Tapping inspections of structures are commonly performed manually by technicians. However, in the case of nuclear structures and other hazardous environments, maintaining a safe distance from the inspection target is preferable. Additionally, there is a growing demand for automated inspection methods. This study proposes a novel remote tapping inspection method that eliminates the need for close proximity to the object. Our approach employs a String-Shoot Impactor, a device inspired by a string shooter toy, which propels a looped string into the air using rollers. By attaching a 4 mm diameter stainless steel ball to the string, we enable remote tapping of inspection targets. In this study, remote tapping tests were conducted from a distance of 2 meters, and the impact sounds were analyzed using frequency spectrum mapping. The results successfully distinguished defect areas from intact regions in a concrete specimen with a 300 mm diameter void defect. To further extend the inspection range, a high-speed String-Shoot Impactor was developed. The previous device, driven by a speed control motor with a maximum rotation speed of 1400 rpm, achieved a maximum launch velocity of 9.2 m/s. By replacing this motor with a brushless motor capable of 4000 rpm, the launch velocity was increased to 26 m/s, enabling an inspection distance of up to 3 meters. Additionally, the impactor was redesigned with three rollers, improving string retrieval performance and stabilizing the launching mechanism. Mounting the impactor on a tripod allowed smooth adjustment of the impact point, enhancing usability. The results demonstrate that this method enables remote tapping inspections from distances of several centimeters to several meters and can be applied in various orientations, from horizontal to vertical. Furthermore, by integrating the device into a suspended inspection setup, it becomes possible to inspect structures that are difficult to access from the ground.

This study presents a novel remote impact echo testing method utilizing pulsed water jets for non-destructive inspection of concrete structures. The method provides advantages over traditional impact methods by enabling efficient long-distance inspections while minimizing water consumption. The pulsed water jets also exhibit improved resistance to wind interference and generate a broader range of excitation frequencies, enhancing defect detection accuracy. To validate the method, experiments were conducted using concrete specimens embedded with artificial cavities to simulate structural defects. The system employed a 4 mm diameter nozzle operating at 1 MPa, generating high-speed water pulses with a velocity of approximately 40 m/s. The resulting impact-induced acoustic signals were recorded using a gun microphone, and frequency spectrograms were analyzed to identify defect-related resonant frequencies. The tests confirmed that defects at a depth of 20 mm and diameter of 300 mm could be successfully detected from a distance of 3 m. Additionally, spatial mapping of impact intensity was performed, revealing that regularly spaced impacts improve defect localization accuracy. The results demonstrate that the pulsed water jet method is a viable and effective alternative for remote defect detection in concrete structures, particularly in areas where direct access is restricted.

In reprocessing plants of Japan, Zr and ultra-low carbon 304 stainless steel (R-SUS304ULC) piping are connected by a joint formed by explosive bonding with Ta sandwiched between R-SUS304ULC and Zr. The joint exhibits excellent corrosion resistance during normal operation. However, Ta causes corrosion and generates hydrogen in NaOH solutions, which are used to decontaminate the equipment in reprocessing plants. This has led to concerns about hydrogen embrittlement of the joints via hydrogen absorption. However, there is a lack of studies on the hydrogen absorption behavior of such joints, and it is difficult to evaluate the amount of hydrogen absorbed by the joints under various decontamination conditions. In this study, we conducted immersion tests of the R-SUS304ULC/Ta/Zr joint in NaOH solution to investigate the effect of immersion environment on hydrogen absorption behavior. Electrochemical measurements were conducted to examine the hydrogen absorption environment. The results showed that the amount of hydrogen absorbed into Ta in the joints decreased compared with that in pure Ta, regardless of the immersion time. The galvanic current measurements of Ta connected R-SUS304ULC or Zr in an NaOH solution indicated that the hydrogen evolution reaction was separated to the R-SUS304ULC and Zr surfaces and that the hydrogen absorption of Ta was suppressed.

The shape of axial primary water stress corrosion cracking (PWSCC) flaws in a dissimilar material weld (DMW) joint is relatively rectangular rather than semi-elliptical. The K-solutions for a rectangular flaw as a PWSCC flaw for a Code Case of ASME Section XI were proposed in the ASME Sec. XI Standard Committee. During the discussion in a WG of the Code Committee, sample problems were proposed to confirm necessity of K-solutions for a rectangular flaw. In the sample problems, the K-solutions, that is Gi coefficients, of a rectangular flaw and a semi-elliptical flaw were compared for flaws with a different flaw depth and length. The deeper and the narrower the flaw, the larger the difference of the Gi coefficients between a rectangular flaw and a semielliptical flaw. Also, PWSCC propagation calculations of both types of the flaws assumed in a DMW joint of a pipe with double V groove, with single V groove or with single V groove were performed by using the K-solutions of a rectangular flaw and a semi-elliptical flaw. It was assumed that the initial semi-circular flaw grew with a semi-elliptical shape and the initial rectangular flaw grew with a rectangular shape. These calculation results were compared with the result of Advanced FE (AFEA) analyses which simulated actual axial flaw growth behavior. In the sample problems, the initial flaw was a semi-circular flaw within a weld width or a rectangular flaw with a length of the weld width. As a result, the calculation results of semi-elliptical flaws were quite similar to those of AFEA. The condition of a rectangular flaw with the initial flaw length of the weld width was too conservative, which was in the code description of the first draft Code Case. If the initial semi-circular flaw reached the weld boundary at the surface point and changed to a rectangular flaw, the PWSCC propagation behaviors were reasonably conservative. The results of the sample problems were reflected to the draft Code Case, which was approved by the Standard Committee of ASME Section XI on January 2025.

