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flightgear/src/FDM/JSBSim/models/FGLGear.cpp
Erik Hofman 05a2eff317 One step ahead of JSBSim CVS.
2011-04-11 10:06:57 +02:00

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/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Module: FGLGear.cpp
Author: Jon S. Berndt
Norman H. Princen
Bertrand Coconnier
Date started: 11/18/99
Purpose: Encapsulates the landing gear elements
Called by: FGAircraft
------------- Copyright (C) 1999 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
Foundation; either version 2 of the License, or (at your option) any later
version.
This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
details.
You should have received a copy of the GNU Lesser General Public License along with
this program; if not, write to the Free Software Foundation, Inc., 59 Temple
Place - Suite 330, Boston, MA 02111-1307, USA.
Further information about the GNU Lesser General Public License can also be found on
the world wide web at http://www.gnu.org.
FUNCTIONAL DESCRIPTION
--------------------------------------------------------------------------------
HISTORY
--------------------------------------------------------------------------------
11/18/99 JSB Created
01/30/01 NHP Extended gear model to properly simulate steering and braking
07/08/09 BC Modified gear model to support large angles between aircraft and ground
/%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
INCLUDES
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
#include "FGLGear.h"
#include "FGGroundReactions.h"
#include "FGFCS.h"
#include "FGAuxiliary.h"
#include "FGAtmosphere.h"
#include "FGMassBalance.h"
#include "math/FGTable.h"
#include <cstdlib>
#include <cstring>
using namespace std;
namespace JSBSim {
/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
DEFINITIONS
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
GLOBAL DATA
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
static const char *IdSrc = "$Id: FGLGear.cpp,v 1.80 2011/01/24 13:01:56 jberndt Exp $";
static const char *IdHdr = ID_LGEAR;
// Body To Structural (body frame is rotated 180 deg about Y and lengths are given in
// ft instead of inches)
const FGMatrix33 FGLGear::Tb2s(-1./inchtoft, 0., 0., 0., 1./inchtoft, 0., 0., 0., -1./inchtoft);
/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
CLASS IMPLEMENTATION
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
FGLGear::FGLGear(Element* el, FGFDMExec* fdmex, int number) :
FGForce(fdmex),
GearNumber(number),
SteerAngle(0.0),
Castered(false),
StaticFriction(false)
{
Element *force_table=0;
Element *dampCoeff=0;
Element *dampCoeffRebound=0;
string force_type="";
kSpring = bDamp = bDampRebound = dynamicFCoeff = staticFCoeff = rollingFCoeff = maxSteerAngle = 0;
sSteerType = sBrakeGroup = sSteerType = "";
isRetractable = 0;
eDampType = dtLinear;
eDampTypeRebound = dtLinear;
name = el->GetAttributeValue("name");
sContactType = el->GetAttributeValue("type");
if (sContactType == "BOGEY") {
eContactType = ctBOGEY;
} else if (sContactType == "STRUCTURE") {
eContactType = ctSTRUCTURE;
} else {
// Unknown contact point types will be treated as STRUCTURE.
