The Cavermod Device: Force Measurements

1999 ◽  
Vol 121 (2) ◽  
pp. 312-317 ◽  
Author(s):  
E. G. Filali ◽  
J. M. Michel ◽  
S. Hattori ◽  
S. Fujikawa
Keyword(s):  
Solid Wall ◽  
Axial Direction ◽  
Companion Paper ◽  
Point Of View ◽  
Pvdf Film ◽  
Force Measurements ◽  
Hard Materials ◽  
Force Signal ◽  
Ceramic Transducer ◽  
Film Transducer

The Cavermod device, as described in the companion paper (Filali et al., 1999), allows us to produce the axial collapse of a cavitating vortex at high velocities. From a global point of view, we can consider that it produces a high momentum in the axial direction. Large forces, concentrated on a small area and able to produce erosion pits on hard materials, result from the sudden momentum stopping against a solid wall. In this paper, the results of the forces measurements are given. Four different measurements devices are used to analyze the Cavermod performance in both cases of long and short vortex: dislocations in MgO (Magnesium Oxide) single crystal, two special piezoelectric ceramic transducers and a PVDF film transducer. Special attention is given to the PVDF film response which is found twice the response of other devices. In addition, an attempt is made to interpret the temporal force signal given by a ceramic transducer in terms of local erosive pressure.

scholarly journals Two-Dimensional Analytical Solution of the Laminar Forced Convection in a Circular Duct with Periodic Boundary Condition

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
M. R. Astaraki ◽  
N. Ghiasi Tabari
Keyword(s):  
Boundary Condition ◽  
Temperature Distribution ◽  
Analytical Solution ◽  
Periodic Function ◽  
Forced Convection ◽  
Solid Wall ◽  
Convection Heat Transfer ◽  
Axial Direction ◽  
Energy Balance Equation ◽  
Circular Duct

In the present study analytical solution for forced convection heat transfer in a circular duct with a special boundary condition has been presented, because the external wall temperature is a periodic function of axial direction. Local energy balance equation is written with reference to the fully developed regime. Also governing equations are two-dimensionally solved, and the effect of duct wall thickness has been considered. The temperature distribution of fluid and solid phases is assumed as a periodic function of axial direction and finally temperature distribution in the flow field, solid wall, and local Nusselt number, is obtained analytically.

The Cavermod Device: Hydrodynamic Aspects and Erosion Tests

1999 ◽  
Vol 121 (2) ◽  
pp. 305-311 ◽  
Author(s):  
E. G. Filali ◽  
J. M. Michel
Keyword(s):  
Rotation Rate ◽  
Cavitation Erosion ◽  
Companion Paper ◽  
Core Collapse ◽  
Pure Aluminium ◽  
Force Measurements ◽  
Test Device ◽  
Erosion Model ◽  
Erosion Test

The Cavermod (CAVitation ERosion MODel) is an erosion test device first described by Dominguez-Cortazar et al. (1992, 1997). Recently, it was modified in two steps: first by increasing its maximum rotation rate (from 4500 to 8000 rpm) and second by shortening its vapor core (from 156 to 66 mm). This paper plans to present the main results which are obtained in both configurations (long and short vortex) and for “slow” or “rapid” regime of rotation. They mainly concern 1. the hydrodynamic aspects of the vapor core collapse, as deduced from observation of rapid films (evolution of the vortex length, collapse, velocity), 2. the erosion patterns produced on metallic targets such as pure aluminium and copper. A second companion paper will present the results of force measurements in both configuration and an attempt to estimate the local erosive pressures.

Analysis on Microfluids Squeeze Film Damping of Perforated Disks With a Centre Hole

2005 ◽  
Author(s):  
Weidong Wang ◽  
Jianyuan Jia
Keyword(s):  
Solid Wall ◽  
Slip Flow ◽  
Surface Characteristics ◽  
Axial Direction ◽  
Accommodation Coefficient ◽  
Squeeze Film ◽  
Computation Method ◽  
Damping Force ◽  
Analysis And Design ◽  
Fem Method

Based on the equations of gap flow and squeezed flow, the solution for viscosity amendment with slip-flow boundary condition is presented for microfluids damping force on perforated disks with one centre hole, moving along its axial direction in microfluids. The correlation between the kinetic damping of the perforated disk and the parameters, such as the gap height, the radius of the center hole and the thickness of disk, is investigated and obtained. Also an analytical expression of the damping composed of slide film damping and squeezed film damping is given for this kind of perforated disks. Having compared with the numerical solution from FEM method, the analytical solutions match well with those from FEM method. It shows that the microfluids damping on micro-disk has relationship with the surface characteristics of solid wall. Through amending the momentum accommodation coefficient, the accurate effective viscosity can be obtained. Thereby the microfluids damping force on the moving object can be calculated correctly. A simple computation method is presented for analysis and design on microfluids damping of a perforated disk with one centre hole.

