[haze_1986]

Hi all, I am trying to understand the idea behind the leapfrog motion and orientation adjustments and I am not sure why during the adjustments. Q() from the previous time step Q0() is used with pi() from the current time step, is there any reason for this?

       // Leapfrog orientation adjustment
        Tuple2<tensor, vector> Qpi = rotate(Q0(), pi(), deltaT, deltaT0);
        Q() = Qpi.first();
        pi() = rConstraints_ & Qpi.second();

As we can see the leapfrog translation part uses the current velocity v()

        // Leapfrog move part
        centreOfRotation() = centreOfRotation0() + deltaT*v();

Details regarding rotate()

inline Foam::Tuple2<Foam::tensor, Foam::vector>
Foam::sixDoFRigidBodyMotion::rotate
(
    const tensor& Q0,
    const vector& pi0,
    const scalar deltaT
) const
{
    Tuple2<tensor, vector> Qpi(Q0, pi0);
    tensor& Q = Qpi.first();
    vector& pi = Qpi.second();

    tensor R = rotationTensorX(0.5*deltaT*pi.x()/momentOfInertia_.xx());
    pi = pi & R;
    Q = Q & R;

    R = rotationTensorY(0.5*deltaT*pi.y()/momentOfInertia_.yy());
    pi = pi & R;
    Q = Q & R;

    R = rotationTensorZ(deltaT*pi.z()/momentOfInertia_.zz());
    pi = pi & R;
    Q = Q & R;

    R = rotationTensorY(0.5*deltaT*pi.y()/momentOfInertia_.yy());
    pi = pi & R;
    Q = Q & R;

    R = rotationTensorX(0.5*deltaT*pi.x()/momentOfInertia_.xx());
    pi = pi & R;
    Q = Q & R;

    return Qpi;
}

Any help is appreciated, thanks!