• Journal of Ocean Engineering and Technology
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• v.18 no.4 s.59
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• pp.15-22
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• 2004

Static and dynamic analyses of a very flexible and light riser, for upwelling the deep ocean water, is performed. In this numerical study, an implicit finite difference algorithm is employed for three-dimensional riser equations. Fluid non-linearity and bending stiffness are considered and solved, using the Newton-Raphson iteration. Maintaining the depth of end point of a flexible and light riser is very important for upwelling deep ocean water in a floating type development system. Weight is attached at the end point of the riser in order to maintain its intake depth. It is designed under the strong surface current and the configuration of the rise is predicted. In the dynamic analysis, the tension variation at the top point of the riser is presented. T e results of this study can contribute to the design of the development system in floating type for upwelling deep ocean water.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.9
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• pp.172-178
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• 1999

3D linear and circular interpolations are a basic part for the machining of complex shapes. Until now, because of the absence of appropriate algorithms for the generation of 3D lines and circles, a full accomplishment for available machine tool resolution is difficult. this paper presents new algorithms for 3D linear and circular interpolation in the reference pulse technique. In 3D space, the line or circle is not expressed as an implicit function, it is only defined as the intersection of two surfaces. A 3D line is defined as the intersection of two planes, and a 3D circle is defined as the intersection of a plane and the surface of a sphere. Based on these concepts, interpolation algorithms are designed to follow intersection curves in 3D space, and a real-time 3D linear and circular interpolator was developed in software using a PC. The algorithm implemented in a PC showed promising results in interpolation error and speed performance. It is expected that it can be applied to the next generation computerized numerical control systems for the machining of 3D lines, circles and some other complex shapes.

• Language and Information
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• v.18 no.2
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• pp.141-168
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• 2014

Recognizing spatial information associated with events expressed in natural language text is essential not only for the interpretation of such events and but also for the understanding of the relations among them. However, spatial information is rarely mentioned as compared to events and the association between event and spatial expressions is also highly implicit in a text. This would make it difficult to automate the extraction of spatial information associated with events from the text. In this paper, we give a linguistic analysis of how spatial expressions are associated with event expressions in a text. We first present issues in annotating narrative texts with reference relations between event and spatial expressions, and then discuss surface-level linguistic characteristics of such relations based on the annotated corpus to give a helpful insight into developing an automated recognition method.

• Geomechanics and Engineering
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• v.16 no.6
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• pp.655-667
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• 2018

To evaluate the stability of a rock slope with one pre-exiting vertical crack, this paper performs corresponding probabilistic stability analysis. The existence of cracks is generally ignored in traditional deterministic stability analysis. However, they are widely found in either cohesive soil or rock slopes. The influence of one pre-exiting vertical crack on a rock slope is considered in this study. The safety factor, which is usually adopted to quantity the stability of slopes, is derived through the deterministic computation based on the strength reduction technique. The generalized Hoek-Brown (HB) failure criterion is adopted to characterize the failure of rock masses. Considering high nonlinearity of the limit state function as using nonlinear HB criterion, the multivariate adaptive regression splines (MARS) is used to accurately approximate the implicit limit state function of a rock slope. Then the MARS is integrated with Monte Carlo simulation to implement reliability analysis, and the influences of distribution types, level of uncertainty, and constants on the probability density functions and failure probability are discussed. It is found that distribution types of random variables have little influence on reliability results. The reliability results are affected by a combination of the uncertainty level and the constants. Finally, a reliability-based design figure is provided to evaluate the safety factor of a slope required for a target failure probability.

• Nuclear Engineering and Technology
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• v.53 no.6
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• pp.1810-1820
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• 2021

Study of single bubble behavior under rolling motions can prove useful for fundamental understanding of flow field inside the modern small modular nuclear reactors. The objective of the present study is to simulate the influence of rolling conditions on single rising bubble in a liquid using multiphase Moving Particle Semi-implicit (MPS) method. Rolling force term was added to 2D Navier-Stokes equations and a computer program was written using C language employing OpenACC to port the code to GPU. Computational results obtained were found to be in good agreement with the results available in literature. The impact of rolling parameters on trajectory and velocity of the rising bubble has been studied. It has been found that bubble rise velocity increases with rolling amplitude due to modification of flow field around the bubble. It has also been concluded that the oscillations of free surface, caused by rolling, influence the bubble trajectory. Furthermore, it has been discovered that smaller vessel width reduces the impact of rolling motions on the rising bubble. The effect of liquid viscosity on bubble rising under rolling was also investigated and it was found that effects of rolling became more pronounced with the increase of liquid viscosity.

