Closed-Loop Stall Control System

In the present study, an experimental investigation is conducted for the research of the turbulent open channel flow field at the three directions with the aid of one component Laser Doppler Anemometer and x Hot Film sensors. The instrumentation is used in an efficient manner for the extraction of three turbulent statistics with one measurement. The application of the present technique is conducted on fully developed uniform open channel turbulent flow and on flow with suction from the bed. With the aid of assumption for zero correlation between velocity and direction fluctuations the required number of measurements in the plane of flow direction for turbulent statistics is reduced. Using the Hot film sensor in the streamwise- spanwise orientation and with the LDA beam plane inclined in streamwise - vertical plane for the extraction a component of streamwise velocity direction, the three turbulent statistics are estimated. Also, with the assumption of randomness of velocity fluctuations of the open channel flow in the zero correlation assumption, the dependence of turbulent statistics with the angle is possible to be calculated. The influence of suction from the bed on the uniform open channel flow, alters the turbulent flow field characteristics and in the present paper the distribution of turbulent intensities are presented for various suction rates in the flow depth. In the form of covariance and autocovariance, angle dependence is examined for uniform flow and for flow with suction from the bed.

The influence of spanwise-uniform (linear) forcing applied by a dielectric barrier discharge (DBD) plasma actuator on the growth of a plane mixing layer and the dynamics of large-scale spanwise vortices within, are investigated experimentally. Quantitative spatio-temporal measurement of the flow field is acquired using high-speed planar particle image velocimetry. The DBD actuator is used to impart perturbations into the mixing layer to force the fundamental Kelvin-Helmholtz instability and its first sub-harmonic. Forcing the fundamental instability resulted in the inhibition of vortex pairing due to the attenuation of sub-harmonic instabilities. Correspondingly, the growth of the mixing layer is halted initially. With sub-harmonic instability forcing, two vortices interact with each other and merge together. This results in a higher growth rate compared to the unforced mixing layer at the streamwise location of this vortex interaction. Eventually, the growth rate of the forced mixing layer becomes similar to that of the unforced mixing layer. These results demonstrate the influence of the applied forcing on the growth of the turbulent mixing layer and the dynamics of the coherent vortical structures within.

The paper presents the results of a research activity that aims to investigate the control effect of fast rising pulse Dielectric Barrier Discharge actuators (DBD) in high speed flow conditions. At this aim, several experimental tests have been performed on a 2D wind tunnel model in subsonic and transonic conditions to collect information concerning effects of DBD actuators on the main aerodynamic aerofoil performance. The Mach number was varied between 0.4 and 0.85 at angles of attack ranging between -2° and 8° and Reynolds numbers between Re=1.7∙10 6 and Re=2.5∙10 6 . The aerofoil geometry selected for these tests was the supercritical BAC3-11 profile with 11% of maximum thickness. During the experiments, quantitative measurements have been made through steady and instantaneous pressure sensors. In particular, 45 pressure taps and 10 high frequency pressure transducers were installed on the surface of the model. The experimental data were used to develop and validate numerical tools, able to predict the plasma behaviour in presence of convective fields and, therefore, to support the design and setting of more effectiveness DBD actuator. A Computational Fluid Dynamics (CFD) solver developed at CIRA has been used for numerical simulations. A theoretical model for dielectric barrier discharge (DBD) via bodyforce and power density terms has been implemented in order to support the experimental test campaign.

1 - The Basics

Ice accretion on aircraft surfaces, especially on wings, may do harm to the aerodynamic performance and safety of an aircraft. In this work, de-icing experiments on an NACA0012 airfoil model were conducted in an icing wind tunnel using nanosecond pulsed surface dielectric barrier discharge (nSDBD) actuator under typical glaze icing conditions. The spatial-temporal distribution of the temperature and the dynamic process of de-icing on the surface of the airfoil were obtained and analyzed. Accreted ice with an average thickness of 3 mm can be removed within 4 s by nSDBD, and then the ice never appeared again on the plasma-protected zone. In the whole de-icing process, the ice on the plasma-protected zone was “cut” and the adhesion force between the ice layer and airfoil surface was reduced by the heat generated by the plasma actuator. The “cut” ice layer was blown downstream by aerodynamic force of the incoming flow. It can be concluded that both the thermal effects of the nSDBD actuator and the aerodynamic force of the incoming flow contribute to the de-icing performance.

Active Unsteady Flow Control experiments were performed on a Natural Laminar Flow, NLF 0414 airfoil at Rec = 1.0 × 10 6 . The goal of this study was to control boundary-layer separation across the trailing-edge region of the airfoil in off-design conditions. Both openloop and closed-loop control approaches were used. Active control of separation was achieved using a series of blowing slots at the x/c = 0.75 location. Open loop control parameters were varied across a parametric range of jet amplitudes, actuation frequencies and duty cycles and performance measurements were acquired to identify the effectiveness of these actuation schemes. PIV measurements were acquired across a horizontal plane near the trailing edge region of the model to understand the effects of actuation on flow separation and the vortex dynamics associated with unsteady actuation. A closed loop controller was developed to vary the actuation parameters in-situ using sensory feedback from the unsteady surface pressure measurements and adaptive modal decomposition methods. This closed-loop system was able to automatically control the extent of separation such that a desired value of Cl was obtained.

