Premixed Compression Ignition (PCI) engine has a potential to improve transient performance as well as exhaust emissions. In this paper, a one-dimensional engine model combined with a heat transfer model is used to analyze heat flux between in-cylinder gas and cylinder wall under steady-state operation and transient characteristics of heat loss and torque under transient operation. PCI combustion is initiated by spontaneous multi-point ignition, generating high in-cylinder pressure. According to Woschni equation, heat transfer coefficient is high under high in-cylinder pressure condition. In addition, the rapid combustion near the top dead center which can be seen under PCI combustion causes high in-cylinder gas temperature. Consequently, the temperature difference between in-cylinder gas and cylinder wall is large under PCI combustion. These phenomena which can be seen under PCI combustion induce a higher heat flux than diesel combustion. The analysis results of transient operation show that a slight difference in the ignition delay due to wall surface temperature has a small effect on the combustion characteristics under PCI combustion and it contributes to the improvement of convergence performance. The present results suggest that transient performance of torque will be improved by applying PCI combustion.

A novel total hydrocarbon (THC) emission concentration estimation model is proposed for reduction of engine development cost as well as simplification of measurement system. The model is based on machine learning algorithm including the least absolute shrinkage and selection operator (LASSO) regression and bagging techniques. Major features of the proposal model are taking the absorbance spectrum of Fourier transform infrared (FTIR) spectrometer as input and incorporating not only spectra of the engine exhaust gas but also those of individual hydrocarbon and inorganic gas components as training data set. This method was validated on the exhaust gas before the catalyst of a gasoline engine. The results show an error of less than 5% in both steady and transient operating conditions, outperforming the 20 % error of conventional regression model using only the reference hydrocarbon concentrations. We also evaluate the contribution to performance improvements in THC estimation of employing FTIR spectrum and incorporating spectrum information of gas components, respectively.

The fuel generated from CO₂ and H₂ derived from renewable energy is called “e-fuel”. Among the e-fuels, polyoxymethylene dimethyl ether (OME) is expected as a promising drop-in fuel for CI engines because it has good ignitability and low-soot combustion characteristics. However, the fuel properties such as density, heating value, and stoichiometric air-fuel ratio are different from those of diesel fuel. In this study, the spray and combustion characteristics of OME-diesel blends fuel were investigated and compared with diesel spray under engine-relevant condition at 920K-6.0MPa in a constant volume vessel. First, the fuel sprays were observed using high speed cameras under the non-reacting condition with O₂ concentration of 0%. The result showed that spray-tip penetration length of OME-diesel blends was almost the same as diesel fuel, irrespective of the OME blend ratios, while the spray cone angle and spray projected area increased as the OME blend ratio increased. Moreover, the liquid phase length and width of OME spray were smaller than diesel spray. Then the reacting sprays were observed under the combustion condition with O₂ concentration of 16% to understand combustion characteristics. The result showed that the ignition delay and the flame lift-off length were shortened as the OME blend ratio increased.

Particle number (PN) emissions and particle mass (PM) emissions have been evaluated from a diesel passenger car with diesel particulate filter (DPF) and seven gasoline direct injection passenger cars. PN and PM at upstream of DPF were also measured to evaluate DPF filtering efficiency. Particle mass emissions were obtained with photoacoustic soot measurement method. Particle number emissions were measured using a method which is adopted to European type approval tests for vehicles emissions, but cut-off diameter of this method changed to 10 nm from 23 nm. PN at upstream of DPF in cold start mode was higher than that at downstream of DPF. DPF reduced PM and PN almost zero level. PN and PM results with gasoline direct injection vehicles indicated that 6×10¹¹ #/km of PN is almost equal to 0.1 mg/km of PM. According to this relationship, PN regulation in Europe (6×10¹¹ #/km) is stricter than PM regulation in Japan (5 mg/km).

The prechamber combustion characteristics were studied using a rapid compression and expansion machine (RCEM) to improve the efficiency of cogeneration natural gas engines. The torch flames generated by a prechamber were used to investigate the effect that a prechamber has on the main combustion. In our previous study, we observed the correlation between the torch flame and the main flame (which is a so-called “prechamber combustion”). In this study, the effects of prechamber parameters such as initial pressure and nozzle diameter of injection holes, equivalence ratio on prechamber combustion characteristics were investigated in detail. Especially, by comparing the combustion characteristics of methane, which is the main component of natural gas, and propane, which is a representative of small-volume components, the effects of fuel types on the ignition and combustion characteristics of pre-chamber ignition system were investigated to elucidate of the effect of fuel property. In conclusions, regarding the mechanism of prechamber-ignition combustion, it was inferred that the jet erupted from the prechamber did not directly propagate in the main chamber but included the "ignition phenomenon" of the main chamber due to the jet. In addition, under the experimental conditions of this study, it was found that the ignition delay time and the combustion period can be predicted by simple calculation, which can lead to the important guideline for the pre-chamber design.

