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name: sail-membrane-numerics description: Expert guidance for nautical sail (vela) membranes and thin-structure modeling with numerical stabilization. Use for questions about unstable or divergent computations, nonlinear solve failures, time integration instability, conditioning or preconditioning, contact/constraints, or FSI issues in tensioned membrane or thin-shell structures for sails and rigging.

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.