• 한국해양공학회지
• /
• 제24권4호
• /
• pp.8-12
• /
• 2010

The use of a tidal-current power system is one source of renewable energy that can minimize the environmental impact of power production and offer many other advantages compared to conventional energy sources. Unlike other energy production approaches, rate of energy production can be precisely predicted and the operational rate is very high. The performance of the rotor, which has a vital role in energy production using tidal currents, is determined by various design factors, and it should be optimized for the specific ocean environment in the field. The horizontal-axis turbine is very sensitive to the direction of flow, and flow direction changes due to rise and fall of the tides. To investigate the performance of the rotor considering the interaction problems with incidence angle of flow, a series of experiments were conducted, and a 3D CFD model was designed and analyzed by ANSYS CFX. The results and findings are summarized in the paper.

• Journal of Advanced Marine Engineering and Technology
• /
• 제38권10호
• /
• pp.1333-1339
• /
• 2014

As the demand for petroleum resources increases, and oilfields on lands and in shallow-sea become exhausted, the areas for oil production are expanding to the deep sea and therefore technologies for flow assurance are coming into the highlight. In low temperature environment such as the deep sea, wax is accumulated and prevents stable oil production. Therefore, the development of flow assurance technologies is required. Wax is precipitated in crystalline form when the oil temperature decreases below the wax appearance temperature; it then accumulates on the inner walls of pipelines causing blockages. In particular, in subsea pipelines, which have a large surface contact area with the surrounding seawater, wax deposition problems are frequent. The internal tubular coating can effectively reduce wax deposition without pausing oil production when the coating is appropriately designed. This study carried out wax deposition tests on a number of internal tubular coatings under single flow conditions. The results were analyzed for the effects that the physical properties of the coatings had on wax deposition.

• 대한조선학회 특별논문집
• /
• 대한조선학회 2005년도 특별논문집
• /
• pp.151-158
• /
• 2005

It is important to control material flow in shipbuilding as it decides the productivity of production, cost and period of production. The weight of material in a big shipyard is even more one million tons. The results contained in this paper can provide the valuable information on the effect of reduction of cost and competitive power. The intention of this paper is to let ship builders pay attention to material flow. This paper refers to other manufacture's methods to improve their material flow and also give one example to show how to pursue to improve material flow in a shop. We have still lots of room to improve material flow.

• 산업공학
• /
• 제12권3호
• /
• pp.468-479
• /
• 1999

Lean production system can be defined as customer(product)-oriented production system with small lot size and flow-shop layout based on the JIT(Just-in-time) principles. In this paper, we introduce a case example of implementation of the Lean product ion system for manufacturing line of electronic component which has both machine processes and manual jobs. We also investigate the issues of implementing the Lean production system with the viewpoints of layout design scheme and JIT management rules. In the layout design, we propose the cell-line which has flow-shop layout with small lot size. In the management rules, the superior cell rule is applied in order to boost the needs of kaisen up. As the results of implementing the Lean production system, production lead time is decreased from 5 days to 1.5 days and also productivity and quality level arc surprisingly increased.

• 대한산업공학회지
• /
• 제18권1호
• /
• pp.47-62
• /
• 1992

This paper describes a procedure for optimizing the route selection and production conditions in alternate process plans under a cellular manufacturing environment. The type of production is mainly production-to-order which deals with unexpected products as the changes factor. The flexible cellular manufacturing can be viewed as a complete unification of both flexible manufacturing process and flexible production management. The integrated problem for designing flexible cellular manufacturing associated with determining the optimal values of the machining speeds, overtime, and intercell flow is formulated as Nonlinear Mixed Integer Programming(NMIP) in order to minimize total production change cost. This is achieved by introducing the marginal cost analysis into the NMIP, which will compute the optimal machining speed, overtime, intercell flow, and routing. The application of this procedure offers greater flexibility to take advantage of the cellular manufacturing due to the optimum use of resources. A solution procedure for this problem was developed and a numerical example is included.