In the present study, a mixed timescale subgrid model of large eddy simulation (LES) is applied to simulate detailed mixture formation, combustion and soot formation influenced by turbulence in diesel engine combustion. The combustion model uses the direct integration approach with a fast explicit ODE solver and additionally parallelized by OpenMP. The Diesel oil surrogate mechanism was used which was developed at Chalmers University of Technology, consisting of 74 species and 320 reactions. The soot mass production within a computation cell was determined from a phenomenological soot formation model developed by Waseda University. The model was combined with the LES code mentioned above, including the following important steps: particle inception in which naphthalene grows irreversibly to form soot, surface growth with the addition of C₂H₂, surface oxidation with OH radical and O₂ attack, and particle coagulation. Computational results are compared with experimental data from a high-boosted heavy-duty diesel engine. The predicted soot emissions are compared with experimental data under various EGR conditions. The results show that the in-cylinder pressure and the heat release rate obtained from the engine test are in good agreement with calculation data. In the soot emission calculation, the simulated results show the exponential increases with increasing EGR rate. Furthermore, the steep rise of soot mass increase with increasing EGR rate from 30% EGR is reproduced. The process and spatial distribution of soot formation in a high-boosted heavy duty engine are studied.

In order to evaluate low cycle fatigue life under thermo-mechanical loading including high temperature regions, it is necessary to understand the basic deformation characteristics of a target material. In the case of thermo-mechanical loading, especially, the strain rate dependence for each temperature region must be clarified because there are some temperature regions that are greatly affected by the creep deformation. However, a few studies have investigated the effect of creep deformation on low-cycle fatigue life evaluation considering thermo-mechanical fatigue evaluation. In this study, a low cycle fatigue test at 623 K, which is a higher temperature region than T_m/2 for aluminium alloys is conducted, and a new fatigue life evaluation method using creep strain as an index is also discussed. Namely, a low-cycle fatigue test is performed with a cyclic tension-compression loading with a constant strain amplitude under different strain rates in the tension side and compression side. Furthermore, using the method for separating plastic strain and creep strain, which is proposed by the authors (Ohguchi and Sasaki), the inelastic strain is separated into plastic and creep strain. The correlations between the creep, and plastic strain and the low cycle fatigue life are clarified. Also, the low cycle fatigue life evaluation method using creep strain as an index is verified.

In order to develop a new crash energy absorb structure, in this paper, we propose a new reverse torsion type origami structure (RTO) and a partial heating torsion method. The RTO can adjust the distribution of crash buckling wrinkles by arranging polygonal lines along the side surface, and can have the property of stably continuing accordion-type crushing deformation during the crushing process. In the newly proposed partial heating torsion method, the square pipe material is divided into multiple stages along the axial direction, and a formed RTO can be obtained by repeating partial heating and simple torsion forming for each stage. In addition, by applying the method of heating only to the torsional deformed part, it is possible to process with a small processing load, and it is possible to realize the simplification of the jig for fixing the square tube material. This study examines the problems of forming RTO by the partial heating and torsion method and the forming shape quality. We will also examine whether the obtained RTO has sufficient crash energy absorption performance.

Data analysis was conducted to investigate the causes of the difference in creep strength between the heats of Gr. 91 steel. Creep rupture data were divided into multiple regions and fitted with an exponential degradation model. The Larson-Miller constant of each heat obtained by the fitting was used as the objective variable, and chemical concentrations of important elements, hardness and grain size were used as explanatory variables. The stepwise method was used for the data analysis. As a result of the data analysis, it is found that hardness in region H, grain size in region G, and Cr and C concentrations in regions M and L are the causes of the difference in creep strength between the heats.

