• Journal of Advanced Marine Engineering and Technology
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• 제22권3호
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• pp.371-380
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• 1998

The flow patterns and dynamic properties of ship's propulsion mechanism of two-stage Weis-Fogh type are studied by the discrete vortex method. In order to study the effects of the interaction of the two wings two cases of the phase differences of the wing's motion are considered the same phase and the reverse phase. The flow patterns by simulations correspond to the photographs obtained by flow visualization and flowfield of the propulsion mechanism which is unsteady and complex is clearly visualized by numerical simulations. The time histories of the thrust an the drag coefficients on the wings are also calculated and the effects of the interaction of the two wings are numerically clarified.

• 한국유체기계학회 논문집
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• 제13권3호
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• pp.12-17
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• 2010

The orifice establishment which is improper does to change the entity differential pressure and occurs an error in flow measurement data. Because of this, the thermal power of nuclear power plant could be evaluated excessively and the safety margin could be decreased. In this paper, characters of orifice which is established abnormally was investigated. Specially, the orifice plate which is established in opposition case was modeled and analyzed. Finally, 14.4% was lowly measured differential pressure, when being established in the resultant opposition. And this result with EPRI and NRC experiences was similar.

• 대한기계학회논문집B
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• 제20권11호
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• pp.3639-3648
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• 1996

The effect of 15% pinched diffuser in a centrifugal air compressor with a cascade airfoil diffuser on the aerodynamic performance is investigated using a numerical approach. The commercial CFD code for three-dimensional, turbulent, compressible flow fields is executed for various mass flow rates at a design speed which can be obtained as long as the calculation succeeds. The pinched diffuser is found to help improve the instability of flow within vaneless diffuser space, especially the reverse flow near shroud, and to change both stall/surge line and choking line to increase the surge margin. It is also found to generate more favorable increase of static pressure in diffuser region, and to increase the resulting pressure ratio and efficiency.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2007년도 하계종합학술대회 논문집
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• pp.261-262
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• 2007

This paper proposes a new IFFT(Inverse Fast Fourier Transform) algorithm, which is proper for IMDCT(Inverse Modified Discrete Cosine Transform) of MPEG-2 AAC(Advanced Audio Coding) decoder. The IFFT used in $2^N$-point IMDCT employ the bit-reverse data arrangement of inputs and N/4-IFFT to reduce the calculation cycles. We devised a new data arrangement algorithm of IFFT input and N/$4^{n+1}$-IFFT and can reduce multiplication cycles, addition cycles, and ROM size.

• 열처리공학회지
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• 제8권1호
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• pp.12-23
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• 1995

In this a set of constitutive equation relevant to the analysis of thermo-elasto-plastic materials with phase transformation during quenching process was presented on the basis of continuum thermo-dynamic. In calculating the transient thermal stresses, temperature between coolant and specimen(SM45C) surface was determined from the heat transfer coefficient. A calculation was made for specimen with 40mm in diameter quenched in coolant from $820^{\circ}C$ and the results are as follow. Stresses at starting point of transformation always show the maximum tensile value. Reverse of stresses takes place after completion of transformation of inner part at specimen.

• 한국유기농업학회지
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• 제26권4호
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• pp.619-628
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• 2018

This study analyze the economic effect of chemical fertilizer. We used the input and output data, and the analysis variables include production output nitrogen, phosphoric acid, potassium, seeds, and labor. The main results are as follows. First, for spring potatoes, potassium increases to a certain level of output, but over a certain stage, the output decreases as the input increases. Optimal use of potassium in the calculation of spring potatoes can achieve the effect of reducing input costs and increasing output simultaneously. Second, radish In autumn, nitrogen increases to a certain level, but over a certain stage it represents a reverse U-shaped relationship in which output decreases as input increases. This means that reducing the amount of fertilizer input increases the output. This means that soil-related agricultural big data can contribute to the management of nutrients and greenhouse gas reduction in agricultural land.

