Rotating Reference Frame Research Articles

Duty Cycle-Rotor Angular Speed Reverse Acting Relationship Steady State Analysis Based on a PMSG d–q Transform Modeling

Multilevel converters have been broadly used in wind energy conversion systems (WECS) to set the generator angular speed to a certain value, which allows maximizing wind power extraction; nevertheless, power that is drawn out from WECS strongly depends on the power coefficient and the ability to operate at the optimal tip speed ratio that corresponds to the maximum power coefficient. This work presents a novel and formal steady-state analysis to demonstrate the reverse relationship between the duty cycle of a multilevel boost converter (MBC) and the angular speed of a permanent magnet synchronous generator (PMSG). The study was based on the d–q transformation using the rotor reference frame. It was carried out by employing a reduced order dynamic system that included an equivalent electrical load resistance as a representation for the subsystems that were cascade-connected at the terminals of the PMSG. The steady-state characteristic was obtained by using the definition of equilibrium point. The set of nonlinear equations that represents the steady state of this WECS was solved by using the Newton method; besides, an analysis that considers the equivalent load as a bifurcation parameter demonstrates that the number of equilibria never changes.

Kinematics of the East Pacific Rise Retrodicted From Pacific and Farallon/Nazca Subduction‐Related Torques: Support for Significant Deep Mantle Buoyancy Controlling EPR Spreading

AbstractSlab‐pull together with other boundary‐related torques of the Pacific and Farallon/Nazca plates are reconstructed from paleo‐agegrid datasets over the past 80 Ma in the no‐net rotation (NNR) frame of reference. The resulting reconstructions of both the retrodicted Pacific‐Farallon/Nazca age distribution and relative motion history of the East Pacific Rise (EPR) are compared with global plate kinematic reconstructions of these same aspects of Pacific basin evolution. There are mismatches between the predicted and observed age distributions and relative motion history of the EPR. Slab‐pull related torques mostly retrodict west to east motion of the EPR, whereas global kinematics result in south to north motions, orthogonal to each other. Slab‐pull torques are augmented with estimates of subduction and transform resistances together with spatially variable viscosities to assess their potential contributions to Pacific‐Farallon/Nazca relative motions and EPR motions in the NNR frame of reference. We argue that the discrepancies between these different reconstructed histories result from contributions associated with basal tractions acting on the Pacific and Farallon/Nazca plates resulting from deep mantle buoyancy. We propose that the latter has controlled the EPR evolution over the past 80 Ma and significantly contributed to driving plate motions at least in the Pacific basin.

Comment on: ‘A doubly anharmonic oscillator in an induced electric dipole system’

We argue that recent conclusions about a doubly anharmonic oscillator appear to be wrong. The radial eigenvalue equation is conditionally solvable and the authors derived some analytical eigenvalues for states with polynomial solutions. The allowed discrete values of the cyclotron frequency or intensity of the uniform magnetic field are an artefact of the approach used to obtain such particular solutions. There are bound states when the angular velocity of the rotating reference frame is null, contrary to what the authors claimed.

Urinary Bladder Volume Monitoring Using Magnetic Induction Tomography: A Rotational Simulation Model for Anatomical Slices Within the Pelvic Region.

Urinary bladder volume monitoring can benefit from contactless measurements, as alternative to the traditional medical methods of transurethral catheterization or ultrasound examination. The emerging modality of Magnetic Induction Tomography (MIT) offers the possibility for estimation of the intravesical volume in the physiological and pathological states using conductivity map reconstructions of the tissues present in the pelvic region. Within MIT, eddy currents originating from the conductive urine can produce their own magnetic field in response to an external magnetic source that is susceptible of being detected outside the body by means of a static ring of sensing coils. However, the ill-conditioned and ill-posed nature of the MIT Inverse Problem make the numerical implementation and conductivity estimation highly laborious. In this paper, we present a rotational frame model based on the MIT principles with application in urodynamic studies, which allows to extend the number of contactless measurements without increasing the overall dimension of the simulation domain, at the expense of solving multiple MIT Forward Problems. On the inversion process, the single-step Gauss-Newton method with Laplacian regularizer is recruited to estimate the bladder volume non-invasively and remotely (estimation error of 19%) using a simplified (quasi 2D) approximation to the distribution of eddy currents in the examined region, therefore paving the way for this technique to surpass the current limitations found in intravesical volume monitoring.

