Elastic moving body have attracted many researchers because the elastic moving body is superior to rigid moving body. Flapping motion of butterfly wing is one of the examples of elastic moving airfoil. Vortex ring is the evidence for fluid force generated by moving body. However, it is not easy to grasp the entire structure of vortex ring and estimate fluid force from vortex ring. In this study, we clarified not only the dynamic behavior of a pair of vortex rings but also the dynamic lift generated by flapping motion of butterfly wing. We implemented the 2DPIV to the flow field around butterfly wing from only two directions in order to cut off the quantity of information. From the visualization results, we predicted the dynamic behavior of vortex rings. It found that the vortex ring generated by upstroke is interfered by the induced flow of vortex ring generated by downstroke. That interference is resulted in the disturbance of developing and moving upward of vortex ring’s rear part generated by upstroke. From prediction result of vortex rings, we proposed the change and amplitude of dynamic lift generated by each stroke. Eventually, the dynamic lift tendency is matched with not only the estimation results but also direct measurement result. From that, we could predict the dynamic lift from the dynamic behavior of vortex rings. In addition, it found that upstroke of the butterfly wing hardly contributes the generation of dynamic lift because dynamic lift is negative and small on upstroke.

Aerodynamic characteristics of wings are determined generally by geometrical shape and Reynolds number. Wings in flows might deform and vibrate, which would affect the aerodynamics, provided wings have appropriate physical properties. In this study, self-excited vibration of torsional mode on rectangular wings with various densities and elasticities are focused on. Two non-dimensional parameters are introduced from the equation of torsional motion and relation with torsional vibration on the rectangular wings are investigated. It is found that occurrence of the torsional vibration is determined by the two non-dimensional parameters.

This study numerically investigates the unsteady aerodynamics of a small airfoil under a discrete longitudinal gust with large amplitude in low Reynolds number flow. A significant change in lift and drag forces appears in the freestream variation and is followed by transient forces with the same order amplitude in the forces. A shear layer separated from the leading edge of the wing generates small vortices. The pressure distribution around the airfoil with velocity vectors clearly suggested that the small vortices generate a low-pressure region on the airfoil surface.

When water with free surface in a reservoir is pressurized with air and jetted out from a nozzle attached to the bottom of the reservoir, the jets may periodically align outward in the radial direction and splash. Upstream of the periodic droplets splashing, water is sucked in as it swirls toward the nozzle. This suction vortex grows and enters the nozzle as a column of air. The process has been shown to be related to the shape of the suction vortex and its swirling velocity near the nozzle inlet and the occurrence of periodic droplets splashing. In this study, we investigated the relationship between nozzle inlet flow conditions and periodic droplets splashing in the case of sustained periodic droplet splashing. It was found that the swirling near the nozzle entrance affected the periodic droplets splashing.

In recent years, environmental issues such as carbon dioxide emissions have become a concern, and flow separation control such as vortex generators (hereinafter referred to as "VG") have attracted attention. However, VG has the disadvantage that the drag coefficient is reduced at low Reynolds numbers, but at higher Reynolds numbers, VG conversely becomes a drag. Therefore, we decided to compensate for this shortcoming by creating VG with ice. Specifically, the procedure is to produce ice at low Reynolds numbers and melt ice at high Reynolds numbers. In addition, previous studies have used the technique of freezing water droplets, which has the disadvantage that the height of the droplets is limited by gravity. We proposed a method in which a tube is filled with water, frozen in a cooling device, and pushed out with a syringe like a tokoroten, which does not limit the height of the tube. The following results were obtained by forming a VG with an object that reproduced ice and checking the change in drag coefficient. (1) It was confirmed that a rectangular VG shape reduces drag more than a cylindrical one. (2) The maximum drag reduction of about 8% was observed at a flow velocity of 2m/s with a VG breadth of 5mm and a height of 6mm. (3) The maximum drag reduction of about 17% was observed at a flow velocity of 5m/s with a VG breadth of 5mm and a height of 3mm.

In this study, the effect of the vertical direction and nozzle diameter d_N on heat transfer on the heated disc in cylindrical flow channel was investigated. When the heated disc was installed vertically downward (+g), for d_N = 10mm the Nusselt number Nu had a maximum value at the center of the disc due to impinging jet flow while for d_N = 180 mm the Nu had a maximum value at the edge of the disc due to natural convection. The average Nusselt number Nu_av along the radial direction on the disc decreased drastically with Richardson number Ri. The validation of the Nusselt number ζ had a minimum value of about 0.5 at 100 < Ri < 10000. On the other hand, when the heated disc was installed vertically upward (-g), the Nu became almost uniform along the radial direction on the heated disc for d_N > 50 mm. The Nu_av was two times higher than that for +g condition while the ζ had about 0.2 at (-Ri) > 100000.

