• 융합신호처리학회논문지
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• 제22권4호
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• pp.164-170
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• 2021

해상 풍력발전기의 운동 성능 분석 및 개선을 위한 연구가 수행되었다. 본 연구에 사용된 형상은 과거 연구를 참고하여 가져온 것이며 이를 바탕으로 수선면적의 크기를 80% 60% 40% 20%로 각각 설계하여 이에 따른 운동성능을 확인해 보았다. 해상상태는 Sea State 4, 5, 6에서 계산을 수행하였다. 계산과정에서는 상업용 전산 유체역학(ANSYS)과 AQUA를 사용하여 계산을 수행하였다. 전반적인 운동성능의 경우 이론과 동일하게 수선면적의 크기가 줄어들수록 HEAVE, ROll, PITCH와 같은 운동이 줄어드는 것을 확인할 수 있었다. 하지만 수선면적의 크기가 급격히 줄어든 형상의 경우 복원성 계산을 진행하였을 때 복원성능에서 만족하지 못하는 경우가 발생할 수도 있다는 것을 확인할 수 있었다. 또한 해상상태에 따른 적정의 수선면이 있을 수도 있다는 것을 확인할 수 있었다.

• 한국초전도ㆍ저온공학회논문지
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• 제19권1호
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• pp.26-29
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• 2017

We studied the distribution of the current density and its magnetic-field dependence in GdBCO coated conductors with AC bias currents using low temperature scanning Hall probe microscopy. We selectively measured magnetic field profiles from AC signal obtained by Lock-in technique and calculated current distributions by inversion calculation. In order to confirm the AC measurement results, we applied DC current corresponding to RMS value of AC current and compared distribution of AC and DC transport current. We carried out the same measurements at various external DC magnetic fields, and investigated field dependence of AC current distribution. We notice that the AC current distribution unaffected by external magnetic fields and preserved their own path on the contrary to DC current.

• Journal of Advanced Marine Engineering and Technology
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• 제30권1호
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• pp.73-80
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• 2006

In order to compute the radiated sound from a vibrating structure, the Rayleigh's integral equation has to be derived from the Helmholtz equation using Green's function. Generally, the surface velocity in the Rayleigh's integral equation uses the root mean square(rms) velocity. The calculation value is too large, because it's not considered cancelation. On the other hand. using the complex velocity, the sound pressure is calculated too small, because it considers that sound is perfectly canceled out. Therefore, this thesis proposes a correction factor(CF) which considers vibration modes and the method by which to calculate the radiating sound pressure. The theoretical results are compared with the experimental values, and the proposed method can be verified with confluence.

• 전자공학회논문지A
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• 제32A권1호
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• pp.36-44
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• 1995

For a parabolic reflector antenna, a simple method is presented for computing efficiently the average power pattern degradations caused by the surface roughness of the reflector and misalignments between the reflector and the feed. In this procedure, both nonuniform surface errors and nonuniform illuminations are employed. The assumptions to derive the expressions are that in each annular region of the antenna, the rms value of the surface roughness is known, and in a zone in a annular region, the phase error by misalignments is constant, and can be taken to its value at the center of the zone. Detailed parametric studies are performed with derived expressions to determine the effects of those errors and illumination tapers on parameters such as gain and sidelobe levels.

• 한국태양에너지학회 논문집
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• 제30권1호
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• pp.7-12
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• 2010

As many grid-connected photovoltaic power conditioning systems (PVPCS)are installed in many residential areas simultaneously, these have raised potential problems of network protection on electrical power system. One of the numerous problems is an Islanding phenomenon. In this paper, active frequency drift (AFD) method, one of the anti-islanding methods which is analyzed by current magnitude compensation and calculation of the fundamental component. Both harmonic component and RMS value of the output current for THD analysis are provided and verified by simulation.

• 한국태양에너지학회 논문집
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• 제29권6호
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• pp.75-80
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• 2009

Recently, as the grid-connected photovoltaic power conditioning systems (PVPCS) are installed in many residential areas, these have raised potential problems of network protection on electrical power system. One of the numerous problems is an Islanding phenomenon. In this paper, active frequency drift (AFD) method, one of the anti-islanding methods which is analyzed by current magnitude compensation and calculation of RMS value of the output power is proposed and verified by simulation.

• 한국전기전자재료학회논문지
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• 제20권3호
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• pp.250-256
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• 2007

We analyzed the effect of a pixel and all the inter-electrode capacitances in a unit pixel of TFT-LCDs on the gray scale capability. The pixel and all the inter-electrode parasitic capacitances were obtained from the tree dimensional profiles of potential distribution and molecular director considering lateral fields generated at the edge of the pixel. To obtain the RMS and kickback voltages of the pixel, we constructed an equivalent circuit of the panel containing all the parasitic capacitances. The calculation was performed though H-SPICE. As results, we confirmed that the pixel becomes smaller, the effect of parasitic capacitances on the gray scale capability becomes larger.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.1358-1365
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• 2008

By Computational Fluid Dynamics simulation, general information about an internal gas flow can be achieved. This will be very useful to improve flow inside the pipes and snubber system. Relating with hydrogen compressing system, which plays an important role in hydrogen energy utilization, this method should be a powerful tool to observe the flow quickly and clearly. Flow pressure characteristic analysis of hydrogen gas flowing through the snubber of a reciprocating compressor is presented in this paper. The CFD calculation of pressure pulsation and pressure loss are very close to the experiment. Therefore, consequently development of the better hydrogen compressing system will be observed with better understanding by CFD.

• Journal of Advanced Marine Engineering and Technology
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• 제23권5호
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• pp.711-718
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• 1999

Current turbulence models including modified $K-{\varepsilon}-{\tau}$ turbulence model do not predict compression effect on turbulence accurately in an internal combustion engine. The $K-{\varepsilon}-{\tau}$ turbulence model was suggested to improve the predictability of compression effect by We et al. In this paper a numeri-cal study was performed to clarify the applicability of the $K-{\varepsilon}-{\tau}$ turbulenc model to the calculation of the in-cylinder flow of an axisymmetric engine. THe results using $K-{\varepsilon}-{\tau}$ turbulence model are compared to those from the modified $K-{\varepsilon}-{\tau}$ turbulence model and experimental data. The mean veloc-ity and rms velocity profiles using $K-{\varepsilon}-{\tau}$ turbulence model showed a better agreement with an experimental data than those of modifid $K-{\varepsilon}-e$ turbulence model.

• Journal of Advanced Marine Engineering and Technology
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• 제23권5호
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• pp.662-670
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• 1999

A numerical prediction was performed to clarify the air motion in the cylinder of an axisymmet-ric four-stroke reciprocating engine at its intake and compression stage. A scheme of finite volume method is used for the calculation. Modified $k-{\varepsilon}$ turbulence model is adopted and wall function is applied to the grids near the wall. The predicted mean velocity and rms velocity profiles showed a reasonable agreement with an available experimental data at its intake and compression stage. The predicted in-cylinder flow fields show that a strong turbulent twin vortex structure is pro-duced during induction but it commences to decay rapidly around inlet valve closure. The mean velocity continues to fall to a low level during compression but the turbulence intensity attains an approximate constant level.