Analysis and computer programs to calculate acoustic wave properties of baffled chambers

Analytical methods and four computer programs have been developed for calculating wave motion in closed, baffled chambers with rigid and non-rigid boundaries. Application of these methods to design of injector-face baffles in liquid propellant engines will provide significant insight into effects of baffles on combustion stability

Further analysis of the effects of baffles on combustion instability

A computerized analytical model, developed to predict the effects of baffles on combustion instability, was modified in an effort to improve the ability to properly predict stability effects. The model was modified: (1) to replace a single spatially-averaged response factor by separate values for each baffle compartment; (2) to calculate the axial component of the acoustic energy flux, and (3) to permit analysis of traveling waves in a thin annular chamber. Allowance for separate average response factors in each baffle compartment was found to significantly affect the predicted results. With this modification, an optimum baffle length was predicted which gave maximum stability

Advanced acoustic cavity technology

A series of rocket motor firings was performed in a modified linear aerospike thrust chamber with the H2/O2 propellant combination to allow determination of the physical properties of the combustion gases in acoustic cavities located in the chamber side walls. A preliminary analytical study was first conducted to define theoretically both the appropriate cavity dimensions and the combustion gas flow field adjacent to the cavity openings. During the subsequent motor firings, cavity gas temperature profiles were measured and gas samples were withdrawn from the bottom of the cavities for compositional analysis by measurement of pressure/temperature variation and gas chromatography. Data were obtained with both radially and axially oriented cavities and with and without hydrogen bleed flow through the cavities. A simplified procedure was developed for predicting gas cavity and acoustic velocity for use in acoustic cavity design analyses

High-temperature earth-storable propellant acoustic cavity technology

Design criteria, methods and data, were developed to permit effective design of acoustic cavities for use in regeneratively cooled OME-type engines. This information was developed experimentally from two series of motor firings with high-temperature fuel during which the engine stability was evaluated under various conditions and with various cavity configurations. Supplementary analyses and acoustic model testing were used to aid cavity design and interpretation of results. Results from this program clearly indicate that dynamic stability in regeneratively cooled OME-type engines can be ensured through the use of acoustic cavities. Moreover, multiple modes of instability were successfully suppressed with the cavity

Space shuttle maneuvering engine reusable thrust chamber program. Task 11: Stability analyses and acoustic model testing data dump

The combustion stability characteristics of engines applicable to the Space Shuttle Orbit Maneuvering System and the adequacy of acoustic cavities as a means of assuring stability in these engines were investigated. The study comprised full-scale stability rating tests, bench-scale acoustic model tests and analysis. Two series of stability rating tests were made. Acoustic model tests were made to determine the resonance characteristics and effects of acoustic cavities. Analytical studies were done to aid design of the cavity configurations to be tested and, also, to aid evaluation of the effectiveness of acoustic cavities from available test results

Analysis of the effects of baffles on combustion instability

An analytical model has been developed for predicting the effects of baffles on combustion instability. This model has been developed by coupling an acoustic analysis of the wave motion within baffled chambers with a model for the oscillatory combustion response of a propellant droplet developed by Heidmann. A computer program was developed for numerical solution of the resultant coupled equations. Diagnostic calculations were made to determine the reasons for the improper prediction. These calculations showed that the chosen method of representing the combustion response was a very poor approximation. At the end of the program, attempts were made to minimize this effect but the model still improperly predicts the stability trends. Therefore, it is recommended that additional analysis be done with an improved approximation

Understanding Cost-of-Care Conversations

Healthcare costs are increasing for patients. Choosing Wisely is an initiative of the American Board of Internal Medicine (AIMB) Foundation in partnership with Consumer Reports to promote conversations between physicians and patients to avoid unnecessary tests, procedures, and medications. The Choosing Wisely Initiative developed the resource “Five Questions to Ask Your Doctor” to support patient engagement in cost conversations and empower patients to ask questions about what care is right for them. The purpose of this study was to understand patients’ response to the “Five Questions”. Four focus groups were conducted in English and Spanish in rural and urban communities in Central California. Participants represented an ethnically, racially, and socioeconomically diverse sample (including those who are below the 400% Federal Poverty Level), and those who were between 30 and 64 years of age. In each focus group patients provided information about their individual healthcare costs, completed a scenarios survey, watched a patient/doctor interaction video, and responded to the “Five Questions”. Analysis of the interview transcripts focused on the following: identifying overarching themes, identifying ways to tailor messages to patients, and characterizing themes of preservation of trust during cost-of-care conversations. Patients’ trust in the authority of their doctor was a common theme across participants that reoccurred throughout the interview. Other themes included asking about options, variable quality of care, limited time with their doctor, educating yourself, and self-advocacy. Results suggest that the “Five Questions” to ask your doctor is an effective approach to promote patient-doctor conversations about cost and self-advocacy among patients

Analysis of combustion instability in liquid propellant engines with or without acoustic cavities

Analytical studies have been made of the relative combustion stability of various propellant combinations when used with hardware configurations representative of current design practices and with or without acoustic cavities. Two combustion instability models, a Priem-type model and a modification of the Northern Research and Engineering (NREC) instability model, were used to predict the variation in engine stability with changes in operating conditions, hardware characteristics or propellant combination, exclusive of acoustic cavity effects. The NREC model was developed for turbojet engines but is applicable to liquid propellant engines. A steady-state combustion model was used to predict the needed input for the instability models. In addition, preliminary development was completed on a new model to predict the influence of an acoustic cavity with specific allowance for the effects the nozzle, steady flow and combustion

Effect of Short-Term Exposure to Low pH and Low Dissolved Oxygen on the Swimming Performance of Juvenile Rockfish

Organisms living in coastal habitats off northern California coast are exposed to low pH and low dissolved oxygen water during strong upwelling events, but the effects of these events on coastal fishes is poorly understood. We examined the effects of short-term (1 to 24 hour) exposures to low pH (pH ~ 7.5) or low dissolved oxygen (DO; 50% O2 saturation) on the swimming performance of juvenile rockfish (Sebastes spp.). Juvenile copper rockfish (Sebastes caurinus) were collected from Trinidad Bay, and, following acclimation to laboratory conditions, were exposed to treatment conditions for intervals of 0 (control), 1, 2, 4, 8, or 24 hours. We measured critical swimming speed (uCrit)—a metric of swimming performance that integrates speed and endurance—by placing each fish into a swimming flume and increasing current speed according to a timed, stepwise sequence until exhaustion. Short-term exposures cause a decline in uCrit, with increasingly strong effect developing from 0-4 hours. Swimming performance remains depressed over longer exposures, but it is possible that recovery from initial handling stress might offset continued declines in swimming performance. Ongoing work is addressing a potential size-dependence in response to exposure, and will examine the effect of simultaneous exposure to low-pH/low-DO water, as these conditions naturally co-occur. Insights from this study address the potential ecological effects of upwelling events, which may have important demographic consequences for these ecologically and economically important species, as well as the potential consequences of increasing frequency, duration, and intensity of upwelling-driven exposures and increasing levels of global ocean acidification predicted under ongoing climate change