Application of Streamline Simulation for Gas Displacement Processes

Performance evaluation of miscible and near-miscible gas injection processes is available through conventional finite difference (FD) compositional simulation, which is widely used for solving large-scale multiphase displacement problems that always require large computation time. A step can be taken to reduce the time needed by considering low-resolution compositional simulation. The model can be adversely affected by numerical dispersion and may fail to represent geological heterogeneities adequately. The number of fluid components can possibly be reduced at the price of less accurate representation of phase behaviour. Streamline methods have been developed in which fluid is transported along the streamlines instead of the finite difference grid. In streamline-based simulation, a 3D flow problem is decoupled into a set of 1D problems solved along streamlines, reducing simulation time and suppressing any numerical dispersion. Larger time steps and higher spatial resolution can be achieved in these simulations, particularly when sensitivity runs are needed to reduce study uncertainties. Streamline-based reservoir simulation, being orders of magnitude faster than the conventional finite difference methods, may mitigate many of the challenges noted above. For gas injection, the streamline approach could not provide a high resolution or adequate representation for the multiphase displacement. In this work, the streamline simulations for both compositional and miscible gas injection were tested. In addition, the conventional gas injection scheme and detailed comparison between the FD simulation and the streamline approach are illustrated. A detailed comparison is given between the results of conventional FD simulation and the streamline approach for gas displacement processes. Finally, some guidelines are given on how the streamline method can potentially be used to enhance for gas displacement processes

Effects of axisymmetric contractions on turbulence of various scales

Digitally acquired and processed results from an experimental investigation of grid generated turbulence of various scales through and downstream of nine matched cubic contour contractions ranging in area ratio from 2 to 36, and in length to inlet diameter ratio from 0.25 to 1.50 are reported. An additional contraction with a fifth order contour was also utilized for studying the shape effect. Thirteen homogeneous and nearly isotropic test flow conditions with a range of turbulence intensities, length scales and Reynolds numbers were generated and used to examine the sensitivity of the contractions to upstream turbulence. The extent to which the turbulence is altered by the contraction depends on the incoming turbulence scales, the total strain experienced by the fluid, as well as the contraction ratio and the strain rate. Varying the turbulence integral scale influences the transverse turbulence components more than the streamwise component. In general, the larger the turbulence scale, the lesser the reduction in the turbulence intensity of the transverse components. Best agreement with rapid distortion theory was obtained for large scale turbulence, where viscous decay over the contraction length was negligible, or when a first order correction for viscous decay was applied to the results

Textual and Visual Representation of Hijab in Internet Memes and GIFs

This study provides a preliminary report of veil/hijab representation in the modern social media tools of communication; internet memes and GIFs. It bridges a gap in visual communication research by conducting an integrative -textual and visual- framing analysis of 400 memes and GIFs that used the hashtag #Hijab, to unravel the frames and stereotypes of veiled women in such online visuals. Hijabi Muslim women have been visually represented in media in overgeneralized stereotyped ways, being shown as either oppressed and subservient to others with no individual opinions, or as liberated progressives who resist western hegemony (Khan & Zahra, 2015). The research timeframe comes right after the two terrorist attacks on Muslim mosques in Christchurch, New Zealand, that occurred on 15 March 2019, where an extremist Australian gunman killed 50 people and injured another 50 in the first ever livestreamed shooting video on Facebook (BBC, 2019). Utilizing a visual analysis dual-modality technique, of both textual and visual elements, and through conducting a quantitative content analysis of the most popular, viral, and retweeted hijab memes and GIFs in March 2019, the study contributes to the growing literature of memes and GIFs, and their representation of Muslim women and their body coverage hijab . It, therefore, allows for a deeper understanding of internet memes and GIF\u27 usage, the frames they used in portraying hijab, and their stereotypical effects on the image of contemporary veil and veiled women on digital media, specifically social media platforms. The study codes a sample of 200 internet memes and 200 GIFs based on 9 coding variables to analyze both textual and visual elements. Findings highlight how veil/hijab is represented in modern digital communication tools and suggest that, opposite to negative stereotypes of Muslim women in traditional media, memes and GIFs support hijab and depict veiled Muslim women as happy and respected females. The study also shows that internet memes and GIFs are not the same thing and should be examined accordingly