eContactType = ctSTRUCTURE;
}
if (el->FindElement("spring_coeff"))
kSpring = el->FindElementValueAsNumberConvertTo("spring_coeff", "LBS/FT");
if (el->FindElement("damping_coeff")) {
dampCoeff = el->FindElement("damping_coeff");
if (dampCoeff->GetAttributeValue("type") == "SQUARE") {
eDampType = dtSquare;
bDamp = el->FindElementValueAsNumberConvertTo("damping_coeff", "LBS/FT2/SEC2");
} else {
bDamp = el->FindElementValueAsNumberConvertTo("damping_coeff", "LBS/FT/SEC");
}
}
if (el->FindElement("damping_coeff_rebound")) {
dampCoeffRebound = el->FindElement("damping_coeff_rebound");
if (dampCoeffRebound->GetAttributeValue("type") == "SQUARE") {
eDampTypeRebound = dtSquare;
bDampRebound = el->FindElementValueAsNumberConvertTo("damping_coeff_rebound", "LBS/FT2/SEC2");
} else {
bDampRebound = el->FindElementValueAsNumberConvertTo("damping_coeff_rebound", "LBS/FT/SEC");
}
} else {
bDampRebound = bDamp;
eDampTypeRebound = eDampType;
}
if (el->FindElement("dynamic_friction"))
dynamicFCoeff = el->FindElementValueAsNumber("dynamic_friction");
if (el->FindElement("static_friction"))
staticFCoeff = el->FindElementValueAsNumber("static_friction");
if (el->FindElement("rolling_friction"))
rollingFCoeff = el->FindElementValueAsNumber("rolling_friction");
if (el->FindElement("max_steer"))
maxSteerAngle = el->FindElementValueAsNumberConvertTo("max_steer", "DEG");
if (el->FindElement("retractable"))
isRetractable = ((unsigned int)el->FindElementValueAsNumber("retractable"))>0.0?true:false;
ForceY_Table = 0;
force_table = el->FindElement("table");
while (force_table) {
force_type = force_table->GetAttributeValue("type");
if (force_type == "CORNERING_COEFF") {
ForceY_Table = new FGTable(fdmex->GetPropertyManager(), force_table);
} else {
cerr << "Undefined force table for " << name << " contact point" << endl;
}
force_table = el->FindNextElement("table");
}
sBrakeGroup = el->FindElementValue("brake_group");
if (maxSteerAngle == 360) sSteerType = "CASTERED";
else if (maxSteerAngle == 0.0) sSteerType = "FIXED";
else sSteerType = "STEERABLE";
Element* element = el->FindElement("location");
if (element) vXYZn = element->FindElementTripletConvertTo("IN");
else {cerr << "No location given for contact " << name << endl; exit(-1);}
SetTransformType(FGForce::tCustom);
element = el->FindElement("orientation");
if (element && (eContactType == ctBOGEY)) {
vGearOrient = element->FindElementTripletConvertTo("RAD");
double cp,sp,cr,sr,cy,sy;
cp=cos(vGearOrient(ePitch)); sp=sin(vGearOrient(ePitch));
cr=cos(vGearOrient(eRoll)); sr=sin(vGearOrient(eRoll));
cy=cos(vGearOrient(eYaw)); sy=sin(vGearOrient(eYaw));
mTGear(1,1) = cp*cy;
mTGear(2,1) = cp*sy;
mTGear(3,1) = -sp;
mTGear(1,2) = sr*sp*cy - cr*sy;
mTGear(2,2) = sr*sp*sy + cr*cy;
mTGear(3,2) = sr*cp;
mTGear(1,3) = cr*sp*cy + sr*sy;
mTGear(2,3) = cr*sp*sy - sr*cy;
mTGear(3,3) = cr*cp;
}
else {
mTGear(1,1) = 1.;
mTGear(2,2) = 1.;
mTGear(3,3) = 1.;
}
if (sBrakeGroup == "LEFT" ) eBrakeGrp = bgLeft;
else if (sBrakeGroup == "RIGHT" ) eBrakeGrp = bgRight;
else if (sBrakeGroup == "CENTER") eBrakeGrp = bgCenter;
else if (sBrakeGroup == "NOSE" ) eBrakeGrp = bgNose;
else if (sBrakeGroup == "TAIL" ) eBrakeGrp = bgTail;
else if (sBrakeGroup == "NONE" ) eBrakeGrp = bgNone;
else if (sBrakeGroup.empty() ) {eBrakeGrp = bgNone;
sBrakeGroup = "NONE (defaulted)";}
else {
cerr << "Improper braking group specification in config file: "
<< sBrakeGroup << " is undefined." << endl;
}
if (sSteerType == "STEERABLE") eSteerType = stSteer;
else if (sSteerType == "FIXED" ) eSteerType = stFixed;
else if (sSteerType == "CASTERED" ) {eSteerType = stCaster; Castered = true;}
else if (sSteerType.empty() ) {eSteerType = stFixed;
sSteerType = "FIXED (defaulted)";}
else {
cerr << "Improper steering type specification in config file: "
<< sSteerType << " is undefined." << endl;
}
Auxiliary = fdmex->GetAuxiliary();
Propagate = fdmex->GetPropagate();
FCS = fdmex->GetFCS();
MassBalance = fdmex->GetMassBalance();
GroundReactions = fdmex->GetGroundReactions();
GearUp = false;
GearDown = true;
GearPos = 1.0;
useFCSGearPos = false;
Servicable = true;
// Add some AI here to determine if gear is located properly according to its
// brake group type ??
