Numerical studies were carried out to investigate the flat-plate boundary layer receptivity to vorticity disturbances. The disturbances were introduced indirectly as a wall boundary condition. As a result, it is shown that only the low wavenumber fluctuations in the freestream could generate the vorticity pattern on the wall. It is also shown that the interaction between the streamwise vortices and the boundary layer promotes the rapid growth of the velocity fluctuations.

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Zonostrophy, which was discovered by Balk in 1991, is a quasi-invariant for the two-dimensional quasi-geostrophic equation on a beta-plane. Zonostrophy is useful for explaining the anisotropic energy cascade that favors zonally elongated structures, that is, the Rhines effect. In the present study, we propose a general procedure to numerically obtain a quasi-invariant for discrete wavenumber systems, which correspond to finite physical domains, and derive a discrete counterpart of zonostrophy, which we refer to as the third quasi-invariant. We also conduct numerical experiments to compare the conservation properties of the third quasi- invariant and the zonostrophy. In addition, we show that the third quasi-invariant is closely related to the concept of near-resonant triad interactions, which was introduced by Lee and Smith in 2007.

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We numerically study a point sink flow of stratified viscous fluid in a reservoir of finite depth under a rigid rotation of the whole system. In the initial stage after starting a discharge, selective withdrawal is formed and only a layer of fluid adjacent to the sink level is withdrawn. As time elapses more, this withdrawal layer increases its thickness gradually. The speed of such withdrawal-layer thickening is found to be a function of the Reynolds number only and does not depend on the other parameters if the time is non-dimensionalized using the rotating speed of the system. Based on our numerical results, we also discuss the effect of the earth’s rotation on sink flow in the actual situation.

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Numerical simulation is performed for steady state flows in a driven cavity at low Reynolds numbers. The flows of incompressible viscous fluid are driven by the top lid of the cubic cavity which slides at constant speed in directions not parallel to the sidewalls. The Reynolds number Re and the angle of lid motion θ are adopted as the governing parameters. Structure of streamlines is studied by means of the Poincarémap and the rotation number N of the tori formed by streamlines. The rotation number N of the tori is given as a function of (Re, θ). The appropriateness of using N as an index of mixing efficiency is discussed.

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Stochastic resonance, in which a type of noise amplifies weak signals, has been observed in various fields, however, its oceanic applications have not been investigated in detail. Therefore, in this study, we examined basic responses of oceanic double-gyre to constant external wind forcing with noise generated by the Ornstein-Uhlenbeck equation by using a 1.5 layer quasi-geostrophic model. For cases with adequate noise, potential signals in the system appear at the front as actual signals such as intermittent large variations in energy. In addition, the flow patterns show intense meandering of strong current extension. These variations are more frequent and stronger for cases with long decorrelation time than for cases with short decorrelation time although intermittent variations can be observed even for cases with white noise.

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We present numerical results for vibration responses, obtained by three-dimensional computations, of two circular cylinders which move to in-line and cross-flow directions along a smooth flow, with a low Scruton number, and which are arranged at a spacing larger than the critical spacing of the center-to-center of the cylinders. In the case of the in-line vibration which occurs at a low Scruton number, there are two kinds of excited vibration regions, named first- and second-excited vibrations, in the range of low reduced velocities. In order to capture such vibration responses, numerical computations of the Navier-Stokes equations are carried out by means of the finite element method and the arbitrary Lagrangian-Eulerian method. In addition, the numerical solution stabilization of the Navier-Stokes equations is performed by the third-order upwind scheme. From our numerical results, we discuss the response mechanisms of the cylinders in detail.

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In order to investigate the segregation behavior induced by the size difference in suspended particles, we conduct a two-dimensional numerical simulation for suspensions of fluid droplets of two different sizes subjected to a Poiseuille flow between two parallel plates. The large and small droplets are assumed to have equal surface tensions and equal internal viscosities. From the temporal evolutions of the lateral positions of the large and small droplets, it is obtained that the small droplets are displaced closer to the channel walls with increasing fraction of the large droplets whereas the large droplets accumulate more preferentially near the channel centerline with increasing fraction of the small droplets. The probability distribution functions for the droplets indicate that a line of small droplets is formed next to the channel walls at high area fractions, which enhances the size segregation of the droplets.

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The dependence of the structure of numerical solutions of the compressible Euler equations on forcibly added randomness is discussed. The compressible Euler equations are solved numerically by using Harten type total variation diminishing(TVD) method for the subsonic flow around a two-dimensional NACA0012 airfoil. We investigated the behavior of the fluctuating shock waves under insertion of randomness. The mean position of the fluctuating shock wave induced by randomness is different from that of stationary shock wave calculated without randomness. We also study the dependence of behavior of shock wave on types of pseudo-random number rows. It is clarified that statistical values of the position of shock wave are affected by the period of pseudo-random number row.

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In this paper we investigate the Euler-Maruyama approximate solution for SDE with unbounded coefficients and estimate the mean square error. From the result we obtain a confidence interval of the SDE.