The Rules on Fitness-for-Service of the Japan Society of Mechanical Engineers (the rules on FFS) stipulates the limit load evaluation method based on the plastic collapse strength as one of the fracture evaluation methods for pipes with circumferential flaws. However, since the limit load evaluation method treats flaws as a decrease in thickness regardless of their location, the internal pressure acting on the flaw surface is not taken into consideration even when the flaws are on the inner surface of the pipe. The limit load evaluation method that takes into account the effect of the internal pressure acting on the flaw surface was derived, and the results were compared for plastic collapse loads with and without considering the internal pressure acting on the flaw surface. When the flaw was shallow and its angle was small, both plastic collapse loads were almost the same. However, when the flaw was deep and its angle was large, the plastic collapse load decreased due to the internal pressure acting on the flaw surface. Especially when the internal pressure was high, the impact was large. In the rules on FFS, the safety factor is taken into consideration in the evaluation of allowable stress, and the flaw depth is limited by a regulatory requirement when the flaw angle exceeds 60°. Due to this consideration and requirement, the impact of internal pressure acting on the flaw surface on collapse strength is negligible. If the flaw depth limitation is eliminated when the flaw angle exceeds 60° or when accurate fracture strength has to be evaluated such as in reliability evaluation, the plastic collapse evaluation formula that take into account the effect of pressure acting on the flaw surface should be employed.

We have aimed to realize high-fidelity neutronics/thermal-hydraulics coupling simulation to provide simulation results that can be used as validation data for reactor analysis codes. We have developed a multi-physics platform, JAMPAN, to conduct neutronics/thermal-hydraulics coupling simulation by connecting independent codes. It is required to reduce empirical correlations as far as possible to perform high-fidelity neutronics/thermal-hydraulics coupling simulation. Hence, a continuous energy Monte Carlo code MVP is adopted as a neutronics analysis code and a detailed and phenomenological numerical analysis code JUPITER is adopted as a thermal-hydraulics analysis code. Our simulation target is a single BWR fuel assembly. Hence, the simulation results need to reproduce the varying heat generation owing to the varying void fraction. Therefore, we carried out MVP/JUPITER coupling simulation in a BWR 8 × 8 single fuel assembly and confirmed that the void fraction and heat generation distribution are reasonable qualitatively. Furthermore, it is necessary to clarify the effect of the parameters of the coupling simulation on the results, and the time interval is one of the coupling parameters to improve the reliability of the simulations. We carried out MVP/JUPITER coupling simulation in a 2 × 2 fuel pin system using the multi-physics platform JAMPAN to investigate the effect of the time interval on the results. The 2 × 2 fuel pin system, which is the smaller unit of the actual single fuel assembly for a BWR, is adopted as a simulation target to investigate the effect with efficiently. It is found that the effect of the time interval on the simulation results is small.

At the Fukushima Daiichi nuclear power station, fuel debris is cooled under immersion. However, under an unexpected significant drop in water level, the water comes into contact with fuel debris that possesses a porous structure. In this scenario, rapid cooling of the fuel debris is essential. However, the cooling time has not been estimated, because the thermal behavior of high-temperature debris, including capillary phenomena, is not well understood. In the present study, the droplet evaporation characteristics on metallic porous media featuring pores smaller than 1 mm were investigated. To derive lifetime curves for droplets, the authors conducted experiments using 316L stainless steel and bronze porous materials with pore diameters of 1, 40, and 100 μm to establish droplet lifetime curves. The experimental findings indicate that the Leidenfrost phenomenon is mitigated on porous surfaces because the vapor escapes through the pores of the porous material. Further, as the temperature increases, an oxide film having a fine structure activates capillary action in bronze porous media. By contrast, a stainless-steel porous medium prevents capillary phenomena owing to its low wettability, inhibiting droplet absorption and dispersion into the pores. Consequently, if the fuel debris has similar characteristics to steel porous media, rapid cooling via the capillary action is unexpected. Finally, the cooling heat flux and cooling time of fuel debris are estimated according to experimental results. The estimation indicates that even in the case of stainless steel, the fuel debris can be cooled from 200 to 100 °C within 60 min under a low-decay heat condition. However, when the decay heat exceeds a certain value, the fuel debris cannot be cooled in either the stainless steel or bronze cases. Therefore, for risk management, the cooling system should be established for situations where the decay heat is substantial and simple spray cooling is not sufficient.

When a molten jet falls into a shallow pool in the containment vessel during a severe accident in a light water reactor, melt spreading is expected to occur on the floor surface with extremely complex fluid phenomena. In order to analyze such complex behavior, the authors identified important phenomena related to the melt spreading behavior based on experiments conducted under dry and wet conditions. The identified influential factors in under-water melt spreading are the heat transfer between the melt and overlying water, melt-coolant interaction caused by water confinement at the time of molten jet impingement, molten jet breakup into melt slugs, dispersion of melt slugs and cooling by water recirculating inside the partially solidified debris bed. In particular, a numerical model to treat the above-mentioned melt-coolant interaction and the subsequent chain of phenomena was developed. The model was named as "molten jet quench model" by the authors and was implemented in MSPREAD. In the developed model, the diameter of the spherical melt slugs and the radius of the floor surface region where melt continues to be slugs can be given as user inputs. Four sensitivity analysis cases were performed with varying diameter of spherical melt slugs and the radius of the floor surface region together with no quench cases based on the PULiMS-E10 test conducted by the Royal Institute of Technology in Sweden. Comparisons of the time histories of the spreading area, pool water temperature, spreading shapes, and post-test debris cross section indicate that the molten jet quench model can explain the short spreading distances, thicker solidified debris, and even higher pool water temperatures observed in PULiMS-E10.

