Cavitation erosion incubation period

To evaluate the “incubation period” (IP) stage of cavitation erosion, short-duration vibratory horn tests in tap water were made on soft aluminum alloy (aluminum alloy 1100-O) and also on a much more resistant alloy (316 stainless steel). Curves of weight loss versus time, and corresponding scanning electron microscopy photomicrographs taken during the IP, are presented and discussed. The effects of horn amplitude and temperature are investigated for “open-beaker” tests. The IP for 316 stainless steel is found to be about 500 times that for aluminum alloy 1100-O for the same amplitude and temperature. This ratio can be predicted almost exactly by applying an assumed relation between MDPR_max and IP, i.e. MDPR_max^?1 = k(IP)ⁿ.Fatigue cracks and individual-blow craters were found for 316 stainless steel but only individual craters were found for aluminum alloy 1100-O, although their ductilities are approximately equal. It is found that the IP based on the eroded area only, IP_erod, is much less than the conventional IP (based on the total specimen area) if IP is based on the attainment of a given mean depth of erosion MDP.Relations between the eventual erosion rate MDPR_max and the IP are considered. It is found that IP data can often be used to predict eventual MDPR_max values according to the relation MDPR_max^?1 ∝ (IP)ⁿ where n ≈ 0.93 and n ≈ 0.95 for our vibratory and Venturi data respectively. However, different values for n have been reported in the literature. By assuming a “characteristic” erosion-time curve the time of occurrence of MDPR_max can also be estimated.It is verified that only bubble collapse stresses are important in the vibratory horn test, although specimens are vibrated under very high accelerations.     

Bubble sizes and shapes in a counter-current bubble column with pure and binary liquid phases

It is generally admitted that the “global-scale” behavior of bubble columns is imposed by the “local-scale” phenomena. For this reason, understanding the fluid dynamics in bubble columns relies on the precise knowledge of the so-called “birth and life” of bubbles. A-priori knowledge of the bubble sizes and shapes is required to characterize the “local-scale”, to understand the “global-scale”, to set-up and validate numerical models, as well as to support scaling-up methods towards the “industrial-scale”. This paper contributes to the present-day discussion by proposing an experimental research devoted to clarify the relationships between the bubble sizes and shapes, the integral flow parameters, and the liquid phase properties. The experimental study, based on a bubble-identification methods, was performed in a “large-scale” bubble column (inner diameter equal to 0.24 m, height equal to 5.3 m) operated in the batch and in the counter-current modes with pure (deionized water) and binary (mixture of ethanol and deionized water) liquid phases. The system was operated in the pseudo-homogeneous flow regime with superficial gas velocities in the range of 0.0037–0.0188 m/s and superficial liquid velocity, in the counter-current mode, equal to −0.066 m/s. In the different experimental runs, bubble size distributions and shapes were obtained at different radial and axial locations. The experimental observations have been presented, compared with literature correlations, used to develop novel correlations (to be applied in practical applications), compared with previously obtained experimental data and interpreted in a multi-scale point of view. The comprehensive dataset obtained within this research may be used to improve the validation of numerical approaches and, in particular, to tackle the unsolved issue of developing break-up and coalescence kernels.     

Experimental study of effects of water-cement ratio on the acoustic emission rate “<Emphasis Type="Italic">a</Emphasis>” values in concrete

The critical microcracks make durability of the concrete seriously weakened, and the water-cement (w/c) ratio plays a key role in the durability of concrete, acoustic emission (AE) rate “a” value is an effective parameter to evaluate the amount of critical microcracks quantitatively, so the study on the influence factors and the distribution of w/c ratio on the value “a” can provide a promising reference value for the practical engineering. A total of 90 specimens in different w/c ratio are tested under axial compression in the experiment. The whole damage evolution processes are monitored by fulldigital AE acquisition system. The differences of the amount of critical microcracks in different w/c ratio are explored based on the AE rate process theory, and the rule of the effects of w/c ratio on the rate “a” value is revealed through the analysis of fracture energy and cumulative AE energy in the failure process. The results show that a linear relationship was observed between cumulative AE energy and rate “a” value, the amount of critical microcracks and the rate “a” value increase with the increase of w/c ratio, while the cumulative AE energy and cumulative AE hits are on the contrary.     

