Choosing a Layer Growth Method

Layer Growth Method enables you to select one of these methods for determining the heights of the boundary layers:

  • Total Thickness creates the specified Number of Layers using the constant Growth Rate to obtain a total Maximum Thickness.

  • First Layer Thickness generates the specified Number of Layers, in which the First Layer Height is specified and each subsequent layer is calculated from the previous using the constant Growth Rate.

  • Smooth Transition uses the local element size to compute each local initial height and total height so that the rate of volume change is smooth.

    Each prism that is grown from a triangular surface element will have an initial height that is computed with respect to its base area, averaged at the nodes. For a uniform mesh, the initial heights will be roughly the same, while for a varying mesh, the initial heights will vary. The mesher uses these computations for prism layer growth:

    • The following value is computed at each node on the prism base:Height of last prism (H) = Transition Ratio * average_edge_length
    • The height of the first layer (h) is computed using the following formula, where g = Growth Rate and n = Number of Layers:H = h * (g ^ (n - 1))

    Increasing the value of Growth Rate reduces the total height of the boundary layers. The total height approaches an asymptotic value with respect to the number of boundary layers.

  • First Aspect Ratio calculates the heights of the boundary layers starting with the desired aspect ratio of the elements adjacent to the surface mesh. With this method, you can specify the First aspect ratio, Maximum layers, and Growth rate. The first layer height is calculated from the First aspect ratio and the local mesh base size. Subsequent layer heights are calculated using the Growth rate and the previous layer height.

  • Last Aspect Ratio also calculates the heights of the boundary layers using a desired aspect ratio.

    With the Last Aspect Ratio method, the First Layer Height is specified. The offset height for the last layer is calculated from the local base mesh size and specified Aspect Ratio (base/height). For example, if you specify a value of 3 for Aspect Ratio (base/height), the offset height of the last layer will be the local base mesh size divided by 3. The local growth rate is calculated using Maximum layers to create exponential growth through the intermediate layers.