To develop turbomachinery blades with high reliability, it is indispensable to verify the natural frequency, damping, resonant stress, etc. under operating condition, and utilize these data in the mechanical design of a new blade. BTT (Blade Tip Timing) and the telemetry system have been widely used to measure the modal parameters of turbomachinery blades. In measurement of the modal parameters of blades under rotation, it is pointed out that the mistuning phenomena make the identification of modal parameters difficult. Namely, because, in a mistuned bladed disk, responses of many vibration modes are superposed, it becomes difficult to correctly identify the natural frequency and damping of an individual blade. This is one of the critical issues to be overcome for developing blades with high reliability. In this study, a novel identification method of modal parameters of a mistuned system is proposed, where the modal parameters of a mistuned bladed disk are identified using the frequency responses consisting of many vibration modes. To verify the validity of the identification method proposed, typical mistuned systems of a turbocharger are analyzed, and the modal parameters are identified. The effect of the noise included in the measured frequency response on the accuracy of the identification is examined in detail.

Evaluation of bolt tightening plays an important role to keep a performance of a mechanical structure. Lack of the fastening force induces slack and falling of the tightening bolt. Excessive fastening force induces a plastic deformation of screw thread and causes the decline of the fastening force. Therefore, guarantee of the bolt tightening is an important subject in order to secure the mechanical structure against unforeseen accidents. However, most of preceding studies are restricted within qualitative evaluation of the slackness. In the field of industrial manufacturing, quantitative evaluation of the bolt tightening is strongly required. In this paper, the authors propose a technique for quantitative evaluation of bolt tightening, and in this technique, the flank of the screw thread is assumed to contact through a contact stiffness. The transmissivity and reflectivity of an ultrasonic pulse wave through the flank are derived as a function of contact stiffness, and the contact stiffness is capable of being identified from experimentally acquired amplitude of ultrasonic pulse wave. The contact stiffness is quantitatively identified and the surface pressure on the screw thread is estimated by the identified contact stiffness through the results of the preceding study. The proposed technique treats an ultrasonic pulse perpendicularly transmits a fastening bolt, and is applied to an experimentally acquired ultrasonic pulse which enters a side surface of nut and transmits a bolt-nut fastening element. The identified contact stiffness is shown to be adequate for the given fastening force to the bolt-nut fastening element, and validity of the proposed technique is demonstrated.

This study focuses on the energy transmissibility, which is called coupling loss factor (CLF) in Statistical Energy Analysis (SEA) framework, for two degree of freedom vibration system. The aim of this study is to obtain a new interpretation of the energy transfer viewpoint of the phenomena represented by the two-degree-of-freedom vibration system and to utilize it for vibration control and structural design. In this paper, the energy transfer characteristics of one-degree-of-freedom and two-degree-of-freedom vibration systems are explicitly derived from the equations of motion under broadband excitation through the energy (power) equilibrium and the frequency average concept. And then it is shown that the derived energy transmissibility can be described by a mathematical equation and is a single value. The transmissibility is determined by three parameters, which are the properties concerning each two uncoupled one degree of freedom vibration system, the uncoupled natural angular frequencies, the damping and the coupling properties. Then the energy transmissibility can be easily used for understanding phenomena described by the two degree of freedom systems and for control and design them. Furthermore, as an example of vibration control based on the energy transmissibility, the reduction of engine shake in automobiles is presented, and its effectiveness is compared and discussed with the results in the reference.

Vibration measures can be taken at three main locations: the vibration source, the propagating part, and the radiating part. However, measures at the vibration source are often difficult to implement, and countermeasures at the radiating part are inefficient. Therefore, measures at the propagation part are expected. For measures at the propagation part, the technique of structural intensity (SI) is used, which is effective in understanding the propagation path. Then, we attempt to reduce the vibration by a viscous damper layout based on the SI distribution. In this paper, the most effective layout for vibration reduction is presented for 2 and 3 DOF systems. As a result, it was found that adding a damper on the response side is effective. For beam system, the relationship between the ratio of change of SI and the velocity was also discussed. Based on these findings, a method for identifying the damper location by SI is newly proposed, and its effectiveness is verified.

This study considers electric circuits for dielectric elastomer generators (DEG) supplying to low-voltage devices such as sensors for wireless networks. The DEG convert the mechanical energy to the electrical one owing to their capacitance change according to the deformation, and they are expected as the generators utilizing low-frequency vibrations. To supply the electric charge to the DEG for power generation, the self-priming circuit (SPC) comprising capacitors and diodes is widely used. To use the DEG as the power source for the low-voltage devices, voltage step-down elements such as Zener diodes are conventionally introduced, however, the energy loss caused by the elements deteriorates the efficiency. Moreover, to quickly boost the voltage to the operational region from the initial state, smaller capacitors are usually used in the SPC. However, the choice makes the generators sensitive to the leakage charge flowing through the dielectric layers, which is problematic especially when the DEG are operated by low-frequency vibrations. This study proposes a DEG with a voltage-difference-type output circuit that utilizes a rectifier as the output circuit elements connected serially between the DEG and SPC, instead of the step-down elements connected parallel to them. The current flow to the load is governed by the voltage difference between the DEG and SPC, hence we can choose larger SPC capacitors because the quick voltage boost is not required. The output charge as well as the voltage increment and the acceptable leakage charge per cycle is precisely analyzed, from which a systematic way to choose the SPC parameters is also deduced. Experimental results show the validity of the derived formulae and the efficiency of the proposed circuit.

