• The korean journal of orthodontics
• /
• v.31 no.2 s.85
• /
• pp.271-281
• /
• 2001

The Purpose of this study was fourfold - to evaluate the general laws of friction applied to orthodontic conditions, to compare archwire materials under these controlled conditions, to compare ligation method, and to measure the effect of the artificial saliva on friction with these materials Three wire alloys (Cobalt-chromium, Nickel-titanium, Beta-titanium) in two size wires (.016" , .016" ${\times}$.022" ) were examined respect to the bracket (.018" ${\times}$.025" standard), and two ligature material (stainless steel, elastomeric) in dry and wet conditions The results were as follows, 1. The order of frictional force against alloy materials was Co-Cr (lowest), Ni-Ti, and ${\beta}$-Ti(highest) - with the exception of elastomeric ligation under wet conditions. 2. S.S. ligation gave rise to significantly greater friction than elastomeric ligation did. 3. Testing in the presence of saliva, rather than in dry conditions, decreased the frictional force for S.S. ligation with .016" Co-Cr, Ni-Ti, ${\beta}$-Ti. but, increased the frictional force for S.S. ligation with .016" ${\times}$ .022" Co-Cr, Ni-Ti, ${\beta}$-Ti. 4. .016" ${\times}$.022 " wire generated more friction than .016" wire.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.2087_2088
• /
• 2009

최근 도심지 전력수요의 증가로 송전선로 건설의 필요성이 증대되고 있으나, 가공송전선로가 가지고 있는 한계 때문에 지중송전선로의 건설이 증대되고 있는 추세이다. 이러한 상황에서 지중 및 가공을 포함하는 거시적인 관점에서 지락 및 단락과 같은 고장시의 대전류 현상에 대한 연구는 어느 정도 시도된 바가 있으나, 지중케이블 시스템 자체에 미치는 영향에 대해서는 그 연구가 미비한 것이 현실이다. 특히 단락고장의 경우 고장전류의 크기도 크지만 고장전류 발생에 따른 전자력을 동반하게 되어 케이블 및 접속함, 각종 금구류에 전기적, 기계적인 스트레스를 야기할 수 있다. 따라서 본 논문에서는 최근 발생한 단락고장 상황을 고려하여 전자력에 의한 케이블의 거동특성을 확인하기 위해 154kV OF케이블 3상단락 실증시험을 시행하였고, 실증시험시 촬영된 고속카메라 영상을 이용한 변위분석 결과와 유한요소법을 이용하여 계산된 케이블의 변위 특성을 비교 분석하여 유한요소법을 이용한 계산방법이 케이블 거동특성 분석에 적합한지 그 실효성을 검증하고자 한다.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.2091_2092
• /
• 2009

지중케이블 시스템에서의 고장은 필연적으로 대전류 현상을 수반하는 경우가 대부분으로서 고장전류는 고장 케이블 자체와 인접해 있는 타 선로 및 통신선 등에 악영향을 미칠 가능성이 크고, 초고압 케이블의 운전전압 레벨이 지속적으로 증가하고 있는 상황에서 사고의 파급 및 위험정도 또한 지속적으로 증가하고 있다. 특히, 단락 고장의 경우 고장전류의 크기도 크지만 고장전류 발생에 따른 전자력을 동반하게 되어 케이블 및 접속함, 각종 금구류에 전기적, 기계적인 스트레스를 야기할 수 있다[1]. 따라서 본 논문에서는 지중케이블의 삼각배열 구간의 단락전자력 영향을 최소화하기 위한 방안을 모색하기 위하여 154kV OF케이블 3상 단락 실증시험을 2회 시행하였고, 유한요소법을 이용하여 단락전자력 발생시 클리트 설치간격에 따른 케이블 변위를 계산함으로써 케이블의 단락 전자력 영향 검토결과를 기술하였다.

• Smart Structures and Systems
• /
• v.18 no.4
• /
• pp.683-705
• /
• 2016

A semi-active algorithm for edgewise vibration control of the spar-type floating offshore wind turbine (SFOWT) blades, nacelle and spar platform is developed in this paper. A tuned mass damper (TMD) is placed in each blade, in the nacelle and on the spar to control the vibrations for these components. A Short Time Fourier Transform algorithm is used for semi-active control of the TMDs. The mathematical formulation of the integrated SFOWT-TMDs system is derived by using Euler-Lagrangian equations. The theoretical model derived is a time-varying system considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar, mooring system and the TMDs, the hydrodynamic effects, the restoring moment and the buoyancy force. The aerodynamic loads on the nacelle and the spar due to their coupling with the blades are also considered. The effectiveness of the semi-active TMDs is investigated in the numerical examples where the mooring cable tension, rotor speed and the blade stiffness are varying over time. Except for excessively large strokes of the nacelle TMD, the semi-active algorithm is considerably more effective than the passive one in all cases and its effectiveness is restricted by the low-frequency nature of the nacelle and the spar responses.

