Blade Pitch Research Articles

THEORETICAL STUDIES OF DRILLING FROZEN SOILS WITH A SCREW DRILL

Link for citation: Martyuchenko I.G., Zenin M.I., Kolesnikov A.Yu., Boikov E.V. Theoretical studies of drilling frozen soils with a screw drill. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 194-202. In Rus. The relevance of the study is caused by the need to create a new drilling tool to drill frozen soil in difficult conditions. This line of research is important and relevant for ensuring the formation of wells on frozen sands, since the screw drilling tool performs the deformation of frozen soil separation, which makes it possible to drill hard-to-drill soils, namely frozen sands. The main aim: to study the interaction of the destructive part of the helical drill with frozen soil and determine the rational values of the geometric parameters of the helical blade when achieving the lowest value of the force of soil separation and the highest value of the productivity of drilling. Objects: interaction of the destructive part of the helical blade of a helical drill with frozen soil. Methods: plotting dependencies of factors showing the energy intensity of drilling, on the angle of rotation of the radius of the helical blade, at which it increments, and on the pitch of the helical blade in the second section of the destructive part of the helical drill; analysis of the obtained results of theoretical studies of the force of soil separation and the efficiency of drilling from the geometric parameters of the helical blade of a drilling tool on frozen soils. Results. The authors have studied the influence of the geometrical parameters of the helical drill on well formation, obtained the dependences of the efforts and constructed the graphs for soil separation, as well as the dependence of the productivity of drilling on the angle of rotation of the radius of the helical blade, at which it increments, and on the pitch of the helical blade in the second section of the destructive part of the helical drill. Based on the results of theoretical studies, an analysis of the obtained dependencies was carried out and the area of rational values of the geometric parameters of the helical blade of a helical drill on frozen soils was found.

Mixing tank hydrodynamics and mixing efficiency for propeller impellers

In this study, the distribution of axial and radial velocities with the use of a PIV laser system was determined and the mixing power in a mixing tank with narrow and wide propeller impellers was measured. The pumping capacity and secondary circulation values in the mixing tank were calculated and on this basis, the energy efficiency of the operation of both types of propeller impellers was determined and compared with the efficiency of turbine impellers with inclined blades. It turned out that propeller impellers with wide blades are most effective as regards the amount of energy that should be supplied to the mixing tank to achieve the required mixing time. It was found that the share of pumping capacity in the total secondary circulation is almost twice as high as the share of induced circulation. Correlation equations for the dependence of the mixing power and dimensionless flow numbers on the pitch of the propeller blade were also formulated. All the results obtained were compared with the works of other authors. The paper also found that propeller impellers with a variable angle of inclination of the blade α depending on the current radius do not meet the theoretical assumption of a constant axial velocity of the liquid flowing out from of the impeller zone. For small radii of the impeller the explanation for this observation is the presence of the hub and shaft in the axis of the mixer and the effect of liquid slip for the steep agitator blades near the hub. For radii close to the radius of the stirrer, the reason is generation of induced circulation as the expense of the kinetic energy of the liquid flowing out of the impeller area.

Robust multi‐loop control of a floating wind turbine

AbstractA principal challenge facing the control of floating offshore wind turbines (FOWTs) is the problem of instability, or “negative damping,” when using blade pitch feedback to control generator speed. This closed‐loop instability can be attributed to non‐minimum phase zeros in the transfer function from blade pitch to generator speed. Standard approaches to improving stability and performance include robust tuning of control gains and introducing multiple feedback loops to respond to platform motion. Combining these approaches is nontrivial because multiple control loops complicate the impact of coupling in the system dynamics. The single‐loop approach to analyzing stability robustness neglects inter‐loop coupling, while a simplistic multi‐loop approach is highly sensitive to dimensional scaling and overestimates the robustness of the single‐loop controller. This work proposes a sensitivity representation that separates some of the natural FOWT dynamic coupling into a parallel feedback loop in the sensitivity function loop to address both of these concerns. The modified robustness measure is used with a simplified linear FOWT model to optimize scheduled multi‐loop control parameters in an automated tuning procedure. This controller is implemented for the 10‐MW Ultraflexible Smart FLoating Offshore Wind Turbine (USFLOWT) and compared against conventional single‐ and multi‐loop controllers tuned using frequency‐domain analysis and high‐fidelity OpenFAST simulations. The multi‐loop robust controller shows the highest overall performance in generator speed regulation and tower load reduction, though consideration of power quality, actuator usage, and other structural loading leads to additional trade‐offs.

