Journal of Japan Society of Civil Engineers, Ser. A2 (Applied Mechanics (AM))
Online ISSN : 2185-4661
ISSN-L : 2185-4661
Volume 75 , Issue 2
Showing 1-50 articles out of 63 articles from the selected issue
Journal of Applied Mechanics Vol.22 (Special Feature)
  • Isao SAIKI, Xun ZHENG, Takeki YAMAMOTO
    2019 Volume 75 Issue 2 Pages I_3-I_12
    Published: 2019
    Released: February 06, 2020
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    Although the Timoshenko beam theory assumes that cross sections remain plane, the shear stress is not constant through the beam thickness. Therefore, the shear stiffness of beams has to be modified by a shear correction factor through taking into account warping of cross sections. In this beam theory, warping is assumed to be proportional to the shear force. Whereas the shear force can be discontinuous, warping must be continuous due to compatibility condition of deformation. Therefore, the warping can not be proportional to the shear deformation. This paper proposes a beam theory taking into account the warping independent of the beam shear deformation. The effect of independently considered warping is evaluated through a series of analyses of simple cantilever beams. As a result, we conclude that the present theory predicts the deformation more accurately compared with other beam theories and that the effect of constraint of the cross-sectional deformation reduces the shear deformation within the length equivalent to the height of the beam.

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  • Yoshinao KISHIMOTO, Yukiyoshi KOBAYASHI, Toshihisa OHTSUKA, Kanta KOMU ...
    2019 Volume 75 Issue 2 Pages I_13-I_24
    Published: 2019
    Released: February 06, 2020
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    This study has developed a novel technique for vibration simulation by using interfacial element that simulates contact of micro asperities formed on interfaces of bolted joints. The stiffness of the interfacial element is derived by the assumption in which peak heights of the asperities obey the Gaussian distribution and the contact of the asperities is the Hertzian contact. Due to this assumption, the stiffness of the interfacial element is determined by compressive stress and surface texture of the interfaces. Finite element simulations with the interfacial element and hammering tests were performed by using a miniature specimen of bolted joints composed of steel and concrete. The results of the finite element simulations and the hammering tests have shown the validity of the proposed technique. Moreover, the methodology to estimate the clamping force of the bolted joints from the natural vibration has been discussed. The hammering tests and the finite element simulations were also conducted under the condition in which the clamping force of the screw bolts was varied. The results have shown that loosen bolts can be detected by the difference of the power spectra obtained with accelerometers.

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  • Shuya KANAGAWA
    2019 Volume 75 Issue 2 Pages I_25-I_29
    Published: 2019
    Released: February 06, 2020
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    We investigate the daily share prices of the Nikkei 225 stock market index to identify jump times of the stock index using a jump diffusion model, which consists of the Black-Scholes model with stochastic volatility and a compound Poisson process. Since the data of daily share prices of the Nikkei 225 stock index are observed at discrete times, it is difficult to find real jump times from the data. In this paper, we consider how to separate jump times from the observed times. The volatility of the stock index is estimated by the historical volatility from the observation of daily share prices. We also refer to the number of daily share prices for historical volatility and show that the number is essential for the accuracy of identifying of jump times.

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  • Hiroaki T-KANEKIYO, Kensuke KASAYUKI, Toshiyuki ISHIKAWA
    2019 Volume 75 Issue 2 Pages I_31-I_40
    Published: 2019
    Released: February 06, 2020
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    Spatially random variation of stress appearing in adhesive for a steel plate bonded by a CFRP plate is theoretically discussed by taking into account spatially random variation of longitudinal elastic modulus and shear elastic modulus associated with the adhesive. First, a new probabilistic model is proposed for describing spatially random variation of a longitudinal elastic modulus, shear elastic modulus and Poisson ratio of the adhesive, in which statistical correlation among these factors is introduced. Then, a system of differential equation of static mechanics describing axial force of the steel plate and shear force of the CFRP plate is extended to a system of spatially random differential equations. By constructing a numerically solving scheme for them, a probability distribution of a maximum of principal stress of the adhesive is estimated through computer simulations to generate solution of the system of random differential equations, which is directly applied to estimate probability of detachment of the adhesive. It is clarified that (i) probability distribution of a maximum of principal stress of the adhesive is well approximated by Gaussian distribution and (ii) probability of detachment of the adhesive is hardly affected by statistical correlation among longitudinal elastic modulus and shear elastic modulus of the adhesive.

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  • Takahiro SAITOH, Masahiko TASHIRO, Hikaru MORIKAWA, Kazushi KIMOTO
    2019 Volume 75 Issue 2 Pages I_41-I_49
    Published: 2019
    Released: February 06, 2020
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    In this paper, a novel shape reconstruction method based on the time-reversal technique is presented for the purpose of quantification of the ultrasonic nondestructive testing. First, a forward analysis of 3-D scalar wave scattering by rigid scatterers in an infinite region is solved by using the convolution quadrature time-domain boundary element method (CQBEM), which can produce higher accuracy than conventional time-domain boundary element method (BEM). In the proposed method, the topological sensitivity is used to identify the shape and position of defects in 3-D infinite space, and it is obtained by solving the corresponding adjoint problem of the forward one with the aid of CQBEM for 3-D scalar wave propagation. As numerical examples, some numerical results of shape reconstruction of a scatterer and multi-scatterers in an infinite space using the proposed method are demonstrated. The reconstruction ability of the proposed method is investigated by changing the radiation pattern of ultrasound from a phased array transducer and the number of scatterers, and by comparing the results obtained by the synthetic aperture focusing technique (SAFT).

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  • Yosuke KONDO, Gen HAYASHI, Yoshinobu OSHIMA, Chul-Woo KIM
    2019 Volume 75 Issue 2 Pages I_51-I_62
    Published: 2019
    Released: February 06, 2020
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    This study aims to examine how changes in load resistance capacity of a prestressed concrete bridge (PC bridge) influence on their modal properties. Static loading test was carried out under step-by-step loading until failure. In addition, forced vibration tests were carried out along the static loading test in order to assess the changes in the modal properties of the PC bridge with different health conditions. Energy performance calculated by load-displacement relation is used in order to estimate the structural performance of the PC bridge. Observations showed strong relationships between 2nd bending modal frequency and the level of structural performance. This indicates the usefulness of the 2nd bending mode in vibration-based bridge health monitoring for PC bridges.

