• Uncertainty in fish counting using an echo-counting technique as applied to data from a single-beam sonar

      Lai, Zhiguo (2002-08)
      A model of fish distribution in time and space and a single-beam sonar model are presented. Simulated sonar data are obtained and analyzed using the echo-counting method to determine the estimated number of fish. The results show that (1) when the fish rate is less than 1 fish/s, the error is within plus minus 15% and fish are overcounted more often than undercounted, (2) this method underestimates the number of fish by 57% of the actual number of fish for a fish rate of 5 fish/s, (3) fish counts are dominated by the noise if the threshold is lower than the noise level, (4) by varying the ping rate, the error could be as much as 72% for a fish rate of 10 fish/s and a ping rate of 10 pings/s, (5) by varying the pulse width, the error could be as much as 80% for a fish rate of 10 fish/s and a pulse width of 1.0 ms.
    • Uncertainty in fish location using a split beam sonar

      Ayers, Mark L. (2001-05)
      The enumeration of fish is of critical importance to the management of both commercial and sport fisheries in Alaska and worldwide. Current methods for riverine fish enumeration are inaccurate and unreliable. Improved fish counting accuracy in Alaskan rivers by acoustic methods is required. A split beam sonar system in the presence of noise is modeled. The sonar system including the received sonar pulse, receiver system, transducer beam pattern, propagation losses, and noise are modeled. An analysis of the effects of noise, pulse duration and sampling frequency on the uncertainty in fish location is presented. Signal to noise ratios less than 5 dB can cause significant errors in the calculation of received signal phase. A stationary fish with a signal to noise ratio of 15 dB has approximately plus-minus 0.001 degrees of uncertainty in the angles of arrival. Reducing the SNR to 3 dB the uncertainty increases to plus-minus 3.6 degrees in the angles of arrival.
    • Uncertainty quantification of gas production in the Barnett shale using time series analysis

      Joshi, Kishan Ghanshyambhai; Awoleke, Obadare; Hanks, Catherine; Ahmadi, Mohabbat (2015-12)
      Deterministic methods for evaluating uncertainty in production forecasts for unconventional shale plays are either unreliable or time intensive. This thesis presents an improved methodology for quantifying uncertainty in production forecasts using Logistic Growth Analysis (LGA) and time series modeling. The applicability of the proposed method is tested by history matching production data and providing uncertainty bounds for forecasts from eight Barnett Shale counties. The 80% confidence interval (CI) generated by this method successfully bracketed true production values for all the counties, even when approximately one-third of the data was used for history matching. In the methodology presented, the trend in the production data was determined using two different non-linear regression schemes. The predicted trends were subtracted from the actual production data to generate two sets of stationary residual time series. Time series analysis techniques (Auto Regressive Moving Average models) were thereafter used to model and forecast residuals. These residual forecasts were incorporated with trend forecasts to generate our final 80% CI. To check the reliability of the proposed method, I tested it on 100 gas wells with at least 100 months of available production data. The CIs generated covered true production 84% and 92% of the time when 40 and 60 months of production data were used for history matching, respectively. An auto-regressive model of lag 1 best fit the residual time series in each case. The proposed methodology is an efficient way to generate production forecasts and to reliably estimate uncertainty for short to medium time periods. It includes uncertainty due to parameter estimation using two different regression schemes. It also incorporates the uncertainty due to the variance of the residuals. The method is computationally inexpensive and easy to implement. The utility of the procedure presented is not limited to gas wells; it can be applied to any type of well or group of related wells.
    • Understanding reservoir engineering aspects of shale gas development on the Alaska North Slope

      Nyulund, Anna; Dandekar, Abhijit; Patil, Shirish; Ahmadi, Mohabbat (2015-12)
      Horizontal drilling and multi-stage hydraulic fracturing made it possible to develop US shale resources. Shublik shale is one of such US shale resources - it is one of the largest source rocks for hydrocarbon accumulations located on the Alaska North Slope. This study used the workflow introduced by Mirzaei and Cipolla in 2012 to investigate the effects of fracturing fluid flowback; shale porosity; matrix, fracture and unpropped zone permeability; hydraulic fracture spacing; permeability anisotropy; non-Darcy flow; gas adsorption/desorption using the complex-fracture-network model, referred to as an Unconventional Fracture Model (UFM), and Voronoi grid on well performance in the Shublik shale formation. In addition, the effects of natural fracture network orientation, fracture spacing and length were examined using a single porosity model with incorporated Discrete Fracture Network (DFN). The Schlumberger Mangrove Plug-In for Petrel platform was used to conduct the study. Mangrove has the DFN feature, which can be deactivated in the single porosity model. The results suggested that ignoring fracturing fluid flowback and non-Darcy effects can lead to overestimation of the gas recovery factor. Neglecting gas adsorption/desorption effects leads to underestimation of the gas recovery factor. In addition, smaller fracture spacing leads to a higher gas recovery factor. DFN orientation, fracture spacing and length affect the propped fracture area and should be incorporated into analysis from shale plays since it can result in either overestimation or underestimation of the gas recovery factor depending on fracture network propagation. Finally, examining multiple hydraulic fractures instead of one fracture is more accurate due to the stress shadowing effects and fracture network propagation.
    • Understanding reservoir engineering aspects of shale oil development on the Alaska North Slope

