Recent Submissions

  • Investigation of the friction and noise of automotive rubber belt

    Narravula, Vikram R. (2011-05)
    The objective of this research was to study the frictional properties of an automotive v-ribbed belt-pulley system. In order to evaluate the friction and noise, a new test setup was constructed. The assembly was run under various environmental and operational conditions and the results were quantified, studied, and compared among themselves. The environmental conditions included dry interface and wet interface, conducted at both room temperature (23°C) and cold temperature ( -20°C). Operational parameters varied during the experiment were wrap angle, load attached, and acceleration. Frictional forces and associated noises generated were recorded. Some of the results generated were compared with previous research work, and the setup was also used to generate new data for conditions not previously studied. Dry room temperature results show close correlation with previous research. The presence of water in liquid state in the interface induces larger adhesion as water film in the interface changes friction mechanisms in the rubber belt-pulley interface. The high stiction of wet friction can lead to stick-slip vibrations and squeal noise. The theoretical stiction model for wet belt-pulley interface is presented. The stiction-related noise test is conducted, and the result is used to identify the spectrum pattern. The belt friction under cold conditions is found to have a higher value than that in room temperature conditions. The belt noise under cold conditions is found to have much higher squeal frequency than that in room temperature conditions.
  • The measurement of anisotropic thermal conductivity in snow with needle probes

    Holbrook, Joshua (2011-05)
    A new method for measuring thermal conductivity is being adapted from the method of measuring isotropic thermal conductivity in snow with needle probes as used by Sturm, Johnson and others, in order to enable the determination of anisotropic thermal conductivities. This method has particular relevance to measuring thermal conductivity of natural snowpacks where conductivity can be strongly anisotropic due to structures that develop from vapor transport-induced metamorphism, self-compaction and other mechanisms, and where there are known discrepancies between density-conductivity relations empirically derived from guarded hot plate and needle probe methods. Both analytically-based solutions and finite element numerical solutions to the anisotropic case are used to calculate the expected effective thermal conductivity as a function of anisotropic thermal conductivity and needle orientation. Additionally, preliminary measurements of both anisotropic salt/sugar layered samples and of snow were taken. Both suggest that detecting anisotropy in such materials is possible, though made difficult by variability between measurements and the requirement of multiple measurements at various angles. These studies suggest that anisotropy in snow may be able to explain in part the discrepancies between guarded hot plate and needle probe measurements in certain cases.
  • Water-in-air droplet formation in plasma bonded microchannels fabricated by Shrinky-Dink® lithography

    Bender, Christopher J. Jr. (2011-08)
    This thesis presents the first work on water-in-air droplet microfluidics. Polymeric microchannels were prototyped to illustrate water droplet formation in air by the T-junction meditated design. The first part of the thesis is on the proof of using unfiltered air as the process gas for plasma-assisted bonding of polydimethylsiloxane (PDMS) microchannels. A series of bilayered PDMS prototypes were plasma bonded under various plasma treatment parameters to determine the optimal settings for high-strength bonding. Pressure rupture tests were conducted to measure the bonding interface strength, which were shown to be as high as 135 psi. The second part of the thesis illustrates the formation and dispersion of water droplets in a continuous air flow in microchannels, and discusses the mechanisms of how droplets are formed. The Shrinky Dinks lithography and plasma-assisted bonding were used to prototype leakage-free microcbannels for testing droplet production. Droplets are formed under the competition between the fluid viscosity and surface tension forces. The channel dimensions and the fluid flow rates dictate the mechanism of droplet formation. The major finding is that the droplet length increases and droplet velocity decreases with increasing water flow rates, but some droplets were not formed at the T-Junction. These findings are discussed.
  • Renewable energy development in Alaska: policy implications for the development of renewable energy for remote areas of the circumpolar Arctic

