Browsing by Author "Stansloski, Mitchell, committee member"
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Item Open Access A tabu search evolutionary algorithm for multiobjective optimization: application to a bi-criterion aircraft structural reliability problem(Colorado State University. Libraries, 2015) Long, Kim Chenming, author; Duff, William S., advisor; Labadie, John W., advisor; Stansloski, Mitchell, committee member; Chong, Edwin K. P., committee member; Sampath, Walajabad S., committee memberReal-world engineering optimization problems often require the consideration of multiple conflicting and noncommensurate objectives, subject to nonconvex constraint regions in a high-dimensional decision space. Further challenges occur for combinatorial multiobjective problems in which the decision variables are not continuous. Traditional multiobjective optimization methods of operations research, such as weighting and epsilon constraint methods, are ill-suited to solving these complex, multiobjective problems. This has given rise to the application of a wide range of metaheuristic optimization algorithms, such as evolutionary, particle swarm, simulated annealing, and ant colony methods, to multiobjective optimization. Several multiobjective evolutionary algorithms have been developed, including the strength Pareto evolutionary algorithm (SPEA) and the non-dominated sorting genetic algorithm (NSGA), for determining the Pareto-optimal set of non-dominated solutions. Although numerous researchers have developed a wide range of multiobjective optimization algorithms, there is a continuing need to construct computationally efficient algorithms with an improved ability to converge to globally non-dominated solutions along the Pareto-optimal front for complex, large-scale, multiobjective engineering optimization problems. This is particularly important when the multiple objective functions and constraints of the real-world system cannot be expressed in explicit mathematical representations. This research presents a novel metaheuristic evolutionary algorithm for complex multiobjective optimization problems, which combines the metaheuristic tabu search algorithm with the evolutionary algorithm (TSEA), as embodied in genetic algorithms. TSEA is successfully applied to bicriteria (i.e., structural reliability and retrofit cost) optimization of the aircraft tail structure fatigue life, which increases its reliability by prolonging fatigue life. A comparison for this application of the proposed algorithm, TSEA, with several state-of-the-art multiobjective optimization algorithms reveals that TSEA outperforms these algorithms by providing retrofit solutions with greater reliability for the same costs (i.e., closer to the Pareto-optimal front) after the algorithms are executed for the same number of generations. This research also demonstrates that TSEA competes with and, in some situations, outperforms state-of-the-art multiobjective optimization algorithms such as NSGA II and SPEA 2 when applied to classic bicriteria test problems in the technical literature and other complex, sizable real-world applications. The successful implementation of TSEA contributes to the safety of aeronautical structures by providing a systematic way to guide aircraft structural retrofitting efforts, as well as a potentially useful algorithm for a wide range of multiobjective optimization problems in engineering and other fields.Item Open Access Design, modeling, and optimization of 3D printed compliant mechanisms with applications to miniature walking robots(Colorado State University. Libraries, 2018) DeMario, Anthony R., author; Zhao, Jianguo, advisor; Stansloski, Mitchell, committee member; Maciejewski, Anthony, committee memberMiniature robots have many applications ranging from military surveillance to search and rescue assistance in disaster areas. Traditionally, fabrication of these robots has been labor intensive, time-consuming, and expensive. This thesis proposes to leverage recent advances in 3D printing technology to fabricate centimeter-scale walking robots utilizing compliant elements printed directly into the walking mechanisms in replacement of traditional revolute joints or rigid links. The ability to design around the capabilities of 3D printers and novel material choices gives miniature robots the ability to have multiple functions in the same mechanism, reduces the overall number of parts that must be assembled to make a functional robot, and decrease the time and cost of prototyping. This thesis details three areas of study for compliant mechanisms with applications to walking robots. First, we utilize multi-material 3D printing to fabricate a miniature walking robot (49 x 38 x 25mm) that directly replaces the traditional revolute joints in the designed walking mechanism with a custom, soft joint. Some links are also printed with soft materials to enhance the robustness and durability of the robot. Along with design and testing of the robot, we develop two numerical models to simulate the effects of the soft elements on the mechanism trajectory. Second, we leverage the numerical models to optimize the design of the walking mechanism to produce a trajectory similar to that of the same mechanism using all revolute joints. Third, we redesign the original robot to utilize a conductive polylactic acid (PLA) material to 3D print linkages that allow for changing joints locations by softening the desired part through applied electricity. This variable joint mechanism can create multiple trajectories without changing the mechanical structure, therefore creating a multi-functional compliant mechianism. Such capabilities are demonstrated