1,720,957 research outputs found
Hydrodynamic behaviour of compacted granite sawdust from the dimension stone industry of Pontevedra (Spain): experimental and modelling
Get PDFTwo large-scale column experiments have been performed to test the hydrodynamic behaviour of unsaturated, compacted granite sawdust—a material produced during the dressing of dimension stone in Pontevedra (Spain). One of the columns was equipped with psychrometers and capacitance probes while, in the other, a radial array of 80 electrodes made possible a time-dependent 3D electrical resistivity survey. All these devices allowed investigating and modelling the progressive saturation of the material. The study includes a straightforward methodology developed to calibrate the resistivity signals based on standard Proctor-compacted specimens. The progressive saturation of the granite sawdust reveals different stages: initially, an uneven advance of the saturation front (fingering) occurs; later on, this feature vanishes and is replaced by a more regular advance of the saturation front. Numerical analysis of the results shows that the yield capacity of the granite sawdust is ~0.39 m3 m?3 and a saturated hydraulic conductivity ~2 × 10?6 m s?1. The latter, which corresponds to the specific standard Proctor compaction, is not sufficient to support the use of granite sawdust for compacted-single-layer capping structures. Nonetheless, increased compaction efforts or improved design criteria (multilayer systems or capillary barriers) can keep bearing when considering granite sawdust for this purpose
Seismic Risk Assessment For Geothermal Projects: With The Creation Of A Physical Screening Model
No full textGeothermal energy can be a great solution for the downscaling fossil fuel society, but it can potentially lead to seismic hazards. A doublet system, with a cold water injection well and a hot water production well, alters the stress situation in the subsurface, which can result in (micro)fracturing and fault reactivation. Even in water filled reservoirs, aquifers, with relatively good permeabilities, the acting in-situ stress on already existing fault can be changed such that there can be a seismic hazard. The three dominant phenomena that influence the fault reactivation and are triggered by geothermal water injection and production are the direct pore pressure change, poro-elastic stress change and thermo-elastic stress change. To predict and subsequently diminish or limit the seismic hazards in geothermal operations, Seismic Risk Analysis (SRA) are to be completed before such operations can take place in an often seismic risky location, like densely populated areas. In the current (Dutch) geothermal environment mainly three SRA’s are used; “Methodiek voor risicoanalyse ontrent geinduceerde beving door gaswinning” by the Staatstoezicht op de Mijnen (SodM), “Defining the Framework for Seismic Hazard Assessment in Geothermal Projects V0.1” by Q-con/IF-technology [6] and an Excel-model created by TNO/Geomech. By investigating and reviewing these three SRA’s in this thesis their shortcoming and limitations are exposed, for example their lack of physical foundation and explanatory results. From the foundation of the currently excising SRA’s a new alternative SRA, which corresponds in some steps with the older SRA’s, is created in this thesis. In order to successfully finish the new SRA one of the three steps should be completed, starting with SRA Step 1. In this first step of the new SRA a new Physical Screening Model (PSM) is created. When completing the SRA an indication of what type of seismic monitoring there should be done during production. This PSM is a fairly quick and simple in its use but provides sufficient informative data to investigate the seismic hazard for most geothermal operations in the Netherlands. In four different steps in the PSM, the potential reactivation of faults over the whole reservoir during production will be evaluated. With the spatio-temporal evolution of ΔP, Δσporo, ΔT (PSM Step 1) this model can predict fault reactivation at any place and time inside the reservoir, while it can also look at which parameter dominated this reactivation. In this thesis the physical background and results of the PSM will be explained step by step. Eventually there are three final results from the PSM; a Mohr plot that predicts if certain faults (at certain locations) are stable or not and the maximum Moment magnitude (Mw) in combinations with the Peak Ground Velocity (PGV), which predict the severity of a possible event. Sensitivity analyses and case studies done with the PSM in this thesis show the influence of dominating parameters, like permeability and injection rate, and what results can be expected when using this model.Applied Earth Science
Soil Constitutive Modelling Using Neural Networks
