DTRUSS

Bulk Data Entry Activates Truss Layout Optimization and defines the corresponding parameters for design optimization, including truss cross-sectional area limits, stress, symmetry, and buckling constraints.

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
DTRUSS ID AINIT AMAX SCOMP SEXTEN VRELAX
SYMMETRY AXIS LOC
METHOD TYPE
BUCKLING ALPHA

Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
DTRUSS 10 0.2 1.3 150.0 150.0 0.02
SYMMETRY X 45.0
BUCKLING 10.0

Definition

Field Contents SI Unit Example
ID Identification number

No default (Integer > 0)

AINIT Initial cross-section area of truss members

No default (Real > 0.0)

AMAX Maximum cross-sectional area of truss members

No default (Real > 0.0)

SCOMP Compression stress limit on truss members

No default (Real > 0.0)

SEXTEN Extension stress limit on truss members

No default (Real > 0.0)

VRELAX Volume relaxation parameter, which is the ratio of how much volume can be added to simplify the structure. 8

Default = 0.02 (Real > 0.0)

SYMMETRY Flag to activate symmetry constraints in truss layout optimization; the corresponding parameters are to follow.
AXIS Indicates that the plane of symmetry is perpendicular to the defined axis.

No default (X, Y, Z)

LOC The plane of symmetry is perpendicular to the defined axis on the AXIS field and located at the corresponding location defined by LOC on the specified axis.

No default (Real)

METHOD Flag to control the method type for truss layout optimization and indicate that the corresponding parameters are to follow.
TYPE Controls the method type for truss layout optimization.
0
Local stress constraints are used for the entire solution (single phase approach).
1
Global stress constraints are used for the entire solution (single phase approach).
2 (Default)
Global stress constraints are used first, followed by local stress constraints being used; the switch occurs based on certain conditions (two phase approach). 11
BUCKLING Buckling continuation line to activate the consideration of Euler Buckling constraints during truss layout optimization. 12
ALPHA Diameter-thickness ratio to adjust the stress bound for truss layout optimization.

Comments

  1. The DTRUSS Bulk Data Entry activates truss layout optimization. It is currently only supported for Linear Static Analysis.
  2. Truss layout optimization is useful for applications where structures include trusses such as in the architectural industry for building design.
  3. If truss layout optimization is activated (DTRUSS is present), then all shell and solid elements in the model are automatically converted into non-tapered CROD elements to generate the ground structure. From the ground structure of CROD elements, during the initial adaptive member handling process, some CROD's can be added into the structure.
    1. Some nearby grids can be connected with CROD elements
    2. Some far-away grids can be connected with CROD elements
  4. After the initial adaptive member handling process, a filtering process is performed in which some CROD elements with small cross-section are removed. This simplifies the Truss structure.
  5. Subsequently, a Geometry optimization process is carried out, where:
    1. The location of grids can change
    2. The length of each CROD can change
    3. The cross-section CROD elements can change
  6. Subsequently, some additional operations may also be performed.
    1. If some CROD elements cross over each other, new grids are added to divide the intersecting rods.
    2. If some grids are very close to each other, they are merged to form a single grid.
  7. The filtering process, geometry optimization, and grid operations are carried out iteratively until a steady state is reached.
  8. The final optimized truss design is saved in the <filename>_opt.fem file in the working directory. This file can be opened in a Text Editor or imported into HyperWorks and the corresponding final design can be visualized. Additionally, if a more simplified structure could be generated during the optimization, this is saved in an optionally generated <filename>_opt_simp.fem file. This simplification is carried out by sacrificing some amount of volume, which is controlled by the parameter VRELAX.
    Note: Sometimes the simplification process cannot find a simpler structure. In such cases, a <filename>_opt_simp.fem file is not generated.
  9. Since local stress constraints are applied to each rod, the number of constraints can be very high even for small models. Therefore, the recommended number of CROD elements during truss layout optimization is lower than 2000. Hence, it is recommended to use coarse meshes for truss layout optimization.
  10. During Geometry optimization, OptiStruct internally creates an optimization setup to minimize volume subject to local stress constraints during geometry optimization. User-defined responses via DRESP1, DRESP2, and DRESP3 and corresponding user-defined constraints via DCONSTR or objective via DESOBJ are currently not supported in conjunction with truss layout optimization.
  11. If the TYPE field is set to 2 (Default), the two-phase approach is used. Phase 1 is driven by global stress constraints and Phase 2 is driven by local stress constraints. The switch to local stress constraints occurs:
    1. After the filtering and validation stage, if the number of rod elements is less than 500, OR,
    2. After joint merging stage, if the number of rod elements is less than 500, OR,
    3. Before the simplification stage.
  12. Euler buckling constraints are only considered at the final stages of truss layout optimization (at the sizing optimization step). At this step, the stress bound of the CROD truss elements are updated based on the defined ALPHA value. The general formulation of truss layout optimization is updated to consider Euler buckling constraints as:
    Minimize volume, subject to
    σ pc σ i σ pe MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeyOeI0Iaeq 4Wdm3aaSbaaSqaaiaadchacaWGJbaabeaakiabgsMiJkabeo8aZnaa BaaaleaacaWGPbaabeaakiabgsMiJkabeo8aZnaaBaaaleaacaWGWb Gaamyzaaqabaaaaa@44D6@
    σ ¯ i = min σ i b , σ p c MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGafq4WdmNbae badaWgaaWcbaGaamyAaaqabaGccqGH9aqpciGGTbGaaiyAaiaac6ga daGadaqaaiabeo8aZnaaBaaaleaacaWGPbGaamOyaaqabaGccaGGSa Gaeq4Wdm3aaSbaaSqaaiaadchacaWGJbaabeaaaOGaay5Eaiaaw2ha aaaa@474F@
    σ i b = α E A i 8 L i 2 MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Wdm3aaS baaSqaaiaadMgacaWGIbaabeaakiabg2da9maalaaabaGaeqySdeMa amyraiaadgeadaWgaaWcbaGaamyAaaqabaaakeaacaaI4aGaamitam aaDaaaleaacaWGPbaabaGaaGOmaaaaaaaaaa@4294@
    Where,
    σ i MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Wdm3aaS baaSqaaiaadMgaaeqaaaaa@38D0@
    Stress in the truss element,
    σ i b MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Wdm3aaS baaSqaaiaadMgacaWGIbaabeaaaaa@39B7@
    Updated stress bound based on the buckling constraint.
    σ p e MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Wdm3aaS baaSqaaiaadchacaWGLbaabeaaaaa@39C1@
    Permissible extension stress limit.
    σ p c MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Wdm3aaS baaSqaaiaadchacaWGJbaabeaaaaa@39BF@
    Permissible compression stress limit.
    α MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqySdegaaa@3792@
    Diameter-thickness ratio given by the ALPHA field.
    E MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyraaaa@36BD@
    Young's modulus.
    A i MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyqamaaBa aaleaacaWGPbaabeaaaaa@37D3@
    Cross-sectional area of rod element i MathType@MTEF@5@5@+= feaahqart1ev3aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamyAaaaa@36E2@ .
    L i MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamitamaaDa aaleaacaWGPbaabaaaaaaa@37DF@
    Length of rod element L i MathType@MTEF@5@5@+= feaahqart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamitamaaDa aaleaacaWGPbaabaaaaaaa@37DF@ .