PythonModels/components/amesim_pneumatic_line.py

@@ -343,10 +343,10 @@ class AmesimPnl0001Pipe(_DarcyPipeResistanceMixin, DynamicComponent):
         connected_h_2: float,
     ) -> VolumeState:
         internal = self.properties()
-        # PNL0001 is a fixed-volume distributed line store. Its transported
-        # energy variable therefore follows specific internal energy, not the
-        # chamber-style stagnation enthalpy contract. For this ideal gas,
-        # h = gamma * u. Outflow always carries the local u.
+        # Default first-pass PNL0001 behavior uses the historical internal-energy
+        # approximation. AMESim-specific transport-enthalpy corrections are kept
+        # behind derivatives_from_transport_enthalpy_connections so they can be
+        # applied only where validated against baseline data.
         inlet_u_1 = (
             connected_h_1 / self.gas.gamma
             if port_1_m_flow > 0.0
@@ -367,6 +367,27 @@ class AmesimPnl0001Pipe(_DarcyPipeResistanceMixin, DynamicComponent):
             U=port_1_m_flow * inlet_u_1 + port_2_m_flow * inlet_u_2 + heat_flow,
         )
 
+    def derivatives_from_transport_enthalpy_connections(
+        self,
+        *,
+        port_1_m_flow: float,
+        connected_h_1: float,
+        port_2_m_flow: float,
+        connected_h_2: float,
+    ) -> VolumeState:
+        internal = self.properties()
+        inlet_h_1 = connected_h_1 if port_1_m_flow > 0.0 else internal.h
+        inlet_h_2 = connected_h_2 if port_2_m_flow > 0.0 else internal.h
+        heat_flow = (
+            self.heat_transfer_coefficient
+            * self.heat_transfer_area
+            * (self.external_temperature - internal.T)
+        )
+        return VolumeState(
+            m=port_1_m_flow + port_2_m_flow,
+            U=port_1_m_flow * inlet_h_1 + port_2_m_flow * inlet_h_2 + heat_flow,
+        )
+
 
 class AmesimPnl0003Pipe(_DarcyPipeResistanceMixin, DynamicComponent):
     """First-pass AMESim ``PNL0003`` (C-R-C) pipe.

PythonModels/scripts/run_test_mql_full_state_comparison.py

@@ -1056,14 +1056,14 @@ def _pnl0001_energy_flow_diagnostic(
             snapshot.p4_port3_remote_balance.port_2_enthalpy_flow_w
             / p4_node_port_2_mass_flow_kg_s
         )
-    p4_node_port_2_inlet_u = (
-        p4_node_port_2_connected_h / line.gas.gamma
+    p4_node_port_2_inlet_h = (
+        p4_node_port_2_connected_h
         if rhs_diagnostic.node_to_line_flow_kg_s > 0.0
-        else line_properties.u
+        else line_properties.h
     )
     p4_node_port_2_counterfactual_energy_derivative = (
         rhs_diagnostic.port_1_energy_flow_w
-        + rhs_diagnostic.node_to_line_flow_kg_s * p4_node_port_2_inlet_u
+        + rhs_diagnostic.node_to_line_flow_kg_s * p4_node_port_2_inlet_h
         + rhs_diagnostic.thermal_energy_flow_w
     )
     p4_node_port_2_counterfactual_dtemp = (

PythonModels/systems/test_mql.py

@@ -4190,21 +4190,24 @@ class TestMqlFullStateClosure:
         chamber_properties = getattr(snapshot.pneumatic, chamber_field)
         chamber_to_line_flow = getattr(snapshot.pneumatic, chamber_flow_field)
         node_to_line_flow = getattr(snapshot.pneumatic, node_flow_field)
-        line_derivative = line.derivatives_from_connections(
+        p4_balance = snapshot.pneumatic.p4_port3_remote_balance
+        p4_port_2_mass_flow_kg_s = p4_balance.port_2_mass_flow_g_s * 1.0e-3
+        node_connected_h = (
+            line_properties.h
+            if abs(p4_port_2_mass_flow_kg_s) <= 1.0e-12
+            else p4_balance.port_2_enthalpy_flow_w / p4_port_2_mass_flow_kg_s
+        )
+        line_derivative = line.derivatives_from_transport_enthalpy_connections(
             port_1_m_flow=chamber_to_line_flow,
             connected_h_1=chamber_properties.h,
             port_2_m_flow=node_to_line_flow,
-            connected_h_2=line_properties.h,
+            connected_h_2=node_connected_h,
         )
-        port_1_inlet_u = (
-            chamber_properties.h / line.gas.gamma
-            if chamber_to_line_flow > 0.0
-            else line_properties.u
+        port_1_inlet_h = (
+            chamber_properties.h if chamber_to_line_flow > 0.0 else line_properties.h
         )
-        port_2_inlet_u = (
-            line_properties.h / line.gas.gamma
-            if node_to_line_flow > 0.0
-            else line_properties.u
+        port_2_inlet_h = (
+            node_connected_h if node_to_line_flow > 0.0 else line_properties.h
         )
         thermal_energy_flow = (
             line.heat_transfer_coefficient
@@ -4221,8 +4224,8 @@ class TestMqlFullStateClosure:
             chamber_to_line_flow_kg_s=chamber_to_line_flow,
             node_to_line_flow_kg_s=node_to_line_flow,
             mass_derivative_kg_s=line_derivative.m,
-            port_1_energy_flow_w=chamber_to_line_flow * port_1_inlet_u,
-            port_2_energy_flow_w=node_to_line_flow * port_2_inlet_u,
+            port_1_energy_flow_w=chamber_to_line_flow * port_1_inlet_h,
+            port_2_energy_flow_w=node_to_line_flow * port_2_inlet_h,
             thermal_energy_flow_w=thermal_energy_flow,
             energy_derivative_w=line_derivative.U,
         )

