This paper shows the development and analysis method of a single element strain gage (K value gage) used to analyze the stress intensity factor of mode I (opening type) cracks. The K-value gage reported in the previous report collected the strain εθ with a grid angle of 52 °, and was able to obtain the stress intensity factor within an error of 10% from the theoretical value. The purpose of this study was to develop a K-value gage with even higher accuracy. As a result, the developed single-element K-value gage had a total grid angle of 104 ° extended to ± 52° from the crack tip extension line. Using the developed 104° K-value gage, two types of experiments were conducted to investigate the analysis accuracy of the stress intensity factor. One is a comparative experiment with a conventional grid angle 52 ° K value gage. The second was to change the simulated crack length of the test piece by three types. The following was found from the experiment. (1) The 52 ° K-value gage had a maximum error of 10% from the theoretical value, while the 104 ° K-value gage was obtained within a maximum of 5%. (2) All three types of test pieces with different simulated crack lengths were obtained within 5% of the theoretical value and the maximum error.
In the present study, we have addressed a dispersion composed of magnetic cubic particles in an alternating magnetic field to investigate the time change in the local internal structure of particle aggregates by means of quasi-two-dimensional Brownian dynamics simulations. An alternating magnetic field is applied along the x-direction. In the situation of a relatively weak magnetic field, if the magnetic particle-particle interaction strength is small, single particles remain in the system. The magnetic moments of single particles follow the change in the switched direction of the alternating magnetic field. As the magnetic particle-particle interaction strength is increased, particles aggregate to form closely-packed structures with a perfect face-to-face configuration. Since the orientation of the magnetic moments of constituent particles is strongly restricted due to the influence of the magnetic particle-particle interaction between neighboring particles, they do not follow the change in the alternating magnetic field direction. As the magnetic particle-field interaction strength is increased, closely-packed structures tend to collapse, and loosely-packed structures are formed in the system. As the magnetic particle-field interaction strength is further increased, the magnetic moments of constituent particles are restricted to the direction of the alternating magnetic field. Therefore, the aggregates with an offset face-to-face configuration are formed along the magnetic field direction. If the alternating magnetic field switches from the positive x-direction to the negative x-direction, the aggregates with an offset face-to-face configuration collapse temporarily because the magnetic moments reorient in the switched direction of the alternating magnetic field. After that, the orientation of the magnetic moments is strongly restricted to the switched magnetic field direction, and aggregates with an offset face-to-face configuration are re-formed in the system.
We propose a method to evaluate time-dependent rheological properties, shear stress, effective viscosity and shear rate, of coagulating curd of the skimmed milk as an analog of cheese products. Ultrasonic spinning rheometry was adopted for the rheological evaluation, where the rheological properties were calculated via the equation of motion from spatio-temporal velocity information of oscillatory shear flow in a cylindrical vessel measured by ultrasonic velocity profiler (UVP). Dispersed small gels formed immediately after the addition of rennet to the skimmed milk allow UVP measurements without seeding tracer particles for ultrasonic wave. Shear distribution in the vessel due to the oscillatory rotation of the cylinder wall formed two distinct regions. In the inner region, the gel structure was developed because of the sufficiently weak shear. Consequently, in the near-wall region, sol-like state in which small gels were floating in the whey dehydrated from the developing gel in the inner region was maintained. The rheological evaluation performed on the near-wall region elucidated a time-dependent trend of the decreasing effective viscosity representing the state that whey gradually accumulated in the region. The increase of amount of whey reduces the volume fraction of floating gels in the near-wall region. The results suggested that we can estimate the physical states of developed curd in the inner region from the information of rheological property changes in the near-wall region.
