• Journal of Welding and Joining
• /
• v.27 no.6
• /
• pp.74-79
• /
• 2009

Titanium and titanium alloy can be reproduced immediately even if oxide films($TiO_2$) break apart in sea water. Therefore, since titanium demonstrates large specific strength and outstanding resistance to stress corrosion cracking, crevice corrosion, pitting and microbiologically influenced corrosion in sea water environment, it has been widely applied to heat exchanger for ships. In particular, with excellent elongation, pure titanium may be deemed as optimal material for production of heat exchanger plate which is used with wrinkles formed for efficient heat exchange. Conventional plate type heat exchanger prevented leakage of liquid through insertion of gasket between plates and mechanical tightening by bolts and nuts, but in high temperature and high pressure environment, gasket deterioration and leakage occur, so heat exchanger for LPG re-liquefaction device etc do not use gasket but weld heat exchanger plate for use. On the other hand, since welded plate cannot be separated, it is important to obtain high quality reliable welds. In addition, for better workability and production performance, lasers that can obtain weldment with large aspect ratio and demonstrate fast welding speed even in atmospheric condition not in vacuum condition are used in producing products. So far, 1st report and 2nd report compared and analyzed embrittlement degrees by bead colors of weldment through quantitative analysis of oxygen and nitrogen and measurement of hardness as fundamental experiment for the evaluation of titanium laser welding, and evaluated the welding performance and mechanical properties of butt welding. This study welded specimens in various conditions by using laser and GTA welding machine to apply edge welding to heat exchanger, and evaluated the mechanical strength through tensile stress test. As a result of tensile test, laser weldment demonstrated tensile strength 4 times higher than GTA welds, and porosity could be controlled by increasing and decreasing slope of laser power at overlap area.

• Earthquakes and Structures
• /
• v.25 no.5
• /
• pp.359-367
• /
• 2023

High-rise structures are considered as symbols of economic power and leadership. Developing countries like India are also emerging as centers for new high-rise buildings (HRB). As the land is expensive and scarce everywhere, construction of tall buildings becomes the best solution to resolve the problem. But, as building's height increases, its stiffness reduces making it more susceptible to vibrations due to wind and earthquake forces. Several systems are available to control vibrations or deflections; however, outrigger systems are considered to be the most effective systems in improving lateral stiffness and overall stability of HRB. In this paper, a 42-storey RCC HRB is analyzed to determine the optimum position of outriggers of different materials. The linear static analysis of the building is performed with and without the provision of virtual outriggers of reinforced cement concrete (RCC) and pre-stressed concrete (PSC) at different storey levels by response spectrum method using finite element based Extended3D Analysis of building System (ETABS) software for determining responses viz. storey displacement, base shear and storey drift for individual models. The maximum allowable limit and percentage variations in earthquake responses are verified using the guidelines of Indian seismic codes. Results indicate that the outriggers contribute in significantly reducing the storey displacement and storey drift up to 28% and 20% respectively. Also, it is observed that the PSC outriggers are found to be more efficient over RCC outriggers. The optimum location of both types of outriggers is found to be at the mid height of building.

• The Journal of the Acoustical Society of Korea
• /
• v.28 no.8
• /
• pp.768-773
• /
• 2009

This paper demonstrates the digital communication in air using the parametric array. The stepped-plate transducer which is suitable for high-power and high-efficient radiation is used to generate the difference frequency wave with the parametric array. The primary frequencies are selected to 83 kHz and 122 kHz and the resulting difference frequency wave at the frequency of 39 kHz is used for the communication. The modulation method is selected to On-Off Keying method. The waveform and signal-to-noise ratio (SNR) is measured and analyzed to see the characteristics of the digital communication using the parametric array. The proper distance for the communication using parametric array is about 3 m. The measured beam width of the 3dB SNR reduction was $14^{\circ}$. The possibility of the communication in air using the parametric array is confirmed and the high directional characteristic of the communication using the parametric array is expected to have the advantages for the multi path and the security problems.

