Browsing by Subject "Pressure"

Now showing 1 - 6 of 6

Collapse of internally corroded pipe under external pressure
(2008-08) Sakakibara, Naoto; Kyriakides, S.
This thesis is concerned with the effect of internal corrosion or erosion defects on the collapse of pipelines under external pressure. Experiments are conducted on SS-304 tubes with D/ts of 21.0 and 18.7 with axially uniform grooves of several thicknesses and angular spans of 6 − 60°. All specimens exhibited the classical ovalization mode of collapse with the grooved side being more deformed. For groove angles between 6° and 20° the collapse pressure decreases as the angle increases but remains essentially constant for angles between 20° and 60°. The collapse pressure was found to decrease with groove depth, reducing by nearly 50% when the groove depth reached 50% of the pipe wall thickness. The experiments were simulated numerically using both the custom computer code BEPTICO as well as an axially uniform finite element model. The predictions were found to follow the trends of the experimental results and to be usually somewhat lower than the measured collapse pressures. Using a 3-D finite element model that includes the seals used at the ends of the test specimens it was confirmed that the seal provided some rotational constraint that increased the measured collapse pressure. The three-dimensionality of grooves was examined using appropriate finite element models. It was found that grooves shorter than about 8D constitute local imperfections and accurate prediction of their effect on collapse pressure requires fully 3-D modeling. By contrast, grooves 10D long or longer behave essentially as "long" grooves and can be analyzed using 2-D models.
Determination of the energy flux of internal gravity waves
(2017-12) Lee, Frank Moonyoung; Morrison, Philip J.; Swinney, Harry L; Hazeltine, Richard D; Horton, Claude W; Gamba, Irene M
Internal gravity waves are traveling disturbances that propagate within a fluid whose density varies with depth, and two prominent examples where these occur are the atmosphere and the ocean. In the latter case, which is the focus of this work, the tidal forcing by the moon creates internal gravity waves (oftentimes referred to simply as "internal waves") that originate from the ocean bottom topography. The energy generated in the internal waves by this mechanism contributes significantly to the energy budget of the ocean. Hence it is important to determine the energy flux in the internal waves. However, it is not possible to obtain the energy flux J = p v directly because the pressure and velocity perturbation fields, p and v, cannot be simultaneously measured at the present time. The two primary methods for measuring internal waves in the laboratory are particle image velocimetry (PIV), which gives velocity perturbation fields v(x,z,t), and synthetic schlieren, which gives density perturbation fields [rho](x,z,t). We present one method for obtaining the time-averaged energy flux (J) from PIV data by calculating the stream function [psi](x,z,t), whose results agree to within 0.5% when compared with direct numerical simulations of the Navier-Stokes equations. The method was also applied to laboratory data, and again using direct numerical simulations, the agreement was found to be very good. A MATLAB code was developed with a graphical user interface that can be used to compute the energy flux and power from any two-dimensional velocity field data. Another method, using a Green's function approach, was developed to obtain the instantaneous energy flux J(x,z,t) from density perturbation data [rho](x,z,t) such as that from synthetic schlieren. This was done for a uniform, tanh, and linear buoyancy frequency N(z). Additionally, a finite-difference method was developed for the case of arbitrary N(z). The results for J(x,z,t) are found to agree with results from direct numerical simulations, typically to within 6%. These methods can be applied to any density perturbation data using the MATLAB graphical user interface EnergyFlux.
Exploring the physics of methane-foam generation for gas mobility control in high-temperature, proppant-fractured reservoirs
(2022-12-05) Parekh, Aashish Trilok; Nguyen, Quoc P.; Katiyar, Amit
Gas EOR through HnP is an increasingly important method of recovering additional oil from fracture-stimulated reservoirs. HnP productivity, however, is hampered by well interference and fracture channeling leading to early gas breakthrough and poor areal sweep efficiency. To mitigate these issues and improve conformance control, foam-generating surfactants have been developed as a method of reducing mobility of the injected gas phase and increasing oil recovery. The experiments outlined in this work investigated foam generation and propagation by an anionic and amphoteric surfactant blend in high-temperature, high-pressure, high-permeability, and high-shear conditions meant to simulate the actual environment of a proppant-filled fracture. Bulk foam tests confirmed the aqueous stability and foaming viability of the surfactant at the proposed temperature, pressure, and salinity. Through several series of floods co-injecting methane gas and the surfactant solution through a proppant-pack at residual oil, the effects of several injection parameters on apparent foam viscosity were investigated. The surfactant exhibited an unusually high transition foam quality at about or greater than 95% as well as expected shear-thinning behavior. When analyzing the effect of pressure on foam generation, an important finding was observed in that foam viscosity linearly decreased with increasing pressure. Another flood series was conducted in an oil free proppant pack and showed that residual oil had no effect on the apparent foam viscosity, meaning oil swelling at higher pressures could not be the reason the inversely linear pressure trend was seen. An additional flood series with nitrogen as the injection gas was completed to see if the hydrophobic attraction between the methane and surfactant tail was responsible for the observed pressure trend, but, despite an increase in apparent foam viscosity, the pressure trend persisted even with nitrogen. Though a conclusion could not be made on the cause of the pressure dependency, previous tests confirmed that the trend is not the result of a system artifact and supported that it must be due to the effect of pressure on surface properties of foam film stabilized by this particular surfactant formulation. Additional tests focused on the effect of pressure on surfactant adsorption and micellar size could prove fruitful in finding an answer.
