Under the Analysis tab in the Project Settings dialog, you can specify:
Number of Boundary Elements (default = 100)
Boundary Element Type (constant, linear, quadratic)
These options are described below.
Number of Boundary Elements
The boundary element analysis requires that the model boundaries (i.e. Excavation boundaries and Ground Surface boundary), be discretized into a number of smaller segments, referred to as "boundary elements". This discretization is performed automatically by Examine2D (no user action is required), prior to the computation of results.
The default value of Number of Boundary Elements = 100. This default value is recommended for the initial analysis of a model. Increasing the Number of Boundary Elements may improve the accuracy of the results (e.g. stress, displacement, strength factor contours). However, the computation time will increase as you increase the number of elements. This will be most noticeable if you are using the interactive editing features of Examine2D (i.e. real time contour updates as you move an excavation boundary, for example). If computation speed is not an issue, then you can experiment with the Number of Boundary Elements, to determine the lowest value which provides sufficiently accurate analysis results. Accuracy of the result contours is also dependent on the density of computation points within the Stress Grid.
NOTE:
If you have multiple excavation boundaries, the Number of Boundary Elements is the total number of elements for ALL excavations.
If you have defined a Ground Surface, then the Number of Boundary Elements is applied independently to the Ground Surface. For example, if the Number of Boundary Elements = 100, then the excavation boundaries and the ground surface will EACH be discretized into approximately 100 boundary elements, for a total of 200 elements.
The Number of Boundary Elements (in Project Settings) is an approximate number. In general, the actual number of boundary elements generated by the automatic discretization of the excavation (and ground surface) boundaries, may be slightly different from the Number of Boundary Elements specified in the Project Settings dialog. The actual number of boundary elements used in the analysis, is listed in the Info Viewer and will generally be very close to the value in Project Settings.
The boundary element discretization can be displayed on the model, by selecting the Show Element Discretization checkbox under the General tab in the Display Options dialog. The discretization is indicated by red crosses distributed uniformly along the boundary line segments (you may have to zoom in to view the elements).
Boundary Element Type
The Boundary Element Type defines the assumed stress distribution along each boundary element. You can choose one of the following three options:
Constant
Linear
Quadratic
The default selection = Constant. If you choose a higher order element (i.e. Linear or Quadratic), this may improve the accuracy of the results, however you may notice a slight increase in Compute time, due to the increase in the number of degrees of freedom.
NOTE: if you are using Transversely Isotropic Elastic Properties, the Boundary Element Type will automatically be set to Constant. You cannot use Linear or Quadratic elements in conjunction with Transversely Isotropic elasticity.