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Articles 9571 - 9600 of 30045

Full-Text Articles in Mechanical Engineering

Multiscale Modeling Of Fracture In Quasi-Brittle Materials Using Bifurcation Analysis And Element Elimination Method, Keyvan Zare Rami Dec 2019

Multiscale Modeling Of Fracture In Quasi-Brittle Materials Using Bifurcation Analysis And Element Elimination Method, Keyvan Zare Rami

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Analyzing the fracture of heterogeneous materials is a complex problem, due to the fact that the mechanical behavior of a heterogeneous material is strongly dependent on a variety of factors, such as its microstructure, the properties of each constituent, and interactions between them. Therefore, these factors must be effectively taken into account for accurate analysis, for which the multiscale method has been widely used. In this scheme, the computational homogenization method is used to obtain the effective macroscopic properties of a heterogeneous material based on the response of a Representative Volume Element (RVE). The growth of damage in an RVE …

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Mems 411: Improved Greens Harvester, Matthew Celentano, Nicholas Watts, Sam Friedrich, Ava Mennin Dec 2019

Mems 411: Improved Greens Harvester, Matthew Celentano, Nicholas Watts, Sam Friedrich, Ava Mennin

Mechanical Engineering Design Project Class

Earth Dance Organic Farm School has asked that we design an improved version of their “Quick-Cut” greens harvester. The redesign should be capable of cutting a 36 inch wide bed of greens, should roll on wheels, and should be able to operate for long periods without interruption. This report details the concept generation and selection phases of the project, wherein we elect to design the system with an aluminum extrusion frame, four- wheeled custom band saw system, and rope sweepers, among other key features. In the concept embodiment phase, we explore the features of our initial prototype and areas for …

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Thermodynamic Model Of Co2 Deposition In Cold Climates, Sandra K. S. Boetcher, Ted Von Hippel, Matthew J. Traum Dec 2019

Thermodynamic Model Of Co2 Deposition In Cold Climates, Sandra K. S. Boetcher, Ted Von Hippel, Matthew J. Traum

Publications

A thermodynamic model, borrowing ideas from psychrometric principles, of a cryogenic direct-air CO2-capture system utilizing a precooler is used to estimate the optimal CO2 removal fraction to minimize energy input per tonne of CO2. Energy costs to operate the system scale almost linearly with the temperature drop between the ingested air and the cryogenic desublimation temperature of CO2, driving siting to the coldest accessible locations. System performance in three Arctic/Antarctic regions where the proposed system can potentially be located is analyzed. Colder ambient temperatures provide colder system input air temperature yielding lower CO2 removal energy requirements. A case is also …

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Generalized Ultrasonic Scattering Model For Arbitrary Transducer Configurations, Andrea P. Arguelles, Joseph A. Turner Dec 2019

Generalized Ultrasonic Scattering Model For Arbitrary Transducer Configurations, Andrea P. Arguelles, Joseph A. Turner

Department of Mechanical and Materials Engineering: Faculty Publications

Ultrasonic scattering in polycrystalline media is directly tied to microstructural features. As a result, modeling efforts of scattering from microstructure have been abundant. The inclusion of beam modeling for the ultrasonic transducers greatly simplified the ability to perform quantitative, fully calibrated experiments. In this article, a theoretical scattering model is generalized to allow for arbitrary source and receiver configurations, while accounting for beam behavior through the total propagation path. This extension elucidates the importance and potential of out-of-plane scattering modes in the context of microstructure characterization. The scattering coefficient is explicitly written for the case of statistical isotropy and ellipsoidal …

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Pulsed Detonation Engine Nozzle Design And Analysis, Rahul Kumar Dec 2019

Pulsed Detonation Engine Nozzle Design And Analysis, Rahul Kumar

Mechanical and Aerospace Engineering Dissertations - Archive

For a hypersonic flight mission, different flight regimes have been recognized. The successful and efficient operation of the aircraft to traverse through all the flight regimes requires the integration of various propulsion cycles into a single flow path. Using the phenomenon of detonation initiation and propagation, a multi-mode detonation based propulsion concept was proposed for hypersonic flight. Of the different modes proposed, it was recognized that the efficient operation of Normal Detonation Wave Engine (NDWE) mode and Oblique Detonation Wave Engine (ODWE) mode played an important role as they delivered thrust at critical parts of the trajectory. For this study, …