The effect of layer thickness of prepreg on the static and dynamic flexural properties of quasi-isotropic carbon fiber reinforced polyamide 6 laminates were investigated. The layer thickness of each ply was set to 40, 80 and 120 μm by using thin-ply prepreg with a thickness of about 40 μm made by tow-spreading technology. Four-point flexural tests were carried out to evaluate the static flexural properties of the laminated materials. The results showed that the flexural strength and modulus did not change much as the layer thickness change. The delamination at interlaminar was interestingly inhibited with decrease of layer thickness. Charpy impact strength evaluated as the dynamic flexural properties was affected by the layer thickness depending on the impact direction. In the impact test where the applied load was parallel to the laminates (edgewise test), the Charpy impact strength was almost unaffected by the layer thickness change. In contrast, Charpy impact strength increased with increasing layer thickness where the applied load was normal to the laminates (flatwise test). In the observation of the fracture appearance after edgewise test, the fiber fractures were observed independent of the layer thickness. Meanwhile, the occurrence of the cracking and delamination at interlaminar were effectively suppressed with decrease of layer thickness in the specimen after flatwise test. The delamination at interlaminar progressed in the in-plane direction with increasing layer thickness, resulting in large-scale delamination. As a result, a large amount of fracture energy could be absorbed. In conclusion, the layer thickness of the laminate is an important material design factor for controlling the impact properties of the composite materials.

In order to clarify the effect of internal hydrogen on the fatigue life properties of SUS304, SUS316 and SUS316L, tensile tests and low- and high-cycle fatigue life tests were carried out in air at room temperature using 10, 68 and 100 MPa hydrogen-charged specimens. High-cycle fatigue life tests demonstrated that S-N curve (i.e., relationship between stress amplitude, σ_a, and number of cycles to failure, N_f) of each steel was higher in hydrogen-charged specimen than in uncharged specimen. The increase in fatigue limit, Δσ_w, with internal hydrogen was 40 MPa in 100 MPa hydrogen-charged specimens, 20 or 30 MPa in 68 MPa hydrogen-charged specimens, and 0 or 10 MPa in 10 MPa hydrogen-charged specimens. Low-cycle fatigue life tests manifested that ε_ta-N_f curve (i.e., relationship between total strain amplitude, ε_ta, and number of cycles to failure, N_f) of 68 MPa hydrogen-charged specimen was nearly coincident with that of uncharged specimen in SUS316L, whereas 68 MPa hydrogen-charging markedly lowered ε_ta-N_f curve in SUS304. The fraction of strain-induced martensite was measured on specimens fractured by tensile tests and low- and high-cycle fatigue life tests. The critical value of the martensite fraction below which 68~100 MPa hydrogen-charging does not cause hydrogen embrittlement, f_mH, was 1 % in tensile tests. On the other hand, the f_mH value was 9% in low- and high-cycle fatigue life tests. The increase in fatigue limit due hydrogen-induced solid solution strengthening, Δσ_w, in high-cycle fatigue life tests was expressed as Δσ_w (MPa) = 15.4 × 237H, where H is the hydrogen content (mass %). In addition, the hydrogen-induced strengthening of stress amplitude, Δσ_a, and 0.2% proof strength, Δσ_0.2, in low-cycle fatigue life tests was expressed as Δσ_a+0.2 (MPa) = 15.4 × 296H. The results inferred that the contribution of hydrogen to solid solution strengthening was about 10 times larger than that of carbon and nitrogen when compared at the same mass concentration.

Disruption of gas-filled microcapsules under pulsed ultrasound irradiation is experimentally studied. The goal of this study is to evaluate the disruption rate of the polymer-shelled microcapsules as a function of the mean number concentration of the microcapsule population. In the present study, we defined the disruption of a microcapsule as decapsulation of the shell layer followed by exposure of an internal gas bubble, growing to visually detectable size through mass diffusion. An experimental setup has been designed to sonicate two-dimensionally dispersed microcapsules in a planar microchamber. Pulsed ultrasound at 1 MHz is irradiated normal to the chamber from a planar ultrasound transducer. Pure water and glycerol aqueous solution of 30 wt. % were used as the dispersion media. Image processing of the recorded microscopic images yields capsule size distribution and local concentration distribution defined as an inverse of the occupied area of the capsule position (Voronoi area). The mean number concentration is controlled over a wide range from 5 to 200 capsules/mm², while the mean capsule diameter is controlled between 25 and 40 μm regardless of the concentration. The disruption rate is evaluated comparing the number of disrupted microcapsules (gas bubbles) and the total number of microcapsules in the target area of the ultrasound irradiation. The disruption rate turned out to decrease with the mean concentration and is inversely proportional to the mean concentration for the particular case of the two-dimensional spatial distribution.

