In recent years, automobile manufacturing requires both weight reduction for environmental measures and high strength for safety. For this reason, the use of ultra-high tensile strength steel sheets for frame components is increasing. For the application of ultra-high tensile strength steel sheets, it is necessary to pay attention to measures to ensure dimensional accuracy for press forming. Among them, wall curvature countermeasures are very important technologies. In this study, a novel forming method without generating wall curvature was developed using a simple hat model, and then a prototype mold was produced and confirmed. This novel forming method is a combination of the advantages for draw forming and cam bending forming. To form a shape so as not to fracture or wrinkle in a process similar to drawing, and to prevent wall curvature of a vertical wall part of a hat section in a process similar to cam bending. The forming motion consists of downward descent and multi-step sliding while holding the specimen in one forming process. In the FEM analysis before the production of the prototype mold, the conventional forming method and the novel forming method were evaluated from the viewpoint of the wall curvature, and the novel forming method gave the best results with the minimum wall curvature. The evaluation of the formed panel using the prototype mold also gave the same results as the FEM analysis. This paper shows that the developed forming method hardly generates the wall curvature even when the ultra-high tensile steel sheet is used.

Metal shock absorbers of nuclear spent fuel casks for storage have been developed. The shock absorbers are equipped at both ends of the cylindrical cask to reduce the impact force and maintain the safety functions of the cask in the event of an unexpected drop accident. As a countermeasure to meet long-term storage requirement (against material degradation), the shock absorber was designed with metal instead of usual wood and its energy absorption performance against 2.5 m height drop (maximum hypothetical handling height in nuclear power plants during storage) was evaluated. With the aim of reducing compression stiffness the metal shock absorber was designed from a perforated aluminum block. Two tests were done for static compression characteristics using cubic specimens and energy absorption capacity against 2.5 m drop using 1/4 scale mockup of metal shock absorber. In addition, a drop test using 1/10 scale mockup cask with metal shock absorbers confirmed that it could deform as assumed and reduce the applied acceleration on the cask to a safety level at crash. As a result of the finite element analysis of the cask with designed shock absorbers dropped from a height of 2.5 m that was verified by the drop test, the fitting portion between body and primary lid in the cask remained within elastic deformation thus confirming the design’s validity.

Rail corrosion is one of the causes of rail breaks. The relationship between rail corrosion state and fatigue strength is still unclear. Therefore, to accurately estimate the fatigue strength of corroded rails, the prediction method for fatigue strength of corroded rails with pitting corrosion by actual stress and stress gradient was investigated. Bending fatigue tests were performed on the rails with pitting corrosion on the bottom surface. At this time, models based on the shape of the rail bottom surface were created, and actual stresses and stress gradients generated at the rail bottom surface were evaluated by the finite element method. When the fatigue test results were evaluated by the actual stress, the bending fatigue strength appeared to be higher when the fracture origin position was inside of pitting corrosion than when it was outside. This was an apparent phenomenon due to the use of actual stress, which could be explained in terms of stress gradients. Furthermore, using the relationship between the correction factor of time strength q, which expresses the relationship between the fatigue strength of new rails and the apparent fatigue strength of the corroded rails, and the stress gradient χ, it is possible to estimate the number of loading cycles that the corroded rails break in the fatigue tests.

With the recent development of additive manufacturing technology represented by 3D printers, various lattice structures have emerged because their mechanical properties can be designed artificially according to their structural characteristics. This study aims to develop knowledge that will contribute to the design of lattice structures with tailored and desired mechanical properties. Among the many unit cell topologies in the lattice structures that have been designed in numerous studies, there are several basic structures and a variety of additional structures that were derived from these basic structures. However, there is a degree of ambiguity as to which of these structures should be regarded as the basic structures. In this study, the basic structures of a lattice structure with orthogonal symmetry were derived by determining the edges of the struts using a mathematical combination approach. Then, the deformation characteristics of them were evaluated through elasto-plastic finite element analysis. Five basic structures were determined by designing the unit cell of the lattice structure such that the struts pass through the vertices, the midpoints of the edges, and the centers of the faces in the cubic design region. It was found that structures with the same strut directions in their unit cells have similar stiffness distributions, and the basic structures obtained can be classified accordingly into three types. Finite element analysis of the compression of a micro-lattice structure composed of these basic structures confirmed that different deformation characteristics appeared during plastic collapse for each type of classified basic structure, and that the strut deformation type determined the overall deformation characteristics. Evaluation of the stiffness and the plastic collapse stress showed that with stretch-dominant strut deformation, lattice structures can be made lighter in weight while still maintaining some stiffness and some plastic collapse stress.

