Obtained Frequency Response Research Articles

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.

Determining auditory-evoked activities from multiple cells in layer 1 of the dorsal cortex of the inferior colliculus of mice by in vivo calcium imaging

Layer 1 of the dorsal cortex of the inferior colliculus (DCIC) is distinguished from other layers by its cytoarchitecture and fiber connections. However, the information of the sound types represented in layer 1 of the DCIC remains unclear because placing electrodes on such thin structures is challenging. In this study, we utilized in vivo calcium imaging to assess auditory-evoked activities in multiple cells in layer 1 of DCIC and to characterize sound stimuli producing strong activity. Most cells examined showed strong responses to broad-band noise and low-frequency tone bursts of high sound intensity. In some cases, we successfully obtained frequency response areas, which are receptive fields to tone frequencies and intensities, and ~30% of these showed V-shape tunings. This is the first systematic study to record auditory responses of cells in layer 1 of DCIC. These results indicate that cells in this area are selective to tones with low frequency, implying the importance of such auditory information in the neural circuitry of layer 1 of DCIC.

Damage identification based on response-only measurements using cepstrum analysis and artificial neural networks

This article presents a response-only structural health monitoring technique that utilises cepstrum analysis and artificial neural networks for the identification of damage in civil engineering structures. The method begins by applying cepstrum-based operational modal analysis, which separates source and transmission path effects to determine the structure’s frequency response functions from response measurements only. Principal component analysis is applied to the obtained frequency response functions to reduce the data size, and structural damage is then detected using a two-stage ensemble of artificial neural networks. The proposed method is verified both experimentally and numerically using a laboratory two-storey framed structure and a finite element representation, both subjected to a single excitation. The laboratory structure is tested on a large-scale shake table generating ambient loading of Gaussian distribution. In the numerical investigation, the same input is applied to the finite model, but the obtained responses are polluted with different levels of white Gaussian noise to better replicate real-life conditions. The damage is simulated in the experimental and numerical investigations by changing the condition of individual joint elements from fixed to pinned. In total, four single joint changes are investigated. The results of the investigation show that the proposed method is effective in identifying joint damage in a multi-storey structure based on response-only measurements in the presence of a single input. Because the technique does not require a precise knowledge of the excitation, it has the potential for use in online structural health monitoring. Recommendations are given as to how the method could be applied to the more general multiple-input case.

Invited Presentation: Impedance Analysis of Lithium-Ion Battery for Future

Batteries have become one of the most important devices because green vehicles, such as hybrid electric vehicles, battery electric vehicles, and even fuel cell electric vehicles, mount batteries. Also, solar power and wind power plants require batteries, in which the power leveling are demanded to stabilize electrical power systems. In order to operate the batteries in those systems, an understanding of the state of batteries, such as the state of charge and state of health of batteries, is very important for effective and safe operation of the batteries. Therefore, a non-destructive analysis of the condition is in high demand for the premonitory diagnosis of the on-board batteries of electric vehicles, and of installed batteries in load leveling systems. Electrochemical impedance spectroscopy (EIS), in which a small-amplitude sinusoidal potential perturbation is applied to a cell, is one of the most powerful tools for the non-destructive analysis of energy devices such as lithium-ion batteries (LIB) 1-4]and fuel cells 5,6. However, the capacity and the internal resistance of large-scale LIBs become higher and lower, respectively, for the application to electric vehicles and large-scale power storage systems: EIS using conventional frequency response analyzer (FRA) – potentiostat systems is not easy to measure the impedance of the LIB because of its low internal resistance. In this situation, we focused on the power controller of LIB system to create a signal for analyzing the battery health. In the present study, application of square wave potential/current for input signals of EIS was investigated firstly in simple electrochemical reaction to verify a new technique called “Square-potential/current electrochemical impedance spectroscopy (SP-EIS, SC-EIS)” which is a method for EIS without using FRA systems. And then, we applied SC-EIS to evaluate a degradation of commercial LIB with the chargedischarge cycling.Firstly, a redox reaction of Fe(Ⅱ)/(Ⅲ) was investigated as a simple electrochemical reaction. On the basis of the technique of fourier transform in ref. 7, 8, EIS was carried out using square potential input. Figure 1A shows Nyqust plots of [Fe(CN)6]4-/[Fe(CN)6]3- electrolyte using square potential input generated by potentiostat. The value of frequency response as ten times higher than that of input frequency was successfully obtained. The value was as almost same as that was obtained by the FRA system. From Fig.1B, applying this method to LIB, we successfully obtained frequency response using several square current inputs generated by a power controller.A commercially available laminated LIB with a nominal capacity of 5 Ah for an electric power assisted bicycle was also evaluated. As the results, fine Nyquist plots could be obtained by means of SC-EIS as well as that by means of the FRA system even in the case of degraded LIBs. Specifically, there was a good accordance between Nyquist plots obtained by SC-EIS on an LIB cell and those obtained by EIS using the FRA system with the error of each plot being less than 3% in the range of 1 kHz – 1 Hz. Therefore, the SC-EIS must be a method of great promise for widespread use in society.