Drag and velocity measurement on a two-dimensional bluff body has been performed in a pulsatile flow. Circular and rectangular cylinders were selected in the present study. The projected width and length of the cylinders were d =30 mm and L =300 mm, respectively. The cycle-averaged velocity was 〈V_θ〉 ≅15 m/s and the amplitude was in the range of V′_θm =0.45 to 3.6 m/s. The pulsation period of the flow was set in the range of T =1.5 to 10.0 s. The Reynolds number based on the phaseaveraged mean velocity and the projected width was in the range of R_eθ =20000 to 40000. The cycle-averaged drag coefficient increases with the root mean value of the deviation from the cycle-averaged velocity of approaching flow to the cylinder. The cycle-averaged drag coefficient for T <6.0 s ( T〈V_θ〉/d <3.0× 10³) increases compared with that estimated from the drag coefficient in the steady flow. For T ≥6.0 s ( T〈V_θ〉/d ≥3.0× 10³), the drag coefficient of the steady flow can be used to calculate the cycle-averaged drag. The effect of the pulsation period on the phase-averaged drag occurs during temporal deceleration of the pulsatile flow and can be related with the increase of the velocity deficit and width in the wake behind the cylinder. The phase-averaged drag will be represented as the sum of the momentum deficit due to the phase-averaged flow, which contributes to the cycle-averaged drag, and the pressure gradient by the pulsatile flow. This can be formulated semi-empirically with the cycle-averaged value of the phase-averaged drag coefficient, phase-averaged velocity and the derivative of the pulsatile flow with respect to time.

This study aims to develop a design methodology for district heating network based on linear heat density. In the previous study, district heating systems including network were designed by applying mixed integer linear programming (MILP), however, number of demands was small because MILP takes long computational time. In this study, we have designed a district heating network design as a spanning tree problem, and have analyzed it based on Prim’s algorithm. First of all, heat demand was analyzed and heat density maps in target municipals were drawn according to the geographical information of buildings, and the statistical data of the energy consumptions. The target buildings as the demand of district heating systems (DHSs) were selected from the higher heat density area in the drawn heat density maps. In the developed methodology in this study, it is assumed that the heat source is installed in the higher heat demand building. Three heat pipe networks were designed based on linear heat density (LHD case), distance (Distance case), and heat demand (Demand case), and their heat loss and cost were analyzed. As a case study, DHSs in Koriyama city and Akita city were designed and compared. The average pipe diameter and the average linear heat density in the LHD case showed similar trend to experiential curve. The trend in heat loss and pipe cost showed rapid increasing as supplied heat increased in LHD case. It can help to select demand buildings for superior performance of DHS. In the Distance case, the minimum heat loss and cost were obtained when supplied heat were higher, however, there were no clear trend in heat loss and pipe cost because they depended on demand distribution.

Droplet impingement to wet wall is observed and classified. The wet wall has a thin liquid film which is different kind of liquid from the droplets. The present study models the droplets impingements to wet engine walls in gasoline engine. The alternative fuel droplets injected by the injector for port injection system impinge to the silicon oil film simulating wet cylinder wall of actual gasoline engine. In this experiment, a rectangular flow section is used as an example of collision between different liquids in a port injection engine. The viscosity of the liquid film was varied as experimental parameter. The experimental results are well organized using Weber number calculated by using vertical velocity. As Weber number increases, the impingement type changes from rebound to deposit then splash. The tendency is same as impingement regime under the case of same liquid for wet wall and droplets, however critical Weber number is different from them. The liquid film viscosity strongly affects the droplet impingement form. Splash does not occur under the large liquid film viscosity. It is difficult to categorize the impingement regime by common Laplace number based on droplet viscosity. The modified Laplace number which is based on the viscosity of the liquid film is proposed. In the case of different kinds of liquids droplet-film impingement, the phenomenon can be categorized by modified Laplace number and Weber number based on the vertical velocity component of droplet velocity.

Vibration power generators that generate electricity using environmental vibrations are attracting attention as independent power sources for IoT sensors and the like. We are paying attention to the electromagnetic induction method, which can be composed of general-purpose and easily available materials and is less likely to cause aging deterioration of the members related to power generation. In the past, we reported that the effect of the magnetic parameters of the electromagnetic induction vibration generator on the generated power when the environmental vibration is a sine wave, and validated the model. We also discussed the design guidelines for improving the generated power when the angular frequency of environmental vibration matches the natural angular frequency. It is suggested that this guideline improves the frequency characteristics of generated power. On the other hand, there are many experimental reports in an actual vibration environment as an evaluation example of a vibration power generator, but it is difficult to make a general discussion because the frequency characteristics of environmental vibration differ depending on the application. In addition, although there are experimental reports and theoretical studies when the environmental vibration is white noise, there are no reports that experimentally verified the theory of average generated power for an electromagnetic induction type vibration power generator using a one-degree-of-freedom oscillator as far as we investigated. In the paper, we constructed a mathematical model for the time average of generated power against white noise vibration containing various frequency components and clarified the effect of magnetic parameters on generated power. Furthermore, the effectiveness of the model was verified by comparing the results of evaluating the power generation performance of the prototype using white noise as the excitation signal and the calculations.

