This study describes a method to reliably search and determine design points required for constructing importance sampling probability density functions (p.d.f.s) in the method of estimating the structural failure probability based on multiple importance sampling simulation. In order to search out and determine all of design points without any omission, the initial points of Rackwitz Fiessler (RF) algorithm that performs the design point search are proposed to be set on limit state surfaces within the entire quadrants of the basic random variables space. First, from the standardized normal p.d.f., several samples, referred to as real samples, are generated in the specific quadrants. Using the newly proposed "inter-quadrant relational expression", the coordinates of the real sample points are converted to the coordinates of the sample points called pseudo samples in all the quadrants except those of the real sample points. In this way, real samples or pseudo samples are generated and determined in all quadrants. Next, the coordinates of intersection points of the limit state surface and straight lines extending from the origin and passing through respective real and pseudo sample points are determined. And the intersections determined on the limit state surfaces in all quadrants are proposed to adopt as initial points of RF algorithm. By executing RF algorithm from respective initial points determined, all of design points are searched out completely, and the importance sampling p.d.f.s are constructed by making use of the respective design points determined. Numerical examples for estimating the failure probability of structural systems having multivariable nonlinear limit state functions are shown based on multiple importance sampling simulation using all of the constructed importance sampling p.d.f.s and the proposed method shows accurate estimations of structural failure probabilities.
Carbon nanotube yarn, which is an aggregate form of carbon nanotubes (CNTs), is expected to be practically used as a lightweight wiring material. In recent years, CNT/metal composite yarn has been fabricated for making the CNT yarn highly conductive. While improving conductivity in the CNT/metal composite yarns, current capacity, which determines durable current value of the wiring material, has not reached practical value. In this study, composite material of untwisted CNT yarn and copper was fabricated by plating treatment for the purpose of creating a lightweight wiring with larger ampacity than metal wiring. In addition, CNT/copper composite yarns having different composite structures were fabricated and the relationships between the composite structure and electric characteristics were evaluated. One of the composite yarns had a two-layer structure in which copper was deposited on the surface of the CNT yarn, and the other had a structure in which copper precipitated to the inside of the CNT yarn. As a result of the plating treatment using a copper sulfate bath, current capacity of the composite yarn reached 6.87×108 A/m2 at the copper volume fraction of 28.9%, and the specific current capacity was 1.29 times larger than copper wire. From evaluation of the fracture mechanism, it was revealed that combustion of the CNTs and melting of the metal part were suppressed by combining the CNT yarn with copper, and it led to the large ampacity. In addition, it was possible to electroplate inside of the yarn by adding a dipping step to the plating process. In the case of the composite yarn plated the inside, an increase in resistance under large current was suppressed and further improvement of the current capacity was achieved.
In this paper, we have proposed a simple buckling evaluation method for plate structures of which original shapes and boundary conditions do not change before buckling, and buckling modes of the plates are uniform along longitudinal directions of the plates. Buckling forces of the plates in the structures are derived from the product of the Euler buckling forces and buckling coefficients of the plates. For the establishment of a relationship between the buckling coefficient and support stiffness of plates elastically supported by adjoining plates, buckling analyses by FE models were executed under conditions of different support stiffness for the adjoining plates, and then an approximate function between the support stiffness and the buckling coefficient was derived. This function was applied to examples with another moment ratio, a plurality of adjoining plates and asymmetric adjoining plates, and the buckling coefficients predicted by the function. It was then found that the buckling coefficients obtained by the proposed method matched those of the buckling analysis results. Furthermore, this buckling evaluation method was applied to plate structures, and a buckling force of a buckling plate was compared with a buckling analysis result. It was found that the buckling force could be evaluated within a difference of 6.8 %.
Effect of grain boundary microstructure, such as the spatial distribution and the connectivity of grain boundaries with different character, on the process of fatigue crack propagation in SUS430 ferritic stainless steel was investigated using the technique combined in-situ observations of crack propagation with EBSD measurements. The ratio of intergranular fracture to the overall fracture path increased with decreasing stress intensity factor range. Particularly, the ratio of intergranular fracture reached about 60 %, when the stress intensity factor range was less than 40 MPa m1/2. Moreover, the larger deflection of crack propagation occurred by the cyclic deformation at the higher stress intensity factor range more than 50 MPa m1/2, depending on the grain boundary microstructure. The intergranular fatigue cracks mainly propagated along random boundaries, and the deflection of intergranular crack path occurred at grain boundary triple junctions, owing to the further propagation along random boundary ahead. Moreover, when the fatigue crack propagation along random boundaries was inhibited by a triple junction composed of low-∑ CSL boundaries, the branching of fatigue crack occurred at a triple junction behind and the crack subsequently propagated along another random boundary. The propagation of fatigue crack was inhibited for a while by crossing low-∑ CSL boundaries and triple junctions. The possible grain boundary microstructure for control of fatigue crack propagation in SUS430 stainless steel was discussed based on the observed results.
