Stress fields affect various characteristics of materials. However, measurement methods for three-dimensional stress fields tend to be complicated because stress tensors generally consist of six independent components. We therefore propose a simple method for measuring axisymmetric three-dimensional stress fields by measuring deflection angles of light rays using the background-oriented schlieren technique. Assuming axial symmetry of the stress field, we use the Lagrangian optics to derive a relationship between two-dimensional deflection angle and three-dimensional stress. Using independent ray polarizations, the method can reconstruct the respective refractive indices from the deflection angle. Equilibrium equations for the stress tensor can be written under the assumption of axial symmetry. By applying appropriate approximations, we formulate normal and shear stress-tensor components, which enables reconstruction of these components from refractive indices. Stress-tensor components can be experimentally generated by applying a load to a glass plate surface on the basis of the Hertz contact theory. The proposed method reconstructs the stress-tensor components from a refractive index field that is induced by the stress in the glass. The reconstructed axial-stress tensor σzz and shear-stress tensor τrz well agree with numeric calculations using structural analysis software. Other stress-tensor components, however, slightly deviate from those of the numeric calculations.
Aircraft impact analysis is needed for safety assessment of nuclear power plants. One of the items which should be analyzed for aircraft impact is physical damage to a reinforced concrete (RC) building and this can be estimated by numerical simulation. In the simulation, a simulation model which has been validated by some experimental data needs to be established. In 1988, an aircraft impact test using an F4 Phantom fighter was conducted at the Sandia National Laboratories in the US and a lot of important experimental data were measured. The numerical simulation results for this aircraft impact test are also introduced in this paper. The relationship between the thickness and the deceleration of the aircraft model is studied and then the differences in the deceleration between the simulation and test results are discussed. The relationship between the failure strain and the destruction modes of the aircraft and the target in the simulation are also studied, and then the differences between the simulation and test results are discussed as well. Through these parametric simulations, the validations of the aircraft and the target model are demonstrated. In evaluating the physical damage area inside the buildings, or discussing the necessary numbers of RC walls until the impacting aircraft stops, it is important to estimate whether the RC walls are perforated by an impacting aircraft. Besides numerical simulations, some empirical equations to estimate them are reported. One of them is the UKAEA equation. This equation estimates a dynamic punching strength of a RC wall. It is determined whether an impacting aircraft perforates a RC wall by comparing the dynamic punching strength with the dynamic impact load of the aircraft. In this paper, several aircraft impact simulations using the established aircraft model with different RC wall thicknesses are conducted. Dynamic punching strength of these RC walls are measured in each simulation. The obtained values in the simulations are compared with the estimated values by the UKAEA equation. The differences between them are investigated and the reasons of these differences are discussed.
Sintered materials are superior in productivity because of their simple process, but their mechanical properties are low. To improve the mechanical properties of sintered materials, we focus on liquid-phase sintering. In this study, we selected boron as sintering aids and evaluated on the effect of the addition quantity of boron (0-0.6 mass%) to the mechanical properties of liquid-phase sintered and heat-treated materials. In the test range of this study, the tensile strength of material with an additional quantity of boron of 0.1 mass% showed the highest value, 1386 MPa, which is about 35% higher compared to the tensile strength of material without adding boron. On the other hand, materials with an additional quantity of boron of 0.2 mass% or higher showed higher-density than material with an additional quantity of boron of 0.1 mass%, but both their elongation and tensile strength were significantly decreased. The precipitates changed between the boundary of the quantity of boron added of 0.1 and that of 0.2 mass%. Only Fe23B6 was formed in the material with the boron addition amount of 0.1 mass% or less, and Fe23B6 and Fe2B were formed in the material with the boron addition amount of 0.2 mass% or more. By cross-sectional observation of the test specimen after the tensile test, it was confirmed that in the material with the boron addition amount of 0.2 mass% or more cracks occurred and propagated at the Fe23B6/Fe2B interface and finally resulted in fracture. In the material with the boron addition amount of 0.1 mass%, however, such a fracture was not confirmed. The phenomena could be explained the fact that the mechanical properties were sharply changed between the quantity of boron added of 0.1 mass% and 0.2 mass%. The existence of Fe23B6/Fe2B interface would significantly affect the strength of the liquid-phase sintered materials.
