Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 325-353). / Many industrial processes involve multicomponent or composite materials in which one component can undergo a phase transition leading to the appearance of a solid phase dispersed in a liquid-like continuous phase. Examples of soft phase-change materials can be found in a variety of applications from food products (e.g., organogels, casein gels and gelatin), pharmaceutical products (e.g., tissue mimicking phantoms and encapsulating agents), cosmetics (e.g., foundations and lipsticks), and in the oil and gas industry, where formation of paraffin waxes and clathrate hydrates represent major issues for upstream production and flow assurance. / Historically, phase-changing materials have been exploited for their unique thermal properties in energy storage applications, however soft solids and complex fluids that undergo phase transformation have broader impact in industrial and biomedical applications because of the dramatic changes in mechanical properties that result from the conditions across the phase transition. Typically, these soft phase-change materials are part of the broader class of elasto-visco-plastic materials, showing both viscoelasticity at small deformations and plasticity at large deformations. However, their material properties are greatly influenced by the specific processing conditions during formation, such as temperature and applied deformation, leading to a thermo-rheological complexity that still poses major challenges for their experimental and theoretical characterization. / In this Thesis, we develop novel experimental protocols and theoretical frameworks to characterize and describe the complex rheological behavior of soft phase-changing materials, under both linear and non-linear deformations. We focus mainly on two types of materials that are of major importance in the oil and gas industry: paraffin gels, as model waxy crude oils, and clathrate hydrate suspensions. In the limit of small deformations, we are usually interested in measuring the frequency response of the material as it evolves, or mutates, over time. Current state-of-the-art techniques have major limitations in providing both time- and frequency-resolution primarily due to the type of input signals used. To overcome this, we develop a robust excitation signal that allows us to perform time-resolved mechanical spectroscopy of fast mutating systems. Inspired by the biosonar signals of bats and dolphins, we introduce a joint frequency- and amplitude- modulated chirp signal. / Combining experiments and numerical simulations, we show that there exists an optimized range of amplitude modulation that minimizes the estimation error while reducing the total acquisition time by almost two orders of magnitude. With this new technique, which we call the Optimally Windowed Chirp (or OWCh), we then explore the phase transition during gelation of a series of mutating, phase-changing materials, including casein gels, gelatin and paraffin gels. To address large, non-linear deformations, we start from a thorough investigation of the steady state and transient response of paraffin gels under shear. We develop a robust protocol that enables us to systematically extract the main rheological features including the thermokinematic memory (i.e. the effect of thermal and shear history on the rheological behavior of the gel) and thixotropy (i.e. the time-dependent behavior under constant applied deformation). / We show that these features can be understood in terms of microstructural rearrangements of the underlying solid particle network, which can be quantified through differential scanning calorimetry, birefringence imaging and rheometry. Based on this understanding, we present a constitutive framework that captures all of the different features while respecting thermodynamic and objectivity constraints. We also investigate mechanical instabilities that may arise during rheological measurements. Combining ultrasonic image velocimetry and rheometry, we show that both shear banding and slip can take place during steady shear below a critical value of the shear rate. However, the thixotropic nature of these materials precludes the banding instability from growing in the sheared region of the gap, ensuring that the measured stress response corresponds to the real bulk behavior. Finally, we study the visco-plastic response of clathrate hydrate suspensions. / To do so, we develop a novel method to robustly control their formation, which so far has been a major issue in experimental studies due to uncontrolled nucleation and growth of hydrate crystals. Our method, based on the use of "frozen emulsions", decreases the induction time by orders of magnitude while guaranteeing that all the water droplets initially frozen into ice particles are converted into hydrate particles. Rheological measurements for different water volume fractions and shear rates reveal that the macroscopic rheological response is again governed by rearrangements of the microstructure; however, due to the very strong interparticle forces (which are the result of a continuous sintering process) the microstructure evolves towards a fully connected network that behaves as a porous solid structure. / Incorporating this limit into our theoretical model, we show that the framework developed for softer interparticle interaction can also capture the macroscopic plastic response of hydrate suspensions. The results from this Thesis have the potential to impact many industrial processes that involve soft phase-change materials, such as flow assurance and oil extraction, thermal energy storage, gas transport and storage, and other processes where the dynamics of gelation are used to control the rheological properties of the ultimate product. / by Michela Geri. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Mechanical Engineering

