Mechanical Engineering Journal
Online ISSN : 2187-9745
ISSN-L : 2187-9745
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Solid Mechanics and Materials Engineering
  • Yasuhiro MAEDA, Yoshihito OZAWA, Wataru TAKANO, Naoto TAKEHANA, Yuta O ...
    2020 Volume 7 Issue 1 Pages 19-00186
    Published: 2020
    Released: February 15, 2020
    [Advance publication] Released: January 14, 2020
    JOURNALS FREE ACCESS

    In recent years, accidents have frequently occurred under the rapid spread of the photovoltaic power generation system in Japan. In order to make the design procedure for the support structure safety, in the previous studies, the authors have compared the experimental results with the FEM analytical results by using the beam element model. The results show that it can evaluate the deformation of the support structure qualitatively, determine the buckling member, and calculate the buckling load. However, it was not easy to quantitatively evaluate the deformation of the support structure in the analysis with the beam element model. In this study, in order to do quantitative evaluation for the deformation of the support structure, FEM analysis was performed by using the shell element model and through comparing experimental results with analytical results. From these results, it is found that the buckling member was determined and its bucking load could be calculated precisely. Furthermore, in order to examine the deformation and fracture process of the angle members, we conducted elastoplastic FEM analysis for the angle member. We will clarify the deformation behavior of the angle steel member until the buckling, and show new knowledge in the destruction of the whole of the support structure.

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  • Hao Dinh DUONG, Masakazu OKAZAKI, Tra Hung TRAN
    2020 Volume 7 Issue 1 Pages 19-00490
    Published: 2020
    Released: February 15, 2020
    [Advance publication] Released: January 27, 2020
    JOURNALS FREE ACCESS

    The effects of tool offset and the reversed metal flow induced by a double-pass friction stir welding (FSW) on the welding interface characteristics were investigated in a dissimilar thickness T-lap joint between 7075-T651 and 5083-H116 aluminum alloys. The performance of the joint was evaluated by the skin and stringer tensile tests. The experimental results showed that the bonding interface could be improved by applying double-pass welding which the tool was offsetted toward advancing side. An employment of the double-pass welding significantly improved the strength so that the joint efficiency reached about 90% in comparison with the 5083 base metal strength while the tensile strength of the joint produced by the single-pass welding was quite low. The kissing bond defects were found to be the main culprit in the tensile behavior of the T-lap joint. The reversed metal flow and the gap distance between pin and die played a key role in the formation of the welding interface.

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Fluid Engineering
  • Keigo SHIMIZU, Takuji NAKASHIMA, Takenori HIRAOKA, Yusuke NAKAMURA, Ta ...
    2020 Volume 7 Issue 1 Pages 19-00366
    Published: 2020
    Released: February 15, 2020
    [Advance publication] Released: February 05, 2020
    JOURNALS FREE ACCESS

    On-road turbulence caused by atmospheric winds and other automobiles influences the flow field of automobiles and causes variations in aerodynamic forces. Furthermore, the disturbance caused by passing vehicles has a significant impact on drag increase and vehicle stability. Therefore, designing flow control techniques considering this impact will effectively improve the robustness of automobiles under on-road conditions. In this study, we investigated flow phenomena responsible for drag changes under passing vehicle conditions to reduce drag. Two simplified vehicle models were adopted for the test vehicle. These models are one-fifth scale models, which reproduce the flow structure of production vehicles. The tests were conducted in a wind tunnel that simulated the passing environment where the truck model was placed in the adjacent lane. The drag change and flow characteristics of the truck model were measured by changing the relative positions of the vehicle model and the truck model. The Reynolds number was 1.1×106 at the transition to the turbulent boundary layer in front of the vehicle model. An analysis procedure was proposed to identify the components affecting the drag change using the flow characteristics of a passing vehicle. As a result, three key factors that change drag were identified; variations in the pressure field, crosswind generated by passing vehicles, and the remaining part. Crosswinds are especially important for reducing drag because the contribution of the pressure field to the drag is uniquely determined by the flow characteristics of the passing vehicles and almost zero when the overtaking/being overtaken process is considered. These results provide guidance for designing flow control techniques that are robust against disturbances under on-road conditions.

