Gradient Recovery Method Research Articles

Steady state simulation of electrode processes with a new error bounded adaptive finite element algorithm

In a series of papers, Harriman et al. [1–5] have presented a reliable means of simulating steady state currents with adaptive finite element. They have demonstrated that multi-step, even non-linear, mechanisms, alongside convection, can be incorporated. However, there is considerable complication in the mathematical approach taken, and it would seem to be limited as it stands to certain types of electrode reaction models – notably those without heterogeneous kinetics or transient effects. In this paper we discuss alternative approaches to error estimation and adaptivity, and present a simpler formulation, capable of simulating systems with heterogeneous kinetics; transient simulations also appear more attainable. We introduce, apparently for the first time in electrochemistry, the use of gradient recovery methods [6] to both error estimation and accurate current calculations. The result is an algorithm with considerably more potential for generalisation, closer to the ideal of an entirely flexible automatic simulation program, capable of dealing with any mechanism or electrode geometry. In tests we find our method to perform more efficiently than that cited above, producing accurate results with simpler meshes in less time.

THREE‐DIMENSIONAL GRADIENT RECOVERY BY LOCAL SMOOTHING OF FINITE‐ELEMENT SOLUTIONS

The gradient recovery method proposed by Zhu and Zienkiewicz for one‐dimensional problems and extended to two dimensions by Silvester and Omeragi? is generalized to three‐dimensional solutions based on rectangular prism (brick) elements. The extension is not obvious so its details are presented, and the method compared with conventional local smoothing and direct differentiation. Illustrative examples are given, with an extensive experimental study of error. The method is computationally cheap and provides better accuracy than conventional local smoothing, but its accuracy is position dependent.

A TWO‐DIMENSIONAL ZHU—ZIENKIEWICZ METHOD FOR GRADIENT RECOVERY FROM FINITE‐ELEMENT SOLUTIONS

The gradient recovery method proposed by Zhu and Zienkiewicz for one‐dimensional problems is generalized to two dimensions, using quadrilateral elements. Its performance is compared with that of conventional local smoothing techniques and of direct differentiation of the finite‐element solution, on finite‐element approximations to analytically known polynomial and transcendental functions on a quadrilateral second‐order finite‐element mesh. The new method appears to be reliable and more stable than local smoothing, and to provide better accuracy than direct differentiation, at low computational cost.

A comparison of gradient recovery methods in finite‐element calculations

AbstractIn this paper we consider methods of gradient recovery in the context of primitive‐variable finite‐element solutions of viscous flow problems. Two methods are considered: a global method based on a Galerkin weighted residual procedure, and a direct method where gradients are recovered directly at individual nodes. The direct method has the benefit of utilizing the property of superconvergence as a natural consequence of its formulation, and furthermore requires no smoothing matrix to obtain the gradients at the nodal points. The two recovery schemes are considered with respect to two benchmark viscous flow problems of differing complexity. Both schemes are shown to produce comparable results, although the direct recovery method is found to be significantly more cost‐effective than the global method.