Aerodynamic performance analysis of a supercritical airfoil in the helicopter main rotor

Helicopters can be considered as any-terrain vehicles, as they can take off and land at any location. The aerodynamic characteristics of helicopters are more complicated than those of fixed-wing aircraft. The rotor is the source of lift and thrust for helicopters. The complex aerodynamic characteristics of helicopters are due to their rotational frame and variations in the velocity and pressure throughout the blades. Moreover, the airfoil undergoes phase changes because half of the phase exhibits a trailing edge toward the flow. In this study, four isolated helicopter rotor blades were analyzed using ANSYS Fluent in terms of flow in a static domain under non-rotating conditions. Supercritical airfoils used in high-speed aircraft have been found to be incredibly useful in the transonic region. They increased the critical and drag divergence Mach numbers. Incorporating supercritical airfoils in helicopter rotor blades ensures suitable flow characteristics and more than 50% efficiency compared to those of the HH02 blade in a stationary frame. Analyses were conducted for HH02 and NASA SC(2)-0714 airfoils with Mach numbers of 0.3, 0.4, and 0.5 without rotation. The post-processing results prove that the NASA SC(2)-0714 airfoil rotor achieves a better aerodynamic performance than the HH02 airfoil rotor.

Compensation of Torque-Producing Stator Current Error for Vector-Controlled Induction Motor Drives

This paper presents a detailed analysis of dynamic properties and accuracy issues of the torque-producing stator current control loop for vector-controlled induction motor drives. In this paper, a necessary mathematical description of vector control of an induction motor is shown with respect to the x-axis and y-axis current control in the rotating reference frame. A derivation of a steady-state error for the torque-producing stator current control scheme with and without a decoupling algorithm is described. The presented derivation and dynamic behavior of both these schemes were extensively tested in the MATLAB-SIMULINK software, considering different values for the moment of inertia. This solution was implemented in a DSC-based induction motor drive using a voltage source inverter to obtain experimental results. Moreover, the advantages of using the presented decoupling block for compensation of the problem are discussed at the end of the paper.

Tracking raw material flow through a continuous direct compression line Part I of II: Residence time distribution modeling and sensitivity analysis enabling increased process yield

Continuous manufacturing (CM) offers advantages in quality and space–time yield compared to common batch manufacturing. However, higher yield losses due to the start-up procedure make a broad application uneconomical. This work discusses the possibility of reducing yield losses by adjusting the degree of back-mixing. Back-mixing of nonconforming material from disturbances or start-up will result in the contamination of subsequent material. Therefore, higher degrees of back-mixing cause the discharge of additional material. Choosing an advantageous setting of operational parameters may be a simple way to change the degree of back-mixing. Based on direct compression, this work demonstrates the identification of promising parameters. Therefore, step-change experiments using color-marked material in the feeder, blender, and tablet press quantify the impact of three operational parameters per device. Models for the devices and the entire process result from those measurements. Subsequently, a global variance-based sensitivity analysis identifies the most influential parameters. As a result, adjusting the minimal filling level of the feeder and the rotational feed frame speed of the tablet press reduces back-mixing by more than 30 %. At high costs of the raw materials, the resulting savings can significantly improve the economic performance of CM compared to batch manufacturing.

Angular super-resolution in X-ray projection radiography using deep neural network: Implementation on rotational angiography

BackgroundRotational angiography acquires radiographs at multiple projection angles to demonstrate superimposed vasculature. However, this comes at the expense of the inherent risk of increased ionizing radiation. In this paper, building upon a successful deep learning model, we developed a novel technique to super-resolve the radiography at different projection angles to reduce the actual projections needed for a diagnosable radiographic procedure. MethodsTen models were trained for different levels of angular super-resolution (ASR), denoted as ASRN, where for every N+2 frames, the first and the last frames were submitted as inputs to super-resolve the intermediate N frames. ResultsThe results show that large arterial structures were well preserved in all ASR levels. Small arteries were adequately visualized in lower ASR levels but progressively blurred out in higher ASR levels. Noninferiority of image quality was demonstrated in ASR1–4 (99.75% confidence intervals: −0.16–0.03, −0.19–0.04, −0.17–0.01, −0.15–0.05 respectively). ConclusionsASR technique is capable of super-resolving rotational angiographic frames at intermediate projection angles.

