ABSTRACT In the trenching, one of the working targets of underwater construction robots, a long ditch for cable laying is dug by rotational torque of the trenching cutter generated by the force of bringing the trenching cutter into contact with the underwater ground. This contact force is generated by operating the boom cylinder which enables up and down movement of the trenching cutter or by the propulsive force of the track. This contact force applied to trenching cutter for trenching work should be maintained properly because when this force is excessive or insufficient, the trenching cutter stops or the work efficiency is not ensured, respectively. For the remote-controlled underwater construction robot, the operator should maintain the optimum torque of the trenching cutter by repeatedly operating the proportional control valve for driving the track drive motor or boom cylinder. This work requires a period of skill practice for proficient performance even on the ground and also causes fatigue quickly by repeated work even to expert. In the case of the seafloor, the work condition is more severe by the difficulty in obtaining visibility due to high concentration of float in the water caused from trenching work. The present paper proposes an active control technique for maintaining the optimal torque and speed for the trenching work. In order to evaluate the effect of the proposed control method for the trenching work, the experiments were performed. INTRODUCTION As the marine energy and plant projects attract increasingly more attention of government and businesses, the need for construction equipment to develop the oceans has been raised, which led to the development of deep-sea robots to perform various tasks required for marine construction work [Lee et al., 2015]. Deep sea robots, based on the moving method, are divided into, into thruster-based underwater swimming robot, waterjet propelled skid-based mobile robot, and track- based mobile robot [Hettinger et al., 2005, Kim et al., 2016]. Track-based underwater construction robots are designed to perform underwater works such as pipeline burial and rock crushing under underwater ground conditions of compressive strength of 20 MPa or more. The track-based underwater construction robots are required to have impact resistance because of such need for heavy works. The underwater construction robot uses valve control type hydraulic system, a flexible power transmission system that has higher impact resistance than electric motor system and that generates power in Hydraulic Power Unit (HPU) and supplies the power to each actuator by adjusting the proportional control valve [Cho et al., 2010, Kim et al., 2016, Wang et al., 2012].

ABSTRACT This paper introduces the Light-weight Work Class ROV URI-L for underwater construction. And the design and implementation of an underwater precision navigation system and dynamic positioning system that is essential for the underwater construction, position maintenance control, path tracking control and precision mapping are described. In this study, to develop an underwater precise navigation system which is the key technology in the operation of underwater robot, USBL, DVL and FOG sensor data are fused to realize a fast and accurate navigation system with high update rate. The developed navigation and DP algorithm was verified by a sea trial test. INTRODUCTION KRISO is currently conducting a sixth year research project on ROV development for underwater light work to support underwater construction projects. The production of ROV URI-L for light work was completed as shown in Fig. 1, and an underwater precision navigation algorithm was developed and verified by the November sea trial test in order to develop and verify precision mapping, automatic control technology, and smart ROV operation technology. In this project, KRISO has been developing underwater robots in the past, and it has been improving the control performance of ROVs with the production company Red One Technology. It is equipped with intelligent algorithms that are easy to operate by main pilots, navigators and supervisors. We are trying to implement a smart ROV system. It is a high-performance underwater robot that uses multi-beam imaging sonar and forward looking scanning sonar to easily recognize the surrounding environment even in turbid water of the bad sight. The URI-L weighs about 1.5 tons in air and is ballasted slightly positive buoyancy in water. In order for the ROV to operate freely at a depth of 400m or more, a cage-type TMS (Tether Management System) as shown in Fig.2 is required. The TMS is a home-like type of ROV with a weight of about 1.5 tons. It separates the movement of the ship excited by the wave so as not to affect the ROV. In addition, the underwater precise and continuous navigation system up to 10Hz that can be considered as the strength of this research is very helpful for the implementation of the precise dynamic positioning control system.

