Optimal Pitch Research Articles

Optimal Adaptive Robust Pitch Control with Load Mitigation for Uncertain Variable Speed Wind Turbines

In this paper, an optimal adaptive robust pitch controller is proposed for variable speed wind turbines (VSWTs). The proposed pitch controller has stability analysis, while it simultaneously keeps the generated power of the wind turbine at the rated power and mitigates the mechanical loads on the gearbox. The proposed pitch controller in this paper has two terms. The first term is a radial basis function neural network (RBFNN), to approximate unknown nonlinear functions of the wind turbine. Another term is a chattering-free continuous robust structure, which can cope with the approximation error. The weights of RBFNN and the gain of the robust structure are derived via the Lyapunov synthesis approach. It is proved that the closed-loop signals are semi-globally uniformed and ultimately bounded. The optimal parameters of the proposed controller are derived by solving a proposed multi-objective optimization problem using non-dominated sorting genetic algorithm-II (NSGA-II) and multi-objective particle swarm optimization (MOPSO) algorithm. The effectiveness of the proposed controller is compared to the baseline PI controller designed by NREL. First, both the proposed and the baseline PI controllers are applied to the general model (2-mass model) of the wind turbine, and then they are validated via a highly reliable simulator called FAST. The results demonstrate the effectiveness and applicability of the proposed pitch controller.

The study of nucleation site interactions on the mixed wettability rough surface

In order to achieve the best heat transfer performance on a mixed wettability surface, engineering of the wettability pattern is often used as heat transfer performance is significantly dependent on pitch distance between hydrophobic spots, which is maybe linked to the nucleation site interaction effects. In this work, the effects of nucleation site interactions between two hydrophobic cavities on a hydrophilic surface (a mixed wettability rough surface) are investigated, using a two-dimensional pseudopotential phase-change lattice Boltzmann method. The results of the mixed wettability rough surface are compared with completely hydrophilic rough surface and mixed wettability smooth surface to understand the effects of wettability and surface roughness. The focus is placed on the hydrodynamic interaction (which has promotive effect on the bubble formation activity) and thermal interaction (which has inhibitive effect). There exists an optimum pitch distance at which the heat flux and heat transfer coefficient are highest for mixed wettability surface, which are due to larger intensity of hydrodynamic interaction and nearly zero intensity of thermal interaction. Moreover, heat flux is found to be larger for the mixed wettability rough surface than the mixed wettability smooth surface. The bubble nucleation mechanism and time are found to be different for all surfaces.

Analysis on Hull Block Erection Process Considering Variability

The hull block erection network process, which is performed during the master production planning stage of the shipyard, is frequently delayed because of limited resources, workspace, and block preparation ratio. In this study, a study to predict the delay with respect to the block erection schedule is conducted by considering the variability of the block preparation ratio based on the discrete event simulation algorithm. It is confirmed that the variation of the key event observance ratio is confirmed according to the variability caused by the block erection process, which has the minimum lead time in a limited resource environment, and the block preparation ratio. Furthermore, the optimal pitch value for the key event concordance is calculated based on simulation results.

Empirical Assessment Method of Ultimate Capability of Steel Stiffened Panel under Longitudinal Compressive Load

The hull block erection network process, which is performed during the master production planning stage of the shipyard, is frequently delayed because of limited resources, workspace, and block preparation ratio. In this study, a study to predict the delay with respect to the block erection schedule is conducted by considering the variability of the block preparation ratio based on the discrete event simulation algorithm. It is confirmed that the variation of the key event observance ratio is confirmed according to the variability caused by the block erection process, which has the minimum lead time in a limited resource environment, and the block preparation ratio. Furthermore, the optimal pitch value for the key event concordance is calculated based on simulation results.

Experimental Testing of a Preview-Enabled Model Predictive Controller for Blade Pitch Control of Wind Turbines

Model predictive control (MPC) is a control method that involves determining the input to a dynamical system as the solution to an optimization problem that is solved online. In the wind turbine research literature, MPC has received considerable attention for its ability to handle both actuator constraints and preview disturbance information about the oncoming wind, which can be provided by a lidar scanner. However, while many studies simulate the wind turbine response under MPC, very few physical tests have been carried out, likely due in part to the difficulties associated with solving the MPC problem in real time. In this work, we implement MPC on an experimental, scaled wind turbine operating in a wind tunnel testbed, using an active grid to create reproducible wind sequences and a hot-wire anemometer to generate upstream wind measurements. To our knowledge, this work presents the first physical test of MPC for blade pitch control of a scaled wind turbine. We compare two MPC strategies: one including preview disturbance information and one without. Our results provide further evidence that feedforward control can improve wind turbine performance in transition and above-rated conditions without increasing actuation requirements, which we hope will encourage industry experimentation and uptake of feedforward control methods. We also provide a high-level analysis and interpretation of the computational performance of the chosen approach. This work builds upon the results of an earlier study, which considered unconstrained optimal blade pitch control.

