As the share of power electronics-based renewable energy sources increases in power systems, the system inertia provided by conventional generation is reduced. Inertia is an important factor in the grid's frequency stability, and with its reduction comes challenges to ensure the reliability of the grid. The frequency stabilising service of frequency containment reserves will need to work in conjunction with the faster, stabilising service of fast frequency reserves to avoid power failures in case of sudden disturbances. This project aims to examine the impact of inertia and methods of improving frequency stability in a future low inertia power system. The frequency behaviour is studied using a simplified and linearised model of the Nordic power system implemented in Matlab/Simulink. The model is extended by implementing supplementary battery control to support the frequency response. The simulation results show that there is an evident correlation between the reduction of system inertia and frequency instability. Moreover, it is concluded that the implemented battery support is successful in stabilising frequency following a disturbance. / Då andelen kraftelektronikbaserade förnybara energikällor ökar i kraftsystem så kommer systemets tröghet, tillfört av konventionell generering av elektricitet, att minska. Trögheten är en viktig faktor för elnätets frekvensstabilitet. Då trögheten minskar utmanas tillförlitligheten av elnätet. Frekvensstabiliserande frekvenshållningsreserver behöver fungera i samspel med de snabbare och stabiliserade frekvensreserverna för att undvika strömavbrott vid plötsliga störningar. Projektet ämnar undersöka trögheten och metoder som används vid förbättring av frekvensstabilitet i framtida kraftsystem med låg tröghet. Beteendet hos frekvenser studeras med en förenklad och linjäriserad modell av det nordiska kraftsystemet implementerat i Matlab/Simulink. Modellen utökas genom att inkludera en batterikontrollmetod för att tillförse ett snabbt frekvenssvar. Resultatet av simuleringarna visar att det finns en korrelation mellan minskning av systemets tröghet och frekvensinstabilitet. Vidare visas det att implementationen av batteristöd lyckas förbättra frekvensen i fallet av en störning. / Kandidatexjobb i elektroteknik 2022, KTH, Stockholm

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In the search for green energy to combat climatechange, a shift from conventional energy sources such as coal,oil, and nuclear towards Renewable Energy Sources (RES) isneeded. This shift poses a threat to the stability of the powergrids as RES do not contribute with rotating mass in the system.A lack of rotating mass, or in other words inertia, jeopardizesthe ability of power systems to counteract large disturbances.Frequency Containment Reserves (FCR) units are responsiblefor controlling the frequency in power systems by regulatingthe balance between the generated and consumed power. If thefrequency deviates outside of the defined range from the nominalvalue, it can lead to system separation, blackouts, and systemequipment damage. The frequency deviations are faster in lowinertia systems, making it more difficult for FCR to keep thefrequency within accepted ranges. Hydro turbines are often usedas FCR units, but additional means of support could be neededfor low inertia systems. Viable support could be battery systems.This project investigates the change towards low inertia and thepossible implementation of a battery system as fast step-wisepower support with a frequency trigger. The investigation is donethrough case studies of simulated system models in Matlab andSimulink. / I jakten på grön energi för att bekämpaklimatförändringarna behövs en övergång från konventionellaenergikällor som kol, olja och kärnkraft mot förnyelsebaraenergikällor. Denna övergång utgör ett hot mot kraftnätensstabilitet då förnyelsebara energikällor inte bidrar med roterandemassa. Brist på roterande massa eller med andra ord tröghetäventyrar kraftsystemens förmåga att motverka stora störningar.Frequency Containment Reserves (FCR) är system som aktivt arbetarmed att styra frekvensen i kraftsystemet genom att reglerabalansen mellan den producerade och konsumerade effekten.Om detta misslyckas och frekvensen avviker för mycket frånden nominella frekvensen kan detta leda till systemseparation,strömavbrott eller skada hos systemkomponenter. I ett systemmed låg tröghet blir frekvensavvikelserna snabbare. Detta gördet svårare att använda sig av FCR för att hålla frekvenseninom accepterade intervall. Vattenkraftverk används ofta somFCR enheter, men för system med låg tröghet kan ytterliggarestöd behövas. Ett möjligt effektstöd kan vara batterisystem.Detta projekt undersöker förändringen till lägre tröghet i ettkraftsystem och möjlig implementering av ett batterisystemmed ett snabbt stegsvar för effektstöd, vilket aktiveras vid enförbestämd frekvens. Undersökningen görs genom studier avspecifika fall med en linjäriserad modell av ett kraftsystemet,simulerade i Matlab och Simulink. / Kandidatexjobb i elektroteknik 2021, KTH, Stockholm

