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In this paper, we investigate small amplitude oscillations of a thin shape-morphing plate submerged in a quiescent, Newtonian, incompressible, viscous fluid in the vicinity of a solid wall. The plate undergoes prescribed, time-varying shape-morphing deformation in phase with the transverse oscillation, consisting of periodic curvature to an arc of a circle. As the presence of the solid wall in close proximity of the oscillating plate is known to significantly increase hydrodynamic damping on the structure due to squeeze film effects, shape-morphing is considered as a potential strategy to modulate and control hydrodynamic forces, as well as power dissipation. Via a rigorous formulation based on unsteady Stokes equations and the boundary element method, we show that the shape-morphing strategy is effective in reducing hydrodynamic forces on the structure as well as hydrodynamic power dissipation due to viscous effects. Additionally, such a reduction is enhanced as the gap between the oscillating plate and the solid wall is reduced. We present a comprehensive parametric study which investigates the effect of oscillation frequency, gap size, and imposed curvature on the hydrodynamic performance of the system and support our findings with asymptotics from inviscid flow theory and lubrication theory. These findings are of direct interest and applicability in several cantilever-based sensing and actuation systems, such as atomic force microscopy and microelectromechanical systems in liquids. [ABSTRACT FROM AUTHOR]

A novel contact resonance atomic force microscopy (CR-AFM) method utilizing a two-dimensional Kirchhoff-Love plate framework is presented. Theoretical formulations are discussed, and the classic CR-AFM problem is re-cast into an easily implementable generalized eigenvalue problem. An analysis is performed to determine the optimal placement of the sensing tip for plates of different aspect ratios. Finally, an experiment is conducted using the finite element method to numerically verify the proposed technique. By using a plate geometry for CR-AFM and optimizing the sensor tip location, we achieve a higher measurement sensitivity and modal density when compared with standard AFM cantilever geometries. A higher modal density allows CR-AFM measurement to be conducted using more information extracting eigenmodes in a given frequency bandwidth. [ABSTRACT FROM AUTHOR]

Nanostructured bimetallic reactive multilayers can be conveniently produced by ball milling of elemental powders. This research explores the non-equilibrium microscale conductive thermal transport in ball-milled particulate fractal structures during fabrication, arising from heat dissipation by bulk plastic deformation and surface friction. Upon impactor collisions, temperature increments are determined at interface joints and domain volumes using Green's functions, mirrored by source images with respect to warped ellipsoid domain boundaries. Heat source efficiency is calibrated via laboratory data to compensate for thermal expansion and impactor inelasticity, and the thermal analysis is coupled to a dynamic mechanics model of the particulate fracture. This thermomechanical model shows good agreement with the fractal dimensions of the observed microstructure from ball milling experiments. The model is intended to provide a comprehensive physical understanding of the fundamental process mechanism. In addition, the model could serve as a realtime thermal observer for closed-loop process control, as well as for interfacial diffusion and reaction analysis during ball milling. [ABSTRACT FROM AUTHOR]

This paper investigates and compares four commonly used flow transport equation-based cavitation models and their applicability to predict the cavitation performance of an industrial centrifugal pump with a helical inducer. The main purpose of this study is to identify, for this specific application, the most appropriate cavitation model and the associated empirical constants. Each cavitation model is reviewed in detail and the uniqueness of each model is outlined. Each cavitation model is incorporated in a computational fluid dynamics code to study the vaporization and condensation transport rate of the fluid. Experimental tests are conducted on a pump system to determine the true cavitation performance in terms of net positive suction head (NPSH). Experimental results are compared to simulation results for different cavitation models to validate cavitation performance predictions, along with the empirical constants. Lastly, bubble formation, cavitation inception, and bubble growth predicted by each cavitation model are compared with the experimental results. A sensitivity analysis is conducted in order to determine the impact of each set of empirical constants to the condensation and the vaporization rate in the centrifugal pump. Results show that two of the cavitation models exhibit high dependency on the empirical constants in terms of change in vaporization rate. Modifications to empirical constants for two of the four cavitation models are suggested to obtain agreement with the experimentally observed cavitation behavior and better predict NPSH performance for the industrial pump studied. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the inducer tip clearance is studied to understand its impact on the cavitating and noncavitating performance of centrifugal pumps. Helical inducers with constant pitch and with variable (progressive) pitch are considered. Computational fluid dynamics (CFD) simulations of a single stage pump are conducted on each inducer type to determine the cavitating (two-phase) and noncavitating (single-phase) performance for varying inducer tip clearance. The Rayleigh-Plesset cavitation model is used to understand the bubble dynamics under the assumptions of single fluid undergoing no thermal energy transfer between each phase. Experimental tests are conducted on a pump with the variable pitch inducer to determine the true performance in cavitating and noncavitating operating conditions. Experimental results are compared to the simulations to validate the accuracy of the proposed numerical modeling. Net positive suction head (NPSH) with 3% differential head drop is used as a criterion to identify the true cavitation performance of each inducer configuration. It is found that, as the inducer tip clearance increases, excessive back leakage and larger vortex recirculation occur at the tip location. This results in pressure loss within the inducer and, consequently, degrades the cavitation performance. In addition, the change in cavitation performance with the tip clearance is much more evident for variable pitch inducer geometries as compared to the constant pitch case. Furthermore, the impact on the noncavitating performance of inducer tip clearance is found to be minimal. [ABSTRACT FROM AUTHOR]

