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Academic Commons Search Resultsen-usThe Stability at the Solid-Solid and Liquid-Solid Interfaces
http://academiccommons.columbia.edu/catalog/ac:198539
Xiao, Junfenghttp://dx.doi.org/10.7916/D8KK9BS1Wed, 04 May 2016 15:33:41 +0000In this thesis, we studied three small subjects in the realm of continuum mechanics: imbibition in fluid mechanics, beam and rod buckling in solid mechanics and shell buckling at the solid-liquid interface.
In chapter 2, we examined the radial imbibition into a homogenous semi-infinite porous media from a point source with infinite liquid supply. We proved that in the absence of gravity (or in the regime while gravity is negligible compared to surface tension), the shape of the wet area is a hemisphere, and the radius of the wet area evolves as a function with respect to time. This new law with respect to time has been verified by Finite Element Method simulation in software COMSOL and a series of experiments using packed glass microsphere as the porous media. We also found that even though the imbibition slows down, the flow rate through the point source remains constant. This new result for three dimensional radial imbibition complements the classic Lucas-Washburn law in one dimension and two dimensional radial imbibition in one plane.
In chapter 3, we studied the elastic beam/rod buckling under lateral constraints in two dimension as well as in three dimension. For the two dimensional case with unique boundary conditions at both ends, the buckled beam can be divided into segments with alternate curved section and straight section. The curved section can be solved by the Euler beam equation. The straight sections, however, are key to the transition between different buckling modes, and the redistributed length of straight sections sets the upper limit and lower limit for the transition. We compared our theoretical model of varying straight sections with Finite Element Method simulation in software ABAQUS, and good agreements are found. We then attempted to employ this model as an explanation with qualitative feasibility for the crawling snake in horizontal plane between parallel walls, which shows unique shape like square wave. For the three dimensional buckling beam/rod confined in cylindrical constraints, three stages are found for the buckling and post buckling processes: initial two dimensional shape, three dimensional spiral/helix shape and final foldup/alpha shape. We characterized the shape at each stage, and then we calculated the transition points between the three stages using geometrical arguments for energy arguments. The theoretical analysis for three dimensional beam/rod are also complemented with Finite Element Method simulations from ABAQUS.
In chapter 4, we investigated the buckling shape of solid shell filled with liquid core in two dimension and three dimension. A material model for liquid is first described that can be readily incorporated in the framework of solid mechanics. We then applied this material model in two dimensional and three dimensional Finite Element Method simulation using software ABAQUS. For the two dimensional liquid core solid shell model, a linear analysis is first performed to identify that ellipse corresponds to lowest order of buckling with smallest elastic energy. Finite Element Method simulation is then performed to determine the nonlinear post-buckling process. We discovered that two dimensional liquid core solid shell structures converge to peanut shape eventually while the evolution process is determined by two dimensionless parameters Kτ/μ and ρR^2/μτ. Amorphous shape exists before final peanut shape for certain models with specific Kτ/μ and ρR^2/μτ. The two dimensional peanut shape is also verified with Lattice Boltzmann simulations. For the three dimensional liquid core solid shell model, the post buckling shape is studied from Finite Element Method simulations in ABAQUS. Depending on the strain loading rate, the deformations show distinctive patterns. Large loading rate induces herringbone pattern on the surface of solid shell which resembles solid core solid shell structure, while small loading rate induces major concave pattern which resemble empty solid shell structure. For both two dimensional and three dimensional liquid core system, small scale ordered deformation pattern can be generated by increasing the shear stress in liquid core.
In the final chapter, we summarized the discoveries in the dissertation with highlights on the role that geometry plays in all of the three subjects. Recommendations for future studies are also discussed.Mechanical engineering, Mechanicsjx2151Mechanical Engineering, Earth and Environmental EngineeringDissertationsNanofluidics: Fundamentals and Applications in Energy Conversion
http://academiccommons.columbia.edu/catalog/ac:152478
Liu, Linghttp://hdl.handle.net/10022/AC:P:14671Wed, 12 Sep 2012 00:00:00 +0000As a nonwetting liquid is forced to invade the cavities of nanoporous materials, the liquid-solid interfacial tension and the internal friction over the ultra-large specific surface area (usually billions of times larger than that of bulk materials) can lead to a nanoporous energy absorption system (or, composite) of unprecedented performance. Meanwhile, while functional liquids, e.g. electrolytes, are confined inside the nanopores, impressive mechanical-to-electrical and thermal-to-electrical effects have been demonstrated, thus making the nanoporous composite a promising candidate for harvesting/scavenging energy from various environmental energy sources, including low grade heat, vibrations, and human motion. Moreover, by taking advantage of the inverse process of the energy absorption/harvesting, thermally/electrically controllable actuators can be designed with simultaneous volume memory characteristics and large mechanical energy output. In light of all these attractive functionalities, the nanoporous composite becomes a very promising building block for developing the next-generation multifunctional (self-powered, protective and adaptive) structures and systems, with wide potential consumer, military, and national security applications. In essence, all the functionalities of the proposed nanofluidic energy conversion system are governed by nanofluidics , namely, the behavior of liquid molecules and ions when confined in ultra-small nanopores. Nanofluidics is an emerging research frontier where solid mechanics and fluid mechanics meet at the nanoscale. The complex interactions between liquid molecules/ions and solid atoms at the nanointerface, as well as the unique structural, thermal and electrical