Distributed Acoustic Sensing using straight, sinusoidally and helically shaped fibres for seismic applications

Distributed Acoustic Sensing (DAS) is a versatile dynamic strain sensing method that has been adopted for a wide range of seismic applications. In DAS, optical fibres are interrogated and used as sensors, where a strain or strain-rate measurement is made along a specific length of the fibre, called the gauge length. Its main appeal is the spatially dense data over long distances. The main limitations of DAS, however, are that it is mainly sensitive along the axial direction of the fibre and that the signal-to-noise ratio is worse than that of standard geophones. The first issue limits its adoption in surface reflection seismic when the fibre is deployed horizontally. Also, due to the very nature of the measurement (i.e. elongation and contraction of the fibre), it is commonly considered as a single-component measurement, therefore it lacks the information from the other components.This thesis studies the potential of obtaining multi-component information from DAS as well as investigating the use of combined fibre configurations for surface-seismic applications. We approach this by examining several fibre-shaping approaches with static and dynamic strain measurements. First, the concept of the sinusoidally shaped fibre is examined to make a directional strain sensor in a direction other than the fibres’ axial direction using a static-strain approach. Secondly, the combined use of straight and helically wound fibres for obtaining multi-component information from DAS data as well as assessing the usefulness of using such a combination is investigated in a surface-seismic setting.'Using the sinusoidally shaped fibre, two approaches are investigated. The first approach involves the use of the sinusoidally shaped fibre embedded in a homogenous material. An analytical model is presented to describe what happens to the deformed fibre in three main directions, which was validated via a finite-element model. Along with the model, loading experiments were performed on a sinusoidally shaped fibre embedding in a polyurethane-type (i.e. called Conathane®) strip in the following directions: in-line (i.e. transversal in-plane with the sinusoidal fibre), broadside (i.e. perpendicular to the sinusoidal fibre), and along-strip (i.e. along the strip’s longest dimension). We saw that the fibre is mainly sensitive to the in-line and broadside directions, and it is slightly more sensitive in the in-line direction relative to the broadside direction. We also saw that the geometrical parameters of the fibre, as well as the mechanical properties of the embedding material, affect its directional sensitivity. This is exploited in the second approach where the embedding material is now adapted to a low Poisson’s ratio metamaterial as well as further adaptations in the geometry of the fibre, aiming to create a unidirectional strain sensor. Experimental results showed improvements in the sensitivity but not as much as predicted by the analytical or numerical modelling.Using DAS in field settings, multiple configurations of straight (SF) and helically wound fibres (HWF) with different wrapping angles (α) were buried in a 2-m trench in farmland in the province of Groningen in the Netherlands. Significant amplitude differences are observed between the straight and helically wound fibres. It is observed that shaping the fibre into a helix dampens the amplitude inside the surface wave significantly. Also, a polarity flip is observed with the use of HWF with a wrapping angle of 30◦. This hints that there is a contribution of the vertical component on the response measured by the HWF as also supported by the theoretical models. The reflection response is also examined using a set of engineered SF and HWF fibres. The main seismic reflections are present in both fibres with higher amplitude in SF compared to HWF, contrary to what was expected. Also, using post-stack images we see that the SF and HWF provide reflection structural images comparable to surface-deployed geophones but with an (expected) lower signal-to-noise ratio. We show that the combined use of SF and HWF is useful, as reflections were better shown for the shallow section, unlike HWF which provided better reflections in deeper sections. Furthermore, we discuss the effect of gauge length on the retrieval of surface waves along with the use of different fibre shapes using active and passive sources.With the active-source data, we show that the gauge length plays an essential role in the retrieval of surface waves depending on their wavelength range, as it might cause distortions in the waveform which appears as notches in the (frequency, horizontal-wavenumber)–domain, as well as complicates picking the dispersion curves of these waves. On the other hand, the helically wound fibres might require a longer gauge length to retrieve the surface wave properly. This decreased sensitivity of the helically wound fibres is also shown from virtual shots obtained by passive interferometry as well as a recorded earthquake in the area.Applied Geophysics and Petrophysic

System behaviour in prestressed concrete T-beam bridges

About 70 prestressed concrete T-beam bridges, constructed in the Netherlands between 1953–1977, are still in use today with many located in the main highway network. This type of bridge consists of prefabricated and prestressed T-shaped beams, with an integrated deck slab, cross-beams and transverse prestressing. Even if these bridges are well maintained, two important factors demand the current need for assessment: (1) increased traffic loading and (2) potential lack of shear resistance. Using traditional assessment methods it was concluded that about 50% of these bridges do not fulfil the current design code requirements. However, this does not automatically imply that these bridges are structurally unsafe, since some potentially significant additional load-transfer mechanisms are not taken into account in a traditional assessment. This is strengthened by the observation that, in general, these bridges do not show any signs of distress....Concrete Structure

Flight Testing Reinforcement Learning based Online Adaptive Flight Control Laws on CS-25 Class Aircraft

