• 한국음향학회지
• /
• 제30권1호
• /
• pp.42-48
• /
• 2011

본 연구는 능동 방음벽의 성능과 관련하여 제어 음원으로서 복합음원의 사용 가능성을 알아보았다. 복합음원은 근접거리에 위치하며 위상이 반대인 두 개의 단극음원으로 구성된다. 한 조의 복합음원 내 두 개의 단극음원의 세기는 각각 별도의 제어 채널을 구성하여 제어 되는 것이 아닌, 수음점 쪽에 위치한 음원의 세기에 다른 하나가 상수배로 비례하여 제어된다. 따라서 제어 시스템의 하드웨어 구성 비용이 낮아지며, 단극음원 하나당 한 채널로 구성되는 제어시스템에 비하여 비교적 세밀한 음장 형성이 가능하다고 알려져 있다. 본 연구에서는 이러한 복합음원을 방음벽 양쪽에 무반사 바닥면을 가지는 비교적 간단한 시스템에 적용하여 단극음원 대비 어느 정도의 효용성이 있는지 컴퓨터 시뮬레이션을 통하여 알아보았으며 30~40 % 정도의 성능 향상이 가능함을 보여주었다.

• 한국소음진동공학회논문집
• /
• 제13권10호
• /
• pp.743-750
• /
• 2003

The equivalent source method(ESM) is used for the calculation of the internal pressure field for an enclosure which can have arbitrary boundary conditions and nay include internal objects which scatter the sound field. The advantage of using ESM is that it requires relatively low computing cost and is easy to model the internal diffracting objects. Typical ESM modeling uses two groups of equivalent source positions. One group includes the first order images of the source inside the enclosure. The Positions of the other group are usually on a spherical surface some distance outside the enclosure. The normal velocity on the surfaces of the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and the expected is minimized by adjusting the strength of the equivalent sources. This study is on the optimal far field sources positions when using the equivalent source method. In general, the far field sources are evenly distributed on a surface of a virtual sphere which is centered at the enclosure with a sufficiently large radius. In this study. optimal far field source locations are searched using simulated annealing method for various radii of spheres where far field sources are located. Simulation results showed that optimally located sources with adequate distance away from the enclosure center gave better result than sources with even distribution even with a smaller number of far field sources.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집B
• /
• pp.216-221
• /
• 2001

The equivalent source method(ESM) is used for the calculation of the internal pressure field for an enclosure which can have arbitrary boundary conditions and may include internal objects which scatter the sound field. The advantage of using ESM is that it requires relatively low computing cost and is easy to model the internal diffracting objects. In the ESM modelling, some of the equivalent positions are chosen to be the same as the first order images of the source inside the enclosure, some are positioned on a spherical surface some distance outside the enclosure. The normal velocity on the surfaces of the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and the expected is minimized by adjusting the strength of the equivalent sources. This study is on the optimal equivalent source positions, the far field sources. Typically, the far field sources are evenly distributed on a surface of a virtual sphere which is centered at the enclosure with a sufficiently large radius. In this study, optimal far field source locations are searched using simulated annealing method and simulation results showed that optimally located sources gave better accuracy even with a smaller number of far field sources.

• 한국의학물리학회지:의학물리
• /
• 제14권2호
• /
• pp.81-89
• /
• 2003

근접조사용 선원으로 직경이 0.5 mm에 길이 3.5 mm인 Ir-192선원을 고안하고, 선량알고리즘을 개발하였다. 선원을 0.1 mm 두께로 균등분할하고 총 875개의 미소선원으로부터 조직에 도달되는 선량을 계산하고 선량분포를 조사하였다. 선원을 감싸는 캡슐용기의 두께는 0.3 mm이며, 선량기준점인 Ir선원의 Air-kerma strength(S$_{k}$ ) 는 mCi당 4.108U를 얻었으며 선원 측방의 1 cm에서 1.154 Uh$^{-1}$ (1.3167${\times}$$10^{-3}$cGy/mCi-sec)의 조직선량률을 얻었다. Air-kerma strength로부터 조직내 선량률상수(Λ)는 Ir-192에너지 스펙트럼과 실험치인 조직내 산란보정계수를 적용하여 1.154 cGy h$^{-1}$U$^{-1}$ 얻었다. 선량분포의 특성은 선원 축방향으로 56%의 상대선량률을 보였고, 케이블측의 선량감쇠는 50%를 보였다. 마이크로선원의 중심에서 반경 1 cm 주위의 선량분포와 5 cm의 선량분포를 비교한 결과 반경이 큰 경우의 측방선량에 비해 축 방향의 선량이 약 2% 감쇠함을 보았다. 선원자체의 필터효과는 점선원에 비해 88.3%의 선량률을 얻어 약 12%의 감쇠를 보였으며, 캘슐벽의 필터효과는 약 3% 정도로 미미하게 나타났으며 기준점에서 선량필터효과는 약 15.6% 감쇠되는 것으로 나타났다. Ir-192 선원과 같이 에너지가 낮은 선원을 사용하는 경우 선량분포특성에 따라 아프리케이터의 직경을 크게 하여 선원 축 방향의 선량저하를 피할 수 있음을 알 수 있었다.

