Pitch Angle Changes Research Articles

Computational Fluid Dynamics Analysis and Validation with Field Test of 1 MW Hydropower Turbine System

This study analyzed and validated a 1 MW hydropower turbine system using computational fluid dynamics (CFD) in conjunction with field test data. The fluid domain of the hydropower system includes the runner blade, vane, duct, and both inflow and outflow free surface flows. An implicit unsteady flow solver and the SST k-ω turbulence model were employed. The rotational motion of the rotor blade was simulated using the moving reference frame (MRF) method. To handle a non-conformal mesh among the intake, runner, and outlet domains, an internal interface boundary condition was applied. System performance was evaluated by adjusting the guide vane opening ratio and the runner blade pitch angle. A free surface model was also developed to accurately represent the water level. The results show that the CFD analysis predicted the turbine’s power output with a maximum deviation of 1.7% from field test measurements under different tide conditions. The numerical analysis also confirmed the influence of the runner blade pitch angle, with a 1° change in pitch angle leading to a 68 kW variation in power output. The accuracy of the CFD analysis was verified by comparing it to performance data from actual field tests.

Research on Control Technology of Variable Load Gun Pitch Servo System

Abstract The artillery pitch servo system has a significant unbalanced torque within its pitch range, which varies greatly with the change of pitch angle. The conventional control method is designed based on the control model of the controlled object. Due to load changes, the control model of the controlled object in the system changes, resulting in poor consistency of control characteristics in different pitch intervals, and even exceeding the dynamic and static performance and system instability in large unbalanced torque pitch intervals. On the basis of analyzing the composition, working principle, and torque variation of the pitch servo system, this article analyzes the problems of conventional control methods and proposes a control method for artillery pitch servo system based on SMVC control. Through MATLAB simulation and experiments, it is shown that this control method can effectively overcome the impact of variable loads on the pitch servo system, significantly improve the dynamic and static performance of the system, and improve the control effect of the system.

Rotor solidity and blade pitch influence on horizontal axis small wind turbine performance – Experimental study

The urgent need to reduce greenhouse gas emissions has accelerated the adoption of renewable energy sources such as wind power. In this context, small wind turbines (SWTs) have emerged as a viable solution for decentralized electricity generation. This paper investigates the combined influence of rotor solidity and pitch angle variation on the performance of a small horizontal axis wind turbine through experimental analysis conducted in a wind tunnel. Results show that increasing rotor solidity generally improves Cpmax, particularly for shorter chord blades, with up to a 25–35 % increase observed by increasing the number of blades and a 10–15 % increase by employing longer chord blades compared to benchmark designs. Additionally, the study highlights the significant sensitivity of turbine performance to slight changes in pitch angle resulting in a 4–8 % rise in Cpmax. Higher solidity rotors exhibit reduced sensitivity to pitch angle changes and reference velocity variations, contributing to improved stability in varying environmental conditions. The study highlights the influence of aerofoil Reynolds number on turbine performance, underscoring the importance of careful aerodynamic design considerations. It provides valuable insights for SWT design to enhance energy efficiency and promote the widespread adoption of wind energy technology.

Influence of Initial Proton Energy on the Nonlinear Interactions Between Ring Current Protons and He+ Band EMIC Waves

AbstractThe energy of ring current protons is believed to influence the pitch angle scattering due to electromagnetic ion cyclotron (EMIC) waves and is typically analyzed using quasi‐linear theory. However, nonlinear behavior becomes significant as the wave amplitude intensifies. In this study, we aim to explore how the nonlinear behavior depends on the initial proton energy under various background plasma density conditions. The frequency of EMIC waves is 0.96ΩHe (where ΩHe is the gyrofrequency of He+ at the equator). It is found that the higher energy protons with nonlinear phase trapping experience more resonances, causing these trapped protons to move away from the loss cone more quickly compared to lower energy protons. However, the proportion of phase‐trapped protons significantly decreases as the initial proton energy increases. This declining trend is more pronounced for a background plasma condition in the plasmapause than within the plasmasphere. The number of phase‐trapped protons goes to zero as initial proton energy increases to above approximately 60 keV. Additionally, nonlinear phase bunching is more pronounced for lower energy protons (e.g., below 60 keV) compared to higher energy protons. As a result, both nonlinear phase trapping and phase bunching contribute to larger standard deviations in the net changes of equatorial pitch angle (Δαeq), suggesting a larger pitch agnel diffusion coefficient compared to the prediction of quasi‐linear theory.

