The objective of the work described in this paper is to evaluate the significance of storm waves and drift forces in generating the driving force for iceberg-structure interaction.
The current paper is based on both experimental and analytical studies conducted at the University of California, Berkeley. Tests were made to simulate the impact of different wave driven icebergs with a fixed caisson type structure. A numerical model for calculating impacts with different eccentricities was developed and this model forms the basis for a reliability evaluation.
For the proposed offshore developments in the Eastern Canada continental shelf, iceberg impact with a structure has to be considered. This paper presents a extensive study carried out at the University of California, Berkeley which consisted of the following main tasks:
Laboratory experiments to simulate iceberg-structure interaction phenomena and identify the key parameters in the process.
The development of a reliability model to predict the magnitudes of impact forces and their probability distribution.
A sample application of the procedures that were developed was then carried out using publicly available environmental data in the Grand Banks area offshore Newfoundland.
The experimental studies included a range of iceberg and structure sizes as well as conditions characteristic of the Grand Banks area, and were conducted in a wave tank 4.3m wide by 7.3m long.
Russel at 0.1. (1) provided a description of the modeling rationale for simulation of iceberg drift. The dynamic similitude between a model and its prototype in which an object is moving in an incompressible viscous fluid is obtained by keeping the Froude and Reynolds numbers the same. Froude scaling ensures similitude in inertial and gravitational forces and Reynolds scaling reproduces the inertial viscous effects correctly. Both numbers cannot be modeled correctly and because of the blunt shape of icebergs inertial forces dominate and so Froude number scaling is chosen.
Lever (2) has discussed the importance of Reynolds number in the simulation and argues that if the iceberg is very much smaller than the wave length then it will move with a trajectory similar to the water particle orbitals. In this case the viscous force generated on the iceberg surface will be small and so Froude scaling will be appropriate. If the iceberg has a horizontal dimension greater than about. 1/5 of the wavelength, the diffraction regime dominates the viscous drag effects and again Froude scaling would be the best choice. Iceberg motions can be subdivided into first order motions (heave, yaw, pitch, roll, sway, and surge) and the higher order drift motions. Both types of motions are considered in Lever's experimental work. Small icebergs with a dimension of 1/10 of the wave length maintain orbital motions, those with a dimension of up to 2/3 of the wavelength have horizontal velocities close to the maximum wave velocity and large icebergs tend to have steady motions close to the drift velocity.