Stable Poles Research Articles

Directional DIC method with automatic feature selection

Using displacement identification via high-speed cameras is a non-contact, full-field technique for characterizing the dynamic properties of engineered structures. Achieving reliable measurements of structural deformation through conventional Digital Image Correlation (DIC) requires a well-defined spatial gradient in two orthogonal directions within an image subset of pixels. However, DIC is susceptible to the aperture problem, which leads to an ill-conditioned optimization problem. An example of such a case is cable systems on which no speckle patterns can be applied. This study proposes Directional DIC (D-DIC) as an alternative technique to overcome the limitations posed by the aperture problem in conventional DIC methods. Directional DIC assumes the local direction of motion, which is often a valid assumption in structural vibration tests, as individual vibration shapes are often unidirectional at localized parts of the structure. This alleviates some restrictions on trackable image subsets, enabling more trackable locations. A parameter for quantifying expected tracking performance for D-DIC is introduced. The parameter enables automatic feature selection for D-DIC, making optical methods more accessible for displacement identification on structures where no speckle patterns can be applied. Experimental modal tests are conducted using a flexible spider web-like structure to validate the D-DIC method and compare it to conventional DIC. The experimental findings show that the Directional DIC method allows for measuring displacements at significantly more locations than conventional DIC. Additionally, D-DIC provided less noisy frequency response functions, more retrieved stable poles, and more fitted vibrational modes. Lastly, the findings show that D-DIC is especially superior to DIC when using small subsets since D-DIC is less inhibited by the aperture problem.

Analysis, Simulation, and Experiments of Dynamics and Control of a Hydrostatic Wind Turbine Under Partial Load

Abstract Kω2 control, also called torque control, is a popular method for maximizing wind turbine power. For hydrostatic wind turbines, torque control becomes pressure control with pc=K'ω2 because pressure is proportional to torque. Inverse Kω2 control is an alternative approach using rotor speed control with pc=(p/K')1/2. This work analyzes the dynamics of hydrostatic wind turbines using forward and inverse Kω2 control with P-, PD-, PI-, and PID-control for feedback. Dimensionless, linearized models are used. Analysis shows that the mechanical rotor dynamics are much slower than the hydrostatic transmission dynamics and that frictional and leakage losses are negligible. Linear perturbation of the nonlinear model reveals that the closed-loop control is not in Evan's form, so that closed-loop poles and zeros both vary with the loop gain. Pole and zero root locus analysis shows how systems responses change with controller gains. Both control approaches require derivative controller action to sufficiently dampen their responses; both are also fundamentally limited in speed of response by a slow stable pole regardless of controller loop gains. Nonlinear system simulation shows that both control approaches track the maximum power point with nearly identical transient behavior and have nearly identical power losses when using suboptimal values of the control law gain, K. Pressure control has a gain margin of infinity and a phase margin of 99.3 degrees, while speed control has a gain margin of 22.4 dB and a phase margin of 73.8 degrees showing that pressure control is more robust than speed control. Experiments using the power regenerative hydrostatic test stand at the University of Minnesota show that the control approaches have different transient responses but capture comparable power under steady and turbulent conditions.

Development of a 12 mm period cryogenic permanent magnet undulator for time-resolved X-ray beamline on HEPS

In order to obtain hard x-rays with the fundamental harmonic energy over 20 keV, a Pr2Fe14B based cryogenic permanent magnet undulator (CPMU) with the period length of 12 mm has been developed on High Energy Photon Source (HEPS) for time-resolved beamline. Several technical difficulties arise with the further shortening of the CPMU period length such as magnets and poles clamping, constitutionally stable pole height shimming, multipoles shimming within the small horizontal area according to the dynamic apertures of ultra-low emittance storage ring. Some specific treatments are adopted in response to these difficulties and proved to be effective. Details of development process including design, assembling, methods of optimization, measurement and shimming are presented.

