Mechanical Engineering Letters
Online ISSN : 2189-5236
ISSN-L : 2189-5236
Volume 2
Showing 1-32 articles out of 32 articles from the selected issue
  • Farhana MOHD FOUDZI, Ikuo IHARA
    2016 Volume 2 Pages 15-00727
    Published: 2016
    Released: January 08, 2016
    JOURNAL FREE ACCESS
    Ultrasonic waveguides have been widely used for material characterizations, flaw detections and health monitoring by ultrasonic pulse-echo methods. Although a clad waveguide consisting of a core rod and a cladding layer has been expected to be the most promising waveguide for practical applications, little is known about an appropriate material combination for the cladding and core. In this work, numerical simulations are performed to investigate an optimum combination of the materials for the cladding and core of a clad waveguide. Wave propagations are examined for a series of clad waveguides having different combinations of material properties using a two-dimensional finite different analysis. In the analysis, steel is used as the core material, and the density and ultrasonic wave velocity of the cladding material are systematically changed, and the signal-to-noise ratios (SNRs) of ultrasonic pulse waves propagating through the clad waveguides are estimated. It is found that the SNR changes drastically with the material combination for the cladding and core and the highest SNR is appeared when the velocity and density of the cladding are approximately 120% and 70% of the core, respectively. It should be noted that an appropriate SNR is obtained when the velocity of cladding is approximately 110% of the core regardless of the density value of the cladding on the condition that the density value is within the range from 75% to 150% of the core. This fact obtained here could be useful for designing desirable ultrasonic clad waveguides used for practical applications.
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  • Hirofumi HIDAI, Souta MATUSAKA, Akira CHIBA, Noboru MORITA
    2016 Volume 2 Pages 15-00686
    Published: 2016
    Released: January 14, 2016
    JOURNAL FREE ACCESS
    There have been many investigations into the changes in the properties of transparent materials, e.g. optical, physical and chemical properties, induced by focused ultrafast laser beams. In this letter, we report the modification of borosilicate glass using an ultraviolet nanosecond laser. A laser beam operating at a wavelength of 266 nm was focused inside the glass. Interestingly, although penetration depth of the laser beam was only 110 μm, emission was observed in the glass at the depth of approximately 1100 μm after several laser shots. The emission moved toward the light source with further laser illumination, and modification of the glass along the trajectory of the emission was observed. The modified area became deeper with increasing focusing depth. The deepest modified area was located at a depth of approximately 1800 μm. No clear dependence of the modification on the pulse repetition rate was found; therefore, heat accumulation was not prominent in the modification process. The subsequent etching rate of the modified area was faster than that of the unmodified area. The etching rate in aqueous KOH was 60 μm/h where continuous modification was obtained. A microchannel with a depth of approximately 400 μm and a diameter of approximately 30 μm was formed after 10 h etching.
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  • Toshiharu KAZAMA
    2016 Volume 2 Pages 15-00699
    Published: 2016
    Released: January 14, 2016
    JOURNAL FREE ACCESS
    The possibility of improving the static characteristics of hydrodynamic bearings using the inverse viscosity-temperature relations of liquid lubricants is theoretically examined. A simplified model that comprises the Reynolds equation with a change in the mean oil viscosity across the film as a function of temperature and that is based on the thermal lubrication theory is applied. The solutions are numerically obtained for linear sliding bearings, tapered land bearings, and cosine pad bearings, wherein the temperature distributions are given as known values and the viscosity distributions are determined beforehand. The bearing geometry and temperature profiles are selected as parameters. When the temperature in the converged region close to the minimum clearance is low, the fluid pressure becomes larger; thus, the friction coefficient becomes smaller, whereas the leakage flow rate changes slightly. This behavior may contribute to improving the static characteristics of hydrodynamic bearings.
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  • Fumiyoshi YOSHINAKA, Takashi NAKAMURA
    2016 Volume 2 Pages 15-00730
    Published: 2016
    Released: January 25, 2016
    JOURNAL FREE ACCESS
    Fatigue cracks often initiate inside materials in the very high cycle region (VHCF), although they always initiate at the surface of materials in usual high cycle fatigue. However, the mechanism behind internal crack propagation is not yet clear due to difficulties in observation. The environment inside internal cracks is likely similar to a vacuum environment since it is shut off from air, leading to negligible effect of oxidation or gas absorption. In the present work, the effect of vacuum on fatigue fracture surfaces of high strength steel SNCM439 was investigated quantitatively to estimate the effect of the vacuum-like environment inside the internal crack on the crack propagation process. Uniaxial fatigue tests were carried out in vacuum and air environments and then 3D fractography was performed to measure surface roughness of the fracture surface. These analyses targeted three typical fracture surfaces: (a) surface fracture in air, (b) surface fracture in vacuum, and (c) subsurface fracture. Results of fatigue tests showed that fatigue lives were longer in vacuum than in air. Fracture surface roughness of surface fracture in air was greater than that in vacuum, while fracture surface roughness of subsurface fracture agreed quite well with that of surface fracture in vacuum. These results indicate that the effects of vacuum environment and the environment inside internal crack on fatigue crack propagation are almost the same. This leads us to conclude that the behavior of internal crack propagation can probably be estimated from surface crack propagation in vacuum environment.
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  • Keiichiro YOSHIDA
    2016 Volume 2 Pages 15-00484
    Published: 2016
    Released: February 03, 2016
    JOURNAL FREE ACCESS
    This study numerically investigates mechanisms of NOx reduction when pure NO is injected into a diesel engine intake. In a previous experiment, emissions were reduced successfully with NO concentrations above 600 ppm at the intake. However, the NOx suppression was significantly smaller when premixed NO concentrations were 600 ppm or below. To explain these observations, the contributions of active species O, OH, H, and N to the production of thermal NO were estimated numerically. First, the equilibrium concentrations of CO2, CO, H2O, H2, O2, O, OH, H, and N2 in flames with various equivalence ratios were calculated. The concentrations of quasi-steady-state N and the NO production rate were then calculated based on the active species concentrations. The analysis shows that the reduced NO suppression at lower premixed NO concentration is primarily due to the role of N changing from production to decomposition of NO in fuel-rich regions when the NO concentration exceeds around 1200 ppm.
