%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
#include "FGAtmosphere.h"
-#include "FGState.h"
-#include "FGFDMExec.h"
#include "FGAircraft.h"
#include "FGPropagate.h"
#include "FGInertial.h"
+#include "FGAuxiliary.h"
+#include "FGFDMExec.h"
#include "input_output/FGPropertyManager.h"
#include <iostream>
#include <cstdlib>
namespace JSBSim {
-static const char *IdSrc = "$Id$";
+static const char *IdSrc = "$Id: FGAtmosphere.cpp,v 1.38 2010/09/16 11:01:24 jberndt Exp $";
static const char *IdHdr = ID_ATMOSPHERE;
/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
vGustNED.InitMatrix();
vTurbulenceNED.InitMatrix();
+ // Milspec turbulence model
+ windspeed_at_20ft = 0.;
+ probability_of_exceedence_index = 0;
+ POE_Table = new FGTable(7,12);
+ // this is Figure 7 from p. 49 of MIL-F-8785C
+ // rows: probability of exceedance curve index, cols: altitude in ft
+ *POE_Table
+ << 500.0 << 1750.0 << 3750.0 << 7500.0 << 15000.0 << 25000.0 << 35000.0 << 45000.0 << 55000.0 << 65000.0 << 75000.0 << 80000.0
+ << 1 << 3.2 << 2.2 << 1.5 << 0.0 << 0.0 << 0.0 << 0.0 << 0.0 << 0.0 << 0.0 << 0.0 << 0.0
+ << 2 << 4.2 << 3.6 << 3.3 << 1.6 << 0.0 << 0.0 << 0.0 << 0.0 << 0.0 << 0.0 << 0.0 << 0.0
+ << 3 << 6.6 << 6.9 << 7.4 << 6.7 << 4.6 << 2.7 << 0.4 << 0.0 << 0.0 << 0.0 << 0.0 << 0.0
+ << 4 << 8.6 << 9.6 << 10.6 << 10.1 << 8.0 << 6.6 << 5.0 << 4.2 << 2.7 << 0.0 << 0.0 << 0.0
+ << 5 << 11.8 << 13.0 << 16.0 << 15.1 << 11.6 << 9.7 << 8.1 << 8.2 << 7.9 << 4.9 << 3.2 << 2.1
+ << 6 << 15.6 << 17.6 << 23.0 << 23.6 << 22.1 << 20.0 << 16.0 << 15.1 << 12.1 << 7.9 << 6.2 << 5.1
+ << 7 << 18.7 << 21.5 << 28.4 << 30.2 << 30.7 << 31.0 << 25.2 << 23.1 << 17.5 << 10.7 << 8.4 << 7.2;
+
bind();
Debug(0);
}
void FGAtmosphere::CalculateDerived(void)
{
T_dev = (*temperature) - GetTemperature(h);
- density_altitude = h + T_dev * 66.7;
+
+ if (T_dev == 0.0) density_altitude = h;
+ else density_altitude = 518.67/0.00356616 * (1.0 - pow(GetDensityRatio(),0.235));
if (turbType != ttNone) Turbulence();
return value * value;
}
+/// simply square a value
+static inline double sqr(double x) { return x*x; }
+
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
//
// psi is the angle that the wind is blowing *towards*
void FGAtmosphere::Turbulence(void)
{
- double DeltaT = rate*State->Getdt();
+ double DeltaT = rate*FDMExec->GetDeltaT();
switch (turbType) {
case ttStandard: {
spike = spike * 0.9;
break;
}
+ case ttMilspec:
+ case ttTustin: {
+ // an index of zero means turbulence is disabled
+ if (probability_of_exceedence_index == 0) {
+ vTurbulenceNED(1) = vTurbulenceNED(2) = vTurbulenceNED(3) = 0.0;
+ vTurbPQR(1) = vTurbPQR(2) = vTurbPQR(3) = 0.0;
+ return;
+ }
+
+ // Turbulence model according to MIL-F-8785C (Flying Qualities of Piloted Aircraft)
+ double
+ h = Propagate->GetDistanceAGL(),
+ V = Auxiliary->GetVt(), // true airspeed in ft/s
+ b_w = Aircraft->GetWingSpan(),
+ L_u, L_w, sig_u, sig_w;
+
+ // clip height functions at 10 ft
+ if (h <= 10.) h = 10;
+
+ // Scale lengths L and amplitudes sigma as function of height
+ if (h <= 1000) {
+ L_u = h/pow(0.177 + 0.000823*h, 1.2); // MIL-F-8785c, Fig. 10, p. 55
+ L_w = h;
+ sig_w = 0.1*windspeed_at_20ft;
+ sig_u = sig_w/pow(0.177 + 0.000823*h, 0.4); // MIL-F-8785c, Fig. 11, p. 56
+ } else if (h <= 2000) {
+ // linear interpolation between low altitude and high altitude models
+ L_u = L_w = 1000 + (h-1000.)/1000.*750.;
+ sig_u = sig_w = 0.1*windspeed_at_20ft
+ + (h-1000.)/1000.*(POE_Table->GetValue(probability_of_exceedence_index, h) - 0.1*windspeed_at_20ft);
+ } else {
+ L_u = L_w = 1750.; // MIL-F-8785c, Sec. 3.7.2.1, p. 48
+ sig_u = sig_w = POE_Table->GetValue(probability_of_exceedence_index, h);
+ }
+
+ // keep values from last timesteps
+ // TODO maybe use deque?
