Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physreve.106.045109

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevE.106.045109/fulltext

Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physreve.104.025111

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevE.104.025111/fulltext

Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

DOI： 10.1016/j.jcis.2020.03.019

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Publishing type：Research paper (scientific journal)   Publisher：Cambridge University Press ({CUP})  

DOI： 10.1017/jfm.2018.16

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

In this study, the dynamics of a contact line passing a single defect, which was represented by a locally wettable part (whose static contact angle is less than the other part, namely, chemically heterogeneous and physically flat part), was analyzed using numerical simulations employing the front-tracking method and the generalized Navier boundary condition. We observed that the contact line was distorted with a logarithmic shape far from the defect; however, the distortion was dependent on the wall velocity. The apparent (averaged) dynamic contact angle of the wall with a defect was evaluated using a macroscopic energy balance. The apparent dynamic contact angles estimated from the energy balance agree well with the arithmetic averaged angles obtained from the present simulations. The macroscopic energy balance is useful to consider the effect of heterogeneity or roughness of the wall on the relation between the dynamic contact angle and contact line speed. Published by AIP Publishing.

DOI： 10.1063/1.4961490

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Language：English   Publisher：THE JAPANESE SOCIETY FOR MULTIPHASE FLOW  

Dynamic wetting of a solid sphere has been simulated numerically. We have developed the model for the description of the moving contact lines on curved solid surfaces by combining the GNBC-Front-tracking method and the immersed boundary method. The model was applied to the simulation of a quasi-static penetration of a water-repellent sphere into the water. As a result, the shape of the interface for different wettability is in good agreement with the previous experimental results. The residual bubble volume was evaluated under the different sphere size, static contact angle, and penetrating velocity conditions. The present results show a similar trend to the experimental and theoretical ones that the water-repellent sphere has a larger bubble since it incorporates more volume of air into the water, indicating the dynamic wetting of the sphere surface can be reproduced by the model.

DOI： 10.3811/jjmf.29.443

CiNii Books

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Other Link： https://jlc.jst.go.jp/DN/JLC/20022372701?from=CiNii

Language：English   Publisher：THE JAPANESE SOCIETY FOR MULTIPHASE FLOW  

Estimation of the contact angle on a moving contact line is one of the important factors for the prediction of the liquid surface geometry contacting with solid. In this study the dynamic contact angle on an accelerating vertical glass rod is investigated both experimentally and numerically to elucidate the effect of the acceleration of the contact line. The experiment was held by using ethylene-glycol and its aqueous solution as test fluid. The measured contact angle in the transient state clearly deviated from that for the steady state, depending on the acceleration of the rod. Numerical simulation shows that the acceleration and the gravity terms in the momentum equation, which are relatively remarkable in macroscopic scale, are not responsible for such deviation in the contact angle. Rather, the dependence of the microscopic contact angle on the acceleration, estimated with the viscous bending model, should be the primary factor on the deviation of the contact angle.

DOI： 10.3811/jjmf.29.421

CiNii Books

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Other Link： https://jlc.jst.go.jp/DN/JLC/20022372725?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Behavior of concentration interfaces, which are apparent interfaces between a suspension and pure liquid, was studied using numerical techniques. Two types of numerical simulations were used to classify whether collective or individual behavior occurred in the ratio of the average particle separation to the wavelength of the fastest growing perturbation. The first is Lagrangian tracking of individual particles in fluid, and the second type is interface tracking of two immiscible continuum phases. These two extremely different approaches represent the dual nature of the concentration interface: immiscible with no interfacial tension and miscible with no diffusion. These results reflect the experimentally-observed behavior of particles, which is both collective and individual. Sealing of the concentration interface by particle-induced flow is crucial to collective motion of suspended particles. A proposed dimensionless parameter describes quantitatively the transition from collective to individual settling of suspended particles. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijmultiphaseflow.2015.03.007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE INC  

