Actual Sea Area Research Articles

Research on Multibeam Line Measurement Problem Based on Iterative Algorithms

With the continuous advancement of marine resource development, an efficient and reasonable multi beam acoustic survey line design scheme is crucial for accurate sea area measurement. Firstly, in order to make the model closer to the actual complex scene, a three-dimensional coverage model was derived that comprehensively considers the relative angle between the measurement line and the normal direction of the seabed terrain slope projected on the horizontal plane, referring to the three-dimensional sound beam propagation characteristics of multi beam sound waves. Then, based on the working principle and geometric relationship of multi beam recording, a formula for calculating the recording coverage width under multi-directional slope conditions considering measurement equipment parameters was derived, and an expression for the overlap rate of adjacent measurement lines was given. In addition, different measurement lines and slope normal direction angles . Finally, based on the actual sea area situation of the rectangular area within the specific given range, iteratively traverse and set different combinations of survey lines, calculate the total length of the combination and the corresponding coverage area, and calculate the coverage rate. Select the survey line combination with the shortest total length and the highest coverage rate as the optimal solution. This article focuses on the design of multi beam acoustic survey lines and establishes a universal mathematical model to achieve optimization solutions in different practical scenarios.

Unmanned Surface Vehicle Using a Leader–Follower Swarm Control Algorithm

To overcome the limitations of a single unmanned surface vehicle (USV), this study investigated the swarm control algorithms of USVs. Among various swarm control methods, a leader–follower swarm control method was selected and studied. The performance of the swarm algorithm proposed in this study was verified through an actual sea area test. A USV was designed and manufactured by dividing the power and communication parts. The power system was equipped with a coulometer to monitor the battery state in real time to protect the system through a switch linked to the coulometer in the case of abnormalities in the battery and to prevent accidents. In addition, a communication system was established to process the sensor data and camera image data of the USV in real time. Consequently, the desired swarm formation was achieved through the separately constructed swarm control algorithm. Before the actual sea area test, individual performance tests of each sensor were conducted. Finally, the performance of the swarm algorithm was verified by conducting a sea area test. The performance of the controllers was confirmed to be good, and the swarm formation was confirmed to be successful.

Development of an Underwater Robot for Detecting Shallow Water in a Port

Water depth is an important piece of information for the ship navigator when entering the port. However, the depth is not always accurate as indicated in the chart due to tides and sedimentation. This study aimed to develop an underwater robot to easily measure water depth. To measure the water depth at the place where the ship is moored at the quay, this paper proposed the method of measuring the water depth by submerging an underwater robot under the moored ship. Actual sea area experiments indicated the effectiveness of the underwater robot.

Characteristics of Storm Surge by Forward Speed of Typhoon in the South Coast of Korea

The damage caused by typhoons is gradually increasing due to the climate change recently. Hence, many studies have been conducted over a long period of time on various factors that determine the characteristics of storm surge, and most of relationships have been discovered. Because storm surge is complexly determined by various factors, it often show different results and draw different conclusions. For this reason, this study was conducted to understand the various characteristics of storm surge caused by changes in the forward speed of typhoons. This study was carried out with a numerical model, and the effect of forward speed could be analyzed by simplifying other factors as much as possible. When forward speed is increased, storm surges caused by typhoons tended to increase gradually. The storm surge showed a wide and gentle increase at a slow speed, but a narrow and steep one at a fast speed. In the case of the same forward speed, it was found that the storm surge was significantly influenced by the water depth of actual sea area. It was confirmed that the change in forward speed after passing Jeju Island did not significant affect on the storm surge in the south coast of Korea.

1st Report on the Basic Performance Verification by the Actual Sea Model Tests for the Higher Holding Performance New Type Anchor Development

Authors are studying and developing the higher holding performance new type anchor to prevent the marine accident due to the dragging anchor. The purpose of this research is to indicate the usefulness and applicability of our higher holding performance new type anchor in actual sea area. For that purpose, the actual sea model tests were carried out in September and November 2019. Shioji-maru, the training ship belonging to the TUMSAT, was used for the actual sea model tests. The actual sea model tests were carried in Tateyama Bay and Off Tokyo Bay Urayasu. The dragging tests were carried out in the actual sea areas and, the basic holding performance of the new type model anchor was verified. In this paper, it is considered the holding resistance, the holding resistance coefficient, and stability. From this consideration, it was revealed that the new type anchor has the possibility and usefulness as the higher performance new type anchor of the next generation. In addition, the issues for practical use were shown.

