Mechanical Engineering Masters Theses Collection

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https://hdl.handle.net/20.500.14394/148

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Thermodynamic Analysis of a Combined Cycle District Heating System
(2012-09) Suresh, Sharan
Power plant performance can be assessed by the method of thermodynamic analysis. The goal of this thesis is to perform a thermodynamic analysis on the University of Massachusetts’ Combined Heat and Power (CHP) District Heating System. Energy and exergy analyses are performed based on the first and second laws of thermodynamics for power generation systems that include a 10-MW Solar combustion gas turbine, a 4-MW low pressure steam turbine, a 2-MW high pressure steam turbine, a 100,000 pph heat recovery steam generator (HRSG), three 125,000 pph package boilers, and auxiliary equipment. The University of Massachusetts’ CHP plant delivers all of the campus’ steam and nearly all its electricity to the more than 200 buildings and nearly 10 million gross square feet of building space. Two 20-inch main steam transmission lines connect the plant to the campus. On an annual basis the plant generates approximately 1,100,000,000 pounds of steam and 100,000,000 kWh of electric power. The plant has a SCADA (Supervisory Control and Data Acquisition) system. Rockwell Automation’s RSLinx OPC (Object Linking and Embedding for Process Control) server acquires data from up to 675 field instruments in the plant which is used for carrying out the analyses. The latest pollution control technologies, including advanced combustion turbine low NOx burners, advanced Selective Catalytic Reduction and Oxidation Catalyst pollution control technologies are employed in the plant. System efficiencies are calculated for a wide range of component operating loads. Factors affecting efficiency of the CHP district heating system are analyzed. In the analysis, actual system data is used to assess the district heating system performance, energy and exergy efficiencies and exergy losses. Energy and exergy calculations are conducted for the whole year on an hourly basis. Factors affecting efficiency of the CHP district heating system are analyzed and recommendations made to improve the operating efficiency. The results show how thermodynamic analysis can be used to identify the magnitudes and location of energy losses in order to improve the existing system, processes or components.
A Nonlinear Model for Wind-Induced Oscillations of Trees
(2012-09) Ramanujam, Lakshmi Narayanan
Ambient wind causes trees to oscillate. Wind-induced oscillations of trees constitute a fluid-structure interaction problem, which has been studied by many researchers from various points of view. However, there is yet a lot to be done. From an engineering point of view, the complex structure of trees, which are very different from man-made structures, as well as the highly nonlinear interaction between wind and tree, makes it a challenging task to predict the amplitude and frequency of the resulting oscillations. From a biological point of view, the influence of wind on photosynthesis as well as the growth and death of plants is crucial. A nonlinear model is derived for wind-induced oscillations of trees to investigate the effect of structural nonlinearities. It is shown that the structural nonlinearities in the system can result in a hardening behavior of the tree, indicating the importance of taking such nonlinearities into account. The influence of various system parameters such as tree’s age, taper and slenderness ratio on the tree oscillations is studied using this nonlinear model.
Vibration Reduction of Offshore Wind Turbines Using Tuned Liquid Column Dampers
(2012) Roderick, Colin
Offshore wind turbines (OWTs) are becoming an accepted method for generating electricity. The environmental conditions of offshore locations often impose high wind and wave forces on OWTs making them susceptible to intense loading and undesirable vibrations. One method to reduce system vibrations is through the use of structural control devices typically utilized in civil structures. Tuned liquid column dampers (TLCDs) show great promise in the application to OWTs due to their high performance and low cost. This thesis examines the use of TLCDs in OWTs. Equations of motion for limited degree-of-freedom TLCD-turbine models are presented. A baseline analysis of each OWT is performed to generate a quantitative comparison to show how a TLCD would affect the overall dynamics of the system. The models are then subjected to two methods of testing. Optimal TLCD dimensions are derived for the models using a deterministic sweep method. The TLCD configurations examined include those with a uniform and non-uniform column cross-sectional area. The TLCD is shown to successfully reduce overall tower top displacement of each of the OWTs as well as the platform pitch when applicable. In some cases, use of the TLCD actually increases overall tower and platform motion. This thesis also examines the use of idealized tuned mass dampers (TMDs) in OWTs. Comparisons between the optimized TLCD and the idealized TMD are made with regards to motion reduction and parameter values.
