• 대한조선학회논문집
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• 제51권1호
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• pp.88-98
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• 2014

A supercavitation is modern technology that can be used to reduce the frictional resistance of the underwater vehicle. In the process of reaching the supercavity condition which cavity envelops whole vehicle body, a vehicle passes through transition phase from fully-wetted to supercaviting operation. During this phase of flight, unsteady hydrodynamic forces and moments are created by partial cavity. In this paper, analytical and numerical investigations into the dynamics of supercavitating vehicle in transition phase are presented. The ventilated cavity model is used to lead rapid supercavity condition, when the cavitation number is relatively high. Immersion depth of fins and body, which is decided by the cavity profile, is calculated to determine hydrodynamical effects on the body. Additionally, the frictional drag reduction associated by the downstream flow is considered. Numerical simulation for depth tracking control is performed to verify modeling quality using PID controller. Depth command is transformed to attitude control using double loop control structure.

• 대한기계학회논문집
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• 제12권6호
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• pp.1238-1245
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• 1988

본 연구에서는 단섬유가 첨가된 복합재료의 마찰 및 마멸특성에 대하여 보고 하고자 하며, 최근 공업용 고분자(engineering plastic)로 중오시되고 있는 PAI를 모 재로 하여 탄소섬유(graphite fiber), 유리섬유(glass fiber), TiO$_{2}$ 등이 첨가된 복합재료의 트라이볼로지(tribology) 특성에 대하여 고찰하고자 한다. 본 연구에서 사용된 복합재료에 포함된 단섬유들은 일정한 배열방향이 없이 마구잡이로 분포되어 있으며, 섬유특성에 따라 마멸메카니즘에 큰 차이가 있음을 본 연구 결과를 통하여 알 수 있다.

• 대한의용생체공학회:의공학회지
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• 제18권3호
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• pp.205-210
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• 1997

본 시험조사는 정형외과, 신경외과, 재활의학과 등에서 경부 척추를 물리적으로 고정하는 데 널리 사용되고 있는 연성, 토마스, 미네르바 및 필라델피아 경추보조기의 물성을 조사하여 새로운 경추보조기를 고안하기위한 기초자료를 얻기 위하여 이루어 졌다. 인장강도는 토마스 보조기가 가장 우수했으며 지속적인 마모를 통한 재료 관통시험에서는 미네르바 보조기가 가장 우수한 내구력을 가진 것으로 나타났다. 이러한 결과로 미루어 볼 때, 에틸렌수지를 구조체로 사용하고 피부에 통기성을 부여하기 위해 재료에 다공성을 제공하는 것이 좋을 것으로 사료된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.744-749
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• 2005

In this paper, a lens actuator for mobile devices is proposed using stack type piezoelectric materials. In general, the deformation of PZT actuators is not enough for lens motion when the allowed voltage is applied. The small stroke problem can be solved by accumulating a lot of small displacements in high frequency. In this paper, a new inch-worm type model for focusing actuator is suggested based on the interaction of inertial and frictional forces. Theoretical analysis and simulation using ANSYS are performed to verify the feasibility of the inch-worm PZT actuator model. Various types of clamps are considered to determine the effect of frictional force on the motion, and appropriate clamp-actuator models are proposed. The proposed models are experimentally verified and the experimental results show high correspondence with theoretical and simulated values. The inch-worm type focusing actuator enable a large stroke with 7.79 mm/sec with 10kHz and 10V.

• 한국공간구조학회논문집
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• 제20권4호
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• pp.185-192
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• 2020

A new lighting support structure composing of two-way wires and pulley, a pulley-type wireway system, was developed to improve the seismic performance of a ceiling type lighting equipment. This study verifies the seismic performance of the pulley-type wireway system using a numerical approach. A theoretical model fitted to the physical features of the newly-developed system was proposed, and it was utilized to compute a frictional coefficient between the wire and pulley sections under tension forces. The frictional coefficient was implemented to a finite element model representing the pulley-type wireway system. Using the numerical model, the seismic responses of the pulley-type wireway system were compared to those of the existing lighting support structure, a one-way wire system. The addition of the pulley component resulted in the increasement of energy absorption capacity as well as friction effect and showed in significant reduction in maximum displacement and oscillation after the peak responses. Thus, the newly-developed wireway system can minimize earthquake-induced vibration and damage on electric equipment.

