We have developed a finite element model to reproduce the axial and radial stiffnesses of IWRC 6×Fi(29) wire ropes for cranes. Since IWRC 6×Fi(29) employs steel-wire core, the number of contact points is much larger than that of fiber-core rope. Therefore, complicated modelling of contact between wires is required. Firstly, we have developed finite element models of Fi(29) and IWRC. Then, we have realized the modelling of IWRC 6×Fi(29) by twisting them. In order to reproduce the actual shape and contact conditions of wires, cross-sectional images taken by the X-ray CT are used. For the validation of the model, the axial tensile tests and radial compression tests are conducted for Fi(29), IWRC and IWRC 6×Fi(29). As for axial tensile stiffness, the finite element model well reproduces the experimental results. As for radial compression stiffness, the finite element model reproduces the nonlinearity and hysteresis of the compressive force-displacement curves and the radial stiffness in the low-loading region. The difference in the radial-direction stiffness in the high-loading region might be caused by the difference in contact situation between wires. From the comparison with the our previous results of fiber-core rope 8×S(19), high resistance against the lateral pressure of steel-core rope is proved.

Thermoplastic resins, which can be used for matrix materials in fiber reinforced thermoplastics (FRTP), have distinctive nonlinear characteristics that depend on temperature and strain rate compared to conventional materials such as metals and thermosets. Therefore, in order to use FRTP as a structural material, it is necessary to properly measure its material behavior, adopt an appropriate constitutive law, and accurately identify the material parameters. Conventionally, although there have been reports on the nonlinear behavior of thermoplastic resins, most of them employ a single constitutive law such as plasticity or creep using data measured under specific conditions. In this study, adopting a viscoelastic-viscoplastic-damage constitutive law to represent the material behavior of thermoplastic resin, we propose a hybrid identification method that can determine the material properties of by the combined use of the results of dynamic mechanical analysis and uniaxial cyclic loading-unloading test. Specifically, material parameters for viscoelasticity are identified from the complex moduli of elasticity obtained from the dynamic mechanical analysis, and those for viscoplasticity as well as the damage and time-temperature shift factor in low temperature range are identified from the uniaxial cyclic loading-unloading test. Differential Evolution, one of the optimization algorithm, is adopted to identify the parameters. Conducting some material tests, we confirm the effectiveness of the proposed method in reproducing the nonlinear material behavior of three typical thermoplastic resins: polycarbonate, acrylic resin and thermoplastic epoxy resin. In addition, the identification accuracy is significantly improved by the modification of the time-temperature shift factor, which has been determined by dynamic mechanical analysis, using the results of uniaxial cyclic loading-unloading tests in the low temperature range.

In this study, micromechanical modeling and analysis is performed for a composite material containing many double inhomogeneous inclusions which consist of a nested sequence of two inhomogeneous inclusions, whose shapes are spheroids that are different from each other. Applying double inclusion method and Mori-Tanaka theorem to this composite material, macroscopic elastic constants and thermal expansion coefficients of the material are formulated explicitly by terms of the difference in shape between inner region and outer one of a double inhomogeneous inclusion. It is shown that the independent number of macroscopic elastic constants of the composite material is the same as that of a hexagonal material. It is also examined the solution of macroscopic elastic constants for the special case where the shape of inner region and outer one of a double inhomogeneous inclusion are similar and coaxial. Furthermore, it is confirmed that the independent number of macroscopic elastic constants and thermal expansion coefficients is the same as that of an isotropic material, when shapes of two region of a double inhomogeneous inclusion are spherical.

In the previous study, solutions of macroscopic elastic constants and thermal expansion coefficients for a composite material containing many spheroidal double inhomogeneous inclusions were formulated explicitly by using double inclusion method and Mori-Tanaka theorem. The purpose of this study is to verify the validity of the solutions of macroscopic elastic constants derived in the previous analysis. First, by homogenizing the elastic constants inside the double inhomogeneous inclusions, continuity to the solution for the single inhomogeneous inclusion is confirmed. Secondly, for the cases where shapes of the inner and outer regions of the double inhomogeneous inclusions are both sphere and fiber, analytical results of macroscopic elastic constants are compared with analytical solutions obtained by other research groups, and the accuracy of this analytical solution is examined. Furthermore, the usefulness of this analytical solution is also investigated by calculating the macroscopic elastic constants in the case that shapes of the inner and the outer regions of the double inhomogeneous inclusions are not similar.

