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Accurate simulation of the continuous icebreaking process in level ice is crucial for the design of icebreakers. The crushing and bending failures of ice sheet, as well as the rotating, sliding and accumulating of ice cusps broken from the ice sheet constitute a complex system for the icebreaking process. In this paper, cohesive element method is combined with an elastoplastic softening constitutive model to simulate continuous icebreaking process in level ice. Firstly, the elastoplastic softening constitutive model in modelling ice local crushing is calibrated by simulating the ice cone crushing tests. Three different softening laws are proposed and their effects on simulation results are evaluated by comparing with the experimental data. Then, the continuous icebreaking process in level ice is simulated by cohesive element method. The regular tri-prism mesh is applied to ice bulk elements to realize the random propagation of crack. The mesh dependency study is carried out, and the simulation results are validated by comparing with model test results in both of time domain and frequency domain. The ice failure patterns during continuous icebreaking process are also compared between the simulated and experimental results. Finally, the influences of ship velocity on ice resistance and ice failure patterns are investigated by numerical methods and semi-empirical formulas.

In ice-infested waters, propellers of a polar ship are likely to be exposed to ice loads in different scenarios. Propeller milling with ice is one of the most dangerous cases for ice-propeller interaction. In this study, we try to simulate dynamic milling process of ice-propeller and reproduce resulting physical phenomena. Cohesive element method is used to model ice in the simulation. To simulate material properties of ice, an elastoplastic softening constitutive law is developed. Both crushing and fracture failures are included in the ice-propeller milling process. The ice loads in 6 Dofs acting on blades of a propeller are calculated in time domain. The average and standard deviations of simulated dominant ice loads are compared with those from model test. A good agreement is achieved. By varying propeller rotation speed, advance velocity and cutting depth on ice block, the sensitivity study has been carried out. The results show that dominant ice loads are affected much by the three parameters. It is shown that decreasing rotation speed, or increasing advance velocity and cutting depth may lead to higher ice loads. Care should be taken to avoid over-loading on propeller when operating in ice for polar ship.

The microbiological spoilage of stored grain is important for human health and economic loss. Two major predominant grain spoilage fungi (M15 and M16) were isolated from maize from a granary in China. Morphological observation of the fungal isolates, analysis of their ITS sequences and construction of their phylogenetic trees were conducted on these two strains, which were identified as Fusarium solani (M15) and Aspergillus sclerotiorum (M16). This method was shown to be a feasible, accurate and convenient way to identify fungi in stored grain.

Under torsion and beyond the buckling point, multi-walled carbon nanotubes (MWCNTs) develop a periodic wave-like rippling morphology. Here, we show that torsional rippling deformations can be accurately described by a simple sinusoidal shape function. Combining this observation with the geometry optimization, we develop an effective coarse-grained model that reproduces the complex nonlinear mechanical responses of thick MWCNTs under torsion predicted by large-scale atomistic simulations. Furthermore, the model allows us to simulate super-thick tubes, inaccessible by other coarse-grained methods. With this effective coarse-grained model, we show from an energetic analysis that the rippling deformation is a result of in-plane strain energy relaxation, penalized by the increase in the interlayer van der Waals interaction energy. Our simulations reveal that the torsional response of MWCNTs with up to 100 layers approximately follows a simple bilinear law, and the ratio of the torsional rigidities in the pre- and post-buckling regimes is nearly a constant, independent of the tube radius. In contrast, the bifurcation torsional strain powerly scales with the tube radius. We also find that the wave number in the circumferential direction linearly increases with tube radius, while the wavelength monotonically increases with tube radius, and approaches a constant in the limit of bulk graphite. The bilinear constitutive relation, together with the scaling law of the bifurcation torsional strain, furnishes a simple nonlinear beam theory, which facilitates the analysis of MWCNT bundles and networks., Peer Reviewed, Postprint (published version)