Browsing by Subject "Density"

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Changes in freeway level of service with the introduction of autonomous and connected vehicles
(2018-12) Espinoza, Edoardo; Machemehl, Randy B.
Connected and Autonomous vehicles (CAVs) have risen in popularity in recent years and are expected to bring with them many changes including driver safety, expansion of ridership from people currently unable to drive, and more travel miles from long trip commuters. From an engineering standpoint, CAVs are expected to bring with them an increase in highway capacities because of their ability to react faster than human drivers and produce shorter time headways between successive vehicles. CAVs are not anticipated to dominate the traffic stream until another 20 to 40 years and are expected to be introduced gradually into the transportation system. Shorter time headways suggest that freeways may be positively affected by the new technology and new procedures will need to be established in order to analyze highway capacities in the future. The 6th Edition Highway Capacity Manual is one of the main sources that is used by the engineering community to estimate capacities of freeway segments. This study documents a new simulation tool to discover the capacity implications for a basic freeway segment of different CAV market penetrations and reduced time headways
CO₂ solubility and dissolution rate: the epic battle between ions and CO₂ for water, energy and space
(2015-12) Gilbert, Kimberly Dawn; Bennett, Philip C. (Philip Charles), 1959-; Cardenas, Meinhard B; Breecker, Daniel O; Zhang, Tongwei; Cygan, Randall T
CO₂ dissolution into deep subsurface brines is regarded as a viable means of reducing CO₂ atmospheric emissions. Dissolved ions affect CO₂ solubility (CCO₂) and the rate of dissolution, but the mechanisms of the effect are not clearly understood and thus CCO₂ prediction is difficult. We measured CCO2 and solution density up to 140°C and 35.5 MPa-PCO₂ in water, NaCl, CaCl₂, Na2SO₄, and NaHCO₃ solutions up to 3.4 molal and Bravo Dome mixed brine. CCO₂ weakly correlated to ionic strength and water activity. Strong correlations (R² > 0.92) were identified between CCO₂ and each of ΔGhydr, ΔHhydr, ΔShydr, and the electrostricted water concentration, ha; calculated from ion concentration and hydration number. Traditional empirical CCO₂ prediction models require extensive experimental work to determine parameters. We use a novel prediction approach by applying a mole balance on water, then evaluating the energy required to remove water from hydrated ions to solvate CO₂. The resulting model developed using moderated multiple regression shows that CCO₂ is dependent on CO₂fugacity (f), temperature (T), ha, and the solution hydration energy (G): all of which are specified or previously catalogued variables. A model (R²=0.92) is generated from 503 data points from this study and literature and includes the squares of each variable and interactions. Interactions between f, T, ha and G evaluated using spot-light analysis indicate that: 1) competition for water molecules significantly impacts CCO₂; 2) T and f interact to exacerbate a decrease in open water structure concentration; and 3) hydrated ions may dampen thermal agitation and reduce open structure collapse caused by increased T. The interactions of this research are likely extensible to the dissolution of any non-polar gas into a salt solution. CO₂ dissolution rate measurements demonstrated that convection occurred in experimental reactors with dissolving CO₂; however, the system was diffusion limited due to a thin diffusion layer. Density measurements revealed salt solution volume decreases with increasing CO₂, which results in: 1) faster mass transfer of dissolved CO₂ and 2) increased CO₂ total storage capacity (TSC). In 1 m Na₂SO₄ at 60°C and 10 MPa volume decreases yielded a 20% TSC increase.
