Statistical predictions of crack propagation are requested to evaluate remaining lifetime of operating welded structures. Today, crack growth rate for each observed crack cannot be evaluated accurately without neutron diffraction and synchrotron X-ray diffraction due to the difficulty of nondestructive measurements of welding residual stresses in the thickness direction. However, it is difficult to apply those nondestructive diffraction methods as on-site measurement techniques because the higher energy diffraction methods are available only in special irradiation facilities. To make things worse, measured results by diffraction methods cannot be directly applied to the FEM (finite element method) model for crack propagation prediction. From this view point, the methods based on the eigenstrain methodology have been proposed. In the bead flush method, for example, three-dimensional welding residual stresses are calculated by an elastic FEM analysis from eigenstrains which can be estimated by the inverse analysis from released strains during the removal of the weld reinforcement. Here, the removal of the excess metal is nondestructive treatment essentially because it is effective to eliminate stress concentration zone. In this study, numerical simulations for a welded pipe under SCC (stress corrosion cracking) were carried out to evaluate crack propagation statistically. As well, estimation accuracies of crack propagation using residual stresses estimated by the bead flush method were compared with the accuracy using residual stresses assumed to be measured by diffraction methods. Prediction accuracies of crack propagation estimated by this method were higher than that by diffraction methods. It is because estimated results base on the eigenstrain methodology satisfy the self-equilibrium condition of residual stress.
Fatigue property in gigacycle regime is focused as an important subject in recent years. In such a long-life region, a tremendous long period is required to perform the fatigue tests. In order to overcome this difficulty, special types of fatigue testing machines in rotating bending whose loading type is cantilever bending has been developed. It is known that this type of fatigue machine can be performed much quickly comparing with the tension and compression fatigue testing machines. And these experimental results are consistent with much data obtained by using traditional testing machines like tension and compression fatigue testing machines and the rotating bending fatigue test machines whose loading type is uniform bending named as Ono type, though it is unclear that much data of an ultrasonic fatigue testing machine are consistent with them. Although it prefers to perform the fatigue tests as fast as possible, but the maximum frequency of a rotating bending fatigue test are limited because of the possibility of temperature rise in specimen caused by the cyclic plastic work and the heat transfer from fatigue testing machine. Such local temperature rise might affect the fatigue property. However, the appropriate loading frequency limit is unclear because of the difficulty of the temperature measurement in the fracture portion of a specimen precisely during the rotating bending fatigue test. An in-situ temperature measuring technique is proposed to measure the temperature at the fracture portion of the specimen in real time during the fatigue testing, and the validity to determine the loading frequency of a rotating bending fatigue testing machine is discussed in this study.
It has been shown that rolling contact fatigue (RCF) test using specimen having a small drilled hole is a useful method for evaluating the effect of small defect on flaking strength of steels. In this study, RCF tests of rolling bearings having a small drilled hole were carried out. The flaking failure was considered as a problem of shear-mode fatigue crack emanating from the small defect. As a first step to quantify the crack-growth threshold on the basis of fracture mechanics, mode II stress intensity factor range, ΔKII, of a ring-shaped crack emanated around the edge of a drilled hole under the passing of a rolling element was analyzed by using finite element method. And then, the obtained values were correlated with the ΔKII values of penny-shaped cracks in an infinite body under uniform shear through the intermediary of a correlation factor, fdrill. The stress intensity factor of the ring-shaped crack was uniformly correlated with that of the penny-shaped crack by the single factor fdrill irrespective of hole diameter, d, depth of hole edge, h’, and maximum contact pressure, qmax, within the ranges: d = 0.05 ~ 0.2 mm, h’ = 0.05 ~ 0.345 mm and qmax = 2.0 ~ 3.0 GPa. The obtained results will be applied for the quantification of RCF test results shown in the subsequent paper.
Rolling contact fatigue (RCF) tests were conducted using rolling bearings with a micro-drilled hole on the raceway. In all the tests, fatigue crack initiated at the edge near the bottom of the hole, and then propagated by shear mode. Even in the unbroken specimens tested up to N = 1×108 cycles, a short fatigue crack was found at the edge. By using stress intensity factor (SIF) range calculated for initial defect size, fatigue life data were uniformly gathered inside a small band irrespective of the diameter and depth of the hole. In addition, it was found that the crack size dependency of threshold SIF range, which is well-known for mode I fatigue crack, also exists in mode II fatigue crack emanating under the rolling contact. The values of threshold SIF ranges obtained by the RCF tests were in good agreement with those obtained in the torsional fatigue tests under a static compression.
A new finite element model of textile green composites is proposed to simulate thermoforming process in this study. The model is assembled with actual configuration of the green composites and the interface between yarn and matrix has certain GAP. The mechanical behavior of yarn was considered by using truss element. To verify these models, deep drawing tests were performed with experiment. As a result, orientation of yarn and thickness of drawn cup agreed with experiment well. After this process, strength of drawn cup was evaluated with compression test in both finite element method (FEM) and experiment. In FEM, to remove GAP between yarn and matrix, tied contact method that adjust the unconformity of mesh was used. The deformation behavior of the drawn cup agreed with experiment. The effectiveness of thermoforming process to design products with FEM was verified.
