Actuator Surface Research Articles

Simulation of Rotorcraft Fuselage with Rotor Effects Using An Immersed Boundary Method

Computational fluid dynamics simulations of the flow around the ROtor Body INteraction (ROBIN)-mod7 fuselage with pressure-sensitive paint rotor are conducted using an immersed boundary method and an actuator surface model in OpenFOAM. The ROBIN-mod7 fuselage is represented by the immersed boundary method, while the unsteady rotor is modeled using the actuator surface model. A comprehensive analysis of the generic helicopter configuration is carried out for the hovering flight condition; the isolated fuselage is simulated to provide its baseline aerodynamics, and the isolated rotor and rotor–fuselage cases are studied to measure the rotor performance in hover and the fuselage effect on the performance. The validation of each test case is conducted against both experimental measurements and computational data from the literature. The surface pressure data from the isolated fuselage case shows good agreement with the experimental measurements. Also, the rotor performance predicted on the isolated and installed rotors (rotor–fuselage) has excellent agreement with the reference data; in particular, the performance data on the installed rotor agree with the experimental data better than the previous numerical study does. The fuselage effect has been analyzed by comparing the isolated rotor and rotor–fuselage datasets. The computational effort for different grid levels of each test case is provided. Overall, the results have demonstrated an equivalent level of accuracy compared to the previous high-fidelity simulation results at their fraction of setup and computational expenses.

A comprehensive RFD-FTC-DCA system for hypersonic vehicles with saturation constraints

A comprehensive RFD-FTC-DCA system is proposed for the hypersonic vehicle with saturation constraints to resist the control surface damage, actuator faults, disturbances and parameter perturbation. Firstly, the hypersonic vehicle fault model is established. Secondly, the robust fault detection (RFD) observer is designed to detect the control surface damage and actuator faults accurately under the influences of disturbances and parameter perturbation. Thirdly, the fault-tolerant control (FTC) law is designed to resist the control surface damage, actuator faults, disturbances and parameter perturbation simultaneously. Finally, a dynamic control allocation (DCA) algorithm is designed to reallocate the FTC law and limit the deflection angle and velocity within saturation constraint. The comparison simulation results are presented to demonstrate that the RFD observer can detect the faults accurately and reduce false alarm rates effectively, the FTC law can resist the control surface damage, actuator faults, disturbances and parameter perturbation simultaneously, and the tracing errors of attack angle, side-slip angle and roll angle are only , and , respectively, and the DCA algorithm can reallocate the FTC law and limit the deflection angle and velocity within saturation values.

Closed‐loop adaptive model predictive control of a bluff body wake

AbstractA machine learning methodology is outlined to achieve robust closed‐loop feedback control of a bluff body turbulent wake. A Long Short‐Term Memory (LSTM) Neural Network is implemented with Model Predictive Control (MPC) to achieve closed‐loop flow control. The LSTM model is trained using actuation and pressure sensor data to forecast future pressure states. The candidate system is a square cross‐sectional cylinder with two modulated moving surface actuators embedded in the windward face leading corners. The controller performance is tested experimentally for three objective functions: recovery of mean‐base pressure set‐point after perturbation; and minimization of drag or wake fluctuation intensity. An adaptive learning strategy is implemented to adjust the model to new Reynolds number (Re) conditions without user intervention, thereby extending the controller performance and achieving more robust control. The identified minimum drag and wake fluctuation cases are analysed using velocity field data measured with particle image velocimetry.

Study on Characteristics of an AC Sliding Discharge Plasma Actuator Operating at Different Pressures

Dielectric barrier discharge (DBD) has been one of the most promising techniques for flow control, but the practical application needs a large plasma surface. A three-electrode sliding discharge plasma actuator (SDPA) can generate plasma filling the inter-electrode distance. In this study, the performance of an SDPA for practical flight at low pressures is reported. When the pressure decreases, plasma discharge becomes more intensive. Current peaks and power consumption of electrode 1 become higher at low pressure. Sliding discharge is fully developed at 54 kPa, and the plasma morphology resembles plumes. PIV results show vortex structures and an induced wall jet above the actuator surface. A ‘potential-arc-discharge’ is observed at 38 kPa, leading to an inhomogeneous surface temperature distribution and a velocity decrease of the jet.

