An Edge-Based Smoothed Finite Element for Free Vibration Analysis of Functionally Graded Porous (FGP) Plates on Elastic Foundation Taking into Mass (EFTIM)

In this paper, free vibration analysis of the functionally graded porous (FGP) plates on the elastic foundation taking into mass (EFTIM) is presented. .e fundamental equations of the FGP plate are derived using Hamilton’s principle. .e mixed interpolation of the tensorial components (MITC) approach and the edge-based smoothed finite element method (ES-FEM) is employed to avoid the shear locking as well as to improve the accuracy for the triangular element. .e EFTIM is a foundation model based on the two-parameter Winkler–Pasternak model but added a mass parameter of foundation. Materials of the plate are FGP with a power-law distribution and maximum porosity distributions in the forms of cosine functions. Some numerical examples are examined to demonstrate the accuracy and reliability of the proposed method in comparison with those available in the literature.


Introduction
e plate resting on the elastic foundation (EF) is one of the most common types of structures which have practical applications in civil and industrial constructions, especially in transportation and irrigation. In particular, the structures of beams and plates on the EF are subjected to moving loads of means of transport such as roadbeds affected by vehicles, railway tracks, and aircraft runways. In most publications, when investigating the mechanical behavior of structures on the EF, the researchers mainly use the one-parameter Winkler foundation model [1] or two-parameter Winkler-Pasternak foundation model [2,3]. e analysis of plates resting on the Winkler-Pasternak foundation was previously addressed by several authors. For instance, Fazzolari [3] used an analytical method to consider free vibration and buckling of porous FG Sandwich beams resting on the EF with the Winkler-Pasternak foundation model. Leissa [4] presented results for the free vibration of rectangular plates. Xiang et al. [5] studied free vibration for Mindlin plates on the Winkler-Pasternak foundation using an analytical method. Omurtag et al. [6] used the finite element method (FEM) for the free vibration analysis of the Kirchhoff plates resting on the EF.Özçelikörs et al. [7] analyzed the exact solutions of bending, buckling, and vibration problems of a Levy-plate on the two-parameter foundation. Matsunaga [8] used a special higher-order plate theory (HSDT) to analyze vibration and buckling of thick plates on the EF. Ayvaz et al. [9] developed a modified Vlasov model to consider the earthquake response of thin plates on the EF. Shen et al. [10] based on the Rayleigh-Ritz method to study free and forced vibration of the Reissner-Mindlin plates resting on the EF. Liew et al. [11,12] and Han and Liew [13] analyzed the free vibration of rectangular plates resting on the EF using a differential quadrature method. Zhou et al. [14] considered the vibration of rectangular plates on the EF using the Ritz method. Chucheepsakul and Chinnaboon [15] investigated plates by a two-parameter foundation model using a boundary element method. Civalek and Acar [16] investigated the bending of Mindlin plates on the EF by developing a singular convolution method. Ferreira et al. [17] presented bending and free vibration analyses of the FGP plates on the Winkler-Pasternak foundation by using radial basis functions. Shahsavari et al. [18] used a new quasi-3D hyperbolic theory for the free vibration analysis of the FGP plates resting on the EF. Zenkour and Radwan [19] proposed an exact analytical approach for free vibration analysis of laminated composite and Sandwich plates resting on the EF using a four-unknown plate theory. Duc et al. [20] presented the analysis of nonlinear thermal dynamic response of shear deformable functionally graded plates on the EF. Mahmoudi et al. [21] developed a refined quasi-three-dimensional shear deformation theory to analyze the functionally graded Sandwich plates resting on the two-parameter EF under thermomechanical loading. Duc et al. [22] used an analytical method to calculate static bending and free vibration of FG carbon nanotube-reinforced composite plate resting on Winkler-Pasternak foundations. ang et al. [23] considered the effects of variable thickness on buckling and postbuckling behavior of imperfect sigmoid FGM plates on elastic medium subjected to compressive loading. Banhien et al. [24] developed the isogeometric analysis for buckling analysis of nonuniform thickness nanoplates in an elastic medium.
In recent years, the FGP materials have attracted great interest from many researchers over the world due to their lightness and high strength. As a result, they are widely applied for civil engineering, aerospace structures, nuclear plants, and other applications. Kim et al. [25] investigated bending, vibration, and buckling of the FGP microplates using a modified couples stress based on the analytical method. Coskun et al. [26] presented analytical solutions to analyze the bending, vibration, and buckling of the FG microplates based on the third-order shear deformation theory (TSDT). Chen et al. [27] investigated the static bending and buckling of the FGP beams by using the Timoshenko beam theory. Rezaei and Saidi [28,29] studied the vibration of rectangular and porous-cellular plates based on an analytical method. e vibration of the FGP shallow shells using an improve Fourier method was examined by Zhao et al. [30]. Moreover, the dynamics of the FGP doubly-curved panels and shells were also investigated in [31]. Li et al. [32] analyzed the nonlinear vibration and dynamic buckling of the Sandwich FGP plates with graphene platelet reinforcement (GPL) on the EF. For nonlinear problems, Sahmani et al. [33] used the nonlocal method to analyze nonlinear large-amplitude vibrations of the FGP micro-/nanoplates with GPL reinforce. Wu et al. [34] studied the dynamic of the FGP structures by using FEM. ang et al. [35] investigated the elastic buckling and free vibration of porous cellular plates based on the first-order shear deformation theory (FSDT). Although the FGP materials have many different types, in this paper, the authors only use the distribution of porosity as presented in [25,26].
In the other front of the development of numerical methods for computational mechanics, Liu et al. [36] have recently proposed an edge-based smoothed FEM (ES-FEM) using triangular elements which show some following excellent properties for the 2D solid mechanics analyses such as (1) the numerical results are often found superconvergent and very accurate; (2) the method is stable and works well for dynamic analysis; and (3) the implementation of the method is straightforward and no penalty parameter is used. e ES-FEM has been developed for n-sided polygonal elements [37], viscoelastoplastic analyses [38], 2D piezoelectric [39], primal-dual shakedown analyses [40], fluid structure interaction [41,42], and various applications [43][44][45]. Recently, in an effort to improve the accuracy of the plate and shell structural analyses, the classical MITC3 element [46] incorporated with the ES-FEM [36], has been proposed to give the so-called ES-MITC3 element [47][48][49][50][51]. In the formulation of the ES-MITC3, the system stiffness matrix is employed using strains smoothed over the smoothing domains associated with the edges of the MITC3 elements. e numerical results demonstrated that the ES-MITC3 has the following great properties [47]: (1) the ES-MITC3 can eliminate transverse shear locking even with the ratio of the thickness to the length of the structures reach 10 − 8 and (2) the ES-MITC3 has better accuracy than the existing triangular elements such as MITC3 [46], DSG3 [52], and CS-DSG3 [53] and is a good competitor with the quadrilateral element MITC4 element [54]. e objective of this research now is to further extend the ES-MITC3 method for free vibration analyses of the FGP plates resting on the EFTIM. e governing equations are derived from the FSDT and the Reissner-Mindlin plate theory due to simplicity and computational efficiency. Besides, the EFTIM is modelled based on a two-parameter Winkler-Pasternak foundation model and added in a mass parameter of foundation. e plate is made from the FGP materials with a power-law distribution (k) and maximum porosity distributions (Ω) in the forms of cosine functions. e accuracy and reliability of the present formulation are verified by comparing with those of other available numerical results. Moreover, the effects of some geometric parameters and material properties on the free vibration of the FGP plates are also examined in detail.