A large amount of concrete contaminated by ¹⁴CO₂ will be discharged during the decommissioning of aged nuclear power plants. Rubbing, which separates cements from concrete debris, is one method available to reduce the volume of the waste if most of the ¹⁴C is present in the cement inside the concrete. We confirmed that more ¹⁴CO₂ adsorbs onto the cements than onto the aggregates by a factor of approximately 100. A rubbing test was performed to obtain the mass balance and decontamination factor (DF) using simulated concrete debris not contaminated with ¹⁴CO₂. The cements and fine aggregates were removed from the debris as fines by rubbing using a Los Angeles testing machine. Steel balls with larger sizes and in greater quantities were used to increase the rubbing effect. In addition, the production rates of the fines for debris subjected to a heat treatment were compared with those of the fines for debris not subjected to a heat treatment. Residues in the mill of the Los Angeles testing machine were washed to remove deposits remaining on the surface. We concluded that an effective volume reduction could be achieved by rubbing the heat-treated debris using additional steel balls with a larger size. The DF was not improved by washing the surface residues. However, washing can resolve concerns regarding radiation protection because of scattering of fines contaminated with ¹⁴CO₂ in the treatment of the residues after rubbing. If the volume reduction is performed using a system similar to that used in a concrete recycling plant, the production of class H aggregates is necessary to achieve a sufficient DF. In this case, air ventilation and removal of radioactive dust in the exhaust air using, e.g., a bug filter, should be required to reduce the radiation hazard to workers and to the surrounding environment.

As an outer protective engineering structure for a nuclear power plant (NPP), a reinforced concrete (RC) containment wall of NPP should be evaluated for safety requirement related to external threats. Therefore, much attention has been paid to investigate the impact resistance ability of the RC plate structure subjected to projectile impact. In these studies, most of them focused on local damage of RC plate structures struck by a rigid projectile along the normal direction of the impact surface, while only few studies have focused on oblique impact. We have therefore conducted a series of impact tests under different impact conditions covering impact angles, stiffnesses of projectiles, etc. The objective is to figure out the different impact behaviors of the RC plate structures. We also intended to put forward a numerical method based on the test results, and to validate the proposed method through comparisons between experimental and numerical results. In the test results, the reaction forces of RC plate were measured by using the load cells installed on the four corners of RC plate’s back surface. In the oblique impact, a special support structure was manufactured to fix the RC plate. It is speculated that the different supporting structure may influence the test results of reaction force. Thus, this work concentrates on the effect of the stiffnesses of the supports for oblique impact on the reaction forces of RC plate. Until now, static loading tests were carried out to confirm the stiffnesses of the components of supporting parts. This paper reports the findings obtained from the comparison between the numerical results using the experimental values as spring constants in the finite element (FE) model and the reaction force measurement results.

This study investigates the effects of the Fluid-Structure-Soil Interaction (FSSI) on the seismic responses of a deeply embedded nuclear facility with large water pools under severe earthquakes. This paper presents an efficient seismic analysis method for considering FSSI using 3D FEM for deeply embedded typical RC (Reinforced Concrete) shear wall nuclear buildings. In the proposed method, the commercial SSI analysis software, ACS SASSI was used with Option AA-F, which treats ANSYS fluid element FLUID80 dynamic matrices in ACS SASSI environment. Using the proposed method, it was confirmed that large pool water in the building provides significant local deformation of the pool walls, while the effects on other parts of the structure are almost negligible from engineering point of view. To capture the structure behavior during severe earthquakes, the nonlinear behavior of the structure was taken into account. The proposed FSSI method was applied using the ACS SASSI NQA Option NON software. To model the RC walls nonlinear behavior, their nonlinear back-bone curves (BBCs) were computed using both Japanese and US standards. Then, the nonlinear analysis SSI responses with both standards were compared. It was confirmed that the nonlinear structure behavior produced a visible shift of the ISRS (In-Structure Response Spectra) peak responses to the lower frequencies in comparison with the response of linear analysis. It was also confirmed that the amplification of ISRS in nonlinear analyses comparing with elastic linear analyses are strongly influenced by the frequency content of in the in-column input motion at foundation level. Consequently, it was shown that differences between the formulations and requirements in the two standards could affect seismic responses more or less depending on the frequency content of in-column input motion, structure dynamics, and nonlinear modeling of structural behavior.

After the Fukushima Daiichi nuclear power plants accident, the scope of Probabilistic Risk Assessment (PRA) application was enhanced to meet the new Japanese regulatory standard for nuclear power plants. In addition to that, an importance for risk management has come to be re-recognized in Japan. To use PRA in risk management, Japanese utilities are proceeding the projects for enhancing the quality of PRA model to comply with international standards. The Chugoku Electric Power Company is also upgrading the internal event at power PRA model of the Shimane Unit 2 Nuclear Power Plant (Boiling Water Reactor (BWR)) including both the level 1 and level 2 (except the source term analysis) and enhancing PRA quality to reflect international state-of-the-practice approaches and to meet (ASME/ANS, 2013) requirements (Capability Category II (CC-II) or higher). Our PRA upgrading process is divided into 3 phases: “Phase I”, “Phase II” and “As-is”. In the Phase I and Phase II, the PRA model was upgraded. An external expert review was conducted using (NEI, 2019) and (ASME/ANS, 2013) in the end of Phase II. In the As-is Phase, Shimane Unit 2 PRA is further being updated and upgraded. PRA was updated to reflect the as-built and as-operated plant features resulted from changes made to the plant design and procedure by licensing activities which were performed in parallel with PRA enhancement in the Phase I and Phase II. In addition, we updated the component failure data newly issued for Japanese nuclear power plant and reflected the findings on PRA for other Japanese plant. We addressed Facts and Observations (F&Os) raised in the external expert review conducted in the Phase II. This paper reports the processes and the details of improvements of the internal event at-power PRA for Shimane Unit 2 implemented in the As-is Phase.

