Showing papers on "Metacentric height published in 2019"

Practical maneuvering simulation method of ships considering the roll-coupling effect

Abstract: In this study, a practical maneuvering simulation method is presented considering the roll-coupling effect by extending an ordinal simulation model (3D-MMG model) proposed by Yasukawa and Yoshimura (J Mar Sci Technol 20:37–52, 2015), and adding the motion equation of roll. The roll moment acting on the hull is estimated by multiplying the hull lateral force with the vertical acting point. With respect to the surge force, lateral force, and yaw moment, the derivative expression model is employed. Subsequently, hydrodynamic derivatives with the exception of the roll-related terms are obtained by a captive model test based on the 3D-MMG model. The roll-related derivatives and the vertical acting point of the hull lateral force are estimated by simple formulae constructed based on the experimental data of four ship models. To validate the proposed simulation method, turning simulations are conducted for a pure car carrier model with variations in the metacentric height $${\overline{\mathrm{GM}}}$$ and are compared with free-running model test results. The simulation method exhibits sufficient accuracy with respect to its practical use and is useful to conventionally predict turning motions by considering the roll-coupling effect.

Estimation of metacentric height using onboard monitoring roll data based on time series analysis

Abstract: In this study, a novel procedure to estimate the metacentric height (GM) is proposed based on an autoregressive modeling procedure and a self-organizing state space modeling with respect to the onboard monitoring of roll data. First, the autoregressive modeling procedure is applied to estimate a natural frequency of the roll motion. Subsequently, a self-organizing state space modeling procedure is applied to estimate the GM using the estimated natural frequency. Model and onboard experiments were performed to verify the proposed procedure. The results confirmed that the proposed procedure achieves a good estimation in which the estimated results are in agreement with those obtained in the model experiments and are close to those derived from the stability manual corresponding to the ship condition in onboard experiments.

Tuning parameters sensitivity analysis study for a DP roll–pitch motion controller for small waterplane surface vessels

Abstract: For surface vessels with small waterplane area and low metacentric height, which results in relatively low hydrostatic restoring force compared to inertial forces, an unintentional coupling between the vertical and horizontal plane motions can be invoked through the thruster action. A novel controller dedicated to mitigating the unintentional roll and pitch motions of a dynamically positioned vessel has been proposed by the authors. As a continual study of that, this paper conducts a sensitivity analysis of the controller tuning parameters. A possible criterion comprised of several key variables representing different perspectives of the controller performance is proposed, followed by a guide for optimization their weighting factors by non-dominated sorting genetic algorithms algorithm. The sensitivity analysis was performed by a time domain simulation of a dynamically positioned semi-submersible platform. The simulation results reveal that the controller performance is crucially affected by the advance coefficient, that determines how large the ratio of the roll and pitch angles to their limiting angles that activates the proportional roll–pitch controller. The proposed parameter sensitivity analysis methodology can be used as a tool to determine appropriate roll–pitch controller gains with high positioning performance.

Experimental Validation of Transverse Stability Monitoring System for Fishing Vessels

Abstract: Active monitoring of transverse stability in fishing vessels is paramount due to its significant incidence in operational accidents. Access to systems for automatic detection of changes in vessel’s stability related parameters would better support the crew during fishing and navigation operations. The paper presents an initial experimental validation of a signal-based transverse stability monitoring system, which consists of an estimator-detector kernel that solely uses measurements of roll motion to identify changes in vessel’s metacentric height by estimating the roll natural frequency. Its performance is evaluated based on experimental data from a towing tank scale model test campaign. The proposed transverse stability monitoring system well performs by identifying the potential risks and changes in loading condition.

Numerical Study on Swimming Performance Based on Flapping Orientations of Caudal Fins for Bio-robotic Systems

Abstract: Set in the context of the development of bioinspired robotics systems, this paper seeks to understand the influence of the choice of the flapping orientation of fins on the propulsive performance of small underwater vehicles. In particular, the thunniform mode of Body and/or Caudal Fin (BCF) propelled systems is studied. This research is motivated by the fact that not much literature is available on the influence of flapping orientation of marine organisms and a number of mechanisms are found in nature. Dorso-ventral flapping with a positive metacentric height is shown to yield better self-stabilizing effects and lesser energy consumption compared to sideways flapping. Moreover, with dorso-ventral flapping, the choice of metacentric height could lead to the possibility of adjusting the body's rotational oscillation amplitudes to positively affect the downstream fluid interactions for the caudal fin. This is not possible with sideways flapping where the designer would be forced to change the flapping kinematics or the body shape in the sagittal plane, to adjust the body oscillation amplitudes. While the main body of results are obtained using simulations for underwater vehicle dynamics with coefficients of the REMUS underwater vehicle, stability analysis for a generalised case is also presented.