Design and development of an X-ray sensor to measure the density and flow rate of drilling fluids in high pressure lines
(2018-12) Singhal, Vivek, Ph. D.; Oort, Eric van; Chen, Dongmei; Bovik, Alan C; Barr, Ronald E; DiCarlo, David
There is a need for advanced technology that can accurately measure the density and mass flow rate of drilling fluids at the high pressure well inlet in real-time. Current reliance on antiquated metering technologies such as the pressurized mud balance and the pump stroke counter to make these measurements greatly impedes our ability to accurately predict the near well bore pressure profile and measure the delta flow rate, which is one of the primary indicators for trouble events such as kicks or lost circulation. In order to address this gap in technology an X-ray sensor was developed to make real-time measurements at greater than 99% percent accuracy and 1 Hz measurement frequency. The X-ray sensor can measure the density of drilling fluids in the 8 ppg to 20 ppg range and with flow rates of up to 1200 gpm. These measurements are made using 320 kV/1500W polychromatic X-ray source, which is well within the range of readily available industrial X-ray tubes. In the past such measurements would require X-ray voltages that could only be achieved with linear accelerators thereby making the cost and size of equipment non-conducive to the drilling environment. However, recent advances in pipe manufacturing, particularly using a class of low density and high pressure materials known as carbon fiber reinforced polymers (CRPs) and, are now making it viable to re-visit relatively low cost X-rays systems for density and mass flowrate measurements. Windows constructed from CRPs allow us to bypass the high density carbon steel standpipe and make measurements at voltages that do not require a linear accelerator. In this paper we discuss the design and implementation of a CRP based X-ray sensor that is used to measure drilling mud density and mass flowrate at the high pressure well inlet.
Effects of local environmental factors and spatial habitat characteristics on the density of a marine gastropod, Megastraea undosa (Wood 1828)
(2010-08) Abshire, Courtney Burke; Gonzalez-Guzman, Laura Imelda; Keitt, Timothy H.
The ability to identify and define factors which affect the abundance of marine species has been a primary goal of many ecologists. The need to accurately quantify the relationship between an organism and its environment is of critical importance in cases where that organism is the object of commercial harvest and tied to the economic well being of communities. This is especially evident for communities located along the Pacific coast of the Baja California peninsula where local fishing cooperative and their associated communities are dependent on the continuing successful harvest of a limited number of marine species, one of these being the marine gastropod Megastraea undosa (Wood, 1828). I conducted a multi-scale observational study investigating the effects of scale and selected local environmental and regional habitat characteristics of subtidal rocky reefs on the density of M. undosa. The study showed that M. undosa density varied significantly at two scales: quadrat (m2) and reef (100s m2). At the reef level, area and percent total cover were found to have a significant positive relationship with M. undosa density. No measured variable showed a significant association to M. undosa density at the quadrat level. Results suggest that both local and regional factors combine to affect M. undosa density and that their impacts on M. undosa density warrants further study.
Estimation of in-situ fluid properties from the combined interpretation of nuclear, dielectric, optical, and magnetic resonance measurements
(2018-12) Lee, Hyungjoo; Torres-Verdín, Carlos; Daigle, Hugh; Heidari, Zoya; Okuno, Ryosuke; Raizen, Mark
During the last few decades, the quantification of hydrocarbon pore volume from borehole measurements has been widely studied for reservoir descriptions. Relatively less effort has been devoted to estimating in-situ fluid properties because (1) acquiring fluid samples is expensive, (2) reservoir fluids are a complex mixture of various miscible and non-miscible phases, and (3) they depend on environmental factors such as temperature and pressure. This dissertation investigates the properties of fluid mixtures based on various manifestations of their electromagnetic properties from the MHz to the THz frequency ranges. A variety of fluids, including water, alcohol, alkane, aromatics, cyclics, ether, and their mixtures, are analyzed with both laboratory experiments and numerical simulations. A new method is introduced to quantify in-situ hydrocarbon properties from borehole nuclear measurements. The inversion-based estimation