• Current Optics and Photonics
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• 제4권6호
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• pp.566-570
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• 2020

The present paper computes the refractive indices of different corona viruses (H5N1, H5N2, H9N2, H4N6, FAdV and IBV) through reflectance analysis of a virus solution. The computational analysis indicates that the refractive indices of all viruses are negative at the signal of 412 nm. Further the numerical output shows that the infectious bronchitis viruses (family of novel corona viruses, COVID-19) have higher negative refractive indices as compared to other corona viruses. Finally refractive indices of the family of COVID-19 are investigated with respect to the EID (Electronic infusion Device) concentration of the viruses, showing that the refractive index which ranges from "-0.96725 to -0.999998" corresponds to '0.01 to 10000' EID virus concentration.

• 국제학술발표논문집
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• The 7th International Conference on Construction Engineering and Project Management Summit Forum on Sustainable Construction and Management
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• pp.133-137
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• 2017

Nuclear power plants in Korea are usually built based on a duplicated model; so the project cost data of the preceding unit can be used as reference when estimating the project cost for the succeeding unit. However, since the contracting method is oriented towards the price, empirical factors such as making top-down estimations using the reverse calculation method based on the completion cost of the preceding unit is dominant. In order to develop a project cost database to resolve such problems, the detailed cost boundary of the project cost data must be categorized by project and by system. This study proposes a method to connect the code of account with the base quantities and the IAEA account, and proposes a database structure for the development of a project cost estimation system. The estimation system developed in the future is expected to utilize the proposed project cost data structure.

• 전력전자학회논문지
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• 제14권5호
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• pp.372-378
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• 2009

태양광 발전시스템의 설치 용량이 증가함에 따라 시스템 효율을 개선하기 위한 연구가 활발히 진행되고 있다. 고성능 시스템의 설계 및 시험을 위해서는 태양전지의 모델링을 바탕으로 태양전지의 물리적 특성에 관해 정확히 이해하는 것이 중요하다. 그러나 태양전지의 모델은 다수의 파라미터가 얽힌 비선형 형태이며, 모델식의 파라미터 값을 얻기 위한 기존의 방식에서는 오차를 동반하는 실제와 다른 가정을 전제로 하므로 결과적으로 추출된 파라미터의 정확도가 저하되게 되는 단점이 있다. 따라서 본 논문에서는 제조사가 표준상태에서 측정하여 공개하는 태양전지의 I-V 커브로부터 다이오드의 이상계수와 역포화 전류를 구하고 이로부터 저항 성분이 없는 이상적인 태양전지의 I-V 커브를 도출한 뒤, 실측된 I-V 커브와 차이를 최소화하는 직·병렬 저항값을 추출하는 새로운 방식을 제안한다. 기존의 방식과 제안된 방식의 모델링을 통하여 얻은 파라미터를 이용해 구현한 I-V 커브와 실측 I-V 커브와의 상관관계를 최소자승법을 통해 계산함으로써 제안된 방법의 유용함을 증명하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제34권1호
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• pp.76-83
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• 2010

본 연구는 정렬배열 및 엇갈림배열 상태에 놓인 원주군 주위의 유동장 특성을 와법으로 수치계산한 것이다. 계산은 피치 비 Pt/D=1.25~2.0, 레이놀즈 수 Re=$4.0{\times}10^1{\sim}4.0{\times}10^4$의 범위 내에서 각 유동장의 순간 볼텍스 분포, 순간 속도분포를 계산하였다. 정렬배열 및 엇갈림 배열 모두 각 원주의 상방에서는 시계방향의, 하방에서는 반시계방향의 볼텍스가 발생하였다. 각 배열 모두 원주군 후방에서 역류의 발생여부는 피치 비와 레이놀즈 수에 기인하며, 같은 레이놀즈 수에서는 피치 비가 작을수록, 그리고 같은 피치 비에서는 레이놀즈 수가 클수록 원주군 후방에서 역류발생이 쉽게 일어났다. 그리고 그 경계영역은 정렬배열의 경우 피치 비 Pt/D=1.5, 레이놀즈 수 Re=400~4,000, 엇갈림 배열의 경우 피치 비 Pt/D=1.4, 레이놀즈 수 Re=40~400에 존재했다.