Design parameters and mechanical efficiency of jet wind turbine under high wind speed conditions

Abstract Turbines are one of the most important means of producing clean energy, as they do not cause any negative emissions affecting the environment. Recently, the need to design turbines capable of facing strong winds has appeared because the currently designed turbines must be cut off in such circumstances. This study aims to find the best design parameters and investigate the efficiency of the jet turbine at high wind speed conditions. SolidWorks and MatLab are used to design and analyze small jet wind turbines. The design parameters were chosen to obtain the best efficiency. The turbine diameter is 0.5 m, and the short blade length helps withstand the generated stresses due to strong wind, especially fatigue stress, and resists bending. Blade pitch angle beta starts from 2° from the vertical axis at the hub and changes harmonically along the length to end at an angle of 88° at the blade’s tip to allow air to pass through and not form a wall. The blade number has chosen 15 blades, corresponding to the Betz limit, to obtain the maximum power coefficient. As a result, the assigned power was obtained at a wind speed of 28 m/s. At a lower wind speed, it will work with acceptable efficiency and more efficiently at higher speeds. Therefore, this turbine is suitable to use in such cases.

Actuator-Line CFD Simulation of Tidal-Stream Turbines in a Compact Array

An actuator-line CFD model is used to simulate tidal-stream turbines acting alone or in a compact 3-turbine staggered array. CFD results confirm that the accelerated bypass flow between two proximal turbines in shallow water can enhance the power output for a close downstream turbine, with additional smaller effect of the upstream turbines’ operating point. Comparison with other authors’ experimental data in a narrow flume (IFREMER) and circular wave-current tank (FloWave) show some difference in relative loads between the turbines, possibly associated with ambiguity in overall blade pitch and difficulty in characterising onset flow in the FloWave tank. The accelerated bypass flow is persistent and largely established on the rotor plane of the upstream turbines, indicating how local array effects might be incorporated in simpler blade-element/momentum-theory design tools.

Objective Functions for the Blade Shape Optimisation of a Cross-Flow Tidal Turbine under Constraints

Hydro-kinetic cross-flow tidal turbines (CFTT) are omni-directional and offer higher area-based power density compared to horizontal-axis tidal turbines, making them very attractive for tidal energy exploitation. However, the rotating motion around the vertical axis results in continuously varying angles of attack, causing alternating loads, which may lead to fatigue failure and structural damage. The OPTIDE Project addresses these challenges by implementing intracycle blade pitching to individually control the angle of attack, increasing the power coefficient CP and reducing structural loads. For this purpose a Darrieus turbine is designed with embedded actuators in each blade. Firstly a blade shape optimization will be conducted to fit the actuator at the quarter-chord position while ensuring sufficient thickness. The optimization procedure couples Computational Fluid Dynamics (CFD) with a Genetic Algorithm. The employed optimizer OPAL++ sets ten variables for each individual, which describe the hydrofoil shape, length and tip speed ratio (TSR). A smooth hydrofoil shape is generated from the variables, followed by an automatic mesh generation. Subsequently, numerical simulations of each individual at the desired TSR are conducted, while keeping the blade pitch angle constant. Simulation results provide the CP and stress acting on the turbine blades, which are the two optimization objectives (maximize CP while minimizing stress). This process is repeated during the optimization, aiming to determine the most suitable blade shape, that fits the actuator, and operating point (TSR) in a trade-off between CP and structural loads. This will lead to the increase of efficiency and a longer turbine lifetime.