In order to assess the fatigue damage of austenitic stainless steels by electron backscatter diffraction (EBSD) method more simply and easily, it should be more preferable to use a commercially available general-purpose EBSD analysis software rather than to employ an in-house developed EBSD analysis programme. In the present study, EBSD measurement was performed for Type 316 austenitic stainless steels subjected to cyclic loading, and the applicability of the EBSD parameter relevant to the pattern quality, which could be obtained by the commercial software, to the fatigue damage assessment was discussed by comparing the other EBSD parameter of the averaged local misorientation (Mave), which could be calculated by the in-house developed programme. As a result, the EBSD parameter relevant to the pattern quality, which signified the full width at half maximum (FWHM) of the histogram distribution of the image quality (IQ), was saturated at the beginning stage of the fatigue cycles, while Mave was increased monotonically with the cycles. This suggested that the FWHM of IQ could be useful to detect the initial stage of the fatigue damage, while Mave was suitable for the quantitative evaluation of the fatigue damage. XRD measurement was also carried out for the same samples employed in the EBSD measurement, and the XRD data was compared with the EBSD data to discuss the crystallographic mechanism of the change in the FWHM of IQ. As a result, it was found that the FWHM of the (111) XRD peak correlated well with the FWHM of IQ. Because the (111) plane in fcc metal such as austenitic stainless steel was most preferable for slip system, this implied that the change in the distribution of the pattern quality generated by the fatigue loading could be due to the slip deformation.
Si wafer diameter tends to be increased from 300 mm to 450 mm in order to increase semiconductor device productivity. To this end, the authors developed a rotary grinding machine with high stiffness, equipped with water hydrostatic bearings. This grinding spindle is designed to govern infeed motion of the grinding wheel. This study investigates the basic design and performance of the grinding spindle system. This system itself is composed of a constant pressure water hydrostatic bearing as a radial bearing and a magnetic actuator as a thrust bearing. The magnetic actuator combine the infeed device and the thrust bearing. The measured results show that the static stiffness, Ks, is 1.06 kN/μm, the natural frequency is 353 Hz, and the positioning accuracy is 0.2 μm. These results meet the performance requirements necessary to grind φ450 mm Si wafer.
The radiation shielding effects on the gamma ray with the effective energy Ee = 661.7 keV and X-rays with that of Ee = 74 keV and 38 keV were examined by using the tungsten-mesh (W-Mesh) made of the tungsten wires of 18μm and 50μm, as candidate for radiation shielding materials having breathability and flexibility. The results showed that the radiation shield rate “η” of W-Mesh sample material represented by mass “Ma” per unit area was almost the same value as in that of the tungsten plate and the lead plate, excepted for the irradiation of gamma-ray at the range under Ma = 1 kg/m2. The value of η at the region of less than Ma = 0.3 kg/m2 also transited to the negative range on the gamma ray irradiation. Therefore, we found that use of W-mesh in the region of Ma = 0.3 kg/m2 or below should be avoided.
Icing is one of important problems that have to be prevented in jet engine of airplane. If thin ice layer deposited on the surface of blade is detached in fight, the debris is scattered and then impacts to a rear stage blade. Such impact of the debris could lead to catastrophic fracture of the blades. Numerical simulation is a powerful tool to understand how the icing is grown and detached. Thus, the icing phenomenon has been focused on the point of view from fluid mechanics. However, fundamental knowledge for mechanical property of ice itself and the adhesion of the ice layer is still very poor. The aim of this study is to examine about the mechanical property including Young's modulus, fracture toughness and adhesive strength at a low temperature. First of all, as a result of bending test on ice, it was found that the Young's modulus and fracture toughness of ice was increased as ambient temperature being low and loading speed being increased. Then, a shear force test was performed using ice/aluminum alloy to evaluate the interfacial fracture toughness as adhesive strength. As a result, the interfacial fracture toughness was decreased as ambient temperature being low and loading speed being increased. Based on those results, it is concluded that the mechanical property and adhesive strength are strongly affected by ambient temperature and loading speed.
This study aims to evaluate strength of a diamond-like carbon (DLC) film on a metal for glass press molding at high temperature. Static and cyclic indentation tests at high temperature up to 300℃ with AE monitoring technique were performed. AE monitoring reveled crack generation load or cyclic number during the indentation tests. The static strength of the films at each temperature was determined from maximum stress in the film in the radial direction induced by sink-in deformation due to static indentation. The maximum stress at each temperature was estimated with indentation loads at first AE generation and FEM analysis. Thermal stress in DLC film was at each temperature also calculated. The film strength estimated by taking the thermal stresses into account was decreased with an increase of temperature. In cyclic indentation test, AE due to cracks in film was detected after 1.0×104 cycles at the load where no crack generated under one loading cycle. The cyclic number to crack initiation for the sample in 300℃ was 1/50 smaller than that in room temperature.