WOW = lastWOW = false;
ReportEnable = true;
FirstContact = false;
StartedGroundRun = false;
TakeoffReported = LandingReported = false;
LandingDistanceTraveled = TakeoffDistanceTraveled = TakeoffDistanceTraveled50ft = 0.0;
MaximumStrutForce = MaximumStrutTravel = 0.0;
SinkRate = GroundSpeed = 0.0;
vWhlBodyVec = MassBalance->StructuralToBody(vXYZn);
vLocalGear = Propagate->GetTb2l() * vWhlBodyVec;
vWhlVelVec.InitMatrix();
compressLength = 0.0;
compressSpeed = 0.0;
brakePct = 0.0;
maxCompLen = 0.0;
WheelSlip = 0.0;
TirePressureNorm = 1.0;
// Set Pacejka terms
Stiffness = 0.06;
Shape = 2.8;
Peak = staticFCoeff;
Curvature = 1.03;
// Initialize Lagrange multipliers
memset(LMultiplier, 0, sizeof(LMultiplier));
Debug(0);
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
FGLGear::~FGLGear()
{
delete ForceY_Table;
Debug(1);
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
FGColumnVector3& FGLGear::GetBodyForces(void)
{
double t = fdmex->GetSimTime();
dT = fdmex->GetDeltaT()*GroundReactions->GetRate();
vFn.InitMatrix();
if (isRetractable) ComputeRetractionState();
if (GearDown) {
FGColumnVector3 angularVel;
vWhlBodyVec = MassBalance->StructuralToBody(vXYZn); // Get wheel in body frame
vLocalGear = Propagate->GetTb2l() * vWhlBodyVec; // Get local frame wheel location
gearLoc = Propagate->GetLocation().LocalToLocation(vLocalGear);
// Compute the height of the theoretical location of the wheel (if strut is
// not compressed) with respect to the ground level
double height = fdmex->GetGroundCallback()->GetAGLevel(t, gearLoc, contact, normal, cvel, angularVel);
vGroundNormal = Propagate->GetTec2b() * normal;
// The height returned above is the AGL and is expressed in the Z direction
// of the ECEF coordinate frame. We now need to transform this height in
// actual compression of the strut (BOGEY) of in the normal direction to the
// ground (STRUCTURE)
double normalZ = (Propagate->GetTec2l()*normal)(eZ);
double LGearProj = -(mTGear.Transposed() * vGroundNormal)(eZ);
switch (eContactType) {
case ctBOGEY:
compressLength = LGearProj > 0.0 ? height * normalZ / LGearProj : 0.0;
break;
case ctSTRUCTURE:
compressLength = height * normalZ / DotProduct(normal, normal);
break;
}
if (compressLength > 0.00) {
WOW = true;
// The following equations use the vector to the tire contact patch
// including the strut compression.
FGColumnVector3 vWhlDisplVec;
switch(eContactType) {
case ctBOGEY:
vWhlDisplVec = mTGear * FGColumnVector3(0., 0., -compressLength);
break;
case ctSTRUCTURE:
vWhlDisplVec = compressLength * vGroundNormal;
break;
}
FGColumnVector3 vWhlContactVec = vWhlBodyVec + vWhlDisplVec;
vActingXYZn = vXYZn + Tb2s * vWhlDisplVec;
FGColumnVector3 vBodyWhlVel = Propagate->GetPQR() * vWhlContactVec;
vBodyWhlVel += Propagate->GetUVW() - Propagate->GetTec2b() * cvel;
vWhlVelVec = mTGear.Transposed() * vBodyWhlVel;
InitializeReporting();
ComputeSteeringAngle();
ComputeGroundCoordSys();
vLocalWhlVel = Transform().Transposed() * vBodyWhlVel;
compressSpeed = -vLocalWhlVel(eX);
if (eContactType == ctBOGEY)
compressSpeed /= LGearProj;
ComputeVerticalStrutForce();
// Compute the friction coefficients in the wheel ground plane.
if (eContactType == ctBOGEY) {
ComputeSlipAngle();
ComputeBrakeForceCoefficient();
ComputeSideForceCoefficient();
}
// Prepare the Jacobians and the Lagrange multipliers for later friction
// forces calculations.
