Structure Of Transfer Function Research Articles

Investigation of the mechanism of noise radiation reduction from an ABH-cavity under interior acoustic excitation considering multistage coupling

The acoustic black hole (ABH) structure exhibits superior vibration and sound radiation control capability compared to its flat counterpart. However, for a coupled plate-cavity system under interior acoustic excitation, the underlying suppression mechanism of noise radiation has not been explored, especially below the critical frequency of the structure. In this paper, the noise suppression mechanism of an ABH-cavity system under interior acoustic excitation is investigated both theoretically and numerically. Based on the theoretical analysis, the noise radiation depends on both the structural modes and the cavity modes, which can be suppressed in two ways. One is to lower the magnitude of structural transfer functions. The other is to change the mapping matrix which maps the structural modal amplitude to the amplitude of radiation modes. For the former, numerical analysis based on FEM demonstrates that a lower structural transfer function is obtained in the ABH-cavity system compared to its flat counterpart because of the damping enhancement characteristic of the ABH structure. Therefore, attenuated flexural vibrations and reduced sound radiation are achieved at corresponding modal frequencies. For the latter, ABH-cavity systems with varying numbers of ABHs are constructed to demonstrate a simple solution of manipulating the mapping matrix to achieve the reduced radiation efficiency of structural panels and the enhanced suppressing effect of noise radiation. The study in this paper indicates a feasible direction for the further optimization analysis of noise radiation suppression of the ABH-cavity system.

Numerical simulation of on-road wind conditions for interior wind noise of passenger vehicles

Traditionally vehicles are designed for wind noise under ideal steady wind conditions. But, passenger comfort is affected by high modulation of cabin noise while cruising in traffic due to variations of instantaneous wind speed and direction from driving through large-scale turbulence. In consequence, designing a vehicle for the best performance in a low-turbulence wind tunnel may lead to issues during on-road conditions. To predict the interior noise corresponding to on-road turbulence, a simulation approach is proposed combining an upstream turbulence flow simulation with an SEA vehicle model. This work is an extension of existing well validated procedures for steady wind conditions. Time-segmented transient loads on panels and steady-state structural acoustics transfer functions are combined, producing interior noise results for a series of overlapping time segments. This interior noise prediction, as a function of time, captures the modulation of wind noise results, which are then visualized using a spectrogram, plotting sound pressure level indicated by color as a function of time and frequency bands. Audio signals are also created from the interior noise results, allowing detailed signal analysis from this simulation. This capability enables designers to reduce wind noise modulation in time caused by on-road turbulence, improving speech intelligibility and passenger comfort.

Electric machine noise and vibration prediction and validation through test

In this paper, a finite element (FE) simulation process for the NVH prediction of electric motors is proposed. The proposed process first simulates the motor excitation forces using a 2D electromagnetic force model which is derived from Maxwell and then it applies these forces to a simplified 3D electric machine model. This simplified 3D model is validated by comparing the structural transfer functions calculated from impact hammer test and FE simulation. Finally, the proposed simulation process is validated by comparing predicted sound pressure levels at different selected locations to an electric motor NVH test results from a semi-anechoic chamber.

Low-story damage detection of buildings using deep neural network from frequency phase angle differences within a low-frequency band

Lower stories of buildings are much more vulnerable due to the critically dead load from high stories. Vibration-based damage detection methods are commonly used to quantify damage with indicators and early assess structural deterioration. However, these indicators are usually not directly related to structural performance and can be distorted by the modeling errors or sensing uncertainties. In addition, damage detection of structures can be realized from sensor data by the remaining useful life estimation framework in machine learning. Meanwhile, a machine learning model, which detects structural damage, can be trained by the generated data from a numerical/identified model, e.g., phase angle differences of structural transfer functions. Moreover, the bounded nature of phase angles coincides with the needs of machine learning algorithms, and the combined stiffness and damping changes involved in damaged structures can also be considered in a learning model. Therefore, this study proposes a neural network damage detection method based on frequency response phase angle differences for low-story damage of buildings. In this proposed method, a simplified model is established from identified modal parameters of a structure and optimized using the least-squared stiffness approach, and the transfer function phase angle differences are generated from the model considering the stiffness and damping changes in various damage scenarios. The generated data are exploited to train a deep learning model which predicts the residual stiffness percentages as the condition parameters in the remaining useful life estimation framework. In this study, a numerical example provides detailed procedure to develop the neural network damage detection model and evaluate the effectiveness of the learning model. The proposed method is also employed in a scaled six-story steel-frame building for experimental verification. As seen in the results, the neural network damage detection method can estimate the residual stiffness percentages in the lower stories of a building based on frequency response phase angle differences.

