Local Projection-Based Stabilized Mixed Finite Element Methods for Kirchhoff Plate Bending Problems
Abstract
Based on stress-deflection variational formulation, we propose a family of local projection-based stabilized mixed finite element methods for Kirchhoff plate bending problems. According to the error equations, we obtain the error estimates of the approximation to stress tensor in energy norm. And by duality argument, error estimates of the approximation to deflection in H1-norm are achieved. Then we design an a posteriori error estimator which is closely related to the equilibrium equation, constitutive equation, and nonconformity of the finite element spaces. With the help of Zienkiewicz-Guzmán-Neilan element spaces, we prove the reliability of the a posteriori error estimator. And the efficiency of the a posteriori error estimator is proved by standard bubble function argument.
1. Introduction
To design conforming finite element method for fourth-order elliptic partial differential equation, it requires C1-continuity finite element space which is arduous to construct (cf. [1]). Alternatively, mixed finite element methods are preferred because C0-continuity finite element space is sufficient for deflection. Another advantage of mixed finite element methods is that the stress or Δu can be approximated simultaneously.
One kind of mixed finite element methods is based on Ciarlet-Raviart method whose unknowns are Δu and deflection u (cf. [2]). Optimal convergence rate of the approximation to u and suboptimal convergence rate of the approximation to Δu of Ciarlet-Raviart method were obtained in [3–5], and a posteriori error analysis was given by [6]. It is worth to mention that mixed discontinuous Galerkin method for biharmonic equation advanced in [7] is on the basis of Ciarlet-Raviart method. Based on a first-order system and using single face-hybridizable technique in [8], Cockburn et al. derived a hybridizable and superconvergent DG method in [9] which improved the convergence rate of the approximation to Δu.
Another kind of mixed finite element methods for Kirchhoff plate bending problems is based on stress-deflection formulation. Standard stress-deflection mixed finite element methods require the finite element space for stress belonging to H(div, Ω, 𝕊), which is substantially difficult to construct since the tensor-valued function must be symmetric and belong to H(div, Ω) simultaneously. As far as we know, the only standard mixed finite element method of this kind mentioned in [10] adopts composite element. Fortunately, several H(div, Ω, 𝕊)-conforming elements have been developed in the last decade. Arnold and Winther designed the first pure polynomial H(div, Ω, 𝕊)-conforming elements in two dimensions in [11], which were extended to three dimensions in [12, 13]. The vertex degrees of freedom are unavoidable when using pure polynomial shape function spaces, which is demonstrated in [11]. With regard to this, Guzmán and Neilan constructed H(div, Ω, 𝕊)-conforming elements by enriching the polynomial shape function spaces with rational bubble functions which can avoid vertex degrees of freedom in [14]. On the other hand, some efforts have been made to lower the requirement of H(div, Ω, 𝕊)-conforming finite element space for stress. Along this way, Hellan-Herrmann-Johnson method raised in [15–17] is a wonderful mixed method for plate bending problems whose convergence rates for both variables are optimal. Behrens and Guzmán introduced a new mixed method which is based on a system of first-order equations and uses nonsymmetric finite element tensor space to approximate stress in [18]. And a hybrid technique is used for this mixed method to reduce the globally coupled degrees of freedom to only those associated with Lagrange multipliers, which is very efficient in implementation. Moreover, a local postprocessing technique is used to produce new approximation of u with superconvergence rate. In the context of DG methods, LCDG method using fully discontinuous finite element space for stress devised in [19] is also based on stress-deflection formulation.
In this paper, we propose a family of local projection-based stabilized mixed finite element methods for problem (1) based on the stress-deflection variational formulation. The stress tensor will be approximated in Arnold-Winther element spaces [11] which uses polynomial shape functions, and deflection will be approximated in Lagrangian element spaces [1, 20] in our mixed methods. To ensure the well-posedness of our mixed methods, we use local projection method which has been widely used in Stokes equation (cf. [21, 22]), second-order elliptic problems (cf. [23–25]), and fourth-order obstacle problem (cf. [26]). According to the error equations, we obtain that the convergence rate of the approximation to stress tensor in energy norm is O(hmin {m−1+α,k−1−α}). And by duality argument, the convergence rate of the approximation to deflection in H1-norm is shown to be O(hmin {m−1+2α,k−1}). An error estimator is proposed which is closely related to the second-order system (equilibrium equation and constitutive equation) and nonconformity of the finite element spaces. Using the similar argument as in [6] by replacing Hsieh-Clough-Tocher element space by Zienkiewicz-Guzmán-Neilan element space proposed in [27], we prove the reliability of the a posteriori error estimator with all orders. However, by using Hsieh-Clough-Tocher element space which includes the third-order polynomials, the a posteriori error estimator is only proved to be reliable for k = 2,3 in [6]. Furthermore, efficiency of the a posteriori error estimator is achieved by bubble function argument.
