Carbon steel pipe specimens, which had been experimentally ruptured or deformed by hydrogen-oxygen detonation, were analysed by dynamic analysis using a finite element method (FEM). Pressure load histories induced by detonation were estimated by computational fluid dynamics (CFD). These pressures were applied to the inner surface of finite element models of pipe specimens. The relationship between stress and strain for piping material was obtained by performing a tensile test at a high strain rate of up to 5000 s^-1. The thickness of the pipe specimens measured by an ultra sonic thickness meter was used for the FEM model geometry. In the case of the straight pipe specimens with a closed valve, FEM analyses estimated larger deformation caused by a detonation pressure than that of the test specimens. For the ruptured elbow specimen, the rate of increase in circumferential strain calculated by FEM was as high as or higher than that of the experiment. In the case of an elbow specimen deformed by detonation pressure, CFD predicted that the peak pressure at the extrados of the elbow was increased by reflection off the pipe wall. However, it did not deform the extrados of the elbow by a large amount in both the experiment and FEM analysis. In all cases, analyses of the strains caused by detonation pressure showed that they were as high as or higher than those of the measured results in the pipe specimens. Therefore, piping design using the proposed analysis method conservatively estimates the strength of piping against detonation pressure.

View full abstract

This paper describes the elucidation about the influence of NaCl electrolyzed oxidizing water (It abbreviates as EO water) on the surface of kovar alloy (Fe-29.72wt%Ni-16.28wt%Co). First, the etching characteristic of NaCl EO water against the surface of kovar alloy was clarified using chemicals for comparative immersion experiments. The comparative study showed that as for the etching efficiency on the surface of kovar alloy, NaCl EO water was superior, and the selective etching tendency is weak to HCl solution. Next, by the observation using SEM image, the influence of NaCl EO water on the surface shape of kovar alloy was clarified. The results indicated that when using NaCl EO water, the test pieces surface of only polishing becomes smooth but in the test pieces surface of heating processing, the small pit occurs. Lastly, as for the test pieces after heating processing, it did the surface oxidation layer removal experiment by the immersion. The results show that NaCl EO water can remove the surface oxidation layer like HCl solution approximately. However, the surface oxidation layer which is thin newly is formed in the surface which was processed with NaCl EO water. By this study, we got the suggestion that NaCl EO water can be applied to the surface treatment such as the etching of kovar alloy.

View full abstract

Mod.9Cr-1Mo steel(P91) is widely used for high temperature pipes in ultra-super-critical thermal power plants. However it was recently reported that the creep damage was detected at heat affected zone(HAZ) in welded joints of the pipes so-called the “Type IV” damage. So far, study on damage and life assessment methods for the welded joints of the P91 steel were concentrated on longitudinal welded pipes. On the other hand, circumferential welded joints are also susceptible to yield creep damage because of increase of axial stress by thermal stress superimposed with pipe weight itself. In this study, the effect of additional axial stress to the axial stress by the internal pressure on damage and rupture property is discussed based on internal pressure creep tests adding different levels of the axial stress using the P91 circumferential welded pipe. Rupture time of the circumferential welded pipe decreases with increasing additional axial stress level. The longitudinal cracking in the weld metal was observed in the specimen tested under lower additional stress level, and the “Type IV” cracking was observed in those under higher additional stress levels. The stress analysis results indicate that axial stress in the HAZ increases as increasing the additional stress level causing the “Type IV” cracking at a certain value of ratio of the total axial stress to the circumferential stress. Under the test condition where the “Type IV” cracking occurs is significantly shorter than predicted rupture time based on internal creep rupture data of the longitudinal welded pipes. The limited creep strain is introduced to predict rupture time of the circumferential welded pipe by considering the effect of stress multiaxiality. Eventually, times to rupture caused by the “Type IV” cracking of both the longitudinal and the circumferential welded pipes were accurately predicted by the limited creep strain concept.

View full abstract

This paper deals with the analysis of the thermal stress intensity factor for small edge interfacial crack between bonded dissimilar plates subjected to uniform change of temperature by using the crack tip stress method. The stress intensity factor of edge interface crack is strongly controlled by the singular stress field at the interface edge of the bonded plates without the crack when the crack becomes extremely short. In this study, the small edge interface crack problem under thermal stress is solved by superposing the uniaxial tension problem with edge singularity and the uniform stress problem having the boundary condition of temperature change and uniaxial compression. The calculation shows that the stress intensity factors of the small edge interface crack under thermal stress can be evaluated from four factors related only to the Dundurs' parameters α and β. In addition, the expression of the stress intensity factor for the small edge interface crack under the logarithmic edge singularity is presented when the material combination is α=2β.

View full abstract

To assess the integrity of piping under the detonation pressure of accumulated hydrogen-oxygen, the fracture strain of the pipe material must be identified. In carbon steel pipe specimens that had been experimentally ruptured by hydrogen-oxygen detonation, the strain rate of the measured hoop strains was around 2000 s^-1. To obtain fracture strains at such a high strain rate, tensile tests were conducted at strain rates of up to 5000 s^-1 using specimens cut from carbon steel pipes, low alloy steel pipes, and weld metals. For all the different strain rates and materials, elongation was over 24 % and dimple patterns were found in the fracture surfaces. From this, it is apparent that the fracture mode of piping material subjected to a high-speed tensile load is ductile fracture. We had previously measured the strain history of the carbon steel pipe specimens ruptured by hydrogen-oxygen detonation, but we had not measured a strain higher than about 14 % because of the limitations of strain gauge measurement. FEM analyses of the ruptured pipe specimens were conducted to estimate the fracture strain at pipe rupture. We estimated that the strain at the pipe rupture was 20 - 22 %. The results of the material tensile tests and the estimated fracture strains of the pipe specimens revealed that steel pipes have sufficient ductility even if they are subjected to detonation pressure. Because pipe rupture is accompanied by large strains, we propose a method for assessing the integrity of a pipe subjected to detonation pressure by comparing the strain on a pipe estimated by FEM and the limiting strain of the pipe material. We propose a limiting strain of 8 %, which is reduced to one-third of the minimum elongation in material tensile tests in order to ensure a sufficient safety margin.

