MNE / EAS Ph.D. Dissertation Defense: Ms. Jinya Liu
Mechanical Engineering (MNE) / Engineering Applied Science (EAS) Ph.D. Dissertation Defense by Ms. Jinya Liu DATE: August 25, 2017 TIME: 2:00 p.m. - 4:00 p.m. LOCATION: Textile Building, Room 101E TOPIC: Statistical Regular-Fractal Topography Modeling and Contact Analysis of RF MEMS Surface ABSTRACT: Surface contact quality of electrodes has been recognized as a key factor in RF MEMS switch performance and reliability design. Topography of the surfaces and contact mechanics determine the quality of the contact. Surface topography contains complex and random features, which make measurement, surface characterization/modeling and contact simulation a big challenge in predicting the contact quality. The objective of our research is to develop a methodology to measure, characterize, and model topography for contact modeling and correlating contact properties to the surface characterization. An interdisciplinary approach, which integrates metrology, statistics, fractal mathematics, and contact mechanics, is proposed to achieve the research goal. Specifically it includes: · Multi-scale sampling plan design: A sampling plan is proposed for surface measurement using atomic force microscopy (AFM). Topography on RF MEMS switch contacting surfaces are scanned by AFM at different length scales (e.g. 1x1, 10x10 and 60x60 mm2). A sample allocation plan is designed to maximize the spatial representative of the AFM scanning patches with different resolutions and uniformly distributed sample patches. The scanning data are used for characterizing, model estimation and contact analysis. · Topography characterization and statistical modeling: A flexible framework is created to accommodate various pattern structures. Regular patterns are found at coarser scales (e.g. 10x10 and 60x60 mm2). Random irregularity and the fractal structure are observed at finer scales (e.g. 1x1 mm2). A regular-fractal model is proposed to decompose and characterize the regular and fractal structures with two model components: one for the regular geometric pattern and the other for fractal irregularity. The model validation is made through the comparisons of topography and conventional roughness parameters between the results of simulation from the proposed model and that derived from AFM scanned data. · Elasto-plastic contact analysis: A non-adhesive, frictionless contact analysis is carried out to investigate the contact aspects of RF MEMS capacitive switches by finite element software COMSOL. Elastic-plastic contact model is employed based on the AFM data of different scales (e.g. 1x1, 10x10 and 60x60 mm2) to represent the regular pattern dominate surface, and regular-fractal and fractal structure dominate surfaces. Loading/ unloading cycles are applied to simulate the working status of RF MEMS switch. Dimensionless contact area vs dimensionless load curve were determined and compared for different cycles. Dominant micro-scale regular patterns were found to significantly change the contact behavior. Contact areas mainly clusters around the regular pattern. The contribution from fractal structure is not significant. Under cyclic loading conditions, plastic deformation in 1st loading/unloading cycle smoothen the surface. The subsequent repetitive loading-unloading cycles undergo elastic contact without changing the morphology of the contacting surfaces. The work is expected to shed light on the quality of switch surface contact as well as optimum design of RF MEM switch surfaces. ADVISORS: Dr. Wenzhen Huang (firstname.lastname@example.org, 508-910-6568) Dr. Vijaya B. Chalivendra (email@example.com, 508-910-6572) COMMITTEE MEMBERS: Dr. Wenzhen Huang, Department Mechanical Engineering, UMD Dr. Vijaya B. Chalivendra, Department of Mechanical Engineering, UMD Dr. Sherif D. El Wakil, Department of Mechanical Engineering, UMD Dr. Jianyi Jay Wang, Department of Physics, UMD Dr. Charles L. Goldsmith, President, MEMtronics Corporation Open to the public and all are welcome! Mechanical Engineering and Engineering Applied Science students are encouraged to attend. For more information, please contact Dr. Wenzhen Huang (firstname.lastname@example.org) or Dr. Vijaya Chalivendra (email@example.com).
Academic year commences
The academic year begins.
Convocation is a ceremony that celebrates the beginning of the academic year and welcomes our new students to campus.
