Uncertain Frequency Research Articles

Numerical analysis of uncertain frequency of rotating composites using NURBS-based isogeometric HSDT approach: Rim-driven configuration

This study delves into the impact of material and fabrication uncertainties on the natural frequencies of rim-driven rotating structures. Utilizing a higher-order shear deformation theory (HSDT), an isogeometric analysis (IGA) model predicts these frequencies. Sensitivity analysis via a radial basis function network (RBFN) model, validated with Monte Carlo simulation, highlights parameter influence. Parametric investigations unveil sensitivity patterns and influential parameters. Employing a stochastic approach, the study compares the effects of random material properties on the free vibration response of rotating and non-rotating plates. Additionally, the RBFN-based surrogate model assesses reliability parameters concerning resonance failure in rim-driven rotating composite structures.

Sufficient active control of uncertain low-frequency space micro-vibrations near measurement limit of acceleration sensors

High-precision payloads such as ultra-stable optical clocks for next-generation space missions are greatly sensitive to the low-frequency micro-vibrations induced by various flexible appendages equipped on the spacecraft. The frequencies of such micro-vibrations are uncertain and near the measurement limit of acceleration sensors, leading to insufficient vibration control performance of classical feedback control. To solve this problem, a hybrid control algorithm which combines PI controller and the filter-x least-mean-square (FxLMS) algorithm is proposed in the paper. In particular, a frequency estimation algorithm is designed for the active vibration control system to provide the reference signal. In the new system, the rough estimation of disturbance frequency is given by the adaptive notch filter. Then, the frequency is refined by Kalman filter and provided into the autoregressive model, which fine-tunes the estimated frequency and offers the reference signal for the hybrid PI-FxLMS algorithm. Finally, the experimental prototype of active vibration control system is developed and the proposed control algorithm is adopted. The experimental results demonstrate the effectiveness of the frequency estimation algorithm and further validate that the proposed hybrid PI-FxLMS algorithm can effectively suppress the low-frequency micro-vibrations near the measurement limit of acceleration sensors and with uncertain frequency.

The Impact of Projected Changes in Hurricane Frequencies on U.S. Hurricane Wind and Surge Damage

Abstract We use a simple risk model for U.S. hurricane wind and surge economic damage to investigate the impact of projected changes in the frequencies of hurricanes of different intensities due to climate change. For average annual damage, we find that changes in the frequency of category-4 storms dominate. For distributions of annual damage, we find that changes in the frequency of category-4 storms again dominate for all except the shortest return periods. Sensitivity tests show that accounting for landfall, uncertainties, and correlations leads to increases in damage estimates. When we propagate the distributions of uncertain frequency changes to give a best estimate of the changes in damage, the changes are moderate. When we pick individual scenarios from within the distributions of frequency changes, we find a significant probability of much larger changes in damage. The inputs on which our study depends are highly uncertain, and our methods are approximate, leading to high levels of uncertainty in our results. Also, the damage changes we consider are only part of the total possible change in hurricane damage due to climate change. Total damage change estimates would also need to include changes due to other factors, including possible changes in genesis, tracks, size, forward speed, sea level, rainfall, and exposure. Nevertheless, we believe that our results give important new insights into U.S. hurricane risk under climate change. Significance Statement We investigate how changes in the frequencies of hurricanes of different intensities as a result of climate change may contribute to changes in U.S. economic damage due to wind and surge. We find that economic damage will likely increase as a result of projected increases in the frequency of landfalling hurricanes. Analysis of our results shows that increases in the frequency of category-4 storms are the main driver of the changes. Our best estimate results, based on a multimodel ensemble, give modest increases in damage, but within the ensemble there are individual scenarios that give much larger increases in damage. The large range of individual damage estimates is a motivation for continuing efforts to reduce the uncertainty around hurricane projections under climate change.