This paper describes a practical wheel/rail tangential contact force model for railway dynamics analysis under running in rainy conditions. In our previous studies, it was confirmed that experimental results of tangential contact force measurement are agree well with Kalker’s rolling contact theory under dry condition with low humidity around contact surfaces. Here, it can be considered that if the ambient humidity around the contact surface become high infinity, the contact surface is under wet lubrication conditions. On the basis of this assumption, in this study, a practical estimation model for characteristics of tangential contact force under running in rainy conditions is proposed by combining the relationship between the adhesive coefficient and velocity measured on running experiments using actual railway vehicles and Kalker’s linear rolling contact theory. Therefore, to verify the proposed model, the tangential contact force measurement experiment using a twin-disk rolling sliding machine was carried out. As a result, it is confirmed that estimated formulae based on the proposed model are well agreed with experimental results even under different velocity conditions, comparing the relationship between tangential contact force coefficient and slip ratio. From these verified results, the proposed model is considered to be a practical wheel/rail tangential contact force model for vehicle dynamics analysis under rain conditions, because the proposed model has the advantage of low calculation cost and can be easily applied to vehicle dynamics analysis based on multi-body dynamics theories.

The structural health monitoring is a very important technology for realizing a sustainable society. Building structures are subjected to random vibrations from the surrounding environment such as wind, and it is necessary to identify the random external forces for structural health monitoring. In this study, we assumed the case where the random external force such as wind acts on the layered structure, and proposed the identification method of the random external force. The identification method is to identify the power and cross spectrums of the random external force from the measured power and cross spectrums of the response and the frequency response function of the structure previously identified. In the governing equations of this inverse problem, the fact that the power spectrum is a real number and the conjugate relationship of a certain variables are used to reduce the ill-posedness of the inverse problem by reducing the variables in advance. After constructing a concrete identification procedure for a three-layered structure, the validity was verified by numerical simulation. It was shown that the spectrums of the random external force acting on the structure could be identified with sufficient accuracy. Next, we conducted an experiment to verify applicability. A simple three-layered structure was constructed, and inertia type exciters were installed on all layers. Then, when the vibration exciters are operated, the actual external force acting on the structure was measured with a load cell, and the external force was identified by applying the proposed method using the measured response data. Furthermore, numerical simulations were carried out to reproduce the experiments, and it was shown that the proposed method could identify random external forces.

Recent increase of low-grade, finer iron ore leads to development of powder handling methodology applicable for fine powders. In order to reduce developing time of mechanical facilities, development of optimization methodology of mechanical property in powder mixer was conducted. This methodology was combination of mixing experiment and novel discrete element method (DEM). Conventional DEM tracks particle movements to evaluate mixing of particles; in this model in addition enabled to evaluate moisture content as it tracked exchange of moisture content between particles upon contact. This DEM model was validated in comparison with experimental PIV surface flow and DEM surface flow, in lab-scale (diameter of 390 mm) of high speed shear mixer. Using this method enabled to estimate mixing time of high speed shear mixer with accuracy of t < 10 s where estimation time varied from around 20 to 100 s.

In this study, methods for automatically controlling load transportation by a swivel crane with high speed and suppressed swing motion of suspended load at the target position are proposed. First, highly versatile trajectories for each of swivel and straight transport of load are proposed on the basis of a linearized and simplified analytical model and the optimal control theory. The proposed method has the versatility that it can be applied even with different swivel radii and swivel angles. The effectiveness and limitations of the proposed methods are shown with computer simulations and experiments with a laboratory model. Next, we propose a new method that expands the proposed method and uses the measurement data of the swing information of the load. It is shown that by using this method, even if the load swings at the start of transport, it is possible to suppress the swing of the load at the target point of transport.

The seismic resistance of nuclear power plants, particularly those using Sodium-Cooled Fast Reactor (SFR) design, is of crucial significance. This paper presents an innovative three-dimensional seismic isolation system developed to address the inherent challenges of SFR design. Given that these designs necessitate components with a thin wall thickness for achieving high-temperature structural integrity, this can inadvertently lead to a disadvantageous seismic design. Hence, reducing seismic forces in both horizontal and vertical directions is crucial to ensure seismic resistance. This isolation system, designed for application to the reactor building, aims to make it an effectively isolated entity within the larger plant structure. It has been developed to manage seismic forces acting on components, thereby balancing the requirements of both seismic and high-temperature structural designs. The feasibility and effectiveness of this design have been verified through static loading tests conducted on a half-scale model of the system, investigating force-displacement relationships in both horizontal and vertical directions. The results demonstrate that the system's horizontal supporting function provides a stable load path. Additionally, it validates the decoupling of force-displacement interactions under the condition of simultaneous horizontal and vertical loading, an essential presumption in the formulation of the design basis ground motion.

In automotive development, it is important to balance various phenomena with a simplified vehicle body model in the initial design phase. Additionally, idling vibration, engine shake, and road noise are phenomena that affect vehicle ride comfort. Since they have different exciting components and target frequencies, each simplified vehicle model examined in the past report is different. Therefore, it is necessary to represent of each phenomenon in a single vehicle model. Therefore, in recent years, much research has been done in initial design techniques called Model Based Development (MBD) and 1D CAE. We have studied using the Statistical Energy Analysis (SEA) for the initial design. Especially an energy transmissibility parameter of SEA which is called by coupling loss factor (CLF) is focused on describing the phenomenon for various kinds of vibration and noise problem. In this paper, a fundamental study is conducted to examine the balance of multiple phenomena in the initial design phase by the energy transmissibility. At first, a simplified vehicle model that represents each phenomenon is constructed. Next, the energy transmissibility is used to represent each phenomenon, and vibration reduction guidelines are obtained and verified through balance design. The obtained guidelines are then applied numerically to the actual vehicle to confirm vibration reduction.

