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Accurate frequency estimation is crucial for researchers and engineers engaged in audio processing, communication, and vibration analysis. In the case of short signals containing low-frequency components and a non-integer number of periods, conventional frequency estimation algorithms, such as DFT, prove inadequate in precisely identifying signal frequencies due to inherent limitations in frequency resolution and the presence of the leakage phenomenon. Interpolation methods offer the potential to enhance frequency estimation by discerning frequencies at intermediate positions within the spectrum. Precisely determining amplitude values across spectral bins is critical when employing such methods. Remarkably, while the initial phase of a signal can significantly alter the spectrum, its influence on amplitude distribution remains an aspect yet to be thoroughly researched. In this study, we use Python to implement the DFT algorithm and analyze how the initial phase affects the results. We are conducting tests using generated sinusoidal signals and signals processed with Hamming and Hanning windowing functions to determine the extent of changes in amplitude. The findings indicate that a signal's time shift can influence the spectrum significantly, resulting in inaccurate frequency estimations and erroneous conclusions in signal analysis. [ABSTRACT FROM AUTHOR]

Thispaper presentssimulations that highlight the influence of the friction pendulum radius on the behavior of isolated structures. A model was created in SolidWorks, whichis employed to find out the structural response. The excitationin term ofdisplacements, ensured by a feature of the software program,follows asine function. The study has shown the frequencyevolution with the radius increase, along with the displacement of the isolated structure.

This paper introduces a device dedicated to acoustic excitation for modal analysis of plates. A particular setup is requested since the system should produce acoustic excitation with high power in the 10...120 Hz frequency range. The system comprises a signal generator, an amplifier powered by a car starter or a battery, and a subwoofer. This system permits setting the generated frequency around the resonance frequency with reasonable frequency and amplitude stability. We present the system's design and test its performance on a rectangular plate. In our laboratory experiments, we achieved the desired structural behavior. [ABSTRACT FROM AUTHOR]

The current paper explores a novel approach for determining temperature variations by integrating the modal parameters and AI techniques. The research focuses on the development of a comprehensive dataset for training an AI model encompassing an analytical method that considers thermal conditions and natural frequencies. Traditional methods of temperature measurement, like infrared and platinum resistance thermometers, often face limitations in terms of accuracy, especially in complex or dynamic environments having an uncertainty of ±3.6 °C [1], respectively ±0.2 °C [2]. In this study, we propose a methodology that harnesses the inherent relationship between axial loads caused by temperature variations and the change in natural frequencies of a double clamped steel beam. The measured natural frequency data is collected and fed into the AI model, specifically, for a robust temperature estimation, obtaining a maximum predicted temperature deviation of 0.386 °C. [ABSTRACT FROM AUTHOR]

Signals of short duration and containing a small number of cycles require special procedures if the precise estimation of their frequencies is intended. In this paper, we present an algorithm that allows accurate estimation of frequencies and simultaneously explains the decision regarding the prediction made. We first show why predictions regarding the frequency of signals mentioned above can contain significant errors and the prediction dependency on the analysis time. We then prove that the errors are systematic, and it is possible to train a neural network to quantify the errors and later correct the predictions. The algorithm also indicates the level of error by analyzing the signal-to-noise ratio. The algorithm was tested for numerous similar cases and proved to be reliable. At the end of the paper, we present how to use the algorithm using a signal generated with a known frequency. [ABSTRACT FROM AUTHOR]

When considering damage detection using the natural frequencies of structures, small frequency drops can indicate either the presence of cracks or a temperature change. This change can lead to additional stress affecting the modal parameters for specific structures, making it much harder to detect, locate, and evaluate damage accurately. The current research aims to describe a method for detecting transverse cracks in beams, considering temperature variations. The considered beam is fixed at both ends, thus inducing axial forces when the temperature is increased. The influence of temperature is considered using adjustment coefficients developed for each vibration mode. This coefficient can be used to accurately calculate the natural frequency for an intact or damaged beam. An analytical method for determining the natural frequencies caused by the changing temperature and the presence of a transverse crack is described and used to generate data for training a feedforward artificial neural network (ANN). The ANN's capability of determining the position of transverse cracks in double-clamped beams subjected to small temperature changes is proven by creating numerical simulations with known crack positions and thermal conditions for testing the developed method. [ABSTRACT FROM AUTHOR]

The paper focus on showing using statistical analysis the relevance of vibration, temperature, and humidity on a crimped connection between a copper wire and copper terminal. As a primary metric it was used, as baseline, the behavior of the resistivity of a crimped assembly after vibration, humidity, and temperature tests in order to analyze and conclude if there is a significant relation between all these environmental factors and the crimped height. The core activity of this experiment consists in the analysis performed on 50 crimped assemblies where the main dimensional characteristics were achieved using a specific crimping normative, followed by a sequence of environmental testing steps, in order to obtain a significant number of data points that enable us to create a proper statistical model to analyze and conclude the influence of vibration (one of the main environmental factors tracked) over the crimped assembly. [ABSTRACT FROM AUTHOR]

Ultrasonic welding parameters originally provided by the components supplier caused negative pull/peel tension results. In this paper, we present a method to find the optimal parameters for the ultrasonic welding of copper elements. These elements represent components inside an electrical harness from automotive industry: coper plate and copper wire strands. The design of experiments (DoE) was used as a method within the Six Sigma approach. We succeeded in obtaining welding parameters that ensure successfully passing the pull/peel tension test. [ABSTRACT FROM AUTHOR]

This paper presents a method for detecting a crack in simply supported beams by identifying its location and severity (depth). The method is based on the measured natural frequencies for several bending vibration modes of an intact and cracked beam and the Particle Swarm Optimization (PSO). To explain the approach, we calculate the relative frequency shifts (RFS) for eight vibration modes for all possible damage cases. To this aim, we use a mathematical relation deduced in previous research. Next, we monitor the natural frequencies, and in case of arising changes, we calculate the RFSs. We subtract, separately for all modes, the measured RFSs from all calculated RFSs. Considering the absolute values the subtractions achieve, we obtain eight surfaces that achieve elevation zero if the calculated and measured RFSs coincide. The zero-elevation points form curves with different shapes for the different vibration modes. The intersection of these curves, thus the location where all surfaces have zero elevation, indicates the damage location and severity. Adding the elevation values of the eight surfaces point by point, we obtain a new surface that has two points (due to symmetry) with zero elevation. The coordinates of these points indicate the damage parameters. We use the generated surface as an objective function and find the coordinates of the minima involving PSO. Using this method, we accurately identified the damage location and severity. [ABSTRACT FROM AUTHOR]

The paper presents the strain energy of the circular plate clamped all around through a relation obtained analytically and the graphic representation of the modal shapes and the maximum normalized strain energy along the x axis. Depending on the number of nodal circles s and the nodal diameters n, the maximum strain energy can be both in the center of the circular plate clamped all around, as well as the first ventral points from the center of the circular plate towards the outside of the plate. [ABSTRACT FROM AUTHOR]

The first part of the paper presents a study regarding the dynamics behavior of thin circular plate clamped all around. An analytical investigation is performed and the results in terms of mode shapes are used to highlight the plate's dynamics. The modal shapes are obtained using Bessel functions and their graphic representation is presented in 3D by using MS Excel software. [ABSTRACT FROM AUTHOR]