Decrease vertical space between text and equation

Question

I am a new user of LaTex, I have some struggle. I want to reduce the vertical space between text and equation. There is a big gap between the equation and the text "Linearization of motion equations". I don't know how to do it, I've searched on the internet but it doesn't work for me:

\setlength{\belowdisplayskip}{0pt}
\setlength{\belowdisplayshortskip}{0pt}
\setlength{\abovedisplayskip}{0pt}
\setlength{\abovedisplayshortskip}{0pt}

You will find down below my code:

\begin{align*}
m\dot{v} &= Y + mg\sin\varphi\cos\theta + m(pw - ru) \\
I_{XX}\dot{p} &= L + (I_{YY} - I_{ZZ})qr \\
I_{ZZ}\dot{r} &= N +(I_{XX}-I_{YY})pq \\
\end{align*}

Linearization of motion equations
\begin{align*}
u &= U_0 + u(t) & v &= 0 + v(t) \\
p &= 0 + p(t) & r &= 0 + r(t) \\
\theta &= \theta_0 + \theta (t) & \varphi &= 0 + \varphi (t) 
\end{align*}

Thank you for your help :)

Answer 1

Considering that first of all are very important also the comments, just I have used \intertext option.

\documentclass[a4paper,12pt]{article}
\usepackage{mathtools,amssymb}

\begin{document}

\begin{align*}
m\dot{v} &= Y + mg\sin\varphi\cos\theta + m(pw - ru) \\
I_{XX}\dot{p} &= L + (I_{YY} - I_{ZZ})qr \\
I_{ZZ}\dot{r} &= N +(I_{XX}-I_{YY})pq \\
\intertext{Linearization of motion equations}
u &= U_0 + u(t) & v &= 0 + v(t) \\
p &= 0 + p(t) & r &= 0 + r(t) \\
\theta &= \theta_0 + \theta (t) & \varphi &= 0 + \varphi (t) 
\end{align*}

\end{document}