Exploratory Research

Exploratory Research in FY 2014

 Exploratory researches considered to have potential for development in the future are appropriately evaluated and promoted considering their potential and mobility.

1 Development of calculation models that can estimate high-order wave transformation covering from shallow waters to deep waters
2 Establishment of techniques for quick, high-precision detection of cavities in port facilities
3 Establishment of techniques for tsunami propagation calculation using a neural network
4 Development of techniques for reconstructing soil particle arrangement and application to mechanical evaluation
5 Development of a resolution variable scheme for predicting the deformation of structures and ground using the particle method
6 Development of a simple sensor for the prevention of cavitation
7 Feasibility study of biomarkers for detecting separated pavements

Examples of Exploratory Research

Development of calculation models that can estimate high-order wave transformation covering from shallow waters to deep waters

  • In this study, by introducing a water depth gradient term in the numericalmodel based on the nonlinear Schrödinger equation that can solve the development of third-order nonlinear interference during propagation through deep waters (infinite depth), we successfully developed a new calculation model that can estimate high-order wave transformation covering from shallow waters to deep waters. We will continue to verify the model while reducing the calculation costs.
  • As a result of hydraulic model experiments, we found that, regarding seabed topographies having the same propagation distance of waves to slope topography and different slope gradients, the spatial distribution of the kurtosis (μ4) varied depending on the difference of the wave-breaking pattern due to the difference of the slope gradient, but the kurtosis (μ4) developed regardless of the slope gradient outside the wave-breaking band. We also found that, regarding seabed topographies having the same slope gradient,the longer the propagation distance of waves to slope topography (x) was, the more conspicuously the kurtosis (μ4) developed,and the effect remains even in shallow waters (Figure 1.1.3.2).

Figure 1.1.3.1 Relation between depth of kurtosis and slope gradient

Figure 1.1.3.2 Relation between depth of kurtosis and slope position

Establishment of techniques for quick,high-precision detection of cavities in port facilities

  • In this study, we developed new techniques for cavity exploration and verified their on-site feasibility.
  • Cavity exploration requires knowledge and skills as to the selection of devices and interpretation of the output data, and therefore the accuracy of detecting cavities significantly varies depending on the researcher. In this study, we developed techniques for detecting cavities with higher accuracy regardless of knowledge and skills, including software that can quickly receive reflected waves coming from underground using an electromagnetic wave radar as well as fast imaging of the waves.
  • Figures 1.1.3.3 and 1.1.3.4 show examples of the results verified at the simulated cavity site in the Nobi Experiment Station. The top figure shows the result of detection by the conventional technique, and the bottom one shows the result obtained in this study. At the points circled in the bottom figure (simulated cavities), the differences from the peripheral image are easily confirmed compared to the conventional technique.

 

Figure 1.1.3.3 Detection result (Two (small) cavities)

Figure 1.1.3.4 Detection result (One (large) cavity)

Establishment of techniques for tsunami propagation calculation using a neural network

  • At present, damage estimation including the prediction of tsunami propagation and seepage, is performed by numerically solving dominant equations such as differentiated RANS equations,and therefore many detailed calculation cells are required when applying a 3D non-hydrostatic model to a large area, resulting in a large calculation cost and extremely long calculation time.
  • Meanwhile, tsunami damage must be estimated by trial and error for many cases such as various structural arrangements, and therefore the long calculation time seriously hinders the estimation. In this study, we proposed a database-type tsunami estimation model using a neural network and investigated its applicability in order to shorten the calculation time while ensuring calculation accuracy.
  • We verified the estimation accuracy of this model regarding the flow velocity and pressure of tsunamis propagating at a constant depth,while regarding the result of calculation using a 3D non-hydrostatic model as the true value (Figure 1.1.3.8 Example of verification result).
  • We confirmed the validity of this model, though its applicability requires further study.

 

Figure 1.1.3.8 Estimation accuracy of flow velocity and pressure
(Horizontal axis: True value, Vertical axis: Estimated value)

Development of techniques for reconstructing soil particle arrangement and application to mechanical evaluation

  • In this study, we tried to reconstruct samples having an arbitrary soil particle arrangement by using an X-ray CT scanner and a 3D printer in order to propose a new technique for evaluating the mechanical characteristics of granular material.
  • We carried out tri-axial compression tests using samples duplicated based on X-ray tomographic images of granular samples and experimentally examined the geometrical and mechanical reproducibilities with respect to the original sample. Photograph 1.1.3.1 shows the particles of both the gravel material used in this study and the duplicated sample. Furthermore, Figure 1.1.3.9 shows X-ray horizontal tomographic images of the original and the duplicated samples. As shown in the figure, the granularity, shape, and soil particle arrangement of the original sample were well reproduced by the restoration. Figure 1.1.3.10 shows the result of performing tri-axial compression tests three times for the original and duplicated samples. The three duplicated samples show similar stress-strain curves and much less variation compared to the original samples.
  • If this technique can be used to evaluate the influence of the difference of soil particle arrangement on the mechanical characteristics of soil, it would be extremely helpful in the field of geotechnical engineering.

