Modified Nyquist analysis for PFM‐continuous-time hybrid systems

A graphical method is proposed for analysing PFM‐continuous-time hybrid systems. The method is an improved version of the authors' earlier method, which was practical, but had two shortcomings that remained to be addressed. One is that the influence of the included parameter upon stability estimation is not clear, the other being that extension to the network case is not straightforward. The present paper proposes a modified Nyquist analysis method that can overcome the above two problems with little effect on sharpness in the estimation of stability.     

Simulation of heat transfer in the cool storage unit of a liquid–air energy storage system

An energy storage system that stores energy in the form of liquid air was studied. In this system, the cool storage unit was the most important unit. From the viewpoint of safety and economy, it was most promising to store the cold energy as the sensitive heat of a solid such as pebbles or concrete. A simulator was developed to predict temperature variations of the solid cool storage unit. The simulator calculated unsteady heat transfer between a supercritical gas flow and the solid material. Comparison of calculated and experimental results showed that the temperature variation of the metal cool storage medium was accurate within 11%. The calculated results showed for the concrete cool storage unit that a smaller quantity of medium was required with a smaller pitch of the tube. The minimum quantity of concrete calculated at the smallest pitch was three times that of concrete, which was simply estimated from the heat capacity of concrete and air. The volume required for concrete cool storage was less than 1/100 that of reservoirs for a pumped‐hydro power station having a vertical drop of 500 m. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 284–296, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10035     

Tool life prediction for cup shaped cold forgings with fuzzy language risk analysis and fuzzy inference

A method of Die-life prediction is suggested for cup shaped forgings.Authors theorize that forge specialists can make die-life prediction by comparing a “target” forging process” with other standard processor whose actual life are known. The authors make comparison by calculation of risk (that which shortens die-life span). Risk is estimated by using a risk tree network, based on information compiled from a survey of forge experts. The risk rate of an “end node” is estimated by a computer-aided forging process planning system. Comparing dimensions of the target and standard forging processes has effect on the risk rate. Once risk is determined, it is used to predict dielife span using Fuzzy inference. The Fuzzy inference rule is estimated based on data received from the interview of experts.     

Mode I fracture modeling of elastomer toughened epoxy adhesive joints

An analytical model is developed to correlate the mode I fracture energy of toughened epoxy adhesive joints with microdamage mechanisms generated around a crack tip. The analytical expression for the mode I fracture energy is derived on the basis of total energy dissipation during crack extension. Three dominant damage modes, plastic shear band formation, plastic void growth, and plastic deformation of the entire matrix resin in a crack-tip region, are identified in the proposed model as the primary energy dissipation mechanisms. Numerical results show that the models can predict the effects of adhesive thickness on the mode I fracture energy of toughened adhesive joints. The analytical model involving material constants and microstructural variables should provide some guidelines toward achieving optimum fracture toughness for these types of adhesive joints. This revised version was published online in July 2006 with corrections to the Cover Date.     

Immune algorithm combined with estimation of distribution for traveling salesman problem

This paper describes an artificial immune algorithm (IA) combined with estimation of distribution algorithm (EDA), named IA‐EDA, for the traveling salesman problem (TSP). Two components are incorporated in IA‐EDA to further improve the performance of the conventional IA. First, aiming to strengthen the information exchange during different solutions, two kinds of EDAs involving univariate marginal distribution algorithm and population‐based incremental learning are altered based on the permutation representation of TSP. It is expected that new promising candidate solutions can be sampled from the constructed probabilistic model of EDA. Second, a heuristic refinement local search operator is proposed to repair the infeasible solutions sampled by EDA. Therefore, IA‐EDA can alleviate the deficiencies of the conventional IA and can find better solutions for TSP by well balancing the exploitation and exploration of the search. Experiments are conducted based on a number of benchmark instances with size up to 100 000 cities. Simulation results show that IA‐EDA is effective for improving the performance of the conventional IA and can produce better or competitive solutions than other hybrid algorithms. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Effect of carbon deposition by carbon monoxide disproportionation on electrochemical characteristics at low temperature operation for solid oxide fuel cells

The deterioration by carbon deposition was evaluated for electrolyte- and anode-supported solid oxide fuel cells (SOFCs) in comparison with carbon monoxide disproportionation and methane cracking. The polarization resistance of the nickel-yttria stabilized zirconia (Ni-YSZ) anode increased with a rise in CO concentration in H₂-CO-CO₂ mixture for the electrolyte-supported cells at 923 K. The resistance, however, did not change against CO concentration for the anode-supported cells. In a methane fuel with a steam/carbon (S/C) ratio of 0.1, the cell performance decreased for both of the cells at 1073 K. A large amount of agglomerated amorphous carbon was deposited from the anode surface to the interface between the anode and the electrolyte after power generation at S/C = 0.1 in methane fuel. On the other hand, the crystalline graphite was deposited only at the anode surface for the anode-supported cell after power generation in CO-CO₂ mixture. These results suggest that the reaction rate of CO disproportionation is faster than that of methane cracking. The deposited carbon near the anode/electrolyte interface caused the increase in the polarization resistance.