Obtained Frequency Response Research Articles

Design of High Power Handling Filter Using Cascaded Quadruplet Superconducting Bulk Resonators

We designed transmit bandpass filters that have a four-pole cascaded quadruplet (CQ) structure with high-temperature superconducting (HTS) bulk disk resonators. We developed a trimming device that can change the electric-coupling coefficients simply by adjusting the height of a pair of copper rods. We analyzed the frequency response of the filters using an electromagnetic simulator and found that the trimming device can provide the targeted value for the coupling coefficient. In addition, from simulation of the filters, we obtained frequency responses with a center frequency of 5.04 GHz, a bandwidth of 124 MHz, and a skirt characteristic of 3.23 dB/5 MHz. To our knowledge, this is the first CQ filter structure yet developed using HTS disk resonators and a trimming system for electric coupling.

AC and DC Impedance Extraction for 3-Phase and 9-Phase Diode Rectifiers Utilizing Improved Average Mathematical Models

Switching models possess discontinuous and nonlinear behavior, rendering difficulties in simulations in terms of time consumption and computational complexity, leading to mathematical instability and an increase in its vulnerability to errors. This issue can be countered by averaging detailed models over the entire switching period. An attempt is made for deriving improved dynamic average models of three phase (six-pulse) and nine phase (18-pulse) diode rectifiers by approximating load current through first order Taylor series. Small signal AC/DC impedances transfer functions of the average models are obtained using a small signal current injection technique in Simulink, while transfer functions are obtained through identification of the frequency response into the second order system. For the switch models in Simulink and the experimental setup, a small signal line to line shunt current injection technique is used and the obtained frequency response is then identified into second order systems. Sufficient matching among these results proves the validity of the modelling procedure. Exact impedances of the integral parts, in interconnected AC/DC/AC systems, are required for determining the stability through input-output impedances.

음강성을 갖는 비틀림 진동 절연 시스템의 성능 분석

A novel torsional vibration isolator with negative stiffness is proposed in this paper. Unlike most previous isolators achieving vibration isolation in translational direction, a torsional vibration isolator employing negative stiffness is devised in this study. The torsional vibration isolator proposed in this study consists of a linear torsional spring and two pre-compressed translational springs that create negative torsional stiffness. Vibration isolation performance of the proposed system is investigated using an analytical model which is obtained with the Lagrange’s method. The harmonic balance method (HBM) is employed to obtain frequency response curves (FRCs) from the equation of motion. The proposed system exhibits vibration isolation performance superior to linear vibration isolators especially in low frequency range. Therefore, the proposed torsional vibration isolator can be usefully employed to attenuate the low torsional frequency response characteristics.

Chatter stability prediction in high-speed micromilling of Ti6Al4V via finite element based microend mill dynamics

High-speed micromilling (spindle speeds 100 000 r/min) can create complex three-dimensional microfeatures in difficult-to-machine materials. The micromachined surface must be of high quality, to meet functional requirements. However, chatter-induced dynamic instability deteriorates the surface quality and can be detrimental to tool life. Chatter-free machining can be accomplished by identifying stable process parameters via stability lobe diagram. To generate accurate stability lobe diagram, it is essential to determine the microend mill dynamics. Frequency response function is required to determine the tool-tip dynamics obtained by experimental impact analysis. Note that application of impact load at the microend mill tip (typically 100 – 500 μm) is not feasible as it would invariably end with tool failure. Consequently, alternative methods need to be developed to identify the microend mill dynamics. In the present work, the frequency response function for the microend mill is obtained by finite element method modal analysis. The frequency response function obtained from modal analysis has been verified from the experimentally obtained frequency response function. The experimental frequency response function was obtained by impacting the microend mill near the taper portion with an impact hammer and measuring the vibration of the tool-tip with a laser displacement sensor. The fundamental frequency obtained from finite element method modal analysis shows a difference of 6.6% from the experimental fundamental frequency. Microend mill dynamics obtained from the finite element method is used for chatter prediction in high-speed micromilling operations. The stability lobe diagram predicts the stability boundary accurately at 60 000 r · min–1 and 80 000 r/min; however, a slight deviation is observed at 100 000 r/min.

