Angle Oscillations Research Articles

Power System Stabilizer PSS4B Model for Iraqi National Grid using PSS/E Software

To damp the low-frequency oscillations which occurred due to the disturbances in the electrical power system, the generators are equipped with Power System Stabilizer (PSS) that provide supplementary feedback stabilizing signals. The low-frequency oscillations in power system are classified as local mode oscillations, intra-area mode oscillation, and interarea mode oscillations. Double input multiband Power system stabilizers (PSSs) were used to damp out low-frequency oscillations in power system. Among dual-input PSSs, PSS4B offers superior transient performance. Power system simulator for engineering (PSS/E) software was adopted to test and evaluate the dynamic performance of PSS4B model on Iraqi national grid. The results showed that after installing the PSS in a specific plant the oscillation of rotor angle, bus frequency, speed, power flow is better than without PSS during the disturbances that occurred during the simulations. All the PSS/E simulation and tests were done in the National dispatch center (NDC) laboratory, Ministry of Electricity. 

A System Transient Stability Enhancement Control Method Using Doubly Fed Induction Generator Wind Turbine with Considering Its Power Constraints

With the rapid development of wind power, the effects of doubly fed induction generators (DFIGs) on the transient stability of power system have attracted more attention. However, the effects are still not clear due to the lack of deep and theoretical analysis. A control method for enhancing system rotor angle stability enhancement is proposed with considering the power constraints of DFIG. The rotor angle oscillation of the synchronous generator (SG) can be reduced and overspeed and the overcurrent of DFIG can be avoided. In this paper, the effects of the DFIG on the rotor angle characteristics of SG are analyzed. The change law of system rotor angle varying with transient power of the DFIG is obtained. Then, the power equation in the emergency pitch control process is explored. The reactive power constraints of the stator and grid-side converter are deduced. Finally, the system rotor angle stability enhancement control method is proposed based on the power constraints of DFIG. The effectiveness of proposed method is proven by simulations.

Power System Transient Stability Enhancement by Tuning of SSSC and PSS Parameters Using PSO Technique

In this paper, the tuning design of SSSC and PSS was examined in increasing the damping of system oscillations and improve the stability of the power system during disturbances. The design problem of the SSSC controller and PSS is designed as problem of optimization and the technique uses (PSO) technique to find for optimal control parameters. By minimizing the objective function based on the speed deviation and time domain, which deliberately deviates at the oscillation angle of the alternator rotor to improve performance of transient stability of the system. The proposed controllers are tested on the system of weak bonding ability exposed to severe disturbance. Nonlinear simulation results are presented to demonstrate the proposed controller's effectiveness and its ability to give efficient damping. It is also noted that the proposed controllers of SSSC and PSS greatly improves the power system stability.

Experimental Study and Neural Network Modeling of Aerodynamic Characteristics of Canard Aircraft at High Angles of Attack

Flow over an aircraft at high angles of attack is characterized by a combination of separated and vortical flows that interact with each other and with the airframe. As a result, there is a set of phenomena negatively affecting the aircraft’s performance, stability and control, namely, degradation of lifting force, nonlinear variation of pitching moment, positive damping, etc. Wind tunnel study of aerodynamic characteristics of a prospective transonic aircraft, which is in a canard configuration, is discussed in the paper. A three-stage experimental campaign was undertaken. In the first stage, a steady aerodynamic experiment was conducted. The influence of a reduced oscillation frequency and angle of attack on unsteady aerodynamic characteristics was studied in the second stage. In the third stage, forced large-amplitude oscillation tests were carried out for the detailed investigation of the unsteady aerodynamics in the extended flight envelope. The experimental results demonstrate the strongly nonlinear behavior of the aerodynamic characteristics because of canard vortex effects on the wing. The obtained data are used to design and test mathematical models of unsteady aerodynamics via different popular approaches, namely the Neural Network (NN) technique and the phenomenological state space modeling technique. Different NN architectures, namely feed-forward and recurrent, are considered and compared. Thorough analysis of the performance of the models revealed that the Recurrent Neural Network (RNN) is a universal approximation tool for modeling of dynamic processes with high generalization abilities.

