System identification procedure is recently developed to evaluate dynamic properties of building structures, Present study is concerned with adaptive health-monitoring systems adequate for finding variable characteristics of wounded constructions under strong quake excitations. Adaptive observers are effectively utilized to carry out corresponding on-line operation whatever initial conditions are arranged.

View full abstract

Fiber opening technology is expected to improve mechanical performance of woven fabric composites by high impregnation of matrix resin and reduction of undulation of yarns. In this paper, a three-dimensional finite element method based on damage mechanics has been applied to spread woven fabric composites fabricated by fiber opening technology, and the effect of fiber opening on progressive fracture behaviors under on-axis tensile load has been investigated computationally. Finite element models composed of weave yarns and matrix were employed, the flattening ratio between width and height of opened yarns were changed under the condition that volume fraction of fiber was constant. Computational results indicated that spread woven fabric composites show different progressive fracture in a mesoscopic scale according to geometric change of opened yarns. Overall tensile strength proved to be maximized by geometric design of opened yarns.

View full abstract

Three 2-D stress concentration problems are treated for a fluid-saturated, poroelastic, infinite plate with a rigid circular inclusion, a permeable or an impermeable circular hole, subjected to a step-like, uniform, uniaxial tension at infinity, with account of a full range of drained Poisson's ratio. Those are analytically solved in the Laplace space and numerically inverted into the time domain. The numerical results and various limiting solutions are discussed. It is found that the stress concentration is in general alleviated by the existence of pore fluid for the three problems and that a discontinuity in the pore fluid pressure and tangential stress takes place immediately after loading at the hole periphery. It is also found that the mechanical response in the case of (the lower limit of drained Poisson's ratio) is counter-intuitive and shows another discontinuity for infinite time elapsing.

View full abstract

The present paper deals with the instabilities of a bending tube. When an increasingly large amount of bending moment is applied to the ends of a circular tube, ovalization occurs at its cross-section before it finally buckles. This ovalization is referred to as the Brazier effect and the result of which is the decrease in the tube's geometrical stiffness. After buckling, the tube collapses with a local kink in the longitudinal direction. The tube responses described above are, in this paper, investigated with a nonlinear finite element method that uses the hyperelastic shell model. By conducting numerical analysis, we detect the bifurcation paths,trace the post-buckling equilibrium paths and depict the corresponding buckled configurations.From the numerical analyses, it is revealed that there are two critical points, a bifurcation point and a limit or turning point, before the limit point that Brazier estimated. Symmetrical kinks are observed along the primary path as final largely deformed configuration, while only one kink along the furcation path. In the both cases, the deformation suddenly jumps to the kink mode at the same rotation angle. The numerical results demonstrate the ability of presented approach and examine the bending instabilities of a tube.

View full abstract

The fundamental reason of deterioration is the repetitional scaling of the surface layer; further, it has been basically analyzed that the freezing and thawing actions make concrete neutralize from the outside by virtue of the environmental contact water. The wet-dry action is one of the principal deterioration causes. It has been already understood that both actions contribute to the neutralizing acceleration of concrete. The present paper particularly deals with the quantification of the concentration dilution of pore solution and the neutralization of the matrix of concrete, from the viewpoint of the potential Hydrogen (pH) range of general environmental water; in addition, it has been clarified that the equilibration-concentration and the neutralized depth can be obtained, assuming to be the semipermeable membrane on the shell interface. The critical thickness as to the hypothetical thick shell with the through microcrack has been derived for the first time; thus, finally the mechanical cover can be perfectly neutralized due to the approximately fifty cycles of water-microcirculation.

View full abstract

Some strain rate types of constitutive equations have been proposed to express macroscopic dynamic phenomena of solid materials. However, they can’t express volume change of dynamic behaviour since they are assumed to be incompressible under inelastic deformation. In addition, theoretical propagation speed of stress waves deduced from elastic-viscoplastic constitutive equations can’t express experimental results since the theoretical one is constant. The purpose of this work is to mathematically derive a constitutive equation which is able to express strain and strain rate dependence of stress, and volume change under dynamic inelastic deformation. Each Poisson’s ratio for plastic, viscoplastic and inelastic strain is newly defined and introduced into the proposed equation to express volume change in addition to the existing Poisson’s ratio foe elastic strain.

