In this paper, we deal with vibration damping analysis of acoustic black hole models. We created an acoustic black hole model that has a bidirectional residual plate thickness for the target of study. For comparison, we also made two acoustic black hole models, that has a unidirectional residual plate thickness type and that has no residual plate thickness type. These three models were created by using CAD and FEM. Using these three models, we calculated resonance frequencies and modal loss factors in each mode and compared the vibration damping performance.

Vibration and sound damping are important industrial and environmental technologies for automobiles and structures. The proposed damping device consists of a viscoelastic gel partially sandwiched between a box-sectioned highly rigid constraining layer and a frame member. This damping structure converts vibration energy into thermal energy, thereby providing damping. In this paper, numerical analysis using FEM and the proposed SEA method are used for the L-shaped panel structure including two beads. A model in which a vibration-damping device is installed in the center of the bead panel parallel to the long side of the bead. And this bead panel is connected with a flat plate in L-shape. This paper focuses on the validation of the proposed SEA method and the effects of the presence or absence of the damping device on the wave propagation characteristics between two panels in an L-shaped panel structure.

In conventional pipe support structures, the frictional force between the pipe and the support structure becomes unstable, making it difficult to reflect this in seismic response analysis. Therefore, the axial direction of the pipe was treated as unconstrained, and the frictional force between the pipe and the support structure was not considered. The authors propose a support structure consisting of friction materials and elastic bodies to stabilize the frictional force between the pipe and the support structure. They verified its force-displacement relationship through loading experiments. The results confirmed that the proposed structure's force-displacement relationship maintains a stable hysteresis loop shape regardless of the input displacement speed, vibration frequency, or the pipe's surface condition. However, to reflect this support structure in seismic response analysis, it is necessary to model its force-displacement relationship. This paper presents a modeling method for this support structure from the perspectives of a nonlinear spring element and a finite element model. Analysis conducted on both methods showed good agreement with experimental results. Therefore, seismic response analysis incorporating these two models will rationalize the design to reduce the seismic response acceleration and response displacement.

We proposed a new vibration control device consisting of a constraining frame and a viscoelastic layer to realize high vibration control performance. The proposed new vibration control device consists of a viscoelastic gel partially sandwiched between a highly rigid constraining layer with a box cross section and a frame member. We evaluated this vibration system and obtained very high damping effects in the lower eigenmodes for high rigid bead panels. However, for higher eigenmodes, we could not get sufficient damping effects because local modes occur in the flat regions without the damping device outside of the two beads. To improve this situation in this study, we add double-layer-type damping sheets on the flat regions as hybrid damping structure. This structure is modeled and analyzed numerically by FEM, and the changes in vibration reduction characteristics are obtained using the MSE method．

In Japan, where earthquakes occur frequently in recent years, systems and structures to reduce the damage caused by earthquakes have been attracting attention.The purpose of this study is to investigate efficient vibration and wave damping methods by focusing on the acoustic black hole proposed by Mironov.Since acoustic black holes are dangerous due to their sharp tips, this paper employs a crater-type acoustic black hole in which the thickness of the panels decreases in a circular manner toward the center. And a hybrid vibration analysis using statistical energy analysis (SEA) and FEM for a model of two panels connected in an L-shape and given a crater-type acoustic black hole with a damping layer on one side. We focused on the validation of the proposed SEA method and discuss the effects on the wave propagation characteristics between two panels in an L-shaped panel structure when a crater-type acoustic acoustic black hole is given.

As an approach to demonstrate the seismic resilience of structures, seismic response analysis has been increasingly used to evaluate structural integrity. Generally, analytical models capable of expressing intricate nonlinear behavior tend to become complex, requiring numerous variables to be set. It has been confirmed that employing metaheuristic optimization methods, such as genetic algorithms, is effective for identifying these variables. However, optimization methods like genetic algorithms necessitate parameter settings, which significantly impact the search accuracy (convergence accuracy of the objective function). In response, we have developed an optimization method (FHPFO) that does not require parameter settings. Its effectiveness has been verified using benchmark functions and engineering benchmarks. However, it remains unverified for the hysteresis models of dampers. Therefore, this paper demonstrates variable identification for a steel damper which exhibits strong nonlinearity and cannot be represented by simple bilinear models. Moreover, the FHPFO was compared with other optimization methods using the highly multimodal CEC2017 benchmark functions. These analytical results reveal that even for variable identifications with strong nonlinearity, appropriate variables can be derived, and the effectiveness of FHPFO was confirmed in the high-dimensional and highly multimodal CEC2017 benchmarks.

