Maneuverability is an important characteristic of a ship, which affects not only the performance during its daily operation but also its safety under urgent conditions, such as danger of collision. Currently, it draws increasing attention from naval architects during the design stage. The characteristics of hydrodynamic derivatives in maneuvering equations are traditionally obtained from towing tank experiments. In this paper, we present several numerical simulations of typical ship maneuvering using a RANS-based computational fluid dynamics tool. In order to resolve the transient phenomena properly, the explicit volume of fluid method is applied to solve the free surface. The motions of the vessel are captured through an embedded 6-DOF dynamic solver. This kind of simulation provides a more direct reference to naval architects for their design and optimization work. All simulations can be achieved with practical turnaround times on a single workstation.
This paper presents the application of a direct time-domain solver to simulate the influence of the incident wave height on the maneuvering characteristics of a container ship in waves. A body-exact potential flow model is used to compute the wave loads on the vessel. In the present body - exact scheme, the perturbation free surface boundary conditions are transferred to a representative incident wave surface at each station at each time. The hydrodynamic pressure components are integrated under the intersection surface of the incident wave surface and the exact body position. A strip theory formulation is used, which has been found to be numerically stable, robust and computationally efficient. These are all critical aspects when performing long time maneuvering simulations. The hull maneuvering, rudder and propeller forces are carefully modelled from a systems-based approach, typically used for simulating calm water maneuvers. The computational model is validated using available free-running model test data. The influence of wave characteristics including wave height, frequency and heading on the turning maneuver of a containership is presented.
The paper presents a rational methodology for the simulation of the maneuvering ability of ships, while accounting for the vessel’s maneuvering properties and the ensuing environmental and navigational conditions. In this context, the effect of different rudders and weather scenarios is demonstrated and a real ship to ship collision accident under adverse weather conditions has been simulated. The presented methodology can form the basis for a decision support tool for ship's navigation in adverse weather conditions and the assessment of ship’s maneuvering devices.
Propeller-hull interaction may have a relevant role in the overall propulsion efficiency of an underwater vehicle (UV) driven by single propeller: the modification of the boundary layer characteristics at the stern due to the momentum introduced in the flow by the propeller may determine a significant relative change of the hull drag and determine a very different effective inflow to the propeller, with respect to the bare hull condition. These effects are exacerbated for the current size Autonomous UVs (AUVs) whose cruising speed is kept low to increase range and endurance. Knutsson and Larsson (2011) studied different longitudinal positions of a large diameter propeller in the stern of a singlescrew tanker. While they demonstrated the general principle that larger propeller diameters and larger longitudinal clearances may lead to higher propulsion efficiencies, in their study, the propeller design was kept fixed. Changing position and diameter of the propeller, obviously changes the self-propulsion coefficients, but it also changes the nominal wake at the propeller disk. Eslamdoost et al. (2017) performed a CFD study on the effect on hull-propeller interactions with varying propeller diameters. However, they used the same design of propeller which remained un-optimized in terms of open water efficiency, pitch and RPM for each of these cases. Conceptually, when the propeller gets a larger diameter and it is moved further downstream from the underwater vehicle tail, the hull efficiency initially increases and then start decreasing again (the thrust deduction at first decreases more rapidly than the decrease of wake fraction).
In recent years, the need for a quantification of “maneuvering in waves” has increased due to both requirements for heading and track keeping of naval hulls, and to quantify the ability of low-powered ships to recover and keep the (presumably safe) head seas heading in adverse weather. To address these requirements, the CRS has been working since 2011 on a new time domain simulation tool able to predict the ship’s sustained speed, track and drift angle in wind and wave conditions with sufficient accuracy. Due to the difficulty in accurately combining the wave frequency forces with the maneuvering forces, a reformulated simulation tool was developed which only considers the low frequency wave drift forces and the maneuvering forces. The present paper presents how this new approach (ManWav) performs compare to the experimental results and compare to a fully coupled semi-nonlinear time domain tool (FREDYN). To assess the performances of this approach, an extensive validation test campaign was carried out on the 5415M model. This test campaign included captive and free sailing maneuvering tests in calm water, in regular and irregular waves for multiple wave directions and ship speeds.
The problem of interest in this work is the numerical simulation of a ship maneuvering in a seaway. A key challenge of this problem is the time-scale disparity between the high-frequency seakeeping response and the slowly varying maneuvering motion, both of which are coupled with the interaction of the hull, propeller, and rudder. The time-scale disparity becomes extreme when the rotation of the propeller is resolved in a time-accurate manner, requiring small time-step increments relative to the seakeeping and, in particular, the maneuvering time scales. Our novel approach to the maneuvering-in-waves problem is a hybrid simulation method that combines a fast-running computational fluid dynamics solver, a semi-empirical propulsion model, and a higher-order boundary element method. The hybrid simulation method is compared to a new numerical benchmark for the Duisburg Test Case Hull turning in waves.