Determination of the economical policy of a three-echelon inventory system with (R, Q) ordering policy and information sharing

In this work, we consider a three-echelon serial inventory system with two warehouses (suppliers) and one retailer with information exchange. The retailer applies continuous review (R, Q) policy. The warehouses have online information on the inventory position and demand activities of the retailer. We present a new ordering policy to share information among inventory echelons. The warehouse I and II start with m ₁ and m ₂ initial batches of the same order size of the retailer, respectively. The warehouse I places an order to an outside source immediately after the retailer’s inventory position reaches an amount equal to the retailer’s order point plus a fixed value s ₁, and the warehouse II places an order to the warehouse I immediately after the retailer’s inventory position reaches an amount equal to the retailer’s order point plus a fixed value s ₂. Transportation times are constant and the retailer faces independent Poisson demand. The lead times of the retailer and the warehouse II are determined not only by the constant transportation time but also by the random delay incurred due to the availability of stock at the warehouses. In this paper using the idea of the one-for-one policy, we implicitly incorporate the distribution function of the random delay to obtain the exact value of the expected inventory system cost. Resorting some numerical examples in three different scenarios, we show how information sharing reduces the inventory costs.     

Comparison of cavitation erosion test results from venturi and vibratory facilities

A detailed comparison of cavitation erosion performance in tap water for five alloys in a vibratory (no-flow) system and a Venturi (flow) system was made. The effects of temperature variation (80 – 200 °F), Venturi throat velocity (34 – 49 m s^?1) and vibratory horn double amplitude were studied. Correlations between maximum erosion rate (maximum mean depth of penetration rate (MDPR_max)) and incubation period IP, and the material mechanical properties Brinell hardness and ultimate resilience $\text{UR =}\text{UTS}{}^2\text{2E}$. (where UTS is the ultimate tensile strength and E is the elastic modulus), were examined. Only moderate success was achieved in correlations between “erosion resistance” MDPR_max^?1 and IP and these mechanical properties. However, a good correlation was found between MDPR_max and IP, pertinent to both facilities, of the form MDPR_max^?1 = aIPⁿ, where n is near unity (0.94). The cavitation intensity, as measured by MDPR_max, was found to be 10–20 times greater in the vibratory system, depending on horn amplitude and material. This ratio varies between 5 and 30 if individual materials are considered separately, being greatest for 1018 carbon steel and least for 316 stainless steel. This indicates the important differences in form between these cavitating regimes and the imprecision of material comparisons made in both regimes.     

Table Tennis: Preliminary Displacement in Pimples-Out Rubber

Following the recent trend of applying a more scientific approach to the study of all aspects of racket sports, we have developed a simple tribological method allowing to characterize unequivocally and unbiased by human factor the frictional behavior of table tennis rubber racket covering. This technique suggests examining the performance of rubber coverings at the onset of sliding against the table tennis ball by using three non-dimensional parameters, “friction,” “stickiness,” and “grip.” However, while “friction” and “stickiness” parameters were elaborated well, the “grip” parameter was only outlined due to the lack of actual determination of preliminary displacement on which it is based. To fill this gap, here we focus on studying preliminary displacement in four short and four long pimples-out rubbers. It is also found that a particular attention should be paid for the environmental conditions under which the three parameters are determined.     

Decision diagram based methods and reliability analysis for k-out-of-n: G systems

Binary k-out-of-n systems are commonly used reliability models in engineering practice. Many authors have extended the concept of k-out-of-n system to multi-state k-out-of-n systems. This paper proposes a binary decision diagram (BDD) based approach for binary k-out-of-n: G system and a multi-state multi-valued decision diagram (MMDD) based approach for multi-state k-out-of-n: G system. BDD and MMDD have been extensively used for representing and manipulating logic functions in many areas, including reliability modeling and analysis. In this paper, patterns of BDD/MMDD for binary/multi-state k-out-of-n: G system are summarized and proved, a two-step algorithmic process is proposed for modeling the BDD/MMDD and three case studies are implemented to demonstrate the presented methods. Complexity analysis shows that the presented method is more computationally efficient than the traditional algorithms for k-out-of-n: G system.     