Many countries worldwide are advancing the development of next-generation reactors to improve safety. In Japan, rubber-bearing technology is being considered as part of earthquake countermeasures in these reactors. The force-displacement relationship of rubber bearings varies with compressive stress and shear strain, exhibiting strong nonlinear characteristics near ultimate behavior. Additionally, due to the recent increase in seismic activity levels, vertical seismic responses are considered significant when evaluating structural integrity. The authors have developed a hysteresis model that accounts for these characteristics in horizontal and vertical directions. Seismic response analysis beyond the design basis ground motion was conducted using this model, confirming the strong nonlinear relationships. Consequently, this model can accurately reproduce the force-displacement relationship in horizontal and vertical directions up to ultimate behavior. This paper presents the composition of the hysteresis model, considering these hysteresis characteristics.

Large earthquakes occur frequently in Japan, and it is expected that the occurrence of large earthquakes may cause the shutdown or destruction of a variety of equipment and structures. Therefore, this study investigates the effect of installing vibration control devices on ground-mounted photovoltaic panels to reduce their seismic response. As part of this study, Shaking table tests were conducted on a reduced test specimen and loading tests were carried out using the vibration control device. Finally, the appropriate installation method of the vibration control device has been studied, and the ideal vibration control device for solar panels was considered. In conclusion, the response reduction effect was evaluated based on the shaking table test results. Evaluation methods for actual equipment are also being considered. As a future prospect, based on the results, efforts will be made to improve safety during actual earthquakes, study the appropriate installation method of the vibration control device, and consider the optimal vibration control device itself. Simulations are performed when a vibration control device is added to the actual machine.

The research purpose is to improve the functional maintenance performance of elevators during earthquakes. The study has been examined on both experimental and analytical studies. A five-story building model and an analytical model of the seismically isolated elevatorway were constructed and response analysis was conducted. As a result, the results showed that the response acceleration and displacement of the isolated hoistway were reduced, and it was considered that the seismic function maintenance performance of the isolated hoistway would be maintained if the clearance between the building and the hoistway was sufficient. A test specimen was created based on the analytical parameters. Shaking table tests were conducted using the test specimens. The effectiveness of the isolated hoistway is examined from shaking table experiments as well as analysis.

Predictive maintenance is attracting attention as a low-cost and efficient maintenance method compared to preventive maintenance and after-the-fact maintenance. However, one of the challenges in predictive maintenance is the need to accurately detect and identify equipment anomalies. Therefore, this research aims to perform predictive maintenance with high accuracy using AI. In this paper, from the viewpoint of vibration engineering, the condition of the target equipment is monitored through vibration monitoring to predict the possibility of detecting abnormalities. FRS analysis of the time history acceleration data of the equipment makes it easier to extract the characteristics of the vibration. However, there are many issues to be considered, such as the possibility of erasing important vibration features if the attenuation setting is too large when using FRS, and the relationship between the number of dimensions and accuracy when performing machine learning. Taking them into consideration, whether the machine learning of changes in waveforms due to damping and differences in discrimination results depending on the number of dimensions can accurately detect abnormalities was verified. As a result, the use of FRS with a small amount of damping in the feature extraction confirmed the reduction of extra noise and waveform deviations.

Floating seismic isolation building has been proposed as a measure to reduce seismic response of small modular reactor (SMR). Demonstration experiment on floating seismic isolation building was conducted in February 2024. Seismic response analysis model for OpenFOAM was built by reference to the demonstration experiment. The analytical model consists of a pool, water, and a floating structure on the water. To confirm the availability of the analytical model, the time history analysis was conducted using a sine wave with an amplitude of 0.05 m in the vertical direction and horizontal direction, respectively. As a result, the maximum response displacement in horizontal direction by the horizontal input was reduced by 53.8 % compared to the input wave, but the maximum response displacement in the vertical direction by the vertical input was amplified by 515 % compared to the input wave, due to the noticeable drift in the vertical response displacement. The result indicated that the current analytical model has a problem in reproducing behavior in the vertical direction, and we will continue to improve the analytical model.

Seismic isolation structures, using devices such as laminated rubber bearing, shift the natural period of the structure to avoid resonance phenomena and significantly reduce seismic forces by incorporating damping properties. This approach has been considered not only for general buildings, but also for critical infrastructure such as nuclear power plants. However, in recent years, earthquakes exceeding the maximum seismic events designed for nuclear power plants have been observed on several occasions. Therefore, it is crucial to assess the safety of structures against beyond design ground motions. In this study, a nonlinear seismic response was performed to investigate the impact of retaining wall collisions on the isolation building and internal equipment under large earthquake scenarios. The parameters considered include the seismic ground motion, amplification factor, clearance amount, collision restitution stiffness, etc. As a result of this study, we confirmed that not only the damage to the isolation building but also the damage to the internal equipment should be considered for the seismic risk analysis with collision.