View full abstract

Rice Bran is a residual product of rice and the amount of it is about 0.9 million tons per year in Japan. The rice bran carbon (RBC) is manufactured by impregnating a phenol resin with the rice bran, and carbonizing in 900 °C nitrogen gas atmosphere. The RBC is expected as an industrial material with a low environmental impact from a viewpoint of recycling. Moreover, since the RBC has a natural porous structure, it has excellent frictional properties and to be a friction element such as brake and clutch. In this study, the authors prepared some friction materials with the RBC particle to discuss the possibility of the RBC as alternative material of graphite. Especially, the frictional properties and the mechanical strength were measured to evaluate the possibility of the RBC. The friction coefficient was almost the same for the samples which was mixed with graphite and RBC. On the other hand, the specific wear rate in the sample with RBC was decreased to the one half of that in sample with graphite. The mechanical strength was almost the same in samples with RBC and graphite. Therefore, the RBC was expected to be a high performance frictional material to reduce the specific wear rate.

View full abstract

Spot-welding is widely used in various fields of industries. Since the size and quality of a welded nugget are closely related to the bonding strength of the weld, its quantitative evaluation is important to improve the reliability of the welded structure. In this work, a nugget sizing method based on measuring Lamb waves diffracted at the nugget boundary of a spot weld is proposed. In this method, the nugget size is estimated from the amplitude distribution of Lamb wave diffracted at the nugget boundary when a pair of air-coupled ultrasonic transducers is being scanned near a spot weld. A pair of focused transducers of center frequency of 0.3 MHz is employed. An imitation specimen is firstly evaluated to verify to the validity of the proposed method. Based on the result, the method is applied to the nugget sizing of three spot welds fabricated with different electric currents. Although the estimated values almost agree with those obtained by a water-immersion ultrasonic method, there are certain discrepancies between them due to structural disorders at the nugget/base material interface.

View full abstract

To systematically investigate the aerodynamic characteristics of wings with 30, 45 and 60 degree swept-back angles, and different taper ratios, Navier-Stokes (N-S) simulations for flows over a wing have been conducted. The Mach numbers of the flows range from 0.8 to 2.8. The planforms of wings are in various shapes whose half span aspect ratios are identically fixed in 2.0. The simulation and investigation has revealed new knowledge on the relation between swept-back angles and aerodynamic characteristics of a wing in a supersonic flow. As the aerodynamic characteristics, drag coefficient CD variation is primarily observed along flow Mach number increase. Results of N-S simulations show a realistic profile of the variation which is substantially different from that by the thin-wing theory commonly printed in a textbook. Moreover, the simulation results indicate not only the swept-back angle of a leading edge but also that of a trailing edge take important role on aerodynamics of a wing. Finely, the effect of drag coefficients induced by lift is analyzed using simulation results. It is found that the induced drag in realistic supersonic flows can be treated by the thin-wing theory if three-dimensionality is properly evaluated.

View full abstract

This paper reports a numerical investigation of the motion of spherical and non-spherical particles with/without gas blowing-out in a vertical uniform flow. A sphere, spheroid and pulverized coal particle are targeted in this study. The shape of coal particle is three-dimensionally modeled by scanning a coal particle using the X-ray CT method. As a first stage of the research, the Arbitrary Lagrangian-Eulerian (ALE) method is validated by comparing with the experiment. Secondly, the simulations of spherical and non-spherical particles with or without gas blowing-out in a vertical uniform flow are performed. The results show that the spheroidal particle with equivalent volume has a more similar accelerating motion to that of coal particle than spherical particle. For spheroidal particle, its distribution of PDF of C_D shows a possibility to make a C_D equation with Re and particle's orientation. It is also revealed that the motion of coal particle with irregular shape is significantly dependent on its shape, especially with gas blowing-out. A new model in which this complex shape effects can be considered is required to describe the irregular shape particle.

View full abstract

This work aims at developing a new cooling fan for vehicle engine. This fan can operate as a cooling fan at low vehicle speed. At high vehicle speed, however, the fan is rarely used as a cooling fan. Therefore the fan can be used as a wind turbine, which generates electric power. In the previous report we had confirmed the effect of S-Shaped blade profile on the wind turbine efficiency by CFD analysis and the experiments. The present paper reports the improvement of wind turbine efficiency by adopting high solidity for the rotor. The tip portion of the low solidity rotor works as the cooling fan even in the wind turbine operation. However, high solidity rotor can work as the wind turbine at the whole portion. Therefore high solidity increases the wind turbine efficiency and can regenerate more electric power than the original rotor.

