forked from 1b-agent/fieldcraft-upstream
solver: heat transfer across ties (#358)
Ties constrain temperatures with the displacement tie's mortar weights in steady and transient heat and in coupled temperature-displacement steps; the heat solver eliminates them with the prescribed temperatures through constraints::Reduction. refuse_ties is gone. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo
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jyvikoandClaude Opus 5.5 authored and Irakli Kourtis committed
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@@ -1,5 +1,6 @@
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//! Contact in nonlinear static steps against closed forms: the contact patch test on
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//! non-matching meshes, Newton's convergence with contact, and what implicit contact refuses.
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//! non-matching meshes, Newton's convergence with contact, and what implicit contact refuses;
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//! ties of non-matching meshes for displacement and for heat.
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//! Run with `--nocapture` to see the iterations.
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use std::collections::BTreeMap;
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@@ -546,10 +547,6 @@ fn a_tie_passes_the_patch_test() {
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#[test]
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fn what_ties_refuse() {
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let (mut b, _) = tied(ElementKind::Hex8, ElementKind::Hex8, false, Procedure::Static {});
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b.model.add_step(Step::new("Heat", Procedure::HeatTransfer { transient: None }), None).unwrap();
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let e = fieldcraft_solver::solve_heat(&b.model, Some("Heat"), &Limits::default()).unwrap_err().to_string();
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assert!(e.contains("tie `glue`") && e.contains("heat transfer"), "{e}");
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let (mut b, _) = tied(ElementKind::Hex8, ElementKind::Hex8, false, Procedure::Static {});
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// (Touching surfaces are tied within any tolerance.)
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b.model.replace_tie("glue", Tie { position_tolerance: Some(1e-9), ..Tie::new("lower_top", "upper_bottom") }).unwrap();
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@@ -557,6 +554,160 @@ fn what_ties_refuse() {
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assert!(r.warnings.iter().all(|w| !w.contains("stay free")), "{:?}", r.warnings);
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}
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/// Two blocks tied at z = 1, conducting heat: `lower` (`lower_n` cells, graded unless `n`
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/// divides evenly, conductivity `k_lower`) below and `upper` (2 × 2 × 2, `k_upper`) above, the
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/// lower block secondary, in step "Step" of `procedure`. ρc = 1 and α = 1e-5 (reference 0) in
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/// both.
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fn tied_conductor(lower: ElementKind, lower_n: [usize; 3], graded: bool, upper: ElementKind, k: [f64; 2], procedure: Procedure) -> Blocks {
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let mut b = Blocks::default();
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let low = b.block(lower, lower_n, |p| if graded { [p[0].powf(1.4), p[1].powf(0.8), p[2]] } else { p });
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let up = b.block(upper, [2, 2, 2], |p| [p[0], p[1], 1.0 + p[2]]);
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for (name, elements, k) in [("low", &low, k[0]), ("up", &up, k[1])] {
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b.model.add_set(name, Set { elements: elements.clone(), ..Set::default() }).unwrap();
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let thermal = Thermal {
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conductivity: Some(Directional::Isotropic(k)),
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specific_heat: Some(1.0),
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expansion: Some(Directional::Isotropic(1e-5)),
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..Thermal::default()
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};
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let material = Material {
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elastic: Some(Elastic::Isotropic { young: 1000.0, poisson: 0.3 }),
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density: Some(1.0),
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thermal: Some(thermal),
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..Material::default()
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};
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b.model.add_material(name, material).unwrap();
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b.model
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.add_section(name, Section { set: name.into(), material: name.into(), kind: SectionKind::Solid {}, formulation: Formulation::default() })
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.unwrap();
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}
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b.model.add_step(Step::new("Step", procedure), None).unwrap();
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b.face_set("lower_top", &low, |x| near(x[2], 1.0));
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b.face_set("upper_bottom", &up, |x| near(x[2], 1.0));
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b.model.add_tie("glue", Tie::new("upper_bottom", "lower_top")).unwrap();
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b
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}
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/// Hold the nodes satisfying `f` at temperature `value` in step "Step".
