In order to clarify the effect of surface profile on friction characteristics of viscoelastic material used for oil seal, sliding test was conducted under oil lubrication with the NBR (Nitrile Butadiene Rubber) specimen in combination with steel specimen. The sliding surface profiles with different feature in the steel specimens were introduced by polish process and blast process. The NBR specimens with different surface feature were also employed. Under a low load condition, steel specimens with plateau surface showed the lower friction coefficient. The reduction of contact area and pocket effect could lead to the lower friction coefficient. Similar effect was provided by the NBR specimens with rough surface or dimples. Friction behavior under a low load condition was influenced by adhesion force. The adhesion force decreased with increasing surface roughness, that is with decreasing contact area. Therefore, the friction coefficient decreased with increasing surface roughness in NBR specimen. The friction coefficient of the NBR specimen with dimples which had small asperity and large concave portion was remarkably small under a low load condition. On the other hand, under a high load condition, where the deformation of NBR specimen was rather large, the effect of surface profile on friction coefficient was small.
Amorphous Carbon Nitride (a-CNx) coating is an attractive material that satisfies both relatively high hardness and ultra-low friction coefficient. We have tried to obtain a-CNx by using plasma-enhanced chemical vapor deposition (PECVD), which is more suitable for 3-dimensional coating than typical physical vapor deposition methods. However, considering the application of a-CNx coatings for real machine parts, ultra-low friction property is expected to express under oil lubrication. Thus in this work, the friction characteristic under oil lubricated of Si-containing a-CNxHy films deposited by PECVD was evaluated especially by analyzing the relation between the Raman spectrum, which is a proper index of carbon structure, and the friction coefficient of the films. In particular, the relation between friction coefficient and ID/IG ratio from Raman spectroscopic analysis of Si-containing a-CNxHy films was focused on. The friction coefficient decreased with the increasing of ID/IG ratio in the range of 0.63-0.78, and the minimum low friction coefficient of 0.055 was shown for the ID/IG ratio of 0.78. However, even for a film with the ID/IG ratio of 0.32, similar low friction coefficient of 0.051 was shown. Moreover, for a film with the ID/IG ratio of 0.34, which is almost unchanged from 0.32, the increased friction coefficient of 0.105 was shown. In these films, the amount of hydrogen in Si-containing a-CNxHy film increased from 33% to 37%, which is considered to mainly cause the increased of friction from 0.051 to 0.105. Two more exceptions were seen for some films where the friction characteristic is not correlated with ID/IG ratio, but may be affected by maximum height roughness (Rz) and C=N combination. When maximum height roughness (Rz) was in the range of 203 nm-414 nm, transfer layer formed on counter material, and it showed lowest friction coefficient of 0.02. In addition, the friction coefficient was linearly decreased with the increase of C=N bond amount; the friction coefficient of 0.027 was achieved for the IC=N/IG ratio of 0.44.
In this study, case-hardened steel rollers with an effective case-hardened depth of 2 mm were fatigue-tested using a roller testing machine in order to elucidate their rolling contact fatigue life. They were made of three kinds of steels. These experimental results were compared with the results of the case-hardened steel roller with an effective case-hardened depth of 0.7 mm. The surface properties of all the test rollers were almost the same. The failure mode of all the test rollers was pitting due to surface cracking. The fatigue life and the surface durability of the rollers with an effective case-hardened depth of 2 mm were improved by the toughness effect due to nickel and the reduction of sulfur content in this experimental range. On the other hand, those with an effective case-hardened depth of 2 mm were far superior to those with an effective case-hardened depth of 0.7 mm. It was confirmed that the surface durability of the case-hardened steel rollers increased as their effective case-hardened depth increased under the same surface hardness.
High carbon chromium bearing steel (SUJ2) is generally used for the rolling element of ball bearing as its material. Normal form of the bearing steel is wire rod. Then rough spheres are made by forging and they are developed gradually into high accurate rolling elements by heat treatment and polishing. However, it is known heretofore that there is inhomogeneous stress distribution caused by forging and heat treatment inside the rolling element. Recently, usage environment of rolling bearings tightens, in other words, high-speed and high temperature conditions are increasingly applied. Though increasing the environmental temperature is well-known as a stress releasing technique for metal stock, moderate deformation arises in the material. When such stress releasing inside the rolling element is enforced at work with being heated to a high temperature, the geometrical form error of rolling element enlarge and the bearing performance will decay. Therefore in this research, relating to the bearing steel ball and silicon nitride ball, the relationship between the non-repetitive run-out (NRRO) of the bearing and the changes in dimensional and geometrical form (roundness) of the rolling element which is exposed to high temperature for one year, assuming its use in a hot environment, are described. As a result, the followings were clarified. (1) For SUJ2 ball, high temperature environment enforced the change of not only geometrical form error but also diameter insomuch as differing accuracy grade. This causes the deterioration of bearing performance. (2) For silicon nitride (Si3N4) ball, under the same condition, the changes of geometrical form error and diameter are very few. Then, the authors confirmed that the silicon nitride ball has a beneficial effect on the usage in a hot environment.
The authors have been developing a pipe bender based on the penetration bending method using a 3-RPSR parallel mechanism as the movable-die drive mechanism and a fixed die on the ground. In this paper, a theoretical model to estimate the curvature of bent pipe in the penetration bending process has been developed by constructing an algorithm to calculate the center line of the bent pipe from the pose of the movable die taking into consideration the springback effect of the pipe and clearances at the dies. Based on this model, maps of estimated curvature radius of bent pipe and bending force have been obtained, and a bending strategy to perform precise bending, in which the pose of the movable die is determined so that the tilt of the movable die is maximized, has been proposed. Improvement of accuracy in radius of curvature of bent pipe based on the proposed model and bending strategy has been shown by experimental results obtained by our prototype pipe bender. In experiments, error of 2% and 4% in bent pipes with shapes of uniform curvature and clothoid curve was achieved while error without the proposed method was around 10-20%.
