Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 63-66). / This thesis proposes a transactive control mechanism that minimizes the operational costs of individual trains and integrates rail-side distributed energy resources (DERs) within an electric railway system. The operation of each individual train is posed as an energy cost minimization problem that is constrained by both the dynamics of the train and the specific schedule it must meet. The solution of this problem yields an optimal power profile for the train to follow. For each of the railway's segments, the proposed transactive controller determines the minimum average cost of electricity and the dispatch of the DERs based on the energy usage of the trains across space and time. By iterating between the transactive controller and the cost minimization scheme of the individual trains, the proposed methodology yields optimal power profiles of all the trains in the system and the dispatch of the generation assets. This methodology is tested through numerical simulation of the Amtrak Northeast Corridor service between University Park Station in the outskirts of Boston, Massachusetts and New Haven Station in Connecticut. Simulations of the southbound service over the course of a year demonstrate that the minimum cost operation reduces retail energy supply and delivery charges by 10% when compared to minimum work operation. We test the addition of solar generation across the system as an example of DER integration. The price signal of the transactive controller converges to within 1% after just 3 iterations for a single PV array and one train and within 4 iterations for two PV arrays and two trains. / Supported by award 1644877 from National Science Foundation, Cyber-Physical Systems program / by David Humberto D'Achiardi Pascualy. / S.M. / S.M. Massachusetts Institute of Technology, Department of Mechanical Engineering

The present numerical investigation aims to uncover the inherent instability in compressible cavity flows and aid designs of effective flow control to alter undesirable flow features. Two-dimensional (2D) and three-dimensional (3D) global stabilities of compressible open-cavity flows are examined in detail, which provides insights into designs of active flow control to reduce the pressure fluctuations over the cavity. The stability characteristics of compressible spanwise-periodic open-cavity flows are investigated with direct numerical simulation (DNS) and biglobal stability analysis for rectangular cavities with length-to-depth ratios of $L/D=2$ and 6. This study examines the behavior of instabilities with respect to stable and unstable steady states in the laminar regimes for subsonic as well as transonic conditions where compressibility plays an important role. It is observed that an increase in Mach number destabilizes the flow in the subsonic regime and stabilizes the flow in the transonic regime. Biglobal stability analysis for spanwise-periodic flows over rectangular cavities with large aspect ratio is closely examined in this study due to its importance in aerodynamic applications. Moreover, biglobal stability analysis is conducted to extract 2D and 3D eigenmodes for prescribed spanwise wavelengths $\lambda/D$ about the 2D steady state. The properties of 2D eigenmodes agree well with those observed in the 2D DNS. In the analysis of 3D eigenmodes, it is found that an increase of Mach number stabilizes dominant 3D eigenmodes. For a short cavity with $L/D=2$, the 3D eigenmodes primarily stem from centrifugal instabilities. For a long cavity with $L/D=6$, other types of eigenmodes appear whose structures extend from the aft-region to the mid-region of the cavity, in addition to the centrifugal stability mode located in the rear part of the cavity. A selected number of 3D DNS are performed at $M_\infty=0.6$ for cavities with $L/D=2$ and 6. For $L/D=2$, the properties of 3D structures present in the 3D nonlinear flow correspond closely to those obtained from linear stability analysis. However, for $L/D=6$, the 3D eigenmodes cannot be clearly observed in the 3D DNS, due to the strong nonlinearity that develops over the length of the cavity. In addition, it is noted that three-dimensionality in the flow helps alleviate violent oscillations for the long cavity. The analysis performed in this paper can provide valuable insights for designing effective flow control strategies to suppress undesirable aerodynamic and pressure fluctuations in compressible open-cavity flows. Three-dimensional nonlinear simulations (DNS and LES) are also conducted to examine influence of cavity width, sidewall boundary conditions, free stream Mach numbers, and Reynolds numbers on open-cavity flows. DNS and large eddy simulations (LES) are performed with $L/D=6$, width-to-depth ratios of $W/D$=1 and 2 for Reynolds number of $Re_D = 502$ and $10^4$. To numerically study the effects of cavity width on the flows, we consider (1) 2D cavities with spanwise periodicity and (2) finite-span cavities with no-slip adiabatic walls. Furthermore, the analyses are conducted for subsonic ($M_\infty=0.6$) and supersonic ($M_\infty=1.4$) speeds to reveal compressibility effects. It is found that, at low $Re_D=502$, widening the cavity can decrease the velocity fluctuations of the flow by introducing spanwise variations in the shear layer to reduce the kinetic energy from spanwise vortices associated with Rossiter modes. Both velocity and pressure fluctuations decrease in the finite-span cavity compared to those with spanwise periodic boundary conditions. With the characteristics of base flows revealed, flow control is implemented for turbulent cavity flows where steady blowing is introduced along the leading edge of the cavity for both subsonic ($M_\infty=0.6$) and supersonic ($M_\infty=1.4$) flows. We examine how the actuations interact with the flows and reduce the velocity and pressure fluctuations with and without sidewalls. From the control study, we find that pressure reduction on the cavity surfaces can be achieved in an effective manner by taking advantage of 3D flow physics. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2017. / November 3, 2017. / Compressible cavity flow, Flow control of cavity flows, Global stability analysis / Includes bibliographical references. / Kunihiko Taira, Professor Directing Dissertation; Weikuan Yu, University Representative; Louis N. Cattafesta, III, Committee Member; Lawrence S. Ukeiley, Committee Member; Shangchao Lin, Committee Member.