Functionally Graded Porous Material Plates on Elastic Foundation
Let us consider an FGP plate resting on EFTIM, as shown in Figure 1. e FGP materials with a variation of two 2 Mathematical Problems in Engineering constituents and three different distributions of porosity through-thickness are presented as follows [25,26]: where Ω is the maximum porosity value. A typical material property of the FGP materials can be considered as in the following power-law relations: where P t and P b are the typical material properties at the top and the bottom surfaces, respectively; and k is the power-law index. e normalized distributions of porosity through the thickness are shown in Figure 2 where w is the displacement of FGP plate; k 1 and k 2 are, respectively, Winkler foundation stiffness and shear layer stiffness of the Pasternak foundation. In order to mention the effectiveness of the foundation mass involved in the oscillation as well as the continuous interaction of the spring with the plate, the parameter β with unit kg −1 is added. It characterizes the effective level of the foundation mass involved in vibration, which is determined based on an experimental basis and the ratio of the density of the foundation to the density of plate material which is defined as μ F � ρ F /ρ. us, the density of mass m f involved vibration with the foundation is determined m f � βμ F ρ. From equation (3) we see that, for the static problem, the EFTIM model and Winkler-Pasternak foundation model are the same. But, for the dynamic problems, these two models have differences, and when omitting the influence parameters of the foundation mass, the EFTIM model is equivalent to the Winkler-Pasternak foundation model. In addition, this foundation model also covers the Winkler foundation model when the influence of shear parameters and foundation mass parameters ignored. It was found that the EFTIM model closely resembles the true feature of the foundation, including the Pasternak and Winkler foundation models.

First-Order Shear Deformation eory for FGP Plates.
e displacement of the FGP plates in the present work based on the FSDT model can be expressed as where u, v, w, θ x , and θ y are five unknown displacements of the midsurface of the plate. For a bending plate, the strain field can be expressed as follows: where the membrane strain is given as e bending and transverse shear strains are written as From Hooke's law, the linear stress-strain relations of the FGP plates can be expressed as where where E(z) presents for effective Young's modulus and υ represents Poisson's ratio.