A two-stage Polynomial Chaos Expansion application for bound estimation of uncertain FRFs

Polynomial Chaos Expansion (PCE) is a method for analysing uncertain vibratory structures with lower computational effort. It may simply be described as a curve fitting method with orthogonal basis terms, where the polynomial type, dimension and order are predefined for the uncertain responses. However, the polynomial order in PCE must be very high to accurately estimate statistical moments of the frequency response function in resonance regions of lightly damped and uncertain structures. To solve this issue different transformation techniques are reported in the literature, where implementations of PCE produce higher accuracy with a lower order polynomial. However, these transformations lose the attraction for using PCE, since they require some additional mathematical operations and, mostly, they present high accuracy if the higher orders of polynomials are again of interest. In this study, an efficient approach is presented for the upper bound estimation of the uncertain frequency response functions (FRFs) via PCE with lower order terms without performing any transformation. Rather than one-stage application of PCE for the desired response of an uncertain problem, the approach comprises a two-stage application of the classical PCE, i.e. first for the natural frequencies and then for the FRF calculations. As an example application of the approach, a thin beam for two different uncertainty cases is considered, namely local and global uncertainty. The local and global input uncertainties are generated by variability of lumped masses added at the boundary and Young's modulus, respectively. The FRF bounds are compared with extensive experimental and numerical Monte Carlo simulations, showing that low order polynomials are sufficient to calculate the bounds accurately with the technique described.

Robust Adaptive Resonant Controller for PMSM Speed Regulation Considering Uncertain Periodic and Aperiodic Disturbances

This paper studies a robust adaptive resonant controller (RARC) for the speed loop of permanent magnet synchronous motor (PMSM) drives to attenuate periodic speed fluctuation of uncertain frequency. The conventional adaptive resonant controller is susceptible to the aperiodic disturbances (e.g., load torque, parameter variation, and friction torque), so it has poor robustness to the aperiodic disturbance. To solve this problem, a linear extended state observer is applied to estimate the aperiodic disturbances, and then the estimated disturbances are adapted to the adaptive resonant controller to enhance its robustness. Thus, the proposed scheme can suppress the uncertain periodic and aperiodic disturbances simultaneously. Also, the stability of the closed-loop system with the proposed scheme is analyzed by the singular perturbation theory and the averaging theorem, which can guide the tuning of control parameters. Therefore, even if there exist aperiodic disturbances, the studied RARC can also stably operate to suppress the periodic disturbance of uncertain frequency. The effectiveness of the studied RARC is validated on a 2.2-kW PMSM drive platform.

Uncertain frequency responses of CNT – reinforced polymeric graded structure using fuzzified elastic properties – fuzzy finite element approach

A novel fuzzy finite element computational model is prepared to predict the frequency responses of the functionally graded carbon nanotube (FG-CNT) reinforced composite panel structure. The nanotube distributions in the matrix have an affinity towards the agglomeration and affect final properties. The model incurred the fuzzification of elastic properties (E 11, E 22, G 12, and υ 12) considering a ±20% as the degree of uncertainty via Mamdani’s fuzzy inference system (FIS). The extended rule of the mixture has been adopted to count the CNT properties for different grading patterns to achieve the realistic one in the framework of the higher-order polynomial model. Further, a set of fuzzy rules have been adopted to count the uncertainty in elastic properties with the help of the design of the experiment (Taguchi-L25 orthogonal array). The equation of motion is derived for the CNT-reinforced composite in association with Hamilton’s principle for the computation of natural frequency. An in-house computer code is derived in MATLAB with the help of a higher-order fuzzified finite element model (FFEM) for the computation. The suitability of the proposed model has been tested by solving a series of numerical examples and the output is discussed in detail.

Discrete-Time Design of Dual Internal Model-Based Repetitive Control Systems

This paper presents a novel design of discrete-time dual internal model-based repetitive control systems. The design strategy is accomplished by combining general and high-order modified repetitive control schemes for simultaneous tracking repetitive tasks and rejection of uncertain periodic disturbances. The proposed controller is constructed from two different discrete-time internal models, rendering a dual internal model-based repetitive controller (DIMRC). The first internal model is intended to track repetitive commands with a fixed fundamental frequency. Meanwhile, the second internal model is coupled to compensate for an exogenous periodic disturbance with an uncertain frequency. The controller structure, stability conditions, and convergence analysis are discussed in this paper. The performance of the proposed controller is validated through simulation studies showing accurate tracking and excellent disturbance rejection simultaneously.

