46 results on '"Zeno-Iosif Praisach"'
Search Results
2. Eigenvalues of a continuous beam with two spans
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Patric-Timotei STAN and Zeno-Iosif PRAISACH
- Subjects
eigenvalues ,continuous beam ,dynamic behavior ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
Continuous beams can be found in various engineering applications. The dynamic behavior of continuous beams is strongly influenced by the location of the intermediate support. The paper presents the determination of the frequency equation depending on the location of the intermediate support for a continuous beam with two openings for the case that this support can be placed in any position along the length of the beam. Finally, the obtained curves of the eigenvalues for the first six vibration modes are represented.
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- 2024
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3. Dynamic behavior of a simply supported circular plate
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Ionela HAREA and Zeno-Iosif PRAISACH
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Bessel functions ,circular plate ,mode shape ,eigenvalue ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
The paper presents a study regarding the dynamics behavior of thin circular plate simply supported with a relation obtained analytically and the graphic representation of the modal shapes. The modal shapes are obtained using Bessel functions and their graphic representation are compared with Finite Element Method (FEM) by using modal analysis. For the analyzed case, the first 70 eigenvalues and natural frequencies are calculated.
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- 2024
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4. Forward Fall Detection Using Inertial Data and Machine Learning
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Cristian Tufisi, Zeno-Iosif Praisach, Gilbert-Rainer Gillich, Andrade Ionuț Bichescu, and Teodora-Liliana Heler
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forward fall detection ,inertial data ,acceleration ,machine learning ,digital model ,Technology ,Engineering (General). Civil engineering (General) ,TA1-2040 ,Biology (General) ,QH301-705.5 ,Physics ,QC1-999 ,Chemistry ,QD1-999 - Abstract
Fall risk assessment is becoming an important concern, with the realization that falls, and more importantly fainting occurrences, in most cases require immediate medical attention and can pose huge health risks, as well as financial and social burdens. The development of an accurate inertial sensor-based fall risk assessment tool combined with machine learning algorithms could significantly advance healthcare. This research aims to investigate the development of a machine learning approach for falling and fainting detection, using wearable sensors with an emphasis on forward falls. In the current paper we address the problem of the lack of inertial time-series data to differentiate the forward fall event from normal activities, which are difficult to obtain from real subjects. To solve this problem, we proposed a forward dynamics method to generate necessary training data using the OpenSim software, version 4.5. To develop a model as close to the real world as possible, anthropometric data taken from the literature was used. The raw X and Y axes acceleration data was generated using OpenSim software, and ML fall prediction methods were trained. The machine learning (ML) accuracy was validated by testing with data acquired from six unique volunteers, considering the forward fall type.
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- 2024
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5. Essential biomechanical aspects in athletics
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Daniel-Mihai Amariei, Zeno-Iosif Praisach, Zoltan Iosif Korka, and Andrade-Ionuț Bichescu
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biomechanical model ,optimization ,performance ,evaluation ,objectives ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
The aim of this paper is to present theoretical aspects of the study of biomechanics in athletics, which is essential for performance optimization, injury prevention, and improvement of athletes' capabilities. This study contains various research directions in athlete biomechanics as well as biodynamic modeling and simulation in athletics. Finally, aspects of athlete training design and optimization are presented, which are essential for tailoring training programs to the individual needs and goals of athletes.
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- 2023
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6. Determining the Temperature Using Natural Frequencies and Artificial Intelligence
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Alexandra-Teodora AMAN, Zeno-Iosif PRAISACH, Gilbert-Rainer GILLICH, and Vasile Cătălin RUSU
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temperature, natural frequency, artificial intelligence, finite element method, thermal condition ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
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.
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- 2023
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7. Crimping Standard DIN vs USCAR Gap Analysis
- Author
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Florin DRAGOMIR, Tiberiu Ștefan MĂNESCU, and Zeno-Iosif PRAISACH
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crimping standard, gap analysis, crimping microsection, statistical analysis, crimping compression ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
In this paper, the main objective is to present the current status of the automotive specifications related to the crimping process, an in particular how these specifications were adopted by the suppliers of the crimping components (e.g. Terminals and cables). For this reason, we took as reference two of the most worldwide used standards form the automotive manufacturing industry: DIN (“Deutsches Institut für Normung”) with the corresponding Romanian standard SR EN 60352-2:2006 and SAE/USCAR-21 REVISION 3.
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- 2023
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8. The strain energy in loosening the clamped end of a beam (part II)
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Dan-Alexandru PÎRȘAN, Zeno-Iosif PRAISACH, Gilbert-Rainer GILLICH, and Cornel HAȚIEGAN
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weak clamped end, mode shapes, strain energy ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
In the second part of the paper, the dynamic behavior of a doubly clamped beam is presented, where the right clamped end of the beam is weakened by introducing a weakening coefficient. The analytical calculation is based on the determination of the bending moment from the weakened clamped end expressed as a function of slope, after which the modal function, strain energy, and the characteristic equation are determined to obtain the eigenvalues of the first six vibration modes depending on the weakened coefficient of the clamped end. The obtained mode shapes and strain energies are determined for seven values of the weakened coefficient.
