DSIZE – Design Variable for Free-Size Optimization
Defines parameters for the generation of free-size design variables.
Format
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DSIZE |
ID |
PTYPE |
PID1 |
PID2 |
PID3 |
PID4 |
PID5 |
PID6 |
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PID7 |
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Optional continuation lines for thickness definition:
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THICK |
T0 |
T1 |
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Optional continuation lines for stress constraint definition:
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STRESS |
UBOUND |
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Optional continuation lines for member size constraint definition:
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MEMBSIZ |
MINDIM |
MAXDIM |
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Optional continuation lines for pattern grouping constraint definition:
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PATRN |
TYP |
AID/XA |
YA |
ZA |
FID/XF |
YF |
ZF |
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UCYC |
SID/XS |
YS |
ZS |
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Optional continuation lines for "Master" definition for pattern repetition constraint:
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MASTER |
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COORD |
CID |
CAID/XCA |
YCA |
ZCA |
CFID/XCF |
YCF |
ZCF |
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CSID/XCS |
YCS |
ZCS |
CTID/XCT |
YCT |
ZCT |
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Optional continuation lines for "Slave" definition for pattern repetition constraint:
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SLAVE |
DTPL_ID |
SX |
SY |
SZ |
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COORD |
CID |
CAID/XCA |
YCA |
ZCA |
CFID/XCF |
YCF |
ZCF |
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CSID/XCS |
YCS |
ZCS |
CTID/XCT |
YCT |
ZCT |
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Field |
Contents |
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ID |
Each DSIZE card must have a unique ID. No default (Integer > 0) |
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PTYPE |
Property type for which DSIZE card is defined. No default (PCOMP, or PSHELL) |
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PID# |
Property identification numbers. List of properties of type PTYPE for which this DSIZE card is defined. Use ALL in PID1 field if it applies to all properties of type PTYPE in the model. No default (Integer > 0, or ALL) |
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THICK |
THICK flag indicating that minimum and possibly maximum thickness value are to follow. |
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T0 |
Minimum thickness. For PTYPE = PSHELL, this refers to the minimum thickness of the shell. If no value is entered for T0, the T0 value on the PSHELL card is used. If T0 is not defined on the PSHELL card, then T0=0.0 is assumed. This option does not apply for PTYPE = PCOMP. Default = blank (Real > 0.0) |
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T1 |
Maximum thickness. For PTYPE = PSHELL, this refers to the maximum thickness of the shell. If no value is entered for T1, the T value on the PSHELL card is used. This option does not apply for PTYPE = PCOMP. Default = blank (Real > T0) |
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STRESS |
STRESS flag indicating that von Mises stress constraints are active and that an upper bound value for the stress is to follow. See comment 5 below. |
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UBOUND |
Upper bound constraint on von Mises stress. No default (Real > 0.0) |
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MEMBSIZ |
MEMBSIZ flag indicating that member size control is active for the properties listed. Indicates that MINDIM and possibly MAXDIM are to follow. |
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MINDIM |
Specifies the minimum diameter of members formed. This command is used to eliminate small members. It also eliminates checkerboard results. See comment 3 below. Default = No minimum member size control (Real > 0.0) |
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MAXDIM |
Specifies the maximum diameter of members formed. This command is used to prevent the formation of large members. It can only be used in combination with MINDIM. See comment 4 below. Default = No maximum member size control (Real > MINDIM) |
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PATRN |
PATRN flag indicating that pattern grouping is active for the properties listed. Indicates that information for pattern grouping is to follow. |
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TYP |
Indicates the type of pattern grouping requested. See comment 1 below. Default = No pattern grouping (1, 2, 3, 10, or 11) |
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AID/XA, YA, ZA |
Anchor point for pattern grouping. The point may be defined by entering a grid ID in the AID field or by entering X, Y, and Z coordinates in the XA, YA, and ZA fields. These coordinates will be in the basic coordinate system. See comment 1 below. Default = origin (Real in all three fields or integer in first field) |