• 열처리공학회지
• /
• 제34권6호
• /
• pp.272-280
• /
• 2021

The influence of acetylene flow rates on the carburizing behavior of an AISI 4115 steel in 1 ton-class mass production-type vacuum carburizing furnace has been studied through microstructure, carbon concentration, hardness analyses. The AISI 4115 steels were carburized with various flow rates (20, 32.7, 60 l/min) and locations in the furnace (top, center, bottom) at 950℃. The acetylene flow rate played an important role in controlling the carburizing properties of carburized samples, such as effective case depth and uniformity carburizing according to location in the furnace. At an acetylene flow rate of 20 l/min, the carburized samples had a shallow average hardened layer (0.645 mm) compared to the target hardening depth (1 mm) due to low carbon flux and spatial uniformity of carburization (17.8%) in the furnace. At a flow rate of 60 l/min, the carburized samples showed an average hardened layer (1.449 mm) deeper than the target hardening depth and had the spatial uniformity of carburization (98.8%). In particular, at a flow rate of 32.7 l/min, the carburized samples had an average hardened layer (1.13 mm) close to the target hardening depth and had the highest carburizing uniformity (99.1%). As a result, an appropriate flow rate of 32.7 l/min was derived to satisfy the target hardening depth and to have spatial uniform hardened layer in the furnace.

• 한국건설관리학회:학술대회논문집
• /
• 한국건설관리학회 2001년도 학술대회지
• /
• pp.416-421
• /
• 2001

국내 철근 콘크리트 공사는 철근현장가공조립을 주로 하고있는데 철근공사는 거푸집공사와 더불어 건축물의 구조적 안정성과 내구성 및 공기에 가장 큰 영향을 미치고 있는 공사이다. 이와 같은 철근현장가공조립의 프로세스를 린 생산원리를 적용하여 가치흐름분석을 하였다. 가치흐름분석은 가치분석과 가치흐름맵핑을 통해서 건설프로세스 상의 가치창출작업과 비 가치창출작업을 분석하였다 그 결과 비 가치창출 작업으로 인한 낭비로 많은 작업 단계와 인력, 장비, 자재, 시간 등이 낭비되고 있었다. 또한 밀어내기 생산(Push-driven Production)으로 과잉생산을 하는 등 생산의 낙후성이 조사되었다. 이러한 프로세스상의 문제점을 개선하기 위해 이 연구에서는 부가가치를 창출하는 가치창출 작업을 최대화하고, 비 가치창출작업을 최소화하여 낭비요소를 제거하는데 목적이 있다. 특히 진행간 재고를 최소화하여 흐름생산(Flow Production)과 당김생산(Pull-driven Production)이 될 수 있도록 하였다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.2154-2159
• /
• 2007

The potential of using a double-faced wall stagnation flow burner in mass production of carbon nanotubes was evaluated experimentally and computationally. With nitrogen-diluted premixed ethylene-air flames established on the Nickel-coated stainless steel double-faced wall, the propensities of carbon nanotube formation were experimentally determined using SEM and FE-TEM images and Raman spectroscopy, while the flame structure was computationally predicted using a 3-dimensional CFD code with a reduced reaction mechanism. The uniformity and yields of synthesized carbon nanotubes were evaluated in terms of the flame stretch rates. Results show substantial increase of area on the wall surface where uniform carbon nanotubes are synthesized with using the double-faced wall stagnation flow burner due to enhanced uniformity of temperature distribution along the wall surface and support the potential of using a double-faced wall stagnation flow burner in mass production of carbon nanotubes.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2012년도 제44회 KOSCO SYMPOSIUM 초록집
• /
• pp.29-31
• /
• 2012

The effects of combustion parameters on the characteristics of a steam-methane reformer. The reformer system was numerically simulated using a simplified two-dimensional axisymmetric model domain with an appropriate user-defined function. The fuel ratio, defined as the ratio of methane flow rate in the combustor to that in the reactor, was varied from 20 to 80%. The equivalence ratio was changed from 0.5 to 1.0. The results indicated that as the fuel ratio increased, the production rates of hydrogen and carbon monoxide increased, although their rates of increase diminished. In fact, at the highest heat supply rates, hydrogen production was actually slightly decreased. Simulations showed that equivalence ratio of 0.7 yielded the highest steam-methane mixture temperature despite a 43% higher air flow rate than the stoichiometric flow rate. This means that the production of hydrogen and carbon monoxide can be increased by adjusting the equivalence ratio, especially when the heat supply is insufficient.

• 한국자동차공학회논문집
• /
• 제7권7호
• /
• pp.1-14
• /
• 1999

In the present study, the flame factor which primarily influence the simulation accuracy of the combustion process in a gasoline engine was modeled as a nonlinear function of turbulent intensity to laminar flame speed ratio. Multi-length-scale production rate model for turbulent kinetic energy equation was introduced to consider the different length scales of the swirling and tumbling motions in cylinder on the production rte of turbulent kinetic energy. By7 introducing the multi-length-scale production rate model for the turbulent kinetic energy equation, the predictions of turbulent burning velocity , cylinder pressure, mass burning rate and engine performance of a gasoline engine can much be improved.