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  • Tatsuya KURIHARA, Tokuo TSUJI
    2019 Volume 75 Issue 2 Pages I_63-I_70
    Published: 2019
    Released: February 06, 2020
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    The social infrastructure structure which was built for the rapid economic growth period becomes deterioration. Load bearing deterioration of existing transmission towers due to aging is estimated by periodic inspections and numerical analyses. However, efficient classification of the deterioration level is inevitably requested, since a lot of anxious towers may exist.This study is intended to evaluate the aging deterioration phenomenon of the transmission tower from vibration characteristic. The representative of deterioration phenomenon is loose bolt , material corrosion and basic displacement in transmission tower, and aimed at the detection of the basic displacement using a high resolution camera and an accelerometer.

    In this paper, we simulated the member corrosion and base displacement of transmission tower, then analyzed to what extent it will affect the vibration characteristics of the tower.In addition, we also analyzed the change in vibration characteristics of a transmission tower that was actually diagnosed with base displacement. Then, by utilizing high-resolution camera and accelerometer to measure the vibration characteristics of the diagnosed tower, it was verified that the analysis results were consistent with the actual vibration characteristics.

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  • Kazuyuki NAKAHATA, Yuui AMANO, Hirohisa MIZOTA, Takahiro SAITOH, Kazus ...
    2019 Volume 75 Issue 2 Pages I_71-I_81
    Published: 2019
    Released: February 06, 2020
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    The simulation-aided time reversal imaging method has been proposed for nondestructive ultrasonic testing. In this study, we describe the theory of the time reversal imaging method in detail and validate it for an anisotropic material using ultrasonic measured signals. First the incident wave arrives at the flaw, which is called ’illumination’, and then scattered waves from flaws are recorded at the array elements. Next the time-reversed signals are emitted into a finite element model which imitates the target material. The time reversal waves propagate in the model and focus on the flaw location. By calculating a crosscorrelation of the incident and the reverse propagated waves, the flaw shape can be uniquely determined. In the measurement, the elastic constants of the anisotropic material were estimated using wavefield data measured by a laser ultrasonic method. An artificial flaw in the target material can be reconstructed by the proposed method. It was shown that the flaw imaging area depends on the first illumination, and the frequency components contribute the intensity of the flaw shape.

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  • Naohiko WATANABE, Ryo MATSUI, Daisuke AOKI, Satoshi NAMEDA, Yoshiyuki ...
    2019 Volume 75 Issue 2 Pages I_83-I_92
    Published: 2019
    Released: February 06, 2020
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    To investigate the applicability of a mechanical model to estimate the bulging response of an isolated rectangular water storage tank, sweep excitation and scaled real earthquake-wave excitation were performed on a model tank with various liquid levels and its response was measured. A comparison of the response value calculated by the mechanical model and the results of excitation tests showed that the mechanical model is effective in predicting the waveform and peak value response characteristics of the isolated tank.

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  • Tomoki KURASAWA, Kazuya INOUE
    2019 Volume 75 Issue 2 Pages I_93-I_104
    Published: 2019
    Released: February 06, 2020
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    Intermediate-scale laboratory solute transport experiments were conducted in physically heterogeneous and homogeneous porous formations to investigate the impacts of upscaling of hydraulic conductivity on the behavior of solute macrodispersion. Solute transport in porous media based on geostatistics was visualized and solute macrodispersion parameters were quantified by using dye tracer imaging technique. The results showed the longitudinal and transverse macrodispersivity estimates decrease with the increase of the degree of upscaling due to a lower heterogeneity corresponding to the upscaling. The macrodispersivity estimates were almost constant in heterogeneous porous formations having the cell size of less than 6 cm, which is the correlation length of non-upscaled porous formation, whereas for large cell sizes macrodispersivity estimates depended strongly on the length of the cell. As the degree of upscaling increased, the horizontal distance between forward and backward edges of the solute plume decreased.

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  • Masataka HASHIMOTO, Hiroshi TAKAHASHI
    2019 Volume 75 Issue 2 Pages I_105-I_111
    Published: 2019
    Released: February 06, 2020
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    Stochastic differential delay equations (SDDEs) are generalizations of stochastic differential equations (SDEs) because SDDEs may include information of the past process. SDDEs are used for describing models that the future states of systems depend on not only the present state but their past states. Solutions of SDDEs do not necessarily have the Markov property, and representations of the solutions are more complicated than those of SDEs. For this reason, approximate solutions of SDDEs have been studied. In this paper, we focus on error estimations of the Euler-Maruyama approximate solutions of SDDEs and consider confidence intervals for the approximate solutions.

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  • Kazushi KIMOTO
    2019 Volume 75 Issue 2 Pages I_113-I_124
    Published: 2019
    Released: February 06, 2020
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    This study develops a numerical technique for the analysis of mass diffusion in unsaturated porous media. In the present approach, a periodic porous solid model is generated numerically by packing arbitrary shaped particles into the unit cell. The pore water of predetermined amount is then distributed over the pore space so that the total interfacial free energy is minimized. Finally, a random walk particle tracking is implemented on the rectangular grid generated uniformly over the fluid phase domain. To characterize the macroscopic diffusion, an overall diffusion constant and the abnormality of the macro diffusion are evaluated quantitatively based on the temporal evolution of random walkers’ mean-square displacement. With the numerical methods, the effects of such parameters as the degree of saturation, solid phase packing structure, and the solid particle size distribution on the macro diffusion characteristics are investigated. It was found, as the results, that the origin of the anomalous diffusion is the tortuosity of the diffusion paths, while the grain size distribution has more to do with the magnitude of the macro diffusion constant.