Double-Helical Tiled Chain Structure of the Twist-Bend Liquid Crystal Phase in CB7CB

The twist-bend nematic liquid crystal phase is a three-dimensional fluid in which achiral bent molecules spontaneously form an orientationally ordered, macroscopically chiral, heliconical winding of a ten nanometer-scale pitch in the absence of positional ordering. Here, the structure of the twist-bend phase of the bent dimer CB7CB and its mixtures with 5CB is characterized, revealing a hidden invariance of the self-assembly of the twist-bend structure of CB7CB, such that over a wide range of concentrations and temperatures, the helix pitch and cone angle change as if the ground state for a pitch of the TB helix is an inextensible heliconical ribbon along the contour formed by following the local molecular long axis (the director). Remarkably, the distance along the length for a single turn of this helix is given by 2πRmol, where Rmol is the radius of bend curvature of a single all-trans CB7CB molecule. This relationship emerges from frustrated steric packing due to the bent molecular shape: space in the fluid that is hard to fill attracts the most flexible molecular subcomponents, a theme of nanosegregation that generates self-assembled, oligomer-like correlations of interlocking bent molecules in the form of a brickwork-like tiling of pairs of molecular strands into duplex double-helical chains. At higher temperatures in the twist-bend phase, the cone angle is small, the director contour is nearly along the helix axis z, and the duplex chains are sequences of biaxial elements formed by overlapping half-molecule pairs, with an approximately 45° rotation of the biaxis between each such element along the chain.

Сравнительный анализ клинических результатов двух способов хирургического лечения пациентов с полой стопой: удаление ладьевидной кости с остеотомией кубовидной кости и остеотомия Cole

Rationale: Cole osteotomy is performed in patients having a cavus deformity with the apex of the deformity in a plantigrade foot. We invented a new approach in cavus foot surgery: removing the navicular bone and wedge-shaped osteotomy of the cuboid bone. We retrospectively reviewed and compared the clinical and radiographic results of 16 feet (16 patients) that underwent Cole midfoot osteotomy, and 11 feet (11 patients) that underwent removing of the navicular bone ande midfoot. Correction of the deformity at this midfoot level improves foot and ankle stability by creatin wedge-shaped osteotomy of the cuboid bone (2020–2023). Objective: to compare clinical results of two methods of surgical treatment of the cavus foot: removal of the navicular bone with osteotomy of the cuboid bone and osteotomy of Cole. Methods: The patients had two etiologies (idiopathic pes cavus and Charcot-Marie-Tooth disease). In the first group dorsal and slightly laterally based transverse wedge osteotomy through the navicular bone medially and the cuboid bone laterally was performed, in the second group — removal of the navicular bone and wedge-shaped osteotomy of the cuboid bone. Patients were under routine clinical follow-up. We evaluated clinical and radiographic results. Results: Mean clinical follow-up was 15.7 months (range, 6–36 months). The mean preoperative and postoperative talo–first metatarsal angles on lateral radiographs were 29,9 and 8,7, respectively (р<0,05) after the Cole osteotomy and 27,2 and 5,4, respectively (P , .05) after the navicular bone removal. The mean postoperative calcaneal pitch angle changes were 10,8 on the lateral radiograph (р<0,05) after the Cole osteotomy and 15,6 after the navicular bone removal (р<0,05). At final follow-up, all patients were independently active, had plantigrade feet,and were able to wear conventional shoes. The mean American Orthopaedic Foot and Ankle Society questionnaire score was 38.8 preoperatively and 79.5 postoperatively (р<0,05) in the first group and 37,4 preoperatively and 83,5 postoperatively р<0,05) in the second group. One patient after the Cole osteotomy did not have full bony union. Conclusions: removing the navicular bone and wedge-shaped osteotomy of the cuboid bone is a safe procedure to correct adult pes cavus deformity with the apex in midfoot, and has similar results as Cole osteotomy.

