American football is characterized by its intense collision, which can induce serious injuries such as concussions and head trauma. Therefore, the evaluation of the safety of players is mandatory. In this study, we have developed a new finite element analysis model to evaluate the head kinematic response in American football. The novelty of our model is the incorporation of the effect of cervical muscle strength and pre-impact cervical muscle activation on head kinematics response. This model is based on the head-neck model extracted from the Total HUman Model for Safety (THUMS). The finite element analysis of the hit movement, which is frequently seen during the American football practices, is performed with four different cervical muscle conditions; (i) early pre-impact activation, (ii) late pre-impact activation, (iii) weak muscle strength, and (iv) No pre-impact activation. We also performed an experiment to measure head kinematics response and torso rotation in the hit movement of American football players by mouthguard sensors and video motion capture system for model validation. The four conditions parameter study shows that the time history of head angular velocity with pre-impact muscle activation is better agreement with our experimental results. Therefore, it is important to model the pre-impact cervical muscle activation in the finite element analysis for evaluating the head kinematic response accurately. We also found that higher cervical muscle strength and earlier cervical muscle activation decrease the head angular acceleration at 20-35 ms after the head collision. This suggests that, in the case of low-intensity head collision, strengthening cervical muscles and activating them before the head impact by anticipating the collision can reduce head angular acceleration.

Since it is known that tensile strength and hardness are roughly proportional, a hardness test is often used as a simple and substitute test. However, it has been reported that the proportional relationship between tensile strength and hardness is broken above 595 HV (≈55 HRC). Besides, there are few examples of mechanical properties determined by compression tests despite the fact that high-hardness and high-strength materials subjected to significant compressive stress are used in machine element parts, e.g. bearings. Tensile strength is used instead of compressive strength for the design. Thus, the relationship between hardness and compressive strength in hard materials, quenched medium carbon steel, was revealed. The compressive strength at 8% plastic strain (compressive strength) was almost the same as the maximum compressive strength. The compressive strength and hardness were at their maximum in the as-quenched specimen and decreased with the increase in tempering temperature. The compressive strength and hardness had a linear relationship up to 2000 MPa similar to the relationship of tensile tests. However, the compressive strength increased slightly in relation to the hardness above 2000 MPa in contrast to tensile tests. Thus, the work-hardening index was introduced as a variation parameter to the function that expresses the relationship between compressive strength and hardness to obtain better estimation. The estimated compressive strengths using the work-hardening index are agreed well to the experimental results.

Using a high-speed multistage scale model compressor simulating a middle stage of a gas turbine compressor for power generation, the effects of 3 types of rotor tip clearances on performance and operating range, and the vortex structure of rotor tip leakage vortices were investigated numerically and experimentally. To clarify the mechanism of the unsteady development of tip leakage vortices from vortex breakdown to stall cells, which was confirmed to occur in the condition of largest tip clearance, details were investigated by unsteady numerical analysis. In both CFD and experiments, the tip leakage loss increased rapidly when the tip clearance increased, and the load increased. The tip leakage flow is determined by the tip clearance and differential pressure between suction and pressure side. Under the condition of the largest clearance, the axial momentum of the tip leakage flow decreases with increasing blade load. At this time, a rapid increase in loss was observed at the 30 %chord of the rotor, suggesting that the double leakage increased and the backflow from the trailing edge reached the mid-chord position of the adjacent blades, contributing to the increased loss. At the condition of the highest-pressure ratio of the largest clearance, vortex breakdown occurred. Spiral vortex breakdown of the tip leakage vortex causes the vortex to swing and then begin to interfere with the adjacent blade leading edge, and the vortex feet attach to the adjacent blade pressure side and the blockage develops. This starts the generation of spillage and initiates the formation of a stall cell.

Turbulent diffusion in homogeneous isotropic turbulence is numerically investigated using the direct numerical simulation (DNS). The four-dimensional turbulence database allows us to track fluid particles not only in the forward direction of time but also in the backward direction. Two-particle dispersion has been studied in previous studies and it is known that backward diffusion is faster than forward diffusion. However, little is known about multi-particle dispersion due to the difficulty of observing it experimentally. Studies on backward diffusion are also limited. In this study, multi-particle dispersion is numerically investigated and its properties are discussed, e.g., direction of time and geometry of a tetrahedron. The results show that forward and backward diffusions of multi-particles behave differently at the beginning and evolve similarly after the transient time, but the coefficients of the backward direction are larger than those of the forward direction.

An experimental study was made on burning velocity in powder-gas hybrid combustion in order to investigate the determination factor to alter the burning velocity caused by the addition of power in the premixed gas. A burner system was newly developed to visualize the dynamic flame behavior originally stabilized in a stagnation point flow field. Using the system, the instantaneous burning velocity and burning area by powder loading were obtained and analyzed. It was found that the burning velocity and burning area varied substantially in accordance with the powder loading amount. Data analyses exhibited that a positive correlation was found between them, suggesting that wrinkling shall be a major cause to alter the burning velocity. To understand the mechanism of wrinkle formation, the change of the flow field ahead of the flame with powder loading was measured. It is suggested that the wrinkles could be attributed to the pyrolysis gases evolved in the preheating zone, which could both increase the local burning velocity by increasing the local equivalence ratio and change the flow field due to the divergence flow generated by each powder. Further study would be needed to confirm the suggested mechanism.