Recently, plasma actuators have attracted attention as a new fluid control device. In this study, micro plasma actuators with an electrode width of millimeter order or less was applied to suppress the flow separation from NACA airfoil. The electrode geometry of the micro plasma actuators was sinusoidal electrodes. Jets induced by wavy electrodes collide with each other to form streamwise vortex. Streamwise vortex mixes the momentum inside and outside the boundary layer around the airfoil and suppresses flow separation. We used the square-type and staggered-type with four rows of sinusoidal electrodes. These plasma actuators were attached to the surface of airfoil. Flow visualization and PIV analysis were used to verify how the suppression of flow separation differs depending on the streamwise vortex and jet. The results showed that staggered-type, which induced streamwise vortex as the jet due to the plasma actuators was not pushed by the reverse flow and winds up, was more effective in suppression of flow separation than square-type.

An aeroelastic analysis method for vertical axis wind turbines based on the double multiple streamtube model has been developed using MATLAB Simulink/Simscape. In the multibody model of the new method, a blade was constructed by using only three elastic elements, i.e. upper, lower, and middle parts, instead of a number of equally-divided elastic elements adopted in the previous model to reduce the computational cost．In order to demonstrate the validity, the new method was applied to the aeroelastic analysis of a two-bladed H-Darrieus wind turbine. Turbulent inflow generated greater rotor torque, including fluctuation caused by structure displacements of the blade elements, than that in the constant wind speed case.

Atomization characteristics of superheated water jet sprayed from a swirl nozzle were experimentally investigated with the immersion method which captures atomized water droplets into a sampler filled with silicone oil. The spay nozzle is used for a water / liquid nitrogen rocket engine (WNE) that utilizes the vapor pressure of nitrogen evaporation as a thrust source when the heat is supplied from superheated water by mixing these two propellants in a mixing chamber. The effects of the parameters such as superheated water temperature and injection pressure on the Sauter mean particle diameter (SMD) and particle size distribution were investigated. The results indicated that the SMD decreased as the temperature increased. Compared to the fan spray nozzle at the same flow rate, the swirl nozzle was found to be able to obtain the same or lower SMD at any dimensionless degree of superheat, suggesting that the swirl nozzle can improve the performance of this engine.

Flow separation has been attracting great interest because it affects lift reduction and drag increase. In particular, development of control methods designed to reduce flow separation requires predicting the occurrence of separation. However, predicting the occurrence of flow separation is a challenging problem due to the strong nonlinearity and high degrees of freedom of flow phenomena. Additionally, the importance of physical quantities for accurate prediction remains unclear. To address these challenges, machine learning methods are considered effective as they are data-driven and superior in capturing nonlinearities embedded in data. In this study, we use machine learning methods to predict the occurrence of flow separation. We deal with flow separation phenomena in a channel flow with a bump. As a specific problem setting, we demonstrate the prediction of the time evolution of the wall shear stress field behind the bump using a machine learning model. Then, reattachment points are determined using the sign of the predicted wall shear stress field to identify the occurrence of flow separation. The results show that the proposed method can well predict the occurrence of flow separation. In addition, we investigate the dependence of prediction accuracy on the input components and the prediction time range.

This paper describes the flow characteristics of air injected from a slit nozzle into a rectangular container. The effects of the position and the length of nozzle brims at the nozzle exit, and of Reynolds number on the flow in a rectangular container, were investigated experimentally. The velocity distributions were measured using particle image velocimetry (PIV). The length of nozzle brims, b_n, was changed from 0 mm to 47.5 mm. When the slit nozzle does not have a nozzle brim, the jet flow does not reach the bottom of the container. However, when the slit nozzle has a nozzle brim with b_n > 20 mm at Re = 2,000, and b_n > 30 mm at Re = 4,000 and 6,000, the jet flow reaches the bottom of the container. When the slit nozzle was offset closer to the right wall side of the container, the jet flow from a slit nozzle with the brim on the left side reaches the bottom of the container as compared with that on the right side.

This paper describes the results of numerical studies on the mixing and diffusion control of coaxial jets.The effect of the exit area ratio between the inner round nozzle and the outer annular nozzle on characteristics of jet was studied. Numerical calculations were carried out using Large Eddy Simulation (LES). Changing the exit area ratio between the inner round nozzle and the outer annular nozzle from 1.5 to 1, it was found that the effect of the outer annular jet on the inner round jet decreased, resulting in a reduction of mixing. An increase in the exit area of the inner round nozzle and a decrease in the exit area of the outer annular nozzle resulted in the central axis of flow velocity along the central axis and a reduction in the jets spread.

