Scaling the Vibrations of Water Pipes: Application to Industrial Case Studies

ABSTRACT A scaling approach for the vibrations of water pipes was proposed in the ASME PVP 2005 Conference. Using a single hole orifice in non-cavitating conditions as a reference noise source, the vibrations of a piping system were estimated on the basis of plane wave propagation for the acoustics, and on the basis of vibrating beams for the structure. The scaling of the velocity Power Spectral Density (PSD) of a pipe is then a function of the pressure drop of the device considered, of the inner and outer diameters of the pipe, of the flow velocity, of the support spacing and of the densities of steel and water. The present paper describes the application of the scaling approach to industrial case studies: velocity PSD were measured on a sample of piping systems with pressures varying from 3 to 100 bars, with flows varying from 30 to 1000 m 3 /h and with hydraulic powers varying from 10 to 200 kW. The sources of vibrations were orifices, globe valves and butterfly valves in turbulent or cavitating regimes, and centrifugal pumps operating at nominal or partial flow regimes. In most cases, the measured data match the scaling law based on the single hole orifice noise, as an order of magnitude. A closer look reveals that different sources of vibrations exhibit recognizable patterns; the partial flow regime of a centrifugal pump generates a velocity PSD different from the nominal regime, and the cavitation of a globe valve generates a velocity PSD very different from the one generated by the cavitation of a single hole orifice. Typical non-dimensional spectra are proposed for each type of noise generating device. INTRODUCTION Scientific works about water pipes vibrations in the low frequency range are rare (see the review in [1] an

Foveal thickness after phacoemulsification as measured by optical coherence tomography

Gerasimos Th Georgopoulos, Dimitrios Papaconstantinou, Maria Niskopoulou, Marilita Moschos, Ilias Georgalas, Chrysanthi KoutsandreaGlaucoma Department, Medical School, Athens University, Athens, GreeceBackground: Despite a significant body of research, no consistency on postoperative foveal thickness as measured by optical coherence tomography (OCT), can be recorded. The purpose of our study was to evaluate the effect of uncomplicated cataract surgery in the thickness of the retina in the foveal area during the early postoperative period.Methods: In a prospective study, 79 eyes were assessed by OCT, on day 1, and weeks 2 and 4 after uncomplicated phacoemulsification with intraocular lens implantation in the Athens University Clinic. The outcome measure was the thickness of the retina in the foveal area.Results: The thickness of the retina preoperatively is significantly smaller (150.4 ± 18.8) (p < 0.05) than the thickness of the retina on day 1 (171.8 ± 21) and week 2 (159.7 ± 19) and returned to the initial levels on week 4 (152 ± 17.1). The estimated correlation coefficients between preoperative and postoperative thickness of the retina were significant (p < 0.05). Conversely, no association was found between postoperative visual acuity and thickness of the retina, neither between the phacoemulsification energy and retinal thickness. Operation time, although inversely related with postoperative visual acuity, was not associated with the thickness of the retina.Conclusions: Following phacoemulsification, an increase in the foveal thickness was detected in the early postoperative period, quantified and followed up by OCT. The foveal thickness returned to the preoperative level, 1 month following surgery in our study. No association was shown between intraoperative parameters and increased postoperative retinal thickness.Keywords: optical coherence tomography, phacoemulsification, retinal thicknes