• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4B
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• pp.315-322
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• 2011

This study reviewed the Weiss model, probably the only theoretical study available on the fixed- to true-interval rainfall conversion factor (CF), and implemented to propose a modified Weiss model. Also, the characteristics of the temporal distribution of rainfall were considered in the estimation of CF to overcome the problem of these two models, whose results were compared with those estimated empirically. As results, the CF was found to be differently estimated depending on the temporal distribution of rainfall. Especially, the theoretical CF estimate for the center-concentrated rainfall distribution was found to be very similar to that of empirical results of domestic and foreign studies.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.7
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• pp.571-577
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• 2006

The characteristics of ice packing factor (IPF) at the ice slurry system using one line type are compared with the system using two lines type. The installation space for one transporting line is saved at the one line system. For the one line type, the ice packing factor is reduced along the downstream, but for the two lines type, the ice packing factor is fixed. For the one line system, mass flow rate in the main line is fixed along the down-stream, but for two lines system, the mass flow rate in the main line is reduced along the downstream. For one line system, along the down stream after IPF=0, the temperature at the main steam is increased, and the extracted mass flow is increased. The initial IPF, at which the IPF is not arrived at zero upto the final node, is proposed for the B area.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.12 no.2
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• pp.59-70
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• 2004

Most of studies on aircraft accidents have been conducted mainly for fixed-wing aircraft, while the studies on helicopter accidents have been done less even though the helicopter accidents occurred quite more than those of the fixed-wing. There are lots of differences between helicopter and fixed-wing accidents, in aspect of causes and occurrence of accidents as well as aerodynamics and operation. In Korea, helicopter accidents have occurred 2 or 3 times annually since 2000, while the number of fixed-wing aircraft accidents has been reduced considerably. The goal of this study is to solve the present safety problems in helicopter accidents by reviewing the characteristics of past accidents and comparing differences between two types of aircraft.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.3
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• pp.408-415
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• 2019

Basically the dynamics of the fixed-wing aircraft is based on the airspeed which is relative to the wind, but when it comes to the track guidance and control, ground speed is the factor to be considered. Especially in the case of low-speed fixed-wing unmanned aerial vehicles the difference between the airspeed and the ground speed is significant depending on wind conditions, so that the heading control and the course control have to be designed separately. This paper represents the course control method using the pre-designed heading control gains which meet the desired characteristics. Also, waypoint guidance and control algorithms are suggested applying this control method. Finally the robustness of the proposed method is confirmed by 6-DoF nonlinear simulation.

• Journal of Environmental Science International
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• v.23 no.1
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• pp.53-60
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• 2014

Adsorption of phenol on activated carbon in a fixed bed was studied. The effects of fixed-bed length, superficial velocity (flow rate) and particle size of adsorbent on fixed-bed performance were investigated. Some characteristic parameters such as the breakthrough time ($t_{0.05}$), saturation time ($t_{0.95}$), length of mass transfer zone ($L_{MTZ}$), adsorptive capacity (W), and adsorption rate constant ($K_a$) were derived from the breakthrough curves. Adsorbent particle sizes significantly affected the shape of the breakthrough curve. Larger particle sizes resulted in an earlier breakthrough, a longer $L_{MTZ}$ and a lower adsorption rate. Superficial velocity was a critical factor for the external mass transfer during fixed-bed adsorption process. The external mass transfer resistance was dominant as increasing superficial velocity.

• Journal of the Korean Solar Energy Society
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• v.37 no.6
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• pp.69-77
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• 2017

The amount of solar irradiation obtained by a photovoltaic (PV) solar panel is the major factor determining the power generated by a PV system, and the array tilt angle is critical for maximizing panel radiation acquisition. There are three types of PV systems based on the manner of setting the array tilt angle: fixed, semi-fixed, and tracking systems. A fixed system cannot respond to seasonal solar altitude angle changes, and therefore cannot absorb the maximum available solar radiation. The tracking system continually adjusts the tilt angle to absorb the maximum available radiation, but requires additional cost for equipment, installation, operation, and maintenance. The semi-fixed system is only adjusted periodically (usually seasonally) to obtain more energy than a fixed system at an overall cost that is less than a tracking system. To maximize semi-fixed system efficiency, determining the optimal tilt angle adjustment schedule are required. In this research, we conducted a simulation to derive an optimal operation schedule for a semi-fixed system in Seoul, Korea (latitude $37.5^{\circ}$). We implemented a solar radiation acquisition model and PV genereation model on MATLAB. The optimal operation schedule was derived by changing the number of tilt angle adjustments throughout a year using a Dynamic Algorithm. The results show that adjusting the tilt angle 4 times a year was the most appropriate. and then, generation amount of PV system increased 2.80% compared with the fixed system. This corresponds to 99% compared to daily adjustment model. This increase would be quite valid as the PV system installation area increased.

• Journal of Communications and Networks
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• v.16 no.2
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• pp.130-139
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• 2014

Due to the unpredictable nature of channel availability, carrying delay-sensitive traffic in cognitive radio networks (CRNs) is very challenging. Spectrum leasing of radio resources has been proposed in the so called coordinated CRNs to improve the quality of service (QoS) experienced by secondary users (SUs). In this paper, the performance of coordinated CRNs under fixed-rate with hard-delay-constraints traffic is analyzed. For the adequate and fair performance comparison, call admission control strategies with fractional channel reservation to prioritize ongoing secondary calls over new ones are considered. Maximum Erlang capacity is obtained by optimizing the number of reserved channels. Numerical results reveal that system performance strongly depends on the value of the mean secondary service time relative to the mean primary service time. Additionally, numerical results show that, in CRNs without spectrum leasing, there exists a critical utilization factor of the primary resources from which it is not longer possible to guarantee the required QoS of SUs and, therefore, services with hard delay constraints cannot be even supported in CRNs. Thus, spectrum leasing can be essential for CRN operators to provide the QoS demanded by fixed-rate applications with hard delay constraints. Finally, the cost per capacity Erlang as function of both the utilization factor of the primary resources and the maximum allowed number of simultaneously rented channels is evaluated.

• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.290-293
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• 2000

In this paper the algorithm which controls output voltage and power factor independently and the algorithm which controls output voltage with fixed unity power factor are compared and analyzed. These algorithms are applied to single-phase AC/DC parallel are applied to single-phase AC/DC parallel converters for a high speed train system. The control characteristic of the algorithms are compared and analyzed with respect to the output voltage and input power factor when system parameters vary.

• Journal of the Korean Data and Information Science Society
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• v.15 no.2
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• pp.339-345
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• 2004

This paper deals with a mixed logit model for ordered polytomous data. There are two types of factors affecting the response varable in this paper. One is a fixed factor with finite quantitative levels and the other is a random factor coming from an experimental structure such as a randomized complete block design. It is discussed how to set up the model for analyzing ordered polytomous data and illustrated how to estimate the paramers in the given model.

• Honam Mathematical Journal
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• v.7 no.1
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• pp.119-127
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• 1985

A study is made of a special type of $C^{\ast}$ -dynamical systems, consisting of a class $n^{\infty}$ uniformly hyperfinite $C^{\ast}$-algebra A, the torus group $G=T^{d}$ ($$1{\leq_-}d{\leq_-}n-1$$) and a natural product action of G on A by $^{*}-automorphisms$. We give some conditions for product states on the fixed point algebra $A^{G}$ of A by G to be factorial.