As a safe long-term management of nuclear wastes, deep geological repositories (DGRs) have been proposed or currently being constructed in several countries. The host rocks in DGRs are saturated with water after the geological disposal facilities (GDFs) are closed and sealed. Significant gas can be generated due to several processes, e.g., the metal corrosion, water radiolysis or microbial reaction of organic materials, etc. The generated gas is anticipated to span throughout the long-term disposal of waste, which may jeopardize the stability of host rocks. Correspondingly, the performance of GDF will be affected since the host rocks provide a final impediment to the radionuclide transport. As gas migration in saturated host rocks is a highly coupled hydro-mechanical (HM) process, either gas-induced micro-fracturing or macro-fracturing may contribute to the development of preferential gas pathways, which needs to be concerned to ensure the feasibility and safety of geological disposal. Current numerical studies on the gas migration behavior devoted to explaining the experimental phenomena in the gas injection tests conducted on the rock materials, in which some behaviors still cannot be well represented, i.e., gas induced fracturing, volulme dilation, anisotropic radial deformation. Therefore, to better represent the actual physical process of preferential gas flow, two modelling frameworks, i.e., macroscopic HM framework and two-scale HM framework, are proposed in the PhD study. For the macroscopic HM framework, a double porosity model is firstly developed based on the dual continuum method, in which the volumetric strains of the porous continuum (PC) and fractured continuum (FC) are work-conjugated to the respective effective stress level. The treatment in two types of porosity allows us to capture that the opening/closure of the fractures is caused by the interaction between the dilation of the PC and the dilation of the FPM, which is beneficial to describe the gas induced fracturing in an implicit way. Then, an enriched embedded fracture model (EFM) is proposed to address the mechanical behavior of fractures. A hyperbolic relation of fracture deformability is incorporated into the rock matrix, as a result the fractured rock shows a nonlinear elastic behavior, which can capture the stiffness degradation due to fracture opening. The equivalent continuum method is provided to derive the effective compliance tensor, which includes the transverse isotropic matrix and two fracture sets. Using the enriched EFM with a three-dimensional (3D) geometry is able to capture the anisotropic radial deformation during gas migration. Although the macroscopic HM framework is able to capture the major HM behaviors related to preferential gas flow, the development of gas dilatant pathways is still represented in an implicit way. Therefore, a two-scale HM framework is developed to explicitly simulate the development of preferential gas pathways. Initiating from the periodically distributed microstructures with microcracks, the asymptotic homogenization method is used to derive the macroscopic governing equations coupled with the normalized damage variable. The time-dependent damage evolution law is obtained from the microscopic mechanical energy analysis for evolving microcracks. Both time effect and size effect are incorporated in the damage model that will affect the overall HM behavior of rocks. The developed two-scale HM framework with single gas flow can qualitatively capture important behaviors, such as the discrete pathways, localized gas flow, unstabilized fracture branching. More specifically, the simulated results demonstrates that the inter-connection of fractures from gas inlet to outlet is a prerequisite for gas breakthrough, accompanied by large amounts of gas flowing out of the sample and a rapid drop in gas injection pressure. Incorporating water flow in the two-scale framework allows the model to quantitatively reproduce the experimental phenomena observed in the laboratory air injection tests, such as gas pressure evolution and mechanical deformation. More importantly, the model exlpaines that the significant differences in controlling gas breakthrough and mechanical deformation are resulting from the arbitrary nature of microstructural heterogeneities. To account for the gas-water interaction in the two-scale HM framework, a fully coupled two-phase flow and elaso-damage model is developed to simulate the laboratory and in-situ gas injection experiments. The model can quantitatively capture the experimental behaviors, e.g., gas pressure evolution and non-desaturation phenomenon. Furthermore, model results show that the highly localized fracture pathways are the major places where gas and water interacts each other, and as a result the rock is still kept fully saturated. As a whole, the obtained numerical results are synthesized and analyzed, the pros and cons of the developed models are discussed. To better improve the model performance, some recommendations are proposed for the future studies.

