Title: Clarkson Distinguished Professor / Robert H. Hill

Title: Aerosols Transport, Dispersion and Deposition- Applications to Industrial, Environmental and Biological Flows including Transmission of COVID-19

Department of Mechanical and Aeronautical Engineering

Email: gahmadi@clarkson.edu

Phone: 315-268-2322

Abstract: Applications of particle transport, deposition, and removal in Industrial, environmental and biological flows are presented. The mechanics of particulate transport and deposition in turbulent flows are discussed. Numerical simulations of airflow with the use of the Reynolds averaged Navier-Stokes (RANS) equation, as well as DNS and LES, are described. The stochastic models for simulation of instantaneous fluctuation velocity are also discussed. The Lagrangian particle trajectory analysis method is presented, and the effects of various forces, including drag, lift, gravity, and Brownian, are described. The dispersion and deposition of airborne particles in turbulent flows are analyzed. Examples of computational modeling of gas-solid flows in ducts and pollutant transport in indoor and outdoor environments are presented. Particular attention is given to the simulation of compact spherical and elongated particulate transport and deposition in human upper airways. Applications to the transmission of the SARS-CoV-2 virus are also presented. It is shown that computational modeling provides an efficient tool for studying gas-solid flows in complex passages and the spreading of virus-laden droplets.

Graduate Student

Title: A 3D Parallel High-Order Spectral Difference Solver with Curved Local Mesh Refinement for Predicting Arterial Flow Through Stenoses of Varied Constriction Degrees

Department of Mechanical Engineering

Email: kuchen@clarkson.edu

Advisor: Chunlei Liang

Abstract: A massively parallel Compressible High-ORder Unstructured Spectral-difference (CHORUS) code was developed by Wang, Liang and Miesch for simulating stratified convection in rotating spherical shells. In this research, a new feature of curved local mesh refinement (LMR) is implemented for CHORUS. CHORUS-LMR is high-order accurate and realized through curved watertight non-conforming interfaces. Several benchmark problems are used to demonstrate the spatial order of accuracy of CHORUS-LMR. Subsequently, CHORUS is used to simulate arterial flows through stenoses of varied radius constriction degrees (50%, 65%, 70% and 75%) at Reynolds number of 500. CHORUS employs high-order curved elements in the vicinity of arterial wall and the LMR technique reduces the overall computational cost by locally distributing more elements over critical regions. Computational results of this research demonstrate that large geometric constriction of stenosis leads to the formation of shear layers and the development of Kelvin- Helmholtz instability. These instabilities propagate downstream in a wave-like motion and roll-up of the shear layers produce a periodic street of vortex rings. Before the flow transitions into turbulence, frequency spectrum of streamwise velocity fluctuation show that the flow is dominated by the frequency associated with the advection of the vortex rings, which increases from 7.5 to 14.0 for the stenoses of 65% and 70% radius constriction. When the flow breaks down into a large bulk region of small-scale turbulence, the chaotic vortical structures are characterized by arch-shaped hairpins with arbitrary orientations. The streamwise location where the flow transitions into turbulence moves upstream when the constriction degree increases. The early transition for the stenosis of 75% radius constriction induces large pressure drop and provides a fluid-dynamic explanation for clinical definition of critical stenosis (i.e. over 75% luminal radius narrowing). This study also discuss high-performance computing related aspects of CHORUS and the scalability of CHORUS has been tested.

Undergraduate Student

Title: Using Computer Vision Techniques to Automate Microscope Control and Material Characterization

Department of Computer Science

Email: kingpz@clarkson.edu

Advisors: Ajit Achuthan, Natasha Banerjee, and Sean Banerjee

Abstract: Understanding the microstructure evolution of a material undergoing deformation is extremely beneficial in correlating the microstructure of the material to its mechanical properties. This can aid in optimizing the microstructure of the material to obtain better mechanical properties. The routine, systematic task of identifying and characterizing individual microstructures, such as grains, can be time consuming and resource intensive. This problem is exacerbated by the microscope going out of focus over time as deformation takes place. As such, this research presents a combination of computer vision methods which aim at maintaining the focus of a microscope and characterize the features of the material sample being analyzed. We present a solution to autofocusing based on theoretical and applied work done in focus measurement and stage height optimization. We also look into the use of unsupervised clustering techniques in segmentation grain microstructures.

