Publications

This paper documents research into the use of an adaptive cultural model and collective intelligence as a means of characterizing the reliability of bulk power networks. Historically, utilities support the reliable design and operation of bulk power networks through first-order contingency analysis. In contingency analyses the list of candidate elements for disruption are identified by engineers a priori based on the rate at which the elements failure through the course of normal grid operation. The new method, an implementation of particle swarm analysis, a swarm of 'virtual power engineers' successfully identified the set of network elements which, if disrupted, would possibly lead to a cascading series of events resulting in the most wide spread damage. The methodology is technology independent: it can be applied on not only for reliability analysis of bulk power systems, but also other energy systems or transportation systems. The methodology is scale neutral: it can be applied to power distribution networks at the local, state or regional level.

A two-dimensional Riemann solver is developed for the spherical harmonics approximation to the time dependent neutron transport equation. The eigenstructure of the resulting equations is explored, giving insight into both the spherical harmonics approximation and the Riemann solver. The classic Roe-type Riemann solver used here was developed for one-dimensional problems, but can be used in multidimensional problems by treating each face of a two-dimensional computation cell in a locally one-dimensional way. Several test problems are used to explore the capabilities of both the Riemann solver and the spherical harmonics approximation. The numerical solution for a simple line source problem is compared to the analytic solution to both the P1 equation and the full transport solution. A lattice problem is used to test the method on a more challenging problem. © 2005 Elsevier Inc. All rights reserved.

We have used density functional theory to investigate diffusion of VN+ in the presence of H+. Optimal migration pathways were determined using the climbing image nudged elastic band and directed dimer methods. Our calculations indicate that the rate-limiting barrier for VN+ migration will be reduced by 0.58 eV by interplay with H+, which will enhance migration by more than an order of magnitude at typical GaN growth temperatures. © 2005 American Institute of Physics.

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A liquid-vapor phase-change membrane actuator is demonstrated which integrates an open groove wicking structure to continuously pump liquid into the heat addition region of the pressure cavity. Integration of the wick yields a higher efficiency and operating speed compared with existing thermal phase-change actuators. This improvement results from control of the liquid thickness, volume, and fill rate. An experimentally validated numerical model is presented which determines the energy budget within the actuator and investigates factors controlling efficiency such as wick thickness, thermal mass, thermal conductivity, and membrane compliance. Work to date for this class of actuators has focused primarily on steady state behavior with detailed transient analyses receiving little attention. This investigation focuses strictly on characterization of transient operation and provides a benchmark for this class of dynamic thermal actuators. The actuator presented in this work develops pressure and deflection excursions of 148kPa and 70μm at 10Hz while consuming 150mW. A peak force of 1.4N is generated during each cycle and the thermal to mechanical efficiency is 11%. © 2005 IEEE.

Mandell et al. have recently presented an updated constant-life diagram (CLD) for a fiberglass composite that is a typical wind turbine blade material. Their formulation uses the MSU/DOE fatigue data base to develop a CLD with detailed S-N information at 13 R-values. This diagram is the most detailed to date, and it includes several loading conditions that have been poorly represented in earlier studies. Sutherland and Mandell have used this formulation to analyze typical loads data from operating wind farms and the failure of coupons subjected to spectral loading. The detailed CLD used in these analyses requires a significant investment in materials testing that is usually outside the bounds of typical design standards for wind turbine blades. Thus, the question has become: How many S-N curves are required for the construction of a CLD that is sufficient for an "accurate" prediction of equivalent fatigue loads and service lifetimes? To answer this question, the load data from two operating wind turbines and the failure of coupons tested using the WISPERX spectra are analyzed using a nonlinear damage model. For the analysis, the predicted service lifetimes that are based on the CLD constructed from 13 R-values are compared to the predictions for CLDs constructed with fewer R-values. The results illustrate the optimum number of R-values is 5 with them concentrated between R-values of -2 and 0.5, or -2 and 0.7. Copyright © 2005 by ASME.