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2019 / Cataloged from PDF version of thesis. "Thesis contains very faint/illegible footnote numbering"--Disclainer Notice page. / Includes bibliographical references. / Water scarcity is an increasing problem globally. Seawater desalination is increasingly being relied upon as a means of mitigating the problem of water scarcity. However, seawater desalination has costs associated with it: capital costs, cost of energy to desalinate and environmental costs from the discharge of high salinity brine. Efficient and cost-effective seawater desalination and desalination brine management systems are necessary to make seawater desalination a sustainable scalable process. This work seeks to improve seawater desalination and seawater desalination brine management in several ways. For the first time, the thermophysical properties of seawater have been characterized as a function of pressure across the full desalination operating regimes of temperature, salinity and pressure. Functions that allow accurate thermodynamic least work of desalination and seawater flow exergy analysis have been developed. / The least work of desalination, brine concentration and salt production was investigated and the performance of state-of-the-art brine concentrators and crystallizers was calculated. Hybrid designs of reverse osmosis (RO) and electrodialysis (ED) were proposed to be integrated with a crystallizer to concentrate desalination brine more efficiently. The RO-ED-crystallizer concept was applied to two separate applications: (a) salt production from seawater and (b) zero brine discharge seawater desalination. A parametric analysis to minimize the specific cost of salt production and water production was conducted. Parameters varied were: the ratio of seawater to RO brine in the ED diluate channel, ED current density, ED diluate outlet salinity, electricity, water and salt prices, and RO recovery by adding a high pressure RO (HPRO) stage. Results showed that significant cost reductions could be achieved in RO-ED systems by increasing the ED current density from 300 A/m² to 600 A/m². / Increasing RO brine salinity by using HPRO and operating at 120 bar pressure reduced salt production costs while increasing water production costs. Transport properties of monovalent selective ED (MSED) membranes were also experimentally obtained for sodium chloride, significantly improving the accuracy of modeling MSED brine concentration systems. MSED cell pairs transported only about ~~50% the water but nearly as much salt as a standard ED cell pair, while having twice the average membrane resistance. / Supported by Center for Clean Water and Clean Energy at MIT and KFUPM Project No. R13-CW-10, King Fahd University of Petroleoum and Minerals (KFUPM), Dhahran, Saudi Arabia / by Kishor Govind Nayar. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Mechanical Engineering

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1987. / Bibliography: leaf 26. / by Steven Michael Griffiths. / B.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1987. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Bibliography: leaves 219-225. / by Shahriar Negahdaripour. / Ph.D.

Characterization of fluid with suspended nanoparticles in microchannels has been studied as a part of a microfluidic based acute myocardial infarction (AMI) detection device. The AMI detection process uses heat stabilized human serum albumin (HSA) magnetic microspheres and specific antibodies to create a magnetic immunoassay used in the detection of AMI. Microanalysis systems have several advantages over conventional analysis systems due to their sensitivity, reliability and the amount of anlaytes needed for the test. The microchannels used in this work were fabricated at Sandia National Laboratories (SNL) using a SwIFT™ microfabrication surface micromaching process. Micro channels made of Poly(dimethylsiloxane)-glass (PDMS-glass) designed and fabricated at the Department of Chemistry at the Florida State University were also used in this work. The SwIFT™ microchannels had dimensions of 6µm in height, 20µm in width and 200µm in length where as the PDMS-glass microchannels had dimensions of 40µm in height, 200µm wide and 13mm in length. Characterization of the microchannels was accomplished using a variety of techniques. The first method used to characterize the microchannels was to used a head pressure-flow set up to determine the pressure and flow characteristics of the SwIFT™ microchannels with the different fluids that the biodiagnostic process calls for, with average mass flow rate being 1.9x10-2 µg/s and Reynolds number of 1.45 at a pressure of 23kPa for a typical channel, these values approach the upper limit of the work accomplished. Since the HSA microspheres, 1µm in diameter and less, play a critical role in the detection protocol their compatibility to the SwIFT™ microchannels was investigated. Results showed the HSA microspheres agglomerated and adsorbed to the walls of the channels. Fluorescence correlation spectroscopy (FCS) was attempted on the SwIFT™ microchannels with 200nm and 40nm beads and the same conclusion of agglomeration and adsorption was reached which made these channels not suitable for adaptation in the microanaylsis system considered for AMI detection. PDMS-glass microchannels head pressure-flow rates were also investigated showing an average mass flow rate of 1.76x10-1µg/s and a Reynolds number of 1.03 at a pressure of 4.5kPa. FCS was preformed on these channels successfully without any signs of agglomeration, though some adsorption of the beads to the walls of the channel was evident. FCS measured max velocity was equal to approximately 6.6 cm/s. Thus it is concluded that microchannels of similar sizes of the PDMS-glass will be needed in the microanalysis system that is being developed to detect for AMI markers. / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Spring Semester, 2004. / Date of Defense: April 15, 2004. / Microfluidics, Bidiagnostics, AMI Detection, MEMS / Includes bibliographical references. / Yousef Haik, Professor Directing Thesis; Ching-Jen Chen, Committee Member; Chiang Shih, Committee Member.

