173 research outputs found
Parametric Instability of an Oscillator moving on a Railway Track
No full textThe instability of a moving mass / oscillator due to surpassing the velocity of the minimum group wave velocity (in a continuous homogeneous structure) has been studied extensively and is well understood. In contrary to that, Parametric Instability of a moving mass / oscillator on a continuous periodic structure has been studied less extensive and therefore the mechanism behind the instability is unknown. Literature that is avaiable on this topic mainly focuses on continuous periodic inhomogeneous structures, namely where the foundation is modeled as a continuous periodic inhomogeneous structure. Even less well studied are models where instead of a continuous periodic inhomogeneous foundation discrete periodic supports have been used. So far as known to the author there has also been no studies where the discrete supports are coupled through a medium. In order to solve the transition curves discerning the stable and unstable domains concerning the parametric instability of a moving mass / oscillator the analogy with the Mathieu equation is used, which tells us that the solution on those transition curves will be periodic with once or twice the period of the parametric excitation. In this thesis we have focussed on studying the use of the analogy on continuous structures founded upon periodic supports. The Mathieu equation describes the motion of a parametric oscillator, for example a pendulum with a length that periodically varies over time. The theory that predicts the solution to the Mathieu equation is called Floquet theory and ascociated with the solution are the Floquet exponents, these exponents dictate whether the solution will be periodic and bounded or unbounded. By solving for the Floquet exponents of the Mathieu one sees that for an increase of the amplitude of the parametric excitation the system will experience a greater exponential growth. For a greater mistuning between the parametric excitation and the natural frequency of the equivalent non-parametrically forced equation we see that the system will experience a smaller exponential growth. Outside the instability domains the solutions will be bounded and periodic and contain a wide variety of frequencies. When damping is introduced, the value of the damping coefficient (if written in the canonical form of a viscously damped single degree of freedom equation) will be subtracted from the value of the undamped Floquet exponents and by that result in an upward shift and narrowing of the transition curves. Furthermore, outside the instability domains we will see two regions: the first lies close the the transition curves and is asymptotically stable with a period equal to that of the transition curve, the second covers the remaining stable region and is asymptotically stable and periodic with a wide variety of frequencies.Regarding the Parametric Instability of a moving mass / oscillator we have studied three different models: a continuous Euler-Bernoulli beam on periodic spring supports, a continuous Euler-Bernoulli beam on periodic supports that are complex (i.e. modeled as an oscillator between two springs), and a continuous Euler-Bernoulli beam on periodic supports that are founded upon a 2-dimensional lattice. Of these models we have conducted a parametric study as to study what the effects are of the various parameters. We have seen that whenever the ratio between the stiffness of the supports and that of the beam is increased, the instability domains will shift to higher velocities and become wider. For certain combinations also 'islands' of instability may appear, where these 'islands' indicate stable areas between regions of instability. If damping is introduced into the system, this will generally narrow the instability domains and shift them to higher values of the mass and lower values of the velocity. However, for certain parameter combinations adding damping will lead to a widening of the instability domain. In the case of a moving oscillator the instability domains will narrow and be shifted to lower values. If the support is modeled with a mass it will affect the general trend of the transition curves through its own resonance, hence for a complex structure it is advised to model the supports with the correct dynamic equations. Last but not least, if the supports are coupled through a medium (a 2-dimensional lattice in this case) one will generally see a similar effect as adding damping has. In this thesis we have also studied three real world cases: a regular railway track, a high-speed railway slab-track, and the Hyperloop. In the first case we have seen that Parametric Instability will most likely have no influence. For the slab-track, being much more stiff, Parametric Instability will be important. However, a more extensive study with several cases must confirm this. In the last case, namely the Hyperloop, we have seen that for a moving mass the instability domains are relatively large as compared with the other cases. We have also studied the Parametric Instability of a test-pod, which showed that its instability domains that are negligible. Of course, this was merely a test-pod not capable of transporting people, hence when a larger pod is studied it may be expected that the instability domains may not be neglected.Civil Engineering | Hydraulic Engineerin
The Public Interior and its Purpose: a re-assessment
