An underexpanded radial jet is generated downstream of intake and exhaust valves of an internal combustion engine, a pressure control valve and so on. In addition, when a supersonic jet issuing from a circular nozzle impinges on a flat plate, the wall jet on the plate often becomes underexpanded and spreads out radially. The underexpanded jet has typical shock-cell structure and strongly oscillates and its behavior is known to cause many industrial problems. In this study, a jet structure and an emitted noise from an underexpanded jet radially discharged from a circular slit nozzle, which consists of two circular tubes, are examined experimentally for different nozzle pressure ratios and different diameters of tube, and the experimental results are compared with those of a two dimensional jet issuing from a rectangular nozzle. As a result, multiple ring-shaped shocks are visualized in the radial underexpanded jet, and the sound source of noise measured is found to be in the vicinity of the end of the second cell. Furthermore, collapse of the cellular structure of radial jet occurs upstream in comparison with the case of rectangular jet and the length of second cell is shown to be one of the most important parameter of a frequency of the emitted screech tone.
Selected from various eigenmodes of blading, nodal diameter κ= 0 and κ= 1 are both related to shaft torsional and/or axial vibration and shaft bending vibrations respectively. In order to avoid the possibility of 2f (f=power system frequency) from torsional vibration resonance, ISO regulates the final calculation results considering the combination betweenκ= 0 blade and torsional shaft vibration. The combination between κ= 1 blade and shaft bending vibration may become increasingly problematic as industry moves toward blade upsizing. This study explains a global method for blade-shaft coupled vibration analysis governing bothκ= 0 and κ= 1 in a systematic manner. According to our methods, the uncoupled blade vibration is first calculated for eigenvalue solutions using a general-purpose code of 3D-FEM (Finite Element Method), such as Nastran®. This solution provides a simplified blade model based on the concept of mode synthesis. Based on this blade model of our small scale test rotor, coupled vibration analysis was completed using the following two methods: -1) A simplified model of a shaft system was also prepared in a similar manner, and the two reduced models were then combined to understand the blade-shaft coupling system. 2) A 1D-FEM code specialized for shaft vibration analysis, defined as only beam elements, was connected with the prepared blade model to analyze the coupling effect. - These two methods provide numerical solutions that are approximate and within practical accuracy. As a result, it is a suitable alternative when a 3D-FullFEM evaluation is not possible on actual machines like large scale turbine generator sets.
A planetary gear train (PGT) is one of the most important components in the hybrid and electric vehicles owing to its high torque-to-weight ratio, light weight, and compactness. But transmission mechanism is still unclear due to structural complexity. Planet gears make PGT complex because of its motion (simultaneous rotation and revolution) and different contact ratio, or meshing stiffness between internal meshing (ring-planet) and external meshing (sun-planet). Although many experimental studies about PGT’s steady condition had been conducted all over the world, no studies have proved motion of planet gear experimentally. In this paper, planet gear instant center of rotation (ICR) is found out based on its velocity distribution and it was proved with direct motion observation on planet gear motion by high speed monitoring. ICR is expected to be effective to estimate meshing transmission errors (MTE) with its feature like light lever. MTEs in a PGT were also discussed based on the fluctuation of trace of ICR, or centrode.
Sound masking is a method that used for protecting speech privacy of conversation at public open space such as a pharmacy or a bank window. In a conventional masking, a masking sound is used to cover contents of conversation. This masking sound which is generated from a loudspeaker allow a third party not to understand what is said, but there is a problem that the sound level is increased because of a masking sound. Against this problem, we proposed Low-noise sound masking method using active noise control (ANC). The approach of this method is to make spectrum of phonemes flat by control sound. It is difficult to recognize phonemes that are processed by this method because the major factor determining the phonemes in speech recognition is the relative relationship of the peaks of its spectrum. In this paper, the sound attenuation performance of the proposed method is validated by control experiments in an anechoic chamber. Moreover, a listening experiment is carried out to investigate the sound masking performance. The result show that comparing with the conventional sound masking method, the proposed method can achieve the sound masking effect with a smaller sound pressure level.
In this paper, we aim to clarify the effect of cutting direction on the cutting characteristics of polyethylene terephthalate (PET) film with mechanical anisotropic properties during the wedge indentation process. In order to reveal the difference in the cutting line force due to the cutting direction, the wedge cutting force on the PET film was experimentally measured by choosing the cutting direction as the machine direction (MD) and the cross machine direction (CD), while the cutting profile of the PET film was observed from the side line direction. From the experiment, the cutting line force of PET film in orthogonal to CD was the larger than the cutting line force of PET film in orthogonal to MD. It was found that there were three deformation modes of the cutting profile and the occurrence frequency of these modes was changed with respect to the cutting direction. In addition, a finite element method (FEM) analysis was carried out to compare the cutting profile and the internal stress state in the sheared zone due to the difference of the cutting direction and the lubrication state. It was clarified that the cutting deformation of the PET film at the necked stage was characterized by the tensile test based mechanical properties and the frictional coefficients with the wedge blade and the underlay.
The relationship among strength, ductility, toughness and microstructure was studied in order to find out microstructure image of stronger and tougher steel. Initial samples with two different microstructures, ferrite-pearlite and martensite (and/or bainite), were prepared and then caliber rolling was conducted at warm working temperature. Two kinds of low carbon steel bars with ultrafine elongated grained (UFEG) structure in transverse grain size of 1.0 μm and 1.3 μm, respectively, were produced. For comparison, conventionally quenched and tempered 0.29%C steel and 1.03%C steel with a martensitic structure and low-carbon steel with ferrite (grain sizes, 10μm and 18μm)/pearlite structure were also prepared. The Charpy impact and static tensile tests were conducted at a temperature range from 200°C to －196°C. The reduction in area and the plastic deformation limit were used as a universal parameter of ductility. In the Charpy impact test, only the UFEG steels fractured with delamination crack, the delamination remarkably appeared near energy transition temperature and the impact energy becomes larger than all other steels. As a result, the UFEG steel with transverse grain size of 1.0 μm was best balance in correlation between strength and ductility and between strength and toughness.
