Natural frequencies of thin rectangular plates using homotopy-perturbation method

A technique based on the Galerkin approach has been developed for determination of the natural frequencies of rectangular plates with discrete masses added. The technique is applied to the rectangular plates with simply supported and clamped boundary conditions, but no difficulty exists in applying the same method to the plates of various forms with different boundary conditions. The results of this technique applied to one particular case are compared to a solution obtained by an exact method; the comparison shows the two methods to be in excellent agreement.

A simple semigraphical method is developed for calculating the natural frequencies of systems made up of two plates rigidly joined to each other at a common edge. The mode shapes are discussed, and the modes for which coupling is most severe are indicated. It is demonstrated that at higher modes the component plates become effectively uncoupled, as one would expect intuitively. Charts for easy determination of the natural frequencies are presented. One of these gives, as a by-product, the natural frequencies of rectangular plates (of any dimensions) having one edge clamped and the remaining three simply supported. (Supported by the Office of Naval Research-Acoustic Branch.)

The determination of natural frequencies of rectangular plates with mixed boundary conditions by discrete singular convolution

Natural frequencies of rectangular plates

In this paper, the nonlinear free vibrations of thin symmetric and non-symmetric cross-ply composite plates subjected to biaxial initial stresses are investigated. Because of their excellent properties such as specific strength and specific stiffness, composite plates have wide applications in aerospace and mechanical structures. Based on Von-Karman's strain-displacement relations and using Galerkin method, the nonlinear differential equation of free vibrations of initially stressed composite plate is obtained. This nonlinear equation is solved using two different analytical perturbation methods, namely method of multiple scales (MTS) and homotopy perturbation method (HPM), to analyze the nonlinear vibrations of initially stressed cross-ply composite plates. Effects of tensile and compressive biaxial initial stresses, initial vibration amplitude, thickness, and aspect ratios of the composite plates on the frequency behavior are investigated. The validity of the results is confirmed by making a comparison with those reported in the literature. According to the results, both analytical solutions show increasing trends for natural frequency parameters by increasing normal initial stresses. Regardless of the value of initial biaxial stresses, for both symmetric and non-symmetric plates, the results of MTS and HPM are in close agreement for the smallest initial amplitude. However, for compressive initial stresses, by increasing initial amplitude ratios, the discrepancies between the results of HPM and MTS increase for symmetric and non-symmetric plates. Although HPM includes less computational effort (smaller length of formulation) than MTS, the linear-to-nonlinear frequency ratios obtained using MTS method become closer to those obtained by HPM as initial vibration amplitude is decreased and initial stress is increased.

An analysis is presented of the forced vibrations of non-homogeneous rectangular plate of variable thickness on the basis of classical plate theory. The non-homogeneity of the plate material is assumed to arise due to the variation in density which is assumed to vary linearly. The thickness of the plate also varies linearly. Approximate formulae are proposed for estimating the maximum deflection of a rectangular plate subject to a uniformly distributed harmonic lateral load. Maximum deflection for the different values of the fundamental frequency of vibration is computed for a simply supported-free-simply supported-free plate for various values of taper constant, non-homogeneity constant and aspect ratios. Results are presented in graphical form.

In this study, we applied the homotopy perturbation (HP) method for solving linear and nonlinear fourth-order boundary value problems. The analytical results of the boundary value problems have been obtained in terms of a convergent series with easily computable components. Comparisons between the results of the HP method and the analytical solution showed that this method gives very precise results with a few terms. In the implied HP method, some unknown parameters in the initial guess are introduced, which are identified after applying boundary conditions. This improvement results in higher accuracy.

Since analytical perturbation methods depend on a small parameter and finding this small parameter is difficult, two powerful analytical methods are introduced to be applied to solve nonlinear heat transfer problems in this article. One is He's variational iteration method ( VIM ) and the other is the homotopy-perturbation method ( HPM ). The VIM is used to construct correction functionals using general Lagrange multipliers identified optimally via the variational theory. The HPM converts a difficult problem into a simple problem which can be easily solved. In this article, the VIM is used to solve some nonlinear heat transfer equations with variable heat transfer coefficient. The results are then compared with those obtained by the HPM and the exact solution.

A novel hybrid numerical/experimental identification procedure for the assessment of welding-induced residual stresses in rectangular plates is proposed and evaluated. This procedure explores the influence of the stress state on the dynamic responses of structural components, according to the so-named stress-stiffening effect. The technique consists in using a set of experimental natural frequencies of the welded plate and a mathematical model relating the residual stresses to the natural frequencies to formulate an optimization problem. The cost function represents the differences between the experimental and model-predicted dynamic responses and the design variables are interpreted as parameters of the mathematical model describing the stress distribution over the plate. A parameterized stress model suitable to the case of welding residual stresses is presented in terms of a differential equation that relates an Airy's stress function to the plastic strains resulting from the welding process. From this stress function, the stress components σx, σy and τxy (assuming plane stress state) are computed. Genetic Algorithms are used to solve the numerical optimization problem. To demonstrate the feasibility of the method, it is used for the assessment of residual stresses generated by TIG (GTAW) welding of a thin rectangular steel plate, for which experimentally measured natural frequencies and numerically computed residual stress distributions are available in the literature.(*) A preliminary version of this article has been presented in the 17th International Congress of Mechanical Engineering, promoted by Brazilian Society of Mechanical Sciences and Engineering, São Paulo, Brazil, 2003.