Coupling of structures using frequency response functions

In the field of structural dynamics is common to predict the behaviour of a structure regarding structural modifications. In this context, the frequency based substructuring method is well-known to perform structural modifications based on the coupling of structures. This process gives the possibility to perform the study of a structure at the level of its components and then assess the response of the coupled system. In practice, it is impossible to attain an experimental complete response model, although one can simulate all the responses of a structure using numerical models. Hence, the substructuring process can be enhanced by the combined use of experimental and numerical responses, as it was demonstrated using numerically obtained frequency response functions. This work presents the enhancement of the frequency based substructuring method using a method to expand experimental frequency response functions over the entire set of degrees of freedom in a finite element model. This expansion process, known as modified Kidder’s method, considers that if one can only measure translations due to exciting force, it is possible to obtain the complete response model, including the rotational frequency response functions due to exciting moments. The combined use of the frequency based substructuring and the modified Kidder’s methods has several advantages, as it avoids modal identification or residual compensation. To evaluate the performance of the proposed procedure a numerical example of a beam structure is presented, and its results are discussed.

Vibration analysis of simulated tyre-vehicle system using frequency-based substructuring

There is a complex relationship between tyre dynamics and the overall ride comfort and noise of a given vehicle. The main source of this complexity is the interaction of the tyre and vehicle subsystems. This interaction is investigated in the present work through an application of frequency-based substructuring techniques to obtain frequency response information for the tyre from a quarter car system. First, these techniques are applied to a simplified, single coupling degree of freedom representation of the quarter car system. Subsequently, the process is repeated for a simulated system containing a rigid ring tyre model. The results show the power of the technique for studying tyre and suspension subsystems as parts of the assembled quarter car system. This process will allow for a more precise estimation of vehicle ride properties without the need to create complex models or test physical models for each tyre-suspension combination.

A Compact Waveguide Bandpass Filter Using Hybrid Combination of CSRR and Koch Fractal

This paper presents a compact, wideband, waveguide bandpass filter using a hybrid combination of complementary split ring resonators (CSRRs) and Koch fractal. Three identical planar structures, printed with CSRRs and Koch fractal, have been placed in the transverse plane of a standard WR-90 waveguide at a quarter wavelength distance to form the filter. The proposed filter has been simulated using Ansoft HFSS (version 14) and the obtained frequency response has been compared with the frequency response of its lumped element equivalent circuit. The filter was also fabricated and its frequency response has been measured. The measured result shows a 3-dB fractional bandwidth of 12.66% at resonant frequency 9.95 GHz. The total length of the fabricated filter is 20.33 mm. Detailed design procedure has been presented along with necessary diagrams. A table has been provided to compare the performance of the proposed filter with those already available in the literatures. The table shows that the proposed filter is compact, has higher bandwidth and better frequency response compared to the rests.

Natural frequency analysis of lattice boom crane theoretically and experimentally

Having knowledge of dynamic properties named as natural frequency and mode shapes during the design process is important to determine proper design criteria. As a main aim of this study, experimental and theoretical modal analysis was carried out using a scaled physical model of selected lattice boom and comparing the frequency responses are evaluated. The 1/30 scaled physical model of a prototype lattice boom crane was designed and manufactured. Free vibration tests are performed and critical frequency values of the system are obtained. After that, physical structure was modeled by using ANSYS. Modal analysis was carried out. Efficiency of the numerical model is discussed by comparing the results which is found from theoretical and experimental studies. The comparative study showed that frequency values can be obtained from the finite element analysis. Thus, it will be possible to obtain frequency response of these kind of crane structures theoretically without needing experimental studies.