ABSTRACT The support structure of offshore wind turbines is working in harsh ocean environments, where uncertainties exist and affect the performance of the whole system. This work presents an efficient methodology for the Reliability Based Design Optimization (RBDO) of the support structure of offshore wind turbines considering uncertainties. Reliability analysis is a feasible option in the absence of field measurement data. Monte Carlo simulations are robust and used as reliability analysis benchmark, but they are very computationally demanding for offshore wind turbine cases. Efficient Fractional Moment reliability analysis method was proposed. The results show that the proposed methodology can obtain a reliable design with better dynamic performance and less weight. Compared with the deterministic optimization, the presented dynamic RBDO of offshore wind turbines is more practical, and this methodology can be applied in the design of other similar offshore structures. INTRODUCTION The support structure of offshore wind turbines is working in harsh ocean environments, reliability analysis is a feasible option in absence of field measurement data (Yang et al., 2017). To ensure that the proposed offshore wind turbine design is cost effective, it is necessary to check whether the decided support structures provides optimal life cycle cost. For a reliable design, it is essential to consider various uncertainties in the dynamic analysis of offshore wind turbine (Xiao and Yang, 2014; Zhang et al., 2017). Due to the random nature of environmental parameters, wave, wind and currents must be modelled as stochastic process (Zhang and Yang, 2014). Hence, there is a need of stochastic dynamic analysis on one hand and the need of developing performance assessment, maintenance and optimization of the offshore wind turbine system with uncertainties. We try to answer the following questions: Can we formulate an efficient and accurate method for reliability analysis to replace Monte Carlo simulations which are robust but too time consuming; How to overcome computational challenges associated with reliability-based optimization methodology of offshore wind turbine system?

ABSTRACT This paper describes an original approach to reduce drastically the analysis time needed for fatigue design of structures by using machine learning techniques. The approach is applied to the spectral fatigue analysis of various structural details on a converted FPSO hull, where design iterations are usually time consuming. For the structural detail example used in the present study, numerical results show that by including the right inputs to the machine learning algorithm, the predicted fatigue life could compare well with the spectral fatigue analysis output with a score of up to 0.997. For the critical elements with high fatigue damage, the predicted fatigue life is found up to 2.5 times of the actual value. Overall an estimated 5.5 hours (out of 6 hours) are saved for one iteration of spectral fatigue analysis. INTRODUCTION Ocean developments for oil and gas and renewables involve site specific floaters designs. For such assets, it is required to perform detailed structural analysis at the design stage to consider all the specificities of the structure and the environments in the design and make sure the floater can operate safely throughout its design life. For fatigue design, the state of the art approach for such floaters is spectral fatigue analysis. The calculations of the fatigue damage using a full spectral direct calculation approach is labor intensive, especially when design iterations are needed. The complete assessment procedure comprises hydrodynamic analysis to compute wave-induced loads; structural analysis for both global coarse mesh and local fine mesh finite element models; statistical analysis to calculate the short-term stress response based on the environmental conditions on site; and lastly fatigue strength evaluation using the applicable fatigue S-N curve. This analysis approach can be rather time consuming in cases where many structural details are assessed or where multiple iterations are needed to reach a satisfactory design.

Abstract It is difficult to make model tests by using the conventional reduced scale for floating structures in the deepwater field. The currently widely used method is the hybrid model test, which requires equivalent truncated designs to be matched first. Using static characteristics similar to the design criteria of equivalent truncated design, selecting appropriate objective function, and using genetic optimization algorithm, the mooring system equivalent truncated mathematical model is designed by in-house computer programs. Restoring force characteristic curves of the truncated mooring system, top tension and displacement characteristic curves of a single mooring line are drawn with the designed various parameters within the written static characteristic calculation programs and compared with that of the full depth mooring system. The results of developed programs are checked by the hydrodynamic calculation software, OrcaFlex, and the dynamic characteristics differences between truncated and full depth system are compared with the software AQWA. Relying on the ocean engineering test tank of Harbin Engineering University and a working depth of 1500m, taut moored Floating Production Storage and Offloading tanker and catenary moored Catenary Anchor Leg Mooring system are to be made equivalent truncated optimized designs of 700m and 500m, respectively. The results show that the developed equivalent truncated optimized design programs are feasible for model tests of deepwater floating system. Introduction The model test becomes difficult with the increase of water depth due to the size limitation of the tanks. So new model test solutions are studied around the world. Studies have shown that despite the scale effects becoming increasingly significant, small-scale model testing is still feasible (Luo, 1994). However, the available depth remains limited in the marine engineering basin, even with small scale model tests, and it is very difficult to measure the varying forces and the motion response in practical applications.

