Added boundary states for correct resonances

Interfaces/Connection.cs

@@ -0,0 +1,15 @@
+namespace FluidSim.Interfaces
+{
+    /// <summary>Pure data link between two ports, with orifice parameters.</summary>
+    public class Connection
+    {
+        public Port PortA { get; }
+        public Port PortB { get; }
+
+        public double Area { get; set; } = 1e-5;          // effective orifice area (m²)
+        public double DischargeCoefficient { get; set; } = 0.62;
+        public double Gamma { get; set; } = 1.4;
+
+        public Connection(Port a, Port b) => (PortA, PortB) = (a, b);
+    }
+}