I'm building a site that allows users to search through an index of articles (all about the same general subject) by topic, time published, people involved, and other attributes. An advanced search function will include the ability to specify these piece-by-piece, perform "OR," "AND," and "NOT" filters, and some other extra functions.
By default, I think these functions should be hidden from view, but whether they are or not I am wondering if seeing multiple search boxes on a page will be confusing. Currently I have a basic search box in the navigation bar at the top of the page (with the text "Search Articles" to prevent confusion about its purpose). I think there's an advantage to being able to create a simple new search from any part of the site, and maintaining a consistent navigation bar seems like a good idea.
Is it bad practice to have redundant functional UI elements on a page? If there are two search boxes on a page (one in the navigation bar and one in the body if they are on the main "Search" page), is there a good way to indicate that they share functionality? If redundancy is likely to cause confusion, is it better to remove the search box from the navigation bar altogether for consistency, or is it permissible to hide it when there is a search box available in the body of the page?