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Dynamics & Control, Robotics & Mechatronics
  • Changan JIANG, Satoshi UENO
    2020 Volume 7 Issue 1 Pages 19-00307
    Published: 2020
    Released: February 15, 2020
    [Advance publication] Released: January 27, 2020
    JOURNALS FREE ACCESS

    This study expresses a novel active vibration control method for structures by using magnetic levitation (MA-GLEV) technologies. When a vibration occurs, a developed MAGLEV device will repeat to levitate and contact to the ceiling of structures properly. According to this movement, frictional force will be generated to consume vibration energy by the friction mechanism of the MAGLEV device. For making the MAGLEV device levitate stably, sliding model control method is employed. By varying levitation distance of the MAGLEV device, normal force which is related to friction can be adjusted. The experimental results show the effect of normal force on vibration control of structures, and verify the effectiveness of the proposed active vibration control method.

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  • Makoto SASAKI, Shumpei ITO, Katsuhiro KAMATA, Masahiro YOSHIKAWA, Isam ...
    2020 Volume 7 Issue 1 Pages 19-00076
    Published: 2020
    Released: February 15, 2020
    [Advance publication] Released: January 27, 2020
    JOURNALS FREE ACCESS

    Several people, particularly the elderly population, have difficulties in swallowing; therefore, to address this issue, we built an oral motion classification system based on the muscle activity pattern of the suprahyoid muscles and tested it on 12 elderly people (seven males and five females) without a history of dysphagia and five healthy young men. Surface electromyography (sEMG) signals of the suprahyoid muscles were measured using a 22-channel electrode that was designed as a thin flexible boomerang-shaped patch attached to the underside of the jaw. Six oral motions involving various tongue, jaw opening, and swallowing exercises were classified from the root mean square (RMS) features and cepstrum coefficients (CC) features of sEMG signals using a support vector machine (SVM) classifier. Results showed that the six oral motions for elderly patients were classified with an accuracy of 95.2% and 95.4% for young patients. There was no statistically significant difference in the mean classification accuracy between the two groups. We also found that the six oral motions can be classified with an accuracy of 95.2% regardless of sex, subcutaneous fat thickness on the underside of the jaw, or the level of oral function. Therefore, it appears that the system proposed here can be an effective tool for accurately measuring oral motions and it can be employed to develop an effective game-based training protocol for the elderly whose swallowing capabilities require maintenance and improvement.

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Bio, Medical, Sports and Human Engineering
  • Kazuki HIRANAI, Akisue KURAMOTO, Akihiko SEO
    2020 Volume 7 Issue 1 Pages 19-00464
    Published: 2020
    Released: February 15, 2020
    [Advance publication] Released: December 18, 2019
    JOURNALS FREE ACCESS

    In the current workplace, most manual labor is composed of high-frequency tasks with low physical workloads. Moreover, traditional ergonomic evaluation methods often have difficulty identifying slight variations in working postures and physical workloads in manual tasks. The aim of this study is to determine whether singular spectrum transformation (SST) can detect changes in human posture during manual tasks. In an experiment, eleven male participants performed lightweight material handling tasks under differing work conditions and task intervals, and an electromagnetic motion-tracking system measured their working postures. An anomaly score for each joint angle was calculated using SST, and the means, coefficients of variation (CV), and over-threshold values recorded during each experimental condition were compared. Lag is an important SST parameter for detecting how working posture differs between tasks. Therefore, the effects of changes in lag on the anomaly score were investigated. For each joint angle, the mean anomaly scores were greater under random task intervals than under constant intervals. In contrast, the CV of the anomaly score was smaller under random intervals than under constant intervals. The number of over-threshold values was significantly larger under random intervals than under constant intervals when SST was applied to the elbow flexion angle. The lag was determined according to the time of the work cycle and agreed with lag times observed in previous studies. This study concludes that the efficacy of SST was shown through detection of working posture changes in a time series, and that lag should be selected in accordance with the work cycle.

