• 한국전자파학회논문지
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• 제17권9호
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• pp.829-835
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• 2006

본 논문에서는 초고출력용 X-band 카세그레인 반사판 안테나 시스템에서 반사판의 표면 형상을 변형시켜 spill-over가 효과적으로 감소하는 현상에 대하여 이론적인 고찰을 수행하였다. 이러한 구조는 이중의 쌍곡면 부 반사판을 적용함으로써 주 반사판의 크기를 확장하지 않고 급전 혼 안테나에서 방사된 전파 패턴의 확장각을 증가시켜 spill-over특성이 감소되도록 설계하였다. 결과적으로 본 논문에서 제안된 카세그레인 반사판 안테나가 기존의 설계 방법에 의한 반사판 안테나에 비해 약 9 %의 효율 향상과 10 dB의 부엽 레벨 감소가 구현됨을 이론적으로 확인하였다.

• 전기학회논문지
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• 제60권6호
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• pp.1245-1254
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• 2011

This paper proposes a target tracking algorithm for wheeled mobile robots using in various fields. For the stable tracking, we apply a vision system to a mobile robot which can extract targets through image processing algorithms. Furthermore, this paper presents an algorithm to position the mobile robot at the desired location from the target by estimating its relative position and attitude. We show the problem in the tracking method using the Position-Based Visual Servo(PBVS) control, and propose a tracking method, which can achieve the stable tracking performance by combining the PBVS control with Image-Based Visual Servo(IBVS) control. When the target is located around the outskirt of the camera image, the target can disappear from the field of view. Thus the proposed algorithm combines the control inputs with of the hyperbolic form the switching function to solve this problem. Through both simulations and experiments for the mobile robot we have confirmed that the proposed visual servo control method is able to enhance the stability compared to of the method using only either PBVS or IBVS control method.

• Geomechanics and Engineering
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• 제4권4호
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• pp.263-279
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• 2012

The present paper deals with the analysis of combined footings resting on geosynthetic reinforced granular fill overlying stone column improved poor soil. An attempt has been made to study the influence of inclusion of geosynthetic layer on the deflection of the footing. The footing has been idealized as a beam having finite flexural rigidity. Granular fill layer has been represented by Pasternak shear layer and stone columns and poor soil have been represented by nonlinear Winkler springs. Nonlinear behavior of granular fill layer, stone columns and the poor soil has been considered by means of hyperbolic stress strain relationships. Governing differential equations for the soil-foundation system have been derived and solution has been obtained employing finite difference scheme by means of iterative Gauss Elimination method. Results of a detailed parametric study have been presented, for a footing supporting typically five columns, in non-dimensional form in respect of deflection with and without geosynthetic inclusion. Geosynthetic layer has been found to significantly reduce the deflection of the footing which has been quantified by means of parametric study.

• 한국항해학회지
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• 제22권3호
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• pp.9-16
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• 1998

Loran C is a low frequently , pulsed. hyperbolic radio aid to navigation system, which operates in the 90 to 110 kHz frequency band. The position accuracy is not excellent but the repeatable and relative accuracy is very good, and it is very useful for fishing vessel in coastal waters. The operation of China north sea chain9GRI 7430) was begun on January, 1996, and in order to evaluate the accuracy of this chain, it was observed with Loran C receiver (LC-90, Furuno) in July 9 and December 30, 1997 at the fixed position of Kunsan national university. The obtained results were as follows : The time difference error of M-X, M-Y pair were $0.5{\mu}s$, $4.4{ \mu}s$ respectively and the mean time difference of M-X, M-Y pair were $15120.4{,\mu}s$ $32085.4{\mu}s$ respectively. The Loran C signals were received steadily and the daily fluctuation of time difference was very small. The longitudinal position error was very much than latitudinal position error, and the mean position error was about 1091.8m.

• KSTLE International Journal
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• 제1권2호
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• pp.101-106
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• 2000

Variable displacement axial piston pumps are widely used for raising the energy level of the fluid in hydraulic systems. And the regulator is the device which regulates the discharge flow of the piston pump by controlling the swivel angle. The regulator receives the hydraulic pilot pressure and controls the pump output flow depending on the machine load and engine speed. This work deals with constant power control (horsepower control) in the design of a regulator by using a bent-axis type piston pump. In order to effectively use engine power, we must keep the horsepower from the engine to the pump constant. Therefore the regulator operates the constant power control. As a result, optimum power usage is obtained by accurately following the power hyperbola. This study focused on developing a simulation model of a regulator. First, the governing equations of the regulator are derived, and analysis is performed by computer simulation, which can identify significant parameters of regulator. As a result, the variation of the swivel angle, flow rate, hyperbolic curve, inner leakage and responsibility are simulated, and significant parameters of a regulator are identified.