Non-destructive damage localization in built-up composite aerospace structures by ultrasonic guided-wave multiple-output scanning

This paper focuses on defect localization in a composite skin-to-stringer stiffened panel representative of modern aircraft construction by an ultrasonic scanning system using multi-channel transfer function extraction. An especially made mini-impactor is utilized as the excitation to generate a broad wave frequency range. At each scanning position, multiple excitations are concatenated to extract the Guided-Wave Structural Transfer Function (GWSTF) between two points of the test structure. This extraction is performed using an averaged, normalized cross-power spectrum operation that minimizes the influence of the excitation and that of uncorrelated noise. The GWSTF extracted from different sensor pairs is then related to the presence of damage at different locations. The system is thus able to locate damage in the panel in 2D (along and across the stringer direction), in a substantial improvement over a 1D scanning system developed by the authors previously. The system is tested on damage in the form of added masses and real damage in the form of through-thickness stringer notches. The results show good detection and location of damage, suggesting the potential for a practical inspection system targeting internal damage in aircraft structures when probed from the outer skin side.

Physical-virtual time reversing of nonlinear Lamb waves for fatigue crack detection and quantification

This article presents the investigation of a nonlinear Lamb wave time reversing technique for fatigue crack detection and quantification. A 2D analytical framework is initially presented, modeling Lamb wave generation, propagation, wave crack linear and nonlinear interaction, and reception. This study extends the Time Reversal (TR) techniques into the realm of nonlinear Lamb waves. Due to the structural transfer function variation between the forward and backward transmission process, the Virtual Time Reversal (VTR) algorithm reveals obvious deviation for predicting nonlinear Lamb waves, given that it replaces the backward TR procedure with the forward transfer function. However, this study demonstrates that the difference between the physical nonlinear TR method and the conventional VTR algorithm proves to be sensitive to detect and quantify fatigue cracks. Fatigue tests on a thin aluminum plate with a rivet hole are conducted to induce a fatigue crack. The experimental results further illuminate that the proposed physical-virtual nonlinear Lamb wave TR technique possesses remarkable sensitivity to the nucleation and growth of fatigue cracks. The paper finishes with discussion, concluding remarks, and suggestions for future work.

A deep convolutional neural network for simultaneous denoising and deblurring in computed tomography

Computed tomography (CT) has been commonly used for providing medical images. However, CT scans have a potential risk of side-effect due to high radiation dose. In order to overcome this limitation, low-dose CT imaging techniques have been developed by using novel scanners, reconstruction algorithms and adjusted scanning protocols. In spite of these strategies, the conventional low-dose CT imaging techniques are hard to compromise between radiation dose and image quality, leading to noise, blur and artifacts in CT images. These drawbacks of the conventional techniques degrade diagnostic accuracy. In this study, we proposed a deep convolutional neural network (CNN)-based low-dose CT imaging technique for simultaneously reducing noise and blur at once. The proposed method, called denoising and deblurring CNN (DnDbCNN), consisted of two networks, and each network was separately trained for reducing noise and blur in CT images. For combining the trained networks, a convolutional layer was added between the two trained networks, and the combined network was re-trained to update the weights of each layer. Denoising convolutional neural network (DnCNN) and super-resolution convolutional neural network (SRCNN) were also implemented for comparison. We evaluated the performance of the DnDbCNN in terms of mean-square error (MSE), peak signal-to-noise ratio (PSNR), structural similarity index measure (SSIM), coefficient-of-variation (COV) and modulation transfer function (MTF). The results showed that the DnDbCNN improved the noise property, spatial resolution and quantitative accuracy of CT images, and the performance of the DnDbCNN was superior to the conventional methods. As a result, the DnDbCNN can simultaneously reduce noise and blur by combining two networks through three training steps. Therefore, the DnDbCNN has a potential for improving CT image quality with low radiation dose and enables precise diagnosis.

Structural-Parametric Model Electromagnetoelastic Actuator Nanodisplacement for Mechatronics

Electromagnetoelastic actuator have been used successfully to nanodisplacement for mechatronics systems in nanotechnology, electronic engineering, microelectronics, nanobiology, power engineering, astronomy. Linear structural-parametric model, parametric structural schematic diagram, transfer functions of the simple electromagnetoelastic actuator nanodisplacement for the mechatronics systems are obtained. For calculation of the mechatronics system with piezoactuator the parametric structural schematic diagram and the transfer functions of the piezoactuator are obtained. A generalized parametric structural schematic diagram and transfer functions of the piezoactuator are constructed. This work describes the linear structural-parametric model of the simple piezoactuator for the mechatronic in the static and dynamic operation modes in contrast solving its electrical equivalent circuit.

