Department of Mechanical Engineering

In a recent paper, Ferraris, Lee and Lifschitz conjectured that the concept of a stable model of a first-order formula can be used to treat some answer set programming expressions as abbreviations. We follow up on that suggestion and introduce an answer set programming language that defines the meaning of counting and choice by reducing these constructs to first-order formulas. For the new language, the concept of a safe program is defined, and its semantic role is investigated. We compare the new language with the concept of a disjunctive program with aggregates introduced by Faber, Leone and Pfeifer, and discuss the possibility of implementing a fragment of the language by translating it into the input language of the answer set solver DLV. The language is also compared with cardinality constraint programs defined by Syrjänen.

Model-mediated teleoperation (MMT) employs an environment model at the master side to compute feedback output to the master at a faster rate. This approach improves system stability in the presence of time delay. MMT, however, does not generally perform well if the employed model is not accurate. Model mismatch is unavoidable when the environment is unknown in advance or varies. This paper proposes MMT employing an adaptive model. The proposed method adaptively moves the reference point of the employed model, whereas the previous MMTs used reference points fixed to the surface of objects in the environment. This can make system stability independent of the time delay. Experiments show that the proposed method improves stability compared to the previous MMTs when there are model mismatches. User studies are conducted to compare the operator's performance in two tasks, control of force exerted to objects in the environment, and discrimination of object stiffness. The result shows that the error in the forces applied to objects in the environment significantly decreases in the proposed method. Errors in forces rendered to the master are also improved by at least 20.2 %. The experiment result also shows that subjects can discriminate up to 40.9 % smaller differences in the stiffness than the previous MMT under the same time delay.

A non-circular drawing sequence was investigated for manufacturing medium carbon steel wires with improved spheroidization of cementite for better cold workability compared to those produced by the conventional wire drawing. The wire drawing and non-circular drawing processes with 20% area reduction per each pass were numerically and experimentally applied up to the fourth pass (total area reduction of 59%). The drawn wire by the non-circular drawing sequence shows higher average effective strain value than the one of the wire drawing in the numerical result. To investigate the effect of prior cold working on spheroidization of the drawn wire, spheroidization annealing was conducted at subcritical temperature of 705 o C for 2 h for both processes. According to the present investigation, the wires subject to subcritical annealing following the non-circular drawing sequence showed the reduced ultimate tensile strength and micro-hardness, and the enhanced reduction of area compared to those for the wire drawing. From upsetting test results, cold workability was also improved for the annealed specimen processed by the non-circular drawing sequence compared to the one produced by the wire drawing. Scanning electron microscopy (SEM) was employed to investigate microstructure changes during spheroidization annealing. Owing to the SEM results, the spheroidization of the annealed specimens processed by the non-circular drawing sequence was improved than the one produced by the wire drawing. It is demonstrated that the non-circular drawing sequence could manufacture the wires with improved spheroidization of cementite and cold workability compared to the wire drawing in the present work.

The effect of Brownian diffusive particle trajectory of nanoparticles on the transfer function of the low pressure Differential Mobility Analyzer (LPDMA) was evaluated by a numerical simulation of the Langevin dynamic equation. The results of the simulation were compared with previously reported experimental results (Seto et al. 1997; Seol et al. 2000) and Stolzenburg's transfer function (1988). As the operational pressure decreased, the peak and FWHM (full width of the transfer function at half of its maximum) values of transfer function, as calculated by numerical simulation, were increased, which was not evident from Stolzenburg's transfer function. In comparison with the experiments of Seto et al., discrepancies in the higher electrical mobility regime than from central mobility were found, which could be caused by the incomplete flow control of their LPDMA. However, the transfer function, as calculated by numerical simulation was in good agreement with experimental results reported by Seol et al., performed with the improved LPDMA at well-controlled operation conditions.

A new instrument having a cross-flow configuration for aerosol and sheath flows is introduced for sizing of nanoparticles and referred to as nanoparticle cross-flow differential mobility analyzer (NCDMA). The flow and electrical fields in the NCDMA are analyzed theoretically, and its sizing characteristics are obtained in relation to the instrument geometry and operating conditions. The theoretical transfer functions compare well with numerical predictions for non-diffusing particles. For smaller particles, the focusing provided by the combination of the cross-flow configuration and electric field results in reduced Brownian diffusion broadening of particle position distribution in the classification region. From the analysis of instrument resolution based on the migration Peclet number, the NCDMA design is seen to provide a higher resolution than that of the TSI short column DMA (nano-DMA) for the same applied voltage. Monte Carlo simulation results of the Langevin equation confirm the theoretical prediction of improved resolution of NCDMA over conventional designs in the Brownian diffusion regime. ᭧

General expressions for the particle position distribution in non-uniform external fields are provided based on an investigation of distribution function. For a case of uniform or vanishing external fields, the particle position distribution with time results in a normal distribution with a variance as obtained for pure Brownian motion. To account for the non-uniformity of external fields, simple linearization methods were applied and the change in particle position distribution was investigated. A procedure to determine time evolution of change in variance of particle position distribution in non-uniform external fields is presented. For any non-uniform external field described by an analytic function, this simple procedure can accurately calculate the spreading characteristics of nanoparticles in the diffusional regime. This approach is used to predict particle diffusional spreading in a coaxial DMA, and the results are seen to closely match Monte Carlo simulations. ᭧