Laser quenching is a partial quenching method that significantly reduces deformation associated with heat treatment compared to conventional methods such as furnace quenching and induction quenching. However, thin parts such as brake disk and miniature-guide rail are subject to large deformation even by laser quenching. To expand the laser quenching applications, we proposed “dummy irradiation method” to complete heat treatment and deformation correction only by laser irradiation. Although the effectiveness of this method has been confirmed in our previous study, more detailed studies on the deformation of thin steel plate caused by laser irradiation are necessary to achieve highly accurate correction by dummy irradiation method. Therefore, laser irradiation experiments were conducted under various laser powers on three types of S50C plates with thicknesses of 2.5 mm, 3.0 mm and 3.5 mm, and the detailed deformation behaviors and the mechanism of the deformations were investigated. By the laser irradiation, the downward convex deformation (positive deformation) was caused in the direction perpendicular to the laser scanning direction, regardless of the laser power or plate thickness. In the laser scanning direction, both positive and negative deformations occurred depending on the laser power. Positive deformation occurred at low laser power and negative occurred at high laser power. Positive and negative deformations occurred at different times during the laser irradiation process: the positive deformations occurred during or immediately after the laser irradiation, while the negative occurred during the cooling process. It was found that the negative deformation in the laser scanning direction that occurs at high laser power could be related to the bending moment generated by the positive deformation in the direction perpendicular to laser scanning. From this result, it was considered that the plate width would affect the deformation caused by laser quenching. In order to correct the deformation by dummy irradiation, it is necessary to consider the plate width of the object as well as the laser irradiation conditions such as laser power and scanning speed.

Flake graphite cast iron has high damping capacity. Among the various theories on the damping mechanism of cast iron, the viscoelastic layer between matrix and graphite is an important factor. This indicates that the increase in surface area and quantity of graphite would be effective for improving the damping capacity of the cast iron. In this research, aluminum, which is a graphitizing element, was added to the flake graphite cast iron. The concentration of aluminum in the cast iron specimens was controlled from 0 to 7 mass%. The graphite and matrix structure were examined by optical microscopy and FE-EPMA, and the perimeter and area ratio of graphite in the cast irons and the damping capacity were measured. Addition of aluminum up to 5 mass% increased the area ratio and surface area of flake graphite in the cast irons. Addition of 3 ~ 5 mass% aluminum improved the damping capacity of the flake graphite cast irons, and that of 5 mass% aluminum cast iron was twice as compared with that of the cast iron without aluminum. This was attributed to the increase in the amount of graphite due to the addition of aluminum and to the refinement of the graphite, which contributed to the increase in the graphite surface area. Although the damping capacity of 7 mass% aluminum cast iron was smaller than that of 5 mass% aluminum one, it was higher than the cast iron specimens with the similar area ratio and surface area of flake graphite. This indicates that the κ phase observed in the as-cast high aluminum specimens and aluminum dissolved in the matrix of the heat-treated high aluminum cast iron specimens would have some effect for improving the damping capacity. The damping capacity at every temperature was decreased due to a heat-treatment in a condition, which decomposed the graphite.

An upswept aft section at the underbody in ground effect can improve the aerodynamic downforce of vehicles. In order to clarify the effect of the upswept aft section, a simplified vehicle with the upswept aft section is examined using Large Eddy Simulations. In the present study, four upsweep angles of the upswept aft section, i.e., θ = 0°, 5°, 10° and 15°, are investigated, where 0° corresponds to the original Ahmed body. It is found that the upswept aft section leads to an increase in flow rates through a cross-section between the underbody of the model and the ground. The high flow rate enhances strong negative pressures not only on the upswept aft section but also on a forward part of the underbody. In addition, induced vortexes are generated near both side edges of the upswept aft section. The induced vortex enhances the negative pressure on the upswept aft section close to the side edge because the vortex develops downstream, approximately along the side edge. In this study, the aerodynamic downforce for θ = 10° is the maximum because of the high negative pressure based on the highest flow rate and the strongest induced vortex. Furthermore, the relationship between the induced vortex and an effective cross-sectional area under the upswept aft section is examined and a blockage effect is discussed. Three-dimensional flows, such as the induced vortex and the underbody inflow, are found to increase the effective cross-sectional area because the three-dimensional flow should improve a flow uniformity in the mainstream direction.

