The growing amount of plastic pollution in the oceans is worldwide a huge problem. There is an increasing amount of projects that try to clean up this pollution. To remove the pollution efficiently, it is useful to know how plastic litter moves, degrades and sinks. Models are being developed that can describe what happens with plastic in the ocean. To model the behaviour of plastic in the ocean a lot of parameters need to be taken into account. The transport of plastic particles is largely determined by processes like the wind and the current but their movement also has a random character due to dispersion. Due to this random movement, the future position of a particle can be described by a probability distribution. To find that probability distribution, the Kolmogorov forward equation (or Fokker-Planck equation), in this context the same as the advection-diffusion equation, needs to be solved. It is also possible that the plastic particles sink and settle on the bottom of the ocean. One goal of this project was to incorporate the settling of particles as an extra term into the advection-diffusion equation. Forward models are used to predict where particles will go to. It can also be useful to have reverse time models that can describe where particles had their origin. To make reverse time models, it is necessary to solve a reverse time advection-diffusion equation. The main goal of this project was to derive and solve the reverse time advection-diffusion equation that includes the settling of particles. This is done by finding the adjoint of the Kolmogorov forward equation and the settling term.

The energy transition will significantly impact distribution transformers as they will have to deal with more load on them, which is also more variable due to renewable energy sources. However, currently, these transformers are often not monitored with sensors. Therefore, the Dutch network operator Stedin asked to investigate the possibilities of a digital twin for distribution transformers without many sensors. This thesis presents two ways to do so: the currently most used but more empirical loading guide and a more analytical method where we solve Maxwell's equations using the finite element method (FEM). Furthermore, the transition to more renewable energy sources and sources that draw instant power from the grid causes the current to get distorted. This distortion can be mathematically analyzed using harmonic functions, and we will consider the impact of these harmonics in both the loading guide and the FEM model. The loading guide is a method written in slightly different ways in the IEEE and IEC standards that takes the load on a transformer and the ambient temperature around the transformer to determine the hot spot temperature inside the transformer. By saying that the hot spot temperature is the warmest point inside the transformer, we can determine the percentage of loss of life of a transformer for a particular loading pattern. However, the loading guide only considers one set of parameter values for distribution transformers, which can vary widely in rating, location and ventilation household, leading to an over-or underestimation of the temperature, which in both cases can lead to extra costs. Additionally, the impact of harmonics is an empirical addition to the loading guide and only considers the effect on temperature rise and not the losses. Therefore, we consider the transformer in a finite element approach. We solve Maxwell's equation on a transformer cross-section with the FEM, resulting in a 2D model that can calculate the losses for a particular geometry. This model is made using COMSOL Multiphysics. Furthermore, we calculate the core and winding losses under a harmonic load, resulting in considerably higher losses than without harmonics. As the FEM model is quick and straightforward to run, it can serve as a first step towards developing a digital twin of distribution transformer, giving a way to determine the losses analytically. With future development, the model can provide better insight into the temperature distribution in the transformer.