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- 2023
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9. Dynamic behavior of a clamped circular plate and strain energy representation (part II)
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Ionela HAREA, Zeno-Iosif PRAISACH, Gilbert-Rainer GILLICH, and Cristian TUFIȘI
- Subjects
circular plate, Bessel functions, strain energy ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
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.
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- 2023
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10. The strain energy in loosening the clamped end of a beam (part I)
- Author
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Patric-Timotei STAN, Zeno-Iosif PRAISACH, Gilbert-Rainer GILLICH, Tiberiu MĂNESCU, and Cristian TUFIȘI
- Subjects
weak clamped end, mode shapes, strain energy ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
Using analytical equations, the paper aims to solve the dynamic behavior of beams where a clamped end of the beam does not respect the ideal boundary conditions by introducing a weakening coefficient. In the paper, the characteristic equation for determining the eigenvalues and the relationship of the modal function and strain energy are derived. The results show the first six vibration modes for different values of the weakening coefficient which is considered in the clamped end and the evolution of the strain energy.
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- 2023
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11. Dynamic behavior of a clamped circular plate and strain energy representation (part I)
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Nestor MANU, Zeno-Iosif PRAISACH, Gilbert-Rainer GILLICH, and Cristian TUFIȘI
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circular plate, mode shape, Bessel functions ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
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.
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- 2023
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12. The influence of the change of the longitudinal modulus of elasticity on the dynamic behavior of a Warren truss
- Author
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Zeno-Iosif Praisach and Dan Alexandru Pîrșan
- Subjects
warren truss ,slenderness ratio ,modal analysis ,relative frequency shift ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
Trusses are commonly used structures and they are present in the most constructions because it use a small amount of material and for the loads they can support. The paper presents the dynamic be-havior of a Warren truss with seven elements when for one member of the truss the modulus of elasticity is much different compared to the other elements. The relative frequency shift for the first seven vibration mode are calculated taking into consideration that the slenderness ratio has a constant value and the transverse section of the elements is changed. The conclusions reveal that by main-taining the constant value of a slenderness ratio, the relative fre-quency shift is not modified for the considered transverse sections of the elements of the Warren truss.
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- 2022
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13. Natural frequencies and mode shapes in zero-force members of a truss
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Dan Pîrșan and Zeno-Iosif Praisach
- Subjects
trusses ,zero-force member ,natural frequency ,mode shape ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
Trusses are everywhere; they are used in bridges, antenna towers, cranes, even in parts of the International Space Station. And for good reason, they allow us to create strong structures while using materials in very efficient and cost-effective way. Trusses it is es-sentially a rigid structure made up of a collection of straight mem-bers. The type of truss depends on how the horizontal and diagonal beams are arranged.
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- 2021
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14. Dimensionless wave numbers evolution of a three spans simply supported beam when the intermediate supports are moving along the whole beam
- Author
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Zeno-Iosif Praisach, Dorel Ardeljan, and Constantin-Viorel Pașcu
- Subjects
natural frequency ,dimensionless wave number ,mode shape ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
Continuous beams simply supported with several intermediate sup-ports are very common in engineering achievements everywhere. The paper shows the evolution of the dimensionless wave number in 3D format, respectively of the eigenfrequencies for a continuous beam with three openings when the intermediate supports take any position inside the beam. The frequency equation for calculating the dimensionless wave number is presented and the modal func-tion is given with an example for the case where the eigenfrequency has the maximum value at fist vibration mode.
- Published
- 2021
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15. Estimation of the severity of damage produced by a transverse crack
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Marius-Vasile Pop, Gilbert-Rainer Gillich, Cristian Tufisi, Zeno-Iosif Praisach, and Lucian Păun
- Subjects
cantilever beam ,transverse crack ,damage severity ,deflection ,statistical method ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
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.
- Published
- 2020
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16. Beam Damage Assessment Using Natural Frequency Shift and Machine Learning
- Author
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Nicoleta Gillich, Cristian Tufisi, Christian Sacarea, Catalin V. Rusu, Gilbert-Rainer Gillich, Zeno-Iosif Praisach, and Mario Ardeljan
- Subjects
damage detection ,linear regression ,random forest ,artificial neural network ,training parameters ,natural frequency ,Chemical technology ,TP1-1185 - Abstract
Damage detection based on modal parameter changes has become popular in the last few decades. Nowadays, there are robust and reliable mathematical relations available to predict natural frequency changes if damage parameters are known. Using these relations, it is possible to create databases containing a large variety of damage scenarios. Damage can be thus assessed by applying an inverse method. The problem is the complexity of the database, especially for structures with more cracks. In this paper, we propose two machine learning methods, namely the random forest (RF), and the artificial neural network (ANN), as search tools. The databases we developed contain damage scenarios for a prismatic cantilever beam with one crack and ideal and non-ideal boundary conditions. The crack assessment was made in two steps. First, a coarse damage location was found from the networks trained for scenarios comprising the whole beam. Afterwards, the assessment was made involving a particular network trained for the segment of the beam on which the crack was previously found. Using the two machine learning methods, we succeeded in estimating the crack location and severity with high accuracy for both simulation and laboratory experiments. Regarding the location of the crack, which was the main goal of the practitioners, the errors were less than 0.6%. Based on these achievements, we concluded that the damage assessment we propose, in conjunction with the machine learning methods, is robust and reliable.