The combustion timing control by the flow control of hydrogen was examined in hydrogen mixed combustion of diesel engine. The 50% mass fraction burning timing can be controlled up to 10.3 deg. Controllable angle of MFB50T doesn’t depend on the diesel fuel type and is dominated by hydrogen mixed ratio. We also examined a new method of combustion phase estimation without cylinder pressure sensor.

In seismic design for a PWR reactor containment vessel (PWR-CV), the reliability assessment about buckling limit state under a seismic loading has been carried out by the method described in JEAG4601 (hereinafter, design by rule). Recently, the static elasto-plastic buckling behavior of PWR-CV has also been evaluated by a finite element method (FEM) (hereinafter, design by analysis). The design by analysis can take into account geometrical nonlinearity and changes of the shape of PWR-CV in the FEM model. However, the buckling capacity obtained by this method may depend on the analysis conditions of the material nonlinear characteristics and the shape of the vessel model. We analyzed the buckling behavior of PWR-CV to expand the knowledge on the design by analysis method. The FEM model and input waves were based on the past shaking-table tests by Nuclear Power Engineering Test Center. In order to examine the buckling capacities depending on the analysis conditions, two conditions were applied: (a) conservative ones and (b) realistic ones. The results demonstrated that the buckling capacity highly depended on the analysis conditions above, and the design by rule provided more conservative buckling capacity than the design by analysis.

If a piping system under high pressure is damaged and steam is ejected into the atmosphere, human safety and safety equipment may be damaged by the impingement of the steam jet. Therefore, it is necessary to evaluate the region affected by the steam jet impinging on the surrounding equipment and people. This study is conducted to identify the problems with the evaluation model of the region affected by the jet specified in the ANSI standard and to reconstruct the evaluation model of the affected region based on the experimental results. From the visualization experiment and CFD analysis results, we found that the ANSI standard can be used to appropriately evaluate the experimental and CFD results for the steam spread angle and asymptotic plane area. On the other hand, the results of asymptotic length were different from the experimental and CFD results owing to the assumption in the ANSI standard that the expanding angle of the steam jet is constant at 45° regardless of any pressure change. A correlation equation for the expansion angle of the steam jet caused by a pressure change was developed referring to the experimental and CFD results, and the improved model was used to evaluate the asymptotic length. By using this improved model, it is possible to evaluate the region affected by the steam jet in the event of pipe failure, under a wide range of pressure and nozzle conditions.

This paper discusses the conditions for the undershoot responses in a circular path-following vehicle control. As a method to follow the circular path, it is known to combine the rotational and expansionary coordinate transformation to the vehicle kinematic model. However, the undershoot responses in which the output moves in the opposite direction to the reference value occurred under certain initial conditions of the vehicle. It is necessary to clarify the cause of the undershoot responses because the undershoot responses delay the time for following the vehicle to the reference value. The occurrence of the undershoot responses is related to the zeros of the transfer function. To derive the initial conditions of the vehicle that occurs the undershoot responses, in this paper, we analyze the zeros of the transfer function including the zero input response. Furthermore, we confirm the conditions for the occurrence of the undershoot responses through the numerical simulations.

Drones, whose applications have been rapidly expanding in recent years, have a wide range of uses, such as transporting goods, spraying pesticides, inspecting structures, and even flying cars, which have become a hot topic in recent years. However, it is difficult to fly in bad weather such as gusty winds. To solve these problems, flight stability has been controlled by manipulating the rotation speed of the propeller. However, it is not desirable to use a propeller for flight stability in bad weather conditions. Therefore, the authors developed a drone equipped with a CMG(Control Moment Gyro), which has the property of rotating in a direction perpendicular to the force applied to the axis of rotation from the outside, and confirmed the suppression effect of pitch angle fluctuation through experiments. In this paper, based on these findings, we developed and tested a drone equipped with two CMGs that can suppress the variation of pitch and roll angles. As a result, the variation of pitch and roll angles without CMGs was 20 degrees and 25 degrees, respectively, while the variation of pitch and roll angles with CMGs was 12 degrees and 16 degrees, respectively. In the case of the CMG, the pitch and roll angles fluctuated by 20 and 25 degrees, respectively. In addition, it is necessary to operate the controller to keep the drone as level as possible before applying disturbance, and we confirmed that the variation of pitch angle and roll angle with CMG is less than that without CMG.

