• Not just small potatoes: a comparison of four agricultural education models in alaska

      Silverman, Annie; Taylor, Karen; Richey, Jean; Herron, Johanna (2016-08)
      Agricultural education is a means of increasing food security, increasing willingness to try new fruits and vegetables, improving test scores, and increasing community resiliency. School gardens, which are one form of agricultural education, are the primary focus of this thesis. In order to identify barriers to maintaining school garden programs, semi-structured interviews were conducted at four school sites in the Fairbanks area. In order to compare emerging themes from the interview data in the Fairbanks area to school sites throughout the state, a survey was also administered through Survey Monkey to schools that received the Alaska state Farm to School grant between the years 2011-2014. Using Diffusion of Innovation Theory as a theoretical lens to perform qualitative data analyses, several emerging themes are highlighted including: An increase in student’s nutritional awareness, children’s love of dirt, participant empowerment, the need for more time, a decrease in productivity where uncertainty is present, and the need to further develop communication channels between agricultural education practitioners. Recommendations are made based upon findings to further support the creation and maintenance of agricultural education projects throughout the state.
    • Not only an athlete: a curriculum for athletes at NCAA institutions

      Sawchuk, Jamie; Cook, Christine; Sheppard, Dani; Simpson, Joni (2016)
      Despite there being plenty of research regarding identity, athletic identity, and athlete transition, there is limited research on assisting athletes with blending their athletic identity with other roles in their life. Most retired athletes have difficulties letting go of their athletic identity, creating a new non-athletic identity and getting a job. Olympic committees, professional sport organizations, and collegiate athletics have created different transition programs for their athletes to aid them in transitioning to their life upon athletic retirement by helping them realize skills learned from sport are transferrable into the workforce and other areas of life. Researchers have found that athletes should not let go of their athletic identity; but rather learn to blend their athletic identity with their other identities. The following examines the extent to which student-athletes identify with their athletic identity, athletic retirement symptoms, and current athlete transition programs. The end product is a four year curriculum geared towards college level student-athletes.
    • A novel low-cost autonomous 3D LIDAR system

      Dial, Ryker L.; Bogosyan, Seta; Hatfield, Michael; Lawlor, Orion (2018-05)
      To aid in humanity's efforts to colonize alien worlds, NASA's Robotic Mining Competition pits universities against one another to design autonomous mining robots that can extract the materials necessary for producing oxygen, water, fuel, and infrastructure. To mine autonomously on the uneven terrain, the robot must be able to produce a 3D map of its surroundings and navigate around obstacles. However, sensors that can be used for 3D mapping are typically expensive, have high computational requirements, and/or are designed primarily for indoor use. This thesis describes the creation of a novel low-cost 3D mapping system utilizing a pair of rotating LIDAR sensors, attached to a mobile testing platform. Also, the use of this system for 3D obstacle detection and navigation is shown. Finally, the use of deep learning to improve the scanning efficiency of the sensors is investigated.
    • Novel methods of disease surveillance in wildlife

      Hansen, Cristina M.; Hueffer, Karsten; O'Hara, Todd; Leigh, Mary Beth; Ferrante, Andrea (2015-05)
      Both infectious and noninfectious disease agents in wildlife impact human health and accurate research, monitoring, and diagnostic methods are necessary. The objectives of the research reported here were to develop and implement novel methods for bacterial and toxicological disease agent surveillance in wildlife. This dissertation begins with a review of tularemia, an important zoonotic disease to the state of Alaska and the Northern hemisphere. In chapter two, I show the development and implementation of broad-based PCR and quantitative PCR (qPCR) surveillance methods for bacterial DNA in tissue samples; 1298 tissue samples were assayed, numerous potential bacterial pathogens were identified and qPCR detection limits were quantified for various tissue matrices. Chapter three describes an investigation into microbial infection as a source of embryo mortality in greater white-fronted geese (Anser albifrons) in Arctic Alaska. This chapter builds upon our previously developed PCR surveillance techniques by which I demonstrated that bacterial infection is responsible for some greater white-fronted goose embryo mortality in Arctic Alaska. Chapter four describes the development and validation of a cellulose filter paper method for quantifying total mercury in whole blood. I determined that filter paper technology is useful for monitoring total mercury in whole blood, with excellent recoveries (82 - 95% of expected values) and R2 values (0.95 - 0.97) when regressed against the concentration of total mercury in whole blood, the technique generally considered as the "gold standard" for mercury detection. These methods will aid in the accurate detection of disease agents in wildlife as demonstrated by our white-fronted goose work.
    • A novel virtual reality-based system for remote environmental monitoring and control using an activity modulated wireless sensor network