In this study, we propose the use of a Plasma Synthetic Jet Actuator (PSJA) for cooling localized heat sources. Previous research on cooling heat sources using PSJAs has mainly relied on experimental investigations. However, we believed that employing numerical analysis could visually elucidate heat transfer within enclosed spaces. By conducting fluid-solid thermal coupling numerical analysis, we were able to confirm that cooling using PSJAs is indeed feasible, similar to the experimental findings.

This paper presents experimental results of DFC of heat source temperature using a plasma synthetic jet actuator（PSJA）. The unique feature of our study is that the control input to the PSJA is the duty ratio, a type of PWN, as the operating quantity. The feedback gain of DFC has not been established in previous studies, but in this study, the feedback gain of DFC was obtained by using LMI. In this study, the feedback gain of DFC derived by LMI was used to achieve efficient cooling of the heat source.

The purpose of this study is to reveal the characteristics of internal flow in wire-parallel plate electrode type electrohydrodynamic (ELD) fan and improve it to be more powerful fan. In order to understand the characteristics of the EHD fan more deeply, visualizations of the air flow in the flow channel and the exit area were conducted by using PIV and CFD analyses. In the experiment, air at atmospheric pressure and room temperature was used as a working fluid. Fan characteristics for the EHD fan, such as velocity profile and cross-sectional average velocity in the flow channel or at the exit area were shown as experimental results and considered in detail. In addition, the flow visualization, the instantaneous and time averaged velocity profiles by PIV analysis were shown while the comparison with experimental results described above, and differences of flow regime for different locations were discussed. Furthermore, two-dimensional steady state flow simulation by CFD analysis were also shown and discussed in consideration of experimental results.

Feedback control of the flow field by a controller using plasma actuators (PA) with a sparse processing PIV (SPPIV) as a observer was implemented in a wind tunnel test. The control target in this study is a Kármán vortex suppression around a circular cylinder. The time delay of the influence of the PAs on the flow field was quantitatively evaluated, and the control laws were set based on it. A particularly high control effect was confirmed by control with Sum-of Absolute-Value control, which determines the control input in the interval. A certain effect of Kármán vortex suppression was confirmed by feedback control. For more effective control, properties of the PA itself, such as burst ratio, should be considered.

In this study, our goal was to enhance boundary layer transition control through the use of plasma actuators. We developed a micro plasma actuator array via photolithography, designed to apply forces near the wall surface. Our analysis, conducted using Particle Image Velocimetry (PIV) measurements, revealed the generation of both positive and negative volumetric forces due to electrode interference, which led to a spreading of the jet flow. It became clear that this aspect needs to be addressed for further optimization. The comparison with conventional plasma actuators indicates a promising potential for the improved control of boundary layer transitions using our micro plasma actuator array, pending modifications to rectify the observed interference issue.

Jet fans are considered as simple components to boost the tunnel ventilation. But they contain some important and complex aspects in them. First, the authors discuss the principle of pressure gaining mechanism in tunnels by jet fans, which was established by Meidinger. Then, a sample calculation of overall efficiency by a jet fan is carried out for a typical case to show it’s just less than 20% with the reason why it takes such low values. Next, problems with the measurement of jet fan performances are discussed. The authors point out inaccuracy of measurement of the discharged air velocities with Pitot tubes and suggest the specification introducing thrust forces be more appropriate to define. Finally, the importance of commissioning on ventilation systems is stressed, and is urged to study it for the adoption.

Jet fans are installed in tunnels on the Metropolitan Expressway to ensure the air quality in tunnels and to provide an evacuation environment in case of fire. The jet fans are suspended above the roadway in the tunnels, and lane restrictions are required for many days for inspection. This experiment was started with the purpose of developing a new inspection method and reducing lane restrictions. In this experiment, the motion was analyzed using an acceleration sensor for the purpose of grasping the abnormality detection of the jet fan motion. From the analysis results, it was possible to obtain data that could be used to two types of abnormality detection: a method based on frequency analysis and a method based on trajectory analysis.

In order to secure the safety of the people at a fire in road tunnels, it is important to get to know about the longitudinal air velocity and the pressure distribution in the tunnel that would occur at the fire. These two parameters make us understand how the smoke moves and expands with time and how pressure difference changes with time between the fire source and the evacuation areas, which is essential to think about the safety of the people. The paper shows that the authors have developed the equation of motion for transient situation in tunnels with transverse ventilation systems and added a sample of the transient changes of the longitudinal air velocity and pressure distribution at an emergency in a transverse ventilated tunnel with plural ventilation sections.