Importance of nonlocal electron correlation in the BaNiS2 semimetal from quantum oscillations studies

By means of Shubnikov-de-Haas and de-Haas-van-Alphen oscillations, and ab initio calculations, we have studied the Fermi surface of high-quality BaNiS$_2$ single crystals, with mean free path $l \sim 400 ~\text{\AA}$. The angle and temperature dependence of quantum oscillations indicates a quasi-two-dimensional Fermi surface, made of an electron-like tube centred at $\Gamma$, and of 4 hole-like cones, generated by Dirac bands, weakly dispersive in the out-of-plane direction. Ab initio electronic structure calculations, in the density functional theory framework, show that the inclusion of screened exchange is necessary to account for the experimental Fermi pockets. Therefore, the choice of the functional becomes crucial. A modified HSE hybrid functional with 7% of exact exchange outperforms both GGA and GGA+U density functionals, signalling the importance of non-local screened-exchange interactions in BaNiS$_2$, and, more generally, in $3d$ compensated semimetals.

The Caveats of observing Inter-Trial Phase-Coherence in Cognitive Neuroscience

Many studies have now consistently reported that the phase angle of ongoing oscillatory activity (measured using EEG/MEG), at time of stimulus presentation influences detection when stimuli are near-threshold. However, studies examining whether the adjustment of the phase angle of oscillations is under top-down attentional control have thus far yielded conflicting results. A possible source for the discrepancy could be that the estimation of the phase of ongoing oscillations as well as its uniformity across trials could be affected by task induced changes in the power of oscillations or concurrent evoked responses. One measure, Inter-Trial Phase-Locking (ITPC), or the uniformity of phase angles across trials, is particularly vulnerable to these factors. Here, using various simulations modelling the common task induced changes in the EEG reported in the literature, we demonstrate that apparent changes in Inter-Trial Phase-Locking of oscillatory activity can occur independent of any actual change in the phase of the ongoing activity.

Aeroelastic Control-Oriented Modeling of an Airbreathing Hypersonic Vehicle

Modeling aeroelastic effects for an airbreathing hypersonic vehicle is challenging due to its tightly integrated airframe and propulsion system that leads to significant deflections in the thrust vector caused by flexing of the airframe. These changes in the orientation of the thrust vector in turn introduce low-frequency oscillations in the flight-path angle, which make control system design a challenging task. The airbreathing hypersonic vehicle considered here is assumed to be a thin-walled structure, where deformations due to axial, bending, shear, and torsional loads are modeled using the six independent displacements of a rigid cross section. Complex interactions between the airframe and the associated hypersonic flowfield may introduce lightly damped high-frequency modes. Such high-frequency free vibration modes are computed accurately using a previously developed novel scheme. The nonlinear equations of motion for the flexible aircraft are derived; these equations are then linearized about a computed cruise condition, and a selective modal analysis is carried out on the linearized system. Furthermore, a linear quadratic regulator is designed to compensate for perturbations in initial conditions, where a novel and practical approach is used to populate the weighting matrices of the linear quadratic regulator objective function.

Phasor Measurement Sensor-Based Angular Stability Retention System for Smart Power Grids With High Penetration of Microgrids

Emerging phasor measurement sensor (PMS) technology is revolutionizing conventional power grids to smart power grids (SPGs). This also paves the way for deregulations in energy market and wide area infusion of distributed energy-based systems like microgrids (MGs). Advanced energy management of MGs for better consumer gratification may pose severe threat to angular stability of SPGs. This paper outlines the angular stability issues that may emerge in SPGs due to high penetration of MGs. PMS-powered stability monitoring and MG operational-based stability retention technique are proposed for retaining the angular stability. Real-time frequency domain analysis of phase angle oscillations measured from PMS across the grid is the backbone of the proposed stability monitoring technique. Wide area optimized control of MGs with the aid of topological genetic algorithm is proposed for restraining the stability. Case studies conducted on standard bus systems portray the impact of high penetration of MGs on angular stability and the effectiveness of proposed techniques in monitoring and retaining the stability.