No full textConstitutive models are one of the main building blocks of the Finite Element Analysis that nowadays is used in almost every geotechnical engineering project. Thus, finding realistic stress-strain behaviour models has been one of the main fields of research in Geotechnical Engineering. However, constitutive equations have become increasingly complex featuring 10 or more parameters as inputs with sometimes small correlations to physical properties (Beaty & Byrne, 1998; Bauer, 1996). Thus, a more data driven approach can be determined to account for that issue. In this thesis, that data driven approach will be attempted by using Neural Networks. The main goal of the thesis is to access if Neural Networks can be used to model constitutive soil behaviour. Specifically, two approaches are used to model stress-strain behaviour of soils.The first approach is classified as a generic approach because the investigation is mostly focused on which techniques of the Neural Network can help with the modelling of stress and strain behaviour. In that way the Network can be thought of as a “black box”. The prediction after the training of the Neural Network is achieved by dataset retrieved inputs and from inputs that are retrieved from the last step of the prediction. The latter has the objective of replicating the prediction as it is achieved from a typical constitutive model. The aim is the minimisation of errors after training. The feedback and the non-feedback predictions do not produce the same results which imply that the network is sensitive towards a certain input. This is further validated by conducting a sensitivity analysis and by looking into the activation of each node for certain loading cases. Dropout and reassessing the inputs and outputs are attempted to resolve this issue but the results remain erroneous.The second approach is to create a component based Neural Network. In this case a link is created between the function of the neural Network and typical soil behaviour. The linear elastic model is modelled with a linear activation function. In this case the network is successful in reproducing the full linear-elastic matrix. The linear elastic perfectly plastic model is modelled by connected the linear elastic matrix with a ReLU layer as it is seen in continuum mechanics. The Neural Network accurately predicts the stress-strain relationship. And it can be used to also predict the stress path of “noisy” datasets. However, when trained with noise the signal added to the training dataset is recognised as a pattern from the Neural Network. Finally, the work hardening model does not successfully model the stress-strain relationship as it tends to exaggerate the contribution of the stress input versus the strain input. All in all, this is an effort towards the development of a Neural Network constitutive model with the final aim of producing data driven constitutive models.<br/
Aquifer thermal energy storage following up on the tu delft geothermal well: A study on how a low-temperature aquifer thermal energy storage system can cool and heat the campus in accordance with its climate goals by 2050
No full textIn 2020 TU Delft will build a geothermal well producing enough energy to power all its faculties and a number of buildings surrounding the campus. This is done to meet the climate goals the TU set itself: an energy neutral campus by 2040. Geothermal plants are designed to produce for 30 years. After this period, by 2050, the TU has to be energy-neutral without the geothermal heat flowing from deep underground. To prevent falling back to fossil fuels there is need for a new energy source. In this feasibility study one of the options is investigated, low temperature aquifer thermal energy storage (LT-ATES). This technology stores heat-energy produced during summertime in aquifers, during wintertime this water is used to heat the faculties. It was found that a LT-ATES system is viable. A 19 MW ATES system containing 23 cold and 23 warm wells to a depth of 180 meters is needed. Cooling during summertime is not sufficient to charge the system to meet the winter heating demand; therefore an additional solar thermal collector field of 35.000 m2 is needed. Designing a strategy for 2050 means that there is a considerable amount of assumptions to be made. To optimize the LT-ATES-system, a more in-depth study should be performed
Centrifuge modelling to study the effect of root spacing on load transfer mechanism in vegetated slope
No full textFailure of slopes has been a frequently occurring hazard, which leads to loss of life and resources. To stabilize the slopes, vegetation has been used, where stump of plant roots act as passive piles by providing mechanical reinforcement. In this research, effect of spacing of trees on load transfer mechanism in a slope has been studied and comparability of passive piles and roots has been investigated. Half portion of an embankment has been taken and simplified instrumented roots were planted in staggered pattern on the slope. Two models with spacing of 3 times the diameter of root and 6 times the diameter of the root were prepared to study the effect of spacing on load transfer mechanism. A model with no reinforcement (fallow) has also been tested. During the test, load was introduced to a foundation at the crest of slope till the slope failed. It was observed that as the spacing increases, load bearing capacity of slopes decreases. As spacing of roots decreases, incidence of failure prolongs. Also, as the spacing of roots decreases, shear failure plane gets deeper in the slope. As these aspects of passive piles were observed, behaviour of roots is comparable to that of passive piles
