Power System Nonlinear Modal Analysis Using Computationally Reduced Normal Form Method

Increasing nonlinearity in today’s grid challenges the conventional small-signal (modal) analysis (SSA) tools. For instance, the interactions among modes, which are not captured by SSA, may play significant roles in a stressed power system. Consequently, alternative nonlinear modal analysis tools, notably Normal Form (NF) and Modal Series (MS) methods are being explored. However, they are computation-intensive due to numerous polynomial coefficients required. This paper proposes a fast NF technique for power system modal interaction investigation, which uses characteristics of system modes to carefully select relevant terms to be considered in the analysis. The Coefficients related to these terms are selectively computed and the resulting approximate model is computationally reduced compared to the one in which all the coefficients are computed. This leads to a very rapid nonlinear modal analysis of the power systems. The reduced model is used to study interactions of modes in a two-area power system where the tested scenarios give same results as the full model, with about 70% reduction in computation time

National Aeronautics and Space Administration (NASA)/American Society for Engineering Education (ASEE) Summer Faculty Fellowship Program, 1993, volume 2

The JSC NASA/ASEE Summer Faculty Fellowship Program was conducted by Texas A&M University and JSC. The objectives of the program, which began nationally in 1964 and at JSC in 1965, are (1) to further the professional knowledge of qualified engineering and science faculty members; (2) to stimulate an exchange of ideas between participants and NASA; (3) to enrich and refresh the research and teaching activities of participant's institutions; and (4) to contribute to the research objectives of the NASA centers. Each faculty fellow spent at least 10 weeks at JSC engaged in a research project in collaboration with a NASA/JSC colleague. A compilation of the final reports on the research projects completed by the faculty fellows during the summer of 1993 is presented

Assessing the Impact of Organizational Practices on the Productivity of University Technology Transfer Offices: An Exploratory Study

We present quantitative and qualitative evidence (field research) on university technology transfer offices (TTOs). These offices negotiate licensing agreements with firms to commercialize university-based technologies. A stochastic frontier production function framework is used to assess the relative productivity of 113 university TTOs. Our field research provided a useful reality check on the specification of the econometric model. The empirical findings imply that licensing activity is characterized by constant returns to scale. Environmental and institutional factors appear to explain some of the variation in TTO efficiency. Relative productivity may also depend on organizational practices in university management of intellectual property, which potentially attenuate palpable differences in the motives, incentives, and organizational cultures of the parties to licensing agreements. Unfortunately, there are no existing data on such practices, so we rely on inductive, qualitative methods to identify them. We present detailed information on our use of these methods. This information may be useful to economists who are contemplating fieldwork. Based on 55 interviews of managers/entrepreneurs and administrators at five research universities, we conclude that the most critical organizational factors are likely to be reward systems for faculty, TTO staffing and compensation practices, and actions taken by administrators to extirpate informational and cultural barriers between universities and firms.

Functions of ZNF516 in embryonic development, health, and disease

Zinc finger protein 516, or ZNF516, is a largely understudied protein. Germline homozygous loss of the murine ortholog, ZFP516, has been previously reported to lead to embryonic lethality in mice. However, the cause of this lethality has not been investigated. With the aid of newly developed Zfp516 knock out mouse line in our laboratory I characterised the phenotypes of Zfp516 knock out animals and concluded that severe and 100% penetrant congenital heart defects were the most likely cause of embryonic lethality in Zfp516-/-. I reported that heart defects were not due to selective Zfp516 deletion in cardiomyocytes, and that only some defects were recapitulated when Zfp516 was deleted in Isl1-expressing cells. I further described spatiotemporal expression of Zfp516 during development and showed that Zfp516 ablation at E9.5 leads to upregulation of genes involved in neuronal migration, growth and synapsogenesis. Moreover, I found genetic synergy between Zfp516 and Sox10 during development. Next, I characterized phenotypes associated with deletions of and polymorphisms in human ZNF516 and adult heterozygous Zfp516 knock out mice. I discovered that manifestation of phenotypes in Zfp516+/- mice was largely gender dependent, and that our mouse model phenocopied some of the phenotypes seen in humans. Lastly, I reported that targeting ZNF516 in HCT116 with CRIPSR/Cas9 can result in chromosome arm truncations. I therefore suggested a screening method for future studies that could preselect clones with correct genotype and without arm truncations before further cell expansion for subsequent downstream experiments

Modeling Settlement Bargaining with Algorithmic Game Theory

Past computational models of settlement bargaining have lacked explicit game theoretic foundations. Algorithmic game theory, however, offers techniques that can find perfect Bayesian equilibria even where closed-form mathematical solutions may be intractable. Some recent mathematical models tackle two-sided asymmetric information, including evidentiary signals models, in which the judgment is a sum of both shared and independent private information, and correlated signals models, in which both parties receive noisy signals about the same information. To relax assumptions inherent in these models, this paper employs several progressively more complicated techniques, including iterative elimination of dominated alternatives, no regret learning, and counterfactual regret minimization. Although these algorithms are not guaranteed to produce Nash equilibria in general-sum games like litigation, they nonetheless succeed in producing either exact or close approximate equilibria on discrete versions of the corresponding mathematical models. A single algorithmic game theory model can incorporate a number of features that state-of-the-art mathematical models cannot handle simultaneously, such as two-sided correlated signals of both liability and damages, risk aversion, and options to concede

Modeling and Analysis for Control of Reactant and Water Distributions in Fuel Cells.