New viscosity measurement technique by using rotational breakup of electrostatically levitated droplet was developed. The new one-dimensional viscosity measurement equation is derived by integrating three-dimensional momentum equation based on the assumptions with axisymmetric shape and internal flow of levitated droplet. From the measurement result obtained, internal flow around the center of the dumbbell shape droplet is axisymmetric along the elongational axis. This result means that the present proposed new method is appropriate. In the present study, high accuracy image processing technique is applied to obtain the shape and curvature around the center of the dumbbell shape droplet by using the transformation to rotating coordinate system. The present technique can be applicable after the breakup start and before the shape of the droplet becomes asymmetric. This is reason why Euler force becomes so large that the symmetricity cannot be sustained. The newly proposed viscosity measurement technique makes it possible to estimate the viscosity within 10 % error in the range of the viscosity which the previous levitation technique cannot be available.
A fuel cell with a simple structure and operating at nearly ambient temperature and pressure is suitable for low cost small-sized generator sets ranging from several to tens Watts for home, outdoor and emergency use. This kind of fuel cell is called passive or self-breathing PEFC. Water management is very important and sometimes crucial for a long term stable operation in the passive type PEFC because control of gas temperature and humidity is inherently not easy for the PEFC. In this paper, various performance characteristics regarding the passive type PEFC were experimentally investigated using a rated 55 W fuel cell module with 20 cells laid out in plane. The properties, such as the output voltage of each cell, the temperature, pressure and humidity of hydrogen and air, were measured with time in the dead-end system and the recirculation system for hydrogen supply. The water balance in the fuel cell module was then calculated and the behavior of generated water, which should cause output power breakdown and voltage fluctuation in certain conditions, was also discussed. Results showed that a sudden power breakdown in a long time continuous operation with dead-end hydrogen supply system was caused by flooding in the anode and that this shortcoming was overcome by introducing a simple hydrogen recirculation system with valves and a water trap. Results also showed that 95% of produced water by the reaction was discharged from the cathode to the atmosphere in the form of vapor and that 5% trapped in the form of liquid in the hydrogen recirculation system.
The energy consumption of air conditioning for the business and home use is about 9% of the total energy consumption in Japan. It is effective for the energy conservation to reduce the consumption. The reduction of air conditioning energy has been promoted mainly by the development of high efficiency equipment. For further reduction, the optimum control of the air conditioning together with the heat supply equipment will make a contribution. A dynamic simulation is expected to be one of the tools for the optimization. The paper presents development of a dynamic simulator for the purpose of the evaluation of district heat and cool (DHC) plant operation and control. A double effect absorption chiller model and a cooling tower model are developed for the simulator. The developed chiller model is based on the dynamic approach which accommodates the heat capacity of the equipment and the sensible and latent heat of the internal liquid to evaluate the energy loss derived from the time delay of the startup. The steam system model which consists of the steam header, pipes and valves has been developed for the study of the impact by the mutual steam accommodation in the neat future with the neighboring combined heat and power plant. The boundary of the simulator is the equipment and system inside the DHC plant and the flow pipes to the district demand is not accommodated. The outputs of developed models suitably describe the equipment test data. These models are applied to the developed DHC plant dynamic simulator and the results of the simulation show good accordance with the DHC plant data. The simulator is confirmed to be a useful tool for the study of optimum DHC plant operation and control. Further, it can be useful for the evaluation of the impact on the DHC plant in the plant expansion and modification or in the plant connection and cooperation with the neighboring plant.
This paper numerically investigated the detail process to appear the asymmetrically spreading flames in narrow channel consisted of combustibles. We have successfully reproduced the transient process to form asymmetrically arranged spreading flame first ever in this work. 2-D, time-dependent mass and energy transport process as well as one-step chemical process in gas-phase is considered. Thick solid combustible plates (PMMA) are placed at both sides, then exactly the same ignition operation is made to initiate symmetrical processes. Pure oxygen is fed into the channel at the fixed rate to promote the spreading. Oxidizer velocity and channel height are varied as numerical parameters in this study. After the forced ignition, the combustibles are pyrolized via one-step reaction to evolve the fuel gas into the gas phase to form the opposed-mode flame spreading. Results show the distinctive three spreading modes (two-symmetric flames spreading, two-asymmetric flames spreading and one flame spreading) and transient process from one to the other mode is successfully simulated, which is hardly achieved in experiment. The asymmetric flame spreading mode appears under the limited combination of channel height and velocity. Moreover the distance between two leading edges of the flame varies depending on the imposed condition. Flow patterns are found to be sinus motion, thus the heated and accelerated oxidizer flow may enhance the reaction in the downstream. In this way, it is suggested that the flowing oxygen is effectively used to burn two fuel slabs. It is obvious that the asymmetrical configuration gives temporary stable condition. To study the details further, systematic study is demanded.