In the safety study of sodium cooled fast reactor, it is important to appropriately evaluate the event progression of Core Disruptive Accident (CDA). In previous studies, the reliability and validity of the SAS4A code was significantly enhanced by applying Phenomena Identification and Ranking Table (PIRT) approach to the Unprotected Loss of Flow (ULOF). SAS4A code has been developed to analyze the early stage of CDA, which is named Initiating Phase (IP). In this study, PIRT approach was applied to Unprotected Transient over Power (UTOP), which was one of the most important and typical events in CDA as well as ULOF. The phenomena were identified by the investigation of UTOP event progression and physical phenomena relating to UTOP were ranked in order of the degree of importance to the figure of merit (FOM), which is the average fuel temperature. 8 key phenomena were identified and the differences in ranking between UTOP and ULOF were clarified. The code validation matrix was completed and an SAS4A model, which was not validated in ULOF, was identified and validated. In this study, SAS4A code became applicable to various scenarios by using PIRT approach to UTOP and the reliability and validity of SAS4A code were significantly enhanced.
An automatic adjustment method of the model-based controller of an HCCI engine was designed in this study. As modeling errors are inevitable, feedback control is usually introduced to reduce the effect of the modeling errors. However, especially under transient conditions, the control performance may deteriorate, because this is a control with the information of the previous cycle. The transient control performance is thought to be improved by taking modeling errors into consideration. Therefore, an algorithm to adjust the feedback input based on the prediction of the modeling error was developed. The modeling error was learned and predicted by ReOS-ELM (Regularized Online Sequential Extreme Learning Machine), which is a method of online machine learning with low computational load. The modeling error learning was conducted every engine cycle. The feedback input was adjusted so that the output prediction by the engine model including its modeling error prediction coincided with the output reference. The reference tracking performance was improved by the proposed method.
An Excel program that uses tri-diagonal matrix algorithm (TDMA) is proposed to calculate one dimensional unsteady heat conduction using implicit method. The program is unified analysis method to calculate symmetric flat plate, solid cylinder, sphere, double-sided flat plate, hollow cylinder, and spherical shell geometries. Three different boundary conditions and arbitrary heat generation rates can be applied. The unsteady numerical analysis is compared with the exact solution to verify the accuracy. Furthermore, the effectiveness of the program is demonstrated by solving various engineering examples using this Excel program.
The vibration characteristics of a bladed disk with the continuous ring type structure have been studied extensively, and the vibration response analyses considering the friction damping between adjacent shrouds have been performed in the recent blade design. The effect of the friction damping on the self-excited vibration also has been studied by several researchers. However, because the most of these studies have been performed using the simple macroslip model, the damping characteristics of bladed disks with the friction damping are not yet clarified sufficiently. In this paper, the damping characteristics of the bladed disks with the continuous ring type structure is studied using the conventional macroslip model and the sophisticated microslip model for the forced and self-excited vibration and the results calculated by both models are compared. From the analysis results, it is concluded that, in the forced vibration, the damping characteristics predicted by both models are almost the same if the excitation force is extremely large or small. However, when the excitation force is medium, the damping characteristics predicted by both models are different. In the self-excited vibration, the stability predicted by both models are qualitatively the same. However, the amplitude of the limit cycle oscillation and the critical aerodynamic damping predicted by both models are quantitatively different.
Jitter Ring is the popular toy which has another name called as “Chatter Ring” or “Gyro Ring”. This toy is composed of a circular ring and the washer inserted into the ring. Just after supplying the washer with an initial angular velocity, the player of this toy has only need to wheel the ring in the vertical state by handling each hand alternately. Then, the washer will continue to rotate with fluctuation by this operation. Further the player will feel the oscillating response through the driving hands. This rotatory motion of the washer is somewhat complicated and the analyses tried up to now concerning this motion don’t almost appear in public. Consequently the author thought that there were the significant meanings in the dynamic analysis for this motion of the washer. Considering the friction between the ring and the washer, he performed the three-dimensional analysis by regarding the washer as the rigid body without a fixed point and adopting Eulerian angles in this research. As a result, the actual behavior with fluctuating rotation of the washer was confirmed by the numerical analysis. Furthermore, he investigated the influence on the motion of the washer by varying each value of parameters in this system.