    Holdmann, Gwen Pamela; Johnson, Ronald; Peterson, Rorik; Greenberg, Joshua; Sfraga, Mike (2019-12)
    The territories that comprise the Arctic region are part of some of wealthiest and most advanced countries on the planet; yet, rural Alaska, northern Canada, the Russian Far East and Greenland--characterized by off-grid communities, regional grids, and higher degrees of energy insecurity--have more in common with the developing world than the southern regions of their own country. This thesis explains this paradox of energy development in the Circumpolar North and tackles the issue of developing renewable energy in remote areas where technical and socioeconomic barriers are significant. The primary research questions are two-fold: 1) Why did the Alaska electrical system develop as a non-integrated patchwork of regional and isolated grids? and 2) What are the major factors in Alaska that have resulted in a greater uptake of renewable energy systems for remote communities, compared to other similar places in the Arctic? This thesis demonstrates that state-building theory provides a cogent framework to understand the context of electrical build-out in the Circumpolar North. A major finding of this thesis is that the buildout of electric infrastructure in the non-Nordic countries, including Alaska, exemplifies a process of incomplete nation-building. Interconnected regional grids, where they exist, are largely due to the twin national priorities in infrastructure development in the north: extracting natural resources and enhancing national security. This thesis also draws on sociotechnical transition theory to explain why Alaska exhibits such high levels of energy innovation when compared to other similar regions across the Arctic. This research concludes that drivers such as extremely high energy costs, a highly deregulated utility market with dozens of certificated utilities, state investment in infrastructure, and modest subsidies that create a technological niche where renewable energy projects are cost-competitive at current market prices have spurred energy innovation throughout Alaska's communities, remote or otherwise. Many of the evolving technical strategies and lessons learned from renewable integration projects in Alaska's remote islanded microgrids are directly applicable to project development in other markets. Despite differences in climate and geography, lessons learned in Alaska could prove invaluable in increasing resiliency and driving down energy costs in remote communities world-wide.
  • Stress-corrosion cracking susceptibility of polystyrene/TiO₂ nanocomposite coated thin-sheet aluminum alloy 2024-T3 with 3.5% NaCl

    Baart, Brian V.; Chen, Cheng-fu; Ahn, Il Sang; Zhang, Lei (2020-05)
    This thesis reports an investigation into the performance of nanocomposite coatings, which consist of titanium dioxide nanoparticles within a polystyrene matrix, on the resistance to stress-corrosion cracking (SCC). The coatings are applied to compact tension specimens subject to conditions that promote failure by (SCC). It has been well documented in the literature that high-strength aluminum alloys such as 2024- T3 are prone to SCC when exposed to chloride media and sufficient levels of stress. The use of polymerbased nanocomposite coatings to protect aluminum alloy 2024-T3 has recently been shown to exhibit anticorrosion properties, which has been motivation for further study. The performance of such coatings on SCC is thus investigated here, using a fracture mechanics approach with compact tension specimens. The specimens are subject to a slow strain rate test using a constant displacement rate of 1.25 nm/s while exposed to periodically supplied 3.5% wt. sodium chloride solution. Measurements of load and crackmouth opening displacement data are recorded from the specimen throughout the test and used to characterize the response of the material to the applied mechanical loading in a corrosive environment. Results from the methods used herein showed a quantitative influence derived from the test results for several criteria of interest such as maximum load, time-to-failure, and fracture toughness. In total, four different coatings were applied; three with different titanium dioxide nanoparticle aspect ratios, and one without any titanium dioxide nanoparticles present in the polystyrene matrix. Characterization of the results showed that the shape of the titanium dioxide nanoparticle is a dominant factor that influences the susceptibility of aluminum alloy 2024-T3 to SCC.
  • Testing and analysis of a ground source heat pump in Interior Alaska

