• 한국기계가공학회지
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• 제10권5호
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• pp.7-12
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• 2011

This study covers the optimum design of the 5-axis machine tool. In addition, the intelligent control secures structural stability through the optimum design of the structure of the 5-axis machine center, main spindle, and the tilting index table. The big requirement, like above, ultimately leads to speed-up operation. And this is inevitable to understand the vibration phenomenon and its related mechanical phenomenon in terms of productivity and its accuracy. In general, the productivity is correlated with the operation speed and it has become bigger by its vibration scale and the operation speed so far. Vibration phenomenon and its heat-transformation of the machine is naturally occurred during the operation. If these entire machinery phenomenons are interpreted through the constructive understanding and the interpretation of the naturally produced vibration and heat-transformation, it would be very useful to improve the rapidity and its stability of the machine operation indeed. In this dissertation, the problems of structure through heating, stability, dynamic aspect and safety about intelligent 5-wheel machine tool are discovered to examine. All these discoveries are applied to the structure in order to enhance the density of it. It aims to improve the stability.

• 한국안전학회지
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• 제28권4호
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• pp.58-65
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• 2013

Transportation and further expansion of social infrastructure was needed along the development of urbanization and population concentration. To use the underground space due to the lack of availability of land, it is inevitable to intersect between present structure and tunnel during construction. Soil grouting is one of the ground improvement methods to reinforce weak soil around the underground structures by injection of grouting liquid. Some of central columns of an upper structure are damaged during injection of grouting liquid by injection pressure. To investigate and improve the stability of the tunnel, three dimensional analysis are performed with full construction stages which includes the construction of present underpass, damaging columns of the underpass, reinforcing the columns by H-pile and shear walls, and excavation and construct tunnel. The arrangement of grouting holes such as curtain and horizontal type affects largely to the stability of upper structure and horizontal arrangement diminish the shear forces which is the cause of damage of central columns. The liquid injection type of reinforcement for tunnel is not recommended while the presence of upper structure with columns. Wall type reinforcing is utilize for permant support of upper structures which is affected by grouting injection pressure. H-pile is utilize for temporary support, but not for permanent since the sharing of shear forces is not much to shear wall during tunnel construction.

• 한국산업융합학회 논문집
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• 제11권4호
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• pp.201-208
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• 2008

This thesis is the result of the study about 'How we should develop the human resources program to gain human strength in the strategic environment of the future?' Once again, regional stability is interdependent with economic stability, political stability, and military stability of all the factors in the region. History shows that if a militarily capable regime lacks economic resources, then there is political pressure on the regime to use their military to acquire needed resources. The purpose of this study is to find the way that how to gain excellent human resources now and in the future. Military man power should be strong whenever. The Ministry of National Defense has "Reform Military Structure Plan". The focus of this Plan is Korean military strategy in the situation of the confrontation between South and North Korea and in the situation of the international relationship and the way of constructing the military strength for the future. To study these subjects, I reviewed the theories of "Acquisition Program of Human Strength" were developed and assessed the future strategic environment of the Korean Peninsula. From these studies, I suggest that The Ministry of National Defense should pursue preparing for the future military strategy and military structure. we should be skillful in supplementing the Human Strength. We should study about Military Revolution Plan and Human Strength structure for the future.

• 한국기계가공학회지
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• 제5권4호
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• pp.72-78
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• 2006

Inherent in machine tool structures are the vibrations which are generated by rotating parts such as motors, spindles and chucks. The vibrations not only hurt the precision machining but also damage the structures, and become more serious with time. Many of the old machine tools show severe vibrations for the desired accuracy of the modern industries. It is too much of a waste, however, to get rid of them as scraps. There have been many researches in order to suppress the vibrations of old machine tool structures using the tool post which utilizes actuators to compensate the existing vibrations and using the dampers or absorbers attached to some critical parts. In this paper, the dynamic properties are analyzed to obtain the natural frequencies and mode shapes of a machine tool structure which reflect the main reasons of the biggest vibrations under the given operating conditions. And the feasibility of improving the stability of the structure has been investigated with minor design changes and expenses. The result of the study shows that simple changes based on proper system identification can considerably improve the stability of the machine tool structure.