- Published
- 2022
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17. Deflection of a beam with a transverse crack under dead load
- Author
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Marius-Vasile Pop, Zeno-Iosif Praisach, and Gilbert-Rainer Gillich
- Subjects
cantilever beam ,deflection ,dead load ,transverse crack ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
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.
- Published
- 2020
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18. Free Vibration of a Perfectly Clamped-Free Beam with Stepwise Eccentric Distributed Masses
- Author
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Gilbert-Rainer Gillich, Zeno-Iosif Praisach, Magd Abdel Wahab, Nicoleta Gillich, Ion Cornel Mituletu, and Codrin Nitescu
- Subjects
Physics ,QC1-999 - Abstract
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.
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- 2016
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19. Early Structural Damage Assessment by Using an Improved Frequency Evaluation Algorithm
- Author
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Gilbert-Rainer Gillich, Nuno M. M. Maia, Ion-Cornel Mituletu, Zeno-Iosif Praisach, Marius Tufoi, and Ionica Negru
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Damage detection ,Frequency shift ,Modal analysis ,Kullback-Leibler Divergence ,Frequency evaluation ,Multi-resolution ,Mechanics of engineering. Applied mechanics ,TA349-359 ,Descriptive and experimental mechanics ,QC120-168.85 - Abstract
Abstract 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.
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20. The influence of the truss bar on the dynamic behavior of a Warren truss by changing the modulus of elasticity
- Author
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Zeno-Iosif Praisach and Dan Alexandru Pîrșan
- Subjects
Materials Science (miscellaneous) ,Business and International Management ,Industrial and Manufacturing Engineering - Abstract
The paper presents the natural frequencies shift of a Warren truss with seven elements in the case that members of the structure are weakened by considering that the modulus of elasticity with a lower value. Taking into consideration that the slenderness ratio has a constant value and the transverse section of the truss bars is changed, the relative frequency shift for the first seven vibration mode were calculated by using the values obtained from numerical modal analysis. The conclusions reveal the fact from the dynamic behavior of the structure it can be obtained templates to identify the weakened truss bar of the structure.
- Published
- 2022
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21. A new approach for imperfect boundary conditions on the dynamic behavior
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Zeno-Iosif Praisach, Dorel Adeljan, Dan Alexander Pîrșan, and Gilbert-Rainer Gillich
- Subjects
General Medicine - Abstract
Real beams have non-ideal boundary conditions and it is necessary to use new models to determine the real modal parameters. Models that use ideal conditions do not fully reflect reality and can lead to unsatisfactory description of the dynamic behavior. The hinged – hinged boundary conditions, which is in the focus of the paper, are not analyzed as a single beam, but as a continuous beam with three spans, free at the ends. The continuous beam with three spans is analyzed for cases in which the intermediate supports can occupy any position along the length of the beam, by an analytical solution of the problem, with the example of cases when the intermediate supports are located very close at the free ends of the continuous beam, thus simulating the real case for an hinged beam at both ends; the situation in which the intermediate supports are very close to one of the ends of the beam, thus simulating the real case of the clamped beam, with an imperfect clamped end; and the situation in which the intermediate supports are very close located anywhere on the beam length, thus simulating the hypothetic case with a continuous beam free at the ends and fix on the hinged supports. The analytic results are compared with numerical results by using finite elements method.
- Published
- 2022
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22. Dimensionless wave numbers evolution of a three spans simply supported beam when the intermediate supports are moving along the whole beam
- Author
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Constantin-Viorel Pașcu, Dorel Ardeljan, and Zeno-Iosif Praisach
- Subjects
Physics ,Wavenumber ,Mechanics ,Beam (structure) ,Dimensionless quantity - Abstract
Continuous beams simply supported with several intermediate supports are very common in engineering achievements everywhere. The paper shows the evolution of the dimensionless wave number in 3D format, respectively of the eigenfrequencies for a continuous beam with three openings when the intermediate supports take any position inside the beam. The frequency equation for calculating the dimensionless wave number is presented and the modal function is given with an example for the case where the eigenfrequency has the maximum value at fist vibration mode.
- Published
- 2021
- Full Text
- View/download PDF
23. Natural frequencies and mode shapes in zero-force members of a truss
- Author
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Zeno-Iosif Praisach and Dan Pîrșan
- Subjects
Physics ,business.industry ,Normal mode ,Truss ,Structural engineering ,business ,Zero force member ,Natural (archaeology) - Abstract
Trusses are everywhere; they are used in bridges, antenna towers, cranes, even in parts of the International Space Station. And for good reason, they allow us to create strong structures while using materials in very efficient and cost-effective way. Trusses it is essentially a rigid structure made up of a collection of straight members. The type of truss depends on how the horizontal and diagonal beams are arranged.
- Published
- 2021
- Full Text
- View/download PDF
24. Modal identification and damage detection in beam-like structures using the power spectrum and time-frequency analysis.