      Montz, Benjamin; Raskovic, Dejan; Mayer, Charles E.; Thorsen, Denise (2019-08)
      The ability to monitor and control a home environment remotely has improved considerably in recent years due to improvements in the computational power, reduction in physical size, reduced implementation cost, and widespread use of both wireless sensor networks and smart home systems. This thesis presents a remote environment management system that integrated a custom wireless sensor network that monitored environmental factors in multiple locations, a smart system that controlled those factors, and a virtual reality system that functioned as a remote interface with the environment. The resulting system enabled a user to efficiently interact with a distant environment using an immersive virtual reality experience. The user was able to interact with the remote environments by issuing voice commands, performing hand gestures, and interacting with virtual objects. This type of system has applications in many fields ranging from healthcare to the industrial sector. The case study system that was designed in this thesis monitored and controlled the environments of several rooms in a home. A novel approach to modulating the activity of the wireless sensor network was implemented in this system. The rate at which the sensor nodes collected and transmitted data was modulated based on the visibility of the virtual objects called VSNs. These virtual sensor nodes displayed the sensor node measurements in virtual reality. This method was expanded upon using a motion prediction algorithm that was used to predict if the virtual sensor nodes were going to be visible to the user. This prediction was then used to modulate the activity of the wireless sensor network. These activity modulation algorithms were used to reduce the power consumption of the wireless sensor network and thus increasing its operational lifespan, while simultaneously reducing unnecessary RF signals in the environment that can interfere with the operation of other wireless systems. These algorithms would be crucial for systems monitoring complex sensor-rich environments where reducing the data transmitted and extending the system's lifespan was paramount, such as managing the environments of many rooms in a large industrial park or controlling the environments of spacecraft from Mission Control on Earth.
    • Nucleic Acid Ratios As An Index Of Growth And Nutritional Ecology In Pacific Cod (Gadus Macrocephalus), Walleye Pollock (Theragra Chalcogramma), And Pacific Herring (Clupea Pallasii )

      Sreenivasan, Ashwin; Smoker, William (2011)
      Pacific cod (Gadus macrocephalus), walleye pollock (Theragra chalcogramma), and Pacific herring (Clupea pallasii) are among the most ecologically and commercially important species in the North Pacific Ocean. In spite of their importance, little is known about larval and juvenile growth strategies in these fish. Since larval and juvenile fish growth may determine future growth, possibly affecting recruitment success, assessments of growth strategies might improve predictive growth models. Nucleic acid ratios (RNA/DNA) can have applications as a sensitive growth index in larval and juvenile Pacific cod, walleye pollock, and Pacific herring, and can potentially be used to determine growth responses and energetic assessments at the cellular level. Determining physiological growth responses in these fish after exposure to different temperatures and nutritional states can help in understanding growth strategies and condition. Nucleic acid ratios from white muscle of juvenile Pacific herring and whole-body Pacific cod and walleye pollock larvae were used as a cellular growth index to provide energetic assessments in these species. Growth responses were studied in these fish across a range of temperatures and nutritional states. Growth was compared between fed, starved/fed and terminally starved Pacific herring cultured at 6.5�C, 8.5�C, and 12.5�C. Relative to fed controls, starved/fed fish showed similar RNA/DNA ratios and soluble protein concentration, but reduced mass. Nucleic acid ratios in starved/fed fish during the starvation phase, and in terminally starved fish, indicated incipient terminal starvation. Also, a seasonal variation of RNA/DNA, protein concentrations and total body lipid concentrations was seen in fed fish, reflecting changes in resource allocation. Early growth was compared in yolk-sac Pacific cod and walleye pollock larvae cultured at 5�C and 8�C, and in yolk-sac Pacific cod larvae cultured in two nutritional states (fed and starved). Growth responses in Pacific cod and walleye pollock larvae were affected by small differences in temperature. Exposure to the lower temperature resulted in higher RNA/DNA in both Pacific cod and walleye pollock larvae. Based on nucleic acid patterns with larval development, it was possible to identify distinct growth stanzas in Pacific cod larvae.
    • Numerical analysis of structural behavior of welded wire reinforcement in reinforced concrete beams