Development of Ship Maneuvering Training Programs Based on Dynamic Positioning Simulator

In recent years, marine development for undersea energy resources and offshore wind power, development areas are expanding from shallow waters along the coast to deep waters in the open ocean due to technological advances. Generally, the DP (Dynamic Positioning) system is used to maintain a fixed point by automatically controlling propellers and thrusters or other propulsion unit against wind/wave disturbances for holding ship’s position. Engineers such as university students and DPOs (Dynamic Positioning Operators) engaged in marine development need to acquire sufficient understanding and knowledge of such marine development-specific operations and ship handling methods. Since a handling error caused by the DPO will cause an operation stop and accidents, it is necessary to conduct training method in the environment that is more suited to the actual situation. In this research, the author constructed a DP simulator that simulates the actual sea area and targets multiple DP ships. The author has also developed six types of classroom and DP simulator hands-on training programs, respectively. Finally, we conducted an educational experiment on the students and evaluated the achievement level and improvement points of this training program using the evaluation method of student questionnaire.

Research on Performance Evaluation of Tidal Energy Turbine under Variable Velocity

Aiming at the performance evaluation problem of tidal energy turbines in the application of periodic time-varying flow velocity, with the goal of maximizing the efficiency of energy harvesting in practical applications, an evaluation system combining the characteristics of flow velocity changes in practical applications is proposed. After long-term monitoring of tidal current flow velocity in the applied sea area, the actual measured tidal current periodic flow velocity is divided into several flow velocity segments by using statistical segmentation, and the evaluation flow velocity of each flow velocity segment and its time proportion in the tidal current cycle are obtained. A test device with constant torque regulation is built, and capture power tests of different torque loads are carried out under each evaluation flow rate. After comparison, the maximum captured power at each evaluation flow rate is determined. We calculate the weight based on the time proportion of each evaluation flow velocity and obtain the turbine average power of the tidal cycle, thereby evaluating the overall energy capture performance of the turbine under the periodic time-varying flow velocity. Finally, the application test of the turbine in the actual sea area shows that the thin-walled airfoil turbine is more suitable for the sea area, which is the same as the pool evaluation result. The result shows that the evaluation system is reliable and effective and has significance for guiding practical engineering.

Validation of dynamic response of a 2-MW hybrid-spar floating wind turbine during typhoon using full-scale field data

Accurate estimation of the dynamic behavior of Floating Offshore Wind Turbines (FOWTs) under typhoon environment is essential to design and install FOWTs in a prone area of typhoons such as around Japan. Up to now, extensive efforts for development of design tools for FOWTs have been made, and nowadays several design tools are available. Needless to say, it is of utmost importance that the engineering design tools have been verified and validated for the real physical phenomena before being applied to real designs/projects with confidence. Much efforts have thus been made as code-to-code comparisons and by validations using model test data. Validations of the design tools using full-scale field data for FOWTs have also been made, but available open literatures are quite limited, particularly for design-driving extreme cases. In this paper, we describe the analysis of the dynamic response of a 2-MW spar-type FOWT at the time of typhoon attack in the actual sea area. The central atmospheric pressure of the typhoon at the closest time was 965 hPa, the maximum instantaneous wind speed at the hub height was 52.2 m/s, and the maximum significant wave height was 6.9 m. The dynamic responses under the typhoon environment are numerically simulated by using the time-series records of the wind speed, the wind direction, the wave height, the wave direction, the current speed, and the current direction which were acquired during the typhoon passing through close to the FOWT. Then the simulated motion responses are compared with the measured motion responses for the same durations. By the comparisons, the numerical simulation tool which was used for the design of the FOWT has been partially validated. It has also been confirmed that the spatial coherence of the wind speed has a significant effect for the platform motions, particularly for yaw motion.

Excavation performance experiment in the actual sea area of the seabed exploration robot with seawater resistant processing.

Excavation performance experiment in the actual sea area of the seabed exploration robot with seawater resistant processing.