• Journal of Korea Water Resources Association
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• v.34 no.1
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• pp.19-30
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• 2001

A laterally averaged 2-dimensional hydrodynamic model is newly developed. The coordinate system is first transformed to minimize the effects of irregularity of bottom and surface. The advection terms of the governing equations are then discretized by an upwind scheme. By employing an explicit scheme for longitudinal direction and an implicit scheme for vertical direction, the model is free from restriction of temporal step size caused by a relatively small grid ratio. To demonstrate the applicability of the model, calculated time histories of free surface displacements and distributions of velocity and salinity are compared with the field measurements of the Keum River Estuary before construction of the estuary dam. A reasonable agreement is observed between them.

• Journal of the Korea Computer Graphics Society
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• v.4 no.1
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• pp.79-88
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• 1998

Till now there are several rendering models for water and simulating other fluids and their dynamics. Especially in order to generate a curved surface of flexible objects such as liquid and snow, the implicit metaball formulation is widely used in favor of its simplicity and flexibility. This paper proposes one excellent method for generating water droplets, which would be deformed in gravitation field. In previous works, a water droplet was simply represented by approximated curved surfaces of a symmetric metaball. Thus the final result of the rendered water droplet was far from a realistic droplet, because they do not consider the gravitational effect in droplets. We propose a new metaball model for rendering water droplets placed on an arbitrary surface considering the gravitation and friction between droplet and plate. Our new metaball model uses a new vector field isosurface function to control the basic scalar metaball with respect to the norm of gravitational force. In several experiments, we could render a photo-realistic water droplets with natural-looking shadows by applying ray-tracing.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.3
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• pp.211-219
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• 2008

A three-dimensional inviscid flow solver has been developed based on unstructured meshes for the investigation of the effect of the external stores on the tail surfaces of a generic fighter aircraft. The numerical method is based on a vertex-centered finite-volume discretization and an implicit point Gauss-Seidel time integration. The calculations were made for a steady flow and the computed results were compared with experimental data to validate the flow solver. An unsteady time-accurate computation of the generic fighter aircraft with external stores at transonic flight conditions showed that the external stores cause unsteady loading on the horizontal tail surface due to the mutual interference between their wake and the horizontal tail surface. It was shown that downward deflection of the trailing edge flap significantly reduces the undesirable interference effect.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.147-155
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• 1993

An urban runoff model is proposed in this study, which is composed of a surface runoff model and a channel routing model. ILLUDAS is selected as the best fit model for the surface runoff computation, and the dynamic wave model using weighted four-point implicit finite difference scheme is used to perform the channel routing. The 3rd Seongbook bridge basin located in Seoul is selected as the test basin for the proposed model, and the rainfall-runoff data are collected to calibrate and verify the urban runoff model. The computed results by this model showed the fair accuracy when compared with the observed hydrographs. So the model proposed in this study could be used to compute the urban river flow as well as the outflow from the urban drainage area.

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.4
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• pp.353-361
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• 2000

In Computer Graphics, to select the element for modeling is very important in aspect of real-time processing of photorealistic images. Especially in modeling of informal objects, the criteria of choice are such as the minimum number of data, the easy rendering technique, and the expansibility. The metaball model which is one of the methods for modeling the implicit surface is excellent in modeling the complicated surface with a few data. However, a greater number of data are required for modeling objects that consist of planar surfaces with metaballs than with polygons. In this paper, we propose the new skeletal element, metacube which has the merits of metaball and improves the modeling ability of informal objects containing planar surfaces. A metacube has two parameters to change freely its shape from the cube to the sphere and can easily do the modeling of objects with curved surfaces and plane surfaces.