nastran中强制激励spcd的使用方法
2013-05-03 19:16阅读：
核心思想：在load中施加SPCD位移载荷的节点，要在spc中约束其6个自由度，否则求解是无结果的。
另：使用spc+spcd，作为rlaod和tload的exciteid项，可以施加力、位移、速度、加速度激励。
There are two methods available to you for specifying an enforced
displacement at a component. The first method is to enter the value
of the enforced displacement directly on an SPC entry.
The alternate method to enforce a displacement at a component is to
use the SPCD Bulk Data entry. The SPCD entry is actually a force,
not a constraint, but it is used in conjunction with an SPC entry
to enforce the displacement. When you use an SPCD entry, internal
forces are computed that are applied to the structure to produce
the desired enforced displacements.
The format of the SPCD entry is as follows:
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
9
|
10
|
SPCD
|
SID
|
G1
|
C1
|
D1
|
G2
|
C2
|
D2
|
|
|
Field
|
Contents
|
SID
|
Identification number of a
static load set.
|
Gi
|
Grid or scalar point
identification number.
|
Ci
|
Component
numbers.
|
Di
|
Value of enforced
displacement for at Gi and Ci.
|
Grid points with an enforced displacement using the SPCD entry must
also appear on an SPC or an SPC1 Bulk Data entry.
The SPCD method of enforcing a nonzero constraint is more efficient
than using an SPC entry alone when you're using multiple subcases
that specify different constraint conditions. Note also that when
you use an SPCD entry, the displacement values entered on the SPC
entry are ignored. The software only uses the SPCD values.
As an example of enforced displacement, consider the flat plate
shown in
Figure 9-7. The plate is modeled
with 2500 CQUAD4 elements.
Figure 9-7. Flat Plate with Various Corner Constraints
The purpose of this example is to compare the efficiency of using
the SPC/SPCD combination to that of using the SPC entry only. For
the plate model, four runs are made, each having two subcases with
different constraint conditions. For the input files “const1.dat”
and “const2.dat”, the locations of the constraints are the same for
both subcases, but the magnitudes of the constraints change. The
file “const1.dat” uses a different SPC for both subcases. The file
“const2.dat” specifies the same SPC for both subcases, but it has
different SPCD entries.
The input files “const3.dat” and “const4.dat” are similar to the
first two; however, the locations of the constraints in the two
subcases are different.
Table 9-1
summarizes the constraints and CPU time for all four
analyses.
Table 9-1. Comparison of the SPC
Versus the SPC/SPCD Combination
|
Location of Enforced
Displacement
|
|
const1.dat
|
const2.dat
|
const3.dat
|
const4.dat
|
|
SPC Only
|
SPC/SPCD
|
SPC Only
|
SPC/SPCD
|
Corner Displacement
(in)
|
Subcase 1
|
Subcase 2
|
Subcase 1
|
Subcase 2
|
Subcase 1
|
Subcase 2
|
Subcase 1
|
Subcase 2
|
Grid 1
|
0
|
0
|
0
|
0
|
-
|
-
|
-
|
-
|
Grid 51
|
0
|
5
|
0
|
5
|
-
|
0
|
-
|
0
|
Grid 2551
|
5
|
5
|
5
|
5
|
0
|
5
|
0
|
5
|
Grid 2601
|
5
|
0
|
5
|
0
|
5
|
-
|
5
|
-
|
CPU Time*
|
7.3 (sec)
|
5.1 (sec)
|
7.3 (sec)
|
7.3 (sec)
|
– free to move
* CPU time on Windows 2000
|
The SPC/SPCD combination is more efficient for both modeling
situations. It is most advantageous to use this combination when
the magnitudes but not the locations of the constraints change. The
larger improvement seen by the magnitude only change is reasonable
because only one SPC needs to be processed; the multiple boundary
conditions are represented as multiple loads. In general, whenever
you have multiple subcases with different constraint conditions,
the SPC/SPCD combination is the preferred method for
efficiency.
As mentioned previously, the SPCD is a force entry, not a
constraint. Therefore, the SPCD is called out in the Case Control
Section with the LOAD command. The input file for “const2.dat” is
shown in
Listing 9-1.
$ FILENAME - CONST2.DAT
ID LINEAR,CONST2
SOL 101
TIME 200
CEND
TITLE = ENFORCED
DISPLACEMENTS USING
SPC1 ONLY
DISP(PLOT) = ALL
SPC = 1
SUBCASE 1
LOAD = 11
SUBCASE 2
LOAD = 12
BEGIN BULK
PARAM POST 0
