Virtual sensor, which is one of the applications of the digital twin, is effective for estimating physical quantities that are difficult to measure. This paper deals with estimation of real-time tool edge temperature by virtual sensor. The tool edge temperature is estimated by inputting the temperature data of the endmill shank obtained from the pyrometer installed in the machine tool to the simulation model created in cyber space. The simulation performed in cyberspace is an unsteady heat transfer analysis, and a state space model with a reduced order of the finite element model using Krylov subspace method is adopted as the simulation model in order to allow real-time simulation. In addition, unknown heat input to the cutting edge was calculated by state feedback control using the temperature data obtained from the pyrometer and the simulation model. The tool edge temperature during cutting was estimated in real time using the developed virtual sensor with the heat transfer analysis block and the input estimation block. The estimated tool edge temperature changed significantly in response to changes such as chipping of the tool edge. The estimated temperature and the measured temperature by the thermocouple method generally matched.

This study presents a computationally efficient one-dimensional (1D) modeling approach for analyzing the frictionless contact behavior between a tire carcass and the ground, successfully demonstrating its effectiveness for early-stage design optimization. We first determine the curvature and bending rigidity distributions along the arclength of the carcass to approximate it as a beam. Then, assuming frictionless contact between the carcass and the ground plane, we perform contact analysis using the finite element method (FEM) and finite difference method (FDM) to elucidate the load-displacement behavior, deformed shapes, strain energy density, and contact pressure distributions for three types of tires: normal/standard tires (STD), low-rigidity run-flat tires (LRT), and high-rigidity run-flat tires (HRT). The developed 1D model is rigorously validated through both FEM and FDM simulations, demonstrating excellent agreement with experimental results up to a compressive displacement of 25 mm, as confirmed by direct comparisons. The HRT demonstrated enhanced strain energy distributions and reduced stress concentrations in high-curvature regions, characteristics that are crucial for durability and safety during zero-pressure operation. The proposed 1D modeling approach significantly reduces computational requirements compared to traditional three-dimensional FEM simulations. It preserves essential mechanical insights, enabling rapid parametric studies and design optimization during the initial development phase.

An elastic moving airfoil is superior to a rigid moving airfoil because the deformation of its shape enables it to generate a larger fluid force. Membrane airfoils, such as butterfly wings, perform well even in low Reynolds number flows and have thus attracted attention. Previous studies have shown that the flapping motion of a butterfly generates a pair of vortex rings. However, it is difficult to determine the entire vortex ring structure and estimate the dynamic fluid force. In this study, we clarify the dynamic behavior of vortex rings generated by the flapping motion of a butterfly and the associated dynamic lift. Two-dimensional particle image velocimetry is used to visualize the flow field around a butterfly wing in two cross sections. The dynamic lift is estimated from the parameters of a pair of vortex rings measured from two directions. The estimation results indicate that the amplitude of dynamic lift is the largest before the butterfly wing reaches the horizontal position in each stroke. In addition, the degree of development of the vortex ring circulation and the projected area on the horizontal plane are the largest before the butterfly reaches the horizontal position, except for the projected area of the vortex ring during the upstroke. Both the dynamic lift and the parameters for the vortex rings are different between the downstroke and the upstroke. It is believed that these differences are mainly caused by the different degrees of elastic deformation of the butterfly wing on the downstroke and the upstroke.

Currently, the environment for human habitation on the Moon and technologies for mining lunar resources are being actively researched. Space rovers are necessary for this purpose. On a planet like the Moon, the ground is soft and covered with sand. When a spacecraft travels on such terrain, it is prone to the “stuck phenomenon,” in which the wheels spin around and the vehicle becomes unable to travel. There is a need for an explorer that is less prone to getting stuck; in other words, one with high traveling performance. However, the conditions for improving mobility performance are not clearly defined. They depend on the shape and physical properties of the terrain. To pursue the conditions that enhance traveling performance, this study first focused on “lug”, one of the key conditions that improve travel performance. Lugs have the function of pushing out sand to generate a reaction force. This improves traveling performance. Commonly, lugs are installed perpendicular to the wheels and crawlers. Therefore, we examined the relationship between mobility performance and the alignment angle of the lugs. In this study, we conducted running experiments on crawlers with different lug attachment angles. The crawlers were single-wheeled and were assumed to run in a straight line. To evaluate the running performance of each crawler, we used the slip ratio. We investigated the adequate lug’s alignment condition for each crawler’s running performance. We discussed the results from the perspective of machining studies on how the lugs enter and exit the sand. We also employed PIV (Particle Image Velocimetry) analysis to investigate the effect of the lugs on the sand during operation.

Undulatory motion is an effective propulsion mechanism widely observed in nature, offering advantages in environments where traditional propulsion systems struggle, such as highly viscous fluids. This study systematically investigates how the number of links and fluid viscosity influence the propulsion characteristics of a multi-link swimmer. A fluid force model incorporating pressure and viscous drag, valid across a wide range of Reynolds numbers, was utilized. Multi-objective optimization was then performed to identify Pareto-optimal solutions for swimming speed and average power by varying the number of links and control inputs across three distinct fluid viscosities. The results reveal several key findings. First, a greater number of links enables higher speeds and more efficient propulsion, with the most significant improvement seen when increasing from four to eight links, after which the gains diminish, a phenomenon potentially linked to the uniform control strategy employed. Second, while a larger tail beat amplitude increases stride length, its effectiveness is reduced in highly viscous fluids where viscous drag becomes the dominant resistive force. Consequently, undulatory motion becomes an inefficient strategy in very low Reynolds number regimes (Re ~ 10⁻²). Finally, the robot’s optimal motion aligns with established scaling laws for aquatic animals, although the constant Strouhal number at high Reynolds numbers (~ 1.0) differs from typical biological values (~ 0.3). This discrepancy suggests that body shape and surface material, in addition to motion patterns, are critical factors for achieving high efficiency. These findings provide design guidelines for bio-inspired robots operating in diverse viscous environments.

The dynamic contact behavior of a minute liquid droplet upon collision with a high-temperature solid is investigated using total reflection imaging. An inkjet water droplet collides with a high temperature surface of a sapphire prism (and a quartz glass prism) and then splashes away. The contact behavior captured from the back side using a nanosecond lighting stroboscope varies significantly with the contact temperature T_c, as determined based on heat-conduction theory, rather than the temperature T_s of the bulk solid. The contact behavior can be classified into four regions: (I) film evaporation, (II) nucleate boiling, (III) spontaneous nucleation and (IV) supercritical state. The contact area decreases significantly in region II and exhibits a minimum at a temperature close to the superheat limit for the liquid. It then increases in region III to reach a maximum at a temperature close to the critical temperature before it decreases at higher temperatures. Even at a contact temperature so high as to exceed the critical temperature, the liquid still contacts the solid surface over a significant area for several microseconds before the surface dries out. The fine bubbles generated due to spontaneous nucleation hinder contact due to the formation of a local dried area as the contact temperature approaches the superheat limit, whereas contact is enhanced at higher temperatures due to the dynamic action of spontaneous nucleation. Similar behavior is observed for the quartz glass prism in the same range of contact temperature.

In the early stages of chassis model-based development, we needed a tire physical model that could be handled easily, and we devised the TM Tire Model. Some tire samples have verified that the TM Tire Model is superior to existing physical characteristic models. The feature of the TM Tire Model is that it enhanced the modeling of tire tread parts. This enhancement has made it possible to embody the mechanism of the cornering force in the small slip angle range. In this paper, we theoretically prove that the way of thinking of the TM Tire Model has universal validity and explains its mechanism.