93 research outputs found
Bulking sludge control. Kinetics, substrate storage, and process design aspects
No full textThe activated sludge process is the preferred technology for biological wastewater treatment. Despite decades of progress and operation serious operating problems still occur with this process. One major problem is the regular occurrence of excessive growth of filamentous bacteria, phenomena known as filamentous bulking sludge. Poor solid-liquid separation can occur as result of this problem, leading to effluent quality deterioration and to process failure due to uncontrollable loss of biomass with the effluent. The goal of this thesis was to achieve a better understanding of bulking sludge and the relevant factors involved. To accomplish these objectives, well-controlled laboratory scale sequencing batch reactors with mixed microbial cultures and defined substrates, were operated under different conditions. Traditionally pure culture microbiology or full scale reactor observations have been the basis for the research. The choosen process engineering approach proved to be a success to study bulking sludge. Not only filamentous bacteria grew very well under specific conditions but also the results were reproducible and trends relating sludge settleability and operational conditions were identified. Design guidelines and operation aspects were proposed to control bulking sludge, leading to more robust, reliable, predictive, and sustainable activated sludge systems. Together with a literature review, the experimental results were the basis to develop a unifying hypothesis about bulking sludge - diffusion based selection. This theory can replace the existing theory based on kinetic selection. Both bacterial morphology and substrate micro-gradients inside microbial aggregates are hypothesized as playing a dominant role in selection for bulking sludge. An individual-based model, originally developed to a biofilm system, is adapted for the first time to model the competition between different bacterial morphotypes in activated sludge flocs. The first modelling results support qualitatively the hypothesis. Several chapters in this PhD thesis have been published by commercial publishers. These chapters can only be found in publications of these publishers. Bibliographical information of these publications can be found in the different chapters.Applied Science
Minimal invasive diagnostic capabilities and effectiveness of cfrp-patches repairs in long-term operated metals
No full textThe paper deals with the subject of diagnostics and the quick repairs of long-term operated metallic materials. Special attention was paid to historical materials, where the structure (e.g., puddle iron) is different from modern structural steels. In such materials, the processes of microstructural degradation occur as a result of several decades of exposure, which could overpass 100 years. In some cases, their intensity can be potentially catastrophic. For this reason, the search for minimally invasive diagnostic methods is ongoing. In this paper, corrosion and fracture toughness tests were conducted, and the results of these studies were presented for two material states: post-operated and normalized (as a state “restoring” virgin state). Moreover, through the use of modern numerical methods, composite crack-resistant patches have been designed to reduce the stress intensity factors under cyclic loads. As a result, fatigue lifetime was extended (propagation phase) by more than 300%
Enabling Continuous Descent Operations in High-Density Traffic
No full textThe Air Traffic Management (ATM) community strives to reduce the environmental impact per flight. Continuous Descent Operation (CDO) has been identified by the ATM community as one of the operational improvements that could reduce aviation’s environmental impact, both in terms of aircraft noise and gaseous emissions. In the current ATM system, CDOs are only feasible in low-density traffic. The ultimate goal is an ATM system that facilitates CDOs in high-density traffic. This research described in this thesis focused on two features of such an ATM system: decision support that enables the air traffic controller to accurately set up traffic for CDO, and delegation of the spacing task to the flight crew during the CDO. Two enablers are real-time availability of meteorological data, and accurate trajectory prediction. In this thesis new methods were developed and validated to infer wind, air pressure, and air temperature profiles from aircraft surveillance data. Trajectory prediction was defined as a machine learning problem, enabling predictions based on historic aircraft trajectory and meteorological data without the need for explicit modeling of the aircraft performance and procedures. A decision support tool was developed further and tested using a human-in-the-loop experiment. The tool enabled the subjects to set up traffic for CDO in high-density traffic at an acceptable work load level and high level of situation awareness. Monte-Carlo simulations were carried out to assess the runway capacity that can be achieved when delegating the spacing task to the flight crew. These simulations showed the feasibility of CDOs in high-density traffic.Control and SimulationAerospace Engineerin
