• Journal of Advanced Marine Engineering and Technology
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• 제33권5호
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• pp.729-737
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• 2009

This paper introduces the machine tools feed system, which can be optimized the control's performance through simulation and the adjustment of the mechanical components. One method simulates the frequency response of the speed-loop with the design value using the MATLAB application, so that all of the interpolation axis can be equal to the response bandwidth, resulting in a high accuracy rate. The other method sees the mechanical component being adjusted by analyzing the results of various experiments. Lastly, this client's program is able to change the parameters that are related to the FFD, as well as the parameters in the friction compensation of the OPEN-CNC.

• 한국정밀공학회지
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• 제18권6호
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• pp.182-187
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• 2001

Much research efforts have been made on the equal-channel angular pressing(ECAP)that produces ultra-fine grain size materials. Recently many materials have been tested for ECAP process, and in this paper pure-Zirconium is considered due to its applicability to nuclear reactors. Among many process parameters of ECAP, frictional effects on the deformation behavior of materials and on the stress distribution of die have been investigated. The finite element method has been employed in order to investigate this issue, and experiments have also been made to verify the numerical results.

• 소성∙가공
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• 제13권4호
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• pp.382-387
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• 2004

The continuous confined strip shearing (CCSS) based on the equal channel angular pressing (ECAP) was modeled by means of a rigid-plastic two-dimensional finite element method (FEM). Parallel to the simulations, samples of AA 1050 sheets were experimentally deformed by CCSS. The CCSS deformation led to the formation of through thickness texture gradients comprising a strong shear texture in the sheet center and weak shear textures in the sheet surfaces. FEM analysis revealed variations in the strain component $\varepsilon_13$ along the sample thickness direction, which gave rise to the evolution of different textures. A high friction between the sample and die surface was responsible for lowering intensities of the shear texture components in thickness layers close to the surfaces.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.523-528
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• 2008

The accurate distribution of flow rate has been a very important part to control the air change rate since introduction of house ventilation system. An inappropriate selection of fan due to incorrect prediction of pressure loss in duct brings energy loss. In the previous study the pressure loss of general spiral duct was measured and database was constructed for finding correct loss factors in fitting upper stream. The purpose of this study is to compare and investigate the error range of flow rate by applying T-Method to bilateral symmetry and asymmetry layout of duct. The results of this study are as following. It is demanded to decide accurate size under duct design for house ventilation system. Because the small amount of Flow rate was considered at that time. The error range was 3.17% on case1 and 3.52% on case2. The error range difference was 0.35%.

• 한국지반공학회논문집
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• 제35권8호
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• pp.31-42
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• 2019

최근에 시공된 건축현장의 73개 설계 자료를 분석하여 매입 PHC말뚝에 대한 설계 현황을 고찰하였다. 매입 PHC말뚝의 설계에서 사용하고 있는 극한지지력 산정공식에 따라 산정한 전체지지력에 대한 주면마찰력의 분담율(SRF)는 20~53%로 나타났다. 극한주면마찰력이 과소평가되는 지지력 산정공식에 대한 개선이 필요한 것으로 판단되었다. PHC말뚝의 재료 성능에 대한 평균 설계 효율은 약 70%이었으며 지반 지지력에 대한 평균 설계 효율은 약 80%이었다. 즉, 지반의 설계 효율은 PHC말뚝의 설계 효율보다 약간 높은 수준으로 나타나고 있었다. 이는 지반 지지력을 설계하중보다 동등한 수준 또는 그것보다 약간 높은 수준으로 계산하고 있는 설계 현황에 기인한 것으로 판단되었다. 지반의 허용지지력을 PHC말뚝의 허용연직압축하중보다 높은 수준으로 산정하여야 할 것으로 판단되었다. 매입 PHC말뚝의 지지력 산정공식에서는 극한주면마찰력이 극한선단지지력보다 상대적으로 2.2배 정도 낮은 수준으로 계산되었다. 매입 PHC말뚝의 설계에서 적용하고 있는 극한지지력 산정공식들은 모두 국외 지반을 대상으로 개발되었으며 국내 지반에 대한 적용성 검증 없이 도입되어 사용되어 오고 있었다. 매입 PHC말뚝의 설계에서 적용할 지지력 산정공식의 개선이 이루어져야 할 것으로 판단되었다.

