Browsing by Subject "Roughness"

Now showing 1 - 9 of 9

Bayesian estimation of finite mixture roughness model
(2016-12) Serigos, Pedro A. (Pedro Antonio); Prozzi, Jorge Alberto; Zhang, Zhanmin; Gilbert, Robert B; Müller, Peter; Mikhail, Magdy
Highway infrastructure systems provide a crucial service to society and constitute a major asset with a significant maintenance and rehabilitation cost, highway pavements comprising a major component of the total cost. The increasing need for greater capital investment, in the face of ever-decreasing federal funding to maintain highway infrastructure, highlights the importance of developing and implementing effective methods for managing pavement assets. A key for the success of pavement management is to accurately predict the future condition of the pavements in the network. This dissertation proposes a mixture of regression models to capture the systematic differences in pavement performance not explained by variables typically available in pavement management systems. This approach assumes that the heterogeneous pavement performance, which results from the combined effect of the several unobserved factors and interactions, is manifested through a finite number of latent groups. The estimation of the proposed model allows for defining the parameters of the group-specific models while clustering the observations into the latent groups. The insights provided by the model-based clustering of performance data can also be incorporated into the design of maintenance and rehabilitation strategies, as clustering of sections according to their deterioration rate allows for identifying pavements in the network with structural deficiencies and tailoring actions in response. The gain in model fit, along with the insights provided by the proposed methodology for the unsupervised model-based clustering of pavement performance was demonstrated using experimental data. In addition, the proposed mixture model was applied to develop a Bayesian pavement roughness model specified with variables from an existing pavement management system, plus climatic and preventive maintenance variables, and estimated using nationwide field data from the Long-Term Pavement Performance program. Lastly, the developed roughness mixture model was calibrated for Texas pavement conditions by combining both the nationwide data and data extracted from the processing and merging of various Texas Department of Transportation databases. The proposed methodology produces accurate predictions of the progression of roughness as well as robust estimates of the factor effects driving the deterioration of pavements, which, ultimately, lead to a more efficient management of highway assets.
Constraining fracture permeability by characterizing fracture surface roughness
(2010-12) Al-Johar, Mishal Mansour; Sharp, John Malcolm, 1944-; Ketcham, Richard A.; Cardenas, Meinhard B.
Open and connected fractures, where present, control fluid flow and dominate solute transport. Flow through fractures has major implications for water resource management, underground waste repositories, contaminant remediation, and hydrocarbon exploitation. Complex fracture morphology makes it difficult to quantify and predict flow and transport accurately. The difficulty in usefully describing the complex morphology of a real fracture from a small 3-D volume or 2-D profile sample remains unresolved. Furthermore, even when complex fracture morphology is measured across three-dimensions, accurate prediction of discharge remains difficult. High resolution x-ray computed tomography (HXRCT) data collected for over 20 rock surfaces and fractures provide a useful dataset to study fracture morphology across scales of several orders of magnitude. Samples include fractured rock of varying lithology, including sandstone, volcanic tuffs and crystalline igneous and metamorphic rocks. Results suggest that the influence of grain size on surface roughness is not readily apparent due to other competing variables such as mechanics, skins and coatings, and weathering and erosion. Flow tests of HXRCT-scanned fractures provide real discharge data allowing the hydraulic aperture to be directly measured. Scale-invariant descriptions of surface roughness can produce constrained estimates of aperture variability and possibly yield better predictions of fluid flow through fractures. Often, a distinction is not made between the apparent and true fracture apertures for rough fractures measured on a 2-D topographic grid. I compare a variety of local aperture measurements, including the apparent aperture, two-dimensional circular tangential aperture, and three-dimensional spherical tangential aperture. The mechanical aperture, the arithmetic mean of the apparent local aperture, is always the largest aperture. The other aperture metrics vary in their ranking, but remain similar. Results suggest that it may not be necessary to differentiate between the apparent and true apertures. Rock fracture aperture is the predominant control on permeability, and surface roughness controls fracture aperture. A variety of surface roughness characterizations using statistical and fractal methods are compared. A combination of the root-mean-square roughness and the surface-to-footprint ratio are found to be the most useful descriptors of rock fracture roughness. Mated fracture surfaces are observed to have nearly identical characterizations of fracture surface roughness, suggesting that rock fractures can be sampled by using only one surface, resulting in a significantly easier sampling requirement. For mated fractures that have at least one point in contact, a maximum potential aperture can be constrained by reflecting and translating a single surface. The maximized aperture has a nearly perfect correlation with the RMS roughness of the surface. These results may allow better predictions of fracture permeability thereby providing a better understanding of subsurface fracture flow for applications to contaminant remediation and water and hydrocarbon management. Further research must address upscaling fracture morphology from hand samples to outcrops and characterizing entire fracture networks from samples of single fractures.