Recent Results from Electron Cyclotron Emission (ECE) Radiometer diagnostics in the presence of Electron Cyclotron Resonance Heating (ECRH)

Besides furnishing localized spatial and temporal electron temperature measurements, Electron Cyclotron Emission (ECE) diagnostics are routinely employed across various tokamaks for diverse physics investigations, encompassing MHD localizations, transport studies, and fluctuation measurements. Variations in the bulk of the electron distribution function manifest as alterations in ECE signatures, often attributable to the presence of fast electrons induced by auxiliary heating mechanisms such as Electron Cyclotron Resonance Heating (ECRH). This manuscript delves into the scrutiny of such interactions on ECE spectra leveraging a newly devised 16-channel ECE radiometer diagnostic. The manuscript delineates the impact of ECRH application, including pre-ionization and heating, resulting in ECE signal saturation and an expected rise in electron temperature (Te) respectively. Furthermore, the discourse explores instabilities potentially induced by high-energy electrons stemming from ECRH, focusing initial observations on runaway discharges characterized by relaxation oscillations in ECE, Soft X-ray (SXR), CIII, and Hα emissions. The backdrop of weakly ionized plasma with low electron density (ne) and temperature (Te), coupled with ECRH, fosters the generation of runaway electrons and corresponding relaxation oscillations in bulk plasma parameters. Additionally, a distinct surge in the ECE signature emerges upon cessation of the ECRH pulse, with no discernible variation in other bulk plasma parameters. Given that ECE signatures are susceptible to changes in both energy and pitch angle, this abrupt amplitude rise likely arises from Pitch Angle Scattering (PAS), potentially prompted by the sudden de-acceleration of fast electrons engendered by the ECRH pulse.

FPP'DEN CPP'YE DÖNÜŞTÜRÜLEN BİR PERVANENİN HİDRODİNAMİK PERFORMANSININ SAYISAL İNCELENMESİ

Present paper investigates the hydrodynamics of a Controllable Pitch Propeller (CPP) which is generated by geometrical modifications applied on a benchmark propeller designed as a fixed pitch propeller (FPP). The aim of the study is to examine the practical feasibility of converting a propeller model designed as a FPP to a new one operating with CPP principles. The flow around propeller models is solved via computational fluid dynamics and the results of the new generated model are presented in comparison with its parent geometry. The well-known KP505 propeller model is chosen as test case. The primary results show that the effect of the geometrical modifications on the propeller efficiency mainly depends on the propeller load and the blade pitch angle. The optimum efficiency point is determined as J=0.8, for the new design model. For the J values below this point, negative pitch angle changes improve the efficiency compared to FPP model. If the J exceeds the above mentioned value, positive pitch angle changes are needed to gain efficiency increase. The results led us to conclude that, it’s possible to convert a FPP to a CPP, but the blade pitch angle should be carefully controlled, for efficient operation

Design of an Integral Fuzzy Logic Controller for a Variable-Speed Wind Turbine Model