Many mechanical systems such as vehicles, robots and space structures are comprised of a lot of interconnected components. The motion of the components is constrained because of mechanical joints or specified motion trajectories. Multibody dynamics is one of effective methods to analyze nonlinear dynamic behavior for such systems. On the other hand, it is quite difficult to obtain all parameters required for numerical simulation by only direct measurement in complex mechanical systems. Therefore, parameter estimation and identification techniques are crucial for simulation in practical problems. This study aims to develop a parameter estimation technique based on the adjoint method which can be applied to mathematical models used in the multibody dynamics, namely, differential algebraic equations. In addition, a feature extraction technique based on the proper orthogonal decomposition is incorporated into the parameter estimation method in order to evaluate effect of model uncertainties on an accuracy of the parameter estimation, because the joint components often involve model uncertainties due to inherent physical characteristics such as friction, contact and so on. The validity of the present method is discussed by numerical experiments using the rigid multibody systems.

Christensen derived solutions of macroscopic elastic constants of composite materials containing randomly oriented fibers (Christensen, 2005). In this study, by extending Christensen’s method, the analysis of macroscopic physical properties of a composite material containing ellipsoidal reinforcements oriented randomly will be performed. Macroscopic elastic constants, thermal expansion coefficients and dielectric constants of the composite material could be expressed explicitly by using solutions for ellipsoidal reinforcement oriented unidirectionally. As a result of calculations for various ellipsoidal shapes of reinforcement by using derived solutions, it was confirmed that these analytical results of macroscopic physical properties exist between the upper and lower bounds of Hashin et al. Furthermore, by comparing the present result with the result of solution based on Mori-Tanaka’s theory and the experimental result, the validity and applicable range of the analytical solutions were examined.

Recently, large-scale welded structures especially in power stations have been designed and operated based on the concept of assurance of structural integrity. Here, fracture mechanics and non-destructive inspections are applied to flaw evaluations, however it is necessary to estimate three-dimensional residual stresses to predict crack growth rate for each observed crack. On the other hand, welding deformations have an influence on manufacturing accuracy and on external appearance of products. Still today, it is relatively difficult to estimate three-dimensional welding residual stresses and welding deformations accurately using the thermo-elasto-plastic FEM (Finite Element Method) analysis due to higher complexity of actual welding process. Authors have proposed a non-destructive method evaluating welding deformations and residual stresses based on the eigen-strain methodology. In this method, welding deformations and residual stresses for whole structure are calculated from eigen-strains which are estimated by the inverse analysis from surface displacements which can be measured by the digital image correlation (DIC) method. However, estimation accuracy near the weld line becomes relatively poor because it is impossible to define deformations and total strains on the weld metal by the DIC method. This study aims to improve the estimation accuracy of both welding deformations and residual stresses by adding surface elastic strains along the weld line which can be measured by X-ray diffraction. Numerical simulations for a butt-welded plate with a V-groove before welding were carried out to evaluate the estimation accuracy of this method. X-ray measurements along the weld line were effective to improve the estimation accuracy when the penalty method is combined with the Truncated Singular Value Decomposition (TSVD) method in the inverse analysis.

A series of tensile tests were conducted for notched plate specimens whose shapes are similar to the pressure shell to clarify the local failure characteristics for the steel nuclear containment. The specimens included the full or partial-width notched plate specimens of 10 mm thickness, and full-width notched thick plate specimens of 34 mm thickness the same as the actual pressure shell. In the full-width notched plate specimens with a small curvature notch, the cracking occurred on the notch bottom, and the crack propagated and finally ruptured. The plate specimens with a large curvature notch failed in shear suddenly without notch bottom cracking. Those failure modes were very unlike notched round-bar specimens, in which failure always starts at the notch section center. In the case of partial-width notch plate specimens, the notch bottom cracking also occurred for a small curvature notch, and the notch section failure happened before the specimen’s rupture for a large curvature notch. The limit strain diagrams were 40% to 50% lower than those of the notched round-bar specimens. The limit failure stress indexes, which correspond to the stress indications for the limit strain diagrams, could be applied to the shear failure of notched plate specimens. The indexes of the notched plate specimens were approximately 10% lower than those of the round-bar specimens. The crack initiation points for small curvature notch specimens were concentrated in the range of stress triaxiality 0.6 and equivalent plastic strain 0.5 to 0.8. In the full-width notched thick plate specimens, notch bottom cracking occurred for all specimens, and the cracking conditions were almost the same as the full and partial notched plate specimens. However, the maximum nominal stress exceeded 2/3 of the design tensile strength, and it was concluded that local failure occurs at more than twice the design pressure.