When there are no stationary vehicles downstream of the fire source, smoke is exhausted downstream to maintain the evacuation environment on the upwind side of the fire in expressway tunnels. However, if there are stationary vehicles on the downwind side, it is necessary to control the movement of smoke until the victims have completed evacuation. In order to maintain a stable evacuation environment and improve the operation of the smoke removal system, which changes depending on the mine conditions during a fire, we have begun developing a system that uses smoke sensors to determine the location of the smoke tip and control the behavior of the smoke. This paper reports on an experiment using an invertercontrolled jet fan to control longitudinal air velocity in a full-scale tunnel.

In the study of tunnel fire safety, we focused on the behavior of evacuees during the first 10 minutes from the start of the fire. This is because the goal is to complete the evacuation within 10 minutes, and after the initial evacuation is completed, the ventilation system shifts to smoke exhaust operation. If there are evacuees who are caught in smoke during evacuation and their evacuation is delayed, the feasibility of smoke exhaust operation has not been examined yet. In this study, we used simulations to examine the effects on human damage caused by the time from the ventilation operation for initial evacuation to the start of smoke exhaust operation.

Longitudinal ventilation is the mainstream ventilation system for road tunnels in Japan, and in many cases, especially in long tunnels, low-speed ventilation control is introduced to reduce the longitudinal wind velocity near the fire point to as close to 0 m/s as possible. In Nihonbashi underground section, there are many underground buried structures such as sewers and subways, which must be avoided, and therefore there are many steep sections with low inner voids. In such sections, it is difficult to ensure an evacuation environment with conventional low air velocity control because smoke flows in an upward direction, which tends to expand the reachable area, and smoke descends quickly due to a decrease in the retention space. Therefore, a "Sectional smoke extraction system" that concentrates smoke extract airflow only in the vicinity of the fire point and its improvement system were studied. As a result, effective smoke evacuation was achieved even in steep sections with low inner airspace.

Austenitic stainless steel used in nuclear power plants sometimes meets a stress corrosion cracking during their long period of operation. The corrosion resistance of stainless steel is attributed to the repassivation of the chromium oxide film when it was damaged. If the corrosion rate exceeds the repassivation rate, the corrosion continues and leads to cracking. The polarization curve is important as an electrochemical property to evaluate the corrosion rate. In this study, we evaluated the effect of oxide film damage on the polarization curve of stainless steel. To neglect the effect of repassivation, we employed a rapid tensile test under a constant potential condition. Multiple tensile tests with different potentials were carried out and they yielded the polarization curve for arbitrary plastic strains, that is, arbitrary damages of oxide film. The results showed that the natural potential decreased and the current density drastically increased as the plastic strain increased. However, we found that the availability of the constant potential test was limited within a fixed range of measurement due to a restriction on the response rate of the measurement circuit.

Fatigue crack growth tests were conducted to clarify the coalescence behavior of multiple cracks due to fatigue fracture. SUS304 was used as the material, the shape of the specimen was plate-shaped, and notches were introduced by electrical discharge machining (EDM) on both sides of the smooth part in the center. The crack position was expressed by the distance between the crack faces and the distance between the crack tips. Slit-type fatigue cracks were adopted assuming cracks initiated by thermal stress in structural materials in fast reactors. The crack tip distance, S, was set to approximately 4.5 mm in order to investigate the relationship between the crack coalescence behavior under fatigue conditions and the crack coalescence behavior with the crack face distance, H. Fatigue tests were performed on specimens with a fixed S and varying H between 1.69 and 6.48 to 6.71. As a result of the experiment, the following facts were found. A white streak thought to be caused by plastic collapse was observed. However, the two cracks did not eventually coalesce. On the other hand, in past creep tests, when H is small (1.78), the cracks coalesce, and the creep test results and fatigue test results differ from past creep test results.

In order to investigate the coalescence behavior of multiple cracks due to creep crack propagation, a creep crack growth test was conducted under a high temperature environment of 600 °C using a specimen with two cracks, and the crack propagation behavior was investigated. The shape of the specimen was a flat plate, and two cracks were introduced by wire electric discharge machining, and fatigue cracks were propagated from the tips. The distance between cracks was expressed by the horizontal distance between the crack tips and the vertical distance between the two crack faces. It was found that the cracks may or may not coalesce depending on the position of the cracks, but the boundaries are not clear at this time. Observation of the fracture surface after the test revealed that the shape of the fatigue crack was curved, and the crack near the center of the cross section progressed more than the surface of the specimen. However, the width of the crack growth part due to creep was the same in the central part and the surface part. In addition, macroscopically, the crack propagated due to creep in the part where the crack propagated obliquely, but microscopically, the fracture surface transitioned from intergranular fracture to plastic collapse.