The interior noise characteristics of railway vehicles vary depending on the position of the cabin. In general, interior noises are louder in the area directly above bogies (ends of the cabin) than in the center of the cabin. It has been known that structure-borne sounds from bogies contribute greatly to the interior noises directly above bogies. This paper describes, using measured data obtained with the rolling stock test plant at Railway Technical Research Institute (RTRI), the application of the operational transfer path analysis (OTPA) to determine the contribution ratio of each transmission path of vibration from bogies to cabin floors. It is considered that structure-borne sounds from bogies propagate mainly through the parts connecting the bogie and car body such as single-link-type traction devices (traction links), yaw dampers, and air springs. As a result of applying the OTPA and determining the contribution ratios, it has been confirmed that the contribution ratios varied depending on the position of the floor and the frequency band. In addition, the validity of the contribution has been verified by examining the linearity of input/output data and the correlations of input data using multiple coherence functions and partial coherence functions. Although a bogie vibrates rigidly in the low frequency range with the very high correlation between the vibrations of the bogie and the parts connecting the bogie and car body, the correlation becomes low in the high frequency region. Therefore, it is expected that the contribution of each transfer path can be well estimated by applying the OTPA in the high frequency range for structure-borne sounds from bogies.

Since abnormal posture of the trunk due to aging decreases walking ability, the use of a trunk device is required to maintain and improve posture. Wearable assistive devices for the purpose of extending healthy life expectancy must be lightweight, have a simple mechanism, and have a drive system that cooperates with human movements. In our previous study, we developed an adjustable stiffness mechanism to correct the posture of the trunk. In this study, we propose a rotation mechanism that can support trunk rotation during walking and posture correction. The mechanism is a simple structure consisting of a bearing mechanism to reduce rotational resistance and a plastic block connected to pneumatic soft actuator bellows. Using a pneumatic soft actuator provides high adaptability to sudden human movements. This paper explains the outline of the proposed mechanism and the mathematical model of the actuator, followed by a description of the rotational stiffness adjustment method to support trunk rotation movements. Finally, the validity of the proposed mechanism and the effectiveness of the stiffness adjustment method are described based on the results of evaluation experiments.

In order to reveal the precursor of buckling by the eigenvalue/vectors of the atomic elastic stiffness, B^a_ij = Δσ^a_i/Δε_j (atomic stress and strain in the Voigt notation), molecular dynamics simulations are performed on a single crystalline Mg nanowire of 5nm×5nm×104nm (infinite bar under periodic boundary) with the three compressive directions of the [0001], [1210] and [1010]. The corner atoms of the nanowires show negative 1st eigenvalue, η^a(1) (the solution of the eigen-equation of {B^a_ij}{Δε_j} = η^a{Δε_i}), or “unstable” in the initial equilibrium; and the other atoms never become η^a(1) < 0 at the onset of bending. Thus we investigated the distribution of the η^a(1) in each corner and found that the position of the minimum η^a(1) was close to the peak point of the Euler buckling curve. The deformation modes of these unstable corner atoms are also visualized by the maximum principal strain direction calculated by the strain compornent of the corresponding eigenvectors, {Δε_i} = {Δε_xx,··· ,Δγ_xy}^T.

In recent years, attention has been focused on failure prediction technology for electronic devices that can ensure the stable operation of the infrastructure, by warning the failure of devices before it happens, and noticing for an early maintenance which can minimize downtime. Different from the HDD, which is a storage medium, the research about the SoC or the CPU, which is an arithmetic unit, is few. One of the reasons is that the SoC or the CPU has a long life and a low failure rate, because of their smaller number of mechanical parts. Also, the number of SoCs or CPUs used in infrastructure control boards is small. Therefore, the problem is that it is difficult to obtain log data and failure data for the SoC or the CPU. Thus, the purpose of this research is to establish an accelerated test method that causes SoC to failure in a short time, with similar failure mode for those works in normal condition, and to acquire log data and failure data for the further development of failure prediction technology. By establishing a system that can locally heat the SoC to promote failure, it is possible to acquire a large amount of SoC failure data and log data in a short time. Finally, using the acquired 17 sets of failure data and log data, we tried to apply them to the failure prediction of the control board SoC. By using machine leaning algorithm OC-SVM, and using CPU calculation time as feature, it was showed that the failure of the SoC can be detected within 5% of the remaining life, with true detection rate of 47.1% and false detection rate of 17.6%. Based on this result, the failure prediction technology developed in this research was considered having a certain level of value in field using, by strengthening the redundancy system.

