Дисертації: "Mechanical and aerospace"

1

Moore, Gareth Edward. "Electro-mechanical interactions in aerospace gas turbines." Thesis, University of Nottingham, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.768249.

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The provision of electrical power on modern aircraft is a necessary and growing aspect of a gas turbine's function. The replacement of traditional pneumatic, hydraulic and mechanical systems with electrical equivalents means that electricity is now the dominant means of power distribution on aircraft. However, the electrical loads seen on aircraft present challenges, as they are time varying and are often non-linear. This is particularly true for loads such as radar. The aviation industry has adopted the term More Electric Aircraft (MEA) to describe the latest generation of aircraft with a high reliance on electrical power. There is potential for significant interaction between the transient variation of electrical loading and the gas turbine (both drive-train and engine core). Engine testing and initial simulation work support this view. Understanding of this phenomenon must now be furthered through modelling and testing. This thesis presents simulation models of a transmission system and generator interface, which provides a useful kernel for a modelled system to assess electro-mechanical interaction. This is extended to multi-domain simulation work through the successful interlinking of transmission, generator and an electrical load model. These models have been validated, at a domain level, against analytical expressions, and also as a complete electro-mechanical system against test data. To allow more control over test conditions, an electro-mechanical test rig is designed and constructed. The data from the test rig is analysed and compared to modelled results. This thesis also presents potential mitigation actions for avoiding unwanted electro-mechanical interactions during electrical load transients. A method of extracting transient mechanical torque information from a gas turbine's electrical generator's terminal quantities is included. At a system level, the simulation work in this thesis potentially enables the development of future designs with improved power systems integration throughout the entire airframe. High level control could allow optimisation of the power conversion process between gas turbine spool and electrical systems, with increased intelligence in the movement of power between components.

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2

Stimac, Andrew K. (Andrew Kenneth) 1977. "Precision navigation for aerospace applications." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16676.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.
Vita.
Includes bibliographical references (p. 162). Includes bibliographical references (p. 162).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Navigation is important in a variety of aerospace applications, and commonly uses a blend of GPS and inertial sensors. In this thesis, a navigation system is designed, developed, and tested. Several alternatives are discussed, but the ultimate design is a loosely-coupled Extended Kalman Filter using rigid body dynamics as the process with a small angle linearization of quaternions. Simulations are run using real flight data. A bench top hardware prototype is tested. Results show good performance and give a variety of insights into the design of navigation systems. Special attention is given to convergence and the validity of linearization.
by Andrew K. Stimac.
S.M.

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3

Cauberghs, Julien. "Out-of-autoclave manufacturing of aerospace representative parts." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106593.

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The use of carbon fibre reinforced composites for aerospace structures has seen a high increase in recent years, and is still growing. The high stiffness-to-weight ratio of these materials makes them ideal for primary structures on airplanes, satellites, and spacecrafts. Nevertheless, the manufacturing of composites remains very costly since it requires equipment investment such as an autoclave, and very qualified workers. Out-of-autoclave manufacturing technology is very promising since it only requires a traditional oven, while still aiming at similar part quality. However, the absence of positive pressure compared with an autoclave makes it more difficult to achieve low porosity parts. This research investigates the manufacturing of complex features with out-of autoclave prepreg technology. The features studied are tight-radius corners with a curvature change, and ply drop-offs. Ply drop-offs tests were conducted to identify if porosity is higher at ply terminations. In corners, the bagging arrangement was modified to achieve the most uniform thickness in areas of curvature change, even with small radii. The conclusions from these studies provided us with guidelines to manufacture larger representative parts, which included these features. The representative parts were tested for porosity, thickness uniformity, mechanical performance, and glass transition temperature(Tg). A total of four representative parts were manufactured with out-of-autoclave technology, and one more was manufactured with an autoclave to allow for a proper comparison between the two processes. The materials used were MTM45-1 5 harness satin and CYCOM5320 plain weave for the out-of-autoclave parts,and CYCOM5276-1 plain weave for the autoclave part. The effect of ply dropoffs on porosity was found to be negligible. Thickness deviation in corners was attributed to a combination of consumable bridging, prepreg's bulk factor and inter-ply shear. Overall, out-of-autoclave prepregs showed performance similar to autoclave prepregs.
L'utilisation de matériaux composites en fibres de carbone pour des structures aéronautiques a connu une croissance rapide ces dernières années, et continue de croitre. Le rapport raideur/masse de ce type de matériaux en fait une solution idéale pour les structures primaires d'avions, de satellites, ou de navettes spatiales. Toutefois, la fabrication de ces pièces en composites demeure extrêmement couteuse puisqu'elle nécessite de lourds investissements d'équipement tels que l'acquisition d'un autoclave, ainsi que de la main-d'oeuvre qualifiée. La technologie hors autoclave semble très prometteuse puisqu'elle ne requiert que l'utilisation d'un four traditionnel, tout en visant à obtenir des pièces de qualité similaire. Cependant, l'absence de pression extérieure provenant de l'autoclave rend plus délicate l'obtention de pièces ayant une faible porosité. Cette recherche a pour thème la fabrication d'éléments complexes avec la technologie hors autoclave. Les éléments étudiés sont des angles convexes et concaves ayant de faibles rayons de courbure, ainsi que des plis partiels. Des tests sur les plis partiels ont été réalisés pour déterminer si ils sont associés à une augmentation de la porosité. Dans les angles, l'arrangement des consommables a été modifié pour obtenir l'épaisseur la plus uniforme possible dans les zones de changement de courbure, et cela même pour de faibles rayons. Les conclusions de ces tests nous ont permis de considérer la fabrication de pièces représentatives de plus grande taille, et qui contiennent les éléments précédemment étudiés. Les pièces représentatives ont été testées pour déterminer leur niveau de porosité, l'uniformité de leur épaisseur, leur performance mécanique, et leur température de transition vitreuse. Au total, quatre pièces représentatives ont été fabriquées par technologie hors autoclave, et une a été fabriquée dans un autoclave afin de permettre une comparaison de bon aloi entre ces deux procédés de fabrication. Les matériaux utilisés pour cette recherche étaient du MTM45-1 5 harness satin et du CYCOM5320 plain weave pour les pièces hors autoclave, ainsi que du CYCOM5276-1 plain weave pour la pièce autoclave. La présence de plis partiels n'a pas été associable à une augmentation notable de la porosité. L'uniformité d'épaisseur s'est révélée être une combinaison de pontage des consommables, du facteur de foisonnement du pré-imprégné, et du cisaillement entre les plis de fibre. Globalement, les pré-imprégnés hors autoclave ont montré des performances similaires aux pré-imprégnés autoclave.

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4

Nill, Scott T. (Scott Thomas). "Aerospace composite manufacturing cost models as geometric programs." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118731.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 108-110).
The introduction of large, composite transport aircraft, such as the Airbus A350 and the Boeing 787, has been fraught with billions of dollars of production cost overruns. This research develops a novel approach to manufacturing cost modeling during the conceptual design phase using Geometric Programming (GP). A new formulation of a closed queuing network as a GP is presented to capture the crucial cost trade-offs between capacity and inventory. Additionally, GP models are presented for modeling unit processes in composite manufacturing and for modeling cost accounting metrics. Applied to the challenges of conceptual design for composite aircraft, the cost models can be used as a tool to help inform decisions about which manufacturing process to use and what type of supply chain should be deployed. The special sensitivity-analysis properties of the GP solutions can be exploited to explain how different aspects of the design drive manufacturing costs and to find highly sensitive areas of the trade-space that would have a large impact on cost if the design needed to be altered. The framework is demonstrated for fast but informative analyses of process trade-offs in composite fuselage fabrication.
by Scott T. Nill.
Ph. D.

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5

Kirtley, Aaron L. (Aaron Lloyd) 1977. "Fostering innovation across aerospace supplier networks." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/82696.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2002.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
"June 2002." Page 187 blank.
Includes bibliographical references (p. 180-184).
by Aaron L. Kirtley.
S.M.

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6

Negri, Christopher Anthony. "Ductile Fracture of Laser Powder Bed Fusion Additively Manufactured Ti-6Al-4V." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1627570434852405.

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7

Chiu, Brendon W. "Additive manufacturing applications and implementation in aerospace." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/126950.

