In this study, the effect of curvature radius of the thread bottom and the pitch difference between of M16 bolt and nut on fatigue strength for bolted joint is considered experimentally. The M16 bolt-nut specimens having the two kinds of thread bottom radii and the pitch differences are prepared. The S-N curves for bolted specimens with different thread shapes are obtained by the stress-controlled fatigue test (stress ratio R>0). The experimental results are compared and discussed in terms of stress analysis. The finite element method is used to make a simulation of the fatigue experiment and the mean stress and stress amplitude at each thread bottom of bolt are analyzed. It is found that the initiation and propagation of crack are changed by introducing the pitch difference of α=15μm, from the crack observation on the surface of the bolt specimens after the experiment. Furthermore, the fatigue limit can be substantially improved by increasing curvature radius of thread bottom and introducing the pitch difference.
This paper deals with the acoustic shielding of especially high-frequency sound by jet (Air Shield). In the shear layer of the jet, sound waves incident on the jet undergo reflection and / or scattering. We investigated the performance of the air shield with two methods. One method is the experiment of a sound source in static field with a finite width rectangular jet under subsonic speed. The other method is the numerical calculation with the similar condition with the experiment as a reference to understand the phenomenon of the experiment. The cause of sound attenuation under the air shield was discussed by considering a reflection model on the surface of jet and scattering effect in the shear layer of jet. As a result, it was found that the scattering occurred when the sound source frequency was 20kHz. When the sound source frequency was 5kHz, the reflectivity was close to the theoretical value. Because of these experimental results, the reduction effect can be obtained at the side, so it is best to install the air shield when the sound source at the position of the potential core as the air shield installation position.
In the present study, we have treated a suspension composed of magnetic cubic particles in a simple shear flow situation in order to investigate the dependence of the magnetorheological properties on the aggregate structures by means of Brownian dynamics simulations. An external magnetic field is applied in the direction normal to the simple shear flow. The main results obtained here are summarized in the following. In a weak applied magnetic field, the cubic particles aggregate to form the closely-packed clusters if the magnetic particle-particle interaction strength is sufficiently large. The closely-packed clusters are transformed into chain-like clusters with increasing magnetic field strength. These chain-like clusters tend to incline in the flow field direction from the magnetic field direction. Since the chain-like clusters give rise to a large resistance to the flow field, the net viscosity of the suspension is increased. As the magnetic field strength is further increased, wall-like structures along the magnetic field direction are formed in the system. In this situation, the force to accelerate the flow field arises due to the characteristic of the particle arrangement within the wall-like clusters, which induces a decrease in the net viscosity. From these results, we conclude that the magnetorheological effect depends on the internal structures of the aggregates formed in the system. Moreover, we suggest that a cubic hematite particle dispersion may have negative magnetorheological characteristics under the certain conditions.
The boundary layer of a bubble is an important factor that determines its rising velocity. But it is generally very thin to simulate using typical interface capturing method, such as volume of fluid method. In this study, we numerically investigated the velocity distribution in the boundary layer, and whether a general method for calculation of bubble describes a correct boundary layer. First, we simulated axisymmetric flow around a spherical bubble to calculate the accurate velocity distribution in the boundary layer using boundary fitted coordinate system. The velocity is first increased until a certain distance from the bubble surface and showed maximum value. And then the velocity is decreased with taking a distance from the bubble. Although this tendency is the same as the theoretical analysis, the magnitude is different. In order to guarantee the accuracy of bubble simulation, high spatial resolution in this very thin region where the velocity is increased near the bubble surface is required. Second, we compared the result of deformed bubbles between boundary fitted coordinate system and volume of fluid method. When 4 points are arranged in the velocity increase region, the velocity difference between two methods is approximately 1%. We conclude that the velocity profile by volume of fluid method matches that by boundary fitted coordinate system when the grid resolution is appropriate.
