• Modeling and analysis of masonry electro-thermal heating and storage for optimal integration with remote stand-alone wind-diesel systems

      Sateriale, Maura Eileen; Peterson, Rorik; Wies, Richard; Kim, Sun Woo (2013-12)
      Due to their remote locations and small populations, many remote villages in Alaska generate electricity with microgrids that employ diesel-electric generators for their primary source of power, and supplement this production with wind turbines. In such communities, it is economically advantageous to minimize fuel consumption by shifting as much of the village's energy demands to the wind system as is feasible. When wind turbines produce in excess of the demand, it is possible to use the excess electricity to power resistance heaters to heat water in tanks or masonry. The heat is then stored so that it can be used immediately or in the future to meet the village's heating demand. This is called electrothermal heating (ETH). The goal of this research work is to use MATLAB/Simulink� to model heating scenarios employing masonry electrothermal heaters to investigate how excess electricity from wind can be used for immediate heating needs and storage. The results demonstrate reduced heating oil consumption using electrothermal heating and increased storage potential in conjunction with oil stoves.
    • Modeling and exploring battery management strategies for use of LiCoO₂ lithium polymer cells in cold climates

      Thompson, Isaac D.; Wies, Richard; Raskovic, Dejan; Lawlor, Orion (2018-05)
      As the use of batteries to power vehicles becomes more common, a robust battery management system becomes necessary to monitor and maintain the batteries. Cold weather places a further burden on this system especially in small electric vehicles such as snowmobiles where it is desirable to use every bit of available energy from the battery cells. The problem with current battery management technology is that use of batteries in cold temperatures is often not addressed. The objective of this research was to develop an appropriate model of a lithium polymer cell with a cathode comprised of LiCoO₂ and develop an optimized charge/discharge method taking into account the effects of extreme cold weather and cell state of charge imbalance. A cell model was adapted and tuned that accurately captures the dynamics of a lithium polymer cell when discharged at temperatures below freezing. The model results were verified against cells discharged in an environmental chamber, which allowed accurate control of ambient temperature. Multiple scenarios were explored, looking at the effects of ambient temperature, cell initial temperature, internal heating, battery pack insulation, and how rapidly the cells were discharged. The results of the optimized battery management strategies showed improvements in the energy delivery capability of lithium polymer battery packs for small vehicles operating in extreme cold environments. In addition, this research extended the LiCoO₂ model down to -20 °C using validated data, showed that perceived cell capacity loss at low temperatures is primarily due to increased internal resistance, demonstrated that measured cell terminal voltage can rise under load at low temperatures, and showed that increasing the capacity of a battery pack has a better than linear gain in usable energy versus increased battery capacity. I.e., doubling battery pack capacity will more than double the useable range of the vehicle.
    • Modeling and optimization of hybrid electric power systems for remote locations in extreme northern climates

      Agrawal, Ashish N. (2003-08)
      This thesis presents a long-term performance model of a hybrid electrical power system for remote locations in various parts of the world. The model incorporates the performance of different components of the hybrid power system in extreme northern climates. The hybrid model presented uses the graphical user interface available in MATLAB Simulink. Two variations of the hybrid model were developed. One model consists of a photo voltaic (PV) array with a diesel-battery system and the other model consists of a wind turbine with a diesel-battery system. The main performance criterion by which the system was evaluated is the percentage of fuel savings relative to the diesel only case. The results show the significant savings in fuel consumption due to the penetration of the battery bank, the photovoltaic module and the wind turbines in the diesel-only system, while increasing the overall efficiency of the system. This simulation tool will help designers to determine the best hybrid mix of diesel generation, battery storage, photovoltaics, and wind generation for optimal performance of the system in remote villages like those found in Alaska and other developing countries. Examples are presented based on actual systems in the remote Alaskan communities of Lime Village (PV with a diesel-battery) and Wales Village (wind with a diesel-battery).
    • Modeling Biosorption Of Cadmium, Zinc And Lead Onto Native And Immobilized Citrus Peels In Batch And Fixed Bed Reactors