Interactions between global and local performance incentives on decision-making and categorization
(2010-08) Worthy, Darrell Andrew; Maddox, W. Todd; Markman, Arthur B.; Love, Bradley C.; Beer, Jennifer S.; Loewenstein, Jeffrey
Recent work has shown that the regulatory fit between global approach/avoidance goals and the local approach/avoidance mechanisms of goal pursuit influence cognition and behavior in predictable ways. A regulatory fit leads to an increase in motivation and engagement relative to a regulatory mismatch. The increase in engagement can lead to an increase in cognitive flexibility on cognitively demanding tasks. This work is composed of three inter-related studies that examine how the fit between global performance incentives and local mechanisms of goal pursuit influence decision-making and categorization. In Study 1 I examine how the interaction between global performance incentives and local goal pursuit mechanisms influences decision-making strategies in an experience-based decision-making paradigm. In this paradigm decision-making strategies can be classified as more exploratory or more exploitative. I find that participants in a regulatory fit would exhibit more exploratory decision-making patterns than participants in a regulatory mismatch. In Study 2 I examine how social pressure is related to approach and avoidance-based performance incentives using two types of category-learning tasks. I test the hypothesis that increasing performance pressure will induce an avoidance-based prevention focus which then interacts with the local mechanism of goal pursuit employed in the task (maximizing points gained or minimizing points lost). Participants either perform an explicit, rule-based category-learning task, or an implicit information-integration category-learning task. Behavioral and model-based analyses support the hypothesis that social pressure induces a prevention focus. When the pressure-induced prevention focus aligns with the local goal-pursuit mechanism participants perform better on the rule-based task, but worse on the information-integration task. Study 3 examines the effects of social pressure on categorization in highly-trained participants. Participants performed over 2500 training trials of either a rule-based or an information-integration category-learning task, and then performed another 640 trials after half received a manipulation designed to raise social pressure. Performance was worse on both the rule-based and information-integration task for participants who were under high social pressure compared to participants under low social pressure. The results from all three projects suggest that motivational incentives have a large effect on cognitively demanding tasks.
Optical and vibrational properties of low-symmetry two-dimensional materials under compressive strain
(2019-08-19) Roberts, Richard Hillman, III; Akinwande, Deji
Due to their remarkable mechanical and electronic properties, twodimensional materials have been the subject of avid interest over the last decade and a half. The successful exfoliation of graphene in 2004 was a watershed moment, prompting search for new monolayered materials that could be used in the next-generation of electronic devices. While many of graphene’s admirable traits—record-setting tensile strength, massless dirac fermions, among others—are a result of its highly symmetric “honeycomb” crystal structure, a new class of monolayered materials with low-symmetry structures has recently been gaining interest. Due to their uniquely anisotropic electronic and thermal properties, low-symmetry materials such as ReS₂ and phosphorene are promising candidate materials for thermoelectric and optoelectronic devices capable of leveraging their anisotropy. In this work, we examine the effect of pressure on monolayer ReS₂ and few-layer phosphorene to determine their suitability for strain-tuned and flexible electronic devices
Transport of nobel gases under pressure in geological materials
(2021-07-25) Lumpkin, Samantha Katharine; Haas, Derek Anderson, 1981-
This report intends to elucidate the ways in which noble gases transport through geological materials, and how pressure plays a role in this process. The role of sand is explored, and future experiments with salt are discussed. These experiments give an idea of how noble gases would behave if released underground into geological materials which contain these substances. This is of particular interest for nuclear monitoring purposes. Radioisotopes of xenon, krypton and argon are all of interest due to their long half-lives, low background levels and non-reactive nature. We have chosen to test xenon-132, krypton-84, and argon-40 in our experiments. These are stable isotopes of key gases, which closely mimic the behavior of their radioactive counterparts while being cheaper and safer alternatives. Our results examined how pressure affects the transport of noble gases through geological material and delve into troubleshooting with the Gas Chromatography Mass Spectrometer (GCMS). Evidence was found showing equilibrium times at pressure are much longer than anticipated, however we also learned the GCMS was not well suited for high pressure work in its current configuration and did not yield the anticipated results.