No full textAfter COVID-19, might one think of the public interior differently? Might the public interior treat the people who use it differently? There is a long history of the public interior shaping or conditioning its subjects and forming subjectivities. Rarely do those subjects challenge the projections of public interiors or alter their conditions. One might imagine (or hope) that the orderly submission to consumption or other subtler exhibitions of power might be diverted by other possibilities, by, say people-watching with civility, or by associations that are independent of prescribed modes of behaviour. One is largely aware that the public interior becomes public by some common consent – it is taken to be public –when it is in fact most often a privately owned, operated and secured space, which implicitly filters its public, and very often does so explicitly, affording limited enfranchisement or denying it entirely as it does so.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Situated Architectur
Deletion of vitamin D receptor leads to premature emphysema/COPD by increased matrix metalloproteinases and lymphoid aggregates formation
No full textDeficiency of vitamin D is associated with accelerated decline in lung function. Vitamin D is a ligand for nuclear hormone vitamin D receptor (VDR), and upon binding it modulates various cellular functions. The level of VDR is reduced in lungs of patients with chronic obstructive pulmonary disease (COPD) which led us to hypothesize that deficiency of VDR leads to significant alterations in lung phenotype that are characteristics of COPD/emphysema associated with increased inflammatory response. We found that VDR knock-out (VDR(-/-)) mice had increased influx of inflammatory cells, phospho-acetylation of nuclear factor-kappaB (NF-κB) associated with increased proinflammatory mediators, and up-regulation of matrix metalloproteinases (MMPs) MMP-2, MMP-9, and MMP-12 in the lung. This was associated with emphysema and decline in lung function associated with lymphoid aggregates formation compared to WT mice. These findings suggest that deficiency of VDR in mouse lung can lead to an early onset of emphysema/COPD because of chronic inflammation, immune dysregulation, and lung destruction
PROJECT C.R.A.N.I.U.M.: Constructing a Real-time Alarm for Nearing Intracranial hypertension Using Machine learning
No full textIntroduction Intracranial hypertension (IH) is a harbinger of secondary brain injury in patients suffering from traumatic brain injury (TBI), can be mitigated at the Intensive Care Unit (ICU) and is associated with a poor prognosis. Current clinical practice consists of treating IH once it has occurred, by medical or surgical interventions. This is later than desired, as secondary injury has already been initiated. A pre-emptive approach may be preferable, and seems possible since many physiological variables that may aggravate IH are known and can be managed clinically. The aim of this research is to develop a machine learning method that is able to predict whether or not a patient will develop IH in the near future during ICU stay. Methods A cohort of 114 patients with TBI admitted to the ICU of Erasmus MC was selected. Long Short Term Memory (LSTM) models were trained and evaluated with 26 clinical variables to predict IH. The effect of the length of the minimal IH period, the length of the prediction window and the number of included variables was evaluated. Primary outcome measures were the model loss, accuracy, and Area Under the receiver operating characteristic Curve (AUC). Results We achieved a mean AUC of 0,83 [95% CI: 0,68-0,98] with a model predicting periods of ICP≥20mmHg lasting at least 15 minutes, using a prediction window of 30 minutes and using only the ICP and mean arterial blood pressure (MAP). All models showed decreasing training and validation loss values during the first few epochs of model training. Thereafter, the training loss continued to decrease while the validation loss started to increase. Conclusion We developed a LSTM model that was able to predict, with a mean AUC of 0.83 [95% CI: 0,68-0,98], the occurrence of IH after half an hour based on the ICP and MAP. Adding more clinical variables resulted in overtrained models. Technical Medicin
Stimulating adolescents' physical well-being by gamification: The design of a product-service combination called: Move on
No full textThis thesis describes the design of the product-service combination called Move on. Move on is designed to stimulate adolescents to be more physically active. This stimulation is done by gamification, which therefore can be considered as serious gaming product. This thesis starts with a literature analysis of the decreasing level of childrens’ physical well-being. Added to this analysis, is a literature research on the increased digitalization among children to see if there is a connection between their increased screen-time and the decreasing level of fitness. A relation between digitalization and emotional behavior, and digitalization and social relationships, has also been taken into account. It seems that there is no clear proof of the coherency between the increasing digitalization and decreasing physical activity. Which was a positive result, since the advantages of the digitalization could be taken into account when designing a product for children. After finding out that the adolescents, of all children, spend the most time stuck to their screens, the target group for the ideation phase was determined. A target group analysis and a market analysis eventually lead, together with the previous insights, to a full program of requirements and therefore the end of the design brief. The design brief created the base for the next phase: the synthesis phase. Within the synthesis phase of the product development, some concept directions were found. These concept directions lead to some iteration steps which eventually resulted in the embodiment phase of the Move on. The embodiment phase describes the final concept with regard to its materials, production method, and price estimation. An important part of the Move on, is that it is able to recognize the user motion. This motion will be converted to a reward, which the user can use in their favorite game. Since this motion recognition plays a big role in the product, a basic machine learning validation is executed. Data from walking and running sessions is used to actually predict if the user is walking or running. This validation succeeded with a hit rate value of 96 percent. The end of the thesis will describe recommended steps fur future development of the product, together with a project and a personal evaluation.Integrated Product Desig