View full abstract

In order to efficiently develop microfluidic devices using electrohydrodynamic (EHD) phenomenon, an appropriate model for the phenomenon and a numerical simulation method for EHD flow in microfluidic devices has been required. In this study, EHD flow in micropumps was modeled and a numerical simulation code based on the model was developed. The numerical simulation code was constructed utilizing an open-source CFD software package OpenFOAM. Numerical simulations were performed using the present numerical simulation code for EHD micropumps developed and experimentally tested by Kazemi, et al. (Journal of Microelectromechanical Systems, Vol.18, No.3 (2009), pp.547-554.), and the simulations were validated by comparing with the experiments. The simulated discharge pressure generated in the micropumps was proportional to both applied voltage and charge density, and the experimental discharge pressure was well reproduced by considering the change of charge density with applied voltage. The electrophoretic mobility was assumed to be constant in the present study. This assumption was discussed based on experimental electric current, and it was shown that the assumption was valid in an applied voltage range where EHD phenomenon was dominant. With increasing applied voltage, the charge density was generated when the average electric field on the electrodes exceeded a threshold, and then the charge density was proportional to the average electric field.

View full abstract

The compressible turbulent flows through a square duct including an adiabatic bottom-wall with three Mach numbers, M = 1,1.5,2 are investigated using the direct numerical simulation. The secondary flows, which are caused by the turbulent anisotropic effects, are drastically changed with respect to the number and flow pattern of the secondary circulation due to the dependency of the Mach number and the existence of an adiabatic wall. At high Mach number case, the secondary flow near the adiabatic wall grows and is strengthened. Thus, due to the strong secondary flow, the heating fluid near the bottom wall is transported to the upper region. As increasing Mach number, the heat is generated near the adiabatic wall and the fluid temperature rises in the whole region except those near the isothermal walls. The strong secondary flow at high Mach number exerts an influence on the distribution of the mean quantities of the streamwise velocity, density and temperature. From the viewpoint of the budget of the streamwise vorticity, the Reynolds shear stress plays a primary part in producing the secondary flow, and the contribution of the difference between the normal stresses is weakened as the Mach number increases unlike the incompressible turbulent flow through a square duct.

View full abstract

Co-generation system and district heating and cooling system have been applied to urban areas to realize a low-carbon society. However, CO₂ emissions from operation division including commercial buildings are still on the increase. Hence researches of micro grid have been conducted as one of the countermeasures to realize a low-carbon society. Here, it seems that the district heating and cooling system is operated effectively under the urban site micro grid network. Thus in this report, a combined system composed of micro grid network and district heating and cooling was investigated to minimize CO₂ emissions with a variation of a combination of energy saving systems. The combined system in this study interconnected 3 commercial-scale utility customers with different electric demands and thermal demands. In addition, a conventional energy supply system and district heating and cooling were selected as subjects of comparison with the combined system. Furthermore, 4 kinds of heat-to-power ratio were set by changing the total floor space of each building. In these conditions, annual CO₂ emission from each energy supply system was simulated by using a numerical software GAMS/BARON. The calculated CO₂ emission was compared with one another in each heat-to-power ratio.

View full abstract

Two color ratio method was applied to measure temperature distributions of a luminous diffusion flame. A small blue butane diffusion flame, 3mm in flame diameter, was used. A small droplets array (300 droplets of 30um in diameter) was injected in the diffusion flame. The component was 85% hexadecane and 15% o-xylene to surrogate diesel oil. A color CMOS high speed camera of 4kpfs in flame speed and 16um/pix in spatial resolution was used to measure the flame shape and the temperature. The flame with the droplet array was luminous and the temperature was measured with optical two color ratio method (green and red). In the two color ratio method, a threshold of the red intensity should be defined. As the flame could be assumed as an axial symmetry, an Abel conversion was used. In the Abel conversion, thresholds of red/green intensities should be defined to form a sextic even polynomial. A thin sheath thermocouple (0.3mm in sheath diameter) was used to compare the two color ratio method results. As a result, the red intensity threshold for the two color method was reasonable and 40 in this experiment. In comparison with a KL value two color method, the two color ratio method could show lower temperature region.

View full abstract

In gas turbine engines, combustion temperature increases in order to reduce CO₂ emissions and to improve thermal efficiency. However, at the same time, this leads to the increase of nitrogen oxide (NOx) emissions. Lean premixed combustion is one of the most effective techniques to reduce NOx emissions. However, lean premixed combustors have a narrow stable combustion range compared with diffusion combustors and have a risk of flashback. Flashback of flame into the fuel nozzle causes serious damage to combustors. In this study, we present characteristics of unsteady flame behavior in a premixed burner with swirling flow. A variable swirler is used in order to investigate the flame behavior under different swirl intensity. The relationship between the flame behavior and flow fields in the premixer have been captured by applying high-speed particle image velocimetry (PIV) measurement. It is clarified that flow velocity of unburned gas upstream the flame tip has effect on flame propagation velocity regardless of swirl intensity from the results of PIV measurement in flashback limit. From the results of PIV measurement in blow-off limit, we clarified the possibility of flame extinction upstream the flame tip in high swirl intensity. It is conceivable that this is because flame is stretched by a steep velocity gradient.

View full abstract

Recently, highly efficient small heat transport devices have been required. In particular, pulsating heat pipes (PHP) have come to draw a lot of attention. The contribution of sensible heat transport and latent heat transport in oscillating working fluid, which plays an important role in heat transport performance of PHP, has not been clarified enough experimentally yet. The purpose of this study is to evaluate the contribution of sensible heat transport and latent heat transport experimentally by making liquid column oscillate sinusoidally in the channel. The channel was initially evacuated, and ethanol was charged to form a liquid column, which is called single component system. In addition, the ethanol was charged in the channel with air in the gas phase at atmospheric pressure, which is called two components system. The effective thermal conductivity of latent heat transport is determined by the difference between the effective thermal conductivity in single component system and that in two component system. In two components system, that is sensible heat transport, the effective thermal conductivity decreases monotonically as oscillation center moves to cooling section under the same amplitude, because residence time of liquid column at heating section decreases. On the other hand, in latent heat transport, the effective thermal conductivity increases as oscillation center moves to cooling section under the same amplitude, because liquid film at cooling section becomes longer. In addition, numerical analysis was conducted for sensible heat transport in oscillating working fluid. The comparison of the numerical results with the experimental results indicates that liquid film at the tip of liquid column would enhance sensible heat transport.