Dynamic Modelling for Automobile Acceleration Response and Ride Quality Over Rough Roadways
(Council for Advanced Transportation Studies, 1974-12) Healey, Anthony J.; Smith, Craig C.; Stearman, Ronald O.; Nathman, Edward
Current interest in dynamics and vibration of ground transportation vehicles arises from the fact that excessive levels can lead to unsafe operation and give an uncomfortable ride to passengers. Current work by the U.S. Department of Transportation in high-speed tracked air-cushion and magnetically levitated vehicles centers around suspension design (both active and passive) for isolating guideway roughness effects from the main body of the vehicle. The work described herein arose from a need to evaluate vibration acceptance criteria for use in both vehicle systems design and guideway specification. This report deals with the first part of a study of automobile riding quality. Three different models of an intermediate sedan together with two different models for roadway roughness are compared. Roadway models compared are, first, a random input single track model with statistics governed by a power spectral density proportional to the square of the wavelength and, second, a model using a data sequence with a zero order hold where the data sequence is obtained from measured evaluation profiles of actual roadway sections. Frequency weighted rms acceleration responses are compared with serviceability indices of roadway test sections. It is concluded that the commonly used roadway model is inadequate and that more complete roadway information regarding statistics of right and left wheel tracks, together with a vehicle model including body roll motions, is necessary to predict ride quality. Use of the ISO Standard on Whole Body Vibration Tolerances as a basis of frequency weighting provides a good correlation with subjective response measured in terms of the roadway servicability index.
The effect of grid scale on calibration of two-dimensional river models through the drag coefficient
(2011-05) Chisolm, Rachel Elizabeth; Hodges, Ben R.; Maidment, David R.
New survey technologies are able to provide detailed data on the form and topography of riverbeds. With this increased data resolution, the required computational time rather than data availability has become the limiting factor for river models. Detailed bathymetric data can be used to provide better empirical representation of drag and roughness at fine scales, allowing a priori selection of roughness using known physics rather than a posteriori calibration. However, we do not have sufficient guidance or understanding from the literature to represent known heterogeneities smaller than our practical grid scale. The problem is what to do with known subgrid-scale bathymetric features and roughness when our models must use a coarser computational grid. In this project, we simplify this complex problem to analyzing flow in a simple open channel with a single patch of relatively high roughness against an otherwise uniform background of low roughness. We model this open channel with a two-dimensional, depth-averaged river model. By running multiple simulations using different grid sizes we gain insight into how the relationship between the grid cell size and the patch size affects the appropriate physical selection of roughness parameter. As the primary focus, the present work proposes and investigates several methods for upscaling known fine-scale drag coefficient data to a coarser grid resolution for a model. For the tested conditions, it appears that a simple area-weighted linear average is simple to apply and creates a flow field very similar to the best results achieved by calibration. As a secondary issue, the present work examines grid-dependent behaviors when using model calibration. Although recalibration of models for different grid scales is a common practice among modelers, we could find relatively little documentation or analysis. In our work, we examine both single-cell calibration (i.e. changing roughness in only the cell containing the rough patch) and multiple-grid cell calibration involving neighbor cells. With either method, improving calibration required multiple model simulations and comparative analysis for each tested grid size and was inefficient compared to the upscaling approach. As expected, the calibration at a given grid size was always inappropriate for a different grid size.
