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Measuring rainfall using microwave links: the influence of temporal sampling
No full textTerrestrial microwave links are increasingly being used to estimate path-averaged precipitation by determining the attenuation caused by rainfall along the link path, mostly with commercial microwave links from cellular telecommunication networks. However, the temporal resolution of these rainfall estimates and the method to derive them are often determined by the temporal sampling strategy that is employed by the mobile network operators. Currently, the links are most often sampled at a temporal resolution of 15 min with a recording of the minimum and maximum values, while more recently, a form of instantaneous sampling with possible intervals up to 1 s has also been set up. For rainfall research purposes, often high temporal resolutions in combination with averaged values are preferred. However, it is uncertain how these various temporal sampling strategies affect the estimated rainfall intensity. Here we aim to understand how temporal sampling strategies affect the measured rainfall intensities using microwave links. To do so, we use data from three collocated microwave links, two 38 GHz and one 26 GHz, sampled at 20 Hz and covering a 2.2 km path over the city of Wageningen, the Netherlands. We aggregate the microwave link power levels to multiple time intervals (1 s to 60 min) and use a mean, instantaneous, and minimum and maximum value to characterize the signal. Based on the aggregated data, we compute rainfall intensities and compare these with 20 Hz rainfall estimates, such that we isolate errors and uncertainties caused by the sampling strategies from instrumental effects, such as different biases between instruments and representativeness errors. In general, our results show that for all sampling strategies, an increase in sampling time interval reduces the performance of the rainfall estimates, which especially holds for the instantaneous sampling strategy. Even the mean sampling strategy, which generally performs best of all strategies, is sensitive to this reduction in temporal resolution and could lead to significant underestimations. This sensitivity of the mean sampling to the temporal resolution seems to be largely affected by the non-linear relation between attenuation and rainfall. The min–max sampling strategy is mostly prone to minor underestimations or large overestimations of the path-averaged rainfall intensities. Moreover, our results, including a comparison with theoretical events, show that the attenuation due to wet antennas not only affects the comparison between the rainfall estimates obtained with a microwave link and another reference instrument but also has a significant influence on the performance of the rainfall retrieval algorithm, especially for devices with relatively long duration of the wet-antenna attenuation combined with the longer sampling time intervals. Overall, this study demonstrates the effect a selected sampling strategy can have on rainfall intensity estimates using (commercial) microwave links.Water Resource
Analysis of Adaptive Individual Pitch Control Schemes for Blade Fatigue Load Reduction on a 15 MW Wind Turbine
No full textIndividual pitch control (IPC) is a method to mitigate periodic blade loads in wind turbines, and it is typically implemented using the multi-blade coordinate (MBC) transform, which converts the blade load measurements from a rotating frame into the non-rotating tilt axis and yaw axis. Previous studies have shown that by including an additional tuning parameter in the MBC, the azimuth offset reduces the coupling between non-rotating axes, allowing for higher performance levels for diagonal controller structures. In these studies, the decentralized control of IPC was composed of two identical integral controllers. This work analyzes and compares the improvement that the azimuth offset can provide in different adaptive gain scheduling IPCs where the diagonal controllers can have integral or proportional action with different gains. They are applied to a 15 MW wind turbine simulated with OpenFAST v3.5 software. The controller parameter tuning is addressed as an optimization that reduces blade fatigue load based on the damage equivalent load (DEL) and is resolved through genetic algorithms. Simulations show that only using different controller gains in IPC does not provide significant improvements; however, including azimuth offset in the optimal IPC schemes with integral controllers allows for the greatest DEL reduction with a lower actuator effort.Team MuldersTeam Jan-Willem van Wingerde
Impact of different energy types of military vehicles on the supply chain: A MILP model for an optimal military Vehicle Energy Supply Chain
No full textThe Dutch Ministry of Defence (NLMoD) has stated the goal of reducing dependency on fossil fuels by at least 20% by the year 2030 and at least 70% by the year 2050 compared to the year 2010. Research in the NLMoD explores the possibility of changing diesel-fuelled vehicles and weapon platforms to alternative forms of energy such as electric or sustainable fuels. In these projects, the focus is on (part of) the vehicle or energy source itself, but the impact on the Military Supply Chain (MSC) is missing.This research has developed a Mixed Integer Linear Programming model that can be used to gain insight into the impact of the energy type of tactical vehicles and weapon platforms on the MSC and therefore is able to see what energy type has the lowest impact on that MSC. The impact on the MSC is measured by minimizing the refuel time, number of supply trips, and