An application of bubble collapse pulse height spectra to venturi cavitation erosion of 1100-o aluminum

Venturi cavitation erosion tests were performed and correlated with bubble collapse pulse height spectra measured by a microtransducer. The effects of the throat velocity and the cavitation number σ (referred to the downstream pressure and throat velocity) on the erosion rate (MDPR) were studied. The velocity damage exponent was 4.11 for 0.62 ? σ ? 0.80, while the MDPR is almost independent of velocity for σ = 0.85. The MDPR decreases with increased σ for 0.62 ? σ ? 0.85. The data were reduced to “acoustic power” (from pulse height spectra) and “erosion power” (the ultimate resilience multiplied by the MDPR). A near-linear relationship was found between these. Their reciprocal ratio η_cav ≈ 7 × 10^?11. For σ = 0.62, the data deviated from the others, possibly because of the work hardening of the eroded surface.     

Quantitative analysis of noninvasive diagnostic procedures for induction motor drives

This paper reports quantitative analyses of spectral fault components in five noninvasive diagnostic procedures that use input electric signals to detect different types of abnormalities in induction motors. Besides the traditional one phase current spectrum analysis “SC”, the diagnostic procedures based on spectrum analysis of the instantaneous partial powers “P_ab”, “P_cb”, total power “P_abc”, and the current space vector modulus “csvm” are considered. The aim of this comparison study is to improve the diagnosis tools for detection of electromechanical faults in electrical machines by using the best suitable diagnostic procedure knowing some motor and fault characteristics. Defining a severity factor as the increase in amplitude of the fault characteristic frequency, with respect to the healthy condition, enables us to study the sensitivity of the electrical diagnostic tools. As a result, it is shown that the relationship between the angular displacement of the current side-bands components at frequencies (f±f_osc) is directly related to the type of induction motor faults. It is also proved that the total instantaneous power diagnostic procedure was observed to exhibit the highest values of the detection criterion in case of mechanical faults while in case of electrical ones the most reliable diagnostic procedure is tightly related to the value of the motor power factor angle and the group motor-load inertia. Finally, simulation and experimental results show good agreement with the fault modeling theoretical results.     

Exploring injection prevention technologies for security-aware distributed collaborative manufacturing on the Semantic Web

Security is one of the key challenges for the development of distributed collaborative manufacturing systems. Most of the access control models of collaborative systems cannot prevent illegal accesses to column/row levels of a database table, which could be caused by command injection. This paper firstly presents the possible injection attacks in RDBMS-based collaborative system on the Semantic Web and gives their classification. Based on this classification, the paper then describes an attempt at detecting command injections to the distributed collaborative manufacturing systems by comparing the inputs related nodes that are intended with the resulting parse tree in run time. To validate the proposed approach, a prototype system called “SemGuard” has been developed. By testing on two commonly used RDF databases and one real Semantic Web application, it shows that SemGuard is efficient, taking less than 10 ms overhead to protect the context information of a distributed collaborative manufacturing system.     

Optimal design of \overline {\text{X}} -control chart with Pareto in-control times

Economic control chart models usually assume that the time to occurrence of an assignable cause follows an exponential or Weibull distribution. This paper extends that to the Pareto distribution in order to investigate, in general, the effect on the economic control chart parameters like sample size, time between two successive samples, and the cost per unit time of the distributional assumption. The Pareto distribution arises as a limiting distribution of the waiting time for the number of new observations needed to obtain a value exceeding the greatest among “n” observations. It was found that the economic design of $ \overline {\text{X}} $ chart is greatly influenced by the distributional assumption. Using the cost model, the sensitivity analysis of the statistical economic design of the $ \overline {\text{X}} $ chart with respect to the parameters and costs is studied.     