    Garber-Slaght, Robbin; Das, Debendra K.; Marsik, Tomas; Lin, Chuen-Sen (2019-08)
    Ground source heat pumps (GSHPs) can be an efficient heating and cooling system in much of the world. However, their ability to work in extreme cold climates is not well studied. In a heating-dominated cold climate, the heat extracted from the soil is not actively replaced in the summer because there is very little space cooling. A ground source heat pump was installed at the Cold Climate Housing Research Center (CCHRC) in Fairbanks, Alaska with the intent to collect data on its performance and effects on the soil for at least ten years. Analysis shows GSHPs are viable in the Fairbanks climate; however, their performance may degrade over time. According to two previous finite element models, the CCHRC heat pump seems to reach equilibrium in the soil at a COP of about 2.5 in five to seven years. Data from the first four heating seasons of the ground source heat pump at CCHRC is evaluated. The efficiency of the heat pump degraded from an average coefficient of performance (COP) of 3.7 to a mediocre 2.8 over the first four heating seasons. Nanofluids are potential heat transfer fluids that could be used to enhance the heat transfer in the ground heat exchanger. Improved heat transfer could lower installation costs by making the ground heat exchanger smaller. A theoretical analysis of adding nanoparticles to the fluid in the ground heat exchanger is conducted. Two nanofluids are evaluated to verify improved heat transfer and potential performance of the heat pump system. Data from the CCHRC heat pump system has also been used to analyze a 2-dimensional finite element model of the system's interaction with the soil. A model based on the first four years of data is developed using Temp/W software evaluates the ground heat exchanger for a thirty-year period. This model finds that the ground heat exchanger does not lower the ground temperature in the long term.
  • Comparison of resistance-based strain gauges and fiber bragg gratings in the presence of electromagnetic interference emitted from an electric motor

    Keller, Douglas Jr.; Peterson, Rorik; Fochesatto, Javier; Chen, Cheng-fu (2018-12)
    This thesis reports a performance analysis of resistance based strain gauges and fiber optic fiber Bragg gratings in an environment contaminated by high levels of electromagnetic interference. The obtained results are directly applicable to the development of aerospace vehicles propelled by electrical motors. An area of importance in this relatively new technology is characterizing the mechanical loadings coming off a propulsion device in a stationary setup. This characterization is usually accomplished through the utilization of load cells. The majority of the load cells used in such an application are based on measurements acquired through resistance strain gauges. However, electric motors are known to radiate electromagnetic interference (EMI), which in the case of brushless DC motors is pulsing, alternating, square waves. This EMI severely degrades the signal produced by the resistance strain gauge. This degradation is due to the gauge's metallic construction, acting as an antenna for the EMI. To evaluate the performance of alternative strain measuring methods, a load cell implementing both the resistance strain gauge and fiber Bragg grating sensor, the latter of which is immune to EMI, was designed as a test article. The load cell was calibrated and demonstrated a thrust load sensitivity of 1.93 ±0.04 lbf through the strain gauge system and 0.56 ±0.56 lbf through the fiber Bragg grating system. The device was subjected to both mechanical loading and EMI to quantify the effect of the EMI on the resistance strain gauge. Testing of the device included operating a brushless DC motor, with a coupled flywheel, attached to the load cell at a range of angular velocities from 500 to 2400 RPM. During laboratory testing the resistance strain gauge signal exhibited an important amount of signal spikes and electrical noise, introduced by the EMI contamination; the fiber Bragg grating did not. The spikes increased linearly with the speed of the motor. The electrical noise required bandpass filtering to extract the mechanical signal, which was obtained without noise in the fiber Bragg grating signal. The resistance strain gauge signal, at a maximum, had a signal to noise ratio of 0.0443; the fiber Bragg grating signal, at a minimum, had a signal to noise ratio of 2.0114. These results demonstrated the fiber Bragg grating is more applicable in an EMI contaminated environment.
  • Two-dimensional analysis of natural convection and radiation in utilidors