The demand for electricity is continuously growing around the world and thus the need for renewable and long-lasting sources of energy has become an essential challenge. Wind turbines are considered one of the major sources of renewable electricity generation. Therefore, there is a crucial demand for wind turbine model and control systems that are capable of precisely simulating the actual wind power systems. In this paper, an advanced fuzzy logic controller is proposed to control the speed of a wind turbine system. Initially, aero dynamical, mechanical and electrical models of two mass wind turbines models are derived. Analytical calculation of the power coefficient is adopted through a nonlinear function of six coefficients that mainly depends on pitch angle and tip speed ratio. The ultimate power output from the turbine can reach up to 50 % which is achieved at zero pitch angle with an approximately tip speed ratio of eight. This is then followed by designing a hybrid fuzzy-plus I pitch controller to regulate the speed of the wind turbine shaft. In general, fuzzy logic control strategy have the advantages over traditional control techniques especially when the system is highly non-linear and has to deal with strong disturbances such as wind turbulence. To evaluate the reliability and robustness of the controller, the response of the wind turbine system is tested under several types of disturbances including wind fluctuation, sudden disturbances on high and low speed shafts. Simulation findings reveals that the performance of fuzzy-integral control technique outweighs that of conventional fuzzy approach in terms of multiple performance evaluation indexes such as zero overshoot and steady state error, rise time and a settling time of (32.9 s) (44.7 s) respectively. The reliability and robustness of the controller is tested by applying speed and torque disturbances of 25% of their maximum ranges. Results have revealed that the controller was able to reject all disturbances efficiently with a change in pitch angle up to a maximum of 10 degrees in order to retain a constant rotor speed at 1000 rpm.

Relativistic kinematic effects in the interaction time of whistler-mode chorus waves and electrons in the outer radiation belt

Abstract. Whistler-mode chorus waves propagate outside the plasmasphere, interacting with energetic electrons in the outer radiation belt. This leads to local changes in the phase space density distribution due to energy or pitch angle diffusion. The wave–particle interaction time (Tr) is crucial in estimating time-dependent processes such as the energy and pitch angle diffusion. Although the wave group and particle velocities are a fraction of the speed of light, the kinematics description of the wave–particle interaction for relativistic electrons usually considers the relativistic Doppler shift in the resonance condition and relativistic motion equation. This relativistic kinematics description is incomplete. In this paper, to the literature we add a complete relativistic description of the problem that relies on the relativistic velocity addition (between the electron and the wave) and the implications of the different reference frames for the estimates of the interaction time. We use quasi-linear test particle equations and the special relativity theory applied to whistler-mode chorus waves parallel propagating in cold-plasma magnetosphere interaction with relativistic electrons. Also, we consider that the resonance occurs in the electron's reference frame. At the same time, the result of such interaction and their parameters are measured in the local inertial reference frame of the satellite. The change pitch angle and the average diffusion coefficient rates are then calculated from the relativistic interaction time. The interaction time equation is consistent with previous works in the limit of non-relativistic interactions (Tnr). For the sake of application, we provide the interaction time and average diffusion coefficient Daa for four case studies observed during the Van Allen Probes era. Our results show that the interaction time is generally longer when applying the complete relativistic approach, considering a non-relativistic calculation. From the four case studies, the ratio Tr/Tnr varies in the range 1.7–3.0 and Daa/Daanr in the range 1.9–5.4. Accurately calculating the interaction time with full consideration of special relativity can enhance the modeling of the electron flux in Earth's outer radiation belt. Additionally, the change in pitch angle depends on the time of interaction, and similar discrepancies can be found when the time is calculated with no special relativity consideration. The results described here have several implications for modeling relativistic outer-radiation-belt electron flux resulting from the wave–particle interaction. Finally, since we considered only one wave cycle interaction, the average result from some interactions can bring more reliable results in the final flux modeling.

Wind tunnel investigation of blade pitch effect for performance improvement of an asymmetric bladed H-Darrieus VAWT under low wind speed condition

In this paper experimental investigation is conducted to analyse the blade pitch effect on the performance improvement (self-starting and dynamic performance) of a NACA 63415 asymmetric bladed H-Darrieus VAWT at low wind speed conditions (5.0 and 6.0 m/s). It has been found that the performance of the considered VAWT has improved with a change of blade pitch angle (β) from negative to positive value. A maximum power coefficient (Cp) of 0.086 is obtained at a tip speed ratio (TSR) of 1.73 at a wind speed of 6.0 m/s for β = + 5°. Further turbulence intensity (TI) and flow non-uniformity (NU) are also calculated. In this case, TI of 2.6% and 2.4% is calculated from experimentation along with 4% and 3.33% non-uniformity (NU) for wind speeds 5.0 and 6.0 m/s, respectively, which are responsible for Cp improvement.