      Balasubramanian, Radhakrishnan; பாலசுப்ரமணியன், ராதாகிருஷ்ணன்; Hulsey, J. Leroy; Ahn, Il-Sang; Perreault, Paul V.; Lin, Chuen-Sen (2016-05)
      Modernization and industrialization have paved the way for the construction industry of India to expand. On the other hand the Indian construction industry is set to face an acute workforce shortage. The shortage of construction workers has in fact slowed down the growth of this industry in major cities across the country and escalated its cost by 40 percent. An alternative way to replace the labor force is by automation techniques. This study is a numerical analysis to evaluate structural behavior of simply supported concrete beams reinforced with welded wires in comparison with mild steel reinforced concrete beams. Welding conventional steel bars (60 ksi) reduces their shear strength by 50 percent. Welded Wire Reinforcement (80 ksi), with its greater strength, higher durability, significantly lower placing and overall cost, provides an alternative and perhaps a better substitution for mild steel bars. The commercial finite element analysis program, ABAQUS, was used to model the non-linear behavior of reinforced concrete beams. In order to evaluate the structural behavior of welded wire reinforced concrete beams, different configurations of longitudinal and transverse wires have been considered. First, different types of stirrup configurations in a rectangular reinforced concrete beam are compared with a conventional reinforced beam. Second, a structurally performing welded wire configuration is compared with a Mexican chair styled reinforcement configuration. This part of the analysis is evaluated for a T–beam, used for building roof applications.
    • A numerical analysis of the distribution of the benthic infauna of the southeastern Bering Sea shelf

      Haflinger, Karl E. (1978-12)
      The continental shelf region of the southeastern Bering Sea may be classified into five provinces (station groups) based on infaunal distribution. Three large station groups lie in adjacent bands extending from the Alaskan coast to the shelf break, roughly paralleling the bathymetry. Two smaller groups occupying positions at the head of Bristol Bay and off Nunivak Island were identified. Stations in the northwestern section of the study area (near the Pribilof Islands) show no strong affinity to the major station groups. Fourteen major biocoenoses identified on the basis of species distribution show strong correlation with the spatial positioning of station groups. Spatial patterning of these species groups is described on the basis of their representation at station groups. Characteristic differences in trophic structure between station groups are attributed to the effects of storm-induced turbulence in nearshore environments and periodic intensive input of organic carbon in the midshelf region.
    • Numerical analysis of the stability of a column laterally restrained by a flexible brace

