Reduced models for thick liquid layers with inertia on highly curved substrates

A method is presented for deriving reduced models for fluid flows over highly curved substrates with wider applicability and accuracy than existing models in the literature. This is done by reducing the Navier-Stokes equations to a novel system of boundary layer like equations in a general geometric setting. This is accomplished using a new, relaxed set of scalings that assert only that streamwise variations are ‘slow’. These equations are then solved using the method of weighted residuals, which is demonstrated to be applicable regardless of the geometry selected. A large number of results in the literature can be derived as special cases of our general formulation. A few of the more interesting cases are demonstrated. Finally, the formulation is applied to two thick annular flow systems as well as a conical system in both linear and nonlinear regimes, which traditionally has been considered inaccessible to such reduced models. Comparisons are made with direct numerical simulations of the Stokes equations. The results indicate that reduced models can now be used to model systems involving thick liquid layers

Reduced-order modelling of thick inertial flows around rotating cylinders

A new model for the behaviour of a thick, two-dimensional layer of fluid on the surface of a rotating cylinder is presented, incorporating the effects of inertia, rotation, viscosity, gravity and capillarity. Comparisons against direct numerical simulations (DNS) show good accuracy for fluid layers of thickness of the same order as the cylinder radius, even for Reynolds numbers up to Re∼10. A rich and complex parameter space is revealed, and is elucidated via a variety of analytical and numerical techniques. At moderate rotation rates and fluid masses, the system exhibits either periodic behaviour or converges to a steady state, with the latter generally being favoured by greater masses and lower rotation rates. These behaviours, and the bifurcation structure of the transitions between them, are examined using a combination of both the low-order model and DNS. Specific attention is dedicated to newly accessible regions of parameter space, including the multiple steady state solutions observed for the same parameter values by Lopes et al.(2018), where the corresponding triple limit point bifurcation structure is recovered by the new low-order model. We also inspect states in which the interface becomes multivalued - and thus outside the reach of the reduced-order model - via DNS.This leads to highly nonlinear multivalued periodic structures appearing at moderate thicknesses and relatively large rotation rates. Even much thicker films may eventually reach steady states (following complex early evolution), provided these are maintained by a combination of forces sufficiently large to counteract gravity

Fabrication of lightweight Si/SiC LIDAR mirrors

A new, chemical vapor deposition (CVD) process was developed for fabricating lightweight, polycrystalline silicon/silicon-carbide (Si/SiC) mirrors. The process involves three CVD steps: (1) to produce the mirror faceplate; (2) to form the lightweight backstructure, which is deposited integral to the faceplate; and (3) to deposit a layer of optical-grade material, e.g., Si, onto the front surface of the faceplate. The mirror figure and finish are fabricated into the faceplate

Fluid structure in the immediate vicinity of an equilibrium three-phase contact line and assessment of disjoining pressure models using density functional theory

We examine the nanoscale behavior of an equilibrium three-phase contact line in the presence of long-ranged intermolecular forces by employing a statistical mechanics of fluids approach, namely density functional theory (DFT) together with fundamental measure theory (FMT). This enables us to evaluate the predictive quality of effective Hamiltonian models in the vicinity of the contact line. In particular, we compare the results for mean field effective Hamiltonians with disjoining pressures defined through (I) the adsorption isotherm for a planar liquid film, and (II) the normal force balance at the contact line. We find that the height profile obtained using (I) shows good agreement with the adsorption film thickness of the DFT-FMT equilibrium density profile in terms of maximal curvature and the behavior at large film heights. In contrast, we observe that while the height profile obtained by using (II) satisfies basic sum rules, it shows little agreement with the adsorption film thickness of the DFT results. The results are verified for contact angles of 20, 40 and 60 degrees

Soft Inkjet Circuits: Rapid Multi-Material Fabrication of Soft Circuits using a Commodity Inkjet Printer

Despite the increasing popularity of soft interactive devices, their fabrication remains complex and time consuming. We contribute a process for rapid do-it-yourself fabrication of soft circuits using a conventional desktop inkjet printer. It supports inkjet printing of circuits that are stretchable, ultrathin, high resolution, and integrated with a wide variety of materials used for prototyping. We introduce multi-ink functional printing on a desktop printer for realizing multi-material devices, including conductive and isolating inks. We further present DIY techniques to enhance compatibility between inks and substrates and the circuits' elasticity. This enables circuits on a wide set of materials including temporary tattoo paper, textiles, and thermoplastic. Four application cases demonstrate versatile uses for realizing stretchable devices, e-textiles, body-based and re-shapeable interfaces

Study of the Influence of Substrate Shape and Roughness on Coating Microstructure in Suspension Plasma Spray

