The Lewis number is the ratio of thermal diffusivity to molecular diffusion coefficient, and its influence on premixed-flame propagation has been a topic of extensive combustion research. Diffusive-thermal model, which neglects density variation caused by temperature increase due to combustion, has been frequently used to examine the effect of the Lewis number. Major advantages of the diffusive-thermal model are that it allows computation with a given flow field and that the sole effect of the Lewis number can be investigated. The diffusive-thermal model includes a dimensionless parameter, hereafter denoted by Λ, which corresponds to the pre-exponential factor of reaction rate constant. Its value must be determined such that the correct burning velocity can be reproduced. Although a number of studies use the lowest-order asymptotic expression for evaluating the value of Λ, the expression causes errors as much as several tens of percent depending on the condition. In this study, the value of Λ is numerically determined by seeking a traveling wave solution in a one-dimensional moving coordinate system. The method is simple enough to be implemented in Microsoft Excel using its solver add-in. It was found that even two-term asymptotic expansion of Λ resulted in errors more than 10% in some cases. It is therefore recommended to numerically evaluate the value of Λ under every condition of interest. As an alternative means, this paper proposes an empirical formula that yields the value of Λ with errors less than 1% in most cases (less than 2% in all the cases) tested in this study.

Baby carriage vibrations cause unpleasant sensations for both the babies and carriage operators. This study analyzed the baby carriage vibration generated by passing over a level difference on a road surface because this situation introduces a large physical burden and significant stress. The purpose of this study is to develop simulation models in order to improve the performances of baby carriages under operating conditions efficiently. Furthermore, experiments were conducted using a real baby carriage to verify the accuracy of the simulation models. We focused on vibrations in the front leg because characteristic vibrations were generated in this part. Baby carriage models, such as the rigid body model (modeled as a rigid body other than the elastic deformation of suspension) and the elastic connection model (modeled the movement of joints around the legs), have been developed. However, the accuracy of these models are insufficient because these are not able to model high-frequency vibrations and the trend in the vibration peaks when the baby carriage passes over the level difference. Additionally, we developed the front leg elastic body model considered the elastic deformation of front legs based on the finite segment method. In the front leg elastic body model, front legs were divided into fifths, which were connected by translational and rotational springs because the time is required for analysis using the general finite element method. This model was able to provide the trend similar to the experimental result. Finally, the vibration reduction design for a baby carriage was considered by using the developed simulation model.

A method to conserve the volume of dispersed components (e.g. bubbles and droplets) in a viscous fluid is proposed for the front-tracking method (Unverdi and Tryggvason, 1992; Tryggvason et al., 2001). The method adjusts the coordinates of each nodal points on the interface (or Lagrangian markers) along the velocity vector. A simplified algorithm determines the new position of the marker independently from those of the surrounding nodes, which allows the volume correction to be accomplished efficiently. The results show that the volume of a deformed fluid particle is kept constant within errors of O(10⁻⁷) ～ O(10⁻⁶). The effects of the time step size and the frequency of the volume correction are investigated. The method is applicable to enclosed structures of non-spherical geometry (e.g. oblate/prolate/spherical-cap fluid particles).

In a High-Temperature Gas-cooled Reactor (HTGR), radiation is the dominant form of heat transfer due to the high temperature environment. Therefore, the emissivity of the core materials (mainly nuclear grade graphite) is important for reactor safety assessment. In this paper, the emissivity of nuclear grade graphite IG-110 was measured in the temperature range from 500 °C to 1000 °C by using an infrared thermometer. Besides, the impact of the graphite oxidation, which may take place in a postulated air ingress accident, was also evaluated. As a result, it was found that the emissivity of IG-110 grade graphite decreases slightly as the temperature increase. Moreover, a relatively high emissivity was detected in the pre-oxidized specimen. Based on the measurement data, two experimental correlations were suggested for the engineering applications. It could also be concluded that the commonly used value of the graphite emissivity (0.8), is conservative for engineering judgment.

In finite element analysis, small fillets make mesh generation difficult and accurate evaluation of stress concentration at fillets requires refined meshes. Simplified analysis is often performed using a corner model where the fillets are removed. In the analysis using a corner model, mesh division becomes easier and the number of elements is reduced, which shortens the calculation time. However, the stress concentrations cannot be evaluated, and stress singularities occur at corners. We have developed a method for predicting the stress at a fillet based on the simulation of a simplified corner model and the use of a neural network. We use the stress distribution at a corner as the neural network input such that the method can be applied to arbitrary object shapes, loading, and boundary conditions. We trained and validated the neural network using simple corner and fillet models. It was shown that stress distribution at a corner can express the difference in loading conditions. In addition, we found that the method can predict stress at fillets of models that were not used for the neural network training. These results show the possibility that the method enables efficient stress concentration evaluation in finite element analysis.