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  • Shota UEDA, Hiroshi MADOKORO, Byeongnam JO, Masahiro KONDO, Nejdet ERK ...
    2016 Volume 2 Pages 16-00056
    Published: 2016
    Released: March 01, 2016
    JOURNAL FREE ACCESS
    The liquefaction and relocation of control rods at temperatures over 1200 °C due to the eutectic reaction between boron carbide and stainless steel are important phenomena for the clarification of the Fukushima Daiichi Nuclear Power Plant accident. However, the mechanism and behavior of these phenomena have not yet been understood completely. The time-resolved visualization of the dynamic and unsteady characteristics of the eutectic reaction might provide important insights into the various phenomena occurring in a time sequence. Therefore, this study employed a time-resolved visualization technique under high-temperature conditions to analyze the eutectic reaction between boron carbide and stainless steel. Among the many heating methods available, radiative heating was chosen because it facilitates clear visualization. The main problems that made this visualization difficult were the large thermal expansion, reflected light from heaters, and change in the specimen geometry due to the reaction. These problems were solved by employing novel and simple techniques. In this study, experiments were performed at different temperatures using different specimens to confirm the effectiveness of the developed technique. The maximum temperature used in the experiments was 1250 °C. Clear images were recorded. It was observed that the change in the specimen geometry affected the melt behavior. The developed technique was effective in acquiring geometrical information on dynamic phenomena at high temperatures. The technique may provide a potential data set for the validation of numerical simulations.
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  • Naoki MORITA, Kazuo YONEKURA, Ichiro YASUZUMI, Mitsuyoshi TSUNORI, Gak ...
    2016 Volume 2 Pages 16-00082
    Published: 2016
    Released: March 03, 2016
    JOURNAL FREE ACCESS
    Structural elements which have 6 degrees of freedom (DOFs) at each node, such as shell and beam elements, are widely used in structural analysis. A matrix originating from finite element method (FEM) is stored in some sparse matrix storage format with a suitable block size for the number of DOFs at each node. When both 6 DOF structural elements and general 3 DOF solid elements are employed, the sparse matrix storage format becomes complicated due to combination of different block sizes. High computational efficiency of finite element analysis has become more important in large-scale structural problems. The complicated storage format leads to deterioration of computing performance in solving linear equations by an iterative procedure, conjugate gradient (CG) iterations for example. A computational technique is required that allows us to use existing parallel linear solvers without deteriorating the performance for solving linear equation systems originating from combination of solid and structural elements. This research aims to develop 3×3 DOF blocking structural elements to enhance the computational intensity of iterative linear solver, such as the CG method. As numerical results, the proposed 3×3 DOF blocking elements have shown better performance for each CG iteration than the conventional structural elements. The computational efficiencies are 95.0% with single thread execution and 76.6% with 8-thread execution of a theoretical peak performance based on the STREAM benchmark.
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  • Lijun LIU, Masao OGINO
    2016 Volume 2 Pages 16-00119
    Published: 2016
    Released: March 03, 2016
    JOURNAL FREE ACCESS
    Numerical simulations such as finite element analyses have increased in size thanks to the explosive development of computer technology. However, large amount of data produced by large scale analysis leads to I/O bottlenecks in simulation, data processing and visualization at the same time. To alleviate this problem, we propose to employ JHPCN-DF technique to large scale finite element analysis for providing a powerful way of data compression. To reduce the quantity of transmission data which is used for further analyses and visualizations, we investigate the possibility of post calculations on local computers and evaluate the precision of post-run results which are calculated by JHPCN-DF encoded data. Over our numerical results, JHPCN-DF performs significantly better than the generic zlib compressor and obtained compression rate of 0.83 with a user defined allowed error ε of 10-2 and 0.68 with ε of 10-4. Our results also indicated that the post-run data calculated by reconstructed data with ε lower than 10-4 achieves almost same level of precision with the one calculated by original data.
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  • Satoshi KADOWAKI, Ryutaro NUMATA, Yusuke HASHIMOTO, Toshiyuki KATSUMI
    2016 Volume 2 Pages 16-00170
    Published: 2016
    Released: March 17, 2016
    JOURNAL FREE ACCESS
    Oxy-fuel combustion of methane in small scales was handled to investigate micro counterflow diffusion flames. We observed methane-oxygen diffusion flames in counterflow burners where the burner distance was less than 1 mm, and obtained the flame thickness and flame diameter as functions of the burner distance, inner diameter and gas flow rate. When burners with large inner diameter were used, counterflow diffusion flames were observed in small burner distance, and the flame thickness and flame diameter were large under the same conditions of burner distance and gas flow rate. The flame thickness and flame diameter decreased as the burner distance became smaller, and they increased as the gas flow rate became larger. Moreover, the flame stretch rate had a great influence on the flame thickness. As the flame stretch rate became larger, the flame thickness decreased monotonously, which depended on the inner diameter and gas flow rate. To scrutinize the dependence of flame thickness on the flame stretch rate, we normalized the flame thickness by the inner diameter and the average velocity of methane. We confirmed that the normalized flame thickness depended only on the flame stretch rate.
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  • Ryotaro SAKAMOTO, Hiroaki TANAKA, Yoshiro OGI
    2016 Volume 2 Pages 16-00042
    Published: 2016
    Released: March 23, 2016
    JOURNAL FREE ACCESS
    In this study, a method of improving the positioning accuracy of deployable space structures was developed and its effectiveness demonstrated. When a space structure expands, friction is generated at the joints between different parts. This friction has adverse effects on the positioning accuracy and produces deviations from the expected position during operation. To achieve high positioning accuracy, it is necessary to not only minimize the friction at the joint but also correct the deviation after it occurs. We apply vibration produced by a macro fiber composite (MFC) actuator to correct the deviation caused by friction. A portion of the structure including the joint is simulated by a simple beam and a ball bearing joint. In the results of our experiments, we observed the effect of applying vibration on the correction of deviations. We also determined the effective vibration based on the natural frequency of the beam and the necessary vibration duration. This method may contribute to improving the accuracy of deployment operations.
