Antiplane electro‐mechanical field of a piezoelectric finite wedge under a pair of concentrated forces and free charges

Abstract

This paper presents general antiplane electro‐mechanical field solutions for a piezoelectric finite wedge subjected to a pair of concentrated forces and free charges. The boundary conditions on the circular segment are considered as traction free and insulated. Using finite Mellin transform methods, the stress and electrical displacement in all fields of the piezoelectric finite wedge are derived analytically. Singularity orders and intensity factors of stress and electrical displacement can be obtained too. After being reduced to a problem of an antiplane edge crack or an infinite wedge in a piezoelectric medium, the results compare well with those of previous studies.     

Antiplane electro‐mechanical field of a bimaterial piezoelectric wedge under a pair of concentrated forces and surface charges

Abstract

This paper presents the general solutions of the antiplane electro‐mechanical field for a bimaterial piezoelectric wedge subjected to a pair of concentrated forces and surface charges. Identical wedge angles are assumed here. Using the Mellin transform method, the singularity orders and the generalized stress, strain, electric displacement and electric field intensity factors are derived analytically. The discussion of a semi‐infinite crack at the interface of two bonded piezoelectric half‐planes is also included. Some degenerated cases are investigated to check the accuracy of the obtained solutions.     

Modeling of the Temperature Field on a Thermodiffusion‐Galvanizing Line

Results of mathematical modeling of the temperature field in the working volume of a thermodiffusiongalvanizing unit on the basis of the assumptions of convective heat exchange are given.     

Modeling of the dynamic characteristics of two‐bolt‐joints

Abstract

In this paper, a method to identify the damping and stiffness properties of bolted joints from a substructure synthesis scheme is presented. The easily measured frequency response functions of substructures and the assembled structure are the only data needed in this method. A synthesis formula used to predict the frequency response functions of two‐bolt‐joint structures is proposed. The formula makes use of the extracted properties of a single‐bolt‐joint. Some experiments with two free‐free steel beams jointed with one or two bolts are made to check this method. The close correlation between predicted and measured results demonstrates that this method is acceptable.     

Thermal and mechanical evolution of welding‐induced buckling distortion

Abstract

The evolution of the buckling phenomenon starts during the weld cooling cycle, caused by an onset inelastic strain incompatibility condition. This initial bifurcation phenomenon may continue to grow until the completion of the cooling cycle, which results in the final buckling distortion of the plate. With lower heat input and/or smaller plate dimensions this initial instability may stop during the cooling cycle due to diminishing strain incompatibility and recovering of the plate rigidity. The buckling evolution process is complex due to the highly nonlinear nature of the welding problem. This paper studies this buckling evolution process using an integrated experimental and numerical approach. Bead‐on‐plate welds of AH36 steel were experimentally studied. The welding process was numerically simulated and analyzed using a three‐dimensional, thermo‐elastic‐plastic, large deformation model. The transient stress bifurcation phenomenon and the displacement evolution process were analyzed to understand the critical weld conditions causing the final buckling distortion of the weldment. The critical weld conditions were evaluated on the longitudinal inherent shrinkage (plastic) strain distribution in the weldment.     

Modeling of Rotating and Recirculation Flows on the Basis of a Hybrid Two‐Parameter k–ε Model

A modified twoparameter model of turbulence for calculation of flows with a considerable flow curvature is considered. Account for the effects of anisotropy is based on correction of empirical coefficients, which enter into the equation of transfer of dissipation of turbulent kinetic energy, using the Richardson number. It is suggested to apply a correction not to the entire region of calculation, but to the portions where the Richardson number takes on certain values. Satisfactory agreement of calculation results with experimental data of different authors and a slight increase in computational costs allow one to draw the conclusion on the possibility of employing the suggested approaches in engineering practice.     

Numerical Modeling of the Three‐Dimensional Unsteady Convection of a Silicon Melt in a Vessel Typical of Czochralski‐Method Apparatuses

Calculations of the quasiperiodic and stochastic regimes of threedimensional convection of a silicon melt (Pr = 0.015) have been performed for a rotating vessel whose complicated shape is typical of crucibles used in growing crystals by the Czochralski method. A large set of data on the structure of the convection and the spectral composition of pulsations has been obtained. The influence of the rotation of a crystal and a crucible on the convection and the thermal state of a melt has been investigated.     

Modeling of Heat and Mass Transfer in Systems of Radiation‐Evaporation Thermal Protection

Results of theoretical and experimental studies of models of different systems of radiationevaporation thermal protection are presented; the overalldimensionweight parameters of these systems and of systems of passive radiation thermal protection are compared.     

Modeling of the Thermal Field of a Workpiece in Milling of Austenitic Steel by a Finger‐Type Cutter

The authors report results of modeling thermal fields by the method of finite elements under conditions of milling of 00H17N14M2A austenitic steel by a fingertype cutter. A solution of the problem of unsteady nonlinear heat conduction has made it possible to find the temperature distribution in the surface layers of a workpiece as a function of the cutting rate and the position of the tip of the cutter edge.     

Summary of development of 70 MW class model superconducting generator––research and development of superconducting for electric power application

A 70 MW class superconducting model generator was designed, manufactured, and tested from 1988 to 1999 as Phase I, which was Japan's national project on applications of superconducting technologies to electric power apparatuses that was commissioned by NEDO as part of New Sunshine Program of AIST and MITI. Phase II then is now being carried out by almost same organization as Phase I. With the development of the 70 MW class superconducting model generator, technologies for a 200 MW class pilot generator were established. The world's largest output (79 MW), world's longest continuous operation (1500 h), and other sufficient characteristics were achieved on the 70 MW class superconducting model generator, and key technologies of design and manufacture required for the 200 MW class pilot generator were established. This project contributed to progress of R&D of power apparatuses. Super-GM has started the next project (Phase II), which shall develop the key technologies for larger-capacity and more-compact machine and is scheduled from 2000 to 2003. Phase II shall be the first step for commercialization of superconducting generator.     

