In this paper we evaluate the drag of periodic rough microstructures from near-wall models. With near-wall models we denote Coutte flows which describe the viscous boundary layer of turbulent flows. The structures inside this layer are not the optimal ones but can be used for a deeper understanding of the drag reducing mechanism of riblets due to a valid mathematical theory for viscous flows. Here, the numerical calculations can be validated and the developed calculation strategies can later be extended to the turbulent boundary layer. The focus of this paper is the evaluation of the drag of several microstructures for a better understanding of their action to the turbulent overflow. The influence of the structures will be visible trough a shift in the mean velocity profile which will be quantified. Due to the fixed calculation domain and thus an altered sublayer thickness, the obtained drag values can not be easily compared. We will as well present a theory for the comparison of the drag of rough surfaces calculated from our near-wall models as one for the comparison of rough versus smooth surface.

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This paper quantitatively evaluated the fatigue life of concrete around the air-water boundary layer of bridge piers located in inland rivers, considering the long-term climate. The paper suggests a method to predict the low-cycle fatigue life by demonstrating a thermal-fluid-structural analysis of bridge pier concrete according to long-term climate such as temperature, velocity and pressure of air and water in the process of freezing and thawing in winter. In addition, it proposes a reinforcing method to increase the life of damaged piers and proves the feasibility of the proposed method with numerical comparison experiment.

This article quantitatively evaluated the influence of three-dimensional multi-layer welding on the welding residual stress of super-big diameter welded hollow sphere joint in the large-span spatial steel structure considering the influence of material state change using finite element method. First, this article proposed a conception of equivalent state change time—the virtual time of state change in the analysis of welding and cooling—which represents the heat absorbed or released during the change of solid and fluid states in welding material. The equivalent state change time increases the accuracy of the thermal analysis considering the latent heat of fusion in welding and cooling process. Second, this article simulated the numerical experiments of three welding methods including multi-layer symmetric welding, multi-layer sequential welding, and single-layer symmetric welding, which show that multi-layer symmetric welding not only increases the balance of supporting ability of structure but also decreases the value of maximum tensile residual stress, and it is better than the other two welding methods.