TenneT’s vision of the North Sea Infrastructure (NSI) creates a basis for a joint European approach up to 2050 which focuses specifically on developing the North Sea as a source and distribution hub for Europe’s energy transition. High wind speed, central location and shallow water qualify the Dogger Bank as the location of the central hub. For further development of the NSI, more detailed research is needed. The research gap is recognized that there is not sufficient research on proposing new HVDC grids in the North Sea considering optimization (e.g. following a cost-related objective) of different topology structures within a scope of six surrounding countries (BE, DE, DK, GB, NL and NO), with sensitivity tests regarding uncertainties (e.g. in meteorological condition, load, or industry development). Therefore, the main research objective of this thesis project is to evaluate CAPEX, overall OPEX of participating countries and other operational performances (e.g. energy mix, nodal price, EENS) of possible topologies of HVDC network in the North Sea, including NSI (with a central North Sea Wind Power Hub at the Dogger Bank) and other two competitive topologies, considering uncertainties in green energy technology development, European coordination, load and meteorological condition (e.g. wind speed, solar radiation and hydrology). Three specific research questions were studied in order to achieve the aforementioned research objective: How to define 3 topologies of the North Sea HVDC network with different feasible structures? What are the criteria to optimize each topology and to compare the topologies? What are the implications of each topology, when evaluated against a wide range of uncertainties, on the overall CAPEX and OPEX of countries involved? The simulation considers the scenario in the year 2030. Software PowerGAMA and PowerGIM were used for operation simulation and topology optimization. When calculating OPEX throughout the lifetime of the equipment (assuming 30 years), the year 2030 is taken as a representative year and the 30-year OPEX is obtained by multiplying OPEX in 2030 by an annuity factor. In short, 3 topologies of the North Sea HVDC grid, with hub-and-spoke structure (for the NSI), point-to-point structure and meshed (without central energy hub) structure, respectively, are defined. They are then optimized towards and compared for the lowest overall cost (i.e. the sum of CAPEX and OPEX including CO2 prices) throughout the lifetime. Simulating under different uncertainties/selected critical scenarios (4 Visions from ENTSO-E’s Ten Year Network Development Plan which reflect different RES share target and European coordination level, and extreme RES inflow and load conditions), the optimized NSI design stays most socio-economically preferable (with lowest overall cost) topology. It is also recognized that NSI is able to realize its expected functions, namely transmission of renewable energy, enhancement of system security and price convergence. On the other hand, launching of NSI brings in challenges such as grid congestion and benefit asymmetry. Main contributions of this thesis include: • Creation of the baseline model/dataset for European power system in 2030 as a background/environment for the North Sea HVDC grid planning; • Design and optimization of the North Sea HVDC grid topologies in three different feasible structures; • Verification of NSI’s advantage in cost saving, compared to two competitors, in 4 Visions reflecting different green energy transition and European coordination level, and under extreme RES inflow and load conditions; • Verification of NSI’s function in improving energy sustainability, affordability and security; • Realization of Non-Homogeneous Markov Chain algorithm in Excel to generate wind power inflow time series.

Almost everyone is familiar with games such as poker and checkers, but games can also be found in non-entertaining settings, such as competing companies in a market or conflict resolutions between countries. However, what happens when players want to avoid working together? This thesis provides two game-theoretical models of boycotts based on existing literature and is complemented with new insights. We discuss the dynamic process of a consumer boycott, where the effectiveness can be determined by the predefined consumers’ and firm’s thresholds or by the maximum boycott duration. Besides, we consider a static model using the Shapley value to analyze the impacts of boycotts, which are balanced for 2-player boycotts but not when three players are involved. We extended the existing models by finding supermodularity as a sufficient requirement for the boycott to never be profitable for the involved players, by introducing a direct formula for the coalition value in a boycott game (the boycott-contraction), and by analyzing real-world data, where we observe the effect of boycotts on trading activities with uninvolved players.

Decreasing NOx emissions is becoming increasingly important as it has many lifechanging implications on humanity and nature. In this work several models were constructed to simulate the combustion of methane in a cement rotary kiln, and it was investigated whether oxygen-enhanced combustion leads to less NOx production for the obtained models. This was done using the Cantera software package with Python. Starting off with a single zero-dimensional reactor equipped with a reduced one-step global reaction mechanism, which was expanded to include two-step and four-step reaction mechanisms. Combustion inside this homogeneous reactor was simulated for various stoichiometric conditions for an initial temperature of 1000K. Subsequently, a one-dimensional model of chained reactors to simulate flow was considered, equipped with both the two-step and four-step mechanisms. This was realized using the scalar convection-diffusion equation to compute the flow throughout the reactor. All aforementioned models were adjusted to replace air with oxygen-enhanced air, containing higher levels of oxygen for every iteration. The simulated temperature evolution was examined using the exponential relationship of temperature and thermal NOx.

