Selected experiments in laminar flow: An annotated bibliography

Since the 1930s, there have been attempts to reduce drag on airplanes by delaying laminar to turbulent boundary layer transition. Experiments conducted during the 1940's, while successful in delaying transition, were discouraging because of the careful surface preparation necessary to meet roughness and waviness requirements. The resulting lull in research lasted nearly 30 years. By the late 1970s, airframe construction techniques had advanced sufficiently that the high surface quality required for natural laminar flow (NLF) and laminar flow control (LFC) appeared possible on production aircraft. As a result, NLF and LFC research became widespread. This report is an overview of that research. The experiments summarized herein were selected for their applicability to small transonic aircraft. Both flight and wind tunnel tests are included. The description of each experiment is followed by corresponding references. Part One summarizes NLF experiments; Part Two deals with LFC and hybrid laminar flow control (HLFC) experiments

Dynamic structural analysis of ramming in bighorn sheep

Includes bibliographical references.2015 Fall.Concussions are the most common traumatic brain injury and are caused by impulsive loads applied to the skull, resulting in relative motion of the brain within the brain cavity. Despite wearing helmets, athletes involved in full contact sports, such as football, are highly susceptible to concussive injuries. Short term symptoms of concussions include nausea, headache and confusion and there is evidence of more serious, long term effects from repeated concussions. Furthermore, the physical mechanisms of concussions are not well understood, making them difficult to diagnose and treat clinically. Male bighorn sheep sustain massive impact loads to the head during ramming, which is done as a means of determining hierarchy and gaining mating privileges. These large animals thrust themselves, horns first, at one another and collide violently, repeating this ritual for up to several hours until the subdominant male succumbs. After a collision, the animals are stunned momentarily but otherwise appear to suffer no ill effects, based on behavioral observations. This simple fact provided the motivation to examine the dynamic structural behavior of bighorn sheep horns and skulls. For reference, the average translational brain cavity accelerations observed during finite element model impact were found to be 111g (1091 m/s²) and impacts thought to be damaging to human brains occur at around 100g. A dynamic finite element impact model was produced using the geometry, obtained from a CT scan, of a mature male bighorn sheep’s skull and horns. Quantitative and qualitative results of the simulation were examined to determine mechanisms of energy dissipation and stress distribution during an idealized impact event. Video analysis of particularly forceful ramming sequences of wild bighorn sheep was carried out to estimate the dynamics involved with ramming. In order to investigate the relative contributions of the horn curl as well as the internal foamy bone architecture, three separate finite element models were produced. One model had one half of the horn length removed, another had the internal foam-like bone removed and these models were compared to the fully intact model to determine the structural contributions of these features during impact. Removing one half of the horn curl had the effect of increasing the peak brain cavity translational acceleration by 49%. Eliminating the internal foamy bone architecture resulted in a dramatic 442% increase in brain cavity rotational accelerations. The dynamic (vibrational) response of bighorn sheep horns and skulls was investigated using two, related methods: finite element modal analysis and experimental modal analysis. The finite element modal analysis revealed five dominant natural frequencies with values ranging from 118 to 309 Hz. Experimental modal analysis revealed several natural frequencies between 100 and 300 Hz, however, differentiating specific modes was difficult. For both vibrational analyses the dominant vibrational mode shape was side-to-side oscillations of the horn tip. This study hopes to promote and guide further research on the mechanisms of brain trauma prevention in bighorn sheep, with an emphasis on the structural and material characteristics of the horn and skull, to increase our understanding of, and ways to prevent traumatic brain injuries in humans

Using unmanned aerial vehicles (‘drones’) to collect data from tagged fishers in the environment

Fisher (Pekania pennant) belongs to the weasel family. In October 2014, the United States Fish and Wildlife Service proposed to list the West Coast Distinct Population Segment of fisher as threatened under the Endangered Species Act. We wish to better define where fishers live within their habitats and use that information to improve conservation efforts. Previously, to track the behavior of wild fishers, researchers put tracker collars on the animals and relied on networks of fixed antennas on the ground in the environment to collect data. We are experimenting with using unmanned aerial vehicles (‘drones’) to collect data from tagged fishers in the environment. Using drones could offer advantages over antennas that require a dedicated power source and are placed in the field long-term

Flight Readiness Review (FRR): Are you ready to fly?

