Frequency Response Analysis Research Articles

Frequency response analysis of edge-cracked magneto-electro-elastic functionally graded plates using extended finite element method

This paper studies the frequency response of edge-cracked magneto-electro elastic functionally graded (ECMEE-FG) plates using the extended finite element method (XFEM). First-order shear deformation theory (FSDT), von Karman's nonlinear strain-displacement equations, and a modified power-laware used to develop the numerical model. The coupled equations are derived and analyzed using Hamilton's principle and extended finite element methods. The influence of B-rich bottom and F-rich bottom material gradation, crack orientation, crack length, and aspect ratio on the geometrically nonlinear frequency response was investigated after the current study was validated. Furthermore, crack propagation behavior in the ECMEE-FG plate was examined. The results could be helpful for the design of functionally graded magneto electro elastic structures and devices.

Fast, Accurate and Full Extraction of Coupling-of-Modes Parameters by Finite Element Method

This paper presents a new numerical approach for the full extraction of the coupling-of-modes (COM) parameters by stationary and eigenfrequency analyses in the finite element method (FEM). This is a fast method extracting from the results of static analysis and eigenfrequency analysis. It avoids the long calculation time of admittance frequency response analysis, which is commonly used in extracting COM parameters. In addition to the usual COM parameters (velocity, reflection coefficient, transduction coefficient and capacitance), the phases of reflection and transduction coefficient can be also extracted with this method. The proposed method was applied to different cutting types LiNbO3 with different types of thicknesses in a varying interdigital transducer (IDT). These examples show that our approach has great potential in extracting all the COM parameters of the Rayleigh SAW for all kinds of IDT structures. Therefore, it is a fast, accurate, general and full extraction approach of COM parameters.

IOT Based Evaluation of Internal Fault Detection In Transformer Using V-I Characteristics

The common problem in operating the power transformer is the winding deformation due to the internal and external conditions. It should be controlled and rectified soon as it emerge, as it is progressive in nature. Unfavorably,theonlytechniquetodetect and identifysuchfaultsatthis stage is the frequency response analysis technique which is conducted offline. In this paper, we are proposing an idea to detect power transformer incipient winding deformations in real time by measuring voltage and current level in transformer in online mode. In this method, we are monitoring the live status of transformer using cost efficient and easily available sensors.

Honeywell develops new technology for production of green hydrogen

Composites of high density polyethylene, HDPE, filled with submicrometric particles of BaTiO3, BT, have been prepared. Uniform dispersion of the particles was achieved by high energy ball milling and subsequent hot pressing. Using SEM, FTIR, TGA-DTA and stress-strain tests, studies of the structural, morphological and mechanical features of the composites have been carried out. Frequency response analysis, dielectric strength and resistivity measurements were also performed to evaluate the final electrical properties as a function of the processing and the amount of BaTiO3 particles. From the analysis of the microscopic structure, it can be deduced that any change in the properties of the materials must be solely ascribed to the presence of the BT particles. A balance between an enhancement of space charge polarization with the presence of BT and the existence of permanent dipoles associated to them might explain an initial increase in the dielectric losses with the BT content, and its later decrease at higher BT content. The observed decrease in resistivity and breakdown voltage when increasing the amount of BaTiO3 can be explained by the lower resistivity of BT particles at room temperature and the growing accumulation of space charge.

Run-Time Cutting Force Estimation Based on Learned Nonlinear Frequency Response Function

Abstract The frequency response function (FRF) provides an input–output model that describes the system dynamics. Learning the FRF of a mechanical system can facilitate system identification, adaptive control, and condition-based health monitoring. Traditionally, FRFs can be measured by off-line experimental testing, such as impulse response measurements via impact hammer testing. In this paper, we investigate learning FRFs from operational data with a nonlinear regression approach. A regression model with a learned nonlinear basis is proposed for FRF learning for run-time systems under dynamic steady state. Compared with a classic FRF, the data-driven model accounts for both transient and steady-state responses. With a nonlinear function basis, the FRF model naturally handles nonlinear frequency response analysis. The proposed method is tested and validated for dynamic cutting force estimation of machining spindles under various operating conditions. As shown in the results, instead of being a constant linear ratio, the learned FRF can represent different mapping relationships under different spindle speeds and force levels, which accounts for the nonlinear behavior of the systems. It is shown that the proposed method can predict dynamic cutting forces with high accuracy using measured vibration signals. We also demonstrate that the learned data-driven FRF can be easily applied with the few-shot learning scheme to machine tool spindles with different frequency responses when limited training samples are available.