      Kulchitskaya, Natalia; Кульчицкая, Наталья Борисовна; Hulsey, Leroy; Yang, Liao; Metzger, Andrew; Shur, Yuri (2014-08)
      The paper analyses the behavior of a structure which includes a classically restrained steel column under an axial load and a single flexible brace attached at an arbitrary point along the column to restrict its lateral deformation. The column is assumed to have an initial imperfection limited according to the current code requirements. Focusing on lateral deformations only, the paper studies the maximum load the system can resist before failure, as well as a brace force arisen at this load. Due to the complexity of the problem when it is extended from the elastic region to the plastic domain, a numerical solution is utilized. In the current work, a student version of AbaqusTM provides results of finite-element analysis implemented for a variety of ASTM A992 steel W-Shaped columns. The results confirm that the failure load and brace force highly depend on brace location and its stiffness. It is also shown that the current code provision of a brace load is not always conservative for braces shifted from the center of the column.
    • Numerical investigations of the hydrography, dynamics, and ice distributions of Chukchi Sea shelf

      Lu, Kofan; Danielson, Seth; Weingartner, Thomas; Hedstrom, Kate; Shimada, Koji; Winsor, Peter (2019-08)
      Warm, moderately salty Bering Sea Water (BSW) carried into the Chukchi Sea through Bering Strait provides an oceanic heat flux for melting sea ice comparable to that of the solar heat flux. Intrusions of BSW transport heat and nutrients via intrapycnocline eddies vertically beneath the sea ice and laterally across structural fronts near the ice edge, setting up hydrographic features important to ice edge communities and the seasonal evolution of the ice melt-back. However, the intrapycnocline eddy dynamics and associated hydrography near the fronts have not previously been well described or characterized. Three numerical models using the Regional Ocean Model System (ROMS) are integrated to systematically investigate the importance of the intrapycnocline eddy field and the factors that affect its dynamics. The models suggest that the heat transported by eddies depends on frontal stratification, which is influenced primarily by the Bering Strait inflow discharge and salinity. The eddy field is also indirectly modified by the sea surface height, which varies with strong winds. Two frontal zones near the ice edge are identified according to the model-derived hydrographic structures and eddy dynamics: the Shelf Water Transition Zone (SWTZ) and the Melt Water Transition Zone (MWTZ). Improved understanding of these frontal zones will benefit future research of the ice edge ecosystem. Our models show a noticeable effect of strong wind events on ice edge displacement and vertical transports, both of which may be important to primary production in the frontal zones. Changing winds associated with increasing sea surface temperatures could alter the manifestation of the processes highlighted in this study.
    • Numerical Method For Tsunami Calculation Using Full Navier -Stokes Equations And The Volume Of Fluid Method

      Horrillo, Juan J.; Kowalik, Zygmunt (2006)
      A two-dimensional numerical model was developed to study tsunami wave generation, propagation and runup. The model is based on solving the Navier-Stokes (NS) equations. The free-surface motion is tracked using the Volume of Fluid technique. The finite difference two-step projection method is used to solve NS equations and the forward time difference method to discretize the time derivative. A structured mesh is used to discretize the spatial domain. The model has been conceived as a versatile, efficient and practical numerical tool for tsunami computation, which could address a comprehensive understanding of tsunami physics with the ultimate aim of mitigating tsunami hazards. The prediction capability of tsunami generation, propagation and runup is improved by including more accurately the effects of vertical velocity/acceleration, dispersion and wave breaking. The model has the capability to represent complex curved boundaries within a Cartesian grid system and to deal with arbitrary transient-deformed moving boundaries. The numerical model was validated using laboratory experiments and analytical solutions. The model was used as a tool to determine the adequacy of the shallow water (SW) approximation in the application of tsunami simulations. Numerical results were compared with experimental data, analytical solutions and SW results in terms of the time-history free surface elevations and velocity. Reasonable agreements were observed based on the spatial and temporal distributions of the free surface and velocity.
    • Numerical modeling and remote sensing to determine depths of lava tubes and buried cylindrical hot sources