method allows depth-continuous assessment of compositional gradients at in-situ conditions and provides thermodynamically consistent interpretations of reservoir fluids that depend greatly on phase behavior. Applications of this interpretation method to measurements acquired in two field examples, including one in a gas-oil transition zone, yielded reliable and verifiable hydrocarbon compositions. Dielectric properties of polar liquid mixtures were analyzed in the frequency range from 20 MHz to 20 GHz at ambient conditions. The Havriliak-Negami (HN) model was adapted for the estimation of dielectric permittivity and relaxation time. These experimental dielectric properties were compared to Molecular Dynamics (MD) simulations. Additionally, thermodynamic properties, including excess enthalpy, density, number of hydrogen bonds, and effective self-diffusion coefficient, were computed to cross-validate experimental results. Properties predicted from MD simulations are in excellent agreement with experimental measurements. The three most common optical spectroscopy techniques, i.e. Near Infrared (NIR), Infrared, and Raman, were applied for the estimation of compositions and physical properties of liquid mixtures. Several analytical techniques, including Principal Component Analysis (PCA), Radial Basis Functions (RBF), Partial Least-Squares Regression (PLSR), and Artificial Neural Networks (ANN), were separately implemented for each spectrum to build correlations between spectral data and properties of liquid mixtures. Results show that the proposed methods yield prediction errors from 1.5% to 22.2% smaller than those obtained with standard multivariate methods. Furthermore, the errors can be decreased by combining NIR, Infrared, and Raman spectroscopy measurements. Lastly, the ¹H NMR longitudinal relaxation properties of various liquid mixtures were examined with the objective of detecting individual components. Relaxation times and diffusion coefficients obtained via MD simulations for these mixtures are in agreement with experimental data. Also, the ¹H-¹H dipole-dipole relaxations for fluid mixtures were decomposed into the relaxations emanate from the intramolecular and intermolecular interactions. The quantification of intermolecular interactions between the same molecules and different molecules reveals how much each component contributes to the total NMR longitudinal relaxation of the mixture as well as the level of interactions between different fluids. Both experimental and numerical simulation results documented in this dissertation indicate that selecting measurement techniques that can capture the physical property of interest and maximize the physical contrasts between different components is important for reliable and accurate in-situ fluid identification
Increased Single-Lift Thicknesses for Unbound Aggregate Base Courses
(1998-10) Allen, John J.; Bueno, Jaime L.; Kalinski, Michael E.; Myers, Michael L.; Stokoe, Kenneth H.
A study was conducted to evaluate the feasibility of compacting unbound aggregate base courses in thicker lifts than currently permitted by state departments of transportation (DOTs). At present, the majority of states allow a maximum lift thickness of 8 inches or less. This project constructed and tested full-scale test sections using a variety of material types. Two test pads were constructed in an aggregate quarry in Texas utilizing crushed limestone. Three crushed granite test sections were built as part of a road widening project in Georgia, and two test pads were constructed of uncrushed and partially crushed gravel with loess fines at a gravel production facility near Memphis, Tennessee. Single-lift thicknesses varied from 6 inches to 21 inches. Moisture contents and densities were evaluated using the Nuclear Density Gauge (NDG). Nondestructive seismic testing, using the Spectral-Analysis-of-Surface-Waves (SASW) technique, was used to evaluate stiffness profiles within the compacted lifts. Cyclic plate load tests were accomplished by means of the Rolling Dynamic Deflectometer (RDD), modified for this static application. Results showed that compaction targets could be attained for lifts up to 21 inches thick. Density and stiffness results for 13-inch thick lifts in the Georgia tests were equal to, or better than, the results for the base placed in two lifts, a 7-inch lift followed by a 6-inch lift. Higher moisture contents during compaction yielded lower shear wave velocity and Young’s modulus values. Seismic results show that the upper 3 inches of the final test pads had lower stiffness values, presumably from lower effective stresses near the surface and possibly from some disturbance caused by the compaction equipment. This zone of lower stiffness and slightly less compaction is less evident in the density measurements.