A Flight Readiness Review evaluates the readiness to begin and safely conduct flight tests or flight operations. FRR approval is necessary in order to determine that the system under review can proceed into its test environment having met the standards to be considered airworthy. These standards require that the aviation system be under configuration management, have flight clearance, approved flight test plans, discrepancy tracking, and appropriate risk assessment processes in place. As an Autonomous Flight Lab we are interested in developing a protocol that will make this processes more accessible to individuals trying to utilize UAVs for various research projects. Currently there is no process in place to assist individuals in preparing an FRR. We have been working on generating a user friendly guide to developing quality student presentations in the form of FRRs. We began by observing student FRR presentations, determining the best procedure for risk assessment, and specifying base line operation requirements. In order to do so one must first identify the vehicle being used, the mission details, the necessary crew members, and the operational environment. Ultimately we hope that by having a procedure in place to assist individuals in developing FRRs, we can greatly reduce lab member dependency and need for multiple FRR revisions

Artists have superior local and global processing abilities but show a preference for initially drawing globally

The attentional demands of drawing require both local processing of an object’s details and global processing of its overall structure. In this study, we examined the extent to which artists have superior local and global processing skills, how these skills relate to artists’ ability to draw realistically and to autistic-related traits, and whether artists initially take a local or global approach to drawing. Forty first-year college art students and 41 nonart students completed two tasks assessing local processing and two tasks assessing global processing. Participants completed two drawing tasks that assessed their ability to draw realistically, two copying tasks that assessed whether they showed a preference for initially copying the local or global aspects of an object, and the Autism-Spectrum Quotient that assessed autistic-related traits. We found that art students outperformed nonart students on both the local and global processing tasks and that drawing ability was related to performance on these tasks. We also found that art students were more likely than nonart students to initially copy the global features in their drawings. Finally, we found that art students did not exhibit more autistic-related traits than nonart students and that the number of autistic-related traits was unrelated to performance on the local and global processing, drawing, or copying tasks. These results suggest that art students have an attentional flexibility that allows them to process information at a local and global level but that they have a preference for initially drawing globally

Experimental Modeling and Laboratory Measurements of Drag Embedment Anchors Subjected to In-Plane and Out-Of-Plane Loading

Extreme hurricane events of the past decade are responsible for several drag embedment anchor (DEA) mooring failures of mobile offshore drilling platforms stationed within the Gulf of Mexico. A proposed failure mechanism is caused by out-of-plane loading. The current status of DEA holding capacity is based on empirical design charts and does not include the effects of out-of-plane loading. Experimental modeling using a 1:10 scale generic DEA was performed at the Haynes Coastal Engineering Laboratory at Texas A & M University to examine the effects of out-of-plane load conditions. Instrumentation and specialized devices were constructed to measure the anchor's trajectory through a representative sample of Gulf of Mexico clay with average un-drained shear strength of 0.764 kPa (16 psf). The sediment basin allowed for drag distances of 4.87 m (16 ft) and an embedment depth of 1.37 m (4.5 ft). The measurements included pitch and roll of the anchor and line tension measured at the shank pad-eye. The variables modeled were fluke angle settings of 22°, 36° and 50°. The initial towline angle was varied from a minimum of 5° to upwards of 20°. Surface out-of-plane angles of 45° and 90° and embedment loading of 15°, 30° and 45° were examined. Curves of the ultimate holding capacity with respect to the out-of-plane towline angle and ultimate embedment depth were developed as functions of out-of-plane loading angles. Analysis of the rate effect indicates that a 46 percent increase in towing velocity causes an average 3 percent increase of holding capacity. The 50° fluke angle embeds an average of 0.7 fluke lengths deeper and has a holding capacity of 0.73 units greater than the 36° setting. The surface out-of-plane tests have a 5.1 percent reduction in holding capacity as the out-of-plane load angle increases from 45° to 90°. For all one fluke length initial towing distance tests, the ultimate holding capacity increases and the ultimate embedment depth decreases as the out-of-plane towing angle increases from 15° to 45°. The three fluke length initial towing distance tests indicate a contrasting trend, in that as the out-of-plane tow angle increases, both the ultimate holding capacity and ultimate embedment depth decrease

