• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2365-2372
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• 2011

The Cogging Torgue is non-uniform torgue in motor which causes noise and vibration to synchronous motors such as BLDC motor, and regardless of load current, is generated by the interaction between permanent magnet rotor and stator slot which is the force of tangential direction that tends to move into the position where the magnetic energy of motor system is minimal. such Cogging Torgue shall be considered in design stage since it is the main factor of motor's noise and vibration. Understanding that Cogging Torgue is generated by the interaction between relatively low stage harmonic flux density gab of permanent magnet rotor and steel slot of stator. This study proposes the method if reducing Cogging Torgue using response surface method which is a kind of design if experiment.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1990.06a
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• pp.32-44
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• 1990

유압 Vane pump는 carming, rotor, vane에 의하여 둘러싸인 공간체적이 rotor의 회전과 함께 변화하면서 pump 작용을 한다. 즉 공간체적이 증가하는 동안은 유압이 저압으로 되어 흡입구에서 유압유를 흡입하고 vane의 존환점 (vane이 가장 많이 출한 점)을 지나면 공간용적이 감소하여 유압류는 고압으로 될 수 있도록 되어있다. 이때 vane은 관성력과 점성력 그리고 유압류의 압력에 의한 힘으로 vane 선단이 캠링의 내면에 밀착되어 회전하도록 되어있다. 유압 vane pump 베인 선단부의 윤활문제와 관련된 지금까지의 연구로서는 Hibi 등에 의한 압력평형형 베인모터, W.D Beck, T.C Edwards에 의한 베인형 콤푸렛셔 Ujiie 등에 의한 베인형 진공펌프, Ueno 등에 의한 가변용량형 베인펌프의 마찰특성에 관한 연구 및 베인 이간 현상에 관한 실험적 연구가 있다. 그러나 이와 같은 연구들의 베인과 캠링 슬라이딩 부분에 관한 취급들은 베인선단 슬라이딩 부분에 가해지는 변동가중이 불명확했기 때문데, 단순히 슬라이딩 부분의 면적이 작다는 이유로 단성유체 윤활상태일 것이라는 확정을 하였을 뿐, 실제적으로 어느 정도의 윤활 상태를 파악하기 위하여 회전하는 vane의 가학적인 거동을 확실하게 규명하고자 함이 본 연구의 목적이다.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.3
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• pp.250-257
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• 2017

It is desirable to have a way to predict the pressure drag due to various appendages attached to stern. As a mathematical model for these, a sphere and a singularity behind it, both in the uniform flow can be considered. We may use the Butler's sphere theorem to find the Stokes' stream function when the resulting flow is axisymmetric, and then the extended Lagally's theorem to get the force upon the sphere due to the singularity. Assuming the separation distance between the sphere and the singularity is small, the leading order approximation for the force is obtained and it is found out that if the separation distance and the square root of the strength of the dipole are of the same order, the effect of the image of the dipole with respect to the sphere is the most important.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.20 no.2
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• pp.96-104
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• 1984

This paper is on the prediction and response of the ship hull girder due to slamming of foreward flat bottom plate. The response with respect to foreward flat bottom is divided two kinds by estimating method. One is the estimation of impact forces by slamming, Another is the response of hull girder due to impact forces, that is, displacement, velocity, acceleration, etc. must calculate the values for considered ship hull girder. In this paper, therefore, was estimated only impact forces along ship ordinate of foreward. The analysis of data for estimation followed mainly papers of Ochi. These estimated data shall contribute for ship gull construction for basic optimum design. In particular, the estimated impact forces shall be given for the response of ship gull girder on the foreward flat bottom plate with characteristics of external forces.

• The Korean Journal of Zoology
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• v.39 no.1
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• pp.98-105
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• 1996

Studies on thermal adaptation postulate that optimal temperature of physiological properties matches a usually experienced body temperature (Tb) of organisms. Hibernating bats maintain Tb's that are slighdy higher than ambient temperatures (9$^{\circ}$-12$^{\circ}$C) of their wintering sites. To test the hypothesis that muscle function is adjusted to the Tb range of the hibernating animals, we examined contractile function of the biceps brachil muscle of Korean greater horseshoe bats, Rhinolophus ferrumequlnum korai (n = 5) at tissue temperatures between 1O$^{\circ}$ and 35$^{\circ}$C. Relative tetanic force (% of maximum force) was highest at temperatures of 1O$^{\circ}$-15$^{\circ}$C, which match well their Tb's during hibernation. Because non-hibernating endotherms with Tb of around 37$^{\circ}$C show the optimal temperature for muscle force over 30$^{\circ}$-40$^{\circ}$C, our results strongly suggest that the flight muscle of the bats may exhibit thermal adjustments according to their seasonal Tb's. The capacity to generate strong force at such low body temperatures may be adaptive, because bats must have muscles functioning to fly for occasional watering or excretion, or to move away from potential predators during hibernation.

