In this study, the effect of machined surface layer on residual stress relaxation was investigated. In previous study, low cycle fatigue strength was affected by residual stress. However, residual stress relaxation was complex because local plastic strain occurred by stress near yield stress. Also, machined surface layer affect the yield stress. Therefore, machined surface layer was modeled using the crystal plasticity model, i.e. plasticity model based on crystallographic deformation mechanics. To describe the microstructure of plastic deformation layer, initial dislocation density and back stress near surface were changed. To describe the microstructure of fine grained layer, grain size near surface was changed. Residual stress relaxation was simulated by crystal plasticity finite element method. Three types of machined surface layers were modeled. Two kind of strain amplitude condition was simulated. In simulation results, local plastic strain was occurred under global elastic condition. Residual stress after cyclic load was different from machined surface conditions under low strain loading. Residual stress was largely relaxed in all cases under high strain loading. Comparing fatigue life of experimental results, simulation results were thought to be valid. Therefore, residual stress relaxation is able to be predicted using this model. Hardening in plastic deformation layer prevents yield by tensile load. However, plastic strain was occurred in plastic deformation under compression load. On the other hand, fine grain layer prevent yield by not only tensile but also compression.
Improving national energy security has been recognized as one of the most important perspectives of energy policy in Japan. On the other hand, a notion of higher energy resilience has recently become common to make a domestic energy supply system stable since the Great East Japan earthquake occurred in 2011. Therefore, a purpose of this study is to establish frameworks that evaluate energy security and energy resilience quantitatively to design a sustainable energy system. An advanced framework for energy security evaluation is developed in which Resource Diversity, Import Price, Import Region Diversity, Environmental Impact and Energy Efficiency are selected as criteria, where each criterion is normalized between 0 (extremely low security) and 1 (extremely high security). In addition, a multi-objective analysis using the augmented ε-constraint method (AUGMECON) is conducted to determine the best energy resource configuration for a Japanese energy system from the perspective of both energy security and economic feasibility. On the other hand, energy resilience evaluations are conducted in accordance with four steps: identifying risks, assessing risks, building resilience, and evaluating resilience. Energy resilience is evaluated based on two criteria. The first one is Resilience Index which is calculated by a ratio between energy supply and energy demand. The second one is an economic loss incurred by a sudden energy supply interruption. In conclusion, in order to develop a sustainable energy system in Japan, it is important to increase the proportion of renewable energy consumption, which contributes to enhancing both national energy security and regional energy resilience.
Detonation transition was experimentally investigated using flame jetting through the orifice of a small sub-chamber, which was equipped on the side wall near the closed end of the main channel (square inner closs section, 50 mm on a side) filled with a stoichiometric hydrogen-oxygen mixture at an initial pressure of 80 kPa. The number of sub-chambers and orifice diameters were changed as 1, 2, 4 (called as FJ1, FJ2, FJ4, respectively) and 3, 5, 7 mm, respectively, and the facing flame jets were collided with each other in FJ2 and FJ4. Two regimes of detonation transition were observed: (i) deflagration-to-detonation transition (DDT) accompanied by flame acceleration process and (ii) direction initiation of a detonation near the flame jetting section. The flame propagation distance required for detonation transition was one-half to one-third for regime (i) compared to single-spark ignition without flame jet, and below one-sixth for regime (ii). Except for the case of regime (ii), observed for an orifice diameter of 5 or 7 mm of FJ4, the detonation transition distance had no significant effect on the types of flame jetting and orifice diameters. Time-resolved schlieren recordings showed that the choked jet of combustion products drove the shock wave preceding the flame front, and induced multi-dimensional flame motion and repeated shock-flame interactions in the confinement. These behaviors enhanced flame velocity at the ignition end by a factor of 4 to 7 in FJ1 and FJ2, compared to single-spark ignition. The effect of these enhanced flame velocities on DDT distances was consistent with the semi-empirical model of flame acceleration process in a smooth tube. The schlieren recordings and pressure measurements at the closed end indicated that the possible factors for the initiation of detonation in regime (ii) were the mixing of reacted and unreacted gas induced by the repeated strong shock-flame interaction and the hot spot formed by shock-shock interaction driven by the facing flame jetting.