This paper outlines the methodology and analysis of the at-power Fire Probabilistic Risk Assessment (FPRA) of the Shimane Unit 2 Nuclear Power Plant (BWR). For most BWRs in Japan, the Fire PRA model is in the development phase. The Shimane Unit 2 Nuclear Power Plant is one such plant, for which the FPRA project began in 2018 as a joint effort by The Chugoku Electric Power Company (Chugoku electric) and Hitachi-GE Nuclear Energy. The PRA process followed the EPRI/USNRC Fire PRA Methodology (NUREG/CR-6850, 2005) as main guidance, with various other NUREG documents as supplementary reference. The project was divided into two phases; phase 1 focused on collecting the requisite plant information to develop a conservative initial model for initial quantification, and phase 2, which removed the conservatisms in phase 1 by analyzing the fire scenarios in more detail. This paper provides an analysis of plant features from the perspective of fire PRA elements, focusing on the relative risk mitigation between initial and final quantification for specific compartments of interest. Moving forward, refinement measures will be taken to remove over-conservatism for risk-significant fire scenarios, and the model will be updated to reflect the latest design changes. The effort included plant walkdowns to confirm various as-built plant characteristics. The PRA team, with support from Chugoku Electric, visited the Shimane site a total of four times to collect data regarding plant partitioning, ignition sources, distance between source and target, and control room features. As a key milestone, the project scope also included an online, external review at the end of Quantitative Screening to assess conformance with the ASME/ANS PRA Standard.

We report a triaxial force plate (FP) fabricated by a metal three-dimensional (3D) printer and sampling moiré (SM) method for displacement measurement. Ground reaction force (GRF) is an important index for foot biomechanics. For a detailed analysis of human locomotion, it is desired to examine the GRF distribution across the sole. FPs are widely used to measure GRF. Development of an FP array capable of multipoint measurement by miniaturizing each FP and arraying them is required. However, conventional FPs with built-in force sensor elements are difficult to array due to the proportional increase in wiring complexity with the number of FP elements. Another approach involves FPs that use mechanical components and external displacement meters, which can be arranged in an array, but this also leads to an increase in the number of displacement meters. Recently, we developed an optical FP capable of triaxial force measurements by capturing a two-dimensional grating attached to the mechanical component through a prism by a single camera and analysis with the SM method at a high resolution. This measurement method is applicable to multipoint simultaneous displacement measurements of an FP array owing to the extension of the camera’s field of view. On the other hand, from a mechanical perspective, it is desirable to manufacture the array structure as one batch. Here, we propose an FP mechanical component integrated with a plate and spring fabricated by a metal 3D printer. Experiments for measurement of spring constants were conducted, which showed a linear response to the applied force in each direction. Using the FP system with a prism and camera with the SM method, the proposed FP demonstrated the feasibility of triaxial force measurement. Therefore, the proposed FP could be applicable to the arraying of FPs.

Three-dimensional (3D) cryogenic bioprinting has emerged as a promising technique for fabricating cell-laden structures by freezing bioinks during printing. This method enables precise spatial arrangement of cells while preventing cell degradation during the structural fabrication. However, conventional cryogenic bioprinting often requires cryoprotective agents (CPAs), which may induce cytotoxicity. To address this issue, CPA-free cryogenic 3D printing was examined and evaluated for constructing cell-embedded ice structures. This approach employs inkjet printing to eject ultra-small 70 pL droplets onto a liquid nitrogen-cooled substrate, achieving ultrafast freezing that suppresses ice crystal formation. The effects of droplet ejection frequency on ice structure formation and cell viability were systematically investigated. Ice pillars were printed at frequencies of 5, 20, 50, 100, and 200 Hz, and their morphologies were analyzed. At 5 Hz, droplets remained distinctly separated, forming a well-defined layered structure, whereas at 20 Hz, they partially merged while maintaining a high aspect ratio. In contrast, at 50 Hz and above, incomplete freezing between droplets resulted in lower aspect ratios and structural instability. Cell viability after freezing and thawing showed no clear difference between 5 Hz and 20 Hz frequency ejections, but was lower than that achieved with conventional monolayer freezing. This decrease in viability is considered to result from a combination of factors, including insufficient cooling in the upper regions of the ice pillars, slower warming during thawing, and localized recrystallization. Additionally, overhanging ice structures were successfully fabricated by adjusting droplet spacing, demonstrating the feasibility of support-free complex ice structure printing. These findings highlight the potential of cryogenic 3D printing for producing intricate ice-based architectures. Further optimization of cooling conditions and droplet control is essential to improve the survival rate of embedded cells and enhance the applicability of cryogenic 3D bioprinting in biofabrication and tissue engineering.

Polymer optical fibers (POFs) are promising candidates for sensor applications due to their high strain resistance, flexibility, and cost-effectiveness. The performance of POF-based sensors can be enhanced through precise micro-processing of the fibers. However, conventional methods for observing POF cross-sections often fail to capture the detailed profiles of micro-processed POFs, leading to inaccuracies in sensor design and analysis. In this work, we developed a new protection layer-assisted cross-sectional observation method to preserve the surface profiles of POFs during cutting and polishing. As a proof of concept, we applied this method to perfluorinated (PF)-POFs dry-etched by reactive ion etching (RIE). Epoxy resin was used as a protection layer to maintain the structural integrity of the fibers during the cutting process. The cross-sectional profiles of the micro-processed PF-POFs were successfully captured using a laser microscope. These profiles, previously difficult to predict, were found to be crucial for analyzing the strain sensor performance. Finite element method simulations further demonstrated the impact of these geometric features on the strain characteristics of the PF-POFs. Our results confirm that the proposed method is effective for constructing accurate design and analysis models of micro-processed POFs, paving the way for improved sensor technologies.