This work deals with the design of a small hydro secured control system. The secured control system itself belongs to the Fault Tolerant Systems category. At first the requirements on small hydro control system are discussed. Then the introduction into the basics of Fault Tolerant System theory is given. The requirements on small hydro control system and basics of Fault Tolerant Systems are basis for specification of secured control system which design and construction is the main objective of this work.

The aim of the present master’s thesis is to explore the feasibility of small hydropower plant for cur-rent hydro energetic potential of the weir on Ohře river, located in the city of Terezín in Ústecký re-gion, Czech Republic. The target of the thesis itself was to design minimally two variants of constructional and technological part. Due to requirements related to maintaining of all functions of the weir construction was decided to design small hydropower plant completely under the water surface, with flap mounted to the roof of the hydropower plant. Part of the thesis was also an economical assessment of designed hydropower project.

The object of this diploma thesis is revision of coolant system skid steer loaders “BOBEK” B861, B961 and his eventually optimization for prevention of overheating hydraulic system and engine. The first part dedicate of general issues of coolant skid steer loaders. The second part is the calculation during heat stress hydraulic systems of loader and the third part include proposals for solutions problems of overheating hydraulic systems and combustion engine.

The thesis deals with design and implementation of proportional hydraulic valve, which will be integrated to hydraulic system of small hydro in Rájec - Jestřebí. This valve will be used to control one of the wicket gates of double Francis turbine. The thesis is processed for the company Mavel a.s., which is the owner of SH. The goal of this thesis is to create control of the valve according to the client's requirements, its implementation to the control system and commissioning.

Les agrosystèmes sont soumis à de fortes hétérogénéités spatiales et temporelles, notamment du fait des pratiques agricoles. Les modèles de surface, qui servent à quantifier les échanges d'eau et d'énergie entre le sol, la végétation et la basse atmosphère, dits flux hydrométéorologiques, utilisent la plupart du temps des résolutions spatiales trop larges et une description des pratiques agricoles trop simple pour caractériser ces hétérogénéités, faute d'information spatialisée fiable et à fréquence temporelle suffisante pour paramétrer les simulations. Pourtant, réussir à simuler de manière plus réaliste les agrosystèmes à l'échelle du paysage, comme un bassin versant par exemple, est d'importance cruciale que ce soit pour gérer la répartition des ressources en eau ou évaluer les interactions entre pratiques agricoles et évolution climatique. La télédétection à haute résolution spatiale et temporelle, à l'image de la mission spatiale Sentinel-2 de l'ESA, permet de fournir des informations sur la surface terrestre à des résolutions inégalées (10 m, 5 jours) et sur l'ensemble du globe. Cette thèse visait donc à exploiter ce type de données dans un modèle de surface, le modèle SURFEX-ISBA développé par le CNRM, afin d'améliorer la représentation des pratiques agricoles et évaluer son impact sur les flux hydrométéorologiques à l'échelle du paysage. Le premier volet de la thèse avait pour objectif de représenter l'hétérogénéité spatio-temporelle des cultures, du fait des choix des dates de semis et de récolte ainsi que des rotations de culture, dans le modèle. Pour ce faire, j'ai exploité les produits issus des données du satellite optique Formosat-2 (8m, acquisitions programmées), sous la forme de cartes d'occupation des sols et de cartes multi-temporelles d'indice de surface foliaire (LAI) afin de simuler un agrosystème du Sud-Ouest de la France sur une zone de 576 km2. Afin de simuler de telles étendues en exploitant la haute résolution des produits satellite tout en limitant le temps de calcul, une approche de simulation par parcelle a été mise en place. / Agricultural practices generate strong spatial and temporal heterogeneities of the vegetation in agrosystems. Land Surface Models (LSMs), which simulate water and energy fluxes between soil, vegetation and atmosphere, use coarse spatial resolutions and very simplified agricultural practices representations. Therefore, they cannot characterize such heterogeneities. However, simulating agrosystems in a realistic way is of great interest to manage water resources at landscape scale, like a river basin, or study the interactions between climate evolution and agriculture. High resolution remote sensing, like the ESA's Sentinel-2 space mission, allows monitoring the Earth surface globally with unprecedented spatio-temporal resolution of 10 meters and 5 days. This Ph. D. thesis aimed to exploit such data in the SURFEX-ISBA LSM, developed by the CNRM, to represent agricultural practices in the hydrometeorological fluxes estimation at landscape scale. The first part of the thesis aimed at representing the spatial and temporal heterogeneities of the vegetation due to the choice of sewing and harvesting dates and crop rotations in the model. I used multi-temporal Leaf Area Index and annual land cover maps derived from the Formosat-2 remote sensing date (8m, tasking acquisitions). Simulations were performed on a 576 km2 agricultural plain in southwestern France. In order to keep the interest of high resolution while saving computation time, a plot scale simulation approach was used.

