• Title/Summary/Keyword: Resistance variation

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A Study on the Optimal Forebody Forms for Minimum Wave Resistance (최소조파 저항성능을 갖는 최적 선수형상에 관한 연구)

  • Sung-Eun Kim
    • Journal of the Society of Naval Architects of Korea
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    • v.28 no.2
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    • pp.28-39
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    • 1991
  • A study on the optimization problems to find forebode shapes with minimum wavemaking and frictional resistance was performed. The afterbody was fixed as a given hull and only forebode offsets were treated as design variables. Design variables were divided into the offsets of given hull and small variation from them. For the wavemaking resistance calculation, Neumann-Kelvin theory was applied to the given hull and thin ship theory was applied to the small variation. ITTC 1957 model-ship correlation line was used for the calculation of frictional resistance. Hull surface was represented mathmatically using shape function. As object function, such as wavemaking and frictional rersistance, was quadratic form of offsets and constraints linear, quadratic programing problem could be constructed. The complementary pivot method was used to find the soulution of the quadratic programing problem. Calculations were perfomed for the Series 60 $C_{B}$=0.6. at Fn=0.289. A realistic hull form could be obtained by using proper constraints. From the results of calculation for the Series 60 $C_{B}$=0.6, it was concluded that present method gave optimal shape of bulbous bow showing a slight improvement in the wave resistance performance at design speed Fn=0.289 compared with the results from the ship theory only.

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Study on the Corrosion Characteristics in the Slag Line of SEN Oxide Refractory (산화물계 SEN내화물의 슬래그 라인부 침식특성 연구)

  • Sung, Young Taek;Son, Jeong Hun;Lee, Sung Seok;Bae, Dong Sik
    • Korean Journal of Materials Research
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    • v.24 no.1
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    • pp.53-59
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    • 2014
  • The corrosion resistance of submerged entry nozzle (SEN) materials were investigated for high-class steel manufacturing. Composite samples were fabricated by mixing $ZrO_2$, $Al_2O_3$, MgO, mullite, spinel, and carbon. The raw materials were mixed with attrition milling, compacted in a uniaxial pressure of 200MPa and calcined at $1000^{\circ}C$ for 3 h in $N_2$ atmosphere. The bulk density and apparent porosity of the calcined samples were measured by the liquid displacement method in water using Archimedes's principle. The corrosion resistance of the samples were measured by cup test with mold powder at $1550^{\circ}C$ for 2 h. The microstructure and elemental analysis of samples were observed by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), and X-ray diffraction pattern (XRD). The XRD result shows that the starting raw materials were crystalline phase. The microstructure of fabricated specimen was investigated before and after corrosion tests at $1000^{\circ}C$ and $1550^{\circ}C$ for 2h. $ZrO_2$-C composite showed good resistance in the slag corrosion test. Among the composite oxide materials, $ZrO_2-Al_2O_3$-C and $ZrO_2$-MgO-C showed better resistance than $ZrO_2$-C in the slag corrosion test. The diameter variation index of $ZrO_2$-C refractory was 16.1 at $1000^{\circ}C$ for 2 h. The diameter variation index of the $ZrO_2-Al_2O_3$-C refractory was larger than that of the $ZrO_2$-C refractory at $1550^{\circ}C$ for 2 h.

A Study on Properties of CuInSe2 Thin Film by Annealing (CuInSe2 박막의 열처리에 의한 특성분석)

  • Park, Jung-Cheul;Chu, Soon-Nam
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.24 no.2
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    • pp.162-165
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    • 2011
  • In this paper, $CuInSe_2$ thin film was prepared by use of the co-evaporation method with the variation of the substrate temperature in the range of $100^{\circ}C$ to $400^{\circ}C$. The film was annealed at $300^{\circ}C$ for an hour in a vacuum chamber at $3{\times}10-4$ Pa. After annealing, the thin film prepared at the substrate temperatures of $100^{\circ}C$ and $200^{\circ}C$ was observed. The XRD (x-ray diffraction) pattern of sample prepared at $100^{\circ}C$ showed the single phase formation of $CuInSe_2$. However, at $200^{\circ}C$, there was no apparent difference in the XRD pattern except a variation in the intensity of the peak. As the annealing treatment of substrate improved the crystal structure of the film, it affected to the increase of an electron mobility, resulted in an increase in conductivity and a decrease in resistance. As a results, when the substrate temperature was at $200^{\circ}C$ and $300^{\circ}C$, the sheet resistance was 1.534 $\Omega/\Box$ and 1.554 $\Omega/\Box$, respectively, and the resistivity was $1.76{\times}10-6\;{\Omega}{\cdot}cm$ and $1.7210-6\;{\Omega}{\cdot}cm$, respectively. From the absorption spectrum measurements, there was no variation between the before and after annealing conductions. And it means that the annealing step does not affect the thickness of the thin film.