High Speed Flow Simulation in Fuel Injector Nozzles
(2012-09) Rakshit, Sukanta
Atomization of fuel is essential in controlling combustion inside a direct injection engine. Controlling combustion helps in reducing emissions and boosting efficiency. Cavitation is one of the factors that significantly affect the nature of spray in a combustion chamber. Typical fuel injector nozzles are small and operate at a very high pressure, which limit the study of internal nozzle behavior. The time and length scales further limit the experimental study of a fuel injector nozzle. Simulating cavitation in a fuel injector will help in understanding the phenomenon and will assist in further development. The construction of any simulation of cavitating injector nozzles begins with the fundamental assumptions of which phenomena will be included and which will be neglected. To date, there has been no consensus about whether it is acceptable to assume that small, high-speed cavitating nozzles are in thermal or inertial equilibrium. This diversity of opinions leads to a variety of modeling approaches. If one assumes that the nozzle is in thermal equilibrium, then there is presumably no significant delay in bubble growth or collapse due to heat transfer. Heat transfer is infinitely fast and inertial effects limit phase change. The assumption of inertial equilibrium means that the two phases have negligible slip velocity. Alternatively, on the sub-grid scale level, one may also consider the possibility of small bubbles whose size responds to changes in pressure. Schmidt et al. developed a two dimensional transient homogeneous equilibrium model which was intended for simulating a small, high speed nozzle flows. The HEM uses the assumption of thermal equilibrium to simulate cavitation. It assumes the two-phase flow inside a nozzle in homogeneous mixture of vapor and liquid. This work presents the simulation of high-speed nozzle, using the HEM for cavitation, in a multidimensional and parallel framework. The model is extended to simulate the non-linear effects of the pure phase in the flow and the numerical approach is modified to achieve stable result in multidimensional framework. Two-dimensional validations have been presented with simulation of a venturi nozzle, a sharp nozzle and a throttle from Winklhofer et al. Three-dimensional validations have been presented with simulation of ‘spray A’ and ‘spray H’ injectors from the Engine Combustion Network. The simulated results show that equilibrium assumptions are sufficient to predict the mass flow rate and cavitation incidence in small, high-speed nozzle flows.
Effect of Slip on Flow Past Superhydrophobic Cylinders
(2012-09) Muralidhar, Pranesh
Superhydrophobic surfaces are a class of surfaces that have a microscale roughness imposed on an already hydrophobic surface, akin to a lotus leaf. These surfaces have been shown to produce significant drag reduction for both laminar and turbulent flows of water through large and small-scale channels. The goal of this thesis was to explore how these surfaces alter the vortex shedding dynamics of a cylindrical body when coated on its surface, thus leading to an alteration in drag and lift on these surfaces. A cylindrical body was chosen as it is a very nice representative bluff body and sets the stage for predicting the behavior of hydrofoils and other bluff bodies under flow with a slip boundary condition. In this work, a series of experiments were performed which investigated the effect of superhydrophobic-induced slip on the flow past a circular cylinder. In these experiments, circular cylinders were coated with a series of superhydrophobic surfaces fabricated from PDMS with well-defined micron-sized patterns of surface roughness or random slip surfaces fabricated by sanding Teflon cylinders or spray painting superhydrophobic paint on a smooth cylinder. The presence of the superhydrophobic surface was found to have a significant effect on the vortex shedding dynamics in the wake of the circular cylinder. When compared to a smooth, no-slip cylinder, cylinders coated with superhydrophobic surfaces were found to delay the onset of vortex shedding and increase the length of the recirculation region in the wake of the cylinder. For superhydrophobic surfaces with ridges aligned in the flow direction the separation point was found to move further upstream towards the front stagnation point of the cylinder and the vortex shedding frequency was found to increase. For superhydrophobic surfaces with ridges running normal to the flow direction, the separation point and shedding frequency trends were reversed. The vortices shed from these surfaces were found to be weaker and less interlaced leading to reduced circulation and lift forces on these cylinders. The effect of slip on bluff bodies and separating flow was dealt with in detail in this thesis and the results could be used to predict the impact of these surfaces on the flow past hydrofoils which combine skin friction dominated flow with separating flow.
