1,136 research outputs found
ASSESSING AND MITIGATING AIRBORNE NOISE FROM POWER GENERATION EQUIPMENT
This dissertation examines the assessment and mitigation of airborne noise from power generation equipment.
The first half of the dissertation investigates the diagnosis and treatment of combustion oscillations in boilers. Sound is produced by the flame and is reflected downstream from the combustion chamber. The reflected sound waves perturb the mixture flow or equivalence ratio increasing the heat release pulsations and the accompanying sound produced by the flame. A feedback loop model for determining the likelihood of and diagnosing combustion oscillations was reviewed, enhanced, and then validated. The current work applies the feedback loop stability model to two boilers, which exhibited combustion oscillations. Additionally, a feedback loop model was developed for equivalence ratio fluctuations and validated. For the first boiler, the combustion oscillation problem is primarily related to the geometry of the burner and the intake system. For the second boiler, the model indicated that the combustion oscillations were due to equivalence ratio fluctuations. Principles for both measuring and simulating the acoustic impedance are summarized. An approach for including the effect of structural-acoustic coupling was developed. Additionally, a method for determining the impedance above the plane wave cut-off frequency, using the acoustic FEM, of the boiler was proposed.
The second half of the dissertation examines the modeling of bar silencers. Bar silencers are used to mitigate the airborne noise from large power generation equipment (especially gas turbines). Due to the large dimensions of the full cross section, a small representative cell is isolated from the entire array for analysis purposes. To predict the acoustical performance of the isolated cell for different geometric configurations, a numerical method based on the direct mixed-body boundary element method (BEM) was used. An analytical solution for a simplified circular geometry was also derived to serve as a comparison tool for the BEM. Additionally, a parametric study focusing on the effects of flow resistivity, perforate porosity, length of bars, and cross-sectional area ratio was performed. A new approach was proposed to evaluate the transmission loss based on a reciprocal work identity. Moreover, extension of the transmission loss computation above the plane wave cut-off frequency was demonstrated
Functions of Conversation in Detective Fiction: An Analysis of Smiley’s Duplicate Keys From Grice’s Theory of Conversational Implicature
Duplicate Keys, published in 1984, is a detective novel written by Pulitzer Laureate Jane Smiley. The novel develops around a murder discovered by Alice, the heroine, in Manhattan, in which two band members, Denny and his adopted brother Craig, were shot dead in Denny’s apartment. Since besides Alice, some of their other friends, and even their friends’ friends have duplicate keys, it’s extremely distracting and difficult for Police Detective Honey to solve the case. With suspense resolved and mystery unraveled, it turns out that the killer is Denny’s girlfriend and Alice’s best friend Susan, who pretends to be on a trip far away at the occurrence of the murder. The novel contains an abundance of conversations, which play a crucial part in plot advancement as well as characterization. Guided by Paul Grice’s theory of conversational implicature, the paper analyzes some conversations from Duplicate Keys, especially the disobedience of the cooperative principle in the conversations, deciphers the reasons behind the disobedience, while at the same time exposes characters’ inner world, and exhibits their personality traits. In so doing, functions of conversation in detective fiction are revealed.
A Program Logic for Verifying Secure Routing Protocols
The Internet, as it stands today, is highly vulnerable to attacks. However,
little has been done to understand and verify the formal security guarantees of
proposed secure inter-domain routing protocols, such as Secure BGP (S-BGP). In
this paper, we develop a sound program logic for SANDLog-a declarative
specification language for secure routing protocols for verifying properties of
these protocols. We prove invariant properties of SANDLog programs that run in
an adversarial environment. As a step towards automated verification, we
implement a verification condition generator (VCGen) to automatically extract
proof obligations. VCGen is integrated into a compiler for SANDLog that can
generate executable protocol implementations; and thus, both verification and
empirical evaluation of secure routing protocols can be carried out in this
unified framework. To validate our framework, we encoded several proposed
secure routing mechanisms in SANDLog, verified variants of path authenticity
properties by manually discharging the generated verification conditions in
Coq, and generated executable code based on SANDLog specification and ran the
code in simulation
Efficient Frozen Gaussian Sampling Algorithms for Nonadiabatic Quantum Dynamics at Metal Surfaces
In this article, we propose a Frozen Gaussian Sampling (FGS) algorithm for
simulating nonadiabatic quantum dynamics at metal surfaces with a continuous
spectrum. This method consists of a Monte-Carlo algorithm for sampling the
initial wave packets on the phase space and a surface-hopping type stochastic
time propagation scheme for the wave packets. We prove that to reach a certain
accuracy threshold, the sample size required is independent of both the
semiclassical parameter and the number of metal orbitals ,
which makes it one of the most promising methods to study the nonadiabatic
dynamics. The algorithm and its convergence properties are also validated
numerically. Furthermore, we carry out numerical experiments including
exploring the nuclei dynamics, electron transfer and finite-temperature
effects, and demonstrate that our method captures the physics which can not be
captured by classical surface hopping trajectories.Comment: 41 pages, 10 figure
Noise Folding in Completely Perturbed Compressed Sensing
This paper first presents a new generally perturbed compressed sensing (CS) model y=(A+E)(x+u)+e, which incorporated a general nonzero perturbation E into sensing matrix A and a noise u into signal x simultaneously based on the standard CS model y=Ax+e and is called noise folding in completely perturbed CS model. Our construction mainly will whiten the new proposed CS model and explore in restricted isometry property (RIP) and coherence of the new CS model under some conditions. Finally, we use OMP to give a numerical simulation which shows that our model is feasible although the recovered value of signal is not exact compared with original signal because of measurement noise e, signal noise u, and perturbation E involved
- …