• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.1
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• pp.39-47
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• 2004

In this paper, the defects of two-dimensional anisotropic elastic bodies are identified by using the boundary element method. The use of numerical models that contain only boundary integral terns reduces the dimensionality of the problem by one. This advantage is particularly important in problems such as crack mechanics. Avoiding domain meshing is also particularly advantageous in the solution of inverse problems since it overcomes mesh perturbations and simplifies the procedure. In this paper, nondestructive approaches for the existing isotropic materials are extended to analyze the elastic bodies made of anisotropic materials such as composites. After verifying that the proposing boundary element model is in good agreement with numerical results reported by other investigators, the effect of noise in the measurements on the identifiability is studied with respect to different design parameters of layered composites. Sample studies are carried out for various layup configurations and loading conditions. The effects of the layup sequences in detecting flaw of composites is explored in this paper.

• The Journal of the Korea Contents Association
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• v.11 no.6
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• pp.106-115
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• 2011

In this paper, we evaluate the effectiveness of previous shading algorithms in depicting shape of 3d objects. We perform a study in which people are shown an image of one of ten 3D objects shaded with one of eight styles and asked to orient a gauge to coincide with the surface normal at many positions on the object's surface. The normal estimates are compared with each other and with ground truth data provided by a registered 3D surface model to analyze accuracy and precision. Our experiments suggest that people interpret certain shape differently depending on shading of 3d object. This paper offers substantial evidence that current computer graphics shading algorithms can effectively depict shape of 3d objects where the algorithms have the properties of lots of tone steps and uniformly distributed tone steps. This type of analysis can guide the future development of new CG shading algorithms in computer graphics for the purpose of shape perception.

• Tunnel and Underground Space
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• v.16 no.4 s.63
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• pp.334-346
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• 2006

The discrete element code in 2-D, PFC2D, has been used as a tool to simulate various phenomena in rock mechanics and rock engineering. However, the code has an disadvantage that procedure to determine micro-parameters, namely properties of particles and contacts is repetitive and time-consuming. In this study, we analyzed the effect of micro-parameters(for generation of a contact-bonded model) on macro-properties(that were measured numerically by uniaxial compressive test). Based on the analysis, also, the time-saving and reliable method was suggested to determine a complete set of micro-parameters. In order to verify the suggested method, numerical specimens were generated in PFC2D for 10 different rock types at home and abroad. By the two trials for each specimen, in the result, the Young's modulus, Poisson's ratio and uniaxial compressive strength could be reproduced with being in relative error by about 5% to the values obtained by laboratory tests.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.3
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• pp.226-232
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• 2014

In the present study, the characteristics of laser ultrasound in the ablation regime are investigated using simulations and experiments. The laser ultrasonic technique has been recognized as a noncontact method in the field of nondestructive tests (NDTs). In hostile environments (such as hot temperatures), this method has various advantages over the conventional contact ultrasonic method. In particular, in the ablation regime, the laser ultrasonic technique is suitable for inspecting internal defects because of the high amplitude and directivity of the longitudinal wave. In this paper, a simulation model for laser ultrasound in the ablation regime was developed. This model was subsequently applied to a defective specimen using the B-scan method to locate defects. Finally, we performed an experimental test to verify the simulation results. Consequently, the simulation demonstrated good agreement with the experimental test.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.4
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• pp.189-196
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• 1999

In order to verify a numerical model for the calculation of wave motion around an offshore barrier in shallow water, laboratory physical experiments are necessary. In this study, sample experiments are carried out on the wave and wave induced current fields due to a sloping bottom topography and on that due to an isolated structure from the coastline. The water body is divided into 4 levels, in which the current tracking floaters are deployed to measure the wave induced currents. Data measurement was continued using the limited wave gauges and current tracking floaters including a video camera from the top. The wave heights for the preselected surface and time-averaged velocity distributions at each level were measured in detail. The distribution of wave and current fields was analyzed precisely combining the whole measured laboratory data. Moreover, comprehensive analyses were carried out on non-linearity of wave transformation in terms of skewness and atiltness.

