Mechanical Engineering

The current work aims to develop a reliable theoretical model capable of simulating the depletion process of urea-water-solution (UWS) droplets injected in a hot exhaust stream as experienced in an automotive urea-based selective catalytic reduction system. A modified multicomponent vaporization model is presented and implemented in the current study to simulate the behavior of UWS droplet in heated environment. Although water depletion is modeled as a vaporization process, urea depletion is modeled using two different approaches: (i) vaporization and (ii) direct thermal decomposition. The suitability of both depletion approaches is assessed in the current study by comparison with experimental data of the decay of a single UWS droplet in a quiescent heated environment. The decay rate of UWS droplet is accurately predicted with the multicomponent vaporization model. The possibility of internal gasification is demonstrated. Based on the complex decomposition behavior of urea, the current study proposes a decomposition mechanism for UWS droplet. The suitability of implementing the rapid mixing approach is assessed through comparison with the diffusion limit approach at various operating conditions and initial UWS droplet sizes.

A comprehensive model based on finite volume method was developed to analyze the heat-up and the melting of ceramic particles injected into a microwave excited laminar air plasma flow field. Plasma flow field was simulated as a hot gas flow generated by volumetric heat addition in the microwave coupling region, resulting in a temperature of 6000 K. Alumina and zirconia particles of different diameters were injected into the axisymmetric laminar plasma flow at different injection velocities and locations. Additionally, noncontinuum effects, variation of transport properties of plasma surrounding the spherical particles and absorption of microwave radiation in the ceramic particles were considered in the model. Model predictions suggest that zirconia and alumina particles with diameters less than 50 µm can be effectively melted in a microwave plasma and can produce more uniform melt states. Microwave plasma environment with the ability to inject particles into the plasma core provide the opportunity to create more uniform melt states as compared with dc arc plasmas that are influenced by characteristic arc root fluctuations and turbulent dispersions.

A comprehensive computational model based on finite difference method was developed to study the heat and mass transport within solution precursor droplets injected into a laminar microwave air plasma flow field. Plasma flow field was simulated as hot gas flowing in a quartz tube generated by volumetric heat addition in the microwave coupling region. The resulting air plasma had a maximum temperature of 6000 K. Droplets containing zirconium acetate precursor of different diameters and solute concentrations were injected into the axisymmetric laminar plasma flow along the centerline of the plasma. Variation of transport properties of the plasma surrounding spherical droplets and absorption of microwave radiation within these droplets were considered in the model. Model predictions suggest that solution droplets are not affected by the microwave radiation in the presence of high convective heat flux from microwave plasma. Smaller droplets and high solute concentrations result in formation of thicker precipitate shells around them based on the homogeneous precipitation hypothesis. Mass transport is found to be slower than heat transfer in the droplets. Microwave plasma allowing the possibility of injecting droplets axially into the high temperature plasma environment present the opportunity to produce more consistent precipitate states as compared to DC arc plasmas into which droplets are typically injected transversely in thermal spray applications.

A comprehensive computational model based on finite difference method was developed to study the heat and mass transport within solution precursor droplets injected into a laminar microwave air plasma flow field. Plasma flow field was simulated as hot gas flowing in a quartz tube generated by volumetric heat addition in the microwave coupling region. The resulting air plasma had a maximum temperature of 6000 K. Droplets containing zirconium acetate precursor of different diameters and solute concentrations were injected into the axisymmetric laminar plasma flow along the centerline of the plasma. Variation of transport properties of the plasma surrounding spherical droplets and absorption of microwave radiation within these droplets were considered in the model. Model predictions suggest that solution droplets are not affected by the microwave radiation in the presence of high convective heat flux from microwave plasma. Smaller droplets and high solute concentrations result in formation of thicker precipitate shells around them based on the homogeneous precipitation hypothesis. Mass transport is found to be slower than heat transfer in the droplets. Microwave plasma allowing the possibility of injecting droplets axially into the high temperature plasma environment present the opportunity to produce more consistent precipitate states as compared to DC arc plasmas into which droplets are typically injected transversely in thermal spray applications.

To get better understanding of vortex shedding mechanism, we conducted numerical simulation on NACA 4418 hydrofoil at an angle of attack of 12° for 2D incompressible flow. The numerical method consists of transient, finite volume method using Transient SST turbulent model to capture the turbulent wake flows. At high Reynolds number the occurrence of 2D structures of shed vortices and the modulation of vortex-induced frequency are investigated. The lift, pressure and skin friction coefficients of hydrofoil were studied.