An understanding of the impact response of glass plates is important to protect people from injury. We investigated the fracture mode of a float glass plate that fractured under a low-velocity impact and conducted a numerical simulation. First, an impact fracture experiment of a float glass plate was carried out using a dropping weight, and crack development in the thickness direction of the glass plate was observed by a shadowgraph method. Then the numerical simulation was conducted applying two types of material models to the float glass: the Johnson–Holmquist model and the elastic model with tensile pressure failure. The two models were used in a simulation and the results were compared with the experimental result. At an impact velocity of 4.43 m/s, which correspond to the deformation velocity of the glass plate of 6.1 m/s in deflection, simulation with the Johnson–Holmquist model could reproduce the strain response of the glass plate but it could not reproduce the fracture mode of the glass plate. This result implied the limitation of applying the damage model to low-velocity impact for simulating the fracture mode of a glass plate. In the material model with elastic as the constitutive law and tensile pressure failure as the failure model, the simulated fracture strength of the glass plate was the same as the experimental fracture strength, and the fracture mode showed characteristics of the bending fracture mode that was observed in the experiment, although the fracture initiation time of the glass plate was slightly delayed in the strain history. In the low-velocity impact where the influence of inertia was small, the glass plate response could be reproduced easily using the elastic model. The efficacy of the model was confirmed in the simulation result with several deformation velocities.
The global carbon dioxide emissions issue is the main hindrance of the Paris agreement goals. Biomass has been effectively utilized as a renewable energy in the household heating and the electricity generating sector. However, it is unsuited for use in the heavy industry. Due to the limitation of biomass applied in the steel industry, the pre-carbonized solid biofuel (Kindai Bio-coke) has been developed and studied throughout the years. This research studied the effect of hemicellulose (glucommannan powder from the Konjac tuber) on Japanese cedar base bio-coke apparent density, heating value, and compressive strength at room temperature and 973 K. The bio-coke samples were produced by the vertical laboratory scale compression machine connected with 12 mm mold by loading cell. The mixture of dried glucomannan powder, with 0, 2, 5, 8, 10 and 15 wt. % and Japanese cedar powder are the raw materials in this research. The production conditions were controlled following the trial experiments done by Bio-Coke Research institute. It shows that hemicellulose has blended in with Japanese cedar particles and has increased the bio-coke apparent density significantly. However, the heating value of bio-coke decreased by 3 % with 15 wt. % of hemicellulose. The maximum compressive strength at room temperature results show an open end downward parabola with peak at 5 to 8 wt. %. Bio-coke containing 10 wt. % of hemicellulose has the highest maximum compressive strength at 973 K.
The rolling noise generated by railway vehicles was evaluated in scale-model tests. The similarity relations associated with wheel/rail noise were derived and the full-scale phenomena were estimated from the scale-model tests. When converting scale-model findings to full-scale, the frequency is scaled by the ratio 1/n, accelerances of rail and wheel vibration are scaled by the ratio 1/n3, and a logarithmic term is added to the sound pressure level. To verify the validity of these scaling relations, the scale-model measurements were compared with the results of field tests. Through measurements with an impact hammer, the vibration characteristics of the track and wheel were estimated in scale-model tests, were scaled using the proposed similarity laws, and were compared with field measurements of actual tracks and wheels. The quantitative trends of the actual characteristics were estimated well from the scale-model results. The field tests showed that, though the measured noise in the test rig had an unsuitable signal-noise ratio because of the greater driven noise of the test rig itself, the rail vibrations measured in the scale-model test did have a suitable signal-noise ratio. The rail vibration measured in the scale-model test is in good agreement with the measurements from the field tests. If noise from the test rig can be sufficiently reduced, or if rolling noise in the scale model is sufficiently large, we conclude that scale-model tests can simulate actual rolling noise.