In this paper, the mechanical properties of two-dimensional linked zig-zag structure subjected to in-plane compressive load was investigated. This structure has two counterphase layers consisted of inclined plate. The stiffness and the stored strain energy during the deformation were solved analytically based on the flexible bar theory proposed by Frisch-Fay(1962). In particular, the effects of micro-architecture of the zig-zag model on these mecahnical properties were discussed. The obtained theoretical results agree fairly with FE results. In addition, three cases of the compressive response of a connected zig-zag structure were examined in order to clarify the effective parameters on the equivalent elastic modulus and strain energy stored under certain constraining conditions.

A conservative design methodology which results in overweight winding of helical layer in Type 4 hydrogen tank has been employed since the rupture phenomena in the vicinity of metallic boss of the tank is too complicated to predict precise burst pressure. The complexity comes from both the meso-scale structure constituted by overlapped carbon fiber bundles and local bending deformation in the part. Authors have developed a meso-scale based methodology for precise prediction of the burst pressure of Type 4 hydrogen tank, where carbon fiber bundles and matrix resin are perfectly distinguished for modeling. We investigate resin fracture model for the improvement of burst pressure prediction initiated by the rupture in the vicinity of metallic boss, assuming the reinforcement by means of Automated CFRP Tape Placement to realize ultimately light design of the tank. Specimens representing meso-scopic structure in the part are manufactured and submitted to the three-point bending tests. Through the validation of meso-scale fracture simulations corresponding to the tests, we demonstrate compressive fracture model of resin is decisive for precise description of terminative fracture phenomena in bending test specimen.

This paper describes computational study to investigate the aero-acoustic mechanism observed in Hartmann generator when under-expanded supersonic jet is blown from a convergent nozzle. The Hartmann generator, composed of a nozzle and a resonance tube with small distance, is known to radiate much higher amplitude of tonal sound than a free jet without any interaction. Aiming at establishing compact and efficient fluidic actuators, the authors tried to clarify the fluid-dynamic and acoustic behaviors of this special device by use of computational tool, i.e., UPACS-LES of Japan aerospace exploration agency（JAXA）. The computational results suggested existence of the JRG mode, an alternative flow motion between the nozzle and the resonance tube. This flow motion drives strong pressure fluctuation and forms sound field in the far field. The computational results complied with the fundamental acoustic characteristics in the former studies, such as far-field sound directivity and radiated acoustic power. Based on the results, it was confirmed that some parameters such as nozzle pressure ratio are predominant to intensify the acoustic power in the far field. Especially, the open-end location of the resonance tube governs the acoustic power when it is between Mach disk and shock cell end in the under-expanded supersonic jet.

The effect of the nozzle orientation and the nozzle spacing on the flow characteristics of twin rectangular jets were studied experimentally. The nozzle spacing ratio S/d_e of a rectangular nozzle with an aspect ratio of 2 was varied from 2.75 to 6.875. Two nozzle orientations were tested, i.e., twin nozzles oriented along the minor plane (TwinMinor) and twin nozzles oriented along the major plane (TwinMajor), and the results were compared with a single round jet, a single rectangular jet, and a twin round jet. In each case, the Reynolds number based on the maximum jet velocity and the equivalent diameter was 1.5 × 10⁴. The nozzle orientation has no influence on the flow characteristics of twin rectangular jets along the jet centerline. However, the velocity and turbulence intensity of the twin rectangular jets of TwinMajor increases more than that of TwinMinor near the symmetry line of the twin jets, and the location of the combined point (CP) becomes upstream. The twin rectangular jets with a small nozzle spacing ratio, i.e., S/d_e = 2.75 merge upstream. The velocity near the jet centerline in downstream becomes relatively higher compared to that with a large spacing ratio. The vortex shedding frequency of the twin rectangular jets depends on the nozzle spacing ratio. The flow characteristics of the twin rectangular jets with a large nozzle spacing ratio, i.e., S/d_e = 5.5 and 6.875 are similar to the single rectangular jet.