High temperature pressure sensing is desirable for a broad range of applications related to re-entry of space vehicles and control of combustion processes; however, limited materials can sustain temperatures above 1000C while under time-varying pressure. A sapphire based optical pressure transducer has been proposed for measuring pressure at temperatures approaching 1600C. Manufacturing such sensors has focused on picosecond laser machining. Current research has produced models which can predict ablation depth for longer (ns) pulses and shorter (fs) pulses but there is an underwhelming amount of research focusing on predicting and understanding the mechanics of picosecond pulses. This is partially because of transitions in the mode of ablation processes associated with photothermal versus photochemical behavior. We put forth a general model for laser ablation using Maxwell's equations and a sharp interface equation and compare different constitutive laws which couple the two equations together. The proposed modeling results are compared to laser machining experimental data on sapphire from the literature to illustrate key material parameter uncertainty and sensitivity to the laser machining process. Bayesian uncertainty quantification is used to help validate the approximations within the constitutive equations. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester 2016. / July 8, 2016. / dielectrics, laser ablation, picosecond, sapphire, uncetainty quantificion / Includes bibliographical references. / William S. Oates, Professor Directing Thesis; Shangchao Lin, Committee Member; Wei Guo, Committee Member.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1996. / Includes bibliographical references. / by Byeonghyeok Sohn. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006. / Includes bibliographical references (leaves 35-36). / A device that can measure the dynamic compliance of a material has applications for research, health sciences and for use as a pedagogical tool. A device was created which stochastically perturbs a material while measuring the resulting forces and displacements. A software program then creates a non-parameterized impulse response function in addition to a fit second order model for the material. The device was tested on a compliant sponge sample which exhibited highly nonlinear dynamic behavior. The low frequency compliance of the sponge was measured with the device with 16% to 31% error. Improvements for further dynamic testing on the sponge are presented as well as future improvements to the design of the device. / by Ethan A. Post. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002. / "September 2002." / Includes bibliographical references (p. 61). / by C. Kelly Harper. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 59). / This work takes an in depth look at acoustic propagation through double duct sound speed profiles in the Arctic. While the traditional Arctic sound speed profile has a single surface duct, some portions of the Arctic have a sound speed profile which includes a second, lower duct. These double duct systems are seen through out the Beaufort Sea, dating back to 2004, in data made available by the Ice-Tethered Profiler program at the Woods Hole Oceanographic Institutes. The acoustic propagation through the double duct system is analyzed using normal mode analysis, through the Kraken normal mode code. A simulated lower duct is introduced in order to isolate only those modes which travel within the lower duct. Propagation through the lower duct is compared to propagation in traditional Arctic sound speed profiles, and for certain ducts distinct increases in propagation strength are shown. / by Thomas Howe. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (leaf 54). / The objective of this thesis is the design and implementation of a multi-axis force transducer to be integrated into a set of track and field starting blocks. The feedback from this transducer can be used by athletes and coaches to analyze race starts, with the intention of maximizing the runner's speed and power while decreasing wasted side loads and torques. This thesis describes the design of the transducer itself and the supporting infrastructure that connects it to an existing pair of track starting blocks. The transducer is tested in several field trials and generates a measurable voltage output that varies linearly with applied load and loading position. Data collected from the field trials is further analyzed to give insight into the starting mechanics of a collegiate sprinter. / by Zachary J. Traina. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007. / Includes bibliographical references (p. 73-75). / Unmanned underwater vehicles have various missions within civilian, military and academic sectors. They have the ability to explore areas unavailable to manned assets and to perform duties that are risky to humans. In particular, UUVs have the ability to perform bearings-only tracking in shallow areas near shorelines. This thesis presents a guidance algorithm for this particular mission. This thesis first presents a Modified Polar Extended Kalman Filter for the estimation problem. Bearings-only tracking is a nonlinear problem that requires some sort of estimator to determine the target state. The guidance algorithm is developed based on the relative positions of the observer and the target. In order to develop the guidance algorithm, the effectiveness of a variety of course maneuvers are presented. The effectiveness of these maneuvers are analyzed both quantitatively and qualitatively. The results from this analysis is incorporated into the final guidance algorithm. This thesis also evaluates the developed guidance algorithm through a series of simulation experiments. The experiments explore a variety of scenarios by varying speed, geometry and acoustic environment. The results of the experiments are analyzed based on estimation errors and detection time. The final conclusions indicate that some of the geometries are more favorable than others. In addition, the degree of noise in the acoustic environment affects the range of the UUV's sensors and the UUV's ability to perform bearings-only tracking for an extended period of time. In addition, the desired speed ratio is one in which the observer is either the same speed as or slower than the target. / by Danica Lee Middlebrook. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995. / Includes bibliographical references (leaves 77-78). / by Chad Matthew Brooks. / M.S.