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Thesis: M.B.A., Massachusetts Institute of Technology, Sloan School of Management, May, 2020
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, May, 2020
Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 107-108).
Many aerospace companies are turning to additive manufacturing solutions to stream-line current production processes and open opportunities for on-demand producibility. While many OEMs are drawn to the appeal of the benefits that additive manufacturing brings, they are beginning to understand the difficulties in what it takes to realize those benefits. This paper analyzes additive manufacturing from an industry perspective down to a company perspective to develop a deeper understanding of the practical use cases as well as the various challenges a company faces should they choose to enter this market. This study begins with market research on the additive manufacturing and aerospace industry before honing in on a several use-case parts from rotary aircraft. Selection criterion were created and applied to analyze the value that additive manufacturing would bring in comparison to that of conventional methods, ultimately determining its feasibility for additive manufacturing.
This study applied the selection criterion to various parts of differing functions among the aircraft, resulting in a group of candidate parts. An evaluation method was created and applied to provide an objective assessment on the candidate parts. Initial insights show that additive manufacturing favor casted parts with features that can be optimized to increase performance and reduce costs and weight. In addition, aerospace has the best product mix of low volume parts that are advantageous to the economies of scale for additive manufacturing. Additionally, this study analyzes a company's organization and previous additive manufacturing efforts to propose ways to approach future development. Venturing through the various road maps that lead to the final goal of certification and addressing organizational barriers generate momentum for continuous development.
These road maps, selection criterion, and evaluation method can be applied through many applications within the general aerospace industry.
by Brendon W Chiu.
M.B.A.
S.M.
M.B.A. Massachusetts Institute of Technology, Sloan School of Management
S.M. Massachusetts Institute of Technology, Department of Mechanical Engineering

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8

Mohammed, Mohammed Abdelaziz Elamin. "IMPACT AND POST IMPACT RESPONSE OF COMPOSITE SANDWICH STRUCTURES IN ARCTIC CONDITION." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1518520473027006.

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9

Frauenberger, Douglas H. "Lean transformation in aerospace assembly operations." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39728.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; in conjunction with the Leaders for Manufacturing Program at MIT, 2007.
Includes bibliographical references (p. 81-82).
For the past two decades, virtually all manufacturing companies in the United States have adopted or are in the process of adopting lean manufacturing. Globalization has resulted in the increased availability of reliable, low cost sources putting greater pressures on traditional US manufacturing companies to reduce costs. The need to successfully transform to lean has only grown in importance in this new operating environment, resulting in renewed focus on such initiatives in the United States. This thesis discusses various approaches to lean manufacturing with reference to specific examples from both academia and industry. In particular, lean transformation efforts in Mitchell Engine Company's* Final Assembly Plant will be provided as a case study. Focus on the JP-3525 fan case assembly cell provides specific examples on how shop floor improvements, assembly cell redesign, and flow can improve process cycle time and decrease variability. The direct result of this work has been a 15% decrease in cycle time and a 100% decrease in variability in the JP-3525 fan case assembly cell. Finally, the role front-line supervisors play in change initiatives will be introduced, discussing the position from both management and labor perspectives. Based on past research, recommendations will be made on how to improve cell leader effectiveness, recognizing these changes require systemic change within the organization.
by Douglas H. Frauenberger.
M.B.A.
S.M.

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10

Buettner, Robert W. "Dynamic Modeling and Simulation of a Variable Cycle Turbofan Engine with Controls." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1496179248257409.

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11

Anderson, Mary Ann. "Analysis of flexible assembly implementation in the automotive and aerospace industries." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10285.

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12

Rossie, Kathleen Eaton. "An energy and environmental analysis of aerospace sheet metal part manufacturing." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101487.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 223-246).
In this thesis we analyze the energy and environmental impacts of sheet metal manufacturing, focusing on the aerospace industry. The motivation of this work is the introduction of a new incremental sheet forming (ISF) technology called RAFFT, which substitutes heavy part specific dies for flexible generic tools but with a slower processing rate. The analysis has two sections. The first section analyzes the current aerospace sheet forming technological and economic landscape in order to determine RAFFT's probable adoption rate and predict which technologies it will displace. The second section includes four energy and lifecycle analysis (LCA) case studies on traditional forming technologies. The first section maps the process capabilities of twenty sheet forming technologies. It also describes the business needs and typical practices of the aerospace industry, including a classification of the different business needs for parts. We find that stretch forming and flexforming (also known as a bladder press or hydroforming) dominate current aerospace production, and superplastic forming SPF is used when high formability is required. Machining is used extensively for very low volume production, such as prototyping. We find that the new RAFFT technology is best suited for very low volume production such as the production of replacement parts. The second section includes energy and LCA case studies for titanium SPF, aluminum SPF, flexforming, and stretch forming. Moreover, case studies on kirksite and cast iron die manufacturing are completed because these materials are used in forming dies. We find that SPF uses more energy and has higher impacts than stretch and flexforming. We also find that each technology has high "baseload" (no forming) electricity use due to heat losses in SPF and circulation of hydraulic fluid in stretch and flexforming, meaning that cycle time is a critical factor in electricity use. Lastly, we find that the material for the blank, the die, and the electricity can each dominate impacts depending on the particular characteristics of each case because a) the aerospace industry is willing to invest significant resources, be it time, energy, or material, to produce the desired part and b) the required amount of blank, die, and electricity are dependent on uncorrelated factors.
by Kathleen Eaton Rossie.
S.M.

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13

Dobbs, Daniel C. 1975. "Development of an aerospace manufacturing system design decomposition." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/89302.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M.)--Massachusetts Institute of Technology, Technology and Policy Program, 2000.
Includes bibliographical references (p. 173-175).
by Daniel Charles Dobbs.
S.M.

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14

King, Rachel Marie. "Study of an Adaptive Mechanical Turbulator for Control of Laminar Separation Bubbles." NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20010508-105403.

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Low Reynolds number experiments have been conducted in the North Carolina State University Subsonic Wind Tunnel Facility to determine the feasibility of using an adaptive mechanical turbulator to control in a predetermined manner a laminar separation bubble. The experimental set-up consists of a flat plate with an inverted airfoil mounted above its surface. This set-up permits laminar separation bubbles to be examined over a range of Reynolds numbers and pressure distributions. An SMA-actuated mechanical turbulator is developed in the present work. A multi-element hot-film array is used to detect the laminar separation, transition to turbulence, and turbulent reattachment in the laminar separation bubble. The effects of turbulator height and Reynolds number on the mean, the standard deviation, the skewness, and the kurtosis of the hot-film signals are examined. The experimental results agree well with the theoretical predictions of laminar separation, transition, and turbulent reattachment obtained using a viscous/inviscid analysis code.For the range of trip heights examined, that is up to 30 percent of boundary layer thickness, the adaptive boundary layer trip is not suited to provide proportional control of a laminar separation bubble, as no monotonic variation of location in separation, transition, or reattachment is observed with varying trip height. However, the hot-film measurements show promise for providing in real time the identification of the primary features of the laminar separation bubble.

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15

Boulet, Michael Thomas. "Design of a small fast steering mirror for airborne and aerospace applications." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45955.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.
Includes bibliographical references (p. 177-181).
This thesis presents the analysis and design of a small advanced fast steering mirror (sAFSM) for airborne and aerospace platforms. The sAFSM provides feedback-controlled articulation of two rotational axes for precision optical pointing. The design, useful for both disturbance rejection and high-speed scanning applications, incorporates a flux steering actuator with a ring core magnetic configuration. The novel magnetic concept enables a dramatic size reduction compared with heritage systems. The moving armature is supported with a combination of elastomer sheets and active position control. Local angular and mirror-normal displacement is sensed with integrated capacitive sensors. Analysis content includes specification of performance requirements based on a realistic deep-space laser communication mission, magnetic equivalent circuit and three-dimensional magnetostatic finite element analysis of the actuator, and a 3D structural optimization of the moving armature modal frequencies. The resulting design is one iteration removed from a flight -ready model. The sAFSM hardware is in fabrication, and anticipated performance exceeds 10 krad/s2 angular acceleration, 10 mrad range, and 9 kHz closed-loop bandwidth.
by Michael Thomas Boulet.
S.M.

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16

Bhatti, Wasim. "Mechanical integration of a PEM fuel cell for a multifunctional aerospace structure." Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/21513.