Hydro power plants are an essential part of the infrastructure in Sweden as they stand for a large amount of the produced electricity and are used to regulate supply and demand on the electricity grid. Other renewable energy sources, such as wind and solar power, have become more popular as they contribute to a fossil free society. However, wind and solar power are intermittent energy sources causing the demand for regulating power on the grid to increase. Hydro power turbines are designed to operate at a certain design point with a specific flow rate. The plants are operated away from the design point when used to regulate the supply and demand of electricity. This can cause a specific flow phenomenon to arise in the draft tube at part load conditions called a Rotating Vortex Rope (RVR) which causes dangerous pressure fluctuation able to damage blades and bearings. A solution to mitigate a RVR is to inject pulsating momentum into the draft tube by using an actuator operating at a certain frequency. A literature study was conducted and three techniques were numerically simulated using ANSYS Workbench 19.0 R3; a fluidic oscillator, a piston actuator and a synthetic jet actuator. A dynamic mesh was used to simulate the movement of the piston actuator and diaphragm of the synthetic actuator whilst the mesh of the fluidic oscillator was stationary. The relative errors of the three numerical models were all below 3 %. All devices showed promising results and could potentially be used to mitigate a RVR because they all have the ability to produce high energy jets. The fluidic oscillator had an external supply of water, whereas the other two did not, which means that it could inject the largest mass flow. The piston actuator required a driving motor to move the piston. The diaphragm of the synthetic jet actuator was moved by a Piezoelectric element. Advantages of the fluidic oscillator are that it has no moving parts, in contrary to the two other devices, it can directly be connected to the penstock or draft tube to obtain the required water supply and it is easy to install. It will most likely also be smaller compared to the other two for the same mass flow rate. It does however not generate a pulsating jet, but rather an oscillating jet. The other two devices generate pulsating jets, but have problems with low pressure areas during the intake stroke which can cause cavitation problems. These areas cause the formation of vortex rings close to the outlet. Simulations showed that a coned piston together with a coned cylinder outlet could decrease losses by almost 16 % compared to a normal piston and cylinder. It also decreased the risk for cavitation and the required force to move the piston. Otherwise, a shorter stroke length for a constant cylinder diameter or a longer stroke length for a constant volume displacement also decreased the risk for cavitation and required force. The gasket between the piston and cylinder is a potential risk for leakage. A solution to avoid critical low pressure areas is to install an auxiliary fluid inlet or valve which opens at a certain pressure for the piston actuator as well as the synthetic jet actuator. This will also allow larger mass flow rates and a higher injected momentum. Both devices are more complicated to install and require likely more maintenance compared to the fluidic oscillator. However, there exist many possible design options for the piston actuator. The design of the synthetic jet is more limited because of the diaphragm. The amplitude of the diaphragm also has a direct effect on the pressure levels. The losses increased proportional to the mass flow to the power of three which suggests that it is better to install many small actuators instead of a few large ones.