A general computational framework for the simulation of ships advancing through brash ice based on the coupling of Computational Fluid Dynamics (CFD) to the Discrete Element Method (DEM) as implemented in Simcenter STAR-CCM+ is presented. The method was applied to predict resistance of a bulk carrier advancing through brash ice and explore implications for propulsion and structural responses. The study demonstrated the capabilities for the simulation of ship-ice interactions, encompassed relevant sensitivity studies regarding the modeling of material properties, packing density of brash ice, boundary conditions, the degree of coupling of CFD to DEM and implications for computational cost. Simcenter STAR-CCM+ offers uni- and bidirectional coupling of CFD to DEM. The was to derive best practices for the application to resistance, propulsion, local flow field and maneuvering analysis and related validation exercises. It was shown that different modeling approaches and simulation inputs affect both forces on the hull and local flow field variables. The method can be applied to simulations of ships advancing through a field if scattered ice floes of arbitrary shape and distribution.
For navigation safety, ship behaviors in adverse weather conditions must be captured. As a method to know the navigation limit of a ship under external disturbances such as wind and waves, there is a method to capture the maneuvering limit based on the average (steady) sailing conditions (SSCs), such as check helm, forward ship speed (speed drop), and hull drift angle of a ship moving in adverse weather conditions. These are obtained by solving the motion equations for ship maneuvering in steady wind and waves, and related studies have been performed (for instance, Eda, 1968; Ogawa, 1969; Martin, 1980). However, the check helm, hull drift angle, ship speed, etc. fluctuate owing to the effect of random sea. Therefore, to discuss the navigation safety, it may be insufficient to consider only the average condition, and it may be necessary to consider its fluctuation components.
In the past, the boundary element method (BEM) has been widely used to predict the potential flow around hydrofoils and propellers. The viscosity, which not only causes friction and reduces the efficiency but also affects the pressure distributions, is considered via an empirical skin friction coefficient. In this paper, the three-dimensional VII method, which coupled a lower order panel method with a two-dimensional integral boundary layer solver (the viscous/inviscid interaction method, or VII) is used to solve the flow around three-dimensional wings and propellers. It is assumed that the boundary layer growth is mainly in the chord-wise direction and simplified the three-dimensional boundary layer equations into two-dimensional. The three dimensional velocities, which is from the panel method, are used as the edge velocities, and the influence of boundary layers in other strips are considered. The pressure distributions and open water characteristics are compared with either full-blown RANS simulations or with existing experimental data, and it is shown that the 3D VII method can improve the results significantly.
The cruise industry is seeking new markets and products to trigger a growing customer base around the world. As the more traditional cruise ships have become bigger and more geared towards mass tourism in typical locations like the Mediterranean and the Caribbean, there has also emerged a need for smaller niche type of cruises, typically higher end and more exclusive. Exploration of the Arctic and Antarctic is exotic and is seen as the next step after the popular cruises to places like Alaska has become mainstream.
To enable the cruise industry to conquer Polar region a new generation of cruise ships is entering the market. A common feature for all of these is that they are smaller ships with more luxurious accommodation. Strong focus on safety, customer comfort along with sustainability and low environmental footprint are also all key drivers in this market. To achieve these objectives some of latest technology in terms of propulsion, power generation and distribution, navigation and digital solutions is critical. As per today more than 25 such expedition cruise ships are on order, most of which have been contracted in 2017.
Ensuring the safety, comfort and satisfaction of 100s if not 1000s of passengers and crew in such inhospitable regions is no mean feat. Through the experience and innovation in hip power management and propulsion systems some companies have become the leader in providing these type of solutions to the cruise industry. The past 25 years the leading companies have worked closely with ship owners, operators, designers and shipyards to develop the technical that is now setting the standard in the cruise industry.
Historically, naval architects have tackled these issues independently, working within rules developed by individual classification societies. However, the exhaustive harmonization work done in developing the IMO's new Polar Code has delivered a type of equivalence in structural and machinery specifications, as set out in the International Association of Class Societies Unified Requirements for Polar Class (PC) ships, which come into force on 1 January 2017.
Podded propulsion systems offer major safety benefits for ice-going vessels and has built a strong track-record across the sector, as demonstrated by the fact that it already satisfies IMO's Polar Code requirements and is available with PC notations suitable for a range of ice conditions. This level of confidence stems from past performance, with more than 60 vessels now in operation or ordered working in icy waters, including Pechora Sea, Kara Sea, Ob Bay, and Yenisei River.
In addition to ice-going ships, today, around 100 cruise ships are fitted with podded propulsion, including the world's largest such vessels - Royal Caribbean's Oasis class. In fact, due to better vessel maneuverability, improved passenger and crew safety, greater fuel efficiency and lower total cost of ownership, podded propulsion have largely superseded conventional shaftline propulsion in combination with rudder steering across the cruise market.
Given the strength demonstrated by podded propulsion in these distinct markets, it came as little surprise that PC6 classed Podded propulsion was selected for polar discovery yacht Scenic Eclipse-the world's first passenger vessel to be constructed explicitly to Polar Code standards-and for three Endeavor class ships which will be the world's largest expedition yachts with ice class. Before the end of 2017 Lindblad Expeditions Holdings, Inc. signed an agreement with Norwegian shipbuilder and ship designer Ulstein to build a new ice class expedition ship relying on podded propulsion system. According to recent news VARD Holdings Ltd. will build unique state-of-the-art LNG dual fuel electric hybrid icebreaker expedition vessel with the second highest icebreaking class Polar Class 2. When delivered, this ship equipped with pod propulsion will be revolutionary in its class. Taking all this into account, it is fair to consider the modern propulsion technology as the natural starting point for new generation cruise ships crossing polar and sub polar waters.