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  • Shoko ARITA, Yasuyuki MIYAZAKI
    2016 Volume 2 Pages 15-00677
    Published: 2016
    Released: March 31, 2016
    JOURNAL FREE ACCESS
    Technology of deployable space structures is necessary for spacecraft to challenge advanced missions. It is important in designing the deployable space structures that they are easily deployable and reliably repeatable. Traditional approach for improving the repeatability was conducted by investigating errors and its effect to the deployment. However, the traditional approach has a problem that results change depending on estimation of the errors. With that background, this study proposes numerical methods to enable selection of robust deployable structures against the errors. The repeatability is decreased due to occurrence of the buckling caused by the errors. Therefore, a structure not occurring the buckling should be selected for designing of a reliably repeatable structure. The buckling is detected by non-positive eigenvalues of a stiffness matrix of the structure in static analysis. However, detection of the buckling in dynamic analysis is difficult because the eigenvalue is also non-positive when the structure has rigid-body motion. This study solved the problem by proposing a method to discriminate the buckling from the rigid-body motion. Furthermore, a method to evaluate instability of the structure quantitatively is desired when only structures occurring the buckling are available for the spacecraft. When the buckling occurs, small disturbance sets off grave displacement. Therefore, this study proposed the method to evaluate the instability quantitatively by calculating disturbance force and buckling displacement as index values of the instability based on the equation of motion. Finally, it was confirmed that the proposed methods are appropriate by the dynamic analyses of truss arch.
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  • Hideya ANZAI, Ryo ISHIBASHI, Masumi SAKA
    2016 Volume 2 Pages 15-00632
    Published: 2016
    Released: April 14, 2016
    JOURNAL FREE ACCESS
    To establish an evaluation technique for oxide film thickness in-situ, the applicability of a four-point-probe direct current potential drop method is discussed in this study. Several samples of JIS SUS316L stainless steel with different oxide film thickness were prepared after immersing them in oxygenated pure water at 288°C for different periods. The oxide film thickness was measured by cross sectional observation using a transmission electron microscope. Potential drop on the oxide surface was measured every second during an acquisition period of about 20 s while a constant current was being injected into the sample simultaneously. This kind of measurement was repeatedly carried out at several arbitrary contact positions on the surface of the same sample. The measurement results showed that the potential drop slightly changed during the acquisition period and the tendency varied at the different contact positions. Multiple measurements at different contact positions revealed that the tendency could be categorized into two general types: the decreasing potential drop and the increasing potential drop, defined by the overall trend of the potential drop during the acquisition time. It was found that the ratio of contact positions with a decreasing potential drop tendency to all the contact positions of measurement tended to increase as applied current increased. This tendency depended on the oxide film thickness. The threshold value of applied current was found to correlate well with the oxide film thickness when the occurrence rate of decreasing potential drop ranged from 70 to 90% showing the best correlation at 70%.
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  • Nobuyuki OSHIMA
    2016 Volume 2 Pages 16-00220
    Published: 2016
    Released: April 21, 2016
    JOURNAL FREE ACCESS
    This paper investigates a relation between the scalar conservation equation and the level-set equation based on Liu's local interface speed model for a premixed combustion flame. A new model formulation is introduced for the source term of the conservation equation in three-dimensional interface phenomena, which gives the solution of the level-set equation coupled with a re-initialization procedure for the physical interface problems governed by conservation law. It may be an extensional formulation for a diffusive solution of the level-set equation.
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  • Daisuke YAMAUCHI, Byeongnam JO, Nejdet ERKAN, Shinji TAKAHASHI, Wataru ...
    2016 Volume 2 Pages 16-00092
    Published: 2016
    Released: May 17, 2016
    JOURNAL FREE ACCESS
    This study aimed to verify the characteristics of thermal stratification induced by direct contact condensation using a 1/20-scale suppression pool of the Fukushima Daiichi nuclear power plants. A blow-down nozzle was used to inject steam into the toroidal suppression pool. Vertical temperature profiles were measured by vertically aligned thermocouples at eight positions along the circumferential direction. Flow patterns in the suppression pool were obtained using particle image velocimetry (PIV). Vertical velocity profiles were obtained every 30 min. Results showed that thermal stratification was reproduced in the scaled-down suppression pool. PIV analysis showed that two primary flows existed in the suppression pool and that the interface between the moving part and the stationary part moved according to thermal stratification development. The flow patterns obtained in this study were compared with those of our previous study using a two dimensional suppression pool.
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  • Sho KANO, Akira OBA, Huilong YANG, Yoshitaka MATSUKAWA, Yuhki SATOH, H ...
    2016 Volume 2 Pages 15-00481
    Published: 2016
    Released: May 20, 2016
    JOURNAL FREE ACCESS
    High-Cr steel (Fe-8Cr-2W-0.4Mn-0.2V-0.06Ta, so-called F82H steel) is one of the candidate structure materials for fusion blanket system, and its dissimilar welding technology to stainless steel (SUS316L) is an inevitable issue. Fiber laser welding is a promising technique to joint F82H and SUS materials, because of its non-mandatory vacuum environment during welding, and the reduced distortion and residual stress. Purpose of the present study is to identify the microstructure characteristics of dissimilar joint between F82H and SUS316L fabricated by fiber laser welding. M23C6-type precipitates were evaluated using an electron back-scatter diffraction device equipped with a scanning electron microscope, an electron probe micro analyzer, and a transmission electron microscope. The microstructure of as-welded specimens was composed of heat affected zone (coarse grain (CGHAZ) and fine grain (FGHAZ)) in F82H side, and weld metal (WM). Distributions of size, density and chemical composition of precipitates in HAZ were examined as a function of the distance from WM/HAZ interface. Besides, isochronal annealing experiments on F82H performed to obtain relationship between annealing temperature and Cr (or C) concentration in M23C6 precipitates. Cr-rich M23C6 comparing with original F82H (tempered F82H) one was observed at temperature ranging from 1103 to 1173 K. By comparison of their microstructure with that of HAZ, temperature distribution in HAZ upon welding was evaluated. It is suggested that the HAZ/F82H interface and the FGHAZ/CGHAZ boundary were heated up to 1150 K and 1400 K, respectively. Further applications of this method to clarify the temperature history and its distribution in HAZ, as well as increase in diagnostic accuracy, are greatly expected.
