Showing papers by "Gilbert-Rainer Gillich published in 2014"
TL;DR: A new method, based on natural frequency changes, able to detect damages in beam-like structures and to assess their location and severity, considering the particular manner in which the natural frequencies of the weak-axis bending vibration modes change due to the occurrence of discontinuities is presented.
112 citations
TL;DR: In this article, the authors proposed an algorithm to assess transversal cracks in composite structures based on natural frequency changes due to damage, which is performed in two steps; first the crack location is found, and afterwards an evaluation of its severity is performed.
Abstract: An algorithm to assess transversal cracks in composite structures based on natural frequency changes due to damage is proposed. The damage assessment is performed in two steps; first the crack location is found, and afterwards an evaluation of its severity is performed. The technique is based on a mathematical relation that provides the exact solution for the frequency changes of bending vibration modes, considering two terms. The first term is related to the strain energy stored in the beam, while the second term considers the increase of flexibility due to damage. Thus, it is possible to separate the problems of localization and severity assessment, which makes the localization process independent of the beams cross-section shape and boundary conditions. In fact, the process consists of comparing vectors representing the measured frequency shifts with patterns constructed using the mode shape curvatures of the undamaged beam. Once the damage is localized, the evaluation of its severity is made taking into account the global rigidity reduction. The damage identification algorithm was validated by experiments performed on numerous sandwich panel specimens.
45 citations
TL;DR: In this article, the authors presented the modeling and simulation of the thermal transfer in the transformers from the high electric voltage stations using finite element method, which is based on the creating of a geometrical model which follows the transformer's sizes and material properties, real constants are established by standards.
Abstract: This present paper presents the modeling and simulation of the thermal transfer in the transformers from the high electric voltage stations using finite element method As the transformers are of high power and are inversed in oil, a particular interest represents the maintenance of physical and chemical parameters of oil as long a time during operation For this, one presents the coupled analysis electromagnetic field and thermal field The procedure of coupled analysis consists of a quantity of heat release when passing electric current through the coil of transformers The amount of heat affects the chemical properties of the oil Because overloads occurring in their operation, the chemical properties of the oils worsen in time and may lead to premature aging and scrapping of them The simulation is based on the creating of a geometrical model which follows the transformer’s sizes and material properties, real constants are established by standards After the simulations an optimal solution is obtained regarding the correct usage of the transformers
17 citations
01 Jan 2014
TL;DR: In this paper, the influence of the damage geometry on the natural frequencies of beams considering the two above mentioned aspects was investigated and a relation between frequency changes and damage geometry and location was contrived.
Abstract: Global non-destructive testing methods use changes in modal data as damage indicators. Depending on their geometry, damages influence the modal parameters in different way. While breathing cracks influence the natural frequencies due to only stiffness change, open cracks affect supplementary these frequencies due to loss of mass. This paper describes a study devoted to clarify the influence of the damage geometry on the natural frequencies of beams considering the two above mentioned aspects. First, analytical and numerical analyses are performed, in order to highlight the effect of mass changes on the frequency changes. Afterwards, the study focuses on breathing cracks in open and closing stages as well as on open cracks and emphasizes the influence of the geometrical discontinuity. It was demonstrated that, for beams with a breathing crack, a two degrees of freedom model is necessary to characterize its dynamic behavior. Finally, a relation between frequency changes and damage geometry and location is contrived.
15 citations
01 Jan 2014
TL;DR: In this paper, a finite element analysis (FEA) and analytical investigations are performed on the dynamics of thin circular plates, embedded on the circumference, and the results in terms of frequencies and modes are used to highlight the plate's dynamics.
Abstract: This paper presents a study regarding the dynamics of thin circular plates, embedded on the circumference. A finite element analysis (FEA) as well as analytical investigations is performed, and the results in terms of frequencies and mode shapes are used to highlight the plate's dynamics. First we demonstrated the good fit between the results obtained in different ways. Analyzing the plate's dynamic behavior, we identified vibration modes able to be used to extract patterns characterizing a damage location. These damage signatures can be used, similar as in the case of beams, to find the damage location.
