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Hydrological risk analysis is essential and provides useful information for dam safety management and decision-making. This study presents the application of bivariate flood frequency analysis to risk analysis of dam overtopping for Geheyan Reservoir in China. The dependence between the flood peak and volume is modelled with the copula function. A Monte Carlo procedure is conducted to generate 100,000 random flood peak-volume pairs, which are subsequently transformed to corresponding design flood hydrographs (DFHs) by amplifying the selected annual maximum flood hydrographs (AMFHs). These synthetic DFHs are routed through the reservoir to obtain the frequency curve of maximum water level and assess the risk of dam overtopping. Sensitive analysis is performed to investigate the influence of different AMFH shapes and correlation coefficients of flood peak and volume on estimated overtopping risks. The results show that synthetic DFH with AMFH shape characterized by a delayed time to peak results in higher risk, and therefore highlight the importance of including a range of possible AMFH shapes in the dam risk analysis. It is also demonstrated that the overtopping risk is increased as the correlation coefficient of flood peak and volume increases and underestimated in the independence case (i.e. traditional univariate approach), while overestimated in the full dependence case. The bivariate statistical approach based on copulas can effectively capture the actual dependence between flood peak and volume, which should be preferred in the dam risk analysis practice. [ABSTRACT FROM AUTHOR]

To determine the effect of heating and water-cooling on the mechanical properties of the WC-Co coatings, we conducted a series of mechanical tests on the HVOF (high-velocity oxygen-fuel) sprayed WC-Co samples. These coatings were first heated to the target temperatures (200–800 °C), followed by rapid cooling with water. Mechanical properties were tested after thermal treatments. Microstructural changes were also observed using a scanning electron microscope and optical microscope. According to experimental results, the microhardness, residual stress and adhesive strength of the heated WC-Co coating changed significantly after water-cooling. As heating temperature rises, changes in these properties become more pronounced. However, the number of cycles has less effect on the mechanical properties of the coatings and the effect mainly occurs in the first 30 cycles. Compared with the argon-cooling method, water-cooling induces greater changes in the mechanical properties at higher target temperatures. This indicates that water-cooling can damage the heated WC-Co coatings more remarkably than the other cooling treatment. Nevertheless, after about 30 cycles, changes in mechanical become less pronounced. Additionally, cobalt content has little impact on the mechanical properties of the coating after heating and water-cooling. • The effects of heating and water-cooling on the WC-Co coatings were investigated. • Temperature is the main factor affecting the properties of the coating. • Phase transformation and crack growth affect the properties of the coating. • Reducing vibration of the hammer can increase the service life of the coating. [ABSTRACT FROM AUTHOR]

The impedance-graded material (IGM) systems can be used as a protective structure to attenuate the stress. Due to the fluidic oscillator of the down-the-hole (DTH) hammer made by cemented carbide was broken during the test, it is urgent to design a protective structure to decay the stress transferred to the fluidic oscillator. This paper studied the stress attenuation effect of Steel-Poly-ether-ether-ketone (PEEK) -layered-protective-structure (SPLPS) subjected to low-velocity impact loadings. The contact state of samples is measured by pressure-sensitive test paper. The experiments were carried out by the split Hopkinson pressure bar (SHPB) method. The stress attenuation effect of 5-layer SPLPS was tested at the different impact velocities. A three-dimensional numerical simulation model is established to simulate the SHPB experiments with the same boundary conditions. The stress attenuation effect of different layers of SPLPS is compared by numerical simulation. Besides, the influence of the thickness of steel-sheet and PEEK-sheet is investigated. And the SPLPS made for the DTH hammer has been tested in the hot dry rock drilling field. The results show that the data of numerical simulation are consistent with the SHPB experimental results. It is found that the different impact velocities do not change the contact state of the sample's end face. The stress attenuation ratio of 5-layer SPLPS in numerical simulation and experiment is 77%. The attenuation ratio increases rapidly when the number of SPLPS layers changes from 1 to 4. When the number of SPLPS layers exceed 4, the attenuation ratio does not increase significantly. Additionally, the thickness of 6 mm and 8 mm are suitable parameters for the SPLPS. The field test has proved that the SPLPS could protect the fluidic oscillator effectively. • A Steel-Poly-ether-ether-ketone (PEEK) layered protective structure (SPLPS) is designed for a fluidic DTH hammer. • The stress attenuation ratio of the 5-layer SPLPS is up to 77% under the low-velocity impact. • The SPLPS have the advantages of simple structure, high service life and low cost for engineering application. [ABSTRACT FROM AUTHOR]

Utilization of the rotary–percussive drilling tools can help to reduce friction along the drill string and improve drilling performance in hard rock formations. However, intrinsic vibration and shock loads may severely damage the bottom hole assembly (BHA) and measurement while drilling (MWD). This paper investigates the dynamic response of fluidic hammer with hydraulic-damping-device, a rotary–percussive drilling tool which can provide forward percussion while eliminating harmful backward impact collisions. Descriptive statistical methods are introduced to accurately estimate the required damping length (RDL) and maximize the actual stroke length. In order to evaluate the influence of hydraulic-damping-device on vibration elimination, this paper discusses the effect of principal operating and design parameters on the dynamic responses of the fluidic hammer. In particular, a parametric model is fitted, in which the probability that backward impact collision is sufficiently eliminated is restricted to follow the probability density function. According to this function, when the damping stroke equals 10 mm, it is better than 99.999% to fully eliminate the possibility of backward collision. The improved understanding of the dynamic responses and some optimization proposals of a fluidic hammer will lead to the system reliability enhancement and cost optimization of the drilling engineering by eliminating the harmful shock and reducing shock-related tool failures. • The hydraulic-damping-device can completely eliminate the backward stroke impact collision. • A descriptive statistical approach was introduced to maximize the actual stroke length. • A parametric model was fitted to evaluate the probability that impact collision is sufficiently eliminated. [ABSTRACT FROM AUTHOR]