• Journal of Broadcast Engineering
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• v.15 no.6
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• pp.731-741
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• 2010

In this paper, we propose the methodology of prediction of field strength for a digital television (DTV) receiver by virtue of Recommendation ITU-R P.1546. The curves shown in this recommendation represent the point-to area field strength for 1.0 kW effective radiated power in the 30 MHz ~ 3000 MHz. Based upon the procedures described in this Recommendation, computation results are presented here from the derived formulation of field strength for DTV receiver. To show the validity of this method, some results are compared with the analysis by Okumura-Hata model and it was shown that the error of field strength is in the range of 6.9 ~ 11.5 %. The presented method provides not only the predicted values of field strength for DTV receiving area to check the quality of transmitted signal, but also an appropriate site selection for obtaining good propagation environment. In addition, it can be directly used for analyzing the protection ratio or separated distance for frequency sharing in the same band.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.4 no.2
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• pp.197-207
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• 2006

The engineering performance of a high level waste repository is significantly dependent upon the T-H-M behavior in the engineered barrier system. An engineering-scale test facility (KENTEX) was set up to validate the T-H-M behaviors in the buffer of a reference disposal system developed in the 2002. The validation tests started on May 31, 2005 and is now in progress. The KENTEX facility and validation test programme are introduced, and pre-operation calculations are also presented to give information on the sensitive location of sensors and operational conditions. This test will provide information (e.g., large-scale apparatus, sensors, monitoring system etc.) needed for 'in-situ' tests, make the validation of a T-H-M model for the T-H-M performance assessment of the reference disposal system, and demonstrate the engineering feasibility of fabricating and emplacing the buffer of a repository.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.6
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• pp.2441-2451
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• 2012

This paper presents the design of a control system for improving performance of a washer fluid heating system (WFHS) which is capable of removing frost, ice, snow and/or other debris from windshield. First, for the WFHS, a modeling process is described, and the extraction of characteristic parameters of the model are made by experimental studies. Design variables that affect on performance of the WFHS are also presented. Secondly, a control system is proposed for improving heating performance of the WFHS, and its performance is verified through experiments. The key feature of the proposed control system is to regulate the current of a booster converter input to the WFHS up to the target value that is set to guarantee heating performance. Target current is calculated by using initial temperature value and employing the mathematical model derived in the paper. Computer simulation and experimental results show that the proposed control system can perform heating operations in a way to satisfy per-determined target performance of the WFHS.

• Journal of the Korean Society for Marine Environment & Energy
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• v.1 no.2
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• pp.52-59
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• 1998

Many concerns are placed on preservation of coastal environment from the spilled oil contaminant in the coastal area. And the use of computer simulation model to combat with oil spill has come to play mote important role in forecasting the oil spill trajectory so as to protect coastal area and minimize the damage from oil contaminants. The main concerns of this study is how the movements of spilled oil are affected by currents including tidal, oceanic, and wind-driven currents. Especially, in the present paper, the oil spill trajectory can be predicted by a real-time system that allows prediction of circulation and wind field. The harmonic methods are adopted to simulate the tidal currents as well as it can be possible to achieve the wind-field data and oceanic current data from the established database. System performance is illustrated by the simulation of oil spill in the south-eastern coastal area of Korea. Simulation results are compared with the observed one.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.657-663
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• 2018

In this study, shape optimization was performed to improve the vibration isolation capability of an anti-vibration rubber assembly, which is used in the field option cabin of agricultural tractors. A uniaxial tension test and biaxial tension test were performed to characterize the hyper-elastic material properties of rubber, and the data were used to calibrate the material model used in the finite element analyses. A field test was performed to quantify the input excitation from the tractor and the output response at the cabin frame. To account for the nonlinear behavior of rubber, static analyses were performed and the load-displacement curve of rubber was derived. The stiffness of the rubber was calculated from this curve and input to the harmonic analyses of the cabin. The results were verified using the test data. Taguchi's parameter design method was used to find the optimal shape of the anti-vibration rubber assembly, which indicated a shape with reduced stiffness. The vibration of the cabin frame was reduced by the optimization by as much as 35% compared to the initial design.