1,170 research outputs found
A comparative institutional analysis for the auditing system of internal control in Japan
No full textRarefied gas flows through an in-line array of circular cylinders (Mathematical Analysis in Fluid and Gas Dynamics)
No full textオソイ キタイリュウ ニ タイスル ヒアッシュクセイ NAVIER STOKES ホウテイシキケイ ノ テキヨウセイ ニ ツイテ リュウタイ ト キタイ ノ スウガク カイセキ
No full textApplication of Taguchi Method in the Optimization of Swimming Capability for Robotic Fish
No full textIn this paper, we applied the Taguchi method to evaluate the maximum swimming speed of a robotic fish under the limitation of the output of the motor. Four factors were considered in the optimization: the caudal-fin aspect ratio, the caudal fin stiffness, the oscillating frequency and the stiffness of the spring that transmits forces from the actuators to the foil. Because of the power limitations, the parameter's space was irregular. Since the Taguchi method requires a regular parameter space, we divided the parameter space into a regular space and the remaining irregular spaces. Within only 25 trials, the frequency and the spring stiffness were determined as the main factors in the regular space by the orthogonal design. Six more trials were carried out in the remaining irregular space with a higher frequency and spring stiffness. The fastest swimming speed of 870 mm/s, approximately 2.6 BL (Body Lengths)/s, was acquired, when the frequency reached 12Hz and with infinite spring stiffness. This method is efficient for exploring the maximum locomotor capabilities of robotic fish and may also be useful for other robots as no modelling is required
Molecular dynamics study on Ar ion bombardment effects in amorphous SiO2 deposition processes
No full textM. Taguchi et al., Journal of Applied Physics 100, 123305 (2006) https://doi.org/10.1063/1.2401651Argon ion bombardment effects on growing amorphous Si O2 films during reactive sputtering deposition processes were examined based on molecular dynamics (MD) and Monte Carlo (MC) simulation techniques. The system we have considered here is a film that is subject to energetic Ar bombardment while it is formed by surface reactions of Si and O atoms separately supplied at low kinetic energies. It has been found that (1) Ar injections preferentially sputter O atoms from the surface over Si and (2) also have a compressing effect on the growing film during the deposition process. In other words, our MD/MC simulations have demonstrated at the atomic level that, with higher energy Ar injections, an amorphous Si O2 film grown in a reactive sputtering deposition process is denser and more Si rich. © 2006 American Institute of Physics
A generalized slip-flow theory for a slightly rarefied gas flow induced by discontinuous wall temperature
No full textA system of fluid-dynamic-type equations and their boundary conditions
derived from a system of the Boltzmann equation is of great importance in
kinetic theory when we are concerned with the motion of a slightly rarefied
gas. It offers an efficient alternative to solving the Boltzmann equation
directly and, more importantly, provides a clear picture of the flow structure
in the near-continuum regime. However, the applicability of the existing
slip-flow theory is limited to the case where both the boundary shape and the
kinetic boundary condition are smooth functions of the boundary coordinates,
which precludes, for example, the case where the kinetic boundary condition has
a jump discontinuity. In this paper, we discuss the motion of a slightly
rarefied gas caused by a discontinuous wall temperature in a simple two-surface
problem and illustrate how the existing theory can be extended. The discussion
is based on our recent paper [Taguchi and Tsuji, J. Fluid Mech. 897, A16
(2020)] supported by some preliminary numerical results for the newly
introduced kinetic boundary layer (the Knudsen zone), from which a source-sink
condition for the flow velocity is derived.Comment: 17 pages, 3 figure
Inverse Magnus effect in a rarefied gas
No full textThe transverse force exerted on a rotating sphere immersed in an otherwise
uniform flow of a rarefied gas is investigated based on the
Bhatnagar-Gross-Krook (BGK) model of the Boltzmann equation assuming the
Maxwell boundary condition on the sphere. In several existing studies, it has
been shown that the transverse force acting on the sphere, also known as the
Magnus force, has opposite signs in the free molecular and continuum flows. The
present study intends to clarify the force's transition in terms of the Knudsen
number (i.e., the reciprocal ratio of the sphere radius to the molecular mean
free path) with a particular interest in the impact of the sphere's surface
accommodation. It is found that the threshold of the Knudsen number, at which
the transverse force changes the sign, depends only weakly on the accommodation
coefficient, suggesting certain robustness in the threshold. The present study
is an extension of the previous work [S. Taguchi and T. Tsuji, J. Fluid. Mech.
933, A37 (2022)], in which the case of complete accommodation (diffuse
reflection) is exclusively considered.Comment: 22 pages, 2 figure
Asymptotic far-field behavior of macroscopic quantities in a problem of slow uniform rarefied gas flow past a sphere
No full textThe steady behavior of a low Mach number flow of a rarefied gas past a sphere is considered on the basis of the linearized Boltzmann equation with a special interest in the asymptotic behaviors of the flow velocity and temperature in the region far from the sphere. The study is motivated by the previous one [Taguchi, J. Fluid Mech. 774, 363 (2015)], in which an asymptotic analysis of the Boltzmann equation for small Mach numbers was carried out to derive the expression of the drag up to the second order of the Mach number. The derived expression contains two functions of the Knudsen number, corresponding to the leading-order drag obtained from the linearized problem and the second-order correction due to the weak nonlinear effect. This correction is also obtained through the analysis of the linearized problem; it is given by the factor of the term in the flow velocity whose magnitude is inversely proportional to the distance from the sphere and therefore vanishes at infinity. In this study, this factor (and thus the correction) is obtained for a wide range of the Knudsen number for the hard-sphere gas as well as for the ellipsoidal statistical (ES) model of the Boltzmann equation, under the conventional diffuse reflection boundary condition. The construction is based on the universal relation between the linear drag and the factor (correction). With the available data for the linear drag, this allows us to derive the latter from the former. For the ES model with the Prandtl number Pr=2/3, a series of additional numerical computations of the linearized problem is carried out to obtain the linear drag and then the correction. It is also shown that a factor occurring in the temperature, decaying in proportion to the inverse square of the distance from the sphere, is connected to the thermal force exerted on a sphere (thermophoresis), whose numerical values on the basis of the ES model are obtained as well
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