Diagnosis of Artificial Flaws from Eddy Current Testing Signals Based on Sweep Frequency Non-Destructive Evaluation

An investigation of artificial flaws in electromagnetic non-destructive evaluation using eddy-current frequency-response analysis is carried out in this study. A new approach incorporating innovative solution is proposed. The goal was to increase the resolution of gained signals in contrast to the conventional sweep-frequency method. The proposed procedure was tested on real material specimens where differential responses were gained from artificial electro-discharge machined flaws. Two plate specimens having EDM flaws of various dimensions were inspected. Eddy-current responses due to the material flaws were sensed and compared to a dataset that was obtained by numerical modelling. The presented unique results clearly show that the resolution of a fixed probe driven with sweep-frequency excitation signal can be increased when the appropriate probe instrumentation is used and the characteristics are further mathematically processed.

Unsteady flow simulations in two-stage turbines of a rocket turbopump to estimate blade structural soundness for fatigue

Abstract This study first aims at detailed investigations of three-dimensional unsteady flow field in the reference and optimized rocket turbine stages by performing time-accurate flow simulations based on Transient Blade Row (TBR) method or Time Transformation (TT) method in a commercial software ANSYS CFX. Although TT method is believed to enable relatively low-cost unsteady flow simulation, detailed comparisons between TT method-based and conventional unsteady flow simulations are made before TT method application to Fluid-Structural Interaction (FSI) problem. This study then makes an attempt to conduct structural analyses of the 1st and 2nd stage turbine blades under the influence of unsteady fluid forces caused by rotor-stator interaction predicted by TT method-based flow simulations. The structural analyses are executed by use of MSC Nastran. In this study, two materials are adopted as blade material. After the Fourier-series decomposition of the calculated unsteady pressure distributions, the unsteady pressure information is mapped onto the FEM (Finite Element Method)-modeled turbine blade surface as exciting aerodynamic loading. The frequency response analyses are then performed to calculate alternating stresses of the blade, from which the maximum magnitudes of alternating stress are obtained so as to discuss the rotor blade fatigue life.

Frequency response analysis under faults in weak power systems

The renewable energy sources (RESs) projects are solutions with environmental benefits that are changing the traditional power system operation and concept. Transient stability analysis has opened new research trends to guarantee a secure operation high penetration. Problems such as frequency fluctuations, decoupling between generator angular speed, network frequency fluctuation and kinetic energy storing absence are the main non-conventional RESs penetration in power systems. This paper analyzes short-circuit influence on frequency response, focusing on weak distribution networks and isolated, to demonstrate relevance in frequency stability. A study case considered a generation outage and a load input to analyze frequency response. The paper compares frequency response during a generation outage with a short-circuit occurrence. In addition, modular value and angle generator terminal voltage affectation by electric arc and network ratio R⁄X, failure type influence in power delivered behavior, considering fault location, arc resistance and load. The arc resistance is defined as an added resistance that appears during failure and influences voltage modulus and angle value results showing that intermittent non-conventional RES participation can lead to frequency fluctuations. Results showed that arc resistance, type of failure, location and loadability determine the influence of frequency response factors in weak power systems.

Frequency of the Statistical Methods and Relation with Acceptance Period in Archives of Iranian Medicine Articles: A Review from 2015-2019.