Combustion is and remains for the foreseeable future an essential chemical process. The physical and mathematical modelling of such processes can help to optimise the design and operation of combustion furnaces which is critical for fuel efficiency. Given the combined complexity and interaction of the gas flow dynamics and the reaction processes however, such modelling can become time consuming and demanding when it is comes to computational capacity. It is for this reason that alternative modelling and computational techniques are of interest. This paper serves as a thorough introduction to modelling this process using Chemical Reactor Networks (CRN) – which is known to be a relatively efficient model and computational approach. It provides a step-by-step explanation of the CRN approach, as well as a hands-on implementation for a One-Step Mechanism, ie. a combustion process involving only a single stage oxidisation of the fuel. It also introduces the reader to the industry standard CHEMKIN format and the GRI 3.0 data-base, and investigates the possibility of incorporating the state-of-the-art GRI 3.0 database into Chemical Reactor Networks. Following on from this work it is recommended to validate CRN based results against experimental data and modelling results using different techniques such as Computational Fluid Dynamics to gauge both accuracy and computational efficiency.

In this thesis, the acoustic noise emitted by a small electric outrunner motor, such as the ones commonly used in unmanned areal vehicles, is analyzed using a multiphysics simulation based on the finite element method. The simulation covers the electromagnetic, mechanical and acoustic domain. The electromagnetic simulation is performed in the 2D time domain, the mechanical simulation in the 3D time domain and frequency domain and the acoustic simulation in the 3D frequency domain. The difference between results of the time and frequency domain mechanical study is investigated, as well as the difference between the obtained results and those obtained in other available literature. Furthermore, the results are compared to acoustic noise measurements performed in the laboratory. Based on the obtained results, noise reduction methods, specifically focussed on small electric outrunner PMSMs, are proposed and verified using the developed simulation.

The efficient and clean combustion of liquid fuels is a fundamental requirement in the design of future energy systems. Simulation plays a more and more important role in the design of such burners. In this work the spray combustion simulation approach introduced by Ma (2016) is improved, and validated against the CORIA Jet Spray Flame database (Verdier et al., 2017). The database presents droplet temperatures measured by global rainbow refractometry technique, which gives a unique insight in the flame structure. The two phase flow is treated with an Eulerian-Lagrangian approach. Flamelet Generated Manifold (FGM) is used to model the gas phase combustion. The RANS equations are solved using final volume method, with standard k − ε turbulence modelling. The turbulence-chemistry interaction is addressed with assumed probability density function method. The spray cloud is modelled with the Lagrangian transport of droplets including heat and mass transfer. Ma (2016) developed a solver based on the OpenFOAM 2.3.x libraries. His development is complemented in this work with a novel spray model. The improved spray modelling allows the treatment of droplet evaporation in the context of FGM without limiting the complexity of the chemical mechanism. This improvement is crucial for the modelling of complex fuels and the correct prediction of emissions. The modelling concept is rather light-weight considering the RANS approach. Despite the low computational expenses, most of the results agree fairly well with the measurement data. However the correct prediction of droplet temperature remains an an unresolved problem. Ma, L. (2016). Computational modelling of turbulent spray combustion. PhD Thesis, Delft University of Technology. Verdier, A., Santiago, J. M., Vandel, A., Saengkaew, S., Cabot, G., Grehan, G., and Renou, B. (2017). Experimental study of local flame structures and fuel droplet properties of a spray jet flame. Proceedings of the Combustion Institute , 36(2):2595-2602.

Modelling of fluid-structure interactions (FSI) plays a key role in many engineering applications. However, due to the interaction between fluid and structure the computational cost related to high fidelity models (especially for strongly coupled systems) limits the direct use of current FSI simulation techniques in industry. Since a thorough knowledge of FSI phenomena is very important in design processes, efficient simulation techniques that combine low cost with high accuracy need to be developed. To this end, the use of the space mapping optimization technique as coupling approach for partitioned FSI simulations is investigated.

