• International Journal of Aeronautical and Space Sciences
• /
• 제17권1호
• /
• pp.101-108
• /
• 2016

The RCS characteristics of stealth modified three-surface aircraft are analyzed in this paper. Prototype A is built with CATIA software and the three-dimensional digital models of modified stealth three-surface B and C are also designed based on carrier-based aircraft Su-33; the numerical simulation of RCS characteristics of three-surface aircraft is conducted with RCSAnsys software based on physical optics method and the method of equivalent currents; The following results are obtained by comparative analysis and mathematical statistics: (1) by the use of physical optics method and equivalent electromagnetic current method, the scattering intensity for each part of the model and RCS characteristic of the aircraft can be analyzed efficiently and accurately; (2) compared with model A, the mean RCS value of model B is reduced to 14.1% in forward direction and 48.1% in lateral direction; (3) compared with model A, the mean RCS value of model C decreases to 11.4% in forward direction and 21.6% in lateral direction. The results are expected to provide theoretical basis and technical support to the conceptual design of aircraft and stealth technology research.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2002년도 제24회 KOSCO SYMPOSIUM 논문집
• /
• pp.113-122
• /
• 2002

The purpose of this study is to verify that the modified Lagrangian model can predict temperature, flow and scalar fields in the high temperature recirculation region of swirling confined diffusion flame. In the meantime numerical results from EBU and Equilibrium PDF models as well as experimental results are compared with those from the modified Lagrangian model. Adaption of three different turbulent models were accompanied with this procedure. Look-up table of the ignition characteristic time scale which is one of important factors of the Lagrangian model was referred to the 11-step reduced mechanism. Eventually, results with the Lagrangian model show a good accordance with experimental results, which shows the validity of this model. Results from Chen's model differ from those of the others. Numerical results of ${\widetilde{k}$ show significant deviation from experimental results for three models.

• Communications for Statistical Applications and Methods
• /
• 제10권2호
• /
• pp.585-594
• /
• 2003

It has been generally recognized that conventional binomial or Poisson model provides poor fits to the actual correlated binary data due to the extra-binomial variation. A number of generalized statistical models have been proposed to account for this additional variation. Among them, beta-binomial, correlated-binomial, and modified-binomial models are binomial-related models which are frequently used in modeling the sum of n correlated binary data. In many situations, it is reasonable to assume that n correlated binary data are exchangeable, which is a special case of correlated binary data. The sum of n exchangeable correlated binary data is modeled relatively well when the above three binomial-related models are applied. But the estimation results of correlation coefficient turn to be quite different. Hence, it is important to identify which model provides better estimates of model parameters(success probability, correlation coefficient). For this purpose, a small-scale simulation study is performed to compare the behavior of above three models.

• 한국산업정보학회논문지
• /
• 제15권3호
• /
• pp.59-65
• /
• 2010

This paper proposes a modified heuristic mixed model assembly line (MMAL) balancing algorithm that provides consistent station assignments on a model by model basis as well as on a station by station. Basically, some of single model line balancing techniques are modified and incorporated to be fit into the MMAL. The proposed algorithm is based on N.T. Thomopoulos' [8] method and supplemented with several well proven single model line balancing techniques proposed in the literature until recently. Hoffman's precedence matrix [2] is used to indicate the ordering relations among tasks. Arcus' Rule IX [1] is applied to generate rapidly a fairly large number of feasible solutions. Consequently, this proposed algorithm reduces the fluctuations in operation times among the models as well as the stations and the balance delays. A numerical example shows that the proposed algorithm can provide a good feasible solution in a relatively short time and generate relatively better solutions comparing to other three existing methods.

• Transactions on Control, Automation and Systems Engineering
• /
• 제3권4호
• /
• pp.257-261
• /
• 2001

Nonlinear pulse width modulation (PWM) controlled system is considered to achieve control performance of thruster controlled spacecraft. The actual PWM controlled motions occur, very closely, around the average model trajectory. Furthermore nonlinear PWM controller design can be directly applied to thruster controlled spacecraft to determine thruster on-time. Sliding mode control for attitude tracking of three-axis thruster-controlled spacecraft is presented. Simulation results are shown which use modified Rodrigues parameters and sliding mode control law to achieve attitude tracking of a three-axis spacecraft with thrusters.

• Journal of Power Electronics
• /
• 제13권5호
• /
• pp.829-840
• /
• 2013

The modified sinusoidal pulse-width modulation (SPWM) is one of the PWM techniques used in three-phase AC-DC buck converters. The modified SPWM works without the current sensor (the converter is current sensorless), improves production of sinusoidal AC current, enables obtainment of near-unity power factor, and controls output voltage through modulation gain (ranging from 0 to 1). The main problem of the modified SPWM is the huge starting current and voltage (during transient) that results from a large step change from the reference voltage. When the load changes, the output voltage significantly drops (through switching losses and non-ideal converter elements). The single-input single-output (SISO) approach with minor-loop voltage feedback controller presented here overcomes this problem. This approach is created on a theoretical linear model and verified by discrete-model simulation on MATLAB/Simulink. The capability and effectiveness of the SISO approach in compensating start-up current/voltage and in achieving zero steady-state error were tested for transient cases with step-changed load and step-changed reference voltage for linear and non-linear loads. Tests were done to analyze the transient performance against various controller gains. An experiment prototype was also developed for verification.

