title: Solving Coupled pde in comsol
body: <p>Does anyone know which module in comsol should I use to solve below equations?</p>
  
  <pre><code>$partial_t u1 = -a1 \div ((cos(s), sin(s)) u1) + a2 \div (u1 \grad (u2) )+ a3 \partial_s ((-sin(s), cos(s)) \cdot \nabla c u1) + a4 \nabla^2 u1+a5 \nabla^2 u1+a6 \partial_s^2 u1$
  
  $\partial_t u2= a5 \nabla^2 u2 - k u2 u1$
  </code></pre>