- Author
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Gilbert-Rainer Gillich and Zeno-Iosif Praisach
- Published
- 2014
- Full Text
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25. Circular crack identification in plates based on natural frequency evaluation
- Author
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Zeno-Iosif Praisach, Gilbert-Rainer Gillich, Zoltan Iosif Korka, Constantin-Ioan Barbinta, and Codruta Oana Hamat
- Subjects
Frequency analysis ,Materials science ,Materials Science (miscellaneous) ,Modal analysis ,Geometry ,Natural frequency ,Radius ,Circumference ,Curvature ,Industrial and Manufacturing Engineering ,Physics::Geophysics ,law.invention ,Strain energy ,Condensed Matter::Materials Science ,Normal mode ,law ,mental disorders ,Business and International Management - Abstract
We propose in this paper a method to detect cracks in circular plates clamped at the circumference. It consists in analyzing and interpreting the frequency changes that occur due to a circular arc crack. We show that the effect of the crack depends on the strain energy loss, which actually is proportional to the curvature achieved by the affected region in the radial direction. Three types of cracks are considered herein to demonstrate this dependency, differing by their length. Modal analysis is performed involving a professional simulation software for the intact plate, and that with the generated cracks. We found a perfect fit when we compared the curvature of the plate in the radial direction obtained with the analytical relation with the frequency values for the crack displaced along the radius. Therefore, using the curvature of several vibration modes we can obtain damage patterns that can be used to locate circular cracks.
- Published
- 2020
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26. A New Concept Regarding the Modeling of Steel Cantilever Beams with Branched Cracks: A Case Study
- Author
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Dorian Nedelcu, Gilbert-Rainer Gillich, Cristian Tufisi, Zeno-Iosif Praisach, and Codruta Oana Hamat
- Subjects
Transverse plane ,Materials science ,Cantilever ,Position (vector) ,Bending moment ,Physics::Accelerator Physics ,Rigidity (psychology) ,Mechanics ,Rotation ,Constant (mathematics) ,Beam (structure) - Abstract
In this paper, we present a simple predictive model to estimate the natural frequencies of steel cantilever beams with branched cracks. The model considers the cracked beam as a beam with constant cross-section, on which acts an equivalent bending moment. This bending moment takes into account the modification of the rigidity on the beam segment on which the crack extends in the longitudinal direction and the additional rotation that occurs in the slices located at the ends of the damaged segment. Along with the theoretical background and the deduced mathematical model, we present several cases of deterioration defined by the depth of the transverse crack branch respectively the position and the extension of the longitudinal branch. These examples prove the accuracy of the predictions regarding the change of the natural frequencies due to the damage obtained with the proposed model.
- Published
- 2021
- Full Text
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27. On the Use of Higher-Order Frequencies in Crack Identification in Columns Subjected to Important Tip Mass
- Author
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Gilbert-Rainer Gillich, Zeno-Iosif Praisach, Vasile Iancu, Florian Muntean, Zoltan Iosif Korka, and Codrin Nitescu
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Materials science ,business.industry ,Quantitative Biology::Tissues and Organs ,Order (ring theory) ,General Medicine ,Structural engineering ,Inverse problem ,Finite element method ,Square (algebra) ,Position (vector) ,Normal mode ,business ,Energy (signal processing) ,Beam (structure) - Abstract
The paper present a novel non-destructive evaluation method designed to assess damage in structural elements subjected to important axial loads, as columns are. In the prior research a reliable damage detection method was developed for beams subjected to own mass, that consider the relation existing between the energy stored in the beam in certain vibration modes and the related natural frequencies. First we found the mathematical relations expressing the healthy pillar mode shapes and frequencies with respect to the top mass. Afterward, by means of FEM, we derived the natural frequencies for the numerous damage cases, in order to define the frequency shift curves. Analogous to the case of beams, the damage location is characterized by patterns that are derived from the mode shape curvatures square of the healthy beam. The damage location becomes an inverse problem while the damage position is found by interpreting frequency measurements made on the healthy and damaged beam.
- Published
- 2015
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28. Damage-Caused Frequency Shifts in Beams and their Use in Structural Health Assessment
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Horia Furdui, Zeno-Iosif Praisach, Marius Tufoi, Gilbert-Rainer Gillich, and Silviu Razvan Avram
- Subjects
Engineering ,business.industry ,Mode (statistics) ,Stiffness ,Natural frequency ,General Medicine ,Structural engineering ,Finite element method ,Vibration ,Transverse plane ,medicine ,medicine.symptom ,business ,Constant (mathematics) ,Beam (structure) - Abstract
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 locations along the beam. Simulations have shown that accurate prediction about the natural frequency shifts can be made with the proposed relation.
- Published
- 2015
- Full Text
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29. Crack Localization in L-Shaped Frames
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Gilbert-Rainer Gillich, Jean Louis Ntakpe, Nicoleta Gillich, Zeno-Iosif Praisach, and Codruta Oana Hamat
- Subjects
business.industry ,Computer science ,Evaluation algorithm ,020101 civil engineering ,02 engineering and technology ,Structural engineering ,Low frequency ,021001 nanoscience & nanotechnology ,0201 civil engineering ,Modal ,Distribution (mathematics) ,Normal mode ,Assessment methods ,Evaluation methods ,0210 nano-technology ,business ,Energy (signal processing) - Abstract
This paper introduces a method to detect damages in L-shaped frames. The problem of identifying cracks in such structures arises from the low frequency changes due to damage. In the early stage, cracks are hard to be assessed. We present two distinct parts: the assessment of the dynamic behavior of L-shaped and description of the damage evaluation method. In the first part, the mathematical relations contrived for the natural frequencies and mode shapes respectively curvatures are introduced. Afterward, the distribution of the modal energy is found and associated with effects produced by a crack with a given depth in different locations. Findings are used to identify the crack location and severity. Accurate frequency evaluation, a crucial aspect since low frequency changes are expected, was made by employing an algorithm developed by the authors. The damage assessment method with the integrated frequency evaluation algorithm is employed to evaluate the health of an L-framed structure.
