Bridge resistance and reliability may deteriorate with time due to aggressive environmental conditions and increasing road freight volumes, resulting in an increase of potential economic loss. This is thus a great concern to decision-makers managing the bridges’ continued future service. Reasonable models of bridge resistance and applied loads are the fundamentals of accurate estimation/prediction of a bridge’s serviceability. In this paper, a new model for resistance deterioration is proposed, which enables the non-increasing property and auto-correlation in the stochastic deterioration process to be incorporated. To facilitate the practical application of the model, methods to determine its parameters using obtained data on structural resistance are developed and illustrated through simple numerical examples. Time-dependent reliability analysis is conducted using the proposed resistance deterioration model based on Monte Carlo simulation, and the effect of auto-correlation in the deterioration process on structural time-dependent reliability is investigated.

A good understanding of the mechanical behavior of functionally graded material (FGM) cylindrical shells is necessary for designers and researchers. However, the 3D transient response of FGM cylindrical shells under various boundary conditions has not yet been analyzed. In this paper, the problem is addressed by proposing an approach integrating the state space method, differential quadrature method, and Durbin’s numerical inversion method of Laplace transform. The laminate model is used to obtain the transient solution in the radial direction. At the edges, four kinds of boundary conditions are considered: Clamped-Clamped, Clamped-Simply supported, Clamped-Free, and Simply supported-Simply supported. The results of the proposed method and finite element (FE) method agree with each other excellently. Convergence studies show that the proposed method has a fast convergence rate. The natural frequencies obtained by the proposed method, experiment, and other theoretical methods are in close agreement with each other. The effects of the load frequency and duration, length/outer radius ratio, and the (outer radius−inner radius)/outer radius ratio on the transient response of FGM shells are investigated. Two laws of variation of material properties along the radial direction are considered: the first has material properties varying according to an exponential law along the radial direction, while the second has material properties varying according to a power law. The effect of a functionally graded index on the transient response of FGM shells is investigated in both cases. The results obtained in this paper can serve as benchmark data for further research.

To quantitatively assess the residual strength of wood members after rot and infestation using non-destructive testing (NDT), the multi-point Resistograph method was applied to test six used wood beams with initial imperfections. Each wood beam was then divided into a shorter segment for mechanical tests and a longer one for bending capacity tests. With the help of finite element analysis using ANSYS, bending capacity is predicted by taking account of the initial imperfections. Results show that there is a significant correlation between drill resistance values and strengths for small specimens. Therefore, the strengths of wood at other measurement points may be obtained through drill resistance values. The beams showed a near linear behaviour up to the maximum load with poor ductility performance in bending capacity tests. It can also be found that the effects of initial imperfections on failure modes and ultimate loads are significant. The lateral side of specimen BA1 has serious infestation and the bottom of BA2 has a long longitudinal crack, the ultimate bearing capacities of these specimens are respectively only 67.6% and 64.8% of BA3, which has fewer cracks. BB1 and BB3 have knots at the bottom and their ultimate bearing capacities are respectively 83.9% and 81.0% of BB2, which has fewer cracks as well. Furthermore, there is quite good agreement between test results and numerical prediction using strength values obtained by NDT results. Therefore, the bending capacity of used wood beams can be obtained using NDT, which can provide the basis for the protection and retrofitting of wood structures.

Drag reduction and thermal protection is very important for hypersonic vehicles, and a counterflowing jet and its combinations is one of the most promising drag and heat release reduction strategies. In the current survey, research progress on the drag and heat release reduction induced by a counterflowing jet and its combinations is summarized. Three combinatorial configurations are considered, namely the combination of the counterflowing jet and a forward-facing cavity, the combination of the counterflowing jet and an aerospike, and the combination of the counterflowing jet and energy deposition. In conclusion, some recommendations are provided, especially for jet instability protection, for the tradeoff between drag and heat release reductions, and for the critical points for the operational and geometric parameters in the flow mode transition.

Accurate and reliable short-term prediction of ship motions offers improvements in both safety and control quality in ship motion sensitive maritime operations. Inspired by the satisfactory nonlinear learning capability of a support vector regression (SVR) model and the strong non-stationary processing ability of empirical mode decomposition (EMD), this paper develops a hybrid autoregressive (AR)-EMD-SVR model for the short-term forecast of nonlinear and non-stationary ship motion. The proposed hybrid model is designed by coupling the SVR model with an AR-EMD technique, which employs an AR model in ends extension. In addition to the AR-EMD-SVR model, the linear AR model, non-linear SVR model, and hybrid EMD-AR model are also studied for comparison by using ship motion time series obtained from model testing in a towing tank. Prediction results suggest that the non-stationary difficulty in the SVR model is overcome by using the AR-EMD technique, and better predictions are obtained by the proposed AR-EMD-SVR model than other models.

The operating characteristics are important for design and optimization of pulse tube cryocoolers, in particular for those with high cooling power, which up to now have been seldom extensively investigated. In this study, the dependence of cooling performance on the charge pressure and operating frequency has been investigated, both numerically and experimentally. A numerical model based on Sage software was established. Experiments were performed on a home-made single-stage high power Stirling-type pulse tube cryocooler (SPTC) working at liquid nitrogen temperatures. The results revealed that each charge pressure corresponds to an optimum frequency with respect to compressor and regenerator efficiency. A lower charge pressure results in a higher cryocooler efficiency, but the delivered maximum pV power is significantly reduced due to the stroke limit of the pistons in the linear compressor. The influence of operating characteristics on the temperature non-uniformity in the regenerator was also investigated. By optimizing the charge pressure and frequency, the minimum no-load temperature was decreased to 46.9 K at 56.5 Hz and 2.0 MPa. A cooling power of 300 W at 71.8 K was measured with an electrical input power of 8.9 kW.

Wind tunnel experiments at a model scale have been carried out to investigate the flow characteristics in the near wake of a wind turbine. Time resolved particle image velocimetry (TRPIV) measurements are applied to visualize the wind turbine wake flow. The instantaneous vorticity, average velocities, turbulence kinetic energy, and Reynolds stresses in the near wake have been measured when the wind turbine is operated at tip speed ratios (TSRs) in the range of 3–5. It was found that wind turbine near the wake flow field can be divided into a velocity increased region, a velocity unchanged region, and a velocity deficit region in the radial direction, and the axial average velocities at different TSRs in the wake reach inflow velocity almost at the same radial location. The rotor wake turbulent kinetic energy appears in two peaks at approximately 0.3R and 0.9R regions in the radial direction. The Reynolds shear stress is less than the Reynolds normal stresses, the axial Reynolds normal stress is larger than the Reynolds shear stress and radial Reynolds normal stress in the blade root region, while the radial Reynolds normal stress is larger than the Reynolds shear stress and axial Reynolds normal stress in the blade tip region. The experimental data may also serve as a benchmark for validation of relevant computational fluid dynamics (CFD) models.

The original version of this article unfortunately contained some mistakes.