ComputeJacobian(vWhlContactVec);
} else { // Gear is NOT compressed
WOW = false;
compressLength = 0.0;
compressSpeed = 0.0;
WheelSlip = 0.0;
StrutForce = 0.0;
// Let wheel spin down slowly
vWhlVelVec(eX) -= 13.0*dT;
if (vWhlVelVec(eX) < 0.0) vWhlVelVec(eX) = 0.0;
// Return to neutral position between 1.0 and 0.8 gear pos.
SteerAngle *= max(GetGearUnitPos()-0.8, 0.0)/0.2;
ResetReporting();
}
}
if (!fdmex->GetTrimStatus()) {
ReportTakeoffOrLanding();
// Require both WOW and LastWOW to be true before checking crash conditions
// to allow the WOW flag to be used in terminating a scripted run.
if (WOW && lastWOW) CrashDetect();
lastWOW = WOW;
}
return FGForce::GetBodyForces();
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Build a local "ground" coordinate system defined by
// eX : normal to the ground
// eY : projection of the rolling direction on the ground
// eZ : projection of the sliping direction on the ground
void FGLGear::ComputeGroundCoordSys(void)
{
// Euler angles are built up to create a local frame to describe the forces
// applied to the gear by the ground. Here pitch, yaw and roll do not have
// any physical meaning. It is just a convenient notation.
// First, "pitch" and "yaw" are determined in order to align eX with the
// ground normal.
if (vGroundNormal(eZ) < -1.0)
vOrient(ePitch) = 0.5*M_PI;
else if (1.0 < vGroundNormal(eZ))
vOrient(ePitch) = -0.5*M_PI;
else
vOrient(ePitch) = asin(-vGroundNormal(eZ));
if (fabs(vOrient(ePitch)) == 0.5*M_PI)
vOrient(eYaw) = 0.;
else
vOrient(eYaw) = atan2(vGroundNormal(eY), vGroundNormal(eX));
vOrient(eRoll) = 0.;
UpdateCustomTransformMatrix();
if (eContactType == ctBOGEY) {
// In the case of a bogey, the third angle "roll" is used to align the axis eY and eZ
// to the rolling and sliping direction respectively.
FGColumnVector3 updatedRollingAxis = Transform().Transposed() * mTGear
* FGColumnVector3(-sin(SteerAngle), cos(SteerAngle), 0.);
vOrient(eRoll) = atan2(updatedRollingAxis(eY), -updatedRollingAxis(eZ));
UpdateCustomTransformMatrix();
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
void FGLGear::ComputeRetractionState(void)
{
double gearPos = GetGearUnitPos();
if (gearPos < 0.01) {
GearUp = true;
WOW = false;
GearDown = false;
vWhlVelVec.InitMatrix();
} else if (gearPos > 0.99) {
GearDown = true;
GearUp = false;
} else {
GearUp = false;
GearDown = false;
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Calculate tire slip angle.
void FGLGear::ComputeSlipAngle(void)
{
// Check that the speed is non-null otherwise use the current angle
if (vLocalWhlVel.Magnitude(eY,eZ) > 1E-3)
WheelSlip = -atan2(vLocalWhlVel(eZ), fabs(vLocalWhlVel(eY)))*radtodeg;
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Compute the steering angle in any case.