characteristics of fluids confined in nanocavities collectively represent an outstanding challenge in physical science. A thorough understanding of the science of nanofluids, in particular the detailed molecular mechanisms as well as the roles of various material and system parameters, does not only underpin the development and optimization of the aforementioned nanofluidic energy conversion system, but it also have broad impact on a number of other areas including environmental engineering, chemical engineering, bioengineering, and energy engineering, etc. This dissertation carries out a systematic computational study to explore the fundamental nanofluidic infiltration and transport mechanisms, as well as the thermal and electrical characteristics of the solid-liquid interface. New physical models describing the unique nanofluidic phenomena will be established, where critical parameters, such as the surface tension, contact angle, and viscosity, will be reinvestigated at the nanoscale. The effects of various material and system parameters, such as the solid phase, liquid phase, pore size and pore geometry, as well as the external thermal, electrical and mechanical loads, etc., will be systematically investigated and bridged with the nanofluidic energy conversion processes. The energy conversion efficiencies under various conditions will be evaluated via a synergy between simulation and experiment. Reverse analysis based on the revealed principles can guide the optimization of the various material and system parameters, which potentially may contribute to the design of highly efficient and sustainable nanofluidic energy conversion devices. Besides the direct impact on the nanofluidic energy conversion, the study is also directly relevant to biological conduction and environmental sustainability, in both of which infiltration and transport play important roles.Mechanics, Alternative energy, Energy, Materials sciencell2405Civil Engineering and Engineering Mechanics, Earth and Environmental EngineeringDissertationsScience of Nanofluidics and Energy Conversion
http://academiccommons.columbia.edu/catalog/ac:148244
Xu, Baoxinghttp://hdl.handle.net/10022/AC:P:13570Thu, 21 Jun 2012 00:00:00 +0000The emerging subject of nanofluidics, where solids and fluids interact closely at the nanoscale, has exhibited radically different from their macroscopic counterparts (and sometimes counterintuitive), and yet relatively less explored. On the other hand, the resulting unique properties may contribute to a number of innovative functions with fascinating applications. Among various exciting potential applications, an important and ever expanding one is to provide alternative solutions to energy conversion with high efficiency, including energy absorption, actuation and harvesting. In this dissertation, we first report a novel protection mechanism of energy capture through which an intensive impact or blast energy can be effectively mitigated based on a nonwetting liquid-nanoporous material system. The captured energy is stored in nanopores in the form of potential energy of intercalated water molecules for a while, and not necessarily converted to other forms of energy (e.g. heat). At unloading stage, the captured energy will be released gradually due to the hydrophobic inner surfaces of nanopores through the diffusion of water molecules out of nanopores, thus making this system reusable. Several key controlling factors including impacting velocity, nanopore size, nanopore structure, and liquid phase have been investigated on the capacity of energy capture. The molecular mechanism is elucidated through the study of water molecular distributions inside nanpores. These molecular dynamic (MD) findings are quantitatively verified by a parallel blast experiment on a zeolite/water system. During the transport of confined liquid molecules, the friction resistance exerted by solid atoms of nanopores to liquid molecules will dissipate part of energy, and is highly dependent of temperature of liquid molecules and wall morphology of nanopores. Using MD simulations, the effects of temperature and wall roughness on the transport resistance of water molecules inside nanopores are investigated in Chapter 3. The effective shear stress and nominal viscosity that dominate the nanofluidic transport resistance are extracted and coupled with the nanopore size, transport rate, and liquid property. The molecular-level mechanisms are revealed through the study of the density profile and hydrogen bonding of confined liquid molecules. A parallel experiment on a nanoporous carbon-liquid system is carried out and qualitatively verifies MD findings. Motived by the well-known thermo- and electro-capillary effect, Chapter 4 and Chapter 5 present a conceptual design of thermal and electric actuation system by adjusting the relative hydrophobicity of a liquid-nanoporous system through a thermal and electric field, respectively. The thermally and electrically dependent infiltration behaviors of liquids into nanopores are analyzed by using MD simulations. The fundamental molecular characteristics, including the density profile, contact angle, and surface tension of the confined liquid molecules, are examined to reveal underlying mechanisms. The energy density, power density, and efficiency of both thermal and electric actuation systems are explored and their variations with pore size, solid phase, and liquid phase are evaluated. Thermally and electrically controlled infiltration experiments on a zeolite-water /electrolyte solution system are performed accordingly to qualitatively validate these findings. These energy actuation systems can also become high density thermal or electric storage devices with proper designs. Energy harvesting by the flow of a hydrochloric acid-water solution through a nanopore is explored using atomistic simulations in the last chapter. Through ion configurations near the pore wall, an averaged ion drifting velocity is determined, and the induced voltage along the axial direction is obtained as a function of key material parameters, including the applied flow rate, environmental temperature, solution concentration and nanopore size. The molecular mechanism of ion hopping and motion is revealed. This study shed light on harvesting wasted thermal and mechanical energy from ambient environmental sources such as wasted heat in power plants. Nanofluidics is a novel and thriving research area, whose couplings with other disciplines such as material, mechanical, physical, chemical, electrical engineering are open.Engineering, Mechanics, Materials sciencebx2107Earth and Environmental EngineeringDissertations