RD-E: 5101 Size Optimization of a B-Pillar

This example defines a crash test on B-Pillar. The optimization objective is to minimize the mass of the B-Pillar by changing the shell thickness. The intrusion, which is defined by the optimization constraint is required to not be larger than the original model, to keep the passenger safe.

The Optimization feature in Radioss, makes it easy to set up an optimization problem in Radioss Block Format. The purpose of this example is to show how to set up an optimization, based on a crash test (Radioss Block model).

ex_51_Bpillar
Figure 1.

The setup of optimization in Radioss requires an extra input file apart from the usual Starter and Engine input files. The required file is an optimization input file named <name>.radopt (the Starter and Engine files are named <name>_0000.rad and <name>_0001.rad, respectively). The <name>.radopt file defines optimization entities such as the optimization objective, optimization constraints, design variables, optimization responses and so on.

Options and Keywords Used

Input Files

The input files used in this example include:
B-Pillar (Thickness Optimization)
<install_directory>/hwsolvers/demos/radioss/example/51_RADIOSS_Optimization/Size_Optimization

Model Description

Units: mm, s, ton, N, and MPa

Cut the B-Pillar from the full car model and set the initial velocity in the rigid cylinder.
  • Objective: Minimize mass
  • Constraint: Maximum displacement of node 2021524 in Y direction (inside reinforcement) < 19.7 [mm]

    ex_51_problem
    Figure 2. Problem Description
  • Design variables:
    • Shell thickness of the middle reinforcement - allowable range [0.5mm, 3.0mm]
    • Shell thickness of the inside reinforcement - allowable range [0.5mm, 3.0mm]

Detailed Optimization Setup


ex_51_optimization_setup
Figure 3. Radioss Optimization Setup

Optimization Objective

/DESOBJ is used to define optimization objective. In this example, it defines the minimal response #1.

Response #1 defines an optimization response that is the combination of mass in part group #2000329 (defined in the Radioss Starter file), which includes both parts of the middle reinforcement and the inside reinforcement.

ex_51_desobj
Figure 4. Optimization Objective Setup in Radioss Optimization

Optimization Constraint

In this example, you want to constrain the intrusion to not be larger than the original model (before optimization). In the original model, max. y-displacement in node 2021524 is 19.7mm. Define this value as cmax in /DCONSTR and in response 2, define 19.7 as the max. y-displacement (with RTYPE=5, ATTA=7) in node 2021524 (with PTYPE=1, ATTI=2021524).

Depending on your own optimization criteria, the value in cmax may differ.

ex_51_dresp1
Figure 5. Optimization Constraint Setup in Radioss Optimization

Design Variable

/DESVAR is used to define design variables and /DVPREL1 to relate design variables to analysis model property.

Two different design variables are defined: One for part 2000327 and one for part 2000329

For example, the design variable for inside reinforcement (part 2000327) is defined:
  • In /DESVAR with the range [0.5,3.0] - this will be used in /DVPREL1.

    In /DVPREL1 with prop_typ and prop_fid the above variable can be used for shell thickness, and with prop_ID the thickness in shell property 2000327 will be used in the optimization run.

  • COEF1 in /DVPREL1. In each iteration, Pi (the thickness value) will be equal to C 0 + ( 1.0 ∗ X ) MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aacaWGdbGaaGimaiabgUcaRmaabmaabaGaaGymaiaac6cacaaIWaGa ey4fIOIaamiwaaGaayjkaiaawMcaaaaa@40B7@ , where X ∈ [ 0.5 , 3.0 ] MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aacaWGybGaeyicI48aamWaaeaacaaIWaGaaiOlaiaaiwdacaGGSaGa aG4maiaac6cacaaIWaaacaGLBbGaayzxaaaaaa@422E@ which is defined in /DESVAR.(1)

ex_51_desvar
Figure 6. Design Variable Setup in Radioss Optimization

Radioss Options Used

/INIVEL and /INTER/TYPE7 are also used.

Use /INIVEL to optimize the B-Pillar under same initial kinetic energy.

In this example, you want to change the shell thickness to have minimal mass of B-Pillar. There is initial penetration, due to thickness changes between two contact parts. Defining initial thickness in /PART can avoid this issue and the thickness is only used to calculate the gap in interfaces.

ex_51_part
Figure 7. /PART Card in Radioss Starter File

Results

In the results check the following:
  1. The latest design provides the best results. Verify whether the result is feasible or not. In the *.out file (Neon-b_pillar.out) this data is at end of each iteration.

    FEASIBLE DESIGN (ALL CONSTRAINTS SATISFIED) - indicates that the design is good.

    INFEASIBLE DESIGN (AT LEAST ONE CONSTRAINT VIOLATED). - indicates that the design variable definition needs to be checked/improved.

    This information can also be found in the output file hwsolver.mesg.

  2. In the *.out file (Neon-b_pillar.out), check/verify the optimization definition. Objective Function: Minimize Combined Mass, Run Type: Sizing Optimization and so on.
  3. By running the Optimization in Radioss, an equivalent OptiStruct model will also be automatically created and named *.fem (Neon-b_pillar.fem).
Check the results in the *.eslout (Neon-b_pillar.eslout), in the *h3d file, or in each ANIM, T01 file. The *.eslout file contains the value of optimized objective in each iterations.

ex_51_selout_file
Figure 8. Optimized Results in Each Iterations in *eslout File

In the original model, the mass of the two parts is 3.0011e-3[Ton] and the optimized mass for these two parts is 2.4158e-3[Ton]. The mass is reduced by approximately 19.5%.

The thickness of part #2000327 is 1.328mm and the optimized thickness is 0.5539mm. The thickness is reduced.

The thickness of part #2000329 is 0.7060mm and the optimized thickness is 0.8933mm. The thickness in this model increased in order to get better performance of these two parts (in response 1, ATTB =1 (for COMB) is defined).

ex_51_2000329
Figure 9. Optimized Results of Shell Thickness of Two Reinforcement Parts

ex_51_mass_results
Figure 10. Optimized Results of Total Mass of Two Reinforcement Parts

In the last iteration, the mass was reduced to 2.4158e-3[Ton]. This new design still meets the constraint (< 19.7[mm]), defined in /DCONSTR.

In node 2021524, the max. y-displacement:

19.57[mm] (last iteration) < 19.7 [mm] (in constraint). Meets the constraint.

ex_51_202154
Figure 11. y-displacement on Node 2021524 in Original Model and Optimized Model