The effects of active separation control on the aerodynamic performance of an advanced fighter aircraft configuration have been determined. Lowspeed wind tunnel tests were performed using a 7% scale lambda-wing model with jet actuators on the wing leading edge flaps. The jets were operated in a pulsed mode and their frequency and amplitude were varied during the experiments. The effects of the jet actuators on the model aerodynamic performance were measured using a six component force balance for several flap configurations and for angles-of-attack (a) up to 40 deg. The results indicate that the pulsed jets are effective in delaying separation and augmenting lift. Maximum increases in lift were approximately 7% and occurred near C,max. Experiments performed to determine the influence of pulse frequency, ff, on control effectiveness showed that control was optimized for nondimensional frequencies, based on freestream velocity, UM, and wing chord, c, near Strc =/p c/Ura= 1. In addition, it was found that control effectiveness increased monotonically with increases in pulse amplitude. When operating the jet actuators on one wing alone, roll moment coefficients of CRoll- 0.011 could be produced. The results of these experiments indicate that leading edge pulsed jet actuators are an effective means of enhancing aerodynamic performance and maneuverability of advanced fighters.
The Wind-Driven Dynamic Manipulator is a robotic device which executes multidimensional maneuvers of aircraft models in a wind tunnel. Tunnel freestream kinetic energy is used to power the device. Transmission of reactions to the tunnel structure is thus minimized, and power requirements are negligible compared to conventional devices. Support interference can be minimized by using slender and flexible supports and correcting for deflection errors. The concept and results achieved with the device are summarized, and a new 3-degree of freedom device is described. Several example applications are described. Transient vortex interactions are visualized quantitatively in coupled pitch-yaw maneuvers. Dynamic stability parameters are measured using a second-order dynamic model of the system. An adaptive control algorithm improves trajectory tracking and enables new dynamic characteristics to be learned. WDM design parameters are discussed, and the performance equations of the device show maneuvering rates increasing faster than the reduced frequency as tunnel speed increases.
Mm Pitching moment generated by the model Inverse force measurement using a wind-driven dynamic manipulator is explored. Using system identification techniques, the WDM offers a method of measuring forces and moments on wind tunnel models during rapid, multi-axis maneuvers. Previous work has shown the measurement of dynamic stability parameters for small disturbances using the WDM. System identification has been used to construct simulations of WDM behavior in order to match desired and actual maneuver trajectories. Here the nonlinear behavior of a pitch manipulator is measured over a range of model loads and attitudes. A look-up table constructed from these data is used to measure quasi-steady forces and moments on a rectangular wing and a delta wing. The WDM is used to hold models steady in a wind tunnel under feedback control, at various attitudes. Each model is taken through a range of attitudes, and the control input needed for equilibrium is recorded. By repeating the experiment with 3 model-mounting positions, a set of 3 simultaneous equations is generated for the lift, drag and pitching moment at each angle of attack. The technique is successful in measuring the lift of a rectangular wing and a delta wing. Measurement resolution was inadequate to resolve drag and pitching moment accurately in these tests. Methods for measuring these are discussed. Continuous force measurement from repeated maneuvers is discussed.
Dynamic stall control is of interest for its potential to enhance the performance of rotorcraft. The experiments described used pulsed vortex generator jets, shown previously to prevent separation on steady wings and airfoils, to delay dynamic stall on a rapidly pitching airfoil. In tests performed on a NACA-0012 airfoil at low Reynolds numbers, the jets yielded a 25‐ 35% increase in the lift coefe cient achievable without moment stall. Next, a differential equation model of the dynamic stall process was derived and experimentally validated. Models of this form enable the application of well-known control theory to the design of e ow control systems. In the e nal round of experiments, a state observer based on the mathematical model detected incipient dynamic stall. A controller used the stall prediction to operate the pulsed jets only when needed to prevent stall. The controller turned the jets off for the remainder of the oscillation cycle. The controller only operated the jets for about 25% of the pitch cycle, so that the best lift increases of the early experiments could be achieved with only 25% of the air mass e ow.