On the computation of stable coupled state-space models for dynamic substructuring applications

This paper aims at introducing a methodology to compute stable coupled state-space models for dynamic substructuring applications by introducing two novel approaches targeted to accomplish this task: (a) a procedure to impose Newtons’s second law without relying on the use of undamped RCMs (residual compensation modes) and (b) a novel approach to impose stability on unstable coupled state-space models. The enforcement of stability is performed by dividing the unstable model into two different models, one composed by the stable poles (stable model) and the other composed by the unstable ones (unstable model). Then, the poles of the unstable state-space model are forced to be stable, leading to the computation of a stabilized state-space model. If this model is composed by real poles, it should be divided into two different ones, one composed by the pairs of complex conjugate poles and the other composed by the real poles. Afterwards, to make sure that the Frequency Response Functions (FRFs) of the stabilized model well match the FRFs of the unstable model, the Least-Squares Frequency Domain (LSFD) method is exploited to update the modal parameters of the stabilized model composed by the pairs of complex conjugate poles. The validity of the proposed methodologies is presented and discussed by exploiting experimental data. Indeed, by exploiting the FRFs of a real system, accurate state-space models respecting Newton’s second law are computed. Then, decoupling and coupling operations are performed with the identified state-space models, no matter the models resultant from the decoupling/coupling operations are unstable. Stability is then imposed on the computed unstable coupled model by following the approach proposed in this paper. The methodology proved to work well on these data. Moreover, the paper also shows that the coupled state-space models obtained using this methodology are suitable to be exploited in time-domain analyses and simulations.

Model-assisted clustering for automated operational modal analysis of partially continuous multi-span bridges

Long multi-span bridges represent a broad section of the civil roadway infrastructure. Despite being so common, their condition-based maintenance through vibration-based Structural Health Monitoring (SHM) has been scarcely investigated in the literature. The dynamic identification of such structures through Operational Modal Analysis (OMA) is especially challenging due to of their quasi-periodic nature and the common existence of weak inter-span coupling. Even when designed following an isostatic scheme, there always exists a certain degree of coupling between spans due to the continuity of the deck, the pavement and imperfect expansion joints. Hence, the modal poles of the spans typically appear as dense clusters with closely spaced frequencies and mode shapes with similar wavelengths, which significantly hinders the identification of physical poles through stabilization diagrams. In this light, this paper proposes a model-based machine learning approach to conduct and interpret the OMA results of partially continuous multi-span bridges. The proposed method is a hierarchical clustering approach that leverages on the analytical solution of the vertical free vibration response of multi-span girders with weak inter-span rotational coupling, allowing the estimation of the modal features of any bridge configuration ranging from simply supported to perfectly continuous conditions. Detailed parametric analyses and discussions are presented to appraise the correlation between the inter-span rotational coupling and the clustering of the modal poles of multi-span bridges, as well as the influence of damage conditions of varying severity and extension. On this basis, a model-based cut-off distance threshold for hierarchical clustering of stable poles is proposed to assist the automation of the global OMA of multi-span bridges. The developed formulation is tested in a real-world in-operation seven-spans reinforced concrete girder bridge, the Trigno V Bridge in Italy.

New palaeoproterozoic palaeomagnetic data from Central and Northern Finland indicate a long-lived stable position for Fennoscandia

SUMMARYThe Svecofennian gabbro intrusions coincide temporally with the global 2100–1800 Ma orogens related to the amalgamation of the Mesoproterozoic supercontinent Nuna. We provide a new reliable 1891–1875 Ma palaeomagnetic pole for Fennoscandia based on rock magnetic and palaeomagnetic studies on the Svecofennian intrusions in central Finland to fill gaps in the Palaeoproterozoic palaeomagnetic record. By using the new pole together with other global high-quality data, we propose a new palaeogeographic reconstruction at 1885 Ma. This, together with previous data, supports a long-lived relatively stable position of Fennoscandia at low to moderate latitudes at 1890–1790 Ma. Similar stable pole positions have also been obtained for Kalahari at 1880–1830 Ma, Siberia at 1880–1850 Ma, and possibly India at 1980–1775 Ma. A new reconstruction at the beginning of this period indicates the convergence of several cratons at 1885 Ma in the initial stages of the amalgamation of the Nuna supercontinent at low to moderate latitudes. The close proximity of cratons at low to moderate latitudes is further supported by global and regional palaeoclimatic indicators. Stable position of several cratons could indicate a global period of minimal apparent drift at ca. 1880–1830 Ma. Before this period, the global palaeomagnetic record indicates large back-and-forth swings, most prominently seen in the high-resolution 2020–1870 Ma Coronation loops of the Slave craton. These large back-and-forth movements have been explained as resulting from an unstable geomagnetic field or basin- or local-scale vertical-axis rotations. However, the most likely explanation is inertial interchange true polar wander (IITPW) events, which is in line with the suggestion of large amplitude true polar wander events during the formation of the supercontinent.