Since the boiling heat transfer is much affected by the nucleation of bubble and its growth, estimation of such process is essential for the accurate prediction of the heat transfer. In this study, molecular dynamics simulations were performed in order to clarify the effect of the wall conditions, i.e. the wettability and the slip between fluid and solid wall, on the bubble growth. The simulation results show that the evaporation near the contact line is enhanced and the vapor jet from contact line is observed. The direction of the vapor jet from the contact line is along the solid wall surface in the case of large slip and is along the liquid-gas interface in the case of small slip. The difference in the direction of the vapor jet is due to the flow in the adsorption layer on solid wall surface (in solid-gas interface). In the case of large slip, the fluid molecules in the adsorption layer flow with larger velocity in the direction away from the contact line. The vapor jet thus can develop along the surface of the adsorption layer. In the case of small slip, by contrast, the flow in the adsorption layer is prevented by the wall shear stress and the layer held on the wall surface invokes shear stress between the layer and the vapor jet. Consequently, the slip affects the vapor jet from contact line.

The atomization process of fuel spray injection in internal combustion engines affects the spray mixture formation process, the combustion characteristics, and the formation of toxic substances. Therefore, several optical measurement procedures have been developed and applied to capture spray features, including imaging methods and laser diagnostics. It has been concluded that the spatial resolution of fine spray droplets detection in imaging with silver halide film is much better than with a CCD imaging device. Therefore, the authors previously developed a novel imaging technique called Super High Spatial Resolution Photography (SHSRP), which allows for whole spray imaging while maintaining the spatial resolution of tiny droplets. This is a wide-field, high-resolution imaging method that can measure the entire spray area at the droplet scale. However, the image analysis method analyzes the intensity gradient of the outer edge of the droplet, and the accuracy of droplet analysis deteriorates as the droplet diameter is small. In this study, a new image analysis method with wide-field and high-resolution images acquired by SHSRP was developed to improve the analysis accuracy of spray droplets. The analysis method of depth of object field, which depends on droplet size, was changed from one-dimensional analysis of the intensity gradient of the outer edge of the droplet to two-dimensional analysis using the intensity deviation of the entire droplet area. For the developed analysis method, analysis of error based on scattering theory was conducted and the droplet capture ratio in diesel spray was analyzed to verify the accuracy. As a result, it was found that the particle size distribution obtained has no peaks due to noise effects, and that the presented analysis method is accurate enough to characterize the particle size distribution of diesel spray.

In recent years, there has been active development of robots that play a role in people's lives. These robots require actuators that have high responsiveness and high output force in addition to being small. Furthermore, safety and contact affinity are also required for these actuators. An actuator that can balance high responsiveness, high output, and contact affinity is developed in this study. The proposed system is a hybrid system of hydraulic and pneumatic systems. Hydraulic systems are generally used in machines that require large forces, such as construction machinery, because they have high responsiveness and high output force. However, hydraulic systems have poor contact affinity. On the other hand, pneumatic systems are used in machines that come into contact with people, such as power assist suits and massage chairs, because they have high contact affinity, although their output is inferior to that of hydraulic systems. Generally, the mixing of air bubbles into hydraulic oil is a problem. However, as the pressure increases, the rigidity of the working hydraulic oil mixed with bubbles approaches that of pure working hydraulic oil. If this characteristic is appropriately modeled and controlled, bubbles mixed into the working hydraulic oil can create a cushioning effect. Firstly, the relationship between the pressure and rigidity of hydraulic oil mixed with bubbles is demonstrated in this paper. Secondly, the mechanism of the hybrid system and the prototype model are explained. Lastly, the results of performance evaluation through analysis and experiments are presented. From these results, this paper shows that the proposed system has the potential to balance high responsiveness, high output, and contact affinity.

