, which can produce cheap hydrogen. Electrolysers can be employed to control the frequency of the electricity grid while also making fuel as a by-product. This thesis concerns the intricacies of hydrogen production by electrolysers from renewable energy sources. A generalised, input-based mathematical model of the electrolyser has been developed for various subsystems, such as current-voltage, Faraday efficiency, gas production, gas purity, differential pressure, temperature subsystem, parasitic losses, gas losses and efficiencies at various stages of operation. Some empirical equations have been developed and some adjusted parameters have been used in the model. The model has been tested and verified against the experimental measurements. A generic method has been developed for modelling the Faraday efficiency. Model simulations have been carried out to investigate the sensitivity of the results to the value of the capacitance and how this affects the dynamic response of the electrolyser. A new sizing method of the electrolyser has been developed for a stand-alone energy system such as the HARI project. The electrolyser model has also been simulated for maximum and efficient hydrogen production in a directly coupled mode of electrolysers with solar PV arrays without the maximum power point (MPP) tracker, which leads to an interesting finding that "electrolysers should not be operated at MPP". It has also been found that the dynamic and intermittent power supply from renewables can damage the stability of electrolysers and reduce the energy capture. This is especially true for pressurised electrolysers, which are favoured by the industry at present. The in-depth theoretical and practical analysis of several aspects confirms - contrary to industry trends - that "Pressurised electrolysers are less energy efficient, less durable, more costly and not adequately compatible for renewable energy powered operation, especially in the stand-alone energy systems, compared to atmospheric electrolysers".

Ces travaux visent à améliorer la biofidélité des modèles virtuels de l’être Humain. Les statistiques montrent que la tête humaine est fréquemment sujette à des traumatismes cérébraux, des lésions et autres blessures. Une attention particulière sera donc donnée à la modélisation de la tête. Afin de mieux prédire les mécanismes lésionnels de la tête, la biofidélite des modèles doit être améliorée, pour cela les effets du fluide situé à l’intérieur de la tête doivent être pris en compte. Cependant, la modélisation des interactions entre un fluide corporel visqueux et un matériau mou comme le cerveau reste un verrou scientifique. Il est proposé d’étudier en détail la modélisation des interactions fluide-structure entre un fluide et un corps mou. Premièrement, une étude bibliographique détaillée sur les méthodes numériques de modélisation des interactions fluides-structure a permis d’évaluer chacune d’elles et de juger de celle qui est la mieux adaptée pour la résolution de la problématique. Deuxièmement, lors de travaux de thèse précédents, une expérience a été réalisée montrant l’influence du liquide cérébrospinal sur la cinématique du cerveau lors d’un chargement dynamique. Cette expérience est utilisée dans un premier temps pour caractériser numériquement le gel silicone Sylgard 527 utilisé comme substitut de cerveau. Dans un second temps des méthodes de couplage partitionné disponible dans le code commercial LS-Dyna ICFD sont utilisées pour modéliser l’expérience. Bien que les modèles de gel précédemment caractérisés ont été utilisés, la version avec fluide n’a pas pu être modélisée avec succès. Troisièmement, un code de couplage partitionné est donc développé. Il consiste en un middleware écrit en C++ couplant deux codes éprouvés, OpenFOAM et LS-Dyna pour la modélisation du fluide et du solide respectivement. De plus, parce que très peu d’essais expérimentaux utilisables pour la validation de code d’interaction fluide-structure sont disponibles dans la littérature, une expérience permettant cela a été réalisée dans une soufflerie. La comparaison des prédictions numériques avec les résultats expérimentaux est prometteuse et donne des résultats globaux satisfaisants. Les points qui ne peuvent pas être validés nécessitent de plus amples investigations et permettront d’améliorer les techniques de modélisations et le développement du code. / The purpose of this work is to improve the biofidelity of the human body models. The work is focused on the human head as it is one of the most injured part. In order to improve the traumatic brain injury onset and mechanism, the biofidelity of the head models has to be increased, thus, the fluids embedded inside the head has to be taken into account. Nevertheless, the modelling of the interactions occurring between the viscous corporal fluids and the soft matter as the brain remains a challenge. This study intends to investigate the fluid-structure interactions between a soft structure and a fluid. Firstly, in order to found the most relevant methods to solve the problem, a deep literature survey has pointed-out all the numerical methods available nowadays. Secondly, in a previous PhD work an experimental test has been carried-out to demonstrate the influence of the cerebrospinal fluid on the brain kinematics under dynamical load case. On one hand, the Silicon Sylgard 527 gel used as brain substitut has been characterized . Subsequently the partitioned coupling methods available in LS-Dyna ICFD have been assessed to model the experiment. Although, the previous characterized gel model has been used, the experiment has been unsuccessfully completed. Accordingly, it has been decided to develop an in-house coupling code. Thirdly, a partitioned coupling code has been developed. It is a middleware in C++ between two well establishing solvers OpenFOAM and LS-Dyna respectively for the fluid and the solid. Because there is very few experimental tests for the coupling code validation, it has been carried-out in this work a fluid-structure interaction experiment involving a soft plate in a wind channel. This appealing experiment allows the scientific community to validate easily their coupling algorithms. Subsequently, the developed coupling code is used to model the wind channel. The results depict a good overall agreement between the experiment and the simulation. Nonetheless, in order to get validated results further investigation are required mainly about the flow modelling.