An Angle-Compensating, Complex-Coefficient PI Controller Used for Decoupling Control of a Permanent-Magnet Synchronous Motor

An asymmetric, cross-coupling effect, as well as digital control delays, in a permanent-magnet synchronous motor (PMSM) will deteriorate its current-control performance in the high-speed range, especially for electric motors used in electric vehicles (EVs) with features such as high-power density and a low carrier/modulation frequency ratio. In this paper, an angle-compensating, complex-coefficient, proportional-integrator (ACCC-PI) controller is proposed, which aims to provide an excellent decoupling performance even with considerable digital control delay. Firstly, the current open and closed loop complex-coefficient transfer functions were established in the synchronous rotation coordinate system. The proposed method, along with existing ones, were then evaluated and theoretically compared. On this basis, the parameter-tuning method of the ACCC-PI controller was presented. Finally, simulation and experimental results proved the correctness of the theoretical analysis and the proposed method.

Quantum effects in rotating reference frames

We consider the time delay of interfering single photons oppositely traveling in the Kerr metric of a rotating massive object. Classically, the time delay shows up as a phase difference between coherent sources of light. In quantum mechanics, the loss in visibility due to the indistinguishability of interfering photons is directly related to the time delay. We can thus observe the Kerr frame dragging effect using the Hong–Ou–Mandel dip, a purely quantum mechanical effect. By Einstein's equivalence principle, we can analogously consider a rotating turntable to simulate the Kerr metric. We look at the feasibility of such an experiment using optical fiber and note a cancellation in the second order dispersion but a direction dependent difference in group velocity. However, for the chosen experimental parameters, we can effectively assume light propagating through a vacuum.

Theoretical Model Development for Energy Motion of Dusty Turbulent Flow of Fibre Suspensions in a Rotational Frame

Fibre suspension has garnered considerable attention in turbulent flows that are used in many industries. Solid particles, such as dust particles, notably affect the turbulent flow field in a rotational frame. In assessing their impacts, the dusty turbulent flow for fibre suspensions needs to be studied in a frame of rotation that can be substantially applied in many industries. This study, therefore, aims to build a theoretical model for the energy motion of dusty turbulent flow of fibre suspensions in a rotational frame. The turbulence momentum equation was considered to formulate the model in presence of dusty fluid rotating flow of fibre suspensions. The newly derived equation was derived in second‐order correlation tensors Fi,j, Wi,j, Gi,j, Si,j, Xi,j, Yi,j, Qi,j, and Ri,j at any two points in the flow domain, where the tensors were expressed as space, time, and distance functions. The developed model is a considerable improvement because it takes into account all of the potential influential parameters that could affect the motion of turbulent energy, such as dust particles, suspending particles (fibres), and rotating frame. However, the impact of these parameters on turbulence energy motion must be evaluated in order to assess the performance of turbulence systems utilized in a variety of industries, such as paper manufacturing. The present theoretical development will contribute to open up experimental and numerical research opportunities for the advancement of the industry, science, and technology.

A DC-Side Fault-Tolerant Bidirectional AC-DC Converter for Applications in Distribution Systems

This paper proposes an ac-dc converter for dc distribution systems. The proposed converter has a simple structure, offers bidirectional power flow capability, and is robust to dc-side faults. Based on the developed dynamic model, the converter is current-controlled in a rotating reference frame, meaning it is also protected against ac-side faults. Insight on the design of the specific control parameters for proper operation of the various control loops is also provided. Furthermore, it is shown that the minimum permissible dc-link voltage of the converter is the same as that of a conventional voltage-sourced converter. Time-domain simulation studies in the MATLAB and Simulink software environments, as well as a 1.25- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$kW$ </tex-math></inline-formula> experimental prototype confirm the effectiveness of the proposed converter under various normal and faulted operating scenarios.