Unusually long path length for a nearly scatter-free solar particle event observed by Solar Orbiter at 0.43 au

Context. After their acceleration and release at the Sun, solar energetic particles (SEPs) are injected into the interplanetary medium and are bound to the interplanetary magnetic field (IMF) by the Lorentz force. The expansion of the IMF close to the Sun focuses the particle pitch-angle distribution, and scattering counteracts this focusing. Solar Orbiter observed an unusual solar particle event on 9 April 2022 when it was at 0.43 astronomical units (au) from the Sun. Aims. We show that the inferred IMF along which the SEPs traveled was about three times longer than the nominal length of the Parker spiral and provide an explanation for this apparently long path. Methods. We used velocity dispersion analysis (VDA) information to infer the spiral length along which the electrons and ions traveled and infer their solar release times and arrival direction. Results. The path length inferred from VDA is approximately three times longer than the nominal Parker spiral. Nevertheless, the pitch-angle distribution of the particles of this event is highly anisotropic, and the electrons and ions appear to be streaming along the same IMF structures. The angular width of the streaming population is estimated to be approximately 30 degrees. The highly anisotropic ion beam was observed for more than 12 h. This may be due to the low level of fluctuations in the IMF, which in turn is very probably due to this event being inside an interplanetary coronal mass ejection The slow and small rotation in the IMF suggests a flux-rope structure. Small flux dropouts are associated with very small changes in pitch angle, which may be explained by different flux tubes connecting to different locations in the flare region. Conclusions. The unusually long path length along which the electrons and ions have propagated virtually scatter-free together with the short-term flux dropouts offer excellent opportunities to study the transport of SEPs within interplanetary structures. The 9 April 2022 solar particle event offers an especially rich number of unique observations that can be used to limit SEP transport models.

Particle transport through localized interactions with sharp magnetic field bends in MHD turbulence

When a particle crosses a region of space where the curvature radius of the magnetic field line shrinks below its gyroradius $r_{g}$ , it experiences a non-adiabatic (magnetic moment violating) change in pitch angle. The present paper carries that observation into magnetohydrodynamic (MHD) turbulence to examine the influence of intermittent, sharp bends of the magnetic field lines on particle transport. On the basis of dedicated measurements in a simulation of incompressible turbulence, it is argued that regions of sufficiently large curvature exist in sufficient numbers on all scales to promote scattering. The parallel mean free path predicted by the power-law statistics of the curvature strength scales in proportion to $r_{g}^{0.3}\,\ell _{c}^{0.7}$ ( $\ell _{c}$ is the coherence scale of the turbulence), which is of direct interest for cosmic-ray phenomenology. Particle tracking in that numerical simulation confirms that the magnetic moment diffuses through localized, violent interactions, in agreement with the above picture. Correspondingly, the overall transport process is non-Brownian up to length scales $\gtrsim \ell _{c}$ .

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.

A field measurement on the aerodynamic load evolution in the start-up procedure of a wind turbine

The start-up procedure of wind turbines is one of the most complex operating conditions, which includes the dynamic changes of pitch angle decreasing, rotor speed increasing and generator grid-connected, and implies the complex evolution of attack of angle and aerodynamic load. Besides, the velocity and direction of the inflow have strong unsteadiness in the field, which makes the variation of the angle of attack more complex. To reveal the aerodynamic behaviors of the full-scale wind turbine in the start-up procedure, a field measurement campaign was conduct on a 100 kW wind turbine with blade angle of attack, aerodynamic pressure distribution and operating parameters measured in this paper. Aerodynamic power, lift and drag, angle of attack, lift coefficient and pressure distribution were analyzed. As results, the start-up procedure can be divided into free acceleration stage, fast acceleration stage, tip-speed ratio adjustment stage and normal operation stage. The normal forces of airfoils produce the main power to drive the turbine to accelerate in the acceleration stages. The standard deviation of angle of attack decreases continuously with the increase of rotor speed. The flow around the thick airfoil at the blade inner section presents a three-dimensional stall delay effect, and the effect is weakening with the increase of rotor speed. The results reveal the variation of angle of attack and aerodynamic load during the start-up process of a full-scale wind turbine in the field, and provide valuable field measured data for the validation of aerodynamic model.