Experimental Study of Stability Limits for Slender Wind Turbine Blades
(2012) Ladge, Shruti
There is a growing interest in extracting more power per turbine by increasing the rotor size in offshore wind turbines. As a result, the turbine blades will become longer and therefore more flexible and a flexible blade is susceptible to flow-induced instabilities, such as classical flutter. In order to design and build stable large wind turbine blades, the onset of instability should be considered in the design process. To observe flow-induced instabilities in wind turbine blades, a small-scale flexible blade was built based on NREL 5MW reference wind turbine blade. The blade was placed in the test section of a wind tunnel and its tip displacement was measured using a non-contacting displacement measurement device. The blade was non-rotating and was subjected to uniform incoming flow. For a range of blade angles of attack, instability was observed beyond a critical wind speed. The amplitude of oscillations increases for wind speeds higher than the critical speed, and the frequency of oscillations remains constant. Flow visualizations and force measurements are conducted and the influence of various system parameters including the angle of attack and the blade twist was examined.
Vortex-Induced Vibrations of an Inclined Cylinder in Flow
(2012-09) Jain, Anil B
When a bluff body is placed in flow, vortices are shed downstream of the body. For the case of a bluff body with a circular cross-section (a cylinder) attached to a spring and a damper, when the frequency of vortex shedding is close to the natural frequency of the structure, the cylinder oscillates in a direction perpendicular to the flow. This is called Vortex Induced Vibration (VIV) and is a canonical problem in fluid-structure interactions. The majority of studies on VIV of a flexibly mounted rigid cylinder are for the cases where the flow direction is perpendicular to the long axis of the structure. However, in many engineering applications, such as cable stays in bridges, mooring lines of floating offshore wind turbines and undersea pipelines, the flow direction may not be perpendicular to the structure. The hypothesis is that the VIV in inclined cylinders is similar to a normal-incidence case, if only the component of the free stream velocity normal to the cylinder axis is considered. This is called the Independence Principle (IP). The IP neglects the effect of the axial component of the flow, which is legit for small angles of inclination, but not for large angles. In this Thesis, a series of experiments have been conducted on a flexibly-mounted rigid cylinder placed inclined to the oncoming flow with various angles of inclination (0° < θ < 75°) in a subcritical Reynolds number range of 500 – 4,000 to investigate how the angle of inclination affects VIV. In these experiments, a rigid cylinder was mounted on springs, and air bearings were used to reduce the structural damping of the system. The system was placed in the test section of a recirculating water tunnel and crossflow displacements were measured. Even at high angles of inclination, large-amplitude oscillations were observed. The IP was found to be valid for angles of inclination up to 55°. While for all inclinations the onset of lock-in was observed to be at the same normalized flow velocity, for angles of inclination larger than 55°, the lock-in region (the range of dimensionless flow velocities for which the cylinder oscillates with a large amplitude) was smaller. These results show that the influence of the axial component of the flow is non-negligible for angles of inclination larger than 55°.
Finite Element Analysis of a Femur to Deconstruct the Design Paradox of Bone Curvature
(2012) Jade, Sameer
The femur is the longest limb bone found in humans. Almost all the long limb bones found in terrestrial mammals, including the femur studied herein, have been observed to be loaded in bending and are curved longitudinally. The curvature in these long bones increases the bending stress developed in the bone, potentially reducing the bone’s load carrying capacity, i.e. its mechanical strength. Therefore, bone curvature poses a paradox in terms of the mechanical function of long limb bones. The aim of this study is to investigate and explain the role of longitudinal bone curvature in the design of long bones. In particular, it has been hypothesized that curvature of long bones results in a trade-off between the bone’s mechanical strength and its bending predictability. This thesis employs finite element analysis of human femora to address this issue. Simplified human femora with different curvatures were modeled and analyzed using ANSYS Workbench finite element analysis software. The results obtained are compared between different curvatures including a straight bone. We examined how the bone curvature affects the bending predictability and load carrying capacity of bones. Results were post processed to yield probability density functions (PDFs) for circumferential location of maximum equivalent stress for various bone curvatures to assess the bending predictability of bones. To validate our findings on the geometrically simplified ANSYS Workbench femur models, a digitally reconstructed femur model from a CT scan of a real human femur was employed. For this model we performed finite element analysis in the FEA tool, Strand7, executing multiple simulations for different load cases. The results from the CT scanned femur model and those from the CAD femur model were then compared. We found general agreement in trends but some quantitative differences most likely due to the geometric differences between the digitally reconstructed femur model and the simplified CAD models. As postulated by others, our results support the hypothesis that the bone curvature is a trade-off between the bone strength and its bending predictability. Bone curvature increases bending predictability at the expense of load carrying capacity.
