update_particle_step Subroutine

    pure subroutine update_particle_step(self, particles, dt)
        class(float_object_type), intent(inout) :: self  !! 浮体粒子集
        type(particle_type), intent(inout) :: particles  !! 区域
        real(rk), intent(in) :: dt                       !! 时间步长
        integer :: i

        ! 浮体表面光滑，加速度由位移决定
        self%vel = self%vel + self%acc*dt
        self%ang_vel = self%ang_vel + self%ang_acc*dt

        ! 更新粒子
        do i = self%istart, self%iend
            particles%vel(:, i) = self%vel(:) + cross_product_local2( &
                                  self%ang_vel, &
                                  particles%loc(:, i) - self%loc(:))
            particles%loc(:, i) = particles%loc(:, i) + particles%vel(:, i)*dt
        end do

        self%loc = self%loc + self%vel*dt

    end subroutine update_particle_step