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Improving Compressive Strength Of High Modulus Carbon-Fiber Reinforced Polymeric Composite With Varying Modulus Fibers, Sarvenaz Ghaffari Dec 2019

Improving Compressive Strength Of High Modulus Carbon-Fiber Reinforced Polymeric Composite With Varying Modulus Fibers, Sarvenaz Ghaffari

Mechanical and Aerospace Engineering Dissertations - Archive

There has been a strong demand in using high-modulus (HM) carbon-fiber composites potentially enabling lightweight aircraft structures with significant weight savings. However, extremely low fiber-direction compressive strength has been a well-recognized weakness of the HM composites, preventing their implementation in aircraft platforms. Fiber-direction compressive strength of HM and intermediate-modulus (IM) carbon fiber-reinforced polymers (CFRP’s) is presumably governed by microstructural stability. However, strong decrease in fiber-direction compressive strength of HM carbon-fiber composites, compared to their intermediate modulus (IM) counterparts, contradicts predictions from available microstructural buckling theories. A recent work demonstrated that significant improvement in the fiber-direction compressive strength of HM carbon-fiber …

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Numerical Study Of Detonation Flame Arrestor Performance And Detonation Interaction With The Arrestor Element, Hoden Ali Farah Dec 2019

Numerical Study Of Detonation Flame Arrestor Performance And Detonation Interaction With The Arrestor Element, Hoden Ali Farah

Mechanical and Aerospace Engineering Dissertations - Archive

A numerical study of detonation propagation and interaction with a flame arrestor product in a combustible gas/vapor transport pipeline system is conducted. The flame arrestor element is modeled as a porous medium using the Forchheimer equation, which is incorporated in the governing conservation equations as a momentum sink. The Forchheimer porous medium model is then used to model the flow through a representative four-inch detonation flame arrestor and is validated with experimental data. The detonation propagation simulation is modeled with the Reynolds averaged Navier-Stokes (RANS) equations extended for reacting flow. A 21-step chemical kinetic mechanism with 10 species is used …

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Numerical Study Of High–Frequency Fluidic Valve Injectors For Detonation Engine Applications, Sushma Yalavarthi Dec 2019

Numerical Study Of High–Frequency Fluidic Valve Injectors For Detonation Engine Applications, Sushma Yalavarthi

Mechanical and Aerospace Engineering Dissertations - Archive

The feasibility of fluidic valves for use in detonation-based engines was studied numerically. The fluidic valve acted by shutting off reactant flow through the high pressure behind detonation waves propagating past the valve opening. The valve which featured a plenum cavity was mounted to the side of a pulsed detonation engine, an arrangement that allowed the valve to be characterized under a sustained operation. A series of different cavity lengths were studied. Further, a numerical study of the high-frequency fluidic valve was conducted by using a two-dimensional reactive Euler solver. A 19–step elementary mechanism was employed for the stoichiometric oxyhydrogen …

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Dynamics Of A Pulse Detonation Engine Driven Linear Power Generator, Umang Umeshkumar Dighe Dec 2019

Dynamics Of A Pulse Detonation Engine Driven Linear Power Generator, Umang Umeshkumar Dighe

Mechanical and Aerospace Engineering Dissertations - Archive

The dynamics of a pulse detonation engine driven linear power generator were studied. For an ideal pulse detonation engine, the thrust generated is in the form of a piecewise function given by the Endo-Fujiwara model. Nonlinear electromagnetic damping is also introduced in the system due to the rare earth permanent magnets present in the linear generator architecture. Various linear generator topologies were studied using static magnetic analysis. Two configurations of a single degree-of-freedom oscillator system, one with a linear spring restoring force and another with geometric nonlinear spring restoring force, were investigated to study any potential advantages of using nonlinear …

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Droplet-Based Microextraction Of Dna Enabled By Electrowetting-On-Dielectric Digital Microfluidics, Shubhodeep Paul Dec 2019

Droplet-Based Microextraction Of Dna Enabled By Electrowetting-On-Dielectric Digital Microfluidics, Shubhodeep Paul

Mechanical and Aerospace Engineering Dissertations - Archive

In recent years there have been significant advances in micro/nanotechnologies employing miniaturized platforms to achieve efficient sample pre-processing, separation, and quantification processes. The idea of bringing several lab-scale protocols on to a single chip, i.e., a lab-on-a-chip (LOC) device along with automation, is a reality now. Miniaturization of biochemical operations usually handled in a laboratory has numerous advantages, such as cost effectiveness, multiplexing, assay speed, and sensitivity. Microfluidic technologies used in LOC devices can manipulate tiny volumes of samples and reagents to perform on-chip protocols with minimal human intervention. Electrowetting-on-dielectric (EWOD)-based digital microfluidics (DMF) is one of the LOC platforms …

