decks: ties as Abaqus *TIE and LS-DYNA tied contact

Nastran refuses them by name.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/decks/src/abaqus.rs

@@ -28,6 +28,11 @@
 //! initial overclosure have no Abaqus counterpart and are noted in comments (Abaqus chooses its
 //! own penalty and resolves overclosure in the first increment).
 //!
+//! # Ties
+//!
+//! Each tie is `*TIE, NAME=…, ADJUST=NO` with the secondary surface first and its position
+//! tolerance when it has one: FieldCraft ties the nodes where they are (no adjustment).
+//!
 //! # Steps and the activity table
 //!
 //! The model lists, for every step, exactly the boundary conditions and loads active in it; Abaqus
@@ -187,6 +192,7 @@ pub fn write_resolved(model: &Model, r: &Resolved) -> Result<String> {
     d.discrete_properties(&discrete)?;
     d.couplings(model, r);
     d.contacts(model, r)?;
+    d.ties(model)?;
     d.steps(model, r)?;
     Ok(d.out)
 }
@@ -1042,6 +1048,20 @@ impl Deck {
         Ok(())
     }
 
+    /// Ties: `*TIE` per tie, secondary surface first.
+    fn ties(&mut self, model: &Model) -> Result<()> {
+        if model.ties().is_empty() {
+            return Ok(());
+        }
+        self.comment("Ties: each secondary surface bonded to its main surface");
+        for (name, t) in model.ties() {
+            let tolerance = t.position_tolerance.map_or(String::new(), |v| format!(", POSITION TOLERANCE={v:?}"));
+            self.line(&format!("*TIE, NAME={name}, ADJUST=NO{tolerance}"));
+            self.line(&format!("{}, {}", t.secondary, t.main));
+        }
+        Ok(())
+    }
+
     fn boundary_lines<'n>(&mut self, model: &Model, r: &Resolved, names: impl IntoIterator<Item = &'n String>) -> Result<()> {
         for name in names {
             let Some(bc) = model.boundary_condition(name) else { continue };

crates/decks/src/lsdyna/mod.rs

@@ -23,7 +23,8 @@
 //!   node set), distributing as `*CONSTRAINED_INTERPOLATION` (the reference point dependent on
 //!   the set's translations, equal weights);
 //! - contact: a pair as `*CONTACT_AUTOMATIC_SURFACE_TO_SURFACE` between segment sets (the
-//!   secondary surface first), general contact as `*CONTACT_AUTOMATIC_SINGLE_SURFACE` on a segment
+//!   secondary surface first; a tie as `*CONTACT_TIED_SURFACE_TO_SURFACE` likewise), general
+//!   contact as `*CONTACT_AUTOMATIC_SINGLE_SURFACE` on a segment
 //!   set or on every part (`surfatyp` 5); the static and kinetic coefficients and the decay
 //!   coefficient (`fs`, `fd`, `dc`: the same exponential decay law) and the penalty scale on both
 //!   sides (`sfsa`, `sfsb`, a factor on LS-DYNA's own default stiffness). LS-DYNA moves nodes
@@ -280,6 +281,9 @@ fn plan<'a>(model: &'a Model, r: &Resolved) -> Result<Plan<'a>> {
     for c in model.contacts().values() {
         segment_sets.extend(c.surfaces.sets());
     }
+    for t in model.ties().values() {
+        segment_sets.extend([t.main.as_str(), t.secondary.as_str()]);
+    }
     let mut gravity_sets: BTreeSet<Option<&str>> = BTreeSet::new();
     for step in model.steps() {
         if matches!(step.procedure, Procedure::ExplicitDynamic(_)) {
@@ -733,6 +737,21 @@ fn contacts(d: &mut Deck, model: &Model, plan: &Plan) -> Result<()> {
         d.header(&["sfsa", "sfsb"]);
         d.card([Field::from(c.penalty_scale), Field::from(c.penalty_scale)]);
     }
+    // Ties: a tied surface-to-surface contact between the segment sets, secondary first.
+    for (name, t) in model.ties() {
+        let sid = |set: &str| plan.sets.get(set).copied().ok_or_else(|| broken(format!("tie `{name}`: set `{set}`")));
+        d.comment(&format!("tie `{name}`"));
+        if t.position_tolerance.is_some() {
+            d.comment("FieldCraft's position tolerance: LS-DYNA ties the nodes within its own search distance");
+        }
+        d.line("*CONTACT_TIED_SURFACE_TO_SURFACE");
+        d.header(&["surfa", "surfb", "surfatyp", "surfbtyp"]);
+        d.card([Field::from(sid(&t.secondary)?), Field::from(sid(&t.main)?), Field::from(0), Field::from(0)]);
+        d.header(&["fs", "fd", "dc"]);
+        d.card([Field::from(0.0), Field::from(0.0), Field::from(0.0)]);
+        d.header(&["sfsa", "sfsb"]);
+        d.card([Field::from(1.0), Field::from(1.0)]);
+    }
     Ok(())
 }
 

