Papers by Keyword: Vibration

Abstract: Vibration-based inspection is an area of active research. This task is performed by estimating the effects of structural damage on the eigen parameters of structures. The problem of detecting, locating, and quantifying the extent of damage was under study for several decades. In order to investigate the prevailing effects of damage present in the structure under examination, a mathematical model of the damage must be introduced into the model of the structure at the location of the fault. While focusing on transverse vibrations, a simple stiffness reduction of the damaged region was used. In the present work the vibration parameters (relative first three natural frequencies) of the cracked structure are treated in a controller. The controller is designed using fuzzy logic & genetic algorithm. Here the fuzzy rules are optimized by using genetic algorithm. Using the controller, the crack locations can be determined.

Abstract: This paper presents an investigation methodology for detection of size and location of open edge transverse crack on a rotating beams using continuous wavelength transform. Generally, vibration characteristic of abeam like structure changes significantly due to the presence of crack. However when the crack is relatively small, it is difficult to identify the presence of the crack from the vibration response data only. In the present case, vibration parameter, such as, mode shapes of damaged beams are obtained using the finite element method. The CWT is implemented with different scales on mode shape of the rotating beam to evaluate crack size and its location. It is also shown that this method can produce satisfactory results with some limitation based on mode shape profile. In addition to the the profile quality, other determining factors are scale and resolution of the detection signal

Abstract: A numerical investigation is performed to study the free vibration responses of a width tapered composite beam. The finite element simulation is performed to investigate the effect of taper angle along the longitudinal plane of the beam on the free transverse vibration responses. Experimental investigations are also performed to demonstrate the effectiveness of the developed finite element formulation (FEM) in identifying the free vibration responses of the uniform and tapered composite beam. Further, various parametric studies are performed to investigate the effect of taper angle and boundary conditions on natural frequencies of the uniform and tapered composite beams. It is shown that the natural frequencies of the taper configurations at all the modes considered are higher than those obtained from the uniform composite beam. It is concluded that the stiffness of the composite structures could be tailored according to the requirement by changing the taper angle of the composite along longitudinal plane to obtain the desired natural frequencies.

Abstract: The fighter aircraft transmission system consists of a light weight, High Speed Flexible Coupling (HSFC), used to transmit power from engine gear box to accessory gear box at speed ranging from 10,000 to 18,000 rpm. The HSFC accommodates larger parallel and axial misalignment resulting from differential thermal expansion of the aircraft engine and mounting arrangement. As the HSFC operates at higher rotational speeds close to critical velocities, it is important to analyze, the unbalance exciting forces considering the misalignment. In the present work, prediction of critical speed by camp bell diagram and unbalance response of the HSFC has been carried out using FEA. An experimental investigation also been carried out to study the influence of applied misalignment on a bi-plane dynamically balanced HSFC. The study shows that lower reaction forces are transmitted to HSFC end supports with the applied misalignments, as they are accommodated by the elastic material flexure of flexible plates.

Abstract: In structural applications, plates with cut-out or holes are commonly used. The structure will deteriorate dynamically due to presence of cut-out and experiences amplification in vibrations. This paper presents an experimental study on effect of position of vibratory flap on dynamic response of a clamped rectangular plate with cut-out subjected to harmonic excitation. Vibratory flap is an auxiliary plate attached on the main plate as a cantilever plate and acts as a dynamic vibration absorber, which is used to reduce the vibration of the plate at first and second frequencies. Investigation has been carried out for different combinations of flap location and orientation through experimental sine sweep test. From the test it is found that, there is an optimum position where vibration suppression is more effective with improved dynamic response of the plate with cut-out in the presence of flap. The experimental results have shown good agreement with the published finite element analysis results.

Abstract: The constitutive equations of MEE materials are used to derive the finite element equations involving the coupling between mechanical, electrical and magnetic fields. The candidate materials for this study are piezoelectric (BaTiO₃) and magnetostrictive (CoFe₂O₄) material. The linear buckling and vibration behavior of layered MEE beam under uniform magnetic field is carried out using finite element method. The present study is limited to clamped-clamped boundary conditions. The influence of stacking sequences and piezoelectric coupling on critical buckling magnetic field and vibration behaviour is investigated.

Abstract: Human comfort is of great importance to main powerhouse and vibration level should be controlled below the human comfort limit. Comparison of ISO2631/1-1985 and ISO2631/1-1997 was performed firstly in this study. It points out that weighted root-mean-square acceleration is basic variable for vibration evaluation. The reduced comfort boundary of 2 hours (0.260m/s²) in 1985 version is very close to the comfort threshold (0.315m/s²) in 1997 version. Above two values were selected as human comfort standard in this paper. After that, 3D dynamic finite element model of HongPing pumped storage station was established and vibration analysis under pressure fluctuations was conducted using time history method. The calculation results indicated that vibration of generator floor was mainly caused by the multiples of runner blade number frequency. Vibration level of generator floor would not lead to human discomfort.

Abstract: It is difficult to get a theoretic answer to the water flow load features of high dam flood discharge. Through direct measurement of water flow load features by arranging a surface pressure cell, the complicated point-surface conversion was avoided, and the shock load and surge load features were obtained. For the dam body outlet wall pressure, isolated the fluctuating load applied to the plunge pool floor and the downstream dam surface, the impact of the fluctuating load to the arch dam dynamic response at the flood discharge flow outlet was obtained, and then the equivalent fluctuating load on each discharge flow outlet was obtained by using flow-induced vibration back analysis. The test shows that the energy of the shock load and the surge load mainly centers in a frequency range between 0~1Hz, the shock load is about 2.5-6 times that of the surge load, and the surge load is about 4 times that of the outlet wall pressure.

Abstract: Much concern has been paid on the human-induced vibration of high-speed railway station structures in recent years. But the vibration responses are influenced greatly by are two key factors, which are rational pedestrian load model and accurate structure calculation model. Field test, therefore, is the most directly and valuable method to obtain the vibration responses of large-span railway station structure. The vibration responses of the waiting floor of the Hangzhou East Railway Station, which is just completed, are measured and analyzed. The test results showed that the vibration of waiting room floor under pedestrian load cannot be neglected for vibration comfort evaluation.

Abstract: Structural crack damage will degrade its carrying capacity, and affect the security of the structure. Thus early detection of crack damage is a guarantee of the structure safety. Cracks can change the vibration characteristics of the structure, therefore we proposed a method of identifying the crack damage based on the vibration modal. Take both ends fixed beam as an example, through establish the finite element models of crack-free beam and the crack beam with different location and different depth, we calculate the displacement modal parameters of beam before and after the damage, analyze the variation law of displacement modal horizontal component of change and displacement modal Axial displacement difference rate of change varies with crack depth and location, results show that the variation of displacement modal horizontal component and the change rate of displacement modal Axial displacement difference along crack direction are sensitive to cracks location and depth, these can be used as a basis for identification of beam’s crack damage.