An active, hardware-based retinal tracker is integrated with a clinical optical coherence tomography (OCT) system to investigate the effects of stabilization on acquisition of high-resolution retinal sections. The prototype retinal tracker locks onto common fundus features, detects transverse eye motion via changes in feature reflectance, and positions the OCT diagnostic beam to fixed coordinates on the retina with mirrors driven by a feedback control loop. The system is tested in a full clinical protocol on subjects with normal and glaucomatous eyes. Experimental analysis software is developed to coalign and coadd multiple fundus and OCT images and to extract quantitative information on the location of structures in the images. Tracking is highly accurate and reproducible on all but one subject, resulting in the ability to scan the same retinal location continually over long periods of time. The results show qualitative improvement in 97% of coadded OCT scans and a reduction in the variance of the position of the optic disc cup edge to less than 1 pixel (<60 µm). The tracking system can be easily configured for use in research on ultra-high-resolution OCT systems for advanced image modalities. For example, tracking will enable very high density 3-D scans of the retina, which are susceptible to eye motion artifacts even for new high-speed systems.
Solid bodied electric guitars typically employ one or more magnetic pickups attached to the guitar body in close proximity to the guitar strings. At low frequencies the amplitude of the vibrating string is typically far greater than vibrations transmitted through the guitar body and it is likely therefore that the output current is largely dominated by the string vibrations with little contribution from the guitar body itself. However, musicians often describe subjective differences between instruments made from different body materials, with mahogany often being cited as sounding ‘warm’ for example. Described in the presentation is a method that has been used to determine the contribution to the guitar signal from just the guitar body itself so as to estimate at what frequencies the guitar body may make a significant contribution to a guitar’s ‘tone’ if any. The method is similar to the approach used to diagnose structure borne noise problems in vehicles and aircraft known as transfer path analysis. However, instead of determining forces and their contribution to vehicle interior sound pressure, we determine the forces applied to a guitar body through the bridge and nut together with their contributions to the guitar output signal. In this way the contribution of the string and the guitar body can be found independently and compared to the guitars total output signal. Preliminary experimental findings from a vibro-electric transfer path analysis of a Gibson Les Paul type guitar are presented.
This paper describes the development of an air bearing with high bandwidth load sensing capabilities and a means of delivering high pressure air to the rotating (floating) element. The device will be used to provide nearly frictionless rotation to wind tunnel test models while measuring unsteady aerodynamic loads. Although the current application involves dynamic testing of missiles, it will be useful in the study of longitudinal high-alpha aircraft dynamics. The load sensing is based on measurements of pressures in the bearing gas film using micromachined fast response (1 ms) sensors. The air bearing balance also provides a supply of high pressure air to the test model for reaction control jets and pneumatic flow control devices. This paper describes the design and evaluation of a prototype capable of single-axis rotation. Static calibration experiments confirm that the prototype can sense multi-axis loads precisely. Frequency response tests demonstrated the ability to detect unsteady loads at least as high as 200 Hz. Further demonstrations showed that the balance can deliver high pressure air to the test model without friction and without hampering load sensing. The prototype will serve as the basis for an air bearing balance capable of three-axis rotation.
INTRODUCTION: The prevalence of Metabolic Syndrome (MetS) is progressing globally, with limited research in the young adult population (18-24 years old). It is estimated that approximately 36% of the adult population in the United States meets the criteria for MetS, whereas 3-10% of college students qualify for MetS. MetS identifies conditions of insulin resistance, visceral adiposity, and endothelial dysfunction. Carotid femoral pulse wave velocity (CFPWV), the gold standard measurement of arterial stiffness, is also considered in this discussion of cardiovascular risk. There is limited research on the relationship between MetS, CFPWV, and gender in the young adult population. PURPOSE: To identify the prevalence of MetS in this high school senior population and determine if the number of MetS criteria met and gender are predictive of CFPWV. METHODS: Data were collected to determine MetS criteria met and CFPWV in 55 high school seniors (17.5 ± .5 years). Height, weight, waist circumference, and blood pressure were measured. Arterial stiffness was assessed using CFPWV measurement. Blood samples were collected to measure HDL-C, triglycerides, and fasting blood glucose. For statistical analysis, a multiple regression analysis was used to assess the effect of gender, and the number of criteria of MetS present on CFPWV. RESULTS: There was a 2% prevalence of MetS in this population with variable prevalence of each criterion. The multiple regression model significantly predicted CFPWV, F (2, 53) = 5.412, p < .007, R2 = .170. The number of criteria was the only significant variable of prediction. Gender was kept in the model even though it was not a significant variable of prediction because of its impact on the overall model and explanation of variance. CONCLUSION: The number of MetS criteria met, and gender are independent predictors of CFPWV. Establishing new cut-points for each of the MetS criteria could help identify a more effective screening process and allow for the development of individualized interventions. Adjusted criteria, with gender considerations, could be investigated to better identify cardiovascular/cardiometabolic disease risk in the young adult population.
