fglgear.cpp

6 DOF Missle Simulation

/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

 Module:       FGLGear.cpp
 Author:       Jon S. Berndt
               Norman H. Princen
 Date started: 11/18/99
 Purpose:      Encapsulates the landing gear elements
 Called by:    FGAircraft

 ------------- Copyright (C) 1999  Jon S. Berndt ([e-mail]) -------------

 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

/%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
INCLUDES
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/

#include "FGLGear.h"

namespace JSBSim {

/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
DEFINITIONS
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/

/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
GLOBAL DATA
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/

static const char *IdSrc = "$Id$";
static const char *IdHdr = ID_LGEAR;

/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
CLASS IMPLEMENTATION
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/

FGLGear::FGLGear(Element* el, FGFDMExec* fdmex, int number) : Exec(fdmex),
                 GearNumber(number)
{
  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 {
    eContactType = ctUNKNOWN;
  }

  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(Exec->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) vXYZ = element->FindElementTripletConvertTo("IN");
  else {cerr << "No location given for contact " << name << endl; exit(-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;
  else if (sSteerType.empty()       ) {eSteerType = stFixed;
                                       sSteerType = "FIXED (defaulted)";}
  else {
    cerr << "Improper steering type specification in config file: "
         << sSteerType << " is undefined." << endl;
  }

  RFRV = 0.7;  // Rolling force relaxation velocity, default value
  SFRV = 0.7;  // Side force relaxation velocity, default value

  Element* relax_vel = el->FindElement("relaxation_velocity");
  if (relax_vel) {
    if (relax_vel->FindElement("rolling")) {
      RFRV = relax_vel->FindElementValueAsNumberConvertTo("rolling", "FT/SEC");
    }
    if (relax_vel->FindElement("side")) {
      SFRV = relax_vel->FindElementValueAsNumberConvertTo("side", "FT/SEC");
    }
  }

  State = Exec->GetState();
  LongForceLagFilterCoeff = 1/State->Getdt(); // default longitudinal force filter coefficient
  LatForceLagFilterCoeff  = 1/State->Getdt(); // default lateral force filter coefficient

  Element* force_lag_filter_elem = el->FindElement("force_lag_filter");
  if (force_lag_filter_elem) {
    if (force_lag_filter_elem->FindElement("rolling")) {
      LongForceLagFilterCoeff = force_lag_filter_elem->FindElementValueAsNumber("rolling");
    }
    if (force_lag_filter_elem->FindElement("side")) {
      LatForceLagFilterCoeff = force_lag_filter_elem->FindElementValueAsNumber("side");
    }
  }

  WheelSlipLagFilterCoeff = 1/State->Getdt();

  Element *wheel_slip_angle_lag_elem = el->FindElement("wheel_slip_filter");
  if (wheel_slip_angle_lag_elem) {
    WheelSlipLagFilterCoeff = wheel_slip_angle_lag_elem->GetDataAsNumber();
  }
  
  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 ??

  State       = Exec->GetState();
  Aircraft    = Exec->GetAircraft();
  Propagate   = Exec->GetPropagate();
  Auxiliary   = Exec->GetAuxiliary();
  FCS         = Exec->GetFCS();
  MassBalance = Exec->GetMassBalance();

  WOW = lastWOW = false;
  ReportEnable = true;
  FirstContact = false;
  StartedGroundRun = false;
  TakeoffReported = LandingReported = false;
  LandingDistanceTraveled = TakeoffDistanceTraveled = TakeoffDistanceTraveled50ft = 0.0;
  MaximumStrutForce = MaximumStrutTravel = 0.0;
  SideForce = RollingForce = 0.0;
  SinkRate = GroundSpeed = 0.0;

  vWhlBodyVec = MassBalance->StructuralToBody(vXYZ);

  vLocalGear = Propagate->GetTb2l() * vWhlBodyVec;

  compressLength  = 0.0;
  compressSpeed   = 0.0;
  brakePct        = 0.0;
  maxCompLen      = 0.0;