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  • Tatsuo YANAGITA, Tetsuro KONISHI
    2019 Volume 75 Issue 2 Pages I_125-I_133
    Published: 2019
    Released: February 06, 2020
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    We consider the Hamiltonian dynamics of the bead-spring model. The bead-spring model considered here is that masses are connected linearly with spring and known as the Rouse model, which presents a model of polymer. Despite the bending energy is not included in the Hamiltonian explicitly, the bead-spring model exhibits bending oscillations when the spring energy exceed a critical value. In other words, stiffness emerges dynamically. We show that the critical spring energy is one third of total energy by considering a simple three-beads model.

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  • Takashi NAKAZAWA
    2019 Volume 75 Issue 2 Pages I_135-I_143
    Published: 2019
    Released: February 06, 2020
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    This paper presents optimal design using Shape Optimization Problem considering Snapshot Proper Orthogonal Decomposition (Snapshot POD) which is the same algorithm as Prinary Component Analysis (PCA) and is able to decompose time dependent flow into time average and time fluctuation parts. The method suppresses time periodic flows driven only by the non-stationary boundary condition at a sufficiently low Reynolds number. For shape optimization, the eigenvalue in Snapshot POD is defined as a cost function. The main problems are Reynolds Average Navier-Stokes problem and eigenvalue problem of Snapshot POD. An objective functional is described using Lagrange multipliers and finite element method. Two-dimensional cavity flow with a disk-shaped isolated body is adopted for an initial domain. The non-stationary boundary condition is defined on the top boundary and non-slip boundary condition for side and bottom boundaries and for the disk boundary. For numerical demonstration in Newtonian fluid and Non-Newtonian fluid, the disk boundary is used as the design boundary. Using H 1 gradient method for domain deformation, all triangles over a mesh are deformed as the cost function decreases.

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  • Munemasa TOKUNAGA, Hideki YAGI, Manabu IKEDA, Masamichi SOGABE
    2019 Volume 75 Issue 2 Pages I_145-I_153
    Published: 2019
    Released: February 06, 2020
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    Railway viaducts contain non-structural elements such as track components and bridge railings, which are components of the railway system. Although non-structural elements have a significant effect on main structural rigidity and dynamic response, the same has not been quantified. This study aims to evaluate the influence of non-structural elements and their expansion joints on the vibration characteristics of the main structure of the general railway girder. Three dimensional finite element analysis showed that the natural frequency of the main structure increases differently depending on the type of the non-structural elements, and increases owing to the stiffness of roadbeds by approximately 30%–50% when the girder span is 10 m, and by approximately 10% when the span is 22 m or greater. It decreases by approximately 15%–25% because of the influence of the expansion joints of non-structural elements. Thus, it was found that these effects tend to decrease with the increase in bridge span.

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  • Mitsumasa WADA, Shiori KUBO, Hidenori YOSHIDA, Kohei FUJITA, Tsuyoshi ...
    2019 Volume 75 Issue 2 Pages I_155-I_164
    Published: 2019
    Released: February 06, 2020
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    It is difficult to evacuate a reservoir disaster caused by a massive earthquake if the time to failure is short. Reservoirs that are important for disaster prevention is used to be considered priority reinforcement. It is also equally important to utilize disaster prevention information based on 2D numerical analysis, such as hazard maps. In recent years, large-scale numerical simulations is implemented by improvement of computing power. We aim to clarify that the analytical methods for a reservoirs disaster is able to be shown by a large-scale deformation based on finate element method and an incompressible fluid flow program. Using 3D nonlinear seismic response analysis, the damage location and the damage scale were determined. The first obtained results were incorporated into the 3D flood analysis model. The arrival time of the runoff water, height of inundation, hydrodynamic pressure and flow velocity were acquired by flood analysis. It was shown that the wooden house within 100m from the reservoir collapsed in a few minutes. The application method of analysis technology to evaluate disaster risk is obtained by integrating 3D nonlinear seismic response analysis and 3D flood analysis.

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  • Yuto SOMA, Mao KURUMATANI
    2019 Volume 75 Issue 2 Pages I_165-I_173
    Published: 2019
    Released: February 06, 2020
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    In this paper, we propose a fracture simulation method of reinforced concrete considering detailed bond behavior between reinforcing bar and concrete using a damage model considering frictional contact on interface. The bond between reinforcing bar and concrete consists mainly of adhesive force on interface, frictional force generated by sliding between materials, and pressure on lug of reinforcing bar. The pressure on lug of reinforcing bar is simulated by using a finite element model reflecting the surface shape of reinforcing bar. The fracture and frictional contact on interface are simulated by applying the damage model to thin interfacial phase on surface of reinforcing bar. The damage model is formulated by combining the scalar-valued damage variable and the Coulomb friction law in local coordinate system defined along interface. In order to verify the performance and effectiveness of the proposed method, we simulate pull-out test of round bar and deformed bar. In addition, we compare the experimental and numerical results of 4-point bend tests of RC beams using round bar and deformed bar.

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  • Osamu SHIMAKAWA, Toshiyuki HORIGUCHI, Yoshiharu KOMATSU, Satoshi KATSU ...
    2019 Volume 75 Issue 2 Pages I_175-I_185
    Published: 2019
    Released: February 06, 2020
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    This paper investigates an evaluation method of debris flow impulsive load on steel pipe open sabo dam observed in preliminary experiment. In the experiment, the impulsive load of debris flow was reduced 30 % by the front inclination angle of the dam model. Moreover, the distinct element method is utilized for a numerical simulation of the experiment. Herein, the numerical results reproduced the load duration relation and sedimentary process of experimental results. The load reduction mechanism that was influenced the front inclination angle of the dam, is precisely analyzed by tracing the movement of elements around ‘Dead Zone’ and/or area of colliding with facilities. At last, it is pointed out that the predominant mechanism of load reduction is contact frequency that is intended between the dead zone and the flowing elements along with the dead zone.

