SRM attrition rate study of the aft motor case segments due to water impact cavity collapse loading

The attrition assessment of the aft segments of Solid Rocket Motor due to water impact requires the establishment of a correlation between loading occurrences and structural capability. Each discrete load case, as identified by the water impact velocities and angle, varies longitudinally and radially in magnitude and distribution of the external pressure. The distributions are further required to be shifted forward or aft one-fourth the vehicle diameter to assure minimization of the effect of test instrumentation location for the load determinations. The asymmetrical load distributions result in large geometric nonlinearities in structural response. The critical structural response is progressive buckling of the case. Discrete stiffeners have been added to these aft segments to aid in gaining maximum structural capability for minimum weight addition for resisting these loads. This report presents the development of the attrition assessment of the aft segments and includes the rationale for eliminating all assessable conservatisms from this assessment

Post-Fire Erosion Following the CZU Lightning Complex Fire: Quantifying Hillslope Erosion and Providing Guidance Towards Improving Post-Fire Response

The size and severity of wildfires have increased in California during recent decades. This trend is highlighted through the CZU Lightning Complex fire of August 2020 which burned over 86,000 acres in the Santa Cruz mountains of California. The fire greatly impacted the Little Creek watershed, a roughly 1,300 acre watershed that exists largely within Cal Poly San Luis Obispo’s Swanton Pacific Ranch (SPR). The current trends of California’s increased wildfire regime are expected to continue, raising concerns regarding the direct and secondary effects on forest watersheds and the effectiveness of current post-fire erosion control management. Accelerated rates of erosion following wildfire have been found to occur due to the loss of vegetation cover and changes in soil physical properties. We measured hillslope erosion from ten plots at SPR using a silt fence erosion trap approach to study regional post-fire erosion dynamics in the second winter following the CZU Lightning Complex fire. Slope steepness, percent soil cover, and percent canopy coverage were found to be significant factors driving changes in post-fire hillslope erosion in a multivariate model (R2=0.88). Field-collected data from the erosion plots was used to inform spatial extrapolation of hillslope erosion and sediment delivery rates for the entire Little Creek watershed under different soil cover and precipitation scenarios using the Universal Soil Loss Equation (USLE). A watershed average hillslope erosion rate was found to be 4.23 tons/acre/year during the study period from October 2021-March 2022, a 53-fold increase when compared to pre-fire erosion rates and surpassing the watershed average soil loss tolerance factor. Annual sediment delivery to streams within the Little Creek watershed was quantified at 1.16 tons/acre from contributing hillslopes, a 58-fold increase from pre-fire sediment delivery. Using the information obtained from the results from this study, a review of scientific literature, and interviews with relevant stakeholders, we also identify current issues limiting the effectives of post-fire erosion control and provide recommended policy changes and best management practices to mitigate these problems. The results of this study provide valuable information and context regarding post-fire erosion dynamics in the Santa Cruz region and inform future managing decisions aimed mitigating accelerated rates of erosion following wildfire

SRB water impact velocity trade study

The results of the attrition/cost studies which formulated the data base for the recommendation to reduce the Space Shuttle Solid Rocket Booster's nominal vertical water impact velocity to 85 feet per second is presented

Characterization of the Optical and Electrical Properties of Proton-Irradiated 4H-Silicon Carbide