This paper presents a data-driven modeling approach for damping devices using deep learning, which can be applied to the seismic response analysis. The proposed model consists of four-layer stacked Long Short-Term Memory and is capable of creating hysteresis loops for the damper whose damping coefficient switches at a specific value. The training data for the proposed deep learning model are analytical values of displacement, velocity, and force obtained from the fundamental waves, such as sinusoidal wave inputs. Dynamic analysis is performed using a Single-Degree-of-Freedom system seismic response analysis model in which the proposed model is adapted to both damping and spring elements, and the results are compared with those obtained using the Maxwell model by using response waveforms and response spectrum. This paper demonstrates that the proposed damping model can capture the force-displacement relationship of oil damper, which has nonlinear characteristics without using equations, and that the seismic response analysis results obtained with the proposed model are as accurate as those obtained with the existing methods.

This study aims to develop a new seismic design methodology incorporating elastic-plastic response analysis of piping systems, including piping support structures. An elastic-plastic finite element analysis model was constructed for piping support structures. A gate-type piping support structure was analyzed using ANSYS software. The analysis result was compared with experimental data to improve model accuracy. Because there was a discrepancy in the load-displacement relationship between the experimental result and the analytical result, the boundary conditions at loading points were re-examined. Consequently, the maximum reaction force and the load-displacement relationship of the gate-type support structure showed good agreement with the experimental result.

Oscillating Water Column (OWC) wave power generation system consists of a primary conversion unit that generates air energy from waves and a secondary conversion unit that generates electricity from the air energy. In recent years, it has been confirmed that with dual air chambers in the primary conversion unit, a two-degree-of-freedom vibration is generated, allowing energy absorption over a wide frequency range. In this study, a model with triple air chambers was constructed to determine if a three-degree-of-freedom vibration would occur and if this would improve efficiency. The vibration characteristics were evaluated through tank experiments. As a result, the amplitude and phase of the three air chambers varied with the period. Additionally, it was observed that the contribution of each air chamber to energy conversion changed with the wave period, indicating the characteristic of converting wave energy into air energy across a range of short to long periods.

Surges occur in compressor systems including turbo compressor at low flow rates. Surges not only degrade the performance of the compression system but can also damage the compressor system. There have been few studies on low-flow rate centrifugal compressors, and their dynamic characteristics are still unknown. In this study, the behavior and inception process of surges in a low flow rate centrifugal compressors were investigated. As a result, it was found that surges occur even in low flow rate compressors with small plenum, and that small pressure fluctuations that are precursors to the occurrence of surges occur.

The design basis ground motions have been revised to improve the seismic resistance of nuclear power plants. The reduction of seismic forces not only horizontally but also vertically has required more critical than in the past to ensure the seismic resistance of components. Notably, the design of a Sodium-Cooled Fast Reactor will require reducing the seismic forces applied to the components because of the components with thin wall thickness. To overcome this problem, the authors plan to introduce a seismic isolation system. When the sloshing wave height is small, it can be approximated with a linear vibration model. However, when the sloshing wave height increases and the sloshing becomes nonlinear, it is necessary to evaluate the wave height using other methods such as numerical analysis. Although the evaluation of nonlinear sloshing wave height is important, there are few examples which quantitatively evaluate the wave height of nonlinear sloshing. This paper reports on the study result of the sloshing water test necessary for developing the predictive evaluation method for nonlinear sloshing wave height and impact load acting on the flat roof applied to cylindrical tanks.

The design basis ground motions have been revised to improve the seismic resistance of nuclear power plants. The reduction of seismic forces not only horizontally but also vertically has required more critical than in the past to ensure the seismic resistance of components. Notably, the design of a Sodium-Cooled Fast Reactor will require reducing the seismic forces applied to the components because of the components with thin wall thickness. To overcome this problem, the authors plan to introduce a seismic isolation system. When the sloshing wave height is small, it can be approximated with a linear vibration model. However, when the sloshing wave height increases and the sloshing becomes nonlinear, it is necessary to evaluate the wave height using other methods such as numerical analysis. Although the evaluation of nonlinear sloshing wave height and sloshing load is important, there are few examples which quantitatively evaluate the sloshing load acting on roof . This paper reports the results of the reproduction analysis carried out using the VOF method.

The design basis ground motions have been revised to improve the seismic resistance of nuclear power plants. The reduction of seismic forces not only horizontally but also vertically has required more critical than in the past to ensure the seismic resistance of components. Notably, the design of a Sodium-Cooled Fast Reactor will require reducing the seismic forces applied to the components because of the components with thin wall thickness. To overcome this problem, the authors plan to introduce a seismic isolation system. When the sloshing wave height is small, it can be approximated with a linear vibration model. However, when the sloshing wave height increases and the sloshing becomes nonlinear, it is necessary to evaluate the wave height using other methods such as numerical analysis. Although the evaluation of nonlinear sloshing wave height is important, there are few examples which quantitatively evaluate the wave height of nonlinear sloshing. This paper reports the results of research on the sloshing load evaluation method based on theoretical calculation.