Investigating the Performance of Hyperelastic Constitutive Models in Predicting Dynamic Characteristics of Elastomeric Components

In this paper, the performance of different hyperelastic constitutive models namely Money-Rivlin, Gent, Ogden and Arruda-Boyce to predict the dynamic characteristic of elastomeric components is investigated. An elastomeric engine mount is chosen as case study. Material Parameters of the different models are extracted by curve fitting on uni-axial stress-strain test data. Both static and dynamic response of the finite element model considering the hyperelastic constitutive models are compared with their measured counterparts and each other. To obtain frequency response function of the component for each model, at first considering proportional damping for elastomeric media, the transient analysis due to impulse excitation is performed on the component and then using FFT transformation, the frequency response function is achieved. The results show that hyperelastic constitutive models can be implemented in predicting both static and dynamic behavior of elastomeric components.

Piezoelectric Ceramic Controlled with Platinum Implant as New Isolator in ECG

Recently, a new PLZT bulk single plate, called ceramic-controlled piezoelectric with two Platinum wires (CCP2) has been produced; this CCP2 has two (250 μm of diameter and 1 cm long) Platinum-wire implants. This unconventional isolation device for use with diagnostic ECG devices provides high common mode rejection and low leakage current using piezo isolator based on two Platinum wires implanted Lead Lanthanum Zirconate Titanate bulk ceramic. These isolation was validated using four experimental setups; one of them determine that ceramic-controlled piezoelectric with two Platinum wires (CCP2) support up to 6 kV DC before it cracks (short cut). The second experimental setup determined high resistance about 3.9 × 109 Ω and 1.8 × 109 Ω measured on lateral sides and among Platinum wires of CCP2 respectively. The third experimental setup was to obtain the current leakage from CCP2 and it was 6 nA. The fourth experimental setup was to obtain frequency response that was the maximum up to 2.2 MHz and was a pass band filter. Finally the CCP2 was applied as new isolator in a ECG circuit, where bioelectrical ECG signal is modulating at 16 KHz using the piezoelectric effect obtaining excellent results.

All Fiber Distributed Vibration Sensing Using Modulated Time-Difference Pulses

An optical fiber distributed sensing system merging Mach-Zehnder interferometer (MZI) and phase-sensitive optical time domain reflectometer for vibration measurement with wide frequency response and spatial resolution is proposed and demonstrated. Two acoustic optical modulators are adopted to generate narrow and wide pulses, respectively, on both ends of sensing fiber with a time difference. Narrow pulses are used to generate Rayleigh backscattering light, which locates the vibration point, while wide pulses interfere with reference light as an MZI to obtain frequency response. To simulate the high frequency responses of crack in civil structures, the sudden break of pencils adjacent to the fiber loop has been measured. The experimental results show 5 m spatial resolution and up to 6.3 MHz frequency response with 50 ns pulse width are achieved in 1150 m sensing distance.

Development of an experimental methodology to evaluate the influence of a bamboo frame on the bicycle ride comfort

In the current environment of increased emphasis on sustainable transport, there is manifold increase in the use of bicycles for urban transport. One concern which might restrict the use is the ride comfort and fatigue. There has been limited research in addressing the difficulty in bicycle ride comfort quantification. The current study aims to develop a methodology to quantify bicycle discomfort so that performance of bicycles constructed from bamboo and aluminium alloy can be compared. Experimentally obtained frequency response functions are used to establish a relation between the road input and the seat and rider response. A bicycle track input profile based on standard road profiles is created so as to estimate the acceleration responses. The whole-body-vibration frequency weighting is applied to quantify the perception of vibration intensity so that eventual discomfort ranking can be obtained. The measured frequency response functions provide an insight into the effect of frame dynamics on the overall resonant behaviour of the bicycles. The beneficial effect of frame compliance and damping on lower modes of vibration is very clear in the case of bamboo frame, in turn affecting seat and rider response. In the bamboo frame, because of multiple resonances, the frequency response of the handlebar is smaller at higher frequencies suggesting effective isolation. Further improvements may have come from the joints made from natural composites. Overall, based on the comparative analysis and the methodology developed, bamboo frame shows significant improvement in ride comfort performance compared with the aluminium frame.