Effect of electric conductivity of the supporting rods on Marangoni convection of low-Prandtl-number fluid under the influence of axial magnetic field has been numerically studied. An end of the supporting rod is heated and an opposing end of the rod is cooled both isothermally while the surface of cylindrical liquid bridge is supposed to be adiabatic. An axial magnetic field is applied to this configuration to investigate the influence of such magnetic effect on the liquid metal Marangoni convection. In addition, the Seebeck coefficients in both the liquid and the rod region are taken into consideration. In the numerical analyses, the Joule heating and the induced magnetic field are neglected. The governing equations of mass conservation, momentum, energy, Ohm's law and conservation of electric charge for a cylindrical coordinate system have been numerically solved with a finite difference method using the SMAC algorithm. The numerical results reveal that the conductivity of the rods affects the azimuthal disturbance and tends to prevent transition effectively under the magnetic field. This trend is found especially for the transition to the 1T+R-type oscillation mode. In addition to the conductivity of rods, when the Seebeck effect is taken into account, azimuthal flow is induced and 2T+R type rotating oscillatory mode, which cannot be observed in the Marangoni flow without magnetic effect, takes place.
Shock-induced combustion around a spherical body was experimentally investigated by launching the projectile at supersonic speed into a combustible mixture. This study focused on occurrence conditions for an unsteady combustion which was characterized as combustion instabilities with an oscillating combustion front. A spherical body of 4.76 mm dimeter was used as the projectile, and its flight Mach numbers were ranged from 3.5 to 7.5. Four types of combustible mixtures, which were stoichiometric hydrogen-oxygen and ethylene-oxygen mixtures diluted with argon or nitrogen (2H2 + O2 + 3Ar, 2H2 + O2 + N2, C2H4 + 3O2 + 12Ar, C2H4 + 3O2 + 2.5N2), were used and their initial pressures were varied between 25 and 100 kPa. The combustion regimes around the projectile were observed by using a schlieren optical system and high-speed camera. The combustion regimes generally varied from the steady combustion with smooth combustion front to the unsteady combustion with oscillating combustion front, when the projectile Mach number or the initial pressure increased. The occurrence conditions for the unsteady combustion were expressed by the two dimensionless parameters; dimensionless heat release rate, q*t* and dimensionless induction length, lind*, which were defined by the post-shock state and flow velocity on the stagnation streamline of the projectile and by assuming the chemical reaction as a constant-volume explosion. The q*t* included a temperature gradient in a reaction zone, and represented the strength of the pressure wave driven by the heat release reaction. The lind* included an induction time, and represented the distance between the shock wave and the location where the heat release reaction started. The unsteady combustion occurred when these two dimensionless parameters were above the critical values, and the trend of occurrence condition of the two combustion regimes could be explained by introducing the parameters.
A detonation wave propagating in a straight tube (detonation tube) was reflected off the end wall of the tube, and the pressure profile produced by the propagation of the reflected shock wave was experimentally investigated. The detonation wave was initiated at the opposite end of the reflection end, and two ignition conditions were tested. First, ignition at the closed end of the tube (called as “closed ignition end condition”), where the fluid motion was negligible, was evaluated. Second, ignition at the open end of the tube (called as “opened ignition end condition”), where the burned gas flowed toward the vacuum tank attached to the detonation tube, was evaluated. Karnesky et al. (2013) suggested the empirical model in order to represent the pressure profile near the reflection end in the closed ignition end condition. In this paper, the empirical model of Karnesky et al. was modified in order to represent the pressure profile in the opened ignition end condition, and the effect of two ignition conditions on the pressure profiles was discussed. In these models, the pressure profile at the reflection end was empirically formulated by using two empirical parameters, and a uniform pressure distribution between the reflected shock wave and the reflection end was assumed. In this paper, the empirical parameters were normalized by the characteristic parameters for the propagating reflected shock wave. These parameters expressed the conditions of the combustible mixture and the length of the detonation tube. In the opened ignition end condition, the model well represented the measured pressure profile created by the propagating detonation wave and reflected shock wave in the entire length of the detonation tube because the rarefaction wave existed in the entire region behind the detonation wave, and the pressure behind the reflected shock wave had an approximately uniform distribution. Conversely, the model was applicable for a limited duration for the closed ignition end condition because a pressure gradient gradually developed behind the reflected shock wave when the reflected shock wave began to propagate in the plateau region behind the rarefaction wave.
Theoretical examinations based on absorption line databases were carried out about the influence of turbulence-radiation interaction on the radiative heat transfer arriving at the wall of large-scale industrial furnaces, where the re-absorption of radiative energy by combustion gas on its path toward objects to be heated cannot be neglected. In this study, the efficient and accurate calculation method for non-gray analysis and the effective method for handling turbulent fluctuations of radiation and absorption proposed in our previous paper were coupled. Combining the above coupled method and a governing equation solver for obtaining the spatial distribution of time-averaged values of temperature, concentration, velocity and so on, the heat transfer including radiation in large-scale industrial furnaces enveloping turbulent flames was able to be evaluated with sufficient accuracy equivalent to Line-by-Line analysis and with feasible calculation load. By applying this calculation technique to large-scale furnaces, it was found that negligence of turbulent fluctuation in numerical simulation gives rise to obvious change in heat flux distribution on the side wall and in the spatial distribution of time averaged temperature. In addition, change in the total amount of radiative energy arriving at side wall caused by negligence of turbulent fluctuations is fairly small compared with change observed in the case of a typical optical path indicated in our previous report.
