Hilbert-Schmidt independence criterion least absolute shrinkage and selection operator (HSIC Lasso) and plural long short-term memory (pLSTM) has been implemented in a multi-electrode impedance meter (MIM) to estimate void fraction α^{^} accurately in vertical gas-liquid flows. The MIM measures voltage vector V reflecting the spatial distribution of bubbles in the gas-liquid flows with multiple pairs of electrodes on the inner wall of the pipe. HSIC Lasso selects the electrode pairs which are strongly dependent on the void fraction and flow regime based on the nonlinear assumption to select the voltage vector V^~ without any hyperparameters. pLSTM estimates α^{^} after identifying the time-dependent flow regime. In the experiments, V was measured by MIM under the conditions of 25 points of liquid and gas flow rate in gas-liquid upward flows for training, on the other hand, five points for testing, respectively. As the result, HSIC Lasso successfully selects highly dependent electrode pairs with regression coefficient β over 0.03. pLSTM achieves a 100% accuracy of flow regime identification and time mean relative error η with less than 0.0157 of void fraction estimation in bubble flow and slug flow, which decreases total mean relative error <η> by 69% compared with the existing method.

Drag reduction by bubble injection in turbulent boundary layers was investigated using a 36-m-long flat-bottom model ship. The model ship was towed at 8.0 m/s, resulting in a downstream-distance-based Reynolds number as high as 2.9 × 10⁸. The total resistance exerting on the model ship was reduced, and the resistance reduction increased with the air flow rate for the bubble injection. The local wall shear stress on the bottom plate was measured at multiple locations to clarify the streamwise transition of the drag reduction. The local drag reduction observed at the upstream measurement locations was increased with the air flow rate. The higher gas flow rate, moreover, produced the longer streamwise persistence of the drag-reduction effect. These multiple factors improved the efficiency of the total resistance reduction against the power consumption for the bubble injection. We provide the estimation of total frictional drag reduction for the full-scale ships using the equation of the local friction coefficient obtained experimentally. The results of the model ship experiment and the full-scale estimation consistently indicated that the downstream persistence of the local drag-reduction effect strongly affect the total drag reduction of such the long hulls.

We had proposed a creep life assessment method for boiler piping that can consider the heat-to-heat variations of the creep properties of each welded joint, where the creep properties of the welded joint are estimated from those of each base metal. In the method, it is assumed that the creep properties of each base metal in actual pipe are approximately constant in the wall thickness direction of the pipe, and test results with a small sample cut from base metals at an outer surface of the pipe are useful for representing the creep properties of the pipe. In this work, the assumption was examined for six pipes of modified 9Cr-1Mo steel, which had been used for longer than 100,000 h in 600 °C class thermal power stations, and the thickness of the small sample taken from the piping on site was determined. The microstructure, chemical composition, hardness, creep void, uniaxial creep life and small punch creep life were investigated in detail in the wall thickness direction of the pipes. No difference was observed for these items, except in an area less than 0.4 mm from the outer surface of the pipes, which means that the assumption in the assessment method is valid except in this area. On the basis of the results, we determined the thickness of the small sample taken from the 9Cr steel piping as 2.0 mm. Then, we applied the creep life assessment method using the small sample to 600 °C class boiler piping on site, and demonstrated its usefulness for diagnoses of the piping.

The MH21-S R&D consortium (MH21-S), supported by the Ministry of Economy, Trade, and Industry (METI), is currently developing the commercial production process of methane gas from methane hydrate. In order to develop the gas production method through thermal-hydraulic models, an objective identification method of gas-liquid two-phase flow regime under high-pressure conditions is necessary. Furthermore, in identifying the flow regime, it is necessary to distinguish the transition states and improve the calculation accuracy. Therefore, flow regime identification has been conducted in the present research by classifying the high-speed images using clustering algorithms, namely the principal component analysis (PCA) and the k-means method. Specifically, the sequence images of the upward gas-liquid two-phase flow under high pressure taken with a high-speed camera are merged into a single image by the time-strip method, and these single images were then processed with PCA and classified by the k-means method. Furthermore, the PCA and the Gaussian Mixture Model (GMM) were also applied to quantify the flow regime of the transition region. As a result, PCA has shown that the merged images of bubbly flow and slug flow occupy different regions, and the bubbly flow and slug flow are classified with high recall values. The flow regime map obtained from the classification by the PCA and GMM mostly showed similar trend compared with the transition models studied in the past. Thus, this study has shown that the flow regime identification can be performed using the single images of upward gas-liquid two-phase flow merged by the time-strip method, with clustering algorithms. Moreover, it was shown that the unsupervised machine learning method is capable of clustering the flow regime at transition regions.