Comparative study of prediction methods of power increase and propulsive performances in regular head short waves of KVLCC2 using CFD

  • Lee, Cheol-Min;Seo, Jin-Hyeok;Yu, Jin-Won;Choi, Jung-Eun;Lee, Inwon
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.11 no.2
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    • pp.883-898
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    • 2019
  • This paper employs computational tools to predict power increase (or speed loss) and propulsion performances in waves of KVLCC2. Two-phase unsteady Reynolds averaged Navier-Stokes equations have been solved using finite volume method; and a realizable k-ε model has been applied for the turbulent closure. The free-surface is obtained by solving a VOF equation. Sliding mesh method is applied to simulate the flow around an operating propeller. Towing and self-propulsion computations in calm water are carried out to obtain the towing force, propeller rotating speed, thrust and torque at the self-propulsion point. Towing computations in waves are performed to obtain the added resistance. The regular short head waves of λ/LPP = 0.6 with 4 wave steepness of H/λ = 0.007, 0.017, 0.023 and 0.033 are taken into account. Four methods to predict speed-power relationship in waves are discussed; Taylor expansion, direct powering, load variation, resistance and thrust identity methods. In the load variation method, the revised ITTC-78 method based on the 'thrust identity' is utilized to predict propulsive performances in full scale. The propulsion performances in waves including propeller rotating speed, thrust, torque, thrust deduction and wake fraction, propeller advance coefficient, hull, propeller open water, relative rotative and propulsive efficiencies, and delivered power are investigated.

Investigation of Spudcan Penetration Resistance in Layered Soil Deposits

  • Jan, Muhammad Asad;Nizamani, Zubair Ahmed;Park, Duhee
    • Journal of the Korean GEO-environmental Society
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    • v.22 no.1
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    • pp.13-20
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    • 2021
  • A suite of 3D large deformation finite element (FE) analyses was performed to investigate the load transfer mechanism and penetration resistance of spudcan foundations in heterogeneous soil profile consisting of sand and clay. The Elasto-Plastic models following Mohr-Coulomb and Tresca failure criteria were adopted for sand and clay, respectively. The accuracy of the numerical model was validated against centrifuge test measurements. The dense sand behavior with dilation is modeled using the non-associated flow rule. An investigation study consisting of key parameters, which includes variation in soil stratigraphy (sand-clay, sand-clay-sand), strength parameters of sand and clay (��' and su) and normalized height ratio of the sand layer (Hs/D) was conducted to assess the penetration behavior of spudcan. Based on calculated outputs, it was demonstrated that these parameters have a significant influence on the penetration resistance of spudcan. The calculated penetration resistance profiles are compared with the published (sand overlying clay) analytical model. It is confirmed that for the case of two-layer soil, the available theoretical model provides an accurate estimate of peak penetration resistance (qpeak). In the case of three-layer soil, the presence of a third stiff layer affects the penetration resistance profile due to the squeezing of the soil.

Electrically Programmable Fuse - Application, Program and Reliability (전기적 프로그램이 가능한 퓨즈 - 응용, 프로그램 및 신뢰성)

  • Kim, Deok-Kee
    • Journal of the Microelectronics and Packaging Society
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    • v.19 no.3
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    • pp.21-30
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    • 2012
  • Technology trend and application of laser fuse, anti-fuse, and eFUSE as well as the structure, programming mechanism, and reliability of eFUSE have been reviewed. In order to ensure eFUSE reliability in the field, a sensing circuit trip point consistent with the fuse resistance distribution, process variation, and device degradation in the circuit such as hot carrier or NBTI, as well as fuse resistance reliability must be considered to optimize and define a reliable fuse programming window.

Analysis of Switching Overvoltage on Operating Reclosing in Combined Transmission Systems (혼합송전계통에서 재폐로 시행시 개폐과전압 해석)

  • Lim, Kwang-Sik;Lee, Jong-Boem;Jung, Chae-Kyun;Kang, Ji-Won;Park, Hung-Sok
    • Proceedings of the KIEE Conference
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    • 2008.11a
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    • pp.391-393
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    • 2008
  • This paper is analysed by switching overvoltage on operating reclosing in 154 [kV] combined transmission systems. Combined transmission systems are modeled by EMTP/ATPDraw program. It is fault condition that simulate high resistance earth fault. The simulation is carried out considering variation of parameters such as resistance value of fault point and rate of underground line.

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A study on the Propulsive Characteristics of Stern-End-Bulb (STERN-END-BULB의 추진특성 연구)

  • Kim, Eun-Chan;Gang, Guk-Jin
    • 한국기계연구소 소보
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    • s.12
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    • pp.63-71
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    • 1984
  • A new kind of bulb called Stern-End-Bulb(SEB) for the improvement of the after part of fine hull forms was developed. The reduction of wave resistance and the improvement of the powering performance for the ship with SEB were shown by the ship model tests, At the same time, the characteristics of wave in the vicinity of the stern and the mechanism of the resistance reduction by SEB were investigated. By the systematical variation of the SEB size, the optimum size of SEB was obtained.

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