A variational approach to determination of maximum throw-able workspace of robotic manipulators in optimal ball pitching motion

This study is aimed at finding the entire points that a manipulator can launch an object onto by an optimal motion. These points are called throw-able workspace, which are located outside the reachable workspace of the robot. From an optimization point of view, some throwing parameters can be found to decrease motion cost. In this paper, by using this concept, the best combination of throwing and trajectory planning is attempted. The proposed method consists of two basic ideas: first, defining the optimal throwing problem as the optimal control problem (OCP) and solving it using the indirect solution approach based on the fundamental lemma of calculus of variations. To achieve the best release angle and speed, the throwing equation of motion is applied as a moving-end boundary condition (BC). Second, based on the obtained optimal throwing, an algorithm is presented to calculate the maximum throw-able workspace. The simulation results demonstrate the effectiveness of the proposed framework for both single link and spatial two-degree-of-freedom throwing robots.

Numerical Study of The Airfoil Pitch Angle on The Darrieus-Savonius Combination Turbine

AbstractThe Darrieus turbine is used as an ocean current converter to generate renewable electrical energy. One way to improve turbine performance is to determine the optimal pitch angle. Therefore, the purpose of this study was to determine the optimal pitch angle of the NACA 0018 airfoil with angle variations of -6°, -2°, 0° and 2°. Numerical method with the help of Ansy Fluent software was carried out for the construction of the turbine. The result of this research is that the angle of 2° produces the largest coefficient of power and torque compared to other angles. This happens because the direction of the lifting force on the forward airfoil is in accordance with the rotation of the turbine.Keywords: Ocean Current, Turbine, Pitch Angle

High Light Outcoupling Efficiency from Periodically Corrugated OLEDs.

Organic light-emitting diodes (OLEDs) suffer from poor light outcoupling efficiency (ηout < 20%) due to large internal waveguiding in the high-index layers/substrate, and plasmonic losses at the metal cathode interface. A promising approach to enhance light outcoupling is to utilize internal periodic corrugations that can diffract waveguided and plasmonic modes back to the air cone. Although corrugations can strongly diffract trapped modes, the optimal geometry of corrugations and limits to ηout are not well-established. We develop a general rigorous scattering matrix theory for light emission from corrugated OLEDs, by solving Maxwell’s equations in Fourier space, incorporating the environment-induced modification of the optical emission rate (Purcell effect). We computationally obtain the spectrally emissive power inside and outside the OLED. We find conformally corrugated OLEDs, where all OLED interfaces are conformal with a photonic crystal substrate, having triangular lattice symmetry, exhibit high light outcoupling ηout ∼60–65%, and an enhancement factor exceeding 3 for optimal pitch values between 1 and 2.5 μm. Waveguided and surface plasmon modes are strongly diffracted to the air cone through first-order diffraction. ηout is insensitive to corrugation heights larger than 100 nm. There is a gradual roll-off in ηout for a larger pitch and sharper decreases for small pitch values. Plasmonic losses remain below 10% for all corrugation pitch values. Our predicted OLED designs provide a pathway for achieving very high light outcoupling over the full optical spectrum that can advance organic optoelectronic science and solid-state lighting.

Analytical and Experimental Investigations of Novel Maglev Coupling Based on Opposed Halbach Array for a 2D Valve

In this paper, a novel maglev coupling based on the opposed Halbach array is proposed as the interface between the linear electro-mechanical converter and 2D valve body. This non-contact maglev coupling possesses several advantages over existing mechanical couplings such as zero friction and wear, low vibration and noise, and no lubrication, which is expected to greatly improve the control accuracy and life cycle of the 2D valve. A detailed analytical model of maglev coupling is established based on the electro-magnetic theory. Firstly, the permanent magnets of the Halbach array is decomposed into several types of basic elements to obtain their individual analytical expressions, which are then re-superimposed into the whole coupling to obtain the analytical formula of torque–displacement characteristics. In order to obtain maximum output torque of maglev coupling, a parametric analysis was performed using an analytical model and optimal pitch angle and shifted distance was explored and found. To verify the correctness of the analytical modelling and parametric analysis results, the torque–displacement characteristics were also studied through both the FEM simulation and experimental approach. The results of analytical modelling, FEM simulation and experiment were in a good agreement, which shows that the maximum magnetic torque can reach about 0.579 N·m when the external armature displacement is 1 mm. The research work provides an important reference for the future application of maglev coupling in a 2D valve.