View full abstract

We study the axisymmetric indentation mechanics of an elastic layer overlaid on a rigid foundation. An infinite rigid flat-ended punch with a circular hole is pressed onto the upper surface of the elastic layer causing a small deformation mode. This problem is equivalent to a mixed boundary-value problem in which the displacement prescribed within the contact region of the punch and surface stresses are zero inside the circular hole. The problem is formulated satisfying a solution of an infinite system of simultaneous equations utilizing a method of expressing normal displacement in the circular hole as an appropriate series function. The effects of the layer thickness and the circular hole are addressed with the solution obtained here.

View full abstract

In many cases where a reinforced concrete (RC) slab directly supports the wheel load of large-sized vehicles, the static strength of the slab is generally evaluated as punching shear capacity. Given the situation, this study proposes equations to be used to determine the punching shear capacity for the slab fabricated by applying the limit state design method, which were derived from the relationship between the experimental maximum load-carrying capacity and the reinforcement strain in the static loading experiment conducted using two types of the double reinforcement slab specimens. This is an attempt to perform a theoretical evaluation of such strength with a view to making some contributions to the establishment of a reasonable design method of RC slabs.

View full abstract

In recent years, Ultra High Strength Fiber reinforced Concrete (UFC) attracts attention as new material corresponding to large-sized or high durability structures. Since UFC is reinforced with the steel fiber in addition to 200N/mm2 or more compressive strength, it is also excellent in toughness. In this research, an experiment with (1) static load or (2)running load was performed by three kinds of specimens with different height, and at the same time the influence by running load was evaluated.

View full abstract

Magnetorheological (MR) fluid dampers have been utilized in vibration control for buildings and mechanical structures. As an advanced MR fluid, we have proposed a magnetic functional fluid that composed of micrometers size iron particles and 10 nanometers size magnetite particles. In this paper, four kinds of MR fluids consisting of different proportions of particles are investigated. Then we reached the preliminary conclusion that MR damper utilizing the newly functional fluids can be changed their damping properties by applied magnetic field and their increments of damping force depend on the mixing ratio of their different size of particles.

View full abstract

In this paper, a sliding mode control scheme is proposed to control the chaotic system with unknown parameter. The parameter is estimated by function approximation with Fourier series, while the sliding mode controller keeps robustness against parameter uncertainty. Therefore the sliding mode control can be applied without knowing the bounds of the unknown parameter. The simulation results show that the proposed method can steer Van der Pol system to the desired state.

View full abstract

Discrete breathers (DBs) or intrinsic localized modes (ILMs) are energy localizations in nonlinear lattice systems. One of the characteristic properties of DB is that they can be excited even in higher dimensional systems. Indeed, it has been reported that DB can be formed in two dimensional lattice systems as a result of energy concentration from some perturbations. However detailed studies of DBs in the higher dimensional system have not been done yet. In this paper, we investigate structures and dynamics of quasi-one dimensional DBs in two dimensional Fermi-Pasta-Ulam (FPU) lattice systems.

View full abstract

In recent years, many researches have been proposed various methods to suppress vibrations produced from flexible structures. The purpose of this paper is to show experimentally that impactive and periodic force which is called 'pulsating force' can suppress the vibrations from the flexible structure. Our experimental setup is a typical of the Duffing system which has a buckled thin steel sheet moved by periodic external force. We passively apply the pulsating force toward the steel sheet by collisions with a steel stick fixed near it. As a result of measuring displacements of the steel sheet with or without the pulsating force, large-amplitude vibrations is decreased by applying the pulsating force when our system shows the frequency hysteresis. We consider that the pulsating force is capable of changing the large amplitude vibration to smaller one when a target system is bistable.