In general rehabilitation, the walking stick, parallel bars, and walker are used as walking training devices. Users of these devices bear their weight with the hands or legs, and doing so is painful in some cases. In recent years, population aging has progressed rapidly and a labor shortage in the welfare field has become a serious problem. Against this background, it is necessary to develop a walking training device that can motivate patients to train without assistance from a care worker. In this research, we designed and developed a walker equipped with an assist mechanism that translates simulated walking motion into rotational wheel motion. Using the walker, the patient is supported by a saddle, so the hands and legs are relieved of pain due to supporting body weight. The motion transformer is designed using a planar 6-link mechanism, which transforms oscillating motion to rotational motion. Joint angular displacements were measured with a wearable device. Results showed that general walking trajectories can be obtained. This mechanism is designed such that the pedal follows the foot motion in walking by comparing the coupler curve of the mechanism with the trajectory of an ankle joint in a walking motion. We manufactured four types of walkers for testing. Type I uses a motion transformer consisting of only revolute pairs. Type II uses a motion transformer consisting of revolute pairs and a prismatic pair (sliding joint). Type II-ankle free uses a Type II motion transformer from which two links were removed in order to allow free rotational motion of the ankle joint. Lastly, the Type III walker has an axle in the front in order to facilitate riding from the rear and to allow free rotational motion of the ankle joint. Pedaling force was measured and compared among the four types. It was found that free ankle joint movement was effective in decreasing the pedaling force. The results indicate that the motion transformer could be driven with a small force and with a simulated walking motion as the input. However, the angle between the direction of foot velocity and the direction of pedaling force was approximately π/2, and so driving the device using a pedaling motion could produce a sensation different from that of a normal walking motion. Eliminating discomfort during operation is left as a future task.
The present study proposes a robot arm that can support precise positioning in operation by a human. The robot arm has passive and actuated joints. The passive joint is not mechanically constrained and can move passively with the motion of the output point of the robot arm. Therefore, a human can move the output point of the robot arm by his will. When a human tries to move the output point along an object path, the displacement of the passive joint is determined passively. Then, if the actuated joint is controlled so that the output point may be on the object path, the human can achieve precise positioning. Namely, using the proposed robot arm, the human can adjust the velocity, acceleration, applied force and so on by his will, while the position is preciously compensated by the actuated joint. This paper describes a mechanical form of such robot arm for drawing of planar figures and shows that the robot arm has specific singularity condition. In order to avoid the singularity condition, the proposed robot arm interchanges the actuated joint and the passive one situationally. The study fabricated the two degrees of freedom robot arm for positioning assistance and described its control method. Furthermore, its availability is confirmed by drawing some figures.
This report describes a new self-propelled cleaning robot which cleans floor by a wet rotational brush like a floor polisher. The rotational brush does not only clean floor but also transfer itself. Velocity of the robot is controlled by inclining the rotational axis of the brush. Its moving direction is controlled by direction of the rotational axis and moving speed is controlled by degree of inclination angle of the rotational axis. A cleaning robot which has single rotational brush driven by hydraulic motor and the water passed through the hydraulic motor is used to clean the floor was proposed and designed. An experimental apparatus was fabricated and its moving and cleaning performance was experimentally demonstrated.
The aging population and the ratio of 65 years old or more increase rapidly at time when the baby boom generation and baby boomers enter the aging population, receive lower birthrates afterwards, and increase gradually in recent years. In addition, the number of elderly person single homes increases aging. The animal therapy from which a physiological effect, a psychological effect, and a social effect have been achieved as the solution for these problems is paid attention to. On the other hand, it might be difficult to keep the animal from the problem of pet care, the allergy, and the infectious disease in the hospital and senior citizen's facilities. In this study, we focus on the pet robot in substitution for the pet animal. First of all, to decide externals of the pet robot liked by the senior citizen, it proposed the solution of the problem of the pet robot. It paid attention to "Fabulous animal and character" as a form that filled the solution, and externals of the pet robot that developed were assumed to be "Characterized bear of biped walking type as prettily". Then, the mechanism of four joints was developed by two one foot joints and both feet. The joint of the upper-body arranged three joints in the waist, and arranged four joints in the right hand by two joints and both arms, and arranged two joints as a neck and a head aiming at the improvement of communications. The bear of biped walking type with a short leg liked by the senior citizen was designed, produced, the questionnaire survey with a real machine was executed, and the effect of healing that the pet robot that was developed gave the senior citizen was verified.
There has been increased interest in use of pneumatic actuators in many fields, such as medical care and welfare. In particular, proposed pneumatic soft actuator with soft material has many advantages such as low mass, flexibility, safety and user-friendliness. We therefore focus on the pneumatic soft actuators as a drive source of a rehabilitation device. The purpose of this work is to develop a rehabilitation system to prevent contracture of the finger joints using the pneumatic soft actuators. This paper describes the concept, design, prototype and evaluation of the rehabilitation system with the actuators. The system has two different actuators, stepping motors and pneumatic soft actuators. The stepping motors are used for moving the pneumatic actuator at right position for finger rehabilitation. The pneumatic soft actuators are also used for the range of motion (ROM) and relaxation exercise. We measured the flexion and extension angles of the fingers in the rehabilitation test. As the results, we confirmed that the rehabilitation system is able to provide ROM exercise. The test clarified the problems of rehabilitation system with unlimited to the joint range of motion at the same time.
A stacked piezoelectric actuator is used for precision positioning because of high resolution, large generative force and high responsiveness. When piezoelectric actuators are used in the positioning mechanism it is usually used in compressive pre-load because it is weak for tensile load. There are several reports to investigate characteristics of the piezoelectric actuator in loaded condition. However, there are no detail reports which investigate influences of pre-load on the characteristics of both displacement characteristics and relative permittivity under simultaneous measurement. In this paper, it is shown that the behaviors of displacement and relative permittivity of stacked piezoelectric actuators for the pre-load does not agree with each other at all under the same measurement condition, and that these behaviors are dependent on both amplitude and offset value of input voltage. In the experiments, soft and hard type PZT elements are investigated and difference of the behavior is shown. In addition, influences of the input voltage amplitude and the offset voltage on the behaviors of displacement and relative permittivity for pre-load. As a result, in all types of PZT elements, behaviors of displacement and relative permittivity for pre-load do not agree with each other under the same measurement condition, and these behaviors for load are much different between soft and hard types PZT elements.