To investigate the influence of briquette size and density on the combustion behavior in both flaming and char combustion stage, the combustion experiments with the highly densified columnar briquette made from cypress sawdust were carried out. Three sizes of the briquette, φ30 mm×60 mm, φ35 mm×70 mm and φ40 mm×80 mm, of which diameter/length ratio is kept constant at 1/2 and three types of the briquette density, 900, 1100 and 1300 kg/m3 were employed. The water content of the briquette was kept around 10 wt%. The mass loss rate and the duration in both combustion stages were measured. In the flaming combustion stage, it is observed that the average mass loss rate per unit specific surface area is proportional to the briquette surface area, while it doesn't depend on the briquette density. It is expected by considering Fourier number that the flaming combustion duration is proportional to the product of the inverse square of the specific surface area and the briquette density and it is shown that the experimental results correspond to the expectation. It is found that the relationship between normalized mass loss rate and normalized time is nearly the same regardless of the briquette size and density. In the char combustion stage, normalized mass loss can be approximately expressed with the shrinking core model by assuming the effective oxygen diffusion coefficient in the ash layer for each briquette density used in this study. And it is found that the effective oxygen diffusion coefficient in the ash layer obtained by the shrinking core model decreases with increasing the briquette density.
Experimental study was performed to reveal the response characteristics of a stretched cylindrical diffusion flame to sinusoidal oscillation of air flow velocity. The cylindrical flame used in this study has a convex curvature with respect to air stream and is formed in air stream. The fuel is methane, diluted with nitrogen, and the oxidizer is air. Oscillation frequency f is varied from 5 Hz to 250 Hz. Velocity at the outlet of air supplying nozzle was changed sinusoidally with four speakers. Velocity at the fuel nozzle outlet was kept constant. The air velocity at the nozzle outlet is measured using particle image velocimetry. Flame radius rf, flame thickness δ, and flame luminosity Lf are obtained by using high speed video camera. Results are summarized as follows: Though fluctuation amplitude of the velocity gradient of air stream Δga is constant with increasing f, that of the fuel stream Δgf increases. The fluctuation amplitude of rf varies to quasi-steady at low frequency, while the fluctuation amplitude is reduced with increasing f. Lf does not respond to quasi-steady at low frequency. The fluctuation amplitude of Lf has maximum value at 50 Hz and is larger than that for the steady flame corresponding to the velocity fluctuation. It is considered that this complex change of the flame luminosity with respect to f is related to δ/rf which is associated with the flame curvature effect, ga which affects the flame stretch effect, and gf which impacts fuel transport.
This paper discloses the development of the improved Bouc-Wen model which captures the behavior of the rate dependent hysteresis of a piezoelectric actuator. The basic form of the Bouc-Wen model only exhibits symmetric hysteresis loop for a sinusoidal input with no DC offset, whereas the real world bi-morph type actuator occasionally exhibits asymmetric loop for the same stimuli. The present works also proposes the integration of the FIR filter to the model to capture phase lag caused by the structural oscillation of the actuator. Comparison of the modeling accuracy has been given with our recent work of adaptive Preisach model. The result shows that accuracy of the two models are almost the same but the intrinsic difference lies in the number of parameters to be determined to form a computable model: the proposed model has only 25 parameters whereas the adaptive Preisach model includes 5050 discretized distribution function values to establish a single model.
This paper describes self-excited oscillation caused by coulomb friction of electromagnetic proportional valve. Especially, this research focuses on a hydraulic system in which electromagnetic proportional and pressure proportional valves are located tandem. In the system, the coulomb frictional force effects on the displacement direction of the spool of the former valve and the piston is established in the downstream region of the latter valve. Each valve is stable, but, the connection of them causes instability. This paper analyzes the mechanism of this unstable vibration and then investigates an anti-vibration design method. In analysis, this paper clarifies that the vibration is caused by an elastic deformation delay of the oil in the piston. This delay increases the phase delay of the spool due to the coulomb frictional force. After replacing the coulomb frictional force with hysteresis, the proposed method uses the describing function method to express phase delay phenomenon due to the coulomb frictional force. The describing function is the complex function which expresses an amplitude ratio and phase difference with the input and output of nonlinear element. The delay of a vibration factor is linearized by converting coulomb friction into hysteresis. The effectiveness of the proposed method is demonstrated via practical experiment and non-linear simulation results.
