• Structural Engineering and Mechanics
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• v.74 no.2
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• pp.283-296
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• 2020

The coupled hydro-mechanical loading conditions commonly occur in the geothermal and petroleum engineering projects, which is significantly important influence on the stability of rock masses. In this article, the influence of flaw inclination angle of fracture behaviors in rock-like materials subjected to both mechanical loads and internal hydraulic pressures is experimentally studied using the 3-D X-ray computed tomography combined with 3-D reconstruction techniques. Triaxial compression experiments under confining pressure of 8.0 MPa are first conducted for intact rock-like specimens using a rock mechanics testing system. Four pre-flawed rock-like specimens containing a single open flaw with different inclination angle under the coupled hydro-mechanical loading conditions are carried out. Then, the broken pre-flawed rock-like specimens are analyzed using a 3-D X-ray computed tomography (CT) scanning system. Subsequently, the internal damage behaviors of failed pre-flawed rock-like specimens are evaluated by the 3-D reconstruction techniques, according to the horizontal and vertical cross-sectional CT images. The present experimental does not only focus on the mechanical responses, but also pays attentions to the internal fracture characteristics of rock-like materials under the coupled hydro-mechanical loading conditions. The conclusion remarks are significant for predicting the rock instability in geothermal and unconventional petroleum engineering.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.187-192
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• 2002

The open-connect type eddy current transducer for the flaw detection in continuously connected pipelines was developed. This eddy current transducer is for the on-line inspection of the tubes in industries, to which commercial encircling probes are not applicable. The excitation coil that consists of a ribbon type cable and a flat connector can be opened and closed on purpose. The sensing coils of this transducer are circumferentially arrayed near the outside of the tube wall but axially displaced from the exciter by about one and half tube diameter. In application to steel tubes, and the performance of this transducer was evaluated as a little behind those of magnetic saturation type in signal to noise ratio and flaw size decision, but usable to detect or to locate large size flaws in steel tubes. Surface cracks deeper than 19% of the tube thickness could be detected with good signal to noise ratio.

• Journal of Ocean Engineering and Technology
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• v.8 no.1
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• pp.96-104
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• 1994

The use of advanced composite materials has grown in recent years in aerospace and other structures. Out of various kinds of repairing methods the one selecteh for this study is an idealized case which simulates a situation where a damaged laminate has been repaired by drilling a hole and therefter plugging the hole with reinforcement. Two typesof reinforcement are investigated ;adhesively bonged plug reinforcement or snug-fit unbonded plug in the hole. For each case of reinforcement, four different sizes of hole diameter and three types of reinforcing material(steel, aluminum, plexiglass) are employed for investigation. The experiment are mainloy forced on the evaluation of ultimate strength of laminate with reinforced hole in comparison to its counterpart with the open hole.

• Geomechanics and Engineering
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• v.35 no.4
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• pp.333-366
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• 2023

Rock as a mass generally exhibits discontinuities, commonly witnessed in rock slopes and underground structures like tunnels, rock pillars etc. When these discontinuities experiences loading, a new crack emerges from them which later propagates to a macro scale level of failure. The failure pattern is often influenced by the nature of discontinuity, geometry and loading conditions. The study of crack growth in rocks, namely its initiation and propagation, plays an important role in defining the true strength of rock and corresponding failure patterns. Many researchers have considered the length of the discontinuity to be fully persistent on rock or rock-like specimens by both experimental and numerical methods. However, only during recent decades, there has been a substantial growth in research interest with non-persistent discontinuities where the crack growth and its propagation phenomenon were found to be much more complex than persistent ones. The non-persistence fractures surface is generally considered to be open and closed. Compared to open flaws, there is a difference in crack growth behaviour in closed or narrow flaws due to the effect of surface closure between them. The present paper reviews the literature that has contributed towards studying the crack growth behaviour and its failure characteristics on both open and narrow flaws subjected to uniaxial and biaxial compression loading conditions.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.187-193
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• 2011

In this report, We compared the actual test with the result of pow calculation and Resistance/Self-propulsion of the ship using STAR-CCM+ which is the commercial Reynolds Averaged Navier-Strokes(RANs) Solver. The calculation model was the KRISO Container Ship and 205K Bulk Carrier of Sungdong shipbuilding company. For this calculation, We used Realizable K-Epsilon model for flaw analysis, VOF method for the free surface creation, Moving Reference Frame method for reducing the POW calculation time, and Sliding Mesh method for Self-Propulsion analysis. Calculation of Resistance and Self-Propulsion includes the free-surface. And all calculations in this report were based on unstructured grids.

