• Structural Engineering and Mechanics
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• v.43 no.2
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• pp.179-197
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• 2012

This study presents the findings of the structural health monitoring and the real time system identification of one of the first large scale building instrumentations in Turkey for earthquake safety. Within this context, a thorough review of steps in the instrumentation, monitoring is presented and seismic performance evaluation of structures using both nonlinear pushover and nonlinear dynamic time history analysis is carried out. The sensor locations are determined using the optimal sensor placement techniques used in NASA for on orbit modal identification of large space structures. System identification is carried out via the stochastic subspace technique. The results of the study show that under ambient vibrations, stocky buildings can be substantially stiffer than what is predicted by the finite element models due to the presence of a large number of partitioning walls. However, in a severe earthquake, it will not be safe to rely on this resistance due to the fact that once the partitioning walls crack, the bare frame contributes to the lateral stiffness of the building alone. Consequently, the periods obtained from system identification will be closer to those obtained from the FE analysis. A technique to control the validity of the proportional damping assumption is employed that checks the presence of phase difference in displacements of different stories obtained from band pass filtered records and it is confirmed that the "proportional damping assumption" is valid for this structure. Two different techniques are implemented for identifying the influence of the soil structure interaction. The first technique uses the transfer function between the roof and the basement in both directions. The second technique uses a pre-whitening filter on the data obtained from both the basement and the roof. Subsequently the impulse response function is computed from the scaled cross correlation between the input and the output. The overall results showed that the structure will satisfy the life safety performance level in a future earthquake but some soil structure interaction effects should be expected in the North South direction.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.105-105
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• 2016

Recently, high power impulse magnetron sputtering (HIPIMS) has attracted considerable attentions due to its high potential for industrial applications. By pulsing the sputtering target with high power density and short duration pulses, a high plasma density and high ionization of the sputtered species can be obtained. HIPIMS has exhibited several merits such as increased coating density, good adhesion, microparticle-free and smooth surface, which make the HIPIMS technique desirable for synthesizing hard coatings. However, hard coatings present intrinsic defects (columnar structures, pinholes, pores, discontinuities) which can affect the corrosion behavior, especially when substrates are active alloys like steel or in a wear-corrosion process. Atomic layer deposition (ALD), a CVD derived method with a broad spectrum of applications, has shown great potential for corrosion protection of high-precision metallic parts or systems. In ALD deposition, the growth proceeds through cyclic repetition of self-limiting surface reactions, which leads to the thin films possess high quality, low defect density, uniformity, low-temperature processing and exquisite thickness control. These merits make ALD an ideal candidate for the fabrication of excellent oxide barrier layer which can block the pinhole and other defects left in the coating structure to improve the corrosion protection of hard coatings. In this work, CrN/Al2O3/CrN multilayered coatings were synthesized by a hybrid process of HIPIMS and ALD techniques, aiming to improve the CrN hard coating properties. The influence of the Al2O3 interlayer addition, the thickness and intercalation position of the Al2O3 layer in the coatings on the microstructure, surface roughness, mechanical properties and corrosion behaviors were investigated. The results indicated that the dense Al2O3 interlayer addition by ALD lead to a significant decrease of the average grain size and surface roughness and greatly improved the mechanical properties and corrosion resistance of the CrN coatings. The thickness increase of the Al2O3 layer and intercalation position change to near the coating surface resulted in improved mechanical properties and corrosion resistance. The mechanism can be explained by that the dense Al2O3 interlayer acted as an excellent barrier for dislocation motion and diffusion of the corrosive substance.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.593-596
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• 2004

We are developing a micro-solid propellant rocket array thruster for simple attitude control of a 10 kg class micro-spacecraft. The prototype has ø 0.8 mm solid propellant micro-rockets arrayed at a pitch of 1.2 mm on a 22 x 22 mm substrate. In previous studies, an impulse thrust of 4.6 x 10$^{-4}$ Ns was obtained in vacuum, but we found the problems of unacceptably low ignition success rate and incomplete combustion. This paper describes experiments to improve the ignition rate. In order to achieve this goal, we tried to solidify paste-like ignition aid (RK) on the ignition heaters with strong adhesion. To make the paste-like RK, isoamyl acetate was added to RK powder. We tested 9 rockets, but only 2 rockets were ignited with huge ignition energy. This is because the heat con-duction between the ignition heater and the RK was too low to ignite the RK, since dried RK had a lot of pores. Also, a large cavity was sometimes found just above the ignition heater.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.1
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• pp.18-25
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• 2001

The results of systematic numerical experiments of secondary gas injection thrust vector control are presented. The effects of secondary injection system such as injection location and nozzle divergent cone angle onto the overall performance parameters such as thrust ratio, specific impulse ratio and axial thrust augmentation, are investigated. Complex nozzle exhaust flows induced by the secondary jet penetration is numerically analyzed by solving unsteady three-dimensional Reynolds-averaged Navier-Stokes equations with Baldwin-Lomax turbulence model for closure. Numerical simulations compared with the experiments of secondary air injection into the rocket nozzle of $9.6^{\cire}$ divergent half angle showed good agreement. The results obtained in terms of overall performance parameters showed that locating the secondary injection orifice further downstream of primary nozzle ensures the prevention of occurrence of reflected shock wave, therefore is suitable for efficient and stable thrust vectoring over a wide range of use.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.7
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• pp.784-790
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• 2012

In this paper, an all-digital CMOS ultra-wideband(UWB) pulse generator for high band(6~10 GHz) frequency range is presented. The pulse generator is designed and implemented with extremely low power and low complexity. It is designed to meet the FCC spectral mask requirement by using Gaussian pulse shaping circuit and control the center frequency by using CMOS delay line with shunt capacitor. Measurement results show that the center frequency can be controlled from 4.5 GHz to 7.5 GHz and pulse width is 1.5 ns and pulse amplitude is 310 mV peak to peak at 10 MHz pulse repetition frequency(PRF). The circuit is implemented in 0.13 um CMOS process with a core area of only $182{\times}65um^2$ and dissipates the average power of 11.4 mW at an output buffer with 1.5-V supply voltage. However, the core consumes only 0.26 mW except for output buffer.

