mirror of https://github.com/ArduPilot/ardupilot
314 lines
11 KiB
C++
314 lines
11 KiB
C++
/*
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/*
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Sailboat simulator class
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see explanation of lift and drag explained here: https://en.wikipedia.org/wiki/Forces_on_sails
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To-Do: add heel handling by calculating lateral force from wind vs gravity force from heel to arrive at roll rate or acceleration
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*/
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#include "SIM_Sailboat.h"
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#include <AP_Math/AP_Math.h>
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#include <string.h>
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#include <stdio.h>
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extern const AP_HAL::HAL& hal;
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namespace SITL {
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#define STEERING_SERVO_CH 0 // steering controlled by servo output 1
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#define MAINSAIL_SERVO_CH 3 // main sail controlled by servo output 4
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#define THROTTLE_SERVO_CH 2 // throttle controlled by servo output 3
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#define DIRECT_WING_SERVO_CH 4
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// very roughly sort of a stability factors for waves
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#define WAVE_ANGLE_GAIN 1
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#define WAVE_HEAVE_GAIN 1
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Sailboat::Sailboat(const char *frame_str) :
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Aircraft(frame_str),
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steering_angle_max(35),
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turning_circle(1.8),
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sail_area(1.0)
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{
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motor_connected = (strcmp(frame_str, "sailboat-motor") == 0);
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lock_step_scheduled = true;
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}
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// calculate the lift and drag as values from 0 to 1
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// given an apparent wind speed in m/s and angle-of-attack in degrees
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void Sailboat::calc_lift_and_drag(float wind_speed, float angle_of_attack_deg, float& lift, float& drag) const
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{
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const uint16_t index_width_deg = 10;
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const uint8_t index_max = ARRAY_SIZE(lift_curve) - 1;
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// Convert to expected range
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angle_of_attack_deg = wrap_180(angle_of_attack_deg);
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// assume a symmetrical airfoil
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const float aoa = fabs(angle_of_attack_deg);
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// check extremes
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if (aoa <= 0.0f) {
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lift = lift_curve[0];
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drag = drag_curve[0];
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} else if (aoa >= index_max * index_width_deg) {
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lift = lift_curve[index_max];
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drag = drag_curve[index_max];
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} else {
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uint8_t index = constrain_int16(aoa / index_width_deg, 0, index_max);
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float remainder = aoa - (index * index_width_deg);
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lift = linear_interpolate(lift_curve[index], lift_curve[index+1], remainder, 0.0f, index_width_deg);
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drag = linear_interpolate(drag_curve[index], drag_curve[index+1], remainder, 0.0f, index_width_deg);
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}
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// apply scaling by wind speed
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lift *= wind_speed * sail_area;
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drag *= wind_speed * sail_area;
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if (is_negative(angle_of_attack_deg)) {
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// invert lift for negative aoa
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lift *= -1;
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}
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}
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// return turning circle (diameter) in meters for steering angle proportion in the range -1 to +1
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float Sailboat::get_turn_circle(float steering) const
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{
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if (is_zero(steering)) {
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return 0;
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}
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return turning_circle * sinf(radians(steering_angle_max)) / sinf(radians(steering * steering_angle_max));
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}
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// return yaw rate in deg/sec given a steering input (in the range -1 to +1) and speed in m/s
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float Sailboat::get_yaw_rate(float steering, float speed) const
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{
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if (is_zero(steering) || is_zero(speed)) {
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return 0;
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}
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float d = get_turn_circle(steering);
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float c = M_PI * d;
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float t = c / speed;
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float rate = 360.0f / t;
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return rate;
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}
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// return lateral acceleration in m/s/s given a steering input (in the range -1 to +1) and speed in m/s
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float Sailboat::get_lat_accel(float steering, float speed) const
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{
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float yaw_rate = get_yaw_rate(steering, speed);
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float accel = radians(yaw_rate) * speed;
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return accel;
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}
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// simulate basic waves / swell
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void Sailboat::update_wave(float delta_time)
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{
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const float wave_heading = sitl->wave.direction;
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const float wave_speed = sitl->wave.speed;
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const float wave_lenght = sitl->wave.length;
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const float wave_amp = sitl->wave.amp;