In order to investigate the suitable test methods for determining threshold of hydrogen-induced crack growth, KI,H, JIc, none-unloading JIc, constant-load and constant-displacement tests were conducted in 115 MPa hydrogen gas at room temperature, using SCM435 low alloy steels whose tensile strengths were between 824 and 1127 MPa. Constant-load and constant-displacement tests have been standardized by ASME KD-10 for determining KI,H in hydrogen gas. JIc test has been standardized by ASTM E1820 for determining fracture toughness JIc or KIc in air. Recently, JIc test was done in hydrogen gas to obtain KI,H. In this study, there were many cases when JIc tests were not conducted in hydrogen gas, because CT specimens broke before the first unloading. Then, none-unloading JIc test, where unloading processes were eliminated in JIc test, was employed in hydrogen gas. All four tests were done under small scale yielding in 115 MPa hydrogen gas. KI,H obtained by four tests was almost the same. KD-10 demands that constant-load and constant-displacement tests of ferritic steels such as SCM435 are done for 1000 hours. Contrary to this, none-unloading test at displacement rate of 2×10-3 mm/s was finished within one hour. It was concluded from these results that none-unloading JIc test was the best test for determining KI,H in 115 MPa hydrogen gas. On the other hand, JIc test was the only test for determining KIc in air, because KIc was obtained under large scale yielding.
Because of the stable material property of optical fiber up to 1000℃, fiber-optic Bragg grating (FBG) sensor is considered as one of possible ultrasonic sensors used at ultrahigh temperature. However, disappearance of reflectivity of a normal FBG in the high temperature above 900℃ makes the ultrasonic detection impossible. In order to detect ultrasonic wave under high temperature environments, we conducted an anneal heat treatment to produce a regenerated fiber Bragg grating (RFBG) sensor. Because the RFBG has a stable reflectivity even at temperature of 1000℃, we detected the ultrasonic wave successfully at the temperature. Especially, because a π-phase-shifted FBG (PSFBG) was used as the seed grating, the RFBG sensor possessed very short effective gauge length that resulted in a broad bandwidth response to ultrasonic wave over 1 MHz. Hence, we believe that the ultrasonic RFBG sensors could be potentially applied for ultrasonic detection in non-destructive tests to evaluate microscopic damage in materials under extreme high-temperature environment.
In order to study the hydrogen embrittlement behavior of austenitic stainless steel weld metal, slow strain rate tensile (SSRT) tests and fatigue life tests were performed in high-pressure hydrogen gas. Tensile and fatigue life specimens, in which whole of the gauge section consists of weld metals, were machined out from a TIG welded round bar. The base metal of multi-pass welded bar was SUS316 (hi-Ni), and the filler metal was 317L. Two series of weld metals were tested; one was an as-welded metal having coarse columnar gain with dendrite and δ-ferrite, and the other was a post-welded solution-treated metal. The relative reduction of area, RRA, was 0.55 for 317L as-welded metal, and approximately 0.9 for SUS316 (hi-Ni) base metal and 317L post-welded solution-treated metal. The fracture surface of 317L as-welded metal included lamellar weld (LW) fracture surface, whereas those of SUS316 (hi-Ni) base metal and 317L post-welded solution-treated metal were entirely covered with dimples. Fractographic observation in combination with EDS manifested that δ-ferrite was responsible for the hydrogen-enhanced crack growth leading to the formation of LW, and therefore the post-welded solution-treated metal without δ-ferrite exhibited excellent resistance to hydrogen. Regardless of the heat treatment, the fatigue limit of 317L weld metal was not degraded in hydrogen gas as well as the austenitic stainless steel base metal.
Micro-Raman spectroscopy is used to measure phases, stresses and strains in microstructures comprising semiconductor materials, such as Si. However, the two-dimensional Raman imaging techniques for directly observing phases and measuring stresses and strains in a large area are required. In this study, we develop a new micro-Raman spectroscope equipped with an integral field unit (IFU) for two-dimensional imaging. Two-dimensional Raman images are obtained without scanning laser spots and stages. In addition to the IFU, this instrument primarily comprises an illumination optical system. In the illumination optical system, a diffractive optical element is used to enlarge the area of the laser spot and transform the circular laser beam into a square beam. The IFU simultaneously collects two-dimensional Raman signals using a microlens array, 4 × 4 optical fiber bundle, two-dimensional imaging spectrometer, and highly sensitive two-dimensional charge-coupled device (CCD) detector. Subsequently, we conduct two-dimensional imaging of the Si phase and residual stress components of the (111)-oriented single-crystal Si wafer induced by Vickers indentation. The Raman spectra are measured under polarization conditions to decompose the triple degeneracy of Si, and the residual stress components around Vickers indentation are calculated from the relations between the Raman shift and applied strain.
