• International Journal of Automotive Technology
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• v.8 no.4
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• pp.421-428
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• 2007

This paper investigates the combustion and emission characteristics of a compression ignition engine fueled with neat and blended Shell's gas-to-liquid (GTL) fuel, which was derived from natural gas through the Fischer-Tropsch process. The experiments were conducted in a 6-cylinder DI diesel engine with pump timing settings of $6^{\circ},\;9^{\circ}\;and\;12^{\circ}$crank angle before TDC over ECE R49 and US 13-mode cycles separately and compared to a conventional diesel fuel. The results show that GTL exhibited almost the same power and torque output, improved fuel economy and effective thermal efficiency. It was found that GTL displayed lower peak in-cylinder combustion pressure and maximum heat release rate (HRR), the timings of the peak pressure and the maximum HRR were generally delayed, and the combustion durations were almost equivalent for diesel and GTL under the same speed-load condition. The results also indicate that, compared to diesel fuel, GTL blends showed a trend forward decreasing four regulated emissions simultaneously and a higher GTL fraction in blends contributing to further reductions in the emissions. In particular and on average, neat GTL significantly reduced HC, CO, NOx and PM by 16.4%, 17.8%, 18.3% and 32.4%, respectively, for all cases.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.6
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• pp.144-150
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• 2007

In recent years, the particle number emissions rather than particulate mass emissions in automotive engine have become the subject of controversial discussions. Recent results from the health effects studies imply that it is possible that particulate mass does not properly correlated with the variety of health effects attributed to diesel exhaust. So, the concern is instead now focusing on nano-sized particles emitted from I. C. engine. This study has been performed for the better understanding about the engine nano-particle for 3-measurement systems with different measuring principle. Firstly, EEPS is a newly introduced instrument for size distribution measurement of engine exhaust particles. It can measure nano-particles with an adequate resolution and in real time. In this study, the characteristics of EEPS were compared with ELPI and SMPS. As a research results, EEPS showed a same effect of engine load on the size distribution with ELPI and SMPS. But the quantitative results of EEPS were more similar to SMPS than ELPI, because the EEPS and SMPS use a same principle for classifying particles by size. The capability for transient measurement of EEPS was equivalent to that of ELPI.

• International Journal of Highway Engineering
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• v.8 no.1 s.27
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• pp.25-32
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• 2006

Behavior of concrete pavement due to temperature gradient was investigated for 48 hours at test road using Falling Weight Deflectometer. The deflections at slab center changed similarly to those of ambient temperature and temperature gradients in the slab. And rapid variations in the deflections were observed between 8 to 12 in the morning. However, dynamic modulus of subgrade reaction and joint deflections showed reverse trends to the ambient temperature and temperature gradients. The dynamic modulus of subgrade reaction was significantly affected by temperature gradient when its value got higher. Backcalculated elastic moduli were obtained using AREA method and Method of Equivalent Thickness. The trends of the backcalculated elastic modulus were similar to those of dynamic modulus of subgrade reaction. Measured load transfer efficiencies showed maximum peak in the morning due to dowel locking. However, additional effort is necessary to verify the result.

• Journal of Astronomy and Space Sciences
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• v.23 no.4
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• pp.435-444
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• 2006

Since artificial space objects are observable only in a short period of time and the characteristics of their motion is not exactly predictable, it is difficult to obtain both photometric and spectroscopic data by a set of observations. We have, therefore, designed a mount to load multi-optical instruments on the Kyung Hee University (KHU) satellite tracking and observation system for both photometric and spectroscopic observations of artificial space objects. In this paper, we have calculated the deformation of the remodeled mount using structural analyses for the loading of the multi-optical instruments. We have also deduced pointing errors of the mount occurring at tracking and observing artificial space objects. we have derived tracking reliably artificial space objects in our field of view and confirmed structural safety test of mount utilizing equivalent (von-mises) stress distribution.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.2
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• pp.148-155
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• 2008

The aim of the study is to interpret the distribution of occlusal force by 3-dimensional finite element analysis of ISP(Implant Supported Prosthesis) supported by minimum number of implant to restore the edentulous patients. For this study, the Astra Tech implant system is used. Geometric modeling for 6 and 4 fixture ISP group is performed with respect to the bone, implant and one piece superstructure, respectively. Implants are arbitrarily placed according to the anatomical limit of lower jaw and for the favorable distribution of occlusal force, which is applied at the end of cantilever extension of ISP with 30mm. Element type is tetrahedral for finite element model and the typical mechanical properties, Young's modulus and Poisson's ratio of each material, cortical, cancellous bone and implant material are utilized for the finite element analysis. From this study, we can see the distribution of equivalent stress equal to real situation and speculate the difference in the stress distribution in the whole model and at each implant fixture, From the analysis, the area of maximum stress is distributed on distal contact area between bone and fixture in the crestal bone. The maximum stress is 53MPa at the 0.2mm area from the bone-implant interface in the maximum side for 300N load condition for 4 fixture case, which is slightly less than the stress calculated from allowable strain. This stress has not been deduced to directly cause the loss of crestal bone around implant fixture, but the stress can be much reduced as the old peoples may have lower chewing force. Thus, clinical trial may be performed with this treatment protocol to use 4 fixtured ISP for old patients.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.3
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• pp.29-37
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• 2000

