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Tip vortex cavitation (TVC) is an important cavitation phenomenon in marine propeller. The formation and evolution of tip vortex cavitation are hot topics consistently both in engineering application and mechanism research. In this paper some recent studies on tip vortex cavitation inception and the noise of tip vortex cavitation evolution are presented. The effects of both flow field and water qualities on tip vortex cavitation inception are considered by experiments and numerical simulations. The results show that besides the average minimum pressure in the vortex core the turbulence fluctuation and water qualities including air content and nuclei distribution have great influence on tip vortex cavitation inception. Based on the idea of first nucleus cavitating in tip vortex core new prediction formula for tip vortex cavitation inception is proposed. The synchronous technique of high speed video observation and noise measurement are adopted to study the development of tip vortex cavitation. S-type total noise characteristics are obtained when cavitation number from low to high. Vortex singing is found in the case where the tip vortex cavitation just before leaves the tip region. The excited mechanism of vortex singing is proposed by analyzing the wave propagation on the interface of vortex cavity.

Fracture reorientation affects hydraulic fracturing much in perforated wells. A finite element model used for investigating fracture reorientation is established using the extended finite element m...

It is well known that methane hydrate has been identified as an alternative resource due to its massive reserves and clean property. However, hydrate dissociation during oil and gas development (OGD) process in deep water can affect the stability of subsea equipment and formation. Currently, there is a serious lack of studies over quantitative assessment on the effects of hydrate dissociation on wellhead stability. In order to solve this problem, ABAQUS finite element software was used to develop a model and to evaluate the behavior of wellhead caused by hydrate dissociation. The factors that affect the wellhead stability include dissociation range, depth of hydrate formation and mechanical properties of dissociated hydrate region. Based on these, series of simulations were carried out to determine the wellhead displacement. The results revealed that, continuous dissociation of hydrate in homogeneous and isotropic formations can causes the non-linear increment in vertical displacement of wellhead. The displacement of wellhead showed good agreement with the settlement of overlying formations under the same conditions. In addition, the shallower and thicker hydrate formation can aggravate the influence of hydrate dissociation on the wellhead stability. Further, it was observed that with the declining elastic modulus and Poisson’s ratio, the wellhead displacement increases. Hence, these findings not only confirm the effect of hydrate dissociation on the wellhead stability, but also lend support to the actions, such as cooling the drilling fluid, which can reduce the hydrate dissociation range and further make deepwater operations safer and more efficient.

In this paper, recent measurements of tip vortex flow with and without cavitation carried out in Cavitation Mechanism Tunnel of China Ship Scientific Research Center (CSSRC) are presented. The elliptic hydrofoil with section NACA 662-415 was adopted as test model. High-speed video (HSV) camera was used to visualize the trajectory of tip vortex core and the form of tip vortex cavitation (TVC) in different cavitation situations. Laser Doppler velocimetry (LDV) was employed to measure the tip vortex flow field in some typical sections along the vortex trajectory with the case of cavitation free. Stereo particle image velocimetry (SPIV) system was used to measure the velocity and vorticity distributions with and without cavitation. Series measurement results such as velocity and vorticity distributions, the trajectory of tip vortex core, the vortex core radius, cavity size and cavitation inception number were obtained. The results demonstrated that the minimum pressure coefficient in the vortex core obtained by flow field measurement was quite coincident with the tip vortex cavitation inception number obtained under the condition of high incoming velocity and low air content. And TVC would decrease the vortex strength comparing with the case without cavitation.

The diminishing oil resources make the exploration and development of heavy oil reservoirs more and more important. Heavy oil reservoirs need steam stimulation or other thermal development methods; temperature increasing during the thermal recovery process will inevitably affect the reservoir compressive characteristics. In order to study the variation of the compression coefficient of heavy oil reservoirs in the multi-round steam stimulation process, the compression coefficients of the reservoirs after different temperature and pore pressure cycles were tested. The results show that the compression coefficient of heavy oil reservoir decreases with the increase in effective confining pressure and increases with the increase in test temperature; After the temperature and pore pressure cycle, the compression coefficient of the rock is greatly reduced; the decrease in range of compression coefficient of the reservoir after the temperature and pore pressure cycle increases with the increase in the test temperature, and increases with the increase in maximum effective confining pressure. The dynamic variation of the reservoir compression coefficient must be taken into account in the prediction of the production capacity of multi-round steam stimulation.

Recently, (K, Na, Li)(Nb, Ta, Sb)O3 ceramics have attracted much attention of researchers, and have become one of the most popular systems of KNN-based ceramics. In this paper, Bi4Ti3O12 was added in the (K0.4425Na0.52Li0.0375)(Nb0.87Ta0.06Sb0.07)O3 ceramics (KNLNTS-x mol% BIT) to improve their piezoelectric properties. The phase formation and microstructure of KNLNTS-x mol% BIT ceramics were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). With the addition of BIT, the permittivity maxima of samples shifted toward higher temperature firstly and then shifted to lower temperature. All samples showed well ferroelectric behavior and the density of (1-x)KNLNTS-x mol% BIT ceramics were increased and reached a relative density of 99.4%. High piezoelectric properties of d33 = 255 pC/N, kp = 0.451, Qm = 186 were obtained for the samples containing 0.50 mol% BIT.