Keywords: autofocus, search optimization, microscopy, material deformation, image segmentation

Graduate Student

Title: Ultrawide Bandgap III-Oxides

Department of Electrical and Computer Engineering

Email: ctan@clarkson.edu

Advisor: Chee-Keong Tan

Abstract: First-Principle DFT calculations are carried out to investigate electronic and structural properties of (BxGa1-x)2O3 alloys in both monoclinic and orthorhombic phases. Generally, the alloying with boron results in the increasing of the bandgap energy and reduction of the lattice constants of (BxGa1-x)2O3 alloys. In addition, the formation enthalpy is calculated to predict its growth feasibility. The band alignment between Ga2O3 and B2O3 is also investigated, which shows the type-II offset in monoclinic phase and type-I offset in orthorhombic phase, respectively. Our studies provide important insight regarding the potential of (BxGa1-x)2O3 alloys for III-Oxide based electronic and optoelectronic device applications.

Associate Professor

Title: Multiscale Modeling of Nanoporous Copper/Nickel Alloys

Department: Mechanical and Aeronautical Engineering

Email: imastora@clarkson.edu

Phone: 315-268-7731

Abstract: Metallic nanofoams have cellular structures consisting of networks of thin nanowires and empty pores occupying a large portion of their volume. They have the potential to present clear advantages in a broad spectrum of low density, high surface area applications. However, those structures suffer from macroscopically brittle behavior, which is one of the limiting factors in their applications. The traditional way to fabricate metallic nanofoams is by dealloying, a process that makes strengthening mechanisms impossible. To resolve this issue, we used electrospinning to manufacture a polymeric non-woven fabric containing metal precursors. Then, a pyrolysis method was applied to form the metallic nanofoams. Two types of metallic nanofoams were produced in that way, pure copper and alloyed copper-nickel. The specimens were characterized and tested using nanoindentation. Furthermore, we applied a multiscale approach to study the mechanical response of the metallic nanofoams under compression and explain the experimental findings. Atomistic simulations were performed to model the yield surface of multiaxial compressive loading of different cell structures. A continuum plasticity model using finite element methods was then introduced to study the overall mechanical strength of these nanofoams under uniaxial compression.

Both the experiment and the simulation analysis reveal that the Cu/Ni alloyed nanofoams were stronger than their pure copper counterparts under compression. The simulations suggested that this behavior was attributed mostly to the higher dislocation density inside the alloyed ligaments that resulted in higher strength. The high dislocation density can also explain the tendency of the ligaments to break, which also observed in the experiments leading to a drop in hardness under increased loading. The application of this methodology can be used to provide further insights into predicting and optimizing the mechanical behavior of macroscopic nanofoam specimens under complex loading conditions.

Assistant Professor

Title: Better by Design: (Electro) Catalysis for Renewable Energy Conversion, Storage, and Chemical Production

Department of Chemical and Biomolecular Engineering

Email: imccrum@clarkson.edu

Phone: 315-268-6665

Abstract: By combining atomistic-scale computational modeling with detailed experiments on well-defined catalysts, we can understand the behavior of a catalyst at the most fundamental level. With this understanding, we can predictively design lower-cost, more active, more selective, and more stable catalysts using a computer. As an example, we will discuss our work with the alkaline hydrogen evolution reaction, where intermittent renewable electricity, such as from wind and solar, can be used to split water to make hydrogen. This hydrogen can be stored as a fuel, or used as a renewable chemical feedstock. We have recently identified the mechanism for this reaction in an alkaline electrolyte and provided guidelines for catalyst design.

Graduate Student

Title: Design of Closed-loop Controller for Active Control of Flow over Flapped Airfoil