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A multifunctional structural polymer electrolyte membrane (PEM) fuel cell was designed, developed and manufactured. The structural fuel cell was designed to represent the rear rib section of an aircraft wing. Custom membrane electrode assemblies (MEA s) were manufactured in house. Each MEA had an active area of 25cm2.The platinum loading on each electrode (anode and cathode) was 0.5mg/cm2. Sandwiched between the electrodes was a Nafion 212 electrolyte membrane. Additional components of the structural fuel included metallic bipolar plates and end plates. Initially all the components were manufactured from aluminium in order for the structural fuel cell to closely represent an aircraft wing rib. However due to corrosion problems the bipolar plate had to be manufactured from marine grade 361L stainless steel with a protective coating system. A number of different protective coating systems were tried with wood nickel strike, followed by a 5μm intermediate coat of silver and a 2μm gold top coat being the most successful. Full fuel cell experimental setup was developed which included balance of plant, data acquisition and control unit, and a mechanical loading assembly. Loads were applied to the structural fuel cells tip to achieve a static deflection of ±7mm and dynamic deflections of ±3mm, ±5mm, and ±7mm. Static and dynamic torsion induced 1° to 5° of twist to the structural fuel cell tip. Polarisation curves were produced for each load case. Finite element analysis was used to determine the structural fuel cell displacement, and stress/strain over the range of mechanical loads. The structural fuel cells peak power performance dropped 3.9% from 5.5 watts to 5.3 watts during static bending and 2% from 6.2 watts to 6.1 watts during static torsion. During dynamic bending (2000 cycles) the structural fuel cell peak power performance dropped 11% from 6.7 watts to 6 watts (3mm deflection at 190N), 23% from 6.3 watts to 4.8 watts (5mm deflection at 270N), and 41% from 7.2 watts to 5 watts (7mm deflection at 350N). During dynamic torsion (2000 cycles) the structural fuel cell peak power performance dropped 16% from 6 watts to 5.1 watt (3° of torsional loading), and 30% from 6.4 watts to 4.3 watts (5° of torsional loading). The simulated (finite element modelling) displacement of -6.6mm (At maximum bending load of 364.95N) was within 9% of the actual measured displacement of -7.2mm at 364.95N. Furthermore the majority of the simulated strain values were within 10% of the actual measured strain for the structural fuel cell.

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17

Kousourakis, Asimenia, and asimeniak@hotmail com. "Mechanical Properties and Damage Tolerance of Aerospace Composite Materials Containing CVM Sensors." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2009. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20090506.095922.

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The PhD thesis evaluates the mechanical properties and damage tolerance of aerospace carbon/epoxy laminates containing long, narrow interlaminar galleries. The term 'galleries' refers to thin and long holes in a laminate used for the installation of small measuring devices, such as structural health monitoring (SHM) sensors. The galleries considered in this study are similar to those used in a novel SHM system known as 'Comparative Vacuum Monitoring (CVM)'. CVM was developed by the Australian company - Structural Monitoring Systems (SMS) - for damage detection in aircraft structures. CVM is a SHM system that utilises pressure differentials between a parallel series of galleries at atmospheric or low pressure to detect damage initiation and propagation. Thus far, CVM has been used for the monitoring of surface cracks in metallic structures using surface mounted sensors. Recent research has also demonstrated that it may be possible to monitor damage along the bond- line of both metallic and composite joints using CVM. The ability of CVM sensors to detect delamination damage inside composite structures is less well understood. It is envisaged that CVM can be used for the through-life health monitoring of composite aircraft structures prone to delamination damage. However, a major concern with applying CVM to composite laminates is the open-hole design of the galleries that may initiate damage growth under external loading. Material property data, structural tests, and models for predicting the properties of laminates containing galleries is needed before CVM technology can be certified for use in aircraft composite structures. The primary objectives of this PhD thesis are the development of an optimum process method for introducing multiple interlaminar CVM galleries in composite laminates; the development of a validated model for calculating changes to the mechanical properties of laminates containing CVM galleries; and the determination of optimum CVM gallery shape, size and orientation combinations for minimising the effect of the galleries on the mechanical properties of laminates. The effects of the shape, size and orientation of CVM galleries on the mechanical properties of carbon/epoxy laminates are evaluated by an extensive experimental research program, and the results are presented in the thesis. The properties investigated include the in-plane tensile and compressive properties, tensile and compressive fatigue life, through-thickness tensile strength, interlaminar shear strength, mode I and mode II interlaminar fracture toughness, and impact damage resistance. The results from tensile tests on lap-joints and T-joints containing CVM galleries are also presented.

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18

Fulcher, Jared T. "MECHANICAL CHARACTERIZATIONS OF ENVIRONMENTALLY CONDITIONED SHAPE MEMORY POLYMERS FOR RECONFIGURABLE AEROSPACE STRUCTURES." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_theses/81.

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Shape memory polymers (SMPs) have been candidate materials for morphing applications. However, the SMPs have not been fully tested to work in relevant environments required for Air Force missions. In this study, an epoxy-based SMP was separately exposed to moisture, lubricating oil and UV radiation, which are simulated service environments designed to be reflective of anticipated performance requirements. The thermomechanical properties and shape memory effects were studied by using novel high-temperature nanoindentation technique. Results show that environmental conditions have affected the glass transition temperature and mechanical properties of the SMPs. In most cases, the conditioned SMPs exhibited higher elastic moduli than the unconditioned SMP. The shape recovery ability of the SMP was assessed by creating an indent and then observing the corresponding recovery according to the standard shape memory cycle. It was found that the deformation was mostly recovered for both conditioned and unconditioned SMP samples on heating the material above its glass transition temperature.

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19

Barut, Atila 1966. "Nonlinear thermo-mechanical analysis of stiffened composite laminates by a new finite element." Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/282754.

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A new stiffened shell element combining shallow beam and shallow shell elements is developed for geometrically nonlinear analysis of stiffened composite laminates under thermal and/or mechanical loading. The formulation of this element is based on the principal of virtual displacements in conjunction with the co-rotational form of the total Lagrangian description of motion. In the finite element formulation, both the shell and the beam (stiffener) elements account for transverse shear deformations and material anisotropy. The cross-section of the stiffener (beam) can be arbitrary in geometry and lamination. In order to combine the stiffener with the shell element, constraint conditions are applied to the displacement and rotation fields of the stiffener. These constraint conditions ensure that the cross-section of the stiffener remains co-planar with the shell section after deformation. The resulting expressions for the displacement and rotation fields of the stiffener involve only the nodal unknowns of the shell element, thus reducing the total number of degrees of freedom. Also, the discretization of the entire stiffened shell structure becomes more flexible.

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20

Bennett, William Thomas. "Computational and Experimental Investigations into Aerospace Plasmas." Wright State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=wright1212780703.

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21

Tahhan, Antar Mohammad. "Minimum damage wire electrical discharge machining of aerospace alloys." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/3222/.

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The research focused primarily on the effects of WEDM on the surface / subsurface integrity of Ti-6Al-2Sn-4Zr-6Mo titanium alloy and Udimet 720 nickel base superalloy, and encompassed measurement of surface roughness and contamination, workpiece microhardness, recast layer thickness, residual stresses and fatigue performance. Associated productivity and manufacturing costs were also evaluated in respect of blade root slot machining in aerospace turbine / compressor discs. Preliminary tests results showed that machined surfaces with Ra of ~0.5μm, less than 2μm of recast layer and almost neutral residual stresses were obtained following a roughing and four finishing passes. In a subsequent phase it was possible to reduce the number of finishing passes into only 2 while maintaining similar surface integrity figures, where also it was possible to wire machine firtree slots geometrical accuracy of ±7μm. This phase also entailed extensive assessment of the impact of pulse shape on surface integrity when using similar pulse energies. Fatigue performance tests proved no statistically significant differences between WEDM and flank milling at 5% level. The research also investigated the use of coated wires and oil based dielectric compared to standard brass wire and de-ionised water, where significant differences in productivity were recorded.

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22

Kohorn, Adam B. (Adam Benjamin) 1971. "Influencing process and cultural change in the aerospace industry." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/31081.

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Анотація:

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M.)--Massachusetts Institute of Technology, Sloan School of Management, 1999.
Includes bibliographical references (p. 69).
Aerospace equipment manufacturers have expressed considerable frustration with the lack of success in implementing process and cultural change initiatives within their organizations. The objective of this report is to offer more successful methods of designing and executing change initiatives in the aerospace industry. This report provides an analysis of three particular change initiatives in execution at Pratt&Whitney Aircraft at the time of this writing. The successes and failures of three initiatives are analyzed and compared in the context of the major barriers to change faced by the industry. The arguments made in the discussion and in the following conclusions suggest that success depends on the application of entrepreneurial marketing and negotiations theories: 1. Solving a quantifiable, pressing source of pain for the customer 2. Results selling by providing a solution versus solely a technology 3. Focusing on a single customer with the budget and power to employ the new technology 4. Understanding the positions and interests of the parties involved 5. Establishing a bargaining range when faced with resistance 6. Enabling a give and take of concessions and tradeoffs in the bargaining process.
by Adam B. Kohorn.
S.M.

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23

Roy, Steven. "Mechanical modeling and testing of a composite helicopter structure made by resin transfer moulding." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40829.