Epitaxial n-type 4H-silicon carbide (SiC) is irradiated with 2 MeV protons to evaluate the dislocation damage effects on the optical and electrical characteristics of the material. Semiconductor materials with a high tolerance to radiation fields have applications in several aerospace power and satellite systems. SiC is under investigation due to its potential for such space material applications. The optical properties of the material are investigated using temperature-dependent photoluminescence (PL) and the effects of proton irradiation on the electrical properties are evaluated using current-voltage measurements and constant-voltage deep level transient spectroscopy (CV-DLTS). Subsequent high-temperature thermal annealing and recovery of the irradiated material is investigated over the temperature range of 900 – 1500 °C. Proton-induced irradiation damage is apparent in the 4H-SiC material, affecting both the optical and electrical characteristics of the devices. The radiative behavior of the nitrogen-related near band edge transitions is significantly reduced as a result of the irradiation with partial recovery observed after high-temperature thermal annealing at 1500 °C. A deeper trapping complex (EC-ET ≅ 380 meV) is detected as a result of irradiation and shows signs of activation due to thermal annealing. Initial indications taken from I-V measurements of the Schottky diodes reveal that proton irradiation followed by thermal annealing at 900 °C may, in fact, enhance the rectifying device characteristics. Increasing the anneal temperature (TA = 1300 °C) causes the device to fail entirely. Further annealing of the irradiated 4H-SiC at 1500 °C demonstrates recovery in the rectifying behavior of the material. Significant levels of deep level donor traps are observed, induced by irradiation in n-type material. Three detectable defect pairs emerge with energy levels ranging from 570 – 730 meV below the conduction band. The trap parameters were determined using curve-fitting algorithms. Upon high-temperature thermal annealing of the material, the trap center pairs showed little change in the energy levels and capture cross-sections while the density of traps decreased as temperatures increased. Full recovery of the material characteristics is not apparent after annealing at 1500 °C

Sessile droplet evaporation on superheated superhydrophobic surfaces

This fluid dynamics video depicts the evaporation of sessile water droplets placed on heated superhydrophobic (SH) surfaces of varying cavity fraction, F_c, and surface temperature, T_s, above the saturation temperature, T_sat. Images were captured at 10,000 FPS and are played back at 30 FPS in this video. Teflon-coated silicon surfaces of F_c = 0, 0.5, 0.8, and 0.95 were used for these experiments. T_s ranging from 110{\deg}C to 210{\deg}C were studied. The video clips show how the boiling behavior of sessile droplets is altered with changes in surface microstructure. Quantitative results from heat transfer rate experiments conducted by the authors are briefly discussed near the end of the video.Comment: videos include

Analyses of Nutrient and E. Coli Contamination Within the Otter Creek Watershed, Madison County, KY

The Otter Creek watershed exhibits dissolved nutrient (ammonium, NH41+; nitrate, NO31-; phosphate, PO43-) and Escherichia coli contamination that compromises its water quality. The watershed covers a substantial portion of Madison County (~168 km2) and consists of Lake Reba, Dreaming Creek, and east and west forks, all of which enter the trunk of Otter Creek before flowing into the Kentucky River. Suspected contaminate sources include leaky sewage system pipes, runoff from pasture land, and septic system leachate. We collected 330 water samples on three occasions during summer 2014 to determine the extent and sources of contamination, in hopes to mitigate contamination and improve water quality. Nutrients were measured using colorimetric methods, whereas E. coli counts were determined by using IDEXX materials. We found highest nutrient concentrations immediately below discharge from the Otter Creek sewage treatment plant (STP), which is a point source for nitrate (3.5 – 4.4 mg/L N-NO3) and phosphate (0.8 - 1.0 mg/L P-PO3). Background levels were ~0.4 mg/L N-NO3 and ~0.09 mg/L P-PO4. Nitrate and phosphate values progressively decrease at stations downstream from the STP. Ammonium averages ~0.4 mg/L N-NH4, ranging from 0 to 1.4 mg/L in May, but measurable ammonium occurs only sporadically in June and July. The highest observed value is 1.8 mg/L N-NH4 (station CC, June) with the majority of stations having no measurable ammonium. 53% of samples exceeded EPA E.coli concentration standards for human contact (\u3e575 cfu/100 mL) and are distributed throughout the watershed, displaying classic non-point-source pollution.Phosphate and fecal microbes are the principal contaminants within the watershed. Compared to a national data set, phosphate contamination is most severe, often exceeding the 90th percentile value. Nitrate is generally below the 25th percentile level. Ammonium concentration is not related to STP discharge but exceeds the 90th percentile value in May; concentrations approach those of pristine streams in June and July. Non-point sources for nitrate, phosphate, and E. coli are likely due to leaky sewage pipes within the town of Richmond, and to pasture runoff in rural areas. Ammonium sources are more enigmatic, but seem associated with pasture land and septic systems. Sampling in June and July after rain events saw higher nitrate, phosphate, and E. coli concentrations, but lower ammonium levels relative to measurements in May