Sandro Erceg

Semi-empirical level ice resistance prediction methods

ABSTRACT Ship performance in ice depends on numerous design aspects, such as ensuring adequate thrust, appropriate arrangement of the propellers, as well as a hull designed to reduce the resistance, in both ice and open water. All these efforts require ice resistance estimates. In early design stages, semi-empirical methods represent the most commonly used choice. However, being based on a limited amount of empirical data, these methods are expected to be restricted to ships of similar characteristics to the ones used in their development. This paper reviews six semi-empirical level ice resistance prediction methods, applied to four ships of different sizes and bow shapes. The results are presented along with the available full-scale resistance measurements. It is found that their deviation from the measurements varies substantially with the ship size. The methods show significant discrepancies, with the deviations from one another as large as 100–200%, especially for larger ships.

Ice Resistance Calculation Methods and Their Economic Impact on Ship Design

A ship is an investment and built to create revenue. The decision whether the design of a ship is realized or not is therefore strongly affected by the natural obstacles of mission and route. The occurrence of ice along arctic routes is such an obstacle and affects significantly the resistance and the required propulsion power. Advanced simulation environments, such as panel methods or CFD do not exist yet for ice resistance calculations and hence semi-empirical formulations or model tests need to be employed to assess or validate a design. Ice model tests impose great expenses in terms of time and money, which often does not allow testing design variations. On the other hand, the results of semi-empirical formulas might be accompanied by significant uncertainties. The academic study presented in this paper is a transit simulation on the Northern Sea Route (NSR) for the ice-capable tanker MT Varzuga (formerly MT Uikku). The study evaluates the ice conditions along several NSR alterations and the ice resistance-related performance with available semi-empirical methods and ice model tests. Finally, the economic impact of the applied ice resistance prediction methods is evaluated and the differences are quantified.Copyright

Development of an Approach Towards Mission-Based Design of Arctic Maritime Transport Systems

This paper describes an approach that utilizes a discrete event simulation tool and ice data from a numerical ice prediction model to enable mission-based design of arctic maritime transport systems consisting of a single or multiple arctic cargo ships.For a specific vessel design and route, the developed approach makes it possible to simulate how the transit time varies over time due to both varying ice conditions and stochastic factors such as the weather. Thus, for a given transport scenario (route, transport demand, and period of time), the approach can be used to determine a suitable vessel capacity, propulsion power, and ice class. When necessary, the approach can be used to analyze and design more complex transport system consisting of multiple vessels and routes.A case study is carried out to demonstrate how the approach could be applied in practice. The outcome of the case study indicates that the approach generates realistic figures, and that it is flexible enough to make it possible to vary the number of included parameters and variables as needed.Copyright

Ice Condition Database for the Arctic Sea

Increasing trends in the arctic sea transport lead to the necessity to determine route specific ice conditions to ensure safe vessel transits. In order to achieve this, the comprehensive understanding of ice conditions from the past should be used to predict future trends for arctic sea ice conditions.This paper presents the development of such ice conditions database with the implementation of a satellite data source, which will become a basis for the determination of route specific ice conditions. A case study is performed in order to show how the database could be used to collect the route specific ice data for statistical analyses.Copyright

Ship Performance Assessment for Arctic Transport Routes

The melting ice cap in the Arctic Sea creates greater operational opportunities not only for shipping routes in areas inaccessible in the past due to ice coverage, but also for the existing commercial shipping routes. Therefore, the economic feasibility of higher polar classes (PC5 and PC4) will be discussed for transit operations on the route from Rotterdam to Yamal LNG terminal. Initially, the ice thickness and coverage along the route until 2050 will be identified following recent forecasting trends. This will lead to the permitted round trips per year for the ice class in question. Consequently, a decision towards the choice of ice class must be made. This choice will be accomplished with the help of the ship merit factor (SMF), which considers the potential earnings arising from the increase in operational days for a higher ice class while accounting for the increased expenditure in the ice free season and areas of operation. As a result, a comparative study will be presented for the LNG sea transport operation on the route from Rotterdam to Yamal, which thereby visualizes a decision-support procedure for an arctic transit operation.© 2013 ASME

The influence of the bow design on structural response due to ice loading

ABSTRACT The optimum bow shape for an ice-going vessel in ice conditions is different to open water conditions and research about the influence of the bow shape on the structural response due to ice loading and resistance is required. A framework is developed to study the functional relationship between the bow shape and the structural response for ice-going bows in MATLAB. The structural dimensions are optimised by an automatic link to a parametric finite element model in ANSYS Mechanical. Both the buttock angle and the average waterline angle should be as small as possible to reduce the channel ice resistance. When changing the bow shape angles along an iso-resistance curve, the design pressure is constant and thus the structural response according to the DNVGL rules. It is found that the maximum stress in plates of the bow increases by reducing the average waterline angle while keeping the structural design constant.

Challenges for Using LNG Fueled Ships for Arctic Routes

The utilization of the Northern Sea Route by commercial ships is an official fact. Since 2009 the number of international cargo vessels using the passage has been increasing, and a continuous raise in these numbers is expected if the route establishes itself as reliable. The route saves vessels approximately two weeks’ time in summer over a route via the Suez channel, but the increase brings concerns, regarding environmental impact, safety, and operability on the route.This paper investigates the current challenges of using LNG fueled ships for arctic transport routes. A panorama of the recent conditions and predictions for the arctic environment regarding ice concentration and seasonal route availability is presented. The current development of LNG as a commercial fuel is discussed based on this arctic panorama, approaching key topics such as infrastructure, economic viability, propulsion requirements, and environmental impact. Special attention is given to the performance of LNG propulsion systems under arctic conditions, focusing on powering and air emissions. We conclude the paper by proposing the implementation of a lifecycle model to predict economical and environmental performance indicators when simulating a fleet of LNG fueled ships operating under many possible future ice conditions scenarios.Copyright

A Numerical Model to Initiate the Icebreaking Pattern in Level Ice

Ships navigating in ice-covered waters experience local and global ice loads due to ice-hull interaction. The design of a ship with good ice performance requires adequate assessment of these forces. Recently, an increased activity in developing numerical models of ice-hull interaction in level ice has been observed, owed to the increased computational capabilities. However, certain semi-empirical icebreaking patterns inevitably influencing the interaction process have been implemented in the majority of interaction models used for the assessment of ice performance of ships. Therefore, an attempt using a quasi-static numerical approach to model the initiation of icebreaking pattern in level ice has been made and is presented in this paper. The term initiation herein denotes the creation of circumferential cracks, disregarding thus the succeeding radial cracks.The concept used in the model features a set of radially oriented ice beams at the interaction zone. The model accounts for the bow geometry and the properties of the encountered ice. The icebreaking pattern for a case study ship is simulated using the developed model. Lastly, this paper discusses the sensitivity of the model with respect to the bow shape.Copyright