Velocity and size dependences of the erosion rate in silicon

The results obtained in this investigation for the velocity and size dependences of the steady state erosion rate in silicon single crystals are consistent with the predicted power law relation only if certain modifications are made. The velocity exponent n must depend on the particle size in such a way that n decreases as D increases, and allowance should be made for the onset of an apparent size threshold effect at small particle sizes. Further theoretical work is needed to extend the existing models, taking into account a number of new physical features. Possible mechanism changes and thresholds seem most important in this context. Further systematic experiments are also needed to establish the important parameters and to extract reliably their phenomenological relations. It is pointed out that a cursory analysis of erosion rate data according to simple power law velocity and size dependence is likely to be inconsistent and a suitable range of D and υ values must be systematically analyzed.     

Tribological properties of self-assembled monolayers on Au,SiOx and Si surfaces

Using interfacial force microscopy (IFM), the tribological properties of self-assembled monolayers (SAM) on Si surfaces produced by a new chemical strategy are investigated and compared to those of “classical” SAM systems, which include alkanethiols on Au and alkylsilanes on SiO_x. The new SAM films are prepared by depositing n-alkyl chains with OH-terminations onto Cl-terminated Si substrates. The chemical nature of the actual lubricating molecules, n-dodecyl, is kept constant in all three thin film systems for direct comparison and similarities and differences in tribological properties are observed. The adhesion strength is virtually identical for all three systems; however, frictional properties differ due to differences in film packing. Differences in the chemical bonds that attach the lubricant molecules to the substrate are also discussed as they influence variations in film wear and durability. It is demonstrated that the new SAM films are capable of controlling the friction and adhesion of Si surfaces equally well as the classical SAMs and are potentially more reproducible and more durable.     

A new method to investigate the sliding wear behaviour of materials based on energy dissipation: W–25 wt%Cu composite

A new method is proposed to explain and monitor wear behaviour based on energy dissipation. The wear of a W–25 wt%Cu composite against 52100 steel was used to demonstrate this approach with pin-on-disc tests conducted under three normal loads. An energy-dependent criterion, namely, specific wear volume (wear volume/dissipated energy (mm³/J)), was defined to evaluate the wear of the composite. The specific wear volume can be used as a substitute for the traditional wear rate due to the simultaneous expression of several wear parameters and because of its strong dependence on the wear mode. The specific wear volume appears to be constant in any particular “wear mode” regardless of the active “wear processes”. In the wear of this composite, processes such as particle pull-out, mechanically mixed layer (MML) formation, crack propagation and delamination were observed. But, combination of these processes in each test had identical specific wear volumes. Thus, all of these wear processes were considered to be consecutive stages of the same wear mode: fatigue wear. The amount of dissipated energy and the volumetric loss increased with increasing normal load. Also, changing the normal load changed the rate of energy dissipation per unit sliding distance.     

Evaluation of the impact of information delays on flexible manufacturing systems performance in dynamic scheduling environments

The significance of the adverse effects of information delays (IDs) on flexible manufacturing system (FMS) performance is getting increasing attention from manufacturing systems managers, planners, schedulers, Enterprise Resource Planning software developers, and researchers because of their potential to disrupt production schedules. In this paper, we examine the extent of the adverse impact that IDs have on FMS performance. The FMSs are assumed to operate in a “review period” mode; i.e., the control decisions (e.g., sequencing and dispatching) are taken based on information monitored at predetermined intervals of time called “review periods”. The performance deterioration occurs due to the obsolescence of system status information. Key empirical findings based on extensive simulation experiments are: (1) IDs significantly degrade FMS performance for due date-based measures (mean tardiness and percent of jobs tardy); (2) IDs also degrade FMS performance for non-due date-based measures (mean flowtime and average machine utilization), albeit to a less severe degree; (3) routing flexibility, often regarded as a significant factor to influence FMS performance, is superseded by status review information delay.     