Three methods for predicting pressure loss of gaseous flow in a conduit-system of microchannel heat exchanger are proposed and discussed. In the experiment, the heat transfer plate which is the core of the heat exchanger has 34 rectangular microchannels. The microchannels are 330 μm in width, 200 μm in depth and 20 mm in length. The working fluid is air at room temperature, which is compressed to flow in the heat exchanger and flows out to atmospheric surroundings. The static pressures were measured at the inlet and outlet of the conduit-system. The conduit-system, namely, the heat exchanger and the piping system, includes several factors of pressure loss such as pipe friction, sudden expansion or contraction at the joints of piping system, besides the conventional loss at the heat exchanger core. These additional losses cannot be ignored because the hydraulic diameters of piping system tend to be small for microchannel heat exchangers. The prediction methods are formulated with the assumption that the pressure loss coefficients (such as pipe friction factor) have the same value of those of incompressible flow. One of the methods is simply formulated assuming isothermal flow and constant densities in each conduit-element, and another one is based on one-dimensional adiabatic flow theory. These two methods adopted pressure loss correlation of incompressible flow as approximation. The third method adopted modified pressure loss correlation where the essence of pressure loss is considered as internal heat generation by dissipation, and total pressure loss is calculated based on isobaric curves on h-s chart using entropy increase by the heat generation. When the measured outlet pressure is used as initial value of prediction, the third method gives the best prediction of static pressure difference between the inlet and outlet of the conduit-system within 3.9% difference from the experiment in the range of 371-1460 of channel Reynolds number.
A suction air cooling by water spray has been used for inlet air of gas turbines. The cooling performance depends on spray characteristics and surrounding conditions. The aims of this study are to understand the spray characteristics under the various humidity conditions and to discuss influences of humidity on spray characteristics and cooling performance. A Phase Doppler Anemometry (PDA) provides spray characteristics. Air temperatures before cooling and after cooling are measured under various humidity conditions and the number of nozzles. Two types of nozzles, that is, an impaction PIN Jet nozzle and a Hole type nozzle, are tested. For both nozzles, evaporation of droplets becomes inactive with high humidity condition. For PIN Jet nozzles, spray droplets exist in large area and are smaller than those of Hole nozzle. For Hole nozzle, droplets size is larger at spray outer edge and spray area is smaller compared with PIN Jet nozzle. The cooling performance for PIN Jet nozzle is larger than that of Hole nozzle. The cooling performance becomes better when spray flow rate increases.
Ammonia has been suggested as a potential carbon-free fuel for spark ignition reciprocating engines. As ammonia is a nitrogen compound, nitrogen oxide (NOx) emissions are important subjects to study. This paper clarifies features of NOx emissions of an ammonia-hydrogen fueled engine by experiment and NOx formation and extinction process in the cylinder by numerical simulation. Engine test results show the sensitivities of spark timing, load and equivalence ratio are major differences from gasoline engines. Additionally, the use of hydrogen as a combustion promoter tends to promote NOx emissions. Numerical simulation focused on NO, as greater part of NOx was nitric oxide (NO). Three representative chemical kinetic models were applied and compared each other and with experiment. Each model shows the largest NO concentration at flame zone. The values are several times higher than equilibrium although each model predicts quite different value. Two-step calculations are investigated to simulate NO history in the cylinder. First step calculation is to simulate NO formation at the flame zone. Qualitative effects of hydrogen and load on NO corresponded to the experiment, although the effects of spark timing and equivalence ratio slightly differs from the experiment. Multi zone engine simulator was applied in the second step to estimate extinction of NO in burned gas zone by applying the results of first step NO. It was found for NO to decrease considerably in the burned zone and come closer to the experiment at the end of the expansion stroke. Qualitative trends of NO by spark timing and equivalence ratio corresponded to the experiment by two-step calculation although the effect of hydrogen became small. The results provide a possibility to predict NO emissions by this simplified method.
A pulsating turbulent channel flow at constant wall temperature difference condition is studied by direct numerical simulation (DNS) to clarify the effect of pulsation frequency on turbulence statistics and heat transfer. The flow pulsation was forced to a turbulent channel flow by sinusoidal variation of pressure gradient. Four pulsation frequencies were tested for Womersley number, Wo = 19.8, 28.0, 39.6 and 56.0 at steady-state friction Reynolds number, Reτs = 300. Phase-averaged friction velocity and Nusselt number change periodically, showing different amplitude and phase lag to bulk Reynolds number, depending on Womersley number. Consequently, it is found that the time-local dissimilarity between momentum and heat transfer occurs due to the flow pulsation. Also, the phase-averaged streamwise velocity and turbulent kinetic energy can be scaled with phase-averaged friction velocity at low Womersley number. On the other hand, at high Womersley number, the phase-averaged turbulent kinetic energy is scaled with the time-averaged friction velocity. This fact implies that near-wall turbulent eddy structure changes following bulk Reynolds number variation at low frequency, but it cannot follow the rapid variation at high frequency and ends up holding near steady-state structure. This view is supported by the behavior of vortex structures which virtually does not change during one cycle at high Womersley number.