// This will also make sure that animations will look right.
void FGLGear::ComputeSteeringAngle(void)
{
switch (eSteerType) {
case stSteer:
SteerAngle = degtorad * FCS->GetSteerPosDeg(GearNumber);
break;
case stFixed:
SteerAngle = 0.0;
break;
case stCaster:
if (!Castered)
SteerAngle = degtorad * FCS->GetSteerPosDeg(GearNumber);
else {
// Check that the speed is non-null otherwise use the current angle
if (vWhlVelVec.Magnitude(eX,eY) > 0.1)
SteerAngle = atan2(vWhlVelVec(eY), fabs(vWhlVelVec(eX)));
}
break;
default:
cerr << "Improper steering type membership detected for this gear." << endl;
break;
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Reset reporting functionality after takeoff
void FGLGear::ResetReporting(void)
{
if (Propagate->GetDistanceAGL() > 200.0) {
FirstContact = false;
StartedGroundRun = false;
LandingReported = false;
TakeoffReported = true;
LandingDistanceTraveled = 0.0;
MaximumStrutForce = MaximumStrutTravel = 0.0;
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
void FGLGear::InitializeReporting(void)
{
// If this is the first time the wheel has made contact, remember some values
// for later printout.
if (!FirstContact) {
FirstContact = true;
SinkRate = compressSpeed;
GroundSpeed = Propagate->GetVel().Magnitude();
TakeoffReported = false;
}
// If the takeoff run is starting, initialize.
if ((Propagate->GetVel().Magnitude() > 0.1) &&
(FCS->GetBrake(bgLeft) == 0) &&
(FCS->GetBrake(bgRight) == 0) &&
(FCS->GetThrottlePos(0) > 0.90) && !StartedGroundRun)
{
TakeoffDistanceTraveled = 0;
TakeoffDistanceTraveled50ft = 0;
StartedGroundRun = true;
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Takeoff and landing reporting functionality
void FGLGear::ReportTakeoffOrLanding(void)
{
if (FirstContact)
LandingDistanceTraveled += Auxiliary->GetVground()*dT;
if (StartedGroundRun) {
TakeoffDistanceTraveled50ft += Auxiliary->GetVground()*dT;
if (WOW) TakeoffDistanceTraveled += Auxiliary->GetVground()*dT;
}
if ( ReportEnable
&& Auxiliary->GetVground() <= 0.05
&& !LandingReported
&& GroundReactions->GetWOW())
{
if (debug_lvl > 0) Report(erLand);
}
if ( ReportEnable
&& !TakeoffReported
&& (Propagate->GetDistanceAGL() - vLocalGear(eZ)) > 50.0
&& !GroundReactions->GetWOW())
{
if (debug_lvl > 0) Report(erTakeoff);
}
if (lastWOW != WOW) PutMessage("GEAR_CONTACT: " + name, WOW);
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Crash detection logic (really out-of-bounds detection)
void FGLGear::CrashDetect(void)
{
if ( (compressLength > 500.0 ||
vFn.Magnitude() > 100000000.0 ||
GetMoments().Magnitude() > 5000000000.0 ||
SinkRate > 1.4666*30 ) && !fdmex->IntegrationSuspended())
{
PutMessage("Crash Detected: Simulation FREEZE.");
fdmex->SuspendIntegration();
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// The following needs work regarding friction coefficients and braking and
// steering The BrakeFCoeff formula assumes that an anti-skid system is used.
// It also assumes that we won't be turning and braking at the same time.
// Will fix this later.
// [JSB] The braking force coefficients include normal rolling coefficient +
// a percentage of the static friction coefficient based on braking applied.
void FGLGear::ComputeBrakeForceCoefficient(void)
{
switch (eBrakeGrp) {
case bgLeft:
BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgLeft)) +
staticFCoeff*FCS->GetBrake(bgLeft) );
break;
case bgRight:
BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgRight)) +
staticFCoeff*FCS->GetBrake(bgRight) );
break;
case bgCenter:
BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
staticFCoeff*FCS->GetBrake(bgCenter) );
break;
case bgNose:
BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
staticFCoeff*FCS->GetBrake(bgCenter) );
break;
case bgTail:
BrakeFCoeff = ( rollingFCoeff*(1.0 - FCS->GetBrake(bgCenter)) +
staticFCoeff*FCS->GetBrake(bgCenter) );
break;
case bgNone:
BrakeFCoeff = rollingFCoeff;
break;
default:
cerr << "Improper brake group membership detected for this gear." << endl;
break;
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Compute the sideforce coefficients using Pacejka's Magic Formula.