Digital Image Correlation (DIC) method was applied to measure the strain fields around the crack tip in a Ni-base single crystal superalloy. DIC systems were assembled to appropriately measure the strain fields at room temperature, 700°C and 900°C. Influences of crystallographic orientation and temperature on the crack tip strain fields were investigated. A series of measurement at room temperature revealed that cracks propagated in shearing mode and the strain fields around the crack tip were strongly affected by anisotropic plastic deformation along the octahedral slip system. Based on the shear strain components along the slip systems, effect of the crystal orientation on the strain field was visualized, and the visualized strain field provided a reasonable explanation on the crack propagation path and propagation rate. At 700°C, on the contrary, cracks propagated in opening mode and symmetric shear strain fields were measured around the crack tip. Temperature dependent strain fields and resultant cracking modes were explained by the slip system activity which was also influenced by temperature. The present DIC systems could measure the strain field even at 900°C, and it was found that the strain around the crack tip was higher at 900°C than that at 700°C.
It has been long since the technology for human space flight system was established. In order to realize challenging manned space missions, further improvements in the system reliability and crew safety are essential. Comprehensive design and operation considerations based on the quantitative crew safety analysis are key issues. Crew injury risk prediction method due to the transient dynamic load such as the excessive water landing speed, the explosion overpressure, and the off-nominal acceleration of the launch abort system (LAS) are developed and investigated in this study. In the early design stages, parametric injury risk analysis should be carried out. For this purpose, an anthropomorphic test device (ATD) model based on the multi-body dynamics is suitable to cover the wide range of conditions. In addition, an human finite element model is employed for more detailed crew injury risk analysis. Although there have been comprehensive research efforts in the automotive safety fields for many years, further research efforts are needed for the crew safety of human space flight since a wider range of the magnitude and the direction of the impact load should be considered. This paper deals with the human injuries evaluation using finite element model. The results are compared with those using Hybrid-III and safety margin is evaluated in view of NASA injury criteria to extract highly damaged body region in both models. The validity of brain injury criteria BrIC is investigated by using mechanical properties in brain and new risk curve for BrIC suitable for LAS environment is finally proposed.
Under certain weather conditions, avalanches can occur because of snow cover on a steep slope. Such avalanches can reach snow fences that are arranged as countermeasures. Furthermore, traffic is completely blocked when fences collapse and snow falls on a road. Therefore, prediction of avalanche occurrence is important, but such predictions are considered difficult. To resolve this difficulty, this study assessed measurement of the danger degree by measuring the risk to the avalanche fence at the time of snowfall and falling rock according to changes in the load and the impact of voltage proportional to the avalanche barrier deformation. This measurement system has fixed sensors attached with mounting brackets to a dedicated avalanche prevention measurement fence. It measures the pressure and vibration measurement of the snowfall at the time of avalanche or rock fall occurrence at the main structure of the fence. Furthermore, this fence made of lumber from thinned timber is useful as a defensive barrier countermeasure against avalanches and falling rock. It is designed to withstand a snow load of 3–5 [t/m2] during an avalanche.
A novel two-limb six-degrees-of-freedom (dof) parallel robot redundantly driven by eight actuators is proposed. The proposed robot was named Atarigi Carrier or ATARIGI for short. An atarigi is a long wooden pestle, an instrument used in Japanese cooking. A chef holds an atarigi with his two hands and grinds sesame and miso paste in a large mortar bowl. The precessional motion of the robot is similar to that of a Japanese chef using an atarigi. The mechanism of ATARIGI has a two-layer structure in which the eight-dof actuators control six-dof hand via seven-dof internal mechanism. The first part of the hierarchy from the eight-dof actuators to the seven-dof internal mechanism has actuation redundancy, and the second part of the hierarchy from the seven-dof internal mechanism to the 6-dof hand has kinematic redundancy. ATARIGI is a novel parallel mechanism which simultaneously has kinematic redundancy and actuation redundancy. The kinematic redundancy contributes to singularity avoidance, while the actuation redundancy contributes to backlash removal by acting on the internal forces of the mechanism. These redundancies enable the proposed parallel robot to have a large workspace by avoiding the singularity and high accuracy by removing the backlashes. Closed-form solutions for forward and inverse displacement analysis, and forward and inverse kinetostatic analysis were derived. The derived solution was implemented using MATLAB and Mathematica, and the validity was verified by numerical calculations.
In this study, the automated process planning system for end-milling operation is realized. This study considers to minimize the number of times of tool change and to determine the appropriate machining sequence in the process planning. In our previous process planning system, the machining sequence is calculated geometrically, based on the Total Removal Volume (TRV) and the machining regions split from TRV. However, it remains difficulty to determine the best machining sequence from the large number of the calculated machining sequences. The previous process planning systems also do not consider machining conditions in the determination of the appropriate machining sequence. First, our new process planning system generates the association chart of machining regions, which represents the geometrical constraints to determine machining sequence. According to the association chart, the candidates can be selected from the enormous candidates of the machining sequence. Subsequently, our new process planning system determines the best machining sequence under considering the machining conditions. The best machining sequence is determined to minimize the number of times of tool change. A case study was conducted to show the effectiveness of our new proposed process planning system, and the machining sequence was automatically determined based on the geometrical constraints considered in process planning and the machining conditions considered in operation planning.
It is required to examine the characteristics of turbochargers for automobiles using one-dimensional simulation from the viewpoint of estimating total engine performance. In this study, a mathematical model to predict mechanical loss generated in a turbocharger is proposed. Friction works generated in a journal bearing and a thrust bearing are modeled, separately. As for the calculation of the friction work with the thrust bearing, the thrust force is calculated from the fluid force which is formulated analytically and calculated numerically based on one-dimensional flow taking account of relevant boundary conditions. According to the developed model, the friction work generated in a journal bearing is larger than that in a thrust bearing. Difference of thrust force and flow rate of oil has less impact on the friction works in a turbocharger. Finally, calculated total friction work based on the model proposed in the present study is compared with that obtained from the oil temperature method.