The disturbance observer is widely used in various applications, since it can effectively reject the external disturbances. And it also compensates the plant uncertainties if the system has matched uncertainties. Actual system has actuator to regulate the physical control input. Generally, the response time of actuator is very small enough to be ignored. But, in case of high power system, the response time of actuator is relatively long to affect system properties, and it's often described approximately in first order time lag. Since the disturbance observer rejects the disturbance and uncertainties by subtracting the estimated value of disturbance from the system input, the time lag of actuator increases the disturbance compensation error. So effect of actuator should be considered to design the disturbance observer. In this paper, matched uncertainty system with input actuator is considered and robust control method using disturbance observer is proposed. The gain of robust control input is adaptively determined. All information - states, disturbance and uncertainties - needed for controller are obtained and estimated from system input and output. The relation between estimation error and output boundary is analyzed.

This paper presents a new control law based on type-2 fuzzy logic system (T2FLS) for the Cessna Citation X aircraft during cruise. This methodology combines three control systems: a T2FLS, a sliding mode control (SMC) system, and an adaptive control system. Differing from conventional controllers, this control system can deal with uncertainties and aircraft dynamics variations using the T2FLS approximator. The approximated functions were updated during the simulation iterations using adaptation laws derived from the Lyapunov theorem. The adaptability characteristic of this controller allows updating the approximated functions while the other design parameters remain unchanged. This fact simplifies the controller design process and eliminates the need to use a group of conventional controllers with different gains to control the aircraft in various flight conditions. In addition, the sliding mode control system helps to guarantee the aircraft’s stability and robustness, along with two other methodologies in the presence and absence of turbulence. The performance of this control methodology was validated with a nonlinear simulation platform developed for the Cessna Citation X business aircraft using accurate flight data derived from a Level D flight simulator at the Research Laboratory in Active Controls, Avionics and AeroServoElasticity (LARCASE).

Extrusion blow moulding (EBM) is a polymer forming technique used to manufacture hollow plastic parts, such as fuel tanks. In this work, the feasibility of using closed-loop control in EBM is explored to compensate for machine drift and disturbances. A control system is proposed to regulate the extrusion process in EBM. The extrusion controller aims to increase process consistency by minimizing part thickness deviations. The thickness of the extrudate is measured during the extrusion cycle and any deviation from the desired thickness profile is compensated by changing the die gap in real time. The controller, which offers flexibility in thickness sensor placement, features a Smith predictor configuration embedding an H∞ controller. It compensates for the input-dependent polymer transport delay, the nonlinear steady-state swell, and nonminimum phase necking effects affecting the extrudate. This extrusion control technique may help reduce the production rate of off-specification parts and improve product quality.

The modeling, control, and dynamic stabilization of long-span suspension bridges are considered. By employing leading- and trailing-edge flaps in combination, we show that the critical wind speeds for flutter and torsional divergence can be increased significantly. The relatively less well known aerodynamic properties of leading-edge flaps will be studied in detail prior to their utilization in aeroelastic stability and control system design studies. The optimal approximation of the classical Theodorsen circulation function will be studied as part of the bridge section model building exercise. While a wide variety of control systems is possible, we focus on compensation schemes that can be implemented using passive mechanical components such as springs, dampers, gearboxes, and levers. A single-loop control system that controls the leading- and trailing-edge flaps by sensing the main deck pitch angle is investigated. The key finding is that the critical wind speeds for flutter and torsional divergence of the sectional model of the bridge can be greatly increased, with good robustness characteristics, through passive feedback control. Static winglets are shown to be relatively ineffective.

The closed-loop brain stimulation system can adjust stimulation parameters based on neural activity feedback, so as to provide precise and personalized treatment for neurological and neuropsychiatric diseases. The design of a model-based closed-loop system requires the choice of a suitable system identification framework to learn a dynamic mapping from input and output data to quantify the effect of input stimulation on output neural activity, and design the controller with the identification model. We first designed a control-theory system identification framework to build a dynamic input-output (IO) model of neural activity suitable for closed-loop control design. To achieve effective model-based control, we use a linear state space model (LSSM), which uses low-dimensional hidden neural states to characterize the effect of inputs on neural activity. Secondly, in order to train the model parameters, we choose a pulse sequence with independent modulation of parameters by pseudo-random sequence (PRS), and proved that this is the best choice for collecting informational IO data sets in system identification. The input waveform can be used as a deep brain stimulation (DBS) for treating neuropsychiatric diseases while meeting clinical safety requirements. Thirdly, we take the beta frequency band of the local field potential (LFP) as a biomarker of Parkinson's disease (PD) and system feedback signal to identify the system and design a closed-loop controller. The simulation results show that the closed-loop controller designed based on the LSSM model identified by the PRS modulation waveform can achieve the ideal control effect, and the performance of the model is similar to that of a real physiological IO model describing neural activity. The new PRS modulation waveform and system identification framework can help develop future model-based closed-loop stimulation systems, which is of great significance for the treatment of neuropsychiatric diseases.