Monitoring neural regulation and density effects on the social behavior of freely behaving prairie voles
(2021-08-05) Wallace, Gerard Nicolas; Phelps, Steven Michael, 1970-; Ryan, Mike; Hofmann, Johann; Keitt, Timothy; Di Fiore, Anthony
Understanding social behavior requires observing freely behaving animals in natural environments. Ecological context is required to ask meaningful questions in the lab. Further some behaviors only manifest in the wild. Unfortunately, the small rodents that are common in the lab are exceedingly difficult to observe in the wild. Prairie voles are a prominent model in social biology, important for the study of pair bonding, parental care and social buffering. Though prairie voles are socially monogamous, in natural environments pairing and territorial behavior vary with individual differences in neuroanatomy and with differences in population density. First, I tested the hypothesis that the retrosplenial cortex contributes to social and spatial memory in the field. Male prairie voles received retrosplenial cortex lesion or sham treatment. Then pair-bond formation was assessed with the partner preference test in the lab. Mated pairs were then radio-tracked in the field to assess pair-bond maintenance. Following tracking, male spatial memory was assessed with a homing test following a random displacement. Lesions disrupted partner preference in the lab and homing in the field, suggesting a role for the retrosplenial cortex in social behavior and demonstrating a contribution to spatial memory in the field. Second, I deployed an automated radio-telemetry system in the field to better monitor social behavior of freely living prairie voles. I radio-mapped the field site and radio tracked 48 prairie voles. These data were used to train nonlinear least-squares, nonparametic, and Bayesian trilateration localization models. The most accurate model (the Bayesian trilateration) had a median fix error of 4.5 m. The system was then used to observe the activity of freely living prairie voles, uncovering both circadian and ultradian patterns of behavior. Finally, I use our automated telemetry system to detect differences in social behavior using active-RFID and Bayesian trilateration approaches. Three cohorts of 48 prairie voles were tracked at low and high population densities by manual and automated radiotelemetry. Pairing, territorial classification, same-sex, and opposite sex encounter rates were estimated and compared for each method. Despite lower per-fix accuracy Bayesian trilateration was found to have the best agreement with manual telemetry inference of social behavior. Hopefully these studies will provide ecological validation and new observational tools for the study of prairie vole social behavior in the lab and field
Sensitivity of AVO reflectivity to fluid properties in porous media
(2004-05) Stine, Jason Andrew; Tatham, R. H. (Robert H.), 1943-
The Zoeppritz equations used in a typical reflection amplitude versus source-receiver offset (AVO) study to calculate the reflection and transmission coefficients do not directly consider the fluids filling the pore space in a porous solid medium. Although they account for the effects on the density and P-wave and S wave velocities in porous solids, these equations neglect the movements of fluids with respect to the porous framework. In doing so, the effects of the permeability and viscosity of the fluids during flow are ignored. These properties may affect the energy reflected and transmitted at a boundary; therefore, they must be accounted for to give an accurate wave propagation model. Biot theory considers the propagation of elastic waves in a porous elastic solid saturated by a viscous fluid. This theory accounts for the motion of fluids in the interconnected voids of a porous solid, assuming Darcian fluid flow. Biot theory accounts for the propagation of three waves, one rotational (shear) wave and two dilational waves (P-wave and slow wave). Reflection and transmission coefficients are calculated including Biot theory, showing potentially observable differences from the coefficients calculated using the Zoeppritz equations, for different physical situations. The sensitivity of the reflection coefficients to different physical parameters is examined. The goal is to evaluate how the reflection coefficients change as individual parameters, such as viscosity or permeability, are varied, and which parameters affect the reflection coefficients the most. If the reflection coefficient does not change as a parameter is varied, there is no sensitivity to that parameter and information about that parameter cannot be extracted from the data. The sensitivity analysis is complimented by calculating partial derivatives of the expressions for the reflection coefficients with respect to individual parameters, particularly fluid parameters. With this approach, large values of the partial derivative imply large changes in reflection coefficients with respect to a physical parameter indicate the most sensitivity to that parameter in the reflection coefficient. In Biot theory, the solid properties dominate over those of the fluids alone. The fluid properties only impact the reflection coefficients