Optimization of excitation frequency and guided wave mode in acoustic wavenumber spectroscopy for shallow wall-thinning defect detection

In plate-like structures, wall-thinning defects resulting from corrosion may not be accompanied by any indication of damage on the surface. Thus, inspections are required to ensure that wall-thinning defects are within allowable limits. However, conventional ultrasonic techniques require physical contact to the structure. Alternatively, acoustic wavenumber spectroscopy (AWS) may be used for detecting, locating, and characterizing defects. This paper describes the performance of AWS in the estimation of a wall-thinning defect size in thinplate structures using finite element analysis (FEA). Through a series of FEAs, the structure’s steady-state response to a single-tone ultrasonic excitation is simulated, and the wall-thinning defect-size effect on the wavenumber-estimation accuracy is investigated. In general, the A0 guided wave mode is widely used to visualize defects because of the nature of the wave speed variation in relation to the plate thickness. However, it is not appropriate for the detection of relatively shallow wall-thinning defects, because the rate of change in wave speed with the thickness decreases with increasing plate thickness. To overcome this limitation, we propose a method to optimize excitation frequency and effective guided wave mode instead of utilizing the A0 mode. The results can be used to determine the size of shallow wall-thinning defects in plate-like structures.     

Performance analysis of a triple pressure hrsg

Operating characteristics of a triple pressure reheat HRSG are analyzed using a commercial software package (Gate Cycle by GE Enter Software). The calculation routine determines all the design parameters including configuration and area of each heat exchanger. The off-design calculation part has the capability of simulating the effect of any operating parameters such as power load, process requirements, and operating mode, etc., on the transient performance of the plant. The arrangement of high-temperature and intermediate-temperature components of the HRSG is changed, and its effect on the steam turbine performance and HRSG characteristics is examined. It is shown that there could be a significant difference in HRSG sizes even though thermal performance is not in great deviation. From the viewpoint of both economics and steam turbine performance, it should be carefully reviewed whether the optimum design point could exist. Off-design performance could be one of the main factors in arranging components of the HRSG because power plants operate at various off-design conditions such as ambient tempera-ture and gas turbine load, etc. It is shown that different heat exchanger configurations lead to different performances with ambient temperature, even though they have almost the same performances at design points.     

Optimal vibration image size determination for convolutional neural network based fluid-film rotor-bearing system diagnosis

This paper suggests an image gradient based method that determines the optimal image size for convolutional neural network (CNN)-based diagnosis of fluid-film rotorbearing systems. As distinct patterns improve the diagnosis performance, a criterion is defined to measure the intensity of patterns in an image. The proposed criterion is derived by segmenting an image by the size of the CNN filter and evaluating each segment through the use of image gradient analysis. Vibration signals from a testbed are used to demonstrate the proposed method. First, the signals are transformed into vibration images by using an omnidirectional regeneration technique. Then, vibration images of four different health states are analyzed using the suggested criterion. The analyzed results are compared to the performance of CNN based diagnosis. The results indicate that the proposed criterion can determine the optimal size range of the vibration image that gives the best performance for CNN-based diagnosis.

     

The influence of titanium on the electrochemical properties of the AB5-type metal hydrides

AB₅-type intermetallic compounds were prepared by arc-melting in argon atmosphere. The composition of a stoichiometric compound LaNi_3.6Al_0.4Co_0.7Mn_0.3 with a hexagonal CaCu₅ structure was varied by stoichiometric and nonstoichiometric addition of Ti. With the increase of the Ti y0.05 content in LaNi_3.6Al_0.4Co_0.7Mn_0.3Ti_y, the hydrogen storage capacity is enhanced, whereas when y=0.1–0.3, it is decreased. The discharge capacity and cyclability are increased considerably by addition of titanium in the range of 0.02–0.1 with a maximum value at about 0.1%. The highest maximum capacity is achieved for a nonstoichiometric addition of 0.05% Ti. The kinetic properties are also additionally improved by the formation of a titanium-rich second phase. This can explain the improvement of the capacity for alloys with low Ti content. The decrease in capacity for high Ti content was also correlated with the amount of the Ti-rich phase. Therefore, the improvement of kinetics are due to the catalytic effect, grain boundary diffusion effect or more pronounced alloy pulverization upon cycling. This study has been aimed to improve the electrode properties of a series of multicomponent LaNi_3.6Al_0.4Co_0.7Mn_0.3Ti_y (y=0.0, 0.02, 0.05, 0.1, 0.2, 0.3) alloys which have mutual complementary properties. All the prepared alloys have been subjected to analyses by EDS, SEM and XRD. In order to determine the hydrogen storage capacity, the pressure composition isotherms (P–C–T curves) have been used. The metal hydride electrodes were characterized by galvanostatic cycling test.     

A Geometric Approach to Modelling Friction In Metal Forming

When simulating metal fanning processes It is common practice to describe the friction by using the Coulomb or Tresca model and to assume that the conditions are constant throughout the process. This paper describes an alternative approach that seeks to describe friction by modelling the geometric surface roughness of the tools. Using the ring test analytically a relationship has been established between surface geometry and the friction factor. This model has been validated experimentally also using the ring test. Such a system provides an opportunity to model friction more flexibly and accurately.     

