Tohru Hirano

Multi paradigm expert system architecture based upon the inverse design concept

The architecture consists of an inference engine, an analysis engine, a graphic engine, and a database management system. A multiparadigm expert-system architecture based on the inverse design concept is proposed. The iterative method for the solution of inverse problems, which is interpreted as a general design process, is implemented in a Prolog environment. This environment is used as a kernel of the architecture, which connects symbolic and numerical computation and realizes the automation of the design process. Functionally gradient material (FGM) design is considered as an example.<<ETX>>

Mathematical Modeling and Design

For the design of functionally gradient materials (FGMs), necessary material properties, such as thermal-expansion-coefficient and Youngs modulus in the specific region, are optimized by controlling the distribution profiles of composition and microstructures, as well as micropores in the materials. For this purpose, our research team employs the inverse design procedure in which both the basic material combination and the optimum profile of the composition and microstructures are determined with respect to the objective structural shape and the thermomechanical boundary conditions. Figure 1 shows the inverse design procedure for FGM, in which the final structure to be developed, as well as the boundary conditions, are specified first. After the fabrication method and an allowable material combination are selected from the FGM database, the estimation rules for the material properties of the intermediate compositions are determined based upon the micro-structure. Then, the temperature distribution and the thermal-stress distribution are calculated with the assumed profiles of the distribution functions for the constituents. Other possible combinations and different profiles are also investigated until the optimum is obtained.

Reversal of π-face selectivity in the Evans aldol reaction with fluoral: A computational study on the transition states using semiempirical calculations

Abstract Transition states for aldol reactions of boron enolate derived from N -acyloxazolidinone with acetaldehyde and fluoral were located by semiempirical molecular orbital calculation. For reaction with acetaldehyde, a chair transition structure was found, while two open transition structures were obtained with fluoral. The transition states reproduced the experimental results such that acetaldehyde and fluoral react preferentially on the re and si faces of the double bond of the boron enolate.

A DESIGN EXPERT SYSTEM FOR FUNCTIONALLY GRADIENT MATERIALS

Functionally Gradient Materials (FGM) is a novel material concept in which two different base materials, such as ceramics and metals, are compounded with gradually changing composition and microstructure so as to decrease the thermal stress induced by the high temperature difference within the thickness. In this paper, a design expert system for FGM is presented which encompasses the inverse design procedure. The system also incorporates a hierarchical optimization process which combines numerical optimization methods with heuristic controls. Besides, heuristic and theoretical approaches for estimating the effective material properties of the intermediate compositions are also explained. A design example for space plane applications is presented, and comparison with the experimental results of high temperature simulated environment is discussed.

Life prediction of CIP formed thrust chamber

Abstract The authors previously proposed a new fabrication method of closeout for a regeneratively cooled thrust chamber, the CIP (Cold Isostatic Pressing) forming method, by which a low stiffness closeout is easily obtained. In this study, sintered aluminum alloy was chosen as a porous closeout material which had relatively a lower Youngs modulus and a lighter weight. The forming conditions of the porous closeout and its elastic and plastic behaviors were investigated. Then the fatigue life of the high pressure chamber cooled by liquid hydrogen with the sintered aluminum alloy closeout was analyzed by means of nonlinear FEM (Finite Element Method). The results showed that the optimum design condition for a long-life rocket thrust chamber could be achieved with a low-stiffness closeout consisting of a CIP formed aluminum alloy layer with a porosity of 17% and a TFE (polytetrafluoroethylene) insulation layer with a thickness of 20 mm. The chamber with this low-stiffness closeout had a prolonged fatigue life three times longer than that of a conventional chamber with an electroformed nickel closeout.

Lattice Thermal Conduction across Disordered Interfaces.

Lattice thermal conduction across the disordered interfaces in multilayered materials has been studied. The model consists of an array of slabs of scattering centers (mass defects) embedded in a host material. The layered distribution of the mass defects can be characterized by the structure factor in the scattering probability due to the slabs. We assume that the physical arrangement of the scattering centers within a slab is quenched disorder and is approximately described by the structure factor of a homogeneous liquid interacting via hard sphere pair potentials. By varying the packing fraction of the scattering centers from low density to high density, the calculated thermal conductivity exhibits the minimum which reflects the local structural organization of the scattering centers. The relation to thermoelectric energy conversion has also been discussed.