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  • Takashi NAKAMURA, Fumiyoshi YOSHINAKA, Shinya NAKAYAMA, Hiroyuki OGUMA ...
    2016 Volume 2 Pages 16-00233
    Published: 2016
    Released: May 23, 2016
    JOURNAL FREE ACCESS
    The purpose of this study is to develop a method for detecting small internal fatigue cracks in Ti-6Al-4V by using synchrotron radiation provided at SPring-8. An electro-hydraulic fatigue testing machine was carried into the facility and a combination of uniaxial fatigue tests and micro computed tomography (μCT) imagings were conducted. The small specimen without size effect was newly designed for μCT imaging. The conditions of the fatigue tests were determined to observe internal crack initiations within the available time at the facility. To obtain a clear and accurate image of internal cracks, several important parameters for μCT imaging such as the crack opening load, the distance between detector and specimen, were optimized. As a result, multiple internal fatigue cracks sized around 30 μm or below were successfully detected.
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  • Gai KUBO, Tetsuya MATSUDA
    2016 Volume 2 Pages 16-00248
    Published: 2016
    Released: May 26, 2016
    JOURNAL FREE ACCESS
    In this study, a multiscale damage analysis of plain-woven laminates with laminate misalignment is conducted based on the homogenization theory for misaligned internal structures developed by the authors. For this, the homogenization theory is reconstructed for plain-woven laminates with arbitrary laminate misalignment in two directions using a novel boundary condition for unit cell analysis. The Hoffman's failure criterion is then introduced into the theory to determine the failure of fiber bundles and a matrix material, and the damage modes. The damages are expressed as reduction of stiffness according to the damage modes. The present method can efficiently analyze the macroscopic strength and the microscopic damage development of plain-woven laminates with arbitrary laminate misalignment using only one unit cell. This method is then applied to the damage analysis of plain-woven E-glass/vinylester laminates with 13 cases of laminate misalignment including the non-misaligned case under on-axis uniaxial tension. It is shown that the laminate misalignment noticeably affects the macroscopic strength of the laminates, which is attributable to the difference in the microscopic damage development in the laminates depending on the misalignment.
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  • Yuki HAYASHI, Siddharth LOKACHARI, Satoshi YAMAGISHI, Masakazu OKAZAKI
    2016 Volume 2 Pages 16-00240
    Published: 2016
    Released: May 31, 2016
    JOURNAL FREE ACCESS
    More recently a new type of damage has been pronounced in thermal barrier coatings (TBCs) by calcium-magnesium-alumino-silicates (CMAS) from ingestion of siliceous minerals under certain operating conditions. In order to understand material aspect of CMAS damage, a study on material interaction between molten CMAS and yttria-stabilized zirconia (YSZ) was carried out by using a single crystal YSZ material and a synthetic CMAS product in this work. Here the effect of crystallographic orientation on the interaction was also investigated. The CMAS-covered single crystal bulk YSZ specimens were isothermally exposed at high temperature. The experimental works clearly showed that interaction between the molten CMAS and YSZ was significant resulting in the change in microstructural morphology and composition of YSZ. The extent of interaction between CMAS and YSZ depended on the crystallographic plane of the YSZ: it was the lowest in the {111} crystallographic plane.
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  • Hiroto IKADAI, Yasuhiro KIMURA, Masumi SAKA
    2016 Volume 2 Pages 15-00714
    Published: 2016
    Released: June 08, 2016
    JOURNAL FREE ACCESS
    The influencing factors associated with the temperature dependence of electromigration (EM) damage are discussed. EM is the atomic diffusion in a metal line when the line is stressed with high current density and causes EM damage called voids and hillocks. Voids are the depletion of the metal atoms and lead to breaking of the lines. Hillocks are the accumulation of the metal atoms and cause short circuits. Passivation covering the metal lines has been used as one of the ways to prevent EM damage because it constrains the formation of hillocks and voids at the same time owing to the conservation of mass. The passivation characteristics such as hardness affect the ability to inhibit EM damage. EM damage is significantly affected by temperature, and to reveal the relation of the passivation hardness with temperature contributes to improving EM reliability. In addition, other factors are thought to affect the temperature dependence of EM damage. In the present paper, we investigate the temperature dependence of EM damage measured by means of threshold length product and clarify several factors affecting the temperature dependence of EM damage. A tetraethyl orthosilicate layer is used as passivation on a conventional Al line-type structure sample. Through the experiments, we demonstrate that EM damage can be prevented much more by decreasing temperature and the increase of the passivation hardness with decreasing temperature is assumed to have an influence on the ability of passivation to prevent EM damage. We also discuss the effective bulk modulus and the electrical resistivity of Al as the factors affecting the temperature dependence of EM damage.
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  • Shusuke AKIMOTO, Naoki TAKANO
    2016 Volume 2 Pages 16-00316
    Published: 2016
    Released: June 20, 2016
    JOURNAL FREE ACCESS
    For the probabilistic finite element analysis of structures and materials considering uncertainty parameters, the Monte Carlo (MC) simulation is often used. However, the accuracy to predict the tail distribution of the quantity of interest (QoI) is not always good enough. Therefore, this paper proposes a multi-step MC method focusing on the tail distribution. The first step aims at predicting the expected value of QoI accurately with least number of sampling points. By analyzing the results of sampling points in the first step, a region in the parameter space is determined whose sampling points may result in extreme value in the tail distribution of QoI. The next step employs the sampling points in the above limited region to obtain accurately the tail distribution. The main contribution of this paper is to present the newly developed automated algorithm to determine the above region in parameter space. Its usefulness has been shown in the simulation of tensile test of perforated thin plate considering the scattering of geometrical size of holes due to laser processing. Predicted scattered initial fracture load was compared with experimental results.
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  • Daijiro KAWASAKI, Kentaro KASHIWAGI, Takeshi YOKOMORI, Toshihisa UEDA
    2016 Volume 2 Pages 16-00374
    Published: 2016
    Released: July 21, 2016
    JOURNAL FREE ACCESS

