Numerical computations of resistance of high speed catamaran in calm water

In this paper, the in-house multifunction solver naoe-FOAM-SJTU is applied to study the resistance and wave-making performance of a high-speed catamaran sailing at different velocity in calm water. The volume of fluid（VOF） method is used to capture the free interface and the finite volume method（FVM） is adopted as the discretization scheme. The hull model is fixed with initial trim and sinkage. The numerical results of the presented paper agree very well with the measurement data of model test. Wave making and vortex field are well simulated to analyze the hydrodynamic performance of a catamaran.     

TEM study of nanopores and the embrittlement of CVD nickel foam

Abstract

Ni foam, manufactured by depositing Ni onto polyurethane foam using the carbonyl CVD process, exhibits brittleness which has been correlated with the presence of a high number-density of 'nanopores'. These nanopores, which were typically less than ~25 nm in diameter, tended to be associated with sulphur, which is present in the form of H₂S as a catalyst during the deposition process. The as deposited foam also shows significant hardening, ascribed to the high density of nanopores. This hardening may also help to reduce the ductility compared to well annealed nickel foam. High temperature annealing restores the foam to the high ductility typical of high purity nickel by coarsening the nanopores and removing the sulphur. The failure of the pores to sinter during high temperature annealing indicates the presence of stable gas molecules, the pressure from which balances the surface tension forces that drive sintering.     

Behaviour of surface oxide scale before roll bite in hot rolling of steel

Abstract

Hot stalling rolling tests using mild steel slabs with thin and thick scale layers, and cold stalling rolling simulation tests using lead slabs coated with brittle lacquer layers, have been conducted to investigate the behaviour of the surface oxide scales before hot rolling. The effects of rolling reduction, temperature, scale thickness and structure, and slab geometry were examined. The experimental results indicate that the oxide scale can either adhere and deform with the parent steel, or delaminate from the parent steel, or suffer from cracking before hot rolling, depending on the hot strength of the scale and the stress status in the scale, which depend on rolling reduction and temperature, and scale thickness and structure. Therefore, the cracks observed in the oxide scales on the steel slab after hot rolling are generally the combined results of cracking before rolling and further cracking in the roll gap. On the basis of comparative analysis, the prerolling behaviour of the oxide scales in a laboratory scale rolling mill and in an industrial hot strip mill is discussed.     

Compressive behaviour of open cell Al–Al2O3 composite foams fabricated by sintering and dissolution process

Abstract

The sintering and dissolution process (SDP) was used to produce the fine open cell Al–Al₂O₃ composite and pure Al foams with the relative density of 0·25–0·40 and the pore size of 112–400 μm. The composite foam exhibited much higher yield strength and Young's modulus than the pure Al foam, and thus had an elevated plateau stress. Moreover, the composite foam showed a unique dependence of the compression stress on the pore size, i.e. it increased with increasing pore size, which was quite different from that for the common metal foams.     

湍流氢氧预混燃烧流场的二维数值模拟

基于Cantera化学动力反应模型库,采用工程计算开源软件OpenFOAM建立应用半隐式压力校正方程SIMPLE算法求解定常可压缩湍流燃烧流动问题的数值模拟方法,设计出适合于稳态求解的可压缩燃烧反应的求解程序,并对燃烧室内的氢氧燃烧过程进行二维数值模拟。通过计算结果与试验数据的直观对比分析表明:所建立的数值计算方法对定常可压缩燃烧流动问题有很好的计算仿真效果,体现了其可行性与正确性,同时对解决其他燃烧流动问题也具有较高的参考价值。     

Functionalisation of polypropylene by solid phase graft polymerisation and its effect on the mechanical properties of silica nanocomposites

Abstract

To prepare macromolecular compatibiliser for grafted nano-SiO₂/polypropylene (PP) composites, solid phase graft copolymers of PP with styrene and ethyl acrylate were synthesised, respectively. It was found that both percentage grafting and grafting efficiency can be adjusted by changing initiator concentration, reaction temperature and reaction time. Due to partial chain scission and deterioration of the ordered structure of PP during the graft polymerisation, the grafted PP exhibits worse thermal stability and crystallisability than the unmodified PP. Mechanical tests of grafted nano-SiO₂/PP composites indicated that the addition of PP copolymer with the same species of grafting polymer as that on the nanoparticles further improves the ductility of the composites. Molecular rigidity of the grafting polymers, presence of the homopolymer produced during the graft polymerisation, and strain rate of the load applied have important influences on the toughening effect of the functionalised PP.     