Words are communication media to share a concept in a community. A word involving ambiguity represents multiple concepts depending on a context. Such ambiguity causes misunderstanding between people having different contexts. On the other hands, a community uses words to obtain responses and/or evaluations from target population, such as customers and participants. The word ambiguity causes misunderstanding between a community and a target population due to different contexts. A community dealing with multiple languages (e.g. multinationals) has a difficulty in translation if there are no words in a second language, all meanings of which do not correspond to all meanings of a word one wishes to translate. To deal with above issues caused by word ambiguity, I propose a multilingual semantic networks(MLSN) framework in this paper. The MLSN is a graph where multiple languages words, as nodes, are semantically linked through concepts, as another type nodes. I implemented MLSN in a graph database with datasets of WordNet in three languages: English, Japanese, and French. With MLSN, I conducted two analysis. In the first analysis, I investigate the meanings of ambiguous words such as “design” and Japanese word “Kansei”, and their semantic relations with relevant words in other languages. I found that there are no words corresponding to all meanings of those words in second languages. For the word “Kansei”, I illustrate semantic relations with words such as “emotion”, “affect”, “feeling”, “impression”, and “intuition” which are often used to define “Kansei”. In the second analysis, I discuss how MLSN supports to select and translate a set of words used as evaluation descriptors. I analyze 10 positive emotion words from well-established Geneva Emotion Wheel and their translation in French and Japanese. I demonstrate how MLSN automatically find translation mismatches and semantic independence between emotion descriptors.
Under the existing method based on a detailed equation for evaluating the wind speed that can cause a vehicle to overturn, it is assumed that the crosswind blows the vehicle at the same wind speed uniformly over the entire length of the vehicle body along the track. However, taking into consideration the actual wind state, there is a wind speed distribution over the length of the vehicle body and there is a high possibility that the crosswind does not blow at the same wind speed over the entire length of the vehicle body. Therefore, if the wind speed distribution is considered, it becomes possible to evaluate the critical wind speed in more detail. In previous research, an evaluation formula of aerodynamic force in consideration of the wind speed distribution has been proposed with the natural wind direction assumed to be 90 degrees. On the other hand, the calculation of the wind speed that can cause a vehicle to overturn requires extending the evaluation formula so as to be applicable to the other natural wind directions. In this study we proposed, extending the existing evaluation formula, a method of calculating the critical wind speed in consideration of the spatial fluctuation of wind speed. We also evaluated the critical wind speed for the combination of the vehicle and the track constructions with the proposed method. In addition, we also evaluated the critical wind speed in accordance with changes in the height of the center of the car body from the ground and the roughness length. As a result of the evaluation, we confirmed that the critical wind speed increases by up to 1.4m/s, provided that the vehicles and railway structures are those assumed in this study.
It has been shown that passengers have large reduction effect on the elastic vibration of a railway vehicle car body. That effect is considered due to the viscoelastic motion and multi-directional motion of a human body. This study focuses on the latter one and aims to develop a new vibration reduction device to mimic the multi-directional motion of passengers. In this paper, an experimented multi-directional dynamic vibration absorber (called MDDVA in this report) is developed. The MDDVA consists of a steel ball supported resiliently by elastic balls bottled in a rigid cylindrical vessel. The steel ball can vibrate multi-directionally in the vessel and is expected to work as a MDDVA. In addition, the natural frequency of the MDDVA can be changed by pressing the elastic balls from the top. To evaluate the effectiveness of the MDDVA, excitation tests by means of a scale model of a railway vehicle is conducted. As a result, the MDDVA can reduce the elastic vibration by adjusting the natural frequency of MDDVA to that of the scale model, and multi-modal vibration reduction effect is successfully observed. And then, FEM models of the MDDVA and a scale model of the railway vehicle are constructed to verify the mechanism of the multi-modal vibration reduction. As a result of the FEM analysis, it is confirmed that the multi-directional motion of the steel ball produces the multi-modal vibration reduction effect.
This paper presents motion prediction model of cyclist based on potential field for a hazard-anticipatory collision avoidance braking system to enhance the collision avoidance performance and secure the smoothness of driving. The target situation is chosen as the scene that a cyclist overtakes a pedestrian or another slowcyclist based on the traffic survey. The 1st order motion predictionmethod reaches its limit under the situation that a cyclist runs towards a pedestrian or another cyclist as the prediction is conducted based on the current position and velocity of cyclist within a finite time horizon. If the overtake action of cyclist can be predicted before the cyclist changes moving direction, the vehicle maneuver to avoid collision with cyclist can be executed in advance without activating harsh braking. The trajectories of cyclists overtakes a pedestrian and a slower cyclist is measured to find the characteristics in overtake action.Motion prediction model of cyclist based on potential field is constructed by considering the trajectory analysis. The effectiveness of the proposed prediction model in the target scenario is verified by comparing the measured trajectory with the calculated data based on 1st order prediction and the proposed method.
This paper describes the use of nine-axis motion sensors to evaluate the motion sensor position on the thigh and lower leg during walking. The motion sensors are mounted on a subject's body using adhesive tape. The muscles constantly relax or contract because of human movement. Therefore, joint angle estimation using motion sensors produces different accuracy depending on the position where the motion sensor is mounted. Evaluating the motion sensor position is important for improving the joint angle estimation accuracy. For this study, the authors used six nine-axis motion sensors and a 3D motion analysis system to assess walking exercise. Three motion sensors were mounted to the thigh; three were mounted to the lower leg. The knee joint angle was estimated using a sensor fusion algorithm that corrected the centrifugal acceleration and the tangential acceleration in the acceleration sensor output. We evaluated the accuracy of knee joint angle estimation by comparing the nine-axis motion sensor results and the 3D motion analysis system results. Results demonstrated the possibility of high-accuracy estimation when the motion sensor is attached to a position 50% or 75% from the upper end of the thigh and another sensor is attached to a position 25% or 50% from the upper end of the lower leg.
Weld-joint has been atracting attention to assemble structures of dissimilar metals, particularly in automobile industry. However, the application of weld-joint to steel and aluminum plates is still limited due to uncertainty of the fatigue strength. Fatigue strength of weld-joint is rather complicated to evaluate because both effects of stress concentration at the edge and formation of intermetallic compounds along the interface should be considered carefully. This study focused on finding the key factor that determines the fatigue strength of steel-aluminum brazing joint by considering the variation of strength along interface. The welded part of single lap joint was partially removed by a wire-cut electric discharge machine to investigate the influence of length and location of interface on fatigue strength. When the applied load was relatively low it was found that the numbers of cycles to failure were found to be similar, even though the lengths of interface were different due to partial removal. Furthermore, observation on the fracture surface indicated that early stage of crack propagation showed similar topography regardless of the partial removal of weld part. These results clarified that the number of cycles to failure was mainly consumed at the early stage. Finite element analysis was then conducted to investigate the stress component affecting the fatigue strength. As a result, principal stresses were maximum at the fracture initiation site in all the specimens. Therefore, we concluded that fatigue life of weld-joint is dominant in the early stage of crack propagation, which is characterized by the principal stress.