Mitigation of Turbine Vane Shock Waves Through Trailing Edge Cooling

The immense market demand on the high efficiency and lightweight aero-engines results in designs with compact high-pressure turbine stages experiencing supersonic flow field. In supersonic turbines, shocks appear at the vane trailing edges. The interaction of these shock with the neighbouring airfoils and blades on the adjacent rotor row and consequently create considerable amount of losses on the aerodynamic performance of the turbine. Moreover, periodic excitation created by the interaction of the shock waves and the motion of the turbine rotor causes fatigue problems and reduces the lifetime of the engine. Current study aims to alter the vane shock waves through blowing at the trailing edge. In order to characterize the effect of active blowing on the trailing edge flow field, a series of URANS simulations were conducted on OpenFOAM solver platform. Various blowing schemes were simulated over a simplified trailing edge geometry exposed in supersonic flow. The computations were compared in terms of shock intensity, oscillation frequency and exerted pressure forcing over the downstream components. The results showed that unsteady trailing edge blowing were able to modify the fluctuations observed on the shocks by altering the shock intensity, angle and frequency of oscillations. The classification of the wake unsteadiness, i.e. vortex shedding, in terms of trailing edge characteristics were also accomplished through frequency domain analysis of simulations.

Effects of stray lights on Faraday rotation measurement for polarimeter-interferometer system on EAST.

A double-pass radially view 11 chords polarimeter-interferometer system has been operated on the experimental advanced superconducting tokamak and provides important current profile information for plasma control. Stray light originating from spurious reflections along the optical path (unwanted reflections from various optical components/mounts and transmissive optical elements such as windows, waveplates, and lens as well as the detectors) and also direct feedback from the retro-reflector used to realize the double-pass configuration can both contribute to contamination of the Faraday rotation measurement accuracy. Modulation of the Faraday rotation signal due to the interference from multiple reflections is observable when the interferometer phase (plasma density) varies with time. Direct reflection from the detector itself can be suppressed by employing an optical isolator consisting of a λ/4-waveplate and polarizer positioned in front of the mixer. A Faraday angle oscillation during the density ramping up (or down) can be reduced from 5°-10° to 1°-2° by eliminating reflections from the detector. Residual modulation arising from misalignment and stray light from other sources must be minimized to achieve accurate measurements of Faraday rotation.

Analysis of the formation of filament winding in terms of force interactions between threads

We investigated a problem of filament winding formation in terms of force interactions between threads. It was established that at certain ratios between the frequency of bobbin rotation and the frequency of thread feeder motion the threads are laid on the same place. This results in the formation of the so-called filament winding. In this case, in an extreme case, a turn of the thread is laid exactly on the place of the preceding one. This phenomenon, however, occurs only if the thread is considered ideal, that is, it has no thickness. It is shown that due to sufficient complexity of actual processes a thread cannot be placed exactly on the place of the one laid earlier, which results in that it flies off it. In this case, the turn laid earlier acquires the role of a spreader, that is, it defines the place of laying a thread on the bale. This place can differ significantly from that set by the motion of a thread feeder, resulting in the formation of chords, which cause breaks of thread at subsequent unwinding of the bobbin. It is proposed, in order to eliminate the specified defects of winding in the form of filaments and chords that accompany them, to reduce to the permissible minimum the distance from the eye of a thread feeder to the point of attack. We describe conditions under which a fly-off of the turn occurs, based on which it becomes possible to determine the number of turns, laid with a breach of the kinematic conditions, as one of the basic parameters of the process. The latter means that there is no need for the thread feeder to control it. It is shown that a given parameter depends on the inclination angle of the turn, and the application of the resulting analytical description of this relation does not present any practical difficulties because all actual values of its constituent magnitudes, except for thread twisting stiffness, are known when designing a winding mechanism. It was established that in addition to the proposed design solution it is necessary to maintain the tension not less than 20 sN for the yarn 225´2 tex. In the case of other linear densities, this parameter can be calculated based on the obtained analytical dependences for a thread inclination angle and duration of torsional oscillations of a homogeneous rod suspended in the middle. Such results form the basis of requirements to the design of a winding mechanism, which are aimed at reducing the number of uncontrollably placed turns.