Impact of spring-associated riparian vegetation on channel morphology : insights from Henry Mountains, UT
(2019-09-11) Southard, Paul Johnson; Johnson, Joel P.; Rempe, Daniella M.
Riparian vegetation is a key control on alluvial channel morphology, but a more quantitative understanding of its morphological impacts must be developed in order to predict channel change in the face of riparian succession and prescribe vegetation as a river management tool. Recent studies have focused on vegetation's role as a bank-strengthening agent that hinders braiding, increases depth and decreases width in perennial streams. However, the tendency of vegetation to grow on the channel bed, in addition to the banks, in ephemeral streams suggests that it may have entirely different morphological impacts. I examined dryland channels draining the Henry Mountains in southern Utah that are intersected by perennial bedrock springs along their length. Spatial variability in water availability from the spring produces high spatial variability in vegetation. As a result, these channels provide a unique opportunity to study how channel morphology responds to changes in vegetation, and to identify the morphological impact of riparian vegetation in channels that accommodate ephemeral streams. I used 1m-resolution Digital Elevation Models and AnuGA flow modeling software to simulate five discharge scenarios for two roughness conditions in three of these channels, and produced high-resolution datasets of channel geometry and spatial vegetation density. I tested the hypotheses that 1) riparian vegetation has a quantifiable impact on channel morphology in ephemeral streams and 2) the morphological impact of riparian vegetation in channels with channel bed vegetation is different from that in channels with channel bank vegetation. I quantitatively showed that, for these ephemeral streams, channel morphology is dependent on vegetation characteristics. In channels with channel bed vegetation, vegetation causes widening and decreases flow velocity. In channels with only channel bank vegetation, vegetation causes narrowing and deepening. By performing comparisons of sparsely- and densely-vegetated reaches within individual channels, I provided the following quantitative constraints on the relative magnitude of riparian vegetation's impact on channel geometry: Reaches with dense channel bank vegetation are approximately 25% narrower and 25% deeper than sparsely-vegetated reaches. Channel bank vegetation causes narrowing by 12-16% and deepening by 7-11% per 0.1 increase in calculated LiDAR Vegetation Index from the unvegetated cross-section channel geometry. Reaches with dense channel bed vegetation are approximately 20-100% wider and 5-30% slower than sparsely-vegetated reaches. Channel bed vegetation causes widening by 13-29% and slowing by 2-7% per 0.1 increase in calculated LiDAR Vegetation Index from the unvegetated cross-section channel geometry.
Lattice-Boltzmann modeling of multiphase flow through rough heterogeneously wet fractures
(2018-09-05) Estrada Santos, Javier Andres; Prodanović, Maša
Fractures are widely present in the subsurface, often representing primary channels for fluid flow in low permeability rocks. While fracture surfaces are composed by different minerals and are rough by nature, mathematical models to predict flow properties rarely take in account these heterogeneities. Therefore, the pore-scale mechanisms of flow through fractures are not well understood. Because characterizing multiphase flow phenomena in these geometries has received limited attention, this thesis aims to address this issue, by studying the effect of surface roughness and heterogeneous wettability in immiscible displacement through single fractures. Since analytical solutions are restricted to simple domains and obtaining data from laboratory experiments is unpractical, a 3D direct simulation approach via the lattice Boltzmann method was selected. This was chosen based on its rigorous kinetic derivation, its ability to simulate immiscible displacement, and its versatile boundary conditions. To study the effects of surface heterogeneities, synthetic domains exhibiting geometrical mineral arrangements, and self-affine fractures were created to carry out drainage and imbibition simulations with different input parameters. The relationships of different wetting/non-wetting patterns and surface roughness, with interfacial areas, capillary pressure, and residual fluid saturation were quantified. It has been shown that there is an effective heterogeneous feature size related to the fracture dimensions that modifies the capillary pressure behavior, and the shape of an invasive fluid front. We further found that for increasingly rough surfaces, there is a linear relation between the residual non-wetting saturation and capillary pressure with the aperture distribution. Thus, the shape, mineral size ratio, and surface roughness can have a significant effect on flow behavior. The results of this work can be used to better inform field simulations, by providing physically-accurate input parameters to characterize fracture network models, enhanced flow rate predictions for naturally fractured reservoirs can be obtained.
