The focused acoustic field formed under the water surface raised by ultrasound exposure was numerically investigated to elucidate the relationship with the surface rising prior to ultrasonic atomization. The effect of surface tension was newly added to the computational scheme constructed in the previous paper (Orisaki and Kajishima, 2022) and the direct numerical simulation based on compressible fluid dynamics was conducted. The water surface above the sound source rises. When the risen surface shape changes into a dome due to the effect of surface tension, the acoustic antinode with strong focusing appears inside the dome and the water surface begins to rise rapidly. In case of the insufficient sound source pressure, the gentle risen surface is kept, and acoustic peak spots remain deep due to the small curvature of the surface. These results suggest that the dome formation increases the acoustic pressure amplitude at the dome center and promotes acoustic cavitation there. On the dome surface, the kinetic energy density with the phase opposite to acoustic pressure increases, which causes the increase in the acoustic radiation pressure.

Since boiling is a phenomenon with high heat transfer performance, it is expected to be used in various industrial fields such as emergency cooling in nuclear power plants, power device cooling for EVs and next-generation CPU cooling in data centers. So far, various research on boiling have been carried out in the background of these trends. In particular, many studies have been conducted to improve the critical heat flux (q_CHF) which is the limit of boiling heat transfer. However, since the mechanism of q_CHF is a complex phenomenon, the methods of q_CHF improvement are still unconstructed. Here we demonstrate the high-performance heat transfer surface using electrodeposition which fabricates copper porous plate. We found that this copper porous plate has higher q_CHF (3.7 MW/m²) than the plain surface (1.3 MW/m²) in saturated pool boiling of water at atmospheric pressure. The structure of copper porous plates is investigated by X-ray CT and SEM. The copper porous plates have a honeycomb porous structure consisting of porous area and vapor escape channels extending vertically from the substrate. In addition, the diameter of the vapor escape channels increases from the substrate to the top surface. This surface structure can supply the coolant to the heat transfer surface with the reduction of pressure drop. Our results show that the mechanism of q_CHF improvement using porous plate depends on the wicking phenomenon and structure. We expect that these results will help in the development of high-performance heat transfer surfaces for various industrial applications.

Zinc-air batteries are widely considered as the next-generation rechargeable batteries due to their high energy density, low cost, and high safety. However, internal short circuits caused by zinc dendrite growth and bubble generation by side reaction during high-speed charging can deteriorate battery performance. To address this issue, a zinc-air flow battery with an electrolyte flow has been proposed for high-speed charging, and previous studies have shown improved cycle performance. Optimization of operating conditions for practical use requires elucidation of the behavior of the zinc electrode and bubble with electrolyte flow during battery operation, but this remains unclear. This study utilized operando X-ray imaging to investigate the zinc electrode and bubble behavior of a zinc-air flow battery during charging. The results revealed that when charging without electrolyte flow, zinc was deposited in a dendrite structure, and the dendrite growth rate increased with the charging speed. In contrast, it was observed that dendrite growth was suppressed, and dense zinc deposition was achieved even under high current density conditions when charged with a flowing electrolyte. Furthermore, the voltage fluctuation due to a decrease in the reaction area caused by the bubbles generated by water reduction was successfully suppressed when the flow was present. This was achieved by removing the bubbles through convection, which prevented the increase in overvoltage. Overall, it can be said that the flow of electrolytes has a positive effect on battery performance, as it helps to achieve a more uniform deposition of zinc and to prevent voltage fluctuation.

Particle dampers (PD) can be embedded in structures fabricated via selective laser melting (SLM) because the raw powder (particle diameter : several tens of micrometers) remains in closed spaces during SLM. However, most PD studies have focused on coarse particle sizes larger than 1 mm and low frequencies below 100 Hz; there is insufficient evaluation of PD attenuation characteristics and particle behavior for particle sizes from tens of micrometers to sub-millimeters and in the 100 to 1000 Hz band. In this study, the equivalent viscous damping coefficients of spherical zirconia balls with nominal sizes of 0.05, 0.10, 0.20, and 0.40 mm are measured under different vibration accelerations (from 9 to 148 m/s²(rms)) and frequencies (from 100 to 800 Hz) to experimentally investigate the effect of fine particle diameters on the damping properties. It is deduced that in the frequency range above 200 Hz, the equivalent viscous damping coefficients of the coarse particle diameter are greater than those of fine particles at accelerations below the range of 15.7–22.4 m/s²(rms). In contrast, the equivalent viscous damping coefficients of the fine particles are greater than those of the coarse particles at accelerations above the 15.7–22.4 m/s²(rms) range. In addition, to determine the reason for these tendencies, the behavior of particles with a nominal size of 0.05 mm, which is close to the raw powder, is observed through a window using a high-speed microscope camera. The results reveal that in the low acceleration range, the inertial force does not overcome the static friction force owing to poor flowability caused by adhesion force, and the particles are always stationary with respect to the sealed container.

