Twist Distribution Research Articles

A Design Method for Twist Distribution along Wing Span

A design method for wing jig shape twist is proposed. Target cruising aerodynamic loads are applied to structure model, and the deformation converge gradually using predictor-correction displacement iterative method. When ensuring the relative twist distribution in the streamwise section, a wing jig shape with straight leading ledge is created, then an aeroelastic coupling iteration is started to achieve the deformed elastic cruising shape. Taking a large aspect ratio swept wing as an example, analysis results show that the deformed elastic cruising wing had an identical streamwise twist distribution compared with rigid designed cruising shape. Sectional lift distribution along with pressure distribution matches well with that of the designed cruising shape, and the drag gap among them is not significant. There might be some change in shock wave chord position between elastic cruising wing and designed cruising wing for outboard wing section. By slight adjusting twist with unchanged airfoil profile, the difference above could be improved.

Wideband Omnidirectional Slotted-Waveguide Antenna Array Based on Trapezoidal Slots

This manuscript presents a novel approach for designing wideband omnidirectional slotted-waveguide antenna arrays, which is based on trapezoidal-shaped slots with two different electrical lengths, as well as a twisted distribution of slot groups along the array longitudinal axis. The trapezoidal section is formed by gradually increasing the slot length between the waveguide interior and exterior surfaces. In this way, a smoother impedance transition between waveguide and air is provided in order to enhance the array operating bandwidth. In addition, we propose a twisting technique, responsible to improve the omnidirectional pattern, by means of reducing the gain ripple in the azimuth plane. Experimental results demonstrate 1.09 GHz bandwidth centered at 24 GHz (4.54% fractional bandwidth), gain up to 14.71 dBi over the operating bandwidth, and only 2.7 dB gain variation in the azimuth plane. The proposed antenna array and its enabling techniques present themselves as promising solutions for mm-wave application, including 5G enhanced mobile broadband (eMBB) communications.

A Study of Pre-flare Solar Coronal Magnetic Fields: Magnetic Flux Ropes

Abstract Magnetic flux ropes (MFRs) are thought to be the central structures of solar eruptions, and their ideal MHD instabilities can trigger the eruption. Here we performed a study of all the MFR configurations that lead to major solar flares, either eruptive or confined, from 2011 to 2017 near the solar disk center. The coronal magnetic field is reconstructed from observed magnetograms, and based on magnetic twist distribution, we identified the MFR, which is defined as a coherent group of magnetic field lines winding an axis with more than one turn. It is found that 90% of the events possess pre-flare MFRs, and their three-dimensional structures are much more complex in details than theoretical MFR models. We further constructed a diagram based on two parameters, the magnetic twist number which controls the kink instability (KI), and the decay index which controls the torus instability (TI). It clearly shows lower limits for TI and KI thresholds, which are n crit = 1.3 and , respectively, as all the events above n crit and nearly 90% of the events above erupted. Furthermore, by such criterion, over 70% of the events can be discriminated between eruptive and confined flares, and KI seems to play a nearly equally important role as TI in discriminating between the two types of flares. More than half of the events with both parameters are below the lower limits, and 29% are eruptive. These events might be triggered by magnetic reconnection rather than MHD instabilities.

Geometrical Design of a Rotor Blade for a Small Scale Horizontal Axis Wind Turbine

In the present study, Blade Element Momentum theory (BEMT) has been implemented to heuristically design a rotor blade for a 2kW Fixed Pitch Fixed Speed (FPFS) Small Scale Horizontal Axis Wind Turbine (SSHAWT). Critical geometrical properties viz. Sectional Chord ci and Twist distribution θTi for the idealized, optimized and linearized blades are analytically determined for various operating conditions. Results obtained from BEM theory demonstrate that the average sectional chord ci and twist distribution θTi of the idealized blade are 20.42% and 14.08% more in comparison with optimized blade. Additionally, the employment of linearization technique further reduced the sectional chord ci and twist distribution θTi of the idealized blade by 17.9% and 14% respectively, thus achieving a viable blade bounded by the limits of economic and manufacturing constraints. Finally, the study also reveals that the iteratively reducing blade geometry has an influential effect on the solidity of the blade that in turn affects the performance of the wind turbine.