View full abstract

A ground source heat pump (GSHP) heating system is one of the most effective and realistic renewable energy plants which reduce energy consumption and carbon dioxide to be about a half in comparison with an oil heater in cold climate region. In spite of such superior performance, utilization of GSHP has not been extended in Japan, while that has been remarkably increased in Europe and USA. A design tool which is easy to use for builders is required in Japan. Energy balances in an actual renewable energy house, equipped with a GSHP air conditioning system were observed by real-time continuous monitoring systems from 2005 to 2013 and analyzed in Kitami City, Hokkaido, subarctic region, Japan. Real-time continuous monitoring of soil temperature distributions were also carried out from July in 2007. Thermal demand of heating (=heat loss) from house and thermal input caused by residents were well predicted using house configurations and meteorological data (mainly ambient temperature and wind speed). We set the allowable lowest soil temperature at the vicinity of a heat collecting tube 0°C under a common ambient temperature condition in order to maintain healthiness of soil. Seasonal and cumulative changes in soil temperature distributions were successfully analyzed with FEM from the beginning of GSHP operation in 2005 to the end of that in spring, 2014. A prediction method of required lengths of a U-tube to the required heating demands in various domestic cities which have various soil temperatures has been developed. Builders will easily use these simplified methods as a new design tool.

View full abstract

The critical heat flux (CHF), heat transfer coefficient, and pressure loss were measured systematically for water subcooled flow boiling. A small rectangular channel containing a porous metal plate was used as the test channel (this was called “porous-microchannel” in this work). In the normal rectangular channel that did not contain the porous plate, large bubbles were produced at sufficiently high heat flux. In some experimental conditions, the formation of large bubbles immediately led to the onset of CHF condition. It was hence considered that the CHF value was deteriorated by the formation of large bubbles. Whist, in the porous-microchannel, the mixing effect associated with the complicated channel geometry prevented the formation of large bubbles to enhance the CHF value. The occurrence of flow instability was also mitigated. The effects of the material and the pore size of the porous metal were also investigated. Silver and nickel were selected as the high and low thermal conductivity materials, respectively. It was found that the CHF value was not influenced significantly by the material, but it was dependent noticeably on the pore size. These results supported the hypothesis that the CHF enhancement in the porous-microchannel can mainly be attributed to the mixing effect caused by the complicated channel geometry.

View full abstract

Loop Heat Pipes (LHPs) have been used in thermal control of spacecraft as next generation heat transport devices. Recently, multiple-evaporators LHP (MLHP) is under studied since the MLHP supplies autonomous thermal control function. However, some physical phenomena in the MLHP have not been clarified yet. The purpose of this study is to clarify thermal behavior of the MLHP under the microgravity. The MLHP used in this research has two evaporators and one condenser. Distilled water is used as the working fluid. 40W/40W, 80W/80W, 120W/0W, 0W/120W heat load were applied during the test. This experiment was conducted under microgravity for about 20 seconds, which was realized by parabolic flight. The vapor-liquid distribution in the wick core and the compensation chamber (CC) under the microgravity is presented. The effect of the microgravity for the working the MLHP is also discussed. The heat distributions in the MLHP when one and both evaporators were heated is also clarified

View full abstract

A cooling method is proposed of residual power released after the shutdown of nucleate reactors even when all electricity becomes unavailable. The cooling source is a water reservoir that the initial level is 20 m high from the sea. Only turbine driven pumps are used for circulation of coolant in the reactor. The high-pressure injection system is used to remove residual power directly from the reactor vessel, then cooled with the heat exchanger in the residual heat removal system, to which a turbine-driven pump in the reactor core isolation cooling system supplies water from the suppression pool. The flow system of cooling water consists of feeding pipe, tubes in the heat exchanger and an orifice that controls flow rate. The simulation reveals that the temperature of the suppression pool has its maximum at about 50 hours from the shutdown, though the flow rate is steadily decreasing. It is results from the decrease of residual power. The temperature increases again in the last phase of cooling because the flow rate of cooling water diminishes. The delay of the start of cooling contributes to make the cooling water exit temperature cooler at the last phase of cooling. Two restrictions were applied to minimize the area of the reservoir. One is that the temperature of the suppression pool does not exceed designed temperature of the containment vessel. The other is that the cooling water exit temperature is less than 60°C. The minimized area is 3094 m², a possible area to build. This cooling system is considered very important for reactors located on seashore, where tsunami attack may destroy the residual heat removal sea water system.

View full abstract

In this study, secondary atomization of emulsified fuel spray was visualized, and the effect of ambient temperature on secondary atomization in spray flow was investigated. The W/O emulsified fuel was prepared by adding 10 wt% water and 0.75 wt% emulsifying agent (sorbitan monooleate) to n-dodecane. A shadow imaging system consisting of high-speed video camera (125,000 fps) and metal halide lamp was used to visualize secondary atomization of spray droplets. As a result, it clearly showed that secondary atomization of spray droplet was caused by vapor production inside the spray droplet due to the rapid evaporation of dispersed water. When the furnace wall temperature (T_w) was 823 K, there is no significant difference between the size distribution of emulsified fuel spray and that of n-dodecane spray because the droplet temperature was too low to produce vapor inside the spray droplet, leading to decreasing secondary atomization effect. Meanwhile, at T_w = 923 K and 973 K, the size distribution of emulsified fuel spray droplets was shifted to smaller than that of n-dodecane spray droplets. This is because the droplet temperature was enough to produce vapor inside the droplet and secondary atomization was enhanced. It was indicated that ambient temperature was important in the occurrence of secondary atomization.

