Electrical Engineering and Computer Sciences - Master's degree
http://hdl.handle.net/1721.1/7817
2018-04-13T01:11:42ZPrediction of velocity distribution from the statistics of pore structure in 3D porous media via high-fidelity pore-scale simulation
http://hdl.handle.net/1721.1/113977
Prediction of velocity distribution from the statistics of pore structure in 3D porous media via high-fidelity pore-scale simulation
AlAdwani, Mohammad S. Kh. F. Sh
Fluid flow and particle transport through porous media are determined by the geometry of the host medium itself. Despite the fundamental importance of the velocity distribution in controlling early-time and late-time transport properties (e.g., early breakthrough and superdiffusive spreading), direct relations linking velocity distribution with the statistics of pore structure in 3D porous media have not been established yet. High velocities are controlled by the formation of channels, while low velocities are dominated by stagnation zones. Recent studies have proposed phenomenological models for the distribution of high velocities including stretched exponential and power-exponential distributions but without an underlying mechanistic or statistical physics theory. Here, we investigate the relationship between the structure of the host medium and the resulting fluid flow in random dense spherical packs. We simulate flow at low Reynolds numbers by solving the Stokes equations with the finite volume method and imposing a no-slip boundary condition at the boundary of each sphere. High fidelity numerical simulations of Stokes flow are facilitated with the assist of open source Computational Fluid Dynamics (CFD) tools such as OpenFOAM. We show that the distribution of low velocities in 3D porous media is described by a Gamma distribution, which is robust to variations in the geometry of the porous media. We develop a simple model that predicts the parameters of the gamma distribution in terms of the porosity of the host medium. Despite its simplicity, the analytical predictions from the model agree well with high-resolution simulations in terms of velocity distribution.
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.; Thesis: S.M., Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2017.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 57-60).
2017-01-01T00:00:00ZDecentralized infrastructure for file storage
http://hdl.handle.net/1721.1/113976
Decentralized infrastructure for file storage
Greco, Nicola, S.M. Massachusetts Institute of Technology
How might we incentivize a peer-to-peer network to store users' files? The purpose of this research is to combine ideas from existing peer-to-peer file sharing systems, blockchain technology and Proofs-of-Storage to create an incentivized decentralized storage network, where every participant can earn a reward for storing and serving files or pay the network to store or retrieve their own. More broadly, in this thesis we present the elementary components for building decentralized infrastructure, culminating in a protocol for incentivizing file storage.
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 99-103).
2017-01-01T00:00:00ZThe Traveling Salesman Problem and orienteering for kinodynamic vehicles
http://hdl.handle.net/1721.1/113975
The Traveling Salesman Problem and orienteering for kinodynamic vehicles
Adler, Aviv
The Traveling Salesman Problem is a major foundational problem in the fields of Computer Science, Operations Research, and Applied Mathematics, in which an agent wants to visit a set of target points with the shortest path possible. This problem is of the highest interest both theoretically in practice. When the agent is a vehicle whose trajectory must satisfy a set of dynamic constraints and the target points are distributed over a continuous space, this problem is especially relevant to robotics. Although this problem is considered computationally intractable to solve precisely, in many settings a good approximate path can be computed efficiently. We study the case where the target points are distributed independently at random and ask how the length of the optimal tour grows as the number of such target points increases, a question which has attracted interest from both the robotics and motion planning community and the applied probability community; however, there has been little interaction between the two communities on this problem. By combining the approaches developed independently by these two communities, we re-derive the most general and powerful results with a simplified method. We then demonstrate the power of our method by extending it to show novel stronger results for an important sub-class of vehicles, as well as novel results for an alternative setting in which the target points are distributed by an adversary rather than at random.
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 55-56).
2017-01-01T00:00:00ZScalable design of high-performance on-chip Terahertz source and imager
http://hdl.handle.net/1721.1/113973
Scalable design of high-performance on-chip Terahertz source and imager
Hu, Zhi, S.M. Massachusetts Institute of Technology
In this thesis, two chip designs using the scalable array architecture are introduced. Firstly, we introduce a scalable architecture of coherent harmonic oscillator array for high-power and collimated radiation beam at mid-THz band. The array is 2D-coupled, and each element achieves these functions: (i) maximize oscillation at fundamental frequency fo= 2 50 GHz; (ii) synchronize phase of fo and its harmonics among elements; (iii) cancel near-field radiation of fo, 2fo and 3fo, and (iv) efficiently radiate at 4fo and combine power in free space. The resultant compact design fits into the optimal radiator pitch of [lambda]/2 (half wavelength) for side-lobe suppression and enables high density implementation of THz arrays. An array prototype of 42 coherent radiators, or 91 resonant antennas, at 1 THz is also presented using IHP S13G2 130-nm SiGe process. The chip occupies 1-mm 2 area and consumes 1.1 W of DC power. The measured total radiated power and effective isotropically-radiated power (EIRP) are 80 pW and 13 dBm, respectively. Secondly, we introduce a scalable architecture of coherent receiver array for beam-steerable imaging. The array is also 2D-coupled, and each element achieves theses functions: (i) maximize oscillation at fo=120 GHz; (ii) synchronize phase of fo and its harmonics among elements; (iii) cancel radiation of fo and 2fo; and (iv) receive and down-convert RF signal near 2fo=240 GHz and output baseband signal for digital beam-forming. Chip is fabricated using TSMC 65nm LP CMOS technology.
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 77-80).
2017-01-01T00:00:00Z