• 정보저장시스템학회:학술대회논문집
• /
• 정보저장시스템학회 2005년도 추계학술대회 논문집
• /
• pp.204-209
• /
• 2005

Load/Unload(L/UL) technology includes the benefits, that is, increased areal density, reduced power consumption and improved shock resistance contrary to contact-start-stop(CSS). It has been widely used in portable hard disk drive and will become the key technology far developing the small form factor hard disk drive. The main object of L/UL is no slider-disk contact or no media damage. For realizing those, we must consider many design parameters in L/UL system. In this paper, we focus on lift-off force. The 'lift-off' force, defined as the minimum air bearing force, is another very important indicator of unloading performance. A large amplitude of lift-off force increases the ramp force, the unloading time, the slider oscillation and contact-possibility. To minimize 'lift-off' force we optimizes the slider and suspension using the integrated optimization frame, which automatically integrates the analysis with the optimization and effectively implements the repetitive works between them. In particular, this study is carried out the optimal design considering the process of modes tracking through the entire optimization processes. As a result, we yield the equation which can easily find a lift-off force and structural optimization for suspension.

• 한국지반공학회지:지반
• /
• 제6권3호
• /
• pp.41-52
• /
• 1990

To investigate the liquefaction potential of sands, a series of untrained cyclic triaxial compression tests is carried out on the samples of Ottawa, Joomoonjin, Hn river and Hongseung sands. The constitutive equations of sands are derived to explain the mechanical behavior of sands under cyclic stresses, and are applicable to liquefaction analysis. The following results are obtainded in this study. 1. Sands with the lower confining pressure or relative density are to be easily liquefied, and when the amplitude of cyclic stress are large, liquefaction takes places over only a few cycles. 2. Stress ratio, porewater pressure ratio and cyclic shear strains are to be good criteria to evaluate liquefaction potential of sands. 3. Hongseung sands which contains some silty clay shows higher dynamic properties than other sands. 4. The dynamic behaviors of undisturbed Hongseung sand are about same as those of dense sands. It is noted that undisturbed Hongseung sand shows higher liquefaction potential than the samples made by pluviation under same relative density, 5. The constitutive equations of soils under cyclic loads are developed based on the theory of elasto-plasticity, logarithmic stress-strain rela'tionship, non-associated flow rule and the concept of the boundary surface. The derived equations is applicable to predict the behavior of sands under cyclic loads and liquefaction potential with a higher accuracy. 6. Based on results of the study it may be concluded that cracks of the foundations and dislocation of the structures at Hongseung earthquakes(Oct. 7, 1978, Richter scald 5.2) are not brought by the liquefaction process.

• 천문학회보
• /
• 제36권2호
• /
• pp.64-64
• /
• 2011

We present a new quasi-stellar object (QSO) selection algorithm using a Support Vector Machine, a supervised classification method, on a set of extracted time series features including period, amplitude, color, and autocorrelation value. We train a model that separates QSOs from variable stars, non-variable stars, and microlensing events using 58 known QSOs, 1629 variable stars, and 4288 non-variables in the MAssive Compact Halo Object (MACHO) database as a training set. To estimate the efficiency and the accuracy of the model, we perform a cross-validation test using the training set. The test shows that the model correctly identifies ~80% of known QSOs with a 25% false-positive rate. The majority of the false positives are Be stars. We applied the trained model to the MACHO Large Magellanic Cloud (LMC) data set, which consists of 40 million lightcurves, and found 1620 QSO candidates. During the selection, none of the 33,242 known MACHO variables were misclassified as QSO candidates. In order to estimate the true false-positive rate, we crossmatched the candidates with astronomical catalogs including the Spitzer Surveying the Agents of a Galaxy's Evolution (SAGE) LMC catalog and a few X-ray catalogs. The results further suggest that the majority of the candidates, more than 70%, are QSOs.

• Structural Engineering and Mechanics
• /
• 제55권2호
• /
• pp.365-377
• /
• 2015

Large-amplitude vibration of overhead sign structures can cause unfavorable psychological responses in motorists, interfere with readability of the signs, and lead to fatigue cracking in the sign structures. Field experience in Texas suggests that an overhead sign structure can vibrate excessively when supported within the span of a highway bridge instead of at a bent. This study used finite element modeling to analyze the dynamic displacement response of three hypothetical sign structures subjected to truck-passage-induced vertical oscillations recorded for the girders from four actual bridges. The modeled sign bridge structures included several span lengths based on standard design practices in Texas and were mounted on precast concrete I-girder bridges. Results revealed that resonance with bridge girder vertical vibrations can amplify the dynamic displacement of sign structures, and a specific range of frequency ratios subject to undesirable amplification was identified. Based on these findings, it is suggested that this type of sign structure be located at a bridge bent if its vertical motion frequency is within the identified range of bridge structure excitation frequencies. Several alternatives are investigated for cases where this is not possible, including increasing sign structure stiffness, reducing sign mass, and installing mechanical dampers.

• 대기
• /
• 제24권2호
• /
• pp.207-223
• /
• 2014

The bogussing method was further developed by incorporating the asymmetric component into the symmetric bogus tropical cyclone of the Structure Adjustable Balanced Vortex (SABV). The asymmetric component is separated from the disturbance field associated with the tropical cyclone by establishing local polar coordinates whose center is the location of the tropical cyclone. The relative importance of wave components in azimuthal direction was evaluated, and only two or three wave components with large amplitude are added to the symmetric components. Using the Weather Research and Forecast model (WRF), initialized with the asymmetric bogus vortex, the track and central pressure of tropical cyclones were predicted. Nine tropical cyclones, which passed over Korean peninsula during 2010~2012 were selected to assess the effect of asymmetric components. Compared to the symmetric bogus tropical cyclone, the track forecast error was reduced by about 18.9% and 17.4% for 48 hours and 72 hours forecast, while the central pressure error was not improved significantly. The results suggest that the inclusion of asymmetric component is necessary to improve the track forecast of tropical cyclones.