In recent years, the authors have developed a dedicated strain gage (hereafter referred to as a K-value gage) and an analysis method that can analyze the stress intensity factor of a crack with a single element. The developed single-element K value gage can obtain the opening mode stress intensity factor of the simulated crack within ±5% of the theoretical value. In this study, using this single-element K-value gage, a simulated crack was inserted into one side edge of the strip and an attempt was made to analyze the stress intensity factor when an out-of-plane bending load was applied. M.L.Williams introduced the stress equation for the out-of-plane bending load acting on a strip crack. In this study, the stress equation was converted into the strain ε_θ equation, and the K-value gage equation was derived. The K-value gage formula defined a K-value gage grid angle of 104 degrees for a Poisson's ratio of 0.3. In order to examine the validity of the derived strain gage equation, out-of-plane bending experiments were carried out on strips with simulated cracks inserted. When a/W=0.2 and 0.3, the crack length a with respect to the strip width W was obtained within ±10% of the theoretical value. When a/W=0.1, the error was 10-15%.

We conducted a study on unsteady characteristics of fluid-dynamic force acting on a pitching NACA0012 wing with linear leading edge (Baseline) and with leading edge protuberance (Wave) in low Reynolds number region (Re =4.32×10⁴) for the development of fish-type autonomous underwater vehicle. To investigate the effect of pitching motion on the fluid-dynamic force, force measurement and flow visualization were conducted by using a wind tunnel. In the case of Baseline, increase in pitching frequency and amplitude produced higher lift force than the quasi-steady one in upstroke phase. On the other hand, in downstroke phase, the lift force decreased and become lower than the quasi-steady state. However, at large pitching amplitude such as 15° where the rapid decrease in lift was observed at the end of downstroke phase, the lift change was close to the quasi-steady one. Flow visualization showed that the increase in lift force at upstroke phase was caused by separation control effect of the upstroke motion. In the case of Wave, although the same characteristics of unsteady fluid-dynamic forces as the Baseline case were observed, higher average lift and smaller lift fluctuation than the Baseline case which caused by the separation control effect of leading edge protuberance were confirmed regardless of the pitching conditions. Furthermore, the 2-dimentional potential flow analysis revealed that the effects of unsteady lift and drag forces attributed to the potential flow were considerably small compared with one by flow separation.

I have addressed a polydisperse suspension composed of cubic hematite particles in thermodynamic equilibrium. From the viewpoint of developing a surface modification technique using cubic hematite particles, I have investigated the local internal structures of cubic particle aggregates in a quasi-two-dimensional (quasi-2D) system. The cubic particles have a full three-dimensional (3D) rotational ability in a quasi-2D system. I have conducted quasi-2D Monte Carlo simulations in the situation of no applied magnetic field to investigate the dependence of the local internal structures of particle aggregates on the magnetic particle-particle interaction strength and the standard deviation in the particle size distribution. The results obtained here are summarized as follows. In a polydisperse system with a small standard deviation, cubic particles tend to aggregate to form closely-packed structures with an aligned face-to-face configuration as the magnetic particle-particle interaction strength is increased. In a polydisperse system with a large standard deviation, they tend to aggregate to form loosely-packed structures with unstable face-to-face contact as the magnetic interaction strength is increased. That is, an increase in the value of standard deviation leads to a decrease in the orientation order of the constituent particles in the aggregates. I understood that the orientation order of the cubic particles decreases sharply within a narrow range of the standard deviation in the particle size distribution.

Fluoroplastics have a very high absorptivity to the CO₂ laser (oscillation wavelength: 10.6 μm) widely used industrially, so that only the surface layer of their substrates irradiated with the laser can be melted. It is difficult to weld the overlapping parts with a thickness exceed 1mm deep enough. This study deals with the CO laser welding method for plastics assisted by a solid heat sink transparent to infrared laser beam. The CO laser beam (wavelength: 5.7 μm) is possible to penetrate fluoroplastic sheet deeper than CO₂ laser beam due to the decrease in absorption of fluoroplastics at that wavelength. Firstly, heat transfer analysis was conducted to investigate the influence of the difference in transmission / absorption characteristics of the plastic material on the temperature distribution inside the welded sheets during laser irradiation. Secondly, by using the CO laser, an experimental examination of lap welding of PFA sheets with a thickness of 1 mm was carried out. It was impossible to weld them using a CO₂ laser due to its high absorbance. It was conducted an observation of the internal cross section and evaluating the tensile strength of welded sheets. Under suitable laser irradiation conditions, melting of the interface between the upper and lower sheets was confirmed. In addition, it was confirmed by a tensile test that the welding performance is guaranteed by breaking the base material while the welded line is held integrally.

There are several studies focusing on rapid tapping motion for a robotic finger, including not only a theoretical approach of musculoskeletal modeling of a human finger but also an empirical challenge with robotic finger. Shourijeh had made a success of 6Hz-periodic tapping motion by an index finger model for forward dynamic simulation, however the contribution is restricted to analyzing the validity of a musculoskeletal model of finger and is based only on simulation of not a force control but an angular control of the finger. This paper, therefore, presents a novel three-DOF robotic finger that enables fast tapping motion applicable in piano playing and keyboard typing, which consists of metacarpophalangeal(MCP), proximal interphalangeal(PIP), and distal interphalangeal(DIP) joints. In previous study, we developed Twisted Round-belt Actuator(TbA) capable of producing contraction force by twisting a small-diameter round-belt having high elasticity, and empirically derived a contraction force model applicable only to two-DOF robotic finger. This study, therefore, derives such force model available for an extended three-DOF finger mechanism that is containing Variable-pitch Screw Module(VpSM) newly designed in this paper. This module is able to eliminate irregular twist phenomenon resulting in unexpected discontinuous movement in finger joints. Thus, we first describe the detail mechanism of the three-DOF robotic finger and indicate great advantage of the finger, which is obtained by combining the TbA and VpSM. Finally, we demonstrate a new force feedback method based on fingertip force estimation without any force/pressure sensors, in which the fingertip force can be accurately estimated by using mathematical model of the contraction force by TbA with VpSM. In addition, this paper shows successful experimental results of fast tapping motion by the robotic finger, and clearly reveals that the robot is able to move against sinusoidal force reference up to 5Hz interval.