• Journal of the korean academy of Pediatric Dentistry
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• v.26 no.2
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• pp.323-330
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• 1999

It is well recognized that a cross-bite tends to occur more frequently among Japanese, Chinese and Koreans more than among Europeans. A variety of functional appliances have already invented for the treatment of cross-bites. One of them is the FR III(by Rolf $Fr\ddot{a}nkel$) which applies a quite different philosophy based on the using vestibular region compared with other methods which utilize muscular forces applied directly on the teeth. The FR III also increases both the lack of muscular tension against the dental arch and the dentition and muscular forces which can then influence the teeth indirectly. This mechanism can achieve favorable developments with the basal bone, teeth, and alveolar bone. After using FR III to the anterior cross-bite patient with the eruption of a maxillary incisor the results were as follows: 1. Forward growth of maxilla and proclination of the upper incisor 2. Downward and backward rotation of the mandible 3. Increase the facial height 4. The case which was normal mandible, underdevelopmental maxilla, deeper overbite and more nagative overjet exhibited good prognosis

• Korean Journal of Social Welfare Studies
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• v.49 no.4
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• pp.159-193
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• 2018

This study aims to examine life experiences of single mothers according to three types of single parent families, divorced, widowed and unmarried and how they cope with their difficulties to become self-reliant and to identify strengths promoting self-reliance. The researchers analyzed personal, environmental and life factors by using the strengths perspective and discovered distinctive features of three types of single mothers that promote self-reliance. Data were collected by in-depth interviews with 20 single mothers, 4 widows, 8 divorced mothers and 8 unmarried single mothers. The results show that participants defined their experiences of self-reliance as a process to increase capability to accomplish their responsibilities as a mother, rather than as a completed goal. Increasing capability not only means achieving economic self-sufficiency, but also gaining psychosocial strengths that are developed by embracing one's own life, having sense of control and empowerment. This study identified commonalities and differences of strengths and resources and unique experiences of participants and proposed implications for policy and practice related to the roles of service delivery and support system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.72-79
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• 2019

Concrete is vulnerable to cracks due to volume changes caused by temperature changes, shrinkage during curing, external forces, or poor construction. In particular, concrete placed in electric power tunnel structures can generate cracks by a variety of factors. As a result, these tunnel structures require continuous maintenance. In this study, we investigated the mechanical properties of electric power tunnel concrete using alpha-calcium sulfate hemihydrate, which is an industrial byproduct that has excellent expansion performance. To compensate for the decrease in compressive strength when substituting alpha-calcium sulfate hemihydrate, based on previous research, we added 9% alpha-calcium sulfate hemihydrate and adjusted the amount of admixture while using the same amount of cement. We then evaluated the mechanical properties of the concrete. The results showed that the compressive strength of the concrete was higher than that of ordinary Portland cement (OPC), and the shrinkage of concrete was reduced by more than 30% compared to that of OPC. Therefore, adding 9% of alpha-calcium sulfate hemihydrate is expected to have a significant effect in reducing concrete cracks.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.32-40
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• 2018

In order to avoid excessive vibration, it is required to carry out a vibration analysis of heat-exchanger/nuclear-reactor at the design stage. Information of eigen-frequency in the vibration problem is required to evaluate safety of heat-exchange/nuclear reactor. This paper describes a numerical method, Galerkin's method, to solve the eigenvalue problem occurred in a cantilever beam. The beam is restrained with added mass and spring at the free end or a node point of a mode shape. The numerical results of eigen-frequency were compared with simple analytical and experimental results given by simple approach and simple test, respectively. It is found that Galerkin's method is applicable to estimate the eigen-frequency of the cantilever beam. The frequencies become lower with increasing the added mass and the frequencies increase with the spring force. It is shown the heavy added mass has a role of support on the flexible tube. The eigen-frequency of the first mode, for the system with the added mass mounted at the free end, can be calculated by the approximate analytical method existing with more or less accuracy.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.496-500
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• 2000

대형 구조물의 진동제어를 위하여 MR 유체 댐퍼를 사용한 반능동 제어기법에 대하여 연구하였다. 기존에 많이 사용되고 있는 수동제어기법은 일단 제어장치를 설치한 후에는 구조물에 실제로 작용하고 있는 외부 하중의 현재 특성에 대해서 적절히 반응할 수 없다는 제한을 가지고 있으며, 이를 극복하기 위하여 연구되어온 능동제어기법은 구조물이 진동을 감소시키기 위하여 구조물에 직접적으로 가해지는 커다란 제어력을 요구하며, 이로 인해 경우에 따라서는 불안정한 상태가 유발될 수도 있다는 점이 단점으로 지적되고 있다. 최근에 Spencer 등은 반능동 제어기법을 제안하였는데, 이는 수동제어장치의 제어특성을 On-Line 으로 조절하는 방식으로서 제어 가능한 수동제어기법으로도 불리운다. 구조물의 진동제어에 필요한 제어력이, 특수한 제어기구에서 발생되는 인위적인 힘이 아니라, 적절한 구조부재에서 발생되는 자연적인 부재력이므로, 무엇보다 강인하고 신뢰할 수 있는 제어기법이며, 이때 제어장치의 구조적 특성을, 측정된 구조물의 응답에 맞추어 적절히 조절함으로써 다양한 외부하중에 대해 보다 효율적인 제어가 이루어질 수 있도록 한 방법이다. 반능동제어를 위한 제어기로서는 Variable Orifice Dampers, Friction Controllable Isolators, Variable Stiffness Devices, Electro-Rheological (ER) Fluid Damper, Magneto-Rheological(MR) Fluid Damper등이 제안되고 있으며, 본 논문에서는 반응속도가 빠르고, 적은 파워만을 요구하며, 커다란 제어력을 낼 수 있는 MR Damper를 사용하여 지진하중을 받는 구조물의 반능동 제어게 대하여 연구하였다. MR Damper의 특성이 비선형이므로 이에 적합한 Sliding Mode Fuzzy Control(SMFC)기법을 사용하였으며 이때 SMFC 의 최적 설계를 위하여 Genetic Algorithm을 적용하였다. 제안된 제어기법의 실제 적용성을 검증하기 위하여 기존이 제어결과와 비교 검토하였으며, 그 결과로부터 MR Damper를 사용한 반능동 제어기법이 구조물의 진동제어에 매우 효과적임을 확인할 수 있었다.