For designing a high-performance mixed-flow pump, control and suppression of performance-curve instability is crucial. For doing so, clarification of the essential flow physics that leads to the performance-curve instability is crucial in addition to an accurate prediction of the performance curve. We investigated internal flows of a mixed-flow pump, with performance-curve instability at round 60% of the designed flow rate, by using Large Eddy Simulation (LES). In the previous report, we clarified that drop of the Euler's head caused by stall near the tip of the impeller's blades is the major cause of the performance-curve instability. In the present report, we investigated in detail unsteady internal flows of individual blade passage near the head-drop point. As a result, we clarified the followings. (1) When the flow rate through a blade passage is low, the Euler's head is high for that particular passage, and this condition propagates in the direction of the impeller rotation for the whole impeller while the impeller makes approximately 20 revolutions. (2) Upstream flow of the stalled blade passage is deviated to the downward neighboring blade passage, resulting in increase in the load of the neighboring blade near its trailing edge. The neighboring blade passage will then be stalled. (3) When the flow rate in a stalled blade passage reaches the minimum, the passage starts to recover from stall while the pressure gradient in the streamwise direction will decrease.
Joint statistics between velocity gradient and fluctuating static pressure in a turbulent planar jet are experimentally investigated. The experimental data was acquired by simultaneous measurements of velocity gradient ( ∂u’2/∂x1 and ∂u’1/∂x2, where u’1, u’2, x1 and x2 are fluctuating stereamwise velocity, fluctuating cross-streamwise velocity, streamwise coordinate, and cross-streamwise coordinate, respectively) and fluctuating pressure p′ using two combined probes. One of the combined probe consists of an X-type hot-wire probe and a pressure probe and the other combined probe consists of two I-type hot-wire probes arranged in vertical direction and a pressure probe. In the time-series, it is shown that the events in which the instantaneous Reynolds stress, squared cross-stramwise velocity, and product of velocity gradient and pressure shows significantly large value (so-called “significant events”) occur intermittently with negative pressure fluctuation, this implies that the Reynolds stress transport phenomena are locally active with the large-scale vortex structures observed in a turbulent planar jet. It was also found that the standard deviation of (p’/ρ)(∂u’2/∂x1) conditioned by the negative pressure fluctuation is 21% larger than the unconditioned standard deviation. The cospectra show that the correlation (p’/ρ)(∂u’2/∂x1) greatly contributes the local isotropy of the flow field. On the other hand, we confirmed that ∂u’1/∂x2 is almost unrelated to the pressure fluctuation in the present turbulent planar jet. The results show that there is little contribution on the Reynolds stress transport by the correlation (p’/ρ)(∂u’1/∂x2).
Numerical simulations are carried out aimed at finding a key flow structure which leads to a laminar-turbulent transition of a boundary layer with streaky structures. In the preliminary computation, an array of cuboids is used to form streaky structures inside a boundary layer. Then, a disturbance is introduced into the boundary layer by ejecting a short-duration jet from a hole in the wall into a low-speed region in the streaky structures. Although the boundary layer returns to a laminar state when the jet velocity is set to 18% of the uniform flow velocity, it eventually turns into a turbulent state downstream in the 20% case. The differences are investigated in detail in terms of the vortical structures. As a result, only in the stronger jet case, a flat spanwise vortex is generated beside one leg of a hairpin vortex and it merges with the streamwise vortex nearby forming an inclined streamwise vortex. On the other hand, the flat spanwise vortex disappears without being connected to the streamwise vortex in the weaker jet case. The inclined streamwise vortex is stretched by the mean velocity gradient of the boundary layer growing into a strong vortex, and new vortex structures are generated around the inclined one, which leads to turbulence. Therefore, the results suggest that formation of the inclined vortex is the key to transition of the boundary layer.
The authors develop a small and simple steam-reforming reactor in a home-use size for n-dodecane as a heavy-hydrocarbons fuel. Under the thermal condition controlled by electric heaters and a gas burner with a thermal diffuser, the authors measure the inside-temperature profile and the hydrogen molar fraction (concentration) CH2, together with the molar fractions CCH4, CCO and CCO2 of other main gas components such as CH4, CO and CO2, respectively. As a result, the authors successfully achieve suitable inside-temperature profiles. And, the authors experimentally reveal the effects of the liquid-hourly space velocity LHSV upon the molar fractions, in addition to the LHSV effect upon a conversion ratio XC12H26. Furthermore, the authors reveal the effects of the temperature T inside the reactor upon both the molar fractions and XC12H26, comparing with the chemical-equilibrium theory in a wide range of LHSV. The comparison with the chemical-equilibrium theory indicates that the temperature at the catalyst-layer-bed downstream end could be regarded as the reaction temperature.
Flame height variations of a laminar stagnating premixed flame with gas component transition between fuel mixture A (methane:92%, ethane:6.7%, propane:1.3%) and B(methane:84%, ethane:13.3%, propane:2.7%), and between A and C (methane:76%, ethane:20.0%, propane:4.0%) are discussed. The estimation of the flame speed and the flame temperature of fuel mixtures A, B and C by the Chemkin-Pro show almost the same values for all fuel mixtures. In experiments, the transition between A and B and between A and C were performed. The transition time changes from 1 s to 10 s, keeping flow velocity and equivalence ratio constant at 0.8 m/s and 0.7 respectively. The flame position was measured by using images taken by a high speed camera with 125 fps. Two transition patterns are examined, keeping the total flow rate of premixed mixture constant. One is the constant flow rate transition, which changes the gas component, keeping the fuel mixture flow rate constant. The other is the constant equivalence ratio transition, keeping the equivalence ratio constant. In the case of the constant flow rate transition, the equivalence ratio changes which results in the variation in the flame speed, the flame temperature and the flame height. It means that the combustion state changes with the transition. On the other hand, in the case of the constant equivalence ratio transition, the flame speed, the flame temperature and the flame height keep almost the same state, which means that the gas component can be changed, keeping the combustion state the same.