Through the research of Filtered Containment Venting System (FCVS), air purification methods have been developed, such as technologies of scrubbing, metal fiber, silver zeolite and mobility. Using these technologies, we have been studying the further improvement of air purification systems in the nuclear field. In this study, we conducted adsorption experiments using several metal fiber filters and evaluated the effect of the metal fiber wire diameter on the decontamination factor (DF). It was found that metal fibers with fine wires made a significant contribution to the removal of materials with minute particles. By combining the metal fiber technology with the scrubbing technology, a sufficiently huge DF could be achieved on a laboratory scale. Based on these results, we can propose the mobile air purification system.

A creep rupture life evaluation equation for Gr. 91 steel was proposed, taking account of the region classification and the creep strength difference between heats. The creep rupture life evaluation equation consists of three parts. Each part is related to the region H, ML, or G. The factor dominating the difference in creep strength between heats is hardness in region H, Cr, and C concentrations in region ML, and grain size in region G. The minimum value among the three calculated creep rupture lives is used to draw the creep rupture curve of Gr. 91 steel. By substituting the hardness, Cr and C concentrations, and grain size of the material into the proposed equation, one can easily estimate the temperature and stress conditions under which each region (H, ML, or G) will appear, as well as the creep rupture life in each region. The accuracy of creep life description was compared among the creep rupture life evaluation equation proposed in this study, that of the Ministry of Economy, Trade and Industry (METI) and that of the ECCC. The accuracy of the proposed equation was the highest. The region classification by the proposed equation is helpful to reduce the discrepancy between the actual rupture life and the evaluation result in region G. In addition, the evaluation accuracy was improved by considering the heat dependence of creep strength.

In this study, a finite element (FE) analysis code installing an inelastic constitutive model and crack growth algorithm for thermal barrier coatings (TBCs) developed by Arai et al. was applied to TBCs and porous TBCs (P-TBCs) to evaluate stress, damage and crack initiation and propagation behavior under cycling loading at high temperatures of 673 K and 973 K. The results showed that (i) number of cycles until the crack tip reaching the interface between top coat and bond coat in P-TBC was longer than that in TBC. In other words, the fatigue crack growth rate of P-TBC was slower than that of TBC. (ii) Comparison of the cross-sectional observation results with the finite element analysis showed that the crack initiation location and the crack propagation path in FE analysis results were in good agreement with the observation results. The reason for slow fatigue crack growth rate observed in the P-TBC was as follow: the crack becomes stationary by reaching the wall of open pore. After that, the fresh crack initiates at the edge of open pore by subjecting to more cyclic loading. Consequently, the crack propagates as sewing between pores with cyclic loading which leads to the slow crack growth rate. (iii) Comparison of the surface crack initiation life between test results and the FE analytical results shows that the prediction results by finite element analysis agreed well with the observed results.

In very high cycle fatigue for high strength steels, one can usually observe the fish-eye on the fracture surface and an inclusion is observed at the center of the fish-eye. The fine granular area (FGA) is also found in the vicinity around the inclusion at the crack initiation site on the fracture surface. If the stress cycles required to form the FGA occupies the predominant part of the final fatigue life of these steels, the FGA formation mechanism is one of the most important subjects in the very high cycle fatigue. From this point of view, the authors have attempted to construct the FGA formation model based on the current experimental results obtained by the authors. Supposing four different probabilistic models, the FGA formation is interpreted as intermittent micro-debondings and their coalescence during the long sequence of the cyclic loadings. After the FGA was accomplished, the penny-shape crack tends to grow steadily following the well-known Paris’ law. Based on this analysis of the FGA formation, it was found that polygonization around the inclusion is more important behavior to govern the total fatigue life of the high strength steels.