Apixaban and Valve Thrombosis After Transcatheter Aortic Valve Replacement: The ATLANTIS-4D-CT Randomized Clinical Trial Substudy.

Subclinical obstructive valve thrombosis after transcatheter aortic valve replacement (TAVR) is of uncertain frequency and clinical impact. The aim of this study was to determine the effects of apixaban vs standard of care on post-TAVR valve thrombosis detected by 4-dimensional (4D) computed tomography. The randomized ATLANTIS (Anti-Thrombotic Strategy to Lower All Cardiovascular and Neurologic Ischemic and Hemorrhagic Events After Trans-Aortic Valve Implantation for Aortic Stenosis) trial demonstrated that apixaban 5mg twice daily was not superior to standard of care (vitamin K antagonists or antiplatelet therapy) after successful TAVR and was associated with similar safety but with more noncardiovascular deaths. Three months after randomization, 4D computed tomography was proposed to all patients to determine the percentage of patients with≥1 prosthetic valve leaflet with grade 3 or 4 reduced leaflet motion or grade 3 or 4 hypoattenuated leaflet thickening (the primary endpoint) in the intention-to-treat population. Seven hundred sixty-two participants had complete multiphase datasets and were included in the 4D computed tomographic analysis. The primary endpoint occurred in 33 (8.9%) and 51 (13.0%) patients in the apixaban and standard-of-care groups, respectively. It was reduced with apixaban vs antiplatelet therapy (OR: 0.51; 95%CI: 0.30-0.86) but not vs vitamin K antagonists (OR: 1.80; 95%CI: 0.62-5.25) (Pinteraction=0.037). The composite of death, myocardial infarction, any stroke, or systemic embolism at 1 year occurred in 10.7% (n=9 of 84) and 7.1% (n=48 of 178) of patients with and without subclinical valve thrombosis at 90days, respectively (HR: 1.68; 95%CI: 0.82-3.44). Apixaban reduced subclinical obstructive valve thrombosis in the majority of patients who underwent TAVR without having an established indication for anticoagulation. This study was not powered for clinical outcomes. (Anti-Thrombotic Strategy After Trans-Aortic Valve Implantation for Aortic Stenosis [ATLANTIS]; NCT02664649).

Stochastic model predictive controller for wind farm frequency regulation in waked conditions

As renewable energy penetrations increase, wind farms may be required to provide ancillary services such as frequency regulation. For wind farms, two issues complicate frequency regulation: turbine-wake interactions alter the available wind power, and the future power reference signal is uncertain. This paper presents a stochastic model predictive controller (MPC) for wind farms to track an uncertain frequency regulation signal while accounting for wakes. The controller uses a simplified Park model with wake propagation delay to predict turbine-wake interactions. The controller operates without any knowledge of the future power regulation signal or wind speed. The controller solves a nonconvex stochastic optimization program using scenario optimization. Our stochastic MPC tracks with 7%–10% less error than our deterministic MPC controllers.

Uncertain frequency response analysis of clamp-pipe systems via the coordinate transformed polynomial chaos expansion

The frequency response function (FRF) that links structural responses and external excitations is required to realize the dynamic analysis of a clamp-pipe system. Due to random geometry and stiffness parameters, the FRF becomes a stochastic quantity that is represented by a surrogate model based on the polynomial chaos expansion (PCE) in this paper. Considering that an FRF trajectory is mainly controlled by resonance and anti-resonance frequencies, a reference frequency coordinate characterized by the controlling frequencies associated with a nominal value of input random variables is first determined. By reserving the original amplitude, an FRF sample is projected to the reference coordinate through a linear transform. Then, a PCE surrogate model with coefficients estimated by the Gauss-quadrature scheme is obtained, and the utility of an inverse transform allows one to obtain the predicted FRF result in the original domain. Together with estimations on the confidence intervals and extreme boundary results, engineering applications are demonstrated by the uncertain FRF analysis of straight and L-shape clamp-pipe systems.

