Browsing by Author "Gong, Hanyang"

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3D DEM study on the effect of ridge keel width on rubble resistance on ships
(2018-06-17) Gong, Hanyang; Polojärvi, Arttu; Tuhkuri, Jukka
A4 Artikkeli konferenssijulkaisussa
In this paper, we use 3D discrete element method (DEM) to simulate ship penetration through a non-cohesive rubble pile presenting a ridge keel. We study the effect of the pile width on the rubble resistance and the relation between the resistance records and rubble deformation. The peak rubble resistance increases with the rubble pile width, but the rate of the increase is not constant. The peak rubble resistance values from the simulations with the widest rubble piles are compared to the ones yielded by the analytical models with success.
Comparison of Full-scale and DEM simulation Data on Ice Loads Due to Floe Fields on a Ship Hull
(2021) Polojärvi, Arttu; Tuhkuri, Jukka; Gong, Hanyang
A4 Artikkeli konferenssijulkaisussa
Ship passage through an ice floe field was simulated with 3D discrete element method (DEM). In the simulations, the ship traveled through a 2 km long ice floe field with constant velocity, while the local ice loads, due to the ship contacting with the ice floes, were gauged. Ice floes were simplified in their shape, they were rigid and not allowed to fracture. The ice floe field properties, such as ice floe thickness, average floe size and ice coverage, were varied. The simulated local ice loads were compared to those measured in full-scale.
Discrete Element Simulation of the Resistance of a Ship in Unconsolidated Ridges
(2019-11-01) Gong, Hanyang; Polojärvi, Arttu; Tuhkuri, Jukka
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Resistance on a ship penetrating a sea ice ridge is a key design parameter of ice breaking ships. The resistance of a ship in an unconsolidated ridge has been studied by using a three dimensional discrete element method. Ridges of equal thickness but different widths were used and it was observed that the ridge width has a major effect on the ridge resistance: The ridge resistance is increasing with increasing ridge width, until the ridge width is of the same order as the ship length. The ridge resistance was decomposed into a frictional force and a deformation force. The deformation force is due to the ridge deformation by the ship bow and it was shown that the deformation force is related with the mass of ice blocks accelerated by and moving with the ship.
Discrete-element modelling of ship interaction with unconsolidated ice ridges: ridge resistance and failure behaviour
(2021) Gong, Hanyang
School of Engineering | Doctoral dissertation (monograph)
Safe and efficient shipping in ice-covered waters requires the consideration of multiple sea ice features. Ice ridges can significantly increase the resistance of a ship; understanding this resistance requires knowing the failure mechanism of ice ridges. Traditionally, this failure mechanism has been studied using analogies to soil mechanics. This thesis provides a new approach to studying ice ridge resistance using a three-dimensional discrete element method to calculate the kinetic responses of an unconsolidated ice ridge interacting with a ship. The proposed approach is used to analyse the effect of ice ridge dimensions (width and depth) and ship hull form on ridge resistance and ridge failure behaviour. The analysis indicates that ridge width plays an essential role in ridge resistance—the peak resistance increases with ridge width until the width is of the same order as the ship's length. The analysis further indicates that, for wide ridges, peak ridge resistance increases exponentially with ridge depth following a power-law function with an exponent of 1.5. With regard to hull form, the analysis indicates that the peak ridge resistance and the work needed to penetrate a ridge increase linearly with any of the three main bow angles (waterline angle, stem angle and flare angle). This finding is obtained using a simplified wedge-shaped bow model, which has been shown to yield results similar to those using a realistic reference ship model. A ship-ice ridge interaction is a dynamic ridge failure process involving irreversible ridge deformation. The deformed domain is defined by ice blocks accelerated by and moving with the ship. The deformation force, as part of the ridge resistance, is found to relate to the mass of ice blocks in the deformed domain. The ice ridge failure behaviour at local scale is described by the kinetic responses of individual ice blocks within the deformed domain. The velocity field of the rubble shows that fast-moving ice blocks are in the near-bow field and stationary ice blocks at the far end of the ridge until the entire ridge fails to sustain the ship's penetration. No well-defined shear plane could be observed. Loads within the ice rubble are transmitted through force chains, which develop with the ship's penetration and form into an arch-like pattern normal to the bow. In addition, the ice ridge failure behaviour at large scale is analysed by the average stress and strain state of the ridge in the deformed domain. The ratio of horizontal to vertical normal stresses is less than half the value often used in previous analytical models based on Rankine theory and appears to be related to the ridge width.
Preliminary 3D DEM Simulations on Ridge Keel Resistance on Ships
(2017-06-11) Gong, Hanyang; Polojärvi, Arttu; Tuhkuri, Jukka
A4 Artikkeli konferenssijulkaisussa
Ice ridge resistance of ships operating on Arctic seas is of importance when estimating the ship traffic emissions and the efficiency of ship transport systems. Here we use 3D discrete element method (DEM) to simulate the interaction between a ridge keel and a ship. In this preliminary study, we will present results from simulations with various ridge keel lengths and accounting for the symmetry of the interaction scenario. We also study the effect of ridge keel widths on the keel resistance in our simulations.
A review of DEM-CFD numerical methods for estimating ship resistance in FSICR channel
(2024) Gong, Hanyang; Prasanna, Malith; Matala, Riikka
A4 Artikkeli konferenssijulkaisussa
Modern ice-going merchant ships have been customised for operating in ice and open water. The current model tests granting merchant ships Finnish-Swedish Ice Class may face challenges from the effect of hydrodynamics on the brash icebreaking process. Numerical simulations as alternatives for calculating ice resistance have shown their potential to assist model tests on ice performance prediction. This paper first reviews previous studies on numerical simulations of ships in a brash ice channel. Discrete element method (DEM) of modelling brash ice has become outstanding among other numerical methods, such as physics engine, finite element method and smoothed particle hydrodynamics. Coupling computational fluid mechanics (CFD) with DEM for ship-brash ice channel application have mainly been implemented in commercial software, but accessibility of the software is limited by the significant cost of license. This paper summaries key techniques of DEM, CFD and coupling methods related to the application in model scale and full scale based on open-source software platforms.
Velocity field and force distribution in an unconsolidated ice ridge penetrated by a ship
(2023) Gong, Hanyang; Polojärvi, Arttu; Tuhkuri, Jukka
A4 Artikkeli konferenssijulkaisussa
Estimating ship resistance in ice ridges requires an understanding of ridge failure processes. A three-dimensional discrete element method is used to study a ship passing through a small unconsolidated ridge with a triangular cross-section and the resulting velocity field and force distribution inside the ridge. The kinetic behavior of ice blocks within the ridge suggests a gradual failure process, not a sudden failure. The velocity field shows fast-moving ice blocks near the ship bow, and stationary or slow-moving blocks further away. Loads within the ridge were transmitted through force chains. No unique shear planes were observed.