fixed Free connector

Author: Brad Carman

src/Hydraulic/IsothermalCompressible/components.jl

@@ -506,7 +506,7 @@ dm ────►               │  │ area
 
     ports = @named begin
         port = HydraulicPort(; p_int)
-        flange = MechanicalPort()
+        flange = MechanicalPort(; f_int = p_int*area)
         damper = ValveBase(; p_a_int = p_int, p_b_int = p_int, area_int = 1, Cd,
             Cd_reverse, minimum_area)
     end
@@ -528,8 +528,7 @@ dm ────►               │  │ area
     Δx = ParentScope(x_max) / N
     x₀ = ParentScope(x_int)
 
-    @named moving_volume = VolumeBase(; p_int, x_int = 0, area, dead_volume = 0, Χ1 = 0,
-        Χ2 = 1)
+    @named moving_volume = VolumeBase(; p_int, x_int = 0, area, dead_volume = 0, Χ1 = 0, Χ2 = 1)
 
     volumes = []
     for i in 1:N
@@ -582,6 +581,8 @@ dm ────►               │  │ area
         defaults = [flange.v => 0])
 end
 
+
+
 @component function SpoolValve(reversible = false; p_a_int, p_b_int, x_int, Cd, d, name)
     pars = @parameters begin
         p_a_int = p_a_int

src/Mechanical/Translational/components.jl

@@ -1,17 +1,17 @@
 """
     Free(; name)
 
-Use to close a system that has un-connected `MechanicalPort`'s.  
+Use to close a system that has un-connected `MechanicalPort`'s where the force should not be zero (i.e. you want to solve for the force to produce the given movement of the port)
 
 # Connectors:
 
   - `flange`: 1-dim. translational flange
 """
 @component function Free(; name)
     @named flange = MechanicalPort()
-    vars = []
+    vars = @variables f(t) = 0
     eqs = [
-        flange.f ~ 0,
+        flange.f ~ f
     ]
     return compose(ODESystem(eqs, t, vars, []; name, defaults = [flange.v => 0]),
         flange)

src/Mechanical/Translational/sources.jl

@@ -36,7 +36,7 @@ Linear 1D position input source
   - `flange`: 1-dim. translational flange
   - `s`: real input 
 """
-@component function Position(; s_0 = 0, name)
+@component function Position(solves_force=true; s_0 = 0, name)
     systems = @named begin
         flange = MechanicalPort()
         s = RealInput()
@@ -46,16 +46,17 @@ Linear 1D position input source
     vars = @variables x(t) = s_0
 
     eqs = [
-        flange.f ~ 0
         D(x) ~ flange.v
         s.u ~ x
         ]
 
+    !solves_force && push!(eqs, 0 ~ flange.f)
+
     ODESystem(eqs, t, vars, pars; name, systems, defaults = [flange.v => 0, s.u => s_0])
 end
 
 
-@component function Velocity(; name)
+@component function Velocity(solves_force=true; name)
     systems = @named begin
         flange = MechanicalPort()
         v = RealInput()
@@ -65,15 +66,16 @@ end
     vars = []
 
     eqs = [
-        flange.f ~ 0
         v.u ~ flange.v
         ]
 
+    !solves_force && push!(eqs, 0 ~ flange.f)
+
     ODESystem(eqs, t, vars, pars; name, systems, defaults = [flange.v => 0])
 end
 
 
-@component function Acceleration(; s_0 = 0, name)
+@component function Acceleration(solves_force=true; s_0 = 0, name)
     systems = @named begin
         flange = MechanicalPort()
         a = RealInput()
@@ -83,9 +85,10 @@ end
     vars = @variables v(t) = 0
 
     eqs = [
-        flange.f ~ 0
         v ~ flange.v
         D(v) ~ a.u]
 
+    !solves_force && push!(eqs, 0 ~ flange.f)
+
     ODESystem(eqs, t, vars, pars; name, systems, defaults = [flange.v => 0])
 end

src/Mechanical/Translational/utils.jl

@@ -1,10 +1,13 @@
-@connector function MechanicalPort(; name)
-    pars = []
+@connector function MechanicalPort(; name, f_int=0, v_int=0)
+    pars = @parameters begin
+        f_int = f_int
+        v_int = v_int
+    end
     vars = @variables begin
-        v(t)
+        v(t) = v_int
         f(t), [connect = Flow]
     end
-    ODESystem(Equation[], t, vars, pars, name = name, defaults = [f => 0])
+    ODESystem(Equation[], t, vars, pars; name, defaults=[f=>f_int])
 end
 Base.@doc """
     MechanicalPort(;name)