Department of Mechanical & Aeronautical Engineering

Email: sobeid@clarkson.edu

Advisor: Goodarz Ahmadi

Abstract: The aim of this study is to develop closed-loop feedback control algorithms for turbulent flow separation phenomena over 2-D flapped airfoil equipped with set of synthetic jet actuators (SJAs). The SJA was mounted in the main body of the airfoil near to the leading edge (0.1c) with an inclined injecting orifice flow injection at 30 degrees to the airfoil wall tangent. . The control objective is to delay flow separation or stall by actuating the SJA through a closed-loop control algorithm using surface pressures as sensor data. FLUENT simulation results are validated by wind tunnel test data of turbulent flow over a 0015 airfoil at Re=1x106. The synthetic jet excitation was modeled by a sinusoidal velocity boundary condition. The effect of synthetic jets in improving the aerodynamic performance of the airfoil by significantly modifying the surface pressure distribution was carefully analyzed. Together with their critical roles, the influences of the actuation frequency (f_j), and momentum coefficient ratio, (C_μ), in the performance of the synthetic jets on separation control, were evaluated. Extensive simulations were performed to identify the effects of f_j in the range of 0 -750 Hz and momentum coefficient in the range of 0 - 0.1 on the external flow field. Variations of the synthetic jets momentum coefficient and driving frequency showed the ability to mitigate separated flows as well as the ability to suppress separation and control the flow from massively separated to a fully attached state. The validity of the present simulations was evaluated through comparisons of the present model predictions with the experimental measurements and earlier numerical studies of open-loop control. In agreement with the experimental observations, the numerical results indicated that the efficiency of the synthetic jet control could be improved with the use of specific frequencies for the momentum coefficient larger than a certain minimum. A control system design approach based on system identification using NARMAX is investigated. A NARMAX model of the flow is constructed using data from a pressure sensor which includes nonlinearities in the flow excited by synthetic jets. A synthetic jet actuator model is employed and controller design follows the standard PI algorithm for single-input single-output systems. The response of the resulting closed loop feedback control system (comprised of PI controller, SJA model and NARMAX model) is shown to track the desired pressure command. A significant improvement in the transient response over the open-loop system at high angles of attack is realized. The benefits of closed-loop control versus open-loop control are thoroughly investigated. The NARMAX controller enhances the lift coefficient from 0.787 for the uncontrolled case to 1.315 for the controlled case with an increase of 67.1%.

Research Associate

Title: Horizontal Ribbon Growth (HRG) for Silicon Wafer Production: Let's Have a Better Understanding of the Physics!

Department of Mechanical and Aeronautical Engineering

Email: apirnia@clarkson.edu

Advisor: Brian Helenbrook

Phone: 315-268-6586

Abstract: Horizontal ribbon growth (HRG) is a novel procedure for growing thin sheets of silicon used in the production of solar panels. This method is proven to be more efficient than conventional procedures, such as the Czochralski method, with higher production rates and lower kerf losses. Despite several attempts at modeling and analyzing the HRG procedure, there is still a large difference between experimental observations and analytical simulations, mainly due to a gap of knowledge in understanding the physics of solidification in this problem. This work explores the solidification mechanism in the HRG process using theoretical modeling and numerical simulations. The solidification mechanism is formulated using appropriate kinetic models in the vicinity of the sheet leading edge, where the solidification process is initiated, and temperature distributions, gradients, and facet formation criteria at the solidification front are obtained. The HRG process is also simulated numerically using an accurate hp-finite element procedure, and the solid ribbon properties, such as ribbon thickness, leading edge position, and facet length are obtained. The findings of this study provide valuable information for better understanding of the solidification mechanism in the HRG process.

Undergraduate Student

Title: Effects of Grain Boundary - Dislocation Interaction on High Entropy Alloy Strengthening

Department of Mechanical and Aeronautical Engineering

Email: willissm@clarkson.edu

Advisor: Ioannis Mastorakos

Abstract: Molecular dynamic simulations of dislocations-grain boundary interactions in fcc high entropy alloys were performed to understand the atomistic mechanisms responsible for the grain boundary strengthening in these systems. Dislocations were nucleated using a modeled force indenter close to a Σ=5 grain boundary perpendicular to the top surface of the structure. Further, the effects of changing the grain boundary to that of a Σ=3 boundary and varying the atomistic distribution were considered. The results for the high entropy alloy were compared to that of a similar structure made of single nickel. The difference between single nickel and high entropy alloys detected in this work can be used to quantify the effect of grain boundaries on strengthening of high entropy alloys. From the varying atomic distributions, the local distribution around the grain boundary should be quantifiable and compared the atomic stresses in the region to determine an effect or not.

Graduate Student

Title: Using CFD method to study the particle transportation characteristics through a critical orifice

Department of Mechanical and Aeronautical Engineering

Email: dayang@clarkson.edu

Advisor: Suresh Dhaniyala

Abstract: A critical orifice, commonly used to control gas flow rates, is also deployed to focus aerosol particles into narrow beams. Aerosol beams generated with orifice are critical for aerosol mass spectrometry studies. Modeling the transport of aerosol particles through a critical orifice is complicated by the interaction of super-sonic flow structures, turbulence, non-continuum effects, and strong gradients in flow velocities. With computational fluid mechanics software, FLUENT 18.1, we model flow through orifice under different sampling conditions and compare our simulation results to the experimental data. We demonstrate errors in existing particle trajectory codes and provide solutions to address them. The simulations are being used to understand the existing system to produce particle beams and to improve the design for better throughput.