A nonlinear modeling and prediction method using radial basis function (RBF) network is developed in this paper, where the coordinate system of training data is transformed using the affine transformation. It is difficult to accurately predict the time series by conventional approach using the RBF network, in which the coordinate system is always fixed and this makes the prediction poor. For highly accurate prediction using the RBF network, the coordinate system is transformed using the affine transformation. The coordinate system of training data for the RBF network is transformed, and consequently it is expected that the highly accurate prediction can be made in comparison with the conventional approach. The proposed approach is numerically easy to implement with the computationally inexpensive procedure. The validation and characteristics of the proposed approach are examined through benchmarks.

We investigate the secondary instability of thermocapillary-driven convection in a high-Pr liquid bridge (Pr = 4) of half-zone geometry via direct numerical simulation. The convection is known to exhibit a three-dimensional time-dependent ‘oscillatory’ state with a distinct azimuthal modal structure, that is, spatio-temporally periodic state after the onset of the primary instability. We indicate that the convection exhibits another transition to spatio-temporally quasi-periodic states by increasing the intensity of the thermocapillary effect. The proper orthogonal decomposition (POD) is employed in order to extract the variation of the flow structures before/after the secondary instability. After the primary instability, one finds the oscillatory flow with a fundamental azimuthal modal number. It is indicated that the flow field consists of the primary component with the fundamental modal structure and the components with fundamental modal structures of higher harmonics of the primary components. Those components dominate the whole flow field. After the onset of secondary instability, additional components emerge in the flow; those components consist of the the fundamental azimuthal modal structures, which are different from higher harmonics of the primary flow field. We determine the onset condition or critical Reynolds number for the secondary instability Re_c⁽²⁾ by monitoring the development of the energy of the newley arisen components. It is found that the secondary instability evaluated through decomposed flow structures via nonlinear simulation corresponds to that predicted through Floquet modes via linear stability analysis.

Lithium-ion secondary batteries have become key devices for energy storage for automotive and renewable energy applications. To further improve battery performance, clarification of the ion transport phenomena within the batteries is necessary. However, experimental investigation has not yet been performed. In this study, in situ visualization of lithium-ion batteries with a hard carbon or graphite negative electrode was achieved using low-energy X-ray microscopy. Visualization experiments were conducted on two different negative electrode materials. The concentration distributions of lithium ions (Li⁺) and hexafluorophosphate ions (PF₆⁻) inside the hard carbon negative electrode were investigated. Additionally, stage transformation caused by lithium intercalation was observed in the graphite negative electrode. These results suggest that transport phenomena in the electrodes of operating lithium-ion batteries can be investigated using low-energy X-ray microscopy.

In ocean current and tidal power generation systems, the rotating shaft, which connects the turbine in water phase and the generation system in air phase, experiences a variety of shaft speeds and high water-pressure conditions. The shaft seal is required to separate water and air with a rotating shaft, which should guarantee both a low frictional torque and a low leakage of water. Conventional shaft seals realize the low frictional torque by operating in a hydrodynamic lubrication mode at the dynamic seal face. However, the dynamic seal face suffers to form rich lubrication film against low speed shaft in water environment. Therefore, a hydrated seal ring was proposed for use in the dynamic seal faces to realize the boundary lubrication. The hydrated seal ring made of a polyvinyl formal (PVF) was adopted. Two types of shaft seals using PVF seal ring were designed, which had the similar structure to oil seals or mechanical seals. The design scheme was validated using verification tests in which the shaft rotation speed was varied from 5000 to -5000 revolutions per minute under a water pressure of 0.5 MPa. The hydrated seal ring can be further improved by avoiding deformation of the hydrated seal ring to inhibit the clearance flow in the dynamic seal face. However, it needed to consider the surface profile of the ceramics surface used as a counterface of the hydrated seal ring because the heat generation at the dynamic seal face might be occurred, which changes the material property of the hydrated seal ring.

The borated stainless steel B-SUS304P-1 is used for storage and transport metal casks in the nuclear industry. According to our previous research, the boron addition reduces the fracture toughness but has a minimal effect on the fatigue crack growth. In this study, in situ laser microscopy observation during tensile, fracture toughness and fatigue crack growth tests of B-SUS304P-1 was performed to investigate the mechanism responsible for the effects of the boron addition on static and fatigue crack growth. During the tensile test, the borides were broken, but the base material remained intact. Results obtained using the digital image correlation method revealed that the strain of boride at fracture was very low compared with the macroscopic elongation of B-SUS304P-1. For the fracture toughness test, the borides in front of the crack were broken before static crack growth. The crack propagated along a zigzag path as it grew along the broken borides. Because of this crack growth mechanism, the fracture toughness was reduced by the boron addition. In contrast, for the fatigue crack growth test, only a few broken borides were observed in front of the crack because the stress intensity factor of the fatigue test was smaller than that of the fracture toughness test. The crack thus grew linearly, and the boron addition had a minimal effect on the fatigue crack growth of the stainless steel.

