In order to address the challenge of the future Fukushima Dai-Ichi Nuclear Power Station (1F) debris characterization a new Raman spectroscopy investigation of simulated debris obtained after two control blade degradation tests CLADS-MADE-01 and CLADS-MADE-02 has been performed. A mechanism of the B4C degradation during the beginning phase of a severe accident until approximately 1873 K is described. A sequence of material interactions of B4C with stainless steel resulted in partial transformation of B4C granules into pure graphite, that later experienced oxidation with formation of COx gas. Especially this mechanism is active during melting phase in oxidative environment. At the same time boron was associated with formation of new Cr-B-containing solid phases in liquid melt, that continued relocation depleted by Cr and B, which resulted in redistribution of elements within the degrading reactor core. This knowledge would provide new insights for understanding of the absorber blade degradation mechanism under specific accident conditions close to Fukushima Daiichi Unit 2 and Unit 3 reactors and especially would be helpful during potential characterization of metallic debris of 1F.
Pure copper is utilized as a material for products with complicated shape and high thermal conductivity such as heat exchangers. However, it is difficult to fabricate pure copper parts with high density by the selective laser melting (SLM) process. One of the reasons is considered to be its high thermal conductivity by which the heat in the melt pool rapidly diffuses away. Additionally, the lower rate of energy absorption of fiber laser power for pure copper makes the size of melt pool smaller. In this research, the optimum fabrication condition of high-purity 99.9% copper fabricated by SLM process was investigated by evaluating the density and microstructure. As a result, it was found that the optimum condition of laser power and scan speed are 800~900W and 300 mm/s, respectively, and the optimum energy density is around 1000 J/mm3, which is much higher than that of other materials due to high reflectivity and high thermal conductivity of pure copper. And also, it was found that the hatch pitch is important factor to achieve the densification of the as-built specimen and the optimum hatch pitch was 0.01 mm. The high density parts were successfully fabricated by the optimum fabrication condition. The maximum density of the as-built specimen was 96.6 % and was much higher than that of the as-built part already reported.
X-ray diffraction experiments were carried out to non-destructively study the interior of aluminum single crystals at the pre-deformation, post-deformation and post-annealing stages using synchrotron radiation at SPring-8. Single crystals were grown by the Bridgman method. The as-grown samples were not perfect from the crystallographic perspective, but were composed of several sub-grains with misorientations smaller than 1° across the sub-boundaries. Although the difference in orientation in the cross section of the sample increased about 0.7° by the application of the nominal strain of 8% in tension along the <111> direction, the sub-grain structures remained largely unchanged. No evidence was found of the local accumulation of dislocations at the sub-boundaries. The orientation map of the deformed sample clearly shows that no non-uniformly deformed regions formed inside the sample. The level of residual strain calculated by the strain-scanning method was as low as 1×10-4. After annealing at 480 °C, the whole cross section of the center of the sample was covered by a single recrystallized grain. Although the resolution of the present experiments was insufficient to observe potential nucleation sites of recrystallized grains in <111>-oriented crystals, a possible candidate for the sites may be assumed at the intersections of certain types of slip bands.
Thermal barrier coatings (TBCs) applied to turbine blades indicate nonlinear deformation and complex fracture behavior due to the microstructure which is formed by deposition of molten particles. In this study, in order to accurately simulate these behaviors observed in TBC, finite element analysis based on the brick model combined with cohesive model and the inelastic constitutive equation was established. First, bending tests of freestanding YSZ sample specimens extracted from TBC-coated sample deposited under different particle velocity conditions were performed to identify its deformation and fracture behaviors prior to FE analysis. As a result, the bending test revealed that the maximum load, the maximum deflection, and the crack propagation path varied significantly depending on the particle velocity. Subsequently, the FE procedure combined with the brick and inelastic constitutive models was developed, and it was confirmed that the FE analysis based on the brick model can accurately simulate nonlinear deformation and complex crack propagation path observed in a micro-scale.
The characterization of the product gas of flames is important not only in the design of combustors but also to provide a fundamental understanding of the phenomenon of combustion. To prevent the disturbance of the flow field during gas sampling, the flow rate of the sampled gas must be kept low. However, some gas analyzers require a relatively large flow rate of several liters per minute for gas sampling to increase the response of the gas analysis. In this study, to enable analysis with a low net sampling rate, a method for the dilution of the sampled gas was developed. Although a dilution sampling method has already been proposed, it is difficult to measure the species of interest with this existing method when a tracer species is included in the object mixture. To address this problem, the newly proposed dilution sampling method is appropriate for object gases containing tracer species. In the proposed dilution sampling method, sampling is carried out twice using two dilution gases with different mole fractions of the tracer species. The mole fraction of the target species can be then calculated by solving simultaneous equations. Uncertainty analysis was also conducted for this method, and demonstrations of the dilution sampling method were successfully carried out. In addition, it is suggested that the selection of the dilution gas, i.e., the mole fraction of the tracer species in the dilution gas, is important to reduce the experimental uncertainty in the dilution sampling method.