It is necessary to simulate a eutectic reaction and relocation behavior of boron carbide (B₄C) as a control rod material and stainless steel (SS) during a core disruptive accident (CDA) in an advanced sodium-cooled fast reactor designed in Japan. On that account, Japan Atomic Energy Agency with academic/industrial partners have been conducting a research project consisting of thermophysical property measurement of the B₄C-SS eutectic melt, B₄C-SS eutectic melting and relocation experiments, eutectic reaction mechanism investigation, and physical model development for a CDA simulation code and its reactor application. This project has accomplished the development of a basic physical model to simulate the B₄C-SS eutectic reaction in Phase 1. The objective of Phase 2 (2020-2024) is to upgrade the physical model for the improvement of reactor analysis accuracy. The model improvement is characterized by implementing a variable B₄C mass fraction for the B₄C-SS eutectic material. This paper describes the project overview and progress until JFY2022.

To enhance a safety of sodium-cooled fast reactors (SFRs), decay heat removal systems under natural circulation (NC) with a dipped-type direct heat exchanger (D-DHX) installed in an upper plenum of a reactor vessel (RV) have been investigated. During the D-DHX operation, the flow of the coolant at low temperature from the D-DHX into assemblies and an interwrapper gap (IWG) between them, and the radial heat transfer through a wrapper tube and the IWG among assemblies occur. Such phenomena in the core can remove the decay heat without external electric power supply. In terms of the design study, modeling of an RV using a CFD code (RV-CFD) with a coarse mesh arrangement has an advantage in a reduced computational cost. In this study, focused on the modeling of the IWG, to achieve a lower computational cost while maintaining the prediction accuracy, an influence of combination of the mesh number in the IWG and the pressure loss correlation on the core temperature distribution was investigated through the numerical analysis of a sodium experimental apparatus named PLANDTL-1. The result shows the coarse mesh with correlation reduced the IWF, or a circulation flow with the upward and downward flow in the IWG, and shifted the temperature distribution in the core to the high-temperature side.

The design of a containment vessel in a sodium-cooled fast reactor was optimized from numerical analysis on the hypothetical severe accident including sodium leakage and combustion. The analysis method is one of the base technologies of the design optimization system, ARKADIA, which integrates artificial intelligence, numerical analysis, and knowledge base. The numerical analysis was performed on the different design conditions including volume of the containment vessel and the safety equipment as optimization parameters. Atmosphere pressure in the containment vessel was selected as a safety evaluation figure. The combustion of the leaked sodium from the primary piping increases atmosphere pressure both in the compartment below a floor level and the upper compartment of the containment vessel. The iterative numerical analysis successfully found that the safety under this accident was kept even in the downsized containment vessel by selecting an effective safety equipment. This numerical analysis demonstrated the basic capability of design optimization in ARKADIA.

In order to improve the heat transfer performance of a heat pipe, the screen mesh wick contained in the copper tube container was pre-coated with a silica nanoparticle layer to enhance its capillarity. Pure water was used as the working fluid. In the experiment, the one end of the heat pipe was heated using a nichrome wire heater and the other end was cooled with saturated pool boiling of water. The experimental results showed that in comparison with the normal heat pipe, the thermal resistance decreased up to 46% and the maximum heat transfer rate increased up to 1.5 times if the amount of deposited nanoparticles was sufficient. The hysteresis after the MHTR condition was reached disappeared. The thermal performance was not deteriorated even after the maximum heat transfer rate condition was experienced. It was confirmed that the improvements of the heat transfer performances can mainly be attributed to the high water absorption property of the nanoparticle layer.

Flow Accelerated Corrosion (FAC) is a pipe wall thinning phenomenon to be monitored and managed in the power plants with high priority. Its management has been conducted with conservative evaluation of thinning rate, and residual lifetime of piping based on wall thickness measurements. In T-joint with a curvature part called a "crotch" in the area where pipes meet, the radius of curvature of the crotch becomes small, especially when the pipe diameter is small, and the flat tip of the probe commonly used in conventional UT measurement cannot sufficiently contact the measurement surface of the crotch, making wall thickness measurement difficult. The purpose of this study is to develop a method for estimating the maximum wall thinning of a T-joint based on detailed wall thinning trends at and around the crotch, and to introduce a multiplication factor necessary for estimating the wall thinning. It was found that the local thinning distribution near the crotch changed depending on the inlet conditions of the branch and main pipes. The multiplication factor is greater than 1 under the condition of maximum wall thinning at the crotch, but this value also varies depending on the evaluation conditions, and is shown to be approximately 1.5 at maximum.

Flow-Accelerated Corrosion (FAC) is a pipe wall thinning phenomenon to be monitored and managed in the power plants with high priority. Its management has been conducted with conservative evaluation of thinning rate and residual lifetime of piping based on wall thickness measurements. However, in the actual plants, noticeable case of the wall thinning occurred in branch and junction piping (T tube). There is a problem to manage the wall thickness of the part covered by reinforcing plate of the T tube, because measurement of this area is difficult to be conducted with ordinary ultrasonic testing devices due to the presence of the reinforcing plate. Our previous studies have developed methods for estimating wall thinning in areas where it is difficult to measure pipe wall thickness. The validity of this method was verified by actual plant data. However, considering its application to a new plant, this method may result in overly conservative evaluation results. Therefore, this study examines a simpler method for estimating wall thinning, including the handling of correction values for the estimated evaluation equation.