Orthogonal rational approximation of transfer functions for high‐frequency circuits

SummaryThis paper introduces the orthogonal rational approximation (ORA) algorithm for rational function approximation of transfer functions, based on data available from simulations or measurements. A rational function allows integration of such data in transient solvers for analysis of high‐frequency circuits. In rational function approximation, the unknown denominator polynomial of the model results in a nonlinear problem, which can be replaced with successive solutions of linearized problems following the Sanathanan–Koerner (SK) iteration. An orthogonal basis can be obtained based on Arnoldi resulting in a stabilized SK iteration. We present an extension of the stabilized SK, called ORA, which ensures real polynomial coefficients and stable poles for realizability of electrical networks. We also introduce an efficient implementation of ORA for multiport networks based on a block QR decomposition.

A study of histopathological analysis and clinico-pathological correlation of leprosy in urban industrial area

Leprosy is a chronic infectious granulomatous disease caused by Mycobacterium leprae, with a prevalence rate corresponded to 0.2/10000. Skin and peripheral nerves are mainly affected exhibiting spectrum of clinical and histopathological features based on the immunological status of the individual. The diagnosis is made from adequate clinical information combined with histopathology. The aim of study to asses the clinical and histopathological features and there correlation in diagnosing the cases of leprosy.A cross-sectional study of 2 years was conducted on 99 cases of skin biopsies histopathologically diagnosed with leprosy. Adequate clinical history was obtained and biopsies were stained with hematoxylin and eosin and modified Fite Faraco stain. A clinicopathological correlation was then attempted along with statistical analysis. Out of the total 99 leprosy cases, maximum cases (34.34%) belonged to third decade of life with Male to Female ratio of 1.75:1. About 58.59% of the total cases of leprosy showed decreased sensations and nerve thickening was seen in 79.80% cases. Clinically, 45.46% lesions were erythematous plaques. Borderline tuberculoid leprosy (31.68%) was the most frequently diagnosed subtype of leprosy. Evaluation of agreement and correlation between clinical and histopathological classification of leprosy showed an overall agreement of 57.57%. Correlation was more in stable poles i.e. TT tuberculoid pole (TT) and lepromatous pole (LL). Leprosy is still a prevalent disease which raises the concern about therapeutic approaches and various health programmes. It may not have a classical clinical picture always. Many factors contribute in clinicopathological discordance. Hence, diagnostic efficacy can be improved by clinic- histopathological corroboration which includes morphological examination of the skin lesion along with proper clinical history and correlation of these findings with histopathological examination findings.

능동댐핑 영-극점 상쇄 BLDC모터 속도 제어기를 위한 경사 하강법 기반 자동 동조 알고리즘 설계

This paper presents an auto-tuning mechanism for major design factors adopted for the active damping pole-zero cancellation Brushless DC Motor (BLDCM) speed controller. The proposed auto-tuner is designed to seek the minimum point of the steepest gradient method-based controlled error’s cost function. Moreover, the proposed solution employs the compensation term (σ-modification) to assign the stable pole to the auto-tuner dynamics. The prototype dynamo system, which includes the 500W BLDCM as the test motor, verifies the effectiveness of the closed-loop system driven by the proposed auto-tuner.

Observer-Based PD Controller for a Class of High Order Linear Unstable Delayed Systems

In this paper it is considered the stabilization and control of a class of high order linear systems that are subject to constant time delay at the input-output channel. In particular, systems with two unstable poles and any number of real or complex conjugate stable poles are studied. To improve the solutions existing in the literature, a new proposal for the solution of the considered problem is taken into account consisting in the design of an observer and a ProportionalDerivative PD controller to assure stable closedloop performance, establishing by means of a frequency analysis necessary and sufficient conditions for the proposed control strategy. The proposal novelty is the inclusion of the PD control action in the observer that allows to estimate internal signals used in the solution. This configuration offers advantages in the time delay size that can be handled and on the control performance of the closed loop system. A practical design procedure is presented to determine the value of the controller gains. Numerical simulations examples are presented to show the operation of the proposal.

AAA Algorithm for Rational Transfer Function Approximation With Stable Poles

Signal and power integrity analysis in time-domain requires suitable models for interconnects and power distribution networks, which are often available only in terms of their frequency responses from electromagnetic simulations or measured data. A rational transfer function approximation of such data allows its integration in circuit simulators. Recently the AAA (adaptive Antoulas-Anderson) algorithm has been introduced for rational function approximation. This letter introduces a modification of that algorithm for fitting in terms of the squared variable ( s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), called AAA <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> algorithm, for generating rational transfer functions with stable poles from frequency response available from simulated or measured data.