Since our ultimate target is to realize a simple and inexpensive rehabilitation system of kinesthetic illusion and apply it to rehabilitation training, we need to miniaturize the vibration stimulus device and systematize the vibration stimulus conditions to freely induce and control the illusion. In this paper, we developed a desktop kinesthetic illusion inducement and evaluation system that allows us to investigate the sensory properties of the illusion. When the contact force of a contact head is under 1.5 N, our system can apply vibration stimuli of 100 m/s2 to the tendon between 50 and 300 Hz. Experiments with this system induced kinesthetic illusion of an extension at the right hand joint in all five subjects. We confirmed the efficacy of an estimation system of sensory properties and enhanced gatherings of the vibration stimulus conditions to induce and control the illusion.
It has been known that the high fracture toughness of partially stabilized zirconia (PSZ) is due to a process zone caused by stress induced transformation at a crack tip. The process zone will give an effect not only on fracture toughness but also on fatigue crack growth behavior. In this paper, the R-curve and fatigue crack growth behavior were investigated by some methods using indentation crack specimens. The toughening exponent obtained by the indentation-strength-in-bending method, where beam strength measurements were made using the specimens with indented loads in the range of 48-294 N, is almost zero, that is, a flat R-curve behavior. On the other hand, KI-V curve obtained by constant stress rate tests using indented beam specimens indicated that there was much subcritical crack growth, i.e. a small crack propagation parameter of n=7.4. Moreover, the static and cyclic fatigue tests conducted under static four-point bending and under cyclic reversed plane bending respectively, indicated that there was an appreciable degradation in fatigue lifetime due to cyclic loading, and the crack propagation parameter (n=9.3) obtained from cyclic fatigue test was obviously smaller than that (n=23.9) obtained from static fatigue tests. X-ray diffraction patterns measured in fracture surfaces showed a sign that a part of tetragonal phase is transformed to the monoclinic phase by static and cyclic loading. As the results, it is considered that the high fracture toughness is caused by transformation toughening in process zone, and the degradation of lifetime in cyclic fatigue is due to micro cracks induced by cyclic loading in the process zone.
Aluminum and magnesium alloys dissimilar friction stir spot welds had been fabricated using a tool without probe whose shoulder surface had a scroll groove with the depth of 0.5mm. The scroll groove was designed to induce material flow in the nugget of spot welds. The tensile strengths of dissimilar welds were comparable to those of the magnesium similar welds made by the same tool. Thin intermetallic compound (IMC) layer consisting of Al3Mg2 and Al12Mg17 was formed along the interface between aluminum and magnesium sheets. EDX analysis revealed that the thickness of IMC layer was dependent on the distance from the center of nugget, where the formation of thin IMC layer had resulted in the bonding between the dissimilar alloys. The tensile strengths of dissimilar welds fabricated by the different conditions were dependent on the thickness of IMC layer, and were sensitive to the thickness of IMC layer around the edge of the nugget. Subsequently, tensile shear fatigue tests had been conducted, and the fatigue strengths were nearly the same between dissimilar and magnesium similar welds. Fatigue fracture modes were dependent on the load levels, where fatigue crack propagated along the interface at the higher load levels than 1000N. However, fatigue crack initiated in the lower magnesium sheets at the edge of the nugget and propagated through thickness at the low load level of 750N. Fractographic and EDX analyses revealed that the fatigue crack mainly propagated through the thin IMC layer at the higher load levels.
The subloading-friction model proposed formerly is capable of describing the transition from the static to the kinetic friction and the recovery of static friction, which leads to the negative rate-sensitivity, i.e. the decrease of friction resistance with the increase of sliding velocity. The generalized friction model, called the subloading-overstress friction model, is proposed by extending the subloading-friction model so as to describe not only the negative rate-sensitivity but also the positive rate-sensitivity, i.e. the increase of friction resistance with the increase of sliding velocity in this article. The numerical experiments for several levels of material parameters are shown in order to clarify the influences and the physical meanings of the material parameters in the generalized model. Further, the validity is verified by comparisons with test data obtained by executing the friction test using lubricated steels.
In this paper, we propose a new FE model of a carbon fiber reinforced thermoplastic (CFRTP) in order to capture the deformation during a thermoforming process because the thermoforming process of CFRTP has increased its presence in the automotive industry for its wide applicability to the mass production car. The proposed model can describe temperature dependent non-linear bending property of CFRTP by a set of elements which consists of two shell elements with membrane elements in between them. The membrane elements represent temperature dependent anisotropic in-plane behavior by calculating stress contributions of the textile reinforcement and thermoplastic in a parallel system. By applying Reuss model to the stress calculation of thermoplastic, the in-plane shear behavior which is the key deformation mode during forming can be accurately predicted. FE model is constructed based on the results of three point bending and bias-extension experiments which are conducted in the range of the process temperature. Thermoforming simulations are presented and compared to experimental results. Simulated outline and shear angle are in good agreement with experimental results. It will be shown by sensitivity study that the effect of the temperature plays an important role in deformation during a non-isothermal forming process.
A new procedure using indentation technique was proposed in this study for semi-nondestructive measurement of non-equiaxial residual stress field. The stress evaluation formula using the Vickers and Knoop indenters was constructed based on the addition rule. In the newly proposed procedure, the Vickers and Knoop indenters are used so that the procedure does not require the reference value of hardness or indentation load under non-stress state. In this regard, however the proposed procedure requires two constants for stress determination. One is the load ratio between Vickers and Knoop indenters and the other is the conversion factor determining the relation between existing residual stress and load change due to the existing residual stress. The two constants were quantified by the measurement of the indentation load - depth curve and the existing residual stress using X-ray diffraction method. The accuracy of stress determination using the newly developed procedure was validated using welded specimens of high strength steel with different non-equiaxial stress fields. As the results, it was confirmed that the developed stress measurement using indentation technique provided good agreement with the X-ray stress measurement. Thus the newly developed procedure using indentation technique is expected to be a useful semi-nondestructive technique for determining the non-equiaxial residual stress at welds.
