Networked embedded systems for active flow control in aircraft

Aerodynamic drag is known to be one of the factors contributing more to increased aircraft fuel consumption. The primary source of skin friction drag during flight is the boundary layer separation. This is the layer of air moving smoothly in the immediate vicinity of the aircraft. In this paper we discuss a cyber-physical system approach able of performing an efficient suppression of the turbulent flow by using a dense sensing deployment to detect the low pressure region and a similarly dense deployment of actuators to manage the turbulent flow. With this concept, only the actuators in the vicinity of a separation layer are activated, minimizing power consumption and also the induced drag.

Fabrication and testing of a poly(vinylidene fluoride) (PVDF) microvalve for gas flow control

A microactuator made from poly(vinylidene fluoride) (PVDF), a piezoelectric polymer, was fabricated to control the gas flow rate through a glass micronozzle. The actuator was formed by gluing together two PVDF sheets with opposite polarization directions. The sheets were covered with thin conducting films on one side, that were then used as electrodes to apply an electric field to move the valve. The actuator has a rectangular shape, 3 mm x 6 mm. The device was incorporated with a micronozzle fabricated by a powder blasting technique. Upon applying a DC voltage across the actuator electrodes, one sheet expands while the other contracts, generating an opening motion. A voltage of +300 V DC was used to open the device by moving the actuator 30 mu m, and a voltage of -200 V DC was used to close the device by moving the actuator 20 mu m lower than the relaxed position. Flow measurements were performed in a low-pressure vacuum system, maintaining the microvalve inlet pressure constant at 266 Pa. Tests carried out with the actuator in the open position and with a pressure ratio (inlet pressure divided by outlet pressure) of 0.5, indicated a flow rate of 0.36 sccm. In the closed position, and with a pressure ratio of 0.2, a flow rate of 0.32 sccm was measured.

Development of microvalves for gas flow control in micronozzles using PVDF piezoelectric polymer

This work describes a fabrication and test sequence of microvalves installed on micronozzles. The technique used to fabricate the micronozzles was powder blasting. The microvalves are actuators made from PVDF (polivinylidene fluoride), that is a piezoelectric polymer. The micronozzles have convergent-divergent shape with external diameter of 1mm and throat around 230μm. The polymer have low piezoelectric coefficient, for this reason a bimorph structure with dimensions of 2mm width and 4mm of length was build (two piezoelectric sheets were glued together with opposite polarization). Both sheets are recovered with a conductor thin film used as electrodes. Applying a voltage between the electrodes one sheet expands while the other contracts and this generate a vertical movement to the entire actuator. Appling +300V DC between the electrodes the volume flux rate, for a pressure ratio of 0.5, was 0.36 sccm. Applying -200V DC between the electrodes (that means it closed) the volume flux rate was 0.32 sccm, defining a possible range of flow between 0.32 and 0.36 sccm. The third measurement was performed using AC voltage (200V AC with frequency of 1Hz), where the actuator was oscillating. For pressure ratio of 0.5, the flow rate was 0.62 sccm. © 2008 IOP Publishing Ltd.

Advanced control of managed pressure drilling

Automation of managed pressure drilling (MPD) enhances the safety and increases efficiency of drilling and that drives the development of controllers and observers for MPD. The objective is to maintain the bottom hole pressure (BHP) within the pressure window formed by the reservoir pressure and fracture pressure and also to reject kicks. Practical MPD automation solutions must address the nonlinearities and uncertainties caused by the variations in mud flow rate, choke opening, friction factor, mud density, etc. It is also desired that if pressure constraints are violated the controller must take appropriate actions to reject the ensuing kick. The objectives are addressed by developing two controllers: a gain switching robust controller and a nonlinear model predictive controller (NMPC). The robust gain switching controller is designed using H1 loop shaping technique, which was implemented using high gain bumpless transfer and 2D look up table. Six candidate controllers were designed in such a way they preserve robustness and performance for different choke openings and flow rates. It is demonstrated that uniform performance is maintained under different operating conditions and the controllers are able to reject kicks using pressure control and maintain BHP during drill pipe extension. The NMPC was designed to regulate the BHP and contain the outlet flow rate within certain tunable threshold. The important feature of that controller is that it can reject kicks without requiring any switching and thus there is no scope for shattering due to switching between pressure and flow control. That is achieved by exploiting the constraint handling capability of NMPC. Active set method was used for computing control inputs. It is demonstrated that NMPC is able to contain kicks and maintain BHP during drill pipe extension.

