Iron-based sintered alloy materials have a problem with fatigue strength because the number of pores contained in the material is 10% by volume. Therefore, sintered materials are not applicable to gears used under high speed and high load, such as transmission gears for automobiles. The authors have developed a high fatigue strength sintered gear using the liquid-phase sintering method. In this study, Fe-Ni-Mo-B-C sintered and carburized gears with different boron contents were fatigue-tested using a gear testing machine. The sintering densities of each test gear were controlled to be the same in order to evaluate only the effect of boron addition on fatigue strength. The gear fatigue limit (p_max)_lim of a boron-free gear (the 0.0BG), 0.1 mass% boron added gear (the 0.1BG) and 0.4 mass% boron added gear (the 0.4BG) were 1750 MPa, 2150 MPa and 2000 MPa, respectively. The addition of boron was effective in improving gear fatigue strength. A comparatively large difference was confirmed in the pore shape between the boron-free material (the 0.0BG) and the boron-added material (the 0.1BG, the 0.4BG). That is, while the pores of the 0.0BG were irregularly shaped, those of the 0.1BG and the 0.4BG were spherical. Since these spherical pores suppressed the generation and propagation of cracks during the fatigue test, the fatigue strength could be improved by the addition of boron. In addition, the 0.4BG had a brittle Fe₂₃B₆ network microstructure that was not seen in the 0.1BG. The reason why the fatigue strength of the 0.4BG was lower than that of the 0.1BG was considered to be due to the formation of network-like Fe₂₃B₆ in the 0.4BG.

Mg-based materials with added C₆₀ and/or Fe, i.e., Mg-C₆₀, Mg-Fe and Mg-C₆₀-Fe, were prepared by ball milling. We also added stearic acid (SA) as a process control agent to Mg-Fe + SA and Mg-C₆₀-Fe + SA. We investigated the effects of C₆₀, Fe and stearic acid on the hydrogen storage properties of Mg by X-ray diffraction (XRD), morphology observation, differential scanning calorimetry and pressure-composition-temperature measurements using Sievert apparatus under lower hydrogen pressure (<1.0 MPa). Morphology observation revealed that the particles of Mg-Fe + SA, Mg-C₆₀-Fe and Mg-C₆₀-Fe + SA were less agglomerated than Mg-Fe, and also nanoparticles of C₆₀ were formed on the surface of the C₆₀-added samples. We observed MgO in the as-milled samples of Mg-Fe + SA and Mg-C₆₀-Fe + SA, and MgH₂ in all the Fe-added samples after hydrogenation at 280℃ under a hydrogen pressure of 0.99 MPa with XRD analysis. The Fe-added samples released hydrogen at temperatures 71-152℃ lower than commercial MgH₂ in DSC analysis. The hydrogen storage capacities of Mg-Fe + SA and Mg-C₆₀-Fe + SA were 2.93 wt.% and 2.42 wt.%, respectively, and they did not release hydrogen at 280℃ even the equilibrium pressure as below 0.1 MPa. On the other hand, Mg-Fe and Mg-C₆₀-Fe absorbed hydrogen up to 2.57 wt.% and 3.10 wt.%, respectively, and released hydrogen at 280℃ and about 0.1 MPa. The Fe had a catalytic effect on Mg, and stearic acid oxidized Mg during ball milling, although it refined the particles. In contrast, C₆₀ inhibited agglomeration without oxidizing Mg and dispersed Fe finely on it, and also increased specific surface area by the nanoparticles provided the more active sites for hydrogenation. The co-addition of C₆₀ and Fe exhibit the synergetic effects in enhancing the hydrogen storage properties of Mg.

In this paper, the dynamic fracture problem of a functionally graded piezoelectric material strip (FGPM strip) containing a crack perpendicular to the interface between the FGPM strip and a homogeneous layer is considered. It is assumed that the electro-elastic properties of the FGPM strip vary exponentially in the thickness direction, and that the crack faces are under a normal mechanical impact loading. The integral transform techniques and the dislocation density function are employed to reduce the problem to the solution of a singular integral equation. The dynamic stress intensity factors of the internal crack, the terminated crack and the edge crack are computed and are presented as a function of the normalized time for the various values of the nonhomogeneous and geometric parameters.

Multi-resolution techniques are essential for the performance of large-scale simulations of computational fluid dynamics with particle methods. In this study, a novel adaptive multi-resolution scheme has been developed for the least squares moving particle semi-implicit (LSMPS) method. With the proposed technique, particles are dynamically resized based on a local error estimate. The error estimate is defined by how well the velocity of a particle can be approximated by the Taylor-series expansions of its fluid neighbours, and vice versa for wall neighbours. Due to the adaptiveness of the multi-resolution technique, time-consuming optimization of predefined particle size targets is avoided. The adaptiveness also enables particle resizing which tracks transient resolution changes of the flow. Therefore, the adaptiveness should improve the computational efficiency of the multi-resolution method. In this study, the multi-resolution technique was tested for a two-dimensional eccentric rotating cylinder problem with a small clearance and a known steady-state solution. As expected, initially uniform particle sizes quickly decreased around the clearance. The particle size distribution evolution was smooth in both time and space throughout the simulations. Consequently, the multi-resolution method gave significantly more accurate results than a single resolution method with the same number of particles and time-step length. A drawback with the multi-resolution scheme is that the restrictions on time-step lengths become tighter. This issue is considered by ongoing development of a multi-time stepping scheme.