• 대한치과교정학회지
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• 제46권2호
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• pp.73-80
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• 2016

Objective: The purpose of this study was to investigate the static (SFF) and kinetic frictional forces (KFF) in sliding mechanics of hybrid bracket systems that involve placing a conventional bracket (CB) or active self-ligating bracket (ASLB) on the maxillary anterior teeth (MXAT) and a passive SLB (PSLB) on the maxillary posterior teeth (MXPT). Methods: The samples consisted of two thoroughbred types (group 1, anterior-CB + posterior-CB; group 2, anterior-ASLB + posterior-ASLB) and four hybrid types (group 3, anterior-CB + posterior-PSLB-type 1; group 4, anterior-CB + posterior-PSLB-type 2; group 5, anterior-ASLB + posterior-PSLB-type 1; group 6, anterior-ASLB + posterior-PSLB-type 2) (n = 13 per group). After maxillary dentition alignment and maxillary first premolars removal in the stereolithographically-made typodont system, a $0.019{\times}0.025$-inch stainless steel wire was drawn through the right quadrant of the maxillary arch at 0.5 mm/min for 5 min. The SFF and KFF were measured with a mechanical testing machine and statistical analyses were performed. Results: Four different categories of SFF and KFF were observed among all groups (all p < 0.001). Group 1 demonstrated the highest SFF and KFF; groups 4 and 3 were second and third highest, respectively. The fourth category included groups 2, 5, and 6. Placing PSLBs on the MXPT resulted in significant SFF and KFF reductions in cases with CBs on the MXAT, but not in cases with ASLBs on the MXAT. Conclusions: These data might aid in the development of a hybrid bracket system that enables low-friction sliding of an archwire through the MXPT.

• 대한토목학회논문집
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• 제3권4호
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• pp.1-10
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• 1983

평면내력(平面內力)을 받는 철근(鐵筋)콘크리트슬래브, 판(板) 및 쉘 등(等)의 벽부재(壁部材)의 정확한 변형해석(變形解析)을 위하여 균열의 마찰일팽창거동(摩擦一膨脹擧動), 인장증강효과(引張增剛効果) 및 철근의 연결작용(連結作用)을 고려한 실제적인 해석모델을 수립하였다. 본 연구의 이론(理論)에 입각한 전산(電算)프로그램을 작성(作成)하여 포괄적인 변형해석이 수행되었으며, 새로운 개념의 마찰평형설계(摩擦平衡設計)와 종래(從來)의 무마찰평형설계(無摩擦平衡設計)에 입각한 철근설계에 대하여 각각 균열폭을 계산하여 비교하였다. 마찰설계개념에 의해 철근을 설계했을 경우 종래의 무마찰설계보다 변형량이 상당히 감소됨을 발견하였다. 또한, 철근직경과 균열간격이 균열폭에 미치는 영향을 연구(硏究)하였다. 본(本) 연구(硏究)에서 개발된 해석모델로 철근콘크리트부재(部材)의 좀 더 실제적이고 정확한 변형해석(變形解析)을 할 수 있게 되었다.

• Journal of Ship and Ocean Technology
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• 제1권1호
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• pp.35-47
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• 1997

The consequences associated with ships running aground depend very much on the soil characteristics of the sea bed and the geometrical shape of the ship bow. The penetration into the sea bed depends on these factors and the penetration is an important factor for the ship motion because it influences the ship heave and pitch motions as well as the friction between the ship and the soil. In this paper a rational calculation model is presented for the sea bed soil reaction forces on the ship bottom. The model is based on the assumption that the penetration of the ship bow generates a flow of pore water through the grain skeleton of the soil. The flow is governed by Darcy\`s law and it is driven by the pressure of the pore water at the bow. In addition to this pore water pressure, the bow is subjected to the effective stresses in the grain skeleton at the bow surface. These stresses are determined by the theory of frictional soils in rupture. Frictional stresses on the bow surface are assumed to be related to the normal pressure by a simple Coulomb relation. The total soil reaction as a function of velocity and penetration is found by integration of normal pressure and frictional stresses over the surface of the bow. The analysis procedure is implemented in a computer program for time domain rigid body analysis of ships running aground and it is verified in the paper through a comparison of calculated stopping lengths, effective coefficients of friction, and sea bed penetrations with corresponding experimental results obtained by model tests as well as large, scale tests.