The artificial pancreas (AP) has the potential to improve glycemic control in adolescents. This article presents the first evaluation in adolescents of the Zone Model Predictive Control and Health Monitoring System (ZMPC+HMS) AP algorithms, and their first evaluation in a supervised outpatient setting with frequent exercise. Adolescents with type 1 diabetes underwent 3 days of closed-loop control (CLC) in a hotel setting with the ZMPC+HMS algorithms on the Diabetes Assistant platform. Subjects engaged in twice-daily exercise, including soccer, tennis, and bicycling. Meal size (unrestricted) was estimated and entered into the system by subjects to trigger a bolus, but exercise was not announced. Ten adolescents (11.9-17.7 years) completed 72 h of CLC, with data on 95 ± 14 h of sensor-augmented pump (SAP) therapy before CLC as a comparison to usual therapy. The percentage of time with continuous glucose monitor (CGM) 70-180 mg/dL was 71% ± 10% during CLC, compared to 57% ± 16% during SAP (P = 0.012). Nocturnal control during CLC was safe, with 0% (0%, 0.6%) of time with CGM <70 mg/dL compared to 1.1% (0.0%, 14%) during SAP. Despite large meals (estimated up to 120 g carbohydrate), only 8.0% ± 6.9% of time during CLC was spent with CGM >250 mg/dL (16% ± 14% during SAP). The system remained connected in CLC for 97% ± 2% of the total study time. No adverse events or severe hypoglycemia occurred. The use of the ZMPC+HMS algorithms is feasible in the adolescent outpatient environment and achieved significantly more time in the desired glycemic range than SAP in the face of unannounced exercise and large announced meal challenges.

The production of complex multi-functional, high-strength parts is becoming increasingly important in the industry. Especially with small batch size, the incremental flow forming processes can be advantageous. The production of parts with complex geometry and locally graded material properties currently depicts a great challenge in the flow forming process. At this point, the usage of closed-loop control for the shape and properties could be a feasible new solution. The overall aim in this project is to establish an intelligent closed-loop control system for the wall thickness as well as the α’-martensite content of AISI 304L-workpieces in a flow forming process. To reach this goal, a novel sensor concept for online measurements of the wall thickness reduction and the martensite content during forming process is proposed. It includes the setup of a modified flow forming machine and the integration of the sensor system in the machine control. Additionally, a simulation model for the flow forming process is presented which describes the forming process with regard to the plastic workpiece deformation, the induced α’-martensite fraction, and the sensor behavior. This model was used for designing a closed-loop process control of the wall thickness reduction that was subsequently realized at the real plant including online measured feedback from the sensor system.

NASA's technology program for short takeoff and vertical landing (STOVL) aircraft has included the definition of integrated flightlpropulsion control systems for operation of the aircraft over the low-speed poweredlift flight envelope. The control system employs command modes for attitude, flightpath angle, and flightpath acceleration during transition, and translational velocity command for hover and vertical landing. Piloted evaluations of these integrated control designs have been conducted on Ames Research Center's Vertical Motion Simulator to assess flying qualities over the low-speed flight envelope and to document control power usage and system dynamics characteristics for these operations as a basis for defining design criteria for STOVL controls. Results indicate that Level 1 flying qualities can be achieved with flightpath and translational velocity command control system concepts for low-speed operations over a wide range of wind, atmospheric turbulence, visibility, and sea conditions. Maximum control usage and thrust response dynamics were established for the system for each of the operational conditions. Control power criteria are defined and compared with existing specifications wherever these are available. Also addressed are thrust margin in the presence of ground effect and hot gas ingestion, thrust transfer rates for attitude control, dynamic thrust response for the engine core, and flightpath control envelope during transition.

The capability to minimize vibratory loads with trailing edge flaps on a helicopter rotor is explored in this paper. Predictions with computational structural dynamics (CSD) codes coupled to a lifting-line (LL) aerodynamic model and a computational fluid dynamics (CFD) code are compared. Open and closed-loop controls are explored with both aerodynamic models. Moderate nonlinearities in the CFD/CSD simulation are shown to be present by illustrating that the extracted T-matrix, from open-loop actuation, varies with actuation phase. For example, for a purely linear system, identical T-matrices would be obtained from open-loop phase sweeps with different combinations of positive/negative cosine and sine inputs. However different T-matrices were obtained for these actuation phase permutations for the CFD/CSD simulation. The predictions showed that trailing-edge flaps are capable of simultaneously reducing vibratory thrust, pitch and roll moments by 90%. The rotor performance (L/De) was shown to be reduced for flap inputs which minimize vibratory hub loads; however the predicted performance reduction is less for CFD/CSD than LL/CSD simulations. Calculations were performed to minimize control loads by reducing 3p-5p push-rod loads.