+ static double
+ xi_u_km1 = 0, nu_u_km1 = 0,
+ xi_v_km1 = 0, xi_v_km2 = 0, nu_v_km1 = 0, nu_v_km2 = 0,
+ xi_w_km1 = 0, xi_w_km2 = 0, nu_w_km1 = 0, nu_w_km2 = 0,
+ xi_p_km1 = 0, nu_p_km1 = 0,
+ xi_q_km1 = 0, xi_r_km1 = 0;
+
+
+ double
+ T_V = DeltaT, // for compatibility of nomenclature
+ sig_p = 1.9/sqrt(L_w*b_w)*sig_w, // Yeager1998, eq. (8)
+ sig_q = sqrt(M_PI/2/L_w/b_w), // eq. (14)
+ sig_r = sqrt(2*M_PI/3/L_w/b_w), // eq. (17)
+ L_p = sqrt(L_w*b_w)/2.6, // eq. (10)
+ tau_u = L_u/V, // eq. (6)
+ tau_w = L_w/V, // eq. (3)
+ tau_p = L_p/V, // eq. (9)
+ tau_q = 4*b_w/M_PI/V, // eq. (13)
+ tau_r =3*b_w/M_PI/V, // eq. (17)
+ nu_u = GaussianRandomNumber(),
+ nu_v = GaussianRandomNumber(),
+ nu_w = GaussianRandomNumber(),
+ nu_p = GaussianRandomNumber(),
+ xi_u, xi_v, xi_w, xi_p, xi_q, xi_r;
+
+ // values of turbulence NED velocities
+
+ if (turbType == ttTustin) {
+ // the following is the Tustin formulation of Yeager's report
+ double
+ omega_w = V/L_w, // hidden in nomenclature p. 3
+ omega_v = V/L_u, // this is defined nowhere
+ C_BL = 1/tau_u/tan(T_V/2/tau_u), // eq. (19)
+ C_BLp = 1/tau_p/tan(T_V/2/tau_p), // eq. (22)
+ C_BLq = 1/tau_q/tan(T_V/2/tau_q), // eq. (24)
+ C_BLr = 1/tau_r/tan(T_V/2/tau_r); // eq. (26)
+
+ xi_u = -(1 - C_BL*tau_u)/(1 + C_BL*tau_u)*xi_u_km1
+ + sig_u*sqrt(2*tau_u/T_V)/(1 + C_BL*tau_u)*(nu_u + nu_u_km1); // eq. (18)
+ xi_v = -2*(sqr(omega_v) - sqr(C_BL))/sqr(omega_v + C_BL)*xi_v_km1
+ - sqr(omega_v - C_BL)/sqr(omega_v + C_BL) * xi_v_km2
+ + sig_u*sqrt(3*omega_v/T_V)/sqr(omega_v + C_BL)*(
+ (C_BL + omega_v/sqrt(3.))*nu_v
+ + 2/sqrt(3.)*omega_v*nu_v_km1
+ + (omega_v/sqrt(3.) - C_BL)*nu_v_km2); // eq. (20) for v
+ xi_w = -2*(sqr(omega_w) - sqr(C_BL))/sqr(omega_w + C_BL)*xi_w_km1
+ - sqr(omega_w - C_BL)/sqr(omega_w + C_BL) * xi_w_km2
+ + sig_w*sqrt(3*omega_w/T_V)/sqr(omega_w + C_BL)*(
+ (C_BL + omega_w/sqrt(3.))*nu_w
+ + 2/sqrt(3.)*omega_w*nu_w_km1
+ + (omega_w/sqrt(3.) - C_BL)*nu_w_km2); // eq. (20) for w
+ xi_p = -(1 - C_BLp*tau_p)/(1 + C_BLp*tau_p)*xi_p_km1
+ + sig_p*sqrt(2*tau_p/T_V)/(1 + C_BLp*tau_p) * (nu_p + nu_p_km1); // eq. (21)
+ xi_q = -(1 - 4*b_w*C_BLq/M_PI/V)/(1 + 4*b_w*C_BLq/M_PI/V) * xi_q_km1