Coupling turbulent flow with blade aeroelastics and control modules in large-eddy simulation of utility-scale wind turbines

We present a large-eddy simulation framework capable of control co-design of large wind turbines, coupling the turbulent flow environment with blade aeroelastics and turbine controllers. The geometry and aerodynamics of the rotor blades and the turbine nacelle are parameterized using an actuator surface model. The baseline collective pitch control and individual pitch control (IPC) algorithms, consisting of a single-input, single-output proportional–integral controller and two integral controllers, respectively, are incorporated into the simulation framework. Furthermore, a second-order model based on the Euler–Bernoulli beam theory is implemented to describe the blade deformation. Simulations are carried out to investigate the impact of collective and individual pitch control strategies on the deflection of turbine blades. Our results show that the IPC reduces the blade tip deflection fluctuations in the out-of-plane direction, while the fluctuations of the blade tip deflection along the in-plane direction are barely affected by the IPC. Furthermore, the blade out-of-plane deformation fluctuation is underestimated by the one-way coupling approach compared to the two-way coupling approach. The findings of this study reveal the importance of advanced control systems in reducing the dynamic loads on wind turbine blades and underscore the potential of control co-design to reduce the levelized cost of wind energy.

Photomechanical Solid Polymers: Model for Pressure and Strain Induced by Photoisomerization and Photo-Orientation

Photoactive polymers are important for fundamental studies and applications in several area of photonics such as data storage and holography and nonlinear optics and photomechanics. The latter is perhaps one of the most important applications of such materials, since they act as light to mechanical energy transducers and move under light action. For example, azo-polymers irradiated by inhomogeneous resonant ultra-violet or visible light undergo molecular and macroscopic motion, at sub-glass transition temperatures by photoisomerization of the azo dyes. Our recent research in this field highlighted the fundamentals of mobility enhancement by light, including light-induced viscosity change and acceleration of relaxation times, and photomechanics, encompassing motions in gradients of actinic light leading to surface structuring and actuation. In this paper, we present an original model which predicts the creation of mechanical pressure, i.e., motion, by a photo-induced change in the occupied volume and length of anisometric isomers, and we give simple analytical expressions describing the dynamics of volume as well as strain change upon polarized light irradiation of photomechanic samples.

Event-triggered sliding mode trajectory tracking control for underactuated unmanned surface vessel

This article considers the trajectory tracking control for underactuated unmanned surface vessel and actuator loss caused by frequent updating of the controller. An event-triggered sliding mode trajectory tracking control algorithm is proposed for the problems. A sliding mode tracking controller is designed by the integral sliding surface at the beginning to guarantee global asymptotic tracking of the desired trajectory. Based on the tracking controller, the event-triggered condition is designed in the channel of the controller to actuator, which effectively reduces the update frequency of the controller. Theoretical analysis proves that the states of underactuated unmanned surface vessel are uniformly stable, while the Zeno behavior is prevented. The results of the numerical simulation are presented to demonstrate the effectiveness of the proposed algorithm.

Toward control co-design of utility-scale wind turbines: Collective vs. individual blade pitch control

A large-eddy simulation framework has been coupled with controller modules to systematically investigate the impacts of collective (CPC) and individual (IPC) pitch control strategies on utility-scale wind turbine energy production and fatigue loads. Wind turbine components were parameterized using an actuator surface model to simulate the rotor blades and the turbine nacelle. The baseline CPC and IPC algorithms, consisting of single-input single-output proportional–integral controllers and two integral controllers, respectively, were incorporated into the numerical framework. A series of simulations were carried out to investigate the relative performance of the two controllers under various turbulent inflow conditions, spanning hub-height velocities of 7 to 14 m/s. The numerical simulation results of this study showed that, in comparison to the CPC, the IPC controller could successfully reduce the damage equivalent loads of utility-scale turbines at regions 2 and 3 of turbine operation by about 3% and 40%, respectively, without any penalty on the power production of the turbine. It was also shown that, despite its minor impact on the turbulence kinetic energy of the wake, the IPC controller did not influence the recovery of the turbine wake.

Electromagnetic 2D scanning micromirror fabricated with 3D printed polymer parts for LiDAR applications

In this research, an omnidirectional scanning micromirror fabricated using a three-dimensional (3D) printing process and manual assembly is presented. The core part of the scanning micromirror is printed with photocurable resin using vat polymerization based on digital light processing. Externally fabricated 6mm-diameter aluminum-coated silicon mirror plate, self-supported coils, and permanent magnets were assembled with the printed part to provide a reflective surface and electromagnetic actuation. Two types of devices with different spring shapes were designed and tested. Modal analyses were performed for each model with different magnet combinations in the design phase. To optimize the 3D printing process, resin mixtures with various mixing ratios were tested. An optical scan angle of 8.98° has been obtained for model #1 printed with an ABS-like resin at 309 Hz and an input current of 0.2 A rms . For model #2 printed with a 9:1 mixture of ABS-like resin and B9R-2-Black resin, an optical scan angle of 6.04° at 356 Hz an input current of 0.2 A rms has been obtained. Spiral scan patterns with various modulation depths were generated using model #1. • An omnidirectional scanning micromirror fabricated using a 3D printing process • Core part of the device is printed with vat polymerization using DLP • Resin mixtures with various mixing ratios were tested to optimize the fabrication • Two types of devices with different spring geometries were designed and tested

