This paper introduces a method to identify damages in beam-like structures by analyzing the natural frequency changes of the first six transversal vibration modes. A correlation between the damage location and frequency change is established for each mode separately, by considering the modal strain energy stored in that location. The mathematical relation describing this correlation is used to characterize the dynamic behavior of a beam with a damage of known position and to derive its Damage Location Indicator (DLI) as a six-term vector. The method consists in comparing the vectors describing the damage at any possible location along the beam with the Damage Signature (DS), which is achieved from the measurements that compare the beam's frequencies in healthy and damaged state. A modified Kullback-Leibler Divergence is used to assess the damage location. In order to permit early damage assessment, an improved frequency evaluation algorithm was developed. It is based on signal truncation and consequent spectral lines rearrangement, in order to accurately find the strongest spectral components. The effectiveness of the proposed method is demonstrated by simulations and experiments.

A direct approach for the calculation of the natural frequencies and vibration mode shapes of a perfectly clamped-free beam with additional stepwise eccentric distributed masses is developed, along with its corresponding equations. Firstly there is contrived influence of a mass, located on a given position along the beam, upon the modal energies, via an energy analysis method. Secondly, the mass participation coefficient is defined as a function of the mass location and the bending vibration mode number. The proposed coefficient is employed to deduce the mathematical relation for the frequencies of beams with supplementary eccentric loads, generally available for any boundary conditions. The accuracy of the obtained mathematical relation was examined in comparison with the numerical simulation and experimental results for a cantilever beam. For this aim, several finite element models have been developed, individualized by the disturbance extent and the mass increase or decrease. Also, one real system was tested. The comparisons between the analytically achieved results and those obtained from experiments proved the accuracy of the developed mathematical relation.

Nowadays, the damage severity evaluation in mechanical structures is mostly performed by analyzing the natural frequency shift. The non-isotropic materials, as the multi-layered ones, are wide-spread in industrial applications, due to their interesting physic-mechanical properties. Thus, a deeper approach of multi-layered beams becomes an important request in the research domain. This paper introduces a damage severity estimator by expressing the crack evolution as a function of stored energy. It is well known that the energy stored in a beam without damage is greater than the energy of that damaged beam. As a consequence, the beam deflection can be related to the stored energy. In this regard, the possibility to split the damage localization and the damage severity assessment has been proven, and also the graphical evolution of the natural frequency shift has been achieved as a function of the crack depth. The results achieved by the finite element method (FEM) and experimental tests are given in tables and graphics. For the first five vibration modes, a comparison was made between frequencies accomplished by analytical, numerical and experimental analyses, in order to give more credibility to the accuracy of the research data presented in this paper.

Accurate frequency evaluation is very important in the damage detection processes because the dynamic response is less sensitive to damage. Therefore, to be able to detect transverse cracks in early stage, it is necessary to read precisely the frequencies. In the literature are presented several methods, more or less complex and resource consuming, destined to improve the frequencies readability. In practical applications simple and fast methods for frequency evaluation are requested; the process should be adequate to be automated. The paper presents an original method for identifying the correct frequency of generated or acquired signals. The method is based on the analysis of the original signal cropped by rectangular windows in order to rearrange successively the spectral lines aiming to find the highest peak achieved in a region of interest for the frequency-amplitude pairs.

Frequency and magnitude evaluation are two of the main signal analysis tasks in the electrical power systems. This paper presents a simple and robust algorithm which enables an accurate estimation of the harmonic parameters of signals with unknown frequency. Differing from the existing approaches, frequency and magnitude of harmonic waves are simultaneously and precisely identified. The proposed algorithm can be applied in spectral estimation as well as in system identification, signal reconstruction, and other important signal processing issues. Algorithm operational efficiency was proved by frequency and amplitude estimation of generated signals with known frequency achieved their aim.

The paper presents results obtained for the cooling process of a new-designed SMA-based wave generator (SMA-WG), which represents the deforming component of a harmonic drive. SMA-WG is driven by two-way SMA elements and, due to this, it does not require a driving motor. Correct SMA-WG operation supposes a simulated rotational ellipse performed by SMA elements, which is achieved by a cyclical control of temperature. SMA heating is electrically controlled, but for rapid cooling, a forced air flow is aimed. Therefore, SMA-WG design must involve special characteristics determined by numerical flow simulation.