Sensitivity analysis and its application for dynamic improvement

In order to determine appropriate points where natural frequency or mode shape under consideration can be effectively modified by structural modification, the theoretical background of sensitivity analysis is described, followed by experimental verification with a simple structure. Then it can be extended to (1) operational deflection shape, where a problem arises at offresonance frequency, (2) relative motion, (3) transmitted force through connecting points between components, (4) servo system, which consists of electrical elements with mechanical elements, and (5) acoustics generated by the vibration of the structure. To illusrate its effectiveness, many actual examples are given.     

Characterization of CuMn-spinel catalyst for methanol steam reforming

CuMn-spinel oxide (CuMn(S)) and non-spinel CuMn (CuMn(NS)) oxide have been obtained by calcining the same precursor at 900 °C and 300 °C, respectively. CuMn(S) was composed of Cu_1.5Mn_1.5O₄ spinel and Mn₃O₄, while CuMn(NS) consisted of CuO and Mn₃O₄. XRD, EXAFS, and TEM measurements of the samples reduced in hydrogen revealed that both CuMn(S) and CuMn(NS) were reduced to Cu metal dispersed on MnO and that the particle size of Cu metal from the CuMn(S) was smaller than that from CuMn(NS). In methanol steam reforming, the spinel derived catalyst showed higher activity than the non-spinel due to the higher dispersion of the Cu metal.     

Re‐ignition surge and high‐frequency arc extinction phenomena at 550‐kV shunt reactor current interruption

At substations connected with transmission lines and cables, shunt reactors are sometimes installed to compensate the capacitive current of these lines and cables. It is known that re‐ignitions occur and high‐frequency currents flow during interruption of the shunt reactor currents by switches. When the high‐frequency currents are interrupted immediately after the re‐ignitions (which is called high‐frequency arc extinction), the result is often repetitive re‐ignitions or voltage escalations that produce dangerous overvoltages. The authors investigated the occurrence of high‐frequency arc extinctions in a 550‐kV one‐break SF₆ gas circuit breaker during interruption of a 550‐kV shunt reactor current. Computations for a real 550‐kV substation gave a minimum frequency of 290 kHz for the high‐frequency current. However, 550‐kV reactor current interruption tests showed that high‐frequency arc extinctions did not occur even when this frequency was lowered to 26 kHz. Since high‐frequency arc extinction is generally likely to occur at lower frequencies, it was concluded that high‐frequency arc extinction will not occur in a 550‐kV one‐break SF₆ gas circuit breaker during interruption of shunt reactor current in real substations. © 2001 Scripta Technica, Electr Eng Jpn, 136(2): 18–25, 2001     

Development and application of highly charged ion source

The interaction of slow highly charged ions (HCIs) with solid surfaces is useful for ‘nanoprocess’; the modification, activation, machining and analysis in nanometer scale. An electron beam ion source ‘Kobe EBIS’ has been developed for the application of HCIs to nanoprocesses. The ion source produces ion beams of Ar^q+ (q ≤ 12) HCI in the nanoampere range. The ion source was applied to irradiate samples in order to investigate the structural or electric modification effect of HCIs with high fluence on the topmost layers of sample surfaces.     

DEVELOPMENT OF DIRECT UPGRADING PROCESS FOR HEAVY CRUDE OIL

The direct upgrading process from heavy crude oil to sweet and light oil (IKC process) has been developed for about 10 years in Idemitsu Kosan. Compared with conventional refinery scheme consisting of YR-HDS, VGOHYC and so on, the new refinery scheme combined with IKC process and Topper was always economically feasible with lower cost and smaller energy consumption. In the existing refinery of no middle distillate HDS and residue HDS of HYC plants to supplement IKC process is expected to be one of the efficient methods to cope with the environmental regulations.     

Correction of the thermal neutron capture cross section of 241Am obtained by the Westcott convention

There is large discrepancy among the reported experimental data of the thermal neutron capture cross section of ²⁴¹Am, where the activation measurements provided larger cross sections than those in the time-of-flight ones. The Westcott convention has been widely used for the derivation of the thermal neutron capture cross section in the activation measurements. We have estimated that this large discrepancy is due to the existence of the resonances below the cadmium cut-off energy (E_Cd ～ 0.5 eV). By reviewing the Westcott convention, we developed the correction method taking account of the contribution of the resonances near or below E_Cd. The correction term was evaluated using the JENDL-4.0. Application of the present method successfully improved the existing discrepancy of the thermal capture cross section of ²⁴¹Am.     