Dynamic analysis of an L-shaped liquid-filled pipe with interval uncertainty

In this paper, a fourteen-equation fluid-structure coupling model of an L-shaped liquid-filled pipe with elastic support is established by the transfer matrix method (TMM). The validity of the dynamic model of the liquid-filled pipe is verified by comparing the frequency results obtained from the literature, experiment, and finite element method. The liquid-filled pipe system is inevitably subject to uncertainties due to the manufacture and assembly error, material dispersion, and the change of working conditions. To obtain more reasonable evaluations of the dynamic response of the L-shaped liquid-filled pipe, an uncertain frequency response surrogate function (UFRSF) is proposed to evaluate the uncertainty of the liquid-filled pipe. The pipe parameters, support parameters, and fluid parameters are taken as unknown but bounded interval variables. The frequency responses of the L-shaped liquid-filled pipe under various uncertain variables are calculated. Compared with the Monte Carlo simulation (MCS) results, the efficiency and accuracy of the proposed method for solving the uncertain frequency response of liquid-filled pipe are proved. The proposed method has the advantages of convenience in implementation, high efficiency and transparency, and can provide theoretical guidance for the uncertainty assessment of liquid-filled pipes with unknown sample probability distribution in engineering.

An interval framework for uncertain frequency response of multi-cracked beams with application to vibration reduction via tuned mass dampers

The paper addresses the frequency response of beams in presence of open cracks with interval parameters. On adopting the standard Euler–Bernoulli beam theory, every crack is modelled as a linearly-elastic rotational spring whose stiffness and position are treated as uncertain-but-bounded parameters. A two-step method is proposed to calculate the bounds of all response variables. First, the sensitivity functions of the response are calculated as every uncertain parameter varies within the respective interval. Next, the bounds of the response are computed by either a sensitivity-based method or a global optimization technique, the former if the response is monotonic with respect to all uncertain parameters and the latter if the response is non-monotonic with respect to even one parameter only. The method relies on analytical forms for all response variables and the associated sensitivity functions. The applications focus on the frequency response of multi-cracked beams equipped with tuned mass dampers, showing potential and accuracy of the method.

Use of antimicrobial mouthwashes (gargling) and nasal sprays by healthcare workers to protect them when treating patients with suspected or confirmed COVID-19 infection.

COVID-19 infection poses a serious risk to patients and -due to its contagious nature -to those healthcare workers (HCWs) treating them. If the mouth and nose of HCWs are irrigated with antimicrobial solutions, this may help reduce the risk of active infection being passed from infected patients to HCWs through droplet transmission or direct contact. However,the use of such antimicrobial solutions may be associated with harms related to the toxicity of the solutions themselves, or alterations in the natural microbial flora of the mouth or nose. Understanding these possible side effects is particularly important when the HCWs are otherwise fit and well. To assess the benefits and harms of antimicrobial mouthwashes and nasal sprays used by healthcare workers (HCWs) to protect themselves when treating patients with suspected or confirmed COVID-19 infection. Information Specialists from Cochrane ENT and Cochrane Oral Health searchedthe Central Register of Controlled Trials (CENTRAL 2020, Issue 6); Ovid MEDLINE; Ovid Embaseand additional sources for published and unpublished trials. The date of the search was 1 June 2020. SELECTION CRITERIA: This is a question that urgently requires evidence, however at the present time we did not anticipate finding many completed randomised controlled trials (RCTs). We therefore planned to include the following types of studies:RCTs;quasi-RCTs;non-randomised controlled trials;prospective cohort studies;retrospective cohort studies;cross-sectional studies;controlled before-and-after studies. We set no minimum duration for the studies. We sought studies comparing any antimicrobial mouthwash and/or nasal spray (alone or in combination) at any concentration,delivered to HCWs, with or without the same intervention being given to the patients with COVID-19. We used standard Cochrane methodological procedures. Our primary outcomes were: 1) incidence of symptomatic or test-positive COVID-19 infection in HCWs; 2) significant adverse event: anosmia (or disturbance in sense of smell).Our secondary outcomes were: 3)viral content of aerosol, when present (if intervention administered to patients); 4) other adverse events: changes in microbiome in oral cavity, nasal cavity, oro- or nasopharynx; 5) other adverse events: allergy, irritation/burning of nasal, oral or oropharyngeal mucosa (e.g. erosions, ulcers, bleeding), long-term staining of mucous membranes or teeth, accidental ingestion.We planned to use GRADE to assess the certainty of the evidence for each outcome. We found nocompleted studies to include in this review. We identified three ongoing studies (including two RCTs), which aim to enrol nearly 700participants. The interventionsincluded in these trials arepovidone iodine, nitric oxideand GLS-1200 oral spray (the constituent of this spray is unclear and may not be antimicrobial in nature). AUTHORS' CONCLUSIONS: We identified no studies for inclusion in this review. This is not surprising given the relatively recent emergence of COVID-19 infection. It is promising that the question posed in this review is being addressed by two RCTs and a non-randomised study. Weare concerned that only one of the ongoing studies specifically states that it will evaluate adverse events and it is not clear if this will include changes in the sense of smell or to the oral and nasalmicrobiota, and any consequences thereof. Very few interventions have large and dramatic effect sizes. If a positive treatment effect is demonstrated when studies are available for inclusion in this review,it may not be large. Inthese circumstances in particular, where those receiving theintervention are otherwise fit and well,it may be a challengeto weighup the benefits against the harms if the latter are of uncertain frequency and severity.

