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Fatigue
Published in Mark W. Wiggins, Introduction to Human Factors for Organisational Psychologists, 2022
From an operational perspective, the impact of fatigue was illustrated in the crash of Colgan Air Flight 3407, a Bombardier Q400, on February 12, 2009. The aircraft was on descent to Buffalo, New York, having departed Newark, New Jersey. Light snow and fog resulted in ice forming on the leading edge of the wings, increasing drag, and causing a reduction in the airspeed of the aircraft to a point where the stall warning activated. In responding to an impending stall, pilots are taught to lower the attitude of the aircraft and then to increase power. However, in the case of the Flight 3407, the captain pulled back on the yoke, and subsequently applied power, The result was a further ‘pitch-up’ of the aircraft, further restricting the margin for recovery (NSTB, 2010).
Pump and fan controls
Published in Raymond F. Gardner, Introduction to Plant Automation and Controls, 2020
Figure 8.12 shows the progression of system curves as a discharge damper closes while modulating flow. As the damper closes, the system resistance increases, the fan rides back on the curve decreasing flow and increasing developed pressure, as would be expected (Figure 8.12b). Eventually, the damper closes enough to put the fan into the unstable operating range, where the fan pressure drops as the damper closes, instead of increasing (Figure 8.12c). At low discharge pressure, the fan curve has two possible operating flowrates, as shown as Q1 and Q2 in Figure 8.11, at which point the fan will surge. Surging occurs as the flow separates from the impeller vane in a condition known as stall. The flow separation and stall occurs when the angle of attack of the relative air flow over the vane exceeds the critical angle of attack. Stall can lead to surging, noise, vibration, fatigue, inefficiency, difficult pressure/flow measurement, and poor system behavior. Instability and surge are a low flow phenomenon and even small amounts would be intolerable in systems requiring fine control, such as combustion-air fans.
Going with the Flow: An Optical Basis for the Control of Locomotion
Published in Richard J. Jagacinski, John M. Flach, Control Theory for Humans, 2018
Richard J. Jagacinski, John M. Flach
The ambiguity created by global optical flow rate has been hypothetically linked to a very dangerous situation connected with low altitude flight. The U.S. military loses a significant number of aircraft due to a problem labeled controlled flight into terrain (CFIT; Haber, 1987). CFIT refers to situations where an aircraft flies into the ground with no obvious mechanical failure, no dangerous weather or meteorological conditions, and apparently no medical problems. The cause seems to be pilot control error. The hypothetical explanation is as follows. The first assumption is that pilots utilize the global optical flow rate as a primary indicant of airspeed. As already noted, this is a smart strategy, as long as altitude is roughly constant. Airspeed is a critical determinant of lift. If airspeed becomes too low, then the amount of lift will be less than the pull of gravity, and the aircraft will essentially begin to fall out of the sky. The minimum airspeed necessary to keep the aircraft in flight is referred to as the stall speed. A wing stall is a situation where the lift generated by the wings is less than the force of gravity.
Multiphase SPH Modelling of Supercooled Large Droplets Freezing on Aircraft Surfaces
Published in International Journal of Computational Fluid Dynamics, 2021
Xiangda Cui, Wagdi G. Habashi, Vincent Casseau
In-flight icing poses a serious risk to aviation safety: ice accretion causes increased drag, reduced lift, early stall and erroneous and inoperative sensors and probes. A combination of these adverse effects can result in serious and sudden aircraft performance degradation, leading to incidents and/or accidents (Habashi 2009). Such consequences of icing must be assessed through extensive procedures under airworthiness agencies certification standards, such as the Appendices C and O of Federal Aviation Administration’s Part 25 (FAA 2011; FAA 2016), European Aviation Safety Agency’s CS-25 (EASA 2015), and Transport Canada Civil Aviation’s CARs (TCCA 2019). In addition, Appendix O mandates new aircraft to be protected against supercooled large droplets (SLD) with diameters ranging from 50–1000 µm (FAA 2016). Due to their large size, SLDs behave in a different way from smaller droplets as they may break-up or coalesce before impact, spread and splash during impact, and rebound after impact (Honsek, Habashi, and Aubé 2008). In some cases, splashing and rebounding droplets re-entering the airstream can lead to ice accretion beyond the limits of ice protection systems (IPS); a dangerous situation (Bilodeau et al. 2015).
Hydrodynamic design of a horizontal axis current turbine with passive flow control using vortex generator and inserted tube
Published in International Journal of Green Energy, 2023
Among various possible options to increase the total extracted power from a current turbine, the performance improvement of the blade foil has been considered in this work. Specifically, increasing the lift force coefficients at various angles of attack and delaying the undesirable stall appearance have been targeted by adopting flow control techniques. As suggested by various researchers, this can be achieved through several approaches, such as synthetic jet actuators (Cattafesta and Sheplak 2011), moving object or surface actuators (Cattafesta and Sheplak 2011), plasma actuators (Cattafesta and Sheplak 2011), pulsed combustion actuators (Cattafesta and Sheplak 2011), fluidic actuators (Cattafesta and Sheplak 2011), vortex generators (Manolesos and Voutsinas 2015), rigid flaps (Li et al. 2013), dimples (Beves and Barber 2011), slots (Weick and Wenzinger 1933), etc. Unlike the active flow separation control methods, the passive flow control techniques do not require external energy into the system, i.e., such methods are primarily based on bringing high kinetic energy fluid from the free stream to the area of low kinetic energy fluid which is on the verge of separation. Application of such systems is often a lot easier since aspects like size, additional weight, initial cost, failure risk, and maintenance cost are significantly less compared to active devices. Thus, passive techniques like vortex generators have gained considerable popularity in the aircraft industry. A details discussion on various passive flow control methods has been discussed in (Belamadi et al. 2016; Kundu 2019, 2020a, 2020b; Kundu, Sarkar, and Nagarajan 2019, 2020; Lin 1999).
Design, electromechanical simulation, and control of a variable speed stall-regulated PMSG-based wind turbine
Published in International Journal of Green Energy, 2019
Ebrahim Mohammadi, Roohollah Fadaeinedjad, Hamid Reza Naji
This paper presented a comprehensive study of a 10 kW variable speed stall-regulated wind turbine with PMSG and back-to-back converters. The study included blade design, electromechanical simulation of the entire WT, and the controllers design and analysis. Since the stall-regulated WTs do not require active aerodynamic device to limit the output power in high wind speeds, they are appropriate choices in small-scale wind energy conversion systems. The MPPT strategy was implemented in Region 2 and the captured power was limited in Region 3 using the stall control strategy. Stall is an aerodynamic condition where the angle of attack increases beyond the critical value which results in reducing the lift forces and limiting the captured power. The blades of the stall-regulated WTs should be designed precisely and they are forced to operate in the stall condition by controlling the generator-connected converter. Hence, the stall-regulated blades were initially designed utilizing HARP_Opt software using two S822 and S823 airfoils. To evaluate the performance of the designed blades, the designed blades were utilized in the electromechanical simulation and the results were compared. The turbine was simulated using AeroDyn, FAST, and MATLAB/Simulink software packages to model the details of aerodynamic, mechanical and electrical aspects. Two wind speed profiles including a simple hub-height and a turbulent one, generated by TurbSim, were used to investigate the performance of the WT. The simulation results of both cases showed that the stall-regulated WT with the designed blades has appropriate performance in both MPPT and stall regions. The generator-connected converter controls the rotor speed to track the MPP in Region 2 and limit the captured power in Region 3. The network-connected converter also controls the DC link voltage properly and keeps the system at unity power factor.