The implicit stress integration algorithm was devised in the first report by formulating the return-mapping based on the cutting-plane projection and the consistent tangent modulus tensor due to the numerical method for the subloading surface model. It was incorporated into the implicit finite element program ABAQUS/Standard through the User subroutine UMAT. The high accuracy and efficiency in computation was verified by the numerical experiments adopting the one finite element subjected to the uniaxial loading under the monotonic and cyclic loadings, comparing with the calculation by the forward-Euler method under infinitesimal strain increments. In this article, the simulations of the test data for the cyclic loading under a constant strain amplitude and the small stress amplitude near the yield state are performed by the implicit finite element program, where the accurate simulation is attained. Further, the boundary-value problems, i.e. the cyclic torsional loading of the notched circular bar and the tensional loading of the flange with the hole attached to the bolt are analyzed by the program. The pertinences of these analyses are verified by comparing with the other implicit method with the nonlinear kinematic hardening model.
In this report, the fatigue delamination strength of WC-Co thermal sprayed coatings under combined torsion and tension is evaluated using the torsion-tension pin-test method. First, the effects of both the pin-diameter and the coating thickness on the apparent delamination strength were investigated experimentally. Second, the stress distributions around the interface edge between the pin and the coating were numerically obtained by using the finite element analysis program "MARC". Third, delamination fatigue strength was investigated under cyclic torsion with or without tensile stress, experimentally. It was confirmed that the fractured plane of the torsion pin coincides with the interfacial plane between the coating and the pin. Similar stress distributions were observed at the interface when delaminations occurred for rather thick coatings, independent of the pin diameter. The critical combination of strength of shear stress field (Ks) with that of tensile stress fields (Ka), i.e., the delamination criteria of the coating under combined shear and tensile loadings, was obtained for a WC-12Co thermal sprayed coating. These combinations were found to be independent of pin diameter and coating thickness. The apparent shear fatigue delamination strength obtained experimentally decreased with increasing pin diameter and tensile stress. The normalized shear fatigue delamination strength curves (S/N curves) can be obtained using the strength of shear stress fields (Ks) observed at the interface when delaminations occurred, independent of pin-diameter.
A pressure type homogenizer consists of a plunger pump, and a valve part with a narrow channel. It generates effects such as a shear, a turbulent flow and a cavitation between fluid molecules at very short time, and makes a homogeneous emulsification state. If the flow pattern in a valve can be solved in more detail, the more efficient and stabilized emulsification will be attained. However, since it is difficult to measure the size, the pressure and the flow velocity in a narrow gap space by experiment, the details of the mechanism of emulsification by s shear, a turbulent flow, a cavitation and a collision have not been clarified enough. In this research, the size of gap is first calculated from the theoretical equation assumed to be laminar flow, based on the Reynolds number of the gap flow. Next, the pressure, the flow velocity, shearing stress, etc. are calculated. Then, the emulsification mechanism of each part of the valve is clarified by expressing the droplet size as a function of the gap size, the shearing stress and the exit velocity about two kinds of original solutions in which interfacial tension differs. Furthermore, the prediction expression of droplet size obtained by the emulsification is proposed.
The mean flowfield of a linear array of multiple rectangular jets run through transversely with a normal two-dimensional jet, has been investigated, experimentally. The purpose of this experiment is to operate both the velocity scale and the length scale of the multiple rectangular jets using a two-dimensional jet. The reason of the adoption of this nozzle exit shape was caused by the reports of authors in which the cruciform nozzle jet promoted strongly the inward secondary flows on both the two jet axes. Aspect ratio of the rectangular nozzle used in this experiment was 12.5. Reynolds number based on the nozzle width d and the exit mean velocity Ue (≡39m/s) was kept constant 25000. Longitudinal mean velocity was measured using an X-array Hot-Wire Probe (3.1 μm in diameter, 0.6 mm effective length) operated by the linearized constant temperature anemometers (DANTEC), and the spanwise and the lateral mean velocities were measured using a yaw meter. The signals from the anemometers were passed through the low-pass filters and sampled using A.D. converter. The processing of the signals was made by a personal computer. Acquisition time of the signals was usually 60 seconds. From this experiment, it was revealed that the inward secondary flows on both the y and z axes in the upstream region were promoted by a two-dimensional jet which run through transversely to the multiple rectangular jets, therefore the potential core length on the x axis of the present jet became 2.5 times longer than that of the supposed multiple rectangular jets, and the half-velocity width on the multiple rectangular jet axes of the present jet was suppressed 50% shorter compared with that of the supposed multiple rectangular jets.
The purpose of this study is to clarify the effect of a component for high-pressure water separation, which is included in the air conditioning system of the general commercial aircrafts, on the air-cycle operation (reverse Brayton cycle); the high-pressure water separation consists of water separator and two heat exchangers called reheater and condenser, respectively. This paper briefly describes the typical system configuration of the air-cycle refrigeration progressed with evolutions in turbofan engine. Since nowadays, 4-Wheel air-cycle has been a trend on the aircraft air conditioning system, this paper theoretically shows its advantage on the basis of the thermodynamic cycle study. In the following chapters, an analysis was conducted on the interaction between a reheater and a condenser when each heat transfer performance changes from the baseline operating point. Also, the comparative study was made on the system performances by the 3-wheel and 4-wheel air-cycle. In addition, this paper describes how the heat transfer performance is designed for the reheater and the condenser under the system requirements for the entire air conditioning system.
We examine the effects of temperature non-uniformity and turbulence on homogeneous charge compression ignition (HCCI) of a homogeneous n-heptane/air mixture, using three-dimensional direct numerical simulations of the mixture flows. We use a reduced chemical reaction model for the HCCI combustion. Time evolutions of the flows are obtained under the initial conditions having three different initial velocity fluctuations at 4.0 MPa and with temperature fluctuation around 781 K. Heat-release by the low-temperature oxidation, a key reaction in the ignition process, is analyzed along the trajectories of the temperature gradients, using dissipation-elements decomposition of the temperature fields. It is shown that the high heat-release rate occurs in the membrane-like regions where the temperature is about 870 K. The membrane-like regions move along the trajectories from high to low temperature. The analysis on the trajectories shows that the conditionally averaged moving speed and thickness of the regions are decreasing functions of the magnitude of temperature gradient. When the velocity fluctuation is strong, the turbulent flow is found to play a key role in retarding the ignition: The turbulent flow reduces the maximum temperature and slows down the averaged moving speed of the membrane-like regions.
