99 lines
2.4 KiB
C++
99 lines
2.4 KiB
C++
/*
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* Copyright (c) 2016-2016 Irlan Robson http://www.irlan.net
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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#ifndef PENDULUM_H
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#define PENDULUM_H
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class SinglePendulum : public Test
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{
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public:
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SinglePendulum()
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{
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m_g = -10.0f;
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m_r = 10.0f;
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m_m = 1.0f;
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m_I = m_m * m_r * m_r;
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// Initial state
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m_theta = -0.5f * B3_PI;
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m_omega = 0.0f;
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}
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void Step()
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{
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float32 h = g_testSettings->inv_hertz;
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// Solution (acceleration)
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float32 omega_dot = -m_g / m_r * sin(m_theta);
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// Integrate acceleration
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m_omega += h * omega_dot;
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// Integrate velocity
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m_theta += h * m_omega;
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// Convert from polar coordinates (r, theta) to Cartesian coordinates (x, y)
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b3Vec3 c;
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c.x = m_r * sin(m_theta);
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c.y = m_r * cos(m_theta);
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c.z = 0.0f;
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g_draw->DrawSolidSphere(c, 1.0f, b3Color_white);
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b3Vec3 pole;
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pole.SetZero();
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g_draw->DrawSegment(pole, c, b3Color_white);
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// Kinetic energy
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float32 T = 0.5f * m_I * m_omega * m_omega;
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// Potential energy
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float32 V = -m_m * m_g * m_r * cos(m_theta);
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// Lagrangian
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float32 L = T - V;
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//
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g_draw->DrawString(b3Color_white, "T = %f \nV = %f \nL = %f", T, V, L);
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}
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static Test* Create()
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{
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return new SinglePendulum();
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}
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// Gravity
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float32 m_g;
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// Mass, inertia
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float32 m_m, m_I;
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// Radial coordinate
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float32 m_r;
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// The allowable generalized coordinate in polar coordinate frame.
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// Only motions satisfying the constraints can be described
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// in this frame. Therefore, all solutions satisfy the constraints.
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// This is the so called reduced coordinates approach.
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float32 m_theta;
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// Velocity
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float32 m_omega;
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};
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#endif |