Dynamic wetting behavior was investigated experimentally. First, the movement of a liquid column in a capillary tube was observed. Using the measured dynamic contact angles dependent on the contact line velocity, the solution of the modified Lucas-Washburn equation predicts the time variance of the liquid height in the capillary efficiently. Second, the dynamic contact angles were measured for a two-dimensional meniscus and an axisymmetric droplet to detect the influence of contact line curvature. The measured angles coincide well with each other for a two-dimensional meniscus and droplets of various radii. The dynamic wetting behavior is independent of the triple-phase contact line curvature. The dynamic contact angles measured in this study distribute widely from 10 degrees to 170 degrees. The results cannot be arranged by a single function of contact line velocity proposed by Hoffmann. It is suggested that the roughness or impurities on the solid surface could play an important role on the dynamic wetting behavior. (C) 2014 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.expthermflusci.2014.05.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

In this study, dynamic wetting phenomena in a capillary tube were studied by using numerical simulations based on the front-tracking method employing the generalized Navier boundary condition (GNBC) and by experimental measurements. For the GNBC, based on molecular dynamics simulations, the microscopic dynamic contact angle is estimated from the grid-scale contact angle using Cox's macroscopic-microscopic relation. The experimentally measured correlation between the apparent dynamic contact angle and the moving velocity of the contact line is well reproduced by the present simulation technique considering Cox's macroscopic-microscopic relation. Thus, we found that the dynamics of wetting are well described by combining molecular-scale behavior and macroscopic-microscopic relations. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijmultiphaseflow.2013.10.018

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The dynamic contact angle, the angle between the surfaces of the liquid and the solid at a moving contact line, is one of the primary conditions for the dynamics of the liquid surface confined by solid wall. It has been commonly modeled as a function of the velocity of the contact line relative to the solid surface under steady state condition. Some situations, such as the impact of a drop on a solid surface or sudden release of a contact line stuck on an edge of solid, however, involve a transient motion of the contact line, which would lead to a deviation of the dynamic contact angle from the steady one. In this study, dynamic contact angle for an accelerating or decelerating contact line advancing on glass surface is measured in two experimental systems different with other, i.e. one with a rapid meniscus formation after contact of a descending rod with the liquid surface, and the other with accelerating advance of liquid column in a circular tube. The experimental results revealed that the contact angle is increased with the (positive) acceleration of the contact line relative to the solid and vice versa. The critical condition for the appearance of the deviation of the contact angle brought with the acceleration is also discussed.

DOI： 10.1299/transjsme.2014fe0004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We propose a front-tracking method that considers a moving contact line with a generalized Navier boundary condition (GNBC) and with a delta function distribution approximated on the grid scale. A method of evaluating the interfacial balance at the contact line in the form of a body force, which is straightforward with the front-tracking method, cannot give a natural flow field. In contrast, the proposed method using the GNBC, which includes the unbalanced Young's force as stress on the wall, can give a very stable and reasonable flow field. The proposed front-tracking method was applied for the capillary rise of a liquid in a tube, in which the velocity-dependent contact angle dominates the dynamic characteristics. The validity of the proposed method was confirmed by comparing simulation results with experimental measurements and simple theoretical models. The results of the present simulations with adjusted non-dimensional slip parameters agreed very well with experimental measurements. Under the present simulation conditions, the linearity of the GNBC allows the correlation between the dynamic contact angle and the contact line's velocity to follow a simple linear expression that involves the difference of the cosine with the capillary number. The non-dimensional slip parameter, which represents the dynamic nature of the moving contact line, can therefore be easily adjusted to reproduce experimental observations under small-capillary-number conditions. (c) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijmultiphaseflow.2012.12.002

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Language：Japanese   Publishing type：Research paper (scientific journal)  

A drop actuation utilizing the wettability change by laser beam irradiation was studied by numerical simulations. The drop is actuated because surface tension force acts on the irradiated side more strongly in the wall parallel direction due to the smaller contact angle on that side. On the other hand, the temperature gradient due to laser irradiation causes surface tension gradient, then so-called Marangoni flow is caused. Each flow direction due to the wettability effect and the Marangoni effect is opposite. Those effects were evaluated by numerical simulations by a front-tracking method, which can properly evaluate the surface tension effect even on the solid surface and even with spatial gradient. As the results, we found that a simple model considering the macroscopic force balance could predict the moving condition due to wettability change fairly well although it could not predict the condition of movement caused by Marangoni effect. It is shown that the present numerical approach is very useful to predict such complex interfacial phenomena. ©2013 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaib.79.567

