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• Cleats with non-extension features are commonly developed in coals. • The cleat system characteristic parameters are proposed. • The cleat system characteristic parameters determine the pore characteristics of reconstructed coals. • The box dimension can quantitatively calibrate the pore characteristics of coals. To effectively characterize the characteristics of the pore network of coal and to provide a realistic flow channel for flow simulation, a numerical reconstruction method of coal based on characteristics of the cleat system was proposed. Based on the real coal obtained through high-resolution micrometer CT, the cleat system characteristic parameters are defined and extracted. Then, a series of coals with different pore characteristics at the same scale and the same pore characteristics at different scales were reconstructed. Besides, the applicability of box dimension in calibrating the pore characteristics of coals was quantitatively analyzed. The results show that the coals reconstructed based on the method proposed in this paper can truly restore the pore characteristics of the real coal, especially the non-extension features of cleats; When the cleat system characteristic parameters remain consistent, the reconstructed coals maintain the same pore characteristics, with an average error of 3.37 % in the autocorrelation function, 0.78 % in the variation function and 1.94 % in the average percolation probability function. The box dimension can effectively identify the differences in pore characteristics of coals. At the same scale, as the distance between face cleats increases, the value of the box dimension of the reconstructed coals monotonically decreases, with a fitting slope of −0.22; At different scales, when the cleat system characteristic parameters remain the same, the value of the box dimension of the reconstructed coals is consistent, with an average relative error of 0.34 %. The research results provide a reasonable and effective flow channel for the microscopic/mesoscopic flow simulation of coalbed methane and provide a reference for the quantitative calibration of the pore characteristics of coals. [ABSTRACT FROM AUTHOR]

[Display omitted] • Reaction sequence has a major effect on structural evolution of coal-based carbon. • A panoramic view of structural evolution is revealed by double-round processing. • Double-round processing is better than single in a coal-to-carbon process. • High-rank coal allows for both highly porous surface and internal robustness. • Robust and rough catalyst support lends itself to performance optimization. Structural strengths of carbon-based supports, which hold up catalytically active sites and electron transfer, need to be considered in terms of carbonaceous electrocatalysts because weak supports often give unstable or poor performance in electrochemical environments. Coal can be a reasonable option for an attractive carbon source in view of its low expense, extensive reserve and natural robustness. Conversion of coal to coal-based carbon, instead of conventionally burning it off as fuel to emit CO 2 , is increasingly finding its own niche in the forefront of chemical engineering. However, pore propagation and surface modification of coal are difficult to handle due to its hardness characteristics, limiting performance enhancement of coal-based catalysts. To tackle this problem, we propose a double-round activation/doping method and disclose significant influences of different reaction sequences on structure-performance correlations. The coal-based metal-free N,P-doped porous carbon materials manifest the improved performance of electrocatalytic oxygen reduction in the alkaline, acidic and neutral electrolytes, along with robust behaviours including good resistance to harmful ions and conceptual demonstration of electrochemical devices. It is also revealed that the electrocatalytic performance of coal-based catalysts is closely related both to their textural properties and to concerted effects induced by the coexistence and uniform distributions of N and P atoms doped into carbon matrices, as demonstrated by the experimental and theoretical results. Consequently, this work gives intriguing insights into structural evolution and performance enhancement of robust coal-based electrocatalysts from the perspective of reaction sequences and provides inspiration for low-carbon utilization of coal in regard to coal-to-carbon transformations. [ABSTRACT FROM AUTHOR]

Since the successful application of the Elrod method to the Jakobsson–Floberg–Olsson (JFO) theory, many new alternative methods have been presented. In particular, over the past decade, the efficiency of cavitation algorithms has significantly improved, as demonstrated by the Fischer-Burmeister based unconstrained optimization methods and the modulus-based methods based on the generalized absolute value equation. This paper briefly reviewed the principles of these algorithms and compared their computational efficiency. Pseudocodes were included to illustrate their implementation. Taking advantage of linear direct solvers, a novel equivalent symmetric matrix equation was presented to promote the efficiency of these algorithms. A case of a surface-textured thrust bearing with multiple dimples was studied. The results showed that the method can save more than 2–5 times the computing time. [ABSTRACT FROM AUTHOR]