한국대기환경학회지 제 26 권 제2 호 1. 서 론 전기집진기는 입자상 오염 물질의 배출 저감을 위 해 가장 널리 사용되는 집진설비로서 설치 및 유지 보수의 용이성 및 높은 집진 효율 등의 장점이 있다. (Kim et al., 1994) 전기집진기를 적용하여 높은 집진 효율을 얻기 위해서는 전기집진기 내부 유동의 균일 도가 확보되어야 한다. 발전소 등의 현장에 설치된 전기집진기는 연소실 후단의 탈황설비 후단에 위치 하며, 환경 제어 설비들 사이는 유로(Duct)로 연결되 어 있다. 유로를 통해 전기집진기로 유입되는 유체는 한국대기환경학회지 제 26 권 제 2 호

In recent years, the worldwide use of polyethylene terephthalate (PET) has increased exponentially. PET wastewater contains ethylene glycol (EG) and terephthalic acid (TPA). In this study, we present a unique method for producing combustible gases like CH4 and H2 from PET wastewater by electrochemical reaction of EG and TPA. The non-diaphragm-based electrochemical (NDE) method was used to treat PET wastewater. The electrochemical removal of EG and TPA from PET wastewater was examined and the optimal conditions for their reduction to CH4 and H2 were determined. Using the proposed system, 99.9% of the EG and TPA present in the PET wastewater samples were degraded to produce CH4 and H2, at applied voltages lower than 5 V. The highest Faradaic efficiency achieved for EG and TPA reduction was 62.2% (CH4, 25.6%; H2, 36.6%), at an applied voltage of 0.8 V. Remarkably, CH4 was produced from EG decomposition and H2 from TPA decomposition. To the best of our knowledge, this is the first repor...

Here, we demonstrate a new strategy of air filtration based on an Al-coated conductive fibrous filter for high efficient nanoparticulate removals. The conductive fibrous filter was fabricated by a direct decomposition of Al precursor ink, AlH3{O(C4H9)2}, onto surfaces of a polyester air filter via a cost-effective and scalable solution-dipping process. The prepared conductive filters showed a low sheet resistance (<1.0 Ω sq(-1)), robust mechanical durability and high oxidative stability. By electrostatic force between the charged fibers and particles, the ultrafine particles of 30-400 nm in size were captured with a removal efficiency of ∼99.99%. Moreover, the conductive filters exhibited excellent performances in terms of the pressure drop (∼4.9 Pa at 10 cm s(-1)), quality factor (∼2.2 Pa(-1) at 10 cm s(-1)), and dust holding capacity (12.5 μg mm(-2)). After being cleaned by water, the filtration efficiency and pressure drop of the conductive filter was perfectly recovered, whic...

An adaptive, sliding control algorithm is developed for automated throttle control of an IC engine to be used in drive-by-wire applications such as coordinated engine/transmission gear shiftings, traction control and autonomous vehicle control (IVHS). The paper presents a ...

Abstract—The engineering technology for automotive systems is currently edging toward improving fuel economy. Transmission is one of the major parts to determine overall energy efficiency. The goal of this paper is to investigate the feasibility of a new clutch actuator in order to ...

This paper suggests an adaptation scheme for robust control of Electronic Wedge Brake (EWB) and estimation of pad friction-coefficient. The Electronic Wedge Brake is highly energy-effective as it uses selfreinforcement. But accordingly, it can be sensitive to the parametric variation, particularly to the pad friction-coefficient. The suggested scheme reduces the effect of the variation of pad friction-coefficient on system robustness and provides a way of estimation of the friction-coefficient in real time. The series of simulation results verify the performance of suggested control scheme.

There have been several studies aiming to develop a realistic driver model in accordance with the increased interest in vehicle safety issues and in computer simulation for a vehicle design. This study is especially considering the human driver's steering process; path planning, feed-forward steering, and preview feedback steering. Important human factors, such as the view angle and the neuromuscular system, are also regarded. The suggested driver model is simulated based on the CarSim vehicle model in a Simulink environment. The simulation results are then compared to the actual vehicle test data and to the driving simulator test data with regard to the four human driver levels. The driver model suggested in this study represents the human steering behaviour and well matches the real vehicle test data.

In this paper, a camless engine valve actuator (CEVA) system for robust engine valve timing control is presented. A particularly challenging control obstacle, shown in hydraulic actuation system for camless engine valve actuators, is the sluggish response of valve actuators at a cold operating condition. This is mainly due to the characteristics of oil viscosity with respect to temperature changes. At a low temperature condition, CEVA shows the very sluggish response. The retarded valve opening and closing timing, by CEVA's slow response at low temperature, cause an increase in pollutant emission and cylinder temperature during engine operation. In order to avoid these adverse effects by retarded timing, the new valve timing controller is proposed to control opening timing and closing timing, which is robust against temperature variations. A proposed valve timing controller is for guaranteeing the valve timing repeatability without using expensive position sensors. Experimental results indicate the feasibility of a fully variable valve timing control and CEVA system which can be constructed at a low cost.