Date started: 09/12/2000
Purpose: This module models a rocket engine
- ------------- Copyright (C) 2000 Jon S. Berndt (jsb@hal-pc.org) --------------
+ ------------- Copyright (C) 2000 Jon S. Berndt (jon@jsbsim.org) --------------
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the Free Software
INCLUDES
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
+#include <iostream>
#include <sstream>
-
#include "FGRocket.h"
+#include "FGThruster.h"
+
+using namespace std;
namespace JSBSim {
-static const char *IdSrc = "$Id$";
+static const char *IdSrc = "$Id: FGRocket.cpp,v 1.27 2012/04/08 15:19:08 jberndt Exp $";
static const char *IdHdr = ID_ROCKET;
/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
CLASS IMPLEMENTATION
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
-FGRocket::FGRocket(FGFDMExec* exec, Element *el, int engine_number)
- : FGEngine(exec, el, engine_number)
+FGRocket::FGRocket(FGFDMExec* exec, Element *el, int engine_number, struct Inputs& input)
+ : FGEngine(exec, el, engine_number, input), isp_function(0L)
{
+ Type = etRocket;
Element* thrust_table_element = 0;
ThrustTable = 0L;
BurnTime = 0.0;
+ previousFuelNeedPerTank = 0.0;
+ previousOxiNeedPerTank = 0.0;
+ PropellantFlowRate = 0.0;
+ TotalPropellantExpended = 0.0;
+ FuelFlowRate = FuelExpended = 0.0;
+ OxidizerFlowRate = OxidizerExpended = 0.0;
+ SLOxiFlowMax = SLFuelFlowMax = PropFlowMax = 0.0;
+ MxR = 0.0;
+ BuildupTime = 0.0;
+ It = 0.0;
+ ThrustVariation = 0.0;
+ TotalIspVariation = 0.0;
+ Flameout = false;
// Defaults
- Variance = 0.0;
MinThrottle = 0.0;
MaxThrottle = 1.0;
- if (el->FindElement("shr"))
- SHR = el->FindElementValueAsNumber("shr");
- if (el->FindElement("max_pc"))
- maxPC = el->FindElementValueAsNumberConvertTo("max_pc", "PSF");
- if (el->FindElement("prop_eff"))
- propEff = el->FindElementValueAsNumber("prop_eff");
+ string base_property_name = CreateIndexedPropertyName("propulsion/engine", EngineNumber);
+
+ std::stringstream strEngineNumber;
+ strEngineNumber << EngineNumber;
+
+ Element* isp_el = el->FindElement("isp");
+ Element* isp_func_el=0;
+
+ bindmodel(); // Bind model properties first, since they might be needed in functions.
+
+ // Specific impulse may be specified as a constant value or as a function - perhaps as a function of mixture ratio.
+ if (isp_el) {
+ isp_func_el = isp_el->FindElement("function");
+ if (isp_func_el) {
+ isp_function = new FGFunction(exec->GetPropertyManager(),isp_func_el, strEngineNumber.str());
+ } else {
+ Isp = el->FindElementValueAsNumber("isp");
+ }
+ } else {
+ throw("Specific Impulse <isp> must be specified for a rocket engine");
+ }
+
+ if (el->FindElement("builduptime"))
+ BuildupTime = el->FindElementValueAsNumber("builduptime");
if (el->FindElement("maxthrottle"))
MaxThrottle = el->FindElementValueAsNumber("maxthrottle");
if (el->FindElement("minthrottle"))
MinThrottle = el->FindElementValueAsNumber("minthrottle");
- if (el->FindElement("slfuelflowmax"))
+
+ if (el->FindElement("slfuelflowmax")) {
SLFuelFlowMax = el->FindElementValueAsNumberConvertTo("slfuelflowmax", "LBS/SEC");
- if (el->FindElement("sloxiflowmax"))
+ if (el->FindElement("sloxiflowmax")) {
SLOxiFlowMax = el->FindElementValueAsNumberConvertTo("sloxiflowmax", "LBS/SEC");
- if (el->FindElement("variance"))
- Variance = el->FindElementValueAsNumber("variance");
+ }
+ PropFlowMax = SLOxiFlowMax + SLFuelFlowMax;
+ MxR = SLOxiFlowMax/SLFuelFlowMax;
+ } else if (el->FindElement("propflowmax")) {
+ PropFlowMax = el->FindElementValueAsNumberConvertTo("propflowmax", "LBS/SEC");
+ // Mixture ratio may be specified here, but it can also be specified as a function or via property
+ if (el->FindElement("mixtureratio")) {
+ MxR = el->FindElementValueAsNumber("mixtureratio");
+ }
+ }
+ if (isp_function) Isp = isp_function->GetValue(); // cause Isp function to be executed if present.