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// apply rate propositional to error between boat angle and water angle
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// this gives a 'stability' effect
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float r, p, y;
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dcm.to_euler(&r, &p, &y);
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// if not armed don't do waves, to allow gyro init
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if (sitl->wave.enable == 0 || !hal.util->get_soft_armed() || is_zero(wave_amp) ) {
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wave_gyro = Vector3f(-r,-p,0.0f) * WAVE_ANGLE_GAIN;
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wave_heave = -velocity_ef.z * WAVE_HEAVE_GAIN;
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wave_phase = 0.0f;
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return;
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}
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// calculate the sailboat speed in the direction of the wave
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const float boat_speed = velocity_ef.x * sinf(radians(wave_heading)) + velocity_ef.y * cosf(radians(wave_heading));
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// update the wave phase
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const float aprarent_wave_distance = (wave_speed - boat_speed) * delta_time;
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const float apparent_wave_phase_change = (aprarent_wave_distance / wave_lenght) * M_2PI;
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wave_phase += apparent_wave_phase_change;
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wave_phase = wrap_2PI(wave_phase);
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// calculate the angles at this phase on the wave
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// use basic sine wave, dy/dx of sine = cosine
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// atan( cosine ) = wave angle
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const float wave_slope = (wave_amp * 0.5f) * (M_2PI / wave_lenght) * cosf(wave_phase);
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const float wave_angle = atanf(wave_slope);
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// convert wave angle to vehicle frame
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const float heading_dif = wave_heading - y;
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float angle_error_x = (sinf(heading_dif) * wave_angle) - r;
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float angle_error_y = (cosf(heading_dif) * wave_angle) - p;
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// apply gain
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wave_gyro.x = angle_error_x * WAVE_ANGLE_GAIN;
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wave_gyro.y = angle_error_y * WAVE_ANGLE_GAIN;
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wave_gyro.z = 0.0f;
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// calculate wave height (NED)
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if (sitl->wave.enable == 2) {
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wave_heave = (wave_slope - velocity_ef.z) * WAVE_HEAVE_GAIN;
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} else {
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wave_heave = 0.0f;
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}
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}
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/*
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update the sailboat simulation by one time step
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*/
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void Sailboat::update(const struct sitl_input &input)
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{
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// update wind
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update_wind(input);
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// in sailboats the steering controls the rudder, the throttle controls the main sail position
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float steering = 2*((input.servos[STEERING_SERVO_CH]-1000)/1000.0f - 0.5f);
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// calculate apparent wind in earth-frame (this is the direction the wind is coming from)
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// Note than the SITL wind direction is defined as the direction the wind is travelling to
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// This is accounted for in these calculations
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Vector3f wind_apparent_ef = velocity_ef - wind_ef;
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const float wind_apparent_dir_ef = degrees(atan2f(wind_apparent_ef.y, wind_apparent_ef.x));
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const float wind_apparent_speed = safe_sqrt(sq(wind_apparent_ef.x)+sq(wind_apparent_ef.y));
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float roll, pitch, yaw;
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dcm.to_euler(&roll, &pitch, &yaw);
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const float wind_apparent_dir_bf = wrap_180(wind_apparent_dir_ef - degrees(yaw));
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// set RPM and airspeed from wind speed, allows to test RPM and Airspeed wind vane back end in SITL
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rpm[0] = wind_apparent_speed;
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airspeed_pitot = wind_apparent_speed;
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float aoa_deg = 0.0f;
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if (sitl->sail_type.get() == 1) {
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// directly actuated wing
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float wing_angle_bf = constrain_float((input.servos[DIRECT_WING_SERVO_CH]-1500)/500.0f * 90.0f, -90.0f, 90.0f);
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aoa_deg = wind_apparent_dir_bf - wing_angle_bf;
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} else {
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// mainsail with sheet
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// calculate mainsail angle from servo output 4, 0 to 90 degrees
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float mainsail_angle_bf = constrain_float((input.servos[MAINSAIL_SERVO_CH]-1000)/1000.0f * 90.0f, 0.0f, 90.0f);
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// calculate angle-of-attack from wind to mainsail, cannot have negative angle of attack, sheet would go slack
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aoa_deg = MAX(fabsf(wind_apparent_dir_bf) - mainsail_angle_bf, 0);
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if (is_negative(wind_apparent_dir_bf)) {
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// take into account the current tack
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aoa_deg *= -1;
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}
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}
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// calculate Lift force (perpendicular to wind direction) and Drag force (parallel to wind direction)
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float lift_wf, drag_wf;
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calc_lift_and_drag(wind_apparent_speed, aoa_deg, lift_wf, drag_wf);
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// rotate lift and drag from wind frame into body frame
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const float sin_rot_rad = sinf(radians(wind_apparent_dir_bf));
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const float cos_rot_rad = cosf(radians(wind_apparent_dir_bf));
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const float force_fwd = (lift_wf * sin_rot_rad) - (drag_wf * cos_rot_rad);
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// how much time has passed?