It is shown that the critical task of controlling the water accumulation within the gas diffusion layers (GDL) and channels of a polymer electrolyte membrane fuel cell (PEMFC) benefits from a partial differential equation (PDE) approach. Starting from first principles, a fuel cell model is represented as a boundary value problem for a set of six coupled, nonlinear, second-order PDEs for mass transport across the gas diffusion layer, from channel-to-channel. The multi-input, multi-output model includes nonlinearities related to both switching and PDEs with polynomial coefficients in the dependent variable. The six PDEs are approximated, with justification founded in linear systems theory and a time-scale decomposition approach, by a semi-analytic solution (SAS) model that, compared to the full numeric solution, requires only one-third the number of states to be numerically integrated. This model simplification plays a critical role in the fundamental goal of the research, which is to provide a control-oriented model that maintains the meanings of the states in order to apply physically intuitive control algorithms. The SAS model consists of a set of numeric transient, analytic transient, and analytic steady-state solutions to the system of PDEs. Model accuracy is verified by comparison to the experimental voltage transient response from a 24-cell stack, and to the predictive capability of the full-order numeric model. The SAS model predicts degradation due to liquid water accumulation and voltage variations due to changes in inputs such as stack current, reactant excess ratio, and overall stack temperature with negligible variation versus the full-order model. The SAS model is created for application to real-time automatic control of spatial and temporal water and reactant distributions within a PEMFC. The semianalytic solution is analyzed for open-loop stability and to gain insight into the physics of the equilibrium water distributions. Candidate distributions for vapor and liquid water are then identified which allow maximum membrane hydration while simultaneously avoiding voltage degradation that results from anode liquid water accumulation (flooding). The desired distributions would be maintained via control of the channel conditions (boundary value control) with the ultimate goal to maximize hydrogen utilization and prolong fuel cell life.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58379/1/bmccain_1.pd

Analysis of the shearing instability in nonlinear convection and magnetoconvection

Numerical experiments on two-dimensional convection with or without a vertical magnetic field reveal a bewildering variety of periodic and aperiodic oscillations. Steady rolls can develop a shearing instability, in which rolls turning over in one direction grow at the expense of rolls turning over in the other, resulting in a net shear across the layer. As the temperature difference across the fluid is increased, two-dimensional pulsating waves occur, in which the direction of shear alternates. We analyse the nonlinear dynamics of this behaviour by first constructing appropriate low-order sets of ordinary differential equations, which show the same behaviour, and then analysing the global bifurcations that lead to these oscillations by constructing one-dimensional return maps. We compare the behaviour of the partial differential equations, the models and the maps in systematic two-parameter studies of both the magnetic and the non-magnetic cases, emphasising how the symmetries of periodic solutions change as a result of global bifurcations. Much of the interesting behaviour is associated with a discontinuous change in the leading direction of a fixed point at a global bifurcation; this change occurs when the magnetic field is introduced

Reduced-order modeling of power electronics components and systems

This dissertation addresses the seemingly inevitable compromise between modeling fidelity and simulation speed in power electronics. Higher-order effects are considered at the component and system levels. Order-reduction techniques are applied to provide insight into accurate, computationally efficient component-level (via reduced-order physics-based model) and system-level simulations (via multiresolution simulation). Proposed high-order models, verified with hardware measurements, are, in turn, used to verify the accuracy of final reduced-order models for both small- and large-signal excitations. At the component level, dynamic high-fidelity magnetic equivalent circuits are introduced for laminated and solid magnetic cores. Automated linear and nonlinear order-reduction techniques are introduced for linear magnetic systems, saturated systems, systems with relative motion, and multiple-winding systems, to extract the desired essential system dynamics. Finite-element models of magnetic components incorporating relative motion are set forth and then reduced. At the system level, a framework for multiresolution simulation of switching converters is developed. Multiresolution simulation provides an alternative method to analyze power converters by providing an appropriate amount of detail based on the time scale and phenomenon being considered. A detailed full-order converter model is built based upon high-order component models and accurate switching transitions. Efficient order-reduction techniques are used to extract several lower-order models for the desired resolution of the simulation. This simulation framework is extended to higher-order converters, converters with nonlinear elements, and closed-loop systems. The resulting rapid-to-integrate component models and flexible simulation frameworks could form the computational core of future virtual prototyping design and analysis environments for energy processing units

Proceedings of the Workshop on Identification and Control of Flexible Space Structures, volume 1

Identification and control of flexible space structures were studied. Exploration of the most advanced modeling estimation, identification and control methodologies to flexible space structures was discussed. The following general areas were discussed: space platforms, antennas, and flight experiments; control/structure interactions - modeling, integrated design and optimization, control and stabilization, and shape control; control technology; control of space stations; large antenna control, dynamics and control experiments, and control/structure interaction experiments