    Richmond, Paul W., Iii; Zarling, John; Das, Debendra; Gislason, Gary; Kinney, Thomas (1997)
    Central heating plants are often used on large building complexes such as university campuses or military bases. Utilidors can be used to contain heat distribution lines and other utilities between a utility station and serviced buildings. Traditional thermal analysis of utilidors is one-dimensional, with heat transfer correlations used to estimate the effects of convection, radiation, and two-dimensional geometric effects. The expanding capabilities of computers and numerical methods suggest that more detailed analysis and possibly more energy-efficient designs could be obtained. This work examines current methods of estimating the convection and radiation that occur across an air space in square and rectangular enclosures and compares them with numerical and experimental data. A numerical model was developed that solves the energy, momentum, and continuity equations for the primitive variables in two dimensions; radiation between free surfaces was also included. Physical experiments were conducted with two 10-ft-long apparatuses; one had a 1-ft $\times$ 1-ft cross section, the other was 2 ft $\times$ 4 ft. Several pipe sizes and configurations were studied with the 1-ft $\times$ 1-ft apparatus. The 2-ft $\times$ 4-ft apparatus was limited to containing 4- and 8-inch insulated pipes. Corresponding numerical studies were conducted. Difficulties in modeling large enclosures or those with large temperature differences (Rayleigh numbers above 10$\sp7$) were encountered. Results showed good agreement between numerical and experimental average heat transfer rates, and for insulated pipe cases these results also compared well with rates obtained from one-dimensional analysis. A new effective conductivity correlation for air in a square enclosure was developed, and its use was demonstrated in numerical conduction solutions and compared with full numerical convection and radiation solutions and with experimental data. Reasonably good results were achieved when there was a small temperature difference across the air gap.
  • Pitorifices and small pumps in cold region water distribution systems

    Mauser, Michael William; Zarling, John; Carlson, Robert; Kane, Douglas; Goering, Douglas (1995)
    Most buried potable water distribution systems in colder regions of Alaska rely on pitorifices to provide circulation between the water main and service connections for freeze protection. Pitorifices are scoops which project into the main. When water is circulated in the main, they create a differential head which induces flow through dual service lines. Pitorifices have provided an inexpensive and simple alternative to installing a small pump at each service to provide circulation. However, very little information was available on the hydraulic performance of these devices. The objectives of this study were to: (i) develop techniques to measure pitorifice performance in the field; (ii) characterize performance of commonly used pitorifice shapes with different insertion depths and relative sizes in full-scale testing; (iii) develop an improved shape; (iv) research the competing technology of small pumps; and (v) present the information in a way that is useful to engineers. An inexpensive device for field checks of both differential head and flow rates at service lines was developed and the use of a low head loss meter was initiated. Methods and results of field studies in four different water systems are presented. Five commonly used pitorifice shapes and four new shapes were evaluated. The best shape was found to be one of the existing shapes, which is also one of the easiest to produce but not the most popular. It was also determined using a larger service line size can be cost effective. Test results are graphed and a theoretical framework is provided for designers. Smaller, energy efficient pumps may provide a cost effective alternative to pitorifices in some situations. Requirements for small pumps used for circulation in place of or to supplement pitorifices are given. Performance test results for different pumps are presented, most of which have not been used previously for service line circulation. Pumps with significantly lower operating costs than those in current use are identified. Several of these pumps were installed in services for long term testing.
  • Size Effects In Mesoscale Mechanical Testing Of Snow

    Huang, Daisy; Lee, Jonah; Newman, David; Peterson, Rorik; Truffer, Martin (2013)
    Snow is a naturally-occurring, heterogeneous material whose interactions with humans make it desirable for analysis as a geotechnical engineering material. In this study, clean, undisturbed, natural snows of two common types were collected in and around Fairbanks, Alaska and subjected to laboratory testing, and the results were compiled and analyzed. Three types of tests--flat pin indentation, unconfined compression, and cone penetration--were carried out while varying size parameters, and size effects were observed and studied. From flat-pin indentation testing, it was observed that first peak indentation strength initially fell exponentially with increasing indenter cross-sectional area, with the exponent averaging 0.84. Furthermore, the strength eventually rose to a plateau value, and the compression strength of snow could be calculated from this plateau value. This plateau, too, initially depended exponentially on the pin cross-sectional area for smaller pins. From unconfined compression testing, it was observed that as cross-sectional area of a flat pin indenter increased, plateau strength eventually reached that value found from unconfined compression testing. Furthermore, initial strength, plateau strength, and energy absorption density all increased linearly with increasing aspect ratio. From cone penetration testing, it was found that empirical values of snow strength may be obtained on both a micromechanical and macromechanical scale using cone penetration. Size effects, were also observed--smaller cone diameters and larger cone included angles yielded larger values for apparent snow strength. Some of the mechanisms behind all of these size effects are explainable from theory; others must be regarded for now as empirical in nature. In both cases, the results are quite reliable descriptors for a natural material, and may be safely interpolated from.
  • 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.
  • 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.
  • Theoretical And Experimental Analysis Of Two-Phase Closed Thermosyphons