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Assessment Of Material State In Composites Using Global Dielectric State Variable, Vamsee Vadlamundi Dec 2019

Assessment Of Material State In Composites Using Global Dielectric State Variable, Vamsee Vadlamundi

Mechanical and Aerospace Engineering Dissertations - Archive

Composites are heterogeneous in nature and a fundamental understanding of the material response to applied mechanical, thermal, electrical and other multi-physical fields is required to efficiently design and synthesize the material system and demands attention to long-term behavior in particular. Unlike metals, composites are designed to develop distributed damage and initiation of a single microscopic crack does not individually affect the strength/life of these materials. Therefore, the primary interest is not in single local events but in the process of interaction of multiple events that have a collective global effect on the material behavior. The interaction of these local events …

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Development And Testing Of A Control Strategy For Dynamic Cooling At Rack Level In Data Centers, Amrutha Valli Rachakonda Dec 2019

Development And Testing Of A Control Strategy For Dynamic Cooling At Rack Level In Data Centers, Amrutha Valli Rachakonda

Mechanical and Aerospace Engineering Theses - Archive

Cooling is a critical part of data center’s infrastructure, and with ongoing demands in data processing and storage, thermal management issues are of great concern. Some imperative methods of removing heat are either using air or liquid (preferably water or refrigerant). When high power density modules are involved, liquid cooling addresses some of the problems faced by air cooling as liquid coolants have higher thermal capacitance. Also, in the case of multi-chip modules, a non-uniform heating due to multi-core generates hot-spots and increases temperature gradients across the module. A dynamic cold plate along with a self-regulated flow control device was …

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Autonomous Carrier Landing Of A Fixed-Wing Uav With Airborne Deck Motion Estimation, Metin Kus Dec 2019

Autonomous Carrier Landing Of A Fixed-Wing Uav With Airborne Deck Motion Estimation, Metin Kus

Mechanical and Aerospace Engineering Theses - Archive

This study focuses on the design, implementation, and evaluation of an autonomous carrier landing system featuring an airborne deck motion estimation module. The three-dimensional dynamics of a fixed-wing UAV with the actuator and engine dynamics are considered. A carrier motion model that accounts for the perturbations caused by various sea states is built. An airborne measurement system, which is composed of a calibrated camera and light-emitting beacons, is utilized to detect several coplanar target points on the moving carrier deck. The known correspondence between the locations of the target points and their coordinates on the focal plane of the camera …

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Static Response Calibration Of 3d Printed Thin Walled Structures Using Fused Deposition Modelling, Akhilesh Ravindra Kulkarni Dec 2019

Static Response Calibration Of 3d Printed Thin Walled Structures Using Fused Deposition Modelling, Akhilesh Ravindra Kulkarni

Mechanical and Aerospace Engineering Theses - Archive

3-D printing has enabled flexible, tool-less fabrication that yields numerous benefits. One benefit is unique and complex structural arrangements that increase design freedom to minimize weight. Such arrangements can be guided by advanced topology, shape, and sizing optimization tools using appropriate process constraints to ensure a printable design and can include highly integrated structural details such as stiffeners, flanges, frames, and other connections. 3D printing thin wall aircraft structures presents challenges for material and structural characterization. 3D printing enables integrated structural details, each detail is affected by the print process capability to fabricate the local geometry and deviations from designed …

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Backstepping Approach For Design Of Cascaded Pid Controller With Guaranteed Trajectory Tracking Performance For Micro-Air Uav, Yusuf Kartal Dec 2019

Backstepping Approach For Design Of Cascaded Pid Controller With Guaranteed Trajectory Tracking Performance For Micro-Air Uav, Yusuf Kartal

Mechanical and Aerospace Engineering Theses - Archive

Flight controllers for micro-air UAVs are generally designed using Proportional- Integral-Derivative (PID) methods, where the tuning of gains is difficult and time-consuming, and performance is not guaranteed. In this thesis, we develop a rigorous method based on the sliding mode analysis and nonlinear backstepping to design a PID controller with guaranteed performance. This technique provides the structure and gains for the PID controller, such that a robust and fast response of the UAV for trajectory tracking is achieved. First, the second-order sliding variable errors are used in a rigorous nonlinear backstepping design to obtain guaranteed performance for the nonlinear UAV …

