Azimuthal Position Research Articles

Exceptional-point-enhanced nanoparticle sensor utilizing a linewidth broadening mechanism

Exceptional points (EPs) in non-Hermitian systems, where eigenvalues and eigenvectors coalesce, offer unique advantages in state transitions, non-reciprocal devices, and sensing, owing to their distinctive and extraordinary properties. Most prior studies for sensing at EPs focused on mode splitting, with limited focus on leveraging the linewidth broadening mechanism. In this study, we construct an EP by embedding two nanoholes within a microdisk cavity. With nanoparticle adsorption at the edge of the microcavity at the EP, the linewidth of two split modes exceeds the frequency splitting, enabling the use of the linewidth broadening mechanism for nanoparticle detection. By calculating the linewidth of the transmission spectra with or without the adsorption of the nanoparticle, an enhanced linewidth broadening based on the EP is achieved compared to that based on the diabolic point (DP). We observe that the linewidth broadening based on the EP varies periodically with the azimuthal position of the nanoparticle along the edge of the cavity. Specifically, the maximum of the linewidth broadening based on the EP is several times larger than that based on the diabolic point. This paper not only deepens our understanding of non-Hermitian physics in microcavities but also lays the groundwork for future research and applications in high-sensitivity sensing.

Subcycle modulation of light's orbital angular momentum via a Fourier space-time transformation.

Achieving highly tailored control over both the spatial and temporal evolution of light's orbital angular momentum (OAM) on ultrafast timescales remains a critical challenge in photonics. Here, we introduce a method to modulate the OAM of light on a femtosecond scale by engineering a space-time coupling in ultrashort pulses. By linking azimuthal position with time, we implement an azimuthally varying Fourier transformation to dynamically alter light's spatial distribution in a fixed transverse plane. Our experiments demonstrate self-torqued wave packets that exhibit spiraling motions and rapid temporal OAM changes down to a few femtoseconds. We further extend this concept to generate angularly self-accelerating wave packets that adjust their OAM by redistributing their energy density across their spectral bandwidth, without external forces. The ability to tune the spatial-temporal properties of light on demand opens the possibility for exploring ultrafast light dynamics at fundamental timescales, with far-reaching implications for ultrafast spectroscopy, nano- and microstructure manipulation, condensed matter physics, and other related areas.

Study on the dynamic adjustment of UAV formation based on purely azimuthal passive positioning

In recent years, with the continuous development of unmanned aerial vehicle (UAV) technology, the application of UAV formation flight has also more and more extensive, but the UAV formation is easy to be interfered with by the outside world, which affects the formation. In this paper, we use pure orientation passive positioning, the least squares method to fit the UAV orientation, according to the superior and inferior arc model, cross-positioning, to reduce the UAV formation to emit electromagnetic wave signals to the outside. Firstly, the dynamic adjustment model of UAV formation is established to simulate the dynamic adjustment of two kinds of UAV formation from circular UAV formation to conical UAV formation and from rectangular UAV formation to conical UAV formation, and the simulation results show that the dynamic adjustment scheme of UAV formation under the model has a closer change distance and a shorter change time.

Aeroelastic Simulation of Full-Machine Wind Turbines Using a Two-Way Fluid-Structure Interaction Approach

Two-way fluid–structure interaction (FSI) simulation of wind turbines has gained significant attention in recent years due to the growth of offshore wind energy development. Strong coupling procedures in these simulations predict realistic behavior with higher accuracy but result in increased computational costs and potential numerical instabilities. This paper proposes a mixed weak and strong coupling approach for the FSI simulation of a 5 MW wind turbine. The deformation of the turbine blade is calculated using a weak coupling approach, ensuring blade deflection meets a convergence criterion before rotating to the next azimuthal position. Fluid and solid solvers are partitioned, utilizing the commercial software packages STAR-CCM+ and Abaqus, respectively. Flexible and rigid blade cases are modeled, and the calculated loads, power, and blade tip displacement for the rotor at a constant rotating speed are compared. The proposed model is validated, showing good agreement with the existing literature and results comparable to those from another validated wind turbine simulator. The effect of rotor–tower interaction is evident in the results. Based on our calculations, the power production of flexible blades is evaluated to be 9.6% lower than that of rigid blades.