The arc welding robot uses a weaving motion that periodically oscillates the welding torch installed at the tip of the robot. The weaving motion is used for the arc sensor to follow the weld fusion line, and the error of the oscillation has large effects on the finished shape of the weld metal, so the improvement of motion accuracy is most important foci in arc welding robot control. In this paper, we propose a design method of feedforward control that cancels out the error caused by the effect of Coulomb friction in the periodic motion of the robot and verify its effectiveness using an experimental robot. Based on error analysis using sensitivity to the periodicity of motion, a smooth feedforward compensating torque is derived to reduce the vertical error and the amplitude error, which affects weld quality. In the derivation, the Coulomb friction is regarded as a continuous value and repeated calculations are carried out to calculate feedforward compensating torques that are effective in reducing the effect of friction even when the Coulomb friction coefficients are large. Using an experimental three-link planar manipulator, the effectiveness of the proposed method is verified.

To improve the product performance of turbomachinery and ensure vibration reliability, we propose a method for predicting natural frequencies that considers the decrease in the stiffness of the rotor stepped part. We developed a modeling method that divides the stepped part into a conical part that is responsible for stiffness and a shoulder part that is modeled as an additional mass. We then formulated the stiffness of the conical element based on the static deformation considering the cross-sectional change and verified the stiffness for various conical beams. We also developed a method that determines the boundary between the conical part and the shoulder part based on the axial load distribution in the rotor when the tensile distribution load is applied to the small diameter part of the end face of the stepped part. The primary bending natural frequency under free-free conditions was evaluated for rotors with a large diameter part in the center and small diameter parts at both ends. The calculation accuracies using a conventional model composed of beam elements, a model that reproduces the conical stiffness parts with 100-divided beam elements, and a model using the formulated conical elements were compared and verified with the 3D FEM analysis results. Our findings showed that the stiffness calculation error of the conical element based on the static deformation was 2.81% or less. In addition, the natural frequency calculation error when modeling the stepped parts with the proposed conical elements was 2.3% or less, thus demonstrating that the natural frequency can be predicted accurately.

We consider a linear system under non-Gaussian random excitation modeled by the Cai and Lin’s model and investigate the effects of the non-Gaussianity of the excitation on the displacement and velocity responses based on the bispectrum and cross-bispectrum. Bispectrum is one of the higher-order spectra which are generalization of power spectrum. Just as the power spectrum is the distribution of the 2nd-order moment of a stationary stochastic process in the frequency domain, the bispectrum is the distribution of its 3rd-order moment in the frequency domain. Cross-bispectrum is generalization of cross-spectrum, and the cross-bispectrum between the excitation and the response provides the input-output relation of the non-Gaussianity in the frequency domain. The Cai and Lin’s model for the excitation can represent a wide variety of non-Gaussian processes observed in various engineering problems. In this paper, we derive the bispectrum of the Cai and Lin’s model and show the properties of the non-Gaussianity of the model in the frequency domain. Using the derived bispectrum, we obtain the cross-bispectrum between the excitation and the response, and it reveals that how the effect of the non-Gaussianity of the excitation on the response changes depending on a bandwidth parameter α of the Cai and Lin’s model. It is shown that when α is small, the non-Gaussianity of the excitation concentrated on the DC component is mostly transferred to the DC component of the displacement response, but is hardly transferred to the velocity response. On the other hand, when α is large, the power of the resonant frequency component is dominant in the response, but the resonant frequency component hardly transfers or amplifies the non-Gaussianity of the excitation. These findings can only be obtained from the bispectrum and cross-bispectrum, and cannot from the power spectrum.

A periodic reversal spring (PRS) with permanent magnets is proposed to suppress the torsional vibration of automobile powertrains. Results of numerical dynamic simulations pertaining to automobile powertrains from a previous study show that the magnetic counter torque of a PRS reduces the torsional vibration caused by the internal combustion engine. However, the effectiveness of the PRS has only been verified at one engine operating point. Because the magnetic field of permanent magnets on a PRS is fixed, the waveform of the counter torque of the PRS is uniquely determined. Therefore, a certain mechanism is required to control the amplitude and phase of the counter torque in a PRS to suppress torsional vibrations at several operating points of an engine. In this study, we use a pair of PRSs to control the counter torque and evaluate its effectiveness based on numerical simulations and experiments. First, we show that the amplitudes and phases of the counter torque can be controlled by adjusting the phases of the PRS pair. Next, we perform a three-dimensional electromagnetic field analysis and confirm that the amplitudes and phases of the counter torques are controllable when the phases of the PRS pair are adjusted. Subsequently, we simulate torsional vibrations in powertrains using a dual-mass flywheel (DMF) damper and a DMF damper combined with a controllable PRS as torsional vibration suppression devices. The numerical simulation results show that a controllable PRS can reduce a higher amount of torsional vibration in powertrains at several operating points of an engine compared with a DMF damper. Finally, we construct a prototype of a controllable PRS that uses a simple mechanism to adjust the phases. Experimental results show that a controllable PRS can suppress torsional vibrations in the experimental system at several operating points, wherein the rotational speed and excitation torque are different.