//
// y(x) = D sin {C arctan [Bx - E(Bx - arctan Bx)]}
//
// Where: B = Stiffness Factor (0.06, here)
// C = Shape Factor (2.8, here)
// D = Peak Factor (0.8, here)
// E = Curvature Factor (1.03, here)
void FGLGear::ComputeSideForceCoefficient(void)
{
if (ForceY_Table) {
FCoeff = ForceY_Table->GetValue(WheelSlip);
} else {
double StiffSlip = Stiffness*WheelSlip;
FCoeff = Peak * sin(Shape*atan(StiffSlip - Curvature*(StiffSlip - atan(StiffSlip))));
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Compute the vertical force on the wheel using square-law damping (per comment
// in paper AIAA-2000-4303 - see header prologue comments). We might consider
// allowing for both square and linear damping force calculation. Also need to
// possibly give a "rebound damping factor" that differs from the compression
// case.
void FGLGear::ComputeVerticalStrutForce(void)
{
double springForce = 0;
double dampForce = 0;
springForce = -compressLength * kSpring;
if (compressSpeed >= 0.0) {
if (eDampType == dtLinear) dampForce = -compressSpeed * bDamp;
else dampForce = -compressSpeed * compressSpeed * bDamp;
} else {
if (eDampTypeRebound == dtLinear)
dampForce = -compressSpeed * bDampRebound;
else
dampForce = compressSpeed * compressSpeed * bDampRebound;
}
StrutForce = min(springForce + dampForce, (double)0.0);
// The reaction force of the wheel is always normal to the ground
switch (eContactType) {
case ctBOGEY:
// Project back the strut force in the local coordinate frame of the ground
vFn(eX) = StrutForce / (mTGear.Transposed()*vGroundNormal)(eZ);
break;
case ctSTRUCTURE:
vFn(eX) = -StrutForce;
break;
}
// Remember these values for reporting
MaximumStrutForce = max(MaximumStrutForce, fabs(StrutForce));
MaximumStrutTravel = max(MaximumStrutTravel, fabs(compressLength));
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
double FGLGear::GetGearUnitPos(void)
{
// hack to provide backward compatibility to gear/gear-pos-norm property
if( useFCSGearPos || FCS->GetGearPos() != 1.0 ) {
useFCSGearPos = true;
return FCS->GetGearPos();
}
return GearPos;
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// Compute the jacobian entries for the friction forces resolution later
// in FGPropagate
void FGLGear::ComputeJacobian(const FGColumnVector3& vWhlContactVec)
{
// When the point of contact is moving, dynamic friction is used
// This type of friction is limited to ctSTRUCTURE elements because their
// friction coefficient is the same in every directions
if ((eContactType == ctSTRUCTURE) && (vLocalWhlVel.Magnitude(eY,eZ) > 1E-3)) {
FGColumnVector3 velocityDirection = vLocalWhlVel;
StaticFriction = false;
velocityDirection(eX) = 0.;
velocityDirection.Normalize();
LMultiplier[ftDynamic].ForceJacobian = Transform()*velocityDirection;
LMultiplier[ftDynamic].MomentJacobian = vWhlContactVec * LMultiplier[ftDynamic].ForceJacobian;
LMultiplier[ftDynamic].Max = 0.;
LMultiplier[ftDynamic].Min = -fabs(dynamicFCoeff * vFn(eX));
LMultiplier[ftDynamic].value = Constrain(LMultiplier[ftDynamic].Min, LMultiplier[ftDynamic].value, LMultiplier[ftDynamic].Max);
}
else {
// Static friction is used for ctSTRUCTURE when the contact point is not moving.
// It is always used for ctBOGEY elements because the friction coefficients
// of a tyre depend on the direction of the movement (roll & side directions).
// This cannot be handled properly by the so-called "dynamic friction".