Spray method is used for liquid vaporization. Especially in the internal combustion engine, ICE, the spray specifications are important to improve the efficiency and to reduce the emission amount. The main purpose of spray is vaporization but the necessary heat transfer amount is not enough at the cold-start of ICE. In the use of ethanol, an important alternative and sustainable fuel from biomass, this cold-start problem is much more serious because of the high latent heat and low heating value. The Local-contact Microwave-heating Injector, LMI, was designed and tested in this paper to solve the ethanol cold-start problem. The evaluation parameters of the LMI spray were droplet diameter distribution, Sauter Mean Diameter, SMD, and droplet velocity distribution. As a laser diffraction method (approximately 4mm spot-diameter He-Ne laser) was used to measure the droplet diameter distribution but could not measure other parameters, direct photographs with a high speed camera (512pix x 512pix, color, 12bit for each three colors, 30kfps, 87.7μm in spatial resolution) was used to measure the spray structure change and droplet velocity distribution. A threshold evaluation was important to distinguish the droplets in spray. A watershed method was used to divide exceptionally large droplets. As a result, the microwave heating can improve the atomization.
Polymer electrolyte fuel cells (PEFCs) generally have external humidifiers to supply humidified hydrogen and oxidant gases, preventing dehydration of the membrane electrode assembly (MEA). If a PEFC could be operated without humidification, external humidifiers may be removed, resulting in a very simplified PEFC system with increased total efficiency and reduced cost. One of most important issues to advance the commercial viability of PEFCs is to develop high performance PEFCs that can operate without humidification. In the present study, a water vapor exchange system installed in the cell was developed to enhance the PEFC performance without humidification. A gas diffusion layer coated with a hydrophilic microporous layer, which consists of carbon black and polyvinyl alcohol (PVA), used at the cathode exchange area increases water transport from the wet cathode outlet gas to the dry anode inlet gas. This prevents dehydration of the MEA, thereby reducing the IR (ohmic) overpotential. The exchange area using interdigitated flow channels is effective to achieve further enhancement of water transport from the cathode to the anode, which significantly enhances the ability to prevent dehydration of the MEA. This results in a much higher output power density compared with that for a PEFC without the water vapor exchange area.
Local water behaviors in a PEFC was analyzed by equivalent electric circuit and the temperature distribution with an ultra-fine thermocouples. The thermocouple is tailor-made: thermocouple elements in 50 μm diameter are welded, and electrically insulated with polyimide coating, resulting in the ultra-fine thermocouple. The temperature distribution, which was measured by the thermocouple placed in array configuration, reveals that the cathode catalyst layer shows the highest temperature in the through-plane direction due to the activation over-potential in cathode. Under low humidification condition, however, the anode catalyst layer has the highest temperature triggered by dried polymer electrolyte membrane and increased IR loss. Along gas flow direction, upstream has the highest temperature, because water droplets accumulate in downstream resulting that load current and heat production concentrates in the upstream. In comparison of the temperature in the adjacent channels direction, the tendency of liquid water accumulation under rib makes the temperature under the channel higher.
Exhaust Gas Recirculation (EGR) system with EGR coolers is one of the promising ways for NOx reduction in a diesel engine. Since PM and condensable hydrocarbons are contained in the exhaust gas of a diesel engine, they cause PM deposition on the wall in an EGR cooler. To improve performance of EGR cooler, the PM deposits in it should be reduced because the heat transfer performance is deteriorated by the PM deposition. In this study, effect of wall temperature on PM deposition in an experimental EGR cooler was investigated. The wall temperature of the EGR cooler could be controlled by the temperature of cooling water. The exhaust gas from a diesel engine was passed through the EGR cooler. The thickness of PM deposit was measured by a laser displacement sensor. As a result, the thickness of PM deposit increased with an increase of the exhaust gas passed through it, and the thickness did not so depend on the temperature of cooling water. The PM deposit layer in the upstream region of EGR cooler was thicker than that in the downstream region. It was found that PM deposit layers were separated from the wall in the case of lower cooling water temperature. The separation was probably caused by condensation of water in the exhaust gas.
In this study, we analyze the supply-demand balance in a power system for the year 2030, utilizing an optimal power generation mix model in which the increased amount of renewable energy, high-efficiency thermal power generation, and constraint conditions that reflect realistic operation in a thermal power plant have been successfully incorporated. Our results indicate that the introduction of high-efficiency thermal power generation is capable of yielding a substantial reduction in both the annual costs involved in power generation and the annual amount of CO2 emissions. Moreover, the impact of high penetration of renewable energy on power supply operation is investigated in detail by estimating the daily capacity variation for frequency control at an interval of 15 min. Depending on the season and the weather conditions, our analysis detects that much of the time there is a capacity shortage for frequency control, which implies that high penetration of renewable energy could lead to severe integrity reduction in power operation. Finally, we discuss practical strategies for power supply operation toward resolving this capacity shortage with a particular focus on the resulting economic loss.
The purpose of this study is to establish a two-stage combustion method, which has advantages of a wide range of combustion temperature and high controllability compared to the conventional methods, from the standpoint of promoting the use of woody biomass as solid fuel and the effective utilization of unused wood materials. In this method, we use a vertical grate-type combustor, into which chipped woody biomass is loaded as a batch. The wood chips are burned at a low air ratio of 0.3 to 0.5 from the top to the bottom of a fuel layer, which is opposite to the direction of supplied air flow. The two-stage combustion method can be achieved through the way described above. Under the new method, wood chip combustion can be divided into two stages, namely, pyrolytic combustion process (generation of carbides) and surface combustion process (combustion of carbides). In this paper, the combustion of wood chips with different moisture contents (11, 20, 35%) was investigated, and the effects of the amount of air and moisture contents on the burning characteristics were discussed. The result clarified the mechanisms of combustion under the new method. In addition, we confirmed that combustion temperature and burning rate could be controlled by simply changing the amount of air. The temperature could be changed in the range of about 800 to 1300 K in the pyrolytic combustion process and about 800 to 1500 K in the surface combustion process.