Using PSO Algorithm to Compensate Power Loss Due to the Aeroelastic Effect of the Wind Turbine Blade

Power loss due to the aeroelastic effect of the blade is becoming an important problem of large-scale blade design. Prior work has already employed the pretwisting method to deal with this problem and obtained some good results at reference wind speed. The aim of this study was to compensate for the power loss for all of the wind speeds by using the pretwisting method. Therefore, we developed an aeroelastic coupling optimization model, which takes the pretwist angles along the blade as free variables, the maximum AEP (annual energy production) as the optimal object, and the smooth of the twist distribution as one of the constraint conditions. In this optimization model, a PSO (particle swarm optimization) algorithm is used and combined with the BEM-3DFEM (blade element momentum—three-dimensional finite element method) model. Then, the optimization model was compared with an iteration method, which was recently developed by another study and can well compensate the power loss at reference wind speed. By a design test, we found that the power loss can be reduced by pretwisting the origin blade, whether using the optimization model or the iteration method. Moreover, the optimization model has better ability than the iteration method to compensate the power loss with lower thrust coefficient while keeping the twist distribution smooth.

A CFD Based Application of Support Vector Regression to Determine the Optimum Smooth Twist for Wind Turbine Blades

Computational fluid dynamics (CFD) is a powerful tool to estimate accurately the aerodynamic loads on wind turbine blades at the expense of high requirements like the duration of computation. Such requirements grow in the case of blade shape optimization in which several analyses are needed. A fast and reliable way to mimic the CFD solutions is to use surrogate models. In this study, a machine learning technique, the support vector regression (SVR) method based on a set of CFD solutions, is used as the surrogate model. CFD solutions are calculated by solving the Reynolds-averaged Navier–Stokes equation with the k-epsilon turbulence model using a commercial solver. The support vector regression model is then trained to give a functional relationship between the spanwise twist distribution and the generated torque. The smooth twist distribution is defined using a three-node cubic spline with four parameters in total. The optimum twist is determined for two baseline blade cases: the National Renewable Energy Laboratory (NREL) Phase II and Phase VI rotor blades. In the optimization process, extremum points that give the maximum torque are easily determined since the SVR gives an analytical model. Results show that it is possible to increase the torque generated by the NREL VI blade more than 10% just by redistributing the spanwise twist without carrying out a full geometry optimization of the blade shape with many shape-defining parameters. The increase in torque for the NREL II case is much higher.

Interplanetary flux ropes of any twist distribution

Context. Recent investigations indicate that the magnetic field configuration in interplanetary flux ropes is in contrast with the common magnetic field models that are used to fit them, namely constant-alpha force-free fields, whose twist increases without limits toward the flux-rope boundary. Therefore, magnetic field configurations with a constant twist are now being employed in fits. Aims. Real flux ropes have varying twist. Therefore, analytical magnetic field configurations with prescribed twist distributions are searched for in cylindrical geometry. Methods. Equations for the field solenoidality and for the force-free condition are solved for case when a twist profile is prescribed. Results. A model of a force-free magnetic field configuration with an arbitrarily given twist distribution in a cylinder and its relative helicity per unit length are presented. It is applied to a core-envelope model recently suggested in studies of twist in magnetic clouds.

Design of a Horizontal Axis Tidal Turbine for Less Energetic Current Velocity Profiles

Existing installations of tidal-stream turbines are undertaken in energetic sites with flow speeds greater than 2 m/s. Sites with lower velocities will produce far less power and may not be as economically viable when using “conventional” tidal turbine designs. However, designing turbines for these less energetic conditions may improve the global viability of tidal technology. Lower hydrodynamic loads are expected, allowing for cost reduction through downsizing and using cheaper materials. This work presents a design methodology for low-solidity high tip-speed ratio turbines aimed to operate at less energetic flows with velocities less than 1.5 m/s. Turbines operating under representative real-site conditions in Mexico and the Philippines are evaluated using a quasi-unsteady blade element momentum method. Blade geometry alterations are undertaken using a scaling factor applied to chord and twist distributions. A parametric filtering and multi-objective decision model is used to select the optimum design among the generated blade variations. It was found that the low-solidity high tip-speed ratio blades lead to a slight power drop of less than 8.5% when compared to the “conventional” blade geometries. Nonetheless, an increase in rotational speed, reaching a tip-speed ratio (TSR) of 7.75, combined with huge reduction in the torque requirement of as much as 30% paves the way for reduced costs from generator downsizing and simplified power take-off mechanisms.