The objective of this study is to establish a method of direct combustion that allows safe and effective incineration of difficult-to-process woody waste as well as its utilization as fuel. A tremendous amount of debris including woody waste was washed into the sea by the tsunami of the Great East Japan Earthquake in 2011, and still remains on the coastal seabed. In order to examine the feasibility and effectiveness of incineration of the woody debris containing seawater, combustion experiments are conducted using a small combustor by applying the two-stage combustion method which we developed for woody biomass. Simulated wastes with three different moisture contents (13, 22, 38 %) are prepared by saturating woody chips with artificial seawater. The experiments confirm that the two-stage combustion method is applicable to the combustion of the woody waste containing seawater. In addition, it is clarified that combustion temperature could be widely controlled by changing the amount of air in the range of about 860 to 1250 K in the pyrolytic combustion process and about 820 to 1240 K in the surface combustion process. The results indicate that the two-stage combustion method is effective to reduce salt content in combustion gas, and that a large part of contained salt could be recovered as a residue after incineration. It is also revealed that combustion temperature is an important factor influencing the generation of hydrogen chloride.
Compact power generation systems which consist of methanol reformer and Polymer Electrolyte Fuel Cell (PEFC) are greatly required as emergency power source. In this system, PEFC exhaust heat can be utilized for evaporating methanol solution before reforming. To use PEFC exhaust heat (80 - 90 °C), a microchannel (MC) heat exchanger is suggested as an evaporator because of supplying heat more efficiently. However, phase change phenomena of methanol solution in a MC are not clarified. In this study, the transparent double-pipe heat exchanger including the MC (channel diameter: 0.5 mm) was employed. Then, phase change phenomena in the MC were visualized with varying concentration. As a result, cyclic flow pattern was observed by using a high-speed camera. A small liquid column was generated periodically in the MC and the liquid phase gradually evaporated. Visualized images also indicated existence of thin liquid film on the inner wall of MC. By using an X-ray observation system, thickness of thin liquid film was able to be measured. The distribution of liquid film thickness was affected by the difference of solution and flow rate.
This paper describes how to exploit the dynamic coupling of a multi-link robot to improve the motion ability without depending on only actuator power. The focus is on swing motion (e.g., throwing or kicking motion) in this paper. The prime purpose of swing motion is to increase the kinetic energy of the end-link (e.g., hand or foot). This paper proposed a method to generate the swing motion pattern for the explosive increase of the kinetic energy of the end-link. In general, a multi-link robot has high-power actuators in the base side. The high-power actuators can produce a large amount of mechanical energy. The dynamic coupling can transfer mechanical energy between the links. Mathematical models were constructed to transfer mechanical energy from the base side toward the end side and convert potential energy into kinetic energy in this paper. The swing motion pattern for the explosive increase of the kinetic energy of the end-link was generated on the basis of the models. The results of the simulation experiments showed that the kinetic energy of the end-link increased explosively. The reason was that a large amount of energy produced by the actuators in the base side was transferred toward the end side. Furthermore, they showed that the motion pattern was similar to the trajectory optimized based on energetic cost.
In this paper, aiming to estimate force/torque information from brain activity to help and support the daily lives of human beings, we estimate the human muscular activity from EEG (Electroencephalogram) by PCA (Principal Component Analysis) and RLS (Recursive Least Squares). EEG and EMG (Electromyogram) are measured when a subject is flexing and extending his arm, and their linear model is established by PCA. Then, this linear model between EEG and EMG is updated by the angle, the angular velocity and the angular acceleration of the robot arm. Finally, EMG is estimated from EEG using the updated model. The results show that the estimation of EMG from EEG is possible, and using EEG support human's activities has a great potential.
This paper proposes a structural optimization method for a hexrotor. Structure here means the positions and orientations of the six rotors constituting the hexrotor. In the present optimization method, 6-DOF dynamic manipulability and the maximum translational acceleration are simultaneously considered as structural evaluation indices. The former is introduced as a common evaluation index for motion performance, and the latter with hope for payload flying against the gravity force. A special class of hexrotor structure is first proposed to make the optimization problem tractable, where 6-DOF dynamic manipulability can be provided by the simple product of translational manipulability and rotational one. Then, structual optimization problems are defined and a nonlinear optimization technique is applied. Here, the optimization problems handle two cases: (i) anti-torque of rotors and change of innertia tensor depending on structure are small enough to be neglected, or (ii) they are explicitly considered for structural optimization. Consequently, it is shown that the optimization provides strong symmetry.
In recent study, active thermography has reached a high status as an easy and speedy defects inspection method in a NDT field. This paper newly proposes a non-disassembly and non-contact NDT method using a Vibro-Thermography for detecting and evaluating of fatigue cracks at neck parts of the conveyance roll in the steel making plant. In this method, fatigue cracks are detected as localized high temperature areas caused by friction and collision at crack surfaces with an infrared camera, applying a high-amplitude ultrasonic vibration. In this paper, the most suitable nose-shape of horn type transducer, which is contacted with the curved roll surface, is developed for an effective propagation of ultrasonic vibration. In the case of the roll surface is covered with lubricating grease or dust, the crack detectability is shown. Self-reference lock-in data processing technique is applied for improvement of signal noise ratio in the crack detection process. This technique makes it possible to perform correlating process without an external reference signal. Time and cost saving inspection method in the neck part of conveyance roll is carried out using this NDT technique.