In the development of mechanical structures, it has been required for a long time to establish a modular design method of resonance by controlling the vibration coupling among subsystems. From the analytical perspective of coupled vibration among modules, the kernel compliance analysis (kCA) method exists. The kCA method has the advantage of being able to analyze vibration coupling when modules, which will be called subsystems below, are connected with multiple degrees of freedom. However, the kCA method is not directly applicable to damped systems. This is because the kernel compliance matrix, which is the core of the kCA method, of the damped system is a complex symmetric matrix. To avoid the difficulty, in this paper, the Autonne-Takagi factorization is employed instead of the general eigenvalue decomposition to decompose the complex symmetric matrix. Furthermore, the old-type frequency-based substructuring was introduced so that vibration coupling analysis can be performed among multi-subsystems. With these extensions of the kCA, a method to analyze the energy distribution ratio between subsystems was derived. By using the analysis results, it is possible to shift the resonance frequency and determine the appropriate placement of damping materials.

The authors developed a vibration suppression device (VSD) that has variable moment of inertia using magneto-rheological (MR) fluid in order to get series inertia mass effect for vibration reduction. In previous paper, the proto-type VSD was manufactured and the variable series inertia mass effect was confirmed. From the experimental results, the series inertia mass effect can be switched by the current of electromagnets. And theoretical model of solidified form of the fluid was proposed by formula and the trend were closed the experimental results. Then the vibration tests of 1DOF system with the VSD were conducted by a shaking table. Vibration reduction of the VSD was confirmed. The current of the electromagnet was controlled by using the reinforcement learning. But the fluid behavior inside the flywheel has not investigated before. In this paper, to investigate the fluid behavior inside the flywheel, it is analyzed by computational fluid dynamics (CFD). Three types of the flywheels are manufactured, and 2 types of electromagnets are used here. Equivalent inertia mass in totally 20 cases of the flywheel and the electromagnets are numerically calculated by using the OpenFOAM, and also measured in experiments. From the analytical results, convection is initially occurred in the direction of the magnetic poles when the magnetic field applies, and then the particles are eventually solidified at locations other than near the magnetic poles. Finally, the analytical results are compared with the theoretical and the experimental results.

This paper presents a data augmentation method for generating a surrogate model of numerical analysis results. The proposed method focuses on the relative frequency of learning data for generating a learning model using deep learning techniques. Generally, data augmentation techniques are known to be useful for improving prediction accuracy. Adding noise and data duplication are commonly used for predicting numerical simulation results, but it is essential to carefully consider the amount of noise or choose a duplication target. However, these techniques are not appropriate for generating surrogate models. The reason is that the numerical analysis results mostly have high data imbalance, and no specific solution has been presented. The method proposed in this paper solves this problem and aims to be a simple and highly versatile data augmentation method. This paper describes the application of the proposed method to predict two-dimensional stress fields. It was confirmed that by increasing the number of data augmentations using the proposed method, the prediction errors were reduced for three different stress components stably. Additionally, it was confirmed that the prediction accuracy improved 5.81 to 27.0% compared to that of the data augmentation by simple duplication.