Design and Demonstration of a Passive Pitch System for Tidal Turbines

Tidal currents are renewable and predictable energy sources that could prove fundamental to the transition to a sustainable use of renewable energy resources. Over a tidal period, changes in the flow speed in a tidal channel require that the blade pitch is adjusted to maximise power extraction. This is currently achieved with active pitch actuation, which however increases the capital and maintenance cost of the turbine. Furthermore, because of turbulence in the tidal stream, turbine yaw, wave-induced currents, etc., tidal turbine blades experience high-frequency velocity fluctuations that result in power and thrust unsteadiness, both of which are transmitted to the generator, the tower, and the active pitching mechanism, shortening the operating life due to fatigue loading.
 A passive morphing blade concept capable of reducing the load fluctuations without affecting the mean loads has recently been formulated and demonstrated with low-order simulations (https://doi.org/10.1016/j.renene.2021.10.085) and measurements (https://doi.org/10.1016/j.renene.2023.01.051). The system allows both passive pitch adjustment to changes in the mean flow speed over the tidal period, and the mitigation of high-frequency fluctuations.
 In this paper, we present the recent progress on the development of morphing blade technology, including with numerical simulations and experimental tests on a 1.2-m diameter turbine. Two different design concepts have been tested in the FloWave facility at the University of Edinburgh and in the recirculating channel at the Institute for Marine Engineering of the Italian National Research Council, respectively.
 Experimental results show that the amplitude of power variations over a wide range of flow speeds is substantially decreased, while thrust variations with changes in freestream speed are essentially suppressed. The detrimental effect of yawed inflow is, in addition, almost entirely cancelled. The fluctuations in the root-bending moment, thrust and torque are consistently reduced over a broad range of tip-speed ratios. We also show that such a system, if improperly designed, could result in a negative starting torque, and we show the steps necessary to avoid this issue.
 Furthermore, we present a theoretical and numerical framework that allows the design of passive pitch blades that can cancel either thrust or power fluctuations in specific flow conditions, as well as mitigating both types of fluctuations over a wide range of conditions. Specifically, we show that for any quasi-steady change in the relative flow speed and direction, there is a pitching axis that allows a chosen force component to be kept constant. High-frequency force fluctuations can also be substantially mitigated, and the extent of the mitigation depends on the inertia and friction in the system.
 Overall this paper demonstrates experimentally the effectiveness of morphing blades for tidal turbines and presents a theoretical and numerical framework for the future development of this technology.

Methodology to capture the single blade loads on a cross-flow tidal turbine flume model

The OPTIDE project aims to improve the efficiency and durability of Hydro-kinetic cross-flow tidal turbines (CFTT). These turbines are attractive for the exploitation of tidal energy, as the area-based power density of such turbine arrays is higher in comparison to those from horizontal-axis turbines. CFTT also generally feature a simpler design and the ability to operate under varying flow conditions. Nevertheless, the efficiency of single CFTT is lower relative to the most commonly used axial turbine type. Furthermore the life time can be affected by alternating and pulsating stresses, caused by continuous variations of the angle of attack and hydraulic loads during the rotation. These stresses may lead to structural damage and fatigue-induced material failures. A promising approach to overcome these drawbacks is intracycle blade pitching. In this case the angle of attack is continuously adjusted individually for each blade during the rotation. The consequence is smoothed peaks of the load alternations and a higher power coefficient CP . The project aims to explore the influence of active blade pitching on CFTTs and to optimize it with numerical and experimental means. Therefore, a lab-scaled three-bladed experimental turbine with embedded pitch actuators is developed. The model will subsequently be tested in the lab flume of the Institute of Fluid Dynamics and Thermodynamics of the Otto-von-Guericke University Magdeburg. Blade forces in tangential and radial components as well as the machine torque and the rotational speed are measured during the experiments. The turbine is equipped with two full-bridges of strain gauges for the detection of the blade loads, from which the structural stress is calculated subsequently. To ensure the turbine model’s mechanical durability, weakly coupled fluid-solid-interaction (FSI) simulations have been performed and will be presented. To this purpose, a 2D flow analysis, employing the open-source CFD toolkit OpenFOAM (v2206), has been coupled with a 3D structural analysis, using the Mechanical module of the commercial software package Ansys Workbench (2020 R2). The FSI simulations show that the current setup only allows for the measurement of the radial blade load component, because the pitching moment at blade level interferes with the measurements as soon as the profile stalls. The measurements are further distorted by secondary force paths from the loads on the other rotor blades. Possible measures for an improved instrumentation strategy on the flume model will be presented and discussed. It is shown that multiple equipment options allow for a decent investigation of the forces on blade level.

