Complex mechanical products are composed of thousands to millions of parts, making it essential to utilize numerical calculations such as finite element analysis to improve performance and reduce costs. Recently, advancements in computer performance have promoted the optimization of component shapes, however, a trade-off between the flexibility of shape generation and adherence to design constraints has emerged as a challenge. For example, topology optimization using density methods can yield diverse shapes but often ignores manufacturing constraints. Thus, current methods struggle to balance the exploration of diverse shapes with compliance to manufacturing constraints. Furthermore, the relationship between shape and material selection is also crucial in design. When using multiple materials, the properties of the materials will influence shape design, however, optimization methods like density methods fix material properties during calculations, making it difficult to consider both shape and material concurrently in the optimization process. As a result, designers often rely on experience to select materials and shapes. This study proposes a method that simultaneously allows for high flexibility in shape modifications aligned with the engineer's intentions while optimizing materials and composite structures. In this method, the displacement of node coordinates in finite element analysis is defined as a morphing vector and generates diverse shapes by varying the magnifications of these vectors. By employing Bayesian optimization to minimize stress and maximize flexural rigidity, material selection is also optimized concurrently with shape variation. The optimization calculation is substituted for a machine learning surrogate model to estimate stress in order to keep computational cost low.

It is important to control the vibration of the car body and maintain good ride-comfort especially on high-speed railway. This paper focuses on the vertical vibration of car body. The vibration modes and intensities of actual running rolling stock were analyzed using the Tokaido-Shinkansen as an example. The results showed that the anti-roll damper between cars causes bending vibration peaks at a frequency lower than the first natural bending eigenvalue of the car body. Therefore, we developed a multi-body vehicle dynamics simulation model that can simulate a train set and clarified the vibration mechanism caused by the anti-roll damper between cars. Specifically, it was found that bending vibrations caused by the anti-roll damper between cars occur in the following two cases. The first case occurs when the following two conditions overlap. The first condition is that the even multiple of the half-wavelength of the longitudinal irregularities is close to the distance between the two bogies, and the front and rear bogies are vibrating up and down in the same phase. The second condition is that the odd multiple of the half-wavelength of the longitudinal irregularities is close to the distance between the vehicle centers, and the neighboring vehicles are vibrating up and down in the opposite phase. And the second case occurs when the following two conditions overlap. The first condition is that the odd multiple of the half-wavelength of the longitudinal irregularities is close to the distance between the two bogies, and the front and rear bogies are vibrating up and down in the opposite phase. The second condition is that the even multiple of the half-wavelength of the longitudinal irregularities is close to the distance between the vehicle centers, and the neighboring vehicles are vibrating up and down in the same phase.

NV (Noise and Vibration) performance is one of the key product qualities of a mechanical system. Isolating all resonant frequencies from the frequency band where excitation forces are high is an important strategy for improving NV performance. However, a challenge in designing NV performance is that the resonant frequency is determined by the contributions of all the subsystems that make up the mechanical system. Complex mechanical systems such as automobiles are concurrently developed, in which the supplier subsystem is mounted onto the OEM (Original Equipment Manufacturer) subsystem. As a result, it is not easy to share intellectual property, such as shape information, between companies. For this reason, NV performance, including the assignment of resonant frequencies, is often evaluated in the final stage of product development. However, if NV performance targets are not met at this stage, extensive redevelopment will be required. Therefore, it is necessary to be able to design the NV performance of a whole structure from the supplier's viewpoint at the upstream product development stage. In this paper, we proposed a method to solve the underdetermined inverse problem of appropriately allocating the multiple resonant frequencies of a whole structure, which occurs due to a large contribution from the supplier subsystem, by modifying the structure of only the supplier subsystem. This method is composed of the kCA (kernel Compliance Analysis) and the CMCM (Cross-Model Cross-Mode) method and is realized by using the compliance-FRF matrix of the OEM subsystem provided by the OEM to the supplier in the upstream design stage. Finally, numerical verification of the proposed method was demonstrated.