Particularities of condensation of atoms with increased kinetic energy

Novel universal method for measurement of the condensation coefficient α is developed. Using this method, noticeable difference between measured (α≈0.8) and expected (α≈1) values of the condensation coefficient for sputtered Cr atoms was revealed for the first time. The effect is assumed to be a result of considerable elevation of the surface temperature during atomic condensation induced by the energy delivered to the condensation surface by sputtered atoms and from the plasma.     

Optimization of silicon solar cell fabrication based on neural network and genetic programming modeling

This study describes techniques for the cascade modeling and the optimization that are required to conduct the simulator-based process optimization of solar cell fabrication. Two modeling approaches, neural networks and genetic programming, are employed to model the crucial relation for the consecutively connected two processes in solar cell fabrication. One model (Model 1) is used to map the five inputs (time, amount of nitrogen and DI water in surface texturing and temperature and time in emitter diffusion) to the two outputs (reflectance and sheet resistance) of the first process. The other model (Model 2) is used to connect the two inputs (reflectance and sheet resistance) to the one output (efficiency) of the second process. After modeling of the two processes, genetic algorithms and particle swarm optimization were applied to search for the optimal recipe. In the first optimization stage, we searched for the optimal reflectance and sheet resistance that can provide the best efficiency in the fabrication process. The optimized reflectance and sheet resistance found by the particle swarm optimization were better than those found by the genetic algorithm. In the second optimization stage, the five input parameters were searched by using the reflectance and sheet resistance values obtained in the first stage. The found five variables such as the texturing time, amount of nitrogen, DI water, diffusion time, and temperature are used as a recipe for the solar cell fabrication. The amount of nitrogen, DI water, and diffusion time in the optimized recipes showed considerable differences according to the modeling approaches. More importantly, repeated applications of particle swarm optimization yielded process conditions with smaller variations, implying greater consistency in recipe generation.     

phenanthrene biodegradation in soil slurry systems: Influence of salicylate and triton X-100

The effects of a nonionic surfactant (Triton X-100) and a metabolic inducer (salicylate) were investigated in order to enhance the biodegradation rate of phenanthrene in soil slurry systems. The addition of salicylate reduced the time for the complete degradation of phenanthrene up to about 3 times (12.9 mg/L-d) even at highly concentrated soils of 650 mg/kg. The inducer was beneficial not only by increasing metabolic activity of existing cells, but also by increasing cell mass since it was utilized as an additional carbon source. The fraction of fast growing bacteria in total with salicylate addition was much higher compared to that without salicylate. The addition of Triton X-100 ranging from 0 to 10 g/L increased the apparent solubility of phenanthrene in soil slurry, but significantly inhibited the phenanthrene degradation in both slurry and pure liquid systems without any inhibition to cell growth. The phenanthrene degradation was inhibited much more with increasing the surfactant concentration. The inhibition by surfactant addition might be due to the prevention of bacterial adhesion to phenanthrene sorbed to soil and/or decrease of micellar-phase bioavailability     

A vehicle routing problem solved by using a hybrid genetic algorithm

The main purpose of this study is to find out the best solution of the vehicle routing problem simultaneously considering heterogeneous vehicles, double trips, and multiple depots by using a hybrid genetic algorithm. This study suggested a mathematical programming model with a new numerical formula which presents the amount of delivery and sub-tour elimination. This model gives an optimal solution by using OPL-STUDIO(ILOG CPLEX). This study also suggests a hybrid genetic algorithm (HGA) which considers the improvement of generation for an initial solution, three different heuristic processes, and a float mutation rate for escaping from the local solution in order to find the best solution. The suggested HGA is also compared with the results of a general genetic algorithm and existing problems suggested by Eilon and Fisher. We found better solutions rather than the existing genetic algorithms.     

Compositional effects in the retention of colloids by thermal field-flow fractionation

The retention of polystyrene and silica colloids that have been chemically modified is measured in several aqueous carrier liquids. Retention levels are governed by particle size and composition but are also sensitive to subtle changes in the carrier. Size-based selectivities are higher in aqueous carriers compared to acetonitrile. In aqueous carriers, retention varies dramatically with the nature of the additive, and for a given additive, retention increases with ionic strength, regardless of modifications to the particle surface. The role played by electrostatic effects in retention is studied by varying the ionic strength of the carrier, estimating electrical double layers, determining particle-wall interaction parameters, and calculating the coefficients of mass diffusion and thermal diffusion. Although electrostatic phenomena can affect mass diffusion and particle-wall interactions in carriers of low ionic strength (<10(-3) M), such effects are not great enough to explain the dependence of retention on ionic strength. Therefore, thermal diffusion must be affected directly. Thermal diffusion is found to increase with pH, and at a given pH with the surface tension of the suspended particle. Finally, while the addition of the surfactant FL-70 generally decreases retention, greater retention levels can ultimately be achieved with FL-70 because larger temperature gradients can be used without particle adsorption to the accumulation wall.