Non-dimensional scaling of passive adaptive blades for a marine current turbine

For tidal energy to support access to off-shore electricity, further development is needed to decrease costs and increase reliability of current turbines at relevant scales. Blade pitch control strategies can significantly reduce structural loads in above-rated flow conditions by shedding power through decreased angles of attack. This can be accomplished through an active strategy using motorized blades or a passive adaptive strategy using flexible, self-twisting blades. We focus this study on the passive adaptive approach in which the composite fibers of the blade are oriented off-axis to produce a coupling between bend and twist deformations.
 Extending laboratory results to larger, open-water designs requires an understanding of hydrodynamic and hydroelastic scaling. While dimensionless scaling relations have been extensively studied for current turbines with rigid blades, relatively few studies discuss appropriate hydroelastic scaling for passive adaptive blades. In this study, we experimentally apply non-dimensional scaling laws to laboratory-scale passive adaptive turbine blades and demonstrate similarity in blade deformation and non-dimensional loads across scales.
 When Cauchy similarity is achieved between model and full-scale, the same steady-state blade loading and blade deformation are expected. We define Cauchy number as Ca = ρUo2/E, where ρ is the water density, Uo is the freestream velocity upstream of the turbine, and E is the transverse flexural modulus of the blade (i.e., elasticity corresponding to bending in the flapwise direction). We tested the effectiveness of Cauchy-scaling by designing an experiment in which blade bending stiffness and flow speed varied, but Cauchy number remained constant. The first blade used a 7-ply carbon fiber spar while the second blade used a 5-ply carbon fiber spar, both fabricated with unidirectional fibers oriented 10° off-axis and cast in a semi-rigid polyurethane using the same mold. All other non-dimensional parameters relevant to hydrodynamic scaling were held constant, where possible.
 As hypothesized, we observed agreement in thrust coefficient, deflection, and twist when Cauchy similarity was achieved, particularly when flow remained attached over the entire blade span. Small differences of 0-7% were observed in normalized thrust, deflection, and twist compared to 50-65% when Cauchy number was allowed to vary by 50%. We did not observe this similarity for normalized mechanical power between the 5-ply and 7-ply blades, but hypothesize that the source of the disagreement was a small surface defect in the urethane on the 5-ply blade. The experiment will be repeated to confirm this hypothesis and included in future presentations of this work.
 Our experimental result partially demonstrates the effectiveness of using Cauchy number to scale passive adaptive marine current turbine blades and model their steady-state hydrodynamic and hydroelastic behaviors in a consistent, non-dimensional manner. Accurate experimental models are critical to support the development of passive adaptive blades, which may obviate the need for an active pitch mechanism, thereby increasing reliability and decreasing maintenance costs. Finally, we present initial results from a field-scale turbine equipped with rigid and passive adaptive blades, demonstrating a path towards validating our conclusions from lab-scale testing.

