Maintenance, Reliability and Condition Monitoring
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Forced response characteristics of random mistuned blade disk based on weibull distribution and monte carlo simulation
Get PDFThis paper presents a method of mistuning identification of a random mistuned bladed parameter, to predict the forced vibration characteristics of random mistuned blade disk of aeroengine compressor, based on the prestress mode synthesis method, substructure finite element reduction model was adopted, the identification method combines Weibull distribution with Monte Carlo simulation to identify the random mistuned blade parameters. The vibration characteristics of mistuned bladed disks under different engine orders of excitation were calculated, and the vibration characteristics of mistuned bladed disk systems under different mistuning standard deviations were discussed. Vibration localization characteristics of mistuned bladed disk system were analysed by using localization factor. The correctness of the identification method was verified by calculating the vibration amplitude of mistuned bladed disk system under different mistuning standard deviations
A versatile algorithm for estimating natural frequencies with high accuracy
Get PDFDetection 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
Impact of selected sources of transport vibrations on the perception of vibrations by people in buildings
Get PDFVibrations propagating through the soil into the building can not only be harmful to the building structure or cause its accelerated wear, but can also effect on the vibrational comfort in the rooms. They can also be annoying for residents and building users, and in extreme cases can lead to sleep disorders, headaches and neurotic conditions. Especially vibrations from the low frequency range from 5 to 25 Hz are undesirable, because there are resonance frequencies of human internal organs in this frequency range. The human perception of vibrations in buildings, despite many researches made in the past, despite standards and requirements in this area, is still a topic not fully understood mainly due to the subjective nature of the perception of vibrations by various people. It is widely known that the type of transport vibration source has an impact on human perception. Vibrations generated by above-ground sources are more felt on the upper floors as opposed to vibrations generated from the underground. In this paper three types of transport vibrations are analyzed on one chosen building located in Warsaw. Human perception of vibration is evaluated according to two methods: root mean squared (RMS) and vibration dose value (VDV)
Modal analysis application for the problemof gamma-ray spectrometers resolution improving
Get PDFThe cryostat of gamma-ray spectrometer with HPGe detector cooled by Stirling cycle cryocooler is under consideration. The natural frequencies and modes shapes for components involved to oscillatory systems distinguished in dynamic model of cryostat were calculated by Solidworks simulation. The results obtained for the gamma-ray spectrometer “Monolith” produced by BSI, represent its specific modal portrait and allow identification the components of electrical noise due to microphone effect. The absence of resonant amplification due to coincidence between the harmonics of cryocooler operating frequency and the natural frequencies of the cryostat components is an important condition for reducing the influence of microphonics. The results obtained by modal analysis are also useful for assessing the influence of external mechanical disturbances, such as shocks, external vibration or audible noise
Study on multi-axis sine vibration test control techniques
Get PDFThis paper describes several key aspects about multi-axis sine vibration test control techniques including the identification of the system frequency response function, synchronization of the input and output signals, the generation of the sinewave, the control algorithm, etc. A multi-axis sine vibration controller is developed based on these key techniques and the major framework of the controller is introduced. Finally, a dual axial experiment is carried out by the controller. The test results show the feasibility of the control algorithm and the good control strategy of the multi-axis sine vibration controller in which the key techniques are realized
Uncertain optimization of in-bore launching performance of artillery based on interval method
Get PDFIn order to study the uncertainty optimization of the in-bore launching performance of larger-caliber artillery, the interior ballistic program was compiled and embedded in ABAQUS finite element software for secondary development, and the dynamic model of in-bore launching was built. The structural parameters of bore, the structural parameters of projectile and parameters of launching propellant were considered, and the uncertainty was described by interval number. BP neural network was used to construct a surrogate model for the dynamic model of in-bore launching. The deterministic transformation of uncertain objective function and uncertain constraints was carried out by using interval order model and interval probability model respectively. The interval uncertainty optimization model of the in-bore launching performance artillery was established by taking the interval radius and midpoint of the projectile muzzle velocity as objective functions and the maximum chamber pressure as constraint. Multi-objective genetic algorithm was used to solve the problem, and the optimal solution and reasonable interval of uncertain parameters were obtained
Numerical simulation and experimental analysis of magneto-mechanical behavior of anti-seismic active sandwich structure
Get PDFThis work focuses on the quasi-static behavior study for simply supported sandwich beams with aluminum faces and magnetorheological elastomer core subjected to three points bending subjected to a magneto-mechanical loading by numerical and experimental investigations. The mechanical properties of the magnetorheological elastomer core are measured experimentally and the mechanical behavior of the MRE was identified by the generalized Maxwell rheological model. Depending upon the adjustable properties of the beam, energy dissipation is by core shear. A systematic series of experiments and finite elements simulations have been performed in order to assess the static behavior of the beam. The results obtained show a significant influence of the magnetic field intensity on the flexural displacement of the beam
Near-field acoustic holography for high-frequency weak sound sources under low signal-to-noise ratio
Get PDFThe mechanical noise in the cabin of the ship is so large that the leakage of high-pressure fluid is not easily noticed. In view of this situation, a near-field acoustic holography for high-frequency weak sound source under low signal-to-noise ratio is proposed. The method uses the empirical mode decomposition method to add weights to the time-domain sampling signals of each array element, and then uses the plane equivalent source near-field acoustic holography combined with compressive sensing to find the holographic surface acoustic pressure distribution. The simulation and experiment show that this method has certain feasibility under low signal-to-noise ratio, and the results are better than the method based on Fourier transform and the traditional boundary element method. It is of positive significance to apply it to engineering practice
Fracture strength estimation of L3-L4 intervertebral disc using FEA
Get PDFMechanical stress and fracture analysis of the human lumbar intervertebral discs are important in assessing disorders related to lower back pain and ageing. Finite element modelling and simulation approaches assist in easier prediction of the disc behaviour under different load conditions. The causes of mechanical failure and morphological changes still remain partially speculative. The present study addresses the issue by developing a finite element model of an L3-L4 lumbar intervertebral disc subjected to different axial compressive loadings. The morphological deformations and stress concentration regions within the disc are analyzed and reported. A mathematical relation is established to estimate the breaking strength of an L3-L4 intervertebral disc, thus indicating the risk of disc failure based on the applied load
Cell dynamics and natural frequencies: scaling and shape matters
Get PDFCell dynamics is one of the most investigated areas under the field of biomechanics. Scaling plays a crucial role in determining the dynamic characteristics of biological systems. In the present investigation, cuboidal and cylindrical models of different scales are analysed to depict the dependence of natural frequency on the scaling factors. Three approaches, namely lumped mass system, finite element model (FEM) and numerical approach using Ansys are used to determine the fundamental natural frequencies. Different scaling factors, namely nano, micro (original size), millimeter and meter are considered for the analysis. The results indicate that the natural frequency varies inversely with the size of the cell by the same factor. A simple mathematical relation is derived to support this claim. Results are illustrated with numerical examples and corresponding mode shapes are reported