A numerical simulation of conjugate heat transfer was conducted to analyze the thermal mixing phenomenon at a T-junction, with a specific focus on the reverse flow from the main pipe into the branch pipe. To investigate the causes of temperature fluctuations on the inner surface of the branch pipe, dynamic mode decomposition was applied to the simulated temperature field. The analysis revealed a dominant 66 Hz temperature fluctuation, with a corresponding Strouhal number of approximately 1, at the point where the main stream and branch pipe flow collide. A lower frequency fluctuation of approximately 30 Hz was observed at the right corner. In the reverse flow region along the right wall of the branch pipe, fluctuations of 5.5 Hz and 0.29 Hz were also detected. These findings suggest that the vortex roll-up generated in the central part of the branch pipe collides with the right corner, leading to relatively low-frequency temperature fluctuations on the inner surface. Based on this analysis of temperature fluctuation factors, the possibility of reducing the risk of thermal fatigue damage in the branch pipe was investigated by altering the merging angle of the T-junction. When the merging angle was changed to 45 degrees, the root mean square values of both the inner surface temperature and the fluid temperature near the branch pipe wall decreased compared to the 90-degree case. This change also led to a reduction in the maximum range of temperature fluctuation on the inner surface of the branch pipe, a crucial indicator for fatigue assessment. The results suggest that the amplitude of stress at the upper end of the thermal sleeve installed in the branch pipe can be mitigated by changing the merging angle of the T-junction.

The present study has investigated the effect of passive control devices on the flow characteristics of a rectangular jet with an aspect ratio of 2, and the relation between the three-dimensional developing vortex structures near the nozzle exit and the axis-switching phenomenon in the downstream. The serrated tabs at the exit of the rectangular nozzle, and the convergent deflectors and the convergent tapered triangular tubes in the rectangular nozzle were installed as the passive flow control devices. These additional devices can change the velocity distribution and the turbulent intensity of air flow issuing from a rectangular nozzle. The rectangular nozzle had a height H of 30 mm and a width B of 60 mm. The Reynolds number Re (= U0H/ν; where U0 is the mean bulk velocity at the nozzle exit, and ν is the kinematic viscosity of air) of the jet was 9,000. The mean velocity, the turbulent intensity, the vorticity norm, and the vorticity vector in the three-dimensional flow field were calculated by the measured data from standard and mirror-image X-type hot-wire probes. It is found that the jet spread to the y and z-directions is significantly affected by the passive control devices, and the deformation of the vortex ring relates to the distribution and the intensity of the vorticity. The axis-switching phenomenon for the rectangular jet with serrated tabs moves to the downstream in comparison with the other jets because the vorticity on the long side of the rectangular nozzle becomes weaker than that on the short side. In the case of the rectangular jet with the convergent tapered triangular tubes, at x/H = 4, there is little difference in vorticity between the long and short sides of the rectangular nozzle. As a result, the shape of the jet remains rectangular to the downstream.

This study applies a hybrid finite element-material point method (FEM-MPM) framework to the simulation of pneumatically actuated soft robots undergoing large deformation and contact. Internal forces and pressure boundary conditions are evaluated using an explicit total Lagrangian FEM, while contact—including self-contact—is handled robustly via an MPM formulation with P2G/G2P mappings on a background Eulerian grid. Interactions with external bodies employ a frictional contact model, and self-contact is treated succinctly through MPM’s inherent non-penetration. The cavity volume enclosed by the FEM boundary mesh is updated incrementally via the divergence theorem, and internal pressure is prescribed through an isothermal equation of state, enabling an approximate coupling between deformation and internal pressure while avoiding the need for sophisticated full-scale fluid–structure interaction analysis. As verification, we analyze a self-contacting bending actuator and a four-finger soft gripper assembled from the actuator, reproducing grasping sequences with complex contact in a consistent manner. We further show that global deformation states can be identified from pressure time series alone, providing a basis for numerical analysis and data acquisition toward self-sensing soft robots using only injected volume and actuation profiles. Finally, a case study that systematically varies the initial arrangement and injected air quantity reveals―summarized as a phase diagram―that grasp success depends strongly on spatial configuration and actuation conditions. This application indicates that the hybrid FEM-MPM workflow can serve as a practical foundation for design exploration and future closed-loop control.