A new positioning method for large objects by cooperation of three position-controlled manipulators is proposed. To realize the cooperative positioning system by position-controlled manipulators, it is necessary to avoid excessive inner forces among manipulators caused by mutual positioning errors. To solve this problem, two wires with independent directions are installed between each manipulator tip and the positioned object. As a result, the object is suspended by six wires those directions are linearly independent of each other. Then, if the tensions of all wires are positive during the execution of the positioning tasks, the excessive inner forces don’t generate by positioning errors of the manipulator tips and sway motion of the object doesn’t occur against external forces in some extent. On the other hand, this system has 12 kinematical redundant degrees of freedom. Therefore, we propose a positioning control algorithm to keep all wire tensions positive and to avoid the concentration of tension on any one wire by utilizing kinematical redundancy. The effectiveness of the proposed method and the developed system are verified by a fundamental experiment and simulations.

This paper reports the launching and organizing procedures of Robomech 2020, the first online conference in the history of Robomech series. We discuss the required functions of an online academic conference and show an implementation example. Analysis of the conference results and responses from the participants reveals the advantages and disadvantages of Facebook that is used as a platform of the online conference. The analysis also indicates the constitutive problems of the online conference. Consequently, this paper provides multiple clues for constructing a new platform suitable for more active and efficient online academic conferences.

Drones, whose applications are rapidly expanding in recent years, have a wide range of uses, such as material transportation, pesticide spraying, structure inspection, and even the recently-flying cars, but it is difficult to fly in bad weather such as gusts. On the other hand, CMGs (control moment gyros) are known to have a precession property that tries to rotate in the direction perpendicular to the external force applied to the axis of rotation. Therefore, we wondered if the self-sustained control of the motorcycle using the CMG developed by the authors could be applied to the attitude control of the drone. Although the weight reduction is an important issue for drones, about 1 kg of weight is added when the CMG is mounted. As a result of comparing the control performance between the case where the weight and power consumption corresponding to the CMG are used for control (without CMG) and that where the CMG is installed (with CMG), it was shown that the control effect against wind disturbance was better when the CMG was installed even when the CMG weight was taken into account. In this paper, we confirmed by experiments that mounting a CMG on a drone has a suppressing effect even when a disturbance equivalent to a wind speed of 22 m/s is applied, and furthermore confirmed that the vibration of 2 to 4 Hz was damped.

Although wheelchair is useful as hardware for moving purposes such as the elderly and disability person, it is not suitable for driving in environments other than flat ground such as steps and ditches, and so there is a problem that the range of activities is limited. In this paper, we propose an add-on type step elevating mechanism and its control method that realizes step movement without the need for human visual inspection or intervention of operation in wheelchair elevating operation. The basic configuration of the mechanism consists of two arm rotation mechanisms whose drive source is a linear actuator and auxiliary drive wheels. By cooperative controlling these devices, it is possible to move the step by the chair occupant alone and while maintaining the horizontal posture. Applying a disturbance observer, this paper suggests a method that can estimate the step height without the need for a dedicated sensor even when a wheelchair user encounters the step for the first time. As a result of implementing this step detection method, it is shown that a step of up to 175 mm can be detected without relying on human eyes and its height can be estimated within the tolerance without using a dedicated sensor. In addition, it was confirmed that wheelchair with an adult man actually boarded can ascend and descend step height of 140 mm, as a result of implementing an arm movement model that realizes step up and down while maintaining the posture of the wheelchair body horizontally for the arm mechanism after touchdown.

According to David Marr, three levels are needed to understand information processing systems. Those are “computational theory”, “representation” and “algorithm and hardware implementation”. This idea improves understanding brain function and technological application in a mutually complementary manner. On the other hand, the development of measuring brain function enabled us to apply brain activities to engineering. Measuring brain activity have been used for the evaluation method to information that is difficult to quantify such as emotion and learning levels. This work investigates the relationships between learning levels and brain activities. In the conducted experiment, subjects firstly learned a set of procedures for assembling work by observation and then imitated the procedures in the tasks. After several practices, they participated in the same tasks. The results indicates that activities of regions of dorsolateral prefrontal cortex (DLPFC) have increased at pre-learning and a wide region of prefrontal area have increased at post-learning during the observation. In the imitation, regions of DLPFC were activated at pre-learning. At the post-learning, the regions of DLPFC, frontopolar cortex and inferior prefrontal gyrus were activated. These findings are accorded with the results of the previous studies and suggest the necessity of considering the effects of a default mode network on the brain activities of imitation learning.