      Chatterjee, Abhijit; Schiewer, Silke; Barnes, Dave; Johnson, Ron; Tainor, Tom (2012)
      Biosorption, i.e., the passive uptake of pollutants (heavy metals, dyes) from aqueous phase by biosorbents, obtained cheaply from natural sources or industrial/agricultural waste, can be a cost-effective alternative to conventional metal removal methods. Conventional methods such as chemical precipitation, membrane filtration or ion exchange are not suitable to treat large volumes of dilute discharge, such as mining effluent. This study is a continuation of previous research utilizing citrus peels for metal removal in batch reactors. Since fixed bed reactors feature better mass transfer and are typically used in water or waste water treatment using ion-exchange resins, this thesis focuses on packed bed columns. A number of fixed bed experiments were conducted by varying Cd inlet concentration (5-15 mg/L), bed height (24-75 cm) and flow rate (2-15.5 ml/min). Breakthrough and saturation uptake ranged between 14-29 mg/g and 42-45 mg/g respectively. An empty bed contact time of 10 minutes was required for optimum column operation. Breakthrough curves were described by mathematical models, whereby three popular models were shown to be mathematically identical. Citrus peels were immobilized within an alginate matrix to produce uniform granules with higher uptake capacity than raw peels. All breakthrough curves of native and immobilized peels were predicted using external and intra-particle mass transfer resistances from correlations and batch experiments, respectively. Several analogous mathematical models were identified; other frequently used models were shown to be the approximate derivatives of a single parent model. To determine the influence of competing metals, batch and fixed bed experiments were conducted in different binary combinations of Pb, Cd, Zn and Ca. Equilibrium data were analyzed by applying competitive, uncompetitive and partially competitive models. In column applications, high affinity Pb replaced previously bound Zn and Cd in Pb-Zn and Pb-Cd systems, respectively. However, the Cd-Zn system did not show any overshoot. Calcium, which is weakly bound, did not affect target metal binding as much as other metals. Saturated columns were desorbed with 0.1 N nitric acid to recover the metal, achieving concentration factors of 34-129. Finally, 5 g of citrus peels purified 5.40 L mining wastewater.
    • Modeling fish movement in sonar beam

      Chen, Biao (2002-05)
      Enumerating salmon in the Yukon River drainage allows for assessment of annual harvest management guidelines and prediction of long-term salmon population trends in Alaska. Sonar is currently used to enumerate migrating salmon and determine salmon location in the river. To understand these results, a model of fish movement is required. This thesis analyzes the existing sonar data on fish movement to construct a model that predicts typical spatial and temporal distribution of fish. A model of the sonar measurement system, which includes target strength, transmission loss, transducer beam pattern, time delay, and noise is developed. This system will simulate a sonar signature for an arbitrary distribution of fish by making several simplifying assumptions. This thesis compares the simulated system sonar signature with assumed fish distribution to predict the accuracy of the sonar fish counting system.
    • Modeling Impacts of Cold Climates on Vehicle Emissions

      Chung, Serena (Center for Environmentally Sustainable Transportation in Cold Climates, 2017-01-20)
      This project relates to the research thrust area of ‘environmental impact assessment,' specifically the impact of cold climates on vehicle exhaust emissions. Motor vehicles emit pollutants that are harmful to human. Emissions are thought to be elevated during engine cold starts. During winter, low-lying temperature inversion can trap vehicle emissions near the surface, leading to significantly elevated pollutant concentrations. Despite the importance, vehicle emissions data for cold climates are sparse and the accuracy of vehicle emissions model parameterizations for cold climates is not known. The goal of this project is to improve ability of EPA's Motor Vehicle Emission Simulator (MOVES) model to simulate cold start emissions in cold climates
    • Modeling Of A Novel Triple Turbine Solid Oxide Fuel Cell Gas Turbine Hybrid Engine With A 5:1 Turndown Ratio