Review of Turbine Parameterization Models for Large-Eddy Simulation of Wind Turbine Wakes

Wind turbine parameterization models, which are often employed to avoid the computational cost of resolving the blade aerodynamics, are critical for the capability of large-eddy simulation in predicting wind turbine wakes. In this paper, we review the existing wind turbine parameterization models, i.e., the actuator disk model, the actuator line model, and the actuator surface model, by presenting the fundamental concepts, some advanced issues (i.e., the force distribution approaches, the method for velocity sampling, and the tip loss correction), and their applications to utility-scale wind farms. Emphasis is placed on the predictive capability of different parameterizations for different wake characteristics, such as the blade load, the tip vortices and hub vortex in the near wake, and the meandering of the far wake. The literature demonstrated the importance of taking into account the effects of nacelle and tower in wind turbine wake predictions. The predictive capability of the actuator disk model with different model complexities, which is preferred in wind farm simulations, is systematically reviewed for different inflows and different wind turbine designs. Applications to wind farms show good agreements between simulation results and measurements.

Feed-forward Control of Vortices Using Real-Time Particle Image Velocimetry

Active flow control (AFC) is a topic with enormous potential for improving a wide array of technologies. This work presents the use and evaluation of a novel AFC system to apply feed-forward control to vortices formed in the wake of a wall-mounted spherical cap. A real-time particle image velocimetry (RT-PIV) system served as the sensor for the AFC system. The RT-PIV system produced 7.35 vector fields per second, each consisting of a two-dimensional grid of 5 × 37 velocity vectors. The actuator system consisted of a rubber surface that could deform using 16 independently controlled linear actuators. The actuators were controlled to apply wall-normal surface deformation at velocities proportional to wall-normal velocities measured by the RT-PIV system upstream of each of the 16 actuators. Analysis of the RT-PIV measurements in comparison to those from an offline PIV system run in parallel indicated that the RT-PIV system produced accurate flow measurements. As well, it was found that the RT-PIV system had a delay of approximately 0.09 seconds. The evaluation of the actuator system indicated that the actuator displacements were consistently damped by 20-25% and lagged the control signal by approximately 0.1 seconds relative to the input signal to the actuators. Therefore, the AFC system had a total delay of approximately 0.2 seconds and applied slightly weaker than specified actuations. These results were within anticipated values and, overall, the AFC system functioned adequately. The impacts of the flow control included disruption of the coherent ejection and sweep structures formed in the wake of the spherical cap and the formation of numerous smaller turbulent structures. As well, several of the control cases showed altered wall-normal velocity fluctuation variance fields in comparison to that of the unforced wake. This is a promising result for AFC using deformable surface actuators as it shows that the active control had a significant effect on an average quantity of the flow.

Large-Eddy Simulation of Wakes of Waked Wind Turbines

The wake dynamics of a wind turbine are influenced by the atmospheric turbulence and the wake of its upwind turbine. In this work, we investigate the wake characteristics of a waked wind turbine for four different downwind spacings and three different inflows using large-eddy simulation with a turbine parameterized using the actuator surface model. The wake statistics of the waked turbine are compared with those of the stand-alone wind turbine under the same inflow. The results show that the oncoming wake significantly affects the near wake of the waked turbine, where it accelerates the wake recovery by increasing the turbulent convection, and increases the turbulence kinetic energy. The velocity deficit and turbulence kinetic energy in the far wake, on the other hand, are fairly similar with each other for the considered different turbine spacings, and are close to those of the stand-alone wind turbine. As for the wake meandering of the waked wind turbines, it is initiated quickly and enhanced by the oncoming wake turbulence, as shown by the meandering amplitudes and the power spectral density of the instantaneous wake positions. The growth rates of the wake meandering from the waked wind turbines, on the other hand, are close to that of the stand-alone wind turbine, indicating the critical role of the atmospheric turbulence on wake meandering. The present work details how the oncoming wake influences the wake dynamics of the downwind turbine, and provides physical insights on developing engineering models to take into account such effects.