The study of supersonic cavity flows is of interest both from fundamental fluid dynamics and practical perspectives. The complex nature of this flowfield, consisting of compressible shear layers, compression/expansion waves, and fluid-acoustic interactions, makes it a rich problem to study. A detailed experimental study of supersonic flow (M=1.5 to 2) over a range of three-dimensional rectangular cavities (L/D=1 to 5.2) was conducted. The measurements included unsteady surface pressure measurements, particle image velocimetry, and flow visualization using shadowgraph and schlieren. Large-scale structures in the shear layer and a large recirculation zone in the cavity was observed. Spatial and temporal mode switching was also observed, the nature being different for short and long cavities. The shear layer characteristics of the two cavities are very different in term of curvature and growth. Supersonic microjets were used at the leading edge of the cavities to suppress the resonance in the flow. With a minimal mass flux (0.15%), the activation of microjets led to a large reduction in cavity tones (20 dB) and overall sound pressure levels (9dB). In addition, the microjet injection enhanced the shear layer mixing and reduced the velocity fluctuation in the cavities. The significant reductions together with the low mass flux requirements make this a potentially viable technique for full-scale, practical applications. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Degree Awarded: Spring Semester, 2007. / Date of Defense: March 22, 2007. / Supersonic cavity, Control, Microjet, PIV / Includes bibliographical references. / Farrukh S. Alvi, Professor Co-Directing Dissertation; Chiang Shih, Professor Co-Directing Dissertation; Christopher Tam, Outside Committee Member; Anuradha Annaswamy, Committee Member; Emmanuel G. Collins, Committee Member.

The static synchronous compensator (STATCOM) is increasingly popular in power system application. In general, power factor and stability of the utility system can be improved by STATCOM. Specifically, STATCOM can stabilize a given node voltage and compensate for the power factors of equipment serviced by that node. The dynamic performance of STATCOM is critical to these performance and stability function. STATCOM is a multiple input and multiple output system (MIMO), which can be presented by a mathematic model. Recently, full MIMO state feedback by pole assignment has been shown to be an improvement over classical PI control. In this thesis, an optimal linear quadratic regulator (LQR) design is a compared to the pole assignment design for transient dynamic performance of STATCOM. It was found that LQR controllers do not offer significant performance improvement to pole assignment. However, as a design method the determination of state feedback gains is easier using the LQR method / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Fall Semester, 2003. / Date of Defense: December 12, 2003. / Pole Assigment, Statcom, LQR / Includes bibliographical references.

The magnetic field dependence of critical currents are studied in Bi2Sr2CaCu2O8+x and (Bi,Pb)2Sr2Ca2Cu3O10+x multifilamentary superconducting tapes. The critical current was measured in the magnetic fields up to 5 T, at 4.2 K, with several orientations of the applied magnetic field relative to the tape. The critical current is determined by the normal (c-axis) component of the applied magnetic field over a wide range. At low magnetic fields, the field dependence of the critical current is mainly dominated by weak-links, while at the higher fields it is determined by the strong-links current path limited by intragranular flux pinning. Two-dimensional behavior of the critical current in Bi2Sr2CaCu2O8+x and (Bi,Pb)2Sr2Ca2Cu3O10+x multifilamentary tapes is observed. From 2D behavior it is possible to calculate the average misalignment angle of the grains from critical current measurements in a magnetic field oriented perpendicular and parallel to the tape plane. The results are compared with a reported model that describes the angular dependence of critical currents [*]. The model is based on a Gaussian distribution of the misalignment angles of the grains. With this model it is possible to calculate the standard deviation of the misalignment angle of the grains from critical current measurements in a magnetic field oriented perpendicular and parallel to the tape plane. This model is confirmed experimentally. The angular dependence of the critical current of the measured tapes can be described at 4.2 K in the region between 0 and 5 T by using a standard deviation. [*] O. van der Meer, B. ten Haken, and H.H.J. ten Kate, "A model to describe the angular dependence of the critical current in a Bi-2223/Ag superconducting tape," Physica C 357-360, 1174 (2001). / A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science. / Degree Awarded: Summer Semester, 2004. / Date of Defense: June 28, 2004. / Angular Distribution, Hysteresis, Bi-2223, Bi-2212, Magnetic Field Dependence / Includes bibliographical references. / Justin Schwartz, Professor Directing Thesis; Simone Peterson Hruda, Committee Member; Cesar Luongo, Committee Member.

