CFD-BASED SIMULATION OF THE FLOW AROUND A SHIP IN OBLIQUE MOTION AT LOW SPEED

Ships tend to maneuver in oblique motion at low speed in situations such as turning in a harbor, or during offloading, dynamic positioning and mooring processes. The maneuverability criteria proposed by IMO are valid for ships sailing with relatively high speeds and small drift angles, which are inadequate to predict ship maneuverability in low speed condition. Hydrodynamic performance of ships maneuvering at low speed is needed to know for safety issues. A CFD-based method is employed to predict the flow around an Esso Osaka bare hull model in oblique motion at low speed, where the drift angle varies from 0° to 180°. The URANS method with the SST k-ω model is used for simulating ship flows with drift angles 0°~30° and 150°~180°, and DES method for simulating ship flows with drift angles 40°~150°. Verification and validation studies are conducted for drift angles of 0° and 70°. The vortex structures at typical drift angles of 0°, 30°, 50°, 70°, 90° and 180° are analyzed. The effects of drift angle and ship speed are demonstrated.

Multifunctional simulator for providing ship with data on maneuverability

The article presents the research analysis on the ship safety. It has been found out that due to the lack of a methodology for planning an algorithm for the maneuvering control system, there is no concept of solving technological problems or any understanding of what data are needed to perform the work. Despite the cybernetic devices and programs perform some part of the work and prepare the necessary data, the skipper does not understand how the device generates them. The task was to create a prototype that could allow to get data on the ship maneuverability. After the initial stage of training has been passed the skills should be obtained, which further will transform into the passive and stable abilities. The created hardware and software package allows implementing the concept of the guaranteed safety of maneuvering control in piloting vessels due to improving the methods of forming sustainable skills and bringing it to the automation level. It was recommended to use a simulator with visualization, to introduce the new algorithms of controlling the ship propulsion in the area of responsibility by coastal and to develop the recommendations on divergence, new training methods for pilots on shore. The conclusions were made on improving the level of information support by preparing subject-specific declarative knowledge and presenting it in an easily accessible form for perception when making decisions on maneuvering. The developed methodology is implemented in the training process of pilots in the training complex of Kerch State Maritime Technological University

A novel ship path following method in inland waterways based on adaptive feedforward PID control

Given the complex and time-varying external disturbances of inland waterways, designing an accurate path following controller is challenging. Based on the traditional PID controller, combined with the servo system model and the lead compensator, an adaptive feedforward PID controller for path following of ships in inland waterways is designed considering ship maneuverability and external disturbances. Simulations of a ship in a curved channel in different scenarios are carried out to illustrate the effectiveness of the proposed path following method. Compared with the traditional path following controller, the proposed one based on adaptive feedforward PID control has favorable relative stability, anti-interference ability and high steady-state precision in inland waterways.

Effects of Hull Geometry and Tightness of Turns on Ship Maneuverability: An OSIS-IHI Simulation

OSIS-IHI (Ocean Structure Interaction Simulator – Ice-Hull Interaction) is a ship maneuvering in ice modeling software developed at OCRE for a marine simulator and ship performance assessment applications. A series of OSIS-IHI simulations is conducted to explain the maneuvering behavior observed of the USCGC Polar Icebreaker indicative design previously tested at the centre. The simulation is conducted with the original and a modified version of the USCGC Icebreaker Healy. The Icebreaker USCGC Healy was equipped with doublescrew conventional propellers. The hull geometry of the OSIS-Healy model is appropriately modified to mimic the hull form of two indicated design versions in question and its propulsion units replaced by twin pods prior to studying its maneuverability in order to shed light on the apparently poor maneuvering performance of the podded version of the indicative design. The modified version extends the mid-body leaving just 7.5 % of hull that constitutes the stern section. It is hypothesized that the extended mid-section cost large resisting moment against turning due to the increase of ice breaking at the aft shoulder and mid-body. This hypothesis is validated numerically to explain the poor maneuverability exhibited by the extended mid-body design, based on consideration of ice-hull interaction geometry and basic mechanics of ice breaking as well as existing anecdotal test evidences. This paper presents result of the simulation to explore effects of hull geometry and tightness of turns on ship maneuverability. Important insights gained are summarized and recommendation for further work given.