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The design and mechanical performance of a helicopter horizontal stabilizer slat made by resin transfer moulding (RTM) can be evaluated with finite element analysis (FEA). To verify the validity of the assumptions used in the modelling of the slat structure, static mechanical tests were performed on prototype slats which were half of the full-size length. The slat complex boundary conditions were simplified to make static mechanical testing possible. Two fixtures were designed and built to introduce simplified loads in specimens with two different bracket configurations: a full and a half bracket. A finite element (FE) model of the specimens was made with shell elements and the finite element solution was compared with the experimental results. In most cases, comparison between the finite element analysis solution and experimental results showed good agreement in terms of structure stiffness, strength, strain and damage location. It is believed that out-of-plane stresses should be considered to improve the finite element solution accuracy.
Le design et la performance mécanique d’un bec de bord d’attaque de stabilisateur horizontal d’hélicoptère fabriqué par moulage par injection sur renfort (« resin transfer moulding ») peuvent être évalués par des analyses par éléments finis. Pour vérifier la validité des hypothèses utilisées dans la modélisation du bec de bord d’attaque, des essais mécaniques ont été effectués sur des prototypes demi-longueurs. Les conditions frontières complexes ont été simplifiées pour rendre les essais mécaniques possibles. Deux gabarits ont été conçus et construits pour introduire les chargements simplifiés dans les pièces d’essai possédant deux configurations de support: un support complet et un demi-support. Un modèle par éléments finis des pièces d’essai a été réalisé avec des éléments de type membrane et la solution est comparée avec les résultats expérimentaux. Dans la plupart des cas, la comparaison entre la solution par éléments finis et les résultats expérimentaux coïncide concernant la rigidité de la structure, la résistance, l’allongement et la localisation de l’endommagement. Les contraintes hors du plan devraient être considérées pour améliorer la précision de la solution par éléments finis.

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24

Peters, Brett. "On Accelerating Road Vehicle Aerodynamics." Thesis, The University of North Carolina at Charlotte, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10791882.

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Road vehicle aerodynamics are primarily focused on developing and modeling performance at steady-state conditions, although this does not fully encompass the entire operating envelope. Considerable vehicle acceleration and deceleration occurs during operation, either because of driver input or from transient weather phenomenon such as wind gusting. With this considered, high performance road vehicles experience body acceleration rates well beyond ±1G to navigate courses during efficient transition in and out of corners, accelerating from maximum straight-line speed to manageable cornering speeds, and then back to maximum straight-line speed. This dissertation aims to answer if longitudinal acceleration is important for road vehicle aerodynamics with the use of transient Computational Fluid Dynamics (CFD) to develop a method for obtaining ensemble averages of forces and flow field variables. This method was developed on a simplified bluff body, a channel mounted square cylinder, achieving acceleration through periodic forcing of far field velocity conditions. Then, the method was applied to an open-source road vehicle geometry, the DrivAer model, and a high performance model which was created for this dissertation, the DrivAer-GrandTouringRacing (GTR) variant, as a test model that generates considerable downforce with low ground proximity. Each test body experienced drag force variations greater than ±10% at the tested velocities and acceleration rates with considerable variations to flow field distributions. Finally, an empirical formulation was used to obtain non-dimensional coefficients for each body from their simulated force data, allowing for force comparison between geometries and modeling of aerodynamic force response to accelerating vehicle conditions.

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25

Beal, Roger Zack. "A study comparing changes in loading conditions of an extended service life system using aluminum 2024-T351." Thesis, The University of Utah, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1569706.

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Анотація:

The current fiscally austere environment prevalent in the military and industry is driving extreme measures to save money. In the United States Air Force, this has driven enormous efforts to trim sustainment spending on extended life aircraft. The challenge to the aerospace engineer is to ensure flight safety in the midst of this economic pressure.

One method of cutting costs is to increase the time an aircraft is in service by delaying the point when the aircraft is taken out of service for depot maintenance. To ensure flight safety, in depth fatigue and fracture analysis needs to be accomplished to assess increasing the inspection interval.

The purpose of this study was to determine the sensitivity of Aluminum 2024-T351 alloy, a common material used in tension dominated aerospace applications, to two different loading spectra—one that is aggressive and the other that is benign. This was accomplished by conducting five different combinations of the two spectra, developing computer simulations using the AFGROW software and comparing with the measured data. The results showed that the material demonstrated significantly different behavior between the two spectra. These results provide a valuable tool for the aerospace engineer for fatigue life prediction and inspection interval evaluation.

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26

Meshreki, Mouhab. "Dynamics of thin-walled aerospace structures for fixture design in multi-axis milling." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32614.

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Milling of thin-walled aerospace structures is a critical process due to the high flexibility of the workpiece. Available models for the prediction of the effect of the fixture on the dynamic response of the workpiece are computationally demanding and fail to represent practical cases for milling of thin-walled structures. Based on the analysis of typical structural components encountered in the aerospace industry, a generalized unit-element, with the shape of an asymmetric pocket, was identified to represent the dynamic response of these components. Accordingly, two computationally efficient dynamic models were developed to predict the dynamic response of typical thin-walled aerospace structures. These models were formulated using Rayleigh's energy and the Rayleigh-Ritz methods. In the first model, the dynamics of multi-pocket thin-walled structures is represented by a plate with torsional and translational springs. A methodology was proposed and implemented for an off-line calibration of the stiffness of the springs using Genetic Algorithms. In the second model, the dynamics of a 3D pocket is represented by an equivalent 2D multi-span plate. Through a careful examination of the milling of thin-walled structures, a new formulation was developed to represent the continuous change of thickness of the workpiece due to the material removal action. Two formulations, based on holonomic constraints and springs with finite stiffness, were also developed and implemented to take into account the effect of perfectly rigid and deformable fixture supports. All the developed models and formulations were validated numerically and experimentally for different workpiece geometries and
Le fraisage des structures aérospatiales à parois minces est un processus critique dû à la flexibilité élevée de la pièce. Les modèles disponibles pour la prévision de l'effet du système de fixation sur la réponse dynamique de la pièce sont basés sur des méthodes numériques très lentes et n'arrivent pas à représenter les cas pratiques du fraisage des structures à parois minces. Basé sur une analyse des composants structurels typiques produits dans l'industrie aérospatiale, un élément généralisé de base avec la forme d'une poche asymétrique, a été identifié pour représenter la réponse dynamique de ces composants. En conséquence, deux modèles dynamiques efficaces ont été développés pour prévoir la réponse dynamique des structures aérospatiales types à parois minces. Ces modèles ont été formulés en utilisant les méthodes de Rayleigh et Rayleigh-Ritz. Dans le premier modèle, les réponses dynamiques des structures de poches multiples à parois minces sont représentées par des plaques avec des ressorts de torsion et de translation. Une méthodologie a été proposée et mise en application pour calibrer la rigidité des ressorts en utilisant les algorithmes génétiques. Dans le deuxième modèle, la réponse dynamique d'une poche en 3D est représentée par une plaque équivalente de multi-travées en 2D. À travers une étude approfondie du fraisage des structures à parois minces, une nouvelle formulation a été développée pour représenter le changement continu de l'épaisseur de la pièce durant l'usinage. Deux formulations, basées sur des contraintes holonomes et des ressorts avec des rigidités finies, ont été$

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27

Nicolle, Mathias. "Mechanical and structural conceptof the ISS microgravity experimentpayload: AtmoFlow." Thesis, KTH, Rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-261797.

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Анотація:

This Master Thesis report presents the mechanical concept and design of a microgravity fluid science experiment that is planned to be launched to the International Space Station in approximately five years. Named AtmoFlow, this experiment aims to study the complex flow phenomena occurring in different planets’ atmosphere by implementing a scaled-down model of a planet-atmosphere system in microgravity. The design introduced here focuses on several of the experiment’s systems: the Turn Table, a rotating system involving a Fluid Cell Assembly, a Thermal Control System and two Rotation Drive Systems. Design methods, main choices and crucial conception steps are presented. Components’ dimensioning and choices are motivated. Models and analyses are derived from the selected design to ensure that the design meets the requirements on microgravity disturbances, structural and rotational characteristics stated during previous project’s phases. The Computer Assisted Design model of the experiment’s final concept and its integration sequence are eventually proposed and discussed.
Denna rapport presenterar den mekaniska utformningen av ett mikrogravitationsexperiment som studerar strömningsmekaniska fenomen och som planeras att skickas till den internationella rymdstationen om ungefär fem år. Experimentet heter AtmoFlow och syftar till att studera komplexa flödesfenomen som förekommer i olika planeters atmosfärer genom att implementera en nerskalad modell av en planets atmosfärssystem i mikrogravitation. Utformningen av experimentet som presenteras här fokuserar på flera av experimentets system: rotationsbordet (ett roterande system med en strömningscellhopsättning), ett termiskt reglersystem samt två rotationsdrivsystem. Utformningsmetoder, huvudsakliga val och utformningssteg presenteras. Dimensioneringen av komponenter och deras urval motiveras. Modeller och analyser av den valda konstruktionen har utförts för att säkerställa att den uppfyller kraven på störningar i mikrogravitation, struktur och rotationsegenskaper som specificerats under tidigare faser i utformningen av experimentet. CAD-modellen av den slutliga utformningen av konstruktionen av experimentet presenteras och diskuteras.