Weak Form Equations.
To obtain the motion equations of the FGP plates for the free vibration analysis, Hamilton's principle is applied with the following form: where U and K are the strain and kinetic energies, respectively. e strain energy is expressed as where U f is the strain energy and U p is the strain energy where ε � ε m κ T and and A, B, F, and C can be given by e kinetic energy in equation (11) is given by where K p is the kinetic energy where u T � u 0 v 0 w 0 θ x θ y ϕ x ϕ y is the displacement field and m p is the mass matrix defined by where (I 1 , I 2 , In equation (11), the kinetic energy of the mass of foundation K f is defined as Substituting equations (12) and (18) into equation (11), the weak formulation for the free vibration of the FGP plate is finally obtained as

Formulation of the Finite Element Using the MITC3
Element. e middle surface of plate ψ is discretized into n e finite three-node triangular elements with n n nodes such that ψ ≈ n e e�1 ψ e and ψ i ∩ ψ j � ∅, i ≠ j. en, the generalized displacements at any point u e � [u e j , v e j , w e j , θ e xj , θ e yj ] T of element ψ e can be approximated as where n ne is the number of nodes of ψ e ; N(x) is the shape function matrix; and d e j � [u e j , v e j , w e j , θ e xj , θ e yj ] T is the nodal degrees of freedom (d.o.f ) associated with the j th node of ψ e . e membrane bending strains of MITC3 element can be expressed in matrix forms as follows: where To eliminate the shear locking phenomenon as the thickness of the plate becomes small, the formulation of the transverse shear strains of the MITC3 element based on FSDT [36] in this study can be written as follows: where Mathematical Problems in Engineering with where Here, a � x 2 − x 1 , b � y 2 − y 1 , c � y 3 − y 1 , and d � x 3 − x 1 are pointed out in and A e is the area of the three-node triangular element as shown in Figure 3.
Substituting the discrete displacement field into equation (22), we obtained the discrete system equations for free vibration analysis of FGP plate resting on the EF, respectively, as where K and M are the stiffness and mass matrices, respectively. e stiffness matrix in equation (38) can be written as where where Next, the mass matrix in equation (38) can be defined as where

Formulation of an ES-MITC3 Method for FGP Plates.
e smoothing domains ψ k is constructed based on edges of the triangular elements such that ψ � ∪ n k k�1 ψ k and ψ k i ∩ ψ k j � ∅ for i ≠ j. An edge-based smoothing domain ψ k for the inner edge k is formed by connecting two end-nodes of the edge to the centroids of adjacent triangular MITC3 elements, as shown in Figure 4.
Applying the edge-based smooth technique [36], the smoothed membrane, bending, and shear strain ε k m , κ k , γ k over the smoothing domain ψ k can be created by where ε m , κ, and γ the compatible membrane, bending, and the shear strains, respectively; Φ k (x) is a given smoothing function that satisfies at least unity property In this study, we use the constant smoothing function where A k is the area of the smoothing domain ψ k and is given by where n ek is the number of the adjacent triangular elements in the smoothing domain ψ k ; and A i is the area of the ith triangular element attached to the edge k. By substituting equations (47) where n nk sh is the total number of nodes of the triangular MITC3 elements attached to edge k (n nk sh � 3 for boundary edges and n nk sh � 4 for inner edges as given in Figure 4; d k j is the nodal d.o.f associated with the smoothing domain ψ k ; and B k mj , B k bj , and B k sj are the smoothed membrane, bending, and shear strain gradient matrices, respectively, at the j th node of the elements attached to edge k computed by e stiffness matrix of the FGP plate using the ES-MITC3 is assembled by where K k is the ES-MITC3 stiffness matrix of the smoothing domain ψ k and given by where

Accuracy of the Proposed Method
In this section, the various numerical examples are solved to verify the reliability and accuracy of the proposed method. For convenience, the stiffness factors and nondimensional frequencies of the plates are defined as the following equations: To demonstrate the performance of numerical results, the relative frequency error is defined by where λ pr and λ re are nondimensional frequencies of present method and nondimensional frequencies in [17,18], respectively. e results of the convergence of the first two nondimensional frequencies of the plate in the case of fully simple support (SSSS) plate and a fully clamped (CCCC) plate with h/a � 0.1, K 1 � 100, K 2 � 10, respectively, are shown in Figure 5. From these results, it can be seen that almost all frequencies corresponding to different cases of boundary conditions (BC) converge with 18 × 18 element mesh. For 18 × 18 mesh, we compare the first three nondimensional frequencies of a plate resting on the Winkler-Pasternak foundation with the published results as shown in Table 1. It can be seen that the present results agree well with the results of the authors using analytical methods [5,14,17] and are more accurate than those using the original MITC3 element and FEM [6]. In addition, from Table 2, it is obvious that the relative error of the present results compared to [18] is less than 2%. In [18], they used a new quasi-3D hyperbolic theory to investigate the free vibration of the FGP plate resting on the EF. ese results are the basis to analyze the free vibration of FGP plates on the EFTIM.  Next, we consider an SSSS FGP plate (Al/Al 2 O 3 ) with its material properties as follows: metal (Al) E b � 70 GPa, ρ b � 2702 kg/m 3 and ceramic (Al 2 O 3 ) E t � 380 GPa, ρ t � 3800 kg/m 3 . Poisson's ratio is fixed at υ � 0.3. e FGP plate with even porosities is expressed as in [18]: where ξ(ξ ≤ 1) presents the porosity volume fraction. e stiffness factor and nondimensional frequencies of the plates are shown in equation (58) with H b � (E b h 3 /12(1 − υ 2 )) and  Plates . e first nondimensional frequencies of present work compared with [18] are shown in Table 2.