This paper describes a novel method for blind source separation using multilayer neural networks when an audio signal has been recorded in a room with reverberation or with moving signal sources. In conventional applications, speech-recognition specialists can identify the signal from a specific speaker in a recording of many speakers by analyzing a spectrogram of the recording. The spectrogram is a visual representation of the time series of frequency spectra of a target signal. To use multilayer neural networks for a similar classification task, the proposed method begins by preparing a spectrogram of a mixed signal using the short-time Fourier transform, which is then regarded as a visual object. The spectrogram is then divided into small time-frequency segments and each segment is classified into a class of the corresponding signal source by the multilayer neural networks. After that, an inverse short-time Fourier transform is employed to extract the separated signals. The paper also evaluates the separation performance of this classification algorithm. With the transformation of the blind source separation problem into a classification problem, multilayer neural network classifiers can be used, and they do not require information about the mixing environment, or statistical characteristics of the target signals, or multiple microphones. Simulated tests indicate that the proposed method achieves good separation performance under conditions with reverberation or moving signal sources. The proposed method may be adapted for separating signals from unknown convolutive mixtures and time-varying systems.
A compact and highly efficient motor is proposed in this paper. It is intended to apply to power assist legs. The motor is flat type outer rotor motor which has 16 neodymium PM pole rotor and 18 concentrated wound slot stator. Higher torque and light weight motor is better for leg assost device. Bigger least common multiple of rotor pole and stator slot number produces higher torque and lower cogging. The motor is designed using commercial FEM analysis MagNet to optimize their dimensions. The test motor is fabricated which shows high torque compared with its size than a commercial motor.
Interfaces based on surface electromyography (sEMG) signals are one of the important methods for non-invasively extracting the intention of a severely disabled person and supporting environmental control of wheelchairs and personal computers. However, sEMG-based interfaces generally have a common and maximum disadvantage of vulnerability to changes in electrode position. In this study, we aimed to develop a robust oral motion classification method that is robust to change in electrode position. Five healthy adult male subjects participated in this experiment. sEMG signals of the suprahyoid muscles during five oral motions (right, left, up tongue motion, jaw opening, and clenching) were measured using a boomerang-shaped 22-channel electrode adhered to the underside of the jaw. Oral motion classification from sEMG signals was performed using a support vector machine (SVM). When sEMG signals measured at a position different from the 22-channnel electrode position where the training data for SVM classifier was obtained were used as the test data, the classification accuracy of five oral motions sharply decreased from 92.0% to 72.8%. In contrast, when the 10 trials of sEMG signals obtained in advance at different electrode positions on different days were used as training data, the robustness against electrode position change was improved drastically and the mean classification accuracy of all subjects reached 90.4%. Furthermore, we developed an electric wheelchair control system that can operate based on classified motions and verified its usefulness for wheelchair operability and driving performance thorough the experiment. The results showed that the proposed method can omit the SVM training process required every time after the electrode is attached and can operate the wheelchair immediately after electrode attachment. Such advancement of interfaces eliminates the annoyance caused to the user who uses the interface on a daily basis and is expected to lead to an improvement in the quality of life.
A finite element elastic-plastic seismic response analysis using a full-scale integrated model of Unit 1 of the Fukushima-Daiichi Nuclear Power Plant, which was subjected to the 2011 off the Pacific coast of Tohoku Earthquake, is performed using the K computer in order to obtain both the global and local responses more precisely. The purpose of the present study is to investigate the computational performance and show the feasibility of such an analysis. The high-fidelity finite element mesh for the plant used in the present study was generated using tetrahedral elements in a previous study by Yoshimura et al. (2019a) for the pressure vessel, the containment vessel, the suppression chamber, the vent pipes, a number of supports, and the reactor building. The mesh with linear elements has approximately 200 million DOFs. The elastoplasticity is taken into account for only the steel used in the pressure and containment vessels. However, the material for the reactor building is assumed to be elastic. The dynamic response during 55 s is solved successfully, although yielding occurs at very few points. The total elapsed time for analysis is approximately 14.2 days using 1,032 nodes of the K computer. If the nonlinearity increases, the computation time may be increased by three to four times due to the increase in the number of Newton-Raphson iteration steps. Even in this case, the computation time can be estimated to be less than two months, which means that an elastic-plastic seismic response analysis of the plant using the high-fidelity finite element mesh is feasible. An elastic-plastic seismic response analysis using a quadratic element model with approximately 1.5 billion DOFs is also successfully conducted for 12 time steps (0.12 s) using 4,128 nodes of the K computer.