- Published
- 2017
- Full Text
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30. Integrity evaluation concerning vibrations of a welded structure
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Codrin Nitescu, Gilbert-Rainer Gillich, Zeno-Iosif Praisach, and Emilian Stanciu
- Subjects
Engineering ,business.industry ,Engineering structures ,Structure (category theory) ,Mechanical engineering ,Structural engineering ,Welding ,Kinetic energy ,Finite element method ,law.invention ,Vibration ,Modal ,law ,lcsh:TA1-2040 ,business ,Reduction (mathematics) ,lcsh:Engineering (General). Civil engineering (General) - Abstract
In this paper, a predictive model that describes the structural behavior in the absence and presence of damage, and anticipates the modal parameter changes, is introduced for weld structures. Degradation of engineering structures in the welds or HAZ due to damage affects their safety by reducing the stiffeners of structural components. In this paper was considered the kinetic energy distribution which reflects the mass participation, and the modal strain energy distribution which take into consideration the stiffeners reduction. The relation is successfully proved against FEM simulation results.
- Published
- 2017
31. Evaluation of Loss of Mass due to Corrosion Using Vibration-Based Methods
- Author
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Zeno-Iosif Praisach, Andrea Amalia Minda, Jean Louis Ntakpe, Horea Furdui, and Gilbert-Rainer Gillich
- Subjects
education.field_of_study ,Frequency analysis ,Materials science ,Cantilever ,business.industry ,Stiffness ,Rigidity (psychology) ,General Medicine ,Structural engineering ,Volumetric Mass Density ,Corrosion ,law.invention ,law ,medicine ,medicine.symptom ,business ,education ,Beam (structure) ,Reliability (statistics) - 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.
- Published
- 2014
- Full Text
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32. Vibration-Based Crack Detection in L-Frames
- Author
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Gilbert-Rainer Gillich, Jean Louis Ntakpe, Zeno-Iosif Praisach, Peter Lorenz, and Florian Muntean
- Subjects
Engineering ,Distribution (mathematics) ,Modal ,business.industry ,Modal analysis using FEM ,Modal analysis ,Frame (networking) ,General Medicine ,Real structure ,Structural engineering ,business ,Finite element method ,Strain energy - 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.
- Published
- 2014
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33. Methods of Interpreting the Results of Vibration Measurements to Locate Damages in Beams
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Zeno-Iosif Praisach, Petru Florin Minda, Andrea Amalia Minda, and Gilbert-Rainer Gillich
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Engineering ,business.industry ,Interface (computing) ,Natural frequency ,General Medicine ,Structural engineering ,Vibration ,Noise ,Position (vector) ,Normal mode ,business ,Representation (mathematics) ,Algorithm ,Reliability (statistics) - Abstract
This paper deals with methods of interpreting the results of vibration measurement to identify structural changes in beam-like structures. We briefly presented an own developed damage assess method, that consider a large number of frequencies for the weak-axis banding vibration modes; it allows first a precise localization and afterwards evaluation of the damages. For the first step, recognition of the damage position, we introduce an algorithm implemented in C++ with the interface done using EXCEL features, indicating by one number the damage probable position, based on the Minkowski metrics. To avoid uncertainties, a graphic representation of all results is also presented. The method is tested for values determined by calculus for a randomly selected location, with and without measurement results debased by noise, proving its reliability.
- Published
- 2013
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34. Assessment of Corrosion Damages with Important Loss of Mass and Influences on the Natural Frequencies of Bending Vibration Modes
- Author
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Zeno-Iosif Praisach, Cornel Hatiegan, Daniel Bobos, and Gilbert-Rainer Gillich
- Subjects
Materials science ,Bending vibration ,business.industry ,Frequency shift ,Stiffness ,Natural frequency ,General Medicine ,Structural engineering ,Mathematical relation ,Corrosion ,Vibration ,Discontinuity (geotechnical engineering) ,medicine ,medicine.symptom ,business - Abstract
Corrosion as material destruction affects the safety of structures, leading to more serious consequences than the simple loss of a mass. The effect of corrosion on the dynamic behaviour of structures act in two ways: the loss of mass increases the natural frequencies, opposite to the effect of stiffness loss. This paper present the results of researches made to extend the mathematical relation presenting the influence of damage location and severity on the natural frequency changes, by adding the effect mass loss. Therefore we modeled the beam once with the discontinuity and loss of mass, afterwards the damaged segment is replaced by an intact one but having the mass similar to that of the damaged segment. This permitted to plot frequency shift curves for both cases and to contrive the relations defining that curves. Finally a relation summarizing the both effects was contrived; it was confirmed both by numerical simulations and experiments.