When mascot suits or plush fabrics are used to cover a human-friendly robot, frequent sterilization may be required, depending on the use of the robot. However, the effects of such sterilization are not sufficiently understood. In this study, variations in the strength and color values of plush fabrics were measured and quantitatively evaluated following 50 cycles of sterilization by ethylene oxide gas (EOG). The fabrics were composed of boa fabric, which is commonly used in mascot suits and plush dolls, and cloth reinforced with polyurethane foam. The tensile strength and the elongation were measured by the tensile strength test for clothes or clothing seams, in accordance with the standard JISL1096. In terms of appearance, red-green-blue (RGB) color values were obtained from photographs taken under the same light conditions to evaluate the color tone. A friction test was used to evaluate the tactile sensation. These results showed that EOG sterilization did not notably affect the properties of the fabrics; however, a single cycle of autoclave sterilization degraded the fabrics. Notably, the boa fabric shrunk and hardened. Thus, EOG sterilization, which does not feature elevated temperatures, may be an effective sterilization approach for these materials.

It has not been solved that the fruits and vegetables such as strawberries, cells, blood and a bottle of sake are damaged, broken during transportation. It is the greatest factor in this situation that there is a dangerous vibration frequency range where these are easy to scratch and are prone to death. If there are eigen frequencies within this dangerous frequency range，it is good to be redesigned such that the eigen frequencies within this dangerous frequency range are moved out of the range. But it is difficult to apply the existing topology optimization methods using homogenization method or density method or thickness distribution method. As fundamental research, it is demonstrated the effectiveness of the proposed method based on the strain and kinetic energy density distributions of the targeted eigen modes for a flat plate compared to the conventional topology optimization method using thickness distribution as follows. (1) It is possible to control plural eigen frequencies by deciding interactively how the topology should be changed from the observation of kinetic and strain energy density distributions of the targeted eigen modes in a very short time compared to the conventional topology optimization method. (2) In the case of the proposed method, it is not necessary to get a new topology from the thickness or density distribution after the optimization results. (3) It can be checked the validity of the task set for the conventional topology optimization method by observing the strain and kinetic energy density distributions of the targeted eigen modes which are actively used in the proposed method.

All-terrain wheelchairs are assumed to be used under such conditions that are on the roads along mountain topography, steep slopes, bumpy roads, muddy roads, etc. It is often used for people with disabilities to enjoy outdoor activities in nature with friends and family. In order to deal with such conditions and usages, all-terrain wheelchairs have different structures and features from normal wheelchairs. In this paper, we focus on the type of all-terrain wheelchair that needs to keep the pitch posture during turning. Here, the pitch posture means the state that the front wheel is lifted. It is hard to keep a stable pitch posture on a steep slope and a bumpy road even though the wheelchair is manipulated by an experienced operator. This paper proposes an electric power assist control that keeps this pitch posture stable and reduces the manipulating load of an operator. The most important feature of the control is to control the kinetic energy of the wheelchair, the sum of the energies of longitudinal and pitch motion. This control is implemented on an electrically power assisted wheelchair, and the effectiveness of the control is demonstrated by the experimental results.

A series of numerical material tests based on homogenization theory are carried out to characterize the anisotropic elastoplastic and hardening behavior of thermoplastic resin reinforced in one direction by carbon fibers (UD-CFRTP), and a new constitutive model is proposed to describe the characteristic material behavior. First, macroscopic stress-strain curves are obtained from numerical material tests (NMTs) conducted on a unit cell model, i.e., a representative volume element of periodic microstructures, to which uniaxial and combined stress states are applied under various conditions of stress ratios and stress paths. Using the obtained NMTs results, the initial shape of the yield surface and its evolution are investigated in detail. The results suggest that even if a resin has isotopic hardening characteristics, UD-CFRTP exhibits complex anisotropic post-yielding or, equivalently, hardening behavior. Then, a constitutive model that can describe such material behavior is originally formulated, and a step-wise identification strategy is presented to determine the material parameters. Finally, by carrying out verification analyses, we confirmed that the macroscopic stress-strain curves represented by the proposed model can be fitted to those obtained by NMTs with sufficient accuracy for practical use and that the performance of the proposed model is much better than that of a conventional constitutive law.

