Papers by Gilbert-Rainer Gillich
Vibration-Based Techniques for Damage Detection and Localization in Engineering Structures, 2018
Applied Mechanics and Materials, 2015
Transverse cracks affect the stiffness and consequently the dynamic behavior of beams, by alterin... more Transverse cracks affect the stiffness and consequently the dynamic behavior of beams, by altering the natural frequencies. Actual cracked beam models are not able to explain in-deep the vibration mechanism and, therefore, no mathematical relation able to predict frequency changes due to damage exist. This paper proposes a new damage model which better explain the dynamic behavior of beams with open and closed cracks and a mathematical relation able to predict the frequency changes due to damage. In contrast to actual models, a global approach is used, by considering the influence of the stored energy distribution for each transversal vibration mode. Since the energy loss globally quantifies the state change due to damage, it was possible to replace the cracked beam with an equivalent one having constant but reduced stiffness. Based on it, a relation indicating the frequency drop damage was contrived and tested, by means of the finite element analysis, for various damage types and l...
Vibroengineering PROCEDIA
During functioning time, structures such as beams are subjected to a variety of loads caused by t... more During functioning time, structures such as beams are subjected to a variety of loads caused by the working conditions and environment, which can lead to the development of cracks. The current research is concerned with detecting the presence and location of two transverse breathing cracks, in cantilever beams. Starting from the known fact that damages produce a stiffness degradation in structures altering their dynamic parameters, we performed modal simulations of damaged beams to determine their natural frequencies. By using the simulation data, we trained an artificial neural network (ANN), using the feedforward backpropagation algorithm, that is capable to detect the presence of the cracks, their position and for the case when the damages are in proximity, the model can determine if the cracks occur on the same face or opposite faces.
Romanian Journal of Acoustics and Vibration, Jul 22, 2021
In this paper, we propose a model for detecting transverse cracks in simply supported beams, whic... more In this paper, we propose a model for detecting transverse cracks in simply supported beams, which can be part of more complex structural systems. The relative frequency shifts of the structure are considered a basis for damage identification. An original method developed by the authors is employed to evaluate the required modal parameters. A multi-stage optimization approach based on the rigidity loss suffered by the affected structure is employed to accurately recognize the locations of potential cracks. The outcome presented in this research shows the computational ability of the proposed model to indicate the presence and location of damages in beam-like structures.
This paper introduces a robust method for vibration-based damage assessment, which is based on a ... more This paper introduces a robust method for vibration-based damage assessment, which is based on a mathematical relation contrived by the authors that involves the frequency shifts, the damage size and position. Databases containing damage indicators for all possible damage scenarios, for three types of beams, were developed by involving this mathematical relation. The proposed damage indicator is expressed using the relative frequency shifts. The damage location and severity can be assessed if the relative frequency shifts are derived from measurements at the initial state and periodically afterwards. The paper investigates the effectiveness of several dissimilarity estimators, to find damage involving frequencies measured without and in the presence of noise.
IOP Conference Series: Materials Science and Engineering, 2020
Detecting damage in the incipient state is of crucial importance in monitoring the health of engi... more Detecting damage in the incipient state is of crucial importance in monitoring the health of engineering structures. Approaching damage detection as an inverse problem is a common method when vibration-based techniques are used. It implies a precise a priori estimation of the modal parameters. We present in this paper a model to predict the frequency changes due to cracks in the side frames of bogies used to detect the welding defects in T-joints. To this aim, we model the structure and perform simulations using the SolidWorks software. The frequencies for the first thirteen modes are derived for the intact structure and the structure with different damage lengths and positions. By these tests, we first desire to find the optimal fixing of the side frame to reduce the number of vibration modes that are not of interest to the damage detection process. After finding the ideal fixing system, we derive patterns, for different defects, in the form of relative frequency shifts. Finally, w...
