1,200 research outputs found
The My Lai Massacre in American history and memory
No full textThis book examines the response of American society to the massacre and its ambiguous place in American national memory. The author argues that the massacre revelations left many Americans untroubled, and it was only when the soldiers most immediately responsible came to be tried that the controversy really came to public attention. He finds that, contrary to interpretations of the Vietnam conflict as an unhealed national trauma or wound, many Americans have assimilated the war and its violence rather too well, and they were able to do so even when that violence was most conspicuous and current. Consistent with the view that US soldiers have subsequently been cast in national culture as the conflict’s principal victims, it was the American perpetrators of the massacre and not the Vietnamese they brutalized who, even in the case of My Lai, became the central object of popular concern
Thick-bedded deep-marine sandstones: The use of analogs for reservoir appraisal
No full textCivil Engineering and Geoscience
Characterization of deltaic rocks for numerical reservoir simulation
No full textCivil Engineering and Geoscience
Upscaling of permeability heterogeneities in reservoir rocks; an integrated approach
No full textThis thesis presents a hierarchical and geologically constrained deterministic approach to incorporate small-scale heterogeneities into reservoir flow simulators. We use a hierarchical structure to encompass all scales from laminae to an entire depositional system. For the geological models under consideration we propose a five-scale hierarchy with sedimentary structure and subfacies as key elements. The five scales are the lamina, sedimentary structure or bed, subfacies, facies, and depositional system. We use the term subfacies to denote a rock type, i.e. a body of rock with internally consistent sedimentary properties. The term facies denotes an assemblage of subfacies. The depositional system may be thought of as a sequence, i.e. an assemblage of genetically related deposits formed during periods between "catastrophic" events such as an abrupt sea level rise. Although sedimentary architecture is very complicated, the hierarchical approach lends itself naturally to implementation of heterogeneity in a reservoir simulator. For this reason we distinguish flow units, flow cells and grid cells. Flow units are subfacies schematised in a rectangular structure. The building block of the flow unit is a particular type of flow cell. Flow cells are periodic unit cells (PUC) that contain one or more sedimentary structures. The advantage of the assumed periodicity is that PUC's can be used to obtain average flow characteristics over the representative elementary volume (REV) of the flow unit. Such an REV consists of a large collection of PUC's. For flow simulations on the oil field scale we divide the flow units into rectangular grid cells that contain the flow characteristics of the flow cell. The simulations based on SPE 9th comparative program show the importance of incorporating small-scale heterogeneities.Civil Engineering and Geoscience
Permeability heterogeneity in cross-bedded sandstones: Impact on water/oil displacement in fluvial reservoirs
No full textCivil Engineering and Geoscience
The structural, paleogeographical and hydrocarbon systems analysis of the Ghadamis and Murzuq Basins, West Libya, with emphasis on their relation to the intervening Al Qarqaf Arch
No full textCivil Engineering and Geoscience
Toepassing van het caisson-systeem bij het filtergebouw op het terrein van de Centrale Gelderland-Zuid te Nijmegen
No full textBeschrijving van de uitvoering van een caissonfundering
Improving the Evolutionary Optimization of Interplanetary Low-Thrust Trajectories Using a Neural Network Surrogate Model
No full textBuilding on recent advances in the fields of low-thrust trajectory optimization based on shaping methods, Artificial Neural Networks, and surrogate models in Evolutionary Algorithms, an investigation into a novel optimization routine is conducted. A flexible Python tool to evaluate linked trajectories in a two-body model based on hodographic shaping is implemented and used to develop a novel evolutionary optimization approach where a Genetic Algorithm is assisted in finding new candidate solutions by an online surrogate. The algorithm and different surrogate designs are experimentally investigated on two example problems based on the Dawn trajectory and the GTOC2 problem. Employing the surrogate yields new candidate solutions that improve the population’s fitness especially when the surrogate is used to approximate the shaping computation. Additionally, the use of a surrogate pretrained on a general data set of low-thrust transfers is tested and found to considerably improve the initial quality of the model, meaning that more good candidate solutions are found early on, accelerating the algorithm’s convergence.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.Astrodynamics & Space Mission
Behaviour of segment joints in immersed tunnels under seismic loading
No full textThe immersed tunnel technique is a common used technique for river crossings in the Netherlands, but also in the United States and Japan. 80% of the immersed tunnels are built in these 3 countries. The design of the immersed tunnels differs for the different countries, because of the possibility of seismic loading on the tunnel structure. This seismic loading can occur at the west coast of the United States and in Japan, because of their position close to tectonic earth plates. The immersed tunnels in the Netherlands are built with elements of 100-150 meter consisting of segments of 20-25 meters. For transportation these segments are pre-stressed forming one element, after immersion on the river bottom they are released again. In this way the tunnel is flexible and can follow the settlement differences of the river bed. The water tightness in the joints is secured with rubber sealing profiles in the segment joints (W9U) and compressible rubber profiles in the immersion joint (Gina). In areas where risk of seismic activity is severe, the immersed tunnels are built different. The pre-stressed tunnel elements are kept as one element, the same as they are for transportation, to prevent joint opening and leakage. This results in large deformations in the immersion joints and Gina gaskets and stresses in the tunnel structure. For this reason a research is performed on the behaviour of the segmental immersed tunnel subjected to seismic loading and especially on the sensitive segment joint. Most earthquakes are created by the movement of tectonic plates. The release of energy involved with this movement creates seismic waves which will propagate through the soil. When these waves reach an immersed tunnel, it will respond to the soil movements with a certain behaviour. The design seismic wave that causes the tunnel to deform is the shear wave (S-wave). When this wave propagates parallel to the tunnel axis, the tunnel will bend in lateral direction causing the snaking effect. This can occur in horizontal and vertical direction, but the horizontal direction is determining. When the wave reaches the tunnel under an angle of 45 °, the tunnel can be deformed in axial direction. This is called the worming effect. Both the worming and snaking effect are modeled to determine the influence of the different seismic design parameters like the wave length of the seismic wave, the construction depth and the tunnel element length. Other important model properties are the stiffness of the rubber gaskets in the segment joints and the immersion joints. All the properties and loads due to the seismic soil movement are included in two different beam models to determine the worming and snaking effect for a representative immersed tunnel. The modeling of the worming and snaking effect shows that the gasket properties and the seismic wave length are the most important parameters. The compressibility of the Gina gasket and the elongation capacity of the W9U determines the total axial deformation of the immersed tunnel. For the snaking effect the rotation capacity and the number of Gina gaskets are of importance. The segment joints act relatively stiff and are of less importance until their moment capacity is reached. Then joint opening and leakage could occur. It can be concluded that the propagation speed and wave length of the seismic wave are important factors when modeling the worming and snaking effect of immersed tunnels. It is not clear from literature what the seismic design wave is for tunnels in soft soil. This needs to be investigated further to make a final judgment on the behaviour of the segment joints. For the used design parameters the tunnel can withstand the worming effect, but snaking could cause joint opening and leakage based on the free-field approach. For the snaking effect a soil-tunnel- interaction approach should be performed to determine the real tunnel response and make a final judgment of the behaviour of the segment joint.Hydraulic StructuresHydraulic EngineeringCivil Engineering and Geoscience
Sand Underflow of Immersed tunnels (in Dutch). Onderstromen van tunnels
No full textSummary report on the underflow method for Foundations of Immersed TunnelsWesterscheld
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