+ + C_BLq/V/(1 + 4*b_w*C_BLq/M_PI/V) * (xi_w - xi_w_km1); // eq. (23)
+ xi_r = - (1 - 3*b_w*C_BLr/M_PI/V)/(1 + 3*b_w*C_BLr/M_PI/V) * xi_r_km1
+ + C_BLr/V/(1 + 3*b_w*C_BLr/M_PI/V) * (xi_v - xi_v_km1); // eq. (25)
+
+ } else if (turbType == ttMilspec) {
+ // the following is the MIL-STD-1797A formulation
+ // as cited in Yeager's report
+ xi_u = (1 - T_V/tau_u) *xi_u_km1 + sig_u*sqrt(2*T_V/tau_u)*nu_u; // eq. (30)
+ xi_v = (1 - 2*T_V/tau_u)*xi_v_km1 + sig_u*sqrt(4*T_V/tau_u)*nu_v; // eq. (31)
+ xi_w = (1 - 2*T_V/tau_w)*xi_w_km1 + sig_w*sqrt(4*T_V/tau_w)*nu_w; // eq. (32)
+ xi_p = (1 - T_V/tau_p) *xi_p_km1 + sig_p*sqrt(2*T_V/tau_p)*nu_p; // eq. (33)
+ xi_q = (1 - T_V/tau_q) *xi_q_km1 + M_PI/4/b_w*(xi_w - xi_w_km1); // eq. (34)
+ xi_r = (1 - T_V/tau_r) *xi_r_km1 + M_PI/3/b_w*(xi_v - xi_v_km1); // eq. (35)
+ }
+
+ // rotate by wind azimuth and assign the velocities
+ double cospsi = cos(psiw), sinpsi = sin(psiw);
+ vTurbulenceNED(1) = cospsi*xi_u + sinpsi*xi_v;
+ vTurbulenceNED(2) = -sinpsi*xi_u + cospsi*xi_v;
+ vTurbulenceNED(3) = xi_w;
+
+ vTurbPQR(1) = cospsi*xi_p + sinpsi*xi_q;
+ vTurbPQR(2) = -sinpsi*xi_p + cospsi*xi_q;
+ vTurbPQR(3) = xi_r;
+
+ // vTurbPQR is in the body fixed frame, not NED
+ vTurbPQR = Propagate->GetTl2b()*vTurbPQR;
+
+ // hand on the values for the next timestep
+ xi_u_km1 = xi_u; nu_u_km1 = nu_u;
+ xi_v_km2 = xi_v_km1; xi_v_km1 = xi_v; nu_v_km2 = nu_v_km1; nu_v_km1 = nu_v;
+ xi_w_km2 = xi_w_km1; xi_w_km1 = xi_w; nu_w_km2 = nu_w_km1; nu_w_km1 = nu_w;
+ xi_p_km1 = xi_p; nu_p_km1 = nu_p;
+ xi_q_km1 = xi_q;
+ xi_r_km1 = xi_r;
+
+ }
default:
break;
}
PropertyManager->Tie("atmosphere/turb-gain", this, &FGAtmosphere::GetTurbGain, &FGAtmosphere::SetTurbGain);
PropertyManager->Tie("atmosphere/turb-rhythmicity", this, &FGAtmosphere::GetRhythmicity,
&FGAtmosphere::SetRhythmicity);
+
+ PropertyManager->Tie("atmosphere/turbulence/milspec/windspeed_at_20ft_AGL-fps",
+ this, &FGAtmosphere::GetWindspeed20ft,
+ &FGAtmosphere::SetWindspeed20ft);
+ PropertyManager->Tie("atmosphere/turbulence/milspec/severity",
+ this, &FGAtmosphere::GetProbabilityOfExceedence,
+ &FGAtmosphere::SetProbabilityOfExceedence);
+
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
projects / flightgear.git / blobdiff