Measurement of roadway roughness and automobile ride acceleration spectra
(Council for Advanced Transportation Studies, 1974-07) Healey, Anthony J.; Stearman, Ronald O.
The present study is designed to support an overall program for the evaluation and establishment of ride quality criteria in transportation systems. This report, which is restricted to the automobile, outlines the procedures and equipment employed to measure, record, and analyze automotive vibrations and highway or roadway roughness. Detailed automobile vibration responses and corresponding roadway roughness have been measured and recorded here for 20 different roadway sections which are typical of those found in the Austin - Travis County, Texas, area. Our highway roughness models are also compared to some of the roughness models found in the literature.
Mechanistic investigation of paraffin deposition in oil-dominated pipes
(2023-12) Burmaster, Derek; Lu, Yingda; Nguyen, Quoc; Prodanovic, Masa; Bahadur, Vaibhav; Bommer, Paul
Paraffin deposition is a complex process that has posed a significant issue for the oil and gas industry for more than half a century. About two decades ago, it was shown that molecular diffusion mechanism was the main driver for the deposition process, leading to the development of several powerful models. The quick progress of those modeling projects has since stagnated, however, despite continued research efforts into the topic. This work presents results from a series of experimental investigations into several previously neglected parameters. The first of those parameters was the material that the deposit is formed on. A custom cold finger experimental apparatus was created. Several data acquisition systems were used to generate both discrete and real-time data on deposit mass, thickness, and composition. Special care was taken to create a series of interchangeable cold fingers with equivalent thermal properties, despite the significant differences in thermal properties of the materials under investigation. The improved thermal control allowed for meaningful analysis between different deposition surface materials, which demonstrated that previous uncontrolled experiments likely overstated the effectiveness of pipeline coating materials. Deposition tests were also conducted on various steels to investigate the possibility of an optimal choice for bare pipelines. It was shown that differences exist between steels, though the benefits may not be worth the differences in cost. The second parameter investigated was the roughness of the surface the deposit is formed on. This work also relied on the cold finger test apparatus but used a set of fingers whose surfaces had been finished in several different methods. As in the previous cold finger experiments, data on deposit mass, thickness, and composition were collected and analyzed. Roughness was shown to play a significant role in the deposition process, affecting all three deposition data sets considered. To further investigate this, an additional test system, the finger press, was also created. The finger press generates direct measurements of the shear strength of the adhesive bond between the deposit and the wall in the actual deposition state, which has never been achieved before. In light of this new type of experimental data and the observations that resulted from it, an expansion of the standard diffusion-gelation model is outlined that includes macroscopic failures of adhesive and cohesive bonds. The third parameter investigated was the inclination of the flow line in which the deposit was formed. These experiments necessitated a third novel experimental apparatus: an inclinable flow loop. The loop can be set to any angle from horizontal to vertical, and has two test sections in opposite directions, allowing for data to be collected at any inclination. As in the cold finger tests, the flow loop tests generated mass, thickness, and composition data. The horizontal case produced the most wax deposition, with symmetrical drops in mass as the inclination was increased or decreased away from the horizontal. Deposit composition seemed to be markedly affected by inclination as well, particularly in laminar flow.
Passenger Response to Random Vibration in Transportation Vehicles: Literature Review
(Council for Advanced Transportation Studies, 1975-06) Healey, Anthony J.
The design concepts used to implement a computer simulation of a land use decision model are described. Sources delineated by a literature search are examined for the statements made ("source postulates") concerning the interactions of leaders of dominant and subdominant social groups when making land use decisions. Specific attention is paid to the role of leader personalities and the power of the social groups represented in the final decision outcome. Source postulates are rewritten in a symbolic logic notation, and a set of "rules of behavior" is derived. Consistency among source postulates and correct implication procedures in deriving rules can be checked via theorem-proving methodology. The second phase of design entails replacing symbolic logic statements with "fuzzy logic" statements and algorithms. The set of rules in either notation constitutes a model, and both notations are programmable.