Many sensitivity calculations are necessary to evaluate the effect of the uncertainties of Core Disruptive Accident (CDA) scenarios on debris bed coolability for Sodium-cooled Fast Reactors (SFR). This paper describes a calculation model and a technique for high-speed calculations of debris bed coolability. Firstly, the detailed coolability calculation model taking into account phase change and vapor-liquid advection for a boiling zone in the debris bed is derived as a single equation. The vapor-liquid advection is based on the momentum equation including inertial, viscous, capillary and gravitational effects. In addition, the streamlined calculation which ignores inertial and gravitational effects for the boiling zone is proposed. Secondly, both the detailed and streamlined calculation models are validated through the analysis of the Sandia ACRR-D10 in-pile experiments. Then, the effects of the ignoring on debris bed coolability are evaluated through sensitivity calculations. Thirdly, the speed-up technique for the streamlined calculation model is proposed which solves the boiling zone by the combination of transient and steady state calculations and allows using coarse mesh size and time step. Owing to the technique, the calculation time becomes about 1/50. The application of the speed-up technique to the streamlined calculation model is confirmed under typical SFR conditions. Finally, it is demonstrated that the streamlined calculation model and the speed-up technique enable us to perform many sensitivity calculations in a realistic time. The model and technique developed in this study is practical to evaluate the effect of the uncertainties of CDA scenarios on debris bed coolability for SFR.
Precise positioning technologies are widely used in industrial machines such as device manufacturing equipment. Many studies have been done on feedback control systems for precise positioning stages that improve accuracy by using sensor signal feedback. However, the sensor output does not always directly indicate the performance of the industrial machines because the final requirement of a stage system is generally to adjust a movable stage to a target structure. Therefore, the relative displacement between the stage and the target structure must be controlled. However, the stage and other structures must be considered as elastic elements, especially for precise positioning devices. Thus, this study aims to achieve precise positioning in relative displacement between flexible structures. The authors previously proposed a relative displacement observer that estimated the relative displacement between the stage and the target structure by using only the stage displacement. In this paper, we propose additional control system for relative displacement by using self resonance cancellation technique. The positioning performance of the proposed system is evaluated in numerical simulation and experimental stage system. Results of numerical simulation and experiments show that the proposed control system improves the relative positioning performance.
Because double-mass dynamic vibration absorbers (DVAs) are superior to single-mass DVAs in terms of their vibration suppression performance and robustness, they have been increasingly studied recently. The optimization of double-mass DVAs is much more difficult than that of single-mass DVAs. However, recently, the ability of formula manipulation solvers typified by Mathematica has greatly improved, and exact algebraic solutions have been obtained for double-mass DVAs. The optimal solution for a double-mass DVA attached to a damped primary system has been reported in the form of an exact algebraic solution in a previous report. That paper reported the algebraic optimal solutions for a series-type double-mass DVA for the compliance and mobility transfer functions of the primary system successfully obtained by applying three different optimization criteria: H∞ optimization, H2 optimization, and stability maximization. In the present article, the numerical solutions to optimization problems for double-mass DVAs that cannot be algebraically solved are presented. There are two types of double-mass DVAs: series- and parallel-type DVAs. When applying the three optimization criteria mentioned above to each of them, there exist a total of 22 different optimal solutions because there are three transfer functions— the compliance, mobility, and accelerance transfer functions—that are typically used to describe the absolute response of the primary system. Of these 22 solutions, 10 solutions for the compliance transfer function are introduced in this article.
In the optimization of dynamic vibration absorbers (DVAs), it is generally assumed that the damping force changes in proportion to the velocity of the object; this damping is called viscous damping. However, many DVAs used in practical applications are made of polymeric rubber materials having both restorative and damping effects. This polymer material is considered to show a hysteretic damping force that is proportional to the displacement rather than the velocity of the object. Despite the widespread use of such hysteretically damped DVAs, there are very few studies on their optimal design, and the design formula of the well-known general viscously damped DVA is presently used for the design of this type of DVA. This article reports the optimal solution of this hysteretically damped DVA. For generality, it is assumed that the primary system also has structural damping that can be treated as hysteretic damping. Three optimization criteria, namely the H∞ optimization, H2 optimization, and stability maximization criteria, were adopted for the optimization of the DVA. For the H∞ optimization and stability maximization criteria, exact algebraic solutions were successfully derived, and for the H2 criterion, simultaneous equations with six unknowns and their numerical solutions were obtained.
Methods for presenting information by utilizing a visual field (such as driver peripheral vision) are attracting increased attention in association with an increase in the amount of information required for driver assistance. However, studies on interfaces utilizing such a visual field are currently insufficient. In addition, to avoid information overload, it is important to evaluate different interfaces in terms of the amount of information presented. The authors researched those interfaces from the viewpoint of ergonomics with the purpose that the result is possible to be applied to various researches mainly in the field of automobiles. Through an in-house experiment, participants viewed video clips presenting dot patterns within their peripheral vision or effective visual field (which is nearer to the gazing point than peripheral vision), and then answered questions regarding the positions and moving directions of the dots and the mental workload they experienced. The authors prepared two types of dotted patterns (fixed and moving) based on the perceptive characteristics of peripheral vision. The number of dots varied from one to six. The rate of misperception and participant mental workload were calculated. The results showed a tendency for the effect of the visual fields to depend on the type of dot pattern. It appears that the interface for peripheral vision may have resulted in a lower accuracy when fixed objects were presented, whereas fewer differences occurred when moving dots were shown. This implies that information with motion can be more suitable for interfaces utilizing peripheral vision. A larger amount of information and number of tasks resulted in lower accuracy and higher workload. Moreover, the relation between the number of dots and the rate of misperception (estimated based on percentage) suggests that the rate of misperception may increase significantly when either four or more fixed objects, or three or more moving objects, are presented.