      Burbank, Winston Starr, Jr.; Witmer, Dennis E. (2009)
      Electrical production using solid oxide fuel cell gas turbine (SOFC-GT) hybrid systems has received much attention due to high-predicted efficiencies, low pollution and the availability of natural gas. Solid oxide fuel cell (SOFC) systems and hybrid variants designed to date have had narrow operating ranges due largely to the lack of control variables available to control the thermal requirements within the SOFC. Due to the higher value of peak power, a system able to meet fluctuating power demands while retaining high efficiencies is strongly preferable to only base load operation. This thesis presents results of a novel SOFC-GT hybrid configuration designed to operate over a 5:1 turndown ratio. The proposed system utilizes two control variables that allow the hybrid to maintain the SOFC stack exit temperature at a constant 1000�C throughout the turndown. The first control variable is the setting of a variable-geometry inlet nozzle turbine, which most directly influences the system airflow. The second control variable is an auxiliary combustor, which allows control of the thermal and power needs of the turbomachinery independently from that of the SOFC. At low turndown the proposed hybrid operates similarly to previous hybrids, in that roughly 80% of the power is delivered from the SOFC. However, the newly proposed hybrid uses the unique turbomachinery to drastically increase the delivered power at higher power demands. A unique aspect of the proposed hybrid is the contribution of half the rated power being supplied by the inexpensive turbomachinery with the expensive SOFC contributing the other half. This will significantly lower system capital costs compared to previous hybrid designs. The proposed hybrid has high efficiencies throughout turndown with peak efficiencies occurring at low turndown levels.
    • Modeling Of Depressurization And Thermal Reservoir Simulation To Predict Gas Production From Methane -Hydrate Formations

      Patil, Shirish L.; Chen, Gang; Huang, Scott L.; Sonwalkar, Vikas S.; Reynolds, Douglas B. (2007)
      Gas hydrates represent a huge potential future resource of natural gas. However, significant technical issues need to be resolved before this enormous resource can be considered to be an economically producible reserve. Developments in numerical reservoir simulations give useful information in predicting the technical and economic analysis of the hydrate-dissociation process. For this reason, a commercial reservoir simulator, CMG (Computer Modeling Group) STARS (Steam, Thermal, and Advanced Processes Reservoir Simulator) has been adapted in this study to model gas hydrate dissociation caused by several production mechanisms (depressurization, hot water injection and steam injection). Even though CMG is a commercially available simulator capable of handling thermal oil recovery processes, the novel approach of this work is the way by which the simulator was modified by formulating a kinetic and thermodynamic model to describe the hydrate decomposition. The simulator can calculate gas and water production rates from a well, and the profiles of pressure, temperature and saturation distributions in the formation for various operating conditions. Results indicate that a significant amount of gas can be produced from a hypothetical hydrate formation overlying a free gas accumulation by several different production scenarios. However, steam injection remarkably improves gas production over depressurization and hot water injection. A revised axisymmetric model for simulating gas production from hydrate decomposition in porous media by a depressurization method is also presented. Self-similar solutions are obtained for constant well pressure and fixed natural gas output. A comparison of these two boundary conditions at the well showed that a higher gas flow rate can be achieved in the long run in the case of constant well pressure over that of fixed gas output in spite of slower movement of the dissociation front. For different reservoir temperatures and various well boundary conditions, distributions of temperature and pressure profiles, as well as the gas flow rate in the hydrate zone and the gas zone, are evaluated.
    • Modeling of wax precipitation

      Bhangale, Amit Y. (2007-12)
      Due to increasing oil demand, oil companies are moving into deep water and arctic environments for oil production. In these regions, due to lower temperature, wax starts depositing when the temperature in wellbore falls below Wax Appearance Temperature (WAT). This leads to reduced production rates and larger pressure drops. Wax problems in production wells are very costly due to production down time and removal of wax. Therefore, it is necessary to develop the solution to overcome wax deposition. Wax precipitation is one of the most important phenomena in wax deposition, and hence, it needs to be modeled. There are various models present in literature. The purpose of this study is to compare two major classes of wax precipitation models. Won's model which considers the wax phase as a non-ideal solution and Pedersen's model which considers the wax phase as an ideal-solution were compared. Comparison indicated that Pedersen's model gives better results but the assumption of wax phase as an ideal solution is not realistic. Hence, Won's model was modified to consider different precipitation characteristics of the different constituents in the hydrocarbon fraction. The results obtained from the modified Won's model were compared with existing models and it was found that predictions from the modified model are encouraging.
    • Modeling snowmelt runoff in an arctic coastal plain

