Tensegrity structures are lightweight structures, often deployable, consisting of axial members (rods and cables). One of their design problems is to determine the minimum member mass to support an external force under the buckling and yielding conditions. In the previous work, the deformation of the structure is not considered, and the equilibrium position is assumed to be known in advance. However, when the structure is subjected to an asymmetric force, for example, the equilibrium position is not obvious and is typically unknown. As a more realistic problem setting, this study discusses a minimal mass design considering the deformation by an asymmetric external force. The self-equilibrated configuration is chosen as the initial configuration for the optimization. The internal force at this configuration is called the prestress, and is often utilized to improve structural stability and stiffness. The problem setting in this paper also allows us to introduce the prestress in the design. Mechanical formulae considering the deformation without the prestress are first derived. A minimal mass design problem allowing the deformation can be formulated by using these formulae. The problem is a nonlinear problem with many variables, and requires proper initial estimates. The paper also addresses this issue by employing dynamical simulation. The prestress can be introduced by modifying the member force calculation in the above formulae. Numerical examples are conducted to show the efficiency of the proposed method.

In order to understand rocking vibration characteristics of a small structure installed on the seismic isolation system using sliding mechanical system under various condition, we have performed vibration test and proposed a numerical analysis model using 2-DOF. From results of vibration test using sine waves and observed seismic ground motions as inputs, it was indicated that the rocking vibration and overturning behavior of a structure can be suppressed by setting the dynamic friction coefficient. The rocking vibration and overturning behavior of the structure could be suppressed by the dynamic friction coefficient on the small seismic isolation system in which the small friction coefficient that could not reach the overturning limit acceleration amplitude of the structure was set. In case of input as sine waves and seismic ground motions, it was good agreement between response wave forms in vibration test and numerical analysis. Therefore, the numerical model using 2-DOF proposed in the study is effective to evaluate vibration behavior of small structure installed on the seismic isolation systems with sliding mechanical system.

The damping performance of a rolling-ball damper was examined experimentally and numerically. The damper consists of multiple rolling balls on a circular track attached to the main vibration body. Since, unlike mass-spring-tuned mass dampers, it does not use a spring, it is far superior in durability. Moreover, the cover of the damper ensures that the rolling balls will not jump out from the track. However, determining the combination of parameters that maximize performance remains challenging. In this study, we used a novel evolutionary algorithm and the discrete element method. In terms of convergence and calculation time, we compared the particle swarm optimization (PSO) and cuckoo search algorithms and chose PSO as the evolutionary algorithm. To verify the validity of the numerical method, an experimental apparatus that acts as an equivalent horizontal single-degree-of-freedom system was used. The main vibration body is excited sinusoidally at the support using a motor and a slider-crank mechanism. Steel balls were used as rolling balls. The displacement of the support and the main vibration body was measured using two laser displacement sensors. The numerical results were compared with the experimental results for the relationship between amplitude and frequency to verify the validity of the numerical method.

This study examines Operational Transfer Path Analysis (OTPA) for vibration-acoustic dynamics in complex vehicle systems. OTPA simplifies data collection by avoiding structural transfer function pre-measurement, overcoming traditional method limitations on complex paths. It uses multivariate regression for transfer function estimation but faces noise and multicollinearity. Conventional PCR-based OTPA for vibration-acoustic coupling often misidentifies dominant sound contributors by prioritizing high-energy vibrations, potentially overlooking critical low-energy components or the low radiation efficiency of high-energy ones. To address this, a Partial Least Squares (PLS) regression-based OTPA is proposed. PLS extracts 'acoustic latent modes' by maximizing covariance between reference vibrations and response sound, better linking vibrations to acoustics. The PLS-OTPA is verified to extract key sound-constituting vibration modes and shows improved accuracy over PCR methods in analyzing an air-conditioning outdoor unit's piping. This approach significantly refines transfer path analysis accuracy, advancing vibration and acoustic analysis.