A counter-flow diffusion flame formed of a fuel consisting of methane and nitrogen, and a oxidizer of air heated to 500℃ was applied to clarify the influence on the extinction limit when fine powder of polymethyl methacrylate (PMMA) was added to the fuel. The flame stretch rate at the time of extinguishing flame was measured as function of the powder size and the weight concentration of powder in the fuel. The sizes of PMMA powder used are 15 μm, 30 μm and 50 μm. The weight concentration of PMMA powder in the fuel was changed to 20%, 25% and 30%. The flame stretch rate at the extinction limit for the methane fuel and air was increased with the increase of the air temperature. When the PMMA powder were mixed in the fuel, the flame stretch rate at the extinction limit increased with the larger fuel size, because the larger powders had slip to gas and did not trace on the gas flow. Therefore, the powder stayed longer in the flame. The flame stretch rate at the extinction limit was decreased with the increase of the weight concentration of the PMMA powder, because the combustion of powder needed longer time to that of gas.
This study investigated experimentally a response of premixed Bunsen flame to transient change in a fuel composition and a method to control the variation. Fuel mixtures were composed of methane, ethane and propane. The volumetric fraction of methane was varied from 92 % to 76 % by 4 % and the ethane/propane ratio was 5. Transition time of the fuel composition was 1, 5, 10 and 20 s. Flow velocity and the equivalence ratio were 0.8 m/s and 0.85 respectively before the transition. Channel length L between the merging point of fuels and the point of air was 0, 500, 1000, 1500 mm. The motion of flame was recorded by a high-speed video camera at 60 fps. The experiment was conducted under the fuel flow rate constant and the equivalence ratio constant conditions. In the former condition, the flame height varied almost linearly not depending on the conditions. In the latter condition, variation of the steady flame height was smaller than the former condition. However, the unsteady flame height exceeded or fell below temporarily the steady flame height. This is due to the time lag between the transmission of fuel flow rate variation and fuel compositions variation. Therefore, considering this time lag, the experiment was conducted with a system which had a density meter to detect the fuel composition variation. The system controlled automatically the fuel flow rate. At long L and short transition time, there were some peaks in the flame height variation. It is considered that this is caused by the difference between the actual density and the output of the density meter due to Taylor dispersion and response time of the density meter. However, the flame height variation was smaller than the variation without control, and particularly at long transition time, the variation was suppressed sufficiently.
In this paper, we present a new design of the robust observer called integral sliding mode observer (ISM observer) for nonlinear strict feedback systems. Many controllers that have been proposed in control engineering require full information of states. However, we may not be able to measure full states because of cost of sensors or physical constraints. Therefore, it is important to estimate the states of the systems. Many researchers proposed various observers for estimating the states. Luenberger observer is the most common observer in control engineering, and Luenberger observer applied to the nonlinear system is called nonlinear observer. However, nonlinear observer may not work well when it is applied to nonlinear systems with uncertainties. Therefore, the robustness of the observer is an important issue. In this research, we propose ISM observer by introducing some kind of auxiliary system to nonlinear observer. Even if the system has uncertainties, the proposed observer guarantees the stability and the robustness of the origin of estimation error system if the observer gains satisfy the conditions for generating sliding mode. We design sliding mode controller based on ISM observer and simulate van der pol oscillator and an unmanned airship with various uncertainties. The simulation results on the estimation errors and the control errors show the robustness of state estimation by ISM observer and the effectiveness of the controller based on ISM observer, respectively.
In general, mechanical systems are stabilized on their equilibrium point. Equilibrium point is often not unique and they are continuously connected, which is an equilibrium manifold. To stabilize the mechanical system on an equilibrium manifold will enable optimal control including the selection of the stabilizing position. In this paper, we propose a controller design method that stabilizes a mechanical system on an equilibrium manifold based on vector field. The equilibrium manifold is derived from dynamic equations, and by setting an appropriate evaluation function, (1) an optimal equilibrium point from arbitrary initial value is calculated, (2) a trajectory, input and vector field are derived based on linear control theory, (3) a controller is designed using functional approximation. Simulations show that different initial values are stabilized to different equilibrium points, and experimental results show the effectiveness of the proposed method.