Robust non-destructive inspection of composite aerospace structures by extraction of ultrasonic guided-wave transfer function in single-input dual-output scanning systems

Ultrasonic guided-wave testing is widely utilized for damage detection in plate-like structural components, including composite aircraft fuselage and wing panels. Many guided-wave tests involve transducer scanning to cover finite areas, a task that is most effectively performed by non-contact wave transduction means. The most common guided-wave test implementation consists of a “single-input single-output” scheme. The single-input single-output scheme leads to a transfer function that is convolved with the particular frequency response of the transducers and that of the transducer-to-structure paths (in both excitation and detection). These responses can be unknown or generally variable, especially in non-contact scanning systems and impact excitations. This article proposes a “single-input dual-output” scheme for ultrasonic guided-wave testing in scanning systems that is based on a deconvolution operation. The single-input dual-output scheme better isolates the structural transfer function that is the only property affected by the presence of possible damage. The single-input dual-output scheme was applied to two guided-wave scanning systems under development to detect impact-type damage in stiffened skin-to-stringer panels representative of modern composite aircraft construction. The results demonstrate the dual-output technique and also shed some light on the role of the different frequency bands for the detection of damage at different locations of the skin-to-stringer assembly.

Transmission Matrices for Physical-System Modeling [Lecture Notes

Power transmission matrices (PTMs) for structures are 2 X 2 matrices that relate force and velocity at one terminal to force and velocity at another terminal. This technique provides an elegant approach to deriving transfer functions for structures consisting of masses, springs, and dashpots, that is, dampers. PTMs were developed during the 1970s and 1980s, but they are rarely mentioned today except briefly in textbooks. The first goal of this tutorial is to highlight the utility of this modeling technique. A related aim is to bring inerters into this framework. The article revisits the classical topic of analogies by deriving PTMs for twoport networks. The across-through analogy is used to construct circuits whose transfer functions match those of the analogous structure. This article is intended for all students and practitioners of control systems who may benefit from awareness of this modeling technique.

Convergence of the Newton Structure Transfer Function to the Ideal Fractional Delay Filter

This letter presents a rigorous demonstration of the convergence of the Newton fractional delay filter to the ideal fractional delay filter. The Newton structure is a very efficient implementation of Lagrange interpolation using a variable fractional delay filter structure. Through the developed demonstration, a new approach is proposed to define the ideal fractional delay filter as the limit of any digital filter implementing on Lagrange interpolation. This letter also proves that the Z -transform expression of the ideal fractional delay has a fully defined frequency response on the unit circle.

The Numerical Investigation of Optical Error Compensation for Dynamic Target by FSM in Photoelectric Mast

In this paper, firstly, based on the basic control equations of fluid mechanics, the effects of the fluid on force and vortex induced vibration around underwater submarine model are studied and discussed, employing the finite volume method by hierarchy grids. Secondly, the structural characteristics, transfer functions and control strategies of Steering Mirror Fast (FSM) are analyzed and obtained. The disturbance of moment also has been resolved to optical axis coordinate system. Finally, take the optical model of submarine as the research background, the effects of the FSM on the stability improvement of photoelectric tracking system are discussed. The results show that the disturbance of submarine moments mainly origin from the vortex induced vibration. The dynamic target tracking error could be suppressed. This research explores vortex induced vibration control in optical filter. Therefore, it holds certain scientific significance and practical value.

Specific modes of vibratory technological machines: mathematical models, peculiarities of interaction of system elements

The methodological basis of constructing mathematical models of vibratory technological machines is developed in the article. An approach is proposed that makes it possible to introduce a vibration table in a specific mode that provides conditions for the dynamic damping of oscillations for the zone of placement of a vibration exciter while providing specified vibration parameters in the working zone of the vibration table. The aim of the work is to develop methods of mathematical modeling, oriented to technological processes with long cycles. The technologies of structural mathematical modeling are used with structural schemes, transfer functions and amplitude-frequency characteristics. The concept of the work is to test the possibilities of combining the conditions for reducing loads with working components of a vibration exciter while simultaneously maintaining sufficiently wide limits in variating the parameters of the vibrational field.

Lorentz force filtering and fast steering mirror optical compensation in optical axis stability control for photoelectric mast

The photoelectric mast equipped on the underwater vehicle is the key equipment for photoelectric tracking. While the vehicle moves under water, especially, at high speed, more complex vortexes are generated at the surface, which will give rise to great disturbance to the stability of optical axis. In this paper, firstly, based on the basic control equations of electromagnetic field and fluid mechanics, the effects of the Lorentz force on flow field structure and vortex induced vibration are numerical simulated with using the finite volume method with hierarchy grids. Secondly, the structural characteristics, transfer functions and PID control strategies of fast steering mirror (FSM) are analyzed. Finally, combining the transfer function of FSM and the force characteristics, the effect of the composite control on the stability of submarine photoelectric tracking system is discussed by MATLAB. The results show that the Lorentz force can adjust the boundary layer and suppress vortex induced vibration, based on which the FSM can be used to further improve the accuracy of the optical tracking system. This research offers a new exploration in the field of electromagnetic fluid control, as well as a novel development of the traditional research direction of fluid mechanics. Therefore it appears to have a certain scientific significance and practical value.