In dieser Dissertation wird eine allgemeine zweiskalige Homogenisierungsmethode für große Deformationen entwickelt, welche die Trägheitskräfte der Mikroskala konsistent berücksichtigt. Die energetische Skalenkopplung der Methode basiert auf der erweiterten Hill-Mandel Bedingung für Makrohomogenität. Darüber hinaus wird die kinematische Skalenkopplung diskutiert und eine Volumenintegrals-Verschiebungsbedingung aufgezeigt, die eine allgemeine dynamische Betrachtung ermöglicht. Um einen effizienten Algorithmus zu gewährleisten, werden vier makroskopischen Tangenten-Module in geschlossener Form hergeleitet. Es werden zwei Rechenbeispiele genutzt, um allgemeine Eigenschaften der Methode zu analysieren. Dazu gehören das makroskopische Konvergenzverhalten und die Übereinstimmung mit einskaligen Referenzsimulationen. Des Weiteren wird der Einfluss der Verschiebungsbedingung und die Wahl der Einheitszelle als representatives Volumenelement auf die Antwort der Makroskale untersucht. Der Fokus der Arbeit wird im Anschluss auf die Modellierung hochduktiler Betone (Engl.: Strain-Hardening Cementitious Composites – SHCC) unter Stoßbelastung gelegt. Zunächst wird anhand von experimentellen Daten ein vereinfachtes Materialmodell kalibriert, welches das homogenisierte Faserauszugsverhalten repräsentiert. Danach wird dieses Faserauszugsmodell auf der Mikroskale eingesetzt und mit der vorgestellten Homogenisierungsmethode untersucht. Schließlich wird ein Split-Hopkinson-Bar Zugversuch numerisch repliziert. Dieser wird verwendet um die Funktionaltät der Methode aufzuzeigen, wie dynamische Effekte des Materials und der Struktur untersucht werden können. / A general numerical two-scale homogenization method for large strains is developed, which consistently takes into account inertia forces at the microscale. The energetic scale coupling of the framework is based on the extended Hill-Mandel condition of macro-homogeneity. Furthermore, kinematic scale links are discussed and a volume integral displacement constraint is proposed. To enable an efficient algorithm, closed form formulations of four macroscopic tangent moduli are derived. These consistently include the microscale inertia effects as well as the proposed displacement constraint. Two numerical examples are presented, a layered microstructure and a locally resonant material. These examples are used to analyze general properties of the presented framework, namely the macroscopic convergence behavior and the overall match with single-scale reference calculations. In addition, both the displacement constraint and the choice of unit cell as representative volume element are studied with respect to their influence on the macroscopic response. Subsequently, the thesis focuses on the modeling of strain-hardening cementitious composites under impact loading. First, a simplified material model representing the homogenized fiber pullout behavior is calibrated using experimental data. Then, this fiber pullout model is used at the microscale and studied using the proposed dynamic homogenization framework. Finally, a split Hopkinson bar tension test is numerically replicated and used to showcase the ability of the framework to thoroughly study the dynamic effects of the material and structure.

[pt] Na emergência global das mudanças climáticas, um eixo fundamental para a mitigação é associado ao setor energético, que representa 77% das emissões globais de gases de efeito estufa. O fenômeno global caracterizado pela substituição de fontes de energia fósseis por fontes de energia renováveis, visando a redução das emissões é denominado de ‘Transição Energética’. Neste contexto, as empresas incumbentes do setor de óleo & gás se encontram no centro deste dilema estratégico, uma vez que este setor responde por 50% da demanda global de energia e são focadas em fontes de energia fósseis, emissoras de gases de efeito-estufa. Este estudo visa esclarecer os fatores que precedem o engajamento na transição energética por empresas incumbentes do setor de óleo & gás, fazendo-as vencer a inércia organizacional e adotar estratégias que as levem a se adaptar à mudança de cenário global pela qual passa este setor. Com estudo plurianual (2017-2022) e ampla base de dados (168 empresas do setor) foram aplicados testes empíricos para verificar os fatores antecedentes ao engajamento das empresas incumbentes do setor de óleo & gás. Observou-se que a vigência do acordo de Paris, a natureza do controle acionário e a importância do segmento de upstream são fatores que influenciam no engajamento das empresas incumbentes do setor de óleo & gás. / [en] In the global climate change emergency, a fundamental axis for mitigation is associated with the energy sector, which accounts for 77% of global greenhouse gas emissions. The international phenomenon characterized by replacing fossil energy sources with renewable energy sources, aiming at emissions reduction, is termed Energy Transition. In this context, incumbent oil and gas sector companies find themselves at the center of this strategic dilemma, as this sector accounts for 50% of global energy demand and is focused on fossil energy sources that emit greenhouse gases. This study aims to elucidate the factors preceding engagement in the energy transition by incumbent oil and gas sector companies, enabling them to overcome organizational inertia and adopt strategies that lead them to adapt to the changing global landscape that this sector is undergoing. Through a multi-year empirical study (2017-2022) and a comprehensive database (168 companies in the industry), empirical tests were applied to verify the factors preceding incumbent oil and gas companies engagement. It was seen that the enforcement of the Paris Agreement, the nature of shareholder control, and the importance of the upstream segment influence incumbent companies engagement in the oil & gas sector.