Recently, detection and separation techniques of micro- and nanoparticles using micro- and nanofluidic channels have been developed. Especially, micro- and nanoplastics have attracted significant attention as pollutants of the water environment. On the other hand, it is known that the separation and recovery of nanoobjects that widely disperse in water are quite difficult. In this study, we investigate the behavior of nanoparticles in nanochannels where nanoparticle transport driven by pressure-driven flow is modified by electrostatic force and electroosmotic flow. Furthermore, nanoparticles are effectively separated by size and captured in the nanochannel by the balance between the Stokes drag and the electrostatic forces acting on particles passing through the nanochannel. The present methods are expected to be one of effective methods for separation, condensation, and recovery of nanoplastics from wastewater as well as transport velocity control for single particle analysis.

Soft actuators have garnered significant attention for applications in medical and wearable devices owing to their lightweight properties and inherent safety. Nevertheless, standardized performance charts for such actuators remain scarce, complicating the selection of suitable actuators for specific applications. One of the fundamental characteristics of soft actuators is that the force–displacement relationship is influenced by the stiffness of the object with which they interact. To evaluate the sensor characteristics, conventional methods employ rigid load cells, which hinders the simultaneous measurement of force and displacement under varying stiffness conditions. Here, we propose a force sensor consisting of a seesaw-type beam embedded with an internal magnet and a laser displacement meter. External magnets are installed above and below the internal magnet, enabling modulation of the beam’s effective spring constant by varying the distance to the external magnets and their magnetic polarity. This configuration enables both repulsive and attractive magnetic forces, facilitating continuous and wide-range stiffness adjustment. The sensor structure was fabricated using a 3D printer. Experimental validation confirmed that the spring constant was tunable within the range of 5.9 to 20 N/m. Furthermore, the sensitivity of the laser displacement meter remained consistent, with a standard deviation corresponding to an error of approximately 2.2% across varying stiffness conditions. These results suggest that the proposed sensor can measure force while adjusting its stiffness, making it useful for evaluating the performance of soft actuators under different mechanical stiffness conditions.

We report on the effect of elastomer materials on the time response characteristics of tactile sensors using microcantilevers embedded in the elastomer. Our previous work has shown that different electrical time response characteristics of the sensor output can be obtained using piezoelectric or resistive elements. In this paper, focusing on mechanical time response control, we evaluated the response differences based on the viscoelasticity of the elastomer used to embed the microcantilever as a sensing element for tactile sensors. The microcantilever embedded in an acrylic elastomer, which has higher viscoelasticity than the previously used PDMS, exhibits nonlinear responses that are significantly dependent on the rate of deformation. Furthermore, we found that even when the elastomer used to embed the microcantilever is the same material, the time response characteristics vary depending on the material of the contact surface with the object.

A vibration energy harvester generates power by utilizing resonance. Stationary sine-wave excitation is a common method of evaluating vibration energy harvesters. However, environmental vibrations are often non-stationary. For example, human vibrations are often impulse vibrations with large instantaneous accelerations. In this study, we applied impulse vibrations to a piezoelectric vibration energy harvester (PVEH) and evaluated the input acceleration of the impulse vibrations, deflection, and output power waveforms. The PVEH was fabricated into a cantilever shape, and the resonance frequencies were varied by attaching different proof masses. Based on the results of the experiment and FEM analysis, it was observed that the pulse width of the input impulse vibration and the resonance frequency of the PVEH at which the maximum output power was obtained were inversely proportional. The conventional design method of matching the resonance frequency of a PVEH to the number of impulse vibrations per second results in challenges regarding the size and complexity of the device. However, the proposed method focuses on the acceleration waveform of impulse vibrations, making it effective even when the input vibrations are non-periodic. In addition, the proposed design method can generate high power with a small and simple structure. Therefore, it is promising for application in wearable devices.

In this study, we propose a sensor probe utilizing electromagnetic metamaterial perfect absorbers to enable the evaluation of soil properties. This device consists of periodically arrayed copper split-ring resonators (SRRs), a moisture-absorbing material, and a mesh-like aluminum structure, forming a perfect absorbing metamaterial. The mesh-like aluminum placed at the bottom surface prevents interference with soil moisture absorption while blocking reflections from the soil, thereby allowing robust soil property evaluation independent of soil reflection waves. The finite element method (FEM) simulations showed that the device with a mesh-like aluminum structure absorbed approximately 83% of the incident electromagnetic waves, compared to a configuration with no material on the bottom surface. Reflection measurements demonstrated that changes in soil moisture levels could be detected in both air and on soil surfaces without being affected by reflection waves. This study enables measurements of soil surface environments by eliminating the artifacts caused by soil reflection waves, contributing to the realization of wide-area soil property monitoring, independent of soil surface conditions.

In this study, we report on the fabrication of microscale structures that induce photothermal effects using SU-8/Cu composite material and evaluate the directional changes in microtubule movement relative to these structures, as well as velocity changes in response to the irradiance of excitation light. Evaluation of the temperature rise in SU-8/Cu composite structures under excitation light showed a proportional relationship between temperature increase and irradiance, with a maximum rise of 9.5°C at 43.2 W/cm². Microtubule motility experiments conducted on the fabricated device revealed that the average probability of microtubules changing their movement direction along the structure was 61%. Microtubule velocity was higher in regions closer to the SU-8/Cu composite structures than in more distant regions. Additionally, the velocities measured at irradiances of 1.0 W/cm² and 43.2 W/cm² were 0.308 µm/s and 0.464 µm/s, respectively, indicating a maximum increase of 1.5 times. These findings suggest that integrating directional and velocity control mechanisms for microtubule movement onto a single substrate is feasible. Furthermore, they demonstrate the potential utility of the fabricated device as a system capable of simultaneously observing and controlling microtubule movement using a microscopic observation system.