• Computers and Concrete
• /
• 제34권2호
• /
• pp.169-178
• /
• 2024

To circumvent the constraints of time-consuming experimental methods, numerical simulation can be one of the most effective approaches to investigating chloride diffusion behaviors in concrete. However, except for the effect of the external environments, the transport direction of the chloride cannot be neglected when the concrete is exposed to the marine tidal zone, especially in certain areas of concrete members. In this study, based on Fick's second law, considering the effects of timevarying, chloride binding capacity, concrete stress state, ambient temperature, and relative humidity on chloride diffusion coefficient, the modified one-dimensional, two-dimensional, and three-dimensional novel modified chloride diffusion theoretical models were established through defining the current boundary conditions. The simulated results based on the novel modified multi-dimensional model were compared with the experimental results obtained from some previous pieces of literature. The comparing results showed that the modified multi-dimensional model was well-fitted with experimental data, confirming the high accuracy of the novel modified model. The experimental results in literature showed that the chloride diffusion in the corner area of the concrete structure cannot be simulated by a simple one-dimensional diffusion model, where it is necessary to select a suitable multi-dimensional chloride diffusion model for simulation calculation. Therefore, the novel modified multi-dimensional model established in this study has a stronger applicability for practical engineering.

• 한국농업기계학회:학술대회논문집
• /
• 한국농업기계학회 1996년도 International Conference on Agricultural Machinery Engineering Proceedings
• /
• pp.886-895
• /
• 1996

To fit the desorption isotherm and adsorption isotherm for Pangola grass, the modified Henderson model, Chung-Pfost model, modified Halsey model, and modified Oswin model were used to fit the experimental EMC /ERH data. A step-by -step ERH measuring technique was used in this study. The ERH data were collected at three temperature levels of 5 $^{\circ}C$, $25^{\circ}C$ and 5$0^{\circ}C$ for Pangola grass whole plant, stem , and foliage. The modified Halsey model has the best fit for both desorption isotherm and adsorption isotherm of Pangola grass whole plant as compared with other models.

• Structural Engineering and Mechanics
• /
• 제44권5호
• /
• pp.585-600
• /
• 2012

This paper presents a Modified Tikhonov Regularization (MTR) method in model updating for damage identification with model errors and measurement noise influences consideration. The identification equation based on sensitivity approach from the dynamic responses is ill-conditioned and is usually solved with regularization method. When the structural system contains model errors and measurement noise, the identified results from Tikhonov Regularization (TR) method often diverge after several iterations. In the MTR method, new side conditions with limits on the identification of physical parameters allow for the presence of model errors and ensure the physical meanings of the identified parameters. Chebyshev polynomial is applied to approximate the acceleration response for moderation of measurement noise. The identified physical parameter can converge to a relative correct direction. A three-dimensional unsymmetrical frame structure with different scenarios is studied to illustrate the proposed method. Results revealed show that the proposed method has superior performance than TR Method when there are both model errors and measurement noise in the structure system.

• 한국수자원학회논문집
• /
• 제43권9호
• /
• pp.823-833
• /
• 2010

침수식생 개수로 흐름은 식생영역과 상부영역에 서로 다른 흐름구조를 보인다. 즉, 식생영역에서 전단으로 인해 생성되는 난류는 억제되며 비교적 균일한 유속 분포를 보이며 상부영역에서는 일반 개수로 흐름과 유사한 흐름구조를 보인다. 이와 같이 두 상이한흐름구조가 결합된 복잡한 흐름특성으로 인해 침수식생 개수로흐름은 공학적인 관심의 대상이 되어왔다. 본 연구에서는 침수식생 개수로 흐름의 층적분 모형의 비교 분석을 수행하였다. 일반적으로 식생흐름의 층적분 모형은 층의 수에 따라 2층 및 3층모형으로 구분한다. 즉, 전체 수심을 식생영역과 상부영역으로 구분하는 2층모형과 식생영역을 바닥 조도의 영향 유무에 따라 내부 및 외부 식생영역으로 구분하는 3층모형으로 분류된다. 본 연구에서는 2층모형과 3층모형을 비교하였다. 다양한 실험조건에 적용한 결과, 3층모형이 식생영역에서 유속의 변화를 고려할 수 있으나 결과는 레이놀즈응력 분포에 민감하며, 적분된 유속은 2층모형에 의한 예측 결과가 더욱 정확한 것으로 나타났다. 3층모형에서 내부 식생영역의 결과가 전체 흐름구조에 미치는 영향이 무시할 수 있으므로 이 점을 착안하여 식생영역에서 유속 변화가 고려되는 수정 2층모형을 제시하였다. 수정 2층모형에서 가정하는 레이놀즈응력 분포는 상부영역에서는 선형, 식생영역에서는 멱함수 형으로 변화한다. 다양한 조건에 적용한 결과, 수정 2층모형이 대체로 기존의 모형과 비슷한 정도의 예측을 수행하나 식생밀도가 매우 작은 흐름의 경우 예측 결과가 불량한 것으로 나타났다.