This study evaluates the effectiveness and risks of using AR goggles in a hands-free standing-type Personal Mobility Vehicle (PMV). AR goggles, which overlay digital information onto the real world, have significant potential for enhancing efficient information access and entertainment experiences during travel. In the experiment, Apple Vision Pro was utilized to compare conditions with and without AR goggles, as well as to evaluate the effects of different screen positions. Foot pressure data and questionnaire were collected. The results showed that wearing AR goggles increased the maximum displacement of foot pressure during turns, indicating a higher risk of falling. Increased COP (Center of Pressure) oscillation was also observed, suggesting potential instability. Survey responses indicated that wearing AR goggles led to increased fatigue and instability, negatively affecting ride comfort. However, the visual entertainment aspect of AR goggles was highly appreciated. In conclusion, AR goggles are effective for enhancing information access and entertainment during travel, but they pose risks of falling and reduced ride comfort in a hands-free standing-type PMV.

This study discusses the concept of resilient multi-agent systems and algorithms for their realization. Specifically, we focus on improving the optimization algorithm for task assignments and applying it to a mid-air retrieval mission. In particular, this study highlights the mid-air retrieval of a low-speed descending object, supported by a parachute, by one of three unmanned aerial vehicles (UAVs) that constitute a multi-agent system as a representative case. The results demonstrate that the optimal task assignments can be achieved within practical computation times. This capability enables prompt and appropriate adjustments to task assignments in response to dynamic changes in situations and environments, marking a significant step toward realizing practical resilient multi-agent systems. Different from the conventional methods such that they pursue mathematically rigorous optimal solutions, this study aims to obtain solutions suitable for practical applications within shorter time frames. Therefore, we propose a method to derive optimal task assignments based on approximate trajectory planning, as verified through numerical simulations. These simulations demonstrate that, in the case study, one of the UAVs can successfully capture a low-speed descending object with feasible maneuvers. In this paper, the issue of deriving exact optimal trajectories using the obtained approximate trajectories as initial solutions still remains. This issue is one of the important subjects in this study and we will discuss it in another paper.

Active control of flow separation on a bluff body model utilizing dielectric barrier discharge plasma actuators (DBD-PAs) was experimentally demonstrated at Re = 28,000. The model consisting of a flat side plate and a quarter cylinder with a radius of 84.5 mm was placed 200 mm downstream from the exit of the blowing-type wind tunnel and fixed at a yaw angle of 10 degrees relative to the main flow. In the conventional spanwise arrangement of exposed electrode utilizing a string-array-type plasma actuator consisting of six Cu wires coated with silicone rubber and exposed electrodes, the control effect significantly decreased as the distance from the separation point increases. Therefore, blowing-type and suction-type vortex generating plasma actuators (VG-PAs) with exposed electrodes arranged in the streamwise direction were prototyped by combining the string- array-type DBD-PAs, and the effects of suppressing flow separation were verified by generating blowing and suction jets. Both blowing-type and suction-type VG-PAs were effective in suppressing flow separation, with the blowing jet reducing the displacement thickness by 64% and the suction one reducing it by 85% compared to the no control case. Strain rate analysis of the Y-Z cross section revealed that the control effect of the suction-type VG-PA can be obtained over a wider range in the spanwise direction than that of the blowing type VG-PA.

This paper proposes a novel inspection system for seismic isolation and vibration control devices using unsupervised deep learning to enhance evaluation reliability and objectivity. Conventional force and stiffness assessments through loading tests require human inspectors, creating potential subjective bias and necessitating impartial third-party evaluation. The proposed deep learning system minimizes human intervention, significantly improving test result consistency while eliminating operator bias. The unsupervised learning approach enables the model to learn exclusively from normal operational data, facilitating detection of anomalies in previously unseen patterns with high sensitivity. This paper presents a comprehensive framework encompassing data generation, preprocessing, and model inference. Experimental validation using oil dampers and laminated rubber bearings, representative components in seismic isolation technology, demonstrates the method's effectiveness with approximately 98% classification accuracy for oil dampers and 100% for rubber bearings in distinguishing normal from anomaly conditions. These results confirm the system's viability for large-scale manufacturing deployment. Furthermore, anomaly visualization capabilities provide valuable insights for manufacturers and regulatory bodies, reinforcing the importance of objective and transparent evaluation. This inspection system establishes a robust foundation for quality control in seismic isolation and vibration control technologies, with significant potential for broader adoption toward ensuring safer and more reliable infrastructure.