The design basis ground motions have been revised to improve the seismic resistance of nuclear power plants. The reduction of seismic forces not only horizontally but also vertically has required more critical than in the past to ensure the seismic resistance of components. Notably, the design of a Sodium-Cooled Fast Reactor will require reducing the seismic forces applied to the components because of the components with thin wall thickness. To overcome this problem, the authors plan to introduce a seismic isolation system. However, the natural frequency of first order sloshing may be close to the response frequency of the Sodium-Cooled Fast Reactor with the seismic isolation system, and the sloshing wave height and the vertical load is expected to increase. Therefore, the authors studied the predictive evaluation method of load on the roof under seismic wave excitation. This paper reports on an overview of this method.

This study investigates the phenomenon of in-line vibration of a square prism, one of the structural elements, in the flow direction. The purpose of this study was to control vibrations by directly controlling the flow separating from the object by attaching control plates to the corner of the object surface of the square prism. The number of control plates installed at the corners of the square prism and the method of installation were varied. Moreover, the control plates were perforated and non-perforated. In the experiment, the test model was installed in a free vibration apparatus that can vibrate only in the flow direction in a wind tunnel, and the flow-induced vibration response characteristics were investigated by changing the number and the presence of the control plates. Instantaneous displacement of the model was measured by means of Laser Displacement Anemometer. From the experimental results, it was found that the vibration effect obtained differs depending on the method of installation and shape of the control plates. Therefore, the method used in this study can suppress the displacement of flow-induced vibration in the-line direction.

A study on the noise characteristics and blade performance of propellers with leading edge protuberance (LEP) was conducted in order to reduce the fluid dynamic noise generated by drone propellers. Noise, thrust and torque measurements were carried out to investigate the effectiveness of a LEP on reducing noise and improving wing performance. As a results, neither noise reduction nor improvement of wing performance were found for the wing with LEP compared to the wing with straight leading edge. The investigation in which the mounting position of the LEP was changed found that the LEP mounted near the wing tips, where the rotation speed increases, has a significant effect on the deterioration of the noise. In addition, the investigation using wing models with different wavelength and amplitude found that longer wavelength and smaller amplitude of LEP improves the noise characteristic and wing performance because the leading-edge shape becomes more similar like the linear leading edge.

Small axial fans are widely used for cooling electronic devices, where the installation of fans in a small space such as a narrow duct can lead to the radiation of intense aerodynamic noise. The methods for reducing the aerodynamic noise from the axial fans are necessary to be established. As a one of noise reduction technique, a resonator-type silencer to an axial fan is focused on. The objective of this study is to evaluate the effects of the resonator on the acoustic radiation from a small axial fan installed in a narrow duct. The narrow-band tones at the blade passing frequency, its harmonic frequencies and the first harmonic frequency of rotational number of the fan were observed from the fan without a resonator. The control effects of a resonant tube with adjustable depth installed in the fan casing on the acoustic radiation were investigated. As a result, the acoustic radiation were weakened at the blade passing frequency and its first harmonic frequency for different resonator depths. The resonance frequencies of the three-quarter- and one-quarter-wavelength modes of the resonator with these depths agreed with the blade passing frequency and its first harmonic frequency, respectively. Meanwhile, these tones were often intensified with other resonator depths. For the acoustic radiation at the frequency of the first harmonic frequency of the rotational number, sound reduction effects were obtained over a wide range of resonator depth, where the frequency did not match the resonance frequencies of the resonator.

This study investigates the self-excited vibration of concentric tubes subjected to double axial annular flow. Recent designs in nuclear reactor components involve a long circular cylinder containing an elastic hollow tube, which in turn houses an elastic solid bar. Axial flow through the annulus between these components can induce vibrations of tubes. While previous research has extensively examined vibration in concentric tube systems subjected to single annular flow, research on concentric tube systems subjected to double annular flows are not seen. In this research the equations of motion for a concentric tube system subjected to double annular flows are shown and the stability of self-excited vibrations using complex eigenvalue analysis are investigated. The coupled vibration modes of the hollow tube and solid bar are derived by superpositions of vacuum modes. Based on this theory, the simulation studies are performed. Simulations are validated by comparing the results with those of concentric tube systems subjected to single annular flow. In addition, this study investigates how the Young's modulus and length of the tubes affect the critical flow velocity. It is found that the smaller the Young's modulus and the larger the length of the structure, the smaller the critical flow velocity. The coupled modes are also displayed, and it is confirmed that the modes are distorted at the critical flow velocity.