A Root Cause Study on AOA-PWR and CDA-VVER: A Point of View of “Long-Cell Action” Corrosion Mechanism

2006 ◽  
Author(s):  
Genn Saji
Keyword(s):  
Electrical Potential ◽  
Companion Paper ◽  
Ionic Concentration ◽  
Point Of View ◽  
Corrosion Mechanism ◽  
Nickel Iron ◽  
Erosion Rates ◽  
Root Cause ◽  
Excess Electrons ◽  
Iron Ferrite

The author has investigated the characteristics of boron co-deposition with crud experienced in AOA and iron ferrite deposition in CDA. Corrosion product deposits found in cores with appreciable AOA have been reported in mostly nickel-based (as NiO or elemental nickel) as opposed to nickel ferrite deposits common to non-boiling cores. Significant quantities of meta-ZrO2 and nickel iron oxyborates (bonaccordite), notably Ni2FeBO5 have also been found in deposits on cores with AOA. On the basis of this general characterization information, the author has constructed a potential-pH diagram of Ni2FeB(OH)10, which is a hydrated state of FeNi2(BO3)O2 as summarized in this paper. Although preliminary, the estimated E-pH diagram suggests some interesting observation, including: growth of bonaccordite “needles” on the clad is associated with a local anodic electrochemical reaction necessary to remove excess electrons from the system to a cathode. During the AOA cycle, the concentration of nickel and iron ions must have been unusually high as they should be for a significant amount of crud deposits. The author thinks such an acceleration of the anodic dissolution of metal cations is due to the effect of the long cell action corrosion mechanism. As early as 1949, an Italian scientist Petracchi demonstrated that electrochemical effects significantly influence the erosion rate. He constructed a flow nozzle with specimens kept under external electrical potential. Upon inducing as low as 0.1 mA/cm2 of the positive current, the erosion rates were reported drastically increased. No erosion was observed by reversing the polarity of the potential. As discussed in a companion paper also presented at this conference [1], the author discusses various mechanisms (electrochemical cell configurations) that induce potential differences, including those differences in ionic concentration, aeration, temperature, flow velocity, radiation and corrosion potentials. In this paper, the author discusses how these potential differences are related to the AOA/CDA issues in PWR/VVER plants. The author is calling for further verification experiments regarding this corrosion mechanism as a joint international project.

scholarly journals The Lax–Oleinik semi-group: a Hamiltonian point of view

2012 ◽  
Vol 142 (6) ◽  
pp. 1131-1177 ◽  
Author(s):  
Patrick Bernard
Keyword(s):  
Hamiltonian Systems ◽  
Viscosity Solutions ◽  
Jacobi Equation ◽  
Kam Theory ◽  
Companion Paper ◽  
Point Of View ◽  
Invariant Sets ◽  
Evolution Operators ◽  
Weak Kam Theory ◽  
Hamilton Jacobi Equation

The weak KAM theory was developed by Fathi in order to study the dynamics of convex Hamiltonian systems. It somehow makes a bridge between viscosity solutions of the Hamilton–Jacobi equation and Mather invariant sets of Hamiltonian systems, although this was fully understood only a posteriori. These theories converge under the hypothesis of convexity, and the richness of applications mostly comes from this remarkable convergence. In this paper, we provide an elementary exposition of some of the basic concepts of weak KAM theory. In a companion paper, Albert Fathi exposed the aspects of his theory which are more directly related to viscosity solutions. Here, on the contrary, we focus on dynamical applications, even if we also discuss some viscosity aspects to underline the connections with Fathi's lecture. The fundamental reference on weak KAM theory is the still unpublished book Weak KAM theorem in Lagrangian dynamics by Albert Fathi. Although we do not offer new results, our exposition is original in several aspects. We only work with the Hamiltonian and do not rely on the Lagrangian, even if some proofs are directly inspired by the classical Lagrangian proofs. This approach is made easier by the choice of a somewhat specific setting. We work on ℝd and make uniform hypotheses on the Hamiltonian. This allows us to replace some compactness arguments by explicit estimates. For the most interesting dynamical applications, however, the compactness of the configuration space remains a useful hypothesis and we retrieve it by considering periodic (in space) Hamiltonians. Our exposition is centred on the Cauchy problem for the Hamilton–Jacobi equation and the Lax–Oleinik evolution operators associated to it. Dynamical applications are reached by considering fixed points of these evolution operators, the weak KAM solutions. The evolution operators can also be used for their regularizing properties; this opens an alternative route to dynamical applications.

