Adapt
An Adapt node () provides the possibility to use adaptive mesh refinement based on some error estimate from a computed solution. Adapt nodes are part of mesh sequences that the adaptive solver creates. You can also add Adapt nodes by right-clicking a Mesh node and select it from the More Operations submenu. An Adapt node modifies an existing mesh based on an expression, typically by refining the mesh based on error information from a solution.
If you want to perform adaptive mesh refinement by manually adding an Adapt node, first create a new meshing sequence and copy the original mesh into that mesh sequence before adding an Adapt node.
The Adapt node’s Settings window contains the following sections.
Domain Selection
From the Geometric entity list, choose Entire geometry (the default) or Domain to select a set of domains for which the adaptation is active.
Adaptation
From the Solution list, select the solution to use for evaluation.
From the Solution selection list, select which solution that should be used to evaluate error estimates:
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Select Use last to use the last solution.
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Select Use first to use the first solution.
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Select All (the default for Eigenvalue studies) to use all solutions from that study.
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Select Manual to use a specific solution number that you specify as solution indices in the Index field.
In the Weights field (only available when Solution selection is Manual or All), enter weights as a space-separated list of positive (relative) weights so that the error estimate is a weighted sum of the error estimates for the various solutions (eigenmodes). The default value is 1, which means that all the weight is put on the first solution (eigenmode). That is, any omitted weight components are treated as zero weight.
From the Type of expression list, choose Error indicator (the default) or Absolute size.
Error Indicator
If you select Error indicator, the following settings appear:
The Error expression list, where you can add expressions for the error, for example, in terms of the dependent variables (including the variables for error estimation). Use the Move Up (), Move Down (), Add ()and Delete () buttons as needed. If you use several expressions, such as one for each solution component, the error expressions are added to form the sum of all of them. Or right-click a table cell and select Move Up, Move Down, Add, or Delete.
In 2D, use the Refinement method list to control how to refine mesh elements. Select:
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Longest to make the solver refine only the longest edge of an element.
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Regular to make the solver refine elements in a regular pattern.
Use the Element selection list to specify how the element refinement vector is determined from the error expression. Select:
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Rough global minimum to minimize the L2 norm of the error by refining a fraction of the elements with the largest error in such a way that the total number of elements increases roughly by a factor greater than 1 specified in the accompanying Element growth rate field. The default value is 1.7, which means that the number of elements increases by roughly 70%. The Error orders field is an array of h-exponents for the decrease of the error expression. This array has the same indexing as the error expression’s indexing. (for an error expression with two expressions such as errexpr1, errexpr2 and error orders = 2, 3, it means that errexpr1 = O(h2) and errexpr2 = O(h3)). When the adaptation method is used, these numbers are filled in automatically based on the Residual order and Error estimate settings (on the adaptation study). The shape functions can also influence this order. Note that these order numbers need to be positive to generate additional elements (element growth).
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Fraction of worst error to refine elements whose local error indicator is larger than a given fraction of the largest local error indicator. Use the accompanying Element fraction field to specify the fraction. The default value is 0.5, which means that the fraction contains the elements with more than 50% of the largest local error.
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Fraction of elements to refine a given fraction of the elements. Use the accompanying Element fraction field to specify the fraction. The default value is 0.5, which means that the solver refines about 50% of the elements with the largest local error indicator.
Absolute Size
If you select Absolute size, the following settings appear:
In the Size expression field, type an expression for the element size (in terms of variables defined by the solution).
When you evaluate on a solution, the spatial variables (and any other length dependent variable, such as the local mesh size h), has the units of the component. So if your 2D geometry use units km and has a unit square, assuming the component uses the SI unit system, the range of x and y would be 0 to 1000 (m) on the same geometry. Also note that the evaluated value of the expression is interpreted as a length in the geometry’s unit system.
In 2D, use the Refinement method list to control how to refine mesh elements. Select:
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Longest to make the solver refine only the longest edge of an element.
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Regular to make the solver refine elements in a regular pattern.