Perturbed soliton and director deformation in a ferronematic liquid crystal

The nonlinear molecular deformation of the ferronematic liquid crystal in the presence of external applied magnetic field intensity is investigated in view of solitons for the director axis. The Frank’s free energy density of the nematic liquid crystal comprising the basic elastic deformations, molecular deformation associated with the nematic molecules and the suspended ferromagnetic particles and their interactions with magnetic field intensity is deduced to a sine-Gordon like equation using the classical Euler–Lagrange’s equation. Using the small angle approximation we establish the Ginzburg–Landau (GL) equation and a class of solutions are obtained. In the normal condition of large angle oscillation of the director axis, we constructed a damped sine-Gordon (sG) equation with the additional perturbation appears in the form of cosine function. The sG equation is solved using numerical simulation and kink excitations were obtained as the molecular deformation for the case of constant damping and distorted kink to a planar configuration transition as we increase the damping.

Semi-empirical estimation and experimental method for determining inertial properties of the Unmanned Aerial System – UAS-S4 of Hydra Technologies

ABSTRACTThis article presents a structural analysis of the Unmanned Aerial System UAS-S4 ETHECATL. Mass, centre of gravity position and principal mass moment of inertia are numerically determined and further experimentally verified using the ‘pendulum method’. The numerical estimations are computed through Raymer and DATCOM statistical-empirical methods coupled with mechanical calculations. The mass of the UAS-S4 parts are estimated according to their sizes and the UAS-S4 class, by the means of Raymer statistical equations. The UAS-S4 is also decomposed in several simple geometrical figures which centres of gravity are individually computed, weighted and then arithmetically averaged to find the whole UAS-S4 centre of gravity. In the same way, DATCOM equations allows us to estimate the mass moments of inertia of each UAS-S4 parts that are finally sum up according to the Huygens-Steiner theorem for computing the principal moment of inertia of the whole UAS-S4. The mass of de UAS-S4 is experimentally determined with two scales. Its centre of gravity coordinates and its mass moment of inertia are found using the pendulum method. A bifilar torsion-type pendulum methodology is used for the vertical axis(14)and a simple pendulum methodology is used for the longitudinal and transversal axes(12). The test object is installed on a pendulum (simple or bifilar torsion pendulum) which is led to oscillate freely while recording the oscillation's angles and speed, by the means of three sensors (an accelerometer, a gyroscope and a magnetometer) that the calibration is also discussed. Simultaneously, nonlinear dynamic models are developed for the rotational motion of pendulums, including the effects of large-angle oscillations, aerodynamic drag, viscous damping and additional momentum of air. ‘Algorithms of minimization’ are then used to simulate and actualise the dynamic models and finally chose the model that simulated data best fit the experimentally recorded one. Pendulum parameters, such as mass moment of inertia, are lastly extracted from the chosen model. To determine the accuracy of the nonlinear dynamics approach of the pendulum method, the experimental results for an object of uniform density for which the mass moments of inertia are computed numerically from geometrical data are presented along with the experimental results obtained for the UAS-S4 ETHECATL. For the uniform density object, the experimental method gives, with respect to the numerical results, an error of 4.4% for the mass moment of inertia around theZaxis and 9.5% for the moment of inertia around theXandYaxes. In addition, the experimental results for the UAS-S4 inertial values validate the numerical calculation through DATCOM method with a relative error of 6.52% on average.