Decentralized robust control of multi‐machine power systems with a prescribed degree of stability

Abstract

This paper presents a completely decentralized scheme for the robust control of multi‐machine power systems with a prescribed degree of stability. By applying the optimal control technique to the nominal dynamics of each decomposed machine, the calculated optimal gains are multiplied by appropriate factors to account for the intrinsic uncertainties and nonlinear interactions among the machines. This subsystem‐based method can give the overall system an arbitrarily chosen degree of stability, where no state information is transferred. An example of a three‐machine power system is given below.     

Possibilities and sustainability of “biomass for power” solutions in the case of a coal-based power utility

This paper investigates the possibilities and the sustainability of “biomass for power” solutions on a real power system. The case example is JP Elektroprivreda BiH d.d.—Sarajevo (EPBiH), a typical conventional coal-based power utility operating in the region of South East Europe. Biomass use is one of the solutions considered in EPBiH as a means of increasing shares of renewable energy sources (RES) in final energy production and reducing CO₂ emissions. This ultimately is a requirement for all conventional coal-based power utilities on track to meet their greenhouse gas (GHG) cut targets by 2050. The paper offers a discussion of possible options as a function of sustainability principles, considering environmental, economic and social aspects of biomass use. In the case of EPBiH, the most beneficial would be waste woody biomass and energy crop co-firing on existing coal-based power plants, as suggested by biomass market analyses and associated technological studies. To assess the sustainability of the different biomass co-firing options, a multicriteria sustainability assessment (MSA) and single criteria analysis (SCA) were used. Four different options were considered, based on different ratios of biomass for co-firing: 0 wt%-reference case, and 5, 7 and 10 wt% of biomass. Both the MSA and the SCA confirmed that the option with the highest share of biomass is the most preferable one for the considered case. In addition to that, the CO₂ parameter proved to be a key sustainability indicator, effecting the most decision making with regard to preference of options from the point of sustainability. Following up on the results of the analyses, the long-term projection of biomass use in EPBiH has shown an increase in biomass utilization of up to 450,000 t/y in 2030 and beyond, with associated CO₂ cuts of up to 395,000 t/y. This resulted in a 4 % CO₂ cut achieved with biomass co-firing, compared to the 1990 CO₂ emission level. It should be noted that the proposed assessment model for biomass use may be applied to any conventional coal-based power utility as an option in contributing to meeting specific CO₂ cut targets, provided that the set of input data is available and reliable.     

Two‐Dimensional Calculation of the Parameters of a Steam‐Air Mixture in a Film‐Type Heat and Mass Exchanger

A mathematical model for twodimensional calculation of the temperature and density of the steam in a steamair mixture which rises between two water films flowing down adiabatic shields has been proposed. The parameters of the films have been calculated in a onedimensional approximation. The results of calculating the parameters of air according to the onedimensional and twodimensional models of the processes of heat and mass transfer have been compared. The range of applicability of the former to a filmtype heat and mass exchanger has been determined.     

Modeling of the Process of Electric‐Discharge Sintering of Metal Powders

Consideration has been given to the process of electricdischarge sintering (EDS) of a powder fill in passing an electric current through it. The dependences for calculation of the heat release, the efficiency of an EDS unit, the resistance of a powder fill, and the temperature in the contact zone have been obtained. An algorithm for calculation of the technological parameters of the process of EDS has been given.     

Modeling of Thermal Strains of Multilayer Shell‐Type Space Structures

A procedure of modeling of the stressedstrained state of largesize space structures is considered. Using the mirror of the concentrator of a solar power plant as an example, results of the modeling are shown.     

Modeling of the Temperature State of Large‐Size Space Structures

A procedure of modeling of the temperature state of largesize space structures is considered. Results of modeling of the temperature state of a truss structure, the reflector of a reflectortype aerial, and the concentrator of a solar power unit are reported.     

Stochastic Modeling of Impurity Motion and Scattering in the Mechanics of Turbulent Gas‐Dispersed Flows

Issues associated with the development and realization of stochastic models of the impurity particle motion and scattering in a turbulent flow are considered. The proposed model is used to calculate turbulent flows of a lowconcentration gas suspension in channels and jets. We compare the results of the calculations obtained from the viewpoint of different models and the results of numerical simulation with the data in which the influence of turbulent pulsations on the particle motion was ignored.     

Modification of a One‐Dimensional Lagrangian Grid for Modeling of Dynamic Processes in Pipelines of Variable Cross Section

Consideration is given to a mathematical model of the nonseparating nonstationary motion of an ideal compressible gas in a pipeline with a variable cross section. A method which enables one to calculate changes in the pressure, density, and the velocity at the sites of contraction and expansion of the pipeline without going beyond the scope of a onedimensional model is presented.     

A fuzzy‐neural approach for output projection in a semiconductor fabrication factory

Abstract

Output projection is a critical task for a semiconductor fabrication factory. There are two steps in output projection: predicting the output time for every job in the factory, and projecting the outputs into each period. For enhancing the effectiveness of output projection, a fuzzy‐neural approach is proposed in this study. Firstly, a fuzzy back propagation network (FBPN) is applied to generate fuzzy‐valued output time forecasts. Then, the fuzzy output projection function is proposed to project the outputs into each period. To evaluate the effectiveness of the proposed methodology and to make comparison with some traditional approaches, production simulation is also applied in this study to generate test data.