 

(a) Original sample                   (b) Duplicated sample

Photograph 1.1.3.1 Appearance of samples

(a) Original sample                  (b) Duplicated sample

Figure 1.1.3.9 X-ray CT images of samples

Figure 1.1.3.10 Triaxial compression test result

Development of a resolution variable scheme for predicting the deformation of structures and ground using the particle method

  • In this study, we tried to introduce variable mixed-size particles into the particle method, which is a fluid analysis technique that is excellent for tracking interfaces between different phases, in other words, to develop the method into multi resolutions and thus develop a high-precision fluctuation estimation tool for comprehensively handling composition phenomena in which extremely different scales, such as scouring in wave places and suction phenomena,coexist, and to clarify poorly-understood issues. The particle method expresses the dynamic relation of fluid fields using the interaction force between a particle and adjacent particles via local averaging, where the isotropic distribution of physical quantities must be ensured for stable calculation via local averaging. Meanwhile,the introduction of mixed-size particles makes the particle sizes and weighting of them uneven and therefore causes pressure disturbance. This is why the particle method has not yet been developed into multi resolutions. In particular, this problem is almost impossible to solve as an algorithm based on incompressible fluids using the particle number density for the Poisson equation.
  • In this study, we developed a new interaction model for stably handling the uneven arrangement of the Kernel distribution caused by mixed-size particles. Furthermore, regarding the treatment of geometrically uneven voids caused by mixed-size particles, we successfully achieved a high-precision, stable calculation method for particle flow simulation (MPS method) using mixed-size particles,which was previously difficult, by introducing space potential particles in order to give the mathematical meaning of spatial characteristics to the voids without calculation points.
  • We examined the reproducibility of hydrostatic pressure distribution as the benchmark of the restriction of pressure disturbance by comparing the result of numerical simulation using the conventional mixed-size particle model based on the MPS method and that using the proposed model. The conventional model shows a non-physical pressure distribution due to pressure disturbance, but the proposed model shows that pressure distribution is sufficiently suppressed.
  • To examine the applicability of the proposed model under highly non-stationary conditions, we conducted numerical simulation of a dam break using both the conventional model and the proposed model, as with the benchmark test described above. Then, we confirmed that the proposed model provided a smoother water surface system compared to the conventional model.
  • We developed a mixed-size particle model based on the particle method, which enables high-precision, stable calculation even under highly non-stationary conditions compared to the conventional model. We will try to construct a framework with a dynamically variable particle size and thus improve numerical wave tanks based on the particle method.

Development of a simple sensor for the prevention of cavitation

  • Cavitation of port facilities is normally detected using an electromagnetic wave radar, which is expensive and requires expert knowledge.Meanwhile, outflow of back reclamation soil due to the corrosion of steel sheet piles or the like is considered to be one of the causes of cavitation of steel port facilities, but the corrosion occurs under water and therefore the points are difficult to confirm. In this study, we developed a simple sensor that can detect the corrosion of steel members from the land without requiring expert knowledge.
  • The developed sensor consists of a steel pipe with caps on both ends (Photograph 1.1.3.2), and it is used by directly attaching it to a steel member of facilities, such as a steel sheet pile. The sensor will be corroded as with the steel members of facilities, and eventually,through-holes will be generated. When the sensor detects seawater invading the sensor through such a hole, it means that steel members have been corroded by the thickness of the sensor. By determining the wall thickness of the sensor so that through-holes are generated in the sensor before occurring in the steel members of the facility, it is possible to make repairs before through-holes occur in the steel members, thus preventing the generation of cavities.
  • Electrometers used for measuring the electrolytic protection potential are also used for detecting seawater. Before seawater invades, the inside of the sensor is isolated, and therefore no electric potential is measured, but when seawater invades,the sensor is energized and therefore the electric potential becomes the same as the outside of the sensor. In an indoor test, we confirmed energization of the sensor when seawater invaded to reach a height of approx. 10 mm in the sensor.
  • This sensor enables the corrosion of steel members to be detected from the land. Furthermore, since no expert knowledge is required, facility managers can conduct inspections themselves.
  • This sensor can also be used to prevent the generation of through-holes in the steel pipe piles of piers. In addition, by combining the sensor with other sensors such as water pressure gauges, remote continuous monitoring is possible.

Photograph 1.1.3.2 Developed sensor

Feasibility study of biomarkers for detecting separated pavements

  • The purpose of this study is to develop technologies for labeling the points
    of delamination of asphalt pavements using magnetic bacteria, which
    have magnetism in their bodies (hereafter referred to as “biomarker”).
  • In this study, we examined the culture conditions for generating magnetism
    in the bodies of magnetic bacteria (Photograph 1.1.3.3) and evaluated
    the magnetism generated by magnetic bacteria using a Gauss meter.
  • As a result, we revealed that the magnetic flux density of a
    solution containing magnetic bacteria is approx. 0.4 μT when
    the cell weight of the solution is 33.3 g/L (Figure 1.1.3.13).

Photograph 1.1.3.3 Transmission electron microscope photograph (Left:Single bacterium, Right:String of bacteria)

 Figure 1.1.3.13 Measurement result of the magnetic flux density of magnetic bacteria (The numbers above the bars are the cell weight.)

 

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