Statistical methods (SM) are a ubiquitous tool in research. This study aimed to review SM used in original article published in the Archives of Iranian Medicine (AIM) and assess their effect on article acceptance period. The original articles published in the period 2015-2019 from volumes 18 to 22 and issues 1 to 12 of the AIM were reviewed and six items such as SM, study design, statistical population, sample size, software and acceptance period were extracted. Mean (SD), frequency (percentage) and multiple response analysis (MRA) were used for description. The Kruskal-Wallis test and Spearman correlation coefficient were used for data analysis in SPSS 26 with significance level at 5%. During the study period, 423 original articles were reviewed. The statistical population in most of them was patients (38.8% and 164 articles), and most studies (51.5% and 218 articles) had a sample size of less than 500 people. The study design in most of the articles was analytical-observational (55.1% and 233 articles), and 79.7% (337 articles) used SPSS for data analysis. The median (IQR) acceptance period was 194 (134.25). MRA results showed that the highest rate of use of SM was related to descriptive statistics (277 articles, 30.3%) and Chi square test (130 articles, 14.2%). In the last two years, the acceptance period had a declining trend. There was no significant relation between mentioned variables and acceptance period (P>0.05). Contrary to the researchers' misconceptions, the acceptance period was not affected by SM, study design, statistical population, sample size, or type of software.

SPICE-Based Circuit Analysis of Power Flow Coupling Effect in Double-Input Cuk--Buck DC–DC Converters

An equivalent simulation program with integrated circuit emphasis (SPICE) based circuit is derived from the proposed small-signal averaged model of double-input Cuk--Buck dc–dc converter so that the power flow coupling effect amongst input/output ports is easy to be analyzed in terms of circuit theory rather than pure mathematics. Based on the equivalent SPICE-based circuit, common mode and differential mode power flow decomposition is presented to unveil the power flow coupling between three ports, and furthermore benefits frequency response analysis. It is shown that common mode perturbation analysis reveals the power flow coupling amongst input and output ports, whereas differential mode perturbation analysis does the power flow coupling between input ports. Meanwhile, the explanation of circuit knowledge is provided for power flow coupling effect. Particularly, it is found that the occurrence of the pseudo resonant phenomenon is the result of counteract effect of the common mode and differential mode components in power mismatched condition. Besides, the application of frequency-selective decoupling is proposed to weaken the power flow coupling between ports. Finally, theoretical analysis is verified by experimental ones. These results are useful to understand coupling effects in multiple-input converters and provide a guidance to the controller optimization and engineering application.

Low-Rank Approximation of Frequency Response Analysis of Perforated Cylinders under Uncertainty

Frequency response analysis under uncertainty is computationally expensive. Low-rank approximation techniques can significantly reduce the solution times. Thin perforated cylinders, as with all shells, have specific features affecting the approximation error. There exists a rich thickness-dependent boundary layer structure, leading to local features becoming dominant as the thickness tends to zero. Related to boundary layers, there is also a connection between eigenmodes and the perforation patterns. The Krylov subspace approach for proportionally damped systems with uncertain Young’s modulus is compared with the full system, and via numerical experiments, it is shown that the relative accuracy of the low-rank approximation of perforated shells measured in energy depends on the dimensionless thickness. In the context of frequency response analysis, it then becomes possible that, at some critical thicknesses, the most energetic response within the observed frequency range is not identified correctly. The reference structure used in the experiments is a trommel screen with a non-regular perforation pattern with two different perforation zones. The low-rank approximation scheme is shown to be feasible in computational asymptotic analysis of trommel designs when the proportional damping model is used.

A Novel Approach to Assess Power Transformer Winding Conditions Using Regression Analysis and Frequency Response Measurements

A frequency response analysis (FRA) is a well-known technique for evaluating the mechanical stability of a power transformer’s active part components. FRA’s measuring practices have been industrialised and are codified in IEEE and IEC standards. However, because there is no valid coding in the standard, the interpretation of FRA data is still far from being a widely acknowledged and authoritative approach. This study proposes an innovative fault segmentation and localisation technique based on FRA data. The algorithm is based on regression analysis to estimate the repeatability and relationship between the FRA fingerprint and the latest measured data. Initially, the measuring frequency is discretised into three regions to narrow the location of the fault; the regression model of the fingerprint and current FRA data are then evaluated. As a benchmark, two statistical indicators are the employed benchmark against the proposed method. Finally, the proposed scheme identifies and characterises various transformer conditions, such as healthy windings, axial and radial winding deformations, core deformation and electrical faults. The database used in this study consists of FRA measurements from 70 mineral-oil-immersed power transformers of different designs, ratings and manufacturers that were physically inspected for various faults and comparable frequency regions. The results achieved corroborate the efficacy of the proposed regression analysis fault recognition algorithm (RAFRA) model for transformer fault diagnosis using FRA. Further recommendations are made to address the reproducibility concerns induced by multiple FRA testing conditions.