      Carlson, Robert F.; Norton, William; McDougall, James (University of Alaska, Institute of Water Resources, 1974-01)
      Present and impending oil exploration and development activity on Alaska's Arctic Coastal Plain has created a need to better understand the region's water resources. The remoteness of the area and an almost complete lack of hydrologic data preclude the use of usual hydrologic analysis techniques. Attempts by the Institute of Water Resources to synthesize this data led to the development of snowmelt runoff models which simulate the spring runoff, an important part of the hydrologic system. The snowmelt model produces a snowmelt hydrograph which is converted by the runoff model into a runoff hydrograph. The snowmelt model subdivides the snowpack into two layers. Daily climatological parameters govern the heat transfer between snowpack and atmosphere. Once the heat flux received or emitted by the snowpack has been computed, the melting processes within the snowpack are considered. Computed parameters of the snowpack are density, depth, water equivalent, water content, temperature, and thermal quality. The runoff model uses a three-parameter linear storage model to transform the snowmelt hydrograph into a runoff hydrograph. The parameters represent the amount of storage, the rate of runoff, and the lag between snowmelt and runoff. Using Prudhoe Bay weather data as input, and comparing the output to runoff data from the Kuparuk, Putuligayuk, and Sagavanirktok Rivers for the years 1970 and 1971, produced results which indicate that the models perform satisfactorily.
    • Modeling the injection of CO₂-N₂ in gas hydrates to recover methane using CMG STARS

      Oza, Shruti; Patil, Shirish; Dandekar, Abhijit; Khataniar, Santanu; Zhang, Yin (2015-08)
      The objective of this project was to develop a reservoir simulation model using CMG STARS for gas hydrates to simulate the Ignik Sikumi#1 field trial performed by ConocoPhillips at the North Slope, Alaska in 2013. The modeling efforts were focused exclusively on the injection of CO₂-N₂ in gas hydrate deposits to recover methane after an endothermic reaction. The model was history matched with the available production data from the field trial. Sensitivity analysis on hydrate saturation, intrinsic permeability, relative permeability curves, and hydrate zone size was done to determine the impact on the production. This was followed by checking the technical feasibility of the reservoir model for a long-term production of 360 days. This study describes the details of the reservoir simulation modeling concepts for gas hydrate reservoirs using CMG STARS, the impact on the long term production profile, and challenges and development schemes for future work. The results show that appropriate gas mixture can be successfully injected into hydrate bearing reservoir. The reservoir heat exchange was favorable, mitigating concerns for well bore freezing. It can be stated that CO₂-CH₄ exchange can be accomplished in hydrate reservoir although the extent is not yet known since the production declined for long term production period during forecasting study.
    • Modeling the interaction between hydraulic and natural fractures using three dimensional finite element analysis