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  • Yusuke IMOTO, Mitsuteru ASAI, Takehiro FUJII
    2019 Volume 75 Issue 2 Pages I_187-I_194
    Published: 2019
    Released: February 06, 2020
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    The stabilized ISPH method is a particle method for the incompressible Navier–Stokes equations and has a characteristic of adding a relaxation term with respect to a particle density in the pressure Poisson equation. The relaxation term contributes to keeping uniformness of particle distribution, then, enhancements of stability, volume conservation, and accuracy are confirmed by numerical results. For the stabilized ISPH method, it was shown by our previous study that the stabilization term is theoretically derived as an approximate solution of an energy minimization problem with respect to errors of incompressibility of fluid and uniformness of particle distributions weighted by a relaxation coefficient. However, a theoretical derivation of the optimal value of the relaxation coefficient remained unsolved. Then, this paper derives an optimal relaxation coefficient in the sense that minimizing an upper bound of errors derived by error analysis. Moreover, it is shown that the value and tendency of the optimal relaxation coefficient coincide with experimental results.

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  • Ryosuke FUJIOKA, Naoto MITSUME, Tomonori YAMADA, Shinobu YOSHIMURA
    2019 Volume 75 Issue 2 Pages I_195-I_201
    Published: 2019
    Released: February 06, 2020
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    We develop a hybrid method using the finite difference method (FDM) and the smoothed particle hydrodynamics (SPH) to simulate evacuation of pedestrian. A distribution of potential that corresponds to the shortest path between arbitrary two points is determined by the FDM-based fast marching method. Using the potential distribution a partial differential equation model of pedestrian flow is solved by the SPH. We conduct simulations to discuss qualitative validity of our proposed method.

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  • Kumpei TSUJI, Mitsuteru ASAI, Yasuhiko KONISHI, Shuichi OOMINE
    2019 Volume 75 Issue 2 Pages I_203-I_213
    Published: 2019
    Released: February 06, 2020
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    Recently, the ground collapse caused by deterioration of sewer pipes, which is constructed during the period of high economic growth, has occurred frequently. In this study, 3-dimensional numerical analysis is conducted to understand the mechanism of ground collapse. As an analysis method, we developed a fluidsoil multi-phase flow analysis method based on particle method that can follow large deformation and discontinuous motion. By introducing the liquid bridging force, which has been studied in the field of powder engineering, the apparent cohesion due to water content was taken into consideration and improvements were made to adapt to unsaturated ground. We succeeded in reproducing the qualitative collapse phenomenon by the analysis of the depression phenomenon using this method.

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  • Yuki YAMAKURI, Shun-ichi KOBAYASHI, Jun SAITO, Tatsunori MATSUMOTO
    2019 Volume 75 Issue 2 Pages I_215-I_224
    Published: 2019
    Released: February 06, 2020
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    A rigid plastic finite element method is a numerical tool based on the limit theorem to solve directly the failure mode and its ultimate capacity, such as bearing capacity of shallow foundations. To model a soil-reinforcement effect by linear reinforcement members, the introduction of a constant length condition between two nodes can be found in the literature. In this article, the authors re-investigate this constant length condition and extend it for more general cases. Based on Lagrangian duality theory, a Lagrangian multiplier for this constant length condition can be interpreted as a constraint force between the two nodes. The authors introduce an additional inequality constraint on this Lagrangian multiplier in a hybrid formulation of a rigid plastic finite element method to express finite and anisotropic strength properties of linear reinforcement members. Some numerical examples are presented to demonstrate the ability of the proposed method.

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  • Kiyomichi YAMAGUCHI, Kazuto YAMAMURA, Norio TAKEUCHI, Kenjiro TERADA
    2019 Volume 75 Issue 2 Pages I_225-I_236
    Published: 2019
    Released: February 06, 2020
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    In this paper, we developed a method using HPM to the multi stage failure simulation (MSFS) of framed structures. The algorithm of static elasto-plastic large displacement analysis by an implicit method was applied to the analysis until the structure forms mechanism. The failure mechanism was detected using the degree of indeterminacy, the degree of instability, the maximum displacement and the loaddisplacement relationship. The algorithm of dynamic motion analysis by a quasi implicit method was applied to post-collapse analysis because the mechanism is formed. The beam elements were computed by dynamic explicit method, and the pin elements without mass were corrected the position by a static implicit method. In the case of contact with the boundary, the algorithm of contact correction was applied not to cause penetration into the boundary surface like the augmented Lagrangian method. In MSFS method using HPM, discretization method with the same numerical model and the same rigid body degree of freedom before and after collapse can be applied consistently. Finally, we verified the characteristic features of this seamless analysis by HPM with simple numerical examples.

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  • Koji NISHIGUCHI, Tokimasa SHIMADA, Masafumi OTAKA, Shigenobu OKAZAWA, ...
    2019 Volume 75 Issue 2 Pages I_237-I_248
    Published: 2019
    Released: February 06, 2020
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    We propose a finite volume formulation for compressible solid using marker particles on the Eulerian mesh based on the building-cube method, which can generate computational meshes automatically and quickly for complex geometries. Velocity boundary conditions at solid interfaces are imposed using marker particles that interpolate velocity to the Eulerian mesh. The validity of the proposed method is verified by tensile and shear analysis of a circular plate with holes. We also clarify the spatial mesh resolution, the spatial density of marker particles, and the compute cost to obtain a certain computational accuracy. We demonstrate that the proposed method can compute a car body stiffness analysis in 3.6 hours, which is much shorter than turnaround time by the conventional finite element method.

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  • Takehiro FUJII, Mitsuteru ASAI, Satoru USHIJIMA, Daisuke TORIU
    2019 Volume 75 Issue 2 Pages I_249-I_258
    Published: 2019
    Released: February 06, 2020
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    The mechanisms of the seawall destruction have been studied and the following three causes have been investigated in general; 1) horizontal force due to the water level difference, 2) soil scour and erosion behind the seawall during overflow, 3) seepage failure associated with the reduction of the bearing capacity. Whereas, the collapse predictions by complex destruction factors have not ever been realized.