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These days, the use of single nucleotide polymorphisms (SNP) is increasing for the genetic dissection of complex common diseases, and many studies have been conducted to identify SNPs associated with diseases. If the number of subjects with the objective disease is large enough, then we detect disease-associated SNPs with statistical tests by a two-stage replication study design. For the design, several ways to calculate a power of a test have been considered. They show that the well-constructed two-stage replication study designs maintain enough powers of the tests. However, we cannot handle a large quantity of data well for all diseases, and we perform statistical tests by a one-stage design for diseases with small sample sizes. In this paper, we propose a method to estimate the proportion of significant results of the tests for such diseases by using a similar method to calculate the power of statistical tests with the two-stage replication study design.

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In the paper, we present numerical experiments for investigation of a property of functions. Especially, we focus on the smoothness. Two kinds of methods are used in numerical experiments. One is the interpolation and the other is the Cauchy problem for the Laplace operator. Numerical experiments are performed by using the spectral collocation method and a multiple-precision arithmetic. Numerical results show the possibility of the numerical computation for the distinction between smooth functions and analytic functions.

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For the sake of spacecraft mission design, it is indispensable to develop a low energy transfer of spacecrafts using very little fuel for interplanetary transport network. The Planar Circular Restricted Three-Body Problem (PCR3BP) has been a fundamental tool for the analysis \ of such a space mission design. In this paper, we explore stable and unstable invariant manifolds associated with the collinear Lagrange points L₁, L₂ of the PCR3BP, in which geometric structures of the invariant manifolds are clarified on a Poincar\'a5'e section. Further, we compute the Finite Time Lyapunov Exponent fields (FTLE fields) to obtain Lagrangian Coherent Structures (LCS) as the ridges of the FTLE fields. In particular, we compare the LCS with the invariant manifolds on the Poincaré section from the viewpoint of the numerical integration times.

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Flash flooding due to a dam failure brings about catastrophic consequences involving destruction of buildings and loss of human lives. Numerical models based on the 1-D shallow water equations serve as essential tools for effective flood risk analysis. However, conventional models have difficulties in consistently handling rapidly varying transcritical flows involving steep slopes, general cross-sections, wet and dry interfaces, and junctions. This study proposes an efficient and easily implementable numerical model for flash flooding, referred to as CDFVM, utilizing a simple finite volume algorithm with local Froude number as a weight. The CDFVM has a model parameter to be tuned, whose optimal value is determined so that wet and dry interfaces in idealized dam break problems are accurately captured. The CDFVM is successfully applied to numerical simulation of a dam break problem with wet and dry interfaces in a multiply connected (looped) open channel network.

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The East Japan Earthquake and Tsunami caused serious damages in the coastal area of eastern Japan. Many houses and cars on the road were swept away by the tsunami. Also, industrial facilities such as chemical plants in the coastal area were completely destroyed. Damage from saline seawater was not limited only to the rice field areas, and there were also serious anxieties regarding the possibility of ground contamination as a result of harmful heavy metals that leaked from destroyed chemical plants. In light of this scenario, we carried out a quantitative survey to examine these areas. This paper reports on the results of our survey. It was found that high salt concentrations were detected on the ground surface but predictions state that these concentrations can be diluted with rainfall. It was also revealed that serious ground contamination due to the harmful heavy metals was not detected.

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A new probabilistic model describing temporally random damage accumulation of tunnel concrete linings is proposed, in which independent two compound Poisson processes are used for (i) accumulation of daily small damages and (ii) accumulation of large damages due to severe frost damages, earthquakes or other unusual phenomena. The model is based upon a random differential equation of Itô type driven by the two compound Poisson processes, whose solution and statistical moments are analytically derived. It is clarified that the proposed model can reproduce damage accumulation processes whose statistical tendency shows good agreement with actual damage data.

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The differences in seismic responses in highly nonlinear ranges among various analytical models are not clear. These include such as frame models, and detailed Finite Element Method (FEM) models microscopically reproducing the individual components’ shapes are not clear structures. In this study, the dynamic response of a detailed FEM model is compared to those of frame models. The FEM model was made to reproduce a building’s shape as precisely as possible and analyzed by LS-DYNA that is commercial FE code equipped explicit method. The frame model was macroscopically composed of beam elements. Two frame models were considered; in one model, the P-delta effect was considered, and in the other model, it was neglected. The differences between those frame models and the detailed FEM model in highly non-linear ranges was investigated. As a result, it was assured that the frame model that neglected the P-delta effect tend to underestimate the deflection in these ranges, while the residual deflection of the frame model that considered the P-delta effect was larger than that of the detailed FEM model because of stiffness degradation.

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In this paper, we discuss ways of achieving more accurate tsunami run-up simulations, paying particular attention to the method of setting the friction parameter for tsunami run-up obstacles. To achieve mitigation of a tsunami disaster, real-time tsunami run-up simulations and tsunami inundation warnings are very important issues. In recent years, tsunami observations and the amount of survey data collected have both increased. Using these data, we clarify the effect of land use / land cover on tsunami run-up behavior to realize a tsunami run-up simulation. In this paper, we propose a new method for setting the friction parameter. First, we show the procedure for simulating a tsunami run-up phenomena and modeling the effect of buildings. The effect of buildings means the effect of friction from buildings, which act as obstacles to a tsunami when it runs up to their location. Second, we show existing methods used to determine the friction parameter including this building effect. Then, we propose a new method to determine the friction parameter from observable data. Finally, we show the performance and robustness of this method using a statistical approach.