For robotic teleoperation, semi-autonomous control, i.e. autonomous control allowing human interposition will be an effective way overcoming delay of electrical communication and emergency operation. We have proposed semi-autonomous control method focusing on excavation in teleoperation environments. In the method, a model of human operation is designed and human internal state is estimated by Extended Kalman Filter. In this paper, experimental evaluations are conducted and reported about ”Digging” process. A human skill of excavation is modeled by an attractor-based dynamics embedding shallow and deep digging trajectories for soft and hard soil, respectively. An index parameter is changed based on the load of the bucket, and a seamless motion transition is realized satisfying the restriction by setting a threshold. Moreover, by adding a human operation to the autonomy, the proposed method will cope with the emergency, which is experimentally evaluated.
In aerial industry, to improve the mileage, workpiece such as jet engine turbine case has been lightened and thinned. However, cutting workpiece with thin-walled structure causes vibration called “chatter vibration of workpiece deformation type”. Chatter vibration affects not only processing accuracy but also wear of cutting tool. This paper describes chatter vibration generated in cutting thin-walled cylindrical workpiece. Firstly, by cutting various thickness workpieces, limit thickness and waveform of chatter vibration was investigated. In workpiece with axis length 200mm, 150mm and 100mm, vibration generation limit thickness is 16mm, 12mm and 4mm, respectively. Chatter vibration consists of sine mode vibration with node in tool position and cosine mode vibration with anti-node in tool position. Secondly, natural frequencies and natural vibration modes of the workpieces were measured. A thin-walled cylindrical workpiece has natural vibration similar to chatter vibration in frequency and vibration mode. When tool contacts workpiece, natural vibration is separate in 2 which are sine mode and cosine mode. Finally, coupling of two natural vibrations was investigated. Vibration system from thrust force to translational displacement (cosine mode) and vibration system from principal force to rotational displacement (sine mode) are coupled by two cross feedback in tool position. Cross feedback 1 is transfer characteristics from translational displacement to principal force, and cross feedback 2 is transfer characteristics from rotational displacement to thrust force. When the feedback system which consists of two natural vibration systems and two cross feedback becomes unstable, chatter vibration is generated.
This study was conducted to clarify relationship between putter head motions of golf and ball hitting direction, distance with use of statistical techniques. Measurement was carried out by measuring systems for golf putting which composed of 3D gyro sensor and infrared sensors. From the measurement data, 27 parameters related to putting were selected. From the 27 parameters, 10 parameters related to hitting distance and direction were selected by analysis of variance. 10 parameters were applied principal component analysis to eliminate data redundancy. Using the first to forth principal components obtained by principal component analysis, the hitting distance and direction were learned and identified by the neural network. In addition, it was shown from the principal component analysis, angle around y axis, z axis at impact, angle about z axis, maximum of angular velocity, angular velocity around z axis at impact,the maximum and minimum angles around the y axis are important parameter for expressing the ball hitting result. Moreover it was shown that the parameter that most influence the estimation of the hit ballistic result are the angle around the y axis at the time of impact, and the angular velocity around the z axis at the time of impact.
Two phase lubricant has attracted attention as a lubricating oil with little change in viscosity with temperature change. The two phase lubricant consist of the low and high viscosity base oils which are miscible at high temperature but not at lower temperature. For exmaple, Mineral or synthetic base oil are used as a low viscosity lubricant and PAG（polyalkylene glycol）. In the high temperature region, PAG dissolves into mineral or synthetic base oil and the viscosity reduction is relieved. However, the structure and frictional characteristics of the oil film at the sliding part have not been elucidated. In this paper, in-situ analysis of the oil film formed on the friction surface was carried out with a reflection spectroscopic film thickness meter. And, this paper clarified the influence of the oil film structure and oil film thickness of the two phase lubricant and its friction characteristics. As a result, it was suggested that the oil film of the two phase lubricant in the sliding part was a multilayer due to the adsorption layer of PAG. In addition the two phase lubricant showed a friction coefficient lower by about 0.03 to 0.07 at the experimental temperature compared to PAO, and it was clarified that a thick oil film was formed.
High-density memories and high-speed CPUs are usually realized by reduction of the size of semiconductor cells in Large Scale Integrations (LSIs). Representative length scale of Ultra Large Scale Integration (ULSI) cells is going to be in nano-meter order. Dislocation accumulation during the production process in the electron channel of semiconductor device is one of the most serious problems. Dislocation accumulation has an enormous effect on the electronic state of the device. Therefore, the evaluation and suppression of dislocation accumulation are crucially important for the design and development of semiconductor device structure. In this study, we numerically analyze the suppression of dislocation accumulation in the shallow trench isolation type ULSI cells. Accumulation of dislocations is analyzed by employing a technique of crystal plasticity analysis and we evaluate the dislocation density distribution and total length of dislocations in the silicon substrate. Possibilities for the suppression of dislocation accumulation are discussed.