Global analysis of next-generation utility-scale PV: Tracking bifacial solar farms

The bifacial gain of East-West vertical and South-facing optimally-tilted bifacial solar farms are well established. One wonders if bifacial gain and the associated levelized cost of energy (LCOE) may be further improved by tracking the sun. Tracking bifacial photovoltaics (PV) system has advantages of improved temperature sensitivity, enhanced diffuse and albedo light collection, flattened energy-output, and reduced soiling. Monofacial tracking already provides many of these advantages, therefore the relative merits of bifacial tracking are not obvious. In this paper, we use a detailed illumination and temperature-dependent bifacial solar farm model to show that bifacial tracking PV delivers up to 45% energy gain when compared to fixed-tilt bifacial PV near the equator, and ~10% bifacial energy gain over tracking monofacial farm with an albedo of 0.5. An optimum pitch further improves the gain of a tracking bifacial farm. Our results will broaden the scope and understanding of bifacial technology by demonstrating global trends in energy gain for worldwide deployment.

Mathematical Model of Tubular Linear Induction Motor

Problem of calculation of distribution of magnetic field induction in clearance of tubular linear induction motor (TLIM) is considered. Mathematical model is represented by Fredholm integral equations of second kind for complexes of electric field strength and density of coupled magnetization currents at interface of environments. Algorithm of calculation of distribution of magnetic field induction in TLIM clearance has been developed. Dependence of magnetic field induction in motor clearance on value of pole division is investigated. There is area of optimum pole pitch. Reliability of results of calculations on mathematical model is confirmed by their comparison with results obtained on physical model. Calculated dependence of induction on thickness of runner's iron circuit also has extreme character. Given model can be used at design stage of TLIM. Model allows calculating its optimal geometric dimensions based on criterion of maximum induction in motor clearance, taking into account physical properties of applied materials.

Study of patterned GaAsSbN nanowires using sigmoidal model

This study presents the first report on patterned nanowires (NWs) of dilute nitride GaAsSbN on p-Si (111) substrates by self-catalyzed plasma-assisted molecular beam epitaxy. Patterned NW array with GaAsSbN of Sb composition of 3% as a stem provided the best yield of vertical NWs. Large bandgap tuning of ~ 75 meV, as ascertained from 4 K photoluminescence (PL), over a pitch length variation of 200–1200 nm has been demonstrated. Pitch-dependent axial and radial growth rates show a logistic sigmoidal growth trend different from those commonly observed in other patterned non-nitride III–V NWs. The sigmoidal fitting provides further insight into the PL spectral shift arising from differences in Sb and N incorporation from pitch induced variation in secondary fluxes. Results indicate that sigmoidal fitting can be a potent tool for designing patterned NW arrays of optimal pitch length for dilute nitrides and other highly mismatched alloys and heterostructures.

Heat transfer enhancement in quasi-two-dimensional magnetohydrodynamic duct flows using repeated flow-facing wedge-shaped protrusions

Repeated flow-facing wedge-shaped protrusions are explored as a means to enhance the heat transfer behaviour in a quasi-two-dimensional magnetohydrodynamic duct flow. Quasi-two-dimensionality is achieved under a strong magnetic field which are prevalent in the cooling blankets of fusion reactors. Ranges of Hartmann friction parameters (50 ≤H≤ 500) and Reynolds numbers (1300 ≤Re≤ 3000) are investigated. The effect of blockage β (wedge height to duct height), pitch γ (distance between wedges) and wedge angle ϕ on heat transfer ratio HR and efficiency η are considered. A monotonic increase in HR with β is observed in the range of β investigated. It is possible to further improve HR by changing the geometric parameter to an optimal pitch and optimal wedge angle. Corresponding to each H there exists an optimal β,γ and ϕ where maximum η could be achieved. In contrast to the optimal β which showed a monotonic increase with H, optimal γ and ϕ showed a reversal in the trend after a critical H. Effectiveness of surface modification on the heated wall is also established through a net power analysis.