Proposal of Wear Estimation Method for Mooring Chain of Floating Structures

Up to now, wear estimation method for mooring chain of floating facilities has not been established, and it currently relies on empirical methods. In this research, numerical analysis combining 1) wear analysis between links by finite element method and 2) response analysis of mooring system was performed to establish a method for estimating wear amount of mooring chain during operation. The validity of the proposed method was confirmed by comparing with the actual measurement value in the actual sea area. As a result, it was found that the wear amount estimated by our proposed method is generally close to the measured value. However, it was also confirmed that the estimated wear amount at the touchdown point between the seabed and mooring chain was considerably overestimated. That result could be attributed to insufficient consideration of the effects caused between the links ( e.g. snap load, elastic deformation and friction), the behavior of the links ( e.g. sticking, rolling and non-contact) and the external forces ( e.g. wind and current ).

무인수상선을 위한 경유점 추적 제어 알고리즘에 관한 연구

워터젯이 탑재된 RIB(Rigid Inflatable Boat)형태의 무인수상선을 인한 경유점 추적 제어 알고리즘을 설계하였고, 성능 검증을 위해 실해역 시험을 수행하였다. 본 연구에서 사용된 RIB형 무인수상선의 경유점 추적제어를 위해서는 방향제어를 위해 버킷각을 제어하여야 한다. 우선, 육상 관제소에 미리 입력된 경유점들의 위경도 등의 위치정보들을 바탕으로, 목표 방향각을 실시간 계산한다. 그리고, 무인수상선에 탑재된 마그네틱 콤파스 등의 센서로부터 받은 선수각 및 선수각속도의 값과 PD 제어기법을 이용하여, 버킷각 명령을 실시간 계산한다. 본 연구에서는, 바람 등의 외력으로 인한 표류각을 보정하기 위해 일정속도 이상에서는 실침로(Course Of Ground, COG)를 사용하였다. 또한, 설계된 경유점 추적 제어 알고리즘을 검증하기 위해 부산 광안대교 근처 해역에서 육상관제소를 설치하고, 실선 시험을 수행하였다. 본 논문에서는, 설계된 무인 경유점 추적 제어 알고리즘의 시험결과를, 유인으로 제어한 결과 및 상용추적제어기로 제어한 결과들과 비교 분석하였다. A waypoint tracking algorithm(WTA) is designed for Unmanned Surface Vehicle(USV) in which water-jet system is installed for propulsion To control the heading of USV for waypoint tracking, the steering nozzle of water-jet need, to be controlled. Firstly, target heading is calculated by using the position information of waypoints input from the land control center. Secondly, the command for the steering nozzle of water-jet is calculated in real time by using the heading and the rate-of-turn( ROT) from magnetic compass, In this study, in order to consider the drift angle due to external disturbance such as wind and wave, the course of ground( COG) can be used instead of heading at higher speed than a certain value, To test the performance of newly-designed WTA, the tests were carried out in actual sea area near Gwang-an bridge of Busan. In this paper, the sea trial test results from WTA are analyzed and compared with those from manual control and those from commercial controller.

Field Demonstration test on a Semi-Circular Caisson Breakwater

The first semi-circular breakwaters have been erected at Miyazaki Port in Japan. This type of breakwater, having a hollow structure with a semi-circular cross section, is expected to exhibit superb characteristics in terms of sliding stability and low reflectively under a severe natural environment that includes high waves and poor soil conditions. In addition, its unique design provides excellent scenery enhancement. Field demonstration tests by erecting test breakwaters have been conducted since 1991 at Miyazaki port in an effort to verify stability, member safety and construction ease of the semi-circular breakwater in an actual sea area, as well as to establish practical design and construction methods.

Sound attenuation by barriers in underwater.

Sound attenuation characteristics of barrier for underwater sound propagation was investigated through a reduced scale cistern experiment. From the observed data for a thin barrier, it was found that the sound attenuation characteristics in underwater is almost the same as that in the air, which has been obtained in the noise control engineering field. Next, a useful functional form was derived for predicting the sound attenuation in underwater and it's effectiveness was confirmed experimentally by applying it to the data measured in an actual sea area. Furthermore, a possibility for the prediction of sound attenuation value in the case of a finite wide barrier was considered as well. As a result, sound attenuation characteristics for the wide barrier were understood by a double diffraction process.

DEVELOPMENT OF THE DOUBLE CYLINDER CAISSON BREAKWATER

A double cylinder caisson breakwater was recently developed to create a calm sea area in deep and high wave open sea areas. In order to confirm some subjects on design method and construction work, we conducted a field test in an actual sea area. This paper reports the results of that field test, mainly from the viewpoint of the hydraulic property of this new type of caisson, and the results of hydraulic model tests conducted to complement and verify the results of the sliding tests.