The multi-body hinge-barge wave energy converter has the advantages of high capture width ratio and wide bandwidth of wave-excited response, which is the current hotspot of studies on wave energy converters. However, to correctly and throughfully analyse its overall efficiency, hydrodynamics, mechanical dynamics and electrical dynamics, a fully coupled wave-to-wire approach by numerical analysis and physical validation is required, which is not concerned by current studies. The work conducted in this study improves the overall wave-to-wire efficiency by optimising the mooring system, the structure and geometry of the primary capture system, and the external electric load. Results show that an optimised prototype achieves a wave-to-wire efficiency up to 25 % in flume experiments, where a significant improvement of 53 % is contributed by employing a damping plate to the right barge. Numerical results indicate that a wave-to-wire efficiency of up to 53 % is obtained by further optimisation of the damping plate. • A wave-to-wire model is developed for a hinge-barge wave energy converter, verified by flume experiments. • Adding a damping plate to the right barge can significantly improve power generation. • High wave-to-wire efficiency of 25.02% is experimentally achieved by a prototype. • High wave-to-wire efficiency of 53% is numerically achieved by optimisation. [ABSTRACT FROM AUTHOR]

Lacking a long-term power supply restricts the endurance of unmanned surface vehicles (USVs) and their application in remote sea areas. To address that ptoblem, a reliable solution based on the utilisation of wave energy is proposed in this study, where a wave-excited energy harvester is integrated into the USV. A fully coupled mathematical model is established to describe the dynamics and the electricity generation performance of the integrated system, considering the coupling of the mooring system. Numerical results given by this mathematical model are validated by physical experiments. The influence of the external load, the wave height, the wave period, the pendulum length, the pendulum mass and the mooring system on the system's performance are investigated, respectively. Experimental results of two small-scale prototypes, performed in a wave flume, show that the time-averaged generated electrical power is up to 324.89 mW when the wave height is 9.00 cm and the wave period is 1.72 s , where the corresponding wave-to-wire efficiency is 9.72%. Results indicate that the pendulum length, the pendulum mass, and the configuration of the mooring system significantly influence the resonant period and bandwidth. • A new wave-powered USV based on an inertial pendulum is proposed. • The proposed wave energy harvester has the capability to tune natural frequency. • A time-averaged electric power of 324.89 mW is achieved under a flume wave height of 9 cm. • The mooring system has a significant effect on the bandwidth of the USV. [ABSTRACT FROM AUTHOR]

A micro-impinging stream reactor (MISR) at the size of ~1 mm has been built from commercial T-junctions and steel micro-capillaries, which has advantages of intensified micromixing and easy construction. By using a big-sized and very short outlet tube, the two injecting streams could impinge intensely within the limited chamber of the T-junction to achieve a quick mixing at the micro-scale. The effects of both operating parameters and geometric parameters of MISR, e.g., inlet jet Reynolds number ( Re j ), volumetric flow ratio ( R ), outlet configuration, outlet length ( L ), and inlet diameter ( d i ), on the micromixing efficiency have been studied by experiments with the Villermaux–Dushman reaction as well as by computational fluid dynamics (CFD) method. Both experimental and numerical results agreed well and demonstrated that the inlet jet Reynolds number ( Re j ) and inlet size played a key role for the micromixing performance. The outlet configuration also had a great influence on micromixing, but the effects of the length of outlet channel were insignificant. This work showed that MISR will have a great potential for both reaction and separation process intensifications. [ABSTRACT FROM AUTHOR]

Unmanned surface vehicles (USVs) have been widely used in various fields credited for their high flexibility and excellent manoeuvrability. However, the limited onboard electricity of USVs restricts their applications in long-term working tasks. A promising option to address that problem is employing a wave-powered USV, where a wave energy converter is integrated into the USV. For a wave-powered USV, it is challenging to achieve a precise estimation of its power generation under complex marine environments. Although there are physics-based models of WECs used for the estimation and prediction of power generation of USVs, they cannot achieve satisfactory accuracy in practice because of the linearization and simplification of those mathematical modelling. To fill up this gap, this paper proposes a data-driven modelling method utilizing feature engineering and ensemble learning to estimate the mean power generation of a wave-powered USV, relying on time-serial measurements obtained from real physical wave-flume experiments under regular waves. Results show that the estimation achieves promising performance, where the minimum RMSEs are 3.359 mW and 6.148 mW for a harvester-to-wire model and a wave-to-wire model, respectively. Additionally, the proposed method shows great potential for real-sea applications, such as online power prediction and control. • A data-driven method for power estimation of a wave-powered USV is proposed. • The robustness of the proposed method is verified with the presence of noise. • The proposed method possesses practical significance, such as data-driven control. [ABSTRACT FROM AUTHOR]