We developed a design to achieve the simultaneous tilting of structures to multiple angles by stretching. We focused on the tilting of plates using a kirigami hinge structure and proposed a method of connecting hinges with varying stiffness in series. To characterize the deformation of the kirigami hinge structure, we fabricated test pieces with varying cut line widths, hinge lengths, and beam widths and measured the relationship between load and tilt angle. The experimental results demonstrate that the tilting characteristics of a kirigami hinge structure under load vary with its geometric parameters. On the basis of experimental results, we fabricated a mechanism to simultaneously tilt nine flat plates to three different angles by varying the cut line width. Additionally, we fabricated a kirigami-hinged mirror array for an autostereoscopic display, which achieves a parallax effect by arranging two sets of mirrors with distinct tilt angles.

Maintenance-free wearable energy harvesters are attracting attention as an energy source for sensors within the internet of things (IoT) landscape. The effectiveness of vibration energy harvesting uses resonance; therefore, achieving frequency matching with the vibration source is essential. However, the target vibrations in wearable environments are concentrated in the low-frequency band, making it challenging to achieve device miniaturization and frequency matching. Our previous work proposed polymer-based piezoelectric vibration energy harvesters (PVEHs) incorporating mechanical metamaterials (MMs). This allowed us to achieve low resonance alongside high output power in compact devices. However, concerns regarding decreased yield during the deposition process of the thin-film piezoelectric layer and potential compromises in the microstructure strength have been identified. In response to these challenges, this study focuses on redesigning PVEHs to improve the yield and structural integrity. Using finite element method (FEM) analysis, we examined the effects of the PVEH structure and thickness of the elastic layer on performance, leading to a design of PVEHs that optimize both output power and sufficient strength. The proposed PVEHs were fabricated through photolithography, and their performance was evaluated by vibration experiments. When subjected to a sine wave excitation of 0.2 G, equivalent to walking vibration, the proposed PVEH had a resonance frequency of 25.0 Hz and RMS output power of 11.5 µW. Compared to the conventional solid-type PVEH, this corresponds to an approximately 31% lower resonance frequency and 1.3 times higher output power.

Recently, resistive pulse analysis of single nanoparticles and single biomacromolecules have attracted significant attention. It is known that the volume exclusion in the test section usually causes a decrease in the electrical conductance of ionic current. The amplitude of spike signals and the duration time reflect objects’ characteristics. On the other hand, previously we found that Au nanoparticles (AuNPs) irradiated with near-infrared light showed conductive pulses when the particles passed through the nano-orifice, although a reason why the electrical conductance increased by the light has not yet been clarified. In this study, we investigate the ionic current response to the transport of AuNPs that are confined in a nano-orifice in applied electric fields. The relationship between the current responses induced by AuNPs and near-infrared light irradiation is discussed by classifying the transport modes. It is found that the irradiation of AuNPs is inevitable for the conductive pulses, and on the other hand, the resistive pulses are observed only when the light is turned off. The amplitude of conductive pulse of AuNP with a diameter of 200 nm attains more than 5% of the base current level that is much higher than that of resistive pulses caused by the volume exclusion that is actually at most 1% or less. It has been suggested that conductive pulse analysis has the potential to open the door to novel single particle analysis methods.

P91 steel, known for its excellent creep strength and corrosion resistance, is used in key high-temperature equipment in power plants. This equipment has geometric discontinuities such as notches, where cracks will develop due to creep-fatigue loading by subjecting the equipment to start-up, continuous operation, and shutdown. Therefore, accurately predicting the crack initiation life at such notches is essential. In this study, finite element (FE) analysis was performed on circumferentially notched specimens with different radii of curvature at the notch root using finite element (FE) analysis software that implements the damage-coupled inelastic constitutive equation developed by the authors' group. To validate the FE results, they were compared with test results obtained from a creep-fatigue test we conducted. The comparison revealed that the variation of the peak stress with the number of cycles, the hysteresis loop, and the stress relaxation curve in the FE results were consistent with the test results, regardless of the shape of the radius of curvature and the hold time condition. Additionally, the creep-fatigue crack initiation and growth process obtained based on the non-localization algorithm were compared with the SEM observation results, thereby confirming that both the crack initiation and its propagation path simulated by the FE were consistent with the observed results.

Mechanical components must be designed to prevent wear and seizure. In hydraulic piston pumps, abnormal friction between the piston bore and cylinder as well as bearings can cause failure or breakdown. The slipper-type bearings exhibit complex behavior, as the piston orientation is influenced by various operational factors such as the rotational speed of the camshaft and supply pressure. The orientation of the piston also affects the pressure distribution on the slipper. In this study, the slipper of a radial piston pump was investigated. The behavior was examined by excluding shaft eccentricity. An experimental apparatus was developed to monitor the slipper conditions, including the slipper-shaft clearance, pocket pressure and lubricant flow rate. Experimental results confirmed that the slipper operated under fluid lubrication, as designed. Additionally, static finite element method (FEM) was used for simulation analysis under conditions that were consistent with those of the experiments. Both the experimental and simulation results revealed similar trends in the clearance. The clearance distribution indicated that the wedge film effect considerably influenced the piston orientation, during which the piston did not stand vertically but exhibited a tilted state. The robustness of the bearing was examined using FEM, which revealed that the slipper made a mechanical contact with the shaft when the piston was subjected to an external moment in a certain direction. As a countermeasure, an asymmetric configuration of piston slippers was developed, which enhanced the robustness of the bearing in a constant shaft rotational direction.

