• International Journal of Aeronautical and Space Sciences
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• v.15 no.3
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• pp.335-343
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• 2014

An airbag is an important safety system and is well known as a safety system in cars during an accident. Airbag systems are also used as a shock absorber for UAVs to assist with rapid parachute landings. In this paper, the dynamics and gas dynamics of five airbag shapes, cylindrical, semi-cylindrical, cubic, and two truncated pyramids, were modelled and simulated under conditions of impact acceleration lower than $4m/s^2$ to avoid damage to the UAV. First, the responses of the present modelling were compared and validated against airbag test results under the same conditions. Second, for each airbag shape under the same conditions, the responses in terms of pressure, acceleration, and emerging velocity were investigated. Third, the performance of a pressure relief valve is compared with a fixed-area orifice implemented in the air bag. For each airbag shape under the same conditions, the optimum area of the fixed orifice was determined. By examining the response of pressure and acceleration of the airbag, the optimum shape of the airbag and the venting system is suggested.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.3
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• pp.460-465
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• 2003

Microgravity experiments were conducted to determine the effect of liquid and gas superficial velocities on flow behaviors. Flow behaviors observed under microgravity conditions can be classified into five flow patterns: bubble. Taylor bubble, slug, semi-annular and annular flows. Transition boundary between four flow patterns could be determined by drift-flux model. It was also found that the effect of gravity and pipe inclination on flow pattern transition was not significant in the inertia dominant region.

• Journal of Korean Institute of Industrial Engineers
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• v.28 no.3
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• pp.256-263
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• 2002

This paper addresses a planning problem in a pickup-delivery transportation' system under dynamic vehicle dispatching. We present a procedure to determine a fleet size in which stochastic characteristics of vehicle travels are considered. Statistical approach and queueing theory are applied to estimate vehicle travel time and vehicle waiting time, based on which an appropriate fleet size is determined. Simulation experiments are performed to verify the proposed procedure.

• Journal of Korean Institute of Industrial Engineers
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• v.13 no.2
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• pp.17-34
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• 1987

Modern telecommunication switching systems are SPC (Stored Program Control) machines handling voice, data and other kinds of traffic, in an environment which tends to be fully digital switching and transmission. The throughput of such systems is determined by the real time capacity of its centralized or distributed control processors and by the traffic capacity of the switching network. Designers must verify the traffic and call processing capacity of the switching system and check its performance under traffic load before it is put into service. Verification of traffic and call processing capacity of switching systems is one of the problems treated by teletraffic studies; teletraffic studies are based on stochastic process, queueing theory, simulations and other quantitative methods of decision making. This paper reviews the general methodologies to evaluate the throughput and performance of the digital switching system. TDX-10, which is a fully digital switching system under development in ETRI, is employed to give illustrative examples of the methodologies discussed in this paper.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.273-278
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• 2006

In order to use a GPS antenna for launch vehicles, it should be installed on the skin of the vehicle and be able to normally receive the live GPS signals during the vehicle's full flight mission. The GPS antenna on the surface of the launch vehicle is, however, exposed to higher temperature than inner equipments of the vehicle due to aerodynamic heating generated during the flight. Test specification of the GPS antenna for qualification of hot-temperature is determined to $+95^{\circ}C$ that is higher than inner components by $25^{\circ}C$. Test results in this paper show that the GPS antenna normally operates under the above environment.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.1
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• pp.43-56
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• 2011

An integrated system composed of guidance, navigation and control (GNC) system for autonomous proximity operations and the docking of two spacecraft was developed. The position maneuvers were determined through the integration of the state-dependent Riccati equation formulated from nonlinear relative motion dynamics and relative navigation using rendezvous laser vision (Lidar) and a vision sensor system. In the vision sensor system, a switch between sensors was made along the approach phase in order to provide continuously effective navigation. As an extension of the rendezvous laser vision system, an automated terminal guidance scheme based on the Clohessy-Wiltshire state transition matrix was used to formulate a "V-bar hopping approach" reference trajectory. A proximity operations strategy was then adapted from the approach strategy used with the automated transfer vehicle. The attitude maneuvers, determined from a linear quadratic Gaussian-type control including quaternion based attitude estimation using star trackers or a vision sensor system, provided precise attitude control and robustness under uncertainties in the moments of inertia and external disturbances. These functions were then integrated into an autonomous GNC system that can perform proximity operations and meet all conditions for successful docking. A six-degree of freedom simulation was used to demonstrate the effectiveness of the integrated system.

