The necessity to understand and predict flows that carry large suspended sediment and wash loads has become acute in the Shirakawa River Basin where significant erosion and siltation associated with hyperconcentrated flood give rise to many river problems. Mud flows, debris flows or slurries, made up of a large amount of clay and/or silt particles suspended in water, often show non-Newtonian properties but remain poorly understood concerning the impacts of their rheological properties on fully developed turbulent structure.
In this paper, we experimentally investigated resistance and energy budget of hyper-concentrated sediment laden-flow in an open channel with two-dimensional square ribs by using Particle Image Velocimetry(PIV). The results showed that rheological properties significantly diminished energy transfer between mean flow andturbulence by flow fluctuations in cases where the volumetric sediment concentration CV is lower than 8.5%and augmented distinctly the dissipation of mean flow energy by viscosity when CVis higher than 8.5%. incomparison with the clear water flow.

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The scarce knowledge of bedrock channel morphology has limited our understanding of landscape formation. Bedrock channel's morphology is controlled by various factors like sediment properties, climatic conditions, rock strength and local topography. In this study, laboratory scale experiments were conducted to understand the relationship between sediment feed rate and lateral erosion. We also implemented a numerical model and tested it for reproducing the experiments. The numerical model assumes that lateral erosion depends on an abrasion coefficient and transverse bedload transport rate per unit width. The numerical model could successfully trace lateral erosion in bedrock channels. Simulations were also performed to understand the effect of change in sediment supply on banks of bedrock channels. It can be seen from simulation results that sediment supply can be one of the dominating factors in determining the width of bedrock channels.

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Sea spray is one of the important factors to affect weather conditions over the ocean in terms of constituting an aerosol as well as determining air-sea transport of heat, moisture and momentum. The final goal of this study is to explain the relationship between sea-spray generation and conditions of the atmosphere and ocean for a more accurate prediction of the amount of sea spray. This study conducted three-year field observations of atmospheric aerosol at an offshore observatory in Tanabe Bay, Wakayama. Large-scale (> 100 km) distribution of atmospheric aerosol was found to dominate the concentration of the observed aerosol less than 1 μm in normal weather conditions. During storm events with strong winds from the Pacific Ocean, however, the observed concentration monotonically increased with the wind speed, which is considered to be a result of the increase in oceanic aerosol derived from sea spray.

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In this paper, a process of forming the transverse ribs in the mountainous rivers are focused on. It is difficult to conduct some experiments that mountainous bed structures form, such as step-pool and transverse ribs. On the condition that bed slope is steep, water and sediment flow is too fast to measure sediment movement and to grasp sediment discharge. Therefore, there are a few papers treating flume experiments with sediment supply. That is why we tried to conduct series of experiments that anti-dune and transverse ribs form in the condition that bed composed of sand and cobbles and also the condition that sediment supplied from the upstream of channnel. As results of experiments, we found characteristics of sand and cobbles movement through anti-dune on each conditions of composed ratio of cobbles.

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In the 2011 off the pacific coast of Tohoku Earthquake, coastal near cities are catastrophic damaged by Tsunami. The Tsunami sweeps away houses, ships and a lot of cars during runs up on land. The driftage car caused destruction of the structures and fire. In addition, the supply transportation network was interrupted to block a road by drifted cars. As a reason, the complex disaster is necessary to predict by using inundation and drifting simulation. In this research, it is developed that the numerical simulation model for predicting the driftage behavior during flood. And, the numerical simulation model is discussed to compare with hydraulic experiment.

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Dynamics of river bedforms which is an interfacial instability phenomenon between turbulent open channel flow and movable bed significantly affect the flow structures and sediment transport dynamics in rivers, so that this have been an classical and important research topic in the field of river engineering. Here, we perform a linear stability analysis for several combinations of flow and sediment transport submodels, specifically, a shallow flow model and a Boussinesq type depth-integrate model for hydrodynamic model, and an equilibrium and a non-equilibrium bedload transport model for sediment mass conservation model. We then investigate how the submodels adopted determine the linear stability and the wavelength of river bedforms. The results show that the combination of the Boussinesq model and the non-equilibrium bedload transport model can explain the antidune instability and its finite wavelength observed in several published experiments, whereas, use of each submodel alone is insufficient to explain the finite wavelength of antidunes.

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It is a study for practical use of wave power generation device, which is one of the marine renewable energy. In order to full-scale wave power generation business, it is necessary to proper environmental impact assessment. Although environmental assessment can be evaluated by predicting the wave changes around the device area, in the existing model is not appropriate for the evaluation of the actual sea since it is assumed that the conditions of regular waves. Therefore, we have that to build a predictive model of wave changes in irregular waves you intended to accurately assess the environmental impact necessary in this study as the main goal. In this paper, the loss such as eddy and air bubbles that incident wave under the device by hydraulic experiment occurs when it passes through the extent to which effect has been compiled to investigate whether or not there with respect to the incident wave energy using a two-dimensional wave-making water tank. We have focused on the power generation unit of violent wave conditions can be placed on the high offshore resistant to a floating oscillating water column (OWC) type by the typhoon passes.