Low-temperature-difference indirect heating Stirling engine is the most suitable device for a small-scale wood biomass combined heat and power. To design this type of Stirling engine, conventional design method is not sufficient for optimizing working space temperature difference. Therefore, a new design method is developed. A ratio of working gas displacement to volume change is defined, which is found to be a simple function related to the temperature ratio of the ideal Stirling cycle. Through the preliminary study, it is found that the conventional alpha, beta and gamma Stirling engines are not suitable for practical low-temperature-difference engines. Finally, alpha-plus-type engine which is optimized for low temperature difference operation is proposed. The new engine is developed and the results of the operation test is demonstrated.
Mass transfers in porous electrodes of fuel cells affect the performance of the fuel cells. The aim of this study is to verify effectiveness of a measurement method of a hydrogen gas concentration in a fuel electrode of a solid oxide fuel cell (SOFC) to clarify the mass transfer mechanism. This technique was applied to a SOFC which was composed of 8 mol % Y2O3-ZrO2 (YSZ) electrolyte and Ni-YSZ fuel electrode. A sensor which was made of a platinum wire coated with zirconia and alumina was inserted into the fuel electrode to measure the oxygen partial pressure. The hydrogen gas concentration was determined from the oxygen partial pressure which was obtained from an electromotive force of the sensor using Nernst's equation. The hydrogen gas concentration decreased with increasing the current density up to 0.45 A/cm2 and also with increasing the operating temperature (1173 K to 1273 K) at the same current density. The measured values of the hydrogen gas concentration were proportional to the values calculated by three dimensional numerical simulation. These results indicated the measurement method had a potential for the measurement of hydrogen gas concentrations in fuel electrodes. Furthermore, the effective diffusivity of hydrogen gas in the fuel electrode could be obtained from the hydrogen gas concentration.
The natural convective heat transfer from banks of heated horizontal cylinders to air was investigated experimentally. The experiments were mainly carried out with the in-line tube banks consisted of five stairs of ten-cylinder-row aligned horizontally. The whole cylinders in the bank were heated with identical heat flux and their diameter d, vertical and horizontal gaps Gh, Gv between cylinders were varied as d=8.4, 14.4 mm, Gh=10.6-30.6 mm and Gv=5.6-30.6 mm. The flows induced in the banks were first visualized with smoke and the Nusselt numbers of the whole cylinders in the banks were subsequently measured. The visual results depicted that the smokes issued from the upstream of the bank gather gradually toward the vertical centerline of the bank. With the gathering of the plumes, the Nusselt numbers of the cylinders placed near the center of the horizontal rows show marked reduction in the downstream direction. Their Nusselt numbers were rearranged with several parameters to obtain non-dimensional heat transfer correlations. It was found that the Nusselt numbers NuGv for the second to fifth stairs in the bank are correlated well with the parameter [RaGv*(Gv/d)(Gh/d)], while those for the first stair are predicted well with the parameter [RaGv*(Gv/d)2], where NuGv and RaGv* stand for the Nusselt and the modified Rayleigh numbers based on the vertical gaps Gv.
An experimental study investigated the frequency characteristics of a stretched cylindrical diffusion flame in response to sinusoidal air flow velocity oscillation. The flame has a convex curvature with respect to the air stream. The fuel was methane diluted with nitrogen, and oxidizer air. The flame was formed in the air stream side from the stagnation surface. The oscillation frequency f ranged from 10 Hz to 250 Hz. In order to clarify the influence of an oscillation amplitude A of the air flow velocity on the flame responses, three kinds of amplitude were chosen. The flame was photographed by the high speed video camera, and flame radius rf, flame thickness δ, and flame luminosity Lf were analyzed. The air flow velocity va at the nozzle outlet was measured by using particle image velocimetry. Though velocity gradient of the air flow ga responds quickly to the changing va regardless of f and A, the gradient of the fuel flow gf delays with increasing f and A. Here, ga correlates to the flame stretch effect, and gf impacts the fuel transportation. Response of rf to varying va also delays with increasing f and A. δ/rf, which relates to the flame curvature effect, responds complicated with the change in f and A. Oscillation amplitudes of Lf have maximum values with respect to f regardless of A. These maximum values are greater than those of a steady flame, over the same air velocity fluctuation ranges. This complex change in the Lf with respect to f is closely related to the phase difference in the respective time variations in δ/rf and gf, and the magnitude of these values.