This paper addresses the problem of the coordinated deployment of a swarm of mobile robots in an area with geographical constraints. The objective of our research is to investigate how to build an ad hoc network of robotic sensors in a real-world environment. For attaining scalability and robustness, it is desirable that each robot can configure themselves into an area through local interactions with adjacent robots, using only locally available information. Therefore, a decentralized deployment scheme is presented based on geometric ideas allowing robots to converge to the uniform spatial distribution by forming regular triangle lattices. The convergence of the deployment scheme is mathematically examined, and verified through extensive simulations and experiments. In addition, a new evaluation index is proposed, to estimate a relative convergence degree with respect to a desired geometric configuration. Our results indicate that the deployment scheme can be applied to the problem regarding the coverage of an area of interest by a swarm of mobile robotic sensors.
This paper considers the simultaneous stabilization problem for multiple identical unstable systems using network synchronization. In particular, we attempt to design a coupling such that all systems in networks are synchronized, and each system is stabilized at the equilibrium point. The proposed coupling consists of a linear combination of the projective synchronization errors with a constant scaling factor and the delayed values. To realize the simultaneous stabilization based on synchronization, we consider the local stability of both the equilibrium point of a system in the networks and the synchronization errors between the system and others. From the stability analysis, we show that synchronization for mutual-coupled systems with the proposed coupling can lead to the simultaneous stabilization of systems in the networks. The effectiveness of the proposed coupling is demonstrated through examples of coupled rotary inverted pendulums with the proposed coupling. The simulation results show that it is impossible either to stabilize each system or to synchronize all coupled systems if there is no delay in the coupling, but due to the existence of delay the simultaneous stabilization and synchronization can be achieved in the networks. In addition, it is worth remarking that the stabilization and synchronization of systems with the proposed coupling are not subject to the so-called odd number limitation. Finally, we show an experimental result for two rotary inverted pendulums coupled with the proposed coupling. This result also supports the usefulness of the proposed scheme.
Recently, robots with high degree-of-freedom (DOF) have been used widely in various fields. These robots are able to conduct multiple purposes such as obstacle avoidance, postural control, trajectory tracking, etc. simultaneously using their redundancy. Hence, various motion generation methods are proposed for such robots. However, many conventional methods use the pseudo-inverse and null-space of the Jacobian matrix. Then the dedicated evaluation indexes are needed to solve the redundancy. These processes generally require the advanced expertise. Meanwhile, methods using configuration space have been utilized for a long time. However, these methods require enormous computation since the methods use iterative calculation. Recently, “virtual spring-damper hypothesis” was proposed as the motion generation method without using the expertise and iterative calculation for high redundant systems. In this method, the end-effector of the robot arm and reference point is connected by the virtual spring and damper in simulation space. The dynamic motion simulation is performed, then, from the simulation result, reference motion of the real robot arm is obtained. In this paper, a method that extends the virtual spring-damper hypothesis is proposed. In the proposed method, the virtual external force and torque are used to satisfy multiple constrains. Then, the effectiveness of the method is confirmed through several numerical simulations.
In high-rise buildings, the elevator rope may resonate with the building's sway induced by wind forces and/or by long period ground motion. Therefore, suppression of elevator rope vibration is desired. In previous paper, an exact solution to the free vibration of the rope with vibration suppressors located at 1/N from both ends of the rope was presented in the case where the gap between rope and vibration suppressor was zero. However, in the case where N is an odd number and the gap between rope and vibration suppressor is not zero, no exact solution of the free vibration has yet been obtained. In this paper, an exact solution to the free vibration of this case (N is an odd number and gap between string and vibration suppressor is not zero) is presented, when the center position of the rope is pulled. The rope is modeled with string. Finite difference analyses of the rope vibration with vibration suppressor are also performed. The calculated results of the finite difference analyses are in good agreement with those of the exact solution.
We develop a laminated substrate integrated with thin film coil for application of an electromagnetic induction type energy harvester. Magnet material component is built-in in the center of coil as magnetic core. We verified that electric power that can be applied to the tire pressure monitor is obtained with the prototype.