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FID/XF, YF, ZF |
First point for pattern grouping. The point may be defined by entering a grid ID in the FID field or by entering X, Y, and Z coordinates in the XF, YF, and ZF fields. These coordinates will be in the basic coordinate system. See comment 1 below. No default (Real in all three fields or integer in the first field) |
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UCYC |
Number of cyclical repetitions for cyclical symmetry. This field defines the number of radial "wedges" for cyclical symmetry. The angle of each wedge is computed as 360.0/UCYC. See comment 1 below. Default = blank (Integer > 0 or blank) |
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SID/XS, YS, ZS |
Second point for pattern grouping. The point may be defined by entering a grid ID in the SID field or by entering X, Y, and Z coordinates in the XS, YS, and ZS fields. These coordinates will be in the basic coordinate system. See comment 1 below. No default (Real in all three fields or integer in first field) |
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MASTER |
MASTER flag indicating that this design variable may be used as a master pattern for pattern repetition. See comment 2 below. |
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SLAVE |
SLAVE flag indicating that this design variable is slaved to the master pattern definition referenced by the following DSIZE_ID entry. See comment 2 below. |
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DSIZE_ID |
DSIZE identification number for a master pattern definition. No default (Integer > 0) |
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SX, SY, SZ |
Scale factors for pattern repetition, in X, Y, and Z directions respectively. See comment 2 below. Default = 1.0 (Real > 0.0) |
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COORD |
COORD flag indicating information regarding the coordinate system for pattern repetition is to follow. This is required if either MASTER or SLAVE flags are present. |
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CID |
Coordinate system ID for a rectangular coordinate system that may be used as the pattern repetition coordinate system. See comment 2 below. Default = 0 (Integer > 0) |
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CAID/XCA, YCA, ZCA |
Anchor point for pattern repetition coordinate system. The point may be defined by entering a grid ID in the CAID field or by entering X, Y, and Z coordinates in the XCA, YCA, and ZCA fields. These coordinates will be in the basic coordinate system. See comment 2 below. No default (Real in all three fields or integer in the first field) |
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CFID/XCF, YCF, ZCF |
First point for pattern repetition coordinate system. The point may be defined by entering a grid ID in the CFID field or by entering X, Y, and Z coordinates in the XCF, YCF, and ZCF fields. These coordinates will be in the basic coordinate system. See comment 2 below. No default (Real in all three fields or integer in the first field) |
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CSID/XCS, YCS, ZCS |
Second point for pattern repetition coordinate system. The point may be defined by entering a grid ID in the CSID field or by entering X, Y, and Z coordinates in the XCS, YCS, and ZCS fields. These coordinates will be in the basic coordinate system. See comment 2 below. No default (Real in all three fields or integer in the first field) |
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CTID/XCT, YCT, ZCT |
Third point for pattern repetition coordinate system. The point may be defined by entering a grid ID in the CTID field or by entering X, Y, and Z coordinates in the XCT, YCT, and ZCT fields. These coordinates will be in the basic coordinate system. See comment 2 below. No default (Real in all three fields or integer in the first field) |
Comments
There are currently five pattern grouping options for free-size optimization:
1-plane symmetry (TYP = 1)
This type of pattern grouping requires that the anchor point and the first point be defined. A vector from the anchor point to the first point is normal to the plane of symmetry.
2-plane symmetry (TYP = 2)
This type of pattern grouping requires that the anchor point, first point, and second point be defined. A vector from the anchor point to the first point is normal to the first plane of symmetry. The second point is projected normally onto the first plane of symmetry. A vector from the anchor point to this projected point is normal to the second plane of symmetry.
3-plane symmetry (TYP = 3)
This type of pattern grouping requires that the anchor point, first point, and second point be defined. A vector from the anchor point to the first point is normal to the first plane of symmetry. The second point is projected normally onto the first plane of symmetry. A vector from the anchor point to this projected point is normal to the second plane of symmetry. The third plane of symmetry is orthogonal to both the first and second planes of symmetry, passing through the anchor point.