CO2 equivalent emissions. The model can provide insight into what the minimal requirements of potential energy carriers and conversion devices should be in order to have a similar or better impact on the current diesel MSC. The model is based on the current supply chain of the NLMoD and is expanded with the use of APUs for vehicles, energy generation at Nodes, the use of small supply trucks as energy buffers, compatible supply material, and longer self-sufficient times. Combinations of these are looked at in different policies.Results show the trend that energy types with lower CO2 equivalent emissions have higher refuel time and number of supply trips. An exception to this is HVO and HVO-electric series hybrid, which also have the least impact on the MSC. Energy types such as hydrogen and electric require huge improvements in energy density, fill speed, and FTW efficiency to come close to the results of current diesel.Mechanical Engineerin
Near real-time nautical depth mapping via horizontal optical fibers and distributed acoustic sensing
No full textSafe navigation in ports and waterways subjected to siltation requires nautical depth monitoring. For this purpose, surveying vessels equipped with a zero-offset echo sounder and intrusive point measurements are frequently used. Because these measurements depend on the availability of a surveying vessel and require access to quay walls, such as at the container terminals in seaports, the temporal resolution is limited. Especially at these locations, a high temporal resolution monitoring system could allow for a higher occupancy rate. We propose to use Distributed Acoustic Sensing to monitor the nautical depth using fiber-optical cables. We install five horizontal fibers at different heights between two points and continuously record along the complete installation. Analysing the continuous recordings, we show that horizontal fibers can be used to monitor the water-mud interface depth with a vertical resolution around six mm. Multiple passive sources, like vessel movements and water currents, are used to estimate the water-mud interface.Applied Geophysics and PetrophysicsRivers, Ports, Waterways and Dredging Engineerin
Quantifying myocardial perfusion using 3D magnetic resonance imaging
No full textMyocardial perfusion, the blood flow to the heart muscle, can be evaluated by tracing the passage of a contrast agent using cardiac magnetic resonance (CMR) imaging. This technique, well-established for diagnosing coronary artery disease, is limited by the necessity for breath-holding, subjective assessment, and low myocardial coverage. In this thesis, we aim to address these limitations of contrast-enhanced myocardial perfusion CMR. We developed a pulse sequence and post-processing pipeline to quantify myocardial perfusion using free-breathing 3D contrast-enhanced CMR. To restrict volume acquisition to the diastolic phase, characterized by minimal cardiac motion, we employed optimal slice oversampling, maximal partial Fourier acquisition, and cartesian undersampling in spatial and temporal domains. To mitigate the effects of breathing, respiratory tracking and image registration were performed. Collaborations for the reconstruction of raw data utilizing deep learning and image registration were established. Validation in healthy volunteers demonstrates that the developed pulse sequence enables isotropic 3D acquisition (3.6 x 3.6 x 3.6 mm^3) of an arterial input function (AIF) and myocardial signal during each cardiac cycle, up to heart rates of 76 bpm. Obtained AIF images exhibit sufficient resolution for extracting the left ventricular blood pool signal and registered myocardial images are of good quality. We investigated and validated a method to convert signal intensity to T1, which is required for MBF quantification. While T1 estimates from the AIF images approximate reference values up to 500 ms well, underestimation was observed from the myocardial images and for high T1 values.Applied Physic
Process parameters of 4D printing which affect the shape memory effect of PLA
No full textThis masters thesis investigates the influence of various printing parameters on the shape memory effect of 3D printed objects, with a focus on fixity and recovery rates. Through a series of experimental tests, it was observed that printing temperature had minimal impact on fixity and recovery rates. However, correlations were identified between fixity rate and layer height, as well as between percentage infill and recovery rates. Lengthwise shrinkage, particularly prominent in samples with 0\% infill, was attributed to printing speed the formation of voids within the structure and layer height. Higher printing speeds were found to compromise mechanical properties while facilitating enhanced shape transformation responses. Additionally, changes in layer height led to observable alterations in the printed object's geometry, including bending and bulging, due to retained shape memory of the filaments original form. Moreover, certain 100\% infill samples exhibited an unexpected hardening phenomenon akin to annealing. These findings underscore the intricate interplay of printing parameters in determining shape memory properties, mechanical properties and highlight potential avenues for optimization in 3D printing processes.Mechanical Engineering | Multi-Machine Engineerin
Application of machine learning in the structural design process of bascule bridges: Using an artificial neural network to generate structural bascule bridge designs in Grasshopper