View full abstract

The flow field of a turbulent premixed V flame has been closely examined by using a three-color six-beam LDV system. A bi-modal distribution, composed of the velocity fluctuations of both the high velocity mode and the low velocity mode, is observed within the turbulent flame brush. In the radial component, the high velocity mode is identified as velocity fluctuations of the unburnt mixture and the low velocity mode as velocity fluctuations of the burnt gas. On the other hand, in the axial component, the high velocity mode is identified as velocity fluctuations of the burnt gas and the low velocity mode as velocity fluctuations of the unburnt mixture. Velocity vectors of the unburnt mixture are seen to be directed toward outer side of the burner, indicating that the flow divergence is remarkable in the unburnt mixture. The radial component of the velocity vectors of the unburnt mixture increases in the downstream. On the other hand, the velocity vectors of the burnt gas are slightly directed towards the centerline because of the thermal expansion across the flamelet. The axial component of the velocity vectors of the burnt gas increases in the downstream. The RMS (root-mean-square) of the fluctuations of the radial component of the gas velocity decreases in the unburnt mixture towards the centerline. It increases in the turbulent flame brush. It decreases in the burnt gas toward the centerline. The RMS of the fluctuations of the axial component of the gas velocity decreases both in the unburnt mixture and the burnt gas toward the centerline. Enhancement of turbulence in the turbulent flame brush is remarkable in the radial direction.

View full abstract

The purpose of this paper is to estimate the feasibility of a low-carbon society in Japan through developing an energy flow, carbon flow and cash flow. In addition to total primary energy supply (TPES) and final energy demand, the energy flow contains estimated renewable energy potential, energy services and energy losses. TPES in 2012 is estimated as 18.9 EJ, of which 17.9 EJ (= 17.9 ×10¹⁸ J)was supplied by fossil fuels. Total renewable energy potential is estimated as 21.2 EJ which is enough to meet Japan’s TPES. Wind energy has large potential of 18.3 EJ. As for demand sectors, the transportation sector has the largest energy losses, 2.62 EJ, due to low energy efficiency. Total CO₂ emission in 2012 was 1,223 Mt-CO₂, of which 956 Mt-CO₂ was emitted from both coal and petroleum. Coal is mainly supplied to electricity generation sector, and petroleum is supplied to transportation sector. Total payment for energy supply in final demand sector is estimated to be 41.9 trillion JPY. Total CIF price of 20.6 trillion JPY is paid to foreign countries due to imported fossil fuels. This study indicates that introduction of renewable energy and energy supply system transition, in particular of the transportation sector and electricity generation sector, leads to CO₂ reduction and revitalizes local economies. Wind energy, which has a great potential, is important to design a low-carbon society.

View full abstract

This paper presents laser-based tracking of moving objects by a group of mobile robots located near one another. Each robot detects moving objects such as people, cars, and bicycles in its own laser-scanned images using a binarized occupancy-grid-based method. It then sends laser measurements related to the detected moving objects to a central server. The central server estimates pose (position and velocity) and size of the moving objects via the Kalman filter based on the received measurements; it then feeds that information back to the robots. Rule-based and global-nearest-neighbor-based data associations are applied for matching of tracked objects and laser measurements in multitarget environments. In this cooperative tracking method, the central server collects the laser measurements from all robots; hence, the robots can always track invisible or partially invisible objects. The experimental results for two robots in an outdoor environment validate our tracking method.

View full abstract

5-DOF self-bearing motor possesses the functions of a motor, two radial active magnetic bearings (AMBs), and an axial AMB. It is possible to downsize the AMB system while still maintaining a high level of support performance. In a 5-DOF self-bearing motor, the IPM rotor generates bias fluxes in not only the radial direction but also in the axial and tilt directions without any side surface permanent magnets. However, cogging torques are inherently generates by the magnetic flux flow in a IPM rotor. The proposed flux recovery-type permanent magnets configuration was analyzed using the 3-dimensional finite element method. The results show a significant reduction of the cogging torques and an improvement to motor efficiency.

View full abstract

Bipedal walking ability, which is mainly composed of mechanical stability and moving efficiency, is one of the most important issues in the field of humanoid robots. An effective use of the arms is expected to improve the walking ability under the constraints from limited body. Multiple usages of the arms are required to adapt the robot to various walking conditions because each usage possesses different utility, respectively. We propose two strategies for arm-swing to enhance stability and efficiency. Both the strategies use the selection algorithm for locomotion (SAL) that determines the optimal locomotion for the various walking conditions. One strategy is a use/compensation of moment of swing-leg by hip-rotation/arm-swing. This strategy, called Ro-SAL, selects a rotation rate of hip depending upon a falling risk. Another strategy is a support of the center of gravity (COG) tracking. This strategy, called Su-SAL, employs a predictive control, and a support weight that determines weights of input and output in the predictive control is also selected depending upon the falling risk. From simulation results, we validate that Ro-SAL is effective in a stable state and a state with internal model error, while Su-SAL is effective in states with external force and environmental complexity.

