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The existing discontinuous Galerkin (DG) finite element method (FEM) for the numerical simulation of elastic wave propagation is primarily implemented in two dimensions. Here, a discontinuous FEM (DFEM) for efficient three-dimensional (3D) elastic wave simulation is presented. First, the velocity–stress equations of 3D elastic waves in isotropic media are transformed into first-order coefficient-changed partial differential equations. A DG discretisation method for wave field values on a unit boundary is then defined using the local Lax–Friedrichs flux format. The equations are first transformed into equivalent integral equations, and subsequently into a spatial semi-discrete ordinary differential equation system using a hierarchical orthogonal basis function. The DFEM is extended to an arbitrary high-order accuracy in the time domain using the exponential integrator technique and the explicit optimal strong-stability-preserving Runge–Kutta method. Finally, an efficient method for selecting the calculation area of the geometry of the current shot record is realised. For the computation, a multi-node parallelism with improved resource utilisation and parallelisation efficiency is implemented. The numerical results show that the proposed method can improve both the accuracy of the simulation and the efficiency of the calculation compared with existing methods.

Purpose This paper aims to present the slip/no-slip design in two-dimensional water-lubricated tilting pad thrust bearings (TPTBs) considering the turbulence effect and shifting of pressure centers. Design/methodology/approach A numerical model is established to analyze the slip condition and the effect of turbulence according to a Reynolds number defined in terms of the slip condition. Simulations are carried out for eccentrically and centrally pivoted bearings and the influence of different slip parameters is discussed. Findings A considerable enhancement in load capacity, as well as a reduction in friction, can be achieved by heterogeneous slip/no-slip surface designs for lubricated sliding contacts, especially for near parallel pad configurations. The optimized design largely depends on the pivot position. The load capacity increases by 174 per cent for eccentrically pivoted bearings and 159 per cent for centrally pivoted bearings for a suitable design. When slip zone locates at the middle of the radial direction or close to the inner edge, the performance of the TPTB is better. Research limitations/implications The simplification of slip effect on the turbulence (definition of Reynolds number) can only describe the trend of the increasing turbulence due to slip condition. The accurate turbulence expression considering the boundary slip needs further explorations. Originality/value The shifting of pressure center due to the slip/no-slip design for TPTBs is investigated in this study. The turbulence effect and influence of slip parameters is discussed for large water-lubricated bearings.

Controlling the wettability of surfaces is imperative for the tribology behavior during the friction and wear, especially in aqueous environment. In this work, fiber laser treatment of impregnated graphite was used to achieve a bidirectional wettability transition. The treated surfaces were characterized using scanning electron microscopy, 3D confocal surface topography analysis, Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The surface treated by a low–energy laser became hydrophobic (increase of contact angle from 73.6° to 131.6°) and the surface treated by a high–energy laser became more hydrophilic (decrease of contact angle to 6.7°). Examination of the morphology indicated that with increasing laser energy, the roughness increased and the surface changed from a flocculent to scaly structure. Analysis of the energy spectra revealed an increase of oxygen content on the hydrophilic surface. In addition, Raman spectra analysis indicated a positive correlation between graphite ordering and the contact angle. The FTIR results demonstrated the existence of hydrocarbon on the hydrophobic surface. After ultraviolet/O3 cleaning, the contact angle of the hydrophobic surface decreased to 37°; however, the contact angle of the surface which did not be treated by laser hardly changed. Based on these results, it was concluded that the wettability transition was caused by the changes in surface morphology and chemical composition.

Continuous bi-Gaussian reconstruction approach is applied to two simulated pure bi-Gaussian and four real worn surfaces. It is compared with segmented bi-Gaussian, ISO 13565-3 bi-Gaussian and Johnson reconstruction approaches in terms of surface property, lubrication and asperity contact. The results show that the continuous approach reproduces a surface in good agreement with the original in terms of maximum fluid pressure, cavitation ratio and lift load, because it serves as a concise way to achieve the high resemblance of surface property with the original surface as similar to the ISO approach. The segmented approach sometimes loses efficiency, and the Johnson approach generates a single-stratum surface with steep valleys, inducing large pressure spikes, large cavitation zone and large lift load. The superiority of the continuous approach can be drawn from the contact mechanics study on contact pressure and real contact area.

Shear-wave velocity logs are useful for various seismic interpretation applications, including bright spot analyses, amplitude-versus-offset analyses and multicomponent seismic interpretations. This paper presents a method for predicting the shear-wave velocity of argillaceous sandstone from conventional log data and experimental data, based on Gassmann's equations and the Xu–White model. This variable aspect ratio method takes into account all the influences of the matrix nature, shale content, porosity size and pore geometry, and the properties of pore fluid of argillaceous sandstone, replacing the fixed aspect ratio assumption in the conventional Xu–White model. To achieve this, we first use the Xu–White model to derive the bulk and shear modulus of dry rock in a sand–clay mixture. Secondly, we use Gassmann's equations to calculate the fluid-saturated elastic properties, including compressional and shear-wave velocities. Finally, we use the variable aspect ratio method to estimate the shear-wave velocity. The numerical results indicate that the variable aspect ratio method provides an important improvement in the application of the Xu–White model for sand–clay mixtures and allows for a variable aspect ratio log to be introduced into the Xu–White model instead of the constant aspect ratio assumption. This method shows a significant improvement in predicting velocities over the conventional Xu–White model.