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Analysis Of Laminated Curved Beam With And Without Defects And Imperfections, Wei-Tsen Lu Dec 2019

Analysis Of Laminated Curved Beam With And Without Defects And Imperfections, Wei-Tsen Lu

Mechanical and Aerospace Engineering Dissertations - Archive

Several studies have focused on the modeling and response characterization of composite structural members, with particular emphasis on composite curved beams. The class of curved beam is explored to determine mechanical response in primary aerospace structural applications. The present work focuses on developing analytical closed-form solutions for investigating composite curved beams with and without fiber waviness and delamination. The present work can efficiently characterize the structural behavior of composite curved beams under bending. This work shows the development of a novel mathematical approach to predict structural performance by investigating axial stiffness, bending stiffness with consideration of shear deformation in composite …

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Electrowetting-On-Dielectric (Ewod) Digital Microfluidic Device For Synthetic Organic Chemistry, Matin Torabinia Dec 2019

Electrowetting-On-Dielectric (Ewod) Digital Microfluidic Device For Synthetic Organic Chemistry, Matin Torabinia

Mechanical and Aerospace Engineering Dissertations - Archive

Over the past decades, microscale chemical reaction technology has been attractive in diverse areas of chemistry. It allows the precise control of quantified reagents and highly efficient heat and mass transfer, because of a large interface-to-volume ratio–particularly in case of the exothermic reaction and mixing–, reduced consumption of toxic or expensive agents, improved reaction profiles, and enhanced selectivity compared to macro-scale reactions. The mainstream microscale reaction processes were established using continuous microchannel flow systems, which has emerged as a powerful complement to batch chemistry on the laboratory scale due to relative advantages, some of which include: increased safety, more accurate …

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An Implementation Of The Regularized Extended Finite Element Method In Abaqus, Yu-Jui Liang Dec 2019

An Implementation Of The Regularized Extended Finite Element Method In Abaqus, Yu-Jui Liang

Mechanical and Aerospace Engineering Dissertations - Archive

The Regularized eXtended Finite Element Method (Rx-FEM) methodology is a discrete damage modeling (DDM) technique, which represents an approach to the progressive damage analysis (PDA) in laminated composites when multiple damage events such as matrix cracks and delamination are introduced into the model via the displacement discontinuities. In the Rx-FEM, the Heaviside step function that is typically used to introduce a displacement discontinuity across a crack surface in the eXtended Finite Element Method (x-FEM) is replaced by a continuous function approximated by using the finite element (FE) shape functions. This regularization offers unique possibility for the implementation of the Rx-FEM …

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Material Characterization And Fracture Prediction Of Fdm Printed Parts, Sanchita Sheth Dec 2019

Material Characterization And Fracture Prediction Of Fdm Printed Parts, Sanchita Sheth

Mechanical and Aerospace Engineering Theses - Archive

In order to take advantage of the design freedom that Additive Manufacturing offers, most applications require reliable material characterization. This can ensure that a design performs within its environment and life requirements. This work discusses two models. One investigates the raster angle dependency of stiffness properties and the other numerically predicts fracture in Fused Deposition Modeling (FDM) printed polymer parts. Pre-processing of FDM geometry was done in Abaqus CAE (SIMULIA TM). FEA and post-processing was done in BSAM, which is a damage prediction software developed for composites. BSAM uses a regularized extended finite element approach of Discrete Damage Modeling. In …

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A Robust Controller Design For A Tailless Uav With Effective Control Allocation, Ethem Hakan Orhan Dec 2019

A Robust Controller Design For A Tailless Uav With Effective Control Allocation, Ethem Hakan Orhan

Mechanical and Aerospace Engineering Theses - Archive

Attempts to completely remove the tails from aircraft can be dated back to the early days of modern aviation. A number of stability and control problems arising from the unique characteristics of the configuration resulted in poor handling qualities and some dangerous flight characteristics in the early designs. Lately, this configuration is becoming widespread again and the current state-of-the-art of fly-by wire technology and modern control design techniques enable design of tailless aircraft which are safe to fly. In this thesis, a study on the application of modern robust control design techniques on a tailless UAV is presented. A nonlinear …

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Fluids Demonstrations Ii: Bubbles In Mondrian Painting, Eruption-Like Flow, Rotational Instability, And Wake Vortices, Said Shakerin Dec 2019

