• Journal of the Korean Society for Precision Engineering
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• v.30 no.1
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• pp.113-119
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• 2013

To develop a new nuclear fuel, it needs to make a test fuel rod and carry out burn-up test in the test loop of a research reactor to check the irradiation characteristics of the nuclear fuel. At that time, several sensors such as thermocouples, LVDTs and SPNDs are needed to be attached in and out of the fuel rod and connect them with instrumentation cables. Then, the instrumentation cables deliver the signals measured by the sensors to the measuring device located outside of the reactor pool. In particular, to install a thermocouple in a fuel rod, it needs to drill off holes on the alumina blocks and sintered $UO_2$ pellets. However, because the hardness of a sintered $UO_2$ pellet is 700 Hv (or HRC 61) and that of an alumina block is 1480 Hv, a special drilling machine which adapts a diamond coated drill bit had developed. In this study, several case experiments have been carried out to find an optimal drilling condition of the drilling machine. And, using the optimal drilling condition, minimum numbers of the holes that a drill bit can drill off are verified.

• Geomechanics and Engineering
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• v.22 no.1
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• pp.81-95
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• 2020

Measurement of the unconfined compressive strength (UCS) of the rock is critical to assess the quality of the rock mass ahead of a tunnel face. In this study, extensive field studies have been conducted along 3,885 m of the new Nagasaki tunnel in Japan. To predict UCS, a hybrid model of artificial neural network (ANN) based on genetic algorithm (GA) optimization was developed. A total of 1350 datasets, including six parameters of the Measurement-While- Drilling data and the UCS were considered as input and output parameters respectively. The multiple linear regression (MLR) and the ANN were employed to develop contrast models. The results reveal that the developed GA-ANN hybrid model can predict UCS with higher performance than the ANN and MLR models. This study is of great significance for accurately and effectively evaluating the quality of rock masses in tunnel engineering.

• Journal of Sensor Science and Technology
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• v.13 no.1
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• pp.72-77
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• 2004

In this paper, we fabricated an apparatus of the electro-chemical discharge drilling for boring narrow through-hole into a glass. In the electrolyte, electro-chemical discharge creates high temperature condition by the electro-discharge energy. Therefore, glass are removed by the accelerated chemical reaction with glasses and chemicals in the high temperature condition. For optimization of the electro-chemical discharge drilling, the process condition was studied experimentally as a function of the electrolyte concentration, supply voltage and process time. The optimum condition was from DC25V to DC30V of applied voltage, 35 wt% NaOH solution.

• Journal of the Korean GEO-environmental Society
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• v.24 no.1
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• pp.51-60
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• 2023

Unlike the vertical drilling in the directional drilling should be minimized torque and drag in the well trajectory that avoided problems such as drillstring transformation, casing wear and key-seating. These torque and drag magnitude is determined by variations such as the well trajectory geometry, drilling mud, drillstring type and kick-off point. Therefore, it is essential to consider these variations for designing directional well trajectory. In this study, it was selected well trajectory by the most common build-hold type well and calculated torque and drag on each section by Analytical friction model. Analysis indicates that torque and drag could be minimized by using high lubricity drilling mud, kick-off point appropriate according to the well geometry and possible minimize dogleg severity. The results of this study is useful to minimize torque and drag from directional well trajectory design.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.1287-1288
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• 2011

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.82-96
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• 2019

A semi-submersible structure has been widely used for offshore drilling and production of oil and gas. The small water plane area makes the structure very sensitive to weight increase in terms of payload and stability. Therefore, it is necessary to lighten the substructure from the early design stage. This study aims at an optimization of hull structure based on a sophisticated yield and buckling strength in accordance with classification rules. An in-house strength assessment system is developed to automate the procedure such as a generation of buckling panels, a collection of required panel information, automatic buckling and yield check and so on. The developed system enables an automatic yield and buckling strength check of all panels composing the hull structure at each iteration of the optimization. Design variables are plate thickness and stiffener section profiles. In order to overcome the difficulty of large number of design variables and the computational burden of FE analysis, various methods are proposed. The steepest descent method is selected as the optimization algorithm for an efficient search. For a reduction of the number of design variables and a direct application to practical design, the stiffener section variable is determined by selecting one from a pre-defined standard library. Plate thickness is also discretized at 0.5t interval. The number of FE analysis is reduced by using equations to analytically estimating the stress changes in gradient calculation and line search steps. As an endeavor to robust optimization, the number of design variables to be simultaneously optimized is divided by grouping the scantling variables by the plane. A sequential optimization is performed group by group. As a verification example, a central column of a semi-submersible structure is optimized and compared with a conventional optimization of all design variables at once.

• Tunnel and Underground Space
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• v.22 no.4
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• pp.257-265
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• 2012

In this study, a series of CFD (Computational Fluid Dynamics) simulations carried out to evaluate the optimum design model of the internal flow path of drill bit. The Star-CCM+ code was adopted to simulate the multi-phase discharge flow of rock particles and flushing air during a drilling process. The input parameters for the flow simulation of rock particles and air were obtained from the in-situ drilling test results. After the three design factors were determined, the experimental design method (Taguchi method) was utilized to evaluate the optimum value of each factor.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.60-66
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• 2021

The core is extracted through drilling and used to evaluate the feasibility of developing mineral resources. To extract the core, a bit is installed in the forefront of the drilling device for drilling. Here, the drill bit receives stress due to direct friction against the ground. In addition, a bit appropriate for the given ground condition should be used due to the possibility of damaging a bit as a result of friction. This paper used a current bit model based on an impregnated bit and analyzed a new bit model that uses a stiffener of similar/disparate materials. The hardness and deflective strength were then evaluated by modeling the shape of impregnated bit through a calculation based on a theoretical formula. Through FEM analysis of the existing model and the new model, the stress and strain calculation results were optimized to minimize the stress and strain with a stress of 1.92 × 107 Pa and a strain of 9.6× 10-5 m/m.

• Explosives and Blasting
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• v.31 no.2
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• pp.1-5
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• 2013

Parameters of Swedish bench blast design was analyzed by robust design method. Orthogonal array which is adopted in this study was $L_9(3^4)$ and the parameters were hole diameter, explosive type, hole inclination and rock factor of 3 levels. Result of analysis showed that maximum and minimum burden are most affected by hole diameter, followed by explosive type, rock type and inclination of hole. Parameters affecting specific charge are in the order of rock type, explosive type and to specific drilling are hole diameter and explosive type. Cost analysis showed that robust design is capable of parameter optimization.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.2
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• pp.13-19
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• 2010

Due to the rapid spread of mobile handheld devices, industrial demands for micro-scale holes with a diameter of even smaller than $10{\mu}m$ in sapphire/silicon wafers have been increasing. Holes in sapphire wafers are for heat dissipation from LEDs; and those in silicon wafers for interlayer communication in three-dimensional integrated circuit (IC). We have developed a sapphire wafer driller equipped with a 532nm laser in which a cooling chuck is employed to minimize local heat accumulation in wafer. Through the optimization of process parameters (pulse energy, repetition rate, number of pulses), quality holes with a diameter of $30{\mu}m$ and a depth of $100{\mu}m$ can be drilled at a rate of 30holes/sec. We also have developed a silicon wafer driller equipped with a 355nm laser. It is able to drill quality through-holes of $15{\mu}m$ in diameter and $150{\mu}m$ in depth at a rate of 100holes/sec.