We constructed a coarse-grained (CG) water model based on non-Markovian dissipative particle dynamics (NMDPD) taking into account memory effects. The NMDPD equation of motion was derived from a generalized Langevin equation formulated via the Mori–Zwanzig (MZ) projection operator. We extracted a CG pair potential and memory kernels between clusters comprising 10 water molecules by means of molecular dynamics (MD) simulations. We found that the MZ-guided CG potential followed by an iterative Boltzmann inversion correction resulted in an accurate representation of both a radial distribution function and pressure. Furthermore, in contrast to Markovian DPD, the NMDPD model exploiting MZ-guided memory kernels could reproduce short-time dynamics originating from molecular collisions, which was characterized by decaying nature of a velocity autocorrelation function (VACF). The NMDPD model was also able to reasonably represent the viscosity of the MD system compared to the conventional DPD, where interaction parameters were phenomenologically tuned such that a few macroscopic properties were reproduced, leading to a significant underestimation of a viscosity or Schmidt number. Finally, the differences of the viscosity and long-time behavior of the VACF between MD and NMDPD systems implied the necessity of a more appropriate description for a one-to-one correspondence between a CG particle and a water cluster.
The purpose of this study is to propose the quantitative evaluation indices for the hemiplegic gait characteristics by accelerometers attached to the right and left lumbar part. Subjects are 16 patients with hemiplegia, 8 males and 8 females whose ages are from 46 to 83 years. Twenty-six healthy adults also participated as a control group. An FFT analysis for both hemiplegic gait and healthy normal walking test results is carried out paying attention to the component with frequency of 0.5fw (half frequency component of the gait cycle fw) . Based on these analytical results, it is revealed that the component with frequency of 0.5fw in the fore and after direction is obviously prominent for the hemiplegic gait compared with measured values of healthy normal gait. The parameter PR is defined as the power spectrum ratio of 0.5fw to fw component. The relationship between gait stage (GS) and PR is investigated for both subjects of hemiplegic patients and healthy adults. Dynamic load factor (DLF) corresponding to the vertical walking force and lateral displacement of the waist are also calculated using power spectrum density for time history signals measured by the accelerometers. This led to the conclusion that the parameter PR in the fore and after direction, DLF in the vertical direction and lateral displacement of the waist are the useful evaluation indices for the hemiplegic gait analysis from the viewpoint of rehabilitation medicine.
In recent years, alkaline water electrolysis is receiving much attention on environmental issues because of hydrogen production using renewable energy. However, it is necessary to enhance the efficiency of electrolysis. One of the main causes that have effect on efficiency of alkaline water electrolysis is presence of bubbles in electrolyte. It is important to investigate the relation between bubbles behavior and efficiency of alkaline water electrolysis system. In this study, the calculation model to realize coupled simulation of ion transport, electrochemical reaction and bubbles behavior is developed and the impact of convection induced by bubbles on alkaline water electrolysis is investigated by numerical simulation. As a result, it is found that convection induced by bubbles has impact on mass transport around anode and has an effect on the efficiency of alkaline water electrolysis. Convection induced by bubbles in the vicinity of anode has an effect on ion transport to anode and anodic concentration overpotential. However, as bubbles depart from anode, this effect becomes small because convection removes ion from anode. Moreover, convection induced by bubbles shortens ion transport pass between electrodes and has an effect on ohmic loss.
Cycle-to-cycle variation (CCV) of combustion is an important issue because it affects emissions and drivability. Improvement of CCV of combustion has been carried out using electronic controls (e.g. ignition timing, fuel injection and variable valve timing) in motor vehicle's engines. However, electronic devices are hardly used for motorcycle's engines because of limited space and cost. Therefore, the engine performance itself must be improved to reduce CCV of combustion in motorcycle. Though CCV of combustion is caused by CCV of in-cylinder flow pattern, fuel distribution, temperature and residual gas, and ignition energy, it is difficult to measure and analyze these factors. In this study, the simultaneous measurement of high-speed PIV and direct photographing of flame propagation was carried out. CCV of in-cylinder flow was evaluated as time-averaged flow that was obtained by instantaneous flow using low-pass filtering and cut-off frequency. As a result, in-cylinder timeaveraged flow pattern fluctuated between individual cycles. Especially, the flow pattern on the surface of piston at BDC was different between the highest and the lowest cycle in IMEP. This difference is considered to be due to the location offset of tumble flow. Also the fluctuation of turbulence kinetic energy (TKE) is caused by tumble flow offset. TKE distribution near the spark plug at ignition timing affected the direction and speed of flame propagation.
Possibility of the higher combustion efficiency using the oxy-fuel combustion technology has been studied from the thermodynamic point of view. The energy consumption and the change in entropy were calculated for the case of the normal air combustion, the regenerative combustion, and the oxy-fuel combustion. The energy consumption and the change in entropy were compared and discussed for three cases. For the oxy-fuel combustion, the energy required to produce the pure oxygen from the air was considered. The regenerative combustion was the case in consideration of a heat recovery. As a result, the thermodynamical potential of the oxy-fuel combustion is higher than that of the normal air combustion when the exhaust gas temperature is high. The thermodynamical potential of the regenerative combustion depends on the heat recovery efficiency of the regenerative system. The thermodynamical potential of the oxy-fuel combustion is lower than that of the regenerative combustion for the lower exhaust gas temperature, but for the higher exhaust temperature that of the oxy-fuel combustion is higher than that of the regenerative combustion.
It is well known that the dropwise condensation on a hydrophobic surface has a larger heat transfer coefficient than the filmwise condensation. Larger droplets in ordinary systems depart from the condensing surface by the gravity or the shear-force of vapor flow and the bare surface is created for the rapid condensation, resulting in higher heat transfer performance. However, those forces cannot be expected in the micro- and nano-systems because the spaces for the liquid and vapor flow are limited. In order to obtain the larger condensation heat transfer rate, it is necessary to use high heat transfer characteristics of microscopic droplets together with developing a new method for removing the grown droplets from the condensing surface. A challenging work has been carried out in the present paper to remove the droplets effectively, where the micro-scale groove patterns were fabricated with the hydrophobic and hydrophilic surfaces. The experimental results have shown that the condensation heat flux on the micro-structured surface is 1.4 times enhanced compared with the milli-scale structure. For further heat transfer enhancement, improving the drainage ability is required to reduce the condensate flooding.
