Journal of Engineering and Thermal Sciences
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Damage localization by wavelet analysis of uniform load surface
Get PDFThis paper presents a new technique for identifying damages in beam-type structures based on wavelet analysis of uniform load surface (ULS). Having come into focus in the field of damage detection, wavelet analysis revealed itself as a practical and state-of-the-art signal processing method for discerning abnormalities of mode shapes of structures, where the irregularities are considered as the indications of cracks. ULS is beneficial in terms of participating lower mode shapes and better immunity to noise. Continuous wavelet transform (CWT) is employed to analyze the ULS in order to find the damage site. The proposed method does not require any prior knowledge of the structure and combines the synergistic advantages of ULS technique and CWT to provide more accurate results in the face of high signal to noise ratio. A numerical study is conducted and three kinds of wavelets are utilized to evaluate the technique, namely symmetrical 4, Gaussian 4 and bior 6.8. The procedure is also experimentally investigated using a free-free beam structure
Aeroelastic self-oscillations of gas seal wall
Get PDFThe channel with a moving wall is considered to describe aeroelastic oscillations induced by gas flow. One of the channel walls has two degrees of freedom and it is supported by springs and dampers. The multi-fields investigation method is based on simulation transient gas flow in the channel to calculate aerodynamic forces acting on the wall. Corresponding rigidity and damping gas flow parameters obtained from these loads are included into the wall oscillations model for the stability analysis. The models are developed for two channel types: with smooth and finned wall. Aeroelastic stability boundary is shown for both channels. An effect of structural parameters on the realization of convergent oscillation and self-oscillation modes is shown too. A paradox of system destabilization with the increasing damping is observed for a certain parameter set
Kelvin Voigt’s model of single piezoelectric plate
Get PDFAssemblies and subassemblies based on a piezoelectric effect, in construction and operation of machines, have been used for decades. Among important examples of the piezoelectric elements can be distinguish non-destructive testing methods of a various objects, such as an ultrasonic diagnostic technique, in which a piezoelectric film is glued on a surface of a tested object. In this article an impact of these phenomena on the dynamic characteristics of a modeled system will be examined. It is a base for a study of complex piezoelectric plates by other methods. Moreover, a damping of the systems in a single piezoelectric plate will be considered
Study on analysis method for deepwater TTR coupled vibration of parameter vibration and vortex-induced vibration
Get PDFConsidering the vertical vibration, caused by floating platform, of top tensioned riser (TTR), an analysis method for the coupled vibration of parameter excited vibration and vortex-induced vibration is presented in this paper. With the section rotation and shear deformation due to the bending large displacement of TTR, a coupled vibration model of parameter excited vibration and vortex-induced vibration is put forward. And the vortex-induced vibration (VIV) of a TTR for 1500 m water depth is analyzed based on the model. The results show that the vertical vibration caused by floating platform increases transverse vibration displacement of TTR
Simulation and analysis of blood flow in bypass grafts with a cuff
Get PDFIn the paper the hemodynamics in the blood vessel and in the bypass graft is simulated and analyzed. A new construction of a bypass graft with a cuff is applied. The goal of the research is evaluation of influence of the ratio between the length and the height of the bypass graft cuff upon the structure of the blood flow and pathogenesis of the blood vessel. The results of the analysis indicate that blood flow velocity at a junction of the bypass graft and the blood vessel depends on the parameters of the cuff. The best results are obtained when the said ratio is 1.25 and 1.5 due to uneven distribution of pressure in the cuff. Choosing such parameters of a bypass cuff ensures better hemodynamics and absence of haemostasia, thus reducing a risk of formation of thrombi in the bypass graft and the blood vessel
Instantaneous frequency identification of a time varying structure using wavelet-based state-space method
