RJAV vol XII issue 1/2015 81 ISSN 1584-7284 Finite Element Analysis of thin plates clamped on the rim of different geometric forms. Part II: The Absolute and Relative Variation of Natural Frequencies Cornel HAğIEGAN “Eftimie Murgu” University of Resita, Traian Vuia Square, No. 1-4, 320085, Resita, Romania, c.hatiegan@uem.ro Edwald-Viktor GILLICH University Politehnica of Timisoara, Faculty of Mechanics, Mihai Viteazu, No. 1, 300222, Timisoara, Romania, edwaldgillich@gmail.com Ovidiu VASILE Department of Mechanics, University “Politehnica” of Bucharest, Splaiul IndependenĠei 313, 060042 Bucharest, Romania, ovidiu_vasile2002@yahoo.co.uk Marian-Dumitru NEDELONI “Eftimie Murgu” University of Resita, Traian Vuia Square, No. 1-4, 320085, Resita, Romania, m.nedeloni@uem.ro Marcel JURCU “Eftimie Murgu” University of Resita, Traian Vuia Square, No. 1-4, 320085, Resita, Romania, marcel1jurcu@yahoo.com Petru MAGHEğI “Eftimie Murgu” University of Resita, Traian Vuia Square, No. 1-4, 320085, Resita, Romania, petrumaghy@yahoo.com Abstract: - In this paper, according to the natural frequencies resulted from the simulation for 30 vibration mode shapes of rectangular, square, trapeze and parallelogram plates that are analyzed with the SolidWorks program, the absolute respectively the relative variation has been obtained for thin clamped plates with the same area. The absolute and relative variation of natural frequencies was made for 6 possible cases of the 4 type of plates, namely: rectangle-square, trapeze-rectangle, trapeze-square, parallelogram-rectangle, parallelogram-square and trapeze-parallelogram. Keywords: - Finite Element Analysis, natural frequencies, absolute variation, relative variation 1. INTRODUCTION In the specialty literature, studies in plate’s theory have had authors such as: Timoshenko and Woinowsky-Krieger [1], Thompson [2], Reddy [3], Mindlin [4], Bratu [5] and others. Also, a reference book's Leissa [6] shows for free vibration of plates a considerable number of records frequencies and modal forms useful for researchers in engineering. In paper [7], for precise results by analyzing the free vibration of Timoshenko beam type and a type Mindlin plates, used as a method for combining the basic functions and methods radial pseudo-spectral reports for different lengths of elastic structures. In the paper [8], for transverse vibrations of a rectangular plate with restricted boundary conditions, use an improved method of Fourier series, and the results have shown that the natural frequencies are more influenced by rotational stiffness than the cross so that a very small change in the value of the rotational stiffness can result in a large change in the mode shapes of the plate. By disseminating relevant research results were made also at the University "Eftimie Murgu" of Resita respectively at ICECON (Research Institute for Construction Equipment and Technology) in the vibration analysis in the laboratory [9]-[13], modal analysis through finite element method in SolidWorks program to determine the natural frequencies and mass participation coefficients