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The Tsugaru Strait lying between Hokkaido and Honshu islands of Japan is one of the most powerful site for tidal and ocean energy. Field observations on the velocity field of this site revailed significant increase in the velocity flutuation may occur in summer and autumn. This study conducted a numerical experiment on the effects of the density stratification on the velocity field in the strait. Density stratification was found to strengthen and elongate a wind-driven flow, resulting in significant velocity disturbance near the surface.

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A heavy rainfall attacked the Otofuke river in 2011. Bank levee was eroded at that time, even though the water level at the flood was not reached a height of flood plain. It was assumed that the main factor of this erosion was the deflection of flow due to bar development. Hydraulic experiments were conducted in this paper for clarifying the influence of bar development to the bank erosion. It was found that bar migration speed and development situation of bars influenced bank erosion strongly and bank erosion affected to the form of sandbars.

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In this study, we simulated river flows and morphological changes on a sharp meandering channel, which consists of sand topography, to evaluate the secondary flow effects, the development of point-bar and braided channel with the vegetation effect using a two-dimensional numerical model, iRIC software. In the simulation results, meandering channel with vegetation showed diverse river bed deformations, such as braided channel, sub-meandering channel, mid-channel bars, and a point-bar. In particular, vegetation area is changed by flood events, and then vegetation changes the flow characteristics and river environment.

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In order to investigate features of residual stress distribution generated by patch welding and influences of joint dimeisnions and restraint conditions on the residual stress, a series of experiment and analysis was carried out. The controlled thermal severity weld cracking test specified by JIS could be simulated by the thermal elastic plastic analysis. It was shown that the base plate length did not affect the residual stress at the weld toe. However, the width and thickness of base plate largely affected the residual stress at the weld toe. When the shrinkage of base plate was resitained, the residual stress at the weld toe became higher than that without resitraint. A measure of the degree of restraint for patch welding was proposed based on a simple elastic analysis. It was confirmed that the residual stress might be estimated by the proposed measure.

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The deterioration of bridge should be adequately evaluated to use it safely and to develop an appropriate maintenance strategy. Therefore, the present research proposed a method to quantify damage severity and existence of cracks by use of multipoint acceleration measurement and random forest which is one of the supervised machine learning method. Lots of previous research only used natural frequencies to detect damages, but the accuracy is not necessarily enough. This research therefore increases the amount of information including the maximum and standard deviation of accerelation and logarithmic decrement. Finally, the accuracy of the developed method is verified by leave-one-out cross validation and the vibration test results of actual damaged specimens.

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Plate bonding method is one of the new tentative repair methods for fatigue cracks. So far, the extended fatigue life of crack covered with patch plates is evaluated by using Stress Intensity Factor. However, crack propagation just after bonding patch plates cannot be evaluated by the previous crack propagation analysis based on Stress Intensity Factor. In this study, the main reason of this is assumed that the residual stress before bonding patch plates is not considered in the previous analysis, the crack propagation analysis considering the effect of the residual stress before bonding patch plates was conducted. As the results of the proposed crack propagation analysis, it was clarified that in the specimen cured under unloading condition, early crack growth ratio after bonding patch plates could be evaluated by the proposed analysis. On the other hand, in the specimen cured under cyclic loading condition, since it is difficult to estimate the residual stress before bonding patch plates, early crack growth ratio after bonding patch plates could be estimated a little larger by the previous analysis.

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In recent years, the occurrence case of fatigue crack has been an increase steel piers and steel deck, etc. in the road bridge. Depending on the site of the fatigue crack occurs, the crack is progress, cause brittle fracture. As a result, fatigue cracks will be a significant impact on the safety of the bridge. Therefore, finding them early, it is important to perform appropriate repair. This study is intended to develop a measurement method for detecting fatigue cracks. In this measurement method, first, by heating the steel members to open and close the cracks, and distortion difference before and after heating is measured using a digital image correlation method. This measurement method is a new detection method of crack defects of the steel member that does not require removal of the coating.

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As a new repair method for steel members with corrosion attack and fatigue damages, bonding patch plates have been proposed and used. One of the concerns of this method is prevention of delamination of patch plates, because the adhemsive stresses concentrate at the end of patch plates. In general, the tensile test of single lap joint is applied for quality control of adhensives. However, the tensile shear strength given by the tensile tests of single lap joint is not available for the evaluation of the prevention of delamination of patch plates. Therefore, in this study, the adhensive stresses in single lap joint under tensile or bending load are theoretically given. Furthermore, it was shown that the energy release rate, which often applied for the design of delamination of patch plates, can be calculated by using adhensive stresses at the end of patch plate given by the theory.

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In the seismic design specified in JSHB, the PC girder bridge with the abutment is recommended to have a sufficient expansion joint gap to avoid the collision behavior between girder-end and parapet against level 2 earthquake motion. However, ensuring the large gap size at the expansion joint is uneconomical design to increase cost of construction and seismic reinforcement. This paper presents the result of seismic response analysis with 3D-FEM considering the pounding effect. As a result, it was recognized that the damage of the abutment and the pier at the pounding were clarified. Furthermore, a hybrid reduction methods of seismic response by the isolated pier with seismic isolation rubber were discussed.