Nonlinear Analysis of Bifurcation Phenomenon for a Simple Flexible Rotor System Supported by a Full-Circular Journal Bearing

This paper demonstrates nonlinear theoretical analysis of a flexible rotor system supported by a full-circular journal bearing focusing on the bifurcation phenomenon in the vicinity of the stability limit (bifurcation point). A third-order polynomial approximation model is used for the representation of the oil film force of the journal bearing. The reduced-order model, with modes concerning the bifurcation, is deduced using the center manifold theory. The dynamical equation in the normal form relating the bifurcation which leads to the oil whirl is obtained using the normal form theory. The influences of various parameters are investigated based on the analysis of a deduced dynamical equation in the normal form. Furthermore, the validity of the derived analytical observation is confirmed by comparing it with the numerically obtained frequency response result.

Linear and non-linear vibrations of fluid-filled hollow microcantilevers interacting with small particles

Linear and non-linear vibrations of a U-shaped hollow microcantilever beam filled with fluid and interacting with a small particle are investigated. The microfluidic device is assumed to be subjected to internal flowing fluid carrying a buoyant mass. The equations of motion are derived via extended Hamilton's principle and by using Euler-Bernoulli beam theory retaining geometric and inertial non-linearities. A reduced-order model is obtained applying Galerkin's method and solved by using a pseudo arc-length continuation and collocation scheme to perform bifurcation analysis and obtain frequency response curves. Direct time integration of the equations of motion has also been performed by using Adams-Moulton method to obtain time histories and analyze transient cantilever-particle interactions in depth. It is shown that exploiting near resonant non-linear behavior of the microcantilever could potentially yield enhanced sensor metrics. This is found to be due to the transitions that occur as a matter of particle movement near the saddle-node bifurcation points of the coupled system that lead to jumps between coexisting stable attractors.

Electrical impedance functionality and spin orientation transformation of nanostructured Sr-substituted BaMnO3 hexagonal perovskites

Eliminating the undesirable pyrochlore phase is quite essential in order to determine the viable dielectric and magnetic characteristics of perovskite-based materials. In this work, we report the synthesis of stoichiometric Sr-substituted barium manganite namely, Ba1−xSrxMnO3 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) to reveal the improved structural, dielectric and magnetic properties with increase in Sr contents. X-ray diffraction and subsequent Rietveld refinement reveals that with successful substitution of Sr at Ba-site, the pyrochlore phase diminishes and pure perovskite phase is achieved. Scanning electron microscopy demonstrates gradually improved grain shapes and uniformity in sizes in the series. Electrical impedance spectroscopy was performed using an impedance analyzer, to obtain frequency response of dielectric constant, giving tenable information about a sustainable change in electrical permittivity due to Sr-substitution which could be used for multilayered chip inductors. Dense dielectric materials with low losses are credible for multilayered components which make these oxides more feasible than ferrites to be used as sheets inside the multilayered chip inductors. Contribution of grains and grain boundaries effect on electrical resistivity, losses and quality factors are also distinguished. The coupling between the magnetic and dielectric order is also confirmed through magneto-dielectric measurement. Low temperature magnetic studies reveals the multiferroic characteristic of the material as the ferromagnetic transition temperature of 55 K, found experimentally has never been reported before.

Study on Vibro-acoustics Characteristics of Bamboo-based Violin

Bamboo is knownas fast-growing plant and can easily be obtained in Bandung. This situation leads bamboo to be material that commonly used for constructing various solid structures with particular strength including violin. It is interesting that bamboo violin has a unique sound quality that differs perceptually from common wooden violin. This research is focused on finding the physical parameters in order to get plausible explanations on that sound difference by conducting vibro-acoustic analysis. An automatic bow-moving machine is developed to provide a highly repeatable bowing strokes upon string. The frequency spectrum analysis is used.A piezoelectric is put on the violin resonator surfaces for recording excitation force of bridge while a microphone is used for recording sound pressure level produced by the resonator. This approach is considered in order to obtain frequency response function of soundbox as ratio of the sound pressure level to the vibration one. It is found that the frequency response function on overtones of both violins are different at mid and high frequencies. Meanwhile, at low frequencies it is seen that the both violins share similar pattern of frequency response function hill peaks.

