Mechanical Engineering

This paper investigates the sensitivity of critical parameters in AFM-based nanomanipulation, including the nanoparticle pushing force and time versus changing all parameters of the nanomanipulation process. The presented model includes both adhesional and normal friction forces. Also, pull-off forces are modeled by using the Johnson-Kendall-Roberts (JKR) contact mechanics model. Dynamic equations are developed based on the free body diagram of the pushing system, including AFM cantilever and probe, nanoparticle, and substrate. Dynamic simulation of gold particle manipulation on a silicon substrate is performed. In this model, the nanoparticle can be traced at every moment and at the same time all the dynamics and deformations of nanoparticle can be achieved from numerical simulation. Depending on obtained diagrams for parameters sensitivity, the suggested behavior will be followed by the particle such as rolling, sliding, stick-slip, and rotation. Its novelty is that the sensitivity of critical force and critical time for particle pushing on the substrate are obtained for all parameters. This is important for designing and choosing of geometry and materials of AFM, nanoparticle, and substrate. Also this is effective on choosing of proper initial condition in pushing purposes. Finally, it can be used to adjust proper pushing time and force for an accurate and successful pushing and assembly, and real-time visualization during micro/nanomanipulation using real-time force data.

Decellularized adipose tissue (DAT) has shown great potential for use as a regenerative scaffold in breast reconstruction following mastectomies or lumpectomies. Mechanical properties of such scaffolds are of great importance in order to mimic natural adipose tissue.

This paper proposes a non-cascade -single loop- Direct Speed Control algorithm for surface mounted Permanent Magnet Synchronous Motor (PMSM) fed by Matrix Converter. The proposed method uses Finite Control Set Model Predictive Control (FCS-MPC) to manipulate system speed and currents simultaneously. Also, for better performance of the predictive method, an observer designed to estimate mechanical torque and other uncertain parameters of the mechanical subsystem as a lumped disturbance. Simulation results using Matlab/Simulink demonstrate the performance of proposed algorithm.

Even though some wind turbine manufacturers are no longer active, and are not willing to disclose their intellectual property, their turbines are still in operation. Since the exact values of wind turbine parameters like the aerodynamic model, drive-train model and generator parameters are not always accessible, the design of a controller which does not require prior knowledge of the system parameters can be very useful and effective. As a result, this paper proposes a disturbance observer-based controller to harvest the maximum power from a wind turbine system with fully unknown parameters. To reduce control efforts, a disturbance observer is designed to estimate unknown nonlinear terms caused by unknown model parameters in the presence of unknown control coefficient that uses only the tracking error to estimate nonlinear disturbance. Compared with previously published works, in this paper, both aerodynamic model and drive-train model parameters are assumed to be fully unknown. Clo...

Nanomechanical cantilever sensors (NMCSs) have recently emerged as an effective means for label-free chemical and biological species detection. They operate through the adsorption of species on the functionalized surface of mechanical cantilevers. Through this functionalization, molecular recognition is directly transduced into a micromechanical response. In order to effectively utilize these sensors in practice and correctly relate the micromechanical response to the associated adsorbed species, the chief technical issues related to modeling must be resolved. Along these lines, this paper presents a general nonlinear-comprehensive modeling framework for piezoelectrically actuated microcantilevers and validates it experimentally. The proposed model considers both longitudinal and flexural vibrations and their coupling in addition to the ever-present geometric and material nonlinearities. Utilizing Euler-Bernoulli beam theory and employing the inextensibility conditions, the coupled longitudinal-flexural equations of motion are reduced to one nonlinear partial differential equation describing the flexural vibrations of the sensor. Using a Galerkian expansion, the resulting equation is discretized into a set of nonlinear ordinary differential equations. The method of multiple scales is then implemented to analytically construct the nonlinear response of the sensor near the first modal frequency (primary resonance of the first vibration mode). These solutions are compared to experimental results demonstrating that the sensor exhibits a softeningtype nonlinear response. Such behavior can be attributed to the presence of quadratic material nonlinearities in the piezoelectric layer. This observation is critical, as it suggests that unlike macrocantilevers where the geometric hardening nonlinearities dominate the response behavior, material nonlinearities dominate the response of microcantilevers yielding a softening-type response. This behavior should be accounted for when designing and employing such sensors for practical applications.