In late years, from the viewpoints of drying up of fossil fuels such as oil or coal, and prevention of global warming, the renewable energy such as solar power generation or wind power generation attracts attention. The wind power generation can generate electricity with relatively low cost in renewable energy. A highly efficient propeller type wind turbine is generally used for wind power generation, but disadvantages are that the posture control to the direction of the wind is needed, and propeller type wind turbine is noisy. The Darrieus type wind turbine has the features that the control for wind direction is unnecessary, and the low noise, which is suitable for using in a residential area. In this paper we improve the performance of the wind turbine by mounting the cylinder type flow guide in a Darrieus type wind turbine. The guide ratio defined as the ratio of cylindrical guide diameter against wind turbine diameter was examined by experiment varying chord length. As a result, it was clarified that the wind turbine with guide ratio rd /ld=0.45, number of wings N=3, wing cord length lc=80 mm indicated the highest power coefficient Cpmax =0.172. Moreover the flow around wing was calculated by LES under the conditions with and without cylindrical guide. As a result, it was clarified that the performance of wind turbine with cylindrical guide was improved by decrease of separation on suction side wing surface.
This study investigates the flow control of backward-facing step flow by a dielectric barrier discharge (DBD) plasma actuator. The DBD plasma actuator is mounted onto the edge of the backward-facing step, and is driven by burst modulation. Velocity measurements, flow visualization, and pressure measurements were carried out.The results demonstrated that the reattachment point is dependent on the burst modulation frequency. When the reattachment point is moved upstream, the vortex frequency in the downstream shear layer becomes to equal the burst modulation frequency. When the reattachment point is moved downstream, the fluctuation of the shear layer weakens, and the shear layer narrows to a width that is less than that of downstream non-control. When the duty ratio of the burst modulation drive is outside of a certain range, the effect of control is reduced. In the case that the reattachment point moves upstream, the upper limit of the duty ratio at which the control effect does not change is determined by the off-time length of burst modulation, whereas the lower limit of the duty ratio is determined by the on-time length of burst modulation. In the case that the reattachment point moves downstream, the upper limit of the duty ratio at which the control effect does not change is independent of the modulation frequency.
Today, automation of various work using robots is progressing in the industrial field . For robotized automation, we must teach motion to industrial robots. However, small and medium-sized enterprises which make various products in relatively small scale cannot introduce such robots because teaching takes long time. In this research, in order to solve this problem, we have proposed and developed a new motion teaching method which can be done easily and fast. Motion teaching takes long time because of robot installation error and absolute position error. Therefore, robot motion teacher needs long time to do remote teaching. Thus, we propose a new motion teaching method that can ignore influence of these errors. By marking work places and capturing work targets using RGB-D camera attached to robot's end-effector, we generate motion paths in the robot coordinate system and robot can ignore influence of those errors. In order to verify the feasibility of the proposed method, we constructed a recognition algorithm for work subjects, work places and working environments using RGB-D camera. After that, the time required for motion teaching was compared between the proposed method and remote teaching through actual machine experiments. From the results, we suggest that proposed motion teaching method can perform in about half the time of remote teaching.
We developed a new prediction technique for dynamic stress on a bellows with low computational load, to secure the strength reliability of the multilayer bellows used in the engine exhaust system of hydraulic excavators. In this developed technique, dynamic stress is predicted by constructing the bellows finite element model with single-layer shell elements having stiffness equivalent to that of the multilayer bellows and selecting appropriate excitation conditions for each stress-generating factor. The stress time waveform calculated by the developed prediction technique was verified by actual measurement results, and the following conclusions were obtained: (a) The causes of dynamic stress on the bellows were specified and classified into the two classifications. One is the deformation of the bellows caused by relative displacement. The other is the deformation caused by the bellows vibration modes; (b) Appropriate excitation conditions of the bellows model are forced displacement input for predicting dynamic stress caused by relative displacement, and forced acceleration input for predicting dynamic stress caused by the bellows vibration modes; (c) The calculation results derived by using the above model and the excitation inputs were verified by measuring a vibration bench test. The calculated stress had relative agreement with measured stress in the test.
Conventionally, the transfer path analysis (TPA) targeted in this study is an experimental method capable of specifying a path to be countermeasured, which has a large contribution to response from among multiple paths by multiplying the external force and the transfer function. Although there are practical examples of application to automobile development, enormous experiments using actual equipment are necessary; it is not easy to grasp the transfer characteristics of vibration and to study countermeasures. Therefore, in this study, we focus on TPA method using Finite Element Method (FEM). In previous study, TPA based on FEM was applied to a mechanical structure having the multiple transfer paths, the structural modification guideline for the path structure itself connecting the subsystem including the vibration source and the subsystem including the vibration receiver was proposed. However, the proposed method is effective only when the contribution of one path is dominant at the target frequency, and no improvement method has been proposed when the contributions of multiple paths are dispersed to the same extent. In this study, to solve these problems, we propose a method to evaluate contribution obtained from TPA using numerical model for each degree of freedom component of transmitted force, by calculating the six degrees of freedom component (three direction force and three direction moment) of the macro transmitted force of the object cross section of each transfer path and the transfer function. By evaluating the contribution for each degree of freedom component of each section force, it is possible to intuitively grasp the phenomenon and to propose an effective structural change proposal for the target degree of freedom, so clarification of the structural change guideline can be expected.
This paper proposes a methodology for estimating airborne noise from a mechanical system in the operational conditions by component tests of a certain active subsystem which is a part of the mechanical system and includes all of vibration sources in the mechanical system. The mechanical system consists of the active and passive subsystems, and supporting structure of the active subsystem is different from that in the component test conditions. Hence airborne noise from the active system in these two conditions are different from each other. Therefore the in-situ blocked force approach is expected to estimate airborne noise in the operational conditions by the component tests, because blocked force is a specific characteristic of the active subsystem and independent from its supporting structure. However it is reported that the in-situ blocked force approach is suitable for estimating structure borne noise and cannot be applied to airborne noise, it has been found that the in-situ blocked force approach can be approximately applied to airborne noise in resonant frequency of the mechanical system. This paper describes theoretical derivation of the approximation error caused by applying the in-situ blocked force approach to airborne noise. Furthermore, the error is evaluated by means of a 3-DOF simple model.