Scopus

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Language：Japanese  

DOI： 10.3811/jjmf.24.657

CiNii Books

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Language：Japanese   Publishing type：Research paper (scientific journal)  

For multiphase flow simulations, accurate evaluation of interfacial tension is an important issue, so a front-tracking method which tracks the interface explicitly by marker elements is expected to be very useful. In the front-tracking method, however, treating the elements in 3D space is very tedious. To eliminate this problem, a front-tracking method without connectivity called level contour reconstruction method (LCRM) has been developed. However, the volume conservation property of the method is not so good. In this study, three techniques in reconstruction process of the LCRM are proposed and evaluated for several curvature spheres. As the result, the proposed method shows very high volume conservation property even for 2-grid diameter sphere. And also shape of a single deformable bubble and merging of two bubbles are reasonably expressed. © 2011 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaib.77.237

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Language：Japanese   Publisher：The Visualization Society of Japan  

The defocus method enables the three-dimensional coordinates of particles to be measured using a single camera. By introducing a color camera and color filters to the conventional defocus system, the capabilities and performance of the defocus method are greatly enhanced. The proposed method, referred to as the color-defocus method, can process densely distributed particles, and compared to the conventional method, the depth of the measurable area is approximately double. The color-defocus method generates numerous sets of triangles, the vertexes of which are given by RGB particle images. The colored particle images are recorded separately on RGB planes, so that even overlapping particle images can be resolved. Using this method, separation of particle images and detection of triangular patterns become quick and easy. As a practical example, the flow induced by a spot vortex in a vessel is investigated.

DOI： 10.3154/tvsj.29.43

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

In the first part of this paper, sub-pixel displacement detection methods in particle image velocimetry (PIV) measurements were discussed. Some schemes for calculating the spatial gradient in a gradient method, which is one of sub-pixel displacement detection methods, were evaluated. It was found that the second order central finite difference scheme tends to underestimate the gradient of the tracer-particle's intensity. Consequently it leads to an overestimation of sub-pixel displacements. A first-frame upstream and second-frame downstream finite difference scheme was then proposed and evaluated for one-dimensional flow measurements. Furthermore, the proposed difference scheme was extended to apply to two-dimensional flows. It was shown that taking the direction of the sub-pixel correction into account and using fewer adjacent pixels are important for PIV images consisting of small tracer particle images. Finally, a robust procedure for the execution of the gradient method was proposed, which can eliminate the effect of noises. It was found that the proposed scheme is not only highly accurate but is highly robust to noise.

DOI： 10.1007/s00348-008-0591-4

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

In this paper, we present a front-tracking method containing an accurate representation of solid surface condition, and simulate a drop sliding down an inclined plate employing some slip models. Numerical results are compared with experimental observations by Le Grand et al. (Journal of Fluid Mechanics, 2005), and then which slip model is well-suited is examined. Drop shapes, in particular advancing and receding contact angles, and drop velocity reproduced by our simulations without explicit slip model are qualitatively good agreement with experimental observations for capillary number Ca<0.01.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

An implicit interface method and a level contour reconstruction method (LCRM) are coupled for stable simulation of multiphase flow largely affected by surface tension. For surface tension evaluation, three representations, namely, basic phase indicator function for interface tracking, surface element, and reconstructed indicator function by the LCRM, are combined in four ways. By a drop simulation under the condition of non-gravity and inviscid, the four proposed evaluation methods are compared and evaluated. By the method using the curvature calculated by the surface elements and the gradient of the reconstructed indicator function, rotation of surface tension force acts to suppress development of parasitic currents in connection with production of curvature gradient by small shape change. Thus, by this method, stable flow field can be obtained within the characteristic time scale. Furthermore, numerical results show that the proposed method can reproduce the stable flow field containing an air bubble in oil with large effect of surface tension.