This paper deals with an advanced version of eMDVA (embedded Mass Dynamic Vibration Absorber), which is a passive multi-modal damping device that was proposed by the authors. The eMDVA consists of a mass embedded in a viscoelastic material, and the mass can vibrate freely in all directions. The authors showed in their former works that the eMDVA consisting of a single mass sphere embedded in a spherical or elliptical viscoelastic material with a constrained outer shape is valid for multiple vibration control target frequencies. Considering practical use, the authors are developing another configuration of the eMDVA where many masses are dispersed and embedded in a sheet-like viscoelastic material. While the original eMDVA utilizes the multi-directional vibrations of the embedded mass as a multi-modal dynamic vibration absorber, the sheet-like configuration achieves multi-modal vibration damping by using different sizes of masses. In this work, we take up an eMDVA in which a mass sphere is embedded in a cuboid viscoelastic material, assuming a partial element of the sheet-like eMDVA and the influence of the external shape of the viscoelastic material on the vibration of the embedded mass is investigated using finite element analysis. It is shown that the peak frequencies of the frequency response function (corresponding to natural frequencies of the embedded masses) can be adjusted by changing the diameter of the mass sphere and the thickness of the viscoelastic material, and this means the sheet-like eMDVA can be designed by the size of the embedded mass sphere. The numerical and experimental results are described in this paper, including the configuration of multiple masses embedded in the viscoelastic material side by side. In addition, a series of excitation tests are conducted using a plate-like structure, a 1:10 scale model of a railway vehicle’s underframe, and the multi-modal vibration reduction effect by the eMDVA has been confirmed.

This paper proposes a simple passive device with an adjustment mechanism for spring constant and damping coefficient to realize a dynamic vibration absorber (DVA) that can be used for various vibration control target frequencies. The proposed device consists of a coil spring and an air spring with an auxiliary reservoir and orifice. The active coil of the device's coil spring can be varied to adjust the spring constant. The main tank and reservoir tank are separated by an "orifice disk" with several orifices of different diameters, and the damping coefficient can be changed by selecting one of these orifices. A numerical model was constructed to design the spring constant and damping coefficient, and a DVA equipped with the proposed adjustment mechanism was developed. The results of stand-alone vibration tests showed that the changing trend of vibration response property agreed well with the numerical results, and the proposed adjustment mechanism worked well. Then, vibration control tests were conducted by mounting a dynamic vibration absorber on a plate-like structure that simulates the underframe of a railroad car at approximately 1/10 scale. As a result, a significant vibration reduction was successfully achieved for the bending mode of elastic vibration, and the usefulness of the proposed spring constant and damping coefficient adjustment mechanism was confirmed by adjusting the optimum spring constant and damping coefficient values, which varied at each measurement point.

A shaking table is a device used in vibration testing to investigate the vibration characteristics of structures. Currently, seismic waveforms used in vibration tests are recorded in acceleration. Therefore, acceleration feedback control is suitable for controlling shaking tables. However, while accelerometers have high measurement accuracy in the high-frequency range, they have low measurement accuracy in the low-frequency range. On the other hand, displacement sensors can accurately measure vibrations in the low-frequency range. Therefore, a method of constructing a single control system by fusing an acceleration feedback control system and a displacement feedback control system was considered. However, this method has a problem that the target tracking performance deteriorates near the frequency at which the control systems switch due to interference between the control systems. Therefore, this study proposes a method to suppress interference by using filters. Furthermore, we formulate the conditions for interference suppression and verify them through experiments using a one-degree-of-freedom shaking table. The results show that the influence of interference can be suppressed by designing the target tracking performance of the fused control systems to match near the frequency at which the control systems switch. And, the results show that characteristics that can suppress the influence of specimen reaction force can be obtained by reducing the phase difference of the disturbance suppression characteristics of the control systems to be merged near the frequency at which the control systems switch.

