• Journal of Advanced Marine Engineering and Technology
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• v.41 no.4
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• pp.362-367
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• 2017

This study was conducted to compare the particulate removal efficiency of the developed diesel particulate filter using various measurement methods in a high-speed marine diesel engine. A four-stroke mechanical marine diesel engine is used for the test, which has a maximum output of 403 kW and is coupled to an AC dynamometer to control engine speed and load. The test was conducted based on four steady-state engine operating conditions of E3 engine test cycle for the measurement of PM and soot removal efficiency using partial dilution method considered as gravimetric method and filter smoke number method as light absorption method, respectively. As a result of the removal efficiency measurement according to the application of diesel particulate filter, particulate matter was reduced from 76% to 91% and the soot was reduced by more than 90% while meeting the permissible engine back pressure. From these results, the applicability of diesel particulate filter adopted in high-speed marine diesel engines could be confirmed. In addition, based on the result that the particulate removal efficiency varies with different measurement methods, the necessity of unification of these methods could be identified.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.3
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• pp.57-60
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• 2008

Purpose: The radial speed of plasma current sheath was measured at the plasma focus apparatus. Methods: The measurement was used to time-resolved spectroscopic method and Rogowski coils. Results: Radial current sheath speed was measured with $10^5$ cm/s at Helium and Argon pressure between 5 to 100 torr and discharging voltage of 15 kV. When the gas pressure was increased, the current sheath speeds were decreased. Conclusions: At the optimum condition of plasma focus apparatus, the radial speed is guessed $10^7$ cm/s as a results of the measurement of current sheath speed.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.806-811
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• 1994

Two kinds of static and dynamic state estimation methods are newly discussed for the problem of the measurement disturbance of environmental low-frequency noise in the presence of wind-induced noise. First, the probability characteristics of wind-induced noise are discussed in the form of probability distribution conditioned by wind speed, based on the simultaneous observation of the wind-induced noise and wind speed near a microphone. Next, especially form the viewpoint of simplicity for practical use, two kinds of static and dynamic state estimation methods are discussed. The static estimation method using the information on wind speed is fundamentally supported by the conservation principle of energy sum. The dynamic one is the method by using a recursive digital filter with the parameters successively renewed by the information on wind speed. This can be also simplified by using well-know Kalman filter under the assumption of the Gaussian distribution. The effectiveness of proposed two estimation methods are shown through experiments under a breezy condition in the open filed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.503-507
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• 2004

This paper is concerned with the measurement of low-frequency vibrations of structures using the image processing method. To measure the vibrations visually, the measurement system consists of a camera, an image grabber board, and a computer. The specific target installed on the structure is used to calculate the vibration of structure. The captured image is then converted into a pixel-based data and then analyzed numerically. The limitation of the system depends on the image capturing speed and the size of image. In this paper, we discuss the methodology for the vibration measurement using the image processing method. The method enables us to measure the displacement directly without any contact. The resolution of the vibration measurement can be refined but limited to the sub centimeter displacement.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.303-310
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• 2011

This paper is focused on development of models for measuring lateral and vertical track irregularities from corresponding accelerometers of an in-service high-speed train. Generally, the track irregularity was measured by a special railway inspection vehicle or system with contact or non-contact sensors. However, the sensors are very expensive and vulnerable to a harsh environment. Displacement estimation from an inertial measurement unit and its wave-band filtering was already developed in the previous study, and it was found that their results included not only the track irregularities but also other information such as phase delay of the applied filters, and suspension and conicity of the wheel. To identify the track irregularities from those results, a compensation filtering method was proposed. Each directional compensation filter was derived by using a system identification method with the estimated directional displacement as input and the corresponding track irregularities as output. In this paper, they are integrated into a model for each direction and applied to the measured lateral and vertical acceleration data from the axle-box and bogie of an in-service high-speed train. Their results are compared with the data from the track geometry measurement system. From the comparison, the proposed models are a useful tool for the measurement of the track irregularities using accelerometers of in-service high-speed trains.

