Ilyas, Saad; Alfosail, Feras; Younis, Mohammad I.(Journal of Computational and Nonlinear Dynamics, ASME International, 2019-02-15)[Article]
We investigate modeling the dynamics of an electrostatically actuated resonator using the perturbation method of multiple time scales (MTS). First, we discuss two approaches to treat the nonlinear parallel-plate electrostatic force in the equation of motion and their impact on the application of MTS: expanding the force in Taylor series and multiplying both sides of the equation with the denominator of the forcing term. Considering a spring-mass-damper system excited electrostatically near primary resonance, it is concluded that, with consistent truncation of higher-order terms, both techniques yield same modulation equations. Then, we consider the problem of an electrostatically actuated resonator under simultaneous superharmonic and primary resonance excitation and derive a comprehensive analytical solution using MTS. The results of the analytical solution are compared against the numerical results obtained by long-time integration of the equation of motion. It is demonstrated that along with the direct excitation components at the excitation frequency and twice of that, higher-order parametric terms should also be included. Finally, the contributions of primary and superharmonic resonance toward the overall response of the resonator are examined.
Aznar, Miguel Sierra; Chorou, Farouk; Chen, Jyh Yuan; Dreizler, Andreas; Dibble, Robert W.(Volume 1: Large Bore Engines; Fuels; Advanced Combustion, ASME International, 2019-01-03)[Conference Paper]
Carbon capture has been deemed crucial by the Intergovernmental Panel on Climate Change if the world is to achieve the ambitious goals stated in the Paris agreement. A deeper integration of renewable energy sources is also needed if we are to mitigate the large amount of greenhouse gas emitted as a result of increasing world fossil fuel energy consumption. These new power technologies bring an increased need for distributed fast dispatch power and energy storage that counteract their intermittent nature. A novel technological approach to provide fast dispatch emission free power is the use of the Argon Power Cycle, a technology that makes carbon capture an integral part of its functioning principle. The core concept behind this technology is a closed loop internal combustion engine cycle working with a monoatomic gas in concert with a membrane gas separation unit. By replacing the working fluid of internal combustion engines with a synthetic mixture of monoatomic gases and oxygen, the theoretical thermal efficiency can be increased up to 80%, more than 20% over conventional air cycles. Furthermore, the absence of nitrogen in the system prevents formation of nitrogen oxides, eliminating the need for expensive exhaust gas after-treatment and allowing for efficient use of renewable generated hydrogen fuel. In the case of hydrocarbon fuels, the closed loop nature of the cycle affords to boost the pressure and concentration of gases in the exhaust stream at no penalty to the cycle, providing the driving force to cost effective gas membrane separation of carbon dioxide. In this work we investigated the potential benefits of the Argon Power Cycle to improve upon current stationary power generation systems regarding efficiency, air pollutants and greenhouse gas emissions. A cooperative fuel research engine was used to carry out experiments and evaluate engine performance in relation to its air breathing counterpart. A 30% efficiency improvement was achieved and results showed a reduction on engine heat losses and an overall increase on the indicated mean effective pressure, despite the lesser oxygen content present in the working fluid. Greenhouse gas emissions were reduced as expected due to a substantial increase in efficiency and nitric oxides were eliminated as it was expected. Numerical simulation were carried out to predict the performance and energy penalty of a membrane separation unit. Energy penalties as low as 2% were obtained capturing 100% of the carbon dioxide generated.
Hajjaj, Amal; Alfosail, Feras; Younis, Mohammad I.(Volume 6: 14th International Conference on Multibody Systems, Nonlinear Dynamics, and Control, ASME International, 2018-11-02)[Conference Paper]
In this paper, we investigate experimentally and theoretically the two-to-one (2:1) internal resonance between the first two symmetric vibrational modes of microelectromechanical (MEMS) arch resonator electrothermally tuned and electrostatically driven. Applying electrothermal voltage across the beam anchors controls its stiffness and then its resonance frequencies. Hence the ratio between the two frequencies can be tuned to a ratio of two. Then, we study the dynamic response of the arch beam during internal resonance. In the studied case, the presence of high AC bias excitation leads to the direct simultaneous excitation of the 1st and 3rd frequencies in addition to the activation of the internal resonance. A reduced order model and perturbation techniques are presented to analyze the nonlinear response of the structure. In the perturbation technique, the direct excitation of the 3rd resonance frequency is taken into consideration. Results show the presence of Hopf bifurcations, which can lead to chaotic motion at higher excitation. A good agreement among the theoretical and experimental results is shown.