The oxygen concentration distribution in the porous cathode of a lithium–air battery during discharge has been measured using a fine optical fiber sensor. The lithium–air battery has the highest theoretical capacity. However, for practical application, the lithium–air battery power density needs to be improved. To realize a more powerful aqueous lithium–air battery, sufficient oxygen supply into the porous cathode is required. No previous studies have measured the oxygen concentration in the porous cathode structure. In this study, platinum tetrakis pentafluorophenyl porphine (PtTFPP) was used as the oxygen indicator. When PtTFPP is exposed to excitation light, phosphorescence emission occurs, and its intensity depends on the oxygen partial pressure. Thus, the oxygen concentration can be obtained by measuring the phosphorescence intensity and using calibration data. A fine optical fiber sensor (110 μm in diameter) was constructed with PtTFPP painted on the edge. According to the experimental results, as the current density increases, the oxygen concentration in the porous cathode drastically decreases. Because of slow oxygen transport in the aqueous electrolyte and the existence of an electrolyte between the air layer and the porous cathode, sufficient oxygen is not supplied to the porous cathode. Therefore, only oxygen near the electrode surface can contribute to the discharge.

Focusing on humans’ velocity perceptual characteristics, this study clarified the velocity JNDs that is minimal velocity differences humans can discriminate. For this purpose, using a 2-DOF SCARA-type haptic device, we conducted an experiment, assuming a pattern in which velocities were increased from constant values to other constant ones for shoulder and/or elbow joints. In the experiment, subjects’ upper limbs were enforced to move by the device, while the subjects focused on their hand velocity change using their proprioceptive sensations. After the movements, the subjects answered whether they perceived a velocity change during the movement. Iterating this trial with various velocity difference, velocity JNDs were obtained for each of the subjects and the following two factors. The two factors to be evaluated were the joint factor and the before-acceleration velocity factor: (1) the joint factor was the joints to be moved, of which levels were set as the shoulder, the elbow, and the shoulder-and-elbow, (2) the before-acceleration velocity factor was the nearly-constant tangential velocity of hand motions before velocity change, V_before. As a result, it was confirmed that a linear relationship of the velocity JND against the V_before was confirmed for all the joint factor levels, i.e., the shoulder only, the elbow only, and both the shoulder-and-elbow. Here, it should be noted that the joint angular velocities corresponding to hand tangential velocities are greatly different between the three joint factor levels. Nevertheless, the correspondence between V_before and the velocity JNDs were approximately the same between the three joint-factor levels. Therefore, it is concluded that the hand velocities, not the joint angular velocities, are dominant in human velocity-change perception for passive movements in the shoulder and/or elbow joint.

This paper explores the transmittable power of power transmission elements in fluid power and electric drive systems. We consider a simple model for the piping in hydraulic and pneumatic systems that ignores the fittings and auxiliary equipment and the wiring in electric drive systems that ignores the terminals and auxiliary equipment. We analyze the data based on specifications of hoses for hydraulic systems, tubes for pneumatic systems, and cables for electric drive systems from the manufacturers’ catalogs. We survey the outer and inner diameters, mass per unit length, maximum working pressure, mean flow velocity, rated voltage, and rated current to estimate the maximum transmitted power and examine the relationship between the power and the size and weight and calculate the power density. The influences of mass of oil, return lines of hydraulic circuit, materials of pneumatic tubes, and number of cable cores are also discussed. In conclusion, the transmittable power of the elements of all systems can be approximated by a power function for the mass per unit length. The relation between the transmittable power and the mass for hoses, tubes, and wires is similar. The power density of hydraulic hoses and electrical cables is high; the power density of pneumatic tubes is low. Oil in the pipes and return lines of hydraulic systems is not negligible.

In recent years, the dielectric barrier discharge plasma actuator (DBD-PA), which is a fluid control device, has been investigated for achieving both high aerodynamic performance and pleasing styling of transportation equipment. In this study, the authors installed a DBD-PA system on a simplified three-dimensional bluff automobile body to reduce the aerodynamic drag. In particular, the authors focused on the sides of the rear end of the body, where the local shape has high sensitivity regarding both styling and aerodynamic drag. Atthe rear sides of the automobile-like bluff body, a sharp edge rather than a smooth rounded corner often reduces the aerodynamic drag by promoting airflow separation. Therefore, the authors aimed to reduce the aerodynamic drag by using a DBD-PAsystem to promote flow separation at the rear end while retaining its rounded shape. Aerodynamic measurements using a one-fifth scale simplified automobile model were conducted in a wind tunnel. Preliminary investigation of the aerodynamic effect at the rear clarified how the longitudinal vortices from the rear pillar and the side edge of the trunk deck cause the drag increase at the rear-end corners. Two parallel DBD-PAs were installed on the rear surface to shift these vortices away from the corners by promoting flow separation. The drag reduction rate reached 3% at the highest applied voltage using the DBD-PAsystem on a rounded shape, and it achieved approximately half the effect of the sharp-edged shape. The longitudinal vortices were successfully kept away from the rear-end corners by the DBD-PAs. The surface pressure increased with the displacement of the vortices, which led to the drag reduction observed.