• Journal of Korea Water Resources Association
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• v.41 no.9
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• pp.959-967
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• 2008

Disaggregation techniques are widely used to transform observed daily rainfall values into hourly ones, which serve as important inputs for flood forecasting purposes. However, an important limitation with most of the existing disaggregation techniques is that they treat the rainfall process as a realization of a stochastic process, thus raising questions on the lack of connection between the structure of the models on one hand and the underlying physics of the rainfall process on the other. The present study introduces a nonlinear deterministic (and specifically chaotic) framework to study the dynamic characteristics of rainfall distributions across different temporal scales (i.e. weights between scales), and thus the possibility of rainfall disaggregation. Rainfall data from the Seoul station (recorded by the Korea Meteorological Administration) are considered for the present investigation, and weights between only successively doubled resolutions (i.e., 24-hr to 12-hr, 12-hr to 6-hr, 6-hr to 3-hr) are analyzed. The correlation dimension method is employed to investigate the presence of chaotic behavior in the time series of weights, and a local approximation technique is employed for rainfall disaggregation. The results indicate the presence of chaotic behavior in the dynamics of weights between the successively doubled scales studied. The modeled (disaggregated) rainfall values are found to be in good agreement with the observed ones in their overall matching (e.g. correlation coefficient and low mean square error). While the general trend (rainfall amount and time of occurrence) is clearly captured, an underestimation of the maximum values are found.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.1
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• pp.1-7
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• 2017

In general, the large loads which are applied from explosion, impact, earthquake and wind at a short time caused the materials of structures to large deformations, rotations and strains locally. If such phenomena will be analyzed, hydrocodes which can be considered fluid-structure interaction under computational continuum mechanics are inevitably needed. Also, the explosion mechanism is so complicated, it is reasonable that the behaviors of structure are predicted through explosion analyses and experiment at the same time. But, unfortunately, it is true that explosion experiments are limited to huge cost, large experiment facilities and safety problems. Therefore, in this study, it is shown that the results of explosion analyses using the AUTODYN are agreed with those of existing explosion experiments for reinforced concrete slabs within reasonable error limits. And the explosion damage of the same reinforced concrete slab are assessed for quite different reinforcement arrangement spacings, concrete cover depths, and vertical reinforcements. From the explosion analyses, it is known that the more the ratio of slab thickness to reinforcement arrangement spacing is increased, and small-diameter reinforcements are used than large-diameter reinforcements on the same reinforcement ratio, and vertical reinforcements are used, the more the anti-knock capacities are improved.

• Journal of the Korean association of regional geographers
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• v.22 no.4
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• pp.887-911
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• 2016

The empirical law that transverse dunes migrate inversely with their heights leads logically to the prediction that multiple dune ridges will converse to a single huge dune by merging. This contradicts the existence of the steady state dune fields on the Earth. The recent studies have emphasized dune collisions as a key mechanism to the stability of dunefield. The roles of wind shadow aspect ratio, however, have yet to be fully explored. This research aims to investigate the potential roles of wind shadow aspect ratio in the dynamical behaviors of transverse dune field. The simplified model is established for this, based upon allometric properties of transverse dunes, wind speedup on the stoss slope and sand trapping efficiency. The derived governing equations can be transformed to the zoning criteria and vector field for dune evolution. The dynamics analysis indicates that wind shadow aspect ratios do not produce convergent areas on the behavior space; rather, they just act as one of the factors that affect the trajectories of dune evolution. Though the model cannot represent the stability of dune field, but seem to produce a reasonable exponent for dune spacing-height relations.

• Geophysics and Geophysical Exploration
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• v.8 no.1
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• pp.1-6
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• 2005

Analogue physical modelling using granular materials (i.e., sandbox experiments) has been applied with great success to a number of geological problems at various scales. Such physical experiments can also be simulated numerically with the Discrete Element Method (DEM). In this study, we apply the DEM simulation to the collision between the Indian subcontinent and the Eurasian Plate, one of the most significant current tectonic processes in the Earth. DEM simulation has been applied to various kinds of dynamic modelling, not only in structural geology but also in soil mechanics, rock mechanics, and the like. As the target of the investigation is assumed to be an assembly of many tiny particles, DEM simulation makes it possible to treat an object with large and discontinuous deformations. However, in DEM simulations, we often encounter difficulties when we examine the validity of the input parameters, since little is known about the relationship between the input parameters for each particle and the properties of the whole assembly. Therefore, in our previous studies (Yamada et al.,2002a,2002b,2002c), we were obliged to tune the input parameters by trial and error. To overcome these difficulties, we introduce a numerical biaxial test with the DEM simulation. Using the results of this numerical test, we examine the validity of the input parameters used in the collision model. The resulting collision model is quite similar to the real deformation observed in eastern Asia, and compares well with GPS data and in-situ stress data in eastern Asia.