Papers by Keyword: Natural Frequency

Abstract: In this article a sandwich beam structure with honeycomb core filled of MRE (magnetorheological elastomer) with different ratios of Elastomer and iron particles is proposed. Modal response for structures with Nylon and Resin8000 honeycomb core filled with MRE and sandwiched between aluminum face sheets were analyzed and compared for two different ratios of MRE by placing magnets at free end and center of the structure. The force generated by magnets on the sandwich beam structure was calculated using ANSYS EDT and the modal response of the structure was then observed under generated magnetic force using ANSYS Workbench. The results showed that the resonance frequency of the structure decreased as the magnetic intensity was increased for all the cases specially for the first mode. Secondly structure with Nylon honeycomb core showed lower frequency drop and higher deformation than the structure with Resin8000 honeycomb core.

Abstract: The aim of the present paper is to study the vibration behavior of a sandwich structure with honeycomb core experimentally and numerically with different design parameters. The natural frequency and damping ratio were obtained. Core height, cell angle and face thickness were considered as design parameters. Finite element models for the honeycomb sandwich were developed and analyzed via ANSYS finite element analysis (FEA) software. Response Surface Method (RSM) is used to establish numerical methodology to simulate the effect of the design parameters on natural frequency and damping ration. The employment of (RSM) provides a study of the effect of design parameters on natural frequency and damping ratio, numerical modeling of them in term of design parameters and specifying optimization condition. The experimental tests were conducted on sandwich specimens for the validity goal of the previous models created via the finite element analysis. The obtained results show that the natural frequency is directly proportional to the core height and face thickness, while it is inversely proportional to cell angle, Vice versa for damping ratio. Moreover, the optimum value of natural frequency (209.031 Hz) as minimum and damping ratio (0.0320) as maximum were found at 4.8855 mm of core height, 26.770 cell angle and 0.0614 mm face thickness.

Abstract: Turbine blade failures are among the leading causes of steam turbine failure. Failure types typically include cracking, rubbing, blade fouling, and foreign object damage. There is currently a range of non-destructive testing methods used to detect damage at the blade-disk attachment zone, all of which involve disassembling of the blade from the disk for periodic inspection. Evidence indicate that a method to detect damage at the blade-disk attachment zone using a non-contact, non-destructive in-situ off-line modal-based structural health monitoring technique could be useful under some circumstances. Such a technique would have the advantage of eliminating the necessity to disassemble blades during inspection. This would result in significant cost savings. Also, defects associated with the disassembly and reassembly of blades would be avoided. Thus, the aim of this study was to develop a modal-based turbomachinery blade disk attachment inspection technique. Modal parameters were acquired from a robust experimental modal analysis of freely supported low-pressure steam turbine blade-disk segment assemblies. Artificial single-location cracks were intentionally introduced into the turbine blades by cutting a 1 mm thickness notch at three probable damage locations, namely, at the upper pinhole on the leading-edge pressure side, above the root at the base of the aerofoil on the leading-edge and on the trailing-edge. In this work, a finite element analysis of the bladed disk segment assemblies was carried out with and without damage. To validate the reliability of the numerical models, the numerical results were correlated with the measured values, the results of which showed a strong correlation. Finally, a parametric study was conducted in which various healthy and damaged blade-disk cases were systematically investigated. This was done to examine the sensitivity of the blade natural frequency to damage. The artificial damage above the root was found to cause the largest changes in natural frequency. These changes were even more pronounced for assemblies with two blades. Receiver operating characteristic curves were used to assess the discriminatory ability of the results. Each damage case was found to be unique and therefore identifiable from its corresponding healthy case.

Abstract: Vibration stress relief (VSR) and thermal stress relief (TSR) are important method to eliminate the residual stress of structural parts. The thermal vibratory stress relief (TVSR) is a new method to decrease and homogenize the residual stress. Based on the stress relaxation tests and the equivalent vibration equation of modal analysis, the creep constitutive model and the bilinear isotropic hardening plasticity material model (BISO) are combined to establish the numerical simulation model of TVSR of 7075 aluminum alloy ring part. The simulation results show that four different initial blank residual stress levels are obtained after quenching process, and the residual stress elimination and homogenization effect of TSR and TVSR is better than that of VSR. TVSR has a better effect on both residual stress elimination and homogenization, and the residual stress relief rate can reach more than 20%.

Abstract: The vibration of perforated plates is central to certain engineering applications, such asdroplet-on-demand, inject printing and aerosol generation. To the author’s knowledge, there is limitedpublished literature outlining the effect of perforations on the natural frequency of a flat circular plate.This paper aims to further the understanding in this field research, by determining analytically theeffect of perforations on the natural frequency of boundary clamped flat circular plate. The methodology of this paper outlines the development of a dynamic finite element (FE) model which accurately embodies the effect of perforations on the natural frequency of a boundary clamped flat circular plate using modal analysis. This dynamic FE model aids in optimising the vibrational mechanics of perforated plates for specific engineering applications. The finding from this analysis demonstrates that the published literature is less conservative when compared to the FE method in predicting the effect of perforations on the natural frequency of a boundary clamped flat circular plate. Published literature uses a numerical analysis which underestimates the effect of perforations on the natural frequency of a boundary clamped flat circular plate when compared to the FE analysis reported in this study.