The development of a numerical analysis of fuel atomization is important for engine design but has the problem that the required resolutions for the gas phase and atomized droplets are significantly different. To solve this, an Euler-Lagrange coupling numerical analysis for fuel atomization has been developed. For the improvement of this analysis by including the shape effect of atomized droplets and increasing the number of droplets that can be replaced by Lagrange particles, a new droplet shape representation method using five shape parameters — Sphericity, Bentness, Slenderness, Flatness and Complexity — are proposed. These parameters are defined based on indices that reflect the overall scale of droplets, such as volume and area, and the local distribution of shape features within a droplet. First, a test case with ideal geometries showed how well these parameters qualitatively and quantitatively represent the characteristics of droplet shapes. Then, the distribution of droplet shapes in a crossflow computed by a detailed numerical analysis using the S-CLSVOF method was analyzed by the proposed shape representation method. As a result, it was shown that the parameters expressed the characteristics of actual droplets sampled from the analysis. In addition, it was confirmed that the shape distributions expressed by the proposed five parameters differed depending on the density ratio of gas and liquid and/or the Weber number, and that the analysis result is consistent with the theories of surface tension and linear instability.

Establishing sustainable and economical pathways for the deployment of variable renewable energy (VRE) is essential for reducing greenhouse gas emissions and increasing energy security. However, due to VRE power output fluctuations, high shares of VRE are associated with increases in surplus power generation, which increases the cost of power supply. This paper examines the effects of power fluctuation mitigation measures on the integration of high shares of VRE in power supply systems. The paper takes a systematic approach to evaluate the effects of the geographical distribution of VRE locations, the increase in transmission capacity, and the introduction of large-scale battery storage while increasing the VRE share. The methodology used in this analysis is a linear programming-based power supply mix model which was developed to optimize installed capacities and operation patterns of a power supply system with geographically distributed VRE locations by minimizing the total cost of power supply. The developed methodology is applied to the power supply system of Hokkaido, Japan, as a case study. The results demonstrate that VRE shares of up to 40 % can be achieved by geographically distributing the VRE locations with no increase in the total cost of the power supply. This is because the geographical distribution of VRE locations suppresses the increase in surplus power generation. Further, achieving 40 % to 60 % VRE shares only requires an increase in the power transmission capacity. However, for higher VRE shares from 60 % to 80 %, a combination of the geographical distribution of VRE locations, transmission capacity increase, and the introduction of power storage are required to effectively minimize the amount of surplus power generated.

Physical training enables us to recover from disability in rehabilitation or to acquire motion skill. So far, many devices that assist human’s motion such as power assist suit have been developed. However, these devices do not consider human’s proficiency level or recovery degree, therefore some adjustments of the device i.e. how much the device generates its force, will be required according to the human’s proficiency level. In this paper, focusing on stabilization of an inverted pendulum, we propose a varying controller design method that changes its contribution for stabilization based on human’s proficiency level. The controller is designed based on Model Predictive Control (MPC) for fast on-line calculation. Human’s proficiency level is calculated from convergence level of the inverted pendulum system. The convergence level is obtained by a norm of state variables which is coordinate-transformed so that its norm decreases monotonically according to convergence. Based on human’s proficiency level, the controller is designed to change its contribution. Experimental results show the degree of controller contribution is decreased for high skilled subjects and increased for low skilled subjects.

This paper describes the vibration damping characteristics of elevator ropes acted on by air. High-rise buildings sometimes resonate during earthquakes, and the elevator ropes in the building may swing significantly as a result. The vibration analysis of the elevator ropes is required because the swing of the ropes may interfere with the subsequent operation. However, there is no sufficient study on the damping force of air acting on the elevator rope, which is necessary for vibration analysis. We established a damping theory to estimate the damping force and loss factor of air acting on a vibrating rope, and conducted principle experiments using silicon rope and piano wire. Theoretically, the vibrating rope was considered as a cylindrical object placed in a flow field, and the drag force derived in the field of fluid mechanics was considered as the damping force exerted by the air on the rope. In particular, the vibration damping of ropes by air can be classified into two major types: viscous damping—proportional to the 1.5^th-power of the vibration velocity—and vortex damping—proportional to the square of the velocity. Additionally, the loss factor of the vibrating rope was evaluated from the displacement transfer function of the excitation amplitude and the rope vibration amplitude. As the loss factor exhibited large values for large-amplitude vibrations of the rope, the loss factor was influenced by the vibration velocity of the rope. Moreover, the damping theory presented in this paper can be applied to nonlinear rope vibrations as well.