Flash boiling is known to be a common phenomenon for Gasoline Direct Injection (GDI) engine sprays. Homogeneous Relaxation Model has been adopted in many recent numerical studies for predicting cavitation and flash boiling. Assessment of the Homogeneous Relaxation Model has been presented in this study. Sensitivity analysis of the model parameters has been documented to infer the driving factors for the flash boiling predictions. The model parameters have been varied over a range and the differences in predictions for the extent of flashing have been studied. Apart from flashing in the near-nozzle regions, mild cavitation is also predicted inside the gasoline injectors. The variation in the predicted time-scales through the model parameters for predicting these two different thermodynamic phenomena (cavitation, flash) have been elaborated in this study. ∗Corresponding Author: ksaha@anl.gov

Cavitation-induced erosion is the result of repeated impacts from cavitation collapse events on a solid surface. To improve representation of the incubation period before material rupture within multiphase flow simulations, a new physics-based metric was derived based on cumulative energy absorbed by the solid material from repeated hydrodynamic impacts. Previous work by the authors validated the modeling framework through comparison of critical erosion sites and relative erosion severity with available experimental data. In this study, the predictive capabilities of the cavitation erosion metric are extended by relating the predicted stored energy with the solid material properties to estimate the incubation period. To extend the rigor of validation of the erosion predictions, the turbulent multiphase flow development was simulated over a range of Reynolds (Re = 1.5-2.0·10) and cavitation number (K = 1.60-1.78) conditions in an aluminum channel geometry featuring a sharp inlet corn...

In this paper we introduce a new control strategy for linear time invariant (LTI) systems with a single time delay. The delay appears within the feedback control logic. Earlier research on this class of systems determines the delay intervals for stable operations, exhaustively, exactly and completely. The newly developed inverting control logic suggests a very practical procedure of reversing the sign of the feedback control gain, in order to enlarge the stable delay intervals. This gives some additional capabilities to control system designer. The sign inversion idea is based on a critical mathematical feature of LTI-TDS (Time Delay Systems) which was first recognized under a paradigm called the Cluster Treatment of Characteristic Roots (CTCR). Several example case studies demonstrate the practicality and the advantages of the new control law.

A new perspective is presented for studying the stability robustness of nth order systems with p rationally independent delays. It deploys a holographic mapping procedure over the delay space into a new coordinate system in order to achieve the objective. This mapping collapses the entire set of potential stability switching points on a manageably small number of hypersurfaces, which are explicitly defined in the new domain. This property considerably alleviates the problem, which is otherwise infinite dimensional, and therefore notoriously complex to handle. We further declare some unrecognized features of these switching hypersurfaces, that they are (a) encapsulated within a higher-dimensional cube with edges of length 2 , which we name the 'building block', and (b) the 'offspring' of this building block, which represent the secondary stability switchings, appear within the adjacent and identical building blocks (cubes) stacked up next to each other. The final outlook is an exclusive representation of stability for this general class of systems at any arbitrary point in the delay space. Two example case studies are also provided, which are not possible to analyze using any other methodology known to the authors. . Cross-sectional views of for different 3 values.

In repetitive control, the enhanced servo performance at the fundamental frequency and its higherorder harmonics is usually followed by undesired error amplifications at other frequencies. In this paper, we discuss a new structural configuration of the internal model in repetitive control, wherein designers have more flexibility in the repetitive loop-shaping design, and the amplification of non-repetitive errors can be largely reduced. Compared to conventional repetitive control, the proposed scheme is especially advantageous when the repetitive task is subject to large amounts of non-periodic disturbances.

This paper presents an adaptive control scheme for identifying and rejecting unknown and/or time-varying narrow-band vibrations. We discuss an idea of safely and adaptively inverting a (possibly non-minimum phase) plant dynamics at selected frequency regions, so that structured disturbances (especially vibrations) can be estimated and canceled from the control perspective. By taking advantage of the disturbance model in the design of special infiniteimpulse-response (IIR) filters, we can reduce the adaptation to identify the minimum amount of parameters, achieve accurate parameter estimation under noisy environments, and flexibly reject the narrow-band disturbances with clear tuning intuitions. Evaluation of the algorithm is performed via simulation and experiments on an active-suspension benchmark.

The disturbance observer (DOB) has been a popular robust control approach for servo enhancement in single-input single-output systems. This paper presents a new extension of the DOB idea to dual-and multi-input single-output systems, and discusses an optimal filter design technique for the related loop shaping. The proposed decoupled disturbance observer (DDOB) provides the flexibility to use the most suitable actuators for compensating disturbances with different spectral characteristics. Such a generalization is helpful, e.g., for modern dual-stage hard disk drives, where enhanced servo design is becoming more and more essential in the presence of vibration disturbances. keywords: MISO systems, dual-stage hard disk drives, disturbance observer, audio vibration, optimal filter design Nomenclature DDOB decoupled disturbance observer G yd transfer function from d to y S(z −1 ) sensitivity function (output disturbance-rejection function)

A controller design is presented for directly shaping the sensitivity function in feedback control of dualinput single-output (DISO) systems. We provide special forms of discrete-time Youla-Kucera (YK) parameterization to obtain stabilizing controllers for DISO systems, and discuss concepts to achieve a reduced-complexity formulation. The proposed YK parameterization is based on an inverse of the loop transfer function, which gives benefits such as clearer design intuition and reduced complexity in construction. The algorithm is verified by simulations and experiments on hard disk drive systems, with application to wide-band vibration and harmonic disturbance rejections.