• Geomechanics and Engineering
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• 제11권6호
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• pp.739-756
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• 2016

The shear strength reduction finite element method (SSRFEM) is a powerful tool for slope stability analysis. The factor of safety (FOS) of the slope can be easily calculated only through reducing effective cohesion (c′) and tangent of effective friction angle ($tan{\varphi}^{\prime}$) in equal proportion. However, this method may not be applicable to soil slope under wetting-drying cycles (WDCs), because the influence of WDCs on c′ and $tan{\varphi}^{\prime}$ may be different. To research the method of estimating FOS of soil slopes under WDCs, this paper presents an experimental study firstly to investigate the effects of WDCs on the parameters of shear strength and stiffness. Twelve silty clay samples were subjected to different number of WDCs and then tested with triaxial test equipment. The test results show that WDCs have a degradation effect on shear strength (${\sigma}_1-{\sigma}_3)_f$, secant modulus of elasticity ($E_s$) and c′ while little influence on ${\varphi}^{\prime}$. Hence, conventional SSRFEM which reduces c′ and $tan{\varphi}^{\prime}$ in equal proportion cannot be adopted to compute the FOS of slope under conditions of WDCs. The SSRFEM should be modified. In detail, c′ is merely reduced among shear strength parameters, and elasticity modulus is reduced correspondingly. Besides, a new approach based on sudden substantial changes in the displacement of marked nodes is proposed to identify the slope failure in SSRFEM. Finally, the modified SSRFEM is applied to compute the FOS of a slope example.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.1287-1294
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• 2006

A pile is compressed with settlements when loading and bearing capacity is altered along relative displacement of pile/soil on settlement and compression. Settlements of pile displaying limit skin friction is different from displaying tip resistance. Therefore, it is an error in traditional method that bearing capacity of pile is estimated from the sum of limit skin fraction and tip resistance. Accordingly, development of design method considering behavior of load-settlement is needed. In this study, we would like to establish the base for development of design method considering bearing capacity altering along displacement on settlement and compression. For this, we established system and substance of design method. And in order to establish relationship of load-settlement of pile on the type of soil, we analyzed and arranged existing database and pile loading test. On design method, settlement is assumed gradually on each capacity level being assumed gradually. Bearing capacity developing on the pile is obtained on each settlement level. Until the obtained bearing capacity will be equal to assumed capacity, this process is continued with increasing settlement. Load-settlement curve for soil classification is sketched in the process computing settlement on assumed capacity. This design method will be materialized by computation program.

• 설비공학논문집
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• 제11권6호
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• pp.861-870
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• 1999

An experimental study was carried out to investigate the effects of using various shapes of turbulence promoter on the heat-transfer enhancement of 2-D and 3-D arrays of rectangular modules in a rectangular channel for design of noiseless and low-powered cooling fan in the electronic systems. Measurements of heat/mass transfer coefficients were made using a naphthalene sublimation technique, and the friction factors were measured for Reynolds numbers in the range$3.3{\time}10^3$~$1.6{\time}10^4$. Flow visualization was peformed by oil-film method. It was found that heat transfer and pressure drop increased remarkably due to the existence of the promoter. The results of the performance evaluation based on equal pumping power were showed that substantial heat-transfer enhancement was obtained at low Reynolds number range by use of a turbulence promoter.

• 한국소음진동공학회논문집
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• 제22권7호
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• pp.619-625
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• 2012

Since the fuel is always exposed to turbulent flow, the grid strap shows flow induced vibration characteristics that impact on the nuclear fuel soundness. The dynamic behavior of grids in nuclear fuels is quite complex, since two pairs of spring and dimple support are contacted with rods by friction in the limited space. This paper focuses on investigation of the grid strap(test fuel strap, TFS) vibration in one cell. TFS consists of a single spring and double dimples. To identify the grid strap vibration, modal analysis of the strap is performed using finite element method(FEM). Modal testing on a $5{\times}5$ grid structure without rods is performed. The modal testing results are compared to analytic results. In addition, random test considering rod effect is performed about a $5{\times}5$ grid with rods under real contact condition in the air. Finally, the strap vibration of a $5{\times}5$ fuel bundle in investigation of flow induced vibration(INFINIT) facility is measured in real fluid velocity condition without heating. It is shown that modal frequencies from the test are almost equal to those peak frequencies in the INFINIT test.

• 한국가시화정보학회지
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• 제8권1호
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• pp.53-60
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• 2010

Experimental investigations were conducted to study the characteristics of turbulent swirling flow in an axisymmetric annuli. Swirl angle measurements were performed using a flow visualization technique using smoke and dye liquid for Re=60,00080,000. Using the two-dimensional particle image velocimetry method, we found the time-mean velocity distribution and turbulent intensities in water with swirl for Re=20,000, 30,000, and 40,000 along longitudinal sections. Neutral points occurred for equal axial velocity at y/(R-r)=0.70.75, and the highest axial velocity was recorded near y/(R-r)=0.9. Negative axial velocity was observed near the convex tube along X/(D-d)=3~23. Another experimental study was performed to investigate heat transfer characteristics of turbulent swirling flow in an axisymmetric annuli. Static pressure, and local flow temperature were measured using tangential inlet condition and the friction factors and Nusselt number were calculated for several Reynolds numbers.