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A shell with a void inside.

The void region show with a clip plane.

A plot of a swept mesh.

From left to right: 1) A shell domain with a void region inside it. 2) The void region, shown via a clip plane. 3) A plot of a swept mesh. Some elements have been filtered out for visibility.

如何将源面和目标面连接到域

Let's now focus on the second rule. For each domain, the destination must be a connected face component, and, as of version 6.4, the source faces can be disconnected face components. Another way to interpret this rule on a domain level is to say that the domain can contain steps so that the source faces are located on different heights in the sweep direction. For a geometry that contains steps in both ends of the sweep, try to partition the domain into smaller pieces that can be sweepable (as shown in the image of the steel pipe below), or combine a swept mesh with a free tetrahedral mesh.

On a side note, coincident source and destination faces are allowed so long as the source mesh matches the destination (including any twists of the face), as shown in the animation of the torus below.

A rectangular 3D geometry with the faces shown with mesh elements. This domain can be automatically swept meshed as of COMSOL Multiphysics^® 6.4. The source faces (magenta) form a disconnected component as they are located on different heights while the bottom surface, the destination face, is a connected face component (yellow).

A domain with disconnected face components. A cylindrical 3D geometry is shown assembled, in parts, with the faces colored in yellow, magenta, and blue and mesh elements applied. The steel pipe to the left is one single domain with an indent where the brass clamp is located. By partitioning the steel domain with a work plane parallel to the side of the clamp, it is possible to sweep a mesh through the whole geometry (exploded view to the right).

对扭转环进行的正方形截面网格划分，源的表面网格需要有 180° 的对称性，因为它只转动了半圈。

可视化扫描路径

按照网格的横截面进行扫描，通常有助于形成可视化效果。对前两条标准的解释是，横截面的形状不能有任何突变，similar to what is described in the Source and Destination Faces Requirements section。例如，孔会在横截面上产生空洞，孤立的面会引入新的边，而分岔会在横截面上分割、合并、添加或移除面。虽然这种技术并不是最严谨的，“横截面” 和 “突变” 需要正确定义，但是在大多数情况下，它将有助于定位不可扫掠的域，并为分割域提供线索。See “How to Control the Swept Mesh” for an example of how to partition the geometry in order to sweep parts of it。

直观地解释了之前的域无法进行网格扫略的原因。左边的动画中，横截面被分为两部分。右边的动画中，当到达第一个目标面时，横截面的形状瞬间发生变化。为了直观地演示，在横截面分割的部分显示了部分网格，在该部分如果采用横截面进行分割，可以对域进行网格扫描，但实际上不会生成网格。

可帮助实现上述可视化的一个方法是，添加一个与扫掠横截面平行的剪裁平面 ，然后沿扫掠方向拖动剪裁平面的边框。确保选择显示横截面选项。

这段视频演示了如何从图形窗口手动查看扫掠路径。由于该域包含一个空白域，不符合第一条标准，因此无法扫掠网格。这一点非常明显，因为横截面在扫掠路径的中间部分变成了空心。

孤立实体的特殊示例

孤立边和孤立顶点是指位于域或面内的边和顶点，它们不属于任何一个用于划分面的孤立实体。当存在孤立边和孤立顶点时，网格首先在不考虑孤立实体的情况下生成。然后，第二步，通过移动附近的一些网格节点，将实体包含并黏合到现有网格中。在扫掠过程中，网格与孤立实体保持一致。

If the isolated entities are not needed, consider using Virtual Operations to remove them from the geometry. See this blog post for more information.

The interior of a mesh with and without isolated entities on the linking faces..

域内无（左）或有（右）孤立实体的内部可视化网格。右图中的网格被扭曲，以便在扫掠过程中考虑孤立的实体。

源面和目标面的要求

每个目标面必须对应一个或多个源面，而每个源面必须精确对应一个目标面或其子集。换句话说，源面可以包含比目标面更多的面，只要有一种方法可以将网格映射到目标面上即可（最多可以有一些变形，就像我们在这个动画中看到的那样）。

尽管源面（洋红色）多于目标面（黄色），但仍可对该几何体进行扫掠网格划分。

大多数情况下，源面和目标面之间不会发生变形，只需简单地平移和旋转源面，使其与目标面重叠即可。在这种情况下，我们可以在头脑中想象将源网格复制到目标网格，查看复制操作是否可行。下面的动画演示了这种想法的可视化过程。

图中只显示了源面和目标面，颜色与上一个三维视图相同。请注意，源面比目标面多，每个目标面对应一个或多个源面。

不符合此规则的示例：由于目标面较多，因此无法复制网格。网格复制失败的边用红色标出。因此，对于之前的三维几何结构，扫掠方向无法反转。

Imprinting some of the edges from the source to the destination, or vice versa, is one strategy to be able to sweep a mesh when there is a mismatch between the source and destination faces in domains or to make sure the sweep creates matching meshes along the sweep. The latter case is shown below.

A cylindrical gray 3D geometry has two domains, which are also shown separately on the right, with the mesh elements and faces colored in magenta, blue, and yellow. A geometry with two domains where it helps to imprint the rectangle edges on the middle face to make the geometry sweepable. Otherwise, there is no guarantee that the mesh swept from the top to the middle will be the same as for the mesh swept from the bottom to the middle.

See more examples of imprinting here.

3D geometries of a gray, angled bracket and bolts are shown on the left, and the same geometry is shown on the right, with mesh elements applied and the faces colored in magenta, blue, and yellow. To sweep a mesh through the angle bracket above (left), where there are imprints of the screws on opposite sides of the bracket, the domain can be partitioned in two (right) instead of imprinting the screw surfaces. Note that this geometry can be swept meshed with one Swept operation even though the two domains are swept in opposite directions.

链接边的要求

每个截面必须至少有两条链接边。对这一标准的另一种解释是，每个截面至少应有两个链接面。