Sprayed coatings produced with submicron particles have unique properties when compared to 10-100 micron particles. Suspension Plasma Spray (SPS) is used to deposit coatings from submicron particles. This process, which is a modification of the atmospheric plasma spray (APS) process, uses a liquid carrier to inject the fine particles into the plasma jet. However, this technique is still subject of extensive research efforts due to the complexity of the phenomena related to the liquid stream and the submicron particles in contact with the plasma jet. There is a wide range of parameters that affect the properties and microstructure of the coatings sprayed using SPS. In this study, the influence of the substrate shape on the resulting coating microstructure is investigated. For this purpose, an yttria-stabilized zirconia (YSZ) suspension was sprayed on flat and curved stainless steel substrates by SPS. The suspension was composed of 20 wt.% YSZ particles in ethanol. After spraying, the morphology of the coatings has been characterized by scanning electron microscopy (SEM). The results showed that the substrate shape influences the amount of coating material deposited and column growth. The amount of coating material deposited was seen to decrease as the radius of curvature decreased. Finally, roughness influences the formation of columnar structure

Particulate fouling of dry and liquid coated surfaces

Particulate fouling is the process of deposition of extraneous particulate matter on other surfaces. In particular, particulate fouling is a major cause of concern in energy-intensive heat recovery systems like biomass gasifiers, coal fired boiler and waste incinerators. The thermal energy is extracted from the flue gas using a system of heat exchangers. The flue gas is however contaminated with particulate matter, tar, nitrogen, sulphur and alkali compounds. The contaminants are transported by the flue gas and interact with the heat exchanger surface eventually forming a deposit layer. The deposit layers have very low thermal conductivity and leads to drastic loss in thermal efficiency apart from maintenance problems and capital losses. The focus of this research is to understand the process of particulate fouling from a fundamental view point based on particle surface interactions and the global effects associated with process conditions by experiments. A numerical model to capture the deposition and removal of particles over heat exchanger surfaces is aimed at. Particles which arrive at the heat exchanger surface and undergo inertial impaction can stick to the surface, rebound and might remove other previously deposited particles. In order to model the process, a sticking criterion is necessary. The interaction of a particle with other particles on the heat exchanger surface can be either in a dry state or in the presence of a thin liquid film due to condensation of alkali compounds. Detailed experiments were performed to evaluate the sticking criterion for particle impaction over a liquid coated surface under elastic and elastic-plastic deformation conditions. An empirical relation in terms of Stokes number was evaluated to determine the energy loss in the thin interstitial liquid film. A critical Stokes number range between 3 and 8 was observed below which particles do not rebound from the surface. In the Stokes number range of 8 to 20, the particles were observed to rebound but do not overcome the viscous effects of the liquid layer. A high-temperature closed-loop vertical wind tunnel was designed and constructed to perform fouling experiments under controlled conditions. The effect of gas velocity, particle concentration, particle size distribution, gas temperature, heat exchanger tube orientation and geometry was studied. A measurement technique that allowed the evaluation of temporal evolution of the fouling layer thickness was used. The experimental investigations revealed that the shear induced by the gas flowing around the tube has a major effect on the overall deposit growth dynamics. The geometry and orientation of the tube indicated that deposition and removal of particles is strongly coupled to the flow dynamics and particle surface interactions. A numerical model was implemented in a commercial software package to capture the deposition and removal of particles. The deposition model was based on particle-surface interactions including elastic-plastic deformations and the removal model was based on the rolling moment induced by the flow and on the energy transferred by other impacting particles. The fundamental impaction experiments along with the controlled experiments have provided better insight into the process of particulate fouling and resulted in the development of a numerical model which can be used to devise mitigation strategies for particulate fouling

Intracortical Neural Probes with Post-Implant Self-Deployed Electrodes for Improved Chronic Stability.

This thesis presents a new class of implantable intracortical neural probe with small recording electrodes that deploy away from a larger main shank after insertion. This concept is hypothesized to enhance the performance of the electrodes in chronic applications. Today, electrodes that can be implanted into the brain for months or years, are an irreplaceable tool for brain machine interfaces and neuroscience studies. However, these chronically implanted neural probes suffer from continuous loss of signal quality, limiting their utility. Histological studies found a sheath of scar tissue with decreased neural density forming around probe shanks as part of an ongoing chronic inflammation. This was hypothesized to contribute to the deterioration of recorded signals. The neural probes developed in this thesis are designed to deploy electrodes outside this sheath such that they interface with healthier neurons. To achieve this, an actuation mechanism based on starch-hydrogel coated microsprings was integrated into the shank of neural probes. Recording electrodes were positioned at the tip of micrometer fine and flexible needles that were attached to the springs. Before insertion, the hydrogel dehydrates, retracting the springs. After insertion, the gel rehydrates, releasing the springs, which then deploy the electrodes. The actuation mechanism functions in a one-time release fashion, triggered by contact with biological fluids at body temperature. The deployment of the electrodes occurred over the course of two hours and can be divided into three stages: For the first 20 s, the electrodes did not deploy. Within the first three minutes they deployed by roughly 100 µm (0.5 µm/s). Tor the following two hours they deployed an additional 20 µm (0.17 µm/min). The employed design supported six deploying electrodes, each at the end of a 5 µm wide and thick, and 100 µm long needle. These were attached to a shank with 290 µm width, 12 µm thickness and 3 mm length. The shanks could be inserted into the cortex of rats through an opening in the pia without breaking. The acquired waveforms indicate that some of the deployed electrodes were able to record neural action potentials.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113317/1/egertd_1.pd