View full abstract

In this study, we proposed a sound localization method by using the binaural model for a real environment, in which the reflected sound and background noise is present. In order to estimate of horizontal angle, the reduction method of the initial reflected sound that combining the modified Thomposon-τ method and the modified sub-band peak hold processing, was proposed and its effectiveness has been performed. In addition, to create the ESR database of vertical angle, the modified Thompson-τ method is used for elimination of the abnormal value. In the estimation of the vertical angle, a new method that is called wins calculation method is proposed and it is strong in abrupt noise, without using the traditional cross-correlation method. The experiments were carried by using /a/ sound in real environment with 45[dB] background noise and 300[ms] reverberation time. As the results obtained that the estimate correct rate of the horizontal angle is 94.6%, the correct rate of the vertical angle is next 98.6%, and the validity of the proposed method was confirmed.

View full abstract

The purposes of this study are to propose the seismic isolator which has the new characteristic using the thrust bearing, and to propose a simple method for the seismic isolation design. It is thought that the seismic isolator using the thrust bearing depends on the seismic input motion because it is nonlinear system with the geometric nonlinearity. Therefore, it is found that the response magnification changes with respect to the maximum acceleration of the seismic wave and the rotation spring constant, and the domain which has the response reduction effect on a response reduction map was acquired. It is thought that the proposed seismic isolator has the following characteristics from the analytical result. The initial state of the isolator is important in order to acquire the response reduction effect to the various excitation directions. The response reduction effect is small in the case of a long-period earthquake ground motion, and the seismic isolator carries out seismic isolation effect by making a rotation spring constant small. The response reduction effect is large in the case of a short period earthquake ground motion, and the rotation spring constant of the seismic isolator should be enlarged not to the response becomes unstable. Moreover, it is possible to make the seismic isolation design simply by applying the response reduction map.

View full abstract

This study deals with a generation method of undulatory motion of an aquatic flexible plate, to improve the efficiency of an aquatic propulsion mechanism by suppression of a reflection wave on a trailing edge. Firstly, non-reflection impedance of a flexible plate was derived by using a matrix-based wave approach, and then control forces for trailing edge of a plate was derived by the impedance. Secondly, obtained non-reflection impedance was translated into the relationship of the displacements between leading edge and trailing edge, to generate a pure traveling wave by three linear actuators. By the relationship, appropriate forced displacements of trailing edge are available by referring to driving signals. However, the method uses a wave number of an aquatic planar plate, which is dependent on added mass effect. To overcome this difficulty, an identification method of wave numbers with constant amplitude for various driving frequencies was introduced. Finally the method was applied to an experimental apparatus. Experimental results showed that a quasi-pure traveling wave was generated on an aquatic flexible plate by the method.

View full abstract

In this paper, the hybrid active noise control (HB-ANC) system applied in the active noise barrier (ANB) is improved, and the noise attenuation performace of the ANB is invetigated under four different sound field configurations. This hybird ANB reduces the diffraction noise from top of the ANB and the noise propagated to the head position of the target person behind the ANB simultaneously to achieve higher noise attenuation. However, the waterbed effect of the feedback control part of the HB-ANC system will cause noise enhancement at some frequencies in the control area. In order to solve this problem, the HB-ANC system is improved by adding a filter to cancel the noise enhancement caused by the waterbed effect. Then, the noise attenuation performance of the hybrid ANB under four sound field configurations is evaluated by simulations. The sound field configurations are set up to investigate how the diffraction from side of the ANB and the reflection influence the performance of the ANB. An experiment in the anechoic chamber is also conducted. The results indicate that the low frequency noise attenuation can be obtained in a wide area behind the ANB, and at the head position of the person, the noise attenuation can be ensured within a wider frequency range, even for the sound fields where the uncontrolled diffraction from side and the reflection exist.

View full abstract

In this research, we study on posture control of a two-link torque unit manipulator under the condition of viscous friction. The torque unit is a module which consists of an electric motor and a reaction wheel, and it can be set at any arbitrary position as actuators to control a rotating link system with free joints. In this paper, we propose a control method using a kinetic energy of the reaction wheel. The viscous friction cannot be ignored in the real system. There arises a problem such that angular momentum remains in the reaction wheel of the torque units by the influence of the viscous friction. Then, we clarify the relation between angular momentum of the reaction wheels and rotation angles of the links. First, we try to control the first link to an arbitrary reference position without regard for the angle of the second link. The angle of the first link can be controlled by changing the viscous friction between the first link and the base. Next, we try to control the second link to an arbitrary reference position by using the residual angular momentum of the reaction wheel on the second link. Finally, we propose a control method based on these ideas, and we confirm the feasibility of the proposed method through the numerical simulations.

View full abstract

In industrial scenes, pneumatic anti-vibration apparatuses having both air springs and voice coil motors are widely implemented in semiconductor exposure apparatuses for suppression of disturbance and improvement of vibration transmissibility. Since it is necessary to reduce effect of heat in the semiconductor manufacturing, the voice coil motors, which are exactly heating elements, are forcibly cooled down. Moreover, for a lot of space of the exposure apparatus, temperature is locally managed by means of air conditioning. However, the temperature in the air springs changes due to the intake and exhaust of high pressure air, it has not been managed in semiconductor industries. For the above reason, the heat radiation from the air springs affects the semiconductor manufacturing probably. Furthermore, the pressure in the air springs changes in accordance with the inner temperature. It results in the performance degradation of pressure control. To overcome the temperature changes of the air springs, this paper discusses the suppression of temperature change in air springs used for an anti-vibration apparatus. The thermal equivalent circuit, which corresponds to the heat transfer of the air springs, are derived in order to create mechanical and electrical temperature reduction methods, and to evaluate experimental results. Based on measurement results of the temperature changes and the thermal equivalent circuit, four methods are proposed so as to suppress the temperature change.