A loop thermosyphon is known to have a higher heat transfer performance without a pump. In addition, there is demand for the reduction of the electricity needed for the fan used to cool the CPUs in a rack mount server. We more efficiently designed a new loop thermosyphon that is thinner and applicable to rack mount servers. Thermosyphon uses gravity to return the refrigerant from the condensation part to the boiling part of the system. Therefore, when it is in operation, the water level in the condenser should be higher than that in the evaporator. However, it is slightly more difficult to ensure the water level differences in such a thin loop thermosyphon than the thick one. The dry-out which is the phenomenon that refrigerant does not return to the boiling part is easy to occur, when the loop thermosyphon is inclined and there is less refrigerant in it. Therefore, it is important to clarify the relationship between the angle needed to start the dry-out and the refrigerant enclosure quantity. For this purpose, we conducted experimental measurements while changing the conditions, and showed that the dry-out angles could be estimated by using a geometric water surface model, which is combined with the calculation of the pressure drop in a vapor tube and the calculation of the steam temperature based on the water surface level in the condensation tube. As a result of using this model, we confirmed that the length of the vapor tube and the volumetric capacity of the bottom header affect the dry-out angle.
We have developed a pulsed laser viscometer (PLV) which is a high speed viscosity sensing technique using pulsed volume heating laser of near-infrared wavelength. For the purpose of developing the novel viscometer applicable to the in-situ measurement and the high time-resolution sensing of viscosity change process, the liquid-level height is a critical factor because the principle of this method is based on the physical phenomenon near the surface. Therefore, we developed the liquid-level control system for precisely adjusting the height. This system determines the liquid-level by controlling the sample stage to the target height with the reflected beam of a probing laser. In addition, we fully automated the measurement process for high speed sensing. The automatic system enables to measure viscosity in a few seconds after setting the sample. In this paper, with the developed experimental apparatus, in order to confirm the capability of the liquid-level control system, we successively measured viscosities of four different Newtonian liquids (toluene, water, 1-hexanol and JS20), whose viscosity range is from 0.1 to 10mPa･s. Then each measurement time was within 3~4 seconds and the deviations from the reference values were within ±10.7 %. In addition, as the aim for a verification of viscosity sensing, we measured viscosity of toluene with intervals of 1 second for 20 seconds. Finally, we successively measured the whole human blood viscosity at the coagulation process.
We made polystyrene-block-poly (1,4-isoprene) (PS-b-PI) thin films with different composition and molecular weight. PS-b-PI thin films with well-aligned PI cylinders were made, and porous PS thin films were made by removing PI cylinders through ozone etching. The micro-structures of the films were investigated by AFM, SEM and GI-SAXS measurements. We measured the cross-plane thermal conductivities of the micro-structured thin films by using 3ω method. Thermal conductivity of a PS-b-PI thin film with non-oriented cylinders was as low as that of homopolymer (PS, PI) thin films. Thermal conductivity of micro-phase separated PS-b-PI thin film with well-aligned PI cylinders was 0.38 W/(m⋅K), and it was twice higher than that of a PS-b-PI thin film with non-oriented PI cylinders. Thermal conductivity was enhanced due to the reduction of phonon scattering in the well-aligned structure of the film. Thermal conductivity of the ozone etched porous PS thin film was only 0.15 W/(m⋅K). The measured thermal conductivity of the porous thin film was well agreed with thermal conductivity calculated by the empirical model for a porous material. Thermal conductivity of a polymer thin film can be controlled by micro-structures.
BWR fuels are covered with liquid water under normal operation conditions but in such events as pump trip, supply of water decreases and fuels may touch on vapor directly. Such condition is called dryout. An occurrence of dryout results in increase of fuel surface temperature, which may cause a severe accident. Therefore it is important from a view point of nuclear safety to make an accurate prediction of surface temperature. Though the final target of this study is to develop a prediction method of surface temperature for actual geometry and conditions of BWR fuel assembly, in this study we focused on the heat transfer phenomena for upward flow in a vertical tube as a first step. The prediction was carried out in order of (1) dryout point location, (2) heated surface temperature in pre-dryout region and (3) in post-dryout region. For prediction of dryout point location, a conventional model of liquid film dryout was used. We attempted to improve the prediction accuracy by adopting equations considering the traction at the vapor-liquid interface. In pre-dryout region, conventional equations for subcooling and nucleate boiling were applied. In post-dryout region,surface temperature prediction with a conventional method showed low accuracy at low flow rate. We specified the cause of low accuracy with statistical method and changed the prediction model. Major conclusions are as follows: (1) Prediction results were compared with various experimental data which cover the conditions of actual reactor to show that the developed method provided dryout location in good agreement but didn't bring a significant improvement compared with conventional model. (2) Developed model can accurately predict surface temperature including the range of high temperature (>650◦C) where conventional model showed low accuracy. (3) Calculation results were compared with experimental data of several researchers to confirm that the dependence on experiment geometry is small enough.
In this study, we experimentally examined a combustion field in a triple port burner. There are four flame configurations, consisting of attached flames, inner attached/outer lifted flames, inner lifted/outer attached flames, and twin lifted flames. Focusing on the transition process of these flames, the flow field was investigated when the external air flow velocity was increased at constant internal air flow and fuel flow velocities. Results show that, except for the attached flame, when the flame is lifted, the axial velocity toward the leading-edge flame gradually decreases downstream, takes its minimum, and then increases very rapidly. This minimum velocity is larger than the so-called laminar burning velocity. It should be noted that, different from a single lifted flame, the inner or outer flame is affected by the other flame located more upstream. For example, the downstream lifted flame faces the flow induced by the upstream lifted flame. Resultantly, a unique behavior of flip-flop between inner and outer flames is observed.
The power generation system by waste biomass has lately attracted attention. The system can convert waste biomass such as garbage, paper and wood into energy. As a result, regional energy independence ratio of area increases. However, conditions of waste biomass are different from their properties, so it is difficult to use as a fuel. Superheated steam gasification system is one of the effective energy conversion systems in order to available wide range of waste biomass. Waste biomass consumes a lot of energy so as to make superheated steam. Then, it is necessary to take account from the collection and transport to power generation process in order to evaluate CO2 emission totally by means of Life Cycle Assessment (LCA). Therefore, this study proposes modeling analysis for LCA by the waste energy by means of superheated steam gasification system. In this paper, it was evaluated that the effect of processing speed of gasification, population, waste biomass ratio, and boiler fuel on energy balance, CO2 emission and cost in residential area. It was obtained that the optimal processing speed of gasification effects on utilization method of carbonization gas and waste biomass ratio. As a result of LCA, energy independence ratio is improved and CO2 emission is reduced by use of carbonization gas. However, total energy conversion efficiency and surplus power are reduced.
