Many AC grids suffer from decreased frequency stability due to less system inertia. This has increased the risk of large-scale blackouts. This thesis and its papers address the frequency stability problem from a hydropower perspective. Grid frequency stability assessments often require accurate system inertia estimates. One approach is to estimate the inertia of all individual power plants and sum up the results. We implemented three inertia estimation methods on a Kaplan unit and compared their results. The generator contributed with 92-96% of the unit inertia, which verified the results from previous studies. However, the three methods estimated slightly different values for the unit inertia, which raises the question of when to use which method. Hydropower often deliver frequency control, yet we found no studies which validate Kaplan turbine models for large grid frequency disturbances on strong grids. Therefore, we performed frequency control tests on a Kaplan unit, implemented three hydropower models, and compared the simulation results to the measurement data. The models overestimated the change in output power and energy delivered within the first few seconds after a large change in frequency. Thus, it is important to have sufficient stability margin when using these types of hydropower models to assess the grid frequency stability. The Nordic transmission system operators are updating their frequency control requirements. We used measurement data and simulation models to assess whether improved runner blade angle control could help a Kaplan unit fulfill the coming requirements. The results showed that improved runner control does not improve the performance sufficiently for requirements fulfillment. The requirements are based on an assumption on minimum system inertia and became easier to fulfill if they were implemented with more system inertia. Thus, more inertia could allow more participants to deliver frequency control in the Nordic grid.

The thesis first provides a survey of acceleration tests with the focus on automotive component testing. The survey covers multiple types of acceleration tests and sources of stress. The thesis then includes a MATLAB application for the removal of inertia forces, which is applied on two shaft configuration models developed in Pro Engineer. Both models are subjected to stress analysis using FEM in Ansys. The thesis has been carried out in collaboration with TRW-DAS Dačice.

This diploma thesis is concerned with selecting the appropriate method for determining the moment of inertia to the vertical, lateral and longitudinal axis through the centre of gravity of the vehicle. Using the special mechanical device, constructed on IAE was carried out repeated measurements of known mass properties in each axis. With the aid of obtained data was calculated measurement error. To compare the resulting values was created MBS model.

This diploma thesis deals with measurement of vehicle centre of gravity height position. In the first part is created summary of methods used for measuring centre of gravity position and moment of inertia of the vehicle. In the other parts are designed and analyzed two dynamics method of measuring centre of gravity height position. This thesis presents analysis of the errors of the proposed methods, results of measurements and design of the construct adjustments device for measuring of the moments of inertia enabling its used for measuring centre of gravity height position. Some components are through analyse of tension.

The main aim of this master’s thesis is balancing of the inertia forces of sliding parts of the twin cylinder motorcycle’s engine by dummy connecting rod. There is description of two computing stances to design dummy connecting rod. Then there is comparison of these computing stances. The dummy connecting rod is designed and the strength analysis is done by FEM method (finite element method) to limit the state of material fatigue. Furthermore, a crankshaft is designed while considering rotation parts’ inertia forces balancing. Finally, a strength analysis by FEM method is done to limit state of material fatigue of the crankshaft

[pt] A constante busca pelo desenvolvimento sustentável, com o uso de fontes de energia limpa e renováveis, tem fomentado o crescimento da energia eólica no cenário mundial. Como resultado, a produção de energia elétrica por meio de aerogeradores atingiu um estágio de maturidade que a coloca como participante da matriz energética em vários países onde esse recurso natural é disponível, com projeção para vir a ter participação expressiva na matriz energética mundial nas próximas décadas. A integração de grandes usinas/parques de energia eólica ao sistema elétrico tem despertado preocupações em relação a seus impactos sobre questões de controle/estabilidade de frequência, visto que os parques eólicos com gerador de indução com dupla alimentação (DFIG) e turbinas com conversor de potência não contribuem para a inércia do sistema. Como resultado disso, a substituição de unidades geradoras convencionais por fazendas eólicas resulta na redução do momento total de inércia, acarretando uma deterioração da qualidade da frequência frente a grandes distúrbios no SIN. A indústria de energia eólica desenvolveu um controlador para permitir a resposta inercial em geradores de turbinas eólicas, chamada de Inércia Sintética. Logo, o objetivo principal deste trabalho é descobrir o impacto da integração da energia eólica na estabilidade/manutenção da frequência do sistema e avaliar os efeitos da emulação de inércia em turbinas eólicas com base em conversores de potência e seu impacto no momento de inércia total do sistema após a ocorrência de distúrbios de frequência. / [en] The constant pursuit of sustainable development through the use of clean and renewable energy sources has fostered the growth of wind energy on the world stage. As a result, the production of electric energy through wind turbines reached a maturity stage that places it as a participant in the energy matrix in several countries where this natural resource is available, with a projection to have a significant participation in the world energy matrix in the coming decades. The integration of large wind power plants and wind farms into the electricity system has raised concerns about their impacts on frequency control and stability issues, as wind farms with doubly-fed induction generator (DFIG) engines and turbines with power converters do not contribute to system Inertia. As a result, the replacement of conventional generating units by wind farms results in the reduction of the total moment of inertia, causing a deterioration of the quality of the frequency in front of major disturbances in the SIN. The wind power industry has developed a controller to allow inertial response in wind turbine generators, called Synthetic Inertia. Therefore, the main objective of this work is to discover the impact of integrating wind energy into the stability / maintenance of the frequency of the system and to evaluate the effects of the inertia emulation in wind turbines based on power converters and their impact at the moment of total inertia of the System after the occurrence of frequency disturbances.