Philosophiae Doctor - PhD / The increasing population in search for better social and economic development in coastal areas puts groundwater resources under pressure because of the high fresh water demand for domestic and agriculture use. Seawater intrusion is widely recognised as major concern in coastal aquifers across the globe and is influenced by multiple factors, being climate variation which is projected to adjust recharge of groundwater because of decreased precipitation patterns and to increase sea level variations and over-abstraction due to high freshwater demand as a result of increased population and agricultural practices, thereby inducing salinization in groundwater. The coastal aquifer in Heuningnes Catchment is not exempted from these issues and salinization is a major concern in the area affecting groundwater quality. In Heuningnes Catchment and South Africa in general there is limited knowledge on the application of integrated approach for assessing groundwater quality especially salinization mechanism in coastal aquifers. The main goal of this research is to test and demonstrate the viability of using joint interpretation approach of geophysics, geochemical and geological information to investigate groundwater quality in coastal aquifers thus improving on the understanding of using such approach. This work offers the initial thorough assessment of groundwater quality and understanding of the salinity sources and hydro-geochemical processes governing the chemical composition of groundwater in the region. Thus provide advice on the fitness of this water for consumption and irrigation purposes. Thirty-two groundwater samples were collected and analysed for (Mg2+), (Ca2+), (Na+), (K+), (Cl-), (SO42), (HCO3-), (pH, TDS and EC). To estimate fitness of groundwater quality for consumption purposes WHO (2011) and SANS241 guideline were used and for irrigation utilization the water quality indices (EC), (Na+%), (SAR), (RSC), (KR) and (MR) were used. Statistics approaches were employed to ascertain the primary geochemical processes governing the chemical composition of groundwater in the research region. Lastly, the spatial distribution maps were created by means of ArcGIS. Electrical resistivity method was used to map the extent of saline distribution within the subsurface. The findings of this study revealed that groundwater in the region is alkaline type and TDS, EC, Na+, Cl- exceeded WHO and SANS241 guidelines for consumption water. The geophysical investigation revealed that the sandy clay/clayey sand, fine sand and fractured sandstone units make up the coastal aquifer systems within the area. Further, revealed that these aquifers were saturated with fresh, saline or brackish water depending on the subsurface layer. The presence of saline and brackish was confirmed by the chemical results which indicated a Na+-Cl- type as a dominant water type. Also classifying groundwater based on EC and TDS supports these findings. The foremost hydro-geochemical processes that controls the salinity and quality of groundwater in the study region as indicated by Gibbs plot are water-rock interaction followed by evaporation process. Furthermore, analysis of hydrochemical data also proposes that weathering of silicate minerals, ion-exchange and dissolution of carbonate minerals amended ion concentration in groundwater thus influencing salinisation in certain parts of the study region. Also assessment of ionic-ratios displays influences of marine sprays as well as seawater, on the chemical structure of groundwater within the Heuningnes Catchment aquifer. Valuation of groundwater quality and its fitness for ingestion and irrigation purposes, the results indicated that shallow groundwater in the area is not suitable for any use; however, groundwater from deeper boreholes was found fresh and appropriate for irrigation and household purposes. Findings of this study indicated that salinity is the major groundwater quality issue for this area and that monitoring of groundwater quality in Heuningnes Catchment is limited. The absence of consistent monitoring program on groundwater quality makes it difficult to ascertain long term trends on groundwater quality parameters. Therefore, this study emphasizes the need for regular groundwater quality monitoring to assess the trends of these parameters in order to make an informed decision as to what can be done for mitigation purposes.