Analele Universităţii "Constantin Brâncuşi" din Târgu Jiu: Seria Inginerie, 2018
Thispaper presentssimulations that highlight the influence of the friction pendulum radius on the... more 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.
Studia Universitatis Babeș-Bolyai Engineering, 2020
This paper proposes an analytic relation for the deflection of a cantilever beam with a transvers... more This paper proposes an analytic relation for the deflection of a cantilever beam with a transverse crack subjected to dead load. The mathematical relation is deduced involving the decreased capacity of the beam to store energy, which is in direct relation with the crack position and depth. Eventually, the validity of the relation is proved by means of the finite element method.
Journal of Physics: Conference Series, 2021
Non-destructive testing of structures involving vibration-based damage detection methods implies ... more Non-destructive testing of structures involving vibration-based damage detection methods implies knowing the beam’s boundary conditions. For perfect boundary conditions, numerous damage detection methods are developed and ensure more or less accurate estimation of the crack type, position, and severity. On the contrary, for imperfect boundary conditions, which are the real ones, there are only a few dedicated works. This paper presents a methodology that allows the identification of the weak clamping and the crack if both exist. The weak clamping is modelled as a defect that produces an identical relative frequency shift (RFS) for all vibration modes. Therefore, to find the two defects namely the real crack and defect simulating the weakly clamped end, we apply the principle of superposition. The method is implemented as an application written in the Python programming language. Tests show that defects are successfully identified even if there are uncertainties about the fixing of t...
Studia Universitatis Babeș-Bolyai Engineering, 2020
In this paper we propose a procedure to correct Jain's algorithm, which in certain situations... more In this paper we propose a procedure to correct Jain's algorithm, which in certain situations fails in correctly estimating the frequency by indicating frequency values that are very far from the real frequency. It happens because the two points considered for the method proposed by Jain are not on the same lobe. Thus, a method is proposed according to which these points are chosen so that the results are improved.
Studia Universitatis Babeș-Bolyai Engineering, 2020
This paper presents a method to find the severity of a crack for cantilever beams that can be use... more This paper presents a method to find the severity of a crack for cantilever beams that can be used to estimate the frequency drop due to the crack. The severity is found for the crack located at the location where the biggest curvature (or bending moment) is achieved. Because the fixing condition does not permit a symmetrical deformation around the crack, the apparent severity is smaller as the real one. The latter is found by the estimated value of the trend-line at the fixed end, it being constructed on points that consider the crack position (equidistant points in the proximity of the fixed end) and the resulted deflections.
Frequency estimation for short-time signals is difficult because the raw frequency resolution obt... more Frequency estimation for short-time signals is difficult because the raw frequency resolution obtained. The frequency for these signals fall usually at an inter-line position, and is far from the frequency displayed at the spectral line. To get a better frequency estimate, interpolation methods are used to find the peak between the two spectral lines on which the biggest amplitudes are obtained. The number of points involved in the interpolation are two or three. The inter-line position at which this maximum is found is considered to correspond to the true frequency. This paper presents a comparison of the most common interpolation methods that can be used to increase the precision of the frequency estimation, so necessary in the processes of structural health and condition monitoring. An analysis of the accuracy obtained by these methods is made for a generated signal with an acquisition time of around 1 second.
We introduce in this paper an application developed in the Python programming language that can b... more We introduce in this paper an application developed in the Python programming language that can be used to generate digital signals with known frequencies and amplitudes. These digital signals, since have known parameters, can be used to create benchmarks for test and numerical simulation.
The dynamic behaviour control of a butterfly valve is important because, when one of the valve di... more The dynamic behaviour control of a butterfly valve is important because, when one of the valve disc natural frequency is close to the frequency of vortex shedding, which appears when the valve is fully open or partially closed, resonance may appear and vibration with significant amplitudes is generated. This paper presents an example by how the design of a butterfly valve disc can be improved by using a modal analysis performed by means of the finite element method. For this purpose, the research reveals the way in which the natural frequencies of the disc can be modified by applying stiffening ribs or changing the dimensions, respective the position of these ribs.