Low-intensity pulsed ultrasound (LIPUS) is commonly used for bone fracture healing to mechanically stimulate a fracture site and accelerate the repair process. Recent studies reported that LIPUS stimulation could have various effectiveness such as not only fracture healing but also regenerative medicine of articular cartilage and cognitive dysfunction improvement. However, conventional LIPUS devices stimulate both affected and unaffected sites. To promote healing effects at an affected site and enhance therapeutic applications, LIPUS devices should employ acoustic holography, which can control force fields and provide the desired ones to an affected site. However, conventional control algorisms cannot form desired force fields and have not been used in vivo for therapy. In this study, we experimentally investigate the feasibility to control force fields by acoustic holography using an ultrasound transducer array under water for therapy. First, we designed and prototyped a simple device for generating force fields using a 4×4 ultrasound transducer array under water for therapy. Then, we introduced a force field control algorithm developed in our previous study into the prototype force field generator to experimentally verify the controllability to achieve desired force fields for therapy. The findings show that the prototype force field generator meets acoustic intensity enough for fracture healing by focused ultrasound and that the developed control algorism applied to the prototype force field generator forms a two-dimensional force field similar to a rectangular shape assuming a fracture line as a target area and suppresses the acoustic intensity outside the target area.

Journal bearings are an important mechanical element of rotating machines and support the rotor system by oil film reaction forces. As rotational speeds increase, the shear heat of the oil film causes a significant temperature distribution on the journal surface. As a result, bending of the shaft occurs and vibration modes called Morton effect are generated. The Thermo Hydrodynamic Lubrication (THL) model is used for analyzing of lubricant, and one of the authors has modified and applied it as a simple unsteady model to efficiently analyze the temperature, viscosity, and pressure distribution of the oil film , maintaining computational accuracy. In this paper, the simplified THL model is modified with the boundary condition that both the bearing and journal are adiabatic (ADIADI) in order to construct an accurate and efficient analytical model of the Morton effect in the rotor system. The journal vibration is assumed to be small, and dynamic coefficients of journal bearing are derived considering the temperature distribution. Eigenvalue analysis is performed using these dynamic coefficients to predict the onset speed of instability of the rotor system. The validity of the eigenvalue analysis is verified by direct numerical integration simulation.

In this study, we develop a vibration isolation system using an air suspension with a variable length slit restriction, clarify its dynamic characteristics and build a system that automatically adjusts an equivalent damping coefficient and an equilibrium position of a supported object. The proposed air suspension can provide an optimum damping coefficient by a damping adjustment mechanism. The optimum damping coefficient, which provides the minimum resonance amplitude, increases as mass of the supported object increases. The damping coefficient can be varied by varying slit length of the restriction. In order to vary slit length, the damping adjustment mechanism consists of a fixed plate, which has a partially circular groove and a rotating flat plate faced to the grooved plate. The variable length partially circular slit is formed by the two plates. The damping coefficient is almost proportional to an adjustment angle of the rotating flat plate in the adjustment mechanism. An optimum adjustment angle which provides the minimum resonance amplitude can be obtained by equation showing a relationship between the supported mass and the optimum adjustment angle. The proposed system consists of the air suspension, two pressure sensors measuring atmospheric pressure and static pressure in the cylinder and the reservoir tank, the damping adjustment mechanism, a servo motor rotating the flat plate to tune the adjustment angle and a micro-computer. The micro-computer calculates the optimum adjustment angle which is obtained from the measured pressure data and controls the servo motor to adjust the damping coefficient. The equivalent damping coefficient of the proposed air suspension does not depend on the amplitude even if the slit length is changed by the damping adjustment mechanism. Even if the mass increases up to three times of the nominal value, the minimum resonance amplitude is achieved by using the damping adjustment mechanism.

A method of controlling a cooperative positioning system consisting of three industrial manipulators is proposed. The positioned object is suspended with six wires each two of which are connected to each manipulator tip and remotely controlled by an operator with a joystick. In our previous study, cooperative positioning system with three manipulators has already been developed. However, positioning errors of the object inevitably remain because it is difficult to sufficiently compensate for the geometrical errors within the mechanical system. Therefore, the compensation of the object position by a joystick control is essential. For achieving the joystick control, it is necessary to keep all the tensions positive for the stable positioning. However, if the operator moves the object in arbitrary directions, some wire tensions may become zero because it is impossible to know the positioning error in advance. Therefore, a new control method for not only achieving the positioning of the object but also keeping the proper wire tensions has been developed by two joystick control modes, position control mode and tension control mode. The joystick has three degrees of freedom and control the three translational position parameters or orientation parameters by a selector switch in position control mode. In tension control mode, the minimum wire tension among six is increased by utilizing the kinematical redundancy of the system according to the joystick input. The developed control system has been applied to our experimental system and the effectiveness of the proposed method was verified.