Antimicrobial mouthwashes (gargling) and nasal sprays administered to patients with suspected or confirmed COVID-19 infection to improve patient outcomes and to protect healthcare workers treating them.

COVID-19 infection poses a serious risk to patients and -due to its contagious nature -to those healthcare workers (HCWs) treating them. If the mouth and nose of patients with infection are irrigated with antimicrobial solutions, this may help the patients by killing anycoronavirus present at those sites. It may also reduce the risk of the active infection being passed to HCWs through droplet transmission or direct contact. However,the use of such antimicrobial solutions may be associated with harms related to the toxicity of the solutions themselves or alterations in the natural microbial flora of the mouth or nose. To assess the benefits and harms of antimicrobial mouthwashes and nasal sprays administered to patients with suspected or confirmed COVID-19 infectionto both the patients and the HCWs caring for them. Information Specialists from Cochrane ENT and Cochrane Oral Health searchedthe Central Register of Controlled Trials (CENTRAL 2020, Issue 6); Ovid MEDLINE; Ovid Embaseand additional sources for published and unpublished trials. The date of the search was 1 June 2020. SELECTION CRITERIA: This is a question that urgently requires evidence, however at the present time we did not anticipate finding many completed RCTs. We therefore planned to include the following types of studies:randomised controlled trials (RCTs);quasi-RCTs;non-randomised controlled trials;prospective cohort studies;retrospective cohort studies;cross-sectional studies;controlled before-and-after studies. We set no minimum duration for the studies. We sought studies comparing antimicrobial mouthwash and/or nasal spray (alone or in combination) at any concentration, delivered with any frequency or dosage to suspected/confirmed COVID-19 patients. We used standard Cochrane methodological procedures. Our primary outcomes were: 1)RECOVERY* (www.recoverytrial.net)outcomes in patients (mortality;hospitalisation status;use of ventilation;use of renal dialysis or haemofiltration); 2)incidence of symptomatic or test-positive COVID-19 infection in HCWs; 3)significant adverse event: anosmia (or disturbance in sense of smell). Our secondary outcomes were: 4)change in COVID-19 viral load in patients; 5)COVID-19 viral content of aerosol (when present); 6)other adverse events: changes in microbiome in oral cavity, nasal cavity, oro- or nasopharynx; 7)other adverse events: allergy, irritation/burning of nasal, oral or oropharyngeal mucosa (e.g. erosions, ulcers, bleeding), long-term staining of mucous membranes or teeth, accidental ingestion. We planned to use GRADE to assess the certainty of the evidence for each outcome. We found nocompleted studies to include in this review. We identified 16 ongoing studies (including 14 RCTs), which aim to enrolnearly 1250participants.The interventionsincluded in these trials areArtemiC (artemisinin, curcumin, frankincense and vitamin C),Citrox(a bioflavonoid),cetylpyridiniumchloride,chlorhexidine,chlorine dioxide,essential oils,hydrogen peroxide,hypertonic saline,Kerecis spray (omega 3 viruxide-containingneem oil and St John's wort),neem extract,nitricoxide releasing solution,povidone iodine andsaline with baby shampoo. AUTHORS' CONCLUSIONS: We identified no studies for inclusion in this review. This is not surprising given the relatively recent emergence of COVID-19 infection. It is promising that the question posed in this review is being addressed by a number of RCTs and other studies. Weare concerned that few of the ongoing studies specifically state that they will evaluate adverse events such aschanges in the sense of smell or to the oral and nasalmicrobiota, and any consequences thereof. Very few interventions have large and dramatic effect sizes. If a positive treatment effect is demonstrated when studies are available for inclusion in this review,it may not be large.Inthese circumstances in particularit may be a challengeto weighup the benefits against the harms if the latter are of uncertain frequency and severity.

