• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1995년도 춘계학술대회논문집; 전남대학교, 19 May 1995
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• pp.196-201
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• 1995

The broadband and discrete sources of sound in small cooling fans of propeller type and centrifugal type were investigated to understand the turbulent vortex structures from many bladed fans using ANSI test plenum for small air-moving devices (AMDs). The noise measurement method uses the plenum as a test apparatus to determine the acoustic source spectral density function at each operating conditions similar to real engineering applications based on acoustic similarity laws. The characteristics of fans including the head rise vs. volumetric flow rate performance were measured using a performance test facility. The sound power spectrum is decomposed into two non-dimensional functions: an acoustic source spectral distribution function F(St,.phi.) and an acoustic system response function G(He,.phi.) where St, He, and .phi. are the Strouhal number, the Helmholtz number, and the volumetric flow rate coefficient, respectively. The autospectra of radiated noise measurements for the fan operating at several volumetric flow rates,.phi., are analyzed using acoustical similarity. The rotating stall in the small propeller fan with a bell-mouth guided is mainly due to a leading edge separation. It creates a blockage in the passage and the reduction in the flow rate. The sound power levels with respect to the rotational speeds were measured to reveal the mechanisms of stall and/or surge for different loading conditions and geometries, for example, fans installed with a impinging plate. Lee and Meecham (1993) studied the effect of the large-scale motions like impinging normally on a flat plate using Large-Eddy Simulation(LES) and Lighthill's analogy.[ASME Winter Annual Meeting 1993, 93-WA/NCA-22]. The dipole and quadrupole sources in the fans tested are shown closely related to the vortex structures involved using cross-correlations of the hot-wire and microphone signals.

• 한국작물학회지
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• 제57권3호
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• pp.296-300
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• 2012

국내산 콩과 수입콩의 판별에 NIRS를 도입함으로써 보다 빠르고 정확한 식별분석을 하고자 실험을 수행하였다. NIRS를 사용하여 400~2,500 nm 범위에서 콩 분말의 파장을 측정하였으며, 측정된 spectrum은 WINISI II program 을 이용하여 수처리와 회귀분석을 하였다. 검량식 작성을 위한 수처리는 spectrum을 1차미분 및 4 nm gap으로 조정한 것이 가장 적합하였으며, 회귀식은 변형부분최소자승회귀법(Modified partial least squares regression)이 우수하였다. MPLS 회귀분석시 원산지 판별을 위해 loading value를 국내산 콩은 '100', 수입콩은 '1'로 처리하여 검량식을 작성하고 그 적합성을 검증한 결과 factor가 10일 때 도출된 calibration equation의 상관값이 0.98, 교차검증의 상관값이 0.94를 나타내어 상관도가 높음을 알 수 있었다. 따라서 NIRS를 이용한 국내산 콩과 수입콩의 판별분석이 가능할 것으로 판단되었다.

• 한국광학회지
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• 제3권4호
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• pp.227-233
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• 1992

분할디스크형 글라스레이저 증폭기를 개발하기 위하여 이를 해석 설계할 수 있는 시뮬레이션 코드를 작성했다. 레이저매질에서의 열부하를 감소시키고, 플래시램프의 방사스펙트럼과 레이저글라스의 흡수 스펙트럼 간의 결합효율을 높이기 위해서는 전류밀도를 2000-4000A/$\textrm{cm}^{2}$로 유지하여 단파장에서의 방사에너지를 줄여야 한다. 디스크 증폭기에서 같은 부피를 갖는 매질을 3등분하여 냉각표면적을 3배로 늘렸을 때 온도상승치는 30% 정도로 떨어졌다. 단면펌핑 분할 디스크형 증폭기의 설계에서는 각 글라스 간의 $Nd^{3+}$ 도핑율에 차등을 주어야 하고 플래시램프 앞에 있는 매질의 흡수계수 $\alpha$ 와 두께 d의 곱인 $\alpha$d가 0.26 전후가 적절하다는 것을 알았다.

• 대한조선학회논문집
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• 제43권5호
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• pp.560-567
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• 2006

FPSO and shuttle tanker are connected to each other by a mooring hawser and a loading hose through which cargo oil is off-loaded. Even in mild sea-state. environmental loads can cause unstable large drift motions between two vessels in tandem off-loading operations, which may result in collision incidents. Accordingly. the analysis on the relative motion between two vessels due to the environmental loads should be investigated in initial design stage. In this study, the low speed maneuvering equation is employed to simulate nonlinear motions of FPSO and shuttle tanker. Low frequency wave drift forces including hydrodynamic interactions between two vessels are evaluated by near field approaches. Current loads are determined by mathematical model of MMG and wind loads are calculated by employing the wind spectrum according to the guidelines of API-RP2A. Mooring forces produced by turret mooring lines and a flexible hawser are modeled quasi-statically by catenary equations. The effect of environmental loads that affect nonlinear motion is investigated through variation in their magnitudes and the nonlinear motions between FPSO and shuttle tanker are simulated under wave, current and wind in time domain.