Fluid-Structure Interaction Modeling of A F/A-18 Twin-Tail Buffet Using Non-linear Eddy Viscosity Models

When turbulent flow generates unsteady differential pressure over an aircraft\u27s structure, this may generate buffeting, a random oscillation of the structure. The buffet phenomenon is observed on a wide range of fighter aircraft, especially fighters with twin-tail. More research is needed to better understand the physics behind the vortical flow over a delta wing and the subsequent tail buffet. This dissertation reports the modeling and simulation of a steady-state one-way fluid-structure interaction for the tail buffet problem observed on a F/A-18 fighter. The time-averaged computational results are compared to available experimental data. Next, computations are extended to simulate an unsteady two-way fluid-structure interaction problem of the tail buffet of a F/A-18 fighter. For the modeling herein, a commercial software ANSYS version 14.0, is employed. For the fluid domain, the unsteady Reynolds-averaged Navier Stokes (URANS) equations with different turbulent models are utilized. The first turbulence model selected is the modified Spalart-Allmaras model (SARRC) with a strain-vorticity based production and curvature treatment. The second turbulence model selected is the Non-linear Eddy Viscosity Model (NLEVM) based on the Wilcox k–ω model. This model uses the formulation of an explicit algebraic Reynolds stress model. The structural simulation is conducted by a finite element analysis model with shell elements. Both SARRC and NLEVM turbulence models are in ANSYS software. The experimental data used for validation were conducted on a simplified geometry: a 0.3 Mach number flow past a 76-deg delta wing pitched to 30-deg. Two vertical tails were placed downstream of the delta wing. The present work is the first ever study of the tail buffet problem of the F/A-18 fighter with two-way fluid-structure interaction using the two advanced turbulence models. The steady-state, time-averaged, one-way fluid-structure interaction case of the present investigation indicates that simulations employing the NLEVM and SARRC turbulence models do not match the experimental data. These results are somewhat expected for the steady-state, one-way simulation, because it involves no force and displacement transfer between the fluid and structural domains. For the unsteady two-way fluid-structure interaction case, both models result in more favorable agreement with the experimental data by optimizing the available computational resources particularly when compared to prior simulations by other researchers. Results from the NLEVM model produce improved pressure predictions on the tail as compared to the results from the SARRC model. Based on the simulation results, it is concluded that the buffet problem should be simulated as a two-way fluid-structure interaction. The NLEVM turbulence model is recommended in predicting vortical flow characteristics over a delta wing. The NLEVM turbulence model is necessary to predict the pressure distribution not only over the aircraft surface but also the tails since they experience the wake of vortices

Experiments on identification and control of inflow disturbances in contracting streams

Vorticity from all surfaces and isolated objects in the vicinity of the fan intake, including the outside surfaces of the fan housing, were identified as the major sources for disturbances leading to blade passing frequency noise. The previously proposed mechanism based on atmospheric turbulence is refuted. Flow visualization and hot wire techniques were used in three different facilities to document the evolution of various types of disturbances, including the details of the mean flow and turbulence characteristics. The results suggest that special attention must be devoted to the design of the inlet and that geometric modeling may not lead to adequate simulation of the in flight characteristics. While honeycomb type flow manipulators appear to be effective in reducing some of the disturbances, higher pressure drop devices that generate adequate turbulence, for mixing of isolated nonuniformities, may be necessary to suppress the remaining disturbances. The results are also applicable to the design of inlets of open return wind tunnels and similar flow facilities

Case of escape in cassava, Manihot esculenta Crantz

Two cassava escapes where collected from cultivated fields near natural habitat in Bolivia. They are described morphologically and analyzed cytogenetically in this study. It is suggested that they are the product of backcrosses of cassava interspecific hybrids with the cultigen itself, and that selective conditions have developed in which certain forms of cassava segregates have adapted to grow wildly in natural habitats near cassava fields. These segregates may hybridize with cultivated cassava upon coming in contact with such varieties. Because these escapes have incorporated useful genes from the wild into their genetic structure, they could be used for cassava improvement since their genetic barriers with other forms of cassava are very weak