Numerical simulations, such as the finite element method have been widely used to predict noise and vibration behavior. This allows reducing the development time and production cost of products. However, these results have been calculated based on the governing equations at each physical areas as the idealized conditions. Then, these simulations are not taken into account the fluctuation of response characteristic by the uncertainties of noise factors. Therefore, it is important to restrain the fluctuation of products properties by the uncertainties. In order to mitigate the fluctuation, robust optimization that is combined used of the stochastic finite element method and structural optimization will be introduced. Moreover, finite element models for vibro-acoustic simulations typically induce a high computational cost especially time history response analysis. In order to alleviate this problem, model order reduction is proposed to reduce the number of degrees of freedom while maintaining a desired accuracy. In this paper, focusing on the transient analysis, we propose a robust design method that combined use of the model order reduction and robust optimization. Then, the proposed method is validated by applying it to the vibro-acoustic systems whether the fluctuation of the time history response amplitude and the computational cost are restrained.
In this study, both a new damper concept and its mathematical model are proposed. Basically, a damping force for an oil damper depends on a stroke speed. Therefore, a damper becomes stiff in a high speed stroke if a higher damping coefficient was set up to improve a dynamic performance. As a result, a ride comfort for a vehicle would be spoiled. A relationship between a dynamic performance and a ride comfort are trade-off. It is necessary to consider desirable damping force characteristics. However, it is a complicated issue to treat oil dampers theoretically. The study aims to develop a new nonlinear damper and its mathematical model. The damper has two main features: an ease to design a characteristics of damping force and a damping force reduction mechanism. The damping force generation mechanism of the damper is based on a viscous theory. A mathematical model of the damper is also developed using simple formulations. The simulated result of a damping force vs stroke speed using the mathematical model shows a damping force decrease in high piston speed. In addition, the prototype of the damper was developed and tested for the validation of the mathematical model. The simulated damping force characteristics agreed well with the actual one.
This paper proposes a novel structure of an axial gap self-bearing motor. The axial gap self-bearing motor controls both axial force and motor torque by using a similar structure to a disc motor, thus simplifying its structure and control system. In this paper, for further simplifying the structure, the number of stator coils is reduced to four for the side stators in a 4-pole disc rotor. Because one of the side stators produces only a 4-pole magnetic flux, all of the stator coils can be connected in series and driven by the single amplifier. Two stators are required to produce continuous motor torque and the bidirectional axial force; therefore, the drive system is composed of eight concentrated coils and two power amplifiers. To obtain continuous motor torque, the permanent magnets are attached to the rotor with a phase difference of 45 degrees between the two sides of the disc. In this study, the axial force and motor torque of the proposed structure are analyzed theoretically, and a control method for the axial force and motor torque is derived. Experimental results show that the proposed motor can control the axial position and the rotation speed simultaneously.
In order to satisfy the setting settling time and overshoot, a new design method of controller was developed using a model parameter which was approximated as a second-order lag-time system. Then, an effectiveness was experimentally demonstrated as an engine speed controller. In order to operate wide conditions, however, an adaptive ability was required for parameter change. This paper investigated regarding an on-line execution of non-linear least square problem to obtain the changed controlled plant model parameter. A simulation study were carried out and a suitable adaption were experimentally demonstrated.
In recent years, as a natural disaster in Japan, there were damage from the 2011 Tohoku Region Pacific Offshore Earthquake and the 2016 Kumamoto Earthquake. In the event of a disaster, people who are difficult to evacuate can not escape, and sometimes they die. In this research, we investigate damage situation on natural disasters in recent years, and make basic experiments on running experiments simulating bad roads after disasters. Based on the results obtained from experiments, we aim to propose a wheelchair that can be utilized at the time of a disaster or after a disaster. In addition, riding comfort analysis was carried out using the vibration measuring device during the experiment. From the results of the research, it was shown that the introduction of a wheelchair driven vehicle aimed at reducing the load assuming natural disasters is effective. Also, by increasing the size of the front wheel, it is possible to alleviate the gap between the step and the step. It is possible to reduce the load exerted on the body by using a tire with less electric assistance or less resistance.
In railways, on-track running tests are implemented to assess running safety against flange climb derailment. Results of tests depend on the frequency component of measured data. In this paper, the relationship between the measured data of the derailment quotient, which is the assessment quantity of derailment, and wheel rise are investigated. The data for the investigation are obtained in a flange climb running test at low speed on a test track, which includes two sharp curves with cants. Several types of track irregularities, such as track twist, rail misalignment and angular bent at joints, are added to the test track, which are some of factors causing flange climb derailment. Some static wheel unloading is also set at the test vehicle's leading wheelset to induce flange climbing. We show that the derailment quotient data obtained through filter processing with some cutoff frequencies and the amount of wheel rise of the leading outer wheel have a similar tendency in time sequence, which indicates the usability of the filtered derailment quotient data for the assessment of flange climb derailment at low speed. Further, the cumulative value of the derailment quotient which is larger than the target maximum value is examined in order to evaluate the safety margin for derailment more precisely compared to the ordinary assessment by the derailment quotient only. As a result, we propose a new assessment quantity considering the cumulative value, and its target maximum value derived from the wheel rise and running distance.
In order to improve the running performance of a railway vehicle, the authors developed the axle box suspension with the magnetic elastomer. The magnetic elastomer is composed of magnetic particles and the elastomer such as synthetic rubber. This material is characterized by its hardness variation depending on the magnetic field. In this paper, the authors synthesized the bimodal magnetic elastomer containing nonmagnetic particles. In a characteristic test, the authors confirmed that Young's modulus of the magnetic elastomer changed in the range of about 2.2 times depending on the magnetic field. Moreover, the authors carried out a running test on a test line of the MIHARA Test Center. The authors confirmed that the axle box suspension with the magnetic elastomer were able to secure the running stability at 70 km/h without causing an unstable state. In addition, the authors carried out a running test on a test line of the Railway Technical Research Institute. The authors confirmed that the axle box suspension with the magnetic elastomer were able to reduce the outer lateral force of a leading wheelset.
The steering vibrations include the useful information, such as road condition, for the drivers. Therefore, the various evaluations about relations of the steering vibration characteristics and the road information are carried out. In this paper, the human vibration sensitivities of the steering vibration concerned with the road information were evaluated first. It is clarified that the vibration direction of frequency band more than 20Hz can’t be discriminated and the sensitivity of the vibration power is decrease at an incline of 10dB/dec for frequency. Next, the evaluating method of the steering vibration using the steering simulator was examined based on the human vibration sensitivities. As a result, it was clarified that the steering vibration can be evaluated by the vibration combination of the rotational vibration and the translation vibration more than 20 Hz.