A Multi-Level Hierarchical Finite Element Model for Capillary Failure in Soft Tissue
(2012-09) Huang, Lu
Developing a more scientific way to determine the load threshold for capillary wall failure would be a big step forward in characterizing whether bruising is result from an abuse or an accident. In this thesis, the upper portion of the human arm was modeled and analyzed under dynamic loading conditions. Since the diameter of the arm is much larger than that of the capillary, a four-level hierarchical sub-modeling method was used to mathematically link the transient response of the global arm model to the response of a small volume in the muscle tissue containing one capillary. Soft tissue in the arm was modeled in two distinct ways. In one method each component of soft tissue was modeled used isotropic linear elastic properties to find the loading threshold that produces a hoop stress in the capillary wall equal to the capillary failure stress. In the other approach, nonlinear, hyper-elastic properties for skin, adipose, muscle tissue and capillary wall were employed to make the tissue behavior more realistic to that of a human arm. Material-appropriate constitutive functions were chosen for each layer. A mathematical technique implement in MATLAB was used to estimate and subtract rigid body motion from the total displacement to avoid excessive displacements of sub-models and focus more on the deformation-only displacement. It was found that modeling the skin, adipose, muscle and capillary as hyper-elastic resulted in significantly smaller deformations but larger loads that resulted in capillary failure.
Investigating the Relationship Between Material Property Axes and Strain Orientations in Cebus Apella Crania
(2012) Dzialo, Christine M
Probabilistic finite element analysis was used to determine whether there is a statistically significant relationship between maximum principal strain orientations and orthotropic material stiffness orientations in a primate cranium during mastication. We first sought to validate our cranium finite element model by sampling in-vivo strain and in-vivo muscle activation data during specimen mastication. A comparison of in vivo and finite element predicted (i.e. in silico) strains was performed to establish the realism of the FEM model. To the best of our knowledge, this thesis presents the world’s only complete in-vivo coupled with in-vitro validation data set of a primate cranium FEM. Our results indicate that a validated FEM of a Cebus apella cranium was achieved. Giving collaborating anthropologists, biologists, and engineers the confidence that these models have sufficient accuracy to address the research questions pertaining to cranial structure morphology. Probabilistic finite element analysis design was then utilized to determine the dependence of maximum principal strain orientations on material stiffness orientations in particular craniofacial regions during mastication. It was discovered that the maximum principal strain orientations are more dependent on loading conditions and/or the shape of and location in the cranium rather than the material stiffness orientation of a particular region. It was also uncovered that the material stiffness orientations are not developed in a way that is optimal for feeding biomechanics from the perspective of minimization of total elastic strain energy. Results from this research will provide insights into the co-evolution of bone morphology and material properties in the facial skeleton.
Physical Model of the Feeding Strike of the Mantis Shrimp
(2012-09) Cox, Suzanne M
A physical model was built to study the properties of the feeding strike of the mantis shrimp that are responsible for drag reduction and cavitation control. The model had three goals: 1) The model was to be outfitted with a method to collect kinematic, force and cavitation data. 2) The velocity and acceleration profile of the model were to be predicted with a mathematical model of the mechanism. 3) The model was to match as many drag and cavitation sensitive properties of the mantis shrimp strike as feasible and have a means to control the rest. The first iteration of the model met the first goal but not the second or third. It matched the strike in maximum velocity, appendage size and shape and environmental temperature and salinity but did not control acceleration profile, water quality or pressure. Data collected with high-speed video of strikes of the model and Gonodactylus smithii showed the model to cavitate at speeds at which no cavitation was seen in animal strikes. The model was redesigned to be driven by the stored elastic energy in the deflection of a beam spring. The redesigned model reached the animals maximum accelerations but not velocities. Environmental variation was found to not substantially contribute to the variation in cavitation onset velocity between the model and animal experiments.