Electric vehicles (EVs) generate different cabin noise from internal combustion engine vehicles (ICE) during low-speed driving. In order to identify the cause of the interior noise of EVs at low-speed (30km/h) and to reduce the noise, a Helmholtz resonator made of pulp molds was fabricated and its noise reduction effect was evaluated. First, a Helmholtz resonator to reduce the cavity resonance of the tire is investigated by numerical calculation. Through numerical calculations, it was demonstrated that a stable noise reduction effect could be achieved by installing multiple Helmholtz resonators. Next, we fabricated a Helmholtz resonator using pulp molds as the material and installed multiple resonators in the tire. In the experiment, the resonators were able to reduce the tire cavity resonance by 13.8 dB to 9.7 dB. When driving tests were conducted with these tires installed, the noise at the ear position of the front seats in the cabin was reduced by 11.3 dB. From these results, we were able to identify that tire cavity resonance is the cause of the cabin noise when the EV is running at low-speeds. In addition, a driving test in which the same number of Helmholtz resonators as installed in the tires were installed on the cabin ceiling resulted in an 8.1 dB reduction in cabin noise. This demonstrated that it is possible to reduce the noise caused by tire cavity resonance even with parts inside the vehicle.
In robotic thick plate welding, the welding strength is ensured by periodically oscillating the welding torch attached to the end-effector in the horizontal direction, which is called weaving motion. Because the vertical accuracy of the end-effector affects a quality of the welding, it is necessary to reduce vertical error of the end-effector. In this paper, we focus on periodic motions, such as the weaving motion, and consider the suppression of vertical errors by feed-forward control. To calculate the feed-forward torque, it is necessary to identify the dynamic parameters of the robot. However, since noise and un-modeled dynamics are included in the experimental data, we identify parameters that have small influence on the motion error even though the existence of the parameter errors by considering the parameters as stochastic variables and identifying their error covariance to be the reference one. The reference error covariance is calculated from the sensitivity analysis of the vertical direction of the end-effector in the periodic motion with respect to the minimum set of dynamic parameters. Sensitivity of the dynamic/static motion, and sensitivity of feed-forward control are employed to improve the stability of the iterative calculation. By experiments using the planar 3-link manipulator, we confirm that vertical errors of the weaving motion are reduced by the feed-forward torque using the proposed method compared to the Least Mean Square.
Parametric speaker can radiate an audible sound beam with sharp directivity by using the nonlinear interaction of ultrasonic waves. In recent years, the highly directional audible sound generated by the parametric speaker has been applied to various applications. For example, applications such as active noise control, sound absorption coefficient measurement, and creation of audio spots have been proposed. Numerical analysis of nonlinear sound field is important in application design. Many discrete analyses by using finite difference time domain method have been proposed as analysis methods for parametric speakers, but these methods have problem that the calculation load is heavy. Therefore, there is a need for efficient analysis methods for parametric speakers. In this study, we construct a steady-state response analysis method that can efficiently analyze the audible sound of parametric speakers. The method is combined a nonlinear concentrated mass model and a perturbation method. In addition, the computational load of the constructed model can be reduced by combining the substructure synthesis method. The proposed method is suitable for analysis of parametric speakers because the number of divisions in the axial direction can be set very large. The validity is confirmed by comparing the analysis result of the proposed method with the solution of the KZK equation. In addition, the improvement in calculation efficiency by the substructure synthesis method has been confirmed by numerical calculation.