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A numerical method based on the foundamental mechanism of fault slip is essential for a reliable estimation of surface fault displacement. A rigorous joint element and a time integration method for energy conservation are required for the numerical method. In this paper, a rigorous formulation of joint element for three-dimensional FEM is derived from the variation of Lagrangian on a fault plane. Symplectic time integration is applied for energy conservation. Some numerical tests demonstrate their advantage comparing to conventional methods.

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Crack detection system is developed to rationalize nondestructive testing of fatigue crack. This system judges possibility of existence of fatigue crack beneath the paint crack without removing the paint. The judgement is based on pattern-matching of paint crack pattern and fatigue crack patterns. Paint crack profile is extracted first from the inspection photograph. Mapping transformation is applied on the profile in order to compare 2 different crack images. The original crack profile images are projected on standardized weld bead 2D expansion plan. The image is compared with pattern image of fatigue cracks in crack DB. Those images are previously obtained by same procedure as paint crack pattern image. Possibility of fatigue crack is judged by coincidence factor of pattern matching of 2 images. The performance of this image diagnosis system is accurate and high enough to apply this for preliminary judgments for ordinary NDT.

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GPS wireless sensor network, which is a displacement monitoring system using a low cost L1 GPS receiver as a sensor of wireless sensor network, has been developed by the authors. Since the cost per a single observation point can be decreased, the dense sensor deployment is applicable to the displacement monitoring under a construction site or the estimation of disaster distribution in a large earthquake.
In this research, quasi-static displacement is monitored by using the prototype system developed by the authors. The experimental results show that the accuracy is about 1 cm after applying Kalman filter to the positioning reuslts. In case of estimating a sudden displacement, integer ambiguities should be determeined as an usual GPS positioning analysis. A data mask method and a weight estimation method using SNR (Signal to Noise ratio) of raw carrier phase data are introduced to the anaylsis. A redeterminataion algorithm for fixing integer ambiguities is also developed by the authors. The Fix rate of integer ambiguities is improved by introducing these technique to the GPS positioning analysis.

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Complaints due to traffic vibration of highway bridges have a strong correlation between the vertical vibration of the superstructure of the bridge. Therefore, to determine countermeasure methods, a vehicle load analysis which considers dynamic interaction when the vehicle travels on the bridge, is used. However, this analysis method requires specialized skill and knowledge. In this study, the authors have proposed an analysis method that can be applied using a general-purpose software, by determining an external force of the frequency band which is causing complaints, using the actual measured value of the vehicle vibration. The vibration of the typical plate girder bridges with/without countermeasures has been estimated by the proposed analysis method. It was confirmed that the proposed analysis method simulates roughly and simply the bridge vibration and is feasible for practical use.

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Recently, the polarization resistance method is highly noticed as a non-destructive test method to evaluate the corrosion rate of rebar in concrete structures. The corrosion rate can be estimated from the apparent polarization resistance and the polarized area. The polarized area is often evaluated by numerical methods such as boundary element method. The material heterogeneity such as rebar corrosion or altered concrete is one of the most important affectors on the current propagation in a reinforced concrete. However, it is not well evaluated by boundary element method. Thus, in this study, finite element method is employed to evaluate the current propagation. In the results, the properties of current propagation are strongly affected by the material heterogeneity.

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Corrosive sources, such as water and chrorides, for infractrucrtures are influenced by wind direction, wind velocity, temperature, humidity, rainfall, sea waves and so on. This study discusses relations on corrosive damage on bridges between meteorological data and corrosive responses. With the multiple regression model, the seasonal tendency of corrosive responses is shown; in addition, the evaluation of t-values shows that the simultaneous effects of rainfall and wind predominantly affect to induce corrosive responess.

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Mass Spring-Soil Spring (MSSS) model has been used for seismic response analysis that accounts for soil-structure interaction. This paper seeks to interpret the basic concept of this modeling, based on the meta-modeling theory. It is shown that the MSS model is a mathematical approximation of continuum modeling, without introducing any physical assumption. The values of the mass and spring constant of MSS model is rationally determined. Numerical experiments for a set of simple structure and soil supports the validity of the interpretation of the MSSS model made by this paper.

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A previous study reported that results of operational modal analysis applied to a cable stayed bridge was drasticly changed depending on wind speed. Aiming at investigation of an effective bridge health monitoring technology, it is desired to identify the mechanism of the modal identifiability problem. This study presented a Bayesian estimation method based on frequency domain of ambient vibration data. Modal properties identified from SSI are compared to ones identifed from the Bayesian method. Coefficient of variances of modal parameters and S/N ratio of modal responces indicated uncertainty of modal estimation directry. This observation shows Bayesian estimation can be helpful approach to interpret quarity of the estimation itself.

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The article

Keita NAKAMURA and Mamoru KIKUMOTO: CHARACTERISTIC CURVE MODEL FOR WATER-NAPL-AIR THREE-PHASE SYSTEM,
Journal of JSCE, Series A2(Applied Mechanics),Vol.70, No.2, I_831-I_840, 2014.

has been retracted at the authors’ request.

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