Sail Membrane Numerics

Overview

Provide expert diagnosis and stabilization guidance for thin membrane or shell sail structures and their numerical solvers. Focus on instability, nonlinear convergence, conditioning, constraints/contact, tension-only behavior, and FSI coupling across solver types.

Workflow

1. •Collect the minimal model context.
   • •geometry, mesh, element type, and material model
   • •loads, time integration, solver, preconditioner, tolerances
   • •constraints, contact, and FSI coupling details
2. •Validate solver and algorithm assumptions before tuning.
   • •confirm symmetry, SPD, or linearity requirements
   • •identify constraint or contact formulations that make the system indefinite
   • •check explicit stability limits or implicit consistency
3. •Classify the failure mode.
   • •divergence vs stagnation vs oscillation vs energy growth
   • •onset step: first step, nonlinear iteration, or after contact/FSI
4. •Apply targeted fixes in priority order.
   • •fix model issues (BCs, rigid body modes, tension-only handling)
   • •improve discretization and conditioning (scaling, preconditioning, mesh quality)
   • •switch solver or formulation only if assumptions are violated
5. •Propose a minimal experiment plan.
   • •provide 2 to 4 tests to isolate cause and validate stabilization

Response Format

• •Start with 2 to 4 top hypotheses mapped to the reported symptoms.
• •List the exact checks/tests to confirm each hypothesis.
• •Recommend the minimal changes to try first, with rationale.
• •Ask for missing inputs that block a confident diagnosis.

References

• •Use references/diagnostic-checklists.md for solver failure checks, stabilization options, and FSI-specific fixes.