Optimal Pitch Angle Strategy for Energy Maximization in Offshore Wind Farms Considering Gaussian Wake Model

This paper presents a new approach based on the optimization of the blade pitching strategy of offshore wind turbines in order to maximize the global energy output considering the Gaussian wake model and including the effect of added turbulence. A genetic algorithm is proposed as an optimization tool in the process of finding the optimal setting of the wind turbines, which aims to determine the individual pitch of each turbine so that the overall losses due to the wake effect are minimised. The integration of the Gaussian model, including the added turbulence effect, for the evaluation of the wakes provides a step forward in the development of strategies for optimal operation of offshore wind farms, as it is one of the state-of-the-art analytical wake models that allow the evaluation of the energy output of the project in a more reliable way. The proposed methodology has been tested through the execution of a set of test cases that show the ability of the proposed tool to maximize the energy production of offshore wind farms, as well as highlights the importance of considering the effect of added turbulence in the evaluation of the wake.

Optimal rotor blade control using Grey Wolf Optimizer for small signal stability of SCIG Wind Turbine

The pitch control of Wind Turbine needs to be tuned for optimal pitch control performance. In this paper, the Grey Wolf Optimizer (GWO) is proposed to tune the PI controller in the pitch control of the Squirrel Cage Induction Generator (SCIG) Wind Turbine. The goal is to show that the slow convergence of the Particle Swarm Optimization (PSO), and the trapping into a local optimum of Genetic Algorithm (GA) tuning methods can be overcome by applying the GWO tuning method. The GWO, PSO and GA were applied online to tune the PI controller in pitch control. The tuning results were executed in the PI controller of pitch control of simulated SCIG Wind Turbine connected to a double circuit distribution line. Equally, the Ziegler Nichols (ZN) tuned PI controller was executed in the rotor blade control of the same Wind Turbine. From the simulation results, the GWO tuned PI controller executed in the pitch control of the Wind Turbine provided the least overshoot and the settling time in the aerodynamic power and torque compared to the PSO, GA and ZN tuned PI controllers. The significance of the proposed GWO tuning method for PI controller in the rotor blade control of the SCIG Wind Turbine, it can reduce the stress on the pitch actuator of the Wind Turbine. This is because it reduced overshoot and settling time in the trajectories of blade pitch demand of the Wind Turbine compared to PSO, GA and ZN tuning methods.

Numerical study of heat transfer during solidification in ice-freezing type PCM heat exchanger

In these modern times, the requirement of the energy is not always constant but often periodic. In a hot climatic country like India, a large amount of energy is consumed in cooling application. A heat-exchanger which can store the thermal energy during off-peak hours and use the same energy during peak hours for cooling applications may flatten the periodic energy requirements. Water has a very high value of latent heat of fusion. This latent heat can be utilized to store the thermal energy and use it at a later stage for cooling purposes. The cooling temperature management will be more effective during the phase change process due to the constant fluid temperature. The present study analyzes the heat transfer performance of Ice-Freezing type phase change material (PCM) based heat-exchanger (HEX) during the solidification process. The prediction of solidification time and variation of heat transfer coefficient (HTC) under various configurations is performed. commercialized computational fluid dynamics (CFD) software, Fluent 19 is used to analyze the solidification phenomenon in water. To evaluate the optimum element size, Mesh-independent study is conducted on a single block. Initially, the single block is considered for analyzing the solidification process. The simulations are performed on multiple pipe with varying pitch. The results indicated a drastic change in solidification time as the pitch is decreased. An optimum pitch has to be decided based on the application. The transient variation of the HTC during the solidification process is studied. Initially, during the sensible cooling stage, the HTC decreases at a faster rate. While during the solidification process, the transient variation in HTC is less.