A variety of microscopes have been developed to clarify microstructures. The observation principle of photoacoustic microscope is based on generation and propagation of thermal and elastic waves by heating the sample surface which allows us to observe the detailed microstructure. The resolution of this microscope depends on the characteristic properties of the waves, such as the amplitude and decay rate of the thermal and elastic waves propagating through the sample, and thus requires an accurate understanding how temperature and stress field are changed with time in the medium. However, the classical Fourier heat conduction equation cannot reproduce the propagation of such thermal waves. In this study, we attempt to analyze numerically a two-dimensional dynamic thermoelastic wave problem using the time-domain finite difference method based on the coupled non-Fourier heat conduction equation and the dynamic thermoelastic equation, in which the delay time effect and the thermoelastic effect are considered in classical Fourier's law. In this study, we investigate how thermal and elastic waves propagate in a square plate problem without defect. The results showed that thermal and elastic waves were generated and propagated in concentric circles around the temperature input point, and reflection phenomena were observed at the boundary surface. It was also found that the delay time had a stronger effect on the temperature and stress fields than the thermoelastic coupling effect.
This paper discusses a multiscale stochastic stress analysis of a particle reinforced composite material with a successive approximation based on the local sensitivity analysis of microscopic stresses with respect to a random location variation of particles. A microscopic geometrical random variation will have a significant influence on the microscopic stress fields in a heterogeneous material, and probabilistic analysis of the stresses should be encouraged for estimation of probabilistic properties of the stresses for more reliable structural design. Further, a more complicated microstructure reflecting an actual material considering wider analysis region, for example, including a larger number of inclusions in composite materials will be required for a practical application. This numerical analysis will be very expensive, and therefore a successive local sensitivity analysis-based approximate multiscale stochastic analysis method has been proposed for unidirectional fiber reinforced composite material. In this research, this approach is extended to a three-dimensional problem, and effectiveness of the approach for the multiscale stochastic analysis of a particle reinforced composite material is investigated. In this paper, the problem setting and outline of the methodology are provided, and the effectiveness and accuracy of the presented method are discussed with the numerical results.
In recent years, many types of inchworm mechanisms have been developed as miniature linear actuators for high-resolution positioning. The mechanism can usually move over a long distance regardless of the positioning actuator stroke because it moves like an inchworm by sequentially driving two clamping elements and one positioning actuator. However, most mechanisms equipped with a multi-layered piezoelectric actuator for positioning have difficulty to improve their feed rate because of a small stroke of the actuator, despite their excellent positioning resolution. An inchworm mechanism in this study employs one electromagnet for longitudinally driving a moving bar and two electromagnets for clamping the bar. Use of the electromagnet with a larger stroke enables a high-speed feed rate and allows for the use of inexpensive low-voltage amplifiers. Furthermore, a displacement reducer based on the toggle linkage reduces the actuator displacement and enlarges the thrust force. Since the output displacement of the reducer exponentially increases with an increase in the input displacement, this mechanism achieves not only high-speed positioning but also high-resolution positioning as necessary. This paper describes the principle of proposed mechanism and the design of the electromagnet actuator and clamps. Experiments of a prototype mechanism showed that low reduction ratio of the reducer achieved maximum feed rate of 25 mm/s at a driving frequency of 110 Hz. In addition, high reduction ratio kept the positioning resolution less than 50 nm.
Heat exchangers (HEs) are used in process industries such as power plants and petroleum refineries. It is important to minimize flow maldistribution as well as pressure drop for high performance of HE. A baffle is often installed in the header part of HE in order to achieve the flow uniformity, but the hole sizes of baffle are determined by the engineer’s experience. In this paper, a multi-objective design optimization for minimizing both the flow maldistribution and the pressure drop is performed using numerical simulation. The hole sizes in the baffle are taken as the design variables. In addition, the angle of baffle is newly considered. By introducing the angle of baffle, it is expected that fluid will smoothly flow into the edge of the header. The numerical simulation using computational fluid dynamics (CFD) is so intensive that sequential approximate optimization that response surface is repeatedly constructed and optimized is adopted to determine the optimal solution with a small number of simulations. Through the numerical result, the pareto-frontier between the flow maldistribution and the pressure drop is identified. It is found from the numerical result that several small vortexes are generated in the optimal configuration. This indicates that generating small vortexes will play an important role for improving the performance of HE.