In a circular cylinder blade wind turbine driven by a longitudinal vortex, the torque characteristics of the turbine are greatly affected by the flow field at the blade tip. In general, wind turbines reduce drag by making the blade tips thinner. However, because this wind turbine uses a cylinder as a blade, it is important to control the flow field at the blade tip. From the experiments, it was found that the torque coefficient can be increased by attaching the endplate to the blade tips, and the rotational force can be obtained stably up to very low rotation speeds. The installation of fairing or endplates in circular cylinder blade wind turbines enables stable rotation at low speeds even under high loads, and also reduces drag at high speeds and increases the maximum speed. In the case of a disk-shaped endplate, the torque coefficient can be increased by up to 20 % by attaching an endplate with a diameter 2.5 to 3 times the diameter of the cylinder to the outer blade tip only. The L-type endplate has the effect of shifting the characteristics to the higher rotation side than the disk-type, and increases the torque coefficient at the same tip speed ratio. However, the lower limit of stable rotation becomes higher, and as a result, the value of the maximum torque coefficient obtained at high load decreases. If the endplate attached inside has a negative effect on the stable formation of the necklace vortex, it will inhibit the rotation at a low speed due to high load, making it difficult to obtain high torque.

For the purpose of improving the performance of the Savonius wind turbine, we added ailerons to the turbine to rotate with the turbine buckets. Ailerons with a relatively simple structure were installed within the rotating area of the Savonius wind turbine. As such, the ailerons did not increase the wind-receiving portion of the wind turbine. A semi-circular shape similar to the bucket was chosen as the aileron. Three sizes of ailerons were used, the largest of which was half the size of the wind turbine bucket. Experiments were conducted using wind tunnel test equipment, where the Savonius wind turbines fitted with ailerons were tested under various installation conditions. In the experiment, the torque generated by the wind turbine was measured at different tip speed ratios. Due to the installation of ailerons, the torque generated by the Savonius wind turbine increased mainly at low tip speed ratios. The torque increased the most when the largest aileron of the three types was used. It was also found that it is possible to improve the efficiency of the wind turbine when using large ailerons. From these results, it can be said that the installation of ailerons is effective for improving the performance of the Savonius wind turbine.

When an underwater ultrasonic wave is emitted toward an air-water interface, the water surface rises and droplets are generated from the formed fountain. The rising process of water surface was numerically investigated for better understanding the mechanism of ultrasonic fountain prior to the atomization. To analyze the water surface rising that occurs in a very short time, it is necessary to simulate the rapid increase of acoustic radiation pressure and the rapid development of acoustic streaming. Therefore, the direct numerical simulation based on compressible fluid dynamics was carried out. The water surface rising as observed in the formation process of ultrasonic fountain was successfully reproduced. In the region between sound source and water surface, standing wave is established and acoustic kinetic energy density increases significantly while water surface rises with acceleration. The kinetic energy density is associated with the acoustic radiation pressure acted on free surface based on the theory of Yosioka-Kawasima (1955). After the rising speed becomes to be constant, the standing wave fades and the kinetic energy density decreases. These results suggest that the acoustic radiation pressure acted on water surface increases significantly due to temporary resonance and water surface rises rapidly. By drawing a fluid due to rapid rising of water surface, acoustic streaming is induced toward the risen region.

As a power generation control method for utilization in nuclear power plants, the turbine bleed valve operation known as condensate throttling (CT) which controls the extraction steam flow rate from a steam turbine to increase generating power has been studied. The purpose of this paper was to evaluate the applicability of the CT to nuclear power plants which have been conventionally operated as a base load power source in the future when use of thermal power plants has to be suspended to reduce greenhouse gas emissions. First, in order to evaluate the basic CT characteristics in nuclear power plants, a dynamic characteristics simulator for the nuclear power plant balance of plant (BOP) system was developed. Next, an effective CT operation method for improving the power generation output was devised, and the dynamic characteristics of the BOP system during CT operation were evaluated using the dynamics characteristics simulator.

The feedwater temperature decreased due to the CT operations. The amounts of the decrease were estimated to be 91.3% of the rated temperature in plant rated load for the case that reactor heat output was the rated value, and 93.2% for the case that reactor heat output was increased from the plant partial load of 95% to 100%. The power generation output increased due to the CT operations. The amounts of increase were estimated to be 4.5% of the rated output for the case of the reactor rated heat output operation, and 5% for the case that the reactor heat power was changed from the plant partial load of 95% to 100%. Assuming that the rated power generation output was 1300 MWe, the power generation output increase was equivalent to the capacity of one or two small- and medium-capacity gas turbines or one small-capacity coal-fired power plant. From the above, it was judged that nuclear power plants could be evaluated as having the ability to adjust supply and demand of electric power systems by CT operation.