    Xu, Jianfeng; Goering, Douglas J. (2008)
    This work presents an analytical and numerical model of a long inclined two-phase closed thermosyphon, known as a hairpin thermosyphon, which is representative of a new configuration for thermosyphons used in arctic applications. A laboratory experiment and a full scale road experiment along with associated modeling are described in detail. The laboratory experiment studies the condensation heat transfer performance of carbon dioxide inside the thermosyphon condenser under conditions of limited heat flux. The operating condition is not far from the critical point for carbon dioxide, which has a significant impact on the condensation heat transfer. An experimental correlation is developed to predict the carbon dioxide condensation heat transfer performance under these specific conditions. The full scale road experiment studies the overall performance of hairpin thermosyphons under actual field conditions. The model is a quasi one-dimensional formulation based on two-dimensional two-phase flow simulations at each cross section. The proposed model is useful for predicting steady state system operating characteristics such as pressure, temperature, liquid film thickness, mass flow rate, heat flow rate, etc., at local positions as well as over the entire system. The comparison of the modeling predictions with both laboratory and field experiments showed a strong correlation between modeling predictions and experimental results.
  • Experimental Investigations Of Fluid Dynamic And Thermal Performance Of Nanofluids

    Kulkarni, Devdatta Prakash; Das, Debendra K. (2007)
    The goal of this research was to investigate the fluid dynamic and thermal performance of various nanofluids. Nanofluids are dispersions of metallic nanometer size particles (<100 nm) into the base fluids. The choice of base fluid is an ethylene or propylene glycol and water mixture in cold regions. Initially the rheological characterization of copper oxide (CuO) nanofluids in water and in propylene glycol was performed. Results revealed that higher concentrations of CuO nanoparticles (5 to 15%) in water exhibited time-independent pseudoplastic and shear-thinning behavior. Lower concentrations (1 to 6%) of CuO nanofluids in propylene glycol revealed that these nanofluids behaved as Newtonian fluids. Both nanofluids showed that viscosity decreased exponentially with increase in temperature. Subsequent correlations for viscosities as a function of volume concentration and temperature were developed. Effects of different thermophysical properties on the Prandtl number of CuO, silicon dioxide (SiO2) and aluminum oxide (A12O 3) nanofluids were investigated. Results showed that the Prandtl number increased with increasing volume concentrations, which in turn increased the heat transfer coefficients of the nanofluids. Various nanofluids were compared for their heat transfer rates based on the Mouromtseff number, which is a Figure of Merit for heat transfer fluids. From this analysis, the optimal concentrations of nanoparticles in base fluids were found for CuO-water nanofluids. Experiments were performed to investigate the convective heat transfer enhancement and pressure loss of CuO, SiO2 and A12O 3 nanofluids in the turbulent regime. The increases in heat transfer coefficient by nanofluids for various volume concentrations compared to the base fluid were determined. Pressure loss was observed to increase with nanoparticle volume concentration. It was observed that an increase in particle diameter increased the heat transfer coefficient. Calculations showed that application of nanofluids in heat exchangers in buildings could result in volumetric flow reduction, reduction in the mass flow rate and size, and pumping power savings. Experiments on a diesel electric generator with nanofluids showed a reduction of cogeneration efficiency due to the decrease in specific heat compared to the base fluids. However, it was found that the efficiency of the waste heat recovery heat exchanger increased for nanofluids.
  • Nanotribological Characterization Of Dynamic Surfaces

