aero.cpp

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/***************************************************************************

    file                 : aero.cpp
    created              : Sun Mar 19 00:04:50 CET 2000
    copyright            : (C) 2000-2026 by Eric Espie, Bernhard Wymann
    email                : berniw@bluewin.ch

 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/



#include "sim.h"

void SimAeroConfig(tCar *car)
{
    void *hdle = car->params;
    tdble Cx, FrntArea;

    Cx       = GfParmGetNum(hdle, SECT_AERODYNAMICS, PRM_CX, (char*)NULL, 0.4f);
    FrntArea = GfParmGetNum(hdle, SECT_AERODYNAMICS, PRM_FRNTAREA, (char*)NULL, 2.5f);
    car->aero.Clift[0] = GfParmGetNum(hdle, SECT_AERODYNAMICS, PRM_FCL, (char*)NULL, 0.0f);
    car->aero.Clift[1] = GfParmGetNum(hdle, SECT_AERODYNAMICS, PRM_RCL, (char*)NULL, 0.0f);
    car->aero.SCx2 = 0.645f * Cx * FrntArea;
    car->aero.Cd += car->aero.SCx2;
}


void  SimAeroUpdate(tCar *car, tSituation *s)
{
    tdble hm;
    int i;    
    tCar *otherCar;
    tdble x, y;
    tdble yaw, otherYaw, airSpeed, tmpas, spdang, tmpsdpang, dyaw;
    tdble dragK = 1.0;

    x = car->DynGCg.pos.x;
    y = car->DynGCg.pos.y;
    yaw = car->DynGCg.pos.az;
    airSpeed = car->DynGC.vel.x;
    spdang = (tdble) atan2(car->DynGCg.vel.y, car->DynGCg.vel.x);

    if (airSpeed > 10.0f) {
        for (i = 0; i < s->_ncars; i++) {
            if (i == car->carElt->index) {
                // skip myself
                continue;
            }
            
            otherCar = &(SimCarTable[i]);
            otherYaw = otherCar->DynGCg.pos.az;
            tmpsdpang = spdang - (tdble) atan2(y - otherCar->DynGCg.pos.y, x - otherCar->DynGCg.pos.x);
            NORM_PI_PI(tmpsdpang);
            dyaw = yaw - otherYaw;
            NORM_PI_PI(dyaw);
            
            if ((otherCar->DynGC.vel.x > 10.0f) && (fabs(dyaw) < 0.1396f)) {
                if (fabs(tmpsdpang) > 2.9671f) {        /* 10 degrees */
                    // behind another car
                    tmpas = 1.0f - (tdble) exp(- 2.0f * DIST(x, y, otherCar->DynGCg.pos.x, otherCar->DynGCg.pos.y) /
                                      (otherCar->aero.Cd * otherCar->DynGC.vel.x));
                    if (tmpas < dragK) {
                        dragK = tmpas;
                    }
                } else if (fabs(tmpsdpang) < 0.1396f) {     /* 8 degrees */
                    // before another car, lower drag by maximum 15% (this is just another guess)
                    tmpas = 1.0f - 0.15f * (tdble) exp(- 8.0f * DIST(x, y, otherCar->DynGCg.pos.x, otherCar->DynGCg.pos.y) / (car->aero.Cd * car->DynGC.vel.x));
                    if (tmpas < dragK) {
                        dragK = tmpas;
                    }
                }
            }
        }
    }

    car->airSpeed2 = airSpeed * airSpeed;
    tdble v2 = car->airSpeed2;
    
    // simulate ground effect drop off caused by non-frontal airflow (diffusor stops working etc.)
    tdble cosa = 1.0f;  
    if (car->speed > 1.0f) {
        cosa = car->DynGC.vel.x/car->speed;
    }
    
    if (cosa < 0.0f) {
        cosa = 0.0f;
    }
            
    car->aero.drag = - (tdble) SIGN(car->DynGC.vel.x) * car->aero.SCx2 * v2 * (1.0f + (tdble)car->dammage / 10000.0f) * dragK * dragK;

    hm = 1.5f * (car->wheel[0].rideHeight + car->wheel[1].rideHeight + car->wheel[2].rideHeight + car->wheel[3].rideHeight);
    hm = hm*hm;
    hm = hm*hm;
    hm = 2.0f * (tdble) exp(-3.0f*hm);
    car->aero.lift[0] = - car->aero.Clift[0] * v2 * hm * cosa;
    car->aero.lift[1] = - car->aero.Clift[1] * v2 * hm * cosa;
}

static const char *WingSect[2] = {SECT_FRNTWING, SECT_REARWING};

void SimWingConfig(tCar *car, int index)
{
    void *hdle = car->params;
    tWing *wing = &(car->wing[index]);
    tdble area;

    area              = GfParmGetNum(hdle, WingSect[index], PRM_WINGAREA, (char*)NULL, 0);
    wing->angle       = GfParmGetNum(hdle, WingSect[index], PRM_WINGANGLE, (char*)NULL, 0);
    wing->staticPos.x = GfParmGetNum(hdle, WingSect[index], PRM_XPOS, (char*)NULL, 0);
    wing->staticPos.z = GfParmGetNum(hdle, WingSect[index], PRM_ZPOS, (char*)NULL, 0);
    wing->staticPos.x -= car->statGC.x;
    
    wing->Kx = -1.23f * area;
    wing->Kz = 4.0f * wing->Kx;

    if (index == 1) {
        car->aero.Cd -= wing->Kx* (tdble) sin(wing->angle);
    }
}


void SimWingReConfig(tCar *car, int index)
{
    tCarPitSetupValue* v = &car->carElt->pitcmd.setup.wingangle[index];
    if (SimAdjustPitCarSetupParam(v)) {
        tWing *wing = &(car->wing[index]);
        tdble oldCd = wing->Kx* (tdble) sin(wing->angle);
        wing->angle = v->value;
        
        if (index == 1) {
            car->aero.Cd += oldCd;
            car->aero.Cd -= wing->Kx* (tdble) sin(wing->angle);
        }
    }
}


void SimWingUpdate(tCar *car, int index, tSituation* s)
{
    tWing  *wing = &(car->wing[index]);
    tdble vt2 = car->airSpeed2;
    // compute angle of attack
    tdble aoa = (tdble) atan2(car->DynGC.vel.z, car->DynGC.vel.x);
    aoa += wing->angle;
    // the sinus of the angle of attack
    tdble sinaoa = (tdble) sin(aoa);

    if (car->DynGC.vel.x > 0.0f) {
        wing->forces.x = wing->Kx * vt2 * (1.0f + (tdble)car->dammage / 10000.0f) * sinaoa;
        wing->forces.z = wing->Kz * vt2 * sinaoa;
    } else {
        wing->forces.x = wing->forces.z = 0.0f;
    }
}