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Implementation and Stability Analysis of Synthetic Inertia for Inverter-Based Energy Resources
No full textAbstract
Inverters are being integrated into power systems around the world at a rapid pace due to the shift from traditional energy sources to renewable sources such as wind and solar power. As the number of inverters increases, the inertia in the system with respect to the power level decreases. Since frequency stability in power systems heavily relies on the kinetic energy stored in rotating masses to provide inertia, such as synchronous generators which are now being partly phased out, it may become necessary for inverters to provide synthetic inertia as well.
This thesis work includes the implementation of grid following and grid forming inverters together with an external grid of variable strength and an island grid constituted of a hydro power generator. The simulations are carried out in Matlab and Simulink. The implementation is based on the theory of existing methods and includes an important definition of synthetic inertia, namely that it is proportional to the rate of change of frequency. Contrary to fast frequency response which is proportional to frequency deviation. The models were then tested against grid frequency disturbances to analyze how aggressively the system could be tuned while still maintaining stability. The results showed that grid following inverters are highly dependent on the strength of the external grid, mainly because of their need to synchronize their own frequency with the grid. When operating in synthetic inertia mode, the grid following inverter stability region increased linearly between proportional gain and the filtering time constant. When providing active power based on frequency deviation, the stability
decreased as the filtering increased. The grid forming inverter was highly dependent on its droop constant to remain stable where as the droop constant increased, the stability decreased
CFD Simulation of a Semi-Submersible Floating Wind Platform in Waves. Balancing Accuracy and Efficiency in Simulation of Wave-Structure Interaction
No full textOffshore wind power is a promising solution for large-scale renewable energy production, offering benefits such as abundant offshore space and higher energy output. One type of floating platform is semi-submersibles, which combine buoyancy stabilization with catenary mooring systems. This thesis presents the development of a numerical model of the YFloat semi-submersible floating offshore wind platform using the CFD software StarCCM+, intending to achieve a balance between computational efficiency and solution accuracy.
To support model development, initial wave simulations were conducted without the floater to investigate mesh requirements for accurately capturing wave-induced currents and wave heights. The results indicated that capturing the wave-induced current required a fine mesh with at least 25 cells per wave height and 132 cells per wavelength, while wave heights could be represented adequately with a significantly coarser mesh.
Consecutive full-scale simulations included the floater and were validated against experimental model test data. A free decay simulation was used to confirm the floater’s dynamic properties, showing less than 5 % deviation in rotation around the x-axis compared to test results. Simulations in regular waves focused on the spatial and temporal resolution influence on motion responses and wave height. The best compromise between accuracy and efficiency was achieved with 10 cells per wave height and a time step of Δt = 0.02 s. This configuration required 2.8 hours of simulation time, saving 7.3 hours compared to the finest spatial resolution, which took 10.1 hours (a 72.3% reduction), and 9.7 hours compared to the finest temporal resolution, which took 12.5 hours (a 77.6% reduction). The numerical results showed strong agreement with experimental data, validating the CFD model
A Self–Trained Engine for Atomic Chess
No full textThis thesis concerns the development of a chess engine to play a variant of chess
called atomic chess, utilizing a neural network. The neural network is modeled after
DeepMind’s AlphaZero, which is a model that learned standard chess from only the
rules, and no real-world games (hence “zero”). We demonstrate an adapted model
that improves its playing strength in atomic chess, given enough training time. This
is done using a deep convolutional neural network, trained with data generated by a
modified Monte Carlo tree search in a process called self-play. These two components
feed each other data in a cycle: the neural network guides the tree search, and the
results of the tree search are then used to train the network, repeatedly. The result
is a trained network that is shown to have improved from the untrained model,
which corresponds to an unguided or randomly guided Monte Carlo tree search.
An extensive background aimed at computer engineering students is also included,
explaining the terms used in the thesis
An exploration of low-cost LNA systems intended for LEO satellites
No full textThe increasing demand for low-latency, on-demand services has warranted the transformative
shift from satellites placed in geostationary orbit (GEO) to low Earth orbit
(LEO). To achieve coverage comparable to that of GEO satellites, LEO satellite
constellations such as Starlink require thousands of satellites, potentially leading to
substantial costs if using traditional space-qualified electronics. However, compared
to those in GEO, the less stringent reliability requirements for satellites in LEO
have sparked interest in identifying low-cost solutions for various system modules,
including low-noise amplifier (LNA) systems.