In this study, we proposed a sterilization technique for cutting fluids using plasma treatment under atmospheric pressure and in-liquid and investigated the characteristics of sterilization and the fluids’ surface properties (e.g., wear resistance and wettability). The results show that the number of bacterial colonies in the fluid sterilized by atmospheric-pressure plasma and in-liquid plasma was reduced by more than 90% compared with the number in the untreated fluid. The lubricating properties of the plasma-treated cutting fluids were well improved compared with those of the untreated fluid, as determined from a comparison of the results of specific wear rate tests. The adhesive energy of the plasma-treated cutting fluids was greater than that of the untreated fluid, as revealed by the results of sliding angle measurements. However, the adhesive energy decreased over time; that is, the duration of the effect was limited. The results of this study demonstrate that the life of a cutting fluid can be prolonged by plasma treatment, with an associated improvement in the fluid’s tribological properties. This research can help reduce the frequency of maintenance required for coolants used in cutting applications.

Radioactive aerosols are strongly diffusive and migratory and thus have presented one of the greatest challenges during the decommissioning of the Fukushima Daiichi Nuclear Power Plant (NPP). Although cutting through debris underwater can suppress the generation of radioactive aerosols from pool scrubbing to some extent, the removal efficiency of bubble columns can be influenced by many factors. In this study, fine bubbles (microbubbles and nanobubbles) with large specific surface areas were introduced into a simple scrubber; nanobubbles, in particular, are known to have long residence times in water. The effects of fine bubbles on the aerosol removal efficiency during pool scrubbing were studied for TiO₂ (around 100 nm) and ZrO₂ (around 100 nm) aerosols. Due to the fact that TiO₂ (4.23g/cm³) has similar density with CsOH (3.68g/cm³) and CsI (4.51g/cm³). On the other hand, ZrO₂ was found in the fuel debris (Zirconium-Water Reaction). To clarify the effects of fine bubbles, three kinds of water were prepared (i.e., distilled water, nanobubble water, and microbubble water). As a result, the removal efficiency of fine bubbles for TiO₂ aerosols decreased, while that observed for ZrO₂ aerosols improved in some cases. The improved removal efficiency achieved using fine bubbles may provide a new method for suppressing the generation of radioactive aerosols in the decommissioning of the Fukushima Daiichi NPP.

The objective of this study is to quantify the influence of higher orders of expansion in the formulation of stochastic finite elements method on the linear elastic response in 2-dimensional problems with random physical parameters in the left hand side term. Neumann expansion was used to get an explicit expression of the result. Young’s modulus was considered as a random variable following normal distribution. The coefficient of variance (COV) of this input parameter ranged in this study up to 0.3 (30%), and mainly 20% of COV was analyzed. The displacement was selected as the quantity of interest. The difference in distribution function of the displacement for different orders of expansion was observed in the tail distribution. A fundamental example revealed the limitation of the applicability of first, second and third orders being approximately 3%, 12% and 20% of COV of input parameter. In the analysis of 2-phase composite material, the influence of geometrical random morphology was larger than that of physical parameter, but the latter was not negligible in the microscopic response.

We realized a direct numerical simulation (DNS) of the turbulent flow of liquid along a solid wall with solidification by incorporating the phase-field model. The combination of DNS and phase-field model can clarify the mechanism of modulation of a turbulent boundary layer of liquid solidifying upon a solid wall and assist in constructing a prediction method in the future. The simulations allow observation of turbulent flow along a solid wall surface that grows with the solidification of a flowing liquid under an undercooling condition. In the flow field, turbulence structures such as velocity streaks and quasi-streamwise vortices were noted to diminish, and the turbulent flow tended to be laminar. In contrast, there were no changes in the turbulence statistics in the region above the growing solid-liquid interface. The solidification structure had a bent shape, which was caused by the effects of advection downstream and growing in the upstream direction owing to the undercooled fluid flowing from upstream. The wall surface grew non-uniformly depending on the local flow patterns and temperature distribution caused by turbulence structures close to the wall surface. The complex shape of the wall surface, which was observed during simulation, was originally triggered by the initial distribution of the turbulence structures. Sweep events in the high-speed streaks relatively expedited the growth of the solidification structures, which then modified the turbulence structures. The interaction between the turbulence structure and solidification structure promotes laminarization of the fluid flow.