Pneumatic rubber artificial muscles are nearly ideal for power assistance, medical care, and rehabilitation due to their lightweight drive unit made of rubber, which is soft and safe for human use. However, they have complex nonlinearities, including input saturation, hysteresis, and changes in static characteristics due to shrinkage. Additionally, when used with a human subject, the artificial muscle control system’s characteristics may vary based on the person’s physique, fitness, temperature, and the rubber’s deterioration. Therefore, it is desirable to be able to auto-tune the PID and other controllers in a short time before use. Data-driven controls such as FRIT and VRFT are suitable for auto-tuning in a short time. Among them, V-Tiger presented a procedure for predicting the actual closed-loop response and its Confidence interval. However, V-Tiger is not applicable to nonlinear systems with input saturation. This paper describes a procedure for (1) tuning PID gains by predicting the closed-loop response with V-Tiger in the presence of input saturation, (2) obtaining Confidence intervals for the predicted response affected by input saturation, and (3) how to use the Confidence intervals to apply this method to nonlinear systems.

In this paper, the prediction of crack propagation with two cracks using machine learning is described. The analysis results of crack propagation by s-version FEM (s-FEM), which combines the automatic mesh generation technique, are used for generation of training and validation datasets. Plural crack propagation with the different vertical distance between the two cracks as a variable are analyzed. The analysis cases are divided into training and validation datasets. In training process, the input parameters are the coordinates of 4 crack tip, the output data are crack propagation vectors, the number of cycles for crack propagation of 0.25 mm. Initial crack configurations should be specified. After the specification, the predictor iteratively predicts crack propagation direction and the number of loading cycles. A prediction accuracy depends on the training datasets, which contains 0.25 mm length of each crack propagation in this study. To improve prediction accuracy, the data augmentation is effectively applied. In case of plural crack interaction, when the crack tips close each other, the accuracy gets worse and worse. Reducing datasets which satisfy the crack coalescence condition, it is shown that the prediction accuracy is improved. Even if training datasets are not enough number for accurate prediction, it is shown that the prediction accuracy is improved by the data augmentation.

Magnetic materials exhibit various magnetic orders and are used in many magnetic and mechanical devices. In order to control and design magnetic ordering, the stability of the magnetic phase with mechanical strain has been reported in previous studies. In this study, based on the first-principles calculation, we investigate the stain dependence of the magnetic phase stability in iron with carrier doping. We find that the excess electron doping makes keeping the ferromagnetic (FM) phase for compressive strain loading in the (001) plane. On the other hand, hole doping leads to a multi-step strain-induced magnetic phase transition, and the spin spiral (SS) phase appears under the in-plane tensile strain. The 3d-orbital hybridization of up- and down-spin makes the hybridization gap, which is one origin of stabilized SS phase. FM phase under the in-plane strain and hole doping will be unstable due to the increasing 3d-orbital bands at Fermi energy; that is, SS phase will be the most stable state by the hybridization gap. The present study suggests that the excess electron/hole carrier doping and mechanical loading help to design a non-trivial magnetic phase in magnetic materials.

Sequential press forming of thin sheets is a method in which different locations within a single workpiece are pressed in sequence, and is used to manufacture large structures, such as storage tanks. In the sequential press forming, it is important to estimate bending-defect areas efficiently because a product shape can be corrected not by repairing dies but by only re-pressing the bending-defect areas in the subsequent process. At present, high skill is required to determine bending-defect areas because they are judged by measuring a gap from a template. In this study, a versatile method to estimate bending-defect areas in products obtained with sequential press forming is proposed. Specifically, a cosine similarity is calculated between the product shape and templates of ideal shapes with known defects prepared beforehand. A cosine similarity is calculated based on curvatures. Bending-defect areas are then evaluated from the magnitude of the deviation from the average of the multiple calculated cosine similarities. This paper also presents a procedure to calculate the threshold for estimating bending-defect areas by the proposed method. The effectiveness of the proposed method was confirmed through case studies that considered virtual products and actual workpieces. It was confirmed that the proposed method can estimate bending-defect areas and excess or deficiency of bending even when local deformation and measurement noise exist.

For improving consumer satisfaction, a design process for individual production based on additive manufacturing technology is required to consider appearance as well as functionality. Although topology optimization is a powerful technology to design highly functional structure, it has difficulty considering aesthetic features. This paper presents a new topology optimization method considering aesthetic preferences with a manufacturing constraint by incorporating the image processing used for style transfer and object recognition. To consider aesthetic features, we introduce texture energy which evaluates the similarity between the input preference image and structure represented by the level set method. To identify the unmanufacturable regions disconnected from the main structure, the connected component labeling process based on the object recognition method is applied to the binary image of the level set function. A topology optimization problem of maximizing stiffness is formulated considering aesthetic preferences and imposing the structural connectivity constraint, where the objective function is defined as a combination of minimizing mean compliance and texture energy. A reaction diffusion equation is used to update the level set function, where the Lagrange multiplier of structural connectivity constraint is calculated to eliminate unmanufacturable disconnect regions. Numerical examples are provided to confirm the validity and utility of the proposed method.

There are more and more issues, requirements and complexities that engineering design problems must take into account in industrial applications. Therefore, the number of behavior and design variables tends to increase, making optimization problem harder. PSO was proposed and has been widely used for its simplicity and capability to solve problems, even though their convexity is not guaranteed. However, its effectiveness is limited to a relatively small number of design variables. In this study, we propose the following four ideas to extend its efficacy for the number of design variables - adjustments for PSO parameters, a large explosion, a small explosion, and a genetic estimation technique. The explosion is kind of mutation in GA. The genetic estimation uses a chromosome called Hoxgene to identify variable dependencies, enabling PSO to solve the problem with a smaller number of variables. The results of experiments on benchmark problems showed the highly accurate solutions were stably obtained even for problems with a large number of variables using the proposed method.