crates/decks/src/nastran/mod.rs

@@ -337,6 +337,9 @@ impl<'m> Deck<'m> {
         for name in self.model.contacts().keys() {
             self.problems.insert(format!("contact `{name}` (Nastran's linear solutions SOL 101 and 103 have no contact)"));
         }
+        for name in self.model.ties().keys() {
+            self.problems.insert(format!("tie `{name}` (this writer does not write glued contact yet)"));
+        }
         for sub in &mut self.subcases {
             if matches!(sub.step.procedure, Procedure::Frequency { .. }) {
                 sub.method = Some(next_id(&mut self.next_sid)?);

crates/decks/tests/contact.rs

@@ -4,7 +4,7 @@
 use fieldcraft_decks::{Error, abaqus, lsdyna, nastran};
 use fieldcraft_model::{
     BoundaryCondition, Contact, ContactSurfaces, Elastic, ElementFace, ElementKind, Friction, InitialPenetration, Material, Model, Procedure,
-    Section, SectionKind, Set, Step, Target, UnitSystem,
+    Section, SectionKind, Set, Step, Target, Tie, UnitSystem,
 };
 
 /// Two unit hex8 cubes, the second on top of the first (separate nodes), with face sets for the
@@ -42,6 +42,7 @@ fn model() -> Model {
     m.add_contact("stack", pair).unwrap();
     m.add_contact("everything", Contact { friction: Friction::coulomb(0.1), ..Contact::new(ContactSurfaces::General { surface: None }) }).unwrap();
     m.add_contact("fold", Contact { penalty_scale: 0.5, ..Contact::new(ContactSurfaces::General { surface: Some("upper".into()) }) }).unwrap();
+    m.add_tie("glue", Tie { position_tolerance: Some(0.05), ..Tie::new("lower", "upper") }).unwrap();
     m
 }
 
@@ -56,6 +57,7 @@ fn abaqus_writes_interactions_pairs_and_general_contact() {
         "*SURFACE INTERACTION, NAME=fold-interaction\n*FRICTION\n0.0\n",
         "*CONTACT\n*CONTACT INCLUSIONS, ALL EXTERIOR\n*CONTACT INCLUSIONS\nupper,\n*CONTACT PROPERTY ASSIGNMENT\n, , everything-interaction\nupper, upper, fold-interaction\n",
         "** contact `fold`: penalty scale 0.5",
+        "*TIE, NAME=glue, ADJUST=NO, POSITION TOLERANCE=0.05\nupper, lower\n",
     ] {
         assert!(deck.contains(expected), "{expected}\n{deck}");
     }
@@ -83,6 +85,7 @@ fn lsdyna_writes_automatic_contacts_on_segment_sets() {
     for set in ["lower", "upper"] {
         assert!(deck.contains(&format!("*SET_SEGMENT_TITLE\n{set}\n")), "{set}\n{deck}");
     }
+    assert_eq!(after("*CONTACT_TIED_SURFACE_TO_SURFACE"), ["4 3 0 0", "0.0 0.0 0.0", "1.0 1.0"], "{deck}");
 }
 
 #[test]
@@ -92,6 +95,7 @@ fn nastran_refuses_contact_by_name() {
             for name in ["everything", "fold", "stack"] {
                 assert!(what.contains(&format!("contact `{name}`")), "{what}");
             }
+            assert!(what.contains("tie `glue`"), "{what}");
         }
         other => panic!("{other:?}"),
     }