Environmental Impacts Due to Fixed and Floating Offshore Wind Turbines
(2012-09) Brewer, Micah K
As has been the case for onshore wind systems, the environmental effects of offshore wind farms are expected to play an important part of the development of future large-scale wind energy systems. This paper presents a detailed review of the status of, and recent developments in, research on the environmental impacts of fixed and floating offshore wind turbine systems. The primary information that has been reviewed has come from European sources where there are a significant number of offshore installations, but some work on this subject has been carried out recently in the United States. Information, from an extensive review, is presented on the environmental impacts of fixed and floating offshore wind turbines on benthic organisms, fish, marine mammals, avian species and bats. The environmental impacts of fixed and floating systems are anticipated to vary due to multiple parameters that need to be taken into account when identifying environmental impacts. Additionally, there are variations in the impact throughout the lifecycle of the offshore wind turbines. The primary focus for this paper is on the environmental impacts through the scope of barrier and habitat impacts in addition to the anticipated avian and bat fatalities. A noise propagation model is used to determine the extent of effects due to the installation of fixed and floating support structures using piling installation methods. Finally, a summary of progress in all the major environmental impact areas is given along with recommendations for future research.
A Finite Volume Approach For Cure Kinetics Simulation
(2012-05) Ma, Wei
In our study, the Finite Volume Method (FVM) is successfully implemented to simulate thermal process of polymerization. This application is verified based on the obtained plots compared with those from other two methods as well as experimental data. After the verification, a method is developed to optimize heat history in order to reduce processing time and in the meantime to maintain the uniformity of cure state. Also sensitivities of cure state to different parameters are examined. Besides, a correlation between temperature and the degree of polymerization profile on sample surface is found using on-line monitoring method.
Semi-Active Damping for an Intelligent Adaptive Ankle Prosthesis
(2012) Lapre, Andrew K
Modern lower limb prostheses are devices that replace missing limbs, making it possible for lower limb amputees to walk again. Most commercially available prosthetic limbs lack intelligence and passive adaptive capabilities, and none available can adapt on a step by step basis. Often, amputees experience a loss of terrain adaptability as well as stability, leaving the amputee with a severely altered gait. This work is focused on the development of a semi-active damping system for use in intelligent terrain adaptive ankle prostheses. The system designed consists of an optimized hydraulic cylinder with an electronic servo valve which throttles the hydraulic fluid flowing between the cylinder’s chambers, acting on the prosthesis joint with a moment arm in series with a carbon spring foot. This provides the capability to absorb energy during the amputees gait cycle in a controlled manner, effectively allowing the passive dynamic response to be greatly altered continuously by leveraging a small energy source. A virtual simulation of an amputee gait cycle with the adaptive semi-active ankle design revealed the potential to replicate adaptive abilities of the human ankle. The results showed very similarly that irregularities in amputee biomechanics can be greatly compensated for using semi-active damping.
Viscoelastic Flow through Contraction Geometries
(2012-05) Sankaran, Ashwin Karthik
Contraction flow of viscoelastic fluids has been a benchmark problem in non-Newtonian fluid mechanics because it mimics flows occurring in a number of industrial applications. It is also of considerable interest to academia to gain fundamental understanding of factors that affect the evolution of vortices and a complete understanding of the dynamics for a simple polymeric fluid has not been achieved. In this two part study we investigate the effect of pre deformation of a Boger fluid in a contraction geometry and the flow of surfactants in a parallel contraction geometry. Entry flow of a polymeric fluid results in the formation of upstream vortices,the presence of recirculation zones may lead to a nonuniform residence time and hence inferior quality products. In this work we study the effect of pre-stretching dilute flexible chain polymers by placing a cylinder in front of a contraction in a microfluidic device.This deformation applied to the polymer is remembered before it completely relaxes, this memory effect changes the rheological properties during the fading period of the deformation history. Applying pre-deformation gives rise to new type of vortex evolution that is different from the standard contraction case. Semi-dilute surfactant solutions that exhibit shear thickening nature can be potentially used in enhanced oil recovery to increase the sweep efficiency. Two parallel microfluidic contractions of different cross sectional area are used to investigate the rheological effect on the mass flux of the two channels. Shear thickening micellar solutions were found to increase the mass flux through the small channel compared to a newtonian fluid. This effect was observed only for a small range of flow rates. As flow rates increased inlet instabilities were observed that evolved into a chaotic behavior upon further increase in the net flow rate.