      Zanganeh, Behnam; Hanks, Catherine; Ahmadi, Mohabbat; Awoleke, Obadare (2014-05)
      Horizontal drilling and multi-stage hydraulic fracturing have made the commercial development of nano-darcy shale resources a success. The Shublik shale, a major source rock for hydrocarbon accumulations on the North Slope of Alaska, has huge potential for oil and gas production, with an estimated 463 million barrels of technically recoverable oil. This thesis presents a workflow for proper modeling of flow simulation in shale wells by incorporating results from hydraulic fracturing software into hydraulic fracture flow modeling. The proposed approach allows us to simulate fracture propagation and leak-off of fracturing fluid during hydraulic fracturing. This process honors the real proppant distribution, horizontal and vertical variable fracture conductivity, and presence of fracturing fluid in the fractures and surrounding matrix. Data from the Eagle Ford Shale in Texas was used for this modeling which is believed to be analogous to Alaska's Shublik shale. The performance of a single hydraulic fracture using a black oil model was simulated. Simulation results showed that for the hydraulically fractured zone, the oil recovery factor is 5.8% over thirty years of production, to an assumed economic rate of 200 STB/day. It was found that ignoring flowback overestimated oil recovery by about 17%. Assuming a constant permeability in the hydraulic fracture plane resulted in overestimation of oil recovery by almost 25%. The conductivity of the unpropped zone affected the recovery factor predictions by as much as 10%. For the case investigated, about 25% of the fracturing fluid was recovered during the first 2 months of production; in total, 44% of it was recovered over thirty years. Permeability anisotropy was found to have a significant effect on the results. These results suggest that assuming a constant conductivity for the fractures and ignoring the presence of water in the fractures and the surrounding matrix leads to overestimation of initial production rates and final recovery factors. In addition, the modified workflow developed here more accurately and seamlessly integrates the modeled induced fracture characteristics in the reservoir simulation of shale resource plays.
    • A unified viscoplastic model for the inelastic behavior of ice

      Dasari, Jeevana (2006-08)
      A physics-based SUVIC-I model is proposed for the ductile region of polycrystalline ice. It accounts for mixed hardening and directional softening using the three internal state variables - back stress, yield stress and drag stress. The main objective is to provide the best suitable material parameters for this model. The process to obtain these parameters is discussed in detail. The computational aspect of this model is implemented in the finite element program ABAQUS through a user subroutine UMAT for the axisymmetric and 3D models. The results are validated against the experimental data for constant strain rate and creep tests.
    • Unmanned Aircraft System Assessments of Landslide Safety for Transportation Corridors

      Cunningham, Keith; Olsen, Michael J.; O'Banion, Matt; Wartman, Joseph; Rault, Claire (2016-12)
      An assessment of unmanned aircraft systems (UAS) concluded that current, off-the-shelf UAS aircraft and cameras can be effective for creating the digital surface models used to evaluate rock-slope stability and landslide risk along transportation corridors. The imagery collected with UAS can be processed using a photogrammetry technique called Structure-from-Motion (SfM) which generates a point cloud and surface model, similar to terrestrial laser scanning (TLS). We treated the TLS data as our control, or “truth,” because it is a mature and well-proven technology. The comparisons of the TLS surfaces and the SFM surfaces were impressive – if not comparable is many cases. Thus, the SfM surface models would be suitable for deriving slope morphology to generate rockfall activity indices (RAI) for landslide assessment provided the slopes. This research also revealed that UAS are a safer alternative to the deployment and operation of TLS operating on a road shoulder because UAS can be launched and recovered from a remote location and capable of imaging without flying directly over the road. However both the UAS and TLS approaches still require traditional survey control and photo targets to accurately geo-reference their respective DSM.
    • Unstable Slope Management Program

      Huang, Scott L.; Darrow, Margaret M.; Calvin, Peter (Alaska University Transportation Center, Alaska Department of Transportation and Public Facilities, 2009)
    • Uranium exploration methodology in cold climates

