Experiments by Invited Researchers


Ice loading on a moored structure in a changing ice drift direction

Project acronym: HyIV-Aalto-01
Name of Group Leader: Li Zhou
User-Project Title: Ice loading on a moored structure in a changing ice drift direction
Facility: Ice Tank
Data Management Report: Report

User-Project Objectives

This project addresses a moored icebreaking tanker which may encounter varying ice drift directions. The general objective was to measure ice force and to observe the physical phenomenon in ice breaking process when a ship is experiencing a sudden change of the ice drift direction versus the fore-and-aft direction. Such information is needed to simulate the performance of a vessel operating in ice conditions. The first specific objective was to validate the present numerical model when the heading angle is zero degree in level ice. The second objective was to refine present numerical model considering the ice drift angles effect, where ice accumulation observed in model tests needs to be modeled in level ice. The third one might be to develop a model to simulate ice-hull interaction in broken ice.

Short description of the work carried out

The ice forces on the model in six degree of freedom were measured. A lot of videos were recorded to observe the ice breaking phenomenon. It is observed that ice accumulate severely in front of hull when the heading angle is different from 0 degree. The corresponding thicknesses of ice pile up are measured after every level ice tests. Practical difficulty is encountered as the measured time signals on force in surge are oscillating with large amplitude, but the effect was reduced after the longitudinal acceleration was measured. The connection between model and carriage was found not stiff enough in the first ice model test. Then more screws were used to fix the model to the carriage rigidly in the second ice model test. In addition, there are also some uncertainties with calibration process.

Highlights of important research results

This project is important for us to get insight into the physical process during interaction between hull and ice and assists to model ice accumulation process based on massive observations in ice model tests. It is found from model tests that ice drift direction significantly influences on the ice load level in both surge and sway directions, especially when the drift angle is 90 degree, ice load level gets very large and a lot of broken ice cusps accumulate in front of hull to a relatively steady state rather than go under the hull in mid-ship. The ice breaking pattern is very similar to what we have simulated in present model when the ice drift angle is small, but the ice breaking radius are still needed to be adjusted based on observations. This project provided necessary data and videos to update our present model in level ice and also provided a possibility to develop a model to calculate ice force in broken ice. In addition, the measured data, as an input into dynamic positioning system if applicable, might assist to study and design the dynamic positioning system which performs station-keeping function for a vessel in ice.

Zhou L. , Riska K, von Bock und Polach R., Moan, T, Su, B. Experiments on level ice loading on an icebreaking tanker with different ice drift angles , 2013
Li Zhou, Kaj Riska, Torgeir Moan, Biao Su Numerical modeling of ice loads on an icebreaking tanker: Comparing simulations with model tests , 2013

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