7 citations
01 Jan 2014
TL;DR: In this paper, a mathematical expression relating damage location and depth to the frequency shifts of the bending vibration modes is presented, which permits the extraction of a series of coefficients that characterize each damage location.
Abstract: Vibration-based damage detection techniques use the change in modal data as an indicator to assess damages in the structure. Knowing the structural dynamic characteristics of the healthy and damaged structure, the estimation of the damage location and severity is possible by solving an inverse problem. This paper presents a mathematical expression relating damage location and depth to the frequency shifts of the bending vibration modes. This expression permits the extraction of a series of coefficients that characterize each damage location and are independent of the damage severity. The vector aggregating these coefficients for a given location constitutes a Damage Location Indicator (DLI) that unambiguously characterizes the position of a geometrical discontinuity in the beam. A set of vectors typifying all locations along the beam may be used as patters opposable to the damage signature found by measurements. The similarity between the signature and one of the patterns indicates the location of damage.
3 citations
TL;DR: In this article, the influence of mass changes upon the natural frequencies of beam and to use it as a baseline in damage detection methods is presented. But, the mass decrease is a phenomenon associated with numerous corrosion mechanisms.
Abstract: This paper present a procedure to detect wear or corrosion in structural elements based on frequency changes. Several methods to damage assessment are known, but these are mainly addressed to open cracks without considering the loss of mass. Since the mass decrease is a phenomenon associated with numerous corrosion mechanisms, the idea of this paper was to establish the influence of mass changes upon the natural frequencies of beam and to use it as a baseline in damage detection methods. Consequently, the research was conducted in two steps; first we analyzed the beam dynamics for a segment with reduced volumetric mass density but maintaining the global beam rigidity, succeeding to find the correlation between the frequency changes in the transversal vibration modes and mass loss in form of a mathematical relation. Afterwards, this relation was incorporated in the relation who predicts the frequency decreases due to stiffness diminish, in order to fit it for wear and corrosion assessment. The method’s robustness and reliability was proved by FEM simulations as well as by experiments.
1 citations
TL;DR: In this paper, a non-destructive method to locate and size damages in frame structures, performed by examining and interpreting changes in measured vibration response, is presented, which permits to locate cracks in spatial structures.
Abstract: This paper presents a novel non-destructive method to locate and size damages in frame structures, performed by examining and interpreting changes in measured vibration response. The method bases on a relation, prior contrived by the authors, between the strain energy distribution in the structure for the transversal vibration modes and the modal changes (in terms of natural frequencies) due to damage. Using this relation a damage location indicator DLI was derived, which permits to locate cracks in spatial structures. In this paper an L-frame is considered for proving the applicability of this method. First the mathematical expressions for the modes shapes and their derivatives were determined and simulation result compared with that obtained by finite element analysis. Afterwards patterns characterizing damage locations were derived and compared with measurement results on the real structure; the DLI permitted accurate localization of any crack placed in the two structural elements.
01 Jan 2014
TL;DR: In this paper, the authors compare two methods to determine the severity of a damage occurring in cantilever; the first method is well-known in the literature and base on an approach from fracture mechanics, while the second is contrived by the authors and based on the transversal deflection under small loads.
Abstract: This paper compare two methods to determine the severity of a damage occurring in cantilever; the first method is well-known in the literature and base on an approach from fracture mechanics, while the second is contrived by the authors and base on the transversal deflection under small loads. First the paper demonstrate the relation existing between the stiffness reduction due to damage (i.e. the value of the transversal deflection) and the change of the natural frequencies, exemplified for three shapes of the transversal cross-section. It is proofed that the relation is valid for all three cases, square, hexagon and circle, the damage depth being accurate determined. Afterwards, the results are compared with that provided by numerous researchers which used the fracture mechanics approach; a good concordance can be found, with the mention that the method developed by us is more accurate. This is justified by the fact that our method does not introduce empirical relations, being based on the formulized physical phenomena alone.