If the cooling systems of the spent fuel pool (SFP) is lost, scenarios such as evaporation of pool water, fuel exposure, fuel damage, and environmental release of radioactive materials are possible. As a measure against such a severe accident, SFP has provided portable spray equipment. However, it has been pointed out that the technical knowledge on thermal-hydraulic behavior and fuel damage expected when the SFP water level has lost is not enough. In this study, assuming a severe accident in which the SFP water level dropped abnormally, technical bases were established to evaluate the effectiveness of the spent fuel assembly cooling effect of the spray equipment under these conditions.

In pool scrubbing, one of the measures against severe reactor accidents (SA), a gas (non-condensable gas or condensable gas) containing fission products (FP) is introduced into the suppression pool. This pool scrubbing is expected to have the effect of suppressing damage to the containment vessel, as well as the effect of removing FP by transferring FP from the gas phase to the liquid phase through the gas-liquid interface. CRIEPI has acquired an experimental database on FP removal characteristics in pool scrubbing. In this study, we have obtained the aerosol DF data and empirical model by using CsI aerosol, inner diameter 1.5 m test vessel, aerosol spectrometer (Welas®) and several nozzles. Moreover, using the empirical model, we have compared the trends of the aerosol DF in different experimental systems.

In order to avoid boiling transition (BT) conditions in boiling water reactors (BWR), rewetting is an important mechanism in the quenching process. The effect of a droplet from another plate is observed to determine the importance of the effect of the droplet on the rewetting rate. Two metal plates are used for the heat transfer surface while lower ends of the metal plates are sandwiched between brass block columns and heated to 250-300°C. On the other hand, distilled water is pumped from the nozzle at a flow rate of 0.2-0.5 LPM. The nozzle is installed between two plates and sprays water in the left and right directions on the cooling surface. Wetting velocity is measured using continuous images recorded by a thermal imaging camera. Since the heat transfer mechanism of water vapor and droplets is dominant, it is expected that the collision of droplets will increase the rewetting rate.

A star-type highspeed planetary gear test rig have been developed. It has a power circulating structure, and the planetary gears are supported with flexible pins. The pin loads and the tooth root stresses are measured, and the following conclusions were reached. (1) The test capacity of the prototype is 10000 min-1 and the maximum torque was 287 Nm on the sun gear shaft. (2) The dynamic load of the flexible pin was about 13% of the DC component of the pin load. (3) At the gear resonance speed, the amplitude of the tooth root stress rised to 2.1 times compared with the low speed.

In order to reduce the noise of the spur gear pump, the authors have designed a modified tooth profile to reduce the meshing noise of the gears. The calculation program had created to find the optimum or suitable tooth profile modification. This program calculates the tooth root stress waveform with using the load meshing theory of gears. Then the program calculates differential of tooth root stress to evaluate its smoothness. The program repeats the calculation for various tooth profile modification shapes to find the modification design that achieves the smoothest root stress waveform, because it was presumed that the gear meshing noise was caused by abrupt changes in the root bending stress. In this calculation, constraints on machining of gears and limits on contact ratio were also considered. After the calculation, the suitable tooth profile modification was designed. Then the test gears were produced to verify the effect by the tooth profile modification to reduce noise. Finally, test gear pump with modified gears was driven, and its noise reduction effect was confirmed.

Gear mechanism causes notable noise and vibration synchronized with meshing contact cycle due to fabrication, wear and elastic deformation. To reduce the noise, some researchers have focused on changing cycle of meshing contact. The authors came up with an idea that helical pinion and rack gears that achieve non-constant transmission ratio can be applied to a cylindrical gear pair, and discussed a calculation method of the variable gear’s teeth profile for achieving a target non-uniform transmission ratio given as a function of an input angular displacement of a pinion gear with standard involute profile. This paper shows the experimental validation of a variable gear calculated by such method. The experimental result with respect to angular displacement of that almost matched theoretical one derived from a target transmission ratio, and the calculation method was confirmed as correct. On the other hand, frequency analysis was done to check the cause of transmission error and shows that some of the transmission error was caused by meshing contact error. Other than that, the acceleration caused by a variable of a transmission ratio is considered to rotate the driven gear by the angle of backlash, but the calculations show that the torque is small under the experimental condition.