An evaporation of droplet reaches a minimum time at a temperature of hot surface beyond the saturation temperature. Most of researches have mainly focused on the temperature at the minimum time, only. This paper proposed an exact solution to calculate heat flux after a time when the droplet starts contact with the hot surface. The calculated heat flux until a time of about 1 ms when the droplet starts evaporating on the contact surface is found to be very close to the critical heat flux for subcooled pool boiling at the droplet temperature. The average heat flux at the minimum time is firstly determined for the hot surface from which the corresponding initial surface temperature is dependently determined. The quench temperature, furthermore, in a mist cooling for a high temperature material is found to be estimated well by applying the proposed method

The fuel injection in diesel engines have a significant effect on the engine performance. But there is little knowledge on the characteristics of dispersion of liquid phase concentration. The purpose of this study is to clarify the dispersion process of the liquid phase of diesel spray through quantitative analysis of the liquid phase concentration distribution in non-evaporating diesel spray. In this paper, a quantitative analysis method of the liquid phase concentration of diesel spray under non-evaporative conditions is developed. The cross-sectional mass flow of the fuel was obtained using the momentum theory from the measured concentration distribution of the liquid phase with the laser induced fluorescence method. The relationship between the fluorescence intensity and the liquid phase concentration was estimated. In addition, a scheme was developed to account for the attenuation of the laser light and fluorescence, which results in a quantitative spatial distribution of the liquid phase concentration. Using this method, the dispersion process of the liquid phase in diesel spray was evaluated.

In this paper, we aim to develop a technology that can be commonly used for link mechanisms. We use nonlinear model predictive control to design a control system that enables trajectory generation and trajectory tracking using only a single controller. By using the nonlinear model predictive control, we can expect the versatility that does not depend on the hardware by changing the model, the scalability that can realize multiple objectives by the evaluation function, and the easiness that the trajectory generation and tracking can be realized by a single controller. As an example of a link mechanism, a hydraulic excavator was modeled as a link mechanism with four degrees of freedom, and the effectiveness of the proposed method was verified by numerical simulation. In this simulation, the hydraulic excavator performed the loading operation to load the excavated soil into the dump truck and the repositioning operation to move to the next excavation position. During these operations, the excavator needs to reach the target position while avoiding collision with the dump truck. From the simulation results, it was confirmed that by setting the evaluation function appropriately, the loading and repositioning operation in three-dimensional space can be performed while avoiding collision with obstacles without giving a target trajectory.

There is a growing demand for higher performance and thinner communication cables (LANs and USBs) that can transfer data in large volumes at high speed in the era of IoT, 5G. Fluorine resins having a lower dielectric constant and a lower dielectric dissipation factor are used as coating materials for high performance electric wires. To coat the electric wires stably at high speed, it is necessary for resin pellets to flow smoothly from hopper into cylinder in an extruder. In this paper, we propose a simulation method based on the dynamic explicit FEM (Finite Element Method) to evaluate the flowability of resin pellets which are filled into the hopper by free-fall and then flow out from the hopper by gravity. First, we verify simulation results by statistical method to ensure the randomness of the filled state of resin pellets in the hopper and validate the simulation method with experiment results. Next, using the simulation method, we clarify that the shape of resin pellets has a great influence on their flowability and find an optimal pellet shape that can improve the flowability of resin pellets from the hopper to the cylinder in the extruder. Finally, we confirm that the optimal resin pellet shape is in dependent of the amount of pellet, kind of material and angle of hopper.

To reduce weigh of the transportation machines, joining of the FRP and the light metal is considered as important technique. In this study, the punching rivet method was applied to make joints between a GFRP sheet and an aluminum alloy A6061 sheet and joint strength was examined. The punching rivet method is possible to join the sheets without drilling by using a rivet and a rivet holder. The punching-out process of the sheets using a rivet shank as a punch and the joining process of the sheets using the rivet and the rivet holder are continuously performed. From the experimental results of joining of the GFRP sheet and the A6061 sheet, the joints made by the punching rivet method had no large crack and out-of-plane deformation of the joints was suppressed. From the results of the joint strength tests, the joints made by the punching rivet method had almost the same joint strength as the bolted joints which were tightened by regulated torque. In addition, the fatigue life of the joints made by the punching rivet method was longer than that of bolted joints. It could be confirmed that the punching rivet method was effective to join the GFRP sheet and the A6061 sheet.

