你不知道的CAE小常識（二十七）

*BOUNDARY_NON_REFLECTING
1，0，0
還是
*BOUNDARY_NON_REFLECTING
1，1，1
許多人爭論不休。
要告訴大家的是，LS-DYNA關鍵字手冊關于該*BOUNDARY_NON_REFLECTING的說明
AD Default activation flag for dilatational waves. (on.EQ.0.0, off.NE.0.0)
AS Default activation flag for shear waves. (on.EQ.0.0, off.NE.0.0)
是錯誤的（關鍵字手冊有不少錯誤），恰好說反了。應該是
AD Default activation flag for dilatational waves. (off.EQ.0.0, on.NE.0.0)
AS Default activation flag for shear waves. (off.EQ.0.0, on.NE.0.0)
意思是說等于0的時候，膨脹波和剪切波不會產生，是關閉的，相當于無反射邊界；不等于0的時候，會產生膨脹波和剪切波，相當于有限邊界，自由邊界。
對此，ANSYS的幫助手冊上有說明：
EDNB, Option, Cname, AD, AS
Defines a nonreflecting boundary in an explicit dynamic analysis.
Option
Label identifying the nonreflecting boundary option to be performed.
ADD — Define a nonreflecting boundary (default).
DELE — Delete a nonreflecting boundary.
LIST — List all defined nonreflecting boundaries (remaining fields are ignored). 
Cname
Name of existing nodal component to which the nonreflecting boundary is to be added or deleted. For Option = DELE, use Cname = ALL to delete all defined nonreflecting boundaries.
AD
Activation flag for dilatational waves (dampers normal to waves).
0 — Dilatational activation flag is off (default). 
1 — Dilatational activation flag is on.
AS
Activation flag for shear waves (dampers tangent to waves).
0 — Shear activation flag is off (default).
1 — Shear activation flag is on.
此外，使用TG中無反射邊界的NR命令，輸出為：
*BOUNDARY_NON_REFLECTING
1，0，0
所以，無反射邊界就是
*BOUNDARY_NON_REFLECTING
1，0，0