A review on plate and shell theories for laminated and sandwich structures highlighting the finite element method

It has been over two decades since the publication of pioneer works about the power transformer diagnostics based on monitoring of their acoustic fingerprints. Since then, there has been great progress in this field and the methods used are as complex as ever. Any unnecessary intervention on a power transformer implies its temporary disconnection from the power grid. The inability to supply electricity to the customer means not only financial loss for the utility but also generates a non-material loss, e.g., the loss of reputation to the customer. Faster, more accurate, more reliable, and less invasive diagnosis is the main reason behind development and improvement in this field. The main goal of this paper is to categorize and review state-of-the art of vibro-acoustic diagnostic methods for power transformers. This paper opens with a brief note about continuous condition monitoring, after which we overview the causes of transformer vibrations as well as the collection and preprocessing of diagnostic data. Then, we review and categorize works related to the acoustic condition assessment of power transformers considering both: feature extraction in the time, frequency, time-frequency domain, and mathematical modeling and system identification of dynamic systems.

/pdf/vibro-acoustic-methods-in-the-condition-assessment-of-power-596hhz2h8b.pdf

Vibro-Acoustic Methods in the Condition Assessment of Power Transformers: A Survey

Vibroacoustic analysis of double-wall sandwich panels with viscoelastic core

Windings are the most critical components in power transformers, and the related mechanical degradation assessment has attracted an increasing attention in recent years In this paper, a novel feature extraction method based on an amalgamation of variational mode decomposition (VMD) and wavelet transform (WT) is encouraged, which correlates the nonlinear structural parameters of windings with the mechanical degradation First, the winding vibration mechanism is explored, and the relationship between the transient vibration of windings and the structural parameters is studied Next, the vibrations are decomposed into multiple modes using VMD, and the feature vector is extracted from the modes by means of WT After that, three classification algorithms are employed, including support vector machine, naive Bayes classifier, and artificial neural network In the experiment, the winding structure degradation was simulated via adjusting the clamping force The vibrations from three winding units are used to train and test the classifiers, and their performance is evaluated and compared The results demonstrate that the proposed feature extraction method with an appropriate classifier is effective for winding degradation assessment

A Variational Mode Decomposition Approach for Degradation Assessment of Power Transformer Windings

Numerical modeling of sound and vibration reduction using viscoelastic materials and shunted piezoelectric patches

Noise and vibration of a power transformer under an electrical excitation

This paper presents numerical and experimental validation of results obtained by a shell finite element, which has been developed for modeling of the dynamic behavior of sandwich multilayered structures with a viscoelastic core. The proposed shell finite element is very easy to implement in existing finite element solvers, since it uses only the displacements as degrees of freedom at external faces and at inter-layer interfaces. The displacement field is linearly interpolated in the thickness direction of each layer, and analytical integration is made in the thickness direction in order to avoid meshing of each sandwich layer by solid elements. Only the two dimensional mid-surface of reference is meshed, facilitating the mesh generation task. A simplified modal approach using a real modal basis is also proposed to efficiently calculate the dynamic response of the sandwich structure. The proposed method reduces the memory size and computing time and takes into account the frequency-dependence of the polymer core mechanical properties. Results obtained by the proposed element in conjunction with the simplified modal method have been numerically and experimentally validated by comparison to results obtained by commercial software codes (MSC/nastran and ESI/rayon-vtm), and to measurements done on automobile windscreens.

Finite element analysis of the dynamic behavior of a laminated windscreen with frequency dependent viscoelastic core

Multiphysics model for predicting the sound radiation of a single-layer air-core coil

In this paper, the vibro-acoustic response of a clo sed vehicle (Renault B95) is computed using a proto type tool based on the VPS software developed by ESI Group. This prototype tool takes into account the frequency dependence of the modulus of viscoelastic materials represented by the PVB of the windscreen and joints between the vehicle’s body and glass sur faces. In a first step, the accelerations at differ ent points of the windscreen and pressures inside the cabin are c omputed and compared to those obtained by NASTRAN software. In a second step, these results are compa red with experiments obtained by Renault using accelerometers and those obtained by the University of Technology of Compiegne using a 3D laser vibrometer. Comparisons show an acceptable agreement between different numerical and experimental results.

/pdf/numerical-modelling-of-the-vibro-acoustic-behavior-of-a-4oewe4iwkm.pdf

Numerical modelling of the Vibro-Acoustic behavior of a closed vehicle with frequency dependent polymer materials

The dynamic response of a laminated windshield with a viscoelastic core is computed using a simplified modal method combined with a quadratic sandwich finite element. The method is based on a modal expansion of the displacement field using a constant young modulus of the core layer. The frequency dependence of the complex modulus of the core is taken into account using the residual dynamic stiffness matrix. The method is applied to predict the frequency response of two types of laminated windshield using a standard and acoustic PVB cores. Numerical results are compared in a first step with those obtained using the direct solver of Nastran software, and in a second step with experimental results obtained by a laser vibrometer. Comparisons show a very good agreement between experimental and numerical results and demonstrate the efficiency of the simplified modal solving method and the developed parabolic sandwich element. The method will be applied to compute the coupled vibro-acoustic frequency response of...

A dynamic response of a laminated windshield with viscoelastic core − numerical vs. experimental results

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