• Journal of Advanced Research in Ocean Engineering
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• 제1권4호
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• pp.239-251
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• 2015

In this study, a spectral fatigue analysis was performed for the topside structure of an offshore floating vessel. The topside structure was idealized using beam elements in the SACS program. The fatigue analysis was carried out considering the wave and wind loads separately. For the wave-induced fatigue damage calculation, motion RAOs calculated from a direct wave load analysis and regular waves with different periods and unit wave heights were utilized. Then, the member end force transfer functions were generated covering all the loading conditions. Stress response transfer functions at each joint were produced using the specified SCFs and member end force transfer functions. fatigue damages were calculated using the obtained stress ranges, S-N curve, wave spectrum, heading probability of each loading condition, and their corresponding occurrences in the wave scatter diagrams. For the wind induced fatigue damage calculation, a dynamic wind spectral fatigue analysis was performed. First, a dynamic natural frequency analysis was performed to generate the structural dynamic characteristics, including the eigenvalues (natural frequencies), eigenvectors (mode shapes), and mass matrix. To adequately represent the dynamic characteristic of the structure, the number of modes was appropriately determined in the lateral direction. Second, a wind spectral fatigue analysis was performed using the mode shapes and mass data obtained from the previous results. In this analysis, the Weibull distribution of the wind speed occurrence, occurrence probability in each direction, damping coefficient, S-N curves, and SCF of each joint were defined and used. In particular, the wind fatigue damages were calculated under the assumption that the stress ranges followed a Rayleigh distribution. The total fatigue damages were calculated from the combination with wind and wave fatigue damages according to the DNV rule.

• Wind and Structures
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• 제19권3호
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• pp.339-352
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• 2014

This paper discusses the appropriate duration for basic gust wind speeds in wind loading codes and standards, and in wind engineering generally. Although various proposed definitions are discussed, the 'moving average' gust duration has been widely accepted internationally. The commonly-specified gust duration of 3-seconds, however, is shown to have a significant effect on the high-frequency end of the spectrum of turbulence, and may not be ideally suited for wind engineering purposes. The effective gust durations measured by commonly-used anemometer types are discussed; these are typically considerably shorter than the 'standard' duration of 3 seconds. Using stationary random process theory, the paper gives expected peak factors, $g_u$, as a function of the non-dimensional parameter ($T/{\tau}$), where T is the sample, or reference, time, and ${\tau}$ is the gust duration, and a non-dimensional mean wind speed, $\bar{U}.T/L_u$, where $\bar{U}$ is a mean wind speed, and $L_u$ is the integral length scale of turbulence. The commonly-used Durst relationship, relating gusts of various durations, is shown to correspond to a particular value of turbulence intensity $I_u$, of 16.5%, and is therefore applicable to particular terrain and height situations, and hence should not be applied universally. The effective frontal areas associated with peak gusts of various durations are discussed; this indicates that a gust of 3 seconds has an equivalent frontal area equal to that of a tall building. Finally a generalized gust response factor format, accounting for fluctuating and resonant along-wind loading of structures, applicable to any code is presented.

• Nuclear Engineering and Technology
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• 제48권1호
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• pp.55-63
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• 2016

Calculation of the core neutronic parameters is one of the key components in all nuclear reactors. In this research, the energy spectrum and spatial distribution of the neutron flux in a uranium target have been calculated. In addition, sensitivity of the core neutronic parameters in accelerator-driven subcritical advanced liquid metal reactors, such as electron beam energy ($E_e$) and source multiplication coefficient ($k_s$), has been investigated. A Monte Carlo code (MCNPX_2.6) has been used to calculate neutronic parameters such as effective multiplication coefficient ($k_{eff}$), net neutron multiplication (M), neutron yield ($Y_{n/e}$), energy constant gain ($G_0$), energy gain (G), importance of neutron source (${\varphi}^*$), axial and radial distributions of neutron flux, and power peaking factor ($P_{max}/P_{ave}$) in two axial and radial directions of the reactor core for four fuel loading patterns. According to the results, safety margin and accelerator current ($I_e$) have been decreased in the highest case of $k_s$, but G and ${\varphi}^*$ have increased by 88.9% and 21.6%, respectively. In addition, for LP1 loading pattern, with increasing $E_e$ from 100 MeV up to 1 GeV, $Y_{n/e}$ and G improved by 91.09% and 10.21%, and $I_e$ and $P_{acc}$ decreased by 91.05% and 10.57%, respectively. The results indicate that placement of the Np-Pu assemblies on the periphery allows for a consistent $k_{eff}$ because the Np-Pu assemblies experience less burn-up.