Unforeseen failures during flight can lead to Loss of Control In-Flight, a significant cause of fatal aircraft accidents worldwide. Current offline synthesized flight control methods have limited capability to recover from failures, due to their limited adaptability. Incremental Approximate Dynamic Programming (iADP) control is a model-agnostic online adaptive control method, which integrates an online identified locally linearized incremental model, with a Reinforcement Learning (RL) based optimization technique to minimize an infinite horizon quadratic cost-to-go. A key challenge for adopting these self-learning flight control methods is validation through flight testing. This paper presents the iADP flight control law design for CS-25 class aircraft to achieve rate control. It outlines the controller evaluation strategy, controller integration, verification & validation procedures, and a discussion on flight test results. To the author’s understanding, this flight test marks the world’s first demonstration of an online RL based automatic flight control system for this aircraft category, demonstrating real-time learning and adaptation capabilities to aircraft configurations.Control & Simulatio

Impact of a Heated Wall on the Laminar-to-Turbulent Transition of Crossflow Vortices: an Experimental Study

One of the most critical technological challenges embedded in the electrification of future aircraft revolves around the thermal management of batteries and fuel cells. An innovative idea involves using the aircraft’s aerodynamic surfaces to dissipate the extra heat, thereby reducing the impact that traditional thermal management systems (e.g. ram air heat exchanger) have on the overall aerodynamic efficiency of the aircraft. However, the limited experimental research addressing the influence of a heated surface on the stability and transition of the crossflow instability (CFI) hinders the assessment of the aerodynamic impact of this technology for future aircraft, where swept wings are ubiquitous. Thus, the objective of this work is to experimentally study the effect of a heated wall on the stability and final breakdown of CF vortices. To do so, experiments are conducted on a 45◦ swept flat plate wind tunnel model, where the surface temperature is increased by means of a surface-embedded electrical heater, yielding a mean wall-temperature ratio of T w/T ∞ = 1.055. Overall, the experimental (i.e. HWA) and numerical (i.e. CLST) results show that wall heating leads to significant destabilization of the stationary CFI. Interestingly, a spectral analysis of the HWA signal reveals substantial amplification of the traveling CF mode under wall-heating conditions, which in turn appears significantly more destabilized than the stationary CF mode. Additionally, inspection of the high-frequency content in the HWA measurements indicates premature breakdown of the CF vortices and advancement of the laminar-turbulent transition by Δ x/c x = 6.3% with wall heating. The results presented in this work render a first insight into the impact of a non-adiabatic wall on the development of the crossflow instability and subsequent breakdown to turbulence.AerodynamicsAerospace EngineeringShip Hydromechanics and Structure

High-resolution turbofan intake flow characterization by automated stereoscopic-PIV in an industrial wind tunnel environment

Unsteady inlet flow distortion can influence the stability and performance of any propulsion system, in particular for more novel, short and slim intakes of future aero-engine configurations. As such, the requirement for measurement methods able to provide high spatial resolution data is important to aid the understanding of these flow fields. This work presents flow field characterisations at a crossflow plane within a short aeroengine intake using stereoscopic particle image velocimetry (SPIV). A series of tests were conducted across a range of crosswind and high angle of attack conditions for a representative short and slim aspirated intake configuration at two operating points in terms of mass flow rate. The velocity maps were measured at a crossflow plane within the intake at an axial position L/D = 0.058 from where a fan is expected to be installed. The diameter of the measurement plane was 250 mm, and the final spatial resolution of the velocity fields had a vector pitch of 1.5 mm which is at least two orders of magnitude richer than conventional pressure-based distortion measurements. The work demonstrates the ability to perform robust non-intrusive flow measurements within modern intake systems in an industrial wind tunnel environment across a wide range of operating conditions; hence, it is suggested that SPIV can potentially become part of standard industrial testing. The results provide rich datasets that can notably improve our understanding of unsteady distortions and influence the design of novel, closely coupled engine-intake systems.Aerodynamic

Critical factors for effective resident participation in neighborhood rehabilitation in Wuhan, China: From the perspectives of diverse stakeholders

Resident participation is essential for neighborhood rehabilitation. It requires the active involvement of residents and efficient management by organizers. To improve the effectiveness of resident participation, it is necessary to understand the critical success factors (CSFs) underlying it. However, previous research has examined the critical factors from a single-stakeholder perspective, overlooking potential differences in perceptions among stakeholders with diverse roles and rehabilitation experiences. Based on 30 interviews and 255 questionnaires from six stakeholder groups in Wuhan, China, this study explores how the perception of critical factors for effective resident participation varies among local government, community-based organization, designer, contractor, consulting party, and resident. Thirty-seven factors were identified and compared among the stakeholders. Financial Incentive (for participation organizers) was identified as the most critical factor for effective resident participation, followed by Information Disclosure and Transparency, and Trust. Results from the analysis of variance (ANOVA) show that the six groups differed significantly in the importance of most factors (25/37), especially in Participant Education and Prejudice against the Working Group. Interview results indicate that the COVID-19 pandemic and rehabilitation experience changed stakeholders’ perceived importance of some factors. Specifically, in future RP initiatives, extra emphasis could be placed on Trait and Capacity (of the working group) and Participation-assistance Technologies. Stakeholders regarded these two factors as more critical as their rehabilitation experience accumulated. By understanding stakeholders' conflicting and changing perceptions of effective resident participation, suggestions were proposed to each stakeholder group to fulfill their distinct participation objectives and improve the overall effectiveness of participation practices.Design & Construction ManagementReal Estate Managemen