Empirical Vibration Synthesis Method for Electric Machines by Transfer Functions and Electromagnetic Analysis

This paper proposes an accurate empirical vibration synthesis methodology for the vibration response of electric machines. The proposed method enables designers of the electric machines to synthesize the vibration response of mechanical components that are connected to the electric machine's stator, for given magnetic force profiles. It utilizes the experimentally obtained structural transfer functions by vibration testing, and the magnetic forces computed by magnetostatic finite element analyses. The proposed method has been applied to synthesize vibration responses of an interior permanent magnet machine. The synthesized vibration response agrees very well with the measured vibration response for a wide frequency range and various rotational speeds.

Structural-Parametric Models and Transfer Functions of Electromagnetoelastic Actuators Nano- and Microdisplacement for Mechatronic Systems

Structural-parametric models, parametric structural schematic diagrams and transfer functions of electromagnetoelastic actuators are determined. A generalized parametric structural schematic diagram of the electromagnetoelastic actuator is constructed. Effects of geometric and physical parameters of actuators and external load on its dynamic characteristics are determined. For calculations the mechatronic systems with piezoactuators for nano- and microdisplacement the parametric structural schematic diagrams and the transfer functions of piezoactuators are obtained.

Research on Vibration Transfer Characteristics of the Bolt Connection Structure

Bolt pre-tightening force and the characteristics of contact surfaces have great influence on structural modes and transfer functions, which are usually ignored due to the difficulty in treatment. Using the ANSYS Workbench software, the finite element model of the whole structure and the bolt connection structure are established, and the vibration modes and harmonic responses in different structures are investigated. By comparing the finite element calculation data and test data, the influence of bolt connection structure is analyzed. Comparing the results when the bolt pre-tightening force is varied, the results show that the natural frequencies of bolt connection structure decrease compared with the whole structure. The transfer characteristics of the system are influenced by the pre-tightening force, and the natural frequencies increase with the increase in pre-tightening force.

In-Service Condition Assessment of a Long-Span Suspension Bridge Using Temperature-Induced Strain Data

AbstractMonitoring data of civil structures mainly include load- and temperature-induced structural responses. Traditional damage-detection methods use vibration-based structure responses by eliminating temperature effects from the measured data. In this article, a new structural damage identification method using temperature-induced responses is proposed and applied to a long-span suspension bridge. The novelty of the method is that it derives the structural transfer function by taking temperature load variation and temperature-induced strains input–output data; thus, it is able to accurately reveal inherent structural characteristics, unlike traditional methods that use structural vibration responses from ambient testing. In the proposed method, the temperature-induced strain is separated from measured strain responses with ensemble empirical mode decomposition (EEMD) technology, and a Euclidean distance-based damage index is defined that uses temperature variations and temperature-induced strains for s...

Evaluation of free-field transfer functions in anomalous reverberant fields

The structural-acoustic transfer functions of complex structures are often measured in anomalous reverberant environments. Aiming to eliminating the influences of these reverberant fields on structural-acoustic transfer functions, an impulse-based synchronization average evaluation method is proposed. Structures are actuated according to an impulse signal, and the response signals are synchronized in time and averaged in space. This method does not require complex data processing, and the free-field transfer functions can be obtained based on the measurements in reverberant fields and the transfer characteristics of the structures are preserved. Moreover, in combination with the principle of reciprocity, the proposed method does not require the installation of impulse actuators in structures. The proposed method is verified numerically and validated in a deep lake experiment using a cylindrical model. The results show that the structural-acoustic transfer functions in the profundal zone can be effectively evaluated using the data collected in the shallow zone, and the error is less than 3dB at most frequencies.

Vibration Prediction Method of Electric Machines by using Experimental Transfer Function and Magnetostatic Finite Element Analysis

This paper concerns the noise and structural vibration caused by rotating electric machines. Special attention is given to the magnetic-force induced vibration response of interior-permanent magnet machines. In general, to accurately predict and control the vibration response caused by the electric machines, it is inevitable to model not only the magnetic force induced by the fluctuation of magnetic fields, but also the structural dynamic characteristics of the electric machines and surrounding structural components. However, due to complicated boundary conditions and material properties of the components, such as laminated magnetic cores and varnished windings, it has been a challenge to compute accurate vibration response caused by the electric machines even after their physical models are available. In this paper, we propose a highly-accurate vibration prediction method that couples experimentally-obtained discrete structural transfer functions and numerically-obtained distributed magnetic-forces. The proposed vibration synthesis methodology has been applied to predict vibration responses of an interior permanent magnet machine. The results show that the predicted vibration response of the electric machine agrees very well with the measured vibration response for several load conditions, for wide frequency ranges.