This is in my Application module onBootstrap. I downloaded the library with composer.

gistfile1.txt

return array(
  doctrine => array(
    ...
    'configuration' => array(
          'orm_default' => array(
              'string_functions' => array(
                  'acos'      => 'DoctrineExtensions\Query\Mysql\Acos',
                  'cos'       => 'DoctrineExtensions\Query\Mysql\Cos',
                  'radians'   => 'DoctrineExtensions\Query\Mysql\Radians',
                  'sin'       => 'DoctrineExtensions\Query\Mysql\Sin'
              )
          )
      )
  )
)