Simulating cement microstructural evolution during calcium leaching
No full textCalcium leaching is one of the important degradation mechanisms causing dissolution of the crystalline phases such as, AFm, portlandite increasing capillary porosity. Further it leads to decalcification of an amorphous C-S-H phase causing increase in the gel porosity and in turn degrading the long term performance of concrete structures. In this paper a lattice Boltzmann based pore-scale reactive transport approach in the context of simulating the evolution of microstructure of a hardened cement paste during calcium leaching is presented. This approach is based on fundamental principles of chemical thermodynamics and mass transport. The example presented illustrates influence of location of mineral grains and surface area on overall dissolution rate and pore structure evolution.Structural EngineeringCivil Engineering and Geoscience
On Negotiating discredit in meetings of patients living with Alzheimer’s disease
No full textDans ce texte, l’auteur présente les particularités communicationnelles d’espaces visant à recueillir la parole et les expériences de personnes jeunes vivant avec la maladie d’Alzheimer, et de leurs aidants proches. Cette attention permet de mettre en lumière un dispositif cherchant à la fois à faire participer les personnes directement concernées, et à faire de ces espaces des lieux dans lesquels l’indésirabilité de leurs symptômes est renégociée. À cet effet, l’auteur aborde les modalités pratiques de ces réunions, les normes participatives et les difficultés rencontrées pour les concilier avec la maladie d’Alzheimer. Il compare ensuite la recevabilité du discours des jeunes patients et le travail de réception effectué par l’assemblée.This article presents the communicational specificities of spaces that aim at gathering the voices and experiences from people living with dementia and their carers. This allows focusing on an arrangement that seeks in the same time to involve people with Alzheimer’s disease and to create spaces where the undesirability of their symptoms are renegotiated. In order to do so, the author addresses the practical modalities of those gatherings, the participative norms and the difficulties to meet their standards. He then compares the admissibility of the young onset dementia speeches and the reception work made by the group
Virtual fatigue verification of Glass Fibre-Reinforced Polymer components for civil engineering applications
No full textThe increase in road traffic intensity and loading capacity of a truck over the last decades causes fatigue problems in existing bridges built in the 1960s and 1970s. For steel bridges, this means that the deck structure does not meet the current demands. A solution would be to replace these existing deck structures with Glas Fibre-Reinforced Polymer (GFRP) sandwich webcore deck panels. However, the ministry of infrastructure in the Netherlands has voiced its concern about the fatigue performance and displacements of these deck panels under the high traffic load and intensity. Furthermore, the knowledge about the fatigue performance of GFRP deck panels, applied in the main road network, is still limited. At the time of writing this report, the technical committee, CEN/TC 250 (responsible for developing structural eurocodes), establishes a technical design specification for Fibre-Reinforced Polymer (FRP) structures. This technical specification requires full-scale fatigue testing due to the complex failure modes that can occur. General fatigue damage summation methods like Palmgren-Miner [30, 41] are not allowed by this technical specification. This report discusses the development of Virtual Fatigue Stiffness Simulation (ViFaSS), a numerical non-linear fatigue stiffness reduction model that can predict the fatigue performance of in-plane stress dominated Glass Fibre-Reinforced Polymer components, with a wide range of lay-up compositions, based on existing knowledge and experiments, including the damage development under multi-axial stress states and stress redistribution. The damage development includes damage accumulation dependency on damage history and damage development dependency on the load type, e.g. Tension-Tension (T-T) or Compression-Compression (C-C). With the low utilisation of the material strength in civil engineering applications, the research is limited to the stiffness degradation of the material. The numerical model is coupled with the Finite Element (FE) software SOFiSTiK where the component is modelled with shell finite elements. The fatigue material response is characterised on a unidirectional ply level based on principal ply directions and based on experimental results from the Optidat program [36]. The coupon response predicted by ViFaSS for constant amplitude T-T and bending fatigue loading was in reasonable agreement with experimental results. For future work it is recommended to extended the model with the ability to use non-linear material behaviour and to include the strength degradation caused by fatigue