Many servo systems are subjected to narrowband disturbances that generate vibrations at multiple frequencies. One example is the track-following control in a hard disk drive (HDD) system, where the airflow-excited disk and actuator vibrations introduce strong and uncertain spectral peaks to the position error signal. Such narrowband vibrations differ in each product and can appear at frequencies above the bandwidth of the control system. This paper presents a control scheme that adaptively enhances the servo performance at multiple unknown frequencies, while maintaining the baseline servo loop shape. A minimum parameter model of the disturbance is first introduced, followed by the construction of a novel adaptive multiple narrow-band disturbance observer for selective disturbance cancellation. Evaluation of the proposed algorithm is performed on a simulated HDD benchmark problem.

Vibrations with unknown and/or time-varying frequencies significantly affect the achievable performance of control systems, particularly in precision engineering and manufacturing applications. This paper provides an overview of disturbance-observer based adaptive vibration rejection schemes; studies several new results in algorithm design; and discusses new applications in semiconductor manufacturing. We show the construction of inverse-model-based controller parameterization, and discuss its benefits in decoupled design, algorithm tuning, and parameter adaptation. Also studied are the formulation of recursive least squares and output-error based adaptation algorithms, as well as their corresponding scopes of applications. Experiments on a wafer scanner testbed in semiconductor manufacturing prove the effectiveness of the algorithm in high-precision motion control. 2 extensively studied in the multi-band situation . Many control design algorithms have been studied in the related literature. Adaptive noise cancellation [8] uses sensors and stochasticgradient-based adaptation to cancel the disturbance effect. Adaptive feedforward cancellation composes an estimate of the sinusoidal disturbance using trigonometric functions. In feedback control, it has been understood that for asymptotic disturbance rejection, controllers should be customized to incorporate the model of the disturbance. This internal-modelprinciple approach has been essential for the achieved results in . In the scope of direct adaptive controls, used state-space designs; applied Youla Parameterization with adaptive finite-impulse-response (FIR) filters. Alternatively, indirect adaptive control can be formulated after online identification of the disturbance frequencies. Among the related literature on frequency identification, MUSIC and ESPRIT are two of the most commonly used subspace spectrum estimation methods. Both algorithms are batch processes that require an entire sequence (of sufficient length) of data to find the spectral peaks of the signals. Compared to Fast Fourier Transform (FFT), MUSIC and ESPRIT require less data points to generate accurate identification in noisy environments. For adaptive control, more common than the batch process are the adaptive notch filters and phase lock loops, where improved frequency identification is provided at each time step; and in addition, it is possible to track the change of the disturbance characteristics online. Algorithms of this kind include , among which are statespace constructions suitable for different computation complexities; [22] is a phase locked loop method that is commonly combined with adaptive feedforward cancellation; [17] is a popular adaptive notch filter based on recursive prediction error methods.

A loop-shaping idea for dual-input-singleoutput (DISO) systems is presented in this paper. We explore special forms of Youla parameterization for obtaining stabilizing controllers for DISO systems, and discuss concepts to achieve reduced-complexity formulations with clearer design intuitions. The algorithm is verified by a benchmark control problem of dual-stage hard disk drive systems, using real-system models and actual vibration data.

The disturbance observer (DOB) has been one effective robust control approach for servo enhancement in singleinput-single-output systems. This paper presents a new extension of the DOB idea to dual-input-single-output systems, and discusses an optimal Q-filter design. The proposed decoupled disturbance observer (DDOB) provides a flexible approach to use the most suitable actuators for compensating disturbances at different frequencies. Such a scheme is helpful, e.g., for modern dual-stage hard disk drives, where enhanced servo design is becoming more and more essential in the presence of audio vibrations.

In repetitive control, the enhanced servo performance at multiple repetitive frequencies is usually followed by undesired error amplifications at other frequencies. This paper presents a new structural configuration of the internal model principle in repetitive control, wherein designers have more flexibility in the repetitive loopshaping design, and amplification of non-repetitive errors can be greatly reduced. The proposed algorithm is particularly advantageous when repetitive control is required in environments where large amounts of non-repetitive disturbances exist. Verification of the algorithm is provided in a benchmark regulation problem of hard disk drives.