This study focused on the piston system and targeted vehicle interior noise caused by combustion, which is mainly due to vibration transmission in the high-speed, high-load region. Vehicle interior noise is defined as having both a combustion excitation force, which causes the piston to move due to combustion, and a structural excitation force, which causes the engine block to vibrate due to piston movement. The purpose of this study was to index these forces to develop noise and vibration suppression technologies and adapt them to design concepts. Conventionally, the relationship between combustion and noise and vibration is discussed in terms of ensemble averages. However, due to the nonstationary properties of noise and vibration, this paper analyzed both excitation force characteristics for vibration on a cycle-by-cycle basis. Engine vibration is affected by heat release characteristics, even with the same engine structure specifications. As heat release characteristics, combustion speed: the maximum second derivative of heat release value and combustion phase: CA50 were identified as indicators of the excitation force of combustion. Engine vibration is also affected by piston specifications, even when heat release characteristics are the same. The maximum piston tilt angle, maximum piston tilt speed, and maximum piston translation speed were identified as indicators of the structural excitation force. Based on these indicators, various means have been devised to suppress noise and vibration caused by combustion.

In this study, the effectiveness of the electrical impedance method (EIM) for monitoring lubrication conditions in helical gear systems during actual operation was investigated. A custom-built gear tester equipped with helical gears, and an alternating current circuit was used to monitor the lubrication conditions through EI signals. The temporal changes in EI signals were analyzed to estimate the dimension less thickness and breakdown ratio of the lubricant film at the gear mesh. The results revealed that the EIM effectively monitors the temporal changes in the lubricated conditions at the gear mesh of the helical gear. The technique also demonstrated the ability to monitor lubrication regimes through evaluating the dimension less thickness and breakdown ratio simultaneously. Thus, the EIM presents a promising tool for real-time monitoring of the lubricated conditions in helical gear systems.

This study describes the development of a microcurrent supporter powered by a triboelectric nanogenerator (TENG), designed to be integrated into an ankle supporter. Microcurrent therapy (MCT) is known for promoting tissue repair, reducing pain, and enhancing muscle recovery. However, conventional MCT devices are not suitable for use during exercise due to size and power source constraints. To address this, the authors developed a self-powered, wearable TENG system that harvests biomechanical energy during walking and delivers microcurrent stimulation through the skin via water-soaked conductive sponge electrodes. The TENG structure employs stacked layers of triboelectric films with conductive nonwoven electrodes, achieving peak voltages exceeding 200 V. A tribotronic energy extractor (TEE) was incorporated to regulate and enhance current output to a biologically effective range (50–500 μA), overcoming impedance mismatch between TENG and human skin. Experimental results demonstrated that when the supporter was used with water-soaked sponge electrodes, contact resistance dropped to 0.1–0.5 MΩ, enabling effective current delivery. Muscle stiffness measurements in the gastrocnemius and soleus muscles showed that applying microcurrents via the TENG-supporter system significantly suppressed post-exercise muscle stiffness compared to no current condition, particularly in the gastrocnemius muscle within the first 45 minutes post-exercise. These findings suggest that triboelectric-powered microcurrent delivery systems can be effectively used during physical activity, offering a novel approach to real-time muscle care and recovery.

Heat exchangers for air conditioners are generally composed of aluminum fins and copper tubes, and their performance has been improved over the years since 1970. On the other hand, microchannel heat exchangers achieve significant performance improvements by increasing refrigerant-side heat transfer performance and reducing airflow resistance through the application of microchannel tubes, and by reducing the contact thermal resistance between the fins and tubes through aluminum furnace brazing. It is also possible to reduce material costs by making it all aluminum, and in recent years, this technology has attracted attention as it can be applied to air conditioners to improve system efficiency, make products more compact, and reduce the amount of refrigerant. This paper summarizes the development trends that have been conducted to date in applying microchannel heat exchangers to air conditioners, and presents current challenges and future prospects.