Kinematics of Deformable Blocks: Application to the Opening of the Tyrrhenian Basin and the Formation of the Apennine Chain

We describe the opening of back-arc basins and the associated formation of accretionary wedges through the application of techniques of deformable plate kinematics. These methods have proven to be suitable to describe complex tectonic processes, such as those that are observed along the Africa–Europe collision belt. In the central Mediterranean area, these processes result from the passive subduction of the lithosphere belonging to the Alpine Tethys and Ionian Ocean. In particular, we focus on the opening of the Tyrrhenian basin and the contemporary formation of the Apennine chain. We divide the area of the Apennine Chain and the Tyrrhenian basin into deformable polygons that are identified on the basis of sets of extensional structures that are coherent with unique Euler pole grids. The boundaries between these polygons coincide with large tectonic lineaments that characterize the Tyrrhenian–Apennine area. The tectonic style along these structures reflects the variability of relative velocity vectors between two adjacent blocks. The deformation of tectonic elements is accomplished, allowing different rotation velocities of lines that compose these blocks about the same stable stage poles. The angular velocities of extension are determined on the basis of the stratigraphic records of syn-rift sequences, while the rotation angles are obtained by crustal balancing.

Decentralized Tension Control With Active-Damping Injection for Large-Scale Roll-to-Roll Systems

This article presents a decentralized tension controller for large-scale roll-to-roll machines under the consideration of inherent nonlinearity and parameter variations. First, active-damping injection with specific proportional-integral gain is adopted to render the first-order dynamics for the closed-loop system via stable pole– zero cancelation. Second, the nonlinear disturbance observers for each loop intensify the high-frequency disturbance attenuation capability with a combination of regulation error integral actions. Moreover, the closed-loop analysis results include the proof of performance recovery from the first and second features. Various simulation results validate the effectiveness of the proposed technique from a combination of active-damping and DOBs using MATLAB/Simulink.

Controller Design for Switched Systems with Non-symmetrical Input Saturation

In this paper, a state feedback controller is designed for switched systems with non-symmetrical input saturation based on two classes of parametric Riccati equation (PRE). Through appropriate mathematical transformation, we transform a switched system with non-symmetrical input saturation to a switched system with multiple equilibrium points and symmetrical input saturation. The exponential stability of the switched system is investigated using the good properties of PRE. The main contributions of this paper include (a) solving the non-symmetrical input saturation control problem for the switched system; (b) designing a controller to guarantee the exponential stability of the switched system with the subsystems having the open-loop critical stable poles; (c) the designed controller can be easily computed by solving the PRE. The controller is easy to implement in practical applications. A numerical example is provided to illustrate the effectiveness and potential of the proposed method.

Optimal communications with infinite impulse response matched filters

Abstract Optimal communication waveforms matched to a large and practically important class of filters are investigated and shown to be chaotic. Filters of this class are defined by an infinite impulse response (IIR) and a transfer function comprising a finite number of distinct stable poles. This class contains many of the most popular and widely used filter families, including Butterworth, Chebyshev (type I), and Bessel. For such a filter, a matched basis function is derived and convolved with a random binary sequence to construct a communication waveform. It is shown that this waveform is chaotic in the sense that it is deterministic and characterized by a positive Lyapunov exponent. This result supports a recent conjecture that optimal communication waveforms matched to stable IIR filters are chaotic, and it further establishes that chaos is fundamental to modern communication theory.

Integrated Approach to Design and Implementation of a Single-Phase Current Regulator With Antiwindup Mechanism

An ac-regulated single-phase inverter operating in the stationary frame is designed to accurately track a sinusoidal reference signal at a designated frequency. To achieve such a control objective, resonant controllers with a conjugate set of marginally stable poles are required. The explicit implementation of marginally stable dynamics is prone to wind up in the event of the control signal entering a nonlinear saturation condition, resulting in a degraded or even an unstable dynamic response. This article proposes an integrated approach to the design and implementation of a resonant controller for a single-phase current regulator with an intrinsic antiwindup mechanism. The proposed method utilizes a disturbance observer to embed a pair of complex poles into the controller, leading to accurate tracking of a sinusoidal reference signal. Simultaneously, by using the observer architecture with a set of desired closed-loop poles as the performance specification, the implementation form remains completely stable. Furthermore, the closed-loop performance of the proposed resonant control system is analyzed to assess the impact of unmodeled dynamics. Experimental results are presented to demonstrate the efficacy of the proposed approach.