This study examines a driver's judgment assistance system at a signalized intersection. The assistance system indicates the evaluation indices on a road ahead virtually using the Head-Up Display (HUD). The HUD for the driving simulator consists of a projector, a screen and a combiner. The assistance system informs a driver visually of the distance which the vehicle can advance by maintaining the present vehicle velocity until the red signal onset. The driving simulator experiments are conducted to evaluate the assistance system with the HUD. The assistance system encourages the driver to make the earlier deceleration before the amber signal onset and prevents the emergency braking behavior. In addition, the assistance system with the HUD maintains drivers' braking reaction time to the emergency deceleration of the preceding vehicle in comparison with the assistance system assuming the HUD, which is directly indicated on the road in the simulated front view. Indicating evaluation indices on the road ahead virtually through the HUD helps the driver to decelerate earlier and avoid the emergency braking maneuver. These effects make it possible to suppress the collision risk to the preceding vehicle and contribute to the safety driving.
Static 4-point bending tests have been carried out with poled PZT under various environmental conditions. The average value of applied stress at which fracture occurred within 48 hours was defined as the delayed fracture strength σdf, and the effects of the environment and the electric field on the strength was investigated. When temperature and humidity of the test environment are controlled, the variation of the fracture stresses are smaller than that in uncontrolled laboratory environment. In the laboratory environment, applied electric field of 400 V/mm decreases bending strength compared with the case of no electric field. Furthermore, σdf decreased by 68 % under high temperature of 40 ℃ and high humidity of 80 %. It was found that delayed fracture strength remarkably decreased due to the synergistic effect of environment and electric field. The effect of electric field was sensitive to the intensity of positive field, and σdf decreased drastically up to field intensity of 200 V/mm. However, under the negative field, the degradation behavior of σdf was different from that under the positive filed. Intergranular cracking is dominant in delayed fracture where crack grow slowly under the condition with high temperature, high humidity and electric field.
To investigate and understand conditions of mutual contact and collision impact between a wheel-flat and a roller rig, we first did a bench test of a bogie with the wheel flat on the roller rig. In the bench test, the effect of the rotational speed of the wheel and the sprung mass on the vertical acceleration of an axlebox was observed. Based on the results of the bench test, we built a dynamic simulation model of the bogie composed of the rigid bodies. By comparing the vertical accelerations of the axlebox calculated by the model with those by the bench test, we could verify that the calculation results of the simulation model provided good agreement with the experimental ones. The model calculation made clear that the wheel rotated contacting the roller rig continuously up to the speed of 10 km/h, and at higher speed had a short period during which the wheel did not contact with the roller rig at the beginning of the flat. When there were any contactless periods, the maximum value of the vertical contact force occurred at the moment of the collision impact just after the contactless state. Particularly at 25 km/h, the impact spot was located around the area from the center to the end of the wheel-flat, and it was revealed by the result of the simulation that differences in the potential energy stored in a compressed axle spring result in differences in the collision velocity of the wheel to the roller rig in a higher speed range than 25 km/h according to the load on the bogie.
In recent years, needs for micro drilling are increasing, accompanying the development of higher wiring density of printed circuit board (PCB). When drilling PCB for the purpose of making the electric through holes, it has been said that surface quality of PCB hole wall is affected by drill temperature. The aim of this study is to clarify the effect of depth of hole, tool wear and chip evacuation on temperature on surface of PCB hole wall using cemented carbide drill. Series of drilling tests of PCB have been carried out to investigate the temperature of cutting edge, dill margin and chips, the cutting torque, the amount of drill wear, the chips evacuation behavior out of drilling hole of the drill and the shape of chips produced during drilling hole. The temperature of cutting edge, dill margin and chips are measured with copper-constantan thermocouples. The cutting torque is measured by a dynamometer; Kistler 9329A. The chips evacuation behavior out of drilling hole of the drill is filmed by a high-speed motion camera and the shape of chips is observed by a microscope. The temperature of cutting edge is higher than that of drill margin and chips. The temperature of cutting edge, dill margin and chips are increasing with an increase of the tool wear. Being filled the chips of PCB in the drill flutes causes an increase of friction between chips and hole wall surface, an increase of temperature of chips.
In order to develop the quantitative model to predict the surface characteristics of austenitic stainless steels from shot peening conditions, the response surface model which represents the quantitative relationship between the shot peening conditions and the surface characteristics of austenitic stainless steels has been constructed by using statistical design of experiments, and the validity of the model has also been discussed. As a result of Fisher's F tests in analysis of variance (ANOVA), the response surface models representing surface roughness parameter RSm, surface hardness (Hv) and surface residual stress (σ), which were constructed in the present study, were statistically significant. It was also found that shot diameter and air pressure of the shot peening conditions were statistically significant factors for the response surface models of RSm and σ, while the shot diameter was the statistically significant for Hv. The predicted values of the surface characteristics estimated from the response surface models of RSm, Hv and σ agreed well with the measured values. It was concluded that the surface characteristics of RSm, Hv and σ for austenitic stainless steels could be predictable from shot peening conditions by using the response surface models constructed in the present study.
Four types of strength tests, slow strain rate tensile (SSRT), fatigue life, fatigue crack growth (FCG) and fracture toughness tests, were performed on six types of aluminum alloys, 5083-O, 6061-T6, 6066-T6, 7N01-T5, 7N01-T6 and 7075-T6, in air and 115 MPa hydrogen gas at room temperature. All the strength properties were not deteriorated in every alloy in 115 MPa hydrogen gas. In all the alloys, FCG rates were lower in 115 MPa hydrogen gas than in air. This was considered to be due to a lack of water- or oxygen-adsorbed film at crack tip in hydrogen gas. Relative reduction of area (RRA) of 5083-O, 6061-T6 and 6066-T6, and fracture toughness of all the alloys were higher in 115 MPa hydrogen gas than in air. These improvements were attributed to a hydrostatic pressure produced in 115 MPa hydrogen gas. RRA of 7N01-T5, 7N01-T6 and 7075-T6, and fatigue life of 6061-T6 in 115 MPa hydrogen gas were almost the same as those in air. These results suggest that aluminum alloy components used in high-pressure hydrogen gas can be designed based on the strength properties in air.