Computational Methods for the Analysis of Non-Contact Creep Deformation
(2012-02) Ye, Xiao
Currently, various needs from industry, science and national defense strategy demand materials with cutting-edge ultra-high temperature performances. Typical applications of ultra-high temperature materials (UHTMs) are supersonic airplanes, gas turbines and rocket nozzles which usually require continuous service of critical components at temperatures higher than 1600°C. Creep resistance is a critical criterion in designing materials for these applications. Traditional creep characterization methods, however, due to limitations on cost, accuracy and most importantly temperature capability, gradually emerge as a bottleneck. Since 2004, a group of researchers in the University of Massachusetts, Amherst have been designing a new high temperature characterization scheme that can break through the limits of traditional methods. Their method is based on non-contact creep tests conducted with Electrostatic levitation (ESL) facilities in NASA Marshall Space Flight Center in Huntsville Alabama. The tested sample is levitated in electric field and is heated as well as rotated with specially positioned laser beam. After certain amount of time, the sample deforms under centripetal forces. By comparison of the shape of the deformed sample with results from finite element simulation, creep behavior of the tested material can be characterized. Based on the same theory, this thesis presents a computational creep characterization method based on non-contact method. A finite element model was built to simulate non-contact creep behavior and results were compared to ESL experiments to determine the creep characteristic. This method was validated both theoretically and numerically and then applied to creep characterization of a promising ultra-high temperature composite from General electric (GE).
Load Reduction of Floating Wind Turbines using Tuned Mass Dampers
(2012) Stewart, Gordon M
Offshore wind turbines have the potential to be an important part of the United States' energy production profile in the coming years. In order to accomplish this wind integration, offshore wind turbines need to be made more reliable and cost efficient to be competitive with other sources of energy. To capitalize on high speed and high quality winds over deep water, floating platforms for offshore wind turbines have been developed, but they suffer from greatly increased loading. One method to reduce loads in offshore wind turbines is the application of structural control techniques usually used in skyscrapers and bridges. Tuned mass dampers are one structural control system that have been used to reduce loads in simulations of offshore wind turbines. This thesis adds to the state of the art of offshore wind energy by developing a set of optimum passive tuned mass dampers for four offshore wind turbine platforms and by quantifying the effects of actuator dynamics on an active tuned mass damper design. The set of optimum tuned mass dampers are developed by creating a limited degree-of-freedom model for each of the four offshore wind platforms. These models are then integrated into an optimization function utilizing a genetic algorithm to find a globally optimum design for the tuned mass damper. The tuned mass damper parameters determined by the optimization are integrated into a series of wind turbine design code simulations using FAST. From these simulations, tower fatigue damage reductions of between 5 and 20% are achieved for the various TMD configurations. A previous study developed a set of active tuned mass damper controllers for an offshore wind turbine mounted on a barge. The design of the controller used an ideal actuator in which the commanded force equaled the applied force with no time lag. This thesis develops an actuator model and conducts a frequency analysis on a limited degree-of-freedom model of the barge including this actuator model. Simulations of the barge with the active controller and the actuator model are conducted with FAST, and the results are compared with the ideal actuator case. The realistic actuator model causes the active mass damper power requirements to increase drastically, by as much as 1000%, which confirms the importance of considering an actuator model in controller design.
Techniques for Industrial Implementation of Emerging Semantic Technologies
(2012) Breindel, Jay T.