Hasan, Mohammad H.; Ouakad, Hassen M.; Jaber, Nizar; Hafiz, Md Abdullah Al; Alsaleem, Fadi; Younis, Mohammad I.(Volume 4: 23rd Design for Manufacturing and the Life Cycle Conference; 12th International Conference on Micro- and Nanosystems, ASME International, 2018-11-02)[Conference Paper]
Electrostatic micro-electro-mechanical-system (MEMS) devices show great potential in a variety of applications such as sensing and actuation; however, they are hindered by their high input voltage requirement. Double resonance excitation, which activates the system’s mechanical and electrical resonances simultaneously, was recently demonstrated experimentally to alleviate this problem. In this work, we present a mathematical model, based on the Euler Bernoulli beam model coupled with a circuit model, to simulate double resonance in MEMS devices and to shed light more onto the previously published experimental data. We show good agreement between the theoretical simulation and experimental data when the electrical resonance frequency band is sufficiently high.
Alcheikh, Nouha; Tella, Sherif Adekunle; Younis, Mohammad I.(Volume 4: 23rd Design for Manufacturing and the Life Cycle Conference; 12th International Conference on Micro- and Nanosystems, ASME International, 2018-11-02)[Conference Paper]
Complex logic functions based on micro electromechanical resonators has recently attracted significant attention. Realization of complex logic functions through cascading micro resonators has been deterred by challenges involved in their interconnections and the large required array of resonators. This paper presents a micro electromechanical system MEMS resonator with multiple input (actuation) and output (detection) that enables the realization of complex logic operations. The devices are based on a compound resonator consisting of an in-plane clamped-guided arch beam that is mechanically coupled from its guided side to two flexure beams and to another T-shaped resonant beam. As examples, we experimentally demonstrate using the device to realize a half adder and a 1:2 DEMUX, based on electrothermal and electrostatic tuning of the arch beam and side resonant beam. The logic operation is based on the linear frequency modulation. This paper demonstrates that with such compound MEMS resonators, it is possible to build more complex logic functionalities.
Chong, Shao Teng; Raman, Venkat; Mueller, Michael E.; Im, Hong G.(Volume 4B: Combustion, Fuels, and Emissions, ASME International, 2018-08-30)[Conference Paper]
Recirculation zone plays an important role in flame stabilization in combustors and gas turbines. The location, size, and strength of recirculation zones are important features of a combustor. However, the quantitative role of recirculation zones in affecting soot formation from an aero combustor is not fully understood. In a turbulent flow field with swirling flows and high frequency oscillations of the inflow jets, inner recirculation zones and outer recirculation zones have different functions in determining soot evolution. In this study, large-eddy simulation (LES) of soot formation with detailed physical and chemical models is used in order to study the dynamic aspects of soot formation. The soot population is modeled using the hybrid method of moments (HMOM), while the gas phase precursor evolution is modeled using detailed chemical kinetics. A model aero combustor, studied experimentally at DLR, is used as the baseline flow configuration. The simulations are used to understand the transport of soot particles within such complex flows. In particular, the ability of recirculation regions to increase soot formation by increasing residence times is explored. A Lagrangian particle tracking (LPT) analysis is carried out and statistical roles of recirculation zones are determined from these streamlines. Furthermore, source term analysis of these particles are performed to determine the key physical processes that contribute to soot mass in the recirculation zones. From a numerical stand-point, such soot evolution introduces limitations for statistical convergence, which will also be discussed. In particular, a time-scale analysis will be conducted to determine total computational time needed to obtain converged soot statistics.