    Hence, to predict various destruction due to interaction between water and soil, a multiphase flow simulator utilizing the Incompressible Smoothed Particle Hydrodynamics method (ISPH method) for water and Discrete Element method (DEM) for soil is developed in our research group. In this research, we simulated scouring phenomena due to vertical jet experiment for a validation test. In our SPH model, a turbulence model is adopted, and the velocity in the vicinity of the gravel DEM particles may decrease because of the eddy viscosity effect of the turbulent model. Then, we propose a modification to take into account the influence of unresolved turbulent flow. The modified drag force model shows a better performance to represent the gravel movement during this vertical jet simulation. Consequently, the result in this research indicate possibility that the gravel movement force needs to be supplemented energy.

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  • Keita IMAI, Toru YOSHIMACHI, Kazuo KASHIYAMA
    2019 Volume 75 Issue 2 Pages I_259-I_267
    Published: 2019
    Released: February 06, 2020
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    This paper presents an acoustic simulation method considering the absorption effect of soundproof wall and its auralization using VR Technology. The CIP method using adaptive mesh refinements is employed for the descretization of wave equation, and impulse response analysis which can reproduce various noise problems is adopted, The Rayleigh model is employed for a sound absorption model. The time-variant convolution is employed to treat moving sound sources such as traffic noise, In order to show the validity and efficiency, the present method is applied to several application examples. The present method is shown to be a useful tool for noise evaluation system.

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  • Hiroki TANAKA, Daisuke TORIU, Satoru USHIJIMA
    2019 Volume 75 Issue 2 Pages I_269-I_276
    Published: 2019
    Released: February 06, 2020
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    The effects of time increments ∆t and mesh or cell sizes ∆xi are investigated in the computation methods to predict directly the fluid flows among many solid particles, such as some immersed boundary methods and phase-averaged models, in which no empirical formulations, like a permeability k, are needed. First it was pointed out that the fluid-solid interactive term included in the general form of the momentum equation is possibly affected by the time increments ∆t. Then, from the numerical investigations for the flows among solid particles, it was suggested that the reasonable results can be obtained when the diffusion number (νt/∆x2i ) is less than 6.0 × 10−3 and the cell-size resolution against void volume Rs is larger than 5,000.

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  • Miho ARAKI, Tetuya KAWAMURA
    2019 Volume 75 Issue 2 Pages I_277-I_288
    Published: 2019
    Released: February 06, 2020
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    In this study, we analyze the flows around two S-shaped turbines that rotate inversely by numerical simulation. In general, when investigating the flow around a rotating object, a rotational coordinate system is often used. However, it is difficult to calculate with such coordinate system when two objects rotate in the reverse direction. Therefore, we use the overset grid that consists of two rotational coordinates for each turbine immersed in a steady coordinate to calculate this turbines’ system. In this study, two-dimensional and three-dimensional simulation is performed by changing the distance between two turbines rotating inversely and flow directions, and the influence of interaction is investigated. Moreover, it is found that the end-plates that are attached both sides of the blades play an important role to keep high performance of the tubrine.

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  • Satoru USHIJIMA, Daisuke TORIU, Hirohumi YANAGI, Hiroki TANAKA
    2019 Volume 75 Issue 2 Pages I_289-I_300
    Published: 2019
    Released: February 06, 2020
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    Hydraulic experiments and numerical predictions were conducted for the unsteady process of local scour on the gravel bed, in which the average diameter of gravel particles is about 7 mm, caused by an impinging vertical water jet. The average velocity of the vertical jet was about 1.2 m/s and the flow was stopped at t = 3.18 [s]. In the computations, the fluid-solid interactions are taken into account in a similar way to the so-called an immersed domain method. This method was introduced into our parallel computational method in which governing equations are discretized with a finite volume method in the three-dimensional collocated grid system. The parallel computations were conducted for the local scour with 16,700 gravel particle models with 1,088 processes. The unsteady process of the local scour is categorized into three stages, (A) unsteady-scouring stage, (B) saltation-collapse equilibrium, and (C) stationary state with angle of repose. It was confirmed that the calculated gravel-bed shapes in all three stages are in good agreement with the experimental results. In particular, it was shown that the numbers of rising saltation particles and falling collapsed ones are approximately equivalent and that as a result almost uniform scoured surfaces are maintained during the saltation-collapse equilibrium. In addition, the total traveling lengths of the gravel particles were tracked in a Lagrangian way with the computational results. The distributions of fluid pressure were obtained in the computations and the pore water pressure near the scoured area is estimated higher than the initial hydrostatic pressure.

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  • Hideki SETOUCHI
    2019 Volume 75 Issue 2 Pages I_301-I_311
    Published: 2019
    Released: February 06, 2020
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    The elastoplastic model for soils introduced the power rule of logarithm void gradient into the hardening law of Cam-clay model instead of the compression index is presented. The model would contribute to the improvement of prediction accuracy of the elastoplastic model with the compression index as the hardening law, because the power rule of logarithm void gradient accurately and reasonably predicts the compressibility for soils over a wide range in stress. Furthermore, the soils with any void ratio deviated from the steady state (critical state) for shear are described in the novel logarithm void strain relative to that of the steady state and then the proper evolution law is introduced. The model is capable of describing the dilatancy to translate any void ratio with shear into that of the steady state.

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  • Kazuya HASHIGUCHI, Ryota AIDA, Mao KURUMATANI, Shinichiro OKAZAKI
    2019 Volume 75 Issue 2 Pages I_313-I_321
    Published: 2019
    Released: February 06, 2020
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    This paper develops a three-dimensional digital image correlation (3D-DIC) measurement system for measuring 3D deformation and crack propagation in concrete, and verifies the accuracy and availability. Stereo matching is incorporated with the system to measure out-of-plane displacements. High resolutional digital cameras are used to realize the high accurete measurements. The principle of 3D-DIC measurement based on stereo matching is first explained. The measuring accuracy of the system is then verified for the 3D shape and displacement of concrete’s test specimens. Finally, 3D crack propagation behavior of concrete’s cylinder specimen is measured and visualized to demonstrate the availability of the 3D-DIC system.