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float delta_time = frame_time_us * 1.0e-6f;
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// speed in m/s in body frame
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Vector3f velocity_body = dcm.transposed() * velocity_ef_water;
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// speed along x axis, +ve is forward
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float speed = velocity_body.x;
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// yaw rate in degrees/s
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float yaw_rate = get_yaw_rate(steering, speed);
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gyro = Vector3f(0,0,radians(yaw_rate)) + wave_gyro;
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// update attitude
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dcm.rotate(gyro * delta_time);
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dcm.normalize();
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// hull drag
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float hull_drag = sq(speed) * 0.5f;
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if (!is_positive(speed)) {
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hull_drag *= -1.0f;
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}
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// throttle force (for motor sailing)
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// gives throttle force == hull drag at 10m/s
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float throttle_force = 0.0f;
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if (motor_connected) {
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const uint16_t throttle_out = constrain_int16(input.servos[THROTTLE_SERVO_CH], 1000, 2000);
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throttle_force = (throttle_out-1500) * 0.1f;
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}
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// accel in body frame due acceleration from sail and deceleration from hull friction
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accel_body = Vector3f((throttle_force + force_fwd) - hull_drag, 0, 0);
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accel_body /= mass;
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// add in accel due to direction change
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accel_body.y += radians(yaw_rate) * speed;
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// now in earth frame
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// remove roll and pitch effects from waves
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float r, p, y;
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dcm.to_euler(&r, &p, &y);
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Matrix3f temp_dcm;
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temp_dcm.from_euler(0.0f, 0.0f, y);
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Vector3f accel_earth = temp_dcm * accel_body;
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// we are on the ground, so our vertical accel is zero
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accel_earth.z = 0 + wave_heave;
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// work out acceleration as seen by the accelerometers. It sees the kinematic
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// acceleration (ie. real movement), plus gravity
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accel_body = dcm.transposed() * (accel_earth + Vector3f(0, 0, -GRAVITY_MSS));
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// tide calcs
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Vector3f tide_velocity_ef;
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if (hal.util->get_soft_armed() && !is_zero(sitl->tide.speed) ) {
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tide_velocity_ef.x = -cosf(radians(sitl->tide.direction)) * sitl->tide.speed;
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tide_velocity_ef.y = -sinf(radians(sitl->tide.direction)) * sitl->tide.speed;
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tide_velocity_ef.z = 0.0f;
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}
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// new velocity vector
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velocity_ef_water += accel_earth * delta_time;
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velocity_ef = velocity_ef_water + tide_velocity_ef;
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// new position vector
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position += (velocity_ef * delta_time).todouble();
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// update lat/lon/altitude
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update_position();
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time_advance();
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// update magnetic field
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update_mag_field_bf();
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// update wave calculations
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update_wave(delta_time);
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}
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} // namespace SITL
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