DOI： 10.1299/kikaib.75.758_2003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Holography technique can be used for 3D measurement of particle positions. However, in general in-line holography, accurate determination of the object's position in the optical axis direction is difficult. In order to overcome this defect, we proposed a two-views recording technique combined with a digital in-line holography. The two-views recording is executed by only one camera with the assistance of one mirror, capturing the real image of a particle and the mirror image of the same particle simultaneously. This method keeps simplicity of optical alignment and is free from a difficult calibration of multiple cameras. It was confirmed that the proposed technique can reduce the uncertainty in the depth direction to about 1 pixel. For application of this method to micro-PIV, magnified recording is desired. In this paper, magnified holograms were also taken through a lens. It was confirmed that the uncertainty in the optical-axis direction can be reduced to a few pixels by the proposed technique for the magnified holograms.

DOI： 10.1007/s00348-008-0501-9

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

In this study, a front-tracking (FT) method combined with a solver for the interfacial transport of surfactant is proposed to analyze interfacial flows affected by contamination. Because the interfaces are expressed explicitly in the FT method, the advection-diffusion equation on the interface can be treated easily and can be solved with high accuracy. In this study, a scheme that completely conserves the total amount of surfactant was constructed. Numerical simulations of a water drop sinking in silicone oil were performed, taking into account the Marangoni effect caused by concentrations. The effects of three parameters—a damping coefficient of interfacial tension, a diffusion coefficient, and the total amount of surfactant—were evaluated. Calculated results were compared with experimental results and were in very good agreement with variables including the stagnant cap size, the flow separation point, and the peak of shear stress. We can therefore expect that our simulations can estimate the conditions of surfactant at the interfaces.

DOI： 10.1299/jcst.2.246

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Language：English   Publisher：The Japanese Society for Experimental Mechanics  

In order to develop a simulation method that can treat flows containing various multi-components as one fluid system, we propose a model which can represent the relation of interfacial tensions on three phase contact line faithfully. Our model is based on a front-tacking method. By comparing some schemes of interfacial tension representation, we found that three-point finite difference without extrapolation can represent the curvature and static balance of tension among interfaces very accurately. Then we performed a drop spreading on a solid surface by the proposed model and dynamic contact angles were represented.

DOI： 10.11395/jjsem.8.s43

CiNii Books

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Other Link： https://jlc.jst.go.jp/DN/JALC/00352687218?from=CiNii

Grant-in-Aid for Encouragement of Young Scientists

DOI： 10.3811/pmfr.2.165

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

In this study, a front-tracking (FT) method combined with a solver of interfacial transport of surfactant was proposed in order to resolve interfacial flows affected by contamination. In the FT method, because the interfaces are presented explicitly, advection-diffusion equation on the interface can be easily treated and can be solved highly accurately. In this study, a scheme which conserves the total amount of surfactant completely was constructed. Numerical simulations of a water drop sinking in silicone oil were performed taking the Marangoni effect into account. The effects of three parameters, a damping coefficient of interfacial tension, a diffusion coefficient and a total amount of surfactant, were evaluated. Calculated results were compared with PTV measurement results and were in very good agreement with them on the points of stagnant cap size, flow separation point, peak of shear stress and so on. So, we can expect that our simulations can estimate the conditions of surfactant on the interfaces, which is very difficult to be measured.

DOI： 10.1299/kikaib.72.1913

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

Some calculation schemes of spatial gradient for the spatio-temporal derivative method, which was used for sub-pixel displacement detection in PIV measurements, were evaluated. It was found that the second-order central finite difference scheme tends to underestimate the gradient of tracer-particle's intensity, so that it leads to overestimation of sub-pixel displacements. In this study, a combined upstream and downstream finite difference scheme was proposed and evaluated for one-dimensional flow measurements. Furthermore, the proposed scheme was modified for two-dimensional flow. Two important things for small tracer particle PIV images were shown: 1) the direction of the sub-pixel correction should be taken into account, 2) distant pixels should not be used. It was found that the proposed scheme has high accuracy even if images contain some noises.