Analysis of infiltration in buildings using LES and airflow network models
No full textInfiltration is the uncontrolled flow of air into the building through the envelope, which contributes to a significant amount of heat loss and is estimated to be around 30% of the heating demand. It is therefore essential to estimate the amount of infiltration, to design a suitable heating and cooling system in a building. Empirical relations which are used to determine infiltration, generally overestimate the infiltration rate, since the effects of weather, mechanical ventilation and building geometry are not taken into account. Large Eddy Simulation (LES) is used to determine the pressure distribution around a building along with an airflow network model to determine the infiltration flow rate. Validation studies of the LES model show that the pressure data at the front and back faces of a surface-mounted cube are accurately captured, whereas, the pressure at the top and side faces slightly deviate from reference data with an error of 16%-20%. This occurs due to a shift in the recirculation region at the top towards the leeward part of the cube surface. The reattachment of the flow is not observed at the top and side surfaces, which explains the deviations in pressure. The infiltration rate is analysed in the Matrix VII building using the in-house model, which combines the LES model and the airflow network model. It is then compared with other relevant standards and models like the NTA 8800 and an energy balance model. The comparison is made in terms of the cross-correlation between the models and the heat loss associated with infiltration. The in-house model shows good cross-correlation with the NTA 8800 model, with a Pearson correlation coefficient of 0.8454. The building standards which employ empirical relations, overestimate the heat loss by a factor of 10 compared to the in-house model. The in-house model is then used to develop a database of infiltration values for different building heights and airtightness values. The specific infiltration rate is observed to decrease in buildings taller than 120 m due to the minimal changes in velocity higher up the atmospheric boundary layer. The database is observed to provide values of infiltration with reasonable accuracy, compared to the existing database in the ISSO standard
Flow structure detection using a numerical lidar measurement model
No full textWith the increasing number of wind farm projects, a growing interest is seen towards the extension of wind turbine durability and the optimisation of energy production. A promising technology in this direction, is the use of lidars for remote sensing of wind fields and particularly for lidar-assisted control of wind turbines. Many investigations have been carried out to study the performance of lidars for measuring global wind statistics and test out lidar-assisted control strategies. However there appears to be less research efforts towards identifying and characterising localised and specific flow structures within the wind field, which is the aspect of focus in this study. Whilst the main objective is to detect flow structures, this study also dives into the lidar measurement process. A striking feature of this process is the extensive data processing procedure applied to reduce noise and provide a final output in the form of the line-of-sight velocity. As this consists on relatively large data reduction and condensing steps, the question therefore arises, is useful information lost during this process?To investigate the different stages of the lidar measurement process, a continuous wave lidar emulator was developed and served as the main tool for simulating lidar operation under controlled conditions. The first part of the investigation was performed on the Lamb-Oseen vortex, and was aimed at finding traces of the vortex within the lidar outputs. Besides, the line-of-sight velocity output, the Doppler spectrum was also analysed in a statistical sense with the use of moments. Three main indicators of the presence of the vortex were identified in the velocity envelope and the variations of the Doppler spectrum standard deviation and skewness across the vortex core. Tests were performed to see the effects of varying conditions (core size, noise, line-of-sight effects, etc.) on these patterns. From these sensitivity tests, a possible approach at characterising the vortex position, core radius and circulation was formulated. Further testing was then performed by adapting the methods used to a LES simulated wind turbine tip vortices.In all tests performed, it is clear that the most detrimental obstacle to reliable vortex detection arises from the surrounding flow field which distorts the structure of the vortex and hence the regularity of the patterns identified within the lidar measurement process. An additional barrier are measurement process noise sources which tend to damp the signal rather than distort it, thus weakening but preserving the general shape of the identified features.Applicability of the detection method developed is possible, but challenging in real operating conditions, due to the noisy background wind field and the ignorance of the approximate vortex location in the wind inflow. However, with continued and improved future studies, the approach shown may result in a suitable way of determining wake regions from the detection of tip vortices, thus providing a valuable input for wind turbine control and wind farm power optimisation.European Wind Energy Masters (EWEM) | Rotor Design Trac
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