• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.8
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• pp.692-698
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• 2015

This paper represents a trajectory design and analysis technique which uses invariant manifolds of the circular restricted three body problem. Instead of the classical patched conic method based on 2-body problem, the equation of motion and dynamical behavior of spacecraft in the circular restricted 3-body problem are introduced, and the characteristics of Lyapunov orbits near libration points and their invariant manifolds are covered in this paper. The trajectories from/to Lyapunov orbits are numerically generated with invariant manifolds in the Earth-moon system. The trajectories in the Sun-Jupiter system are also analyzed with various initial conditions in the boundary surface. These methods can be effectively applied to interplanetary trajectory designs.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.1
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• pp.53-60
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• 2005

The use of pipe-bends brings about non-uniform flows at the exit of them due to the velocity difference between inner and outer flows inside the bend. These phenomena may cause turbopump of satellite launch vehicle to run off-design and reduce its efficiency, and also introduce unstable influx of propellants to engine manifold after passing through a turbopump. In order to improve the uniformity of flow at the bend exit, certain turning vanes are set up in the bend pipe normally. Correspondingly the design is an $90^{\circ}\;and\;45^{\circ}$ bend pipes that incorporate with the maximum three turning vanes. All designs were analyzed with numerical analysis by solving the Navier-Stokes equations in three dimensions in case of each respective fuel and oxidizer. Evaluations of the vaned pipe bends designs were accomplished by the velocity magnitude distributions and the predicted pressure drops. We could find that the more vaned bend pipe and larger angle pipe under consideration effectively, the more uniform velocity magnitude of the bend and pressure losses.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.1
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• pp.80-89
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• 1998

The residual gas in an spark-ignition engine is one of important factors on emissions and performance such as combustion stability. With high residual gas fractions, flame speed and maximum combustion temperature are decreased and these are deeply related with combustion stability especially at idle and NOx emission at relatively high engine load. Therefore, there is a need to characterize the residual gas fraction as a function of the engine operating load. Therefore, there is a need to characterize the residual gas fraction as a function of the engine operating parameters. In the present study, the quantitative measurement technique of residual gas fraction was studied by using Fast Response Flame Ionization Detector(FRFID). The measuring technique and model for estimation of residual gas fraction were reported in this paper. By the assuming that the raw signal from FRFID saturates with the same slope for firing and misfiring cycle, in-cylinder hydrocarbon(HC) concentration can be estimated. Residual gas fraction can be obtained from the in-cylinder HC concentration measured at firing and motoring condition. The developed measurement and calibration procedure were applied to the limited engine operating and design condition such as intake manifold pressure and valve overlap. The results show relevant trends by comparing those from previous studies.

• 제어로봇시스템학회:학술대회논문집
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• 1994.10a
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• pp.405-410
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• 1994

The purpose of this paper is to present the details of design procedure of a nonlinear regulator by Riemannian geometric approach and to applied it to the case of a double-effect evaporator. A nonlinear geometric model is proposed on a direct sum space of a state vector and a control vector as well as in the previous parers by the authors. The geometric model is derived by replacing the orthogonal straight coordinate axes of a linear system on the direct sum space with the curvilinear coordinate axes. The integral manifold of the geometric model becomes homeomorphic to that of fictitious linear system. For the geometric model a nonlinear regulator with a performance index is designed renewedly by the procedure of optimization. The construction method of the curvilinear coordinate axes on which the nonlinear system behaves as a linear system is discussed. To apply the above regulator theory to double-effect evaporators especially to the pilot plant at the University of Alberta, a suitable nonlinear model is determined by the plant dynamics. The optimal control law is derived through the calculation of the homeomorphism. As a result it is confirmed that the regulator is effective and superior to that of the conventional control.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.230-231
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• 2005

As environmental problems are important, automotive industries are developing various techniques to prevent air pollution. One of these is Positive Crankcase Ventilation (PCV) system. It removes blowby gas which includes about 30% hydrocarbon of total generated quantity. In this system, a PCV valve is attached in a manifold suction tube to control the flow rate of blowby gas which generates differently according to various operating conditions of an automotive engine. As this valve is very important, designers are feeling to design it because of both small size and high velocity. For this reason, we numerically investigated to understand both spool dynamic motion and internal fluid flow characteristics. As the results, spool dynamic characteristics, i.e. displacement, velocity, acting force, increase in direct proportion to the magnitude of differential pressure and indicate periodic oscillating motions. And, the velocity at the orifice region decreases according to the increase of differential pressure because of energy loss which is caused by the sudden decrease of flow area at the orifice region and the increase of flow volume in the front of spool head. Finally, the mass flow rate at the outlet decreases with the increase of spool displacement. We expect that PCV valve designers can easily understand fluid flow inside a PCV valve with our visual information for their help.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.549-557
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• 2005