Stochastic Control of the External Sling of a Fire Helicopter

The paper describes the motion modeling of a fire helicopter with an external sling and a spillway device. The mathematical model of the fire helicopter with an external sling takes into account the effect of the stochastic disturbances for the sling caused by the rotor vibrations, gusts of wind and convection flows in the fire zone. The stochastic optimal control is synthesized with minimal sling oscillations and control power for its implementation. The solution is obtained due to dynamic programming. The resulting optimal control does not depend on the mass of a spillway device, but it is a function of a sling length. Thus, because of the changing sling length during motion, the length should be measured together with the sling deviation angle and the intensity of the stochastic disturbances. The temporal evolution of the system solution is done for various disturbance intensities. The computer calculation results are presented as a function of the suspension length and the intensity of the stochastic disturbances. Analysis of the results shows that the sling length affects significantly the value of the control signal, especially at high levels of the disturbances. A structure of the helicopter stochastic control system is proposed. It makes it possible to control oscillation of the external sling within an acceptable range. The system includes an oscillation angle, a sensor of the stochastic disturbance intensity and the sling length sensor. Thus, the helicopter control can be obtained through changing the thrust magnitude of the main and tail helicopter rotors.

Network-Based Heading Control and Rudder Oscillation Reduction for Unmanned Surface Vehicles

This paper is concerned with network-based heading control and rudder oscillation reduction for an unmanned surface vehicle (USV) equipped with single rudder in network environments. A novel network-based model is first established by constructing a heading control error system and purposely dropping some control input packets, which are received by a steering machine. Then, a stabilization criterion is derived to guarantee the heading angle tracking performance and to reduce the oscillation of the rudder angle. Some algorithms for selecting the number of purposely dropped control input packets are presented. It is shown through heading control and rudder oscillation reduction performance analysis that compared with the controller design without dropping control input packets purposely, the proposed intentional packet dropouts-based controller design is more effective in improving the control performance of the USV.

Measurement of sin2(2θ13) via neutron capture on hydrogen at Daya Bay

An independent measurement of neutrino oscillation angle θ13 using samples based on neutron captured on hydrogen (nH) was performed at the Daya Bay Reactor Neutrino Experiment. To deal with the challenges due to larger backgrounds, longer neutron capture time and lower detection efficiency, the nH analysis developed several data-driven techniques to precisely measure backgrounds and to control systematic uncertainties. This statistically independent and largely systematically uncorrelated independent analysis provides a firm confirmation of the nGd result and improves the overall uncertainty of sin2(2θ13). With 621 days of data and two newly installed antineutrino detectors, nH analysis yields sin2(2θ13) = 0.071 ± 0.011 in the three neutrino oscillation framework.

Reduced frequency effects on combined oscillations, angle of attack and free stream oscillations, for a wind turbine blade element

The dynamic stall phenomenon in horizontal axis wind turbines causes significant energy waste and sometimes wind turbine failure. For modeling a deep dynamic stall phenomenon of a horizontal axis wind turbine blade element, a numerical simulation of an oscillating NREL's S809 airfoil has been performed at Reynolds number of 106 in an unsteady incident velocity; the velocity oscillates with the same frequency as the airfoil oscillation but with different phase difference (ϕ). Since the sliding mesh technique has been applied for the airfoil oscillation, an O-type grid is created resulting in the reduced number of mesh layers. A specific correction improves the quality of the O-type mesh near the sharp trailing edge. For the combined oscillations, the effects of the reduced frequency (k) in the range of 0.05≤k≤0.15 are investigated with the phase differences of ϕ=−π2, +π2,π. The results show their significant dependency on k at specific ϕ values in particular at ϕ=−π2. Combined effects of k and ϕ can change the aerodynamic loads during dynamic stall significantly compared to loads from a case with a steady incident velocity. These significant changes in the flow structure and aerodynamic loads can affect the wind turbine performance during the dynamic stall phenomenon.