Newly developed 3D scanning optical endoscopic probe consists of φ1.5mm quartz pipe and 2 micro motors that run inside and conduct helical 3D scanning. This research looks into the possibility of accurately measuring the inner wall of extremely small diameter object by combining 3D scanning endoscopic optical probe and OCT (optical coherence tomography). Conventionally, precision measurement of such extreme inner diameter size was not possible due to influence of what is called “fluctuation of light” and “mechanical run-out of the measuring instrument itself” in axial and radial direction. In the new method, the inner wall of quartz pipe is measured in advance by calibration work, and the inner wall of the object is measured based on the quartz pipe. Applying this method, we succeeded in measuring with standard variation 0.07μｍ(σ) repeatedly. This new method also features auto-correction of the incline angle between the optical probe and the measuring object by computing, which prevents setting error and variation.
Visual servoing towards moving target with hand-eye cameras fixed at a hand of a robot is inevitably affected by the hand's dynamical oscillations, therefore it is difficult to keep target's position always at the center of camera's view, because nonlinear dynamical effects of whole manipulator stand against tracking ability of the visual servoing. One possible solution to overcome this problem is that the visual servoing control of the hand and eye-vergence is separated independently, so that the camera can track the target to observe it at the center of camera images to enhance the tracking ability (trackability). In line with this tactics, the authors have developed an eye-vergence visual servoing control system to enhance the trackability. With several experiments, it has been shown that the trackability of the eye-vergence motion is superior to the one of hand-eye system since the eyes' motion can be quicker than the hand's motion.
A pneumatic artificial muscle is a rubber actuator activated by air pressure. It is lightweight and has the high power density compared to other actuators such as motors and fluid powered cylinders. In addition, it can provide high compatibility with human since its flexibility. Authors have developed the Straight-fiber-type pneumatic artificial muscle which has high output and high contraction amount compared to the McKibben type artificial muscle that is widely used. However, the lifetime of the Straight-fiber-type pneumatic artificial muscle has not been considered so far. In this paper, effects of aspect ratio and materials on the lifetime of the artificial muscle are examined for prolonging the lifetime. Firstly, the desirable maximum stretch rate of the material is developed. Secondly, fatigue life is measured by reducing the elongation of the rubber material by changing the aspect ratio of length and inner diameter in the SF-ARM. Finally we measure the influence on the output characteristics by changing aspect ratio. The result shows relationship of the lifetime and the aspect ratio of the artificial muscle. We showed that the artificial muscle’s lifetime and contraction characteristics can be selected according to the application.
In this paper, we proposed a system in which robot swarms autonomously divide or merge themselves according to phase gradients emerged by coupled oscillators. Due to the limitation of communication cost or ability, a large-scale swarm should be controlled in the distributed manner. Although the agents in the proposed system were equipped local communication system only, they successfully organized group formations, and divided or merged them. We employed phase gradients emerged by phase oscillators, which we could find similar phenomena in living slime molds. We implemented a phase oscillator on an agent, and proposed an algorithm to move along the gradients. By controlling phase gradients, we could make the swarms dividing or merging themselves in the self-organization manner. We provided formulations and analyses to guarantee those performances. Simulations and experiments were carried out in order to verify the performance of the proposed system.
This study aims to establish the fundamental theory of function of the practical inerters. Inerter is effective component for mechanical vibration system to control vibration frequency characteristics. Many studies related to inerter had been examined in the past. Although most of the previous studies are examined with ideal inerter which ignore mass and inertia of the devices themselve. We assume that the function of practical inerter can be regarded as the function of ideal inerter with two inertias connected to each terminal. We formulate four types of practical inerters: three types of torsional inerter constracted by planetary gear unit and one linear type inerter using rack and pinion gear mechanism. Re-arranging dynamic characteristics based on the assumption of the practical inerter function, it is confirmed that function of each practical inerter can be represented as the combination of two functions: one is ideal inerter function and the other is inertia-distribution function which is redistributed the inertia of the devices to each terminal. In addition, the inertia-distribution function could furthermore devide three subfunctions: first is inertia transfer, second is the directly connected inertia to the terminals, third is the indirectly connected inertia to the terminals. As the concluding remarks, fundamental theory of the practical inerter function is sucsessfully derived.
The potential of an ultrasonic biometric finger sensor to evaluate the finger load and surface texture in contact opposition was investigated under the range of quasi-static load and low sliding speed. The ultrasonic probe, which has a respective vibration element for reception and transmission, attached to the nail plate has a transducer 5 mm in diameter with 5 MHz center frequency. The reflection echo ratio H1 from the nail bed is reduced with increment of nail bed stiffness (acoustic impedance) due to increasing finger load W. In contrast, the reflection echo ratio H2 from the finger-pad is increased with increment of finger load since the amplitude of interference wave reflected from the finger-pad is increased due to the phase decrement of the reflected wave from there by flattening of the finger pad. Therefore, the potential for the estimation of finger load W using the echo ratio H1 or H2 was cleared. Additionally, it becomes possible to evaluate the surface texture in contact opposition since the finger-pad echo ratio H2 is strongly affected by local displacement on finger-pad. Since the nail bed echo ratio H1 during catalyzed migration of the finger depends on only finger load without being influenced by the texture of the opposition surface, the potential for the substitution of tactile impression of the person by the simultaneous observation of H1 and H2 became clear.