in a significant manner when there is a small contrast in the solid properties across a boundary. If the contrast in solid properties is too large, any effects caused by the fluid properties are insignificant compared to the solid effects. The three shale over sandstone models have too large of a contrast in solid properties to see fluid effects. Conversely, the six models of fluid boundaries within a reservoir sand all have little to no contrast in solid properties, so the fluid effects are evident. For gas-water interfaces, the observable changes in the P-P reflectivity are estimated to be as large as 5% for a 1% change in permeability and 15% for a 1% change in viscosity. When the above criteria for observing the fluid effects are met, the P-wave has sensitivity to viscosity, sensitivity, and porosity, with the reflection coefficients giving the most sensitivity to changes in the fluid viscosity. The apparent sensitivity to porosity is mostly a response to the density change caused by the change in porosity, rather than direct effects of the porosity. Theoretical AVO reflection coefficient curves based on Biot theory are inverted using two and three term AVO inversions based on approximations of Zoeppritz reflectivity. There is significant error in the parameters extracted by the inversion for both the two- and three-term AVO inversions. The three-term Aki and Richards (2002) inversion produces inaccurate values of the physical parameters across the boundary. Standard AVO inversion algorithms based on Zoeppritz reflectivity have problems accurately calculating parameters for a porous medium where fluids can move. An intercept and gradient interpretation algorithm based on Biot theory is desirable to accurately extract physical properties in porous media. A second formulation for reflectivity in a porous elastic solid is examined. In this study the theory developed by de la Cruz and Spanos (1985) is modified from their high viscosity limits, to fit more common lighter-oil viscosity regimes. The equations of motion and boundary conditions developed as part of the Spanos theory are adapted for this application. The reflectivity problem is simplified to an eigenvalue problem, based on a number of assumptions. De la Cruz, Hube, and Spanos (1992) published their computed values of reflection coefficients for high viscosity fluids. However, the complexity of this theory makes it impractical, in this study, to follow through to calculation of reflection coefficients in a porous elastic solid
Spectroscopic measurement of n[subscript e] and T[subscript e] profiles using atomic and kinetic models for Argon in the Texas Helimak
(2013-05) Dodd, Kenneth Carter; Gentle, Kenneth W.
Profiles for electron density and temperature were determined in a self-consistent way using line emission spectroscopy and collisional radiative models for neutral and singly ionized Argon (Ar I and Ar II) in the Texas Helimak. Neutral Argon density profiles were calculated using a kinetic gas model. Electron-impact excitation and Ionization rates were corrected to account for the electron velocity distribution deviating slightly from a true Maxwellian distribution due to inelastic electron-neutral collisions. Results show an electron temperature which roughly agrees with probe diagnostics. This method gives an electron density that is about twice as high, which may be possible from a power balance perspective.
A Study on the Feasibility of Compacting Unbound Graded Aggregate Base Courses in Thicker Lifts Than Presently Allowed by State Departments of Transportation
(1998-10) Bueno, Jaime Luis; Stokoe, Kenneth H.; Allen, John J.
A study was conducted to evaluate the feasibility of compacting unbound aggregates base courses in thicker lifts than currently permitted by state departments of transportation (DOTs). At present, the majority of states allow a maximum lift thickness of 8 inches or less. This project constructed and tested full-scale test sections using a variety of materials types. Two test pads were constructed in an aggregate quarry in Texas utilizing crushed limestone, and three crushed granite test sections were built as part of a road widening project in Georgia. Single-lift thickness varied from 6 inches to 21 inches. Moisture contents and densities were evaluated using the Nuclear Density Gauge (NDG). Nondestructive seismic testing, using the Spectral-Analysis-of Surface-Waves (SASW) techniques, was used to evaluate stiffness profiles within the compacted lifts. Results showed that compaction targets could be attained for lifts up to 21 inches thick. Density and stiffness results for 13-inch thick lifts in the Georgia tests were equal to, or better than, the results for the base placed in two lifts, a 7-inch lift followed by a 6-inch lift. Higher moisture contents during compaction yielded lower shear wave velocity and Young’s modulus values. Seismic results show that the upper 3 inches of the final test pads had lower stiffness values, presumably from lower effective stresses near the surface and possibly from some disturbance caused by the compaction equipment. This zone of lower stiffness and slightly less compaction is less evident in the density measurements.