This project seeks to explore low-cost alternatives to the Ka-band LNA hybrid developed
at Beyond Gravity in Gothenburg. These alternatives were to be based
on commercial off-the-shelf (COTS) components, commercial printed circuit board
(PCB) materials, and various design strategies aimed at reducing the overall system
cost. The project aimed to compare these cost-effective alternatives with a current
high-reliability implementation, to assess the design trade-offs between cost and performance.
Also, the project aimed to establish what criteria a design option must
fulfil to be deemed suitable for use in LNA systems intended for LEO satellites, as
well as highlight the industry-related challenges that hinder the full adoption of the
New Space paradigm.
The design process consisted of distinct phases, ranging from an initial screening
of possible component configurations to the design and optimisation of the final
system implementations. The project resulted in two system alternatives: one that
incorporates the existing WR28 isolator and has the potential to reduce costs to
approximately one-fourth of the original design, and another that explores a system
using a quadrature hybrid coupler (QHC) configuration, which offers a tenfold
reduction in cost. We believe that the greatest potential to reduce cost lies in replacing
the expensive isolators. However, the primary challenge is to maintain sufficient
return loss without compromising the system’s noise figure
Utvärdering av kärnmaterial för vakuumisolerade paneler Jämförelse av fyra VIP-kärnmaterial med viktad multikriterieanalys baserad på fem faktorer
No full textByggsektorn står för en del av energianvändningen och utsläppen av växthusgaser inom Europeiska unionen. En stor andel energi går till uppvärmning, där värmeförluster genom klimatskärm är en utmaning. För att minska energiförbrukningen har Europeiska unionen infört nya regler och mål. En av lösningarna för att nå EU:s är att använda effektivare isolerings lösningar. Vakuumisoleringspaneler (VIP) har upp till åtta gånger bättre termisk prestanda än traditionella material men används sällan i Sverige, delvis på grund av högre kostnader och begränsad svensk forskning.
Detta examensarbete syftar till att öka förståelsen för VIP-teknologin och identifiera det mest lämpade kärnmaterialet för VIP genom att jämföra fyra vanligt förekommande kärnmaterial såsom kiseldioxid, polyuretan/expanderad polystyren (PU/EPS), glasfiber och aerogel, med fokus på värmekonduktivitet, porstorlek, livslängd, kostnad och densitet. Arbetet har genomförts som en litteraturstudie, där relevant vetenskaplig litteratur har analyserat för att möjliggöra en jämförande bedömning av de olika materialen.
Resultatet visar att VIP med aerogel som kärnmaterial har den bästa isoleringsförmåga och minsta porstorlek. VIP med PU/EPS har lägst densitet, VIP med glasfiber är mest kostnadseffektivt, medan VIP med kiseldioxid har längst livslängd. För att jämföra materialen rättvist används en multikriterieanalys. Baserat på denna analys bedöms VIP med aerogel vara det bästa alternativet. Valet av material kan dock variera beroende på projektets prioriteringar, vilket gör resultaten av denna undersökning vägledande snarare än absolut
Tracking meta-dynamic recrystallization in a Ni-based superalloy using timeresolved synchrotron X-ray diffraction
No full textThe drive towards more sustainable aviation has gained traction as the global aviation
industry expands alongside increasing demands to reduce carbon emissions.
This drive has pushed research in materials science aimed at developing alloys capable
of withstanding high operating temperatures while maintaining metallurgical
stability. The nickel-based superalloy Haynes 282 has emerged as a promising material
for use in aero-engine applications. Recrystallization plays a critical role in
determining the final microstructure and, consequently, the mechanical properties of
metallic materials. This project aims to develop computational methods for studying
the dynamics of meta-dynamic recrystallization in Haynes 282, to gain a deeper
understanding of how the recrystallization process evolves.
The superalloy samples were first deformed at elevated temperatures. Right after
the deformation stopped, in situ synchrotron X-ray diffraction (XRD) measurements
were performed while maintaining the constant deformation temperature. Diffraction
patterns were recorded as a function of time. A method was developed to
separate the signal into contributions from the deformed and recrystallized grains.
This enabled the calculation of the recrystallized fraction, and the tracking of recrystallized
grain evolution over time. These analyses were applied to samples deformed
at different temperatures. For the sample deformed at 1100 °C, the recrystallized
fraction increased rapidly, from an initial average of approximately 5% to 90%
within 120 seconds. Higher deformation temperatures resulted in faster recrystallization
kinetics and higher final fractions. The progression of new grains and their
size distribution was also studied, showing an increase in both the number of grains
and their average size over time.