    The criterion for transition from a quasi-steady state to a non-steady state of laminar stagnating lean premixed flame in the presence of oscillation in fuel concentration is discussed experimentally. Two types of mixtures with different Lewis numbers are examined: lean methane/air and lean propane/air mixtures. Sinusoidal oscillation in fuel concentration is effected by an oscillator with two cylinder-piston units that supply leaner and richer mixtures alternately. The flame response under fuel concentration oscillation is measured as a function of frequency. The frequency of fuel concentration oscillation varies within 2-20 Hz, and the burner exit velocity varies within 0.6-1.1 m/s. For both mixtures, oscillator characteristics cause the amplitude of oscillation of the flame position to increase with frequency. The increase in amplitude becomes less sharp as frequency increases further. In the present study, two additional Strouhal numbers, one based on heat transfer and another based on mass transfer, are newly introduced in addition to the ordinary Strouhal number which is based on momentum transfer. When any of these Strouhal numbers exceeds unity, the increase in the amplitude starts to fall off. This indicates that the three Strouhal numbers play equally important role on phenomena with momentum, heat and mass transfer, such as combustion.

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  • Yuki NOGUCHI, Takayuki YAMADA, Takashi YAMAMOTO, Kazuhiro IZUI, Shinji ...
    2016 Volume 2 Pages 16-00246
    Published: 2016
    Released: July 21, 2016
    JOURNAL FREE ACCESS