Optimal transport of surface-actuated microswimmers

We analyze the transport behavior of surface-actuated spheroidal microswimmers that locomote steadily with or without a spatiotemporally uniform external forcing. The surface actuation is in the form of either a tangential surface motion or a zero-net-mass-flux wall-normal transpiration. Starting from a general modal expansion in terms of an appropriate basis set, we link the surface actuation, the force exerted on the spheroid, and its forward speed through a Stokesian representation of the microhydrodynamics. Our analysis is generic and enables a systematic investigation over the complete range of aspect ratios from zero (streamlined needlelike spheroid) to infinity (disc-shaped spheroid). We identify a critical aspect ratio of 1.82 below and above which tangential and wall-normal surface actuations enable transport at minimal energetic cost, irrespective of whether the spheroidal microswimmer is free or forced. Crucially, we find the propulsive performance of a forced spheroidal swimmer to be appreciably higher than the one of an analogous self-propelled swimmer. Most importantly, the optimal energy expenditure minimizing tangential or wall-normal surface actuation for forced transport is passive overall so that the power requirement arises solely from the rate at which work is done by the external forcing. We highlight the complementing roles of external forcing and surface actuation over moderate and extreme aspect ratios and also exemplify the crucial disparities between optimal transport in free and forced environments. Our results indicate that a combination of external forcing and an optimal surface actuation could substantially enhance the transport of generic streamlined and bluff microswimmers.

Predictive capability of actuator disk models for wakes of different wind turbine designs

To evaluate the predictive capability of the actuator disk (AD) models in simulating wakes of different wind turbine designs, we compare the results of the AD simulation with those of the actuator surface (AS) simulation for the EOLOS, NREL and a variant of the NREL (i.e., NREL-V) wind turbine designs. Two types of AD models are considered, i.e., the AD-R and AD-NR models corresponding to the AD model with and without rotational effects, respectively. For the AD models, the force coefficients are both obtained from the corresponding AS simulations. The results from the AD simulation are compared with those of AS simulations. It is observed that the velocity profiles predicted by the AD models agree well with the AS predictions. For the turbulent kinetic energy and the Reynolds shear stress, differences appear at far wake locations (7D, and 9D downwind of the turbine where D is the rotor diameter) for both the EOLOS and the NREL-V turbines. In case of the NREL turbine, on the other hand, there is an overall good agreement except in 3D downwind to the turbine. Furthermore, the modes obtained by using the proper orthogonal decomposition from the AD and AS simulations are also presented and compared with each other, indicating that the distribution of the mode energy, and the location and features of the mode patterns differ for different turbine designs.

Efficacy of graphitic allotrope’s surface area in silicone rubber based composites for reverse piezo-electric actuation: Nano effect

Filler surface areas importantly determine the properties of rubber composites. In this study, the reverse piezo-electric actuation efficacies of three graphitic allotropes were studied in room temperature vulcanized silicone rubber (RTV-SR) based composites. The three fillers examined were graphite, nanographite, and graphene. Specific surface areas were determined using the Brunauer–Emmett–Teller (BET) method in a nitrogen atmosphere. BET testing showed graphite, nanographite, and graphene had surface areas of 30, 110, and 650 m2/g respectively. Mechanical properties showed that fillers with greater BET surface areas had higher compressive moduli, tensile strengths, fracture strains, and tensile moduli. Similarly, actuation measurements obtained at 10 kV showed that composites containing graphene produced significantly greater actuation displacements than those containing nanographite or graphite. The figure of merit showed filler BET surface areas played a key role in determining the mechanical and actuation properties of composites. For example, as the surface area increases, the properties and actuation displacement increases exponentially. To sum-up, graphene filled silicone rubber composites exhibited better mechanical properties and much better actuation displacements than graphite or nanographite filled composites.

A Low Cost Oscillating Membrane for Underwater Applications at Low Reynolds Numbers

Active surface morphing is a nonintrusive flow control technique that can delay separation in laminar and turbulent boundary layers. Most of the experimental studies of such control strategy have been carried out in wind tunnels at low Reynolds numbers with costly actuators. In contrast, the implementation of such a control strategy at low cost for an underwater environment remains vastly unexplored. This paper explores active surface morphing at low cost and at low Reynolds for underwater applications. We do this with a 3D printed foil submerged in a water tunnel. The suction surface of the foil is covered with a magnetoelastic membrane. The membrane is actuated via two electromagnets that are positioned inside of the foil. Three actuation frequencies (slow, intermediate, fast) are tested and the deformation of the membrane is measured with an optosensor. We show that lift increases by 1%, whilst drag decreases by 6% at a Strouhal number of 0.3, i.e., at the fast actuation case. We demonstrate that surface actuation is applicable to the marine environment through an off the shelf approach, and that this method is more economical than existing active surface morphing technologies. Since the actuation mechanism is not energy intensive, it is envisioned that it could be applied to marine energy devices, boat appendages, and autonomous underwater vehicles.

