Comparison of cross-spectral and signal enhancement methods for mapping steady-state acoustic fields in turbomachinery ducts

The conceptual differences between the following two approaches used to measure spatial variations in steady-state acoustic pressure amplitude were examined: taking the cross spectrum between two signals from probes in the same field or taking the difference in complex Fourier transform of enhanced probe signals. Each approach is used to analyze pressure data from the inlets of two different turbomachines. A complete mapping of this steady-state field may then be used to determine its modal content. A problem with long term nonstationarity was found with both methods. Conditions for equivalence of the two methods are discussed

High frequency sound attenuation in short flow ducts

A geometrical acoustics approach is proposed as a practical design tool for absorbent liners in such short flow ducts as may be found in turbofan engine nacelles. As an example, a detailed methodology is presented for three different types of sources in a parallel plate duct containing uniform ambient flow. A plane wave whose wavefronts are not normal to the duct walls, an arbitrarily located point source, and a spatially harmonic line source are each considered. Optimal wall admittance distributions are found, and it is shown how to estimate the insertion loss for any admittance distribution. The extension of the methodology to realistic source distributions in variable area cylindrical or annular ducts containing arbitrary flow is shown to be conceptually straightforward and computationally practical on a vector-hardware digital computer

Effect of nonsymmetrical flow resistance upon orifice impedance resistance

A nonreactive orifice in an infinite baffle is analyzed. The pressure difference delta across the orifice varies sinusoidally with amplitude 1.0 and average value -P. The orifice resistance, delta p is discontinuous at zero velocity and exhibits the constant values R sub + and R sub - for u 0 and u 0, respectively. The resultant velocity has power in all harmonics of the excitation frequency. A quasi-linear resistance is defined and found to be relatively insensitive to the presence or absence of a resonant backing cavity; however, it does vary from 1.33 R sub + to 0.67 R sub + for a resistance ratio R sub +/R sub - between 0.5 and 2.0

Duct liner optimization for turbomachinery noise sources

An acoustical field theory for axisymmetric, multisectioned lined ducts with uniform flow profiles was combined with a numerical minimization algorithm to predict optimal liner configurations having one, two, and three sections. Source models studied include a point source located on the axis of the duct and rotor/outlet-stator viscous wake interaction effects for a typical research compressor operating at an axial flow Mach number of about 0.4. For this latter source, optimal liners for equipartition-of energy, zero-phase, and least-attenuated-mode source variations were also calculated and compared with exact results. It is found that the potential benefits of liner segmentation for the attenuation of turbomachinery noise is greater than would be predicted from point source results. Furthermore, effective liner design requires precise knowledge of the circumferential and radial modal distributions

Silver, Blood and Singing

Silver, Blood and Singing is a novel that is an exploration of the blurred lines between science fiction and fantasy in which the concepts of grief and mourning are explored. This thesis consists of a novel following two sisters and those around them as they try to come to terms with their grief. Along this journey they end up being opened up to worlds more dangerous and stranger than any they have come across before. As they explore these new worlds this functions as a place to examine the understanding of what it means to be a person and how to discern what’s even real

This Land is My Land: The Need for a Feasibility Test in Evaluation of Takings for Public Necessity

Federal and state governments, through the use of eminent domain, may condemn the property of a private landowner and use that property to meet a public necessity. If the landowner challenges the condemnation, the courts generally perform an extremely narrow review of the government\u27s decision to take the land. In order to prevail, the landowner must show either that the taking was in violation of constitutional or statutory provisions, or that some gross impropriety such as fraud or abuse of discretion occurred. However, landowners generally may not base their challenges on the grounds that the proposed project is unfeasible or unlikely to be completed. This notion that the feasibility of public necessity projects should never be judicially examined is clearly evidenced in two recent state cases: Itasca v. Carpenter and Comes v. City of Atlantic. In both of these cases, the government was allowed to condemn private lands for a public necessity, despite evidence that the land might never be used to alleviate that necessity. The practical effect of these holdings was to weaken the security of private land rights by making it easier for the government to exercise eminent domain powers. Although there will always be some possibility that a project designed to meet a public necessity will not be completed, this Note argues that landowners should be allowed to raise feasibility challenges in certain limited circumstances. Specifically, it proposes judicial means to limit the use of eminent domain in cases where the government is unlikely to use the condemned land to complete the necessity project, and suggests that judicial review of the feasibility of proposed necessity projects should be performed, in limited circumstances, through the application of a burden-shifting test. The Note concludes by addressing common arguments against judicial inquiry into the feasibility of necessity projects and by pointing out flaws in the economic reasoning of those arguments

Torque Tension Testing of Fasteners used for NASA Flight Hardware Applications

The effect of various lubricants and other compounds on fastener torque-tension relationships is evaluated. Testing was performed using a unique test apparatus developed by Posey at the NASA Goddard Space Flight Center. A description of the test methodology, including associated data collection and analysis will be presented. Test results for 300 series CRES and A286 heat resistant fasteners, torqued into various types of inserts will be presented. The primary objective of this testing was to obtain torque-tension data for use on NASA flight projects