View full abstract

Numerical simulation for a hydraulic operation stabilizing system of gas circuit breaker (GCB) driven by a hydraulic operating mechanism is treated . Valve collision and hydraulic column separation, created in hydraulic fluid by the movement of valves, are simulated. Constrictions between main piston and latching mechanism which is used to control the movement of the piston is taken into consideration. Results of simulation agree well with the experiments on the characteristics of the movement of valves, piston and hydraulic pressure. It is confirmed that the hydraulic mechanism with a hydraulic operation stabilizing system is stably operated, not affected by hydraulic column separation. Dimension of return circuit and latching mechanism which constitute a hydraulic operation stabilizing system are investigated. The range of diameter of restrictors in the circuit and latch angle to optimize a hydraulic operation stabilizing system are shown.

View full abstract

This paper addresses position and path-tracking problems of robot manipulators subject to constraints on both the magnitude and difference of the control input. Along with the model predictive control (MPC), the disturbance observer (DOB) is used to compensate for disturbances and nominalize the plant dynamics. To constrain the total control input, which is the sum of the MPC output and DOB output, we adopt time-varying input constraints and construct a useful structure of the combined DOB-MPC system. The effectiveness of the proposed control scheme is validated through a few experiments using a real two-link manipulator.

View full abstract

A passive vibration isolation system consisting of a friction damper is advantageous at cost, a maintenance, etc. However, the conventional damper of constant friction force has performance limitations; the isolation performance declines and the residual displacement becomes large when the friction force is large, while the resonant peak becomes large when the friction force is small. It is known that above drawbacks are avoided when the friction force varies in proportion to the relative displacement. Recently, authors proposed a simple linear friction damper mechanism that consists of a cylindrical block and a tilt lever supported with a pivot or a leaf spring. When the cylindrical block moves and pushes the tilt lever, the normal and friction forces at the contact surface vary proportionally to the displacement of the cylindrical block. However, the mechanism is limited to one-dimensional motion. This paper proposes the extended mechanism that can be applied to the motion moving in two dimensions by combining the conical lever and the disc. The conical lever consists of the concave cone supported with the universal joint at the apex side and the tilting movement is constrained by the restoring spring. The rounded edge of the disc is set up to contact the inside flank of the concave cone. When the disc moves in arbitrary direction in the planar floor and pushes the conical lever, the normal and friction forces at the contact portion vary depending on the displacement of the disc. Fundamental property of the proposed mechanism is investigated by the simplified numerical simulation and the experiment.

View full abstract

An elevator rope for high-rise building is forcibly excited by the displacement of the building caused by earthquakes and wind forces. In high-rise building, the elevator rope may resonate with the natural frequency of the building; hence, effective solution to reduce the rope displacement is demanded. In this paper, a method to suppress the transverse vibration of elevator rope using vertical vibration of counterweight is proposed. Rope lateral vibration is controlled by fluctuating rope tension using up-and-down motion of this counterweight. Finite difference analyses of rope vibration with counterweight are performed to verify the validity of this method. Experiments involving forced vibration of a rope whose length is constant are performed. In the experiments, guide bar is used to suppress the rotation motion of the rope. As a result, rope sway is reduced to about 1/2, when the cage is stopped. The optimal natural frequency of vertical vibration of counterweight is about 2 times of the natural frequency of the rope lateral vibration.

View full abstract

To improve the noise proof performance of a cover with apertures, the occurrence of the inner acoustic mode at lower frequencies must be prevented. To do this, the authors propose an interference wave inducing aperture. To overcome the noise propagation from the outer source to inside the cover that has an aperture on the top end, the location and the size of another aperture (interference wave inducing aperture) were optimized by a calculation using boundary element method and validated by experimental measurement. The calculation results show that the first inner acoustic mode to be prevented is the second in the height direction when the noise source is set at the outer cover and the sound pressure evaluation point is set at the cover center. In this mode, the point at the cover center along the height direction has a reverse phase of the location at the original aperture, so the interference wave inducing aperture seems to be set at the cover center along the height direction. The location and the size of the interference wave inducing aperture were optimized by analysis. The results show that if the interference wave inducing aperture is set at the center of the cover along the height direction, both the second inner acoustic mode in the height direction and the second in the width direction are the most prevented. The reduction effect is approximately 9 dB at the peak level. The effect of the interference wave inducing aperture that is caused by these calculations was validated by an experimental measurement. The results show that the effect is approximately 11dB at peak level reduction and approximately 4 dB overall between 220 Hz and 600 Hz.

View full abstract

It is important to develop numerical prediction techniques for solidification and thermal deformation of casting, in order to clarify mechanisms of cast defects, deformation behaviors of cast itself or cracks which appear during solidification. However, non-linearity of such thermo-mechanical phenomena is extremely high, and numerical calculations for such problems often require enormous computational cost. Therefore, there is always a need for simulation method that can allow high efficient calculation on such high non-linearity problems. In this study, a coupled solidification-thermal elasto-plastic simulation model based on dynamic explicit finite element method is developed. Moreover, some numerical approaches such as mass scaling method are applied so as to improve computational efficiency. Using this model, simulation on thermal stress of casting during solidification was conducted for a simple 2D model and a relatively large 3D model of steel ingot casting. In both cases, dynamic effect due to inertia was negligible and mass scaling factor was able to be raised to the order of 10¹⁰ without computational instability, resulting in drastic reduction of computational time. These numerical results indicate that explicit mass scaling method has significant effect on improving calculation efficiency, and such method can be a powerful tool for thermal stress simulation of casting.