Get PDFThis paper presents a method to identify the instantaneous frequency of the time varying structures based on wavelet and state space methods by using free and forced vibration response data. Firstly, the second-order vibration differential equations are rewritten as the first-order state equations using state space theory. Secondly, both excitation and response signals are projected by the Daubechies wavelet scaling functions. Thus, the first-order state equations are transformed into linear algebraic equations using the orthogonality of the scaling functions. Lastly, the equivalent time varying state space system matrices of time varying structure are extracted directly by solving the linear equations. The instantaneous frequencies are determined via eigenvalue decomposition of the state space system matrices. The proposed identification algorithm is investigated with a four degrees-of-freedom spring-mass-damper model. Numerical simulations demonstrate that the proposed method is robust and effective for identification of the abruptly, smoothly and periodically changing instantaneous frequencies of time varying structures
Vibrations, stability and compression of elements of packages made from corrugated board
Get PDFThe paper considers vibrations, stability and compression of a package element made from corrugated board. The analysis is based on a model of a structure consisting from twodimensional beams taking into account the orthotropic properties of the corrugated board. The problem of initial stability was solved and the first eigenmodes of stability were obtained. Performed experimental study allowed to determine the dependence of the vertical compression force on the geometrical parameters of the multilayered board before the development of plastic deformations in the board. The results of investigation are used for the design of package elements
Numerical model of journal bearing lubrication considering a bending stiffness effect
Get PDFAn analysis for operating characteristics of journal bearing lubrication system is performed based on the numerical model. Dynamic bearing lubrication characteristics such as oil film pressure and thickness distribution can be analyzed through a numerical model with an integration of elastohydrodynamics and multi-flexible-body dynamics (MFBD). In particular, the oil film thickness variation by elastic deformation is considered in the elastohydrodynamic analysis by applying the bending stiffness effect of journal. And the oil film thickness variation by the bending stiffness effect is applied to the fluid governing equations to calculate the oil film pressure in the elastohydrodynamic lubrication region. A series of process proposed in this study is available for the analysis of realistic elastohydrodynamic lubrication phenomenon. Also, a numerical example for the journal bearing lubrication system is demonstrated and compared with the experimental results. The numerical results considering the bending stiffness effect show a good agreement with the experimental results
Nonlinear free vibration analysis of the functionally graded beams
Get PDFNonlinear natural oscillations of beams made from functionally graded material (FGM) are studied in this paper. The equation of motion is derived according to the EulerBernoulli beam theory and von Karman geometric nonlinearity. Subsequently, Galerkin’s solution technique is applied to obtain the corresponding ordinary differential equation (ODE) for the FGM beam. This equation represents a kind of a nonlinear ODE containing quadratic and cubic nonlinear terms. This nonlinear equation is then solved by means of three efficient approaches. Homotopy perturbation method is applied at the first stage and the corresponding frequency-amplitude relationship is obtained. Frequency-amplitude formulation and Harmonic balance method are then employed and the consequent frequency responses are determined. In addition, Parameter Expansion Method is utilized for evaluating the nonlinear vibration of the system. A parametric study is then conducted to evaluate the influence of the geometrical and mechanical properties of the FGM beam on its frequency responses. Different types of material properties and boundary conditions are taken into account and frequency responses of the system are evaluated for different gradient indexes. The frequency ratio (nonlinear to linear natural frequency) is obtained in terms of the initial amplitude and compared for different materials and end conditions
Analytical model to determine fundamental frequency of free vibration of perforated plate by using unit step functions to express non-homogeneity
Get PDFIn the current study an analytical model to determine fundamental frequency of perforated plate is formulated. Non-homogeneity in Young’s modulus and density due to perforation is expressed by using unit step function in Rayleigh’s Quotient. In the present analysis the boundary condition considered is clamped at all edges. Perforated plate is considered as plate with uniformly distributed mass and holes are considered as nonhomogeneous patches. The deflected middle surface of the plate is approximated by a function which satisfies the boundary conditions. The proposed approach is validated by comparing results with finite element method modal analysis