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  • Kazuhiro KANEDA, Masamichi AOKI
    2019 Volume 75 Issue 2 Pages I_323-I_328
    Published: 2019
    Released: February 06, 2020
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    The formula to calculate the ultimate vertical bearing capacity is specified in the guidelines by the Architectural Institute of Japan for the design of building foundation. With wider footing, the ultimate bearing capacity becomes smaller than that obtained by Terzaghi’s formula for sandy grounds caused by the decline of the inertial friction angle or progressive failure. Furthermore, the ultimate bearing capacity of embedded and inclined load have not been clarified. In this study, rigid plastic finite element method is employed to discuss the ultimate bearing capacity of large foundation against inclined and embedded loads.

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  • Yukihiro MORIKAWA, Kentaro NAKAI, Kazuki NAKATANI, Yusuke TAKEDA, Keni ...
    2019 Volume 75 Issue 2 Pages I_329-I_339
    Published: 2019
    Released: February 06, 2020
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    Earthquake resistance of important structure have benn promoted based on the lessons learned from the big Earthquake in Japan. However, liquefaction still causes serious damages to many detached houses in the world. Also, most soil improvement methods apply to original ground without structure, and countermeasure against liquefaction for existing small structure has not been sufficiently investigated. Therefore, we investigated reduction effects of liquefaction damage using small grid-type improvement as countermeasure against liquefaction for existing small structure. To this end, 2D model tests under 1g condition and non-linear FEM analyses have been carried out. From the model tests results, it was found that if the interval of improved wall is within 1.2 times of the base width, some degree of counter measure effect agaisnrt subsidence due to liquefaction can be obtained with a small grid-type improvement where the improvement depth is about twice the base width. The numerical simulation has shown a similar result as found in the observations.

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  • Ahmed ElSAYED, Huang HUANG, Zhishen WU
    2019 Volume 75 Issue 2 Pages I_341-I_350
    Published: 2019
    Released: February 06, 2020
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    Majority failure of ductile behavior of the tested flexural bridge columns was buckling of longitudinal bars, which occurred after yielding of the perimeter ties. Increasing the transverse reinforcement specified in design codes for bridge columns in plastic hinge zone to confine and prevent premature buckling of longitudinal bars for column deformation ductility has a limit due to yielding of reinforcement steel ties. Types of fiber-reinforced polymer (FRP) have the strength and yield (rupture) strain higher than steel-reinforcement leads to enhance the confinement. Recently, using FRP ties has been spread especially in the destructive environment to enhance the deformation ductility. This paper presents a numerical investigation model to predicate the behavior of square bridge column confined using a combination of steel and rectangular closed FRP ties in the plastic hinge zone subjected to reversed lateral cyclic load. Results showed enhancement of columns’ deformation ductility and indicated that closed FRP ties provide effective confinement resulting in delay bars’ buckling and increasing the drift ratio more than 16.6%.

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  • Daiki HIZEN, Katsutoshi UENO, Ryosuke UZUOKA
    2019 Volume 75 Issue 2 Pages I_351-I_359
    Published: 2019
    Released: February 06, 2020
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    Verification and validation procedures were applied for numerical analysis of clay ground consolidation. The numerical analysis is a soil-water coupled analysis on finite deformation porous media theory.

    At the verification stage, the code and calculation verification was conducted based on an analytical solution and the concept of order of accuracy. The accuracy and convergence of numerical method were verified.

    At the validation stage, first some elasto-plastic material parameters were assumed as normal distributions from laboratory tests. Second the numerical analyses simulated centrifuge tests of clay ground consolidation using the probabilistic material parameters. By comparing the probability distributions of experimental and numerical results, the uncertainty in the clay ground deformation and validity of numerical method were discussed. The distribution of numerical results overestimated that of experimental results.

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  • Yoshiharu KOMATSU, Toshiyuki HORIGUCHI, Satoshi KATSUKI
    2019 Volume 75 Issue 2 Pages I_361-I_370
    Published: 2019
    Released: February 06, 2020
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    In recent years, accidents in which the steel pipe open sabo dam had a severe damage events occurred by an unexpected level debris flow. In Japan, a new design concept i.e., two level design, have been discussed in these day. In the design concept, the second level design will be associated with combination of a debris flow load of a few frequent occurrence probability and an elasto-plastic limit state. If the new design is adopted, some existing structures will not necessarily satisfy a criteria of a second level design. This paper proposes a reinforcement method setting reinforce members between at the top of an open sabo dam and a neighboring concrete dam as reinforcing members. The reinforcement effect is evaluated by an elasto-plastic analysis.

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  • Masanori TSUYAMA, Kazunari SAKO, Shinichi ITO, Ryosuke KITAMURA
    2019 Volume 75 Issue 2 Pages I_371-I_378
    Published: 2019
    Released: February 06, 2020
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    In this study, the pore-water pressure in unsaturated soil used in slope stability analysis are disucussed. A seepage force in unsaturated soil and A body force by a difference of pressure heads in unsaturated soil are proposed. Then these forces are employed in the infinite slope stability analysises expressed by the body force method or the water pressure method, and the calculation results are discussed. As the results, the safety factors derived from the equations considered unsaturated seepage behavior showed lower values than the traditional slope stability analysis. Moreover, the effect of the area acted pore-water pressure in unsaturated soil on the slope stability analysis was discussed. It was found that the difference between the body force method and the water pressure method was coused by the area acted pore-water pressure in unsaturated soil when the pore-water pressure in unsaturated soil was considered in the Limit Equilibrium Method.

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  • Takahiro YOSHIKAWA, Toshihiro NODA, Takeshi KODAKA, Ying CUI
    2019 Volume 75 Issue 2 Pages I_379-I_388
    Published: 2019
    Released: February 06, 2020
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    Due to heavy rain in northern Kyushu in July 2012, failure of the Yabe River levee occurred, caused by local piping in highly permeable foundation ground, and it was a great shock when river engineers and researchers realized that levees can collapse without overflow. Regarding the Koyoshi River levee slope slip and the Kakehashi River levee slope failure that occurred in July 2013, it is also considered that the damage was the result of highly permeable foundation ground. In this paper, to clarify the seepage failure mechanism of river levee with highly permeable foundation ground, numerical simulations of model tests were conducted using a soil-water-air coupled finite deformation analysis code. As a result, the simulation was able to reproduce the difference between the case when the seepage failure occurred and the case when the seepage failure did not occur in the experiment. In addition, using this analysis code, case studies were conducted and the influence of introducing suction effect to elastoplastic constitutive model on seepage failure behavior was also discussed.