A no-backlash drive control technique which used two motors for forward rotation and reverse rotation to drive one load so as to cancel backlash has been using the same motor so far. However, there is a water gradient on an actual road surface, and we need to turn a steering wheel a little to the right in order to drive the car straight ahead. Therefore, it may be considered to make the right steering motor larger than the left one. In this paper, we examined the effect of the difference in viscous friction between two motors on the control system. We derived the following results through analyses and experiments. The viscous friction of each motor has a different effect on the 1^st natural frequency in the no-backlash drive control system. The damping of the 1^st natural frequency is largely unchanged by changes in the viscous friction of the motor on which position and rate feedback control is performed. Its damping increases in proportion to the viscous friction of the motor on which position and rate feedback control is not performed. Since the poles of the 1^st natural frequency do not change at all with respect to changes in the position control gain, the rate control gain, the current feedback gain, and the motor torque constant, the poles derived from the characteristic equation containing these products are expressed in mathematical formulas. And the formula shows that the viscous friction of the motor on which the position and rate feedback is not performed contributes to the damping of the system's 1^st natural frequency.

Rigid plastic and large deformation analyses of the finite element method (FEM) require multiple remeshing procedures to avoid a decrease in the analysis accuracy. Thus, a three-node triangular element that can perform automatic mesh generation is suitable for these FEM analyses. However, in the FEM analysis of nearly incompressible materials using the displacement-based three-node triangular element, the inhibition of volumetric locking and pressure checkerboarding is required. The generalized finite element method (GFEM) approximation can improve the analysis accuracy for three-node triangular elements without the addition of midpoint nodes. In this study, we performed a detailed performance evaluation of a three-node triangular element based on the GFEM approximation for nearly incompressible materials in the linear elastic analysis. The GFEM approximation employs a polynomial of degree 1–3. Performance investigation using a compression test revealed that each GFEM element required the application of selective reduced integration to avoid volumetric locking and pressure checkerboarding. Furthermore, we investigated the number of constraint degrees of freedom of the GFEM element, which is related to volumetric locking. In the case of the GFEM element, we inferred that the application of this investigation is difficult because of the additional nodal degrees of freedom, which are different from the translational nodal displacement.

For the elderly, the act of “speaking” is important to maintain their physical function. It is known that the listening with nods and giving responses are important to encourage utterances. Also, in elderly nursing homes, conversations are often started when they look at images. We have developed a speech-driven embodied entrainment character called “InterActor” which automatically performs communicative motions such as nodding based on voice input, and have demonstrated the effectiveness of nodding reaction. In this study, we propose a listening system that promotes utterances by recognizing the user’s speech contents by voice input, and presenting images related to the words in speech on the display, and giving nodding reaction from the listener’s InterActor and images. This system has a function to support the intention to listen by having the listener’s InterActor to turn around to the image at the time of display and to gaze it jointly. To verify the effectiveness of this system, a comparative experiment and a sensory evaluation experiment were conducted on care workers at an elderly nursing home under the two conditions, one with or without of nodding image, and another with or without of the word image from the utterance. As a result, it was confirmed that the listening effect by image presentation and nodding motion has an utterance promoting effect that makes it easier for the user to speak.

In recent years, the development of technologies for "connected factories" based on the Internet of Things (IoT) has become important, and industrial robots are required to operate autonomously based on sensing technologies and their data. In this paper, we focused on the polishing work with a cooperative robot, and discussed a method to integrate the technology of the developed wireless vibration monitoring system with the internal information of the servo. In particular, we attempted to construct a novel finishing system that utilizes the internal information of the force sensor installed in the base of the cooperative robot not only to detect human contact but also to improve the accuracy of machining. We estimated the rough-endmilling state from the in-process monitoring the vibration with a wireless tool holder system and the internal information of the servo obtained during endmilling operation, and also integrated the finishing process using the newly developed system considering rough endmilling information with a cooperative robot.