• Ocean and Polar Research
• /
• 제29권4호
• /
• pp.367-378
• /
• 2007

A sediment quality index (SQI) and a mean sediment quality guideline quotient (M-SQGQ) were applied for the assessment of sediment quality in Masan Bay, Korea where metals and organic pollutants are of concern. The SQI was calculated by two functions, 'scope' (the number of variables that do not meet guideline objective) and 'amplitude' (the magnitude by which variables exceed guideline objective), with six different sediment quality guideline values from Canada, USA and Australia/New Zealand. Categorization of sediment quality was on the basis of SQI scores. The SQI values were compared with six guideline values applied as well as with the M-SQGQs. The SQI values were severely influenced by a few variables of high exceedance in the degree of non-compliance. The SQI values were very dependent on both the numbers and values of guideline variables used in index caluculation. Nevertheless, the SQI could provide integrated and simplified information from a large number of chemical data set. It is required to further evaluate protocols and guideline applied for deriving SQI and to compare it with field based sediment toxicity test and ecosystem integrity.

• 한국환경과학회지
• /
• 제12권10호
• /
• pp.1043-1054
• /
• 2003

During the period from April to September 2002, the size distributions of ambient aerosol were measured at the coastal site at Hamduk in Jeju Island. Na$\^$+/, K$\^$+/, Mg$\^$2+/, Ca$\^$2+/and Cl$\^$-/ exhibited mostly a bimodal coarse mode size distribution, while ammonium and sulfate were mainly in the fine size range, with maximum at around 0.54$\mu\textrm{m}$. The average molar concentration ratio of ammonium to sulfate for fine particles was equal to 2.0${\pm}$0.9. Nitrate was evenly found in both the coarse and fine modes. Elements like Al, Fe, Cu, Mg, Na, Ti, Sr and Mn were dominant in coarse particles, with the maximum at around 5.25$\mu\textrm{m}$. S and Pb were mainly in the submicrometer size range. Other elements with a fine and coarse modes were V, Ni, Cu, Ba and Mo. The patterns of the size distributions of trace elements measured at the downtown in Jeju City were very similar to those at the coastal site in Hamduk. However, the amplitude of size fractional concentrations at Jeju City was narrower than that at Hamduk. While the mass median diameters for the chemical species originated from the natural origin such as marine and crust were relatively large, those for ammonium, sulfate, S and Pb were very small.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2010년도 제35회 추계학술대회논문집
• /
• pp.469-473
• /
• 2010

본 연구에서는 빠른 후퇴율을 갖는 용융성 고체연료를 사용한 연소 실험을 수행하여 연소 중 압력진동 특성을 분석하고 연소 불안정의 위해성을 검토하였다. 빠른 후퇴율을 가지는 용융성 고체연료는 기존의 폴리머계 연료에 비해 압력 진동의 진폭이 증가하였다. 그러나 연료 그레인 내부 직경의 증가가 연소실 압력 진동의 증폭을 제한하여 급격한 연소 불안정은 거의 일어나지 않았다. 축방향 인젝터를 사용하는 경우 연료 연소량의 큰 증가와 예연소실에서의 와류 진동이 큰 압력 진동을 유발하였다.

• Smart Structures and Systems
• /
• 제15권3호
• /
• pp.787-806
• /
• 2015

Due to corrosion, a large number of belt conveyors support structure in industrial plants have deteriorated. Severe corrosion may result in collapse of the structures. Therefore, practical and effective structural assessment techniques are needed. In this paper, damage identification methods based on two specific local vibration modes, named periodic and isolated local vibration modes, are proposed. The identification methods utilize the facts that support structures have many identical members repeated along the belt conveyor and there exist some local modes within a small frequency range where vibrations of these identical members are much larger than those of the other members. When one of these identical members is damaged, this member no longer vibrates in those modes. Instead, the member vibrates alone in an isolated mode with a lower frequency. A damage identification method based on frequencies comparison of these vibration modes and another method based on amplitude comparison of the periodic local vibration mode are explained. These methods do not require the baseline measurement records of undamaged structure. The methods is capable of detecting multiple damages simultaneously. The applicability of the methods is experimentally validated with a laboratory model and a real belt-conveyor support structure.

• 대한기계학회논문집B
• /
• 제22권9호
• /
• pp.1195-1207
• /
• 1998

Periodic pulsations in the static pressure near turbine surfaces as blade rows move relative to each other is one of the important sources of turbine unsteadiness. The present experiment aims to investigate the effect of the static pressure pulsations on the interaction of film coolant flows from two rows of staggered holes with mainstream and its effect on film cooling heat transfer. Potential flow pulsations are generated by the rotating shutter mechanism installed downstream of the test section, The free-stream Strouhal number based on the boundary layer thickness is in the range of 0.033 - 0.33, and the amplitude of about 10-20%. Measured are time-averaged and phase-averaged velocity variations, pressure variations and temperature distributions of the flow field. Experimental conditions are identified by boundary layer measurements. Injectant behavior is characterized by the measurements of unsteady pressure in the plenum chamber and free-stream static pressure. The film cooling effectiveness is evaluated from the insulated wall temperature measurement. It has been found that bulk flow pulsation provides very large diffusion of the injectants and the effectiveness is significantly reduced by the flow pulsations.