+ // If there is a thrust table element, this is a solid propellant engine.
thrust_table_element = el->FindElement("thrust_table");
if (thrust_table_element) {
ThrustTable = new FGTable(PropertyManager, thrust_table_element);
+ Element* variation_element = el->FindElement("variation");
+ if (variation_element) {
+ if (variation_element->FindElement("thrust")) {
+ ThrustVariation = variation_element->FindElementValueAsNumber("thrust");
+ }
+ if (variation_element->FindElement("total_isp")) {
+ TotalIspVariation = variation_element->FindElementValueAsNumber("total_isp");
+ }
+ }
}
- Debug(0);
- Type = etRocket;
- Flameout = false;
-
- PC = 0.0;
- kFactor = (2.0*SHR*SHR/(SHR-1.0))*pow(2.0/(SHR+1), (SHR+1)/(SHR-1));
+ Debug(0);
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
FGRocket::~FGRocket(void)
{
+ delete ThrustTable;
Debug(1);
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-double FGRocket::Calculate(void)
+void FGRocket::Calculate(void)
{
- double Cf=0;
+ if (FDMExec->IntegrationSuspended()) return;
+
+ RunPreFunctions();
+
+ PropellantFlowRate = (FuelExpended + OxidizerExpended)/in.TotalDeltaT;
+ TotalPropellantExpended += FuelExpended + OxidizerExpended;
+ // If Isp has been specified as a function, override the value of Isp to that, otherwise
+ // assume a constant value is given.
+ if (isp_function) Isp = isp_function->GetValue();
+
+ // If there is a thrust table, it is a function of propellant burned. The
+ // engine is started when the throttle is advanced to 1.0. After that, it
+ // burns without regard to throttle setting.
+
+ if (ThrustTable != 0L) { // Thrust table given -> Solid fuel used
+
+ if ((in.ThrottlePos[EngineNumber] == 1 || BurnTime > 0.0 ) && !Starved) {
+
+ VacThrust = ThrustTable->GetValue(TotalPropellantExpended)
+ * (ThrustVariation + 1)
+ * (TotalIspVariation + 1);
+ if (BurnTime <= BuildupTime && BuildupTime > 0.0) {
+ VacThrust *= sin((BurnTime/BuildupTime)*M_PI/2.0);
+ // VacThrust *= (1-cos((BurnTime/BuildupTime)*M_PI))/2.0; // 1 - cos approach
+ }
+ BurnTime += in.TotalDeltaT; // Increment burn time
+ } else {
+ VacThrust = 0.0;
+ }
+
+ } else { // liquid fueled rocket assumed
+
+ if (in.ThrottlePos[EngineNumber] < MinThrottle || Starved) { // Combustion not supported
- if (!Flameout && !Starved) ConsumeFuel();
+ PctPower = 0.0; // desired thrust
+ Flameout = true;
+ VacThrust = 0.0;
- Throttle = FCS->GetThrottlePos(EngineNumber);
+ } else { // Calculate thrust
- // If there is a thrust table, it is a function of elapsed burn time. The engine
- // is started when the throttle is advanced to 1.0. After that, it burns
- // without regard to throttle setting. The table returns a value between zero
- // and one, representing the percentage of maximum vacuum thrust being applied.
+ // PctPower = Throttle / MaxThrottle; // Min and MaxThrottle range from 0.0 to 1.0, normally.
+
+ PctPower = in.ThrottlePos[EngineNumber];
+ Flameout = false;
+ VacThrust = Isp * PropellantFlowRate;
- if (ThrustTable != 0L) {
- if (Throttle == 1 || BurnTime > 0.0) {
- BurnTime += State->Getdt();
}
- Throttle = ThrustTable->GetValue(BurnTime);
- }
- if (Throttle < MinThrottle || Starved) {
- PctPower = Thrust = 0.0; // desired thrust
- Flameout = true;
- PC = 0.0;
+ } // End thrust calculations
+
+ LoadThrusterInputs();
+ It += Thruster->Calculate(VacThrust) * in.TotalDeltaT;
+
+ RunPostFunctions();
+}
+
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+//
+// The FuelFlowRate can be affected by the TotalIspVariation value (settable
+// in a config file or via properties). The TotalIspVariation parameter affects
+// thrust, but the thrust determines fuel flow rate, so it must be adjusted
+// for Total Isp Variation.
+
+double FGRocket::CalcFuelNeed(void)
+{
+ if (ThrustTable != 0L) { // Thrust table given - infers solid fuel
+ FuelFlowRate = VacThrust/Isp; // This calculates wdot (weight flow rate in lbs/sec)
+ FuelFlowRate /= (1 + TotalIspVariation);
} else {
- PctPower = Throttle / MaxThrottle;
- //todo: remove Variance?