View full abstract

We consider an inverse scattering problem for the Maxwell equation outside a moving obstacle in inhomogeneous media.Concerning this problem, we obtain our results similar to those of the Lax-Phillips theory; we have the existence and uniqueness of a solution to the Maxwell equation outside the obstacle, and we obtain a recovering of the convex hull of the obstacle under the assumption that the scattering operator exists and the operator is bounded.

View full abstract

In this paper, we investigate the parametrization of all robust stabilizing multi-period repetitive controllers for single-input/single-output systems. The multi-period repetitive controllers were proposed by Goto et al., in order to improve the disturbance attenuation characteristics of the conventional repetitive control systems for the frequency which is different from that of periodic reference input. Yamada et al. proposed a design method of multi-period repetitive controllers to attenuate wide-frequency disturbance that has the same frequency component of periodic reference input based on the idea of changing time-delay. In this way, several design methods of the multi-period repetitive controllers to improve the disturbance attenuation characteristics of the conventional repetitive control systems have been considered. However, the parametrization of all robust stabilizing multi-period repetitive controllers has not been considered yet. In this paper, we propose the parametrization of all robust stabilizing multi-period repetitive controllers. Finally, a numerical example is shown to illustrate the effectiveness of the proposed parametrization.

View full abstract

Multi-component gas transport phenomena in a cathode electrode layer of Polymer Electrolyte Fuel Cells (PEFC) are investigated by using a two-dimensional computational model developed by Yi and Nguyen. In the past research, we encountered a problem that the solution did not converge when the same settings for physical parameters with them were used in our steady simulations. In the present study, we extend our simulation from steady to unsteady simulation to avoid the problem. Also, based on the results, the effect of changing permeability in the simulations is discussed with reporting possible errors regarding the value of permeability shown in the reference at the same time.

View full abstract

In this study, an interface-tracking method, NS-PFM, combining Navier-Stokes (NS) equations with a phase-field model (PFM) is applied to an incompressible two-phase free surface flow problem at a high density ratio equivalent to that of an air-water system, for examining the computational capability. Based on the Cahn-Hilliard free energy theory, PFM describes an interface as a finite volumetric zone across which physical properties vary steeply but continuously. Surface tension is defined as an excessive free energy per unit area induced by local density gradient. Consequently, PFM simplifies the interface-tracking procedure on a fixed spatial grid without any elaborating techniques in conventional numerical methods. It was confirmed through the numerical simulation that (1) the NS-PFM conducts self-organizing reconstruction of the interface with a certain thickness using volume flux driven by chemical potential gradient and (2) predicted collapse of two-dimensional liquid column in a gas under gravity agreed well with available data.

View full abstract

Rigorous theoretical analysis of heat conduction in a very long elliptical cylinder in comparison with its cross section, i.e., an infinite elliptical cylinder, during heating or cooling is carried out using the Mathieu and modified Mathieu functions, which are the solutions of the basic heat-conduction equation expressed in terms of the elliptical cylinder coordinates. By applying the method of separation of variables, the mathematical solution is derived in the form of an infinite Mathieu function series in the most realistic and useful case that takes into consideration the internal and surface resistance of the cylinder. Two special cases of the heat conduction of an infinite elliptical cylinder, neglecting its surface resistance, and that of an infinite circular cylinder, including both its inner and surface resistance, are also discussed in detail. The temperature history and distribution within the cylinder are calculated numerically for various convective heat-transfer coefficients and aspect ratios of the elliptical cross section.

View full abstract

Motion of a circular interface between two fluids with different densities is investigated by use of the vortex method. We have found that initial perturbations with various mode numbers n grow to mushroom-like structures except the case for mode n=1. It is shown that when the inner fluid is heavier than the outer fluid (Atwood number A < 0), the break-down of computations occurs at later time than the reverse case (A > 0) for the same mode number n. We also present that the break-down of computations for the interface with higher mode numbers occurs at later time than the one with the lower modes for a fixed Atwood number A.