As a new means of transportation for short and middle distance, personal mobility vehicle (PMV), which is one or two-seater and has high environmental performance, is recently being developed. It is because many people drive a car when they travel a short distance alone, that is inefficient in cost and space. One of the PMVs which is recently gathering attention is three-wheeled vehicle with leaning mechanism. Leaning mechanism, which gives tires degree of freedom, has an effect of stable cornering in the case of short tread width vehicle. For this reason, this vehicle has two advantages, compact and stability. We research on the vehicle which has two front wheels and one rear wheel. We derived equation of motion by referring to Sharp’s 4 DOF two-wheeled vehicle model, and carried out the numerical analysis to compare three-wheeled vehicle and two wheeled vehicle. However, it’s difficult to find out driver’s sensuous difference between three-wheeled and two-wheeled vehicle by only numerical analysis. Then, we conducted the real-time simulation experiments and questionnaires, search on that difference. Through that experiments, three-wheeled vehicle needs large steering torque and drivers feel sense of security, but steering is difficult when the vehicle speed is fast. On the other hand, two wheeled vehicle needs small steering torque and large output, so drivers steer constantly for maintenance of slalom running.

In this paper, we present a non-parametric material orientation optimization method for tailoring the vibration eigenvalues of laminated shell structures composed of orthotropic carbon-fiber-reinforced plastic (CFRP) materials. Both of the design problems to maximize an arbitrary vibration eigenvalue and to maximize the gap between arbitrarily specified the vibration eigenvalues are formulated as distribution parameter optimization problems based on the variational method. We introduce KS function to solve the multiple roots problem latent in the vibration eigenvalue optimization problem. The sensitivity functions derived are applied to the H1 gradient method for material orientation to determine the optimal material orientation of each layer. The effectiveness of the proposed method are confirmed by the numerical results of a cantilever plate and a three-layer rectangular shell structure. The proposed method makes it possible to tailor the vibration eigenvalues of laminated shell structures without design parametrization while maintaining the smooth material orientation.

CFRP laminates subjected to out-of-plane load may have complex damage such as delamination, matrix crack and fiber failure. In this study, damage propagation analyses for Quasi-Static Indentation (QSI) tests were performed by static implicit method using quasi-3D extended finite element method (XFEM) considering materially, geometrically and boundary nonlinear. In the numerical models, interface elements considering cohesive zone model (CZM) are introduced to model delamination. The accuracy of QSI test analysis was improved by quasi-3D XFEM using multiple matrix crack model, and ZECZM considering the dependence of shear strength on hydrostatic pressure. It was shown that the results including relation between load point displacement and applied load, and delamination obtained by the analyses are in good agreement with the experimental results.

This study concerns the computational accuracy of a particle method for a time-dependent incompressible flow. In recent years, accurate spatial discretization schemes have been developed for a particle method. However, the actual convergence rate in space tends to be much lower than the order of the leading truncation error given by an adopted spatial discretization scheme. This suggests that the Δt-dependent error is comparably significant with respect to the truncation error of the spatial discretization scheme. Under these circumstances, we have developed a new time marching method to improve the computational accuracy by reducing the Δt-dependent error and improving the convergence property. The proposed time marching method is based on the 1st-order fractional step method, just as the conventional methods. However, as opposed to the past studies, the convection term is explicitly included in the provisional velocity calculation, as an Eulerian-based approach. By doing this, the Δt-dependent error caused by the particle movement can be avoided. A numerical test has been carried out using the two-dimensional Taylor-Green vortex problem, where 2nd- and 4th-order spatial discretization schemes are adopted. As a result, the conventional time marching methods gave much lower convergence rate than the order of the spatial discretization scheme. On the other hand, the proposed time marching method showed approximately 2nd- and 4th-order convergence in space with the 2nd- and 4th-order spatial discretization schemes, respectively. Therefore, the proposed method is indicated to highly improve the computational accuracy.

This study presents a method suppressing thermal deformation of a computer numerical control (CNC) lathe. Although the thermal deformation of machine tools often reduces their accuracy, it cannot necessarily be prevented by ensuring their rigidities, etc. Therefore, we have been trying to compensate for the thermal deformation by predicting their variations and adjusting the position of the tool according to predicted values. The previously proposed method determined a prediction equation of the thermal deformation in the CNC lathe by measuring the temperature variations at a few specific points of the body. However, the equation needs to exchange the coefficients of the prediction equation depending on whether cutting fluid is used or not. Thus, this study tries to propose a method to determine the coefficients that can be used for machining with and without cutting fluid. Furthermore, the determined coefficients need to be ensured for a wide range of machining conditions such as temperature variations. In order to obtain such coefficients with a few experiments, the present study determines actual cutting conditions to obtain the coefficients with the experimental design and confirms the prediction equations with the determined coefficients to be applicable under wide machining conditions involving temperatures and cutting fluid.

