Papers by Keyword: Natural Frequency

Abstract: This paper presented vibration analyses of a tapered composite thin-wall box beam with rectangular section. In the numerical results, the effects of taper angle on natural frequencies and the corresponding mode shapes, transient responses of the beam were considered. The algorithm and Matlab code using nine nodded rectangular isoparametric plate element with five degree of freedom per node developed to solve the problems.

Abstract: Conducting surveys of multi-storey buildings is a laborious task, because large volumes of visual and instrumental research should be carried out. Reduction of labor costs with an increase in the reliability of information about the state of damage and technical condition is an actual scientific and practical task. One of the ways to solve it is to use non-destructive vibration diagnostic methods. The purpose of carrying out diagnostics with the use of vibration based damage detection methods is to search for damages in structural elements that can cause the deviation of the dynamic parameters of a structure from calculated ones. Determination of the dynamic parameters of the structure, in particular natural frequencies and mode shapes of mechanical systems, is one of the most important tasks that allows obtaining integral information about the state of a structure. This article presents the results of calculations for the localization of slabs defects in a multi-storey building with a transverse crack, span L = 4.5 (m), height H = 0.2 (m), with prestressed reinforcement d = 0.05 (m). Vibration based Damage Index method was used to localize the defect. During the study, reliable localization values of the defect area of the slab were obtained, this indicates that the vibration method for determining the damage index with a sufficient degree of accuracy allowed predicting the site of damage to the structure.

Abstract: In the present research, imperfect graphene sheets were generated and their vibrational property was studied via finite element analysis. The effect of vacant sites in the arrangement of these nano-structures was examined. The fundamental frequency of the defect free and imperfect nano-sheets was acquired based on two different approaches. The first approach was a pure finite element simulation. The second approach for comparison purpose was a recently reported refined finite element simulation at which the vicinity of a defect was first evaluated according to the density functional theory (DFT) and then the refined geometry was implemented into a finite element model. The findings of this research show that the fundamental frequency of graphene sheets decreases by presenting microscopic imperfection to the formation of these nano-materials. In addition, it was pointed out that the geometry based on the more precise DFT simulations gives a higher decrease in the fundamental frequency of the sheets for all considered cases.

Abstract: The objective of the present work is an analysis of vibratory responses due to the impact of projectile in steel against a glass/polyester composite material under hygrothermal conditions with different energy levels. In the first part of this study, by means of a data acquisition system, a signal processing analysis of the contact force and acceleration of the projectile is carried out in order to deduce the oscillations of the responses. These are generated by the vibrations induced by the contact between the plate and the impactor. The analysis of the vibrations by the calculation of the Fast Fourier Transform (FFT) applied to the oscillations of the contact force allows to defining the resonance frequencies of the plate for the different energy levels. The measure of the Frequency Response Functions (FRF) from the obtained responses allows the determination of the damping of the impacted composite material.In the second part of this study highlights quantitatively and puts into evidence the influence of hygrothermal conditions on the mechanical responses such as contact force, acceleration, frequency and damping of aged and non-aged composite plates.

Abstract: In this research aims to study the damping characteristics of hybrid polymer composite, which can be used in engineering structures and in many other applications. Hybrid composites are namely Glass fiber and carbon filler reinforced with polyester and epoxy matrix have been prepared by vacuum bag molding fabrication technique. Then the free vibration test were conducted using FFT analyzer with Lab VIEW software. The damping ratio and natural frequency were investigated for fabricated composites. Then through ANSYS, the mode shapes and natural frequencies were determined and the results were compared with experimental results. The damping ratio increases with increased volume fractions of E-glass fibers for both the types of polymer composites. Vibrations are concerned to large structures such as aircraft, as well as small structures such as electronic equipments.

Abstract: Designing structures with frequency constraints is an important task in aerospace engineering. Aerodynamic loading, gust loading, and engine vibrations all impart dynamic loads upon an airframe. To avoid structural resonance and excessive vibration, the natural frequencies of the structure must be shifted away from the frequency range of any dynamic loads. Care must also be taken to ensure that the modal frequencies of a structure do not coalesce, which can lead to dramatic structural failure. So far in industry, no aircraft lifting surfaces are designed from the ground up with frequency optimisation as the primary goal. This paper will explore computational methods for achieving this task.This paper will present a topology optimisation algorithm employing the Solid Isotropic Microstructure with Penalisation (SIMP) method for the design of an optimal aircraft wing structure for rejection of frequency excitation.

Abstract: New-type floor is composed of three kinds of slabs joined together through fittings. It is a kind of anisotropic two-way slab. In order to study the calculation method of natural frequency, series method, variable thickness method and variable stiffness method are adopted to calculate the natural frequency. The calculation results of three methods are compared with test result and numerical simulation result. The conclusion is that the calculation result of the variable stiffness method is the closest to the real natural frequency of new-type floor.

Abstract: The maintenance and operation of bridges represent a significant investment in both the public and private domains. In practice, the structural damage of a bridge that accumulates over its life-span is a result of continuous degradation caused mainly by traffic conditions and sudden extreme events (e.g. flooding, fires and severe traffic accidents). However, under heavy truck loading, the deterioration rate of a bridge can be accelerated. As the use of heavier articulated trucks becomes increasingly popular in contemporary freight transportation systems, the development of modern Non-Destructive Testing (NDT) techniques in conjunction with computational modelling becomes necessary. The advancement in this area will allow rapid assessment of the structural health of bridges and detection of ongoing damage to enhance the structural performance of bridges.

Abstract: This paper presents the vibration test method of the elastic modulus of glulam beams. Under the condition of simply supported, the elastic modulus of glulam beams is tested based on the vibration method. Compared with the static modulus tested by static load test and the natural frequency tested by finite element method, vibration-based detection method is proved to be feasible and accurate in measuring the elastic modulus of glued laminated beams.

Abstract: Preloads have an important influence on working performance and service life of wheel hub bearing. In order to study the action mechanism, carrying out the study on the effect of wheel hub bearing preload on the natural frequency is particularly important. Aiming at a certain type of car wheel hub bearing, the wheel hub bearing swept-sine vibration test system is built, and the conclusion is got after testing on wheel hub bearings with different preloads. The conclusion is that the natural frequency of wheel hub bearing increases with preload increasing, but increasing trend tends to slow.