Lag-twist coupling sensitivity and design for a composite blade cross-section with D-spar

In this paper, the effect of various parameters of a specific rotor blade cross-section on the effectiveness of a twist morphing concept is investigated. Then, by considering different constraints, a cross-section consistent with this morphing concept with high lag-twist coupling and low extension-twist, is developed. This lag bending-torsion coupling is used to change the twist of the blade during the flight, while the high values of extension-twist coupling is avoided. To this end, a concentrated mass is added to the blade, where its chordwise location varies in flight. When the mass moves in the chordwise direction, a local lag bending is introduced into the blade. This in-plane bending moment then changes the blade twist distribution through lag-twist coupling induced through stiffness tailoring in the blade cross-section. Therefore, this coupling plays an important role in this morphing concept. The one-dimensional dynamics of the blade is modelled by using the geometrically exact fully intrinsic bean equations while the 2D cross-sectional stiffness values are determined by using the VABS software. First, a blade which resembles the BO-105 main rotor blade in the fundamental frequencies is designed. Then, the effect of various parameters of the cross-section on the fundamental frequencies, the lag-twist coupling, and the extension-twist coupling are determined. It is found that the skin of the spar has the highest contribution to both the extension-twist and the lag-twist coupling. Finally, a cross-section compatible with the proposed morphing concept is designed and it is demonstrated that the twist of the blade may be changed significantly.

Improvement of aerodynamic performance of a small wind turbine

The aerodynamic performance of horizontal-axis wind turbines is strongly dependent on many parameters, among which the airfoil type and the blade geometry (mainly defined by the chord and the twist distributions) are considered the most critical ones. In this article, an approach giving the appropriate airfoil for a small wind turbine design was conducted by performing an aerodynamic improvement of the blade’s airfoil. First, a preliminary design of the rotor blades of a small wind turbine (11 kW) was conducted using the small wind turbine rotor design code. This preliminary approach was done for different airfoils, and it resulted in a maximum power coefficient of 0.40. Then, the aerodynamic efficiency of the wind turbine was improved by modifying the geometry of the airfoils. This technique targets the optimization of the lift-to-drag ratio (Cl/Cd) of the airfoil within a range of angles of attack. Also, a non-uniform rational B-spline approximation of the airfoil was adopted in order to reduce the number of the design variables of the optimization. This methodology determined the best airfoil for the design of a small wind turbine, and it gave an improved power coefficient of 0.42.

Theoretical study of the effects on yarn strength in a modified ring spinning system

A modified ring spinning system using a dynamic twist-resistant device has been employed to produce yarn. The modified device blocks twist to propagate to the spinning triangle, which changes the distribution of twist in the spinning area and increases the height of the spinning triangle. In this paper, two kinds of yarn counts (30 and 40 Ne) are spun in the conventional and modified ring spinning with twist multipliers of 3.2, 3.6, and 4.0. The results show that the yarn spun by the modified ring spinning system possesses a higher strength compared with the conventional yarn except in the higher twist multiplier. The increase in yarn strength was theoretically analyzed according to the model of yarn strength. The yarn strength was calculated by considering the original fiber strain in the yarn and the fiber strain due to yarn strain. In the model, the fiber migration was considered and the fiber entanglement caused by fiber migration was ignored to simplify the calculation. Four potentially important parameters of the spinning triangle, the height of the spinning triangle, the migration coefficient, the inclination angle, and the spinning tension, were proposed and their individual and interaction effects on yarn strength were analyzed. The results demonstrate that yarn strength increased with the increase of height of the spinning triangle and the migration coefficient. The inclination angle and the spinning tension have a relatively small influence on yarn strength when the height of the spinning triangle is higher.