      Berthelote, Antony Ray (2005-08)
      Estimating depths of buried lava tubes is important for determining the thermal budgets and effusion rates of certain volcanic systems. This research uses a laboratory experiment scaled to an observed lava tube system to measure the 3D temperature field surrounding a buried depth adjustable glass tube with hot honey flowing through it at varying conditions such as flow rate and temperature. Numerical techniques are used to model the laboratory experiment. The input parameters are then applied to non-laboratory situations. The surface thermal distributions from these models are analyzed to empirically derive a depth estimation function using regression techniques. This depth function is the first scaleable depth estimation technique which can be solved with remote sensing data alone. The minimum temperature, maximum temperature and width of a Lorentzian distribution, fit to a surface thermal transect, are used in the function to predict depth to the hot source. Sensitivity and error analysis of the function is carried out for depths ranging from 0.01 m to ±60 m with good results. The function gives accurate depth estimates of 0.2 m for extreme arctic environments, ±0.3 m for lava tubes and ± 55 m for subsurface coalfires.
    • Numerical modeling of lava flow cooling applied to the 1997 Okmok eruption: comparison with AVHRR thermal imagery

      Patrick, Matthew R. (2002-05)
      Throughout February and March of 1997, Okmok volcano, in the eastern Aleutian Islands of Alaska, erupted a 6 km long lava flow of basaltic a'a within its caldera. A numerical model for lava flow cooling was developed, building upon existing lava cooling models, and applied to the flow to better understand the nature of its cooling. The model predictions were then compared to Advanced Very High Resolution Radiometer (AVHRR) data collected over the flow. Daily data of rainfall and ambient temperature, as opposed to yearly averages used in comparable models, greatly increased the accuracy of the model. Furthermore, convective cooling of the lava surface was observed to be the dominant heat loss process during extended cooling indicating the convective heat transfer coefficient is a prime determinant of the accuracy of the model. The model's flexibility allows application to flows beside that of the 1997 Okmok eruption.
    • Numerical Modeling Of Seasonally Freezing Ground And Permafrost

      Nicolsky, Dmitry J.; Romanovsky, Vladimir (2007)
      This thesis represents a collection of papers on numerical modeling of permafrost and seasonally freezing ground dynamics. An important problem in numerical modeling of temperature dynamics in permafrost and seasonally freezing ground is related to parametrization of already existing models. In this thesis, a variation data assimilation technique is presented to find soil properties by minimizing the discrepancy between in-situ measured temperatures and those computed by the models. The iterative minimization starts from an initial approximation of the soil properties that are found by solving a sequence of simple subproblems. In order to compute the discrepancy, the temperature dynamics is simulated by a new implementation of the finite element method applied to the heat equation with phase change. Despite simplifications in soil physics, the presented technique was successfully applied to recover soil properties, such as thermal conductivity, soil porosity, and the unfrozen water content, at several sites in Alaska. The recovered properties are used in discussion on soil freezing/thawing and permafrost dynamics in other parts of this thesis. Another part of this thesis concerns development of a numerical thermo-mechanical model of seasonal soil freezing on the lateral scale of several meters. The presented model explains observed differential frost heave occurring in non-sorted circle ecosystems north of the Brooks Range in the Alaskan tundra. The model takes into account conservation principles for energy, linear momentum and mass of three constituents: liquid water, ice and solid particles. The conservation principles are reduced to a computationally convenient system of coupled equations for temperature, liquid water pressure, porosity, and the velocity of soil particles in a three-dimensional domain with cylindrical symmetry. Despite a simplified rheology, the model simulates the ground surface motion, temperature, and water dynamics in soil and explains dependence of the frost heave on specific environmental properties of the ecosystem. In the final part, simulation of the soil temperature dynamics on the global scale is addressed. General Circulation Models are used to understand and predict future climate change, but most of them do not simulate permafrost dynamics and its potentially critical feedback on climate. In this part, a widely used climate model is evaluated and the simulated temperatures are compared against observations. Based on this comparison, several modifications to the Global Circulation Models are identified to improve the fidelity of permafrost and soil temperature simulations. These modifications include increasing the total soil depth by adding new layers, incorporating a surface organic layer, and modifying the numerical scheme to include unfrozen water dynamics.
    • Numerical modeling of two-dimensional temperature dynamics across ice-wedge polygons