• Tribology and Lubricants
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• 제35권3호
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• pp.169-175
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• 2019

In lithium-ion batteries (LIBs), the stress induced by the volume change of an electrode during charge-discharge processes may often cause the mechanical integrity of the electrode to degrade. Polymer binders with enhanced mechanical properties are preferred for improved mechanical integrity and cycling stability of the electrode. In addition, given that sliding and shearing between the polymer binder and components in the electrode may readily occur, frictional and adhesion characteristics of the polymer binder may play a critical role in the mechanical integrity of the electrode. In this study, frictional and adhesion characteristics of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) were investigated using a colloidal probe atomic force microscope. Friction loops were obtained under various normal forces ranging from 0 to 159 nN in air and electrolyte and then the interfacial shear strengths of PAN and PVDF in air were calculated to be $1.4{\pm}0.5$ and $1.3{\pm}0.3MPa$, respectively. The results show that in electrolyte, interfacial shear strength of PAN decreased slightly ($1.2{\pm}0.2MPa$), whereas that of PVDF decreased drastically ($0.06{\pm}0.01MPa$). Decreases in mechanical properties and adhesion in electrolyte may be responsible for the decrease in interfacial shear strength in electrolyte. The findings from this study may be helpful in developing polymer binders to improve the mechanical integrity of electrodes in LIBs.

• 대한치과교정학회지
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• 제31권2호통권85호
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• pp.271-281
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• 2001

치아에 부착된 bracket이 교정선을 따라 이동할때 필연적으로 bracket과 교정선, 결찰재 사이에 마찰력이 발생된다. 이에 저자는 동일한 bracket내에서 교정선의 종류, 결찰방법, 건조와 타액상태에 따른 마찰력 차이, 타액의 윤활제로서의 기능을 살펴보기 위해 본 연구를 시행하게 되었다. 본 실험에 사용된 bracket은 .18" ${\times}$ .025" slot의 상악 견치용 standard edgewise bracket(RMO. USA)이며, 교정선은 .016" , .016" ${\times}$ .022" 크기의 Cobalt-chromium(Elgiloy : RMO. USA), Nickel-titanium(Ni-Ti) (ORTHOLLOY : Goldstar Cable Co. KOREA), Beta- titanium(TMA : ORMCO Co., USA)의 2가지 형태의 3종을 이용하여 활주할 때의 마찰력을 만능시험기(Instron, M 1000 EC)를 사용하여 계측하여 다음과 같은 결론을 얻었다. 1. 각각의 동일조건하에서 교정선의 재질에 따른 마찰력은 Co-Cr, Ni-Ti, ${\beta}$-Ti순으로 증가하였다. 단, 타액상태에서 elastomeric으로 결찰한 .016" 군에서는 예외이다. 2. 각 조건하(건조/타액상태, .016" /.016" ${\times}$.022" ) 에서 결찰방법에 따른 마찰력은 elastomeric보다 stainless steel결찰에서 더 크게 나타났다(p<0.05). 3. 각각의 교정선과 결찰방법에서 타액 유무에 따른 마찰력은 stainless steel로 결찰한 .016" Co-Cr, Ni-Ti, ${\beta}$-Ti는 타액상태에서 감소하나, stainless steel로 결찰한 .016" ${\times}$.022" Co-Cr, Ni-Ti, ${\beta}$-Ti는 타액상태에서 증가하였다(p<0.05). 4. 각 조건하(건조/타액상태, elastomeric/stainless steel 결찰) .016" 과 .016" ${\times}$.022" 교정선 사이의 마찰력은 .016" ${\times}$.022" 교정선에서 증가하였다(p<0.05).