PTFE is often used in various fields because of its excellent properties such as low coefficient of friction, heat resistance, and chemical resistance. On the other hand, non-granulated fine powder of PTFE agglomerates easily and tends to fibrillate, therefore, it is difficult to supply it continuously with high accuracy. The purpose of the research is to develop a device that can continuously and accurately supply fine PTFE powder. The authors propose a new method in which combinations of three motions, i.e. vibration, stirring motion and crushing motion, are adopted. The powder in a straight hopper is stirred by a slowly rotating tool while the hopper is vibrated in the horizontal direction. The hopper has stainless steel mesh at its bottom. The powder is dropped through the mesh and supplied into a container. In order to avoid for the powder agglomeration in the hopper, two crushing tools also rotate fast in the hopper. Powder and supply situations are investigated for the supplies by each motion or combination of the motions. Target values and accuracies of one supply are set to 10g±0.1g or 0.8g ±0.02g, respectively. In addition, the target continuity of the supply and target time in one supply are set more than 100 times and less than 40 seconds, respectively. As a result, the target accuracy has been achieved at 95 % or more possibility for both target values. The target conditions of both of the continuity and time have also been cleared.

Magnetic flux modulation gear was proposed in 2001, and many researchers have reported its transmission torque density which has increased dramatically compared to conventional magnetic transmissions. It has some unique characteristics not found in mechanical transmissions such as greaseless drive, high efficiency, quiet drive, low backlash, step-out torque and so on. Therefore, it has potential not only to replace existing mechanical gears but to create new value. For example, it is expected to save maintenance time, improve the working environment (factory or office) by making it quieter, increase efficiency of speed up gears for generators. However, only a few studies about detailed transmission characteristics have been reported. Therefore, authors made a prototype and measured the driving efficiency, loss characteristics, backlash, torsional stiffness, and sound pressure level. In this paper, we report the experimental results and suggest potential used for new applications.

The purpose of this study is to propose an effective model for predicting the slip ratio of a belt transmission mechanism during power transmission, considering the different tensile stiffness of the drive belt. The slip ratio of the belt mechanism was measured under a constant applied torque to compare it with the theoretical value based on belt elastic elongation. The apparent friction coefficient between the belt material and the pulley was measured using a laboratory-made counter-type disc-on-block friction tester under a constant fixed slip velocity condition. The test results showed that when a soft rubber belt was used, the slip ratio of the belt mechanism could be accurately predicted by considering only the elastic elongation of the belt itself. However, when a rigid metal belt was used, the experimental slip ratio of the belt mechanism was larger than the theoretical value. The observed friction coefficient between the belt material and the pulley indicated that the friction force depended on the slip velocity, with the friction force at low slip velocity being smaller than that at high slip velocity. Based on these results, a prediction model for the slip ratio was proposed, considering micro-slip due to the varied frictional coefficient, and its validity was examined.

Suitable friction modifiers and anti-wear additives for hydrogenated amorphas carbon (a-C:H) films have been investigated by many research groups for a decade since it is well-known that the combination of the a-C:H film and the conventional additives hardly exhibits good tribological performances under boundary lubrication. In this study, to confirm the effectiveness of nano-carbon additives for improving the tribological performance of a-C:H films, the tribological performances of the combination of the a-C:H film and multi-walled fullerenes (MWFs) containing oil was investigated under boundary lubrication. Especially, we compared the effects of the MWFs on the tribological performances of two DLCs: a-C:H and tetrahedral amorphous carbon (ta-C) using a ball-on disk tribometer and in-contact Raman tribometer that can monitor the chemical structure of frictional interfaces. All our results suggest that the combination of a-C:Hs and MWFs exhibits an ultralow friction and remarkable wear reduction compared to non-MWF added oils due to the formation of MWF tribofilms uniformly at the frictional interfaces.

The paper describes the critical Reynolds number of soccer balls as a function of the total groove volume on the ball surface. In this study, the aerodynamic drag and separation point of 6 soccer balls with different panel orientations were measured in a wind tunnel. Moreover, the total volume of grooves on the ball’s surface was measured by One shot 3D measuring machine. It was found that the drag coefficient in the supercritical region and the critical Reynolds number depend on the design of the ball surface (shape, number of panels, surface roughness). A negative correlation exists between the total groove volume on the surface and the critical Reynolds number. When the total groove volume is large, the drag in the supercritical region increases. The position of the separation point does not change in the subcritical and supercritical regions even if the orientation of the panel is changed. However, when the groove width is wider, the panel orientation dependence becomes significant in the supercritical region. In the transition region, the position of the separation point differs depending on the panel's orientation.

Recently, the movement and muscle usage principles have been elucidated by analyzing the kinematic and dynamic parameters of various body parts during movements and exercises. Feedback training methods based on these findings have also been proposed to improve athlete performance. For instance, prior research on pedaling exercises has shown that considering muscle contraction patterns and activation states can help cyclists avoid muscle fatigue. However, few studies have investigated the effects of both muscle contraction patterns and muscle activation states during pedaling exercises. Therefore, this study proposes a novel pedaling training system that provides visual and auditory feedback on the muscle contraction and activation of a cyclist's lower limb during pedaling exercise. This may help cyclists better understand and optimize muscle contraction and activation patterns. The proposed system visualizes muscle contraction patterns and activation states during pedaling motion and generates sound for cyclists at the ideal crank angle for optimal muscle activation timing. This allows cyclists to recognize the optimal timing for muscle activation based on these patterns. The effectiveness of the proposed system was validated by performing a trial pedaling training session for an amateur cyclist and comparing the muscle contraction and activation states among the pre-trial, feedback-trial, and post-trial. The experimental results confirmed that the proposed system improves muscle activation timing effectively during pedaling training.