Analysis of the fluid-structure interaction of a 2D model of the savonius rotor, using immersed boundary and fourier pseudospectral methods

Savonius rotors are a unique type of vertical axis wind turbine (VAWT) characterized by its “S” shape, with low rotational speed, low noise and good automatic start-up capability. This turbine has a great profile forsmall businesses and residences. The present work presents a simplified modeling of the fluid-structure interaction problem of a Savonius rotor, using the Fourier pseudospectral method (FPSM) coupled to the immersed bound-ary method (IBM), considering the Newtonian fluid, incompressible flow, without heat transfer and gravitational effects, with constant and two-dimensional (2D) properties. The results presented address the flow over a freely rotating vertical turbine, which allows the analysis of the evolution of the moment coefficient (Cm ) in relation to temporal evolution, azimuthal position (θ) and the blade tip speed ratio (λ).

NSTTF Heliocon Wireless Closed-Loop Controls Test Bed Development

A closed loop controls test bed is in development at the Sandia National Laboratories (SNL), National Solar Thermal Test Facility (NSTTF) as part of the U.S. DOE SETO sponsored Heliostat Consortium (HelioCON) program. This work pertains to preliminary development of advanced feedback controls for a concentrating solar power (CSP) field of 218 heliostats, and the development of a baseline closed-loop controls extremum seeking control (ESC) algorithm. This algorithm utilizes a batch least squares (BLS) technique to facilitate feedback control automation for heliostat pointing. This allows the determination of the optimal highest flux within a Gaussian profile, for both a four-point (QuadCell) aim point strategy, and a concentric aim point strategy. The results of this work determined that both approaches using the ESC BLS were able to reduce pointing errors to zero for both azimuth and elevation heliostat position movements. This work also reviews progress of the test bed which will allow flexible employment of controls and sensors which will be communicating with both wired and wireless protocols. The solar field distributed control system (DCS) will manage the flux distribution of energy across test articles and solar receivers using real-time programmable logic controllers (PLC) at each heliostat, for aiming and closed-loop feedback. Feedback control will be facilitated with a variety of sensors, located: 1. On the heliostat, 2. On the tower or 3. At an ancillary field tower station. The system is also developed to incorporate environmental information to provide real-time feedback into advanced algorithms for solar field management.

Coupling of two helical circular waveguides.

Coupling between optical waveguides has always been an important topic. By using the finite element method (FEM) based on a helicoidal coordinate system, we present a detailed study of the couplings between two helical coupled circular waveguides, showing several important aspects that were not found in previous studies. Our numerical results show that for the two-fold rotationally symmetric cases, intersections will appear in the effective index curves of the two composite modes with increasing twist rate, and we have found that this is related to the different increases of the composite modes in the helical path and the emergence of high-order harmonics. Further, for the one-fold rotationally symmetric structures formed by the two waveguides with the same radical but different azimuthal positions, as the twist rate increases, we observe the emerging asymmetric modal distributions of the composite modes, indicating that couplings between the two waveguides are no longer equivalent.

Controlling the initial separation distance between two electron plasma vortices in a Malmberg–Penning trap

This paper presents a novel method to continuously control the initial separation distance d between two plasma vortices of electrons. In this method, the two electron columns are initially confined individually in two coaxial Malmberg–Penning traps with different axial lengths. They rotate around the trap axis at different rotation frequencies due to the \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{E}\ imes \\varvec{B}$$\\end{document} drift. Their different rotation rates cause periodic changes in their relative azimuthal positions. The initial conditions are established when the two columns are stretched along magnetic field lines of a unified Malmberg–Penning trap. This method precisely provides a simple and continuous adjustment of the initial d and facilitates efficient investigation of the interaction of the two plasma electron vortices.