Abstract: The aim of this paper is to perform a study on how the elevated temperature and gradient of temperature affect the natural frequencies of aluminum honeycomb plate. This study is carried out for temperature range between 200K and 800K, and gradient temperature (ΔT) across the thickness direction of the plate between [0-500K]. Different honeycomb plate geometries have been selected for the analysis, by changing the core thickness, skins thickness and cell size. The obtained results show that the effect of the temperature is noticeable. At temperature 800K, the natural frequencies decrease by 16.1% in comparison to their values at ambient temperature (300K). That means, high temperature makes the material suffers from weak rigidity, which furthermore contribute to high decrease of all the frequencies. In addition, investigations carried out in this work relate to the modal analysis of the honeycomb plate, under various gradients of temperature across the core of the plate. The obtained results show that the gradient of temperature has an effect on the modes of vibration of the honeycomb plate. This effect becomes significant when the gradient of temperature is very high. At ΔT equal 500K, the natural vibration modes decrease by 9.5% in comparison to the case where no gradient of temperature (ΔT = 0K) is applied between the two faces of the plate. Keywords: honeycomb panel; aluminum; natural frequency; finite element method; temperature.

Abstract: This paper presents a free vibration analysis of un-damped woven roving laminated composite plate using Classical Laminate Plate Theory (CLPT), for different boundary conditions. The fiber glass/epoxy woven roving laminated composite plates have been prepared using hand layup method. Three different fiber orientations have been considered for the fiber glass/epoxy laminated composite plate, having 50% each percentage by volume of glass and epoxy. Effects of fiber orientation on different mechanical properties such as density, hardness, impact strength and impact strength have been studied. Finite element modeling of the composite plates has been performed using different boundary conditions such as CCCC, CFCF, and CFFF and the fundamental frequencies obtained from the computational modeling have been compared with the available literature.

Abstract: Modal analysis is a method to describe the dynamic properties of structure such as natural frequency, mode shape and damping ratio. These properties are important for design and analysis of structure in dynamic condition. MATLAB is a high-performance numerical computation and visualization software package. It provides an interactive environment with hundreds of built-in functions for technical computation, graphics, and animation. In present analysis, use of MATLAB is done for finding the free vibrational characteristics of a structure made of composite material. The study involves finding the natural frequencies of structure made of Glass-epoxy, Carbon-epoxy and Graphite fiber reinforced polyamide materials. In this case Euler’s-Bernoulli beam theory is used for analytical solution and to construct MATLAB codes. The structure considered here is a beam with fixed-free condition. The results obtained from the MATLAB are accurate comparatively, the results obtained shows that the MATLAB can be further used to write programs which involve complicated iterations and cannot be done manually. The further work can be extended for writing the programs of much more complex equations in MATLAB and obtains exact solution.

Abstract: The present work proposes a vibration study with different surface and layers orientations at 0°, 15°, 30°, 45°, 60°, 75° and 90°using the Abaqus finite element code, the frequencies Stratified laminate composite panels were studied and the comparison between damaged structures and perfect structures we used stiffened panels based on T-shaped reinforced fibers. Lamb waves (LW) were widely proposed for the long-range inspection of Structural Structural Health Monitoring (SHM) oriented composite structures, the obtained results show the angle effects on the natural frequency increase at a peak then decrease in the form of a sinusoidal half-curve and the numerical results found in this work can be compared to those of other authors in the same area of ​​research, A piezoelectric actuator is used to design acoustic waves and a sensor is used for signal acquisition.

Abstract: Based on the first order shear deformation plate theory (FSDT) in the present studie, static and dynamic behavior of carbon nanotube-reinforced composite sandwich plates has been analysed. Two types of sandwich plates, namely, the sandwich with face sheet reinforced and homogeneous core and the sandwich with homogeneous face sheet and reinforced core are considered. The face sheet or core plates are reinforced by single-walled carbon nanotubes with two types of distributions of uniaxially aligned reinforcement material which uniformly (UD-CNT) and functionally graded (FG-CNT). The analytical equations are derived and the exact solutions for bending and vibration analyses of such type’s plates are obtained. The mathematical models provided and the present solutions are numerically validated by comparison with some available results in the literature. Influence of Various parameters of reinforced sandwich plates such as aspect ratios, volume fraction, types of reinforcement and plate thickness on the bending and vibration analyses of carbon nanotube-reinforced composite sandwich plates are studied and discussed. The findings suggest that the (FG-CNT) face sheet reinforced sandwich plate has a high resistance against deflections compared to other types of reinforcement. It is also revealed that the reduction in the dimensionless natural frequency is most pronounced in core reinforced sandwich plate.