Automated Modal Analysis for Tracking Structural Change during Construction and Operation Phases.

The automated modal analysis (AMA) technique has attracted significant interest over the last few years, because it can track variations in modal parameters and has the potential to detect structural changes. In this paper, an improved density-based spatial clustering of applications with noise (DBSCAN) is introduced to clean the abnormal poles in a stabilization diagram. Moreover, the optimal system model order is also discussed to obtain more stable poles. A numerical simulation and a full-scale experiment of an arch bridge are carried out to validate the effectiveness of the proposed algorithm. Subsequently, the continuous dynamic monitoring system of the bridge and the proposed algorithm are implemented to track the structural changes during the construction phase. Finally, the artificial neural network (ANN) is used to remove the temperature effect on modal frequencies so that a health index can be constructed under operational conditions.

Practical controllability and systematic tuning in a control system of bioethanol purification

For a system of bioethanol purification based on extractive distillation, this work addresses the problem of determining the better control configuration and the systematic tuning of the PI controllers in a framework of physical insight. The purification system is a distillation column train consisting of a preconcentration column, a dehydration column and a entrainer recovery column. To establish the control loops, a parameter called Operability Index (OI) was proposed and applied. All possible control loops were evaluated, and unlike typical works, also impurities in the product streams were considered as control outputs. The outcomes suggested that less control effort is achieved by controlling impurities than controlling purities; this means, the OI for impurities were lower than the ones for purities, and the control configuration was easily established by choosing loops of small OI. In the next step of tuning the linear PI controller for each loop, an approach of stable pole assignment was followed. Through this technique, all controllers were tuned simultaneously, and the values of the controller gains were calculated directly from the static gains and a pseudo time constant identified for every loop; this pseudo time constant corresponds to the best first order dynamics matched to the dynamics of the control output with respect to unit change of the control input. Through simulations in Aspen Plus Dynamics®, the performance of controlling impurities was illustrated and compared with the one of controlling purities, and the simultaneous tuning of controllers was demonstrated.

Structured observer-based controller for delayed systems with two unstable poles and minimum phase zeros.

This paper analyses the problem of control and stabilization of a particular class of Linear Time Invariant (LTI) systems. The system under consideration has two unstable poles, n real stable poles, m minimum phase zeros plus time delay. An observer based controller with four tunable gains is proposed as a control strategy in order to ensure a stable behaviour of the closed-loop system. Sufficient conditions for the existence of the proposed scheme are obtained in terms of the upper limit of time delay size and the poles and zeros position. The controller parameters are tuned using a non-smooth H∞ optimization method. The proposed control strategy is applied to an unstable linearized model of a continuously stirred tank reactor (CSTR) in order to show the effectiveness of the proposed design scheme. Numerical results are presented.

The degenerate Eisenstein series attached to the Heisenberg parabolic subgroups of quasi-split forms of 𝑆𝑝𝑖𝑛₈

In [J. Inst. Math. Jussieu 14 (2015), 149–184] and [Int. Math. Res. Not. IMRN 7 (2017), 2014–2099] a family of Rankin-Selberg integrals was shown to represent the twisted standard L \mathcal {L} -function L ( s , π , χ , s t ) \mathcal {L}(s,\pi ,\chi ,\mathfrak {st}) of a cuspidal representation π \pi of the exceptional group of type G 2 G_2 . These integral representations bind the analytic behavior of this L \mathcal {L} -function with that of a family of degenerate Eisenstein series for quasi-split forms of S p i n 8 Spin_8 associated to an induction from a character on the Heisenberg parabolic subgroup. This paper is divided into two parts. In Part 1 we study the poles of these degenerate Eisenstein series in the right half-plane R e ( s ) &gt; 0 \mathfrak {Re}(s)&gt;0 . In Part 2 we use the results of Part 1 to prove the conjecture, made by J. Hundley and D. Ginzburg in [Israel J. Math. 207 (2015), 835–879], for stable poles and also to give a criterion for π \pi to be a CAP representation with respect to the Borel subgroup of G 2 G_2 in terms of the analytic behavior of L ( s , π , χ , s t ) \mathcal {L}(s,\pi ,\chi ,\mathfrak {st}) at s = 3 2 s=\frac {3}{2} .