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  • Kazushige MATSUO, Kenichi MAEDA, Kosuke HORI, Kentaro SUZUKI, Hisashi ...
    2019 Volume 75 Issue 2 Pages I_389-I_400
    Published: 2019
    Released: February 06, 2020
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    This study researches rock fall trapping performance of a rock-fall protective soil embankment protection method. A rock-fall protective soil embankment protection method is excellent in economy, workability, and maintainability. It can use soil generated on site if there is installation space. The current design manual, Rock Fall Countermeasures Manual, however, only describes the concept of rockfall energy absorption and dispersion mechanisms when designing a rock-fall protective soil embankment. The manual does not consider deformation and fracture modes when evaluating performance. To understand rock fall trapping performance of a rock-fall protective soil embankment, this study performed an experiment to confirm the behavior of a 500 mm height soil embankment model. The study also performed analysis to reproduce the experiment using the two-dimensional discrete element method (2D-DEM).

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  • Kentaro NAKAI, Toshihiro NODA, Takuya OHBA
    2019 Volume 75 Issue 2 Pages I_401-I_410
    Published: 2019
    Released: February 06, 2020
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    In the 2011 off the Pacific Coast of Tohoku Earthquake, the liquefaction damage in the residential area of Urayasu City was huge, and many detached houses suffered uneven settlement. In Japan, however, there has not been sufficient knowledge about liquefaction-induced damage of detached houses. Therefore, in this study, with regard to the liquefaction damage form of the detached houses constructed on the liquefiable ground, the following points were clarified focusing on the influence of the neighboring houses using soil-water coupled finite deformation analysis. 1) In the case of single structure evaluation, even if stability is maintained without tilting, tilting damage may occur when considering neighboring houses. 2) The direction of inclination of neighboring houses can be explained by using the computed direction of post-seismic displacement vector in the case of one house alone.

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  • Mao KURUMATANI, Shinichiro OKAZAKI, Yoshihito YAMAMOTO, Naoshi UEDA, H ...
    2019 Volume 75 Issue 2 Pages I_411-I_420
    Published: 2019
    Released: February 06, 2020
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    Four-point bend tests of reinforced concrete (RC) beams were performed at approximately the same time in five institutions equipped with different test machines, for investigating the uncertainty involved in experiments. The RC beams were produced simultaneously at one location to reduce the variation of materials and specimens. The influence of the difference in boundary conditions on the experimental results were examined. The reproducibility of the test results by numerical simulation was also discussed from the view point of the V&V (Verification and Validation), especially the Validation for computational model. This study may provide experimental data available for the Validation of computational model, and offer valuable insight into the V&V for concrete structure.

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  • Shinnosuke KATAOKA, Masuhiro BEPPU, Hiroyoshi ICHINO
    2019 Volume 75 Issue 2 Pages I_421-I_432
    Published: 2019
    Released: February 06, 2020
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    In recent years, crucial damages to humans and structures caused by the impact due to natural disasters such as tornadoes and volcanic eruptions have occured, and the establishment of a protective design method is urgent. Although many studies have been conducted on the local failure of RC members subjected to a projectile impact, the failure mechanism of RC members was not sufficiently investigated. This study presents an investigation of the local failure mechanism of RC slabs subjected to a projectile impact. In order to investigate the impact response of RC slabs, numerical simulations were conducted. The sectional force of the RC slabs was calculated from the numerical simulation results, and the inertial force and shear force generated in the RC slabs were discussed. It was found that the impact load was balanced with the inertia force before the reaction force was generated, and the diagonal crack progressed according to the shear force generated in the cross section. It was also found that the local failure could be evaluated by comparing the shear force generated in the cross section and the improved capacity of punching shear failure.

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  • Naoto NAITO, Osamu NUNOKAWA, Kenichi MAEDA
    2019 Volume 75 Issue 2 Pages I_433-I_444
    Published: 2019
    Released: February 06, 2020
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    Slope failures may occur under unsaturated conditions before the surface soil reaches saturation due to rainfall. Countermeasures may be installed at the slope toe to prevent the sediment from flowing into the road or railway. In order to select an economic countermeasure, it is necessary to clarify the mechanism of flow down and the generation mechanism of impact force of unsaturated soil. This study aims to elucidate these mechanism not only by experiment but also by numerical simulation.

    In this paper, the applicability of the DEM simulation which introduced the simple cohesion model considering the effect of cohesion to the slope flow and collision behavior of unsaturated soil was examined. As a result, it was shown that the relationship between the condition of the collapsed soil and the maximum impact force obtained by the impact experiment can be roughly reproduced by proposed DEM model. In addition, numerical experiments were conducted on the assumption of full scale, and it was shown that the collapsed soil deposited on the wall may play a role as a shock absorber for the continuing impact of the collapsed soil.

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  • Seiichiro TSUTSUMI, Hirokazu NAGAHAMA, Riccardo FINCATO
    2019 Volume 75 Issue 2 Pages I_445-I_453
    Published: 2019
    Released: February 06, 2020
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    Fatigue damage process is generally divided into two stages, fatigue crack initiation and propagation. Stress intensity factor or J-integral are usually used for driving force of fatigue crack propagation. Various assessment methods for fatigue crack initiation life have been proposed, and the authors have recently proposed an assessment method for fatigue crack initiation life utilizing elasto-plasticity FEM analysis adopting the material model which can describe cyclic hardening or softening. If it is possible to assess the fatigue crack initiation and subsequent propagation which strongly depend on elasto-plastic response of material under the same numerical analysis framework, it is useful to understand the detailed mechanism of fatigue damage process. The purpose of present study is to propose a method which can evaluate the fatigue crack propagation behavior by extending the assessment method for fatigue crack initiation life, and consider the accuracy of its evaluation.