Fluids Demonstrations Ii: Bubbles In Mondrian Painting, Eruption-Like Flow, Rotational Instability, And Wake Vortices, Said Shakerin

All Faculty Articles - School of Engineering and Computer Science

The purpose of this paper is to present five new devices that demonstrate a variety of flow phenomena in liquids and granular materials that exhibit fluid-like behavior. These devices complement and add on to a recent collection of demonstrations that was published in this journal. The devices are self-contained and portable, and can be utilized repeatedly without waiting or cleanup between uses. Furthermore, since the demonstrations result in visually engaging patterns, they are accessible to everyone regardless of age or science background. Descriptions are provided to enable replication by others. Significance of each demonstration is outlined and background information on …

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Experimental Investigation Of Flow Pulsation Waveforms In Rectangular Mesochannels For High Heat Flux Electronics Cooling, Jaakko Mcevoy, Sajad Alimohammadi, Tim Persoons Dec 2019

Experimental Investigation Of Flow Pulsation Waveforms In Rectangular Mesochannels For High Heat Flux Electronics Cooling, Jaakko Mcevoy, Sajad Alimohammadi, Tim Persoons

Articles

The ever rising heat fluxes encountered in electronic devices present a challenging thermal engineering problem. Not only is heat transfer enhancement a goal but more recently control of the enhancement is desired, especially in large scale data facilities where the heated outlet coolant fluid may be of use. Flow pulsation is one of the most common active heat transfer enhancement methods studied across all heat sink sizes. While the effects of pulsation have been shown to increase heat transfer under certain conditions there is still disagreement upon its merit for practical applications, with the majority of previous research has been …

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A Generalisable Bottom-Up Methodology For Deriving A Residential Stock Model From Large Empirical Databases, Ciara Ahern, Brian Norton Dec 2019

A Generalisable Bottom-Up Methodology For Deriving A Residential Stock Model From Large Empirical Databases, Ciara Ahern, Brian Norton

Articles

Specifying representative reference buildings as a prerequisite for calculating cost-optimal energy performance requirements for buildings and building elements. Appropriate characterisation is prerequisite data for an overall national building energy consumption model to produce valid outcomes. Energy Performance Certificates (EPCs) are issued in the EU, for dwellings whenever they are constructed, sold or leased. Where acquiring data for an EPC would be prohibitively costly, nationally applicable default-values are employed for the building envelope thermal transmittance coefficients. Significant levels of retrofits led to the default-values used now being higher than is typical in reality, leading to characterisations of reference dwellings based on …

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2-Axis Electric Off-Road Bucket Seat Bases, Brennan K. Slater, Alexander P. Croteau, Spencer M. Kubik Dec 2019

2-Axis Electric Off-Road Bucket Seat Bases, Brennan K. Slater, Alexander P. Croteau, Spencer M. Kubik

Mechanical Engineering

Off-road vehicle bucket seats are currently restricted to a single position relative to the floor of the vehicle. Drivers and riders desire the ability to adjust their seat position to increase comfort and allow for a greater size range of riders to fit safely within the cabin or roll cage. To develop a viable solution, the team has gone through an extensive design process and has constructed a functioning prototype. This Final Design Report encapsulates the entire design process and concludes with recommendations for changes we would make looking both back in review as well as moving forward with further …

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Experimental Investigation Of N2o/O2 Mixtures As Volumetrically Efficient Oxidizers For Small Spacecraft Hybrid Propulsion Systems, Rob L. Stoddard Dec 2019

Experimental Investigation Of N2o/O2 Mixtures As Volumetrically Efficient Oxidizers For Small Spacecraft Hybrid Propulsion Systems, Rob L. Stoddard

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

A hybrid thruster system utilizes propellants in two different stages, traditionally a solid fuel and a gaseous or liquid oxidizer. Recently hybrid thrusters have become a popular topic of research due to the high demand of a ”green” replacement for hydrazine. Not only are hybrid thruster systems typically much safer than hydrazine, but they are also a low-cost system with a high reliability in performance. The Propulsion Research Laboratory (PRL) at Utah State University (USU) has developed a hybrid thruster system using 3-D printed acrylonitrile butadiene styrene (ABS) as the fuel and gaseous oxygen (GOX) as the oxidizer. This system …

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Generation Of Polarization Singularities With Geometric Metasurfaces, Yuchao Zhang, Xiaodong Yang, Jie Gao Dec 2019