EAS Proposal Defense by Tiffany Ferreira
TITLE: HIGH-ORDER AND GEOMETRICALLY FLEXIBLE NUMERICAL METHOD FOR SYSTEM OF COUPLED TIME-DEPENDENT PARTIAL DIFFERENTIAL EQUATIONS Abstract:Systems of partial differential equations (PDEs) are often encountered in many scientific applications. One particular example related to mathematical biology is a system of coupled, nonlinear reaction diffusion PDEs that models the spread of harmful plaques associated with Alzheimer's disease on the human brain. Numerical collocation methods for computing and simulating solutions for such problems face several challenges including dealing with irregular geometry, capturing local profiles, handling non-linearity, and maintaining stability, efficiency, and accuracy. In our preliminary work, we numerically study this type of system on regular domains using method of lines, where classical finite difference (FD) is used for the spatial discretization and coupled with an Implicit-Explicit (IMEX) time stepping scheme to advance the solution in time. We have solved a system of up to 50 coupled PDEs and tested for convergence in space and time using known solutions. Our next goal, which is the scope of this proposal, is to explore a new approach using Radial Basis Function in finite difference mode (RBF-FD) methods for the spatial discretization that can mitigate drawbacks arising from using FD methods on complex domains. Due to the nature of collocation methods, implementing RBF-FD methods will require minimal modifications to the existing model. We plan to study and address issues that arise from the implementation of RBF-FD methods when coupled with IMEX time integrators on regular and irregular domains with boundary conditions. We will use a variety of numerical techniques to resolve any issues that may arise from this combination of spatial/temporal numerical schemes such as instability, dealing with boundary conditions, preconditioning techniques for solving large systems, and resolving local profiles. Additionally, we will place emphasis on reproducible research codes which will be made publicly available through a git repository.
First Day of Classes
Fall 2017 classes begin today.
EAS Proposal Defence by Jacob Sousa
TITLE: HIGH-ORDER SPACE-TIME COLLOCATION METHOD FOR THE NUMERICAL SOLUTIONS OF TIME-DEPENDENT PARTIAL DIFFERENTIAL EQUATIONS Abstract:Time-dependent partial differential equations (PDEs) appear very often in many different fields of science and engineering. They are commonly solved numerically using a method of lines approach, in which some discretization is applied to all of the spatial dimensions to transform the problem into a system of ordinary differential equation (ODE) initial value problems. These equations can then be integrated in time using one of many numerical integration schemes. This popular approach works well and is well-studied. However, in order to achieve high accuracy in both space and time, the time integration may require unacceptably small time-steps to maintain accuracy and numerical stability. We would like to develop methods which achieve high orders of accuracy in both space and time without unacceptably small time-steps by using a space-time collocation method based on pseudospectral (PS) and radial basis function (RBF) methods. In this method, space and time are discretized together and the PDE is solved as a boundary value problem in space and time domain. This approach has been attempted before for finite element methods, but is comparatively unexplored using collocation. Moreover, the space-time RBF collocation method has the flexibility to handle a problem on a moving domain without reformulating the underlying PDEs. The goals of this research are to demonstrate the effectiveness of this approach numerically, to address difficulties that arise from using these methods, and to develop a theoretical understanding of these methods. As a separate project, we are investigating the possibility of using non-polynomial functions as bases of interpolants for deriving linear multistep methods. In this work, we will study the consistency, accuracy, and stability of the methods based on Gaussian RBF. Our goal is to see if this method can be a viable choice or if it turns out that polynomial-based methods are always superior.
The Jewish Culture Book Club, Friday September 8th, 2017
Jewish Book Club "A Horse walks into a Bar" Novel by David Grossman
Last day to Add, Drop, or Audit
Today is the last day to add/drop a class. Today is the last day to audit a class. Students taking online or continuing education courses please consult the University Extension withdrawal and refund policy. http://www.umassd.edu/extension/tuitionandfees/withdrawalandrefundpolicy/
Science Fiction Book Club September meeting
Join the Science Fiction Book Club for our first fall meeting! We'll be discussing the graphic novel Lumberjanes, Vol. 1: Beware the Kitten Holy (issues 1-4) by Shannon Watters, Grace Ellis, Noelle Stevenson, and Brooke Allen. All are welcome! Questions? Contact Hilary Kraus at firstname.lastname@example.org
Columbus Day Holiday - no classes
Columbus Day, no classes today.
Follow Monday's class schedule
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