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An earthquake forecasting system based on sequential data assimilation of slip on the plate boundary is constructed. Sequential Importance Sampling, a type of particle filter, is used for the data assimilation. A forward calculation is made using an earthquake generation cycle simulation. From the simulation results, we estimate crustal deformation that can be compared with observations of the GNSS Earth Observation Network System (GEONET) on land and the Dense Ocean Floor Network for Earthquakes and Tsunamis (DONET) on the seafloor. We demonstrate a numerical test of this system using synthetic data of seafloor deformation before virtual Nankai earthquakes. We also use a real GEONET data set to compare the results of earthquake generation cycles.

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A microflame, defined in this paper as a diffusion flame established on a burner whose size is less than 1 mm, is used as a small heat source having high heating density. Multiple microflames are often used to achieve a high density and uniform heating performance. However, when the microflames are placed too closely, they merge into a larger flame, which is no longer a microflame. Therefore, the knowledge of the critical burner-burner distance at which two microflames touch each other is important when designing such a device. This paper theoretically discusses the critical distance of two identical micro-slot burners, which are slot burners of the slot widths less than 1 mm. Two micro-slot burners are modeled as line-source burners in a uniform flow. The mixture-fraction model is then used to predict flame shapes, based on which the critical distance is derived.

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Injection of sweeping agent (surfactant, steam, etc) in tertiary recovery will only extract some additional oil; usually 70% of total oil. To produce it, sweeping agent has to make a contact with trapped oil. The existence of oil blobs may cause such a disturbance in injected flow field so that preventing contact between sweeping agent and trapped oil, but there is no strong evidence of it. Advanced micro-focused X-ray CT scanner technology enables us to directly observe water flow phenomena around trapped oil blobs. We injected water upward into packed glass beads, scanned it, and constructed 3-D images from it. Injection of additional miscible fluid representing sweeping agent in actual tertiary recovery process was able to invade pores located just next to trapped oil. There is very thin stagnant water comes from previous water flooding process preventing the contact between trapped oil and additional miscible fluid.

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Currently, the extension of life span of concrete structure is urgently needed. Therefore, it is important to predict the future deterioration of the concrete structure. The deterioration accompanied with alkali-silica reaction is one of the factors associated with durability. Generally, the aggregate expansion which is caused by the alkali-silica reaction brings about cracking, and the crack may decrease the durability with changing the mechanical properties of the concrete structure. Though there are a number of researches on alkali-silica reaction, the deterioration prediction under complex stress condition such as pre-stressed concrete is not well discussed. In this study, the degradation model for pre-stressed concrete structure is proposed and the validity of the model is examined through the comparison with exposure test of alkali-silica reaction using a pre-stressed concrete.

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We analytically investigate breakup phenomena of a viscous liquid column jet in a static electric field. Under a long wave approximation, nonlinear equations of the jet radius, velocity and electric surface charge density are derived. Assuming a constant axial electric field strength, these equations are numerically solved for the initial-boundary condition that a semi-spherical jet emanates from a nozzle exit. It is shown that there exist two types of breakup modes - dripping and cone-jet modes - depending upon the parameters ∧ (=electric force/fluid force) and Pe (=convective current/conductive current). Then a critical curve is found in the ∧ - Pe parameter space, across which the breakup is transfered from the dripping mode to the cone-jet mode as the increase of ∧ and/or the decrease of Pe. In the dripping mode, the produced drop size decreases as the increase of ∧ for larger Pe, while there is a region of ∧ where the drop size increases as increasing ∧ for smaller Pe.

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Embankments are constructed with compacting soil with the aim of improving their stability and deformation characteristics. Typhoons and guerrilla rainstorms are occurring frequently due to the abnormal weather of recent years, and there have been many reports of cases of collapses of embankments due to their effects. Drainage measures for embankments against rainfall are different during construction and after commencement of use, and the effects are sustained intermittently from the start of construction to after the commencement of use. In this study, soil/water/air-coupled F.E. analysis was used to perform analyses of embankments which take into account compaction and the history of rainfall/evaporation. Further, changes in the stresses inside the embankment by the effects of rainfall sustained after commencement of use are considered.

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This paper describes an evaluation of electromagnetic compatibility based on a full-wave analysis of electromagnetic fields using a parallel finite element method. The environment chosen is the interior of a commuter train. A train containing seats, handrails and 48 human bodies is precisely modeled using a large-scale finite element mesh with Nedelec elements and about 21 million degrees of freedom. To improve a convergence of an iterative method for the interface problem in the iterative domain decomposition method, a unit conversion is proposed by considering the wavelength. The results show that the environmental impact of electromagnetic fields due to cellular phone use in the train can be successfully evaluated.

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