Control system design for azimuth position of earth station antennas

Smart earth station antennas have been used for several decades in many applications, from satellite communications to space object detection and tracking. The accuracy of the azimuth position for such antennas plays a crucial role in most steerable ground station antennas. Satellite tracking and space object detection demand precise tracking capabilities from the Earth. Several methods and techniques have been developed and used in industry to control the directions of ground station antennas, including the azimuth position. The challenge of azimuth tracking is increasing with the demand for full-sky coverage and with the exponential increase in space objects, including man-made satellites and operational and nonoperational objects; thus, providing accurate tracking is a key technology that demands continuous enhancement and development. This article presents the use of a PID-proportional-integral-derivative controller, a slide mode controller and a fractional order PID controller. It also introduces a new methodology based on model predictive control (MPC). The manuscript provides the core design for each of these controllers and provides insight into the performance of each controller even in the presence of disturbance. The camel optimization algorithm (COA) was used to obtain the optimal design parameters of each controller in the considered scenarios.

Exposure of employees to very high frequencies: laboratory measurements

Many occupational sectors are subject to noise exposure to very high audible frequencies (VHF) or low frequency ultrasound (LFUS): welding, food cutting, cleaning, etc. Although studies on employee exposure to these sound sources have been carried out since the 1960s, the question of the location of the measuring microphone and the representativeness of the measurement remains. As part of a study focusing on the risks associated with exposure to VHF/LFUS, the INRS conducted laboratory experiments on a mannequin to assess the variability of exposure measurements under controlled conditions as a function of microphone location (shoulder, ear entrance, etc.), source frequency and source position in azimuth. Of particular interest was the appropriateness of positioning the microphone at temple level via a dedicated mounting system suitable for use in the field. The findings of this preliminary work will be used to develop a protocol for measuring VHF/LFUS exposure in situ.

Formation mechanism and evolution of flow patterns for thermal convection in an inner cylinder-heated annular pool

In this paper, a set of numerical simulations were carried out to analyze the evolution and formation mechanism of various flow patterns for thermal convection in inner cylinder-heated annular pools at different depths. The results show that the basic flow bifurcates into the second type of hydrothermal waves, standing waves, petal-like structures, and spoke patterns after the flow destabilization. The formation mechanisms of these four flow patterns are all due to the lag in phase between temperature and velocity fluctuations. The reduction in surface azimuthal temperature fluctuation causes the second type of hydrothermal waves to bifurcate into standing waves. The bifurcation from standing waves to petal-like structures is due to the amplitude of azimuthal velocity fluctuation on the free surface being one order of magnitude smaller than that of radial velocity fluctuation. The bifurcation from petal-like structures to spoke patterns is because basic flow varies as the depth rises. Unlike the second type of hydrothermal waves, for standing waves, petal-like structures, and spoke patterns, the temperature fluctuation on different horizontal planes is different. Besides, for standing waves, the periodical variation process of the flow field depends on the azimuthal position.

Localization of Moving Sound Stimuli under Conditions of Spatial Masking

The aim of this study was to investigate spatial masking of noise signals in the delayed motion paradigm. Spatial effects were created by interaural level differences (ILD). Stationary maskers were located laterally or near the head midline, while test signals moved at different velocities from the head midline towards the ears, or in the opposite direction. The masking effect was measured by shifts in the perceived azimuthal positions of the starting and final points of signal trajectories, compared to their positions in silence. The perceived trajectories of all test signals shifted in the opposite direction from the masker. The masking effect was most pronounced in the spatial regions closest to the maskers, and was stronger when the signal moved towards the masker, compared to moving away from it. The final points were perceptually shifted further than the starting points. Signal velocity and masker presentation side (left or right) did not change the degree of masking.

Performance Improvement of a Straight-Bladed Darrieus Hydrokinetic Turbine through Enhanced Winglet Designs

The global climate and energy crisis have underscored the importance of sustainability in energy systems and their efficiency. In the case of vertical axis turbines (VATs) for hydrokinetic applications, the increment in efficiency is a topic of interest. Using winglets as passive flow control devices has the potential to improve the power coefficient of straight-bladed (SB) Darrieus turbines highly due to their impact in the dynamics of the flow close to the tip blade and the general impact in the hydrodynamic performance of each blade. The aim of the present work is to study the influence of the geometric parameters of a symmetric winglet in the performance of an SB-VAT for hydrokinetic applications via numerical simulations based on Computational Fluid Dynamics (CFD). Several simulations were performed in Star CCM+ v2206 varying the cant and sweep angles of the designed winglet. Numerical results show that a cant angle of 45° in combination with a sweep angle of 60° achieved the highest power coefficient with an increment around 20% with respect to the model without winglets. Furthermore, the vortical flow structures that form around straight and winglet blades are examined. This involves assessing the distribution of pressure and skin friction coefficients at different blade azimuthal positions during a turbine revolution. In general, the predicted increment in performance is related to the influence of the winglets in the strength of the tip vortices and in the delay in the flow separation.