    Ingole, Sudeep Prabhakar; Liang, Hong (2005)
    This dissertation research includes three fundamental areas: utilizing an atomic force microscope (AFM) to study the nanomechanical and tribological properties, to understand friction and wear at nanometer length, and to study wear mechanisms of boride coatings for biological applications. This was the first time that an AFM was used to study the nanomechanical and tribological properties and the performance of the materials. The AFM enables detailed investigation of the wear modes at multi-length scales as well as the surface mechanical properties. Surface analysis using an AFM included the surface texture, profile of indents, wear tracks, and wear scars. The friction force microscope (FFM) revealed the relationship between surface texture and frictional properties, thus contributing to the fundamental understanding of nanotribology. A new wear model was proposed. Also, hardening was discovered under the indents. The multi-scale wear study was focused on fundamental wear mechanisms. New wear modes, different than the traditional ones, were proposed. In this research, nanocracks and other damage (hardening and plastic flow) were found at different scales. Boride coatings on refractory metals were investigated for biological applications. Tribological performance of these coatings was studied in dry and wet (biofluid) conditions. It was found that boron plays an important role in forming amorphous and crystalline wear debris.
  • Maximum weight lifting prediction considering dynamic joint strength

    Rana, G M Rahid uz zaman; Xiang, Yujiang; Chen, Cheng-fu; Peterson, Rorik (2018-05)
    This thesis describes an efficient optimization method for predicting the maximum lifting weight considering dynamic joint strength in symmetric box lifting using a skeletal model. Dynamic joint strength is modeled as a three-dimensional function of joint angle and joint angular velocity based on experimentally obtained joint strength data. The function is further formulated as the joint torque limit constraint in an inverse dynamics optimization formulation to predict the lifting motion. In the proposed optimization formulation, external load is treated as design variables along with joint angle profiles, which are represented by control points of B-spline curves. By using this new formulation, dynamic lifting motion and strategy can be predicted for a symmetric maximum weight box lifting task with given initial and final box locations. Results show that incorporating dynamic strength is critical in predicting the lifting motion in extreme lifting conditions. The prediction outputs in joint space are incorporated in OpenSim software to find out muscles force and activity during the movement. Electromyography data are collected for a regular weight lifting to validate the integration process between the predictive model (joint model) and OpenSim model (muscle model). The proposed algorithm and analysis method based on motion prediction and OpenSim can be further developed as a useful ergonomic tool to protect workers from injury in manual material handling.
  • Dynamics simulation of human box delivering task

    Owens, Paul Davis; Xiang, Yujiang; Peterson, Rorik; Chen, Cheng-fu (2018-05)
    The dynamic optimization of a box delivery motion is a complex task. The key component is to achieve an optimized motion associated with the box weight, delivering speed, and location. This thesis addresses one solution for determining the optimal delivery of a box. The delivering task is divided into five subtasks: lifting, transition step, carrying, transition step, and unloading. Each task is simulated independently with appropriate boundary conditions so that they can be stitched together to render a complete delivering task. Each task is formulated as an optimization problem. The design variables are joint angle profiles. For lifting and carrying task, the objective function is the dynamic effort. The unloading task is a byproduct of the lifting task, but done in reverse, starting with holding the box and ending with it at its final position. In contrast, for transition task, the objective function is the combination of dynamic effort and joint discomfort. The various joint parameters are analyzed consisting of joint torque, joint angles, and ground reactive forces. A viable optimization motion is generated from the simulation results. It is also empirically validated. This research holds significance for professions containing heavy box lifting and delivering tasks and would like to reduce the chance of injury.
  • Buoyancy Effects On Building Pressurization In Extreme Cold Climates