This paper presents a model predictive control algorithm under input and state constraints. The algorithm is designed to track time-varying reference signals and allows for offset-free tracking when the reference signal is a constant or ramp signal. A double integrator is inserted into the controller as a servo compensator, when the cost function is large, the state of the integrator can be reset at each sampling moment, thereby allowing the cost function to decrease rapidly to improve the system’s performance. While the cost function is sufficiently small, an integral action is employed to achieve offset-free tracking. The control algorithm is reduced to a convex optimization problem under linear matrix inequality constraints.

Recently, in vehicle development, the efficiency of the design process and the reduction of development costs are emphasized. Therefore, the development of a human body model that can perform analysis combining various humans and vehicles is required. In this research, we aimed to investigate the effects on posture control motion of vehicle occupants in response to forward deceleration of a vehicle. First, we used multibody dynamics to make a simplified human model consisting of three rigid body segments: head, chest, and lumbar region. Then we performed motion capture experiments to reproduce the motion of the human body when the vehicle decelerates. After this, we used a two-dimensional body model to perform numerical simulations based on the experimental results obtained by motion capture. Then, we identified the parameters for the numerical simulation and simulated the human motion. Next, we used the parameters to reproduce the experimental results. We verified the validity of the human body model by comparing postural changes in the numerical and experimental results. Finally, we conducted a numerical simulation using the identified parameters and clarified how vehicle occupants move their bodies based on the drive torque response of each body segment under different decelerations.

High-speed and high-precision positioning technology is widely used in industrial machinery such as manufacturing equipment and processing machines. In semiconductor manufacturing equipment, a magnetic levitation (maglev) stage is used to prevent the effects of non-linear friction, which deteriorates positioning precision. In the maglev stage, multiple motors and sensors are arranged to enable control of six degrees of freedom, i.e., a multi-input multi-output (MIMO) system. A decoupling method is effective for MIMO control because it reduces the interaction between the motors and sensors and converts the control target into multiple single-input single-output (SISO) systems. The purpose of this study is to develop decoupling that includes vibration cancellation in the high frequency range. The proposed decoupling cancels vibration modes by combining motors for orthogonal translation axes (horizontal and vertical directions) and using orthogonal motors to excite the vibration modes in opposite phases. In the proposed method, the conditions for cancelling vibration modes are derived and shown in the frequency domain. The proposed decoupling method, which includes dynamics, is designed to satisfy the derived conditions. The effectiveness of the proposed approach is verified by analysis and experiments using a prototype coarse-fine maglev stage.

A new optical inclinometer is proposed in this paper. In environments such as buildings under construction, where disturbance vibrations are always present, accurate inclinometer measurements are required. The sensor consists of a light emitting diode (LED) as the light source, a ball lens on a concave lens forming the optical system, and a position-sensitive detector (PSD). Viscous fluid is used around the ball lens both to suppress minor vibrations from the installation site and to serve as an additional optical element. Ray-tracing simulation was employed to design this optical system. It was determined that the silicone oil is the most suitable viscous fluid for the optical inclinometer due to its damping of vibrations, temperature stability, and appropriate refractive index. The resolution of the inclinometer output was estimated to be 0.00052°. Disturbance vibrations with frequencies ranging from 0.1 Hz to 1.0 Hz and accelerations from 0.17 mm/s² to 9.11 mm/s² were applied to the inclinometer to evaluate its stability. Since the output angle during those process was at most approximately ten times the resolution, the inclinometer is considered to be minimally affected by these disturbance vibrations. The developed optical inclinometer offers high resolution for tilt sensing and robust stability against disturbance vibrations.

This study explores the separation and transportation of works using elliptical vibration composed of vertical and horizontal components. When the acceleration amplitude of the vertical component exceeds the jump limit of works on a vibrating table, the works jump. The jump limit varies depending on the gap length at the contact region between the work and the vibrating table. Therefore, face- and reverse-side works can be separated and transported depending on their jump behavior. In this study, the separation and transportation of minuscule face- and reverse-side works were investigated, considering, between both works, the difference in gap length at the contact region. First, the influence of the driving frequency of the elliptical vibration on the jump limit and the positional stability of the jumping works was investigated. Next, the relationship between the transportation velocity and the parameters of the elliptical vibration, particularly the driving frequency and the acceleration amplitude of the horizontal vibration component, was revealed. Finally, experiments on the separation and transportation of minuscule face- and reverse-side works were conducted. By driving the elliptical vibration at a high frequency and high acceleration amplitude of the horizontal vibration component, high-speed and stable separation and transportation of minuscule works were realized.

Soft cable-driven actuators offer flexibility and adaptability but often lack stiffness, limiting their application in tasks requiring high load capacity. A variable stiffness mechanism has been developed to change the stiffness as needed to increase the actuator’s applications further. The layer jamming structure combined with the soft actuator can be tuned to increase the actuator’s stiffness when needed. The mechanical layer jamming using the actuator body to activate the jamming state has been shown as a new method of changing the stiffness of the actuator. The actuator is designed to change stiffness by pulling the cable that is also used for actuator bending. However, it still has low stiffness when jamming, which still limits the applications of actuators. This study focuses on improving the cable-driven actuator’s design to increase stiffness through cable routing and sheet materials. In addition, frame reinforcement was applied to reduce the sheet separation in the mechanical layer jamming. The experiments in each condition of the actuator were conducted by adding an external load to the actuator tip in the bending posture and measuring the displacement of the actuator in order to verify the effectiveness of the design in improving stiffness. The results of experiments show that our approach can successfully increase stiffness and load capacity with variable stiffness capabilities. Moreover, we tested the actuator in the soft gripper application to hold the objects. The results show that the soft gripper can control stiffness and, in the jamming state, is able to grasp the object with 1500g successfully.

