Actuator Surface Research Articles

Conceptual examination of dielectric elastomer for flight control surface actuation

Conceptual examination of dielectric elastomer for flight control surface actuation

Geometry optimization of linear and annular plasma synthetic jet actuators

The electrohydrodynamic (EHD) interaction induced in atmospheric air pressure by a surface dielectric barrier discharge (DBD) actuator has been experimentally investigated. Plasma synthetic jet actuators (PSJAs) are DBD actuators able to induce an air stream perpendicular to the actuator surface. These devices can be used in the field of aerodynamics to prevent or induce flow separation, modify the laminar to turbulent transition inside the boundary layer, and stabilize or mix air flows. They can also be used to enhance indirect plasma treatment effects, increasing the reactive species delivery rate onto surfaces and liquids. This can play a major role in plasma processing and chemical kinetics modelling, where often only diffusive mechanisms are considered.This paper reports on the importance that different electrode geometries can have on the performance of different PSJAs. A series of DBD aerodynamic actuators designed to produce perpendicular jets has been fabricated on two-layer printed circuit boards (PCBs). Both linear and annular geometries were considered, testing different upper electrode distances in the linear case and different diameters in the annular one. An AC voltage supplied at a peak of 11.5 kV and a frequency of 5 kHz was used. Lower electrodes were connected to the ground and buried in epoxy resin to avoid undesired plasma generation on the lower actuator surface.Voltage and current measurements were carried out to evaluate the active power delivered to the discharges. Schlieren imaging allowed the induced jets to be visualized and gave an estimate of their evolution and geometry. Pitot tube measurements were performed to obtain the velocity profiles of the PSJAs and to estimate the mechanical power delivered to the fluid.The optimal values of the inter-electrode distance and diameter were found in order to maximize jet velocity, mechanical power or efficiency. Annular geometries were found to achieve the best performance.

Optimal and robust design of a control surface actuation system within the GLAMOUR project

Optimal and robust design of a control surface actuation system within the GLAMOUR project

Ice Accretion on Helicopter Fuselage Considering Rotor-Wake Effects

To accurately predict the ice shape on the fuselage under rotor-wake effects, discrete modeling of individual tip vortices is essential to determine the local aerodynamic interactions between the vortex and the fuselage. To this end, the actuator surface model is developed and applied to the present study. Then, water-droplet-trajectory prediction, thermal analysis, and ice growth module are seamlessly integrated. This study aims to perform detailed analysis of the rotor downwash effects on ice that accretes on a helicopter fuselage and to determine the variation with respect to the forward flight speed. As a result of comprehensive numerical computations, the following conclusions are reached. First, the rotor inflow transforms the droplet trajectories, the location of ice accretion and the amount of ice are changed. Actually, 16.5% less ice is accumulated on the overall fuselage in the rotor–fuselage interaction case compared to the isolated fuselage case. Second, a clear-cut distinction of the icing locations on the fuselage is observed with various advance ratios. In hovering conditions, massive ice is accumulated on the tail-boom and fuselage nose region, where the tip vortices collide with fuselage. Due to the large collision area with high speed of droplets, 15.2 and 9.1% more ice is accumulated in hovering case than that of forward flight case with the advance ratio 0.075 and 0.15, respectively. However, as the forward speed grows from 0.15 to 0.2, the total mass of ice exponentially increases. In case of the advance ratio 0.2, 36% more ice is accumulated than that of the hovering case.

Adaptive Flight Control Under Actuation and Sensor Failures and Slow-Engine Dynamics

Current approaches to in-flight failure accommodation are focused either on failures of sensors or control surface actuators. Some results also focus on simultaneous sensor and actuator failures. However, there are apparently no results for the case of engine actuation failures when the engine dynamics are slow and its output is not measurable. Hence, the stability proofs for the case of accommodation of simultaneous actuator, engine, and sensor gain failures are not available. On the other hand, overall system stability is crucial in preventing loss of control under flight-critical failures. In this paper, a stable adaptive approach to simultaneous sensor, actuator, and slow-engine gain failure accommodation in flight control is proposed. The approach is broken into two parts: 1) design of a stable adaptive reconfigurable control scheme for accommodation of actuator and engine gain failures in the case of slow-engine dynamics and nonmeasurable engine output, and 2) stable adaptive control design extending part 1 results to the case of failures of air-data sensors. In the latter case, a suitable state estimator, referred to as the virtual sensor, is proposed, and the stability of the overall system is demonstrated. Finally, a multiple-model approach is proposed to achieve effective control strategy selection under multiple simultaneous sensor, actuator, and engine gain failures, and overall system stability is demonstrated. Computer simulations of the generic transport model are included to illustrate the proposed approach.