Numerical investigation of a high pressure hydrogen jet of 82 MPa with adaptive mesh refinement: Concentration and velocity distributions

To investigate the safety properties of high-pressure hydrogen discharge or leakage, an under-expanded hydrogen jet flow with a storage pressure of 82 MPa from a small jet orifice with a diameter of 0.2 mm is studied by three-dimensional (3D) numerical calculations. The full 3D compressible Navier-Stokes equations are utilized in a domain with a size of about 3 × 3 × 6 m which is discretized by employing an adaptive mesh refinement (AMR) technology to reduce the number of grid cells. By AMR, the local mesh resolutions can narrowly cover the Taylor microscale $l_T$ and direct numerical simulations (DNS) are performed. Both the instantaneous and mean hydrogen concentration distributions in the present jet are discussed. The instantaneous concentrations of hydrogen $C_{{\text{H}}_2}$ on the axis presents significant turbulent pulsating oscillations. The centerline value of the intensity of concentration fluctuation ${\stackrel{?}{\sigma }}_{{\text{H}}_2}$ asymptotically comes to 0.23, which is in a good agreement with the existing experimental results. It substantiates the conclusion that the asymptotic centerline value of ${\stackrel{?}{\sigma }}_{{\text{H}}_2}$ is independent of jet density ratio. The probability distributions function (PDF) of instantaneous axial $C_{{\text{H}}_2}$ agree approximately with the Gaussian distribution while skewing a little to the higher range. The time averaged hydrogen concentration ${\overline{C}}_{{\text{H}}_2}$ along the radial directions can also be described as a Gaussian distribution. The axial ${\overline{C}}_{{\text{H}}_2}$ of 82 MPa hydrogen jet tends to obey the distribution discipline approximated with ${\overline{C}}_{{\text{H}}_2}=4200/(z/\theta )$ where z is the axial distance from the nozzle and $\theta$ is the effective ejection diameter, which is consistent with the experimental results. In addition, the hydrogen tip penetration $Z_{\text{tip}}$ is found to be in a linear relationship with the square root of jet flow time $\sqrt{t}$. Meanwhile, the jet's velocity half-width $L_{\text{Vh}}$ approximately gains an linear relation with z which can be expressed as $L_{\text{Vh}}=0.09z$.     

π-Conjugated polymer/GaN Schottky solar cells

We developed heterojunction-based Schottky solar cells consisting of π-conjugated polymers and n-type GaN. Poly (3,4-ethylendioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) was used as the transparent Schottky contact material and their electrical properties were investigated in comparison with those of a polyaniline (PANI) Schottky contact. The PEDOT:PSS/n-GaN/sapphire (0 0 0 1) sample exhibited high-quality rectifying characteristics with a low reverse leakage current of less than 10⁻⁸ A/cm² at a reverse bias voltage of −3 V. While investigating the photovoltaic performance, it was observed that the open-circuit voltage of the PEDOT:PSS/n-GaN/sapphire (0 0 0 1) sample reached 0.8 V, which was much superior to the photovoltage reported for a conventional metal/GaN Schottky photodetector. We also confirmed that the PEDOT:PSS is as promising a material as PANI for π-conjugated polymer/GaN Schottky solar cells.     

Thermocapillary Convection and Buoyant-Thermocapillary Convection in the Annular Pools of Silicon Melt and Silicone Oil

The thermocapillary convection and buoyant-thermocapillary convection in the annular pool of silicon melt (Pr=0.011) and silicone oil (Pr=6.7) with depth d=10 mm differentially heated at the outer wall and cooled at the inner wall are investigated by 2-D numerical simulation. The numerical results exhibit that the thermocapillary flow is enhanced by buoyancy force for silicon melt while it is weakened for silicone oil. Linear stability analysis indicates that the buoyancy force destabilizes the thermocapillary convection, which is different from that for silicone oil. The detailed reason of different influence of buoyancy force on the thermocapillary flow with different Pr numbers is explained according to present numerical results.     

Double-walled reformer tubes using high-temperature thermal storage of molten-salt/MgO composite for solar cavity-type reformer

Composite materials with alkali carbonate and magnesia have been examined for high-temperature thermal storage in solar tubular reformers. The concept of a double-walled reactor tube involves packing a molten-salt/ceramic composite material into the annular region between internal catalyst tube and exterior solar-absorber wall. In this paper, the shape and interior structure of the reactor tube are newly designed for use in solar cavity-type reformers using straight reactor tubes. Na₂CO₃, K₂CO₃, and Li₂CO₃ composite materials with magnesia were tested as thermal storage media for CO₂ reforming of methane during cooling mode of the reactor tube at a laboratory scale. The efficiency of Na₂CO₃/MgO composite with various MgO contents was also estimated. Composite materials of Na₂CO₃ 80–90 wt% and MgO 20–10 wt% were successfully delayed the cooling of the catalyst bed and sustained methane conversion at >90%. A solar cavity-type reformer consisting of multiple straight reactor tubes is expected to enable stable operation of the solar reforming process under fluctuating solar insolation during cloud passage.