In this master thesis a CFD model targetting the combustion in cement kilns is developed. The model is implemented in OpenFoam

The application of Computational Fluid Dynamics to model and simulate flows around flexible and moving objects has grown in the last decades fueled by new technological challenges in particular in the aerospace engineering field because of the introduction of highly deformable materials and complex moving systems. Existing body-fitted mesh methods such as the Arbitrary Lagrangian Eulerian (ALE) approach have been proposed to simulate the flow around moving and deforming structures but their applicability is limited because of the issues arising in deforming the computational grid constrained to the moving/deforming structure. This thesis focuses on the verification, and validation of an Embedded Boundary method (developed at Stanford University by Prof. Farhat research group) for the solution of fluidstructure interaction problems involving large and complex structural motions and deformations. The Embedded Boundary method works on non-body fitted grids, by using a tracking algorithm is able to impose the effects of an ’immersed’ moving and deforming surface mesh on the fixed Eulerian fluid mesh. For this reason this method is gaining popularity because it simplify a number of issues ranging from codes coupling (fluid-structure solvers) to formulating and implementing algorithms for applications that involve very large and complex motions-deformations and for which ALE algorithms are unfeasible.

Heat transfer by radiation is something you experience everyday: when walking outside in the sun or when cooking your diner. This thesis provides understandable models of the role that radiation plays in the transfer of heat. By studying literature we developed a mathematical basis for the heat transfer model, where we discuss diffusive, convective and radiative heat transfer, the weighted sum of grey gases and the chosen solving method: the discrete ordinates method. Using CONVERGE CFD and MATLAB software, we present several one- and threedimensional simulations of a furnace in which we consider different conditions. The overall conclusion is that radiation transports heat from places with high temperatures to their cooler surroundings, where also conditions as isolation, wall emissivity and gas mixture play an important role.

Danieli Corus supplies tailor-made solutions for the global steel industry. Cameras are used in tuyeres of blast furnaces to detect physical aspects and irregularities. No operator could monitor those videos all day, which is why video analyses are needed. A program is written to analyse a test video and give information about the temperature, the injection of pulverized coal and the movement of rocks. The mathematical background of these calculations is presented, which depend on the transport of light from the blast furnace to the camera through the tuyere. Also the implementation of the calculations can be found. The results are interpreted and discussed and further improvements are suggested.

In this thesis work, we strive to describe and apply the modelling methodology for simulating a turbulent jet diffusion flame stabilized behind a bluff body by applying flamelet generated manifold (FGM) model and steady diffusion flamelet model for predicting the pollutant emissions from the flame. The flame under consideration is a CH4/H2 (1:1) bluff-body stabilized flame known as HM1. The numerical calculations of the flow physics has been completed by using a commercial CFD code namely Ansys Fluent 19-R3, where the computational domain is assumed to be two dimensional and axis-symmetric in nature due to the cylindrical symmetry of the burner with an structured grid for meshing. The turbulence is modelled by using a two equation Reynolds averaged Navier Stokes model, namely the standard k – ϵ model with a modification in the Cϵ1 from 1.44 to 1.60. The chemical mechanism used in the project was the GRI 2.11 mechanism developed by the Gas Research Institute, USA. Next, postprocessing tools like the Reactor Network Model (RNM) and Ansys NOx post-processor were used as an alternative, possibly a better way to obtain the NO species concentrations. The acquired results from the simulation are thoroughly analysed and were compared to earlier results on the HM1 flame in the literature and validated by using the experimental data documented by the University of Sydney in collaboration with the TNF Workshop. The results showed that the steady diffusion flamelet performed better than the FGM model and was in acceptable agreement with the experimental data, although some under-prediction and overpredictions were reported for NO and OH species. In regard with the post-processing tools the RNM model performed better than the Ansys NOx post processor.