Rotor Asymmetries Faults Detection in Induction Machines Under the Impacts of Low-Frequency Load Torque Oscillation

Low-frequency torque oscillations (LTOs) characteristic components emerge in the stator current spectrum of induction machines (IMs) as additive frequencies near the rotor asymmetry fault (RAF) indices especially in gearbox-based electromechanical system. The interactions between these two components make the fault detection process complicated and lead to false alarm. In this paper, a new technique for detection and separation of RAF from LTOs in IMs based on single phase stator current data is proposed. The method benefits from a novel pre-processing stage based on several sign functions. Hence, a two-axis rotating reference frame with a single phase of stator current of IMs with no prior knowledge of the rotational speed is introduced. The proposed method maps the static reference frame obtained through single stator current and its associated Hilbert transform to the proposed rotating reference frame which can separate the effects of LTOs from RAF, effectively. The validity of the proposed technique is tested through theoretical analysis, and experiments in both steady-state and transient conditions. In this regard, Synchro-squeezing Wavelet Transforms (SWT) is used for time-frequency analysis of faulty stator current in transient conditions. The obtained results confirm the effectiveness of the proposed approach to separate the RAF characteristic frequency from LTOs even in line-fed IMs applications.

Finding the bulk periodicity of lamellar and cylindrical structures using the pressure tensor.

It has been known for nearly thirty years that in all molecular simulations of periodic ordered morphologies (such as those formed by block copolymers), when the periodic boundary conditions of the simulation box do not match the bulk periodicity L0 of the morphology, they change the structure and even the stability of the morphologies obtained in the simulations. Few studies, however, have focused on finding L0 in simulations. Taking dissipative particle dynamics simulations of asymmetric diblock copolymer melts as an example, we found a simple way of using the pressure tensor, which can be readily calculated in molecular simulations in the continuum, to find L0 of lamellae and (regular-hexagonally packed) cylinders regardless of their orientation in (cuboid) simulation boxes. Variation of the diagonal and off-diagonal elements of the pressure tensor with the orientation of lamellae and cylinders in the box is explained by coordinate system rotation and confirmed by our simulation results. We also showed that the pressure tensor cannot be used to find L0 of 3D periodic ordered structures with a cubic symmetry such as the double gyroid.

Efficient Trajectory Matching Algorithm Based on Spatial Coordinate Rotation

Trajectory similarity estimation is the key to discover vehicle motion characteristics and trajectory classification, but the calculation of trajectory similarity is slow, and improving the speed of trajectory matching can help to carry out trajectory characteristics mining fast. Therefore, an efficient trajectory matching algorithm based on the rotation of spatial coordinate is proposed. Firstly, the trajectory curve is converted into the mean and variance curve which the number of points is equal to the number of rotations by multiple rotation of the spatial coordinate system. Then, Pearson correlation coefficient and Fréchet distance are used to measure the correlation of the mean and variance curves. Finally, the similarity between the original trajectories is determined indirectly according to the values of four parameters: Fréchet mean, Fréchet var, Pearson mean and Pearson var. Based on the taxi trajectory data of Hangzhou, under different trajectory sampling points and spatial coordinate rotation times, compared trajectory matching accuracy and speed with the traditional Hausdorff trajectory matching algorithm. The several experiments show that the algorithm can improve the trajectory matching speed by 85% on average while ensuring the accuracy of trajectory matching. By constructing a visual analysis system that includes three major modules: a map overview showing the results of trajectory matching, several visual interactive components that explore the differences in trajectory matching results, and a module for selecting trajectory matching parameters, explore the differences in the results of the four trajectory matching methods to help road network researchers to match real driving trajectories and find similar trajectory groups faster.

Doppler Analysis of Forward Scattering Radar With Opportunistic Signals From LEO Satellites

Recently microwave communication signals from low Earth orbit (LEO) satellites have been proposed to be used to detect flying objects in a ground-based forward scattering passive radar setup. In this work the Doppler shift and the Doppler spread due to the flying object in such a system are derived directly from the Fresnel-Kirchhoff diffraction formula using a rotational Cartesian coordinate system to accommodate the continuously moving signal source from the LEO satellites. Coordinate transformations for flying objects including those in the atmosphere with rectilinear motion relative to the ground and those in space with circular orbits are investigated. Both analytical and simulation results demonstrate that the Doppler shift and Doppler spread are related to the velocity and volumetric profile of the flying object, thereby in future they may be used to help identify its size and velocity.