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.

Ship roll motion has been the subject of many studies, because of the complexities associated with this mode of ship motion, and its impact on operability, safety, and survivability. Estimation and prediction of the energy transfer and dissipation of the hydrodynamic components, added inertia and damping, is essential to accurately describe the roll motions of a ship. This is especially true for ship operations in moderate to extreme sea conditions. In these conditions, a complex process of energy transfer occurs, which alters the physical behavior of the hydrodynamic components, and ultimately affects the amplitude of ship roll motion. Bilge keels have been used on ships for nearly two centuries, to increase damping and reduce the severity of roll motions experienced by a ship in waves. Because ship motions are more severe in extreme sea conditions, large roll angles may occur. With the possibility of crew injury, cargo damage, or even capsize, it is important to understand the behavior of the roll added inertia and damping for these conditions. Dead ship conditions, where ships may experience excitation from beam, or near beam, seas present a worst case scenario in heavy weather. The behavior of a ship in this condition should be considered in both the design and assessment of seakeeping performance. In this study, hydrodynamic component models of roll added inertia and roll damping were examined and assessed to be unsuitable for accurate prediction of ship motions in heavy weather. A series of model experiments and numerical studies were carried out and analyzed to provide improved understanding of the essential physical phenomena which affect the hydrodynamic components and occur during large amplitude roll motion. These observations served to confirm the hypothesis that the existing models for roll added inertia and damping in large amplitude motions are not sufficient. The change in added inertia and damping behavior for large roll motion is largely due to the effects of hull form geometry, including the bilge keels and topside geometry, and their interactions with the free surface. Therefore, the changes in added inertia and damping must be considered in models to describe and predict roll motions in severe wave environments. Based on the observations and analysis from both experimental and numerical methods, several time-domain model formulations were proposed and examined to model hydrodynamic components of large amplitude roll motions. These time-domain formulations included an analytical model with memory effects, a piecewise formulation, and several possibilities for a bilge keel force model. Although a piecewise model for roll damping was proposed, which can improve the applicability of traditional formulations for roll damping to heavy weather conditions, a further attempt was undertaken to develop a more detailed model specifically for the bilge keel force. This model was based on the consideration of large amplitude effects on the hydrodynamic components of the bilge keel force. Both the piecewise and bilge keel force models have the possibility to enable improved accuracy of potential flow-based numerical prediction of ship roll motion in heavy weather. However, additional development remains to address issues for further practical implementation. / Ph. D.

<p>  </p> <p>Widely recognized as bridging graduate coursework and independent research, doctoral examinations also (re)-produce disciplinary norms and map trajectories for graduate student professionalization. This institutional ethnography investigates doctoral exam processes as a component of curricular infrastructure, a term that I describe in functional, relational, temporal, and heuristic terms. This study begins with a discipline-wide survey (Chapter 3) reaching 81 PhD programs in Rhetoric and Composition, building on previous programmatic research in the field to identify constellations of exam formats and their stated purposes. From this broad view, institutional ethnography re-orients analysis by focusing on the standpoints of individual stakeholders (graduate students and faculty) and the ways that work processes point toward broader structural tendencies and assumptions.  From the survey, individual perspectives through interviews with faculty at nine different universities (Chapter 4) and a large focus group with graduate students (Chapter 5) to identify work practices and the institutional and disciplinary factors that direct them. This project yields an empirically grounded description of current graduate pedagogical practices, and through those practices, describes several contours of curricular infrastructure. Temporal boundary objects describe how the meaning and significance of an experience like a doctoral exam can change across time, yielding insight into how curricular practices transfer from one intuition to another. Institutional inertia appears as common iteration of curricular infrastructure, representing the tendency of intuitions to self-replicate and resist change, and nonverbal visually embodied actions serve as a key to understanding communication about institutions that avoids talking about institutions. The project culminates in Chapter 6 with a three-part heuristic, described as an aspect of curricular infrastructure, designed as a resource to faculty and administrators who are in decision-making positions with respect to doctoral exams.  </p>

4th generation district heating (4GDH) and varying the indoor temperature to store heat are both important concepts that can make it easier to implement more renewable energy and reduce costs of heating. This study looks at these concepts from a customer perspective using one building and looking at how energy can be stored and the performance of 4GDH. Low temperature heat sources from industry, supermarkets, and datacentres are used in combination with heat from a combined heat and power plant to get the required heating. A heat pump has also been modelled as a part of the 4GDH structure. In addition to looking at heat storage in 4GDH a scenario with direct electric heating has also been evaluated. In conclusion 4GDH has lower operating costs than 3rd generation district heating, but it is not worth varying the indoor temperature to store energy when using 4GDH. It is, however, profitable to vary indoor temperature if direct electric heating is used.