Dynamics of Closed Circuit Hydraulic Model Loops

Author(s):  
Bjo̸rnar Svingen ◽  
Morten Kjeldsen ◽  
Roger E. A. Arndt

This paper reviews the issue of making unsteady measurements involving cavitating flow in traditional test loops. Measurements of the dynamic response of a water tunnel during testing of a partially cavitating hydrofoil are presented and reviewed in the context of current theory. Data were collected from an array of pressure transducers that were distributed around the tunnel loop. In the post processing of these data, gain and phase response data were calculated. Theoretical analysis consisted of splitting the system into different elements, and included the compressibility of water in the physics used to describe each element. While solving the global system an eigenvalue solution was found, thus no node specific solution is obtained. This work is currently being extended with the aim of obtaining node specific values such that a more direct comparison between the experimental and theoretical work can be made.

2013 ◽  
Vol 12 (01) ◽  
pp. 1350005 ◽  
Author(s):  
AGNÈS DELAHAIES ◽  
FRANÇOIS CHAPEAU-BLONDEAU ◽  
DAVID ROUSSEAU ◽  
FLORENCE FRANCONI

We demonstrate a new instance of useful-noise effect or stochastic resonance, occurring in magnetic resonance imaging (MRI). Based on the physics of signal–noise coupling specific to MRI, we establish the possibility of regimes where nonlinear post-processing can benefit from an increase in the level of the noise present in the MRI apparatus. The validation is obtained by both theoretical analysis and experimental observations. We especially show that the beneficial tuning of the noise can be practically achieved by controlling the bandwidth of the sampling receiver of the MRI apparatus. These results constitute a nontrivial extension of stochastic resonance in the domain of images, arising here with a signal–noise coupling in MRI which is distinct from the purely additive or multiplicative couplings previously investigated in the framework of useful-noise effect.


2000 ◽  
Author(s):  
Meng-Nian Niu ◽  
Eun Sok Kim

Abstract We experimentally and theoretically confirm that residual stress within a diaphragm is critical in limiting the performance of diaphragm-based piezoelectric microphones even if the stress is low (around 50 MPa). We have fabricated and studied microphones with Al/parylene/ZnO/SiN2/poly-Si/SiN1 (from top to bottom) diaphragm. As the SiN1 supporting layer is removed layer by layer from the backside with CF4 plasma (in an RIE system), we measure both the sensitivity and center displacement of the microphone before and after each RIE etching of the SiN1 from the microphone diaphragm, and find the sensitivity increasing about 5–16 times with the best sensitivity reaching 11 μV/μbar from a mere 0.6 μV/μbar. The center displacement increases very moderately as the SiN1 layer thickness decreases from 0.8 to 0.2 μm. However, the center displacement starts to increase greatly as the SiN1 layer thickness goes below 0.2 μm, which compares with our theoretical analysis well. In the case of the SiN1 layer having compressive residual stress, the compressive stress can enhance the microphone sensitivity and center displacement to a certain extent.


2019 ◽  
Vol 42 (4) ◽  
pp. 743-748
Author(s):  
Andy J Knott ◽  
Ian A Robinson

This paper describes the characterisation of the dynamic response of a range of pressure transducer systems. The transducers were subjected to virtually instantaneous pressure step inputs in the National Physical Laboratory’s shock tube facilities. The magnitudes of these pressure steps were derived from ideal gas theory, with prior commissioning tests having been performed to demonstrate the theory’s validity in this application. The results demonstrate a significant variation in response obtained from various combinations of transducer, instrumentation settings, and mounting arrangement.


2011 ◽  
Vol 97-98 ◽  
pp. 235-240 ◽  
Author(s):  
Lei Liu ◽  
Yan Xuan ◽  
Lan Wang ◽  
Jia Lin Sun

Seriously inhomogeneous track rigidity of turnout will strengthen the dynamic response of wheel/rail system and shorten its service life. Combined with complicated structure characteristics of turnout, the simulation calculation model of track rigidity had been established. Main factors which influence the track rigidity were considered, such as the rail changing section, sharing baseplate, the foundation under rail. Distribution regularity of track rigidity in turnout had been obtained. The calculation result showed that track rigidity of turnout was seriously inhomogeneous. The maximum track rigidity was 162.2kN/mm in point rail of stock line, and the minimum track rigidity was 69.5kN/mm in stock rail of switch line.


2017 ◽  
Vol 88 (6) ◽  
pp. 667-695 ◽  
Author(s):  
Arif Kurbak

In this paper, the load–extension behavior of glass plain knitted fabrics is investigated both experimentally and theoretically. Experiments are carried out by preparing two sets of samples for two directions, namely for the course-wise and wale-wise directions. The load–extension properties are explored by attaching dead weights to the lower ends of the samples. Therefore, while obtaining the load–extension properties in the loading direction, the contraction properties of the samples in the lateral directions are also investigated. By observing the load–extension and load–contraction curves, three stages are distinguished. The first stage can be attributed to the fabric extension or contraction. The second stage can be attributed to the yarn extension or contraction as well as to the changes in the shapes of the samples. The third stage can be attributed to the extension or contraction of the fibers. After obtaining the dimensional properties of a single loop in the knitted fabric, curve fittings are carried out for the three stages. In the rest of the work, a theoretical analysis is carried out to explain the first stage of extension and contraction that was explained above. In the theoretical work, the load–extension or the load–contraction behaviors of the arms of the loops are calculated by using the inflexional elastica theory. The extension behaviors of the loop heads, on the other hand, are calculated by using the extension of the circular ring, which was given in Part I. As a result of the theoretical analysis, some simple equations between the loads applied and the extensions or contractions are obtained. These equations for the extension or contraction rates depend on the initial dimensional properties of the loop, the bending rigidity of the material, frictional restraints and the Poisson ratio. The equations also show that an extension or contraction in the wale-wise direction follows Hooke’s Law, whereas an extension or contraction in the course-wise direction depends on the square root of the applied load. Providing some simple equations about the relation between the load and extension in the loading direction as well as between the load and contraction in the lateral direction are suggested, determining the contractions in the lateral direction in addition to the extensions in the loading direction, which can be used in engineering software in simulating fabric load–extension behaviors under loadings. Finally, the initial and the extended states of the fabric are drawn to scale by using 3DS Max computer software.


In this paper a theoretical analysis is made of the electrokinetic phenomenon known as the ‘electroviscous effect’. A general formula is given for the effective viscosity of a suspension of solid, spherical, charged non-conducting particles in an electrolyte. The increase of the effective viscosity due to the surface charge and the ionic double layer surrounding the particles is determined by a modification of Einstein’s method for the calculation of the viscosity of solid suspensions. The effective viscosity may be expressed in the form η = η 0 {1+2.5 (v/V) (1+Ʃ ∞ r -1 a r Q r )}, where η 0 is the viscosity of the electrolyte, v the volume of suspension in volume V of solution and Qe is the charge on each particle. It is shown that a 1 = 0 and a 2 is determined explicitly. It is found that the electroviscous contribution to η, for a given charge Q , tends to increase as the thickness of the double layer increases. When the thickness of the double layer is small compared with the radius of the particle the effect vanishes. A comparison with previous theoretical work is made, and it is shown that much improved agreement with experiment is obtained.


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