throughwalking on the ground and grasping objects using the same leg mechanism.Item Open Access Dynamic structural analysis of ramming in bighorn sheep(Colorado State University. Libraries, 2015) Drake, Aaron Michael, author; Haut Donahue, Tammy L., advisor; Donahue, Seth W., advisor; Stansloski, Mitchell, committee member; Heyliger, Paul, committee memberConcussions are the most common traumatic brain injury and are caused by impulsive loads applied to the skull, resulting in relative motion of the brain within the brain cavity. Despite wearing helmets, athletes involved in full contact sports, such as football, are highly susceptible to concussive injuries. Short term symptoms of concussions include nausea, headache and confusion and there is evidence of more serious, long term effects from repeated concussions. Furthermore, the physical mechanisms of concussions are not well understood, making them difficult to diagnose and treat clinically. Male bighorn sheep sustain massive impact loads to the head during ramming, which is done as a means of determining hierarchy and gaining mating privileges. These large animals thrust themselves, horns first, at one another and collide violently, repeating this ritual for up to several hours until the subdominant male succumbs. After a collision, the animals are stunned momentarily but otherwise appear to suffer no ill effects, based on behavioral observations. This simple fact provided the motivation to examine the dynamic structural behavior of bighorn sheep horns and skulls. For reference, the average translational brain cavity accelerations observed during finite element model impact were found to be 111g (1091 m/s²) and impacts thought to be damaging to human brains occur at around 100g. A dynamic finite element impact model was produced using the geometry, obtained from a CT scan, of a mature male bighorn sheep’s skull and horns. Quantitative and qualitative results of the simulation were examined to determine mechanisms of energy dissipation and stress distribution during an idealized impact event. Video analysis of particularly forceful ramming sequences of wild bighorn sheep was carried out to estimate the dynamics involved with ramming. In order to investigate the relative contributions of the horn curl as well as the internal foamy bone architecture, three separate finite element models were produced. One model had one half of the horn length removed, another had the internal foam-like bone removed and these models were compared to the fully intact model to determine the structural contributions of these features during impact. Removing one half of the horn curl had the effect of increasing the peak brain cavity translational acceleration by 49%. Eliminating the internal foamy bone architecture resulted in a dramatic 442% increase in brain cavity rotational accelerations. The dynamic (vibrational) response of bighorn sheep horns and skulls was investigated using two, related methods: finite element modal analysis and experimental modal analysis. The finite element modal analysis revealed five dominant natural frequencies with values ranging from 118 to 309 Hz. Experimental modal analysis revealed several natural frequencies between 100 and 300 Hz, however, differentiating specific modes was difficult. For both vibrational analyses the dominant vibrational mode shape was side-to-side oscillations of the horn tip. This study hopes to promote and guide further research on the mechanisms of brain trauma prevention in bighorn sheep, with an emphasis on the structural and material characteristics of the horn and skull, to increase our understanding of, and ways to prevent traumatic brain injuries in humans.Item Open Access Empirical modeling of automotive damper curves and development of shape factors(Colorado State University. Libraries, 2013) Nair, Sreedhu S., author; Fitzhorn, Patrick, advisor; Stansloski, Mitchell, committee member; Catton, Kimberly, committee memberAutomotive dampers are a complex system developed with integration of simple mechanisms. The system comprises of a cylinder filled with hydraulic fluid, a piston dividing cylinder into two chambers known as compression and rebound chambers; a coil spring in some case and nitrogen gas. When a vehicle moves, automotive Damper system deals with damping vibration and giving occupants a comfortable ride. While the system ensures a smooth ride by absorbing all the road vibration, hydraulic fluid inside the Damper system goes through various transformations. Changes and variations happen in properties like pressure and temperature inside the Damper system with time because of displacement of piston which leads to generation of heat which leads to change in damping coefficient. While calculating energy equation, it was observed that constant damping coefficient was used and was not a function of time. In a real world scenario this assumption is not correct because with changes in above mentioned properties, damping coefficient values are affected and they change constantly with time. Research was commenced on coming up with an empirical model that can give information regarding energy inside a Damper system, types of suspension behavior and various characteristics regarding Damper system for any range of velocities. A full-fledged Damper system empirical model will have various constants, parameters, shape factors and form factors. If these parameter values are obtained and used properly, they can give help determining the behavior of any Damper system, different settings that can be used to get required behavior by any Damper system. For a full-fledged empirical model, lots of efforts, resources and years of research