• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.8
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• pp.639-651
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• 2018

An analytical solution to generate attitude command profile for agile spacecraft is proposed. In realistic environment, obtaining analytical minimum-time optimal solution is very difficult because of following constraints-: 1) actuator saturation, 2) flexible mode excitation, 3) uplink command bandwidth limit. For that reasons, this paper applies two simplifications, an eigen-axis rotation and a finite-jerk approximated profile, to derive the solution in an analytical manner. The resulting attitude profile can be used as a feedforward or reference input to on-board attitude controller, and it can enhance spacecraft agility. Equations of attitude command profile are derived in two general boundary conditions: rest-to-rest maneuver and spin-to-spin maneuver. Simulation results demonstrate that the initial and final boundary conditions, in terms of time, attitude, and angular velocities, are well satisfied with the proposed analytical solution. The derived attitude command generation algorithm may be used to minimize a number of parameters to be uploaded to spacecraft or to automate a sequence of attitude command generation on-board.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.899-903
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• 2013

A self-bearing is an electric machine that achieves both rotational actuation and magnetic levitation using a single magnetic structure. To be able to stably levitate the rotor in a self-bearing, one needs to have an inverse of the force-current model. However, the force-current model in a self-bearing motor is typically not square. Furthermore, the elements of the matrix vary with respect to the rotational angle, resulting in singularities of the pseudo-inverse at various angles. In this paper, we propose a new force-current model that eliminates the singularities by adding a constraint in coil currents. This constraint eliminates the flux density in the stator core so that the saturation problem in the previous study is avoided. By implementing this force-current model, we are able to implement a levitation controller for a toroidally-wound self-bearing BLDC motor. The model inversion and levitation are validated experimentally.

• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.443-448
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• 2003

A study on optimum design of the lightweight mirror of a satellite camera is presented. An optical surface deformation of the lightweight mirror, which is a principal component of the camera system, is an important factor affecting the optical performance of the whole camera system. In this study, optimum design of the lightweight mirror is presented. Total weight of the mirror to reduce the optical surface deformation and the launching cost is used as an objective function. Peak-to-valley value and natural frequency of the mirror are given as constraints to the optimization problem. The sensitivities of the objective function and constraint are calculated by a finite difference method. The optimization procedure is carried out by the commercial optimizer, DOT. As a verification of the optimum design of the mirror, two design examples are treated. In the real application example, the lightweight mirror with 600mm effective diameter is treated. The optimized results with various design variables, which are obtained by considering thickness limitations, are analyzed.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.18 no.1
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• pp.39-46
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• 1982

The author has developed the computer program in order to calculate the optimum alignment condition of marine propulsion shafting by linear programming method. The input of program was calculated by the matrix method of three-moment. He compared the calculated values with the experimental values measured by the strain gage on the model shaft, and the values of calculation on actual propulsion shafting with those of Det norske Veritas. The computer program of optimum alignment has been applied to the actual shaft. The results obtained are as follows: 1. To obtain the reaction of supporting points in the straight line necessary to the optimum alignment and the reaction influence number, after the computer program had been developed and then adapted, the result of experimental values and calculated values agreed with each other and the values of the actual shaft were also approximately similar to the values of other program. 2. In this paper, the measuring method on model shaft by strain gage can be effectively used at the time of adjusting alignment condition of actual shaft. 3. The supporting bearing should be considerably readjusted to the vertical direction in order to satisfy some limited condition.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.630-648
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• 1992

The minimum weight design for simply-supported isotropic or symmetrically laminated stiffened cylindrical shells subjected to various loads (axial compression or combined loads) is studied by a nonlinear mathematical search algorithm. The minimum weight design in accomplished with the CONMIN optimizer by Vanderplaats. Several types of buckling modes with maximum allowable stresses and strains are included as constraints in the minimum weight design process, such as general buckling, panel buckling with either stingers or rings smeared out, local skin buckling, local crippling of stiffener segments, and general, panel and local skin buckling including stiffener rolling. The approach allows the consideration of various shapes of stiffening members. Rectangular, I, or T type stringers and rectangular rings are used for stiffened cylindrical shells. Several design examples are analyzed and compared with those in the previous literatures. The unstiffened glass/epoxy, graphite/epoxy(T300/5208), and graphite/epoxy aluminum honeycomb cylindrical shells and stiffened graphite/epoxy cyindrical shells under axial compression are analyzed through the present approach.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1370-1378
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• 2007

High speed railway bridge is affected on safety of bridge by dynamic amplification effect, when dynamic response of bridge is equal to effect cycle load for rolling stock axle according to high speed operation train. And excessive deformation of structure has negative effect on operation safety of train and comfort of passenger due to fluctuation of wheel load by torsion of track etc. and decrease of contact force on vehicle wheel-rail. To ensure the safety of track and train operation safety, it is have to perform the study on resonance and deformation of structure. That criteria and requirement of railway bridge is limitation of vertical acceleration on deck for dynamic behavior of structure, contact of vehicle wheel and rail, limitation of face distortion and rotation angle of end deck, and limitation of vertical displacement by train. Unlike KYEONGBU High Speed Railway, New constructed HONAM High Speed Railway have to applied the new requirement for dynamic behavior safety according to change of condition which is type of ballast (slab ballast), interval of track, and actual rolling stock load. Therefore, in this paper, it was conformed the dynamic characteristic due to parameter, which related with above mentioned criteria, for steel composite bridges.