The investigation of failure in brittle materials, subjected to dynamic transient loading conditions, represents one of the ongoing challenges in the mechanics community. Progresses on this front are required to support the design of engineering components which are employed in applications involving extreme operational regimes. To this purpose, this thesis is devoted to the development of a framework which provides the capabilities to model how crack patterns form and evolve in brittle materials and how they affect the quantitative description of failure. The proposed model is developed within the context of diffusive interfaces which are at the basis of a new class of theories named phase field models. In this work, a set of additional features is proposed to expand their domain of applicability to the modelling of (i) rate and (ii) pressure dependent effects. The path towards the achievement of the first goal has been traced on the desire to account for micro-inertia effects associated with high rates of loading. Pressure dependency has been addressed by postulating a mode-of-failure transition law whose scaling depends upon the local material triaxiality. The governing equations have been derived within a thermodynamically-consistent framework supplemented by the employment of a micro-forces balance approach. The numerical implementation has been carried out within an updated lagrangian finite element scheme with explicit time integration. A series of benchmarks will be provided to appraise the model capabilities in predicting rate-pressure-dependent crack initiation and propagation. Results will be compared against experimental evidences which closely resemble the boundary value problems examined in this work. Concurrently, the design and optimization of a complimentary, improved, experimental characterization platform, based on the split Hopkinson pressure bar, will be presented as a mean for further validation and calibration.

In order to reduce emissions and achieve sustainable energy systems, renewable energy is increasingly being integrated into the power grid. However, the integration of renewable energy into the grid poses several challenges, including maintaining a stable power supply under changing and unpredictable conditions. Low Voltage Ride Through (LVRT) assesses a generator's ability to maintain stable voltage during grid voltage drops, which is crucial for renewables due to their low inertia and vulnerability to voltage disruptions caused by changes in wind or sunlight. LVRT requirements are defined by regional grid codes and regulations, which vary in their diversity. A study was conducted using Matlab Simulink to model and simulate the LVRT phenomenon on Siemens Energy's medium gas turbine generator. The entire power system generation system was simulated to observe the system's response and the generator's behavior during LVRT events. A previous gas turbine power plant project in Romania, delivered by Siemens Energy in Finspång, was simulated for analysis and compared against the grid code requirements. The findings indicated that the Siemens Energy gas turbine model SGT-750 satisfies the Romanian LVRT grid code requirements.

Text in Afrikaans / Summaries in English and Afrikaans / Key terms in English and Afrikaans / Die doel van die studie was om organisasietraagheid as stremmende fenomeen te konseptualiseer en die manifestasie daarvan te ondersoek binne 'n tipiese werkorganisasie. Aandag is gegee aan organisasietransformasie binne die raamwerk van 'n diagnostiese model vir organisasie- en individuele ontwikkeling. Die empiriese studie bevestig die manifestasie van organisasietraagheid ten opsigte van die teikenorganisasie. Resultate bevestig dat respondente ten gunste is van veranderingsinisiatiewe, maar ondergeskiktes toon 'n emstige behoefte aan leierskap. Dit blyk ook dat die organisasie nie die vermoe het om vinnig op omgewingsveranderings te reageer nie. Gesonde bestuurspraktyke word nie gevolg nie en kreatiwiteit word nie aangemoedig nie. By ondergeskiktes bestaan ook twyfel oor veranderingsagente se vermoe om verandering te fasiliteer. / The purpose of the study was to conceptualise organisation inertia as a retarding phenomenon and to investigate its manifestation within a typical work organisation. Attention was given to organisational and individual development within the framework of a diagnostic model. The empirical study focussed on the manifestation of organisational inertia within the target organisation. Results confirmed that respondents are in favour of change initiatives but that the stimulation thereof do not exist. Subordinates are not encouraged to show creativity. The organisation demonstrates an incapability to respond to environmental changes and reflects a non-existence of healthy management practices. Little trust exists in the capability of change agents to facilitate change. / Economics and Management Sciences / M.A. (Industrial Psychology)