Techniques for the industrial implementation of emerging semantic technologies are presented in this research. Every new design, project, and procedure within a company generates a considerable amount of new information and important knowledge. Furthermore, a tremendous amount of legacy knowledge already exists within companies in electronic and non-electronic formats. All of this generated knowledge results in the need for tools and techniques to represent, structure, and reuse this knowledge. Researchers have spent considerable time and effort developing semantic knowledge management systems, with anticipation that these tools will address these knowledge management needs. However, little has been done to implement these systems within an industrial setting. In this thesis, we identify five main requirements for the development of an industry-ready, semantic knowledge management system, and we discuss how each of these requirements can be methodically addressed. The five requirements include the incorporation of legacy information, the ease of new knowledge management software adoption, the robustness of the software to support multiple file types and allow for the sharing of information across platforms, the security of the stored information, and the ease of use of the user interface. In collaboration with Raytheon, a defense and aerospace systems company, we developed and demonstrated a novel approach for the successful adoption of semantic abilities by a commercial company. Salient features of this work include a new tool, the e-Design MemoExtractor Software Tool, custom designed to mine and capture company information, a Raytheon-specific ontology extension to the e-Design Framework, and a novel semantic environment in the form of a customized semantic media wiki SMW+. The advantages of this approach and the associated research issues are discussed in the context of the industrial case study with Raytheon.
Simulations of Non-Contact Creep in Regimes of Mixed Dominance
(2012-02) Benitz, Maija
Improvement of high temperature applications relies on the further development of ultra-high temperature materials (UHTMs). Higher performance and efficiency is driving the need for improvements in energy conversion and propulsion systems. Rocket nozzles, gas turbine engines and hypersonic aircraft depend on a better understanding of a material's performance at high temperatures. More specifically, the characterization of creep properties of high temperature materials is required. Conventional creep testing methods are limited to about 1700 degrees Celsius. Non-contact methods have been developed, which rotate spherical samples up to 33,000 rotations per second. A load is supplied by centripetal acceleration causing deformation of the sample. Non-contact methods have been performed above 2000 degrees Celsius. The induction drive developed in the previous work has decoupled temperature from rotation, greatly expanding the experimental testing range. Creep mechanisms may involve dislocation motion or the diffusional flow of atoms. Creep may be dominated by dislocation glide, dislocation climb, or diffusional-flow mechanisms. Multiple creep mechanisms can be active in a sample, but one is often dominant in a given regime which depends on stress, temperature and grain size. This work studies the creep behavior of samples in regions of transition between dominating creep mechanisms, and the effect on the precision of the measurement. Two finite element models have been developed in the current work. A two-dimensional Norton creep model replaces the more computationally expensive three-dimensional Norton creep model developed in the previous work. Furthermore, a two-dimensional Double Power Law model has been developed to simulate creep behavior of high temperature materials in regimes of mixed dominance. The two-dimensional Norton and Double Power Law models are used to identify and characterize creep in the regions of transition between dominating creep mechanisms. Simulations are analyzed to determine the effect of regimes of mixed dominance on the creep measurements of rotating samples of high temperature materials.
Assessing the Biomechanical Effect of Alveoli, Periodontal Ligaments, and Squamosal Sutures in Mammalian Crania
(2011) Wood, Sarah
The research presented in this thesis focuses on understanding the biomechanical effects of various cranial features that are often ignored in finite element models (FEMs) because their size, position, and complex shapes make them difficult to model. Specifically, this work examines the effects of the alveoli (tooth sockets), periodontal ligament, and squamosal suture on the stress and strain distributions in a cranium under masticatory and dynamic tooth loads. Results from this research will help determine if these features have a significant effect on stress and strain patterns and will yield guidelines as to if or under what conditions they need to be modeled in future FE skull model analyses. As part of this research, three sets of FEMs were developed to address a hypothesis focusing on each cranial feature. The first set of models examined the effect of the tooth sockets on the stress and strain distributions in a cranium under static biting conditions to determine if improperly modeled sockets produce strong global effects in craniofacial regions. The second set of models were used to assess the effect of the PDL's material behavior on the stresses and strains in a cranium under static biting and dynamic tooth loading conditions to determine if the PDL plays an important role in reducing stresses and strains in a model. The final set of models were used to determine the effect of the squamosal suture size on the stresses and strain energies in a cranium under static biting conditions to see if an increase in suture size decreases the risk of separation of the temporal bone from the parietal bone. Results for all analyses indicate the effects of the cranial features are local (i.e. within the vicinity of the feature), with no meaningful global effects. This suggests the sockets, PDL, and squamosal suture do not play an important role in global stress and strain distributions in a cranium under masticatory and dynamic tooth loads. Therefore, it may be safe to ignore the sockets, PDLs, and squamosal sutures during the FE modeling process if the objective of the analysis is to understand global stress and strain patterns.

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