    This letter presents an explicit formulation for the topological derivative of a two-dimensional acoustic-elastic coupled system, expressed with a two-phase material model based on Biot's theory. First, we briefly explain the two-phase material model in which the objective functional is assumed to be a domain integral of a certain function of velocity potential. The shape derivative of the objective functional is obtained using the usual Lagrangian formulation and we then construct the adjoint equation. Since it is known that the limit value of a shape derivative is equal to the topological derivative, asymptotic behavior for the boundary value problem for the state and adjoint variables is searched for and, based on the solutions, an explicit formulation of the topological derivative is thereby obtained. With the objective functional defined as the squared norm of the acoustic pressure, the topological derivatives for equivalent acoustic and elastic material domains are numerically compared with the numerical difference when a hole domain with a finite radius appears, using the FEM. The provided numerical examples demonstrate the validity of our topological derivative formulation and the procedure for calculating topological derivatives.

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  • Masaru OGAWA, Tasuku YAMASAKI, Haruo NAKAMURA
    2016 Volume 2 Pages 16-00247
    Published: 2016
    Released: August 01, 2016
    JOURNAL FREE ACCESS

    The concept of assurance of structural integrity has been taken into accounted especially for energy-related structures where flaw evaluations are conducted based on the fracture mechanics and non-destructive inspections. In evaluations near welded locations, three-dimensional welding residual stresses must be given quantitatively. However, residual stresses only on surfaces can be measured by the X-ray technique. It is inadequate to apply the thermo-elasto-plastic simulation because it gives qualitative information owing to complexity of actual welding process. Moreover, it is required to predict welding deformations in the design process. Authors proposed a new method to evaluate both welding deformations and residual stresses based on the eigen-strain methodology, which is applicable to the finite element (FEM) analysis. In the proposed method, three-dimensional eigen-strains are estimated by the inverse analysis using the Truncated Singular Value Decomposition (TSVD) method and the penalty method. Numerical simulations are carried out for a butt-welded plate with larger angular deformation in the thickness direction. As a result, eigen-strains to express both welding deformations and residual stresses with higher accuracy could be estimated successfully.

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  • Kosuke TAKAHASHI, Takahiro MATSUO, Masakazu FURUTA, Shuzo OSHIMA, Kazu ...
    2016 Volume 2 Pages 16-00227
    Published: 2016
    Released: September 02, 2016
    JOURNAL FREE ACCESS

    Wetting-induced attraction are widely observed in microstructures where liquid flows along solid surfaces. Unexpected bending or collapse occurs if wetting-induced forces are neglected in the structural design, such as high aspect ratio pillars in the process of wet-etching. In this study, a simple experiment is designed to capture the evolving deformation of a cantilever beam due to capillary flow. A pair of polymer plates fixed at one end with a small gap is submerged into liquid, so that capillary rise between the plates and their attraction can be simultaneously observed. The plate dimension is sub-millimeter scale, which is rather large in observation of capillarity, in order to clearly capture deformation process of the plates until their contacts. Different types of liquids are prepared to investigate the influence of wettability, surface tension, and viscosity. Velocity of capillary flow is also considered by changing submergence rate of the plate. The experimental results of plate deflection are compared to analytical estimation obtained from an equation of motion for capillary rise and an equilibrium between capillary attraction and elastic force of plate. This estimation corresponded well with experimental results regardless of liquid types. In addition, the relationship between plate deflection and material constants is derived in a non-dimensional form. Therefore, plate deformation due to wetting-induced attraction, considering velocity of capillary flow, became predictable only from dimension of plates and material constants.