Turbulent structures,integral length scale and turbulent kinetic energy (TKE) dissipation rate in compound channel flow

In the present study, high data rate measurements were obtained for the streamwise and vertical velocity components using 2D Laser Doppler Velocimeter. The turbulent field in a straight compound-channel flow was characterized for three different uniform flow water depths, corresponding to “deep flows”, “intermediate flows” and “shallow flows” conditions. Several methodologies were studied to process the data and to obtain autocorrelation functions, integral length scale and turbulence kinetic energy (TKE) dissipation rate. The Sample and Hold method was adopted to interpolate the unevenly spaced record and calculate the autocorrelation function; the integral-stop-value 1/e was used to estimate the integral length scale; and the TKE dissipation rate was estimated through the velocity energy spectrum. A double shear layer composed of two counter-rotating vertical oriented vortices, interacting with the secondary currents, is observed in the interface region for deep flow conditions. By decreasing the water depth, the interface region becomes dominated by a strong mixing layer of vertical oriented vortices with high TKE dissipation rate and large integral length scale, acting as a vertical wall to the weak secondary currents that develop at the main channel. The determination of the integral length scale permits to confirm the existence and the strength of these turbulence structures, unveiling the strong mixing layer as the origin of the largest integral length scales, even larger than the flow depth, and as the most efficient mechanism to redistribute turbulence generated at the bottom towards upper flow regions. Despite the high complexity of turbulence structures present in the flow, for all water depths, a linear dependence is depicted between integral length scale, TKE dissipation rate, and streamwise turbulence intensity.     

Determining electrophysical characteristics of metal-oxide-semiconductor structures from the data of voltage-capacitance analysis of the depletion region of a semiconductor surface

The oxide layer in nanotransistors with metal-oxide-semiconductor (MOS) structures may be as thin as 20Å. The physical diagnostics of such structures via conventional methods of voltage-capacitance characteristics (VFCs) is impossible without taking into account the usually disregarded effects of degeneracy and dimensional quantization of the electron gas. However, as the oxide-layer thickness decreases, these effects make an increasingly substantial contribution to capacitance C of the MOS structure not only at C?C _i (where C _i is the “oxide capacitance”) but also at C < C _i . In this study, we have developed a general method for determining the principal characteristics of MOS structures from the data of analysis of the VFCs in the region of the Schottky depletion layer. The doping level, the surface potential, the semiconductor surface charge, the voltage of “flat bands,” oxide capacitance C _i , the voltage drop across the oxide, and the sign and density of the charge fixed in it can be found at an accuracy of ?0.1% within the framework of a single experiment regardless of the oxide-layer thickness and without using fitting parameters and a priori assumptions concerning the properties of the electron gas in the accumulation and inversion layers. The stages and results of the implementation of this method are demonstrated by the results of experiments performed on an n-Si-based MOS structure with a 171.2 Å-thick oxide layer.     

Stationary transducer response to planetary-gear vibration excitation II: Effects of torque modulations

The frequency spectra of the outputs of transducers fixed to the ring gears of planetary-gear systems contain useful information pertaining to the health of such systems. The effects on such frequency spectra arising from non-uniform loading carried by the M planets in such systems was derived and illustrated in “Stationary transducer response to planetary-gear vibration excitation with non-uniform planet loading,” by Mark and Hines [W.D. Mark, J.A. Hines, Stationary transducer response to planetary-gear vibration excitation with non-uniform planet loading, Mechanical Systems and Signal Processing 23 (2009) 1366–1381]. The present paper extends this earlier analysis by predicting the added effects on such frequency spectra caused by planet-carrier torque modulations. It is shown that such torque modulations produce “sideband” harmonics on the harmonic contributions arising from uniform loading carried by the planets, and additional “sideband” harmonics on the harmonic contributions arising from the lack of uniformity of loading carried by the planets. An example is discussed for torque modulations with a period of 1/B times the planet-carrier rotation period. This example illustrates the effects of torque modulations on the transducer output spectra of a UH-60A rotorcraft with a B=4 blade rotor and M=5 planets.