In order to experimentally determine the controlled variable values realizing a quasi-zero stiffness of a cable driven continuum robot, this paper presents an experimental method for quantitatively and accurately assessing the stability of a robot in a static equilibrium state with the controlled variables being kept at their target values. Experimental stability assessment requires consideration of the difficulty for an actual robot to achieve the unstable static equilibrium states and the fact that measurement errors can greatly affect stability assessment. Thus, the proposed experimental method assesses the stability of a robot by determining the smallest eigenvalue of the Hessian matrix of the total potential energy through measuring the relationship betweensmalldisplacementandworkdonebyexternalforcesfromastaticequilibriumstatetobeassessed. This measurement sets the controlled variables on an experimental robot that stably achieve the static equilibrium state instead of the controlled variables to be assessed. Moreover, an additional small displacement is given in the same direction as the eigenvector of the smallest eigenvalue of the Hessian once obtained. Then the stability of a planar 3-DOF continuum robot consisting of a variable-length elastic rod and two cables with the controlled variables set as the rod length and the cable tensions was assessed by the derived stability analysis and the proposed experimental method. The experimental results showed that the stability of both stable and unstable static equilibrium states was quantified, with a high repeatability of the results. Additionally, the stability assessment value decreased from positive to negative with the increasing cable tensions, consistent with the theoretical results. Furthermore, giving the additional small displacement enables a more accurate assessment of the stability. Finally, an approximation of the experimental results successfully determined the controlled variable values that allow the experimental robot to realize the neutral static equilibrium state.

In general, the life of a rolling bearing is calculated as the total number of rotations until rolling fatigue occurs on the raceway. However, when rolling bearings are used under light loads and high rotational speeds, they are damaged not by rolling fatigue on the raceways but by cage wear due to lubrication life. In such cases, the conventional method for calculating the rolling bearing life is not applicable. Rolling bearings for traction motors of railway vehicles (hereafter referred to as traction motor bearings) are one example of this and are replaced primarily due to lubrication life. However, there is no practical way to calculate lubrication life and these rolling bearings are replaced empirically. The purpose of this paper is to obtain basic data to create a method for calculating lubrication life. Therefore, traction motor bearings were rotated under conditions like actual operating conditions to reproduce damage due to lubrication life. As a result, damage due to lubrication life could be reproduced, so the next step was to investigate the effect on lubrication life when the operating conditions of traction motor bearings were varied as parameters. The parameters considered were “bearing temperature”, “vibration acceleration”, and “grease mass”. As a result of these verifications, lubrication life decreased exponentially when the bearing temperature was increased. In addition, lubrication life decreased exponentially when vibration acceleration was increased. Furthermore, lubrication life increased logarithmically when the grease mass was increased. The effects of these verified parameters on lubrication life could all be formulated within this paper.

In recent years, condition monitoring technologies have been widely developed aiming at safer railway operation and maintenance cost reduction. Condition monitoring systems of railway for both from onboard and on track have been widely studied thanks to the recent development of sensors. Using equipped sensors on track, as an example of the bogie abnormality detection, the diagonal imbalance of wheel-load for four wheels in a bogie is closely related to the running safety on curve. If serious problem happens in the bogie frame, the diagonal imbalance may change, and wheel load reduction occurs. For these reasons, the monitoring of the diagonal imbalance from track has a potential usefulness. However, in our previous research, the measured imbalance can be varied even though the focused bogies run on the track under almost the same condition such as boarding rate, vehicle velocity and so on. If the cause of variation is clarified, the limit of abnormality detection accuracy can be clarified. Therefore, in this study, variation of the measurement of bogie’s diagonal wheel-load imbalance are investigated. Furthermore, factors that affect the variation of the measurement is investigated using MBD simulation.

This paper describes a method for continuously measuring the contact position between the wheel and rail using strain gauges. The authors investigated the relationship between the bridge output sensitivity rate and the change in the placement of strain gauges using the result of finite element analysis for the instrumented wheelset. It is noted that the bridge output sensitivity rate is defined as the bridge output change per unit distance of the contact position (load position). Based on the result, strain gauges position suitable for measuring contact position was identified. On the other hand, static load tests were conducted on the instrumented wheelset with strain gauges attached to measure contact forces (wheel load, lateral force, and tangential force) and positions, respectively. The test results were found to be generally consistent with the finite element analysis results, and it was also observed that the load position of each contact force influenced each bridge output. Finally, this paper proposes a method for calculating the contact position by solving a nonlinear equation. The calculation uses the results of the load tests and also wheel rotation angle, bridge outputs, wheel load, lateral force and tangential force which measured in running railway vehicle. Simulations were performed for various cases, and the contact positions were obtained stably and continuously. This suggests that the proposed method is reasonable and applicable to various situations.