Search for torsional oscillations in isolated sunspots

In this work we seek evidence for global torsional oscillations in alpha sunspots. We have used long time series of continuum intensity and magnetic field vector maps from the Helioseismic and Magnetic Imager (HMI) instrument on board the Solar Dynamics Observatory (SDO) spacecraft. The time series analysed here span the total disk passage of 25 isolated sunspots. We found no evidence of global long-term periodic oscillations in the azimuthal angle of the sunspot magnetic field within $\sim$ 1 degree. This study could help us to understand the sunspot dynamics and its internal structure.

Decoupled Adaptive Neuro-Interval Type-2 Fuzzy Sliding Mode Control Applied in a 3DCrane System

Moving an object attached to a cable along a predetermined path is a very complex task when the angles of oscillation impose severe constraints. However, to minimize the swing angle, adaptive control laws are necessary, especially in case where the systems dynamics are prone to uncertainties. In this paper, we propose a decoupled adaptive neuro-interval type-2 fuzzy controller based on the sliding mode theory for the control of 3DCrane system. The considered 3DCrane system involves a plan movement in conjunction with a lifting movement. It has three control inputs only (trolley and hoisting forces) with five controlled variables (the trolley position in the XOY plane, the length of the lifting cable, and the two angles of swing). Overall, control subsystems are regarded as being decoupled interactions and that are taken as disturbances acting in the control of each individual subsystem. In the proposed approach, a conventional controller (PD) and the neuro-interval type-2 fuzzy controller are used in parallel; the PD controller ensures the asymptotic stability in compact space, the adaptation parameters of neuro-interval type-2 fuzzy inference system rules are obtained by derivation, and Lyapunov method is used to demonstrate the stability of the online learning algorithm. To validate the proposed approach, the laboratory equipment 3DCrane system is used as an experimental platform. The presented results are obtained for a trajectory tracking with a minimum of oscillations.

Rotational spectrum and structure of the T-shaped cyanoacetylene carbon dioxide complex, HCCCN⋯CO2

The rotational spectrum of the T-shaped cyanoacetylene carbon dioxide dimer, HCCCN⋯CO2, was measured using two Balle-Flygare Fourier transform microwave (FTMW) spectrometers between 1.4GHz and 25GHz. Only the Ka=0, 2, 4 branches of spectrum from J′=1←0 to J″=16←15 transitions were observed. The vanishing of the Ka=1, 3, … transitions demonstrates a C2v symmetry complex with a T-shaped alignment of the subunits. The spectroscopic constants were fit using Pickett’s SPFIT/SPCAT suite of programs obtaining: A0=11273(18)MHz, B0=764.088(21)MHz, C0=716.254(21)MHz, ΔJ=0.50329(34)kHz, ΔJK=0.120867(11)MHz, ΔK=−28.17(36)MHz, δJ=0.0613(21)kHz, δK=44.25(95)kHz, ΦJ=0.0053(12)Hz, ΦJK=9.820(55)Hz, ΦKJ=−0.59325(72)kHz, ΦK=−2.3719(53)MHz, ϕJ=0.0398(42)Hz, ϕJK=6.9(9)Hz, and ϕK=−3.592(13)kHz. The 14N nuclear quadrupole coupling constants were fit to χaa=−4.12753(38)MHz and χbb−χcc=0.103(15)MHz. The small negative inertial defect, Δ0=−0.66(12)uÅ2, indicates a vibrationally averaged planar complex with non-negligible low frequency out-of-plane vibrations. While maintaining near-planar orientation, both binding partners exhibit large-amplitude bending vibrations within the plane. To deal with the intermolecular dynamics, a torsional oscillation model was developed in this work for the structural analysis. According to this model, the vibrational bending amplitude for HCCCN torsional angle is 10.(1)°, with the a-axis of complex; CO2 subtending a 5.4(5)° torsional oscillation angle with the b molecular axis. The van der Waals bond length is 3.0137(3)Å. The stretching force constant, ks=3.9N/m, and the stretching frequency, νs=53cm−1, for the van der Waals bond were calculated using the pseudo-diatomic model. High-level MP2 and DFT calculations of structural parameters, rotational constants, and 14N quadrupole coupling strengths were made and the results compared with experimental results.