• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.6
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• pp.18-28
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• 2016

Numerical analysis was conducted as a preliminary study for evaluating the dual bell nozzle. For future parametric studies, a dual bell nozzle was designed, and thereafter inlet condition, turbulence model, and the number of optimum grids were determined. Dual bell nozzle was designed based on the KSLV-II first stage nozzle. Inlet condition was determined to frozen flow model of non-reacting eight species by comparing with the design values. SST $k-{\omega}$ model turned out to be suitable as turbulence model. About 150 thousand of the grids were selected after grid sensitivity tests. Based on the results determined in this study, we plan to investigate performance gain of the KSLV-II by adopting a proposed dual bell nozzle.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.3
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• pp.46-52
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• 2018

A simple Crocco's $n-{\tau}$ time delay model and linear analysis of fluid flow coupled with acoustics are combined to investigate the high frequency combustion instability in the combustion chamber of LOX/hydrocarbon engines. The partial differential equation of the velocity potential is separated into ordinary differential equations, and eigenvalues that correspond to tangential resonance modes in the cylindrical chamber are determined. A general solution is obtained by solving the differential equation in the axial direction, and boundary conditions at the injector face and nozzle entrance are applied in order to calculate the chamber admittance. Frequency analysis of the transfer function is used to evaluate the stability of system. Stability margin is determined from the system gain and phase angle for the desired frequency range of 1T mode. The chamber model with variable baffle length and configurations are also considered in order to enhance the 1T mode stability of the combustion chamber.

• Journal of Digital Contents Society
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• v.18 no.2
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• pp.411-422
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• 2017

Current policies for sharing bandwidth increase average throughput and improve utilization of the bandwidth in the local network. However, with these policies, a central administer, which is responsible for allocating bandwidth to each network flow, cannot allocate resources based on user characteristics. Thus, it leads to unfair bandwidth allocation because it does not guarantee services based on user characteristics. Therefore, we propose a novel negotiation method to share the bandwidth in a limited bandwidth network, in which, a user negotiates with other users to gain more resource. Ideally, we use a fuzzy system to infer and determine whether a device will request bandwidth or not based on the current usage of the given device. We conduct two experiments consisting of a video streaming simulation in OPNET and a real-time video streaming in WebRTC. The results of the experiment indicate that the proposed method can flexibly share the bandwidth utilization based on user's requirement in the network.

• Journal of Korea Water Resources Association
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• v.32 no.4
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• pp.417-426
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• 1999

A series of numerical experiments is performed to compare the characteristics of outflow hydrograph using linear and nonlinear Muskingum-Cunge methods for two cases: (a) sinusoidal inflow hydrographs and (b) rainfall inputs. The nonlinear method shows the steepening of the rising limb, coupled with a corresponding flattening of the receding limb. The linear method conserves mass exactly. In contrast, the nonlinear method is subject to a gain and a loss of mass. The loss of mass and the subsidence of peak outflow increases with a mild slope, a small baseflow $q_b$ and a large peak inflow to baseflow ratio $q_p/q_b$. A shock wave and associated numerical instability results in the increase of mass for a steep slope and a large $q_p/q_b$ ratio. While the linear method depends on the reference flow per unit-width, the nonlinear method depends on a baseflow and the $q_p/q_b$ ratio. It is found that, unlike for the sinusoidal inflow, the outflow for the rainfall inputs conserves mass fairly exactly in the nonlinear method.

• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1062-1073
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• 2004

We describe a looper controller design for a hot strip finishing mill in steel plants. The main function of the looper system is to balance the mass flow of the strip by accumulating material in the middle of the stands. Another function is to control the strip tension which influences the width of the strip. To ensure strip quality, it is very important to control the tension of the hot strip finishing mill. However, because there is a mutual interaction between the looper angle and the strip tension, it is difficult to control the looper system. Previous researches examined only the operation of a single stand. But it is not sufficient to examine the operation and effect of whole stands because the operation is wholly interdependent. In this paper, we present a full model of the hot strip finishing mill in order to more effectively control strip tension. We propose several control methods for the full-stand hot strip finishing mill, denoted as conventional PI, PI with cross gain, and coefficient diagram method (CDM) PID control. In the real plants, there are some problems by using higher order controllers such as LQ, LQG and H$\_$$\infty$/. By comparison, the PID controller is very simple and easy to apply to all real plants. To that end, we present our findings on PID controls and their potential use in the hot strip finishing mill.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.5
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• pp.2044-2062
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• 2018

