• KIPS Transactions on Software and Data Engineering
• /
• v.4 no.11
• /
• pp.509-520
• /
• 2015

College Scholastic Ability Test(CSAT) is a primary test to evaluate the study achievement of high-school students and used by most universities for admission decision in South Korea. Because its level of difficulty is a significant issue to both students and universities, the government makes a huge effort to have a consistent difficulty level every year. However, the actual levels of difficulty have significantly fluctuated, which causes many problems with university admission. In this paper, we build two types of data-driven prediction models to predict correct answer rate and to identify significant factors for CSAT English test through accumulated test data of CSAT, unlike traditional methods depending on experts' judgments. Initially, we derive candidate question-specific factors that can influence the correct answer rate, such as the position, EBS-relation, readability, from the annual CSAT practices and CSAT for 10 years. In addition, we drive context-specific factors by employing topic modeling which identify the underlying topics over the text. Then, the correct answer rate is predicted by multiple linear regression and level of difficulty is predicted by classification tree. The experimental results show that 90% of accuracy can be achieved by the level of difficulty (difficult/easy) classification model, whereas the error rate for correct answer rate is below 16%. Points and problem category are found to be critical to predict the correct answer rate. In addition, the correct answer rate is also influenced by some of the topics discovered by topic modeling. Based on our study, it will be possible to predict the range of expected correct answer rate for both question-level and entire test-level, which will help CSAT examiners to control the level of difficulties.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.34 no.3
• /
• pp.755-761
• /
• 2014

Internal or external restraint of concrete strain due to drying shrinkage and creep in concrete structures causes mechanical strain and becomes a source of persistent change in creep-causing stress conditions. Mathematical modeling to incorporate the persistent change of creep-inducing stress is generally achieved with consideration of the ages of concrete and concrete properties at the times of loadings, and stress history. This paper presents an incremental format of creep model based on parallel creep concept to depict the creep under time-varying stress history in developing creep strain. Laboratory experiments are carried out to validate the performance of the presented creep model. Typical creep phenomena are addressed through the comparisons between the measured and predicted creep strains.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.19 no.6
• /
• pp.749-754
• /
• 2009

Two gait generation methods using GP(genetic programming) and CPG(Central Pattern Generator) are compared to develop a fast locomotion for quadruped robot. GP based technique is an effective way to generate few joint trajectories instead of the locus of paw positions and lots of stance parameters. The CPGs are neural circuits that generate oscillatory output from a input coming from the brain. Optimization for two proposed methods are executed and analysed using Webots simulation for the quadruped robot which is built by Bioloid. Furthermore, simulation results for two proposed methods are experimented in real quadruped robot and performances and motion features of GP and CPG based methods are investigated.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• v.9 no.2
• /
• pp.204-207
• /
• 2005

Until present, most studies about energy efficiency of quadruped walking robot are mathematical modelings, dynamic analysis or simulation consumption energy per period by basic efficiency evaluate in this paper, a quadruped walking robot Titan-VIII is used for walking experience. The total moving length is about 2[m]. The stride length is 0.1, 0.2, 0.3, walking period is changed by 1.0, 1.5, 2.0, 3.0[sec] per each stride length. So consumption energy of 12 cases are measured. The energy efficiency of quadruped walking robot was analyzed by data that is saved by an experiment.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.9
• /
• pp.444-453
• /
• 2017

This paper proposes an operational algorithm for a Photovoltaic Power-Hardware-In-Loop Simulator that is designed to improve the control algorithm and reliability of the PV Inverter. There was an instability problem in the PV PHILS with the conventional algorithm when it was connected tothe PV inverter. Initially, a real-time based computing unit with mathematical modeling of the PV array is implemented and a DC amplifier and an isolated device for DC power measurement are integrated. Several experiments were performed based on theabove concept undercertain conditions, which showed that the proposed algorithm is more effective for the PV characteristic test and grid evaluation test than the conventional method.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.24 no.3
• /
• pp.245-250
• /
• 2014

Addiction can be largely divided into two categories. One is called medium addiction in which medium itself causes an addiction. Another is called cause addiction that brings addiction through combination of sensitive self and latent personal action. The medium addiction involves addiction phenomena directly caused by illegal drugs, alcohol and various other chemicals. The cause addiction is dependent on personal sensitivities as a sensitive problem of personal and includes cyber addictions such as shopping, work, game, internet, TV, and gambling. In this paper we propose two-dimensional addiction model that are equivalent to using an R-L-C series circuit of Electrical circuit and a Spring-Damper-mass of mechanical system. We also organize a Duffing equation that is added a nonlinear term in the proposed two-dimensional addiction model. We represent periodic motion and chaotic motion as time series and phase portrait according to parameter's variation. We confirm that among parameters chaotic motion had addicted state and periodic motion caused by change in control coefficient had pre-addiction state.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2012.10a
• /
• pp.378-381
• /
• 2012

Increasingly the frequency of use of mathematical modeling and computer simulation, in order to solve complex engineering problems in the field of Applied Science, the researchers need a simulation framework that can make their simulation-based research easier and more convenient. computer simulation framework is composed of various components such as preprocessor, solver, visualization program, computational resources and job scheduler. However until now, no standardized schema for the components of the simulation framework exist, so it is difficult to config that make a general-purpose simulation framework. In other words, most of the existing simulation framework is a structure that provides only limited functionality is dependent on the particular solver code. In this paper, we designed the meta-information schema that can be contained of a various solver code to be used for the simulation framework and we implemented the Web-based simulation environment using our meta-information schema.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.20 no.8
• /
• pp.1487-1493
• /
• 2016