will be required. So, to start with, an empirical model was worked upon that can act as a shape factor for any Damper system for given range of velocities. Any Damper system will give three different types of curves a progressive curve, a linear curve and a digressive curve. The three curve shows three kinds of suspension behavior which is required depending upon the application. Keeping this in mind, a model was created which was able to depict all three damper curves for certain range of values for both compression chambers and rebound chamber inside a damper. The model is a function of various trigonometric functions like sine, arctans, hyperbolic functions and property like velocity. There are constant parameters and changing their values will change shape of damper curve as per the requirement. Developed Empirical Model is able to fulfill the initial requirement of becoming a proper shape factor and can be used to predict behavior of Damper system for both compression and rebound chamber. Main reasons behind obtaining damper curves are the constant parameters associated with it. Those parameters can be related to any characteristics or properties associated with function and performance of a Damper system. Developed Empirical model acts as a foundation for next stage of research because once the shape factor is achieved; the parameters associated with it can be given a meaning based on Damper system's properties and characteristics.Item Open Access Evaluation of wind turbine towers under the simultaneous application of seismic, operation and wind loads(Colorado State University. Libraries, 2013) Smith, Vanessa, author; Mahmoud, Hussam, advisor; Bienkiewicz, Bogusz, committee member; Stansloski, Mitchell, committee memberWind turbines are widely recognized as a renewable energy resource and as such, their safety and reliability must be ensured. Many studies have been completed on the blade rotor and nacelle components of wind turbines under wind and operation loads. While several studies have focused on idealized wind turbine models, significant advancements on the global and local performance of these models under seismic loads in combination with other loads has been lacking. A study on the evaluation and performance of realistic wind turbine models under wind, operation and seismic loads is proposed and successfully completed. First, the geometry and loading for three wind turbine models are developed. A series of finite element analyses is conducted for each model under a variety of load combinations and earthquake records. Both global results and localized behavior were obtained for each analysis in order to identify areas of improvement within the wind turbine structure. Global results include drift ratios, normalized base shear and fast Fourier transformations to evaluate the stability of the wind turbine during operation. Localized performance focused on the welded connection at the base of the turbine and included Von Mises stresses as well as low-cycle fatigue analyses to determine the number of cycles to failure (initiation of through-thickness crack). These results show that certain turbine models are more susceptible to these loads than others. Several analyses indicate yielding at the turbine base and resonant conditions. The results from these analyses identify several critical issues within the wind turbine design and operation protocol.Item Open Access Feasibility assessment of magnetic sensors for measurement of Hall current induced changes to the static magnetic field nearby a Hall thruster(Colorado State University. Libraries, 2013) Morozko, Zoe, author; Williams, John, advisor; Stansloski, Mitchell, committee member; Thornton, Christopher, committee memberA Hall thruster is an electric propulsion device that produces thrust electrostatically by accelerating propellant to velocities 5 to 10 times higher than is achievable using conventional chemical thrusters. This is accomplished through the application of static, crossed electric and magnetic fields that are concentrated in a region close to the exit plane of the thruster. During operation an azimuthal plasma-electron current develops in the region where the electric and magnetic fields are concentrated. This embedded plasma current is referred to as the Hall current. The thrust produced from accelerating the propellant is transferred to a satellite or spacecraft through interaction between the Hall current and the magnetic coils used to produce the static magnetic field within the thruster. The Hall current can be calculated and the thrust can be determined in real time by measuring the magnetic field produced by the Hall current using sensors located external to the thruster. This work investigates the feasibility of placing magnetic sensors in the regions close to the exit of the thruster to measure the external magnetic field and correlate it to the Hall current. A finite element magnetic solver was used to identify several locations outside of the thrust plume and near the pole piece where the magnetic field magnitude changes by several Gauss in a background field level of ~50 Gauss. Magnetic sensors based on the giant magnetoresistive effect were identified as acceptable with regard to sensitivity, and measurements made with these sensors in a simulated high background magnetic field environment demonstrated that changes of 0.5 Gauss could be easily measured. This work also presents the development of a thrust stand that will be useful in future work to demonstrate the overall concept. Special focus was directed to the design of the data acquisition system and in-vacuum calibration system used to make measurements with the thrust stand.