The rest of this paper is organized as follows. A family of local projection based stabilized mixed finite element methods based on stress-deflection variational formulation for Kirchhoff plate bending problems is proposed in Section 2. An a priori error analysis and a posteriori error analysis for the stabilized mixed finite element methods are given in Sections 3 and 4, respectively.
2. Stabilized Mixed Finite Element Methods
- (i)
the values of three components of τ at each vertex of K,
- (ii)
the values of the moments of degree at most k − 2 of τn on each edge e of K,
- (iii)
the values of the moments ∫K τ : ς dx for all ς ∈ Nk−2(K),
Next, let us illustrate the well-posedness of stabilized mixed finite element method (12)-(13).
Proof. Since Σh and Vh are both finite dimensional, it is enough to show that if f = 0, then σh = 0, uh = 0. Taking τ = σh in (12) and v = uh in (13), and adding two equalities, it follows that a(σh, σh) + c(uh, uh) = 0. Thus σh = 0 and ∇uh = Qk−2(∇uh) ∈ Xk−2 in Ω from the definition of a(·, ·) and c(·, ·). Then (12) is reduced to
3. A Priori Error Analysis
In this section, we provide an a priori error analysis for stabilized mixed finite element methods (12)-(13).
3.1. Preliminaries
For simplicity, we still write Ih, Qk−2 and Πh for Ih|K, Qk−2|K and Πh|K. The error estimates for interpolation operators Ih, Qk−2, and Πh are summarized in the following lemma (cf. [1, 4, 5, 11, 20, 31]).
Lemma 2. For all v ∈ Hm+2(K), τ ∈ Hm(Ω, 𝕊) with m a nonnegative integer, and all K ∈ 𝒯h, one has the estimates
3.2. A Priori Error Analysis
Theorem 3. Assume that the solution (σ, u) for mixed formulation (4)-(5) satisfies σ ∈ Hm(Ω, 𝕊) and u ∈ Hm+2(Ω) for some positive integer m, and let (σh, uh) be the solution of stabilized mixed finite element methods (12)-(13). Then
Proof. Choosing τ = Πhσ − σh in (26) and v = Ihu − uh in (27), and subtracting (27) from (26), we get
Lemma 4. Let Ω be a convex bounded polygonal domain. Assume that the solution (σ, u) for mixed formulation (4)-(5) satisfies σ ∈ Hm(Ω, 𝕊) and u ∈ Hm+2(Ω) for some positive integer m; then
Proof. Taking v = Ihu − uh in (37), it holds that
Theorem 5. Let Ω be a convex bounded polygonal domain. Assume that the solution (σ, u) for mixed formulation (4)-(5) satisfies σ ∈ Hm(Ω, 𝕊) and u ∈ Hm+2(Ω) for some positive integer m, and let (σh, uh) be the solution of stabilized mixed finite element methods (12)-(13). Then
Proof. Taking v = Ihu − uh in (34), we have from Lemma 4
4. A Posteriori Error Analysis
In this section, we intend to investigate the a posteriori error estimates of stabilized mixed finite element methods (12)-(13).
4.1. Preliminaries
For any vertex p and edge e of triangulation 𝒯h, denote 𝒯p and 𝒯e by the set of triangles in 𝒯h sharing common vertex p and edge e, respectively. For any subset 𝒮 of 𝒯h, let |𝒮| be the cardinalities of 𝒮. For any edge e of triangulation 𝒯h, ωe means the union of elements in 𝒯e.
4.2. A Posteriori Error Analysis
First, let us consider the reliability of the a posteriori error estimator. We will follow the similar argument as in [6] by replacing Hsieh-Clough-Tocher element space by Zienkiewicz-Guzmán-Neilan element space proposed in [27].
Theorem 6. Let (σ, u) and (σh, uh) be solutions of mixed formulation (4)-(5) and stabilized mixed finite element methods (12)-(13), respectively. Then
Proof. Letting w = u − Lhuh, then . Using integration by parts, (5) and (13), we have
Then, we study the efficiency of the a posteriori error estimator by bubble function argument.
Lemma 7. Let (σ, u) and (σh, uh) be solutions to mixed formulation (4)-(5) and stabilized mixed finite element methods (12)-(13), respectively. Then for all K ∈ 𝒯h,
Proof. Let . It is obvious that and
Lemma 8. Let (σ, u) and (σh, uh) be solutions to mixed formulation (4)-(5) and stabilized mixed finite element methods (12)-(13), respectively. Then for all ,
Proof. Let K1, K2 ∈ 𝒯h such that e is common shared edge of K1 and K2, and define edge bubble function as (cf. [19, 36])
Theorem 9. Let (σ, u) and (σh, uh) be solutions for mixed formulation (4)-(5) and stabilized mixed finite element methods (12)-(13), respectively. Then
Acknowledgments
This work was partly supported by the NNSFC (Grants nos. 11126226 and 11171257) and Zhejiang Provincial Natural Science Foundation of China (Y6110240, LY12A01015).