• Journal of the Chungcheong Mathematical Society
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• v.20 no.4
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• pp.477-484
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• 2007

Let h : M ${\rightarrow}$ M be an almost periodic homeomorphism of a compact metric space M onto itself. We prove that h is topologically transitive iff every element of M has a dense orbit. It follows as a corollary that an almost periodic homeomorphism of a compact metric space onto itself can not be chaotic. Some additional related observations on a Cantor set are made.

• Journal of applied mathematics & informatics
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• v.3 no.1
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• pp.47-54
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• 1996

We prove that if RUC(S) has a left invariant mean ${\rho}={T_{S} : s \;{\in}\; S}$ is a continuous repesentation of S as nonexpansive map-pings on a closed convex subset C of a p-uniformly convex and p-uniformly smooth Banach space and C contains an element of bounded orbit then C contains a common fixed point for ${\rho}$.

• Journal of Mechanical Science and Technology
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• v.20 no.2
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• pp.177-184
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• 2006

An orbital design method of the formation initialization based on the relative orbital element method is presented. It firstly constructed the relative motion equation of the satellite formation flying in terms of the leader and followers' orbital elements. Then the equation was simplified when the orbit eccentricity of the leader satellite was small. And according to the satellites' mission, a general design method for the relative trajectory was proposed. The advantage of this method is that one can get a very simple analytical formula of each follower satellite's orbital elements when the orbital eccentricity of the leader satellite is zero. The simulation results show that the method is effective.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.238-244
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• 2017

A spindle with a built-in motor can be used to simplify the structure of a machine tool system, but the rotor inevitably has unbalanced mass. This paper presents an analysis of the dynamic behavior. The spindle was used in a CNC lathe and investigated using the finite element method and transfer matrices. The high-speed spindle can be very sensitive to the rotation of an unbalanced mass, which has a harmful effect on many machine tools. Thus, a balancing procedure was performed with a spindle-bearing system for the CNC lathe by numerical analysis. The balancing was performed through the influence coefficient method, and the whirl orbit radii before and after balancing were compared to evaluate the effects. The results show that the rotational speed of the spindle seriously affects the whirl responses of the spindle. The whirl responses were also affected by other factors, such as the unbalanced mass and bearing stiffness. The balancing of the assembled spindle model significantly reduced the whirl orbit magnitude.

• Journal of Astronomy and Space Sciences
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• v.32 no.3
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• pp.237-245
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• 2015

A strategy is needed for a regional survey of geosynchronous orbits (GSOs) to monitor known space objects and detect uncataloged space objects. On the basis of the Inter-Agency Debris Committee's recommendation regarding the protected region of geosynchronous Earth orbit (GEO), target satellites with perigee and apogee of $GEO{\pm}200km$ and various inclinations are selected for analysis. The status of the GSO region was analyzed using the satellite distribution based on the orbital characteristics in publicly available two-line element data. Natural perturbation effects cause inactive satellites to drift to two stable longitudinal points. Active satellites usually maintain the designed positions as a result of regular or irregular maneuver operations against their natural drift. To analyze the detection rate of a single optical telescope, 152 out of 412 active satellites and 135 out of 288 inactive satellites in the GSO region were selected on the basis of their visibility at the observation site in Daejeon, Korea. By using various vertical view ranges and various numbers of observations of the GSO region, the detection efficiencies were analyzed for a single night, and the numbers of follow-up observations were determined. The orbital estimation accuracies were also checked using the arc length and number of observed data points to maintain the GSO satellite catalog.

• Journal of the Korean Magnetics Society
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• v.24 no.2
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• pp.66-69
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• 2014

The spreading tube of X-ray cathode tube displayed with an electromagnetic finite element method was designed. To analyze a feature design and the concrete coordinate performance of soft X-ray tube modeling, the orbit of electron beam was simulated by OPERA-3D SW program. The fixed conditions were the applied voltage, the temperature, the work function of thermal electron between cathode and anode of tungsten. Through the analysis of distribution of electron beam and the variation of dividing region, the design of soft X-ray spreading tube equipped with two cross filaments was optimized.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.8
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• pp.692-700
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• 2014

In this work, satellite FE (finite element) model updating for the prediction of the effect of micro-vibration is described. In the case of satellites launched in low earth orbit, high agility and more mission accomplishments are required by the customer in order to procure many images from satellites. To achieve the goal, many mechanisms, including high capacity wheels and antennas with multi-axis gimbals have been widely adopted, but they become a source of micro-vibration which could significantly deteriorate the quality of images. To investigate the effect due to the micro-vibration in orbit on the ground, a prediction is conducted through an integrated model coupling the measured jitter sources with FE (finite element) model. Before prediction, the FE model is updated to match simulation results with the modal survey test. Subsequently, the quality of FE model is evaluated in terms of frequency deviation error, the resemblance of mode shapes and FRFs (frequency response functions) between test and analysis.

• Structural Engineering and Mechanics
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• v.53 no.3
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• pp.443-453
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• 2015

Cable-beam structures characterized by variable stiffness nonlinearities are widely found in various structural engineering applications, for example in space deployable structures. Space deployable structures in orbit experience both high temperature caused by sun's radiation and low temperature by Earth's umbral shadow. The space temperature difference is above 300K at the moment of exiting or entering Earth's umbral shadow, which results in structural thermally induced vibration. To understand the thermally induced oscillations, the analytical expression of Boley parameter of cable-beam structures is firstly deduced. Then, the thermally induced vibration of cable-beam structures is analyzed using finite element method to verify the effectiveness of Boley parameter. Finally, by analyzing the obtained numerical results and the corresponding Boley parameters, it can be concluded that the derived expression of Boley parameter is valid to evaluate the occurrence conditions of thermally induced vibration of cable-beam structures and the key parameters influencing structural thermal flutter are the cable stiffness and thickness of beams.

• Journal of Astronomy and Space Sciences
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• v.29 no.3
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• pp.287-293
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• 2012

Satellite operating agencies are constantly monitoring conjunctions between satellites and space objects. Two line element (TLE) data, published by the Joint Space Operations Center of the United States Strategic Command, are available as raw data for a preliminary analysis of initial conjunction with a space object without any orbital information. However, there exist several sorts of uncertainties in the TLE data. In this paper, we suggest and analyze a method for estimating the uncertainties in the TLE data through mean, standard deviation of state vector residuals and covariance matrix. Also the estimation results are compared with actual results of orbit determination to validate the estimation method. Characteristics of the state vector residuals depending on the orbital elements are examined by applying the analysis to several satellites in various orbits. Main source of difference between the covariance matrices are also analyzed by comparing the matrices. Particularly, for the Korea Multi-Purpose Satellite-2, we examine the characteristics of the residual variation of state vector and covariance matrix depending on the orbital elements. It is confirmed that a realistic consideration on the space situation of space objects is possible using information from the analysis of mean, standard deviation of the state vector residuals of TLE and covariance matrix.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.9
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• pp.805-813
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• 2015

This paper introduces the development of temperature mapping code between thermal mesh and structural mesh in KARI Satellite Design Software. Generally, temperature distribution of a satellite varies with the time by the space environment of the orbit, so thermal expansion of the structure should be analysed in design of the satellite. For the sake of the coupled thermal structural analysis, an interpolation algorithm between two finite element heterogeneous grids has been proposed by which temperature transfer is successively conducted.