关于导入时尺寸问题

请教大家一个问题：
  （1）我在catia里面建立了一个模型单位为mm，比如为1000mm，导入feko中时单位为cm ，那么该尺寸在feko中是1000mm 还是1000cm 。
（2） 如果将单位改成mm，那么在导入的过程中会报错。
请教高手能否给指点指点。

你设为mm，导入就是1000mm。
导入会出错，是因为模型尺寸超过了默认体积限制。修改一下，再导入就OK了。

In general, the mesh size is not allowed to be smaller than the maximum coordinate divided by 1×108. This is the limit of the numerical precision of the geometry. For very small models (which require correspondingly small mesh sizes), the geometry extents (see section 4.1.2) should be decreased. The mesh size is also not allowed to be larger than four times the extents. (For more information regarding the required and suggested mesh
sizes for different mesh elements, see section 2.2.2.)
4.1.2 Geometry extents
Operations on geometry (such as checking if two points are at the same physical location) require a numeric tolerance. This tolerance is dependent on the model size. For example, microwave structures may require dimensions that differ by only few micrometers, but this level of accuracy is clearly not required for studies of propagation around mountains.
CADFEKO therefore allows the specification of the model size — select Geometry → Extents from the main menu. The model extent is the same in all coordinate directions and therefore only one value needs to be specified. This is the Maximum coordinate which gives the largest offset — in either direction — along any of the three axes. For example, if the Maximum coordinate is 500, the entire geometry must fit inside a 1000x1000x1000 box centred at the origin. The size of the extents are specified in the CADFEKO model unit (see section 4.1.1).
The tolerance on the model dimensions can be determined by taking the Maximum coordinate divided by 5 × 108. If coordinate values differ by more than this amount, they are considered unique. Note, however, that values are only guaranteed to be considered identical if the distance between them is less than a hundredth of the model tolerance.
(Between these values is a range where the uniqueness and connectivity cannot be guaranteed.)
The default value for the geometry extents is 5E+02 (500). It is recommend that this value be used except if the model is large (for example, when modelling an automobile in mm model units), or small with a requirement for high dimension-accuracy (accurate CAD model and / or mesh). For extent settings other than the default value of 500, exported Parasolid models will not be in the same unit used in CADFEKO (see section 5.1.2.)
The extents box limitation applies to all geometry. For example, an intersection between two spheres cannot be performed if either sphere exceeds the size box even if the resultant intersection would be within the extents bondary. CADFEKO will display an error if the geometry exceeds the specified size. In this case, the extents can be changed without having to close the dialog that caused the error and the operation re-attempted.
4.1.1 Setting units
To set the unit used for all distances and dimensions in CADFEKO, select Model → Model unit. Besides the standard units provided in the dialog, the user can specify an arbitrary unit conversion factor with respect to metres. For example, the model unit should be 1×10−6 when working in micrometres. The unit is displayed on the status bar (see section 3.1).
Changing the unit does not directly modify any numbers specified in CADFEKO, but rather the interpretation of all numbers (created before and after the unit change) — hence the unit can be changed at any time during construction of the model.
2.2.2 Meshing guidelines regarding element sizes
During meshing the following general rules should be adhered to:
Segments
• The segment length l should be smaller than a tenth of the free space wavelength.
• Note also that the segment current flows only in the axial direction. Thus segments should not be too short relative to the wire radius. Ideally the segment length should be at least four times the radius.
• When modelling a conductive surface by means of a wire grid, the radius should be chosen so that the wire area in one direction is approximately the same as the area of the original surface. This leads to
r =l/2π, (2-1)where r is the radius and l is the segment length which should be about a tenth of a wavelength.
• For wire - surface junctions (so called connection points) the radius of the attached wire segment must be small as compared to the size of the triangular patches attached at this connection basis function. As reference for the triangle size, the triangle edges attached to the connection point are used. The length of these edges must be large as compared to the wire segment radius.
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