A high-resolution hydrological solver that solves on time-adaptive grids is created. The solver uses h-refinement strategies which adapts the resolution of the grid using a posteriori measure. It is based on an open-source scientific computing library named PETSc. With the use of highly scalable time-stepping solvers provided by PETSc, an optimised numerical model is obtained. Validation tests are conducted using dam-break scenarios and flow over humps. Strong scaling tests are conducted to test the scalability of the solver. The model is found to be robust and could thus provide accurate flood-forecasting information.

Flameless combustion, or MILD combustion is a technology that enables stable combustion with high efficiency while maintaining very low NOx and soot emissions. It is characterized by uniform heat flux and can be achieved when fuel and preheated oxidant jets are mixed into a strong recirculating flow. It is a complex process which combines multiple physical phenomena such as, heat transfer and reactions in a turbulent flow and is difficult to capture numerically via simple Computational Fluid Dynamics (CFD) simulations. Therefore, appropriate turbulence, chemistry, radiation and turbulence-chemistry interaction models are required to address this combustion regime via computational modeling. The present work tries to tackle this issue by conducting a comparative study of different radiation, turbulence and chemistry models for the simulation of a labscale MILD combustion furnace using RANS CFD simulations. This assessment was conducted in two steps. Firstly, the importance of radiative heat transfer in furnaces was investigated, by simulating an axisymmetric oxycombustion furnace using advanced radiation models. The SLW, Domain-based WSGG and Cell-based WSGG models were evaluated using simple chemistry and turbulence models. The results were validated based on the work of Webb et al and experimental results. It was concluded that detailed simulation of the radiative gas properties is important and directly influences the resulting temperature field, especially in the bulk flow region. Secondly, a detailed evaluation of a Dutch natural gas fired Delft lab-scale furnace that is operating in MILD combustion was conducted. For the turbulence modeling, the Standard, the Modified Standard, the Realizable k − ε and the k − ω SST Models were compared firstly qualitatively, based on velocity and reaction field contours, and secondly, quantitatively, based on available LDA velocity measurements. The influence of the chemistry modeling was evaluated in two parts. Firstly, the qualitative effect of changing the Cξ constant of the EDC model on temperature and reaction zones of the GRI-Mech 3.0, the DRM-19, the KEE58 and Chen mechanisms, was investigated. And secondly, the quantitative effect on the use of the GRI-Mech 3.0, the KEE58, Chen and Lu-30, based on CARS temperature measurements was researched. Lastly, the influence of the radiation model was investigated qualitatively and quantitatively using the standard 1-RTE domain based WSGG, a 4-RTE WSGG, a cell-based WSGG and the SLW model. Out of the mechanisms coupled with the EDC, the GRI-Mech 3.0 performs well. Of the radiative properties models the domain based WSGG performs worse compared to the other models. The cell based WSGG performs similarly to the more advanced spectral and non-grey (4-RTE) models and has lower computational cost. For these reasons, the best overall combination for the studied flameless furnace is found to be the combination of Standard k−ε model, standard EDC with GRI-Mech 3.0 and cell based WSGG.

Eddy currents are loops of electrical currents induced within conductors by varying magnetic field in the conductor. Eddy currents flow in the closed loops in the conductor, in planes perpendicular to the magnetic field. The eddy current effect plays an important role in the transformer or an actuator system. If there is a coil wound around a cylindrical iron core, system, the AC coil can induce eddy currents in the solid core. The eddy current can change the flux in the core, and further influence the impedance of the system. If such a system is applied to an electromagnetic actuator, a proper modeling approach for the eddy current effect can help the researchers to determine the impedance change and predict the output power of the actuator. This thesis deals with the eddy current modeling improvement problem. A concept of the transformer ring topology is proposed to simplify the actuator model. A brass ring and an iron material ring are studied, in the purpose of realizing modeling optimization and test functions respectively. By using analytical calculation and modeling analysis, the eddy current modeling method is improved and optimized. The practical impedance of the model becomes closer to the simulation results. This research can help the researcher to compute the actuator model, and better simulates it.