• KIPS Transactions on Software and Data Engineering
• /
• v.6 no.11
• /
• pp.527-536
• /
• 2017

With the recent development of smart grid industry, the necessity for efficient EMS(Energy Management System) has been increased. In particular, in order to reduce electric load and energy cost, sophisticated electric load forecasting and efficient smart grid operation strategy are required. In this paper, for more accurate electric load forecasting, we extend the data collected at demand time into high time resolution and construct an artificial neural network-based forecasting model appropriate for the high time resolution data. Furthermore, to improve the accuracy of electric load forecasting, time series data of sequence form are transformed into continuous data of two-dimensional space to solve that problem that machine learning methods cannot reflect the periodicity of time series data. In addition, to consider external factors such as temperature and humidity in accordance with the time resolution, we estimate their value at the time resolution using linear interpolation method. Finally, we apply the PCA(Principal Component Analysis) algorithm to the feature vector composed of external factors to remove data which have little correlation with the power data. Finally, we perform the evaluation of our model through 5-fold cross-validation. The results show that forecasting based on higher time resolution improve the accuracy and the best error rate of 3.71% was achieved at the 3-min resolution.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.43 no.12 s.354
• /
• pp.65-73
• /
• 2006

This work presents a 14b 200KS/s $0.87mm^2$ 1.2mW 0.18um CMOS algorithmic A/D converter (ADC) for intelligent sensors control systems, battery-powered system applications simultaneously requiring high resolution, low power, and small area. The proposed algorithmic ADC not using a conventional sample-and-hold amplifier employs efficient switched-bias power-reduction techniques in analog circuits, a clock selective sampling-capacitor switching in the multiplying D/A converter, and ultra low-power on-chip current and voltage references to optimize sampling rate, resolution, power consumption, and chip area. The prototype ADC implemented in a 0.18um 1P6M CMOS process shows a measured DNL and INL of maximum 0.98LSB and 15.72LSB, respectively. The ADC demonstrates a maximum SNDR and SFDR of 54dB and 69dB, respectively, and a power consumption of 1.2mW at 200KS/s and 1.8V. The occupied active die area is $0.87mm^2$.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.18 no.2_spc
• /
• pp.291-303
• /
• 2020

The Kori-Unit 1 nuclear power plant, which is scheduled to be decommissioned after permanent shutdown, is expected to generate large amounts of various types of radioactive waste during the decommissioning process. Among these, nuclear reactors and internal structures have high levels of radioactivity and the dismantled structure must have the proper size and weight on the primary side. During decommissioning, it is important to prepare an appropriate and efficient disposal method through analysis of the disposal status and the legal restrictions on wastes generated from the reactors and internal structures. Nuclear reactors and internal structures generate radioactive wastes of various levels, such as medium, very low, and clearance. A radiation evaluation indicates that wastes in the clearance level are generated in the reactor head and upper head insulation. In this study, a clearance waste safety evaluation was conducted using the RESRAD-RECYCLE code, which is a safety evaluation code, based on the activation evaluation results for the clearance level wastes. The clearance scenario for the target radioactive waste was selected and the maximum individual and collective exposure doses at the time of clearance were calculated to determine whether the clearance criteria limit prescribed by the Nuclear Safety Act was satisfied. The evaluation results indicated that the doses were significantly low, and the clearance criteria were satisfied. Based on the safety assessment results, an appropriate metal recycle and disposal method were suggested for clearance, which are the subject of the deregulation of internal structures of nuclear power plant.

• Journal of KIISE:Computer Systems and Theory
• /
• v.27 no.7
• /
• pp.650-664
• /
• 2000

NOW(Network of Workstations) is considered as a platform for running parallel programs by many people. One of the fundamental problems that must be addressed to achieve good performance for parallel programs on NOW is the determination of efficient job scheduling policies. Currently most research on NOW assumes that all the workstations in the NOW have the same processing power. In this paper we consider a NOW in which workstations may have different computing power. We introduce 10 classes of space sharing-based scheduling policies that can be applied to the NOW with heterogeneous computing power. We compare the performance of these scheduling policies by using the simulator which accepts synthetically generated sequential and parallel workloads and generates the response time and waiting time of parallel jobs as performance indices of various scheduling strategies. Through the experiments the case when a parallel program is partitioned heterogeneously in proportion to the computing power of workstations is shown to have better performance than when a parallel program is partitioned into parallel processes of the same size. When the owner returns to the workstation which is executing a parallel process, the policy which just lowers the priority of the parallel process shows better performance than the one which migrates the parallel process to a new idle workstation. Among the policies which use heterogeneous partitioning and process priority lowering, the adaptive policy performed best across the wide range of inter-arrival time of parallel programs but when the load imbalance among parallel processes becomes very high, the modified adaptive policy performed better.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.8
• /
• pp.813-822
• /
• 2009