In recent years, the surface quality requirement in die and mold has become severer. In addition, die and mold with surface structure are increasing and it makes polishing process difficult. In order to realize mirror surface finish by cutting, it is necessary to reduce influence of tool non-repeatable run-out (NRRO) on machining surface. Rolling bearings are widely used for machine tools, NRRO of a spindle due to rolling element revolution depends on spindle conditions such as rotational speed, temperature, and cutting load. In order to reduce influence of NRRO on workpiece surface, a prototype of an excitation system which can generate counter excitation force is proposed in this paper. The tool run-out during machining was measured and the results confirmed that the machined surface was affected by this NRRO. In addition, it was confirmed that NRRO has multiple peaks in frequency domain and the state of each peak changes even at the same spindle speed. After developing an excitation system with a voice coil motor, it was confirmed effectiveness of the system that can reduce NRRO component from measured tool run-out signal.
New energy saving methods are required to address global climate change and resource depletion. New structural materials such as Carbon fiber reinforced plastic (CFRP) are used also in nowadays machine tools applications for energy efficiency improvement by weight reduction. This research group succeed in being the first to develop the energy-saving machine tool using new structural materials, mainly CFRP. Furthermore, CFRP is expected to enhance thermal characteristics, which contributes to reduction of warm up drive and implement of idle reduction. First of all, the thermal deformation of the energy-saving machine tool is investigated through single axis feed motion by measuring a test bar. It is obtained that the thermal error is obviously suppressed and shows unique behavior in comparison with a based conventional machine tool. Next, the energy-saving performance is evaluated through machining test. Warm up drive minimization method is proposed in order to realize high precision form accuracy. The warm up drive time is estimated based on an estimation model, and the energy efficiency of warm up drive is improved 57.0% in comparison with the base machine.
In general, a diesel engine does not have ignition system and it can ignite by self-ignition. It has pros that engine manufactures can consist engine components less than normal gasoline engines. However, diesel engines emit more particle matter (PM) rather than normal gasoline engine, so that diesel engines should have diesel particulate filter (DPF) to accumulate them even if it is in not only a exhaust gas but also an engine oil region. In this study, the authors clarified the possibility of PM accumulation method by using an alternating electric field applying between a metal needle and a plate to coagulate them as large particles more than 0.8 μm. The important parameters were an electric field intensity, frequency and applying time. The FESEM observation results indicated that approximately 100 nm-sized particles coagulated to be a large particle. Then, EDS analysis revealed that the particle did not include conventional engine additives such as zinc, molybdenum and calcium. Those results clearly indicated that the alternative electric field method can accumulate nano-sized PM.
Human’s ability to work upon, or manipulate objects in the environment depends on the psychological function to perceive objects’ size appropriately. In daily situation, human recognizes object size by using visual and haptic cues concurrently. In experimental psychology, human visual information processing of object size has long been a major research area, and substantial amount of knowledge has been accumulated, but relatively little is known concerning the haptic information processing. In this study, characteristics of haptic size perception were examined in discrimination and magnitude estimation (ME) experiments for ‘one-dimensional (1D)‘ stimuli (bars of which lengths were varied) and ‘two-dimensional (2D)’ stimuli (circles, triangles and squares of which areas were varied). In the experiments, participants held the 1D standard and comparison stimuli with two fingers (thumb and index or middle finger), or 2D stimuli with three (or four) fingers (thumb, index, and middle (plus third) fingers), and discriminated or evaluated the sizes of the stimuli. The results of the discrimination experiment showed that Weber ratios, defined as discrimination threshold/standard stimulus size, for the two 2D stimuli (circles and squares, but not for triangles) were lower (i.e., discrimination sensitivities were higher) than those for the 1D stimuli. The difference in the discrimination sensitivities was explained by taking into account probability summation between multiple inter-finger distance cues available for the 2D stimuli. Weber ratio for the triangles may be affected by the uncertain factor that the figures were not identified only by the information of contact points. The results of the ME experiment showed that the evaluated value vs. stimulus size functions had different slopes for the 1D and 2D stimuli, suggesting that size perception for the 1D and 2D stimuli may be mediated by different mechanisms specialized for processing of the length and the area of haptic stimuli.