Sulfurnitriding, one of various surface treatments for mechanical components made of steels realizes solid lubrication for decreasing friction force of each contact point and keeping lubricating condition on the surface. Any tribological data on sulfurnitrided steel gears have not been published. In this study, friction performance of sulfurnitrided gears made of low-carbon steels (JIS-S45C) was investigated. Wear tests of the gears were conducted at room temperature without any lubrication. The gears with different treatments such as non-treated, as-nitrided, as-carbonized, as-quenched and as-induction-hardened ones were applied to the same low-carbon steel for comparison. The amount of wear of the gears was decreased by applying the all surface treatments. The gears with the sulfurnitridation show smaller wear than others while the surface hardness of the gears was comparable or lower than the others. In particular, the surface treatment combining of sulfurnitridation and nitridation showed the lowest value of the amount of wear. The FeS layer formed by the sulfurnitriding is approximately 1 μm in thickness which is much lower than the amount of wear after 4 h in test time. Lubrication effects on the FeS layer remains after removing the layer. As well, nitridation after sulfurnitriding is effective to improve a solid lubrication performance for low-carbon gears at room temperature in air.

Selective laser melting (SLM) has been used to fabricate lightweight and complicated structures. Lightweight structures tend to suffer from noise and vibration problems. Hence, to overcome these problems, dynamic vibration absorber (DVA) are embedded in these structures through SLM fabrication. Although SLM can control the stiffness of the DVA by structural design, it is difficult to obtain enough damping effect. To add damping to the DVA in the fabrication process, we embedded powder in the structures so that the powder can work as the damping element of the DVA. This study proposes a fabrication process for tuned particle dampers (TPD), in which the DVA with the embedded powder can be fabricated through a single SLM process. To experimentally demonstrate the vibration reduction performance of the TPD fabricated using the proposed process, we carried out impact testing of plates with multiple undamped DVA (i.e., without powder), and plates with multiple TPD. The maximum acceleration of the plates with multiple TPD and undamped DVA were 19.8 dB and 31.8 dB, lower than that of the plate without dynamic vibration absorber. These results suggest that the proposed fabrication process can effectively add damping to the DVA embedded within the lightweight structures.

In this study, we aimed to elucidate the effect of differences in the viscous load of wheeled–walkers used in rehabilitation on joint movements, muscle activities of the lower extremity, the trunk acceleration, and the trunk angular velocity. The viscous load applied to users was generated by a mechanism that can generate the viscous load according to the movement velocity of the wheeled–walker mounted in front of the wheeled–walker. Twelve young healthy male subjects were instructed to wear an orthosis on the right knee joint to imitate the walking behavior of a patient with a limited range of motion in the knee joint, and to walk with restricted change in the right knee joint angle. From the experimental results, we observed that the effect of the difference in the viscous load on the walking velocity and muscle activities of lower extremity muscle groups differed depending on the recent exercise frequency. Some subjects with low exercise frequency in recent years showed an increase in the hip extension angle and a decrease in the muscle activities of the lower extremity muscle groups in response to an increase in viscous loads. On the other hand, we observed that subjects with a high exercise frequency could maintain their walking velocity by increasing the muscle activity of the lower extremity muscle groups in response to increased viscous load. The maximum viscous load applied on the subjects in the experiment was 5.9 N, which can be easily presented to the patients, even in rehabilitation. Therefore, we believe that the results obtained in this experiment can be utilized in rehabilitation intended for patients with a limited range of motion.

An expanded silencer is well known in all other silencers and widely used in an industry field. As the theory of the expanded silencer has already been established and it is considered to be useful because it has exceptional prospects. There are many studies on the characteristics of the expanded silencer. For example, Davis D.D. et al. constructed the theory under the assumption of no reflection of the tail pipe. Fukuda et al. have left a trail of many fruitful results on the characteristics of the expanded silencer including the effect of the tail pipe. In general, the performance of silencers is evaluated by the silencing effect(ATT) and insertion loss(IL). When we calculated the silencing effect by using the transfer matrix method, we experienced that the silencing effect was completely independent of the inlet tube length. Is the fact true? It is the motivation of this investigation. We noticed the silencing effect was different from the insertion loss in the process of this study. This is considered to be natural and almost all people know that fact. In this paper, it will be verified that the silencing effect is independent of the inlet tube length and we modified the silencer effect by taking into account of radiation effect from the outlet tube and compared the modified silencing effect and the insertion loss. As a result, it was clarified that the both results are good agreement with each other.