Helical gears are commonly used in the gear units of railway vehicles in Japan, and the bearing types used for the gear units are tapered roller bearings. In this gear unit bearing arrangements, it is important to appropriately adjust the combined clearance, called the endplay, of the two bearings supporting the pinion to prevent the damage such as seizure. Our previous research has shown that the smaller the endplay value at gear unit assembly (Initial endplay value) and the lower the ambient temperature, the greater the decrease in endplay value during rotation and the greater the risk of seizure. One of method to prevent seizure is to increase the initial endplay value, but this means an increase in the internal clearance of the bearings, which may reduce the fatigue life of the bearings or cause damage to their cages due to increased vibration. In order to prevent seizure without reducing bearing life, therefore, this study has examined the use of cylindrical roller bearings with ribs that allow a certain degree of axial displacement of inner rings and outer rings, and has compared its performance with that of a conventional structure using tapered roller bearings through various rotating tests. As a result, it is found that the temperature rise immediately after the start of rotation and torque of pinion shaft are lower for the cylindrical roller bearings with ribs than for the tapered roller bearings during the rotation test using the actual gear unit. Further, the results of rotating tests under the radial and axial loads for the pinion bearings alone showed that the torque of cylindrical roller bearings with ribs tended to be lower than that of tapered roller bearings under a large range of flow rate and temperature of lubricants.
When rolling bearings are used under light loads and high rotational speeds, their life may be determined by cage wear rather than raceway flaking. Under these operating conditions, the life and reliability of the bearings can be improved by reducing cage wear. To reduce cage wear, it is necessary to measure and analyze the contact forces acting on the cage due to the interactions between the roller and the cage pocket. In this paper, a measurement system capable of measuring “the contact forces between the roller and the cage pocket” and “the cage center displacement” at the same time has been constructed. Measurements have been conducted using this system for a cylindrical roller bearing at various rotational speeds. As a result of measuring the contact forces, it has been found that “the force to accelerate the cage” is generated continuously in the load zone of the bearing, while “the force to decelerate the cage” is generated intermittently in the non-load zone of the bearing. Since the contact forces are not constant during one rotation of the cage, the impulses due to the interactions have been calculated to evaluate not only the contact force but also the contact time. Results indicate that the impulses per rotation of the cage caused by each force show a tendency to decrease up to 2000 min-1 of rotational speed and not to almost change at higher speeds. In addition, it has been found that the cage center displacement measured becomes a constant velocity circular motion when the rotational speed exceeds 2000 min-1. These findings suggest that the contact between the roller and the cage can be easily modeled when the rotational speed exceeds 2000 min-1. The analysis based on this model created is in general agreement with the impulses obtained from the measurement results.
Differentiation of mesenchymal stem cells (MSCs) into vascular endothelial cells has been demonstrated for application in cardiovascular regenerative medicine. In this study, we evaluated the effect of the combined mechanical stimuli of wall shear stress (SS) and cyclic strain (CS), mimicking hemodynamic conditions of arteries, on endothelial differentiation of MSCs. Immortalized human adipose-derived MSCs were subjected to a combined stimulations of SS (1 Pa) and CS (4%, 1 Hz) by using a developed cell culture chamber. Endothelial differentiation of MSCs was evaluated by immunofluorescent staining of an endothelial protein maker, fetal liver kinase-1 (Flk-1). Morphological changes in MSCs by the stimulation were also examined from the fluorescent images. As a result, the application of the combined stimulation of SS and CS for 24 h induced an increased expression of Flk-1 in MSCs and cell alignment to the direction of flow, whereas the stimulation of only SS or CS did not change Flk-1 expression and morphology of MSCs compared to statically cultured cells. We also found that inhibition of the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) blocked the increased expression of Flk-1 under the combined mechanical condition. These results indicate that the combination of SS and CS effectively induces MSCs differentiation into endothelial cells via activation of ERK1/2 signaling pathway.
