Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005. / Includes bibliographical references (p. 194-198). / Real options analysis is being increasingly used as a tool to evaluate investments under uncertainty; however, traditional real options methodologies have some shortcomings that limit their utility, such as the use of the geometric Brownian motion to model the value of the underlying asset and the assumption of a fixed cost to exercise the option. In this thesis, an alternative real options methodology is developed that overcomes some of the difficulties of traditional approaches. In particular, the methodology proposed here presents an analytical framework that allows the value of completion and the strategy- enabling completion cost (commonly referred to as stock price and strike price in the real options literature, respectively) to be represented by any probability distribution. If these probability distributions can be described analytically, an exact solution to the real options valuation problem can be found. Otherwise, the probability distributions can be generated with numerical simulation (e.g. Monte Carlo simulation), and the answer can then be found numerically. This generalized methodology combines the simplicity of analytical approaches with the flexibility to represent completion costs and the value of completion with any probability distribution. The generalized real options methodology is illustrated with an example from aviation: the decision to launch a new aircraft development program. This type of investment is suitable for real options analysis because of the many uncertainties involved, the long- term nature of the project, and the ability of management to act and influence the project as uncertainties are resolved during its evolution. / (cont.) The analysis shows that investors can use the numerical results of the real options evaluation to determine the investment limits on the different stages of the aircraft program, that managers can use insights from the real options approach to restructure the program to improve the financial feasibility of the project, and that both investors and managers can use the output of derivative analyses to define minimum requirements (in terms of aircraft orders) to ensure program success. / by Bruno Miller. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1993. / Includes bibliographical references (leaves 103-105). / by Jack Barron Aldrich. / 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. 77-80). / This thesis investigates the use of generalized belief propagation (GBP) and belief propagation (BP) algorithms for distributed inference. The concept of a network region graph is introduced, along with several approximation structures that can be distributed across a network. In this formulation, clustered region graphs are introduced to create a network "backbone" across which the computation for inference is distributed. This thesis shows that clustered region graphs have good structural properties for GBP algorithms. We propose the use of network region graphs and GBP for location-aware networks. In particular, a method for representing GBP messages non-parametrically is developed. As an special case, we apply BP algorithms to mobile networks without infrastructure, and we propose heuristics to optimize degree of network cooperation. Numerical results show a five times performance increase in terms of outage probability, when compared to conventional algorithms. / by Ulric John Ferner. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 77-80). / Shielding critical links enhances network robustness and provides a new way of designing robust networks. We first consider shielding critical links to guarantee network connectivity after any failure under geographical and general failure models. We develop a mixed integer linear program (MILP) to obtain the minimum cost shielding to guarantee the connectivity of a single source-destination (SD) pair under a general failure model, and exploit geographical properties to decompose the shielding problem under a geographical failure model. We extend our MILP formulation to guarantee the connectivity of the entire network, and use Benders decomposition to significantly reduce the running time by exploiting its partial separable structure. We extend the algorithms to guarantee partial network connectivity, and observe that significantly less shielding is required, especially when the failure region is small. To mitigate the effect of random link failures on network connectivity, we consider increasing the effective min-cut of the network by shielding, where shielded links cannot be contained in effective cuts. For a single SD pair, we develop an efficient algorithm to increase the effective min-cut by one, and develop a MILP with a small number of constraints to increase the effective min-cut by an arbitrary value. Then we extend the MILP to obtain the optimal shielding to increase the effective min-cut for the entire network, which can be used to solve realistic size problems. Finally, we consider shielding critical nodes in random graphs. We demonstrate the importance of high degree nodes in random graphs constructed under the configuration model. The occupancy of higher degree nodes leads to a larger size of the giant component. Moreover, shielding a small fraction of nodes in power law random graphs guarantees the existence of a giant component if the exponent is less than three. / by Jianan Zhang. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 173-174). / This thesis presents the development of a dimensionless blood microcirculation model for the study of blood microcirculation flows. It is a two dimensional, axially symmetric, incompressible, Newtonian-flow, Krogh cylinder model subjected to axially periodic boundary conditions. This model formulation allows for the use of the streamfunction-vorticity formulation of the Navier-Stokes equation, which offers simplification to boundary conditions and also allows for the use of a non-uniform, collocated mesh. A streamfunction vorticity formulation of the Immersed Boundary Method is also developed, specifically for the boundary conditions along the immersed boundary (red blood cell membrane). Periodic boundary conditions are used, with the assumption of fully-developed flow, in order to focus on the effects of the transient diffusion of oxygen into the surrounding tissue, orthogonal to the capillary flow direction. / by Kevin Sabo. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1996. / Includes bibliographical references (p. 115-116). / by Louis J. Lintereur. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1993. / Includes bibliographical references (leaves 212-213). / by Jabin Todd Bell. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 147-149, 2nd group). / A specimen and an experimental method to observe the behavior of a grooved composite subjected to out-of-plane contact loading is established and verified, and its response is examined. The specimen is designed so that the variability of stress-strain state is negligible across the width of the specimen. The dominant concept of the design is to isolate the response of the specimen around the groove from any other effects. Geometric parameters, stacking sequence (layup), and boundary conditions are determined for the specimen. With simply-supported boundary conditions, specimens fail in a simple beam shear mode as determined from the overall structural response of the specimen, thereby indicating that this configuration is not appropriate for the primary design goal. Thus, the rigid backface boundary condition is chosen and verified as the appropriate configuration. Contact, load transfer, and alignment issues arose in the first set of rigid backface tests and were solved by introducing finer machining, harder material for the indenter, and overall alignment with better accuracy. This resulted in the final test specimen configuration and associated test method, consisting of a specimen with a length of 56.00 mm, a width of 25.00 mm, an approximate thickness of 12.5 mm, and a maximum groove depth of 3.48 mm. The standard layup used for the tests is [F45/0/90]1os, while an alternate layup of [T30/0]13S was also used. In these tests, a number of key behaviors were observed: mode of failure, load-per-stroke slope, and "knee load". / (cont.) Specimens failed in two different modes: a delamination near the bottom of the groove (Mode A), and a crack under the groove propagating to a delamination near the midplane (Mode B). From observations, it is concluded that damage is generated at the bottom of the groove and then propagates in the longitudinal and the thickness direction, resulting in Mode A or B respectively. A "knee load" is defined as a point where the load-per-stroke slope deviates from linear behavior. Failure Mode B and the presence of the "knee load" are observed in the standard layup, but are not applicable to the alternate layup. The presence of 90' plies is indicated as the main cause of the observed differences. The test results clearly show that a specimen and a test method is established and verified for the objectives of the current work, and furthermore is valid for tests with different test parameters. Recommendations are made with regard to extension of the basic testing established herein. / by Yusuke Kobayashi. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012. / 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 (p. 76-80). / In this thesis, I present a framework for achieving a stable bounding gait on the LittleDog robot over rough terrain. The framework relies on an accurate planar model of the dynamics, which I assembled from a model of the motors, a rigid body model, and a novel physically-inspired ground interaction model, and then identied using a series of physical measurements and experiments. I then used the RG-RRT algorithm on the model to generate bounding trajectories of LittleDog over a number of sets of rough terrain in simulation. Despite signicant research in the field, there has been little success in combining motion planning and feedback control for a problem that is as kinematically and dynamically challenging as LittleDog. I have constructed a controller based on transverse linearization and used it to stabilize the planned LittleDog trajectories in simulation. The resulting controller reliably stabilized the planned bounding motions and was relatively robust to signicant amounts of time delays in estimation, process and estimation noise, as well as small model errors. In order to estimate the state of the system in real time, I modified the EKF algorithm to compensate for varying delays between the sensors. The EKF-based filter works reasonably well, but when combined with feedback control, simulated delays, and the model it produces unstable behavior, which I was not able to correct. However, the close loop simulation closely resembles the behavior of the control and estimation on the real robot, including the failure modes, which suggests that improving the feedback loop might result in bounding on the real LittleDog. The control framework and many of the methods developed in this thesis are applicable to other walking systems, particularly when operating in the underactuated regime. / by Michael Yurievich Levashov. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002. / Includes bibliographical references (p. 143-150). / An error correction and grid adaptive method is presented for improving the accuracy of functional outputs of compressible flow simulations. The procedure is based on an adjoint formulation in which the estimated error in the functional can be directly related to the local residual errors of both the primal and adjoint solutions. This relationship allows local error contributions to be used as indicators in a grid adaptive method designed to produce specially tuned grids for accurately estimating the chosen functional. The method is applied to two-dimensional inviscid and viscous (laminar) flows using standard finite volume discretizations, and to scalar convection-diffusion using a Galerkin finite element discretization. Isotropic h-refinement is used to iteratively improve the grids in a series of subsonic, transonic, and supersonic inviscid test cases. A commonly-used adaptive method that employs a curvature sensor based on measures of the local interpolation error in the solution is implemented to comparatively assess the performance of the proposed output-based procedure. In many cases, the curvature-based method fails to terminate or produces erroneous values for the functional at termination. In all test cases, the proposed output-based method succeeds in terminating once the prescribed accuracy level has been achieved for the chosen functional. / (cont.) Output-based adaptive criteria are incorporated into an anisotropic grid-adaptive procedure for laminar Navier-Stokes simulations. The proposed method can be viewed as a merging of Hessian-based adaptation with output error control. A series of airfoil test cases are presented for Reynolds numbers ranging from 5,000 to 100,000. The proposed adaptive method is shown to compare very favorably in terms of output accuracy and computational efficiency relative to pure Hessian-based adaptation. / by David Anthony Venditti. / Ph.D.