Innovative Concepts in Wireline Continuous Coring

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 180017, “Innovative Concepts in Wireline Continuous Coring,” by Rahman Ashena, Walter Vortisch, Michael Prohaska, and Gerhard Thonhauser, University of Leoben, prepared for the 2016 SPE Bergen One Day Seminar, Bergen, Norway, 20 April. The paper has not been peer reviewed. Coring in unconventional reservoirs with typical unconsolidated formations has introduced additional challenges requiring more-innovative concepts to be developed. These requirements have recently led to widespread attention to wireline continuous coring (WCC), which was modified from the mining industry for petroleum-industry applications. This paper is aimed at identifying and addressing complications experienced in the use of WCC. In addition to the challenges and solutions discussed in this summary, others are covered in the complete paper. Basic Bottom-Coring Methods These methods, in the context of petroleum exploration, comprise conventional and WCC methods. Conventional coring is a method of rotary coring by which the inner tube containing the core is retrieved along with the outer-tube assembly to the surface following a conventional drillstring trip. WCC is a method of coring or drilling by which the same outer assembly is used as the bottomhole assembly and the same core bit is applied for both drilling and coring modes; however, changing the inner assembly can be performed easily by wireline in order to switch to the desired mode. WCC has been identified recently as a less-time-consuming coring method to replace conventional coring in certain circumstances. WCC Challenges and Solutions Flushed Inner Tube While Run in Hole. Problem. As a common practice in conventional coring, approximately 90 ft before reaching the bottom (off-bottom), mud circulation is started, still without string rotation. This is because the mud circulation that passes within inner tubes contributes to conditioning and flushing the inner tubes to ensure that the inner tube is free of debris/fill. The most problematic issue with debris/fill is the high risk of jamming off in the core bit, core catcher, or inner tube. Following tagging of the formation to be cored, immediately before beginning the coring, the ball is either dropped from surface or hydraulically actuated by virtue of a drop-ball sub in order to change the mud path from within the inner tube to the annulus between inner and outer tubes so that mud does not flush the core while entering the inner tube. After cutting enough cores or reaching coring termination, the drop ball enables any gas and trapped pressure to be released through the top of the inner assembly. It is noted that, for coring systems with closed inner-tube systems, there is no possibility for drop balls to be used; instead, an enclosed ball and seat.are used. In WCC, an enclosed ball in place is also commonly used in the inner coring assembly (above the inner tubes) instead of dropping a ball from surface or hydraulic actuation using a drop-ball sub. Therefore, before beginning the coring, the mud never passes through the inner tube and thus never flushes the inner tube.

Modeling and control of a torque load system with servo actuator's dynamics

In this work, the models and control strategy of the Electric Servo-torque System(ESS) which is used as an experiment rig for conducting dynamic performance and stability tests of aerial vehicle control surface actuation systems are presented. The detailed dynamics of the load motor and loaded flight actuator’s rotating movement in the ESS are analyzed, leading to an integrated load torque synchronization system. The kinematic dynamics of the loaded control surface driving actuator is an important consideration to estimate the trend of torque variation and to improve the performance of the load system. The load control method is expressed in terms of a multi-loop torque control law, which uses feedback and feedforward loops to meet system design requirements. Numerical examples together with experimental results are included to illustrate the effectiveness of the proposed models and control parameters. This brief addressed a specific utilization of the loaded actuator’s dynamics, revealing that it can reduce both the phase lag and the amplitude gain of the load torque in the Electric Servo-torque System.

Identification and mitigation of T-S waves using localized dynamic surface modification

The control of transition from a laminar to a turbulent flow over a flat plate using localized dynamic surface modifications was explored experimentally in Rensselaer Polytechnic Institute’s subsonic wind tunnel. Dynamic surface modification, via a pair of Piezoelectrically Driven Oscillating Surface (PDOS) actuators, was used to excite and control the T-S wave over a flat plate. Creating an upstream, localized small disturbance at the most amplified frequency of fact = 250 Hz led to phase-locking the T-S wave. This enabled observation of the excited T-S wave using phase-locked stereoscopic particle image velocimetry. The growth of the T-S wave as it moved downstream was also measured using this technique (25% growth over four wavelengths of the excited wave). Activation of a downstream PDOS actuator (in addition to the upstream PDOS) at the appropriate amplitude and phase shift resulted in attenuation of the peak amplitude of the coherent velocity fluctuations (by up to 68%) and a substantial reduction of the degree of coherence of the T-S wave. Since the PDOS actuators used in this work were localized, the effect of the control strategy was confined to the region directly downstream of the PDOS actuator.