• 한국재료학회지
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• 제14권2호
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• pp.94-100
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• 2004

We have investigated the magnetic domain structure and the thermal stability of magnetotransport properties of IrMn biased spin-valves containing Co, CoFe and NiFe. The magnetic domain structures were imaged using a magneto-optical indicator film(MOIF) technique. To investigate the thermal stability, magnetoresistance(MR) was measured at annealing temperature(TANN) and room temperature($T_{RT}$) followed by the annealing. Domain imaging reveal that the increase of annealing temperature led to changes in the exchange coupling between the two ferromagnet(FM) layers through nonmagnetic layer rather than between FM and antiferromagnet. unlike the NiFe biased IrMn spin valve with large domains, MOIF pictures of Co and CoFe biased IrMn spin valve structures show the formation of many small microdomains. The magnetic structure, as revealed by the domain images, appeared unchanged while the MR dropped dramatically. From the combined giant magnetoresistance(GMR) and MOIF results, it was apparent that the decrease of MR ratio was not related to the spin valve magnetic structure up to about $350^{\circ}C$($T_{RT}$ ).

• Earthquakes and Structures
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• 제11권2호
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• pp.297-313
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• 2016

A virtual parameter is introduced into the formulation of the previously published integration method to improve its stability properties. It seems that the numerical properties of this integration method are almost unaffected by this parameter except for the stability property. As a result, it can have second order accuracy, explicit formulation and controllable numerical dissipation in addition to the enhanced stability property. In fact, it can have unconditional stability for the system with the instantaneous degree of nonlinearity less than or equal to the specified value of the virtual parameter for the modes of interest for each time step.

• 대한토목학회논문집
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• 제40권1호
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• pp.35-41
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• 2020

본 연구에서는 피복석으로 피복된 저 마루높이 구조물의 안정성을 검토하기 위해 2차원 수리실험을 수행하였다. 피복석 안정성은 구조물 상부, 전사면 및 후사면을 대상으로 파형경사와 여유고를 변화시키며 검토하였으며, 피복석의 주된 피해는 전사면 상부와 바다측 마루부에서 발생하였다. 수행된 2차원 실험결과를 이용하여 파복석의 안정계수 산정을 위한 경험식을 제안하였다.

• 한국기계가공학회지
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• 제19권1호
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• pp.100-107
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• 2020

As demand for high value-added products with hard materials increases, the line center is used for producing high value-added products in many industries such as aerospace, automobile fields. The line center is a key device for smart factory automation that can improve the production efficiency and the productivity. Therefore, the development of a mill-turn line center is necessary to produce high value-added products with complex shapes flexibly. In the mill-turn process, a milling process and a turning process are combined. In particular, the turning process needs to increase the rigidity of the spindle. The purpose of this study is to analyze the thermal-structural stability through thermo-structural coupled analysis for a mill-turn spindle with a curvic coupling. The maximum temperature and thermal stability of the spindle were analyzed by thermal distribution. In addition, the thermal deformation and thermal-structural stability of the spindle were analyzed through thermo-structural coupled analysis.

• Bulletin of the Korean Chemical Society
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• 제17권11호
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• pp.1045-1052
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• 1996

The effects of G-T mismatches on thermal stability, the base-pair lifetime and the global structure of a d(GCGTGCGC)2 duplex were studied by using 1H NMR, UV and CD spectroscopy. The existence of G-T mismatches was found to cause a noticeable change in the chemical environment of imino protons associated with significant decrease in the base-pair lifetime at the mismatched site as well as in thermal stability of the duplex itself. The melting transition of d(GCGTGCGC)2 was not cooperative at all at 100 mM or lower concentration of NaCl, but became cooperative at 500 mM or higher NaCl concentration. The melting temperature (Tm) of this duplex was 32℃ at 500 mM concentration of NaCl, which is much lower than that of d(GCGCGCGC)2 at the same NaCl concentration. This suggests that the decrease in stability may be ascribed to the decrease in the base-pair lifetime and the deviation from the normal structure due to the G-T mismatches. Adding berenil to d(GCGTGCGC)2 caused no observable change in the global structure but the large decrease in the base-pair lifetime and the stability of the duplex.

• 한국해양공학회지
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• 제35권6호
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• pp.403-413
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• 2021

As the size of ships increases, the size and output power of their thrusters also increase. When a large ship berths or unberths, the jet flow produced from its thruster has an adverse effect on the stability of quay walls. In this study, we conducted a numerical analysis to examine the impact of the thruster jet flow of a 30,000 TEU container ship, which is expected to be built in the near future, on the stability of a quay wall. In the numerical simulation, we used the fluid-structure interaction analysis technique of LS-DYNA, which is calculated by the overlapping capability using an arbitrary Lagrangian Eulerian formulation and Euler-Lagrange coupling algorithm with an explicit finite element method. As the ship approached the quay wall and the vertical position of the thruster approached the mound of the quay wall, the jet flow directly affected the foot-protection blocks and armor stones. The movement and separation of the foot-protection blocks and armor stones were confirmed in the area affected directly by the thruster jet flow of the container ship. Therefore, the thruster jet flows of ultra-large ships must be considered when planning and designing ports. In addition, the stability of existing port structures must be evaluated.