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28

Rana, Akshaykumar A. "Evaluation of Electrical and Mechanical Properties of Carbon-Fiber Composites Using Interleaved Materials." Thesis, California State University, Long Beach, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10979176.

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Carbon-Fiber Reinforced Polymers (CFRPs) provides superior mechanical properties and low weight, enabling their extensive use in the aerospace industry. Susceptibility to internal damage due to out-of-plane loads and poor electrical properties are some of their major challenges that require to be addressed in order to increase the utilization of composites in further aerospace structures. Lightning strikes can lead to catastrophic damage, inflicting high repair and certification costs. Lightning Strike Protection (LSP) solutions such as integration of metallic meshes or foils into the composite structures, even though effective, impose extra costs and hinders the aircraft performance due to the increased weight of the aircraft.

This research aims at the development of a different LSP solution, by enhancing the electrical conductivity of composite, while maintaining a sufficient degree of mechanical properties. The use of non-woven conductive interlayers was proposed for manufacturing of conductive composites. Highly-conductive, low-aerial-weight carbon veil was utilized to manufacture prepreg-based CF/Epoxy laminates, which are generally toughened, in order to improve their conductivity using vacuum bag only (VBO) and heat-pressing techniques. Further, a bi-functional interlayer of graphene coated Polyamide (PA) was developed using interfacial trapping method. This conductive thermoplastic interlayer was then utilized for manufacturing Benzoxazine (BZ) infused carbon fabric laminate with Vacuum-assisted resin transfer molding (VARTM) method, which acted as a conductive toughener and improves the Inter-laminar Fracture Toughness (ILFT) as well as to increase the electrical conductivity.

The effects of the incorporation of non-woven interlayers on the electrical conductivity, thermal behavior of composites, and mechanical properties such as shear strength, compressive strength, and the ILFT (Mode-I and Mode-II) were investigated in this study. In both types of composites, an increase in electrical properties, as well as mechanical properties, were observed. The only exception was in the Mode-I ILFT of the CF/Epoxy prepregs, which decreased with the increase of the areal weight of the interleaved carbon veils. The mechanical properties increased in the range of 9%–138% with the only decrement observed in Mode-I ILFT of CF/Epoxy with carbon veils of 25%. The volume resistivity of the CF/Epoxy samples decreased significantly by approximately 50% due to the incorporation of the conductive interlayer. This added feature was used to develop a structural health monitoring (SHM) procedure. The conductive composite showed an increased sensitivity in detecting the pre-identified damage location in the composites.

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29

Lennox, Kevin Michael. "Implementing pull production within an aerospace assembly operation." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37241.

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Анотація:

Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; in conjunction with the Leaders for Manufacturing Program at MIT, 2006.
Includes bibliographical references (leaf 42).
This thesis presents a detailed analysis of lean implementation at Hamilton Sundstrand, a global supplier of technologically advanced aerospace and industrial products. The main objective of the internship was to convert from a push system, where orders are expedited and scheduled at multiple points in the process, to a pull system driven by a bin size or finished goods supermarket. Some of the key issues addressed include system design for highly variable processes, experimentation with various forms of Kanban, and the use of value stream mapping as a change management tool. This thesis is divided into two separate projects, both directly related to pull production. The first assignment was to redesign a subassembly process to improve fulfillment at the downstream assembly operation. Broader in scope, the second task involved implementation of a constant work-in-process scheduling system or CONWIP. Each project was designed and executed through value stream mapping and continuous improvement. The following discussion focuses on both strategic and tactical challenges of lean transformation because analysis and implementation were equally important throughout the internship.
by Kevin Michael Lennox.
S.M.
M.B.A.

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30

Njuguna, James A. K. "Micro- and macro-mechanical properties of aerospace composite structures and their dynamic behaviour." Thesis, City University London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440734.

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31

Olfati-Saber, Reza. "Nonlinear control of underactuated mechanical systems with application to robotics and aerospace vehicles." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8979.

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Анотація:

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.
Includes bibliographical references (leaves 308-316).
This thesis is devoted to nonlinear control, reduction, and classification of underactuated mechanical systems. Underactuated systems are mechanical control systems with fewer controls than the number of configuration variables. Control of underactuated systems is currently an active field of research due to their broad applications in Robotics, Aerospace Vehicles, and Marine Vehicles. The examples of underactuated systems include flexible-link robots, nobile robots, walking robots, robots on mobile platforms, cars, locomotive systems, snake-type and swimming robots, acrobatic robots, aircraft, spacecraft, helicopters, satellites, surface vessels, and underwater vehicles. Based on recent surveys, control of general underactuated systems is a major open problem. Almost all real-life mechanical systems possess kinetic symmetry properties, i.e. their kinetic energy does not depend on a subset of configuration variables called external variables. In this work, I exploit such symmetry properties as a means of reducing the complexity of control design for underactuated systems. As a result, reduction and nonlinear control of high-order underactuated systems with kinetic symmetry is the main focus of this thesis. By "reduction", we mean a procedure to reduce control design for the original underactuated system to control of a lowerorder nonlinear or mechanical system. One way to achieve such a reduction is by transforming an underactuated system to a cascade nonlinear system with structural properties. If all underactuated systems in a class can be transformed into a specific class of nonlinear systems, we refer to the transformed systems as the "normal form" of the corresponding class of underactuated systems. Our main contribution is to find explicit change of coordinates and control that transform several classes of underactuated systems, which appear in robotics and aerospace applications, into cascade nonlinear systems with structural properties that are convenient for control design purposes. The obtained cascade normal forms are three classes of nonlinear systems, namely, systems in strict feedback form, feedforward form, and nontriangular linear-quadratic form. The names of these three classes are due to the particular lower-triangular, upper-triangular, and nontriangular structure in which the state variables appear in the dynamics of the corresponding nonlinear systems. The triangular normal forms of underactuated systems can be controlled using existing backstepping and feedforwarding procedures. However, control of the nontriangular normal forms is a major open problem. We address this problem for important classes of nontriangular systems of interest by introducing a new stabilization method based on the solutions of fixed-point equations as stabilizing nonlinear state feedback laws. This controller is obtained via a simple recursive method that is convenient for implementation. For special classes of nontriangular nonlinear systems, such fixed-point equations can be solved explicitly ...
by Reza Olfati-Saber.
Ph.D.

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32

Caetano, Sean Michael. "Quantifying the business case for aerospace assembly automation." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111477.

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Анотація:

Thesis: M.B.A., Massachusetts Institute of Technology, Sloan School of Management, in conjunction with the Leaders for Global Operations Program at MIT, 2017.
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, in conjunction with the Leaders for Global Operations Program at MIT, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 87-88).
As aerospace Original Equipment Manufacturer's (OEM's) order backlogs soar to between six to ten years and growing, the community sees automation as vital to increasing throughput. Yet the community seems divided on the quantifiable financial benefits. While automation in aerospace assembly dates back to 1937, there is little substantive research on quantifying its business case. This thesis develops a financial model that predicts the benefit of introducing automation into an OEM's manual assembly line. The hypothesis of this project is that there is, in fact, a quantifiable benefit to implementing assembly automation into a current manual assembly process. Based on an initial automation capital investment, the financial model calculates the Net Present Value (NPV) of an aerospace automation project given various OEM production inputs such as: the annual production schedule, learning curve metrics, labor hour savings through automation, rework, health & safety metrics, and automation operating and downtime costs. A current program was used as a case study against the financial model. One significant finding is the effect production learning has on the labor hours saved from automation introduced in this thesis as the 'Efficiency Factor'. Based on the OEM's conservative production data and an initial automation investment of $12M the NPV for the project is about $16M for the firm order (600 ship sets) and about $27M for the entire program (2000 ship sets).
by Sean Michael Caetano.
M.B.A.
S.M.

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33

Tapley, James Paul. "Development of alternate parts for the aerospace industry." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59181.