We present in this paper a simple approach to estimate the frequency components of a signal acqui... more We present in this paper a simple approach to estimate the frequency components of a signal acquired from a freely vibrating structure. A non-contact excitation technique with a controlled bandwidth is involved, which is obtained by employing a loudspeaker producing for a short time a sine signal. This excitation ensures a strong harmonic component in the frequency range of interest and low components outside this range. In this way, the component of interest is not polluted by noise. The relevant portion of the response signal is extracted for spectral analysis. First, an interpolation by applying zero-padding in order to double the number of the spectral bins is performed. In this way, the main lobe in the spectrum contains four points. Based on three of these points a polynomial interpolation is applied and the function crossing the points is found. The maximum is presumed to be the magnitude, while its ordinate is considered the natural frequency. Simulations involving a generat...
IOP Conference Series: Materials Science and Engineering, 2020
We propose in this paper a method to calculate the antiderivative of signals that have the integr... more We propose in this paper a method to calculate the antiderivative of signals that have the integral close to null, as the signals measured on structures during earthquakes are. The method implies performing a series of numerical integration considering the initial value being zero. Afterward, the average value for the primitive function is calculated and considered as initial value: this solves the initial value problem with acceptable precision. Because of the minor errors, the second antiderivative that is the displacement in our case will gain a continuously slight increase. We overcome this problem by finding the trendline and extracting it from the signal representing the second antiderivative. In this way, we obtain accurate instantaneous values for the displacement as well. The algorithm, nominated as PySEMO, is implemented in the Python programming language and used to demonstrate the accuracy of the method. At the end of the paper, we make recommendations for the acquisitio...
The study presented in this paper shows the results of simulation made on a rigid structure isola... more The study presented in this paper shows the results of simulation made on a rigid structure isolated with four simple friction pendulums. We created a model in SolidWorks that was used to find out how the pendulums radii and friction coefficients respectively the frequency of the excitation influences the structural response. It has also been found that the frequency of the structure does not increase with the frequency of excitation if the latter exceeds the natural frequency of the pendulum, but in the post-resonance domain it remains constant taking the value of the natural frequency of the system.
This paper presents a new approach regarding corrosion assessment in beam-like structures based o... more This paper presents a new approach regarding corrosion assessment in beam-like structures based on the frequency shifts. Uniform corrosion is targeted in this research, which had the aim to find damage corrosion signatures from the vibration response. The effect of mass loss and stiffness decrease upon the natural frequencies of beams due corrosion are presented in form of mathematical relations. Afterward, modal analysis by means of the ANSYS program was performed for intact structures and structures with corrosion simulated as loss of material. Experimental modal analysis on test structures using a noncontact excitation method was also made to extract the natural frequencies. For the real structures corrosion was simulated by cutting on a vise machine. The results achieved by the three methods coincide, proving the reliability of the mathematical relations and that these can be used to define signatures applicable to detect corrosion in large structures.
IOP Conference Series: Materials Science and Engineering, 2020
Detecting damage by using vibration signals is popular because it permits evaluating the structur... more Detecting damage by using vibration signals is popular because it permits evaluating the structural integrity without being necessary scanning of the whole structure. The effect of transverse cracks is presented in detail in the literature, but in reality, the cracks can shift the direction of propagation and even split, resulting in the so-called branched crack. The effect of this type of crack is less investigated due to its complexity. We herein propose a simple model to predict frequency changes that occur due to branched cracks. Initially, we present the effect of stiffness reduction along the damaged section on the structure’s natural frequency. Next, we show that the predicted frequency drop is smaller that happens in reality. This is caused by the sudden cross-section reduction in the slice on which the transverse crack branch is. The phenomenon is similar to the stress concentration for static loads. We propose for dynamic systems a factor that considers the energy stored a...
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Papers by Gilbert-Rainer Gillich