Performance enhancement of small-scale wind turbine based on artificial neural network

<p><span lang="EN-US">Small-scale wind turbine is typically designed to resisted extreme wind; this work aims to adjust their pitch angle based on simulations that use standardization codes for wind turbines. Proportional integral derivative (PID) and artificial neural network (ANN) controllers are used to control the speed of wind turbines. The ideal action for controlling the blade pitch angle can be attained by providing the controller with speed information ahead of time, allowing the controller to provide the best action for blade pitch angle control. The results of this work represent the relationship between the turbine speed with respect to time at different pitch angle. It has been concluded that the ANN controller produced the best time response as compared with the PID controller.</span></p>

Performance optimization of radiator engine parameters during hard conditions by control charts monitoring and evaluating

Recently, engine design and control systems have been developed using data-driven modeling techniques to specify the in-cylinder complicated combustion process. The cooling fan performance is highly influenced by several factors that are determined based on what is called (DOE) «design of experiments». These factors include blade tip clearance, pitch angle, distance from radiator. This work presents a method to improve a cooling fan performance of an engine by designing a Six Sigma technique using Control, Improve, Analyze, Measure, and Define (CIAMD). First, let’s assess the existing cooling fan performance and define its problem. Then, let’s specify the parameters that affect on fan performance to be optimized. Next, let’s conduct sensitivity analysis and evaluate manufacturing control of the developed cool Fan. The primary fan does not distribute air enough by the radiator to maintain the machine cool throughout hard circumstances. First, the work demonstrates how to develop an experiment to examine the influence of three performance elements: blade pitch angle, blade-tip clearance, and fan distance from the radiator. In order to improve the performance of the cooling fan, Box-Behnken design is adopted for testing quadratic (nonlinear) effects. It then indicates how to predict optimal quantities for every element, to produce a technique that makes airflows above the objective of 1486.6 m3/h when utilizing experimental measurements. Finally, it reveals how to operate simulations to confirm that this method creates airflow based on the specifications with more additional fans manufactured performance of 99.999 %. The results of S and X-bar control charts indicate that the manufacturing process is statistically under control

Flow physics and loss mechanisms of tip leakage flow in variable-blade-pitch-angle ducted fans

This paper investigates a ducted fan, which is able to adjust the output characteristics to meet different requirements of VTOL (Vertical Take-Off and Landing) aircrafts at various states, e.g., take-off, landing and high-speed cruise. The variable-blade-pitch-angle method is employed for the ducted fan, so that the fan can present more various performance. The loss mechanisms of the ducted fan are analyzed at seven different blade pitch angles ranging from −15 degrees to 15 degrees, and the importance of the tip leakage flow on the aerodynamic performance of the fan is highlighted. Results show that there exists a critical value for the blade pitch angle, and below the critical value, the tip leakage vortex sweeps to the adjacent blade tip and simultaneously causes the double tip leakage, which results in the high relative-total-pressure loss and a severe deterioration of rotor efficiency. The flow physics and loss mechanisms are discussed in detail. In addition, an analytical model of the tip leakage flow is established, and the effects of blade solidity on the critical blade pitch angle are discussed. The results provide useful guidelines on the design and the control of the variable-blade-pitch-angle fans.

Damping analysis of floating offshore wind turbines (FOWTs): a new control strategy reducing the platform vibrations

Abstract. In this paper, the coupled dynamics of the floating platform and the wind turbine rotor are analyzed. In particular, the damping is explicitly derived from the coupled equations of the rotor and floating platform. The analysis of the damping leads to the study of instability phenomena, thus obtaining the explicit conditions that lead to the non-minimum phase zero (NMPZ). Two NMPZs are analyzed, one related to the rotor dynamics and the other one to the platform pitch dynamics. The latter introduces a novelty, and an explicit condition is provided in this work for its verification. In the second part of the paper, from the analysis of the damping of the floating platform, a new strategy for the control of floating offshore wind turbines (FOWTs) is proposed. This strategy allows one to impose on the controller an explicit level of damping in the platform pitch motion that adapts with wind speed and operating conditions without changing the period of platform pitching. Finally the new strategy is compared to one without compensation and one with a non-adapting compensation by performing aero-hydro-servo-elastic numerical simulations of a reference FOWT. Generated power, motions, blade pitch and tower base fatigue are compared, showing that the new control strategy can reduce fatigue in the structure without affecting the power production.