This paper presents theoretical research on an optimum transition curve with smoothly changing curvature using a multiple clothoid curve for improving the occupant ride comfort of automobiles. At the connecting points between an inlet straight line and a circular arc, or between a circular arc and an outlet straight line, vehicles cannot run smoothly owing to the discontinuity of curvature. Especially, the vehicles equipped with a driving support device which assists driver's steering operation or performs steering operation instead of a driver will increase both unstable movement of vehicle and discomforts of occupant. Moreover, the discontinuity of curvature in the connecting points makes the control of advanced accuracy of apparatus difficult. In order to solve such problems, three dimensional vehicle occupant model which is 21 degrees of freedom is assembled, and the multiple clothoid curve is proposed as a new transition curve. The validity of the multiple clothoid curve is shown as compared with the case where it is interpolated by a single clothoid curve or by a non-interpolation. It was found that the influence of the multiple clothoid curve on vehicle movement and ride comfort is superior to those of the single clothoid curve or the non-interpolation. Some results are presented in the form of parametric plots.
This paper presents a three dimensional flutter analysis of slender webs under tension in cross flow. In the flutter analysis, Doublet-point method based on the unsteady lifting surface theory is used to calculate unsteady fluid force acting on the web surface. The equation of motion of the web under tension is derived by using the finite element method. Flutter velocity, frequency and mode are predicted through the root locus of the flutter determinant of the system with changing flow velocity. The theoretical results are compared to experimental results to confirm validity. Moreover, the local work done by the fluid force acting on the web surface is calculated, and instability mechanism is discussed. Lastly, unified empirical equation of flutter velocities for several parameters of webs is proposed.
This paper describes design formulas and creep characteristics for thick rubber bearing applied to the Sodium-cooled Fast Reactor, which are based on the static loading test and creep test using scale models. The thick rubber bearing, which has a rubber layer roughly two times thicker in comparison with conventional rubber bearings, has been developed by the authors to ensure seismic safety margins for components by reducing the seismic response for the reactor building in the horizontal direction and vertical direction. The static loading tests using a scale model with parameter of first shape factor were conducted to investigate the applicability of proposed design formulas. Moreover, an estimation of creep characteristics due to aging is important issue because the rubber layer of thick rubber bearing which satisfies the design requirement for SFR is larger than conventional rubber layer. The creep test was preformed to estimate the creep characteristics using a scale model. From the above results, the thick rubber bearing is sufficiently rational for use as isolation system for SFR.
This paper proposes a method for assisting standing-up by a robot that utilizes patients' own power to their extent while allowing them to stand up easily. Analyzing the skills of physiotherapists, we extracted two skills that assist patients in standing up by themselves, (1) promoting a forward-bending posture by making their upper body close to a single rigid body, through stretching their back and anteverting their pelvis, and (2) providing minimal balance so the patient does not fall down. In order to implement these skills, we propose (1) a body holder to hold the patient's upper body which reinforces a natural forward-bending posture, and (2) a horizontal position and vertical force assist control system which guides position control in the horizontal direction and assists with exerting force through force control in the vertical direction. We also propose a velocity-switching method as a simplified implementation of the physiotherapist skill. We built a prototype assist robot, which is compact and movable, aiming at the commercialization of standing-up motion assist robots. We implemented the skills of physiotherapists to this prototype robot and confirmed the validity of these skills. We detail the relationship among robot's speed, forces acting on the robot's user and muscular activation. From the results of this analysis we derive indications on the speed appropriate for assisting the sit-to-stand movement.
This paper investigates the free vibrations of double beams, consisting of upper and lower beams, which are discretely connected by N springs. In the theoretical analysis, the modal analysis approach is employed to determine the expressions for the natural frequencies and vibrational modes of the system. In the numerical calculation, two cases, Cases A and B, are examined. In Case A, the two beams are connected by a single spring, while in Case B they are connected by two springs. In Case A, when the two beams have identical materials and dimensions, as the spring constant K1 increases, the natural frequencies of the odd-order vibrational modes are constant because the two beams vibrate in phase in their vibrational modes and the connecting spring is not stretched. The natural frequencies of the even-order vibrational modes are increased with the increase of K1 because the two beams vibrate out of phase. When the spring is attached at the middle of the beams, the natural frequencies p4n-1 (n=1, 2, …) equal p4n. In addition, when K1 reaches the specific values K1,n in this case, a set of three natural frequencies satisfies p4n-2=p4n-1=p4n, and a magnitude relationship of the natural frequencies is switched when K1 crosses the value K1,n. In Case B, when two springs are attached in symmetry with respect to the midpoints of the beams, a set of two natural frequencies satisfies p2n=p2n+1 for the specific values of the spring constants even if the springs are not attached to the positions of the nodes of the independent beams. The validity of the theoretical analysis was confirmed by comparing the theoretical results with the results obtained by the FEM analysis for Case A.
Reaming is a finishing process to be performed in order to improve the accuracy of the prepared hole drilled. In this process, a chatter vibration often occurs and the drilled hole is deformed in a polygonal shape. This polygonal deformation phenomenon becomes a problem in quality control of products, because of decrease in the precision of the borehole. Although a countermeasure by irregular tooth spacing is proposed and the prevention effect is confirmed, the mechanism has not been clarified yet. In this paper, the generating mechanism of the polygonal deformation is considered to be a self-excited vibration caused by time delay. A simple analytical model is proposed, and the stability of the self-excited vibration is analyzed numerically. The numerical result agrees well with the actual phenomenon qualitatively. Furthermore, the effect of irregular tooth spacing on the stability of the self-excited vibration is evaluated numerically.
