scholarly journals Bed-Load Collision Sound Filtering through Separation of Pipe Hydrophone Frequency Bands

Water ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1875
Author(s):  
Jong-Ho Choi ◽  
Kye-Won Jun ◽  
Chang-Deok Jang
Keyword(s):  
Particle Size ◽  
Low Flow ◽  
Bed Load ◽  
Detection Rates ◽  
Frequency Bands ◽  
Acoustic Data ◽  
Fast Fourier Transform Analysis ◽  
Specific Frequency ◽  
Highly Correlated ◽  
Load Discharge

Bed-load discharge of a river can be monitored by indirectly measuring the acoustic pulses generated when the bed load collides with a steel pipe installed on the riverbed (i.e., pipe hydrophone measurement). However, existing methods used for filtering pulses from acoustic signals reflect a combination of bed-load collision frequency bands, thereby limiting characterization capabilities. This study proposes an improved filtering method that separates and efficiently examines frequency bands that are highly correlated with bed-load collision characteristics. Herein, an experimental hydraulic model and bed-load collision sound-measurement system were constructed, and bed-load collision experiments were repeatedly performed for collecting acoustic data using a pipe hydrophone. Fast Fourier Transform analysis was performed on data to select the specific frequency bands and pressures reflecting the bed-load particle size. Furthermore, a bandpass method to examine bed-load collision sounds is also presented herein. Results indicate that in comparison with existing filtering methods, the proposed bandpass method yields higher detection rates under bed-load conditions of low flow rate and small particle size, thereby demonstrating its enhanced effectiveness.

Effect of Geometric Shape of Periodic Cavities in Attenuating Baseframe Vibration

2020 ◽  
Author(s):  
S. N. Das ◽  
Kachita Kohli ◽  
Ayush Kumar ◽  
G. R. Sabareesh
Keyword(s):  
Stop Band ◽  
Rotating Machinery ◽  
Vibration Level ◽  
Structural Vibrations ◽  
Frequency Bands ◽  
Natural Modes ◽  
Vibration Attenuation ◽  
Specific Frequency ◽  
Different Shapes ◽  
Air Cavities

Abstract Vibration attenuation is an important factor while designing rotating machinery since frequency lying in the range corresponding to natural modes of structures can result in resonance and ultimately failure. Damping dissipates energy in the system, which reduces the vibration level. The mitigation of vibrations can be achieved by designing the base frame with periodic air holes. The periodicity in air holes result in vibration attenuation by providing a stop band. A finite element-based approach is developed to predict the modal and frequency response. The analysis is carried out with different shapes of periodic cavities in order to study the effectiveness of periodic stop bands in attenuating vibrations. The amount of mass removed due to the periodic cavities is kept constant. It is seen that better attenuation is obtained in case of periodic cavities compared to a uniform base frame. Among the different geometries tested, rectangular cavities showed better results than circular and square cavities. As a result, it is seen that waves propagate along periodic cells only within specific frequency bands called the “Pass bands”, while these waves are completely blocked within other frequency bands called the “Stopbands”. The air cavities filter structural vibrations in certain frequency bands resulting in effective attenuation.

scholarly journals Regional hydrology controls stream microbial biofilms: evidence from a glacial catchment

2004 ◽  
Vol 1 (1) ◽  
pp. 497-531 ◽  
Author(s):  
T. J. Battin ◽  
A. Wille ◽  
R. Psenner ◽  
A. Richter
Keyword(s):  
Landscape Heterogeneity ◽  
Low Flow ◽  
Detection Rates ◽  
Stream Communities ◽  
Stream Discharge ◽  
Carbon Production ◽  
Microbial Biofilms ◽  
Short Period ◽  
Alpine Stream