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  • Hiroshi YOKOYAMA, Yuu HIROSE, Akiyoshi IIDA
    2016 Volume 2 Pages 16-00412
    Published: 2016
    Released: September 14, 2016
    JOURNAL FREE ACCESS

    In order to clarify the effects of the behaviors of the bubbles of aeration on the productivity of biomass, experiments including cultivation and computation were performed utilizing a bioreactor with a Taylor vortex flow in the annular gap of concentric cylinders. The shape of the inner cylinder and the position of the aeration were changed to vary the floating speed of the bubbles. The flow velocity was measured by Particle Image Velocimetry and the time taken for the floating of the bubbles from the lower wall to the upper surface of the suspension was also measured along with prediction by Large Eddy Simulations. The cultivation of cyanobacteria was also performed. Attaching spiral fins to the inner cylinder induces downward velocity in the region close to the outer cylinder, where a large-scale vortex replaces the original three vortical structures generated in the case of a simple circular inner cylinder. As a result, the time taken for the floating of the bubbles becomes longer when the aeration was performed at a position close to the outer cylinder. When cultivation was performed in these conditions, the cyanobacteria were found to have developed up to a high content and that their growth rate was also high. The present results indicate that the behaviors of the bubbles of aeration are related to the productivity of the biomass.

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  • Zhi-He JIN, Keiichiro TOHGO, Tomoyuki FUJII, Yoshinobu SHIMAMURA
    2016 Volume 2 Pages 16-00436
    Published: 2016
    Released: September 16, 2016
    JOURNAL FREE ACCESS

    It is known that thermal resistance exists at interfaces in bonded dissimilar materials due to imperfect mechanical and chemical bonding as well as phonon scattering at the interface. This thermal resistance influences the temperature distribution as well as thermal stresses in the bonded material. The purpose of this work is to explore the effect of interfacial thermal resistance on thermal fracture behavior of bonded materials. In particular, we consider an edge crack in the coating layer that is bonded to a substrate. The thermal stress intensity factor for the edge crack considering the thermal resistance at the coating-substrate interface is calculated using an integral transform/integral equation method. The numerical results for an Al2O3 coating on a Si3N4 substrate show that the thermal stress field deviates from that for the coating/substrate system without considering interfacial thermal resistance. The thermal stress intensity factor is increased by the interfacial thermal resistance, which indicates that the thermal shock resistance of the coating/substrate system can be degraded by the presence of thermal resistance at the interface between the coating and substrate.

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  • Akira SATOH
    2016 Volume 2 Pages 16-00314
    Published: 2016
    Released: October 07, 2016
    JOURNAL FREE ACCESS

    We discuss the behavior of oblate spheroidal hematite particles in a simple shear flow. Magneto-rheological properties are strongly dependent on the magnetic field direction. For instance, a rod-like hematite particle suspension exhibits negative viscosity characteristics in a certain direction of an applied magnetic field. From this background, we here consider the case of an external magnetic field applied in the direction of the angular velocity vector of a simple shear flow. If the magnetic field is much more dominant than the thermal motion, the particle can almost freely rotate about the direction of the angular velocity vector. This characteristic rotational motion is suppressed or controlled by the shear flow more significantly with increasing shear rate.

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  • Moeto NAGAI, Kei KATO, Takayuki SHIBATA
    2016 Volume 2 Pages 16-00445
    Published: 2016
    Released: October 26, 2016
    JOURNAL FREE ACCESS

    Biohybrid systems, constructed by combining biological cells and artificial components, have the potential to resolve the current technical limits of traditional microactuators. The aim of this study is to bring poly(ethylene glycol) diacrylate (PEG-DA) movable components, formed by microfluidic in situ photolithography, into biohybrid Vorticella-based systems. This paper reports conditions for integrating PEG-DA hydrogels and actuators of Vorticella convallaria (V. convallaria). PEG-DA hydrogels were formed in a polydimethylsiloxane (PDMS) microfluidic channel by in-situ photolithography techniques. Basic photopolymerization properties of PEG-DA hydrogels in a PDMS microchannel were studied by changing the magnification of an objective lens and light intensity. To incorporate a PEG-DA structure with V. convallaria, we studied two possible integration methods: 1) hydrogel formation after cell placement and 2) cell placement after hydrogel formation. To examine the integration methods, we evaluated the viability of V. convallaria in a PEG-DA solution mixed with photoinitiators or in a buffer after the formation of a PEG-DA hydrogel. A viability assay in a PEG-DA solution revealed that lower concentrations of PEG-DA and photoinitiator improved cellular viability. To establish the second integration method, we designed and fabricated a microfluidic device to transport a V. convallaria cell to a microchamber containing a polymerized PEG-DA structure. Cell viability in a microchamber was evaluated after replacing a PEG-DA solution with a culture medium. Vorticella was active and generated a flow, which was characterized by particle image velocimetry (PIV). A higher molecular weight PEG-DA increased V. convallaria viability. The conditions for forming a hydrogel structure while maintaining Vorticella activity were clarified as a method for incorporating a movable component into biohybrid systems.