SIGHTED: A Framework for Semantic Integration of Heterogeneous Sensor Data on the Internet of Things

AbstractSensors are embedded nowadays in a growing number of everyday life objects. Smartphones, wearables, and sensor networks together play an important role in bridging the gap between physical and cyber worlds, a fundamental aspect of the Internet of Things vision. The ability to reuse sensor data integrated from multiple heterogeneous sources is a step towards building innovative applications and services. In this paper SIGHTED, a sensor data integration framework, is proposed exploiting semantic web technologies and linked data principles. It provides a layered structure as a guideline for integrating sensor data from various sources supporting accessibility and usability. DotThing, a demo platform, is implemented as an instantiation of SIGHTED framework and evaluated. Smartphones and sensor nodes are connected to DotThing showing the ability to query and reuse integrated sensor data from multiple sources to create more flexible horizontal applications. DotThing implementation also demonstrates the need for adding a semantic layer to existing IoT cloud-based platforms, like Xively, that generally lack such layer resulting in proprietary vertical solutions with limited data integration and discovery capabilities. DotThing makes use of vocabularies from existing ontologies on the linked data cloud providing a unified model to annotate data and link it to existing resources on the web

The hunt for the K\'arm\'an "constant'' revisited

The logarithmic law of the wall, joining the inner, near-wall mean velocity profile (MVP) to the outer region, has been a permanent fixture of turbulence research for over hundred years, but there is still no general agreement on the value of the pre-factor, the inverse of the K\'arm\'an ``constant'' or on its universality. The choice diagnostic tool to locate logarithmic parts of the MVP is to look for regions where the indicator function $\Xi$ (equal to the wall-normal coordinate $y^+$ times the mean velocity derivative \dd U^+/\dd y^+) is constant. In pressure driven flows however, such as channel and pipe flow, $\Xi$ is significantly affected by a term proportional to the wall-normal coordinate, of order \mathcal{O}(\Reytau^{-1}) in the inner expansion, but moving up across the overlap to the leading $\mathcal{O}(1)$ in the outer expansion. Here we show, that due to this linear overlap term, \Reytau's of the order of $10^6$ and beyond are required to produce one decade of near constant $\Xi$ in channels and pipes. The problem is resolved by considering the common part of the inner asymptotic expansion carried to \mathcal{O}(\Reytau^{-1}), and the leading order of the outer expansion, which is a \textit{superposition} of log law and linear term L_0 \,y^+\Reytau^{-1}. The approach provides a new and robust method to simultaneously determine $\kappa$ and $L_0$ in pressure driven flows at currently accessible \Reytau's, and yields $\kappa$'s which are consistent with the $\kappa$'s deduced from the Reynolds number dependence of centerline velocities. A comparison with the zero-pressure-gradient turbulent boundary layer, henceforth abbreviated ``ZPG TBL'', further clarifies the issues

Experimental Investigation of the Hydrodynamic Stability of Flow in Rotating Pipes Using Thermistors

The hydrodynamic stability of flow in a rotating pipe Is investigated experimentally using thermistors. The experimental apparatus consists of a rotating pipe made of lucite, 3-1/4 inch inside diameter, six feet long, equipped with porous plugs at the ends to minimize recirculation. The working fluid is water and a range of axial and tangential Reynolds numbers up to 7,000 and 20,000, respectively, is covered. Thermistors were chosen for this study since their high electrical resistivity yields strong signals which permit the use of inexpensive and convenient electronics. They also have a high temperature coefficient of electrical resistance which minimizes the problem of noise due to brushes and slip rings. The intensity of the signal and the signal to noise ratio are better by an order of magnitude than those attainable with platinum film probes. The probes are rugged, inexpensive and are commercially available. The major problem encountered is their low frequency response. This, however, does not limit their usefulness in determining transition from laminar to turbulent flow regimes, as can be seen from the results of the present investigation, which were verified by visual diagnostic techniques utilizing dye streaks and hydrogen bubbles