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In rotating machinery, aerodynamic forces and oil film forces often lead to cross-coupling stiffness. This paper is aimed at studying the stick-slip whirling vibrations induced by the piecewise smooth rotor/stator frictions in a modified flexible rotor subjected to cross-coupling stiffness. Governing equations determining the sliding region and boundaries of piecewise discontinuous friction are defined. This analytical study was conducted to discuss the complex vibrations and bifurcations. Various types of sliding motions (continuous pure rolling, continuous crossing, and grazing–sliding) were observed in this research. Further, as for discussing the impacts of the parameters on nonlinear sliding vibrations, a parametric study was conducted. The obtained results reveal that with an increase in the cross-coupling stiffness coefficient, continuous pure rolling occurs earlier, and the disk vibration time around the contact regime becomes shorter. For studying the self-excited backward whirling vibration of stick–slip nonlinear motions, analytical formulations are established. Detailed vibration amplitude and frequency studies of friction-induced backward whirling vibrations were carried out. Numerical simulations were performed to compare them with the analytical solutions and to validate the results as well. The proposed theory and results provide fresh perspectives for predicting friction-induced whirlings and creating proper designs for turbo machinery.

Ultra-high performance concrete (UHPC) has been demonstrated to be a realistic alternative to less maintenance and significantly longer service life due to its better mechanical properties and low permeability. The bond performance of the deformed steel bar embedded in UHPC is critically important for the safety of the UHPC structures. This paper conducted an experimental investigation on the bond behavior of deformed steel bars and UHPC. The impacts of loading method, UHPC strength, steel fiber type and content, rebar diameter, and cover thickness were studied. The testing results revealed that the specimens failed in three modes: pull-out, splitting + pull-out, and cone failure. The main factors affecting the bond strength are UHPC compressive strength, cover thickness, and fiber characteristics. The peak slip of rebar-UHPC increases with cover thickness and rebar diameter. Finally, an analytical model of the bond stress-slip relationship between the UHPC and deformed steel bar is obtained, which is in suitable agreement with the test results.

The design of a post-tensioned transfer plate is typically controlled by shear force—in particular, punching shear at the slab-column connection. To verify the accuracy of the separated model only for one floor currently used in the design of a post-tensioned transfer plate, results were compared to a complete model with multi-story building system for which two representative residential building plans were used to emulate physical structural systems. Punching shear stress for the separated model was calculated using the eccentric shear stress model presented in ACI 318. Punching shear stress was found to be overestimated in the separated model, given that interaction between transfer plates and upper shear walls cannot be reflected therein. Differences at column locations were also noted as the number of stories below the transfer floor increased. Consequently, the separated model is not recommended for design of post-tensioned transfer plates. A complete model is more suitable for more realistic and potential cost-effective design, through the inclusion of the interaction between transfer plates and upper shear walls.

A fixed dual cylindrical oscillating water column (OWC) acting as a breakwater-type wave energy converter (WEC) is proposed to harvest the wave energy effectively for shallow offshore sites. An analytical model is developed to investigate the hydrodynamic characteristics and the energy capture capacity of the cylindrical OWC device in severe waves. Based on the linear potential flow theory, the analytical solutions of the velocity potential in diffraction mode are solved by matching the Eigen-function expansion technique, and the continuous conditions of the velocity potential and fluid velocity between the computational sub-domains are involved in solving the problem for determining a solution. The proposed model is verified against the published data. The effects of the wave height, the angle of chamber clapboard and the radius of the inner and outer cylindrical column on the energy conversion efficiency are investigated in this paper. To improve the energy conversion performance and obtain a faster prediction for structural optimization of the cylindrical OWC, the geometrical parameters are further discussed in the analytical model. The results indicate that the geometrical parameters of the chamber have significant effects on the wave energy absorption efficiency. It is found that the effective frequency bandwidth of the dual cylindrical column can be broadened by improving the angle of the chamber clapboard and the inner−outer cylinder diameter ratio.

An analytical model is developed based on linear potential flow theory and matching eigenfunction expansion technique to investigate the hydrodynamics of a two-dimensional floating structure. This structure is an integration system consisting of a breakwater and an oscillating buoy wave energy converter (WEC). It is constrained to heave motion, and linear power take-off (PTO) damping is used to calculate the absorbed power. The proposed model is verified against the published results. The proposed integrated structure is compared with the fixed structure and free heave-motion structure, respectively. The hydrodynamic properties of the integrated structure with the optimal PTO damping i.e., the transmission coefficient, reflection coefficient, capture width ratio (CWR), and heave response amplitude operator (RAO), are investigated. The effect of the PTO damping on the performance of the integrated system is also evaluated. Results indicate that with the proper adjustment of the PTO damping, the proposed integrated system can produce power efficiently. Meanwhile, the function of coastal protection can be compared with that of the fixed structure.