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Go to Editorial ManagerThe frequency analysis of bones is a new tool to assess bone quality or integrity to characterize osteoporosis. The modal analysis can also be used to determine failure characteristics of remodeled bone in the fractured model. This study describes the numerical characterization of the modal analysis of the standardized femur model. The objective of the numerical procedure is to identify the natural frequencies and mode shapes of an unconstrained femur. The vibration modes of the human femur are studied by digital modal analysis and finite element simulation using ANSYS version 10 programs, with respect to femur dimensions and mechanical properties. The changing of the values of free vibration natural frequencies and mode shapes of the femur due to changing of the femur densities are studied. The results are compared to those obtained experimentally. The comparison of the results shows a good agreement, which indicates that the used model can be utilized in vibration analysis of bones.
A method based on experimentally calibrated rotor model is proposed in this work for unbalance identification of flexible rotors without trial runs. Influence coefficient balancing method especially when applied to flexible rotors is disadvantaged by its low efficiency and lengthy procedure, whilst the proposed method has the advantage of being efficient, applicable to multi-operating spin speeds and do not need trial runs. An accurate model for the rotor and its supports based on rotordynamics and finite elements analysis combined with experimental modal analysis, is produced to identify the unbalance distribution on the rotor. To create digital model of the rotor, frequency response functions (FRFs) are determined from excitation and response data, and then modal parameters (natural frequencies and mode shapes) are extracted and compared with experimental analogies. Unbalance response is measured traditionally on rotor supports, in this work the response measured from rotating disks instead. The obtained results show that the proposed approach provides an effective alternative in rotor balancing. Increasing the number of balancing disks on balancing quality is investigated as well.
Dynamic behavior of pipe conveying fluid at different cross section is investigated. Three kinds of supports are used, which are flexible, simply and rigid supports. The type effect of support on vibration characteristics and dynamic specification are studied. Also, the effect of some design parameters such as pipe material and Reynold numbers are investigated. The governing equations of motion for this system are derived using the finite element method which depends on beam theory. A finite element software (ANSYA-11) is presented to find first three eigenvalue (natural frequency) and eigenvector (mode shape) for pipe system in modal analysis. Velocity and pressure distribution are evaluated in a single phase fluid flow. A coupled field fluid-structure analysis was then performed by transferring fluid forces, solid displacements, and velocity across the fluid-structure interface. Finally the effective stresses (Von mises stress) in piping system are predicted in static analysis at various Reynold numbers, pipe material and pipe supports.
In the present study, the dynamic analysis of jacket type offshore structures under the action of sea waves is carried out. The finite element method is adopted for the solution of the problem. The effect of soil-structure interaction on the dynamic behavior of the offshore structure is taken into account due to the deformations of the soil caused by the motion of the structure, which in turn modify the response of the structure. The supporting elastic foundation is represented by Winkler type model having normal and tangential moduli of subgrade reaction. These moduli may be constant or varying linearly or nonlinearly along the embedded length of the piles that support the offshore structure. The pile tip conditions are also considered. A time domain solution is recommended. The generalized Morison's equation is used to calculate the wave forces and Airy's linear theory to describe the flow characteristics. Both free and forced vibration analyses are studied. The dynamic response has been obtained by modal analysis in conjunction with Wilson-0 method. As an example, a modified model of an actual jacket type offshore platform is analyzed under the action of wave forces.
In the present study, the dynamic analysis of jacket type offshore structures under the action of sea waves is carried out. The finite element method is adopted for the solution of the problem. The effect of soil-structure interaction on the dynamic behavior of the offshore structure is taken into account due to the deformations of the soil caused by the motion of the structure, which in turn modify the response of the structure. The supporting elastic foundation is represented by Winkler type model having normal and tangential moduli of subgrade reaction. These moduli may be constant or varying linearly or nonlinearly along the embedded length of the piles that support the offshore structure. The pile tip conditions are also considered. A time domain solution is recommended. The generalized Morison's equation is used to calculate the wave forces and Airy's linear theory to describe the flow characteristics. Both free and forced vibration analyses are studied. The dynamic response has been obtained by modal analysis in conjunction with Wilson-θ method. As an example, a modified model of an actual jacket type offshore platform is analyzed under the action of wave forces.
The discovery and identification of damages in engineering structures is very important in the field of engineering maintenance, as it is a great challenge in presenting new methods in measuring vibrations and discovering damages with the development in the field of automation and high accuracy in discovering damages. In this study, natural frequencies and mode shapes of transverse vibration for damage detection in structures are investigated. The study is performed for various crack depth and crack location. And suggested a new technique based on Continuous Wavelet Transform (CWT) and Convolution Neural Network (CNN). The comparison will be done by simulating the oscillations of a cantilever steel beam with and without defect as a numerical case. The proposed new technique proved to outperform classical methods and has achieved a100% accuracy in the identification of defect position for the data studied.