Objective Interpretation of SFRA, in the Light of CIGRE TB 812

The SFRA (Sweep Frequency Response Analysis) technique has become quite popular as a condition monitoring technique for transformers. The SFRA technique holds a vast repertoire of data in terms of the electromagnetic behaviour of the transformer. Much research has happened in comprehending this data but no effort has succeeded in determining a universal objective criterion for the interpretation of SFRA data. CIGRE study committee A2.53 has recently released Technical Brochure 812 which has been the result of nearly half a decade of international efforts in arriving at an objective criterion for the interpretation of SFRA. This paper discusses the state of the art in objective interpretation of SFRA data with special reference to TB 812. The paper also presents a case study in HPL where SFRA was compared to a conventional method.

Hybrid k-means-PSO Technique for Transformer Insulation Moisture Determination in the Production Stage Based on Frequency Response Analysis

Hybrid k-means-PSO Technique for Transformer Insulation Moisture Determination in the Production Stage Based on Frequency Response Analysis

머신러닝 기법을 이용한 변압기 주파수 응답 모델 파라미터 추정

Examining power transformer faults is crucial for maintaining the reliability of the power system. The most popular methods for detecting power transformer fault include thermal analysis, vibration analysis, partial discharge analysis, dissolved gas analysis(DGA), and sweep frequency response analysis(SFRA). Especially, the SFRA test is examined to detect transformer internal fault such as winding fault. Simulation-level frequency response analysis enables inspection of the power transformer before connecting to the grid. This paper proposes a parameter estimation method using machine learning for the power transformer frequency response equivalent model.

A New Efficient Approach to Simulate Material Damping in Metals by Modeling Thermoelastic Coupling.

The realistic prediction of material damping is crucial in the design and dynamic simulation of many components in mechanical engineering. Material damping in metals occurs mainly due to the thermoelastic effect. This paper presents a new approach for implementing thermoelastic damping into finite element simulations, which provides an alternative to computationally intensive, fully coupled thermoelastic simulations. A significantly better agreement between simulation results and experimental data was achieved, when compared with the empirical damping values found in the literature. The method is based on the calculation of the generated heat within a vibration cycle. The temperature distribution is determined by the mechanical eigenmodes and the energy converted into heat, and thus dissipated, is calculated. This algorithm leads to modal damping coefficients that can then be used in subsequent analyses of dynamically excited oscillations. The results were validated with experimental data obtained from vibration tests. In order to measure material damping only, a test setup excluding friction and environmental influences was developed. Furthermore, comparisons with fully coupled thermoelastic simulations were performed. It was clear that the new approach achieved results comparable to those of a computationally expensive, coupled simulation with regard to the loss factors and frequency response analyses.

Analysing dynamic deep stall recovery using a nonlinear frequency approach

Based on bifurcation theory, nonlinear frequency response analysis is a recent development in the field of flight dynamics studies. Here, we consider how this method can be used to inform us on how to devise the control input such that the system transitions from an undesirable equilibrium solution—an aircraft deep stall solution in our case—to a desirable solution. We show that it is still possible to induce a large-amplitude oscillation via harmonic forcing of the pitch control device and escape the otherwise unrecoverable deep stall, despite very little control power available in such a high angle-of-attack flight condition. The forcing frequencies that excite these resonances are reflected as asymptotically unstable solutions using bifurcation analysis and Floquet theory. Due to the softening behaviour observed in the frequency response, these unstable (divergent) solutions have slightly lower frequencies than the value predicted using linear analysis. Subharmonic resonances are also detected, which are reflected in the time-domain unforced responses. These nonlinear phenomena show strong dependency on the forcing/perturbation amplitude and result in complex dynamics that can impede recovery if the existing procedures are followed. The proposed method is shown to be a useful tool for nonlinear flight dynamics analysis as well as to complement the rather thin literature on deep stall analysis—a topic of relevance for recent research on unconventional landing techniques in unmanned aerial vehicles. A full description of the aircraft model used, the unstable F-16 fighter jet, is provided in the appendix.