Mullins effect is the phenomenon of stress softening due to prior straining. Stress softening affects the response of facilities isolated by rubber bearings to strong earthquakes because it changes the stiffness of rubber bearings. The influence of the Mullins effect on seismic responses needs to be understood in detail in order to design facilities isolated by rubber bearings based on performance design. The stiffness of rubber isolators which is affected by stress softening, varies over time because stress softening changes depending on the number of repetitions of straining and the magnitude of the generated strain. The magnitude of strain generated in a facility before the principle seismic motion of an earthquake reaches the facility differs depending on whether the earthquake is subduction-zone earthquake or an active fault earthquake because the principle seismic motion of an active fault earthquake reaches the facility in a shorter time. This paper presents the results of a study to investigate the influence of stress softening caused by the Mullins effect and differences in the seismic response of a facility depending on the characteristics of earthquakes.
In this paper, we discuss a modeling method and an altitude control system for a drone type UAV using the image information from the forward camera of the UAV. The model for the UAV dynamics is constructed based on the motion equation and the unknown velocity control logic which was made the internal organs in the drone system, and the parameters of the model are obtained by some experiments of the velocity constant control. The transfer function are expressed the 2 dimensional state space equation, and the optimal control method applied to the system include some limitation of the velocity control logic. This optimal control logic is realized as a PID control system. The P gain range of the PID controller is determined by the parameter of performance index of optimal control logic and the system keep optimal control feature in the range. By the experimental results, we confirmed that this system is stable and efficient.
Karman vortex shedding occurs when the gas passes through the duct with tube bank of the heat exchangers, such as gas heaters and boilers. Very high level sound in called “self-sustained tones” occurs due to the interference of the vortex and the sound field in the duct. In general, baffle plates are used to suppress the self-sustained tone. However, it is difficult to use them effectively, because insertion conditions have not been established. Then, perforated plates are installed in both sides of the duct to suppress the self-sustained tones. As a result, it was clarified that the perforated plate could suppress the self-sustained tone as expected. The perforated plates are generally used with a cavity to obtain the suppression effect effectively. However the perforated plates change the acoustic natural frequency of the sound field of the duct. In previous paper, this was not referred. This paper aims to clarify the role of the perforated plates when it changes the acoustic natural frequency of the duct. In this study, one dimensional duct will be used for simplicity and the relationship between the aperture ratio and the acoustic natural frequency will be obtained analytically and experimentally. As a result, it was clarified that the analytical results are in good agreement with the experimental ones and the plates with holes had a role of acoustic damping in calculation of the acoustic natural frequency of the one dimensional sound field like a duct with plates with holes.
Previously, in order to measure friction coefficients of tire grounding surface in car slipping, a cantilever-type sensor that can detect the vertical load and friction force as well as the direction of the friction force simultaneously has been proposed. The sensing part, which contacts grounding surface, of the proposed sensor is pulled out of the tire tread through a hole. However, penetrating the hole through tire tread part has some problems: leakage of air from the tire, weakening of the rigidity etc. Therefore this study proposes a sensor that can be installed on the inner surface of a tire without penetrating hole through the tire tread by filling the detecting part of the sensor in the inner part of the tire tread. If the detecting part filled in the inner surface has sufficient airtight structure from the integral manufacturing, the durability of the sensor as well as retaining air pressure are expected. This study measured the deformation of the inner part of the tread through the detecting part under high-load at tire slipping state. Furthermore, relation between the measurement values and the force applied to the tire from grounding surface was clarified. As a result, the study confirmed that the proposed method can detect the friction coefficients between the tire and tire grounding surface.
In this study, we propose a fast algorithm for vision-based vibration source tracking that can significantly reduce the computational complexity in pixel-level digital filters. The algorithm reduces the complexity by adjusting the sampling rate to twice the vibration frequency of the target object to be tracked using frame interpolation. The computational complexity and properties of the pixel-level digital filters for downsampled images are evaluated; the proposed algorithm can accelerate the pixel-level digital filters, while retaining the admissible filter property for vibration source tracking unlike the approach used previously in which the input images captured at a high frame rate were directly processed using pixel-level digital filters. The pixel-wise accuracy in vibration source tracking is demonstrated by several evaluation results of offline high-frame-rate videos, which displayed various flight scenarios of a multicopter with its propellers rotating at 90-100 Hz.
In mesh-based fluid-structure interaction (FSI) analysis, mesh moving techniques are essential for preventing mesh distortion and improving the robustness of FSI analysis. In our previous study, we have proposed a new mesh moving technique with minimum-height-based stiffening, which is more robust against the mesh distortion compared to existing techniques. Although this technique provides reasonable distribution of stiffness in space depending on minimum height of each mesh, there is a parameter that determines relationship between the minimum height and the stiffness. Optimal value of this parameter varies depending on problem. However, it is empirically determined in usual. In this study, we develop optimization approaches for the parameter both in space and time directions adopting three optimization methods: static optimization, global optimization and local optimization. Benchmark problems were analyzed for quantitative evaluation of these three approaches. The static optimization provides the best parameter in the minimum-height-based stiffening technique without optimization in time direction. The results with the global optimization contain the best in all results in this study. However, this approach requires unacceptable computational cost from a practical point of view. The local optimization has a good balance between computational cost and robustness since it can achieve comparable to or more robustness against the mesh distortion with much chaper cost compared with the static optimization. This approaches are expected to be applicable to FSI analyses, and improve their accuracy and stability.