  WheelSlip = 0.0;
  TirePressureNorm = 1.0;

  SideWhlVel    = 0.0;
  RollingWhlVel = 0.0;

  SinWheel = 0.0;
  CosWheel = 0.0;

  prevSlipIn  = 0.0;
  prevSlipOut = 0.0;

  Debug(0);
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

FGLGear::FGLGear(const FGLGear& lgear)
{
  GearNumber = lgear.GearNumber;
  State    = lgear.State;
  Aircraft = lgear.Aircraft;
  Propagate = lgear.Propagate;
  Auxiliary = lgear.Auxiliary;
  Exec     = lgear.Exec;
  FCS      = lgear.FCS;
  MassBalance = lgear.MassBalance;

  vXYZ = lgear.vXYZ;
  vMoment = lgear.vMoment;
  vWhlBodyVec = lgear.vWhlBodyVec;
  vLocalGear = lgear.vLocalGear;

  WOW                = lgear.WOW;
  lastWOW            = lgear.lastWOW;
  ReportEnable       = lgear.ReportEnable;
  FirstContact       = lgear.FirstContact;
  StartedGroundRun   = lgear.StartedGroundRun;
  LandingDistanceTraveled   = lgear.LandingDistanceTraveled;
  TakeoffDistanceTraveled   = lgear.TakeoffDistanceTraveled;
  TakeoffDistanceTraveled50ft   = lgear.TakeoffDistanceTraveled50ft;
  MaximumStrutForce  = lgear.MaximumStrutForce;
  MaximumStrutTravel = lgear.MaximumStrutTravel;
  SideForce          = lgear.SideForce;
  RollingForce       = lgear.RollingForce;

  kSpring         = lgear.kSpring;
  bDamp           = lgear.bDamp;
  bDampRebound    = lgear.bDampRebound;
  compressLength  = lgear.compressLength;
  compressSpeed   = lgear.compressSpeed;
  staticFCoeff    = lgear.staticFCoeff;
  dynamicFCoeff   = lgear.dynamicFCoeff;
  rollingFCoeff   = lgear.rollingFCoeff;
  brakePct        = lgear.brakePct;
  maxCompLen      = lgear.maxCompLen;
  SinkRate        = lgear.SinkRate;
  GroundSpeed     = lgear.GroundSpeed;
  LandingReported = lgear.LandingReported;
  TakeoffReported = lgear.TakeoffReported;
  name            = lgear.name;
  sSteerType      = lgear.sSteerType;
  sRetractable    = lgear.sRetractable;
  sContactType    = lgear.sContactType;
  eContactType    = lgear.eContactType;
  sBrakeGroup     = lgear.sBrakeGroup;
  eSteerType      = lgear.eSteerType;
  eBrakeGrp       = lgear.eBrakeGrp;
  maxSteerAngle   = lgear.maxSteerAngle;
  isRetractable   = lgear.isRetractable;
  GearUp          = lgear.GearUp;
  GearDown        = lgear.GearDown;
  GearPos         = lgear.GearPos;
  useFCSGearPos   = lgear.useFCSGearPos;
  WheelSlip       = lgear.WheelSlip;
  TirePressureNorm = lgear.TirePressureNorm;
  Servicable      = lgear.Servicable;
  ForceY_Table    = lgear.ForceY_Table;
  CosWheel        = lgear.CosWheel;
  SinWheel        = lgear.SinWheel;
  prevOut         = lgear.prevOut;
  prevIn          = lgear.prevIn;
  prevSlipIn      = lgear.prevSlipIn;
  prevSlipOut     = lgear.prevSlipOut;
  RFRV            = lgear.RFRV;
  SFRV            = lgear.SFRV;
  LongForceLagFilterCoeff = lgear.LongForceLagFilterCoeff;
  LatForceLagFilterCoeff = lgear.LatForceLagFilterCoeff;
  WheelSlipLagFilterCoeff = lgear.WheelSlipLagFilterCoeff;
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

