-- init vars
DECLARE @sessID int,
		@dbName varchar(50),
		@userName varchar(50)

SET @dbName	= 'DA413'	-- your database name
SET @userName	= 'DA413'	-- sql user account to look for


-- use a cursor to store all session_ids
DECLARE session_cursor CURSOR
FOR
	SELECT	session_id
	FROM	sys.dm_exec_sessions
	WHERE	original_login_name = @userName

	-- open cursor and grab first row
	OPEN session_cursor
	FETCH NEXT FROM session_cursor INTO @sessID

	-- loop through session_ids
	WHILE @@FETCH_STATUS = 0
	BEGIN

		-- kill it
		-- using EXEC because the sproc kill does not like @variables
		EXEC('kill ' + @sessID)

		-- get the next session_id
		FETCH NEXT FROM session_cursor INTO @sessID
	END

-- cursor cleanup
CLOSE session_cursor
DEALLOCATE session_cursor