Spatial rolling contact pair (SRCP) is a kinematic pair of which two links in contact at a line can generate the relative rolling motion along the specified spatial trajectory. By introducing the SRCP into a linkage mechanism with a single degree-of-freedom (DOF), the mechanism can completely generate the specified output motion. However, the conventional constraint method between two links of the SRCP is not strong enough. In order to enforce the connection between the two links, the novel design of the SRCP which has a hybrid elastic constraint with flexible bands and linear springs is proposed. Since flexible bands and linear springs can suppress slippage and separation between the two links, the SRCP can generate the ideal rolling motion. At first, the design methodology of the rolling contact surfaces of the SRCP, which has been proposed by the authors, is reviewed. Next, it is confirmed that constraint with flexible bands can be applied to the designed surfaces with a mathematical approach. In addition, the design methodology of the flexible bands to generate the zero torque around the contact line between the two links is described. Then, the design methodology for the constraint with linear springs is proposed. In this methodology, linear springs are optimally arranged between links so that two links in the SRCP can keep in contact at a line. Some examples of path generators with the SRCP are designed with the proposed design methodology, and it is confirmed that the SRCPs can generate the ideal rolling motion by some simulations. Finally, the designed examples are fabricated and examined to confirm the validity of the proposed design methodology.
This paper discusses the determination of tooth-flank modification on a face gear system in order to improve the handle rotational sensation of a fishing spinning reel (hereafter, fishing reel sensation) and quantification of it. The spinning reel considered in this study uses a face gear system. One of the advantages of a face gear system is that it offers good rotational tactile sensation. However, these systems have a high propensity for assembly errors. If the reel experiences an assembly error, vibration based on the gear-pair engagement occurs when the handle of the reel rotates. The vibration is transmitted to the angler’s finger via the handle. When the vibration is large, the angler feels discomfort, which ultimately has a large influence on the fishing reel sensation. Therefore, reducing gear vibration is our most important objective. It was previously reported that when the tooth flank of the face gear is shaped according to a transmission-error-controlled curve, the reel exhibits robustness against the influence of assembly errors. The report indicated that there is a relationship between the fishing reel sensation and the amplitude of transmission error. However, it did not indicate a relationship between the fishing reel sensation and the waveform of transmission error. Moreover, the amount and width of tooth-flank modification were not optimized in the previous studies. On the other hand, because the fishing reel sensation is conventionally evaluated by human judgment, it is ambiguous and inefficient. To solve these problems, the best factor and level for tooth-flank modification were derived according to a design method based on robust engineering. The fishing reel sensation was quantified by the Mahalanobis–Taguchi system of robust engineering with high correlation. Moreover, a suitable noise factor could be applied in robust design by the accurate measurement of the transmission error. Accordingly, the optimum condition for tooth-flank modification was identified experimentally. This report elucidates the relationship between the fishing reel sensation and the waveform of transmission error and proposes a quantification of the same. Consequently, the face gear design for improving the fishing reel sensation has been established by quantifying the fishing reel sensation using the transmission error instead of sensory human evaluation.
The moon images have been in recent years employed as a referential light source for in-orbit radiometric characterization of on-board radiometer in spacecraft. The irradiance obtained by the integration of the radiance of moon pixels is compared to the referential irradiance that derives from the astrophysical model, and the comparison result includes the gain characteristics of radiometer. In addition to this radiometric purpose, the limb between moon disk and deep space is also an ideal edge in optical aspect. The edge response of radiometer obtained in the limb includes the characteristics of MTF (modulation transfer function) and straylight. In this paper, in-orbit straylight characterization and correction of SGLI (Second Generation Global Imager) radiometer that is flying on JAXA's remote sensing satellite "SHIKISAI" is reported. It is shown that LSF (line spread function) measured in the moon limb is effective trend monitor of radiometer's geometric property in orbit and is also a key to verify the validity of straylight correction model implemented in the ground data processing system. This paper proposes the methodology that constructs PSF (point spread function) by LSFs in two orthogonal direction and corrects straylight of not only the Moon but the earth image by using the constructed PSF.