In this study, one-dimensional simulation was used in this study for internal combustion engines to analyze the exhaust pressure of the mufflers and calculated the exhaust noise from the results of the exhaust pressure at the muffler outlet． The effect of reducing exhaust noise was investigated by changing the internal structure of motorcycle mufflers and compared the differences in exhaust noise between experiments and simulations． As a result, the differences in exhaust noise between original and modified mufflers at stationary noise and constant speed tests were possible to be reproduced even in a one-dimensional simulation if the internal structure was major changed．

This study aims to develop a small water hydraulic motor. In the design of the motor, a rotary piston type was adopted, which does not require a special valve mechanism. The basic shape of the rotary piston is a Reuleaux triangle, with apex seals installed at the three vertices. The internal shape of the housing on which the rotor slides was designed to be the envelope of the arc trajectory of the tip of the apex seal. The tangent to the locus of the center of the arc at the tip of the apex seal was determined, and the housing was designed to have a shape that was expanded outward in the normal direction by the radius of the arc. The rotor was made of gunmetal, the apex seal was made of PEEK, and all other parts were made of stainless steel. The dimensions of the motor body are 50 x 50 x 50 mm. The rated pressure is 3.5 MPa, and rotation in both directions is possible by switching the pressure. Experiments showed that the motor can rotate in both directions at low pressure.

Pneumatic actuators have several advantages for industrial applications, such as, high power/weight ratio, low heat generation in the repeated operation, which is a serious problem for electric motors. However, due to the compliant characteristics of the servo system caused by the air compressibility, it is easily affected by frictional force during position control, making it unsuitable for high-precision application. Ultra-high precision positioning technology has the potential to widely apply pneumatic actuators in precision work and lead to industrial breakthroughs. In this study, we propose a nanometer-order positioning technology using a practical general-purpose pneumatic cylinder sealed with a common rubber gasket, and verify the possibility of industrial application through several experiments.

Torque-unit Manipulator (TUM) is a novel type of space manipulator that does not incorporate motors within its joints. Instead, it attaches torque-units, which combine discs and motors, to each link. TUM can control the links using conventional manipulator control laws, but there is an issue of residual angular velocity in the discs after control. Previous studies have proposed methods to reduce this residual angular velocity to zero. In this research, we focus on the 2-DOF TUM, aiming to find link motion trajectories that bring the link to the target angle while simultaneously reducing the residual angular velocity of the disc to zero through simulation. Our method generates the motion trajectories of the links by adjusting the value of a single free parameter included in a sixth-degree time polynomial, given the target angle and the initial angle. And minimize the Euclidean norm of the residual angular velocities of the two discs.

Additive manufacturing (AM) technology is the layer-by-layer stacking of materials based on a three-dimensional (3D) digital model. It has gained popularity owing to its ability to fabricate complex shapes quickly and at a low cost, while minimizing material loss. This paper presents the development of a novel additive printing system by a slant direct-drive parallel mechanism. The modeling stage has a six degree-of-freedom motion, along with a fixed material supply head. Positioning angle error of the modeling stage affects the accuracy of the modeling. In this report, we describe the repeatability of the positioning angle and tilt control of the modeling stage with angle correction.

We have developed a rotational/linear two-degree-of-freedom switched reluctance motor (2DOF-SRM) as an actuator capable of rotary, linear, and combined motion. Using 2DOF-SRM, we have achieved independent thrust control, torque control, linear speed control, linear position control, and rotational speed control. However, in terms of position control for rotation angle, the double salient pole structure of the SRM limits the stop position of rotation to the angle where the salient poles align, thereby rendering high-resolution control unfeasible. In this study, we investigated the application of a micro-angular position control method to the 2DOF-SRM to overcome the limitation imposed by the SRM's structural constraints on the rotation stop position. Furthermore, with the aim of achieving simultaneous control of angular position and linear position, we developed zero-torque linear position control and conducted demonstration experiments. Finally, we investigated a method for simultaneous rotational and linear position control using micro-angular position control and zero-torque linear position control, and verified its operation through simulation.

Fishing line artificial muscles are fabricated by twisting nylon threads into a coil shape. Due to thermal contraction properties of nylon threads, they contract reversibly in response to temperature change. By using conductive nylon threads or by wrapping electric heating wire, the fishing line artificial muscles can be activated by electrical heating. However, local overheating often leads to breaking. Additionally, without a cooling mechanism, there will be a difference in the response speed of expansion and contraction. In this paper, we aim to realize a heating and cooling system with fluid to prevent breakage and improve response. For this purpose, a prototype of a tube integrated with fishing line artificial muscle is constructed and its response characteristics are verified.

A 3D microstage for high-precision friction force measurement has been developed. This 3D micro-stage is driven in three dimensions by electrostatic actuators and can be employed as a novel driving mechanism for atomic force microscopy (AFM). The 3D microstage is fabricated using MEMS (microelectromechanical systems) technology. The maximum displacements of the 3D microstage were measured to be 6.1 μm, 6.8 μm, and 3.6 μm in the X, Y, and Z directions, respectively. An on-chip AFM was completed by fixing this 3D microstage and a cantilever using magnetic force. The distance between the cantilever probe tip and the stage was approximately 2.9 μm.