Применение тензорных сигналов в системах автоматического управления положением мобильных объектов

The study focuses on using vector-tensor signals in automatic control systems operating in three-dimensional and two-dimensional spaces. The use of tensor signals makes it possible to build a control system in the most physically grounded form without restrictions in space of possible modes. The use of position tensors to close the feedback allows solving the problems of spatial positioning by methods of automatic control theory, including the method of structural diagrams. The study reveals that it is possible to take into consideration the features of working with tensor signals under conditions of relative rotation of coordinate systems in the structural diagram in the form of a variable matrix gain. Calculations showed that the studied class of systems belongs to the class of well linearizable multidimensional automatic control systems.

A Grid Connected Open-End Winding Induction Generator System With Series Compensation

This article presents a new grid connected induction generator (IG) system having open-end stator windings with a series reactive power compensator. The proposed scheme consists of a two-level capacitor fed voltage source inverter (VSI) connected to one side of the stator windings of the IG while the other ends of the windings are directly connected to the grid. A current phasor oriented rotating reference frame based control scheme is developed to control the operation of the VSI to ensure that it compensates the reactive power required by the IG. Thus, the IG system can supply active power to the grid without drawing reactive power from it for excitation. Unlike the shunt compensated IG systems, the proposed scheme does not require an interfacing inductor for connecting to the grid thereby reducing the hardware footprint. The proposed scheme is validated by simulation using PLECS software and the simulation results are presented in the article. A prototype of the system was developed in the laboratory to experimentally verify the proposed scheme and the experimental results are also presented in this article.

Dynamics and Energy Analysis of Nonequatorial Space Elevator Using Three-Dimensional Nonlinear Finite Element Method Extended to Noninertial Coordinate System

A space elevator is a futuristic space transportation technology that enables low-cost and versatile payload transportation using climbers on a tether deployed from the geostationary orbit (GEO). In particular, a nonequatorial space elevator, which contains an anchor in a region with latitudes on the Earth, has recently attracted attention. It has several advantages, such as extending the construction range and avoiding collisions with spacecraft in the GEO. Prior research has focused on rigid-body or spring-mass models with low fidelity. This paper proposes a modeling method for nonequatorial space elevators using a nodal-position finite element method (NPFEM) extended to a rotational coordinate system. The NPFEM is a three-dimensional finite element method that considers geometric nonlinearity. Conventional NPFEMs have only been formulated using inertial coordinate systems. This paper proposes a method to formulate the NPFEM in a noninertial coordinate system and derive the inertial forces and Jacobian matrices. In addition, a three-dimensional analysis of a nonequatorial space elevator was performed based on the proposed method. After determining the equilibrium position of the NPFEM, the dynamic response of the tether during climber ascent was analyzed. Moreover, parametric studies were conducted by varying several properties of the nonequatorial space elevator. Furthermore, the energy exchange between the components was analyzed to validate the proposed method and to discuss the energy perspective of the space elevator. The results revealed that the proposed nonequatorial space elevator model experienced a more tensioned equilibrium and exhibited a more significant dynamic response than conventional models.

이미지와 Voxel 을 이용한 3D 실내 점군 시맨틱 분할

In this paper, we propose a parallel network architecture that exhibits improved performance by fusing two-dimensional (2D) and three-dimensional (3D) features. A voxel-based and a projection-based method were adopted to derive the results through one scan. Our approach consists of two parallel networks, extracts features along each dimension, and converges them in a fusion network. In the fusion network, the voxel blocks and 2D feature maps extracted from each structure are fused to the voxel grid and then trained through convolution. For effective training of 2D networks, we use data augmentation techniques using coordinate system rotation transformation. In addition, a multi-loss with weights applied to each dimension was employed to effectively enhance the performance of the system, and the results revealed that the system exhibited better performance than when a single loss was used. Our proposed method can achieve better performance by changing the performance of the 2D network and 3D network, which can be generalized using other structures.