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Анотація:

Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; in conjunction with the Leaders for Global Operations Program at MIT, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 60-61).
This thesis explores the topic of the development of alternate parts for the aerospace industry, drawing on industry examples to demonstrate methods and approaches and the benefits to firms engaged in these activities. I will explore reverse engineering techniques, obstacles, and the role regulations play in the development of alternate parts. I will also demonstrate that reverse engineering is no longer a back room secret activity, yet instead a innovative engineering discipline that if matured and leveraged properly can provide valuable benefits outside of alternate part development.
by James Paul Tapley.
S.M.
M.B.A.

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34

Kradinov, Vladimir Y. "Optimum design of bolted composite lap joints under mechanical and thermal loading." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/280296.

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Анотація:

A new approach is developed for the analysis and design of mechanically fastened composite lap joints under mechanical and thermal loading. Based on the combined complex potential and variational formulation, the solution method satisfies the equilibrium equations exactly while the boundary conditions are satisfied by minimizing the total potential. This approach is capable of modeling finite laminate planform dimensions, uniform and variable laminate thickness, laminate lay-up, interaction among bolts, bolt torque, bolt flexibility, bolt size, bolt-hole clearance and interference, insert dimensions and insert material properties. Comparing to the finite element analysis, the robustness of the method does not decrease when modeling the interaction of many bolts; also, the method is more suitable for parametric study and design optimization. The Genetic Algorithm (GA), a powerful optimization technique for multiple extrema functions in multiple dimensions search spaces, is applied in conjunction with the complex potential and variational formulation to achieve optimum designs of bolted composite lap joints. The objective of the optimization is to acquire such a design that ensures the highest strength of the joint. The fitness function for the GA optimization is based on the average stress failure criterion predicting net-section, shear-out, and bearing failure modes in bolted lap joints. The criterion accounts for the stress distribution in the thickness direction at the bolt location by applying an approach utilizing a beam on an elastic foundation formulation.

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35

Bhaduri, Debajyoti. "Ultrasonic assisted creep feed grinding and dressing of advanced aerospace alloys." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5415/.

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Анотація:

The research involves the investigation of hybrid ultrasonic assisted creep feed grinding (UACFG) of advanced aeroengine alloys, in particular Inconel 718, CMSX-4 and gamma titanium aluminide (γ-TiAl). For tests with ultrasonic vibration, workpieces were actuated at a constant frequency (~20kHz) via a specially designed block sonotrode attached to a 1kW piezoelectric transducer-generator system. The trials on nickel based superalloys were carried out using open structured alumina wheels whereas γ-TiAl specimens were machined with conventional silicon carbide and single layer diamond superabrasive wheels. Statistically designed experiments involving variation in wheel speed, table speed, depth of cut, grinding condition and vibration amplitude were employed in mainstream testing. Reductions in grinding force components were typically observed albeit at the cost of higher wheel wear and surface roughness of the ground slots when ultrasonic assisted grinding of nickel alloys. Conversely, UACFG of γ-TiAl exhibited lower grinding wheel wear and workpiece surface roughness. Surfaces ground with the assistance of vibration generally revealed greater side flow/ploughing and overlapping grit marks in comparison to standard creep feed ground specimens. Three dimensional topographic measurement of grinding wheel surface replicas indicated that ultrasonic vibration led to an increase in the number of active cutting points on the wheel.

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36

Gerona, Leovigildo Mahon. "Vibration excitation of aerospace composite materials for defect determination using optical NDT techniques (ESPI/Shearography)." Master's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/13432.

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Анотація:

Includes bibliographical references (leaves 87-89).
This project investigates the detection of structural damage in aerospace composite materials using ESPI and/or Shearography. ESPI and shearography are both laser based digital interferometric techniques used to non-destructively identify defects in small and large structures. Vibration excitation is proposed to be used as the excitation method for the above Non-Destructive Testing (NDT) techniques. The material may or may not contain any defects, in which case the flaws are to be artificially induced.

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37

Park, Conrad. "Mechanical Performance and Structure-Property Relations in6061B Aluminum Metal Matrix Composites." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1547842396716777.

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38

Audette, Scott. "Mechanical Properties of Aerospace Composite Parts Made from Stitched Multilayer 3D Carbon Fibre Preforms." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31691.

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Анотація:

Producing composite parts using low-cost processes such as resin transfer moulding (RTM) has received much interest in the aerospace industry. RTM manufactured components require near net shape preforms which closely fit mould cavities. To reduce labour costs associated with composite production, automated preforming processes must be utilized. However, obtaining reproducible high quality preforms is required for manufacturing consistent high quality parts. Stitched multilayer 3D non crimp fabric preforms are well suited for automation and an investigation into quality and performance of components manufactured from these preforms is required. This thesis provides an initial evaluation of quality and mechanical properties of components made from stitched multilayer 3D non crimp fabric preforms using RTM. Similar sized flat plates of varying fibre volume fractions were manufactured to evaluate flexural modulus and strength, short beam shear strength and drop weight impact resistance of the material. Also, integral reinforced panels (IRPs) featuring a reinforcing section joined to a flat plate of varying laminating sequences were manufactured to evaluate debonding strength between sections. Optical microscopy was performed on component samples to determine quality based on void content and was found to be within acceptable limits for production composites. Flexural moduli were found to be comparable with theoretical expected values, however flexural strength was limited by the presence of transverse stitches. Short beam shear strength results showed high consistency between specimens, however were lower than comparable values found in literature. Impact specimens showed consistency among specimens, with greater damage resistance than comparable values found in literature. Determining debonding strength proved difficult as different failure modes were observed between IRPs, however, initial baseline values were acquired.

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39

Wallace, Max Ian. "Real-time dynamic substructuring for mechanical and aerospace applications : control techniques and experimental methods." Thesis, University of Bristol, 2005. http://hdl.handle.net/1983/0d4e8f98-485a-4f92-a4e1-2ba23632b155.

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Анотація:

Real-time dynamic substructuring is an experimental technique for testing the dynamic behaviour of complex structures. It involves creating a hybrid model of the entire structure by combining experimental test piece(s) - the substructure(s) - with a set of numerical model(s) describing the remainder of the system. By employing real-time control techniques to "glue" the numerical and experimental parts together, we create a virtual testing environment that if performed correctly will emulate the dynamic behaviour of the complete structure exactly. In this thesis, we focus on the experimental side of substructuring, specifically concentrating on the influence of delays within the substructured system. These are introduced by the inherent dynamics of the actuation device(s) involved - it is impossible for any controlled transfer system(s) (as they are known) to react instantaneously to a state change in demand. We study the stability of the substructured system in direct relation to the magnitude of this delay error and present two methods for identifying the critical limit of stability; firstly, using a delay differential equation approach by approximating the transfer system to a delayed unit response of the numerical model, and secondly, by observing the magnitude of permissible phase margin of the substructured system. We discuss two different formulations of a compensation scheme; one achieving adaptive forward prediction using polynomial extrapolation and the second achieving lag compensation via the inversion of an identified model of the transfer system. We then extend this control strategy to include the concept of robustness which leads us to develop a four stage testing methodology that can be applied to any substructured system to help ensure successful testing. We build on these fundamental concepts to demonstrate the "proof of concept" of real-time dynamic substructuring for an industrial aerospace application - a helicopter lag damper connected to numerical model of an individual blade excited by flight test data.

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40

English, Orion T. (Orion Tyler). "Quality improvement strategy in a dynamic aerospace manufacturing environment." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90760.

Повний текст джерела

Анотація:

Thesis: M.B.A., Massachusetts Institute of Technology, Sloan School of Management, 2014. In conjunction with the Leaders for Global Operations Program at MIT.
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. In conjunction with the Leaders for Global Operations Program at MIT.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 78-81).
In the manufacturing of any complex product it is a generally accepted phenomenon that defects will occur at various stages in the process. In aircraft modification and repair facilities, the low levels of automation and high degree of manual labor results in a significant increase in the rate of errors and defects caused throughout the production cycle. This results in a significant amount of unplanned rework that is scheduled and executed along with the previously planned work. This thesis presents a project carried out during an internship at Boeing focused on developing and implementing a quality management strategy targeting improvement projects to reduce rework and the occurrence of defects. This includes both the development of analysis and communication tools for identifying the most common causes of rework and working with teams to develop improvement projects to reduce their occurrence. The modification facility where the project took place was still in its early stage of operation, having only been in operation for a short period of time prior to the start of the internship. This created a very dynamic work environment that was constantly evolving and improving at every level of the organization. Previous quality initiatives had been started in the past but a lack of support and commitment from senior management inhibited their adoption. The quality initiative is focused on several key quality metrics that have been identified by the leadership team at the company. The quality management strategy is developed through a cross-functional team effort, bringing a data driven approach and aspects of several common continuous improvement methodologies. Following the framework established during the internship, some project examples are provided along with the methodology behind the root cause and corrective action steps taken.
by Orion T. English.
M.B.A.
S.M.