StaticFriction = true;
LMultiplier[ftRoll].ForceJacobian = Transform()*FGColumnVector3(0.,1.,0.);
LMultiplier[ftSide].ForceJacobian = Transform()*FGColumnVector3(0.,0.,1.);
LMultiplier[ftRoll].MomentJacobian = vWhlContactVec * LMultiplier[ftRoll].ForceJacobian;
LMultiplier[ftSide].MomentJacobian = vWhlContactVec * LMultiplier[ftSide].ForceJacobian;
switch(eContactType) {
case ctBOGEY:
LMultiplier[ftRoll].Max = fabs(BrakeFCoeff * vFn(eX));
LMultiplier[ftSide].Max = fabs(FCoeff * vFn(eX));
break;
case ctSTRUCTURE:
LMultiplier[ftRoll].Max = fabs(staticFCoeff * vFn(eX));
LMultiplier[ftSide].Max = fabs(staticFCoeff * vFn(eX));
break;
}
LMultiplier[ftRoll].Min = -LMultiplier[ftRoll].Max;
LMultiplier[ftSide].Min = -LMultiplier[ftSide].Max;
LMultiplier[ftRoll].value = Constrain(LMultiplier[ftRoll].Min, LMultiplier[ftRoll].value, LMultiplier[ftRoll].Max);
LMultiplier[ftSide].value = Constrain(LMultiplier[ftSide].Min, LMultiplier[ftSide].value, LMultiplier[ftSide].Max);
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// This function is used by the MultiplierIterator class to enumerate the
// Lagrange multipliers of a landing gear. This allows to encapsulate the storage
// of the multipliers in FGLGear without exposing it. From an outside point of
// view, each FGLGear instance has a number of Lagrange multipliers which can be
// accessed through this routine without knowing the exact constraint which they
// model.
FGPropagate::LagrangeMultiplier* FGLGear::GetMultiplierEntry(int entry)
{
switch(entry) {
case 0:
if (StaticFriction)
return &LMultiplier[ftRoll];
else
return &LMultiplier[ftDynamic];
case 1:
if (StaticFriction)
return &LMultiplier[ftSide];
default:
return NULL;
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// This routine is called after the Lagrange multiplier has been computed. The
// friction forces of the landing gear are then updated accordingly.
FGColumnVector3& FGLGear::UpdateForces(void)
{
if (StaticFriction) {
vFn(eY) = LMultiplier[ftRoll].value;
vFn(eZ) = LMultiplier[ftSide].value;
}
else
vFn += LMultiplier[ftDynamic].value * (Transform ().Transposed() * LMultiplier[ftDynamic].ForceJacobian);
// Return the updated force in the body frame
return FGForce::GetBodyForces();
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
void FGLGear::bind(void)
{
string property_name;
string base_property_name;
base_property_name = CreateIndexedPropertyName("gear/unit", GearNumber);
if (eContactType == ctBOGEY) {
property_name = base_property_name + "/slip-angle-deg";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), &WheelSlip );
property_name = base_property_name + "/WOW";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), &WOW );
property_name = base_property_name + "/wheel-speed-fps";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), (FGLGear*)this,
&FGLGear::GetWheelRollVel);
property_name = base_property_name + "/z-position";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), (FGForce*)this,
&FGForce::GetLocationZ, &FGForce::SetLocationZ);
property_name = base_property_name + "/compression-ft";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), &compressLength );
property_name = base_property_name + "/side_friction_coeff";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), &FCoeff );
property_name = base_property_name + "/static_friction_coeff";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), &staticFCoeff );
property_name = base_property_name + "/rolling_friction_coeff";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), &rollingFCoeff );
property_name = base_property_name + "/dynamic_friction_coeff";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), &dynamicFCoeff );
if (eSteerType == stCaster) {
property_name = base_property_name + "/steering-angle-deg";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), this, &FGLGear::GetSteerAngleDeg );
property_name = base_property_name + "/castered";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), &Castered);
}
}
if( isRetractable ) {
property_name = base_property_name + "/pos-norm";
fdmex->GetPropertyManager()->Tie( property_name.c_str(), &GearPos );
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