An embarrassingly simple approach for visual navigation of forest environments.

Navigation in forest environments is a challenging and open problem in the area of field robotics. Rovers in forest environments are required to infer the traversability of a priori unknown terrains, comprising a number of different types of compliant and rigid obstacles, under varying lighting and weather conditions. The challenges are further compounded for inexpensive small-sized (portable) rovers. While such rovers may be useful for collaboratively monitoring large tracts of forests as a swarm, with low environmental impact, their small-size affords them only a low viewpoint of their proximal terrain. Moreover, their limited view may frequently be partially occluded by compliant obstacles in close proximity such as shrubs and tall grass. Perhaps, consequently, most studies on off-road navigation typically use large-sized rovers equipped with expensive exteroceptive navigation sensors. We design a low-cost navigation system tailored for small-sized forest rovers. For navigation, a light-weight convolution neural network is used to predict depth images from RGB input images from a low-viewpoint monocular camera. Subsequently, a simple coarse-grained navigation algorithm aggregates the predicted depth information to steer our mobile platform towards open traversable areas in the forest while avoiding obstacles. In this study, the steering commands output from our navigation algorithm direct an operator pushing the mobile platform. Our navigation algorithm has been extensively tested in high-fidelity forest simulations and in field trials. Using no more than a 16 × 16 pixel depth prediction image from a 32 × 32 pixel RGB image, our algorithm running on a Raspberry Pi was able to successfully navigate a total of over 750 m of real-world forest terrain comprising shrubs, dense bushes, tall grass, fallen branches, fallen tree trunks, small ditches and mounds, and standing trees, under five different weather conditions and four different times of day. Furthermore, our algorithm exhibits robustness to changes in the mobile platform's camera pitch angle, motion blur, low lighting at dusk, and high-contrast lighting conditions.

Dynamic Response Analysis of Airport Pavement under Impact Loading

The safety of the airport runway, as an infrastructure, is of considerable concern. The existing research has problems of hysteresis and unreasonable load application. In this paper, ANSYS is used to construct a coupled tire–pavement model to study the dynamic characteristics of airport asphalt pavements under impact loading. Taking the Boeing 737–800 as an example, the impact of an aircraft landing on an airport pavement is simulated by applying a dynamic load to the landing gear. The effects of tire pressure, landing pitch angle, and sinking speed on the dynamic response of the airport runway are investigated. The effects of each factor of the airport pavement are analyzed by comparing the maximum effective stress, effective strain, and displacement in the vertical direction at the same position of different structures. The results show that when the tire pressure is 2.0 MPa, the maximum values of effective stress, effective strain, and vertical displacement increase by 29.8%, 19.1%, and 22.2%, respectively, compared with 1.0 MPa. The maximum values of effective stress, effective strain, and vertical displacement at the 3.0 m/s sinking speed increase by 25.2%, 93.1%, and 77.1%, respectively, compared with that at the sinking speed of 1 m/s, which indicates that the effect of sinking speed on the dynamic response of the pavement is more significant. However, the change in the landing pitch angle has little impact on the response parameters of the pavement. Meanwhile, the flexural tensile stress at the bottom of the surface and the equivalent effect at the top of the soil foundation must be considered in the design of the airport pavement structure.