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  • Yoshihito OKINAGA, Makoto MURATA, Toshihisa UEDA, Takeshi YOKOMORI
    2020 Volume 7 Issue 1 Pages 19-00335
    Published: 2020
    Released: February 15, 2020
    [Advance publication] Released: February 05, 2020
    JOURNALS FREE ACCESS

    The characteristics of a medical heat and moisture exchanger with filter (HMEF) that contained polyurethane sponges and CaCl2 were investigated experimentally and model analysis was performed. Variations in the temperature and humidity were measured. Saturated air at 37 °C simulating exhalation and dry air at 26 °C simulating inhalation were fed alternatively through the HMEF in opposite directions. The period was set as 256 s, 64 s, 16 s and 4 s. When the period was long (256 and 64 s), the polyurethane sponges and CaCl2 played an important role in condensation and evaporation of water and the amplitudes of the temperature variation was so large that it overshot the input condition. When the period was shortened (4 s), the amplitudes of the temperature and humidity variations decreased and the relative humidity of the patient side of the HMEF gradually reached that of the exhalation conditions. This suggests that the characteristic times of condensation and evaporation were longer than that of the respiration (τb = 4 s). In other words, the unsteady effect is important for the condensation and vaporization mechanism of HMEF. The mechanism was supported by the model analysis. In addition, comparing the results of the experiments and model analysis elucidated the effect of the connecting pipe, which corresponds to the dead space effect in clinical use.

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Environmental and Process Engineering, Safety
  • Kairi MURAMATSU, Takehiko SATO, Tomoki NAKAJIMA, Toshikatsu NAGASAWA, ...
    2020 Volume 7 Issue 1 Pages 19-00431
    Published: 2020
    Released: February 15, 2020
    [Advance publication] Released: February 07, 2020
    JOURNALS FREE ACCESS

    In recent years, cold atmospheric plasma has received attention for medical applications like sterilization, injure treatment, and cancer cell treatment. Plasma sterilization is effective against a wide range of microorganisms. Plasma sterilization devices for contact lens have developed over the years. The purpose of this study is to clarify sterilization characteristics under high ozone, low nitric acid, and nitrous acid concentration in liquids. These concentrations are caused by a new cycle of intermittent discharges. Sterilization efficacy is evaluated by inactivating bacillus spores. Concentrations of HNO3, HNO2 and O3 in water were measured using a pack test. Dielectric surface temperature is measured using a thermocouple and thermography to study relationships between the concentration and the temperature. Sterilization of spores in water was achieved for 80 min. Increasing ozone concentration promotes the generation of hydrogen peroxide, which is a well-known factor for sterilization, and OH, which has strong oxidizing power, however, the concentration of hydrogen peroxide is too low for sterilization, and the life time of OH is as short as microseconds. Meanwhile, a decrease in the concentration of nitric acid and nitrous acid suppresses the formation of peroxynitrite, which has very strong oxidizing powers and a lifetime of 1 sec. These results suggest a critical role of peroxynitrite in sterilization.

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Transportation and Logistics
  • Takuma ITO, Masatsugu SOYA, Kyoichi TOHRIYAMA, Minoru KAMATA
    2020 Volume 7 Issue 1 Pages 19-00119
    Published: 2020
    Released: February 15, 2020
    [Advance publication] Released: February 06, 2020
    JOURNALS FREE ACCESS

    The aim of this study is to develop a risk map generation system on community roads via a data-driven approach. Because there are no roadside cooperative sensing systems on community roads, intelligent motion controls need the prediction of surrounding traffic participants based on a digital map. In addition, to improve the driver acceptance of the system, adaptive motion control considering the risk level at various intersections is desirable. In general, existing risk map preparation methods need too many human resources to prepare the map data for nationwide community roads. To solve this problem, we design a risk map generation system that can be systemized as much as possible for future automated process. First, our proposed system collects the driving data via non-specialized drivers using relatively usual vehicles at various intersections. Next, the system classifies the driving behavior via feature values with regard to the deceleration operation while approaching non-signalized intersections. Based on the driving data of relatively careful drivers, the system extracts the positions of pseudo intersections that are not registered in the digital map. In addition, the system estimates the risk level of intersections based on the driving data of relatively interactive drivers. To confirm the feasibility of the proposed system, we collect the driving data of 45 elderly drivers. According to the evaluation, the system adequately detects the pseudo intersections on actual roads. The estimation results of the risk level show the substantial agreement with the risk evaluations of driving school instructors regarding basic intersections.

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