Ice-structure interaction (ISI) is a complex process, which requires a thorough understanding of the underlying physics to ensure safe operations in the ice-covered regions. Application of discrete element method (DEM) to compute ice loads on structures is a widely accepted approach, where the equations of rigid body motions are solved for all ice pieces in the computational domain. In most ISI simulations, the ice zone is assumed to be resting on a static water foundation omitting the hydrodynamic effects (added mass, water drag, wave damping) of the interacting bodies. This assumption can introduce erroneous results to simulations of the floating ice floes behavior, which in turn will incur uncertainties in planning ice management activities.
In this paper, a smooth particle hydrodynamics (SPH) based computational fluid dynamics (CFD) code is coupled with a three-dimensional DEM model to take the hydrodynamic effects of the interacting bodies including the ice pieces into account. The ice zone is modeled as discrete elements, which allows computing interaction forces by considering contact laws. The water foundation is modeled using smooth particles, which are modelled with the Naiver-Stokes equations.
Several applications of ship and offshore structures interacting with level ice and pack ice are simulated. A scenario of an offshore supply vessel operating in the marginal ice zone (MIZ) that is subject to wave forces is also simulated to show how this approach can be used for modelling complex real-world problems. This scenario is unique in a sense that it yields a multi-physics solution, where ice-structure-wave are all included in a single CFD simulation as a fully coupled analysis. The cost of the simulation is significantly reduced by running the computations on a Graphics Processing Unit (GPU) instead of a typical CPU workstation. Some of the initial results of ice-structure interactions are presented in this paper and a reasonable agreement with reduced scale model test results are found.
Sayeed, Tanvir (OCRE- National Research Council of Canada, Faculty of Engineering and Applied Science, Memorial University of Newfoundland) | Colbourne, Bruce (Faculty of Engineering and Applied Science, Memorial University of Newfoundland) | Molyneux, David (Faculty of Engineering and Applied Science, Memorial University of Newfoundland) | Akinturk, Ayhan (OCRE- National Research Council of Canada)
Wave driven iceberg and bergy bits' impact load with an offshore structure is an important design concern. Hydrodynamic interaction between iceberg / bergy bit and an offshore structure in close proximity is an important factor that governs the impact load. Recently, a set of experiments has been conducted at Ocean Engineering Research Center (OERC) at Memorial University of Newfoundland to measure the wave loads on different sized spherical ice masses at different proximity to a fixed structure. A six component dynamometer was used to measure the loads in a quasi-static manner in six regular head waves. The objective was to investigate change in wave loads as the ice mass approaches to the structure. The experimental results show that the distance to wavelength ratio dictates the corresponding wave loads in horizontal and vertical directions. The mean drift force in the horizontal direction becomes negative (against the direction of wave propagation) for most of the cases when the body is close to the structure. Also, as the body is positioned closer to the structure, the non-dimensional RMS forces in the horizontal direction decrease and the non-dimensional RMS forces in the vertical direction increase.
Although podded propulsor technology has existed for nearly two decades, there has been little research into the use of these propulsors for ice management. Full-scale ice management trials with azimuthing thrusters revealed that it was possible to break and clear ice with the propulsors' wake and that precise ice management could be achieved with the wake of this propulsion system. This means dynamic placement ofpropeller wake wash can facilitate ice breaking and ice management operations. This paper presents preliminary outcome of a research program to evaluate the potentials ofpodded propulsors as an ice management device.
The kinematics i.e. the turbulence and velocity distribution in the propeller wake wash determines the capacity of the propulsor to break, push and clear the ice. In this research, efforts are made to model the propeller wash and data were predicted to quantify the capacity of a podded propulsor to clear ice under a range of operating conditions. A Reynolds-Averaged Navier-Stokes solver is used to predict the propulsive performance of a generic podded propulsor system in various operating conditions and configurations. The effects ofpropeller shaft speed and pod configuration are evaluated. The predicted propeller thrust and torque as well as the loads on the pod are compared with corresponding data acquired in a complimentary experimental program. The simulations and measurements are carried out for both puller and pusher configurations at or near bollard pull condition and in uniform inflow condition. Analysis demonstrates that the RANS solver can accurately predict the performance coefficients of the podded propulsor in straight-ahead condition in both puller and pusher configurations. The kinematics of the propeller wash at multiple downstream locations are studied only to reveal that the pusher propulsor may be more effective in clearing ice than the puller one because of less interaction between the propeller and the strut. The current work aims to provide insight into the effect of propeller shaft speed and pod configurations on the quality of the propeller wake that can be used for ice management.