Bringing Ecological Urbanism and Urban Political Ecology to transformative visions of water sensitivity in cities

Ecological Urbanism and Water Sensitive Urban Design have a central contribution to make in protecting and caring for people, nature and water in cities but readings of Urban Political Ecology evidence how ecological metaphors in urban design can easily translate into discriminatory urban development processes. This paper posits that for UPE to become meaningful for urban design practice, it is necessary to move beyond a critique. Instead, the insights of UPE should be pro-actively mobilized to develop a new vision of water sensitivity. The paper therefore identifies ways in which the key learnings of the critical social sciences, namely UPE, can be mobilized to support Water Sensitive Urban Design practice. How can ecological urbanists imagine new, more politically astute, forms of water sensitive living, charting design processes that not just recognize but also actively question and challenge uneven socio-ecological dynamics? In answering this question, the goal of this article is to make use of critique from UPE to influence Ecological Urbanists' goals and activate their political alignment with agendas that prioritize social equity. In imagining a new form of WSUD, we tried as much as possible not to over-instrumentalize UPE by rejecting the suggestion that some UPE ‘lessons’ or ‘insights’ could simply be inserted into ecological urbanism. On a different direction, we argue for a different emphasis in WSUD that does not deny the causes of current environmental degradation, pollution and depletion but, on the contrary, actively takes issue with and challenges the extractive and exploitative roots of contemporary urbanization processes.Urban DesignSpatial Planning and Strateg

Emergency response in cascading scenarios triggered by natural events

Emergency response is a procedural safety barrier of paramount importance for the mitigation of fire scenarios and the prevention of escalation. However, in Natech scenarios, emergency response may be affected by the natural event impacting the site. Indeed, when contrasting Natech accidents, emergency responders have to face both the natural event and the cascading technological scenario. Despite the criticality of the issue, limited attention was devoted to date to the analysis of emergency response in cascading sequences triggered by natural events. The present study provides a novel and technically sound methodology to assess the performance of emergency response and the required intervention time in Natech scenarios. An expert survey combined with a Bayesian Network model was used to assess the performance of the emergency response. The routing and setup phases were identified as those mostly affected by natural events. Monte Carlo simulations were used to obtain baseline data and specific probability distributions for the time required to carry out the emergency response considering the factors that may hinder the response during natural events. In Natech accidents, the time for effective mitigation resulted higher of at least a factor 2 with respect to that expected in the case of conventional accidents. The methodology developed may be used to support the improvement of the emergency management of Natech scenarios, allowing for a detailed definition of site-specific emergency response plans. Moreover, the results may be used to provide a more accurate assessment of the fire-driven escalation probability in Natech events.Safety and Security Scienc

Three-Dimensional Clustering in the Characterization of Spatiotemporal Drought Dynamics: Cluster Size Filter and Drought Indicator Threshold Optimization

In its three-dimensional (3-D) characterization, drought is an event whose spatial extent changes over time. Each drought event has an onset and end time, a location, a magnitude, and a spatial trajectory. These characteristics help to analyze and describe how drought develops in space and time (i.e., drought dynamics). Methodologies for 3-D characterization of drought include a 3-D clustering technique to extract the drought events from the hydrometeorological data. The application of the clustering method yields small artifact droughts. These small clusters are removed from the analysis with the use of a cluster size filter. However, according to the literature, the filter parameters are usually set arbitrarily, so this study concentrated on a method to calculate the optimal cluster size filter for the 3-D characterization of drought. The effect of different drought indicator thresholds to calculate drought is also analyzed. The approach was tested in South America with data from the Latin American Flood and Drought Monitor for 1950–2017. Analysis of the spatial trajectories and characteristics of the most extreme droughts is also included. Calculated droughts are compared with information reported at a country scale and a reasonably good match is found.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.Digital TechnologiesWater Resource

Seismic acquisition analysis and design using multiple reflections

Seismic survey design deals with determining the acquisition parameters that lead to the best possible imaging and characterization of the subsurface. The design of the survey is constrained by health, safety and environmental considerations and the available budget, seeking for a balance between quality and cost. Because seismic exploration is a widely used geophysical method for revealing underground resources, information about the subsurface is available in many areas. Therefore, it can potentially be used for purposes supplementary to exploration such as the monitoring of producing fields and fluids injection. However, the available budget for these purposes is usually lower than for exploration, and it becomes a priority to maximize the benefits derived from a potentially cheaper acquisition. In this thesis, we propose new methods for the analysis and design of seismic surveys that are based on previous knowledge from existing subsurface models and that aimto maximize image quality with the lowest acquisition efforts.Applied Geophysics and Petrophysic