Bakhsh, Abeer; Samtaney, Ravindra(Journal of Fluids Engineering, ASME International, 2017-12-20)[Article]
We investigate the linear stability of both positive and negative Atwood ratio interfaces accelerated either by a fast magnetosonic or hydrodynamic shock in cylindrical geometry. For the magnetohydrodynamic (MHD) case, we examine the role of an initial seed azimuthal magnetic field on the growth rate of the perturbation. In the absence of a magnetic field, the Richtmyer-Meshkov growth is followed by an exponentially increasing growth associated with the Rayleigh-Taylor instability. In the MHD case, the growth rate of the instability reduces in proportion to the strength of the applied magnetic field. The suppression mechanism is associated with the interference of two waves running parallel and anti-parallel to the interface that transport of vorticity and cause the growth rate to oscillate in time with nearly a zero mean value.
Tella, Sherif Adekunle; Alcheikh, Nouha; Younis, Mohammad I.(Volume 4: 22nd Design for Manufacturing and the Life Cycle Conference; 11th International Conference on Micro- and Nanosystems, ASME International, 2017-11-03)[Conference Paper]
We present axially loaded clamped-guided microbeams that can be used as resonators and actuators of variable stiffness, actuation, and anchor conditions. The applied axial load is implemented by U-shaped electrothermal actuators stacked at one of the beams edges. These can be configured and wired in various ways, which serve as mechanical stiffness elements that control the operating resonance frequency of the structures and their static displacement. The experimental results have shown considerable increase in the resonance frequency and mid-point deflection of the microbeam upon changing the end conditions of the beam. These results can be promising for applications requiring large deflection and high frequency tunability, such as filters, memory devices, and switches. The experimental results are compared to multi-physics finite-element simulations showing good agreement among them.
Ilyas, Saad; Jaber, Nizar; Younis, Mohammad I.(Volume 4: 22nd Design for Manufacturing and the Life Cycle Conference; 11th International Conference on Micro- and Nanosystems, ASME International, 2017-11-03)[Conference Paper]
We present a mechanically coupled MEMS H resonator capable of performing simultaneous amplification and filter operation in air. The device comprises of two doubly clamped polyimide microbeams joined through the middle by a coupling beam of the same size. The resonator is fabricated via a multilayer surface micromachining process. A special fabrication process and device design is employed to enable the device's operation in air and to achieve mechanical amplification of the output response. Moreover, mixed-frequency excitation is used to demonstrate a tunable wide band filter. The device design combined with the mixed-frequency excitation is used to demonstrate simultaneous amplification and filtering in air.
Jaber, Nizar; Ilyas, Saad; Shekhah, Osama; Eddaoudi, Mohamed; Younis, Mohammad I.(Volume 4: 22nd Design for Manufacturing and the Life Cycle Conference; 11th International Conference on Micro- and Nanosystems, ASME International, 2017-11-03)[Conference Paper]
We report a resonant gas sensor, uniformly coated with a metal-organic framework (MOF), and excited it near the higher order modes for a higher attained sensitivity. Also, switching upon exceeding a threshold value is demonstrated by operating the resonator near the bifurcation point and the dynamic pull-in instabilities. The resonator is based on an electrostatically excited clamped-clamped microbeam. The microbeam is fabricated from a polyimide layer coated from the top with Cr/Au and from the bottom with Cr/Au/Cr layer. The geometry of the resonator is optimized to reduce the effect of squeeze film damping, thereby allowing operation under atmospheric pressure. The electrostatic electrode is designed to enhance the excitation of the second mode of vibration with the minimum power required. Significant frequency shift (kHz) is demonstrated for the first time upon water vapor, acetone, and ethanol exposure due to the MOF functionalization and the higher order modes excitation. Also, the adsorption dynamics and MOF selectivity is investigated by studying the decaying time constants of the response upon gas exposure.
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