Control and dynamic analysis of a 10 MW floating wind turbine on a TetraSpar multi-body platform

The role of wind turbine controllers in stabilizing floating offshore wind turbines (FOWTs) is critical in the above-rated operational regions. In this paper, three types of control methods are tested on a 10 MW FOWT mounted on a TetraSpar multi-body platform to numerically investigate the rotor and platform dynamics. A validated aero-hydro-servo-elastic coupling tool based on FAST and AQWA is used to analyse the integrated floating wind turbine model. The results show that the baseline controller designed for the onshore application yields the highest blade pitch and platform pitch fluctuations primarily due to the negative damping effect. Conversely, the detuned controller obtained by derating the control gains reduces these fluctuations and sufficiently mitigates the damping problem. It is also observed that the instabilities caused by the higher frequency baseline controller and the resulting structural penalties are reduced when the detuned controller is employed. On the other hand, the open-loop type fixed blade pitch control method resulted in the highest rotor speed and surge translation. Further analysis found that the tension responses on some of the tendons are dominated by the coupled pitch mode when implementing the detuned and the fixed blade pitch control options.

Characterizing the Wake Effects on Wind Power Generator Operation by Data-Driven Techniques

Wakes between neighboring wind turbines are a significant source of energy loss in wind farm operations. Extensive research has been conducted to analyze and understand wind turbine wakes, ranging from aerodynamic descriptions to advanced control strategies. However, there is a relatively overlooked research area focused on characterizing real-world wind farm operations under wake conditions using Supervisory Control And Data Acquisition (SCADA) parameters. This study aims to address this gap by presenting a detailed discussion based on SCADA data analysis from a real-world test case. The analysis focuses on two selected wind turbines within an onshore wind farm operating under wake conditions. Operation curves and data-driven methods are utilized to describe the turbines’ performance. Particularly, the analysis of the operation curves reveals that a wind turbine operating within a wake experiences reduced power production not only due to the velocity deficit but also due to increased turbulence intensity caused by the wake. This effect is particularly prominent during partial load operation when the rotational speed saturates. The turbulence intensity, manifested in the variability of rotational speed and blade pitch, emerges as the crucial factor determining the extent of wake-induced power loss. The findings indicate that turbulence intensity is strongly correlated with the proximity of the wind direction to the center of the wake sector. However, it is important to consider that these two factors may convey slightly different information, possibly influenced by terrain effects. Therefore, both turbulence intensity and wind direction should be taken into account to accurately describe the behavior of wind turbines operating within wakes.

Finite-Time Suboptimal Control Design for Aerobatic Maneuver of Variable-Pitch Quadrotor

The variable-pitch quadrotors can perform aggressive maneuvers such as aerobatic flip by varying the thrust in both positive and negative vertical directions via the blade pitch, which can provide an additional degree of freedom as opposed to the fixed-pitch quadrotor that only changes the rotational rate of motors. However, an inevitable challenge exists when designing an operative controller for the aerobatic flip due to the resultant singularity of the rotation matrix. In this paper, a finite-time suboptimal control design strategy named finite-time <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta -D$</tex-math></inline-formula> algorithm combined with the geometric control technique is proposed for the aerobatic maneuver control of the variable-pitch quadrotor. Based on this scheme, the singularity issue can be circumvented. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta -D$</tex-math></inline-formula> control design provides a closed-form suboptimal control law by offline solving a differential Riccati equation and a set of linear Lyapunov equations analytically, which does not require complex online numerical and iterative solutions compared with the similar finite-time state dependent Riccati equation technique. Simulation results demonstrate that the proposed geometric finite-time <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta -D$</tex-math></inline-formula> method provides an effective and efficient control of the variable-pitch quadrotor.