We report measurements of the velocity fields in He II forced flow obtained by the Particle Image Velocimetry (PIV) technique, a technique which uses micron scale tracer particles to track the flow. We demonstrate that the micron size solid deuterium particles are the best choice for tracing He II forced flow in a horizontal channel. A novel particle seeding device has been developed to form micron size solid hydrogen isotope tracer particles directly within a He II flow. The tracking mechanism and the fidelity of these particles have been examined and are discussed herein. He II forced flows up to 287 mm/s are created in a square cross-section visualization channel within Liquid Helium Flow Visualization Facility (LHFVF). In the adiabatic flow case, visualization results confirm the existence of the turbulent boundary layer, with the measured velocity profiles being in reasonable agreement with empirical correlations for the classical fluids. No temperature dependence to the velocity profiles is observed within the temperature range tested (1.65 K to 2.10 K). We also tested the case of thermal counterflow in the horizontal channel without net flow. Heater powers ranging from 0.4 kW/m2 to 6.6 kW/m2 were applied to the channel at two different bath temperatures, 1.80 K and 1.95 K. We observe millimeter size vortices randomly located in the transient velocity field as measured by the tracer particles. The mean velocity results confirm that the tracer particles do not exactly track the normal fluid component motion, an effect which was observed by previous researchers with vertically oriented thermal counterflow channels. No turbulent boundary layer is observed in this case. A quantitative comparison with previous research in this area is also presented. Finally, we examine forced flow He II with constant applied heat flux, in which the forced flow is coupled with the thermal counterflow. In this case, the measured particle velocity fields show a similar flow pattern as the adiabatic case and the turbulent boundary layer remains. The mean velocity of the tracer particles is seen to be greater than the flow velocity and increases linearly with the normal fluid velocity; however, the rate of increase is less than predicted based on the two-fluid model. Observing and quantifying He II flow velocity fields can extend our knowledge of He II fundamentals and facilitate the refining of existing He II fluid dynamics models. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Degree Awarded: Fall Semester, 2007. / Date of Defense: October 24, 2007. / PIV, Forced Flow, Hydrogen Particles, PIV, Superfluid Helium, Forced Flow, Superfluid Helium, Hydrogen Particles, Particle Seeding / Includes bibliographical references. / Steven W. Van Sciver, Professor Directing Dissertation; James S. Brooks, Outside Committee Member; Cesar A. Luongo, Committee Member; Justin Schwartz, Committee Member.

This dissertation considers the problem of optimal task allocation for heterogeneous teams, e.g., teams of heterogeneous robots or human-robot teams. It is well known that this problem is NP hard and hence computationally feasible approaches must develop an approximate solution. It will be shown that the global cost of the task allocations obtained with fast greedy algorithms can be improved upon by using a class of cooperative auction methods called Stochastic Clustering Auctions (SCAs). SCAs use stochastic transfers or swaps between the task clusters assigned to each team member, allow both uphill and downhill cost movements, and rely on simulated annealing. The choice of a key annealing parameter and turning the uphill movements on and off enables the converged solution of a SCA to slide in the region between the global optimal performance and the performance associated with a random allocation. The first SCA developed in this research, called GSSCA, is based on a Gibbs sampler, constrains the stochastic cluster reallocations to simple single transfers or swaps, and is applicable to heterogeneous teams. For homogeneous teams this dissertation presents a new and more efficient SCA, called SWSCA, based on the generalized Swendsen-Wang method, which enables more complex and efficient movements between clusters by connecting tasks that appear to be synergistic and then stochastically reassigning these connected tasks. For heterogeneous teams this dissertation proposes a HYbrid Stochastic Clustering Auction, called HYSCA. In HYSCA the auctioneer makes stochastic movements with single tasks when the auctioneer negotiates with heterogeneous agents and makes stochastic movements with interconnected tasks when the auctioneer negotiates with homogeneous agents. For centralized auctioning extensive numerical experiments were used to compare GSSCA with greedy auctioning methods for homogeneous teams and heterogeneous teams in terms of costs and computational and communication requirements. A series of random simulations showed that SWSCA was able to obtain significantly greater cost improvements than GSSCA for both the greedy and non-greedy cases for homogeneous teams and HYSCA was able to obtain significantly greater cost improvements than GSSCA for heterogenous teams. For distributed auctioning simulation results are presented from random scenarios and for selected benchmark auction patterns with a focus on a comparison of the performance achieved with distributed and centralized GSSCA. Finally the distributed SWSCA and HYSCA is evaluated in numerical experiments in which the communication links between agents were motivated by a generic topology called a ``scale free network.' / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Degree Awarded: Summer Semester, 2010. / Date of Defense: June 28, 2010. / Auctions and Market-based Systems, Optimal Task Allocation, Distributed Robot Systems, Networked Agents, Markov Chain Monte Carlo, Simulated Annealing, Swendsen-Wang Method / Includes bibliographical references. / Emmanuel G. Collins, Professor Directing Thesis; Adrian Barbu, University Representative; Leon van Dommelen, Committee Member; David Cartes, Committee Member.