      Garayshin, Viacheslav Valer'evich; Гарайшин, Вячеслав Валерьевич; Romanovsky, Vladimir; Rybkin, Alexei; Nicolsky, Dmitry; Hinzman, Larry (2017-05)
      The ice wedges on the North Slope of Alaska have been forming for many millennia, when the ground cracked and the cracks were filled with snowmelt water. The infiltrated water then became frozen and turned into ice. When the annual and summer air temperatures become higher, the depth of the active layer increases. A deeper seasonal thawing may cause melting of ice wedges from their tops. Consequently, the ground starts to settle and a trough begins to form above the ice wedge. The forming trough creates a local temperature anomaly in the surrounding ground, and the permafrost located immediately under the trough starts degrading further. Once the trough is formed, the winter snow cover becomes deeper at the trough area further degrading the permafrost. In this thesis we present a computational approach to study the seasonal temperature dynamics of the ground surrounding an ice wedge and ground subsidence associated with ice wedge degradation. A thermo-mechanical model of the ice wedge based on principles of macroscopic thermodynamics and continuum mechanics was developed and will be presented. The model includes heat conduction and quasi-static mechanical equilibrium equations, a visco-elastic rheology for ground deformation, and an empirical formula which relates unfrozen water content to temperature. The complete system is reduced to a computationally convenient set of coupled equations for temperature, ground displacement and ground porosity in a two-dimensional domain. A finite element method and an implicit scheme in time were utilized to construct a non-linear system of equations, which was solved iteratively. The model employs temperature and moisture content data collected from a field experiment at the Next-Generation Ecosystem Experiments (NGEE) sites in Barrow, Alaska. The model describes seasonal dynamics of temperature and the long-term ground motion near the ice wedges and helps to explain destabilization of the ice wedges north of Alaska's Brooks Range.
    • Numerical modeling study of the circulation in the Gulf of Alaska

      Bang, Inkweon (1991)
      A series of numerical experiments are performed to simulate the Gulf of Alaska circulation and to examine the dynamical ocean response to the annual mean and seasonal forcing using a primitive equation model (Semtner 1974). The model domain encompasses the North Pacific north of 45$\sp\circ$ N and east of 180$\sp\circ$ and is surrounded by artificial walls in the south and west. Biharmonic diffusion is used in the interior to excite mesoscale eddies. A sponge layer with high Laplacian diffusion is incorporated near the western boundary. Horizontal resolution of 30$\sp\prime$ x 20$\sp\prime$ and 20 vertical levels are used to resolve the mesoscale topography and eddies. Wind stress computed from sea level atmospheric pressure and temperature and salinity data of Levitus (1982) are used. A diagnostic model produces a circulation in the Gulf of Alaska which agrees with observed patterns. In a three-layer flat-bottom baroclinic model, baroclinic Rossby waves propagate at 0.8 cm/sec and it takes a decade for spin-up to be completed. Baroclinic models forced by the annual mean wind and thermohaline forcings show the generation of eddies by baroclinic instability. The eddies in the flat-bottom model have a period of 75 days and are interpreted as barotropic Rossby waves. In the model with topography, the period of dominant eddies is 3-4 years and they are interpreted as baroclinic Rossby waves. Anticyclonic eddies near Sitka show similar characteristics as the Sitka eddy. They propagate westward and cause meanders in the Alaska Stream near Kodiak Island. The abnormal shift of the Alaska gyre in 1981 is probably due to the presence of one of these anticyclonic eddies. A flat-bottom model with seasonal forcing shows a large seasonal variability. When bottom topography is present, however, seasonal response is greatly reduced due to the dissipation of barotropic response by bottom topography. The seasonal baroclinic model shows a similar seasonal variability to the seasonal barotropic model indicating that the seasonal response is mainly barotropic. Eddies are also excited in the seasonal case and are almost identical to those of the annual mean case.
    • Numerical modeling study of the circulation of the Greenland Sea