Accurate simulations of detrimental vibrations observed in a rotor-stator contact system are beneficial. Existing contact models that consider the contact configurations between the rotor and stator cannot deal with the frictional forces simultaneously, thereby not realizing analytical accuracy. This study proposes a contact model that concurrently incorporates these factors for achieving a high-precision expression of detrimental behaviors. The model identifies rotor-stator contact by evaluating their geometric shapes and orientations. In addition, it formulates the influences of contact corresponding to the contact configurations and frictional forces by using external forces and moments derived from the Kelvin–Voigt and smoothed Coulomb models. This study analytically investigates the effects of contact configurations, especially stator thickness, on the nonlinear dynamics of a rotor-stator contact system under frictional forces. The analysis focuses on an overhung rotor modeled via the finite element method. Bifurcation analysis reveals that the bands where key behaviors observed in a rotor-stator contact system under frictional forces such as asynchronous partial contact and backward whirling motions occur expand and shift toward higher rotational speeds as stator thickness increases. This shift is caused by the enhanced stiffening effect resulting from the substantial reduction in clearance and external moments induced by normal forces acting on the side of the stator due to consideration of the stator thickness. Additionally, the stiffening effect is further enhanced by increased penetration, which results from the elevated input energy due to increased frictional forces arising from the substantial reduction in clearance and suppression of rotor deformation because of the external moments induced by frictional forces. The proposed contact model and its findings contribute to improved safety and optimized design in rotating machinery systems.

In this study, a second-order three-node triangular element with drilling and strain degrees of freedom (DOF) (GNTri3-2nd) was developed. GNTri3-2nd was formulated by applying an approximation of the generalized finite element method and a second-order Taylor expansion. The boundary conditions of the extra nodal DOF (drilling, normal strain, and curvature) without the zero-energy mode are discussed through eigenvalue analysis. The analysis accuracy of GNTri3-2nd was higher than that of the conventional six-node triangular element (FEM-Tri6) for the cantilever problem. Furthermore, in the case of plane-strain compression with a nearly incompressible material, the analysis performance of GNTri3-2nd was almost identical to that of FEM-Tri6 when a selective reduced integration was applied to the element stiffness matrix. Finally, we applied the GNTri3-2nd to the fundamental rigid-plastic finite element method. The analysis result of GNTri3-2nd is in good agreement with the slip line method and the conventional four-node quadrilateral element.

Size and weight are two critical factors in the design of automotive inverters. Bus bars form essential components of the inverter assembly and significantly contribute to the overall weight of the assembly. Hence, optimization of the shape of the bus bar is crucial for an optimal unit. The optimal shape should require minimum material without compromising the functional requirements of low-temperature rise in the bus bar assembly. In the present work, we have developed a multiphysics simulation-based topology optimization (TO) algorithm that addresses the thermal trade-offs in the design process. We have used a density-based topology optimization method for optimal material distribution for the DC bus bar. The cell-centered finite volume method (FVM) has been used to discretize the strongly coupled governing equations. The sensitivity is derived for the finite volume global matrix, and the adjoint sensitivity method is used to determine the Lagrange multipliers. The method of moving asymptotes (MMA) is used for the optimization. These algorithms have been implemented in a C++ program. Numerical results are presented for a few sample test cases, which demonstrate the effectiveness of the finite volume-based topology optimization software for bus bar design.

In this study, we developed a numerical analysis technique to optimize the additive manufacturing conditions of the most popular fused deposition modeling (FDM) three-dimensional (3D) printer. First, we additively manufactured filaments on a thin plate fixed on one side, and measured the deflection at the free end. As a numerical analysis technique to simulate the FDM 3D process, we developed a thermal-structural coupled finite element (FE) analysis that models the additive manufacturing process using the quiet element activation technique. We numerically simulated the additive manufacturing process based on slice data, which are 3D printer modeling data. The results confirmed that the in-situ deflection measurements under various manufacturing process conditions were in good agreement with the FE results. An additive manufacturing simulation was also performed for a simple structure. In the simple structure, which was naturally cooled after additive manufacturing, residual deformation occurred in the center of the height direction such that it contracted inward, and high residual stress occurred at all corners of the first layer and the center of the tenth layer. Consequently, the additive manufacturing analysis method developed here can accurately simulate the temperature and stress distributions with changing time under different head speeds and lamination paths, providing a rational tool for determining the optimal manufacturing process conditions.

The purpose of this paper is to discuss a path planning method for navigating narrow L-junctions using iterative reversing maneuvers, as one of the technologies necessary for achieving full self-driving system. First, an analysis of the vehicle's behavior during repeated reversing maneuvers is conducted. Next, based on the analyzed characteristics, a strategy for navigating narrow L-junctions using reversing maneuvers is discussed. Following the proposed strategy, the necessary turning trajectories—constituting segments of the overall path—are formulated sequentially, and the complete path is derived geometrically. Furthermore, an algorithm for generating the entire path from the entrance to the exit is proposed by utilizing the formulated trajectories. The proposed algorithm is validated through numerical simulations. Path generation is performed under varying road width conditions, and it is confirmed that the paths are generated as intended. Additionally, path generation is conducted under a comprehensive range of road width conditions, and it is verified whether the path generation is successful or deemed infeasible. As a result, it is confirmed that the path generation method utilizing reversing maneuvers allows for a wider range of road width conditions to be successfully navigated compared to when reversing maneuvers are not used, indicating the effectiveness of the proposed method. However, after checking for interference with the road boundaries for all path generation results, it is found that in some conditions, the generated paths interfered with the road boundaries, indicating the need for further improvement.