Investigation of Multifrequency Piezoelectric Energy Harvester

This paper presents results of numerical and experimental investigations related to the piezoelectric energy harvester that operates at multifrequency mode. Employment of such operation principle provides an opportunity for obtaining frequency response characteristics of the harvester with several resonant frequencies and in this way increasing efficiency of the harvester at a wide spectrum of excitation frequencies. The proposed design of the energy harvester consists of five cantilevers which forms square type system. Cross sections of the cantilevers are modified by periodical cylindrical gaps in order to increase strain value and to obtain more uniform strain distribution along the cantilevers. Cantilevers are rigidly connected to each other and compose an indissoluble system. Square type harvester has seismic masses at every corner. These masses are placed under specific angle in order to reduce natural frequencies of the system and to create additional rotation moments in the body of harvester. Results of the numerical investigation revealed that harvester has five resonance frequencies in the range from 15 Hz to 300 Hz. Numerical analysis of the harvester revealed that the highest open circuit voltage density is 19.85 mV/mm3. Moreover, density of the total electrical energy reached 27.5 μJ/mm3. Experimental investigation confirmed that frequency response characteristics are obtained during numerical investigation and showed that energy density of the whole system reached 30.8 μJ/mm3.

Numerical models of railway tracks for obtaining frequency response Comparison with analytical results and experimental measurements

Many authors have focused their research on the vibrations caused by railway traffic, and have developed diverse models of railway tracks: from half-track analytical models up to complex numerical models. This paper presents numerical models, built using FEM software, for different types of railway tracks. These models describe in detail the superstructure vibratory response induced by vertical forces acting on the top of the rail head, and include aspects not reflected in the analytical models. The numerical results are compared with previously presented analytical ones, as well as with experimental measurements.

Damage assessment of shear connectors with vibration measurements and power spectral density transmissibility

Shear connectors are generally used to link the slab and girders together in slab-on-girder bridge structures. Damage of shear connectors in such structures will result in shear slippage between the slab and girders, which significantly reduces the load-carrying capacity of the bridge. Because shear connectors are buried inside the structure, routine visual inspection is not able to detect conditions of shear connectors. A few methods have been proposed in the literature to detect the condition of shear connectors based on vibration measurements. This paper proposes a different dynamic condition assessment approach to identify the damage of shear connectors in slab-on-girder bridge structures based on power spectral density transmissibility (PSDT). PSDT formulates the relationship between the auto-spectral densities of two responses in the frequency domain. It can be used to identify shear connector conditions with or without reference data of the undamaged structure (or the baseline). Measured impact force and acceleration responses from hammer tests are analyzed to obtain the frequency response functions at sensor locations by experimental modal analysis. PSDT from the slab response to the girder response is derived with the obtained frequency response functions. PSDT vectors in the undamaged and damaged states can be compared to identify the damage of shear connectors. When the baseline is not available, as in most practical cases, PSDT vectors from the measured response at a reference sensor to those of the slab and girder in the damaged state can be used to detect the damage of shear connectors. Numerical and experimental studies on a concrete slab supported by two steel girders are conducted to investigate the accuracy and efficiency of the proposed approach. Identification results demonstrate that damages of shear connectors are identified accurately and efficiently with and without the baseline. The proposed method is also used to evaluate the conditions of shear connectors in a real composite bridge with in-field testing data.

Investigation of Boring Bar Dynamics for Chatter Suppression

Chatter is a concern in boring process, due to the low dynamic stiffness of long cantilever boring bars. Chatter suppression in machining permits higher productivity and better surface finishes. In order to improve the performance of boring operations, several researchers have investigated electro- and magneto-rheological fluids and piezoelectric and electromagnetic actuators as vibration absorbers. In this study, we investigated the feasibility of shifting the natural frequency of boring bar based on semi-active fluid control. Mass at the end of a boring bar was modulated to tune its natural frequency by adjusting the level of fluid in a reservoir. At the same time, different damping materials were used to improve dynamics of the boring bar. Experimental modal analysis was used to obtain frequency response functions for different system configurations. A finite element model was proposed and validated with experimental results. A chatter stability analysis examined chatter suppression characteristics of the proposed method.