Since the deregulation of the Nordic electricity market in 1996, electricity has become one of the most traded commodities in the Nordic region. The electricity price is characterized by large fluctuations as the supply and demand of electricity are seasonally dependent. The main interest of the hydro power producers is to assure that they can sell their hydro power at an attractive rate over time. This means that there is a demand for hedging against these fluctuations which in turn creates trading opportunities for third party actors that offer solutions between consumers and producers. Telge Krafthandel is one of these actors interested in predicting the future supply of hydro power, and consequently the resulting price of electricity. Several existing models employ the assumption of perfect foresight regarding the weather in the future. In this thesis, the authors develop new models for hydro power optimization that take hydrological uncertainty into account by implementing a variation of multi-stage optimization in order to maximize the income of the hydro power producers. The optimization is performed with respect to prices of financial derivatives on electricity. This gives insights into the expected supply of hydro power in the future which in turn can be used as an indicator of the price of electricity. The thesis also discusses, among other things, different methods for modeling stochastic inflow to the reservoirs and scenario construction. This practice will result in different methods that are suitable for various key players in the industry. / Sedan avregleringen av den Nordiska elmarknaden år 1996 har el blivit en av de mest handlade råvarorna i Norden. Elpriset karaktäriseras av stora svängningar eftersom utbudet och efterfrågan på el är säsongsberoende. Huvudintresset för vattenkraftsproducenter är att säkerställa att de kan sälja sin vattenkraft till ett attraktivt pris över tid. Detta innebär att det finns en efterfrågan för skydd mot dessa variationer, vilket i sin tur skapar affärsmöjligheter för tredjepartsaktörer som erbjuder lösningar mellan konsumenter och producenter. Telge Krafthandel är en av dessa aktörer och är därmed intresserad av att förutsäga det framtida utbudet på vattenkraft, och det resulterande elpriset. Flera befintliga modeller använder antagandet om perfekt förutseende när det gäller vädret i framtiden. I denna rapport utvecklar författarna nya modeller för vattenkraftsoptimering, som tar hänsyn till hydrologisk osäkerhet genom att implementera en variant av flerstegsoptimering för att maximera intäkterna för vattenkraftsproducenter. Optimeringen utförs med hänsyn till priserna på elderivat. Detta ger insikter i den förväntade tillgången på vattenkraft i framtiden, vilket i sin tur kan användas som en indikator på elpriset. I rapporten diskuteras också, bland annat, olika metoder för att modellera stokastiskt inflöde till vattenmagasinen och scenariokonstruktion. Detta kommer att leda till flera metoder som är lämpliga för olika aktörer i branschen.

The power grid faces stability problems due to loss of inertia. The ancillary services balancing the system must be improved to maintain stability. In contrast to earlier studies, this thesis estimates how the future grid frequency quality in both the short and long term is affected by different control methods, using an ensemble of quality measures. The thesis uses conventional one-area models for the power grid and FCR-N (frequency containment reserve – normal operation) but develops new models for FCR-D (– disturbed operation), FFR (fast frequency reserve), and synthetic inertia (SI). To acquire proper input data the thesis uses an inverse model of the power grid to compute the momentary load disturbance, i.e., the difference between load and generation, from the grid frequency. The thesis makes a difference between proportional and derivative SI, where the latter is the one commonly associated with the term SI. The results show that derivative SI can improve some quality measures but requires very high power capacity. In contrast, proportional SI improves almost every measure the most, for a fraction of the required capacity. Derivative SI is therefore worth less from a system perspective. However, it is shown that the quality measures improved by derivative SI are related to hydropower wear and tear, making it more interesting for hydro power owners. Moreover, FFR gives no benefit to long time quality measures. Considering the short-term analysis where a large disturbance occurs, FFR gives almost no benefit and risks worsening the stability. Also, for the large disturbance, proportional SI performs the best. The results are limited by the small number of simulations that were performed and can only provide indications of trends. A more solid conclusion, however, is that one cannot expect transmission system operators (TSO) to introduce an ancillary service that builds on derivative SI.