A multi-resolution based method to precise identify the natural frequencies of beams with application in damage detection

The paper presents a procedure to precisely estimate the natural frequencies of structures. It implies the acoustic excitation of the structure and the evaluation of the frequencies from the response signals, involving an advanced method developed by the authors. The study is performed on a cantilever beam. To demonstrate the efficiency of the contrived procedure, the values of the frequencies by applying this procedure are compared whit those obtained by standard frequency estimation made for the response to an impulsive excitation.

Section: Methodsmentioning

confidence: 99%

“…In previous studies [12,13], we developed an algorithm to accurately evaluate the frequencies of signals achieved by measurements. In this paper, we introduce an acoustic excitation method that transfers the energy to the structure in a narrow frequency band and ensures high-quality signals to be processed for frequency evaluation.…”

Section: Introductionmentioning

confidence: 99%

A procedure for an accurate estimation of the natural frequencies of structures

Gillich¹,

Mituletu²,

Nedelcu³

et al. 2018

“…In previous research [15][16][17][18], the authors developed robust techniques for assessing transverse or complex-shaped cracks for beams and plates, regardless of the structure's boundary conditions. All these techniques are based on the natural frequency shifts and evaluate the severity by energetic methods.…”

Section: Introductionmentioning

confidence: 99%

The effect of a crack near the fixed end on the natural frequencies of a cantilever beam

Tufiși¹,

Gillich²,

Aman³

2019

The paper examines how a transverse crack near the fixed end of a beam affects the natural frequency drop. It is known that the decrease in the frequency due to a crack depends on the position of the damage and its severity. This happens because the slice of the beam on which the crack is located changes its stiffness. Consequently, the damaged beam is no longer able to store the identical amount of energy as the healthy one. In addition, the field of stresses and deformations on an extended area around the crack is disturbed. This alteration can manifest freely for most positions of the crack along the beam. For this case, there is a direct relationship between the defect position and the frequency change, given by the modal curvature of the beam. Close to the fixed end, the field of stress and deformation is hindered on one side of the crack by the fixed end condition. In this way, the crack will produce a lower frequency drop compared with what it is expected. We performed simulations to obtain the frequency drop if the crack is located very close to the fixed end. With these values, we plot the regression curve and estimate the frequencies which should result for a crack located exactly on the fixed end of the beam if symmetric fields of stress and strain are possible. The results are necessary because the frequency drop characterizes the damage severity, further used in the damage detection processes.

“…In previous studies [15][16][17][18], the authors developed a robust method for detecting, locating and evaluating transverse cracks in all types of beams, regardless of the constraining method, based on the natural frequency changes.…”

Section: Introductionmentioning

confidence: 99%

Numerical study on complex shaped cracks in cantilever beams concerning frequency and stiffness changes

Tufiși¹,

Gillich²,

Nedelcu³

et al. 2018

The paper presents a mathematical relation to express the effects of a T-shaped crack on beam-like structures. The study is performed by using the finite element method (FEM) and contrived analytical formulas for proving the existing correlation between deflection, strain energy, and natural frequency changes. The damaged beam static and dynamic behaviors are analyzed by means of the FEM. The frequency shift for the first mode of vibration derived directly was compared with the frequency alteration calculated involving the change in the beam deflection for several scenarios of the T-shaped crack. The frequency shift is derived using the relations between deflection and natural frequency. As the final step in the research, we compared the outcomes for the same crack with the results achieved from a beam suffering a loss of stiffness.