The requirements of multi-resolution models of feature-based solids, which represent an object at many levels of feature detail, are increasing for engineering purposes, such as analysis, network-based collaborative design, virtual prototyping and manufacturing. To provide multi-resolution models for various applications, it is essential to generate adequate solid models at varying levels of detail (LOD) after feature rearrangement, based on the LOD criteria. However, the non-commutative property of the union and subtraction Boolean operations is a severe obstacle to arbitrary feature rearrangement. To solve this problem we propose history-based Boolean operations that satisfy the commutative law between union and subtraction operations by considering the history of the Boolean operations. Because these operations guarantee the same resulting shape as the original and reasonable shapes at the intermediate LODs for an arbitrary rearrangement of its features, various LOD criteria can be applied for multi-resolution modeling in different applications.

• Journal of the Korean Society of Visualization
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• v.10 no.1
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• pp.15-20
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• 2012

PCV(Positive Crankcase Ventilation) system is designed to remove blowby gas. In this system, a PCV valve is attached in a manifold suction tube to control the flow rate of blowby gas which generates various operating conditions of an automotive engine. As this valve plays a crucial role, the demand in its design is high owing to the small size and high velocity. For this reason, a numerical investigation was carried out to understand both the spool dynamic motion and internal fluid flow characteristics. As a result, the spool dynamic characteristics(i.e. displacement, velocity, acting force), increase in direct proportion to the magnitude of the pressure difference and indicate periodic oscillating motions. Moreover, the velocity at the orifice region decreases according to the increase in differential pressure due to energy loss caused by the sudden decrease of flow area at the orifice region and the increase of flow volume in front of the spool head. Finally, the mass flow rate at the outlet decreases with the increase of spool displacement.

• Journal of the Korean Institute of Educational Facilities
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• v.3 no.1
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• pp.39-52
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• 1996

Continuously expanding information technology is changing the world in which our students live. Many schools are using this new technology and many schools are contemplating the use of this new technology. The ways in which teachers and students work, and their dependence on information technology, have evolved significantly-increasing the importance of getting the information technology infrastructure right in schools. Yet, all too often, most of schools are unable to take full advantage of the opportunities that information technology offers since those designing and fitting out school buildings have failed to consider information technology adequately. This study is to guide the physical design of practical networked schools. In this paper, we present the ways to achieve architectural solutions to the manifold problems associated with accommodation of information technology in schools. The practical guidelines for planning and managing information technology infrastructure-that is, the spaces and services provided in the school building to support the user' information technology requirements-are offered. Adherence to these guidelines will provide a substantial degree of adapability and flexibility in school buildings.

• Aerospace Engineering and Technology
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• v.1 no.2
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• pp.113-122
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• 2002

A numerical analysis on the uniformity of propellant injection velocity of KSR-III has been carried out to give design improvements. Injector holes were approximated as porous media with the same pressure drop . The injection velocity is higher at the opposite side of the inlet for both LOX and fuel due to the static pressure rise in the stagnation region. Flow passages at the vertical circular plate in the LOX dome increase the uniformity of LOX injection. Little change was observed in the injection uniformity and pressure drop for the slanted LOX passage. Also provided were the O/ F ratio distributions from the oxidizer/ fuel injection velocity analysis.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.4
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• pp.297-305
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• 1991

Recently, automotive air conditioning system manufacturers have been made a great efforts on the system compactness and high efficiency. This growing interest comes improvements in evaporator thermal performance, one of the most important factors affecting the performance of air conditioning system. In order to improve design of compact type evaporator, this study executes performs to develop a computer program for evaporator thermal performance prediction of automotive air conditioning system. The brief summaries of this study are as follows: 1) To predict the overall thermal performance of serpentine type evaporator, the new simulating method is developed. 2) The calculations are performed as functions of oil mass concentration and refrigerant two-phase distribution at inlet manifold of evaporator. 3) The validity of this simulating program is confirmed by comparing the predicted thermal performance results to experimental results of practical available evaporator. 4) Based on these results, suggestions are made to improve the thermal performance of evaporator.