The surface of a golf ball is provided with innumerable dents called dimples to improve the flight distance. In this study, we manufactured 15 model balls in which the dimple occupancy and the dimple volume ratio was changed by the dimple diameter and the number of dimples, and the dimple shapes. Using these balls, we carried out lift and drag measurements of the rotating balls in wind tunnel experiments. Then, a flight trajectory simulation was performed based on the obtained experimental results. As a result, the influence of the base shape showed different results for both drag and lift coefficients for each occupancy. However, the drag coefficient decreased and the lift coefficient increased as the dimple volume ratio increased regardless of the dimple shape. In addition, the relationship between the lift-drag ratio and the dimple volume ratio showed that the lift-drag ratio decreased as the dimple volume ratio increased. The flight trajectory simulation results showed that the flying distance was greater for O=52.6% and O=63.1% with a conical base when the dimple volume ratio was small and the dimple depth is D_D/d=4.55×10^-3. Two spheres with a spherical base and a conical base at O=83.1%, also exhibited similar flying distances. However, the flight distance tends to increase as the dimple volume ratio decreases. The ball's trajectory was lower when the volume ratio was small, and higher trajectory was obtained when the occupancy ratio was high.

From the previous time, unmanned aircrafts (drones) are being used in fields such as agriculture, logistics, and disaster response. Therefore, it is expected as a machine that creates new technologies and services in the 4th Industrial Revolution. In recent years, there has been a demand for the practical application of drones equipped with a fuel cell as a power source, which enables longer-distance flight. However, in order to operate a fuel cell drone, it is necessary to develop a protector that protects the high-pressure hydrogen tank from the impact of a crash. Therefore, the authors focused on carbon fiber as a protector for hydrogen tanks. Then, in this research, protectors for hydrogen tanks with 6 different layers and weaves were manufactured. And collision tests of these protectors were performed. Based on results obtained in collision tests, energy absorption qualities of protectors were compared and evaluated. As a result, it was clarified that the quality of energy absorption varies depending on the specifications, such as the direction of fibers and the presence or absence of plain weave sheets, even in protectors made from carbon fiber. In particular, the authors clarified the following. In the case of the Carbon Fiber Uni Direction (CFUD) sheet, in which the directional angle of the fibers is the same as the directional angle of the wedge-shaped projections or an angle with a small difference (90 degrees or 72 degrees)., the energy absorption of the protector made of this sheet alone is not good. In addition, a composite sheet that combines a CFUD sheet and a plain weave sheet has better energy absorption than a plain weave sheet alone. After clarifying the foregoing, the authors evaluated protectors with a three-stage evaluation test based on the guideline of the Ministry of Economy, Trade and Industry. Then, it was confirmed that the "Safety requirements for high-pressure hydrogen gas storage containers (tanks) to be mounted on drones" were satisfied by equipped carbon fiber protectors.

Vertical vibrations in railway vehicles are not only induced by track irregularity but also affected by the rotation of wheelsets with small mass imbalance. It is known that the excitation force generated by the rotation of wheelsets is transmitted from bogies to car bodies through longitudinal connecting members such as traction devices and yaw dampers. In this research, we first investigated the influence of yaw dampers on the vertical car body vibration induced by the rotation of wheelsets. Roller rigs rotation tests were performed using a full-scale vehicle with/without yaw dampers. In cases where there was no yaw damper, the vertical vibration of the car body was lower than that of cases where yaw dampers were equipped. This result indicates that vibration transmissibility from bogies to car bodies via yaw dampers should be reduced. In order to suppress this vibration transmission, we developed two vibration reduction devices: a new mounting structure for yaw dampers having a moving beam, and displacement-dependent rubber bushes for yaw dampers. The results of roller rigs rotation tests show that the developed devices reduced the car-body vertical vibrations caused by the excitation forces via yaw dampers. Moreover, we conducted running tests on a commercial track, and the results show that the vertical car body vibrations were reduced by applying displacement-dependent rubber bushes for yaw dampers.

The on-board components mounted on the structural panel of spacecraft are exposed to a severe random vibration environment, mainly induced by the acoustic excitation of the panel structure due to the large acoustic noise from the launch vehicle. To verify the components' resistance against the vibrational environment, random vibration tests of the components are generally performed at the excitation level based on vibroacoustic prediction. In order to consider the prediction uncertainty, there actually needs to add a margin, which often poses an excess of design and testing. JAXA has been involved with predicting wide frequency band vibro-acoustic behavior of the structural panel using SEA (Statistical Energy Analysis), in which we have to add margin to take into account spatial and frequency bandwidth uncertainties. These kinds of uncertainty margin may result in over conservative margin and causes costly over conservative design. To reduce the over conservative margin in SEA method, in this paper, a wavenumber expression of joint acceptance method calculated by fast Fourier transform approach on finite element model parameter of panel, i.e., mode frequency and mode shape is proposed. The proposed method is applied to two structural panels of actual spacecraft and compared with acoustic test results. It is shown by comparison with the test result of an actual panel that the proposed method achieved less conservative prediction in each individual component mounting location rather than enveloping every mounting location that SEA calculates.