In this study, the method of detecting the formation and the dissociation of gas hydrate using AE method was proposed. In the experiment, gas hydrate was formed on the surface of ice particles, which were placed in a copper container filled by propane gas. During the formation process, elastic waves are emitted due to the volume expansion of the ice/hydrate particles, which causes friction between the particle and wall of the container, and contact among the particles. During the dissociation process, elastic waves are emitted due to the melting of ice and formation of propane gas bubbles in the water, which are formed by the dissociation of the hydrate. As a result, it was confirmed that elastic wave can be measured both in formation and dissociation process. Moreover, it was found that the emission of elastic wave increases as the surface area of the ice/hydrate particles increases and the pressure of propane gas increases, because the mass of formed hydrate increases.
In order to elucidate the flow divergence in the rich propane-air turbulent premixed flames, the flow fields of lean and rich propane-air and methane-air turbulent premixed flames of the identical conditions of laminar burning velocity and characteristic of turbulence have been closely examined by using a three-color six-beam LDV system. A bi-modal distribution, composed of both the low velocity mode and the high velocity mode, is obtained from gas velocity fluctuation within the turbulent flame brush. The low velocity mode is composed of velocity fluctuations of the unburnt mixture and the high velocity mode is composed of velocity fluctuations of the burnt gas. The reaction progress variable can be calculated from the bi-modal distribution of the radial component of the gas velocity. Distributions of the reaction progress variable clearly show that the rich propane flame is skinner and shorter than the lean propane flame, indicating that the turbulent burning velocity is larger in the rich propane flame. Comparing the burnt gas mode of the radial component of the gas velocity of the lean and rich propane-air and methane-air flames, the flow divergence is found to be remarkable in the rich propane flame. The cellular instability due to the preferential diffusion causes the turbulent burning velocity and/or the heat release to increase in the rich propane flame.
In this paper, partial load efficiencies of three types of SOFC combined heat and power systems were calculated by cycle analysis. SOFC means Solid Oxide Fuel Cells. The systems were external fuel reforming system (ER type), internal fuel reforming system (IRa type) and internal fuel reforming system with different configuration (IRb type). In each system, the operating temperature of SOFC was 650◦C. The rated point of electrical power generation of SOFC stack was 560W. Fuel was assumed city gas 13A. At the rated points, results of electrical efficiency by cycle analysis were 39.1%, 41.4% and 41.4% at ER type system, IRa type system, IRb type system, respectively. Electrical efficiency of internal reforming system is higher than that of external system. However, the part load area of IRa type system was narrower than that of ER type system because heat recyle was difficult for IRa type system. The part load area of IRb type system was wider than that of IRa type system due to difference of configuration.
In order to investigate the process of accident of Fukushima Nuclear Power Plants, an accident scenario of Fukushima Daiichi Nuclear Power Plant, Unit 1 is analyzed from the data open to the public. Phase equilibrium process model and adiabatic expansion model were introduced. Original data reported in the first stage of the accident were examined to clarify the behavior of the isolation condensers (ICs) which are generally believed unfunctional after the arrival of Tsunami and station blackout. The original data and observation reports verified that the so called “fail safe” system to close the valves in IC did not work properly due to the shutdown of AC power. The reports also showed the evidence that the operators injected water to the storage tank of IC. We proposed a scenario that IC was operational until approximately at 3/12 3:00, small leakage occurred at the reactor pressure vessel (RPV) at the initial stage of the accident, the RPV ruptured at 3/12 6:20, and it ruptured again in approximately at 3/12 16:00. We assumed that PCV ruptured at 3/12 3:00, and the area of rupture did not change after the hydrogen explosion occurred at 3/12 15:36. The present analysis model describes the data measured at the accident, and many evidences and witnesses reported at the early stage of the accident. We also simulated according to the scenario of Tokyo Electric Power Company (TEPCO) that the ICs did not work after the Tsunami arrival. The estimation by the present analysis agrees with the TEPCO's one, however, there are many discrepancies that cannot explain the behavior of the reactor accident.
Accurate evaluation of occurrence location and amplitude of pressure pulsations in a piping system can lead to efficient plant maintenance to prevent fatigue failure of piping and components because the pulsations could be main causes of vibration fatigue and acoustic noise in piping. To measure pressure pulsations easily and directly, a method to combine strain measurement on outer surface of pipe with the formula for thick-walled cylinders was proposed. The experimental validation demonstrated the proposed method could measure amplitudes and behavior of pressure pulsations with a practical accuracy. Furthermore, the applicability of the formula for thin-walled cylinders was examined for various shaped pipes.
The IGCC (integrated gasification combined cycle) is emerging as one of the most advanced and effective systems for electric energy generation. The IGCC consists of pressure vessels such as a gasifier, syngas cooler and gas cleanup unit with the large time constants, so dynamic response of the power plant is delayed. On the other hand, the fluctuating power generation of renewable energies creates the need for flexible operations (e.g. fast start-up and rapid load change) of thermal power plants including IGCC power plants. This paper describes: (1) two new control methods for IGCC power plants that are combined as the proposed control method to reduce the gasifier pressure rise when rapid load changes are required; and (2) a plant-wide dynamic simulation to consider the operability and controllability of the plants. Simulation results showed the gasifier pressure rise rate was reduced from 7.4% to 3.6% due to the new proposed control method, recycle gas flow rate and steam flow rate control, with load change from 100% to 65% at 20%/min. In the case of 15%/min load change, the gasifier pressure rise rate was 2.8% and less than the maximum permissible value of 3.0%.
C4 level cord injury patients can't perform upper limb motion by themselves. Therefore, they need total assistance by care worker in daily life. It disturbs their independence and is burden for care workers. In addition, not moving upper limb makes joint contracture, muscle atrophy and QOL problems, further they can't work on a hobby with upper limb motion. In this study, we support C4 level cervical cord injury patient's upper limb motion. Electromyogram (EMG) signal is used to obtain their intention, then the proposed motion assist robot supports flexion and extension motion at elbow joint as the user intends. Using frequency analysis of the EMG signal, the patient's intention is estimated in real time, and the coefficient of viscosity in admittance controller is varied. Using proposed motion assist method, we realized the arbitrary upper limb motion of C4 level cervical cord injury person.