Dynamic individual pitch control for wake mitigation: Why does the helix handedness in the wake matter?

Wind farm flow control aims at mitigating wake effects in order to maximize power production in wind farms. This work mostly focuses on the Helix strategy, which relies on individual pitch control to radially offset the application point of the thrust force from the rotor center and to dynamically change its azimuthal position. Previous studies have shown that power gains for a downstream turbine are higher for a counter-clockwise (CCW) rotation of the application point than for a clockwise (CW) one. In the CCW case, the wake develops as a right-handed helix, while in the CW case, a left-handed helix is observed. Using Large Eddy Simulations, this paper shows that the helix handedness in the wake matters due to its interaction with the wake swirl. Results of the CCW and CW helix first highlight the formation of streamwise vorticity in the near wake, which is transformed into strong coherent vortices in the far wake. Those vortex structures, to some extent similar to the counter-rotating vortex pair in the wake of yawed wind turbines, are responsible for (i) displacing the wake thanks to their induced velocities and (ii) deforming the shape of the wake.

Impact of rotor blade aerodynamics on tower vortex induced vibration of modern wind turbines

Modern wind turbines in standstill or idling could experience vortex induced vibrations (VIV); the origin of these vibrations is either shedding from the wind turbine blade referred to as blade VIV or shedding from tower termed as tower (or turbine) VIV. When the whole structure of the wind turbine is considered and the blades are pitched out, the dominant 1st order mode for blade deformation in edgewise direction leads to negligible motion of the tower top, while when the whole turbine vibrates with first tower mode, blades also undergo significant periodic translations and deformations. In this study, forced motion is used to study the impact of aerodynamic damping due to rotor moving with 1st tower mode. In the literature no comprehensive work is available to characterize the impact of blades aerodynamics in the turbine mode either using systematic tests or high-fidelity computational fluid dynamics (CFD). In this article high-fidelity numerical simulations are performed to compute the power injections from the rotor blades when the turbine moves in 1st tower mode. Depending on the inflow angle and the azimuthal position, blades can inject significant power. Thus, the estimated damping from tower-only empirical models could severely underestimate the total aerodynamic power if the power injection from the rotor is neglected.

The Underwater Berlin Research Turbine: A Wind Turbine Model for Wake Investigations in a Water Towing Tank

The design of a three-bladed horizontal axis research wind turbine for wake investigations is described. The turbine has a rotor diameter of 1.3 m and will be operated in a large water towing tank at a submergence depth of 2.5 m, yielding 3.3 % blockage. The test rig is configured to allow for underwater-stereo-particle-image-velocimetry measurements of the near and the far wake at chordwise Reynolds numbers approaching 700 000. The low-Reynolds number airfoil SG6040 is selected to constitute the rotor blades. Cavitation-free operation is assured by assigning a rated angle of attack of 1°. The blades are designed to maintain a constant circulation along the blade span and to minimize tip deflections. The blade pitch angles are adjustable. Various blade designs, with and without passive flow control devices, can be tested by replacing individual blade sections. This eliminates the need for multiple sets of blades. Sensors for acquiring the turbine’s thrust, torque, rotational speed, the azimuthal positions of the blades, and the imposed blade root bending moments are incorporated into the design. The wind turbine simulation suite QBlade is utilized to simulate the turbine characteristics. A model of the entire test rig is derived, representing its structural properties. Results from the analytical verification of the structural model are provided. QBlade is utilized to analyze the test rig design by imposing design loads and calculating the modal properties.

