Hallo,

I am new to open modelica. I am trying to model an equation based model of a valve system and found this Software useful. Below is the code of the Throttle valve which is a Basic component in model System. Full model consists of many throttle valves in series and parallel connection. Even the Basic throttle valve model Fails when differential pressure(dp) less than zero or equal to Zero. Érror Analysis indicates that the Format of eqúation (Quadratic equation for flow rate) is causing the trouble. I tried to use if else Statement giving conditions of pressure it works fine. But the Simulation stucks in the middle when it id done on combined throttle models(after connecting 3/4 models in parallel/series). Also i remember about Problems with if else Statements in big models. Is there any way to describe conditions other than mentioned method.


model Throttle
  extends BasicValve;
  Real Hub(unit = "mm")"Stroke of valve cone relative to the position of cone in mm(Hub=0 when D1 closed)";
  Real Kv(unit = "m^3/h")"Flow coeffient of valve";
  Real Q2"Intermediate flow rate value used in inner calculations";
  parameter Real Turn(unit="Nos.") "No of turns on D1 spindle(From close to open state)";
  parameter Real Pitch(unit="mm") "Pitch of the screw thread of valve spindle";
equation
Hub=Turn*Pitch;
  Kv =  0.0319 * Hub;
  outlet.Q = -inlet.Q;
  outlet.P = inlet.P - (Q2 ^ 2 / Kv ^ 2);
  inlet.Q = Q2;

  annotation(
    Icon(graphics = {Line(origin = {0, 50}, points = {{0, 50}, {0, 50}, {0, -50}, {0, -50}}, thickness = 1), Rectangle(origin = {6, 99}, fillPattern = FillPattern.Solid, extent = {{-60, 3}, {48, -3}}), Text(origin = {-46, -25}, extent = {{110, -91}, {-14, 13}}, textString = "D2")}, coordinateSystem(initialScale = 0.1)));
end DrozzleD2;


partial model BasicValve
  Port inlet annotation(
    Placement(visible = true, transformation(origin = {-100, -2}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {-100, -2}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  Port outlet annotation(
    Placement(visible = true, transformation(origin = {100, -2}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {100, -2}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  annotation(
    Diagram,
    Icon(graphics = {Polygon(origin = {-50, 1}, points = {{-50, 99}, {-50, -99}, {50, -1}, {50, -1}, {-50, 99}}), Polygon(origin = {50, 0}, points = {{50, 100}, {-50, 0}, {50, -100}, {50, 100}})}));
end BasicValve;



Port used to connect model between an Input and Output fluid source/sink (Pressure (P), Flow rate (Q) variables). I didn't use modelica library models as the equation i use are different. Sorry if the questions are too naive but i really seek advice from experts

Thanks in advance
Joel