- PC = maxPC*PctPower * (1.0 + Variance * ((double)rand()/(double)RAND_MAX - 0.5));
- // The Cf (below) is CF from Eqn. 3-30, "Rocket Propulsion Elements", Fifth Edition,
- // George P. Sutton. Note that the thruster function GetPowerRequired() might
- // be better called GetResistance() or something; this function returns the
- // nozzle exit pressure.
- Cf = sqrt(kFactor*(1 - pow(Thruster->GetPowerRequired()/(PC), (SHR-1)/SHR)));
- Flameout = false;
+ SLFuelFlowMax = PropFlowMax / (1 + MxR);
+ FuelFlowRate = SLFuelFlowMax * PctPower;
}
- return Thruster->Calculate(Cf*maxPC*PctPower*propEff);
+ FuelExpended = FuelFlowRate * in.TotalDeltaT; // For this time step ...
+ return FuelExpended;
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-string FGRocket::GetEngineLabels(string delimeter)
+double FGRocket::CalcOxidizerNeed(void)
+{
+ SLOxiFlowMax = PropFlowMax * MxR / (1 + MxR);
+ OxidizerFlowRate = SLOxiFlowMax * PctPower;
+ OxidizerExpended = OxidizerFlowRate * in.TotalDeltaT;
+ return OxidizerExpended;
+}
+
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+string FGRocket::GetEngineLabels(const string& delimiter)
{
std::ostringstream buf;
- buf << Name << " Chamber Pressure (engine " << EngineNumber << " in psf)" << delimeter
- << Thruster->GetThrusterLabels(EngineNumber, delimeter);
+ buf << Name << " Total Impulse (engine " << EngineNumber << " in psf)" << delimiter
+ << Thruster->GetThrusterLabels(EngineNumber, delimiter);
return buf.str();
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-string FGRocket::GetEngineValues(string delimeter)
+string FGRocket::GetEngineValues(const string& delimiter)
{
std::ostringstream buf;
- buf << PC << delimeter << Thruster->GetThrusterValues(EngineNumber, delimeter);
+ buf << It << delimiter << Thruster->GetThrusterValues(EngineNumber, delimiter);
return buf.str();
}
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+// This function should tie properties to rocket engine specific properties
+// that are not bound in the base class (FGEngine) code.
+//
+void FGRocket::bindmodel()
+{
+ string property_name, base_property_name;
+ base_property_name = CreateIndexedPropertyName("propulsion/engine", EngineNumber);
+
+ property_name = base_property_name + "/total-impulse";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetTotalImpulse);
+ property_name = base_property_name + "/vacuum-thrust_lbs";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetVacThrust);
+
+ if (ThrustTable) { // Solid rocket motor
+ property_name = base_property_name + "/thrust-variation_pct";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetThrustVariation,
+ &FGRocket::SetThrustVariation);
+ property_name = base_property_name + "/total-isp-variation_pct";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetTotalIspVariation,
+ &FGRocket::SetTotalIspVariation);
+ } else { // Liquid rocket motor
+ property_name = base_property_name + "/oxi-flow-rate-pps";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetOxiFlowRate);
+ property_name = base_property_name + "/mixture-ratio";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetMixtureRatio,
+ &FGRocket::SetMixtureRatio);
+ property_name = base_property_name + "/isp";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetIsp,
+ &FGRocket::SetIsp);
+ }
+}
+
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// The bitmasked value choices are as follows:
// unset: In this case (the default) JSBSim would only print
if (debug_lvl & 1) { // Standard console startup message output
if (from == 0) { // Constructor
cout << " Engine Name: " << Name << endl;
- cout << " Specific Heat Ratio = " << SHR << endl;
- cout << " Maximum Chamber Pressure = " << maxPC << endl;
- cout << " Propulsive Efficiency = " << propEff << endl;
- cout << " MaxThrottle = " << MaxThrottle << endl;
- cout << " MinThrottle = " << MinThrottle << endl;
- cout << " FuelFlowMax = " << SLFuelFlowMax << endl;
- cout << " OxiFlowMax = " << SLOxiFlowMax << endl;
- cout << " Variance = " << Variance << endl;
+ cout << " Vacuum Isp = " << Isp << endl;
+ cout << " Maximum Throttle = " << MaxThrottle << endl;
+ cout << " Minimum Throttle = " << MinThrottle << endl;
+ cout << " Fuel Flow (max) = " << SLFuelFlowMax << endl;
+ cout << " Oxidizer Flow (max) = " << SLOxiFlowMax << endl;
+ if (SLFuelFlowMax > 0)
+ cout << " Mixture ratio = " << SLOxiFlowMax/SLFuelFlowMax << endl;
}
}
if (debug_lvl & 2 ) { // Instantiation/Destruction notification
projects / flightgear.git / blobdiff