This study proposes a method to measure ground force outside the laboratory using motion sensors. The authors estimated ground reaction force (GRF) from the measurements obtained by a motion sensor at an athletics track with no force plates installed. First, experimental data were measured in the laboratory using motion sensors and a 3D motion analysis system and by motion sensors and force plates. Data were compared using three types of prosthetic foot parts with different shapes and rigidities and were evaluated using a root mean square error method. As a result, the estimation accuracy of the displacement of the prosthetic foot and GRFs were high, and the laboratory experiment demonstrates the accuracy of the proposed method. In the second measurement, the authors measured a 60 m run at a stadium comparing two subjects with different competition levels. The GRF of subject A showed values of 2.8 to 3.5 times the body weight whereas subject B showed a value of 1.8 to 2.5 times the body weight. As a result of comparing trunk momentum and prosthesis side, in the stance phase of subject B, the trunk went up, and only the movement on the prosthesis side was used to obtain propulsive force. This may be due to the timing of the trunk and lower limb being unsynchronized. Furthermore, the trunk momentum of both subjects was compared using wavelet analysis. In Subject B, a larger value also appeared at high frequencies other than the main component. This is considered to be due to a difference in the movement of the lower limb during the swing phase. Based on these findings, this analysis method could be useful, and the GRF measured with this analysis method may be an important index in the evaluation of running motion, parts selection, setting of prostheses, and coaching.
A no-backlash drive control technique which used two motors for forward rotation and reverse rotation to drive one load so as to cancel backlash has been using the same motor so far. However, there is a water gradient on an actual road surface, and we need to turn a steering wheel a little to the right in order to drive the car straight ahead. Therefore, it may be considered to make the right steering motor larger than the left one. In this paper, the effect of the two motor inertia difference on the control system is examined. We evaluate the effect by the analysis and experiment:1) the motor equivalent inertia of the two motors is the geometric mean of the respective inertia, when back calculated from the 1st natural frequency, 2) the damping of the 1st natural frequency increases with an increase in the inertia difference, when the position control gain, the rate control gain, and the reduction ratio are set high, 3) the smaller these set values, the larger the change in the damping characteristic with the inertia difference becomes, 4) the rate control gain has remarkable influence on the change of the damping characteristic , 5) the damping characteristic decreases when the motor inertia is equal and both the forward and the reverse motor inertia increase, on the other hand, the damping characteristic increases when the motor inertia difference increases.
The number of whiplash injuries worldwide is at a high level. From the mid-1990s, many researchers have focused into the head-neck S-shaped mode deformation behavior in early rear impacts. Firstly we developed a Japanese male 50th%ile size head-neck FE model, so we attempt to reproduce the same mode in head-neck behaviors in the rear impact sled tests of male subjects. This model has not only the main ligament tissues, but also nearly 40 major muscles such as the sternocleidomastoid muscle, the hyoid muscles, and the erector spinae muscles. Using DOE (Design of Experiments), we analyzed the percent contribution of neck muscles in the relaxed state under 1G, when holding the head neutral posture before rear impact and the muscle force balance was obtained based on the regression equation. Then, we carried out the rear impact simulation using same muscle strength, the results were compared with the head-neck behaviors of male subjects in rear sled impact tests. By balancing the muscular strength before the impact, it found out that the S-shaped mode deformation could be reproduced. This mode is strongly influenced by the muscle force balance, it has little influence on the head maximum rotational angle which occurred in the late rear impact. On the contrary, the muscular strength-up, which is reflexed on muscles such as sternocleidomastoid muscle and hyoid muscle after the impact, has little influence on the S-mode. We introduced an index (S - θmax) to quantify the S - shaped mode deformation, and confirmed that there is a possible correlation between the index value and the muscle strength for holding the head posture. Finally, we investigated the relationship between individual T1 conditions and S - θmax, so we also report these results.
Shape Memory Alloy (SMA) actuators must be continued to be heated generally to retain a shape of a smart structure deformed by the SMA actuators. To save the energy applying to the smart structure, a new control method was proposed utilizing the fact that strain is not single valued even at the same stress and temperature state due to hysteresis in stress-strain-temperature relationship of SMA. Feasibility study of the control method was performed by a fundamental experiment for an antagonistic SMA system. When a pulsed voltage was applied to one SMA, the system moved to some direction, and while the voltage was not applied to the SMA after the pulsed voltage, the system did not return to the original position and was remained at a certain position. Successively, when a larger pulsed voltage was applied to the same SMA or another pulsed voltage was applied to the other SMA, the system moved to the same direction more or the other direction, respectively, and was retained at certain positions without applying the voltages. To explain and confirm the behavior of the system, numerical simulation was also performed. The simulated result agreed with the experiment qualitatively and could explain the mechanism of the behavior. From the results mentioned above, the feasibility of the proposed control method could be shown both experimentally and numerically.
Hunting oscillation is unfavorable to the running stability because it can generate relatively large lateral force between the wheels and tracks. In addition, once hunting oscillation occurs, it lasts until the running speed is reduced to some degree. Therefore, we have studied global stability against hunting oscillation by conducting hunting motion tests using a real bogie on roller rigs. In this study, we confirmed that there exists a clear point where initial lateral displacement of the wheelset caused hunting oscillation. Then, we concluded that the point in question originated from unstable limit cycles, generated by subcritical Hopf bifurcation. On the basis of the obtained global stability, we devised a simple method that could make the hunting oscillation converge to the equilibrium point by oscillating the roller rig, without slowing down the rotational speed of roller rigs.
This paper starts with describing a method of deriving the resonance mode of a pendulum utilizing its equation of motion. This resonance mode is that the equilibrium position of the pendulum locates the vertical plane including its fixed point and the mass accelerates in proportion to the distance from the equilibrium position to its mass. Further, the equation of motion of vehicles was converted to a form conforming to the equation of motion of the pendulum. As a result, it was found that the equilibrium position of yaw resonance is the extension line of the vehicle speed vector at the front wheel position. Moreover, it turned out that its rear wheel accelerates toward this extension line in proportion to the distance from this extension line to the rear wheel is the yaw resonance mode under a special condition. Finally, the step steering response was considered. At the moment of steering input, the mode of the yaw lead time constant appears, and then the yaw resonance mode becomes apparent. Hence, the yaw resonance is revealed in the latter half of the transient response. Therefore, it is considered that the yaw natural frequency is suitable as a metric of the latter half behavior of the transient response.