Different functionalized chord and twist distributions in aerodynamic design of HAWTs

In this study, blade element momentum (BEM) theory has been used to calculate power output and performance of 100 kW and 1 MW horizontal axis wind turbine. Riso‐A1‐21 airfoils are considered as utilized section along the blade span. Generally, Riso family of airfoils is appropriate for wind turbine application. In order to improve the accuracy of turbine performance prediction, lots of corrections have been applied on the BEM method. The aim of this research study is proposing a new procedure to introduce the chord and twist distributions by fitting different types of functions on them. Accordingly, 48 functions are selected as possible distributions for chord and twist angle profiles. These functions are selected in such a way that their behavior is close to the trend of their classical distributions. The utilized design method in this study is optimum in terms of performance and also making distribution of chord and twist functional which is more appropriate for manufacturing process. Finally, the effect of using best functions on blade aerodynamic coefficients has been studied. Results show that despite the changing chord and twist distributions from their classical trends, the aerodynamic coefficients are approximately similar to those in the classical design except in some region of blade. © 2019 American Institute of Chemical Engineers Environ Prog, 38:e13108, 2019

Weighted Least Squares Approach for an Adaptive Aerodynamic Engineered Structure With Twist Transformation

A design concept for a wind turbine blade with an adaptive twist transformation is presented. The design improves partial-load wind capture by adapting the twist distribution in relation to wind speed. Structural adaptability is enabled by actuating a series of compliant sections that are mounted on a relatively rigid spar. The sections are assumed to have a unique stiffness that is achievable through additive manufacturing technology. The authors' prior work employed an aerodynamic model to establish the theoretical blade twist distribution as a function of wind speed. The work in this paper focuses on a method to optimize the stiffness of each blade section that has been previously defined. A mathematical model is proposed to support design optimization. The model is parameterized in terms of actuator locations and the torsional stiffness ratios of each blade section. These parameters are optimized to allow the blade to adapt its twist distribution to match the prescribed configurations. The optimization is completed using a weighted-least squares approach that minimizes the error between the theoretical and practical design. The selected solution is based upon the configuration that maximizes production. Weights are assigned to bias the performance of the blade toward different operating regimes. Our results indicate that quadratically penalizing twist angle errors toward the blade tip increases power capture. A Rayleigh distribution is used to create three sets of wind data, which vary in average speed. These sets of data are used to evaluate the performance of the proposed blade and design technique.

Numerical Investigation of Configurations with Optimum Swirl Recovery for Propeller Propulsion Systems

This paper addresses the design of swirl recovery vanes for propeller propulsion in tractor configuration at cruise conditions using numerical tools. A multifidelity optimization framework is formulated for the design purpose, which exploits low-fidelity potential flow-based analysis results as input for high-fidelity Euler equation-based simulations. Furthermore, a model alignment procedure between low- and high-fidelity models is established based on a shape-preserving response prediction algorithm. Two cases of swirl recovery are examined. The first is the swirl recovery by the trailing wing, which leads to a reduction of the lift-induced drag. This is achieved by the optimization of the wing twist distribution. The second case is swirl recovery by a set of stationary vanes, which leads to production of additional thrust. In the latter case, four configurations are evaluated by locating the vanes at different azimuthal and axial positions relative to the wing. An optimum configuration is identified where the vanes are positioned on the blade-downgoing side downstream of the wing. For the configuration and conditions examined, the wing twist optimization reduces the induced drag by 3.9 counts (5.9% of wing-induced drag), whereas the optimized 4-bladed SRVs lead to an induced-drag reduction of 6.1 counts (9.2% of wing-induced drag).

Non-monotonic, lily-like twist distribution in toroidal nematics.

Toroidal nematics are droplets of nematic liquid crystals in the form of a circular torus. When the nematic director is subject to planar degenerate boundary conditions, the bend-only director field with vector lines along the parallels of all nested torodial shells is an equilibrium solution for all values of the elastic constants. Local stability analyses have shown that an instability is expected to occur for sufficiently small values of the twist elastic constant. It is natural to wonder whether in this regime the global equilibrium would be characterized by a monotonic twist, or not. In the former case, the twist distribution over the torus' circular cross-section would be represented pictorially by a fennel-like surface emanating from the centre. We prove that instead the stable twist distribution is represented by a lily-like surface. Thus, generically the twist distribution is not monotonic and its maximum may fall well within the torus, far away from the boundary. To cope with the peculiar complexity of the elastic free-energy functional in the fully non-linear setting, we developed an ad hoc deep-learning optimization method, which here is also further validated and documented for it promises to be applicable to other similar problems, equally intractable analytically.

