Compared with the conventional vessels and platforms, the water plane area of the sandglass-type FDPSO (floating, drilling, production, storage and offloading unit) under upright condition is ...smaller, which makes its longitudinal metacentric height lower and natural frequency of pitch motion smaller. As a result, coupled surge and pitch motion problem would be caused unexpectedly. In this paper, from the perspective of controlling the metacentric height, a novel dynamic positioning (DP) controller is proposed. The proposed controller can make the natural frequencies of surge and pitch motions away from each other. Consequently, both the surge and pitch motions satisfy the positioning accuracy. Besides, the coupled resonant and non-resonant zones with the control parameters are investigated. Considering the system stability, positioning accuracy and power consumption, a complete analysis process of optimal control parameter selection is proposed. By comparisons with two existing control laws, the novel controller is established with better performances on robustness, positioning accuracy and energy consumption.
•The essential reason of coupled surge and pitch motion problem for the sandglass-type FDPSO was found.•By controlling the longitude metacentric height, a novel controller was proposed to solve the coupled resonance problem.•Considering the stability, ability and consumption, a new design method was proposed to obtain optimal control parameters.
Ship routing process taking into account weather conditions is a constrained multi-objective optimization problem and it should consider various optimization criteria and constraints. Formulation of ...a stability-related, dynamic route optimization constraint is presented in this paper. One of the key objectives of a cross ocean sailing is finding a compromise between ship safety and economics of operation. This compromise should be taken into account by the planning procedure and proper optimization algorithm. In this research complex stability-related phenomena are adopted as the basis for the constraint set formulation in weather routing. Thus, the synchronous roll, parametric resonance, surf riding and broaching-to are considered according to the IMO MSC.1/Circ.1228 guidance. However, the dangerous resonance motion of the ship depends on her natural period of roll and a degree of tuning to the encounter wave period. This natural period strictly depends on the GZ curve shape and, consequently, on the amplitude of roll. In order to properly model the natural period of roll, a new method utilizing equivalent metacentric height is applied and incorporated into the route optimization. Sample calculations of the cross ocean routes are presented and the effect of the dynamic approach to the constraint set is demonstrated and discussed.
•Ship resonance roll-related constraints depending on actual amplitude of roll are proposed.•Reliable modeling of ship synchronous rolling conditions is applied to weather routing and the equivalent metacentric height is utilized in the optimal route finding process.•Significance of equivalent metacentric height application is revealed.•Sample route optimization are run and effects of dynamic constraints implementation are presented.
This paper describes the model test design conducted to investigate the effects of the pitch angle, yaw angle, static metacentric height, and flooding hole on the excess roll problem of an emergent ...buoyantly rising submarine. An increase in the pitch angle can decrease the roll angle prior to surfacing, but will decrease the metacentric height when emerging through the water surface. There was a slight effect of the static metacentric height on the excess roll problem when the submarine had a considerable initial forward speed. The metacentric height of the neck decreased significantly when the area of the flooding hole decreased, but there was only a slight effect of flooding holes near the middle body. The maximum roll and maximum yaw angles were positively correlated. Based on the results from using a computational fluid dynamic (CFD) method to study the coupling and interactions between the roll, yaw, and sway, the rolling moment increased with the increasing velocity and drift angle, and the yawing moment increased with the increasing velocity and roll angle. We also found that the sail accounted for approximately 70% of the rolling moment and 30% of the yawing moment for a rising submarine. The main source of the rolling moment was from the sway velocity on the sail, and the sway velocity and the drift angle were positively correlated with the yaw velocity; thus, the yaw angle must be limited to as small as possible to decrease the maximum roll angle.
Understanding of ship maneuverability and factors effecting to ship maneuverability is important to naval architectures and marine navigators. In ship control problems, the ship maneuvering ...characteristic must be considered before designing the controllers. With the development of science and technology, it allowed the studies of ship maneuvering to be performed in computation simulations. However, there are always the different results between computation simulation and the fact. For that purpose, this article presents an experiment to establish the quantitative relationship between metacentric height and ship maneuverability using scaled model ship.
A large percentage of maritime accidents in coastal seas are related to small fishing vessels. In order to investigate causes of maritime accidents, it is often necessary to carry out dynamic ...simulations for the estimation of trajectories and motions of vessels. Initial conditions of vessels such as main dimensions, loading conditions and hydrostatic properties are required for the accurate simulations. Small fishing vessels usually have few records of hydrostatic properties during their fishing operations. Therefore, in this study, estimation procedures for hydrostatic properties of small fishing vessels are proposed. At first, hull form characteristics of Korean small fishing vessels are investigated. Most of vessels have hard-chines and centerline skegs, they have similar hull forms. Bonjean curves of several small fishing vessels whose gross tonnages are below 10 tons are normalized with vessel breadths and depths. Representative bonjean curves are derived from normalized bonjean curves, and a representative hull plan is obtained as well. If the vessel loading conditions such as total weights and centers of gravity are given, fore and aft drafts can be calculated by using the representative bonjean curves with the constraint that weights and buoyancies are in equilibrium. Metacentric heights are also estimated by using the representative hull plan. Drafts and metacentric heights estimated by proposed iterative estimation procedures are compared with actual vessel data, estimated values are in good agreements with actual values. In addition, normalized fore and aft drafts, metacentric heights of vessels can be formulated as the linear functions of normalized total weights and centers of gravity. Empirical formulas of drafts and metacentric heights are proposed, and it is confirmed that the empirical formulas also provide reasonable results, which are similar to the results by iterative estimation procedures with representative bonjean curves and hull plan.
The reprint presents a collection of contributions to various aspects of ship hydrodynamics and dynamics, a part of which was presented at the MARTECH2020 Conference, and all of which were published ...in a Special Issue of the journal, Marine Science and Engineering. The scope of the collection covers nearly all branches of ship hydrodynamics and dynamics, and so it may be of interest to all specialists in the field as well as for naval architects and applied mechanicians of various levels. The authors are recognized specialists from a number of countries, and to all of whom the Editors express their acknowledgement.
This paper proposes the station-keeping control for an underwater vehicle keeping balance motions and performing accurate manipulations in underwater inspections. In order to control position and ...maintain bilateral balance in deep water, a controller is designed with a Sprott system-based self-synchronization error formulation and a bisection approach algorithm to enhance the performances of brushless dc motors. A sufficiently high but not exceeding metacentric height (GM) is designed for the proposed underwater vehicle. Depth control with a pressure sensor is carried out depth gauge to determine the operated voltages. Using the voltage control mode, the practical tracking controller can maintain the same dynamics for bilateral propellers. Uncertainty dynamic parameters cannot be precisely modeled in a vehicle, and another one can track the pre-specified dynamic responses of a reference model. It keeps the bilateral propeller balancing operations by close-loop controlling the duty ratios of a buck-boost converter. In contrast with the incremental conductance based controller and PID controller, the proposed bilateral propellers controller is used to demonstrate the superior performances in depth and station-keeping tests, operating with armature voltages of 0–30 VDC and rotor speeds of 0–900 rpm in 0–3 m diving depth.
•Keep bi-propeller balance.•Operate via voltage controller.•Design in an embedded system.
PDF