Numerical Results and Discussions
For free vibration problems, a fully simple support (SSSS) FGP plate is considered, e first six nondimensional frequencies of the FGP plate with porosity distribution of Case 1 and stiffener of foundation K 1 � 100, K 2 � 10 are shown in Table 3; and the first six mode shapes are presented in Figure 6. e stiffness factors and nondimensional frequencies of FGP plate are shown in equation (58) with

Influence of the Parameters of the EFTIM to the Free
Vibration for the FGP Plate. Firstly, in order to investigate the effect of the featured-index of the mass of foundation β to free vibration of the FGP plate, the featured-index of mass is changed from 0 to 1. In Figure 7 and Table 4, it is seen that all cases of porosity distribution featured-index of the mass of foundation β significantly influence to free vibration of the FGP plate. As β increases, the mass of the plate increases, and the frequencies of the plate decrease. For all cases of porosity distribution of the FGP plate, the porosity distribution of  Next, the influence of nondimensional parameters of foundation stiffness K 1 and K 2 is investigated. We change K 1 from 100 to 1000 and K 2 from 10 to 100 with respect to β � 0.5 and μ F � 0.5. e first nondimensional frequency of the FGP plate with three cases of porosity distribution is   Table 5 and shown in Figure 8. As shown in these figure and table, when K 1 and K 2 increase, the nondimensional frequency of plate also increases. We also examine the effect of (β, K 1 ) and (β, K 2 ) parameters to nondimensional frequency. e numerical result is presented in Table 6 and Figure 9. Consequently, Winkler foundation stiffness K 1 and shear layer stiffness of Pasternak foundation K 2 make stiffness of plate become greater and the mass of the EF involved in the plate's vibration makes reduce frequencies.
6.2. Influence of the Parameters-FGP to Free Vibration of the Plate on EFTIM. Let us consider the effect of materials property to free vibration of the FGP plate. e power-law index k is changed from 0 to 10, and maximum porosity distributions Ω has the value from 0 to 1. We examine the SSSS FGP plate and fully clamped (CCCC) plate resting on EFTIM.
e parameters of EFTIM are given by β � 0.5, μ F � 0.5, K 1 � 100, and K 1 � 10. e first nondimensional frequencies of plate with three cases of porosity distribution is shown in Table 7 and Figure 10.
As shown in these figures and tables, when k and Ω change, the values of nondimensional frequency change with no rule. It is understandable because with each case of change in porosity distributions k and Ω, the stiffness and the weight of the plate changes. From Figure 10, in the case of the CCCC plate, nondimensional frequency depending on k and Ω value varies more complex than the case of the SSSS plate. If k and Ω values are same, the frequency of the CCCC plate is larger than that of the SSSS plate. e results are quite reasonable because the SSSS boundary condition inherently offers more flexible boundary conditions than the CCCC boundary condition.

Conclusions
In this paper, new numerical results of free vibration of the FGP plate resting on EFTIM are studied. We used the ES-MITC3 to establish the fundamental equation of the FGP plate. e computed results obtained by this approach are in excellent agreement with others published. Our work has the following advantages. e novel ES-MITC3 which computes the free vibration of the plate on EF takes into account the mass of foundation. e numerical results obtained by ES-MITC3 show good agreement with the reference solutions and are more accurate than those obtained by the original MITC3. e elastic foundation of Pasternak with three-parameters is developed by adding the featured-index of mass β to accurately describe the actual elastic foundation. e mass of the elastic foundation involved in the vibration of the plate reduces the frequency of vibration, while two parameters K 1 and K 2 effect the stiffness of the plate. e material parameters k, Ω and the case of porosity distribution effect of vibration of the plate. Numerical results are useful for calculation, design, and testing of material parameters in engineering and technologies.
is study suggests some further works on the dynamic response and heat transfer problems of the FGP plate resting on EF using different plate theories.

Data Availability
e data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.