Assessment of the azimuthal loads variation by a bi-rotor configuration

Multi wind turbine configurations are emerging in the offshore wind energy market. The modelling of the aerodynamics of these systems is challenging, due to the small lateral distance between rotors and the subsequent interaction between wakes. Previous analysis in the literature showed that, due to this interaction, multi wind turbine concepts present the advantage of an increment in power production, if the rotors are laterally aligned. However, the counterpart in the variation of the blade loads throughout the revolution, has yet to be analysed in depth. This study focuses on the differences observed in azimuthal cycles of blade aerodynamic loads in side-by-side bi-rotor configurations, as an initial analysis of their potential impact on fatigue loads. The analysis has been developed using two aerodynamic codes, with different levels of fidelity. These models are: a Free Vortex filament Method (FVM) combined with an unsteady Lifting Line (LL) model, and a URANS-blade resolved approach. The simulations show that the sectional blade loads are affected by the adjacent rotor, changing the shape of the aerodynamic load cycles along the azimuth. The load azimuthal distributions predicted by a FVM and a URANS models have been compared, showing agreement on the shape of the cycle with slight differences on maximum peak values, specially at the inner sections of the blade. The FVM model has predicted increments in the blade load cycles, with respect to a single rotor case, with a maximum amplitude of a 3% for out-of-plane forces, and a 8% for in-plane forces. The difference in the azimuthal position of both rotors (phase shift angle) mainly affects the azimuthal shape and not so much the characteristic amplitude of these cycles. Finally, including geometric angles as tilt or pre-cone, produces imbalances between the blade sectional forces of the different rotors.

Wind tunnel investigations of an individual pitch control strategy for wind farm power optimization

Abstract. This article presents the results of an experimental wind tunnel study which investigates a new control strategy named Helix. The Helix control employs individual pitch control for sinusoidally varying yaw and tilt moments to induce an additional rotational component in the wake, aiming to enhance wake mixing. The experiments are conducted in a closed-loop wind tunnel under low-turbulence conditions to emphasize wake effects. Highly sensorized model wind turbines with control capabilities similar to full-scale machines are employed in a two-turbine setup to assess wake recovery potential and explore loads on both upstream and downstream turbines. In a single-turbine study, detailed wake measurements are carried out using a fast-response five-hole pressure probe. The results demonstrate a significant improvement in energy content within the wake, with distinct peaks for clockwise and counterclockwise movements at Strouhal numbers of approximately 0.47. Both upstream and downstream turbine dynamic equivalent loads increase when applying the Helix control. The time-averaged wake flow streamwise velocity and rms value reveal a faster wake recovery for actuated cases in comparison to the baseline. Phase-locked results with azimuthal position display a leapfrogging behavior in the baseline case in contrast to the actuated cases, where distorted shedding structures in the longitudinal direction are observed due to a changed thrust coefficient and an accompanying lateral vortex shedding location. Additionally, phase-locked results with the additional frequency reveal a tip vortex meandering, which enhances faster wake recovery. Comparing the Helix cases with clockwise and counterclockwise rotations, the latter exhibits slightly higher gains and faster wake recovery. This difference is attributed to Helix' additional rotational component acting in either the same or the opposite direction as the wake rotation. Overall, both Helix cases exhibit significantly faster wake recovery compared to the baseline, indicating the potential of this technique for improved wind farm control.

Research on purely azimuthal passive positioning of unmanned aerial vehicles based on geometric analysis and three-point intersection circle positioning

With the development of UAV technology, this paper discusses the problem of the positioning model of UAVs passively receiving radio signals in UAV clusters. For the case of a circular formation, two possible point distributions are analysed, and the positioning model of UAVs passively receiving signals is established by geometric analysis. In the case where the positions of UAVs numbered FY00 and FY01 are known, the problem of determining how many UAVs need to transmit signals in order to effectively locate a certain UAV with a slightly deviated position is addressed. The paper goes on to prove that only one UAV of unknown number is required to transmit signals for effective localization by analyzing the structure of a positive nine-sided shape on a circle. The article establishes a model of the problem through geometric analysis and proposes a corresponding solution, which provides some theoretical support for the formation flight of UAV clusters.

Optimizing Antenna Azimuth Position Control using Fuzzy PD, Fuzzy PD-I, and Fuzzy PD-plus-I Controllers

Optimizing Antenna Azimuth Position Control using Fuzzy PD, Fuzzy PD-I, and Fuzzy PD-plus-I Controllers