We have investigated operation of a 1:2:2 asymmetric 3-stage Doherty PA(Power Amplifier) and implemented using the Freescale's 4 W, 10 W PEP LDMOSFETS at 1 GHz. By employing the three peak efficiency characteristics, compared to the two peak N-way Doherty PA, the asymmetric 3-stage Doherty can overcome the serious efficiency degradation along the backed-off output power region and maximize the average efficiency for the modulation signal. To maximize the efficiency characteristic, the inverse class F PA has been designed as carrier and peaking amplifiers. Furthermore, to extract the proper load modulation operation, the adaptive gate bias control signal has been applied to the two peaking PAs based on the envelope tracking technique. For the 802.16e Mobile WiMAX(World Interoperability for Microwave Access) signal with 8.5 dB PAPR(Peak to Average Power Ratio), the proposed Doherty PA has shown 55.46 % of high efficiency at an average output power of 36.85 dBm while maintaining the -37.23 dB of excellent RCE(Relative Constellation Error) characteristic. This is the first time demonstration of applying the saturated PA and adaptive gate bias control technique to the asymmetric 3-stage Doherty PA for the highly efficient transmitter of the base-station application.

• Journal of the Korean Society of Radiology
• /
• v.4 no.1
• /
• pp.11-17
• /
• 2010

A urolithiasis, also called calculus, is one of the brutal illnesses, which has constantly harassed humanbeings from time immemorial. However, there is no appropriate method of prevention so far. So, Urological therapy must be followed upon those patients. The biggest problem of urolithiasis is usually causing harsh pain, fever, and throw up. The pain would be more intensified when something came through the ureter or the moment of convulsion caused beyond transmission of urinary calculus. Even strong painkillers, such as fentanyl and Pethidine, can not handle those harshly pain easily. Therefore, a prompt action of medical check up and its therapy must be required to those patients. This thesis paper has put the accent on the specific therapy, known as ESWL (Extracorpereal Shock Wave Lithotripsy), which have generated quite optimum resolution to patients, who received harsh pain from Proximal ureteral stone and Mid ureteral stone and because of its low provability of pulverization. The results of the experiment confirmed that the stone, located between Proximal and Mid ureter, has lower provability of pulverization than distal ureter, because its accuracy rate on shock wave, in respect of breathing, are low. However, decrease in discharge interval have enhanced provability of pulverization. it can also intensify probability of pulverization and its safety by discharging high power with appropriate intervals, and that is more efficient than discharging low power with frequent time.

• Korean Journal of Optics and Photonics
• /
• v.32 no.3
• /
• pp.120-125
• /
• 2021

We have developed a linearly polarized high-power Yb-doped fiber laser in the master oscillator power amplifier (MOPA) scheme for efficient spectral beam combining. We modulated the phase of the seed laser by pseudo-random binary sequence (PRBS), with the bit length optimized to suppress stimulated Brillouin scattering (SBS), and subsequently amplified seed power in a 3-stage amplifier system. We have constructed by coiling the polarization-maintaining (PM) Yb-doped fiber, with core and cladding diameters of 20 ㎛ and 400 ㎛ respectively, to a diameter of 9-12 cm for suppression of the mode instability (MI). Finally, we obtained an output power of 1.004 kW with a slope efficiency of 83.7% in the main amplification stage. The beam quality factor M² and the polarization extinction ratio (PER) were measured to be 1.12 and 21.5 dB respectively. Furthermore, the peak-intensity difference between the Rayleigh signal and SBS signal was observed to be 2.36 dB in the backward spectra, indicating that SBS is successfully suppressed. In addition, it can be expected that the MI does not occur because not only there is no decrease in slope efficiency, but also the beam quality for each amplified output is maintained.