Information theory progression along with the advancements being made in the field of Vehicular Ad hoc NETworks (VANETs) supports the use of coding-aware opportunistic routing for efficient data forwarding. In this work, we propose and investigate an adaptive coding-aware routing scheme in a specific VANET scenario known as a vehicular platoon. Availability of coding opportunities may vary with time and therefore, the accurate identification of available coding opportunities at a specific time is a quite challenging task in the highly dynamic scenario of VANETs. In the proposed approach, while estimating the topology of the network at any time instance, a forwarding vehicle contemplates the composition of multiple unicast data flows to encode the correct data packets that can be decoded successfully at destinations. The results obtained by using OMNeT++ simulator reveal that higher throughput can be achieved with minimum possible packet transmissions through the proposed adaptive coding-aware routing approach. In addition, the proposed adaptive scheme outperforms static transmissions of the encoded packets in terms of coding gain, transmission percentage, and encoded packet transmission. To the best of our knowledge, the use of coding-aware opportunistic routing has not been exploited extensively in available literature with reference to its implications in VANETs.

• Journal of fish pathology
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• v.23 no.3
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• pp.409-420
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• 2010

Effects of various concentrations of garlic powder and garlic extract in the diets on growth, serum chemistry and immune response of olive flounder were determined. Thirty-five juvenile fish averaging 5.1 g were randomly distributed into 21 of 180 L flow-through tanks. Seven experimental diets with various concentrations of garlic powder (GP) and garlic extract (GE) were prepared in triplicate: GP-0 without garlic supplementation, GP-0.5, GP-1, GP-2, GP-3 and GP-5 diets containing garlic powder at the concentrations of 0.5, 1, 2, 3 and 5%, respectively at the expense of wheat flour and finally, GE-0.4 diet containing 0.4% garlic extract were prepared. At the end of the 8-week feeding trial, serum chemistry of fish was measured. In addition, twenty fish from each tank were artificially infected with E. tarda for the following 96 h to monitor cumulative mortality. Weight gain of fish fed GP-0 diet was higher than that of fish fed GP-1, GP-2, GP-3 and GP-5 diets. No difference in serum criteria (total protein, glucose, glutamate oxaloacetate transaminase, cholesterol and triglyceride levels) of olive flounder was found among the experimental diets except for glutamate pyruvate transaminase. Lysozyme activity of fish fed GP-0, GP-1, GP-3 and GE-0.4 diets was higher than that of fish fed GP-5 diet. The highest cumulative mortality was 93.3% in fish fed GP-0 diet at 96 h after E. tarda infection, followed by GP-3, GP-1, GP-5, GP-2, GP-0.5 and GE-0.4 diets. In considering these results, dietary inclusion of garlic powder and garlic extract has no distinctive positive effect on improvement in growth, serum chemistry and immune response of olive flounder in this experimental conditions, therefore, its application should be carefully considered.

• Journal of the Korean Solar Energy Society
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• v.31 no.2
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• pp.89-98
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• 2011

This study examined the energy performance according to the main design parameters of a solar water heating system for an office building using the life cycle cost (LCC) optimization simulations. The LCC optimization simulations of the system were conducted with TRNSYS and GenOpt employing the Hooke-Jeeves algorithm for cases where water temperature was $60^{\circ}C$ and $50^{\circ}C$. The results showed that for water temperature at $60^{\circ}C$ and $50^{\circ}C$ the global radiation incident on the collector could be decreased by 16.98% and 28.52%, collector useful energy gain could be decreased by 15.04% and 22.59%, energy to load from storage tank could be decreased by 10.86% and 18.06% and AH energy to load could be increased by 16.86% and 38.50% respectively compared to a non-optimized system. The annual average collection efficiency of the collector was increased by 0.88% for $60^{\circ}C$ and 2.78% for $50^{\circ}C$ because of increase of collector slope and decrease of the mass flow rate per collector area. The annual average efficiency of the system was increased by 1.74% and 3.47% compared to the basis system. However, the annual solar fraction of the system was decreased by 6.68% for $60^{\circ}C$ and 11.26% for $50^{\circ}C$ due to decrease of collector area and storage tank volume.