PythonModels/systems/test_mql_closure.py

@@ -1913,6 +1913,17 @@ class TestMqlPn3P4NodeChamberSegmentClosure:
             port_3_mass_flow_g_s=port_3.port_mass_flow_kg_s * 1.0e3,
         )
 
+    @staticmethod
+    def _p4_node_port_2_connected_h(
+        *,
+        balance: TestMqlPneumaticNode4Balance,
+        fallback_h: float,
+    ) -> float:
+        mass_flow_kg_s = balance.port_2_mass_flow_g_s * 1.0e-3
+        if abs(mass_flow_kg_s) <= 1.0e-12:
+            return fallback_h
+        return balance.port_2_enthalpy_flow_w / mass_flow_kg_s
+
     def _p4_node_balance(
         self,
         *,
@@ -2073,12 +2084,20 @@ class TestMqlPn3P4NodeChamberSegmentClosure:
         chamber_properties: ThermodynamicProperties,
         chamber_to_line_flow: float,
         node_to_line_flow: float,
+        node_connected_h: float | None = None,
     ) -> tuple[VolumeState, VolumeState]:
-        line_derivative = line.derivatives_from_connections(
+        derivative_method = (
+            line.derivatives_from_connections
+            if node_connected_h is None
+            else line.derivatives_from_transport_enthalpy_connections
+        )
+        line_derivative = derivative_method(
             port_1_m_flow=chamber_to_line_flow,
             connected_h_1=chamber_properties.h,
             port_2_m_flow=node_to_line_flow,
-            connected_h_2=line_properties.h,
+            connected_h_2=(
+                line_properties.h if node_connected_h is None else node_connected_h
+            ),
         )
         chamber_derivative = chamber.derivatives_from_two_connections(
             port_a_m_flow=-chamber_to_line_flow,
@@ -2791,6 +2810,10 @@ class TestMqlPn3P4NodeChamberSegmentClosure:
             chamber_properties=snapshot.p4_port3_remote_primary_chamber,
             chamber_to_line_flow=snapshot.p4_port3_remote_chamber_to_line_flow,
             node_to_line_flow=snapshot.p4_port3_remote_node_to_primary_line_flow,
+            node_connected_h=self._p4_node_port_2_connected_h(
+                balance=snapshot.p4_port3_remote_balance,
+                fallback_h=snapshot.p4_port3_remote_primary_line.h,
+            ),
         )
         p4_port3_remote_port3_derivative = self._connection_line_derivative(
             line=self.components.p4_port3_remote_port3_line,

tests/test_amesim_pnl0001_pipe.py

@@ -115,6 +115,29 @@ class AmesimPnl0001PipeTests(unittest.TestCase):
             - 0.1 * internal.u,
         )
 
+    def test_transport_enthalpy_derivative_preserves_pn2vol_energy_basis(self) -> None:
+        internal = self.pipe.properties()
+        derivative = self.pipe.derivatives_from_transport_enthalpy_connections(
+            port_1_m_flow=0.2,
+            connected_h_1=internal.h + 1000.0,
+            port_2_m_flow=-0.1,
+            connected_h_2=internal.h - 1000.0,
+        )
+
+        self.assertAlmostEqual(derivative.m, 0.1)
+        self.assertAlmostEqual(
+            derivative.U,
+            0.2 * (internal.h + 1000.0) - 0.1 * internal.h,
+        )
+        temperature_derivative = (
+            derivative.U - internal.u * derivative.m
+        ) / (self.pipe.state.m * self.pipe.gas.cv)
+        expected_temperature_derivative = (
+            0.2 * (internal.h + 1000.0 - internal.u)
+            - 0.1 * (internal.h - internal.u)
+        ) / (self.pipe.state.m * self.pipe.gas.cv)
+        self.assertAlmostEqual(temperature_derivative, expected_temperature_derivative)
+
 
 if __name__ == "__main__":
     unittest.main()

tests/test_test_mql_pnl0001_segment.py

@@ -773,7 +773,8 @@ class TestMqlPn3P4NodeChamberSegmentTests(unittest.TestCase):
         )
         rhs = closure.rhs_at(0.04, state)
         line = closure.pneumatic_closure.components.p4_port3_remote_primary_line
-        expected_line_derivative = line.derivatives_from_connections(
+        expected_line_derivative = (
+            line.derivatives_from_transport_enthalpy_connections(
             port_1_m_flow=(
                 open_snapshot.p4_port3_remote_chamber_to_line_flow
             ),
@@ -781,7 +782,8 @@ class TestMqlPn3P4NodeChamberSegmentTests(unittest.TestCase):
             port_2_m_flow=(
                 open_snapshot.p4_port3_remote_node_to_primary_line_flow
             ),
-            connected_h_2=node_inlet_h,
+                connected_h_2=node_inlet_h,
+            )
         )
         self.assertAlmostEqual(rhs[45], expected_line_derivative.U)
         self.assertAlmostEqual(