• Journal of Nutrition and Health
• /
• 제36권7호
• /
• pp.684-690
• /
• 2003

This study has investigated the bioavailability of calcium in eggshell powder (ESP) for the purpose of reutilizing eggshells as the calcium source. The experiment was designed 2 ${\times}$ 2 factorial method with two sources, CaCO$_3$ and ESP, and two levels, 0.2% and 0.4% calcium. Weanling SD rats were assigned randomly to one of 4 groups and provided by one of the isocaloric, 20% casein based 4 different experimental diets for 4weeks. Deionized water was given and environment was kept from any contamination of minerals. The body weight, diet intake, feed efficiency ratio (FER), bone growth, Ca contents of bones, and apparent absorption were measured. FER (0.38 - 0.40) and kidney weight were not different among groups and the weight and length, Ca content, strength of two bones Tibia and Femur were not affected by Ca sources except Femur Ca content. Ca content of Femur was greater in ESP groups than that of CaCO$_3$ groups. The body weight gain, bone growth, the Ca contents and strength of bones were significantly greater in 0.4% calcium groups suggesting 0.2% calcium is not sufficient for the optimum growth in the growing rats. These results indicate that ESP be a proper Ca source comparable or superior to CaCO$_3$. However the apparent absorption rate of final 3 days of feeding did not support the observed results showing lower rate in ESP than CaCO$_3$ groups. Further study be needed in the absorption aspect.

• Elastomers and Composites
• /
• 제51권4호
• /
• pp.301-307
• /
• 2016

Additive manufacturing (AM), so called 3D Printing is a new manufacturing process and is getting attraction from many industries. There are several methods of 3D printing. Among them fused deposition modeling (FDM) type is most widely used by reason of cheap maintenance, easy operation and variety of polymeric materials. Articles manufactured by 3D printing have weak deposition strength compared with conventionally manufactured products. Deposition strength of FDM type 3D printed article is highly dependent of deposition temperature. Subsequently the nozzle temperature in the FDM type 3D printing is very important and it is controlled by heat source in the 3D printer. Nozzle is connected with heat block and barrel, and heat block contains heat source. Nozzle becomes hot through heat conduction from heat source. Nozzle temperature has been predicted for various thermal boundary conditions by computer simulation and compared with experimental measurement. Nozzle temperature highly depends upon thermal conductivities of heat block and nozzle. Simulation results are good agreement with experiment.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2001년도 추계학술대회 논문집
• /
• pp.45-49
• /
• 2001

The length and the breadth or a very large floating airport are determined by airplane types and airport facilities. However, the depth affect not only the structural strength but also the functional requirement such as a possibility of taking off and landing. The optimization problem for determining the depth is to select a design so that the cost is minimized. In this paper, a general arrangement and a method to decide the depth are proposed. Strength, functional requirement, and possibility of occurrence of deck wetness and slamming are considered in order to determine the depth of structure. Hydrodynamic forces of the diffraction and radiatin problems are predicted by applying the source-dipole distribution method, and the structural responses are obtained by the finite element method.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
• /
• pp.177-179
• /
• 2011

The purpose of this study is to enhance an adhesion between substrate and Diamond-like Carbon (DLC) film. DLC has many outstanding properties such as low friction, high wear resistance and corrosion resistance. However, it is difficult to achieve enough adhesion because of weak bonding between DLC film and the substrate. For improvement adhesion, a layer between DLC film and the substrate was prepared by dual post plasma. DLC film was deposited on nitrided layer by linear ion source. The composed compound layer between substrate and DLC film was investigated by Glow Discharge Spectrometer (GDS) and Scanning Electron Microscope (SEM). The synthesized bonding structure of DLC film was analyzed using a micro raman spectrometer. Mechanical properties were measured by nano-indentation. In order to clarify the mechanism for improvement in adhesive strength, it was observed by scratch test.

• 한국농공학회지
• /
• 제18권4호
• /
• pp.4265-4273
• /
• 1976

1. Fine aggregates of concrete are very important for the construction works and construction cost determination. Most of fine aggregates are from the river sand, but the amount of storage in the river side is steadily decreasing due to continuous construction works. Therefore, another source of fine aggregates is needed to meet increasied demand of sand. 2. Beach sand is a possible source of fine aggregates. But rust of steel bar is caused by CL-chemical of beach sand. Therefore, desalinization of beach sand is requested to get durable reinforced concrete. Economical methods of desalinization are as follows. (a) Flooding and drainage method. (b) Washing of beach sand with water supply and mixing. (c) Spreading of beach sand on the land and leaching by rain water for a few month. 3. Hardening of concrete with beach sand is accelerated due to salt, Thus early stage strength increase leads to make cracks. Also later stage strength decreases and durability becomes worse. By using appropriate admixture, the quality of concrete can be improved.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2013년도 추계학술대회 논문집
• /
• pp.564-569
• /
• 2013

An accurate railway environmental noise prediction model is required to make the proper solution of the railway noise problems. In this paper, an engineering model for predicting the noise of conventional passenger cars is presented considering the acoustic source strength in octave-band frequencies and the propagation over grounds with varying surface properties. Since the formation of a train can be variable, the source strength of each locomotive and passenger car was estimated by measuring the pass-by noise and analysing the wheel-rail rolling noise. Some validation cases show on the average small differences between the predictions of the present model and the measurement results.