High-throughput mechanotransduction in Drosophila embryos with mesofluidics.

Developing embryos create complexity by expressing genes to coordinate movement which generates mechanical force. An emerging theory is that mechanical force can also serve as an input signal to regulate developmental gene expression. Experimental methods to apply mechanical stimulation to whole embryos have been limited, mainly to aspiration, indentation, or moving a coverslip; these approaches stimulate only a few embryos at a time and require manual alignment. A powerful approach for automation is microfluidic devices, which can precisely manipulate hundreds of samples. However, using microfluidics to apply mechanical stimulation has been limited to small cellular systems, with fewer applications for larger scale whole embryos. We developed a mesofluidic device that applies the precision and automation of microfluidics to the Drosophila embryo: high-throughput automatic alignment, immobilization, compression, real-time imaging, and recovery of hundreds of live embryos. We then use twist:eGFP embryos to show that the mechanical induction of twist depends on the dose and duration of compression. This device allows us to quantify responses to compression, map the distribution of ectopic twist, and measure embryo stiffness. For building mesofluidic devices, we describe modifications on ultra-thick photolithography, derive an analytical model that predicts the deflection of sidewalls, and discuss parametric calibration. This "mesomechanics" approach combines the high-throughput automation and precision of microfluidics with the biological relevance of live embryos to examine mechanotransduction. These analytical models facilitate the design of future devices to process multicellular organisms such as larvae, organoids, and mesoscale tissue samples.

A design methodology for quiet and long endurance MAV rotors

Over the last 10 years, the use of micro air vehicles has rapidly covered a broad range of civilian and military applications. While most missions require optimizing the endurance, a growing number of applications also require acoustic covertness. For rotorcraft micro air vehicles, combining endurance and covertness heavily relies on the capability to design new propulsion systems. The present paper aims at describing a complete methodology for designing quiet and efficient micro air vehicle rotors, ranging from preliminary aerodynamic prediction to aeroacoustic optimization to experimental validation. The present approach is suitable for engineering purposes and can be applied to any multirotor micro air vehicle. A fast-response and reliable aerodynamic design method based on the blade-element momentum theory has been used and coupled with an extended acoustic model based on the Ffowcs Williams and Hawkings equation as well as analytical formulations for broadband noise. The aerodynamic and acoustic solvers have been coupled within an optimization tool. Key design parameters include the number of blades, twist and chord distribution along the blade, as well as the choice of an optimal airfoil. An experimental test bench suitable for non-anechoic environment has been developed in order to assess the benefit of the new rotor designs. Optimal rotors can maintain high aerodynamic efficiency and low acoustic signature with noise reductions in the order of 10 dB(A).

Application of double cylindrical tube having arbitrary twist distribution to twistable morphing wing and experimental demonstration

Application of double cylindrical tube having arbitrary twist distribution to twistable morphing wing and experimental demonstration

KUBeetle-S: An insect-like, tailless, hover-capable robot that can fly with a low-torque control mechanism

For an insect-like tailless flying robot, flapping wings should be able to produce control force as well as flight force to keep the robot staying airborne. This capability requires an active control mechanism, which should be integrated with lightweight microcontrol actuators that can produce sufficient control torques to stabilize the robot due to its inherent instability. In this work, we propose a control mechanism integrated in a hover-capable, two-winged, flapping-wing, 16.4 g flying robot (KUBeetle-S) that can simultaneously change the wing stroke-plane and wing twist. Tilting the stroke plane causes changes in the direction of average thrust and the wing twist distribution to produce control torques for pitch and roll. For yaw (heading change), root spars of left and right wings are adjusted asymmetrically to change the wing twist during flapping motion, resulting in yaw torque generation. Changes in wing kinematics were validated by measuring wing kinematics using three synchronized high-speed cameras. We then performed a series of experiments using a six-axis force/torque load cell to evaluate the effectiveness of the control mechanism via torque generation. We prototyped the robot by integrating the control mechanism with sub-micro servos as control actuators and flight control board. Free flight tests were finally conducted to verify the possibility of attitude control.

Investigation of Twisting Moment of Twistable Morphing Wing Having Arbitrary Twist Distribution

Investigation of Twisting Moment of Twistable Morphing Wing Having Arbitrary Twist Distribution