The susceptible, exposed, infectious, and recovered model (SEIR) is used extensively in the field of epidemiology. On the other hand, dissemination information among users through internet grows exponentially. This information spreading can be modeled as an epidemic. In this paper, we derive the mathematical model of SEIR in viral communication from the view of optimal control theory. Overall the methods based on classical calculus, In order to solve the optimal control problem, proved to be more efficient and accurate. According to Pontryagin's minimum principle (PMP) the Hamiltonian function must be optimized by the control variables at all points along the solution trajectory. We present our method based on the PMP and forward backward algorithm. In this algorithm, one should integrate forward in time for the state equations then integrate backward in time for the adjoint equations resulting from the optimality conditions. The problem is mathematically analyzed and numerically solved as well.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1993.04a
• /
• pp.86-92
• /
• 1993

자동차의 현가장치에 대한 능동제어연구는 국내외적으로 활발히 진행되어 왔다. 수동식현가장치는 단순히 스프링과 감쇠기로 차체의 진동을 수동 제어 하므로 성능 향상에 한계가 존재하게 된다. 수동식 현가장치가 강성계수와 감쇠계수를 조절함으로써 차체로 들어오는 진동을 억제하는 반면, 능동식제 어는 보통 유압을 이용하여 효율적으로 차체에 들어오는 진동을 억제시키게 된다. 일반적으로 자동차가 능동현가장치 설계시 요구되는 사항은 탑승자의 승차감, 조종성, 현가장치의 공간확보 문제, 경제성(제어력), 실제적으로 자동 차에 적용할 수 있는 능동제어기법인가 하는 문제이다. 자동차 능동식 현가 장치는 보통 1/4 car (2자유도계), Full-car 모델 (7자유도계) 등으로 모델링 을 하여 능동제어기를 설계한다. 1/4 car 모델의 특징은 해석이 비교적 단순 하고 현가장치의 동적거동을 이해하는데 유용하고 실험을 하거나 실제 자동 차에 적용하기 쉬운 반면에 Full-car 모델에 비해 제어력의 효율이 떨어진다 는 단점이 있다. 그 이유는 1/4 car 모델은 차체의 동역학적 특성을 고려하 여 설계하지 않았기 때문에 4개의 독립현가차축에서는 오직 그 현가축방향 으로 발생하는 수직방향의 진동만을 제어하기 때문이다. 따라서 동역학적 역 성에 기인하는 운동을 제어하는 비효율적인 제어력이 공급된다는 단점을 갖 는다. 이에 비해 full-car 모델은 주행모드(수직, 롤링, 피칭운동)간의 연성을 고려하여 제어기를 설계할 수 있기 때문에 1/4 car 모델에 비해 제어력의 효 율이 높다는 장점이 있는 반면에 모델이 수학적으로 복잡하므로 제어력을 구하는데 계산량이 많고, 실제 자동차에 적용하기에 복잡하다는 단점을 갖고 있다. 따라서 본 논문에서는 쉽게 실험할 수 있고, 실용화할 수 있는 1/4 car 모델에 대하여 능동제어기를 설계하여 실제자동차에 능동제어기를 적용할 때 참고가 될 수 있도록 하였다. 자동차는 저주파영역의 밴드통과필터 역할 을 하므로 저주파에서의 성능, 특히 탑승자가 민감하게 느끼는 0.5Hz - 10Hz 부근의 주파수성능은 승차감, 조종성에 상당히 중요하다. 이에 본 논문 에서는 0.5Hz - 10Hz 부근의 승차감, 조종성의 향상에 초점을 두고 차체의 속도를 출력변수로 한 LQG/LTR 제어기를 설계하였다. LQG/LTR 설계기법 은 안정도-강인성이 좋은 체계적인 설계기법으로서 전 상태를 측정할 필요 가 없으므로 실제 적용시 효과적이다. 또한 자동차의 제원의 변화에 대한 고 유치의 민감도해석과 새로운 개념으로 안정도-강인성(Robustness)해석을 하 여 수동시스템과 능동시스템의 강인성을 비교하였다.

• Korean Chemical Engineering Research
• /
• v.57 no.1
• /
• pp.51-57
• /
• 2019

A plant layout problem has a large impact on the overall construction cost of a plant. When determining a plant layout, various constraints associating with safety, environment, sufficient maintenance area, passages for workers, etc have to be considered together. In general plant layout problems, the main goal is to minimize the length of piping connecting equipments as satisfying various constraints. Since the process may suffer from the heat and friction loss, the piping length between equipments should be shorter. This problem can be represented by the mathematical formulation and the optimal solutions can be investigated by an optimization solver. General researches have overlooked many constraints such as maintenance spaces and safety distances between equipments. And, previous researches have tested benchmark processes. What the lack of general researches is that there is no realistic comparison. In this study, the plant layout of a real industrial C3MR (Propane precooling Mixed Refrigerant) process is studied. A MILP (Mixed Integer Linear Programming) including various constraints is developed. To avoid the violation of constraints, penalty functions are introduced. However, conventional optimization solvers handling the derivatives of an objective functions can not solve this problem due to the complexities of equations. Therefore, the PSO (Particle Swarm Optimization), which investigate an optimal solutions without differential equations, is selected to solve this problem. The results show that a proposed method contributes to saving the capital expenditures.