In this study, we conducted real road tests using a series HV (hybrid) that is popular in Japan, and compared the results with the analysis results of a series-parallel HV that the authors have previously investigated, with the aim of proposing an eco-driving method for series HV on real roads. As a result of a comparative analysis of the fuel efficiency of series HV and series-parallel HV on real roads, we found that the series HV has less change in fuel efficiency in urban areas, rural areas, and on highways compared to the series-parallel HV. In addition, for series HV, there is no correlation between fuel efficiency and driving conditions such as frequency of acceleration and deceleration. Therefore, Series HV is considered to be a system that has little change in fuel efficiency in response to changes in vehicle speed due to traffic flow on real roads and changes in driving conditions such as the frequency of acceleration and deceleration due to driving operations by the driver.

Reliable hydrogen combustion aero engines will be needed for future aircrafts including UAVs (Unmanned Aerial Vehicles). In our previous study, we established how to supply a lubricant into a micro reciprocating engine (FG-11, originally a 4-stroke gasoline engine) and succeeded in its continuous operations with hydrogen. Delayed ignition timing was needed to prevent the engine stalls at higher hydrogen flow rates. In this study, the engine was operated with various ignition timings with hydrogen and break power and thermal efficiency were measured. Also, the pressure in the cylinder was measured to clear its combustion process. When the ignition timings are far before TDC, the break powers are low, and it will cause the engine stall because the compression work increased. To maximize the power in a micro reciprocation hydrogen engine, it is important to spark in the narrow range near the TDC due to the short ignition delay and high burning velocity of hydrogen.

Thermoacoustic systems enable mutual energy conversion between heat and sound. Thermoacoustic devices have no moving parts, which makes them simple and reliable with a long lifespan. Thermoacoustic technology has been the subject of many research studies in the recent past because of its simplicity and potential uses in renewable energy systems. Numerical simulation plays a key role in the development of thermoacoustic systems. The computational fluid dynamics and thermoviscous acoustic simulation approaches are used for numerical analysis of a traveling-wave thermoacoustic engine in this study. The simulations are performed using the commercial software COMSOL Multiphysics^®. The results are compared in terms of computational speed and accuracy.

Urea-SCR catalysts for NOx purification exhibit lower purification performance at the low-temperature below 200°C. An electrically heated catalyst (EHC) is one of the effective methods to improve conversion rates.

In this study, reactor tests were carried out using EHC test pieces to compare the deNOx performance of catalyst heating and gas heating. In the former, the catalyst substrate was heated directly, while in the latter, the gas flowing into the catalyst was heated. The results showed that catalyst heating was superior in terms of heating rate until about 50 s after the start of heating, after which gas heating became dominant. Furthermore, the wall temperature inside the catalyst was on average about 13 °C higher with gas heating than with catalyst heating at steady state. Gas heating was superior to catalyst heating in terms of the time it took for the conversion rate to reach steady state and the conversion rate at that point at the same power output. The study concluded that gas heating improves the purification rate more effectively than catalytic heating.

Due to global warming, industries are focusing on reducing CO2 emissions by exploring e-fuel. E-fuel, produced via Fischer-Tropsch synthesis using H2 from renewable energy and CO2 from the atmosphere, resembles diesel and can power existing diesel engines. Its composition can be easily adjusted during production to enhance combustions. To optimize combustion performance, an experiment was conducted using a 0.5-liter, single-cylinder Diesel engine with an externally driven supercharger. The study involved three types of e-fuel at low, medium, and high loads under steady state conditions: engine speed 2000 rpm, injection pressure 140 MPa, and EGR 0%. Various properties of e-fuel such as density, distillation, cetane number, kinematic viscosity, and reaction rate were analyzed for their impact on ignitability, heat balance, and emissions (NOx and soot). The goal was to identify conditions that optimize combustion efficiency.

Ammonia possesses excellent properties such as high energy density and easy liquefaction conditions, making it an attractive carbon-free fuel. However, its low laminar burning velocity makes it difficult to use in spark-ignition engines, and its use in HCCI engines is also being considered. We have confirmed that ammonia HCCI combustion can be achieved by heating the intake air at compression ratios of 22-26. This study investigates the effect of onboard hydrogen addition, obtained through reforming, on improving ignition properties while using an ammonia-only fuel system through simulations. Simulations were performed by varying intake temperature and ammount of hydrogen addition, using a zero-dimensional model constructed with Cantera and reaction schemes which has shown good agreement with pressure traces of an ammonia-hydrogen dual-fuel HCCI engine. The results showed that adding about 5 mol% hydrogen significantly improved the ignitability of the ammonia-air premixed gas, and reduced the required intake temperature for ignition by 60 K. Additionally, a sensitivity analysis of ammonia oxidation was conducted for both pure ammonia and ammonia-hydrogen combustion, revealing that hydrogen addition did not significantly affect the ammonia oxidation mechanism. The improvement in ignitability was concluded to be due to the heat release from hydrogen reactions at relatively low ignition temperatures, raising the mixture temperature.