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41

Roets, Philip J. "Development of a hybrid light alloy - carbon fibre aerospace structural panel." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4151.

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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010.
ENGLISH ABSTRACT: The development of light and sti aerospace structural panels is very important in the aerospace industry, e.g. a lighter satellite requires less fuel to launch it into space which in turn saves money for the owner of the satellite. This thesis describes the design, optimisation, manufacturing and testing of a ribbed light alloy core - carbon bre face sheets, sandwich-type, satellite panel operating at launch loading conditions (115 m/s2 accelerations and requiring a minimum structural natural frequency of 90 Hz) to determine the optimum sti ness per mass ratio of the panel. The panel layout was based on a satellite panel designed by SunSpace and Information Systems for the Sumbandila satellite. Only the black box mounting positions of the original panel were used in the optimisation of the new panel. The core of the evaluation panel was manufactured from aluminium (6082-T6). The carbon bre skins were manufactured from unidirectional high modulus carbon bre (K63712) in a [0/90/0] wet layup with the 0± direction in the longitudinal direction of the panel. A three-dimensional model of the panel consisting of 3D wedge elements and containing all the boundary conditions was modelled with the use of the nite element software MSC Patran. The model was optimised with the use of optimisation software Genesis to locate the rib positions. Genesis removes all the elements containing the least amount of stress; only 30% of the core elements were kept while restricting the elements to form an extruded con guration (for milling machining) throughout the thickness of the panel. The rib elements remaining were replaced in MSC Patran by shell elements and the shell element thicknesses were optimised with the use of Genesis to ensure the lightest and sti est possible structure. The optimised rib thicknesses were imported into MSC Patran and the numerically optimised model could then be analysed with MSC Nastran. The numerical model was converted into a manufacturable structure and the core was machined from a solid aluminium sheet. The ribs were machined in the shape of an Ibeam to allow for minimum weight and a su cient bonding area for the two carbon bre face sheets. Elevated circular surfaces, protruding through the carbon bre sheets, were machined in the position of the black box mountings to allow for better heat transfer away from the black boxes. The carbon bre face sheets were bonded to the metal core (3M Scotch-Weld 9323 B/A). The nished panel was put through various tests to determine whether it is suitable for use in the aviation industry. The tests included modal testing, random vibration testing and temperature testing to determine if the structure is durable enough for use in satellites. The test results are promising and show that a substantive amount of money can be saved by reducing the mass on the structure. By using optimisation software and ribbed light alloy - carbon bre face sheets sandwich structures the performance of the structures can be improved without adding mass to the structure.
AFRIKAANSE OPSOMMING: Die ontwikkeling van ligter en stywer lugvaartstruktuur panele is baie belangrik in die lugvaart-industrie, bv. 'n ligter satelliet benodig minder brandstof om tot in 'n wentelbaan lanseer te word. Dit bespaar sodoende lanseerkostes vir die eienaar van die satelliet. In die verslag word die ontwerp, optimering, vervaardiging en toets van 'n gewebde, ligte allooi kern - koolstofveselvel, saamgestelde materiaal, satelliet struktuurpaneel wat onderwerp word aan lanseer belastingstoestande van ongeveer 115 m/s2 versnellings ondersoek. Die tegnieke word gebruik om die optimale styfheid per eenheidsmassa-verhouding te bepaal. Die paneel benodig 'n minimum strukturele eerste natuurlike frekwensie van 90 Hz. Die basiese paneel uitleg is verkry vanaf 'n satellietpaneel wat deur SunSpace and Information Systems ontwerp is vir die basisplaat van die Sumbandila satelliet. Die enigste geometrie wat van die oorspronklike struktuur behou is om die nuwe struktuur te optimeer is die vashegtingspunt-posisies van die swart-kassies. Die kern van die ge-optimeerde struktuur is vervaardig uit gemasjieneerde aluminium (6082-T6). Die koolstofvesel-velle is vervaardig uit enkelrigting hoë-modulus koolstofvesel-doek (K63712). Die oplegging is gedoen met 'n nat-opleggingsproses waar die drie lae van elke vel 'n [0/90/0] oriëntasie het met, die 0± lae in die langsrigting van die paneel. 'n Drie-dimensionele eindige element model van die paneel is geskep met behulp van die MSC Patran sagteware pakket met die model hoofsaaklik opgebou uit 3D wig-elemente. Al die lanseertuig vashegtingsrandwaardes is in die eindige element model ingebou. Om die web posisies te bepaal is die Genesis optimeringsagteware pakket gebruik. Verskeie ontwerpsvoorwaardes is gespesi seer waaraan die optimeringsproses moes voldoen. Slegs 30% van die wig-elemente mag behoue bly in die optimeringsproses en al die elemente deur die dikte van die paneel moet of behou of verwyder word. Dit verseker dat die resultaat masjieneerbaar is met 'n freesmasjien. Die oorblywende wig-elemente is in MSC Patran vervang met dop-elemente. Die dopelemente se diktes is ge-optimeer met Genesis om die ligste en styfste struktuur moontlik te kry. Die ge-optimeerde dop-element diktes is in die MSC Patran model ingetrek. Die numeries ge-optimeerde model is daarna met behulp van MSC Nastran ge-analiseer. Nadat die numeriese model omgeskakel is in 'n vervaardigbare struktuur is die kern gemasjieneer uit 'n soliede blok aluminium. Die webbe is ontwerp en vervaardig in 'n I-balk vorm. Dit laat toe dat die webbe 'n minimum gewig en genoegsame area het waarop die koolstofvesel velle geheg kan word. Verhewe vlakke is gemasjieneer op die aluminium kern in die posisies van die swart-kassie vashegtingpunte. Hierdie verhewe vlakke steek deur die koolstofvesel-vel aan die kant waar die swart-kassies vasgeheg word. Dit verseker 'n metaal-op-metaal verbinding tussen die kern en die swart-kassies vir beter hittegeleiding. 3M Scotch-Weld 9323 B/A epoksie is gebruik om die koolstofvesel-velle aan die aluminium kern te heg. Die voltooide struktuur is aan 'n reeks toetse onderwerp om te bepaal of dit geskik is om in die ruimtevaart-industrie gebruik te kan word. Dit sluit modale toetse, lukrake vibrasie toetse en temperatuursverandering toetse in. Die toetsresultate sal bepaal of die struktuur duursaam genoeg is om in satelliete gebruik te word. Die toetsresultate is belowend en dui daarop dat deur massa te bespaar op die struktuur, 'n aansienlike bedrag op satelliet lanseer-kostes bespaar kan word. Deur optimeringsagteware tesame met gewebde ligte allooi kern - koolstofvesel vel, saamgestelde materiaal strukture te gebruik kan die werksverrigting van die strukture verbeter sonder dat massa bygevoeg word.

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42

Harman, Steven R. (Steven Robert). "Implementation of lean manufacturing and one-piece flow at Allied Signal Aerospace." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10157.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997, and Thesis (M.S.)--Massachusetts Institute of Technology, Sloan School of Management, 1997.
Includes bibliographical references (p. 69).
by Steven R. Harman.
M.S.

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43

Drivas, Thanos. "Manufacturing Three-dimensional Carbon-fibre Preforms for Aerospace Composites." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31577.

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Carbon fibre reinforced polymer matrix composites (CF PMCs) are increasingly used in state-of-the-art aerospace applications. Aerospace manufacturers favour components made of CF PMCs over those made of traditional metallic alloys because of their light weight and corrosion resistance, which lead to significant improvements in fuel consump- tion, increased payload capability, and reduced maintenance and inspection costs. How- ever, manufacturing of CF PMC components is performed differently than traditional material in all stages – design, prototyping and production – and therefore, many com- mercial manufacturers have only recently begun producing components with CF PMCs. The first half of this thesis was written as a contribution to the CRIAQ COMP-501 project, which focusses on investigating the cost-effective procurement of airframe com- ponents that are manufactured from final-thickness, net-shaped, and through-thickness reinforced CF preforms. Reinforcement preforms were assembled from commercial 2D woven fabric using stacks of various configurations of structural through-thickness CF stitch. The contribution herein provides the results obtained from investigations into the mechanical behaviour of the relevant reinforcements, when subjected to pre-infusion op- erations typical to RTM VARTM; mechanical behaviour in compaction, shear (draping) and bending (forming). The second half of this thesis presents the major developments which were made to an alternative process for producing thick 3D preforms with great versatility, a process originally proposed as a candidate for supplying preforms to the COMP-501 project. This process interfaces a proprietary kinematic drape optimization (CAD) software with proprietary automated dry fibre placement assembly (CAM) machinery to produce vari- able or final-thickness reinforcements which are highly-drapable and can lay steered tow yarns.