Parametric analysis of pitch angle scattering and losses of relativistic electrons by oblique EMIC waves

This study analyzes the effects of electromagnetic ion cyclotron (EMIC) waves on relativistic electron scattering and losses in the Earth’s outer radiation belt. EMIC emissions are commonly observed in the inner magnetosphere and are known to reach high amplitudes, causing significant pitch angle changes in primarily >1 MeV electrons via cyclotron resonance interactions. We run test-particle simulations of electrons streaming through helium band waves with different amplitudes and wave normal angles and assess the sensitivity of advective and diffusive scattering behaviors to these two parameters, including the possibility of very oblique propagation. The numerical analysis confirms the importance of harmonic resonances for oblique waves, and the very oblique waves are observed to efficiently scatter both co-streaming and counter-streaming electrons. However, strong finite Larmor radius effects limit the scattering efficiency at high pitch angles. Recently discussed force-bunching effects and associated strong positive advection at low pitch angles are, surprisingly, shown to cause no decrease in the phase space density of precipitating electrons, and it is demonstrated that the transport of electrons into the loss cone balances out the scattering out of the loss cone. In the case of high-amplitude obliquely propagating waves, weak but non-negligible losses are detected well below the minimum resonance energy, and we identify them as the result of non-linear fractional resonances. Simulations and theoretical analysis suggest that these resonances might contribute to subrelativistic electron precipitation but are likely to be overshadowed by non-resonant effects.

Thrust Vector Controller Comparison for a Finless Rocket

The paper focuses on comparing applicability, tuning, and performance of different controllers implemented and tested on a finless rocket during its boost phase. The objective was to evaluate the advantages and disadvantages of each controller, such that the most appropriate one would then be developed and implemented in real-time in the finless rocket. The compared controllers were Linear Quadratic Regulator (LQR), Linear Quadratic Gaussian (LQG), and Proportional Integral Derivative (PID). To control the attitude of the rocket, emphasis is given to the Thrust Vector Control (TVC) component (sub-system) through the gimballing of the rocket engine. The launcher is commanded through the control input thrust gimbal angle δ, while the output parameter is expressed in terms of the pitch angle θ. After deriving a linearized state–space model, rocket stability is addressed before controller implementation and testing. The comparative study showed that both LQR and LQG track pitch angle changes rapidly, thus providing efficient closed-loop dynamic tracking. Tuning of the LQR controller, through the Q and R weighting matrices, illustrates how variations directly affect performance of the closed-loop system by varying the values of the feedback gain (K). The LQG controller provides a more realistic profile because, in general, not all variables are measurable and available for feedback. However, disturbances affecting the system are better handled and reduced with the PID controller, thus overcoming steady-state errors due to aerodynamic and model uncertainty. Overall controller performance is evaluated in terms of overshoot, settling and rise time, and steady-state error.

Study Method of Pitch-Angle Control on Load and the Performance of a Floating Offshore Wind Turbine by Experiments

Offshore wind energy is a renewable energy source that is developing fast. It is considered to be the most promising energy source in the next decade. Besides, the expanding trend for this technology requires the consideration of diversified seabeds. In deep seabeds, floating offshore wind technology (FOWT) is needed. For this latter technology, such as for conventional WT, we need to consider aspects related to performance, aerodynamic force, and forces during operation. In this paper, a two-bladed downwind wind turbine model is utilized to conduct experiments. The collective pitch and cyclic pitch angle are adjusted using swashplated equipment. The fluid forces and moments acting on the rotor surface are measured by a six-component balancing system. By changing the pitch angle of the wind turbine blades, attempts are made to manage the fluid forces generated on the rotor surface. Under varied uniform wind velocities of 7, 8, 9, and 10 m/s, the effect of collective pitch control and cyclic pitch control on the power coefficient and thrust coefficient of FOWT is then discussed. Furthermore, at a wind speed of 10 m/s, both the power coefficient and loads are investigated as the pitch angle and yaw angle change. Experimental results indicate that the combined moment magnitude can be controlled by changing the pitch-angle amplitude. The power coefficient is adjusted by the cyclic pitch-angle controller when the pitch-angle phase changes. In addition, the thrust coefficient fluctuated when the pitch angle changed in the oblique inflow wind condition.