Damage Detection of Shear Connectors Based on Power Spectral Density Transmissibility

Damage of shear connectors in slab-on-girder structures will result in shear slippage between slab and girder, which significantly reduces the load-carrying capacity of the bridge. This paper proposes a dynamic damage detection approach to identify the damage of shear connectors in slab-on-girder bridges with power spectral density transmissibility (PSDT). PSDT formulates the relationship between the auto-spectral density functions of two responses. Measured impact force and acceleration responses from hammer tests are analyzed to obtain the frequency response functions at the slab and girder sensor locations by experimental modal analysis. When measurement data from the undamaged structure are available, PSDT from the slab response to the girder response is derived with the obtained frequency response functions. PSDT matrices in the undamaged and damaged states are directly compared to identify the damage of shear connectors. When the measurement data from the undamaged structure are not available, PSDT matrices from measured response at a reference sensor response to those of the slab and girder in the damaged state can also be used to detect the damage of shear connectors. Experimental studies with a concrete slab supported by two steel girders are conducted to investigate the accuracy and efficiency of the proposed approach. Identification results demonstrated that damage of shear connectors can be identified accurately and efficiently with and without measurement data from the undamaged structure.

Post-buckling bifurcations and stability of high-speed axially moving beams

The nonlinear forced dynamics of an axially moving beam in the supercritical speed regime is numerically investigated in this paper, with special consideration to the case possessing an internal resonance between the first two modes. At critical speed, the initial equilibrium configuration of the beam becomes unstable and a new stable non-trivial equilibrium solution together with its symmetric counterpart arises. A closed-form solution for the post-buckling configuration is introduced and the system is assumed to be subject to a transverse harmonic excitation load at its buckled state. The equation of motion is cast into new coordinates which gives the equation governing the motion of the beam about the buckled state. This equation is discretized via the Galerkin method which yields a set of nonlinear ordinary differential equations (NODEs) with quadratic and cubic nonlinear terms. The set of NODEs are solved either via the pseudo-arclength continuation technique or by means of direct time integration so as to obtain frequency–response curves as well as bifurcation diagrams of Poincaré sections about the buckled state. Results are shown through time histories, phase-plane diagrams, and Poincaré sections.

Effects of machining accuracy on frequency response properties of thick-screen frequency selective surface

Electromagnetic theory shows that a thick-screen frequency selective surface (FSS) has many advantages in its frequency response characteristics. In addition, it can be used to make a stealth radome. Therefore, we research in detail how machining accuracy affects the frequency response properties of the FSS in the gigahertz range. Specifically, by using the least squares method applied to machining data, the effects of different machining precision in the samples can be calculated thus obtaining frequency response curves which were verified by testing in the near-field in a microwave dark room. The results show that decreasing roughness and flatness variation leads to an increase in the bandwidth and that an increase in spacing error leads to the center frequency drifting lower. Finally, an increase in aperture error leads to an increase in bandwidth. Therefore, the conclusion is that machining accuracy should be controlled and that a spatial error less than 0.05 mm is required in order to avoid unwanted center frequency drift and a transmittance decrease.

Bidirectional Electrothermal Actuator With Z-Shaped Beams

A bidirectional micro-actuator powered by electrothermal force is successfully demonstrated under both dc and ac operations, without the assistance of magnetic field, using MetalMUMPs process. To achieve small stiffness without buckling, which tends to occur in V-shaped actuators, a new Z-shaped electrothermal actuator is designed. With the actuation current from -13 mA to +13 mA, the electrothermal actuator can achieve a bidirectional motion in a dynamic range from -11.6 μm to +12.8 μm. Experimentally obtained frequency response of the actuator indicates that it has a bandwidth of 49 Hz.

Design and fabrication of a resonant scanning micromirror suspended by V shaped beams with vertical electrostatic comb drives

A scanning micromirror suspended by a pair of V-shaped beams with vertical electrostatic comb drives was designed, modeled, fabricated and characterized. The dynamic analyses were carried out by both theory calculation and FEM simulation to obtain frequency response, stiffness characteristics, oscillation modes and their resonance frequencies. The device was fabricated using the silicon-on-insulator process by only two photolithography masks. Some problems during the process such as the micromirror distortion and the side sticking of the comb fingers were effectively solved by thermal annealing and alcohol-replacement methods, respectively. Based on the fabricated device, the typical scanning patterns for 1-D and 2-D operation were obtained. The experimental results reveal that the micromirror can work in resonant mode with the resonant frequency of 2.38 kHz. The maximum deflection angles can reach ±4.8°, corresponding to a total optical scanning range of 19.2° at a driving voltage of 21 V.

Dynamics of damped rotating solids of revolution through an Eulerian modal approach

This article presents a technique for modelling the dynamic response of rotating flexible solids with internal modal damping. The method is applicable to solids with geometry of revolution that rotate around their main axis at constant spinning velocity. The model makes use of an Eulerian modal coordinate system which adopts the vibration modes in a non-rotating frame as basis functions. Due to the coordinate system, the technique is particularly suitable for studying the dynamic interaction between rotating solids and non-rotating structures and permits to obtain Frequency Response Functions. The current investigation presents the development of the proposed technique from a previous Lagrangian model, and consequently the mathematical relationships between the two coordinate sets are found. The approach has been adopted to study the dynamics of a simply supported cylinder including damping in order to obtain the receptance function and the modal properties of the rotating solid.