Cyclic (TYP = 10)
This type of pattern grouping requires that the anchor point, first point, and number of cyclical repetitions be defined. A vector from the anchor point to the first point defines the axis of symmetry.
Cyclic with symmetry (TYP = 11)
This type of pattern grouping requires that the anchor point, first point, second point, and number of cyclical repetitions be defined. A vector from the anchor point to the first point defines the axis of symmetry. The anchor point, first point, and second point all lay on a plane of symmetry. A plane of symmetry lies at the center of each cyclical repetition.
For a more detailed description, please refer to the Pattern Grouping for Free-Size Optimization page contained within the User’s Guide section Manufacturability for Free-Size Optimization.
Pattern repetition allows similar regions of the design domain to be linked together so as to produce similar topological layouts. This is facilitated through the definition of "Master" and "Slave" regions. A DSIZE card may only contain one MASTER or SLAVE flag. For both "Master" and "Slave" regions, a pattern repetition coordinate system is required and is described following the COORD flag. In order to facilitate reflection, the coordinate system may be a left-handed or right-handed Cartesian system. The coordinate system may be defined in one of two ways, listed here in order of precedence:
· Four points are defined and these are utilized as follows to define the coordinate system (this is the only way to define a left-handed system):
- A vector from the anchor point to the first point defines the x-axis.
- The second point lies on the x-y plane, indicating the positive sense of the y-axis.
- The third point indicates the positive sense of the z-axis.
· A rectangular coordinate system and an anchor point are defined. If only an anchor point is defined, it is assumed that the basic coordinate system is to be used.
Multiple "Slaves" may reference the same "Master."
Scale factors may be defined for "Slave" regions, allowing the "Master" layout to be adjusted.
For a more detailed description, please refer to the Pattern Repetition for Free-Size Optimization contained within the User’s Guide section Manufacturability for Free-Size Optimization.
It is recommended that a MINDIM value be chosen which allows for the formation of members that are at least three elements thick. When pattern grouping constraints are active, a MINDIM value of three times the average element edge length is enforced, and user-defined values (which are smaller than this value) will be replaced by this value.
MAXDIM should be at least twice the value of MINDIM, and OptiStruct will terminate with an error if a MAXDIM of less than six times the average element edge length is defined.
Von Mises stress constraints may be defined for topology and free-size optimization through the STRESS optional continuation line on the DTPL or the DSIZE card. There are a number of restrictions with this constraint:
· The definition of stress constraints is limited to a single von Mises permissible stress. The phenomenon of singular topology is pronounced when different materials with different permissible stresses exist in a structure. Singular topology refers to the problem associated with the conditional nature of stress constraints, i.e. the stress constraint of an element disappears when the element vanishes. This creates another problem in that a huge number of reduced problems exist with solutions that cannot usually be found by a gradient-based optimizer in the full design space.
· Stress constraints for a partial domain of the structure are not allowed because they often create an ill-posed optimization problem since elimination of the partial domain would remove all stress constraints. Consequently, the stress constraint applies to the entire model when active, including both design and non-design regions, and stress constraint settings must be identical for all DSIZE and DTPL cards.
· The capability has built-in intelligence to filter out artificial stress concentrations around point loads and point boundary conditions. Stress concentrations due to boundary geometry are also filtered to some extent as they can be improved more effectively with local shape optimization.
· Due to the large number of elements with active stress constraints, no element stress report is given in the table of retained constraints in the .out file. The iterative history of the stress state of the model can be viewed in HyperView or HyperMesh.
· Stress constraints do not apply to 1-D elements.
· Stress constraints may not be used when enforced displacements are present in the model.
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Guidelines for Bulk Data Entries
Alphabetical List of Bulk Data Entries