Impact of Secondary Flow on the Exergetic Performance of a Cost-Effective Solar Air Heater Design: CFD and Experimental Study

An experimental and computational fluid dynamics (CFD) study is carried out to investigate the impact of the strength of secondary flow on the thermo-hydraulic performance of discrete multiple inclined baffles in a flat plate solar air heater (SAH) with semi-cylindrical sidewalls. Initially, for a fixed relative baffle height (Rh = 0.1), the relative baffle pitch (Rp) for continuous baffles is varied in the range of 0.6 to 1 to obtain the optimum baffle pitch for 6000 < Re < 14000. The maximum thermohydraulic performance parameter (THPP) is obtained as 2.28 for Rp = 0.75 at Re = 6000. With this optimum Rp, the impact of gaps at leading, at trailing, and at both leading and trailing apices is studied as three different configurations. Maximum heat transfer enhancement of 2.47 times is obtained for multiple inclined baffles with the gap at trailing apex for Re = 14000 with a corresponding increment of 3.07 times in friction factor (f). Maximum THPP is obtained as 2.69 for gap at the trailing apex for Re = 6000. With lower exergy losses, the present SAH design has higher exergetic efficiency, collector efficiency and is cost-effective compared to ribbed rectangular SAH.

A Study on Relationship among Blade Camber Direction and Pitch Angle and Performance of a Small Straight-Blade Darrieus Wind Turbine by Using Scale Test Model and Gurney Flap

Straight-blade Darrieus vertical axis wind turbines are used as medium and small size wind turbine because of higher power output in vertical axis wind turbine (VAWT). In our previous study, the relationship between the performance and Reynolds number based on airfoil chord length had been investigated by using small-scale test models of lift-type VAWT, and the results showed that the performance of tested wind turbine models with small diameter was clearly lower than that of the large-scale field test machine, and its performance also varies significantly with the blade pitch angle. In this study, we focused on the performance of a small-scale straight-blade Darrieus VAWT, the relationship among the blade airfoil camber direction and the pitch angle, and the performance of the small-scale VAWT was examined experimentally by using a small-scale VAWT test model with Gurney flap which was a small flat plate. Gurney flaps with its height h, as a ratio to the blade chord length c, h/c = 0.036 to 0.055, were attached to the blades of the VAWT test model, in addition, the attaching direction of the Gurney flap on the blade was examined for both inward and outward of the rotor, and the pitch angle was also examined for a range of −5 to 10 degrees. These results are discussed comparing with the result of the VAWT without Gurney flap and considering the numerical results for the single blade with/without the Gurney flap. The results showed that the performance of the tested VAWT was reversed between the inward and outward Gurney flaps around a pitch angle of 10 degrees. That is, the inward Gurney flap was superior at a pitch angle of less than 10 degrees, while the outward Gurney flap was effective at a pitch angle of more than 10 degrees. Furthermore, for the tested small-scale VAWT model, the optimum pitch angle was about 5 degrees, and the inward and shorter Gurney flap showed higher power performance of the VAWT under this pitch angle condition.

Retrieval Effectiveness of Google on Reverse Image Search

In this study, uniform films of nanocomposite glass frits (GFs) were printed on a ceramic surface using an inkjet printing technique. For the uniform inkjet printing of GF films, a theoretical model was employed to predict the optimal pitch of ink droplets for the inkjet printing of uniform lines. This model predicted that uniform GF lines could be printed at ink-droplet pitches smaller than 62 μm. Using this theoretical understanding, uniform and crack-free GF films with a thickness of 6 μm were printed by one-time printing. The inkjet-printed GF films were sintered at 850 ◦ C to enhance the film density and surface roughness. The thickness of the post-sintered film decreased by half compared to the as-deposited film. The root-mean-square roughness of the GF films also decreased from 43 nm for the as-printed film to 8 nm for the post-sintered film. This work opens up an opportunity to inkjet print not only the GF coating layers but also complex GF patterns for various industrial applications.

Inkjet Printing of Glass Frit Suspensions: From Uniform Lines to Uniform Films

In this study, uniform films of nanocomposite glass frits (GFs) were printed on a ceramic surface using an inkjet printing technique. For the uniform inkjet printing of GF films, a theoretical model was employed to predict the optimal pitch of ink droplets for the inkjet printing of uniform lines. This model predicted that uniform GF lines could be printed at ink-droplet pitches smaller than 62 μm. Using this theoretical understanding, uniform and crack-free GF films with a thickness of 6 μm were printed by one-time printing. The inkjet-printed GF films were sintered at 850 ◦ C to enhance the film density and surface roughness. The thickness of the post-sintered film decreased by half compared to the as-deposited film. The root-mean-square roughness of the GF films also decreased from 43 nm for the as-printed film to 8 nm for the post-sintered film. This work opens up an opportunity to inkjet print not only the GF coating layers but also complex GF patterns for various industrial applications.