No full textThis research has aimed to investigate the possibility of applying a neural network algorithm into the structural design process of bascule bridge leaves, by creating a workflow in Grasshopper. The demand for this tool, originates from the fact that the current design process is experienced as linear and slow, and does not fit the dynamic design environment within Amsterdam.The foundation for the generative design workflow, is a parametric model for an orthotropic bridge deck made out of steel. The model is made out of main beams, which are modeled as tubular profiles, cross beams and rib elements, which are modeled as line elements, and a bridge deck plate on top, to which all elements are welded. The parametric model is controlled by a total of 24 parameters which describe its dimensions, profiles and spacing of elements. Based on the user input for three parameters, namely the bridge deck length, bridge deck width and distance to the rotational axis, the neural network algorithm does a suggestion for the remaining parameters, based on information in the bridge database. The bridge database consists of 35 bascule bridges. A design for a steel bridge leaf is then generated. In the next step, the generated structure is forwarded into SCIA Engineer via a.xml file, for structural analysis. Within SCIA Engineer, the structural performance is assessed based on occurring Von Mises stresses under defined load combinations. In the validation stage of the research, three steps were undertaken. In the first validation step, the predicting behavior of the neural network was optimized based on the mean squared error. The predicting behavior of the workflow was assessed using 5-fold cross validation. It appeared that the neural network had a prediction accuracy of 25.91%. Therefore, in the second validation step, the neural network’s complexity was reduced. In the improved model, the neural network predicts fourteen parameters. The total predicting accuracy of the improved model is equal to 61.07%.In the last validation step, five random cases were generated, of which their SCIA model output was compared to simplified models and the predicting behavior of the neural network was assessed. In two out of five cases, the neural network immediately suggests a good structure, while in two others, only one parameter had to be altered to create a viable structure. From validation of the SCIA models, it appeared that the moment, shear force and stress distribution for both the main beam and crossbeam showed consistent behavior through all five models. For the main beams, a simple MatrixFrame model was constructed for comparison. There were significant differences in the magnitude of occurring moments and shear forces between the MatrixFrame model and SCIA model. The magnitudes of moments, shear forces and stresses in the cross beams were compared to a hand calculation of a clamped beam. It was concluded that the SCIA models generated in the validation stage of the research, behaved correctly. In the results section, the output of the workflow was compared to two reference cases, the Berlagebrug and Elizabeth Admiraalbrug. For the Berlagebrug, the SCIA model had such a significant error that no useful results could be extracted from this case study. For the Elizabeth Admiraalbrug, the workflow generated a structure which was approximately twice as large in steel mass. This has resulted in lower unity checks compared to the original design. A qualitative comparison between the current design process and when the created workflow would be implemented, was also done.Based on the quantitative results obtained in the research, it was concluded that the neural network algorithm in the application developed in its current form, will not significantly improve the structural design process, due to a lack of consistency in generated results.Civil Engineering | Building Engineering - Structural Desig
On-Site Characterization of Automotive Diffuser Aerodynamics by 3D LPT
No full textRace cars use aerodynamic downforce to reduce the lap times by increasing grip. Diffusers, upswept ramps located at the rear of a vehicle, are often used to enhance downforce. This investigation proposes a novel LPT facility featuring HFSB, LED illumination, and high-speed cameras to characterize the flow inside automotive diffusers. An RC car, fitted with a custom floor and diffuser, traverses a region of seeded air following the Ring of Fire methodology. Underground cameras view the car through a transparent panel, providing unparalleled optical access to the diffuser of the car. The on-site construction of the setup and the intrinsically realistic interaction with the ground, contribute to realism and fidelity while potentially reducing testing costs associated with wind tunnel operation. The setup was shown to be a valid alternative to conventional testing grounds to capture separation, 3D flow evolution and differences in the flow field between the diffusers with varying angles. The 15° diffuser led to the largest velocity (u/U=1.3) under the car, the 10° diffuser produced the most downforce overall while the 20° diffuser showcased the most prominent separation, heavily affecting its ability to sustain low pressures under the car. The results highlighted the impact of the tyres in disrupting the mechanism of downforce generation through mass flow leakage through the sides of the car.Aerospace Engineering | Aerodynamic
Distributed rail traffic management under moving-block signalling
