Stray current-induced corrosion in cathodic protection installations of steel-reinforced concrete structures: FEM study of the critical parameters

A wide range of parameters was investigated by numerical calculations concerning their impact on DC stray current corrosion of reinforced concrete (RC) structures. A simplified model geometry was used to extract the relevant parameters and their interaction in terms of stray current-affected structures. This study mainly focuses on RC structures that are fitted with cathodic protection installations. The findings reveal a complex interaction between the investigated parameters. The possible relevance of further parameters, which is not the subject of this study, was emphasised.     

Up-pulling force analysis for ESC hollow cylindrical casting

Electroslag casting(ESC)is an important method to produce high quality castings.In this study,the ESC up-pulling inner mold method(EUPIM)was used to produce hollow cylindrical castings with the multiple consumable electrodes.The radial deformation,the axial and radial internal stress of the inner mold,and the axial internal stress of the slag shell were analyzed using the finite element method(FEM)with the aid of ANSYS software.The ProCAST software was used to calculate the specific heat,heat conductivity and density curve of Cu.Simulation results show that the radial deformation,the axial and radial internal stress of the inner mold,and the axial internal stress of the slag shell near the slag-metal interface of hollow cylndrical casting gradually increase from 0 s to 360 s after the ESC starting(slagging)process but before applying the up-pulling force.The suitable initial up-pulling moment of the inner mold is at around 180-198 s after the starting process.     

Performance analysis of hybrid/single nanofluids on augmentation of heat transport in lid-driven undulated cavity

This numerical study reveals the heat transfer performance of hybrid/single nanofluids inside a lid-driven sinusoidal trapezoidal-shaped enclosure. The right and left inclined surfaces of the trapezium have been considered as insulated, whereas the bottom sinusoidal wavy and the flat top surfaces of the enclosure as hot and cold, respectively. The governing partial differential equations of fluid's velocity and temperature have been resolved by applying the finite element method. The implications of Prandtl number (4.2-6.2), Richardson number (0.1-10.0), undulation number (0-3), nanoparticles volume fraction (0%-3%), and nanofluid/base fluid (water, water–copper (Cu), water–Cu–carbon nanotube, water–Cu–copper oxide (CuO), water–Cu–TiO₂, and water–Cu–Al₂O₃) on the velocity and temperature profiles have been studied. Simulated findings have been represented by means of streamlines, isothermal lines, and average Nusselt number of above-mentioned hybrid nanofluids for varying the governing parameters. The comparison of heat transfer rates using hybrid nanofluids and pure water has been also shown. The heat transfer rate is increased about 15% for varying Richardson number from 0.1 to 10.0. Blending of two nanoparticles suspension in base fluid has a higher heat transfer rate—approximately 5% than a mononanoparticle. Moreover, a higher average Nusselt number is obtained by 14.7% using the wavy surface than the flat surface of the enclosure. Thus, this study showed that applying hybrid nanofluid may be beneficial to obtain expected thermal performance.     

A novel multiscale approach to brittle fracture of nano/micro‐sized components

Principles and advantages of a new concept based on the ab initio aided strain gradient elasticity theory are shown in comparison with the classical Barenblatt cohesive model. The method is applied to the theoretical prediction of the critical energy release rate and the crack tip opening displacement at the crack instability in nanopanels made of germanium and molybdenum crystals. The necessary length scale parameter l₁ is determined for germanium and molybdenum by the best gradient elasticity fits of ab initio computed screw dislocation displacements and phonon dispersions. Values of ab initio computed critical energy release rates and crack opening profiles revealed that the length l₁ is related to inflexion points of profiles. A novel ab initio method in combination with continuum mechanics was successfully tested to replace molecular statics dependent of availability of interatomic potentials. The asymptotic strain gradient elasticity solution for displacement components near the crack tip in materials with cubic lattice was also derived.     

