embedded3 S2-2b (host lever): narrow-band φ re-evaluation for moving bodies (max_surface_speed) — bit-identical, the flag body's ny 62 rebuild 3.54 → 0.30 s; the flag driver uses it

Co-Authored-By: Claude Fable 5.1 <[email protected]>

crates/specialized/rtx-cfd/src/solvers/incompressible/embedded3/step/mod.rs

@@ -74,6 +74,11 @@ pub struct Parameters {
     pub inner_stop_factor: f64,
     /// The wall treatment of an embedded body.
     pub wall_scheme: WallScheme,
+    /// A moving body's largest surface speed: with it the cut geometry's
+    /// φ is re-evaluated only within three cells of the surface each step
+    /// (identical results; the far corners keep their sign). `None` =
+    /// every corner every step.
+    pub max_surface_speed: Option<f64>,
 }
 
 impl Default for Parameters {
@@ -87,6 +92,7 @@ impl Default for Parameters {
             convection_scheme: ConvectionScheme::Upwind,
             inner_stop_factor: 1e-2,
             wall_scheme: WallScheme::GhostBinary,
+            max_surface_speed: None,
         }
     }
 }
@@ -182,10 +188,17 @@ impl Solver {
         self.mask = None;
     }
 
-    fn build_mask(&self, body: &Body, g: Grid, t: f64) -> Mask {
+    fn build_mask(&self, body: &Body, g: Grid, t: f64, dt: f64) -> Mask {
         match self.params.wall_scheme {
             WallScheme::GhostBinary => Mask::build(body, g, t, self.params.boundaries),
-            WallScheme::CutCell => Mask::build_cut(body, g, t, self.params.boundaries),
+            WallScheme::CutCell => {
+                let h = g.dx.min(g.dy).min(g.dz);
+                let prev = match (self.params.max_surface_speed, &self.mask) {
+                    (Some(speed), Some(m)) => m.cut().map(|c| (c, 3.0 * h, speed * dt)),
+                    _ => None,
+                };
+                Mask::build_cut_from(body, g, t, self.params.boundaries, prev)
+            }
         }
         .expect("embedded mask")
     }
@@ -453,7 +466,7 @@ impl Solver {
         let t = self.time;
         if let Some(body) = &self.body {
             if self.mask.is_none() {
-                self.mask = Some(self.build_mask(body, field.grid, t));
+                self.mask = Some(self.build_mask(body, field.grid, t, 0.0));
             }
         }
         self.apply_boundary_normals(field, t);
@@ -486,7 +499,7 @@ impl Solver {
             return 0;
         };
         let mut fresh_cells = 0;
-        let mut new_mask = self.build_mask(body, field.grid, t_new);
+        let mut new_mask = self.build_mask(body, field.grid, t_new, dt);
         if let Some(old_mask) = &self.mask {
             fresh_cells = refill_fresh_cells(old_mask, &new_mask, field);
             new_mask.set_step_apertures(old_mask);