Experimental Investigation of the Time Delay Between a Varying Applied Normal Force and the Resulting Friction Force

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Guangxiong Chen ◽  
Xiaolu Cui
Keyword(s):  
Time Delay ◽  
Friction Force ◽  
Normal Force ◽  
Excitation Frequency ◽  
Experimental Tests ◽  
Generation Mechanism ◽  
Test Results ◽  
Test Apparatus ◽  
Force Measurements ◽  
Force Signal

Recently, one of the present authors proposed a new model to explain the generation mechanism of brake squeal based on the time delay between a varying applied normal force and the resulting friction force. The present work conducts a series of experimental tests examining the behavior of this time delay using a special test apparatus. The test apparatus suppresses the effect of interference in the time delay owing to the excitation normal force to the greatest extent possible. Several calibration tests of the test apparatus are conducted to ensure the validity of the normal force and friction force measurements. The varying friction force is extracted from the overall friction force signal without phase distortion using a zero-phase filter. The test results demonstrate a time delay between the varying normal force and the resulting friction force under various testing parameters. The time delay is found to increase with increasing excitation frequency. The generation mechanism of the time delay is also discussed.

scholarly journals Experimental and Finite Element Studies on Man-Rifle Reaction Force

2017 ◽  
Vol 8 (1) ◽  
pp. 7-22
Author(s):  
Cyprian SUCHOCKI ◽  
Janusz EWERTOWSKI
Keyword(s):  
Finite Element ◽  
Human Body ◽  
Reaction Force ◽  
Point Of View ◽  
Fe Model ◽  
Velocity Data ◽  
Force Measurements ◽  
Displacement Fields ◽  
Projectile Velocity ◽  
Recoil Force

The study concerns a man-weapon interaction during a gunshot. The recoil force measurements obtained for the Kalashnikov automatic rifle are presented and analyzed. The influence of shooter’s mass, height and position is described. The breech pressure and projectile velocity data are presented as well. In addition, a finite element (FE) model of the shooter-rifle system is developed in order to qualitatively assess the quantities which could not be determined experimentally, i.e. the stress, strain and displacement fields which are generated in the human body due to the rifle recoil. Several conclusions are drawn that allow for better understanding of the recoil phenomenon and can be useful from the weapon designer’s point of view.

scholarly journals Investigation of the Possibilities to Improve Hydrodynamic Performances of Micro-Hydrokinetic Turbines

Energies ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 4560 ◽  
Author(s):  
Marina Barbarić ◽  
Zvonimir Guzović
Keyword(s):  
Cross Sections ◽  
Axial Direction ◽  
Energy Conversion Efficiency ◽  
Diameter Ratio ◽  
Point Of View ◽  
Power Coefficient ◽  
Hydrokinetic Turbines ◽  
Length Increase ◽  
The Impact ◽  
Length To Diameter Ratio

Horizontal axis turbines are commonly used for harnessing renewable hydrokinetic energy, contained in marine and river currents. In order to encourage the expansion of electricity generation using micro-hydrokinetic turbines, several design improvements are investigated. Firstly, optimization-based design of rotor blade is used to get as close as possible to the efficiency limit of 59.3% (known as Betz limit), that counts for bare turbine rotors, placed in the free flow. Additional diffuser elements are further added to examine the potential to overcome the theoretical efficiency limit by accelerating water at the axial direction. Various diffuser geometrical configurations are investigated using the computational fluid dynamics (CFD) to obtain insight into hydrodynamics of augmented micro-hydrokinetic turbines. Moreover, the turbines are compared from the energy conversion efficiency point of view. The highest maximum power coefficient increase of 81% is obtained with brimmed (flanged) diffuser. Diffusers with foil-shaped cross-sections have also been analyzed but power augmentation is not significantly greater than in the case of simple cross-section designs of the same dimensions. The power coefficients’ comparison indicate that considerable power augmentation is achievable using brimmed diffuser with higher value of length-to-diameter ratio. However, the impact of diffuser length increase on the power coefficient enhancement becomes weaker as the length-to-diameter ratio reaches a value of 1.

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