Designing a Bandpass Frequency Selective Surface Based on an Analytical Approach Using Hexagonal Patch-Strip Unit Cell

This article introduces analytical formulas to obtain frequency response for a periodic array of hexagon metallic patches and strip cells. The validity of analytic expressions obtained from analysis is verified using full-wave simulations. The formulas are then employed for designing a first-order bandpass frequency selective surface. The proposed frequency selective surface is composed of a periodic array of metallic patches separated by thin air gaps backed by a wire mesh having the same periodicity. The array of metallic patches and the wire mesh constitute a capacitive surface and a coupled inductive surface, respectively, which together act as a resonant structure in the path of an incident plane wave. The frequency response of the proposed frequency selective surface is obtained for various angles of incidence. Moreover, principles of operation, detailed synthesis procedure, and designing guideline for this type of frequency selective surface are presented and discussed in this article.

Model-based force and state estimation in experimental ice-induced vibrations by means of Kalman filtering

Bottom-founded structures deployed in ice-choked waters may experience severe ice-induced vibrations. A direct monitoring of the level-ice forces requires installation and use of load panels. This is often cumbersome and costly. Indirect measurements interpreted by inverse techniques are therefore favourable since sensors for response measurements are easier to install, less expensive and provide information as to the structural motion. In this paper, the level-ice forces exerted on a scale model of a compliant bottom-founded structure are identified from non-collocated strain and acceleration measurements by means of a joint input-state estimation algorithm. The algorithm allows for uncertainty in the model equations, can be applied to full-scale structures and reconstructs forces without any prior assumptions on their dynamic evolution. The identification is performed employing two different finite element models. One is entirely based on the blueprints of the structure. The other is tuned to reproduce the measured first natural frequency more accurately. Results are presented for two different excitation scenarios characterized by the ice failure process and ice velocity. These scenarios are known as the intermittent crushing and the continuous brittle crushing regimes. The accuracy of the identified forces is assessed by comparing them with those obtained by a frequency domain deconvolution, on the basis of experimentally obtained frequency response functions. The results show successful identification of the level-ice forces for both the intermittent and continuous brittle crushing regimes even when significant modelling errors are present. The response (displacements) identified in conjunction with the forces is also compared to those measured during the experiment. Here the estimated response is found to be sensitive to the modelling errors in the blueprint model. Simple tuning of the model, however, enables high accuracy response estimation.

Spectral analysis of multiple cracked beam subjected to moving load

In present paper, the spectral approach is proposed for analysis of multiple cracked beam subjected to general moving load that allows us to obtain explicitly dynamic response of the beam in frequency domain. The obtained frequency response is straightforward to calculate time history response by using the FFT algorithm and provides a novel tool to investigate effect of position and depth of multiple cracks on the dynamic response. The analysis is important to develop the spectral method for identification of multiple cracked beam by using its response to moving load. The theoretical development is illustrated and validated by numerical case study.

Geometrically-exact unsteady model for airfoils undergoing large amplitude maneuvers

A semi-analytical, geometrically-exact, unsteady potential flow model is developed for airfoils undergoing large amplitude maneuvers. For this objective, the classical unsteady theory of Theodorsen is revisited relaxing some of the major assumptions such as (1) flat wake, (2) small angle of attack, (3) small disturbances to the mean flow components, and (4) time-invariant free-stream. The kinematics of the wake vortices is simulated numerically while the wake and bound circulation distribution and, consequently, the associated pressure distribution are determined analytically. The steady and unsteady behaviors of the developed model are validated against experimental and computational results. The model is then used to determine the lift frequency response at different mean angles of attack. Both qualitative and quantitative discrepancies are found between the obtained frequency response and that of Theodorsen at high angles of attack.