In this study, we investigated the effect of the chemical composition of the fuel on the combustion characteristics when dimethyl carbonate (DMC) and DMC+ is dropped into an existing fuel. In this study, combustion behavior was observed using an optically accessible engine capable of flame velocity analysis. As a result, when DMC and DMC+ was blend in the existing fuel, the flame propagation speed decreased, and the fuel containing 40% DMC+ showed the smallest value. In addition, under the spark plug washer temperature Tsp= 473 K condition of DMC+80, combustion was unstable and continuous operation could not be performed. On the other hand, under the DMC+80 condition of Tsp=573 K, improvements were found in combustion stability and maximum heat release.

As global warming becomes more serious, decarbonization of internal combustion engines is being promoted and electric vehicles are expected to play a more active role. We focused on the opposed piston engine as an engine for this purpose. Opposed piston engines are considered to be suitable for power generation engines because of their features such as low cooling loss and low vibration. This paper reports the results of a study on the basic characteristics of a two-stroke opposed piston engine, the effects of the number and position of spark plugs on combustion in order to shorten the combustion time, and the validity of a Pre-chamber combustion effective in improving the combustion period, with the aim of solving vibration problems and further improving thermal efficiency. Experiments were conducted at a constant engine speed of 3000 rpm, ignition timing of -25, -30, and -35 [deg. ATDC], and gasoline was used as test fuel. From the experimental results, it was found that the in-cylinder pressure was higher in the two-point ignition than in the one-point ignition because the flame spread distance was shorter in the two-point ignition. Since the experiments could not be conducted in the stable combustion region of the Pre-chamber combustion, experiments in the stable combustion region are needed.

In the rolling contact fatigue conditions for steel materials, it is known that pitting occurs at the surface when slip is present on the lubricated contact surface. Although it is important to understand how the specimen surface is affected by the different friction modes caused by slip, it is difficult to directly observe the phenomenon because it occurs below the contact surface. Therefore, in this study, rolling-slip tests with different slip conditions were conducted using a two-cylinder friction and wear tester. The influence of different friction modes on the specimen surface were measured using an acoustic emission (AE) sensor and an acceleration sensor. The results showed that there were differences in the number of cycles to damage occurrence and the amount of wear due to the different friction modes. Furthermore, analysis of the AE signals from each test revealed that changes in surface conditions due to friction modes, which cannot be captured by the acceleration sensor, appeared in changes in the amplitude values and frequency bands of the AE signals.

In recent years, there has been a demand for technology for achieving carbon neutrality. To meet this demand, improvements in gear transmission efficiency are being studied for vehicle on-board electrical equipment motors. And the lubricating oil and solid lubricant used in the gear will affect the transmission efficiency. In this study, we experimentally analyzed the effect of the particle size of the solid lubricant in the lubricating oil on the tribological characteristics with a pin-on-disk friction tester and PAO lubricating oil to which PTFE solid lubricant was dispersed. As a result, we obtained the following findings. The difference in the particle size of the solid lubricant dispersed to the lubricating oil affects the tribological characteristics. And as the particle size increases, the coefficient of friction tends to increase.

Friction stir welding (FSW) is a joining method which uses the frictional heat generation between a rotating tool and joining metals. Wear of the rotating tool decrease the plastic flow of the materials, so that the welding strength will decrease. Therefore, preventing the wear of the rotating tool is an important technology of FSW. Welding of aluminum alloys are the most common FSW process, in that case, the rotating tool materials are tool steels. However, wear properties of steels in the plastic flow of aluminum alloy, such as FSW, is not clear. We carried out the general reciprocating wear test up to 500 °C for carbon steels versus an aluminum alloy. And we analyzed the under structure of wear scar using transmission EBSD, EDS and TEM.

To improve the accuracy of numerical simulations of plastic forming, it is important to model the friction between the workpiece and the die. Typical friction models commonly used are Coulomb's friction law (τ = μp) under low contact pressure conditions and constant shear stress measurement (τ = mk) under high contact pressure conditions where the surface roughness is plastic deformed. However, it is clear that μ and k depend on changes in surface properties and slip distance (e.g., as the slip distance increases, the friction coefficient should increase due to oil loss) as machining progresses, and there are limitations to using the simplified friction model described above. From this background, this study focused on the change in the surface area expansion rate of the work material and the junction growth model, which is widely known in the field of tribology, to develop a friction model under boundary lubrication conditions. In order to investigate the validity of the proposed model, comparison between the experimental results and the results of a finite element analysis implementing the model were performed.