With the current trend toward larger and larger horizontal axis wind turbines, classical flutter is becoming a more critical issue. Recent studies have indicated that for a single blade turning in still air the flutter speed for a modern 35 m blade occurs at approximately twice its operating speed (2 per rev), whereas for smaller blades (5-9 m), both modern and early designs, the flutter speeds are in the range of 3.5-6 per rev. Scaling studies demonstrate that the per rev flutter speed should not change with scale. Thus, design requirements that change with increasing blade size are producing the concurrent reduction in per rev flutter speeds. In comparison with an early small blade design (5 m blade), flutter computations indicate that the non rotating modes which combine to create the flutter mode change as the blade becomes larger (i.e., for the larger blade the second flapwise mode, as opposed to the first flapwise mode for the smaller blade, combines with the first torsional mode to produce the flutter mode). For the more modern smaller blade design (9 m blade), results show that the non rotating modes that couple are similar to those of the larger blade. For the wings of fixed-wing aircraft, it is common knowledge that judicious selection of certain design parameters can increase the airspeed associated with the onset of flutter. Two parameters, the chord-wise location of the center of mass and the ratio of the flapwise natural frequency to the torsional natural frequency, are especially significant. In this paper studies are performed to determine the sensitivity of the per rev flutter speed to these parameters for a 35 m wind turbine blade. Additional studies are performed to determine which structural characteristics of the blade are most significant in explaining the previously mentioned per rev flutter speed differences. As a point of interest, flutter results are also reported for two recently designed 9 m twist/coupled blades.Copyright © 2005 by ASME.

One of the key issues in the aftermath of an exploded radiological dispersal device from a terrorist event is that of the contaminated victim and the concern among healthcare providers for the harmful exposures they may receive in treating patients, especially if the patient has not been thoroughly decontaminated. This is critically important in the event of mass casualties from a nuclear or radiological incident because of the essential rapidity of acute medical decisions and that those who have life- or limb-threatening injuries may have treatment unduly delayed by a decontamination process that may be unnecessary for protecting the health and safety of the patient or the healthcare provider. To estimate potential contamination of those exposed in a radiological dispersal device event, results were used from explosive aerosolization tests of surrogate radionuclides detonated with high explosives at the Sandia National Laboratories. Computer modeling was also used to assess radiation dose rates to surgical personnel treating patients with blast injuries who are contaminated with any of a variety of common radionuclides. It is demonstrated that exceptional but plausible cases may require special precautions by the healthcare provider, even while managing life-threatening injuries of a contaminated victim from a radiological dispersal device event. Copyright © 2005 Health Physics Society.

Results are shown demonstrating the application of the interfacial force microscope to a study of the micro-scale mechanical properties of an extreme example of a viscoelastic material, one that is often referred to as a "solid liquid." Experiments involve relaxation measurements taken over a range of deformations, to establish linearity, and scaled according to the optically determined contact radius. In addition, the data is Fourier analyzed to obtain the frequency response of both the real and imaginary components of the shear modulus. The results from such an analysis of a single 3s measurement are shown to be in remarkable agreement with published results from a series of single-frequency measurements using a classical rheometer. © 2005 Wiley Periodicals, Inc.

Micromachined microphones with diffraction-based optical displacement detection are introduced. The approach enables interferometric displacement detection sensitivity in a system that can be optoelectronically integrated with a multichip module into mm3 volumes without beamsplitters, focusing optics, or critical alignment problems. Prototype devices fabricated using Sandia National Laboratories' silicon based SwIFT-Lite™ process are presented and characterized in detail. Integrated electrostatic actuation capabilities of the microphone diaphragm are used to perform dynamic characterization in vacuum and air environments to study the acoustic impedances in an equivalent circuit model of the device. The characterization results are used to predict the thermal mechanical noise spectrum, which is in excellent agreement with measurements performed in an anechoic test chamber. An A weighted displacement noise of 2.4 × 10-2 Å measured from individual prototype 2100 μm × 2100 μm diaphragms demonstrates the potential for achieving precision measurement quality microphone performance from elements 1 mm2 in size. The high sensitivity to size ratio coupled with the ability to fabricate elements with precisely matched properties on the same silicon chip may make the approach ideal for realizing high fidelity miniature microphone arrays (sub-cm2 aperture) employing recently developed signal processing algorithms for sound source separation and localization in the audio frequency range. © 2005 Acoustical Society of America.

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