Macro-Fiber Composite Actuators for Flow Control of a Variable Camber Airfoil

This research employs solid-state actuators for delay of flow separation seen in airfoils at low Reynolds numbers. The flow control technique investigated here is aimed for a variable camber airfoil that employs two active surfaces and a single four-bar (box) mechanism as the internal structure. To reduce separation, periodic excitation to the flow around the leading edge of the airfoil is induced by a total of nine piezocomposite actuated clamped-free unimorph benders distributed in the spanwise direction. An electromechanical model is employed to design an actuator capable of high deformations at the desired frequency for lift improvement at post-stall angles. The optimum spanwise distribution of excitation for increasing lift coefficient is identified experimentally in the wind tunnel. A 3D (non-uniform) excitation distribution achieved higher lift enhancement in the post-stall region with lower power consumption when compared to the 2D (uniform) excitation distribution. A lift coefficient increase of 18.4% is achieved with the identified non-uniform excitation mode at the bender resonance frequency of 125 Hz, the flow velocity of 5 m/s and at the reduced frequency of 3.78. The maximum lift (Clmax) is increased 5.2% from the baseline. The total power consumption of the flow control technique is 639 mW(RMS).

Piezoceramic Composite Actuators for Flow Control in Low Reynolds Number Airflow

The research presented here employs solid-state actuators for flow separation delay or for forced attachment of separated flow seen in airfoils at low Reynolds numbers. To reduce separation, periodic excitation to the flow around the leading edge of the airfoil is induced by Macro-Fiber Composite actuated clamped-free unimorph benders. An electromechanical model of the unimorph is briefly presented and parametric study is conducted to aid the design of a unimorph to output high deformation at a desired frequency. The optimum frequency and amplitude for lift improvement at post-stall angles are identified experimentally. Along with aerodynamic force and structural displacement measurements, helium bubble flow visualization is used to verify existing separated flow, and the attached flow induced by flow control. The lift enhancement induced by several flow control techniques is compared. A symmetric and non-uniform (3D) flow excitation results in the maximum lift enhancement at post-stall region at the lowest power consumption level. A maximum lift coefficient increase of 27.5% (in the post-stall region) is achieved at 125 Hz periodic excitation, with the 3D symmetric actuation mode at 5 m/s and the reduced frequency of 3.78. C(l,max) is increased 7.6% from the baseline.

Optimization of filling systems for low pressure by Flow 3D

Dissertação de mestrado integrado em Engenharia Mecânica

Prediction of sustained antihypertensive efficacy of chronic captopril therapy: relationships to immediate blood pressure response and control plasma renin activity

The blood pressure (BP) lowering effect of the orally active angiotensin converting enzyme inhibitor, captopril (SQ14225), was studied in 59 hypertensive patients maintained on a constant sodium intake. Within 2 hours of the first dose of captopril BP fell from 171/107 to a maximum low of 142/92 mm Hg (p less than 0.001), and after 4 to 8 days to treatment BP averaged 145/94 mm Hg (p less than 0.001). The magnitude of BP drop induced by captopril was significantly correlated to baseline plasma renin activity (PRA) both during the acute phase (r = -0.38, p less than 0.01) and after the 4 to 8-day interval (r = -0.33, p less than 0.01). Because of considerable scatter in individual data, renin profiling was not precisely predictive of the immediate or delayed BP response of separate patients. However, the BP levels achieved following the initial dose of captopril were closely correlated to BP measured after 4 to 8 days of therapy, and appeared to have greater predictive value than control PRA of the long-term efficacy of chronic captopril therapy despite marked BP changes occurring in some patients during the intermediate period. Because of these intermediate BP changes, addition of a diuretic to enhance antihypertensive effectiveness of angiotensin blockade should be restrained for several days after initiation of captopril therapy.