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fn hold_temperature(b: &mut Blocks, name: &str, value: f64, f: impl Fn([f64; 3]) -> bool) {
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b.node_set(name, f);
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b.model.add_boundary_condition(name, BoundaryCondition::Temperature { target: Target::Set(name.into()), value }).unwrap();
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b.model.set_boundary_condition_active("Step", name, true).unwrap();
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}
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fn temperature(r: &fieldcraft_solver::HeatResult, label: u32) -> f64 {
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r.temperature()[r.nodes.binary_search(&label).unwrap()]
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}
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/// Steady conduction through two tied blocks of non-matching meshes, 20 at z = 0 and 100 at
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/// z = 2: with one conductivity the profile is the linear T = 20 + 40 z everywhere, the interface
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/// nodes included, the flux −k ∂T/∂z in every element and the heat flow k A ΔT / L in at the hot
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/// end and out at the cold one (A = 1); with k₁ below and k₂ above, the series-resistance
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/// solution, linear in each block with the kink at the interface temperature
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/// T_i = (k₁ T₀ + k₂ T₁)/(k₁ + k₂) and the heat flow ΔT/(1/k₁ + 1/k₂).
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#[test]
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fn heat_crosses_a_tie_exactly() {
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for (lower, upper, n, graded, name) in [
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(ElementKind::Hex8, ElementKind::Hex8, [2, 2, 2], false, "matching hex8"),
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(ElementKind::Hex8, ElementKind::Hex8, [3, 3, 2], true, "hex8 on graded hex8"),
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(ElementKind::Tet4, ElementKind::Hex8, [3, 3, 2], false, "hex8 on tet4"),
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(ElementKind::Hex8, ElementKind::Tet4, [3, 3, 2], true, "tet4 on graded hex8"),
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(ElementKind::Tet4, ElementKind::Tet4, [3, 3, 2], false, "tet4 on tet4"),
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] {
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for k in [[45.0, 45.0], [10.0, 40.0]] {
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let mut b = tied_conductor(lower, n, graded, upper, k, Procedure::HeatTransfer { transient: None });
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hold_temperature(&mut b, "cold", 20.0, |x| near(x[2], 0.0));
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hold_temperature(&mut b, "hot", 100.0, |x| near(x[2], 2.0));
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let r = fieldcraft_solver::solve_heat(&b.model, Some("Step"), &Limits::default()).unwrap();
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assert!(r.warnings.iter().all(|w| !w.contains("stay free")), "{name}: {:?}", r.warnings);
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let interface = (k[0] * 20.0 + k[1] * 100.0) / (k[0] + k[1]);
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let q = 80.0 / (1.0 / k[0] + 1.0 / k[1]);
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let want = |z: f64| if z <= 1.0 { 20.0 + (interface - 20.0) * z } else { interface + (100.0 - interface) * (z - 1.0) };
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for (l, x) in &b.xyz {
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let t = temperature(&r, *l);
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assert!((t - want(x[2])).abs() < 1e-9 * 100.0, "{name} {k:?}: node {l} at {x:?}: {t} vs {}", want(x[2]));
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}
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for e in &r.elements {
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for p in &e.points {
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assert!(
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(p.flux[2] + q).abs() < 1e-9 * q && p.flux[0].abs() < 1e-9 * q && p.flux[1].abs() < 1e-9 * q,
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"{name} {k:?}: element {} {:?}",
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e.label,
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p.flux
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);
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}
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}
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// The heat flow: in at the hot end, out at the cold one, nothing lost at the tie.
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let flow = |f: &dyn Fn([f64; 3]) -> bool| -> f64 { b.nodes(f).iter().map(|l| r.reaction[r.nodes.binary_search(l).unwrap()]).sum() };
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assert!((flow(&|x| near(x[2], 2.0)) - q).abs() < 1e-9 * q, "{name} {k:?}: {}", flow(&|x| near(x[2], 2.0)));
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assert!((flow(&|x| near(x[2], 0.0)) + q).abs() < 1e-9 * q, "{name} {k:?}: {}", flow(&|x| near(x[2], 0.0)));
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assert!(r.reaction_total.abs() < 1e-9 * q && r.applied_total.abs() < 1e-9 * q, "{name} {k:?}");
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}
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}
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}
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/// Transient conduction into a bar of two tied blocks (backward Euler, 0 initially, the top held
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/// at 100 from the start): the single-body bar's history to round-off, with matching meshes and
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/// with a graded 3 × 3 lower block (the field varies along the bar alone, which both hexahedral
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/// meshes represent alike, so the tie is the only difference).
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#[test]
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fn transient_heat_through_a_tie_is_the_single_body_s() {
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let tr = Procedure::HeatTransfer { transient: Some(Transient { theta: 1.0, ..Transient::new(1.0, 0.05) }) };
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// The single body: one 2 × 2 × 4 block of the same material.
