Ehrlich Desa

Evaluation of Pressure Transducers under Turbid Natural Waters

Abstract Pressure measurements made in two turbid natural waters have led to the inference that the effective depth-mean in situ density values, ρeff, of these waters are less than (≈2.70%–6.5%) their bulk densities (i.e., densities of water–sediment mixture), and also less than (≈0.4%–4.5%) that of the density of the same water after removal of suspended sediment. The values of ρeff in a given site differed from one tidal cycle to another (≈1.9%). These values varied slightly (<0.8%) from midtide to slack water period of the same tidal cycle, with ρeff being lower at midtide. It was found that the use of bulk density to estimate tidal elevation yielded an underestimation of tidal range (up to 7%). The underestimation has been corrected (to within ±1.5%) with the use of ρeff parameter. For clear waters there was no measurable underestimation in tidal range. The observations indicate an apparent in situ density reduction for turbid natural waters. With the use of two pressure transducers at a known vertica...

Evaluation and Performance Enhancement of a Pressure Transducer under Flows, Waves, and a Combination of Flows and Waves*

Abstract The performance of a pressure transducer, with its inlet attached to differing hydromechanical front ends, has been evaluated in flow flume and wave flume experiments in which laminar and turbulent flows, and regular progressive gravity waves and combinations of flows and waves, were generated. For steady laminar flows, and for waves propagating on quiescent waters, the transducer’s performance improved when the inlet was at the center and flush with a large, thin, and smooth circular horizontal end plate. This enhancement is likely to have been achieved because of the isolation of the pressure inlet from the separated flows and vortices generated by the transducer housing. Flow disturbances, generated by nearby solid structures, deteriorated the performance of the pressure transducer. However, its performance could be significantly improved by protecting the pressure inlet by a sturdy, curved perforated shield. The dynamic pressure error in this case was 2 mb at 100 cm s−1, compared to 8 mb in t...

An Evaluation of Free- and Fixed-Vane Flowmeters with Curved- and Flat-Bladed Savonius Rotors

Abstract Speed and direction performances of flowmeters, designed by the authors for in-house use, employing an Aanderaa-type curved-bladed Savonius rotor and a free vane and an Aanderaa-type flat-bladed Savonius rotor and a fixed vane, are discussed. It has been observed that accuracy, linearity, and tilt response of a meter using the Aanderaa curved-bladed rotor is superior to those of a meter using the Aanderaa flat-bladed rotor. Analysis showed that the azimuth response of a flowmeter is affected by the presence of support rods surrounding its rotor. The change in azimuth response arises from flow pattern modifications in the vicinity of the rotor, imposed by the changes in the horizontal angle of the support rods of the rotor relative to the flow streamlines. While the use of two support rods may be suitable for a fixed-vane system, it is undesirable for a free-vane system where the meters orientation with respect to the flow direction is not defined. Flow direction calibration results indicated tha...