Vibrating beam gyroscopes are fast becoming the most widely used gyroscopes in many commercial applications. This paper deals with a vibrating beam gyroscope consisting of a cantilever beam with rigid mass attached to its end and undergoing coupled flexural-torsional vibrations. The gyroscope can be used to measure the angular velocity of the rotating base of the beam. The primary (flexural) vibrations are produced in the beam using a piezoelectric patch (bender type) actuator. Due to the base rotation, a gyroscopic effect is generated which induces secondary (torsional) vibrations in the beam. First, a detailed mathematical modeling of the system is developed using extended Hamilton's Principle. The system governing equations are solved and simulated using assumed mode model expansion to analyze the gyroscopic coupling produced due to the base rotations. Finally, the effects of secondary base rotation (cross-axis effects) on the performance of the gyroscope are presented. Also, it is shown that the gyroscopic effect increases with increase in base rotation rate, primary excitation amplitude and length of the beam. It is further proven that the secondary base rotations (cross-axis effects) have an adverse effect on the gyroscope performance. Such detailed analysis on the effects of secondary rotation can be utilized to devise elimination strategies in order to improve gyroscopic performance. r

The nonlinear vibration analysis of a directly excited cantilever beam modeled as an inextensible viscoelastic Euler-Bernoulli beam has been studied by the authors and is reported in the literature. The viscoelastic damping was modeled as Kelvin-Voigt damping, and the nonlinearities arisen from the inextensibility assumption. This paper extends our theoretical developments presented in the previous papers and utilizes the method of multiple scales in order to arrive at the modulation equations and the closed-form frequency response function. The analytically derived frequency response is experimentally verified through harmonic force excitation of samples of carbon nanotube-reinforced beams. The beam used in experiment consists of two elastic layers of high-carbon steel sandwiched together through a viscoelastic layer of carbon nanotube-epoxy mixture. The results demonstrate that increasing the excitation amplitude or decreasing damping ratio can cause a minor decrease in the nonlinear resonance frequency despite the significant increase in the amplitude of vibration due to reduced damping. r

Microcantilevers are one the most commonly utilized microelectromechanical systems in a variant of the ultra-precise scanning and characterization application. Of particular interest, the problem of vibrations of microcantilevers has recently received considerable attention due to its application in several nanotechnological instruments such as atomic force microscopy, nanomechanical cantilever sensors and friction force microscopy. For applications such as these, the problem of coupled flexural-torsional nonlinear vibrations of a piezoelectrically-actuated microcantilever beam is considered in this dissertation. The actuation and sensing are both facilitated through bonding a piezoelectric layer (here, ZnO) vii

Atomic Force Microscopy (AFM) uses a scanning process performed by a microcantilever probe to create a three dimensional image of a nano-scale physical surface. The dynamics of the AFM microcantilever motion and tip-sample force is needed to generate accurate images. In this paper, the non-linear dynamics of a piezoelectric microcantilever probe in tapping AFM will be investigated. The equations of motion are derived for a non-linear contact force, the analytical expressions for natural frequencies and mode shapes are obtained, and the method of multiple scales is used to find the analytical frequency response of the microcantilever. Results show that the non-linear excitation force creates a shift in the frequency response curve during contact mode. This frequency shift is an important consideration in the modeling of AFM dynamics for generation of accurate images as well as for accurate readings when using the AFM microcantilever for other applications. The frequency shift also leads to a bistable region, in which a high and a low amplitude solution coexist. The response of the microcantilever at a single input frequency and voltage are analyzed for both high and low amplitude solutions with the main difference being that the high amplitude solution makes contact with the sample while the low amplitude solution does not. This contact results in higher harmonics of the microcantilever being excited. The response in the bistable region is compared to the response in the monostable region. Additionally, a convergence analysis is used to determine the number of modes necessary to describe the motion of the microcantilever in tapping mode. It is determined that one mode is insufficient, two modes are sufficient for most applications, and five modes is the most that would be necessary for applications that require very precise readings.