FGLGear::~FGLGear()
{
  Debug(1);
}

//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

FGColumnVector3& FGLGear::Force(void)
{
  double t = Exec->GetState()->Getsim_time();
  dT = State->Getdt()*Exec->GetGroundReactions()->GetRate();

  vForce.InitMatrix();
  vMoment.InitMatrix();

  if (isRetractable) ComputeRetractionState();

  if (!GearDown) return vForce; // return the null vForce column vector

  vWhlBodyVec = MassBalance->StructuralToBody(vXYZ); // Get wheel in body frame
  vLocalGear = Propagate->GetTb2l() * vWhlBodyVec; // Get local frame wheel location

  gearLoc = Propagate->GetLocation().LocalToLocation(vLocalGear);
  compressLength = -Exec->GetGroundCallback()->GetAGLevel(t, gearLoc, contact, normal, cvel);

  // The compression length is measured in the Z-axis, only, at this time.

  if (compressLength > 0.00) {

    WOW = true;

    // [The next equation should really use the vector to the contact patch of
    // the tire including the strut compression and not the original vWhlBodyVec.]

    vWhlVelVec      =  Propagate->GetTb2l() * (Propagate->GetPQR() * vWhlBodyVec);
    vWhlVelVec     +=  Propagate->GetVel() - cvel;
    compressSpeed   =  vWhlVelVec(eZ);

    InitializeReporting();
    ComputeBrakeForceCoefficient();
    ComputeSteeringAngle();
    ComputeSlipAngle();
    ComputeSideForceCoefficient();
    ComputeVerticalStrutForce();

    // Compute the forces in the wheel ground plane.

    double sign = RollingWhlVel>0?1.0:(RollingWhlVel<0?-1.0:0.0);
    RollingForce = ((1.0 - TirePressureNorm) * 30 + vLocalForce(eZ) * BrakeFCoeff) * sign;
    SideForce    = vLocalForce(eZ) * FCoeff;

    // Transform these forces back to the local reference frame.

    vLocalForce(eX) = RollingForce*CosWheel - SideForce*SinWheel;
    vLocalForce(eY) = SideForce*CosWheel    + RollingForce*SinWheel;

    // Transform the forces back to the body frame and compute the moment.

    vForce  = Propagate->GetTl2b() * vLocalForce;

// Start experimental section for gear jitter reduction
//
// Lag and attenuate the XY-plane forces dependent on velocity

    double ca, cb, denom;
    FGColumnVector3 Output;

// This code implements a lag filter, C/(s + C) where
// "C" is the filter coefficient. When "C" is chosen at the 
// frame rate (in Hz), the jittering is significantly reduced. This is because
// the jitter is present *at* the execution rate.
// If a coefficient is set to something equal to or less than zero, the filter
// is bypassed.

    if (LongForceLagFilterCoeff > 0) { 
      denom = 2.00 + dT*LongForceLagFilterCoeff;
      ca = dT*LongForceLagFilterCoeff / denom;
      cb = (2.00 - dT*LongForceLagFilterCoeff) / denom;
      Output(eX) = vForce(eX) * ca + prevIn(eX) * ca + prevOut(eX) * cb;
      vForce(eX) = Output(eX);
    }
    if (LatForceLagFilterCoeff > 0) { 
      denom = 2.00 + dT*LatForceLagFilterCoeff;
      ca = dT*LatForceLagFilterCoeff / denom;
      cb = (2.00 - dT*LatForceLagFilterCoeff) / denom;
      Output(eY) = vForce(eY) * ca + prevIn(eY) * ca + prevOut(eY) * cb;
      vForce(eY) = Output(eY);
    }

    prevIn = vForce;
    prevOut = Output;

    if ((fabs(RollingWhlVel) <= RFRV) && RFRV > 0) vForce(eX) *= fabs(RollingWhlVel)/RFRV;
    if ((fabs(SideWhlVel) <= SFRV) && SFRV > 0) vForce(eY) *= fabs(SideWhlVel)/SFRV;

// End section for attentuating gear jitter

    vMoment = vWhlBodyVec * vForce;

  } else { // Gear is NOT compressed