ardupilot/libraries/SITL/SIM_Submarine.h

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/*
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 3 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*
ROV/AUV/Submarine simulator class
*/
#pragma once
#include "SIM_Aircraft.h"
#include "SIM_Motor.h"
#include "SIM_Frame.h"
namespace SITL {
/*
a submarine simulator
*/
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class Thruster {
public:
Thruster(int8_t _servo, float roll_fac, float pitch_fac, float yaw_fac, float throttle_fac, float forward_fac, float lat_fac) :
servo(_servo)
{
linear = Vector3f(forward_fac, lat_fac, -throttle_fac);
rotational = Vector3f(roll_fac, pitch_fac, yaw_fac);
};
int8_t servo;
Vector3f linear;
Vector3f rotational;
};
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class Submarine : public Aircraft {
public:
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Submarine(const char *frame_str);
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/* update model by one time step */
void update(const struct sitl_input &input) override;
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/* static object creator */
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static Aircraft *create(const char *frame_str) {
return new Submarine(frame_str);
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}
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protected:
const float water_density = 1023.6; // (kg/m^3) At a temperature of 25 °C, salinity of 35 g/kg and 1 atm pressure
const struct {
float length = 0.457; // x direction (meters)
float width = 0.338; // y direction (meters)
float height = 0.254; // z direction (meters)
float weight = 10.5; // (kg)
float thrust = 51.48; // (N)
float thruster_mount_radius = 0.25; // distance in meters from thrusters to center of mass. Used to calculate torque.
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float equivalent_sphere_radius = 0.2;
// volume = 4.pi.r³/3
float volume = 4 * M_PI * pow(equivalent_sphere_radius, 3) / 3;
float density = 500;
float mass = volume * density; // 16.75 kg
// Moment of Inertia (I)(kg.m²) approximated with a sphere with a 25 cm radius (r) and same density as water
// I = 2.m.r²/5
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float moment_of_inertia = 2 * (mass * pow(equivalent_sphere_radius, 2) / 5);
// Frame drag coefficient
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const Vector3f linear_drag_coefficient = Vector3f(1.4, 1.8, 2.0);
// Angular drag coefficient CD for a cube is 1.05. This is subject to change based on experimentation.
const Vector3f angular_drag_coefficient = Vector3f(1.05, 1.05, 1.05);
// Calculate equivalent sphere area for drag force
// $ A = pi * r^2 / 4 $
// $ V = 4 * pi * r^3 / 3 $
// $ r ^2 = (V * 3 / 4) ^ (2/3) $
// A = area (m^3), r = sphere radius (m)
float equivalent_sphere_area = M_PI_4 * pow(volume * 3.0f / 4.0f, 2.0f / 3.0f);
} frame_property;
bool on_ground() const override;
// calculate sea floor depth based for terrain follow
float calculate_sea_floor_depth(const Vector3d &/*position*/);
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// calculate rotational and linear accelerations
void calculate_forces(const struct sitl_input &input, Vector3f &rot_accel, Vector3f &body_accel);
// calculate buoyancy
float calculate_buoyancy_acceleration();
// calculate drag from velocity and drag coefficient
void calculate_drag_force(const Vector3f &velocity, const Vector3f &drag_coefficient, Vector3f &force) const;
// calculate torque water resistance
void calculate_angular_drag_torque(const Vector3f &angular_velocity, const Vector3f &drag_coefficient, Vector3f &torque) const;
// calculate torque induced by buoyancy foams
void calculate_buoyancy_torque(Vector3f &torque);
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Frame *frame;
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Thruster* thrusters;
uint8_t n_thrusters;
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};
}