The prior research includes the development of a speech-driven embodied entrainment computer-generated character called InterActor, which automatically generates communicative motions and actions such as nods for entrained interaction from voice rhythm based on only speech input. Because the conventional InterActor character generates only positive actions from the verbal content but no negative actions, it is possible to aggravate a speaker's negative emotions by performing positive gestures in response to negative verbal content. In this paper, we develop an advanced speech-driven embodied entrainment character system that can respond to and improve the speaker's emotional state using speech recognition. In this system, the speaker's words are converted to text by speech recognition; their emotions are then estimated from character strings in the converted text. The system uses a database that quantifies each word and estimates the emotion associated with it. Then, the system automatically generates negative/positive motions based on the semantic orientations of words in utterance as well as entrained motions. Furthermore, we demonstrate the effectiveness of the system through three experiments: two role-play experiments for one user involving positive/negative scenarios, and a communication experiment for two remote users using the developed system.
In this study, a new technique has been proposed to quantitatively evaluate the hitting performance of baseball bats without affecting their initial pitching velocity; this technique is based on an earlier evaluation system developed to measure the same. The experiments conducted in this study were used to calculate two parameters, namely “hitting efficiency index” and “hitting velocity index,” to demonstrate the relation between the pitching and hitting velocity of the baseball bat and evaluate the bat's hitting performance. To evaluate the hitting performance, this method required fewer experiments than the previously developed method. Furthermore, on the basis of the calculations of these two parameters, the swinging ability of a baseball bat was found to be corresponded to the bat's moment of inertia. Using the parameters proposed in this method along with the pitching velocity, a player can estimate the hitting velocity of the bat when used in a match. Therefore, this method, when adopted, can help players choose baseball bats depending on their individual playing abilities.
In order to predict how much the human ligamentum flavum (LF) will be deformed during insertion of an epidural needle, the elastic modulus of a porcine LF was determined with a tensile test. LF specimens collected from porcine spines in a slaughterhouse were prepared into a rectangular shape with connecting vertebral bones. Preconditioning was repeated 20 times up to 0.1 MPa before the porcine LF specimens were tested. Strain rate was set at 0.03 and 0.5 s-1, in reference to previous studies. To calculate strain, we divided elongation length, measured with a laser distance sensor, by the initial length of each specimen. The stress-strain diagram exhibited a linear relation up to 30% strain. When tensile test stopped at 30% strain, force maintained a constant value without stress relaxation, which meant the specimen was exhibiting an elastic property only. Average Young's modulus was 0.13 ± 0.054 MPa (mean ± SD) for 0.03 s-1, and 0.14 ± 0.055 MPa (mean ± SD) for 0.5 s-1. Effect of strain rate was not statistically significant. Elastica-von-Gison stained image of the specimens revealed that they consisted of the LF and adipose, and that the average thickness of the porcine LF was thinner than that of specimens. Young's modulus of the porcine LF was estimated as 0.21 MPa in the thoracic and 0.19 MPa in the lumbar.
DNA damage induced by the radiation, including ultraviolet (UV) light, exerts adverse effects on genome stability, alters the normal state of life, and causes many kinds of diseases. Thus, a biochemical or biomechanical method in DNA damage repair and protection is well required. Hear we investigated the effects of mechanical factors, such as mechanical deformation of the nucleus, on UV radiation resistance of DNA in epithelial-like cells derived from Xenopus laevis (XTC-YF). XTC-YF cells spread normally in the spaces between micropillars whose diameter, length, and center to center spacing was 3, 9, and 9 μm, respectively. Their nuclei showed remarkable deformation and appeared to be “trapped” mechanically on the array of pillars. We compared the cells cultured on the normal flat substrates and on the pillar substrates and found that the UV radiation-induced DNA damage estimated by the fluorescent intensity of the phospho-histone γ-H2A.X, was significantly inhibited in the cells cultured on the pillar substrates. The significant positive correlation was observed between fluorescent intensity of intranuclear DNA and γ-H2A.X in the cells cultured on the flat substrates following UV irradiation, while in the cells on the pillar substrate, their correlation became lower. These results indicate that the inhibition of UV radiation-induced DNA damages might be resulted from structural change of DNA caused by the mechanical stress of the nucleus of the cells on the pillars. Our study first demonstrated the nuclear stress-induced inhibition of DNA damages in living cells.
