Hydraulic turbine generator sets are crucial for harnessing water energy. However, the nonlinear phenomena resulting from the combination of unbalanced magnetic pull (UMP) and oil film forces remain unclear. A mathematical model of the rotor-bearing system is introduced to investigate the effects of UMP and the nonlinear oil film force on system. The UMP and nonlinear oil film force are derived from the air-gap magnetic energy and short bearing theory, respectively. The proposed model is verified by the stability experiments of hydraulic turbine generator set in the idling, no-load, and load conditions. The results show that, firstly, the system turns unstable for oil whip and oil swirl, and which experiences bifurcation and undergoes dynamical motions such as period-1 to period-5, quasi-periodic, and chaotic motions. Then, at moderate speeds, the rotor eccentricity has the greatest effect on the bifurcation at idle. While the nonlinear characteristics of the system are most sensitive to the rotor eccentricity at loaded condition. Finally, the existence of UMP reduces the instability caused by oil film forces.

The cooling medium of the guide bearing heat exchanger in hydro generator sets comes from the upstream dam area, which contains numerous impurities even though it has undergone preliminary treatment. These impurities settle, accumulate, and adhere and form scaling layers in the heat exchanger, seriously affecting its heat transfer performance. This paper presents an innovative investigation of heat exchanger performance under impurity-laden cooling water conditions and proposes an optimization by replacing the conventional round tube structure with a spiral flat tube structure. Numerical simulations are conducted to analyze the flow velocity, pressure, impurity deposition, and temperature distribution of the cooler under actual operating conditions. The results show that the optimized cooler achieves improved velocity uniformity with a lower standard deviation, effectively reducing sediment accumulation. Compared to the prototype, the maximum pressure increases by 55.2% (from 0.562 MPa to 0.872 MPa), which enhances turbulence and improves heat transfer. The sediment volume fraction is significantly reduced by 49% in low-flow operating conditions and 73.7% in high-flow operating conditions. Furthermore, the maximum temperature drops by 5.43 °C, indicating improved thermal performance. These findings confirm the effectiveness of the spiral flat tube design in impurity-rich environments.

The heat exchanger in a hydropower unit plays a critical role in ensuring the stability of the unit and improving operational efficiency. This paper conducted a global flow-field/heat-transfer numerical analysis of multi-tube heat exchangers in hydropower units (with 98 tubes) and applied it to optimization research under actual operating conditions. Using a three-dimensional two-phase flow model, this work systematically analyzes the effects of different sand content and particle size on heat-transfer performance, revealing the impact of particle-flow and fluid-flow nonuniformity on heat-exchange efficiency. This research fills the gap in existing studies regarding the analysis of the impact of complex operating conditions on hydropower unit radiators. To address the issues of nonuniform flow fields and poor flow mixing in existing heat exchangers, an improved inlet/outlet structural-optimization plan is proposed. The original cylindrical inlet/outlet is replaced with a square structure, and its area is increased. The optimized structure improves flow uniformity, reduces flow losses, enhances heat-transfer performance by 7.7%, and achieves a significant reduction of 0.53 K in oil temperature. The findings of this study provide theoretical and engineering guidance for the design and optimization of heat exchangers in hydropower units and are of high value for practical applications.

Structural deformation control of constructed bridges not only affects the alignment of the bridge, it is also the key to ensure safety. Factors such as temperature and time interval in actual construction can make the bridge deviate from the design state, therefore, this paper proposes a method based on error analysis and correction to eliminate these errors, and realize the structural deformation control in bridge construction control. The cantilever deflection in main girder is modeled and the effect of subsequent cantilevers on deflection at current section is further considered. The error in elevation caused by factors such as temperature and time interval is calculated, and a linear minimum variance estimate is employed to reduce this error. Practical engineering verification is carried out on a bridge in Shanxi, where the proposed error analysis method is further implemented by measuring the current cantilever elevation and comparing it with the original design value, with a purpose of obtaining a reasonable elevation for the next cantilever. The results show that, with the application of error analysis and correction, the elevation error generated during construction process is less than 20 mm, and the elevation error after the completion of bridge is less than 30 mm, the linear shape and internal condition of the bridge structure can also be further conformed to design requirements.