A semi-implicit immersed boundary method and its application to viscous mixing

Computational fluid dynamics (CFD) simulations in the context of single-phase mixing remain challenging notably due the presence of a complex rotating geometry within the domain. In this work, we develop a parallel semi-implicit immersed boundary method based on Open∇FOAM, which is applicable to unstructured meshes. This method is first verified on academic test cases before it is applied to single phase mixing. It is then applied to baffled and unbaffled stirred tanks equipped with a pitched blade impeller. The results obtained are compared to experimental data and those predicted with the single rotating frame and sliding mesh techniques. The proposed method is found to be of comparable accuracy in predicting the flow patterns and the torque values while being straightforwardly applicable to complex systems with multiples impellers for which the swept volumes overlap.     

聚酰亚胺泡沫材料吸声性能对比研究

通过阻抗管法研究了聚酰亚胺(PI)、三聚氰胺(MFF)和聚氨酯(PU)3种泡沫材料对声音的吸收特性。结果表明:与MFF和PU泡沫材料相比,PI泡沫材料具有优异的吸声降噪性能;随着材料密度的增大,3种泡沫的吸声降噪性能都有相应提高。     

Damping properties of open cell microcellular pure Al foams

Abstract

Damping behaviours of the open cell microcellular pure Al foams fabricated by sintering and dissolution process with the relative density of 0·31–0·42 and the pore size of 112–325 μm were investigated. The damping characterisation was conducted on a multifunction internal friction apparatus. The internal friction (IF) was measured at frequencies of 1·0, 3·0 and 6·0 Hz over the temperature range of 298–725 K. The measured IF shows that the open cell pure Al foam has a damping capacity that is enhanced in comparison with pure Al. At a lower temperature (～400 K), the IF of the open cell pure Al foams increases with decreasing relative density, with decreasing pore size and with increasing frequency. The IF peak was found at the temperature range of 433–593 K in the IF curves. It is clear that the IF peak is relaxational type and the activation energy associated with the IF peak is about 1·60 ± 0·02 eV. Defect effects can be used to interpret the damping mechanisms.     

Effects of process conditions on mixing between molten iron and slag in smelting reduction vessel via water model study

Abstract

The present study has been conducted to investigate the effects of operating conditions, which include gas flowrate, tuyere size, tuyere number, and height of iron phase, on the extent of mixing between molten iron and molten slag in the direct iron ore smelting reduction process. A transparent acrylic water model, 30% of the size of the actual smelter, was constructed to study the mass transfer phenomena. In the water model, water and spindle oil were used to simulate molten iron and molten slag, respectively, while air was used to replace the bottom blown nitrogen gas. In addition, thymol (C₁₀H₁₄O₆) was used as a tracer material in the water model, added to the water at the beginning of the experiment. As mixing between water and spindle oil proceeded owing to stirring by the bottom blown gas, the concentration of thymol in the water decreased and that in the spindle oil increased. Water samples were taken from the bottom and 12 cm above the bottom of the water model at various operating times. Concentrations of thymol were then measured using a diode array ultraviolet visible spectrophotometer. By analysing the concentration data, the mass transfer rate k_wA, which is a direct index for evaluating the mixing efficiency, could be derived. The process conditions under investigation included 40-500 L min^-1 gas flowrate, 0·3^-1 cm tuyere size, four or five tuyeres, and 20-30 cm height of the water phase. The test results indicate that when the gas flowrate increases, the value of k_wA increases, which indicates better mixing between oil and water phases. However, as the gas flowrate approaches 40 L min^-1, the improvement becomes less obvious. The smaller tuyere gives better mixing, and the design of five tuyeres results in better mixing compared with four tuyeres when they are blown with the same total gas flowrate. However, mixing efficiency decreases with increased height of the water phase. Also, as the gas flowrate of bottom blowing approaches 40 L min^-1, gas blowing from the top has little effect on the mixing behaviour in the liquid bath. For a four tuyere system, the process conditions of height of oil phase 5 cm, height of water phase 25 cm, diameter of tuyere 0·75 cm, and gas flowrate for each tuyere 40 L min^-1, appear to be the optimal design.