A Field Test to Determine PSS Effectiveness at Multigenerator Power Plants

This paper presents a new field test to adequately assess the oscillation damping effectiveness of the PSSs in a multigenerator power plant. The test allows estimating the location of the dominant open-loop poles (i.e., in the absence of PSSs at the multigenerator plant) from frequency response measurements of the closed-loop multivariable system. This test was first carried out at the Itaipu 60-Hz power station, which was generating 4000 MW at the time. The test validation was made through comparison of obtained frequency response measurements with computer simulations of a detailed dynamic model of the Brazilian interconnected power system.

Experimental Comparison of Conventional and Optical VTs, and Circuit Model for Optical VT

This paper compares the performances of an optical voltage transformer (OVT) and a conventional voltage transformer (VT) in a laboratory for steady state and transients. It also presents a developed equivalent circuit model for OVT. In addition, OVT impulse response has been investigated, and field records have been evaluated to confirm that optical systems can satisfactorily replace magnetic transformers. Both experimental results and field records show that the transient performance of an OVT is better than that of a conventional one, and the performance of OVT is comparable to that of the magnetic VT. Differences are found within experimental errors. A transfer function for OVT is derived by using the obtained frequency response characteristics. A circuit model is developed from the derived transfer function by using a network synthesis method. The model is verified through the frequency response results and tested with PSPICE simulation program. The results show that the developed model can be used as a legitimate OVT model.

Area Method for a Biased Relay Feedback System

The relay feedback system often shows an asymmetric response because of initial transient states, disturbances, and process nonlinearity. To restore a symmetric response of the relay feedback system, an iterative adjustment of input or output bias is required. Instead of trying to obtain a symmetric response, the asymmetric response can be analyzed to estimate the ultimate data or a parametric model of process. However, the asymmetric response causes additional errors in estimating the ultimate properties of the process. An area method is proposed to reduce these errors. Because integrals (areas) of the relay responses reduce the effects of the high-order harmonic terms significantly, the proposed method shows better accuracy in obtaining frequency response data and parametric models compared with previous approaches.

Analytical Prediction of Part Dynamics for Machining Stability Analysis

An analytical procedure is developed to predict workpiece dynamics in a complete machining cycle in order to obtain frequency response functions (FRF), which are needed in chatter stability analyses. For this purpose, a structural modification method that is an efficient tool for updating FRFs is used. The mass removed by machining is considered to be a structural modification in order to determine the FRFs at different stages of the process. The method is implemented in a computer code and demonstrated on different geometries. The predictions are compared and verified by FEA. Predicted FRFs are used in chatter stability analyses, and the effect of part dynamics on stability is studied. Different cutting strategies are compared for increased chatter-free material removal rates considering part dynamics.

A new damping modelling approach and its application in thin wall machining

In this paper, a new approach to modelling the damping parameters and its application in thin wall machining is presented. The approach to predicting the damping parameters proposed in this paper eliminates the need for experiments otherwise used to acquire these parameters. The damping model proposed was compared with available damping models and experimental results. A finite element analysis and Fourier transform approach has been used to obtain frequency response function (FRF) needed for stability lobes prediction. Several predicted stable regions using both experimental and numerical FRF’s for various examples gave a good comparison.

Dynamic characterization and modification of dynamic properties of a micro scanner

Micro electro mechanical systems (MEMS) are used in many application areas in different disciplines and took their place among the most promising technologies. The performance of such systems is primarily related to their dynamical characteristics. This study presents the dynamic characterization techniques that are used to identify the modal parameters of a MEMS device and the methods that can be implemented to change its dynamic response. An electrostatic scanner is chosen as the case study to demonstrate the developed methodologies. Initially, the micro scanner is characterized using experimental modal analysis techniques to obtain frequency response function, modal damping, resonance frequencies, and mode shapes. Then, velocity and position feedback control loops are implemented to the scanner system to alter the damping and stiffness characteristics. A closed-loop Simulink model of the scanner is developed to verify the experimental measurements. Several curve fitting methods are used in order to have an accurate representation of the scanner system. Using the model, the influence of both position and velocity feedback on the effective damping, resonance frequency and the transient behavior of the scanner is investigated. The stability limits of the scanner under velocity feedback are also studied via numerical simulations. Based on the experimental and simulation results, the methodology developed in this study proves itself to be very efficient to alter the dynamical characteristics of the MEMS structures and it can be easily adapted to other MEMS applications.