Implementation of Discrete Capability into the Enhanced Multipoint Approximation Method for Solving Mixed Integer-Continuous Optimization Problems

Multipoint approximation method (MAM) focuses on the development of metamodels for the objective and constraint functions in solving a mid-range optimization problem within a trust region. To develop an optimization technique applicable to mixed integer-continuous design optimization problems in which the objective and constraint functions are computationally expensive and could be impossible to evaluate at some combinations of design variables, a simple and efficient algorithm, coordinate search, is implemented in the MAM. This discrete optimization capability is examined by the well established benchmark problem and its effectiveness is also evaluated as the discreteness interval for discrete design variables is increased from 0.2 to 1. Furthermore, an application to the optimization of a lattice composite fuselage structure where one of design variables (number of helical ribs) is integer is also presented to demonstrate the efficiency of this capability.     

A new algorithm for reduction of number of press-forming stages in forging processes using numerical optimization and FE simulation

This study presents a new simulation-based technique for the optimum design of a multi-stage forging process aiming at reduction of the number of press-forming stages. This iterative design technique involves response-surface-based numerical optimization and a finite element analysis of the process. The design procedure starts with an initial process design that is deemed too conservative, i.e. allows to arrive at the desired product but involves an excessive number of stages. To obtain a better process design, one stage of the existing multi-stage process is eliminated using numerical optimization in conjunction with an FE simulation. This is repeated by reducing the number of stages one by one until the minimum possible number of stages is reached. This design technique is applied to stage reduction of a three-stage forging process of an axisymmetric aluminum billet. It is confirmed that a new two-stage process design is obtained successfully and the developed design optimization technique showed its effectiveness in reduction of the number of press-forming stages in a multi-stage forming process.     

Evolution of the photoresponse time of the GaAs/AlGaAs cyclotron resonance quantum Hall effect detector

The photoresponse time of the cyclotron resonance detector to terahertz radiation under integer quantum Hall effect conditions in the GaAs/AlGaAs heterostructure is shown to have a deep minimum at the Hall plateau center and two sharp maxima at the plateau edges. The minimum at the plateau center is associated with the fundamental property of vanishing of the random impurity potential screening under quantum Hall effect conditions. The decrease in the response time outside the plateau is related to the equilibrium population of the Landau level above (under) the Fermi level by electrons (holes), respectively, which increases the probability of photoexcited carrier recombination. It is shown that, under conditions of background radiation (300 K), relaxation times decrease by two orders of magnitude while retaining the characteristic magnetic field dependence.     

Use of various methods for suppressing internal corrosion of the thermal network at the Novomoskovsk state regional electric power plant

The results of using several water-chemical regimes for the thermal network (pH = 8.3–9.0; pH greater than 10; pH = 8.6–8.9 in the presence of a corrosion inhibitor) are reported. The rates of internal corrosion under these regimes are estimated. The regime with pH = 8.6–8.9 and a corrosion inhibitor and the regime with pH greater than 10 are found to produce the same effect. Translated from élektricheskie Stantsii, No. 10, October 2008, pp. 36–38.     

Estimation of noise error when measuring virtual height during diffusivity of ionospheric F layer

It is shown that during diffusivity of ionosphere its bandwidth of coherence may shrink to hundreds of hertz. Frequency-selective fading appears in these cases and the noise error when measuring ionospheric virtual height increases by 1–2 orders if compared to the normal ionospheric conditions.     

Functions of the density distribution, describing the character of changes in the stray current field parameters

As we showed earlier [4–6], corrosion studies involve numerous measurements and observations, the results of which require statistical processing. The procedure of the processing depends on the specific features inherent in the obtained data and characterizes their distributions. Generally, many problems can be best solved when the distribution function is at hand. Original Russian Text ? A.M. Kerimov, P.A. Spirin, R.A. Kerimov, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 6, pp. 661–664.