- Published
- 2013
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- View/download PDF
35. Evaluation of Crack Depth in Beams for Known Damage Location Based on Vibration Modes Analysis
- Author
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Gilbert-Rainer Gillich, Carla Protocsil, Florian Muntean, and Zeno-Iosif Praisach
- Subjects
Vibration ,Severity assessment ,Normal mode ,business.industry ,Deflection (engineering) ,Frequency shift ,Natural frequency ,Fracture mechanics ,General Medicine ,Structural engineering ,business ,Geology ,Beam (structure) - Abstract
The paper presents a method to assess the crack depth in beams for which the damage location is known. Previous researches lead us to a method to identify damage locations in beams, based on a relation providing frequency changes in respect to damage location and depth. Separating the two variables it is possible to find first the damage location, and afterwards to derive the term controlling the severity. Comparing it with values indicating the frequency shift in respect to damage depth, the severity can be assessed. The paper presents a relation reflecting this dependency for any cross-section type, involving the static deflection for the healthy and damaged beam alone; it has a general character, being not influenced by the cross-section shape.
- Published
- 2013
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36. Detection and Quantitative Assessment of Damages in Beam Structures Using Frequency and Stiffness Changes
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Zeno-Iosif Praisach and Gilbert-Rainer Gillich
- Subjects
Engineering ,Cantilever ,business.industry ,Mechanical Engineering ,Mode (statistics) ,Stiffness ,Natural frequency ,Structural engineering ,Curvature ,Term (time) ,Mechanics of Materials ,Normal mode ,medicine ,General Materials Science ,medicine.symptom ,business ,Beam (structure) - Abstract
This paper is concerned with vibration based non-destructive evaluation of structures, with a focus on quantitative assessment of damage. In previous works, a reliable method to locate open cracks in beams has been proposed and tested using both data from numerical simulations and laboratory experiments. It bases on the fact the natural frequency of a bending vibrations mode attend different changes, depending on the loss of stored energy for the slice on which the damage is located. As bigger the mode shape curvature value on that location, so bigger the loss of stored energy and consequently the natural frequency decrease in that mode. Analyzing the natural frequency changes for a larger series of vibration modes, it’s possible to precisely locate damages. The authors succeed to find a single mathematical relation describing the frequency changes for all bending vibration modes, involving one term defining damage’s location and one defining its depth. While the first term changes for different modes, being defined by the mode shape curvature, the second maintain its value for all modes, being affected just by damage depth. This finding permits decoupling the location issue with that of quantitative assessment of damage. Latest researches, presented in this paper, succeed by finding the relation between the second term of the relation and some mechanical characteristics of the beam, i.e. extending the proposed method by including evaluation of damage severity. The approach is illustrated on a cantilever beam, modeled with 3D elements.
- Published
- 2013
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37. On the Mesh Influence upon the Frequency Results Obtained by FEM Simulations
- Author
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Ionică Negru, Carla Protocsil, Zeno-Iosif Praisach, and Gilbert-Rainer Gillich
- Subjects
mesh ,lcsh:TA1-2040 ,beam ,FEM analysis ,natural frequency ,lcsh:Engineering (General). Civil engineering (General) ,error - Abstract
The paper presents a research performed by the authors, in order to establish the optimal element dimensions for a given beam, so that FEM simulations should offer highest accuracy by minimum time consumption. To achieve this desire, we made FEM simulations with elements of various dimensions for seven cross-section dimensions
- Published
- 2012
38. Considerations Regarding the use of Beam Models for Accurate Calculus of Natural Frequencies
- Author
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Carla Protocsil, Ionică Negru, Zeno-Iosif Praisach, and Gilbert-Rainer Gillich
- Subjects
Euler-Bernoulli model ,lcsh:TA1-2040 ,Share model ,beam ,FEM analysis ,natural frequency ,lcsh:Engineering (General). Civil engineering (General) - Abstract
The paper reflects the research performed by the authors, in destined to find out the proper beam model, in concordance with its geometrical characteristics. This knowledge is needed to establish the adequate relations in the difficult process of damage detection. First, we calculated the natural frequencies for two cases: the Euler-Bernoulli model and the Share model. Afterwards, using FEM simulations we determined these frequencies again. Comparison between analytic results and FEM analysis allow seeing which theoretical models best fit for the various investigated cases.
- Published
- 2012
39. Natural Frequencies Distribution on the Damaged Beams
- Author
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Zeno-Iosif Praisach, Gilbert-Rainer Gillich, and Peter Lorenz
- Subjects
lcsh:TA1-2040 ,natural frequencies distribution ,Physics::Accelerator Physics ,beam ,lcsh:Engineering (General). Civil engineering (General) ,damage - Abstract
This paper presents the natural frequencies distribution on the damaged beams. The frequencies distributions was analyzed for three types of beams: cantilever, double clamped and simple supported. The analysis was performed using the finite element method (FEM), for the undamaged beam and for the beam having damages at around 190 locations, considered one by one, and nine levels of depth. The authors deduced analytical relationships for damaged beam frequency shift and presents the results.