The metal bats are more advantageous than the traditional wooden bats due to their specific properties such as improved strength, lower cost, and durability. The National Collegiate Athletic Association (NCAA) only allows the use of bats whose bat-ball coefficient of restitution (BBCOR) is ≤0.50. Since there is a possibility that the value of BBCOR will be standardized in Japan as well, building the design method has become extremely important for controlling the value of the BBCOR. In previous studies, the BBCOR has been shown to decrease with an increase in the hoop frequency of the bat and the impact velocity of the ball. In this study, the equation for predicting the BBCOR from the relationship between the BBCOR and the impact velocity or the hoop frequency has been investigated by using a power law. From the BBCOR prediction equation, for an impact velocity of 61 m/s (as regulated by the NCAA), the hoop frequency in which the BBCOR is ≤0.5 has been determined. Furthermore, the hoop frequency was calculated using a finite element method that mostly corroborated the experimental value. The BBCOR could then be estimated when the hoop frequency was substituted back into the BBCOR prediction equation. It was shown that designing a bat may be possible without resorting to physical experimentation.
In the event of a level crossing accident, train passengers seated in a rotating and reclining seat have a risk of getting injured due to collision with seats in front of them. In order to evaluate the passenger's kinematic behavior and injury quantitatively in this situation, firstly the authors carried out dynamic tests by striking the seats with an impactor to grasp the physical properties of the seat in terms of dynamic strength. Secondly, the authors carried out impact tests using crash-test dummies, and FE analyses under the same condition as the tests. As a result, it was clarified numerically that the most important passenger's part to which attention should be paid was the femur, and the head and the chest had a low risk of serious injury. However, if the impact acceleration was increased, the forward seat was not able to catch the passenger because of its revolution or deformation and there was a possibility of injury caused by jumping out forward. Furthermore, the numerical results obtained by the FE analyses by means of a rigid dummy model developed for the automobile were generally consistent with the empirical results in terms of dummy's behavior and injury values.
This paper presents a basic study to develop a new damping device against flexural vibration of railway vehicle carbody utilizing elastic deformation of an elastic body as a dynamic vibration absorber (DVA). A donut-shaped elastic body (called ”elastic torus” in this study) is proposed considering practical application to rail vehicles. Vibration measurement tests using some existing elastic tori are carried out to examine the effect by their size and infill upon natural frequency. In addition, excitation tests for a 1:5 scale model of a Shinkansen vehicle carbody are conducted, and the DVA effect by applying such elastic torus against the first mode of flexural vibration of the carbody is demonstrated. Then, numerical studies using finite element (FE) analysis are carried out and it has been found that the shape and the size of an elastic torus having desired natural frequency can be determined by the numerical model. Finally, an elastic torus dedicated as a DVA for rail vehicles made of rubber filled with water is designed using the FE model and manufactured actually.
A new vibration reduction device against flexural vibration of railway vehicle carbody utilizing deformation of a donut-shaped elastic body called elastic torus is presented in this paper. The vibration properties of the elastic torus specially designed and manifactured for rail vehicles are firstly presented, and simple one degree of freedom (1DOF) model and detailed finite element (FE) model of the elastic torus are developed. In order to check the vibration reduction effect by the elastic torus, a series of excitation tests using a Shinkansen-type test vehicle are conducted by applying up to 20 elastic tori. Large vibration reduction effect has been observed against flexural vibrations of the carbody, and multi-modal vibration reduction effect has also been demonstrated. Then, numerical studies using simple beam model applied with 1DOF torus model and detailed FE carbody and torus models are carried out to check the vibration reduction mechanism. It has been confirmed that the reduction mechanism by the elastic torus is due to the effect that the elastic torus act as dynamic vibration absorber. And it has also found that different elastic deformation modes of the torus lead to the multi-modal reduction effect.
The derailment coefficient is calculated from wheel-rail contact forces and it indicates the running safety of the railway vehicle especially in sharp curves. The derailment coefficient is affected by many factors such as the track irregularities, the vehicle parameters and the friction characteristics between wheel and rail. Therefore, monitoring of the derailment coefficient is desired to evaluate the running safety of the vehicle. Recently, a new monitoring bogie which can collect time series data of the derailment coefficient during commercial operation has been developed, and a large scale data is collected. However, there was no way to use such a data efficiently because an efficient method and an analysis tool have not been developed. In this research, a new analysis tool which can easily handle a large scale data and assist analysis of the derailment coefficient has been designed using MATLAB. In addition to measuring the derailment coefficient, the wheel load reduction and the track irregularity of twist are also measured. The tool can extract points where the derailment coefficient increases from a large scale data, and quickly show detailed information. On the basis of the information displayed on the user-interface, the data analyst can identify factors that increase the derailment coefficient. Not only analysis focused on a particular curve, but also the tool has the function for comparison of some curves. Analysis of the time change of the derailment coefficient is also possible. This paper shows the basic design of the analysis tool and gives some examples of analysis using this tool.