In this paper, we analyzed the effort of vehicle frontal collision deceleration waveform and seatbelt pretensioner on chest deceleration using one-dimensional spring-mass model. The chest deceleration based on designed one-dimensional spring-mass model have chest deceleration component generated by relative velocity between vehicle and chest before pretensioner is activated, chest deceleration component generated by connecting vehicle and chest using seatbelt after pretensioner is activated, and chest deceleration component generated pretensioner force. In order to confirm the validity of this one dimensional spring-mass calculation model, we compared with the calculation of MADYMO. The result of comparing spring-mass calculation model with MADYMO was qualitatively consistent and we proved the validity of the spring-mass calculation model that calculates chest deceleration by dividing it into three components. We proved that the various vehicle frontal collision deceleration waveform with the same crash stroke and the relative velocity that occur between vehicle and chest before pretensioner is activated have a critical value that minimizes chest deceleration, and we proved that vehicle deceleration before pretensioner activation timing has the same effort on the chest deceleration regardless of the waveform of vehicle deceleration if relative velocity between vehicle and chest is the same.

The variation in driving or braking force between the wheel and rail, which may cause longitudinal vibrations of the vehicle, sometimes causes reduction in adhesion and increases gliding. It is essential to elucidate the relationship between tractive force and longitudinal vibration in consideration of the electric and mechanical system in order to build a motor control method which can improve tractive force and reduce longitudinal vibration in the train set. In previous researches, numerical analysis methods for coupled motions in the vertical and longitudinal directions have been developed by introducing a sophisticated model of forces acting on the coupler. In the past, this analysis method has not been applied to the study of vehicle longitudinal vibration in a train. However, in recent years, the applicability to the analysis of vehicle longitudinal vibration has been studied, but it has not yet been fully studied. Therefore, in this report, the authors compare the test results with the numerical results when the fluctuating driving force is given to the numerical analysis model in order to confirm the effectiveness of numerical analysis. Furthermore, by using the numerical analysis, it is clarified that the frequency characteristics of the longitudinal vibration of the car body generated in the train due to the fluctuation of the driving force.

Fatigue design of the railway wheel web is carried out in compliance with the JRIS J 0405 standard. However, this standard does not specify any evaluation method considering the thermal stress on the wheel web owing to tread braking. The thermal stress in fatigue design should be evaluated as the average stress in the endurance limit diagrams. In addition, it is necessary to evaluate it considering the variations in the actual mass productions and the fatigue strength in the design of actual wheels. In this study, plane bending fatigue tests using the cut wheels were conducted, and various properties of the actual mass productions were measured to evaluate the variations in them statistically. These tests clarified the fatigue limits and the standard deviation at stress ratios of -1 and 0.7. It was found that a curve, which was a combination of σ_a － σ_T and σ_max = σ_f diagrams, corresponded well to the test results. The equivalent standard deviation in the fatigue limit was obtained from the variations in the fatigue properties and the properties of the actual mass production wheels. The fatigue design curve of the wheel web, based on the proposed endurance limit diagram, was determined so that the fracture probability at all the stress ratios was less than 10^-6 by using the equivalent standard deviation.

The coefficient of friction (COF) between the outer rail and the leading-outside wheel flange of a railway bogie running on sharp curved track is an important parameter for the progress of wheel/rail wear and running safety. Therefore, it is desired to grasp the actual state of COF of wheels especially at the leading-outside wheel flange. In the author’s previous studies, a roller-rig experiment was conducted with changing lubrication condition of each wheel of the bogie to figure out relationship between lubrication conditions and wheel/rail contact forces such as tangential, lateral and vertical directions. In this paper, a method to estimate the value of COF of leading-outside wheel with look-up tables built by repetitive numerical simulations is explained. In the construction of the look-up tables, friction coefficients for each wheel in the numerical simulation model are changed while collecting calculated wheel/rail contact forces. A railway bogie running on roller-rig test is considered for both numerical simulations and experiment with different lubrication condition, therefore look-up tables are built with a half-vehicle model running on the roller-rig. By inputting the wheel/rail contact forces measured in roller-rig test into the look-up tables built by simulations, and the COF of leading-outside wheel flange is estimated. The result shows that the lubrication condition of leading-outside wheel flange can be estimated by the proposed method especially when the value of COF is large and is useful for the detection of high COF condition.