Generation Of Polarization Singularities With Geometric Metasurfaces, Yuchao Zhang, Xiaodong Yang, Jie Gao

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The polarization singularities are directly generated by using plasmonic metasurfaces with the geometric phase profiles designed to form the Poincaré beams. Different morphologies of polarization topological structures of lemon, star, monstar, spiral, dipole and quadrupole are created by the superpositions of Laguerre-Gauss modes with different orders under orthogonal circular or linear polarization basis. The polarization ellipse patterns and topological features of the produced optical vector fields are analyzed to reveal the properties of the polarization singularities of C-points and L-lines, and the orbital angular momentum states are also measured. The demonstrated polarization singularities generated from the geometric metasurfaces will promise …

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3d Janus Plasmonic Helical Nanoapertures For Polarization-Encrypted Data Storage, Yang Chen, Xiaodong Yang, Jie Gao Dec 2019

3d Janus Plasmonic Helical Nanoapertures For Polarization-Encrypted Data Storage, Yang Chen, Xiaodong Yang, Jie Gao

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Helical structures have attracted considerable attention due to their inherent optical chirality. Here, we report a unique type of 3D Janus plasmonic helical nanoaperture with direction-controlled polarization sensitivity, which is simply fabricated via the one-step grayscale focused ion beam milling method. Circular dichroism in transmission of as large as 0.72 is experimentally realized in the forward direction due to the spin-dependent mode coupling process inside the helical nanoaperture. However, in the backward direction, the nanoaperture acquires giant linear dichroism in transmission of up to 0.87. By encoding the Janus metasurface with the two nanoaperture enantiomers having specified rotation angles, direction-controlled …

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Orbital Angular Momentum Transformation Of Optical Vortex With Aluminum Metasurfaces, Yuchao Zhang, Xiaodong Yang, Jie Gao Dec 2019

Orbital Angular Momentum Transformation Of Optical Vortex With Aluminum Metasurfaces, Yuchao Zhang, Xiaodong Yang, Jie Gao

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The orbital angular momentum (OAM) transformation of optical vortex is realized upon using aluminum metasurfaces with phase distributions derived from the caustic theory. The generated OAM transformation beam has the well-defined Bessel-like patterns with multiple designed topological charges from -1 to +2.5 including both the integer-order and fractional-order optical vortices along the propagation. The detailed OAM transformation process is observed in terms of the variations of both beam intensity and phase profiles. The dynamic distributions of OAM mode density in the transformation are further analyzed to illustrate the conservation of the total OAM. The demonstration of transforming OAM states arbitrarily …

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Pore Elimination Mechanisms During 3d Printing Of Metals, S. Mohammad H. Hojjatzadeh, Niranjan D. Parab, Wentao Yan, Lianyi Chen, For Full List Of Authors, See Publisher's Website. Dec 2019

Pore Elimination Mechanisms During 3d Printing Of Metals, S. Mohammad H. Hojjatzadeh, Niranjan D. Parab, Wentao Yan, Lianyi Chen, For Full List Of Authors, See Publisher's Website.

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Laser powder bed fusion (LPBF) is a 3D printing technology that can print metal parts with complex geometries without the design constraints of traditional manufacturing routes. However, the parts printed by LPBF normally contain many more pores than those made by conventional methods, which severely deteriorates their properties. Here, by combining in-situ high-speed high-resolution synchrotron x-ray imaging experiments and multi-physics modeling, we unveil the dynamics and mechanisms of pore motion and elimination in the LPBF process. We find that the high thermocapillary force, induced by the high temperature gradient in the laser interaction region, can rapidly eliminate pores from the …

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Spatial Variation Of Vector Vortex Beams With Plasmonic Metasurfaces, Yuchao Zhang, Jie Gao, Xiaodong Yang Dec 2019

Spatial Variation Of Vector Vortex Beams With Plasmonic Metasurfaces, Yuchao Zhang, Jie Gao, Xiaodong Yang

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The spatial variation of vector vortex beams with arbitrary polarization states and orbital angular momentum (OAM) values along the beam propagation is demonstrated by using plasmonic metasurfaces with the initial geometric phase profiles determined from the caustic theory. The vector vortex beam is produced by the superposition of deflected right- and left-handed circularly polarized component vortices with different helical phase charges, which are simultaneously generated off-axially by the single metasurface. Besides, the detailed evolution processes of intensity profile, polarization distribution and OAM value along the beam propagation distance is analyzed. The demonstrated arbitrary space-variant vector vortex beam will pave the …

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