      Masllowski, Wiesllaw (1994)
      This study is a simulation of the circulation of the Greenland Sea aimed at modeling some of the issues related to the Great Salinity Anomaly (GSA) and deep water formation using a primitive equation ocean general circulation model (Semtner, 1974). The features of the model include: (1) a high resolution, (2) real topography, (3) open boundaries at the south and north, and (4) temporally variable wind and thermohaline forcing. The model is used to study: (1) the spreading of a fresh water anomaly, (2) the mechanisms of cross frontal mixing that lead to deep water formation, (3) the general circulation of the deep and upper layers of the ocean and their dependence on wind and thermohaline forcing, and (4) the possible implications of meso-scale and large-scale variability on climate change. One of the major results of this work is the simulation of continental shelf waves propagating along the shelf slope of Greenland between 77$\sp\circ$N and 72$\sp\circ$N. Waves with a subinertial period of 17.2 hrs, a wavelength of 363 km, a phase speed of 586 cm/s and a group velocity of 409 cm/s, are found. Possible mechanism for generation of shelf waves is presented. It is suggested that some energy related with wave activity may support cross-frontal mixing in the East Greenland Current (EGC), where formation of the two main sources of North Atlantic Deep Water (e.g. Norwegian Sea Deep Water and Denmark Strait Overflow Water) have been reported. The results from the GSA simulation suggest that during the early stage of the GSA (e.g. during its propagation with the EGC to the south, in the late 1960s) when no observations are available, the fresh water signal is not being mixed into the interior circulation of the Greenland Sea gyre. The second experiment, representing recirculation of the GSA from the North Atlantic back into the Greenland Sea, in the late 1970s, shows freshening in the Greenland Sea gyre of comparable magnitudes ($-$0.05 to $-$0.1 psu) to the observed ones. These results agree with the earlier indirect measurements (Rhein, 1991; Schlosser et al., 1991) indicating dramatic reduction of deep water renewal in the Greenland Sea in the late 1970s and early 1980s. From the general circulation experiments it has been found that the ocean response to seasonal forcing is mainly barotropic. This implies a strong topographic control in the distribution of currents and hydrographic variables. Most of the areas of topographic steering which are simulated in the region have been reported in the literature. The so-called Molloy Deep eddy shows its direct dependence on the large scale dynamics affecting the northward flow of the West Spitsbergen Current (WSC), controlling this way a net mass transport into the Arctic Ocean. Simulations with different wind forcing suggest dependence of the Greenland Sea gyre circulation on the variations with time of the local wind forcing. Results indicate that monthly mean wind stress forcing probably underestimate wind forcing in the model. Analysis of surface, intermediate and deep ocean velocity fields compare reasonably well with observations.
    • Numerical modelling of electromagnetic wave propagation in a hallway

      Venkatasubramanian, Arun (2003-08)
      This research involves the numerical modelling of electromagnetic wave propagation, (1) to calculate the electric and magnetic fields at any point in a hallway for a known transmitter and receiver antenna pattern and orientation and (2) to determine the wave normal direction of the electromagnetic wave using the electric fields calculated in (1). The results of the numerical simulation are compared with measurements for two hallways. Both the transmitter and receiver employ vertically oriented /4 dipoles operating at 2.4 GHz. Our work has led to the following new results: (1) The calculated signal power varies as 1/r² whereas the measured data varies as 1/r¹·⁴, where r is the transmitter receiver separation distance, (2) The temporal clustering of calculated multipath arrival times qualitatively agrees with the Saleh-Valenzuela model [1987], (3) For an SNR of 0 dB, the standard deviation of the error in the DOA estimate for the direct path signal is 2̃° and 4̃ ̊for the azimuth and elevation angles respectively. (4) In the presence of multi path, the DOA estimate shows an error of 50 ̊in the elevation and 125 ̊in the azimuth.
    • Numerical realization of the generalized Carrier-Greenspan Transform for the shallow water wave equations

