Mechanical Engineering Letters
Online ISSN : 2189-5236
ISSN-L : 2189-5236
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    2021 Volume 7 Pages 21-00048
    Published: 2021
    Released: March 18, 2021

    This paper presents numerical solution to a shape optimization for stationary fluid structure interactive fields. In the fluid structure interactive analysis, a weak coupled analysis is used to alternately analyze the governing equations of the flow field domain and the structural field considering geometrically nonlinear. A mean compliance minimization problem is formulated in order to achieve stiffness maximization on the structural field. Shape derivative, which means the sensitivity in the shape optimization problem, is derived theoretically by using the Lagrange multiplier method and adjoint variable method, and the formulae of the shape derivative with respect to domain variation of the distribution function. Reshaping is carried out by the H1 gradient method proposed as an approach to solving shape optimization problems. Numerical analysis program for the problem is developed by using FreeFEM, and validity of proposed method is confirmed by numerical results of 2D problems.

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  • Masanobu IIDA, Katsuhiro KIKUCHI
    2021 Volume 7 Pages 21-00006
    Published: 2021
    Released: June 12, 2021

    A one-dimensional theoretical analysis is made of the pressure field around a train running in a long tube with a constant width slit, which is a simplified model of partially enclosed structures (or vented tubes) of railway, such as snow shelters or whole covered stations. It is shown from field measurement results in Shinkansen that the pressure field produced in such partially enclosed structures exhibits a pattern of ‘a combination of single sawtooth and its reverse’. The present analysis of a tube with a slit reproduces this unique pressure pattern and shows that one-dimensional pressure field ahead of the train nose and tail can be expressed by elementary functions. It also reveals that the magnitude of the pressure change around the tail can exceed that around the nose, which is also a unique feature that is different from the cases of open air spaces and fully enclosed spaces (i.e., tunnels).

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    2021 Volume 7 Pages 21-00163
    Published: 2021
    Released: August 05, 2021

    In this study, we developed a method for obtaining high contributing part (reference point) to the response point at the operational condition by operational TPA (OTPA) using several measurement systems. OTPA calculates contribution of each reference point to the response point using only operational signals. All reference and response signals are necessary to be measured simultaneously by single measurement system because the method calculates the contribution using their correlation along time. However, this occasionally requires preparing large measurement system depending on the number of measurement points and the size of products. This may decrease the applicability of the method. We then considered a post processing procedure to obtain accurate contribution of each reference point to the response point by using several measurement systems instead of preparing large single measurement system. In the proposed method, all signals are measured using different several systems at around same timing. The exact sampling timing gaps among systems are estimated by using the estimation error between the calculated and actual measured response signal. After then, all reference signals compensated by the estimated time gap in each system are regarded to be measured simultaneously and contribution of all reference signals are calculated by OTPA. As the verification of the proposed method, the procedure was applied to a simple vehicle model. As the result, the contribution of the proposed method was similar with the contribution by single measurement system and clarified to have an ability to obtain correct contribution by several measurement systems.

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  • Younghwa CHO, Rahul BALE, Makoto TSUBOKURA, Nobuyuki OSHIMA
    2021 Volume 7 Pages 21-00136
    Published: 2021
    Released: September 10, 2021

    In this work, we propose a semi-implicit, density-based solver for compressible, evaporating particle-laden flow, and investigate its efficiency. It is established on a Cartesian-grid-based, scalable, numerical framework named CUBE. In this solver, the governing equation system is divided into three subsystems (compressible Navier-Stokes, species transport, and Lagrangian), and these subsystems are weakly coupled in two ways. In the Lagrangian domain, the fuel spray is treated as a set of discrete particles, and the particle-source-in-cell (PSI-Cell) method is employed for the coupling between the Eulerian and Lagrangian domains. Furthermore, the species transport and Lagrangian subsystems are subcycled with smaller time step, and the Navier-Stokes equation is temporally integrated with a larger step size. The proposed solver's verification and evaluation is conducted on the supercomputer Fugaku by comparing the results with those of the original, fully explicit solver where all equations have the same time step. The results show that this solver reduces the computational cost while ensuring similar accuracy. The solution of the proposed solver is consistent with that of the original solver. Finally, we brief our perspective on the future application of the proposed solver to our target problem: the large-scale simulation of evaporating particle-laden flow in a combustor of an aviation engine.

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