DOI： 10.1299/kikaib.70.1703

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOS PRESS  

A new high-speed super-resolution PIV was proposed using characteristic pixel selection to accelerate the successive abandonment (SA) with recursive window subdivision. The performance and applicability of the proposed PIV were evaluated. In the SA calculation with the characteristic pixel selection, 1000 candidates are narrowed down to only one at over 50% of the measurement points, and the number of error vectors is reduced because the difference between the cumulative intensities of a correct candidate and of other ones becomes clear due to the characteristics of selected pixels. In all recursive processes, error checks are carefully performed using the summation of the distribution of the cumulative intensity difference distribution, which is suitable for the SA method. In a comparison of the time per velocity vector, the present super-resolution PIV was shown to be 10 times faster than the former ordinary resolution PIV. Another feature of the present super resolution PIV is that the velocity vectors are obtained in the region very close to the image boundaries and masked regions by using the recursive algorithm.

DOI： 10.1007/BF03181467

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

The interaction between a turbulent gas flow and particle motion was investigated by numerical simulations of gas-particle turbulent downward flow in a vertical channel. In particular the effect of inter-particle collision on the two-phase flow field was investigated. The gas flow field was obtained by large-eddy simulation (LES). Particles were treated by a Lagrangian method, with inter-particle collisions calculated by a deterministic method. The spatial resolution for LES of gas-solid two-phase turbulent flow was examined and relations between grid resolution and Stokes number are presented. Profiles of particle mean velocity, particle wall-normal fluctuation velocity and number density are flattened as a result of inter-particle collisions and these results are in good agreement with experimental measurements. Calculated turbulence attenuation by particles agrees well with experimental measurements for small Stokes numbers, but not for large Stokes number particle. The shape and scale of particle concentrations calculated considering inter-particle collision are in good agreement with experimental observations.

DOI： 10.1017/S0022112001005092

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Language：English   Publisher：Japan Society of Civil Engineers  

High-resolution videographic P. I. V. is applied to measure cross-stream velocity components at 15 Hz and 1 Hz in the lower half of a smooth-bed open channel flow at <I>Re*=u*d /v</I>= 300 (where <I>d</I> is the flow depth of 10.0 cm). We emphasize analysis of the quantity <I>Q<SUB>x</SUB>=(ω<SUB>x</SUB><SUP>2</SUP>-S<SUB>x</SUB><SUP>2</SUP>)/2</I> (ω<SUB>x</SUB>: streamwise vorticity, <I>S<SUB>x</SUB></I>: rate of strain in the cross-stream plane) which expresses the relative strength of rotational and straining motion in the illuminated plane. Instantaneous flow fields, confirmed by two-point correlations, show that regions of negative <I>Q<SUB>x</SUB></I>lie above, below, or beside regions of strongly positive <I>Q<SUB>x</SUB></I>.Isosurfaces of a suitably conditioned spatio-temporal correlation of <I>Q<SUB>x</SUB></I>reveals a tilt and inclination of streamwise vortices ("SV") which agrees substantially with previous results from DNS [e.g. Stretch (1990), Jeong at al.(1997)], and suggest a consistent lattice-type spatial relationship with neighboring SV.

DOI： 10.2208/prohe.45.523

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER  

Illuminating in a quasi-cross-stream plane of an open channel flow of water at low Re and injecting fluorescene dye from a bed slit, mushroom patterns reliably inferred to result from counter-rotating streamwise vortices are found to be typically oriented at some 30 degrees from the cross-stream vertical. PIV in the cross-stream plane shows that the averaged held, and two-point correlation, of the quantity
[GRAPHICS]
exhibit preferred directions in the cross-stream plane at about 45 degrees to the vertical. Spatio-temporal measurements of streamwise vorticity provide direct experimental evidence, possibly the first, for the staggered arrangement of streamwise vortices previously educed from DNS data.

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DOI： 10.1299/kikaib.65.1878

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DOI： 10.1299/kikaib.65.490

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/kikaib.65.166

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/cite.330701007

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Venue：オンライン  

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Venue：オンライン  

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Venue：静岡大学（オンライン）  

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Venue：静岡大学（オンライン）  

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Venue：静岡大学（オンライン）  

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Venue：静岡大学（オンライン）  

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Venue：同志社大学  

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Venue：北海道大学  

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Venue：北海道大学  

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Venue：北海道大学  

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Venue：北海道大学  

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Venue：福岡大学  

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Venue：北見工業大学  

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