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  • Toshiharu KAZAMA, Yamato KOHIRUIMAKI, Kento KUMAGAI
    2016 Volume 2 Pages 16-00442
    Published: 2016
    Released: November 02, 2016
    JOURNAL FREE ACCESS

    Erosion of non-collision surfaces by cavitating oil jets was investigated experimentally using hollow cylindrical specimens. The stainless steel chamber with an inner diameter of 170 mm was utilized, including the nozzle of 1 mm in diameter and 4 mm in length. The aluminum specimens with a length of 20 mm, an outer diameter of 20 mm, and inner diameters of 3, 5, and 7 mm were prepared. The test fluid was hydraulic oil with a viscosity grade of 32 and the temperature was maintained at 40°C. The upstream and downstream absolute pressure were set at 10.1 MPa and 0.2 MPa, respectively, so that the cavitation number defined by the ratio of the downstream pressure to the upstream pressure was 0.02. The stand-off distance was varied from 10 to 25 mm in increments of 2.5 mm. The specimens were observed at 1 hour intervals and the exposure time was up to 8 hours. The specimens were cut in half by a precision machine tool after the completion of the experiments to observe and examine the eroded surfaces. The specimens were partially eroded on their inner walls close to the downstream ends. The eroded region shifted slightly upstream as the stand-off distance increased. The erosion was less pronounced for specimens with a large inner diameter.

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  • Yutaka HAYAMA, Fumihiro OHSHIMA, Junichi IBUKURO, Akira MATSUO, Seiya ...
    2016 Volume 2 Pages 16-00502
    Published: 2016
    Released: November 10, 2016
    JOURNAL FREE ACCESS

    In the energy sector, structures such as offshore wind power plants typically operate for long periods of time in harsh environments. Therefore, remote monitoring systems are required for maintenance. Optical fiber sensors are suitable for this purpose because the transmission loss in the optical fiber lines is very small. For the optical fiber sensor is small transmission loss, the measurement data can be far transmission. Therefore, optical fiber sensing systems are widely used to monitor the structures of wind power plants. Wind power generation systems contain many rotary shafts that are constantly subjected to severe operating loads. It is important to maintain rotary shafts and other rotating components. Their health can be monitored by measuring the strain in the rotary shaft. Optical fiber sensors are line sensors that have a length of measuring section. However, the effects of surface curvature, such as that of a rotary shaft, on the measured strain are not known in detail. These sensors are considered more susceptible to the effects of curvature than conventional point sensors. Therefore, the effect on strain measurement accuracy must be determined. In this study, a high-precision torsional strain sensor system is proposed that uses a fiber Bragg grating (FBG)optical fiber sensor. Torsional load tests were conducted to confirm the effects of curvature on the strain distribution measurement and the performance of the FBG sensor attached to the cylindrical shaft. The proposed measurement technique was evaluated for measurement of the torsional strain distribution and temperature. Experimental and FEM analysis results were compared to verify the measurement accuracy.

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  • Masahiro SUZUKI, Nobuyuki OKURA
    2016 Volume 2 Pages 16-00505
    Published: 2016
    Released: November 10, 2016
    JOURNAL FREE ACCESS

    A novel experiment was conducted to investigate the aerodynamic forces acting on a train traveling through a tornado, in which we developed a moving model rig with a tornado simulator. The flow field generated by the tornado simulator was validated by comparison with those of real tornadoes and the Rankine vortex model. Using this setup, we measured unsteady surface pressures on a model train as it passed through the vortex center. The side force, lift force, and yawing moment were estimated from the pressure data. The results were as follows: 1) the side force acting on the train changed its direction from negative to positive while passing through the tornado-like swirling flow; 2) the lift force increased as the train approached the flow and became maximum around the vortex center; 3) the yawing moment first decreased slightly and then reached its maximum around the vortex center. Asymmetric wave forms of the forces and moment at the center of the tornado simulator suggested that the train itself may have affected the vortex structure of the flow.

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  • Balavenkatesh RENGARAJ, Masakazu OKAZAKI, Masahiro TOSA, Seiji KURODA
    2016 Volume 2 Pages 16-00552
    Published: 2016
    Released: December 27, 2016
    JOURNAL FREE ACCESS

    Investigation on the effects of crystallographic surface and sliding orientations of CMSX-4 single crystal Ni-base superalloy (SC) on the cyclic sliding friction (CSF) behavior against IN718 polycrystalline Ni-base superalloy (PC) has been carried out at room temperature and at 600°C. Tests have been conducted on three different surface orientations (crystallographic orientation of sliding surface) and two different sliding orientations (crystallographic orientation toward the sliding direction), in order to explore the anisotropic friction response of SC/PC sliding contact pair. A significant normal load depended anisotropic tribological behavior was observed. On a given contact surface orientation, a specific effect of sliding direction was also established. This anisotropic behavior was found to be significant and was independent of test temperature. Discussions were made on the above experimental results. It was suggested that both the stress and the deformation field near the contact area which are closely influenced by the anisotropic mechanical properties in longitudinal and transverse elastic moduli and in yield strength would play extrinsic roles there.

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