      Sims, J.M. (University of Alaska Mineral Industry Research Laboratory, 1980-03)
      The uranium prospecting boom of the past decade had, as a major consequence, the rapid development and proliferation of exploration methods for source materials. Numerous established methods were developed and refined whilst new techniques were introduced proving, in some instances, to be highly successful. To the explorationist the proliferation of instrumental hardware and detection systems was something of a headache with the result that in uranium exploration, more so than in other types of prospecting, the choice of exploration method at the appropriate stage of prospecting was frequently ill founded. The situation also spawned ‘black box’ purveyors who made extravagant claims for their equipment. Money was wasted through over kill applications of exploration method accompanied in many instances by deficiencies in the interpretation of results. This project was originally conceived as a means of evaluating, reviewing and filtering from a burgeoning array of systems the most appropriate exploration techniques applicable to cold climate environments. This goal has been trimmed somewhat since it had been hoped to incorporate site investigation data assembled in the field by the writer as appropriate case history material. This was not possible and as a consequence this report is a 'state of the art review' of the applicability of currently available techniques in Arctic and Subarctic environments. Reference is made to published case history data, where appropriate, supportive of the techniques or methods reviewed.
    • Use of adaptive filtering techniques for estimating low-frequency electromechanical modes in power systems

      Balasubramanian, Ashok (2006-08)
      Information about the location and strength of low frequency electromechanical modes in power systems reflects the stability of the system. Highly recommended and used techniques like Prony analysis and eigenanalysis require ring down from a disturbance and tedious matrix calculations, respectively, for mode estimation. This work proposes the use of the Least Mean Squares (LMS) adaptive filtering algorithms and its combination with other algorithms for estimating and tracking the modes with respect to time. The mode of interest in this work was the 0.26 Hz mode. An Adaptive Step Size Least Mean Squares (ASLMS) algorithm was introduced in this work to reduce variability in mode estimation for non-stationary environments. The ASLMS algorithms achieved quicker convergence than LMS algorithms. A combination of the ASLMS and the LMS algorithm called the Error Tracking (ET) algorithm was tested, based on the running error in the estimate, to reduce variability while also maintaining reasonable convergence time. The ET algorithm achieved high accuracy, less variable performance and quicker convergence of estimates compared to all the other algorithms. The ET algorithm tracked the 0.26 Hz mode in both the simulated data and the real time data with the least amount of error.
    • Use of Cellular Concrete for Air Convection Embankment to Protect Permafrost Foundations in Cold Regions: Feasibility Study

      Liu, Jenny; Wu, Hanli (2019-08-15)
      The air convection embankment (ACE) is a technique used to protect permafrost from thawing in road construction in cold regions. However, the desired materials needed for ACE are not readily available, which prevents its extensive use in Alaska. To overcome the limitation of traditional ACE, and further improve the cooling effect of ACE, this study investigated the feasibility of using cellular concrete as an alternative material for ACE in cold regions. The heat transfer patterns of the cellular concrete ACE, the crushed-rock ACE, and the sand/gravel embankment were studied using the numerical simulation. The results of the present study show that the cooling performance of both cellular concrete ACE and crushed-rock ACE are superior to the traditional sand/gravel embankment. The cellular concrete ACE has better heat insulation property in the summer, and the crushed-rock ACE has stronger natural convection in winter. For the annual cooling efficiency of the two different ACE techniques, the proposed cellular concrete ACE has a better cooling effect on the foundation soil than the crushed-rock ACE. These results indicate that the thermal conductivity and specific heat capacity of construction materials have significant impacts on the performance of the ACE.
    • The use of flocculants to control turbidity in placer mining effluents

      Shen, Yun-Hwei (University of Alaska Mineral Industry Research Laboratory, 1987)
      In this study, two placer mine discharge waters of different characteristics were tested in order to determine the applicability of organic polymer flocculants to achieve reduced levels of turbidity. The water samples from both mines were characterized both as to their chemical and physical properties. The jar test was employed to establish the optimum operation conditions of the flocculation process. The best results were obtained employing a cationic polymer Superfloc 340 produced by American Cyanamid Company. The optimum dosage for water samples from both mines were 15 ppm and 40 ppm respectively. Optimum agitation time was within the range of 3 to 9 minutes depending on the agitation rate and the pulp density of water sample. The utilization of settling ponds, in conjunction with flocculation is believed to be a practical method to control the turbidity level of placer mine discharge water.
    • The Use of Geofiber and Synthetic Fluid for Stabilizing Marginal Soils

      Hazirbaba, Kenan; Connor, Billy; Davis, Duane; Zhang, Yu (Alaska University Transportation Center, 2007)
    • The Use of Geofibers and Synthetic Fluids Kwigillingok Airport

      Collins, Rodney; Connor, Billy (Alaska University Transportation Center, 2011)
    • Use of Geogrids for Limiting Longitudinal Cracking in Roads on Permafrost