- Published
- 2011
40. Early Structural Damage Assessment by Using an Improved Frequency Evaluation Algorithm
- Author
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Ionica Negru, Zeno-Iosif Praisach, Marius Tufoi, Nuno M. M. Maia, Ion Cornel Mituletu, and Gilbert-Rainer Gillich
- Subjects
Kullback–Leibler divergence ,Computer science ,Truncation ,Modal analysis ,Quantitative Biology::Tissues and Organs ,Aerospace Engineering ,Ocean Engineering ,Frequency shift ,Signal ,Position (vector) ,General Materials Science ,Frequency evaluation ,Divergence (statistics) ,Civil and Structural Engineering ,lcsh:QC120-168.85 ,business.industry ,Mechanical Engineering ,Natural frequency ,Structural engineering ,Damage detection ,Mechanics of Materials ,Kullback-Leibler Divergence ,Automotive Engineering ,Multi-resolution ,lcsh:Descriptive and experimental mechanics ,business ,lcsh:Mechanics of engineering. Applied mechanics ,lcsh:TA349-359 ,Algorithm ,Beam (structure) - Abstract
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.
- Published
- 2015
41. Nondestructive evaluation of piers
- Author
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Edwald-Viktor Gillich, Ionica Negru, Gilbert-Rainer Gillich, Marius Tufoi, and Zeno-Iosif Praisach
- Subjects
Physics ,Vibration ,Optics ,business.industry ,Normal mode ,Nondestructive testing ,Shear force ,Fictitious force ,Mode (statistics) ,Natural frequency ,Structural engineering ,business ,Curvature - Abstract
This paper proposes a vibration-based damage detection method designed for structural elements subjected to important vertical loads, as columns or pillars. The method is based on the relation existing between the energy stored in the pillar in several vibration modes and the corresponding natural frequencies. For a certain mode, this energy results as the sum of the energies stored in all pillar slices, being dependent on the rigidity and the squared of the corresponding mode shape curvature. This means that the energy distribution along the pillar is different for each mode. Thus, reducing the rigidity of one slice due to damage, the frequencies will decrease in different ways, depending on the slice location. This fact permits to contrive patterns able to characterize the effect of damage at any location along the pillar. Since the mode shapes (and the natural frequencies) are influenced by inertial forces, but in the meantime by the compression and shear forces induced by the top mass, the patterns have to be derived for each load case. The paper presents a simple mathematical expression able to predict frequency changes if damage occurs at any location along the pillar and for any top mass value. Patterns that characterize the damage location are consequently derived by using the squared mode shape curvatures of the healthy beam. The damage location becomes an inverse problem, it being found by interpreting the results of frequency measurements for the healthy and damaged state. The process of damage location is exemplified by numerical simulations.
- Published
- 2015
- Full Text
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42. Natural frequency changes due to severe corrosion in metallic structures
- Author
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Horia Furdui, Zeno-Iosif Praisach, Vasile Iancu, Gilbert-Rainer Gillich, and Ionica Negru
- Subjects
Cantilever ,Materials science ,Engineering structures ,business.industry ,Mechanical Engineering ,Stiffness ,Natural frequency ,Structural engineering ,Mechanics ,Kinetic energy ,Corrosion ,Metal ,Mechanics of Materials ,visual_art ,visual_art.visual_art_medium ,medicine ,sense organs ,medicine.symptom ,business ,Degradation (telecommunications) - Abstract
Degradation of engineering structures due to corrosion affects their safety by reducing the cross-section of structural components and altering the material's mechanical characteristics. These parameter changes are observable in the shift of the natural frequencies. In the study presented in this paper, it was demonstrated that the kinetic energy distribution reflects the mass participation, thus being able to predict frequency changes due to mass loss, while the modal strain energy distribution can be properly used to indicate the location of the damage. As a result, two mathematical relations were developed by the authors, predicting the frequency changes due to the main effects of corrosion: loss of mass and loss of stiffness. Degradacija tehničnih konstrukcij zaradi korozije vpliva na njihovo varnost, saj zmanjšuje presek nosilnih komponent in spreminja mehanske lastnosti materiala. Te spremembe parametrov lahko spremljamo prek premika lastnih frekvenc. Namen članka je predstavitev matematičnih relacij, ki napovedujejo spremembe frekvenc zaradi splošne ali lokalne korozije na podlagi znane izgube mase in zmanjšanja upogibne togosti. Analitična raziskava se začne z vplivom mase rezin na različnih mestih nosilca. Rezultati so pokazali, da položaj rezine določa količino energije, ki prispeva k celotni energiji, shranjeni v nosilcu v danem vibracijskem načinu. Količina energije v različnih načinih se razlikuje in je odvisna od kvadrata oblike načina na mestu rezine. Na ta način je bilo pokazano, da porazdelitev kinetične energije odraža prispevek mase v celotni shranjeni energiji in tako omogoča napovedovanje spremembe frekvenc zaradi izgubljene mase.
