The use of virtual instruments in engineering education

AbstractVirtual instruments are used nowadays for measurement and control, but also as educational tools for students, being well accepted and stimulating innovation in the process of exploring the real world. It leads to discover interrelations, the phenomena are easier undersold and theory is better assimilated. The tool can be used in real laboratories as well as in virtual laboratories, constituting a support for self-learning or distance learning. This article presents how virtual instruments can be used in engineering education, with examples from our Vibration Laboratory, together with a qualitative research regarding the perception of students to this issue

A versatile algorithm for estimating natural frequencies with high accuracy

Detection of damage requires an accurate estimation of the natural frequencies of the monitored structure. This paper introduces an algorithm implemented in Python which improves the frequency readability by increasing the number of spectral lines without requiring a signal extension in the time domain. We achieve this by overlapping several spectra calculated from the acquired signal repeatedly shortened. In this way, the overlapped spectrum gets an increased number of spectral lines. The dense mesh of spectral lines permits us to obtain a fine frequency resolution without being necessary an extension of the signal in the time domain. The high density of the spectral lines ensures a sufficient number of points on the main lobes that permits performing an efficient quadratic polynomial interpolation to find the maximizer. It represents the amplitude of the real frequency and is typically located on an inter-line position, thus cannot be found by standard frequency estimation. We implemented the algorithm in Python and tested it successfully for generated signals, containing one or more harmonics, with known frequencies

The Influence of the Number of Finite Elements upon the Accuracy of the Results Obtained Using Discrete Models

Discrete models are often used because they require a simple mathematical approach, even if their accuracy is inferior to continues models. This paper presents a study regarding the influence of the number of used elements upon the accuracy with which the natural frequencies of straight beams can determined. The results show that, to achieve a reasonable accuracy, it is necessary to use at least ten elements, while for rigorous calculus, more than three hundred elements must be considered

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

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

Modeling of Complex Shaped Cracks

The paper proposes modeling approaches of complex shape cracks. Structures may present many types of defects, of different irregular shapes and sizes, due to various reasons, and so it is very important for the model of the crack used to be accurate. There are three main categories for modeling of cracks; local stiffness reduction, discrete spring models, and complex models in two or three dimensions each proving to be reliable methods for generating finite element models

The Influence of the Weight Loss upon Natural Frequency Changes in Case of Severe Defects

The paper presents a research regarding the use of a "virtual" material in order to compensate the loss of mass in the case of the damaged beam. Because of the loss of mass, the frequency of the beam suffer an increase over the natural frequency of the undamaged beam and so we have proposed the use of this material, having the same density with the density of the beam, in the gap left by damage

Intelligent infrastructures systems for sustainable urban environment

Extensive research is now under way around the world to develop advanced technologies to enhance the performances of infrastructure systems. While these technological advances are incremental in nature, they will eventually lead to structures which are distinctly different from the actual infrastructure systems. These new structures will be therefore capable of Structural Health Monitoring (SHM), involving applications of electronics and smart materials, aiming to assist engineers in realizing the full benefits of structural health monitoring.intelligent infrastructures, environment, optimization

Gabor frames and topology-based strategies for astronomical images

The topic of this paper is the description of procedures to remove the fringes from complicated astronomical data sets, where the interference pattern is not regular, combining topological and Gabor-based analysis. A first method is given and it involves two successive steps: first we perform an identification of the fringes using Gabor frames and latter we filter the connected components using computational topology methods. This is a new approach trying to get the benefit of filtering the harmonic representation by means of topological methods