Rüdiger von Bock und Polach

Design and Modelling of Accidental Ship Collisions With Ice Masses at Laboratory-Scale

Knowledge about the level of damage after a collision with an ice mass is necessary for designing ships and offshore structures operating in ice-infested waters. An understanding of the physical processes during such a collision is needed to prevent (or limit) accidents, causing loss of life, the loss of a ship or environmental pollution. This study was motivated by the lack of experimental data on ship collisions with ice masses where both the ship and the structure undergo deformations. Laboratory experiments of accidental collisions with ice masses (ACIM) are essential to verify current methods for integrated analysis of the crushing and deformation of the ice and the steel structure. ACIM tests are sensitive to the structural design, i.e., the design of a structure that is flexible enough in relation to the ice mass. Both the ice and the structure should be able to deform during the collision event. The paper addresses issues related to the planning of ACIM at laboratory scale with special emphasis on the choice of: (i) process of ice manufacturing and ice mechanical properties; (ii) flexibility of impacted structure; (iii) scaling of the experiment. Experimental setup of laboratory-scale ACIM for the Aalto Ice Tank is proposed. Non-linear finite element analysis is used as a tool to predict structural damage and to guide the planning of collision experiments. The predicted damage of the test specimens caused by collision is presented. NOMENCLATURE

On the Scalability of Model-Scale Ice Experiments

Ice model tests are a frequently used mean to assess and predict the performance of ships and structures in ice. The model ice composition is adjusted to comply with Froude and Cauchy similitude. Recent research indicates that the internal mechanics of Aalto model-scale ice and sea ice differ significantly. This consequently limits the scalability and challenges state-of-the-art scaling procedures. This paper presents a qualitative assessment on selected topics to assess the differences between model-scale ice and sea ice and the influence of related experiments on determined mechanical properties. Furthermore, existing scaling approaches are discussed in context of recent research findings.

A Decision-based Design Approach for Ships Operating in Open Water and Ice

Designing ships for open water and ice requires a suitable design method to account for the distinct challenges in open water and ice. Ships with multienvironment capabilities are of high complexity as a result of design-coupling, which is illustrated by design matrices. In this context, this article presents a method that includes a ship performance evaluation method based on the Ship Merit Factor (SMF). The method combines the SMF with a route specific ship-dependent productivity and allows to compare the technoeconomic performance of ships operating in open water and ice. Consequently, the method is applied to a case study comparing the performance of different ship designs operating along the route Rotterdam to Yokohama through the Suez Canal and the Northern Sea Route. The resulting design approach indicates the necessity to include and develop novel simulation-based methods for the reliable assessment of ice-capable ships is discussed.

Challenges With Oil Spill Risk Assessment in Arctic Regions: Shipping Along the Northern Sea Route

Arctic regions, and thus ice-covered waters, are continuously getting higher in the national and international political agenda. The world demand in energy resources and the need in development of new transportation routes are pushing industrial activities up North where we see prospects and expectations on one side, and gaps and challenges on the other. Industrial development of the new geographic area is complex, and the priority in transportation is given to marine shipping. For the recent years, transit cargo shipping through the North Eastern Passage or the Northern Sea Route (NSR) increased more than 10 times from 0.11 million tons (4 passages) in 2010 to 1.36 million tons (71 passages) in 2013. Although, the numbers are small compared to global cargo shipping, the sensitive Arctic environment requires the establishment of a oil spill recovery system as well as risk mitigation measures. This, in turn, requires the preceding development of a risk assessment methodology for oil spills in ice-covered waters. Therefore, this paper presents the challenges involved in Arctic shipping along the NSR and identifies the knowledge gaps with respect to environmental risk assessment of accidental oil spill.Copyright

Ice Model Tests in Context of the Investment Value of an Offshore Vessel

Offshore activities and shipping in Arctic regions increased significantly in the past decade due to fossil resources. These areas hold about 15% of the worlds oil and gas. Exploration or transportation in such harsh Arctic environments possesses additional risks for the crew, the material and the environment. Hence, ships need to be able to handle low temperatures and ice impacts. Ice class certificates issued by classification societies reflect the ships level of ice capability. They are further required to be admitted to ice covered waters or particular regions in seasons with a certain probability of ice occurrence. In most cases, offshore operations are not continued in ice and ships need to transit through ice after abandoning a site upon ice arrival. However, the daily costs of such specialized vessels are high with up to 0.5M

Ice Resistance Calculation Methods and Their Economic Impact on Ship Design

day that are not reimbursed in downtimes or transit. Therefore, in Northern Arctic regions a higher ice class can significantly enhance the ships workability and therewith its economic value.The lower Polar ice classes, respectively Baltic ice classes, can only be determined analytically with empirically validated formulae for common cargo ships. Other ship types and ships with low L/B ratios are typically required to prove their ice capability through ice model tests. Nevertheless, ice model tests determine only the ice class of the propulsion system, whereas the ice class of the hull structure is determined by calculations. Furthermore, ice model tests are typically conducted towards the end of the design phase where eventual modifications are expensive and potentially threaten the construction schedule of the vessel. Often steel and equipment have already been procured and the manufacturing has begun. This paper presents an iterative procedure of ice model testing and design updates in order to enhance the performance of a particular offshore vessel to meet the requirements for a particular ice class. Thereby, it will be shown how an increase in investment costs for the design changes is compensated by the increasing value of the ships capabilities due to the higher ice class. Furthermore, the drop in value of the ship for the next lower ice class will be indicated as well as the economic consequences should the ship fail to reach the targeted ice class.Copyright

Ship Performance Assessment for Arctic Transport Routes

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

A Numerical Model to Initiate the Icebreaking Pattern in Level Ice

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

Experiments on level ice loading on an icebreaking tanker with different ice drift angles

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