In the structural design of intermediate heat exchanger (IHX) of high temperature gas-cooled reactor (HTGR) for hydrogen production, creep-fatigue damage evaluation at high temperature up to 950 ℃ is important. In this paper, inelastic behavior and creep-fatigue damage of IHX components such as heat-transfer helical tubes and manifold perforated pipe made of Alloy Ni-22Cr-9Mo-18Fe-B, was clarified by detailed inelastic analysis. A simplified creep-fatigue damage evaluation method on the basis of elastic analysis was proposed, which is suitable for parametric study in an initial stage of structural design. This method considers the characteristics of inelastic behavior as follows; stresses are in elastic range; elastic follow-up coefficient during stress relaxation in a steady state is below 3; and a post relaxation stress is a primary stress of structures. The simplified method was applied to both heat-transfer helical tubes and manifold perforated pipe subjected to primary stress and thermal stress. Predicted creep damages were conservative within a factor of 3 compared with the results of detailed inelastic analysis. Influence of temperature, initial stress and post relaxation stress on creep damage was also discussed.

As semiconductors become higher capacity and more complex, 3D packaging technology is gaining attention. In this structure, multiple chips are stacked, leading to complex wiring structures and stress concentration. In addition to thermal stress, the impact of external vibration is also a concern, creating a risk of wire breakage. Molybdenum is attracting attention as a candidate material for future wiring due to its characteristic of exhibiting extremely little increase in resistivity during thin-film formation. Traditionally, measuring the fracture strength of thin films required single-layer test specimens. Since the thin film could not stand independently, this necessitated specialized test specimens and equipment. To address this challenge, we developed a multilayer bulge method. This method constructs the area surrounding the test specimen using a silicon substrate approximately 1 mm thick, making handling easier and enabling simplification of the test equipment. In this study, we evaluated the fracture strength of a 220 nm thick molybdenum thin film using the multilayer bulge method, which accounts for elastoplastic deformation. The results revealed that the fracture strength of the molybdenum thin film is estimated to be 2.6 GPa, approximately 3 to 5 times higher than that of bulk molybdenum.

In recent years, drones have been increasingly introduced across a range of industries, however, their adoption in Japan remains limited. This is primarily due to inherent constraints such as limited payload capacity and a high risk of malfunction or accidents resulting from crashes. To address these challenges, this study proposes a novel method for enhancing both payload capacity and operational reliability by physically connecting and coordinating multiple drones. The proposed approach leverages the concept of cooperative control through mechanical coupling. In such a system, if one drone experiences partial failure, such as a loss of thrust or control, other connected drones can provide compensatory support to maintain stable flight and potentially prevent catastrophic failure. Moreover, the collective lift generated by multiple drones enables the transportation of heavier payloads that would be unmanageable for a single unit. To investigate the feasibility of this concept, a dynamics simulator based on multibody dynamics is developed to predict the behavior of physically interconnected drone systems. Initially, a three-dimensional dynamic model of a single drone is formulated, along with its governing equations of motion. Subsequently, two coupling methods of three mechanically coupled drones are proposed, and corresponding multibody dynamics models are constructed. Numerical simulations are then conducted to evaluate and compare the dynamic behaviors of each configuration. Based on these results, key considerations for the design and implementation of physically coupled drone systems are discussed.

Pressure-sensitive conductive materials are composed of vapor-grown carbon fiber (VGCF) and polymer nanocomposites and are used in a variety of pressure sensors. VGCF has attracted attention in recent years as a filler that imparts various functional properties, including electrical ones, to resins. Polycarbonate (PC) composites containing uniformly dispersed VGCF fabricated by injection molding (IM-PC/VGCF) exhibit a decreasing resistance with increasing load. IM-PC/VGCF is conductive when the VCGF content is at least approximately 12.5 vol.%. By actively forming conductive paths within composite material, VCGF makes it possible for electricity to flow with a small amount of conductive material. In this study, the conduction mechanism in PC/VGCF formed by powder metallurgy (PM-PC/VGCF) was clarified. PM-PC/VGCF samples were fabricated at varying temperatures, and their electrical and mechanical properties were measured. The results demonstrate that increasing the molding temperature improves the material’s mechanical properties but decreases its electrical resistance. Furthermore, microstructural observations using focused ion beam scanning electron microscopy revealed that low forming temperatures produced a large amount of localized VGCF; however, the VGCF was also accompanied by voids, resulting in poor mechanical properties.