DSIZE

Format

Definitions

Comments

1. 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.

   Uniform pattern grouping (TYP = 9)

   This type of pattern grouping requires only the TYP field to be set equal to 9. All elements included in this DSIZE entry are automatically considered for uniform pattern grouping. All elements on this DSIZE entry are set equal to the same thickness.

   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.

   Linear Pattern Grouping (TYP = 20)

   Linear pattern grouping requires that the anchor point and first point be defined. A vector from the anchor point to the first point defines the direction in which the thickness is set to be constant. Linear pattern grouping is typically designed to handle models with minimal or no curvature in the specified vector direction (which is typically orthogonal to the rolling direction in rolling applications). For models with low curvature in the vector direction, appropriate projections to the surface are used to determine the direction on the surface. For models with high curvature in the vector direction, depending on the direction of the specified vector, the direction may become orthogonal to the surface whereby the pattern grouping direction cannot be determined. In such cases, Planar Pattern Grouping (TYP = 21) is recommended.

   Planar Pattern Grouping (TYP = 21)

   Planar pattern grouping requires that the anchor point and first point be defined. A vector from the anchor point to the first point is defined and thickness of the model in the various orthogonal planes to this vector is set to be constant. Planar pattern grouping is designed to handle models with high curvature in the orthogonal planes of the defined vector, and with minimal or no curvature in the direction of the defined vector. The vector defined in planar pattern grouping should typically lie in the rolling direction in rolling applications. This feature can handle large curvature in the slicing plane orthogonal to the defined vector. Planar pattern grouping cannot be used if large curvature exists in the rolling direction.

   Note: Multiple continuation lines defining pattern grouping is allowed. However, this is currently only supported for TYP=20 or TYP=21 in conjunction with TYP=1, TYP=2, or TYP=3.

   For a more detailed description, refer to Pattern Grouping for Free-Size (Parameter) Optimization contained within the User Guide section Free-size Optimization Manufacturability.

2. 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 "Main" and "Secondary" regions. A DSIZE card may only contain one MAIN or SECOND flag. For both "Main" and "Secondary" 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 "Secondary" may reference the same "Main."

   Scale factors may be defined for "Secondary" regions, allowing the "Main" layout to be adjusted.

   For a more detailed description, refer to Pattern Repetition for Free-Size (Parameter) Optimization contained within the User Guide section Free-size Optimization Manufacturability.

3. 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.
4. The 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 that is 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 1D elements.
   • Stress constraints may not be used when enforced displacements are present in the model.
     Note: The functionality of the STRESS continuation line to define topology and free-size stress constraints consists of many limitations. It is recommended to use DRESP1-based Stress Responses instead. Actual Stress Responses for Topology and Free-Size (Parameter) Optimization are available through corresponding Stress response RTYPE's on the DRESP1 Bulk Data Entry. The Stress-NORM aggregation is internally used to calculate the Stress Responses for groups of elements in the model.
5. The following manufacturing constraints are available for composite free-sizing optimization:
   • Lower and upper bounds on the total thickness of the laminate (LAMTHK).
   • Lower and upper bounds on the thickness of a given orientation (PLYTHK).
   • Lower and upper bounds on the thickness percentage of a given orientation (PLYPCT).
   • Linking between the thicknesses of two given orientations (BALANCE).
   • Constant (non-designable) thickness of a given orientation (CONST).
   • LAMTHK, PLYTHK, PLYPCT, and PLYMAN can be applied locally to sets of elements. There can be elements that do not belong to any set.

   For a more detailed description and an example, refer to Optimization of Composite Structures in the User Guide.

6. Elements within each group will have uniform ply thicknesses.
7. The core is designable by default. It can be made non-designable through the CONST manufacturing constraint. To facilitate this, the keyword CORE can be used instead of a ply ID when BYPLY is activated.
8. The core is excluded from the LAMTHK, PLYTHK, PLYPCT and PLYMAN manufacturing constraints by default.
9. Legacy data field PTMAN (for manufacturable ply thickness) defined on the PLYTHK and PLYPCT entries is supported. However, it is now recommended to define the manufacturable ply thickness in the PMMAN field through the PLYMAN continuation line as this offers more control.
10. The options for selecting the type of drop-off constraints for PDTYP are defined for a set of plies.

    
    
    Figure 1.

    Assuming that the plies are stacked as shown above, you have the following definitions:

    
    
    Figure 2.

    
    
    Figure 3.

    
    
    Figure 4.

    
    
    Figure 5.

    When OUTPUT,FSTOSZ is used to generate a Sizing input deck, the Ply drop-off manufacturing constraints are converted into equivalent TOTDRP constraints. Check that the estimated TOTDRP values on the DCOMP entry(s) are meaningful, or adjust the values manually, if necessary.
11. The optional PDDEF definition is used to fine-tune the drop-off constraint. Currently, only the DIRECT option is available for the PDDEF field.

    PDDEF

    DIRECT This option allows you to fine-tune the drop-off constraint by requesting directional drop-off. The direction of drop-off can be specified by defining a directional vector with respect to the basic coordinate system. The directional vector is defined using the PDX, PDY and PDZ values.

    PDX, PDY, PDZ

    PDX, PDY and PDZ are real numbers.

    These values are used to specify the drop-off direction when DIRECT is input in the PDDEF field. They specify the three components of a directional vector defined with respect to the basic coordinate system.

    Example: If drop-off control is required in the X-direction, then 1,0,0 can be defined in the PDX, PDY, PDZ fields, respectively. 0,1,0 can be defined for Y-direction drop-off control.

12. Other manufacturing constraints (except BALANCE) can be used along with tape laying.
13. If there are multiple plies of the same orientation, the corresponding tapes are automatically offset with respect to one another. This increases the design freedom by allowing OptiStruct to choose the optimum layout for a particular configuration.
14. Symmetry is available only at the laminate level for tape laying. Opposite orientations (for example, 45 degrees and -45 degrees) are reflections of each other, instead of being reflected across the plane of symmetry. 0 and 90 degree plies are still reflected across the plane of symmetry.
15. Discrete design variables are internally created based on the thickness step defined via PMDIS. The thickness step indicates that the design variables are created as integer multiples of the PMDIS value. For example, if PMDIS is 0.2, then the design variables can be 0.2, 0.4, 0.6 and so on.
    Note: PMDIS and PMMAN can be different. PMDIS is inactive by default and PMMAN=PMDIS by default if PMMAN is not specified.
16. When PTYPE=SET on DSIZE entry, then:
    • The referenced element set can contain elements referring only to PSHELL property.
    • If T0 is defined on the DSIZE entry and/or the PSHELL entry, they must be consistent. That is,
      • T0 on all the DSIZE entries using elements from the same PSHELL should match.

        For example, DSIZE#1 with T0=0.0 and DSIZE#2 with T0=1.0 and both referring to elements from the same PSHELL is not allowed.

      • If T0 on a PSHELL is defined, then its value should match with T0 defined on all DSIZE entries with PTYPE=SET that reference elements from this PSHELL.
    • Multi-material, level set and lattice optimization are not supported
17. This card is represented as an optimization design variables in HyperMesh.