      Harris, Matthew W.; Rybkin, Alexei; Williams, Gordon; Nikolsky, Dmitry (2015-08)
      We study the development of two numerical algorithms for long nonlinear wave runup that utilize the generalized Carrier-Greenspan transform. The Carrier-Greenspan transform is a hodograph transform that allows the Shallow Water Wave equations to be transformed into a linear second order wave equation with nonconstant coefficients. In both numerical algorithms the transform is numerically implemented, the resulting linear system is numerically solved and then the inverse transformation is implemented. The first method we develop is based on an implicit finite difference method and is applicable to constantly sloping bays of arbitrary cross-section. The resulting scheme is extremely fast and shows promise as a fast tsunami runup solver for wave runup in coastal fjords and narrow inlets. For the second scheme, we develop an initial value boundary problem corresponding to an Inclined bay with U or V shaped cross-sections that has a wall some distance from the shore. A spectral method is applied to the resulting linear equation in order to and a series solution. Both methods are verified against an analytical solution in an inclined parabolic bay with positive results and the first scheme is compared to the 3D numerical solver FUNWAVE with positive results.
    • Numerical Simulation Of Single Phase And Boiling Microjet Impingement

      Ragunathan, Srivathsan (2008)
      This work presents results from the numerical simulation of single phase and boiling microjets primarily for high density electronics cooling. For the single phase microjets, numerical simulation results for the flow fields and heat transfer characteristics in a laminar, confined microjet (76 mum in diameter) impingement arrangement are presented. The parameters varied included the jet Reynolds Number, the fluid Prandtl Number and the ratio of the nozzle-to-plate distance to the jet diameter. Primary and secondary recirculation zones were observed in the stagnation region and the radial outflow region which had a significant impact on the local Nusselt Number distribution on the heated surface. The location and the displacement of the primary and secondary recirculation zones are of particular importance and are associated with secondary peaks in the Nusselt Number similar to those observed for turbulent jet impingement in larger conventional jets. Numerical simulation results are presented for boiling microjet impingement in a confined arrangement. The Rensselaer Polytechnic Institute (RPI) model was modified for laminar flow boiling for simulating these types of flows. The model primarily proposes three different heat transfer components, the single phase heat transfer, the quenching heat transfer and the evaporative heat transfer. The model was first validated with experimental results from the literature and then extended to study the effects of liquid subcooling, microjet Reynolds Number based on the nozzle inlet, and heat flux levels. The simulation results were in good agreement with results from comparable experiments in the literature. The average wall temperature increases as the applied wall heat flux is increased. The slopes of the temperature curves in the radial direction flatten out at higher heat fluxes and lower levels of subcooling indicating the effectiveness of boiling heat transfer. For the cases considered in this study, the single phase heat transfer component dominates the other two modes of heat transfer The liquid velocity profile has a considerable impact on the vapor bubble nucleation, vapor drag and the bubble departure diameter. Lower levels of subcooling are associated with boiling inception and more vigorous boiling in the vicinity of the stagnation zone rather than those with higher levels of subcooling. The degree of subcooling emerged as the single largest factor controlling the lateral temperature rise in an electronic chip cooled by a single, confined impinging microjet. Increases in the jet inlet Reynolds Number for the same heat flux and subcooling levels increased the dominance of forced convection heat transfer over the boiling heat transfer. Lower Reynolds Number flows are marked by partial nucleate boiling in contrast to higher Reynolds Number flows marked by forced convection boiling. For all the cases considered in this work, the single phase heat transfer component dominated the other two modes of heat transfer. The evaporative mode dominates the quenching heat transfer mode, an observation that is markedly different from those observed for turbulent evaporative jets found in the literature.