Numerical Estimation of Hull Hydrodynamic Derivatives in Ship Maneuvering Prediction

Prediction of the maneuvering characteristics of a ship at the design stage can be done by means of model tests, computational simulations or a combination of both. The model tests can be realized as a direct simulation of the standard maneuvers with the free running model, which gives the most accurate results but is also the least affordable, as it requires a very large tank or natural lake, as well as the complex equipment of the model. Alternatively, a captive model test can be used to identify the hydrodynamic characteristics of the hull, which can be used to simulate the standard maneuvers with the use of dedicated software. Two types of captive model tests are distinguished: circular motion tests (CMT) and planar motion mechanism tests (PMM). The paper presents an attempt to develop a computational method for ship maneuverability prediction in which the hydrodynamic characteristics of the hull are identified by means of computational fluid dynamics (CFD). The CFD analyses presented here directly simulate the circular motion test. The resulting hull characteristics are verified against the available literature data, and the results of the simulations are verified against the results of free running model tests. Reasonable agreement shows the large potential of the proposed method.

Estimation of Maneuverability of Fishing Vessel Considering Hull-Form Characteristics

Fishing vessels with a length (LBP) of less than 100 m are generally not required to comply with the mandatory IMO Ship Maneuverability Standards. Therefore, an analytical method using empirical formula is preferred rather than a model test, which consumes a lot of time and monetary resources in estimating the maneuverability at the design stage. However, most empirical formulas have been derived from the model test results of merchant ships, and in the process, estimation errors may occur when hull-form parameters (L/B or CbB/L) with high correlation are applied to fishing vessel hull form whose characteristics are different from those of merchant ships. Therefore, a modified empirical formula was derived from previous research by including major parameters of fishing vessel hull form in the Kijima 90 empirical formula. In this study, maneuverability of stern trawler hull form is estimated for validating a modified empirical formula. The study confirmed that including characteristic parameters of the fishing vessel hull form in the empirical formula developed for merchant ships could improve the accuracy of estimation.

Algorithm of Berthing and Maneuvering for Catamaran Unmanned Surface Vehicle Based on Ship Maneuverability

In the complex port environment, ship berthing manipulation is one of the most difficult operations. In this study, an algorithm of berthing and maneuvering was designed for a catamaran unmanned surface vehicle (USV), which is used for port patrol and protection. Considering the influence of wind, waves, and currents, the mathematical model of the maneuvering movement for the twin-hull and twin-propeller USV was established. Based on the Visual Studio development platform, the USV’s berthing manipulation simulation software was designed. Through the turning simulation experiment of the catamaran USV under different differential rotation speeds of the twin propellers, the relationship between the ship’s turning radius and the propeller speed difference was obtained. A simulation experiment of decelerating and stopping ships at different speeds was carried out, which can provide a reference for speed control when berthing. A berthing maneuvering algorithm based on ship maneuverability was proposed. USV’s berthing algorithm includes three stages: approach process, turning process, and berthing process. In the approach process, the appropriate approach speed was select according to the rotation angle. In the turning process, the right and left propeller speed differences were select. In the berthing process, the berthing speed was controlled according to the berthing distance. In the port environment, a berthing simulation experiment for catamaran USV was carried out. The simulation results show that based on the berthing and maneuvering algorithm, the efficiency and safety of catamaran USV berthing can be improved.

Captive Model Tests for Assessing Maneuverability of a Damaged Surface Combatant with Initial Heel Angle

The present study is about the application of a four-degree-of-freedom (4DOF) maneuvering mathematical model based on Abkowitz’s model for assessing damaged ship maneuverability with initial asymmetry. A scaled model of the Office of Naval Research Tumblehome hull with a damaged compartment was used as the test model. Based on the survivability regulations for naval vessels, the damaged compartment was designed and located near the bow, such that it had an initial heel and trim. Static and dynamic captive model tests were performed on the damaged ship model to determine the maneuvering coefficients for the maneuvering mathematical model. Maneuvering simulations were carried out with the captive model test data and 4DOF maneuvering mathematical model. The advance speed in the maneuver reduced more in the damaged condition than in the intact condition, and maneuverability was severely degraded during starboard turning.