Silicon as an anisotropic mechanical material: Deflection of thin crystalline plates

This paper investigates the parametric resonance of electrostatically actuated MicroElectroMechanicalSystems (MEMS) cantilever resonators. The electrostatic force is modeled to include fringe effect. The MEMS consists of a cantilever over a parallel ground plate and an AC voltage between them. The actuation frequency is near first natural frequency of the cantilever beam. This leads to parametric resonance. It is of interest to investigate the amplitude frequency response of MEMS cantilever resonators. This paper uses the Homotopy Analysis Method (HAM), which is able to capture nonlinear behaviors for higher amplitudes, large parameters, and strong nonlinearities. The base method used for comparison in this work is the method of multiple scales (MMS). MMS is a perturbation method. It requires a relatively short computational time for simulations. Although the CPU time is advantageous, MMS is only accurate for weak nonlinearities and low amplitudes. It is in the interest to compare how well HAM captures the softening behavior of this system as opposed to MMS. In this paper the influences of Casimir forces and Van der Waals effects are included. Electrostatic, Van der Waals and Casimir forces are nonlinear. HAM is a deformation technique that continuously deforms the initial guess, provided to the procedure, to the exact solution. In this work the first and second order deformation equations are constructed for the equation of motion governing the behavior of the MEMS cantilever beam. In the first order deformation, HAM deviates from the solution obtained by MMS. This deviation demonstrates the power of the method to capture the softening behavior more accurately than MMS even at the 1st order deformation HAM. In the second order deformation construction, the HAM’s solution softens more than the previous, demonstrating that higher order deformation approximations result in higher accuracy. In the second order deformation, HAM contains the convergence control parameter. This parameter is chosen via the c0 curve approach. Up to 2nd order HAM deformations are evaluated for this paper. These higher order homotopy deformation solutions were developed and automated symbolically in the software Mathematica and tested numerically using Matlab software.

In this note, the hybrid method (combination of the homotopy perturbation method (HPM) and the Gauss elimination method (GEM)) is developed as a semi-analytical solution for the first kind system of Cauchy-type singular integral equations (CSIEs) with constant coefficients. Before applying the HPM, we have to first reduce the system of CSIEs into a triangle system of algebraic equations using GEM, which is then carried out using the HPM. Using the theory of the bounded, unbounded and semi-bounded solutions of CSIEs, we are able to find inverse operators for the system of CSIEs of the first kind. A stability analysis and convergent of the proposed method has been conducted in the weighted Lp space. Moreover, the proposed method is proven to be exact in the Holder class of functions for the system of characteristic SIEs for any type of initial guess. For each of the four cases, several examples are provided and examined to demonstrate the proposed method’s validity and accuracy. Obtained results are compared with the Chebyshev collocation method and modified HPM (MHPM). Example 3 reveals that the error term of the MHPM is slightly superior to that of the HPM. One of the features of the proposed method is that it can be solved as a complex-valued system of CSIEs. Numerical results revealed that the hybrid method dominates others.

Chapter Nine - The BEM for Time Dependent Problems

A nine-node isoparametric plate element in conjunction with first-order shear deformation theory is used for free vibration analysis of rectangular plates with central cutouts. Both thick and thin plate problems are solved for various aspect ratios and boundary conditions. In this article, primary focus is given to the effect of rotary inertia on natural frequencies of perforated rectangular plates. It is found that rotary inertia has significant effect on thick plates, while for thin plates the rotary inertia term can be ignored. It is seen that the numerical convergence is very rapid and based on comparison with experimental and analytical data from literature, it is proposed that the present formulation is capable of yielding highly accurate results. Finally, some new numerical solutions are provided here, which may serve as benchmark for future research on similar problems.

In this paper, the Homotopy Analysis Method (HAM) proposed by Liao (1992a, 1992b, 1992c, 1992e, 1995a, 1997a) is greatly improved by introducing a nonzero variable ℏ. Based on the HAM, a new numerical approach for strongly non-linear problems is proposed and applied to solve, as an example, a non-linear heat transfer problem, i.e. microwave heating of an unit plate, so as to verify its validity and great potential. Our numerical experiments show that, by the proposed approach, iteration is not absolutely necessary for solving non-linear problems. This fact may deepen our understanding about numerical techniques for non-linear problems and widen our field of vision. Moreover, the basic ideas proposed in this paper may afford us a great possibility to greatly improve our current numerical techniques.