Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)
Online ISSN : 1883-8944
Print ISSN : 1884-2399
ISSN-L : 1883-8944
Volume 68 , Issue 1
Showing 1-6 articles out of 6 articles from the selected issue
Paper (In Japanese)
  • Tadataka WATANABE, Tsunakiyo IRIBE, Eizo NAKAZA
    2012 Volume 68 Issue 1 Pages 6-16
    Published: 2012
    Released: April 20, 2012
     In the coastal engineering field, particle method is expected for three-dimensional numerical simulations on fluid-structure interaction. Although in realistic three-dimensional numerical simulation, an increase of memory utilization and a computational time are very serious problems due to resolution of distance of particles and increase of number of particles. In this research, the authors develop a hybrid (openMP/MPI) parallel simulation code of MPS method and simulate large-scale simulations for coastal engineering. The simulation of a static water problem evaluates the parallel performance of the proposed simulation code. And the simulation of a collapse of water column and the progressive wave verifies the accuracy. The result of large-scale simulation of ocean wave showed the wave concentration into cavities of structures, and generation of spray as three-dimensional hydraulic phenomenon. This study shows that we can evaluate three-dimensional hydraulic phenomenon more fully with the proposed simulation code.
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  • Seiya ITORI, Tsunakiyo IRIBE, Eizo NAKAZA
    2012 Volume 68 Issue 1 Pages 17-28
    Published: 2012
    Released: May 18, 2012
     In the coastal engineering field, the particle method called MPS method is expected to apply to simulate fluid-structure interaction problems such as wave pressure on a breakwater. However, it has been revealed that the accuracy of the particle method for hydraulic pressure is less than other numerical method, since the numerical result by the particle method usually has numerical irregular oscillations of pressure value. The authors propose improvement methods of judgment of dirichlet boundary conditions for the Poisson equation of pressure. The accuracy of the proposed method is verified for the simulation of a static water problem and the collapse of water column. In addition, the results of numerical simulation of a tank sloshing of water are compared with experimental results. The improved MPS method showed high reduction of irregular numerical oscillations of pressure. It can be expected to apply to numerical simulations of high frequency hydraulic pressure oscillations such as a shock wave pressure.
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  • Takaaki UDA, Hiroaki FUJIWARA, Shiho MIYAHARA, Toshiro SAN-NAMI, Masum ...
    2012 Volume 68 Issue 1 Pages 35-53
    Published: 2012
    Released: August 20, 2012
     Long-term shoreline changes between 1899 and 1967 under the natural conditions and between 1967 and 2010 after the various alterations along the Kaike coast extending along Yumigahama Peninsula in Tottori Prefecture were investigated on the basis of old geographical maps and aerial photographs. The changes in fluvial sand supply from the Hino River, being a major sand source to the Kaike coast, and the distribution of longshore sand transport during these periods were estimated. The bathymetric survey data obtained since 1980 when various coastal structures had been constructed was also analyzed. Given the estimated fluvial sand supply from the Hino River, long-term beach changes of the coast were reproduced using the contour-line-change model considering the change in grain size as a reduction process of the Hino River delta. Then the beach changes triggered by various artificial changes were reproduced. The measured and predicted three-dimensional beach changes were in good agreement. Furthermore, beach changes after the suspension of sand back pass which has been carried out on the Kaike coast and the exhaustion of sand supply from the Hino River were predicted using the contour-line-change model. It was concluded that sand back pass and appropriate volume of sand supply from the Hino River was important to maintain the sandy beach of the Kaike coast.
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Technical Note (In Japanese)
  • Yukinari FUKUMOTO, Hiroyuki SUKEGAWA, Nobuyuki IWAMAE, Tsuyoshi IKEYA
    2012 Volume 68 Issue 1 Pages 1-5
    Published: 2012
    Released: January 20, 2012
     The 2011 off the Pacific coast of Tohoku Earthquake, Mw9.0, occurred on the 11th March 2011. High tsunamis were observed on the Pacific coast of Japan and caused devastating damages. The temporal variation of water depth, hydraulic pressure and horizontal components of current velocity was observed by using the Ultrasonic-type wave gauge placed on th e sea bottom 11m deep and 3km offshore of Choshi city, Chiba prefecture, Japan. The following findings were made. 1) Tsunamis and the largest aftershock may occur simultaneously. 2) The amount of water depth decrease due to drawback is larger than that of water depth increase due to runup. 3) The tsunami coming after the drawback can be breaking wave.
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  • Takayuki HASHIMOTO, Kazunori ITO
    2012 Volume 68 Issue 1 Pages 29-34
    Published: 2012
    Released: May 18, 2012
     The 2011 tohoku earthquake tsunami inflicted catastrophe on Tohoku region in Japan. Magnitude of the tsunami exceeded design conditions of tsunami breakwater, seawalls and so on. A difficulty of fixing a design tsunami was re-recognized from the view point of disaster prevention. Of course, since total faults rupture scale was huge, the tsunami became so large that we were not able to anticipate in advance. Seismic researchers, that analyzed the 2011 tohoku earthquake, are pointing out that several faults slid with time lag. The faults rupture time lag should be also considered as one of the reason why the tsunami became large. However, even if the parameters of faults rupture could be set in terms of a disaster prevention design, it is so hard to determine faults rupture time lag.
     Therefore, this paper investigated influence of faults rupture time lag on tsunami height by numerical simulation. Case studies were carried out to evaluate tsunami that was generated two faults with time lag. Two simulation methods were applied. One of them is that tsunami generated by two faults with time lag calculated simultaneously (simultaneous simulation). Another one is a method based on the superposition. Simulation of tsunami caused by each fault is conducted independently. The tsunami profiles from two simulations are added considering with the time lag of faults rupture. This is positioned as a convenient method in order to reduce computational cost. Case studies were performed in Japan Sea and both simulation results were compared at 33 locations. As the results, faults rupture time lag affected tsunami height. And the time lag, makes to occur maximum tsunami height, was different at each location. Finally, it was confirmed that the convenient method based on the superposition could give almost same result as simultaneous simulation.
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  • Taro MINATO, Yuka YOKOYAMA, Tomohiko OISHI, Yoshio SATO
    2012 Volume 68 Issue 1 Pages 54-59
    Published: 2012
    Released: October 19, 2012
     In this study, the change in dissolved oxygen concentration in water by supplying light with Light Emitting Diode (LED)was investigatedon the column experiments. 12 red and 4 blue LEDs were used in this experiment. The irradiance was about 45 W/m2. From the column experiment results, it was found that the dissolved oxygen concentration could be increase from about 0 mg/L to 11 mg/L through the photosynthesis of benthic diatom by supplying light with LED. It was also determined that the orthophosphate and silicate ion concentration in water decreased during the supply of light. Therefore, it should be possible to improve the condition of anoxic bottom water and reductive sediment surface by supplying light with LED.
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