Fact versus Fiction: a Review of the Evidence behind Alcohol and Antibiotic Interactions.

Many antibiotics carry caution stickers that warn against alcohol consumption. Data regarding concurrent use are sparse. An awareness of data that address this common clinical scenario is important so health care professionals can make informed clinical decisions and address questions in an evidence-based manner. The purpose of this systematic review was to determine the evidence behind alcohol warnings issued for many common antimicrobials. The search was conducted from inception of each database to 2018 using PubMed, Medline via Ovid, and Embase. It included studies that involved interactions, effects on efficacy, and toxicity/adverse drug reactions (ADR) due to concomitant alcohol consumption and antimicrobials. All interactions were considered in terms of three components: (i) alteration in pharmacokinetics/pharmacodynamics (PK/PD) of antimicrobials and/or alcohol, (ii) change in antimicrobial efficacy, and (iii) development of toxicity/ADR. Available data support that oral penicillins, cefdinir, cefpodoxime, fluoroquinolones, azithromycin, tetracycline, nitrofurantoin, secnidazole, tinidazole, and fluconazole can be safely used with concomitant alcohol consumption. Data are equivocal for trimethoprim-sulfamethoxazole. Erythromycin may have reduced efficacy with alcohol consumption, and doxycycline may have reduced efficacy in chronic alcoholism. Alcohol low in tyramine may be consumed with oxazolidinones. The disulfiram-like reaction, though classically associated with metronidazole, occurs with uncertain frequency and with varied severity. Cephalosporins with a methylthiotetrazole (MTT) side chain or a methylthiodioxotriazine (MTDT) ring, ketoconazole, and griseofulvin have an increased risk of a disulfiram-like reaction. Alcohol and antimicrobial interactions are often lacking evidence. This review questions common beliefs due to poor, often conflicting data and identifies important knowledge gaps.

Uncertain Frequency Responses of Clamp-Pipeline Systems Using an Interval-Based Method

Due to manufacturing errors and material deteriorations in the metal rubber of clamps, the clamp stiffness of the pipeline is uncertain. This paper presents a non-intrusive multi-dimensional Chebyshev polynomial approximation method (M-CPAM) to evaluate uncertain characteristics of the frequency response function (FRF) of the clamp-pipeline system (CPS), where the clamp stiffness parameters are taken as unknown but bounded interval variables. Firstly, a finite element model of the clamp-pipeline system is established. Secondly, the variance-based global sensitivity analysis is implemented to determine significant stiffness parameters. Then, the uncertain intervals of the clamp stiffness are measured by experiments and the dispersion of the clamp stiffness is described. Finally, based on the measured stiffness interval, the uncertain frequency responses of the CPS under different tightening torques are analyzed by the proposed M-CPAM, and the effectiveness of simulation results is verified by experiments. Compared with the results obtained from the Monte Carlo simulation, the experimental measurements, and the polynomial chaos expansion, the proposed M-CPAM provides a more accurate, time-saving and practical method for solving the uncertain frequency responses of the CPS with interval stiffness variables. The results show that the clamp stiffness has great dispersion under the same tightening torque. A frequency shift phenomenon will be observed when the clamp stiffness is uncertain. Moreover, the dispersion of the frequency response of the CPS tends to be concentrated with the increase of the tightening torques.