Design and Development of Naval Architecture Test Platforms and Experimental Procedures for Test and Evaluation

Abstract: To streamline and simplify current testing procedures within the Naval Architecture course the design, development and testing of current experimental procedures was investigated. The purpose of the investigation was to develop and simplify current test procedures through the delivery of current course content whilst providing students a platform from which they could develop a solid understanding of the first principles of ship and propeller design and efficiency. Two experimental suites were designed and modelled, a Stability and Metacentric Height Experiment, complete with pontoon prismatic reference hull, technical specification data and measurement equipment, to facilitate students understanding of the impacts of hull design on stability and metacentric height. The hull form was further designed with the inherent ability to test free surface effect and its readiness for possible interoperability between tests. The second suite of testing included Propeller Design, Propeller Thrust and Bollard Pull Experiments. This included designing a series of reference screw fixed pitch propellers using the Wageningen-B Series propeller curves. Propeller reference datum was established to support comparative testing against thrust and pull efficiency parameters of student designed propellers. Test platforms were designed and developed to determine the thrust efficiency and bollard pull of a propeller. Test procedures were also developed to support the developmental requirements of fourth year engineering students undertaking Naval Architecture.

Predicting Extreme Parametric Roll in Container Ships

Abstract: Parametric roll resonance is an unstable phenomenon that can lead a ship into dangerous situations such as possibly capsizing or loss of cargo. Container ships are particularly susceptible to parametric roll due to the time variance of the metacentric height. Recent incidents have reinvigorated the conversation concerning parametric roll which in turn has caused many to wonder what types of early stage design tools could be developed to provide parametric roll design guidance. This paper presents several predictive modeling techniques that were used to investigate if parametric roll leading indicators can possibly be identified and then considered in early stage design to avoid parametric roll resonance. This paper will utilize four predictive models that utilize and are trained by the parametric roll data created through the execution of a nonlinear non-homogenous damped Mathieu equation, subject to stochastic stiffness and forcing. The ultimate goal of the execution of these techniques is to expand the understanding the potential for parametric roll in early stage design.

The Risk Analysis of Parametric Rolling to Semi-Submersible Vessel Sailing at Sea

Abstract: Scholars usually studied parametric rolling of container ship, as its speed was very fast. Semi-submersible vessel didn’t have fast speed like container ship, but the special way of floating on/off heavy cargo in long waves could cause the requirement of parametric rolling. Because there was a small semi-submersible fleet size in the world, the problem of parametric rolling was neglected by scholars. This paper studied the methods to prevent semi-submersible vessel generating parametric rolling. During the research, we firstly used case calculation to prove semi-submersible vessel that could also generate parametric rolling like container ships. Secondly, we built semi-submersible vessel motion model and found the key factors that influenced parametric rolling occurring or not. Then the method of variable control parameters was employed, and the different parameters including wavelength, wave height, metacentric height and ship speed were changed to quantitatively calculate their influencing degree and rule. Finally, by the case analyzing, parameters value were gotten.

Design requirements for stability and minimal motions in a storm

Abstract: The hydrodynamics of a ship in a storm is not limited to the hull below the calm-water waterline. In a storm, the operating waterline varies between the bilge and the deck, causing unpredictable wave forces on the hull as well as the possibility of slamming on flat surfaces and the flared sections of the vessel. The present work describes the early stage of a design process for a hull form that accounts for the range of changing of the waterline in order to insure stability under severe heave. With this approach, it is possible to reduce the metacentric height, which minimizes roll resonance. The concept is part of a consistent ship design process; conventional naval architectural approaches will still be needed for successful solutions for reducing the pitching and yawing of the vessel and as a necessary condition for using active stabilizers and other seaworthiness improvements.

Virtual Laboratory with Algodoo for the Determination of the Metacentric Height of a Rectangular Vessel

Abstract: In the present work, a virtual laboratory using the Algodoo App was implemented in order to determine the metacentric height of a rectangular Ship in 2D. Experiments were carried out with different rectangular Ships, of different densities and geometries, which floated on a density fluid of fresh or salt water. Vertically and horizontally sliding pieces of different weights were placed on each Ship, causingtilt on the Ship, which could be measured for determining the stability gradient. Following, dispersion graphs of the vertical gravity center position versus the stability gradient were made, and with a linear data adjustment, the Ships transverse stability metacenter was determined. Finally, with a statistical treatment, the Ships metacentric height and its respective interpretation of the stability were determined. It was concluded that the method could serve as an option for instruction in understanding the stability of Ships and this method could serve as an option for instruction in understanding the stability of ships and in suggesting the future work with more complicated ship geometries.