Improved hyper-reduction approach for the forced vibration analysis of rotating components

Forced vibration analysis is an indispensable process for the design of a rotating component. However, rather expensive nonlinear static and linear frequency response analyses are usually accompanied by a frequency domain analysis. The traditional mode-superposition method (MSM) effectively reduces the cost of the frequency response analysis. However, the nonlinear static analysis of earlier processes remains as the computational bottleneck. In this paper, the application of the hyper-reduction method will be proposed along with the model order reduction (MOR) framework for rotating component forced vibration analysis. The energy-conserving sampling and weighting (ECSW) method will be employed for the nonlinear iterative computation. The pre-stressed stiffness matrix of the reduced finite elements (FEs) resulting from the ECSW will be used for the post computation stage. Also, a variety of MOR will be attempted for the performance comparison, including MSM, proper orthogonal decomposition (POD)-based reduced order model (ROM), and a hybrid approach. It is found that the present ECSW-combined MOR will significantly relieve the computational bottleneck, provide a minimal loss of accuracy, and be compatible with both nonlinear and linear analyses of the rotating component forced vibration analysis.

Application of Frequency Response Analysis Method to Detect Short-Circuit Faults in Three-Phase Induction Motors

The industry has widely accepted Frequency Response Analysis (FRA) as a reliable method to detect power transformers mechanical deformations. While the FRA technique has been recommended in recent literature as a potential diagnostic method to detect internal faults within rotating machines, detailed feasibility studies have not been fully addressed yet. This paper investigates the feasibility of using the FRA technique to detect several short circuit faults in the stator winding of three-phase induction motors (TPIMs). In this regard, FRA testing is conducted on two sets of induction motors with various short circuit faults. Investigated faults include short circuits between two phases, short circuit turns within the same phase, phase-to-ground, and phase-to-neutral short circuit. The measured FRA signatures are divided into three frequency ranges: low, medium, and high. Several statistical indicators are employed to quantify the variation between faulty and healthy signatures in each frequency range. Experimental results attest the feasibility of the FRA technique as a diagnostic tool to detect internal faults in rotating machines, such as induction motors.

A Ternary Seismic Metamaterial for Low Frequency Vibration Attenuation.

Structural vibration induced by low frequency elastic waves presents a great threat to infrastructure such as buildings, bridges, and nuclear structures. In order to reduce the damage of low frequency structural vibration, researchers proposed the structure of seismic metamaterial, which can be used to block the propagation of low frequency elastic wave by adjusting the frequency range of elastic wave propagation. In this study, based on the concept of phononic crystal, a ternary seismic metamaterial is proposed to attenuate low frequency vibration by generating band gaps. The proposed metamaterial structure is periodically arranged by cube units, which consist of rubber coating, steel scatter, and soft matrix (like soil). The finite element analysis shows that the proposed metamaterial structure has a low frequency band gap with 8.5 Hz bandwidth in the range of 0–20 Hz, which demonstrates that the metamaterial can block the elastic waves propagation in a fairly wide frequency range within 0–20 Hz. The frequency response analysis demonstrates that the proposed metamaterial can effectively attenuate the low frequency vibration. A simplified equivalent mass–spring model is further proposed to analyze the band gap range which agrees well with the finite element results. This model provides a more convenient method to calculate the band gap range. Combining the proposed equivalent mass–spring model with finite element analysis, the effect of material parameters and geometric parameters on the band gap characteristic is investigated. This study can provide new insights for low frequency vibration attenuation.