A Heating Mechanism via Magnetic Pumping in the Intracluster Medium

Turbulence driven by AGN activity, cluster mergers and galaxy motion constitutes an attractive energy source for heating the intracluster medium (ICM). How this energy dissipates into the ICM plasma remains unclear, given its low collisionality and high magnetization (precluding viscous heating by Coulomb processes). Kunz et al. 2011 proposed a viable heating mechanism based on the anisotropy of the plasma pressure (gyroviscous heating) under ICM conditions. The present paper builds upon that work and shows that particles can be gyroviscously heated by large-scale turbulent fluctuations via magnetic pumping. We study how the anisotropy evolves under a range of forcing frequencies, what waves and instabilities are generated and demonstrate that the particle distribution function acquires a high energy tail. For this, we perform particle-in-cell simulations where we periodically vary the mean magnetic field $\textbf{B}(t)$. When $\textbf{B}(t)$ grows (dwindles), a pressure anisotropy $P_{\perp}>P_{\parallel}$ ($P_{\perp}< P_{\parallel}$) builds up ($P_{\perp}$ and $P_{\parallel}$ are, respectively, the pressures perpendicular and parallel to $\textbf{B}(t)$). These pressure anisotropies excite mirror ($P_{\perp}>P_{\parallel}$) and oblique firehose ($P_{\parallel}>P_{\perp}$) instabilities, which trap and scatter the particles, limiting the anisotropy and providing a channel to heat the plasma. The efficiency of this mechanism depends on the frequency of the large-scale turbulent fluctuations and the efficiency of the scattering the instabilities provide in their nonlinear stage. We provide a simplified analytical heating model that captures the phenomenology involved. Our results show that this process can be relevant in dissipating and distributing turbulent energy at kinetic scales in the ICM.Comment: 24 pages, 17 figures, submitted to Ap

A new physical interpretation of optical and infrared variability in quasars

Changing-look quasars are a recently identified class of active galaxies in which the strong UV continuum and/or broad optical hydrogen emission lines associated with unobscured quasars either appear or disappear on timescales of months to years. The physical processes responsible for this behaviour are still debated, but changes in the black hole accretion rate or accretion disk structure appear more likely than changes in obscuration. Here we report on four epochs of spectroscopy of SDSS J110057.70-005304.5, a quasar at a redshift of $z=0.378$ whose UV continuum and broad hydrogen emission lines have faded, and then returned over the past $\approx$20 years. The change in this quasar was initially identified in the infrared, and an archival spectrum from 2010 shows an intermediate phase of the transition during which the flux below rest-frame $\approx$3400\AA\ has decreased by close to an order of magnitude. This combination is unique compared to previously published examples of changing-look quasars, and is best explained by dramatic changes in the innermost regions of the accretion disk. The optical continuum has been rising since mid-2016, leading to a prediction of a rise in hydrogen emission line flux in the next year. Increases in the infrared flux are beginning to follow, delayed by a $\sim$3 year observed timescale. If our model is confirmed, the physics of changing-look quasars are governed by processes at the innermost stable circular orbit (ISCO) around the black hole, and the structure of the innermost disk. The easily identifiable and monitored changing-look quasars would then provide a new probe and laboratory of the nuclear central engine.Comment: 13 pages, 4 figures, 3 tables. Published in MNRAS. All code and data links on GitHub, https://github.com/d80b2t/WISE_L

Designing a remote aerial system to image and analyze the health of grape crops at Cal Poly San Luis Obispo

In the last decade the prevalence of unmanned aerial vehicles (UAVs) has exploded; however, the presence of UAVs in research situations is still a relatively new and untested field. The autonomous flight lab (AFL) at Cal Poly San Luis Obispo is a new lab site that is dedicated to using UAVs to benefit research for all backgrounds. Before AFL was able to fly missions we first needed to actually receive our vehicles, create a lab space that would provide all of the necessary resources and equipment necessary to fly, and to be granted permission by the Federal Aviation Administration (FAA) to fly. AFL’s first contract was with the Cal Poly Agricultural Department to photograph their vineyards and analyze the health of the grape crops using a hyperspectral camera. The camera used was the Selectable Hyperspectral Airborne Remote sensing Kit (SHARK) that uses a Visible/Near Infra-Red (visNIR) scanning spectrometer to image the grape crops. Throughout the 9-week STAR placement the SHARK was obtained and a lab station was created to test, troubleshoot, and train new operators in the use of the SHARK. The SHARK has been used to take preliminary pictures to ensure that it will operate correctly on its first aerial helikite mission. Work still needs to be done to determine a safe and user-friendly way of mounting the SHARK to the helikite and powering the SHARK while airborne. The work done during the 9-week placement will allow for AFL to begin field-testing of the SHARK and to begin collecting data in the months to come