• Journal of Mechanical Science and Technology
• /
• 제16권12호
• /
• pp.1613-1626
• /
• 2002

This paper presents hybrid control of an active suspension system with a full-car model by using H$\sub$$\infty$/ and nonlinear adaptive control methods. The full-car model has seven degrees of freedom including heaving, pitching and rolling motions. In the active suspension system, the controller shows good performance: small gains from the road disturbances to the heaving, pitching and rolling accelerations of the car body. Also the controlled system must be robust to system parameter variations. As the control method, H$\sub$$\infty$/ controller is designed so as to guarantee the robustness of a closed-loop system in the presence of uncertainties and disturbances. The system parameter variations are taken into account by multiplicative uncertainty model and the system robustness is guaranteed by small gain theorem. The active system with H$\sub$$\infty$/ controller can reduce the accelerations of the car body in the heaving, pitching and rolling directions. The nonlinearity of a hydraulic actuator is handled by nonlinear adaptive control based on the back-stepping method. The effectiveness of the controllers is verified through simulation results in both frequency and time domains.

• 전자공학회논문지CI
• /
• 제38권2호
• /
• pp.27-32
• /
• 2001

본 논문은 패러렐 카메라 모델을 사용한 카메라 캘리브레이션과 3차원 스캐닝 알고리즘에 관한 것이다. 레이저 스트립라인이 스테레오 매칭을 위해 보조적으로 사용하였으나 원리적으로는 불필요하다. 피측정 물체는 스뎀핑모터에 의해 플레이트 위에서 360도 회전하며, 카메라로부터 거리를 측정하여 월드좌표를 구한다. 피측정 물체의 월드좌표는 모델좌표로 변환되며 다수의 군집 모델좌표로부터 모델링을 위한 면을 추출하고 OpenGL을 이용하여 렌더링 한다. 본 알고리즘은 에피폴라 라인의 매칭점의 유효성을 검사하여 잘못된 매칭값을 버리고 무효한 매칭값은 유효한 값으로부터 보간법으로 산출한다.

• 한국전산유체공학회지
• /
• 제17권1호
• /
• pp.94-100
• /
• 2012

In this paper, the cavitating flows around a hydrofoil have been numerically investigated by using a 2-d multi-phase RANS flow solver based on pseudo-compressibility and a homogeneous mixture model on unstructured meshes. For this purpose, a vertex-centered finite-volume method was utilized in conjunction with 2nd-order Roe's FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing. The Spalart-Allmaras one equation model was employed for the closure of turbulence. A dual-time stepping method and the Gauss-Seidel iteration were used for unsteady time integration. The phase change rate between the liquid and vapor phases was determined by Merkle's cavitation model based on the difference between local and vapor pressure. Steady state calculations were made for the modified NACA66 hydrofoil at several flow conditions. Good agreements were obtained between the present results and the experiment for the pressure coefficient on a hydrofoil surface. Additional calculation was made for cloud cavitation around the hydrofoil. The observation of the vapor structure, such as cavity size and shape, was made, and the flow characteristics around the cavity were analyzed. Good agreements were obtained between the present results and the experiment for the frequency and the Strouhal number of cavity oscillation.

• 한국컴퓨터정보학회논문지
• /
• 제7권1호
• /
• pp.94-102
• /
• 2002

본 논문에서는 국내 전파자원 관리를 위한 전파자원의 중장기 수요예측 방법론 개발의 전 단계로서 전파자원, 즉 주파수의 수요예측 방법론을 제시한다. 특히, 기존 공급자 위주의 하향식(Top-down) 개념의 수요예측 방법론이 아니라 무선자원을 실질적으로 소비하는 사용자를 중심으로 하는 상향식(Bottom-up) 개념의 주파수 수요예측 모형을 제시한다. 이는 크게 서비스 정의, 서비스 특성 분류, 서비스별 대표 속성 도출, 서비스 수요예측, 전파자원과의 매핑 검증 및 주파수 수요예측의 7단계로 이루어지며 각 단계에서 수행하여야 할 주요 업무를 설명한다. 아울러 PCS개인통신환경에서의 주파수 소요량 산출 예를 제시함으로서 개발된 모형의 타당성을 입증한다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
• /
• 제49권2호
• /
• pp.93-101
• /
• 2000

This paper presents a novel method for the transient of eddy currents in the dampers of a super-conducting synchronous generator(SCG). The method proposes a 2-D corrected model which takes into account the influence of leakage fluxes of the field winding ends by increasing the effective air gap in order to consider the high precision of the analysis for the conventional 2-D model. The electromagnetic fields for the corrected model are analyzed by the time-stepping finite element method, thus the eddy currents in the dampers and electro-motive forces(EMF) in the stator windings are calculated. As the results, it is proved the presented method is comparatively accurate by comparing measured phase EMF values and the simulation ones, where about 6.4% error at the maximum value of EMF is occurred between them.