The results were compared to previous experimental measurements of Haynes 282,
where electron backscatter diffraction was used to quantify the recrystallization
and grain growth. The findings of this project align with conclusions previously
drawn. The methodology developed in this work demonstrates that time-resolved
synchrotron XRD data can be used to effectively study recrystallization, enabling
high temporal resolution and potentially greater sensitivity to small grains
Quantum Optics with Giant Atoms in 2D Structured Environments
No full textOne of the major hurdles in the ongoing efforts to construct a working large-scale quantum
computer is achieving rapid interactions between qubits without risking a loss of energy
(and thus information) to their surroundings. This loss of energy is known as decoherence.
In recent years, one possible solution to this problem that has shown promise is the use of
so-called giant atoms. In certain configurations, these systems have been shown to exhibit
decoherence-free interaction (DFI) when coupled to one-dimensional environments, such
as transmission lines or photonic crystal waveguides. For DFI to be possible, the atoms
involved must be perfectly subradiant – that is, they must not spontaneously decay into
their environments. In this study, we used numerical simulations combined with the
methods of resolvent formalism to examine under what conditions giant atoms exhibit
perfect subradiance and DFI when coupled to two-dimensional (2D) environments. More
specifically, structured 2D environments – i.e. resonator lattices – were considered. In
such environments, there are finite energy bands and band gaps, which causes effects
that are not predicted by the so-called Born-Markov approximation, e.g. time delay.
Multiple generalisations of previously known setups exhibiting perfect subradiance were
found. Furthermore, a number of different configurations exhibiting DFI were discovered,
including grid-like ones that in principle could be extended indefinitely
The impact of digitalization on environment and maritime safety within the shipping industry
No full textAs the maritime industry is experiencing a shift towards digitalization to enhance efficiency, safety, and operational effectiveness, maritime professionals are
increasingly required to interact with complex digital systems. While the technologies offer significant advantages, they also introduce challenges related to system reliability,
workload, usability, and maritime professionals’ well-being. This study investigates the impact of digitalization on maritime professionals’ work environment and maritime
safety through a quantitative research approach. A structured questionnaire was distributed to maritime professionals across deck and engine departments, shipping
companies, port authorities, navy personnel, and other maritime-related roles. Findings reveal that frequent system errors, poor user-centred design, and insufficient technical
support contribute to increased workload and decreased trust in digital tools. Over 90% of participants reported experiencing technostress, with many mentionaing frustration,
pressure to adapt quickly, and fear of making mistakes due to system complexity. The study concludes that while digitalization is a necessary evolution in maritime
operations, its implementation must be carefully managed to ensure it supports rather than hinders the maritime professionals’ performance training. Improved training,
standardized system design, and stronger support structures are critical to maximizing the benefits of digital technologies used on maritime working environment
Investigation of Ground Borne Noise Transmission by Numerical Simulation
No full textGround borne noise and vibrations from underground railway tunnels can pose significant
challenges in urban environments, negatively affecting the quality of life of nearby residents.
This thesis investigates the transmission of ground-borne vibration from underground railway
tunnels in bedrock, with a focus on the influence of fracture zones, tunnel geometry, and
model dimensionality. The aim is to improve understanding of how vibrations propagate
through stiff geological media and how the resulting vibrations at the surface are affected by
subsurface inhomogeneities.
A series of numerical simulations were carried out using COMSOL Multiphysics in both 2D
and 3D, analyzing single and twin tunnel configurations under various conditions. Special
attention was given to the presence of vertical fracture zones, which were modeled as weakened
regions within the rock mass. The effect of tunnel depth and structural layout was also
examined. In addition, a parametric study was conducted to determine which material
properties of the fracture zones affect the most the wave propagation.
Simulation results showed that when vibration travels from the source through the fracture
zone, attenuation increases significantly at the ground surface beyond the fractures, especially
at mid-to-high frequencies (250-800 Hz). Tunnel depth and geometry were also found to
influence surface vibration levels, with deeper tunnels and certain twin tunnel configurations
reducing amplitudes. Both 2D and 3D simulations exhibited similar trends in how frequency
influenced the results. However, the 3D model, by incorporating the third spatial dimension,
provided a more realistic representation and captured greater spatial detail in how the effects
varied across the environment.
The findings were compared with site measurements conducted above an operational railway
tunnel. The measurements confirmed key simulation trends, including the dominant
frequency range and the general decay of vibration levels with distance