This research addresses an evaluation method of business value considering risk-hedging options from the first stage of the product development. A scenario planning method is introduced into the estimating method of the business value in order to identify uncertain factors, which affect to the business value. Generally, the scenario planning method has a weak point that it is difficult to apply its result into the project plan, because the specified factors are relatively qualitative. Proposed uncertainty analysis organizes the qualitative factors into four types of stochastic distributions. By combining the risk-hedge options and probabilistic distributions, a decision tree diagram, which contains the numerical estimated values about product development project, is calculated. The decision tree diagram describes project's EPV (Expected Present Value), so that the best combination of options is derived. The proposed method is applied to the i-Painter development project, which is automatic repairing robot of the buildings as an example. Two risks about future technological change in painting mechanics and flooding around factory are identified, calculated, and compared. The application result shows that the proposed method can surely help the development member to specify the economical external element change. In addition, the result indicates that the best business value is estimated and best risk hedge option can be calculated.
Single-crystal SiC is an important material for high-power semiconductors, optoelectronic applications because of its good material properties. Compared with silicon, SiC is harder and more difficult to slice, although high precision slicing process is required for a thinner slicing width. A SiC ingot is conventionally sliced using a fixed-abrasive diamond wire, where the core wire diameter is wide approximately 160 μm and diamond grain size is 20 μm. In this study, precision slicing tests were performed for single-crystal SiC by using an extremely fine diamond wire which was a half width of the conventional one. The used diamond wire had two types of core wire diameter, 60 μm and 80 μm, and the grain size was 5-10 μm and 6-12 μm, respectively. The diamond wire was driven in a single direction at a high speed of 1750 m/min. The slicing width, chipping width, workpiece surface roughness, slicing force and diamond protrusion after slicing were investigated experimentally, and a diamond blade which was usually used for slicing SiC was adopted for comparison. During slicing, the Ni plating that covered the diamond grains on the wire was partially removed which maintained the sharp protrusion of the diamond grain. The results showed that by using the proposed extremely fine diamond wire, the chipping width was significantly lowered and the normal slicing force was stable and low. Furthermore, the present study provides high-precision continuous slicing without interval dressing of the diamond wire.
This paper focuses on the design optimization of clad structures composed of different materials, which are expected to earn better characteristic physical and mechanical properties than structures with single materials. In particular, a non-parametric shape optimization method is proposed for designing the interface shapes of three dimensional composite structures composed of dissimilar materials in natural vibration problem. The objective functional consisting of a set of specified vibration eigenvalues with weighting coefficients is maximized under the volume constraint and repeated eigenvalues. Because the positive weighting coefficient maximizes the eigenvalue, whereas the negative weighting coefficient minimizes the eigenvalue, this optimization method makes it possible to control the sum or the gap of the specified eigenvalues by setting positive of negative of the weighting coefficients of the specified eigenmodes. The shape gradient function is derived using the Lagrange multiplier method and the material derivative method, and is applied in shape update based on the H1 gradient method. A cantilever cylinder composed of 2 different materials with repeated eigenvalues and a composite inlaid plate are optimized in this work with two patterns of weighting coefficients to illustrate the shape optimization algorithm. The results show that the proposed interface shape optimization method can successfully control the vibration eigenvalues, while maintaining the smoothness of the interface boundary.
The slider/disk spacing of magnetic disk drives has been reduced in order to increase the recording density. Especially, the thermal flying-height control technology, where the electromagnetic transducer is protruded into the slider/disk spacing by heating the slider partially, contributes to make the flying height less than 2nm. Because of the narrower gas bearing clearance, the bearing pressure rises up to several tens times of atmospheric pressure. This pressure rise causes the deformation of slider and disk surface. The slider and disk surface deformation causes the change of gas bearing clearance and consequently the change of air bearing pressure. The pressure change causes the flying attitude. The flying characteristics also may be different from that of expected at the design, where the effect of deformation is not included. It is important to estimate correct flying characteristics affected by the deformation to realize stable flying and accurate recording. We introduced iterative method for searching the flying attitude affected by the slider/disk deformation. We obtained the air bearing pressure by solving the molecular gas lubrication equation numerically. And the simple numerical method, which utilizes the elastic half-space assumption, was employed for calculating the deformation of pressurized disk surface. The finite element method was applied to analyze the slider deformation. And the effect of deformation on the slider attitude is evaluated.