This paper presents numerical solution to shape design problems of viscous flow field for unsteady fluid-structure-interactive (FSI) fields. In the FSI analysis, a strong coupled analysis is used to analyze the governing equation of the flow domain and the structural domain considering nonlinearity of strain. A minimization problem for total dissipation energy is formulated for the shape optimization of viscous flow domain in the FSI fields. Also, a shape design problem is formulated to control the flow velocity distribution in the sub-domains of the flow domain. This latter problem can be treated as an inverse problem for minimizing the square error integration between the actual flow velocity distribution and the target flow velocity distribution in the sub-domains. Shape gradient of these shape design problems are derived theoretically using the Lagrange multiplier method, adjoint variable method, and the formulae of the material derivative. Reshaping is carried out by the H¹ gradient method proposed as an approach to solving shape optimization problems. Numerical analysis programs for these shape optimization problems are developed by using FreeFEM, and the validity of proposed method is confirmed by results of 2D numerical analyses.

“Digital Triplet” is a concept proposed to support manufacturing system engineers by combining the knowledge and know-how of expert engineers with digital technology. This study proposes a method to represent engineering processes executed by engineers in a reusable manner based on Digital Triplet. Specifically, we develop a procedure to create a "log-level description" that records an engineering process as it is and a “generalized process model” that generalizes multiple log-level descriptions, using a process modeling language named “PD3” (Process Modeling Language for Digital Triplet). In a case study, expert engineers first executed engineering processes to improve production speed on a simplified production line. Next, log-level descriptions and a generalized process model were created for the engineering processes by the proposed procedure. Furthermore, an experiment was conducted on novice engineers using the generalized process model, and the results suggested that the model is effective for education. Currently, creating log-level descriptions or generalized process models is a labor-intensive task as it is done manually based on the subjective judgment of the person representing the processes. However, we showed the application of "process mining" techniques has the potential to partially automate the task of creating the models.

This paper presents a conceptual design approach for planar link mechanisms by utilizing continuum topology optimization based on micropolar continuum theory. To effectively simulate the behavior of link mechanisms as continuum elasticity, we introduce a mathematical model utilizing micropolar elasticity. Although topology optimization is commonly used for single mechanical components, extending it to mechanisms with multiple interconnected parts presents inherent challenges. To address these challenges, we model the link mechanism using micropolar elasticity, leveraging its bendiness-related material property, which can apply to topology optimization. Subsequently, we formulate a topology optimization problem to generate link mechanisms using our proposed model. The optimized structure achieves the desired motion and deformation characteristics like traditional linkages with proper degrees of freedom while minimizing the objective function that considers both output motion error and link compliance. The design variables of the topology optimization problem are defined using the Solid Isotropic Material with Penalization (SIMP) method, which is further updated using a gradient-based optimizer. The governing equations of linear micropolar elasticity are solved using the Finite Element Method (FEM). The effectiveness and validity of our proposed method are evaluated through numerical examples, which conclusively demonstrate its ability to synthesize the number, dimensions, and structure of link mechanisms.

The variation in stride length is an important index of gait stability. The evaluation requires a device that can accurately measure the stride length during ground walking. However, there are currently no practical and reliable measurement systems for clinical use. The purpose of this study was to improve the stride estimation method using a single inertial sensor and to verify the accuracy of stride length estimation. Stride length was estimated by integrating the horizontal acceleration at the ankle joint. To reduce the impact acceleration at ground contact, which is the primary factor causing estimation errors, we mounted an inertial sensor on the lower leg. In the present method, the following four factors contribute to the stride length estimation error: the sensitivity of the inertial sensor, consideration of the directional angle, detection of integral intervals, and estimation of the relative position vector from the inertial sensor to the ankle joint. This study presents solutions to these problems and verifies the accuracy of stride length estimation by comparing it with optical motion capture measurements. The results indicated that the sensitivity of the inertial sensor improved the accuracy of the stride length estimation. Furthermore, we found that the standard deviation of stride estimation per step was approximately 32 mm, regardless of cadence and stride length. We conclude that the stride length estimation by the acceleration integral method is applicable to the estimation of the average stride length; however, it is difficult to apply it to the evaluation of stride variation from step to step.