In this paper, a new method is proposed for improving a piezoelectric energy harvester’s output power. A piezoelectric vibration energy harvester has an inherent internal capacitance. The new approach adopts inductance to reduce the reactance of the internal capacitance and enhance the output power. To show the practicality of this method, four electrical circuits are investigated numerically and experimentally for a piezoelectric beam energy harvester: Simple Resistive Load, Inductive Load, standard AC-DC, and Inductive AC-DC circuits. An Inductive Load circuit is built by adding an inductor to a Simple Resistive Load circuit, while an Inductive AC-DC circuit is built by adding an inductor to a standard AC-DC circuit. Experimental results indicate that the Inductive Load and the Inductive AC-DC circuits avail the Simple Resistive Load and standard AC-DC circuits respectively. The inductive AC-DC circuit shows a 6.7% increase in the output power compared to the standard AC-DC circuit.

Integral Consensus Control (ICC) is proposed and implemented in this paper for the first time, as a novel approach for vibration control in distributed parameter flexible structures. The ICC consists of multiple parallel first-order lossy integrators, with the goal of targeting all major participating resonant modes in the oscillation of the structure. The vibration control design is taken to a different level, by integrating the concept of consensus control design into the new dynamics. Each control patch on the flexible structure is considered as a node of a network, and a communication topology with consensus control terms are augmented in the controller design dynamics. The result is an effective vibration controller, which is also robust to failures and inconsistencies in the control system. A cantilever is used as a sample flexible structure to investigate the control method. Multiagent representation of the system, state estimator dynamics and the ICC model are designed for the structure. Extensive numerical simulations have been conducted to show the suppression performance of the ICC under different input disturbances. A comparative study is presented to show the advantage of the decentralized design over the conventional centralized approach. The new consensus control design provides new possibilities to vibration control problems, where an effective, robust and synchronized suppression is needed.

A new nonlinear integral resonant controller (NIRC) is introduced in this paper to suppress vibration in nonlinear oscillatory smart structures. The NIRC consists of a first-order resonant integrator that provides additional damping in a closed-loop system response to reduce highamplitude nonlinear vibration around the fundamental resonance frequency. The method of multiple scales is used to obtain an approximate solution for the closed-loop system. Then closed-loop system stability is investigated using the resulting modulation equation. Finally, the effects of different control system parameters are illustrated and an approximate solution response is verified via numerical simulation results. The advantages and disadvantages of the proposed controller are presented and extensively discussed in the results. The controlled system via the NIRC shows no high-amplitude peaks in the neighboring frequencies of the resonant mode, unlike conventional second-order compensation methods. This makes the NIRC controlled system robust to excitation frequency variations.

version of an article including any changes made following the peer review process but excluding any editing, typesetting or other changes made by IOP Publishing and/or its licensors. During the embargo period (the 12 month period from publication of the Version of Record of this article), the Accepted Manuscript: • is fully protected by copyright and can only be accessed by subscribers to the journal; • cannot be reused or reposted elsewhere by anyone unless an exception to this policy has been agreed in writing with IOP Publishing As the Version of Record of this article is going to be/has been published on a subscription basis, this Accepted Manuscript will be available for reuse under a CC BY-NC-ND 3.0 licence after a 12 month embargo period. After the embargo period, everyone is permitted to copy and redistribute this article for Non-Commercial purposes only, provided they*: • give appropriate credit and provide the appropriate copyright notice; • show that this article is published under a CC BY-NC-ND 3.0 licence; • provide a link to the CC BY-NC-ND 3.0 licence; • provide a link to the Version of Record; • do not use this article for commercial advantage or monetary compensation; and • only use this article in its entirety and do not make derivatives from it. *Please see CC BY-NC-ND 3.0 licence for full terms.