MIMO adaptive control for suppression the vibrations of a nonlinear interconnected structure with abrupt changes in the excitation loads

The presented paper, for the first time, deals with the simultaneous suppression of elastically coupled interconnected Timoshenko beams at different nodes by employing a simple virtual absorber (control algorithm). The main system is discretized into interconnected Timoshenko beams using finite element method with unknown parameters. The system is excited externally by applying harmonic disturbances with unknown amplitudes and uncertain time-varying frequency. The aim of the article is to utilize a virtual absorber with adjustable stiffness which is capable of suppressing the vibration of the elastically coupled model at multiple nodes and also identifying the uncertain frequency of the excitations. In addition, the uncertain parameters and their effects on the behavior of the nonlinear formulations of the MIMO system are, practically, included through the dynamic of the model and the adaptable algorithm (embedded in the virtual controller) is employed to annihilate the nonlinear vibration of such complex system only based on its output. The results demonstrate that the proposed adaptive algorithm is able to simultaneously cease the vertical and rotational oscillations of a nonlinear multi-beam system at a wide range of frequencies.

Chance-Constrained Frequency Regulation with Energy Storage Systems in Distribution Networks

One of the applications of energy storage systems (ESSs) is to support frequency regulation in power systems. In this paper, we consider such an application and address the challenges of uncertain frequency changes, limited energy storage, as well as distribution network constraints. We formulate a bi-level optimization problem that includes the operation objectives of the system operator and the ESSs, using chance constraints to account for uncertain frequency changes. The frequency regulation decision of the system operator depends on the ESSs decision to participate in the regulation service as well as the distribution network constraints. Due to the interdependencies between the ESSs demand fluctuations and the distribution network power flow changes, the system operator requires the ESSs’ operation information for frequency regulation decisions, which may not be available from the ESSs. Therefore, we propose a decentralized algorithm such that the system operator and the ESSs can pursue their own operation objectives, while ensuring the distribution network constraints are satisfied. We evaluate the performance of our method on IEEE 37-bus and 123-bus test feeders by considering combinations of ESSs with different sizes. Simulation results demonstrate that our approach can successfully coordinate the ESSs to regulate the frequency deviations.

Efficiently extracting frequent patterns from continuous uncertain data

ABSTRACTUncertain frequent pattern mining has been much discussed in recent decades. It is widely used in various fields and helps analysts to comprehend the deep meaning of collected data from the frequencies of items. In past studies, researchers have focused on discrete models. However, a discrete model only explains the presence of combinations of items without giving specific data intervals. To compensate for the drawbacks of discrete models, we focus on continuous uncertain data and improve a continuous uncertain frequent tree for the extraction of frequent patterns, notably time costs. Attribute overlapping usually causes the high time cost in the extraction phase. To avoid long branches in the tree, two approaches are proposed. The first approach is to name each attribute at given level with an uncertain frequent pattern. By using links and reshaping the uncertain frequency tree, the number of combinations decreases. The second approach is called uncertain frequent pattern map transforming. It uses a discrete transformation to decrease the time cost. In experiments, our two approaches were compared with different mainstream approaches. According to the results, our approaches not only cost less time to explore frequent patterns but also exhibited high accuracy for continuous uncertain data.

Duty ratio modulation direct torque control of brushless doubly-fed machines

ABSTRACTFor the brushless doubly-fed machine (BDFM), traditional direct torque control (DTC) has many problems such as big output torque ripple and uncertain inverter switch frequency. Based on the analysis of traditional DTC, this paper proposed a new torque control which applied duty ratio modulation into direct torque control. This new control method can decrease the torque ripple effectively by adding zero voltage in each control cycle. According to the brushless BDFM state equation and the prediction of torque, flux linkage in the next moment and the theory of electromagnetic torque equals to referenced value at the instant moment in one control cycle, torque ripple can be decreased. Through theoretical analysis and experiments, the proposed control method has all advantages of traditional direct torque control and can decrease torque ripple and flux linkage ripple, which can optimize the performance of direct torque control.