No full textWith the ambition of policy makers to encourage a modal shift to rail, an increase in the demand for running trains can be expected. Capacity wise, this increase in demand could be facilitated by applying moving-block signalling. If railway traffic increases however, so does the difficulty of managing it. Rescheduling systems are currently being developed to help traffic managers with this task. An increase in traffic does however increase the computation time needed for solving the conflict resolution optimization problem tackled by these systems. This could pose a problem since traffic management is a task performed in real-time. An often proposed technique to reduce computation time for conflict resolution is decomposing the problem into multiple coordinated sub-problems. Until now, no research has been performed combining moving-block signalling with decomposition of the conflict resolution problem. This research addresses this gap by developing and testing a distributed moving-block conflict resolution model. The effect of the model on computation time and solution quality in comparison to a centralized model is investigated through a case study of the rail network of the Dutch province Noord-Brabant. The results show a clear improvement in computation time for the distributed model while the solution quality improves or remains the same in the majority of tested scenarios.Civil Engineering | Transport and Plannin
Mega-Constellation Design Optimisation
No full textGiven the rapid growth in popularity of mega-constellations for telecommunication purposes, this thesis aims to identify methods for designing orbital layouts of such constellations. Traditional optimisation methods for regularly sized constellations do not scale due to the number of satellites involved. Therefore, this thesis investigates the design of mega-constellations and how to achieve an optimal layout within a reasonable timeframe.Initially, the figures of merit most commonly used in mega-constellation design were identified. The most important figure of merit used in all types of missions, except for Earth observation, is visibility, i.e., the number of satellites visible from a point on the ground. For Earth observation missions, the revisit time is more relevant than visibility. Thus, the thesis focused on mission objectives where visibility is the main figure of merit, such as Satcom, Satnav, IoT, etc. There is also more literature and data available on such constellations, including Starlink, OneWeb, Project Kuiper, and others. Consequently, two closely related figures of merit were selected for this study: minimum visibility and mean visibility. The former ensures an N-fold uninterrupted coverage, while the latter provides a general metric of how many satellites are visible over time. Also, the main focus was on Walker constellations as this is the most common geometry used for mega-constellations.The visibility computation begins with constellation propagation. Due to the large number of satellites in a mega-constellation, existing tools used at ESOC, such as Godot, are insufficient. Therefore, a self-written tool was developed, named mcdo (Mega-Constellation Design Optimisation), which utilises the basic functionality of Godot and takes advantage of NumPy by applying vectorisation to notoriously slow Python. This approach resulted in a decrease in computational time by a factor of 100x with respect to godot.cosmos.BallisticPropagator.Moreover, the visibility computation was accelerated with the utilisation of graphic processing units (GPU) and simplifications such as North-South symmetry, longitude averaging, or estimating visibility for a single time instance. Depending on the methods and simulation setups used, a reduction of 400x-120,000x in computational time was achieved for visibility computation.Additionally, the parametric analysis of large Walker constellations yielded some valuable discoveries. For instance, the number of planes P and phasing parameter F do not influence the mean visibility but may have a significant effect on minimum visibility. This means that P and F can be omitted when designing for the mean visibility. It was also revealed that the mean visibility curve scales linearly with the number of satellites N, allowing to avoid propagation of very large constellations, and to scale up the mean visibility curve from smaller constellations instead. Parametric analysis of other parameters provided a general insight into their effect on visibility.The improved computational efficiency of visibility computation for large Walker constellations enabled the application of multi-shell constellation design. A case study was set up with a requirement of uninterrupted coverage of 50 satellites over European latitudes (35-70 deg), assuming that all shells were at the same altitude of 700 km with a goal to minimise N. The analysis revealed that for two- and three-shell layouts, the minimum N was attained when higher-inclination shells had more satellites than lower-inclination ones. Moreover, methods for design acceleration were discussed.The "building blocks" method was proposed for designing mega-constellations with more than three shells. This method starts from placing shells at high inclinations and then gradually lowers the inclination of the subsequent shells. It takes advantage of visibility properties of Walker constellations: the higher-inclination shells can cover both high and low latitudes, while the lower-inclination shells can only cover low latitudes. This method reduces the computational time drastically: by a factor of 150x for three-shell layouts and even more for larger numbers of shells.The presented research offered valuable insights into initial phases of design of the orbital layout of mega-constellations. The mcdo tool and the obtained results were already applied for internal projects at ESA, demonstrating their relevance and usefulness.Aerospace Engineerin