• Journal of Preventive Medicine and Public Health
• /
• 제26권3호
• /
• pp.442-456
• /
• 1993

Financial stability is the foremost prerequisite for the continuous growth and development of hospitals. The present study aimed at developing a deterministic model using the factors which affect the hospitals profitability and at discovering which factor affected the hospital profitability. The study conducted questionnaire surveys on all general hospitals, with the exception of special hospitals, with over eighty hospital beds. Of the 274 subject hospitals, 136 of them, consituting 49.6% of the whole, were used in the study. The results are as follows. 1. In the deterministic model, outpatient revenue was affected more by the number of physician visits than by outpatient service intensity. Inpatient revenue was found to be affected more by the number of discharged patients than by inpatient service intensity. However, the increase rate of the service intensity not only contributed in stepping up the operating margin by $4{\sim}8%$ in outpatient and $3{\sim}6%$ in inpatient, but it was statistically significant. 2. Among the factors which determined the operating cost within the deterministic model, the number of patients had a greater impact on the operating cost than the resource consumption per patient. 3. The resource consumption per patient were proved to have the greatest effect on the profitability within the probabilistic model. The management cost per adjusted patient, in particular, was proven to have a statistically significant effect on the profitability in all hospitals.

• 한국항공우주학회지
• /
• 제33권10호
• /
• pp.10-16
• /
• 2005

본 연구에서는 3차원 시간 정확도를 가진 오일러 공탄성 해석 기법을 개발하였다. 유체-구조를 연계 시 발생할 수 있는 지연(lagging) 오차를 감소시키기 위해서 2차의 staggered 알고리즘을 적용하였다. 비정상 공력 해석과정에서 시간 정확도와 계산 시간을 줄이기 위해 사용된 병렬화된 다중격자기법(parallelized multi-grid method)과 DADI 기법을 기반으로 된 이중시간전진기법(dual-time stepping method)을 사용하였다. 오일러 공탄성 코드의 검증을 위해서 AGARD 445.6 날개 모델의 공탄성 해석을 수행하였다. 해석 결과는 실험값 및 다른 참고문헌의 해석 결과와 비교하였으며, 본 연구의 해석 결과가 다른 참고 문헌의 해석 결과들과 비교하여 상대적으로 실험값에 근접하였다.

• 한국지구과학회지
• /
• 제39권4호
• /
• pp.317-326
• /
• 2018

Effect of the nonuniform grid on the two-dimensional transport equation was investigated in terms of theoretical analysis and finite difference method (FDM). The nonuniform grid having a typical structure of the numerical weather forecast model was incorporated in the vertical direction, while the uniform grid was used in the zonal direction. The staggered and non-staggered grid were placed in the vertical and zonal direction, respectively. Time stepping was performed with the third-order Runge Kutta scheme. An error analysis of the spatial discretization on the nonuniform grid was carried out, which indicated that the combined effect of the nonuniform grid and advection velocity produced either numerical diffusion or numerical adverse-diffusion. An analytic function is used for the quantitative evaluation of the errors associated with the discretized transport equation. Numerical experiments with the non-uniformity of vertical grid were found to support the analysis.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 1998년도 추계 학술대회논문집
• /
• pp.90-95
• /
• 1998

The two-dimensional incompressible and compressible Navier-Stokes codes are developed for the computation of the viscous turbulent flow over high-lift airfoils. Incompressible code using pseudo-compressibility and dual-time stepping method involves a conventional upwind differencing scheme for the convective terms and LU-SGS scheme for time integration. Compressible code also adopts an FDS scheme and LU-SGS scheme. Several two-equation turbulence models (the standard $k-{\varepsilon}$ model, the $k-{\omega}$ model. and $k-{\omega}$ SST model) are evaluated by computing the flow over single and multi-element airfoils. The compressible and incompressible codes are validated by computing the flow around the transonic RAE2822 airfoil and the NACA4412 airfoil, respectively. Both the results show a good agreement with experimental surface pressure coefficients and velocity profiles in the boundary layers. Also, the GA(W)-1 single airfoil and the NLR7301 airfoil with a flap are computed using the two-equation turbulence models. The grid systems around two- and three-element airfoil are efficiently generated using Chimera grid scheme, one of the overlapping grid generation methods.

• 노동경제논집
• /
• 제41권3호
• /
• pp.95-128
• /
• 2018

본 연구는 우리나라 기혼여성들의 시간제, 전일제 등 근로형태가 오래 지속되는지 아니면 근로형태간 이동이 활발한지를 상태의존성(state dependence) 추정을 통하여 살펴보고, 최근의 변화를 분석하였다. 동태적 다항로짓모형(dynamic multinomial logit model) 추정결과 시간제와 전일제 상호간 이동성이 최근 낮아지면서 각 근로형태의 상태의존성은 강화되는 모습을 보였다. 따라서 시간제일자리는 전일제와 미취업 사이에서 근로형태간 이동을 활발하게 하는 디딤돌 또는 쉼터의 역할이 약화되고 전일제 외에 노동시장 참여 옵션을 제공하는, 전일제와는 구분된 추가적 일자리형태로 기능하고 있는 것으로 판단된다.