Acoustical evaluation of the NASA Langley full-scale wind tunnel

Determining types of acoustical measurements suitable for test section of NASA Langley wind tunne

Acoustical modeling study of the open test section of the NASA Langley V/STOL wind tunnel

An acoustic model study was carried out to identify effective sound absorbing treatment of strategically located surfaces in an open wind tunnel test section. Also an aerodynamic study done concurrently, sought to find measures to control low frequency jet pulsations which occur when the tunnel is operated in its open test section configuration. The acoustical modeling study indicated that lining of the raised ceiling and the test section floor immediately below it, results in a substantial improvement. The aerodynamic model study indicated that: (1) the low frequency jet pulsations are most likely caused or maintained by coupling of aerodynamic and aeroacoustic phenomena in the closed tunnel circuit, (2) replacing the hard collector cowl with a geometrically identical but porous fiber metal surface of 100 mks rayls flow resistance does not result in any noticable reduction of the test section noise caused by the impingement of the turbulent flow on the cowl

Potential uses of vacuum bubbles in noise and vibration control

Vacuum bubbles are new acoustic elements which are dynamically more compliant than the gas volume they replace, but which are statically robust. They are made of a thin metallic shell with vacuum in their cavity. Consequently, they pose no danger in terms of contamination or fire hazard. The potential of the vacuum bubble concept for noise and vibration control was assessed with special emphases on spacecraft and aircraft applications. The following potential uses were identified: (1) as a cladding, to reduce sound radiation of vibrating surfaces and the sound excitation of structures, (2) as a screen, to reflect or absorb an incident sound wave, and (3) as a liner, to increase low frequency sound transmission loss of double walls and to increase the low frequency sound attenuation of muffler baffles. It was found that geometric and material parameters must be controlled to a very high accuracy to obtain optimal performance and that performance is highly sensitive to variations in static pressure. Consequently, it was concluded that vacuum bubbles have more potential in spacecraft applications where static pressure is controlled more than in aircraft applications where large fluctuations in static pressure are common

Acoustical Evaluation of the NASA Langley V/STOL Wind Tunnel

The results are presented of the acoustical measurements made to supply NASA Langley operating personnel with the acoustical characteristics of the tunnel test section needed for the planning of acoustical measurements and to identify the major noise sources. The results of the preliminary measurements of the spatial distribution of the sound field in the closed tunnel configuration indicate that the total sound power output of an unknown sound source placed in the test section could most probably be evaluated by measuring the sound pressure in two properly chosen locations in the duct - one upstream and one downstream of the test section. However, it is recommended that the practicability of this method of sound power output measurements be further investigated, preferably in a small scale model of the V/STOL Tunnel

Reciprocity-based experimental determination of dynamic forces and moments: A feasibility study

BBN Systems and Technologies has been tasked by the Georgia Tech Research Center to carry Task Assignment No. 7 for the NASA Langley Research Center to explore the feasibility of 'In-Situ Experimental Evaluation of the Source Strength of Complex Vibration Sources Utilizing Reciprocity.' The task was carried out under NASA Contract No. NAS1-19061. In flight it is not feasible to connect the vibration sources to their mounting points on the fuselage through force gauges to measure dynamic forces and moments directly. However, it is possible to measure the interior sound field or vibration response caused by these structureborne sound sources at many locations and invoke principle of reciprocity to predict the dynamic forces and moments. The work carried out in the framework of Task 7 was directed to explore the feasibility of reciprocity-based measurements of vibration forces and moments

Measurements of the reflection factor of flat ground surfaces

Measurements are made of the reflection factors of asphalt, concrete, and sod at oblique angles of incidence. Initial measurements were carried out in an anechoic chamber to eliminate the effects of wind and temperature gradients. These were followed by measurements made outdoors over a wider frequency range. Data are presented for the magnitudes of the reflection factors of asphalt, concrete, and sod at angles of incidence of 38 deg and 45 deg

Case history of the Fortymile Caribou Herd, 1920-1990

Early this century, the Fortymile caribou herd was the largest in Alaska and one of the largest in the world. Since the 1940s the herd has remained relatively small, fluctuating between 6000-8000 and about 50 000. To determine possible limiting factors, we reviewed historical fluctuations in herd since and harvest, historical data on wolf numbers and summer and winter weather. The major decline in herd size from 1963 to 1973 was accompanied by high wolf numbers, some years of unfavorable winter and summer weather, and some years of high harvests. From 1974 to 1990 the Fortymile herd failed to recover as well as the adjacent Nelchi-na herd and provided less than one-fourth the harvest despite favorable winter conditions in both areas. Two notable differences between these herds were that (1) wolves were less strongly limited within the range of the Fortymile herd, and (2) moose as alternate prey for wolves remained more abundant within the range of the Nelchina herd

Cholecystectomy Is Risker in Male Patients

Introduction: While cholecystitis has a female preponderance, some observe a trend towards more challenging disease in male patients. The confluence of sex and patient acuity has not been thoroughly investigated. We hypothesize that men present with worse disease compared with women, as evidenced by higher rates of open surgery and higher resource consumption. Methods: An inpatient registry from a 5-hospital system was queried for cholecystectomy procedures not associated with neoplasm or malignancy. Cases from 2015 to 2021 were included. Demographics, clinical and outcome variables were analyzed. Univariate analysis and multivariate logistic regression were performed. The data were de-identified before analysis and deemed exempt from IRB review, and were analyzed using R within R-Studio. Results: There were 2789 cholecystectomy patients, 1616 (58%) were women and 1173 (42%) were men. Demographics and baseline health characteristics differed across sex. Univariate analysis highlighted that males experienced more harms (1.35 vs 1.14; p = 0.002), more open approaches (18% vs 11%; p \u3c 0.001), longer inpatient lengths of stays (median: 4 vs 3 days; p \u3c 0.001), higher hospital cost ($15,694 vs$13,173; p \u3c 0.001), increased laboratory orders (37.65 vs 30.01; p \u3c 0.001), higher MS-DRG weight (2.104 vs 1.842; p \u3c 0.001) and greater mortality risk (56% vs 36%; p \u3c 0.001). Further, multivariate analysis found male cholecystectomy patients were correlated with higher instances of open surgical approach (OR: 1.80; p \u3c 0.001), hospital readmission (OR: 1.50; p = 0.008), and higher cost (β: $981; R2: 0.27; p = 0.006). Conclusion: Inpatient male cholecystectomy patients present with worse disease and require more hospital resources