This article suggests the machine operation mode can be estimated from sensors attached to the machine in the production line. An injection molding machine (IMM), which is widely operated in the plastics industry, was used in this research within an actual production line. Four strain sensors were attached to the IMM to measure the clamping force in each production cycle. Auto or semi-auto mode was estimated from the clamping force sequence. Auto mode is continuous production by the machine itself, while semi-auto mode involves intermittent human operation and includes such functions as machine start, machine finish, and trouble shooting. Approximately 340000 cycle data were obtained in 10-week production. The changing value was calculated by the binomial filter statistical technique, as well as the differencing of time series data from the clamping force in each cycle. And the relationship between changing value and operation mode is evaluated by the area under the curve (AUC) calculated from the receiver operating characteristic curve (ROC curve). As a result, we obtained that AUC value was 0.86 from 10-week production data, which means operation mode can be estimated from the changing value of clamping force in a high level. This estimating method has a low computational cost; therefore it is easy to install on a machine's board control system. We expect that this method will be used to detect the defective product, the machine malfunction or the mold failure.
This study aims to develop a monitoring system, which can automatically detect tool wear in end-milling operation. A feature of this system is the utilization of the predicted cutting torque for detecting the difference between normal and cutting trouble. The cutting torque predicted by a cutting force simulator is compared with the cutting torque measured and evaluated from the driving torque of a spindle motor. Because the dynamic change of the cutting torque can be predicted by the cutting force simulator as the reference cutting torque, it is possible to detect cutting trouble correctly without disturbance arise from the changes of the cutting conditions and the machining form at every moment. In the cutting simulator, this study uses the workpiece voxel model in order to calculate the uncut chip thickness for the estimation of the cutting force. For the tool wear detection, 200 % increase of the average cutting torque is set as the threshold to detect 300 μm flank wear. In an experimental milling of a workpiece with holes using a worn square end mill, it is confirmed that the increase of the average cutting torque can be identified clearly in both of stationary and transient milling situations. It was verified that the tool flank wear could be detected correctly even in the dynamic change of milling operation.
Even in a state that the person is resting, the person vibrates with a small amplitude. This vibration is called human tremor. For example, when performing precise work such as watch assembly or surgical operation, the tremor will have an influence on the accuracy of work. In order to suppress the tremor, frequency spectrum analysis of the tremor is necessary. However, only dominant frequency of the tremor have been calculated in previous works. In this paper, human tremor model for frequency spectrum analysis is proposed. In the model, the tremor is regarded as forced vibration. Forearm is modeled as a rigid link, which is antagonistically driven by two Hill's muscle models. The stiffness of muscle model is considered as non-linear. This makes it possible to estimate the difference of frequency spectrum of the tremor occurs due to different angle of the elbow. Moreover, the force driving the forearm is generated from muscle by using leaky Integrate-and-Fire cell model. In a previous study, it was confirmed that neural cell had a refractory period, and there was randomness in the period. Therefore, in this study, the refractory period of the cell model is set to the normal distribution. Because the force is intermittently generated by the random period, the forearm is vibrated. The vibration spectrum obtained from the simulations and that obtained from the experiments quantitatively agreed.
This paper describes the use of nine-axis motion sensors to evaluate knee joint angle estimation accuracy during walking. The nine-axis motion sensor comprises a three-axis gyro sensor, a three-axis acceleration sensor and a three-axis geomagnetic sensor. It can estimate joint angles during exercise by correcting the drift of the three-axis gyro sensor using information obtained from the other two sensors. Human movement results from the rotational motion of the respective joints, so that the proportion of the centrifugal acceleration and the tangential acceleration in the output of the acceleration sensor increases during exercise. Processing the centrifugal acceleration and tangential acceleration appropriately and ascertaining the degree of estimation error are important for improving the joint angle estimation accuracy. For this study, the authors produced a sensor fusion algorithm using an extended Kalman filter to correct the acceleration sensor output. The sensor fusion algorithm uses information obtained from the nine-axis motion sensors to estimate the knee joint angle by correcting the centrifugal acceleration and tangential acceleration. During the experiment, the 3D motion analysis system and two nine-axis motion sensors measured walking exercise. The knee joint angle was estimated using an extended Kalman filter with information obtained from the nine-axis motion sensors. We evaluated the system accuracy for knee joint angle estimation by comparing the nine-axis motion sensor results and the 3D motion analysis system results. This analytical method is anticipated for use in estimating motion in sports and healthcare applications.
An intelligent snatching detection system (ISDES) for autonomous detection of criminal incident by using machine learning approach is presented in this paper. Also, ESSM (Extended Snatching Situation Model) is presented to give an effective definition of the whole snatching situation including victim's behaviors. Rule-based decision making and machine intelligence are primary components of the proposed system to act without being explicitly programmed for data dispersion. Some motion characteristics are determined from video streams, also using the ESSM and machine intelligence, the system automatically classifies the situation of the video streams into criminal or non-criminal scenes. After constructing the system, we use test sequences that are continuous video streams of human behavior consisting of several actions in succession. We consider six types of scenarios for the experiments including victime's behaviors as the snatching incidents performed with motorcycle. The experimental results show that the system can effectively detect criminal scenes with an accuracy of 95.83 ％.