Abstract. Glaciers are highly responsive to global warming and important agents of landscape heterogeneity. While it is well established that glacial ablation and snowmelt regulate stream discharge, linkage among streams and streamwater hydrogeochemistry, the controls of these factors on stream microbial biofilms remain insufficiently understood. We investigated glacial (metakryal, hypokryal), groundwater-fed (krenal) and snow-fed (rhithral) streams – all of them representative for alpine stream networks – and present evidence that these hydrologic and hydrogeochemical factors differentially affect sediment microbial biofilms. Average microbial biomass and bacterial carbon production were low in the glacial streams, whereas bacterial cell size, biomass, and carbon production were higher in the tributaries, most notably in the krenal stream. Whole-cell in situ fluorescence hybridization revealed reduced detection rates of the Eubacteria and higher abundance of α-Proteobacteria in the glacial stream, a pattern that most probably reflects the trophic status of this ecosystem. Our data suggest low flow during the onset of snowmelt and autumn as a short period (hot moment) of favorable environmental conditions with pulsed inputs of allochthonous nitrate and dissolved organic carbon, and with disproportional high microbial growth. Krenal and rhithral streams with more constant and favorable environments serve as possible sources of microbes and organic matter to the main glacial channel during periods (e.g. snowmelt) of elevated hydrologic linkage among streams. Ice and snow dynamics have a crucial impact on microbial biofilms, and we thus need better understanding of the microbial ecology and enhanced consideration of critical hydrological episodes in future models predicting alpine stream communities.

Bed Load Discharge Coefficient

1981 ◽  
Vol 107 (11) ◽  
pp. 1445-1454
Author(s):  
Peter Engel ◽  
Y. Lam Lau
Keyword(s):  
Discharge Coefficient ◽  
Bed Load ◽  
Load Discharge

scholarly journals Numerical assessment of bed-load discharge formulations for transient flow in 1D and 2D situations

2013 ◽  
Vol 15 (4) ◽  
pp. 1234-1257 ◽  
Author(s):  
Carmelo Juez ◽  
Javier Murillo ◽  
Pilar García-Navarro
Keyword(s):  
Shallow Water ◽  
Shallow Water Equations ◽  
Numerical Scheme ◽  
Transient Flow ◽  
Morphological Evolution ◽  
Bed Load ◽  
Steady Flows ◽  
Numerical Experimentation ◽  
Load Discharge ◽  
Hydrodynamic Situation

Two-dimensional (2D) transient flow over an erodible bed can be modelled using shallow-water equations and the Exner equation to describe the morphological evolution of the bed. Considering the fact that well-proven capacity formulae are based on one-dimensional (1D) experimental steady flows, the assessment of these empirical relations under unsteady 1D and 2D situations is important. In order to ensure the reliability of the numerical experimentation, the formulation has to be general enough to allow the use of different empirical laws. Moreover, the numerical scheme must handle correctly the coupling between the 2D shallow-water equations and the Exner equation under any condition. In this work, a finite-volume numerical scheme that includes these two main features will be exploited here in 1D and 2D laboratory test cases. The relative performances of Meyer-Peter and Müller, Ashida and Michiue, Engelund and Fredsoe, Fernandez Luque and Van Beek, Parker, Smart, Nielsen, Wong and Camenen and Larson formulations are analysed in terms of the root mean square error. A new discretization of the Smart formula is provided, leading to promising predictions of the erosion/deposition rates. The results arising from this work are useful to justify the use of an empirical sediment bed-load discharge formula among the ones studied, regardless of the hydrodynamic situation.

Passive Periodic Engine Mount

2008 ◽  
Author(s):  
Ling Zheng ◽  
Woojin Jung ◽  
Zheng Gu ◽  
A. Baz
Keyword(s):  
Spectral Width ◽  
Shear Mode ◽  
Effective Width ◽  
Frequency Bands ◽  
Automotive Engine ◽  
New Class ◽  
Mechanical Filter ◽  
Transfer Matrix Approach ◽  
Specific Frequency ◽  
Engine Mount

The transmission of automotive engine vibrations to the chassis is isolated using a new class of mounts which rely in their operation on optimally designed and periodically distributed viscoelastic inserts. The proposed mount acts as mechanical filter for impeding the propagation of vibration within specific frequency bands called the ‘Stop Bands’. The spectral width of these bands is enhanced by making the viscoelastic inserts operate in a shear mode rather than compression mode. The theory governing the operation of this class of periodic mounts is presented using the theory of finite elements combined with the transfer matrix approach. The predictions of the performance of the mount are validated against the predictions of the commercial finite element code ANSYS and against experimental results obtained from prototypes of plain and periodic mounts. The obtained results demonstrate the feasibility of the shear mode periodic mount as an effectiveness means for blocking the transmission of vibration over a broad frequency band. Extending the effective width of the operating frequency bands of this class of mount through active control means is the ultimate goal of this study.

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