• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.32 no.1
• /
• pp.11-16
• /
• 2020

The rotational stability of an interlocking caisson breakwater was studied. Using the analytical solution for the linear wave incident to the infinite breakwater, the phase difference effect of wave pressures in the direction of the breakwater baseline is considered, and Goda's wave pressure formula in the design code is adopted to consider the nonlinearity of the design wave. The rotational safety factor of the breakwater was defined as the ratio of the rotational frictional resistance moment due to caisson's own weight and the acting rotational moment due to the horizontal and vertical wave forces. An analytical solution for the rotational center point location and the minimum safety factor is presented. Stability assessment formula were proposed to be applicable to all design wave conditions used in current port and harbor structure design such as regular waves, irregular waves and multi-directional irregular waves.

• Journal of the Society of Naval Architects of Korea
• /
• v.32 no.4
• /
• pp.105-113
• /
• 1995

A mechanical actuator to generate adjustable force ants its active control algorithm to minimize ship structural vibration are developed. The algorithms comprise initial algorithm which determines optimal phase and force magnitude of the actuator using the variation of vibration response according to the phase difference between the main engine and the actuator, and regulating algorithm which performs continuous optimal control to track the change of the engine speed. This control system can be applied without any prior identification for the dynamic characteristics of the controlled structure. In the control experiments for the deckhouse structural vibration of a 300,000 DWT crude oil carrier and a 2,270 TEU container carrier, the developed system showed good performance to reduce the vibration levels to $1/2{\sim}1/6$ of the uncontrolled levels.

• The Journal of the Acoustical Society of Korea
• /
• v.40 no.5
• /
• pp.428-438
• /
• 2021

For long-range communication in deep water, low carrier frequency is efficient due to a decrease in transmission loss. However, there is a limitation in that the data rate decreases due to a narrow bandwith. In order to increase the data rate in an environment with a limited bandwidth, it is necessary to design a higher-order modulation scheme. This paper analyzes the long-range communication data modulated by higher-order modulation schemes. The long-range communication experiment (23 km ~) was conducted in East Sea in October 2020. During the experiment, a vertical line array was utilized and communication sequences were modulated by Phase Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM) schemes and transmitted by a towed source. In more detail, PSK modulation consists of quadrature PSK and 8PSK, QAM modulation consists of 8QAM and 16QAM. Time reversal processing is applied to mitigate inter-symbol interference by utilizing the correlation between received signals and channel impulse responses. All modulation schemes show successful results at 23 km range, demonstrating the feasibility of higher-order modulation in long-range communication.

• Journal of Convergence for Information Technology
• /
• v.12 no.2
• /
• pp.142-148
• /
• 2022

In this paper, the weight reduction design of the yaw gearbox for wind turbine was performed through the finite element analysis method, and the stability was checked by performing the critical speed analysis. The weight reduction product can improve engine efficiency, save parts materials, and earn economic benefits. The yaw gearbox is lightweighted with the goal of achieving a safety rate of 1.3 or higher for wind turbine as indicated by IEC61400-1. In order to reduce the weight of the carrier, a topology optimization method was performed. The safety factor was verified by performing finite element analysis on the carrier. In addition, the housing and carrier were modeled using the finite element method, and the gear train was modeled using MASTA. For the yaw gearbox, the housing and carrier FE model and the gear train model were connected by the partial structural synthesis method to perform the rotational vibration analysis. Vibration excitation sources are mass unbalance and gear mesh frrequemcy, and as a result of the critical speed analysis, it was found that there was no resonance within the operating speed range.

• Asia Marketing Journal
• /
• v.9 no.3
• /
• pp.233-255
• /
• 2007

본 사례는 외환위기 및 대우 그룹 해체로 인해 존폐의 위기에 처했던 대우증권이 선도업체 위상을 탈환하기까지의 재건 과정에서 실행했던 마케팅 전략 및 영업활동을 분석하고 있다. 이를 통해 경영위기를 효과적으로 극복하고 새롭게 도약하기 위해 활용 가능한 마케팅 및 영업 전략의 일례를 소개하고자 한다. 끝으로 대우증권의 향후 마케팅 과제와 관련된 토의 주제가 제시된다. 국내 증권업계 선두주자였던 대우증권은 1999년 '대우 사태'로 인해 한때 업계 5위까지 추락하고 1조 2,000억원의 적자를 기록하였으며 신용등급은 투자부적격 단계인 CCC+까지 하락하는 등 위기를 맞이하게 되었다. 대우증권이 회생과 재도약을 위해 채택한 마케팅 전략은 '선택과 집중'이었다. 즉, 최대 수익원이자 경쟁력이 있는 사업 분야인 위탁매매(brokerage)에 역량을 우선 집중하여 안정적으로 수익 기반을 다진 뒤 이를 바탕으로 IB(Investment Bank)와 자산 관리(Wealth Management) 등 여타 분야에서의 역량도 점진적으로 강화하는 전략이다. 전략의 실행 방향은 높은 효율성 확보 및 자원의 확충을 통해 시장 지배력과 수익성을 창출하는 것이었다. 전략적 공감대, 오프라인 영업 강화, 현장 및 고객 중시를 위한 기업 자원의 확충 배치를 바탕으로 영업 프로세스, 영업 인프라, 영업 관리, 고객 서비스, 영업 문화의 혁신을 실행한 결과, 대우증권은 증권명가의 옛 명성과 위치를 성공적으로 탈환하게 되었다. 대우증권은 2004년 위탁매매 영업 부문에서 1위 위상을 되찾은 이래 전 사업 분야에서 성장을 지속하였다. 2006년 증권업종 시가총액 1위를 회복하는 등 각종 경영지표는 큰 폭으로 개선되었고, 신용등급은 AA-로 상향 조정되었다. 나아가 자본시장통합법 시대에 걸맞는 선도 글로벌 투자은행으로서 진화한다는 계획을 추진하고 있다.

