Manometer tubes for monitoring coastal water levels: New frequency response factors

Abstract

This paper presents findings of new laboratory experiments on the frequency response of semi-rigid manometer tubes for use in monitoring coastal hydrodynamic processes, extending and improving upon the previous work of Nielsen et al. (1993). An adjustable speed rotary electromotor was used to drive a known water level variation at one end of the tube and the pressure was measured at both ends of the tube, enabling a direct determination of the tube's frequency response. Testing was conducted over a range of frequencies (0.0067 Hzbf b2 Hz) and tube lengths (10 mbLb900 m). New frequency response factors were determined by fitting the semi-empirical gain function equation of Nielsen et al. (1993) to the observed gain data. New predictive formulas for the empirical coefficients are provided which yields substantial improvements over the existing constants deduced by Nielsen et al. (1993).