Data Interpolation

Most visualization objects such as plots, reports, and scalar displayers allow for smooth and non-smooth values. For example, the contour style for scalar displayers provides a Smooth Filled option (smooth) and a Filled option (non-smooth). The way these values are calculated depends on the discretization method.

Finite Volume Interpolation

For finite volume solvers, the values of the computed fields are typically stored on one specific native stencil (either cell, face, or vertex). When evaluating field values on a stencil other than the native one, Simcenter STAR-CCM+ applies a geometry-based interpolation scheme that computes the field values at the new locations. The interpolation scheme is 1st-order accurate.

Most visualization objects such as plots, reports, and scalar displayers allow for two options:
  • Smooth: the physical field is interpolated to vertex values. The interpolated field is continuous.
  • Non-smooth: the physical field is interpolated to the face or cell centroid (one constant value per face, or cell). The interpolated field is generally discontinuous.

Finite Element Interpolation

For finite element solvers, the computed values are also stored on one or more stencils (either cell, face, or vertex). However, the stored values are coefficients that are related to the element shape functions (see Shape Functions). In addition, the continuity of the solution depends on the type of shape functions, which are specific to the physical quantity that is computed.

Depending on the field continuity, smooth and non-smooth values are calculated as follows:
Primary Continuous Fields:
Every component of the computed field is continuous across element faces. This category includes fields that use H1 Lagrange shape functions (see Shape Functions), such as temperature, displacement, and their time derivatives.
  • Smooth: the field is continuously evaluated using the shape functions of the element (either 1st or 2nd order, depending on the mesh element type).
  • Non-smooth: equivalent to smooth except for resampled volume derived parts where the field is evaluated at the face or cell centroids (one constant value per face, or cell) and is generally discontinuous.
Spatially Derived, Discontinuous Field:
Only the tangential or normal component of the computed field is continuous across element faces. This category includes fields that are based on the gradient, curl, or divergence of another quantity, such as the temperature gradient and the mechanical strain, and fields that use H(curl) shape functions (see Shape Functions) such as the magnetic vector potential.
  • Smooth:
    • The field is projected (L2-projection) from integration points to vertex values.
    • Vertex values are averaged across neighboring elements
    • Averaged vertex values are interpolated using the 1st or 2nd-order shape functions of the element
  • Non-smooth:
    • The field is projected (L2-projection) from integration points to vertex values without averaging across neighboring elements.
    • Element local vertex values are interpolated using the 1st or 2nd-order shape functions of the element

    For resampled volume derived parts and scalar and vector warps the field is evaluated at the face or cell centroids (one constant value per face, or cell) and is generally discontinuous.