• Tunnel and Underground Space
• /
• v.5 no.2
• /
• pp.104-113
• /
• 1995

Shear strength of the discontinuity on which the pre-failure of rock slope was occurred during surface excavation was measured through the direct shear test using core samples obtained in-situ. Internal friction angle was increased as the roughness of discontinuity surface(JRC) was increased. Results of the tilt test using core samples of higher JRC also showed very similar trend as those of the direct shear test. When the samples replicated from natural cores were used int he tilt test, results of friction angles showed almost perfect continuation of the residual friction angles from the direct shear test. However, when the gouge material existed in the discontinuity the internal friction angle strongly depended upon the rate of filling thickness to the height of asperity irrespective of the JRC. Based on the results of both direct shear test and tilt test internal friction angle and cohesion of discontinuity, which reflect the in-situ conditions fo pre-sliding failure and also can be used for the optimum design of support system, were assessed. Two kinds of support measures which were expected to increase the stability of rock slope were considered; lowering of slope face angle and installation of rock cable. But, it was found that the first method might lead to more unstable conditions of rock slope when the cohesion of discontinuity plane was negligibly low and in that case the support systems of any kind which could exert actual resisting force were needed to ensure the permanent stability of rock slope.

• Journal of the Korean Society of Safety
• /
• v.20 no.1 s.69
• /
• pp.1-6
• /
• 2005

Stick type ignition coil is new development that connect directly with ECU(Electronic control unit), without needing a spark plug cable and distributor. Glass-fiber reinforced ploymeric composites provide the desirable properties of high stiffness and strength as well as low specific weight. Stick type ignition coil jacket is using PBT CF30 resin. PBT CF30 resin is a kind of electric insulation which is a superior engineering plastic that is used to prevent the leakage of the electrical current. If PET receive a mistake of design or excessive force when HV terminal oppress on jacket, it can happen to crack. Local stress concentrations occurring on the contact surface, the contact phenomenon becomes a direct cause to the wear and failure of mechanical structures. When it is cracked, it can allow a leakage of the electrical current. So, in this study, we analyze the contact stress to PBT jacket using ANSYS program, when HV terminal oppress on jacket. We suppose PBT to be Jacket and we analyzed contact stress that happens in PET like PBT analysis method. We compared the use of PBT and PET.

• Steel and Composite Structures
• /
• v.19 no.3
• /
• pp.615-633
• /
• 2015

Composite steel-concrete beams are used frequently in situations where axial forces are introduced. Some examples include the use in cable-stayed bridges or inclined members in stadia and bridge approach spans. In these situations, the beam may be subjected to any combination of flexure and axial load. However, modern steel and composite construction codes currently do not address the effects of these combined actions. This study presents an analysis of composite beams subjected to combined loadings. An analytical model is developed based on a cross-sectional analysis method using a strategy of successive iterations. Results derived from the model show an excellent agreement with existing experimental results. A parametric study is conducted to investigate the effect of axial load on the flexural strength of composite beams. The parametric study is then extended to a number of section sizes and employs various degrees of shear connection. Design models are proposed for estimating the flexural strength of an axially loaded member with full and partial shear connection.

• Journal of Ocean Engineering and Technology
• /
• v.17 no.3 s.52
• /
• pp.7-12
• /
• 2003

The Navy has tested the holding capacity of many kinds of anchors in order to propose the design chart for the holding capacity of drag-embedment anchors. The design chart is only applicable up to the cable bottom angle 60 when load is raised to the ultimate weight. However, the anchor experiences a significant uplift force when the angle is above 60 in shallow seas. In this paper, the procedure for the estimation of the holding capacity of anchors in mud is proposed. Drag-embedment anchors do not function well when there is a significant uplift component of load in soft seafloor materials, such as mud. Under these loading and seafloor conditions, gravity anchors seems to be more efficient. However, they are too heavy for their holding capacity. Therefore, suction pile (hollow concrete block) is more beneficial to the foundntion of silt protector in shallow sea with mud seafloor materials.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.21 no.3
• /
• pp.43-50
• /
• 1984

A body form, which experiences minimum vertical wave-exciting forces in the vicinity of a prescribed wave frequency in water of finite depth, is obtained by an approximate method. Its configuration has the symmetry with respect to the vertical axis, expressed in terms of exponential functions. By distributing three-dimensional pulsating sources and dipoles on the immersed surface of the body, a velocity potential is determined and subsequently hydrodynamic forces including the 2nd-order time-mean drift forces are calculated. The dynamic behavior of the body moored in irregular waves is investigated numerically by using central difference method. Hereby irregular wave trains are simulated with examining its repeatability by comparing the resulting spectrum with original one. Numerical results indicated that the body form obtained from the present analysis possesses in general a favorable hydrodynamic characteristics in comparison with a spherical buoy and that the maximum excursion of the body can be significantly reduced by setting pre-tension of an appropriate amount in the mooring cable.

• Geomechanics and Engineering
• /
• v.18 no.3
• /
• pp.277-289
• /
• 2019

In this study, an innovative anchoring approach has been developed dealing with all relevant aspects in consideration of previous works. An ultimate pulling force calculation of anchor is presented from a geotechnical point of view. The proposed umbrella anchor focuses not only on the friction resistance capacity, but also on the axial capacity of the composite end structure and the friction capacity occurring around the wedge. Even though the theoretical background is proposed, in-situ application requires high-level mechanical design. Hence, the required parts have been carefully improved and are composed of anchor body, anchor cap, connection brackets, cutter vanes, open-close ring, support elements and grouting system. Besides, stretcher element made of aramid fabric, interior grouting system, guide tube and cable-locking apparatus are the unique parts of this design. The production and placement steps of real sized anchors are explained in detail. Experimental results of 52 pullout tests on the weak dry soils and 12 in-situ tests inside natural soil indicate that the proposed approach is conservative and its peak pullout value is directly limited by a maximum strength of anchored soil layer if other failure possibilities are eliminated. Umbrella anchor is an alternative to conventional anchor applications used in all types of soils. It not only provides time and workmanship benefits, but also a high level of economic gain and safe design.