Selected Publications
Kent L. Gee, Tracianne B. Neilsen, and Alan T. Wall (et al.)
Noise measurements near the F-35A Joint Strike Fighter at military power are analyzed via spatial maps of overall and band pressure levels and skewness. Relative constancy of the pressure waveform skewness reveals that waveform asymmetry, characteristic of supersonic jets, is a source phenomenon originating farther upstream than the maximum overall level. Conversely, growth of the skewness of the time derivative with distance indicates that acoustic shocks largely form through the course of near-field propagation and are not generated explicitly by a source mechanism. These results potentially counter previous arguments that jet "crackle" is a source phenomenon. (C) 2013 Acoustical Society of America
Kent L. Gee, Tracianne B. Neilsen, and Trevor W. Jerome (et al.)
As part of investigations into the design of next-generation launch vehicles, near and far-field data were collected during horizontal static firings of reusable solid rocket motors. In addition to spectral analysis at individual microphone locations, the spatial and temporal variation of overall and one-third octave band pressure levels at sideline and polar arc arrays is considered. Analysis of the probability density functions reveals positively skewed pressure waveforms, but extreme skewness in the first-order estimate of the time derivative because of the presence of significant acoustic shocks. However, plume impingement is the likely cause of reduced high-frequency levels and skewness at far-downstream positions.
As noise continues to grow as a significant design concern, the importance of proper measurement techniques is becoming more crucial. The focus of this chapter is to provide a working knowledge of the basic acoustical or sound measurements and measurement techniques for the practicing engineer. The chapter will also provide a broad overview and introduction to more advanced acoustical measurement methods. There are several published documents including tutorials on the proper methods for measuring sound. This chapter is heavily referenced pointing the reader to these excellent sources of infonnation.
Alan T. Wall, Kent L. Gee, and Tracianne B. Neilsen (et al.)
It is desirable to isolate independent noise sources in jets for targeted noise reduction methodologies. The application of traditional partial field decomposition (PFD) techniques to jet noise fields is useful for estimating the number of incoherent (equivalent) noise sources within a jet and for implementing near-field acoustical holography, but it does not generally provide physically meaningful partial fields (i.e. partial fields related to individual sources). The method developed by Kim et al. [JASA 115(4), 2004] finds the optimal locations of references in a sound field and places virtual references at those locations. In past investigations this method has been successfully applied to locate discrete numerical and physical sources and to generate partial fields related to each source. In this study, Kim's method is applied to a full-scale jet installed on a military aircraft to obtain physically meaningful partial fields. [Work supported by ONR.]
Troy Taylor, Kent L. Gee, Jarom H. Giraud, Scott D. Sommerfeldt, and Jonathan D. Blotter (et al.)
The acoustic field near large-scale solid rocket motors represents a harsh, high-amplitude noise environment rich with high-bandwidth acoustic shocks. Type-1 prepolarized microphones may be used in these environments with the benefit of reduced cost and measurement because they require only a constant-current supply available in many data acquisition systems. However, there are two potential issues related to microphone response that should be considered. The first is a well-known RC-lowpass filter effect that is associated with using insufficient current to drive long cables with relatively high capacitance. The second has to do with temporary failure of the constant-current supply due to an insufficiently fast response time in representing rapid voltage changes at shocks, which results in spurious, capacitive-like effects in the waveform data that are also manifest as a low-frequency roll-up in the spectrum noise floor. An experiment was conducted to identify under what circumstances these waveform effects arise. Data were measured from a solid rocket motor using several combinations of transducer, cable type, cable length and constant current supply. Results and mitigation methods found from the experiment are discussed. These include increasing the supply current, using low-impedance cables, and selecting microphones with low sensitivities.
The current acoustics program at Brigham Young University reflects efforts intended to better prepare students for jobs in industry, research, and academia. In the classroom, ongoing modifications to courses are intended to provide students with a solid foundation in core acoustics principles and practices. A new advanced undergraduate course has been developed to provide students with formal training in acoustics prior to the graduate level and prepare them for research, internships, and entry-level acoustics positions. In the laboratory, graduate students not only carry out research of significance, but often serve as peer mentors to undergraduate students new to the group. This permits undergraduate students greater opportunity to participate meaningfully in research activities and has resulted in an increase in undergraduate-authored presentations and publications.