The suitability of High Temperature – Aquifer Thermal Energy Storage in Holland-Rijnland
No full textHigh Temperature – Aquifer Thermal Energy Storage (HT-ATES) is a way to efficiently store heat with use of the subsurface. Region Holland-Rijnland has the vision to be free of the use of natural gas in 2050. A proposed high temperature heating network from the port of Rotterdam to the households of Leiden, combined with the use of an HT-ATES system as a buffer, could be the next step to achieve the laid-out vision. This research is a first step in the possibility of placing an HT-ATES system near Leiden. An interpretation of the subsurface near Leiden is done based on information from DINOloket to find potential formations and aquifers. Then, combined with different scenarios for the heat demand from the proposed heat network, a preliminary design of an HT-ATES system is made to test the viability of the potential aquifers. The most suitable aquifer is found in the Maassluis formation at a depth of 230 meters. Per scenario, this aquifer needs the least number of wells for the desired pumping rate. Depending on the scenario, the aquifer has a thermal recovery efficiency ratio between 0,16 – 0,26 and an area – to – volume ratio between 0,051 – 0,056. Other suitable aquifers can be found in the Maassluis formation at a depth of 170 meters and in the Oosterhout formation at a depth of 320 meters. The subsurface near Leiden is suitable for an HT-ATES system, but more research needs to be done on the conflict between heat supply from the port of Rotterdam and heat demand from the proposed network in order for an HT-ATES system to fully supply the seasonal heat demands.Applied Earth Science
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Modelling of borehole heat exchangers and heat transfer along horizontal connection pipes
No full textThe use of geothermal energy with shallow borehole heat exchangers (BHEs) is growing steadily. BHEs are the underground components of heat pump systems that uses the ground as source or sink of thermal energy for conditioning of buildings. Larger systems with tens to hundreds of boreholes are being built. Analytical calculation approaches are successfully used for the design of such systems and mechanical plants. To simulate and optimise the actual operating conditions, more complex models that take into account transient conditions may be required. In addition, large BHE fields often require hundreds of meters of horizontal connection pipes to connect the BHE to the manifolds and the building. Heat transfer along these pipes is often neglected. This thesis presents a hybrid simulation approach for BHEs based on a novel combination of existing solutions for the simulation of heat transfer processes within the borehole and the surrounding ground. Heat transfer is modelled using a combination of analytically determinedg-functions and a borehole thermal resistance capacity model. The computational efficiency of long-term simulations is drastically increased by dividing the simulation time into multiple periods, where the influence of past periods on future periods is calculated using the FastFourier Transform. Based on monitoring data from a BHE field with 40 BHEs and a combined connection pipe length of 900 m, heat transfer along connection pipes is investigated. The heat transfer alongthe connection pipes is correlated with parameters such as surface types or solar radiation above the pipes using multiple linear regression analysis, showing that solar radiation above the pipes has the greatest effect. A comparison of three soil and three pipe models of varying complexity is carried out to investigate their suitability in the context of connection pipes and BHE simulation. Basedon the results, a computationally efficient approach is proposed using a novel combination of established steady-state models for the BHE and the connection pipes. The model isused to investigate the effect of horizontal connection pipes attached to a BHE for the 25most representative climate zones. The consideration of the connection pipes leads to thebiggest BHE load reduction in tropical climates, followed by temperate, arid and continentalclimates. In the case of existing BHE fields where the connection pipes have not been considered in the design, various options for the subsequent use of heat gains along the pipes are investigated. The study explores the potential of extended operation, increased loads and an optimised operating strategy to exploit the idle capacity gain from the horizontal connection pipes. Finally, a simple and fast methodology to account for changing thermal properties by using the g-function method is presented. The simulation time is divided into periods according to the changes in thermal properties. By transforming the temperature response from one period to the next and subsequent superposition, any changes in the thermal conductivity properties can be taken into account. The computational time is significantly shorter than comparable numerical simulations
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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