Submerged Vanes for Flow Control and Bank Protection in Streams, HR-255, 1984

This study was conducted for the purpose of evaluating a new concept for a bank-protection structure: The Iowa Vane . The underlying idea involves countering the torque exerted on the primary flow by its curvature and vertical velocity gradient, thereby eliminating or significantly reducing the secondary flow and thus reducing the undermining of the outer banks and the high-velocity attack on it. The new structure consists of an array of short, vertical, submerged vanes installed with a certain orientation on the channel bed. A relatively small number of vanes can produce bend flows which are practically uniform across the channel. The height of the vanes is less than half the water depth, and their angle with the flow direction is of the order of l0 degrees. In this study, design relations have been established. The relations, and the vanes' overall performance, have been tested in a laboratory model under different flow and sediment conditions. The results are used for the design of an Iowa-Vane bank protection structure for a section of East Nishnabotna River along U.S. Highway 34 at Red Oak, Iowa.

Does altering brachial artery tone with lower-body negative pressure and flow-mediated dilation affect arterial stiffness?

Although medium sized, muscular vessels normally respond to sympathetic stimulation by reducing compliance, it is unclear whether the large brachial artery is similarly affected by sympathetic stimulation induced via lower-body negative pressure (LBNP). Similarly, the impact of flow-mediated dilation (FMD) on brachial artery compliance and distensibility remains unresolved, hi addition, before such measures can be used as prognostic tools, it is important to investigate the reliability and repeatability of both techniques. Using a randomized order design, the effects of LBNP and FMD on the mechanical properties of the brachial artery were examined in nine healthy male subjects (mean age 24y). Non-invasive Doppler ultrasound and a Finometer were used to measure simultaneously the variation in systolic and diastolic diameter, and brachial blood pressure, respectively. These values were used to calculate compliance and distensibility values at baseline, and during both LBNP and FMD. The within-day and between-day repeatability of arterial diameter, compliance, distensibility, and FMD measures were assessed using the error coefficient and intra-class correlation coefficient (ICC). While heart rate (P<0.01) and peripheral resistance increased during LBNP (P<0.05), forearm blood flow and pulse pressure decreased (P<0.01). hi terms of mechanical properties, vessel diameters decreased (P<0.05), but both compliance and distensibility were not changed. On the other hand, FMD resulted in a significant increase in diameter (P<0.001), with no change in compliance or distensibility. hi summary, LBNP and FMD do not appear to alter brachial artery compliance or distensibility in young, healthy males. Whereas measures ofFMD were not found to be repeatable between days, the ICC indicated that compliance and distensibility were repeatable only within-day.

High-Frequency Oscillatory Ventilation Associated With Inhaled Nitric Oxide Compared to Pressure-Controlled Assist/Control Ventilation and Inhaled Nitric Oxide in Children: Randomized, Non-Blinded, Crossover Study

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Simplified architecture of a neurofuzzy controller applied on industrial systems for fluid flow control

This work presents a simplified architecture of a neurofuzzy controller for general purpose applications that tries to minimize the processing used in the several stages of hazy modeling of systems. The basic procedures of fuzzification and defuzzification are simplified to the maximum while the inference procedures are computed in a private way. The simplified architecture allows a fast and easy configuration of the neurofuzzy controller and the structuring rules that define the control actions is automatic. Th controller's Limits and performance are standardized and the control actions are previously calculated. For application, the industrial systems of fluid flow control will be considered.

Robust control applied to power flow control in single-phase inverter with LCL filter, using droop control and D-stability

This paper proposes a new methodology to control the power flow between a distributed generator (DG) and the electrical power distribution grid. It is used the droop voltage control to manage the active and reactive power. Through this control a sinusoidal voltage reference is generated to be tracked by voltage loop and this loop generates the current reference for the current loop. The proposed control introduces feed-forward states improving the control performance in order to obtain high quality for the current injected to the grid. The controllers were obtained through the linear matrix inequalities (LMI) using the D-stability analysis to allocate the closed-loop controller poles. Therefore, the results show quick transient response with low oscillations. Thus, this paper presents the proposed control technique, the main simulation results and a prototype with 1000VA was developed in the laboratory in order to demonstrate the feasibility of the proposed control. © 2012 IEEE.