Hardware-in-the-loop platform for development of redundant smart actuators

Purpose Fault tolerant control surface actuation of unmanned aerial systems with take-off weights below 150 kg offers new design challenges due to limitations in mass, weight and cost. Conventional redundancy concepts need to be amended by smart operational strategies, enhanced sensor data provision and advanced failure mitigation. The paper aims for the design of a hardware-in-the-loop platform that enables the model-based development, verification, performance analysis and safety assessment of redundant and smart electromechanical actuators.

Controlling Corner Stall Separation With Plasma Actuators in a Compressor Cascade

This paper presents a numerical and experimental assessment of a plasma actuation concept for controlling corner stall separation in a highly loaded compressor cascade. CFD simulations were first carried out to assess actuator effectiveness and determine the best actuation parameters. Subsequently, experiments were performed to demonstrate the concept and confirmed the CFD tool validity at a Reynolds number of 1.5 × 105. Finally, the validated CFD tool was used to simulate the concept at higher velocities, beyond the experimental capability of existing plasma actuators. These results were used to obtain a preliminary scaling law that would allow approximation of the plasma actuation requirements at realistic operating conditions. Several configurations were examined, but the most effective setup was found to be when plasma actuators were mounted upstream of the separation point on both the suction surface and the endwall. Most of the improvement in total pressure loss stemmed from the suction surface actuator. Comparison with experimental data showed that the CFD simulations could capture the flow features and the effect of plasma actuation reasonably well. Simulations at higher flow velocities indicated that the required plasma actuator strength scales approximately with the square of the Reynolds number.

Reversible Electrochemically Triggered Delamination Blistering of Hydrogel Films on Micropatterned Electrodes

Stimuli responsive elastic instabilities provide opportunities for controlling the structures and properties of polymer surfaces, offering a range of potential applications. Here, a surface actuator based on a temperature and electrically responsive poly(N‐isopropyl acrylamide‐co‐sodium acrylate) hydrogel that undergoes a two‐step delamination and buckling instability triggered using micropatterned electrodes is described. The electrically actuated structures entail large out‐of‐plane displacements that take place on time‐scales of less than 1 s, in response to modest triggering voltages (−3–6 V). Alongside these experimental observations, finite element simulations are conducted to better understand the two‐step nature of the instability. In the first step, hydrogel films undergo delamination and formation of blisters, facilitated by electrochemical reduction of the thiol groups anchoring the film to the electrodes. Subsequently, at larger reducing potentials, the electrolytic current is sufficient to nucleate a gas bubble between the electrode and the gel, causing the delaminated region to adopt a straight‐sided blister shape. Finally, thermally induced deswelling of the gel allows the film to be returned to its flat state and readhered to the electrode, thereby allowing for repeated actuation.

Stability Augmentation and Active Flutter Suppression of a Flexible Flying-Wing Drone

Integrated control laws are developed for stability augmentation and active flutter suppression of a flexible flying-wing research drone. The vehicle is a 12 lb unmanned flying-wing research aircraft with a 10 ft wingspan. Active flutter suppression is flight critical, since the subject vehicle is designed to flutter within its flight envelope. The critical flutter condition involves aeroelastic interactions between the rigid body and elastic degrees of freedom; hence, the control laws must simultaneously address both rigid-body stability augmentation and flutter suppression. The conventional control-synthesis approach is motivated by the concept of identically located force and acceleration, which was successfully applied on some previous operational aircraft. Based on the flutter characteristics and on conventional stability-augmentation concepts, two simple loop closures are suggested. It is shown that this control architecture robustly stabilizes the body-freedom-flutter condition, increases the damping of the second aeroelastic mode (which becomes a second flutter mode at higher velocity), and provides a reasonably conventional vehicle pitch-attitude response. The critical factors limiting the performance of the feedback system are identified to be the bandwidth of the surface actuators and the pitch effectiveness of the control surfaces.