View full abstract

In this paper a typical inverse problem called a backward heat conduction problem is simulated directly and globally. Several bounding transforms are introduced for avoiding unboundedness of the domain and the solution. However, by using the bounding transform unboundedness is replaced by discontinuity. Thus, a method to overcome this difficulty is presented. Numerical results show that it is useful for estimating the growth rate and it enables the global simulation.

View full abstract

We present numerical results for aerodynamic vibrations of two elastically supported circular cylinders, which are placed at a certain distance between two cylinders, by two-dimensional computation. The computation is achieved by means of the finite element method and the arbitrary Lagrangian-Eulerian method, and numerical stabilization of solutions of the Navier-Stokes equations is performed by a third-order upwind scheme. In our computation we show clearly aerodynamic characteristics of two vibrating circular cylinders in side-by-side arrangement.

View full abstract

A feedback control technique of vortex shedding behind a circular cylinder is investigated through two-dimensional numerical simulations. In order to suppress the vortex shedding, periodic velocity excitation is applied from the cylinder surface to the separated shear flows with a time delay and feedback gain for the fluid velocity behind the cylinder or pressure on the cylinder surface. It is shown that the feedback excitation generated by the velocity feedback method can suppress the vortex shedding considerably with appropriate time delay and feedback gain. However, the control using the pressure feedback method cannot suppress the vortex shedding effectively because of the unsteadiness of the pressure fluctuation on the cylinder surface.

View full abstract

Topography and solar heating are incorporated in our Venus-like AGCM. Superrotation is fully developed at the cloud top. Stationary waves and slowly propagating waves with phase velocities of about 0 m/s are predominant because of the topographic and thermal forcings. The topography leads to the north-south asymmetries of the angular momentum and the vertical EP flux in the lower atmosphere. Since the winds near the surface are weak and the static stability is low, the vertical eddy momentum flux of stationary mountain wave with phase velocity of 0 m/s is not large near Maxwell Montes at high latitude. Rather than the stationary wave, slowly propagating waves produce large vertical EP flux. In the equatorial region where Aphrodite Terra is located, the vertical eddy momentum flux of stationary wave is locally predominant near the surface.

View full abstract

Two-dimensional incompressible Navier-Stokes flow on a rotating hemisphere bounded by a meridional line, is studied numerically in the presence of a modeled wind forcing for triple-gyre flow. A stable westward intensification of meridional flow is found when the wind forcing is weak. As the forcing is intensified, a temporal oscillation emerges in the flow field, and the dependence of the oscillation amplitude on the forcing strength indicates a Hopf bifurcation to oscillating solutions. The position of the maximum amplitude of the oscillation is located near a point of the separation of the boundary layer current.

View full abstract

We study liquid film flows falling down a vertical wall, focusing our attention to the limit of high viscosity. For highly viscous liquids (small Kapitza number), it is possible to find a limit in which both Reynolds number R and Weber number W vanish;the governing equations are then reduced to the Stokes equation with free-surface boundary conditions. Theoretical analysis with regularized long-wave expansion yields the modified Benjamin-Bona-Mahony equation as a reduced equation describing one-dimensional surface dynamics. The surface dynamics exhibits a soliton-like behavior: two solitary waves are seen to collide elastically in our numerical calculation. This phenomenon arises in highly viscous situation (described by the Stokes equation), which is opposite to that of inviscid "water waves" (described by the Euler equation). As a step toward comparison with real experiments, a preliminary calculation of two-dimensional surface dynamics (three-dimensional flows) is also presented.

View full abstract

We study the RSA encryption from the viewpoint of dynamical-system. We constitute a “discrete RSA dynamical-system” corresponding to the RSA encryption, present extension of concept of dynamical systems suitable for analyze the encryption system, and then show that it is a new type of solvable -chaotic systems. We consider that the discrete RSA dynamical-system possesses many synchronous periodic points, and show that constituting the pair of keys from the period and corresponding the plaintexts to the periodic points make a public-key encryption possible. Furthermore we show the properties that a chaotic map which is able to constitute a type of RSA encryption must satisfy, by extracting properties of the discrete RSA dynamical-system.