• Journal of The Korean Association For Science Education
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• v.29 no.8
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• pp.848-860
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• 2009

This study examined the characteristics of scientists' writing on the laboratory reports written in the authentic open inquiry, and explored the possibility that the class discussion after the inquiries could influence the laboratory report writing. The samples were 131 10th graders in a science high school in Seoul. The control group (n=45) practiced traditional school science inquiries, the experimental group 1 (n=43) practiced the authentic open inquiries, and the experimental group 2 (n=43) practiced the authentic open inquiries and the class discussion after the laboratory activities. Their laboratory reports were analyzed into three parts - prediction (prediction with background and apposite description), data analysis (data transformation and critical analysis), and conclusion (objective description based on evidence). The frequency of the characteristics of scientist's writing in the experimental group was higher than the control group. Particularly, the differences of the prediction with background (p<.01) and the critical analysis of data (p<.05) were statistically significant. However, the frequency of writing the conclusion based on evidence was very low in all of the three groups. The result from comparing descriptions of reports showed that the writing prediction in experimental groups were more elaborate, and the data transformation in experimental groups were more correct, and the evaluation to data in experimental groups were more critical than the control group. And the descriptions of the critical evaluation to data and the finding flaw in methods were found in experimental groups 2, indicating that the class discussion can stimulate students' scientific thinking.

• Journal of the Korean Institute of Gas
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• v.4 no.1 s.9
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• pp.55-62
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• 2000

A surface acoustic wave method for the evaluation of small fatigue crack initiated from a pit-type surface flaw is presented. In-situ ultrasonic experiments are performed for aluminum 2024-T3 alloy samples under the fatigue test. During the fatigue test, the surface acoustic wave reflection signal from the pit and crack is measured under different hold-stress levels. From the measured and predicted surface wave reflections the depths of fully and partially open cracks are determined and results are verified by comparing with SEM fractography The crack opening behavior of the fatigue crack is evaluated from the predicted effective crack depths. The method developed in this study can be applied to monitor and characterize crack initiation and propagation from pit-type surface flaws in the early stage of fatigue life.

• International journal of advanced smart convergence
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• v.13 no.2
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• pp.48-60
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• 2024

With the exponential growth of satellite data utilization, machine learning has become pivotal in enhancing innovation and cybersecurity in satellite systems. This paper investigates the role of machine learning techniques in identifying and mitigating vulnerabilities and code smells within satellite software. We explore satellite system architecture and survey applications like vulnerability analysis, source code refactoring, and security flaw detection, emphasizing feature extraction methodologies such as Abstract Syntax Trees (AST) and Control Flow Graphs (CFG). We present practical examples of feature extraction and training models using machine learning techniques like Random Forests, Support Vector Machines, and Gradient Boosting. Additionally, we review open-access satellite datasets and address prevalent code smells through systematic refactoring solutions. By integrating continuous code review and refactoring into satellite software development, this research aims to improve maintainability, scalability, and cybersecurity, providing novel insights for the advancement of satellite software development and security. The value of this paper lies in its focus on addressing the identification of vulnerabilities and resolution of code smells in satellite software. In terms of the authors' contributions, we detail methods for applying machine learning to identify potential vulnerabilities and code smells in satellite software. Furthermore, the study presents techniques for feature extraction and model training, utilizing Abstract Syntax Trees (AST) and Control Flow Graphs (CFG) to extract relevant features for machine learning training. Regarding the results, we discuss the analysis of vulnerabilities, the identification of code smells, maintenance, and security enhancement through practical examples. This underscores the significant improvement in the maintainability and scalability of satellite software through continuous code review and refactoring.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.2
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• pp.34-34
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• 1987

Friction welding has emerged as a reliable process for high-production commercial application with significant economic and technical advantages. But nondestructive test in friction weld was not clearly developed. Therefore the experimental verification is necessary in order to understand the characteristics of the pulse echo effects according to various change in welding conditions. This paper presents a new attempt to detect the bond strength of friction welds by ultrasonic. Instead of looking for a flaw or cracks at the interface, the new approach evaluates the coefficient by reflection which provides a single quantitative indicator involving the acoustic energy reflected at the interface. The objective of this study is to find the relationship between the reflection coefficients and the weld strength. Results of the bar-to-bar friction welding of aluminum to copper and stainless steel and such relationship investigation are presented and interpreted.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.2
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• pp.80-85
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• 1987

Friction welding has emerged as a reliable process for high-production commercial application with significant economic and technical advantages. But nondestructive test in friction weld was not clearly developed. Therefore the experimental verification is necessary in order to understand the characteristics of the pulse echo effects according to various change in welding conditions. This paper presents a new attempt to detect the bond strength of friction welds by ultrasonic. Instead of looking for a flaw or cracks at the interface, the new approach evaluates the coefficient by reflection which provides a single quantitative indicator involving the acoustic energy reflected at the interface. The objective of this study is to find the relationship between the reflection coefficients and the weld strength. Results of the bar-to-bar friction welding of aluminum to copper and stainless steel and such relationship investigation are presented and interpreted.