Advances in Science and Technology Vol. 169

Abstract: In a nuclear power plant, the tubes array component that constitutes a cooling water heat exchanger is often subjected to cold and hot fluid flow impact, which are affected by axial stress due to thermal strain cause by these cold and hot flow impact. So, the dynamic characteristics of this tube would be changed significantly by this flow impact and even lead to failure. The axial load caused by thermal strain, the cold and hot flow impact, also markedly changes the dynamic characteristics of the tube.

Abstract: In this study, CFD simulations were conducted to investigate the optimal design parameters for the diffuser vane slit, which is one of the means to suppress diffuser rotating stall (DRS), in terms of slit width, height, and position, to maximize the DRS suppression effect while maintaining diffuser performance. The investigated pump is a centrifugal pump with a specific speed of Ns = 138 m³/min, m, rpm and the diffuser is an axial-flow type. The simple prediction method of DRS by CFD simulation used in the previous study was applied and evaluated in terms of the coefficient of variation C.V., static pressure recovery coefficient C_P, and total pressure loss coefficient C_T in the diffuser flow channel. As a result, it was found that the slit position was the best at 18% of the vane axial chord length regardless of the slit width, and that the slit height from the hub to the tip provided the best DRS suppression. A wider slit width increases the flow rate through the slit and enhances the DRS suppression effect, but it causes lower diffuser performance and results in a trade-off relationship. Therefore, the slit width should be set to an appropriate value depending on the required operating range.

Abstract: In this paper, the stress behaviors of the single lap joint having orthotropic inclusion in the adhesive layer under tensile load were analyzed. In these analyses, a more realistic approach was taken by considering the heterogeneous nature of the adhesive layer. In the study, there are three different orthotropic inclusion materials in the adhesive layers of the connections: glass-epoxy, graphite-epoxy and boron-epoxy. The effects of the selected inclusion material on the stresses in the connections were analyzed using the finite element method. When single lap connections are examined in terms of material, the stresses have the highest value for boron-epoxy inclusion and the lowest value for glass-epoxy inclusion Additionally, the effect of both the adherend material and the thickness of the inclusion material on the stresses was examined. According to this, in single lap connections, the highest peeling, shear and von-Mises stress values were observed on the adhesive layer when the t_o/t_i value was 0.5. The possibility of delamination near the inclusion area has been taken into account.

Abstract: This paper presents a comprehensive modal analysis of a 15-meter span footbridge constructed using fiber-reinforced polymer structures (FRPs) integrated with natural resource fibers and a partial bio-based resin. The bridge was erected at the Floriade Expo 2022 located in Almere, the Netherlands. The lightweight nature of FRPs, coupled with their sensitivity to vibrations, necessitates the satisfaction of specific design requirements to ensure the safety and comfort of pedestrians. The initial phase of this study entails determining the natural frequencies of the bridge via Finite Element Analysis (FEA). Comparative assessment between the footbridge's natural frequency and excitation frequencies evaluates the risk of resonance induced by pedestrian loading. The FEA employs a composite layup technique to replicate the same ply configuration as the actual bridge model. Following the initial assessment, a comprehensive analysis is undertaken to meticulously examine the dynamic response of the footbridge. This analysis prioritizes the evaluation of critical acceleration parameters under diverse conditions, encompassing scenarios such as walking, jogging, and crowded pedestrian traffic. Bridge peak acceleration is assessed and juxtaposed against design values based on site usage, route redundancy, and structural height, and for the target bridge is 0.77 m/s². The results indicate that the footbridge successfully fulfills the specified design criteria for ensuring pedestrian comfort under various dynamic loading conditions. This finding underscores the significance of including the footbridge in the building application process. This study underscores the successful application of FRPs, augmented with natural fibers and bio-based resin, in ensuring the structural integrity and comfort of footbridges subjected to real-world dynamic conditions.