• Journal of Korea Multimedia Society
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• v.12 no.3
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• pp.372-382
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• 2009

When the range of projection angles is limited, tomographic reconstruction suffers from artifacts caused by incomplete data. One can consider a data completion technique, which estimates projection data at unobserved angles using a prior knowledge or mathematical exploration, but the result is often not improved; the improvement by the data completion often undermined by the artifacts by inaccurate estimation, In this paper, we propose an iterative method, which computes projection data at unobserved angles by using the current estimate on the image, links the computed projection data to the observed ones by using the consistence condition of Radon transform, and reconstruct the next estimate on the image by filtered backprojection. The proposed method does not require a prior knowledge on the image, and has much faster approximation rate than the expectation maximization method. The performance of the proposed method was tested through several simulation studies.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.4
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• pp.67-71
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• 1990

This study is concerned with the optimum design of stiffened cylindrical members frequently found in floating offshore platforms with constraints on reliability. Minimised is the expected total cost which is composed of the structural cost and the expected failure cost. Some design requirements drawn from variotus design codes are also considered as constraints. Reliability of critical component in a structure only is considered in this paper and the system failure is discarded since the probability of system failure is in general much smaller than the probability of component failure and it is very difficult to evaluate the cost due to system failure. Ultimate strength only is considered and not the fatigue strength. Several parametric studies are illustrated and the optimum solutions for different strength models which are now in use for the design of stiffened cylinders are derived to show the optimum designs against different strength models for the same type of structural component. The present results lead to the important conclusions relating to the posibility of more cost saving in the design of such structure through the reliability-based optimisation process.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.6
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• pp.106-113
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• 2017

In this paper, we propose a suitable network topology for the Ethernet based Train Communication Network (TCN) for control system in a autonomous multi-articulated vehicle. We propose a network topology considering the structural constraints such as the number of cables and ports, and the performance constraints such as network response time and maximum throughput. We compare the network performances of star topology and daisy chain topology as well as hybrid topology, which is proposed in previous studies and a compromise between daisy chain and star topology. Here, the appropriate number of nodes in a group is obtained for the configuration of the hybrid topology. We first derive estimates of the network performance through simulation with different topologies, and then, implement the network by connecting the actual devices with each network topology. The performance of each topology is measured using various network performance measurement programs and the superiority of the proposed topology is described through comparison.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.163.1-163.1
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• 2012

이 연구는 우주물체에 대한 광학감시 및 추적을 수행하기 위한 선행연구로, 궤도전파 시뮬레이터를 개발하여 궤도상 위성의 광학관측가능성을 분석하고 광학관측 여부를 판단하는 것을 목표로 한다. 연구의 주 내용은 주어진 궤도정보를 바탕으로 하는 태양동기궤도(Sun-Synchronous Orbit; SSO) 위성, Dawn-dusk 위성, 저궤도(Low Earth Orbit; LEO) 위성, 정지궤도(Geostationary Orbit; GEO) 위성 등 궤도상 위성의 추정궤도 전파와 자국위성의 광학관측가능성 분석으로 구성된다. 각각의 궤도전파 정밀도 및 광학관측가능성 분석성능을 확인하기 위해 AGI(Analytical Graphics Incorporated)사의 STK(Satellite Tool Kit) 시뮬레이션 프로그램을 사용하여 개발된 궤도전파 시뮬레이터와 비교하였다. 시뮬레이션 과정에서 광학관측의 제한조건을, 지구반영(penumbra)과 태양직사광(direct sun)에서만 관측하며, 고도(elevation angle)의 최소값은 20도, 태양고도(Sun elevation angle)의 최대값은 -10도로 설정하였다. 광학관측이 이루어지는 가상의 관측소는 임의로 선정하였으며, 기본적인 관측시간은 1년으로 잡고, 계절의 변화에 따른 광학관측가능성 궤적의 변화를 보기위해 춘하추동에 대해서 각각 3일이내의 기간 동안 시뮬레이션을 수행하였다. 결과적으로, 우주물체 광학감시 및 추적을 수행하기 위한 광학관측가능성 분석성능은 궤도전파 시뮬레이터 및 초기궤도요소 정밀도, 좌표변환과정 오차 등의 영향을 받으며, 설정된 제한조건에 따라 광학관측 지속시간의 차이가 발생한다. 연구결과를 통해 궤도상 위성의 궤도를 추정하기 위한 위성의 궤도전파 시뮬레이터를 개발하고, 자국위성의 관측가능성 분석을 통해 광학감시 및 추적시스템의 운영이 원활히 이루어질 수 있도록 한다.