Magnesium alloy is the lightest of all practical metals and has the highest specific strength. However, there is a need for improved formability at ambient temperature. It is known that deep drawing of lightweight magnesium alloy sheets has poor workability due to the anisotropy of the crystal structure. Since non-bottom slipping is particularly difficult to occur at room temperature, molding is generally performed in warm conditions. In the present study, we focused on frictional heat generation in friction stir welding and attempted warm deep drawing of magnesium alloy using a punch incorporating a frictional heat generation jig. The test material is a steel material such as tool steel or stainless steel. The punch generated heat due to the friction between the heater jig and the rotary jig. As a result, it was found that a heat generation of over 400 °C could be obtained within a few minutes of friction machining time. It was found that deep drawing of magnesium alloys is possible using punches in a warm state of 200 to 300 °C.

In recent years, efforts to conserve the environment include energy and resource conservation in the production process. One of these is energy reduction through tribology. To improve the wear resistance of tool materials, surface treatments such as coating and heat treatment are performed on the surface. When machining cutting tools, however, the temperature of the surface of the tool and material becomes extremely high due to plastic deformation and friction, resulting in oxidation and adhesion of the surface, causing wear problems. There has been little research on oxide films and adhesion caused by tool wear on coatings. In the present study, we investigated the effects of heat treatment conditions on the surface condition and wear characteristics of various PVD films, with the aim of producing tools with excellent wear resistance and adhesion resistance. Test material is a cemented carbide with a thickness of approximately 5 mm. PVD uses the arc ion plating method, and there are five types of coatings, including TiN and TiCN. Heat treatment was performed at 573 to 873 K for 3.6 ks in the air. Wear test was performed using a ball-on-disk friction test device. It was found that the thickness and surface roughness of all films increased as the heat treatment temperature increased. Although the TiN film had a large friction coefficient and a large amount of film wear, it was found that there was almost no change in the wear characteristics after heat treatment.

Floating bush bearings are widely used as bearings for high-speed rotating turbochargers because the double oil film formed inside and outside of the floating bush can reduce friction and vibration. However, it is difficult to find the oil film formation conditions, and many aspects of its characteristics remain unexplained. Under this background, the authors have attempted to observe the double oil film of the floating bush bearing utilizing X-ray CT. In this study, the observation of the double oil film using X-ray CT was conducted, focusing on bushes with different clearance ratios and conducting comparative experiments on their characteristics.

Inspired by the water-repellent and self-cleaning properties of the lotus leaf found in nature, artificial superhydrophobic surfaces have garnered extensive attention across academia and industry. Dynamic hydrophobicity is an important phenomenon in both everyday life and various industrial processes. However, only a few studies have explored the dynamic characteristics of droplets on hydrophobic surfaces. This study measures the frictional forces of water droplets to investigate their sliding behaviors on a hydrophobic surface. It is observed that the frictional force is linearly related to the effective shear displacement. The dynamic frictional forces are also measured as the sliding speed increases. Results are analyzed based on molecular kinetic theory, with calculated and compared average molecular displacement distances and frequencies of adsorption-desorption events around the contact line.

The effects of surface roughness on the molecular gas lubrication (MGL) characteristics have been studied in order to confirm the application limit of the MGL equation against the surface roughness. The study has been done by comparing the calculated results by the MGL equation with those by direct simulation Monte-Carlo (DSMC) method which is expected to give more correct solution. In this study, we investigated the applicability of MGL equation in the case of pressure flow, where the pressure at the one side of the lubrication film is higher than that of the other. The lubrication film is assume to be two dimensional and consists of two stationary parallel wall with random rough surface. It is clarified that the transverse flow, which causes the difference of two calculated results, is generated at the wall by the effect of slip flow. The roughness slope of the surface has the great deal in generation of transverse flow. The difference of both calculation methods starts to increase against the roughness slope greater than the specific value. These characteristics, resulted from this study, are same as those shown in the previous study related to the shear flow.

The linear oil film coefficients of journal bearings are calculated, assuming a small vibration of journal at a steady-state equilibrium position. Two methods are known for calculating the coefficients: one obtains them from the variation of oil film reaction forces before and after the vibration, while the other from the variation of oil film pressure with the vibration that is known as the perturbation method. In this report, the coefficients are firstly calculated by applying the latter method under a restriction for the oil film pressure after the vibration, which was not considered in the previous report, and are found to be comparable to those by the former method and also the measured values. Then, the theoretical stability threshold speed of a horizontal rotor supported in cylindrical journal bearings whose oil film coefficients are calculated with the present method is shown to be comparable to the speed with the coefficients by the former method and also the measurement.