• Korean Journal of Optics and Photonics
• /
• v.15 no.4
• /
• pp.385-390
• /
• 2004

In this paper, we designed a 4-bit optical true time-delay(TTD) for phased array antennas(PAAs), which is composed of a wavelength-fixed optical source, 2 ${\times}$ 2 optical MEMS switches, and fiber-optic delay lines. A 4-bit TTD with a unit time delay difference of 6 ps for 10-GHz PAAs has been implemented. Measurement results on time delay show an error of -0.4 ps at maximum, corresponding to a radiation angle error of less than 1.63$^{\circ}$. Thus, the TTD implemented in this research performs in excellent agreement with theory. Each TTD line, composed of MEMS switches and fiber-optic delay lines, connected to the corresponding antenna element has insertion loss in between 1.36 ㏈ and 2.40 ㏈ depending upon the setup of the switches. On the other hand, the insertion loss difference between TTD lines was 0.32 ㏈ at maximum for a fixed radiation angle. The TTD structure proposed in this paper might be more reliable and economical than those previously proposed using tunable wavelength sources if proper power equalization either with gain control of RF amplifiers or variable attenuators is achieved.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.32 no.4
• /
• pp.203-210
• /
• 2020

Spatial variation of diffracting wave amplitudes along a semi-infinite breakwater is investigated using the analytical solution of Penney and Price (1952) for wave diffraction. On the front side of the breakwater, the fluctuation of wave amplitudes due to diffracting waves would cause a wave force greater than that of superposed incident and reflected waves. The diffracting wave phase varies in circular shape from the breakwater tip of (x, y) = (0, 0) whereas the incident and reflected wave phases vary in planar shape. So, the total wave amplitude of the incident (or reflected) waves and the diffracting waves would fluctuate at a position away from the energy discontinuity line. The position (x, y) = (0, y) on the front and lee sides of the breakwater is at a distance y(π/2 - β) of the point on the energy discontinuity line along the diffracting wave crest line. The degree of reduction of the diffraction wave energy is proportional to the distance from the point on the energy discontinuity line along the diffracting wave crest line. Therefore, the diffracting wave amplitudes on the front and lee sides of the breakwater would be inversely proportional to the square root of y(π/2 - β).

• Journal of the Korean earth science society
• /
• v.29 no.2
• /
• pp.163-174
• /
• 2008

In this study, we compared textbook knowledge organization with students' mental models to contribute to a more well-designed instruction scheme. The selected science content was the cause of moon phases. We investigated 9 textbooks and 25 third-year middle school students. Patterns and features in participants' mental models were identified through cross inter-rater data analysis by 9 researchers, including in service teachers and experts in science education. According to the results, observing and modeling are the main activities engaged in when dealing with moon phases. The activities consisted of such concepts as: lunar revolution, the sun's parallel rays, the illuminated half of moon, and the relative positions of the sun, moon, and earth. Each concept involved inquiry skills such as: creating and manipulating models, utilizing the relationship between time and space, and communicating. However, the most important skills which are required for authentic scientific inquiry, namely controlling variables and formulating hypotheses, were missing. We categorized students' mental models into three types: scientific models, mixed models, and alternative models. The knowledge structure of each of the models was also discussed in this paper. Consequently, it was found that, typically, students were not given enough opportunities to strengthen the connection among ideas.

• Journal of Astronomy and Space Sciences
• /
• v.21 no.4
• /
• pp.371-382
• /
• 2004

To improve the precision of relative positioning for GPS single frequency(L1) receiver, we accomplished the GPS data processing using the weighted smoothing techniques. The weighted phase smoothing technique is used to minimize the measurement error of pseudorange and position domain smoothing technique is adopted to make the complement of cycle-slip affection. we also considered some component errors like as ionospheric error, which are related with baseline length, and processed for several baselines (5, 10, 30, 40, and 150 km) to check the coverage area of this algorithm. This paper shows that weighted phase smoothing technique give more stable results after using this technique and the position domain smoothing technique can reduce the errors which are sensitive to the observational environment. Based on the results, we could find out that this algorithm is available for post-time and real-time applications and these techniques can be substitution methods which is able to get the high accuracy and precision without resolving the Integer ambiguity.

• Geophysics and Geophysical Exploration
• /
• v.12 no.3
• /
• pp.225-232
• /
• 2009

As part of seismic experiments investigating crustal velocity structures of the Korean peninsula, permanent (fixed) seismographs of the Korea Meteorological Administration (KMA) network recorded seismic signals from four and eight large explosions in Korean Crustal Research Team (KCRT) profiles shot in 2004 and 2008, respectively. Among the seismograms recorded by 43 velocity sensors and 103 accelerometers at KMA stations distributed throughout the southern Korean Peninsula, 156 records with epicentral distances less than 120 km and high signal-to-noise ratios were analyzed to determine velocity anisotropy of the Pg phase. Relative elevation corrections of -101.6 to 105.3 ms were made using velocity information derived from the 2004 KCRT profile data and differences in elevation between the permanent KMA stations and the temporary stations in the KCRT profiles at the same source-receiver offsets. To remove site effects, receiver-station corrections of -89.6 to 192.2 ms were additionally made to the KMA station data by subtracting the average differences in traveltimes between KMA stations and portable stations at the same offsets for all available shots with different azimuths. With the exception of anomalously fast velocities along trends of the Chugaryeong fault zone and the Okchon fold belt and anomalously slow velocities in the regions of high terrestrial heat near Yeongduk and Ulsan, the analysis of crustal velocity anisotropy using the Pg phase indicates overall isotropy in the southern half of the Korean peninsula.