• Journal of Power System Engineering
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• v.13 no.3
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• pp.40-46
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• 2009

This study on the bolt elongation and torque measuring method by ultrasonic nod-destructive method. In the past, The dial gage was used for the elongation measurement of gas turbine bolts. The purpose of this study is to improve the traditional bolt elongation measurement method. The old method using dial gage measures the elongation of the gas turbine bolt. If the length differences among the loading bolts are within the required range, The loading torques of bolts consider as acceptable. But this method can not give the information about torque differences among the loading bolts. It could bring out vibration of turbine due to loading torque differences among the bolts. So the elongation and torque must be measured simultaneously. The new technology using ultrasonic non-destructive method can give the information about bolt elongation and torque. The ultrasonic method basically measures the speed in the bolt material for the calculation the bolt elongation. But the ultrasonic speed varies according to temperature and loading torque of bolts. So the factors of temperature and loading power were investigated and reflected to the calculation of bolt elongation and torque. The results of this study shows the big difference among the bolts torque in the old method and the torque differences among the bolts can be adjusted by reflecting the result of this study. And this torque adjusting method can decrease gas turbine vibration problem due to torque difference among the bolts. So this paper shows ultrasonic method is better than old method for the measurement of bolt elongation and torque.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.12
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• pp.649-654
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• 2003

The simplest method for measuring output currents of the three phase inverters is to measure them with three current sensors such as hall sensors. This method requires at least two current sensors, and these types of sensors are somewhat expensive. More economical method is measuring DC link current with a simple shunt resistor, then, reconstructing output current using the DC link current value and the switching status. However, in low speed region, the measurement becomes difficult and even impossible due to the requirement of minimum switching duration for A/D conversion. These problems can be overcome by limitation of switching duration. Limitation of switching, however, causes voltage and current distortion. Owing to compensation, distortion can be effectively suppressed. However these increase acoustic noise due to increment of current ripple. In this paper, a current measurement method is proposed, which can reduce minimum switching duration resulting in reduction of acoustic noise. The validity of proposed method is confirmed through experiment.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.7 s.172
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• pp.88-93
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• 2005

$Moir\acute{e}$ topography method is a well-known non-contacting 3-D measurement method. Recently, the automatic 3-D measurement by $Moir\acute{e}$ topography has been required, since the method was frequently applied to the engineering and medical fields. The 3-D measurement using projection $Moir\acute{e}$ topography is very attractive because of its high measuring speed and high sensitivity. In this paper, using two-wavelength method of projection $Moir\acute{e}$ topography was tested to measuring object with $2\pi-ambiguity$ problems. The experimental results prove that the proposed scheme is capable of finding absolute fringe orders, so that the $2\pi-ambiguity$ problems can be effectively overcome so as to treat large step discontinuities in measured objects.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.3
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• pp.311-319
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• 1998

DC Motors have been widely used in industry as driving power motors for electrical vehicles cranes and winches due to their strong starting torques and as servo-motors for position and speed control systems due to their convenience of speed control etc. Generally in the speed control systems of motors speed sensors are required and this fact results in he increased price and operating cost and in the limitted applications. This paper presents a new speed control method for sensorless DC motors. In this scheme the speed signal is estimatd by the measurement values of the armature voltage and current. A Fuzzy feedback controller instead of the conventional PID controller. Through simulations the effectiveness and usefullness of the proposed method are illustrated.

• Journal of Welding and Joining
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• v.17 no.1
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• pp.71-76
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• 1999

The real-time holographic interferometer with digital high-speed camera is applied to the experimental study of laser induced plasma/plume in pulsed Nd:YAG laser welding. A pulsed Nd:YAG laser with 1.2 kW average power is applied to generate laser induced plume. The recording speed of the high-speed camera is 3,000 f/s. The high speed photographs of weld plume without another visualization method, are compared with the visualization photographs with holographic interferometer. The radiation intensity from the laser induced plume is recorded by the high speed photographs, which fluctuated during laser radiation and disappeared after laser end. The density distribution of the plume is recorded by the holographic visualization method. The experimental results show the process of generation of the laser induced plasma/plume, and give the feasibility of quantitative measurement of laser induced plume in laser welding.