void FGLGear::Report(ReportType repType)
{
if (fabs(TakeoffDistanceTraveled) < 0.001) return; // Don't print superfluous reports
switch(repType) {
case erLand:
cout << endl << "Touchdown report for " << name << " (WOW at time: "
<< fdmex->GetSimTime() << " seconds)" << endl;
cout << " Sink rate at contact: " << SinkRate << " fps, "
<< SinkRate*0.3048 << " mps" << endl;
cout << " Contact ground speed: " << GroundSpeed*.5925 << " knots, "
<< GroundSpeed*0.3048 << " mps" << endl;
cout << " Maximum contact force: " << MaximumStrutForce << " lbs, "
<< MaximumStrutForce*4.448 << " Newtons" << endl;
cout << " Maximum strut travel: " << MaximumStrutTravel*12.0 << " inches, "
<< MaximumStrutTravel*30.48 << " cm" << endl;
cout << " Distance traveled: " << LandingDistanceTraveled << " ft, "
<< LandingDistanceTraveled*0.3048 << " meters" << endl;
LandingReported = true;
break;
case erTakeoff:
cout << endl << "Takeoff report for " << name << " (Liftoff at time: "
<< fdmex->GetSimTime() << " seconds)" << endl;
cout << " Distance traveled: " << TakeoffDistanceTraveled
<< " ft, " << TakeoffDistanceTraveled*0.3048 << " meters" << endl;
cout << " Distance traveled (over 50'): " << TakeoffDistanceTraveled50ft
<< " ft, " << TakeoffDistanceTraveled50ft*0.3048 << " meters" << endl;
cout << " [Altitude (ASL): " << Propagate->GetAltitudeASL() << " ft. / "
<< Propagate->GetAltitudeASLmeters() << " m | Temperature: "
<< fdmex->GetAtmosphere()->GetTemperature() - 459.67 << " F / "
<< RankineToCelsius(fdmex->GetAtmosphere()->GetTemperature()) << " C]" << endl;
cout << " [Velocity (KCAS): " << Auxiliary->GetVcalibratedKTS() << "]" << endl;
TakeoffReported = true;
break;
case erNone:
break;
}
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// The bitmasked value choices are as follows:
// unset: In this case (the default) JSBSim would only print
// out the normally expected messages, essentially echoing
// the config files as they are read. If the environment
// variable is not set, debug_lvl is set to 1 internally
// 0: This requests JSBSim not to output any messages
// whatsoever.
// 1: This value explicity requests the normal JSBSim
// startup messages
// 2: This value asks for a message to be printed out when
// a class is instantiated
// 4: When this value is set, a message is displayed when a
// FGModel object executes its Run() method
// 8: When this value is set, various runtime state variables
// are printed out periodically
// 16: When set various parameters are sanity checked and
// a message is printed out when they go out of bounds
void FGLGear::Debug(int from)
{
if (debug_lvl <= 0) return;
if (debug_lvl & 1) { // Standard console startup message output
if (from == 0) { // Constructor - loading and initialization
cout << " " << sContactType << " " << name << endl;
cout << " Location: " << vXYZn << endl;
cout << " Spring Constant: " << kSpring << endl;
if (eDampType == dtLinear)
cout << " Damping Constant: " << bDamp << " (linear)" << endl;
else
cout << " Damping Constant: " << bDamp << " (square law)" << endl;
if (eDampTypeRebound == dtLinear)
cout << " Rebound Damping Constant: " << bDampRebound << " (linear)" << endl;
else
cout << " Rebound Damping Constant: " << bDampRebound << " (square law)" << endl;
cout << " Dynamic Friction: " << dynamicFCoeff << endl;
cout << " Static Friction: " << staticFCoeff << endl;
if (eContactType == ctBOGEY) {
cout << " Rolling Friction: " << rollingFCoeff << endl;
cout << " Steering Type: " << sSteerType << endl;
cout << " Grouping: " << sBrakeGroup << endl;
cout << " Max Steer Angle: " << maxSteerAngle << endl;
cout << " Retractable: " << isRetractable << endl;
}
}
}
if (debug_lvl & 2 ) { // Instantiation/Destruction notification
if (from == 0) cout << "Instantiated: FGLGear" << endl;
if (from == 1) cout << "Destroyed: FGLGear" << endl;
}
if (debug_lvl & 4 ) { // Run() method entry print for FGModel-derived objects
}
if (debug_lvl & 8 ) { // Runtime state variables
}
if (debug_lvl & 16) { // Sanity checking
}
if (debug_lvl & 64) {
if (from == 0) { // Constructor
cout << IdSrc << endl;
cout << IdHdr << endl;
}
}
}
} // namespace JSBSim
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