Abstract Prediction of tsunami wave parameters at certain locations should be made as early as possible to provide enough time for decision making, population warning, and evacuation measures. Modern deep ocean "tsunameters" (pressure recorders, GPS, and other) provide direct measurement of the passing tsunami wave in the real time mode. This paper concerns real time tsunami risk mitigation by using the advantages of modern computer architectures. These are graphic processing units (GPU) and field programmable gates arrays (FPGA). Among many important aspects of tsunami simulation we study time consumable calculation of the wave propagation over a given water area. A comparison of performances achieved at a range of architectures is given.

Abstract Laser scanning technology, LiDAR, has been used to measure free- surface water profiles in the laboratory and in the field and the effect of scale has been investigated in the application of wave breaking theory. As a result of the calculation of wave parameters, such as breaker index and crest elevation, the difference between flume generated waves and waves in the surf zone were observed. The results show that while in most cases the field and laboratory derived breaking waves behave similarly, under some conditions in the flume waves can break outside the theoretical breaker criteria and whether this is a result of the scale effect is investigated.

ABSTRACT: The algorithm of autonomous underwater vehicles /AUVs/ trajectories planning for mapping of oceanographic data is considered in the paper. The problem of this research consists in adaptive data sampling by single AUV or group of vehicles for further high-precision mapping of environment parameters under restriction of whole given area covering. For simulation a bathymetry scalar field was considered, which is given by a digital elevation model. Some simulation results of considered algorithm operation are supplemented. INTRODUCTION Consider the problem of 2D distributed oceanographic scalar field mapping like temperature in horizontal plane or bathymetry. Traditional sampling methods using vessels and towed sensors are in general expensive and do not provide detailed aquatic area coverage. Using this technology, area of interest is covered by nets of tacks. However, this method can take much time if the purpose of research is a detailed survey of inhomogeneous underwater environment. In this case it would be more appropriate to use an AUV with according algorithms of trajectory planning, designed for more fast and precise solution of this problem. The problem can be resolved by taking more samples in fast-changing data areas and few samples in slow-changing data areas. Our task consists in an algorithm designing, which builds such adaptive trajectory for AUV that covers the aquatic square without gaps. The basic idea is to build a trajectory, consisting of meander patterns of different ―levels‖. Patterns of larger level use smaller step between tacks. An AUV control system has to make a decision if the current meander level should be changed according to measured data. A simulation was performed to verify of considered algorithm efficiency. Scalar bathymetric field, provided by digital elevation model /DEM/, was used for survey. Algorithm effectiveness was estimated by time of operation and resulting map precision for used bathymetric field.

ABSTRACT : This paper addresses the autonomous underwater vehicle (AUV) positioning by means of a single mobile acoustic beacon. It is assumed that beacon is towing by autonomous surface vehicle (ASV) in the operation area and its coordinates are determining by means of GPS. As the range measurement allows to localize AUV only in radial direction, the algorithm of beacon motion relative AUV is suggested. According with this algorithm, the mobile beacon moves in a circle around the moving AUV. Presented simulation results verify that using such technique allows to hold position error in desired bounds and to achieve adequate navigation accuracy of AUV. INTRODUCTION Navigation support is a critical importance for successful execution of the missions by autonomous underwater vehicle (AUV). That is the reason why one of the main problems facing the researchers is development of reliable and precise navigation systems for AUV. Commonly AUV uses integrated positioning system (IPS) which based on reckoning navigation system or/and inertial navigation system (INS). IPS fuses data from many different sensors namely depth meter, Doppler velocity log (DVL), attitude and angular velocity sensors (heading, pitch and roll), global positioning system (GPS) receiver etc. The main disadvantage of INS and reckoning navigation system is performance degrading as time goes by. Hence, to guarantee long-term stable operation of AUV it is necessary to periodically correct its coordinates by means of any drift-free positioning system. Since seawater is opaque to the radio waves, GPS can be used by AUV only for surface position fix. The modern underwater robotics is confronted with tasks, demanding not only accuracy but also high mobility and cost effectiveness from underwater robotic system. Among these are search and inspection of stretched objects (e.g. pipe lines, cables etc.), ecological monitoring and many other underwater investigations.