Dry etching using oxygen plasma was conducted on a single-point cutting tool made of nano-polycrystalline diamond to clarify the shapeable cutting edge radius (CER). The CER of the tool was measured by atomic force microscopy (AFM). The cantilever employed was made of single crystal silicon and had a tetrahedral shape with a probe tip radius of 4 to 10 nm. The CER can be identified by subtracting the probe tip radius from a measured CER when the probe tip radius is fixed at a certain value. Dry etching tests revealed that the measured CER decreased and converged to a constant value equivalent to the probe tip radius with increasing etching time. Utilizing this phenomenon, a standard tool suitable for calibrating the probe tip radius was fabricated. The CER and the variation in the CER of the standard tool were less than 0.1 nm. This calibration using the standard tool made it possible to identify the CER from the measured CER. It became clear that the CER converged to less than 0.1 nm, and the variation in converged CER was less than 0.5 nm. Hence, it can be concluded that the shapeable CER that can be formed by dry etching using oxygen plasma is less than 0.5 nm.

Ultrasound transmission gel has been normally used as a material fills the gap between the transducer of the ultrasound and patient’s skin. Alternatively, however, it can be used as a trial bioink for the 3D bio-printer, which is identified as one material for checking its printability at the preliminary phase. The purpose of this study was to clarify whether the ultrasound transmission gel can be used as the trial bioink. For this purpose, we investigated the viscosity of some kinds of the ultrasound transmission gel, and compared with commercially available one. And also we measured the width of the printed lines with the ultrasound transmission gel in comparison with the perspective width. According to our results, we concluded that the ultrasound transmission gel can be used as the trial bioink as long as selecting appropriate viscosity type.

Thumb carpometacarpal (CM) joint osteoarthritis is a common disease in elderly. To clarify the thumb CM joint motion is critical to reveal the factor of disease and improve treatment methods. The thumb CM joint, which has a specific structure called the saddle joint, consists of the first metacarpal bone and the trapezium. The saddle-shaped articular surface allows us to perform a wide range of motion and screw home torque rotation. However, the kinematics of the thumb CM joint is not clarified. The factor of disease and the optimal treatment is also unclear. Recent motion analysis often uses the Euler angle method with three-dimensional CT, whose calculated value may be inaccurate because the coordinate axis used for evaluation does not always coincide with the actual rotation axis. Besides, previous analyses do not capture localized motion changes due to the limited number of limb positions for analysis. Therefore, this study proposed a new analysis method to calculate the rotation axis and performed the 3-dimensional analysis of the thumb by dividing its motion into several segments with CT imaging. As a result, the conventional method often underestimates the motion of the thumb CM joint motion more than our method. The screw home torque rotation occurred in the specific flexion segment. This kinematics may cause a heavy load on the joint surface and be a factor in diseases.

Since the early days of spacecraft development, accurate and simple vibro-acoustic prediction of equipment on the spacecraft panels subjected to acoustic excitation has been conducted in order to mitigate the over-conservative environmental test conditions. The conventional prediction methods are based on numerical solution of equation of motion, such as FEM/BEM and SEA, the so-called deductive approach. However, in a spacecraft with complex structures, there are many structural and non-structural objects, such as wiring harnesses, connecting cables and electronic boards in the equipment, which are usually difficult to be modelled into these methods. These un-modeled objects are usually treated by uncertainty of models, which always results in overly conservative prediction. In order to mitigate this uncertainty caused by model limitation of deductive approach, this study proposes a more accurate and simple inductive approach for vibro-acoustic prediction using Gradient Boosting Decision Trees (GBDT), which is one of the machine learning algorithms based on measured data. In addition, in order to take into account the vibration modes of the structural panels and waveform trends of vibration response spectrum in the creation of the learning model, explanatory variables based on the design drawing information were added, and the concept of bidirectional recurrent neural networks (BRNN), which is used for predicting time histories waveforms, was incorporated. This approach was applied to the vibro-acoustic prediction using the measured data of the equipment on the spacecraft panels in the acoustic tests of 7 spacecrafts developed by JAXA, and the results showed that this approach can make a reasonable prediction with the uncertainty margin mitigated by about 2 to 4 dB compared with the conventional approach.