In this paper, we study torsional vibrations of cantilever beams undergoing moderately large oscillations within a quiescent viscous fluid. The structure is modeled as an Euler-Bernoulli beam, with thin rectangular cross section, under base excitation. The distributed hydrodynamic loading experienced by the vibrating structure is described through a complex-valued hydrodynamic function which incorporates added mass and fluid damping elicited by moderately large rotations. We conduct a parametric study on the two dimensional computational fluid dynamics of a pitching rigid lamina, representative of a generic beam cross section, to investigate the dependence of the hydrodynamic function on the governing flow parameters. As the frequency and amplitude of the oscillation increase, vortex shedding and convection phenomena increase, thus resulting into nonlinear hydrodynamic damping. We derive a handleable nonlinear correction to the classical hydrodynamic function developed for small amplitude torsional vibrations for use in a reduced order nonlinear modal model and we validate theoretical results against experimental findings. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the chemoelectrical behavior of ionic polymer metal composites (IPMCs) in the small voltage range with a novel hypothesis on the charge dynamics in proximity of the electrodes. In particular, we homogenize the microscopic properties of the interfacial region through a so-called composite layer which extends between the polymer membrane and the metal electrode. This layer accounts for the dissimilar properties of its constituents by describing the charge distribution via two species of charge carriers, that is, electrons and mobile counterions. We model the charge dynamics in the IPMC by adapting the multiphysics formulation based on the Poisson-Nernst-Planck (PNP) framework, which is enriched through an additional term to capture the electron transport in the composite layer. Under the hypothesis of small voltage input, we use the linearized PNP model to derive an equivalent IPMC circuit model with lumped elements. The equivalent model comprises a resistor connected in series with the parallel of a capacitor and a Warburg impedance element. These elements idealize the phenomena of charge build up in the double layer region and the faradaic impedance related to mass transfer, respectively. We validate the equivalent model through measurements on in-house fabricated samples addressing both IPMC step response and impedance, while assessing the influence of repeated plating cycles on the electrical properties of IPMCs. Experimental results are compared with theoretical findings to identify the equivalent circuit parameters. Findings from this study are compared with alternative impedance models proposed in the literature. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the effect of electrode surface roughness on ionic polymer metal composite (IPMC) capacitance. We use the linearized Poisson¿Nernst¿Planck model to describe the charge and electric potential distribution in response to a small voltage applied across the IPMC electrodes. We use perturbation methods to develop a comprehensive understanding of the interplay among the scale of the electrode roughness, the Debye screening length, and the IPMC nominal dimensions on the electrical behavior of IPMCs. We derive a closed-form expression of the IPMC capacitance per unit nominal surface area in terms of the Debye screening length, the IPMC nominal thickness, and physically relevant statistical properties of the rough landscape. We find that IPMC capacitance is largely dictated by the effective electrode surface area when the Debye screening length is considerably smaller than the polymer thickness. In this case, the diffuse charge layers that form at the polymer-electrode interface closely follow the rough electrodes profile. As the Debye screening length increases, diffuse layers do not completely adhere to the electrode profile, and local curvature changes and additional geometric factors contribute to the overall IPMC capacitance. We specialize our findings to different electrode models, including fractal electrodes that have been recently observed in IPMC morphological studies. We corroborate our theoretical findings with experimental data on the capacitance of in-house fabricated IPMCs. [ABSTRACT FROM AUTHOR]