View full abstract

In this paper, a free form optimization method is proposed for achieving a desired static deformation of a frame structure. Deformation control is one of the important problems in stiffness design of frame structures, and it also enables to give a function to frame structures. As an objective functional, we introduce the sum of squared error norms to the desired displacements on specified members, and the assumption that each frame member varies in the off-axis direction. The shape gradient function and the optimality conditions for this problem are theoretically derived with the Lagrange multiplier method and the material derivative method. The optimal shape variation that minimizes the objective functional is determined as the displacement-field by applying the negative shape gradient function as fictitious external forces to the frame members. With the proposed method, the optimal arbitrarily formed frame structure can be obtained without any shape parameterization while maintaining the smoothness. The validity and practical utilities of this method for the static deformation control of frame structures are verified through design examples.

View full abstract

This report is described the study on the lubrication characteristics of porous circular journal bearing made with oil impregnate sintered materials as a DC spindle motor's bearing system. It was examined experimentally to optimize the diametral clearance of porous journal bearing with pivot supported condition by measuring the lubrication characteristics. In this report, it is especially referred the experimental examination for Settling Time, Lissajous Curve diagram or Shaft Whirling Behavior by measuring the Time History Waveform of shaft such as above mentioned lubrication characteristics under shaft starting condition. Furthermore, it was investigated to discuss the influences of diametral clearance changes to the lubrication characteristics by measuring the Time History Waveform of shaft under same condition. In addition, in order to investigate more detailed rotating behavior of shaft, authors practiced the Frequency Spectrum Analysis of Time History Waveform with FFT.

View full abstract

Lure fishing and fly-fishing have been positioned as sports deliberately different from the traditional Japanese fishing-style. In the case of fly-fishing, casting is the element which anglers must master in order to cast a fly, done so by using the weight of a line. This study uses experimental and computational analysis to investigate the dynamic behavior of a fly line. Fly-fishing is constituted by various elements, but the importance that casting holds is extremely large. Fling speed, the casting process and the loop shape of the line while in flight are important that casting holds is extremely large. Fling speed, the casting process and the loop shape of the line while in flight are important for the proper presentation of flies. Moreover, the shape of a fly line is also important for a long cast or controlled cast. Fly is a lure that imitates an aquatic insect or a small fish, and becomes the prey of the target fish. And, there are countless of fly patterns. Therefore, anglers necessary to select an appropriate rod or line according to the size of the fly. In this paper, a rod, a line and arms are modeled by using rigid bodies and links. The time history behavior of the model is calculated by pseudo angler velocity of the arms. The validity of the model in detail is investigated. And, proper rod and line in accordance with the fly of the size is verified.

View full abstract

The primary objective of this study was to numerically simulate the carpal bone kinematics during radioulnar deviation of the wrist. Based on computed tomography (CT) images of the human arm, we constructed a biomechanical model comprising the arm and wrist (humerus, ulna, radius, and the bones of the hand). The carpal bones were fused into a single functional unit, while the humerus, ulna, and radius were rigidly fixed, allowing only the wrist joint to move. Further, the ligaments connecting the radius and the ulna to the carpal bones were approximated by wire models. In this study, five palmar and four dorsal ligaments were included. For the muscles controlling radial deviation, the flexor carpi radialis and extensor carpi radialis longus were selected. For the muscles responsible for ulnar deviation, the flexor carpi ulnaris and extensor carpi ulnaris were selected. These muscles were represented with muscle spring models. Two types of muscle spring models were employed: a linear muscle spring model and tendon-modulated muscle spring model. In the linear muscle spring model, the points of muscle origin and insertion were linked with linear springs. These springs simulated muscle stretching and relaxation, without allowing for deformations. The tendon-modulated muscle spring model comprised elements simulating contractible the muscle fibers and elastic tendons that transmitted muscle force to the bone. To compare with the simulation results, CT images of the human wrist joint were obtained at different radioulnar deviation angles. The results of having carried out radioulnar deviation in both models, the linear muscle spring model yielded a maximum ulnar deviation angle of 10° and a maximum radial deviation angle of 3.5°. The tendon-modulated muscle spring model provided a maximum ulnar deviation angle of no less than 30° and a maximum radial deviation angle of no less than 20°. We used the tendon-modulated muscle spring model to estimate the translation of anatomic landmarks (the trapezium and scaphoid) at different degrees of radioulnar deviation, and these simulation results were compared with the human imaging data. For the trapezium, the traveled distances were comparable, whereas the results were incongruent for the scaphoideum. These discrepancies were probably attributable to the improper modeling of the proximal carpal row movement associated with ulnar deviation.

View full abstract

In this paper, we focused on the fact that the ease of driving changed according to torsional rigidity of the electric power steering system for the purpose of the improvement in control performance of vehicle. First, the influence on transfer characteristics from a steering angle(steering wheel) to front wheel angle(front tires) by torsional rigidity was considered theoretically. As a result, it turned out that a front wheel angle was determined by not only a steering angle but also the influence of the dynamic state of vehicle, and it was shown that the influence of the dynamic state of vehicle can be shut by making steering torsional rigidity into high torsional rigidity. Next, the validity of a theoretical verification was confirmed through numerical simulation of steering correction at the time of a disturbance input. Finally, the lower limit value of torsional rigidity for practical use of a high torsional rigidity steering was determined.

View full abstract