In 1990 Flödeskommittén released new guidelines which redefined the method used to determine design flows. The method, combined with more complete measurements of flow variations, has resulted in higher design flows which in turn call for increases in the discharge capacity of hydropower plants. This work is still in progress. Since many Swedish hydropower stations were constructed in the 1950's and 60's they require modernization. Today Statkraft owns and operates 55 hydropower stations in Sweden several of which have a discharge capacity below the design flow. For this reason, the dam safety of these hydropower stations is reduced. According to current guidelines the turbine flow is not added to the discharge capacity since the availability of the electrical grid is not guaranteed during extreme flows. When the electric grid is unavailable the generator has no load and cannot produce an electric torque. Without the electric torque the turbine accelerates which may result in equipment failure. This thesis considers the introduction of an alternative local load where the generator power can be dumped as heat, hence termed dump load. The dump load has the potential to increase the discharge capacity by adding the turbine flow. However, operation of the dump load requires the availability of the generator and turbine, making the discharge capacity dependent on the status of the plant. In turn, achieving a sufficient discharge capacity is of primary concern to dam operators since it determines dam safety. Consequently, this thesis evaluates the effects on dam safety when utilizing a local load to increase the discharge capacity. Three different designs were evaluated; a medium to high voltage electrode water boiler, electrodes submerged in the river and a low voltage electric water boiler. The evaluation shows that all three designs are feasible and can be used to increase the discharge capacity provided the generator and turbine have high availability. The complexity and number of components constituting the dump load should be minimized to reduce the risk of malfunctions and redundancy should be introduced for key components when feasible. The dump load power should be controlled using voltage regulation but further work is required to determine the specifics of this governor. The results also show that the cost of the dump load is a fraction of the cost of a new spillway. However, the topic is controversial and the dump load requires practical testing in order to evaluate operational reliability.

At the Torpshammar dam two rectangular beams are situated upstream of the spillway gates to stabilize the sidewalls holding the embankment of the dam. A computational fluid dynamics (CFD) simulation of the dam with the bottom outlets open was made to investigate how the flow and discharge capacity is affected by the beams. The results can be used to avoid unexpected consequences due to turbulence caused by the beams, make the beams strong enough to hold the pressure from the flow and get an estimation of the discharge capacity with the beams. Turbulence is one of the hardest things to simulate so the results were compared with previous simulation work made without the beams and physical model tests to validate the results. Also, a sensitivity analysis was made to investigate the method used. The beams lowered the velocity (to 17 m/s) and the discharge capacity (to 255 m3/s) compared to the previous work. The force on the beams was directed upward and downstream. The beams increased the turbulence and the vortex shedding frequency was higher for the beam closest to the outlet. The velocity and discharge capacity differed with 6 % compared to model test results. The results can therefore only be used as an estimation, a more detailed computational model and more computational cells are needed to get a better result. The sensitivity analysis showed that the velocity and turbulence depend on the method and further studies need to be made to decide which method gives the closest similarity with reality.

CFD is today a big part of the design process in hydraulic engineering and is more economical and time efficient than traditional scale models. But, there are still issues concerning the agreement with scale models in large and complex geometries. In this degree project a high head, five channeled, slotted flip bucket spillway system is analyzed with the CFD software FLUENT and compared with existing scale model results. The sought hydraulic parameters in each channel were the discharge capacity, the pressure distribution and the throw distance from the flip buckets. The discharge capacity and pressure distribution was practically equal for all five channels and only the throw distance from Channel 1 deviated from the others. The agreement with data from the scale model is quite low. The biggest error sources behind the bad agreement may depend on the lack of computational power which led to bad choice of cell size, model delimitations and simplifications. CFD models can easily be built up by people without experience in hydraulics which can lead to fatal errors when building up the model and interpreting results. Hence, long experience in CFD or verification of the numerical results with several different hydraulic parameters is the only way to guarantee qualitative results from CFD modeling.

No description available.