In this paper, the thrust control of PWM Inverter-fed SLIM(Single-sided Linear Induction Motor) is achieved by vector control and PID control with DSP(TMS320C32). SLIM which used as a conveyor has required the quick response and the constant operating without air gap trembling while it conveys load.Thus, SLIM should have the smallest trembling of air gap length. First, voltage equations for SLIM are calculated from the proposed equivalent circuit in this peper, and not only the exciting current but also the thrust component are obtained from them. The thrust current ripple can be reduced by the vector controller using a slip angle frequency, and the PID controller is also use for the position control.

• Wind and Structures
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• v.19 no.3
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• pp.339-352
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• 2014

This paper discusses the appropriate duration for basic gust wind speeds in wind loading codes and standards, and in wind engineering generally. Although various proposed definitions are discussed, the 'moving average' gust duration has been widely accepted internationally. The commonly-specified gust duration of 3-seconds, however, is shown to have a significant effect on the high-frequency end of the spectrum of turbulence, and may not be ideally suited for wind engineering purposes. The effective gust durations measured by commonly-used anemometer types are discussed; these are typically considerably shorter than the 'standard' duration of 3 seconds. Using stationary random process theory, the paper gives expected peak factors, $g_u$, as a function of the non-dimensional parameter ($T/{\tau}$), where T is the sample, or reference, time, and ${\tau}$ is the gust duration, and a non-dimensional mean wind speed, $\bar{U}.T/L_u$, where $\bar{U}$ is a mean wind speed, and $L_u$ is the integral length scale of turbulence. The commonly-used Durst relationship, relating gusts of various durations, is shown to correspond to a particular value of turbulence intensity $I_u$, of 16.5%, and is therefore applicable to particular terrain and height situations, and hence should not be applied universally. The effective frontal areas associated with peak gusts of various durations are discussed; this indicates that a gust of 3 seconds has an equivalent frontal area equal to that of a tall building. Finally a generalized gust response factor format, accounting for fluctuating and resonant along-wind loading of structures, applicable to any code is presented.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.1
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• pp.97-103
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• 2006

In this paper, a control method of a mini ozone generator is proposed, and also a cooling technique is described which is cooling down the flowing air gap into a silent discharger to $2^{\circ}C$ to generate ozone of high density and diffusing power. As the digital control system for this method, a double feedback loop is designed which detects the voltage and current of equivalent capacitor of the discharger and compensates for the poor power waveform caused by the noise at high discharging frequency. During the plant modeling of this system, computing time factor is considered as a unique parameter of the power system to improve the transient responses with regard to fluctuating load and to replenish the computing time delay of the controller. Through the experiment, sinusoidal input current for discharger can be acquired and all the effectiveness of this accurate control system over unstable ozone discharger are proved.

• Applied Biological Chemistry
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• v.45 no.1
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• pp.25-29
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• 2002

The kernel of wastewater treatment by activated sludge is elimination of organic substances and maintenance of well-flocculated sludge sedimentation. By the conventional activated sludge treatment, the optimum F/M ratio of soybean wastewater treatment was 0.24 (kg-BOD/kg-MLVSS day) and sludge bulking was generated at 0.48 (kg-BOD/kg-MLVSS day). To improve the treatment capacity and operation quality in higher loading of soybean wastewater, influent pH was constantly controlled by 9.0 using NaOH as a coagulant agent. In this process, higher loading up to 2.88 (kg-BOD/kg-MLVSS day) was possible and SVI was maintained under 150 without bulking. This was equivalent to 7.2 times higher than maximum permissible load of the conventional activated sludge process.

• Geomechanics and Engineering
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• v.15 no.2
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• pp.793-803
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• 2018

Based on the theory of porous media, an interaction system of a floating pile and a saturated soil in cylindrical coordinates subjected to vertical harmonic load is presented in this paper. The surrounding soil is separated into two distinct layers. The upper soil layer above the level of pile base is described as a saturated viscoelastic medium and the lower soil layer is idealized as equivalent spring-dashpot elements with complex stiffness. Considering the cylindrically symmetry and the pile-soil compatibility condition of the interaction system, a frequency-domain analytical solution for dynamic impedance of the floating pile embedded in saturated viscoelastic soil is also derived, and reduced to verify it with existing solutions. An extensive parametric analysis has been conducted to reveal the effects of the impedance of the lower soil base, the interaction coefficient and the damping coefficient of the saturated viscoelastic soil layer on the vertical vibration of the pile-soil interaction system. It is shown that the vertical dynamic impedance of the floating pile significantly depends on the real stiffness of the impedance of the lower soil base, but is less sensitive to its dynamic damping variation; the behavior of the pile in poro-visco-elastic soils is totally different with that in single-phase elastic soils due to the existence of pore liquid; the effect of the interaction coefficient of solid and liquid on the pile-soil system is limited.