When manufacturing the variable gear ratio rack, it is necessary to determine the allowable range of tooth surface error. In this study, I propose a method to determine the allowable range of machining error. At first, determine the allowable range of gear ratio error. Next, based on the allowable gear ratio error, the tolerance for machining error is determined by comparing the calculated tooth surface of the rack with the modeled error and the theoretical tooth surface. The test gear is manufactured, and tooth surface measurement and output performance measurement are performed. It was confirmed that the proposed method for machining error is useful.

The purpose of this study was to simplify the design of the tooth surface of face gear and to clarify the optimization method of the specification setting. Face gears have long been used in fishing spinning reels as a speed-increasing gear. Recently, face gears have also been adapted to geared motors for orthogonal reduction gears. However, the design method of the face gear is not supported by a standard theory, and its application is not common. To clarify the meshing of the face gear, the author introduced the idea that the meshing contact progresses along a straight line of action. The meshing point between the involute helical and face gear proceeds at a constant speed along the straight line of action. The velocity vector at the meshing point was divided into the direction of the line of action and the direction orthogonal to the line of action, and defined as the vector of the relative sliding velocity on the tooth flank. This clarified the sliding state of the tooth surface of the face gear.

The possibility of a tandem drive system combining two motors and a planetary gear train is being considered in response to the shift to EVs in the automotive industry. However, in order to take advantage of the ability to change drive conditions according to situations such as road conditions, it is necessary to clarify the torque characteristics of the planetary gear train during gear shifting. In this study, the effect of the moment of inertia of the ring gear on the torque fluctuation during gear shifting was examined through experiments and simulations of tandem drive of a planetary gear train.

In order to confirm the effect of material on the load-carrying-capacity, we compare the failure modes and load-carrying-capacities of phosphor-bronze micro-crossed-helical-gear, alloy-tool-steel micro-crossed-helical-gear and micro-crossed-helical-gear consisting of phosphor-bronze and alloy-tool-steel. We carried out acceleration endurance test on a crossed-helical-gear with a 0.2 mm module under the lubricant dropping condition only at the start of the experiment. As a result, in case of phosphor-bronze micro-crossed-helical-gear, extremely minute wear powder was spread thinly over the entire tooth surface, which was quite different from the tendency of wear powder in the alloy-tool-steel micro-crossed-helical-gear and micro-crossed-helical-gear consisting of phosphor-bronze and alloy-tool-steel. In case of alloy-tool-steel micro-crossed-helical-gear, At the stage where wear has not progressed and there are not many scratches on the tooth surface, the tooth surface does not retain the lubricant well and the lubricant may be discharged outside the tooth surface. The phosphor-bronze micro-crossed-helical-gear had failed tooth tips due to progressive wear, the alloy-tool-steel-micro-crossed-helical-gears had failed by plastic flow due to extremely high maximum hertzian pressure without progressive wear. On the other hand, the micro-crossed-helical-gear consisting of phosphor-bronze and alloy-tool-steel had failed due to localized high contact pressure caused by tooth tip interference. Therefore, the failure mode was different on the material.

The authors conducted operational tests on spur gears injection-molded with a composite resin of polyacetal and cellulose nanofibril (POM/CNF) and investigated the bulk temperature, noise, and fatigue life of test gears. As a result, several findings were obtained regarding the usefulness of CNF as a reinforcing material for plastic gears. However, there are still many unknowns about the effect of CNF. This paper investigates the mechanism of fracture of POM/CNF gears. Test gears were fabricated from POM/CNF composites. Endurance tests were conducted without lubrication. The test gears were operated at constant transmitted torque and rotational speed until failure. The results indicated that adding CNF improved fatigue life and caused less wear on the tooth face. Therefore, the fatigue life of POM/CNF gears is not affected by heat by tooth friction and wear. In addition, the addition of CNF deteriorates flowability during injection molding and forms many voids, so the cracks formed at the tooth root due to fatigue propagates toward the voids, and then test gears are breakage.

In recent years, there has been a demand for technology for achieving carbon neutrality. To meet this demand, technologies such as reduction of production energy, weight reduction of raw materials, and recycling have been studied for vehicle on-board electrical equipment. Aluminum bronze, which is one of the metal materials with low melting point and low density, has the properties that facilitate achievement of carbon neutrality. In this study, oil-impregnated porous aluminum bronze and tin bronze were exposed to a high temperature for a long time, and both materials were examined for changes in their tribological characteristics and sliding surfaces with a pin-on-disk friction tester and a chemical analysis instrument. The findings in this study are that oxides of the impregnated oil are formed on the sliding surface of each oil-impregnated porous material exposed to a high temperature, and tin bronze shows larger amount of oxides than aluminum bronze, and the formation of oxides contributes to decreasing the friction coefficient.