View full abstract

We investigate the stability of a numerical method using the Combined Compact Difference (sp-CCD) method with spectral-like resolution for a 1-D advection diffusion problem. The sp-CCD method was proposed by Nihei and Ishii and has high-accuracy and high-resolution. The finite difference representation of the equation consists of the sp-CCD method for the spatial derivatives and the Runge-Kutta (RK) method for the time marching. In order to investigate the influence of the boundary conditions we use the matrix method in the stability analysis. It is shown that the numerical method with some parameters is stable in the problem with periodic boundaries, but it is unstable in the problem with nonperiodic boundaries. We also propose a new stable boundary scheme for the problem with nonperiodic boundary.

View full abstract

In this study, we present a scheme for analyzing structures that have complex shape models. Targets of the structural analysis usually consist of a combination of simple shape models generated using modeling tools such as CAD systems. On the other hand, in the field of computer graphics, there have been proposed a number of techniques that make it possible to create complex shape models from point clouds obtained by 3D range scanners. One effective way of the modeling is to represent the surface as an implicit function. A scheme for the structural analysis combined with the modeling technique based on implicit surface representation is described in this paper. We also present some numerical results of 3D stress problems.

View full abstract

We examine a design method for learning controllers for multiple-input/multiple-output systems using 2-delay digital control. Learning control systems, in which the present operation is modified by the error between the desired trajectory and the output at the previous trial, endeavor to make the output follow the desired trajectory without error. Many papers on the theory and applications of learning control systems have been published. Learning control for discretized plant is unstable when the discretized plant has unstable zeros. Hayakawa et al. make use of the characteristics of the discretized plant using 2-delay digital control to be of minimum phase and propose a design method for a learning control system using 2-delay digital control. However, the Hayakawa et al. design method is for single-input/single-output plant learning control systems. Since the method by Hayakawa et al. is based on the transfer function method, it is not straightforward to expand their result to multiple-input/multiple-output plants. In this paper, we propose a design method for learning control systems for multiple-input/multiple-output plant using 2-delay digital control.

View full abstract

In order to investigate effects of ablated gases originating from carbon ablation materials on a shock layer around an earth reentry capsule, numerical analyses along a stagnation streamline are conducted by the extended merged shock-layer theory based upon a 4-temperature and 16-chemical species model which includes the detailed nonequilibrium chemical reactions and energy exchanges among internal energy modes. The analysis is based upon an assumption of continuum, and the governing system of equations constitutes a two-point boundary value problem that is solved by using a simple finite difference method called successive accelerated replacement. It is found that the shock standoff distance in the presence of ablation increases in comparison to that without ablation, and that the ablated gases have significant influences on thermal and chemical properties of the entire shock layer.

View full abstract

To help diagnosis of diseases of the circulatory, we have developed the system to perform computational mechanical approach. We have designed so that the system will be based on "Weak Coupling". So the system has capability to be improved easily in the future.
This system performs five subsystems: voxel generation, fluid analysis, define loads, construct elastic wall, structure analysis, and volume morphing.
By using this system, we analyzed an interaction between flow and structure in actual blood vessel from Computer Tomography (CT) image of real patient. The blood vessel we computed was coronary artery stenosis from actual patient image of CT, and we used pulsation inflow condition. A swirl generation and degeneration according to the inflow pulsation was found. And we qualitatively confirmed that the system has ability to handle Fluid-Structure-Interaction (FSI) by observing tube deformation according to flow pulsation.

View full abstract

In LPE, slide of the entire melt before the growth induces flow in the melt. For short growth times, the forced convection may cause compositional variation of solid. Recently, a new calculation method for the variation was proposed.
In this paper, the growth time 0.01 - 0.5 s was treated using the method. The scales of the flow and transport of solutes are different. Then an one-dimensional model was adopted as the first calculation with the forced convection. The flow was approximated to the solution of Stokes's first problem. The boundary layers of solutes in the liquid become same each other by the flow. The initial behavior of solid composition in calculation was consistent with the experiment.

View full abstract