The balancing domain decomposition (BDD) method is an effective preconditioner for the substructuring-based iterative solver, which is a kind of the domain decomposition method. The BDD method is a powerful tool for the large-scale implicit structural analysis using the finite element method. It is a kind of the multi-grid method whose coarse grid is defined by the null spaces in subdomain problems. Shioya et al. proposed a method to construct the null spaces for the structural analysis using the rigid body modes of each subdomain. In the present study, the Shioya's method is improved, that is, the rigid body modes are defined using a local coordinate system of each subdomain instead of using the global coordinate system. In the original method, components with very different values are contained in the prolongation and restriction matrices that are used for making the coarse grid stiffness matrix. The proposed method reduces the difference of the values and improves the property of the coarse-grid stiffness matrix. In the numerical experiments, the proposed method reduces computation time and amount of used memory when the coarse grid problem is solved by a sparse direct solver with the pivoting. In addition, the convergence property of the CG method is improved in some numerical examples.
A discontinuous material behavior such as ductile fracture and fatigue failure is predicted actively in various fields by FEM. There is continuum damage mechanics as a method to evaluate the discontinuous material behavior in a framework of continuum mechanics. However, the predicted behavior based on the method depends strongly on finite element size. Then, improvement of damage evolution equation and damage limit equation in continuum damage mechanics is discussed to reduce the mesh-dependence. These equations are extended based on finite element size and evaluated strain gradient. The predicted material property such as fracture strain in tensile test based on new equations corresponds to experimental result. Additionally, the prediction accuracy is higher than conventional mesh-independence model. Especially, the higher the tensile strength of material is, the higher the prediction accuracy is.
The objective of this study is to develop a novel finger-tactile interface employing “active wheel”: the wheel is rotated around its central axis, and the central axis is swiveled around in a vertical axis with any speeds and duration times. The swivel and the rotation, respectively, result in the direction and the speed of slippage on finger-pad skin. The peripheral surface of the wheel provides the slippage, the skin-stretch, the curvature and the edge stimulus to the finger-pad skin, where the push-in quantity of the wheel peripheral surface into skin is considered to be important for the slippage perception and to be dependent on the wheel thickness. Therefore, for improving the slippage perceptual characteristics, we examined an effect owing to a wheel thickness factor, of which levels are a disc or a drum. In addition, we introduced raised-dots on the wheel peripheral surface: the raised-dot creates a sinkage. The dotted wheel rotation provides a dislocation stimulus of the sinkage, which is expected to be effective for slippage perception. Thus, in order to determine the slippage perceptual characteristics, and to select the better wheel configurations with respect to the wheel-thickness and the raised-dots, psychophysical experiments were conducted by introducing four kinds of wheels: “Dot‣Drum”, “Dot‣Disc”, “Smooth‣Drum” and “Smooth‣Disc” wheel. As a result, we found the followings: (1) Dot‣Drum, i.e., the thick wheel with raised dots, is better than the other three wheels for the systematic errors not for the random errors in length perception, (2) Dot‣Drum and Dot‣Disc, i.e., the two dotted wheels are better than the other two smooth wheels for the random errors not for the systematic errors in direction perception.
In plastic injection molding (PIM), the process parameters such as melt temperature, mold temperature, injection time, and so on strongly affect the energy consumption as well as the product quality. It is preferable to produce plastic products with a small clamping force for the energy consumption. Weldlines, which are formed when two or more melt fronts meet, influence not only the strength of products but also the appearance, so it is preferable to reduce the weldlines as much as possible. In order to reduce the weldlines with the small clamping force, a simultaneous optimization of the process parameters in PIM is performed and the pareto-frontier is identified. The weldline temperature is maximized for the weldlines reduction, whereas the clamping force is minimized. The numerical simulation in PIM is so intensive that a sequential approximate optimization using radial basis function network is adopted. The difference between conformal and conventional cooling channel is also discussed. The numerical result shows that the trade-off between the weldline temperature and the clamping force is clarified and the effectiveness of conformal cooling channel is clarified.
Of all occupational accidents in industries in Japan, the most frequently occurring accidents are falls. In conventional studies on falls, their characteristics have been evaluated by assessing balance on rapidly moving and steeply sloped floorboards considering that the main cause of falls is a decline in balance control. It is speculated that this decline is caused by the development of aging-related muscle weakness. However, resultant trauma to the back of the subject's head could not be replicated in the conventional studies on falls. Therefore, after deriving the physical equation of the fall model, we developed a new equipment for testing falls that simulates a fall consistent with the physical equation. Using this equipment, the test is started by opening a rope toggle, thereby causing the floorboard to suddenly move horizontally and downward at the same time. This equipment could achieve a backward rollover fall that results in hitting the back of the head of the subject, but safely without injury. It was thus possible to confirm that the fall rate was age- and work style-related and there was no relation with height. This study showed that it is possible to identify a decline in balance control as subjects get older using this equipment to execute a falling experience as part of regular safety education. By performing this test regularly, balance control in workers could be assessed and it was also understood that most falls are caused by diminishing balance control. In addition, it would be beneficial if workers exercised on a daily basis to reduce aging-related muscle-weakening effect.