- Published
- 2015
43. Damage-patterns-based method to locate discontinuities in beams
- Author
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Gilbert-Rainer Gillich and Zeno-Iosif Praisach
- Subjects
Vibration ,Discontinuity (linguistics) ,Normal mode ,Acoustics ,Mode (statistics) ,Natural frequency ,Classification of discontinuities ,Curvature ,Geology ,Beam (structure) - Abstract
The paper presents a method to locate discontinuities in form of transversal cracks in beams, based on vibration measurements. Patterns characterizing frequency changes of the first ten weak-axis bending vibration modes are determined for all possible locations on the structure, using a relation contrived by the authors. It base on the correlation between the strain energy stored in a segment of the beam, which is proportional with the square of the mode shape curvature of the considered vibration mode at that location, and the frequency change for this mode by the occurrence of a discontinuity on that segment. The patters consist from a series of ten values representing the normalized relative frequency shifts for the first ten vibration modes. For a structure similarly supported, by continuous or periodical measurements, potential frequency changes can be detected. By processing these data the so-called damage location index for that crack is found out, also as a series of ten values representing the relative frequency shifts of the ten vibration modes. To precise locate the crack a pattern matching method involving the database with all possible patterns and the damage location index is used. Knowing the location, it is easy to determine by analytic calculus the crack depth. The method is easy to be used, provide accurate results, demands modest computational effort and has the advantage that the measurements may be carried out in situ with rather simple equipment. The method was validated by experiments.
- Published
- 2013
- Full Text
- View/download PDF
44. Reliable Method to Detect and Assess Damages in Beams Based on Frequency Changes
- Author
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Zeno-Iosif Praisach, Claudiu Mirel Iavornic, and Gilbert-Rainer Gillich
- Subjects
business.industry ,Computer science ,Mode (statistics) ,Stiffness ,Structural engineering ,Curvature ,Strain energy ,Vibration ,medicine ,sense organs ,medicine.symptom ,skin and connective tissue diseases ,business ,Reduction (mathematics) ,Beam (structure) - Abstract
The paper presents a method to detect, locate and evaluate damage severity of Euler-Bernoulli beams, based on how natural frequencies change due to damages. Previous researches that dealt with this issue focused only on quantitative changes, mainly considering a global stiffness reduction in the damaged area. The authors have contrived a correlation between the strain energy stored in a segment of the beam, which is proportional with the mode shape curvature of a considered vibration mode at that location, and the frequency change for this mode if damage appears on that segment. This reveals that for an element of the beam, the stiffness change of a certain mode for a given damage varies between zero and a maximum, depending solely on the location of that element. Moreover, one has to consider different stiffness changes for a damaged element placed on a certain location, depending on the vibration mode. This rule how frequencies of various modes change due to damage are used to create patterns, based on relative frequency shifts, which characterize damaged beams in respect to defect location and severity. The method was validated by numerous experiments, which proved its accuracy and reliability.Copyright © 2012 by ASME
- Published
- 2012
- Full Text
- View/download PDF
45. Robust method to identify damages in beams based on frequency shift analysis
- Author
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Zeno-Iosif Praisach and Gilbert-Rainer Gillich
- Subjects
Vibration ,Physics ,Optics ,business.industry ,Normal mode ,Inflection point ,Acoustics ,Mode (statistics) ,Natural frequency ,Bending ,business ,Curvature ,Beam (structure) - Abstract
The paper presents a method to assess damages in beams, based on how natural frequencies of bending vibration modes change due to damages. The authors have contrived a correlation between the strain energy stored in a segment of the beam, which is proportional with the mode shape curvature of a considered vibration mode at that location, and the frequency change for this mode if damage appears on that segment. For a certain mode, damages placed on inflection points of the mode shape curvature, where the strain energy is null, will not produce changes in frequency, while damages placed on maxima will produce the highest changes in frequency. For other locations of damage, the frequency shift will be proportional with the mode shape curvature of the vibration mode at that location. We worked out a general relation, which gives the frequency shift of all bending modes, with one coefficient depending on the support type. To evaluate damages, we determine analytically the relative frequency shift as ratio between the frequency change and the natural frequency of the undamaged beam, for the first ten vibration modes, considering various damage depths and locations. Comparison of results with that obtained by measurements on the real beam permits detection, location and assessment of damages in beams with high accuracy. The method was validated by experiments.
- Published
- 2012
- Full Text
- View/download PDF
46. The influence of operational and environmental loads on the process of assessing damages in beams
- Author
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Horia Furdui, Zeno-Iosif Praisach, Florian Muntean, Andrea Amalia Minda, and Nicoleta Gillich
- Subjects
History ,Engineering ,Damage detection ,business.industry ,Process (computing) ,Truss ,Large range ,Structural engineering ,Finite element method ,Computer Science Applications ,Education ,Vibration ,Modal ,business - Abstract
Damage detection methods based on vibration analysis make use of the modal parameter changes. Natural frequencies are the features that can be acquired most simply and inexpensively. But this parameter is influenced by environmental conditions, e.g. temperature and operational loads as additional masses or axial loads induced by restraint displacements. The effect of these factors is not completely known, but in the numerous actual research it is considered that they affect negatively the damage assessment process. This is justified by the small frequency changes occurring due to damage, which can be masked by the frequency shifts due to external loads. The paper intends to clarify the effect of external loads on the natural frequencies of beams and truss elements, and to show in which manner the damage detection process is affected by these loads. The finite element analysis, performed on diverse structures for a large range of temperature values, has shown that the temperature itself has a very limited effect on the frequency changes. Thus, axial forces resulted due to obstructed displacements can influence more substantially the frequency changes. These facts are demonstrated by experimental and theoretical studies. Finally, we succeed to adapt a prior contrived relation providing the frequency changes due to damage in order to fit the case of known external loads. Whereas a new baseline for damage detection was found, considering the effect of temperature and external loads, this process can be performed without other complication.
- Published
- 2015
- Full Text
- View/download PDF
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