ABSTRACT: A fully coupled aero-elastic simulation technology is developed with enough sophistication to have the features required to perform loads analyses for a variety of wind turbine configurations. Blade and tower are modeled multiple rigid bodies which are connected beam elements to represent a flexibility for their bending and torsional behaviors. AeroDyn which is developed by NREL are chosen for aerodynamic analysis. This is a popular and open code and needs hub-height wind data, full field turbulent wind data and airfoil data to calculate an aerodynamic force. DAFUL, which is a commercial multi-body and structure dynamics analysis tool, is used for multi-body dynamics analysis considering a flexibility of the blade and tower. The interface to perform coupled analysis between these two softwares is developed with a user-subroutine of vector force in DAFUL. Analysis results of a sample model to verify This proposed simulation technology is applied to the analysis of a sample model for verification of the developed program. INTRODUCTION When there are no obstacles, the wind has fast and consistent speed. That wind is very useful for wind turbine. A sea provides the good wind and proper environment. A wind power generation can be classified into two groups, onshore wind turbines and offshore wind turbines, and offshore wind turbines can be sorted by the fixed type and the floating type wind turbines. Fixed type wind turbine systems are set up at relatively low depth of water near shore but floating type wind turbines are to be set up at more deep sea. The tower of the fixed type wind turbine is fixed on the ocean floor like onshore type, but the tower of a floating offshore wind turbine is to be fixed on the float and the movement of the float is to be controlled by a mooring system.

ABSTRACT: The algorithms of unmanned underwater vehicle motion detection based on image processing are considered in the paper. The approach is based on detection of the same objects on the consecutive frames and their joint displacement calculation. The motion detection system structure and algorithms of their operation onboard of UUV TSL are considered and results of marine trials are supplemented. INTRODUCTION High precise motion detection of unmanned underwater vehicle/UUV/is important task for UUV station-keeping or docking in the presence of various types of disturbances such as underwater currents or sea waves. The station-keeping mode is intended for maintaining of particular position and orientation of UUV without continuous operator supervision. This mode is a critical UUV capability for inspection and repair of underwater construction, bottom data collection and surveillance missions. Usually the UUV navigation system is based on autonomous onboard reckoning system. It consists of velocity log (absolute or relative), heading meter (flux gate or gyro compass) and depth meter. UUV position is estimated by velocity components calculation and integration. The constant error in velocitymeasuring d v leads to the error dr = t* d v in position estimation. Doppler velocity log /DVL/ is usually used for UUV speed measuring. Modern DVL has the precision of about 0.2% ± 1 mm/sec. The error of position estimation is about 8 meters per hour of operation when the UUV velocity is 1 m/s. The constant error in heading dj leads to the error in the vehicle location of about dr ≈ t* v*dj. The heading error of 2° is usual for magnetic transducer allowing for deviation. It can reach up to 10° and more in the regions of anomaly or near the big mass of magnetic materials However, currently FOGhasnot beenwidely used on themean cost UUVbecause of its high price.

