Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002. / "June 2002." / Includes bibliographical references (p. 93-96). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / This thesis considers the application of shape memory alloy (SMA) actuators for shape control of the undertray of a sports car. By deforming the shape of the structure that provides aerodynamic stability to the car, we expect to improve the overall performance of the vehicle by adapting its aerodynamics according to the vehicle speed. We then develop a methodology for designing SMA actuators in this application. The methodology is based on the integration of the different models involved: mechanical, thermal, and electrical. The constraints imposed on the device are also incorporated. Unfortunately, the analysis predicts an actuation time that is too slow for this particular application. Still, we use our assembled model to sketch the expected characteristics of SMA actuators. A significant result is that the actuation time is a function of the amount of energy the active material has to provide, and that there is a necessary trade-off between the mass of actuators and the actuation time. In particular, the expected energy density may have to be decreased to achieve acceptable actuation times. Finally, we propose a way to estimate a priori the suitability of SMA actuators for a particular application. / by Stéphane Lederlé. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1995. / Includes bibliographical references (p. 199-204). / by Bhavesh T. Patel. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 135-138). / Current aircraft engine designs tend towards higher bypass ratio, low-speed fan designs for improved fuel burn, reduced emissions and noise. Alternative propulsion concepts include counter-rotating propfans (CRPs) which have been investigated intensively in the 1970s and 1980s and demonstrated significant reductions in fuel burn. Currently, propfans are being studied again due to their inherent noise challenge and the potential for reduced environmental impact. A newly developed, integrated noise and performance assessment methodology for advanced propfan powered aircraft configurations is introduced. The approach is based on first principles and combines a coupled aircraft and propulsion system performance analysis with 3-D unsteady, full-wheel CRP CFD computations and aero-acoustic simulations. Special emphasis is put on computing CRP interaction tones. The method is capable of dealing with parametric studies and exploring noise reduction technologies. An aircraft performance and mission analysis was first conducted on a candidate CRP powered configuration. In addition, a comparable aircraft with advanced turbofan engines was defined for performance and noise comparisons. / (cont.) Guided by data available in the literature, a detailed aerodynamic design of a pusher CRP was carried out using vortex-lattice methods and 3-D steady RANS computations of the counter-rotating stage. Full-wheel unsteady 3-D RANS simulations were then used to determine the time varying blade surface pressures and unsteady flow features necessary to define the acoustic source terms. A frequency domain approach based on Goldstein's formulation of the acoustic analogy for moving media and Hanson's single rotor noise method was extended to counter-rotating configurations. The far field noise predictions were compared to experimental data and demonstrated good agreement between the computed and measured interaction tones. The underlying noise source mechanisms due to front-rotor wake interaction, aft-rotor upstream influence, hub-endwall secondary flows and front-rotor tip vortices were dissected and quantified. Based on this investigation, the CRP was re-designed for reduced noise incorporating a clipped rear-rotor and an increased rotor-rotor spacing to reduce upstream influence, tip vortex, and wake interaction effects. Maintaining the thrust and propulsive efficiency at takeoff conditions, the noise was calculated for both designs. At the interaction tone frequencies, the re-designed CRP exhibited an average reduction of 7.25 dB in mean SPL computed over the forward and aft polar angle arcs. On the engine/aircraft system level, the re-designed CRP demonstrated a reduction of 9.2 EPNdB and 8.6 EPNdB at the FAR 36 flyover and sideline observer locations, respectively. The results suggest that advanced open rotor designs can possibly meet Stage 4 noise requirements. / by Andreas Peters. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001. / Includes bibliographical references (p. 177-179). / This thesis focuses on the use of aspiration on compressor blade design. The pressure ratio can be significantly increased by controlling the development of the blade and endwall boundary layers. This concept is validated through an aspirated fan stage experiment performed in the MIT Blowdown Compressor Facility. The fan stage was designed to produce a pressure ratio of 1.6 at a throughflow adiabatic efficiency of 89% at a rotor tip speed of 750 ft/s. Aspiration equal to 0.5% of the inlet flow was applied to the blade surface of both the rotor and stator. Aspiration was also used on the endwall boundary layers. Detailed flowfield measurements are made behind the rotor and stator, and the ensemble-averaged data is compared with a 3-D, viscous analysis tool. The time-accurate flow measurements show a large blade to blade variation due to unsteady vortex shedding, which is not captured by conventional 3-D, viscous analysis tools. An incompressible, vortex shedding model calibrated to the experimental data shows that the vortex shedding induces radial flows that redistribute flow properties in the spanwise direction. 'Correction' of the experimental data using the model gives a better comparison with the 3-D, viscous analysis solution. In order to understand the possible benefits of aspiration, a meanline parameter study is performed over a range of rotor inlet Mach numbers, flow coefficients, and work coefficients. Viscous and shock losses are estimated for both conventional and aspirated stages. The results suggest that aspiration can have the largest impact on compressor performance at high stage pressure ratios. / by Brian Joseph Schuler. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013. / This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from department-submitted PDF version of thesis / Includes bibliographical references (p. 113-115). / Spacecraft formation flight has been identified as a critical enabling technology for achieving many scientific, commercial, and military objectives. One of the primary challenges of a formation flight mission is the control of the relative motion between spacecraft. Before any flagship missions will launch, technology development missions will be required to demonstrate the utility and functionality of formation flying systems. This thesis describes the complete attitude and formation control design for the MotherCube formation flight technology demonstration mission in LEO. A model of the spacecraft's sensors and actuators is developed and analyzed. Using curvilinear orbit theory, a simple LQR control law is used to generate a set of desired relative accelerations for formation control. A newly developed two-tier numerical allocation scheme is used alongside an independent PD attitude control law to generate a set of actuator commands which provides 3-axis attitude stabilization as well as formation control with guaranteed feasibility of actuator commands. An Extended Kalman Filter was developed to estimate the system attitude and angular rate from sensor measurements. To test these algorithms, a simulation environment was developed. This environment includes realistic models of space environment and the major perturbation effects which a LEO spacecraft formation would encounter. In order to improve the fidelity, a new intermediate-accuracy method for computing attitude-dependent aerodynamic and solar effects was also developed. Finally, results from the simulation are used numerically validate the dual-allocator approach, assess the performance of the control laws and provide system level metrics such as fuel use and required maneuver time. / by Austin Kyle Nicholas. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 185-191). / Humans experience strong physiological deconditioning during space missions, primarily due to the weightlessness conditions. Some of these adverse consequences include bone loss, muscle atrophy, sensory-motor deconditioning, and cardiovascular adaptation, which may lead to orthostatic intolerance when astronauts are back on Earth. In order to mitigate the negative effects of weightlessness, several countermeasures are currently in place, particularly very intensive exercise protocols. However, despite these countermeasures, astronaut physiological deconditioning persists, highlighting the need for new approaches to maintain the astronauts' physiological state within acceptable limits. Artificial gravity has long been suggested as a comprehensive countermeasure that is capable of challenging all the physiological systems at the same time, therefore maintaining overall health during extended weightlessness. Ground studies have shown that intermittent artificial gravity using a short-radius centrifuge combined with ergometer exercise is effective in preventing cardiovascular and musculoskeletal deconditioning. However, these studies have been done in very different conditions, and confounding factors between the studies (including centrifuge configuration, exposure time, gravity level, gravity gradient, and use/intensity of exercise) make it very difficult to draw clear conclusions about the stimuli needed to maintain physiological conditioning in space. The first objective of this research effort is to analyze the effects of different artificial gravity levels and ergometer exercise workload on musculoskeletal and cardiovascular functions, motion sickness and comfort. Human experiments are conducted using a new configuration of the MIT Compact Radius Centrifuge, which has been constrained to a radius of 1.4 meters, the upper radial limit to fit within an ISS module without extensive structural alterations. The second objective is to develop a computational model of the cardiovascular system to gain a better understanding of the effects of exercise under a high gravity gradient on the cardiovascular system. The gravity gradient generated when using a short-radius centrifuge has not previously been investigated in detail. The model is validated with the experimental measurements from the MIT CRC. Then, the model is used to explore the cardiovascular responses to new centrifuge configurations and from 0g adapted subjects. / by Ana Diaz Artiles. / Ph. D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 139-142). / Two investigations of current problems in the field of compressor stability are presented. The first is of the formation of spike-type rotating stall precursors. Recently, high fidelity computations have attributed pre-cursor formation to a leading-edge separation and consequent shedding of vorticity near the rotor tip due to high incidence. This hypothesis is assessed via experiments in a low-speed compressor and a linear cascade, supported by unsteady computations. Fast-response pressure measurements at the blade tip show spike pre-cursors propagating in the cascade environment at a rate consistent with the low-speed compressor. The cascade design produces high incidence at the mid-span and fast-response velocity measurements show pre-cursor formation away from the tip region. Unsteady computations confirm leading-edge separation and vortex shedding in both the compressor and cascade. A single blade was instrumented with smoke injection at the leading-edge to visualize the separation and the effect of Reynolds number on pre-cursor formation was quantified to facilitate smoke visualization. The resultant visualizations confirm the leading-edge separation and propagation of shed vorticity. The second investigation is of the effects of heat transfer between the compressor structure and gas path during transient operation. A mean line model of an advanced, high pressure ratio compressor is extended to include the effects of heat transfer. Diabatic, transient calculations show a 9.9 point reduction in stall margin from the adiabatic case. 2.5 points are attributed to the effect of heat transfer on blade row deviation and the remainder is attributed to stage rematching. Heat transfer increases loading in the front stages and the stalling pressure ratio is set by front stage stall, suggesting heat transfer effects are greater for compressors with highly loaded front stages. Sensitivity studies of heat flow rate and deviation show a linear dependence of stall margin loss for ratios of heat flow rate to inlet stagnation enthalpy flux much less than unity. / by Andras Laszlo Andor Kiss. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. Vita. / Includes bibliographical references (pages 326-339). / As modern engineering projects increase in size and complexity, they have also tended to increase the number of people affected, thus expanding the set of involved stakeholders. The majority of research in tradespace exploration (TSE), as a paradigm for solving complex design problems, has focused on the analysis of the space of alternatives with the goal of uncovering design choices that are optimal or near-optimal. These designs feature desirable combinations of attributes for a given system stakeholder, including technical attributes, cost, and, more recently, -ilities. Less tradespace research has been devoted to the multi-stakeholder problem, in which there are multiple parties with different desired attributes, who must agree on a single design selection in order to proceed with development. Many standard value-measuring techniques, such as utility theory, operate on individuals only and have been shown to break down when used to combine the preferences of groups. Because of these limitations, multi-stakeholder tradespace exploration (MSTSE) has largely relied on the best practices for individual tradespace exploration, with all stakeholders using those methods in parallel. This parallel exploration has the goal of uncovering as many interesting or desirable alternatives as possible, empowering stakeholders to make an educated decision on how best to negotiate with their counterparts. The group decision problem, however, is not just a series of individual decisions and must incorporate interpersonal dynamics and psychological considerations of what makes a "good" decision, and what constitutes a "fair" solution in the minds of the participants. This thesis describes a research effort to develop the foundations of MSTSE by incorporating fundamental insights from the negotiation and framing literatures. A literature review is used to show that TSE is naturally aligned with the goals of productive negotiation. The framing of data in MSTSE is confirmed, via controlled experiment, to have impacts on negotiation which can be controlled through the visualizations given to the participating stakeholders. A combination of practitioner interviews, analysis of procedures for modern systems engineering methods, and case studies (on aerospace and transportation infrastructure systems) is used to create recommendations for applying MSTSE and demonstrate the new types of insights that can be achieved by doing so, beyond those of prior analyses. / by Matthew Edward Fitzgerald. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1994. / Includes bibliographical references (p. 269-275). / by Gary H. Blackwood. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002. / Includes bibliographical references (v. 2, leaves 267-276). / The integration of piezoelectric actuators into a structure can lead to an active structural surface that can adapt by bending or straining to different operational conditions. This can be used to tune desired properties of the active system to their optimal levels. Due to their fast response time, high bandwidth, and the level of force that the actuator can apply, it has been proposed that monolithic piezoelectric materials be used for active structural control. Monolithic piezoelectric materials for planar actuation have several drawbacks including: (a) use of the lower 3-1 actuation for planar actuation, (b) low strain before failure, (c) inability to conform to curved surfaces. Active Fiber Composites (AFCs) have been developed to address some of these shortcomings of monolithic piezoceramic materials. AFCs are thin composite plies comprised of unidirectional piezoelectric fibers imbedded in a thermoset matrix. An electric field is supplied to the fibers by use of an interdigitated electrode pattern adhered to either side of the AFC. The benefits of AFCs include: the interdigital electrode design uses 3-3 actuation offering increased levels of actuation, AFCs allows for anisotropic planar actuation, the AFCs matrix provides load transfer and load distribution, AFCs allows for coverage of curved shapes. A major drawback of the AFCs with PZT-5A fibers is that the level of actuation is 60% lower than that of the 3-3 actuation of monolithic PZT-5A. This is due primarily to a small layer of low dielectric matrix material that is trapped between the electrodes and the high dielectric fibers during manufacturing. / (cont.) This dielectric mismatch causes a large voltage drop in the matrix thereby reducing actuation. A method that has been developed to reduce this matrix gap, and thus increasing actuation, is to transfer the electrode pattern onto plastic sheets, and heat and press the sheets around the fibers to make Thermoplastic Active Fiber Composites (tmAFCs). tmAFCs also have simpler processing when compared to AFCs and are reshapeable. The focus of this research is to analyze, manufacture, and test tmAFCs to be used in structural control applications with the goal of producing high quality and high performance actuators. / by Christopher T. Dunn. / Ph.D.