Does the optimality-criteria move limit decide whether a robust topology optimisation survives its beta steps?

What it found

Diagnoses two unexplained poor runs from simdesign-robustmesh. The robust eroded / blueprint / dilated half-MBB design is rerun at move limits 0.2, 0.1 and 0.05 over nine mesh-and-radius cases (27 deterministic runs). At 0.2, the value every earlier project used, five of nine blueprint compliances are more than 1.5× the best (e.g. 742 against about 200 on 60×20); at 0.1 and 0.05 none are. The failing runs show worst-case compliance jumping up to 400× in one iteration after β reaches 32–64. The mechanism (a thin member breaking when the eroded field sharpens) is a hypothesis, not tested. Stylised: 2D, dimensionless, one problem.

A figure from its own output

Paper, code and results

• README and method
• Experiments and results
• Code
• Tests

More in Simulation-first design

• Can an adaptive move limit that shrinks after a compliance spike rescue a robust topology optimisation as well as a fixed small one?Can a move limit that halves after a compliance spike rescue a robust topology optimisation? Partly: fixed 0.2 failed 5 of 9 cases, fixed 0.05 none, the adaptive rule 2 of 9, because it reacts after the damaging step (stylised, one run per cell).
• Does rolling back a robust topology-optimisation step that spikes compliance, and redoing it at half the move, beat shrinking the move afterwards?Does rolling back a robust topology-optimisation step that spikes compliance and redoing it at half the move beat shrinking the move afterwards? Mostly: fixed 0.2 failed 5 of 9 cases, adaptive 2, retry 1, fixed 0.1/0.05 none, but retry never beat fixed 0.05 (stylised, one run per cell).
• Can penalty continuation free SIMP topology-optimisation starts that stay stuck in a different local optimum?Can penalty continuation free SIMP starts stuck in a different local optimum? No: it sends all 5 stuck starts of 20 to one design (c 204.01) worse than the 202.83 three reach by running longer at p = 3. Stylised.
• Is the start-dependence of fixed-penalty SIMP topology optimisation just slow convergence?Is the start-dependence of fixed-penalty SIMP just slow convergence? Over 1200 iterations the median of 20 random starts reaches the uniform-start design (0.0% of elements differ, from 3.9% at 150), but the compliance spread only falls 1.43% → 0.85% (stylised, 2D, one mesh).
• How much does a SIMP topology optimisation depend on its starting density field, and does penalty continuation remove it?How much does a SIMP topology optimisation depend on its starting density field? With a fixed penalty, final compliance spreads 1.4–2.8% over 30 random starts and 2–23% of elements change state; with penalty continuation the spread is 0–0.4% (stylised, 2D, 150 iterations).
• How short can SIMP penalty continuation be and still remove the dependence on the starting density field?How short can SIMP penalty continuation be and still remove the start dependence? A ramp of 25 iterations or fewer leaves much of it (worst start differs in 16–23% of elements, 27–31% for a fixed penalty); 50 iterations cuts compliance spread to 0.01–0.23%, and a 112-iteration ramp is most repeatable but ends at a worse compliance (stylised, 2D, 150 iterations).

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Produced with AI assistance (Claude). Results are from the code in this repository and are simulated or stylised unless the abstract says otherwise; nothing here implies affiliation with or endorsement by any lab, researcher or company cited. MIT licensed.