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let mut single = Blocks::default();
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let all = single.block(ElementKind::Hex8, [2, 2, 4], |p| [p[0], p[1], 2.0 * p[2]]);
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single.model.add_set("all", Set { elements: all, ..Set::default() }).unwrap();
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let thermal = Thermal { conductivity: Some(Directional::Isotropic(1.0)), specific_heat: Some(1.0), ..Thermal::default() };
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single.model.add_material("Mat", Material { density: Some(1.0), thermal: Some(thermal), ..Material::default() }).unwrap();
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single
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.model
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.add_section("solid", Section { set: "all".into(), material: "Mat".into(), kind: SectionKind::Solid {}, formulation: Formulation::default() })
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.unwrap();
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single.model.add_step(Step::new("Step", tr.clone()), None).unwrap();
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hold_temperature(&mut single, "hot", 100.0, |x| near(x[2], 2.0));
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let reference = fieldcraft_solver::solve_heat(&single.model, Some("Step"), &Limits::default()).unwrap();
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let at = |r: &fieldcraft_solver::HeatResult, xyz: &BTreeMap<u32, [f64; 3]>, z: f64| -> f64 {
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let nodes: Vec<u32> = xyz.iter().filter(|(_, x)| near(x[2], z)).map(|(l, _)| *l).collect();
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nodes.iter().map(|l| temperature(r, *l)).sum::<f64>() / nodes.len() as f64
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};
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for (n, graded) in [([2, 2, 2], false), ([3, 3, 2], true)] {
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let mut b = tied_conductor(ElementKind::Hex8, n, graded, ElementKind::Hex8, [1.0, 1.0], tr.clone());
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hold_temperature(&mut b, "hot", 100.0, |x| near(x[2], 2.0));
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let r = fieldcraft_solver::solve_heat(&b.model, Some("Step"), &Limits::default()).unwrap();
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assert_eq!(r.times.len(), reference.times.len());
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for z in [0.0, 0.5, 1.0, 1.5] {
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let (a, want) = (at(&r, &b.xyz, z), at(&reference, &single.xyz, z));
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assert!(want > 1.0, "z {z}: the heat reaches it ({want})");
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assert!((a - want).abs() < 1e-9 * want, "{n:?} z {z}: {a} vs {want}");
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}
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}
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}
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/// A coupled temperature–displacement step with a tie, held at a uniform 100 above the reference
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/// 0: the temperature is uniform through the tie and both blocks expand freely, u = α ΔT x, with
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/// no stress.
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#[test]
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fn a_tied_body_expands_freely_under_a_uniform_temperature() {
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let mut b = tied_conductor(ElementKind::Hex8, [3, 3, 2], true, ElementKind::Tet4, [10.0, 40.0], Procedure::CoupledTemperatureDisplacement {});
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hold_temperature(&mut b, "cold", 100.0, |x| near(x[2], 0.0));
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hold_temperature(&mut b, "hot", 100.0, |x| near(x[2], 2.0));
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// Statically determinate supports: the origin fixed, (1, 0, 0) held in y and z, (0, 1, 0) in z.
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b.bc("o", [Some(0.0), Some(0.0), Some(0.0)], |x| near(x[0], 0.0) && near(x[1], 0.0) && near(x[2], 0.0));
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b.bc("a", [None, Some(0.0), Some(0.0)], |x| near(x[0], 1.0) && near(x[1], 0.0) && near(x[2], 0.0));
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b.bc("c", [None, None, Some(0.0)], |x| near(x[0], 0.0) && near(x[1], 1.0) && near(x[2], 0.0));
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let r = fieldcraft_solver::solve_static(&b.model, Some("Step"), &Limits::default()).unwrap();
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let temps = r.temperature.clone().unwrap();
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assert!(temps.iter().all(|t| (t - 100.0).abs() < 1e-9), "{temps:?}");
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let strain = 1e-5 * 100.0;
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for (i, l) in r.nodes.iter().enumerate() {
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let x = b.xyz[l];
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for (u, x) in r.displacement[i].iter().zip(x) {
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assert!((u - strain * x).abs() < 1e-9 * strain, "node {l}: {:?}", r.displacement[i]);
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}
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}
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assert!(r.elements.iter().flat_map(|e| &e.nodal).flatten().all(|s| s.abs() < 1e-6), "stress-free");
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}
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/// A C-shaped ring of rubber (an annulus of radii 1 and 1.5 with a 10° opening at +x, one hex8
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/// layer thick in z with z held: plane strain) whose two ends are pressed together through the
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/// outer nodes two elements from each end, against general (single-surface) contact on every
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