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  • Hirohito KOYAMA, Kenichi MAEDA, Kaiga YASUE, Yuma SUZUKI
    2019 Volume 75 Issue 2 Pages I_455-I_466
    Published: 2019
    Released: February 06, 2020
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    Understanding the soil-water-structure interaction mechanism is important to control foundation skirt suction settling. Therefore, we used model testing to observe foundation subsidence due to upward seepage. Then we compared it with the ultimate bearing capacity formula and numerical analysis, such as 3D seepage analysis and smoothed particle hydrodynamics (SPH). Although the start of subsidence was controlled by the ultimate bearing capacity formula and the amount of subsidence was quantified by hydraulic gradient management, localized phenomena—such as sand boil and piping by seepage—made control difficult. Subsidence timing of the model test was reproduced through numerical analysis, and important knowledge was obtained for actual foundation penetration control.

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  • Seiichiro TSUTSUMI, Homare SHIBATA, Riccardo FINCATO
    2019 Volume 75 Issue 2 Pages I_467-I_476
    Published: 2019
    Released: February 06, 2020
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    In recent years, fatigue has become a major problem in infrastructures, and many failure cases have been reported. Above all, the cracks initiated from weld joint root are difficult to detect visually from the surface of the weld bead, so it is important to clarify the factors governing the fatigue performance and to make an evaluation method with high accuracy. In this study, we investigated the various factors that affect fatigue damage starting from the weld joint root by numerical analysis. In particular, the local behavior of the root was analyzed by nonlinear FEM analysis and X-FEM analysis based on linear fracture mechanics, and crack intiation life and propagation life were discussed. As a result, it was found that the fatigue crack propagation process dominates the fatigue damage of the weld root where the stress concentration factor is high, and the influence by the local material property and the root gap is small. On the other hand, the effect of angular distortion correction on the fatigue life is large, and the result that the fatigue life extension effect is suggested by the additional process of introducing compressive stress at the weld root was obtained.

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  • Norihiko SUGIMOTO, Mirai ABE, Yukako KIKUCHI, Asako HOSONO, Hiroki AND ...
    2019 Volume 75 Issue 2 Pages I_477-I_486
    Published: 2019
    Released: February 06, 2020
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    We have developed the Venus AFES (atmospheric GCM (general circulation model) for the Earth Simulator) LETKF (local ensemble transform Kalman filter) data assimilation system (VALEDAS) to make full use of observations. In this study, radio occultation measurements among small satellites are evaluated by the observing system simulation experiment (OSSE) of VALEDAS. Idealized observations are prepared by a French Venus Atmospheric GCM in which the cold collar is realistically reproduced. Reproducibility of the cold collar in VALEDAS is tested by several types of observations. The results show that the cold collar is successfully reproduced by assimilating at least 2 or 3 vertical temperature profiles in the polar region every 4 or 6 hours. Therefore, the radio occultation measurements among three satellites in polar orbits would be promising to improve the polar atmospheric structures at about 40–90 km altitudes.

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  • Obaidullah SAFIE, Akihiro TOMINAGA
    2019 Volume 75 Issue 2 Pages I_487-I_498
    Published: 2019
    Released: February 06, 2020
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    Many pile-group dikes have been built along the banks of the Kiso River in Japan for several decades to control the riverbank erosion. However, flow and bed characteristics around pile-group dikes are not treated sufficiently, and no detailed explanation has been found in the literature. This study investigates the effects of different pile-group dikes on the flow and sediment deposition. Different numbers of piles per group, which was defined as pile density, with two types of pile arrangement, namely in-line and staggered arrays were compared. The results indicate that the pile-group dikes can reduce the velocity and enhance sand deposition in the downstream along the bank. Consequently, both can increase riverbank stability. A staggered case had a lower velocity and higher deposition along the bank than an in-line case with the same pile density. Furthermore, the staggered type significantly reduced the turbulence in the downstream. From an economic point of view, a lower pile density in staggered arrays can perform like a higher pile density in an in-line arrangement.

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  • Takafumi KAMEI, Takahiro AYUKAI, Tetsuya KANAGAWA
    2019 Volume 75 Issue 2 Pages I_499-I_508
    Published: 2019
    Released: February 06, 2020
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    This study theoretically clarifies the effect of the liquid viscosity and the thermal conductivity on weakly nonlinear propagation of pressure waves in liquids containing many spherical microbubbles. By the use of the method of multiple scales, a KdV–Burgers equation describing the long-range propagation of a low frequency long wave is derived from the basic equations incorporating the liquid viscosity and the thermal conductivity. As a result, the liquid viscosity and the thermal conductivity affect the dissipation effect. A thermodynamical process of the gas inside bubbles also affects the nonlinear, dissipation, and dispersion effects. From numerical solution of the KdV–Burgers equation, the wave properties appear in the order of the nonlinear and dispersion effects. Comparing the result with the previous study (Kanagawa et al., Trans of the JSME, Ser. B, 76, 1802, 2010) ignoring the liquid viscosity and the thermal conductivity, strong dissipation and dispersion effects appear.

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  • Yoshiki SAKURAI, Hiroki SHIRAISHI, Takashi ISHIHARA
    2019 Volume 75 Issue 2 Pages I_509-I_518
    Published: 2019
    Released: February 06, 2020
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    Self-similar clustering of inertial particles in homogeneous isotropic turbulence has been suggested both by numerically and theoretically. The self-similar clustering may be explained by the co-existing self-similar multi-scale coherent eddies in the turbulence. However, such self-similar relationship between particle clustering and multi-scale eddies has not been directly extracted yet. In this paper, we analyze the data from direct numerical simulation of incompressible homogeneous turbulence, by sampling high vorticity regions in coarse-grained fields and by taking their average using the frame of eigenvectors of the coarse-grained rate-of-strain tensor. The results show that the high vorticity regions make a low particle density region whose size and shape depend on the coarse-grained level and the particle inertia. By tracking the motion of the inertial particles in the averaged velocity field, we find that the particles orbit an elliptical region whose size depends on the coarse-grained level and the particle inertia.

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