The thesis presents a novel computational method for analysing the static and dynamic behaviour of a multi-damaged beam using local and non-local elasticity theories. Most of the lumped damage beam models proposed to date are based on slender beam theory in classical (local) elasticity and are limited by inaccuracies caused by the implicit assumption of the Euler-Bernoulli beam model and by the spring model itself, which simplifies the real beam behaviour around the crack. In addition, size effects and material heterogeneity cannot be taken into account using the classical elasticity theory due to the absence of any microstructural parameter. The proposed work is based on the inhomogeneous Euler-Bernoulli beam theory in which a Dirac's delta function is added to the bending flexibility at the position of each crack: that is, the severer the damage, the larger is the resulting impulsive term. The crack is assumed to be always open, resulting in a linear system (i.e. nonlinear phenomena associated with breathing cracks are not considered). In order to provide an accurate representation of the structure's behaviour, a new multi-cracked beam element including shear effects and rotatory inertia is developed using the flexibility approach for the concentrated damage. The resulting stiffness matrix and load vector terms are evaluated by the unit-displacement method, employing the closed-form solutions for the multi-cracked beam problem. The same deformed shapes are used to derive the consistent mass matrix, also including the rotatory inertia terms. The two-node multi-damaged beam model has been validated through comparison of the results of static and dynamic analyses for two numerical examples against those provided by a commercial finite element code. The proposed model is shown to improve the computational efficiency as well as the accuracy, thanks to the inclusion of both shear deformations and rotatory inertia. The inaccuracy of the spring model, where for example for a rotational spring a finite jump appears on the rotations' profile, has been tackled by the enrichment of the elastic constitutive law with higher order stress and strain gradients. In particular, a new phenomenological approach based upon a convenient form of non-local elasticity beam theory has been presented. This hybrid non-local beam model is able to take into account the distortion on the stress/strain field around the crack as well as to include the microstructure of the material, without introducing any additional crack related parameters. The Laplace's transform method applied to the differential equation of the problem allowed deriving the static closed-form solution for the multi-cracked Euler-Bernoulli beams with hybrid non-local elasticity. The dynamic analysis has been performed using a new computational meshless method, where the equation of motions are discretised by a Galerkin-type approximation, with convenient shape functions able to ensure the same grade of approximation as the beam element for the classical elasticity. The importance of the inclusion of microstructural parameters is addressed and their effects are quantified also in comparison with those obtained using the classical elasticity theory.

組織慣性通常是組織對外在變化的適應與變革的阻礙。特別是在目前外在商業環境變化劇烈的時代，如何有效化解組織慣性以適應現況，變成一個重要的策略與管理課題；而企業資源規劃(ERP)的導入過程中，由於對組織的流程反思與再造，對企業會產生管理變革。本研究透過Godkin與Allcorn (2008) 以組織學習的觀點所發展的三構面組織慣性（思想、行動、心理）與化解方式模型，對於海峽兩岸的九個企業個案在導入ERP過程中所發生過管理變革的抗拒與化解的手法，辨識出其在管理模型中的組織慣性與化解的類型。在個案的研討之下發現，思想慣性是發生最普遍的一種組織慣性，心理慣性則發生在較為成立較久、地處偏僻或管理方式特殊的企業，行動慣性則較易發生在具科技背景的公司。而化解的手法中，思想慣性的反映實踐因為與ERP的導入方式相近因此較為常見，而雙回路學習則是要將管理變革的影響範圍擴大到高層。化解行動慣性的跨功能小組以及系統性問題解法與前提控制會同時採用，且需要高階主管的強勢領導。領導/組織容忍與過渡空間與時間是化解心理慣性的主要方式，也都有個案使用，但都需要考量組織所處的環境與成員特性來進行，以符合實際環境的狀況與需求。