扫描隧道显微镜钨针尖的制备与表征

采用直流电化学刻蚀方法制备扫描隧道显微镜钨针尖,研究了电化学刻蚀过程中NaOH溶液浓度、钨丝浸入长度和刻蚀电压对针尖形貌的影响。通过扫描电子显微镜(SEM)测量针尖曲率半径和针尖纵横比值,以表征针尖的尺寸和形状;通过能谱仪(EDS)分析针尖表面成分,以表征表面清洁度;通过场发射显微镜(FEM)得到Fowler-Nordheim (F-N)曲线来检测针尖发射性能。实验结果表明,当溶液浓度为2 mol/L、钨丝浸入长度为4 mm、刻蚀电压为3 V时,可以得到曲率半径约为100 nm、纵横比值为13的针尖,且表面无钨的氧化层。FEM结果显示当对针尖施加500 V的负偏压时,针尖可以稳定发射50 nA量级的电流,且针尖性能具有良好的一致性。     

Comparative study of granular solid-structure interaction in a uni-axial compression system

Interaction between granular solids and confining structures is an elementary problem encountered in subsurface structural design and bulk solids storing and handling. A classic scenario is uni-axial compression of granular solids in a deformable cylindrical container. Despite being apparently simple in loading condition, the understanding of this scenario remains limited, mainly due to complex interactive deformation between the two components via frictional interfaces. This paper comparatively examines such a uni-axial compression particulate system by a laboratory experiment and two different numerical approaches, namely, continuum finite element method (FEM) and linked discrete-finite element method (linked DEM-FEM). In the continuum FEM approach, two intendedly chosen simple material models, linear elastic and porous elastic models, are attempted. The comparative study reveals that the majority of resultant characteristics show satisfactory agreement amongst the numerical predictions and the experimental measurements. The simple elastic continuum FEM models can hence be a useful alternative in modelling such problems with mild structural flexibility under a monotonic loading scenario. However, precise prediction of some characteristics, such as lateral pressure ratio, may demand more elaborated material model or parameter selection. The enhancements needed for each numerical approach in order to achieve an improved result are further discussed.     

Potential of plasmonic microreactor for Photothermal hydrogen-enriched fuel production from biomethane

In the present article, a series of coupled computational physics - fluid dynamics models were developed aiming at assessing the feasibility of photothermal synthetic fuel production from biogas (biomethane) and steam blends using plasmonic nanostructure Ag/TiO₂ substrate (each, 0.1 μm in thickness) inside a thermal, momentum and mass transport boundary layer in a microreactor. A chain of partial and complete biogas reforming and water-gas shift reactions were modelled as the dominant chemical reactions responsible for synthetic fuel production from biomethane. Using equilibrium analysis, plausible thermodynamic operating conditions were identified and applied to the computational models. The effect of light wavelength (λ) on the reaction rate, chemical conversion extent, syngas quality, exergy partitioned in synthetic fuel, and composition of gas products were investigated. The results showed that the performance of the microreactor is wavelength-dependent. It was found that the highest production rate for the synthetic fuel was achieved at 580 nm < λ < 620 nm. Within the same wavelength range, the chemical conversion of biomethane to synthetic fuel reached 85% at steam to methane ratio of 3 and the synthetic fuel quality was >2.05, which is suitable for a Fischer-Tropsch process. It was also identified that the syngas quality of the synthetic fuel can be regulated by adjusting the wavelength of the light. The exposure time was also identified to be a critical parameter affecting the performance of the microreactor. For an exposure duration of up to 10 ns, high quality of synthetic fuel >2.05 can be achieved within the optimum wavelength range of 580 nm < λ < 620 nm.     

低热水泥混凝土在特高拱坝中应用的可行性分析

针对低热水泥混凝土早期强度低,在大坝主体中应用较少,低热水泥混凝土能否应用于高拱坝工程仍存疑虑的情况,以白鹤滩工程为例,采用室内试验资料对比和有限元仿真结果对比相结合的方法,对白鹤滩拱坝拟采用的中热水泥混凝土和低热水泥混凝土的材料特性和温度应力仿真结果进行了对比分析。结果表明,从材料特性的角度来看,低热水泥与中热水泥混凝土各有优劣,低热水泥混凝土早龄期强度低不利于防裂,但低热水泥的绝热温升低、早期发热慢、弹模小、徐变大这些因素均有利降低整体应力水平,后期强度高则有利于提高后期安全系数,降低开裂风险。此外,有限元计算结果表明,在相同的温控措施和边界条件下,低热水泥混凝土最高温度比中热水泥混凝土低2～3℃,低热水泥混凝土冷却全过程的安全系数均要大于中热水泥混凝土,且在2. 0以上。研究成果进一步证实了低热水泥混凝土比中热水泥混凝土具有更好的抗裂特性,可以应用于特高拱坝,也为白鹤滩拱坝全坝采用低热水泥混凝土提供了重要支撑。