Squirming through shear-thinning fluids

Many micro-organisms find themselves immersed in fluids displaying non-Newtonian rheological properties such as viscoelasticity and shear-thinning viscosity. The effects of viscoelasticity on swimming at low Reynolds numbers have already received considerable attention, but much less is known about swimming in shear-thinning fluids. A general understanding of the fundamental question of how shear-thinning rheology influences swimming still remains elusive. To probe this question further, we study a spherical squirmer in a shear-thinning fluid using a combination of asymptotic analysis and numerical simulations. Shear-thinning rheology is found to affect a squirming swimmer in non-trivial and surprising ways; we predict and show instances of both faster and slower swimming depending on the surface actuation of the squirmer. We also illustrate that while a drag and thrust decomposition can provide insights into swimming in Newtonian fluids, extending this intuition to problems in complex media can prove problematic.

An adaptive controller for nonlinear flutter suppression and free-play compensation

A technique aimed at neutralizing the presence of free-play effects in a control surface actuation chain is presented. It is based on an adaptive inversion of a function approximating such a nonlinearity. A simple, yet robust, on-line adaptive algorithm is proposed to identify the free-play parameters, i.e. free-play width, the equivalent control stiffness and friction. The procedure is then coupled to an immersion and invariance control law to drastically reduce possible residual closed-loop limit cycle oscillations due to the free-play nonlinearity. Within such a framework, the so chosen compensation technique can be interpreted as a control augmentation, easily extendable to multiple control surfaces. The methodology is then verified on a four-degree-of-freedom airfoil in a transonic regime, characterized by highly nonlinear unsteady aerodynamic loads, producing significant shock motions and large limit cycles, at a relatively high frequency. The presence of both aerodynamic and structural nonlinearities makes such a system bistable, leading to complex responses dependent on the initial conditions and the input used to excite the system. The effective suppression of these auto-induced vibrations becomes even more challenging because the limit cycle oscillations generated by different sources are characterized by differing amplitudes and frequencies.

A curvature-controllable, convex-mirror actuator based on carbon nanotube film composites

A novel round shape electrothermal actuator based on a bimorph structure with a cross-stacked superaligned carbon nanotube film and polydimethylsiloxane has been designed and fabricated. The coated silver film (100 nm thickness) makes the actuator surface like a mirror. Compared with common polymer nanocomposites based electrothermal actuators, our actuator exhibits a distinctive shape change. Due to the different coefficients of thermal expansion of the two material layers, it turns into a convex shape (a concave shape on the other surface) by using low electric field strengths such as < 200 V m−1. The curvature of the convex shape can be controlled by the voltage precisely. It can lift almost four times of its own weight. The cyclic actuation test shows the excellent stability of the actuator (over 2000 times). Owing to the advantages of low driving voltages, muscle-like responses, distinctive shape changes, mirror-like surface, stability, we think the novel actuator will have great potential usages in various applications, such as artificial muscles, optical devices, microsensors, microrobots, and so on.

Investigation of a Micro Dielectric Barrier Discharge Plasma Actuator for Regional Aircraft Active Flow Control

This paper reports a multitechnique investigation of a micro dielectric barrier discharge plasma actuator (DBDPA) as a promising system to control separated flows. The device was manufactured through a photolithographic technique and its performances and capabilities were compared with the ones of conventional macro DBDPAs. Alternate current operation under sinusoidal voltage excitation was studied in the absence of external flow by means of many experimental techniques like discharge imaging, flow visualizations, particle image velocimetry, infrared thermography, and electrical characterization. The influence of the operating parameters was investigated. The main results underlined that an increase in the voltage amplitude or frequency brought to a rise in the maximum induced velocity, electrical power dissipation, and actuator surface temperature. Moreover, it was assessed that the small heating of the micro DBDPA did not affect the actuated flow. A jet velocity up to 1.36 m/s was obtained at a 9.01 W/m electrical power dissipation per unit electrode length. The device realized by microelectronic fabrication technology allowed reaching a flow velocity magnitude comparable with the one of conventional macro DBDPAs, with a reduction in applied voltage, power dissipation, and actuator size. Furthermore, the induced wall jet was more confined in the area in proximity of the device, because of the limited plasma discharge extension.