      Savage, Bonnie Mae (1991-05)
      Longitudinal cracking of road embankments results from lateral movement of the subbase which creates a subsurface void space. The void spaces propogate to the surface causing cracks and voids. This is hazardous to motorists and expensive to repair. This thesis examines the use of geogrids to limit lateral spreading thereby preserving safe and useable road surfaces. A field experiment, a full-scale laboratory experiment, a soil arching experiment, and behavioral and theoretical analyses are presented. Soil arching forces are quantified and developed using an experiment based on work done by Terzaghi and Kienzl. A theoretical analysis for quantifying the shear force redistribution to be used for geosynthetic embankment systems, was derived from the Soil Arching Experiment. Relationships of load, embankment resistance, deflection and geometric factors are presented. A comparison of geogrid performance to a geotextile performance for the given relationship is presented as well.
    • Use of H2Ri Wicking Fabric to Prevent Frost Boils in the Dalton Highway Beaver Slide Area, Alaska

      Zhang, Xiong; Presler, Wendy (Alaska University Transportation Center, Alaska Department of Transportation and Public Facilities, 2012)
    • Use of the Micro-Deval Test for Assessing Alaska Aggregates

      Liu, Juanyu; Mullin, Anthony; Rein, Jason (Alaska University Transportation Center, Alaska Department of Transportation and Public Facilities, 2012)
    • User interface and function library for ground robot navigation

      Smith, Micah; Lawlor, Orion; Genetti, Jon; Chappell, Glenn (2017-05)
      A web application user interface and function library were developed to enable a user to program a ground robot to navigate autonomously. The user interface includes modules for generating a grid of obstacles from a map image, setting waypoints for a path through the map, and programming a robot in a code editor to navigate autonomously. The algorithm used for navigation is an A* algorithm modified with obstacle padding to accommodate the width of the robot and path smoothing to simplify the paths. The user interface and functions were designed to be simple so that users without technical backgrounds can use them, and by doing so they can engage in the development process of human-centered robots. The navigation functions were successful in finding paths in test configurations, and the performance of the algorithms was fast enough for user interactivity up to a certain limit of grid cell sizes.
    • User's guide for atmospheric carbon monoxide transport model

      Norton, William R.; Carlson, Robert F. (University of Alaska, Institute of Water Resources, 1976-06)
      In the winter months of Fairbanks, Alaska, a highly stable air temperature inversion creates high levels of carbon monoxide (CO) concentrations. As an aid to understanding this problem, a CO transport computer model has been created which provides a useful tool when used in conjunction with other measurement and analytic studies of traffic, meteorology, emissions control, zoning, and parking management. The model is completely documented and illustrated with several examples. Named ACOSP (Atmospheric CO Simulation Program), it predicts expected CO concentrations within a specific geographic area for a defined set of CO sources. At the present time, the model is programmed to consider automobile emissions as the major CO source and may include estimates of stationary sources. The model is coded for computer solution in the FORTRAN programming language and uses the finite-element method of numerical solution of the basic convective-diffusion equations. Although it has a potential for real-time analysis and control, at the present time the model will be most valuable for investigating and understanding the physical processes which are responsible for high CO levels and for testing remedial control measures at high speed and low cost.
    • Using experimental design and response surface methodology to model induced fracture geometry in Shublik shale

      Poludasu, Venkatasai Sri Chand; Ahmadi, Mohabbat; Hanks, Catherine; Awoleke, Obadare (2014-12)
      The Triassic Shublik Formation of the Alaska North Slope is a world-class resource rock and has been identified as the major source of many of the conventional hydrocarbon accumulations on the North Slope, including Prudhoe Bay. Recent interest in the Shublik as a potential shale resource play has highlighted the need for robust hydraulic fracture modeling and simulation of the interval, but little geologic information is available because of the remote nature of the region and the complex character of the Shublik. In this study, a methodology was developed for identifying the critical variables needed for accurate planning of a hydraulic fracturing treatment in a play like the Shublik where much of the geology remains unconstrained. These identified critical variables can be used to develop a proxy model that can be used in lieu of a numerical simulator. This study was conducted in two stages. The first stage used 2-level fractional factorial design to identify the statistical significance of the input variables on the simulated fracture geometry. This stage was conducted in three phases, each phase incorporating progressively more complex assumptions about geology. Using the three most significant variables identified from first stage, the second stage of this study applies Box-Behnken experimental design and response surface methodology for quantifying functional relationships between input variables and the predicted fracture geometry. A pseudo 3D numerical simulator (Fracpro PT) and MATLAB were used to develop proxy models. These proxy models, typically a polynomial equation, are an easier alternative to Fracpro PT and can predict the fracture geometry with very less computational time. The use of experimental design drastically reduces the number of simulations required to evaluate large number of variables. With only 137 simulations, 26 variables were ranked based on their statistical significance and a non-linear proxy model was developed. Predicted values of the fracture geometry obtained using the proxy models were in good agreement with the simulated values of the fracture geometry (R2 value of 99.39% for fracture length, R2 value of 99.54% for fracture height and R2 value of 98.17% for fracture width).