      Nikam, Aditya Balasaheb; Awoleke, Obadare; Ahmadi, Mohabbat; Dandekar, Abhijit; Chen, Gang; Ahn, Il Sang (2016-08)
      Natural fractures are present in almost every formation and their size and density definitely affect the hydraulic fracturing job. Some of the analysis done in the past shed light on hydraulic fracture (HF) and natural fracture (NF) geometries. The interaction of the HF with existing NF in a formation results in a denser fracture network. The volume of rock covering this fracture network is called the stimulated reservoir volume (SRV). This SRV governs the hydrocarbon production and the ultimate revenue generation. Moreover, past studies show that a microseismic interpreted SRV can be different than the actual SRV. Additionally, there is always limited subsurface access, which makes it imperative to understand the HF – NF interaction to plan and execute a successful hydraulic fracturing job. A three layered, three dimensional complex geomechanical model is built using commercially available finite element analysis (FEA) software. A propagating HF approaching mainly orthogonal NF is studied and analyzed. Cohesive pore pressure elements in FEA software capable of modeling fluid continuity at HF – NF intersection are used to model the HF – NF interaction. Furthermore, a detailed sensitivity analysis considering the effect of stress contrast, job design parameters, NF properties, and properties of the formation is conducted. The sensitivity analysis of properties such as principal horizontal stress contrast, job design parameters, NF properties and properties of target formation reveals a broad variation in the impact of the sensitivity parameters on the HF, NF, and HF-NF geometry and interaction. The observations and the corresponding conclusions were based on broadly classified sensitivity parameters. The most important parameters solely for HF resultant geometry are observed to be a high stress contrast with stress reversal, highest injection rate, and farther NF distance from the injection point. The least important parameter is observed to be the scenario with almost equal horizontal stresses. However, the most important parameter solely for resulting NF geometry is only the high stress contrast with stress reversal. Conversely, for the considered sensitivity cases, the least important parameters are the injection rate, lower injection viscosity (10 cP), higher NF leak-off coefficient, target formation thickness, Young’s modulus, and lowest value of target formation Poisson’s ratio. Collective conclusions for considering HF-NF are also obtained.
    • Modeling the natural freezeback of piles using COMSOL Multiphysics®

      Clausen, Elliot D.; Peterson, Rorik; Shur, Yuri; Perkins, Robert (2017-05)
      Slurried pile foundations installed in predrilled holes are one of the most common foundations for building major structures on permafrost. This installation method relies on the cold permafrost to freeze the backfilled slurry around the piles to provide the strength required to support loads of a structure. Nearly all evaluations of freezeback time to date stems from the work of Frederick Crory presented to the First International Conference on Permafrost in 1963 and published in 1966. Crory never published field data but he provided an equation to determine freezeback time. This work was later expanded upon by G.H. Johnston in 1981 however Johnston gives no explanation for how or why he varied from what Crory had done. The purpose of this research is to check the results predicted by both Crory and Johnston with a contemporary computer modeling using COMSOL ® Multiphysics. Due to the advancement in technology and the power of COMSOL as a program more variables and situations will be able to be examined than what was available to Crory or Johnston at the times of their publications. This will be the first research in over 50 years to revise the work first published by Crory and show that his equation produces results that are significantly shorter than what the model calculates.
    • Moisture-Temperature Realtionships in a Sand Due to Outward, Radial Freezing

      Juel, Erling A. (1989-05)
      A "clean" sand is commonly specified as backfill around the evaporator section of thermosyphons designed to maintain the thermal regime of pernnially, frozen, thaw-unstable soils. A series of laboratory tests were performed to determine the magnitude of moisture migration. The test results indicate the moisture migration can result due to outward radial freezing in a nonfrost susceptible sand possessing a low to moderate degree of saturation. Moisture did not migrate when the sand was saturated prior to freezing. The redistribution of moisture changes the thermal properties of the soil system which effects the maximum radius of freezing by desiccating soil at the outermost radius of influence and increasing the degree of saturation around the evaporator. The desiccated soil region will experience an accelerated rate of thaw due to a lower volumetric latent heat of fusion. In addition, the radius of freezing is reduced as moisture migrates towards the evaporator section. These effects warrant additional considerations that must be addressed when designing refrigerated foundations with thermosyphons.
    • Molecular dynamics simulations to study the effect of fracturing on the efficiency of CH₄ - CO₂ replacement in hydrates

