Design variables

Design variables are independent quantities that the solver can vary to perform a design sensitivity analysis or to achieve an optimum design. Upper and lower limits define the allowable range of variation. For example, you can create a design variable to modify the shell thickness between 0.001 mm and 10 mm from a starting thickness of 0.15 mm. You can add design variables only to a solution, not a subcase.

You can define four types of design variables: property, composite property, material, and connectivity.

Property

This design variable type lets you choose physical properties, such as the T field (thickness) in a PSHELL, the DIM1 in a PBEAML, and so on. In Nastran, this creates a DESVAR and DVPREL1 combination. The following physical property types are supported:

Property type	Supported fields
PBAR	A, I1, I2, J, NSM, C1, C2, D1, D2, E1, E2, F1, F2, K1, K2, I12
PBARL	DIM1, DIM2, DIM3, DIM4, DIM5, DIM6, NSM
PBEAM	A(A), I1(A), I2(A), I12(A), J(A), NSM(A), C1(A), C2(A), D1(A), D2(A), E1(A), E2(A), F1(A), F2(A), A(B), I1(B), I2(B), I12(B), J(B), NSM(B), C1(B), C2(B), D1(B), D2(B), E1(B), E2(B), F1(B), F2(B), CW(A), CW(B), N1(A), N2(A), N1(B), N2(B)
PBEAML	DIM1(A), DIM2(A), DIM3(A), DIM4(A),DIM5(A), DIM6(A), NSM(A), DIM1(B), DIM2(B), DIM3(B), DIM4(B), DIM5(B), DIM6(B), NSM(B)
PBUSH	K1, K2, K3, K4, K5, K6, B1, B2 ,B3, B4 ,B5, B6, GE1, SA, ST, EA, ET, GE2, GE3, GE4, GE5, GE6
PDAMP	B1
PELAS	K1, GE1, S1
PGAP	U0, F0, KA, KB, KT, MU1, MU2
PMASS	M1
PROD	A, J, C, NSM
PSHEAR	T, NSM, F1, F2
PSHELL	T, 12I/T**3, TS/T, NSM, Z1, Z2
PTUBE	OD, T, NSM
PVISC	CE1, CR1

Composite Property

This design variable type lets you choose composite or laminate physical properties such as the NSM field (nonstructural mass) in a PCOMP. In Nastran, this creates a DESVAR and DVPREL1 combination.

You can specify a type of PCOMP or Laminate. The following property fields are supported:

Reference Plane to Bottom Surface Distance (Z0)Nonstructural Mass (NSM)Allowable Bonding Material Shear Stress (SB)Reference Temperature (TREF)	Damping Coefficient (GE)Ply Thickness (T)Ply Orientation Angle (THETA)

If you select Ply Thickness (T) or Ply Orientation Angle (THETA), you must specify whether the design variable affects a single ply or multiple plies.

For multiple plies, the thickness or the orientation angle of the selected plies (specified by material ID in the Plies list) will vary with the same ratio as the design variable changes. For example, if the design variable change is 2.0, the thickness or the orientation angle is doubled for all the selected plies.

In addition, when you select Ply Thickness (T) or Ply Orientation Angle (THETA), you can select the Include Reference Plane to Bottom Fiber Distance (Z0) check box to make sure that a specific relation DVPREL1 is written out at export for the Z0 field in the PCOMP property. The DVPREL1 card is written out only if Z0 represents the middle or top plane of the composite. If Z0 is 0.0 (equivalent to bottom), the relation is not needed. If Z0 is user-defined, an error message is issued at export. For more information, see Design Optimization with Composite Materials.

Material

This design variable type lets you choose material properties such as the Young's Modulus value in a MAT1 material. In Nastran, this creates a DESVAR and DVMREL1 combination. The following material types and properties are supported:

Material types	Supported fields
MAT1	E, G, NU, RHO, A, TREF, GE
MAT2	G11, G12, G13, G22, G23, G33, RHO, A1, A2, A3, TREF, GE
MAT8	E1, E2, NU12, G12, G1Z, G2Z, RHO, A1, A2, TREF, XT, XC, YT, YC, S, GE
MAT9	G11, G12, G13, G14, G15, G16, G22, G23, G24, G25, G26, G33, G34, G35, G36, G44, G45, G46, G55

Connectivity (fields in the element definition)

This design variable type lets you choose element fields such as the ZOFFS field (Z offset) in a CQUAD4 element. In Nastran, this creates a DESVAR and DVCREL1 combination. Fields on the following element types are supported:

Connectivity entry	Supported fields
CBAR	X1, X2, X3, W1A, W2A, W3A, W1B, W2B, W3B
CBEAM	X1, X2, X3, W1A, W2A, W3A, W1B, W2B, W3B
CBUSH	X1, X2, X3, S, S1, S2, S3
CDAMP2	B
CELAS2	K, GE, S
CGAP	X1, X2, X3
CMASS2	M
CONM1	M11, M21, M22, M31, M32, M33, M41, M42, M43, M44, M51, M52, M53, M54, M55, M61, M62, M63, M64, M65, M66
CONM2	M, X1, X2, X3, I11, I21, I22, I31, I32, I33
CONROD	A, J, C, NSM
CQUAD4	THETA, ZOFFS, T1, T2, T3, T4
CQUAD8	THETA, ZOFFS, T1, T2, T3, T4
CQUADR	THETA, ZOFFS, T1, T2, T3, T4
CTRIA3	THETA, ZOFFS, T1, T2, T3
CTRIA6	THETA, ZOFFS, T1, T2, T3
CTRIAR	THETA, ZOFFS, T1, T2, T3

Where do I find it?

SOL 200 Design Optimization

Application	Pre/Post
Prerequisite	A Simulation file as the work part and displayed partSimcenter Nastran as the specified solverStructural as the specified analysis typeSOL 200 Design Optimization as the specified solution type
Command Finder	Modeling Objects →Type set to Design Variable - Composite Property, Design Variable - Connectivity, Design Variable - Material, or Design Variable - Property
Location in dialog box	Solution dialog box→Bulk Data tab→Create Design Variables (next to Design Variables)

SOL 200 Design Sensitivity Analysis

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSimcenter Nastran or MSC Nastran as the specified solverStructural or Vibro-Acoustic as the specified analysis typeSOL 200 Design Sensitivity Analysis as the specified solution type
Command Finder	Modeling Objects →Type set to Design Variable - Composite Property, Design Variable - Connectivity, Design Variable - Material, or Design Variable - Property

How do I

Create a design variable for design optimization

Quick links

Command reference

Pre/Post video examples

Bulk Entry Descriptions

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Design variables, Simcenter 3D 2021.1 Series

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