• Journal of the Korean Society of Safety
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• v.28 no.1
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• pp.88-94
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• 2013

The purpose of this study is to find out the difference of foot pressure according to the firefighter's work postures for providing the basic information to prevent Musculoskeletal disorders. This study was conducted by 9 male firefighters. Work postures were selected for rescuee handling, fire hose and hydraulic rescue equipment work postures. These were divided into 3 position, "High", "Middle" and the postures of taking out and letting down hydraulic rescue equipment were analyzed as starting point and end point respectively. Foot Pressure was used to analyze contact area, peak pressure, and maximum force in terms of work postures, and compared between fire hose and hydraulic rescue equipment work postures. The results of foot pressure are as follows. According to the results of rescuee handling work postures, one person handling posture showed wide contact area and foot pressure showed the highest at right foot. Accoridng to the (High), (Middle), (Low) postures of fire hose, the results didn't show the difference among the contact area, peak pressure and maximum force. As the results of hydraulic rescue equipment work postures, (Low) postures showed the highest in terms of the right foot of contact area, peak pressure and maximum force and (High) postures showed the highest in left foot. The increase of foot pressure lead to be inconvenience of low extremity and muscle fatigue for maintaining postural control cause pain. Thus, it is necessary to design insole-equipped working shoe for reduce the impulse and effect of foot during the rescuee handling work which standing out as foot pressure.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.109-114
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• 2008

This paper presents the development status of a subscale precooled turbojet engine "S-engine" for the hypersonic cruiser and space place. S-engine employs the precooled-cycle using liquid hydrogen as fuel and coolant. It has $23cm{\times}23cm$ of rectangular cross section, 2.6 m of the overall length and about 100 kg of the target weight employing composite materials for a variable-geometry rectangular air-intake and nozzle. The design thrust and specific impulse at sea-level-static(SLS) are 1.2 kN and 2,000 sec respectively. After the system design and component tests, a prototype engine made of metal was manufactured and provided for the system firing test using gaseous hydrogen in March 2007. The core engine performance could be verified in this test. The second firing test using liquid hydrogen was conducted in October 2007. The engine, fuel supplying system and control system for the next flight test were used in this test. We verified the engine start-up sequence, compressor-turbine matching and performance of system and components. A flight test of S-engine is to be conducted by the Balloon-based Operation Vehicle(BOV) at Taiki town in Hokkaido in October 2008. The vehicle is about 5 m in length, 0.55 m in diameter and 500 kg in weight. The vehicle is dropped from an altitude of 40 km by a high-altitude observation balloon. After 40 second free-fall, the vehicle pulls up and S-engine operates for 60 seconds up to Mach 2. High altitude tests of the engine components corresponding to the BOV flight condition are also conducted.

• Journal of the Institute of Convergence Signal Processing
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• v.21 no.3
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• pp.113-120
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• 2020

With the recent development of communication equipment, the demand for communication equipment is gradually increasing. Accordingly, various signal processing has been studied. In the case of an image, noise removal is an indispensable step because noise propagation problems may occur if noise is not removed in the pre-processing process. Salt and Pepper noise is a typical impulse noise with two extremes. Various studies have been conducted to remove such noise, and there are CWMF, MF and MMF. However, the existing methods are somewhat insufficient in the high-density noise region. Therefore, in this study, we have proposed an algorithm that filters the size of the mask according to the number of noises inside the 7×7 mask and filters it with a modified switching filter using the histogram distribution of the image. In the case of the proposed algorithm, noise can be effectively removed in a high-density noise region. For objective judgment, PSNR was used to compare and analyze with existing algorithms.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.11
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• pp.1431-1436
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• 2020

In modern society, various video devices such as CCTV and black boxes are used for convenience. However, noise is frequently generated in the process of transmitting and receiving video images and video signals photographed at night. If such noise is not eliminated, the problem that the image is difficult to identify is generated. Accordingly, noise elimination of images in the image information is an indispensable step. Salt and Pepper noises are typical impulse noises among image noises. Previous research has been carried out as a method for eliminating noise, and CWMF, MMF and A-TMF are typical methods. In common, such a filter exhibits excellent performance in a low-density noise area, but a disadvantage is that noise elimination performance in a high-density noise area is somewhat insufficient. Accordingly, the proposed algorithm uses the inflection point of the histogram graph to separate areas and remove singular points, and proposes a weighting filter utilizing histogram distribution. PSNR was used for objective judgment.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.5
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• pp.65-72
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• 2021

700 W class laboratory model Hall thruster, which can be used for the orbit control or station keeping of small satellites, was developed. The size of the discharge channel was determined using a scaling law, and the magnetic field was designed to be symmetric with respect to the midline of the discharge channel and to be maximized outside the discharge channel. Base pressure of a vacuum chamber was maintained below 2.0×10^-5 Torr during experiments, and the thrust was measured by a thrust stand. The anode flow rate and coil current were varied with the fixed anode voltage at 300 V. Under the operation condition at 2.36 mg/s anode flow rate and 2.4 A coil current, performance was optimized as 38 mN thrust, 1,540 s total specific impulse, and 50 % anode efficiency at 620 W anode power.