      Akheramka, Aditaya O.; Dandekar, Abhijit; Patil, Shirish; Ahmadi, Mohabbat; Ismail, Ahmed E. (2018-05)
      Feasible techniques for long-term methane production from naturally occurring gas hydrates are being explored in both marine and permafrost geological formations around the world. Most of the deposits are found in low-permeability reservoirs and the economic and efficient exploitation of these is an important issue. One of the techniques gaining momentum in recent years is the replacement of CH₄-hydrates with CO₂-hydrates. Studies have been performed, at both laboratory and field based experimental and simulation scale, to evaluate the feasibility of the in situ mass transfer by injecting CO₂ in gaseous, liquid, supercritical and emulsion form. Although thermodynamically feasible, these processes are limited by reaction kinetics and diffusive transport mechanisms. Increasing the permeability and the available surface area can lead to increased heat, mass and pressure transfer across the reservoir. Fracturing technology has been perfected over the years to provide a solution in such low-permeability reservoirs for surface-dependent processes. This work attempts to understand the effects of fracturing technology on the efficiency of this CH₄-CO₂ replacement process. Simulations are performed at the molecular scale to understand the effect of temperature, initial CO₂ concentration and initial surface area on the amount of CH₄ hydrates dissociated. A fully saturated methane hydrate lattice is subjected to a uniaxial tensile loading to validate the elastic mechanical properties and create a fracture opening for CO₂ injection. The Isothermal Young's modulus was found to be very close to literature values and equal to 8.25 GPa at 270 K. Liquid CO₂ molecules were then injected into an artificial fracture cavity, of known surface area, and the system was equilibrated to reach conditions suitable for CH₄ hydrate dissociation and CO₂ hydrate formation. The author finds that as the simulation progresses, CH₄ molecules are released into the cavity and the presence of CO₂ molecules aids in the rapid formation of CH₄ nanobubbles. These nanobubbles formed in the vicinity of the hydrate/liquid interface and not near the mouth of the cavity. The CO₂ molecules were observed to diffuse into the liquid region and were not a part of the nanobubble. Dissolved gas and water molecules are found to accumulate near the mouth of the cavity in all cases, potentially leading to secondary hydrate formation at longer time scales. Temperatures studied in this work did not have a significant effect on the replacement process. Simulations with varying initial CO₂ concentration, keeping the fracture surface area constant, show that the number of methane molecules released is directly proportional to the initial CO₂ concentration. It was also seen that the number of methane molecules released increases with the increase in the initial surface area available for mass transfer. On comparing the positive effect of the two parameters, the initial CO₂ concentration proved to have greater positive impact on the number of methane molecules released as compared to the surface area. These results provide some insight into the mechanism of combining the two recovery techniques. They lay the groundwork for further work exploring the use of fracturing as a primary kick-off technique prior to CO₂ injection for methane production from hydrates.
    • Monitoring and Analysis of Frozen Debris Lobes, Phase I

      Darrow, Margaret M.; Daanen, Ronald P.; Simpson, Jocelyn M. (Alaska University Transportation Center, Alaska Department of Transportation and Public Facilities, 2012)
    • Monitoring and Analysis of Frozen Debris Lobes, Phase IB

      Darrow, Margaret M. (Alaska University Transportation Center, 2015)
    • Monitoring Winter Flow Conditions on the Ivishak River, Alaska

      Toniolo, Horacio; Vas, D.; Keech, J.; Bailey, J. (Center for Environmentally Sustainable Transportation in Cold Climates, 2017-09)
      The Sagavanirktok River, a braided river on the Alaska North Slope, flows adjacent to the trans-Alaska pipeline for approximately 100 miles south of Prudhoe Bay. During an unprecedented flooding event in mid-May 2015, the pipeline was exposed in an area located approximately 20 miles south of Prudhoe Bay. The Ivishak River is a main tributary of the Sagavanirktok River, but little is known about its water flow characteristics and contribution to the Sagavanirktok River, especially in winter and during spring breakup. To gather this information, we installed water level sensors on two main tributaries of the Ivishak River (Upper Ivishak and Saviukviayak rivers), early in winter season 2016–2017, in open-water channels that showed promise as locations for long-term gauging stations. Our ultimate goal was to find a location for permanent deployment of water level sensors. By February, the first sites chosen were ice covered, so two additional sensors, one on each river, were deployed in different locations. Some of the sensors were lost (i.e., carried away by the current or buried under a thick layer of sediments). Water level data gathered from the sensors showed a maximum change of 1.07 m. Winter discharge measurements indicate a 44% reduction between February and April 2017. A summer discharge measurement shows a 430% increase from winter to summer.
    • Multi-Dimensional Frost Heave Modeling With Sp Porosity Growth Function