• Asian-Australasian Journal of Animal Sciences
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• v.32 no.2
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• pp.233-240
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• 2019

Objective: This study was to investigate the effects of dietary cotton stalk on nitrogen and free gossypol in sheep. Methods: Treatments included 25% cotton stalk (Treat 1), 50% cotton stalk (Treat 2), and a control (no cotton stalk). Six Xinjiang daolang wethers were cannulated at the rumen and duodenum and fed one of these diets. The effects of these diets on nitrogen and free gossypol absorption and metabolism were determined. Fifteen healthy Xinjiang daolang wethers were assessed for daily gain, tissue lesions, and free gossypol accumulation. Results: Dry matter intake decreased with increasing dietary cotton stalk. Total tract dry matter digestibility did not significantly differ among treatments. Dietary cotton stalk significantly decreased volatile fatty acids and increased ammonium nitrogen in the rumen. Nitrogen intake was significantly higher in Treat 2 than in the control or Treat 1. Nitrogen retention and free gossypol intake increased with dietary cotton stalk. Duodenal free gossypol flow did not increase, and free gossypol almost disappeared from the rumen. The free gossypol content of plasma and tissue was increased with dietary cotton stalk with liver free gossypol>muscle free gossypol>kidney free gossypol. Elevated dietary free gossypol decreased platelets, hemoglobin, and serum iron. Aspartate aminotransferase and ${\gamma}$-glutamyltransferase increased in Treat 2. With high long-term dietary cotton stalk intake, liver cells were swollen, and their nuclei dissolved. Renal cells were necrotic and the interstitia were enlarged. Conclusion: With short-term cotton stalk administration, only a small amount of free gossypol is retained in the body. In response to long-term or high free gossypol cotton stalk feeding, however, free gossypol accumulates in, and damages the liver and kidneys.

• Advances in concrete construction
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• v.6 no.6
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• pp.561-583
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• 2018

A variety of polycarboxylate ether (PCE)-based superplasticizers are commercially available. Their influence on the rheological retention and slump loss in respect of concrete differ considerably. Fluidity and slump loss are the cardinal features responsible for the quality of concrete. These are related to the dispersion of cement particles and the hydration process which are greatly influenced by type of polycarboxylate ether (PCE)-based superplasticizers. On the backdrop of relatively less studies in the context of rheological retention of high strength self-consolidating concrete (HS-SCC), the experimental investigations were carried out aiming at quantifying the effect of the six different PCE polymers (PCE 1-6) on the rheological retention of HS-SCC mixes containing two types of Ordinary Portland Cements (OPC) and unwashed crushed sand as the fine aggregate. The tests that were carried out included $T_{500}$, V-Funnel, yield stress and viscosity retention tests. The supplementary cementitious materials such as fly ash (FA) and micro-silica (MS) were also used in ternary blend keeping the mix paste volume and flow of concrete constant. Low water to binder ratio was used. The results reveal that not only the PCEs of different polymer groups behave differently, but even the PCEs of same polymer groups also behave differently. The study also indicates that the HS-SCC mixes containing PCE 6 and PCE 5 performed better as compared to the mixes containing PCE 1, PCE 2, PCE 3 and PCE 4 in respect of all the rheological tests. The PCE 6 is a new class of chemical admixtures known as Polyaryl Ether (PAE) developed by BASF to provide better rheological properties in even in HS-SCC mixes at low water to binder mix. In the present study, the PCE 6, is found to help not only in reduction in the plastic viscosity and yield stress, but also provide good rheological retention over the period of 180 minutes. Further, the early compressive strength properties (one day compressive strength) highly depend on the type of PCE polymer. The side chain length of PCE polymer and the fineness of the cement considerably affect the early strength gain.