ABSTRACT: In autonomous system, it is important to establish a control scheme that works with stability even near singularity con£gurations. In this report, an on-line trajectory control scheme that uses the manipulability measure as a distance criteria to avoid manipulator singularities is described for robotic manipulators with dynamic change of the task priority. First, given tasks are reconstructed using a geometric projection on the given index function. Then, the reconstructed tasks are analyzed in the framework of task priority based method. From this analysis, the proposed algorithm is shown to have the property that the task priority is assigned dynamically. Using this algorithm, we easily set the criteria of changing task priority and estimate the performance of the given index function. Considering the measure of manipulability as a index function, the approach is suitable for avoiding kinematic singularities for autonomous operation of, for example, underwater robot. Based on a real-time evaluation of the measure of manipulability, this method does not require a preliminary knowledge of the singular con£gurations. The result shows a good performance near the singular con£gurations, as shown by simulation results. And, the proposed algorithm is also validated by experimental results. INTRODUCTION In the repeating tasks or simple tasks, the desired task trajectory can be planned avoiding the singular points. And, it can be also overcome by mechanical design. In the manageable area, even though the manipulator are fallen into the singular points, the damage and emergency situation can be restored manually after stopping the task. However, in the uncontrollable area-space, underwater, and etc.–, we can not desire the manual labor and the tele-operation is also limited. So, the stability over singularity is the most important in those cases. Comparing with the manipulability of each 1-DOF task, it sets the task priorities.

ABSTRACT: An adaptive operation of a disturbance accommodating controller(DAC) depending on the seastate number for roll motion of a ship is suggested. DAC suggested in this paper assumes the shape of the disturbance, i. e. the wave slope excitation as a harmonic signal that consists of two sine waves of different frequencies and the dynamic model of this kind of disturbance is adopted in the controller to estimate the disturbance from the measurement of roll and to generate the control force to counteract exactly the estimated disturbance. Frequencies of the disturbance model used in the controller are selected so that the energy of the roll response in each seastate is to be minimized. Pole placement technique is combined to enhance the performance of DAC. A necessity of an adaptation scheme i. e. tuning the suggested DAC according to the varying sea environment is also shown by the results of the performance assessment of DAC's with different sets of design frequencies optimized for each seastate. INTRODUCTION Major developments of ship motion theories have been said to be attributed to two important foundations : the development of strip theory and the treatment of ship motions in irregular waves as the ‘black box’ eletronic filter. "The signal received by the filter contains a number of different frequency components and these are amplified or attenuated to produce some modified output signal according to the characteristics of the filter. Extendng the latter idea further into modeling the wave elevation or the wave slope as a filter of the white noise lets us adopt the stochastic control theory in suppressing the unwanted ship motions (Sgobbo and Parsons, 1999) or enhancing the estimation of the state-variables of ship motions in irregular waves (Reid et al., 1984; Triantafyllou and Athans, 1981).

ABATRACT: In this paper we propose a projection based observer that can be used to estimate state vectors such as position and velocity for its motion control using non-uniform interval multi-sensor outputs. The output measurement we will use in estimating the state is a series of known multi-sensor asynchronous outputs. The idea for the proposed projection based observer is that each measurement output give us a piece of information which we can use to project the state vector onto the null space of C (output matrix) in order to reduce the error of state estimation. We will explain how to construct the projection operator in a Hilbert space and show the noise rejection of this algorithm by using Lyapunov method. The applicability of the proposed based observer to SAUV (semi-Autonomous Underwater Vehicles) navigation system is demonstrated through computational analysis with theoretical data. Its comparison with traditional Kalman filtering is assessed for computer simulations of the KRISO SAUV and experiments of the FAU Ocean Voyager II Autonomous Underwater Vehicle. INTRODUCTION There are numerous applications where the usage of an Autonomous Underwater Vehicle is desired. Born from the military requirements for stand-off weapons, remote sensing, mine field mapping and clearance, and coupled with the rapid commercialization of microcomputer technology, it is now possible to foresee some civilian use for AUVs in ocean science, offshore operations, environmental monitoring and underwater inspection. One continuing issue is the precise navigation of such vehicles underwater. While differential GPS (DGPS) is widely used for survey ships and underwater vehicle while surfaced, the navigation problem underwater requires the fusion of data from sensors such as Doppler sonar in a ground locked mode, compass data (a three axis magnetometer), acoustic systems like a SSBL and low cost inertial units.