      Kim, Koui; Huang, Scott L. (2011)
      This dissertation presents a multi-dimensional frost-heave modeling with coupled heat transfer, moisture transfer, and mechanical analysis. A series of laboratory frost-heave tests was conducted to determine segregation potential (SP) values using the effect of cooling rate and overburden pressure in two different freezing modes. Regardless of the freezing mode, consistent SP values were obtained at the formation of the final ice lens. Continuous heave and water-intake measurements made it possible to determine the time at the formation of the final ice lens. The SP porosity growth function was developed using simulations of the growing ice lens and frozen fringe. The developed frost-heave model was verified by laboratory frost-heave tests in one dimension. The simulated temperature distribution and amount of heave were in good agreement with experimental values. The SP porosity growth function was then expanded to two dimensions to simulate the soil-pipeline interaction of an experimental buried chilled pipeline constructed in Fairbanks, Alaska in the early 2000s. A two-dimensional frost-heave simulation was conducted at the free-field area, where the influence of pipeline resistance in frozen ground was negligible. This model, which considers the effect of frozen soil creep on stress distribution due to temperature variation, analyzed the influence of stress fields on soil frost-heave susceptibility and deformation. Simulations of pipe displacement were conducted for two cases, with and without the use of the long-term creep characteristics of frozen soils. Using the long-term creep characteristics, the simulated result agreed well with the observed value, differing by only a few percentage points. However, without using long-term creep characteristics, the simulated pipe heave was approximately 75% of the observed heave because of an unrealistic stress buildup. Finally, the SP porosity growth function was expanded to predict soil-pipeline interaction around a frozen-unfrozen boundary. Temperature distribution was successfully predicted in both the pre-frozen soil and the unfrozen zones, as well as at the time when differential pipeline movement started. The developed three-dimensional frost-heave model could predict pipe movement and induced bending due to differential frost heave for a 20-year period.
    • Multiphysics Modeling Of Gaseous Contaminant Transport In Deep Open Pit Mines Under Arctic Air Inversions

      Choudhury, Abhishek; Bandopadhyay, Sukumar (2011)
      Entrapment of pollutants in a deep open pit operating in a cold climate could occur due to atmospheric inversion. The process of air inversion is complex and requires thorough understanding in order to design a mine ventilation plan to remove trapped pollutants in open-pit mines operating in the arctic/sub-arctic regions. The objective of this dissertation is to develop a model using Computational Fluid Dynamics (CFD) tools for analysis of gaseous pollutant transport in deep, open pit mines under air inversion in arctic or subarctic regions. An Eulerian 3-D model was used for the development and validation of the CFD model of pollutant transport in an idealized open pit mine. No prior assumptions, turbulent or laminar, were considered for the nature of the flow. The 2-D model results indicated that air velocity, air temperature, diffusivity coefficient and slope angle were important controlling parameters in the inversion process. The flow regime was laminar at the origin, but as the flow progressed toward the center of the pit it changed to quasi-laminar and generated local eddies towards the pit bottom. The total energy of the quasi-laminar flow as well as the small local eddies was not enough to lift the inversion cap. However, a combination of quasi-turbulent flow and the local eddy transport resulted in removal of some of the pollutant mass from the pit bottom, either due to turbulent mixing, or due to advection. Presence of backflow may appear to be a logical mode of flow in deep open-pit mines in arctic regions. Next, the 3D model was validated using data from a selected open-pit mine. Influent air velocity, diffusivity coefficient, larger pit geometry were found to influence the retention and transport of pollutant out of the pit. The most important conclusion that was drawn from this research is that natural ventilation alone cannot remove the pollutants from an open pit or lift the inversion cap.