Fatigue crack propagation behavior of old puddle iron including crack closure effects
No full textAbstractIn this paper the fatigue crack growth behavior in structural components from the old 19th century structures (e.g. bridges) has been investigated. The delivered material for investigation was extracted from a beam made of puddled iron, commonly used in 19th century. The obtained results from several ancient railway metallic bridges (located in Lower Silesia, Poland) have shown the presence of microstructural degradation processes in puddled iron. In all analyzed materials (low carbon puddled iron) microstructure degradation processes were related to: the presence of numerous precipitations of carbides and nitrides (or the carbides–nitrides) of iron inside the ferrite grains, the presence of continuous precipitations of cementite at ferrite grain boundaries. In order to restore the initial state of the microstructure, all tests were carried out in two stages of heat treatment; as-received state and after normalization (950°C, 2h, cooled in air) state. The kinetic fatigue fracture diagrams (KFFD) have been obtained. The problem of crack closure has been involved in fatigue crack growth process during the experiments and its understanding is fundamental for the analysis of stress ratio effects on KFFD. In the paper, a few experimental and numerical techniques for the evaluation of the crack closure/opening forces based on the experimental data have been compared. The implemented algorithm in the numerical environment gives promising results in description of the kinetics of fatigue crack growth of the old puddled iron with consideration of crack closure effect
Beleidsbevoegdheid regionale luchthavens gedecentraliseerd: Een onderzoek naar de weerstand tegen de decentralisatie van het regionale luchthavenbeleid aan de hand van de situatie rondom de Rotterdamse luchthaven
No full textTechnology, Policy and Managemen
Global Fatigue Life Modelling of Steel Half-pipes Bolted Connections
No full textAbstractA steel hybrid structural solution for onshore wind turbine towers was proposed in the European project SHOWTIME. This solution is used in the lattice structure for the lower portion of the tower. Recently, a procedure for fatigue life estimation of steel half-pipes bolted connections applied in global structural models using multiaxial Smith-Watson-Topper (SWT) criteria was proposed by Öztürk et al. In this paper a procedure for design S-N curve modelling of steel half-pipes bolted connections is proposed. This procedure is based on a local approach using multiaxial fatigue criteria together with an elastoplastic analysis using the finite element method. The materials to be used in this analysis are the S355 and S690 steels. This evaluation to be performed is calibrated with experimental results of fatigue tests of the connection under consideration
Identification of the net effective strain-life model for a puddle iron from the Portuguese Fão riveted road bridge
No full textAbstractThis paper presents low-cycle fatigue data derived for a sample of puddle iron removed from an ancient Portuguese riveted road bridge - the Fão bridge. Constant amplitude strain-life data is presented for strain ratios equal to 0 and −1. This data was correlated using the classical strain-life model, known as Morrow’s model. Additionally, overloading strain-controlled fatigue tests were carried out to identify the net effective strain-life model, as proposed by D.L. DuQuesnay. Finally, models are applied to assess variable amplitude (variable amplitude blocks) strain-life data derived for smooth specimens
Mechanical behaviour of wood T-joints. Experimental and numerical investigation
No full textResults of a double-shear single-dowel wood connection tested under monotonic quasi-static
compression loading are presented and discussed in this paper. The wood used in this study was a pine wood,
namely the Pinus pinaster species, which is one of the most important Portuguese species. Each connection
(specimen) consists of three wood members: a centre member, loaded in compression along the parallel-tograin
direction and two simply supported side members, loaded along the perpendicular-to-grain direction (Tconnection).
The load transfer between wood members was assured by means of a steel dowel, which is
representative of the most common joining technique applied for structural details in wooden structures. The
complete load-slip behaviour of the joint is obtained until failure. In particular, the values of the stiffness, the
ultimate loads and the ductility were evaluated. Additionally, this investigation proposed non-linear 3D finite
element models to simulate the T-joint behaviour. The interaction between the dowel and the wood members
was simulated using contact finite elements. A plasticity model, based on Hill’s criterion, was used to simulate
the joint ductility and cohesive damage modelling was applied to simulate the brittle failure modes (splitting)
observed in the side members of the joint. The simulation procedure allowed a satisfactory description of the
non-linear behaviour of the T-joint including the collapse prediction
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