• Journal of Soil and Groundwater Environment
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• v.20 no.4
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• pp.22-30
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• 2015

For the preliminary investigations of the bioclogging on groundwater artificial recharge system, studies for conditions and analytical methods of biofilm formation on sediments were performed. Based on the tested results, following conditions were determined for biofilm formation on batch process: optimum period for biofilm formation (30 days), the proper inoculating water (pond water), medium (minimum salt medium with 0.1% yeast extract). Procedures for the measurement of ATP and DHA were also determined. Biomass extract was used for ATP measurement, while sediment itself for DHA. Effects of metals on the biofilm formation were investigated under the determined conditions. Different sensitivities and orders were found depending on tested metals and measurement methods. In general, biomass measurement by ATP and viable cell count showed higher sensitivity than that of DHA. Following toxicity orders were also appeared for ATP and viable cell: Cu ≈ Cd > As(III).

• The Journal of Korean Medicine
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• v.26 no.3 s.63
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• pp.162-175
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• 2005

Backgrounds : Two stress pathways, the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system, regulate immune system responses through release of corticosteroids, norepinephrine and epinephrine. respectively. These neuromediators act on immune cells via specific receptors on their surface to modulate the production of key regulatory cytokines. Objectives : To evaluate the preventive effects of oriental medicine Hyeolbuchukyeo-tang (HC) on stress. Methods : Mice were divided into three groups: nounal group, control group under immobilization stress and HC group which received Hyeolbuchukyeo-tang (HC) under immobilization stress. following sacrifice, their splenocytes were isolated and splenocyte surface markers were determined. The brains were removed and mRNA determined. In vivo, we separated RNA Iron cultured macrophages (RAW264.7). Results : In our study, immune functions were decreased in stress due mainly to changes of various neuromediators, cytokines and macrophage activities, and the treatment of HC increased those expressions. Conclusions : In summary, the present study documents the anti-stress effects of HC through stress-immune regulation.

• Structural Engineering and Mechanics
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• v.43 no.5
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• pp.561-582
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• 2012

Despite popularity of FEM in analysis of static and dynamic structural problems and the routine applicability of FE softwares, analytical methods based on simple mathematical relations is still largely sought by many researchers and practicing engineers around the world. Development of such analytical methods for analysis of free vibration of non-prismatic beams is also of primary concern. In this paper a new and simple method is proposed for determination of vibration frequencies of non-prismatic beams under variable axial forces. The governing differential equation is first obtained and, according to a harmonic vibration, is converted into a single variable equation in terms of location. Through repetitive integrations, integral equation for the weak form of governing equation is derived. The integration constants are determined using the boundary conditions applied to the problem. The mode shape functions are approximated by a power series. Substitution of the power series into the integral equation transforms it into a system of linear algebraic equations. Natural frequencies are determined using a non-trivial solution for system of equations. Presented method is formulated for beams having various end conditions and is extended for determination of the buckling load of non-prismatic beams. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained to those obtained using available finite element software.

• International Journal of Fluid Machinery and Systems
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• v.10 no.1
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• pp.47-53
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• 2017

Surface pressure integration and momentum method were respectively performed to evaluate the impeller thrust and the system thrust of a contra-rotating axial flow water jet propulsion, and an interesting phenomenon so-called thrust paradox was revealed. To explain the paradox, the impeller thrust and the system thrust were physically and theoretically analyzed, the results show that the impeller thrust is head involved and is determined by the hydraulic parameters upstream and downstream the impeller, while the momentum method depicted by a classic equation is valid simply under the best efficiency point. Consequently, the role of a water jet propulsion nozzle was deduced that the nozzle is mainly to limit the flow rate that crosses the impeller and to assure the system working under the best efficiency condition apart from its ability to produce momentum difference. Related mathematical formula expressed the nozzle diameter is the dominant variable used to calculate the working condition of the water jet propulsion. Therefore the nozzle diameter can be steadily estimated by the former expression. The system thrust scaling characteristics under various speeds were displayed lastly.