The purpose of this study was to clarify the factors that make transitions efficient using the positional information of the players. The independent variable in this analysis was the positional data gathered from the Vector X7 system (10 Hz) during 20 official matches of the second division of the Japan Professional Soccer League for the 2022 season. The positional data included metrics such as team convex area, length, width, foremost position, rearmost position, rightmost position, and leftmost position. Statistical analysis revealed that the team convex area, foremost position, rearmost position, and width were significantly higher during successful transitions than failed transitions (p = 0.032, p < 0.001, p < 0.001, and p = 0.030, respectively). Conversely, the leftmost position was significantly lower during successful transitions than failed transitions (p = 0.012). Moreover, the results obtained from the decision tree analysis demonstrated that the rearmost team position emerged as the most influential factor determining the success or failure of transitions. The results of the present investigation demonstrated that the positional information of the players at the time of ball recovery is an explanatory factor for efficient transitions. The novel contribution of this study is that the factor that determines efficient transitions was found to be the rearmost position and the leftmost position of the team at the time of ball recovery.

In recent years, condition monitoring methods have been widely developed. Any failure of the overhead catenary system or pantographs will raise the long downtime of railway operation. Therefore, condition monitoring methods of pantograph failure is required with the overhead catenary system. Furthermore, wear mechanism of contact wire has not been clarified yet due to its complex kinematics between contact wire and pantographs. For preventing these failure efficiently and finding out the wear mechanism of contact wire, the authors have developed a method to measure contact forces of all pantographs during trains passing on sections with sensors installed on the catenary. In the developed method, the contact forces are measured from the sum of dropper forces, inertia force of the contact wire and vertical components of the tensile force of contact wire in measurement section. However, some difficult issues have been left in the method measuring the inertial force from contact wire acceleration at some measurement points. This paper proposes a method selecting effective measurement points of contact wire acceleration. LASSO regression, which is known as one of the sparse modelling technique, is applied to the proposed method so that suitable acceleration measuring points are selected to measure inertia force. The results obtained by the proposed method are shown using dynamic simulation data. It also reports that the proposed method is effective even when the measurement frequency is changed.

To evaluate stresses including stress concentration at weld toes for fatigue evaluation of complex shape welded structures such as railway bogie frames, previous studies proposed the stress assessment procedure through measuring strains of actual structures by attaching strain gauges with its edges to be at weld toes. This paper evaluates design fatigue strength in terms of the measured stress from published fatigue data and re-analysis of those fatigue tests. The obtained fatigue strength fell into danger side by 12-29% if compared to the fatigue strength estimated based on the current version of JIS. The result also showed that fatigue strength at 2×10⁶ cycles with 0.13% failure probability had a similar value with that at 1×10⁷ cycles with 2.3% failure probability. The fatigue strength in terms of the aforementioned strain measuring system was comparable with those in terms of structural hot-spot stress approach.

The present study discusses the effects of wheel steered trailer with stability control for multi-articulated vehicles on the lane-keeping performance. For the stability control, the vector follower control is applied to align the direction of the velocity vector at the articulation point with the trailer centerline by steering each trailer wheel. 16 simulations for the tractor and four-trailer combination model, combining with and without a wheel steering of each trailer, are performed. Trailer wheel steering suppresses the direction difference angle at the articulation point and reduces the lateral deviation of the trailer. The forward trailer wheel steering also suppresses the lateral deviation of the unsteered rearward trailer. Based on the relation between the amount of steering input required for stability control and the lateral deviation of each trailer, the lateral deviation is suppressed by steering, however, the steering input required for the stability control is also generated, so the control efficiency depends on the balance between the reduction of the lateral deviation and the required steering input.