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44

Sebastian, Christopher. "Towards the validation of thermoacoustic modelling in aerospace structures." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2012079/.

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The research presented in this thesis has been performed over the course of three years under funding from the European Office of the United States Air Force (EAORD) as a part of a long-term project to collect high quality data for the validation of computational mechanics models of thermoacoustic loading. The focus is on the adaptation of stereoscopic (3D) Digital Image Correlation for use in a combined thermal and high temperature measurements. To that end, a background is provided which highlights the current state of the art in high temperature, vibration experiments and data acquisition. A system is described in which a pulsed laser of duration 4 nanoseconds is used to capture high-quality displacement and strain data from vibrating components (PL- DIC). Based on this a novel method of capturing data from a component subjected to random excitation was developed. A laser vibrometer was used along with a custom LabVIEW program to trigger the pulsed laser relative to points of maximum velocity in the components vibration cycle. A dynamic calibration procedure was performed of both a high speed DIC system and the Pulsed-Laser DIC system to assess and compare the measurement uncertainty from the respective systems. It is crucial to know the uncertainty in experimental data when using it for the validation of computational models. A new way to validate computational models of vibration behavior using full-field DIC data and image decomposition is described. This is a phasic approach in which data from the entire cycle of vibration is used. The validation assessment is performed using the expanded uncertainty calculated and a concordance correlation coefficient. An example is provided using an aerospace component to validate four different simulation conditions of a modal frequency response model. An apparatus was designed and built which uses a 10 kW array of quartz lamps to reproduce some aspects of the heating provided by the Air Force test chambers. Experiments were performed in collaboration with the University of Illinois using induction heating and a small Hastelloy plate. A thermal buckling phenomena was observed using the PL-DIC system, the first full-field results of such.

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45

Ma, Kevin Yuan. "Mechanical design and manufacturing of an insect-scale flapping-wing robot." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:23845433.

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Despite the prevalence of insect flight as a form of locomotion in nature, manmade aerial systems have yet to match the aerial prowess of flying insects. Within a tiny body volume, flying insects embody the capabilities to flap seemingly insubstantial wings at very high frequencies and sustain beyond their own body weight in flight. A precise authority over their wing motions enables them to respond to obstacles and threats in flight with unrivaled speed and grace. Motivated by a desire for comparably agile flying machines, research efforts in the last decade have generated crucial developments for realizing an artificial instantiation of insect flight. The need for tiny, high-efficiency mechanical components has produced unconventional solutions for propulsion, actuation, and manufacturing. Early vehicle designs proved to be flightworthy but were critically limited by the inability to produce control torques in flight. In this thesis, we synthesize all existing technologies for insect-scale manufacturing and actuation, and we introduce a new vehicle design, the "dual actuator bee," to address the need for flight control. Our work culminates in the first demonstration of controlled, hovering flight of an insect-scale, flapping-wing robot. As the ultimate goal for this research effort is the creation of fully autonomous flying robots, these vehicles must sustain their own power sources and intelligence. To that end, we explore the challenges of scaling flapping-wing flight to attain greater lift forces. Using a scaling heuristic to determine key vehicle specifications, we develop and successfully demonstrate a hover-capable vehicle design that possesses the requisite payload capacity for the full suite of components required for control autonomy. With this operational vehicle as a point of reference, we introduce an iterative sizing procedure for specifying a vehicle design with payload capacity capable of supporting power autonomy. In the development of these vehicles, the reliability of their construction has been a substantial challenge. We present strategies for systematically addressing issues of vehicle construction. Together, this suite of results demonstrates the feasibility of achieving artificial, insect-like flight.
Engineering and Applied Sciences - Engineering Sciences

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46

Cheng, Zhaoquan. "Dynamic inversion and model predictive control for unmanned aerial vehicles." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/26603.

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Unmanned Aerial Vehicles (UAVs) have attracted considerable interest in the commercial markets for the military and civilian uses, such as surveillance and reconnaissance, aerial surveys for natural sources, traffic monitoring, and early forest fire detection, etc. Presently, UAVs are being proven as a cost-effective platform for the military and civilian applications because they gather information without endangering the lives of the pilots, increase maneuverability without limitations from human abilities, cost much less than the traditional aircrafts and do not need human-pilot interfaces. Although UAVs present numerous advantages over the manned aircrafts, they face challenges in achieving autonomous control. Model Predictive Control (MPC) is an interesting solution for UAV control to improve the level of autonomous control, but is mostly applicable to a linear or linearized system at this time. In this thesis, first is presented a complete kinematics and dynamic model of Unmanned Aerial Vehicles which is programmed in Simulink. Second, a control scheme based on a proportional controller for the inner loop and a proportional-integral controller for the outer loop is investigated. Model predictive control is applied to a linearized UAV using dynamic inversion, and simulation results obtained using a nonlinear UAV model are presented and analyzed in view of the suitability for UAV autonomous control.

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47

Fancy, Michael A. "Design, analysis, and fabrication of a prototype non-invasive system for assessment of biological and synthetic tissues." Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/26899.

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A new instrument system for the non-invasive assessment of biological systems has been designed, built and validated. This system utilizes the optical characteristics of a biological system to assess both its static and dynamic response over time. The changes in the optical properties can then be used to quantify the response of the biological system to external or internal stimuli. This new system incorporates an efficient light delivery system, as well as a novel light collection system to provide high repeatability, reproducibility, sensitivity, and detection thresholds. The system incorporates simultaneous measurement of transmitted light, forward scattered light, specularly reflected light, and non-specularly reflected light in across the visible spectrum, to provide flexibility in the biological systems that can be measured. It is shown that typical values are 0.02% for repeatability and 0.15% for reproducibility. Sensitivity in transmission and backscatter measurements was improved by a factor of 20 compared to a previously built instrument, which was the basis for the new design. The system is capable of detecting light attenuated down to 0.0063% of the maximum intensity, resulting in a superior threshold. The system was then validated by measuring the optical properties of various biological samples, both natural and engineered. These samples include bovine, porcine, and human corneas and lenses, as well as synthetic materials. Biological sample testing were consistent with published results on the back vertex distance (BVD) test (bovine lenses), the bovine corneal opacity test (BCOP, bovine corneas), and published results obtained with the precursor to the new device.

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48

Sexton, Scott Michael. "Progress Toward Analytic Predictions of Supersonic Hydrocarbon-Air Combustion| Computation of Ignition Times and Supersonic Mixing Layers." Thesis, University of California, San Diego, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10687717.

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Combustion in scramjet engines is faced with the limitation of brief residence time in the combustion chamber, requiring fuel and preheated air streams to mix and ignite in a matter of milliseconds. Accurate predictions of autoignition times are needed to design reliable supersonic combustion chambers. Most efforts in estimating non-premixed autoignition times have been devoted to hydrogen-air mixtures. The present work addresses hydrocarbon-air combustion, which is of interest for future scramjet engines.

Computation of ignition in supersonic flows requires adequate characterization of ignition chemistry and description of the flow, both of which are derived in this work. In particular, we have shown that activation energy asymptotics combined with a previously derived reduced chemical kinetic mechanism provides analytic predictions of autoignition times in homogeneous systems. Results are compared with data from shock tube experiments, and previous expressions which employ a fuel depletion criterion.

Ignition in scramjet engines has a strong dependence on temperature, which is found by perturbing the chemically frozen mixing layer solution. The frozen solution is obtained here, accounting for effects of viscous dissipation between the fuel and air streams. We investigate variations of thermodynamic and transport properties, and compare these to simplified mixing layers which neglect these variations. Numerically integrating the mixing layer problem reveals a nonmonotonic temperature profile, with a peak occurring inside the shear layer for sufficiently high Mach numbers.

These results will be essential in computation of ignition distances in supersonic combustion chambers.

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49

Fragiskatos, Gerasimos. "Non-linear response and instabilities of a two-degree-of-freedom airfoil oscillating in dynamic stall." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0024/MQ50606.pdf.

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50

Lalonde, Stéphanie. "Investigation into the static and fatigue behaviour of a helicopter main rotor yoke made of composite materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0030/MQ64232.pdf.

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Дисертації з теми "Mechanical and aerospace"

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