Ceramics are used in rolling bearings because they are lighter than metals, have excellent heat resistance, and have insulating properties. On the other hand, another feature of ceramics is that some have high Young's modulus. In rolling friction, it is well known that surface elastic deformation affects rolling resistance. In other words, it is possible to suppress rolling resistance by using materials with high rigidity, that is, high Young's modulus. In this study, we measured the rotational torque of a ball bearing whose rolling elements were changed to ceramics, and clarified the influence of the material of the rolling elements on the torque. Rolling elements of ball bearings made of SUJ₂, ZrO₂, and Si₃N₄ were used, axial loads of 10N and 100N were applied, the inner ring was rotated at 5400min^-1, and the rotational torque was measured. At both loads, the rotational torque of Si₃N₄ was the lowest. On the other hand, when SUJ₂ and ZrO₂ are compared, ZrO₂ has low rotational torque at 10N, and SUJ2 has low rotational torque at 100N.

This paper investigates Interior Permanent Magnet Synchronous Motor (IPMSM) in numerical simulation by COMSOL Multiphysics^Ⓡ. Four kinds of rotor structure of IPMSM, V-shape type, straight shape type, inner forward curve type and outer forward curve type, are proposed and investigated to reduce torque ripple of rotor. Comparison of their torque performance are carried out. It was found that V-type rotor structure shows best torque performance in the same condition of stator. Furthermore, one customized application case is developed and confirmed for designing rotor structure conveniently.

In the tightening of a large number of bolts, the coefficient of friction has a large influence on the variation of initial axial force. The tightening work coefficient a, which indicates the variation of tightening torque, also affects the variation of initial axial force, but has not been studied in detail. Based on the results of tightening tests conducted by the Japan Screw Research Association, a was estimated to be 0.080 for oil-lubricated fastening, 0.048 for rust-preventive oil-lubricated fastening, and 0.140 for fastening without lubrication at the 90% confidence limit, when initial axial tension is 70% of yield point. According to the experimental results using the design of experiment method (L₈(2⁷)) orthogonal table), a was 0.059 for fastening with anaerobic adhesive and 0.131 for fastening without lubrication at the 90% confidence limit with human error.

Loosening of the screw can be classified into types depending on the cause and the phenomenon, there is a "loose by the fluctuation of the axial load" as one of them. Loosening mechanism according to fluctuation the axial load is the sliding of the bearing surface caused by sliding of the threaded portion by fluctuation the axial force and a rotation of the nut by torsion torque accumulated in the bolt shaft. In this study, the effect of preventing "loosening due to changes in axial load" of bolts and nuts that have been developed aimed at loosening prevention effect was investigated from these viewpoints. As a result, the axial impact load decreased the most for Active-X bolts and nuts compared to other conditions. In addition, the amount of reduction in axial force after impact is also the smallest for the Active-X bolt and nut among the four conditions. From the above, it is considered that both the magnitude of the impact load and the amount of depression of the bearing surface affect the reduction in axial force due to the axial impact load.

When bending fatigue strength was evaluated using the actual stress (maximum stress) at the critical point, the bending fatigue strength depends on the geometry near the critical point. In order to propose a bending fatigue design method applicable to machine elements of arbitrary shape, it is necessary to verify the shape dependence of the bending fatigue strength. Since the notched bending fatigue specimen and the notched tensile fatigue specimen have similar normal stress distributions near the critical point, a correspondence is considered between the tensile fatigue strength and bending fatigue strength. In this study, the relationship between the fatigue strength and stress gradient was investigated by tensile and bending fatigue tests. As a result, the equivalence of tensile fatigue strength and bending fatigue strength was recognized, and a method to estimate the bending fatigue strength from the stress gradient was proposed.

The connection of bolts and nuts is an important mechanical component. In the case of a single nut, there is a high likelihood of the nut becoming loose, which will lead to a serious accident. In the case of double nuts, the nuts are less likely to loosen, but their removal becomes more difficult. To solve these problems, a new bolt called PLB has been developed. In this study, Junker vibration tests in which bolted fasteners are subjected to vibration and numerical analysis modeling the experiments will be conducted to investigate the phenomena that cause loosening. The experiment was performed 3 times and the result was calculated as the average value. The bolt was vibrated 2000 times by moving the vibration plate up and down with an axial force of 20kN and a vibration frequency of 12.5Hz. After that, this experiment was modeled by computer and numerical analysis was performed. Marc/Mentat2018, a general-purpose finite element code, was used for numerical analysis. Regarding the single nut, the reason for the loss of residual axial force is thought to be that the directions of the tangential force acting on the nut were scattered when vibration was applied. The high locking performance of the double nut is because the two nuts pull the bolt in opposite directions. Regarding PLB, it was found that high locking performance was obtained because the contact state between the bolt and nut resembled a double nut.