This paper presents a proposed method for center of gravity (COG) velocity estimation during squatting using information obtained from lower limb motion measurements. A squat exercise uses the lower limb joints and the muscles around these joints. The squat exercise velocity changes according to the lower limb muscle activity. Some earlier reports of relevant studies have suggested that muscle weakness and neurological deterioration influence the COG velocity when standing up. Therefore, it is important to clarify the relation between the COG velocity and lower limb motion for efficient training and the prevention of falls among older people. For this study, we constructed a squat velocity model that represents the relation between the COG velocity and lower limb joint power during squatting. Although no joint power indicates each muscle activity in detail, it is possible to estimate muscle activities around the joints approximately by using the joint power. For this experiment, the squat exercise was measured using a 3D motion analysis system. The experiment was conducted for three stance widths. The COG velocity and the lower limb joint powers were calculated using information from the 3D motion analysis system. We estimated the squat velocity model parameters by application of Kalman filter using the measurement information. The analysis results for the squat velocity model indicated a quantitative relation between the COG velocity and the lower limb joint power during squatting. Furthermore, comparable results were obtained from three stance widths. This analytical method is anticipated for use in evaluation of motor function and exercise assisting device design.
Preceding vehicle following control system has been investigated widely. In many previous studies, the vehicular gap is assumed to be short, so the following vehicle can travel stably only by using heading angle toward preceding vehicle. However, the vehicle gap sometimes becomes longer at the complex surroundings such as intersection, so there is a problem that the following vehicle tends to travel along a shortcut path. Therefore, the preceding vehicle trajectory needs to be recognized correctly, but it is impossible because the system can use only current preceding vehicle position. We proposed the algorithm of the preceding vehicle trajectory generation. In the algorithm, the relative preceding vehicle position that is recognized at each period is hold. And each position is converted into the coordinate fixed to the present ego-vehicle. After that point sequence is generated by each position data. By using least squares method, the preceding vehicle point sequence is approximated by a curve line as the preceding vehicle trajectory. By using the trajectory as the target path for course following control, it becomes possible to follow the preceding vehicle regardless of the vehicular gap. Moreover, the validity of the proposed method is confirmed by the experiment conducted with an actual vehicle.
The purpose of this paper is to clarify the effect of vehicle dynamics and steering system parameter on steering feel. The objective evaluation method for on-center and off-center evaluates steering effort, steering torque gradient, torque hysteresis and other values. Steering effort characteristics such as steering torque-steering angle, steering torque-yaw velocity or steering angle-yaw velocity are important properties for steering feel. Therefore the performance design of steering feel should be based on the steering characteristics. For example, some studies focus on the stability factor for steering feel by changing tire performance. However changing stability factor also changes yaw gain (yaw velocity/steering angle) and self-alignment torque (SAT) characteristics. The steering effort and the steering damping are under influenced of vehicle dynamics. The steering system parameters i.e. stiffness of linkages, frictions and setting of power steering (PS), such as assistance curve, damping control and others, also has influences the steering characteristics. Since many parameters are necessary in the detailed model, it is difficult to clarify the effect of each parameter on the steering characteristics. This paper examines the influence of steering system parameters and vehicle dynamics on the steering characteristics analytically and formulates. The model of the investigation consists of bicycles vehicle model and steering system with three frictions, three damping element, steering linkage, PS assistance curve and damping control. These steering system stiffness components and PS assistance torque decrease the effect of the friction or the damping on torque hysteresis. This study assists to understand the effect of the steering system and vehicle dynamics on the steering effort characteristics.
Soil-vehicle interaction is an important factor for predicting trafficability of off-road vehicles. Tractive forces on the wheel to drive the vehicle can be estimated by soil deformation analysis around the contact area of the wheel. Sand deformation and flow under a rolling wheel with slippage were observed from the side through a transparent acrylic wall by 2-dimensional Particle Image Velocimetry (PIV) method. The flow velocities of sand particles obtained on allocated grids revealed that periodic fluctuations of sand flow make ripple patterns on the sand surface behind the wheel. We discussed the effect of wheel slip ratios on the density of the ripples, sinkage, drawbar pull, torque and the depth of influence for the traveling wheel. The result showed that the slipping wheel forms a ripple with each scratch by the wheel rotation corresponding to the front half contact length with sand. The thickness of sand flow layer under the wheel showed thinner for large slip ratios. The finite element method was also conducted to simulate the traveling wheel experiment to discuss the possibility of the numerical simulation. The result of simulation qualitatively reproduced the experiment. However, there was a quantitative difference on the drawbar pull of the wheel, which shows that the method needs modification on the numerical model.