The most dominant failure mode of piping components under seismic loading is fatigue failure with ratcheting. While it was confirmed via the experimental tests in the past, the Primary stress limit is applied to seismic loading to prevent plastic collapse. The plastic collapse due to seismic loading was first confirmed at Pipe-Fitting Dynamic Reliability Program (PFDRP) conducted by EPRI in 1980s. But, the mechanism and occurrence condition of this failure has not been clarified yet. In this research, a composite failure mode of the ratchet-induced collapse, which represents the behavior of the plastic collapse failure induced by ratchet deformation, is introduced. The transition of the failure modes along ratcheting is explained with the seismic failure mode map which identifies the occurrence condition of ratcheting and first-excursion failure, and the X-Y trajectory, which explains the excitation condition of structures under ratcheting, is introduced to project the transition. With the X-Y trajectory and the occurrence condition of the plastic collapse, this study conceptually proposes the prediction approach of the ratchet-induced collapse without the simulation analyses.

Transfer functions are often employed to evaluate the vibration characteristics of mechanical and electrical systems. Within a group of transfer functions, some particular ones have the property that swapping the coefficients of the two terms in the equation does not change the properties of the original function. Such functions are said to have a reciprocity property. Mechanical vibratory systems typically have three transfer functions; namely, compliance, mobility, and accelerance. For a single-degree-of-freedom system, the mobility transfer function has the reciprocity property; for a two-degree-of-freedom system, no transfer function has the reciprocity property; and for a three-degree-of-freedom system, one transfer function has the reciprocity property. This paper shows that the presence of transfer functions with the reciprocity property is extremely important for obtaining simple optimal design formulas for dynamic vibration absorbers.

In this study, a formulation of the inverse problem to identify the shape of a hyperelastic body in which the vibration mode is similar to the swimming mode of a fish is presented. This research aims to demonstrate the possibility of creating a fish robot that swims with a vibration mode in the water when excited with a vibration generator embedded in the body. Before this study, Chancharoen et al. attempted to formulate an inverse problem as a shape optimization problem for a linear elastic body without considering water. In this study, a cost function was defined by the squared error norm of the vibration mode and the ideal swimming mode. The result of a numerical example confirmed that the approach decreased the cost function, but the obtained vibration model was different from the ideal one. In contrast, in this study, a hyperelastic body is used to approach the actual movement of a fish. Using this replacement, the finite deformation theory is employed to formulate the periodic vibration of the hyperelastic body. The cost function is formulated using the squared error norm of the finite deformation in the cycle. Its shape derivative is evaluated using the solutions of the periodic vibration problem and its adjoint problem with respect to the cost function. To solve the shape optimization problem, an iterative scheme based on the H¹ gradient method for domain variation problems is used. The effectiveness of this approach is illustrated through numerical examples using finite-element models.

This paper presents a method for reducing the computational time required to solve the shape optimization problem of a hyperelastic body. In a previous report, the authors presented a method for applying a model order reduction technique based on the Karhunen-Loève expansion (KLE) in a shape optimization problem of a linear elastic body. In the investigated case, we applied this method solely to solve a linear state determination problem. In this paper, we show that this idea is applicable not only to the adjoint problem and to the problems seeking domain variations through the H¹ gradient method, but also to a nonlinear state determination problem. From a theoretical perspective, we assume that the solutions to these three problems for the domain obtained using a conventional shape optimization method at a prescribed number of iterations are random variables, and we apply the idea of KLE to such variables using the solutions obtained in the steps prior to the prescribed number of iterations through a conventional method as a sampling dataset. The orthonormal bases of KLE are defined as the eigenfunctions of the eigenvalue problems obtained as the optimality conditions of the variance maximization problems for the random variables. In the case of a nonlinear state determination problem, we use the incremental solutions instead of the solutions themselves. When using the finite element method to solve the three problems, these eigenfunctions become eigenvectors. Using the eigenvectors as the orthonormal bases in KLE, we define transformations from the coordinates of KLE to the physical coordinates and construct small problems for the variables of KLE. Our proposal is to solve the small problems instead of the original ones. The feasibility of the proposed method is illustrated by testing the numerical schemes using an end mean compliance minimization problem of a three-dimensional hyper elastic body.

The center of gravity of a vehicle (CG) is a critical parameter in influencing the quality of driveability and safety, such as for preventing rollover accidents. Therefore, it is important to identify a vehicle’s CG in practical situations. In particular, it is strongly desired to make it possible to measure the height of the CG of trucks and trailers freighted with various voluminous and heavy loads on business operation. The technology of Weigh-In-Motion (WIM) is being developed to identify the gross weight of trucks and trailers and detect overload. In this paper, the authors propose a method for the estimation of a vehicle’s CG, especially the height of CG, based on the WIM system. The basic theory is described at first, and the validity is shown by means of basic experiments using a light truck and a motorbike.