A fluidized bed can efficiently filter dust particles, but its performance depends significantly on the fluidization state. To further develop the fluidized-bed filtration method, it is important to understand the filtration mechanisms in detail. Numerical simulation via the discrete element method is useful for solving these problems because the motion of each bed and dust particle is demonstrated. This system has large number of particles, and bias of the particle distribution is generated owing to the fluidization and supply of dust particles. Parallel computing on a distributed-memory computer is necessary to simulate many particles. Additionally, dynamic load balancing is a key technique for solving these problems. In this study, we developed a simple implementation of three-dimensional slice grid method and periodically used this method to balance the workload while keeping contact information such as the pair of colliding particles and its overlap. The computational efficiency of our method was assessed through an ideal problem involving a packed particle system and dust filtration in a fluidized bed. The changes in the particle number and particle distribution were examined. In the packed particle system, linear speed-up was obtained at particle number of 100 million and a message passing interface-process number of 1024. Moreover, the effectiveness of the dynamic domain decomposition method was confirmed by solving through the dust filtration problem.

Gaskets are widely used as static seals in industry, machinery, and living ware. Generally, leakage is reduced or eliminated by clamping seal components and blocking flow passages. However, strong clamping sometimes leads to surface damage. Surface roughness and waviness form partial paths and excitation and vibration loosen clamping bolts. Leakage is directly proportional to the cube of gap height and inversely proportional to viscosity. Moreover, the viscosity of fluids, particularly oil, strongly depends on temperature, as lower temperatures correspond to higher viscosities. In other words, oil leakage can be reduced by decreasing its temperature. Therefore, it is possible to control leakage by changing the gap temperatures. In this paper, a flange-type gasket with a gap is modeled using two circular plates with a central recess. The thermohydrodynamic lubrication (THL) theory is applied to the gap flow. The effects of wall temperature, gap height, and recess pressure on the leakage flow rate are numerically solved. The basic equations comprise the generalized Reynolds equation, the energy equation, and the heat conduction equation and the THL solutions are compared with a simple model based on the iso-viscous theory. In conclusion, the oil temperature in the gap can be controlled by the wall temperature. If the wall temperature is decreased, the oil temperature falls. Subsequently, viscosity increases, helping to decrease leakage in a wide range of operating conditions. The leakage can be estimated by the iso-viscous model with the viscosity at the wall temperature.

This short paper studies a robust optimization problem of a structure subjected to frictionless unilateral contacts. We suppose that initial gaps possess non-probabilistic uncertainty, and attempt to maximize the worst-case stiffness of the structure. It is often that a structural optimization problem involving contact conditions is formulated as a mathematical programming problem with complementarity constraints (an MPCC problem). Since any feasible solution of an MPCC problem does not satisfy standard constraint qualifications, special treatment is required to solve an MPCC problem. In contrast, the formulation developed in this paper is free from complementarity constraints, and hence can be handled as a standard nonlinear programming problem. It is shown that this formulation is readily derived as a natural extension of the recently proposed optimal design problem formulation that does not consider uncertainty.

The accurate measurement of thin liquid films in various environments is essential for several industrial applications. In this regard, measurement procedures involving the use of optical fibers are preferred because such fibers are resistant to heat and pressure. Herein, we propose a high-accuracy method to measure liquid films with thicknesses of <100 μm (about fiber diameter) on the basis of the variation in the intensity distribution of the laser light emitted from the optical fiber; the thickness is measured by using the light reflected from the air-liquid interface (called the glare light in this study). First, instead of using light with a Gaussian distribution (characteristic of conventional graded-index fibers), we consider a stepped-index-type optical fiber with a step distribution. We model the distribution of the light emitted from the optical fiber and analyze the reflected light, i.e., glare light, via the ray-tracing method. We model three distributions: the Gaussian, point-like, and step distributions, and then we found that the step-distribution-based approach facilitates high-resolution measurements of liquid films with thicknesses less than optical fiber diameter. Moreover, the reflected light intensities for different film thicknesses closely agreed with the experimental results obtained using a stepped-index fiber. Remarkably, the intensity of the reflected light linearly decreases with the increase in the film thickness when using the step distribution. The numerical results quantitatively agreed with experiments; therefore, these results indicate the possibility of numerical calibration for liquid-film measurements with the use of the proposed step distribution model.