spring.hpp

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#ifndef SPRING_HPP
#define SPRING_HPP
#include "mecacell/utilities/utils.hpp"
namespace MecaCell {
//                SPRING STRUCTURE
// This is just a classic spring-damper
 
struct Spring {
    double k = 1.0;           // stiffness
    double c = 1.0;           // damp coef
    double restLength = 1.0;  // rest length
    double length = 1.0;      // current length
    double prevLength = 1.0;
    double minLengthRatio = 0.5;  // max compression
 
    Spring(){};
    Spring(const double &K, const double &C, const double &L)
        : k(K), c(C), restLength(L), length(L){};
 
    void updateLength(double l) {
        prevLength = length;
        length = l;
    }
 
    double computeForce(double dt) {
        double v = (length - prevLength) / dt;
        return 0.5 * (k * (length - restLength) + c * v);
    }
 
    template <typename A, typename B>
    void applyForce(A &a, B &b, const Vector3D &direction, double dt) {
        // direction = a -> b
        double f = computeForce(dt);
        a.receiveForce(direction * f);
        b.receiveForce(-direction * f);
    }
};
 
//                       JOINT STRUCTURE
// flexible joint. Can be used for flexure (torque + force) or torsion (torque only)
struct Joint {
    double k = 1.0;                // angular stiffness
    double c = 1.0;                // damp
    double maxTeta = M_PI / 10.0;  // maximum angle
    Rotation<Vec> r;               // rotation from node to joint
    Rotation<Vec> delta;           // current rotation
    Rotation<Vec> prevDelta;
    Vec direction;                   // current direction
    Vec target;                      // targeted direction
    bool maxTetaAutoCorrect = true;  // do we need to handle maxTeta?
    bool targetUpdateEnabled = true;
    Joint(){};
 
    Joint(const double &K, const double &C, const double &MTETA, bool handleMteta = true)
        : k(K), c(C), maxTeta(MTETA), maxTetaAutoCorrect(handleMteta) {}
 
    // current direction is computed using a reference Vector v rotated with rotation rot
    void updateDirection(const Vec &v, const Rotation<Vec> &rot) {
        direction = v.rotated(r.rotated(rot));
    }
    void updateDelta() { delta = Vec::getRotation(direction, target); }
};
}  // namespace MecaCell
 
#endif