Active noise control of a vibrating surface: Continuum and non-continuum investigations on vibroacoustic sound reduction by a secondary heat-flux source

We study the effect of surface heating on sound radiation by a vibrating boundary. Focusing on a setup of an infinite planar wall interacting with a semi-infinite expanse of a gas, the system response to arbitrary (small-amplitude) vibro-thermal excitation is investigated. Starting with the case of sinusoidal actuations, the superposed effect of boundary heat-flux excitation at a common frequency ω is examined. The entire range of frequencies is considered, where, depending on the ratio between ω and gas kinetic collision frequency ωcoll, fundamentally different flow regimes follow. The two limit cases of ω⪡ωcoll (continuum-flow conditions) and ω⪢ωcoll (ballistic flow regime) are investigated analytically, based on continuum equations and collisionless Boltzmann equation, respectively. In between, an intermediate interval of frequencies ω~ωcoll is analyzed numerically, based on the direct simulation Monte Carlo method. In search for optimal conditions for acoustic sound reduction, it is found that effective attenuation is obtained when boundary heat flux is applied at opposite phase to surface actuation. Amplitude-wise, conditions for minimization of the acoustic field vary between the limits: at low-frequency conditions, wave radiation extends over large distances from the wall, and optimal sound reduction is achieved when the ratio between wall-inserted thermal and kinetic energies |Eq/Ek|opt equals γ/(γ−1) (with γ denoting the ratio between gas specific heat capacities). At high-frequency conditions, wall signal affects only a thin gas layer (of the order of the mean free path) in the vicinity of the boundary, and optimal attenuation is achieved when |Eq/Ek|opt=1. The analysis is extended to consider the system response to non-periodic excitations, for the specific case of a delta-function input. Making use of the above collisionless- and continuum-limit analyses, early- and late-time system responses are computed. While conditions for optimal sound reduction at late times coincide with the low-frequency predictions in the periodic case, no counterpart agreement is found between early-time analysis and high-frequency periodic behavior.

Efficient needle plasma actuators for flow control and surface cooling

We introduce a milliwatt class needle actuator suitable for plasma channels, vortex generation, and surface cooling. Electrode configurations tested for a channel configuration show 1400% and 300% increase in energy conversion efficiency as compared to conventional surface and channel corona actuators, respectively, generating up to 3.4 m/s air jet across the channel outlet. The positive polarity of the needle is shown to have a beneficial effect on actuator efficiency. Needle-plate configuration is demonstrated for improving cooling of a flat surface with a 57% increase in convective heat transfer coefficient. Vortex generation by selective input signal manipulation is also demonstrated.

A transparent visuo-haptic input device with optical waveguide based thin film display, sensor and surface actuator

We demonstrate a transparent visuo-haptic input device. The device consists of optical waveguide based thin film display, sensor, and surface actuator. Highly transparent flexible display and sensor with high are fabricated by using Bisphenol A ethoxylate diacrylate (na=1.5647 @ 632nm) and Tetra diacrylate (na= 1.5031 @ 632nm) for core and clad, respectively. The display and sensor are thin (thickness:<70μm), highly transparent (optical transmittance: as high as 90%) and designed as a form of 3×9 matrix. Surface actuator is fabricated as a combination of ITO electrode coated two rectangular glass plates, which are sandwiched with a constant air gap. The surface actuator produces electrically induced dynamic deformation responses of displacement as high as 157μm and output force as large as 60mN under a sinusoidal input voltage signal of 2kV at 140Hz. The visuo-haptic display integrating the three functional components is capable of realizing sufficient and human perceivable vibro-tactile response on a touch interface for QWERTY keypad.

A case study involving continuous system methods of inverse simulation for an unmanned aerial vehicle application

Inverse simulation allows input time histories to be found that generate specified outputs for non-linear dynamic models in cases where analytical methods of inversion present difficulties. The two approaches considered involve continuous system simulation principles. One is an approximate differentiation method while the second involves feedback principles. These approaches are compared for a non-linear six-degrees-of-freedom flight-mechanics model of a fixed-wing unmanned aerial vehicle incorporating actuator sub-models with saturation and rate limits. Additional insight is provided through analysis of a linearised version of the vehicle model. It is concluded that both the continuous system simulation methods for finding inverse solutions, for the type of application described in this paper, provide a useful alternative to more conventional iterative methods of inverse simulation based on discrete models. In many cases, including those involving hard non-linearities in control surface actuator sub-systems, they allow issues of vehicle handling and manoeuvrability to be addressed in a more direct fashion than is possible using conventional simulation methods alone.