To support engineers in solving engineering problems utilizing digital twin, we are proposing ‘digital triplet’ concept. We are also developing a problem-solving process support method by using the Log Level Description (LLD) that describes an executed problem-solving process and the Generic Process Model (GPM) that describes a generalized and prescriptive process. This paper illustrates a support method for describing LLDs to put the proposed method into practical use. Through an attempt to describe LLDs, three time-consuming operations were identified: viz., interviewing, structuring the information, and relating each action with the GPM. To save the labor of these operations, we propose the method that the engineer who executes the process sequentially describes the LLD by oneself based on the GPM. This paper also illustrates an LLD description support system based on the proposed method. Finally, a case study was conducted to describe the actual fault detection system design processes with the developed support system. By comparing the LLDs created with the support system in the case study with the ones created manually, the effectiveness of the proposed method was discussed. In addition, by interviewing engineers who created the LLDs in the case study, the usefulness and feasibility of the proposed method were discussed.

As products become large-scale and complex, manufacturing industry faces problems in communication between workers. Among the information to be communicated, design rationale, such as reasons for decided design and the process of consideration leading to the decisions, is rarely expressed in shared design data. This paper proposes a information extraction method of design rationale. While design are conducted, conversations are recorded. Recorded sounds are transcribed using the voice input functions in Google Docs. The transcribed data is analyzed by TF/IDF, which evaluates importance of each word in the script by its frequency and rarity. By extracting sentences that contains important words, it is assumed that most design rationales can be depicted. The proposed method was applied to the design of scissors. The case shows that the proposed method has potential for extracting design rationale.

Aluminum alloy double skin extruded materials are used for carbody and interior materials of the Tokaido Shinkansen rolling stock. In previous rolling stock (e.g. series 700 and series N700), all of these extrusions used alloys based on virgin aluminum ingots. In addition, the aluminum alloys obtained from discarded Shinkansen vehicles contain a mixture of 5000 series, 6000 series, and 7000 series alloys, so that these alloys have been cascade-recycled to acid agents, die casting mold, and not recycled to railway vehicles. This research is a multifaceted study on horizontal recycling to the same aluminum alloy types used in railway vehicles, as a part of efforts to reduce indirect CO₂ emission in the supply chain under partnerships with the companies involved in the lifecycle of railway vehicles. As a result of the verification through the comparison and evaluation of prototypes, it was proved that it is possible to simplify the sorting process and establish a highly accurate and low-cost recycling method by implementing highly accurate separate dismantling in the dismantling process of discarded vehicles, which corresponds to the upstream process of recycling. By applying this recycling method to a part of the roof structure of Series N700S rolling stock of the Tokaido Shinkansen, it enabled to reduce CO₂ emission by approximately 50 tons per trainset.

Due to the shortage of truck drivers, the challenge of improving transportation efficiency through collaboration has been receiving increased attention by both government and private sector. We propose a new methodology to introduce a two-stage stochastic program and cooperative game theory to design a transport network that incorporates truck sharing and Less-Than-Truckload (LTL) shipping under demand uncertainty. The method is focused on the number of suppliers’ own trucks in the first stage, and the flow of parts and trucks from suppliers to manufacturers and in the second stage. We analyze the value of collaboration on three different sets of demand scenarios with two manufacturers and four collaborating suppliers. Our analysis suggests that LTL shipping can reduce the number of trucks more than FTL (Full TruckLoad) shipping when the demand is expected to increase. It is also observed that LTL shipping can be more beneficial than 3PL even for long-distance transportation and reduces the total cost about twice as much as FTL shipping does, which is more than 5% of that of the non-collaborative scenario. Further, LTL shipping cost is allocated to each supplier according to the Shapley value. The results show that LTL shipping is a more cost-effective transportation mode for suppliers with high freight volumes and trucks, and all suppliers acquire cost reduction at almost the same rate.

Marman clamp band separation mechanism is often used to separate a satellite from a launch vehicle. During the separation, the Marman clamp band releases its clamped force and to expose the satellite to a harsh environment of high-magnitude acceleration with high-frequency in a short period of time, which is named by shock environment in spacecraft developments. Estimation of the shock environment is necessary to specify the equipment design condition which is used to design the equipment’s capability to endure shock environment. Empirical methods based on past development shock test data, due to their convenience and simplicity, are often used to estimate the shock environment. However, the accuracy of empirical methods derived by the past shock test data may be affected by the different structural characteristic of the satellite which was not involved in the methods. There are two typical empirical methods, named by conventional empirical methods in this paper, which are widely used in space development. However, there are no discussions and comments regarding the uncertainty of the estimation and this unknown uncertainty will lead to over conservation safety margin assigned when applying the estimated results to specify the design condition of equipment. To answer the questions as mentioned about the conventional empirical methods, first, we investigate the applicability of conventional empirical methods by two different structural characteristics of JAXA satellites, and second, we propose the improved empirical methods for the two different types of structural characteristics based on shock test data during Marman clamp band separation test. Furthermore, a margin used to envelope the uncertainty of individual test data is statistically derived and its applicability is demonstrated from the test data.