Aerodynamic analysis of a novel pitch control strategy and parameter combination for vertical axis wind turbines

The performance of a vertical axis wind turbine (VAWT) deteriorates at low tip speed ratios (TSR) and it is mainly characterized by flow separation and dynamic stall. Several mitigating techniques have been developed recently based on flow separation and dynamic stall research activities. One of such techniques is the use of blade pitch angle control, which shows very promising optimal performance in VAWTs. However, its adaptation for periodic variation of the angle of attack remains an important issue that needs to be addressed urgently. Therefore, this paper proposes a novel pitch control strategy based on the VAWT-shape pitch motion to achieve blade dynamic pitch with the rotational parameters (TSR and azimuth angle). The pitch scale factor (μ) is introduced to proportionally vary the angle of attack. High accuracy computational fluid dynamics (CFD) methods are used to simulate dynamic changes in pitch angle, flow field and vortex shedding vorticity, with the turbulence modelled using the SST k-ω model. The results show that a 146% increase in power coefficient can be achieved using a μ of 0.3 at TSR of 1.25. Additionally, the use of dual pitch scale factors (dpsf) in the windward and leeward regions causes intense transient torque fluctuations at 0° (360°) and 180° azimuths due to a breaking distance in pitch angular velocity at these azimuths. Adding a weight function into the fitting process of the dpsf pitch curve effectively minimize these fluctuations.

Global sensitivity analysis of a semi-submersible floating wind turbine using a neural network fitting method

The stochastic platform motions of a floating offshore wind turbine (FOWT) significantly affect its load characteristics and power production. It is vital to understand the influence of various input parameters on the global performance of an FOWT to ensure structural safety and power efficiency. This study investigates the influence of key design parameters related to metocean conditions and natural periods of platform motions on wind turbine performance. A global sensitivity analysis (GSA) framework is proposed to map the input-output relation of a 4-MW semi-submersible FOWT. This framework uses fully-coupled numerical analysis and neural network fitting (NNF). Several important parameters are selected, including natural periods of the platform motions, mean wind speed, turbulence intensity, wave spectral peak period and significant wave height. Results demonstrate that natural periods of platform motions and wave conditions have a significant influence on the dynamic responses of the FOWT. Furthermore, statistical analysis reveals that severe sea states and low natural periods of platform motions can increase the operation cycles of the blade pitch system by 20%. The use of NNF method effectively increases the efficiency of the GSA by at least forty times. The proposed framework can be applied to other areas of FOWTs.

Servomotor Pitching Control Method for H-Type Darrieus Turbine

This research article discusses the active pitching technique for the H-Type Darrieus turbine and its importance for the turbine’s self-starting and enhanced power coefficient. The pitch of the turbine blades is changed at various points while the turbine is whirling using the servomotor pitching control system. The performance of the turbine is enhanced by the present blade pitching method. The current analytical analysis made use of the DMST (Double Multiple Stream Tube) model. Parametric study is done to create a turbine design suitable for pre-fabrication. Currently, a turbine with a servomotor is being employed in the research. The paper’s conclusion is that the current pitching schedule can increase initial torque to initiate starting of the turbine and improve efficiency of turbine in terms of power coefficient up to 45% for operating tip speed ratio, 0 = 2.5 at wind velocity of 10 m/s.

Sensitivity Analysis of Modal Parameters of a Jacket Offshore Wind Turbine to Operational Conditions

Accurate estimation of offshore wind turbine (OWT) modal parameters has a prominent effect on the design loads, lifetime prediction, and dynamic response of the system. Modal parameters can vary during the operation of OWTs. This paper studies the variation and sensitivity analysis of an OWT’s modal parameters with respect to operational and environmental conditions. Three finite element models of a jacket-supported OWT at the Block Island Wind Farm are created within the OpenSees, SAP2000, and OpenFAST platforms and validated using experimental measurements. The OpenFAST model is used to simulate the modal parameters of the turbine under various wind speed, rotor speed, power, yaw angle, mean sea level, blade pitch angle, and soil spring values. The model-predicted modal parameters of the first fore–aft (FA) and side–side (SS) modes are compared to those identified from experimental measurements. Results from the simulations show that the first FA natural frequency and damping ratio mostly depend on the rotor speed and wind speed, respectively, while yaw angle and mean sea level do not have a visible effect. It is observed that there is about 8% stiffening in the first FA frequency and an aerodynamic damping of 7.5% during the operation of the OWT.