• 국제강구조저널
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• 제18권4호
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• pp.1191-1199
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• 2018

Concepts of submerged floating tunnels (SFTs) for land connection have been continuously suggested and developed by several researchers and institutes. To maintain their predefined positions under various dynamic environmental loading conditions, the submerged floating tunnels should be effectively moored by reasonable mooring systems. With rational mooring systems, the design of SFTs should be confirmed to satisfy the structural safety, fatigue, and operability design criteria related to tunnel motion, internal forces, structural stresses, and the fatigue life of the main structural members. This paper presents a feasibility study of a submerged floating tunnel moored by an inclined tendon system. The basic structural concept was developed based on the concept of conventional cable-stayed bridges to minimize the seabed excavation, penetration, and anchoring work by applying tower-inclined tendon systems instead of conventional tendons with individual seabed anchors. To evaluate the structural performance of the new type of SFT, a hydrodynamic analysis was performed in the time domain using the commercial nonlinear finite element code ABAQUS-AQUA. For the main dynamic environmental loading condition, an irregular wave load was examined. A JONSWAP wave spectrum was used to generate a time-series wave-induced hydrodynamic load considering the specific significant wave height and peak period for predetermined wave conditions. By performing a time-domain hydrodynamic analysis on the submerged floating structure under irregular waves, the motional characteristics, structural stresses, and fatigue damage of the floating tunnel and mooring members were analyzed to evaluate the structural safety and fatigue performance. According to the analytical study, the suggested conceptual model for SFTs shows very good hydrodynamic structural performance. It can be concluded that the concept can be considered as a reasonable structural type of SFT.

• Nuclear Engineering and Technology
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• 제53권2호
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• pp.423-429
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• 2021

The investigation of the utilization of enriched ²⁰⁸Pb as a coolant to enhance the performance of a long-life fast reactor with a Modified CANDLE (Constant Axial shape of Neutron flux, nuclide densities, and power shape During Life of Energy production) burnup scheme has performed. The analyzes were performed on a reactor with thermal power of 800 MegaWatt Thermal (MWTh) with a refueling process every 15 years. Uranium Nitride (enriched ¹⁵N), ²⁰⁸Pb, and High-Cr martensitic steel HT-9 were employed as fuel, coolant, and cladding materials, respectively. One of the Pb-nat isotopes, ²⁰⁸Pb, has the smallest neutron capture cross-section (0.23 mb) among other liquid metal coolants. Furthermore, the neutron-producing cross-section (n, 2n) of ²⁰⁸Pb is larger than sodium (Na). On the other hand, the inelastic scattering energy threshold of ²⁰⁸Pb is the highest among Na, ^natPb, and Bi. The small inelastic scattering cross-section of ²⁰⁸Pb can harden the neutron energy spectrum. Therefore, ²⁰⁸Pb is a better neutron multiplier than any other liquid metal coolant. The excess neutrons cause more production than consumption of ²³⁹Pu. Hence, it can reduce the initial fuel loading of the reactor. The selective photoreaction process was developing to obtain enriched ²⁰⁸Pb. The neutronic was calculated using SRAC and JENDL 4.0 as a nuclear data library. We obtained that the modified CANDLE reactor with enriched ²⁰⁸Pb as coolant and reflector has the highest k-eff among all reactors. Meanwhile, the ^natPb cooled reactor has the lowest k-eff. Thus, the utilization of the enriched ²⁰⁸Pb as the coolant can reduce reactor initial fuel loading. Moreover, the enriched ²⁰⁸Pb-cooled reactor has the smallest power peaking factor among all reactors. Therefore, the enriched ²⁰⁸Pb can enhance the performance of a long-life Modified CANDLE fast reactor.

• 한국지반환경공학회 논문집
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• 제11권6호
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• pp.5-20
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• 2010

1차원 등가선형 지반응답해석은 지반에 의한 지진동의 증폭현상을 모사하는데 널리 사용되고 있다. 등가선형해석은 적은 수의 입력변수를 필요로하므로 사용하기 편리하며 해석 소요시간이 짧다는 장점을 가지고 있는 반면, 시간에 따라서 변화하는 지반의 비선형 거동을 모사할 수 없으며 일정한 전단탄성계수와 감쇠비를 해석 내내 적용하는 선형해석이라는 단점을 가지고 있다. 이와 같은 등가선형해석의 단점을 보완하기 위하여 진동 주파수와 변형률과의 관계를 모사하는 다양한 형태의 수정된 등가선형해석기법들이 개발되었다. 수정된 기법들은 전단변형률 푸리에 스펙트럼을 사용한다는 점에서는 동일하지만, 이로부터 변형률의 주파수 의존도를 정의하는 과정에서는 차이를 보이고 있다. 본 연구에서는 두 가지 수정된 등가선형해석기법들의 정확성을 평가하기 위하여 국내에서 조사된 두 개의 토층에서 일련의 비선형, 등가선형, 수정된 등가선형 지반응답해석을 수행하였다. 해석 결과, 수정된 등가선형해석기법들은 고주파수 요소를 과대 예측할 수 있으며, 특히 고주파수 요소가 풍부한 인공지진파를 입력 지진파로 사용하였을 경우 비현실적인 응답이 계산될 수 있는 것으로 나타났다.