Papers by Keyword: Mode Shape

Abstract: Modal analysis plays an important role at design stage which helps in diagnosing problems related to structural vibration. This paper delineates about the experimental work to investigate the modal parameters, such as mode shapes and natural frequencies of a metallic container. The modal parameters have been experimentally determined for the empty container, the container filled with one liter of water and the container filled with two liters of water. Theoretical analysis is also carried out through finite element analysis using ANSYS workbench 14 for finding out modal parameters of the empty container only. The boundary conditions of the container in the experimental and FEM analysis have been kept same. The values of modal parameters obtained by the two methods then compared for their proximity

Abstract: In order to identify structural damage locations and extent, a method based on ridge estimation and modal strain energy is presented in this paper. First, structural modal strain energy is given and a modal strain energy sensitivity damage equation is obtained. Then, considering the TikhonovTT regularization theoryTT, a ridge estimation method is proposed to solve the damage equation and ridge parameter of the method is optimized. Simulation results demonstrate that the proposed damage detection method based on ridge estimation and modal strain energy can identify structural damage locations and extent with good accuracy.

Abstract: A methodology to detect multi crack, with crack location and size due to transverse loading is presented in this paper taking the advantage of Adaptive neuro-fuzzy inference system (ANFIS) using modal analysis of cracked shaft. A simple supported shaft is subjected with axial and bending load for same angular position along with its longitudinal direction. The natural frequency of the shaft with its various crack positions and size are accurately determined analytically using strain energy release rate and stress intensity factor. The vibration parameters such as first three relative natural frequencies with their mode shapes at different locations and size are supplied to ANFIS to optimize the results. The crack location and size predicted from ANFIS model are verified with the theoretical data with acceptable error. The present method used in this paper is suitable and can be easily extended to complex structure with different orientation of multiple cracks.

Abstract: Stepped distributed dynamic systems are widely used in the engineering fields, and the dynamic characteristics analysis of them is very important. In this paper, the axial vibration of a stepped bar consisting of two uniform sections is studied, in order to solve the dynamic equation, the differential transformation method is used, the governing differential equation and the boundary conditions of the bar become simple algebraic equations. Doing some simple algebraic operations for these equations, the closed form solution of natural frequency, mode shape and the dynamic response can be obtained. Comparison the results obtained by the differential transformation method and finite element method, excellent agreement is achieved, and the effects of the stiffness of spring is discussed in this paper.

Abstract: Damage detection of a structure has drawn much attention in the aspect of maintenance and safety. In these aspects, vibration characteristics of a building have been constantly used in order to obtain a damage index of the whole building, but practical methodologies have not been presented yet. This study proposes a practical methodology to detect damage of a structure by using only the first natural frequency and mode shape of a building. The validity of the proposed methodology has been verified by experiments and numerical analyses. A result of verification confirms degree and location of damage may be detected with a relatively small error by the proposed methodology.

Abstract: The dynamic stability of a timber shell roof structure of the Palasport located in Bologna, has been investigated by means of reduced 1/30 scale model tested on seismic shaking table at Dynamic Testing Laboratory of IZIIS, Skopje, Macedonia. The model was physically modeled according to similitude lows and Buckingham's theorem as an artificial mass simulation model, using the same material as for the prototype structure. The supporting structure of the model was constructed by 26 micro-concrete foundations, 52 micro-concrete columns and 52 steel braces. The roof structure made of wooden lamellar beams forming triangles. The roof consists of a central cylindrical part and 2 lateral spherical parts. The connection between the beams was made by steel rings. The total number of the wooden beams was 550 forming 203 internal and external joints. The model was tested in vertical and horizontal direction considering various loading conditions: symmetrical and non-symmetrical. After definition of dynamic characteristics of the model, it was subjected to seismic excitation of Ancona, as well as Montenegro earthquakes. It was found out that the cylindrical part is more flexible than the spherical one. The largest amplitudes during the tests were obtained in vertical direction. The highest stress concentration was at the cylindrical central arches. The asymmetric load produced more unfavorable behavior than the symmetric one.

Abstract: Focusing on the damage detection using the fractal dimension analysis in plates, this study begins by giving a fractal dimension scanning method for beams. Then extend the algorithm to the plates by degrading the plate mode shape into transverse and longitudinal directions. With the affine transformation, the proposed method overcomes the incapability of identifying damage when using the higher-order mode shapes of the existing fractal dimension methods. Numerical results show that different types of cracks, crack locations and lengths can be detected using this method.

Abstract: This paper concerns with free vibration analysis of single-walled carbon nanotubes including the effect of small length scale based on the nonlocal elasticity theory. The governing equation of nanotube is derived from Euler beam theory including a nonlocal parameter in the function of masses. Classical solutions are obtained and then compared with the numerical solutions provided by finite element models. Effect of tube chirality and various geometrically boundary conditions are considered. The finite element models of nanotubes are assumed as the virtually analogous frame structures. In the numerical technique, the atomic masses existing on the both ends of beams are assigned by physical and chemical properties of carbon element. The results show that the natural frequencies significantly increase when the nonlocal parameters decrease. The numerical results are in good agreement with the classical solutions for the nanotubes with low aspect ratios and are acceptable for high aspect ratios. Furthermore, the first-ten mode shapes are demonstrated for various aspect ratios and boundary conditions, and the repeated natural frequencies are also highlighted in this study.

Abstract: Paradela Bridge is a metallic bridge located along the bank of the Tua River in northern Portugal. While the bridge is not currently in service, its structure is representative of many metallic truss structures built across the continent between the XIX and the XX century. Tua Line belongs to the Douro area that UNESCO recently declared as world heritage. This study acquires its importance since it might serve as an insight for the study of many other similar structures all over the country. This paper comprises a historic investigation of archived documents, an on-site survey to evaluate its present conditions, a dynamic testing and the construction and calibration of numerical models in finite element analysis (FEA) software, structural assessment and capacity rating estimation. The purpose of constructing numerical models was to evaluate the suitability of the bridge under the original loading and in accordance to modern design standards. The historical research revealed that the truss bridge was designed as a simply supported element and that a series of hand calculations were carried out on individual structural elements (e.g. main trusses, stringers and floor beams). Furthermore, a dynamic test was conducted in order to identify the global dynamic properties of the structure and to calibrate numerical models that ensure reliability and representativeness. FE models served through the structural assessment of the bridge in accordance with modern design codes and to estimate the safety of the bridge. Likewise, a nonlinear failure analysis was also conducted in order to estimate the capacity rate of the bridge and the likely failure modes.

Abstract: Active damping using piezoelectric element is one of the effective techniques to counter vibration problems. A 3D finite-element model is developed as part of investigation for damping control. The piezoelectric patches are surface bonded on quadrilateral thin plate and supported with spring damper elements. The main goal of this paper is to investigate mechanical characteristics of piezoceramic array on membrane and the effect of force excitation using small motor and electric excitation on the system. The system setup produced small vibration displacement and does not displace the plate beyond elastic strain region. The results show the linear behavior of piezoceramic and the correlation between electric excitation, motor vibration and displacement at the centre of the plate at different frequency range. The mode shapes and natural frequencies at low frequency spectrum are also presented. Therefore, the results can be used as reference to develop damping system with aid of piezoelectric patches.