Electrolyte is the key to improve the safety, cycle performance and temperature adaptation of lithium batteries. In this paper, we introduce a novel electrolyte that based on ionic liquids (ILs) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR14-TFSI) and fluorinated solvent 1,1,1,3,3,3-hexafluoroisopropyl methyl ether (HFPM). HFPM can significantly reduce the viscosity of PYR14-TFSI and enhance the wettability with Celgard separators. In addition, the coordination of PYR14-TFSI and HFPM promotes the local dissolution of lithium nitrate and helps to form a stable cathode/anode interface film. The electrochemical test shows that the electrochemical window of the electrolyte can reach to 5.35 V. For the Li/LiNi0.6Co0.2Mn0.2O2 half cells, the capacity retention is 94% and the Coulomb efficiency is 99.9% after 100 cycles at 0.5 C. The uniform and dense interface film is characterized and confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy, etc. Furthermore, the half-cell also exhibits good thermal stability at high temperature. Considering ILs and fluoroether are non-flammable solvent, this work may pave the way for designing future generation high-performance electrolyte for lithium batteries.

(1-x)BaTiO3-xSiO2 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol%) ceramics were prepared by microwave sintering method, which nanopowders of BaTiO3 and SiO2 were successfully synthetized by conventional hydrothermal method and Stober method, respectively. The effect of SiO2 content on microstructure and dielectric properties was investigated. X-ray diffraction result suggested that tetragonality (c/a) of the samples increased with increasing content of SiO2. It was found that there existed an increase in density and grain size of the samples for x≤0.4, which was mainly attributed to the presence of liquid phase during sintering process. BaTiO3 ceramics containing such amount of SiO2 also showed improved dielectric properties.

In this paper, we report a mussel-inspired polydopamine coating on the Si/C electrode via a simple immersion process to improve the electrochemical performance such as cycle stability and rate capability. The nanometer-thick polydopamine coating layer enables fast Li+ transport at the interfaces and takes part in the formation of SEI due to the electron-rich amine group. The PD coated Si/C electrode exhibits good performance in long cycling test. Compare with the uncoated Si/C electrode, the capacity retention of the coated electrode is improved from 59.5% to 80% after 200 cycles. X-ray photoelectron spectroscopy, transmission electron microscopy and scanning electron microscopy prove that PD coating really promotes the formation of uniform and dense SEI and reduces cracks on the electrode surface. Meanwhile, the pulverization of electrodes which breaks the electrical contact with the current collector is alleviated.

The ever-decreasing oil resources receive more and more attention for the exploration and development of heavy oil reservoirs. Owing to the high viscosity and poor fluidity of heavy oil, it is necessary to use the method of injecting high-temperature fluid in the development process. But, this will cause a significant increase in the temperature in oil reservoir, and thus the compression coefficient of reservoir rock has a greater impact. The compression coefficient of heavy oil reservoirs at different temperatures was tested. The results show that the compression coefficient of rock is closely related to the nature of rock itself and its stress and temperature environment: the compression coefficient increases with the increase in rock porosity; the compression coefficient decreases with the increase in the effective confining pressure and increases with the increase in temperature. When the temperature is low, the increase in the compression coefficient is larger. As the temperature increases, the increase in the compression coefficient tends to decrease gradually. Because the temperature of the reservoir is higher than that of the ground, the influence of the temperature on the reservoir compression coefficient should be taken into account when carrying out the production forecast.

Natural gas hydrate is widely distributed all over the world and may be a potential resource in the near future, whereas hydrate dissociation during the development affects wellbore stability and drilling safety. However, the present modeling of hydrate reservoir parameters ignored the influence of effective stress and only considered the hydrate saturation. In this paper, a series of stress sensitivity experiments for the unconsolidated sandstone were carried out, and the influence of mean effective stress on physical parameters was obtained; a comprehensive model for the physical parameters of hydrate reservoir was developed subsequently. With the help of ABAQUS finite element software, the established comprehensive model was verified by the use of the wellbore stability numerical model of hydrate reservoir. The verification results show that ignoring the effect of mean effective stress on the parameters of hydrate formation aggravates the invasion of drilling fluid into the hydrate formation. Besides, ignoring the stress sensitivity of reservoir physical parameters will underestimate the wellbore instability during hydrate drilling, which will be a threat to the safety of gas hydrate drilling. At the end of the drilling operation, the maximum plastic strain of the model for considering and not considering stress sensitivity was 0.0145 and 0.0138, respectively. Therefore, the established comprehensive model will provide a theoretical support for accurately predicting the engineering geological disasters in hydrate development process.