    Bargar, Harold Edward; Das, Debendra K.; Goering, Douglas J.; Johnson, Ronald A.; Lin, Chuen-Sen; Quang, Pham X. (2003)
    This research investigates building pressurization due to buoyancy effect. The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) presents an idealized equation to calculate the buoyancy effect. This dissertation compares differential pressure measurements from an actual building exposed to extremely cold temperatures to this idealized model. It also presents new statistical models based on the collected data. These new models should provide engineers with improved tools to properly account for building pressurization for designs in extreme cold climates. Building pressurization, the differential pressure between the interior of a building and its exterior surroundings, is an important design consideration. Pressurization is the driving force in building infiltration/exfiltration. It also affects air flow within building zones. Improper calculation of pressurization can result in under-sizing the building's heating and cooling systems, improper operation of air distribution systems, improper operation of elevators, and freezing and failure of water distribution and circulation systems. Building pressurization is affected by: wind (speed and direction), exterior-to-interior temperature difference, and mechanical equipment operation. In extreme cold climates, the predominant effect is air buoyancy due to temperature differences across the building envelope. The larger the temperature difference, the larger the buoyancy effect. In extreme cold climates, the largest temperature differences often occur at times when wind speed is negligible. This dissertation also demonstrates the use of existing data sources such as building automation systems to collect data for basic research. Modern systems automation provides a tremendous amount of data that, in the past, had to be collected through separate instrumentation and data acquisition systems. Taking advantage of existing automation systems can provide the required data at greatly reduced costs when compared to previous industry practices. The statistical analysis approach taken in this research expands the tools for engineering design. Actual interactions of real world variables are analyzed and used to produce prediction models. These techniques allow the model to incorporate relationships which may not be fully understood at the underlying principle level but are evidenced in the data collected from actual installations.* *This dissertation includes a CD that is compound (contains both a paper copy and CD as part of the dissertation). The CD requires the following applications: Internet Browser; Adobe Acrobat; Microsoft Office; Image Viewer.
  • Performance Prediction Of A Folding Fin Aircraft Rocket Using Datcom, Sens5D, And 6Dof Gem

    Kralewski, Sara Louise; Goering, Douglas; Lin, Chuen-Sen; Das, Debendra (1998)
    An approach for the performance prediction of a Folding Fin Aircraft Rocket (FFAR) is presented. This prediction was compiled by calculating the gravimetrics, aerodynamics, and trajectory for a FFAR. The trajectory analysis utilized four computer codes: Rogers Aeroscience Rocket Performance Software, NASA Wallops Sens5d Trajectory and Wind-Sensitivity Calculations for Unguided Rockets, the United States Air Force (USAF) Stability and Control DATCOM, and the NASA Langley Research Center LRC-MASS program (GEM). Computations were performed for a rigid body configuration. This analysis was compared to radar data collected during the flight of a FFAR launched in February 1997 at the Poker-Flat Research Range. The comparison shows good agreement between the flight data and the predicted apogee and impact point of the vehicle. In addition, static and dynamic stability analyses were completed for the FFAR. <p>
  • An experimental study on the interaction of coaxial and co-rotating vortex rings

    Satti, Jagannadha Reddy (2012-05)
    The study investigated the role of formation time, Reynolds Number, and non-dimensional frequency number, the three most significant parameters in the dynamics of vortex rings, in the interaction between co-axial and co-rotating vortex rings and in the ring behaviors of merging and leapfrogging. To generate and investigate vortex rings with the required characteristics, two laminar vortex rings were generated consecutively from a piston-cylinder apparatus such that the rings propagated in the same direction and that the spatial separation between them decreased until they began merging. Using digital particle image velocimetry to measure the flow fields as well as the trajectory and circulation of the individual rings, a series of experiments were conducted at three formation times, with the experiments at each formation time repeated at different Reynolds Numbers, and the experiments at each Reynolds Number in turn repeated at different non-dimensional frequency numbers. The results indicate that at low Reynolds Numbers, the total circulation in the flow is relatively constant before and after the rings merge. However, at high Reynolds Numbers, the total circulation begins rapidly decreasing upon the contact of two vortex ring cores, indicating a transition to a turbulent vortex ring during merging, before stabilizing at a lower level, indicating that the merged ring has transitioned back to a laminar vortex ring after shedding some circulation.

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