For a closed end we have odd harmonics.
fo, 3fo, 5fo, 7fo, 9fo, .......   fo = V/ wavelength. = V / 4L
Wavelength = 4L.
For a open end we have natural number harmonics.
fo, 2fo, 3fo, 4fo, 5fo, .......   fo = V/ wavelength. = V / 2L
Wavelength = 2L.