A reduced-order model for the near wake dynamics of a wind turbine: Model development and uncertainty quantification

Wind turbine power production and its variability are affected by unsteady, turbulent structures that are induced in the wake and emerge over a range of disparate length scales. However, the inclusion of the unsteady dynamics in wake models remains difficult in kinematic modeling where steady-state conditions are assumed. We develop and quantify the uncertainty of an unsteady wake model by leveraging model-order reduction. The wake is modeled as a dynamical system based on dynamic mode decomposition and compressive sensing, where the system is reduced by designating an objective function to select energetic turbulent structures represented by dynamic modes. A series of large-eddy simulations are undertaken using the actuator line model and the actuator surface with nacelle model for training and testing data. Differences in the turbine parameterizations of near wake simulations are used to identify how modes are related to turbulent structures and are selected through compressive sensing. The results showed that the flow field can be constructed with few modes. The modes are the most energetic and have frequencies related to pertinent features such as tip and hub vortices. While the error in the training phase is dependent on the number of modes, the relative error remains less than 6% and is largely independent of the number of modes during the prediction phase if certain modes are retained. The error accumulates over time near the turbine blades. However, error accumulation does not have a significant impact on the prediction of instantaneous velocity in the wake further downwind.

Control Allocation Reconfiguration for Actuator Failure on a Coaxial-Pusher Helicopter

An elastic blade flight dynamics model for a coaxial helicopter platform based on the Sikorsky X2 Technology™ Demonstrator is presented and validated with steady trim and frequency response flight-test data. A full authority explicit model following control architecture along with pseudoinverse control allocation is implemented for the model in hover and cruise at 180 kt using CONDUIT® in order to stabilize the vehicle and meet a set of stability, handling qualities, and performance requirements. Different fault scenarios are considered including failure of rotor swashplate actuators and tail surface actuators in hover and forward flight, which are compensated for by recalculating the pseudoinverse control mixing accordingly. The approach is shown to maintain aircraft stability through the fault transient and into a new steady trim state for the vehicle. Though the implemented controller is successful in maintaining the aircraft state, different fault cases lead to violations in rotor tip clearance limits, which will require additional effort to account for in flight.

동축 로터 해석을 위한 Actuator Model을 포함한 압력 기반의 압축성 유동 해석자 개발

The purpose of present study is to develop a pressure based compressible flow solver with actuator models to estimate the performance of coaxial rotor. In order to aim this purpose, actuator models which used developed for the single rotor performance was modified to analyze the coaxial rotor performance by isolating and correcting the effect of each rotor blade. In addition, the suggested Actuator models were combined with a pressure based compressible solver which was developed previous research. The hovering rotor analysis results calculated by the developed solver were compared with Full-CFD results with a body fitted mesh. The proposed actuator methods can predict the thrust and power of a coaxial rotor as accurately as a full-CFD method. Moreover, the suggested actuator surface model well predicts the interaction effects between near blades than previous manner.

Time-Averaged Wind Turbine Wake Flow Field Prediction Using Autoencoder Convolutional Neural Networks

A convolutional neural network (CNN) autoencoder model has been developed to generate 3D realizations of time-averaged velocity in the wake of the wind turbines at the Sandia National Laboratories Scaled Wind Farm Technology (SWiFT) facility. Large-eddy simulations (LES) of the SWiFT site are conducted using an actuator surface model to simulate the turbine structures to produce training and validation datasets of the CNN. The simulations are validated using the SpinnerLidar measurements of turbine wakes at the SWiFT site and the instantaneous and time-averaged velocity fields from the training LES are used to train the CNN. The trained CNN is then applied to predict 3D realizations of time-averaged velocity in the wake of the SWiFT turbines under flow conditions different than those for which the CNN was trained. LES results for the validation cases are used to evaluate the performance of the CNN predictions. Comparing the validation LES results and CNN predictions, we show that the developed CNN autoencoder model holds great potential for predicting time-averaged flow fields and the power production of wind turbines while being several orders of magnitude computationally more efficient than LES.