USV 수중 무선광통신 정렬·추적 시스템의 RAO 기반 기초 설계 연구

다국어 초록 (Multilingual Abstract)

The seabed topography and nearshore environment are constantly changing due to waves, currents, sedimentation, and scour. Existing quantitative bathymetric measurement methods use SONAR (Sound Navigation and Ranging), LiDAR (Light Detection and Ranging), SDB (Satellite-Derived Bathymetry), and X-band radar images, but it is difficult to observe changes over time because they provide time-discrete snapshots. To address this limitation, subsea observation platforms for long-term monitoring are being studied, and underwater wireless optical communication (UWOC) is attracting attention for wireless data offloading. Laser-based UWOC requires precise alignment and tracking performance due to its high directionality, and it is necessary to quantitatively estimate the required motor performance for system design and control algorithm development.

This study presents a procedure for estimating the motor requirements of the UWOC alignment and tracking system for a small USV (Unmanned Surface Vessel) using motion response amplitude operators (RAOs) based on linear potential-flow theory. The allowable misalignment angle was calculated from the geometric relationship between the transmitter and receiver for a slant range of approximately 33.1 m (30 m horizontal distance, 14 m water depth), and an allowable misalignment of about 0.15 deg was derived based on a 50% overlap ratio with a laser beam divergence angle of 4 mrad. Next, a measurement device was developed to obtain the center of gravity (COG) and mass moment of inertia (MOI) of the USV, and the motion RAOs were calculated using NEMOH and Orcawave. To validate the numerical results, a 1:2 scale model was produced and a model test was conducted in a 2D wave basin. The estimated RAOs were compared with the numerical analysis results by applying a Kalman filter to the measured raw roll and pitch time-series data to mitigate the effects of transient periods and reflected waves.

Based on the verified RAOs, time-domain analysis was performed in Orcaflex to calculate the angular velocity and angular acceleration requirements of the pan/tilt motor axes under irregular wave conditions. The sea states were set in two cases: Hs = 0.4 m, Tz = 5 s corresponding to Sea state 2, and Hs = 5 m, Tz = 10 s corresponding to Sea state 6. Sea state 2 represents a typical operating condition, and Sea state 6 corresponds to the condition under which the USV manufacturer indicated a risk of capsize. As a result, the required motor-axis angular velocity was peak/RMS = 26.6/5.6 deg/s and the angular acceleration was peak/RMS = 149.8/34 deg/s^2 under Sea state 2. Under Sea state 6, it was calculated as peak/RMS = 41/10.9 deg/s and the angular acceleration was peak/RMS = 125/33.5 deg/s^2. In addition, the torque was estimated based on the angular acceleration, and the results indicate that the inertial component tends to dominate the drag component in a first-order approximation model that sums the inertial torque and the hydrodynamic drag torque. On the other hand, since the allowable alignment angle is about 0.15 deg, the motor's resolution may be more precise or the allowable alignment angle may be mitigated through changes in optical design conditions, suggesting that the integrated design and verification of optics, instruments, and controls is necessary to determine the actual allowable alignment angle.

In conclusion, this study demonstrated that the system can be designed on a quantitative basis through (i) the frequency domain motion RAO analysis, (ii) the time domain analysis using RAO, and (iii) the process of calculating the motor requirements of the alignment and tracking system. However, the actual torque required may be higher because the reduction model experiment uses a simplified model that excludes the added mass, viscosity, and mechanical characteristics, and the influence of current and wind is omitted. In future research, it is necessary to implement and verify alignment and tracking algorithms and develop and install an underwater wireless optical communication system to re-verify the exercise response.


Keywords: Underwater wireless optical communication (UWOC), Unmanned surface vessel (USV), 'Pointing, acquisition, and tracking (PAT)', Response amplitude operator (RAO), Linear potential-flow theory, Boundary element method (BEM), Orcaflex, Orcawave, NEMOH, Motor performance requirements

목차 (Table of Contents)

• List of Tables ⅲ
• List of Figures ⅳ
• ABSTRACT ⅷ
• 1. 서 론 1
• 1.1 연구 배경 및 필요성 1
• 1.2 최근 연구 동향 4
• 1.3 연구 목적 및 범위 6
• 2. 수중 무선광통신의 정렬·추적 시스템 8
• 2.1 시스템 개요 및 운용 시나리오 8
• 2.2 정렬·추적 시스템 개념 설계 9
• 2.2.1 전체 시스템 및 모델링 개요 9
• 2.2.2 짐벌 및 구동계 구조 개념 10
• 2.3 정렬 허용 각도와 설계 기준 11
• 3. USV의 동적 거동에 대한 연구 15
• 3.1 COG, MOI 측정 및 산정 15
• 3.1.1 COG 측정장치 제작 및 측정 절차 15
• 3.1.2 MOI 측정장치 제작 및 산정 절차 17
• 3.1.3 측정 결과 요약 및 한계 22
• 3.2 운동 RAO 해석 25
• 3.2.1 이론적 배경 25
• 3.2.2 USV의 형상 및 제원 32
• 3.2.3 격자 품질 평가 34
• 3.2.4 운동 RAO 결과 및 분석 37
• 3.3 축소 모형실험을 통한 RAO 검증 53
• 3.3.1 개요 53
• 3.3.2 축소 모형 제작 및 세팅 56
• 3.3.3 실험 및 해석 결과 비교 57
• 4. 정렬·추적 시스템의 모터 요구 성능 평가 65
• 4.1 환경 및 하중 조합 65
• 4.2 해석 방법 70
• 4.3 해석 결과 72
• 4.4 모터 성능 검토 80
• 5. 결 론 81
• 참고문헌 83
• 국문초록 87