An urgent transformation from fossil fuels to cleaner energy sources to combat climate change has led to the utilization of renewable energies like solar, wind, and tidal power. However, the intermittency of these sources hinders their wider implementation. To address this, large-scale electrical energy storage (EES) systems are needed. These systems store excess energy during periods of surplus and release it during peak demand, enhancing grid reliability. Secondary batteries have been developed as promising EES solutions due to their reliability, independence from weather, and ease of maintenance. While lithium-ion batteries (LIBs) are popular as secondary batteries, their limited lithium supply, and rising costs demand for cost-effective alternatives. This study focuses on developing sodium iron fluorophosphate (Na2FePO4F) as a promising cathode material for SIBs. Because of its iron-based composition, which is generated from sustainable sources, Na2FePO4F offers a potential solution to the cost and supply difficulties related with LIBs. However, challenges exist, including low electronic conductivity and inferior electrochemical performance. To address these challenges, this research explores mechanochemically assisted solid-state synthesis routes as a low-cost and environmentally friendly approach. The characterization and performance evaluation of Na2FePO4F (NFPF) and NFPF/C positive electrode materials for sodium-ion batteries (SIBs) were systematically investigated through a range of analytical techniques, including XRD, TGA, SEM-EDS, FT-IR, and Raman analyses. A single-step solid-state synthesis demonstrates effectiveness in producing NFPF and NFPF/C-positive electrode materials. Moreover, Fe2O3 nanoparticles serve as the primary iron source in the solid-state synthesis of iron-based fluorophosphate Na2FePO4F/C, successfully producing both NFPF pristine phase and NFPF carbon-coated active materials. Finally, a comparison between the two synthesis pathways reveals that the active material from single-step solid-state synthesis exhibits a superior initial discharge specific capacity of 74.24 mAh⋅g−1 at 0.005 C, outperforming the double-step solid-state synthesis. These findings can contribute to the development of affordable and sustainable energy storage solutions, offering alternatives to traditional LIBs. / En akut omvandling från fossila bränslen till renare energikällor för att bekämpa klimatförändringarna har lett till ett utnyttjande av förnybar energi som sol-, vind- och tidvattenkraft. Emellertid hindrar dessa källors intermittenser deras bredare genomförande. För att komma till rätta med detta behövs storskaliga system för lagring av elektrisk energi (EES). Dessa system lagrar överskottsenergi under perioder med överskott och släpper ut den under toppbelastning, vilket förbättrar nätets tillförlitlighet. Sekundära batterier har utvecklats som lovande EES-lösningar på grund av deras tillförlitlighet, väderberoende och enkla underhåll. Medan litiumjonbatterier (LIB) är populära som sekundära batterier, kräver deras begränsade litiumtillgång och stigande kostnader kostnadseffektiva alternativ. Denna studie fokuserar på att utveckla natriumjärnfluorfosfat (Na2FePO4F) som ett lovande katodmaterial för SIB. På grund av sin järnbaserade sammansättning, som genereras från hållbara källor, erbjuder Na2FePO4F en potentiell lösning på kostnads- och försörjningssvårigheter relaterade till LIB. Men det finns utmaningar, inklusive låg elektronisk konduktivitet och sämre elektrokemisk prestanda. För att möta dessa utmaningar undersöker denna forskning mekanokemiskt assisterade syntesvägar i fast tillstånd som ett billigt och miljövänligt tillvägagångssätt. Karakteriseringen och prestandautvärderingen av Na2FePO4F (NFPF) och NFPF/C positiva elektrodmaterial för natriumjonbatterier (SIB) undersöktes systematiskt genom en rad analytiska tekniker, inklusive XRD, TGA, SEM-EDS, FT-IR och Raman analyser. En enstegs solid state-syntes visar effektivitet vid framställning av NFPF och NFPF/C-positiva elektrodmaterial. Dessutom tjänar Fe2O3-nanopartiklar som den primära järnkällan i solid state-syntesen av järnbaserat fluorfosfat Na2FePO4F/C, vilket framgångsrikt producerar både NFPF orörd fas och NFPF kolbelagda aktiva material. Slutligen avslöjar en jämförelse mellan de två syntesvägarna att det aktiva materialet från enstegs-solid-state-syntes uppvisar en överlägsen initial urladdningsspecifik kapacitet på 74,24 mAh⋅g−1 vid 0,005 C, vilket överträffar dubbelstegs-solid-state-syntesen. Dessa resultat kan bidra till utvecklingen av prisvärda och hållbara energilagringslösningar, som erbjuder alternativ till traditionella LIB.