• Structural Engineering and Mechanics
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• 제52권1호
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• pp.19-33
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• 2014

Structural robustness refers to the ability of a structure to avoid disproportionate consequences to the original cause. Currently attentions focus on the concepts of structural robustness, and discussions on methods of robustness based structural design are rare. Firstly, taking basis in robust $H_{\infty}$ control theory, structural robustness is assessed by $H_{\infty}$ norm of the system transfer function. Then using the SIMP material model, robustness based design of grid structures is formulated as a continuum topology optimization problem, where the relative density of each element and structural robustness are considered as the design variable and the optimization objective respectively. Generalized elitist genetic algorithm is used to solve the optimization problem. As examples, robustness configurations of plane stress model and the rectangular hyperbolic shell model were obtained by robustness based structural design. Finally, two models of single-layer grid structures were designed by conventional and robustness based method respectively. Different interference scenarios were simulated by static and impact experiments, and robustness of the models were analyzed and compared. The results show that the $H_{\infty}$ structural robustness index can indicate whether the structural response is proportional to the original cause. Robustness based structural design improves structural robustness effectively, and it can provide a conceptual design in the initial stage of structural design.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.948-955
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• 2005

In this case of study, Incheon International Airport 2nd phase site preparation 1st section estimated final settlement to improve soft ground. Final settlement is very important in preloading method. Recently, Hyperbolic method, Hoshino method and Asaoka method are used mostly in prediction of final settlement and this paper, Comparing a result of Final settlement, used to Artificial Neural Network. The structure of Dynamic Artificial Neural Network which predicted Final settlement, has application to Young_Jong Island other site, If new investigation data will be added. Also, It is expected to save measuring_system cost in soft ground.

• 대한기계학회논문집
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• 제18권4호
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• pp.1039-1049
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• 1994

The intermitternt and transient fuel spray have been investigated from the simultaneous measurement of droplet sizes and velocities by using Phase/Doppler Particle Analyzer(PDPA). Measurement have been done on the spray axis and at the edge of the spray near nozzle at various gas-to-liquid density ratios(.rho./sub g//.rho./sub l/) that ranges from those found in free atmospheric jets to conditions typical of diesel engines. Probability density distributions of the droplet size and velocity were obtained from raw data and mathematical probability density functions which can fit the experimental distribations were extracted using the principle of maximum likelihood. In the near nozzle region on the spray axis, droplet sizes ranged from the lower limit of the measurement system to the order of nozzle diameter for all (.rho./sub g/ /.rho./sub l/) and droplet sizes tended to be small on the spray edge. At the edge of spray, average droplet velocity peaked during needle opening and needle closing. The rms intensity is greatly incresed as the radial distance from the nozzle is increased. The probability density function which can best fit the physical breakage process such as breakup of fuel drops is exponecially decreasing log-hypebolic function with 4 parameters.

• Journal of Mechanical Science and Technology
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• 제15권8호
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• pp.1165-1173
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• 2001

This paper deals with dynamic analysis of Pipeline Inspection Gauge (PIG) flow control in natural gas pipelines. The dynamic behaviour of PIG depends on the pressure differential generated by injected gas flow behind the tail of the PIG and expelled gas flow in front of its nose. To analyze dynamic behaviour characteristics (e.g. gas flow, the PIG position and velocity) mathematical models are derived. Tow types of nonlinear hyperbolic partial differential equations are developed for unsteady flow analysis of the PIG driving and expelled gas. Also, a non-homogeneous differential equation for dynamic analysis of the PIG is given. The nonlinear equations are solved by method of characteristics (MOC) with a regular rectangular grid under appropriate initial and boundary conditions. Runge-Kutta method is used for solving the steady flow equations to get the initial flow values and for solving the dynamic equation of the PIG. The upstream and downstream regions are divided into a number of elements of equal length. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. Simulation is performed with a pipeline segment in the Korea gas corporation (KOGAS) low pressure system. Ueijungboo-Sangye line. The simulation results show that the derived mathematical models and the proposed computational scheme are effective for estimating the position and velocity of the PIG with a given operational condition of pipeline.

• 한국공작기계학회논문집
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• 제16권5호
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• pp.134-139
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• 2007

This paper presents a computer-based analysis on the thermal shock characteristics of Pb-free solder joints and UBM in flip chip assemblies. Among four types of popular UBM systems, TiW/Cu system with 95.5Sn-3.9Ag-0.6Cu solder joints was chosen for simulation. A simple 3D finite element model was first created only including silicon die, mixture between underfill and solder joints, and substrate. The displacements due to CTE mismatch between silicon die and substrate was then obtained through FE analysis. Finally, the obtained displacements were applied as mechanical loads to the whole 2D FE model and the characteristics of flip chip assemblies were analyzed. In addition, based on the hyperbolic sine law, the accumulated creep strain of Pb-free solder joints was calculated to predict the fatigue life of flip chip assemblies under thermal shock environments. The proposed method for fatigue life prediction will be evaluated through the cross check of the test results in the future work.