Many people with lower limb disabilities use wheelchairs, but their degrees of physical impairment vary greatly. We direct our investigation to manual wheelchair users who are able to lift the front wheelchair casters independently. They hope to establish an independent life without assistance to the greatest extent possible. We developed a pair of step-climbing units that can be installed in a standard manual wheelchair. This mechanism is simpler than any other because it uses the remaining capabilities of the wheelchair user. Each unit comprises two actuators and has two degrees of freedom: a telescopic motion and a rotational motion. We mainly discuss the step-climbing motion using this system. Experimental results obtained when ascending and descending a step of 15 cm height confirm the design's effectiveness.
A self-tuning negative capacitor is proposed for a piezoelectric shunt damping system; unknown capacitance of the piezoelectric element is estimated by an online estimator without introducing additional sensors and the negative capacitor is tuned based on the estimated capacitance. Appropriate selection of bandpass filters and an excitation signal is studied in the frequency domain analysis. Then, it is shown that the estimated capacitance includes the piezoelectric effect coupled with the mechanical system and that the estimated capacitance is actually applicable to the adaptive negative capacitor. The effectiveness of the proposed method is demonstrated by experiments.
In this paper, the phenomenon of vibration and noise in a small fan motor caused by electromagnetic forces were experimentally investigated. First, vibration characteristics of the fan motor in a non-operating state were determined by experimental modal analysis. Next, vibration and noise characteristics of the fan motor in an operating state were determined. The rotational speed was continuously decreased from 2200 r/min to 1200 r/min while the measurements were taken. A detailed frequency analysis was also performed to investigate the directional patterns of noise at the rotational speed which the significant resonance were confirmed. In addition, analysis on the vibration and noise of the fan motor after turning off its power were performed. As a result, it was found out that the significant vibration and noise were generated in the axial direction, and were resonance phenomena between harmonic frequency of electromagnetic force and natural frequency of the fan.
In this paper, a new vibration isolator using origami-based foldable structures is proposed and numerical simulation is performed to evaluate the performance of the isolator to prevent structural vibration. It has been known that the origami-based foldable structures using Kresling's pattern have bistability. However, that is true only if the bar elements which the structure comprises are uniformly distorted in order that the structure is symmetrically folded. To realize the bistability of the structure, we propose to apply additional linear springs to the original structure. In the first design, linear springs are applied, connecting diagonal nodes of the bar elements. In the second design, they are applied along to the axial direction of the structure. It is confirmed by numerical simulation that these designs successfully provide the bistable folding behavior and therefore, the structure with additional linear springs can work as a vibration isolator around the region that the total spring stiffness of the whole structure reaches the relative minimum value that is close to zero.
We aim to clarify the mechanism of the release point of the golf swing and the effect of the parameters of a club and a human body on dynamic behavior at the release point. First, the mathematical model of the golf swing is assumed to be a 2-dimensional double pendulum connected with a nonlinear rotational spring at the wrist joint. By applying Lagrange's equation to this system, we derive equations of motion of the golf swing. We consider that the wrist joint begins to turn naturally under the centrifugal force of the swing. When the angular velocity of the arm and the centrifugal force become to be sufficiently large compared to the angular acceleration and tangential inertial force, uncocking begins naturally without driving torque applied to the wrist joint. We derive simple approximate equations which express the relationship between angular velocity and acceleration at the release point. By using the derived equations and the equations of motion , we also derive some expressions demonstrating the effect of the parameters of a golf club on the dynamic behavior at the release point which may affect significantly on the head speed by using new modeling method, and calculation and discussion are carried out on the effect of the parameters of the club , the cock angle and the active wrist torque on the release point. Through the discussion, it can be seen that the derived simple approximate equations give us physical insight of the phenomena at the release point and help us to understand the effect of the club parameters on the dynamic behavior of the double pendulum at the release point.
In general, internal cells are required to solve nonhomogeneous elastic problems using a conventional boundary element method (BEM). However, in this case, the merit of the BEM, which is an ease of data preparation, is lost. In this study, it is shown that two-dimensional nonhomogeneous elastic problems of functionally gradient materials can be solved without the use of internal cells, using the triple-reciprocity BEM. The triple-reciprocity BEM can be applied to thermo-elastoplastic problems with arbitrary heat generation and to three-dimensional elastoplastic problems without internal cells. In this paper, Young's modulus and Poisson's ratio are variable in nonhomogeneous elastic materials. In this method, boundary elements and arbitrary internal points are used. The distribution of fictitious body force generated by a nonhomogeneous material is interpolated using boundary integral equations. This interpolation corresponds to a thin plate spline. In this paper, elastic analysis is carried out for laminated materials, porous materials and a particle-dispersed composite as special cases of functionally gradient materials. In the case of composite materials or a layer structure, the distribution of Lame's constant is not continuous. However, the same interpolation method can be used for special case of nonhomogeneous material. A new computer program is developed and applied to several nonhomogeneous elastic problems to clearly demonstrate the theory.
An analysis program of predicting the movement of magnetic particles in flow, gravity, and magnetic fields was applied for magnetic separation process in a small vessel of an in-vitro diagnostic system. This program evaluates not only the drag, gravity, and magnetic force in a flow field but also the friction force between a particle and a wall. The friction force was simply modeled as static and dynamic friction forces. The coefficients of the static and dynamic friction forces were determined by comparing simulated and measured magnetic particles capturing distributions. Using this program, we evaluated capturing time and distribution on the wall of the vessel by changing number of magnets, magnet arrangements, and magnetic coercive forces. Capturing distribution of the magnetic particles depends on number of magnets and magnet arrangement, and becomes specific pattern according to the magnetic field generated by magnets. Number of magnets and magnet arrangement can also change capturing time. Especially, magnet arrangement with alternate magnetic pole becomes more uniform distribution and shortens capturing time. Magnet arrangement with stronger magnetic coercive force makes the capturing time short. This simulation method for solving multi physics problems is very effective at predicting the movements of magnetic particles and is an excellent tool for the development and design of devices.