Currently, the maintenance of railway tracks is carried out based on track irregularity measurement data. The vibration data of running vehicles are easy to measure and can be the base of track maintenance, but they have not been used by basic data of track maintenance because of the shortage of repeatability. However, there are an increasing number of cases where small portable information terminals are used as simple and inexpensive vehicle vibration measuring devices. Therefore, the authors tried to construct the method for track management based on vehicle vibration data measured by permanently installed small terminals on in-service trains with high frequency. Data accumulation of vehicle vibration of in-service trains have been carried out for more than one year in a regional railway line. After the analysis of collected vibration data, the authors successfully conclude the possibility of the “vehicle-vibration-based track maintenance”. In this paper, the authors propose the method to obtain accurate positioning data of the trains from GPS speed data. The relationship between car-body vertical acceleration and track irregularity showed the possibility of track maintenance based on car-body vibration.
In the event of a collision accident, if a coupler is failed, the distance between railway adjacent vehicles cannot be maintained at a constant space, which may result in a collision between the ends of those railway vehicles. Therefore, it is important to understand the fracture behavior of a coupler in order to study the crashworthiness of a train set. We conducted quasi-static compressive fracture tests to obtain the deformation characteristics and fracture modes for each coupler angle. As a result, it is clarified that there are two fracture modes depending on the coupler angle. In order to understand the dynamic fracture characteristics of a coupler, a Finite Element (FE) model was constructed which validate the quasi-static compressive fracture test. And the fracture characteristics of each coupler angle were estimated when dynamic loads were applied. In addition, by extending the FE model of a coupler to a car body model, a collision analysis model of a train set with elasto-plastic body of the front and end structures was developed. As a basic study, a collision analysis was conducted assuming a level crossing accident. We consider the improvement of the crashworthiness of a train set with not requiring major changes to a car body structure. As a result, we confirm that reinforcing an under support plate and adopting a coupler with energy absorbing element will prevent the fracture of a coupler and increase the crashworthiness of a train set.
The aerodynamic forces acting on a train travelling in a tornado-like swirling flow were investigated using a tornado simulator and a moving model rig. Rectangular shaped vehicles in scale 1/40 and 1/67 and a round-roofed vehicle in scale 1/40 were used. Two types of tornado-like swirling flow, one-cell vortex and two-cell vortex, were generated by the tornado simulator. By changing the train speed and the train’s path, the model trains of 1 car composition and 3 car composition were passed through the swirling flow on a flat ground, and the aerodynamic forces acting on the vehicle were estimated. The main findings are as follows: 1) The aerodynamic forces acting on the leading car are greater than those of the other cars. 2) The aerodynamic forces of the leading car vary with the vehicle speed, but those of the middle vehicle show little dependence on the vehicle speed. 3) There is no significant difference in the aerodynamic forces acting on the train between a one-cell and a two-cell vortices. 4) The aerodynamic forces acting on the middle car increase when the train’s path is shifted by the core radius from the vortex center so that the flow becomes the headwind. 5) Rounding the roof of the vehicle may reduce the side force.
Elevators are essential for means of vertical transportation. Recently elevators, which are installed in high buildings, are long stroke. These elevator ropes are longer than conventional elevator ropes. The natural period of the elevator rope becomes longer for the long elevator rope. The natural period of the elevator rope gets closer to that of the building. The elevator ropes severely vibrate by the external force, such as strong winds and earthquakes. Accordingly, the division of lift stroke has been suggested for decrease of the rope response in the conventional research. The effectiveness of the lift stroke division has been confirmed by the investigation of the time history response analysis. However, the investigation of the optimum division position at the time history response analysis is taken tremendous effort. Accordingly, the simple design method of the optimum division position is necessary at the commencement of design. In this study, the simple decision procedure of the optimum division position is suggested. The optimum division position of the simple decision procedure is compared with the optimum division position of the time history response analysis. As a result, the calculation of the optimum division position is relatively simple and high precision. Furthermore, the sensitivity analysis of the simple decision procedure is carried out. As a result, the initial tension fluctuation has small influence against the optimum division position. Therefore, the simple decision procedure proposed in this study is effective method at the commencement of design.