DTPG

Format

Example 1

Example 2

Definitions

Comments

1. The bead minimum width and draw angles are used to determine the geometry of the shape variables. The figure below shows a cross-section of a single shape variable fully extended normal to the plane of the design elements. The top of the bead is flat across the circular area with a diameter equal to the minimum bead width parameter. The sides of the bead taper down at an angle equal to the draw angle parameter.

   
   
   Figure 1. Bead Width and Draw Angle Definitions

2. The buffer zone is a parameter that controls how the interfaces between design and non-design elements are treated. If active, OptiStruct will place the shape variables far enough away from the non-design elements so that the proper bead widths and draw angles are maintained. If inactive, the boundary between the beads and non-design elements will have an abrupt transition. Any nodes that were skipped due to the boundary skip parameter (field 10) will also have a buffer zone created around them.

   
   
   Figure 2. Transitions Between Design and Non-design Elements With and Without Buffer Zone

3. Symmetry of topography optimization can be enforced across one, two, or three planes. Defining symmetry planes for symmetric model and loading conditions is recommended because automatic variable generation may not be symmetric if it is not enforced. A symmetric mesh is not necessary, OptiStruct will create variables that are very close to identical across the plane(s) of symmetry. If the mesh is larger on one side of the plane(s) of symmetry than the other, OptiStruct will reflect variables created on the 'positive' side of the plane(s) of symmetry to the other side(s) but will not create variables on the 'negative' side(s) of the plane(s) of symmetry that do not overlap with the positive side. The positive side of the plane(s) of symmetry is the one in which the first vector, second vector, and cross product thereof are pointing toward.
4. Variable pattern grouping may be defined for a DTPG card. OptiStruct will generate shape variables based on the type of pattern selected in field 20. For variable grouping pattern types 1 through 14, only the first vector and anchor node need to be defined. For variable pattern grouping types 20 or higher, the first and second vectors need to be defined as well as the anchor node. If a grid is used to define the first vector, the normal vector will begin at the anchor point and extend towards the given grid (see below). Grids or xyz data may be used for either the first vector, second vector, or anchor point and can be a mixture, (that is the anchor point may be determined by a grid and the first vector determined by xyz data or vice-versa).
   One very useful feature for topography optimization in OptiStruct is the automatic generation of shape variables in simple patterns. In many cases, due to manufacturing constraints or the risk of elements being collapsed upon them during shape optimization, it is required to create shape variables in patterns that conform to the desired shape of the part. In basic topography optimization (TYP = 0), OptiStruct creates shape variables that are circular. OptiStruct contains a library of different shape variable patterns which can be accessed using the TYP parameter on the DTPG card.

   
   
   Figure 3. Defining the First Vector Using a Grid Point

   The second vector is calculated by taking the grid point or vector defined in fields 22, 23, and 24 and projecting it onto plane 1. If a grid point was used to define the second vector, the second vector is a vector running from the anchor node to the projected grid point. If a vector was used to define the second vector, the base of the projected vector is placed at the anchor point.

   
   
   Figure 4. Second Vector is Normal to Plane 2

   
   
   Figure 5. Plane 3 is Determined to be Normal to Both Plane 1 and Plane 2

5. For a list of patterns supported by OptiStruct, refer to Pattern Grouping Options.
6. Pattern repetition allows similar regions of the design domain to be linked together so as to produce similar topographical layouts. This is facilitated through the definition of "Master" and "Slave" regions. A DTPG card may only contain one MASTER or SLAVE flag. Bead parameters will not be exported for any DTPG cards containing the 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, refer to Pattern Repetition contained within the User Guide section Topography Optimization Manufacturability.

7. REMESH function uses mixed type of elements, if input mesh contains any QUAD elements; otherwise, it only uses TRIA elements.
8. This card is represented as an optimization design variable in HyperMesh.